Chemistry and Characterization of Coal Macerals 9780841208384, 9780841210806, 0-8412-0838-7

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Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.fw001

Chemistry and Characterization of Coal Macerals

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.fw001

ACS SYMPOSIUM SERIES

252

Chemistry and Characterization of Coal Macerals Randall E. Winans, EDITOR Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.fw001

Argonne National Laboratory

John C. Crelling,

EDITOR Southern Illinois University at Carbondale

Based on a symposium sponsored by the Division of Fuel Chemistry at the 185th Meeting of the American Chemical Society, Seattle, Washington, March 20-25, 1983

American Chemical Society, Washington, D.C. 1984

Library of Congress Cataloging in Publication Data Chemistry and characterization of coal macérais. (ACS symposium series, ISSN 0097-6156; 252) Bibliography: p. Includes indexes.

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.fw001

1. Maceral—Congresses. I. Winans, Randall E., 1949. II. Crelling, John C. III. American Chemical Society. Division of Fuel Chemistry. IV. Series. TP325.C4416 1984 ISBN 0-8412-0838-7

662.6'2

84-6260

Copyright © 1984 American Chemical Society All 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 pay the stated per copy fee through the Copyright Clearance Center, Inc., 21 Congress Street, Salem, M A 01970, 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 THE UNITED STATES OF AMERICA

ACS Symposium Series M. Joan Comstock, Series Editor

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.fw001

Advisory Board Robert Baker U.S. Geological Survey

Geoffrey D. Parfitt Carnegie-Mellon University

Martin L . Gorbaty Exxon Research and Engineering Co.

Theodore Provder Glidden Coatings and Resins

Herbert D. Kaesz University of California-Los Angeles

James C. Randall Phillips Petroleum Company

Rudolph J. Marcus Office of Naval Research

Charles N. Satterfield Massachusetts Institute of Technology

Marvin Margoshes Technicon Instruments Corporation

Dennis Schuetzle Ford Motor Company Research Laboratory

Donald E . Moreland USDA, Agricultural Research Service W. H . Norton J. T. Baker Chemical Company Robert Ory USDA, Southern Regional Research Center

Davis L . Temple, Jr. Mead Johnson Charles S. Tuesday General Motors Research Laboratory C. Grant Willson IBM Research Department

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.fw001

FOREWORD 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 since symposia may embrace both types of presentation.

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.pr001

PREFACE C O A L IS AN E X T R E M E L Y C O M P L E X , heterogeneous material that is difficult to characterize. It is a rock formed by geological processes and composed of a number of distinct organic substances called macérais and of lesser amounts of inorganic entities called minerals. Each coal maceral and mineral has a unique set of physical and chemical properties that contributes to the overall behavior of coal. Although much is known about the mineral properties of coal, surprisingly little is known about the properties of the individual macérais. This volume covers a wide range of fundamental topics in coal maceral science that varies from the biological origin of macérais to their chemical reactivity. Several chapters report novel applications of instrumental techniques for maceral characterization. These new approaches include solid C NMR, electron spin resonance, IR spectroscopy, fluorescence microscopy, and mass spectrometry. A recently developed method for maceral separation is also presented; many of the new instrumental approaches have been applied to macérais separated by this new method. The contributions in this volume present a sampling of the new directions being taken in the study of coal macérais to further our knowledge of coal petrology and coal chemistry. , 3

R A N D A L L E . WINANS

Argonne National Laboratory JOHN C. CRELLING

Southern Illinois University at Carbondale January 23, 1984

ix

1 Chemistry and Characterization of Coal Macerals: Overview RANDALL E. WINANS Chemistry Division, Argonne National Laboratory, Argonne, IL 60439

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JOHN C. CRELLING Department of Geology, Southern Illinois University at Carbondale, Carbondale, IL 62901 The Maceral Concept All of the papers i n t h i s book deal with the chemistry and c h a r a c t e r i z a t i o n of coal macerals and, as such, recognize the heterogeneous nature of c o a l . Coal is, i n f a c t , a rock derived from a v a r i e t y of plant m a t e r i a l s which have undergone a v a r i e t y of p h y s i c a l and chemical t r a n s f o r m a t i o n s . While a number of chemical s t u d i e s of coal have found the concept of a s i n g l e "coal molecule" u s e f u l , the papers i n t h i s book are aimed at c h a r a c t e r i z i n g i n some way the various macromolecules that comp r i s e the many kinds of coal macerals. Although the heterogeneous nature of coal has long been recognized i n m i c r o s c o p i c a l s t u d i e s , for example by White and Thiessen i n 1913 (1) and i n 1920 ( 2 ) , the term "maceral" was introduced only i n 1935 by Marie C. Stopes ( 3 ) . In t h i s paper (page 11) she says: "I now propose the new word "Maceral" (from the L a t i n macerare, to macerate) as a distinctive and comprehensive word tallying with the word "mineral". I t s d e r i v a t i o n from the L a t i n word t o "macerate" appears to make it p e c u l i a r l y a p p l i c a b l e to c o a l , f o r whatever the o r i g i n a l nature of the c o a l s , they now all c o n s i s t of the macerated f r a g ments of v e g e t a t i o n , accumulated under w a t e r . " The concept behind the word "macerals" i s that the complex of b i o l o g i c a l u n i t s represented by a f o r e s t t r e e which crashed i n t o a watery swamp and there p a r t l y decomposed and was macerated i n the process of coal formation, d i d not i n that process become uniform throughout but still retains delimited regions optically differing under the 0097-6156/84/0252-000106.00/0 © 1984 American Chemical Society

2

COAL MACERALS

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch001

microscope, which may or may not have d i f f e r e n t chemical formulae and p r o p e r t i e s . These organic u n i t s , composing the coal mass I proposed to c a l l m a c é r a i s , and they are the d e s c r i p t i v e equivalent of the i n o r g a n i c u n i t s composing rock masses and u n i v e r s a l l y c a l l e d m i n e r a l s , and to which p e n o l o g i s t s are well accustomed t o give distinctive names." The concept was well received and the term maceral i s now recognized around the w o r l d . Today, many coal s c i e n t i s t s , e s p e c i a l l y those outside of North America, regard coal m a c é r a i s as the smallest m i c r o s c o p i c a l l y recognizable u n i t present i n a sample. However, i n 1958 Spackman ( 4 J presented a concept of m a c é r a i s that i s s i g n i f i c a n t l y d i f f e r e n t and more useful i n the chemical aspects of coal s c i e n c e : ". . . macérais are organic substances, or o p t i c a l l y homogeneous aggregates of organic substances, possessing distinctive physical and chemical p r o p e r t i e s , and o c c u r r i n g n a t u r a l l y i n the sedimentary, metamorphic, and igneous m a t e r i a l s of the e a r t h . " The essence of t h i s concept i s that m a c é r a i s are d i s t i n g u i s h e d by t h e i r p h y s i c a l and chemical p r o p e r t i e s and not n e c e s s a r i l y by t h e i r p é t r o g r a p h i e form; t h u s , even though two substances may be derived from the same kind of plant t i s s u e , f o r example, c e l l w a l l m a t e r i a l , and have a s i m i l a r p é t r o g r a p h i e appearance, they would be d i f f e r e n t m a c é r a i s i f they had d i f f e r e n t chemical or physical properties. Maceral

Characterization

Two serious problems confront the coal s c i e n t i s t t r y i n g to c h a r a c t e r i z e coal m a c é r a i s . F i r s t , the m a c é r a i s are very d i f f i c u l t to separate from the coal matrix and i t i s , t h e r e f o r e , rare to have a pure maceral concentrate to study. For t h i s reason much of the maceral c h a r a c t e r i z a t i o n has been done i n s i t u with pétrographie methods i n c l u d i n g r e f l e c t a n c e and fluorescence analysis. The second problem i s that coal i s , i n t r u t h , a metamorphic rock; any given coal sample i s part of a metamorphic (rank) s e r i e s ranging from peat through l i g n i t e , sub-bituminous c o a l , bituminous c o a l , to a n t h r a c i t e . As the rank of coal i n c r e a s e s , the p h y s i c a l and chemical p r o p e r t i e s of the coal change, and t h e r e f o r e , the various m a c é r a i s change a l s o . The nature of t h i s change i s poorly understood; f o r example, i t may be a continuous change analogous to s o l i d s o l u t i o n i n m i n e r a l s , or i t may be discontinuous i n some way. The inescapable cons t r a i n t of the rank property of coal m a c é r a i s i s that i n any

1. W I N A N S A N D C R E L L I N G

Overview

3

study of maceral p r o p e r t i e s , the coal rank must always be d e t e r mined and i n c l u d e d i n maceral c h a r a c t e r i z a t i o n . Even i n s t u d i e s of s i m i l a r m a c é r a i s i n the same coal seam, v a r i a t i o n i n coal rank can occur and, t h e r e f o r e , cause d i f f e r e n c e s i n maceral properties.

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Development of P é t r o g r a p h i e

Characterization

The development of the p é t r o g r a p h i e c h a r a c t e r i z a t i o n of coal m a c é r a i s c l o s e l y f o l l o w e d the development of p é t r o g r a p h i e techniques. Some of the e a r l i e s t p é t r o g r a p h i e c h a r a c t e r i z a t i o n of coal m a c é r a i s used mainly t r a n s m i t t e d l i g h t techniques and examples can be found i n the papers of Cady ( 5 J , Marshall ( 6 ) , and Parks and O'Donnell (_7J. Although the technique of r e f l e c t e d l i g h t microscopy was a l s o used elsewhere, i t was developed and used e x t e n s i v e l y i n Germany ( 8 - 1 0 ) , A l s o , during the l a t e 1 9 4 0 ' s Hoffmann and Jenkner ( 1 1 ) developed the use of optical r e f l e c t a n c e measurements t o c h a r a c t e r i z e some coal macérais. In the l a t e 1950's and e a r l y 1960's the r e f l e c t a n c e charact e r i z a t i o n of coal m a c é r a i s was used with great success i n c a r bonization studies. For example, i t was shown by Spackman _et_ al. ( 1 2 ) that the p r o p e r t i e s of the various coal m a c é r a i s c o n t r o l l e d the c a r b o n i z a t i o n behavior of c o a l . Based on t h i s work and that of Ammosov et_ _al_. ( 1 3 ) methods were developed t o p r e d i c t the c a r b o n i z a t i o n p r o p e r t i e s of s i n g l e coals and coal blends (14-17), These methods use a maceral point count a n a l y s i s to give the maceral d i s t r i b u t i o n and a r e f l e c t a n c e a n a l y s i s to c h a r a c t e r i z e the thermal p r o p e r t i e s of the m a c é r a i s . The most recent p é t r o g r a p h i e method used to c h a r a c t e r i z e coal m a c é r a i s i s q u a n t i t a t i v e f l u o r e s c e n c e a n a l y s i s . In t h i s method the m a c é r a i s are e x c i t e d by i n c i d e n t u l t r a v i o l e t l i g h t and the spectrum of the r e s u l t i n g f l u o r e s c e n t l i g h t i s used t o c h a r a c t e r i z e the m a c é r a i s . This technique has led to the d i s covery of new m a c é r a i s ( 1 8 ) , the q u a n t i t a t i v e d i s c r i m i n a t i o n between c e r t a i n m a c é r a i s i n a given coal ( 1 9 ) , and the c o r r e l a t i o n of the f l u o r e s c e n c e p r o p e r t i e s of m a c é r a i s to the rank, and t e c h n o l o g i c a l p r o p e r t i e s of coal ( 2 0 - 2 2 ) , Previous P é t r o g r a p h i e

Characterization

As Stopes seems to have a n t i c i p a t e d , a l a r g e number of m a c é r a i s have been i d e n t i f i e d and named. A l l m a c é r a i s , however, can be conveniently grouped i n t o three major s u b d i v i s i o n s v i t r i n i t e , l i p t i n i t e , and i n e r t i n i t e . The v i t r i n i t e group of macérais are derived from plant c e l l w a l l material (woody t i s s u e ) and u s u a l l y make up 50-90% of most North American coals. Although there are a large number of named v a r i e t i e s of

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4

COAL MACERALS

vitrinite macérais, it is i n t e r e s t i n g to note that most researchers studying the v i t r i n i t e m a c é r a i s d i v i d e them i n t o two general groups. The terms t e l e c o l u n i t e and d e s m o c o l u n i t e are used i n many cases to d i s t i n g u i s h these two groups. Brown _et_ a l . (23) used the term v i t r i n i t e A to separate a homogeneous higher r e f l e c t a n c e v a r i e t y from a d u l l e r , f i n e l y laminated, matrix v a r i e t y ( v i t r i n i t e B ) . T a y l o r (24) used t r a n s m i s s i o n e l e c t r o n microscopy (TEM) to show that at high m a g n i f i c a t i o n v i t r i n i t e A was homogeneous w h i l e v i t r i n i t e Β contained i n c l u ­ sions of other m a c é r a i s . Al pern (25) d i s t i n g u i s h e d homocol1 i ni t e and heterocol u n i t e along the same l i n e s . In c a r b o n i z a t i o n s t u d i e s Benedict et_ _al_. (26) found a l e s s r e a c t i v e v a r i e t y , p s e u d o v i t r i n i t e , c h a r a c t e r i z e d by a higher r e f l e c t a n c e and a more homogeneous nature than normal v i t r i n i t e . Although the terms are not s t r i c t l y synonymous, p s e u d o v i t r i n i t e , homocoll i n i t e , v i t r i n i t e A, and t e l e c o l l i n i t e , have the c o i n c i d e n t p r o p e r t i e s of higher r e f l e c t a n c e , greater homogeneity, and lower c a r b o n i z a t i o n r e a c t i v i t y than normal v i t r i n i t e , h e t e r o c o l l i n i t e , v i t r i n i t e B, and desmocol u n i t e . The appearance of pseudov i t r i n i t e under r e f l e c t e d white l i g h t i s shown i n Figure 1A. It a l s o should be noted that i t i s p s e u d o v i t r i n i t e that tends to occur i n homogeneous v i t r e o u s layers i n coal seams and, t h e r e f o r e , the material c o l l e c t e d i n the hand p i c k i n g of these l a y e r s tends to be p s e u d o v i t r i n i t e and not, i n f a c t , the more abundant normal v i t r i n i t e . The 1i p t i ni t e group of m a c é r a i s i s derived from the resinous and waxy parts of plants such as r e s i n , spores, and pollen. This group makes up 5-15% of most North American coals and i s the most a l i p h a t i c and hydrogen r i c h group of m a c é r a i s . The most common v a r i e t i e s of l i p t i n i t e m a c é r a i s are s p o r i n i t e , c u t i n i t e , and r e s i n i t e . S p o r i n i t e i s u s u a l l y the most abundant v a r i e t y and the study of s p o r i n i t e i n coal and other rocks i s the essence of the science of palynology i n which the various s p o r i n i t e morphologies are examined to d i s c e r n both age and botanical relationships. A good c o l l e c t i o n of papers on s p o r i n i t e i s found i n S p o r o p o l l e n i n (27), C u t i n i t e i s derived from c u t i c l e , the waxy c o a t i n g on l e a v e s , r o o t s , and stems. C u t i n i t e i s q u i t e r e s i s t a n t to weathering and i s sometimes concentrated as "paper c o a l " or "leaf c o a l " where i t can be e a s i l y e x t r a c t e d and c h a r a c t e r i z e d . One such occurrence i n Indiana has been s t u d i e d by Neavel e t . l l . (28-30), The r e s i n i t e m a c é r a i s are i n some ways the most varied group. They are derived from both the wound r e s i n s (terpenes) of p l a n t s and various other plant f a t s and waxes making up the l i p i d resins. The terpene-derived r e s i n i t e s are the most abundant type and they are found i n most North American coals as ovoid masses. However, i n some c o a l s , e s p e c i a l l y i n the western USA the r e s i n i t e occurs mainly as a secondary form showing

I.

WINANS A N D CRELLING

Overview

5

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch001

evidence of having been m o b i l i z e d (see Figure I B ) . This form i s of considerable interest because it can be commercially e x p l o i t e d and marketed as a chemical raw material ( 3 1 , 3 2 ) , The occurrence and i n f r a r e d s p e c t r a l p r o p e r t i e s of various r e s i n i t e s have been w e l l studied by Murchison and Jones (33-36), TeichmCfller has reported on the origin and fluorescence p r o p e r t i e s of secondary r e s i n i t e s (20), The i n e r t i n i t e group of m a c é r a i s i s derived from degraded woody t i s s u e and u s u a l l y makes up 5-40% of most North American c o a l s , although in some western Canadian, and a l l southern hemisphere c o a l s , i t can make up a greater percentage. The i n e r t i n i t e m a c é r a i s have the highest r e f l e c t a n c e , as seen i n Figure 1A and C, and carbon content i n any given coal and are u s u a l l y d i v i d e d i n t o f i v e general t y p e s . F u s i n i t e and semif u s i n i t e are c h a r a c t e r i z e d by w e l l - d e f i n e d c e l l t e x t u r e with f u s i n i t e having the highest r e f l e c t a n c e (see Figure ID). Semif u s i n i t e i s the most abundant i n e r t i n i t e maceral type and has the l a r g e s t range of r e f l e c t a n c e - between v i t r i n i t e and fusinite. M a c r i n i t e and semi-macrinite are s i m i l a r i n r e f l e c tance to f u s i n i t e and s e m i - f u s i n i t e , r e s p e c t i v e l y , but without the presence of c e l l t e x t u r e . The processes of both f o r e s t - f i r e c h a r r i n g and biochemical degradation (composting) have both been thought to be involved i n the o r i g i n of a l l of these maceral types (37-39), The f i f t h i n e r t i n i t e v a r i e t y , m i c r i n i t e , i s a granular h i g h - r e f l e c t a n c e material that may be both h i g h l y r e a c t i v e and of secondary o r i g i n ( 1 8 , 4 0 , 4 1 ) , In the f i r s t h a l f of t h i s i n t r o d u c t o r y chapter the maceral concept has been discussed and the main maceral groups and t h e i r important maceral types d e s c r i b e d . Emphasis has been placed on i n s i t u c h a r a c t e r i z a t i o n techniques which r e l y mostly on m i c r o scopy. The rest of t h i s chapter w i l l examine other techniques used f o r chemical c h a r a c t e r i z a t i o n and examine the r e a c t i v i t y of coal m a c é r a i s i n thermal processes. The a v a i l a b i l i t y of separated maceral concentrates was a necessary component of the s t u d i e s which w i l l be d e s c r i b e d . Separations The preparation of maceral concentrates f o r study has been achieved by one of two approaches, e i t h e r by hand p i c k i n g or by a v a r i e t y of techniques which e x p l o i t the v a r i a t i o n i n density between the various maceral groups. The f i r s t l e v e l of hand p i c k i n g i s the j u d i c i o u s sampling of l i t h o t y p e s . This term i s used to i d e n t i f y the various layers found i n a coal seam. For humic coals there are f o u r main designations of lithotypes v i t r a i n , c l a r a i n , d u r a i n , and f u s a i n ( 4 2 ) , V i t r a i n bands are sources of f a i r l y pure v i t r i n i t e group m a c é r a i s while f u s i n i t e and s e m i - f u s i n i t e can be obtained from f u s a i n . These are the

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6

COAL MACERALS

Figure 1. Photomicrographs of coal m a c é r a i s from the Elkhorn No. 3 seam Eastern Kentucky - hvA bituminous rank. Reflected l i g h t i n o i l , diameter of f i e l d , 300 microns, crushed p a r t i c l e pellets. A.

Large p a r t i c l e of p s e u d o v i t r i n i t e at r i g h t showing s e r r a t e d edges and well-developed c e l l t e x t u r e . P a r t i c l e at l e f t i s normal v i t r i n i t e with i n c l u s i o n s of s p o r i n i t e (dark gray) and i n e r t i n i t e ( w h i t e ) .

B.

P a r t i c l e s of v i t r i n i t e with c e l l - f i l l i n g s of dark r e s i n i t e .

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1.

WINANS A N D CRELLING

C.

P a r t i c l e made matrix with a i n the middle v i t r i n i t e are

D.

Inertinite right.

7

Overview

up of i n e r t i n i t e fragments i n a v i t r i n i t e zone of v i t r i n i t e running from l e f t to r i g h t of the p a r t i c l e . Dark zones at boundaries of cutinite.

macérais,

s e i n i - f u s i n i t e at

left

and f u s i n i t e at

8

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t y p i c a l m a c é r a i s which are concentrated by d i t i o n t o , i n some cases, r e s i n i t e s ( 4 3 ) . and the i n e r t i n i t e , m i c r i n i t e , tend to be the other m a c é r a i s which makes hand p i c k i n g

COAL MACERALS

hand p i c k i n g i n adThe other l i p t i n i t e s well dispersed among very d i f f i c u l t .

Due to the v a r i a t i o n i n chemical make up of coal m a c é r a i s , t h e i r d e n s i t i e s are d i f f e r e n t and t h i s property has been exp l o i t e d to produce maceral c o n c e n t r a t e s . Early studies in t h i s area have been reviewed by Golouskin ( 4 4 ) . Typically the m a c é r a i s are f r a c t i o n a t e d by the f l o a t - s i n k technique using heavy l i q u i d s ranging i n density from 1 . 2 - 1 . 5 g/cc. KrOger and coworkers (45) used mixtures of C C ^ - t o l u e n e to f r a c t i o n a t e each of four Ruhr c o a l s i n t o three groups. They found that l i p t i n i t e s f e l l i n the range p=1.20-1.25, v i t r i n i t e s p=1.30-1.35 and i n e r t i n i t e s which they claimed were mostly m i c r i n i t e p=1.401.45. A problem with using CCI4 i s that i t cannot be completely removed from the maceral f r a c t i o n s a f t e r separation ( 4 6 ) . A l s o , a p o r t i o n of the coal can be s o l u b i l i z e d i n these solvent mixtures. Others have used aqueous s a l t s o l u t i o n s . An example i s the technique used by van Krevelen and coworkers where coals crushed t o ~10 pm were f r a c t i o n a t e d i n aqueous ZnCl2 ( 4 7 ) . A problem with aqueous s o l u t i o n s i s the tendency for coal p a r t i c l e s to agglomerate, a tendency that increases as the s i z e of the p a r t i c l e s decreases. P o l a r solvents have been added to the aqueous s o l u t i o n s to d i s p e r s e the coal p a r t i c l e s . Normally, the f l o a t - s i n k method i s a c c e l e r a t e d by c e n t r i f u g i n g the s o l u tions. Kroger developed a continuous flow c e n t r i f u g a t i o n method f o r maceral group separation (45). F l o t a t i o n methods f o r maceral s e p a r a t i o n have up to now y i e l d e d l i m i t e d r e s u l t s , howe v e r , i n one study i t has been found that e x i n i t e s could be concentrated ( 4 8 ) . R e c e n t l y , a new approach f o r e x p l o i t i n g the density v a r i a t i o n i n m a c é r a i s to achieve s e p a r a t i o n has been developed. Dyrkacz and coworkers (49,50) have a p p l i e d density gradient c e n t r i f u g a t i o n (DGC) to d i v i d e coals i n t o narrow density f r a c tions which can y i e l d maceral concentrates of very high purity. The m u l t i - s t e p technique requires a two-stage g r i n d i n g procedure to produce a f a i r l y uniform p a r t i c l e s i z e d i s t r i b u t i o n of 3 microns, f i r s t by b a l l m i l l i n g and second by g r i n d i n g w i t h h i g h - v e l o c i t y nitrogen gas i n a f l u i d - e n e r g y m i l l . Next, the coal i s demineralized by HC1 and HF under nitrogen and f i n a l l y separated i n an aqueous CSCI2 gradient with a n o n - i o n i c s u r f a c tant to d i s p e r s e the p a r t i c l e s . D e m i n e r a l i z a t i o n has been found to be necessary to achieve h i g h - r e s o l u t i o n s e p a r a t i o n s . In the p a s t , i t was thought that 3 micron p a r t i c l e s were too small f o r pétrographie identification. Dyrkacz has shown that although d i f f i c u l t , i t i s p o s s i b l e to d i s t i n g u i s h the three main groups e s p e c i a l l y with the use of fluorescence microscopy f o r the liptinites. In f a c t , s p o r i n i t e and a l g i n i t e can be separated

1.

WINANS A N D CRELLING

Overview

9

w i t h the DGC technique and d i s t i n g u i s h e d petrographically (50). Five of the chapters i n t h i s book d e s c r i b e s t u d i e s of m a c é r a i s concentrated by t h i s technique. Two other sets of separated m a c é r a i s have been s t u d i e d f a i r l y e x t e n s i v e l y i n c l u d i n g the samples prepared by Fenton and Smith (51) which have been termed the " B r i t i s h M a c é r a i s " and more r e c e n t l y a set obtained by A l l a n (52) separated by e i t h e r hand p i c k i n g or by a modified van Krevelen method ( 4 7 ) . Charact e r i z a t i o n of these samples w i l l be described i n the next section.

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch001

Characterization E a r l y s t u d i e s on separated m a c é r a i s were done by Kroger ( 4 5 , 4 8 . 5 3 - 5 8 ) , van Krevelen ( 4 7 , 5 9 ) , and Given ( 6 0 , 6 1 ) . KrCJger and coworkers c h a r a c t e r i z e d t h e i r set of m a c é r a i s from composit i o n parameters ( 5 3 ) , heats of wetting ( 5 4 ) , p y r o l y s i s (55,56) x-ray d i f f r a c t i o n " ^ ? ^ ) and by process behavior such as c a r b o n i zation (53,58). In a s i n g l e paper, Dormans, Huntjens, and van Krevelen presented a s i g n i f i c a n t amount of information on t h e i r set of m a c é r a i s which i s f u r t h e r discussed i n van Krevelen's book (59). They proposed a method of presenting elemental a n a l y s i s data which i s now r e f e r r e d t o as a van Krevelen p l o t and used e x t e n s i v e l y by organic geochemists. An example of such a p l o t i s shown i n Figure 2 with the t y p i c a l d i s t r i b u t i o n f o r the three main maceral groups. The p l o t shows the d i f f e r e n c e s between m a c é r a i s , the v a r i a t i o n w i t h i n m a c é r a i s and the changes i n t h e i r composition with i n c r e a s i n g c o a l i f i c a t i o n . Given and coworkers studying the " B r i t i s h M a c é r a i s " took more of an organic chemist's approach to c h a r a c t e r i z a t i o n . The m a c é r a i s were subjected to solvent e x t r a c t i o n , l i t h i u m reduction, hydroxyl d e t e r m i n a t i o n , o x i d a t i o n , and r e a c t i o n with various reagents. N-bromosuccinimide (NBS) was used to brominate a l i p h a t i c carbons which i n the case f o r four m a c é r a i s from an Aldwarke S i l k s t o n e coal y i e l d e d per 100 carbon atoms the f o l l o w i n g d i s t r i b u t i o n of hydrogen which i s replaced by bromine (61): v i t r i n i t e 16, e x i n i t e 25 1/2, m i c r i n i t e 12, and f u s i n i t e 6. These values were s i m i l a r to those obtained by the c a t a l y t i c dehydrogenation (62) of hvA bituminous coal m a c é r a i s which y i e l d e d i n atoms of hydrogen per 100 carbons: v i t r i n i t e 25, e x i n i t e 3 1 , m i c r i n i t e 18, and f u s i n i t e 5. Such r e s u l t s would suggest that v i t r i n i t e s and e x i n i t e s should be more r e a c t i v e i n thermal processes and indeed t h i s has been found to be t r u e and w i l l be discussed i n the s e c t i o n on r e a c t i v i t y .

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch001

10

COAL MACERALS

Figure 2 . A van Krevelen p l o t showing approximate bands f o r the three main maceral groups.

11

Overview

1. WINANS AND CRELLING

Given determined hydroxy1 groups i n the separated m a c é r a i s by a c e t y l a t i o n (60,61). A c i d i c hydroxyl group abundance decreased from v i t r i n i t e > e x i n i t e > f u s i n i t e . The percentages of oxygen as OH i n f u s i n i t e s were low, averaging about 12% and were independent of rank. Both v i t r i n i t e and e x i n i t e hydroxyl content decrease with rank a f t e r passing through a maximum. Krtfger and BCfrger (63) presented data which d i f f e r from that reported by Given perhaps because of v a r i a t i o n s i n the samples. Aromaticity. One c h a r a c t e r i s t i c t h a t describes coal m a c é r a i s which has received much a t t e n t i o n i s the f r a c t i o n of aromatic carbons ( f ) . In an e a r l y study, van Krevelen used a densimetric technique to estimate the f values f o r a s e r i e s of m a c é r a i s (47). In g e n e r a l , the f values were found to increase from l i p t i n i t e < v i t r i n i t e < i n e r t i n i t e f o r any given c o a l . Using broad l i n e proton NMR Ladner and Stacey estimated hydrogen d i s t r i b u t i o n s and f ' s f o r a set of " B r i t i s h M a c é r a i s " ( 6 4 ) . A g a i n , the data i n d i c a t e d that l i p t i n i t e s and v i t r i n i t e s contain a s i g n i f i c a n t amount of hydroaromatics. Broad l i n e NMR data on i l l - d e f i n e d "dull c o a l " m a c é r a i s have been reported (65). a

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch001

a

a

The interest

advent

of

solid

i n this

area.

ιο C NMR has

Retcofsky

resulted

and V a n d e r h a r t

i n an increased (66) r e p o r t

f

a

values f o r m a c é r a i s from a Hernshaw hvA bituminous coal using cross p o l a r i z a t i o n (CP). Z i l m et a l . (67) used a combination of CP and magic angle s p i n n i n g ( f i  S T ~ t o examine some of A l l a n ' s macérais.

Analyses

o f t h e Hernshaw

samples

have

been

repeated

using CP/MAS (68) and i n the paper the authors concluded t h a t m a c é r a i s although more homogenous than whole c o a l s , are s t i l l q u i t e complex. Recently the f values of m a c é r a i s separated by d e n s i t y gradient c e n t r i f u g a t i o n have been reported ( 6 9 , 7 0 ) . Selected values from these s t u d i e s are presented i n Table I. The general trend f i r s t noted by van Krevelen i s e v i d e n t , but t o t a l agreement between d i f f e r e n t s t u d i e s i s not e v i d e n t . The v a r i a t i o n may be due to the techniques used or to v a r i a t i o n s in samples. a

Free R a d i c a l s in M a c é r a i s . E l e c t r o n spin resonance (ESR) has been used to study carbon f r e e r a d i c a l s i n c o a l s , and t o some e x t e n t , separated m a c é r a i s . The technique provides i n f o r mation on r a d i c a l density and the environment of the r a d i c a l s . The resonance p o s i t i o n , termed the g - v a l u e , i s dependent on the s t r u c t u r e of the molecule which contains the f r e e e l e c t r o n . The l i n e width i s a l s o s e n s i t i v e to the environment of the unpaired electron. In an e a r l y study, KrOger (71) reported that the s p i n c o n c e n t r a t i o n varied between maceral groups with l i p t i n i t e < vitrinite « inertinite. For t h i s l i m i t e d set of samples the s p i n c o n c e n t r a t i o n increases with rank f o r l i p t i n i t e s and v i t r i n i t e s and decreases f o r the m i c r i n i t e samples. On the other hand, van Krevelen (72) found the same general r e s u l t s except

Vitrinite

Liptinite

Inertinite

Maceral Group Densimetric CP CP/MAS CP CP/MAS CP/MAS Broad!ine H NMR CP/MAS Densimetric CP CP/MAS CP/MAS Broadline H NMR CP/MAS CP/MAS CP/MAS CP/MAS Densimetric CP CP/MAS CP/MAS Broadline H NMR CP/MAS CP/MAS

87.2 85.9 85.9 91.5 91.5 91.6 91.6 80.2 85.7 86.2 86.2 82.6 82.6 80.2 81.6 87.1 82.8 85.0 85.2 85.2 82.6 82.6 78.4 86.6

Average Hernshaw II II II Markham Main Il II Ohio No. 5 Average Hernshaw II Markham Main Il II Ohio No. 5 Il II II Silkstone Torbane H i l l Average Hernshaw II Markham Main Il II Ohio No. 5 Silkstone

Micrinite II II Fusinite

Sporinite Algini te Sporinite Alginite

Technique

Macérais

%C

of Separated

Sample

a

Aromaticities (f )

Maceral

I.

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch001

47 66 68 70 64 69 69 67 67 47 66 68 70 64 69 67

0.73 0.66 0.67 0.45 0.46 0.45 0.18 0.51 0.13 0.85 0.85 0.78 0.76 0.61 0.68 0.66

Ref. 47 66 68 66 68 70 64 69

a

0.92 0.85 0.78 0.94 0.92 0.82 0.92 0.75

f

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch001

1. W I N A N S A N D C R E L L I N G

Overview

13

that spin density f o r mi c r i ni tes increased with rank. It i s p o s s i b l e that the m a c é r a i s termed m i c r i n i t e i n these s t u d i e s were a c t u a l l y other low r e f l e c t a n c e i n e r t i n i t e s . In l a t e r studies, i t was shown that at l e a s t f o r the inertinite, f u s i n i t e , s p i n concentration i s f a i r l y independent of rank (73,74). Austen et_ aj_. (73) found that v i t r i n i t e s and l i p t i n i t e s e x h i b i t e d s i m i l a r esr l i n e w i d t h s which were rank dependent and decreased i n samples with a carbon content greater than -82%, w h i l e f u s i n i t e had narrower l i n e w i d t h s which were rank independent. Upon p y r o l y s i s , the f r e e spin concentration f o r v i t r a i n increased while t h e i r l i n e w i d t h s decreased. Furthermore l i t t l e change was observed f o r f u s a i n s up to about 650°C. These results have been r e c e n t l y confirmed (75). The authors concluded that f u s i n i t e s are formed p r i o r to i n c o r p o r a t i o n i n t o the sediment (73). Retcofsky (74) found higher g-values f o r lower rank v i t r a i n s which i s probably due to the heteroatom content which decreases with i n c r e a s i n g rank. Organic S t r u c t u r a l A n a l y s i s . Several approaches have been taken to obtain more d e t a i l e d information on the v a r i a t i o n of organic s t r u c t u r e s found i n m a c é r a i s . A widely used technique i s p y r o l y s i s (Py) combined with e i t h e r gas chromatography (GC), mass spectrometry (MS) or GCMS. Another method which has been used e x t e n s i v e l y with whole coals and only to a l i m i t e d extend with coal m a c é r a i s i s s e l e c t i v e o x i d a t i v e d e g r a d a t i o n . Recent s t u d i e s i n c l u d e a s e r i e s of papers by Douglas and coworkers on the maceral samples separated by A l l a n ( 5 2 ) . GC was used t o examine the v a r i a t i o n s i n hydrocarbon d i s t r i b u t i o n s between e x t r a c t s of v i t r i n i t e s and s p o r i n i t e s of various ranks (76,77) and a l g i n i t e s (78) and Py-GCMS to c h a r a c t e r i z e a l l three sets of whole m a c é r a i s ( 7 9 ) . Triterpanes were found i n a l l the e x t r a c t s and i t i s i n t e r e s t i n g to note that the amount of n-alkanes f o r v i t r i n i t e s and s p o r i n i t e s increased with rank. n-Alkanes were more abundant i n the s p o r i n i t e s and were longer i n chain length (]7_). L a r t e r and Douglas (79) demonstrated that Py-GCMS has potential as a chemical fingerprinting method for coal macérais. More r e c e n t l y , A l l a n and L a r t e r (80) have proposed that s i m i l a r i t i e s observed f o r s p o r i n i t e and v i t r i n i t e s of the same rank may be due to " d i f f e r e n t molecular combinations of s i m i l a r unit structures". R e c e n t l y , P h i l p and Saxby have c h a r a c t e r i z e d a set of A u s t r a l i a n m a c é r a i s by C u r i e - p o i n t PyGCMS (81). Another r a p i d technique f o r c h a r a c t e r i z i n g n o n - v o l a t i l e m a t e r i a l s which has been a p p l i e d to coal m a c é r a i s i s p y r o l y s i s mass spectrometry (Py-MS) (82-84). The e v a l u a t i o n of the complex data produced by t h i s technique has been aided by the use of s t a t i s t i c a l a n a l y s i s . Homologous s e r i e s of molecules can be i d e n t i f i e d and v a r i a t i o n between the various maceral groups i s quite evident.

14

COAL MACERALS

P i r e c t C h a r a c t e r ! z a t i o n Techniques. The J_n_ s i t u a n a l y s i s of elemental composition of coals by ion microprobe was f i r s t demonstrated by Dutcher et_ aj_. (85). Raymond (86) has a p p l i e d t h i s technique to examine the v a r i a t i o n i n composition of coal m a c é r a i s which has been e s p e c i a l l y e f f e c t i v e f o r l o o k i n g at s u l f u r d i s t r i b u t i o n . An example of the organic s u l f u r d i s t r i b u t i o n f o r two bituminous coals i s shown i n Table II which i s taken from reference ( 8 6 ) . Note that the l i p t i n i t e s contain the Table I I . Distribution M a c é r a i s (86_)

of

Organic

Sulfur

in

Bituminous Coal

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch001

U. Elkhorn hvAb Coal

wt% of sample wt% S Q

V

Pv

F

Sf

Ma

Mi

S

R

38.9 0.73

2.2 0.45

7.1 0.30

5.3 0.38

13.2 13.3 17.6 2.4 0.64 0.60 0.94 1.03

Ohio #4 hvBb Coal

wt% of sample wt% S Q

V

Pv

F

Sf

Ma

Mi

S

72.0 2.93

3.0 2.56

3.9 0.73

5.7 1.51

0.3 0.92

7.8 7.3 2.90 3.89

( A l l wt% on dmmf b a s i s ) V = v i t r i n i t e , Pv = p s e u d o v i t r i n i t e , F = f u s i n i t e , Sf = s e m i - f u s i n i t e , Ma = m a c r i n i t e , Mi = m i c r i n i t e , S = sporinite, R = resinite. greatest concentration of s u l f u r w h i l e the f u s i n i t e s and semif u s i n i t e s have the l e a s t amount. A l s o , Raymond has found that t y p i c a l l y the s u l f u r content i n v i t r i n i t e i s c l o s e to the average value f o r whole coal even when v i t r i n i t e i s not the major component. An i n i t i a l study on the use of secondary ion mass spectrometry (SIMS) to analyze m a c é r a i s has been reported (87) and appears to have p o t e n t i a l as a c h a r a c t e r i z a t i o n t e c h nique. The c l a s s i c IR paper on coal m a c é r a i s was published by Bent and Brown (88). They examined the v a r i a t i o n i n a l i p h a t i c and aromatic hydrocarbons f o r a set of the " B r i t i s h M a c é r a i s " . In the conclusions they noted that the d i f f e r e n c e s between " e x i n i t e " and v i t r i n i t e i s i n the "degree of a r o m a t i c i t y rather than of kind" and that with i n c r e a s i n g rank t h i s d i f f e r e n c e disappears.

1.

WINANS A N D CRELLING

Overview

15

R e a c t i v i t y of M a c é r a i s in Conversion Processes The behavior of coal m a c é r a i s in processes other than coking has received l i m i t e d a t t e n t i o n . Neavel (89) reviewed some of the important work i n r e l a t i o n to coal coking g a s i f i c a t i o n , combustion, and p y r o l y s i s . The r e a c t i v i t y of m a c é r a i s i n l i q u e f a c t i o n has r e c e n t l y received more a t t e n t i o n . E a r l y work was done at the U.S. Bureau of Mines and has been reviewed by Davis . e t _ l l - (22.) Given _et_.al_. (91 ) . In these reviews, the authors noted that there i s a d i f f i c u l t y i n comparing t h i s e a r l y work to recent studies due to the d i f f e r e n c e in how the m a c é r a i s are i d e n t i f i e d . However, t h i s e a r l y work does i n d i c a t e that i n e r t i n i t e s are l e s s r e a c t i v e i n l i q u e f a c t i o n . More r e c e n t l y , batch autoclave runs using t e t r a l i n as a solvent (90) demons t r a t e d that v i t r i n i t e s and e x i n i t e s ( s p o r i n i t e and c u t i n i t e ) are q u i t e r e a c t i v e . In two papers (91,92) i t has been noted that Utah r e s i n i t e s are g r e a t l y s o l u b i l i z e d . However, the question of actual r e s i n i t e r e a c t i v i t y i s s t i l l unclear s i n c e at l e a s t the Utah r e s i n i t e s tend to be n a t u r a l l y very s o l u b l e in organic s o l v e n t s .

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch001

a

n

d

L i q u e f a c t i o n of i n e r t i n i t e s i s not always as poor as the name would i m p l y . Table III shows some conversion data taken from Ref. (91 ), where conversion i s defined as ethyl acetate s o l u b l e s plus gases. The low r e f l e c t i n g A u s t r a l i a n f u s i n i t e s and semi-fusinites are reactive compared to the Illinois samples. This has been confirmed by a recent study on A u s t r a l i a n i n e r t i n i t e s (93) where i t has been found that at higher temperatures ( 4 5 ( Η Γ ) up to 54% of the i n e r t i n i t e was c a l c u l a t e d to be converted. This d i f f e r e n c e between the A u s t r a l i a n and North American i n e r t i n i t e s has a l s o been observed in c a r b o n i z a t i o n reactions (94). Product c h a r a c t e r i z a t i o n from l i q u e f a c t i o n has not been extensive. P h i l ρ and R u s s e l l (95) have examined products by PyGCMS from metal h a l i d e c a t a l y z e d h y d r o g é n a t i o n of a v i t r i n i t e , a l g i n i t e , and i n e r t i n i t e , each from a d i f f e r e n t s o u r c e . They were able to c o r r e l a t e Py-GCMS r e s u l t s with r e a c t i o n temperature. K i n g , et_ al_. (96) examined the short contact time l i q u e f a c t i o n of m a c é r a i s separated by DGC from a s i n g l e hvB b i t u m i nous c o a l . They found c o r r e l a t i o n s between density and r e a c t i v i t y and composition of the products. Conclusions This introduction is intended to h i g h l i g h t the past research on coal m a c é r a i s which has led to many of the s t u d i e s presented i n t h i s book. Coal science i s a very complex f i e l d , but i t i s important to recognize that the study of m a c é r a i s

16

COAL MACERALS

e i t h e r i n s i t u or a f t e r separation i s a big step i n the t i o n of reducing the complexity of the s c i e n c e .

direc­

Acknowledgments

R.E.W. acknowledges the support of the O f f i c e of B a s i c Energy S c i e n c e s , D i v i s i o n of Chemical S c i e n c e s , U.S. Department of Energy under contract W-31-109-ENG-38. J . C . C . would l i k e to acknowledge support by the Gas Research I n s t i t u t e . Table I I I .

L i q u e f a c t i o n of F u s i n i t e and S e m i - F u s i n i t e

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch001

1 PSOC 303 C a l l i d e Seam Australia

Maceral Per Cent F SF Γ"

(91)

R^ax (F+SF)

Conversion % daf

15

4

73

3

1.26

40

31

14

44

9

1.49

41

21

65

12

2

3.50

25

17

68

14

0

3.52

15

PSOC 304 Big seam Australia PSOC 261, Fusain I l l i n o i s No. 6 PSOC 261A, Fusain I l l i n o i s No. 6 PSOC 262, Fusain I l l i n o i s No. 6 Williamson C o . , IL PSOC 263, Fusain I l l i n o i s No. 6 P e o r i a C o . , IL

16

69

14

0

4.18

21

8

48

44

0

3.05

13.5

PSOC 264, Fusain C o l c h e s t e r No. 2 Fulton C o . , IL

10

62

27

0

4.23

12

V = v i t r i n i t e ; F = f u s i n i t e ; SF i n e r t i n i t e s R max = r e f l e c t a n c e .

= semi-fusinite;

I

=

other

Q

Literature Cited 1.

White, D.; 390 pp.

Thiessen,

R. U.S. Bur. Mines

Bull.

No. 38 1913,

1. W I N A N S A N D C R E L L I N G

2. 3. 4. 5. 6. 7. 8. 9.

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch001

10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28.

Overview

17

Thiessen, R. U.S. Bur. Mines Bull. No. 117 1920, 296 pp. Stopes, Marie C. Fuel 1935, 14, 4 - 1 3 . Spackman, W. Trans Ν . Y . Acad. Sci. 1958, 20, No. 4, 411423. Cady, G.H. J o u r . G e o l . 1942, 50, 337-356. M a r s h a l l , C.E. Econ. G e o l . 1955, 50th Anniv. V o l . 757-834. P a r k s , B . C . ; O'Donnell, H.J. U.S. Bur. Mines Bull. No. 344 1956, 193 pp. Stach, E. Lehrbuch der Kohlenmikroskopie Gluckauf, K e t t w i g , 1949, 285 pp. Abramski, C . ; Mackowsky, M.T.; M a n t e l , W.; and S t a c h , E. "Atlas für Angewandte Steinkohlenpetrographie"; Gluckauf:Essen 1951, 329 pp. Freund, H. "Handbuch der Microskopie i n der Technik"; Umschau V e r l a g : F r a n k f u r t am Main, 2 , 1952, 759 pp. Hoffmann, E.; Jenkner, A. Gluckauf 1932, 68, 81-88. Spackman, W.; B e r r y , W.F.; Dutcher, R.R.; B r i s s e , A . H . Yearbook Am. Iron and Steel I n s t . 1960, 403-449. Ammosov, I.I.; Eremin, I.V.; Sukhenko, S.F.; and Oshurkova, L . S . Koks i Khim 1957, 12, 9 - 1 2 . S c h a p i r o , W.; Gray, R . J . ; Eusner, G.R. B l a s t Furnace, Coke Oven, and Raw M a t e r i a l s Proc, A . I . M . E . 1961, 20, 89-112. S c h a p i r o , N.; Gray, R . J . Fuel 1964, 11, 234-242. B e n e d i c t , L . G . ; Thompson, R.R.; Wenger, R.O. B l a s t Furnace and S t e e l Plant 1968, 56, 217. B e n e d i c t , L . G . ; Thompson, R.R. Ironmaking P r o c . A . I . M . E . 1976, 35, 276-288. T e i c h m ü l l e r , M. F o r t s c h r . G e o l . R h e i n l d . u. Westf. 1974, 24, 37-64. Crelling, J.C. J o u r . Microscopy 1983, 132, p t . 3 , 251-266. Teichmüller, M. F o r t s c h r . G e o l . Rheinld u. Westf. 1974, 24, 65-112. O t t e n j a n n , K.; T e i c h m ü l l e r , M . ; Wolf, M. i n "Petrographic Organique et Potential Petrolier"; Alpern, B., Ed.; C.N.R.S.:Paris, 1975, 49-65. Teichmüller, M . ; Durand, B. I n t . J o u r . C o a l . G e o l . 1983, 2, 197-230. Brown, H.R.; Cook, A . C . ; T a y l o r , G.H. Fuel 1964, 4 3 , 111124. T a y l o r , G.H. i n "Coal Science"; Given, P . H . ; Advances i n Chemistry S e r i e s 55, Am. Chem. Soc.:Washington, D.C., 1966, 274-283. A l p e r n , B. i n "Adv. Org. Geochem. 1964"; Pergamon P r e s s : O x f o r d , 1966, 129-145. B e n e d i c t , L . G . ; Thompson, R.R.; Shigo, J.J.; Aikman, R.P. Fuel 1968, 47, 125-143. Brooks, J.; G r a n t , P.R.; M u i r , M.D.; van Gijzel, P.; Shaw, G. "Sporopollenin"; Academic Press:New York, 1971; 718 pp. Guennel, G.K.; Neavel, R.C. Science 1959, 129, 1671-1672.

18 29. 30. 31. 32. 33. 34.

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch001

35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66.

COAL MACERALS

Neavel, R . C . ; Guennel, G.K. J o u r . Sed. P e t . 1960, 30, 241248. Neavel, R . C . ; Miller, L.V. Fuel 1960, 39, 217-222. White, D. U.S. G e o l . Sur. P r o f . Paper 8 5 - E . 1914, 65-96. Crelling, J.C.; Dutcher, R.R.; Lange, R.V. Utah G e o l . and M i n . Sur. Bull. 118 1982, 187-191. Jones, J . M . ; Murchison, D.G. Econ. G e o l . 1963, 58, 263273. Murchison, D.G., and Jones, J . M . i n "Adv. i n Organic Geochem. 1962"; Pergamon Press:London, 1964; 1-21. Murchison, D.G.; Jones, J . M . i n "Coal Science"; Given, P.H.; Advances i n Chemistry S e r i e s No. 55, American Chemical Society:Washington, D.C., 1966; 307-331. Murchison, D.G. Fuel 1976, 55, 79-83. M a r s h a l l , C.E. Fuel 1954, 33, 134-144. S k o l n i c k , H. Bull. A . A . P . G . 1958, 4 2 , 2223-2236. Nandi, B . N . ; Montgomery, D.S. Fuel 1975, 54, 193-196. McCartney, J . T . Fuel 1970, 59, 409-414. Shibaoka, M. Fuel 1978, 57, 7 3 - 7 7 . S t a c h , E. in " T e x t b o o k of Coal Petrology" 3rd Ed; S t a c h , E. E d . ; Gebruder B o r n t r a e g e r : B e r l i n , 1982; p. 172. Murchison, D.G.; Jones, J . M . Fuel 1963, 42, 141. G o l o u s k i n , N.S. J. A p p l . Chem. USSR 1959, 32, 2016. K r ö g e r , C . ; P o h l , Α.; Kuthe, F. Gluckauf 1957, 93, 122. Horton, L. Fuel 1952, 3 1 , 341. Dormans, H.N.M.; Huntjens, F . J . ; van K r e v e l e n , D.W. Fuel 1957, 36, 321. K r ö g e r , C . ; Bade, E. Gluckauf 1960, 96, 741. Dyrkacz, G.R.; Bloomquist, C . A . A . ; Horwitz, E.P. Sep. Sci. T e c h n o l . 1981, 16, 1571. Dyrkacz, G.R.; Horwitz, E.P. Fuel 1982, 6 1 , 3 . Fenton, G.W.; Smith, A.K. Gas World 1959, 54, 8 1 . A l l a n , J. Ph.D. Thesis U. of Newcastle, England, 1975. K r ö g e r , C . ; P o h l , Α.; Kuthe, F r . ; Hovesatadt, H.; Burger, H. Brennstoff-Chem. 1957, 38, 3 3 . K r ö g e r , C . ; Bukenecker, J. Brennstoff-Chem. 1957, 38, 82. K r ö g e r , C . ; P o h l , A. Brennstoff-Chem. 1957, 38, 102. K r ö g e r , C . ; Bruecker, R. Brennstoff-Chem. 1961, 4 2 , 305. K r ö g e r , C . ; Ruland, W. Brennstoff-Chem. 1958, 39, 1. K r ö g e r , C . ; Gondermann, H. Brennstoff-Chem. 1957, 38, 231. van K r e v e l e n , D.W. "Coal"; Elsevier:Amsterdam, 1961. Given, P . H . ; Peover, M . E . ; Wyss, W.F. Fuel 1960, 39, 323. Given, P . H . ; Peover, M . E . ; Wyss, W.F. Fuel 1965, 44, 425. Reggel, L.; Wender, I.; Raymond, R. Fuel 1970, 49, 281. K r ö g e r , C . ; Burger, H. Brennstoff-Chem. 1959, 40, 76. Ladner, W.R.; Stacey, A . E . Fuel 1963, 42, 75. Tschamler, H.; DeRuiter, E. i n "Coal Science"; G i v e n , P . H . , E d . ; Adv. i n Chem. S e r i e s No. 55, American Chemical Society:Washington, D . C , 1966, p. 332. R e t c o f s k y , H.L.; Vanderhart, D.L. Fuel 1978, 57, 421.

1. W I N A N S A N D C R E L L I N G

67. 68. 69. 70.

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch001

71. 72. 73.

74.

75. 76. 77. 78. 79. 80. 81. 82. 83. 84. 85. 86.

Overview

19

Z i l m , K.W.; Pugmire, R . J . ; L a r t e r , S . R . ; A l l a n , J.; Grant, D.M. Fuel 1981, 60, 717. M a c i e l , G . E . ; S u l l i v a n , M . J . ; P e t r a k i s , L.; Grandy, D.W. Fuel 1982, 6 1 , 411. Pugmire, R . J . ; Z i l m , K.W.; Woolfenden, W.R.; Grant, D.M.; Dyrkacz, G.R.; Bloomquist, C . A . A . ; H o r w i t z , E.P. Org. Geochem. 1982, 4, 79. Pugmire, R . J . ; Woolfenden, W.R.; Mayne, C . L . ; Karas, J.; Grant, D.M. This Volume, Chapter 6. K r ö g e r , C. Brenstoff-Chem. 1958, 39, 62. Ref. ( 5 9 ) , p. 395 Austen, D . E . G . ; Ingram, D . J . E . ; Given, P . H . ; B i n d e r , C . R . ; Hill. L.W. i n "Coal Science"; G i v e n , P . H . , E d . ; Adv. i n Chem. S e r i e s No. 55, American Chemical Society:Washington, D.C. 1966; p. 344. R e t c o f s k y , H.L.; Thompson, G . P . ; Hough, M . ; Friedel, R.A. i n "Organic Chemistry of C o a l " ; L a r s e n , J.W., E d . ; Symp. S e r i e s No. 7 1 , American Chemical Society:Washington, D.C., 1978; p. 142. P e t r a k i s , L.; Grandy, D.W. Fuel 1981, 60, 115. Allan, J.; Bjorøy, M . ; Douglas, A . G . i n "Advances i n Organic Geochemistry 1975"; Campos, R.; G o n i , J., E d s . ; Pergamon:Oxford, 1977, p. 633. A l l a n , J.; Douglas, A . G . Geochim. Cosmochim. Acta 1977, 41, 1223. Allan, J.; Bjorøy, M . ; Douglas, A . G . i n "Advances i n Organic Geochemistry 1979"; Douglas, A . G . ; Maxwell, J . R . , E d s . ; Pergamon:Oxford, 1980; p. 599. Larter, S . ; Douglas, A . G . in "Environmental Biogeochemistry and Geomicrobiology"; Krumbein, W.E., E d . ; Ann Arbor: 1978; Vol. 1 p. 373. A l l a n , J.; L a r t e r , S.R. "Advances i n Organic Geochemistry 1981"; Bjorøy, M . , E d . , Pergamon:Oxford, 1983, p. 534. P h i l p , R . P . ; Saxby, J . D . "Advances i n Organic Geochemistry 1979"; Douglas, A.G,.; Maxwell, J.R., Eds.; Pergamon:Oxford 1981; p. 639. van Graas, G . ; de Leeuw, J.W.; Schenck, P.A. i n "Advances i n Organic Geochemistry 1979"; Douglas, A . G . ; Maxwell, J.R., E d s . ; Pergamon Press:Oxford 1980, p. 485. Winans, R . E . ; Dyrkacz, G.R.; McBeth, R . L . ; S c o t t , R . G . ; Hayatsu, R. Proceedings I n t e r . Conf. Coal Sci. 1981 p. 2 2 . Meuzelaar, H . L . C . ; Harper, A . M . ; Pugmire, R . J . P r e p r i n t D i v . of Fuel Chemistry. ACS 1983, 2 8 ( 1 ) , 97. Dutcher, R.R.; White, E.W.; Spackman, W. P r o c . 22nd I r o n ­ -making C o n f . , Iron and Steel D i v . , M e t a l l . Soc. AIME, Ν . Y . 1964, 463. Raymond, R. i n "Coal and Coal Products: Analytical Characterization Techniques"; Fuller, E.L., E d . ; ACS Symposium Series No. 205, American Chemical Society:Washington, D . C ., 1982; p. 191.

20 87. 88. 89. 90.

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch001

91.

92. 93. 94. 95. 96.

COAL MACERALS

Wolf, M . ; Migeon, H.N.; Butterworth, M . ; Gaines, A . F . ; Owen, N . ; Page, F.M. I n t . J . Mass Spectrom. Ion Phys. 1983, 46, 487. Bent, R.; Brown, J . K . Fuel 1961, 4 0 , 47. Neavel, R.C. i n "Chemistry of Coal Utilization, 2nd S u p p l . V o l . " ; Elliot, M.A., E d . ; W i l e y : N . Y . 1981, p. 9 1 . D a v i s , Α.; Spackman, W.; Given, P.H. Energy Sources 1976, 3 ( 1 ) , 55. Given, P . H . ; Spackman, W.; D a v i s , Α.; J e n k i n s , R.G. i n "Coal L i q u e f a c t i o n Fundamentals"; Whitehurst, D.D., E d . ; ACS Symp. Series No. 139, American Chemical Society:Washington, D . C ., 1980; pp. 3 - 3 4 . P e t r a k i s , L.; Grandy, D.W. Fuel 1981, 60, 120. Heng, S . ; Shibaoka, M. Fuel 1983, 6 2 , 610. D i e s s e l , C . F . K . Fuel 1985, 62, 883. P h i l p , R.D.; R u s s e l l , N.J. i n "Advances i n Organic Geo­ chemistry 1979"; Douglas, A . G . ; Maxwell, J . R . , Eds.; Pergamon:Oxford 1981; p. 653. K i n g , H.H.; Dyrkacz, G.R.; Winans, R.E. Fuel ( i n p r e s s ) .

RECEIVED January 23, 1984

2 Premaceral Contents of Peats Correlated with Proximate and Ultimate Analyses 1

A. D. COHEN and M. J. ANDRΕJKO

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch002

Earth and Space Sciences Division, MS D462, Los Alamos National Laboratory, Los Alamos, NM 87545

P r o p o r t i o n s o f premacerals and b o t a n i c a l c o n s t i t u ­ ents composing s e l e c t e d peat samples from Minnesota, Maine, North C a r o l i n a , and Georgia were determined by m i c r o s c o p i c a n a l y s i s o f o r i e n t e d microtome t h i n s e c t i o n s . These r e s u l t s were compared w i t h p r o x i ­ mate and u l t i m a t e analyses o f the same samples. Peats w i t h the h i g h e s t p r o p o r t i o n s o f b i r e f r i n g e n t premacerals tended to have the h i g h e s t volatile matter (and H, O, and Ν c o n t e n t s ) . Peats w i t h a dominance o f premacerals i n the light y e l l o w t o red range tended to be higher in volatile matter (and lower in f i x e d carbon) than those w i t h a significant component o f brown t o black i n g r e d i e n t s (preinertinites). V o l a t i l e matter a l s o tended t o i n c r e a s e as root content increased and to decrease as stem content i n c r e a s e d . On the other hand, BTU tended t o c o r r e l a t e more w i t h ash content than w i t h premaceral composition.

In a number o f p u b l i c a t i o n s , peat types have been d e f i n e d p e t r o g r a p h i c a l l y by t h e i r b o t a n i c a l and "premaceral compositions (1-4). "Premacerals" are the o r g a n i c components i n the peats which, due t o t h e i r c o l o r , o p a c i t y , shape, and f l u o r e s c e n c e , can be p r o j e c t e d as the probable p r o g e n i t o r s o f p a r t i c u l a r c o r r e s ­ ponding macérais i n c o a l s . Although the pétrographie c h a r a c t e r i z a t i o n o f peats c o n s t i t u t e s an important " f i r s t s t e p " i n understanding the o r i g i n and i n p r e d i c t i n g the general composition o f the r e s u l t a n t c o a l s , i t i s important t h a t premaceral types and amounts i n peats be c o r r e l a t e d w i t h v a r i o u s c o a l - q u a l i t y t e s t s (such as "proximate" and " u l t i m a t e " a n a l y s e s ) . With these r e s u l t s i t then becomes p o s s i b l e t o develop a s e r i e s of models 11

'Current address: Department of Geology, Washington State University, Pullman, WA 99164-2812

0097-6156/ 84/ 0252-0021 $06.00/0 © 1984 American Chemical Society

COAL MACERALS

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch002

22

with which to p r e d i c t more p r e c i s e l y the chemical and p h y s i c a l composition of the r e s u l t i n g t h e o r e t i c a l c o a l s . These p r e d i c t i v e c h a r a c t e r i z a t i o n s can be a p p l i e d not only to the projected seam-wide v a r i a b i l i t y i n c o a l q u a l i t y f o r c o a l s produced i n s i m i l a r d e p o s i t i o n a l s e t t i n g s as that of the s t u d i e d peats, but a l s o to the p r e d i c t i o n of the v a r i a t i o n s i n i n d u s t r i a l p r o p e r t i e s of the peats themselves, such as f o r g a s i f i c a t i o n , l i q u i f a c t i o n , s o i l c o n d i t i o n i n g , organic chemical production and so f o r t h . I t i s f o r these reasons that we have i n i t i a t e d t h i s c o r r e l a t i v e study of peat petrography and peat i n d u s t r i a l - c h e m i c a l ( c o a l q u a l i t y ) p r o p e r t i e s . Note that the information reported h e r e i n represents p r e l i m i n a r y r e s u l t s based on a l i m i t e d number of d i f f e r e n t types of peats that were analyzed f o r only a few " c o a l q u a l i t y t e s t s " ( i . e . , proximate a n a l y s i s , u l t i m a t e a n a l y s i s , and BTU c o n t e n t ) . Future s t u d i e s w i l l i n v o l v e measurement of other pétrographie parameters and i n c l u d e other i n d u s t r i a l analyses (such as, gas and l i q u i d y i e l d s , p h y s i c a l p r o p e r t i e s , organic chemical y i e l d s , and so f o r t h ) . Objectives The 1. 2.

3.

o b j e c t i v e s of t h i s study are t o : Determine the v a r i a t i o n s i n premaceral types and proportions w i t h i n a wide v a r i e t y of peat types. C o r r e l a t e premaceral contents with corresponding proximate ( f i x e d carbon, moisture, ash, v o l a t i l e m a t t e r ) , u l t i m a t e (C, Η, 0, N, S) and heating value (3TU) analyses. P r e d i c t the probable v a r i a t i o n s i n the proximate and u l t i m a t e makeup and BTU l e v e l s f o r c o a l s which formed i n s i m i l a r v e g e t a t i o n a l and d e p o s i t i o n a l s e t t i n g s to those of the peats studied i n t h i s p r o j e c t .

Methods C a r e f u l l y extracted samples of peat were slowly dehydrated i n a s e r i e s of a l c o h o l s o l u t i o n s and then embedded i n p a r a f f i n . A f t e r embedding, t h i n - s e c t i o n s (15 microns i n t h i c k n e s s ) were cut from these samples with a s l i d i n g microtome and mounted i n Canada Balsam. D e t a i l s of the procedure f o r the embedding and s e c t i o n ­ ing of peats have p r e v i o u s l y been described by Cohen.(2,3). Premaceral i d e n t i f i c a t i o n was made i n t r a n s m i t t e d white l i g h t , i n p o l a r i z e d l i g h t ( b i r e f r i n g e n c e ) and blue l i g h t f l u o r e s ­ cence. Premaceral proportions were determined by area p o i n t counting at 200 X. Proximate and u l t i m a t e analyses and BTU were obtained from commercial t e s t i n g l a b o r a t o r i e s and a l s o from the Department of Energy's Energy Technology Center at Grand Forks, North Dakota.

2.

C O H E N A N D A N D R Ε J KO

Premaceral Contents of Peats

23

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch002

Results and D i s c u s s i o n B o t a n i c a l Composition. F i g u r e 1a shows the r e l a t i v e abundances of p l a n t groups observed i n microtome s e c t i o n s o f the peats. Note t h a t these peats v a r i e d c o n s i d e r a b l y i n t h e i r b o t a n i c a l compositions. The Minnesota peat c o n s i s t e d predominantly o f Sphagnum (peat moss) d e b r i s w i t h some grasses and c o n i f e r s . The Maine peat was composed mostly o f a l g a l m a t e r i a l w i t h some Sphagnum and Nymphaea (water l i l y ) d e b r i s . The North C a r o l i n a peat was dominated by bay t r e e (Magnolia, Persea, Gordonia) and gum t r e e (Nyssa) d e b r i s ; w h i l e the Georgia Nymphaea peat con­ s i s t e d predominantly o f Nymphaea d e b r i s . Figure 1b shows the abundance o f p l a n t organs comprising the peat. Again the d i f f e r e n c e s between peat types are pronounced. The Minnesota peat i s dominated by r o o t s but w i t h l e s s e r but equal amounts o f stem and l e a f d e b r i s . On the other hand, t h e Maine peat has the highest c o n c e n t r a t i o n o f l e a v e s ; the North C a r o l i n a peat has the highest wood content (stems) and lowest l e a f content, w h i l e the Georgia (Nymphaea) peat has the h i g h e s t p r o p o r t i o n of r o o t s . Premaceral Types and P r o p o r t i o n s . One s i m p l i f i e d but u s e f u l means o f d i s p l a y i n g pétrographie composition o f peats i n t h i n s e c t i o n i s by graphing the area percentages o f i n g r e d i e n t s o f d i f f e r e n t c o l o r s . F i g u r e 2 shows such a point-count f o r four r e p r e s e n t a t i v e types o f peat from t h i s study. Note t h a t the Minnesota Sphagnum and Georgia Nymphaea peats have approximately the same range o f c o l o r s (peaking between l i g h t - y e l l o w and l i g h t brown) but t h a t the Maine peat peaked i n the c l e a r t o l i g h t y e l l o w range w h i l e t h a t o f the North C a r o l i n a peat had peaks i n the l i g h t - y e l l o w t o red-brown range and a l s o i n the dark-brown and b l a c k c a t e g o r i e s . The Georgia Nymphaea and Minnesota Sphagnum peats tended t o have the highest p r e v i t r i n i t e s w h i l e the North C a r o l i n a and Georgia Taxodium peat (not shown) had the highest prephlobaphenites (and p r e c o r p o c o l l i n i t e s ) and a l s o the h i g h e s t p r e i n e r t i n i t e s ( p r e m i c r i n i t e s , p r e f u s i n i t e s , and p r e s c l e r o t i n i t e s ) . F i g u r e s 3 and 4 give the area percentages o f biréfringent premacerals found i n the samples s t u d i e d . Since b i r e f r i n g e n c e has been equated w i t h c e l l u l o s e content, i t might t h e r e f o r e be expected t h a t b i r e f r i n g e n c e would decrease w i t h depth i n a deposit as a r e s u l t o f c e l l u l o s e decomposition. However, as can be seen i n Figure 3 ( r e p r e s e n t i n g two cores from the Okefenokee Swamp o f G e o r g i a ) , b i r e f r i n g e n c e may i n c r e a s e or decrease w i t h depth depending on successions o f peat types and moisture c o n d i t i o n s d u r i n g i n i t i a l d e p o s i t i o n . F i g u r e 4 shows t h a t Georgia Nymphaea and Minnesota Sphagnum peats have the h i g h e s t proport i o n s o f biréfringent c o n s t i t u e n t s . The c o n c e n t r a t i o n o f f l u o r e s c e n t premacerals tended t o c o r r e l a t e s l i g h t l y w i t h the p r o p o r t i o n o f biréfringent premacerals.

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch002

COAL

5 UJ < < 5 l o g Ι *

ι

< ω

2 5 ζ en

MACERALS

ω < J s flc Ο ω < 5 uj 8 ί 5 ο a ω

α.

^ (Λ Ζ

< m

ÛC

ο

MINN

N.CAR.

MAINE

Ο

GEORGIA

Figure 1a. R e l a t i v e p r o p o r t i o n s o f p l a n t types i d e n t i f i e d from microtome s e c t i o n s o f peats from Minnesota, Maine, North C a r o l i n a , and Georgia (A = abundant, C = common, Ρ = present, R = r a r e , and 0 = absent).

55

'Φι J

a-

.ο

MINN

MAINE

N.CAR.

GEORGIA

Figure 1b. R e l a t i v e abundances of p l a n t organs i d e n t i f i e d from microtome s e c t i o n s of peats from the same samples as i n Figure 1a.

2.

COHEN AND ANDREJKO

1)

Il

J:

l

25

Premaceral Contents of Peats

c η I

-τ—γ-

100

-Γ-

Ο

j£ CO CO

Û

"Ο Ο) -Û

90-

ο2 Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch002

Ο 2

80-

70 60-

50 40

< 5

30 20 10 0

MINN

GEORGIA

F i g u r e 2. C o l o r o f a l l i n g r e d i e n t s i n t h e f o u r p e a t t y p e s as d e t e r m i n e d by a r e a p o i n t c o u n t s o f m i c r o t o m e s e c t i o n s . ( A v e r a g e o f t h r e e samples from e a c h a r e a )

COAL MACERALS

Minnie's

Lake

Transect

Chesser

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch002

STATION 41

Prairie

Transect

STATION 6

V'V

0

j 65

ι ι ι ιII I I II I I I I I I I I 50 75 100 25 BIREFRINGENCE (%)

[/7TJ|

ι ι ι ι I ι ι ι ι I I I ι ι I I II 25 50 75 100 BIREFRINGENCE (%)

PEAT TYPES

TAXODIUM

Η

NYMPHAEA

[gjg

TRANSITIONAL

Figure 3 . Percentage o f biréfringent o r g a n i c s compared w i t h peat types i n two cores from the Okefenokee Swamp.

Premaceral Contents of Peats

COHEN AND AN DR E J KO

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch002

72 63 54 45 36

if

27

Ί

18 9

!

{/.

I

é

///

H

I

0

MINN

MAINE

Ν. CAR.

GEORGIA

Figure 4. Percentage o f biréfringent o r g a n i c s i n each o f 3 samples o f peat from Minnesota, Maine, North C a r o l i n a , and Georgia.

28

COAL MACERALS

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch002

However, d i f f e r e n t p l a n t types were found t o produce d i f f e r e n t f l u o r e s c e n t c o l o r s and i n t e n s i t i e s . Furthermore, n a t u r a l " s t a i n i n g " ( i . e . , darkening or c o l o r i n g by n a t u r a l impregnation or chemical a l t e r a t i o n ) o f c e l l w a l l s tended t o e f f e c t b i r e f r i n g e n c e and f l u o r e s c e n c e i n very d i f f e r e n t ways ( F i g u r e s 5 and 6 ) . N a t u r a l s t a i n i n g tended t o c o r r e l a t e s t r o n g l y w i t h b i r e f r i n g e n c e ( i . e . , the darker the s t a i n i n g the l e s s the b i r e f r i n g e n c e ) , but d i d not c o r r e l a t e w e l l w i t h o v e r a l l f l u o r e s c e n c e p r o p e r t i e s . For example, some t i s s u e s t h a t were h i g h l y s t a i n e d tended t o have higher f l u o r e s c e n c e i n t e n s i t i e s than those t h a t were unstained (Figure 6 ) . Proximate and U l t i m a t e Analyses and BTU. F i g u r e 7 shows the r e s u l t s o f proximate and u l t i m a t e analyses and BTU measurement. Note that the peat from North C a r o l i n a (a l o w e r - c o a s t a l - p l a i n , woody, dark, more i n e r t i n i t e - r i c h sample) had the h i g h e s t f i x e d carbon, elemental carbon and s u l f u r content. Woody Taxodium peats from Georgia (not shown) and South C a r o l i n a (not shown) were s i m i l a r i n c h a r a c t e r t o the North C a r o l i n a samples. The Georgia Nymphaea peats, which had the h i g h e s t p r e v i t r i n i t e s , can be seen t o have the h i g h e s t oxygen, hydrogen, and v o l a t i l e matter contents. Note that BTU values tended t o c o r r e l a t e more s t r o n g l y w i t h ash contents than w i t h maceral c o n t e n t s . Summary and Conclusions P r e l i m i n a r y c o r r e l a t i o n s o f pétrographie c h a r a c t e r i s t i c s o f peats ( i . e . , peat types, premaceral p r o p o r t i o n s , and premaceral types) w i t h p r o x i m a t e and u l t i m a t e a n a l y s e s s u g g e s t t h e f o l l o w i n g trends: 1. Peats w i t h the h i g h e s t p r o p o r t i o n s o f biréfringent macérais tend t o have the h i g h e s t v o l a t i l e matter (and H and 0 contents). 2. Fluorescence o f macérais, on the other hand, seems t o c o r r e l a t e only s l i g h t l y w i t h proximate and u l t i m a t e analyses. 3. Higher p r e v i t r i n i t e contents (determined by c o l o r ) tend t o c o r r e l a t e w i t h higher v o l a t i l e matter c o n t e n t s . 4. Peats with higher p r e i n e r t i n i t e s , prephlobaphenites (and p r e c o r p o c o l l i n i t e s ) , .and p r e s c l e r o t i n i t e s have the h i g h e s t f i x e d carbon. 5. BTU c o r r e l a t e s s t r o n g l y w i t h ash content and o n l y s l i g h t l y w i t h maceral content. Acknowledgments This work was funded i n p a r t by Grant #EAR-79-26382 from the N a t i o n a l Science Foundation and i n p a r t by funding from the O f f i c e o f B a s i c Energy Sciences o f the Department o f Energy.

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch002

2.

C O H E N A N D A N DR EJ KO

Premaceral Contents of Peats

Figure 5a. Photomicrograph o f a microtome s e c t i o n o f peat i n transmitted l i g h t . Note that the c e l l w a l l s i n the upper l e f t h a l f o f the f i g u r e (even though f i l l e d w i t h reddish-brown t a n n i f e r o u s m a t e r i a l ) are not as d a r k l y s t a i n e d as the c e l l s i n the lower r i g h t h a l f o f the f i g u r e . Scale bar equals 100 microns.

Figure 5b. Same view as 5a except under c r o s s - p o l a r i z e d l i g h t t o show biréfringent i n g r e d i e n t s . The l e s s s t a i n e d w a l l s are the most biréfringent.

29

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch002

COAL MACERALS

Figure 6a. Photomicrograph of a microtome s e c t i o n o f peat showing a cross s e c t i o n o f a n a t u r a l l y s t a i n e d Woodwardia v i r g i n i c a (chain fern) r o o t l e t ( t r a n s m i t t e d l i g h t ) . Scale bar equals 250 microns.

Figure 6b. A s i m i l a r view as i n F i g . 6a o f a s l i g h t l y l a r g e r root o f Woodwardia but observed under blue l i g h t f l u o r e s c e n c e . Note that ( i n c o n t r a s t t o b i r e f r i n g e n c e ) the more d a r k l y s t a i n e d t i s s u e s tend here t o be more h i g h l y fluorescent.

Premaceral Contents of Peats

2. COHEN AND AN DR EJ KO

Ultimate

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch002

OXYGEN Τ CARBON 70605040? 30? 20 % lo­ ot MIMANCGAMIMANCGA

Analyses

HYDROGEN

s

MOISTURE

SULFUR

NITROGEN

m esd

Ml MA NC GA Ml MA NC GA Ml MA NC GA

Proximate

70 60 50 40 30 r 20* 10

31

Analyses

MAT.

VOL.

FIXED C

ASH

Ml MA NC GA Ml MA NC GA Ml MA NC GA Ml MA NC GA

Heating Value

10.000

8 8,000;?

5

6,000*

ω

4,000* 2,000 « 0

Ml MA NC GA

Figure 7. Proximate and u l t i m a t e analyses o f samples from Minnesota (MI), Maine (MA), North C a r o l i n a (NC), and Georgia (GA).

COAL MACERALS

32

Literature Cited 1. 2. 3.

4.

Cohen, A. D. Ph.D. T h e s i s , Pennsylvania State U n i v e r s i t y , 1968. Cohen, A. D.; Spackman, W. Geol. Soc. Am. Bull. 1972, 83, 129-142. Cohen, A. D. T e s t i n g o f Peats and Organic Soils, STP 820, Am. Soc. f o r T e s t i n g and M a t e r i a l s , P h i l a d e l p h i a , PA, 21-36, 1982. Corvinus, D. Α.; Cohen, A. D. Compt. Rendu. IX I n t e r . Carb. Congress, In Press.

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch002

RECEIVED January 6, 1984

3 Characterization of Coal Macerals by Fluorescence Microscopy JOHN C. CRELLING Department of Geology, Southern Illinois University at Carbondale, Carbondale, IL 62901 DAVID F. BENSLEY

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch003

Coal Research Section, The Pennsylvania State University, University Park, PA 16802 The use o f fluorescence microscopy to c h a r a c t e r i z e c o a l macerals is a s u c c e s s f u l recent innovation. Compared to conventional w h i t e - l i g h t a n a l y s i s , fluorescence microscopy r e v e a l s a greater number and v a r i e t y of macerals, as w e l l as, c h a r a c t e r i s t i c textures and s t r u c t u r e s . Although the s p e c t r a of f l u o r e s c e n t macerals are broad-peaked and, a t t h i s time, not s u i t a b l e f o r chemical s t r u c t u r e a n a l y s i s , they are c h a r a c t e r i s t i c of maceral types and rank. S p e c t r a l a n a l y s i s of the liptinite macerals in s i n g l e c o a l s of the Illinois Basin shows that the macerals can be grouped or d i s c r i m i n a t e d both p e t r o g r a p h i c a l l y and statistically using v a r i o u s s p e c t r a l parameters, specifically the wavelength of maximum i n t e n s i t y (λ max) and the red/green quotient (Q = i n t e n s i t y 650nm/500nm). In a num­ ber of cases the s p e c t r a l data r e v e a l the pres­ ence of more than one v a r i e t y of a given maceral type i n some samples. Maceral groupings on the b a s i s of i n c r e a s i n g λ max and Q c o n s i s t e n t l y show the same order: fluorinite, resinite, sporinite, cutinite. For example, i n the B r a z i l Block Seam (Indiana) the f o l l o w i n g maceral groups can be d i s ­ tinguished: f l u o r i n i t e (λ max = 520 nm, Q = 0.58), s p o r i n i t e type I (λ max =550 nm, Q = 0.85), s p o r i ­ n i t e type I I (λ max = 590 nm, Q = 1.00), c u t i n i t e (λ max = 610 nm, Q = 1.47). In a d d i t i o n , a l t e r e d (weathered) forms o f s p o r i n i t e (λ max = 690 nm, Q = 1.22) and c u t i n i t e (λ max = 650 nm, Q = 2.27) were a l s o observed. Studies on other c o a l samples of d i f f e r e n t ranks i n d i c a t e that the fluorescence p r o p e r t i e s are very s e n s i t i v e t o changes in rank. One of the major problems of c o a l science i s that very l i t t l e i s known about the b a s i c p r o p e r t i e s of the v a r i o u s macérais that make

0097-6156/84/0252-0033$06.00/0 © 1984 American Chemical Society

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch003

34

COAL

MACERALS

up c o a l . Two of the main reasons f o r t h i s l a c k of knowledge are that they are extremely d i f f i c u l t to separate from c o a l and that they are n o n - c r y s t a l l i n e organic compounds and, t h e r e f o r e , not good subjects to analyze with such standard methods as x-ray d i f f r a c t i o n or electron-microprobe a n a l y s i s . Some of the most succ e s s f u l c h a r a c t e r i z a t i o n of c o a l macérais to date has been done by pétrographie methods, i n which the i n d i v i d u a l macérais do not have to be separated. In the s t e e l i n d u s t r y , f o r example, pétrographie techniques have proven so s u c c e s s f u l i n allowing the p r e d i c t i o n of the coking p r o p e r t i e s of c o a l that most major s t e e l companies have now e s t a b l i s h e d pétrographie l a b o r a t o r i e s . Another pétrographie technique that has only r e c e n t l y been a p p l i e d to c o a l a n a l y s i s i s q u a n t i t a t i v e fluorescence microscopy. With t h i s technique, the v i s i b l e f l u o r e s c e n t l i g h t e x c i t e d from the macérais r e v e a l s shapes textures, and c o l o r s not v i s i b l e i n normal w h i t e - l i g h t viewing. The technique a l s o y i e l d s q u a n t i t a t i v e spectra that are charact e r i s t i c of both the i n d i v i d u a l maceral type and the rank of the coal. I t i s now a l s o w e l l e s t a b l i s h e d that a l l of the l i p t i n i t e macérais (coal components derived from the resinous and waxy plant m a t e r i a l ) and many of the v i t r i n i t e macérais (coal components derived from woody t i s s u e of p l a n t s ) w i l l f l u o r e s c e , and that some r e c e n t l y discovered l i p t i n i t e macérais can only be i d e n t i f i e d by t h e i r fluorescence p r o p e r t i e s . Some of the f i r s t measurements of the absolute i n t e n s i t y of fluorescence of c o a l macérais at s p e c i f i c wavelengths were made by Jacob (1,_2). R e l a t i v e i n t e n s i t y measurements of f l u o r e s c e n t spect r a of modern plant m a t e r i a l s , peats and coals have been reported by van G i j z e l (_3,_4,J>). Teichmuller (6,_Z,_8) described three prev i o u s l y u n i d e n t i f i e d members of the l i p t i n i t e group of macérais i n part by demonstrating t h e i r d i s t i n c t i v e s p e c t r a l p r o p e r t i e s . Ottenjann et a l (9.), Teichmuller (10). and Teichmuller and Durand (11), i l l u s t r a t e d the c o r r e l a t i o n of changes i n fluorescence spect r a of s p o r i n i t e with rank, and C r e l l i n g and others (12) and C r e l l i n g (13) have demonstrated the use of fluorescence spectra to d i s c r i m i n a t e macérais. In a d d i t i o n , Ottenjann et a l , F i s h e r (14), Teichmuller (10), and Teichmuller and Durand (11) have been able to r e l a t e the fluorescence spectra of v i t r i n i t e macérais to the t e c h n o l o g i c a l p r o p e r t i e s of c o a l . These studies have shown the p o t e n t i a l of using fluorescence measurements i n the study of l i p t i n i t e and v i t r i n i t e macérais. The o v e r a l l o b j e c t i v e of current fluorescence s t u d i e s at Southern I l l i n o i s U n i v e r s i t y at Carbondale i s to determine the kinds and r e l a t i v e amounts of f l u o r e s c e n t macérais i n various coals and to c l a s s i f y and d i s c r i m i n t e them on the b a s i s of t h e i r fluorescence s p e c t r a . A d d i t i o n a l o b j e c t i v e s are to d e f i n e the manner i n which the f l u o r e s c e n t macérais vary with c o a l rank, and to determine which of the macérais are of primary and secondary origin.

3.

CRELLING A N D BENSLEY

Fluorescence

Microscopy

35

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch003

Equipment and Methods The f l u o r e s c e n c e microscopy system used f o r t h i s study i n the SIUC Coal C h a r a c t e r i z a t i o n Laboratory i s a L e i t z MPV I I r e f l e c t a n c e microscope which i s f i t t e d with a 100 watt mercury arc lamp, a Pleom i l l u m i n a t o r and a L e i t z o i l immersion 40X o b j e c t i v e with a 1.3 numerical aperture. For s p e c t r a l measurements the l i g h t from the mercury a r c passes through a UG1 u l t r a - v i o l e t f i l t e r to a TK400 d i c h r o i c m i r r o r which r e f l e c t s l i g h t with wavelengths l e s s than 400 nm to the sample. The f l u o r e s c e n t l i g h t e x c i t e d from the sample i s passed through a 430 nm b a r r i e r f i l t e r to a motorized i n t e r f e r e n c e wedge i n f r o n t of the photometer. The i n t e r f e r e n c e wedge c o n t r o l s the wavelength of the f l u o r e s c e n t l i g h t h i t t i n g the photometer so that the i n t e n s i t y v a r i a t i o n s from 430 to 700 nm can be scanned and recorded i n about 20 seconds. The s p e c t r a l data are then fed from the microscope system i n t o a computer and d i g i ­ t i z e d , c o r r e c t e d , and analyzed. Each spectrum i s c o r r e c t e d f o r the e f f e c t s of background f l u o r e s c e n c e and f o r the e f f e c t s o f the microscope system, e s p e c i a l l y the s e n s i t i v i t y o f the photomultip l i e r tube, f o l l o w i n g c o r r e c t i o n procedures described by van G i j z e l (13). For comparison, the v a r i o u s s p e c t r a a r e normalized and reduced to a number of parameters such as: 1) the wavelength of maximum i n t e n s i t y peak (λ max); 2) the red/green quotient (Q) where Q = r e l a t i v e i n t e n s i t y a t 650 nm/relative i n t e n s i t y a t 500 nm; 3) the area l e s s than λ max; 4) the area greater than λ max; 5) area blue (430 to 500 nm); 6) area green (500 to 570 nm); 7) area yellow (570 to 630 nm); and 8) area r e d (630 to 700 nm). Results and D i s c u s s i o n In c o a l s of the I l l i n o i s Basin, standard w h i t e - l i g h t pétrographie methods g e n e r a l l y r e v e a l three types of l i p t i n i t e macérais; r e s i n i t e , s p o r i n i t e and c u t i n i t e . These macérais a r e i d e n t i f i e d on the b a s i s of t h e i r pétrographie p r o p e r t i e s such as r e f l e c t a n c e , s i z e , shape and t e x t u r e . When f l u o r e s c e n c e microscopy i s used, the fluorescence c o l o r s and i n t e n s i t i e s r e v e a l the presence of l a r g e r amounts of these macérais plus the presence of the new maceral, fluorinite. The combined r e s u l t s of maceral analyses i n both w h i t e - l i g h t and f l u o r e s c e n t l i g h t as w e l l as the r e f l e c t a n c e value for the H e r r i n (No. 6) B r a z i l Block and Hiawatha c o a l s a r e given i n Table 1. F l u o r i n i t e was f i r s t defined by Teichmuller (6) and i s chara c t e r i z e d by a very high f l u o r e s c e n c e i n t e n s i t y . I t commonly occurs i n most c o a l s of the I l l i n o i s Basin and i s shown i n F i g ures 1 and 2 along with photomicrographs of s p o r i n i t e and c u t i n i t e . When f l u o r e s c e n c e s p e c t r a l a n a l y s i s i s used on these samp l e s , the r e s u l t i n g s p e c t r a l data d i s t i n g u i s h these four types of l i p t i n i t e macérais plus a d d i t i o n a l v a r i e t i e s of r e s i n i t e , s p o r i n i t e and c u t i n i t e . For example, s p e c t r a l a n a l y s i s o f the v a r i o u s l i p t i n i t e macérais i n samples of H e r r i n (No. 6) c o a l seam with a

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch003

36

COAL MACERALS

Figure 1. W h i t e - l i g h t ( r e f l e c t e d ) photomicrographs o f l i p t i n i t e macérais. Diameter of frames i s 300 urn. l a (upper l e f t ) v e r t i c a l zones o f l i p t i n i t e (dark gray) a t l e f t and center. Bright spot i n center i s a p y r i t e c r y s t a l , l b (upper r i g h t ) some s p o r i n i t e lenses (dark gray) i n center of frame, l c (lower l e f t ) - l a r g e l i p t i n i t e mass a t center and some s c a t t e r e d spores (dark gray), Id (lower r i g h t ) - some l i p t i n i t e s t r i n g e r s running from top l e f t to bottom r i g h t .

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch003

3. CRELLING AND BENSLEY

Fluorescence

Microscopy

37

Figure 2. B l u e - l i g h t photomicrographs of l i p t i n i t e macérais. Diameter of frames i s 300 urn. 2a (upper l e f t ) same frame as l a , center zone of f l u o r i n i t e showing intense yellow f l u o r e s c e n c e , s p o r i n i t e with l e s s intense range f l u o r e s c e n c e i s seen a t l e f t , green at lower r i g h t i s the f l u o r e s c e n c e from the mounting medium, 2b (upper r i g h t ) same frame as l b - f l u o r e s c e n c e r e v e a l s spore (yellow ovoids) and a mass of granulated l i p t i n i t e i n center of frame, 2c (lower l e f t ) same frame as l c - f l u o r e s c e n c e r e v e a l s l a r g e mass a t center as a spore sac (sporangium), yellow ovoids are s p o r i n i t e and yellow s t r i n g e r s a r e c u t i n i t e . 2d (lower r i g h t ) same frame as Id - fluorescence r e v e a l s two d i f f e r e n t types of c u t i n i t e - a b r i g h t e r t h i c k e r v a r i e t y on the l e f t and a darker thinner v a r i e t y on the r i g h t .

38 Table 1.

COAL MACERALS

Results

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch003

Coal Seam Reflectance ( i n o i l a t 546 nm) Vitrinite Pseudovitrinite Fluorinite Resinite Sporinite Cutinite Amorphous Liptinite Semi-fusinite Fusinite Micrinite

of Combined White-Light and Fluorescent Pétrographie Analyses

H e r r i n (No, 6) S a l i n e Co,, IL 0.65%

B r a z i l Block Parke Co., IN 0.58%

Light

Hiawatha Carbon Co., UT 0.52%

65.1 19.8 0.3 0.1 3.0 0.4

56.3 8.7 0.2 0.7 14.1 2.0

73.7 7.8 0 6.9 0.5 0.8

1.8 5.7 2.1 1.7

4.2 4.9 3.4 5.5

1.0 4.2 1.3 3.8

r e f l e c t a n c e of 0.65% ( i n o i l at 546 nm) showed d i s t i n c t i v e spectra f o r the macérais f l u o r i n i t e , r e s i n i t e , s p o r i n i t e and c u t i n i t e . In t h i s case (Herrin No. 6 ) , the s p e c t r a were assigned to maceral groups on the b a s i s of the pétrographie i d e n t i f i c a t i o n of macérais from which the s p e c t r a were obtained. When the groups of s p e c t r a l data f o r each maceral type were subjected to d i s c r i m i n a n t f u n c t i o n a n a l y s i s of the eight d i f f e r e n t parameters f o r each spectrum, the maceral types were w e l l separated. From t h i s a n a l y s i s i t was e a s i l y seen that there are two d i f f e r e n t groups of r e s i n i t e macérais. Thus, the s t a t i s t i c a l a n a l y s i s of the s p e c t r a l parameters of the macérais revealed two v a e t i e s of the r e s i n i t e maceral group that could not be r e a d i l y d i s t i n g u i s h e d by normal pétrographie means. The average s p e c t r a of the v a r i o u s maceral types d i s t i n g u i s h e d by the d i s c r i m i n a t e f u n c t i o n a n a l y s i s are p l o t t e d i n Figures 3-6. A d d i t i o n a l study of these samples i n d i c a t e s that there are a l s o two v a r i e t i e s of f l u o r i n i t e present. The average s p e c t r a l data f o r a l l of the v a r i e t i e s of the f l u o r e s c e n t macérais i n these samples are given i n Table I I . In a study of the fluorescence p r o p e r t i e s of the B r a z i l Block seam (Parke Co., IN), a somewhat d i f f e r e n t approach was used. In t h i s case, about a hundred i n d i v i d u a l spectra were taken on a v a r i e t y of f l u o r e s c i n g l i p t i n i t e macérais. Although the macérais from which the spectra were tkane were not i d e n t i f i e d at the time of measurement, photomicrographs i n both normal w h i t e - l i g h t and f l u o r e s c e n t l i g h t were taken f o r documentation. The s p e c t r a l parameters f o r each spectrum were c a l c u l a t e d and these data were subjected to c l u s t e r a n a l y s i s to t e s t the degree to which the

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch003

450

500

550

Wavelength

600

650

700

(nm)

Figure 3. Average fluorescence s p e c t r a f o r two v a r i e t i e s o f f l u o r i n i t e i n the H e r r i n (No. 6) seam. The r e f l e c t a n c e of the seam i s 0.65%.

450

500

550

Wavelength

600

650

700

(nm)

Figure 4. Average fluorescence s p e c t r a f o r two v a r i e t i e s of r e s i n i t e i n the H e r r i n (No. 6) c o a l seam. The r e f l e c t a n c e of the seam i s 0.65%.

40

COAL MACERALS

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch003

Relative Intensity (%)

450

500

550

Wavelength

600

650

700

(nm)

Figure 5. Average f l u o r e s c e n c e spectrum f o r s p o r i n i t e i n the H e r r i n (No. 6) c o a l seam. The r e f l e c t a n c e of the seams i s 0.65%.

450

500

550

Wavelength

600

650

700

(nm)

Figure 6. Average fluorescence spectrum f o r c u t i n i t e i n the H e r r i n (No. 6) c o a l seam. The r e f l e c t a n c e of the seam i s 0.65%.

Fluorescence

3. CRELLING AND BENSLEY

Microscopy

41

Table I I . S p e c t r a l Parameter of the Average S p e c t r a l of Maceral V a r i e t i e s i n the H e r r i n No. 6 Coal Seam ( S a l i n e Co. - R = 0.65%)

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch003

Q

Parameter

Fluorinite I II

Resinite I II

Peak (nm)

500

524

553

Red/Green Quotient

0.47

0.57

0.94

Sporinite

Cutinite

604

657

682

1.67

1.63

2.99

groups could be separated on the b a s i s of t h e i r s p e c t r a l parameters. I t was found that seven groups could be d i s t i n g u i s h e d . The b a s i c pétrographie data f o r the B r a z i l Block c o a l seam are given i n Table I and the average s p e c t r a l parameters f o r each maceral group are given i n Table I I I . When the macérais from which the spectra were taken were i d e n t i f i e d from the photomicrogrphs, i t was found that each group corresponded to a separate maceral type or a v a r i e t y of a maceral type. There wae type of f l u o r i n i t e , one type of r e s i n i t e , three types of s p o r i n i t e and two types of c u t i n i t e . While t h i s correspondence o f maceral types and v a r i e t i e s to s t a t i s t i c a l groupings of s p e c t r a l data was not unexpected, i t i s f u r t h e r c o n f i r m a t i o n that the s p e c t r a l parameters of macérais are unique to maceral type and v a r i e t y . Table I I I .

Parameter

S p e c t r a l Parameters of Average Spectra of the B r a z i l Block Coal Seam

Fluorinite

Peak (nm) 480 Red/Green 0.32 Quotient Area Blue (%) 37 Area Green (%) 38 Area Yellow 15 (%) Area Red (%) 10 Area L e f t 21 of Peak (%) Area Right 79 of Peak (%)

Sporinite II III

Cutinite I II

Resinite

I

520 0.58

550 0.85

590 1.00

690 1.22

610 1.47

650 2.27

19 43 23

16 36 25

14 34 28

13 31 26

12 32 28

7 29 29

15 33

23 40

24 53

30 93

28 59

35 60

67

60

47

7

41

40

An i n t e r e s t i n g r e s u l t of t h i s a n a l y s i s i s that one of the

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch003

42

COAL

MACERALS

s p o r i n i t e v a r i e t i e s (II) and one of the c u t i n i t e v a r i e t i e s (II) d i s t i n g u i s h e d by s t a t i s t i c a l means showed pétrographie evidence of a l t e r a t i o n (weathering). Because the c o a l sample i t s e l f was c o l l e c t e d from a f r e s h exposure at an a c t i v e mine, i t appears that the weathered maceral v a r i e t i e s were weathered before they were incorporated i n t o the peat that was l a t e r c o a l i f i e d . The r e s u l t s of these two s t u d i e s show that fluorescence s p e c t r a l a n a l y s i s can d i s t i n g u i s h , on a q u a n t i t a t i v e b a s i s , the v a r i o u s types of l i p t i n i t e macérais and, indeed, even v a r i e t i e s of each type. That the v a r i o u s spectra are unique to the i n d i v i d u a l macérais i s f u r t h e r i n d i c a t e d by the recurrent order of the spect r a l parameters, e s p e c i a l l y the wavelength of maximum i n t e n s i t y (λ max) and the red/green quotient i n any given c o a l . For example as shown i n Figures 3-6 f o r the H e r r i n (No. 6) seam and as seen i n Table I I I f o r the B r a z i l Block seam, the order of the maceral types on the b a s i s of i n c r e a s i n g λ max and Q i s f l u o r i n i t e , r e s i ­ n i t e , s p o r i n i t e and c u t i n i t e . I t should be noted, however, that as the rank of c o a l i n c r e a s e s , a l l of the s p e c t r a l peaks s h i f t toward longer wavelengths and d i m i n i s h i n i n t e n s i t y and are, thus, even­ t u a l l y d i f f i c u l t or impossible to d i s t i n g u i s h from each other. Weathering of the macérais has a s i m i l a r e f f e c t . The p r e l i m i n a r y r e s u l t s of s t u d i e s now underway suggest that the s p e c t r a l peak (λ max) of some macérais, i s more s e n s i t i v e to v a r i a t i o n i n c o a l rank than p r e v i o u s l y b e l i e v e d . In the high v o l a t i l e bituminous c o a l s s t u d i e d , an increase of 3 V-types (0.45 0.75% r e f l e c t a n c e ) r e s u l t e d i n about a 50 nm increase of λ max. Even when macérais have been a l t e r e d by l a r g e increases i n rank, or weathering, or other processes, fluorescence microscopy can s t i l l be q u i t e u s e f u l i n c h a r a c t e r i z i n g c o a l macérais. For example, some c o a l seams i n the western U.S. have an abundance of r e s i n i t e which i n some cases i s being extracted and commercially e x p l o i t e d as a chemical raw m a t e r i a l . The r e s i n i t e i n these seams most o f t e n occurs as a secondary m a t e r i a l , f i l l i n g f i s s u r e s and voids i n the c o a l . Numerous flow t e x t u r e s , i n c l u s i o n s of c o a l i n r e s i n i t e v e i n l e t s , and i n t r u s i v e r e l a t i o n s h i p s throughout c o a l seams i n d i c a t e that the r e s i n i t e was m o b i l i z e d at some point i n i t s h i s t o r y . These secondary r e s i n i t e s are o f t e n d i f f i c u l t to detect i n normal w h i t e - l i g h t viewing; however, they a l l tend to f l u o r e s c e s t r o n g l y d i s p l a y i n g a v a r i e t y of c o l o r s and are theref o r e , q u i t e amenable to fluorescence a n a l y s i s . When samples of the Hiawatha seam from Utah were examined by C r e l l i n g et a l (12) four types of secondary r e s i n i t e s , each w i t h a d i f f e r e n t f l u o r e s cence c o l o r - grren, yellow, orange, red-brown - were seen. Each r e s i n i t e type has a spectrum that i s d i s t i n c t i v e and the v a r i o u s types can be s t a t i s t i c a l l y separated on the b a s i s of t h e i r spect r a l parameters. The average spectra of the four r e s i n i t e types are shown i n Figure 7 and the b a s i c pétrographie a n a l y s i s of the sample from the Hiawatha seam i s given i n Table I. I t should be noted t h a t , at t h i s time, the only way to d i s t i n g u i s h the v a r i o u s types of secondary r e s i n i t e i s with fluorescence microscopy.

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch003

3.

Fluorescence

CRELLING A N D BENSLEY

o I

i-H 450

Microscopy

43

1

1

1

1

500

550

600

650

Wavelength

\ 700

(nm)

Figure 7. Average fluorescence s p e c t r a f o r four v a r i e t i e s of r e s i n i t e from the Hiawatha Seam, Utah. V a r i e t i e s 1, 2, and 3 have a d e f i n i t e shape and a b r i t t l e f r a c t u r e while v a r i e t y 4 occurs only as a v o i d f i l l i n g . The r e f l e c t a n c e of the seam i s 0.65%.

44

COAL MACERALS

Work i s now underway to separate these v a r i o u s r e s i n i t e types using d e n s i t y gradient techniques and to chemically c h a r a c t e r i z e the separated r e s i n i t e f r a c t i o n s .

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch003

Summary Although the c h a r a c t e r i z a t i o n of c o a l macérais on the b a s i s of t h e i r f l u o r e s c e n c e s p e c t r a i s a recent innovation, i t has already proven to be an e x c e l l e n t f i n g e r p r i n t i n g t o o l f o r the v a r i o u s macérais. In some cases, i t i s even more s e n s i t i v e than normal pétrographie a n a l y s i s . The i n i t i a l r e s u l t s of fluorescence spect r a l s t u d i e s show that the v a r i o u s f l u o r e s c e n t macérais i n s i n g l e c o a l s can be s t a t i s t i c a l l y d i s c r i m i n a t e d on the b a s i s of t h e i r s p e c t r a l parameters and that even v a r i e t i e s of a s i n g l e maceral type can be d i s t i n g u i s h e d . Although the spectra obtained at t h i s time are r a t h e r broad and not s u i t a b l e f o r chemical s t r u c t u r e a n a l y s i s , the p o t e n t i a l f o r s t r u c t u r a l a n a l y s i s e x i s t s and may be r e a l i z e d with improvements i n instrumentation. Acknowledgments Much of t h i s work has been supported by the Gas Research I n s t i t u t e under Grant No. 5082-260-0618 and a l s o by the Coal Research Center at SIUC. This support i s g r a t e f u l l y acknowledged. Literature Cited 1.

2.

3.

4.

5.

6.

7.

Jacob, Η., Neue Erkenntnisse auf dem Gebiet der LumineszensMikroskopie f o s s i l e r Brennstoffe. - F o r t s c h r . Geol. Rheinld. u. Westf. 1964, 12, 569-588. Jacob, Η., Mikroskop-Photometrie der organischen S t o f f e von Boden I. Organopetrographische Nomenklatur und mikroskop­ -photometrische Methodik. -Die Bodenkultur, 1972, 23, 217226. van G i j z e l , P., Autofluorescence of fossil p o l l e n and spores with s p e c i a l reference to age determination and coalification. Leidse Geol. Meded., 1967, 50, 263-317. van G i j z e l , P., Review of the UV-fluorescence microphotometry of f r e s h and fossil exines and exosporia. "Sporopollenin"; Brooks, J . , Grant, P. R., Muir, M. D., van G i j z e l , P., and Shaw, G., Eds.; Academic Press: New York, 1971, pp. 659-685. van G i j z e l , P., Polychromatic UV-fluorescence microphotometry of f r e s h and fossil p l a n t substances with s p e c i a l reference to the l o c a t i o n and i d e n t i f i c a t i o n of dispersed organic m a t e r i a l i n rocks, i n "Petrographic Organique et P o t e n t i a l Pétrolier"; Alpern, B., Ed.; CNRS: P a r i s , 1975, pp. 67-91. Teichmuller, M., Uber neue Macerale der L i p t i n i t - G r u p p e und d i e Entstehung von M i c r i n i t . F o r t s c h r . Geol. Rheinld. u. Westf., 1974a, 24, 37-64. Teichmuller, M., Entstehung and Veranderung bituminoser Sub-

3.

8.

9.

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch003

10.

11.

12.

13.

14.

15.

CRELLING AND BENSLEY

Fluorescence

Microscopy

45

stanzen i n Kohlen i n Beziehung zur Entstehung and Umwandlung des E r d o l s . F o r t s c h r . , Geol. Rheinld. u. Westf., 1974b, 24, 65-112. Teichmuller, Μ., Generation of p e t r o l e u m - l i k e substances i n c o a l seams as seen under the microscope. Advances i n Organic Geochemistry-1973. Ottenjann, Κ., Teichmuller, Μ., and Wolf, Μ., S p e c t r a l f l u o r e s c e n c e measurements i n s p o r i n i t e s i n r e f l e c t e d l i g h t and t h e i r a p p l i c a b i l i t y f o r coalification s t u d i e s , i n "Petro­ graphic Organique et P o t e n t i e l Petolier"; A l p e r n , Β., Ed.; CNRS: P a r i s , 1974c, pp. 379-407. T e i c h m u l l e r , M a r l i e s , Fluoreszenzmikroskopische Anderungen von L i p t i n i t e n und Vitriniten mit zunehmendem Inkohlungsgrad und i h r e Beziehungen zu Bitumenbildung und Verkokungsverhalten. Geologischer Landesamt Nordrhein-Westfalen, K r e f e l d , 1982, pp. 1-119. Teichmuller, M., and B. Durand, Fluorescence m i c r o s c o p i c a l rank s t u d i e s on liptinites and vitrinites i n peat and c o a l s and comparison with r e s u l t s of the r o c k - e v a l p y r o l y s i s . Int. Jour. of Coal Geology, 1983, 2, pp. 197-230. C r e l l i n g , John C., Dutcher, R u s s e l l R., and Lange, R o l f V., Petrographic and f l u o r e s c e n c e p r o p e r t i e s of r e s i n i t e macerals from western U.S. c o a l s . Proceedings of the Fifth Symposium on the Geology of Rocky Mountain Coal., 1982, pp. 187-191. C r e l l i n g , John C., Current uses of f l u o r e s c e n c e microscopy i n c o a l p e t r o l o g y . J o u r n a l of Microscopy, 1983, 132, p t . 3, 132-147. Ottenjann, Κ., Wolf, M. and W o l f - F i s c h e r , Ε., Beziehugen zwurischen der Fluoreszenz von Vitriniten und den t e c h n o l o g i schen Eigenschaften von Kohlen. Proc. I n t e r n a t i o n a l Conf. of Coal Science, 1981, pp. 86-89. van Gijzel, P., Manual of the techniques and some g e o l o g i c a l a p p l i c a t i o n s of f l u o r e s c e n t microscopy. Workshop sponsored by Am. Assoc. of S t r a t . P a l y n o l o g i s t , Core L a b o r a t o r i e s , Inc., D a l l a s .

RECEIVED January 1, 1984

4 Microscopic IR Spectroscopy of Coals DOUGLAS BRENNER

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch004

Exxon Research and Engineering Company, Linden, N J 07036

A new microscopic IR ( i n f r a r e d ) spectroscopy technique now makes p o s s i b l e chemical f u n c t i o n a l group a n a l y s i s of i n d i v i d u a l macerals i n c o a l s . Regions as small as 20 micrometers across can be a n a l y z e d . The technique utilizes a computer- c o n t r o l l e d IR microspectrophotometer i n c o n j u n c t i o n w i t h newly-developed procedures f o r preparing uncontaminated t h i n s e c t i o n s of coals. D u r i n g p r e p a r a t i o n , the coal is held by a completely s o l u b l e adhesive. The adhesive i s removed from the ground t h i n s e c t i o n using a solvent chosen to have minimal e f f e c t on the coal. This new IR technique differs from most analyses of chemical functionalities in coals which use ground-up p a r t i c u l a t e samples. These samples g e n e r a l l y contain a great v a r i e t y of o r g a n i c maceral types which are intermixed on a microscopic level, as well as various m i n e r a l s . Analyses of such samples give only averaged i n f o r m a t i o n , rather than being characteristic of any i n d i v i d u a l component. In c o n t r a s t , w i t h the microscopic IR spectroscopy technique described here, i n d i v i d u a l subcomponents of the coal are IR analyzed and i n a d d i t i o n they can be observed visually i n the microspectrometer i n the context of their surroundings. Using this t e c h n i q u e , v a r i a t i o n s from specimen t o specimen w i t h i n a given maceral t y p e , or even h e t e r o g e n e i t i e s w i t h i n a s i n g l e maceral, can be s t u d i e d . In this c h a p t e r , d e t a i l s of this new technique are d i s c u s s e d and r e p r e s e n t a t i v e s p e c t r a of s i n g l e macerals of vitrinite, and i n d i v i d u a l megaspores in Illinois No. 6 coal are d e s c r i b e d .

0097-6156/84/0252-0047$06.00/0 © 1984 American Chemical Society

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch004

48

COAL MACERALS

Coals are heterogeneous on a m i c r o s c o p i c s c a l e . Because of t h i s i t i s d e s i r a b l e to c h a r a c t e r i z e the coal at as f i n e a s p a t i a l l e v e l as p o s s i b l e . IR ( i n f r a r e d ) spectroscopy i s widely used i n coal science and technology to i d e n t i f y both o r g a n i c and i n o r g a n i c f u n c t i o n a l groupings i n c o a l s ; however, i t has only been able t o analyze macroscopic samples. The conventional preparation of coals f o r i n f r a r e d a n a l y s i s uses f i n e l y ground samples. This i s because of the opacity of the coal i n some s p e c t r a l ranges. For t h i s reason, the p a r t i c l e s should g e n e r a l l y be l e s s than about 20 micrometers t h i c k . Techniques i n common use i n c l u d e i n c o r p o r a t i n g the p a r t i c l e s i n potassium bromide d i s k s (_1), or s l u r r y i n g them i n a hydrocarbon o i l such as Nujol [2). Such p a r t i c u l a t e samples generally i n c l u d e a wide range of types of v i t r i n i t e and other m a c é r a i s which are derived from d i f f e r e n t p l a n t s (such as t r e e s , bushes, and grasses) and from various parts of each plant (such as t r u n k s , stems, r o o t s , l e a v e s , e t c . ) . In a d d i t i o n , i n o r g a n i c substances of various types and degrees of d i s p e r s i o n are g e n e r a l l y mixed i n . Because of t h e i r d i f f e r e n t d e r i v a t i o n s , the various organic plant remnants are l i k e l y to have d i f f e r e n t physicochemical c h a r a c t e r i s t i c s ; however, because of the i n t i m a t e mixing of these subcomponents, which u s u a l l y occurs on a microscopic s c a l e , i t i s d i f f i c u l t to separately c h a r a c t e r i z e the d i f f e r e n t maceral components. Therefore, IR spectra obtained on p u l v e r i z e d coal samples give averaged information rather than being c h a r a c t e r i s t i c of any i n d i v i d u a l component i n the c o a l . A few techniques have been u t i l i z e d i n the past to overcome t h i s problem. These i n c l u d e the hand separation of m a c é r a i s (3_,4), s i n k - f l o a t t e c h n i q u e s , and the recently developed meThod of c e n t r i f u g a l separation of very f i n e l y p u l v e r i z e d coal (J5). These p r e p a r a t i o n techniques provide a mixture of material which i s h i g h l y enriched i n a s e l e c t e d maceral t y p e . These maceral concentrates can then be analyzed by a v a r i e t y of chemical procedures. The averaged p r o p e r t i e s o f a maceral type can be c h a r a c t e r i z e d using these procedures, but they do not enable the IR a n a l y s i s of i n d i v i d u a l microscopic m a c é r a i s . The p a r t i c u l a t e samples of coal used f o r i n f r a r e d a n a l y s i s must be f i n e l y ground because of the high absorbance of the c o a l . The p a r t i c l e s must be l e s s than roughly 20 micrometers t h i c k (depending on the rank) f o r s u b s t a n t i a l transmission o f the IR r a d i a t i o n i n the more absorbing regions of the spectrum. The small p a r t i c l e s of coal cause c o n s i d e r a b l e s c a t t e r i n g t o appear i n the IR spectrum. Other c o m p l i c a t i o n s are the d i f f e r e n c e s i n the t h i c k n e s s e s of the various p a r t i c l e s o f the sample, and the v a r i a t i o n s i n t h i c k n e s s along each particle. For example, the t h i n n e r edges (with respect to the i l l u m i n a t i n g beam) of the p a r t i c l e s w i l l be more transparent than the c e n t r a l r e g i o n s , so the volume of the p a r t i c l e s may

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch004

4. B R E N N E R

Microscopic

IR Spectroscopy

49

not be sampled u n i f o r m l y . This can be a problem f o r a heterogeneous material such as c o a l . "Thin s e c t i o n samples o f coal having a r e l a t i v e l y uniform t h i c k n e s s of 20 micrometers or l e s s have been used o c c a s i o n a l l y i n the past (_6). However, the d i f f i c u l t i e s i n preparing these t h i n s e c t i o n samples and problems of contamination with the adhesives used i n the p r e p a r a t i o n of the s e c t i o n s {]_) has l i m i t e d t h e i r usage. A l s o , because the cross s e c t i o n a l area of the samples must be s e v e r a l square m i l l i m e t e r s or more f o r a n a l y s i s w i t h most IR spectrometers, microscopic components of the t h i n s e c t i o n s could not be i n d i v i d u a l l y a n a l y z e d . In t h i s chapter a new technique f o r the IR s p e c t r o s c o p i c a n a l y s i s of i n d i v i d u a l microscopic components i n coals i s d e s c r i b e d . This method combines new procedures f o r preparing uncontaminated t h i n s e c t i o n specimens of coal w i t h a s e n s i t i v e IR microspectrophotometer which has r e c e n t l y become commercially a v a i l a b l e . D e t a i l s of t h i s new technique are discussed and some r e p r e s e n t a t i v e s p e c t r a are d e s c r i b e d . Experimental The technique used to prepare uncontaminated t h i n s e c t i o n samples of c o a l s was as f o l l o w s . A chunk of coal about 1.5 cm across was cut p e r p e n d i c u l a r to the bedding plane to produce a roughly f l a t s u r f a c e . This surface was ground smooth on a 20 cm diameter wheel using 600 g r i t and then 8 micrometer s i l i c o n carbide on d i s k s . To avoid surface r e l i e f i n the sample, o n l y hard surface abrasive d i s k s were used; p o l i s h i n g c l o t h s were not employed. The f l a t surface was cemented to a glass s l i d e w i t h a t h e r m o p l a s t i c hydrocarbon-based adhesive ( P a r a p l a s t , manufactured by the Lancer Company) which i s s o l u b l e i n hexane. Hexane i s a good choice f o r the solvent s i n c e i t has r e l a t i v e l y l i t t l e e f f e c t on the c o a l . A temperature of about 70°C was used i n m e l t i n g and a p p l y i n g the adhesive. The coal was exposed t o t h i s temperature f o r only about a minute before c o o l i n g was s t a r t e d . The coal on the s l i d e was ground t o a t h i c k n e s s of 15 micrometers using the abrasives described above. The g r i n d i n g of p é t r o g r a p h i e samples using standard techniques on a conventional h o r i z o n t a l g r i n d i n g wheel having a hard abrasive surface i s well known t o produce highly f l a t , low r e l i e f s u r f a c e s . For the t h i n s e c t i o n , the upper and lower surfaces may not be p r e c i s e l y p a r a l l e l . However, t h i s causes only very s l i g h t d i f f e r e n c e s i n t h i c k n e s s across the observed o r analyzed area because one sees only a very s m a l l , highly magnified region of the s u r f a c e . In any c a s e , i t i s p o s s i b l e t o detect d i f f e r e n c e s i n t h i c k n e s s of l e s s than a micron across a sample by using a high numerical aperature o b j e c t i v e having a very shallow depth of f i e l d .

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch004

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The completed sample was soaked i n hexane at room temperature u n t i l the t h i n specimen f l o a t e d o f f of the s l i d e . The sample came o f f as a number of small pieces of various s i z e s from l e s s than a m i l l i m e t e r across t o several m i l l i m e t e r s l o n g . Although no r e s i d u a l adhesive could be observed on the pieces of c o a l , to i n s u r e complete removal of the adhesive the samples were immersed i n a l a r g e excess of f r e s h solvent f o r several days. Then the hexane was decanted o f f and the specimens were stored i n nitrogen at room temperature u n t i l they were used. If d e s i r e d , the p r e p a r a t i o n process can be c a r r i e d out i n an i n e r t atmosphere by e n c l o s i n g the equipment i n a dry box, a p l a s t i c glove bag or simply i n a p l a s t i c bag w i t h s l i t s f o r the hands. An i n e r t atmosphere may be d e s i r a b l e f o r cementing the coal to the s l i d e e s p e c i a l l y i f temperatures above about 100°C are used f o r m e l t i n g the t h e r m o p l a s t i c . For other p a r t s of the p r e p a r a t i o n an i n e r t atmosphere i s not as important s i n c e o x i d a t i o n at room temperature i s much s l o w e r . The choice of the t h e r m o p l a s t i c adhesive and the s o l v e n t used t o remove i t from the coal are important f o r o b t a i n i n g t h i n s e c t i o n s of coal which are only minimally a f f e c t e d by the preparation p r o c e s s . Some c o n s i d e r a t i o n s i n choosing the adhesive are l i s t e d below. (1) The adhesive should have reasonably good adhesion to the coal and to the g l a s s s l i d e . (2) The adhesive should be r e a d i l y s o l u b l e i n the solvent and should leave no r e s i d u e . (3) The solvent used should have minimal e f f e c t on the coal w i t h respect to chemical and p h y s i c a l i n t e r a c t i o n s , e x t r a c t i o n , and s w e l l a b i l i t y . (4) The s o l v e n t should be completely removed from the coal on d r y i n g . (5) The temperature required f o r cementing the coal should be as low as p o s s i b l e to avoid thermal changes i n the c o a l , but not so low t h a t the adhesive w i l l be softened during subsequent g r i n d i n g . (6) The adhesive should be r e l a t i v e l y i n e r t to avoid r e a c t i o n w i t h , or attachment t o , the c o a l . (7) The v i s c o s i t y of the adhesive during cementing of the coal should be no lower than necessary i n order to minimize penetration o f the adhesive i n t o the m i c r o s t r u c t u r e of the c o a l . (8) The molecular weight of the adhesive should p r e f e r a b l y be high t o minimize d i f f u s i o n of the adhesive molecules i n t o the coal structure. (9) It i s d e s i r a b l e t h a t the adhesive not have absorption peaks i n regions where the coal has important s p e c t r a l peaks. A l s o , i t i s d e s i r a b l e t h a t the adhesive have one of i t s strongest absorptions i n a region where the coal has no strong peaks so t h a t any r e s i d u a l adhesive could be e a s i l y detected and compensated f o r . (10) The adhesive should p r e f e r a b l y be a reasonably pure m a t e r i a l so that the p o s s i b i l i t y of minor c o n s t i t u e n t s being s e l e c t i v e l y absorbed or r e a c t i n g with the coal i s a v o i d e d . It i s d i f f i c u l t t o simultaneously optimize a l l of these c r i t e r i a , so the adhesive employed i s g e n e r a l l y a compromise.

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch004

4. B R E N N E R

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The microscopic i n f r a r e d spectrophotometer used i n t h i s work (NanoSpec/20IR manufactured by Manometries Inc.) operates i n t r a n s m i s s i o n and contains r e f l e c t i n g l e n s e s . The v i s u a l as well as the IR image i s normally observed i n the t r a n s m i t t e d r a d i a t i o n mode. Though, i f d e s i r e d , the sample can a l s o be i l l u m i n a t e d with a l i g h t source from above and viewed v i s u a l l y i n r e f l e c t e d l i g h t . A schematic diagram of the apparatus i s shown i n Figure 1. Because of the r e f l e c t i n g o p t i c s , the v i s u a l and IR images of the sample correspond and the region of the sample being analyzed can r e a d i l y be i d e n t i f i e d v i s u a l l y w h i l e i t i s i n place i n the IR microscope. This enables unambiguous c o r r e l a t i o n of v i s u a l microscopic c h a r a c t e r i z a t i o n and IR a n a l y s i s f o r the same area of the sample. The condenser and the o b j e c t i v e of the microscope are both 15 power, 0.28 numerical aperature r e f l e c t i n g l e n s e s . The part of the sample to be IR analyzed i s o p t i c a l l y d e l i n e a t e d by an a d j u s t a b l e aperature at the image plane of the o b j e c t i v e , so no masking i s needed at the sample i t s e l f to d e f i n e the analyzed a r e a . The useful IR range of the instrument i s from about 4000 t o 700 cm" (2.5 t o 14 micrometers). The IR monochromator i s a variable interference f i l t e r . The r e s o l u t i o n i s only about 1% of the wave number value over the IR range; however, t h i s should be adequate f o r many a p p l i c a t i o n s w i t h coal because of the breadth of most of the absorbances. The IR source i s a Nernst Glower and the d e t e c t o r i s a l i q u i d nitrogen cooled mercury cadmium t e l l u r i d e photodetector having high sensitivity. The operation of the spectrometer i s computerc o n t r o l l e d and the d a t a , which i s stored d i g i t a l l y , can be a u t o m a t i c a l l y averaged and d i f f e r e n c e spectra can be o b t a i n e d . 1

Results In t h i s p r e l i m i n a r y study, s p e c t r a l c h a r a c t e r i s t i c s of v i t r i n i t e and l i p t i n i t e m a c é r a i s i n I l l i n o i s No. 6 coal (high v o l a t i l e C bituminous rank) were examined to evaluate the u t i l i t y of t h i s new technique f o r microscopic IR a n a l y s i s of coals. In Figure 2, a photomicrograph of a t h i n s e c t i o n specimen c o n s i s t i n g of a megaspore (a form of l i p t i n i t e ) surrounded by r e l a t i v e l y homogeneous v i t r i n i t e i s shown. The t h i n s e c t i o n was placed on a barium f l u o r i d e d i s k on the stage of the IR microscope. The megaspore and a region of the v i t r i n i t e l y i n g c l o s e to the megaspore on the same specimen were analyzed w i t h the IR microscope. The analyzed regions are i n d i c a t e d by rectangles drawn on the photograph of the sample; they are each about 55 micrometers wide by 180 micrometers l o n g . Spectra of the two regions were taken i n a i r at room temperature; they are compared i n Figure 3 . The spectra are d i s p l a c e d v e r t i c a l l y t o avoid o v e r l a p p i n g . The d i s p l a y e d spectra a c t u a l l y i n v o l v e a reference or background scan which

COAL MACERALS

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DETECTOR TARGET (LIQ. Ν COOLED H C T.) 2

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Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch004

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Figure 1.

Optical diagram of microspectrophotometer.

Microscopic

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch004

4. BRENNER

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IR Spectroscopy

Figure 2. Thin s e c t i o n sample of I l l i n o i s No. 6 coal c o n t a i n i n g regions of v i t r i n i t e and l i p t i n i t e .

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Figure 3 . IR spectra of microscopic regions of v i t r i n i t e and l i p t i n i t e i n the same t h i n s e c t i o n sample of I l l i n o i s No. 6 c o a l .

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was taken without the sample present but with a l l other c o n d i t i o n s the same. The subsequent sample spectra are a u t o m a t i c a l l y normalized w i t h respect t o the background spectrum which i s stored i n the microcomputer. Each of the two sample spectra i n Figure 3 are 2 minute s c a n s . There i s a very high s i g n a l to noise r a t i o f o r the scans i n Figure 3 . Subsequently a 1 minute scan was made on a s i m i l a r sample of v i t r i n i t e . This spectrum was taken on a s m a l l e r region which measured only 25 by 100 micrometers. For t h i s scan there was no obvious noise on the t r a c e from 4000 cm down to 1400 c m ' . Below about 1400 cm" noise was e a s i l y seen. A f t e r the f i r s t s c a n , a second 1 minute scan was t a k e n . The repeat scan l a y almost e x a c t l y on top of the f i r s t scan from 4000 cm" down t o 1400 cm" i n d i c a t i n g good r e p r o d u c i b i l i t y . Below about 1400 cm" the scans were l e s s c o i n c i d e n t because of the s l i g h t amount of n o i s e . A number of d i f f e r e n c e s between the l i p t i n i t e and v i t r i n i t e s p e c t r a are apparent i n Figure 3 . Note t h a t s i n c e t h e t h i c k n e s s e s of the l i p t i n i t e and v i t r i n i t e regions are very nearly the same and s i n c e s c a t t e r i n g i s m i n i m a l , these s p e c t r a can be d i r e c t l y compared q u a n t i t a t i v e l y on a per u n i t volume b a s i s . Some of the more prominent of the d i f f e r e n c e s are as f o l l o w s . The broad hydroxyl peak around 3350 cm" i s much deeper f o r the v i t r i n i t e . This probably i s caused c h i e f l y by a much l a r g e r number of phenols i n the v i t r i n i t e , but water absorbed i n the v i t r i n i t e could a l s o c o n t r i b u t e to t h i s peak. Between 2800 and 2975 cm" the l i p t i n i t e shows a much stronger absorption than the v i t r i n i t e . This i n d i c a t e s much more a l i p h a t i c hydrogen i n -CH, - C H , and -CH3 groups i n the liptinite. In t h i s a l i p h a t i c absorbing region i t i s a l s o evident t h a t at about 2850 cm" the l i p t i n i t e shows a s u b s t a n t i a l l y l a r g e r peak than the v i t r i n i t e on the s i d e of t h e l a r g e r a b s o r p t i o n . At about 1600 cm" the v i t r i n i t e peak i s much l a r g e r than the l i p t i n i t e peak probably i n d i c a t i n g much more aromatic c h a r a c t e r i n the v i t r i n i t e . (Note, however, t h a t oxygen-containing f u n c t i o n a l groups can a l s o c o n t r i b u t e to t h i s r e g i o n . ) Conversely, the c a r b o x y l i c a c i d peak near 1700 cm" and the C H , CHo peak around 1440 cm" are much more pronounced f o r the l i p t i n i t e . The s p e c t r a c l e a r l y c o n t r a s t the more aromatic and hydroxyl (or p o s s i b l y water) c o n t a i n i n g s t r u c t u r e of the v i t r i n i t e to the more a l i p h a t i c s t r u c t u r e of the liptinite. Mention should be made of some a r t i f a c t s which appear i n the spectra of Figure 3 . At about 2350 cm" there i s a peak caused by changes i n the CO2 c o n c e n t r a t i o n of the a i r . The major c o n t r i b u t o r to the changes i s probably the operator's b r e a t h i n g . Smoking i n the v i c i n i t y can cause p a r t i c u l a r l y l a r g e changes. (This peak could be e l i m i n a t e d , i f d e s i r e d , by s e a l i n g the region of the beam path and m a i n t a i n i n g a n i t r o g e n 1

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atmosphere). At about 2250 cm" and 1230 cm" are peaks caused by changes i n the IR f i l t e r s . Three f i l t e r s are used t o o b t a i n the f u l l spectrum, and small peaks occur where the second and t h i r d f i l t e r s are brought i n t o use. These peaks are probably a consequence of the abrupt changes i n transmittance which occur when the f i l t e r s are changed. Another a r t i f a c t i s broad peaks seen around 2100 cm" i n the l i p t i n i t e spectrum, 1950 cm" i n the v i t r i n i t e spectrum and i n some other a r e a s . These peaks are caused by i n t e r f e r e n c e f r i n g e s which a r i s e from the IR r a d i a t i o n being i n t e r n a l l y r e f l e c t e d from the top and bottom surfaces of the sample. The f r i n g e s can be m i s l e a d i n g i f they are not c o r r e c t l y i d e n t i f i e d . One other e f f e c t which could p o t e n t i a l l y lead to spurious peaks i s small d e v i a t i o n s i n the p o s i t i o n i n g of the f i l t e r s by the stepping motor. These p o s i t i o n a l d e v i a t i o n s are f a r below the r e s o l u t i o n of the instrument, but i f sharp peaks are present i n the background spectrum, these d e v i a t i o n s could cause small peaks to appear at the p o s i t i o n s of the steepest slopes of the n u l l e d - o u t background peaks. The a p p l i c a b i l i t y of t h i s technique f o r "in s i t u " IR analyses during chemical treatments and the a b i l i t y to perform k i n e t i c measurements was t e s t e d by observing the e f f e c t of applying deuterated p y r i d i n e to a t h i n s e c t i o n of v i t r i n i t e and then a l l o w i n g i t to d r y . An area 40 X 180 micrometers was a n a l y z e d . (Although the t h i n sample had been stored at room temperature i n dry nitrogen gas, i t q u i c k l y e q u i l i b r a t e s w i t h the room a i r . ) F i r s t a spectrum was taken of the untreated sample. Then the solvent was placed on the sample and r e p e t i t i v e scans were made to monitor changes i n the IR spectrum as the deuterated p y r i d i n e evaporated. Figure 4 shows spectra of the untreated sample, the sample wet with p y r i d i n e , and the sample a f t e r d r y i n g f o r about 20 minutes. For t h i s l a s t spectrum, peaks c h a r a c t e r i s t i c of deuterated p y r i d i n e are s t i l l prominent, such as those at about 950 and 820 cm" . Scans at l a t e r times showed no a p p r e c i a b l e l e s s e n i n g of the peaks. The r e t e n t i o n of some of the p y r i d i n e i s c o n s i s t e n t with the r e s u l t s of C o l l i n s et. ^1_. (_8). Tests were made t o determine the minimum area of a n a l y s i s which could be conveniently used with t h i n s e c t i o n s of coal by t h i s t e c h n i q u e . Figure 5 shows s p e c t r a of regions of a t i n y , roughly 30 X 30 micrometer, piece of v i t r i n i t e . One spectrum was taken using a 21 X 21 micrometer a n a l y z i n g a r e a , and the other spectrum was taken using a 20 X 30 micrometer a n a l y z i n g area. Four minutes were used f o r each scan, for t h i s scan t i m e , the smaller area gives q u i t e a noisy spectrum, but the 20 X 30 micrometer spectrum i s much b e t t e r . By using a longer scanning t i m e , or by accumulating r e p e t i t i v e scans t h i s spectrum could probably be made q u i t e r e s p e c t a b l e . The s p e c t r a l region having the greatest problem i n the a n a l y s i s of 1

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Figure 4. IR spectra of a m i c r o s c o p i c region of v i t r i n i t e i n a t h i n s e c t i o n of I l l i n o i s Ν ο · 6 c o a l . Top: untreated sample; m i d d l e : l i q u i d deuterated p y r i d i n e on the sample; bottom: a f t e r p y r i d i n e has evaporated.

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch004

BRENNER

Microscopic

IR Spectroscopy

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Figure 5 . IR spectra of a t h i n s e c t i o n sample of I l l i n o i s No. 6 coal having an area of 30 ym χ 30 Top: d e l i n e a t e d area i s 2 1 p m x 2 1 ym; bottom: d e l i n e a t e d area i s 20 pm χ 30 ym.

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such very small areas i s below 1000 cm" where the s e n s i t i v i t y of the spectrometer f a l l s o f f . Subcomponents or m a c é r a i s i n the coal which are somewhat l e s s than 25 micrometers across can probably be IR analyzed by using long data accumulation t i m e s . Preferably such small subcomponents should be p h y s i c a l l y separated from the surrounding m a t e r i a l . A l t e r n a t i v e l y , the spectrum of a region i n c l u d i n g the subcomponent as well as some of the surrounding material could be substracted (using an appropriate n o r m a l i z a t i o n f a c t o r ) from a spectrum only of the surrounding m a t e r i a l i n order to i s o l a t e the c o n t r i b u t i o n of the subcomponent. Note, however, t h a t f o r subcomponent s i z e s near the wavelength of the IR r a d i a t i o n the p o s s i b i l i t y of i n t e r f e r e n c e e f f e c t s from the edges of the sample must be c o n s i d e r e d . Such e f f e c t s ought to be made apparent by comparing s p e c t r a from subcomponents having d i f f e r e n t s i z e s or shapes.

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch004

1

Discussion Infrared spectra of good q u a l i t y have been obtained on uncontaminated i n d i v i d u a l microscopic m a c é r a i s and microscopic subregions i n c o a l s . This development enables the IR c h a r a c t e r i z a t i o n of microscopic i n d i v i d u a l subcomponents of coals and other s o l i d f o s s i l f u e l s as opposed t o o b t a i n i n g s t a t i s t i c a l l y averaged data on complex m i x t u r e s . In a d d i t i o n t o c h a r a c t e r i z i n g the chemical f u n c t i o n a l i t i e s of the major c l a s s i f i c a t i o n s of m a c é r a i s i n bituminous and brown c o a l s , v a r i a t i o n s of chemical f u n c t i o n a l i t i e s w i t h i n each maceral c l a s s i f i c a t i o n can be s t u d i e d . S u b s t a n t i a l d i f f e r e n c e s are t o be expected, e s p e c i a l l y i n the younger coals i n view of the range of b i o l o g i c a l d e r i v a t i o n s w i t h i n each maceral c l a s s i f i c a t i o n . V a r i a t i o n s i n f u n c t i o n a l i t i e s over microscopic d i s t a n c e s w i t h i n a s i n g l e maceral can a l s o be s t u d i e d . Effects of chemical and thermal treatments on the various maceral types can be examined e i t h e r by t r e a t i n g the coal on the stage of the IR microscope or by s p e c t r o s c o p i c a l l y a n a l y z i n g the same microscopic region of a sample before and a f t e r treatment. This technique should a l s o be a p p l i c a b l e f o r the a n a l y s i s of v i r t u a l l y any chemical process or chemical treatment of coal which causes changes i n the IR spectrum and i n which the area of i n t e r e s t i s i d e n t i f i a b l e a f t e r the t r e a t m e n t . In Figure 3 the IR spectrum of a subregion of v i t r i n i t e about 0.010 mm i n area i s compared with the IR spectrum from an equal area which i s w i t h i n a s i n g l e megaspore. The two regions of a n a l y s i s are on the same piece of t h i n s e c t i o n and they are separated by only about 160 micrometers. The two minute scans of the 15 micrometer t h i c k samples give e x c e l l e n t s i g n a l t o noise r a t i o s . As described i n the r e s u l t s s e c t i o n , these spectra c l e a r l y c o n t r a s t the more aromatic and h y d r o x y l 2

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c o n t a i n i n g s t r u c t u r e of the v i t r i n i t e t o the more a l i p h a t i c s t r u c t u r e of the megaspore. The a b i l i t y to analyze c l o s e l y l y i n g regions having i d e n t i c a l p r e p a r a t i o n , equal areas being a n a l y z e d , and the same t h i c k n e s s , f a c i l i t a t e s q u a n t i t a t i v e comparisons of the r e g i o n s . Thus, w h i l e these data are g e n e r a l l y c o n s i s t e n t with the r e s u l t s of Bent and Brown (_9) taken on maceral c o n c e n t r a t e s , the present technique enables a more d i r e c t q u a n t i t a t i v e comparison of the s p e c t r a . The s p e c t r a i n Figure 4 demonstrate the "in s i t u " treatment of an uncontaminated t h i n s e c t i o n of c o a l . One o p e r a t i o n a l d i f f i c u l t y i s the p o s s i b i l i t y of movement of the sample during treatment which would make a n a l y s i s of the same microscopic region before and a f t e r treatment d i f f i c u l t . For example, a p p l i c a t i o n of a drop of s o l u t i o n t o the coal i s l i k e l y to cause movement. Movement can be avoided by securing the sample, but t h i s may be d i f f i c u l t f o r small samples or i t may a f f e c t the sample. A l t e r n a t i v e l y , i f the region under a n a l y s i s i s c a r e f u l l y recorded, such as on a photograph, then during or a f t e r treatment the sample can be accurately r e p o s i t i o n e d on the s t a g e . Figure 5 demonstrates t h a t i s o l a t e d samples of coal l e s s than 30 micrometers across can be s a t i s f a c t o r i l y IR analyzed and t h a t d e l i n e a t e d regions of a sample l e s s than 25 micrometers across can be c h a r a c t e r i z e d by IR. Signal t o noise l e v e l s which are improved over those shown i n Figure 5 can be obtained by using longer data accumulation t i m e s . A l t e r n a t i v e l y , i f b e t t e r q u a l i t y data i s required only f o r some small regions of the spectrum, then those regions alone can be scanned to shorten the time needed t o o b t a i n an acceptable s i g n a l t o noise l e v e l . The a b i l i t y t o analyze small regions of a coal sample i s important even f o r a s i n g l e maceral type such as v i t r i n i t e . For example, s u b s t a n t i a l v a r i a t i o n s occur i n the s t r u c t u r e ( 1 0 , 1 1 ) and swell a b i l i t y (12J of d i f f e r e n t microscopic areas of v i t r i n i t e from the same c o a l . In the IR microscope the region of the sample being analyzed i s d e l i n e a t e d by a v a r i a b l e aperature at the image plane of the o b j e c t i v e . Therefore, no s p a c i a l r e s t r i c t i o n s are placed around or near the sample i t s e l f . Since the image of the sample has been s u b s t a n t i a l l y magnified at t h i s image p l a n e , i t i s r e l a t i v e l y easy t o a c c u r a t e l y d e f i n e even very small subregions of the sample f o r a n a l y s i s w i t h the a p e r a t u r e . However, the geometrical region d e l i n e a t e d by the v a r i a b l e aperature which i s observed v i s u a l l y i s not nearly so well defined f o r the i n f r a r e d r a d i a t i o n because of d i f f r a c t i o n effects. The s p a t i a l u n c e r t a i n t y i s p r o p o r t i o n a l to the wavelength, so the r e s o l u t i o n i s c o n s i d e r a b l y poorer near the long wavelength end of the IR range. The divergence or angular spread of the IR beam passing through the sample, which i s determined by the numerical a p e r a t u r e , w i l l f u r t h e r d i m i n i s h

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the s p a t i a l s p e c i f i c i t y of the d e l i n e a t e d a r e a . Of course, the t h i c k e r the sample, the more of a problem t h i s becomes. For a n a l y s i s of a very small subregion i n the c o a l , the most unambiguous way to avoid c o n t r i b u t i o n s from contiguous m a t e r i a l i s to p h y s i c a l l y remove the subcomponent from the surrounding material. The 15 micrometer t h i c k n e s s of the I l l i n o i s No. 6 coal used f o r these spectra i s q u i t e s a t i s f a c t o r y s i n c e the percent t r a n s m i s s i o n s of a number of the l a r g e r peaks are below 40 p e r c e n t , but without s a t u r a t i o n . A l s o , at t h i s t h i c k n e s s the t h i n s e c t i o n s can be conveniently manipulated without fracturing. Using the described g r i n d i n g technique f o r p r e p a r a t i o n , samples c o n t a i n i n g any maceral types and even s u b s t a n t i a l amounts of mineral matter can be prepared. There appears t o be no reason why the technique can not be a p p l i e d t o peat on up i n rank through the bituminous coal range - - perhaps even to a n t h r a c i t e s i f samples can be made t h i n enough. The only requirement i s the preparation of samples s u f f i c i e n t l y t h i n f o r the IR r a d i a t i o n to penetrate and which are more than about 20 micrometers a c r o s s . So f a r we have s u c c e s s f u l l y examined c o a l s of ranks from subbituminous to high v o l a t i l e A bituminous. The i n t e r f e r e n c e peaks which occur i n the spectra of Figure 3 can be m i s l e a d i n g when t r y i n g to i n t e r p r e t the s p e c t r a . These f r i n g e s occur when some of the IR r a d i a t i o n r e f l e c t s from the top and bottom surfaces of the sample and then i n t e r f e r e s w i t h the u n r e f l e c t e d beam. The f r i n g e s are p a r t i c u l a r l y a problem where the top and bottom surfaces are nearly p a r a l l e l and where the t h i c k n e s s of the sample i s comparable t o the wavelengths of the r a d i a t i o n , such as f o r the t h i n s e c t i o n specimens used i n the technique described here. However, the i n t e n s i t y of the i n t e r f e r i n g beam i s not l a r g e s i n c e i t i s r e f l e c t e d t w i c e and i t passes through the sample three times i n s t e a d of once. Thus, as seen i n Figure 3 , the f r i n g e s are most prominent i n the s p e c t r a l regions having low absorbance. The f r i n g e s can be p a r t i a l l y compensated f o r by determining t h e i r p o s i t i o n and i n t e n s i t y i n a low absorbance region and then c a l c u l a t i n g and s u b t r a c t i n g out t h e i r c o n t r i b u t i o n t o other parts of the spectrum where t h e i r presence i s l e s s o b v i o u s . A l t e r n a t i v e l y , t i l t i n g the sample, or using samples of d i f f e r e n t t h i c k n e s s e s and of higher adsorbance can be used t o i d e n t i f y the e f f e c t s of the f r i n g e s on a spectrum so t h a t they can be compensated f o r . In conventional t r a n s m i s s i o n IR of coal where crushed p a r t i c u l a t e samples are used, the v a r i a t i o n of t h i c k n e s s along each p a r t i c l e may cause a problem i n t h e i r q u a n t i t a t i v e a n a l y s i s . This problem occurs because the amount of r a d i a t i o n passing through an o b j e c t decreases e x p o n e n t i a l l y w i t h t h i c k n e s s r a t h e r than l i n e a r l y . So, f o r peaks which absorb a

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s u b s t a n t i a l f r a c t i o n of the r a d i a t i o n , the t h i c k e r regions of the p a r t i c l e are "sampled" by the IR beam d i f f e r e n t l y from the t h i n n e r ( e . g . edges) r e g i o n s . Among the consequences of such nonuniform sampling would be e f f e c t s on the peak heights and peak shapes. S i m i l a r l y , i f the r a d i a t i o n passes through a number of p a r t i c l e s i n t r a v e r s i n g the sample, then a p p r e c i a b l e v a r i a t i o n s i n the cumulative amount of m a t e r i a l passed through at d i f f e r e n t points i n the cross s e c t i o n would cause problems. Ihe problem i s i l l u s t r a t e d i n Figure 6. Oh the l e f t i n the f i g u r e i s a uniform d i s t r i b u t i o n of m a t e r i a l . On the r i g h t i s the same q u a n t i t y of m a t e r i a l but i t has a t h i c k n e s s of one u n i t over o n e - h a l f of the area and a t h i c k n e s s of seven u n i t s over the other h a l f . If the a b s o r p t i v i t y of the m a t e r i a l i s such t h a t i t t r a n s m i t s 37 percent of the i n c i d e n t r a d i a t i o n f o r the uniform t h i c k n e s s shown i n the f i g u r e , then the same q u a n t i t y of material with the nonuniform t h i c k n e s s shown on the r i g h t of the f i g u r e w i l l t r a n s m i t 48 percent of the i n c i d e n t r a d i a t i o n . Only f o r samples which at t h e i r t h i c k e s t part absorb only a small f r a c t i o n of the i n c i d e n t r a d i a t i o n ( f o r the s e l e c t e d wavelengths) w i l l the i n t e n s i t y of r a d i a t i o n passing through a sample of nonuniform t h i c k n e s s c l o s e l y approximate the i n t e n s i t y t r a n s m i t t e d by the same q u a n t i t y of m a t e r i a l of uniform t h i c k n e s s . (For high v o l a t i l e C bituminous coal having a t h i c k n e s s of 15 micrometers, the stronger bands absorb over 50 percent of the i n c i d e n t r a d i a t i o n . ) Grinding coal much below 15 micrometers i s d i f f i c u l t with many conventional mechanical g r i n d e r s . In a d d i t i o n , nonuniform d i s t r i b u t i o n of the p a r t i c l e s sometimes o c c u r s . It should be noted t h a t even when nonuniform sampling of the coal p a r t i c l e s by the IR beam o c c u r s , l i n e a r increases i n absorbance w i t h increased sample c o n c e n t r a t i o n ( e . g . s a t i s f y i n g Beer's law) can o c c u r . In p a r t i c u l a r , Beer's law holds approximately f o r a sample i n which the p a r t i c l e s cover only a small f r a c t i o n of the cross s e c t i o n a l area of the r a d i a t i o n beam, even though w i t h i n the i n d i v i d u a l p a r t i c l e s , regions of d i f f e r e n t t h i c k n e s s are averaged d i f f e r e n t l y . For t h i s reason, i n q u a n t i t a t i v e IR work w i t h p a r t i c u l a t e samples of c o a l , i t i s d e s i r a b l e t o examine the sample w i t h an o p t i c a l microscope to estimate the transparency or t h i c k n e s s of the i n d i v i d u a l p a r t i c l e s and the u n i f o r m i t y of d i s t r i b u t i o n of the p a r t i c l e s . For example, i f p a r t i c l e s f i v e micrometers or more across cover an a p p r e c i a b l e f r a c t i o n of the cross s e c t i o n a l area of the sample, or i f the sample appears mottled or grainy i n c o l o r under, say, 20 power m a g n i f i c a t i o n i n t r a n s m i t t e d l i g h t , then problems with q u a n t i t a t i v e a n a l y s i s are a p o s s i b i l i t y . Uhless c o n s i d e r a b l e care i n sample preparation i s t a k e n , nonuniform p a r t i c l e d i s t r i b u t i o n s and/or s u b s t a n t i a l q u a n t i t i e s of p a r t i c l e s or p a r t i c l e agglomerates over f i v e micrometers t h i c k may o c c u r . The d i f f i c u l t i e s from nonuniform t h i c k n e s s described above f o r

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Figure 6. The i n t e n s i t y of r a d i a t i o n t r a n s m i t t e d through the same amount of m a t e r i a l i s d i f f e r e n t f o r uniform versus nonuniform t h i c k n e s s .

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch004

4. B R E N N E R

Microscopic

IR Spectroscopy

IR a n a l y s i s of p a r t i c u l a t e coal do not occur with the t h i n s e c t i o n samples used i n t h i s work which have h i g h l y uniform t h i c k n e s s e s . However, a r e l a t e d problem r e s u l t i n g from the convergent beam of the IR microscope can occur and i s d e s c r i b e d below. High N.A.'s (numerical apertures) f o r the condensor and the o b j e c t i v e are d e s i r a b l e i n microscopes i n order to achieve good r e s o l u t i o n and have good l i g h t gathering q u a l i t i e s . However, high N. A . ' s mean t h a t the r a d i a t i o n s t r i k e s the sample over a wide range of a n g l e s . For r a d i a t i o n passing through a sample of uniform t h i c k n e s s , the greater the angle from the normal, the greater w i l l be the d i s t a n c e through the sample which the r a d i a t i o n t r a v e l s and the greater w i l l be the a b s o r p t i o n . Therefore, the average t h i c k n e s s of m a t e r i a l through which the beam t r a v e l s w i l l be greater than the t r u e t h i c k n e s s of the sample. Furthermore, the r a d i a t i o n i s attenuated e x p o n e n t i a l l y with d i s t a n c e t r a v e l l e d i n the sample r a t h e r than l i n e a r l y . This means t h a t f o r IR bands which have s u b s t a n t i a l a b s o r p t i o n , r a d i a t i o n passing through the sample at the d i f f e r e n t angles w i l l not average together l i n e a r l y w i t h respect t o d i s t a n c e t r a v e l l e d i n the sample. If necessary, these e f f e c t s can be compensated f o r e i t h e r by experimental c a l i b r a t i o n or by c a l c u l a t i o n i f the i n t e n s i t y of r a d i a t i o n at the various angles i s known. For bands w i t h high absorbances the e f f e c t s of the d i f f e r e n t angles w i l l depend on the amount of r a d i a t i o n absorbed and t h e r e f o r e c a l i b r a t i o n must be done over a range of absorbances. Summary and Conclusions Microscopic m a c é r a i s and subregions i n coal have been c h a r a c t e r i z e d by i n f r a r e d spectroscopy using a new t e c h n i q u e . I n d i v i d u a l m a c é r a i s or subcomponents of the coal as small as about 20 micrometers across can be a n a l y z e d . The technique u t i l i z e s new procedures f o r preparing uncontaminated t h i n s e c t i o n s of coal i n combination w i t h a r e c e n t l y a v a i l a b l e microscopic IR spectrometer. Because the t h i n s e c t i o n specimens are not contaminated with adhesives or embedding m a t e r i a l s , and because the samples are r e a d i l y a c c e s s i b l e on the stage of the IR microscope, t h i s technique i s well s u i t e d f o r "in s i t u " treatments of the c o a l . A l t e r n a t i v e l y , s i n c e the 15 micrometer t h i c k specimens of coal can o r d i n a r i l y be handled and transported without damage ( i f proper care i s t a k e n ) , an untreated sample can be i n i t i a l l y a n a l y z e d , then i t can be removed from the instrument f o r chemical or thermal treatment, and f i n a l l y , the same specimen can be returned to the microspectrometer f o r determination of the changes i n the IR spectrum. The a n a l y s i s of the same specimen before and a f t e r treatment i s h i g h l y d e s i r a b l e f o r micro-heterogeneous substances such as c o a l s .

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The m i c r o s c o p i c IR spectroscopy technique described here d i f f e r s from and complements p r i o r IR work on maceral concentrates i n being able to s p a t i a l l y d e l i n e a t e an i n d i v i d u a l subcomponent being IR analyzed and to c h a r a c t e r i z e i t v i s u a l l y i n the context of i t s surroundings. P r e l i m i n a r y IR measurements on microscopic subregions o f i n d i v i d u a l m a c é r a i s of homogeneous-appearing v i t r i n i t e and of megaspores i n I l l i n o i s No. 6 coal c l e a r l y demonstrate q u a n t i t a t i v e as well as q u a l i t a t i v e chemical d i f f e r e n c e s between these m a c é r a i s . This work demonstrates t h a t good q u a l i t y IR s p e c t r a of m i c r o s c o p i c subregions of coal can be obtained.

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Acknowledgments

The author wishes t o acknowledge the e x c e l l e n t t e c h n i c a l a s s i s t e n c e of Mark S. Beam i n the preparation of the samples f o r these s t u d i e s . Literature 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

Cited

Gordon, R. R.; Adams, W. N . ; Pitt, G. J.; Watson, G. H. Nature 1 9 5 4 ,174,1 0 9 8 . Brooks, J. D.; Durie, R. Α.; S t e r n h e l l , S. J. A p p l . Sci. 1 9 5 8 , 9, 63.

Fenton, G. W.; Smith, Α. Η . V. Gas World 1 9 5 9 , 1 4 9 . van Krevelen, D. W.; Schuyer, J. "Coal Science;" Elsevier: Amsterdam, 1 9 5 7 ; p. 2 4 0 . Dyrkacz, G. R.; Horwitz, E. P. Fuel 1 9 8 2 , 61, 3. Cannon, C. G.; Sutherland, G. Β . Β . M. Trans. Faraday Soc. 1 9 4 5 , 41, 2 7 9 .

Mackowsky, M.-Th. i n "Stach's Textbook of Coal Petrology" Gebruder Bontraeger: B e r l i n 1 9 7 5 , p. 2 4 3 . C o l l i n s , C. J.; Hagaman, E. W.; Jones, R. M.; Raaen, V. F. Fuel 1 9 8 1 , 60, 359. Bent, R.; Brown, J. K. Fuel 1 9 6 1 , 40, 47. T a y l o r , G. H. i n "Coal Science;" Given, P. H. E d . ; ADVANCES IN CHEMISTRY SERIES No. 5 5 , American Chemical S o c i e t y : Washington D.C., 1 9 6 6 ; p. 2 7 4 . Brenner, D. Proceedings of the I n t e r n a t i o n a l Conference on Coal S c i e n c e , 1 9 8 1 , Verlag Gluckauf GmbH: Essen, p. 1 6 3 . Brenner, D. i n "Preprints of the D i v i s i o n of Fuel Chemistry;" American Chemical S o c i e t y , National Meeting, 1 9 8 2 , V o l . 2 7 , No. 3 - 4 , p. 2 4 4 .

RECEIVED October 13, 1983

5 Variations in Properties of Coal Macerals Elucidated by Density Gradient Separation GARY R. DYRKACZ, C. A. A. BLOOMQUIST, L. RUSCIC, and E. PHILIP HORWITZ

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch005

Chemistry Division, Argonne National Laboratory, Argonne, IL 60439

Based on a r e c e n t l y developed separation procedure f o r c o a l macerals, c l o s e l y spaced narrow d e n s i t y fractions of macerals have been examined f o r petrographic content and ultimate a n a l y s i s . Each maceral group or maceral type c l e a r l y e x h i b i t s a range of d e n s i t i e s (a density band) and c o r r e s ponding range of atomic r a t i o s . In g e n e r a l , the H/C and S/C r a t i o s decrease monotonically with d e n s i t y , r e f l e c t i n g changes i n the macerals since as d e n s i t y increases the macerals separate i n the order: exinite, vitrinite, inertinite. The overall range of H/C values f o r t y p i c a l high v o l a t i l e bituminous coals can vary from as much as 1.2 to 0.4 w i t h i n the same coal if all three maceral groups are represented. Within each maceral group, less variation i s observed. In most bituminous coals, there i s 15 to 20% t o t a l variation i n H/C r a t i o across the i n d i v i d u a l maceral bands. The O/C and N/C r a t i o s show d i f f e r e n t behavior. R e l a t i v e to the vitrinite O/C and N/C r a t i o s the e x i n i t e r a t i o s are very low, but r i s e s t e a d i l y as density i n c r e a s e s . Within the vitrinite band there i s some additional increase before finally l e v e l i n g o f f . The inertinite r a t i o s have intermediate values between those of vitrinite and e x i n i t e and vary only s l i g h t l y with d e n s i t y .

Our recent development of a new procedure f o r the d e n s i t y separation of macérais o f f e r s a method f o r obtaining high r e s o l u t i o n separation of the three maceral groups: e x i n i t e , v i t r i n i t e , and i n e r t i n i t e , and can f u r t h e r resolve i n d i v i d u a l maceral types w i t h i n these macérais groups, e.g., s p o r i n i t e from a l g i n i t e i n the e x i n i t e group (1,2). The procedure

0097-6156/ 84/ 0252-0065506.00/ 0 © 1984 American Chemical Society

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utilizes well-known techniques of density gradient c e n t r i f u g a t i o n (DGC) to separate the c o a l i n t o i t s components i n an aqueous CsCl continuous density gradient. Density gradient c e n t r i f u g a t i o n has been used f o r many years i n the biosciences. We have taken that knowledge and technology and a p p l i e d i t to c o a l . The technique of d e n s i t y gradient c e n t r i f u g a t i o n r e s u l t s i n a s e r i e s of bands representing the d e n s i t y v a r i a t i o n s i n maceral groups and maceral types. The informat i o n obtained i s s i m i l a r to a chromatographic t r a c e . At the simplest level this density p r o f i l e represents a density " f i n g e r p r i n t " of a c o a l . When coupled with micropetrographic analyses, the d e n s i t y d i s t r i b u t i o n of each maceral group can be obtained. The observed changes i n d e n s i t y are r e l a t e d i n a complex way to the chemical s t r u c t u r e of the c o a l or maceral ( 3 ) . In order to b e t t e r understand the chemical v a r i a t i o n s o c c u r r i n g i n c o a l macérais we have examined the ultimate a n a l y s i s of s e l e c t e d d e n s i t y f r a c t i o n s separated from the same c o a l . EXPERIMENTAL Separation The basic advantages (1,2).

procedures f o r DGC separation of macérais with and disadvantages has been discussed p r e v i o u s l y

Chemical A n a l y s i s Because of the small samples often generated, ultimate a n a l y s i s of s e l e c t e d d e n s i t y f r a c t i o n s was performed with a modified Perkin-Elmer 240, C, H, N, analyzer ( m o d i f i c a t i o n XA by Control Equipment Corp.) using a modified burn procedure which includes i n c r e a s i n g the time of burn and the amount of 02 used i n the burn. Good c o r r e l a t i o n f o r carbon and hydrogen ( r = 0.98) with ASTM methods was found f o r a range of coals from sub-bituminous to a n t h r a c i t e s . 2

Maceral A n a l y s i s The microscopic analyses of the coals follows standard practices. D e t a i l s of the a n a l y s i s of the f i n e maceral p a r t i c l e s has been documented (1). We use the term maceral type and maceral group i n a s p e c i f i c sense i n t h i s a r t i c l e . Maceral type r e f e r s to the i n d i v i d u a l maceral species which comprise the three maceral groups: e x i n i t e , v i t r i n i t e , and inertinite. Separation Scheme Since very d e t a i l e d explanations f o r most of the procedures have been published, we w i l l only provide a b r i e f summary of the important aspects of the separation process (1,2). The methodology we have developed f o r the separation of the

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch005

5.

D Y R K A C Z ET A L .

Density Gradient

Separation

67

macérais i s shown i n Figure 1. One of the most important aspects i s the liberation of one maceral from another. Inadequate comminution w i l l severely r e s t r i c t the density r e s o l u t i o n of the various macérais. However, there are p r a c t i c a l l i m i t a t i o n s on the s e v e r i t y of comminution that can be t o l e r a t e d . The most s i g n i f i c a n t l i m i t for general maceral separation and c h a r a c t e r i z a t i o n i s the a b i l i t y to m i c r o s c o p i c a l l y resolve the p a r t i c l e s i n t o the three maceral groups. This places a lower l i m i t on p a r t i c l e s i z e of two to three microns. In our case, g r i n d i n g i s c a r r i e d out under n i t r o g e n i n two stages: F i r s t , to r

m m H

53

ο

-ο c

ON

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch006

94

Figure

COAL MACERALS

5. S p e c t r a l

slices

a t 977 Hz i n t e r v a l s

taken

from

Figure4.

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch006

6.

PUGMIRE ET AL.

B

Dephasing C-NMR

Techniques

Figure 6. Three dimensional p l o t of aromatic region. Shaded p o r t i o n i s nonprotonated carbon on top of resonance from protonated aromatic carbon.

95

COAL MACERALS

96

Literature

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch006

1.

Cited

P. W. Van K r e v e l e n , "Coal" E l s e v i e r P u b l i s h i n g Company, New York, 1961. 2. B. S. Ignasiak, T. M. Ignasiak, and N. Berkowitz, Reviews i n A n a l y t i c a l Chemistry, 1975, 2 , 278. 3. G. L. Tingey, and J. R. Morrey, "Coal S t r u c t u r e and R e a c t i v i t y " , TID-16627 B a t e l l e Pacific Northwest Labs, R i c h l a n d Washington, 1973. 4. R. M. Davidson, "Molecular S t r u c t u r e of Coal" IEA Coal Research, London, 1980. 5. J . W. Larsen, "Organic Chemistry of Coal" ACS Symposium S e r i e s 7 1 , Washington, D. C. 1978. 6. C. K a r r , " A n a l y t i c a l Methods f o r Coal and Coal Products", Vol. I - I I I , Academic P r e s s , New York, 1978. 7. H. L. Retcofsky, A p p l i e d Spectroscopy, 1977, 3 1 , 166. 8. S. K. Chakrabartty, and H. O. Kretschmer, F u e l , 1974, 53, 132. 9. J . L. Huston, et al, F u e l , 1976, 5 5 , 281. 10. A . P i n e s , H. G. Gibby, and J. S. Waugh, J. Chem. P h y s i c s , 1973, 5 9 , 569. 11. D. L. VanderHart, and H. L. Retcofsky, F u e l , 1976, 5 5 , 202. 12. V. J. B a r t u s k a , G. E. M a c i e l , J. Schaefer, and E. O. Stejskal, F u e l , 1977, 5 6 , 354. 13. V. J. B a r t u s k a , G. E. M a c i e l , and F. P. M i k n i s , "C-13 NMR Studies of Coals and O i l S h a l e s , " American Chemical S o c i e t y , D i v i s i o n of Fuel Chemistry, P r e p r i n t s , 1978, 2 3 . 14. K. W. Z i l m , R. J. Pugmire, D. M. Grant, W. A. Wiser, and R. E. Wood, F u e l , 1979, 58, 1 1 . 15. K. W. Z i l m , R. J. Pugmire, S. R. L a r t e r , J. Allen, and D. M. Grant, F u e l , 1981, 6 0 , 717. 16. R. J. Pugmire, D. M. Grant, S. R. L a r t e r , J. A l l e n , A . D a v i s , W. Spackman, and J. S e n t f l e , New Approaches i n Coal Chemistry, ACS Symposium S e r i e s No. 169, 1981, ρ 2 3 . 17. R. J. Pugmire, K. W. Z i l m , W. R. Woolfenden, D. M. Grant, G R. Dyrkacz, C. A. A. Bloomquist, and E. P. Horwitz, Proceedings of the I n t e r n a t i o n a l Conference on Coal S c i e n c e , D u s s e l d o r f , Germany, September 7 - 9 , 1981, p. 798-806. 18. R. J. Pugmire, K. W. Z i l m , W. R. Woolfenden, D. M. Grant, G. R. Dyrkacz, C. A. A. Bloomquist, and E. P. Horwitz, Carbon-13 NMR Spectra of Macerals Separated from I n d i v i d u a l C o a l s , Org. Geochem., 1982, 4, 7 9 . 19. A. Pines and D. Ε. Wemmer, "Developments i n S o l i d State NMR and P o t e n t i a l A p p l i c a t i o n s to Fuel Research", ACS Division of Fuel Chemistry, P r e p r i n t s , 1978, 2 3 , 15. 20. N. C. Deno, B. A. G r e i g g e r , and S. G. S t r o u d , F u e l , 1978, 57, 455. 21. S . J. O p e l l a , and M. H. Fry, J. Amer. Chem. S o c . , 1979, 101, 5854. 22. S. J. O p e l l a , M. H. Fry, and T. A. C r o s s , J. Amer. Chem. S o c . , 1979, 101, 5856.

6.

23. 24. 25. 26. 27.

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28.

PUGMIRE ET AL.

I3

Dephasing C-NMR

Techniques

97

B. C. G e r s t e i n , P. D. Murphy, and L. M. Ryan, "Aromaticity in Coal" i n Coal S t r u c t u r e , E d . , R. A. Meyers, Academic P r e s s , New York, 1982, pp. 87-129. P. D. Murphy, B. C. G e r s t e i n , V. L. Weinberg, and T. F. Yen, A n a l . Chem., 1982, 54, 522. P. D. Murphy, T. J. Cassady, and B. C. G e r s t e i n , F u e l , 1982, 6 1 , 1233. K. W. Zilm, D. W. Alderman, and D. M. Grant, J. Mag. R e s . , 1978, 3 0 , 563. See a l s o M. J. S u l l i v a n and G. E. M a c i e l , A n a l . Chem. 1982, 54, 1615. The q u a n t i t a t i v e nature of t h i s assumption has been s t u d i e d i n our l a b o r a t o r y on a set of s i x d i f f e r e n t c o a l s ranging i n rank from lignite to a n t h r a c i t e . The average c o r r e c t i o n f a c t o r f o r nonprotonated aromatic carbons i s 6%. See M. A. W i l s o n , L. B. Alemany, W. R. Woolfenden, R. J. Pugmire, P. H. Given, D. M. Grant, and J. K a r a s , "Carbon Distribution i n Coals and Coal Macerals as Determined by CP/MAS C NMR S t u d i e s " , sub­ mitted for p u b l i c a t i o n . G. R. Dyrkacz and E. P. Horwitz, F u e l , 1982, 6 1 , 3 . G. R. Drykacz, C. A. A. Bloomquist and E. P. Horwitz, Sep. Sci. and T e c h . , 1981, 1 5 , 1571. L. B. Alemany, R. J. Pugmire, D. M. Grant, T. D. A l g e r , and K. W. Z i l m , Cross P o l a r i z a t i o n and Magic Angle Spinning NMR Spectra of Model Organic Compounds I I I . The E f f e c t of D i p o l a r I n t e r a c t i o n on Cross Polarization and Carbon-Proton Dephasing, J. Am. Chem. Soc., i n p r e s s . The d i p o l a r dephasing data on an I l l i n o i s No. 6 coal has allowed the s e m i - q u a n t i t a t i v e separation of methyl, CH p l u s aliphatic methine, and protonated and nonprotonated aromatic carbons, L. B. Alemany, D. M. Grant, R. J. Pugmire, and L. M. Stock, S o l i d State Magnetic Resonance Spectra of I l l i n o i s No. 6 Coal and Some Reductive Alkylation Products, F u e l , ( i n p r e s s ) . E. F. Rybaczewski, B. L. B e f f , J. S. Waugh, and J. S. Sherfinski, J. Chem. P h y s . , 1977, 6 7 , 1231. R. E. Richards and R. W. York, J. Chem. S o c . , (London), 1960, 2489. H. Tschamler and E. d e R u i t e r , Coal S c i e n c e , R. F. Gould, E d . , Advances i n Chemistry S e r i e s 5 5 , American Chemical S o c i e t y , Washington, D.C., 1966, ρ 332. Η . Ν. M. Dormans, F. J. Hutjens, and D. W. Van K r e v e l e n , F u e l , 1957, 36, 321. 13

29. 30. 31.

2

32. 33. 34. 35.

RECEIVED January 6, 1984

7 Relationships Between the Organic Structure of Vitrinite and Selected Parameters of Coalification as Indicated by Fourier Transform IR Spectra 1

DEBORAH W. KUEHN , ALAN DAVIS, and PAUL C. PAINTER College of Earth and Mineral Sciences, The Pennsylvania State University, University Park, PA 16802

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch007

Q u a n t i t a t i v e data f o r the organic f u n c t i o n a l groups in 24 vitrinite concentrates were obtained by FTIR a n a l y s i s of samples c o l l e c t e d from the Lower Kittanning coal seam i n western Pennsylvania and eastern Ohio. Absorption areas f o r aliphatic and aromatic CH groups were determined and compared t o s e l e c t e d parameters of coalification i n b i v a r i a t e and principal components a n a l y s e s . A l i p h a t i c C H and CH groups d i s p l a y e d a slight p o s i t i v e increase w i t h i n c r e a s i n g coalification and v a r i e d dependently w i t h calorific value and moisture content. A l i p h a t i c C H groups decreased with an increase i n coalification and components a n a l y s i s revealed partial dependent relationships with volatile matter, carbon content, and r e f l e c t a n c e . Aromatic bands at 884, 815, 8 0 1 , and 750 c m - 1 r e p r e s e n t i n g 1, 2 , 3 , and 4 adjacent hydrogens, r e s p e c t i v e l y , and total aromatic content all showed strong p o s i t i v e c o r r e l a t i o n s with i n c r e a s i n g coalification. P r i n c i p a l components a n a l y s i s r e vealed interdependent r e l a t i o n s h i p s and similar patterns of v a r i a t i o n among these bands. The a r o matic bands at 864, 834, and 785 cm e x h i b i t e d differing patterns of v a r i a t i o n and it is suggested that t h e y , in fact, may not be aromatic i n nature. 3

2

-1

V a r i a t i o n s i n organic s t r u c t u r e of v i t r i n i t e concentrates were determined with F o u r i e r transform i n f r a r e d spectroscopy (FTIR). FTIR i s a r e l a t i v e l y new method f o r o b t a i n i n g q u a n t i t a t i v e data from the organic c o n s t i t u e n t s of coal and provides s p e c t r a of greater q u a l i t y than conventional i n f r a r e d spectrometers. The system employs an o n - l i n e minicomputer which enables the user to analyze data and perform a v a r i e t y of mathematical m a n i p u l a t i o n s . Current address: Department of Geosciences, University of Tennessee at Chattanooga, Chattanooga, T N 37402 1

0097-6156/ 84/ 0252-0099S06.00/ 0 © 1984 American Chemical Society

COAL MACERALS

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch007

100

The o b j e c t i v e s of t h i s study were (1) t o reveal trends be­ tween s e l e c t e d regions of the i n f r a r e d spectrum and accepted i n d i ­ c a t o r s of c o a l i f i c a t i o n ; (2) t o determine the nature and degree of interdependency among these data using s t a t i s t i c a l a n a l y s e s ; and (3) to evaluate the usefulness of FTIR data i n measuring degree of coalification. Twenty-four v i t r i n i t e concentrates were obtained from samples of the Lower K i t t a n n i n g coal seam i n western Pennsylvania and eastern Ohio by hand p i c k i n g the b r i g h t bands i n the c o a l . A l o ­ c a t i o n map of sample s i t e s with t h e i r designated i d e n t i f i c a t i o n numbers i s given i n Figure 1. The Lower K i t t a n n i n g seam i s w e l l s u i t e d f o r t h i s study because i t i s known t o d i s p l a y a broad range of c o a l i f i c a t i o n (high v o l a t i l e Β to low v o l a t i l e bituminous). Some chamical and o p t i c a l parameters of c o a l i f i c a t i o n are reported in Table I f o r the v i t r i n i t e c o n c e n t r a t e s . T o t a l v i t r i n i t e con­ tent i s included as an i n d i c a t i o n of sample p u r i t y . Equipment FTIR analyses were performed on a D i g i l a b FTS 15/B spectrophotom­ e t e r having a s p e c t r a l range of 10,000 - 10 cm" . The system i s c a l i b r a t e d a u t o m a t i c a l l y with a helium-neon l a s e r and i s accurate to 0.2 cm" . The o n - l i n e computer system i s a 16 bit/word m i n i ­ computer c o n t a i n i n g 32 Κ words of memory. Disk storage of 256 Κ words contains the system programs, user programs, and i n f r a r e d d a t a , among o t h e r s . 1

1

Sample Preparation Pressed d i s k s were prepared from a mixture c o n t a i n i n g 300.0 mg of potassium bromide and 1.2 mg of c o a l . T h i s mixture was ground in a v i b r a t i n g m i l l f o r 30 sec and placed i n a d e s i c c a t o r f o r 24 h. A f t e r d r y i n g , the mixture was pressed under vacuum f o r 1 min using 9000 kg of l o a d . Potassium bromide was s e l e c t e d as the binder because i t does not have s p e c i f i c absorption bands i n the m i d - i n f r a r e d region although i t does absorb water r e a d i l y . Water masks the OH ab­ s o r p t i o n at 3400 cm" , making i n t e r p r e t a t i o n of t h i s region difficult. U t i l i z i n g such small weights of coal (1.2 mg) i n each d i s k can permit r e l a t i v e l y large sampling e r r o r s . Previous e x p e r i ­ ments on the r e p r o d u c i b i l i t y of such small samples have revealed n o n s i g n i f i c a n t e r r o r s over the s p e c t r a l regions under i n v e s t i g a ­ t i o n . The average standard e r r o r was found to be Î 3 % . 1

Procedure V i t r i n i t e concentrates were analyzed i n the m i d - i n f r a r e d region between 3800 and 450 c n r using a s p e c t r a l r e s o l u t i o n of 2 c m " . Four hundred scans were co-added f o r each sample and a r a t i o was 1

1

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch007

Figure 1. Sample s i t e s of v i t r i n i t e concentrates from the Lower K i t t a n n i n g seam.

C (dmmf)

86.6 85.8 85.4 84.6 83.0 84.3 85.1 88.8 88.3 90.1 91.3 89.8 89.4 83.7 83.3 80.2 84.7 82.2 83.2 87.0 85.2 87.3 85.5 88.7

Total V i t r i n i t e (mmf) Vol %

98.4 98.1 99.0 98.4 99.0 98.8 98.8 97.8 98.0 94.2 97.6 89.3 98.4 98.8 95.5 98.6 98.8 96.5 97.8 99.2 96.1 96.8 96.2 97.4

16 18 20 30 33 36 39 48 49 50 52 54 56 58 59 60 62 65 67 68 69 70 71 72

5.6 5.6 6.0 5.2 5.3 5.3 5.7 5.4 5.3 5.2 4.8 4.7 5.3 5.3 5.6 5.3 5.5 5.3 5.6 5.5 5.2 5.6 5.6 5.6

H (dmmf)

Volatile Matter (dmmf) 33.3 37.6 40.7 35.5 39.4 34.9 40.7 29.8 26.4 24.2 21.8 18.5 30.7 40.7 42.0 37.7 36.4 37.8 41.4 38.0 28.9 36.8 33.6 25.9

Moisture (mmf) 2.1 2.1 2.2 3.1 2.1 2.6 1.8 1.0 0.9 0.8 1.0 1.8 1.2 7.4 4.1 7.1 3.7 6.7 5.4 1.6 1.1 2.2 2.4 1.3

Chemical and P é t r o g r a p h i e Data f o r V i t r i n i t e

ID #

Table I.

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch007

15085 14883 15194 14407 14674 14405 15127 15628 15643 15846 15854 15378 15738 13675 14208 12932 14357 13407 13891 15441 15595 15278 14780 15703

Calorific Value (mmmf)

Concentrates

1.03 0.87 0.83 0.89 0.87 0.96 0.83 1.19 1.34 1.43 1.50 1.71 1.14 0.55 0.60 0.60 0.80 0.64 0.57 0.92 1.26 0.89 1.03 1.31

Reflectance in O i l , %

7. KUEHN ET AL.

Vitrinite and Coalification:

FTIR

103

Spectra

taken to 400 scans of the atmosphere w i t h i n the sample chamber. This step removed the e f f e c t s of any water vapor which was not e l i m i n a t e d by the normal purge of the sample chamber with dry a i r . Several computer programs were employed on the D i g i l a b s y s tem f o r the adjustment of s p e c t r a . In order to e l i m i n a t e e f f e c t s due to v a r i a t i o n i n sample weights, a l l spectra were normalized to 1 mg using appropriate s c a l i n g f a c t o r s . A l s o , a program f o r s p e c t r a l s u b t r a c t i o n was used to remove mineral c a l c i t e which appears as a small shoulder on the 864 crrr band i n the aromatic o u t - o f - p l a n e bending region [1). Other techniques used to obtain q u a n t i t a t i v e data were d e r i v a t i v e spectroscopy, i n t e g r a t i o n , and l e a s t - s q u a r e s curve f i t t i n g . A t y p i c a l i n f r a r e d spectrum of a v i t r i n i t e concentrate i s presented i n Figure 2 . Three regions of t h i s spectrum are of i n t e r e s t here: aromatic s t r e t c h i n g between 3100 and 3000 cm" , a l i p h a t i c s t r e t c h i n g between 3000 and 2750 cm" , and aromatic o u t - o f - p l a n e bending between 900 and 700 c m - . Q u a n t i t a t i v e data were obtained f o r these regions both by i n t e g r a t i o n and l e a s t squares curve f i t t i n g . I n t e g r a t i o n i s a method f o r determining the area under a s e l e c t e d region of the spectrum. I t can provide data very q u i c k l y ; however, i t cannot provide data from the i n d i v i d u a l absorption bands found w i t h i n a r e g i o n . Least-squares curve f i t t i n g i s a method which r e s o l v e s a region i n t o component bands. In a l e a s t - s q u a r e s a n a l y s i s , parameters are s e l e c t e d so t h a t the d i f f e r e n c e s between observed data and data c a l c u l a t e d from a model are minimized ( 2 ) . F i r s t , the number of major component bands i s ascertained By t a k i n g the second d e r i v a t i v e of the spectrum. D e r i v a t i v e spectroscopy enhances very weak s h o u l ders i n spectra so long as the peaks are separated by more than h a l f t h e i r h a l f w i d t h . D e t a i l s of t h i s technique, as a p p l i e d to these s p e c t r a l r e g i o n s , are reported elsewhere ( 1 , 3 , 4 ) . Weak absorption i n the aromatic s t r e t c h i n g region does not permit the use of d e r i v a t i v e spectroscopy, so i n d i v i d u a l component bands were not o b t a i n e d . Second, a s u i t a b l e mathematical f u n c t i o n f o r c h a r a c t e r i z i n g the observed band shapes i s chosen. Maddams (ji) r e c e n t l y has reviewed methods f o r curve f i t t i n g and suggested employing a Lorentzian band shape. Other workers have used products or sums of Gaussian and Lorentzian curves ( 6 , 7 ) . Solomon, et al_. (8) used Gaussian band shapes, e x c l u s i v e l y . Our method was adopted from Jones, et a l . {9) who obtained t h e i r best r e s u l t s using a sum of Gaussian and"Torentzian f u n c t i o n s . In t h i s study, curve f i t t i n g was performed on the a l i p h a t i c s t r e t c h i n g region (using f i v e component bands) and the aromatic o u t - o f - p l a n e bending region (using seven component bands). Table II l i s t s the peak l o c a t i o n s and assigned f u n c t i o n a l groups f o r both of these r e g i o n s . The peak l o c a t i o n s were not held constant f o r a l l samples so t h a t the wavenumbers reported i n Table II represent average v a l u e s . When curve f i t t i n g was completed, areas f o r the component bands were c a l c u l a t e d by i n t e g r a t i o n . 1

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch007

1

1

1

COAL M A C E R A L S

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch007

OH groups, water

τ — ι — ' — ' — ι — I — ι — ι — τ — f — ι — ι — ι — ι — ι — ι — ι — ι — i — i — ι ι ' — r — ι — f — ι — ι — ι ι—r'T 3600 3200 2800 2400 2000 1600 1200 800 Wave Numbers (cm- ) 1

Figure 2 .

FTIR spectrum of a v i t r i n i t e

concentrate.

7. KUEHN ET AL.

Table I I .

Vitrinite and Coalification: FTIR

Spectra

105

Band Assignments f o r the A l i p h a t i c S t r e t c h i n g and Aromatic Out-of-plane Bending Regions

Region

Peak P o s i t i o n (cm- )

Assignment

1

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch007

Aliphatic Stretching

Aromatic Out-of-plane Bending

2956 2923 2891 2864 2853 884 864 834 815 801 785 750

CH3 groups (asymmetric s t r e t c h ) Composite of CH3 & CH (asymmetric s t r e t c h ) CH groups CH3 groups (symmetric s t r e t c h ) CH2 groups (symmetric s t r e t c h ) 2

1 Adjacent Hydrogen 1 Adjacent Hydrogen Possible a l i p h a t i c rocking & secondary aromatic o u t - o f plane bending modes 2 Adjacent Hydrogens 3 Adjacent Hydrogens P o s s i b l e i s o l a t e d and 2 adjacent CH2 u n i t s 4 Adjacent Hydrogens

R e s u l t s and Discussion Q u a n t i t a t i v e FTIR data were combined with chemical and p é t r o graphie data f o r the 24 v i t r i n i t e concentrates and subjected to b i v a r i a t e and m u l t i v a r i a t e s t a t i s t i c a l analyses i n order to i d e n t i f y the e f f e c t s of c o a l i f i c a t i o n on the a l i p h a t i c and aromatic f u n c t i o n a l groups. B i v a r i a t e A n a l y s i s . C o r r e l a t i o n c o e f f i c i e n t s were c a l c u l a t e d f o r every p o s s i b l e p a i r of v a r i a b l e s in order to determine the nature and degree of l i n e a r interdependence between them. The c o r r e l a t i o n c o e f f i c i e n t (r) ranges from +1 to - 1 , with the end members i n d i c a t i n g a complete l i n e a r dependence and a zero i n d i c a t i n g complete independence. A p o s i t i v e value f o r r i n d i c a t e s a d i r e c t r e l a t i o n s h i p e x i s t s between a given p a i r of v a r i a b l e s and a negat i v e value s i g n i f i e s an inverse r e l a t i o n s h i p . The s i g n i f i c a n c e of each r value was determined by comparison to t a b l e d values (10). At the 95% confidence l e v e l , a c o r r e l a t i o n c o e f f i c i e n t must exceed 0.404 to be s i g n i f i c a n t based on a sample set of t w e n t y - f o u r . Anything l e s s than 0.404 i s n o n s i g n i f i c a n t , meaning i t can be explained by random e r r o r . Data obtained both by i n t e g r a t i o n and l e a s t - s q u a r e s curve f i t t i n g are compared in order to reveal p o s s i b l e d i f f e r e n c e s i n the q u a l i t y of data produced. I n t e g r a t i o n over a s p e c t r a l region takes only the time needed to input the i n f o r m a t i o n , whereas curve f i t t i n g may take 30 min to r e s o l v e the component bands be-

COAL MACERALS

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106

f o r e i n t e g r a t i o n can be performed. T h e r e f o r e , curve f i t t i n g should improve the r e s u l t s to j u s t i f y i t s use. Table III l i s t s c o r r e l a t i o n c o e f f i c i e n t s f o r both methods with s e l e c t e d parame t e r s of c o a l i f i c a t i o n . T o t a l area by curve f i t t i n g i s obtained by adding the i n t e g r a t e d areas of the component bands. There i s l i t t l e d i f f e r e n c e in c o r r e l a t i o n c o e f f i c i e n t s f o r t o t a l a l i p h a t i c CH; some c o r r e l a t i o n s are higher f o r area by curve f i t t i n g , some are lower. A l l but the c o r r e l a t i o n s with moisture and c a l o r i f i c value are n o n s i g n i f i c a n t . Therefore, curve f i t t i n g does not appear to improve the data f o r t o t a l area of a l i p h a t i c CH groups. The remaining s i g n i f i c a n t c o r r e l a t i o n s are low and suggest only a s l i g h t increase in a l i p h a t i c content as c o a l i f i c a t i o n i n c r e a s e s . Areas determined by i n t e g r a t i o n both before and a f t e r curve f i t t i n g produce s i g n i f i c a n t c o r r e l a t i o n s with parameters of c o a l i f i c a t i o n f o r the aromatic o u t - o f - p l a n e bending r e g i o n . However, c o r r e l a t i o n c o e f f i c i e n t s f o r the area obtained a f t e r curve f i t t i n g are c o n s i s t e n t l y h i g h e r . Only f i v e of the seven bands reported i n Table II f o r t h i s region are included i n the t o t a l area by curve f i t t i n g because two bands do not appear to be aromatic i n nature. Bands representing both i s o l a t e d and two adjacent CH u n i t s were reported at 834 and 785 cm" by D r u s h e l , et aT. (11) and supported by P a i n t e r , et a l . ( 1 2 ) . These must Be i n c l u d e d , however, in the t o t a l area o ï ï t a i n ê ï ï by i n t e g r a t i o n and probably account f o r the lower c o r r e l a t i o n s using t h i s method alone. A l s o included i n Table III i s the integrated area f o r the aromatic s t r e t c h i n g r e g i o n . This region e x h i b i t s some of the highest c o r r e l a t i o n s with parameters of c o a l i f i c a t i o n and appears to be a s l i g h t l y b e t t e r i n d i c a t o r of degree of c o a l i f i c a t i o n than the aromatic o u t - o f - p l a n e bending r e g i o n . A comparision of the two methods f o r o b t a i n i n g data f o r t o t a l aromatic CH r e v e a l s t h a t l e a s t - s q u a r e s curve f i t t i n g i s j u s t i f i e d f o r the aromatic o u t - o f - p l a n e bending r e g i o n , producing higher c o r r e l a t i o n c o e f f i c i e n t s than i n t e g r a t i o n a l o n e . However, the highest c o r r e l a t i o n s are obtained f o r the aromatic s t r e t c h i n g region by i n t e g r a t i o n , which suggests that t h i s region should be used f o r determining aromatic CH content. Although l e a s t - s q u a r e s curve f i t t i n g may not be a u s e f u l method i n determining t o t a l area of a given s p e c t r a l r e g i o n , i t does supply information on component bands not o b t a i n a b l e by i n t e g r a t i o n a l o n e . Areas f o r the component bands i n the a l i p h a t i c s t r e t c h i n g and aromatic o u t - o f - p l a n e bending regions are compared to the same parameters of c o a l i f i c a t i o n and presented as a c o r r e l a t i o n matrix i n Table IV. No one parameter shows the best overa l l c o r r e l a t i o n s with a l l bands. C a l o r i f i c value gives the best c o r r e l a t i o n s f o r f i v e c a s e s , v i t r i n i t e r e f l e c t a n c e and elemental carbon each f o r t h r e e , and v o l a t i l e matter f o r one. The c o r r e l a t i o n c o e f f i c i e n t s f o r the a l i p h a t i c bands at 2956 and 2864 cm" , both of which belong to CH3 groups, are j n e x p l a i n ably d i f f e r e n t . The asymmetric CH3 s t r e t c h at 2956 cm" produces 1

2

1

1

Integration

Aromatic S t r e t c h i n g Region

Integration Least-squares Curve Fitting

Aromatic Out-of-plane Bending Region

Integration Least-squares Curve Fitting

-0.728

-0.749

0.903

0.888

-0.675

-0.501

0.274

0.867

-0.489

Moisture (mmf)

0.203

Carbon (dmmf)

-0.932

-0.800

-0.683

0.185

0.266

Volatile Matter (dmmf)

0.821

0.830

0.783

0.528

0.475

Calorific Value ( b t u / l b , mmmf)

0.965

0.868

0.743

0.019

-0.056

Reflectance in O i l , %

C o r r e l a t i o n s Between Methods of Determining T o t a l Areas of A l i p h a t i c and Aromatic Regions and Parameters of C o a l i f i c a t i o n

A l i p h a t i c S t r e t c h i n g Region

Table I I I .

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch007

Volatile Matter -0.421 -0.176 -0.123 0.323 0.837 0.185 -0.877 -0.516 0.124 -0.738 -0.862 -0.502 -0.837 -0.800

Moisture (mmf) -0.817 -0.748 -0.733 -0.346 0.436 -0.501 -0.620 -0.697 -0.218 -0.716 -0.691 -0.574 -0.765 -0.749

Carbon (dmmf) 0.659 0.549 0.560 0.146 -0.555 0.274 0.846 0.732 0.244 0.847 0.877 0.667 0.909 0.903

2956 2923 2891 2864 2853 T o t a l A l i p h a t i c Area 884 864 834 815 801 785 750 T o t a l Aromatic Area

0.849 0.782 0.768 0.377 -0.445 0.528 0.709 0.734 0.225 0.790 0.769 0.639 0.849 0.830

Calorific Value ( b t u / l b , mmmf)

0.585 0.374 0.321 -0.149 -0.771 0.019 0.904 0.604 -0.024 0.797 0.914 0.589 0.911 0.868

Reflectance in O i l , %

C o r r e l a t i o n Matrix f o r Areas of FTIR Absorption Bands and Parameters of C o a l i f i c a t i o n

Areas (dmmf) (Band L o c a t i o n , cm-1)

Table IV.

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch007

7.

KUEHN ET AL.

Vitrinite and Coalification:

FTIR

Spectra

109

s i g n i f i c a n t and higher c o r r e l a t i o n s compared to the symmetric CH3 s t r e t c h at 2864 cm" whose c o r r e l a t i o n s are n o n s i g n i f i c a n t . This suggests that the assignment f o r the band at 2864 cm" should be re-examined. As shown i n Figure 3 , area of the 2956 cm" band increases as c o a l i f i c a t i o n ( c a l o r i f i c value) i n c r e a s e s . A c a l c u l a t e d r value of 72% means t h a t c o a l i f i c a t i o n expressed by c a l o r i f i c value e x p l a i n s 72% of the v a r i a b i l i t y observed i n a l i phatic CH3 groups. A s i m i l a r d i r e c t r e l a t i o n s h i p i s found between the area at 2891 c m (assigned to lone CH groups) and c a l o r i f i c v a l u e . F i n a l l y , the symmetric CH s t r e t c h at 2853 cm- shows the only i n d i r e c t r e l a t i o n s h i p with i n c r e a s i n g c o a l i f i c a t i o n (Figure 4) with an r of 70% ( v o l a t i l e matter i s highest f o r low l e v e l s of c o a l i f i c a t i o n ) . C o r r e l a t i o n c o e f f i c i e n t s f o r the composite of CH and CH3 s t r e t c h at 2923 cm" suggest t h a t the c o n t r i b u t i o n of CH i s only minor. Not only are the values c l o s e r to those f o r asymmetric CH3 s t r e t c h but, more important, they are p o s i t i v e . If the cont r i b u t i o n s of CH and CHo to the 2923 cm" band were n e a r l y e q u a l , i t would seem l i k e l y t h a t t h e i r opposing trends would cancel and no s i g n i f i c a n t c o r r e l a t i o n s would be observed f o r t h i s band. T o t a l a l i p h a t i c area has a p o s i t i v e c o r r e l a t i o n w i t h c o a l i f i c a t i o n f o r moisture and c a l o r i f i c v a l u e ; however, the c o r r e l a t i o n s are weak. The highest r value obtained i s only 28%. The reason f o r the low c o r r e l a t i o n s i s the inverse r e l a t i o n s h i p with i n c r e a s i n g c o a l i f i c a t i o n shown by CH groups at 2853 c m - . If the trend had been p o s i t i v e , the c o r r e l a t i o n s f o r t o t a l area p r o bably would have been h i g h e r . The aromatic o u t - o f - p l a n e bending region has c o n s i s t e n t l y higher c o r r e l a t i o n s with parameters of c o a l i f i c a t i o n than the a l i p h a t i c region and a l l of them vary d i r e c t l y w i t h i n c r e a s i n g c o a l i f i c a t i o n . Figures 5 and 6 show examples of trends f o r the bands at 884 and 750 c m - having r values of 82% and 83%, r e s p e c t i v e l y . The data suggest t h a t any one of the aromatic bands would appear to work e q u a l l y w e l l i n expressing the degree of c o a l i f i c a t i o n of the c o a l . Since t h e i r trends show the same patterns with c o a l i f i c a t i o n , i t i s not s u r p r i s i n g t h a t the t o t a l aromatic area a l s o shows high p o s i t i v e c o r r e l a t i o n s with i n creasing c o a l i f i c a t i o n . Some workers have reported t h a t under i n c r e a s i n g c o a l i f i c a t i o n the degree of s u b s t i t u t i o n w i t h i n aromatic u n i t s decreases, meaning t h a t more hydrogens are attached to the aromatic nucleus (13-15). This f i n d i n g a l s o i s suggested here. Although the band at 884 cm" assigned to one adjacent hydrogen shows the same p o s i t i v e c o r r e l a t i o n with c o a l i f i c a t i o n as the band at 750 c n r a s signed to four adjacent hydrogens, the slopes of the l i n e s i n Figures 5 and 6 are d i f f e r e n t . The slope f o r area at 884 cm" versus r e f l e c t a n c e i s 145.4, whereas f o r 750 cm" i t i s 2 0 4 . 5 . T h e r e f o r e , the i n t e n s i t y of the 750 cm" band increases at a greater r a t e than the band at 884 cm- as c o a l i f i c a t i o n i n c r e a s e s . 1

1

1

2

- 1

1

2

2

2

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1

2

1

2

2

1

2

1

2

1

1

1

1

1

1

COAL MACERALS

110

400

C-

320

Ε

·· ·

τ

Ε υ

240

Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch007

CM