Pyrolysis Oils from Biomass. Producing, Analyzing, and Upgrading 9780841215368, 9780841212282, 0-8412-1536-7

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Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.fw001

Pyrolysis Oils from Biomass

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.fw001

ACS SYMPOSIUM SERIES

376

Pyrolysis Oils from Biomass Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.fw001

Producing, Analyzing, and Upgrading Ed J. Soltes, EDITOR Texas A&M University

Thomas A. Milne,

EDITOR Solar Energy Research Institute

Developed from a symposium sponsored by the Cellulose, Paper, and Textile Division and the Division of Fuel Chemistry at the 193rd Meeting of the American Chemical Society, Denver, Colorado, April 5-10, 1987

American Chemical Society, Washington, DC 1988

Library of Congress Cataloging-in-Publication Data Pyrolysis oils from biomass producing, analyzing, and upgrading. Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.fw001

(ACS Symposium Series; 376). Developed from a symposium sponsored by the Cellulose, Paper, and Textile Division and the Division of Fuel Chemistry at the 193rd Meeting of the American Chemical Society, Denver, Colorado, April 5-10, 1987. Includes index. Bibliography: p. 1. Biomass energy—Congresses. 2. Pyrolysis— Congresses. 3. Hydrocarbons—Congresses. I. Milne, Thomas Α. II. American Chemical Society. Cellulose, Paper, and Textile Division. III. American Chemical Society. Division of Fuel Chemistry. IV. Title. V. Series. TP360.P95 1988 662'.8 ISBN 0-8412-1536-7

88-24172

Copyright ©1988 American Chemical Society A l l Rights Reserved. The appearance of the code at the bottom of the first page of each chapter in this volume indicates the copyright owner's consent that reprographic copies of the chapter may be made for personal or internal use or for the personal or internal use of specific clients. This consent is given on the condition, however, that the copier paythestated per-copy fee through the Copyright Clearance Center, Inc., 27 Congress Street, Salem,MA01970, for copying beyond that permitted by Sections 107 or 108 of the U.S. Copyright Law. This consent does not extend to copying or transmission by any means—graphic or electronic—for any other purpose, such as for general distribution, for advertising or promotional purposes, for creating a new collective work, for resale, or for information storage and retrieval systems. The copying fee for each chapter is indicated in the code at the bottom of the first page of the chapter. The citation of trade names and/or names of manufacturers in this publication is not to be construed as an endorsement or as approval by ACS of the commercial products or services referenced herein; nor should the mere reference herein to any drawing, specification, chemical process, or other data be regarded as a license or as a conveyance of any right or permission to the holder, reader, or any other person or corporation, to manufacture, reproduce, use, or sell any patented invention or copyrighted work that may in any way be related thereto. Registered names, trademarks, etc., used in this publication, even without specific indication thereof, are not to be considered unprotected by law. PRINTED IN T H E UNITED STATES O F A M E R I C A

American Chemical Society Library 1155 18th St., N.W. Washington, D.C. 20036

ACS Symposium Series

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.fw001

M. Joan Comstock, Series Editor 1988 ACS Books Advisory Board Paul S. Anderson

Vincent D. McGinniss

Merck Sharp & Dohme Research Laboratories

Battelle Columbus Laboratories

Harvey W. Blanch University of California—Berkeley

Malcolm H. Chisholm

Daniel M. Quinn University of Iowa

James C. Randall

Indiana University

Exxon Chemical Company

Alan Elzerman

E. Reichmanis

Clemson University

AT&T Bell Laboratories

John W. Finley Nabisco Brands, Inc.

Natalie Foster Lehigh University

C. M. Roland U.S. Naval Research Laboratory

W. D. Shults Oak Ridge National Laboratory

Marye Anne Fox The University of Texas—Austin

Geoffrey K. Smith Rohm & Haas Co.

RolandF.Hirsch U.S. Department of Energy

G. Wayne Ivie USDA, Agricultural Research Service

Douglas B. Walters National Institute of Environmental Health

Michael R. Ladisch

Wendy A. Warr

Purdue University

Imperial Chemical Industries

Foreword

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.fw001

The ACS SYMPOSIUM SERIES was founded in 1974 to provide a

medium for publishing symposia quickly in book form. The format of the Series parallels that of the continuing ADVANCES IN CHEMISTRY SERIES except that, in order to save time, the papers are not typeset but are reproduced as they are submitted by the authors in camera-ready form. Papers are reviewed under the supervision of the Editors with the assistance of the Series Advisory Board and are selected to maintain the integrity of the symposia; however, verbatim reproductions of previously published papers are not accepted. Both reviews and reports of research are acceptable, because symposia may embrace both types of presentation.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.pr001

Preface PROLYSIS O F BIOMASS HAS undergone a technological renaissance in the past decade, thanks to new concepts and processes for high oil yields, new analytical techniques to decipher the mechanisms of formation and constitution of the oil, and catalytic approaches to upgrading the oil fuel used for transportation. Governments have given priority to pyrolysis and direct liquefaction, following bench and pilot success in gasification and indirect liquefaction, to offer industry concepts for renewable liquid fuels, particularly premium fuels. Following the Workshop on Fast Pyrolysis in 1980, and a series of liquefaction workshops in Canada in 1980, 1982, and 1983, it seemed timely to convene scientists and engineers from North America and elsewhere to report on the present progress in integrated pyrolysis oil production, characterization, and upgrading studies. As the book name implies, we attempted to bring together specialists to present the state of the science in the complete fuel cycle, from feedstock to upgraded liquid fuels suitable as replacements for petroleum-derived fuels. The introductory chapter contains a discussion of biomass pyrolysis and its place in a renewable fuel economy. Contributions to this book were received fromfivecountries, a fact indicating the widespread interest in this conversion option for biomass, and permitting the enhancement and establishment of collaborative efforts. At the time this preface was written, the U.S. newspapers reported a two-year low in crude oil prices ($15/Bbl), fleet auto efficiency standards were being relaxed, and oil imports were rising steadily. At the same time, through perhaps a short-term statistical fluctuation in rainfall, the public wasfinallybecoming aware of the implication of the real, longterm rise in C 0 levels from deforestation and the burning of fossil fuels. Perhaps the promise of a renewable source of liquid transportation fuels, coupled with extensive reforestation, as mitigators of the rise in C 0 levels, will spur progress in the conversion of C 0 , through photosynthesis, to plant materials. Such plant materials could provide facile and economic routes to substitutes for fossil-based fuels, chemicals, and biobased materials. 1

2

2

2

2

1. Diebold, J. P., Editor. Proceeding? of the Specialists Workshop on the Fast Pyrolysis of Biomass. Copper Mountain, Colorado, Oct. 20-22 SERI/CP-622-10%. 2. ENFOR Program and National Research Council of Canada. Biomass Liquefaction Specialists' Review Meetings in Toronto, Aug. 13, 1980; Saskatoon, Feb. 16-17, 1982; and Sherbrooke, Sept. 29-30, 1983.

xi

We thank the sponsoring divisions and all contributors to this volume and hope that their results will foster both interest in, and support of, continuing work on the fascinating chemistry and engineering of biomass pyrolysis, oil characterization, and upgrading for many uses. ED J. S O L T E S

TexasA&MUniversity College Station, TX 77843

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.pr001

T H O M A S A. M I L N E

Solar Energy Research Institute Golden, CO 80401 July 5, 1988

xii

Chapter 1

Of Biomass, Pyrolysis, and Liquids Therefrom Ed

J.

Soltes

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch001

Department of Forest Science, Texas Agricultural Experiment Station, Texas A&M University System, College Station, TX 77843-2135 Renewable biomass (harvest and process residues in forestry and agricultural operations, specific terrestrial or aquatic crops grown for fuel, often animal wastes, refuse derived fiber, etc.) represents an important energy resource in the United States, with future potentials especially important as fossil fuels are depleted (1). Biomass is however generally poorly suited for direct energy use, with pretreatments necessary for altering physical and chemical form. Moisture content can be in excess of 50%, so costs of collection, transportation, and energy conversion become relatively inefficient. Further, biomass availability (e.g., from row crops) is sometimes seasonal, so storage is necessary. As biomass can spoil, it has to be covered and processed soon after receipt. Fortunately, thermal conversion processes are somewhat insensitive to type, form and shape, and can convert biomass into stable, storable and transportable energy forms, and in physical or chemical forms that can be used in higher efficiency energy conversion processes developed for liquid petroleum, coal and natural gas. Under pyrolysis process conditions, a liquid tar (pyrolysis oil) can be produced which can be upgraded to liquid engine fuels (2). Why liquid? It can be argued that the principal advantage of petroleum is that it is a liquid (3): liquid fuels, besides being energy dense, are especially easy to store, transport and meter, thus being really the only choice for transportation fuels. Biomass conversion processes (specifically pyrolysis) which have potential for producing liquid fuels, especially liquid fuels that can be direct replacements for gasoline or diesel engine fuels, are then of much interest. The Nature of Biomass Pyrolysis Biomass thermochemical processes have been studied for at least two reasons: (1) a better understanding of the combustion process to control biomass flammability; and, (2) research into improved processes for converting biomass into useful energy forms. The late Fred Shafizadeh (see, e.g., 4,5) laid the groundwork for all recent studies in both arenas. The work on combustion mechanisms continues at the Wood Chemistry Laboratory of the University of Montana in Missoula (see, e.g., 6). Antal has recently (7,8) reviewed all aspects of biomass pyrolysis, and the reader is directed to his reviews for detail study of the processes involved. Chatterjee has produced an excellent summary (9) of biomass pyrolysis 0097-6156/88/0376-0001$06.00/0 ° 1988 American Chemical Society

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PYROLYSIS OILS FROM BIOMASS

rocesses relative to application in lesser developed countries. This author as also written several reviews on biomass thermochemical processes, and specifically pyrolysis (2,3,13). Several volumes have been published recently on thermal conversion (10,11), with another on the way for the 1988 Phoenix conference (12). The opening paragraph to this overview chapter relates the need for pyrolysis relative to liquid transportation fuels production. This is a rather specific energy need, and in fact, biomass can serve other energy needs as well. Charcoal from wood is the principal fuel of rural regions of most lesser developed countries. The gas from biomass gasification has found use in the retrofit of natural gas furnaces and engines, and highly efficient cogeneration plants. The energy content of residues from forestry and agricultural operations can often serve on-site process energy needs, but the biomass materials are generally poorly suited for direct use. Modern agricultural and process machinery seldom use solid fuels, therefore pretreatments are often required to change their chemical or physical nature to liquids or gases. Similar considerations apply to the conversion of biomass crops and to the use of biomass fuels off-farm. Thermochemical processes for biomass are basically pretreatment processes, processes that alter the chemical and physical nature of biomass to permit higher efficiency use. Thermochemical processes are often characterized as combustion, gasification, pyrolysis, carbonization or tarification processes. Except for pyrolysis, these names reflect types of products produced. Thermochemical processing is variable and flexible. Depending on conditions used, (primarily the temperature, the oxygen-to-fuel ratio, and residence time at temperature), biomass can be altered very slightly, or be completely changed. These three variables define conditions for pyrolysis, gasification and combustion but there is often little distinction between these processes. In fact, there is a continuum of process conditions. Selection of treatment conditions permits a variety of outcomes of importance to the production of bioenergy products. The mechanisms for the formation of these products are indeed complex, and are still unfolding (see e.g., 7,8,14). Knowledge of these mechanisms has permitted the identification of conditions under which it is possible to produce tars in good yield from large, moist wood particles (15), or novel reactor design for the production and capture of desired tar products (16). Still, gases, liquids and solids are always produced, with relative yields and chemical or elemental compositions dependent on process variables. Definition of Pyrolysis. The word pyrolysis has had some problems in definition, especially when applied to biomass. The older literature generally equates pyrolysis to carbonization, in which the principal p r o duct is a solid char. Today, the term pyrolysis is generally used to describe processes in which liquid oils are preferred products. This symposium was concerned with the latter pyrolysis - processes which offer enhanced yields of liquid oils, especially those with desirable chemical compositions and physical attributes for liquid fuels, fuel supplements and chemical feedstocks. Definition of Pyrolysis Oil vs. Tar. Throughout this volume, "pyrolysis oil", "tar" and "pyrolytic tar" are used almost interchangeably. Tar or pyrolytic tar is a more generic term, now becoming used in reference to its formation in a secondary sense, e.g., as undesired in gasification, or the "creosote tar" of incomplete combustion or the usually

1. SOLTES

Of Biomass, Pyrolysis, and Liquids Therefrom

3

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wasted tar byproducts of charcoal manufacture. Oil or pyrolysis oil refers specifically to the liquid product of biomass pyrolysis when the oil is the principal product of interest* Thus, not only "pyrolysis" but also "tar" and "oil" definitions are being cast while research is being conducted in this area. To add to this confusion, this author more than once tried (in retrospect fortunately unsuccessful) to coin the term "tarification" as any pyrolytic process where the product of interest was the liquid tar product! Other Feedstocks and Processes. Although most of the papers in the symposium deal with thermochemical conversion of wood in what may be called the conventional pyrolysis process mode (heating in the absence of air, or under air-starve conditions), other papers were invited which cover the conversion of other biomass materials, such as from municipal solid waste (17) or black liquor (18), or conversion under more novel processing conditions. Mention is made of liquefaction relative to pyrolysis. Although there has not been an attempt to define liquefaction in the literature, to the author's knowledge, it usually refers to the one-step high liquid yield process incorporating heat in combination with reducing gases and/or catalysts (19), but may now also include water-based processes (20). Liquids are also produced in acid solution (21), alkaline solution (22) and in solvolysis (23). Characterization of Biomass Pyrolysis Oils The chemical compositions of pyrolysis oils are very complex. High temperature reactions in the absence of oxygen or under air-starve conditions are not specific, and the availability of sufficient energy for alternative pathways results in a series of complex concurrent and consecutive reactions which provide a wide spectrum of pyrolytic products, usually in small yields (3,14). Most of the literature in the past, including that by the author (13), reflected composition of tars produced as a byproduct of charcoal manufacture. These tars, from different biomass materials, exhibit like chemical compositions. The chars produced under similar carbonization conditions also exhibit similar physical and chemical properties (24). During the last decade or so, pyrolysis process research has confirmed that both the yield and chemical composition of pyrolysis oils are v e r y dependent on reaction conditions (see e.g., 14-16,25,26). All biomass oils are not the same: oil formation conditions determine oil composition. Similarly, it has been reported that different biomass feedstocks pyrolyzed under similar process conditions can give oil products with similarities in chemical composition (e.g., 27-30). Characterization Tools for Pyrolysis Oils. It wasn't too many years ago that the only tools available to the scientist interested in pyrolysis oil composition were gas chromatography and thermogravi-metric analysis. The complexity of the pyrolysis oils demands high performance equipment, and a list of such equipment mentioned during the symposium would include proton and carbon nuclear magnetic resonance spectroscopy, free-jet molecular beam/mass spectrometry (16,25), diffuse reflectance Fourier transform infrared spectrometry (31), photoelectron spectroscopy (31), as well as procedures such as computerized multivariate analysis methods (32) - truly a display of the some of the most sophisticated analytical tools known to man, and a reflection of the difficulty of the oil composition problem.

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PYROLYSIS OILS FROM BIOMASS

Not all scientists have access to this type of equipment, and gas chromatography (GC) is still used extensively, especially in capillary mode (see, e.g., 26,27). The higher resolution of capillary GC is preferred over column chromatography because of the many oxygenated species of similar polarity in pyrolysis oils. Much (usually most) of the pyrolysis oil is also non-volatile, and this causes additional problems for capillary columns: nonvolatiles can cause column deterioration of the stationary phase. It is usually with much trepidation that the average scientist injects for the first time a black, viscous, mostly non-volatile pyrolysis oil into his pristine capillary column (especially when coupled to someone else's mass spectrometer), but be assured that it works, and that the column can live a long and useful life after many such experiences! Column deterioration can be minimized by periodic cleaning or rejuvenation of the column, as well as by occasionally removing the first centimeter or two of the column at the injection end containing the nonvolatiles. Prior separations of complex oils into volatile or functional fractions such as with the use of High Performance Size Exclusion Chromatography (HPSEC) (27,33), or silica gel column chromatography (26) can help the researcher in obtaining more suitable fractions for capillary GC work. Although a number of phases are used in capillary GC for separating the volatiles of pyrolysis oils, the most popular appears to be a bonded silica of moderate polarity, such as the DB-5 column in 30 cm length. HPS EC by itself is becoming increasingly used as a tool for characterizing pyrolysis oils (see, e.g., 27,34). Post-Pyrolysis Processing The utility of biomass pyrolysis oils in any fuel or chemical sense must recognize this complexity in chemical composition, and it is commonly suggested that the tar either be fractionated into simpler mixtures, or be reprocessed or converted into more useful mixtures. Unfortunately, oils usually do not fractionate well (depends on storage conditions and type of oil), and will even undergo changes upon storage, resulting in higher concentrations of non-volatile high molecular weight materials. Extraction techniques work, but these processes are unwieldy. Further, functional fractions are generally poor feedstocks for conversion. Other than a limited amount of work conducted in using the phenolic fractions for adhesives (35-37), most product research has been concerned with reprocessing the oils into a more useful mixture of compounds, usually fuel hydrocarbons. As detailed above, composition of the oils will depend on pyrolysis process conditions. If the oils are primarily phenolic, then hydrotreating (oxygen removal) is necessary to produce hydrocarbon fuels. Single ring phenolics and cyclic ketones present in the biomass pyrolytic oils can be upgraded through deoxygenation to hydrocarbons (a low oxygen content mixture of all types) in the gasoline (19,29) and diesel (29) boiling point ranges. Heavier, higher molecular weight products like the polycyclic aromatics need also be hydrocracked, with at least partial ring saturation prior to cracking. A number of catalysts have been tried, initially at high pressures with typical petroleum hydrotreating or hydrocracking catalysts (19,29), but more recently at lower pressures with acidic zeolites (e.g., 38,39). Kinetics of the hydrotreating/hydrocracking reactions are being studied (33). Other post-pyrolysis process variations include the treating of primary pyrolysis vapors to gasoline hydrocarbons (40), and pyrolysis oil cofed over zeolite catalyst with methanol derived from char gasification

1.

SOLTES

Of Biomass, Pyrolysis, and Liquids Therefrom

5

(41). New characterization tools such as molecular beam mass spectrometry help in understanding the mechanisms by which wood vapor and related compounds react over catalysts.

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Prospects for Biomass Pyrolysis It's easy to say that the key to commercial implementation of biomass pyrolysis for tar production will be the identification of economically competitive technology for the production of higher-valued products. As the primary virtues of pyrolysis oils are those attributable to petroleum (liquid fuels and, under some pyrolytic conditions, also olefins), it can be assumed that pyrolysis can become an avenue to petroleum-type products from renewable biomass. Is biomass pyrolysis, coupled with oil upgrading, the renewable route to petroleum? Pyrolysis, after all, allows for the production of biomass-derived fuels in efficient-to-use petroleum forms. Fuels are however not the highest values obtainable from biomass (nor are they from petroleum, coal or natural gas), nor oil the only product of pyrolysis - nor is pyrolysis the only, or even most efficient, biomass conversion process. Perhaps biomass pyrolysis can provide the economic base that would permit the further exploitation of the chemical values of biomass materials to enhance overall process profitability (cf. history of olefins usage in petroleum). This author is bold in suggesting that, more appropriately, pyrolysis should be considered as an upgrading process for residues from chemical/ materials options for biomass, that efficient fuel/energy processes such as pyrolysis be considered in tandem with, if not after, efficient biochemical or chemical processing of biomass for polymer and oxychemical production. Biomass is composed of complex structures and polymers that have merit in their complexity, and usage of biomass should first consider chemicals/ materials production based on this complexity, geared to market demand, with only higher entropy states of biomass, process residues, relegated to fuel use status. Literature Cited 1.

2.

3.

4.

5.

6.

Stevens, D.J. "An overview of biomass thermochemical liquefaction research sponsored by the U.S. Department of Energy." In Production, Analysis and Upgrading of Oils from Biomass, Vorres, K.S., Ed., American Chemical Society, Division of Fuel Chemistry Abstracts, 1987, 32(2), 223. Soltes, E.J. "Thermochemical processes for bioenergy production." In Biomass Energy Development, Smith, W.H., Ed., Plenum Press: New York, 1986, 321. Soltes, E.J. "Thermochemical routes to chemicals, fuels and energy from forestry and agricultural wastes." In Biomass Utilization, Cote, W.A., Ed., Plenum Press: New York, 1983, 537. Shafizadeh, F. "Introduction to pyrolysis of biomass." In Proc. Specialists' Workshop on Fast Pyrolysis of Biomass, Copper Mountain, Diebold, J . , Ed., SERI/CP-622-1096, Solar Energy Research Institute: Golden CO, 1980, 79. Shafizadeh, F. "The Chemistry of Pyrolysis and Combustion." In The Chemistry of Solid Wood, Rowell, R.M., Ed. Advances in Chemistry Series 207, American Chemical Society: Washington DC, 1984. DeGroot, W.F.; Pan, W-P.; Rahman, M.D.; Richards, G.N. "Early products of pyrolysis of wood." In Production, Analysis and Upgrading of Oils from Biomass, Vorres, K.S., Ed., American Chemical Society, Division of Fuel Chemistry Abstracts, 1987, 32(2), 36.

6 7. 8. 9. 10. 11.

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12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27.

28.

PYROLYSIS OILS FROM BIOMASS Antal, M.J., Jr. "Biomass pyrolysis: a review of the literature, Part I– carbohydrate pyrolysis." In Adv. in Solar Energy, Boer, K.W.; Duffie, J.W.; Eds., American Solar Energy Society: Boulder CO, 1984, 1, 61. Antal, M.J., Jr. "Biomass pyrolysis: a review of the literature, Part II– lignocellulose pyrolysis." In Adv. in Solar Energy, Boer, K.W.; Duffie, J.W.; Eds., American Solar Energy Society: Boulder CO, 1985, 2, 175. Chatterjee, A.K. State-of-the-Art Review on Pyrolysis of Wood and Agricultural Biomass. Final Report, Contract No. 53-319-R-0-206, AC Project P0380, USDA Forest Service: Washington DC, 1981. Bridgwater, A.V. Thermochemical Processing of Biomass, Butterworths: London, 1984. Overend, R.P.; Milne, T.A.; Mudge, L.K.; Eds. Fundamentals of Thermochemical Biomass Conversion, Elsevier: New York, 1985. Proceedings of the International Thermochemical Biomass Conversion Conference, Phoenix, AR. Elsevier: New York, 1988, in press. Soltes, E.J.; Elder, T.J. "Pyrolysis." In Organic Chemicals from Biomass, Goldstein, I.S., Ed., CRC Press: Boca Raton FL, 1981, 63. Elliott, D.C. "Relation of reaction time/temperature to the chemical composition of pyrolysis oils." In This Volume. Lede, J.; Li, H.Z.; Villermaux, J. "Pyrolysis of biomass: evidences for a fusion-like phenomena." In This Volume. Diebold, J.P.; Scahill, J.W. "Production of primary pyrolysis oils in a vortex reactor." In This Volume. Helt, J.E.; Agrawal, R.K. "Liquids from municipal solid waste." In This Volume. McKeough, P.J.; Johansson, A.A. "Oil production by high-pressure thermal treatment of black liquors: aqueous-phase products." In This Volume. Baker, E.G.; Elliott, D.C. "Catalytic hydrotreating of biomass-derived oils." In This Volume. Boocock, D.G.B.; Allen, S.G.; Chowdhury, Α.; Fruchtl, R. "The production, evaluation and upgrading of oils from the steam liquefaction of poplar chips." In This Volume. Nelson, D.A.; Hallen, R.T.; Theander, O. "Formation of aromatic compounds from carbohydrates: X. Reaction of xylose, glucose and gluconic acid in acidic solution at 300°C." In This Volume. Krochta, J.M.; Hudson, J.S.; Tillin, S.J. "Kinetics of alkaline thermochemical degradation of polysaccharides to organic acids." In This Volume. Bouvier, J.M.; Gelus, M.; Maugendre. S. "Direct liquefaction of wood by solvolysis." In This Volume. Wenzl, H.F.J. The Chemical Technology of Wood. Academic Press: New York, 1970, 267. Piskorz, J.; Scott, J.S.; Radlein, D. "The composition of oils obtained by the fast pyrolysis of different woods." In This Volume. Pakdel, H.; Roy, C. "Chemical characterization of wood oils obtained in a vacuum pyrolysis multiple hearth reactor." In This Volume. Soltes, E.J.; Lin, S-C.K. "Chromatography of non-derivatized pyrolysis oils and upgraded products." In Production, Analysis and Upgrading of Oils from Biomass, Vorres, K.S., Ed., American Chemical Society, Division of Fuel Chemistry Abstracts, 1987, 32(2), 178. Soltes, E.J.; Lin, S-C.K.; Sheu, Y-H.E. "Catalyst specificities in high pressure hydroprocessing of pyrolysis and gasification tars." In Production, Analysis and Upgrading of Oils from Biomass, Vorres,

1. SOLTES

29. 30. 31.

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32. 33. 34. 35. 36.

37. 38. 39. 40. 41. 42.

Of Biomass, Pyrolysis, and Liquids Therefrom

K.S., Ed., American Chemical Society, Division of Fuel Chemistry Abstracts, 1987, 32(2), 229. Soltes, E.J.; Lin, S-C.K. "Hydroprocessing of biomass tars for liquid engine fuels." In Progress in Biomass Conversion, Tillman, D.A.; Jahn,E.C., Eds., Academic Press: New York, 1984, 5, 1. Elliott, D.C.; Sealock, J.J., Jr.; Butner, R.S. "Product analysis from direct liquefaction of several high-moisture biomass feedstocks." In This Volume. Grandmaison, J.L.; Ahmed, Α.; Kalaiguine, S. "Solid residues from supercritical extraction of wood: characterization of their constituents." In This Volume. Hoesterey, B.L.; Windig, W.; Meuzelaar, H.L.C.; Eyring, E.M.; Grant, D.M.; Pugmire, R.J. "An integrated spectroscopic approach to the chemical characterization of pyrolysis oils." In This Volume. Sheu, Y-H.E. Kinetic Studies of Upgrading Pine Pyrolytic Oil by Hydrotreatment, Ph.D. Dissertation, Texas A&M University, 1985. Johnson, D.K.; Chum, H.L. "Some aspects of pyrolysis oils characterization by high performance size exclusion chromatography (HPSEC)." In This Volume. Elder, T.J. The Characterization and Potential Utilization of the Phenolic Compounds Found in a Pyrolytic Oil, Ph.D. Dissertation, Texas A&M University, 1981. Chum, H.; Diebold, J.; Scahill.; Johnson, D.K.; Black, S.; Schroeder, H.A.; Kreibich, R.E. "Biomass pyrolysis oil feedstocks for phenolic adhesives". In Adhesives from Renewable Resources, Conner, Α.; Hemingway, R., Eds., American Chemical Society: Washington DC, 1988, in press. Soltes, E.J.; Lin, S-C.K. "Adhesives from natural resources." In Progress in Biomass Conversion, Tillman, D.A.; Jahn,E.C., Eds., Academic Press: New York, 1983, 4, 79. Renaud, M.; Grandmaison, J.L.; Roy, C.; Kaliaguine, S. "Low pressure upgrading vacuum pyrolysis oils from wood." In This Volume. Dao, L.H.; Haniff, M.; Houle, Α.; Lamothe, D. "Reactions of model compounds of biomass pyrolysis oils over ZSM-5 zeolite catalysts." In This Volume. Diebold, J.P.; Scahill, J.W. "Biomass to gasoline (BTG): upgrading pyrolysis vapors to aromatic gasoline with zeolite catalysts at atmospheric pressure." In This Volume. Chen, N.Y.; Walsh, D.E.; Koenig, L.R. "Fluidized bed upgrading of wood pyrolysis liquids and related compounds." In This Volume. Evans, R.J.; Milne, T.A. "Molecular beam mass spectrometric studies of wood vapor and model compounds over HZSM-5 catalyst." In This Volume.

RECEIVED May 26, 1988

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Chapter 2

Biomass Pyrolysis Technology and Products A Canadian Viewpoint

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch002

R. D. Hayes Renewable Energy Branch, Energy, Mines, and Resources, Ottawa, Canada K1A 0E4 By way of introduction, this paper presents four "views" on pyrolysis, including an international view, a technical review, a strategic point of view, and a general Canadian bioenergy overview. From a basic definition of pyrolysis as the thermal conversion of material in the absence of oxygen, the following discussion includes vacuum, atmospheric and pressurized pyrolysis technologies for the production of gas, liquid, or char products.

Canadian B i o e n e r g y

Overview

Canada i s w e l l endowed w i t h energy a l t e r n a t i v e s t o c o n v e n t i o n a l petroleum. A number o f these r e s o u r c e s a r e v a s t , i n c l u d i n g t a r s a n d s , a r c t i c and o f f s h o r e o i l , n a t u r a l gas, c o a l , n u c l e a r , b i o e n e r g y and o t h e r renewables. They a r e a l s o , i n g e n e r a l , e x p e n s i v e r e l a t i v e t o c u r r e n t domestic and imported l i g h t crude o i l p r i c e s . B i o e n e r g y , however, has c a r r i e d out an i m p r e s s i v e impact on Canada's p r i m a r y energy s u p p l y , by r i s i n g from 3% i n 1978 t o 6.8% i n 1987. I t s c u r r e n t c o n t r i b u t i o n s i n t h e i n d u s t r i a l and r e s i d e n t i a l s e c t o r s a r e 17% and 14%, r e s p e c t i v e l y . Most o f t h e o i l s u b s t i t u t i o n from biomass i n Canada has been i n l i g h t and heavy f u e l o i l markets. So f a r , very few o f Canada's a l t e r n a t i v e s have made much impact i n t h e t r a n s p o r t a t i o n s e c t o r , n o r a r e t h e r e any obvious e x p e c t a t i o n s o f near-term o i l s u b s t i t u t i o n i n t r a n s p o r t a t i o n o t h e r than a s m a l l n i c h e o f v e h i c l e s running on propane o r n a t u r a l g a s . A g a i n s t t h i s backdrop, Canadian b i o e n e r g y R&D i s very b r o a d l y t a r g e t t e d t o near-term o p p o r t u n i t i e s f o r n o n - t r a n s p o r t a t i o n uses and t o medium and l o n g e r term o p p o r t u n i t i e s f o r t r a n s p o r t a t i o n uses. The term " b r o a d l y " i s emphasized because t h e r e a r e e x c e p t i o n s t o this generalization. Canada's b i o e n e r g y R&D a c t i v i t i e s d i d not b e g i n i n e a r n e s t u n t i l 1978, l a g g i n g somewhat behind other p a r t s o f t h e w o r l d . I n 1980, t h e f e d e r a l N a t i o n a l Energy Program g r e a t l y i n c r e a s e d R&D f u n d i n g i n 0097-6156/88/0376-0008$06.00/0 © 1988 American Chemical Society

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HAYES

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Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch002

a l l c o n s e r v a t i o n and a l t e r n a t i v e energy a r e a s . B i o e n e r g y R&D e f f o r t grew t o $22 m i l l i o n (Cdn) i n 1983-84. Then as o i l p r i c e s s e t t l e d , Canada's energy R&D program e x p e r i e n c e d the "Crash of '84" the government decreased spending by 50%. Bioenergy R&D i s c u r r e n t l y c e n t r e d i n two f e d e r a l departments. Energy, Mines and Resources Canada manages the Bioenergy Development Program a t a p p r o x i m a t e l y $6 m i l l i o n (Cdn) f o r biomass c o n v e r s i o n , and a l e v e l of a p p r o x i m a t e l y $1.5 m i l l i o n (Cdn) f o r biomass p r o d u c t i o n i s managed by t h e Canadian Forestry Service. An approximate breakdown o f 1987 Bioenergy C o n v e r s i o n R&D e x p e n d i t u r e s i n g e n e r a l t e c h n o l o g y areas i s as f o l l o w s : Biochemical conversion Thermochemical c o n v e r s i o n Combustion Biomass h a n d l i n g and p r e p a r a t i o n Peat mining and p r o c e s s i n g Information t r a n s f e r

39% 16% 22% 12% 6% 5%

Of s p e c i a l i n t e r e s t t o the audience o f t h i s paper i s t h a t t h e bulk of t h e thermochemical R&D i s devoted t o some form or o t h e r of pyrolysis. H i s t o r y and S t r a t e g y , 1978-1987 Amidst the p a n i c of petroleum s h o r t a g e s and r i s i n g p r i c e s o f 1979, some i n d i v i d u a l s expected t o produce o i l s from biomass, a l s o known as b i o - c r u d e , p r o t o - o i l , bunker b i o - o i l . . . T h i s e x p e c t a t i o n was f a i r l y s h o r t - l i v e d however. A l t h o u g h t o u t e d as something, someday d e s t i n e d t o r e p l a c e o r reduce o i l i m p o r t s , p y r o l y s i s o i l from biomass had very l i t t l e i n common w i t h p e t r o l e u m . Its q u a l i f i c a t i o n s as "a crude" were very rudimentary. I t looked b l a c k , s m e l l e d bad, and u s u a l l y f l o w e d i f t h e r e was enough water i n i t ; but t h a t i s where the resemblance ended. Biomass, i n those days, was modelled by some r e s e a r c h e r s as a young c o a l , and i t s p y r o l y s i s o i l as a young o i l or a c o a l l i q u i d . N e i t h e r assumption was very a c c u r a t e . Those who f o l l o w e d c o a l l i q u e f a c t i o n development had a head s t a r t i n a p p l y i n g t h a t enormous knowledge base t o biomass. However, perhaps due t o t h a t knowledge base, e a r l y biomass p r o c e s s development d i d not f u l l y t a k e advantage of t h e unique o p p o r t u n i t y f o r s p e c i a l i z e d p r o c e s s i n g t h a t biomass c o u l d p r o v i d e . Biomass i s not a homogeneous c h e m i c a l conglomerate, but r a t h e r a composite of t h r e e major polymers namely c e l l u l o s e , h e m i c e l l u l o s e and l i g n i n . A g a i n s t t h i s background, Canadian r e s e a r c h e r s j o i n e d the i n t e r n a t i o n a l f l u r r y of r e s e a r c h a c t i v i t y i n t h i s a r e a . By 1980, t h e r e were t w e l v e l a b o r a t o r i e s , mostly u n i v e r s i t i e s , i n v o l v e d i n some v a r i a t i o n of biomass p y r o l y s i s r e s e a r c h . The major f o c u s of t h e i r work was t o produce a f u e l o r h e a t i n g o i l . There was v e r y l i t t l e work done on upgrading b i o - o i l t o a t r a n s p o r t a t i o n f u e l or ven a r e f i n e r y f e e d s t o c k . A l s o , t h e r e was l i t t l e i n t e r e s t i n the o p t i m i z e d p r o d u c t i o n of gas or char i n Canada s i n c e Canada i s b l e s s e d w i t h s u b s t a n t i a l r e s e r v e s o f n a t u r a l gas and c o a l .

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PYROLYSIS OILS FROM BIOMASS

In 1980, the f e d e r a l government embraced an " o f f - o i l " p o l i c y under the N a t i o n a l Energy Program. A number of programs p r o v i d e d a s s i s t a n c e d i r e c t l y or i n d i r e c t l y t o homeowners and i n d u s t r y f o r s u b s t i t u t i n g heavy and l i g h t f u e l o i l , by o t h e r energy forms such as n a t u r a l gas, e l e c t r i c i t y and biomass ( v i a c o m b u s t i o n ) . 3 i o - o i l was not t e c h n i c a l l y ready t o t a k e advantage of a market o p p o r t u n i t y , and more i m p o r t a n t l y , i t had no commercial or i n d u s t r i a l i n f r a s t r u c t u r e t o b u i l d upon. T h e r e f o r e , i n s p i t e o f w o r l d r e c o r d p e t r o l e u m p r i c e s , apparent s h o r t f a l l s i n imported and domestic o i l s u p p l i e s , and a p o l i c y environment t h a t was a c t i v e l y encouraging energy a l t e r n a t i v e s i n Canada, b i o - o i l became a long term c u r i o s i t y . R&D was i m p o r t a n t , but i t was supported under the o b j e c t i v e of long term s e c u r i t y of s u p p l y of l i q u i d f u e l s . Canada's R&D e f f o r t s c o n t i n u e d t o down-play upgrading over the next f o u r y e a r s and c o n c e n t r a t e d almost e x c l u s i v e l y on p r i m a r y o i l p r o d u c t i o n . By 1984, o i l p r i c e s appeared t o be more s e t t l e d and the time frame f o r c o m m e r c i a l i z i n g t r a n s p o r t a t i o n f u e l s from b i o - o i l was l i k e l y t o be w e l l beyond 2000. There appeared t o be p l e n t y of time t o p e r f e c t o i l upgrading a t a l a t e r d a t e , e i t h e r through h y d r o t r e a t i n g or u s i n g s h a p e - s e l e c t i v e z e o l i t e c a t a l y s i s . Then came t h e "Crash of '84" r e f e r r e d t o e a r l i e r . B i o e n e r g y R&D f u n d i n g r e s o u r c e s were d e c l i n i n g r a p i d l y . Government seemed t o want more near term r e s u l t s from an a l r e a d y s h r i n k i n g energy f u n d i n g base. Between 1980 and 1984, biomass p y r o l y s i s R&D f u n d i n g had been s l o w l y i n c r e a s i n g w h i l e the number o f Canadian l a b o r a t o r i e s working i n t h i s a r e a had decreased from t w e l v e t o s i x . By 1984/85 thermochemical R&D and o t h e r long-term o p t i o n s w i t h i n the Bioenergy Development Program o f Energy, Mines and Resources had become v u l n e r a b l e t o f u n d i n g r e d u c t i o n s . I t was important not t o l o s e t h e advances a l r e a d y a c h i e v e d and the w o r l d c l a s s e x p e r t i s e developed i n Canada. The d e c i s i o n was t a k e n t h e r e f o r e t o wind up the r e s e a r c h i n Canada over the next two t o t h r e e y e a r p e r i o d i n o r d e r t o l e a v e a r e t r i e v a b l e a c c o u n t i n g of developments f o r f u t u r e r e s e a r c h e r s . The second o b j e c t i v e was t o m a i n t a i n ( o r s a l v a g e ) a base c o r e of e x c e l l e n c e i n Canada a t a reduced f u n d i n g l e v e l s . T h i s d e c i s i o n d i d not u n f o l d as planned however. Three y e a r s l a t e r , the Canadian program i n p y r o l y s i s i s s t r o n g e r than e v e r . The 1987 R&D program o f work i n c l u d e s work i n f i v e o f the s i x l a b o r a t o r i e s , a t f u n d i n g l e v e l s s l i g h t l y h i g h e r than i n 1984. The f o l l o w i n g t h r e e e x p l a n a t i o n s can h e l p e x p l a i n why t h e s t r a t e g i c p l a n changed so f u n d a m e n t a l l y . 1. I n d u s t r y I n t e r e s t . One o f Canada's l e a d i n g s o l a r and biomass c o n v e r s i o n equipment companies, Petro-Sun I n t e r n a t i o n a l I n c . became i n t e r e s t e d i n s c a l i n g up the Université Laval/Université de Sherbrooke vacuum p y r o l y s i s p r o c e s s on a c o s t - s h a r e d b a s i s . S p e c i a l Note. As o f January 1988, Petro-Sun I n t e r n a t i o n a l I n c . was f o r c e d i n t o r e c e i v e r s h i p f o r reasons u n r e l a t e d t o t h e i r a c t i v i t i e s i n biomass p y r o l y s i s . The Université L a v a l i s s e e k i n g a l t e r n a t i v e i n d u s t r i a l p a r t n e r s . Another company, Ensyn E n g i n e e r ing L t d . , was e s t a b l i s h e d , and proposed a c o s t - s h a r e d , s c a l e d - u p development of the U n i v e r s i t y of Western O n t a r i o u l t r a p y r o l y s i s . S i m i l a r l y , t h e r e has been a number of i n d u s t r i a l e x p r e s s i o n s o f i n t e r e s t i n t h e U n i v e r s i t y of Waterloo f l a s h p y r o l y s i s .

2. HAYES 2.

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Diversification. An approach has e v o l v e d i n Canada whereby, u n l i k e e a r l i e r e f f o r t s , a whole range o f p r o d u c t s and r e a c t a n t s a r e now c o n s i d e r e d . Products include o i l s of varying q u a l i t y , sugar s o l u t i o n s i n h i g h y i e l d , c h e m i c a l s ( o l e f i n s , p h e n o l i c s , as w e l l as h i g h v a l u e s p e c i a l t y c h e m i c a l s ) , g a s o l i n e o r d i e s e l f u e l , and h i g h e r v a l u e c a r b o n . D i v e r s i f i c a t i o n of reactants i n c l u d e whole biomass (wood and s t r a w ) , f r a c t i o n a t e d biomass components, p e a t , m u n i c i p a l s o l i d waste, i n c l u d i n g used t i r e s , etc. Another important a r e a o f r e s e a r c h i s t h e t r e a t m e n t , and e s p e c i a l l y , t h e c o n v e r s i o n , o f waste aqueous e f f l u e n c e from p y r o l y s i s i n t o value-added c o - p r o d u c t c r e d i t s . Left unprocessed, t h e s e e f f l u e n c e would o t h e r w i s e i n c u r a c o s t f o r waste t r e a t m e n t . TEA C o l l a b o r a t i o n . By working t o g e t h e r w i t h t h r e e o t h e r member c o u n t r i e s o f t h e I n t e r n a t i o n a l E n e r g y Agency's B i o e n e r g y Agreement, Canada has been a b l e t o combine r e s o u r c e s w i t h USA, Sweden, and F i n l a n d t o d e t e r m i n e t h a t Canadian biomass p y r o l y s i s t e c h n o l o g i e s appear t o be as good as any i n t h e w o r l d . Canada has a l s o had i t s p y r o l y s i s o i l s upgraded and a s s e s s e d by c o l l a b o r a t o r s i n t h e USA· P r e l i m i n a r y r e s u l t s i n d i c a t e t h a t Canada s h o u l d review i t s t r a d i t i o n a l s t r a t e g y o f n o t immediately p u r s u i n g u p g r a d i n g R&D.

T e c h n i c a l Review Over t h e p a s t s e v e r a l y e a r s r e s e a r c h e r s W.J.M. Douglas and D.G. Cooper a t M c G i l l u n i v e r s i t y have been s t u d y i n g an i n t e r e s t i n g thermochemical approach t o wood l i q u e f a c t i o n u s i n g aqueous hydrogen i o d i d e i n f a i r l y m i l d c o n d i t i o n s o f p r e s s u r e and temperature (125°C). S t i l l f a r from c e r t a i n i s t h e e x a c t n a t u r e o f t h e l i q u i d p r o d u c t s and t h e techno-economic p r a c t i c a l i t y o f hydrogen i o d i d e r e c o v e r y and r e c y c l e . On t h e p o s i t i v e s i d e , i n a d d i t i o n t o t h e low s e v e r i t y c o n d i t i o n s o f r e a c t i o n , t h e p r o c e s s removes about 80% o f the oxygen i n t h e wood, and t h e c h a r y i e l d i s v e r y low. D.G.B. Boocock and co-workers a t t h e U n i v e r s i t y o f T o r o n t o have u n d e r t a k e n t h e i n v e s t i g a t i o n o f a steam p y r o l y s i s o r h y d r o t h e r m o l y s i s o f wood. Based on t h e i r e a r l i e r work, they r e c e n t l y d e s i g n e d and c o n s t r u c t e d a l a b o r a t o r y s c a l e c a s c a d e a u t o c l a v e which c a n accommodate up t o 100 g o f wood c h i p s o r 170g o f a s i n g l e l a r g e r p i e c e (3.8 cm r e a c t o r I.D., 600ml volume). It i s r a t e d a t 24.1 MPa (3500 p s i . ) a t 350°C a l l o w i n g f o r 7.6 MPa (1100 p s i ) gas o v e r p r e s s u r e above t h e vapour p r e s s u r e o f water a t t h a t temperature. R e s u l t s t o d a t e a r e p r e l i m i n a r y s i n c e t h e u n i t was commissioned o n l y i n e a r l y 1987. Reproduced r e s u l t s i n d i c a t e t h a t o i l y i e l d i n c r e a s e s with increased c h i p s i z e . Product o i l y i e l d s a r e v e r y h i g h (up t o 50%) w i t h no s o l i d s c o n t a m i n a t i o n , and t h e o i l i s e a s i l y s e p a r a b l e from t h e aqueous phase. Coupled w i t h an upgrading p r o c e s s , t h i s t e c h n o l o g y may someday w e l l l e n d i t s e l f w e l l to commercialization. I n a d d i t i o n t o t h e i r p r o c e s s development work, Boocock's group has c o n t r i b u t e d g r e a t l y t o t h e b a s i c u n d e r s t a n d i n g o f biomass l i q u e f a c t i o n , e s p e c i a l l y through t h e i r s c a n n i n g e l e c t r o n m i c r o s c o p i c s t u d i e s . Of p o t e n t i a l i n t e r e s t t o o i s t h e i r d i s c o v e r y i n 1984 t h a t a p a r t i c u l a r c l o n e o f h y b r i d p o p l a r y i e l d e d 6% p h e n o l .

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PYROLYSIS OILS FROM BIOMASS

Ε . Chornet, R.P. Overend and co-workers a t t h e Université de Sherbrooke have been working on a l i q u e f a c t i o n p r o c e s s i n p r e s s u r i z e d s o l v e n t f o r some y e a r s . T h e i r approach i n v o l v e s an o v e r a l l i n t e g r a t i o n o f biomass p r e t r e a t m e n t , f r a c t i o n a t i o n , a c i d p r o c e s s i n g , thermochemical and b i o c h e m i c a l t r e a t m e n t . D.S. S c o t t , J . P i s k o r z , D, R a d l e i n and co-workers a t t h e U n i v e r s i t y o f Waterloo a r e w e l l known f o r t h e i r f l u i d i z e d bed f l a s h p y r o l y s i s development, a l s o known as t h e WFPP (Waterloo P a s t P y r o l y s i s P r o c e s s ) . The WPPP a c t u a l l y i n c l u d e s f o u r p r o c e s s o p t i o n s as f o l l o w s : 1. D i r e c t t h e r m a l p r o c e s s i n g a t 450-550°C, atmospheric p r e s s u r e and about 500 ms vapour r e s i d e n c e t i m e . They r e p o r t t h e h i g h e s t l i q u i d y i e l d s (80% i n c l u d i n g water, based on i n p u t wood) t h a t i s a suitable f u e l f o r conventional b o i l e r s . 2. By v a r y i n g t h e p r o c e s s c o n d i t i o n s and a d o p t i n g a m i l d s u l p h u r i c a c i d p r e t r e a t m e n t f o l l o w e d by f l u i d i z e d bed t h e r m o p y r o l y s i s , t h e WPPP produces a h i g h y i e l d and c o n c e n t r a t i o n o f a n h y d r o - o l i g o s a c c h a r i d e s , mostly l e v o g l u c o s a n r a t h e r than o i l p r o d u c t s . T h e i r r e p r o d u c i b l e y i e l d s o f sugars from pure c e l l u l o s e a r e about 80% i n a c o n c e n t r a t e d form. One c a n e a s i l y s p e c u l a t e whether t h i s development c o u l d c h a l l e n g e some o f t h e e q u a l l y e x c i t i n g b i o c o n v e r s i o n methods o f c o n v e r t i n g l i g n o c e l l u l o s i c s t o fermentable sugars. 3. Waterloo's h y d r o g a s i f i c a t i o n work has been t e c h n i c a l l y h i g h l y s u c c e s s f u l , r e s u l t i n g i n 75% c o n v e r s i o n o f carbon from wood t o methane v i a p y r o l y s i s over a n i c k e l - a l u m i n a c a t a l y s t w i t h hydrogen a t about 550°C and 440 ms r e s i d e n c e t i m e . 4. Under c u r r e n t i n v e s t i g a t i o n i s a f o u r t h p r o c e s s o p t i o n s o f p r o d u c i n g u n s a t u r a t e d hydrocarbons i n a c a t a l y s e d r e a c t i o n . A p a r t from t h e use of c a t a l y s t s , t h e p r o c e s s equipment and o p e r a t i n g c o n d i t i o n s a r e very s i m i l a r f o r a l l o f t h e above process o p t i o n s . M. Bergougnou, R. Graham and co-workers have developed an U l t r a - R a p i d P y r o l y s i s or U l t r a p y r o l y s i s process at the U n i v e r s i t y of Western O n t a r i o . A l t h o u g h t h e r e a r e s i m i l a r i t i e s i n t h i s work and the r e s e a r c h a t t h e U n i v e r s i t y o f W a t e r l o o , t h e r e a r e important d i f f e r e n c e s . Whereas Waterloo u t i l i z e s f l u i d i z e d bed heat t r a n s f e r , Bergougnou employees a very r a p i d (30ms) m i x i n g and heat t r a n s f e r i n a v o r t i c a l c o n t a c t o r o r v o r t a c t o r f o l l o w e d by a p l u g - f l o w e n t r a i n e d bed down f l o w r e a c t o r (50-900ms) and quenching (30ms) w i t h c r y o g e n i c n i t r o g e n i n a c r y o v o r t a c t o r . A l s o d i s s i m i l a r t o t h e Waterloo p r o c e s s a r e t h e p r o c e s s c o n d i t i o n s (650-1000°C, 50-900 ms r e s i d e n c e time) and t h e main product a t t h e s e temperatures i s gas r a t h e r than liquid. S i n c e p y r o l y t i c f u e l gas p r o d u c t i o n has not been o f h i g h p r i o r i t y i n Canada's b i o e n e r g y R&D s t r a t e g y , t h e c u r r e n t o b j e c t i v e , i n c o l l a b o r a t i o n w i t h Ensyn E n g i n e e r i n g , i s c h e m i c a l p r o d u c t i o n , olefins i n particular. Tt i s i n t e r e s t i n g t o note here t h a t t h e U n i v e r s i t i e s o f Waterloo and Western O n t a r i o conducted an experiment of d a t a comparison from each o f t h e i r r e a c t o r systems. U s i n g s e l e c t e d d a t a from both groups at around 500 ms r e s i d e n c e t i m e , l i q u i d and gas p r o d u c t i o n d a t a were p l o t t e d vs temperature. The temperature ranges were as f o l l o w s : Waterloo a t 400°-750°C, and Western O n t a r i o a t 650°-900°C. With combined d a t a f o r each o f t h e gas y i e l d vs temperature and l i q u i d

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch002

2.

HAYES

Biomass Pyrolysis Technology and Products

13

y i e l d vs temperature d a t a , t h e r e was, as expected, c o n s i d e r a b l e c o n c u r r e n c e o f o v e r l a p p i n g d a t a . In f a c t a s i m p l e f i r s t o r d e r k i n e t i c model i s a b l e t o d e s c r i b e the o i l y i e l d over t h e temperature range o f both e x p e r i m e n t s , Rnsyn E n g i n e e r i n g i s a r e c e n t l y formed company whose p r i n c i p a l i n v e s t i g a t o r , R. Graham has s c a l e d up the u n i v e r s i t y of Western O n t a r i o U l t r a p y r o l y s i s r e a c t o r by a f a c t o r o f 20 t o a 5-10 kg/hr c a p a c i t y RTP ( R a p i d Thermal P r o c e s s o r ) , The r e a c t o r i s designed t o accept any carbonaceous feed ( s o l i d , l i q u i d , or gas) by i n j e c t i n g i n t o a t u r b u l e n t c l o u d of hot s o l i d s . The mixed f e e d p l u s s o l i d s i s c a r r i e d through a t u b u l a r t r a n s p o r t r e a c t o r t o an i n e r t i a l s e p a r a t o r where vapour p r o d u c t s a r e removed. R e s u l t s t o date a r e very p r e l i m i n a r y . The concept f o r m u l a t e d by Ensyn i s t h a t t h e RTP would be a c e n t r a l p r o c e s s o r of p r i m a r y p y r o l y s i s o i l s from s m a l l e r , perhaps m o b i l e , p l a n t s . The m u l t i - s t a g e vacuum p y r o l y s i s was developed by C. Roy and co-workers, i n i t i a l l y at the Université de Sherbrooke and, c u r r e n t l y , a t the Université L a v a l . In c o l l a b o r a t i o n w i t h Petro-Sun I n t e r n a t i o n a l I n c . t h e r e i s a p i l o t d e m o n s t r a t i o n of a s i n g l e - s t a g e p l a n t at St-Amable, Quebec. The u n i t has a c a p a c i t y of 200 kg/hr and i s designed f o r used t i r e s . The t e c h n o l o g y i s based on a m u l t i p l e h e a r t h vacuum p y r o l y s i s p r o c e s s development u n i t l o c a t e d near t h e Université L a v a l and o p e r a t i n g at a 30 kg/hr biomass capacity. A l t h o u g h the m u l t i p l e h e a r t h concept s u f f e r s from low heat t r a n s f e r r e l a t i v e t o o t h e r p y r o l y s i s p r o c e s s e s , and, a t f i r s t g l a n c e , i s c a p i t a l c o s t i n t e n s i v e , i t has a number of f e a t u r e s t h a t show commercial promise as f o l l o w s : 1. A r e a s o n a b l y h i g h y i e l d of p y r o l y s i s o i l (50% based on wood). 2. The p r o d u c t i o n of co-product c a r b o x y l i c a c i d s and h i g h v a l u e chemicals. 3. R e a c t i v e c h a r c o a l a t 25% of i n p u t wood. 4. The aqueous phase i s recovered s e p a r a t e l y as p a r t of the p r o c e s s l e a v i n g a w a t e r - f r e e p y r o l y s i s o i l ready f o r u p g r a d i n g . 5. The m u l t i p l e h e a r t h performs a product f r a c t i o n a t i o n f u n c t i o n t h a t c o u l d reduce e x t r a c t i o n c o s t s of h i g h v a l u e c h e m i c a l s . Centralized Analysis One f i n a l work of i n t e r e s t i n Canada i s the C e n t r a l i z e d A n a l y s i s p r o j e c t at B.C. Research. I n 1984, a t r i a l p r o j e c t was set-up whereby d i f f e r e n t Canadian b i o - o i l s c o u l d be compared i n a c o n s i s t e n t manner. The p r o j e c t embraced a three-pronged approach. Under t h e guidance o f J . Howard and J . M c K i n l e y , B.C. Research performed and/or c o o r d i n a t e d the c e n t r a l i z e d a n a l y s e s o f o p t i m i z e d o i l s produced by each r e s e a r c h e r . I f a p a r t i c u l a r a n a l y t i c a l c a p a b i l i t y was not a v a i l a b l e a t B.C. R e s e a r c h , another l a b o r a t o r y w i t h t h a t s t r e n g t h was c o n t r a c t e d t o do i t . I n d i v i d u a l r e s e a r c h e r s a l s o d i d some of t h e i r own a n a l y s e s t o o b t a i n immediate e x p e r i m e n t a l feedback. The second prong o f the approach was t h a t a l l r e s e a r c h e r s were p r o v i d e d w i t h a s t a n d a r d wood sample Populus deltoïdes by P o r i n t e k Canada Corp. The i d e a was t h a t when each p r o c e s s development became somewhat o p t i m i z e d , the r e s e a r c h e r would submit o i l from the s t a n d a r d wood sample t o the c e n t r a l i z e d a n a l y s i s team.

14

PYROLYSIS OILS FROM BIOMASS

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch002

The t h i r d prong was a computer communications network l i n k c a l l e d CoSy, through the u n i v e r s i t y o f Guelph, t o p r o v i d e f a s t communication of a n a l y t i c a l d a t a . I t was a l s o used t o encourage m u l t i l a t e r a l and b i l a t e r a l c o l l a b o r a t i o n and problem s o l v i n g . The c e n t r a l i z e d a n a l y s i s p r o j e c t i s e n t e r i n g Phase I I . Learning from the s u c c e s s e s and p i t f a l l s of the f i r s t two and one h a l f y e a r s , the scope of t h i s p r o j e c t has changed somewhat. The consensus of program managers and r e s e a r c h e r s i s t h a t Phase I I w i l l have two major t a s k s . Task 1 i s a s e t o f a n a l y t i c a l t e c h n i q u e s a l o n g the same l i n e s as the i n i t i a l p r o j e c t except the methods t h a t were c o n s i d e r e d t o be l e s s i n t e r e s t i n g t o the e n t i r e group a r e not i n c l u d e d . The b a s i c a n a l y s e s i n c l u d e the f o l l o w i n g : -

Elemental

-

Water Content Density Carboxylic Acids Gas L i q u i d Chromatography Carbon-13 NMR G e l P e r m e a t i o n Chromatography

Analysis

Task 2 c o n s i s t s l a r g e l y of s p e c i a l a n a l y t i c a l p r o j e c t s t o meet the needs of i n d i v i d u a l s or groups of thermochemical c o n v e r s i o n r e s e a r c h e r s t h a t may a r i s e over the next two years. I n t e r n a t i o n a l View -

IEA

Under the I n t e r n a t i o n a l E n e r g y Agency, e l e v e n c o u n t r i e s s i g n e d a t h r e e y e a r B i o e n e r g y Implementing Agreement, e f f e c t i v e January 1, 1986 - December 31, 1988. Canada, USA, Sweden and F i n l a n d agreed t o c o l l a b o r a t e on a p r o j e c t e n t i t l e d D i r e c t Biomass L i q u e f a c t i o n (DBL). A Working Group o f e n g i n e e r s and o t h e r s p e c i a l i s t s a r e p r e p a r i n g a d e t a i l e d t e c h n i c a l - e c o n o m i c assessment (TEA) f o r s c a l e - u p and o p e r a t i o n a t commercial s i z e , o f the most p r o m i s i n g h i g h and low p r e s s u r e p y r o l y s i s p r o c e s s e s . Both p r i m a r y o i l p r o d u c t i o n and upgrading a r e c o n s i d e r e d i n the TEA. The u p g r a d i n g work on Canadian a t m o s p h e r i c and vacuum p y r o l y s i s o i l s has been conducted by D. E l l i o t a t B a t e l l e P a c i f i c Northwest L a b o r a t o r i e s . Y i e l d s of p r o d u c t s i n the g a s o l i n e b o i l i n g range have so f a r reached 35% of p r i m a r y o i l by h y d r o t r e a t i n g . The Working Group i s a t t e m p t i n g two t y p e s of a n a l y s e s , one based on c u r r e n t s t a t e of the a r t and the second based on p r o j e c t e d improvements and developments i n the technologies. Canada has b e n e f i t t e d g r e a t l y from t h i s p r o j e c t . In a f u n d i n g environment t h a t r e s t r i c t e d major t h r u s t s i n u p g r a d i n g R&D i n Canada's n a t i o n a l program, t h e r e i s t h i s element a v a i l a b l e i n the i n t e r n a t i o n a l program. Another b e n e f i t t o Canada i s t h a t the IEA Working Group, independent of s e l f - i n t e r e s t s or b i a s e s toward the v a r i o u s processes, concluded that Canadian primary p y r o l y s i s o i l s have t e c h n i c a l and economic advantages t o o t h e r p r o c e s s e s under development.

2. HAYES

Biomass Pyrolysis Technology and Products

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch002

Acknowledgments The a u t h o r wishes t o acknowledge the v a r i o u s r e s e a r c h e r s a c r o s s Canada w i t h o u t whose i d e a s , open d i s c u s s i o n , and d e d i c a t i o n t o r e s e a r c h i n thermochemical c o n v e r s i o n o f biomass, t h i s paper would not have been p o s s i b l e . Each has c o n t r i b u t e d t o t h i s paper, e i t h e r d i r e c t l y or i n d i r e c t l y . The f o l l o w i n g l i s t i s not c o m p l e t e , but i n c l u d e s t h e p r i n c i p a l i n v e s t i g a t o r s i n Canadian l a b o r a t o r i e s and other notable i n t e r n a t i o n a l c o l l a b o r a t o r s . In a l p h a b e t i c a l order, many thanks t o Narendra B a k h s h i , Dave Beckman, Dave Boocock, Jean Bouchard, M a u r i c e Bergougnou, E s t e b a n C h o r n e t , Helena Chum, J i m D i e b o l d , Murray D o u g l a s , D i c k E a g e r , Doug E l l i o t , Bob Graham, John Howard, Serge K a l i a g u i n e , B j o r n K j e l l s t r o m , Tom M i l n e , Hugh Menard, J i m M c K i n l e y , R a l p h Overend, Hooshang P a k d e l , J i m Pepper, Jan P i s k o r z , Desmond R a d l e i n , Tom Reed, C h r i s t i a n Roy, Don S c o t t , Jacques S i c o t t e , and t h e i r many c o l l e a g u e s , s t a f f , and s t u d e n t s . References This paper contains technical contributions from a l l the Canadian and other work mentioned here. The reader is referred to these articles as primary references. RECEIVED June 10,

1988

15

Chapter 3

Processing of Wood Chips in a Semicontinuous Multiple-Hearth Vacuum-Pyrolysis Reactor

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch003

Christian Roy, Richard Lemieux, Bruno de Caumia, and Daniel Blanchette Department of Chemical Engineering, Université Laval, Sainte-Foy, Quebec F1K 7P4, Canada A process for the pyrolysis under vacuum of biomass and waste materials has been under development since 1978 in Canada. Background data regarding the yields and qualities of the pyrolysis products derived from materials such as wood, bark, agricultural residues, peat, municipal solid wastes, activated sludges and scrap tires, have been obtained at the bench scale level. A Process Development Unit having a feedthrough capacity of up to 25 kg h and using a multiple-hearth furnace reactor has been designed and built. The objectives of the P.D.U. was twofold. First, the unit was used to determine engineering data such as the overall thermal efficiency and the heat requirement for the reactions. Secondly, the configuration and mechanical operation of the ractor had to be tested before its scale-up for the pilot plant phase of the project. This paper reports on the role of several process parameters which are key factors to be considered for the design of a biomass vacuum pyrolysis unit. -1

The thermal decomposition of wood into charcoal and tar i s an old process. One example of the e x i s t i n g technology f o r wood carbonization i s the Lambiotte process. The ATOCHEM plant located in Premery, France, i s based on the p r i n c i p l e of external gas c i r c u l a t i o n and i s a completely continuous process (1). The heating gas moves upward in the retort and constantly releases i t s heat into the wood, which i s moving downward. The annual wood charcoal production of this plant i s currently 20 000 t. The charcoal finds i t s use i n barbecues and the iron industries. Another example i s the B r a z i l i a n beehive k i l n f o r charcoal production i n a batch mode, i n B r a z i l , charcoal i s mainly sold to the iron, the cement and the barbecue industries. In 1985, the t o t a l annual production of wood charcoal i n B r a z i l was 8,7 Χ 10 t (2). 6

β

0097-6156/88/0376-0016$06.00/0 1988 American Chemical Society

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch003

3. ROY ET AL.

Processing of Wood Chips in a Pyrolysis Reactor

17

The recovery of by-products i s important f o r the economy o f both processes. The French recover high-value chemicals such as food aromas from the pyroligneous liquors (3). The B r a z i l i a n s market the wood tar by-product as a bunker fuel o i l (2). However, further studies are s t i l l needed and are being conducted by the industry in order to make a better use o f the tar and o i l fractions. Laboratory (4) and Process Development Unit (5*6) studies o r i g i n a l l y conducted at the Université de Sherbrooke, and now conducted j o i n t l y with the private industry at Université Laval, province of Quebec, have led to the conclusion that thermal decomposition under reduced pressure i s an a t t r a c t i v e approach f o r the conversion o f biomass into chemicals and fuels products. The process uses a multiple-hearth furnace for wood p y r o l y s i s . This approach i s characterized by a low pressure and a short residence time of the vapor products i n the reactor. When compared with conventional, atmospher i c pressure carbonization, vacuum pyrolysis has the potential to s i g n i f i c a n t l y enhance the y i e l d s of organic l i q u i d products with respect to s o l i d and gaseous products. The pyrolysis o i l s ( b i o o i l s ) obtained from t h i s process can be deoxygenated into transportation fuels upon further upgrading (7). Specialty as well as commodity (Pakdei, H.; Roy, C. Bipmass, i n press) chemicals can also be extracted from the pyrolysis o i l product. This paper discusses the preliminary engineering data leading to the construction of a vacuum pyrolysis p i l o t plant for the conversion of wood into o i l s , chemicals and charcoal. Experimental A schematic of the Process Development Unit (P.D.U.) used i n t h i s study i s shown i n Figure 1. The reactor i s a multiple-hearth furnace 2 m high and 0.7 m diameter, with s i x hearths. Heat i s provided from heating elements. At the onset o f an experiment wood chips are poured batchwise into a hopper that s i t s on top of the reactor. The hopper i s equipped with a feeding device and i s hermetically sealed. For the experiments reported, 6 to 16 kg of wood chips, with a granulometry of 1/4" to 1/2" Tyler Sieves, were fed at a constant rate o f 0.8 to 4 kg h " . A mechanical vacuum pump removed the organic vapor and gas products form the reactor through a series of outlet manifolds set along the reactor cylinder (H-I to H-VI). Each outlet was connected to a heat exchanger where the vapors were condensed and recovered as l i q u i d i n individual glass receivers. Cold tap water c i r c u l a t i n g on the s h e l l side of the exchangers was used as cooling medium. The vapors from the heat exchangers were c o l l e c t e d i n a t r a i n of receivers that served as a secondary condensing unit (C-l to C-4). The f i r s t reveiver was immersed i n a bath of water-ethylene glycol mixture. Receivers 2 and 3 were immersed in baths of dry i c e acetone. Receiver 4 was f i l l e d with glass wool at room temperature. Pressure i n the system was lower than 11 kPa (absolute) under steady- state conditions. The noncondensable gas was continuously pumped into a 500 L vessel that was set under vacuum at the beginning of the run. The s o l i d residue was directed toward the bottom of the 1

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch003

PYROLYSIS OILS FROM BIOMASS

Figure 1. Schematic Development Unit

of

the

Vacuum

Pyrolysis

Process

3. ROY ET AL.

19

Processing of Wood Chips in a Pyrolysis Reactor

reactor. The residual charcoal was colLected in a metallic vessel i n s t a l l e d on a load c e l l . At time zero of the run, wood chips were fed to the preheated reactor. The heating plate temperatures increased from top to bottom of the reactor. A t y p i c a l temperature p r o f i l e was 200°C to 450°C. The r a d i a l temperature gradient for any heating plate was lower than 5°C during a typical run. The P.D.U. was attached to a central microprocessor which enabled simultaneous data acquisition and control of some 75 operating parameters (64 are recorded and 11 are controlled). A i r leakage through the system was lower than °.0013 atm I. s * . The experiments conducted with the P.D.U. were performed with Populus deltoïdes. The 8-year old fast-growing poplar clone D-38 was grown in Brockville, Ontario. The sample was e s s e n t i a l l y a l l sapwood with no bark. I t was supplied to our laboratories i n the form of chips by Forintek Canada Corp., Ottawa. Its elemental composition was determined to be 48.2% C, 6.4% H, 45.3% 0, 0.09% N, and 0.05% S. It gross heating values was 4660 kcal kg" with an average ash content of 0.6%. Moisture of the air-dry feedstock was 5,9%.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch003

1

1

Results and Discussion Yield..and ^ Q u a l i t y P r o d u c l s . Results for the operation of the multiple-hearth furnace at varying f i n a l thermal decomposition temperatures and reactor pressures are presented i n Table I of the paper. B i o o i l , p y r o l y t i c water, charcoal and gas yields arc presented along with the mass balance calculation f o r each run. Table I indicates that the largest amount of o i l was produced at the lower pressure conditions. The o i l y i e l d drops rapidly with even a s l i g h t increase in pressure. Table I also indicates that a reactor temperature i n the range of 425 450°C i s optimum f o r the maximum o i l production. The general c h a r a c t e r i s t i c s of b i o o i l s , gas and charcoal produced under optimum conditions are presented i n Table II of the paper. It can be observed that the gross c a l o r i f i c value of both charcoal and o i l products increases compared with that of raw wood. The gas has a very low c a l o r i f i c value (1660 c a l g" ) but i s burnable. The composition o f the noncondensable gas phase i s shown in Table III of the paper. 1

SpPMation._of, Watjex^ jTrpm^the . O r g a n _ Liqui d_Phase. One objective of the vacuum pyrolysis process i s to produce large quantities of l i q u i d fuels and chemicals from wood. However during the process organic substances are produced simultaneously with water (moisture and p y r o l y t i c water). The aqueous phase i s highly a c i d i c in nature (Pakdel, H.; Roy, C. Biomass, in press). Its organic content ranges between 45 and 55% but further improvement of the process should reduce this concentration down to 10-20%. Since extraction of chemicals or further processing of p y r o l y t i c o i l s mixed with water i s d i f f i c u l t and expensive, i t i s highly desirable to recover in separate sections the bulk of the aqueous phase from the organicl i q u i d phase. The separation of water and the organics was achieved during

COIO C012 C014 C015 C019 C023 0024 C025

RUN

425 363 450 425 465 450 450 450

FINAL TEMPERATURE (°C)

1.6 2.4 3.3 1.9 10.7 1.6 4.0 1.3 5.98 5.99 6.03 6.00 3.39 15.43 18.30 15.99

WOOD FEEDSTOCK (kg)

46.4 41.6 45.8 50.1 39.7 50.9 47.4 50.0

YIELDS OIL

18.2 14.9 17.0 15.2 21.6 16.5 16.9 15.6 24.2 33.0 25.6 25.0 24.7 21.3 25.5 23.0

11.2 10.5 11.6 9.7 14.0 11.3 10.2 11.4

(% wt. , ash-free, dry wood basis) WATER CHARCOAL GAS

Yields and Mass Balances for Vacuum Pyrolysis of Wood

REACTOR PRESSURE (kPa)

Table I.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch003

96.7 97.5 96.1 96.3 96.7 98.3 97.9 98.6

MASS BALANCE CLOSURE (%)

3. ROY ET AL.

Table II. Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch003

21

Processing of Wood Chips in a Pyrolysis Reactor

General Characteristics of B i o o i l and Charcoal

Water content (*) Gross c a l o r i f i c value ( k J . k g , anhydrous basis)

BIOOIL

CHARCOAL

4.4 22 500

< 1 32 000

55.6 5.8 0.7 0.6 37.3

84.4 3.5 0.2 0.8 11.1

- 1

Elemental analysis (%) C H Ν S 0 (by d i f f . ) Proximate analysis (%) Ash V o l a t i l e matter Fixed carbon Specific surface (BET, m g" ) 2

1

0.13

2.8 18.5 78.7

*

3

425 363 450 425 465 450 450 450

FINAL TEMPERATURE (°C)

1.6 2.4 3.3 1.9 10.7 1.6 4.0 1.3

REACTOR PRESSURE (kPa)

11.2 10.5 11.6 9.7 14.0 11.3 10.2 11.4

TOTAL GAS YIELD (% wt., ashfree, dry wood basis 2

59.2 60.4 65.7 63.8 60.0 60.7 63.5 64.6

C0

33.6 34.9 28.1 30.5 31.4 31.6 29.8 30.3

CO 4

2.4 0.9 1.4 1.5 3.3 2.7 2.6 1.9

CH

0.9 0.1 1.0 0.8 0.7 0.0 0.7 0.4

H2

1.5 0.9 1.6 1.3 2.8 1.4 1.5 1.0

C2-C4

GAS COMPOSITION (% wt. )

2.4 2.8 2.2 2.1 1.8 3.6 1.9 1.8

OTHERS*

* Others gases were among the followings: methanol, ethanol, acetone and acetaldehyde

C010 C012 CO 14 CO 15 C019 C023 C024 C025

HUN

Table I I I . Gas Phase Composition During Vacuum Pyrolysis of Wood

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch003

0.57 0.57 0.43 0.48 0.52 0.52 0.47 0.47

CO/CO2

3. ROY ET AL.

Processing of Wood Chips in a Pyrolysis Reactor

23

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch003

this study by using a series of s h e l l and tube heat exchangers with cool to warm water c i r c u l a t i n g i n the s h e l l side. This series of heat exchangers served as a primary condensing stage for the recovery of the l i q u i d organic f r a c t i o n . Water was primarily recovered in the series of traps that followed (see Figure 1). The r e l a t i v e proportion of water and o i l i n both condensing sections i s shown in Table IV of the paper. Table IV indicates that the lower the pressure, the better the separation between o i l and water (see runs C019 and C025 for example). On the other hand at s i m i l a r operating pressure, the lower the cooling temperature, the more e f f i c i e n t the recovery of o i l in the primary condensing section (see runs C023 and C025). Further studies are underway with the objec­ t i v e to find the optimum operating conditions for the maximum recovery of b i o o i l s with the least amount of water i n i t . O i l Refining. Further fractionation of the wood o i l product is necessary when the objective i s to either recover pure chemical compounds, or upgrade or process s p e c i f i c chemical group components. Results which are reported elsewhere by Renaud et a l (7) and Pakdel et a l (8) show that the multiple-hearth reactor can be operated in a mode that enables the separation and recovery of selected fractions of l i q u i d fuels and chemicals. Mean Residence Time of the Vapor Products i n the Reactor. One important feature of the vacuum pyrolysis process i s the short residence time of the gases and vapors in the reactor. In a previous investigation (4), the residence time of the vapor products in the laboratory scale batch reactor used was estimated to be about 2s. In the present investigation, a different pumping unit and a very large p y r o l y s i s unit have been used, so that a new estimate of the mean residence time was necessary. The mean residence time τ of the gas and vapor products i n the reactor can be defined as the r a t i o between the reactor volume V and the volumetric feed rate v of the gases and vapours flowing through the reactor under steady state pressure conditions. 0

V τ = — v

(1)

0

I f the ideal gas law applies which pressure conditions used, we have:

where Ρ V m M Τ R

= = = = =

is

gas pressure gas volume mass of gas average molecular weight of the gas gas temperature gas constant

likely

under

the low

PYROLYSIS OILS FROM BIOMASS

24 "Equation 2" respect to time:

can

be

expressed

d(PV)

in

a d i f f e r e n t i a l form with

RT

drn^ /dm>

M

\dt>

(3) dt

where the mass of gas in the reactor i s expected to vary with time while the average molecular weight of the gas should remain constant with time. Development of "Equation 3" leads to "Equation 4"

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch003

(4)

Vdt

\dt/v

/ p

M \dt/

Under study state operation of the P.D.U. at constant pressure, the term dP/dt in "Equation 4" i s equal to 0 which reduces "Equation 4" to:

ρ

=-

ί—\ \dt/

ρ

M

(-)

(5)

\dt/

In another special circumstance, the evacuation of gas from the reactor was interrupted during the experiment. As a r e s u l t , the gas pressure b u i l t up in the reactor as depicted in Figure 2. In such case, V i s constant and the term dV/dt i n "Equation 4" i s equal to 0 which reduces "Equation 4" to: /dP\

RT /dm\ (6)

Vdt/

ν

M \dt'

"Equation 5" i s i d e n t i c a l to "Equation 6" i f the term RT dm Μ" 1 dt/ in "Equations 5 and 6" i s the same. This i s true i f the y i e l d and q u a l i t y of the gas phase products which are present i n the reactor remain constant with respect to time in both modes of operation of the reactor as shown i n Figure 2. With t h i s hypothesis, we have: β

(7)

and

(8)

3. ROY ET AL.

25

ProcessingofWood Chips in a Pyrolysis Reactor

hence Ρ τ (9)

"Equation 9" can be calculated using the data available in Figure 2. The average gas pressure i n the reactor during steady state operation was 1.6 kPa. The rate of pressure b u i l t up in the closed reactor was determined to be approximately 150 kPa h " . As a r e s u l t , the average residence time of the gas and vapour phase in the reactor was found to be about 40 s. Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch003

1

Heat Requirement for the Pyrolysis Reaction. Another engineering parameter to be considered when designing a f u l l scale p y r o l y s i s plant i s the amount of energy required for the pyrolysis of each mass unit of wood fed to the reactor. Such value has been empirically determined using the P.D.U. described in this paper, and the detailed procedure has been published elsewhere (.9 ). The determination was based on the difference of e l e c t r i c energy consumed before of after wood was fed to the reactor (heat loss to the atmosphere), and that of the e l e c t r i c energy required for maintaining the multiple-hearth furnace at predetermined set-point temperature with wood chips flowing through the reactor. The amount of heat required to decompose wood ( A H r ) w i l l depend on the operating conditions used and the degree of conversion that has been reached. Under usual carbonization conditions, o v e r a l l the reaction i s known to be exothermic. Under vacuum pressure conditions, o v e r a l l the reaction is slightly endothermic as i l l u s t r a t e d in Table V of the paper. It can be concluded that some of the secondary reactions (e.g. thermal and c a t a l y t i c cracking, repolymerization, recondensation, oxidation and reduction reactions) which occur under the higher pressure conditions are exothermic and hence contribute to the o v e r a l l exothermicity of such reactions. In Table V, A H r for run C019 at 11 kPa i s less endothermic than A H r for reactions C023, C024 and C025 which have been conducted at a s i m i l a r temperature but under a s i g n i f i c a n t l y lower pressure. Several D.T.A. studies suggest that the i n i t i a l stage of thermal decomposition of wood i s endothermic. As a consequence, i t is expected that A H r w i l l vary with the degree of conversion of wood during p y r o l y s i s . In Table V, the r e s u l t s for the A H r calculations have been a l t e r n a t i v e l y reported on the percentage of wood converted basis, as well as on an as-received anhydrous wood basis. Conver­ sion i s defined as: Amount of b i o o i l + p y r o l y t i c water + gas Amount of i n i t i a l feedstock (org. basis) In Table V, the maximum conversion which has been reached i s s i m i l a r for the four reported experiments. It can be concluded that the heat required for vacuum pyrolysis of aspen wood between 1.3 and 3.9 kPa i s about 733 kJ kg" of organic wood converted. Overall, the reaction i s s l i g h t l y endothermic. 1

465 450 450 450

10.7 1.6 4.0 1.3

FINAL TEMPERATURE (°C)

465 450 450 450

C019 C023 C024 C025

(kg)

2.06 10.45 11.85 10.53

11-28 50-55 30-35 15-20

TOTAL LIQUIDS

(°C)

COOLING TEMPERATURE

52.2 32.2 39.8 47.8

(*)

OIL

7.4 36.7 27.2 27.2

19.2 1.5 1.5 3.4

10.7 1.6 4.0 1.3

REACTOR PRESSURE (kPa)

75.3 78.7 74.5 77.1

(%)

CONVERSION

450 570 550 560

1

Alt (kJ.kg* dry wood feedstock)

21.2 29.6 31.4 21.6

WATER (*)

600 720 730 730

Aft? (kJ.kg" of wood converted) 1

(*)

OIL

(*)

WATER

CONDENSING UNITS PRIMARY SECONDARY

V a r i a t i o n of Heat of Pyrolysis With Pressure

(°C)

(kPa)

Table V.

FINAL TEMPERATURE

Separation of Water and B i o o i l s During Condensation

REACTOR PRESSURE

RUN

C019 C023 C024 C025

RUN

Table IV.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch003

s

^ 3 Ο S w

Ο

jf g S

3. ROY ET AL.

27

ProcessingofWood Chips in a Pyrolysis Reactor

Heat Required for Cooling of the Vapors Products. The amount of heat removed when cooling the organic vapor products at the primary condensing stage was also experimentally determined (see Figure 1). The heat exchange ( Q w ) between the cooling medium (water) and the hot vapor products was calculated using the "Equation 10". Qw

=

(Tw,in

mCp

-

Tw,out)

(10)

where m i s the water flowrate, C i s the heat capacity for water and Tw,in and T w , o u t i s the water temperature at the i n l e t and the outlet of the heat exchanger, respectively. Taking into account the heat loss to the atmosphere, the o v e r a l l heat exchanged for cooling of the gas and vapor product to 50°C was found to be 469 kJ kg" of a i r - d r y wood. The experimental set-up simultaneously enabled the c a l c u l a t i o n of the o v e r a l l heat-transfer coefficient U for the heat exchangers. The data were used i n "Equation 11". P

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch003

1

=

Qw

UA

(A

T)

(11)

i n

where A i s the heat transfer area and ( A T ) i n i s the temperature d r i v i n g force. It was found that the U values varied betwen 8 and 15 W.m" .°C" according to the position of the heat exchanger attached to the multiple-hearth furnace (9). 2

1

Determination of the Standard Heat of Reaction. The equipment used also enabled us to determine the standard heat of reaction for pyrolysis of a i r - d r y wood chips. For matter of convenience the standard state for wood considered as "a pure substance" was 323 Κ (50°C) and 1.6 kPa. The standard heat of reaction was calculated using the "Equation 12": ΔΗ°323

where

=

AH°t

-

ΔΗ°Γ

-

ΔΗ°

(12)

Ρ

Δ Η ° i s the t o t a l enthalpy change for the reactants from temperature Τ to 323 Κ Γ

0

ΔΗ ρ i s the t o t a l enthalpy change for the products from 323 Κ to temperature Τ i s the enthalpy change for the three-step process including the enthalpy change during the isothermal reaction at 323 K. Figure 3 i l l u s t r a t e s how each term in "Equation 12" was empirically determined during run C023. Δ H ° r a n d Δ H p in "Equation 12" were calculated using an average heat capacity of 2 J.f ,^ for wood and 1 J . g - . K for wood charcoal . The value for ΔΗ°323 i n "Equation 12" was found to be 92 kJ kg" of a i r - d r y wood which confirms that the reaction i s s l i g h t l y endothermic. Although t h i s value has l i m i t i n g p r a c t i c a l use, i t should be viewed as an attempt to improve our theoretical knowledge of thermodynamics of wood p y r o l y s i s . AH°t

0

1

1

l

- 1

1

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch003

28

PYROLYSIS OILS FROM BIOMASS

Time (h)

Figure 2.

Variation of Reactor Pressure as a function of time AIR-DRY WOOD (5,9% moisture) 1 25»C , 1000 g

SENSIBLE HEAT

HEAT REMOVED

HEAT REMOVED

NON CONDENSABLE GAS ÊECONDARYX UNKNOWN T, 103 g CONDENSING) STAGE

SENSIBLE HEAT ·

AQUEOUS PHASE UNKNOWN T, 448 g

19 kcal ;

CHARCOAL 50*C , 200 g Figure 3.

Mass and Energy balance around the Reactor

3. ROY ET AL.

ProcessingofWood Chips in a Pyrolysis Reactor

29

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch003

Calculation of the Thermal E f f i c i e n c y of the Multiple - Hearth Reactor. The thermal e f f i c i e n c y of the system defined as the r a t i o of useful energy provided by the vacuum p y r o l y s i s reactor, to the energy supplied to i t during a s p e c i f i c run, has been calculated for experiment C023. The c a l o r i f i c values of the end-products represented the following percentages of the heating value of the i n i t i a l feedstock: wood charcoal 36*, wood o i l 41* and gas, 5*. Using these data together with values from Figure 3 enabled us to determine that the thermal e f f i c i e n c y was 82*. For t h i s c a l c u l a t i o n i t was assumed that the e l e c t r i c energy required for the mechanical pump was n e g l i g i b l e and that the reactor was p e r f e c t l y insulated. Heat Transfer Phenomena in the Reactor. In the pyrolysis reactor, heat can be transferred by conduction, by radiation and by convection. Heat transfer by convection i s n e g l i g i b l e due to the low pressure conditions i n the reactor. In p r i n c i p l e , both conduction and radiation can play a s i g n i f i c a n t role during pyrolysis. An o v e r a l l heat-transfer coefficient of 25 W . m - . C ~ was found in a previous study where the multiple hearth furnace was viewed as a heat exchanger. One weakness of t h i s heat transfer model by conduction i s that phase changes occur during the thermal decomposition of wood and t h i s might lead to inaccurate conclusions. A more recent study of the heat fluxes inside the reactor as well as a comparison of the t h e o r e t i c a l data predicted by a radiation heat transfer model showed that radiation i s the main mode of heat transfer i n the multiple hearth reactor configuration used (10). 2

0

1

Conclusions A multiple-hearth reactor has been successfully tested for the production of high y i e l d s of l i q u i d fuels and chemicals. The reactor enabled the separation and recovery of water on the one hand and o i l fractions or the other hand. B i o o i l yields reached about 50* by weight of the a i r - d r y feedstock. Both the o i l and charcoal have a higher c a l o r i f i c value than the raw wood feedstock. Heat required for the p y r o l y s i s of wood i s s l i g h t l y endothermic and was determined to be 733 kJ k g of organic wood converted. The standard heat of reaction at 323 Κ and 1.6 kPa was found to be approximately 92 kJ kg" of a i r - d r y wood. The thermal e f f i c i e n c y of the process i s high at 82*. The mean residence time of the gas and vapour phase product in the reactor was e m p i r i c a l l y found to be about 40 s. Heat i s mainly transferred by radiation i n the type of reactor used. - 1

1

Acknowledgments This study was supported by the Bioenergy Development Program, Energy, Mines and Resources Canada and Petro-Sun R and D, Boucherv i l l e , Québec. Literature c i t e d 1.

Wenzl, H.F.J. The Chemical Technology of Wood; Academic Press: New York, 1970; p 285.

30 2. 3. 4.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch003

5.

6. 7.

8. 9. 10.

PYROLYSIS OILS FROM BIOMASS Rodrigues de Almeida, M. International Workshop on Pyrolysis as a Basic Technology for Large Agro-Energy Projects, L'Aquila, Italy. 15-16 October, 1987. Perdrieux, S.; Lemaire, A. Le bois National. 2 juillet 1983, 23-26. Roy, C.; de Caumia, B.; Brouillard, D.; Ménard, H. In Fundamentals of Thermochemical Biomass Conversion: An International Conference. Overend, R.P., Milne, T.A. and Mudge, L . K . , Eds. Elsevier Applied Science Publishers: New York, 1984; p. 237256. Roy, C.; de Caumia, B.; Blanchette, D.; Lemieux, R.; Kaliaguine, S. Energy from Biomass and Wastes IX, IGT Symposium. Lake Buena Vista, Florida. January 28-February 1, 1985, p. 1085-1106 Roy, C.; Lemieux, R.; de Caumia, B. and Pakdel, H. Biotechnology and Bioengineering. Symp. No. 15., 1985, p. 107113. Renaud, M.; Grandmaison, J . L . ; Roy, C.; Kaliaguine, S. "Production, Analysis and Upgrading of Pyrolysis Oils from Biomass". ACS Division of Fuel Chemistry Preprints, Denver, Co. April 5-10, 1987; 32, (2), p. 276-286. Pakdel, H.; Roy, C. Production, Analysis and Upgrading of Pyrolysis Oils from Biomass". ACS Division of Fuel Chemistry Preprints, Denver, Co. April 5-10, 1987; 32, (2), p. 203-214. Lemieux, R. M.Sc.A. Thesis. Université de Sherbrooke, Québec, 1988. (In French). Labrecque, Β. M.Sc.A. Thesis, Université de Sherbrooke, Québec, 1988. (In French).

Received March 31, 1988

Chapter 4

Production of Primary Pyrolysis Oils in a Vortex Reactor

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch004

James Diebold and John Scahill Chemical Conversion Research Branch, Solar Energy Research Institute, 1617 Cole Boulevard, Golden, CO 80401 A vortex tube has certain advantages as a chemical reactor, especially if the reactions are endothermic, the reaction pathways are temperature dependent, and the products are temperature sensitive. With low temperature differences, the vortex reactor can transmit enormous heat fluxes to a process stream containing entrained solids. This reactor is ideally suited for the production of pyrolysis oils from biomass at low pressures and residence times to produce about 10 wt % char, 13% water, 7% gas, and 70% oxygenated primary oil vapors based on mass balances. This product distribution was verified by carbon, hydrogen, and oxygen elemental balances. The oil production appears to form by fragmenting all of the major constituents of the biomass.

The pyrolysis of biomass follows a complex set of different chemical pathways, which have thus far not been well established. However, several global pathways have been established, which explain most of the observed phenomena. As shown in Figure 1, the f i r s t reaction in fast pyrolysis of biomass is the depolymerization of the 1 ignocellulose macropolymers to form viscous primary o i l precursors. These precursors are formed with almost no by-products, and consequently their elemental composition is very similar to the original biomass. With low heating rates, much of the primary o i l precursors can repolymerize to thermally stable polymers through the elimination of mostly water to eventually form the material known as char. Evidence for a l i q u i d or p l a s t i c phase intermediate in the formation of char is the physical shrinkage of the macrodimensions of wood, which takes place during charring {!) in a manner analogous to heat shrinkable polyethylene tubing. If the heating of the biomass proceeds very quickly to temperatures above 450"C, most of the primary o i l

c

0097-6156/88/0376-0031$06.00/0 1988 American Chemical Society

32

PYROLYSIS OILS FROM BIOMASS

precursors can crack and vaporize before they form char. In the vapor state, the primary o i l molecules are quite d i l u t e , which slows possible second-order polymerization reactions. This d i l u t i o n allows any unstable primary o i l vapors to be converted by first-order reactions to more stable compounds, which can be collected from a reactor designed to have a short gaseous residence time followed by rapid quenching. Thermal s t a b i l i t y is r e l a t i v e , however, and these s t a b i l i z e d primary o i l vapors readily crack to gases following a global f i r s t - o r d e r reaction (2_). The cracking of the primary o i l vapors proceeds with a 10% loss in 36 ms at 700°C and extrapolated 10% losses in 6 ms at 900°C and 591 ms at 500°C.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch004

Pyrolysis Reactor Design Considerations Obviously, the lower the temperature of the primary vapors in the reactor, the greater the y i e l d of primary vapors which can survive passing through the reactor to the quench zone. Minimizing the time required to travel from the vapor formation zone in the reactor to a lower temperature quench zone also helps to maximize the primary o i l vapor y i e l d s . The ideal reactor would thus provide large heat fluxes preferentially to the pyrolyzing biomass p a r t i c l e , while not overheating the surface of the p a r t i c l e to cause cracking of the primary vapors to gases as the vapors escape the surface of the p a r t i c l e . The ideal reactor would allow the vapors to be immediately swept away by a cooler c a r r i e r gas stream out of the reactor to a cold quench zone in order to preserve as much of the vapors as possible. The residence time of the biomass particles in the ideal reactor must be long enough to ensure complete p y r o l y s i s , but the accumulation of dead char in the reactor is undesirable. It would also be advantageous i f the reactor could s e l e c t i v e l y remove dead char and recycle p a r t i a l l y pyrolyzed p a r t i c l e s . The use of thermal radiation for fast pyrolysis has been explored, as this approach preferentially heats the solid with potentially high heat fluxes. However, heating the p a r t i c l e with a high temperature heat source can drive the surface temperature of the p a r t i c l e too high and some cracking of the vapors to gases would be expected. The use of hot flue gases or hot solids as a heat transfer medium usually requires that they be at very high temperatures to lessen the amount of the medium which must be generated or recycled; flue gases or hot sand at 900° to 1000°C have been used for fast pyrolysis, but tend to produce higher y i e l d s of noncondensible gases from cracking the primary pyrolysis oil vapors to gases as described above. Conversely, the use of gases or solids at lower temperatures for the heat source requires that much more of them be used, which increases the process energy required. Large amounts of gases dilute the process stream and promote the loss of v o l a t i l e organics in the gas stream from the condensation part of the system. The ideal reactor for the fast pyrolysis of biomass to primary o i l s would achieve high heat transfer rates through the use of a mechanism which has an inherently high heat-transfer c o e f f i c i e n t , rather than through the use of a high-temperature source. Such a heat transfer mechanism

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch004

4. DIEBOLD & SCAHILL

Production of Primary Pyrolysis OUs

33

is attained by the conduction of heat from a moderately hot reactor wall d i r e c t l y to the biomass p a r t i c l e . It can be readily demonstrated that when a stainless steel wire at 500° to 900°C is contacted with a monolithic piece of b i o ­ mass, the biomass surface is ablatively pyrolyzed and converted to liquids and vapors, which allow passage of the wire through the biomass. If the stored energy in the wire is transferred to the biomass by s l i d i n g the wire across the biomass, pyrolysis rates over 3 cm/sec are observed (3). This method of heat transfer has been studied by pushing a wooden rod into a heated, stainless steel disk, and the pyrolysis rate has been found to be proportional to the pressure exerted and to the temperature d i f f e r e n c e , where the biomass surface was calculated to be pyrolyzing at 4 6 6 ° C . Heat transfer c o e f f i c i e n t s as high as 8 W/cnr Κ were reported, which is over 300 times higher than thermal radiation from a wall at 900°C having an emissivity of one ( ! ) ·

Although a reactor can be designed to push wooden rods into a hot surface for research purposes (4-5), most practical biomass feedstocks are expected to be in the form of sawdust or chips. A modified entrained-bed reactor was selected in which the entrained p a r t i c l e s enter the reactor tangentially so that centrifugal forces push the feedstock particles onto the externally heated cylindrical wall. Drag forces induced on the p a r t i c l e by the entraining gas stream serve to keep the particles moving on the w a l l . Since the p a r t i c l e s are on or very nearly on the w a l l , they tend to intercept p r e f e r e n t i a l l y the heat, which is conducted through the reactor wall. With nonreacting solid p a r t i c l e s in a heat exchanger made from a cyclone separator, the total heat transferred to the process stream was r e l a t i v e l y independent of the solids' content at c a r r i e r - t o - s o l i d s (C/S) mass ratios as low as one, whereas with more s o l i d s , the heat transferred increased dramatically. The temperature rise in the gas stream was as l i t t l e as half of that seen in the solids at these low C/S ratios. The heat transfer c o e f f i c i e n t from the wall to a s o l i d s free gas was found to follow t r a d i t i o n a l convective heat transfer relationships, but to be 1.8 times higher in the cyclone than in a straight tube for the same entering tube diameter and entering gas v e l o c i t i e s (_6). A reported property of a cyclone is that above an entering Reynold's number of 3000, the cyclone has plug flow (_7). The cyclone is an interesting reactor concept for the pyrolysis of biomass, as reported in the l i t e r a t u r e (7-8). However, the reactor of interest in this paper is a vortex tube, which has many s i m i l a r i t i e s to a cyclone separator. Vortex Reactor Considerations The vortex tube of interest has a tangential entrance into one end of a c y c l i n d r i c a l tube and an axial exit at the other end of the tube. Research into the aerodynamics of the vortex tube revealed that the pitch of the vortex near the c y l i n d r i c a l wall was about 1.2 times the diameter of the vortex tube. This results in a coarse h e l i c a l path of the gases near the wall, as measured by Pi tot tubes (9-10). This coarse h e l i c a l path on the wall also

PYROLYSIS OILS FROM BIOMASS

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch004

34

exists for the c y l i n d r i c a l part of the more conventional cyclone separator (11). The effect of the coarse, gaseous path is that entrained s o l i d s , which are centrifuged to the w a l l , follow the same coarse path through the reactor. This has two deleterious effects: only a narrow path of the c y l i n d r i c a l wall would be used for heat transfer; and the residence time of the solid p a r t i c l e s is only a fraction of what i t would be with a tighter h e l i c a l path. The vortex tube reactor which we developed is shown in Figure 2 and is about 14 cm in diameter and 69 cm in length. It has some unique features, which were found necessary to achieve the desired reactor performance in the fast pyrolysis of biomass. The c a r r i e r gas is usually steam between 500 and 1000 kPa, depending upon the desired flow rate, and passes through a supersonic nozzle. Biomass in the form of minus 3-mm sawdust is metered into, and is entrained by, the supersonic c a r r i e r gas stream. Cold-flow studies in a clear p l a s t i c model with 4000frames-per-second movie coverage established that this entrainment method results in rapid acceleration of the sawdust particles to v e l o c i t i e s over 125 m/s. The cold-flow studies also v e r i f i e d that the entrained p a r t i c l e s were following the reported coarse path of the gas flow near the w a l l . This coarse h e l i c a l path appeared to be independent of the entrance angle, the entrance duct shape, and the flow rate of the c a r r i e r gas (13). The pitch angle of the solids flow in the conical section of a conventional cyclone was observed to be about o n e - f i f t h that in the c y c l i n d r i c a l section (11), but the c y l i n d r i c a l vortex tube has more heat-transfer surface area per unit length. To force the entrained p a r t i c l e s into a tight helical path, the 316 SS c y l i n d r i c a l vortex tube wall was machined to leave a 3-mm high and 3-mm wide raised h e l i c a l rib. High-speed movies taken through a clear p l a s t i c bulkhead with cold-flow v e r i f i e d that the raised rib forced the solids to take the desired tight helical path (14). A tracer gas experiment, following the progress of propane pyrolysis, v e r i f i e d that this reactor design was essentially plug flow, with the inner vortices contributing a very small amount of internal recycling (15). Vortex Reactor Operation I n i t i a l operation with this vortex tube as a reactor for the fast pyrolysis of biomass was with heating the reactor wall to r e l a t i v e l y high temperatures of 800°C or so. At that time, the goal was to crack the primary vapors to gases, rather than the preservation of the primary o i l s . Under these conditions, the sawdust had ample time to pyrolyze, as well as the char having time to partially gasify to produce char yields of only about 5%. However, as the vortex reactor wall became hotter, the tendency increased to accumulate a layer of secondary tar and char on the wall. By reducing the wall temperature to 625°C, the buildup of an insulating char-tar layer became n e g l i g i b l e , but the rate of pyrolysis of the sawdust p a r t i c l e s was so low that about 30% of the feed could be recovered in the char cyclone as scorched feed. A tangential exit was then added to the vortex tube reactor

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch004

4.

DIEBOLD & SCAHILL

35

Production ofPrimary Pyrolysis Oik

MACROPOLYMERIC

OLIGOMERIC

MONOMERIC

BIOMASS SOLIDS

LIQUIDS

PRIMARY

SECONDARY

VAPORS

*~

GASES

MACROPOLYMER CHAR S O L I D S

Figure 1.

+

H

2°

+

CO

x

Global Reactions in Fast Pyrolysis

Biomass chips

-50/ym char

Figure 2. Vortex Reactor Schematic. (Reproduced with permission from ref. 19. Copyright 1985 Solar Energy Research Institute.)

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch004

36

PYROLYSIS OILS FROM BIOMASS

to allow the unreacted feed and large char particles to be recycled to the entrance of the reactor as shown in Fig 2. The c a r r i e r gas nozzle acts as an ejector to create the pressure d i f f e r e n t i a l to drive the recycle loop. The recycle stream blows the sawdust off the feeder screws to positively entrain the feed to the carrier gas ejector. The temperature at the exit of the insulated, but unheated, recycle loop is t y p i c a l l y 400° to 450°C. The carrier gas is pre­ heated to between 600° and 700°C prior to expansion through the ejector nozzle. With these conditions, the temperature of the pyrolysis stream is 480° to 520°C, as i t exits the vortex reactor system. About 10% of the feed is converted to char, which is re­ cycled with the scorched feed until i t is a t t r i t e d to less than 50 micrometers in s i z e . The vortex reactor system acts as a par­ t i c l e size c l a s s i f i e r , with the char fines being entrained out of the vortex system to be removed by a cyclone separator having a higher c o l l e c t i o n e f f i c i e n c y . The fine char has a v o l a t i l e content of 15% to 20% and burns readily, especially when hot. The bulk density of the fine char is between 0.18 and 0.24 g/mL, depending upon whether i t was freshly poured or has been allowed to s e t t l e (the bulk density of the sawdust feedstock was 0.24 g/mL). The empirical formula for this v o l a t i l e char is Q . 5 3 ° 0 12» heating value (HHV) of 33 kJ/g (141000 6tu/lb). A microscopic examination of the char fines shows that the p a r t i c l e s have the appearance of broken thin-walled tubes; i . e . , charred and broken cell walls. Although the reactor has not been optimized to maximum throughout, sawdust feeding rate of 22 kg/hr have resulted in good operation with a steam-tobiomass ratio of 1.0 (Run 93). As noted above, the primary vapors are cracking s i g n i f i c a n t l y even at 500°C and a residence time of half a second. If the re­ cycle loop of the vortex reactor is removed, the y i e l d of permanent gases is about 4%, based on the reacted feed. The initial gases, which are formed under these conditions, are extraordinarily rich in carbon dioxide and are associated with the formation of char. With the recycle loop open, some of the primary pyrolysis vapors are recycled along with the c a r r i e r gas, unreacted s o l i d s , and large char. The additional time, which the recycled primary vapors spend in the vortex reactor leads to a small loss in the y i e l d of primary vapors and a higher y i e l d of noncondensible gases of about 7% to 12%. The composition of the gases s h i f t s considerably from the i n i t i a l gases formed to that associated with a small loss of primary vapors. An even greater s h i f t in the gas composition occurs with more extensive cracking of the primary vapors to produce an assymptotic gas composition as the primary vapors near extinction, which is low in carbon dioxide, as shown in Table I. The experimental determination of the feed consumed, the char y i e l d , and the noncondensible gas yields are r e l a t i v e l y s t r a i g h t ­ forward. However, the primary vapor and water yields have proven d i f f i c u l t to measure d i r e c t l y due to the formation of aerosols. These aerosols escape high-pressure sprays, cyclonic separators, and impingement or i n e r t i a l c o l l e c t i o n techniques. The use of condensible steam as the carrier gas makes the water y i e l d very C H

a

n

d

η

h

a

s

a

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch004

4. DIEBOLD & SCAHILL

Production ofPrimary Pyrolysis Oils

37

sensitive to small measurement errors in the steam c a r r i e r gas flow. The use of noncondensible gases as the c a r r i e r tends to s t r i p the v o l a t i l e organics and the water of pyrolysis from the condensate. These considerations have led to the use of a noncondensible c a r r i e r gas, nitrogen, and to the determination of the water formed during pyrolysis and the primary o i l y i e l d by d i f f e rence. By analyzing the recovered condensate for water, the y i e l d of water may be determined. These techniques led to the conclusion that yields of about 70% primary vapors were achieved, based on taking the difference between the sawdust fed and the measured gas flow and char c o l l e c t e d , correcting for the water content of the condensates. After elemental compositions were obtained for the feed and the collected products, an elemental balance was computed which v e r i f i e d the high primary vapor yields of 69 to 77 wt % , as shown in Table II, based on the y i e l d of recovered char (2_). However, our best recovery of dry o i l s has been 55 wt % of the dry feed with a 94% mass closure, when operating the system with 9 kg dry feed per hour and a nitrogen c a r r i e r gas flow rate of 20 kg per hour. The primary pyrolysis o i l s , which have been recovered from the vortex reactor, are highly oxygenated and have nearly the same elemental composition as the biomass feedstock. The o i l s have a dark brown color and are acidic with a pH between two and three. The heating value (HHV) of the dry o i l s i s 20 to 22 kJ/g (8700 to 9500 Btu/lb). The o i l s can absorb up to about 25% water before forming two phases. The viscosity of the o i l s was 1300 cp at 3 0 ° C , and the density was 1.3 g/mL (16). Although the primary vapors have a low molecular weight as determined by the FJMBMS (17), they rapidly polymerize upon physical condensation to form high-molecular-weight compounds in the o i l s (18). Attempts to slowly d i s t i l l the o i l s led to the rapid polymerization of the o i l s boiling above 100°C Q 6 ) . The o i l s have s i g n i f i c a n t chemical activity, which suggests their potential use in low-cost adhesives, coatings, and p l a s t i c s . Scale-up Potential The concept of supplying heat through the wall of a vortex reactor to drive endothermic processes is in i t s early development. The scale-up potential of this concept depends upon the angular momentum of the swirling c a r r i e r gases to keep the entrained feed p a r t i c l e s moving on the wall. The heat flux delivered to tubular pyrolysis reactors t y p i c a l l y ranges between 5 and 15 W/cnr (20,000 to 50,000 B t u / h r - f t ) . Reported data for vortex tubes indicates that with diameters larger than 2.5 cm most of the angular momentum is retained even after traveling a tube length equivalent to 20 tube diameters. The major momentum losses are due to the f r i c t i o n a l contact of the solids and the gases with the vortextube w a l l . With larger vortex tubes needed for scale-up, the angular momentum of the process stream w i l l increase more than the f r i c t i o n a l losses. The heat transferred to the reactor w i l l scale by the product of the diameter and the length. These considerations have led to calculations which suggest that a vortex reactor with a 250 TPD capacity would have a diameter of only 2

38

PYROLYSIS OILS FROM BIOMASS

Table I. Pyrolysis Gas Composition at Various Cracking Severities (mol %) Vortex Exit Gases w/o Recycle (Run 34)

H

3.4

co

2

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch004

CH

Severely Cracked Vapor Gases (Run 5c

8.3

17.8

46.2

49.2

52.2

43.1

27.6

7.5

4.6

8.9

12.0

—

0.1

1.1

1.3

2.4

5.9 0.6

2

CO

4

C2H2

0.3

0.7

H

0.1

0.1

—

H

0.4

0.8

0.8

0.3

0.3

0.6

0.5

1.4

1.4

C H 2

C

Vortex Exit Gases w/Recycle (Run 58)

6

3 8

C 6 3

C H 4

8

wt % y i e l d of gases

f6

f4

65%

Source: Reprinted with permission from r e f . 12. Solar Energy Research Institute. Table II.

Copyright 1983

Elemental Balance for Fast Pyrolysis to Primary Vapors

Feed Τ Primary Vapors + Water + Char + Gas C H

1.4°0.62

T

w

CHi.2Oo.49

+

X

¥

+

Y

C H

0.53°0.12

+

1

C H

0.38°1.33

Calculated Product Values, Wt % Exp. Char Yield

Primary Vapors

Water

Prompt Gas

7.5

76.8

11.7

4.0

10.5

73.1

12.8

4.1

12.7

69.0

14.0

4.3

Source: Reprinted with permission from r e f . 12. Solar Energy Research I n s t i t u t e .

Copyright 1983

4. DIEBOLD & SCAHILL

Production ofPrimary Pyrolysis Oils

about 0.5 m and a length of 9 to 12 m. The fabrication technique would most l i k e l y be by the welding up of a s p i r a l l y wrapped tube to form the raised, helical r i b .

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch004

Conclusions For the fast pyrolysis of biomass, a vortex reactor has s i g n i f ­ icant advantages for the production of primary pyrolysis vapors, including: high heat transfer c o e f f i c i e n t s which allow the use of moderately low temperatures of the vortex reactor walls to supply the endothermic heat of pyrolysis; separation of the p a r t i a l l y pyrolyzed feed p a r t i c l e s from the char; the a b i l i t y to recycle the p a r t i a l l y pyrolyzed feed; the a b i l i t y to accept a wide spectrum of p a r t i c l e sizes in the feed; short gaseous residence times; and preferential heating of the s o l i d feed over the vapor stream to preserve the primary vapors. Primary pyrolysis vapor yields in the 70% range have been calculated by mass balances and v e r i f i e d by elemental balances, although physical c o l l e c t i o n of these vapors has proven to be elusive due to the formation of persistent aerosols and due to the v o l a t i l i t y of the vapors in the c a r r i e r gas (methods to recover these vapors more completely with p r a c t i ­ cal means are under development). Acknowledgments The financial support for the development of the vortex reactor and the c a t a l y t i c conversion of the primary vapors to high-octane gasoline has been provided by the Biofuels and Municipal Waste Technology Division of DOE (FTP 646) with Mr. Simon Friedrich as the DOE program manager and Dr. Don J . Stevens of PNL as the technical monitor. The physical recovery of the primary o i l s for use as chemicals and adhesives is being developed through the financial support of the Office of Industrial Programs of DOE with Mr. Al Schroeder as the DOE program manager (FTP 587). Literature Cited 1. 2. 3.

4. 5.

6.

McGuinnes, E. A. J r . ; Harlow, C. Α.; Beall, F. C. Proc. Plant Sci. Appl. SEM, 1976, p. 543. Diebold, J . P., MS Thesis T-3007, Colorado School of Mines Golden, CO, 1985. Diebold, J . P., In Proceedings of Specialists Workshop on Fast Pyrolysis of Biomass, Diebold, J., ed.; Solar Energy Research Institute, Golden, CO 1980; SERI/CP-622-1096; p. 237. Lede, J.; Panagopoulos, J.; L i , Η. Z . ; Vettermaux, J . Fuel 1985, 64, 1514-1520. Reed, T. B . , ACS Symposium on Production, Analysis, and Upgrading of "Pyrolysis Oils from Biomass, Denver, CO, April 5-10, 1987. Szekely, J.; and Carr, R. Chem. Eng. S c i . , 1966, 21, 11191132.

39

40

PYROLYSIS OILS FROM BIOMASS

7.

8. 9. 10.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch004

11. 12.

13.

14.

15. 16. 17.

18. 19.

Lede, J.; Verzaro, F . ; Antoine, Β.; Villermaux, J . In Proceedings of Specialists Workshop on Fast Pyrolysis of Biomass, Diebold, J., ed.; Solar Energy Research Institute, Golden, CO, 1980, SERI/CP-622-1096, p. 327. Diebold, J . P.; Benham, C. B.; Smith, G. D. Monograph on Alternate Fuel Resources, Hendel, F . , ed.; AIAA Monograph Series 1976, 20, 322-325. Hartnett, J . P.; and Eckert, E. R. G . , Trans. ASME 1957, May, 751-758. Scheller, W.; Brown, G . , Ind. Eng. Chem. 1957, 49, No. 6, 1013-1016. ter Linden, Α., Inst. Mech. Eng. J. 1949, 160, 233-251. Diebold, J . P.; "Entrained-Flow, Fast Pyrolysis of Biomass. Annual Report. 1, December 1982 - 30, September 1983", 1984, Solar Energy Research Institute, Golden, CO, SERI/PR-234-2144 Diebold, J . P.; Scahill, J . W. In Proceedings of the 13th Biomass Thermocontractor's Meeting, Pacific Northwest Laboratory, Richland, WA, 1981, CONF-8110115. PNL-SA-10093; p. 332. Diebold, J . P.; Scahill, J . W. Proceedings of the 15th Βiomass Thermocontractor's Meeting, Pacific Northwest Laboratory, Richland, WA, 1983, CONF-830323, PNL-SA-11306, p. 300. Diebold, J . P.; Scahill, J . W. AIChE Winter National Meeting, Atlanta, GA, 1984, paper 31d. E l l i o t t , D. C.; "Analysis and Comparison of Biomass Pyrolysis/Gasification Condensates - Final Report" Pacific Northwest Laboratory, Richland, WA, 1986. PNL-5943/UC - 61D. Evans, R. J., Appendix C in "Entrained-Flow, Fast Pyrolysis of Biomass, Annual Report, 1 October 1983 - 30 November 1984," by J . P. Diebold and J . W. Scahill, Solar Energy Research Institute, Golden, CO, 1985. SERI/PR-234-2665. Johnson, D. K.; Chum, H. L., ACS Symposium on Production, Analysis, and Upgrading of Pyrolysis Oils from Biomass, 1987, Denver, CO. pp. 167-177. Diebold, J . P.; Scahill, J. W.; Evans, R. J. Entrained-Flow, Fast Ablative Pyrolysis of Biomass. Annual Report 1 December 1984-31 December 1985, 1986, Solar Energy Research Institute, Golden, CO. SERI/PR-234-3012.

Received April 14, 1988

Chapter 5

Conditions That Favor Tar Production from Pyrolysis of Large, Moist Wood Particles

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch005

Marcia Kelbon, Scott Bousman, and Barbara Krieger-Brockett Department of Chemical Engineering, BF-10, University of Washington, Seattle,WA98195 The experiments described in this paper w i l l aid in identifying favorable feedstock properties and process settings for tar production from large (about 1 cm) wood p a r t i c l e s . Conversion of biomass to pyrolytic oils will be greatly facilitated if large, undried particles can be used directly as a feedstock. The experiments have been conducted using well-defined, reactor-independent conditions and the results indicate that an optimum moisture content can facilitate tar production. The reacted fraction that is tar is greater for intermediate moisture contents, particle sizes, and heating rates, and the optimum tar production conditions for moist feeds change with both heating intensity and particle size.

The economics o f making p y r o l y t i c o i l s from biomass w i l l be improved i f l a r g e , and p e r h a p s m o i s t , p a r t i c l e s c a n be u s e d d i r e c t l y as a f e e d s t o c k . T h i s i s a r e s u l t o f t h e h i g h c o s t o f s i z e r e d u c t i o n and d r y i n g o f f i b r o u s and o f t e n green biomass. Both p r e s e n t and p l a n n e d i n d u s t r i a l biomass c o n v e r t e r s employ l a r g e p a r t i c l e s , u s u a l l y t h e r e a d i l y a v a i l a b l e wood c h i p s , sometimes u s i n g them i n f l u i d i z e d beds which a r e l e s s s e n s i t i v e t o f e e d s i z e d i s t r i b u t i o n s ( 1 ) . However, t h e p y r o l y s i s o f r e a l i s t i c a l l y s i z e d p a r t i c l e s (about 0.01 χ 0.01 χ 0.005 m o r g r e a t e r ) i s c o m p l i c a t e d b y n o n - u n i f o r m t e m p e r a t u r e p r o f i l e s w i t h i n t h e p a r t i c l e , and t h e s y n e r g i s t i c e f f e c t s t h a t h e a t i n g i n t e n s i t y , p a r t i c l e m o i s t u r e , and s i z e have i n a l t e r i n g t h e i n t r a p a r t i c l e temperature h i s t o r i e s . S e l e c t i v e l y p r o d u c i n g f r o m wood a p a r t i c u l a r pyrolysis f r a c t i o n such as t a r , o r s p e c i f i c components i n any f r a c t i o n , i s difficult. To enhance s e l e c t i v i t y , t h e m a j o r i t y o f s t u d i e s t o d a t e have u s e d f i n e l y ground (< 100 mm d i a m e t e r ) wood samples i n which heat t r a n s f e r r a t e s a r e r a p i d enough t o cause a u n i f o r m particle t e m p e r a t u r e , and mass t r a n s f e r i s f a s t enough t o m i n i m i z e s e c o n d a r y r e a c t i o n s . F o r t h e s e powders, p y r o l y s i s w i t h a h i g h h e a t i n g r a t e t o moderately h i g h temperatures g e n e r a l l y favors t a r f o r m a t i o n , i f the

β

0097-6156/88/0376-0041$06.00/0 1988 American Chemical Society

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch005

42

PYROLYSIS OILS FROM BIOMASS

t a r c a n be q u i c k l y removed from t h e r e a c t i o n zone. However, i n wood c h i p p y r o l y s i s , t h e p a r t i c l e i n t e r i o r h e a t s s l o w l y owing t o i t s low c o n d u c t i v i t y , and secondary reactions of t a r are s i g n i f i c a n t . As y e t , t h e b e s t c o n d i t i o n s f o r t a r f o r m a t i o n from c h i p s have n o t been identified. S i n c e r e a l i s t i c wood f e e d s t o c k s a r e heterogeneous, t h e u n i f o r m e n t i t y a p p r o p r i a t e f o r fundamental s t u d i e s t o i d e n t i f y improved conditions f o r t a r formation i s the single p a r t i c l e . In i t , the i n t r a p a r t i c l e c o n d i t i o n s c a n be measured and r e l a t e d t o p r o c e s s c o n d i t i o n s t h a t can be m a n i p u l a t e d . I n a d d i t i o n , t h e e f f e c t o f heat and mass t r a n s f e r r a t e s on r e a c t i o n p r o d u c t s c a n be d e t e r m i n e d . The f i n d i n g s c a n be r a t i o n a l i z e d t o a l l r e a c t o r s i n which t h e s t u d i e d experimental conditions p r e v a i l . The i n v e s t i g a t i o n o f r e a c t i n g s i n g l e p a r t i c l e s has p r o v e n e x t r e m e l y s u c c e s s f u l i n t h e development o f c a t a l y t i c r e a c t o r s (2) and c o a l p y r o l y s i s (3,4,5). One g o a l o f t h i s s t u d y was t o i n v e s t i g a t e t h e s y n e r g i s t i c i n f l u e n c e o f p a r t i c l e s i z e , h e a t i n g i n t e n s i t y , and moisture on p a r t i c l e t e m p e r a t u r e , a dependent v a r i a b l e f o r l a r g e p y r o l y z i n g p a r t i c l e s . The e f f e c t o f t h e r m a l o r h e a t t r a n s f e r p r o p e r t i e s was s t u d i e d b y m a n i p u l a t i n g t h e d e n s i t y (6) . These manipulated v a r i a b l e s , by d e t e r m i n i n g t h e temperature p r o f i l e , a l s o determine t h e t a r y i e l d and c o m p o s i t i o n . The 0.005 t o 0.015 m t h i c k p a r t i c l e s i z e range was i n v e s t i g a t e d because o f i t s p r a c t i c a l i m p o r t a n c e . I n a d d i t i o n , Kung (7) d e m o n s t r a t e d t h a t t h i s s i z e range spans t h e t r a n s i t i o n from f l a t temperature p r o f i l e s t o steep temperature g r a d i e n t s f o r t h e h e a t i n g i n t e n s i t i e s normally found i n i n d u s t r i a l converters. One d i m e n s i o n a l (1-D) h e a t i n g h a s b e e n used experimentally (8,9) a n d t y p i f i e s t h e t y p e o f h e a t transfer e x p e r i e n c e d by most wood c h i p s owing t o t h e l a r g e a s p e c t r a t i o s t h e y u s u a l l y have ( 1 0 ) . One d i m e n s i o n a l h e a t i n g i n t e n s i t y i s made p r e c i s e e x p e r i m e n t a l l y b y c o n t r o l l i n g t h e a p p l i e d heat f l u x a t one f a c e o f a wood c y l i n d e r w i t h i n s u l a t e d s i d e s . The l o w e s t heating i n t e n s i t y s t u d i e d , 8.4 χ 1 0 ~ W/m (2 c a l / c m - s ) , b a r e l y chars t h i c k samples ( o r causes s m o l d e r i n g combustion i f oxygen i s p r e s e n t ) . The h i g h e s t , 2.5 χ 1 0 ~ W/m (6 c a l / c m - s ) , i s t y p i c a l i n f u r n a c e s o r h i g h t e m p e r a t u r e r e a c t o r s d e s i g n e d f o r maximum h e a t i n g of p a r t i c l e s . Biomass m o i s t u r e v a r i e s w i t h s p e c i e s and age as w e l l as w i t h growing r e g i o n . T y p i c a l moisture contents (dry b a s i s ) found f o r f e e d p i l e s i n t h e P a c i f i c Northwest range f r o m 10% t o 110%, hence the c h o i c e s i n our experiments (11). Simultaneous v a r i a t i o n s i n two or three o f t h e above experimental c o n d i t i o n s were s y s t e m a t i c a l l y i n v e s t i g a t e d u s i n g a Box-Behnken e x p e r i m e n t a l d e s i g n (12) . 4

2

3

Experimental

2

2

2

Details

Apparatus . A d e s c r i p t i o n and diagram o f t h e s i n g l e p a r t i c l e p y r o l y s i s r e a c t o r a p p e a r s i n Chan, e t a l . (13) b u t a b r i e f p r e s e n t a t i o n i s g i v e n f o r completeness. A wood c y l i n d e r was p l a c e d s n u g l y i n a g l a s s s l e e v e and r e a c t o r assembly. One f a c e o f t h e c y l i n d e r was h e a t e d b y an a r c lamp. I t provided radiative, s p a t i a l l y u n i f o r m , 1-D a x i a l h e a t i n g a s v e r i f i e d b y a b s o l u t e c a l i b r a t i o n o f t h e heat f l u x (6,14, 1 5 ) . The h e a t i n g p e r i o d was t h e

5. KELBONETAL.

Tar ProductionfromPyrolysis ojWoodParticles

43

same f o r a l l e x p e r i m e n t s , 12 m i n , c h o s e n specifically t o be s u f f i c i e n t l y short t o enable t h e study o f a c t i v e d e v o l a t i l i z a t i o n , not char gasification, i n the thinnest wood cylinders. T h e r m o c o u p l e s i n t h e wood a t 2, 4, a n d 6 mm f r o m t h e h e a t e d f a c e measured t h e t e m p e r a t u r e . An i n f r a r e d p y r o m e t e r , mounted o f f - a x i s from t h e a r c lamp beam a p p r o x i m a t e l y measured t h e s u r f a c e temperature o f t h e p e l l e t . The d e s i g n o f t h e g l a s s r e a c t o r and b a f f l e allowed the uniform i r r a d i a t i o n b u t p r e v e n t e d v o l a t i l e s from c o n d e n s i n g on t h e window. A l a r g e h e l i u m c a r r i e r gas f l o w r a t e was d i r e c t e d past the heated surface of the p a r t i c l e . The c a r r i e r quenched t h e v o l a t i l e s and swept them w i t h o u t s i g n i f i c a n t b a c k m i x i n g o r r e a c t i o n (6 ) t o t h e a n a l y s i s system. The h e l i u m p r e s s u r e on t h e u n h e a t e d f a c e was s l i g h t l y e l e v a t e d t o e n s u r e v o l a t i l e s f l o w i n t h e p a r t i c l e toward t h e h e a t e d f a c e , which i n t u r n e n s u r e d maximum volatiles recovery. I t has been v e r i f i e d (8) t h a t during d e v o l a t i l i z a t i o n of a large authentic p a r t i c l e s , nearly a l l of the v o l a t i l e s f l o w t o w a r d t h e h e a t e d s u r f a c e owing t o t h e d e c r e a s e d p o r o s i t y behind the reaction front. A c o l d t r a p (packed w i t h g l a s s wool a n d a t -40 C) i m m e d i a t e l y downstream from t h e r e a c t o r condensed t a r s and w a t e r f r o m t h e v o l a t i l e s . Permanent g a s e s f l o w e d t h r o u g h t h i s t r a p w i t h o u t c o n d e n s a t i o n a n d were sampled n e a r i t s e x i t a t p r e s e l e c t e d t i m e s d u r i n g t h e e x p e r i m e n t u s i n g two a u t o m a t e d g a s sampling v a l v e s . T h i s p r o v i d e d i n f o r m a t i o n on e v o l u t i o n r a t e s o f gaseous p r o d u c t s . A l lvolatiles were l a t e r a n a l y z e d by gas chromatography.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch005

f

Sample P r e p a r a t i o n . The wood p e l l e t s were a l l c u t a n d sanded, w i t h g r e a t a t t e n t i o n t o g r a i n d i r e c t i o n , f r o m u n i f o r m sapwood s e c t i o n s o f t h e same l o d g e p o l e p i n e (Pinus contorta) tree p r o v i d e d by Weyerhauser Co. (Corvallis M i l l ) . The c y l i n d e r s were o v e n - d r i e d a t 90 C f o r a t l e a s t t h r e e weeks. D r y p a r t i c l e s u s e d i n some o f t h e p y r o l y s e s a t t a i n e d an e q u i l i b r i u m m o i s t u r e c o n t e n t o f a b o u t 5% d u r i n g h a n d l i n g a t t h e normal l a b o r a t o r y c o n d i t i o n s . M o i s t u r e was q u a n t i t a t i v e l y added ( f o r some p y r o l y s e s ) u s i n g a m i c r o s y r i n g e a n d b a l a n c e , a n d a l l o w e d t o come t o a u n i f o r m d i s t r i b u t i o n as d e s c r i b e d by K e l b o n (14). Gas Analysis. Permanent g a s e s , o p e r a t i o n a l l y d e f i n e d a s a l l components p a s s i n g t h r o u g h t h e -40°C c o l d t r a p , were c o l l e c t e d i n 30 s t a i n l e s s s t e e l sample l o o p s o f known volume. Immediately a f t e r t h e e x p e r i m e n t , samples were a u t o m a t i c a l l y i n j e c t e d i n t o a P e r k i n - E l m e r Sigma 2 Gas Chromatograph u s i n g a S u p e l c o 100/120 mesh C a r b o s i e v e S column 0.5 mm d i a m e t e r a n d 1.5 m long. The peaks were i n t e g r a t e d and q u a n t i f i e d b y a P e r k i n - E l m e r Sigma 15 C h r o m a t o g r a p h y D a t a Station. Both a thermal conductivity d e t e c t o r and a flame i o n i z a t i o n d e t e c t o r were u s e d as d e s c r i b e d i n Bousman (15). Tar Analysis. The t a r i s washed f r o m t h e t r a p a n d a h i g h e r m o l e c u l a r weight, b u t s m a l l amount, was washed from t h e r e a c t o r . An a l i q u o t o f t h e f o r m e r was a n a l y z e d f o r w a t e r a n d low m o l e c u l a r w e i g h t compounds by g a s c h r o m a t o g r a p h y u s i n g a S u p e l c o 80/100 mesh Porapak Q column 0.5 mm d i a m e t e r and 0.5 m l o n g . The remainder from t h e t a r t r a p was t r e a t e d w i t h a p p r o x i m a t e l y 2 g o f MgS04 t o remove water and t h e n f i l t e r e d . A known q u a n t i t y o f p-bromophenol was

44

PYROLYSIS OILS FROM BIOMASS

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch005

added to both the trapped sample and reactor washings as an i n t e r n a l standard. Each was concentrated using a Kaderna Danish evaporator i n order to remove THF while minimizing the l o s s of the other compounds. The r e s u l t i n g high molecular weight t a r f r a c t i o n was analyzed by gas chromatography using e i t h e r a J and W S c i e n t i f i c DBWAX or Carbowax 20M fused s i l i c a c a p i l l a r y column 0.25 mm ID, 30 m long with a Perkin-Elmer s p l i t t i n g i n j e c t i o n port. Only major peaks which appeared i n a l l samples are presented i n t h i s paper as composite, chromatogram-like f i g u r e s . The component i d e n t i f i c a t i o n number versus absolute y i e l d i s p l o t t e d for several conditions. Char A n a l y s i s . The f r a g i l e char was c a r e f u l l y separated with a s c a l p e l from the l i g h t color, unreacted portion of the wood p e l l e t , and each f r a c t i o n weighed. A q u a l i t a t i v e chemical analysis of some char samples was performed using a F o u r i e r Transform I n f r a r e d Spectrometer (FTIRS) with preparation as described i n Bousman (15). The surface areas of some chars were also characterized using C O 2 adsorption. E x p e r i m e n t a l Design and Data A n a l y s i s . With such lengthy experiments and chemical analyses, only a f r a c t i o n of the independent v a r i a b l e combinations could be s t u d i e d . These were picked according to a type of incomplete f a c t o r i a l experimental design which f a c i l i t a t e s i d e n t i f i c a t i o n of optimum conditions (12). The r e s u l t i n g measurements (Table 1) were f i t to empirical models of the class given i n Equation 1 (12,16) to i d e n t i f y and quantify major effects : Yk

=

b

0

+

^

b

x

i i

+

b^jx^xj, f o r i< j (1) where ν^ = k-th product y i e l d of interest, (or other dependent variable) X £ , X J = independent variables (process controllables) and b Q f b^ and b^j = least square parameter estimates obtained from multiple regression. The independent v a r i a b l e s e t t i n g s were a l l e q u a l l y spaced, and were s c a l e d to a range between -1 and +1 making them dimensionless before f i t t i n g the data as shown i n Table 1. In t h i s way, the units or range of a studied variable do not contribute to the magnitude of the c o e f f i c i e n t s , the b's i n Equation 1 above. The i n t r i n s i c importance of a squared term can also be determined by t h i s s c a l i n g since the second order terms are of the same magnitude as the l i n e a r terms. The units of the c o e f f i c i e n t s b are the same as the dependent variable, y, and represent changes i n i t f o r a now "unit change" i n the independent v a r i a b l e from the mean value studied. When process c o n t r o l l a b l e s such as moisture and p a r t i c l e size combine to affect the pyrolysis i n a non-additive (synergistic) way, as when the l a s t term of Equation 1 i s large, non-linear dependence of y i e l d s on the process controllables i s demonstrated. Trend l i n e s i n subsequent f i g u r e s are p l o t s of Equation 1 f o r p a r t i c u l a r values of the other variables.

5.

KELBON ETAK

Tar Production from Pyrolysis of Wood Particles

45

R e s u l t s and D i s c u s s i o n The range of i n t r a p a r t i c l e temperatures measured f o r the p y r o l y s i s conditions studied are shown i n Figures 1-3. The temperatures achieved are consistent with those found i n other studies f o r both small (17-19) and large (20) wood p a r t i c l e s . Comparing Figure 1 to Figure 2 i l l u s t r a t e s the e f f e c t of i n i t i a l moisture at 110% and 10% r e s p e c t i v e l y , on temperature h i s t o r y . When moisture i s present during p y r o l y s i s , the temperature r i s e s to a plateau at 100°C u n t i l the water has l o c a l l y evaporated, and then more slowly a t t a i n s a somewhat lower ultimate temperature than found i n d r i e r wood p a r t i c l e s at the same conditions (see Figure 2 ) . The duration of the 100°C plateau and time to reach ultimate temperature are prolonged the greater the i n i t i a l moisture of the p a r t i c l e . The surface temperature measurement i n F i g s 1 and 2 i s of some q u a l i t a t i v e value but once v o l a t i l e s are produced, the i n f r a r e d pyrometer cannot a c c u r a t e l y "see" the surface and the measured temperature i s a r t i f i c i a l l y low. In Figures 1 and 2, examine the r e l a t i v e l y greater temperature d i f f e r e n c e (~20 0°C) between the traces at 2 and 4 mm depth compared to that (~50°C) between 4 and 6 mm. It i s i n d i c a t i v e of the steep temperature gradient experienced by the 15 mm thick p a r t i c l e . This i s i n contrast to the shallow temperature gradients i n Figure 3. Presented are the temperatures in the very moist, 10 mm thick p a r t i c l e f o r the highest and lowest heating intensities studied (8.4 and 25.1 χ 1 0 " W/m ) , respectively. For low heating i n t e n s i t i e s , the temperature gradient i s s l i g h t as suggested by Kung ( 7 ) , but a l l zones of the p a r t i c l e pyrolyze at low temperature. At 25.1 χ 1 0 ~ W/m, the temperature of p y r o l y s i s i s high and i n the range that favors t a r formation, but the temperature drops o f f r a p i d l y with distance from the surface. Note that reaction zones near the p a r t i c l e surface experience quite high heating rates even f o r moist p a r t i c l e s , which should favor t a r production early i n the d e v o l a t i l i z a t i o n of a large p a r t i c l e . F r a c t i o n a l y i e l d s are an important measure of s e l e c t i v i t y and are useful f o r downstream separation process considerations. When i n t e r p r e t i n g the f r a c t i o n a l y i e l d data from l a r g e p a r t i c l e p y r o l y s i s , several points should be kept i n mind. The i n d i v i d u a l product y i e l d s are expressed as weight f r a c t i o n s of that which reacted i n the 12 min p y r o l y s i s duration. The f r a c t i o n a l y i e l d s p r e s e n t e d here are d i r e c t l y comparable t o data from other investigators i f i n those studies, p a r t i c l e s had s u f f i c i e n t time to react completely, but not undergo extensive char g a s i f i c a t i o n a f t e r a l l the v o l a t i l e s were gone. The f r a c t i o n of the p a r t i c l e which reacts i n the f i x e d p y r o l y s i s time i s given i n Table 1. It can be seen that the 12 min duration s u c c e s s f u l l y studies the a c t i v e d e v o l a t i l i z a t i o n period because a l l but 1 of the % reacted values are under 100%. A second point i s that the reported y i e l d s r e f l e c t the non-uniform temperature h i s t o r i e s presented i n Figures 1-3. The appropriate measure of r e p r o d u c i b i l i t y of the experiments i s the standard deviation f o r t a r y i e l d c a l c u l a t e d from 3 r e p l i c a t e runs, and these appear at the bottom of Table 1. Their standard d e v i a t i o n i s 2%. However, because of the inherent d i f f i c u l t y i n recovering a l l products, e s p e c i a l l y t a r s , the mass balances do not always add to 100%. Thus, another measure of uncertainty i s the

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch005

f

4

4

2

2

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch005

46

PYROLYSIS OILS FROM

BIOMASS

SECONDS

Figure 1. Temperature h i s t o r i e s at the indicated locations i n a 1.5 cm thick wood p a r t i c l e pyrolyzed with a constant heat flux of 1.6E-4 W/m. I n i t i a l p a r t i c l e moisture was 110% (dry b a s i s ) . 2

500 J

400

300 J

200. /

/

s

///

0.0 0.2 0.4 0. β

100.1\ / /

7/ I 200

10

1— 400

500

CM CM CM CM

—I— 600

—Γ 700

SECONDS

Figure 2. Temperature h i s t o r i e s at the indicated locations i n a 1.5 cm thick wood p a r t i c l e pyrolyzed with a constant heat flux of 1.6E-4 W/m. I n i t i a l p a r t i c l e moisture was 10% (dry basis). 2

5. KELBONETAK

47

Tar ProductionfromPyrolysis ofWood Particles

Table 1 - Experimental Conditions and Pyrolysis Product Yields

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch005

Actual values of independent variables: moisture content

heat particle flux thickness W/m^ cm

110 110 10 10 110 110 10 10 60 60 60 60

2. .5E-3 8. .4E-4 2. .5E-3 8..4E-4 1..6E-3 1,.6E-3 1,.6E-3 1,.6E-3 2 .5E-3 2 .5E-3 8 .4E-4 8 .4E-4

1 1 1 1 1.5 0.5 1.5 0.5 1.5 0.5 1.5 0.5

60 60 60

1 .6E-3 1 .6E-3 1 .6E-3

1 1 1

Scaled values of independent variables: M.C.

flux thickness

1 1 -1 -1 1 1 -1 -1 0 0 0 0

1 -1 1 -1 0 0 0 0 1 1 -1 -1

0 0 0 0 1 -1 1 -1 1 -1 1 -1

0 0 0

0 0 0

0 0 0

mean of the r e p l i c a t e s s t a n d a r d d e v i a t i o n of t h e r e p l i c a t e s

percent reacted

American Chemical Society Library 1155 16th St., N.W. Washington, D.C. 20036

% tar

% mass balance

73. 3 41. 8 12. 0 53. ,4 95. 6 51. ,4 7. 1 40. ,6 33. 5 60. ,8 78. ,5 63. ,8 35. ,6 62. .6 97. ,9 64. .4 67. ,8 58. .6 100. .0 60. .8 8. .8 66. .4 16. .2 60. .9

84. .2 71, .5 83, .0 98, .8 85, .0 61 .6 83 .7 74 .4 79 .5 66 .5 86 .2 73 .8

73. .3 59. .7 59. .3

59, .0 58, .4 61, .0

67 .9 83 .7 57 .9

64.1 8,.0

59 .5 1 .4

69 .8 13 .0

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48

PYROLYSIS OILS FROM BIOMASS

discrepancy i n the mass balance. For a l l the experiments with moisture added, not just the r e p l i c a t e d , the average mass balance closure was 80%, with a standard deviation of 11%. For another set of experiments not presented i n Table 1 but shown i n Figure 4 f o r dry p a r t i c l e s , the mass balance c l o s e s to w i t h i n 6%. The discrepancy was usually assumed to be t a r that condensed on the system surfaces. The synergy, or i n t e r a c t i o n of p a r t i c l e size and heat f l u x to a l t e r the t a r y i e l d can be c l e a r l y seen i n Figure 4. Presented i s the weight f r a c t i o n water-free t a r produced from the f i x e d duration p y r o l y s i s of dry wood p a r t i c l e s of several thicknesses. The trend l i n e s result from regression of a l l the data to Equation 1. Recall that the experimental uncertainty as evidenced by the r e p l i c a t e runs i s about 2%. The data points show runs i n which the density was changed by a factor of three using compressed sawdust p e l l e t s ( 6 ) . It can be seen to have a small e f f e c t . If there were no "combined" e f f e c t of heating i n t e n s i t y and p a r t i c l e thickness, the t a r trend l i n e s f o r d i f f e r e n t p a r t i c l e sizes would be e s s e n t i a l l y p a r a l l e l . However, the reduction i n t a r f o r an increase i n heating rate, as c h a r a c t e r i z e d by the slope of the t r e n d l i n e s at any point, i n c r e a s e s as the p a r t i c l e t h i c k n e s s i n c r e a s e s . The t h i n n e s t p a r t i c l e , 5 mm, produces nearly a constant t a r y i e l d between 30 and 40% when heated over t h i s wide, p r a c t i c a l range of intensities. The t h i c k e s t p a r t i c l e pyrolyzed at the lowest heat f l u x produces over 65% t a r , and i t decreases to 20% at the maximum heating i n t e n s i t y investigated. This i s consistent with the extensive t a r cracking that l i k e l y occurs i n the p a r t i c l e surface char where high temperatures p r e v a i l f o r severe heating. Note that when heating at the i n t e r m e d i a t e heat f l u x s t u d i e d , dry p a r t i c l e s of a l l t h i c k n e s s e s y i e l d approximately the same 3 0 % - 3 5 % t a r . This condition represents a t a r y i e l d that i s i n s e n s i t i v e to p a r t i c l e size over t h i s range. The temperature p r o f i l e i n a dry p a r t i c l e i s a f f e c t e d p r i n c i p a l l y by only two process v a r i a b l e s , the p a r t i c l e s i z e and a p p l i e d heat f l u x . Thus, i t can be p l o t t e d i n a graph such as Figure 4. However, when i n i t i a l moisture of the p a r t i c l e i s also varied i n combination with these variables, the presentation of the data must be d i v i d e d i n t o several graphs, one f o r each p a r t i c l e s i z e , f o r example. The y i e l d of t a r produced from p y r o l y s i s of moist wood i s presented i n Figure 5 as a function of both i n i t i a l moisture content (abcissa) and heating i n t e n s i t y f o r the thickest p a r t i c l e s i z e used i n t h i s study, 15 mm. The uncertainty i n the tar from wet p a r t i c l e p y r o l y s i s i s about 5%. Note that moisture causes the optimum t a r conditions to occur at 16.7 χ 1 0 ~ W/m, rather than the 8.4 χ 1 0 " W/m f o r dry p a r t i c l e s (Figure 4 ) , consistent with the higher heating i n t e n s i t y required to vaporize the water and cause p y r o l y s i s . Overall, the l e v e l of t a r produced i s higher, 50-70%, than f o r dry wood p a r t i c l e s . It can be speculated that the reason f o r the higher t a r y i e l d i s a combination of a lower average p y r o l y s i s temperature, as w e l l as a reduced extent of c r a c k i n g reactions as the v o l a t i l e s leave the cooler p a r t i c l e . Hydrogen i s measurable i n the gases, as well. The data i n Figure 5 are d i f f i c u l t to v i s u a l i z e since t a r y i e l d s depend on more variables than can c l e a r l y be presented i n a 4

4

2

2

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KELBON ET AL.

Tar ProductionfromPyrolysis of Wood Particles

Figure 3. Temperature h i s t o r i e s at the indicated locations i n 1.0 cm thick wood p a r i c l e pyrolyzed with two d i f f e r e n t heat fluxes. I n i t i a l p a r t i c l e moisture was 110% (dry b a s i s ) .

Figure 4. Weight f r a c t i o n t a r y i e l d f o r the p y r o l y s i s of dry wood p a r t i c l e s at varying surface heat fluxes f o r three thicknesses; trend l i n e s are least-square f i t s and symbols are some of the experimental data.

PYROLYSIS OILS FROM BIOMASS

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch005

50

î i

i 10 J w I

10

ι 35

I

I

60 inftiol molature (dry bosla)

I

83

110

F i g u r e 5. Measured weight f r a c t i o n t a r p r o d u c e d from a 1.5 cm t h i c k wood p a r t i c l e as a f u n c t i o n o f m o i s t u r e c o n t e n t f o r 3 different heating rates.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch005

5.

KELBONETAL.

Tar Production from Pyrolysis of Wood Particles

51

two d i m e n s i o n a l p l o t . A n o t h e r way t o v i s u a l i z e t h i s dependence uses c o n t o u r s o f c o n s t a n t t a r p r o d u c t i o n p r e d i c t e d by t h e r e g r e s s i o n of a l l t h e t a r y i e l d d a t a f r o m t h e e x p e r i m e n t s where i n i t i a l m o i s t u r e was v a r i e d . F i g u r e 6 (a-c) shows how p a r t i c l e s i z e and h e a t i n g r a t e a f f e c t t a r y i e l d a t each o f t h e t h r e e i n i t i a l m o i s t u r e l e v e l s t h a t were s t u d i e d . Each c o n t o u r i s a 1% change i n t a r y i e l d , and r e c a l l t h a t t h e e x p e r i m e n t a l u n c e r t a i n t y i s e s t i m a t e d a t 2% from replicates. Thus, t h e n a t u r e o f t h e c o n t o u r s a r e not p r e c i s e l y known, b u t t h e graph s e r v e s t o i l l u s t r a t e t h e c o m p l i c a t e d b e h a v i o r of optimum y i e l d s . Note by t h e m a g n i t u d e s on e a c h c o n t o u r l i n e , t h a t t h e t a r y i e l d i n c r e a s e s from a " s a d d l e p o i n t " f o r b o t h l a r g e r and s m a l l e r p a r t i c l e t h i c k n e s s e s , but d e c r e a s e s f r o m t h e " s a d d l e " f o r l a r g e and s m a l l e r h e a t i n g r a t e s . Note the p o s i t i o n of the s a d d l e moves t o l o w e r heat f l u x e s f o r h i g h e r i n i t i a l m o i s t u r e o f t h e p a r t i c l e s b e i n g p y r o l y z e d . The h i g h e s t t a r y i e l d s o b s e r v e d approach 70% f o r t h e s m a l l e s t and l a r g e s t p a r t i c l e s s t u d i e d . In F i g u r e 7, a c o m p o s i t i o n p r o f i l e o f some components o f b o t h t h e t a r and gas f r a c t i o n i s p r e s e n t e d f o r p y r o l y s i s o f a 1 cm t h i c k , moist p a r t i c l e . Changes i n t h i s p r o f i l e s i m p l y h i g h l i g h t changes i n p r o d u c t c o m p o s i t i o n as p r o c e s s c o n d i t i o n s change, w h i c h i s i m p o r t a n t i n f o r m a t i o n f o r t h e d e s i g n o f downstream s e p a r a t i o n operations. For d i f f e r e n t c o n d i t i o n s t h a t manipulate the p a r t i c l e temperature h i s t o r y a f t e r t h e f a s h i o n shown i n F i g u r e s 1-3, d i f f e r e n t amounts o f t h e p a r t i c l e r e a c t as can be v e r i f i e d i n T a b l e 1. If t h e amount r e a c t e d i s n o r m a l i z e d t o r e p r e s e n t 100%, t h e o r d i n a t e i s t h e w e i g h t f r a c t i o n o f e a c h component i n t h e o f f g a s . Thus a l l components p l o t t e d a r e each l e s s t h a n 2% o f t h e m o i s t wood p a r t i c l e p y r o l y s i s products. The e r r o r as e s t i m a t e d from r e p l i c a t e d e t e r m i n a t i o n s i s about ±0.5% a b s o l u t e , o r 25% r e l a t i v e p r e c i s i o n . The h i g h m o l e c u l a r weight s p e c i e s c o m p o s i t i o n appears t o v a r y l i t t l e as p a r t i c l e temperature i s m a n i p u l a t e d by c h a n g i n g b o t h m o i s t u r e and h e a t i n g i n t e n s i t y of the p y r o l y s i s . However, t h e low m o l e c u l a r weight t a r compounds a r e i n g r e a t e r c o n c e n t r a t i o n f o r m i l d i n t e n s i t y h e a t i n g (8.4 χ 1 0 ~ W/m ) t h a n f o r s e v e r e h e a t i n g which appears t o f a v o r t h e hydrocarbon gases and hydrogen. A l t h o u g h t h e c o m p o s i t i o n d i f f e r e n c e s are n e a r l y w i t h i n the experimental e r r o r , moisture a p p e a r s t o s l i g h t l y enhance t h e p r o d u c t i o n o f m e t h a n o l and a c e t i c a c i d f o r t h e s e experiments (1 cm p a r t i c l e ) . 4

2

Conclusions Data has been p r e s e n t e d which s u g g e s t s t h a t m o i s t u r e can enhance t h e p r o d u c t i o n o f t a r from t h e p y r o l y s i s o f l a r g e wood p a r t i c l e s u s i n g c o n d i t i o n s t h a t o c c u r i n a l a r g e s c a l e r e a c t o r where t h e heat f l u x a p a r t i c l e experiences i s quite constant. The most f a v o r a b l e c o n d i t i o n s r e s u l t i n about 70% o f t h e r e a c t e d biomass becoming t a r . I f one assumes t h a t t h e mass b a l a n c e d i s c r e p a n c y r e s u l t s from tar c o n d e n s i n g on r e a c t o r s u r f a c e s , t h i s i s a c o n s e r v a t i v e e s t i m a t e . Acknowledgment s T h i s work was s u p p o r t e d by t h e N a t i o n a l S c i e n c e F o u n d a t i o n , Grant No. CPE-8400655. M a r c i a Kelbon g r a t e f u l l y acknowledges t h e p a r t i a l s u p p o r t o f a Weyerhauser F e l l o w s h i p and S c o t t Bousman acknowledges t h e p a r t i a l s u p p o r t o f a f e l l o w s h i p from Chevron Corp.

F i g u r e 6. Contour l i n e s of c o n s t a n t t a r y i e l d p l o t t e d a g a i n s t b o t h p a r t i c l e t h i c k n e s s ( v e r t i c a l s c a l e ) and heating intensity ( h o r i z o n t a l s c a l e ) f o r (a) 10% i n i t i a l m o i s t u r e ; (b) 60% i n i t i a l m o i s t u r e ; and (c) 110% i n i t i a l m o i s t u r e .

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch005

C/î en

5 δ

ι

53 ο

I

Ο

a

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch005

KELBON ET AL.

Tar Production front Pyrolysis of Wood Particles

53

Symbol Key 4110% Initial moisture, heated at 2 cal/cm -s 010% initial moisture, heated at 2 cal/cm -s • 110% Initial moisture, heated at 6 cal/cm -s Δ10% initial moisture, heated at 6 cal/cm -s 2

2

2

2

F i g u r e 7. Tar p r o d u c t c o m p o s i t i o n p r o f i l e f o r 1. cm t h i c k p a r t i c l e s w i t h two d i f f e r e n t i n i t i a l m o i s t u r e c o n t e n t s , h e a t e d a t two d i f f e r e n t h e a t i n g r a t e s .

54

PYROLYSIS OILS FROM BIOMASS

Literature Cited

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch005

1.

Reuther, J.J.; Golike, G.P.; Taylor, P.H.; Karsner, G.G. In Applications of Chemical Engineering Principles in the Forest Products and Related Industries: American Inst. of Chemical Engineers, Forest Products Div.; Seattle, WA, 1986; p 160. 2. Petersen, E.E. In Chemical Reaction Analysis, Prentice Hall, N.Y., 1965. 3. Russel, W.A.; Saville, D.A.; Greene, M.I. AIChE J 1979, 25, 65. 4. Srinivas, B.; Amundson, N.R. AIChE J 1980, 26, 487. 5. Massaquoi, J.G.M.; Riggs, J.B. AIChE J 1983, 29, 975. 6. Chan, W.C.R. Ph.D. Thesis, Dept. Chem. Engrg., U. Washington, Seattle, WA, 1983. 7. Kung, H.C. Combustion and Flame 1972, 18, 185-192. 8. Lee, C.K.; R.F. Chaiken; Singer, J.M. 16th International Symposium on Combustion, Combustion Institute, Pittsburgh, PA, 1976, p 1459. 9. Ohlemiller, T.; Kashiwagi, T.; Werner, K. NBSIR 85-3127, Dept. of Commerce, National Bureau of Standards, Center for Fire Research, Gaithersburg, MD, April 1985. 10. Miles, T.R. In Thermochemical Processing of Biomass, Ed. by A.V. Bridgewater, Butterworths, London, 1984, p 69. 11. Chan, W.C.R.; Krieger, B.B., submitted to I.E.C. Proc. Des. Dev., 1986. 12. Box, G.E.P.; Behnken, D.W. Technometrics 1960, 2, p 455. 13. Chan, W.C.R.; Kelbon, M.; Krieger, B.B. Fuel 1985, 64, 1505. 14. Kelbon, M., M.S. Thesis, Dept. Chem. Engrg., U. Washington, Seattle, WA, 1983. 15. Bousman, W.S. M.S. Thesis, Dept. Chem. Engrg., U. Washington, Seattle, WA, 1986. 16. Box, G.E.P.; Hunter, J.S.; Hunter, W.G. Statistics for Experimenters, wiley, N.Y. 1978. 17. Scott, D.S.; Piskorz, J.; Radlein, D. I.E.C. Proc. Des. Dev. 1985, 24, 581. 18. Nunn, T.R.; Howard, J.B.; Longwell, J.B.; Peters, W.A. I.E.C. Proc. Des. Dev. 1985, 24, 836. 19. Bradbury, A.G.W.; Sakai, F.; Shafizadeh, F. J. Appl. Poly. Sol. 1979, 23, 3271. 20. Kanury, A.M. Combustion and Flame, 1972, 18, 75. Received March 31, 1988

Chapter 6

Relation of Reaction Time and Temperature to Chemical Composition of Pyrolysis Oils Douglas C. Elliott Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch006

1

Pacific NorthwestLaboratory ,P. O. Box 999, Richland,WA99352 Biomass pyrolysis tars have widely varying chemical compositions. As a result of this variation, the physical properties of the tars also vary over a wide range. For short-residence-time processing there is a direct correlation between chemical composition and operating temperature. As the temperature increases the oxygen content decreases and the hydrogen to carbon ratio decreases. Biological activity, as measured by mutagenic and tumor-initiating activity, also correlates with temperature. The activity appears only in the high-temperature tars which contain high levels of polycyclic aromatic hydrocarbons. The effect of pressure and residence time on pyrolysis tar yield and quality is also shown. The addition of reducing gas and catalysts to the pressurized system results in product improvements which make comparisons to pyrolysis less straightforward. The recognition of the production of tars by pyrolysis of wood dates to ancient times (1). The composition of these complex mixtures was studied over the years and many components were i d e n t i f i e d (2). U n t i l the last several decades the results reported i n the l i t e r a ture accurately portrayed the composition of wood pyrolyzate tar since e s s e n t i a l l y a l l of such tars were byproducts of charcoal production, a slow process operated at temperatures limited to less than 500°C. As the processing technology has developed during this century, the processing environment has moved to higher temperatures and shorter residence times i n attempts to optimize product d i s t r i bution to either l i q u i d or gas products and minimize s o l i d char production. As processes developed to minimize tar production (as for g a s i f i c a t i o n ) or maximize tar production (as for l i q u e f a c t i o n ) , the v a r i a t i o n i n the tar composition has not always been recognized. As a result of the study of biomass pyrolysis tar composition which has occurred over the past decade, i t i s now obvious that a l l biomass tars are not the same 03). When considering the tar product 1

Operated by Battelle Memorial Institute for the U.S. Department of Energy under Contract DE-AC06-76RLO-1830. 0097-6156/88/0376-0055$06.00/0 1988 American Chemical Society c

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch006

56

PYROLYSIS OILS FROM BIOMASS

of a given biomass conversion process i t i s not enough to deal only with the quantity of tar but the quality of the tar must also be considered. It i s apparent that further processing, either chemi­ c a l l y or b i o l o g i c a l l y , of the tar as a byproduct or as the major product w i l l be e n t i r e l y dependent on the tar formation conditions which determine the tar composition. Early recognition of the changes i n tar composition as a result of p y r o l y t i c processes was reported by Diebold i n 1980 (4). The pyrolysis pathways reported (see Figure 1) depict the conversion of primary pyrolysis tars to two types of secondary t a r . The "second­ ary t a r " from Figure 1 i s the high-pressure l i q u e f a c t i o n product which has been widely studied. The other secondary tar i s the "Vapor Phase Derived Tar." This material i s also suggested as being favored at high pressure with further reaction at high pressure leading to carbon black. However, neither of these secondary tar formation pathways addresses the change i n tar composition as i t i s held at high temperatures without high pressure. Only transient oxygenated fragments and gases are produced from primary tar at low pressure and high temperature according to these reaction pathways. A somewhat more complete series of pyrolysis pathways was presented recently by Evans & Milne (_5). In this series of reac­ tions (see Figure 2) biomass i s pyrolyzed at low pressure to primary o i l which i s further converted sequentially to oxygenates, aromatics, p o l y c y c l i c aromatics and, eventually, soot. This series correlates well with the progression of chemicals e a r l i e r i d e n t i f i e d by this author (6) which i s repeated below. Mixed ^ Phenolic ^ Alkyl ^ Heterocyclic Oxygenates • Ethers • Phenolics ψ Ethers 400°C 500°C 600°C 700°C

^ Ψ

Λ PAH • 800°C

Larger PAH 900°C

These chemical groups are representative of the type of components found i n condensate produced by short-residence-time processing of wood at the given temperature. As such these chemical groups sug­ gest the types of chemical mechanisms occurring i n high-temperature pyrolysis of biomass, i . e . , dehydrogenation and condensation (aromat i z a t i o n ) , dealkylation and deoxygenation. Experimental Systems The data i n this paper are drawn from a number of studies performed at P a c i f i c Northwest Laboratory (3,7-9). We have examined biomass pyrolysis tar samples from many types of p y r o l y t i c g a s i f i c a t i o n and liquefaction systems through the U.S. Department of Energy support of domestic biomass thermochemical conversion research and i n t e r ­ national cooperative e f f o r t s . Many of these can be compared d i r e c t l y as a function of temperature since they are a l l produced at short residence time, approximately one second. Others produced at longer residence time or pressure require discussion separately. The bulk of this chapter w i l l deal with tar produced i n shortresidence-time reactors. There are four convenient groups i n which to categorize these processes: conventional f l a s h pyrolysis (10-13), high-temperature f l a s h pyrolysis,(14) conventional steam g a s i f i c a t i o n (15-17) and high-temperature steam g a s i f i c a t i o n (18). The effects of these four process groups and their operating tem­ perature regimes on product d i s t r i b u t i o n i s presented i n Figure 3.

6. ELLIOTT

57

Relation of Time and Temperature to Oil Composition

Low Temp < 400°C < High Temp

Vapor Phase Derived Tar.(V or L)

Fast < 0.1 sec < Slow Low Ρ < 75kPa < High Ρ

Carbon Black

High τ _ High Ρ

H ,CO, CH . C0 , H 0 2

4

2

High Τ

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch006

Biomass,,

High Τ

Primary Tar(L)

Primary Tar,(V)

V

Secondary

Slow High Ρ

Transient • Oxygenated Fragments^)

v°

s ighT H

Ta/cL,

4

Olefins

Water Soluble Refractory Oxygenated Compounds

Charcoal (S) C0 , H 0 2

CO CH

High Τ Slow High Ρ

Med. Τ Slow Med. Ρ

r

Lo P

Low Τ Slow High Ρ

High Τ Fast

(

2

( V )

2

Dlebold, 1980 Figure 1. Biomass pyrolysis global mechanism, c i r c a 1980

Primary Oils Vapors and Gases

H 0, C0 , CO 2

2

Primary Oil Vapors (Oxygenates)

Ο

Light Hydrocarbons, Aromatics and Oxygenates

Tertiary Oils (Tars) Olefins, Aromatics CO, C 0 , H, H 0 2

2

PNA |CO, H , C 0 H 0, CH 2

2

CO, H C 0 , H 0| 2

2

2

4

2

M

Primary Oil Liquids

Liquids

Secondary Oils

High Pressure Condensed Oils (Phenols, Aromatics)

High f Pressure Solids

Biomass

Evans and Milne, 1986

Charcoal

Coke

Soot

Pyrolysis Severity •

Figure 2. Biomass pyrolysis global mechanism, c i r c a 1986

2

PYROLYSIS OILS FROM BIOMASS

58

As has been reported numerous times previously i n the l i t e r a t u r e the amount of tar product decreases steadily above 500°C while the amount of gas product increases. The amount of char i s low even at 500°C and also decreases over the temperature range. The quality of both the tar and the char as indicated by the oxygen content changes dramatically.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch006

Results and Discussion Chemical Properties of Tars. In addition to the change i n quantitative y i e l d of wood pyrolysis tar there i s also a substantial change i n chemical composition of the tar as a function of temperature. As shown i n Figure 4 the oxygen content as well as the hydrogen to carbon atomic r a t i o can be plotted vs. temperature to show a strong r e l a t i o n s h i p . These data are for tar elemental compositions calculated to a water-free basis from analyses of crude tars. As stated e a r l i e r these data are from a number of different reactor systems yet the strong correlation i s evident. With increasing processing temperature the oxygen content declines as does the hydrogen to carbon r a t i o . These changes represent the conversion of the highly oxygenated pyrolyzates to more thermally stable less oxygenated species which are eventually deoxygenated leaving highly aromatic structures. The relationship of tar composition to processing temperature i s further substantiated by the l i s t i n g of chemical components of the tars as found i n Table I. These chemicals were i d e n t i f i e d through the use of gas chromatography-mass spectrometry (for procedures see r e f . 3). Since gas chromatography was used for separating these components, certain limitations of the data can be assumed. For example, low v o l a t i l i t y of a compound w i l l interfere with the i d e n t i f i c a t i o n of a compound i n a gas chromatography system. Therefore, high-molecular-weight components would not be i d e n t i f i e d i n this system nor would highly polar compounds. High-molecular-weight hydrocarbons, up to 276 molecular weight, have been i d e n t i f i e d i n our analyses. Single-hydroxy, double-ring aromatic compounds

Table I.

Chemical Components i n Biomass Tars

Conventional Flash Pyrolysis (450-500°C)

Hi-Temperature Flash Pyrolysis (600-650°C)

Conventional Steam Gasification (700-800°C)

Hi-Temperature Steam Gasification (900-1000°C)

Acids Aldehydes Ketones Furans Alcohols Complex Oxygenates Phenols Guaiacols Syringols Complex Phenolics

Benzenes Phenols Catechols Naphthalenes Biphenyls Phenanthrenes Benzofurans Benzaldehydes

Naphthalenes Acenaphthylenes Fluorenes Phenanthrenes Benzaldehydes Phenols Naphthofurans Benzanthracenes

Naphthalene Acenaphthylene Phenanthrene Fluoranthene Pyrene Acephenanthrylene Benzanthracenes Benzopyrenes 226 MW PAHs 276 MW PAHs

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ELLIOTT

Relation of Time and Temperature to Oil Composition

Conventional Flash Pyrolysis

450-.500°C

High Temp. Flash Pyrolysis

600-650°C

Low Temp. Steam Gasification

700-800°C

High Temp. Steam Gasification

900-1000°C

Figure

Figure range

4. of

3.

Biomass

Elemental temperatures

Liquids

Gas

Char

Maximum (High Oxygen)

Minimum

Low (High Oxygen)

(Low Oxygen) Minimum

Maximum

pyrolysis

composition

î AI tar producing

of dry tars

(Low Oxygen) Low

systems

produced

over

a

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch006

60

PYROLYSIS OILS FROM BIOMASS

( p h e n y l p h e n o l s and n a p h t h o l s ) seem t o be the upper l i m i t f o r h i g h m o l e c u l a r - w e i g h t p o l a r compounds. S p e c i f i c isomer i d e n t i f i c a t i o n i s d i f f i c u l t w i t h our type of a n a l y s i s . O f t e n no r e f e r e n c e l i s t i n g can be found f o r many of the a l k y l a t e d a r o m a t i c s and p h e n o l i c s found i n these t a r s . Therefore, i d e n t i f i c a t i o n i s usually l i m i t e d to funct i o n a l type and m o l e c u l a r w e i g h t . The l i s t i n g s i n T a b l e I f u r t h e r c o n f i r m the m u l t i s t e p t r a n s f o r m a t i o n as a f u n c t i o n of temperature of the h i g h l y oxygenated p y r o l y z a t e s t o the condensed a r o m a t i c s . The s c i s s i o n of l a b i l e bonds around a r o m a t i c r i n g s t o e l i m i n a t e s i d e c h a i n s c o n t a i n i n g c a r b o n y l and methoxyl groups l e a d s to c a t e c h o l s . F o r example, the p y r o l y s i s of g u a i a c o l to c a t e c h o l i s w e l l documented i n the l i t e r a ture (19). Other c o n d e n s a t i o n r e a c t i o n s t o produce b e n z o f u r a n s , b i p h e n y l s and n a p h t h a l e n e s from p h e n o l i c s have a l s o been r e c e n t l y demonstrated i n t h e s e h i g h - t e m p e r a t u r e environments ( 2 0 ) . At h i g h e r temperatures the p h e n o l i c s and f u r a n s d i s a p p e a r w h i l e the m o l e c u l a r weight of the more s t a b l e a r o m a t i c s c o n t i n u e t o i n c r e a s e . In a d d i t i o n t o e l i m i n a t i o n of oxygen, a l k y l s i d e c h a i n s a r e no l o n g e r o b s e r v e d a t the h i g h e s t temperatures t e s t e d . T h i s same s e r i e s of r e a c t i o n pathways can a l s o be found i n t h e coal pyrolysis literature. The r e l a t i o n s h i p of p h e n o l and n a p h t h a l e n e c o n t e n t i n c o a l t a r i s the same as t h a t found f o r wood tar. As g r a p h i c a l l y p r e s e n t e d i n Lowry (21) n a p h t h a l e n e i n c r e a s e s w h i l e p h e n o l d e c r e a s e s as the c o a l t a r p r o c e s s i n g temperature increases. S i m i l a r l y , F i g u r e 5 shows d a t a f o r aqueous condensate components from wood g a s i f i c a t i o n systems. However, i n the case o f F i g u r e 5 the weight p e r c e n t of a l l p h e n o l i c s and Cg t o aromatics are summed f o r the d a t a p r e s e n t a t i o n . The t h e r m a l environment a t t e m p e r a t u r e s above 800°C l e a v e s l i t t l e d i f f e r e n c e between the c o a l t a r c o m p o s i t i o n and t h a t produced from wood. P h y s i c a l P r o p e r t i e s of T a r s . Due t o the d i f f e r e n c e s i n c h e m i c a l c o m p o s i t i o n of the t a r s , the p h y s i c a l p r o p e r t i e s a l s o v a r y s i g nificantly. The p y r o l y t i c oxygenates e x h i b i t c o n s i d e r a b l e water solubility. In a d d i t i o n t o water, o t h e r l i g h t w e i g h t p o l a r compounds s u c h as a c e t i c a c i d , h y d r o x y a c e t a l d e h y d e , methanol, and h y d r o x y p r o panone a r e p r e s e n t which a l s o a c t as s o l v e n t s . As a r e s u l t , t h e c o n v e n t i o n a l f l a s h p y r o l y s i s o i l can be thought of as a s o l u t i o n of p o l a r o r g a n i c s i n a water, a c i d , ketone s o l v e n t . T h i s s o l u t i o n has a h i g h d e n s i t y (>1.2 g/ml) and a r e l a t i v e l y low v i s c o s i t y (60 cps a t

40°C). H i g h e r temperature p r o d u c t s show a t r e n d t o lower d e n s i t y i n d i c a t i v e of the t r a n s f o r m a t i o n of oxygenates t o h y d r o c a r b o n s . V i s c o s i t y can v a r y w i d e l y depending on the degree of water i n c o r p o r a t i o n i n t o the t a r and the c o n d e n s a t i o n temperature which d e t e r mines the amount of l i g h t h y d r o c a r b o n s c o l l e c t e d i n the t a r . In the h i g h e r temperature ranges the h i g h m o l e c u l a r weight h y d r o c a r b o n s can be c o l l e c t e d from the t a r as t o l u e n e i n s o l u b l e c h a r . The amount of t h i s m a t e r i a l i n c r e a s e s from 19.0 weight p e r c e n t t o 41.2 weight p e r c e n t i n t a r samples r e c o v e r e d o v e r the o p e r a t i n g temperature range from 880°C to 1000°C Ç 7 ) . B i o l o g i c a l P r o p e r t i e s of T a r s . J u s t as p h y s i c a l p r o p e r t i e s of t a r s can be r e l a t e d t o t h e i r c h e m i c a l c o m p o s i t i o n , so can b i o l o g i c a l a c t i v i t i e s of the t a r s . B i o l o g i c a l a c t i v i t y can be c a t e g o r i z e d as e i t h e r s h o r t - t e r m , as i n a c u t e t o x i c i t y , or l o n g - t e r m , as i n

Relation of Time and Temperature to Oil Composition

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch006

ELLIOTT

700

800

900

Degrees Celsius

Figure 5. Shift i n chemical composition of aqueous ph condensate from f l u i d i z e d bed g a s i f i e r s

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch006

62

PYROLYSIS OILS FROM BIOMASS

carcinogenicity which i s often measured as mutagenicity or tumori n i t i a t i n g a c t i v i t y . The short-term acute t o x i c i t y of these tars i s a v a l i d concern. However, one would expect a wide range of effects based on the variation i n chemical composition. The lack of such t o x i c o l o g i c a l tests for biomass tars i s a major shortcoming of the current state of knowledge. Long-term t o x i c i t y as measured by Ames Assay for mutagenicity and mammalian c e l l tumor-initiating a c t i v i t y was measured i n this study and was found to vary widely depending on the biomass processing temperature. Ames Assay was used as an i n i t i a l survey for a l l the tars and aqueous condensates. A c t i v i t y was limited to high-temperature process tars (> 800°C). Results of more lengthy tests of mouse skin painting and tumor counting (30 mice per treatment group) confirm the Ames Assay r e s u l t s . The results depicted i n Figure 6 and 7 show that a c t i v i t y i n the high temperatures was equal to or greater than that of the benzo(a)pyrene a c t i v i t y standard. The a c t i v i t y of the tar produced at 750°C was much l e s s , yet s t i l l s t a t i s t i c a l l y s i g n i f i c a n t . The low-temperature tar (485°C) showed no a c t i v i t y above that of the control. The a c t i v i t y i n these tars i s attributed to p o l y c y c l i c aromatic hydrocarbons. For example, the concentration of benzo(a)pyrene i n the high-temperature tars was so great that the amount added to the animal skin was actually greater than the amount of pure compound used as a standard. There were e s s e n t i a l l y no p o l y c y c l i c aromatic hydrocarbons i n the low-temperature pyrolysis t a r . The E f f e c t of Time and Pressure on Tar Properties. An inadequate data base i s currently available to truly evaluate the effect of time and pressure on biomass pyrolysis tar composition. Most pressurized pyrolysis tests with biomass have been performed at lower temperatures and longer residence times than f l a s h p y r o l y s i s . In addition, a reducing gas and catalyst are sometimes added i n pressurized experiments. Considering the elemental composition of high-pressure processed biomass o i l s (22) a trade-off i n temperature and residence time can be envisioned i n order to make the data comparable to f l a s h pyrolysis tars as i n Figure 4. Typical catalyzed, high-pressure o i l composition (12% oxygen, 1.23 H/C) (9) can be compared to f l a s h pyrolysis o i l s produced at between 550°C (based on the H/C r a t i o ) and 700°C (based on the oxygen content). Apparently due to the reducing gas and c a t a l y s i s , the oxygen content i s reduced while the hydrogen to carbon r a t i o remains higher i n the highpressure o i l s than i s t y p i c a l for f l a s h pyrolyzates. However, the chemical components i d e n t i f i e d i n the high-temperature f l a s h pyrolyzates representative of this temperature (see Table 1) are not obviously different from those found i n the high-pressure o i l s (9). In the case of uncatalyzed, high-pressure processing, as reported by Boocock (22), the o i l has a composition (24% oxygen, 1.10 H/C) which f a l l s at the 600°C l e v e l for a f l a s h pyrolyzate. In extending this comparison to i t s l o g i c a l conclusion, one finds that a similar product can be produced at lower temperature (300°C l e s s ) with an increase i n residence time (100 times) and increased pressure (100 times). Equivalent comparisons with the catalyzed case are not so straightforward, apparently due to d i f f e r e n t reaction mechanisms favoring an improved product composition, i . e . , lower oxygen and higher hydrogen to carbon.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch006

ELLIOTT

37

Relation of Time and Temperature to Oil Composition

51

65

79

93

107

121

135

149

163

177 196

Days Post Initiation

Figure 6·

Tumor i n c i d e n c e as a percentage o f a n i m a l s a f f e c t e d

F i g u r e 7. T o t a l number o f tumors r e s u l t i n g from s k i n application

PYROLYSIS OILS FROM BIOMASS

64 Acknowledgments

The following researchers provided biomass pyrolysis tar samples, the analyses of which produced the data that are the basis f o r this paper:

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch006

M. J. Porter D. S. Scott

Biomass Liquefaction Experimental Facility University of Waterloo

J. J. M. V. L. S. H.

Georgia Tech Research Institute Solar Energy Research Institute P a c i f i c Northwest Laboratory University of Missouri-Rolla P a c i f i c Northwest Laboratory Institute of Gas Technology B a t t e l l e Memorial Institute

A. P. D. J. K. P. F.

Knight Diebold Brown Flanigan Mudge Babu Feldman

Albany, OR Waterloo, Ontario Canada Atlanta, GA Golden, CO Richland, WA Rolla, MO Richland, WA Chicago, IL Columbus, OH

F i n a n c i a l support f o r this research was provided by the Biofuels and Municipal Waste Technology Division of the U.S. Department of Energy, through the Biomass Thermochemical Conversion Technical F i e l d Office at P a c i f i c Northwest Laboratory. The author appreciates the support of Mr. Simon F r i e d r i c h , manager of the Biomass Thermochemical Conversion Program at DOE Headquarters and Mr. Gary F. Schiefelbein, Mr. Mark A. Gerber and Dr. Don J. Stevens of the Technical F i e l d O f f i c e . Literature Cited

1.

Emrich, W. Handbook of Charcoal Making: The Traditional and Industrial Methods; D. Reidel Publishing Co.: Dordecht, Holland. 2. Soltes, E. J.; Elder, T. J. In Organic Chemicals from Biomass, Goldstein, I. S., Ed. CRC Press Inc.: Boca Raton, FL, 1981; Chapter 5, 74-81. 3. Elliott, D. C. Analysis and Comparison of Biomass Pyrolysis/ Gasification Condensates - Final Report, PNL-5943, Pacific Northwest Laboratory: Richland, WA, 1986. 4. Diebold, J. In Proc. Specialists' Workshop on Fast Pyrolysis of Biomass, SERI-CP-622-1096, Solar Energy Research Institute, Golden, CO, 1980, p.3. 5. Evans, R. J.; Milne, T. A. Fundamental Pyrolysis Studies: Final Report 1 October 1980 - 30 December 1985, SERI/PR234-3026, Solar Energy Research Institute: Golden, CO, 1986. 6. Elliott, D. C. Analysis and Comparison of Biomass Pyrolysis/ Gasification Condensates - An Interim Report, PNL-5555, Pacific Northwest Laboratory: Richland, WA, 1985. 7. Elliott, D. C. Analysis of Medium-BTU Gasification Condensates: June 1985 - June 1986, PNL-5979, Pacific Northwest Laboratory: Richland, WA, 1987. 8. Elliott, D. C. Analysis and Upgrading of Biomass Liquefaction Products, Final Report, Volume 4 of International Energy Agency Cooperative Project D-1, Biomass Liquefaction Test Facility. National Energy Administration: Stockholm, 1985.

6. ELLIOTT 9. 10.

11.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch006

12. 13.

14. 15.

16. 17.

18.

19.

20. 21. 22.

Relation of Time and Temperature to Oil Composition

65

Elliott, D. C. In Fundamentals of Thermochemical Biomass Con­ version; Overend, R. P., Milne, Τ. Α., and Mudge, L. Κ., Eds.; Elsevier Applied Science Publishers: London, 1985; Chapter 55. Diebold, J. P.; Scahill, J. "Progress in the Entrained Flow Pyrolysis of Biomass," presented at the 12th Biomass Thermochemical Conversion Contractors' Meeting, Washington, D.C., March 1981. SERI/PR-622-1151, Solar Energy Research Institute: Golden, CO, 1981. Knight, J. Α., Gorton, C. W.; Kovac, R. J. In Proceedings of the 16th Biomass Thermochemical Conversion Contractors' Meet­ ing, CONF-8405157, National Technical Information Service: Springfield, VA, 1984, pp. 287-297. Scott, D. S.; Piskorz, J. Can. J. Chem. Eng. 1984, 62, 404-412. Roy, C.; deCaumia, B.; Brouilland, D.; Ménard, H. In Fundamentals of Thermochemical Biomass Conversion, Overend, R. P., Milne, Τ. Α., and Mudge, L. Κ., Eds.; Elsevier Applier Science Publishers: London, 1985; Chapter 13. Elliott, D. C. "A Process for Direct Production of Hydrocarbon Fuels from Biomass" Invention Report E-639 Battelle-Northwest: Richland, WA, 1985. Mudge, L. K.; Baker, E. G.; Brown, M. D.; and Wilcox, W. A. In Proc. of the 1985 Biomass Thermochemical Conversion Con­ tractor's Meeting, CONF-8510167, National Technical Information Service: Springfield, VA, 1986, pp. 235-256. Flanigan, V. J.; Punyakumleard, Α.; Sitton, O. C. Biotech. and Bioeng. Symp. 14, 1985, pp. 3-14. Kosowski, G. M.; Onischak, M.; Babu, S. P. In Proc. of the 16th Biomass Thermochemical Conversion Contractors' Meeting, CONF-8405157, National Technical Information Service: Springfield, VA, 1984, pp. 39-60. Feldman, H. F.; Paisley, Μ. Α.; Appelbaum, H. R. In Proc. of the 16th Biomass Thermochemical Conversion Contractors' Meet­ ing, CONF-8405157, National Technical Information Service: Springfield, VA, 1984, pp. 13-38. Vuori, A. "Thermal and Catalytic Reactions of the C-O Bond in Lignin and Coal Related Aromatic Methyl Ethers." Acta Polytechnica Scandinavica, Chem. Tech. and Met. Series No. 176, 1986. Cypres, R. Fuel Proc Tech. 1987, 15, 1-15. Weiler, J. F. In Chemistry of Coal Utilization, Supplementary Volume, Lowry, H. H., Ed.; John Wiley & Sons: New York, 1973; Chapter 14, 582. Boocock, D. G. B.; Chowdhury, Α.; Allen, S. Α.; Hayes, R. D. Amer. Chem. Soc., Div. Fuel Chem. Prepts, 1987, 32(2), 90-97.

Received March 31, 1988

Chapter 7

Pyrolysis of Biomass Evidence for a Fusionlike Phenomenon Jacques Lede, Huai Zhi Li, and Jacques Villermaux

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch007

Laboratoire des Sciences du Génie Chimique, Centre National de la Recherche Scientifique-ENSIC, rue Grandville 54042 Nancy, France This paper presents an outline of the main ideas and results illustrating the fusion like behaviour of biomass pyrolysis. The ablative pyrolysis rate of wood rods applied on a hot spinning disk or on a stationnary heated surface is studied. The observations are quite similar to those made in the same conditions with rods of true melting solids (ice, paraffin, ...) in agreement with a theoretical approach. The "fusion" temperature of wood is found close to 739 Κ in agreement with a limited number of experiments of wood sawdust fast pyrolysis in a hot cyclone reactor. The results show also that in most of the experimental devices, the direct measurement of wood pyrolysis reaction rate constant is impossible above about 800 K.

Considering a thermal reaction of a S o l i d-->F l u i d type, the apparent rate of reaction can be controlled by chemistry, thermal and mass transfer resistances. I f the chemical processes are very f a s t , and i f the f l u i d products are e a s i l y eliminated from the medium, the o v e r a l l rate of reaction i s controlled by heat transfer. This i s the case of the ablation regime ( J _ ) , characterized by a steep temperature gra­ dient at the wood surface and consequently by a thin s u p e r f i c i a l layer e of reacting s o l i d moving at a constant v e l o c i t y ν towards the cold unreacted parts of the s o l i d (Figure 1). Suppose now that heat i s provided by a surface at T . A theore­ t i c a l increase of the surface temperature T^ of the s o l i d (by increa­ sing T ) would lead to a subsequent increase of the heat flux demand. Such a demand would be s a t i s f i e d by an equal external heat flux sup­ ply, a condition f u l l f i l l e d only i f large temperature gradients exist (large T - T^ differences). The consequence i s that T j seems to reach a stable value, leading to a fusion l i k e behaviour of the reac­ tion. Wood pyrolysis carried out i n conditions of high available heat flux and e f f i c i e n t elimination of products has been found to occur i n ablation regime with production of very low fractions of char (2,3,4) and could therefore be interpreted as a simple fusion. This w

w

w

0097-6156/88/0376-0066$06.00/0 • 1988 American Chemical Society

7.

LEDEET AL.

67

Pyrolysis of Biomass

paper presents a b r i e f outline of the main ideas and results i l l u s ­ trating this e f f e c t observed under d i f f e r e n t experimental conditions. More d e t a i l s can be found i n related papers (5,6,7,8). The reaction has been carried out i n three d i f f e r e n t conditions: heating against a hot spinning disk ; against a fixed heated surface; i n a continuous cyclone reactor. In the f i r s t two cases, the beha­ viour of the reaction i s compared to that of s o l i d s undergoing simple fusion i n the same conditions.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch007

Spinning Disk Experiments The melting of i c e , p a r a f f i n and " r i l s a n " (polyamide 11) and the py­ r o l y s i s of wood have been c a r r i e d out by applying under known pres­ sures p, rods of the corresponding solids against a hot spinning stainless s t e e l disk (temperature T )(5,6). In wood experiments, the reaction produces almost exclusively gases and l i q u i d s , the s o l i d s being mainly ashes deposited on the disk. The liquids produced are rapidly extracted from the wood surface and eliminated by the fast moving disk on which they undergo further decomposition to gases at a rate depending on T . The presence of the thin l i q u i d layer acts as a kind of lubricant. Figure 2 reveals that under comparable values of p, the beha­ viour of ν as a function of v i s s i m i l a r , the orders of magnitude of ν being the same f o r the four types of s o l i d s . For ν > 2 m s~^, ν increases with ρ following : w

w

R

ν = a p

F

(1)

a depends on T and F on the material. The mean values of F (ice : 0.035 ; p a r a f f i n : 0.29 ; " r i l s a n " : 0.83 ; wood : 1) can be f a i r l y well represented by : w

Cp ι · - i - j N F(melting s o l i d ) =

s

τ,/

(T.-T ) f o y

,v

or F(wood) = *s

f

ο

Cp (T,-T ) *s d o' (τ -Τ )+ΔΗ s d ο

.

r o ( 2 )

F being close to 1 for wood shows that i t i s probable that ΔΗ, the enthalpy of p y r o l y s i s , i s small with respect to sensible heat i n agreement with the littérature. The equations of heat f l u x density balances between the disk and the rod are : melting s o l i d : h ( T - T ) = v p C p ( T w

wood

f

g

s

: h(T - T ) = vp Cp (T w

d

s

s

f

- T ) + vp L

d

- T ) + vp AH

Q

q

g

s

Assuming that the heat transfer c o e f f i c i e n t h i s the only parameter depending on the pressure (h = Kp ) i t can be deduced : F

ν — p

, , . - . ,χ Κ (melting solid) = — s

Τ

*s

w

— Τ

f

ο

f

ν ; -j ρ

Τ — Τ w d

, j v Κ (wood) = —

(

s

r

s

)

α

+

Δ

Η

ο (4)

PYROLYSIS OILS FROM BIOMASS

68

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch007

Rod of melting or reacting solid

Reacting zone Elimination of liquid products Hot surface

Figure 1. Ablative pyrolysis (melting) of a s o l i d cylinder pres­ sed against a heated surface.

Figure 2. Experimental variations of ablation v e l o c i t i e s ν with disk v e l o c i t y V f o r four kinds of solids : a ( i c e , T = 348 K, ρ = 2 χ 10 Pa), b ( " r i l s a n " , T = 723 Κ, ρ = 3,45 χ 10 Pa), c (paraffin, T = 373 Κ, ρ = 3.45 χ 10 Pa), and d (wood, T = 1073 Κ, ρ = 3.7 χ 10 Pa). R

w

5

5

w

5

w

5

w

7.

LEDEETAL.

69

Pyrolysisof Biomass

In agreement with Equation 4, Figures3(a,b,c,d) show that the variations of v / p with T are l i n e a r f o r the three melting solids and also for wood. The values of calculated from the extrapolation of the straight lines to ν = 0 are i n very good agreement with the known values of melting points (better than 2 % accuracy). The correspon­ ding "fusion" temperature of wood i s then calculated close to 739 K. The apparent large magnitude of errors observed i n figure 3d f o r wood (the error bars correspond to extreme measured values of v / p for a given T^) i s a consequence of the s l i g h t theoretical dépendance of T^ with T and h as mentioned i n the f i n a l discussion. This " f u sion temperature of 739 Κ must then be considered as a mean value (figure 8). The values of heat transfer c o e f f i c i e n t s obtained from the slopes of the straight lines i n figures 3(a,b,c,d) are of the same order of magnitude (around 10^ W nf^ κ"^) whatever the s o l i d showing that the mechanisms of heat transfer are probably s i m i l a r for wood^ and melting solids (6). For wood, h varies as h = 0.017 p(W m~^ Κ ) (5). These values reveal very e f f i c i e n t transfers. F

w

F

w

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch007

11

Fixed Heated Wall The same experiments as before have been made with rods of i c e , pa­ r a f f i n and wood pressed against a stationnary piece of brass heated at T . An analytic solution has been found for representing the rate of ablative melting of a s o l i d cylinder pressed against a horizontal wall maintened at T (7). In steady state, a l i q u i d layer of constant thickness i s formed between the hot surface and the rod, with a r a ­ d i a l flow of l i q u i d . The resolution of the equation of l i q u i d flow associated with that of energy balance between the two surfaces allows to derive the following relationship : w

w

1/4 Pe

(Ph) ρ

(5)

Mo*

where Pe i s a Peclet number, a function of a phase change number Ph : C

P £

(T

W

-

T ) F

Ph =

with Pe =

Ph 5/6 1 + 0,33 Ph

0.25 The Equation 5 shows that ν varies as ρ ' whatever the type of s o l i d . In reduced form, the Equation 5 can be w r i t t e n as follows : 3

V = \ [Pe P] with V = —

—

1/4

(6)

ν and Ρ =

R

2 „.3

„Jl/4

t

By p l o t t i n g V against =k Pe Ρ one should obtain a straight l i n e of slope one whatever the nature of melting s o l i d and wall temperature

70

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch007

PYROLYSIS OILS FROM BIOMASS

700

800

900

1000

1100

1200

Figure 3. Experimental variations of v/p with disk temperature T . The straight lines have been determined from the least square method. F i g . 3a : ice ; F i g . 3b : " r i l s a n " ; F i g . 3c : p a r a f f i n ; F i g . 3d : wood. w

7. LEDE ET AL.

71

Pyrolysis ofBiomass

As i n the case of i c e and p a r a f f i n Ç7 ), ablation rate ν f o r wood pyrolysis varies as p^ with a mean value of F close to the theo­ r e t i c a l one : 0.25 (figure 4). The figure 5 gathers a l l the experi­ mental points. I t shows a s i m i l a r behaviour for wood, i c e and paraf­ f i n i n agreement with the theoretical s t r a i g h t l i n e . The physical pro­ perties used f o r the c a l c u l a t i o n of V and Ρ f o r ice and p a r a f f i n are reported i n r e f . (7,8). In the case of wood, the factor containing these properties i n Equation (5) has been f i t t e d to the experimental results (figure 4) leading to ν = 1.55 χ 10~ (Pe p/po) ' (m.s ). The f i t t e d constant associated with estimated values f o r p^(500 kg. m' ), Cp£ (3.65 kJ.kg-^K" ) and o£ (0.3 χ 10" m s" ) allows us to calculate μ£ = 72.5 χ 10~ Pa.s, a reasonable value f o r the v i s c o s i t y of a l i q u i d at a melting point of 739 Κ (7,8). 3

3

1

3

7

2

1

1

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch007

3

L i f e Time of Liquids Produced The same pyrolysis conditions can be achieved with a moving piece of wood pressed upon a fixed heated surface. In that case, i t i s easy to measure the necessary time t of decomposition of the l i q u i d s l e f t behind the wood on the surface. Figure 6 reports the l i n e a r v a r i a ­ tions of the experimental values of \/t (pseudo f i r s t order k i n e t i c constant) as a function of 1/T . Assuming that the liquids are rapidly heated to surface temperature before decomposition i t i s possible to estimate the k i n e t i c parameters of the reaction of liquids decomp o s i t i o n : A = 2.7 χ 10 s and Ε = 116 kJ. Compared to the parame­ ters used i n Diebold k i n e t i c model (14) the experimental points could represent the two possible processes : "Active" primary vapors or "Active" -> char. e

œ

W

7

Cyclone Reactor

- 1

Experiments

The continuous fast pyrolysis of wood sawdust has been studied i n a Lapple type (2.8 χ 10" m diameter) cyclone reactor heated between 893 and 1330 Κ (2). The wood p a r t i c l e s carried away by a flow of steam enter tangentially into the cyclone on the inner hot walls of which they move and undergo decomposition. Mass balances show i n a l l the cases, a very low f r a c t i o n of char (< 4 %) while the g a s i f i c a t i o n • -ι J ν /v weight of dry gas evolved . . . 2

N

i n

y i e l d X (X = — r - s - — — / ?— ) increases with wall tempeweight of dry wood pyrolysed rature T . I t appears from figure 7 that the reaction seems to occur only for wall temperatures greater than about 800 Κ i n good agrément with tusion"temperature of 739 K. The v a r i a t i o n of X with T i s approximately l i n e a r up to about 1300 K. For higher temperatures, the g a s i f i c a t i o n y i e l d must tend to the theoretical constant value of 1. In such a model, the decomposition temperature of p a r t i c l e s being roughly constant, the g a s i f i c a t i o n y i e l d increase with T would then result from further vaporization and/or decomposition of primary products (mainly l i q u i d s ) at the wall and/or i n the gas phase with an e f f i c i e n c y depending on T . Discussion T

w

f

w

w

w

A l l these results obtained i n d i f f e r e n t experimental conditions, show s t r i k i n g s i m i l a r i t i e s between ablative wood pyrolysis and melting of

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch007

PYROLYSIS OILS FROM BIOMASS

IT Figure 4. Ablative pyrolysis rate of wood ν as a function of applied pressure ρ for d i f f e r e n t wall temperatures. Ο ' 823 Κ ; Φ: 873 Κ ; Δ 923 Κ ; Ο : 973 Κ.

Figure 5. Dimensionless representation of reduced v e l o c i t y V as a function of reduced pressure Ρ f o r three kinds of s o l i d s . Ο · p a r a f f i n ; X : i c e ; α : wood.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch007

LEDE ET AL.

Pyrolysis ofBiomass

Figure 6. Variations of the observed k i n e t i c constant of l i q u i d decomposition with wall temperature i n an Arrhenius representa­ tion. A comparison with the scheme of Diebold (14).

X

01

500

L - i

.

600

700

800

ι

.

I

ι

.

90a

1000

1100

1200

1300

L -

1400

Figure 7. V a r i a t i o n of the g a s i f i c a t i o n y i e l d X as a function of wall temperature T i n the fast pyrolysis of wood sawdust i n a cyclone reactor : comparison with the "fusion" temperature of 739 K. w

74

PYROLYSIS OILS FROM BIOMASS

s o l i d s . Nevertheless the equivalent fusion temperature of 739 Κ has been calculated from Equation 4 based on the assumption that is constant. Let suppose now that depends on external physical condi­ tions (p, T ) under the assumption that ΔΗ using the d i f f u s e reflectance FTIR spectrometry (DRIFT). The technique i s simple and applicable to powdered s o l i d s and dark samples -Li and (2

3 )

( 5

1 3 )

C

(

0097-6156/88/0376-0139$06.00/0 « 1988 American Chemical Society

)

140

PYROLYSIS OILS F R O M

BIOMASS

can be used f o r the characterization of the chemical bonds and t h e i r modifications by thermal processes. In t h i s paper we report our e f f o r t s to characterize the s o l i d residues produced in a s e r i e s of experiments with the semicontinuous extraction of Populus tremuloides (aspen wood) in s u p e r c r i t i c a l methanoH-LS.) , at temperatures ranging from 250 to 350°C ( S u p e r c r i t i c a l Extraction residues or SCE residues), by using wet chemistry and chromâtographic JJËL , thermogravimetric and spectral methods such as DRIFT* 12 and ESCA . (

)

)

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch014

Experimental

Procedure

The s o l i d residues analyzed here were produced by s u p e r c r i t i c a l ext r a c t i o n with methanol of Populus tremuloides in a tubular reactor JJi.> . The a n a l y t i c a l procedures used f o r these residues were described previously as elemental analysis, Klason l i g n i n test, thioglycolic acid lignin test, recondensed material and carbohydrates*i£>, thermogravimebric (TG/DTG) and FTIR and ESCA JL£ . Table 1 reports r e s u l t s obtained using these procedures as well as conditions of extraction for each SCE residue. (

(

)

Results and Discussion Wet Chemistry and Chromatography. For the analysis of wood, the Klason l i g n i n test, performed in concentrated s u l f u r i c acid, i s the accepted method f o r the determination of l i g n i n content. We performed s i m i l a r tests using also t r i f l u o r o a c e t i c acid (TFA), the r e s u l t s of which are almost i d e n t i c a l to those of the Klason tests. TFA has the advantage of allowing further analysis of the saccharides i n the acid soluble f r a c t i o n , as i t can e a s i l y be evaporated from the s o l u t i o n . The a c i d insoluble f r a c t i o n , usually designated as "Klason l i g n i n " , i s referred to i n t h i s work as Klason residue. Figure L shows that f o r the most severe extraction conditions the SCE residue i s almost e n t i r e l y constituted of Klason residue. The fact that t h i s Klason residue cannot be considered as l i g n i n has been established through elemental analysis and IR spectroscopy i n KBr p e l l e t s * 1L> . In order to determine i f the so Lid residues s t i l l contain l i g n i n , the o l d method of forming a soluble l i g n i n derivative with t h i o g l y c o l i c acid was used. This reagent reacts by displacement of α-hydroxy1 and α -alkoxyl groups in l i g n i n , and the derivative so produced can be s o l u b i l i z e d by a l k a l i and recovered. Results are reported i n Table 1 and Figure 1 showing that t h i o g l y c o l i c acid l i g n i n (TGAL) decreases from 15.6% i n wood to 3.3-5.9% in the sam­ ples prepared at 350°C. It was shown by IR spectrometry that the TGAL keeps the c h a r a c t e r i s t i c features of l i g n i n even f o r SCE tem­ peratures of 350 C. This confirms our b e l i e f that the t h i o g l y c o l i c acid test i s a s u i t a b l e method f o r the determination of uncondensed l i g n i n i n SCE residues. In s p i t e of the fact that: I) the Klason test induces some condensation reactions, and 2) the t h i o g l y c o l i c acid test may only extract those l i g n i n fragments containing benzyl alcohol groups or a r y l ether groups*.Li> , we would l i k e to suggest that: 1) the o

47.4 44.2 41.2 48.6 48.9

29.2 19.0 16.8 15.0 14.8 29.7 21.6

19.8

20.8 11.6 3.33 18.8

6. 50 5. 84 5.,29 6. 4 9 6.,97

5. 82 5.,12 4.,96 4.,62 5.,35 5..47 5.,17

6..08

4,.34 4 .89 3 .84 5 .00

46.1 50.0 53.5 45.0 44.1

64.9 75.9 78.2 80.4 79.8 64.8 73.3

27.,2 18.,0 12.,8 19.,2 12.,3

7.,9 0.,0 0.,0 0..0 0.,0 3..3 0.,0

47.,6 45.,7 38.,1 38. 0 26..9

25. 9 0.,0 0.,0 0.,6 0.,0 10.,3 0.,7

78.5 70.8 64.1 89.9 90.6

46.4

74.8 83.5 92.8 76.3

1..5 0 .0 0 .0 0 .0 4,.8 0,.0 0 .0 0 .0 11.1 0.8 1.2 3.1 85 .1 88 .5 89 .2 77 .0

5,.2 3 .8 5 .9 3 .3

90.0 92.3 95.1 80.3

26.9 18.2 10.2 6.1

1.5 0.5 2.5 1.5

3.4 10.3 10.3 17.2

350 350 350 350

MP-14 MP-11 MP-8 MP-24

D r y wood b a s i s . D r y SCE r e s i d u e b a s i s . C a l c u l a t e d by d i f f e r e n c e .

74.1 0,.0 7,.1 19.8

66,.7

4..8

71.4

8.4

1.2

17.2

330

MP--27

-

5.0 1.6 2.4 27.2 4.0

30.,1 65.,8 87.,8 88..7 84..7 59..8 81,.3

12.,1 12..3 4.,3 3..8 4..5 6.,0 5..3

42.2 78.1 92.1 92.5 89.2 65.8 86.7

40.5 31.0 16.4 15.9 15.7 18.4 15.0

0.5 2.5 1.5 1.5 1.5 0.5 2.5

(a) (b) (c)

%0 (b,c)

Wt%

(b)

(b) Wt&< b>

%H

%c

xyl

and a n a l y s i s

Glu

conditions

TFA soluble Wt%(b >

extraction

3.4 3.4 10.3 10.3 10.3 17.2 17.2

11..8 8.,3 4.,1 2.,0

15.,6 14.,3 22.,2 6.,5 5..4

Recond. material Wt%(b>

17.6 26.1 30.5 10.6 7.6

Wt%(b>

TGAL

100.0 74.8 55.4 69.7 68.4

Κlason residue wtS»< b )

from Populus tremuloides:

Residue yield Wt*(a)

(SCE) r e s i d u e s

1.5 0.5 2.5 1.5

SCE Flowrate L/h

extraction

3.4 10.3 10.3 17.2

SCK Pressure MPa

Supercritical

300 300 300 300 300 300 300

250 250 250 250

SCE Temperature °C

I.

MP-16 MP-20 MP-9 MP-12 MP-21 MP-13 MP-18

MP-15

Wood MP-22 MP--6 MP-17

Sample

Table

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch014

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch014

PYROLYSIS OILS FROM BIOMASS

Figure 1. Klason residue and t h i o g l y c o l i c a c i d l i g n i n (TGAL) in SCE s o l i d residues (expressed on dry SCE residue b a s i s ) .

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch014

14. GRANDMAISON ET AL.

ResiduesfromSupercritical Extraction of Wood

t h i o g l y c o l i c acid l i g n i n represents a good estimate of unconverted l i g n i n , and 2)the Klason residue represents the summation of unconverted l i g n i n and of condensation products formed by p y r o l y s i s reactions during the SCE process. As a consequence, we suggest that the difference between the Klason residue and the t h i o g l y c o l i c acid l i g n i n i s representative of recondensed material (RM) in SCE residues. The calculated values for recondensed material in these residues are reported in Table I. Figure 2 gives the values for the percent recondensed material expressed on a dry wood basis. Figure 3 shows the percentage of recondensed m a t e r i a l , expressed on dry wood basis, plotted as a function of l i g n i n conversion. This graph suggests different condensation reactions at 250°C and at 3 0 0 - 3 5 0 ° C . At 250°C in p a r t i c u l a r , the condensation seems to be a secondary reaction of l i g n i n conversion. As also shown on the figure, for several experiments the percents of recondensed material are higher than the value which would be calculated assuming that a l l converted l i g n i n i s transformed to recondensed material ( l i n e A). It i s believed that this indicates that the condensation reaction involves not only products of degradation of l i g n i n but also some of carbohydrates. The glucose and xylose contents were determined i n the soluble TFA acid hydrolysis f r a c t i o n by l i q u i d chromatography using a cation exchanged r e s i n ( C a form) column. The results are reported i n Table 1. Most of the samples prepared at 300-350°C show only minor amounts of hydrolyzed material, except for samples MP-16, MP-13 and MP-14 which were prepared at low pressure or low flow rate. The percents of glucose and xylose for these samples as well as those for the samples prepared at 250°C, expressed on dry wood b a s i s , are plotted on Figure 4. The rather well defined curve indicates that c e l l u l o s e and hemicellulose are simultaneously degraded at or below 250°C. ++

Thermogravimetric Analysis. Thermogravimetric analysis (TG and DTG) under nitrogen atmosphere was performed for aspen wood and the 16 p a r t i a l l y converted wood residues. The TG and DTG curves are r e produced in Figure 5 for untreated wood and for 4 selected representative SCE residues. The examination of TG and DTG curves, shows that: a) aspen wood loses weight s t a r t i n g near 230°C (pyrolysis of hemicellulose < 2 i ) ) j between 350 and 4 2 0 ° C , with a maximum rate of weight loss at 385°C (cellulose and l i g n i n p y r o l y s i s ^ i ) ) ; the weight lost at 700°C i s 89.4%. b) the SCE residues can be c l a s s i f i e d according to t h e i r temperature of extraction. For the residues of type I prepared at 250°C (e.g. sample MP6), the weight loss takes place between 350 and 4 2 0 ° C , with a maximum rate at 3 7 5 - 3 9 0 ° C . The weight lost at 700°C i s between 82.5 and 94.6%. For the type II residues produced at 300°C (e.g. sample MP12), a continuous weight loss i s observed from 300 to 6 0 0 - 7 0 0 ° C , with a maximum rate at temperatures ranging from 380°C to 5 1 0 ° C . The t o t a l weight loss at 700°C is less important than for samples of the previous type, ranging from 27.2 to 57%. )

a n (

c

143

144

PYROLYSIS OILS FROM BIOMASS

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch014

2«ι

Ttmperoturc, *C

Figure 2. Effect of SCE conditions on (expressed on dry wood b a s i s ) .

recondensed material

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch014

14. GRANDMAISON ET AL.

Residuesfrom Supercritical Extraction of Wood

Figure 3 . Recondensed material (expressed on dry wood basis) as a function of l i g n i n conversion (experiment number shown i n parentheses).

146

PYROLYSIS OILS FROM BIOMASS

4β

bod

44

40

36 Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch014


. The band at 1740 cm is due to uronic acid and acetyl groups i n hemicellulose . The bands from 1235 to 1605 cm , s p e c i a l l y the one at 1505 cm , are representative of l i g n i n

-1

-1

-1

Spectral region 2870-3050 cm . A band at 3050 cm (aromatic and/or alkene C-H stretching) becomes evident at 300°C (MP-12, Figure 7-III) and dominates this region at 350°C (MP-8, Figure 7-V). The band in the 2900 cm" region ( a l i p h a t i c C-H stretching) which i s broad in the i n i t i a l wood sample, i s progressively resolved in three separate bands (2870, 2930 and 2955 cm ) as the SCE temperature i s 1

-1

GRANDMAISON ET AL.

ResiduesfrontSupercritical Extraction of Wood

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch014

ο

SCE TEMPERATURE CO

Figure 6. DTG peak temperature as a function o f ture and pressure.

4000

ι

4000

3000

2000

SCE tempera­

1000

1 1 1 1 1 1

3000

2000

1000

WAVENUMBERS (cm" ) 1

Figure 7. DRIFT spectra ( i n KC1) o f Populus tremuloides and of four SCE residues.

149

PYROLYSIS OILS FROM BIOMASS

150

increased (MP-12, MP-11, and MP-8, Figures 7JII, IV and V). The o v e r a l l pattern i n Figure 7V corresponding to the most carbonized sample i s s i m i l a r to the ones reported for higher rank bituminuous coal and f o r v i t r i n i t e , with the 3050 cnr even more i n ­ tense i n our MP-8 sample. As i t was shown e a r l i e r that t h i s sample contains 89.2% of recondensed material, i t may be concluded that t h i s material has a c o a l - l i k e polyaromatic nature. This i s supported by the changes i n the next spectral region. 1

1

-1

Spectral Region 700-950 c n r . The band at 895 cm is discernible in wood and MP-6 (SCE temperature 250°C) but disappears from spectra of samples treated at higher temperatures where saccharides analysis has also shown the absence of c e l l u l o s e . As carbonization proceeds, the out-of-plane bending below 900 cm" (at 870-881, 800-833 and 752-766 cm" ) increases i n intensity; the position for some of the bands ( 800 and 750 cm ) can suggest condensed ring systems. The band at 950 cm* , which i s v i s i b l e i n MP-8, i s probably due to elimination reaction giving t - a l k e n e s .

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch014

1

1

-1

1

( 1 9 )

1

Spectral Region 1450-1595 cm" . The c h a r a c t e r i s t i c aromatic r i n g v i b r a t i o n at 1505 cm , c l e a r l y v i s i b l e in the spectrum of wood, i s gradually hidden with an increase i n the SCE temperature. This corresponds to the progressive decrease in l i g n i n content of the residue. Inversely, two bands near 1450 and 1595 cm" become very intense and dominate i n the spectra of residues produced at 300 and 350°C (Figures 7-III, IV and V). These changes p a r a l l e l the modifi­ cations i n the 2870-3050 cm" region. The band at 1450-1460 cm" can be attributed to methyl and methylene bonding and also to aroma­ t i c r i n g modes . The band at 1595 cm i s also assigned to aromatic r i n g stretching. Its high i n t e n s i t y i n spectra 7-III, IV and V, could possibly be given the three following explanations 1) aromatic r i n g stretching i n combination with a chelated conjugated carbonyl structure, 2) aromatic r i n g stretching mode, with possible i n t e n s i t y enhancement due to phenolic groups, 3) aro­ matic r i n g s t r e t c h i n g of aromatic e n t i t i e s linked by methylene and possibly ether linkages. -1

1

1

1

-1

1

Spectral Regions 1035-1370 and 1705-1740 cm" . The bands from 1035 to 1171 cm" (C-0 bonds in polysaccharides, l i g n i n alcohols and l i g n i n ethers), present i n wood and samples obtained at 250°C, drop in the spectra of SCE residues produced at and above 300°C. The aromatic ethers bands (up to 1330 cm* ), and the phenolic s t r e t c h i n g near 1250 cm" , decrease also. The hemicellulose band, at 1740 cm* , present on untreated wood almost disappears i n residues prepared at 250°C. The unconjugated carbonyl and/or carboxyl and/or ester of conjugated acids at 1710•1720 cm from o r i g i n a l l i g n i n i s s t i l l v i s i b l e at 250°C when hemi c e l l u l o s e i s p a r t l y removed, but at higher SCE temperatures i t i s hidden by the highly intense 1705 cm* band. This last band can be a t t r i b u t e d to a conjugated carbonyl or carboxyl structure, but i t would be s u r p r i s i n g that carboxyl could r e s i s t at severe SCE con­ d i t i o n s . Further study i s necessary f o r d e f i n i t e assignment of t h i s band. 1

1

1

1

-1

1

14.

ResiduesfromSupercritical Extraction of Wood

GRANDMAISON ET AL.

151

Quantification. Schultz et alLL? reported correlations of FTIH absorbance r a t i o s with such variables as percent glucose, xylose and Klason l i g n i n for wood chips pretreated by the RASH process at temperature ranging from 140 to 280°C. These correlations do not f i t c o r r e c t l y our data, so we developed our own equations by non-linear least squares regression. For quantitative evaluation of absorbances, baseline was defined as shown on spectra on Figure 7. These equations are described i n Table I I . In equations 1-5, the i n t e n s i t i e s (I) are expressed in Kubelka-Munk units. Selection of the independent variables in equations 1-5 was done by f i r s t s e l e c t ing 16 s i g n i f i c a n t bands i n the 17 DRIFT spectra. A l l l i n e a r regression equations describing the f i v e dependent variables, as function of a l l possible combinations of i n t e n s i t y r a t i o s , were obtained using two to s i x of these variables. A preliminary s e l e c tion was made on the basis of R values and F test s i g n i f i c a n c e l e v e l s . A f i n a l s e l e c t i o n was performed, among the s t a t i s t i c a l l y equivalent regression equations, on the basis of the a n a l y t i c a l s i g n i f i c a n c e of the bands selected, y i e l d i n g equations 1-5.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch014

2

KSÇA ESCA i s a surface s e n s i t i v e technique, based on the measurement of k i n e t i c energies of photoelectrons ejected from a given atomic energy l e v e l under the action of a monoenergetic X-ray beam. I t provides quantitative information on the elemental composition as well as on the chemical environment of each atom (bonding and oxidation s t a t e ) . The k i n e t i c energy o f photoelectrons ( E k ) , as measured with respect to the vacuum l e v e l , i s expressed as: Ek

=

Ex

- (EB +

Φ

+

E

C

)

(6)

where E x i s the energy of the incident photon, EB i s the binding energy of the electron on i t s o r i g i n a l l e v e l , φ i s the work function of the spectrometer, and E c i s the energy lost i n counteracting the p o t e n t i a l associated with the steady charging o f the surface. Φ and E c are e s s e n t i a l l y corrections, φ depends on the spectrometer and i s not l i a b l e to be modified between experiments. E c i s high on low conductivity samples and can be made lower by the use o f a flood gun. ESCA spectra corresponding to carbon Is peaks of Populus tremuloides and 3 samples i s o l a t e d at three different SCE temperatures are i l l u s t r a t e d i n Figure 8. There i s a general agreement i n the l i t e r a t u r e on the assigment of components C i , C 2 and C 3 in wood derived materials: C i corresponds to carbon linked to Η or C, C 2 has one l i n k to oxygen, whereas C 3 has two. In the s o l i d phase, C i i s referenced at 285.0 eV and C 2 and C 3 are usually close to 287.0 and 289.5 eV C2s>. In a l l SCE residues, a fourth C i s component i s found on the low binding energy side of the spectrum, s h i f t e d from the C i component by 1.4 +0.5 eV. This i s thereafter designated as the Co component. As the temperature of extraction i s increased from 250 to 300°C, the C o component increases continuously whereas the general trend o f C i , C 2 and C 3 components in a continuous decrease.

17.2

-42.8

* Klason residue =

% Glucose =

+

+

35.3

20.0

(

(

x

114.1

(

31.1

(

97.7

( χ

x

=

.879

=

.967

Il370/

]

J

=

-

+

.961

IlSQs/

Ιΐ2β0\

= .940

11595/ 2

-

l30S0\ J

=

J

I l 505 ν

Η

χ

2

-

.962

IlS95/

R

χ

2

l29SS\

H

Iisos'

J

I30S0\

-

*

V

V

141.8

/

^

\

(9.1

/

χ

χ

ί 69.5

/

162.2

/

Î77.7 χ

/

+

Il595 '

1

IlS9S/

Ιΐ2β0\

*

-

j -

Il370'

/

V

*

>

(33.2

/

χ I l 5 9 5 '

J

IlS0S\

I i s o s /

J

I l 370 \

+

/ \

[12.5

*

χ Il595

\

'

J

J

\

Ιΐ595'

l89S

Ιβ95

χ

I i 3 7 0 '

/ IlSOS \ ί 111. 1 x I -

χ

ί 54.9

/

122.8

/

ί51.1

1 -

12930 \

Ιΐ21θ\

χ

χ

IlS95'

)

l2870\

Iisos'

1 +

12870 \

IlS9s/

)

I l l 6 0 \

*

Il370/

/ Ιβ95 \ 1181.2 χ J

χ

Table I I . Regression equations' to c a l c u l a t e f i v e parameters i n SCE residues

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch014

(5)

(4)

(3)

(2)

Cl)

δ

en Ο

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Residuesfrom Supercritical Extraction of Wood

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch014

GRANDMAISON ET AL.

Figure 8. ESCA spectra o f and for 3 SCE residues.

Cie peak

f o r Populus tremuloides

153

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PYROLYSIS OILS FROM BIOMASS

It i s i n t e r e s t i n g to note that the uncorrected experimental C i s binding energy f o r dibenz (a,h) anthracene and for a sample of high rank commercial coal i s very close to the binding energy for t h i s C o peak. As polyaromatics are e l e c t r i c a l conductors, the charging i s expected to be low and E c close to 0. On this basis, C o component i s assigned to carbon in polyaromatics. This complementes the i n ­ frared conclusion about the polyaromatic nature of recondensed material. The r a t i o CRM/CSR (where CSR i s the carbon content of the whole s o l i d residue as determined by elemental analysis, whereas CRM i s the calculated mass of carbon i n the recondensed material contained in a given sample) was calculated for 6 samples. Figure 9 shows that t h i s r a t i o i s correlated to the C o f r a c t i o n of the C i s peak f o r ground chars, but also that both values are almost the same f o r each sample; t h i s represents the case where residues are well ground (black dots on the f i g u r e ) . For two samples, MP-22 and MP-16, the ESCA analysis were ran on p a r t i a l l y ground samples. When the grind­ ing i s less severe (MP-22-a and MP-16-a), the f i b e r s are only separated and not broken. The C o area value i s the same as f o r nonground samples. Otherwise, by increasing the e f f i c i e n c y of the grinding (MP-22-b and MP-16-b), the Co% value decreases and, ultimately i s equal to the bulk % carbon in recondensed material. It can be concluded that i n p a r t i a l l y converted material, the recon­ densed material i s located at the external surface of the f i b e r s but uniformally d i s t r i b u t e d within the raw samples. 100 MP-1K 80

-

MP-160

MP-20

60 MP-22Q

σ ω σ

MP-16b

MP-22b o °

4

0

20 0 0

20

40 C

RM

/ C

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60

80

100

0/ο

Figure 9. Relation between carbon i n recondensed material of some SCE residues and ESCA C o peak. Therefore a simple means reactions by a nent i n the C i s

i t may be concluded that the ESCA technique provides for the determination of the extent of recondensation mere determination of the proportion of the C o compo­ band of the s o l i d residue.

Ackn ow1edgement s We thank A. Adnot f o r performing ESCA spectra; P. Chantai (CANMET, Ottawa) f o r running thermogravimetric analysis; G. Chauvette (DREV,

14. GRANDMAISON ET AL.

Residuesfrom Supercritical Extraction of Wood

V a l c a r t i e r ) f o r having allowed the use of his FTS-40 spectrometer for running some infrared spectra and J . Thibault for c a l c u l a t i n g the regression equations.

Literature Cited 1. 2. 3.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch014

4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25.

Fifth Canadian Bioenergy R & D Seminar, Ed. Hasnain, S.; Elsevier, New-York, 1984. McDonald, E.; Howard, J.; Fourth Bio-Energy R & D Seminar, Winnipeg, Canada, March 29-31, 1982. Biermann, C.; Schultz, T.P.; McGinnis, G.D. J. Wood Chem. Technol. 1984, 4, 111-128. Nguyen, T.; Zavarin, E.; Barrall II, E.M. J . Macromol. Sci.Rev. Macromol. Chem a) 1985, C20, 1-65; b) 1985, C21, 1-60. Schultz, T.P.; Templeton, M.C.; McGinnis, G.D. Anal. Chem. 1985, 57, 2867-2869. Chua, M.G.S.; Wayman, M. Can. J. Chem. 1979, 57, 2603-2611. Marchessault, R.H.; Coulombe, S.; Morikawa, H. Can. J . Chem. 1982, 60, 2372-2382. Nassar, M.M.; Mackay, G.D.M. Wood and Fiber Sc. 1984, 16, 441453. Meier, D.; Larimer, D.R.; Faix, O. Fuel 1986, 65, 916-921. Lephardt, J.O.; Fenner, R.A. Appl. Spectrosc. 1981, 35, 95-101. Haw, J.F.; Schultz, T.P. Holzforshung 1985, 39, 289-296. Dollimore, D.; Hoath, J.M. Thermochimica Acta 1981, 45, 103113. Shafizadeh, F.; Sekiguchi, Y. Carbon 1983, 21, 511-516. Fuller, M.P.; Griffiths, P.R. Anal. Chem. 1978, 50, 1906-1910. Poirier, M.; Ahmed, Α.; Grandmaison, J . L . ; Kaliaguine, S. I & EC Research, 1987, 26, 1738-1743. Ahmed, Α.; Grandmaison, J . L . ; Kaliaguine, S. J. Wood Chem. Technol. 1986, 6, 219-248. Grandmaison, J . L . ; Thibault, J.; Kaliaguine, S.; Chantal, P.D. Anal. Chem., 1987, 59, 2153-2157. Ahmed, Α.; Adnot, Α.; Kaliaguine, S. J . Appl. Polym. Sci., 1987, 34, 359-375. Lignins. Occurence. Formation. Structure and Reactions; Ed. Sarkanen, K.V.; Ludwig, C.H.; John Wiley and Sons; 1971. Grandmaison, J . L . ; Kaliaguine, S.; Ahmed, A. in Comptes Rendus de l'atelier de travail sur la liquéfaction de la biomasse, Sherbrooke, Canada, NRCC 23130, Sept. 29-30, 1983. Shafizadeh, F. J. Anal. and Appl. Pyrolysis 1982, 3, 283-305. Nakanishi, K.; Infrared Absorption Spectroscopy-Practical; Holden-Day, Inc.: San Francisco, 1962. Gerson, D.J.; McClelland, J.F.; Veysey, S.; Markuszewski, R. Appl. Spectrosc. 1984, 38, 902-904. Painter, P.C.; Snyder, R.W.; Starsinic, M.; Coleman, M.M.; Kvehn, D.W.; Davis A. Appl. Spectrosc. 1981, 35, 475-485. Gelius, U.; Heden, P.F.; Hedman, J.; Lindberg, B.J.; Manne, R.; Nordberg, R.; Nordling, C.; Siegbahn, K. Physica Scripta, 1970, 2, 70.

Received March 31, 1988

155

Chapter 15

Some Aspects of Pyrolysis Oils Characterization by High-Performance Size Exclusion Chromatography

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch015

David K. Johnson and Helena L. Chum Chemical Conversion Research Branch, Solar Energy Research Institute, 1617 Cole Boulevard, Golden, CO 80401 The utilization of biomass pyrolysis oils or isolated fractions of these feedstocks requires a fast overall characterization technique. Gas chromatographic techniques typically analyze only the volatile fraction (5%-50%) of underivatized oils. With proper choice of solvent and detector systems the HPSEC, on polystyrene-divinylbenzene copolymer gels, of the whole oils can provide valuable information on their apparent molecular weight distributions and changes that occur upon aging or chemical fractionation. Several pyrolysis oils have been analyzed as well as fractions isolated by solvent elution chromatography. In order to better understand the observed low– molecular-weight region, a number of model substances of the main classes of compounds found in pyrolysis oils have been investigated. While hydrogen bonding between the phenolic groups and tetrahydrofuran occurs, solute-solute interactions can be kept very small by operating at very low concentrations of solute; solute-gel interactions do occur with polycyclic aromatic compounds. HPSEC provides very good information on the shelf life and reactivity of pyrolysis oils, and can be used to compare oils produced under different process conditions. Many biomass pyrolysis processes convert 55%-65% of dry biomass to a very inexpensive pyrolysis oil (1-3). Costs of the o i l s w i l l range from $0.02-$0.08/lb of oil, depending on the biomass feedstock cost ($10-$40/dry ton biomass). Therefore, these inexpensive o i l s , rich in phenolic f r a c t i o n s , acids, and furanderivatives could be feedstocks for further upgrading or could be used because of their reactivity, in applications such as thermosetting resins and other wood-bonding methods. One of the 0097-6156/88/0376-0156$06.00/0 « 1988 American Chemical Society

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Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch015

important considerations for this use or further processing is the stability of the o i l . Fast techniques to determine such properties become necessary. We present a method of characterization of pyrolysis oils and chemically isolated fractions using high-performance size exclusion chromatography (45), a technique commonly employed in the determination of the molecular weight d i s t r i b u t i o n of polymers. We discuss the potential of the method and i t s l i m i t a t i o n s . Classes of model compounds commonly found in these o i l s have been investigated in the low-molecular-weight range to shed light on interactions between solute and solvent, solute and gel material (polystyrenedivinylbenzene), and solute-solute which can be kept to a minimum by operating at very dilute conditions.

Experimental High performance size exclusion chromatography was performed on Hewlett-Packard 1084 and 1090 liquid chromatographs using HP1040A diode array and HP-1037A refractive index detectors. Data were stored on a HP 85 microcomputer. The columns (300 χ 7 mm) used in this study were purchased from Polymer Laboratories Inc. and were a PL Gel 100 A (10 μ p a r t i c l e s ) and a PL Gel 50 A (5 μ particles). The solvent employed was tetrahydrofuran (Burdick and Jackson, chromatographic grade) used as received. Details on the preparation of pyrolysis o i l s at SERI in the entrained-flow, fast ablative pyrolysis reactor can be found in a report by Diebold and Scahill (2). The o i l s in Figure 1 were obtained from two runs, #40 (c and d) and #41 (a and b), the o i l s being collected from a packed scrubber (a and c) and a cyclone scrubber (b and d ) . The o i l obtained from the packed scrubber in run 41 was subjected to sequential elution by solvents chromatography (SESC) according to the method of Davis et al (7). The HPSEC of fractions 1 through 6 appear in Figure 3. Fraction 1 was eluted with 15% toluene in hexane (yield 0.4%), Fraction 2 was eluted with chloroform (yield 1.5%), Fraction 3 was eluted with 7.5% ether in chloroform (yield 7.5%), Fraction 4 was eluted with 5% ethanol in ether (yield 19.5%), Fraction 5 was eluted with methanol (yield 38.1%), and Fraction 6 was eluted with 4% ethanol in THF (yield 3.1%). The o i l s displayed in Figures 4 and 5 were produced from run 66. The details of the methods of preparation of the o i l s shown in Figure 2 can be obtained by writing to t h e i r suppliers. B r i e f l y , Oil 1 was supplied by D. S. Scott of the University of Waterloo and was produced by flash pyrolysis of a poplar-aspen hybrid. Oils 2, 3 and 6 were supplied by C. Roy of the University of Sherbrooke. Oil 2 was produced by vacuum pyrolysis of Avicel at 360° C, Oil 3 by vacuum pyrolysis of an aspen-poplar hybrid at 534° C and 2.2 t o r r , and Oil 4 by vacuum pyrolysis of aspen at 315° C and 0.7 t o r r . Oil 4 was supplied by J . Howard, of B.C. Research, Vancouver and was produced by extraction of aspen using s u p e r c r i t i c a l acetone. Oil 5 was supplied by S. Kaliaguine of the University of Laval and was produced by extraction of aspen with s u p e r c r i t i c a l methanol at 350° C and 1500 p s i .

PYROLYSIS OILS FROM BIOMASS

158

The aromatic hydrocarbons, acids and naphthalenes used for Figure 6 were purchased from the Aldrich Chemical Co. and were toluene ( 1 ) , propyl benzene ( 2 ) , s-butyl benzene ( 3 ) , naphthalene (4) , 1,4-dimethyl naphthalene ( 5 ) , 1-phenyl naphthalene ( 6 ) , v a n i l l i c acid ( 7 ) , and 4-hydroxy-3-methoxy cinnamic acid ( 8 ) . The l i g n i n model compounds used for Figure 7 were prepared by J . A. Hyatt (6) and were a 5, 5'-biphenyl tetramer hexaol, C42H54O14 (A), a β-0-4 tetramer heptaol, C 4 H o 0 c (b), and a β-04 d i m e r t r i o l , C H o O g (C). The phenols used for Figure 7 were purchased from the Aldrich Chemical Co. and were phenol ( 1 ) , p-cresol ( 2 ) , 2-propyl phenol ( 3 ) , guaiacol ( 4 ) , syringyl alcohol (5) and acetovani1 lone (6). 1

1 7

5

1

2

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch015

Results and Discussion Comparison of Pyrolysis Oils Obtained from Various Sources. The HPSEC of four wood pyrolysis o i l s obtained from the entrained flow, fast ablative pyrolysis reactor at SERI are shown in Figure 1. The o i l s were obtained from two separate runs and collected from two different scrubbers. The apparent molecular weight distributions of the four o i l s are very s i m i l a r , indicating little selectivity on the basis of molecular weight distribution. Figure 2, however, shows the HPSE chromatograms of a number of other pyrolysis o i l s obtained under a variety of conditions from many different sources. C l e a r l y , some of the o i l s contain components of high apparent molecular weight even to the extent that some are excluded from the pores of the column polymer, indicated by the peaks at about 4.5 minutes in the chromatograms. The o i l s also have varying amounts of more sharply resolved components at lower apparent molecular weight. Thus, HPSEC may be used to characterize pyrolysis o i l s obtained from different sources, and comparisons may be drawn regarding their r e l a t i v e apparent molecular weight distributions as long as the analyses were carried out under the same chromatographic conditions. The wood o i l obtained from the packed scrubber in Run 41 at SERI was also subjected to fractionation by sequential elution by solvents chromatography (SESC) according to the method of Davis et. a l . ( 7 ) . The fractions obtained were analyzed by HPSEC and the chromatograms are shown in Figure 3. The HPSEC shows a general trend to higher apparent molecular weight as the polarity of the eluting solvent was increased up to methanol. A number of the fractions appear to contain r e l a t i v e l y large amounts of d i s t i n c t components (the sharp peaks) of lower apparent molecular weight. The sixth fraction was produced by going back to a less polar solvent. A seventh fraction was produced using a more polar eluant of 10% acetic acid in methanol which could not be analyzed by HPSEC because i t was insoluble in tetrahydrofuran. About three-quarters of the o i l was found in Fractions 3, 4, and 5, the last being the major f r a c t i o n . If the chromatograms in Figure 3 were combined taking into account the yields of the various fractions then, as expected, a close comparison could be made with the chromatogram in Figure 1 of the unfractionated o i l .

JOHNSON & CHUM

Pyrolysis Oils by HPSEC

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch015

2000

5

500

200

6

100 App.

7

Wt

8 Timelmin.l

Figure 1. HPSEC of wood pyrolysis o i l s from the SERI entrained-flow, fast ablative pyrolysis reactor. Analysis on 100 Â , 10 μ GPC column using THF at 1 ml/min" with detection at 330 nm (bandwidth 140 nm), see Experimental for a description of the o i l s . 1

2000

500

100 App.M.Wt.

200

— 1 Λ

"

—

7

2

5

8 Timelmin.l

Figure 2. HPSEC of wood pyrolysis o i l s from a variety of sources. Analysis conditions as per Figure 1, see Experimental for a description of the o i l s .

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PYROLYSIS OILS FROM BIOMASS

Doubts have been expressed that these pyrolysis o i l s could have molecular weights as high as indicated by these chromatograms as they are obtained by condensation of the primary vapors from pyrolysis. Analysis by techniques requiring revaporization of the o i l s consistently do not detect high-molecular-weight components, possibly because they are d i f f i c u l t to vaporize and also because they may be thermally degraded to either higher or lower molecular weight components (8) or both. It has been suggested that the high apparent molecular weights observed by HPSEC are the result of solute-solute or solute-solvent associations producing highmolecular-weight complexes. To verify the results obtained by HPSEC, the three major fractions and the original unfractionated oil were subjected to proton ΝMR analysis. The spectra of Fraction 5 and the original o i l contain broad peaks c h a r a c t e r i s t i c of irregular polymers such as l i g n i n , while the spectrum of Fraction 3 contains sharp peaks indicative of a mixture of simpler, low-molecular-weight compounds; Fraction 4 is intermediate between 3 and 5. Thus, the HPSEC and proton NMR spectra appear to be in general agreement in that this pyrolysis o i l contains mixtures of possibly higher molecular weight polymeric components and simpler low-molecular-weight compounds. Many of the chromatograms shown here are of samples whose history of handling and age are not known in d e t a i l . It has been suggested that because of the very reactive and acidic nature of these o i l s that the high molecular weights observed are produced as the o i l s get older and are exposed to ambient conditions. Consequently, a study has been started to examine the effects of aging and the conditions under which pyrolysis o i l s are stored. A pyrolysis o i l was produced in the SERI entrained-flow, fast ablative pyrolysis reactor. In this reactor, the primary vapors are scrubbed out with water such that about 90% are dissolved out. One sample of this aqueous solution of pyrolysis o i l was stored at 4°C and the other was analyzed by HPSEC. The sample to be analyzed was made up by dissolving a small amount of the aqueous solution in tetrahydrofuran. Storage was under ambient conditions. The THF solution was analyzed several times over the period of a week to look for changes in i t s HPSE chromatogram as shown in Figure 4. At the end of this period, the sample kept at 4°C was also analyzed to determine the effect of aging on the oil. Actually, a physical change took place in the aqueous sample stored at 4°C in that a small amount of tar separated out on the bottom of the v i a l . Consequently, two samples were made up in THF from the cooled sample, one from the aqueous part and one from the tar. Figure 5 compares the HPSEC of the sample kept at ambient conditions to those of the cooled samples. The HPSEC of the tar sample shows i t consists of r e l a t i v e l y much larger amounts of material higher in apparent molecular weight. The aqueous fraction of the cooled sample appears very similar to the sample stored at 25°C, although the l a t t e r does appear to contain a s l i g h t l y larger relative amount of apparently higher molecular weight material. The degree to which storage at lower temperature has prevented any increase in molecular weight of the pyrolysis oil with time is difficult to ascertain because of the

15. JOHNSON & CHUM

Pyrolysis Oik by HPSEC

100 App.M.Wt. I I

ι

ι

1

1

\ —

1

\---4

— 2 -"5

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch015

ν

—

3

— 6

10

12

14

16

1

Figure 3. HPSEC of SESC fractions from a SERI pyrolysis oil. Analysis on a 100Â 10 μ GPC column using THF at 0.5 ml/min~ with detection at 330 nm (bandwidth 140nm), see Experimental for a description of the f r a c t i o n s . r

2000

t

500

200

*

100 App.M.Wt.

i " Time (min.)

Figure 4. HPSEC of a SERI pyrolysis o i l kept under ambient conditions, after 5 hours ( ), 3 days ( ), and 7 days ( ), Analysis on a 50 Â 5μ GPC column using THF at 1.0 ml/min" with detection at 270 nm (bandwidth 10 nm). 1

162

PYROLYSIS OILS FROM BIOMASS

fractionation of the refrigerated sample. The sample kept at ambient conditions did not have the opportunity to fractionate because of the solvent i t was dissolved i n . The HPSEC of the unrefrigerated sample (Figure 4) does indicate that the pyrolysis o i l "aged" over the period of a week with increasing amounts of apparently higher molecular weight components being produced with time. Most of the samples obtained from outside of SERI are much older than one week. Pyrolysis o i l s are generally very reactive so that unless they are e f f e c t i v e l y s t a b i l i z e d in some way, increasing molecular weight should be expected as they get older.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch015

What are the Limitations of HPSEC as a Technique When Applied to Pyrolysis Oil Characterization. One of the major advantages of HPSEC as a technique is that with the proper choice of solvent to dissolve the sample, the whole of the sample may be analyzed under very mild conditions. Because HPSEC is an i s o c r a t i c technique, d i f f e r e n t i a l refTactometers may be used as detectors so that, again, a l l of the sample may be detected. This is not a great concern when applied to pyrolysis o i l s , as they tend to absorb quite strongly in the u l t r a v i o l e t . With a modern UV-visible diode array detector, a number of wavelengths can be monitored to ensure a l l the components of the o i l are monitored. However, the eluting solvent must be chosen such that a l l the sample is dissolved, and as pyrolysis o i l s are f a i r l y polar and often contain water, the solvent w i l l also need to be f a i r l y polar. The combination of polar solutes and polar solvents means that solute-solvent interactions through hydrogen bonding must be a concern. Tetrahydrofuran, probably the most popular solvent for HPSEC, can form hydrogen bonds with certain species such as phenols producing a complex molecule exhibiting greater molecular size and lower retention volume than would be expected (9). When nonpolar solvents are used such as toluene or chloroform, the molecular size should be r e l a t i v e l y unaffected, but o i l s o l u b i l i t y then becomes very l i m i t e d . The use of solvents of greater solvating power, such as dimethyl formamide, also generates problems (10) due to solute-solute association, interaction between polystyrene standards and the column gel and column gel-solvent interactions. The other major limitation of HPSEC as a technique comes from the desire to correlate solute elution time with molecular weight. As stated in i t s name, this is a method of separation based on molecular s i z e . HPSEC columns contain a polymer gel of polystyrene-divinylbenzene produced with a controlled pore size distribution. Solutes of different size are separated by the different degrees of their penetration into the pores of the gel. The parameter that can be obtained from HPSEC is e f f e c t i v e molecular length; e . g . , material excluded from a column containing gel with 100 Â pores should have an effective molecular length of 100 Â or greater. To correlate retention times to molecular weight, i t is necessary to use c a l i b r a t i o n standards similar in structure to the solute whose molecular weight is being determined. The most common c a l i b r a t i o n materials used are polystyrenes of low polydispersity. Others used include straight chain alkanes, polyethylene glycols, and the related materials

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch015

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Pyrolysis OUs by HPSEC

163

IGEPALS™ that are 4-nonylphenyl terminated. If a column were calibrated with straight chain alkanes, i t is unlikely to be much good for obtaining molecular weights of aromatic solutes, as a benzene ring is only about as long as propane, and anthracene is only about as long as hexane. When dealing with much larger molecules, i t is d i f f i c u l t to estimate what their size might be in three dimensions in solution. Although pyrolysis o i l s have a high level of aromatic components, especially phenolics, they are a very complex mixture of components, and so i t is unlikely that any one set of c a l i b r a t i o n standards would do a very good job. Despite these l i m i t a t i o n s , HPSEC can give an idea of the molecular weight d i s t r i b u t i o n of an o i l and certainly can be used in comparing o i l s . Establishing molecular weights for low-molecularweight components is probably the most d i f f i c u l t task. Figures 6 and 7 compare the actual molecular weights of a variety of different types of compounds with their apparent molecular weights calculated from their retention times on a 50 Â 5 μ HPSEC column calibrated with polystyrenes and IGEPALS. If the c a l i b r a t i o n was good for a l l compounds, then they should a l l f a l l on the straight lines. The aromatic hydrocarbons follow the c a l i b r a t i o n , but the aromatic acids and naphthalenes deviate greatly and in opposite directions. The aromatic acids contain both carboxylic and phenolic groups and so probably have higher apparent molecular weights than their actual molecular weights because of hydrogen bonding with the solvent tetrahydrofuran. The naphthalenes have lower apparent molecular weights than actual not only because their condensed structure makes them r e l a t i v e l y small for t h e i r molecular weight, but also because of interactions between these solutes and the column g e l . P h i l i p and Anthony (9) observed retention volumes that were longer than expected for anthracene, benzopyrene, and coronene, considering their molecular s i z e . They attributed this behavior to interaction of these highly aromatic solutes with the phenyl groups of the polymer chains of the gels. The phenols and l i g n i n model compounds follow the c a l i b r a t i o n quite c l o s e l y , tending to show s l i g h t l y higher apparent molecular weights than they actually have, probably because of association with the solvent. This is encouraging for the HPSEC of pyrolysis o i l s as these types of compounds are more l i k e l y to be present. Heavily cracked o i l s , however, can be rich in polynuclear aromatics. Solute-solute association has not been observed for any of these molecules or for others when using tetrahydrofuran as solvent. Retention time changes of less than 0.01 minutes were observed in changing sample concentrations in the mg/mL range (~4 mg/mL) to the μg/mL range (~3 μg/mL) when injecting 5 μ ΐ of these solutions. HPSEC of pyrolysis o i l samples made up in this concentration range should also be free of solute-solute association which would artifically increase the apparent molecular weight of the o i l s .

Conclusions HPSEC has been shown to be a useful method of characterizing pyrolysis o i l s because i t examines the whole of the o i l . When

164

PYROLYSIS OILS FROM BIOMASS 2000 , 500

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch015

I

L—J

200

100 App. M.Wt.

' Tfe

i

Time (min.)

Figure 5 . HPSEC of a SERI pyrolysis o i l after 7 days kept under ambient conditions ( ), tar fraction of refrigerated sample ( ) and aqueous fraction of refrigerated sample ( ). Analysis conditions as per Figure 4.

Figure 6. A p p l i c a b i l i t y of c a l i b r a t i o n using polystyrenes and IGEPALS™ for aromatic hydrocarbons, acids, and naphthalenes, see Experimental for a description of the compounds.

Actual Mol. Wt

Figure 7. A p p l i c a b i l i t y of calibration using polystyrenes and IGEPALS " for phenols and lignin model compounds, see Experimental for a description of the compounds. 1

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Pyrolysis Oils by HPSEC

using polystyrene-divinyl benzene polymer gel columns, tetrahydrofuran as solvent and polystyrenes and IGEPALS " as c a l i b r a t i o n standards a good indication of molecular weight d i s t r i b u t i o n can be obtained for o i l s from a variety of sources. The high apparent molecular weights observed appear to be r e a l , and some corroboration is seen in proton NMR spectra. Although some solute-solvent association can be expected, use of phenolic model compounds has shown that HPSEC can give a good indication of molecular weight. However, i f the o i l s contained large amounts of either much more polar compounds or condensed aromatic compounds, then interpretation of HPSEC on the basis of molecular weight would be much more d i f f i c u l t . Pyrolysis o i l s are reactive materials and an awareness of the length of time and conditions under which they are kept must be maintained and is important for further processing.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch015

1

Acknowledgment s This work was supported by the Office of Industrial Programs of the U.S. Department of Energy (FTP 587). Thanks are due to Mr. A. Schroeder, Program Manager, and to a l l producers of pyrolysis oils: J. Diebold, T. Reed, J. S c a h i l l , C. Roy, S. Kaliaguine, J. Howard, and to R. Evans and T. Milne for profitable discussions. Special thanks to J. A. Hyatt for supplying three of the l i g n i n model compounds employed.

Literature Cited 1. Diebold, J. P., Ed. Proc. Specialists Workshop on Fast Pyrolysis of Biomass, Copper Mountain, SERI/CP-622-1096, Solar Energy Research Institute: Golden, Colorado, October 1980. 2. Diebold, J. P.; Scahill, J. W. Entrained-Flow Fast Ablative Pyrolysis of Biomass, SERI/PR-234-2665, Solar Energy Research Institute: Golden, Colorado, 1985. 3. Overend, R. P.; Milne, Τ. Α.; Mudge, L. K., Eds. Fundamentals of Thermochemical Biomass Conversion; Elsevier: New York, 1985. 4. Provder, T., Ed. Size Exclusion Chromatography: Methodology and Characterization of Polymers and Related Materials; ACS Symposium Series No. 245; American Chemical Society: Washington, D.C., 1984. 5. Yau, W. W.; Kirland, J. J.; Bly, D. D. Modern Size Exclusion Chromatography: Practice of Gel Permeation and Gel Filtration Chromatograhy; Wiley: New York, 1979. 6. Hyatt, J. A. Holzforschung 1987, 41, 363-70. 7. Davis, H. G.; Eames, Μ. Α.; Figueroa, C.; Gansley, Κ. K.; Schaleger, L. L.; Watt, D. W. In Fundamentals of Thermochemical Biomass Conversion; Overend, R. P.; Milne, Τ. Α.; Mudge, L. Κ., Eds.; Elsevier: London, 1985, pp. 10271038. 8. Evans, R. J.; Milne, T. A. Energy and Fuels, 1987, 1, 123137.

166

9·

10.

PYROLYSIS OILS FROM BIOMASS

Philip, C. V.; Anthony, R. G. In Size Exclusion Chromatography; Provder T., Ed.; ACS Symposium Series No. 245; American Chemical Society: Washington, DC, 1984, 257270. Chum, H. L.; Johnson, D. K.; Tucker, M. P.; Himmel, M. E. Holzforchung 1987, 41, 97-107.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch015

Received March 31, 1988

Chapter 16

Composition of Oils Obtained by Fast Pyrolysis of Different Woods Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch016

J. Piskorz, D. S. Scott, and D. Radlein Department of Chemical Engineering, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada Liquids obtained by fast pyrolysis of four different woods were analysed. On addition of excess water they separated into water-soluble and water-insoluble fractions. The former which is principally of carbohydrate origin was shown by HPLC analysis to consist of sugars, anhydrosugars and low molecular weight carbonyl compounds. The latter was shown by C NMR to be a "pyrolytic lignin". In this way 81% to 92% of the organic content of the liquids has been characterised. 13

During

the

biomass Waterloo 70%

of

last

has

Fast yet

liquids

reported

cess.

A fluidized

yields

are

0.5

or

gas

gms/hr,

Details

of

the

publications Several flash at

liquid the type

Roy e t

of

of

are

reactor.

pyrolysis

of

as

pyrolysis

of

process

or a

process

Waterloo gives

yields

of

which are

pyrolytic

conversion

reactor

range

of

one

and

450° of

with

throughput

of

p u b l i s h e d by

to

550°C

throughput

1

to

the

proabout

mm d i a m e -

a

4

to

liquid

at

1.5

up

the

optimum

about

for

(The

softwoods,

particles

use,

of

20

kg/hr.

authors

published describing

Most of

and were work

[5]

have

for

these

intended of

described

al.

to

under a

from biomass,

the

studies

in

[6]

several

of

from

carried

biomass

[4]

vacuum p y r o l y s i s on a

developed liquids

biomass.

0097-6156/88/0376-0167$06.00/0 « 1988 American Chemical Society

hearth

an upward the

high More

system

multiple from

the out

gas

reported

vacuum c o n d i t i o n s .

based

have

production

results were

promote

Roy and C h o r n e t

pyrolysis

Knight et

pyrolyzer

a

been

been

the

liquids

entrained

the in

fast

[3]. have

al.

This

with

with

from biomass

production

bed

University

used

in

biomass.

However,

yields

recently,

of

is

time

have

[2],

studies

the

non-catalytic

another

temperatures

production.

a bed

obtained

process

[1],

pyrolysis

higher

for

Two u n i t s and

fluidized at

Process).

residence

smaller.

100

a

from hardwoods

sand

normally

seconds

ter to

years

developed

Pyrolysis

organic

highest

six

been

flow

thermal

for

168

PYROLYSIS OILS FROM BIOMASS

However, few d e t a i l s o f t h e c h e m i c a l n a t u r e o f the p y r o l y t i c o i l s produced f r o m wood o r o t h e r biomass have been r e p o r t e d . Some recent s t u d i e s of the composition of p y r o l y s i s o i l s obtained from p o p l a r wood were c a r r i e d o u t by w o r k e r s of t h e P a c i f i c N o r t h w e s t L a b o r a t o r i e s o f B a t t e l l e I n s t i t u t e [7] and the Université de Sherbrooke [ 8 ] . Methods o f q u a n t i t a t i v e d e t e r m i n a t i o n o f f u n c t i o n a l groups i n t h e p y r o l y t i c o i l s from wood were t e s t e d i n our l a b o r a t o r y by N i c o l a i d e s [ 9 ] . However, more d e t a i l e d c h a r a c t e r i s a t i o n e x i s t s i n t h e l i t e r a t u r e f o r the p r o d u c t s of the t h e r m a l d e g r a d a t i o n o f c e l l u l o s e [10,11,12,13,14].

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch016

Results In p r e v i o u s l y r e p o r t e d t e s t s (3), y i e l d s have been c l a s s i f i e d as gases, o r g a n i c l i q u i d s , char and p r o d u c t water. Mass b a l a n c e s were g e n e r a l l y c l o s e t o 95% o r b e t t e r . E l e m e n t a l a n a l y s e s were a l s o r e p o r t e d f o r many runs, b u t i d e n t i f i c a t i o n of i n d i v i d u a l compounds was done o n l y f o r non-condensable gases and f o r some v o l a t i l e o r g a n i c s such as methanol, a c e t a l d e h y d e , f u r a n , e t c . However, more det a i l e d a n a l y s e s o f l i q u i d p r o d u c t s have r e c e n t l y been c a r r i e d o u t , and some of these p r e l i m i n a r y r e s u l t s w h i c h a r e o f p a r t i c u l a r s i g n i f i c a n c e a r e r e p o r t e d here. A l l e x p e r i m e n t a l r e s u l t s g i v e n were o b t a i n e d a t c o n d i t i o n s of c l o s e t o o p t i m a l f e e d r a t e , p a r t i c l e s i z e and r e s i d e n c e t i m e f o r maximum l i q u i d y i e l d a t t h e s t a t e d t e m p e r a t u r e s , as d e t e r m i n e d by over 200 bench s c a l e runs and 90 p i l o t s c a l e runs. These o p t i m a l c o n d i t i o n s a r e those shown i n Table I , t h a t i s , 480° t o 520°C, 0.5 t o 0.7 seconds apparent r e s i d e n c e t i m e and a maximum p a r t i c l e s i z e o f 1 mm. Table I shows the e x p e r i m e n t a l y i e l d s o f p r o d u c t s from s e l e c t e d runs f o r f o u r d i f f e r e n t woods whose p r o p e r t i e s a r e g i v e n i n T a b l e I I . High o r g a n i c l i q u i d y i e l d s a r e c h a r a c t e r i s t i c o f a l l f o u r mater i a l s when u n d e r g o i n g f a s t p y r o l y s i s i n our p r o c e s s . The t o t a l l i q u i d y i e l d , i n c l u d i n g w a t e r o f r e a c t i o n , v a r i e s from 70% t o 80% o f the d r y biomass f e d , a l l o f w h i c h can be d i r e c t l y used as a s u b s t i t u t e f u e l o i l i f d e s i r e d . The l i q u i d s a r e s i n g l e - p h a s e , homogeneous f l u i d s , w h i c h pour r e a d i l y , and w h i c h c o n t a i n from 15% t o 25% w a t e r depending on t h e f e e d m a t e r i a l and i t s m o i s t u r e c o n t e n t . These l i q u i d s a r e q u i t e s t a b l e a t room temperature. The w a t e r c o n t e n t , i n a p e r i o d o f t w e l v e months, was found t o i n c r e a s e s l i g h t l y p r e s u m a b l y due t o t h e s l o w p r o c e s s e s o f c o n d e n s a t i o n - p o l y m e r i z a t i o n g o i n g on even a t room temperature. A t h i g h e r t e m p e r a t u r e s , 120°C and above, the o i l s become i n c r e a s i n g l y u n s t a b l e and decompose w i t h e v o l u t i o n o f gas, and f i n a l l y c h a r i f i c a t i o n of a p o l y m e r i c r e s i d u e . A l l t h e p y r o l y s i s vapors produce an o i l m i s t f o l l o w i n g r a p i d quenchi n g , b u t t h e i r p o l a r c h a r a c t e r a l l o w s t h e easy u t i l i s a t i o n of e l e c t r o s t a t i c p r e c i p i t a t i o n i n the r e c o v e r y system o f a p y r o l y s i s p r o c e s s . P r e l i m i n a r y s m a l l s c a l e c o m b u s t i o n t e s t s c a r r i e d o u t w i t h the p y r o l y s i s o i l as produced (20% w a t e r c o n t e n t ) showed t h a t i t burns r e a d i l y i n a f u r n a c e w i t h a c o n v e n t i o n a l p r e s s u r e a t o m i z i n g burner, p r o v i d i n g the c o m b u s t i o n box i s preheated. I f an a i r a t o m i z i n g n o z z l e i s used w i t h a p i l o t f l a m e , no p r e - h e a t i n g o f t h e c o m b u s t i o n chamber i s n e c e s s a r y . L a r g e r s c a l e t e s t s f o r extended p e r i o d s have n o t y e t been done, b u t p r e l i m i n a r y work shows t h a t the p y r o l y s i s o i l has p o t e n t i a l as a s u b s t i t u t e f u e l o i l .

*

Z

2

3

6

Bench Scale Unit

Overall recovery wt%, m.f.

Total Gas

c

C H

4

2

C0 Cll

CO

H

Water Char Gas:

Yields, wt% of m.f. wood Organic l i q u i d

Apparent Residence Time, s Feed Rate, kg/hr

Moisture content, wt% P a r t i c l e Top Size, pin

Run » Temperature, °C

99.7

12.0

11.5

0.02 4.71 5.89 0.44 0.19 0.05 0.07 0.16

9.7 16.5

62.9

100.5

0.02 4.95 6.14 0.45 0.22 0.06 0.06 0.13

10.3 14.4

62.9

0.47 2.10

5.2 1000

««-

0.64 2.24

58 504

51 497

97.2

17.4 97.7

8.1 97.8

7.8

0.03

0.02 3.82 3.37 0.30 0.17 0.03 0.04

0.04 4.16 3.38 0.34 0.16 0.02

11.6 12.2

10.7 16.3

0.65 1.91

7.0 1000

43 500

66.5

0.70 2.07

«·

42 485

96.7

7.4

0.06

j

0.01 4.01 2.69 0.43 0.16 0.05 )

11.1 12.3

66.1

0.62 1.58

45 520

White Spruce

63.1

1

0.07 8.40 7.06 0.97 0.40 0.11 0.10 I 0.28 11

10.2 10.6

59.0

0.57 4.12

50 555

Brockville Poplar

95.7

12.1

0.04

101 .2

9.8

0.01 4.12 4.89 0.36 0.16 0.04 0.07 0.14

98.7

11.6

0.02 4.83 5.36 0.57 0.21 0.07 0.10 I 0.41 »

99.7

12.4

0.09

0.02 5.32 6.30 0.48 0.20 0.04

99*8

11.0

0.01 4.44 5.75 0.37 0.13 0.05 0.08 0.19

96.4

10.8

0.09 3.10

—

5.34 4.78 0.41 0.19

—

12.2 7.7

10.7 11.8 9.3 12.1 10.0 12.1

9.8 13.7

7.4 9.0 0.04 6.96 4.02 0.75 0.24

65.7

0.46 0.05

66.2

0.48 1.85

3.3 590

A-2* 497

65.8

0.55 2.24

4.6 1000

59 504

65.0

0.44 1.32

6.2 590

27 500

67.9

0.47 1.98

0.69 2.16

9.5 1000

81 515

IEA Poplar

67.3

5.9 590

63 508

Red Maple

3.8 590

14 532

Pyrolysis Yields from Different Woods

Table I

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch016

170

PYROLYSIS OILS FROM BIOMASS

o a m

ζ CO

Σ η ο ι ο ο ο

νο

Ό ι to

Ο

C Ό Π3 4-> 03 C Γ —

Ό-

Ό-

Ό-

Ο

ο

Ό" Ό*

Ό·

C

Ο Ο

Γ —

Ο

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch016

ο

in CM I 00 CO

CL

ω

ο

Ό-

•

ο

CO

α» (Ό

L.

ω «j

4->

•Μ

Η Η ω

r— -Q

-α Φ Lu

to

ί­

ο Ο

ω

ο 3

£_

CL

00 0) 4-> •rJC

ω •r—

c (Ό Ό 4-3 Ο

CL ·Γ-

c α> c_

ίο υ « Ο

ω

vo ο

ι— Χ c u e

α»

I/)

ΌΗ

U I O U

Ο

Ό-

co C\J vo

ΟΟ

vo CO Ό-

ο ι—I

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch016

16.

PISKORZ ET AL.

Composition of Oik Obtained by Fast Pyrolysis

171

Some properties of "wet" liquids as produced are given i n Table III. The elemental analyses of the p y r o l y t i c l i q u i d s as given i n Table III are very s i m i l a r to those of the s t a r t i n g materials - wood. One could probably f a i r l y accurately describe these l i q u i d s , there­ fore, by the term " l i q u i d wood". Two major c h a r a c t e r i s t i c s of these liquids are high oxygen content and high density (much higher than wood). Another s p e c i f i c property i s a l i m i t e d water s o l u b i l i t y . In the case of p y r o l y t i c sirups produced by the Waterloo process, water i s dissolved i n the organic phase. The addition of more water to the l e v e l of about 60% by weight causes a phase separation and this be­ haviour has been u t i l i z e d i n our work for a n a l y t i c a l purposes, i n that both fractions were analyzed separately after d i l u t i o n of the o r i g i n a l o i l product. The d e t a i l s of the HPLC technique developed for analysis of the water soluble f r a c t i o n are given below: Column

Eluant Flow Rate Temperature Detector Internal Standard

Aminex HPX-87H, high performance cation exchange resin i n hydrogen form 300 χ 7.8 mm from Biorad H P0 , 0.007 Ν 0.80 ml/min, i s o c a t i c 65°C Waters R 401 D i f f e r e n t i a l RefTactometer n-propanol 3

4

The quantitative data obtained by the HPLC technique are pre­ sented i n Table IV. A t y p i c a l HPLC-chromatogram i s shown i n Figure 1. To obtain r e l a t i v e response factors and retention times, the pure compounds were fed and then eluted, although some of them, such as cellobiosan and 1,6 anhydro-3-D-glucofuranose, had to be synthe­ sized in-house [13]. Confirmation of compound i d e n t i f i c a t i o n was obtained by GC-MS [Hewlett-Packard 5970 Mass Selective Detector cou­ pled to 5890A Gas Chromatograph]. For GC-MS analysis, sugars and anhydrosugars were f i r s t t r i m e t h y l s i l y l a t e d to the corresponding ethers. Small amounts of simple phenols and of furanoid compounds were also detected by GC-MS i n the water soluble f r a c t i o n . These components were not quantified by HPLC. The yields of the water insoluble f r a c t i o n are given also i n Table IV. This f r a c t i o n separated as a dark brown viscous l i q u i d which s o l i d i f i e d during drying into a hard, black, e a s i l y powdered material. The carbon-13 NMR spectrum of this p y r o l y t i c product i s shown i n Figure 2 together with s i m i l a r spectra published by Marchessault e t a l . [15] f o r milled wood l i g n i n (MW) and steam exploded l i g n i n (EXW). The s i m i l a r i t y of the spectra of the steam exploded l i g n i n and our p y r o l y t i c l i g n i n i s quite s t r i k i n g . I t appears that the o i l s produced by the Waterloo Fast Pyrolysis process contain a s i g n i f i c a n t f r a c t i o n which i s apparently derived from the natural wood l i g n i n . This "pyro­ l y t i c l i g n i n " represents nearly 80% of the o r i g i n a l content of wood l i g n i n . Evidence for this conclusion was f i r s t reported from the work of H. Menard [16] using thermogravimetric and infrared analysis. The Waterloo NMR spectrum was recorded using a 9% solution i n DMS0-d at 62.9 MHz and 50°C with broad-band proton decoupling. Delay time between pulses was 10 seconds. 6

19.8 2.6

Water content, wtX pH

Carbon Hydrogen

Elemental a n a l y s i s , wt%, m.f.

54.1 7.1

1.19

74.1

Yields, wt% of wood as fed

Density, g/cc

51

Run t

54.7 6.9

1.20

18.7 2.4

73.3

58

Brockville

in

55.6 6.9

1.18

21.7 2.8

70.5

50

Poplar

53.5 6.6

1.22

21.9 2.1

75.2

42

Liquids

54.0 6.8

1.22

22.4 2.1

79.2

43

56.6 6.9

1.22

21.8 2.3

78.5

45

White Spruce

Properties of P y r o l i t i c

Table

54.7 6.4

1.19

18.0 2.4

77.9

63

Red Maple

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch016

53.6 7.0

1.23

18.6 2.4

77.6

59

IEA Poplar

-

-

29.9 20.9 17.1

20.6 12.9

24.8 10.5

Pyrolytic Lignin

Amount not accounted for (losses, water soluble phenols, furans, etc.)

0.77

0.42

1.11 0.30 0.05

0.63 0.46 0.18

Methanol

Furfural

Methyl furfural

by G.C.

Water-Solubles - Total Above

-

0.63 1.15

-5.81

33.0

-

3.86 0.89 1.24

-

6.30 0.87 1.70

7.55 6.35

-7.67

6.47 5.40 7.15

2.84

3.96

2.52

-

1.62 0.64 1.51 1.75

-•

2.49 0.99 2.27 2.47

67.9

66.5

1.11 0.55 1.34 1.42

62.9

63 508

43 500

58 504

27.7

1. Oligosaccharides 2. Cellobiosan 3. Glucose 4. Fructose 5. Glyoxal 6. Methylglyoxal 7. Levoglucosan 8. 1,6 anhydroglucofuranose 9. Hydroxyacetaldehyde 10. Formic Acid 11. Formaldehyde 12. Acetic Acid 13. Ethylene Glycol 14. Acetol 15. Acetaldehyde

Organic Liquid

Yields, wt % of feed, m.f.

Run if Temperature

Red Maple

White Spruce

Brockville Poplar

Analysis of Liquid Products

Table IV

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch016

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch016

174

PYROLYSIS OILS FROM

BIOMASS

Figure 1. Typical HPLC chromatogram f o r water soluble fractions of p y r o l y t i c o i l from poplar wood. Peak numbers correspond to those i n Table IV.

16. PISKORZ ET AL.

Composition of Oils Obtained by Fast Pyrolysis

175

M W Lignin (POPUIUS TRIMUIA)

K)

1 3

20 26

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch016

VA

J

EX W Lignin iroruius TMMUIAI

UJWIL I Pû_. 50

•8

150

200 1 3

100

19 20.21,.

ppm

0

.

50

F i g u r e 2. C NMR s p e c t r a o f A) m i l l e d wood l i g n i n ; B) steam e x p l o d e d l i g n i n (from M a r c h e s s a u l t e t a l [ 1 5 ] ) ; C) W a t e r l o o p y r o lytic lignin. A l l from p o p l a r wood.

PYROLYSIS OILS FROM BIOMASS

Wood sawdust (7.% H2O) 125 grams pyrolysis liquid product

100 grams (22.4 g of H2O)

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch016

add water

phase separation

insoluble "pyrolytic Iignin" 24.2 gram

soluble

ι

5 3 . 4 g (in water solution)

Cellobiosan y Glucose Fructose Glyoxai Levoglucosan Hydroxyacetaldëhyde Formic Acid Acetic Acid Ethylene Glycol Acetol

3.1 gram 1.2 2.8 3.1 4.9 9.6 8.9 4.8 1.1 1.5

Final balance of Liquid Product

"Iignin" water organics solu ble in water

24.2 22.4 53.4 41.1 gm clearly identifiable 100.0 gram

Figure 3 . M a t e r i a l balance f o r separation of l i q u i d p r o d u c t f r o m e a s t e r n s p r u c e wood.

pyrolysis

16. PISKORZ ET AL.

Composition of Oils Obtained by Fast Pyrolysis

177

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch016

Conclusions Four d i f f e r e n t woods under conditions of f a s t pyrolysis yielded very s i m i l a r l i q u i d products. Analyses show that this product i s a complex mixture of chemicals. The p y r o l y t i c "wet" tar-sirup can be readily separated into two p r i n c i p a l fractions by water extraction. The water-insoluble f r a c ­ tion i s derived from l i g n i n while the water-soluble f r a c t i o n i s carbo­ hydrate i n origin. A n a l y t i c a l results indicate large amounts of low molecular weight (-"100) lactones and aldehydes, and a s i g n i f i c a n t f r a c t i o n of these are multifunctional i n nature. Four major classes of chemicals can be d i f f e r e n t i a t e d , 1· sugars and anhydrosugars 2. carbonyl and hydroxycarbonyl compounds 3. acids - formic, acetic 4. " p y r o l y t i c " l i g n i n . Results i n Table IV show that 81% to 92% of the content of the pyrolysis o i l s produced i n this work from wood has been quantitative­ ly i d e n t i f i e d . A schematic of the material balance for a t y p i c a l separation i s shown i n Figure 3 to i l l u s t r a t e the yields obtained f o r the various fractions. Detailed analysis of p y r o l y t i c o i l s i s needed i n order to allow possible mechanistic or k i n e t i c models to be formulated which can explain the various observed aspects of f a s t biomass thermal degrada­ tion. A knowledge of chemical composition of these o i l s may also a s s i s t i n the eventual future u t i l i z a t i o n , upgrading or separation of these compounds as higher value products. Acknowledgments The f i n a n c i a l supportfor this work of the National Research Council of Canada and of the Natural Sciences and Engineering Research Council of Canada are gratefully acknowledged by the authors. The assistance of P. Majerski and A. Grinshpun with experimental measurements i s also acknowledged with pleasure.

Literature Cited 1. 2. 3. 4. 5. 6. 7.

Scott, D. S.; Piskorz, J. Can. J. Chem. Eng., 1982, 60, 666. Scott, D. S.; Piskorz, J. Can. J. Chem. Eng., 1984, 62, 404. Scott, D. S.; Piskorz, J.; Radlein, D. Ind. Eng. Chem. Process Res. Devel., 1985, 24, 581. Roy, C.; Chornet, E. Proc. 2nd World Congress Chem. Eng., Montreal, 1985, Vol. II, p 315. Roy, C.; Lalancette, Α.; DeCaumia, B.; Blanchette, D.; Cote, B.; Renaud, M.; Rivard, P. Bio Energy 84; Egneus, H.; Ellegard, A. (Eds.), 1984; Vol. III, 31, Elsevier App. Sc. Publ., London. Knight, J.A.;Gorton C.W.; Stevens, D. J. Bio Energy 84, Egneus, H.; Ellegard, A. (Eds.), 1984; Vol. III, 9, Elsevier App. Sc. Publ., London. Elliott, D.C. International Energy Agency Co-operative Project D-1, Biomass Liquefaction Test Facility, National Energy Administration, Stockholm, Vol. 4.

178 8.

9. 10. 11. 12. Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch016

13. 14. 15. 16.

PYROLYSIS OILS FROM BIOMASS Menard, H.; Belanger, D.;Chauvette, G.; Khorami, J.; Grise, M.; Martel, Α.; Potvin, Ε.; Roy, C.; Langlois, R. in Hasnain, S. (Ed.), Proc. 5th Bioenergy R & D Seminar, Elsevier, New York, 1984, p 418. Nicolaides, G. M. The Chemical Characterization of Pyrolysis Oils, MASc Thesis, Dept. of Chemical Engineering, University of Waterloo, Waterloo, Ontario, Canada, 1984. Shafizadeh, F. J. Anal. Appl. Pyrol., 1982, 3, 283. Funazukuri, T. A Study of Flash Pyrolysis of Cellulose, Ph.D. Thesis, Dept. of Chemical Engineering, University of Waterloo, Waterloo, Ontario, Canada, 1983. Piskorz, J.; Radlein, D.; Scott, D.S. J. Anal. Appl. Pyr., 1986, 9, 121. Radlein, D.;Grinshpun, Α.; Piskorz, J.; Scott, D.S. J. Anal. Appl. Pyr., 1987, 12, 39. Golova, O.P. Russian Chemical Reviews, 1975, 44 (8). Marchessault, R. H.; Coulombe, S.; Morikawa, H.; Robert, D. Can. J. Chem., 1982, 60, 2372. Menard, H. Universite de Sherbrooke - private communication.

Received June 9, 1988

Chapter 17

Product Analysis from Direct Liquefaction of Several High-Moisture Biomass Feedstocks Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch017

Douglas C. Elliott, L. John Sealock, Jr., and R. Scott Butner 1

Pacific NorthwestLaboratory ,P. O. Box 999, Richland,WA99352 Experimental results are reported for high-pressure liquefaction of high-moisture biomass. The feedstocks included macrocystis kelp, water hyacinths, spent grain from a brewery, grain sorghum field residue and napier grass. The biomass was processed in a batch autoclave as a ten weight percent slurry in water with sodium carbonate catalyst and carbon monoxide gas. Thirty-minute experiments were performed at 350°C with operating pressures ranging from 270 to 340 atmospheres. The o i l products were collected by methylene chloride and acetone extractions. Oil yields ranged from 19 to 35 mass percent on a moisture and ash-free basis. The o i l products contained from 9.9 to 16.7 percent oxygen with hydrogen to carbon atomic ratios from 1.36 to 1.61. Significant nitrogen content was noted in the o i l product from those feedstocks containing nitrogen (kelp, hyacinth, spent grain). Chemical composition analysis by gas chromatography/mass spectrometry demonstrated many similarities between these products and wood-derived oils. The nitrogen components were found to be mainly saturated heterocyclics.

Significant progress has been made over the past f i f t e e n years toward the development of processes for direct production of l i q u i d fuels from biomass. Process research has generally progressed along two lines — f l a s h pyrolysis and high-pressure processing. Extensive analysis of the l i q u i d products from these two types of processes has demonstrated the s i g n i f i c a n t process-related differences i n product composition. However, the effect of feedstock has received a lesser degree of attention. 1

Operated by Battelle Memorial Institute for the U.S. Department of Energy under Contract DE-AC06-76RLO-1830.

0097-6156/88/0376-0179$06.00/0 * 1988 American Chemical Society

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PYROLYSIS OILS FROM BIOMASS

Process Research i n Direct Liquefaction of Biomass

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch017

Two generalized categories of direct liquefaction processes can be i d e n t i f i e d (1_). The f i r s t , f l a s h pyrolysis, i s characterized by a short residence time i n the reactor (~1 second) at r e l a t i v e l y high temperature (450-500°C) i n order to obtain maximum y i e l d of l i q u i d product. The second, high-pressure processing, i s usually performed at lower temperature (300-400°C) and longer residence time (0.21.0 h r ) . A t y p i c a l operating pressure i s 200 atm and often reducing gas and/or a catalyst i s included i n the process. The differences i n processing conditions result i n s i g n i f i c a n t differences i n product y i e l d and product composition. Product Analyses. Product analysis i n support of the process development research i n biomass direct liquefaction began at the rudimentary l e v e l of determining solvent-soluble portions of the product. Analysis was soon extended to elemental analyses and proximate analyses, such as ash and moisture. Later, spectrometric analyses were performed followed by detailed chemical analyses used i n conjunction with chromatographic separation techniques. At a l l stages of development, the s i g n i f i c a n t differences i n composition between the products of f l a s h pyrolysis and highpressure processing have been evident. While polar solvents are most e f f e c t i v e for both products, less polar solvents such as methylene chloride and even benzene and toluene have been used as extractants for high-pressure product o i l s . Comparative analysis has demonstrated the higher oxygen content and higher dissolved water content i n the f l a s h pyrolysis o i l s . Detailed analyses with spectrometric and chromatographic methods have added supporting evidence to these findings. Variations i n Product Due to Feedstock. While process-related d i f ferences i n product composition have been evident, extensive study of the effect of feedstock on product composition has never been undertaken. Some limited comparative tests can be gleaned from the l i t e r a t u r e ; however, most process research i n direct l i q u e f a c t i o n of biomass has been performed with woods of various species. Table I provides some of the results available i n the l i t e r a t u r e for nonwoody feedstocks. Significant differences i n heteroatom content are evident, but only limited chemical analysis i s available i n most cases. The researchers at the Pittsburgh Energy Research Center (2-4) steadfastly maintained i n their pioneering work on high-pressure l i q u e f a c t i o n that their o i l products obtained from c e l l u l o s i c wastes were p a r a f f i n i e and c y c l o p a r a f f i n i e i n nature. These products were formed i n the presence of sodium carbonate catalyst with an i n i t i a l overpressure of carbon monoxide at temperatures from 250 to 380°C and pressures from 10.4 to 34.6 MPa with batch residence times of 20 to 60 minutes. They reported the presence of carbonyl and carboxyl functional groups but maintained that there was e s s e n t i a l l y no aromatic material produced except at higher temperature (then only i n very small amounts). These conclusions were based on infrared and mass spectral analysis (_2). Later analysis of the sucrosederived o i l (3_) included proton nuclear magnetic resonance spectral evaluation but resulted i n the same conclusion. Most of the hydrogen was i n methylene or methyl groups and about 4 percent

17. ELLIOTT ET AL.

181

Product AnalysisfromDirect Liquefaction

Table I. Product Analyses from Liquefaction Tests with Various Biomasses Feedstock

Temp. (°C)

Pressure (MPa)

C

H

Ν (percent)

0

S

H/C

.90)

89 84 94 81

71 81 87 69

f

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch018

The variance that was not retained i n the CV's represents noncorrelating variance and was not treated further .

diagnostics. More than 90% of the o r i g i n a l factor variance were used from each data set. Canonical c o r r e l a t i o n of the factor analysis results from the MS, IR, PMR and CMR data using 6 factors from each data set gave four canonical variate functions with c o r r e l a t i o n c o e f f i c i e n t greater than 0.90. Figure 5 i s a score plot of CV1 vs. CV2 for the four data sets. The scores from each f r a c t i o n analyzed by the four methods are connected by l i n e s . A small polyhedron implies that the methods describe the sample i n a similar way i n t h i s dimension. The l a t e r eluting samples (9-13) appear to group into clusters that are widely separated from one another (e.g., 9 and 10, 11 and 12, 13) whereas early eluting samples (1-7) are close together i n t h i s space. Figure 5b shows a consensus picture of the component directions from each method found i n t h i s CV space. Correlated variables consistent with an interpretation of a l i p h a t i c compounds are clustered around CV1-, near fractions 1-4. Only the MS found an axis of C H2 (alkene, cycloparaffin) components i n t h i s d i r e c t i o n . Fraction 7 appears also in t h i s d i r e c t i o n . A component axis of a l k y l benzenes (m/z 92, 106...) from the MS data loads weakly i n t h i s CV space. From the o r i g i n a l factor analyses i t can be seen that the mass spectral and PMR data c l e a r l y d i f f e r e n t i a t e d f r a c t i o n 7 from the other fractions in the F l + F2 factor spaces shown. The PMR data showed no unique component associated with f r a c t i o n 7. This says that the mass spectral picture of f r a c t i o n 7 i s i n a sense unique, since confirmation by other data sets i s not apparent. A component axis corresponding to o l e f i n i c variables (IR, PMR, CMR) appears at 150°, in the d i r e c t i o n of fractions 5 and 6. The mass spectral data shows ion series with 2 and 3 units of unsaturation, one or more of these apparently being a double bond. The p o s i t i v e h a l f of CVI reveals three components, each one consistent with an assignment of aromaticity. The PMR and IR (CH in-plane bend modes) show increasing fused ring aromaticity i n the ccw d i r e c t i o n (300° to 50°). The mass spectral data i d e n t i f i e d the component at 300° with indane/tetralin, the 0° component as >C^ a l k y l substituted naphthalenes and the 50° component as acenaphthene/- biphenyls. The CMR data showed a variable 142 ppm at 300° consistent with an assignment of an indane bridgehead carbon ( l i t e r a t u r e value 143.9 i n CHCI3). A component axis at 80° (mass spectral data only) near sample 13 showed peaks c h a r a c t e r i s t i c of a l k y l anthracene/ phenanthrenes. The o r i g i n a l CMR factor analysis showed correlated n

n

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch018

18.

HOESTEREY ET AL.

Chemical Characterization ofPyrolysis Oils

201

peaks near sample 13 which f i t an interpretation of phenanthrenes better than anthracenes. The CV3 and CV4 dimensions also showed c o r r e l a t i o n c o e f f i c i e n t s of >0.9. The variance i n these dimensions ranged from 7% (PMR) to 21% (MS). Since one variable i n the PMR data accounts for 12.5% of the variance, no variables were found to load above 0.4 i n t h i s dimension, and PMR data w i l l not be further discussed. Both the CMR and the MS data sets presented a similar space on CV3 and and 4. Samples 7 and 13 were grouped together along CV3+. Variables from the MS with appreciable loadings i n t h i s dimension were m/z 92, 106, 134... ("alkyl benzenes") and m/z 146, 160, 174 ("indane/tetralins"). The a l k y l benzene components appeared with weak loadings i n the CV1 + CV2 space near sample 7 only. The infrared data showed two variables with low loadings that were i n common between samples 7 and 13, 2950 and 1450 cm . These variables are small portions of the broadest IR peaks and t h e i r significance i s not clear. Variables from the CMR data, 14 and 34 ppm, implied similar a l k y l f u n c t i o n a l i z a t i o n , e.g., ethyl. From evidence i n the factor analysis of ms data from samples 1 to 15 (not presented here) of fragmentation/pyrolysis dominant i n samples 14 and 15 and to a lesser extent 13, and evaporation dominating e a r l i e r samples, i t i s l i k e l y that the tetralin/indane ms ion series i n samples 7 and 13 arose from d i f f e r e n t sources. GC/MS data, not completely interpreted yet, determined that sample 13 was dominated by 2 and 3 ring p o l y c y c l i c aromatics, e.g., higher substituted naphthalenes, biphenyls and larger, whereas sample 7 had benzene and toluene a l k y l substituted compounds. Samples 8 and 9 had associated components from both MS and CMR i n CV3 and CV4. Fragment ions m/z 145, 159 and 173 loaded moderately i n t h i s space, as did the CMR variable 142 ppm. These are not inconsistent with the interpretation of indane/tetralin found i n the CV1 + CV2 space. Sample 10 had associated variables of m/z 142 and 156, Ci and C 2 a l k y l substituted naphthalenes and an "acenaphthene/biphenyl" (m/z 144, 158...) component. The lone variable from CMR, at 131 ppm, might a r i s e from either of these components (2 methyl naphthalene 131.7 ppm or acenaphthene 131.5 ppm C D C I 3 ) considering that we chose variables as v i r t u a l l y + 1 ppm. The only variable loading strongly on CV3 or CV4 from the IR data i s 791 cm" , a CH out-of-plane bend, pointing d i r e c t l y opposite samples 7 and 13, and probably showing some relationship i n aromatic substitution patterns. -1

1

Conclusions A consensus interpretation of the major components contained i n LC eluted samples from a pyrolysis o i l was attempted using MS, IR, PMR and CMR data. Valuable information was gained by correlating the four a n a l y t i c a l techniques. For example, mass spectral peaks of samples containing 2 and 3 units of unsaturation, such as samples 4-6, were shown by PMR, IR and CMR to contain double bonds, whereas mass spectral peaks corresponding to molecules containing one unit of unsaturation such as samples 1 and 2, were apparently c y c l i c , since only a l i p h a t i c functional groups were found by the other methods.

202

PYROLYSIS OILS FROM BIOMASS

A l k y l benzene components i n sample 7 were not represented i n the canonical variate space. Mass spectral peaks corresponding to indane/tetralins i n samples 8 and 9 were found by CMR to contain indanes, and anthracene/phenanthrene mass spectral molecular ions were found to be predominantly phenanthrene.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch018

Acknowledgments The expert assistance of Dr. Jim Liang, Mary West and A l i r e z a Pezeshk in obtaining the a n a l y t i c a l data, and of Dr. Liang and Dr. Charles Mayne i n interpreting the r e s u l t s i s g r a t e f u l l y acknowledged. Drs. George R. H i l l and Larry L. Anderson are thanked for t h e i r stimulating support of t h i s research. The work reported here i s part of the research carried out at the University of Utah, under the auspices of the Consortium for F o s s i l Fuel Liquefaction Science funded under DOE contract RF-4-21033-86-24.

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8.

Thimsen, David; et a l . , Fixed Bed Gasification Research Using U.S. Coals; Vol. 1 Program & Facility Description, USBM HO222001. McClennen, W. H.; Meuzelaar, H. L. C.; Metcalf, G.S.; Hill, G. R. Fuel 1983, 62, 1422. Meuzelaar, H. L. C.; Hoesterey, B. L . ; McClennen, W. H.; Hill, G.R. Proc. 10th Ann. EPRI Contractors Conference on Liquid & Solid Fuels, 1985. Tandem Mass Spectrometric Analysis (MS/MS) of Jet Fuels, Part I and II, Air Force Aero Propulsion Laboratory, Wright-Patterson Air Force Base, Ohio, AFWAL-TR-85-2047, 1985. Windig, W.; Meuzelaar, H. L. C. Proc. 34th ASMS Conf. on Mass Spec. A l l . Topics., 1986, p 64. Windig, W.; Meuzelaar, H. L. C. Anal. Chem. 1984, 56, 2297-2303. Crelling, J. C.; Pugmire, R. J.; Meuzelaar, H. L. C.; McClennen, W. H.; Karas, J. "The Structure and Petrology of Resinite from the Hiawatha "B" Coal Seam." submitted to Energy & Fuel, 1988. Kuehn, D. W.; Davis, Α.; Painter, P. C. In ACS Symp. Series 252, Chapter 7, 1984; p 100.

Received April 14, 1988

Chapter 19

Chemical Characterization of Wood Pyrolysis Oils Obtained in a Vacuum-Pyrolysis Multiple-Hearth Reactor

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch019

H. Pakdel and Christian Roy Chemical Engineering Department, Université Laval, Pavillion Adrien-Pouliot, Sainte-Foy, Quebec F1K 7P4, Canada A multiple hearth reactor has been used to produce high yield of pyrolysis o i l from aspen poplar. The Process Development Unit (P.D.U.) has the capability of achieving a fair fractionation of wood oils by using six heat exchangers (Primary Condensing Unit, P.C.U.) and a series of cooling trap receivers (Secondary Condensing Unit, S.C.U.) at the outlets of the reactor. While the weight average molecular weights (Mw) of the recovered compounds in the P.C.U. were 342, 528, 572, 393, 233 and 123 from top to bottom of the reactor, the low molecular weight compounds with Mw = 100 or below were recovered in the S.C.U., which contained at least 90% of the total water. Silica-gel column chromatography enabled us to fractionate the oil from P.D.U. into fourteen fractions. Aromatic hydrocarbons were collected in Fraction 1 (F1) and F2 followed by elution of moderately polar compounds in F3 to F11 with about 2335% of P.C.U. o i l which can be fully characterized. 8.1% sugar in P.C.U., mainly glucose, was found in F13. Usefulness of H-FTNMR and infrared spectroscopy was shown for preliminary characterization of the F12, F13 and F14. Overall 27.89% of the P.C.U. including water and low molecular weight carboxylic acids have been measured and identified so far. 1

The i d e n t i f i c a t i o n and extraction of valuable chemicals from woodderived o i l s i s a very important goal for the biomass thermochemical conversion industry (IzZ)· Pyrolysis o i l s have been extensively studied and extensive number of compounds have been i d e n t i f i e d (34). However to our knowledge there are only two general methods which have been reported for the fractionation of pyrolysis o i l s

0097-6156/88A)376-0203$06.00A) « 1988 American Chemical Society

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch019

204

PYROLYSIS OILS FROM BIOMASS

into chemical groups: the* solvent extraction method (5) and the adsorption-ehromatography method (6). The former technique i s rather tedious and quite often the phase separation i s d i f f i c u l t due to the emulsion formation. The y i e l d of extraction strongly depends on the solvent volume and extraction r e p e t i t i o n number. The adsorption-ehromatography method was used f o r t h i s investigation with further modifications which w i l l be discussed i n this paper. Extensive works conducted by d i f f e r e n t authors u t i l i z i n g GC and GC/MS sometimes lead to d i f f e r e n t results which indicate the difficulties of carrying out accurate detailed analysis of the chemical constituents of pyrolysis o i l s . Examples of incomplete or even contradictory results can be found i n the l i t e r a t u r e (3^4) and t h i s paper i n the analysis of vacuum p y r o l y s i s o i l s . Other researchers have studied the functional group d i s t r i b u t i o n in pyrolysis o i l (8). Although those techniques are long and tedious, they w i l l lead to useful information about wood o i l chemistry. The majority of compounds found in pyrolysis o i l s are oxygenated with rather s i m i l a r p o l a r i t y . Therefore t h e i r gas chromatograms, i n general, suffer from low resolution and consequently the quantitative analysis w i l l be less accurate. Although t h i s problem may be p a r t i a l l y obviated by choosing narrow bore and Long c a p i l l a r y columns, but they are very expensive and not very practical. Direct injection of a complex mixture into the gas chromatograph on the other hand tend to deteriorate the column by b u i l d i n g up of non v o l a t i l e matter i n the column i n l e t leading to gradual decomposition of the column stationary phase. Generally gas chromatography has a limited application and i s not meant to be used for very complex and less v o l a t i l e mixtures. GC/MS i s a much more powerful a n a l y t i c a l tool but would not be available in a great majority of cases. Besides i t i s quite c o s t l y and requires s k i l l e d operators for the interpretation of the r e s u l t s . Therefore development of new methods of separation and fractionation i n p a r t i c u l a r are needed. The primary objective of t h i s work i s to develop a separation and fractionation method f o r better and detailed analysis of pyrolysis o i l s and to demonstrate f a i r fractionating c a p a b i l i t y of the multiple hearth vacuum pyrolysis system. This w i l l eventually enable us to make correlations between the o i l properties and pyrolysis operation conditions. Full, characterization of the o i l s w i l l also shed some l i g h t on the possible pyrolysis reaction mechanism and upgrading of o i l s . The secondary objective i s to develop methods for the extraction of valuable chemicals such as s p e c i a l t y and rare chemicals which are i n increasing demand (9). Experimental The wood o i l samples which have been character!zed in t h i s work have been obtained from pyrolysis of Populus deltoïdes (clone D-38) with no bark i n a multiple-hearth vacuum pyrolysis reactor. The Process Development Unit, Fig. 1, (P.D.U.) has been described in d e t a i l by one of the co-authors i n another paper (1). The P.D.U. was tested for the production of high yields of o i l s from wood chips. One objective was to separate the bulk of the aqueous phase from the organic l i q u i d phase by means of

19.

PAKDEL & ROY

Vacuum-Pyroly sisMultiple-Hearth Reactor

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch019

FEEDER

Figure 1. Schematic view of vacuum pyrolysis Process Development Unit (P.D.U.).

205

PYROLYSIS OILS FROM BIOMASS

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch019

206

f r a c t i o n a t i o n of the o i l d i r e c t l y at the outlet of the reactor. This was achieved in the following way. The organic vapor product was removed from the reactor through s i x outlet manifolds which corresponded to the s i x heating plates of the reactor, the hearths. The vapors were condensed i n two condensing units named Primary and Secondary Condensing Units (P.C.U., S.C.U.). P.C.U. consisted of s i x heat exchangers i n p a r a l l e l (H-I to H-VI) and S.C.U. consisted of four receivers placed in series (CI to C4). The pyrolysis o i l s which were obtained i n both condensing units were subjected to sequential elution solvent chromatography. The organic fractions were thon analysed as described below. Relationship of a l l samples and designations are described in Table I. One gram of the o i l sample immediate after pyrolysis was transferred into a glass column with 16 mm i . d . packed with 12.5 g of 60 120 mesh s i l i c a - g e l i n petroleum ether (30-60°C b.p.). Fourteen fractions were c o l l e c t e d using d i f f e r e n t solvents as depicted in Table I I . A l l the solvents were d i s t i l l e d before use and the s i l i ca-gel was washed with dichloromethane and dried in a i r . The o i l fractions were dried by rotary evaporator without heat. A l l the y i e l d s are shown in Table II. H-FTNMR spectra of 5% solution in DMSO were recorded on XI, 200 Varian instrument. Gas chromatographic analyses were performed on a 6000 Varian gas chromâtograph with flame ionization detector with two injectors (on column and s p l i t ) . The c a p i l l a r y columns were J & W fused s i l i c a : DB5, 30 m X 0.25 mm i.d. and UB1, 30 m X 0.32 mm i.d. The c a r r i e r gas was He and N 2 as make up gas. The oven temperature was maintained at 50°C for 2 min then programmed to 150°C and 290°C at rates of 4 and 10°C min' respectively. Water's 840 data and chromatography control station with d i g i t a l professional 350 computer and Ι.Λ50 recorder were used as data processor. Various standard mixtures were prepared with the available compounds. Their r e l a t i v e response factors to benzophenone were measured. S i l i c a -gel eluates were added an accurate quantity of benzophenone as internal standard. Their gas chromât o-grams were compared with the standard mixtures for peaks identificat i o n and followed by integrations f o r t h e i r quantifications. Hydrolysis followed by sugar analysis was c a r r i e d out according to the s i i y l a t i o n technique. The procedure can be found elsewhere (10). Gel permeation chromatographic (G.P.C.) analysis of the s i x o i l s from P.C.U. and one o i l from S.C.U. (CI) were performed on ALC/GPC-20I Water's Associate l i q u i d chromâtograph equipped with a model R-401 refractometer. Four 30 cm X 7.8 mm i . d . columns packed with 100, 500, 10 and 10 μ styragel were used i n series. The sam­ ples were prepared in THF (5*) and 15 μΐ was injected and eluted with THF. The following standards were used to c a l i b r a t e the system: polystyrene (Mw = 4000; 2000; 800 and 600), polyethylene g l y c o l (Mw = 450, 300, 200), guaiacol, syringaldehyde and v a n i l l i n e . l

1

3

4

Results and Discussions Pyrolysis o i l , water, char and gas are the wood pyrolysis products. Depending on the liquefaction process, pyrolysis o i l s composition change s i g n i f i c a n t l y . Lack of a standard pyrolysis o i l characteriz­ ation technique has i n i t i a t e d us at the f i r s t stage to develop a

Primary Condensing Unit Secondary Condensing Unit Obtained from the s i x hearths Fourteen fractions of H-I to H o i l s by SESC Receiver 1 See Fig. 2

P.C.II. S.C.U HI F l to F14

CI hearth I to hearth-VI

phase

Oil

Aqueous phase

Pyrolysis o i l

PCU o i l

SCU o i l

S o l i d residue

Vacuum p y r o l y s i s

Vacuum pyrolysis

Vacuum p y r o l y s i s

SESC, GPC, GC, NMR

GPC

1R

SESC = Sequential elution s o l i d chromatography; GPC = Gel permeation chromatography; GC - Gas chromatography; NMR ~ Nuclear magnetic resonance; 1R - Infrared

to H- VI

Remarks

Designation

Nature of Sample

Relationship of the samples studied i n the text (See réf. 1 for more d e t a i l s )

Experimental Technique

Table I.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch019

95.37 3.28 28.26

29.09

33.18

0.12

1.44

H-VI

Fraction 12: Fraction 13: Fraction 14:

Fraction 1: Fraction 2-11:

128 ml with petroleum ether. 128 ml each with C H 2 C I 2 / Petroleum ether mixture, from 10 to 100% F2 to F l l respectively. 128 ml with ether. 128 ml with water. 60 ml with 10% formic acid in methanol.

(a) See the text and table I for description of the classes. A l l figures are expressed in weight percentage (as-received o i l basis).

(10* increments) for

92.41 2.79 29.48

35.35

24.24

0.10

0.45

H-V

CH2CI2

91.35 2.24 30.70

35.60

22.32

0.16

0.33

H-IV

90.12 2.34

26.93

36.80

22.99

0.21

0.85

H-III

87.69 1.65

26.28

32.52

26.37

0.23

0.64

H-II

86.87 1.67

27.16

31.06

26.83

0.04

0.11

H-I

TOTAL

FRACTION 12

FRACTION 14

FRACTION 3-11

FRACTION 2

PYROLYSIS OIL SAMPLES FROM

FRACTION 1

FRACTION 13

Table II. Primary Condensing Unit Pyrolytic Oils and the Yield of Various Classes of Compounds Obtained by Silica-Gel Column Chromatographic Analysis (a)

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch019

ce

S δ

§

g

Ο

I

Ο

1

00

ο

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch019

19.

PAKDEL & ROY

Vacuum-Pyrolysis Multiple-Hearth Reactor

209

sub-fractionation technique followed by quantitative gas chromato­ graphic analysis. Interestingly, vacuum p y r o l y s i s y i e l d s r e l a t i v e l y low percentage of high molecular weight compounds. The high molecu­ l a r weight compounds with Mw > 300 represent approximately 25* of the t o t a l vacuum pyrolysis o i l s . It has been suggested that the high molecular weight less v o l a t i l e and presumably more polar com­ pounds are produced by incomplete thermal degradation of l i g n o c e l l u l o s i c materials (8). The following characterization technique enabled us to f i n d app. 5% oligosaccharides with Mw > 300. Due to GC l i m i t a t i o n , the rest of the high molecular weight compounds can be characterized u t i l i z i n g GPC, M S - M S , HPLC or combination of those. The work i n t h i s l i n e i s presently under investigation i n our laboratory. The s i x o i l s from the P.C.U. (H-I to H-VI) and an o i l sample from the S.C.U. (CI) were analysed by GPC f o r t h e i r molecular weight range d i s t r i b u t i o n . The weight average molecular weights f o r the H~ I to VI were: 342, 528, 572, 393, 233 and 123 respectively. The test f o r CI showed weight average molecular weight of about .100. The molecular weight d i s t r i b u t i o n of CI was as below: Mw^lOO (40*); 100 1000 of lignin oligomers whose average conformed to the PDF of Figures 1, 2, and 3. Monte Carlo simulation of the reaction of each allowed mathematical description of lignin liquefaction.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch022

Lignin Depolvmerization The simulation of lignin liquefaction combined a stochastic interpretation of depolymerization kinetics with models for catalyst deactivation and polymer diffusion. The stochastic model was based on discrete mathematics, which allowed the transformations of a system between its discrete states to be chronicled by comparing random numbers to transition probabilities. The transition probability was dependent on both the time interval of reaction and a global reaction rate constant. McDermott's (6) analysis of the random reaction trajectory of the linear polymer shown in Figure 6 permits illustration. Initially, the 11 monomer units depicted (0) were connected by 10 reactive bonds. These bonds could be either intact or cleaved at all subsequent times. The simulated depolymerization proceeded by allowing fixed time intervals, At, to pass in series. After the passage of At, each of the bonds was tested for reaction by comparing the value of a random number against the associated transition probability. If the transition probability was greater than the random number, the reaction occurred. Otherwise, the bond remained intact. The result of testing each bond then defined the new state of the polymer. This procedure is analogous to a first-order Markov chain through time, in which each discrete polymer state is dependent soley on the immediately previous state. Averaging the results of N = 10,000 Markov chains provided a result of desired accuracy. Application of these ideas to lignin liquefaction required definition of allowable lignin states and the probabilities associated with transitions from one state to another. The random construction just considered provided the initial (t = 0) states. The model compound reaction pathways provided the set of allowable states for t > 0, and the model compound kinetics and selectivities provided the transition probabilities. McDermott (6) et aL developed therigorousexpressions shown in Table II for the transition probabilities of bonds reacting according to the prototype reaction sequences of: A • B, first order; A ^-B and A * - C , first order; A • B ^ C , first order; A ^-B, second order, etc. For example, the transition probability for the irreversible first-order reaction of A to Β has the general form: s

k

(1)

A

P=l- - AB t e

where Ρ is the transition probability, k ^ is derivedfromthe deterministic (model compound) rate constant and other extrinsic factors, and At is the length of time allowed in the test for a transition. In the present simulation the global rate constant kAB had the form kAB =rç(t>Cû k + kt to account for catalyst and effectiveness and thermal-to-catalytic ratios, as developed below. The results summarized in Table II were used herein as the basis for the dependence of the transition probability on the global rate constant. The details of c

c

American Chemical Society. Library 1155 16th St. N.W. Washington, D.C. 20036 f

248

PYROLYSIS OILS FROM BIOMASS

φ-φ-φ-φ-φ-φ-φ-φ-φ-φ-φ

I Ι* Ι"

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch022

At

φ—φ—φ—φ

φ—φ

φ—φ—φ—φ

φ—φ

φ—φ—φ—φ—φ

φ—φ—φ—φ

φ

φ—φ—φ

φ

φ—φ

φ—φ—φ—φ

φ

φ—φ—φ

φ

φ~~φ

φ—φ—φ—φ

φ

φ—φ

φ

φ

ψ~ψ

ψ~ψ

Ψ~Ψ

Ψ

Figure 6. Random Trajectory of the Reaction of a Linear Polymer. A

P

• B. First-order, Irreversible

A

> Β and

A

• C , First-order,

AB =

1

P

Selectivity*products:

^ " ^ B ^ B C

>Β

> C , First-order

kO/l „ • Βj

A A

k

l/2

AB =

1

2

c x

K

PB

K

Δ Ί

>

Irreversible

Probability ofreactionof A :

A

CX

" P

-

B

C

^

A

B

= 1 - cxp(- k ^ t )

kN.i/N > ... B . j

> B , First-order

N

N

Ν p.. 1

>

(-l)N-i

iKl k

^

M/i

ni-i

k

k

J-^

ρ

rii-i i

k

< j-i/j - i-i/i>

k

< M/i -

+

k

M/p

1

1

4

i=l

A

(

2 A

> B , First-order, Reversible: conceptually similar lo a series A - • Β - » A -> B...

• B , Secoad-order, Irreversible

The transition probability b updated after each time step: Ρ^Β(0 * 1 - cxp(- k ^ t ) At)

1

1

kÂB® = d * PABC" ) ) k A B ^ ) :

k

K

AB = e" c

(2)

The molecular weight differences between lignin and its model compounds also complicate the use of model compound kinetics in a predictive simulation. The mobility of a high-molecular weight polymer would be much less than that of smaller model substrates (14). As for catalyst decay, a simple model was used to probe transport issues. For a first order, irreversible reaction in an isothermal, spherical catalyst pellet with equimolar counterdiffusion, the catalyst effectiveness factor and Thiele modulus provide the relevant information as

1 3»coth3»-l Φ 3φ

φ=ϊ(^)

-=

0.03

υ

0.02

3

Product Yields

— Guaiacols — - Catechols — - Phenols — · Hydrocarbons — Anisoles

0.01

0 00 20

40

60

80

100

120

Time (minutes)

Figure 9. Predicted Tar Fraction Product Yields of Kraft Lignin Pyrolysis at 380°C. a. Oligomers'Totals. b. Monomers' Totals

256

PYROLYSIS OILS FROM BIOMASS

0.30

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch022

0.25

— Monomer Yield - Dimer Yield - Trimer Yield

0.15

υ

0.10

"D

0.05

0.00

10

15

20

25

30

Time (minutes)

Figure 10. Predicted Tar Fraction Product Yields of Kraft Lignin Liquefaction at 380°C. a. Oligomers'Totals. b. Monomers'Totals.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch022

22. TRAIN & KLEIN

Chemical Modeling of Lignin

Fi gure 11. Influence of Catalyst Decay and Effectiveness on Monomers' Yield.

257

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch022

258

PYROLYSIS OILS FROM BIOMASS

The effects of polymer diffusion and catalyst deactivation were also considered separately. The remaining curves of Figure 11 illustrate. The diffusional limitation was largest initially, where polymer molecular weight was high, and single-ring products evolved at lower rates initially than in the limiting case of no internal transport limitations. Moreover, inspection of the monomer yield after 30 min showed that transport had little effect on the ultimate evolution of single-ring products. Finally, the remaining curve in Figure 11 illustrates that the effect of catalyst deactivation was largest at longer reaction times, and lower ultimate yields of single-ring products were achieved. Summary of Kraft Lignin Simulations. The foregoing simulations reveal the dramatic influence of the catalyst on the yields of single-ring products; the residue yield correspondingly decreased by roughly 50% when a catalyst was added. The identities of the major products in the single-ring product fraction were also affected. Whereas products with two oxygen-containing substituents (guaiacols and catechols) accounted for nearly 50% of the monomelic products evolved from pyrolysis, they accounted for only 5% of the products resulting from catalytic liquefaction. This was attended by an increase in the yields of phenols and hydrocarbons upon addition of the catalyst. Milled-Wood Lignin. Simulation of the thermal and catalytic liquefaction of milled-wood lignin was at 380°C and, for catalysis, 2250 psig H and a loading of CoMo/Y-Al 0 of 2.47 gn Jg Pyrolysis. The temporal variation of the yields of predicted products are illustrated in Figure 12. The total yield of single-ring products rapidly reached 0.43 by 10 min, after which time their reaction to char caused their yields to decrease to 0.32 by 120 min. The yields of two-and three-ring products reached 0.13 and 0.05, respectively, by 10 min, and thereafter decreased to 0.07 and 0.03 by 120 min. Within the single-ring product fraction, the guaiacols' yield shown in Figure 12b reached 0.33 by about 10 min. Their secondary decomposition to catechols, phenols and char led to a rapid decrease in their yield to a value of 0.07 by 120 min. The yields of catechols and phenols reached about 0.08 and 0.16, respectively, by about 120 min. The catechols underwent secondary decomposition to phenols and char; neither hydrocarbons nor anisoles formed. Thus, the tar fraction was composed primarily of compounds with two oxygencontaining substituents. Methane and CO were the only light products since phenolic hydroxyls were thermally stable. The yield of the former reached 0.010, whereas the maximum CO yield was 0.0064. After rapid decreasing to 0.43, as the reactive other linkages cleaved, the residue yield increased to 0.6 by 120 min while the single-ring product yield decreased. This was a result of the secondary reactions of the guaiacyl- and dihydroxyl-containing compounds to char. Catalytic Liquefaction. Results of the simulated catalytic liquefaction of milled-wood lignin are illustrated in Figure 13. The total yield of single-ring products in Figure 13a increased with time to 0.57 after 30 min. Dimer and trimer yields attained maxima of 0.13 and 0.05, respectively, at 2 min, after which time they decreased to 0.08 and 0.01 by 30 min. The variations with time of the yields of the single-ring products are illustrated in Figure 13b. Yields of guaiacols reached 0.13 by 2 min, and decreased to trace levels by 30 min. The formation of catechols was not as rapid, as product yields reached 0.12 after 4 min. The yield of catechol decreased to zero through secondary reactions to phenols. Their yield rose to 0.43 by 15 min, 2

3

gn

caV

Chemical Modeling of Lignin

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch022

22. TRAIN & KLEIN

Figure 12. Predicted Tar Fraction Product Yields of Milled-Wood Lignin Pyrolysis at 380°C. a. Oligomers'Totals. b. Monomers' Totals.

259

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch022

260

PYROLYSIS OILS FROM BIOMASS

10

15

20

25

30

Time (minutes)

10

15

20

30

Time (minutes)

Figure 13. Predicted Tar Fraction Product Yields of Milled-Wood Lignin Liquefaction at 380°C. a. Oligomers'Totals. b. Monomers' Totals.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch022

22. TRAIN & KLEIN

Chemical Modeling ofLignin

261

and their secondary decomposition was to hydrocarbons, which accounted for C.16 of the tar fraction at 30 min. The light products were methane, CO, and H2O. Both methane and carbon monoxide were primary products, and their respective yields reached 0.007 and 0.011 by 15 min. A secondary product, water, attained yields of 0.015 by 30 min. The yield of water was high because HDO reactions of catechols were facile over the catalyst. The residue fraction decreased to 0.35 by 5 min. The effects of catalyst decay and transport were qualitatively similar to those discussed for the simulation of kraft lignin. Intrinsic kinetics resulted in the highest yields of monomelic products, and the presence of both deactivation and internal transport limitations resulted in the lowest. In summary, the addition of the catalyst increased the yield of the singlering product fraction. The sum of the yields of single-ring products formed from thermolysis reached a maximum value of 0.43 before decreasing to 0.36 by 120 min. In the catalytic simulation, secondary reactions to stable single-ring products were competitive with reactions forming char. This is because HDO of phenolics with two oxygen-containing substitutents, which, thermally, char readily, was facile over the catalyst. Thus the yield of single-ring products resulting from the simulation of catalytic liquefaction increased rapidly to 0.53, and thereafter rose gradually to 0.61 after 120 min.

Simimary A stochastic formalism for using the experimental results of model systems in the analysis of the reaction of complex macromolecular substrates has been developed. The approach is flexible and renders lignin structure and its implications explicit; the Monte Carlo model can easily accommodate a variety of molecular weight distributions, lignin types and processing strategies. In addition, the effects of catalyst deactivation and transport limitations in catalyst pores were modelled easily by coupling a diffusion model to species' molecular weights. Evaluation of the approach is forthcoming in a detailed comparison of predictions vs. pyrolysis and catalytic liquefaction experiments with actual lignins. Acknowledgments

This work was supported by the NSF (Grant No. CPE 840 4452). We are grateful for useful discussions with Dr. John B. McDermott. Notation kAB η

pseudo first-order rate constant, s-1 effectiveness factor

0

catalyst activity function

ω

0

catalyst loading, g^lcrt?

kç

catalytic rate constant, cm~7gs

k

thermal rate constant, s~*

t

c

φ

Thiele Modulus

r

pellet radius, cm

p

262

PYROLYSIS OILS FROM BIOMASS -3

Pc D Ρ

e

catalyst density, g/car effective diffusivity, cm^/s probability

DP

degree of polymerization

Δι α

time interval deactivation rate constant, gc/mol 0 unrecovered

C

mol oxygen unrecovered per unit mass of catalyst, mol 0/g

c

c

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch022

Literature Cited [1] Boudart, Michel. Kinetics of Chemical Processes; Prentice-Hall, Englewood Cliffs, NJ, 1968. [2] Spry,J.C.and Sawyer, W.H., Paper presented at 68th Annual A.I.Ch.E. Meeting; Los Angeles, CA (November 1975) [3] Klein, M.T. and Virk, P.S. MIT Press Energy Lab Series, 1981.5. [4] Petrocelli, F.P. and Klein, M.T. Chem. Eng. Commun., 30(6), 343, 1984. [4b] Petrocelli, F.P. and Klein, M.T. Fuel Science and Technology International 5(3), 291-327, 1987. [5] Squire, K.R., Solomon, P.R., Di Taranton, M.B., and Caragelo, R.M. ACS Division of Fuel Chemistry Preprints 30(1):386, 1985. [6] McDermott,J.B.,Libanati,C.,LaMarca,C.,and Klein, M.T. A Stochastic Model of Depolymerization Kinetics 1. Development Approach. (in press) [7] Pellinen,J.and Salkinoja-Salonen, M. J. Chromotagr. 328:299, 1985. [8] Soundararajan,T N. and Wayman, M. J. PolymerSci.,Part C 30(1):386, 1985. [9] Marton,J.Lignins: Occurrence. Formation. Structure and Reactions. Wiley, New York, 1971. [10] Freudenberg, K. Science 148:595, 1965. [11] Froment, G.F. and Bischoff, K.B. Chemical Reactor Analysis and Design. Wiley, New York, 1979 [12] Vogelzang, M.W., Li, C-L., Schuit, G.C.A., Gates, B.C. and Petrakis, L. Journal of Catalysis 84:170,1983 [13] Train, P.M. Stochastic and Chemical Modelling of Lignin Liquefaction. Ph.D. Thesis, University of Delaware, 1987. [14] Baltus, R.E. and Anderson,J.L.Chem. Eng. Sci., 38(12), 1959-1969, 1983. [15] Rouse, P.E. Journal of Chemical Physics 21(7):1272, 1953. [16] de Gennes, P.-G. Journal of Chemical Physics 55(2), 1971. [17] Sherwood, T.K., Pigford, R.L. and Wilke, C.R. Mass Transfer. McGraw-Hill, New York, 1975. [18] McDermott,J.B.,Klein, M.T. and Obst,J.R.Ind. Eng. Chem. Process Des. Dev., 25(4), 1986. [19] Klein, M.T. Model Pathways in Lignin Thermolysis.. Ph.D. Thesis, Massachusetts Institute of Technology, 1981. [20] Jegers, H.E. Thermolysis of Lignin.. Masters thesis, University of Delaware, 1982. [21] Petrocelli, F.P. and Klein, M.T. Macromolecules 17:161, 1984. [22] Klein, M.T. and Virk, P.S. Ind. Eng. Chem. Fundam. 22:35, 1983.

22. TRAIN & KLEIN

Chemical Modeling of Lignin

263

[23] McDermott, J.B. Chemical and Stochastic Modelling of Complex Reactions: A Lignin Depolymerization Example. Ph.D. Thesis. University of Delaware. 1986 [24] Petrocelli, F.P. Chemical Modelling of the Thermal and Catalytic Depolymerization of Lignin. Ph.D. Thesis, University of Delaware, 1985. [25] Hurff, S.J. and Klein, M.T. Ind. Eng. Chem. Fundam. 22:426, 1983.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch022

Received April 14, 1988

Chapter 23

Biomass to Gasoline Upgrading Pyrolysis Vapors to Aromatic Gasoline with Zeolite Catalysis at Atmospheric Pressure

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch023

James Diebold and John Scahill Chemical Conversion Research Branch, Solar Energy Research Institute, 1617 Cole Boulevard, Golden,CO80401 The primary pyrolysis vapors generated by the fast pyrolysis of biomass at atmospheric pressures consist initially of low-molecular-weight compounds, but which polymerize upon condensation. Prior to condensation, these primary vapors have been found to be very reactive with ZSM-5 catalyst to produce methyl benzenes boiling in the gasoline range. This gasoline is predicted to have very high blending octane numbers. By-products are coke, carbon oxides, water, naphthalenes, ethylene, propylene, and some phenols. The effect of different by-products on the theoretical gasoline yield is examined. Preliminary results, generated with a reactor having a fixed bed of 100 g of catalyst, are examined for the continuous feeding of never-condensed primary vapors and compared to feeding methanol in the same reactor. The conversion of primary pyrolysis vapors made from biomass is a relatively new research and development area which is showing early promise. The extent to which the product slate can be manipulated by process variables will impact heavily on the viability of this process. The conversion of biomass materials to high octane gasoline has been actively pursued for many years. H i s t o r i c a l l y , methanol was made in very low yields by the destructive d i s t i l l a t i o n of hardwoods. More recently, the manufacture of methanol has been by the reaction of synthesis gas over catalysts at high pressures. In theory, any carbon source can be used for this c a t a l y t i c generation of methanol, but in p r a c t i c e , biomass has not been advantageous relative to coal or natural gas. Other approaches to making l i q u i d fuel from biomass have involved the fermentation of biomass to ethanol in a rather slow process. The conversion of biomass to alcohols is technically f e a s i b l e , but the u t i l i z a t i o n of the alcohols as transportation fuels w i l l require modifications to the 0097-6156/88/0376-0264$06.00/0 ° 1988 American Chemical Society

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch023

23.

DIEBOLD & SCAHILL

Biomass to Gasoline

265

d i s t r i b u t i o n systems and to the individual automobiles. The highpressure liquefaction of biomass to oxygenated liquids followed by high-pressure c a t a l y t i c h y d r o g é n a t i o n to form hydrocarbons is one approach to convert biomass to liquid f u e l s . {I) However, in the last decade, Mobil has developed the use of a zeolite catalyst for the conversion of methanol to gasoline at atmospheric pressures. (2_) This process has recently been commercialized and is now in operation in New Zealand. (_3) The zeolite catalyst used in the Mobil process is a medium pore z e o l i t e , which has shape s e l e c t i v i t y to r e s t r i c t the products from methanol to methylated benzenes, i s o p a r a f f i n s , and o l e f i n s , while preventing the formation of coke in the catalyst pores. (4) This catalyst is known as ZSM-5, and its commercial use is controlled by Mobil. The reactivity of high-molecular-weight vegetable o i l s with ZSM-5 was reported in 1979 (5) and, in f a c t , ZSM-5 catalyst is very reactive toward most small oxygenated species to convert them to methylated benzenes and other products. (6-7) Although alcohols appear to be some of the best feedstocks for ZSM-5 catalysis due to t h e i r low coking tendencies, the petroleum industry has long made use of zeolite catalysts for the cracking of very heavy hydrocarbons to produce gasoline and about 5 to 15 weight percent coke. This suggests that the formation of coke and the need for frequent catalyst regeneration w i l l heavily impact the reactor design, but that s i g n i f i c a n t coke formation can be part of a viable commercial process. The thrusts of our early efforts were to briefly examine the effect of possible stoichiometries and to generate preliminary experimental results from passing primary pyrolysis vapors, made by the fast pyrolysis of sawdust at atmospheric pressure in a vortex reactor, over a fixed bed of ZSM-5 catalyst. The production of these oxygenated vapors is addressed in another chapter of this book. Stoichiometry

Considerations

Although the hydrocarbon products have an unusual feedstock independence, the chemistry involved with different feedstocks over the ZSM-5 catalyst varies considerably with the functionality of the oxygen in the feedstock. As seen in Table I, hydroxy! and methoxy groups tend to reject oxygen in the form of water; aryl ethers reject a nearly equal amount of oxygen in water and carbon monoxide; carbonyl and formate groups reject oxygen largely as carbon monoxide, and carboxyl groups reject oxygen mostly as carbon dioxide and water. With the model compounds l i s t e d in Table I, many of these trends may also be a function of reaction conditions as well as reactants. A model compound study coupled with a process variable study is in progress at SERI with the f r e e - j e t , molecular beam/mass spectrometer (FJMBMS) (see chapter in this book by Evans and Milne). The method of oxygen rejection which occurs over the catalyst has a very important impact on the potential y i e l d of hydrocarbons, especially for a feedstock like biomass which has a r e l a t i v e l y low hydrogen content. Although the products formed from a few compounds reacted with ZSM-5 are known for certain conditions, methods to manipulate the by-product slate are essentially unreported.

266

PYROLYSIS OILS FROM BIOMASS

TABLE I.

Reported Distribution of Oxygen in Inorganic By-Products with Various Feedstocks over ZSM-5 Catalyst

% of Oxygen in By-Products

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch023

Compound methanol dimethyl ether guaiacol glycerol xylenol eugenol anisole 2,4 dimethyl phenol o-cresol starch isoeugenol glucose dimethoxymethane xylose sucrose η - b u t y l formate diphenyl ether furfural methyl acetate acetic acid

Oxygen Radical in Reactant* H, Ε, Η, Η Η Η, Μ Η

M M M

Μ

Η Η, Ε Η, Μ C l , Η, Ε Μ, Ε Cl, Η, Ε Η, Ε C2 Ε Cl, Ε C2 C2

H0

CO C0

100 100 96 92 93 89 88 87

__

3 7.5 6 9 12 12

80 78 77 75 73 60 56 54 46 14-22 54 50

17 20 19 20 6 35 36 46 46 75-84 10 4

2

2

—

Ref.

1 0.5 1 2 tr 1

(8) (8) (10) (9) (10) (10) (10) (10)

3 2 4 5 21 5 8 0 8 2.5-3. 0 36 46

(10) (7) (10) (7) (8) (7) (7) (8) (10) (9,7) (H) (H)

—

*H = hydroxy; M = methoxy; Ε = C-0-C; Cl = carbonyl; C2 = carboxy

23.

DIEBOLD & SCAHILL

Biomass to Gasoline

267

However, the d e s i r a b i l i t y to reject oxygen as carbon oxides becomes quite obvious by examining potential product slates which are possible from the stoichiometry of the reacting primary pyrolysis vapors, CH °o.49* hydrocarbon yields would be attained with oxygen* rejection as carbon dioxide, with the excess hydrogen used to reject oxygen as water. If the liquid hydrocarbon product corresponds to xylene, C Q H , rather than to more hydrogen-rich hydrocarbons such as o l e f i n s , C H2p, then the potential hydrocarbon y i e l d w i l l be higher from a hydrogen-poor feedstock l i k e wood pyrolysis vapors. If carbon monoxide is the assumed carbon oxide, more carbon is needed to reject the oxygen, which decreases the potential hydrocarbon y i e l d s . If the by-product gases are a mixture of carbon oxides, methane, o l e f i n s , e t c . , then the gasoline yields would be lowered due to the noncondensible hydrocarbons in the gases. If the olefins in the by-product gases were recycled through the catalyst bed to extinction, the gasoline yields should increase not only due to the conversion of the olefins to aromatics, but also due to the release of hydrogen in the aromatization process which could help counter coke forming (dehydrogenation) reactions. Coke formation is t y p i c a l l y an aromatization reaction to produce polycyclic aromatic hydrocarbons containing residual hydrogen, so a reasonable coking reaction to assume is one which produces water and coke but no gasoline at all. In summary, the more desired reactions produce carbon oxides and water as by-products. Undesired reactions produce noncondensible hydrocarbons and/or coke and water.(12) 1#2

T

h

e

b

e

s

t

1 0

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch023

n

Experimental The primary pyrolysis vapors, used as feedstock, were produced by fast pyrolysis in a vortex reactor from coarse softwood sawdust, as discussed in another chapter of this book. After the vapors l e f t the vortex reactor system, they were allowed to cool to the desired c a t a l y t i c reaction temperature, as they passed through a tubular transfer line to the c a t a l y t i c reactor. The transfer line was located inside of a series of six tubular furnaces, which allowed the vapor stream to equilibrate to the desired temperature. The residence time of the vapor in the transfer line was about one-half second prior to reaching the 2.5-cm diameter c a t a l y t i c reactor, shown in cross-sectional view in Figure 1. The c a t a l y t i c reactor used with the pyrolysis vapors had a 30-cm-long fixed bed of 100 g of ZSM-5 containing catalyst (MCS6-2), which was located in the middle of the sixth furnace section. Only a small slipstream of the pyrolysis vapors passed through the c a t a l y t i c reactor. The catalyst was in the form of 1.4-mm diameter extrudate and supplied by Mobil Research and Development Corp. in a cooperative agreement with the Solar Energy Research Institute. Although the catalyst composition is proprietary to Mobil, the a b i l i t y of the catalyst to maintain good a c t i v i t y in the presence of high-temperature-steam environments implies a f a i r l y high s i l i c o n to aluminum ratio in the ZSM-5 crystal l a t t i c e . The temperature of the catalyst bed was measured with an axial thermocouple inside a 6-mm thermowell. The temperature p r o f i l e of the bed was determined by moving the axial thermocouple within the thermowell. A sintered stainless steel

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268

PYROLYSIS OILS FROM BIOMASS

f i l t e r rated at 5 micrometers was used to remove char fines from the pyrolysis vapors. The products were collected in water-cooled condensers. The pressure in the reactor was s l i g h t l y above the local atmospheric pressure at about 95 kPa. Analysis of the organic condensates was with a 5-micrometer, wide bore c a p i l l a r y column having a length of 60 m. The c a p i l l a r y column was coated with one micrometer of cross-linked methyl silicones. With helium as the carrier gas, the temperature p r o f i l e started at 0°C for 4 minutes, followed by a temperature ramp of 8°C/min until a temperature of 260°C was reached. Detection of the eluted organics was by flame ionization detection (FID). Identification of the major peaks was by reference materials, whereas the minor peaks were i d e n t i f i e d by a combination of the FJMBMS at SERI and a Hewlett-Packard 5890 gas chromatograph/5970 Mass Selective Detector (GC/MSD) using a 1.5-m high-performance cross-linked methyl s i l i c o n e c a p i l l a r y column. The noncondensible gases were analyzed with a Carle GC designed for refinery gas analysis, which used thermal conductivity detection (TCD) and was calibrated with a gravimetrically prepared reference mixture. Electronic grade methanol (99.9% pure) was used for comparison to the softwood feedstock. Experimental

Runs

Methanol. To verify the a c t i v i t y of the catalyst and to gain experience in the operation of the catalyst system, methanol was metered into a preheater tube located inside of the transfer line heated to 500°C. This preheating proved to be too severe and the products which emerged from the c a t a l y t i c reactor were dominated by hydrogen and carbon monoxide in a 2:1 r a t i o , as shown in Table II. This would be expected from thermal decomposition of the methanol prior to reaching the c a t a l y s t . This experiment was repeated using a preheating temperature ramp to just reach 400°C at the entrance to the c a t a l y t i c reactor. The c a t a l y t i c reactor was held at a nominal 400°C prior to the addition of the methanol at a space velocity (WHSV) of 0.9 g methanol per gram of catalyst per hour. The noncondensible gas composition is shown in Table II and was rich in hydrogen, olefins (ethylene and propylene), and alkanes (methane, propane, and isobutane) The gaseous olefins could be used to alkylate the reactive isobutane to result in a highly branched-chain gasoline f r a c t i o n . (13) The l i q u i d product contained r e l a t i v e l y l i t t l e alkanes or olefins and was dominated by methylated benzenes, such as toluene, xylenes, and trimethyl benzenes. Relatively very small amounts of naphthalenes were seen. The temperature p r o f i l e of the c a t a l y t i c reactor immediately prior to and also during this experiment is shown in Figure 2. The location of the temperature-profile maximum was quite stable, which indicates that the catalyst was not s i g n i f i c a n t l y deactivated during the short time of the experiment. This low rate of catalyst deactivation is consistent with published data. (14) The ratio of gasoline to water in the condensates suggests that the gasoline y i e l d was only about one-third of the potential due to the f o r mation of the noncondensible hydrocarbons. This product slate is

23.

DIEBOLD & SCAHILL

TABLE II

269

Biomass to Gasoline

Calculated Molar Compositions of Net Product Gases Produced During Cracking of Primary Pyrolysis Vapors or Methanol (ZSM-5 containing catalyst - Mobil's MCSG2)

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch023

Softwood Pyrolysis Vapor Feed

Thermal Catalytic Thermal Catalytic (Run 55) (Run 76-C) (Run 88-C) (Run 74-C)* (Run 75-C) (650°C) (500°C) (400°C) (485°C) (400°C)

2

CO

10.6

-0.6

0.7

62.8

18.4

59.4

69.8

62.4

31.1

4.4

15.2

14.0

co

2

5.6

CH

4

12.2

2 4 C H C

H

2

C

6

3 8 H

4 8 iso-C H

C

H

4

n-C H 4

C

5

4

C H

Reactor

H

Methanol (CH 0)

( 1.2°0.49)

1 0

1 0

Empirical Formula

C H

16.2

2.2

2.1

0.5

—

—

—

—

5.3

5.0

8.2

1.6

5.3

1.1

0.3

0.3

0.3

4.1

1.9

6.0

6.7

0.7

—

0.5

0.2

0.4

1.1

1.2

1.2

—

—

0.2

0.1

0.1

—

—

—

—

2.4

+

2.8

1.4

1.4

1.3°0.65

5.3 17.8 2.3 14.4 5.3 3.6

3.9

C H

0.65°0.82

C H

0.87°0.61

C H

3.6°0.8

*In this run, the methanol is thought to have thermally for the most part prior to reaching the c a t a l y s t .

C H

2.7°0.05

decomposed

270

PYROLYSIS OILS FROM BIOMASS

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch023

2 Inch Vapo

Figure 1.

Cross-sectional view of c a t a l y t i c reactor

4

6

RERCTOR LENGTH

Figure 2.

12

8

( inches >

Temperature p r o f i l e of reactor with methanol feed (lower curve prior to feeding)

23.

DIEBOLD & SCAHILL

in general agreement with data reported action conditions. (15)

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch023

271

Biomass to Gasoline by Mobil

for

similar

re-

Primary Pyrolysis Vapors. After a catalyst regeneration cycle to remove residue from the methanol experiments, a slipstream of the primary pyrolysis vapors was passed over the ZSM-5 c a t a l y s t . Steam was used as the carrier gas at a weight ratio of two parts of steam to one part of wood feed. The pyrolysis vapors were cooled from 510°C at the exit of the vortex reactor to 400°C at the entrance of the c a t a l y t i c reactor. Figure 3 shows the temperature p r o f i l e immediately prior to feeding the biomass, as well as 5-10 minutes later. The temperature p r o f i l e with pyrolysis vapors as feed was not as large in magnitude as that seen with methanol and i t had a very broad maximum. The heat of reaction of the pyrolysis vapors is less exothermic than for methanol and the steam c a r r i e r gas also has a moderating effect on the temperature r i s e . The broadness of the temperature p r o f i l e r e f l e c t s that the pyrolysis vapors are a complex mixture of compounds, which are probably reacting at d i f ferent rates. The broader and lower temperature p r o f i l e would make temperature control easier in a biomass-to-gasoline (BTG) reactor than in a methanol-to-gasoline (MTG) reactor. The location of the temperature maximum was monitored during the run, as shown in Figure 4. During the f a i r l y short experiment, the temperature maximum was observed to move to the end of the reactor, indicating that a f a i r l y rapid deactivation of the catalyst had occurred. During this time, the composition of the hydrocarbon products appeared to be r e l a t i v e l y constant. The gasoline fraction (eluting before naphthalene) made from wood is very similar by GC to that made from methanol, except for the presence of some phenolics in the former. The composition of the gas formed over the catalyst from the pyrolysis vapors is shown in Table II, as calculated from tracer gas concentrations before and after the reactor, along with the gas composition formed by the thermal decomposition of the pyrolysis vapors as determined previously (16); the c a t a l y t i c a l l y formed gases had s i g n i f i c a n t l y less hydrogen and methane, but more carbon dioxide and propylene than the thermally formed gases. In comparing the composition of the gases formed by the c a t a l y t i c conversion of the pyrolysis vapors to the c a t a l y t i c conversion of the methanol, the relative hydrogen richness of the methanol becomes apparent in the r e l a t i v e l y high hydrogen, methane, propane, and isobutane y i e l d s . This r e l a t i v e hydrogen richness is summarized by the empirical formulas for the two gas streams, in which the hydrogen-to-carbon ratio for the wood-derived gases is one-fourth that for the methanol-derived gases. This excessive amount of hydrogen in the methanol-derived gases suggests that methanol could be used as a hydrogen donor to hydrogen-poor feedstocks and this has been explored by several researchers. (7,9-11) The very low y i e l d of isobutane from pyrolysis vapors would preclude the use of alkylation to incorporate the ethylene, propylene, and b u t è n e s into the gasoline product with a stand-alone process. Adsorption of the gaseous o l e f i n s from the by-product gases onto cold ZSM-5 or activated carbon at low pressures may be a viable method to recycle them into the c a t a l y t i c reactor. Since gaseous olefins are known to be intermediate

272

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PYROLYSIS OILS FROM BIOMASS

TIME

(minutes)

Figure 4. Location of temperature maximum with vapors feed

pyrolysis

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch023

23.

DIEBOLD & SCAHILL

Biomass to Gasoline

273

compounds in the methanol-to-gasoline process, recycling olefins would be expected to have a beneficial impact similar to cofeeding methanol with wood pyrolysis vapors. A six-element i n - l i n e s t a t i c mixer was i n s t a l l e d at the entrance to the vapor cracker (transfer line) to ensure the complete mixing of the pyrolysis vapors, the tracer gas, and the c a r r i e r steam prior to reaching the slipstream c a t a l y t i c reactor. Experimentation verified the elimination of diametrical gradients of tracer-gas concentration downstream of the s t a t i c mixer. In Run 88-C, the steam-to-biomass mass ratio was 1.2 and the softwood sawdust feed rate was 18.5 kg/hr (41 lb/hr). The temperature of the pyrolysis product stream was 475°C at the exit of the vortex reactor. Nitrogen was used as a tracer gas at a flow rate of 0.224 kg/hr to result in a concentration of 10.1 wt % in the permanent pyrolysis gases and 3.6% in the permanent catalyst off-gases. Based on the nitrogen content and the flow measured with a gravimetrically calibrated o r i f i c e meter, the slipstream fed into the c a t a l y t i c reactor was 1.4 wt % of the main stream. The weight hourly space velocity (WHSV) was 2.44 g dry biomass/g catalyst (MCSG-2) hr. By GC analysis, the gasoline hydrocarbon fraction of the organic condensate was about 75% and the naphthalenic/phenolic fraction was 25%. The gasoline fraction was q u a l i t a t i v e l y similar to that made previously and was heavily dominated by toluene, xylenes, and trimethyl benzenes. The olefins and C c + hydrocarbons in the catalyst off-gases were 4 and 2.4 wt % of the dry feed respectively. The total l i q u i d hydrocarbon y i e l d was 10.1 wt % which is equivalent to 28 gal/ton of dry feed, assuming the density of xylene. Assuming that the olefins can be recycled and converted to gasoline, the potential y i e l d shown is 39 gal/ton. If the phenolics were reacted with methanol to form the methyl aryl ethers, the potential l i q u i d fuel yields would then be increased to about 16% (16 wt % y i e l d of the gasoline is one barrel per ton of dry wood). The gasoline boiling fraction of this fuel is projected to be about 85%; the other 15% is composed almost e n t i r e l y of methylated naphthalenes which could be hydrocracked in a typical refinery to a gasoline f r a c t i o n . The y i e l d of methyl naphthalenes has been shown by the MBMS experiments (see chapter by Evans and Milne in this book) to be sensitive to the operating conditions in the zeolite reactor and i t is expected that i t can be reduced in the future. The composition of the permanent gases formed over the catalyst was calculated by subtracting the pyrolysis gas yields from the total gas y i e l d s , as shown in Table II. These catalyst formed gases from Run 88 are similar to those previously shown in that the hydrogen y i e l d was essentially zero and the y i e l d of methane and other paraffins was very low compared to ethylene, propylene, and b u t è n e s . It is interesting to note that the amount of carbon dioxide and carbon monoxide calculated to have been formed by the catalyst in Run 88 corresponds to a potential y i e l d of 16% gasoline (xylene) by the stoichiometry of global equations (12), which is in good agreement with the sum of the olefins and organic condensates produced. The overall yields from Run 88 are shown in Table III.

PYROLYSIS OILS FROM BIOMASS

274 TABLE III.

Wt % Dry Feed

Product

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch023

Run 88 Yields Method of Determination

Pyrolysis Char Gases

12 11

Gravimetric Tracer gas/GC/ gravimetric

Catalysis Coke Fuel gases

8 16

Gravimetric Tracer gas/GC/orifice meter Tracer gas/GC/orifice meter

Gaseous o l e f i n s Gasoline Phenolics/ napthalenics Water

(Total)

4 10 2 37 100

Gravimetric/GC Gravimetric/GC Difference

Conclusions Pyrolysis vapors made by the fast pyrolysis of softwood are very reactive with ZSM-5 catalyst to form a liquid hydrocarbon product, which is similar to that formed from methanol. Although the catalyst is deactivated r e l a t i v e l y quickly with pyrolysis vapors compared to methanol, experimentation indicates that the catalyst can be repeatedly regenerated by oxidation. This suggests that a c a t a l y t i c reactor, which can maintain a high level of c a t a l y t i c a c t i v i t y in spite of high coking rates, would be desired. This problem has been addressed and resolved by the petroleum refining industry which u t i l i z e s an entrained-bed reactor ( r i s e r - c r a c k e r ) , to crack heavy hydrocarbons to gasoline and about 5% to 15% coke, coupled with a fluidized-bed oxidative regenerator for the r e l a t i v e l y slow, controlled oxidative coke combustion and catalyst regeneration. (17) For the conversion of biomass to gasoline, these preliminary data are quite encouraging that a nearly direct conversion of biomass to gasoline can be accomplished at atmospheric pressures in one very rapid thermal cycle without the cost of producing hydrogen and operating at high pressures. With the calculated thermal e f f i c i e n c i e s , i t appears that there w i l l be s u f f i c i e n t energy in the by-products to operate the process, even including the drying of a rather wet biomass feedstock prior to pyrolysis. The gasoline product is almost entirely alkylated benzenes with only a small amount of benzene. This gasoline would be expected to have octane ratings in excess of 100 and to have blending octane numbers between 115 and 135 based on reported

23. DIEBOLD & SCAHILL

Biomass to Gasoline

275

blending octane values for the various alkylated benzenes. (18) Due to the expected continued demand for unleaded gasoline having higher octane numbers, the gasoline made from biomass by this process would be expected to command premium prices i f sold to a petroleum refinery for blending purposes. The naphthalenic fraction of the organic products could easily be hydrocracked to increase the gasoline yields in a modern refinery. (19) At this time, the phenolic by-products appear to be present in minor amounts and could be reacted with methanol to form methyl aryl ethers which are proven octane enhancers. (20) Ongoing research is being directed toward o l e f i n recycling and the improvement of product d i s t r i b u t i o n and y i e l d s .

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch023

Acknowledgments The financial support of the Biofuels and Municipal Waste Technol­ ogy Division of the Department of Energy, FTP 619, with Mr. Simon Friedrich as DOE Program Manager and the technical direction of the Program Monitor, Dr. Don J. Stevens, of PNL, are gratefully ac­ knowledged. Dr. M. Maholland of the Colorado School of Mines and Drs. T. A. Milne and R. J. Evans contributed product i d e n t i f i c a t i o n of many of the hydrocarbon products.

Literature Cited 1. 2. 3. 4. 5. 6.

7. 8. 9. 10. 11. 12.

Baker, E. G.; Elliott, D. C. Preprints of 193rd ACS Meeting, Div. Fuel Chemistry, Denver, CO, April 5-10, 1987, Vol. 32, No. 2, pp. 257-263. Meisel, S. L.; McCullough, J. P.; Lechthaler, C. H.; Weiz, P. B. 1976. CHEMTECH February, 86-89. Anon. Chem. Eng., March 3, 1986, p. 10. Dejaive, P.; Auroux, Α.; Gravelle, P. C.; Vedrine, J. C.; Gabelica, Z.; Derouane, E. G. J. Cat. 1981, 70, 123-136. Weisz, P. B.; Haag,W.O.;Rodewald, P. G. Science 1979, 206, 5 October, 57-58. Diebold, J. P.; Chum, H. L.; Evans, R. J.: Milne, Τ. Α.; Reed, T. B.; Scahill, J. W. In Energy from Biomass and Wastes X, 1987, Klass, D., ed; Elsevier Applied Science Publishers: London, p. 801. Chen, N. Y.; Degnan, T. F. Jr.; Koenig, L. R.; CHEMTECH 1986, August, 506-511. Chang, C. D.; Silvestri, A. J.; J. Cat. 1977, 47, 249-259. Hanniff, M. I.; Dao, L. H.; Energy from Biomass and Wastes X 1987, Klass, D., ed; Elsevier Applied Science Publishers: London, p. 831-843. Chantal, P. D.; Kaliaguine, S.; Grandmaison, J. L. Appl. Cat. 1985, 18, 133-145. Chang, C. D.; Chen, Ν. Y,; Koenig, L. R.; Walsh, D. E. Pre­ prints of 185th ACS Meeting, Div. of Fuel Chem. 1983, Seattle, WA, March 20-25, 146-152. Diebold, J. D.; Scahill, J. W. Annual AICHE Meeting, Houston, TX., March 29-April 2, 1987, Paper 39a. (to appear in Energy Progress).

276 13.

14. 15. 16. 17.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch023

18. 19. 20.

PYROLYSIS OILS FROM BIOMASS Kam, A. Y.; Lee, W. Fluid Bed Process Studies on Selective Conversion of Methanol to High-Octane Gasoline, Mobil Research and Development Corp. 1978, U.S. DOE Contract No. EX-76-C-012490 FE-2490-15. Chang, C. D. Hydrocarbons from Methanol, Marcel Dekker, NY, 1983. Yurchak, S.; Voltz, S. E.; Warner, J. P. Ind. Eng. Chem. Process. Des. Dev. 1979, 18(3), 527-534. Diebold, J. P. MS Thesis T-3007, Colorado School of Mines, Golden, CO 1985. Decroocq, D. Catalytic Cracking of Heavy Petroleum Fractions, Gulf Publishing Company 1984, Houston, TX. Lovell, W. G. Ind. Eng. Chem. 1948, 40(12), 2388-2438. Gary, J. H.; Handwerk, G. E. Petroleum Refining, Technology, and Economics, Marcel Dekker, NY, 1975, pp. 121-141. Singerman, G. M. Methyl Aryl Ethers from Coal Liquids as Gasoline Extenders and Octane Improvers. Gulf Research and Development Co., Pittsburgh, PA. 1980. DOE/CE/50022-1.

Received July 1, 1988

Chapter 24

Fluidized-Bed Upgrading of Wood Pyrolysis Liquids and Related Compounds

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch024

Ν. Y. Chen, D. E. Walsh, and L . R. Koenig Mobil Research and Development Corporation, Central Research Laboratory, P.O. Box 1025, Princeton, N J 08540

The effective hydrogen index (EHI) is a calculated indicator of the "net" hydrogen/ carbon ratio of a pure or mixed heteroatom­ -containing feed, after debiting the feed's hydrogen content for complete conversion of heteroatoms to NH , H S, and H O. Compounds with EHI's less than about 1 are difficult to upgrade to premium products over ZSM-5 catalyst due to rapid catalyst aging in continuous fixed bed processing. However, high conversions of such feeds (acetic acid, methyl acetate, and wood pyrolysis liquids) can be maintained in a fluidized bed system operating under methanol-to-gasoline conditions and employing frequent catalyst regenerations. Also, synergistic effects were observed for blends of low and high EHI model compounds, as well as for wood pyrolysis liquids coprocessed with methanol. Based on these results, a processing scheme is described in which the char from the wood pyrolysis step is gasified to make methanol which is cofed with the pyrolysis liquids over ZSM-5. 3

2

2

Z e o l i t e ZSM-5 i s p a r t i c u l a r l y e f f e c t i v e f o r the conversion of methanol t o g a s o l i n e range hydrocarbons (1). I n a d d i t i o n t o methanol, other oxygenates, i n c l u d i n g t h e i r complex mixtures, can be converted as w e l l (see, f o r example, r e f e r e n c e s 2-8). 0097-6156/88/0376-0277$06.00/0 ©1988 American Chemical Society

278

PYROLYSIS OILS FROM BIOMASS

The

e f f e c t i v e hydrogen index i s d e f i n e d as: H-20-3N-2S (H/C) ££ective or EHI e

C

where H, C, 0, N, and S are atoms per u n i t weight of sample of hydrogen, carbon, oxygen, n i t r o g e n and sulfur, respectively. Model oxygen c o n t a i n i n g compounds, or "oxygena t e s , having EHI's 91.0 (94.9) 90.4 (89.2)

(1.8) (15.8) (42.1) (10.8) (11.4)

1.3 95

1.1 5.2 48.8 5.2 9.9

0.0 0.2 55.8 1.4 19.0

3.7 31.4 28.4 20.2 3.8

6.2 17.6 21.5 13.9 6.0

2.1 9.4 45.3 9.6 7.9

23.3

10.6

32.1

24.9 (17.0)

28.7 (19.1)

42.3

14.4

38.1

32.8 (28.4)

38.6 (33.0)

0.3

1.9

2.7

(1.2). (10.6) (46.7) ( 7.7) (13.9)

4

0.8 ( i . i )

1.1 ( 0.8)

7.6 5.4 7.2 1.5 5.6 0.6 1.6 0.1 0.7 0.4 14.2 25.9 13.8 6.7 5.2 0.5 %5.5 0.4 0.5 0.3 0.1 0.4 0.1 0.3 0.0 ic ' 1.9 5.8 1.6 15.7 1.4 nC.' 24.9 "(37.5) 44.6 14.7 23.5 (34.0) 23.3 Total C 72.3 (58.1) 54.7 74.1 (59.8) 65.0 78.7 Cg+ (gasoline) 2.8 ( 4.4) 0.7 11.7 6.6 2.4 ( 6.2) Coke 1.4*** 1.3 1.3 H/C (effective)* * 1.7 of C + * Numbers shown i n parentheses are the calculated values which would be expected i f the mixture's behavior was the arithmetic average of i t s two components. ** Small amounts of oxygen were observed i n the Cg+ l i q u i d . The use of the effective hydrogen index corrects for this. *** Approximate numbers. 2

4

4

5

284

PYROLYSIS OILS FROM BIOMASS

On a weight b a s i s , a c e t i c a c i d y i e l d s only 40% as much hydrocarbon as methanol. The lower y i e l d i n ZSM-5 p r o c e s s i n g r e s u l t s p r i m a r i l y from a c e t i c a c i d ' s carbon l o s s due t o oxygen r e j e c t i o n through d e c a r b o x y l a t i o n t o

co .

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch024

2

Methylacetate has an EHI of 0.67 and thus, o r d i n a r i l y , would a l s o be considered d i f f i c u l t to process. I t s net hydrogen content, however, i s s u b s t a n t i a l l y higher than t h a t of a c e t i c a c i d . Because of i t s higher carbon content (48.6% C), and d e s p i t e d e c a r b o x y l a t i o n and coking r e a c t i o n s , the observed hydrocarbon y i e l d remains comparable t o t h a t of methanol. Moreover, hydrocarbon s e l e c t i v i t y f o r d i r e c t conversion t o C-+ g a s o l i n e i s higher than a c e t i c a c i d or methanol. Thus, the d i r e c t y i e l d of Cg+ g a s o l i n e i s 32.1% on charge vs 23.3% f o r methanol. From a hydrogen balance standpoint, both a c e t i c a c i d and methyl acetate r e j e c t l e s s HgO and more 0 0 than methanol, with r e s u l t a n t Cg+ l i q u i d s having e f f e c t i v e H/C's of approximately 1.3 vs 1.7 - 2 f o r methanol p r o c e s s i n g . χ

Mixtures of A c e t i c A c i d and Methanol. P r o c e s s i n g a 1.9/1 or a 3.8/1 molar mixture of CH^OH and a c e t i c a c i d provided o b s e r v a t i o n s s i m i l a r t o those already d i s c l o s e d by Chang e t a l (8), v i z , an enhancement i n Cg+ l i q u i d y i e l d a t the expense of C^- vs what might be expected i f the mixture behaved as the average of i t s two components, the c a l c u l a t e d values f o r which are shown i n parentheses i n Table I I . The s e l e c t i v i t i e s of the hydrocarbon products amplify the observed synergism with r e s p e c t t o Cg+ l i q u i d s . Furthermore, there i s an enhancement i n t o t a l hydrocarbon y i e l d vs l i n e a r combination expectations. As shown i n Table I I , the e f f e c t of i n c r e a s i n g mole percent methanol i n the MeOH/acetic a c i d charge i s an attendant decrease i n oxygen r e j e c t i o n as COg and an i n c r e a s e i n oxygen removal as HgO. Thus, more carbon remains a v a i l a b l e t o form hydrocarbon products, much of i t becoming Cg+ l i q u i d s . The above f i n d i n g s demonstrate t h a t a short contact time f l u i d bed r e a c t o r o p e r a t i n g i n a c y c l i c mode can be used t o process low EHI compounds to y i e l d s u b s t a n t i a l amounts of C + l i q u i d hydrocarbon products. K

CHENET AL.

Fluidized-Bed Upgrading of Wood Pyrolysis Liquids

285

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch024

By co-processing a low EHI m a t e r i a l with a high EHI compound such as methanol, a s h i f t i n oxygen r e j e c t i o n from d e c a r b o x y l a t i o n t o dehydration takes p l a c e . The s h i f t r e s u l t s i n an i n c r e a s e d y i e l d of hydrocarbons. The r e a c t i o n of a c e t i c a c i d may have p o t e n t i a l a p p l i c a t i o n i n c o n v e r t i n g fermentation products t o hydrocarbons. A c e t i c a c i d i s a major by-product i n b a c t e r i a l fermentation of biomass t o ethanol (13). Mixtures of a c e t i c a c i d and ethanol may a l s o be processed t o hydrocarbons (14). Upgrading of Wood P y r o l y s i s L i q u i d s . The products from sawdust p y r o l y s i s a t 520°C i n f l o w i n g helium a t atmospheric pressure produced the y i e l d s shown i n Table III. Table I I I .

e

Wood P y r o l y s i s a t 520 C and 1 atm.

Product CH CO C0 L i q u i d Oxygenates Char 4

2

Wt.% 1.4 7.1 8.5 55.0 28.0

Because the o b j e c t of these experiments was t o t r a c k the amount of wood carbon which could be converted t o hydrocarbons by pyrolysis/ZSM-5 upgrading schemes, the amount of water produced by p y r o l y s i s was not measured, and water i n the p y r o l y s i s l i q u i d s was f e d along with the oxygenated products i n subsequent ZSM-5 p r o c e s s i n g . Elemental analyses and the apparent EHI's ( i n c l u d i n g any water) are presented i n Table IV. I n s p e c t i o n of these data i n d i c a t e t h a t the l i q u i d products c o n t a i n about 31% o f the o r i g i n a l wood carbon. The char product accounts f o r another 49 wt% of the o r i g i n a l wood carbon, and i s a v a i l a b l e f o r i n d i r e c t l i q u e f a c t i o n v i a g a s i f i c a t i o n and methanol s y n t h e s i s . The remaining 20% of the wood carbon becomes CO, COg and methane, about h a l f of which (as C H and CO) i s a l s o p o t e n t i a l l y a v a i l a b l e f o r conversion t o methanol. When processed i n the presence of methanol, wood p y r o l y s i s l i q u i d s e x h i b i t e d synergisms and s e l e c t i v i t y s h i f t s s i m i l a r t o those d i s c u s s e d above f o r the model 4

286

PYROLYSIS OILS FROM BIOMASS

Table IV.

wt%

Aqueous L i q u i d Laver (51%}

Organic L i q u i d Laver (4%)

Char

25.9 8.8 65.3

55.0 7.5 37.5

87.3 3.9 8.0

Ash

49.2 6.8 43.4 0.6

-

-

EHI

0.3

0.3

0.6

Sawdust

c H

0

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch024

Elemental A n a l y s i s ,

-

compounds. The d e t a i l s of t h i s behavior are presented below w i t h i n the context of two p o t e n t i a l p r o c e s s i n g arrangements shown i n F i g u r e s 2 and 3. A major f e a t u r e common t o both i s the use of the p y r o l y s i s char as a cheap source of methanol. F i g u r e 2 shows the products obtained i n a scheme i n which d i r e c t upgrading of the wood p y r o l y s i s l i q u i d s over ZSM-5 occurs i n p a r a l l e l with upgrading of methanol obtained from s y n t h e s i s gas d e r i v e d from g a s i f i c a t i o n of the p y r o l y s i s char. In F i g u r e 3, the methanol i s mixed with the p y r o l y s i s l i q u i d s p r i o r to co-processing over ZSM-5. Approximately 40 l b s . of methanol per 100 l b s . of dry wood feed i s p o t e n t i a l l y a v a i l a b l e from the char and p y r o l y s i s gas products. T h i s amount would provide a weight r a t i o of methanol/pyrolysis l i q u i d s of 0.73. In the p a r a l l e l p r o c e s s i n g scheme, a t o t a l of 2 0 . 6 l b s . of hydrocarbon (approximately 85% Cg+ g a s o l i n e , i n c l u d i n g a l k y l a t e ) per 95 l b s . of t o t a l feed ( p y r o l y s i s l i q u i d and methanol) i s obtained. In the co-processing mode, approximately 3 l b s . of a d d i t i o n a l hydrocarbon r e s u l t concomitant with reduced oxygenates and coke. Stated d i f f e r e n t l y , without char g a s i f i c a t i o n , o n l y about 6% of the carbon i n the wood could be upgraded t o hydrocarbon products even i f a l l the oxygenates produced by p y r o l y s i s were r e c y c l e d to e x t i n c t i o n . P a r a l l e l upgrading of methanol d e r i v e d from char g a s i f i c a t i o n can i n c r e a s e t h i s value to approximately 36%, i . e . , about 6% from the p y r o l y s i s l i q u i d s and 30% from methanol. Methanol co-processing boosts the percent of wood carbon transformed i n t o

24.

CHEN ET AL.

Fluidized-Bed Upgrading of Wood Pyrolysis Liquids

17 LBS. GAS ( C O . C 0 . C H ) 2

100 LBS. DRY WOOD

4

28 L B S . CHAR

PYROLYSIS

GASIFICATION AND SHIFT

OXYGEN WATER

SYNTHESIS GAS

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch024

55 LBS. PYROLYSIS I LIQUIDS

METHANOL CONVERSION

40 LBS. METHANOL

ZSM-5 PROCESSING

ZSM-5 PROCESSING

7"

J

3.2 LBS. HYDROCARBON 17.6 LBS. OXYCENATES 26.4 LBS. WATER 4.2 L B S . C 0 3.6 LBS. C O K E

17.4 LBS. HYDROCARBON 22.6 LBS. WATER

2

Figure 2 .

P a r a l l e l Processing

Scheme

17 LBS. GAS (CO, C 0 , C H ) 2

100 LBS. DRY WOOD"

PYROLYSIS

4

28 LBS. CHAR

GASIFICATION AND SHIFT

OXYGEN WATER

SYNTHESIS GAS 55 LBS. PYROLYSIS LIQUIDS

METHANOL CONVERSION 40 LBS. METHANOL

ZSM-5 PROCESSING

23.6 LBS. HYDROCARBON 10.6 LBS. O X Y C E N A T E S 59.0 LBS. WATER 1.8 LBS. C O K E

Figure

3.

C o p r o c e s s i n g Scheme

287

288

PYROLYSIS OILS FROM BIOMASS

hydrocarbon products t o approximately 42%, i . e . , about 12% from the p y r o l y s i s l i q u i d s and 30% from methanol.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch024

Conclusions Hydrocarbon y i e l d s can be increased s i g n i f i c a n t l y when wood p y r o l y s i s l i q u i d s are coprocessed with methanol over ZSM-5 c a t a l y s t vs separate p r o c e s s i n g of the two streams over the same c a t a l y s t . Thus, coprocessing p y r o l y s i s l i q u i d s with methanol produced from char g a s i f i c a t i o n i s one means of producing hydrocarbon f u e l s from wood. R e s u l t s obtained i n t h i s study provide a b a s i s f o r comparison with other p r o c e s s i n g schemes such as wood g a s i f i c a t i o n followed by e i t h e r F i s c h e r - T r o p s c h s y n t h e s i s o r methanol s y n t h e s i s plus Mobil's MTG process. Literature

Cited

1. Chang, C. D. and Lang, W. H., U. S. Patent 3 894 103, 1975 . 2. Chang, C. D. and Silvestri, A. J., J. Catal. 1977, 47, 249. 3. Kuo, J. C., Prater, C. D. and Wise, J. J., U. S. Patent 4 041 094, 1977. 4. Ireland, H. R., Peters, A. W. and Stein, T. R., U.S. Patent 4 045 505, 1977. 5. Haag, W. O., Rodewald, P. G. and Weisz, P. B., U. S. Patent 4 300 009, 1981. 6. Brennan, J. Α., Caesar, P. D., Ciric, J. and Garwood, W. E., U. S. Patent 4 304 871, 1981. 7. Weisz, P. B., Haag, W. O. and Rodewald, P. G., Science, 1979, 206, 57. 8. Chang, C. D., Chen, Ν. Υ., Koenig, L. R. and Walsh, D. E., "Synergism in Acetic Acid/Methanol Reactions Over ZSM-5 Zeolites", Am. Chem. Soc. Div. Fuel Chem. Preprints, 1983, 28 (2) 146. 9. Chang, C. D., Lang, W. H. and Silvestri, A. J., U.S. Patent 3 998 898, 1976. 10. Chantal, P., Kaliaguine, S., Grandmaison, J. L. and Mahay, Α., Appl. Catal., 1984, 10, 317. 11. Walsh, D. E., U. S. Patent 4 419 328, 1983. 12. Lee, W., Maziuk, J., Weekman, Jr., V. W. and Yurchak, S., "Mobil Methanol-to-Gasoline Process," Large Chemical Plants, Elsevier Scientific Publishing Co., Amsterdam, The Netherlands, 1979.

24. CHEN ET AL.

Fluidized-Bed Upgrading of Wood Pyrolysis Liquids

289

13. Cooney, C. L., Wang, D. I. C., Wang, S. D., Gordon, J. and Jiminez, Μ., Biotech. Bioeng. Symp., 1978, 8, 103. 14. Chen, N. Y., Degnan, T. F. and Koenig, L. R., Chemtech, 1986, 16, 506.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch024

RECEIVED March 31, 1988

Chapter 25

Low-Pressure

Upgrading of Vacuum-Pyrolysis Oils from Wood

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch025

M . Renaud, J. L . Grandmaison, Christian Roy, and S. Kaliaguine Department of Chemical Engineering, Université Laval, Sainte-Foy, Quebec G 1 K 7P4, Canada

The oil fractions collected on the six hearthes of a wood vacuum pyrolysis process demonstration unit have been upgraded to hydrocarbons in the C -C range on a ZSM-5 catalyst. The use of a precoker at reaction temperature has been demonstrated and C -C hydrocarbons yields of the order of 30 wt% of oil fed, have been reached. GC/FTIR analyses of the heavier liquids collected after the precoker indicate that the acids in the oils play a dominant role in the gas phase reactions occurring in the precoker. 5

10

5

10

As b i o m a t e r i a l s a r e s t r u c t u r a l l y a n d c h e m i c a l l y complex, biomass thermochemical c o n v e r s i o n p r o c e s s e s (1,2) produce complex f r a c t i o n s i n c l u d i n g a l i q u i d f r a c t i o n w h i c h , depending on t h e p r o c e s s , c a n be obtained i n large ( l i q u e f a c t i o n , p y r o l y s i s ) or small y i e l d s ( g a s i f i c a t i o n ) . These l i q u i d s have found l i t t l e u t i l i t y because o f t h e i r l a r g e c o n t e n t s i n oxygen w h i c h i m p l i e s low heat v a l u e s , i n s t a b i l i t y and c o r r o s i v e p r o p e r t i e s . Two r o u t e s have been t e s t e d (3,4) i n o r d e r t o produce h y d r o c a r b o n s from t h e s e l i q u i d s . The f i r s t one i n v o l v e s h y d r o t r e a t m e n t w i t h e i t h e r H2 o r H2 + CO o v e r c l a s s i c a l hydrotreatment c a t a l y s t s . The second r o u t e i s t h e s i m u l t a n e o u s d e h y d r a t i o n and d e c a r b o x y l a t i o n o v e r HZSM-5 z e o l i t e c a t a l y s t i n t h e absence o f any r e d u c i n g g a s . S o l tes and L i n (5) a c h i e v e d s i g n i f i c a n t d e o x y g e n a t i o n o f v a r i o u s biomass t a r s from g a s i f i c a t i o n / p y r o l y s i s p r o c e s s e s , i n t h e p r e s e n c e o f hydrogen-donor s o l v e n t s ( c y c l o h e x a n e , t e t r a l i n , d e c a l i n ) and v a r i o u s s i l i c a - a l u m i n a s u p p o r t e d m e t a l s c a t a l y s t s . E l l i o t and Baker (6) performed h y d r o d e o x y g e n a t i o n o f t h e p r o d u c t s o f a p r o c e s s of l i q u e f a c t i o n i n t h e p r e s e n c e o f CO a t h i g h p r e s s u r e , u s i n g N i S , CoS and M0S2 c a t a l y s t s . Hydrodeoxygenation o f a biomass t a r c a n be a c h i e v e d when p h e n o l i c compounds a r e i n h i g h c o n c e n t r a t i o n s . In wood p y r o l y s i s however, t h e l i q u i d p r o d u c t s c o n t a i n l a r g e amounts o f low m o l e c u l a r w e i g h t o r g a n i c a c i d s , k e t o n e s , a l d e h y d e s and f u r a n s a s w e l l a s p h e n o l i c compounds i n t h e methoxy- o r dimethoxy (6-8) 7

0097-6156/88/0376-0290$06.25/0 ©1988 American Chemical Society

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch025

25.

RENAUD ET AL.

Low-Pressure Upgrading of Vacuum-Pyrolysis Oils

291

s u b s t i t u t e d forms. These m i x t u r e s a r e t h e r m a l l y i n s t a b l e i n t y p i c a l h y d r o t r e a t i n g c o n d i t i o n s (6). The second r o u t e however seems more a p p r o p r i a t e f o r t h e c o n v e r sion of pyrolytic o i l s . I t was i n d e e d shown t h a t a l a r g e v a r i e t y o f oxygenated compounds c a n be c o n v e r t e d i n t o h y d r o c a r b o n s o v e r H-ZSM+5 (9-20). I n a l l c a s e s h y d r o c a r b o n s i n t h e g a s o l i n e range a r e o b t a i n e d due t o t h e shape s e l e c t i v e p r o p e r t i e s o f t h i s z e o l i t e c a t a l y s t ( 2 1 ) . Moreover a remarkable r e s i s t a n c e t o c o k i n g i s o b s e r ved due t o t h e s t e r i c a l l y r e s t r i c t e d t r a n s i t i o n s t a t e s e l e c t i v i t y e f f e c t s , and t h e s e p r o p e r t i e s a r e a l s o o f c o n s i d e r a b l e i n t e r e s t i n t h e c o n t e x t o f p y r o l y t i c o i l s u p g r a d i n g . Works a l o n g t h i s l i n e have been performed b y C h a n t a i e t a l . (22,25) w o r k i n g w i t h o i l s d e r i v e d from Aspen P o p l a r b y dense gas e x t r a c t i o n , F r a n k i e w i c z (23) who used a d u a l p r o c e s s combining p y r o l y s i s o f s o l i d wastes w i t h a c a t a l y t i c c o n v e r t e r and Mathews e t a l (24) who t r e a t e d s m a l l f r a c t i o n s o f t h e o i l s produced from wood b y t h e i r thermochemical p r o c e s s . I n t h e p r e s e n t paper we r e p o r t a s t u d y o f t h e c o n v e r s i o n o v e r H-ZSM-5 c a t a l y s t s , o f t h e f r a c t i o n a t e d o i l produced by vacuum p y r o l y s i s o f P o p u l u s Deltoïdes wood i n a P r o c e s s D e m o n s t r a t i o n U n i t (PDU) (26). Experimental P y r o l y t i c O i l . The o i l under s t u d y was produced by t h e vacuum p y r o l y s i s p r o c e s s , c u r r e n t l y under development a t LAVAL U n i v e r s i t y and CRIQ ( 2 6 ) . The PDU i s a s i x - h e a r t h f u r n a c e , 2m h i g h and O.7 m i n diameter. I n t h i s u n i t , t h e o r g a n i c vapours and gaseous p r o d u c t s a r e r a p i d l y removed from t h e r e a c t o r t h r o u g h a s e r i e s o f o u t l e t manifolds. Then t h e vapours a r e condensed i n a p r i m a r y c o o l i n g u n i t , and r e c o v e r e d a s a l i q u i d f r a c t i o n f o r each h e a r t h . As shown i n Figure 1 four a d d i t i o n a l l i q u i d f r a c t i o n s are c o l l e c t e d i n the secondary c o o l i n g u n i t . I n t h i s work o n l y t h e f r a c t i o n s from t h e p r i m a r y c o o l i n g u n i t have been s t u d i e d and d e s i g n a t e d a s o i l s #1 t o #6 c o r r e s p o n d i n g t o t h e s i x h e a r t h e s from t o p t o bottom. I n s t a n d a r d p y r o l y s i s e x p e r i m e n t s u s i n g P o p u l u s Deltoïdes c h i p s , t h e p r e s s u r e i n t h e r e a c t o r was l o w e r than 80 T o r r and t h e h e a r t h t e m p e r a t u r e s were 215, 275, 325, 370, 415 and 465°C from t o p t o bottom r e s p e c t i v e l y . T a b l e I g i v e s some a n a l y t i c a l r e s u l t s f o r these s i x o i l s . The low w a t e r c o n t e n t s a r e due t o t h e f r a c t i o n a l T a b l e I . Some C h a r a c t e r i s t i c s o f t h e P y r o l y t i c O i l s

Oil #

% Water*

1

7.8 5.4 4.4 3.9 7.0 3.8

οc o

4 5 6

Formic a c i d wt % 2.64 2.34 3.73 4.40 7.25 2.60

* determined by K a r l - F i s h e r ** d e t e r m i n e d by GPC

Acetic a c i d wt % 3.63 4.13 5.18 3.26 3.16 2.26

Mw** Average M o l e c u l a r weight 342 528 572 393 233 123

292

PYROLYSIS OILS FROM BIOMASS

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch025

FEEDER

Figure 1. unit.

Scheme

of the vacuum pyrolysis process development

25.

RENAUD ET AL.

Low-Pressure Upgrading of Vacuum-Pyrolysis Oils

293

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch025

condensation of p y r o l y s i s products i n the primary c o o l i n g u n i t . Formic and a c e t i c a c i d s a r e c o n s i d e r e d t h e most abundant s i n g l e o r g a n i c compounds i n t h e s e o i l s . Conversion Reactor. The e x p e r i m e n t a l s e t - u p i s a s l i g h t l y m o d i f i e d v e r s i o n of a r e a c t o r d e s c r i b e d p r e v i o u s l y (22). As h e a t i n g t h e p y r o l y t i c o i l s t o t h e r e a c t i o n temperature i s b e l i e v e d t o induce t h e r m a l p o l y m e r i s a t i o n / c o n d e n s a t i o n r e a c t i o n s , a d e v i c e was d e s i g n e d i n o r d e r t o preheat t h e v a p o r i z e d f e e d and condense a t an a p p r o p r i a t e temperature t h e h e a v i e r p r o d u c t s . This device i s described i n F i g u r e 2. U s i n g a s y r i n g e pump (SAGE 220) t h e l i q u i d o i l i s injected i n a c o n t r o l l e d flow of helium ( 6.0 SCC/min) and f i r s t f e d t o an empty p y r e x tube m a i n t a i n e d a t t h e same temperature than t h e t u b u l a r r e a c t o r [ i n l e t o i l p a r t i a l p r e s s u r e 50-300 T o r r , r e s i dence t i m e 5-15 s ] . A t t h e o u t l e t o f t h i s tube t h e gas p a s s e s through a hot t r a p (150°C) where a heavy f r a c t i o n i s condensed. The gas flow then e n t e r s t h e m i c r o c a t a l y t i c p y r e x t u b u l a r r e a c t o r and i t i s l e d t o t h e heated (200°C) a u t o m a t i c sampling v a l v e o f a Gas Chromatograph ( P e r k i n E l m e r , Sigma 115) through a heated l i n e (160°C). A f t e r t h e v a l v e t h e p r o d u c t s a r e c o l l e c t e d as t h r e e f r a c t i o n s i n t h r e e s u c c e s s i v e t r a p s m a i n t a i n e d a t 4, -76 and -196°C respectively. A f t e r a t e s t t h e t u b u l a r r e a c t o r s c a n be t r a n s p o r t e d t o a n o t h e r s e t - u p where t h e y can be r e g e n e r a t e d i n a c o n t r o l l e d f l o w o f d r y a i r a t 500°C. The CO2 and H2O produced a r e adsorbed o v e r a s c a r i t e and d r i e r i t e r e s p e c t i v e l y and weighed. The sum o f t h e masses o f c a r b o n i n CO2 and hydrogen i n H2O was d e t e r m i n e d and compared t o t h e measur e d mass o f t h e coke d e p o s i t e d i n each o f t h e two p y r e x t u b e s . Each experiment was performed u s i n g 1.0 ± O.2 g o f t h e c a t a l y s t d e s i g n a t e d as H-22, u n d i l u t e d . T h i s i s t h e H form o f a ZSM-5 sample p r e p a r e d by t h e procedure d e s c r i b e d as method B* by GABELICA e t a l ( 2 8 ) . I t has S i / A l r a t i o o f 22, and i t s sodium c o n t e n t i s l e s s than 220 ppm as determined by PIXGE ( 2 9 ) . The GC on l i n e w i t h t h e r e a c t o r was equipped w i t h TC and FID d e t e c t o r s and a Porapak-Q column (6 f t , 1/8" OD, 80-100 mesh). I n i n s t a n c e s were peak i d e n t i f i c a t i o n was i n doubt, t h e f r a c t i o n i n t h e 4°C t r a p was f u r t h e r a n a l y z e d u s i n g a n o t h e r GC ( P e r k i n Elmer Sigma 3) equipped w i t h a FID d e t e c t o r and a c a p i l l a r y column DB-1 (30 m). In t y p i c a l r u n s , o i l was i n j e c t e d f o r about 3 000 s but chromat o g r a p h i c a n a l y s i s was s t a r t e d a t 2 000 s f o r a l l e x p e r i m e n t s . T

Experimental Design. A s t a t i s t i c a l e x p e r i m e n t a l d e s i g n was employed t o s t u d y t h e e f f e c t o f t h e p r o c e s s parameters, namely, temperature (350-450°C), space v e l o c i t y (LHSV = O.5-2.5 h" ) and o i l f r a c t i o n , on v a r i o u s response v a r i a b l e s . I n o r d e r t o reduce t h e number o f e x p e r i m e n t s , a Box-Behnken e x p e r i m e n t a l d e s i g n (30) was s e l e c t e d . T h i s d e s i g n i s v i s u a l i z e d as a cube i n F i g u r e 3. S i n c e 6 o i l f r a c t i o n s were s t u d i e d two Box-Behnken cubes were used i n o r d e r t o m i n i m i z e the number o f e x p e r i m e n t s by s t u d y i n g t h r e e o i l s i n each cube. Eventhough a d i s c r e t e v a r i a b l e i s employed t o r e p r e s e n t the o i l , i n r e a l i t y t h e h e a r t h number (1 t o 6) f o l l o w s t h e r e a c t i o n temperature on t h e h e a r t h which i s c o n t i n u o u s . The e x p e r i m e n t s were p e r f o r m e d i n a random manner. 1

294

PYROLYSIS OILS FROM BIOMASS

J

T

°

G

C

°

N

D

C

0

0

U

N

G

T

R

A

P

S

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INJECTION

Figure 2.

Scheme of the o i l precoker and reactor.

25.

Low-Pressure Upgrading of Vaeuum-Pyrolysis OUs

RENAUD ET AL.

295

GC/FTIR A n a l y s i s o f O i l s and R e s i d u a . A n a l y s e s o f o i l s and r e s i d u a ( c o l l e c t e d i n t h e h o t t r a p a t t h e o u t l e t o f t h e empty P y r e x tube) were performed u s i n g a GC/FTIR D i g i l a b FTS60 system equipped w i t h a H e w l e t t - P a c k a r d 5890 gas chromatograph. The c a p i l l a r y column was a DB-WAX c o a t e d column o f O.25 mm d i a m e t e r and 60 m l e n g t h . The i n j e c t i o n was i n the on-column mode and the oven temperature program was 50°C (10 min) 5°C/min + 240°C. The s p e c t r a l d a t a a c q u i s i t i o n r a t e was 1/1.1 s~ ( w i t h c o - a d d i n g o f 4 s p e c t r a ) and t h e s p e c t r a l r e s o l u t i o n was 8 cm . The peak component i d e n t i f i c a t i o n was p e r ­ formed u s i n g an a u t o m a t i c l i b r a r y s e a r c h a g a i n s t t h e vapour phase SADTLER l i b r a r y (9000 compounds). 1

-1

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R e s u l t s and D i s c u s s i o n Table I I shows the e x p e r i m e n t a l r e s u l t s and c o n d i t i o n s f o r t h e c a t a l y t i c upgrading t e s t s of the s i x p y r o l y t i c o i l s . I t g i v e s the weight percents of the v a r i o u s f r a c t i o n s of products c o l l e c t e d . Coke #1 c o r r e s p o n d s f o r example t o t h e t o t a l weight o f the m a t e r i a l d e p o s i t e d on the w a l l o f t h e empty p y r e x tube whereas coke #2 i s t h e one l e f t i n the t u b u l a r r e a c t o r (on t h e c a t a l y s t ) a t t h e end o f a t e s t . The t a r c o l l e c t e d i n t h e h o t t r a p i s d e s i g n a t e d as the r e s i d ­ uum, whereas the c u m u l a t i v e mass r e c o v e r e d i n a l l three cold traps i s i n d i c a t e d as " t r a p s " . The c o m p o s i t i o n o f t h e " t r a p s " f r a c t i o n i s the one o f the stream l e a v i n g t h e r e a c t o r . I t i s g i v e n i n T a b l e I I i n a condensed manner as weight p e r c e n t s o f v a r i o u s components i n c l u d i n g Cs-Ci υ h y d r o c a r b o n s , C i o hydrocarbons and oxygenates. These oxygenates a r e m o s t l y c o m p r i s i n g p h e n o l i c and f u r a n i c compounds. F i g u r e 4 shows some o f t h e c h a r a c t e r i s t i c s o f t h e s i x p y r o l y t i c o i l s . The average m o l e c u l a r w e i g h t v a r i e s i n a c o n t i n u o u s manner w i t h t h e h e a r t h number, showing a maximum v a l u e f o r t h e o i l produced on t h e 3rd h e a r t h and a minimum v a l u e f o r t h e one from h e a r t h No 6. I t must be n o t e d t h a t t h e sum o f weight f r a c t i o n s o f a c e t i c and f o r m i c a c i d s i s f o l l o w i n g a s i m i l a r p a t t e r n e x c e p t f o r t h e o i l No 5 which c o n t a i n s much f o r m i c a c i d and i s t h e r e f o r e much more a c i d i c . The low content i n f o r m i c a c i d o f o i l No 6 i s a c l e a r i n d i c a t i o n t h a t t h e s o l i d r e s i d u e l e a v i n g h e a r t h No 5 i s v e r y d i f f e r e n t i n na­ t u r e from t h e one from h e a r t h No 4 b e a r i n g much l e s s i n t a c t o r s l i g h t l y degraded c e l l u l o s e ( t h e main s o u r c e o f f o r m i c a c i d ) and much more recondensed m a t e r i a l . F i g u r e 5 shows f o r each o i l t h e average v a l u e s o f t h e w e i g h t p e r c e n t s o f coke #1, residuum and t h e y i e l d i n C 5 - C 1 0 hydrocarbons. I t i s i n t e r e s t i n g t o note t h a t at l e a s t f o r the f i r s t four o i l s these values are o b v i o u s l y c o r r e l a t e d w i t h b o t h o i l average m o l e c u l a r w e i g h t and a c i d i t y (Figure 4). As e x p e c t e d , coke #1 i s h i g h e r when t h e o i l i s h e a v i e r , b u t t h e r e s i d ­ uum i s much s m a l l e r . T h i s l a s t r e s u l t can o n l y be u n d e r s t o o d i f t h e residuum i s seen as an i n t e r m e d i a t e product o f gas phase d e p o l y m e r i z a t i o n which would be f a s t e r f o r the most a c i d i c m i x t u r e s . Indeed f o r example t h e low residuum v a l u e o b t a i n e d w i t h o i l No 5 would t h e n be the r e s u l t o f t h i s o i l b e i n g much more a c i d i c t h a n t h e o t h e r s . The C 5 - C 1 0 y i e l d i s a l s o c o r r e l a t e d w i t h Mw (up t o o i l No 5) but t h i s c o r r e l a t i o n i s the r e s u l t o f a more i n t r i c a t e i n t e r a c t i o n o f v a r i o u s f a c t o r s . C 5 - C 1 0 y i e l d does n o t depend o n l y on m o l e c u l a r s i z e o r a c i d i t y o f t h e o i l b u t a l s o on i t s c h e m i c a l n a t u r e . O i l No 3 which c o n t a i n s more l i g n i n fragments i s l i a b l e t o y i e l d s m a l l phe+

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296

PYROLYSIS OILS FROM BIOMASS

1

2

4

5 OIL

*

6 -400 C

• Β

Η

Ο

V-450C

O.5 LHSV 1.2 LHSV

® 400°C 2.5 LHSV

GB

10

V-350°C

1.2 LHSV

ο

I 1 225

1 2 265

Figure 7.

1 3 305 C5-C10

1 4 345

I 5 385

1

6 HEARTH NUMBER 425 HEARTH TEMPERATURE (°C

hydrocarbon yields.

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302

PYROLYSIS OILS FROM BIOMASS

Figure 8. Weight % of oxygenates i n the products a t the reactor outlet.

Low-Pressure Upgrading of Vacuum-Pyrolysis Oils

303

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RENAUD ET AL.

Figure 9.

Product d i s t r i b u t i o n as a function of time on stream.

304

PYROLYSIS OILS FROM BIOMASS

CO, CO2 and t h e i n c r e a s e i n oxygenates. The appearance o f C i o a r o matics i n the products i s of special interest. S i n c e such l a r g e compounds c a n n o t be g e n e r a t e d w i t h i n t h e p o r e s o f t h e ZSM-ô z e c l i t e ( 2 1 ) , t h e y c a n o n l y be g e n e r a t e d e i t h e r on t h e e x t e r n a l a c i d s i t e s or from t h e coke d e p o s i t a s p o s t u l a t e d r e c e n t l y ( 1 3 ) . T h i s would a l s o e x p l a i n t h e e v o l u t i o n o f t h e Ce-Cio a r o m a t i c s d i s t r i b u t i o n w i t h t i m e on stream, showing a r e l a t i v e i n c r e a s e i n C10 a s w e l l a s C i o . The t i m e s c a l e f o r c a t a l y s t d e a c t i v a t i o n i s showing t h e g r e a t r e s i s t a n c e o f t h e ZSM-5 c a t a l y s t t o c o k i n g . A t s i m i l a r t e m p e r a t u r e s f o r example a p e l l e t o f H-Y c r a c k i n g c a t a l y s t i s d e a c t i v a t e d w i t h i n 2-3 seconds i n t h e FCC p r o c e s s . +

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch025

+

GC/FTIR Data. T a b l e I I I r e p o r t s GC/FTIR a n a l y s e s f o r o i l #5 a n d t h r e e r e s i d u a o b t a i n e d i n t h r e e e x p e r i m e n t s performed a t 350, 400 and 450°C., u s i n g o i l #5 a s t h e f e e d . A l l compounds d e t e c t e d e i t h e r as major (Μ), l a r g e (X) o r t r a c e (T) components have been c h a r a c t e r ­ i z e d by t h e i r i n f r a r e d s p e c t r a . The number f o l l o w i n g each i d e n t i ­ f i c a t i o n i n Table I I I i s the f i t q u a l i t y index o f the experimental spectrum t o t h e one i n t h e l i b r a r y . The lower t h i s number, t h e b e t ­ t e r the f i t . T a b l e IV.

Peak number 13B 16 34

Compounds p r e s e n t i n o i l and n o t ( o r low) i n residuum

Abundance in o i l M X M

55 63

Χ Τ

7

M

acids

F o r m i c a c i d (O.05) P r o p a n o i c a c i d (O.03) C y c l o a l k a n e w i t h a ketone and an acid functions B u t y r i c a c i d ; 2-hydroxy, 2 methyl L e v u l i n i c a c i d (O.08) ( 2-propanone-1-hydroxy (O.05)

ketones 8

Τ

62B

Χ

( l-cyclopentene-3

ethers 72

τ

one (O.03)

ί E t h e r , 2-methoxy e t h y l v i n y l ] (O.21) ( P y r o c a t e c h o l , 3-methoxy (O.07)

T a b l e IV l i s t s a l l t h e compounds p r e s e n t i n o i l #5 and n o t found ( o r i n v e r y low c o n c e n t r a t i o n ) i n the residua. I t includes f i v e a c i d s , two k e t o n e s and two e t h e r s . A c e t i c a c i d i s n o t i n c l u d e d i n t h i s l i s t s i n c e i t i s s t i l l p r e s e n t i n r e s i d u a w i t h i t s concen­ t r a t i o n o n l y d e c r e a s i n g a t 450°C. T a b l e V g i v e s a l l t h e compounds w h i c h a c c o r d i n g t o the r e s u l t s o f T a b l e I I I , were p r e s e n t i n t h e r e s i d u a b u t were not found i n o i l #5. These compounds i n c l u d e e l e v e n e s t e r s , some o f w h i c h a s major components, f i v e l a c t o n e s o r d i o n e s , s i x p h e n o l i c compounds and o n l y two a c i d s found a s t r a c e s . From the c o m p a r i s o n o f T a b l e s I I I , I V and V t h e f o l l o w i n g c o n ­ c l u s i o n s can be drawn on t h e c h e m i c a l t r a n s f o r m a t i o n s o c c u r r i n g i n t h e empty P y r e x tube used a s a p r e c o k e r : 1/ A c i d s i n t h e o i l a r e h e a v i l y e s t e r i f i e d .

M

1 2 5 7 9B 10 11 12 13B 15 16 20B 25 30B 32 33 34 35 38 42 44 45 45B 46 48 51B 54 55

χ χ χ

-

χ

τ τ

-

-

Χ Χ

Μ

Τ

Χ

M

-

M

O i l #5

Peak number

Χ

-

-

Τ χ Μ

Μ Χ Χ Τ

-

Χ Τ Μ

Τ

-

Μ

Μ

-

350· C O.5 h-* Τ Μ Τ Τ Χ

χ χ Μ Τ X Τ

τ

-

Μ Χ Χ Χ

-

χ Μ

χ

Χ

χ

Χ Μ Χ

Μ

Residuum 400° C 1.2 h-i Μ Μ Χ

χ

-

χ χ χ

-

τ

χ

χ

Μ Χ

Χ

-

Μ

Χ -

-

450· C O.5 η-ι Χ Χ

Continued on next page

Methyl formate (O.03) Methyl acetate (O.03) 1,3-Cyclohexanedione (O.15) 2-Propanone-1-hydroxy (O.05) G l y c o l i c acid, methyl ester (O.03) Butyric acid, 4,4-dimethyl (O.15) Acetic acid (O.03) 2-Propanone, hydroxy-acetate (O.08) Formic acid (O.05) Furfuryl alcohol, tetrahydro, proprionate (O.08) Propanoic a c i d (O.03) Propionic acid, ester Butyric acid, 4-hydroxy, G-lactone (O.04) Adipic acid, monoethyl ester (O.10) Butyrolactone, 2-carboxy, ethyl, ester (O.10) Crotonic acid, 4-hydroxy, G-lactone (O.02) C y c l i c a l i p h a t i c + ketone + acid Cyclopentane-1,2-dione, 3-methyl (O.03) Guaiacol (O.04) Cyclopentane-1,2-dione, 4-methyl Lactone 4H-pyran-4-one, 3-hydroxy (O.06) 4H-pyran-4-one, 3-hydroxy, 2-methyl (O.07) p-Cresol, 2-methoxy (O.02) Phenol (O.06) 1-3-cyclohexanedione (O.16) Unidentified a l i p h a t i c a c i d Butyric acid; 2-hydroxy, 2-methyl

Compounds ( f i t t i n g )

Table I I I . GC/FTIR Analysis

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X

56 58 61 62 62B 65 68 68B 69 71 77 80B 81

X

X -

X

M X

O i l #5

Peak number

Χ

M Χ Χ

-

Χ

Τ

-

-

-

-

M

Μ Χ

O.5 h-*

1.2 h-* Χ Χ Μ Μ

-

-

-

-

-

M Τ Χ

M

-

450ο C

400ο C

Residuum

M Χ

-

M

M

350°C O.5 h-i M

Table I I I .

Acetic acid, methoxy or ethoxy Lactic acid, methyl ester Phenol, 2-6 dimethoxy (O.02) Unidentified ester Ether, 2-methoxyethyl v i n y l (O.21) Phenol, 4-allyl-2,6-dimethoxy (O.04) Phenol, 4-propenyl-2,6-dimethoxy Acrolein, d i e t h y l acetal (O.16) Benzoic acid (O.05) Phenol 2-6-dimethoxy compound Benzaldehyde, 4-hydroxy, 3-methoxy (O.03) Butyric acid, 4-hydroxy-G-lactone (O.10) Acetophenone, 4PR-hydroxy, 3PR-methoxy (O.05)

Compounds ( f i t t i n g )

Continued

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch025

25.

Table V. Peak number 1 2 6 9B

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Low-Pressure Upgrading of Vacuum-Pyrolysis Oils

RENAUD ET AL.

Ck>mpounds not found i n o i l but present i n residuum

Abundance i n residuum a t 350 400 450C Τ Μ Χ M Μ χ Τ

-

-

Χ

Μ

Μ

15

M

Χ

Χ

20B 22

-

Χ Τ

Χ

24

Τ

τ

30B

Χ

-

58 62

M

-

χ Μ

Μ

32

Τ

Χ

25

Τ

Χ

-

33

Μ

Μ

Μ

42

Χ

Χ

Τ

5

Τ

χ

-

48 68

Μ Χ

Μ Χ

69 71

Μ Χ

-

77

Χ

τ

81

Χ

-

-

29

-

Τ

-

-

esters

lactones and diones

Τ

phenolic compounds

acids 54B

307

=

Τ

'Formiate, methyl (O.03) Acetate, methyl (O.03) L a c t i c acid, methyl ester (O.08) G l y c o l i c acid, methyl ester (O.03) Furfuryl alcohol, tetrahydro proprionate (O.08) Propionic acid, ester \ Pyruvic acid, 3 hydroxy3 phenyl-methyl ester (O.15) Acetic acid, 2 hydroxyethyl ester (O.15) Adipic acid, monoethyl ester (O.10) L a c t i c acid, methyl ester ^Unidentified ester

ι

'Butyrolactone,-2 carboxy, ethyl ester (O.10) Butyric acid, 4-hydroxy, G-lactone (O.04) { Crotonic acid, 4 hydroxy, G-lactone (O.02) Cyclopentane-1,2-dione, 4-methyl ^1,3-Cyclohexane dione (O.15)

"Phenol (O.06) Phenol, 4 propenyl-2,6-dimetoxy Benzoic a c i d (O.05) j/ Phenol 2-6-dimethoxy V

derivative Benzaldehyde, 4 hydroxy, 3 methoxy (O.03) Aceto phenone, 4 Pr-hydroxy, V. 3 Pr-methoxy (O.05)

f V a l e r i c acid, 4-hydroxy < (O.11) ^ G l u t a r i c acid, 2 methyl

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308

PYROLYSIS OILS FROM BIOMASS

2/ L a c t o n e s and d i o n e s a r e o b t a i n e d q u i t e p r o b a b l y by dehydrat i o n and c o n d e n s a t i o n r e a c t i o n s i n v o l v i n g c a r b o h y d r a t e d e r i v a t i v e s . 3/ Among t h e p h e n o l i c compounds, phenol w h i c h i s absent i n o i l #5 i s found as a major component i n r e s i d u a . C r a c k i n g r e a c t i o n s i n v o l v i n g s i d e c h a i n s l i k e p r o p e n y l and methoxy groups on p h e n o l i c compounds have t h e r e f o r e o c c u r r e d . A l l t h r e e r e a c t i o n t y p e s must be l i n k e d t o t h e h i g h c o n c e n t r a t i o n s o f o a r b o x y l i c a c i d s i n t h e o i l . These a c i d s o b v i o u s l y a c t a s reactants i n e s t e r i f i c a t i o n s . A c i d s a r e a l s o good c a t a l y s t s f o r d e h y d r a t i o n , c o n d e n s a t i o n , c r a c k i n g and h y d r o l y s i s o f e t h e r l i n k a g e s i n t h e range o f temperature under c o n s i d e r a t i o n . I t i s t h e r e f o r e h i g h l y p r o b a b l e t h a t t h e c a r b o x y l i c a c i d s i n t h e o i l a c t a s homogeneous c a t a l y s t s o f t h e s e r e a c t i o n s . The h i g h o b s e r v e d r a t e s o f cokéfaction must a l s o be a s s o c i a t e d w i t h t h e h i g h a c i d i t y o f t h e gas phase. These r e s u l t s u n d e r l i n e t h e e f f i c i e n c y o f t h e vacuum p y r o l y s i s p r o c e s s i n a v o i d i n g secondary r e a c t i o n s o f a c i d s s i n c e o i l #5 was produced a t 415°C i n t h e vacuum p y r o l y s i s d e m o n s t r a t i o n u n i t and t h e r e a c t i o n s i n t h e p r e c o k e r were o b s e r v e d a t 350°-450°C. I t i s t h e r e f o r e c l e a r t h a t t h e vacuum p y r o l y s i s has an i m p o r t a n t a s s e t due t o i t s a b i l i t y t o preserve intermediate products o f thermal degradation which may i n c l u d e h i g h l y p r i c e d f i n e c h e m i c a l s . Conclusions The e x p e r i m e n t a l s e t - u p used i n t h i s work a l l o w e d t o d e c o u p l e t h e gas phase t h e r m a l c o n v e r s i o n o f t h e p y r o l y t i c o i l s from t h e c a t a l y t i c u p g r a d i n g . These two s e t s o f r e a c t i o n s happen i n t h e same temperature range and a r e t h e r e f o r e s i m u l t a n e o u s when t h e o i l i s d i r e c t l y f e d t o the c a t a l y s t . P r e l i m i n a r y thermal conversions i n c l u d e some c o k i n g and an i m p o r t a n t t h e r m a l d e p o l y m e r i z a t i o n . Both r e a c t i o n s a r e a c c e l e r a t e d i n t h e presence o f v o l a t i l e a c i d s i n t h e gas phase. Moreover p e r f o r m i n g both r e a c t i o n s i n a p r e h e a t e r i s b e n e f i c i a l t o t h e c a t a l y t i c c o n v e r s i o n f i r s t because t h e d e a c t i v a t i o n o f t h e c a t a l y s t i s l e s s i m p o r t a n t and s e c o n d l y because d e p o l y m e r i z e d fragments y i e l d h i g h e r conversions t o hydrocarbons. C5-C10 h y d r o c a r b o n y i e l d s a s h i g h a s 30 wt% have been c o n s i s t e n t l y o b t a i n e d f o r r e a c t i o n t i m e s o f 2 000 s'. Literature 1.

2.

3. 4.

Cited

SIMONS RESOURCE CONSULTANTS & B.H. Levelton, "A Comparative Assessment of Forest Biomass Conversion to Energy Forms" Phase I-Proven and Near-Proven Technology Vol I-IX - Phase II - Further development, ENFOR PROJECT C-258, Canada, 1983. E. Chornet & R.P. Overend, "Biomass Liquefaction: An Overview" in "Fundamentals of Thermochemical Biomass Conversion" ed. R.P. Overend, T.A. Milne & L.K. Mudge, Elsevier 1985 p. 967-1002 - 2-B K.L. Tuttle, "Review of Biomass Gasification Technology" in "Progress in Biomass Conversion Vol. 5" ed. D.A. Tillman & E.C. John, Academic Press, 1984, p. 263-279. S. Kaliaguine, "Upgrading pyrolytic oils from wood and other biomasses". Energy Project Office, NRCC, Ottawa, 1981. S. Kaliaguine, Proc. Specialists Meeting on Biomass Liquefaction, Saskatoon, 1982, p. 75-125.

25. RENAUD ET AL. 5.

6.

7.

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8.

9.

10. 11.

12.

13.

14. 15.

16.

17.

18. 19.

20.

21.

22.

Low-Pressure UpgradingofVacuum-Pyrolysis Oils

309

E.J. Soltes & S.C.K. Lin, "Hydroprocessing of Biomass Tars for Liquid Engine Fuels" in "Progress in Biomass Conversion" Vol. 5, Ed. D.A. Tillman & E.C. John, AC Press 1984, p. 1-68. D.C. Elliot & E.G. Baker, "Upgrading Biomass Liquefaction Products through Hydrodeoxygenation", Biotechnology & Bioengineering Symp. 14, 159-174 (1984). H. Ménard, C. Roy, A. Gaboury, D. Bélanger & G. Chauvette, "Analyse totale du pyroligneux provenant du Populus Tremuloides par HPLC", Compte-rendu du 4° Séminaire R & D Bioénergique, Winnipeg, Manitoba 29-31 mars 1982. C. Roy, B. de Caumia, D. Brouillard & H. Ménard, "The Pyrolysis under Vacuum of Aspen Poplar" in "Fundamentals of Thermochemical Biomass Conversion", ed. R.P. Overend, T.A. Milne &. L.K. Mudge Elsevier, N.Y. 1985, p. 237-256. C.D. Chang & A.J. Silvestri, "The Conversion of Methanol and other O-compounds to Hydrocarbons over Zeolite Catalysts", J. Catal., 47, 249-259 (1977). B.L. Maiorella, "Fermentation Alcohol: better to convert to fuel", Hydrocarbon Processing, August 1982, p. 95-97. P.D. Chantal, S. Kaliaguine & J.L. Grandmaison, "Reactions of Phenolic Compounds on H-ZSM5", Catalysis on the Energy Scene, Elsevier, 93-100, 1984. P.D. Chantal, S. Kaliaguine & J.L. Grandmaison, "Reactions of Phenolic Compounds over H-ZSM5", Appl. Catal., 18, 133-145 (1985). M. Renaud, P.D. Chantal & S. Kaliaguine, "Anisole Production by Alkylation of Phenol over HSM-5", Can. J. Chem. Eng., 64, 787-791 (1986). C.D. Chang, W.H. Lang, A.J. Silvestri, "Manufacture of Gasoline", U.S. Patent #3, 998-898 (1976). W.O. Haag, D.G. Rodewald, P.B. Weisz, "Conversion of Biological Materials to liquid fuels", U.S. Patent #4,300,009, 1981. P.B. Weisz, W.O. Haag, D.G. Rodewald, "Catalytic Production of High Grade Fuel (Gasoline) from Biomass Compounds by Shape-Selective Catalysis", Science, 206, 57-58 (1979). Y.S. Prasad, N.N. Bakhshi, J.F. Mathews & R.L. Eager, "Catalytic Conversion of Canola Oil to Fuels and Chemical Feedstocks Part I Effect of Process Conditions on the Performance of HZSM-5 Catalyst", Can. J. Chem. Eng., 64, 278-293 (1986). N.Y. Chen & L.R. Koenig, "Process for converting carbohydrates to Hydrocarbons", U.S. Patent #4,503,278 (1985). P.A. Pesa, M.W. Blaskie & D.R. Fox, "Decarbonylation of N.Butyraldehyde using Zeolite Catalysts. "U.S. Patents #4,517,400, (1985). R.M. Gould & S.A. Tabak, "Multistage Process for Converting Oxygenates to Liquid Hydrocarbons with Ethene recycle", U.S. Patents #4,543,435, (1985). E.G. Derouane, "Molecular Shape-Selective Catalysis in Zeolites - Selected Topics", Catalysis on the Energy Scene, Elsevier, p. 1-17 (1984). P.D. Chantal, S. Kaliaguine, J.L. Grandmaison and A. Mahay, "Production of Hydrocarbons from Aspen Poplar Pyrolytic oils over H-ZSM5", Appl. Catal., 10, 317-332 (1984).

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23.

T.C. Frankiewicz, "Process for Converting Oxygenated Hydro­ carbons into Hydrocarbons", U.S. Patents #4,308,411 (1981). 24. J.F. Mathews, M.G. Tepylo, R.L. Eager & J.M. Pepper, "Upgrading of Aspen Poplar Wood Oil Over HZSM5 Zeolite Cata­ lyst", Can. J. Chem. Eng., 63, 686-689, (1985). 25. R. Labrecque, S. Kaliaguine & J.L. Grandmaison, "Supercri­ tical Gas extraction of Wood with Methanol", Ind. Eng. Chem. Prod. Res. Dev., 23, (1), 177-182 (1984). 26(a). C. Roy, R. Lemieux, B. de Caumia & H. Pakdel, "Vacuum Pyrolysis of Biomass in a Multiple-Hearth Furnace", Biotechn. & Bioeng. Symp. 15, 107-113 (1985). 26(b). C. Roy, R. Lemieux, B. de Caumia and D. Blanchette, "Proces­ sing of Wood Chips in a Semi-Continuous Multiple Hearth Vacuum Pyrolysis Reactor", This symposium. 26(c). H. Pakdel and C. Roy, "Chemical Characterization of Wood Pyrolysis Oils Obtained in a Vacuum Pyrolysis Multiple Hearth Reactor", This symposium. 27. C. Roy, A. Lalancette, B. de Caumia, D. Rlanchette et Β. Côté, "Design et construction d'un réacteur de pyrolyse sous vide fonctionnant en mode semi-continu et. basé sur le concept du four à soles multiples", in Third Biomass Liquefaction Specialists Meeting Sherbrooke 29-30 Sept 1983. 28. Z. Gabelica, N. Blom & E.G. Derouane, "Synthesis and Characterization of ZSM5 type zeolites III. A critical evaluation of the role of alkali and ammonium cations", Appl. Catal. 5, 227-248 (1983). 29. I.M. Szoghy, A. Mahay & S. Kaliaguine, "Elemental analysis of zeolites by PIXGE". Zeolites 6, 39-46 (1986). 30. G.P.E. Box & D.W. Behnken, "Some new three level designs for the study of quantitative variables", Technometrics, 2, (4), 455-475 (1960). 31. P.B. Weisz, "The remarkable active sites: Al in SiO ", Ind. Eng. Chem. Fundam, 25, 58-62 (1986). 32. Anon. "SAS User's Guide", SAS Institute inc. Carry North Carolina, 1979. 2

RECEIVED March31,1988

Chapter 26

Molecular-Beam, Mass-Spectrometric Studies of Wood Vapor and Model Compounds over an H Z S M - 5 Catalyst

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch026

Robert J . Evans and Thomas Milne Solar Energy Research Institute, 1617 Cole Boulevard, Golden, C O 80401 Molecular beam mass spectrometry and a quartz microreactor operating in the pulsed mode, have been used to characterize the direct conversion of biomass pyrolysis products over an HZSM-5 zeolite. This technique allows the observation of the reaction products in real time and is ideally suited to screen a variety of catalysts, operating conditions, and model compounds to determine relative reactivity and variation in product composi­ tion as a function of operating conditions. The rela­ tive advantages of shape-selective catalysts with strong acid sites are apparant for wood pyrolysis pro­ ducts. The effect of temperature and weight hourly space velocity on product composition was screened and shows differences in reaction pathways between biomass pyrolysis products and methanol. The synergistic ef­ fect of co-feeding methanol and biomass was observed, using this technique, and showed that more aromatic gasoline products were formed. Methods of calibration have been implemented so that yield estimates can be made. Replicate runs gave hydrocarbon yields from wood of 18 ±4 wt %, with equal amounts of light olefins and aromatics. Screening of model compounds has shown that the methoxyphenols, derived from lignins, give low yields of hydrocarbon products, while carbohydrate­ -derived ring structures, such as furfural and α - a n g e l i ­ -calactones, are good sources of light aromatics.

The goal of the molecular-beam, mass-spectrometry (MBMS) studies of biomass pyrolysis product conversion over zeolite catalysts is to provide rapid c h a r a c t e r i z a t i o n , in real time, of the fate of the complex reactants as a function of reaction parameters. This tech­ nique allows the qualitative observation of transient, reactive and high molecular weight reactants and products that might otherwise escape detection by conventional c o l l e c t i o n and analysis methods. The goal is to optimize gasoline yields from biomass, at this small s c a l e , by evaluating a typical Mobil HZSM-5 z e o l i t e in i t s a b i l i t y 0097-6156/88/0376-0311$06.00/0 ©1988 American Chemical Society

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to deoxygenate wood vapors and to provide support and guidance for the bench-scale reactor studies described elsewhere in this volume. The screening results allow an assessment of several important aspects of the conversion process: the i d e n t i f i c a t i o n of promising catalysts; the determination of the c r i t i c a l variables in y i e l d optimization; the effect of catalyst composition, structural properties, and physical form on product formation; the behavior of model compounds that represent the range of functionality found in biomass pyrolysis vapors; the determination of relative coking rates for various catalysts and feedstocks; and the regenerability of catalysts. This screening approach is not a stand-alone technique, however, and bench-scale experimentation is needed to provide data for parameters which the screening approach does not adequately address: i s o l a t i o n and confirmation of isomers of products, product mass balance, long-term studies in accessing catalyst l i f e , and the variation of certain reactor operating conditions which have limited ranges at this scale, such as feed partial pressure. The c a t a l y t i c conversion of wood pyrolysis products w i l l be discussed in a screening context in this paper. Previous Work in Zeolite Conversion of Biomass Vapors. Applications of zeolites for the conversion of oxygenates in general and biomass pyrolysis products in particular has been previously reviewed ( 1 , 2 ) . Over the last decade, Mobil researchers ( e . g . , 3-5) and others (6-17) have examined a variety of oxygenated compounds over HZSM-5 catalysts of various o r i g i n s . Several investigators have converted wood pyrolysis products (10-14). Recent work at SERI has focussed on the study of direct woodvapor conversion without an o i l condensation step (1). The MBMS experimental system (18-21) has been used to show that the biomass pyrolysis vapors were reactive on the HZSM-5 z e o l i t e c a t a l y s t . The complete destruction of a l l primary products was observed, and a method of monitoring deactivation of the catalyst was demonstrated. S p e c i f i c a l l y , the carbohydrates were converted beyond the furans to l i g h t olefins and aromatics and the lignin products were also completely destroyed with the same classes of gaseous products. However, the coking tendency of each class of starting material was not quantified at that time. In this paper, we report results for the effects of weight hourly space velocity (WHSV), temperature, the co-feeding of methanol, y i e l d estimates, and the relative performance of selected model compounds. Experimental The experimental apparatus and approach have been previously described (18,19) and are summarized b r i e f l y here. The sampling mode is an extractive method in which a sampling probe i s immersed in the system to be studied. A small o r i f i c e at the apex of the cone extracts gas and with a downstream pressure (stage one pressure = 10"^ torr) that is s i g n i f i c a n t l y lower than the source pressure, (one atmosphere in this case) f u l l y developed sonic flow is established. Such an expansion leads to extensive cooling and a more or less abrupt t r a n s i t i o n to c o l l i s i o n l e s s flow. A second conical

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26. EVANS & MILNE

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313

o r i f i c e extracts or col limâtes a central core of gas leading to molecular beam formation. The molecular beam is introduced into the ion source of a quadrupole mass spectrometer. Low-energy electron ionization (EI) (approximately 25 eV) is used to minimize fragmentation within the ion source. The mass range of interest is repeatedly scanned and each scan is stored by the data system for l a t e r analysis. In the case of the pyrolysis-vapor reactants, the mass spectrum is very complex and many ions have multiple origin (20,21). In addition, isomers can seldom be distinguished by mass spectrometry alone. Nevertheless, even in the worst case of primary o i l s composed of hundreds of compounds, a s i g n i f i c a n t number can be i d e n t i f i e d with l i t t l e ambiguity (20). In the case of the product slates observed so far over active ZSM-5, the mass spectrometry is quite simple and unambiguous, except for isomers. Thus pure compounds representing a l l the major products are added both to determine their fragmentation pattern, and possible interference, and to achieve semi-quantitative c a l i b r a t i o n . Only in the case of ethylene and carbon monoxide, is there an overlap of parent and fragment ion (28 amu). In this case, electron impact fragmentation is used b e n e f i c i a l l y (as is often the case) to permit the ion at 27 amu (C Ho+) to be used to moniter ethylene, while correcting the ion at 28 amu to measure CO. Proportions of isomers such as ο - , ρ - , and m-toluene, w i l l eventually be estimated by comparison with companion studies by Diebold et a l . (14) using gas chromatography and GC-MS on collected gasoline-range products. Batch pyrolysis experiments were carried out by inserting wood s p l i n t s , or boats of wood powder or pure compounds into the pre­ heated reactor with hot carrier gas flowing and simultaneously starting the data aquisition system. Under typical conditions, a 30 mg wood splint was pyrolyzed over approximately 30 s giving a weight of carrier gas/weight of wood vapor of approximately 4 (a vapor concentration of approximately 1% by volume in the helium assuming an average molecular weight of the primary vapors of about 100). This resulted in a range of WHSV's from O.6 to 3, depending on the amount of catalyst present. After i n i t i a l screening, with pure HZSM-5 (1), the catalyst was replaced with one-sixteenth inch diameter extruded pellets of HZSM-5 in an unspecified binder. This catalyst was provided by Mobil (22) and was also used in the larger bench-scale testing (14). The catalyst was ground to a 25/45 mesh size (250/350 microns) and catalyst weight was varied to control the WHSV. For i n i t i a l screening, we have operated our micro-catalytic reactor in a pulsed mode. As is shown below (Results & Discussion, Figure 2), the catalyst appears to rather quickly achieve steadystate response, after the f i r s t few samples of wood ( e . g . , 80 % t y p i c a l l y ) from summation of a l l gaseous spe­ cies evolving from each wood-vapor pulse, plus measured char yields for each pulse, and overall coke yields of 5-10 weight percent (See Table II under Results & Discussion). There is some evidence of absorption of water and l i g h t aromatics when vapor f i r s t contacts the c a t a l y s t , so that the reported y i e l d s of l i q u i d products are probably conservative. We plan to insert wood dowels in a contin­ uous manner to v e r i f y the behavior under steady state of wood ad­ dition. 2

PYROLYSIS OILS FROM BIOMASS

314 Results and Discussion

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch026

The goals of this catalyst screening project are to gain insight into the conversion of biomass pyrolysis products with a variety of catalysts and under a range of conditions. Three topics w i l l be discussed here: catalyst and parameter screening, MBMS estimation of y i e l d , and model compound conversion. Methanol and Wood Conversion Product Classes. Methanol has been used in this screening work to ascertain catalyst a c t i v i t y . The methanol relative product d i s t r i b u t i o n on an active, pure catalyst is shown in Figure 1A. (Table II gives the i d e n t i f i c a t i o n of the ions observed). No methanol (m/z 31 and 32) breakthrough was observed, and the f i r s t formed product, dimethyl ether (m/z 45 and 46), has been consumed to form a mixture of C to Cg o l e f i n s and toluene, xylene, and trimethyl-benzene. Note the lack of benzene and alkanes. With lower space v e l o c i t i e s and higher methanol part i a l pressure, the alkenes are known to disproportionate to branched alkanes and to form more aromatics (11). The absence of products above m/z 120 indicates the well-known shape s e l e c t i v i t y of the c a t a l y s t . The conversion of the primary pyrolysis products of birch wood for 2 grams of fresh catalyst and for the catalyst subjected to the pyrolysis vapors from about 2.6 grams of wood are shown in Figure 1C and ID, respectively. The primary pyrolysis products of birch are shown in Figure IB, and the detailed interpretation of the ion peaks is given in Reference 20. A l l the primary products appear to be converted, regardless of s i z e , even though most of the zeolite active sites are within 5.1-5.6 angstrom c a v i t i e s . One possible explanation for this observation is that the larger molecules are i n i t i a l l y cracked on acid sites on the macro surface of the c a t a l yst or binder, or are converted to coke. The products on the active c a t a l y s t , however, do appear to be shape selective with most products below m/z 156. We also screened conversion behavior on other acid type catalyst including wide-bore molecular sieves and silica/alumnia. The formation of higher molecular weight products such as the methylated naphthalenes (m/z 142, 156, and 170) were much more pronounced than in the shape selective HZSM-5. The f o r mation of water, CO, and C0 are the major paths for the rejection of oxygen and represent a substantial portion of the y i e l d . They are under-represented by the i n t e n s i t i e s in the mass spectra because the instrument was tuned to favor heavy organics, so conversion of primary products could be monitored. See Table II and Figure 5 below, for more quantitative indications of the relative proportions of the various product species. The products from the p a r t i a l l y deactivated catalyst are shown in Figure ID. They are a mixture of the peaks in the primary spectrum and the f u l l y active catalyst spectrum. The l i g n i n - d e r i v e d peaks are more prevalent, such as m/z 154, 168, 180 and 194. The carbohydrate-derived products are s t i l l p a r t i a l l y converted to furan derivatives ( e . g . , furan, m/z 68 and methylfuran, m/z 82). The l i g n i n derived methoxyphenols are s t i l l p a r t i a l l y converted to phenols: e . g . , phenol, m/z 94, and c r e s o l , m/z 108. These products are the only unique intermediate oxygen-containing products i d e n t i fied so far in the zeolite conversion of biomass primary vapors. 2

2

26. EVANS & MILNE

315

Wood Vapor and Model Compounds

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch026

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Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch026

316

PYROLYSIS OILS FROM

BIOMASS

The higher proportions of aromatics relative to alkenes for wood vapors, v i s - a - v i s methanol, suggests a direct formation path not involving l i g h t o l e f i n s . The furans are only minor products on active catalysts, but are s t i l l formed on deactivated c a t a l y s t s , even when the aromatics are reduced. This may indicate that the conversion of carbohydrates to furans occurs on weak acid s i t e s , somewhat analogous to the formation of dimethylether from methanol, which also forms as an intermediate. Figure 2 shows the progressive evolution of a variety of products from catalyst conversions as 2.6 grams of wood were pyrolyzed and the vapors passed over 2 gms of c a t a l y s t . Also shown are the steady emergence of primary products. The gradual and consistent changes in the different types of products shown in Figure 2 over the complete catalyst aging cycle are strong evidence against a s i g n i f i c a n t contribution of transient processes to the pulse mode/mass spectrometric detection method of catalyst screening. The gradual decrease in toluene, an obvious product of internal pore c a t a l y t i c s i t e s , is consistent with the gradual increase of the intermediates, furan and phenol, and the primary pyrolysis products, represented by m/z 60 for carbohydratederived products and m/z 194 for lignin-derived products. The different rates of appearance of m/z 60 and 194 show the r e l a t i v e r e a c t i v i t y of these different classes of wood pyrolysis products on the c a t a l y s t . These changes in product ratios with catalyst l i f e shown in Figure 2 support the early and late wood product spectra shown in Figure 1. The mass balances obtained in the quantitative studies that are described below provide further evidence that the experimental approach r e f l e c t s complete wood product behavior on the catalyst and not transient phenomena dominated by macro surface chemisorption of single pulses of pyrolysis products. Effect of Temperature and Weight Hourly Space V e l o c i t y . The proportions of organic products that form over HZSM-5 vary systemati c a l l y with WHSV and temperature. The effects of these two parameters on the r e l a t i v e abundance of selected products from the conversion of pine pyrolysis vapors over HZSM-5 are shown in Figure 3. The temperature was varied from 300° to 550°C and the WHSV from O.7 to 2. These are relative abundance plots and do not d i r e c t l y show the y i e l d of these components since coke and inorganic gases w i l l vary with these parameters and are not reflected in the product d i s t r i b u t i o n . The plots of trimethylbenzene, toluene, and benzene show a trend of dealkylation with increased temperature. Trimethylbenzene decreased with temperature, while toluene i n creased to a maximum at 500°C and then decreased at higher temperatures. Xylene decreased steadily over this temperature range, but not as pronounced as trimethylbenzene. This indicates that the dealkylation of trimethylbenzene and xylene lead to increased abundances of toluene reaching a maximum at 500°C where the depletion of these heavier species and the dealkylation of toluene leads to a decrease in i t s relative abundance. Benzene increased throughout the temperature range studied. At higher temperatures, benzene's r e l a t i v e abundance also increased with lower WHSV's. The intermediates .are represented in Figure 3 by m/z 118 (probably benzofuran) which shows a maximum at 400°C for a l l three WHSV's although the relative abundance increased with WHSV. The

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Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch026

318

PYROLYSIS OILS FROM BIOMASS

TEMPERATURE, °C Figure 3. The effect of temperature and WHSV on the d i s t r i b u tion of selected products from the conversion of pine wood pyr o l y s i s vapors over HZSM-5 c a t a l y s t . (Note: % of total ion abundance should not be equated with % of neutral products since mass spectrometer tuning and cross sections favor aromatics.)

26. EVANS & MILNE

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319

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alkenes showed a steady increase with temperature and a dependence on WHSV at the higher temperatures as i l l u s t r a t e d by propylene. The generation of alkenes under extreme reaction conditions i n d i cate that the mechanism of aromatic formation from the alkenes in methanol conversion is not as dominant in wood pyrolysis product conversion. A large fraction of the aromatics formed from wood are apparently formed more d i r e c t l y by the deoxygenation and aromatization of the primary pyrolysis products rather than through alkenes, as in methanol conversion. Increased formation of the alkenes at higher temperatures may be associated with dealkylation of the aromatics. The formation of condensed aromatics is also enhanced at higher temperatures as demonstrated by naphthalene in Figure 3. The Effect of Co-Feeding Wood and Methanol over HZSM-5. The r e l a t i v e l y low levels of hydrogen in biomass, coupled with the high amount of oxygen to be rejected, are the reasons for the 34 wt % theoretical maximum y i e l d of hydrocarbons from dry wood (where the hydrocarbon products are assumed to have the average stoichiometry of xylene) ( J j . The low hydrogen content of wood and many oxygenated materials that have been tested since the introduction of HZSM-5, has led several researchers to experimentation with the cofeeding of methanol to enrich the feedstock in hydrogen and i n crease the potential hydrocarbon y i e l d . Chang et a l . (23) showed that hydrogen deficient oxygenates could be successfully converted on HZSM-5 i f co-fed with an adequate amount of hydrogen rich material, such as methanol. Chantel et a l . co-fed methanol with pyrolysis o i l ( 9 ) and phenols ( 8 , 1 0 ) , but only at 10 % methanol, which is below the optimum levels found by Chang et a l . (23). Chen et a l . ( 1 2 ) studied the conversion of wood pyrolysis o i l s with an equal weight of methanol and observed a net increase of 63% in hydrocarbons. We b r i e f l y explored the cofeeding of equal weights of methanol with wood pyrolysis vapors. The use of d i r e c t l y formed vapors distinguishes this experiment from the above studies. Selected changes in product ratios are shown in Figure 4 for wood, methanol, and wood plus methanol with the methanol-alone effect subtracted so that wood plus the synergistic effect is shown. The aromatic/inorganic ratio gives an indication of liquid fuel y i e l d and the wood plus methanol enhancement is s i g n i f i c a n t l y higher than either the wood or methanol alone. This is in agreement with past r e s u l t s . As stated previously, the mode of oxygen rejection is an important consideration for biomass due to i t s hydrogen deficiency. This leads to the conclusion that the preferred mode of oxygen rejection from wood is as CO2 or CO. Chen et a l . ( 1 2 ) point out that when a hydrogen donor is present, the prefered route of oxygen rejection is as HoO to preserve carbon. The CO^/ H 0 ratio was increased by the methanol cofeedings in this experiment. This observation does not agree with past results ( 9 , 1 2 ) where increased water y i e l d s and decreased C 0 y i e l d s were found when cofeeding methanol. Since only ratios nave been calculated in this experiment, i t is impossible to say whether the increase in the C 0 / H 0 ratio is due to changes in both C 0 and H 0 or just one product. The presence in this experiment of the C 0 and H 0 from the prompt gases and char formation in the i n i t i a l pyrolysis step could contribute to the 2

2

2

2

2

2

2

2

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320

PYROLYSIS OILS FROM

BIOMASS

difference between these results and past results (9,12). The nature of the aromatic products is also improved by the methanol synergism. The trimethylbenzene/toluene is greatly increased due to the presence of methanol and moves the aromatic product d i s t r i ­ bution from wood closer to that observed for methanol. This means less benzene in the gasoline and more of the higher octane, methylated benzenes. A hypothesis for the synergistic behavior is that methanol, in the presence of wood conversion products, does not have to undergo the dimethyl ether conversion step to alkenes, but rather can react d i r e c t l y with the reactive wood-derived products to alkylate aro­ matics. This increase in methylated benzenes would be expected to occur at the expense of the normal slate of products formed from pure methanol. Chantai et a l . (8,10) have studied the effect of methanol cofeeding on product d i s t r i b u t i o n from phenolic compounds. They proposed an oxonium mechanism to explain alkylation where oxonium ions are generated from diphenylether and anisole, intermediates that were formed from phenolic starting materials. They used low levels of methanol in these experiments: 90/10 (phenol/methanol) vs 1/1 (wood pyrolzate/methanol) in the results reported in this paper and by Chen et a l . (12). Under conditions of high methanol concen­ t r a t i o n s , and in the presence of carbohydrate-derived material, the formation of an oxonium ion from methanol (0Η ΟΗ ) as proposed by Aranson et a l . (24) is also possible. Direct reaction with either wood-derived reactants or various products from zeolite catalysis could explain the observed synergistis e f f e c t . 3

2

+

Hydrocarbon Y i e l d s . Despite encouraging results that the wood pyrolysis products are a l l destroyed on the catalyst and the high quality composition of the organic products, the i n i t i a l indirect estimates of y i e l d (25) were approximately 11% hydrocarbon products or about a third of the theoretical y i e l d based on oxygen rejection considerations (1). Therefore, i t was important to include an estimate of y i e l d in the MBMS catalyst screening work based on improved c a l i b r a t i o n procedures. The i n i t i a l results are reported here. Calibration factors for the products of interest were deter­ mined by injecting known amounts of l i q u i d and gaseous products in the reactor prior to packing the c a t a l y s t . Before each run, the gaseous calibrants were also bled into the flowing helium above the catalyst bed and the c a l i b r a t i o n table was updated based on the ob­ served response factors. The products calibrated were water, CO, C0 , methane, ethylene, propylene, butene, butane, pentene, benzene, toluene, xylene, and methyl naphthalene. Products not calibrated were estimated by using c a l i b r a t i o n factors for similar materials ( e . g . , using the c a l i b r a t i o n factor for methylnaphthalene for naphthalene). The products not calibrated were present in low amounts, so error caused by this procedure was probably within the goals of this screening e f f o r t . Estimates of yields for runs made in t r i p l i c a t e at 500°C and WHSV = 4, on two days, are shown in Figure 5. The error bars are the standard deviation (only positive deviation is shown) of three replicates on each day. Water was s i g n i f i c a n t l y different for the two days, but the CO and C0 estimates were quite close. The total 2

2

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch026

26. EVANS & MILNE

Wood Vapor and Model Compounds

AROM/INORG •1

COj/WATER

(WOOD+MEOH)-MEOH

IH

321

TMB/TOL

WOOD

LH3

METHANOL

Figure 4. The effect of co-feeding methanol with wood. Selected product ratios for wood alone, methanol alone, and wood co-fed with methanol with the methanol products subtracted. The ratios are: l i g h t aromatics/ H 0 + CO + COo, (arom/inorg); COo/water; and trimethylbenzene/toluene (TMB/TOL). Temperature = 500°C; wood WHSV= 2.9; methanol WHSV= 2.8. 2

ALKENES 3-26-87

AROMATICS TOT. ORGAN

4-2-87

Figure 5. Yields on a dry-weight basis from wood pyrolysis products over HZSM-5 for two different runs. Error bars show posit i v e standard deviation based on t r i p l i c a t e determinations. Total organics include alkenes, light aromatics, furnans, indenes and naphthalenes. Table II contains the breakdown of products.

322

PYROLYSIS OILS FROM BIOMASS

organics y i e l d was s i g n i f i c a n t l y less on the second day. The total organic y i e l d contains the light aromatics, alkenes, furans, naphthalenes, and indenes. The estimated product mass balances for these two runs are shown in Table I. These values assume 10% coke formation, which was determined in other experiments by weight gain of the catalyst. The 3-26-87 data are quite close to the calculated values, but the 4-2-87 data are s i g n i f i c a n t l y high in oxygen, which can be explained by the high water value for that day.

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch026

TABLE I.

Product Mass Balances (dry weight basis) for the Average Product Composition for Runs on Two Days. Results Assume 10% Coke Which is A l l Carbon and a Char Composition of C H

.53°.12

Element

Run 3-26-87

54 5.2

Run 4-2-87

Calculated 52

48

6.2

5.7

43_

5£

102

108

42_ 100

The complete product slates for the y i e l d estimates are given in Table II Summations ranged from 96 to 114, with an average of 106. The biggest source of error is probable the quantitation of coke and water (since H 0 is a major constituent detected with lower s e n s i t i v i t y than the other constituents). 2

Model Compound Products over ZSM-5 P e l l e t s . The behavior of i n d i vidual wood pyrolysis products on the catalyst gives insight into the behavior of the major compound classes. If certain compound classes are p a r t i c u l a r l y good or bad performers, then perhaps pyrol y s i s conditions can be changed to enhance the good performers or minimize the bad ones. The experimental approach used here allows compounds to be tested that would not be feasible at a larger scale. However, methods for controlling WHSV and c a l i b r a t i o n are s t i l l under development. Results are presented here, for selected compounds over HZSM-5 that represent the major compound classes, as uncalibrated spectra. The behavior of model compounds has given some insight toward potential y i e l d . The product spectra of four model compounds are shown in Figure 6. The best use of these model compound screening results is for product slate comparisons. The spectra of hydroxyacetaldehyde (Figure 6A) is typical of the light oxygenates with high H2O, CO, and C0 and moderate amounts of olefins and l i g h t aromatics. Even at the high WHSV of 6 a l l the starting material is destroyed. The 5-hydroxymethylfurfural (Figure 6B) products show higher relative amounts of organic products, including the furans and light aromatics, but also 2

Total * Estimate

2

**

18 28 44 16 58 28 42 56 70 78 92 106 128 142 116 130 68 82 118 132

Mass

Not measured

co Methane Butane Ethylene Propylene Butènes Pentenes Benzene Toluene Xylene Naphthelene Me-Naphthelene Indene Me Indene Furan Me Furan Benzofuran Me Benzofuran J Aromatics (monocyclic) V alkenes > Furans I Organics

c8

HoO

Char Coke*

Assumed Species

0.5 6.4 8.3 1.8 22.1 96

110

106

-

-

0.7 0.6

#34 16.7 10 15.1 15.9 16.1 1.0 2.5 2.8 1.8 1.9 1.8 1.1 3.1 2.2 0.5 0.7 0.6

#26 16.3 10 21.1 21.9 18.4 1.0 1.3 3.0 2.1 1.9 0.6 1.3 4.1 2.8 0.5 0.7 0.6 0.6 0.6 0.2 0.5 0.3 8.2 7.6 1.6 21.9

3/26/87 #18 15.9 10 20.5 21.0 17.6 0.9 1.2 2.9 2.0 1.6 0.4 1.3 3.9 2.5 0.6 0.9 0.6 0.5 0.5 0.2 0.5 0.2 7.7 6.9 1.4 20.5 #14 13.1 10 29.7 20.3 18.2 0.7 1.5 2.6 2.0 1.2 0.5 0.8 3.1 2.1 0.5 0.7 0.4 0.3 0.4 0.1 0.3 NM** 6.0 6.3 0.8 17.4 109

4/2/87 #13 12.8 10 28.1 20.2 17.1 0.6 0.1 2.5 1.9 1.3 1.2 0.8 2.9 2.1 0.4 0.6 0.3 0.3 0.4 0.1 0.4 NM** 5.8 6.9 0.9 16.3 104

-

114

0.7 2.7 1.6 0.3 0.4 0.3 0.2 0.4 0.1 0.2 NM** 5.1 4.8 0.7 12.3

#15 17.9 10 34.7 21.0 17.6 0.2 0.3 2.0 1.8 1.0

TABLE II Yields of Total Products from Calibrated MBMS Runs With Birch Wood Dowels HZSM-5, 2 gms; WHSV= 4; T= 500°C; Values are in wt % y i e l d (Moisture Free).

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch026

106

Avg of 6 Runs 15.4 10.0 24.9 20.1 17.5 0.7 1.2 2.6 1.9 1.5 0.8 1.0 3.3 2.2 0.5 0.7 0.5 0.3 0.5 0.2 0.3 0.3 6.5 6.8 1.2 18.4

324

PYROLYSIS OILS FROM BIOMASS

A)

'

75

"

199

•II.... m»125' ι '

'""159' "

175"

'268

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch026

5Θ

Figure 6. Mass spectra of the products of the conversion of Model compounds over HZSM-5: (A) hydroxyacetaldehyde, 500°C WHSV ~ 6; (B) 5-hydroxymethylfurfural, 500°C WHSV ~ 4; (C) a angelicalactone, 500°C WHSV- 4; (D) isoeugenol, 500°C, WHSV ~ 2. Spectra do not contain corrections for s e n s i t i v i t y f a c t o r s .

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch026

26. EVANS & MILNE

Wood Vapor and Model Compounds

325

high amounts of the naphthalenes. The α - a n g e l i c a l a c t o n e results (Figure 6C) show the highest abundances of aromatics of the model compounds that were studied. The products include more m/z 70 ( l i k e l y pentene) than the spectra for other feedstocks. The i s o eugenol results (Figure 6D) show larger amounts of unconverted feedstock (m/z 164) and phenols (phenol, m/z 94; c r e s o l , m/z 108) than observed for whole wood at this WHSV. This low reactivity is confirmed by the work of Chantai et a l . (8,10). The species at m/z 132 could possible be explained by the c y c l i z a t i o n of the side chain to form hydroxyindene with the loss of the methoxy group. It may be that at the e f f e c t i v e l y lower space v e l o c i t i e s for l i g n i n vapors in whole wood, the complete disappearance of lignin products is due to coking. Several trends are summarized here for the model compounds studied to date: (1) The light oxygenates, such as hydroxyacetalde­ hyde, gave high yields of water, CO and C0 with r e l a t i v e l y low yields of hydrocarbon products; (2) The carbohydrate-derived ring compounds, such as α - a n g e l i c a l a c t o n e , gave the greatest yields of aromatics; (3) The methoxyphenols showed lower conversion rates at the r e l a t i v e l y high space v e l o c i t i e s used. It is thought that these materials have a high coking p o t e n t i a l , based on tests per­ formed at lower space v e l o c i t i e s . The presence of unconverted materials and phenols in the product stream may be more desireable than increased coking rates. 2

Summary The use of MBMS for real time screening of wood pyrolysis product conversion over Mobil's HZSM-5 allows the rapid, q u a l i t a t i v e evalu­ ation of performance of different c a t a l y s t s , reaction conditions and feedstocks. This information can help guide more extensive testing at the bench-scale level and provide insight into the chem­ istry of conversion. The following conclusions can be drawn from the work to date: (1) No s i g n i f i c a n t breakthrough of primary wood vapor organics occurs until the weight of wood/weight of catalyst is about 1 (at a WHSV of 4-5); (2) There were few intermediates from wood (furans from the carbo­ hydrates and phenols from the methoxyphenols) on the way to alkenes, l i g h t aromatics, and naphthalenes; (3) The light aromatics/alkenes ratio is 1 for the nonoptimized and low-partial-pressure conditions studied to date; (4) Much of the oxygen is favorably rejected as CO and C 0 ; (5) The coke y i e l d is -10% in these experiments at around"500°C in He; (6) The hydrocarbon y i e l d was ~ 1 8 ± 4 wt % based on two sets of pre­ liminary calibrated experiments; (7) Methanol is a poor model for wood because the mechanism of hydrocarbon formation is apparently d i f f e r e n t . The co-feeding of methanol with wood appears to provide synergistic benefits. 2

Future work w i l l focus on the optimization of parameters, such as the partial pressure of the pyrolysis vapors, for maximizing the y i e l d of C - C I Q hydrocarbons, and the effect of HZSM-5 structural parameters on oiomass conversion. 5

326

PYROLYSIS OILS FROM BIOMASS

Acknowledgments The authors are pleased to acknowledge the technical assistance of Mike Maholland and K r i s t a l Seder and stimulating discussions with Jim Diebold and Helena Chum. The support of the Biofuels and Muni­ cipal Waste Technology Division of DOE is appreciated, as is the technical monitorship of Don Stevens, Gary Schiefelbein, and Si Friedrich. Mobil Research and Development Corporation supplied the samples of HZSM-5.

References

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch026

1.

2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

Diebold, J. P.; Chum, H. L.; Evans, R. J.; Milne, Τ. Α.; Reed, T. B.; Scahill, J. W. In Energy from Biomass and Wastes X; Klass, D. L., Ed.; Institute of Gas Technology, Chicago, and Elsevier Applied Sciences Publishers: London, 1987; p 801. Kaliaquine, S. In Wood Liguefaction Specialists Meeting; Univ. of Saskatchewan; Feb. 16-17, 1982; p 75. Chang, C. D.; Silvestri, A. J. J. Catalysis 1977, 47, 249. Chang, C. D. Hydrocarbons from Methanol; Marcel Dekker, Inc: New York, 1983; p 129. Chen, N. Y.; Degnan, T. F.; Koenig, L. R. Chemtech 1986, 506. Frankiewicz, T. C. In Proceedings of Specialists' Workshop on Fast Pyrolysis of Biomass; Diebold, J., Ed.; CopperMountain, Colorado, Oct. 19-22, SERI/CP-622-1096; 1980; p 123. Hanniff, M. I.; Dao, L. H. In Energy from Biomass and Wastes X; Klass, D. L., Ed.; Institute of Gas Technology, Chicago, and Elsevier Applied Sciences Publishers: London, 1987; p 831. Chantal, P. D.; Kaliaguine, S.; Grandmaison, J. L. In Cata­ lysis on the Energy Scene, Elsevier Science Publ.: Amsterdam, 1984; p 93. Chantal, P. D.; Kaliaguine, S.; Grandmaison, J. L.; Mahay, S. Applied Catalysts 1984, 10, 317. Chantal, P. D.; Kaliaguine, S.; Grandmaison, J. L. Applied Catalysis 1985, 18, 133. Matthew, J. F.; Tepylo, M. G.; Eager, R. L.; Pepper, J. M. Can. J. Chem. Eng 1985, 63, 686. Chen, Ν. Y.; Walsh, D. E.; Koenig, L. R. Prepr. of 193rd ACS Mtg., Div. Fuel Chem., Denver, CO, April 5-10, 1987, 32, No. 2, p 264 and this volume. Renaud, M.; Grandmaison, J. L.; Roy, C.; Kaliaguine, S. Prepr. of 193rd ACS Mtg., Div. Fuel Chem., Denver, CO, April 5-10, 1987, 32, No. 2, p 276 and this volume. Diebold, J. P.; Scahill, J. W. Prepr. of 193rd ACS Mtg., Div. Fuel Chem., Denver, CO, April 5-10, 1987, 32, No. 2, p 297 and this volume. Costa, E.; Uguina, Α.; Aguadok, J.; Herinandez, P. J. Ind. Eng. Chem. Proc. Des. Dev. 1985, 24, 239. Prasad, Y. S.; Bakhshi, Ν. M. Applied Catalysis 1985, 8, 71. Prasad, Y. S.; Bakhshi, Ν. N.; Matthews, J. F.; Eager, R. L. Can J. Chem. Eng. 1986, 64, 278. Milne, Τ. Α.; Soltys, M. N.; J. Anal. Appl. Pyrol. 1983, 5, 93. Milne, Τ. Α.; Soltys, M. N.; J. Anal. Appl. Pyrol. 1983, 5, 111.

26. EVANS & MILNE

20. 21. 22. 23. 24. 25.

Wood Vapor and Model Compounds

Evans, R. J.; Milne, Τ. Α.; Energy and Fuels 1987, 1, 123. Evans, R. J.; Milne, Τ. Α.; Energy and Fuels 1987, 1, 311. Mobil Research and Development Corporation, courtesy of Ν. Y. Chen. Chang, C. D.; Lang, W. H.; Silvestri, A. J. U.S. Patent 3 998 898, 1976. Aronson, M. T.; Gorte, R. J.; Farneth, W. E. J. Catalysis 1986, 98, 434. Evans, R. J.; Milne, T. A. Preprints of 193rd ACS Meeting, Div. Fuel Chem., Denver, CO, April 5-10, 1987, 32, No. 2, p 287.

RECEIVED March 31, 1988

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327

Chapter 27

of

Reactions of Model Compounds Biomass-Pyrolysis Oils over ZSM—5 Zeolite Catalysts

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch027

Le H . Dao, Mohammed Haniff, André Houle, and Denis Lamothe Laboratoire de Recherche Sur les Matériaux Avancés, INRS-Energie, Institut National de la Recherche Scientifique, 1650, Montée Sainte—Julie, Varennes, Quebec J 0 L 2P0, Canada

The catalytic conversion of model compounds (e.g. cyclopentanone, cyclopentenone, furfural, glycerol, glucose, fructose and their derivatives usually found in the pyrolysis oils of biomass materials) to hydrocarbon products over H-ZSM-5, Zn-ZSM-5 and Mn-ZSM-5 zeolite catalysts have been studied in a fixed bed microreactor at temperatures ranging from 350°C to 500°C. Although the deoxygenation of cyclopentanone was completed at 400°C, low yields of hydrocarbons were obtained for furfural, glycerol and carbohydrate derivatives. This is due possibly to thermal polymerization at reaction temperatures of 400°C and higher. Increasing the (H/C) ratio of the feed with methanol increased significantly the hydrocarbon yield of furfural but not that of carbohydrates. Reaction mechanisms for deoxygenation and tar formation are proposed. eff

I t has been shown t h a t s y n t h e t i c z e o l i t e s such as ZSM-5 c a n be used t o c o n v e r t oxygenated compounds d e r i v e d from biomass m a t e r i a l s i n t o h y d r o c a r b o n s which c a n be used as f u e l s o r c h e m i c a l s f e e d s t o c k s (1,2,3,4). However, t h e p y r o l y s i s o i l s o b t a i n e d from biomass mater i a l s by d i f f e r e n t t h e r m a l and t h e r m o c h e m i c a l p r o c e s s e s (5,6) showed poor h y d r o c a r b o n y i e l d s and h i g h t a r c o n t e n t when c o n t a c t e d o v e r ZSM-5 z e o l i t e c a t a l y s t s a t h i g h temperatures ( 7 , 8 ) . S i n c e the p y r o l y s i s o i l s a r e composed o f a wide v a r i e t y of oxygenated compounds s u c h as c y c l o p e n t a n o n e , c y c l o p e n t e n o n e , f u r f u r a l , p h e n o l , c a r b o h y d r a t e and c a r b o x y l i c a c i d d e r i v a t i v e s (9,10); i t i s d i f f i c u l t to p o i n t out e x a c t l y which f a m i l y o f compounds i s c o n t r i b u t i n g more t o the o b s e r v e d t a r and t o t h e r a p i d d e a c t i v a t i o n o f the c a t a l y s t s . C a t a l y t i c s t u d i e s on model compounds which a r e u s u a l l y found i n t h e biomass p y r o l y s i s o i l s a r e t h e r e f o r e p r i m o r d i a l i n o r d e r t o d e t e r m i ne t h e b e s t c a t a l y t i c system f o r the u p - g r a d i n g o f p y r o l y s i s o i l s t o u s e f u l h y d r o c a r b o n p r o d u c t s . The r e a c t i o n s of some p h e n o l i c , c a r b o n y l and c a r b o x y l i c a c i d d e r i v a t i v e s over ZSM-5 c a t a l y s t s a r e a l r e a d y

0097-6156/88/0376-0328$06.00/0 © 1988 American Chemical Society

27. DAO ET AL.

Model Compounds of Biomass-Pyrolysis Oils

329

reported (7,11). The p r e s e n t paper thus r e p o r t s t h e r e s u l t s f o r t h e conversion of cyclopentanone, cyclopentenone, furfural, glycerol, g l u c o s e and f r u c t o s e , and t h e i r i s o p r o p y l e n e d e r i v a t i v e s over H-ZSM5 and Zn and Mn-exchanged ZSM-5 z e o l i t e c a t a l y s t s a t temperatures r a n g i n g from 350°C t o 500°C. Some r e a c t i o n s a r e supplemented w i t h methanol i n t h e i r f e e d s , so as t o determine t h e e f f e c t of i n c r e a s e d (H/C) r a t i o ( s e e T a b l e 1 f o r d e f i n i t i o n ) on t h e d e o x y g e n a t i o n yields. e f f

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch027

Experimental P r e p a r a t i o n and c h a r a c t e r i z a t i o n o f t h e c a t a l y s t s . The s y n t h e s i s of t h e sodium form o f ZSM-5 was done a c c o r d i n g t o p r o c e d u r e #2 g i v e n i n t h e p a t e n t of Derouane and V a l y o c s i k ( 1 2 ) . The o n l y d i f f e r e n c e was t h e use of s i l i c a f i b e r (Strem C h e m i c a l s ) i n s t e a d o f s i l i c a g e l powder. The Na-ZSM-5 z e o l i t e was exchanged s e v e r a l times w i t h 10% aqueous s o l u t i o n o f Ν Η ^ Ν 0 (10 ml p e r g of z e o l i t e ) a t 80°C. The z e o l i t e was then d r i e d a t 100°C and c a l c i n a t e d a t 500°C so as t o o b t a i n t h e H-ZSM-5 c a t a l y s t . Mn-ZSM-5 c a t a l y s t was p r e p a r e d by h e a t i n g t h e ammonium exchanged z e o l i t e w i t h a 10% s o l u t i o n of manga­ nese n i t r a t e a t 80°C f o r 3 hours (10 ml p e r g z e o l i t e ) . A f t e r wash­ ing and d r y i n g , t h e c a t a l y s t was c a l c i n a t e d a t 500°C. Zn-ZSM-5 c a t a l y s t was p r e p a r e d i n a s i m i l a r f a s h i o n t o t h a t of t h e manganese f o r m u s i n g a 10% s o l u t i o n of z i n c n i t r a t e . The X-ray d i f f r a c t i o n p a t t e r n o f the z e o l i t e i s s i m i l a r t o those r e p o r t e d i n t h e l i t e r a t u ­ re. The c h e m i c a l c o m p o s i t i o n i s shown i n T a b l e 1. 3

P r e p a r a t i o n o f t h e c a r b o h y d r a t e i s o p r o p y l e n e d e r i v a t i v e s ( 1 3 ) . 20 g of the c a r b o h y d r a t e was mixed w i t h 250 ml of acetone and 10 ml o f cone. I1 S0^. The m i x t u r e was s t i r r e d a t room temperature f o r about 24 hours and then f i l t e r e d t o remove any u n r e a c t e d s o l i d . The f i l ­ t r a t e was n e u t r a l i z e d w i t h s o l i d NaHC0 d r i e d o v e r MgSO^, f i l t e r e d and t h e excess acetone was removed on a r o t a r y e v a p o r a t o r t o y i e l d the y e l l o w s o l i d d e r i v a t i v e s . 2

3

Apparatus. The c a t a l y t i c c o n v e r s i o n was s t u d i e d i n a c o n t i n u o u s f l o w q u a r t z m i c r o r e a c t o r w i t h a f i x e d - b e d o f d i l u t e d c a t a l y s t s . The r e a c t i o n c o n d i t i o n s a r e r e p o r t e d i n T a b l e 1. A f t e r an e x p e r i m e n t a l r u n (about 3 t o 4 h o u r s ) , t h e t a r on t h e c a t a l y t i c bed was d e t e r m i ­ ned by t a k i n g the d i f f e r e n c e i n weight of t h e r e a c t o r b e f o r e and a f t e r p l a c i n g i t i n a f u r n a c e s e t a t 500°C i n t h e p r e s e n c e o f a i r . The r e a c t i o n p r o d u c t s were a n a l y z e d by GC and GC/MS ( T a b l e 1 ) . Results F i g u r e 1 shows the y i e l d s o f c o n v e r s i o n and the p r o d u c t s d i s t r i b u ­ tion (Cj'Cg h y d r o c a r b o n s , a r o m a t i c , p o l y a r o m a t i c s and t a r ) as a f u n c t i o n of r e a c t o r temperature f o r pure c y c l o p e n t a n o n e over H-ZSM5 / b e n t o n i t e (80/20 Wt.%) c a t a l y s t . The c o n v e r s i o n i s completed a t 350°C. The main r e a c t i o n i s a t h e r m a l d e c a r b o n y l a t i o n of c y c l o p e n ­ tanone, g i v i n g h y d r o c a r b o n fragment t h a t r e a c t s f u r t h e r on t h e c a t a l y t i c bed t o produce a l i p h a t i c , a r o m a t i c and p o l y a r o m a t i c h y d r o ­ carbons. C y c l o p e n t e n o n e which i s p a r t i a l l y deoxygenated (32%) over H-ZSM-5/bentonite (80/20 Wt.%) a t 450°C, c a n be c o m p l e t e l y c o n v e r t e d

330

PYROLYSIS OILS FROM BIOMASS TABLE 1 C h e m i c a l c o m p o s i t i o n o f ZSM-5 samples Component (WT%) Na 0 Al 0~ 2

o

sio

2

3

MnO ZnO Ti0 L.O.I.*

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch027

2

Zn-ZSM-5

H-ZSM-5

Mn-ZSM-5

0.55 2.25 86.86

0.69 2.33 91.05 0.78

0.59 7.02

0.64 3.26

0.26 0.38 6.68

65.47 0.40

66.32 0.49

70.80 0.38

0.49 2.10 87.62

Molar Ratio

sio M i o 2

Na 0/Al 0 2

2

3 3

* L.0.1. means l o s s on i g n i t i o n o f sample w e i g h t . REACTION CONDITIONS C a t a l y s t weight Temperature Pressure I n e r t gas WHSV ** R e a c t i o n time **

The weight h o u r l y

10 g ( 8 0 % ZSM-5 + 20% b e n t o n i t e ) 350-560°C atmospheric pressure h e l i u m (~ 3 mfc/min) variable 3 hours

space v e l o c i t y (WHSV) i s d e f i n e d a s : WHSV

β

g o f i n j e c t e d feed per hour g of c a t a l y s t

ANALYTICAL CONDITIONS •

Gas chromatography: HP 5890 GC w i t h DB-5 (SE-54) column (30m χ 0.25mm, 1.0 μ ) For l i q u i d : 70°C (4 m i n ) , t h e n 4°C/min t o 160°C t h e n 20 m i n a t 160°C Gas : 33°C ( i s o t h e r m a l ) • GC/MS : HP 5890 GC and MS d e t e c t o r Pona column and DB-5 column HYDROGEN/CARBON EFFECTIVE RATIO ( l i a ) The e f f e c t i v e hydrogen i n d e x (EHI) i s d e f i n e d a s : EHI

(H/C) e f f

H

20 - 3N

2S

where H, C, 0, Ν and S a r e atoms p e r u n i t weight o f sample of* hydro­ gen, carbon, oxygen, n i t r o g e n and s u l f u r , r e s p e c t i v e l y .

27. DAO ET AL. to hydrocarbons

Model Compounds of Biomass-Pyrolysis Oils

331

by the a d d i t i o n of methanol t o the f e e d ( c y c l o p e n t e -

none /methanol 70/30 Wt.%). T a b l e 2 shows the r e a c t i o n of pure f u r f u r a l ( ( H / C ) =* 0) o v e r v a r i o u s c a t i o n exchanged ZSM-5 c a t a l y s t s a t 400°C. The h y d r o c a r b o n y i e l d s range from 6.6 t o 9.4% and the oxygenated compounds y i e l d s v a r y from 25.6 t o 50%. These v a l u e s r e f l e c t the poor performance of a l l the t h r e e c a t a l y s t s i n d e o x y g e n a t i n g f u r f u r a l . The l a r g e quant i t i e s of f u r a n and CO o b s e r v e d a r e m a i n l y due t o the t h e r m a l d e c a r b o n y l a t i o n of f u r f u r a l . H i g h e r t a r c o n t e n t s were o b t a i n e d f o r the m e t a l exchanged c a t a l y s t s (21.2 and 25.9%) than the H-ZSM-5 form (14.2%). The low water c o n t e n t s ( r a n g i n g from 2.7 t o 7.0%) produced f r o m t h e s e d i f f e r e n t r e a c t i o n s i n d i c a t e poor c a t a l y t i c d e o x y g e n a t i o n of f u r f u r a l . C0 which i s produced from p y r o l y t i c r e a c t i o n i s obt a i n e d i n low y i e l d s . The y i e l d s f o r the a l i p h a t i c (9.0%) and o l e fin (8.5%) a r e r e l a t i v e l y s m a l l e r than those f o r the a r o m a t i c (47.7%) and p o l y a r o m a t i c . e f f

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch027

2

F i g u r e 2 shows the p r o d u c t d i s t r i b u t i o n s f o r the r e a c t i o n of various f u r f u r a l / m e t h a n o l mixtures o v e r H-ZSM-5/bentonite (80/20 Wt.%) a t 450°C.; o n l y the major components i n the p r o d u c t s a r e shown. The a b s c i s s a i n F i g u r e 2 i s g i v e n i n both i n c r e a s i n g p e r c e n t a g e of methanol and i n c r e a s i n g ( H / C ) f £ r a t i o f o r the f e e d . As the c o n t e n t of methanol i n c r e a s e s , the y i e l d s f o r h y d r o c a r b o n s and water i n c r e a s e w h i l e t h o s e f o r t a r , f u r a n and CO d e c r e a s e . The d r a s t i c augmentation of h y d r o c a r b o n s and water y i e l d s c o n j u g a t e d w i t h the d i m i n u t i o n of f u r a n w i t h i n c r e a s i n g methanol c o n c e n t r a t i o n i n d i c a t e that s i g n i f i c a n t c a t a l y t i c deoxygenation i s t a k i n g p l a c e . For a m i x t u r e o f 55/45 Wt.% m e t h a n o l / f u r f u r a l ( ( H / C ) - 0.85), f u r a n i s c o m p l e t e l y removed from the r e a c t i o n p r o d u c t s ana o n l y s m a l l q u a n t i t i e s of o t h e r oxygenated compounds were p r e s e n t (< 0.3%). The y i e l d s f o r the o t h e r p r o d u c t s were s i m i l a r t o t h o s e o b s e r v e d p r e viously for furfural. Only a t 70/30 Wt.% m e t h a n o l / f u r f u r a l m i x t u r e t h e r e was a s i g n i f i c a n t r e d u c t i o n i n the t a r c o n t e n t (6.7 o r 14.1% on carbon b a s i s ) . The average C 0 p r e s e n t was 0.3%. e

e i f

2

T a b l e 3 shows the p r o d u c t d i s t r i b u t i o n f o r r e a c t i o n s of f u r f u - , r a l / m e t h a n o l (30/70 Wt.%) o v e r v a r i o u s c o n c e n t r a t i o n of H-ZSM-5/supp o r t a t 450°C. By d i l u t i n g the c a t a l y s t w i t h b e n t o n i t e from 80 t o 18 Wt.%, the h y d r o c a r b o n s y i e l d s r a i s e d from 30.6 t o 41.4%. Changi n g the s u p p o r t m a t e r i a l from b e n t o n i t e to S i 0 - A l 0 caused a s m a l l r e d u c t i o n i n the h y d r o c a r b o n y i e l d ( 3 6 . 3 % ) ; however, t h e r e was l e s s t a r formed when compared t o the o t h e r c a s e s . The p r o d u c t s s e l e c t i v i t i e s were s i m i l a r t o those of p r e v i o u s c a s e s . T a b l e 4 shows the p r o d u c t s from the r e a c t i o n of glycerol [ ( H / C ) £ £ o f 0.67] o v e r v a r i o u s c a t i o n exchanged ZSM-5 z e o l i t e s a t 400°C. The r e a c t i o n w i t h Zn-ZSM-5 gave the b e s t y i e l d of h y d r o c a r bons (14.4%) and the lowest y i e l d of oxygenated compounds ( 1 1 . 5 % ) . The t a r and CO c o n t e n t s f o r the t h r e e c a t a l y t i c systems were h i g h ( t h e t a r ranged from 14.0 t o 19.3% and the carbon monoxide from 5.1 t o 7.8%). I t s h o u l d be noted t h a t the major component i n the oxygenated p r o d u c t s i s 2 - p r o p e n a l . T a b l e 5 shows the p r o d u c t s d i s t r i b u t i o n f o r the r e a c t i o n of a m i x t u r e g l y c e r o l / m e t h a n o l f e e d ( 5 5 / 4 4 Wt.%) w i t h ( H / C ) - 1.25 o v e r H-ZSM-5 at 400°C. Compared t o the r e s u l t s i n T a b l e 4, an i n c r e a s e i n h y d r o c a r b o n s y i e l d s and a d e c r e a s e i n t a r and oxygenated compounds y i e l d s were o b s e r v e d . By d i l u t i n g H-ZSM-5 w i t h b e n t o n i t e 2

2

3

e

e f f

PYROLYSIS OILS FROM BIOMASS

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch027

332

00

400

500

TEMPERATURE (°C)

Figure 1. Reaction of cyclopentanone over H-ZSM-5/bentonite (80/20) at a d i f f e r e n t reactor temperature.

Figure 2. Reaction of furfural/methanol mixtures over H-ZSM-5/bentonite (80/20g) at a reactor temperature of 400 °C and a WHSV of 0.238 ± 0.018 h r - . 1

333

Model Compounds of Biomass-Pyrolysis Oils

27. DAO ET AL.

TABLE 2 R e a c t i o n o f f u r f u r a l o v e r c a t i o n exchanged ZSM-5 a t 400°C and WHSV o f 0.281 hr~* Experimental conditions: Catalyst

composition:

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch027

T o t a l product

80% H-ZSM-5, 80% Zn-ZSM-5, 80% Mn-ZSM-5 20% b e n t o n i t e , 20% b e n t o n i t e , 20% b e n t o n i t e

distribution

(Wt.%)

Furan J Oxygenated hydrocarbons Tar CO C0 H 0 Hydrocarbons 2

2

Product

selectivity

Aliphatics, 0 - C Olefins, C - C Aromatics Polyaromatics χ

2

47.0 50.0 14.2 22.8 0.6 4.4 8.00

23.8 25.6 21.2 36.3 4.8 2.7 9.42

27.8 40.7 25.9 17.9 1.9 7.0 6.6

8.8 8.5 50.6 32.1

7.6 10.6 48.8 32.9

10.5 6.5 43.9 39.1

(Wt.%)

8

g

TABLE 3 R e a c t i o n o f f u r f u r a l / m e t h a n o l (30/70) f e e d { ( H / C ) over H-ZSM-5 a t 450°C

e f f

- 1.17}

Experimental c o n d i t i o n s : Catalyst WHSV

c o m p o s i t i o n : 80% H-ZSM-5, 18% 20% b e n t o n i t e , 82% (hr~l) 0.029

T o t a l product Oxygenated Tar CO

co

hydrocarbons* 6.7 9.4 0.5 52.7 h y d r o c a r b o n s 30.6

Deoxygenated

selectivity

Aliphatics, C - C Olefins, C - C Aromatics Polyaromatics 1

2

Mainly

H-ZSM-5 SiO - A l 0 o

i.zi

d i s t r i b u t i o n. (Wt.%)

2

Product

18% H-ZSM-5, b e n t o n i t e , 82% 1.26

g

Q

1.4 7.6 7.8 0.6 41.6 41.1

0.8 4.9 7.2 0.3 50.4 36.3

11.6 3.0 72.8 12.6

20.7 3.6 60.8 14.8

(Wt.%) 1.8 2.9 83.5 11.9

f u r a n and b e n z o f u r a n ,

d e r i v a t i v e s and d i m e t h y l e t h e r .

2

3

a

334

PYROLYSIS OILS FROM BIOMASS TABLE 4 R e a c t i o n of g l y c e r o l ( ( H / C ) ^ ^ = 0.67) over v a r i o u s c a t i o n exchanged ZSM-5 a t 400°C and a WHSV o f 0.228 h r " e

1

Experimental c o n d i t i o n s : Catalyst

c o m p o s i t i o n : 80% H-ZSM-5, 80% Zn-ZSM-5, 80% Mn-ZSM-5 20% b e n t o n i t e , 20% b e n t o n i t e , 20% B e n t o n i t e

T o t a l product

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch027

Oxygenated Tar CO

d i s t r i b u t i o n (Wt.%)

hydrocarbons*

co

2

Hydrocarbons Product

selectivity

A l i p h a t i c s , Cj - C Olefins, C - C Aromatics Polyaromatics 2

32.7 14.0 7.8 0.3 40.2 5.0

11,5 15.8 6.1 3.7 48.2 14.4

16,7 19.3 5.1 1.4 49.6 7.8

15.8 5.9 60.1 18.5

5.5 9.6 63.5 21.4

9.4 8.4 44.1 38.1

(Wt.%)

Q

6

Mainly 2-propenal

and t r a c e s o f a c e t o n e

TABLE 5 R e a c t i o n o f g l y c e r o l / m e t h a n o l (55/45) f e e d {(H/C) ~ - 1.25} o v e r H-ZSM-5 a t 400°C and WHSV o f 1.44 h r ^ Experimental c o n d i t i o n s : Catalyst

composition:

T o t a l product Oxygenated Tar CO

80% H-ZSM-5 20% b e n t o n i t e

d i s t r i b u t i o n (Wt.%)

hydrocarbons*

co t^o 2

Hydrocarbons Product

selectivity

Aliphatics, 0 - C > Olefins, C - C Aromatics Polyaromatic Q

χ

2

18% H-ZSM-5 82% b e n t o n i t e

g

Mainly 2-propenal,

18.0 11.8 4.9 0.9 45.4 19.1

25.6 5.9 1.1 0.6 50.6 16.2

15.2 8.9 56.8 19.0

16.0 11.7 59.2 13.0

(Wt.%)

and t r a c e s o f methanol and d i m e t h y l e t h e r

27. DAO ET AL. from

335

Model Compounds of Biomass-Pyrolysis Oils

80 t o 18%, l e s s

t a r was formed

(5.9%) but t h e y i e l d

of hydro­

carbons a l s o d i m i n i s h e d . T a b l e 6 shows r e s u l t s f o r r e a c t i o n s o f g l u c o s e and g l u c o s e d e r i v a t i v e done over H-ZSM-5 a t 450°C. W i t h t h e a d d i t i o n o f metha­ n o l , t h u s a n i n c r e a s e o f ( H / C ) f £ , t h e r e was a n i n c r e a s e i n t h e hydrocarbon y i e l d s f o r the g l u c o s e / w a t e r / m e t h a n o l (20/50/30) and g l u c o s e d e r i v a t i v e / w a t e r / m e t h a n o l (27.6/12.2/60.2) c a s e s compared t o t h a t o f t h e g l u c o s e / w a t e r (20.3/79.7) c a s e . A l s o , t h e r e was a s i ­ m u l t a n e o u s d e c r e a s e i n t a r c o n t e n t w i t h an i n c r e a s e i n ( H / C ) of the feed. However i n a l l cases t h e h y d r o c a r b o n y i e l d s a r e low and the t a r c o n t e n t s too h i g h f o r a v i a b l e c a t a l y t i c p r o c e s s . The h i g h w a t e r c o n t e n t o b s e r v e d i n a l l experiments (29.2 t o 66.1%) i s not o n l y due t o c a t a l y t i c d e o x y g e n a t i o n through l o s s o f water but a l s o due t o p o l y c o n d e n s a t i o n r e a c t i o n s o f g l u c o s e and i t s d e r i v a t i v e . These c o n d e n s a t i o n r e a c t i o n s produce p o l y m e r i c oxygenated compounds which are r e s p o n s i b l e f o r the h i g h t a r content observed. Oxygenated compounds, CO and C 0 a r e minor p r o d u c t s which a r e n o r m a l l y o b t a i n e d from t h e r m a l d e c o m p o s i t i o n o f biomass m a t e r i a l s ( 1 4 ) . The p r o d u c t s e l e c t i v i t y i n d i c a t e s a h i g h p e r c e n t a g e o f a l i p h a t i c (23.6 t o 50.5%) and a r o m a t i c (34.2 t o 53.2%). E x c e p t f o r the r e a c t i o n w i t h g l u c o ­ se/water, t h e o l e f i n c o n t e n t s a r e low f o r t h e o t h e r two r e a c t i o n s . The p r o d u c t i o n o f p o l y a r o m a t i c s ( m a i n l y indene and naphthalene d e r i ­ vatives) i s rather high. e

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch027

e f f

2

To t e s t t h e e f f e c t o f s u p p o r t and t h e c a t a l y s t efficiency, e x p e r i m e n t s were done w i t h 18% H-ZSM-5 ( i n s t e a d o f 80%) d i s p e r s e d i n 82% b e n t o n i t e . The c a t a l y t i c bed would have l e s s a c i d i c s i t e s which a r e known t o promote p o l y m e r i z a t i o n o f t h e c a r b o h y d r a t e s and hence t o reduce t h e h y d r o c a r b o n y i e l d s . T a b l e 7 shows t h e r e s u l t s f o r e x p e r i m e n t s done on t h e d i l u t e d c a t a l y t i c bed. Only i n t h e methanol added f e e d s t h e r e was a s i g n i f i c a n t i n c r e a s e i n t h e h y d r o c a r b o n y i e l d s and a d e c r e a s e i n t h e t a r c o n t e n t . Thus, r e d u c i n g t h e number o f a c i d i c s i t e s does not seem t o reduce t h e e x t e n t o f t h e p o l y m e r i ­ z a t i o n of carbohydrates. When t h e c a t a l y t i c s u p p o r t m a t e r i a l was changed from b e n t o n i t e t o S i O - A 1 0 , t h e y i e l d s o f hydrocarbons i n c r e a s e d f o r both cases as shown i n T a b l e 8. Deoxygenation of g l u c o s e / w a t e r f e e d (20.3/79.7 Wt.%) w i t h Mn and Zn exchanged ZSM-5 a r e r e p o r t e d i n T a b l e 9. T h e r e was a r e d u c t i o n i n t h e h y d r o c a r b o n s y i e l d s when compared t o s i m i l a r r e a c t i o n s w i t h H-ZSM-5. The t a r c o n t e n t s were as h i g h as those r e a c t i o n s r e p o r t e d b e f o r e . 2

3

The d e o x y g e n a t i o n o f f r u c t o s e and i t s d e r i v a t i v e over ZSM-5 c a t a l y s t s a r e shown i n T a b l e 10. The r e s u l t s o b t a i n e d a r e s i m i l a r t o those r e p o r t e d b e f o r e f o r g l u c o s e and i t s d e r i v a t i v e . As t h e (H/C) r a t i o i n c r e a s e d , t h e h y d r o c a r b o n s y i e l d s i n c r e a s e d and the tar contents decreased. e f f

Discussion Cyclopentanone c a n be deoxygenated i n h i g h y i e l d t o h y d r o c a r b o n s o v e r H-ZSM-5 above 350°C. The main r e a c t i o n i s a t h e r m a l d e c a r b o n y l a t i o n o f c y c l o p e n t a n o n e t o g i v e CO and C^Hg fragment t h a t c a n r e a c t f u r t h e r on t h e c a t a l y t i c bed t o produce a l i p h a t i c , a r o m a t i c and polyaromatic hydrocarbons. Cyclopentenone with ( H / C ) f f 0.8 i s more d i f f i c u l t t o deoxygenated. The a d d i t i o n o f methanol r a i s e s t h e (H/C) r a t i o and p e r m i t s t h e complete d e o x y g e n a t i o n o v e r H-ZSM-5. β

e

f

f

336

PYROLYSIS OILS FROM BIOMASS TABLE 6 R e a c t i o n o f g l u c o s e and g l u c o s e d e r i v a t i v e o v e r 80% H-ZSM-5 and 20% b e n t o n i t e a t 450 °C

Experimental conditions: R e a c t a n t c o m p o s i t i o n : 20 .3% 79 .7% WHSV

(hr"l)

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch027

0i/O

g l u c o s e , 20.0% water, 0.062 0.0

e f f

27.6% g l u c o s e derivative 30.0% methanol, 60.2% methanol 12.2% water 50.0% water 0.313 0.195 1.59 1.36 glucose

T o t a l p r o d u c t d i s t r i b u t i o n (Wt.%) Oxygenated hydrocarbons Tar 65.1 CO 2.1 co 1.5 29.1 H6 Hydrocarbons 2.2

0.7 * 33.3 0.5 1.4 59.7 4.4

3.9 ** 14.1 0.2 0.9 66.1 14.8

P r o d u c t s e l e c t i v i t y (Wt.%) Aliphatics, - C 23.6 Olefins, C - C 41.6 Aromatics 34.8 Polyaromatics***

35.7 3.8 53.3 7.2

50.5 2.7 43.2 3.6

2

2

8

2

6

R e a c t i o n o f g l u c o s e and and 82% Experimental conditions: R e a c t a n t c o m p o s i t i o n : 20 .3%

TABLE 7 glucose d e r i v a t i v e over b e n t o n i t e a t 450°C

18% h-ZSM-5

glucose

27.6%

79 .7% water 1

WHSV (hr"" ) (H/C)

0.862 0.0

e f f

20.0%

glucose

glucose derivative 30.0% methanol 60.2% methanol 12.2% water 50.0% water 1.12 1.195 1.59 1.46

T o t a l p r o d u c t d i s t r i b u t i o n (Wt.%) Oxygenated hydrocarbons 0.6 * Tar 51.3 CO 3.8 co 2.8 39.4 H6 Hydrocarbons 2.1

1.0 * 21.0 1.8 0.3 57.9 18.1

4.2 ** 11.1 0.8 0.8 64.3 18.8

P r o d u c t s e l e c t i v i t y (Wt.%) Aliphatics, C - C 29.0 Olefins, C - C 7.3 Aromatics 45.2 Polyaromatics*** 18.3

43.6 1.2 45.3 10.0

17.5 14.0 55.8 12.7

2

2

Q

x

2

6

M a i n l y f u r a n and b e n z o f u r a n d e r i v a t i v e s ; ** M a i n l y acetone and furan derivatives; * * * M a i n l y indene and naphthalene derivatives

337

Model Compounds of Biomass-Pyrolysis Oils

27. DAO ET AL.

TABLE 8 R e a c t i o n o f g l u c o s e and g l u c o s e d e r i v a t i v e and 82% S i O ^ A L , 0

over

18% H-ZSM-5

?

Experimental conditions: Reactant composition:

WHSV

(hr"l)

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch027

(H/C)

eff

T o t a l product d i s t r i b u t i o n Oxygenated hydrocarbons Tar CO

co

2

H 0 Hydrocarbons 2

Product s e l e c t i v i t y Aliphatics, 0 - C Olefins, C - C Aromatics Polyaromatics χ

2

20.0% g l u c o s e 30.0% methanol 50.0% water 1.18 1.59

27.6% g l u c o s e d e r i v a t i v e 60.2% methanol 12.2% water 1.11 1.46

(Wt.%) 0.1 14.3 1.6 0.4 62.4 21.2

0.2 6.9 1.8 0.5 53.5 37.2

19.0 12.0 65.6 3.4

21.0 8.3 62.0 8.7

(Wt.%)

Q

6

TABLE 9 R e a c t i o n o f 20.3% g l u c o s e and 79.7% water o v e r and z i n c exchanged ZSM-5 Experimental conditions: Catalyst composition WHSV

0i/O

(hr~l) e f f

80% Mn-ZSM-5 20% b e n t o n i t e 0.046 0.0

T o t a l p r o d u c t d i s t r i b u t i o n (Wt.%) Oxygenated hydrocarbons Tar 72.3 CO 2.6 co 1.9 H 0 22.3 0.9 Hydrocarbons 2

2

Product s e l e c t i v i t y Aliphatics, C - C Olefins, C - C Aromatics Polyaromatics L

2

Q

g

80% Zn-ZSM-5 20% b e n t o n i t e 0.055 0.0

53.1 2.2 4.2 39.8 0.7

(Wt.%) 26.0 42.8 31.0

manganes

35.4 2.6 62.0

338

PYROLYSIS OILS FROM BIOMASS

TABLE 10 R e a c t i o n o f f r u c t o s e and f r u c t o s e d e r i v a t i v e o v e r v a r i o u s ZSM-5 a t 450°C Experimental

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch027

Reactant

conditions:

composition:

Catalyst composition:

80% H-ZSM-5 20% bentonite

WHSV ( h r ~ l ) (H/C)

0.06 0.0

e f f

T o t a l product

0.0 37.3 2.6 2.2 60.6 0.7

2

H6 2

Hydrocarbons Product

selectivity

Aliphatics C -C Olefins, C - C Aromatics Polyaromatic*** x

2

19.8% fructose 29.8% methanol 50.4% water

80% H-ZSM-5 20% bentonite 0.14 1.17

27.6% fructose derivative 60.2% methanol 12.2% water

80% H-ZSM-5 20% bentonite

80% Zn-ZSM-5 20% bentonite

80% Mn-ZSM-5 20% bentonite

0.22 1.49

0.19 1.49

0.157 1.49

0. 1* 28. 9 2. 8 2. 1 58. 5 7. 7

3.6** 14.91 0.8 1.2 46.2 33.4

0.6** 10.7 1.2 1.6 61.4 24.9

0.3** 13.2 1.3 1.0 58.7 25.5

21.5 14.1 52.1 12.3

33.2 5.6 54.8 6.3

9.8 8.1 70.7 11.4

8.6 9.7 71.4 10.2

d i s t r i b u t i o n (Wt.%)

Oxygenated hydrocarbons Tar CO

co

19.8% fructose 80.2% water

Q

6

(Wt.%)

17.4 18.8 48.5 15.3

M a i n l y f u r a n and b e n z o f u r a n d e r i v a t i v e s and d i m e t h y l e t h e r M a i n l y a c e t o n e and f u r a n d e r i v a t i v e s and benzofurane d e r i v a t i v e s and d i m e t h y l e t h e r M a i n l y indene and naphthalene d e r i v a t i v e s

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch027

27. DAO ET AL.

339

Model Compounds of Biomass-Pyrolysis Oils

Both f u r f u r a l and g l y c e r o l c a n undergo p y r o l y t i c r e a c t i o n s a t t h e temperature s t u d i e d . Both t h e p y r o l y t i c p r o d u c t s and t h e f e e d s c a n take p a r t i n the c a t a l y t i c d e o x y g e n a t i o n o v e r ZSM-5 t o produce h y ­ drocarbons. The h i g h t a r c o n t e n t o b s e r v e d i n many of t h e r e a c t i o n s r e p o r t e d c a n be e x p l a i n e d by t h e p y r o l y t i c r e a c t i o n s . A t h i g h tem­ p e r a t u r e s , f u r f u r a l c a n undergo many t h e r m a l r e a c t i o n s . I t has been shown (15) t h a t f u r f u r a l , under a c i d i c c o n d i t i o n s , c a n p o l y m e r i z e d by an a l d o l - t y p e r e a c t i o n t o produce h i g h m o l e c u l a r r e s i n r e f e r r e d as f u r f u r a l b l a c k . The major p y r o l y t i c r e a c t i o n of f u r f u r a l i s d e c a r b o n y l a t i o n t o produce f u r a n and CO as r e p o r t e d i n t h e l i t e r a t u ­ r e (16) and a l s o o b s e r v e d i n most of t h e r e a c t i o n s o f f u r f u r a l ( T a ­ b l e s 2 and 3 ) . Under h i g h temperature and a c i d i c c o n d i t i o n s , f u r a n c a n p o l y m e r i z e d t o humin ( 1 6 ) . G l y c e r o l c a n undergo d e h y d r a t i o n a t h i g h temperature t o produce a c r o l e i n ( 2 - p r o p e n a l ) (17) w h i c h c a n r e a c t f u r t h e r t o form polymers ( p o l y a c r o l e i n ) (18) ( T a b l e s 4 and 5 ) . Once a l l t h e s e polymers a r e formed, they remain on t h e c a t a l y t i c bed c o n t r i b u t i n g t h e n t o t h e t a r c o n t e n t s and t h e d e a c t i v a t i o n o f t h e catalysts. T a b l e s 6 t o 10 show t h a t t h e y i e l d s o f h y d r o c a r b o n s obtained f o r most of t h e r e a c t i o n o f c a r b o h y d r a t e s over ZSM-5 c a t a l y s t s were low when compared t o t h e y i e l d s o f t a r formed on t h e r e a c t o r bed. The r e s u l t s a l s o i n d i c a t e t h a t t h e z e o l i t e c a t a l y s t s a r e not r e s p o n ­ s i b l e f o r t h e h i g h t a r c o n t e n t s o b s e r v e d , s i n c e most of the t a r s were formed on t h e top o f t h e c a t a l y t i c bed. Two p o s s i b l e reasons f o r t h e h i g h t a r c o n t e n t a r e t h e low ( H / C ) f r a t i o i n t h e f e e d as a l s o r e p o r t e d by o t h e r a u t h o r s (11) and t h e p o l y m e r i z a t i o n of t h e c a r b o h y d r a t e s and t h e i r d e r i v a t i v e s a t temperatures above 150°C. F i r s t l y , i f the ( H / C ) i s lower than 1, t h e c o n v e r s i o n t o h y d r o ­ c a r b o n w i l l be s m a l l because t h e main d e o x y g e n a t i o n r e a c t i o n i s the e l i m i n a t i o n o f water which i s dependant o f t h e a v a i l a b i l i t y o f t h e h y d r o g e n i n t h e o r g a n i c components of t h e f e e d (2,4,11). Glucose a n d f r u c t o s e a n d t h e i r d e r i v a t i v e s w i t h ( H / C ) ^ * r a t i o < 0.7 a r e t h e r e f o r e e x p e c t e d t o g i v e poor h y d r o c a r b o n s y i e l d s ( T a b l e s 6-10). However, s u p p l e m e n t i n g t h e s e c a r b o h y d r a t e s w i t h compounds w i t h h i g h (H/C) (e.g. methanol with ( H / C ) 2 . 0 ) , i t i s p o s s i b l e to i n c r e a s e the ( H / C ) of the feed. T a b l e s 6, 7 and 10 show t h e e f f e c t o f a d d i n g methanol t o t h e c a r b o h y d r a t e s f e e d s ; t h e r e was a simultaneous i n c r e a s e i n hydrocarbons y i e l d s with i n c r e a s e (H/C) ff· N e v e r t h e l e s s , as t h e i n c r e a s e i s s m a l l and t h e t a r c o n t e n t s t i l l t o o h i g h , t h e c a t a l y t i c u p g r a d i n g would be d i f f i c u l t i n a f i x e d - b e d reactor. T h e r e f o r e more c o s t l y p r o c e s s e s such as a f l u i d i z e d bed s y s t e m (11a) a r e n e c e s s a r y . The h i g h t a r c o n t e n t c a n be produced by t h e d e c o m p o s i t i o n and p o l y m e r i z a t i o n o f c a r b o h y d r a t e s . I t I s known t h a t g l u c o s e can undergo t h e r m a l p o l y m e r i z a t i o n and d e c o m p o s i t i o n a t temperatures h i g h e r than 150°C ( 1 9 ) . P o l y c o n d e n s a t i o n o f g l u c o s e c a t a l y z e d by a c i d produced polymers ( p o l y g l u c o s e ) w i t h a wide range of molecular weights. Other n o n - v o l a t i l e decomposition products which c o n t r i b u t e t o the t a r c o n t e n t a r e l e v o g l u c o s a n and 1,6-anhyd r o g l u c o f u r a n o s e ( 2 0 ) . One consequence o f t h e n o n - v o l a t i l e p r o d u c t s on t h e c a t a l y t i c bed i s t h a t they c a n b l o c k t h e pores of ZSM-5 and, hence, p r e v e n t i n g d e o x y g e n a t i o n of the v o l a t i l e compounds. Thermal d e c o m p o s i t i o n o f g l u c o s e c a n a l s o produce v o l a t i l e p r o d u c t s (5-hydroxymethyl f u r f u r a l , f u r f u r a l , f u r y l hydroxymethyl ketone) which c a n undergo d e o x y g e n a t i o n over ZSM-5 c a t a l y s t s t o y i e l d t h e s m a l l e

f

e f f

β

e f f

e f f

e f f

e

340

PYROLYSIS OILS FROM BIOMASS

amount of h y d r o c a r b o n s o b s e r v e d . The e x p e r i m e n t a l r e s u l t s s u g g e s t t h a t the r a t e of p r o d u c t i o n o f v o l a t i l e p r o d u c t s i s much s l o w e r than the r a t e of p r o d u c t i o n o f n o n - v o l a t i l e p r o d u c t s i n a f i x e d - b e d c a t a ­ l y t i c system. Hence, t h e poor h y d r o c a r b o n y i e l d and the h i g h t a r content. The d e r i v a t i v e s o f g l u c o s e and f r u c t o s e g i v e b e t t e r h y d r o ­ c a r b o n y i e l d s , p r o b a b l y b e c a u s e o f t h e i r h i g h e r R/C ff r a t i o and a l s o because most of the hydroxy groups r e s p o n s i b l e f o r the forma­ t i o n of p o l y g l u c o s e a r e blocked. However, t h e t a r c o n t e n t s f o r t h e s e d e r i v a t i v e s r e a c t i o n s a r e s t i l l too h i g h . e

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch027

Conclusion C y c l o p e n t a n o n e c a n be deoxygenated w i t h h i g h y i e l d t o h y d r o c a r b o n s o v e r ZSM-5 a t 400°C. The a d d i t i o n o f methanol t o c y c l o p e n t e n o n e p e r m i t s t o r a i s e t h e ( H / C ) f £ r a t i o o f t h e f e e d and, hence, i t s complete d e o x y g e n a t i o n . The r e a c t i o n o f f u r f u r a l and g l y c e r o l o v e r ZSM-5 c a t a l y s t s a t temperatures between 400°C and 500°C produces p y r o l y t i c p r o d u c t s o f d i f f e r e n t degree o f v o l a t i l i t y . The v o l a t i l e f r a c t i o n i s deoxygenated by t h e c a t a l y s t s t o produce h y d r o c a r b o n s w h i l e the n o n - v o l a t i l e f r a c t i o n remained on the c a t a l y t i c bed c a u s ­ i n g the d e a c t i v a t i o n o f the z e o l i t e and the enhancement o f the t a r content. G l u c o s e and f r u c t o s e undergo t h e r m a l r e a c t i o n s which p r o ­ duce a s i g n i f i c a n t amount o f t a r and a s m a l l amount o f v o l a t i l e products. The v o l a t i l e f r a c t i o n i s deoxygenatd by ZSM-5 c a t a l y s t s to produce h y d r o c a r b o n s . e

Acknowledgments T h i s work was s u p p o r t e d by g r a n t s from t h e N a t u r a l S c i e n c e s and E n g i n e e r i n g R e s e a r c h C o u n c i l o f Canada and from the Quebec M i n i s t r y of S c i e n c e s and T e c h n o l o g y . Literature

cited

1. Weiz, P.B., Hagg, W.O., Rodewald, P.G., Science, 1979, 206, 57. 2. Frankiewicz, T.C., U.S. Patent 4 308 411, 1981. 3. Dao, L.H., Haniff, Μ., Preprint tenth Canadian Symposium on Catalysis, 1986, p. 278. 4. Chen, N.Y., Koenig, L.R., U.S. Patent 4 503 273, 1985. 5. Hasnain, S., Editor Fifth Canadian Bioenergy R&D Seminar; Elsevier: London, 1984. 6. Chornet, E., Overend, R., Editor Compte-rendu de l'atelier de travail sur la liquefaction de la biomasse, 1983. 7. Chantal, P.D., Kaliaguine, S., Grandmaison, J.L., Applied Catalysis, 1985, 8, 133. 8. Dao, L.H., Canadian Patent 1.201.080, 1985. 9. Schirmer, R.E., Pahl, T.R., Eliot Fuel, 1984, 368. 10. Dao, L.H., Hebert, P., Houle, Α., Haniff, M., Proceeding of the Ninth Biennal Congress of the International solar Energy Society, 1986, Vol. 3, 1812. 11. a. Chen, N.Y., Walsh, D.E., Koenig, L.R., Preprint Amer. Chem. Soc. Div. Fuel Chem, 1987, 32(2), p. 264.; b. Chang, C.D., Silvestri, A.J., J. Catalysis, 1977, 47, 249; c. Chang, C.D., Silvestri, A.J., U.S. Patent 3,998,898, 1976.

27. DAO ET AL.

Model Compounds of Biomass-Pyrolysis Oils

341

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch027

12. Derouane, E.G., Valyacsik, E.W., European Patent 157521, 1985. 13. Shafizadek, F., Fu, Y.J., Carbohydr. Res., 1973, 29, 113. 14. Neuth, F.H., Adv. Carbohydr. Chem, 1951, 6, 83. 15. Kraushaar, B., Kompa, H., Schrolliens, H., Schulz-Eskloff, G., Acta Phys. et Chim. (Szeged), 1985, 31, 581. 16. Acheson, R.M., An Introduction to the Chemistry of Heterocyclic Compounds, Johns Wiley and Sons, NY, 1976, p. 126. 17. Segur, J.B., In Glycerol, Miner C.S., Dalton N.M., Editor Reinhold: NY, 1953, p. 335. 18. Derouane, E.G., J. Catalysis, 1981, 70, 123. 19. Smith, P.C., Guehtlein, H.E., Converse, A.O., Solar Energy, 1982, 28, 41. 20. Houminer, Y., Patai, S., Israel J. Chem, 1969, 7, 513. RECEIVED March 31, 1988

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ix001

Author Index Johnson, David K., 156 Kaliaguine, S., 139,290 K e l b o n , M a r c i a , 41 K l e i n , M i c h a e l T., 241 K o e n i g , L . R., 277 Krieger-Brockett, Barbara, 41 K r o c h t a , J o h n M . , 119 Lamothe, Denis, 328 Lede, Jacques, 66 Lemieux, R i c h a r d , 16 L i , H u a i Z h i , 66 Maugendre, S., 129 M c K e o u g h , P. J . , 104 Meuzelaar, H e n k L . G , 189 M i l n e , Thomas, 311 Nelson, D a v i d Α., 113 Pakdel, R , 203 Piskorz, J . , 167 Pugmire, R o n a l d J . , 189 R a d l e i n , D . , 167 Renaud, M . , 290 R o y , Christian, 16,203,290 Scahill, J o h n , 31,264 Scott, D . S., 167 Sealock, L . J o h n , Jr., 179 Soltes, E d J . , 1 Soyer, N . , 220 Theander, Olof, 113 T i l l i n , Sandra J . , 119 T r a i n , Peter M . , 241 Villermaux, Jacques, 66 Walsh, D . E . , 277 W i n d i g , W i l l e m , 189

Agrawal, Ravindra IC, 79 A h m e d , A , 139 A l l e n , S. G . , 92 Baker, E d d i e G . , 228 Boocock, D . G . B., 92 Bouvier, J . M . , 129 Blanchette, D a n i e l , 16 Bousman, Scott, 41 Brault, Α., 220 Bruneau, C , 220 Butner, R. Scott, 179 Chen, Ν. Y . , 277 Chowdhury, A , 92 C h u m , H e l e n a L., 156 D a o , L e R , 328 de C a u m i a , B r u n o , 16 D i e b o l d , James, 31,264 E l l i o t t , Douglas C , 55,179,228 Evans, Robert J . , 311 Eyring, Edward M . , 189 Fruchtl, R., 104 Gelus, M . , 129 Grandmaison, J . L., 139,290 Grant, D a v i d M . , 189 H a l l e n , R i c h a r d T., 113 Haniff, M o h a m m e d , 328 Hayes, R . D., 8 Helt, James E . , 79 Hoesterey, Barbara L., 189 H o u l e , André, 328 H u d s o n , Joyce S., 119 Hyvrard, R , 220 Johansson, Α . Α., 104

Affiliation Index A g r i c u l t u r a l Research Service, 119 A r g o n n e N a t i o n a l Laboratory, 79 Centre N a t i o n a l de la Recherche Scientifique, 66 E c o l e Nationale Supérieure de C h i m i e de Rennes, 220 Institut N a t i o n a l de la Recherche Scientifique, 328 M o b i l Research and Development Corporation, 277 Pacific Northwest Laboratory, 55,113,179,228 Renewable Energy Branch, Energy, M i n e s , and Resources, 8

Solar Energy Research Institute, 31,156,264,311 Technical Research Centre of Finland, 104 Texas A & M University System, 1 Université Laval, 16,139,203,290 University of A g r i c u l t u r a l Sciences, 113 University of Delaware, 241 University of Technology, 129 University of Toronto, 92 University of U t a h , 189 University of Washington, 41 University of Waterloo, 167

345

PYROLYSIS OILS F R O M

346

BIOMASS

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ix002

Subject Index

Ablative pyrolysis cyclone reactor experiments, 71,73/ determination o f rate constant for wood decomposition, 76 fixed heated wall experiments, 68,71,72/ lifetime of liquids produced, 71,73/ schematic, 66,6Sy spinning disk experiments, 67-68,69-7Qf wood surface temperature vs. heat source temperature, 74,75/ Adsorption-chromatographic method of o i l fractionation, advantages, 204 A l k a l i n e degradation of cellulose production o f organic acids, 124,125/,126i,127 reaction parameters, 122/ reaction rate constants, 124,125/ second-order kinetics, 122,123/124 A l k a l i n e degradation of starch H P L C chromatograms, 124 production of organic acids, 124,125/126r,127 rate reaction constants, 124,125/ reaction parameters, 122/ second-order kinetics, 122,123/124 A l k a l i n e thermochemical degradation of polysaccharides commercial application, 119 degradation o f cellulose, 121-125 degradation of starch, 121-125 experimental materials, 120 experimental procedures, 120-121 G C analysis, 121 H P L C analysis, 121 production of organic acids, 119 A l k a l i n e thermochemical degradation of polysaccharides to organic acids, kinetics, 119-127 A r o m a t i c compounds, formation from carbohydrates, 113-117

Β Batch pyrolysis, experimental procedure, 313 Bioenergy overview, Canadian reports, 8 - 9 Biological properties, tars, 60,62,63/ Biomass, definition, 9 Biomass-derived oils, catalytic hydrotreating, 2 2 8 - 2 3 8

Biomass liquids applications, 290 routes to gasoline hydrocarbon production, 290-291 Biomass materials to high-octane gasoline, conversion, 264-274 Biomass pyrolysis Canadian research, 9 - 1 1 fusionlike behavior, 6 6 - 7 6 nature, 1-3 prospects, 5 Biomass tars biological properties, 60,62,63/ chemical properties, 58/,5Sy,60,61/ effect of formation conditions o n composition, 5 5 - 5 6 effect of time and pressure o n properties, 56 physical properties, 60 pyrolysis mechanisms, 56,57/ Biomass thermotechnical processes characterization, 2 reasons for study, 1 use as pretreatment processes, 2 B i o o i l , general characteristics, 19,21/ Black liquors, o i l production by high-pressure thermal treatment, 104-111

Canadian bioenergy, research and development activities, 8 - 9 Canonical correlation analysis for pyrolysis o i l characterization diagnostics, 199,200/ variate functions, 198f,200-201 Carbohydrates biomass conversion over zeolite catalyst, 3 3 9 - 3 4 0 formation of aromatic compounds, 113-117 Carbohydrate isopropylene derivatives, preparation, 329 Catalyst deactivation causes, 236 example, 236,238f Catalytic hydrotreating of biomass-derived oils catalysts, 230,232/ catalyst deactivation, 236,238/" composition of feedstock oils, 228,229/ discussion, 228 effect of catalysts o n quality of o i l , 234,236,237/

INDEX

347

Catalytic hydrotreating—Continued

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ix002

o i l preparation, 233 oxygen content of oils, 234,235/ results with pyrolysis oils, 236 schematic o f reactor system, 230,231/ tests with C o - M o catalysts, 233-234/ two-phase flow pattern, 230 yield o f gas boiling range o i l , 234,235/ Cellulose composition, 83,85/ production of organic acids, 124-237 pyrolysis, 80 thermochemical degradation, 121-125 Cellulose chars atomic ratios, 85 composition, 83,85/ heating value, 85 Centralized Analysis Project, description, 13-14 Char, analysis, 44 Characterization, pyrolysis oils, 3 - 4 Charcoal, general characteristics, 19,21/ Chemical modeling o f lignin application, 241 definition, 241 lignin depolymerization, 247-253 model predictions, 251,254-261 stochastic description o f lignin structure, 242-247 Chemical properties, tars, 58/,5S>f,60,61/ Composition o f pyrolysis oils, effect of pyrolysis process conditions, 4 - 5 Conventional pyrolysis process mode, definition, 3 Cyclone reactor, experiments, 71,73/ Cyclopentanone, biomass conversion over zeolite catalyst, 335339

D Diffuse reflectance Fourier-transform infrared spectrometry ( D R I F T ) , application, 139-140 Diffuse reflectance infrared spectrometry of supercritical extraction residues quantification, 151,152/ spectral region 700-950 c m , 1 5 0 spectral region 1035-1370 and 1

1705-1740 c m , 1 5 0 spectral region 2870-3050 cm" ,148,150 Direct Biomass Liquefaction Project, description, 14 1

1

Effective hydrogen index, definition, 278 Electron spectroscopy for chemical analysis ( E S C A ) carbon content ratio, 153/154 description, 151 spectra, 151,153/154

Factor analysis for pyrolysis o i l characterization combined loading plots, 197,198^,199 combined score plots, 197,198^,199 factor score plots, 193,19^,197 types o f spectral data, 193,197/ variance diagram, 199 Fast pyrolysis class o f chemicals, 177 combustion test o n oils, 168 description o f process, 167 H P L C analysis o f liquid products, 171,173/ H P L C analytical technique, 171 H P L C chromatogram of water-soluable o i l fracton, 171,174/ properties o f feed materials, 168,170f properties o f liquids, 171,172/ schematic o f material balance for typical separation, 176f,177 yields from different woods, 168,169/ Fast pyrolysis o f biomass, See Pyrolysis of biomass, fast Feedstock, effect o n liquefaction product, 180,181/,182 Flash pyrolysis, description, 180 Fluidized bed flash pyrolysis development, description, 12 Fraction 1 composition, 210 I R spectra, 210,211/ Fraction 2, composition, 210 Fractions 3 - 1 1 characterization o f low molecular weight carbolylic acids, 215 chromatograms, 210,214^,215 identification o f compounds, 210,212-213/ yield, 210 Fraction 12, hydrogen distribution, 215,216/ Fraction 13 composition, 215 hydrolysis, 218 N M R spectra, 215,217/218

348

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ix002

Fraction 14, composition, 218 Furfural, biomass conversion over zeolite catalyst, 339-340 Fusionlike behavior of biomass pyrolysis cyclone reactor experiments, 71,73/ determination o f rate constant for wood decomposition, 76 fixed heated wall experiments, 68,71,72/" lifetime o f liquids produced, 71,73 spinning disk experiments, 67-68,69-70/" wood surface temperature vs. heat source temperature, 74,75/

Gas, analysis, 43 Gas chromatography ( G C ) characterization o f pyrolysis liquids, 82-83,84/ characterization o f pyrolysis oils, 4 thermal degradation products, 121 Glucose biomass conversion over zeolite catalyst, 339-340 structure of isolated liquefaction products, 116^ yields o f aromatic compounds upon liquefaction, 115,116/ Glucuronic acid structures o f isolated liquefaction products, 116/ yields o f aromatic compounds upon liquefaction, 116/,117 Glycerol, biomass conversion over zeolite catalyst, 339-340 H Heat flux density balances, equations, 67 Heat transfer coefficients calculation, 67 values, 68 High-performance liquid chromatography ( H P L C ) , thermal degradation products, 121 High-performance size-exclusion chromatography ( H P S E C ) apparatus, 157 applicability o f calibration, 163,164f characterization o f pyrolysis oils, 4 comparison o f oils from various sources, 158,159f,160,161f

PYROLYSIS

OILS

FROM

BIOMASS

HPSEC—Continued effect o f ambient conditions, 160,161/162,164/ limitations for characterization, 162-163 preparation o f pyrolysis oils, 157 High-pressure liquefaction o f high-moisture biomass categories, 180 chemical functional groups i n products, 184,185/ comparison o f results to earlier results, 185-186 effect o f feedstock o n products, 180,181/,182 experimental results, 184/ feedstock description and analysis, 182,183/ history, 179 implications for future research, 186-187 product analysis, 180,183-184 product recovery, 183 reactor conditions, 183 utilization of o i l products, 179 High-pressure processing, description, 180 High-pressure thermal treatment o f black liquors analysis o f kraft black liquor, 105/ composition o f reducing gas, 109/ description, 104 experimental procedure, 105-106 formation o f o i l phase, 106 implications for process development, 110 interactions between gaseous and aqueous components, 106-108 preliminary scheme for process, 110,111/ reactions o f organic acid salts, 108-109 results o f autoclave experiments, 106,107/ types o f applications, 104-105 Hydrogen/carbon effective ratio, definition, 330 Hydrothermolysis, See Liquefaction Hydrothermolysis o f wood, o i l yield, 11

Infrared spectrometry, analysis o f lignocellulosic material, 139-140 Infrared spectroscopy for pyrolysis o i l characterization experimental procedures, 190-191 spectra, 193,194/

349

INDEX Integrated spectroscopic technique for pyrolysis o i l characterization advantages, 189-190 calculated elution volumes, 190,192/ canonical correction analysis, 199-201 experimental procedures, 190-191 factor analysis, 193,196-199 IR, 193 M S , 191,192f,193 N M R , 193,195/ International Energy Agency, Bioenergy Implementing Agreement, 14 Iron, effect o n wood liquefaction, 220

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ix002

Κ Kinetic energy o f photoelectrons, calculation, 151 Kraft black liquor, analysis, 105r Kraft lignin catalytic liquefaction, 254,256/ description, 242 effects o f catalyst deactivation and internal transport limitations o n liquefaction, 254,257/258 liquefaction, 251 probality distribution functions for molecular weight, 242,244/ pyrolysis, 254,256/" structure, 242-243,246/

Lambiotte process, description, 16-17 Large, moist wood particles, tar production, 4 1 - 5 3 Lignin chemical modeling, 241-261 description, 242 example o f model oligomer construction, 243,246f,247 model polymer generation, 243,245/ probality distribution functions for molecular weight, 242,244/ L i g n i n depolymerization catalyst deactivation, 249 catalyst effectiveness factor, 249 model compound reaction pathways and kinetics, 251,252/ P-position reaction pathways, 251,253/ random trajectory o f polymer reaction, 247,248/" reaction trajectory o f model oligomer, 251-252,253/ simulation o f liquefaction, 249-250 Thiele modulus, 249 transition probabilities for M o n t e C a r l o simulation, 247,248/,249

Lignocellulosic material analysis by I R spectrometry, 139 analysis by thermal methods, 139 Liquefaction definition, 3 first-generation processes, 129 second-generation processes, 129-130 solvolysis, 130 Liquefaction o f carbohydrates experimental procedures, 114 yields o f aromatic compounds, 115,116/ yields o f solvent-free extracts, 114,115/ Liquefaction o f wood effect o f heating rate and temperature, 221/,222-223,224/ experimental procedures, 221 history, 220 H P S E C o f oils, 222,224/ influence o f iron, 223/,225,226/",227 influence o f residue time, 223/ thermogravimetry o f oils, 223 226f yields, 222/,223 yields vs. residence time, 223,225/ L i q u i d fuels, advantages, 1 Low-pressure upgrading o f t

vacuum-pyro lys is oils from wood average values o f coke, residuum, and hydrocarbon yield for

oils, 295,299/300 characteristics o f pyrolysis oils, 295,29ty" experimental conditions and results, 295,297-298/ experimental design, 293,296/" experimental procedures, 293 G C - F T I R analyses, 304,305-306/ G C - F T I R analysis o f oils and residues, 295 identification o f compounds, 304/.307/ product distribution vs. time o n stream, 300,303/304 pyrolysis o i l , 291/.293 reactions, 304,308 schematic o f o i l precoker and reactor, 293,294/ weight percent o f oxygenates i n products, 300,302/" weight percent o f products, 300,301/

Mass spectrometry for pyrolysis o i l characterization experimental procedures, 190-191 low-voltage mass spectra, 191,192/",193

Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ix002

350 Milled-wood lignin catalytic liquefaction, 258,26Qf,261 description, 242 effects of catalyst decay and transport o n liquefaction, 261 probability distribution functions for molecular weight, 242,244/ pyrolysis, 258,25S>f structure, 242-243,246/ M o i s t biomass high-pressure liquefaction, 179-186 utilization of o i l products, 186 Molecular-beam mass spectrometry of biomass pyrolysis product conversion effect of cofeeding wood and methanol over H Z S M - 5 effect of temperature o n product distribution, 316318/319 effect of weight hourly space velocity o n product distribution, 316,318/319 experimental apparatus and approach, 3 1 2 - 3 1 3 goal, 311-312 hydrocarbon yields, 320,321/322-323/ methanol and wood conversion product classes, 314315/316,317/ model compound products over Z S M - 5 pellets, 322,324/325 Multiple-hearth reactor heat transfer phenomena, 29 thermal efficiency, 29 See also V a c u u m pyrolysis multiple-hearth reactor Multistage vacuum pyrolysis, description, 13 M u n i c i p a l solid waste analytical results from pyrolysis, 83,85-86/ basic research programs o n pyrolysis, 8 0 - 8 2 bench-scale studies o n pyrolysis, 82 characterization of liquids, 82-83,84/" composition ranges, 79,80/ pyrolytic reactions, 7 9 - 8 0

Ν Nickel-hydrogen liquefaction system description, 93 See also Steam liquefaction of poplar chips, 93 Nuclear magnetic resonance for pyrolysis o i l characterization experimental procedures, 191 integrated intensities of aliphatic, olefinic, and aromatic regions, 193,195/

PYROLYSIS OILS F R O M

BIOMASS

O i l production, high-pressure thermal treatment of black liquors, 104-111 O i l s , molecular weight reduction, 101-102

Physical properties, tars, 60 Poplar wood chips, steam liquefaction, 9 2 - 1 0 2 Postpyrolysis processing, effect o n composition of pyrolysis oils, 4 - 5 Primary pyrolysis oils physical and chemical properties, 37 production i n vortex reactor, 3 1 - 3 9 Primary vapors o f pyrolysis, elemental balance, 3738/ Pyrolysis definition, 2 progression of chemicals, 56 types of processes, 56,5