Synthetic Membranes: Volume II. Hyper- and Ultrafiltration Uses 9780841206236, 9780841208056

Table of contents :
Title Page......Page 1
Half Title Page......Page 3
Copyright......Page 4
ACS Symposium Series......Page 5
FOREWORD......Page 6
PREFACE......Page 7
DEDICATION......Page 9
PdftkEmptyString......Page 0
Experimental......Page 10
Results and discussions......Page 11
System design......Page 15
Performance of the semicommercial equipment......Page 21
References......Page 25
2 Membrane Processes in Must and Wine Treatment......Page 26
EXPERIMENTAL......Page 28
LITERATURE CITED......Page 35
Feta Cheese......Page 36
Proteins......Page 40
DDS-Nakskov......Page 45
Whey Properties......Page 46
Membrane Processing of Whey......Page 47
Membrane Fouling Studies on Whey......Page 48
Whey Pretreatments to Reduce Fouling......Page 49
Membrane Fouling Models......Page 50
Conclusions......Page 51
Literature Cited......Page 52
5 Development of a Cellulose Acetate Membrane and a Module for Hemofiltration......Page 54
Membrane development......Page 55
Experimental......Page 56
Results and discussions......Page 57
Module development......Page 68
References......Page 69
6 Pressure Control of the Ultrafiltration Rate During Hemodialysis with High-Flux Dialyzers and the Time Dependence of Membrane Transport Parameters......Page 70
Description of a Simple Means of Controlling Ultrafiltration.......Page 72
Equipment and Methods.......Page 74
Results......Page 76
Discussion......Page 81
Literature Cited......Page 83
7 Ultrafiltration Rates and Rejection of Solutes by Cellulosic Hollow Fibers......Page 84
Data Reduction......Page 91
Experimental......Page 99
Results......Page 102
Conclusions......Page 113
Appendix......Page 114
Acknowledgment......Page 115
Literature Cited......Page 116
8 Dialysis Processing of Cryopreserved Red Blood Cells......Page 118
Advantages of Frozen Red Cells Using Current Processing Methods.......Page 119
Disadvantages of Frozen Red Cells Using Current Processing Methods.......Page 120
Methods.......Page 121
Results With Discussion.......Page 125
Literature Cited......Page 126
The concentration and the resistance of gel layer......Page 127
Characterization of ultrafiltration membrane......Page 130
The rejection of solutes by gel......Page 135
Conclusion......Page 139
Literature Cited......Page 140
10 Application of Ultra- and Hyperfiltration During Production of Enzymatically Modified Proteins......Page 141
Highly Functional Soy Proteins......Page 142
Methods of Analysis......Page 147
Results and Discussion......Page 148
Isoelectric Soluble Protein Hydrolysates......Page 152
Continuous Protein Hydrolysis in a Membrane Reactor......Page 156
General considerations......Page 163
The steady-state equations......Page 165
Stability of the steady state......Page 168
Quasi-stationary conditions......Page 171
Yield Calculations......Page 174
Literature cited......Page 176
11 Separation of Biopolymer from Fermentation Broths......Page 178
Experimental......Page 180
Results......Page 185
Discussion......Page 198
Literature Cited......Page 199
System Description......Page 200
Membranes......Page 201
Support Structures......Page 205
Sealants......Page 206
Helical Winding Process......Page 207
Modular Assemblies......Page 209
Rotary Modules......Page 210
Areas of Application......Page 212
13 Membrane Development, Production, and Use in Hyperfiltration Systems......Page 213
Review of Membrane Development......Page 214
Membrane Development......Page 218
Membrane Utilization......Page 221
Membranes in the Future......Page 224
Literature......Page 225
14 Multiyear Experience with Oily and Organic Chemical Waste Treatment Using Reverse Osmosis......Page 226
Discussion......Page 227
Case History - Whitestone Chemical Co.......Page 231
Case History #2 - Cummins Engine Company, Charleston, South Carolina......Page 234
Conclusion......Page 240
Acknowledgements......Page 241
15 A Novel Membrane System for the Ultrafiltration of Oil Emulsions......Page 242
Experimental......Page 247
Results and Discussion......Page 248
Nomenclature......Page 258
Appendix 1......Page 259
REFERENCES......Page 262
16 Engineering Aspects of the Continuous Membrane Column......Page 264
Multicomponents Systems......Page 265
Composition Minima......Page 272
Simulation Difficulties......Page 275
Conclusions......Page 279
Nomenclature......Page 281
Abstract......Page 282
Literature Cited......Page 283
Material used......Page 285
Properties of the membranes......Page 286
Literature Cited......Page 295
Solute Preferential Sorption......Page 296
Literature Review......Page 297
Separation of Aromatic Hydrocarbons......Page 300
Experimental......Page 301
Results and Discussions......Page 302
Legend of Symbols......Page 315
Literature Cited......Page 316
Experimental......Page 318
Theoretical......Page 320
Analysis of High Performance Liquid Chromatography (HPLC) Data......Page 324
Frictional Function......Page 328
Results and Discussion......Page 331
Conclusion......Page 337
Nomenclature......Page 339
Subscripts......Page 340
Literature Cited......Page 341
20 Reverse-Osmosis Separations of Alkali Metal Halides in Methanol Solutions Using Cellulose Acetate Membranes......Page 342
Results and Discussion......Page 347
Nomenclature......Page 359
Literature Cited......Page 360
21 Ultrafiltration and Hyperfiltration in the Pulp and Paper Industry for By-Product Recovery and Energy Savings......Page 363
Literature Cited......Page 374
22 Pressure-Independent Ultrafiltration—Is It Gel Limited or Osmotic Pressure Limited?......Page 375
Theoretical Development......Page 379
Experimental Procedure......Page 395
Results and Discussion......Page 396
Conclusions......Page 404
Nomenclature......Page 406
Greek Letters......Page 407
Abstract......Page 408
Literature Cited......Page 409
Steric Rejection......Page 412
Solute Velocity Lag......Page 413
Polydisperse Solute......Page 414
Membrane Pore Size Distribution......Page 416
Presence of Holes......Page 418
Van der Waals Attractive Forces......Page 420
Theory of Steric Rejection and Experimental Results......Page 426
Conclusions......Page 428
List of Symbols......Page 433
Literature Cited......Page 435
Separation of Dye Manufacturing Process Effluent......Page 436
Renovation of Dye Range Wash Water for Reuse......Page 444
Acknowledgements......Page 453
References......Page 454
B......Page 455
C......Page 456
D......Page 457
E......Page 458
F......Page 459
H......Page 460
K......Page 461
M......Page 462
P......Page 464
R......Page 466
S......Page 467
T......Page 469
U......Page 470
W......Page 471
Z......Page 472

Citation preview

Synthetic Membranes: Volume II Hyper- and Ultrafiltration Uses

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Synthetic Membranes: Volume II Hyper- and Ultrafiltration Uses Albin F. Turbak, EDITOR ITT

Rayonier

Inc.

Based on the 20th Anniversary Symposium honoring Drs. Loeb and Sourirajan sponsored by the Cellulose, Paper, and Textile Division at the Second Chemical Congress of the North American Continent, Las Vegas, Nevada, August 25-29, 1980.

ACS

SYMPOSIUM

AMERICAN

SERIES

CHEMICAL

WASHINGTON, D. C .

154

SOCIETY 1 9 81

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

L i b r a r y o f Congress CIP D a t a Synthetic membranes. ( A C S symposium series, I S S N 0 0 9 7 - 6 1 5 6 ; 153-154) Includes bibliographies and index. Contents: v. 1. Desalination—v. 2. Hyper- and ultrafiltration uses. 1. Membranes (Technology)—Congresses. I. Loeb, Sidney. II. Sourirajan, S. III. Turbak, A l b i n F . , 1929I V . American Chemical Society. Cellulose, Paper, and Textile D i v i s i o n . V . Series. TP159.M4S95 660.2'8424 81-1259 I S B N 0 - 8 4 1 2 - 0 6 2 3 - 6 (v. 2 ) AACR2 I S B N 0 - 8 4 1 2 - 0 6 2 5 - 2 (set) A C S M C 8 154 1-474 1981

Copyright © 1981 American Chemical Society A ll Rights Reserved. T h e appearance of the code at the bottom of the first page of each article in this volume indicates the copyright owner's consent that reprographic copies of the article may be made for personal or internal use or for the personal or internal use of specific clients. T h i s consent is given o n the condition, however, that the copier pay the stated per copy fee through the Copyright Clearance Center, I n c. 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 new collective work, for resale, or for information storage and retrieval systems. T h e citation of trade names and/or names of manufacturers in this publication is not to be construed as an endorsement or as approval by A C S 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. PRINTED I N T H E UNITED STATES O F AMERICA

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

ACS Symposium Series M . Joan Comstock

Series Editor

Advisory Board David L. Allara

James P. Lodge

Kenneth B. Bischoff

Marvin Margoshes

Donald D. Dollberg

Leon Petrakis

Robert E. Feeney

Theodore Provder

Jack Halpern

F. Sherwood Rowland

Brian M . Harney

Dennis Schuetzle

W. Jeffrey Howe

Davis L. Temple, Jr.

James D. Idol, Jr.

Gunter Zweig

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

FOREWORD The ACS SYMPOSIU SERIES was founded in 1974 to provide a medium for publishin format of the Series parallels that of the continuing ADVANCES I N 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.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

PREFACE

T

his volume is the result of a symposium honoring Drs. Sidney Loeb and S. Sourirajan on the 20th anniversary of their discovery of the first functionally useful reverse osmosis membrane. During this four-day symposium membrane experts from 13 countries participated in paying tribute to Drs. Loeb and Sourirajan's pioneering efforts and 55 papers were presented covering most areas of membrane uses. These included the salt-rejecting dense membranes for reverse osmosis, which, as Dr. Sourirajan noted in his plenary lecture, is really a misnomer and might be described more accurately as hyperfiltration, and the more porous membranes for ultrafiltration. The large number o in two volumes. Volum salt-rejecting hyperfiltration membranes. Volume II covers hyper- and ultrafiltration membrane utilization in the following areas: food, medicine, pulp, paper, and textile industries, oily waste stream purification, and in the separation of gases, polymers, organic solutes, and biopolymers. Many of these uses are very significant since they are described from the point of extensive commercial experience. This is particularly true of the food, medical, and waste treatment fields. For example, cheese whey solids that previously were pollution problems are recovered now at the rate of several hundred tons/day and sold as valuable food. Similarly the recent advances of hemofiltration over hemodialysis are improving the quality of life for thousands of patients who suffer from renal failure. Also pollution abatement by ultra- and hyperfiltration in the pulp, textile, and steel-processing industries is now a commercial reality for certain types of waste streams. As the membrane field continues to expand, specific membranes will be available to perform an ever-widening series of important functions and much of the impetus for such expansion will be based on the original efforts of Drs. Loeb and Sourirajan. The overwhelming number of papers originally submitted for consideration for this symposium coupled with the outstanding attendance at the symposium attest to the high esteem in which these two gentlemen are held by their peers. It was a distinct honor to take part in this 20th anniversary tribute. I would like to thank all of the participants for their wonderful cooperation in making this occasion such a great success. I.T.T. Rayonier, Inc.

ALBIN F . TURBAK

Eastern Research Division Whippany, NJ 07981

December 24, 1980. ix

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

S. Sourirajan, Albin Turbak, and Sidney Loeb

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

DEDICATION

T

wenty years ago two researchers laboring diligently at the University of California at Los Angeles developed the first modified asymmetric membranes which seemed to have commercial potential for what was to become the exciting field that today is known as hyperfiltration or reverse osmosis. Since that time, these dedicated scientists have given freely of themselves and their talents not only to further contribute technically, but also to help guide, teach d trai other t i thi frontie It is little wonder the countries throughout the world responded so enthusiastically to the initial announcement regarding the organization of a symposium to recognize, honor, and pay tribute to Drs. Sidney Loeb and S. Sourirajan on the 20th anniversary of their initial contribution. From the beginning it was apparent that this four-day symposium covering a seeming myriad of membrane information and uses would be one of the major events of the Fall 1980 Las Vegas A.C.S. National Meeting. This symposium, highlighted by plenary lectures from Drs. Loeb and Sourirajan, had an outstanding attendance. Even on the fourth day there were still more people attending this symposium than normally are present for the initial phases of most other sessions. This in itself says more than anyone could say regarding the universal interest in membranes and the high esteem in which Sid Loeb and S. Sourirajan are held by their peers throughout the world. Today their initial work on the preparation of suitable asymmetric membranes has touched nearly every aspect of life including uses in water purification, food technology, biological separations, waste treatment, medical applications, and bioengineering, and this appears to be just the beginning. I know that I speak for all of their many friends when I take this opportunity to wish Drs. Loeb and Sourirajan continued good health and, if possible, even more success in their future research and development efforts. ALBIN F. TURBAK

xi

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

1 Development of a Tomato Juice Concentration System by Reverse Osmosis K. ISHII, S. KONOMI, K. KOJIMA, and M. KAI Daicel Chemical Industries, Ltd., 1 Teppo-cho, Sakai-shi, 590, Japan N. UKAI and N. UNO Kagome Co., Ltd., 3-14-15, Nishiki, Naka-ku, Nagoya-shi, 460, Japan

There have been man technology to food i n d u s t r i e s m e r c i a l success except those of d a i r y processes ( 1 ) . DAICEL has been studying s i n c e 1971 the a p p l i c a t i o n of its cellulose a c e t a t e RO membranes and polyacrylonitrile UF membranes to food, pharmaceutical, m e d i c a l , paper and other i n d u s t r i e s . As t o the use o f membranes in food i n d u s t r i e s other than d a i r y processes, o n l y two cases were developed to a semicommercial s c a l e , that is, grape juice c o n c e n t r a t i o n f o r wine must and tomato juice c o n c e n t r a t i o n f o r p r o c e s s i n g and storage of the j u i c e till next h a r v e s t . The RO c o n c e n t r a t i o n of f r e s h fruit j u i c e has two diffculties. The one is that the h i g h osmotic pressure of fruit juice prevents c o n c e n t r a t i n g the j u i c e to the r e q u i r e d c o n c e n t r a t i o n , and the other is the l o s s of light f l a v o r . In case o f tomato j u i c e c o n c e n t r a t i o n , the r e q u i r e d product sugar content is ca. 20%, which i s e x c e p t i o n a l l y low enough to be a t t a i n e d by RO process. In a d d i t i o n , the l o s s of l i g h t f l a v o r does not s i g n i f i c a n t l y s p o i l the commercial v a l u e . The expected advantages of membrane process over c o n v e n t i o n a l evaporation process was the improvement of the product q u a l i t y e s p e c i a l l y i n t a s t e and c o l o r . The major problem was to develop a system which produces h i g h q u a l i t y condensed j u i c e without adding t o the cost over that of the c o n v e n t i o n a l process. A j o i n t study s t a r t e d i n 1971 at DAICEL s l a b o r a t o r y , and a f t e r three seasons' f i e l d t e s t s a t Kozakai, F u j i m i and I b a r a g i p l a n t s of Kagome Co., L t d . , a semicommercial equipment was b u i l t a t I b a r a g i p l a n t i n 1975. Since then i t has been producing ca. 1 m /hr of concentrated f r e s h t o mato j u i c e . 1

3

Experimental Tomato j u i c e . D i l u t e d canned tomato paste was used f o r l a b o r a t o r y experiments w i t h 28 cm f l a t membrane c e l l s . For f i e l d t e s t s w i t h t u b u l a r membranes, s t e r i l i z e d f r e s h j u i c e was used. 2

0097-6156/81/0154-0001$05.00/0 © 1981 American Chemical Society In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

2

SYNTHETIC MEMBRANES:

HF

AND

UF

USES

.Membranes. Three d i f f e r e n t grades of.DAICEL's c e l l u l o s e acetate RO membranes, DRS-97, DRS-95 and DRS-90 were used both i n f l a t sheets and tubes. T h e i r NaCl r e j e c t i o n v a l u e s were 97%, 95% and 90%, r e s p e c t i v e l y . Apparatus and equipment. For l a b o r a t o r y experiments, two to s i x f l a t membrane c e l l s of 28 cm e f f e c t i v e area and 0.3 mm chann e l t h i c k n e s s were used i n s e r i e s w i t h a plunger pump of v a r i a b l e output up to 50 1/hr under the pressure of up to 100 Kg/cm . For f i e l d t e s t s , 12 to 192 membrane tubes (1.4 cm i n n e r diameter and 4.5 m by l e n g t h each) were used both i n s e r i e s and p a r a l l e l w i t h one or two plunger pumps of v a r i a b l e output up to 2 m /hr under the pressure of up to 70 Kg/cm . Both a s i n g l e - and a two-stage system were examined. 2

2

3

2

Measurement and a n a l y s i s measured using Tokyokeik Sodium c h l o r i d e c o n c e n t r a t i o n was measured u s i n g TOA HA5a e l e c t r i c c o n d u c t i v i t y meter. Sugar c o n c e n t r a t i o n was determined by reversed phase l i q u i d chromatograph w i t h a 4.6 mm99 .9 >99 .9 99 .8 >99 .9 >99 .9

.47 .37 .38 .36 .40 .49

CONDITIONS: MEMBRANE AREA: 28 cm CONCENTRATIONS: 0.35% PRESSURE: 40 Kg/cm TEMPERATURE: 25°C

DRS--90 FLUX REJ. m/d %

DRS--95 REJ FLUX m/d % 1.31 1.31 1.24 1.13 1.33 1.34

90.0 97.3 96.7 91.8 99.3 99.6

1 .71 1 .67 1 .64 1 .43 1 .64 1 .73

95 .4 99 .3 99 .2 96 .8 >99 .9 >99 .9

2

The sugar content of raw tomato j u i c e i s about 4.5% R e f r a c t i v e Index ( R I ) . The sugar l o s s d u r i n g the c o n c e n t r a t i o n up t o 20% RI must not exceed 5% of the t o t a l sugar contained i n raw j u i c e . From the r e l a t i o n s h i p between c o n c e n t r a t i o n r a t i o and s o l u t e r e t e n t i o n shown i n F i g u r e 1, the sugar r e j e c t i o n o f the membrane to be employed must be over 97%. As l i s t e d i n Table 1, a l l the membranes t e s t e d has r e j e c t i o n v a l u e s higher than ca. 97% f o r glucose, f r u c t o s e and sucrose. The curves i l l u s t r a t e d i n F i g u r e 1 were c a l c u l a t e d from the equation 3 d e r i v e d from mass balance equation 1 and the r e l a t i o n s h i p between v o l u m e t r i c and c o c e n t r a t i o n a l condensation r a t i o s 2 assuming that the membrane r e j e c t i o n i s uniform throughout the whole membrane a r e a . C

V x R e t e n t i o n (%)/100 = CV

0

(1)

0

(C/C ) = ( V / V ) 0

R

(2)

0

R e t e n t i o n (%) = 1 0 0 ( V o / V )

R_1

Loss (%) = 100-Retention (%) where V V Co C R 0

= = = = =

1

= 100(C/C ) " 0

1 / R

(3) (4)

i n i t i a l volume f i n a l volume i n i t i a l concentration f i n a l concentration r e j e c t i o n of the membrane

Table I I demonstrates a l l the membranes t e s t e d have amino a c i d r e j e c t i o n v a l u e s over ca. 97%.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

4

SYNTHETIC MEMBRANES: H F AND U F

USES

Table I I MEMBRANE PERFORMANCE ON AMINOACID AQ. SOLN. SOLUTE

CONTENT (mg%)

SERINE VALINE ARGININE ASPARAGINE GLUT AMINE GLYCINE GLUTAMIC ACID PHENYLALANINE LEUCINE LYSINE

DRS-97

/PRETENTION DRS-95

DRS-90

99.6 99.4 99.7

99.1 99.0 99.2

97.6 97.7 97.6

99.9 99.7

99.6 98.6

98.8 96.5

99.8 99.8 99.6

98.9 99.3 99.2

96.7 97.7 98.1

10.1 9.2 6.8 6.6 6.6 4.8 4.0 2.4 2.1 1.9

MEMBRANE AREA: 2 CONCENTRATION: 10-2 mg pH: 4.2 (ADJUSTED BY ADDING CITRIC ACID) PRESSURE: 40 Kg/cm TEMPERATURE: 25°C 2

As f o r sour t a s t i n g o r g a n i c a c i d s , p e r m i s s i b l e l o s s up t o 10% corresponds t o the membrane r e j e c t i o n of no l e s s than 93% which w i l l be a l s o f u l f i l l e d by a l l the membranes t e s t e d as shown i n Table I I I , as more than 90% of the organic a c i d i n tomato j u i c e i s c i t r i c acid. Table I I I MEMBRANE PERFORMANCE ON ACID AQ. SOLUTION

SOLUTE CITRIC ACID LACTIC ACID

DRS--97 FLUX REJ. (m/d) (%) .54 .52

98.0 84.3

DRS--95 REJ. FLUX (m/d) (%) ' 1.50 1.46

97.1 70.0

DRS--90 REJ. FLUX (m/d) (%) 1.93 1.89

94.5 64.0

2

MEMBRANE AREA: 28 cm CONCENTRATION: 0.1 wt% PRESSURE: 40 Kg/cm TEMPERATURE: 25°C CIRCULATION RATE: 8 ml/min CHANNEL THICKNESS: 0.3 mm 2

As t o water f l u x , DRS-90 membrane showed the h i g h e s t value i n a l l cases; we concluded that DRS-90 i s best s u i t e d f o r m i n i mizing the membrane a r e a . By the way, r e l a t i v e l y low f l u x and r e j e c t i o n v a l u e s f o r D-ribose represented i n Table I suggest that D-ribose might have a s p e c i f i c a l l y strong i n t e r a c t i o n w i t h c e l l u l o s e a c e t a t e RO membranes.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

ISHII E T A L .

Tomato Juice Concentration System

Figure 2. Osmotic pressure of tomato juice

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

5

6

SYNTHETIC MEMBRANES:

HF

AND

UF

USES

Water f l u x . Secondly, the e f f e c t s of f a c t o r s which were ant i c i p a t e d to i n f l u e n c e the membrane performance and the system e f f i c i e n c y were evaluated. They were the osmotic pressure and the v i s c o s i t y of tomato j u i c e as the f u n c t i o n of j u i c e concentrat i o n and feed v e l o c i t y , and o p e r a t i n g pressure. I t was observed that the r i s e i n temperature i n c r e a s e s water f l u x . F i g u r e 2 shows that the osmotic pressure of tomato j u i c e i n creases w i t h c o n c e n t r a t i o n . The osmotic pressure of 20%RI tomato j u i c e was about 20 Kg/cm . F i g u r e 3 i l l u s t r a t e s t h a t water f l u x decreases i n p r o p o r t i o n to the l o g a r i t h m of j u i c e c o n c e n t r a t i o n . This r e l a t i o n s h i p suggests that tomato j u i c e forms a g e l l a y e r which c o n t r o l s the wat e r f l u x . In order to e l i m i n a t e the i n f l u e n c e of osmotic p r e s sure which e x p o n e n t i a l l y r i s e s w i t h j u i c e c o n c e n t r a t i o n , a s e r i e s of experiments was c a r r i e d out, u s i n g a f l a t UF membrane which permeates sugars and s a l t completely A i l l u s t r a t e d i Figur 4, water f l u x i s not s i g n i f i c a n t l s i d e r i n g that t h i s UF membran permeate proportio pressure up to 3 Kg/cm when pure water i s f e d , i t can be supposed that water f l u x of tomato j u i c e i s governed by a g e l l a y e r . The e f f e c t of j u i c e v e l o c i t y on water f l u x i s demonstrated i n F i g u r e 5. This e f f e c t i s smaller than a n t i c i p a t e d from the data shown i n F i g u r e 4. One reason of t h i s discrepancy might be the d i f f e r e n c e of the tomato j u i c e used. Fresh j u i c e was used to o b t a i n the r e l a t i o n s h i p summarized i n F i g u r e 5, w h i l e canned t o mato paste was used i n d i l u t e d form f o r the experiments shown i n Figure 4. Another reason might be the d i f f e r e n c e i n flow chann e l s , 1.4 cm i n n e r diameter tube and t h i n f l a t channel of 0.040.06 cm t h i c k n e s s . Although the exact reason i s not c l e a r , the r e s u l t s i l l u s t r a t e d i n F i g u r e 5 suggest that i t i s not necessary to feed f r e s h tomato j u i c e at high v e l o c i t y to get h i g h water flux. F i g u r e 6 represents the r e l a t i o n s h i p between tomato j u i c e v i s c o s i t y and f l o w v e l o c i t y . The measurement was done w i t h the j u i c e prepared from canned paste, u s i n g a d i s c r o t a t i n g v i s c o s i meter. The v a l u e , v i s c o s i t y m u l t i p l i e d by v e l o c i t y was n e a r l y independent of the v e l o c i t y . This suggests that the e f f e c t of f l o w v e l o c i t y on the pressure drop would be s m a l l . This a l l o w s the v a r i a t i o n of j u i c e feed v e l o c i t y i n a wide range without s i g n i f i c a n t change i n pressure drop. In F i g u r e 7, the v i s c o s i t y of tomato j u i c e i n c r e a s e s n e a r l y e x p o n e n t i a l l y w i t h j u i c e c o n c e n t r a t i o n . As a n t i c i p a t e d from the r e s u l t s shown i n Figure 7, pressure drop r i s e s almost exponent i a l l y w i t h i n c r e a s e i n c o n c e n t r a t i o n when f r e s h tomato j u i c e was fed i n a t h i n tube of 0.4 cm inner diameter (Figure 8 ) . 2

2

System

design

I f there were not a pressure drop along w i t h feed f l o w ! I f so, i t would be easy to concentrate any s o l u t i o n up to the con-

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Tomato Juice Concentration System

ISHII E T A L .

7

JUICE CONCENTRATION (REFRACTIVE INDEX)

Figure 3. Water flux as a function of tomato juice concentration observed by using 12 membrane tubes. Circulating the juice and discarding the permeate.

KEY VELOCITY(cm/s) THICKNESS(cm) 37.8 0.04 • 13.9 0.04 A 0.062 2U.U • 8.97 0.062

•

i

3

2 2

PRESSURE(Kg/cm )

Figure 4. Water flux as a function of pressure. A UF membrane (DUY-L) dcut-off molecular weight was 5 X 10 daltons.

w

a

s

use

T

n

e

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

8

SYNTHETIC MEMBRANES:

H F AND U F

USES

R1--9.0

5

-3

.2

L

20

Figure 5.

30 AO 50 60 80 100 120 JUICE FLOW VELOCITY ( cm/sec )

Effect of tomato juiceflowvelocity on waterfluxobserved by using 12 membrane tubes

KEY

•

A •

£

o 8 S

RI 24.8 13.5 4.5

6

4

2

3 4 VELOCITY(cm/sec)

Figure 6. The viscosity of tomato juice decreases in proportion to the reciprocal of juice velocity. Measured at 20°C by using a disc-rotating viscosimeter.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

ISHII E T A L .

Figure 7.

Tomato Juice Concentration System

The effect of tomato juice concentration on the viscosity observed at 20°C by using a disc-rotating viscosimeter

Figure 8. The effect of tomato juice concentration on the pressure drop of the juiceflowingthrough 4 mm X 4 mL tube at a velocity of 110 cm/s. Temperature: 24°-30°C.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

10

SYNTHETIC MEMBRANES:

H F AND U F

USES

c e n t r a t i o n l i m i t e d by the osmotic pressure of the feed s o l u t i o n , u s i n g a one-through s i n g l e - s t a g e system by simply extending the feed f l o w l e n g t h . P r a c t i c a l l y , however, e f f e c t i v e pressure goes down so much that the membrane performance and/or system e f f i c i e n c y a r e g r e a t l y decreased, and i t i s necessary to i n s e r t a second pump i n the long f l o w l i n e and add pressure and v e l o c i t y to the flow. Some devices t o match the d i v i d e d flows i s necessary. The l o s s of s o l u t e s can be decreased by r e p l a c i n g the second stage membrane w i t h that of higher r e j e c t i o n . I n a s o p h i s t i c a t e d scheme shown i n F i g u r e 9 ( 2 ) , the water f l u x or the o u t l e t conc e n t r a t i o n can be r a i s e d by employing a c o n s i d e r a b l y low r e j e c t i o n membrane a t the o u t l e t stage, w h i l e the use of a high r e j e c t i o n membrane i s r e q u i r e d a t the permeate d i s c a r d i n g stage i n o r der t o minimize the s o l u t e l o s s to the permeate. From the s a n i t a r y p o i n t of view, i t i s necessary to minimize the number of a r t i c l e s , such as r e s e r v o i r s , pumps, v a l v e s , gages e t c . , which may cause contaminatio i f these a r t i c l e s are s a n i t a r a l s o u n d e s i r a b l e f o r s a n i t a r y reason s i n c e i t y i e l d s the everstaying-in-the-system p o r t i o n of the feed j u i c e . A c i r c u l a t i n g system g e n e r a l l y r e q u i r e s more frequent c l e a n i n g and s t e r i l i z a t i o n than a one-through system. As a l r e a d y been discussed i n the preceeding p a r t of t h i s paper, the water f l u x and the pressure drop are both s t r o n g l y a f f e c t e d by the j u i c e c o n c e n t r a t i o n , w h i l e they a r e i n s e n s i t i v e to the feed f l o w r a t e . The l a t t e r c h a r a c t e r i s t i c a l l o w s to i n c r e a s e or decrease the feed f l o w v e l o c i t y a t w i l l w i t h s l i g h t change of water f l u x and pressure drop. This makes i t p o s s i b l e to a t t a i n the r e q u i r e d o u t l e t c o n c e n t r a t i o n w i t h one-through s i n g l e - s t a g e system by simply decreasing the feed r a t e . The decrease i n feed r a t e enhances the r a t i o , water f l u x to feed r a t e , hence r a i s e s the v o l u m e t r i c c o n c e n t r a t i o n r a t i o as e l u c i d a t e d by equation 5: (V /V) = V / ( V 0

0

0

- F) = 1/[1-(F/V )]

(5)

0

3

where Vo = feed r a t e (m /hr) = feed v e l o c i t y (m/hr) x cross s e c t i o n (m ) V = o u t l e t r a t e (m ) = o u t l e t v e l o c i t y x cross s e c t i o n F = water removal r a t e (m /m hr) = water f l u x (m /m hr) x membrane area (m ) 2

3

3

2

3

2

2

The o n l y p o s s i b l e problem of decreasing the feed r a t e was whether the t h i c k e n i n g of g e l l a y e r and c o n c e n t r a t i o n p o l a r i z a t i o n due to the slow j u i c e speed would r a i s e the osmotic pressure on the membrane surface as h i g h as the o p e r a t i n g pressure before the bulk c o n c e n t r a t i o n reaches the r e q u i r e d v a l u e . A f t e r the o p e r a t i n g c o n d i t i o n s f o r producing 20% RI concent r a t e d j u i c e had been mastered by u s i n g a 12 to 96 tube s i n g l e pass equipment ( 3 ) , i t was decided to b u i l d a semicommercial system c o n s i s t e d of 1440 tubes. The flow diagram of the semicommer-

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

1.

ISHII E T A L .

Tomato Juice Concentration System

SINGLE-STAGE

-KE>-

CIRCULATING

ONE-THROUGH

if

TWO-STAGE

Journal of Applied Polymer Symposia

Figure 9.

Four types of concentration systems (2)

i

STERILIZED FRESH JUICE

A

A

A

A

A

A

A

1 -1.2 mHEAT EX. RESERVOIR

UP TO 92(Ucm0xA.5mL)TUBES/LINE 72 TUBES(K.Am2) 20 LINES = 288m 2

x

3

5m/h 3

~T~3£~4 m /h

Figure 10.

Flow diagram of the semicommercial equipment built at Ibaragi Plant, Kagome Co., Ltd

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

12

SYNTHETIC MEMBRANES:

H F AND U F

USES

3

c i a l system i s shown i n F i g u r e 10. Approximately 5 m /hr s t e r i l i z e d f r e s h j u i c e i s f i r s t cooled to 30°C. R e s e r v o i r i s s e t i n order to absorb the temporary unbalance of f l o w r a t e s . The j u i c e i s then d i s t r i b u t e d to 20 l i n e s , each equipped w i t h 72 tubes. T o t a l membrane area i s 288 m . About 4 m /hr o f permeate and c a , 1 m /hr of product were expected. I t i s necessary to r i n s e the outer surface of membrane tubes i n order t o prevent m i c r o b i a l growth on i t . 2

3

3

Performance of the semicommercial equipment In order to see how the j u i c e c o n c e n t r a t i o n goes up and how the pressure and the f l o w v e l o c i t y go down as the j u i c e courses the 72 tubes, gages and sampling p o r t s were b u i l t i n 2 l i n e s . T y p i c a l observations are shown i n F i g u r e 11 and 12. Figure 11 demonstrates that the product c o n c e n t r a t i o n r i s e s t o 20% RI b decreasing the feed v e l o c i t under the i n l e t pressur Kg/cm j u i c e was f e d a t 45 cm/sec, the l a s t s e v e r a l tubes h a r d l y cont r i b u t e d t o c o n c e n t r a t i o n , perhaps due to both low pressure caused by pressure drop and h i g h osmotic pressure on the membrane surface as the r e s u l t of the higher c o n c e n t r a t i o n and lower v e locity. As i l l u s t r a t e d i n F i g u r e 12, the slower the feed v e l o c i t y , the more r a p i d l y diminishes the o p e r a t i n g pressure along w i t h the j u i c e f l o w . This behavior corresponds to the experimental observ a t i o n that the v i s c o s i t y of the j u i c e goes up n e a r l y exponent i a l l y w i t h i n c r e a s e i n c o n c e n t r a t i o n and i t goes down almost i n p r o p o r t i o n to the r e c i p r o c a l of feed v e l o c i t y . Considering t h a t the c o n c e n t r a t i o n of the j u i c e s u p p l i e d a t 45 cm/sec h a r d l y r i s e s i n the l a s t s e v e r a l tubes, the osmotic pressure on the membrane surface can be estimated to be 30 t o 35. Kg/cm . While the osmom e t r i c r e s u l t s shown i n F i g u r e 2 suggests that the osmotic p r e s sure of the bulk f l o w j u i c e must be about 20 Kg/cm. The r e l a t i o n s h i p between water f l u x and j u i c e c o n c e n t r a t i o n (Figure 13) observed by the semicommercial equipment i s n e a r l y the same to that observed i n f i e l d t e s t s summarized i n F i g u r e 3. F i g u r e 14 shows that the j u i c e v e l o c i t y dependance of water f l u x i s s i m i l a r to that observed by the f i e l d t e s t s . As i s seen i n Figure 15, the pressure drop rose e x p o n e n t i a l l y w i t h i n c r e a s e i n j u i c e c o n c e n t r a t i o n as had been observed i n the model experiments i l l u s t r a t e d i n F i g u r e 8. The q u a l i t y of the product i s s u p e r i o r to that of the conv e n t i o n a l i n c o l o r and t a s t e as shown i n Table IV. The r e t e n t i o n of s o l u t e s i s more than r e q u i r e d as l i s t e d i n Table V. 2

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Tomato Juice Concentration System

ISHII E T A L .

JUICE VELOCITY • • 4 5 - 1 0 cm/sec O 52-* 1 2 • 59-15 O 89*26

20

15

- 20

15

10

-

10

Figure 11.

20 30 AO 50 60 NUMBER OF MEMBRANE TUBES

5

70

Tomato juice concentration observed along the juice flow through 72 membrane tubes at various feed velocities

70

70

60

50

AO

UJ

30

£ 20

30

JUICE VELOCITY • • A5*10 cm/sec O 52*12 • 59*15 O 89*26

20

10 -

- 10

10

Figure 12.

20 30 AO 50 60 NUMBER OF MEMBRANE TUBES

70

Tomato juice pressure observed along the juice flow through 72 membrane tubes at various feed velocities

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

14

SYNTHETIC MEMBRANES:

H F AND U F

USES

Figure 13.

Water flux as the junction of tomato juice concentration. Semicommercial plant (72 membrane tubes X 20 lines).

Figure 14.

Effect of tomato juice flow velocity on water flux. Semicommercial plant (72 membrane tubes X 20 lines).

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

1.

ISHII E T A L .

Tomato Juice Concentration System

15

VELOCITY (cm/sec) ® 300
E even though that form i s t r u l y exact a t E>>E f o r a given w a l l P e c l e t number. L o c a l l y , the e x p o n e n t i a l form f o r C /C^ can be much l a r g e r tha the choice of E would sum of the i n t e g r a l s along the e n t i r e f i b e r l e n g t h that helps determine R, not the l o c a l v a l u e s . To t e s t the s e n s i t i v i t y of R to the choice of E , the sum of i n t e g r a l s i n Equation 41 which help determine R was c a l c u l a t e d , c

c

c

a t

E > E

C

s

J

o

A

[R+(l-R)(C /C )](l-E) w

+

[R+d-R)^/^)^]

b

c

c

a

r

(44)

e

Here (C /C, ) and ( / ) given by Equations 20 and 17, r e s p e c t i v e l y ; E i s a n asiumed v a l u e f o r E>_E , and E^ i s E f o r a given experiment. I n F i g u r e 6 i s a graph of the percentage e r r o r i n I i n c u r r e d by u s i n g E >E , [ I (E ) - I (E ) ] x 100/1 (E ) , versus E^, f o r R = 0.5, P =°0.5 I n d ^ = 8.3$0. Three values of E^ were used. A remarkabfe i n s e n s i t i v i t y t o the choice of EA^E i s shown f o r these c o n d i t i o n s , which a r e i n the midrange of values f o r most of the s a l i n e experiments. Thus, although a l l of the data was reduced by u s i n g Equation 41 w i t h E given by Equation 22, f o r most experiments the choice of 6 was not c r i t i c a l . Only f o r values of E >0.5 can the choice cause a p p r e c i a b l e e r r o r i n c a l c u l a t i o n s of R from R . I n f a c t , f o r experiments w i t h E 0.6 x 10~ cm/sec from a p l a t e a u when s a l i n e was the s o l v e n t , whereas i n serum the R versus J graphs were as p r e d i c t e d from the Spiegler-Kedem equation. The r e l a t i v e e f f e c t s of serum or BSA on R , and on r e s u l t a n t values f o r a and P^ f o r the two l a r g e s o l u t l s , are s m a l l . For cytochrome C i n serum and s a l i n e the d i f f e r e n c e between values i s at most 11%, and f o r myoglobin the d i f f e r e n c e i s about 4% (Table I I I ) . In summary, p r o t e i n i n the s o l v e n t r e s u l t s i n n e g l i g i b l y s m a l l i n c r e a s e s i n s o l u t e r e j e c t i o n by the c e l l u l o s i c membranes s t u d i e d i n t h i s work. F i n a l l y , we note the r a t h e r s m a l l d i f f e r e n c e s given i n Table I I between R c a l c u l a t e d according to u n i f o r m - w a l l - f l u x c

c

w

b

R = 1

v

m

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

3 .06

0 92

3 06

3 .06

Serum

Serum

Saline

II

II

II

3

4

5

3 06

3 06

Saline

0.71 + 0.10

0 55 + 0.30

0. 25 + 0. 05

0 81 + 0.60

0 11 + 0.04

V

0 10 + 0 03

0.73 + 0.03

V

0 09 + 0 03

0.75 + 0.05

-

14

Serum

-

13

0 92

Serum

-

-

V

12

0 06 + 0 08

0.03 + 0.02

0.09 + 0.03 0.82 + 0.02

0.03

0.07 + 0.03

± 0.84

0.85 + 0.05

0.04 + 0.02

0.76 + 0.04 0 07 + 0 04 0.66 + 0.06

0.02 + 0.02

1 73 + 4.28

0.02 + 0.02 0.03 0.77 + 0.03

0. 62 + 1. 27

0 86 + 0.69

0 10 + 0.03

0 70

Saline

IV

11

0.86

-

0.03 + 0.02

0 09 + 0 09

-

0. 31 + 0. 17

0.63 + 0.07

0.81 + 0.02

-

0.04 + 0.01

0.04 + 0.02

0.01 + 0.01

0 01 + 0 02

0.84 + 0.01

0.72 + 0.01

-

0 28 + 0.10

0.02 + 0.01

0.87 + 0.01

0 70 + 0.66

1 .40

Saline

IV

-

1 70 + 1.79

-

0 18 + 0.11

0 70

BAS (10%)

IV

9

-

-

-

1 30 + 1,26

0 24 + 0.16

10

(0.5%) 1 40

BAS

-

-

IV

0 04 + 0 02

8

0.89 + 0.05 0.91 + 0.03

0 04 + 0 02

0.83 + 0.04 0.82 + 0.03

-

-

-

3 06

-

0 92

Serum

Serum

III

III

7

0. 24 + 0. 03

0 90 + 0.60

0 14 + 0.02

0.04 + 0.01

0.88 + 0.02

0 03

0 05 + 0 01

0.03 + 0.03

0 06

0.89 + 0.03

4

0.83 + 0.03

0 04 + 0 01

K 10

0.85 + 0.02

0.82 + 0.01

-

-

-

-

0.05 + 0.01

Myoglobin Pm

0.84 + 0.05

a

-

A

-

10

-

X

0 04 + 0 01

CytochrotnePm

0.79 + 0.02

0

-

10*

-

X

-

Tnulin Pm

-

a

-

A

A

-

10

1.10 + 6.4

X

-

Pm

VALUES FOR o AND Pin MEASURED IN REJECTION EXPERIMENTS

0 10 + 0.39

a

B- 12

TABLE I I I .

6

0 .92

Serum

I

2

Serum

I

1

So Lvent

Uo cm/s

Bundle No.

System No.

100

SYNTHETIC MEMBRANES:

HF

AND

UF

USES

theory, and c a l c u l a t e d from the R , according to Equations 8, 9 (with E = ET/2), and 14. Appreciable d i f f e r e n c e s occurr only for E >0.2. P r o t e i n U l t r a f i l t r a t i o n Experiments. In Table IV and i n Figures 16 through 19, t y p i c a l data obtained i n u l t r a f i l t r a t i o n experiments w i t h serum and BSA are shown. Values f o r TT i n Table IV were c a l c u l a t e d by using a rearrangement of Equation 5, 7 = P - J /L v p

(50)

w i t h P = AP, the average transmembrane pressure and J the average f i l t r a t e v e l o c i t y . Graphs of TT versus C f o r serum and BSA (Figure 7) were used to c a l c u l a t e the average w a l l c o n c e n t r a t i o n , C , which produced the reverse-osmotic pressure and the consequent r e d u c t i o n of f i l t r a t e v e l o c i t y of p r o t e i n systems below that obtained i n s a l i n e at comparable pressures (cf dashed l i n e s i n Figures 16 through 18) C never was l a r g e r tha trie s o l u b i l i t y has been independently measured to be about 580 g/% (17), w e l l above the estimated w a l l concentrations i n our experiments. A l s o , the graphs of J versus P never reach a^ h o r i z o n t a l p l a t e a u r e g i o n where J becomes independent of P. Therefore, there can be no j u s t i f i c a t i o n f o r i n v o k i n g a _ g e l - l a y e r hypothesis to e x p l a i n the observed graphs of J versus P. Instead, as explained p r e v i o u s l y , a boundary l a y e r theory must be used to p r e d i c t C , TT, and hence J at the given o p e r a t i n g _ c o n d i t i o n s . The remarkable independence of the J versus P graphs from a x i a l v e l o c i t y and f i b e r l e n g t h , i l l u s t r a t e d i n Figures 14 through 17, suggests the e x i s t a n c e of an asymptotic boundary l a y e r r e g i o n of f u l l y developed flow. C a l c u l a t e d values f o r D, obtained by u s i n g the u n i f o r m - w a l l - f l u x are shown i n Tables V and VI. For serum, data p o i n t s f o r P >0.5 atm were excluded; f o r BSA, data p o i n t s at a l l pressures were included to c a l c u l a t e D. For serum (Table V) there i s a s m a l l trend to i n c r e a s e D w h i l e i n ^ r e a ^ i n g L and decreasing U , but an average v a l u e , D"= 1.41 x 10~ cm /sec, c o r r e l a t e s a l l o? the serum data f o r bundles I - I I I w e l l f o r P 0 for the determination of o-. PEG#4000 (\>); Vitamin B (O); raffinose (\7); sucrose (•); glucose (A); glycerin (0). v

V

100

80 Ovalbumin and Vitamin Bl2

55

60

=

40

T 5 / A - 6 membrane

Vitamin B12

20

J Figure 10.

0

Rejection of Vitamin B vs. pressure

2

4

6

I

L_

8

10

12

Pressure

J

( Kg/cm )

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

12

9.

NAKAO A N D KIMURA

129

Effect of Gel Layer on Rejection

Table 1 Molecular weights, d i f f u s i v i t i e s and Stokes r a d i i of s o l u t e s

Solute PEG #4000 Vitamin B Raffinose Sucrose Glucose Glycerin

Molecular weight

D x 10 (cm /s)

3000 1355 504 342 180 92

1.5 3.3 4.2 5.2 6.9 9.5

l 2

r

s

2

x io (cm)

8

16.3 7.4 5.8 4.7 3.6 2.6

Table 2 Parameters O and P, and i t s standard d e v i a t i o n of the T4/A membrane determined by the method of curve f i t t i n g

Solute

P x 10 (cm/s)

a

PEG #4000 Vitamin B12 Raffinose Sucrose Glucose Glycerin

Standard deviation

4

1,7 3.1 3.9 1.8 4.5 1.7

0.52 3.0 7.8 17 17 55

0.93 0.81 0.66 0.63 0.30 0.18

x 10" x 10 x 10 x 10 x 10 ' x 10

Table 3 Values of Q and P of ovalbumin gel layer. Solute ; vitamin B ^ * g

R

g (atm/cm. s 40000 20000 10000 8000

)

g 0.99 0.99 0.99 0.99

m

m

P

O

Values of 0* and P a

g

m

g

1.4 2.9 5.6 6.8

of a membrane a r e ;

= 0.89, P = 1.1 x l ( T m

x 10 (cm/s)

3

(cm/s)

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

!

;

:

1

130

SYNTHETIC

MEMBRANES:

HF AND U F

USES

100 Rg=40000

oc 4 0

Figure 11. Plots of rejection of Vitamin B against i / J : ( ) determined by a method of curve fitting; black, Vitamin B single solute; white, ovalbumin + Vitamin B, two solutes.

Vitamin B12 one solute

v

5

12

10 1/J *10~

i

I

Figure 12.

Relationship between P of Vitamin B and R

15 (s/cm)

3

V

2

10

i

i

3

1

1 10

20

1

r

1

1—J

4

10

K

12

K

Rg

1

( Kg cm7cm s" )

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

5

9.

NAKAO AND KIMURA

Effect of Gel Layer on Rejection

131

index to s p e c i f y the thickness i s the g e l l a y e r r e s i s t a n c e , Rg. To determine 0~ and Pg values i t i s necessary to measure the r e j e c t i o n at d i f f e r e n t volume f l u x , Jv, that means i t i s necessary to perform experiment at d i f f e r e n t pressures. And at d i f f e r e n t pressures Rg changes, when the bulk c o n c e n t r a t i o n i s kept constant. To keep Rg value constant at d i f f e r e n t pressure i t i s necessary t o change bulk c o n c e n t r a t i o n or the feed v e l o c i t y . In our experiment the l a t t e r was kept constant, w h i l e the bulk c o n c e n t r a t i o n was adj u s t e d to keep Rg constant. Even so i t i s hard to keep Rg prec i s e l y constant. Therefore f i n a l l y the experimental r e l a t i o n s between Rg and r e j e c t i o n , R, were obtained by p l o t t i n g data on the graph and R values were read at appropriate Rg by i n t e r p o l a t i o n . A f t e r o b t a i n i n g the o r i g i n a l data i t i s necessary to c o r r e c t the e f f e c t of the c o n c e n t r a t i o n p o l a r i z a t i o n . In the mixed sol u t i o n s i t i s not c e r t a i n whether i t i s p o s s i b l e to use the mass t r a n s f e r c o e f f i c i e n t determine value are used s i n c e n r e j e c t i o n , R, thus obtained are shown i n F i g . 10 f o r v i t a m i n B 1 2 only and f o r the case w i t h ovalbumin g e l l a y e r . I n t h i s f i g u r e i t i s shown the r e j e c t i o n of d i f f e r e n t membrane are same due t o the g e l l a y e r formation of ovalbumin. The p l o t of R against 1 / J i s shown i n F i g . 11. In the f i g u r e s o l i d l i n e s are drawn by curve f i t t i n g using Eq. (15) a t each Rg value. Values of Og and Pg are shown i n Table 3. (Jg i s 0.99 and not dependent on Rg, but P i s dependent on Rg. The r e l a t i o n between Pg and Rg i s shown i n F i g . 12, which shows Pg i s i n v e r s e l y p r o p o r t i o n a l to Rg. That means P i s i n v e r s e l y prop o r t i o n a l to the g e l l a y e r t h i c k n e s s , which i s considered to be the reasonable c o n c l u s i o n . Further progress i s being attempted to check these r e s u l t s w i t h other s o l u t e s - g e l l a y e r systems. V

g

g

Conclusion I t was found that the g e l l a y e r c o n c e n t r a t i o n i s not cons t a n t , but v a r i a b l e , which can be p r e d i c t e d by u s i n g the o r d i n a r y c o n c e n t r a t i o n p o l a r i z a t i o n model w i t h appropriate mass t r a n s f e r c o e f f i c i e n t . A l s o t h i s c o n c e n t r a t i o n has a p a r t i c u l a r r e l a t i o n w i t h the g e l l a y e r r e s i s t a n c e . Using t h i s r e l a t i o n the f l u x through the membrane can be c a l c u l a t e d f o r the case of g e l l a y e r formation. R e j e c t i o n c h a r a c t e r i s t i c s of u l t r a f i l t r a t i o n membrane were analysed and method to determine the t r a n s p o r t c o e f f i c i e n t s i s developed. A l s o the r e j e c t i o n c h a r a c t e r i s t i c s of membrane w i t h g e l l a y e r were analysed and i t i s found that the t r a n s p o r t coe f f i c i e n t s of g e l l a y e r have a d e f i n i t e r e l a t i o n w i t h the g e l l a y e r r e s i s t a n c e , and perhaps w i t h g e l l a y e r t h i c k n e s s .

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

132

SYNTHETIC MEMBRANES:

H F AND U F

USES

Notation C = c o n c e n t r a t i o n of s o l u t e , wt% D = d i f f u s i v i t y , cm /s J = permeation v e l o c i t y of s o l u t e through membrane, cm/s J = volume f l u x through membrane, cm /cm *s fe = mass t r a n s f e r c o e f f i c i e n t , cm/s Lp = pure water p e r m e a b i l i t y , cm /cm «S-atm NRe = Reynolds number Nsc Schmidt number Sh Sherwood number Ap = pressure d i f f e r e n c e , Kg/cm P = s o l u t e p e r m e a b i l i t y , cm/s R = r e s i s t a n c e to a flow, Kg.cm" /cm-s~ 2

s

3

v

3

z

=

N

=

2

2

or R = real rejection X = d i s t a n c e , cm 6 = boundary l a y e r t h i c k n e s s , cm All = osmotic pressure d i f f e r e n c e , atm 0 = reflection coefficient Subscripts b g m p

= = =

bulk g e l layer membrane product

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

Kimura, S; Nakao, S. D e s a l i n a t i o n , 1975, 17, 267. Nakao, S; Nomura, T; Kimura, S. AICHE J., 1979, 25, 615. Nakao, S; Kimura, S. J . Chem. Eng. Japan, in press. Kedem, O; Katchalsky, A. Biochim. Biophys. Acta, 1958,27,229. S p i e g l e r , K.S; Kedem, O. D e s a l i n a t i o n , 1966, 1, 311. J a g u r - G r o d z i n s k i , J ; Kedem, O. D e s a l i n a t i o n , 1966, 1, 327.

RECEIVED

December 4,

1980.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

10 Application of Ultra- and Hyperfiltration During Production of Enzymatically Modified Proteins H. SEJR OLSEN and J. ADLER-NISSEN Enzyme Applications Research and Development, Novo Industri A/S, Novo Allé, DK-2880 Bagsvaerd, Denmark A p p l i c a t i o n of membrane processes during production of purified food p r o t e i n s i s a functional properties o These p r o p e r t i e s are mostly found t o be s u p e r i o r t o those of de natured p r o t e i n s . However, not all p o s s i b l e needs o f the modern food i n d u s t r y are fulfilled by using n a t i v e p r o t e i n s i n s t e a d of denatured ones. Therefore, enzymatic m o d i f i c a t i o n of p r o t e i n s has been demonstrated as a p o s s i b l e means o f meeting the needs of the food i n d u s t r y f o r h i g h - q u a l i t y p r o t e i n i n g r e d i e n t s ( 2 ) , (13), (14). Membrane processes have a potential a p p l i c a t i o n w i t h i n many areas of industrial enzymatic h y d r o l y s i s of p r o t e i n s . Table I shows how membrane processes can be a p p l i e d i n the d i f f e r e n t types of enzymatic m o d i f i c a t i o n of p r o t e i n . Thus membrane processes may be used f o r pre-treatment of p r o t e i n s , f o r the r e a c t i o n step and as an essential p a r t of the purification o r post­ -treatment step. In the f o l l o w i n g , r e s u l t s from our work w i t h these processes i n Novo's pilot p l a n t f o r Enzyme A p p l i c a t i o n will be presented. The r e s u l t s demonstrate t h a t the f u n c t i o n a l p r o p e r t i e s of some of the p r o t e i n products obtained were improved to such an extent that the membrane processes may become very important in the modern p r o t e i n technology. Owing to the i n t e r e s t i n g p r e l i m i n a r y r e s u l t s obtained regarding f u n c t i o n a l p r o p e r t i e s , l e s s a t t e n t i o n has been paid to a thorough i n v e s t i g a t i o n of the u n i t operations as such. General C h a r a c t e r i s t i c s of Enzymatic H y d r o l y s i s . As e a r l i e r reported (2_) , a l i m i t e d h y d r o l y s i s of a p r o t e i n product may improve c e r t a i n f u n c t i o n a l p r o p e r t i e s such as whipping and emulsifying capacity. These improvements are dependent on the enzyme and on the p r i n c i p l e by which the r e a c t i o n i s c o n t r o l l e d . The p r e f e r a b l e way of c o n t r o l l i n g the m o d i f i c a t i o n i s by a p p l i c a t i o n of the pH-stattechnique, by which the base consumption used f o r maintaining pH 0097-6156/81/0154-0133$09.25/0 © 1981 American Chemical Society

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

134

SYNTHETIC

MEMBRANES:

H F AND U F

USES

during the p r o t e o l y t i c r e a c t i o n i s d i r e c t l y converted to degree of h y d r o l y s i s 02). Degree of h y d r o l y s i s , DH, i s the p r o p o r t i o n between the number of peptide bonds cleaved and the t o t a l number of peptide bonds i n the i n t a c t p r o t e i n ( 3 ) . P r o t e o l y t i c a l l y modified p r o t e i n s which have been thoroughly enzyme digested are low molecular p r o t e i n h y d r o l y s a t e s . Such products have o f t e n l e s s pronounced foaming o r e m u l s i f y i n g propert i e s than p r o t e i n s which have been only s l i g h t l y hydrolyzed (2) . However, a need f o r t h i s k i n d of p r o t e i n products appears i n the beverage i n d u s t r y f o r enrichment o f s o f t d r i n k s w i t h p r o t e i n and i n the meat i n d u s t r y f o r pumping of whole meat cuts w i t h low cost p r o t e i n s . Important p r o p e r t i e s of low molecular p r o t e i n h y d r o l y sates are a bland t a s t e and a complete s o l u b i l i t y over the wide pH-range used i n foods. The production method f o r low molecular p r o t e i n hydrolysates has been described e a r l i e r (40 A c o n t r o l l e d batch h y d r o l y s i s using the pH-stat i s performed then recovered by e.g. s o l i d used f o r c o n c e n t r a t i o n and/or d e s a l i n a t i o n . Instead of using the c o n t r o l l e d batch h y d r o l y s i s and s o l i d s s e p a r a t i o n processes, the s e p a r a t i o n of peptides may be performed from an enzyme-substrate r e a c t i o n mixture under continuous u l t r a f i l t r a t i o n i n a s o - c a l l e d membrane r e a c t o r . H i g h l y F u n c t i o n a l Soy P r o t e i n s Native soy p r o t e i n i s o l a t e may be produced by u l t r a f i l t r a t i o n of an aqueous e x t r a c t of d e f a t t e d soy bean meal, (1), ( 5 ) . The process layout i s shown i n F i g . 1. A c a r e f u l s e l e c t i o n of membrane parameters such as flow v e l o c i t y , pressure drop, temper a t u r e , and of the type of membrane and modules i s important i n order to o b t a i n a bean p r o t e i n i s o l a t e by a d i r e c t u l t r a f i l t r a t i o n of the c l a r i f i e d e x t r a c t ( 5 ) . The p r o t e i n i s o l a t e has a prot e i n - d r y matter r a t i o higher than 90% (N x 6.25), when using t h i s process. H i t h e r t o , enzymatic m o d i f i c a t i o n of u l t r a f i l t e r e d soy prot e i n s has not been described. The present i n v e s t i g a t i o n shows that p r o t e i n products w i t h b e t t e r p r o p e r t i e s than e n z y m a t i c a l l y modified a c i d p r e c i p i t a t e d p r o t e i n s can be produced by a s u i t a b l e combination of the i n v o l v e d u n i t o p e r a t i o n s . M o d i f i c a t i o n of U l t r a f i l t e r e d versus A c i d P r e c i p i t a t e d Soy P r o t e i n . When the r e t e n t a t e obtained from the u l t r a f i l t r a t i o n of soybean e x t r a c t i s subjected to an enzymatic h y d r o l y s i s as described e a r l i e r (2) f o r a c i d p r e c i p i t a t e d p r o t e i n , a h y d r o l y s i s curve (DH versus time) may be drawn. A comparison of such h y d r o l y s i s curves i s shown i n F i g . 2 f o r a c i d p r e c i p i t a t e d soy p r o t e i n i s o l a t e and u l t r a f i l t e r e d soy p r o t e i n i s o l a t e . The curves a r e drawn on the b a s i s of the same h y d r o l y s i s parameters. The enzyme used i s the m i c r o b i a l a l k a l i n e protease s u b t i l i s i n C a r l s b e r g (ALCALASE® ).

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

O L S E N A N D ADLER—NISSEN

Table I.

TYPES

OF

MATIC

Enzymatically Modified Proteins

1

Application of Membrane Processes During Enzymatic Modification of Proteins

ENZY-

ENZYMATIC

MODIFIED

PRETREATMENTS

REACTION

STEP

POSTTREATMENTS

PROTEINS

HIGHLY

PRODUCTION

FUNCTIONAL

NATIVE

PROTEINS

ISOLATE

OF

MOLECULAR

-

PROTEIN

SEPARATION

BY UF

BY

UF

CONCENTRATION

LOW

-

AND/OR

MOLECULAR

PROTEIN

HYDRO-

LYZATES

MEMBRANE

-

REACTOR

CONCENTRATION BY

AND/OR

UF

UF

~

ULTRAFILTRATION

HF

~

HYPERFILTRATION

Soy

DESA-

meal

50% (Nx6.25)

DESA-

LINATION

BY HF

Water

T\ Extraction

(Liq./solid-ratio:

Extract

4% ( N x 6 . 2 5 )

10:1)

_j

C oonncceei n t r a t e 2 2 - 2 5 %

(Nx6.25)

Centrifuge

Remanence (sludge) 8% ( N x 6 . 2 5 )

filtration (batch)

meate 0.15% (Nx6.25) Spray drying

Figure 1.

Protein Q

Q

%

isolate

( N x 6 > 2

5)

Production of soy protein isolate by UF in pilot plant

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

136

SYNTHETIC

MEMBRANES:

HF

AND

UF

USES

I t appears from F i g . 2 t h a t the u l t r a f i l t e r e d soy p r o t e i n i s o l a t e i s hydrolyzed c o n s i d e r a b l y more slowly than the a c i d prec i p i t a t e d p r o t e i n . This i s due to the compact molecular s t r u c t u r e of the u l t r a f i l t e r e d p r o t e i n , which i s s t i l l i n the n a t i v e s t a t e . That the degree of denaturation of a p r o t e i n s u b s t r a t e has a profound i n f l u e n c e on the k i n e t i c s of the p r o t e o l y s i s has been known f o r long, see Christensen ( 6 ) . I t should be noted that s u b t i l i s i n C a r l s b e r g i s not i n h i b i t e d by the protease i n h i b i t o r s present i n n a t i v e bean p r o t e i n ( 7 ) . Using the u l t r a f i l t e r e d soy p r o t e i n i s o l a t e described prev i o u s l y ( F i g . 1 ) , a s e r i e s of hydrolysates covering a range of DH-values (DH = 0 to DH = 6%) was made i n the l a b o r a t o r y using the method o u t l i n e d i n F i g . 3. In a l l cases the h y d r o l y s i s was terminated by a d d i t i o n of HC1 to pH = 4.2 to i n a c t i v a t e the enzyme. A f t e r 30 minutes, pH was readjusted to pH = 7.0 by using NaOH. NaCl was added u n t i l the f i n a l c o n c e n t r a t i o n i n a 10% prot e i n (N x 6.25) s o l u t i o The whipping expansio a s o l u t i o n having 3% p r o t e i n ( 2 ) . F i g u r e 4 shows whipping expans i o n versus DH f o r u l t r a f i l t e r e d and a c i d - p r e c i p i t a t e d soy prot e i n s modified by A l c a l a s e . S i m i l a r r e s u l t s have a l s o been found f o r u l t r a f i l t e r e d and a c i d - p r e c i p i t a t e d p r o t e i n s from faba beans ( V i c i a faba) ( S e j r Olsen, unpublished r e s u l t s ) . I t appears from F i g . 4 that i n the case of the a c i d - p r e c i p i t a t e d p r o t e i n , higher DH-values cause a d i s t i n c t r e d u c t i o n of the whipping expansion. The i n c r e a s i n g content of small peptides r e s u l t i n g from a more pronounced degradation of the p r o t e i n s at the high DH values i s assumed to be r e s p o n s i b l e f o r t h i s r e d u c t i o n of foaming a b i l i t y . Removal of the small peptides during the proc e s s i n g of the u n r e f i n e d soy meal to the f i n a l whipping agent might t h e r e f o r e have a p o s i t i v e e f f e c t on the foaming a b i l i t y . Experimental D e t a i l s . In order to examine the above hypot h e s i s , the enzymatic h y d r o l y s i s was c a r r i e d out at d i f f e r e n t stages during the soy i s o l a t e process. Four process combinations examined i n our p i l o t p l a n t are o u t l i n e d s c h e m a t i c a l l y i n F i g . 5. In a l l cases the f o l l o w i n g procedure was used: D e f a t t e d , dehulled white soy meal from Aarhus O l i e f a b r i k A/S was e x t r a c t e d w i t h water at pH = 8.0 using a l i q u i d : s o l i d r a t i o of 10 : 1. A l l c e n t r i f u g a t i o n s were c a r r i e d out i n a W e s t f a l i a solids ejecting centrifuge.

SB-7

A l l u l t r a f i l t r a t i o n s were made on a DDS-modul type 35 at 50°C using polysulphone membranes type GR6-P at 3 kp/cm . The module had 2.25 m2 of membrane area. 2

Hydrolyses were made by use of ALCALASE 0.6 i n pH-stat.

L at pH =

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

8.0

OLSEN A N D ADLER—NISSEN

Emymatically Modified Proteins

137

% DH' Soy

Cone, of substrate: _ S= 8% N x 6 . 2 5

16

pH -

12

protein

Purin?.

isolate

500 E ^

8.0

50°C

Cone, o f enzyme: E/S = 2 . 0 % A l c a l a s e (E = 0 . 1 6 % )

0.6L

-

8

Soy p r o t e i n i s o l a t e ultrafi1tered

4

r

_

i 3 min

Figure 2.

Hydrolysis curves for soy protein isolates

> ^ ^ D i l u t e d (Soy

UF-retentate

V^_8%

Nx6.25

ALCALASE

pH-STAT

4N

at

6N

NaOH

HC1

pH

j y

hydrolysis

=

8 . 0 ,

50°C

\

Enzyme

i n a c t i v a t i o n

pH

50°C,

4 . 2 ,

30

min.

• 4N

NaOH

»•

Adjustment pH

to

of

7.0

• Sol i d

NaCl

Adjustment 14.6g

Freeze

Figure 3.

to

NaCl/lOOg

Nx6.25

drying

Laboratory method for proteolytic modification of ultraflltered soy protein isolate

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

138

SYNTHETIC

i

i

i

% Whipping

i

T

r— i

MEMBRANES:

1

H F A N D U F USES

•

expansion

1600 Ultrafiltered

-

1200

800

- i

/

/ /

/ /

/ /

400

A*

Acid

/ T 1

precipitated

i 2 % DH

Figure 4.

Whipping expansions vs. DH for soy protein hydrolysates

EXTRACTION

EXTRACTION

1 HYDROLYSIS

CENTRIFUGATION

1 INACTIVATION

CENTRIFUGATION

1

1

1

ULTRAPILTRATIOR"

•OLTRAPIETRATION"

1

1

' H Y D R O L Y S I S '

' H ? G R 0 C ? 5 I 5 '

1 CENTRIFUGATION

1 DRYING

CENTRIFUGATION

1 INACTIVATION

1

"OCTRAFILTRATIUR"

EXTRACTION

1 HYDROLYSIS

1 CENTRIFUGATION

EXTRACTION

!

INACTIVATION 1

1

1 "OCrariCTRATTOR"

1

1 INACTIVATION

DRYING

CENTRIFUGATION

I

I

DRYING

1 III

'OCTRAPICTRATIOflJ l

II DRYING

IY Figure 5.

Process combinations investigated for production of highly functional enzymatically modified soy proteins

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

10.

OLSEN A N D ADLER—NISSEN

Enzymatically Modified Proteins

139

In a l l cases h y d r o l y s i s to DH = 3% and DH = 6% was made and i n a c t i v a t i o n was c a r r i e d out a t pH = 4.0 (50°C) f o r 30 minutes. The general h y d r o l y s i s parameters were: Substrate c o n c e n t r a t i o n s : Enzyme/substrate r a t i o : Temperature: pH:

S = 3 to 8% (N x 6.25) E/S = 2% ALCALASE 0.6 L T = 50°C pH = 8.0

Some of the d i f f e r e n t u l t r a f i l t r a t i o n processes w i t h i n the four process combinations i n c l u d e d i a f i l t r a t i o n as w e l l . When d i a f i l t r a t i o n was included at a stage, the sequence, u l t r a f i l t r a t i o n - d i a f i l t r a t i o n - u l t r a f i l t r a t i o n , was used i n order to obt a i n a high s e p a r a t i o n e f f i c i e n c y and membrane c a p a c i t y ( 8 ) . The f i n a l p r o t e i n products were analysed and evaluated f o r t h e i r whipping expansion, foam s t a b i l i t y and i n the case of the DH-6%-products f o r bakin performanc i meringu b a t t e w e l l . The a n a l y t i c a l procedure Methods of A n a l y s i s Whipping Expansion.

C a r r i e d out as d e s c r i b e d p r e v i o u s l y

(2). Foam S t a b i l i t y . A p l a s t i c c y l i n d e r (diameter 7 cm, h e i g h t 9 cm) having a w i r e net w i t h a mesh s i z e of 1 mm x 1 mm i s f i l led w i t h foam and the amount of foam i s found by weighing (A gram) . The c y l i n d e r i s then placed on a funnel on top of a g l a s s c y l i n d e r of 100 ml. A f t e r 30 minutes the weight (B) of drained l i q u i d i n the g l a s s c y l i n d e r i s determined. The foam s t a b i l i t y FS i s d e f i n e d by the equation: A

FS =

B

~ A

x 100%

Baking Performance of Meringue B a t t e r . To 100 ml of a 12% w/w (N x 6.25) s o l u t i o n a t pH = 7.0 of the whipping agent, 150 g of saccharose i s added. The saccharose i s completely d i s s o l v e d by gentle s t i r r i n g at room temperature. The s o l u t i o n i s then whipped a t speed I I I (260 rpm) f o r 10 minutes i n a Hobart Mixer (model N - 50) u s i n g a w i r e whisk. Immediately a f t e r w a r d s , t e n samples of 10 ml are t r a n s f e r r e d to an aluminium t r a y a t separate p o s i t i o n s by means of a s y r i n g e . Baking i s then performed a t 130°C f o r 1 hour. A f t e r c o o l i n g t o ambient temperature, the weight, the height (h) and the diameter (d) are determined. The volume i s c a l c u l a t e d assuming that the meringue i s a s p h e r i c a l segment having the volume: 1 2 ^ 2 V=-g-xTrx(h +|- x ) Z

z

d

The apparent d e n s i t y i s then c a l c u l a t e d , and the s m a l l e r the dens i t y , the b e t t e r the baking performance, provided that the s u r face i s s t i l l smooth and the shape i s maintained.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

140

SYNTHETIC

Amino-acid Analyses. K o l d i n g , Denmark.

MEMBRANES:

HF

AND

UF

USES

C a r r i e d out by B i o t e k n i s k I n s t i t u t ,

TCA-soluble N i t r o g e n . Measured i n 0.8 N t r i c h l o r o a c e t i c a c i d (TCA) u s i n g the method of Becker et a l . ( 9 ) . Nitrogen S o l u b i l i t y .

C a r r i e d out as d e s c r i b e d p r e v i o u s l y

(2). Free Alpha-amino Groups.

Measured by the TNBS-method (10).

Crossed Immunoelectrophoresis. Weeke (11) .

The method i s d e s c r i b e d by

R e s u l t s and D i s c u s s i o n Data from the membran l i b . Average permeate f l u x e s of the same order of magnitude were seen i n a l l combinations, whether the u l t r a f i l t r a t i o n s were performed on enzyme t r e a t e d p r o t e i n s or on raw bean e x t r a c t . This i n d i c a t e s that p r o t e i n molecules capable of forming a g e l on the membrane surface are s t i l l present a f t e r the enzymatic m o d i f i c a t i o n . The s i z e of the permeate f l u x e s obtained i s i n the i n t e r v a l of about 20-40 l/h/m2, which i s i n the economically a t t r a c t i v e range of the process ( 5 ) . The p r o t e i n y i e l d s shown i n Table I l i a and I l l b are based on 100% recovery of phases. The reason f o r the r a t h e r low y i e l d s are low n i t r o g e n s o l u b i l i t y of the soy meal used, v i z . about 60% at pH = 8. As about 90% of p r o t e i n may be water e x t r a c t e d from a l e s s denatured soy meal (12), the o v e r a l l y i e l d s would be about 50% higher i f such a raw m a t e r i a l i s used. I f the combinations I , I I and IV are compared w i t h respect to the y i e l d s and f u n c t i o n a l p r o p e r t i e s , i t appears that both whipping expansion and foam s t a b i l i t y are h i g h e s t at the h i g h DHv a l u e . However, due to h i g h e r content of low molecular peptides at the high DH-value, the o v e r a l l p r o t e i n (N x 6.25) y i e l d s are lower. The processes have to be evaluated more thoroughly i n o r der to f i n d a compromise between the p r o t e i n y i e l d s and the funct i o n a l i t y wanted. When comparing the f u n c t i o n a l i t y s t u d i e s w i t h the chemical p r o p e r t i e s of the DH = 3%-products g i v e n i n Table I l i a , no s i g n i f i c a n t c o r r e l a t i o n i s found between T C A - s o l u b i l i t y , p s i ( p r o t e i n s o l u b i l i t y index) at pH = 4.5 or the p s i at pH = 7.0. Omitting the I I I combination which i s made by a method which r e t a i n s some denatured p r o t e i n (see ( 2 ) ) , only the content of leu-NH^ equival e n t s s i g n i f i c a n t l y c o r r e l a t e s w i t h the whipping expansion and the foam s t a b i l i t y . I n c l u d i n g the r e s u l t s from Table I l l b , the curves shown i n F i g . 6 and F i g . 7 c l e a r l y show that the higher the content of f r e e NTJ^-groups, the h i g h e r the whipping expansion and foam s t a b i l i t y of the i s o l a t e d p r o t e i n s , although the process combinations were d i f f e r e n t . This confirms the s i g n i f i c a n c e of

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

10.

O L S E N A N D ADLER—NISSEN

Enzymatically Modified Proteins

Table H a . Ultrafiltration/Diafiltration Processing Data ( D H =

Retentates Process combination

I

UF or DF

%(Nx6.25)

%(Nx6.25)

UF DF UF

2.9 9.3 9.3

9.3 9.3 18.0

Final

Before

3%)

Average Average

permeate

Prot.re-

flux

tention %

7

1/h/nT

70.7

30.1 26.7 20.0

UF

2.3

10.9

75.5

35.6

DF

10.9

10.1

92.9

34.7

UF

2.8

18.3

93.1

36.0

IV 1 s t

UF DF

3.2

9.8

92.2

41.9

9.8

15.7

98.2

26.7

IV 2 n d

UF

3.3

10.4

84.4

II

141

U

III

no

data

Table l i b . Ultrafiltration/Diafiltration Processing Data ( D H =

Retentates Process combination

UF Before or DF % ( N x 6 . 2 5 )

Final %(Nx6.25)

Average Prot.retention

UF DF

3.1 7.4

6.7

55.8 83.2

II

UF

1.8

12.4

69.1

III

UF

I

IV 1 s t IV 2 n d

UF

See

7.4

table

2a

See

%

Average permeate flux 7 1/h/ni 38.5 no d a t a

31.1

6 - 1061a

2.8 9.9

9.9 12.5

95.4

43.4

DF

98.5

21.7

UF

3.3

6.3

74.2

39.1

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

6%)

142

SYNTHETIC

MEMBRANES:

H F A N D U F USES

Table Ilia. Protein Yields and Some Properties of the D H 3 % Products Made by Different Process Combinations

Process combination

I

II

III

IV

% Protein y i e l d (based on soy meal)

39.5

30.9

55.3

28.6

96.0

93.1

77.9

95.5

Coniposi t i o n : % PY/HY Functionality: % Whipping exp. ) 7o Foam s t a b i 1 i t y Chemical prop.: % psi i n TCA % psi at pH - 4.5 % psi a t pH = 7. leu-NH^, mol/kg prot Immuno precip. l

1566 no data

733 12

667 9

13.2 47.8

10.0 42.7

13.4 49.7

17.7 42.6

DH = 0.8 DH = 3.1 6 archs 6 archs

DH= -0.2 6 archs

1650 42

DH = 1.8 6 archs

) at pH 7.0

Table Illb. Protein Yields and Some Properties of the D H Products Made by Different Process Combinations

6%

Process combination

I

II

III

IV

7o P r o t e i n y i e l d (based on soy meal)

34.3

22.3

55.3

23.8

Composition: % PY/HY Methionin (g/16gN) C y s t i n (g/16gN)

90.1 1.06 1.76

91.1 1.10 1.93

77.6 1 .36 1.44

91.2 0.95 1.75

Functionali ty: % Whipping exp. * % Foam s t a b i 1 i t y Density o f mering. g/m3 **

833 20 0.11 ± O.Ol

1317 50 0.096 ± 0.004

1570 no data 0.21 ± 0.01

2484 69 0.17 ± 0.02

Chemical prop.: % psi i n TCA % psi at pH = 4.5 % psi a t pH = 7.0 leu-NH^,mol/kg protein

20.0 51.0 92.0 0.42 ~ DH = 0.9

19.0 54.6 100.0 0.49 ~ DH = 1.7

32.0 53.8 68.9 0.87 ~ DH = 6.4

30.1 71.7 99.5 0.67 ~ DH = 4.0

3 archs

5 archs

4 archs

2 archs

Immuno p r e c i p . * a t pH 7.0

** w i t h

eggwhites:

0.12 g/cm

3

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

10.

OLSEN AND ADLER—NISSEN

%

0.3

Enzymatically Modified Proteins

WHIPPING

143

EXPANSION

0.

Figure 6.

Whipping expansion vs. the number of free NH groups for highly functional soy protein ultraflltered after hydrolysis

Figure 7.

Foam stability vs. the number of free NH groups for highly functional soy protein ultraflltered after hydrolysis

2

2

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

144

SYNTHETIC

MEMBRANES:

HF

AND

UF

USES

using DH as the c o n t r o l l i n g parameter during p r o t e i n h y d r o l y s i s . The values of p s i i n TCA and p s i a t pH = 4.5 give a rough measure of the content of low molecular p r o t e i n s . The presence of arches determined by crossed Immunoelectrophoresis demonstrates that some high molecular p r o t e i n s are r e t a i n e d i n the modified products. For example IV-DH 6%, which has the best f u n c t i o n a l i t y , c o n s i s t s of only two s i n g l e high molecular p r o t e i n f r a c t i o n s compared to the IV-DH 3% which has s i x f r a c t i o n s . Further studies are r e q u i r e d to e l u c i d a t e the s t r u c t u r a l composition of these high molecular p r o t e i n f r a c t i o n s i n r e l a t i o n to the f u n c t i o n a l i t y . The presence of c y s t i n e i s important f o r i r r e v e r s i b l e g e l formation, but as the content of c y s t i n e i s p r a c t i c a l l y the same i n the hydrolysate made by I , I I and IV as shown i n Table I l l b , i t i s concluded that the c y s t i n e content i s not r e s p o n s i b l e f o r the d i f f e r e n c e s seen i n whipping p r o p e r t i e s . A preliminary organolepti evaluatio di not show any b i t t e r n e s s the b i t t e r n e s s of soy p r o t e i n hydrolyzed w i t h A l c a l a s e only be comes pronounced a t DH-values of 7% and above ( 2 ) . Therefore, the present products may be used as n u t r i t i o u s i n g r e d i e n t s and h i g h l y f u n c t i o n a l p r o t e i n s as w e l l . I n many food formulations they may serve as s u b s t i t u t e s f o r egg-white. This was f o r example demons t r a t e d i n meringue b a t t e r s (see Table I l l b ) . I s o e l e c t r i c Soluble P r o t e i n Hydrolysates An i n d u s t r i a l process has been developed f o r production of i s o e l e c t r i c s o l u b l e soy p r o t e i n hydrolysate w i t h no b i t t e r n e s s and a bland t a s t e (13). The raw m a t e r i a l may be a c i d washed soy white f l a k e s , soy p r o t e i n concentrate o r soy p r o t e i n i s o l a t e The raw m a t e r i a l i s hydrolyzed by the a l k a l i n e protease ALCALASE® to a s p e c i f i e d degree o f h y d r o l y s i s using the pH-stat a t pH = 8.0 (4). Extensive p r o t e o l y s i s of a p r o t e i n o f t e n r e s u l t s i n the f o r mation of b i t t e r peptides ( 2 ) . Therefore, a compromise between high p r o t e i n y i e l d and low b i t t e r n e s s has to be found when choosing the DH-value a t which the h y d r o l y s i s r e a c t i o n should be terminated. For the present process a DH-value of about 10% seems to be a reasonable value. The t e r m i n a t i o n i s performed by a c i d i n a c t i v a t i o n of the enzyme and the a c i d used should be chosen i n accordance w i t h the d e s i r e d o r g a n o l e p t i c c h a r a c t e r i s t i c s of the f i n a l h y d r o l y s a t e . A t o t a l l y n o n - b i t t e r product can be produced by use of an organic a c i d l i k e m a l i c or c i t r i c a c i d . Due to the masking e f f e c t s o f such a c i d s , a b s o l u t e l y no b i t t e r n e s s can be detected even when the t a s t e e v a l u a t i o n i s performed a t n e u t r a l pH. Such products are found most s u i t a b l e f o r s o f t d r i n k s . However, when i n o r g a n i c a c i d s , e.g. h y d r o c h l o r i c or phosphoric acids are used, a s l i g h t b i t t e r n e s s may be detected i n the pure h y d r o l y sate. However, when evaluated i n f o r instance a meat product, no b i t t e r n e s s a t a l l can be t a s t e d even when the hydrolysate i s added up to a p r o p o r t i o n of 1 : 3 of hydrolyzed p r o t e i n to meat p r o t e i n . v

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

10.

OLSEN AND ADLER—NISSEN

Enzymatically Modified Proteins

145

A flow sheet of ISSPH-production i s given i n F i g . 8. The carbon treatment removes the l a s t t r a c e s of soy o f f - f l a v o u r s . Using the recommended process parameters, the f i l t e r e d hyd r o l y s a t e c o n t a i n s about 3% p r o t e i n . H y p e r f i l t r a t i o n i s t h e r e f o r e an a t t r a c t i v e process to use f o r c o n c e n t r a t i o n before d r y i n g . In p i l o t p l a n t experiments we have used a 7 m^ DDS-module type 40 w i t h t i g h t c e l l u l o s e acetate membranes type DDS-990. Conc e n t r a t i o n has been performed at pH = 4.0-4.5 i n a batch system at ambient temperature using 30 kp/m^ d e l i v e r e d by a Rannie p i s ton pump. In Table IV the composition of r e t e n t a t e s and average permeate f l u x e s are shown f o r d i f f e r e n t types of ISSPH. Volumes^of 700-900 l i t r e s of c l e a r h y d r o l y s a t e s were t r e a t e d on the 7 m DDSmodule, except f o r one experiment i n which o n l y 60 l i t r e s were t r e a t e d on a 0.36 m DDS-LAB-module. The p r o t e i n l o s s i n the permeate was below 3% i n a l experiments F i g u r 9 typica f l u x and dry matter curv permeate. U n f o r t u n a t e l y the f l u x decreases r a t h e r much d u r i n g the process. Both increase i n osmotic pressure and c o n c e n t r a t i o n pol a r i z a t i o n are r e s p o n s i b l e f o r t h i s dependence. L a t e r s t u d i e s have shown that the f l u x r a t e can be improved by i n c r e a s i n g the flow v e l o c i t y over the membrane s u r f a c e . D e s a l i n a t i o n of ISSPH. S p e c i f i c a p p l i c a t i o n s of ISSPH may r e q u i r e a reduced content of s a l t s , mainly NaCl. The membrane DDS-865, a c e l l u l o s e membrane, has been used f o r both d i r e c t hyp e r f i l t r a t i o n and f o r d i a f i l t r a t i o n , and i t appears that i t has a h i g h r e t e n t i o n of hydrolyzed p r o t e i n and a low r e t e n t i o n of s a l t . In Table V r e s u l t s are shown from an experiment i n which a h y d r o l y s a t e of soy p r o t e i n i s o l a t e c o n t a i n i n g NaCl-HCl i s d e s a l i nated. From a mass balance on n i t r o g e n (N) as w e l l as on n o n - n i t r o gen m a t e r i a l (NNM) the f o l l o w i n g has been found: direct hyperfiltration: hyperfiltration and d i a f i l t r a t i o n :

11% l o s s of N, 74%removing of NNM 23% l o s s of N, 93% removing of NNM.

For most a p p l i c a t i o n s the product which may be obtained by the d i r e c t h y p e r f i l t r a t i o n i s s u f f i c i e n t l y d e s a l i n a t e d and the p r o t e i n l o s s of about 11% may be accepted. P r e l i m i n a r y r e s u l t s a l s o seem to i n d i c a t e a s l i g h t r e d u c t i o n i n b i t t e r n e s s and soy o f f - f l a v o u r due to removal of very small b i t t e r peptides and other f l a v o u r compounds i n the permeate when t h i s d e s a l i n a t i o n membrane i s used. Process f o r D e c o l o r a t i o n of Slaughterhouse Blood. A novel p r o t e i n i n g r e d i e n t can be manufactured by a c o n t r o l l e d enzymatic

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

146

SYNTHETIC

MIXING

MEMBRANES: HF

H20, S5°C Protei n (Soy concentrate

or

UF

USES

isolate)

HYDROLYSIS IN S T I R R E D TANK

NaOH (pH-stat)

S = 8% protein E/S = 2.0% A l c a l a s e 0.6 50-55°C, pH 8.0

ENZYME INACTIVATION

Acid

DH = 10% - 3 h organic acid, pH 4.0-4.2

1.

AND

Soli ds-ejecting c e n t r i fuge

CENTRIFUGATION H20

FURTHER

CENTR.

FILTRATION

~1 SIudge (unconverted protein and other insoluble material)

w/v

0.1%

FILTRATION

Further

treatment

Figure 8. Flow sheet: production of a nonbitter, soluble soy protein hydrolysate suitable for incorporation into soft drinks and other low pH foods.

__1 20

1 40

1

1

60

80

1 X%

2

Figure 9. Hyperfiltration of HCl-containing ISSPH: flux in 1/h/m ; X, percentage of water removed; DM, percentage of dry matter (rejractometer).

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

OLSEN

A N D ADLER—NISSEN

Table I V .

Enzymatically Modified Proteins

Processing Data Regarding Hyperfiltration of ISSPH

Average Av. p r e s - permeate flux « sure Bar l/h/nf

Retentate

Type o f ISSPH

Vol. cone. ratio

Final

Before

DH(%)

A c i d used for inact.

10

ma 1 i c

2.7

4.5

14.3

22.3

5.1

20

3.80

10

HC1

3.5

4.3

21.1

26.2

6.1

34

4.46

10

HC1

2.0

2.8

14.2

17.6

6.7

34

4.67

15

mal i c

1.8

3.2

13.0

23.3

7.3

29

4.80

10

ma 1 i c

3.9

5.6

12.4

19.8

3.4

32

4.03

15

mal i c

3.5

5.4

16.8

27.5

4.9

32

7.08

10

HC1

30.2*

7.1

30

7.48

10

mal i c

10

malic

-

* by r e f r a c t o m e t e r

Table V .

Permeate flux o 1/h/nT

%x6.25

X /iwater removed

3.9*

**60 l i t r e s

Y %water added

13.0

83.3

7.0

87.5

8.7

87.5

0

7.8

33.0

33.0

0

45.0

16.7

38.3

41.7

25.3

66.6

-

%DM

t r e a t e d on a D D S - L A B - m o d u l e

Desalination of ISSPH by Hyperfiltration on a DDS-865 C A Membrane

-

51.7

%Nx6.25

%DM

8.3

133.0

133.0

8.0

233.3

233.3

8.7

300.0

300.0

Retentate

Permeate

0.25

1.25

-

3.44

/o

4.20

6.00

0.80

2.52

(10.44) ( Z l . 0 8 )

-

0/

%Nx6.25

%Nx6.25

-

Nx6.25 DM 81.9

6.89

87.1

-

-

-

18.31

19.90

92.0

-

-

-

1.38

2.23

20.38

21.27

95.8

0.69

0.77

18.50

18.23

101.5

(10.94) (11.28) 2

DDS-LAB-module, average pressure: 29 kp/cm , 20-30°C

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

148

SYNTHETIC MEMBRANES:

HF

AND

UF

USES

h y d r o l y s i s and subsequent d e c o l o r a t i o n of the red blood c e l l f r a c t i o n a r i s i n g as a by-product i n plasma recovery (14). A flow sheet of t h i s process i s shown i n F i g . 10. The process i s much s i m i l a r to t h a t of ISSPH-production. H y p e r f i l t r a t i o n serves the purpose of c o n c e n t r a t i o n of both plasma and h y d r o l y s a t e s e p a r a t e l y . F l u x data are very s i m i l a r to those obtained on soy p r o t e i n h y d r o l y s a t e s , and a l s o the t o t a l economy of such process seems a t t r a c t i v e . The main reason i s that slaughterhouse blood i n most cases i s regarded as a waste product having no v a l u e , or even a negative v a l u e . D i s c u s s i o n . In the above-mentioned examples membrane processes are found u s e f u l f o r both c o n c e n t r a t i o n and d e s a l i n a t i o n . One reason f o r recommending h y p e r f i l t r a t i o n i n s t e a d of evaporat i o n i n t h i s area i s the economical f a c t o r s . M u l t i - s t e p - e v a p o r a t o r s are s t i l l more economi tha osmosi i bi p l a n t s , but the productio p r o b a b i l i t y be d i s t r i b u t e p l a n t s r e q u i r i n g new investments. At a time w i t h i n c r e a s i n g costs of energy, h y p e r f i l t r a t i o n i s recommendable i n such p l a n t s . A l s o , the freedom of choosing membranes which may improve the q u a l i t y of the p r o t e i n s , f o r example by removing of o f f - f l a v o u r s and s a l t , speaks f o r h y p e r f i l t r a t i o n . Continuous P r o t e i n H y d r o l y s i s i n a Membrane Reactor The membrane r e a c t o r i s an u l t r a f i l t r a t i o n system, i n which a high c o n c e n t r a t i o n of h y d r o l y t i c enzyme i s confined. High mol e c u l a r weight s u b s t r a t e i s fed continuously to the r e a c t o r , and the low molecular weight products are removed simultaneously as permeate. I d e a l l y , a steady s t a t e i s reached, i n which the degrad a t i o n of the s u b s t r a t e i s c a r r i e d out i n d e f i n i t e l y w i t h high e f f i c i e n c y and n e g l i g i b l e l o s s of enzyme. The membrane r e a c t o r concept was demonstrated i n l a b o r a t o r y scale a decade ago by Butterworth et a l . (15) and by Ghose and K o s t i c k (16) i n s t u d i e s on the h y d r o l y s i s of s t a r c h and c e l l u l o se, r e s p e c t i v e l y . L a t e r on s e v e r a l p u b l i c a t i o n s have appeared d e s c r i b i n g the analogous, continuous conversion of v a r i o u s prot e i n s i n t o peptides intended f o r human n u t r i t i o n (17-22). Among these works only that of Iaccobucci et a l . (18) presents a quant i t a t i v e model of the membrane r e a c t o r i n continuous p r o t e i n hyd r o l y s i s , and i t i s a l s o the only demonstration of the p r a c t i c a l f e a s i b i l i t y of the concept i n p i l o t p l a n t s c a l e . Iaccobucci et a l . (18) a p p l i e d an a c i d , thermostable fungal protease from P e n i c i l l i u m duponti i n t h e i r work. The choice of t h i s enzyme had two advantages: The h y d r o l y s i s c o n d i t i o n s ensured v i r t u a l s t e r i l i t y (pH = 3.7, 60°C) and the peptides were q u i t e p a l a t a b l e (23). A major disadvantage of working i n the a c i d range i s that soy p r o t e i n i s o l a t e , which was used as s u b s t r a t e , i s i n s o l u b l e . In p r a c t i c e t h i s causes mechanical problems i f the subs t r a t e c o n c e n t r a t i o n i s not kept s u f f i c i e n t l y low (18).

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

10.

OLSEN A N D ADLER—NISSEN

Enzymatically Modified Proteins

149

As described p r e v i o u s l y i n the present p u b l i c a t i o n , we have developed a batch process f o r producing i s o e l e c t r i c s o l u b l e soy p r o t e i n hydrolysate (ISSPH) w i t h a bland t a s t e . From s t u d i e s o f the k i n e t i c s of the h y d r o l y s i s r e a c t i o n , which takes place i n t h i s process, we have come to the c o n c l u s i o n that the r e a c t i o n i s adequately c o n t r o l l e d by keeping pH constant and monitoring DH. Termination of the r e a c t i o n at a preset value of DH ensures a r e p r o d u c i b l e , optimal o r g a n o l e p t i c q u a l i t y of the product. In the f o l l o w i n g the p o s s i b i l i t i e s are discussed of produc i n g ISSPH w i t h a f i x e d DH-value during a continuous h y d r o l y s i s r e a c t i o n i n a membrane r e a c t o r using s i m i l a r h y d r o l y s i s c o n d i t i o n s as i n the batch process. The s l i g h t l y a l k a l i n e c o n d i t i o n s are advantageous from a mechanical p o i n t of view, because the substrate i s d i s p e r s i b l e / s o l u b l e , but may a l s o imply a greater r i s k of i n f e c t i o n . The change from an i n s o l u b l e to a s o l u b l e subs t r a t e , and i n p a r t i c u l a r the a p p l i c a t i o n of the DH concent immediately l e d to the c o n c l u s i o described by Iaccobucc s u b s t i t u t e d by an independently derived and more complete model, which only on c e r t a i n p o i n t s i s i n s p i r e d by the former. The f u l l d e r i v a t i o n of the model i s described i n the Appendix of the present p u b l i c a t i o n . Based on the k i n e t i c s of the batch h y d r o l y s i s i t i s demonstrated i n t h i s model that i t i s p o s s i b l e to run the membrane r e a c t o r i n steady s t a t e , i . e . DH can be kept constant i n the r e a c t o r . The steady s t a t e i s i n t r i n s i c a l l y s t a b l e and can be achieved immediately by c a r r y i n g out the h y d r o l y s i s as a batch r e a c t i o n w i t h zero membrane f l u x u n t i l the d e s i r e d DH-value i s reached, c f . F i g . 11. A t t h i s p o i n t , the f l u x i s increased to a preset v a l u e , and i f the various parameters i n the system have been chosen c o r r e c t l y , DH w i l l be maintained constant. A few experiments have been c a r r i e d out i n the l a b o r a t o r y s c a l e w i t h a one l i t r e h y d r o l y s i s v e s s e l , connected to a small i m p e l l e r pump and a S a r t o r i u s l a b o r a t o r y module f i t t e d w i t h DDS GR6-P membranes (0.2 m^). However, the flow r e s i s t a n c e i n t h i s module was too l a r g e , and i t was soon concluded that a resonably constant f l u x was u n a t t a i n a b l e . Despite these d i f f i c u l t i e s , the q u a l i t a t i v e behaviour of the r e a c t o r v a r i a b l e s could be p r e d i c t e d from the model and v e r i f i e d e x p e r i m e n t a l l y . For example, w i t h dec r e a s i n g f l u x DH i n c r e a s e d , but the r a t e of the base consumption decreased, w h i l e the p r o t e i n c o n c e n t r a t i o n i n the permeate r e mained q u i t e s t a b l e as p r e d i c t e d . The hydrolysate was evaluated and found comparable i n q u a l i t y t o ISSPH produced i n the batch process. These r e s u l t s have encouraged us to continue the work i n p i l o t p l a n t w i t h the DDS-35 module, where we can expect cons i d e r a b l y more favourable flow c o n d i t i o n s . The f i r s t experiments c a r r i e d o^t so f a r i n d i c a t e ^ t h a t a reasonable f l u x i n the order of 50 1/m /h (approx. 1 1/m /min.) can be a t t a i n e d but that foaming problems n e c e s s i t a t e the c o n s t r u c t i o n of p r e s s u r i z e d a i r f r e e r e a c t o r . Future s t u d i e s w i l l t h e r e f o r e be needed t o produce a complete experimental v e r i f i c a t i o n of the derived model.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

150

SYNTHETIC

MEMBRANES:

Bl ood CENTRIFU6ATI0NL__^

Cell 40

H F A N D U F USES

Plasma fraction 60 % v / v

fraction

% v/v

HEMOLYSIS Acid HYDROLYSIS

IN

STIRRED

S = 8 % protein E/S = 4 % A l c a l a s e 0 . 6 T = 550C, pH = 8.5

ENZYME

TANK

L

K

SEPARATION

FILTRATION

^Sludg

H20

SEPARATION

INACTIVATION

DH = 1 8 % pH 4 . 0 HCL o r o r g a n i c acid

II

FILTRATION

OR

EVAPORATION

1 Sludge^ Dark

coloured

CARBON

TREATMENT

-

1

SPRAY

DRYING

insolubles Decoloured

Figure 10.

Figure 11.

product

Enzymatic decoloration of blood

Base Consumption—ideal steady-state protein concentration at t = Po

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

0

10.

OLSEN AND ADLER—NISSEN

Enzymatically Modified Proteins

151

An overview of the v a r i a b l e s i n the membrane r e a c t o r process i s given i n F i g . 12, and those equations, which are most r e l e v a n t from an engineering p o i n t of view, are summarized i n Box 1. The s i g n i f i c a n c e of most of the v a r i a b l e s should appear from F i g . 13 and Box 1 immediately, - f o r a f u l l e x p l a n a t i o n , the reader i s r e f e r r e d to the appendix. The main r a t i o n a l e behind the membrane r e a c t o r g e n e r a l l y appears to be savings of enzyme and the high conversion y i e l d , compared w i t h a batch h y d r o l y s i s process, I t should perhaps be ment i o n e d that the emphasis on enzyme c o s t s i s not p a r t i c u l a r l y r e levant i n the present case, as the major cost f a c t o r s f o r the exi s t i n g batch process are the raw m a t e r i a l s and the c a p i t a l costs (13). In any case the r a t i o n a l e i s based on the assumption that the r e a c t i o n can be c a r r i e d on f o r many c y c l e s w i t h no or only a s l i g h t purging. However, i f a s u b s t a n t i a l f r a c t i o n of the subs t r a t e i s non-degradable i n e r t m a t e r i a l w i l l r a p i d l y b u i l d up i n the r e a c t o r causing i s necessary i f the c o n c e n t r a t i o at a reasonably low l e v e l . This has a d r a s t i c , negative i n f l u e n c e on the instantaneous y i e l d , as demonstrated i n F i g . 14 and Table VI. A l s o the enzyme l o s s d u r i n g purging w i l l be c o n s i d e r a b l e unl e s s the f r a c t i o n (y) of degradable p r o t e i n i n the s u b s t r a t e i s c l o s e to 100%. For soy p r o t e i n i s o l a t e Iaccobucci et a l . (18) found t h a t 6.2% of the p r o t e i n i n the s u b s t r a t e accumulated as i n e r t m a t e r i a l - i n other words, when comparing the membrane process w i t h the batch process, i t seems most r e l e v a n t to use y = 94%. I f a short c y c l e time i s chosen (e.g. 10 min.) Table V I shows that the enzyme consumption w i l l be much higher than i n the batch process, as soon as purging s t a r t s (1.8 hours from s t a r t ) . The enzyme consumption can be decreased by e n l a r g i n g the r e a c t o r s i z e , as enzyme c o n c e n t r a t i o n and r e a c t o r s i z e are i n v e r s e l y prop o r t i o n a l (eq. I , Box 1 ) , but i t w i l l s t i l l be of the same order of magnitude as i n the batch process. The i n c r e a s e i n r e a c t o r s i z e has, however, the disadvantage that more p r o t e i n s u b s t r a t e i s confined and l o s t i n the end (Table V I ) . The concomitant l o s s of confined enzyme i s found to be the same i n both cases, which i s obvious from eq. I . I f we look at Table V I I , the f i g u r e s f o r a t o t a l run of twelve hours are g i v e n , and i t appears that the short c y c l e time w i l l give a 1% higher p r o t e i n y i e l d than the long c y c l e time, but at the expense of a much higher enzyme consumption. A y i e l d above 80% appears at the f i r s t glance favourable compared w i t h the batch process where the h y d r o l y s i s process y i e l d s a l i t t l e above 60% (13). However, the y i e l d s must be compared w i t h respect t o the o r i g i n a l raw m a t e r i a l : soy white f l a k e s . I t i s , of course, necessary to feed the r e a c t o r w i t h soy i s o l a t e and t h i s i s produced from white f l a k e s i n a y i e l d of 60-65%. Based on white f l a k e s the p r o t e i n y i e l d of the membrane process as w e l l as the batch process w i l l be approximately 50%.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

152

SYNTHETIC

MEMBRANES:

H F A N D U F USES

INPUT: SUBSTRATE NaOH

FEED FROM

pH-STAT

(ENZYME)

(COMPENSATED FLOWS)

FOR

PR

= PROTEIN

CONCENTRATION

SR

= A C C E S S I B L E PROTEIN

FEED

VELOCITY

NaOH AND

= &

ENZYME

CONC.

x(l+&)

REACTOR: MEMBRANE REACTOR pH

8.0

= PROTEIN

= A C C E S S I B L E PROTEIN SUBSTRATE CONC.

OS

= SOLUBILIZED, PERMEABLE PROTEIN CONC.

50°C

i—r

PERMEATE FLUX = *

P S

PURG =

E

ENZYME

CONCENTRATION =

CONC

OUTPUT: PY

= PROTEIN (-OS)

3

= PURGE

CONC.

IN

PERMEATE

COEFFICIENT

Figure 12.

Variables in reactor model

Figure 13.

SHC for soy isolate & alcalase

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

O L S E N A N D ADLER—NISSEN

Enzymatically Modified Proteins

Table V I . Some Key Figures for the Production of ISSPH on the Membrane Reactor

M/ $

3

y

V

b

n

a

%

AU/kg

Substrate processed

M/*

% 98

10 mi n .

hours

% 2.7

6

98

2.7

24

96

5.6

11.3

at

Q

, kg

150

AU

15.0

5.0

150

AU

27.8

&

94. 1

9.9

94.1

2.5

88.3

96 94

40 mi n .

c

94

8.7

7.3

82.7

7.5

92

11.9

5.3

77.3

10.0

90

15.4

4.0

72.0

12.5

a)

Enzyme c o n s u m p t i o n

b)

Enzyme a n d s u b s t r a t e

c)

Unrealistic

Table VII.

y

5 8 . 2

10.2

present

in practice

at start

because

in

10

98

mi n .

96

n

t

n

o

prm2

E

AU/1 36 72

17

15

11 36

98 94

deterioration

Total-Yield Calculations on the Membrane Reactor

94

96

reactor

of microbial

used

%

13.4

kg

per kg substrate

cycle time

C

18.2

2.4

Subst.

40 min.

n

18

17 11

3.75

kg

membrane E n z . / subst. Enz. ratio used AU/kg AU

Total yield

%

29.8

296

9.9

94.0

30.6

612

20.0

88.0

31 . 5

946

30.0

82.3

31 . 2

150

4.8

31 . 3 32.2

158 241

5.0

87.2

7.5

81.3

89.7

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

154

SYNTHETIC

I:

E ~

MEMBRANES:

HF

AND

UF

USES

1

i x PR x (E/S) „ x M ' 'SHC k(DH) cu

v

PR

III:

e

IV:

n

p = y x |\ - -2. x ( i - y ) ] m

n

= (t-t ) x ~

VI:

[PR X (1-y)

(number of c y c l e s )

Q

Z m n = b PR x (1-y)

P o PR

Substrate used:

M x [p^ + PR x ( n + 3 x

(n -n ))]

Enzyme used:

MxEx

(n -n )]

t

n Total y i e l d :

Box 1.

Q

[ l + n

t

t

x C + $ x

t

Q

Q

x y + ( n - n ) x T] - P /PR t

Q

Q

^

Equations used i n engineering c a l c u l a t i o n s of the membrane r e a c t o r

The d e r i v a t i o n of the equations i s given i n the appendix. I

i s used f o r c a l c u l a t i n g the enzyme c o n c e n t r a t i o n from the k i n e t i c data of the batch h y d r o l y s i s .

II

gives P

III

gives 3, the purge c o e f f i c i e n t from acceptable l e v e l of i n e r t matter = Z

q

( p r o t e i n cone, a t s t a r t i n r e a c t o r )

m IV

gives n, the instantaneous

yield

V

gives the number of c y c l e s f o r a given p e r i o d

VI

gives the number of c y c l e s before purging must be s t a r t e d .

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

10.

O L S E N A N D ADLER—NISSEN

Enzymatically Modified Proteins

155

I f we b r i e f l y consider the main investments i n the two processes f o r a production o f 1000 tons of ISSPH per year and i n clude i n the membrane process equipment f o r producing soy i s o l a t e , the membrane process appears to r e q u i r e s l i g h t l y higher t o t a l investments. The r e s u l t s given above i n d i c a t e that there i s no obvious advantage o f s u b s t i t u t i n g the e x i s t i n g batch process f o r product i o n of ISSPH by a membrane r e a c t o r process. However, t h i s does not i n general mean that continuous p r o t e i n h y d r o l y s i s i n a membrane r e a c t o r w i l l be uneconomical. For example i f the subs t r a t e i s more completely degradable than soy p r o t e i n ( c a s e i n might be such a s u b s t r a t e ) , i t i s expected that i n a small s c a l e p l a n t (where the c a p i t a l costs would favour the membrane r e a c t o r ) the membrane r e a c t o r process could be very a t t r a c t i v e . The prod u c t i o n of p r o t e i n hydrolysates f o r d i e t e t i c and medical use, could w e l l be considered i n t h i s context APPENDIX Development of a K i n e t i c Model f o r P r o t e i n H y d r o l y s i s i n a Membrane Reactor General c o n s i d e r a t i o n s Basis f o r the k i n e t i c model i s a standard batch h y d r o l y s i s experiment (2,). F i g . 14 shows the standard h y d r o l y s i s curve f o r soy p r o t e i n i s o l a t e - A l c a l a s e . The r e a c t i o n constant (pseudo f i r s t order r a t e constant) i s c a l c u l a t e d from the standard curve by f i t t i n g the inverse curve i n a small DH-range (ADH ^1.3%) to a second order Newton-Gregory polynomium (24), and f i n d i n g v(DH) by d i f f e r e n t i a t i o n . This procedure has i n our experience proved t o be the simplest and most r e l i a b l e way o f o b t a i n i n g values o f the r e a c t i o n r a t e . k(DH) i s shown i n f i g . 15. - i t v a r i e s s t r o n g l y w i t h DH. As demonstrated p r e v i o u s l y (25) there i s substrate s a t u r a t ion throughout the r e a c t i o n which means that f o r a constant E/S v(DH) and t h e r e f o r e k(DH) i s independent o f S. A l s o , E/S and v(DH) are p r o p o r t i o n a l to each other as usual ( i b i d ) . F i g . 12 gives an overview of the v a r i a b l e s i n the r e a c t o r model. In accordance w i t h what was demonstrated by Iacobucci e t a l . (18) i t i s assumed that the c o n c e n t r a t i o n of s o l u b i l i z e d , permeable p r o t e i n i s equal on both sides of the membrane. This assumption i s s u b s t a n t i a t e d by the f a c t that the p r o t e i n h y d r o l y zate c o n s i s t s mainly o f s m a l l e r , s o l u b l e peptides and unconverted p r o t e i n (2). The c o n c e n t r a t i o n of a c c e s s i b l e p r o t e i n i n the feed stream, SR, w i l l be smaller than PR, as i t i s l i k e l y that a s m a l l , constant percentage of the p r o t e i n i s undegradable, i n accordance w i t h what was found by Iacobucci e t a l . (18). This f r a c t i o n counts as p r o t e i n i n a K j e l d a h l a n a l y s i s , but i s otherwise c o n s i -

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

156

SYNTHETIC

p =6%, PR=4%, 1=3% o m

x

MEMBRANES: HF

(50% o f

AND

UF

USES

PJ o'

100 80 \ 60

Number o f c y c l e s \

b e f o r e purging becomes

40 20 1 ,

Figure 14.

Figure 15.

Relationship between certain important variables in the membrane reactor

The reaction constant, k(DH), from the standard hydrolysis curve

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

10.

OLSEN A N D ADLER—NissEN

157

Enzymatically Modified Proteins

dered i n e r t , i . e . i t i s assumed that i t s accumulation i n the r e tentate does not i n f l u e n c e the h y d r o l y s i s k i n e t i c s a p p r e c i a b l y . This assumption w i l l be s u b s t a n t i a t e d l a t e r . I t has been found i n batch h y d r o l y s i s experiments that the p r o p o r t i o n of s o l u b l e n i t r o g e n to t o t a l n i t r o g e n i s g r a d u a l l y i n creasing w i t h DH (2). For a constant DH t h i s p r o p o r t i o n i s independent of S (26) i n accordance w i t h the f a c t that v(DH) i s independent of S. I t thus seems reasonable to assume that OS/S w i l l be a monotonously i n c r e a s i n g f u n c t i o n of DH and independent of S. The r e l a t i v e increase of OS/S w i l l always be equal to or smaller than the corresponding r e l a t i v e increase i n DH - t h i s i s a mathem a t i c a l consequence of the f a c t that the average peptide chain l e n g t h i n the s o l u b l e f r a c t i o n of a hydrolyzate w i l l be constant or decreasing w i t h DH (26). In batch h y d r o l y s i s experiments we have g e n e r a l l y not d i s t i n g u i s h e d between S dard h y d r o l y s i s curve. i s c r u c i a l i n the present case where i n e r t p r o t e i n (N*6.25) accumulates. P denotes the p r o t e i n c o n c e n t r a t i o n i n the beginning of the experiment. F i g . 11 shows the p r i n c i p l e s i n an i d e a l , steady s t a t e experiment. A t t=0 the h y d r o l y s i s i s s t a r t e d as a batch h y d r o l y s i s ( = 0). When the d e s i r e d DH-value has been reached (DH=DH a t t=t ) the membrane r e a c t o r i s s t a r t e d , i . e . peptides are permeat i n g through the membrane w i t h the volume f l u x , $, and f r e s h subs t r a t e i s added continuously to r e p l a c e the degraded p r o t e i n . In the f o l l o w i n g i t w i l l be proved that i f the values of the i n dependent v a r i a b l e s ( i . e . PR, P , E , M, $ and 3) have been chosen c o r r e c t l y , the r e a c t o r w i l l immediately be i n steady s t a t e , most g e n e r a l l y defined as DH remaining c o n s t a n t l y equal to D H . The equations which describe the r e l a t i o n s h i p between the v a r i a b l e s w i l l be derived i n the f o l l o w i n g s e c t i o n s . The above general c o n s i d e r a t i o n s are summarized i n Box 2. q

Q

q

The steady-state

equations

The most general d e f i n i t i o n of steady s t a t e was given p r e v i o u s l y namely that DH should remain constant. However, t h i s d e f i n i t i o n i s too general to be of p r a c t i c a l use, and i t i s t h e r e f o r e necessary i n the f o l l o w i n g to assume that the f o l l o w i n g parameters a l so remain constant throughout the experiment: PR, M, E, $ (and 3)

a l l constant

(9)

Convenience d i c t a t e s that PR and M should remain constant. E i s kept constant by r e p l a c i n g the l o s s of enzyme through i n a c t i v a t i o n , permeation and purging. $ can be regulated by the pressure drop and can be maintained reasonable constant i n a w e l l b u i l t system i n which high flow rates are obtained. Q u a s i - s t a t i o n a r y c o n d i t i o n s , i . e . slow changes i n the above parameters w i l l be d e a l t w i t h l a t e r .

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

158

SYNTHETIC

MEMBRANES:

HF

Mass balance c o n s i d e r a t i o n s i n the time p e r i o d t lead to the f o l l o w i n g :

AND

Q

UF

USES

to ( t +dt) °

E/P v(DH) =

(E/S) 'SHC

x v(DH) _, which can be w r i t t e n as CIJ

c

d(DH) dt

_E P

=

(E/S) c

x DH x k(DH)

PY = OS

y

(2)

SR S P R P

=

-

,

.

^

.

=

Accumulated Z= OS

o

8.

S e j r Olsen, H., Isolation of Bean P r o t e i n by Ultrafiltration In: Proceedings of the I n t e r n a t i o n a l symp. on Sep. proc. by Membranes, Ion-exchange and Freeze-concentration i n Food I n d u s t r y . IUF0ST and FEEC, P a r i s (1975), p. A 6-1, A6-21.

9.

Becker, H.C., M i l n e r , R.T., and Nagel, R.H., Cereal Chem. (1940) 17, 447-457.

10.

J . Food Sci.

(1976) 24, 1090-93

(1977) 12 ( 6 ) , 18-23,32.

A d l e r - N i s s e n , J . , J. A g r i c . Food Chem., (1979) 27, 1256-62.

11.

Weeke, B., 3. Crossed Immunoelectrophoresis, p. 47-56. I n : N.H. Axelsen, J . Krøll and B. Weeke: A Manual of Q u a n t i t a t i v e Immunoelectrophoresis - Methods and A p p l i c a t i o n s . Universitetsforlaget, Oslo, 1973. 12.

Smith, A.K., and 1414-1418.

Circle,

S.J., Ind. Eng. Chem. (1938) 30,

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

10.

Enzymatically Modified Proteins

OLSEN AND ADLER-NISSEN

169

13.

Sejr Olsen, H., A d l e r - N i s s e n , J . , Process Biochem. (1979) 14 (7) 6-8, 10-11.

14.

Novo I n d u s t r i A/S, " D e c o l o r a t i o n o f Slaughter House Blood by Enzymatic M o d i f i c a t i o n " . IB 225, Bagsvaerd 1980.

15.

Butterworth, T.A., Wang, D.I.C., Sinskey, A . J . , B i o t e c h n o l . Bioengin. (1970), 12, 615-631.

16.

Ghose, T.K., K o s t i c k , J.A., B i o t e c h n o l . B i o e n g i n . (1970), 12, 921-946.

17.

Roozen, J.P,

18.

I a c o b u c c i , G.A., Myers I n t . Cong. Food S c i

19.

Bhumiratana, S., Hill Jr., C.G., Amundson, C.H., J . Food Sci. (1978), 42, 1016-1021.

20.

Payne, R.E., Hill Jr., C.G., Amundson, C.H., J . Food Sci. (1978), 43, 385-389.

21.

Cunningham, S.D., Cater, CM., (1978), 43, 1477-1480.

22.

Roozen, J.P., Pilnik, W., Enzyme Microb. Technol. (1979), J., 122-124.

23.

Myers, D.V., R i c k s , E., Myers, M.J., W i l k i n s o n , M., IacobucG.A., Proc. IV I n t . Congr. Food Sci. Technol., Madrid 1974, 5, 96-102.

24.

Bennet, A.A., M i l n e , W.E., Bateman, H.,"Numerical I n t e g r a t i o n of Differential Equations", Dover P u b l . , I n c . , N.Y. 1956, p. 27.

25.

A d l e r - N i s s e n , J., Ann. Nutr. A l i m . (1978), 32, 205-216

26.

A d l e r - N i s s e n , J., Unpublished

ci,

Pilnik,

W., Process Biochem. (1973), 8, 24-25 M.J. Emi S. Myers

Mattil,

D.V. Proc IV

K.F.,J.Food Sci.

experiments.

R E C E I V E D December 4, 1980.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

11 Separation of Biopolymer from Fermentation Broths W. L . G R I F F I T H , A . L . C O M P E R E , C. G . W E S T M O R E L A N D , and J. S. J O H N S O N , JR. Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830

The separations f e a s i b l mously over the last generation. The developments t h i s symposium has commemorated, and the i n d i v i d u a l s it has honored, have been l a r g e l y r e s p o n s i b l e . The removal o f d i s s o l v e d s o l u t e s o r other low-molecular-weight substances from water by hyperfiltration or reverse osmosis, which the L o e b - S o u r i r i j a n membrane made technically and economically feasible, has become an industrial-scale operation. Ultrafiltration o f colloids and filtration of coarser m a t e r i a l s from liquids have become much more efficient w i t h the use o f cross flow o f liquid to slow the b u i l d u p o f filtercake; a p p r e c i a t i o n o f the b e n e f i t s from shear a t the i n t e r f a c e has become much more general from the n e c e s s i t y of controlling concentration polarization and f o u l i n g in salt filtration. This paper is an account of our attempts t o apply these developments t o a c l a s s which still poses formidable problems: s e p a r a t i o n from each other of two substances, both dispersed in a liquid as aggregates o f different but l a r g e size. Even though filters are now likely to be a v a i l a b l e o f pore dimensions which should d i s c r i m i n a t e , the filter cake o r dynamic membrane that b u i l d s up soon dominates, and the pore s i z e of the filter becomes i r r e l e v a n t . One more than likely ends up concentrating both substances, r a t h e r than passing one w i t h the liquid through the filter. In research aimed a t lower chemical costs f o r enhanced oil recovery, we are attempting a s e p a r a t i o n of t h i s type, biopolymer from fermentation b r o t h . The m o t i v a t i o n is to e l i m i n a t e the conventional precipitation of polymer by a l c o h o l a d d i t i o n , a step which c o n t r i b u t e s a s u b s t a n t i a l fraction of p r o d u c t i o n c o s t , perhaps as much as 40%, w i t h the n e c e s s i t y to recover a l c o h o l for r e c y c l e (Figure l). P r e c i p i t a t i o n i s necessary to prepare a dry product, economical to s h i p . (Concentrated b r o t h , prepared a t a c e n t r a l facility, is a l s o proposed, a t a penalty in t r a n s p o r t a t i o n costs.) Biopolymers are needed in petroleum p r o d u c t i o n to i n c r e a s e viscosities of fluids i n j e c t e d i n t o f o r m a t i o n , to improve sweep 0097-6156/81/0154-0171$05.50/0 © 1981 American Chemical Society In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

172

SYNTHETIC

MEMBRANES:

HF

AND

UF

USES

i n water f l o o d s , and to prevent viscous f i n g e r i n g i n s u r f a c t a n t , or m i c e l l a r , f l o o d s . I f one attempts to d r i v e s u r f a c t a n t o r banked o i l w i t h water, which i s of lower v i s c o s i t y than the d r i v e n banks, an unstable f r o n t develops, and e v e n t u a l l y water breaks through prematurely to the production w e l l . A path of low r e s i s t a n c e to flow between i n j e c t i o n and production w e l l s i s e s t a b l i s h e d , and much of the o i l and expensive chemicals are thus not f o r c e d toward the production w e l l . R a i s i n g v i s c o s i t y of the d r i v e water, and perhaps of the s u r f a c t a n t bank, by polymer a d d i t i o n tends to counteract t h i s d i f f i c u l t y . A wet s e p a r a t i o n of biopolymer from broth would be p a r t i c u l a r l y advantageous i f biopolymer were produced near the s i t e of use. Not only would the expense of a l c o h o l p r e c i p i t a t i o n be bypassed, but a l s o the d i f f i c u l t r e d i s p e r s i o n of dry biopolymer i n t o aqueous s o l u t i o n s and removal of c e l l d e b r i s and p o o r l y dispersed polymer fragments e t c . which would plu th f the formation. Large q u a n t i t i e s woul program In a recent f i e l d p i l o t , f o r example, i n v o l v i n g nine i n j e c t i o n and 16 production w e l l s , about 770,000 pounds of polyacrylamide were used CO . (Approximately the same amount of biopolymer would have been required.) I n a f u l l - s c a l e p r o j e c t , much more would be needed, a rough r u l e of thumb being one to two pounds of polymer per b a r r e l of p r o j e c t e d enhanced o i l . An o n - s i t e production f a c i l i t y i s t h e r e f o r e an o p t i o n . Biopolymers have c e r t a i n advantages over p a r t i a l l y hydrolyzed polyacrylamides, the other l e a d i n g candidate; they are l e s s s e n s i t i v e to s a l i n i t y and hardness ions and are l e s s degraded by shear, among other aspects. They are more expensive, however. Lowering cost through f i e l d production would l e s s e n t h i s disadvantage. The c r i t e r i o n of a good s e p a r a t i o n i s production of a s o l u t i o n of the d e s i r e d v i s c o s i t y which does not unacceptably plug formations, without l o s s of s u b s t a n t i a l f r a c t i o n s of the polymer i n the process. Diatomaceous earth f i l t r a t i o n s have c u s t o m a r i l y been used to remove plugging c o n s t i t u e n t s . In f i l t r a t i o n of fermentation b r o t h s , p a r t i c u l a r l y i n the f i e l d , i t i s d e s i r a b l e to minimize use of these f i l t e r a i d s . I f the biomass i s h e a v i l y contaminated w i t h them, p o s s i b l e b e n e f i c i a l use as a c a t t l e - f e e d supplement may be i n h i b i t e d , and an expensive waste d i s p o s a l problem may be i n c u r r e d : a cost adding 20£ to 40c/lb of polymer i s conceivable. In our e v a l u a t i o n of p o s s i b i l i t i e s of lowering biopolymer costs i n o i l recovery, we concluded that s c l e r o g l u c a n s probably were a b e t t e r choice f o r f i e l d production than the more u s u a l l y considered xanthan gums ( 2 ) . V i s c o s i t y p r o p e r t i e s of s o l u t i o n s of the two are s i m i l a r , but the organisms {Sotevotvum votfst'l^ et a l . ) producing s c l e r o g l u c a n s are more g e n e t i c a l l y s t a b l e than those producing xanthan gums (Xanthanomas campestvis), are l e s s pathogenic to p l a n t s , and because they produce a c i d during f e r mentation, t h e i r b r o t h s , which may reach pH values as low as 1.5,

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

11.

GRIFFITH

Biopolymer from Fermentation Broths

ET AL.

173

are l e s s l i a b l e t o contamination by unwanted s p e c i e s . We have p r e v i o u s l y reported r e s u l t s of fermentation w i t h t h i s c l a s s , both w i t h c o n v e n t i o n a l glucose as carbon source (_3) and w i t h waste o r low-value carbohydrates ( 4 ) . Other scleroglucan-producing organisms (mushrooms) have a l s o been investigated (5) . Some p r e l i m i n ary s t u d i e s of s e p a r a t i o n of biopolymers from b r o t h have been reported e a r l i e r 06, 7 ) , as w e l l as of treatment w i t h enzymes which reduce plugging by degrading p o o r l y d i s p e r s e d polymeric aggregates ( 8 ) . Here we summarize the present s t a t u s , from these and other r e s u l t s . F u r t h e r d e t a i l s can be found i n p e r i o d i c reports (9). Experimental Fermentation and b r o t h treatment. Only an o u t l i n e w i l l be given here; d e t a i l s ma b found i reference 3 d4 Bench s c a l e fermentations wer batches i n a 1 4 - l i t e r Chemapec fermenter, type GF0014, sparged by a i r a t a r a t e of one volume per volume of broth/minute. Mechanical a g i t a t i o n was a t 300 rpm, and a t ambient temperature. The organisms used were Sclerotium rolfsii 15206 o r a p r o d u c t i o n c u l t u r e provided by Ceca, S.A. The medium contained per l i t e r , 3 g NaN0 , 1 g K H P 0 , 0.5 g MgSO^, 0.7 H 0, 0.5 g KC1, 30 g glucose, 0.05 g FeS0 , and 1 g Ambrex 1003 yeast e x t r a c t , plus s m a l l amounts of anti-foam agents. Fermentations were allowed t o proceed u n t i l polymer p r o d u c t i o n was maximal, a c o n d i t i o n u s u a l l y reached when reducing sugar l e v e l was about 0.5%. Biopolymer f o r microscreen t e s t s was produced i n the ORNL B i o l o g y D i v i s i o n 4 0 0 - l i t e r fermenter. Assay of polymer was by p r e c i p i t a t i o n w i t h i s o p r o p y l a l c o h o l . Procedures v a r i e d i n d e t a i l from time to time, but i n g e n e r a l , biomass was removed by c e n t r i f u g a t i o n before p r e c i p i t a t i o n . B i o mass was taken to be " v o l a t i l e suspended s o l i d s , " the weight l o s s of the washed c e n t r i f u g a t e between 102°C and 550°C. Broth i s u s u a l l y heated to stop fermentation, n e u t r a l i z e d , and subjected to shear to r e l e a s e polymer attached to c e l l w a l l s . Figure 2 summarizes e f f e c t s of v a r i o u s orders of c a r r y i n g out these treatments on v i s c o s i t y . I t i s c l e a r that the f i r s t b l e n d ing to which the sample i s subjected has the g r e a t e s t e f f e c t on the v i s c o s i t y . These treatments have some e f f e c t on m y c e l i a l m i c r o s t r u c t u r e , as the photomicrographs o f F i g u r e 3 i l l u s t r a t e . The n e u t r a l i z e d and blended (NB) b r o t h had r e l a t i v e l y s m a l l amounts of p a r t i c l e s other than mycellium. The f i b r i l s were h i g h l y branched and aggregated i n loose t a n g l e s . A f t e r a u t o c l a v i n g (NBA), the tangles were more c l o s e l y packed, and the f i b r i l s s h o r t e r . Further b l e n d i n g (NBAB) broke up the t i g h t aggregates and produced some s m a l l p a r t i c u l a t e s . A d d i t i o n a l a u t o c l a v i n g (NBABA) increased breakdown of c e l l f i b r i l s and r e s u l t e d i n a r e l a t i v e l y l a r g e number of f i n e p a r t i c l e s . Even the f i n e p a r t i c l e s , however, are 3

2

4

2

4

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

174

SYNTHETIC

MEMBRANES:

HF AND U F

USES

Conventional Heat, -neutralIzation, blending, etc.

Diatomaceous • Earth Filtration

' Alcohol Precipitation

—

Drying

Ship t o f i e l d

I

Biomass t o waste

Alcohol recovery and r e c y c l e

Injection into formation

Diatomaceous E a r t h . F i l t r a t i o n , perhaps enzyme t r e a t m e n t

• Redisperse

AttzAncuUvz in-i>Ajhx production

Broth—*

Heat, neutralization,blending, etc.

- Microscreening -

Polishing F i l t r a t i o n , » p e r h a p s enzyme treatment

Injection formation

into

supplement?)

Figure 1.

Separation of biopolymer from fermentation broth. (Application: mobility control for enhanced oil recovery.)

554

476lBlendl 1

Neutrallyre

——*^>C

548 Blend 844

Figure 2. Viscosities of fermenter sample of laboratory-produced glucan after various treatments: blend, 60 s at low speed of blender; heat, to 90°C for ~ 30 min; neutralize, to pH 6.5-7.0. Numbers refer to viscosities in centipoise, measured at 60 rpm Brook field LVT, spindle No. 3, T = 25° ± 1°C.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

GRIFFITH

Figure 3.

ET AL.

Biopolymer from Fermentation Broths

Photomicrographs of culture broth after treatment: upper left, upper right, NBA; lower left, NBAB; lower right, NBABA.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

176

SYNTHETIC

MEMBRANES:

HF

AND

UF

USES

s e v e r a l orders of magnitude l a r g e r than the expected s i z e of biopolymer s p e c i e s . A x i a l f i l t r a t i o n . In most of our bench-scale f i l t r a t i o n s cross flow was e f f e c t e d by use of a x i a l f i l t e r s (10). In t h i s c o n f i g u r a t i o n (Figure 4 ) , a membrane i s wrapped around a r o t o r , which i s spun i n a chamber, i n t o which feed i s introduced under pressure. The r o t o r i s p e r f o r a t e d , and passages are provided f o r f i l t r a t e (e.g., by an i n t e r v e n i n g screen) from the membrane to these h o l e s . F i l t r a t e e x i t s through the a x i s . R o t a t i o n speeds p r o v i d i n g v e l o c i t i e s of up to about 15 f t / s e c at the membranefeed i n t e r f a c e can be a t t a i n e d i n a v a i l a b l e equipment. P l e a t e d u l t r a f i l t r a t i o n module. The a x i a l f i l t e r i s conveni e n t f o r experiments, i n that volumes s m a l l r e l a t i v e to o r d i n a r y u l t r a f i l t r a t i o n systems can be s t u d i e d and i n t h a t pumping of viscous solutions i s l i m i t e t r a t e or concentrate b l e necessary to maintain d e s i r e d cross flow v e l o c i t i e s . There i s no obvious reason i t could not be s c a l e d up to moderate s i z e s f o r p r a c t i c a l s e p a r a t i o n s , but so f a r as we know, no large-volume a x i a l f i l t e r s are a v a i l a b l e . For the operations of i n t e r e s t , any of the commercial u l t r a f i l t r a t i o n systems would be candidates. We have t e s t e d one module, r e c e n t l y developed by Gelman, which i n c o r p o r a t e s a pleated membrane (Figure 5 ) , w i t h somewhat more open feed passages than those of spiral-wound membranes, and which allows backwashing. Other a p p l i c a t i o n s of the module were discussed at t h i s symposium by A. K o r i n i n a paper coauthored by G. B. Tanny, and a w r i t t e n account i s presumably i n these proceedings. Microscreens. In the course of t h i s research, we came to the o p i n i o n that a p r e l i m i n a r y screening to remove most of the biomass was d e s i r a b l e . We s h a l l report e v a l u a t i o n s of microscreens, or m i c r o s t r a i n e r s , f o r t h i s purpose. These devices have been a v a i l a b l e f o r s e v e r a l decades f o r waste water treatment (11). They are low-hydraulic-head f i l t e r s , comprised of a screen mounted on a r o t a t i n g drum. Apertures of a v a i l a b l e screens range down to micron s i z e s . Feed i s introduced i n t o the drum. F i l t e r cake c o n t r o l i s by backwash w i t h a i r or a p o r t i o n of the f i l t r a t e , once each r o t a t i o n , the backwash being caught i n a t r a y . A schematic i s shown i n F i g u r e 6. In p i l o t - s c a l e t e s t s , we used a mobile u n i t provided by the Envirex d i v i s i o n of the Rexnord Company. The drum was four f e e t i n diameter by two f e e t long. To a i d i n planning p i l o t t e s t s , we a l s o c a r r i e d out some p r e l i m i n a r y one-cycle short-time ( l e s s than 30 sec) t e s t s of screens i n bench-scale apparatuses, designed by manufacturers to evaluate the p o t e n t i a l of microscreens.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

11.

GRIFFITH

ET

Biopolymer from Fermentation Broths

AL.

i

111

MOTOR

Figure 5. Gelman pleated crossflowfiltercartridge. Cartridge components: (A) a porous pleated support screen to provide mechanical support under applied pressure; (B) the pleated microporousfiltrationelement; (C) the pleated spacer which creates the thinflowchannel and promotes turbulentflow;(D) the impermeable film which creates theflowchannel; (E) a porous support tube to provide an exit for permeate; (F) open-end cap which provides for exit of productflow;(G) closedend cap completely which seals one end of module; (H) outer seal ring which creates the seal between the impermeable film in the module and the interior of the housing. The back pressure support tube is not pictured. The ends of the cartridge are potted and sealed. A space between the ends of Film D and the end seals is provided to allow the entrance and exit of theflow-channelfluid.

Figure 6. Microscreenflowpattern

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

178

SYNTHETIC

MEMBRANES:

HF

AND

UF

USES

Results Laboratory t e s t s . A p r e l i m i n a r y t e s t of a x i a l f i l t r a t i o n on broth from a s c l e r o g l u c a n fermentation, d i l u t e d to give a s o l u t i o n w i t h i n the range of v i s c o s i t i e s used i n o i l recovery, was encouraging. I n passage through 1.2 um Acropor (Gelman) membranes there was no s i g n i f i c a n t l o s s of v i s c o s i t y , measured under the same shear r a t e , e i t h e r of the broth or of resuspended dry glucan or xanthan polymer (range from 20 to 25 c p ) . The f i l t r a t i o n was c a r r i e d out at 20 p s i g and a t 2000 rpm, corresponding to about 11 f t / s e c a t the membrane s u r f a c e . A x i a l f i l t r a t i o n appeared to lower g r e a t l y the l e v e l of plugging c o n s t i t u e n t s . Figure 7 compares the f l u x d e c l i n e i n passage through 1.2 um f i l t e r s , without c r o s s f l o w , of the three polymer s o l u t i o n s before and a f t e r a x i a l f i l t r a t i o n ( a x i a l f i l t r a t i o n f l u x e s a t the time of c o l l e c t i o n of the samples f o r the plugging t e s t s are l i s t e d i n the f i g u r e legend.) I t can be see the f i l t r a t e s . The fermente was g r e a t e s t before a x i a l f i l t r a t i o n , had the lowest plugging r a t e subsequently. These r e s u l t s were obtained w i t h a d i l u t e d b r o t h , without n e u t r a l i z a t i o n , a u t o c l a v i n g , and b l e n d i n g steps. Although they i n d i c a t e a p o t e n t i a l of cross flow i n these s e p a r a t i o n s , i t i s not s u r p r i s i n g that r e s u l t s o f subsequent t e s t s were not always r e p r o d u c i b l e . Without going i n t o d e t a i l , l a t e r r e s u l t s i m p l i e d that a two-step s e p a r a t i o n , i n v o l v i n g a coarse screening to remove most of the biomass, f o l l o w e d by a p o l i s h i n g f i l t r a t i o n to reduce plugging c o n s t i t u e n t s to a t o l e r a b l e l e v e l , would be advantageous. The b u l k of the biomass would be uncontaminated by diatomaceous earth and might t h e r e f o r e be s u i t a b l e as a c a t t l e - f e e d a d d i t i v e . P o l i s h i n g the e f f l u e n t from screening w i t h f i l t e r a i d would pose much l e s s of a waste d i s p o s a l problem than t r e a t i n g the d i l u t e d b r o t h d i r e c t l y . However, the p o s s i b i l i t y of e l i m i n a t i n g f i l t e r a i d use a l t o g e t h e r by u l t r a f i l t r a t i o n should be improved w i t h lower biomass content. Some bench-scale t e s t s i n d i c a t i n g the p o t e n t i a l of t h i s scheme were d e s c r i b e d i n reference 6. Here we summarize some l a t e r r e s u l t s of experiments designed i n the l i g h t of our e x p e r i ence i n the e a r l i e r runs. I n these, b r o t h was heated, n e u t r a l i z e d , and blended, and d i l u t e d to about one gram of biopolymer per l i t e r . I t was then stored under r e f r i g e r a t i o n u n t i l use. P a r t was subjected to screening w i t h a metal screen of about 125 um apertures, mounted on an a x i a l f i l t e r . Most of the b i o mass was removed i n t h i s s t e p , w i t h no s i g n i f i c a n t l o s s of v i s c o s i t y . Fluxes i n the coarse screening were s e v e r a l hundred g a l l o n s per square f o o t per day. The screened b r o t h was then compared w i t h unscreened b r o t h i n p o l i s h i n g by the a x i a l f i l t e r wrapped w i t h 5 um Nuclepore membranes. F i g u r e 8 compares the f l u x e s . Neither are as h i g h as one might hope, though the screened feed values appear

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

GRIFFITH

ET

AL.

Biopolymer from Fermentation Broths

AXIAL at pH XAN

FLOOD:

500

P P

m

FILTRATE

FILTRATION FLUX, g p d / f t 2 *

• A

6

350

4.5

215

GLUCAN : PPT. BY B U T Y L ALCOHOL , 5 0 0 ppm

•

FILTRATE

•

FERMENTOR BROTH, DILUTED 10/1

•

FILTRATE

O * Average when filtrate collected tor plugging test

Figure 7. Plugging of 1.2-}xm Millipore filter by polymer solutions under 15 psig pressure; before and after axial filtration through 1.2-jxm Acropor filter (20 psig, 2000 rpm or ~ 11 ft/s). Viscosities of all solutions are 20 to 25 cps.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

180

SYNTHETIC

MEMBRANES:

SCREENED

HF

AND U F

UNSCREENED _

3 PSI • 12 PSI O

-

USES

-

1 M

I

«

o c

-

-

E E u m

—o

-

X*

O

—1

•

-

o

0

-

X

•

O

—

-

U.

O

-

—

i

O

•

•

3

1

I

10

20

Figure 8.

.

I

30

.

I

.

40

.

1

50 0 10 TIME (min)

.

1

I

20

30

.

I

.

40

i

1

1

50

60

Fluxes in axial filtration of diluted glucan fermenter broth through 5-^m Nuclepore filters (2000 rpm ~ 11 ft/s)

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

11.

GRIFFITH

ET AL.

Biopolymer from Fermentation Broths

181

somewhat h i g h e r . Figures 9 and 10 compare plugging by the f i l t r a t e s from the p o l i s h i n g a x i a l f i l t r a t i o n w i t h the r e s p e c t i v e feeds, d i l u t e d broth and screened d i l u t e d b r o t h . I t can be seen that the f l u x d e c l i n e w i t h both the f i l t r a t e s i s much l e s s than for the feeds. The slopes o f the f l u x d e c l i n e s are not markedly d i f f e r e n t f o r p o l i s h e d f i l t r a t e s from screened and unscreened feeds. However, the f l u x e s i n plugging t e s t s w i t h the f i l t r a t e from the screened feed appear s i g n i f i c a n t l y h i g h e r than w i t h the f i l t r a t e from the unscreened feed. Figures 11 and 12 compare the v i s c o s i t i e s of the a x i a l f i l t r a t i o n e f f l u e n t s and feeds f o r the screened and unscreened b r o t h s . Here there i s a c l e a r advantage of the screening step. There i s l i t t l e decrease of v i s c o s i t y between feed and f i l t r a t e for the screened m a t e r i a l , but about a 25% decrease f o r the unscreened. There are sometimes decreases i n v i s c o s i t y i n c u r r e d from diatomaceous earth f i l t r a t i o n The r e s u l t s i n Figure r e s u l t s i n reference 6 use here of Nuclepore f i l t e r s , which have c y l i n d r i c a l pores normal to the surface i n a narrow s i z e range, r a t h e r than the Acropor membranes i n reference 6, whose pores are more tortuous. We do not have s u f f i c i e n t i n f o r m a t i o n f o r a d e f i n i t i v e c o n c l u s i o n on t h i s p o i n t . However, a l a t e r comparison of f l u x e s i n a x i a l f i l t r a t i o n by the two types (Figure 13) does not i n d i c a t e any great d i f f e r e n c e . Comparisons of v i s c o s i t y of feeds and f i l t r a t e and of plugging r a t e s of f i l t r a t e s a l s o d i d not support a s i g n i f i c a n t d i f f e r e n c e between Nuclepore and Acropor. Removal of biomass by microscreens. Laboratory t e s t s : P r e l i m i n a r y e v a l u a t i o n of microscreens, or m i c r o s t r a i n e r s , as a commercially a v a i l a b l e device f o r the i n i t i a l removal of the b u l k of the biomass from b r o t h was c a r r i e d out by means of bench once-through t e s t s of f i l t r a t i o n w i t h s m a l l areas of screens of p l a s t i c and of s t a i n l e s s s t e e l having d i f f e r e n t a p e r t u r e s , on broths subjected to d i f f e r e n t p r e l i m i n a r y treatments. These procedures have been designed by the manufacturers to simulate the performance f o r times comparable to backwash i n t e r v a l s and to give i n f o r m a t i o n a l l o w i n g p r o j e c t i o n of the s i z e of a treatment system necessary f o r a given a p p l i c a t i o n . Although the r e s u l t s were u s e f u l i n planning the subsequent t e s t s w i t h the mobile p i l o t u n i t , they were not c l o s e l y p r e d i c t i v e of performance. The reason i s not c l e a r , but i t i s p o s s i b l e that backwash i n the p i l o t u n i t was not complete w i t h these feeds, and there was some c o n t r i b u t i o n of cake to the f i l t r a t i o n . The r e s u l t s d i d i n d i c a t e that under the proper c o n d i t i o n s biomass could be separated from b r o t h without a p p r e c i a b l e f i l t r a t i o n of biopolymer and that performance v a r i e d w i d e l y w i t h the h i s t o r y of the b r o t h . F i g u r e 14 i l l u s t r a t e s e f f e c t s of b r o t h treatment. Large d i f f e r e n c e s i n the f r a c t i o n a l removals of b i o mass are apparent f o r d i f f e r e n t screen apertures and treatments

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

182

SYNTHETIC

MEMBRANES:

HF

AND

UF

USES

Figure 9. Unscreened feed for axial filtration: plugging of 1.2-/xm Nuclepore filters by filtrate from Nuclepore filter mounted on axial filter (plugging test pressure = 12 psi).

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

GRIFFITH

ET

AL.

Biopolymer from Fermentation Broths

183

TIME (min)

Figure 10. Screened feed for axialfiltration:plugging of 1.2-pm Milliporefilterby filtrate from 5-^m Nucleporefiltermounted on axialfilter(plugging test pressure, 12 psi).

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

184

SYNTHETIC MEMBRANES:

"I

1—I

| I I I 11

10

1

1—I

| I I I 11

I I I I 11 100

1

1—I

_l

HF

AND

UF

USES

| I I I LI

I I I I II I

l

SHEAR RATE (••c~ )

Figure 11. Unscreened feed: comparison of viscosities of feed and filtrates from axial filtration (25°C; axial filtration through 5-^m Nuclepore filter)

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

GRIFFITH

1000

ET

Biopolymer from Fermentation Broths

AL.

185

r

•

FEED

100 h

o

Tr-

J

I

L_

I I II

I I

II.I 100

i

mil

1000

SHEAR RATE (NC ')

Figure 12. Screened feed: comparison of viscosities of feed and filtrates from axial filtration (25°C; axial filtration through 5-fim Nuclepore filter).

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

186

SYNTHETIC

i

I

SCREENED THROUGH o 200 MESH • 120 MESH A 200 MESH • 200 MESH E E

MEMBRANES:

HF

AND

UF

USES

I

FILTERED THROUGH ~ 5/xm ACROPOR 5/xm ACROPOR 5/xm NUCLEPORE 3/xm NUCLEPORE

10 D

0.5

O •

A u

T^ TIME (hr)

Figure 13.

Axial filtration at a rotational speed of 2,000 rpm (~ screened fermenter broth at 7.5:1 dilution and 7 psi

11 ft/s) of

Treatment • NB O NBA A NBAB + NBABA O NBABH

Figure 14. Biomass removal. Effect of media aperture and broth treatment at 11-in. hydraulic head.

0

10

20

I

I

1

30

40

50

APERTURE, /um

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

_J_ 60

11.

GRIFFITH

ET AL.

Biopolymer from Fermentation Broths

187

(the treatment symbols were i d e n t i f i e d i n the d i s c u s s i o n of Figure 3, except f o r H, which s i g n i f i e s f i l t e r e d w h i l e h o t ) . However, w i t h i n s c a t t e r , there appeared t o be no d i f f e r e n c e s i n the v i s c o s i t i e s o f feeds and f i l t r a t e s . P i l o t t e s t s : Even w i t h 3 5 0 - l i t e r fermentations, d i l u t e d t o v i s c o s i t i e s i n the i n j e c t i o n range, the volume of feed was l e s s than i d e a l f o r the Rexnord mobile p i l o t u n i t . To make runs over the times and under the c o n d i t i o n s we wished, i t was necessary t o r e c y c l e e f f l u e n t and m a t e r i a l c o l l e c t e d i n backwashing to the feed tank. F o r these t e s t s , feed was n e u t r a l i z e d w i t h NaOH and p a s t e u r i z e d i n the fermenter; i t i s b e l i e v e d that adequate b l e n d i n g was accomplished by shear from s t i r r i n g during d i l u t i o n and from pumps, along w i t h passage through other elements o f the system. Figure 15 presents f r a c t i o n a l biomass removal i n runs w i t h p o l y e s t e r screens of s e v e r a l d i f f e r e n sizes f o r 21 um f i l t e r media above 80%. For some reason, y second-stag screen of 21 um e f f l u e n t gave l i t t l e improvement although s i n g l e stage removal by 1 um screens were good. F i g u r e 16a compares biomass c o n c e n t r a t i o n a t v a r i o u s p o i n t s i n the system f o r the run w i t h 21 um screen. Although biomass removal i n t h i s run was the lowest of the t e s t s i n Figure 14, i t can be seen that biomass i s over a f a c t o r of ten h i g h e r i n backwash than i n f i l t r a t e . Figure 16b i n d i c a t e s that polymer concent r a t i o n i s s i m i l a r a t a l l p o i n t s and i s not being removed by the f i l t e r . This behavior was general i n a l l s i n g l e - s t a g e microscreen runs and was confirmed by the f a c t that v i s c o s i t i e s o f samples a t d i f f e r e n t p o i n t s were not s t a t i s t i c a l l y d i f f e r e n t . The e f f l u e n t from the two-stage (21 um f o l l o w e d by 1 um) screeni n g had a lower v i s c o s i t y than the feed. The p o s s i b i l i t y that microscreening alone might be adequate without p o l i s h i n g f i l t r a t i o n was evaluated i n the plugging t e s t s summarized i n F i g u r e 17a. I t appears that f u r t h e r treatment i s necessary. P o l i s h i n g of microscreen e f f l u e n t s : Diatomaceous earth treatment should be much e a s i e r and l e s s c o s t l y a f t e r microscreening, b u t a l t e r n a t i v e s are s t i l l d e s i r a b l e . F i g u r e 17b compares plugging of microscreen e f f l u e n t before and a f t e r f u r t h e r f i l t r a t i o n through 1.2 um Gelman Acropor AN f i l t e r s i n an a x i a l c o n f i g u r a t i o n and i n the p l e a t e d c a r t r i d g e of F i g u r e 5. Plugging rates are g r e a t l y decreased, the Gelman c a r t r i d g e (loop) g i v i n g s o l u t i o n of the h i g h e s t f l u x e s . However, the f i l t r a t e s from i t were somewhat lower i n v i s c o s i t y than the feeds. The r e s u l t s w i t h the a x i a l f i l t e r appear l e s s f a v o r a b l e than i n e a r l i e r t e s t s w i t h prescreened feeds, and i t i s suspected that there may have been leakage around s e a l s i n t h i s case.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

SYNTHETIC MEMBRANES:

Figure 15.

HF

AND

UF

USES

Volatile suspended solids removal efficiencies for various media: +, 6 fxm; 0 , 1 / z r a ; A, 21 jxm; and 1 n following 21 yjn. m

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

GRIFFITH

ET

Biopolymer from Fermentation Broths

AL.

189

-

1.5 1.4 1.3 CO 9 1.2 _i o 1 1 CO 1.0 Q UJ 0 . 9 Q Z 0,8 UJ Q. CO 0 . 7 z> 0 . 6 C O 0.5 UJ _J 0.4 < 0.3 o_ l 0 . 2 > 0.1 \

0

10 TIME (h)

TIME

(hr)

Figure 16. Concentrations at various points in the microscreen system equipped with 21-fim screens: a, volatile suspended solids; b, polymer. • , feed tank; O, influent; %, effluent; -\~, backwash.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

190

SYNTHETIC

MEMBRANES:

!

!

HF AND U F

"'"I

! ! I 1 11

I

" T"T"

• =91

10

1

1

USES

Mil"

6yLim-

= 146 1/j.m A = 173 21/xm = + =145 Feed

_

o

E

=

i i i n i

10

i

10 E L A P S E D TIME

i

i i i i 111

10 (mm)

(a)

1

IO

10"

10

Figure 17. Plugging test results: a, pilot microscreen effluents; b, filtrates from polishing by crossflow filtration through 1.2-fxm Acropor filter in axial filter (1.5 psi, 1000 rpm) and in pleated cartridge (loop).

E

10°

io

1

E L A P S E D TIME

io (min)

(b)

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

2

11.

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Biopolymer from Fermentation Broths

ET AL.

191

Discussion Although there are a considerable number of questions yet needing answers, the r e s u l t s so f a r are promising w i t h respect t o f i l t r a t i o n without f i l t e r a i d , or w i t h much l e s s than i s customary, for s e p a r a t i o n of biopolymer from fermentation b r o t h . Table 1 summarizes estimates o f c a p i t a l costs and power requirements f o r a ton of biopolymer per day s e p a r a t i o n p l a n t by diatomaceous earth f i l t r a t i o n , c e n t r i f u g a t i o n , and microscreening. The microscreening i s lowest, but a p o l i s h i n g step would have to be added. With respect to microscreening of s c l e r o g l u c a n b r o t h s , t e s t s should be c a r r i e d out on b r o t h n e u t r a l i z e d by l i m e . Because some of the a c i d produced i n the fermentation i s o x a l i c , i t s removal i s probably necessary before i n j e c t i o n , to avoid p r e c i p i t a t i o n as calcium o x a l a t e i n the formation. Lime p r e c i p i t a t i o n should e f f e c t t h i s . I t i s probabl tha f i l t r a t i o w i t h calciu o x a l a t i n the feed w i l l procee i t i s d i f f i c u l t to p r e d i c t whethe performance be b e t t e o worse. Further o p t i m i z a t i o n of the p o l i s h i n g step i s c l e a r l y necessary. The mediocre f l u x e s i n c r o s s - f l o w and a x i a l f i l t r a t i o n suggest that systems a l l o w i n g backwash at frequent i n t e r v a l s may be necessary. Many commercial u l t r a f i l t r a t i o n systems, i n c l u d i n g the one used here, have t h i s c a p a b i l i t y . The biomass c o n c e n t r a t i o n i n the microscreen backwash i s low. We have e s t a b l i s h e d however that c e n t r i f u g a t i o n at 2800 g appears to a l l o w c o n c e n t r a t i o n up to 2 or 3% dry s o l i d s , or by about a f a c t o r of ten. The pasty cake obtained could be used d i r e c t l y as an animal-feed a d d i t i v e i f there were a market nearby, or could be d r i e d f o r shipment. C e n t r i f u g a t i o n of microscreen backwash i s a r e l a t i v e l y low cost o p e r a t i o n ; we estimate that i t would add $10,000 to the c a p i t a l cost and 2 hp to the power requirement o f the estimates i n Table 1. Table 1 3

Cost and energy of processes f o r a 1 0 kg/day (10 l i t e r s / d a y ) i n s t a l l a t i o n 6

Capital Process DE

filter

Centrifuge-'Microscreen^

Cost, 1 0

3

$

Power, hp

155

180

107

40

80

8

Maxium power demands up to 60 hp. P o l i s h i n g step r e q u i r e d .

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

192

SYNTHETIC

MEMBRANES:

HF

AND

UF

USES

Moderate decreases i n v i s c o s i t y i n p o l i s h i n g f i l t r a t i o n do not n e c e s s a r i l y imply biopolymer l o s s . So long as polymer i s not incorporated i n f i l t e r c a k e as i t would be i n diatomaceous earth f i l t r a t i o n (or i f i t can be backwashed o f f , even i f i t i s ) , i t should be p o s s i b l e to operate w i t h a feed of h i g h e r v i s c o s i t y than necessary f o r i n j e c t i o n , and to r e c y c l e feed through the f i l t r a t i o n apparatus, perhaps a f t e r d i l u t i o n . Another p o s s i b i l i t y would be to r e c y c l e p o l i s h i n g f i l t r a t i o n blowdown i n t o the microscreening system. Acknowledgments Research was sponsored by the D i v i s i o n of Chemical Sciences, O f f i c e of B a s i c Energy Sciences, U. S. Department of Energy, under c o n t r a c t W-7405-eng-26 w i t h Union Carbide Corporation. We are indebted to J B Cravens of Rexnord f o r c o l l a b o r a t i o n on bench-scale and p i l o M. V. Long of the ORNL fermentations f o r these t e s t s . S. V. Greene and J . M. Crenshaw provided t e c h n i c a l a s s i s t a n c e i n many aspects of the research. Literature Cited 1.

2.

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

10. 11.

K l e i n s c h m i d t , R. F. "North Burbank U n i t T e r t i a r y Recovery Pilot Test," Final Report, Phillips Petroleum Co. to U. S. Dept. of Energy DOE/ET/13067-60 (1980). Baldwin, W. H., et al., "Chemicals f o r Enhanced Oil Recovery," Annual Report, April 1977-April 1978, U. S. Dept. of Energy BETC/W-26-4. Griffith, W. L.; Compere, A. L. Developments I n d u s t r i a l M i c r o b i o l o g y , 1978, 19, 609. Compere, A. L.; Griffith, W. L. Developments I n d u s t r i a l M i c r o b i o l o g y , 1978, 19, 601. Compere, A. L.; Griffith, W. L.; Greene, S. V. Developments Industrial M i c r o b i o l o g y , 1980, 21, 461 Griffith, W. L.; Tanny, G. B.; Compere, A. L. Developments Industrial M i c r o b i o l o g y , 1979, 20, 743. Griffith, W. L.; Compere, A. L.; Cravens, J. B.; E r i c k s o n , P. R. Developments I n d u s t r i a l M i c r o b i o l o g y , submitted. Griffith, W. L.; Compere, A. L.; Crenshaw, J. M. Developments Industrial M i c r o b i o l o g y , 1980, 21, 451. Compere, A. L., et al., "Chemicals f o r Enhanced Oil Recovery," Q u a r t e r l y r e p o r t s f o r Winter, Summer, and Fall 1979, Department of Energy BETC/W26-5, BETC/W26-10, BETC/W26-15. Kraus, K. A., Proceedings 29th I n d u s t r i a l Waste Conference, Purdue Research Foundation, 1974, 1059. Cravens, J. B.; Kormanik, R. A. J . Water Pollution C o n t r o l F e d e r a t i o n , in p r e s s .

RECEIVED

February 18,

1981.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

12 Externally Wound Tubular Membrane Elements in Modular Assemblies: Production and Application S. M A N J I K I A N A R A M C O , Dhahran, Saudi Arabia C. K . W O J C I K University of Petroleum & Minerals, Dhahran, Saudi Arabia

Tubular R.O. system when compared w i t h the g spiral hollow f i n e f i b e r type R.O. systems. I n the water d e s a l i n a t i o n field, the h i g h membrane packing d e n s i t y of spiral and hollow f i n e fiber systems has given them an overwhelming economic advantage over t u b u l a r systems. However, the advantageous design f e a t u r e of spiral and hollow f i n e fiber u n i t s a l s o serves t o limit t h e i r a p p l i c a t i o n t o relatively c l e a r fluids f r e e of colloidal and particulate matter. This effectively curtails their practical a p p l i c a t i o n in areas such as the s e p a r a t i o n and c o n c e n t r a t i o n of fluid foods, pharmaceutical mixtures and the treatment of industrial wastes. Tubular system can and should effectively fill this gap. The e x t e r n a l l y wound t u b u l a r membrane system and c o n v e n t i o n a l t u b u l a r designs have the necessary d e s i g n , p r o d u c t i o n and functional f e a t u r e s t o meet more demanding task of p r o c e s s i n g fluids of h i g h p a r t i c u l a t e content and, in r o t a r y assemblies, treatment of d e l i c a t e and structurally s e n s i t i v e fluids and chemical mixtures. System D e s c r i p t i o n The e x t e r n a l l y wound membranes were developed by U n i v e r s a l Water Corp., San Diego, C a l i f o r n i a . I n t h i s d e s i g n , the membrane element c o n s i s t s of a porous supporting tube on which are s i m u l taneously wound, i n h e l i c a l f a s h i o n , a s t r i p of permeable f a b r i c o v e r l a i d w i t h a h e l i c a l wound s t r i p of semipermeable membrane f i l m . Adjacent turns of the membrane overlap i n winding, and these overlaps a r e sealed by a bonding solvent so t h a t , the membrane i t s e l f

0097-6156/81/0154-0193$05.00/0 © 1981 American Chemical Society

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forms a u n i t a r y tube e n c l o s i n g the f a b r i c and the porous supporting tube. A diagram of such h e l i c a l l y wound membrane element i s shown i n F i g . 1. Modular assemblies designed t o house a number of h e l i c a l e l e ments a r e constructed by arranging i n d i v i d u a l membrane elements, i n spaced r e l a t i o n s h i p s , w i t h i n f l o w guide tubes i n s i d e a s u i t a b l e pressure v e s s e l . V a r i o u s diameter flow tubes are used t o p r o v i d e the d e s i r e d annular spacing between membrane surfaces and b r i n e flow channel w a l l s . By t h i s means the cross s e c t i o n a l area of b r i n e flow channels around each element can be s e l e c t e d t o p r o v i d e best c o n d i t i o n s f o r s p e c i f i c processing a p p l i c a t i o n s . For example, a r e l a t i v e l y wide spacing may be r e q u i r e d f o r f l u i d s that are v i s cous or have a h i g h content of p a r t i c u l a t e or c o l l o i d a l matter as i n food p r o c e s s i n g a p p l i c a t i o n s . On the other hand, c l o s e spacing may be r e q u i r e d i n water d e s a l i n a t i o n a p p l i c a t i o n s t o prevent conc e n t r a t i o n p o l a r i z a t i o n by producing a t u r b u l e n t f l o w and t o reduce pumping r a t e s . Th F i g . 2. A module j u s t described i s a f i x e d module i n which the membrane elements a r e s t a t i o n a r y . A r a d i c a l departure from the conv e n t i o n a l mode of R.O. systems o p e r a t i o n s i s the r o t a r y system wherein e x t e r n a l l y wound membrane elements c l u s t e r e d around a c e n t r a l s h a f t a r e r o t a t e d i n a s t a t i o n a r y pressure v e s s e l f i l l e d w i t h p r e s s u r i z e d feed stock. Here the separated permeate i s replaced by an equivalent volume of f r e s h feed stock under a constant head. The b a s i c r o t a r y concept i s depicted i n F i g . 3. The most important f e a t u r e s of the e x t e r n a l l y wound membranes are: • Low c o s t . No advanced technology o r s o p h i s t i c a t e d equipment i s i n v o l v e d i n making of such membrane elements. They can be manufactured on s i t e . • S e r v i c e a b i l i t y and maintenance. Being on the outer surface of t u b u l a r elements, the membranes a r e r e a d i l y a c c e s s i b l e to i n s p e c t i o n and c l e a n i n g . Assembly and disassembly of modules can be accomplished e a s i l y and q u i c k l y i n the f l u i d . • Good mechanical r e l i a b i l i t y of the system. The membrane elements a r e subjected t o compressive s t r e s s e s o n l y , t h e r e f o r e , n o n - c o r r o s i v e m a t e r i a l s of lower t e n s i l e s t r e n g t h may be used. Membranes Membranes f o r e x t e r n a l l y wound elements were e i t h e r obtained as f i n i s h e d product from commercial sources, or produced in-house from raw m a t e r i a l s . Purchased membranes were i n i t i a l l y t e s t e d f o r compliance w i t h the s p e c i f i c a t i o n s designed t o assure t h e i r s u i t a b i l i t y f o r winding o p e r a t i o n s ( t h i c k n e s s , t e n s i l e s t r e n g t h and e l o n g a t i o n ) and for t h e i r performance c h a r a c t e r i s t i c s ( f l u x and s a l t r e j e c t i o n )

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w i t h i n the p r e s c r i b e d range of o p e r a t i o n . A f t e r meeting successf u l l y these s p e c i f i c a t i o n s , they were evaluated i n teridb of t h e i r a p p l i c a b i l i t y to h e l i c a l winding and c o m p a t i b i l i t y w i t h overlap s e a l a n t s . Most of the commercial membranes were found to be s u i t able f o r h e l i c a l winding a p p l i c a t i o n . The in-house membranes were f a b r i c a t e d , w i t h minor m o d i f i c a t i o n s , along w e l l e s t a b l i s h e d procedures which i n c l u d e d : formulat i o n , c a s t i n g or forming, g e l l a t i o n and c u r i n g a t elevated tempera t u r e s . Various c a s t i n g s o l u t i o n s were t r i e d f i r s t f o r t h e i r performance as f l a t t e s t membranes before t h e i r s u i t a b i l i t y f o r winding operations was considered. The p r e f e r r e d c a s t i n g f o r m u l a t i o n f o r membranes used i n the h e l i c a l l y wound elements comprises: 24% C e l l u l o s e acetate E-398-6 or -10 29% Formamide 35% Acetone 12% P y r i d i n e A d d i t i o n of p y r i d i n e t o i n membranes having s u p e r i o propertie t h e i r s t r e n g t h and d u c t i l i t y . P r i o r t o c a s t i n g , the mixed formulations were f i l t e r e d f o r removal of p a r t i c u l a t e and i n s o l u a b l e matter and t r a n s f e r r e d to s p e c i a l c a n i s t e r s . Casting was done a t ambient temperatures and water c u r i n g a t 1°C f o r a p e r i o d of 45 minutes. P r i o r t o use, the membranes were f i r s t annealed and then s l i t i n t o s t r i p s , say 1.065 ± 0.005 i n c h wide f o r a 7/16 i n c h diameter element, and r o l l e d on s p e c i a l capsules f o r i n s e r t i o n i n t o winding feeders. The c u r i n g temperatures r e q u i r e d f o r given performance s p e c i f i c a t i o n s f o r the e x t e r n a l l y would membranes were found t o be 2 t o 5 C higher than those f o r f l a t membranes. For b r a c k i s h water a p p l i c a t i o n s , the membrane elements were cured a t 84 C ± 0.2 C f o r the p e r i o d of 10 ± 0.5 minutes. Support S t r u c t u r e s In the c o n s t r u c t i o n and assembly of e x t e r n a l l y wound t u b u l a r membrane systems, the support s t r u c t u r e i s g e n e r a l l y a r i g i d noncompressible t u b u l a r body of s u f f i c i e n t mechanical s t r e n g t h t o withstand r e q u i r e d operating pressures and of adequate p o r o s i t y t o f r e e l y transmit the separated permeate. M a t e r i a l s having uniform p o r o s i t y would be the most d e s i r a b l e , however, c e l l u l a r p o r o s i t y i s o f t e n (at l e a s t i n the cases tested) a s s o c i a t e d w i t h low mechanical s t r e n g t h , l a c k of u n i f j r m i t y and long term r e l i a b i l i t y and a r e l a t i v e l y high cost of production. I n absence of such m a t e r i a l s , p o r o s i t y i n supporting tubes was achieved by d r i l l i n g holes a t spaced i n t e r v a l s u s i n g a s p e c i a l l y designed m u l t i - s p i n d l e d r i l l i n g f i x t u r e . I t was e s t a b l i s h e d experimentally that the most s a t i s f a c t o r y passage of water was achieved through 0.028 i n c h diameter p e r f o r a t i o n s spaced at three i n c h i n t e r v a l s along two s t r a i g h t l i n e s 180 degrees apart.

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D e s i r a b l e p r o p e r t i e s f o r supporting tubes are: c o r r o s i o n r e s i s t a n c e , thermal s t a b i l i t y , dimensional s t a b i l i t y under wet c o n d i t i o n s , c o m p a t i b i l i t y w i t h other components of the module, mechanical s t r e n g t h , and good m a c h i n e a b i l i t y . A h i g h l y p r a c t i c a l m a t e r i a l i s ABS ( a c r y l o n i t r i t e - b u t a d i e n e s t y r e n e ) . Membrane elements, f a b r i c a t e d w i t h 7/16 nominal diameters extruded ABS tubing as support s t r u c t u r e s , were successf u l l y operated a t pressure up t o 1500 p s i g . Backing M a t e r i a l s Backing m a t e r i a l s are used i n the c o n s t r u c t i o n and assembly of e x t e r n a l l y wound t u b u l a r membrane elements t o provide f o r l a t e r a l t r a n s f e r of permeate t o spaced p e r f o r a t i o n s i t e s i n the support s t r u c t u r e . P r i n c i p a l c h a r a c t e r i s t i c s d e s i r a b l e i n membrane backing m a t e r i a l s i n c l u d h i g h p o r o s i t f o adequat l i q u i d meation a t minimum p r e s s u r e s surface t e x t u r e t o minimiz g g membrane s u r f a c e s and mechanical s t r e n g t h t o b r i d g e over p e r f o r a t i o n s i n the support tube. Dacron pressed paper was found t o be h i g h l y adequate f o r permeate t r a n s p o r t w h i l e possessing the wet s t r e n g t h p l a s t i c propert i e s needed i n winding o p e r a t i o n s . Dacron paper was a l s o used i n c a s t i n g membranes d i r e c t l y on support s t r u c t u r e s . Sealants In the f a b r i c a t i o n of e x t e r n a l l y wound t u b u l a r membrane elements and modular assemblies s o l v e n t bonding f l u i d s and 0-rings are commonly used as s e a l a n t s . I n winding o p e r a t i o n s , s t r i p s o f membranes a r e wound i n an overlapping manner t o form a u n i t a r y tube where h e l i c a l winding overlaps a r e s o l v e n t bonded d u r i n g winding w h i l e the ends of the windings are sealed t o the support tube. Commercially a v a i l a b l e glues and bonding mixtures were found t o be i m p r a c t i c a l i n the continuous and immediate s e a l i n g requirements of the winding process. Most of the epoxy formulat i o n s were r e j e c t e d because of t h e i r s e t t i n g and c u r i n g time requirements. Commonly known c e l l u l o s e acetate s o l v e n t s were t e s t e d i n d i v i d u a l l y and i n combination. I n g e n e r a l , pure s o l v e n t s were found t o be too strong f o r t h a t purpose, as they tended t o penetrate membrane surfaces r a t h e r than spread over the overlap i n t e r f a c e , thus, r e s u l t i n g i n an i m p e r f e c t l y bonded seams, w i t h p h y s i c a l l y weak and b r i t t l e areas at the j o i n t . E x p e r i m e n t a l l y , weak s o l v e n t s i n combination w i t h d i l u e n t s and p l a s t i c i z e r s were found t o be h i g h l y acceptable. A composition, found t o be the most e f f e c t i v e , c o n s i s t e d of a mixture of t r i a c e t i n and a l c o h o l . C e l l u l o s e a c e t a t e was added t o the mixture to i n c r e a s e i t s v i s c o s i t y and a dye t o c o l o r i t f o r the q u a l i t y c o n t r o l purposes. This mixture, a weak s o l v e n t by i t s e l f , produced an extremely strong and r e l i a b l e bond of the membrane o v e r l a p s . The composition of t h i s sealant mixture was:

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Triacetin 94 1-Propanol 6* C e l l u l o s e acetate (E 398 - 10) 3 Red commercial dye 1

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p a r t s by volume p a r t s by volume g per 100 ml of t r i a c e t i n g per l i t e r of mix.

The bond obtained u s i n g t h i s sealant was found t o be e f f e c t i v e w i t h both wet and d r y membranes. F u r t h e r , t e n s i l e t e s t s showed that the bond was a t l e a s t as strong as the membrane i t s e l f . Most important, the bonding took p l a c e i n s t a n t a n e o u s l y a t ambient temperatures. No c u r i n g or s e t t i n g time i s r e q u i r e d . Hence, t h i s bonding method was found t o be i d e a l l y s u i t e d f o r the automatic and continuous winding of membrane elements. Pressure adhesive tape was used f o r s e a l i n g membrane winding edges and a f f i x i n g same to the supporting tube. Structural Materials As noted above, e x t e r n a l l y wound t u b u l a r membrane elements are f a b r i c a t e d p r i m a r i l y of extruded ABS tubing ( n a t u r a l ) , c e l l u l o s i c or blend membranes and dacron paper. The c a r t r i d g e assembly designed t o house the membrane elements and provide f o r the u n i form d i s t r i b u t i o n / f l o w of feed stock i s f a b r i c a t e d of extruded t h i n w a l l e d p o l y s t y r e n e headers. Pressure v e s s e l s were f a b r i c a t e d e i t h e r by u s i n g epoxy coated s t e e l pipe or f i b e r g l a s s v e s s e l s . H e l i c a l Winding Process Fabrication/assembly of e x t e r n a l l y wound t u b u l a r membrane elements i s accomplished by s p e c i a l l y designed equipment that simultaneously and c o n t i n u o u s l y winds, i n h e l i c a l f a s h i o n , i n f i n i t e lengths of membrane and backing m a t e r i a l s t r i p s onto p r e f a b r i c a t e d t u b u l a r support s t r u c t u r e s . Membrane s t r i p winding overlaps are solvent bonded during the winding process. A s u c c e s s f u l method f o r a c h i e v i n g t h i s motion i s based on the use of three d r i v i n g r o l l e r s e q u a l l y spaced on the circumference of the support tube. In o p e r a t i o n such r o l l e r s are i n compressive contact w i t h the surface of the supporting tube and p o s i t i o n e d a t an angle t o i t s a x i s . The r o l l e r s are d r i v e n by a s i n g l e motor and thus r o t a t e a t i d e n t i c a l speeds. This arrangement imparts a p r e c i s e h e l i c a l motion t o the element support tubing w i t h respect to the s t a t i o n a r y feeding spools. To maintain a constant h e l i x angle, s y n c h r o n i z a t i o n of r o t a r y and l i n e a r motions i s e s s e n t i a l . A l s o , the determination and use of backing m a t e r i a l s and membrane s t r i p s of proper width i s important i n o p t i m i z i n g the e f f e c t i v e membrane surface area f o r a given support tubing nominal diameter. The geometrical r e l a t i o n ships between these widths and the h e l i x angle are given i n F i g . 4. Here, the h e l i x angle i s denoted by a, d i s the diameter of the

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Figure 4. Winding geometry Backing m a t e r i a l (a)

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supporting tube ( i t i s a l s o the nominal diameter of the element), and c i s the amount of membrane overlap ( u s u a l l y 0.062 t o 0.125 in.). I n p r a c t i c e , the h e l i x angle was s e t i n the range of 35 45°. Another important f a c t o r i n the winding o p e r a t i o n i s t e n s i o n a p p l i e d t o the backing m a t e r i a l and t o the membrane s t r i p . Tension i s needed t o i n s u r e smooth w r i n k l e - f r e e wound surfaces and t o prov i d e the necessary pressure between membrane overlaps t o o b t a i n proper ponding. A minimum t e n s i o n of about 3 l b / i n i s r e q u i r e d f o r winding the backing m a t e r i a l , w h i l e the optimal t e n s i o n f o r membrane s t r i p s amounted t o 1 l b / i n . Winding machinery comprises: (1) a d r i v e mechanism t o provide means f o r imparting simultaneous r o t a r y and l i n e a r motion t o support s t r u c t u r e s i n a continuous manner, (2) membrane and backing m a t e r i a l feeder c a r t r i d g e s , (3) a sealant a p p l i c a t o r assembly, (4) electromechanical c o n t r o l s (5) t off/separatio tooling d (6) completed element handlin Modular

Assemblies

A modular assembly housing e x t e r n a l l y wound t u b u l a r membrane elements may be d e f i n e d as a pressure v e s s e l w i t h i n which a r e assembled a m u l t i p l i c i t y of i n d i v i d u a l elements, means f o r connect i n g and s e a l i n g s a i d elements t o common headers and a feed stock d i s t r i b u t i o n system that provides f o r adequate feed f l o w across membrane s u r f a c e s . In the development and design of modular assemblies^ housing a m u l t i p l i c i t y of e x t e r n a l l y wound t u b u l a r membrane elements, the f o l l o w i n g f a c t o r s were considered: e f f e c t i v e n e s s of element packing arrangements and d e n s i t y , feed stock d i s t r i b u t i o n p a t t e r n s f o r c o n t r o l l e d and uniform feed f l o w across membrane s u r f a c e s , s e a l i n g r e l i a b i l i t y of modular sub-assemblies, o v e r a l l system r e l i a b i l i t y , module s e r v i c e a b i l i t y and ease of maintenance, system p r o d u c t i b i l i t y , and economic v i a b i l i t y . In u t i l i z a t i o n of e x t e r n a l l y wound t u b u l a r membrane elements i n modular assemblies f o r conventional systems o p e r a t i o n s , that i s , s e l e c t i v e s e p a r a t i o n v i a the c i r c u l a t i o n of p r e s s u r i z e d feed across membrane s u r f a c e s , flow guide tubes were found t o be e s s e n t i a l f o r the proper d i s t r i b u t i o n and c o n t r o l of feed flow. This was achieved s i n g u l a r l y by the use of i n d i v i d u a l element shrouds or flow tubes c r e a t i n g an annular gap through which feed stock was c i r c u l a t e d across membrane s u r f a c e s . A r e p r e s e n t a t i v e multi-element modular assembly i s depicted i n F i g . 2. I n t h i s design the module comprises three major components: • 36 membrane element assemblies • flow guide tube c a r t r i d g e assembly • 5 i n . diameter 12 f t . long pressure v e s s e l .

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Rotary Modules Conventional reverse osmosis systems are g e n e r a l l y designed to operate by p r e s s u r i z i n g raw feed f l u i d s to r e q u i r e d operating pressures and c i r c u l a t i n g s a i d f l u i d s across membrane s u r f a c e s . To meet the operating requirements of the reverse osmosis process, a pumping system i s commonly used t o p r e s s u r i z e and c i r c u l a t e feed f l u i d s a t s u f f i c i e n t v e l o c i t i e s to maintain the d e s i r e d turbulence and t o provide p r e s s u r i z e d make-up f l u i d t o r e p l a c e withdrawn permeate and concentrate f l u i d s . The above approach i s o f t e n uneconomical and energy consuming s i n c e i n most cases s u b s t a n t i a l amounts of p r e s s u r i z e d f l u i d are r e q u i r e d t o maintain the d e s i r e d t u r b u l e n t flow. A d d i t i o n a l l y , i n treatment of c e r t a i n f l u i d s c o n t a i n i n g c o l l o i d a l and p a r t i c u l a t e matter, t u r b u l e n t flow of the raw f l u i d does not always accomplish the c l e a n i n g a c t i o n necessar f r e e of f o u l i n g d e p o s i t s A unique and improved method which s u b s t a n t i a l l y reduces the r e q u i r e d amount of p r e s s u r i z e d f l u i d flow has been developed by U n i v e r s a l Water Corporation. I n t h i s approach the pumping system i s p r i m a r i l y employed t o p r e s s u r i z e the raw f l u i d and a r o t a b l e assembly c a r r y i n g membrane elements i s used t o provide turbulence over the membrane s u r f a c e s . This approach separates the f u n c t i o n s of p r e s s u r i z a t i o n and feed f l u i d r e c i r c u l a t i o n . Thus, the pumping system needs t o p r e s s u r i z e and pump only the volume of feed stock necessary t o make up f o r the separated permeate w h i l e r o t a t i o n of the membrane element assembly provides the d e s i r e d turbulence. A d d i t i o n a l l y , and more s p e c i f i c a l l y i n batch processing systems, p r e s s u r i z a t i o n can be achieved by means other than a pump. In essence,a r o t a r y system comprises a pressure v e s s e l cont a i n i n g a r o t a b l e assembly c a r r y i n g membrane elements, means f o r p r e s s u r i z i n g the f l u i d feed, and means f o r r o t a t i n g the membraneelement assembly. A conceptual r e n d i t i o n of a r o t a r y module i s shown i n F i g . 3, and a flow schematic of a r o t a r y system i s shown i n F i g . 5. Main advantages of the r o t a r y approach i n c l u d e : • reduced energy consumption • continuous by-batch operation convenient f o r food processing • minimal exposure of t r e a t e d f l u i d s to pumping system, pressure f l u c t u a t i o n s and contamination • reduced c l e a n i n g and maintenance costs • high s u i t a b i l i t y f o r maximum r e c o v e r i e s and e f f i c i e n t c o n c e n t r a t i o n of t r e a t e d f l u i d r e l a t i v e l y uniform c o n c e n t r a t i o n of feed f l u i d s w i t h i n modules • s u i t a b i l i t y f o r use w i t h f l u i d s c o n t a i n i n g p a r t i c u l a t e and c o l l o i d a l matter. • l i m i t e d exposure of t r e a t e d f l u i d s t o contamination.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Control Box

Electric Motor

Figure 5.

Shutoff Valve

Pump

Pressure Regulator

Flow diagram for rotary module

Accumulator

7N

P r e s s u r e Gage

Module

V V

Tank

Dump valve

EH

> d

w

w >

3 w

H w H

4^

to o

12.

MANJIKIAN

AND WOJCIK

Tubular Membrane Elements

205

The r o t a r y concept makes p o s s i b l e the design of modular assemblies which would t r u l y permit the i n s i t u c l e a n i n g of membranes during operation by simply changing the d i r e c t i o n and r a t e of r o t a t i o n s . Areas of A p p l i c a t i o n R.O. systems u t i l i z i n g e x t e r n a l l y wound t u b u l a r membrane e l e ment i n modular assemblies have been used i n the d e s a l i n a t i o n of b r a c k i s h and sea waters, the treatment and/or concentration of i n d u s t r i a l waste waters, the separation/concentration of f l u i d food, pharmaceuticals and chemical s o l u t i o n s , and the manufacture of water p u r i f i e r s f o r domestic use. G e n e r a l l y , e x t e r n a l l y wound t u b u l a r membrane systems have been found t o be h i g h l y s u i t a b l e f o r u l t r a f i l t r a t i o n a p p l i c a t i o n s i n the processing i n d u s t r y and i n water p o l l u t i o n c o n t r o More s p e c i f i c a l l y conventional mode o r as r o t a r y u n i t s have been s u c c e s s f u l l y u t i l i z e d i n a p p l i c a t i o n s such as the recovery of p r o t e i n and l a c tose from cheese whey^ separation of fermentation products, conc e n t r a t i o n of f l u i d s foods and j u i c e s , manually operable sea water d e s a l i n a t o r s , recovery of s t a r c h from potato processing f l u i d s , and processing/separation of pharmaceutical and chemical mixtures. RECEIVED

December 4, 1980.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

13 Membrane Development, Production, and Use in Hyperfiltration Systems W. KOFOD NIELSEN

A/S De Danske Sukkerfabrikker, Driftteknisk Laboratorium, 4900 Nakskov, Denmark

At an anniversary like this, it is usual to look back through the p e r i o d i n q u e s t i o n The great discover to consider reverse osmosis as an industrial process. The core of membrane filtration i s the membrane, but the core in itself must be surrounded o r supported, and t h i s leads to the system o r module in which the membrane is mounted. During these 20 years, a l a r g e number of module systems has been made. The first idea was t o use the conventional filter press, the plate-and-frame system, as done by A e r o j e t General Corp. However, t h i s system never proved to be very s u c c e s s f u l in the U.S.A., and consequently new c o n f i g u r a t i o n s , such as tubes, hollow f i b e r s , and spiral-wound systems were invented. The red thread through the whole p e r i o d was d e s a l i n a t i o n of sea and b r a c k i s h water, and grants sponsored by the O f f i c e of S a l i n e Water d i r e c t e d the development i n t o t h i s field. In Europe, and e s p e c i a l l y by our company, The Danish Sugar Corporation, DDS, in Denmark, we attacked the problem i n a different way. P r i m a r i l y , we saw a great number of advantages in the plate-and-frame system, and by s o l v i n g some of the problems, such as s e a l i n g s , manufacturing of p l a t e s and frames by injection mouldi n g , e t c . , in 1970 we came up w i t h a system which a t that time we considered to be a competitive product. At that time, we saw the most a c c e s s i b l e market i n the pharmac e u t i c a l and food and d a i r y i n d u s t r i e s , because w i t h i n these industries membrane filtration was so advantageous that the relatively high investment and operating costs were no impediment. L a t e r , our system proved to work s u c c e s s f u l l y a l s o f o r d e s a l i n a t i o n of water, but the development through the pharmaceutical to the food and d a i r y i n d u s t r i e s and pulp and paper i n d u s t r y d i d give a great deal of experience which has been extremely v a l u a b l e f o r our design of water d e s a l i n a t i o n p l a n t s as constructed today.

0097-6156/81/0154-0207$05.00/ 0 © 1981 American Chemical Society

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

SYNTHETIC

208

MEMBRANES:

HF

AND

UF

USES

The Plate-and-Frame Membrane-Filtration System The DDS plate-and-frame system and the p r i n c i p l e of i t are shown i n Figures 1, 2, and 3. I s h a l l not go i n t o d e t a i l s on the p r i n c i p l e , as i t has been published a t s e v e r a l occasions (1, 2 ) , but some c o n s i d e r a t i o n ought t o be given to the reasons why t h i s system has proved to be s u c c e s s f u l w i t h i n such a wide range of a p p l i c a t i o n s , and below we s t a t e some f a c t o r s which i n our o p i n i o n p l a y an important r o l e i n this respect. The System (1) I n j e c t i o n moulding of support and spacer p l a t e s makes a low-cost, l a r g e - s c a l e p r o d u c t i o n method p o s s i b l e . (2) The s p e c i a l l y developed s e a l i n g system i n our p l a s t i c p l a t e s , where the very membran i d l betwee tw p l a t e s , gives a system no 0 - r i n g s e a l i n g s are necessary (3) The flow-channel design can b« optimized, dead spots avoided, and the dead volume minimized. (4) Very high f l e x i b i l i t y i n s e r i e s and p a r a l l e l arrangements w i t h i n one module. (5) Flow v e l o c i t y and f l o w d i s t r i b u t i o n a r e e a s i l y c o n t r o l l e d . (6) The permeate s i d e i s l i q u i d - f i l l e d and kept a t a low i n t e r n a l volume, and there i s flow i n a l l p a r t s of the permeate system, s e c u r i n g safe b a c t e r i o l o g i c a l c o n d i t i o n s . (7) Each membrane p a i r i s e a s i l y i n s p e c t e d , s e c u r i n g productq u a l i t y c o n t r o l , and i n case of membrane r u p t u r e , the membrane can be detected and e a s i l y exchanged. The Membrane (1) Any membrane cast i n sheet form of s u f f i c i e n t dimensions can be mounted i n t o the system. (2) The d i s t a n c e between membrane development and membrane p r o d u c t i o n , u t i l i z a t i o n , and a p p l i c a t i o n i s the s m a l l e s t p o s s i b l e . (3) During p r o d u c t i o n , a very e f f e c t i v e q u a l i t y c o n t r o l i s p o s s i b l e , s i n c e each piece of membrane i s i n s p e c t e d , and membranes w i t h f a u l t s are discharged. I t h i n k , these t e n f a c t o r s e x p l a i n some of the obvious advantages obtained by a plate-and-frame system. However, I would l i k e to add that without the great work c a r r i e d out by Dr. R.F. Madsen i n our company who s t a r t e d a research programme w i t h i n t h i s f i e l d some 15 years ago, there would be no DDS plate-and-frame system today ( 3 ) . Review of Membrane Development The development of reverse-osmosis membranes began w i t h i n v e s t i g a t i o n s made by Reid and Breton (4) i n 1959 on dense f i l m s of

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

13.

NIELSEN

Membrane Development in HF

209

Internal Flow, UF

Concentrate

Internal Flow, HF

Concentrate 4

^1^^!^$^^$^$^

Permeate

232

SYNTHETIC MEMBRANES:

HF

AND UF

USES

Figure 8. A typical RO system with a clean-in-place (CIP) unit adjacent to the RO. The CIP unit is plumbed into the RO unit so that the operator can CIP the RO system by simply changing three valves and making certain that the cleaning chemicals are used.

Figure 9. A bag filter system used for pretreatment prior to an oily waste application. We are using 5-fi-rated bags which we feel are approximately equal to 15-fx cartridge filters. Bags are valuable because the waste that is collected can be thrown away.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

SPATZ

Waste Treatment Using RO

233

Figure 10. The actual operating installation of a system that uses both spiralwound UF and spiral-wound RO to handle oily waste which also is contaminated with phosphates

Figure 11. A beaker containing the concentrate from an RO unit on oily waste and a second beaker showing the permeate from oily waste processing. Normally the oily wastes can be concentrated until the oil "breaks" due to concentration and separate phases are apparent to the naked eye.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

234

SYNTHETIC

2.

3.

4.

5.

MEMBRANES:

HF

AND

UF

USES

The n e x t method o f p r e t r e a t m e n t w h i c h was t r i e d was ultrafiltration. P i l o t s i z e UF u n i t s u s i n g t h e h o l l o w f i b e r b o r e f l o w t y p e c a r t r i d g e and t h e 1" t u b e module w e r e t e s t e d . As w o u l d be e x p e c t e d , t h e permeate from the UF u n i t was q u i t e c l e a r and when used as f e e d f o r the RO, a b s o l u t e l y no f o u l i n g was a p p a r e n t . However, t h e UF f o u l e d a t about t h e same r a t e as t h e RO had f o u l e d . The UF c o u l d be c l e a n e d j u s t as t h e RO c o u l d be c l e a n e d . The Cummins e n g i n e e r s d e c i d e d t h a t UF as a p r e t r e a t m e n t t o RO i n t h i s c a s e was n o t e c o n o m i c a l b e c a u s e o f e x c e s s i v e c a p i t a l and o p e r a t i n g c o s t s and s h o u l d n o t be p u r s u e d . As an a s i d e , Osmonics does have some i n s t a l l a t i o n s where UF p r i o r t o RO i s a v i a b l e p r e t r e a t m e n t and can be e c o n o m i c a l l y j u s t i f i e d . I t j u s t d i d not f i t this application A new p r o c e s s c a l l e uses a c o n v e n t i o n a g and t h e n t h e a d d i t i o n o f e l e c t r i c i t y t o a i d i n f o r m i n g a f l o e o f t h e suspended o r emulsed o i l s . On-site p i l o t d a t a c o u l d n o t be c o l l e c t e d w i t h i n a r e a s o n a b l e t i m e and Cummins d e c i d e d n o t t o p u r s u e t h e e c l e c t i c s y s t e m . C h e m i c a l t r e a t m e n t and s e t t l i n g i s t h e most commonly used method o f t r e a t i n g w a s t e w a t e r . Alum and p o l y m e r f l o c c u l a t i n g a g e n t s were used and were f o u n d t o be s u c c e s s f u l i n p r e t r e a t i n g the waste water p r i o r t o the RO u n i t . One o f t h e b i g a d v a n t a g e s o f a c h e m i c a l s y s t e m i s t h a t i t can be t a i l o r e d on a d a i l y b a s i s t o meet changing requirements. The o p e r a t o r can c o n s i d e r t h e d i f f e r i n g w a t e r coming t o t h e w a s t e t r e a t m e n t p l a n t . However, t h e p r o c e s s i s o p e r a t o r i n t e n s i v e . Cummins has n o t t o t a l l y d e c i d e d t o go w i t h c h e m i c a l treatment s i n c e the cost o f d i s p o s i n g o f the sludge c o u l d be e x c e s s i v e . A f a i r l y new t e c h n o l o g y w h i c h many p e o p l e i n t h e w a s t e treatment o f o i l s f i r m l y b e l i e v e i n i s d i s s o l v e d a i r f l o t a t i o n (DAF). DAF was o r i g i n a l l y t r i e d a t Cummins but e i t h e r t h e o i l a t Cummins was t o o s o l u b l e o r t h e c o n c e n t r a t i o n was t o o low t o h o l d t o g e t h e r t h e f l o e f o r a l o n g enough p e r i o d t o have r e a s o n a b l e f l o t a t i o n . After the f i r s t r e v i e w , t h e a i r f l o t a t i o n p r o c e s s was c o n s i d ered not a p p r o p r i a t e . S u b s e q u e n t t o t h e g e n e r a l t e s t i n g and c o n t i n u e d o p e r a t i o n o f t h e s y s t e m as o r i g i n a l l y i n s t a l l e d , Cummins d i d a d d i t i o n a l t e s t i n g w i t h DAF. They f o u n d t h a t t h e DAF w o r k e d f i n e i f t h e o i l c o n c e n t r a t i o n i n t h e w a s t e s o l u t i o n was s u f f i c i e n t l y h i g h . A f t e r a program o f w a t e r c o n s e r v a t i o n gave a r e d u c e d t o t a l e f f l u e n t f l o w and an i n c r e a s e d o i l c o n c e n t r a t i o n , a d d i t i o n a l t e s t s w e r e run w i t h DAF. A g a i n , alum and p o l y m e r w e r e added. A t

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

14.

SPATZ

Waste Treatment Using RO

235

t h i s s t a g e t h e DAF p r o v e d t o be a r e a s o n a b l e and a t t r a c t i n g method o f removing a good s h a r e o f t h e h e a v i e r o i l s and o t h e r c o n t a m i n a n t s w h i c h w e r e p r o b a b l y f o u l i n g t h e RO u n i t . At t h e p r e s e n t t i m e , Cummins has d e c i d e d t o i n s t a l l a p r e t r e a t m e n t s y s t e m u s i n g d i s s o l v e d a i r f l o t a t i o n as t h e p r i m a r y t r e a t m e n t f o l l o w e d by an a n t h r a c i t e / s a n d b a c k w a s h a b l e f i l t e r and an a c t i v a t e d c a r b o n p o l i s h i n g f i l t e r . The e f f l u e n t from t h e f i l t e r s t h e n goes t o t h e RO u n i t . The RO w i l l remove t h e l a s t t r a c e s o f the most s o l u b l e o i l s and o r g a n i c s . I t i s Cummins' i n t e n t i o n t o have t h e e f f l u e n t f r o m t h e f i l t e r s a t a t u r b i d i t y o f l e s s t h a n kS JTU's. T h i s s h o u l d keep t h e RO u n i t s f r o m f o u l i n g and w i l l a l l o w t h e RO t o be used w i t h m i n i m a l c l e a n i n g . L i k e a l l u n i t c h e m i c a l p r o c e s s e s , t h e RO i s u s u a l l y n o t c a p a b l e o f s t a n d i n g e n t i r e l y by i t s e l f . The i m p o r t a n t t h i n g t o remember i s t h a t a s y s t e product. In t h e c a s e o dissolved a i r f l o t a t i o n , anthracite/sand f i l t r a t i o n , activated c a r b o n f i l t r a t i o n and RO. In t h e c a s e o f W h i t e s t o n e C h e m i c a l , t h e c o m p l e t e s y s t e m i n c l u d e s RO and a c l e a n i n g regimen t o m a i n t a i n the RO a t t h e r e q u i r e d p e r m e a t e f l o w r a t e . Time w i l l t e l l w h i c h of t h e s e a l t e r n a t i v e s has t h e b e s t e c o n o m i c s . The e c o n o m i c s and the p r o p e r s y s t e m u s i n g RO a r e b o t h dependent on t h e p r o b l e m t h a t requires a solution. Cone 1 us i o n In

c o n c l u s i o n , I w o u l d l i k e t o l e a v e you w i t h two t h o u g h t s : F i r s t , I am o f t e n a s k e d by i n v e s t m e n t b a n k e r s and t h o s e who f o l l o w o u r t e c h n o l o g y , why t h i s t e c h n o l o g y has n o t grown as f a s t as e v e r y o n e s a i d i t w o u l d . A t f i r s t my i n c l i n a t i o n was somewhat d e f e n s i v e , but t h e n I d i d some r e s e a r c h i n t o t h e g r o w t h o f o t h e r new t e c h n o l o g i e s . I looked a t : - S e m i c o n d u c t o r s w h i c h were i n v e n t e d a t t h e t u r n o f t h e c e n t u r y and have o n l y seen g r o w t h i n t h e l a s t decade. - C o l o r e d t e l e v i s i o n w h i c h was a r o u n d i n 1925 but n e v e r became a v i a b l e p r o d u c t u n t i l I 9 6 0 — 3 5 y e a r s l a t e r . - N u c l e a r r e a c t i o n s , w o u l d we say 1933 f o r t h e i n v e n t i o n ? Is t h e b u s i n e s s r e a l l y t h a t b i g even now? My f e l l o w membrane t e c h n o l o g i s t s , d o n o t become d e f e n s i v e when someone a s k s t h e g r o w t h q u e s t i o n , i n s t e a d a s k them t o t e l l y o u one o t h e r t e c h n o l o g y w h i c h 10 y e a r s a f t e r i t s i n v e n t i o n had more t h a n 10 a c t i v e companies s e l l i n g p r o d u c t s u s i n g t h i s t e c h n o l o g y and now o n l y 2 0 y e a r s l a t e r has p r o b a b l y 3 0 a c t i v e m a n u f a c t u r i n g companies and as many more who are r e s e a r c h i n g t h e p o s s i b i l i t y o f e n t e r i n g t h e f i e l d . S e c o n d l y , I want t o remind a l l o f y o u t h a t t h e o n l y t r u e t e s t o f t h e w o r t h o f any r e s e a r c h i s t h e u l t i m a t e e f f e c t o f t h a t r e s e a r c h on s o c i e t y i n g e n e r a l and i n t h e m a r k e t p l a c e i n particular. Twenty y e a r s a f t e r t h e b e g i n n i n g o f r e v e r s e

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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SYNTHETIC

MEMBRANES:

HF

AND

UF

USES

o s m o s i s and u l t r a f i l t r a t i o n , t h e m a r k e t p l a c e has p r o c l a i m e d t h a t t h i s membrane t e c h n o l o g y i s a s u c c e s s . We a l l l o o k forward t o t h e next twenty y e a r s which w i l l see t h i s t e c h n o l o g y emerge as one o f t h e g r e a t e s t b a s i c i n v e n t i o n s o f the 20th Century. Acknow1edgemen t s I w i s h t o e x t e n d my d e e p e s t a p p r e c i a t i o n t o Dr. S. S o u r i r a j a n who f o r o v e r 16 y e a r s has h e l p e d me t o g a i n a b e t t e r u n d e r s t a n d i n g o f t h i s u n i q u e f i e l d o f r e v e r s e o s m o s i s and u l t r a f i l t r a t i o n and t o t h e f o l l o w i n g f o u r i n d i v i d u a l s whose p e r s o n a l a t t e n t i o n t o my r e q u e s t s f o r i n f o r m a t i o n on t h e c a s e s t u d i e s h e l p e d me i n p r e p a r i n g this talk. B e a l , Thomas W., O p e r a t i o n BASF W y a n d o t t e C o r p . , S p a r t a n b u r g F r a n k l i n , P a t r i c i a V., P.E., Cummins C h a r l e s t o n , I n c . , C h a r l e s t o n , SC K a r a s i e w i c z , W. R i c h a r d , P.E., M c N a i r , G o r d o n , J o h n s o n and K a r a s i e w i c z Company, C o l u m b i a , SC Davis, W i l l i a m , Sepratech RECEIVED

I n c . , Rock H i l l ,

SC

February 18, 1981.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

15 A Novel Membrane System for the Ultrafiltration of Oil Emulsions G. B. TANNY and A. KORIN Gelman Sciences, Inc., 600 S. Wagner Rd., Ann Arbor, MI 48106

The c o n c e n t r a t i o n importance, encompassin c o o l i n g or c u t t i n g f l u i d s ( 1 ) , the p r o c e s s i n g o f foods, and c e r t a i n pharmaceutical p r e p a r a t i o n s . When one takes i n t o cons i d e r a t i o n the increased use o f microemulsions(2), f u r t h e r growth in this area may be a n t i c i p a t e d . Ultrafiltration has q u i c k l y become the method o f choice f o r c a r r y i n g out t h i s pro­ cess (1), and in the past a r e p o r t has been made on the use o f a new c o n v e n t i o n a l thin-film composite UF membrane(3) t o accomplish t h i s g o a l . The present c o n t r i b u t i o n d e s c r i b e s a novel low pressure, high f l u x system which utilizes an "in situ" dynamically formed silica membrane particularly s u i t e d f o r the ultrafiltration of emulsions. The support f o r this s e l e c t i v e l a y e r o f silica was a p l e a t e d , t h i n channel c r o s s f l o w module(4) (tradename "Acroflux", Gelman Sciences, Inc.) c o n t a i n i n g 0.1 m o f 0.2 um pore size acrylonitrile copolymer membrane. This design c o n f i g u r a t i o n f o r flat sheet microporous membrane is relatively new and t h e r e f o r e bears d e s c r i p t i o n . Through the p l e a t i n g process one creates a p l e a t pack o f flow channels c o n s i s t i n g o f : (1) a cover channel m a t e r i a l ; ( 2 ) a t u r b u l e n t flow promoting spacer; and ( 3 ) the microporous membrane support. A cross s e c t i o n o f one o f these p l e a t e d channels is shown in Figure 1 a . The p l e a t pack is then arranged about a c e n t r a l d r a i n tube, glue seamed down the l o n g i t u d i n a l a x i s , and a s e a l r i n g is added t o prevent fluid bypass. A schematic o f the c a r t r i d g e in i t s housing is shown i n F i g u r e 1 b . Since the cover channel m a t e r i a l does not extend i n t o the glue s e a l s a t each end of the c a r t r i d g e , and is somewhat f r e e t o move, i t facilitates backwashing and is thus e s p e c i a l l y s u i t e d t o the membrane regene r a t i o n aspect o f dynamically formed membrane a p p l i c a t i o n s . In the s e c t i o n s which f o l l o w , we shall examine (a) the hydrodynamics o f this new module, (b) the formation and p r o p e r t i e s 2

0097-6156/81/0154-0237$05.50/0 © 1981 American Chemical Society

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

238

SYNTHETIC

Figure lb.

MEMBRANES:

HF

AND

UF

Schematic of an Aeroflux cartridge in a housing

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

USES

15.

TANNY

AND

KORIN

239

UF of Oil Emulsions

of the s i l i c a dynamic membrane, and (c) i t s performance i n the module w i t h o i l / w a t e r emulsions under v a r i o u s c o n d i t i o n s . A.

Theory: Operation and Hydrodynamic A n a l y s i s o f the A e r o f l u x Module. The schematic cross s e c t i o n o f a s i n g l e p l e a t e d channel o f a u n i t mounted i n i t s housing i s shown i n F i g u r e 2. I n the case under c o n s i d e r a t i o n , the f l e x i b l e channel cover w a l l m a t e r i a l i s impermeable to flow and a l l the space between i t and the w a l l o f the housing becomes p r e s s u r i z e d to Pp, the feed entrance pressure. Thus, at any p o i n t w i t h i n the l e n g t h o f the channel, a pressure drop, Pp-P(x), e x i s t s both along the channel and across the channel cover w a l l . T h i s pressure drop helps to seat the channel cover w a l l on the spacer and maintain channel dimensions. (On the other hand, during the b a c k f l u s h o p e r a t i o n , the channel cover w a l l i s somewhat f r e e to move away from the spacer to f a c i l i t a t Let us conside ment dx along the channel. Assuming u n i t a r y w i d t h , the change i n the flow r a t e , dQ, i s given by:

-dQ =

P(x) - P ^ m

(1)

dx

The change i n pressure down the channel element dx i s given by the equation (JL): -dP = aQ

n

over

the same

(2)

dx

where "a" i s the constant r e f l e c t i n g the f r i c t i o n and height of the spacer ( i d e n t i c a l to that o f the channel) and "n" i s a constant, w i t h the values n = 1, f o r laminar flow, and n = 2 , f o r t u r b u l e n t flow. Combining equations ( 1 ) and ( 2 ) y i e l d s : dQ

_ J

=

dP

aR

L_

m

n

(

3 )

K D J

n Q

Rearranging and i n t e g r a t i n g t o the a p p r o p r i a t e boundary c o n d i t i o n s , one o b t a i n s : ( n Q

d Q

=

_ L

/

( _ P

P p

)

d

P

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

(4)

SYNTHETIC

MEMBRANES:

HF

AND

UF

USES

This equation can now be used to o b t a i n the f o l l o w i n g r e l a t i o n s h i p s between the e x p e r i m e n t a l l y r e l e v a n t f a c t o r s , A p^, the t o t a l trans-channel pressure drop, A P , the average opQ e r a t i n g pressure ,Q, the permeation r a t e , and X = — : (see Appendix No. 1 ) . P 1. For the t u r b u l e n t flow c o n d i t i o n : R

,1/2

A

3/2

-(f)

Y Q

( 5 )

p

where Z = 1/3 [ ( 1 + X )

Y

= 1-

3

(6)

3

-X ]

-=

(8)

2AP APm

and

= R 0 m P

(9)

p

m

These r e l a t i o n s can be used t o generate the d i a gram i n F i g u r e 3 , which d e f i n e s the a n t i c i p a t e d range o f pressure drop and average pressure necessary t o achieve any d e s i r e d permeation r a t e a t some d e s i r e d r a t i o o f r e t e n t a t e to permeation flow r a t e . For laminar flow c o n d i t i o n s

2.

/ s \ A P

where

C

=

(2k)

1 / 2

1/2 < Y


e x

pF

k

P ( / P>

(3)

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

SYNTHETIC

298

ref

AB

AB,ref

MEMBRANES:

HF

AND

UF

USES

(4)

The nomenclature i s d e f i n e d i n the Legend of Symbols s e c t i o n a t the c o n c l u s i o n of t h i s paper and i s i l l u s t r a t e d i n F i g u r e 1. Equation 1 i s an e m p i r i c a l r e l a t i o n which d e s c r i b e s the extent of pore b l o c k i n g , expressed by the pore b l o c k i n g f a c t o r 1-(PF/PWF). In the case of the RO s e p a r a t i o n of a d i l u t e s o l u t e - c o n t a i n i n g feed stream i n which there i s no pore b l o c k i n g by the s o l u t e , the f l u x of the permeating stream i s equal to the f l u x obtained f o r a s i m i l a r experiment i n which the feed stream i s pure water ( i . e . , permeate f l u x (PF) equals pure water f l u x (PWF)). In t h i s case, the f l u x r a t i o PF/PWF i s u n i t y and the pore b l o c k i n g f a c t o r 1-(PF/PWF) i s zero. Conversely, when the pores are completely blocked PF i s zero, and thus, the pore b l o c k i n g f a c t o r i s u n i t y . Equation 1 i n d i c a t e s t h a t the pore b l o c k i n f a c t o i p r o p o r t i o n a l t th c o n c e n t r a t i o n of the boundar This r e l a t i o n s h i p w i l l b Equatio e m p i r i c a l r e l a t i o n which r e l a t e s s o l u t e f l u x (NA) to both X^2 (again r a i s e d to a power of n j ) and the o p e r a t i n g pressure ( r a i s e d to a power of n2). The exponents rii and n2,as w e l l as the proportionality factors and K 2 , are f u n c t i o n s of pore s i z e and the nature of the s o l u t e . Equation 3, which a l l o w s the c a l c u l a t i o n of X ^ from experimental data, i s based on a simple " f i l m " theory f o r mass t r a n s f e r and i s d e r i v e d elsewhere (17,23). Equation 4 a l l o w s the mass t r a n s f e r c o e f f i c i e n t on the feed s i d e , k, to be c a l c u l a t e d f o r any s o l u t e based on the value obtained f o r a r e f e r e n c e s o l u t e ( u s u a l l y sodium c h l o r i d e ) i n the same t e s t c e l l . The p o s s i b i l i t y of u s i n g equations of t h i s form f o r aromatic hydrocarbon s o l u t i o n s w i l l be examined i n t h i s paper. Experimental The c e l l u l o s e a c e t a t e membranes used were batch 316(0/25) type membranes (24) made by the general Loeb-Sourirajan technique (25). The s i x f l a t c a s t membranes were shrunk at d i f f e r e n t temperatures (from 68 to 85°C) p r i o r to l o a d i n g the membranes i n t o the r e v e r s e osmosis t e s t c e l l s . This treatment a d j u s t s the average surface pore s i z e of each membrane so t h a t a range of p o r o s i t i e s could be s t u d i e d . A p r e p r e s s u r i z a t i o n at a pressure of 11 720 kPa f o r 2 hours was used to s t a b i l i z e the membranes f o r subsequent use a t pressures of 6900 kPa or lower. ( A l l pressures l i s t e d are gauge pressure.) The general experimental procedure was s i m i l a r to that r e p o r t e d i n the l i t e r a t u r e (25). The s i x flow type reverse osmosis c e l l s were connected i n s e r i e s and were c o n s t r u c t e d i n a design s i m i l a r to that r e p o r t e d by S o u r i r a j a n (25). The c e l l s were placed i n a constant temperature box and the system was c o n t r o l l e d to 25 ± 1°C. The feed f l o w r a t e was maintained constant at 400

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

18.

DICKSON

A N D LLOYD

Solute Preferential Sorption

299

ml/min. For each experiment, the pure water f l u x (PWF) and the permeate f l u x (PF) were measured. I n a d d i t i o n , the s o l u t e c o n c e n t r a t i o n was determined i n the feed and permeate s o l u t i o n s and the s e p a r a t i o n , f , was c a l c u l a t e d as m

f =T " 3 (5) l where m^ and 1113 are the feed and permeate m o l a l i t i e s r e s p e c t i v e l y . For d i l u t e s o l u t i o n s t h i s can be approximated as m

m

^ _ ppml - ppm3 ppml

(6)

where ppml and ppm3 are the feed and permeate c o n c e n t r a t i o n s expressed i n p a r t s per m i l l i o n . The s o l u t e c o n c e n t r a t i o n s f o r benzene and toluene samples were analyzed u s i n g an Oceanography I n t e r n a t i o n a l C o r p o r a t i o n T o t a l Carbon A n a l y z e r The sodium c h l o r i d e s o l u t i o n s wer C o n t r o l D i f f e r e n t i a l Refractomete y Meter. The water used was d e i o n i z e d and d i s t i l l e d and a l l other chemicals were a n a l y t i c a l reagent grade. R e s u l t s and D i s c u s s i o n s Membrane C h a r a c t e r i z a t i o n . The s i x c e l l u l o s e a c e t a t e membranes were c h a r a c t e r i z e d according t o the sodium c h l o r i d e performance data. These data are presented i n Table I . A c t u a l experiments were repeated a t r e g u l a r i n t e r v a l s i n order t o monitor the membrane change^and the i l l u s t r a t e d data represent the average of nine t e s t s . Since the s o l u t e t r a n s p o r t parameter D^M/KS f o r sodium c h l o r i d e , and hence l n C*N Cl> remained e s s e n t i a l l y constant over the experimental time p e r i o d i t can be assumed that the membrane pore s i z e remained constant. The q u a n t i t y l n C* -^ i s r e p r e s e n t a t i v e of the average pore s i z e on the membrane s u r f a c e and i s independent of the s o l u t e under c o n s i d e r a t i o n (26). B r i e f l y , a decrease i n the v a l u e o f l n C*NaCl i n d i c a t e s a decrease i n the average pore s i z e . The v a l u e s of l n C * N c i f o r the membranes t e s t e d cover a wide range of s u r f a c e pore s i z e , thereby maximizing experimental design. The pure water p e r m e a b i l i t y constant A tended t o decrease over the p e r i o d of s e v e r a l experiments; t h i s decrease was a t t r i b u t e d to membrane compaction. This change i n A v a r i e d from a 10% decrease f o r the membranes of l a r g e s t pore s i z e t o a 5% decrease f o r the membranes of s m a l l e s t pore s i z e . The r a t e o f compaction f o r these hydrocarbon s t u d i e s was s l i g h t l y h i g h e r than would normally be observed f o r s a l t s o l u t i o n experiments. This a c c e l e r a t e d decrease i n A may be the r e s u l t of the d e t r i m e n t a l e f f e c t that h i g h i n t e r f a c i a l c o n c e n t r a t i o n of organics have on the c e l l u l o s e a c e t a t e . The average s e p a r a t i o n and the permeate f l u x f o r aqueous NaCl s o l u t i o n s measured under the i n d i c a t e d c o n d i t i o n s are a l s o l i s t e d i n Table I . a

NaC

a

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

2

?

k,

1.342 -12.59

0.6914 -13.25

3

2

— ^ — , 2 m s

xlO

3

13.27

97.0

61.7 25.80

82.8 24.41

93.5 19.38

-8.69

66.15

2.487

6

29.3

-9.49

29.69

2.331

5

47.0

44.0

-10.73

-11.84

38.5

8.653

1.868

4

2.846

1.268

3

a) F i l m area, 1.443 x l O m ; o p e r a t i n g pressure 6900 kPa; feed c o n c e n t r a t i o n 10 000 ppm NaCl; temperature 25°C; feed f l o w r a t e 400 ml/min.

Permeate f l u x ,

9.05

0

7.43

l

98.1

X

98.8

>

Solute Separation, %

m / s

0.8547

38.2

6

>NaCl>

*NaCl

/K6

0.7051

28.3

C

AM

4

2

Mass t r a n s f e r c o e f f i c i e n t , m/s, x l O

l n

(D

S o l u t e t r a n s p o r t parameter,

2

Pure water p e r m e a b i l i t y constant, A, (mol H 0)/(m s k P a ) , x l O

1

a

F i l m Number

C h a r a c t e r i z a t i o n and Performance of the C e l l u l o s e Acetate Membranes

TABLE I

18.

DICKSON

AND LLOYD

Solute Preferential Sorption

301

Benzene - Water Reverse Osmosis Data. The e x p e r i m e n t a l l y determined performance f o r the s e p a r a t i o n of benzene and water a t four d i f f e r e n t pressures i s i l l u s t r a t e d i n Figures 2 through 5. The s e p a r a t i o n and pore b l o c k i n g f a c t o r observed f o r s e v e r a l d i f f e r e n t feed concentrations are p l o t t e d as a f u n c t i o n of the membrane pore s i z e , l n C * N c i . Although there i s s c a t t e r i n the data, i t i s p o s s i b l e t o observe trends that apply c o n s i s t e n t l y i n Figures 2 through 5. As the pore s i z e decreases the s e p a r a t i o n i n c r e a s e s . As the feed c o n c e n t r a t i o n i n c r e a s e s , the s e p a r a t i o n i n c r e a s e s . The extent of t h i s c o n c e n t r a t i o n e f f e c t i s s m a l l f o r the membranes of l a r g e pore s i z e , and increases w i t h decreasing pore s i z e u n t i l the greatest i n f l u e n c e i s observed f o r the membrane of s m a l l e s t pore s i z e . I n a l l cases, the extent of pore b l o c k i n g increases l i n e a r l y w i t h decreasing pore s i z e . I n a d d i t i o n , i n c r e a s i n g the feed c o n c e n t r a t i o n increases the extent of pore blocking. The e f f e c t of s o l u t i l l u s t r a t e d by e x t r a c t i n g the data f o r any given membrane from the curves i n Figures 2 through 5, and r e p l o t t i n g the data i n the form of s e p a r a t i o n as a f u n c t i o n of s o l u t e c o n c e n t r a t i o n i n the feed stream. T y p i c a l r e s u l t s are shown i n Figure 6. This r e l a t i o n s h i p c l e a r l y i l l u s t r a t e s that s e p a r a t i o n increases w i t h i n c r e a s i n g c o n c e n t r a t i o n , e v e n t u a l l y l e v e l i n g o f f a t a constant v a l u e . This p l o t a l s o a l l o w s the comparison of s e p a r a t i o n a t d i f f e r e n t pressures. For the range of pressures 690 to 3450 kPa, the s e p a r a t i o n increases w i t h decreasing pressure, which i s c o n s i s t e n t w i t h the general behavior of p r e f e r e n t i a l l y sorbed s o l u t e systems as discussed above and w i t h the data p r e v i o u s l y obtained (1). However, the data f o r 6900 kPa does not f o l l o w t h i s trend and i n d i c a t e s that s e p a r a t i o n passes through a minimum w i t h i n c r e a s i n g pressure. This behavior w i l l be i n v e s t i g a t e d i n more d e t a i l i n the f u t u r e . The trends i n Figures 2 to 6 a r e c o n s i s t e n t w i t h the q u a l i t a t i v e f e a t u r e s of s o l u t e p r e f e r e n t i a l s o r p t i o n discussed e a r l i e r i n t h i s paper. The permeate f l u x i s lower than the pure water f l u x due to pore b l o c k i n g . This e f f e c t i s enhanced by e i t h e r decreasing the pore s i z e or i n c r e a s i n g the feed c o n c e n t r a t i o n . Both of these f a c t o r s l e a d to a r e l a t i v e increase i n the s o l u t e content of the pore and thus, to r e s t r i c t e d water t r a n s p o r t through the pore. Since the s o l u t e i s r e l a t i v e l y immobile a t the membrane s u r f a c e , p o s i t i v e s e p a r a t i o n i s observed. Both i n c r e a s i n g the feed c o n c e n t r a t i o n and decreasing the pore s i z e l e a d to higher s e p a r a t i o n . The a d d i t i o n a l s o l u t e r e t a i n e d on the h i g h pressure s i d e must a l s o be r e l a t i v e l y immobile. I t i s hypothesized that benzene can be sorbed i n m u l t i p l e l a y e r s which are bound to the membrane. The l a y e r s i n the immediate v i c i n i t y of the membrane m a t e r i a l / p o r e w a l l are s t r o n g l y bound to the membrane. The s t r e n g t h of the a t t r a c t i o n f o r c e decreases as the d i s t a n c e between each subsequent l a y e r and the membrane surface i n c r e a s e s . a

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

302

SYNTHETIC

MEMBRANES:

HF

AND

UF

USES

BULK FEED SOLUTION UNDER "OPERATING GAUGE PRESSURE P -CONCENTRATED

^A2

BOUNDARY

-PREFERENTIALLY -DENSE

SOLUTION

SORBED INTERFACIAL

LESS DENSE MICROPOROUS "MEMBRANE LAYER -SPONGY

POROUS

TRANSITION

MEMBRANE

P R O D U C T S O L U T I O N AT ATMOSPHERIC PRESSURE

^A3

Figure 1.

FLUID

MICROPOROUS MEMBRANE SURFACE

Schematic of RO transport under steady-state conditions (16)

0.4 —

J

I

I

I

I

-13

-12

I -II

l n

C

-L

I

-10

L_

-9

NaCI

Figure 2. Effect of feed concentration on the RO performance for the benzenewater system. Operating conditions: membrane material = CA; membrane area = 1.443 X IO' m , In C* obtained at 6900 kPa; feedflowrate = 400 mL/min; T = 25°C; operating pressure = 690 kPa. Curve a (O) 20.6 ppm; Curve b (%) 31.7 ppm; Curve c O 54.0 ppm; Curve d (^) 96.0 ppm. 3

2

Nam

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

DICKSON

AND

LLOYD

Solute Preferential Sorption

303

Figure 3. Effect of feed concentration on the RO performance for the benzenewater system. The operating conditions are identical to those of Figure 2 except that the operating pressure = 1725 kPa. Curve a (O) 18.0 ppm; Curve b (%) 29.8 ppm; Curve c O 49.0 ppm; Curve d (U) 98.8 ppm.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

304

SYNTHETIC

MEMBRANES:

HF

AND

UF

USES

Figure 4. Effect of feed concentration on the RO performance for the benzenewater system. The operating conditions are identical to those of Figure 2 except that the operating pressure = 3450 kPa. Curve a (O) 20.9 ppm; Curve b (%) 31.0 ppm; Curve c (Q) 44.8 ppm; Curve d (^) 54.5 ppm; Curve e (A) 92.6 ppm.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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Solute Preferential Sorption

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305

306

SYNTHETIC

80

MEMBRANES: HF

AND

UF

USES

-

0

20

40

60

80

FEED CONCENTRATION (ppm BENZENE)

Figure 6. Effect of feed concentration and operating pressure on separation for the benzene-water system. Data illustrated for the CA membrane with In C* i = -13.25. Curve a (O) 690 kPa; Curve b (%) 1725 kPa; Curve c O 3450 kPa; Curve d ( | ) 6900 kPa. NaC

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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The r e s u l t s observed f o r the benzene-water system can be compared to those observed f o r the p-chlorophenol-water system. I n the l a t t e r case, higher feed concentrations and s m a l l e r pore s i z e l e a d to lower s e p a r a t i o n ( 2 3 ) . As discussed e a r l i e r i n t h i s r e p o r t , t h i s d i f f e r e n c e i n behavior i s c o n s i s t e n t w i t h the d i f f e r e n c e s i n m o b i l i t y of the two s o l u t e s . With both benzene and p-chlorophenol, i n c r e a s i n g the c o n c e n t r a t i o n i n c r e a s e s the amount of s o l u t e bound t o the membrane pore w a l l . Since the p-chlorophenol i s more h i g h l y hydrated i t can move through the pore w i t h the water, which decreases the s e p a r a t i o n . For benzene, the s o l u t e i s r e l a t i v e l y immobilized, and w i t h i n c r e a s i n g c o n c e n t r a t i o n more and more of the pore i s occupied w i t h immobilized s o l u t e . The r e s u l t i s higher s e p a r a t i o n . Thus, i t appears that the s e p a r a t i o n and pore b l o c k i n g f a c t o r a r e both c o n t r o l l e d by the r e l a t i v e amount of immobilized s o l u t e i n the pore. This r e l a t i v e q u a n t i t y of s o l u t e can be increased by i n c r e a s i n th feed c o n c e n t r a t i o t fixed pore s i z e o r by decreasin c o n c e n t r a t i o n . As c o n c e n t r a t i o , s o l u t e assumes a p o s i t i o n i n sorbed l a y e r s which are i n c r e a s i n g l y f a r from the membrane s u r f a c e . Thus, the a t t r a c t i o n f o r c e s exerted by the membrane m a t e r i a l on the s o l u t e are p r o g r e s s i v e l y l e s s , and the a d d i t i o n a l s o l u t e i s not so t i g h t l y bound. The r e s u l t i s the permeation of a p o r t i o n of the concentrated boundary l a y e r . Therefore, there i s a l e v e l i n g o f f i n s e p a r a t i o n w i t h i n c r e a s i n g concentration. C o r r e l a t i o n of X A 2 w i t h Pore B l o c k i n g f o r Benzene-Water Data. The b l o c k i n g of the pores on the membrane surface by the p r e f e r e n t i a l l y sorbed s o l u t e , which was discussed q u a l i t a t i v e l y i n the preceding s e c t i o n , i s now t r e a t e d more q u a n t i t a t i v e l y . Equation 4 was used to estimate the a p p r o p r i a t e k value f o r each c e l l . The d i f f u s i v i t y of the s o l u t e i n water was estimated by the method of Wilke and Chang ( 2 7 ) , and the d i f f u s i v i t y of sodium c h l o r i d e i n water used was 1 . 6 0 x 10~" cm /s ( 2 6 ) . Then X A 2 was c a l c u l a t e d f o r each run from Equation 3 . F i g u r e 7 i l l u s t r a t e s the r e l a t i o n s h i p between 1 -(PF/PWF) and X A 2 - W i t h i n the s c a t t e r of t h i s data, i t i s reasonable to use a s t r a i g h t l i n e through the o r i g i n f o r a l l s i x membranes. This data corresponds to an n i value of 1 . 0 i n Equation 1 . The K j v a l u e s , obtained by l e a s t squares a n a l y s i s of the data i n F i g u r e 7 , a r e p l o t t e d i n Figure 8 as a f u n c t i o n of l n C * N C l * This r e l a t i o n s h i p can be described by the equation 5

2

a

Ki =

-2189

l n C*

N a C 1

-

12840

(7)

For the membranes used i n t h i s study, ¥L\ v a r i e d from 6 x 1 0 t o 1 6 x 1 0 . I t should be noted that F i g u r e s 7 and 8 i n c l u d e d data from a l l pressures t e s t e d and t h e r e f o r e Equation 7 w i l l p r e d i c t K i f o r a l l pressures and c o n c e n t r a t i o n s w i t h i n the range s t u d i e d . The i n v e r s e dependence of on l n C*NaCl r e f l e c t s the increased 3

3

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

o

LO

00

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importance of s o l u t e pore b l o c k i n g f o r the membranes of s m a l l e r pore s i z e , E q u a t i o n 7, t h e r e f o r e , can be used to estimate the extent of pore b l o c k i n g that w i l l be caused by p r e f e r e n t i a l l y sorbed benzene. This e s t i m a t i o n can be performed by simply conducting experiments w i t h NaCl-water systems to determine the l n C*NaCl value f o r the membrane i n use. The a p p l i c a t i o n of Equation 7 to aqueous systems c o n t a i n i n g benzene p l u s a s o l u t e such as NaCl w i l l be explored i n f u t u r e s t u d i e s . Toluene-Water Reverse Osmosis Data. Data f o r the reverse osmosis s e p a r a t i o n of aqueous toluene s o l u t i o n s a t 3450 kPa and three d i f f e r e n t c o n c e n t r a t i o n s , u s i n g the same s i x membranes as above, a r e i l l u s t r a t e d i n Figure 9. These r e s u l t s are q u a l i t a t i v e l y s i m i l a r t o those f o r the benzene s t u d i e s . That i s , s e p a r a t i o n and extent of pore b l o c k i n g i n c r e a s e w i t h both i n c r e a s i n g c o n c e n t r a t i o n and decreasin size studie i n v e s t i g a t e the e f f e c t s C o r r e l a t i o n of XA2 w i t h Pore B l o c k i n g f o r Toluene-Water Data. An a n a l y s i s s i m i l a r t o that used f o r the benzene data was a p p l i e d to the toluene data to i n v e s t i g a t e pore b l o c k i n g as a f u n c t i o n of c o n c e n t r a t i o n . Figure 10 i l l u s t r a t e s t h i s r e l a t i o n s h i p f o r a l l s i x membranes. The data f o r membranes 5 and 6 can be approximated by a s t r a i g h t l i n e ; t h e r e f o r e , n\ was s e t to 1.0 i n Equation 1. For the other f i l m s , a l e a s t squares parameter e s t i m a t i o n was a p p l i e d and the n\ and K j values generated. The r e s u l t s are i l l u s t r a t e d i n F i g u r e 11, where K j ( p l o t t e d as l n K^ f o r convenience) and ni are shown as f u n c t i o n s of l n C*NaCl» r e g i o n of l n C * N d l e s s than -10.5 both n^ and K^ i n c r e a s e w i t h l n C*NaCl« Above t h i s value n i and K j l e v e l o f f a t 1.0 and 40 x 1 0 ( i . e . , l n K i = 10.6), r e s p e c t i v e l y . This r e s u l t i s s i m i l a r to that obtained p r e v i o u s l y i n p-chlorophenol s t u d i e s (23) , where n i was found to l e v e l o f f a t l n C*^ n^ values greater than -12.0. In general, the s e p a r a t i o n and pore b l o c k i n g data f o r the toluene-water system are c o n s i s t e n t w i t h those obtained f o r the benzene-water system. P o s i t i v e s e p a r a t i o n occurs, and the general trends of i n c r e a s i n g s e p a r a t i o n and pore b l o c k i n g w i t h i n c r e a s i n g c o n c e n t r a t i o n and decreasing pore s i z e are observed. This i s not s u r p r i s i n g s i n c e toluene and benzene are s i m i l a r i n s t r u c t u r e . However, based on the modified Small's number f o r these s o l u t e s , as discussed e a r l i e r i n t h i s paper, i t would be expected that toluene would be more s t r o n g l y sorbed by the membrane than i s the benzene. I f t h i s i s t r u e , then a t otherwise i d e n t i c a l c o n d i t i o n s toluene should demonstrate greater pore b l o c k i n g and higher s e p a r a t i o n than benzene. Curve c_ i n Figure 9 f o r toluene and curve a i n Figure 4 f o r benzene a r e a t the same pressure and approximately the same molar c o n c e n t r a t i o n . I n a l l cases, the expected r e s u l t i s found. For example, f o r membrane 2, the separations are 41% and 9% and the pore b l o c k i n g f a c t o r s are 0.30 and 0.08 f o r toluene and benzene, r e s p e c t i v e l y . Thus, the modified Small's F

o

r t

n

e

a

3

a(

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

310

SYNTHETIC

MEMBRANES:

HF AND U F

USES

K.xlO"

Figure 8. Correlation ofK of Equation 1 with membrane pore size (In C* ci) for separation of the benzene-water system t

Na

6

In C .

8 0

i< OC 6 0

& W UJ Z W

40

1-

a

20

_J O 0 -12

-II l n

c

NaCI

Figure 9. Effect of feed concentration on the RO performance for the toluenewater system. The operating conditions are identical to those of Figure 2 except that the operating pressure = 3450 kPa. Curve a (O) 8.7 ppm; Curve b (%) 12.4 ppm; Curve c (Q) 20.8 ppm.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

DICKSON A N D

LLOYD

Solute Preferential Sorption

311

Figure 10. Correlation of the pore-blocking factor, 1-(PF/PWF), and the boundary layer concentration of toluene, X . The operating conditions are the same as in Figure 9 with Membranes 1 (*), 2 (Q), 3 (A), 4 (A), 5 (O), and 6 (M) as designated in Table I. A2

Figure 11. Correlation of In K j and n of Equation 1 with membrane pore size (In C* ci) for separation of the toluenewater system t

Na

NaCl

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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SYNTHETIC

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HF

AND

UF

USES

number i s a u s e f u l t o o l f o r q u a l i t a t i v e l y p r e d i c t i n g d i f f e r e n c e s i n the reverse osmosis performance f o r toluene-water and benzene-water systems. Conclusions In c o n c l u s i o n , s e v e r a l important p o i n t s of t h i s work should be r e i t e r a t e d . An understanding and q u a n t i t a t i v e d e s c r i p t i o n of s o l u t e p r e f e r e n t i a l s o r p t i o n i s imperative to the advancement of a fundamental knowledge of the s e p a r a t i o n mechanism and to the a p p l i c a t i o n of reverse osmosis. For the systems s t u d i e d , i n c r e a s i n g the feed c o n c e n t r a t i o n was found to i n c r e a s e s e p a r a t i o n and decrease permeate f l u x . This behavior can be contrasted to the case of water p r e f e r e n t i a l s o r p t i o n where both s e p a r a t i o n and permeate f l u x would remain constant f o r these d i l u t e c o n c e n t r a t i o n s . The r e s u l t s f o r the benzene s t u d i e s and the toluene s t u d i e s were s i m i l a f l u x decreased w i t h i n c r e a s i n pore s i z e . The benzene s t u d i e s showed a minimum i n s e p a r a t i o n w i t h i n c r e a s i n g pressure. At s i m i l a r experimental c o n d i t i o n s the toluene system showed higher s e p a r a t i o n and lower f l u x than the benzene system. This observation i s c o n s i s t e n t w i t h the d i f f e r e n c e i n the nonpolar character of the s o l u t e s as expressed by the Small's number. Further work i s needed i n order to improve the q u a n t i t a t i v e understanding of systems which e x h i b i t solute p r e f e r e n t i a l sorption. Legend of Symbols A

= pure water p e r m e a b i l i t y constant, mol (m s kPa)

H2O/

2

D^g D

= d i f f u s i v i t y of A i n B, K(

=

AM/ 5

2

m /s

s o l u t e t r a n s p o r t parameter,

f

= separation

k

= mass t r a n s f e r c o e f f i c i e n t ,

Ki,K

m/s

m/s

= p r o p o r t i o n a l i t y f a c t o r s defined i n Equations 1 and 2, r e s p e c t i v e l y

2

ln C*N d

= r e l a t i v e measure of the membrane pore s i z e

mi

= concentration, m o l a l i t y

a

ni,n

2

= exponents defined i n Equations respectively 2

NA

= s o l u t e f l u x , mol/(m

P

= operating pressure, kPa gauge

PF

= permeate f l u x , kg/(m s ) '

1 and

2,

s)

2

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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ppm

= c o n c e n t r a t i o n , p a r t s per m i l l i o n

PWF

= pure water f l u x , kg/(m s)

X

= c o n c e n t r a t i o n , mole f r a c t i o n

p

= s o l u t i o n d e n s i t y , kg/m

313

2

3

Subscripts 1

= feed s o l u t i o n

2

= boundary l a y e r s o l u t i o n

3

= permeate s o l u t i o n

M

= membrane phase

A

= solute

B

= solvent

ref

= referenc

Acknowledgements The authors wish t o thank The Engineering Foundation f o r t h e i r support of t h i s research and the N a t u r a l Sciences and Engineering Research C o u n c i l of Canada f o r the s c h o l a r s h i p support of one of the authors (JMD). Literature Cited 1.

S o u r i r a j a n , S.; Matsuura, T. in "Reverse Osmosis and S y n t h e t i c Membranes"; S o u r i r a j a n , S., Ed.; N a t i o n a l Research C o u n c i l of Canada: Ottawa, 1977; Chapter 2.

2.

Lonsdale, H.K.; Merten, U.; R i l e y , R.L. J. Appl. Polymer Sci. 1965, 9, 1341-1362.

3.

Lonsdale, H.K.; Merten, U.; Tagami, M. J. Appl. Polymer Sci. 1967, 11, 1807-1820.

4.

Merten, U.; Lonsdale, H.K.; R i l e y , R.L.; Tagami, M. presented at NATO Advanced Study Institute on S y n t h e t i c Polymer Membranes, R a v e l l o , Sept. 1966.

5.

Anderson, J.E.; Hoffman, S.J.; P e t e r s , C.R. J. Phys. Chem. 1972, 76, 4006-4011.

6.

Pusch, W.; Burghoff, H.G.; Staude, E. 5 t h I n t e r n . Symp. on Fresh Water from the Sea 1976, 4, 143-156.

7.

Merten, U., Ed. " D e s a l i n a t i o n by Reverse Osmosis"; M.I.T. Press: Cambridge, Mass., 1966; p. 15-54.

8.

S p i e g l e r , K.S. Trans. Faraday Soc. 1958, 54, 1408-1428.

9.

Jonsson, G.; Boesen, C.E. D e s a l i n a t i o n 1975, 17, 145-165.

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SYNTHETIC

MEMBRANES*.

HF

AND

UF

USES

10.

Boesen, C.E.; Jonsson, G. 5 t h I n t e r n . Symp. on Fresh Water from the Sea 1976, 4, 259-266.

11.

Boesen, C.E.; Jonsson, G. 6 t h I n t e r n . Symp. on Fresh Water from the Sea 1978, 3, 157-164.

12.

Jonsson, G. D e s a l i n a t i o n 1978, 24, 19-37.

13.

S p i e g l e r , K.S.; Kedem, O. D e s a l i n a t i o n 1966, 1, 311-326.

14.

Sherwood, T.K.; B r i a n , P.L.T.; F i s h e r , R.E. Ind. Eng. Chem. Fundamentals 1967, 6 ( 1 ) , 2-12.

15.

Pusch, W. Ber. Bunsenges. Physik. Chem. 1977, 81, 269-276.

16.

S o u r i r a j a n , S.; Matsuura Membranes"; S o u r i r a j a n Canada: Ottawa, 1977; Chapter 3.

17.

S o u r i r a j a n , S. "Reverse Osmosis"; Academic P r e s s : New York, 1970; Chapter 3.

18.

Matsuura, T.; Dickson, J.M.; S o u r i r a j a n , S. Ind. Eng. Chem. Process Des. Dev. 1976, 15(1), 149-161.

19.

T a f t , R.W., J r . in " S t e r i c E f f e c t s in Organic Chemistry" Newman, M.S., Ed.; Wiley: New York, 1956; p. 556-675.

20.

Small, P.A. J . A p p l . Chem. 1953, 3, 71-80.

21.

Matsuura, T.; S o u r i r a j a n , S. Ind. Eng. Chem. Process Des. Dev. in press.

22.

Matsuura, T.; S o u r i r a j a n , S. J. A p p l . Polymer Sci. 1973, 17, 3683-3708.

23.

Dickson, J.M.; Matsuura, T.; S o u r i r a j a n , S. Ind. Eng. Chem. Process Des. Dev. 1979, 18(4), 641-647.

24.

Pageau, L.; S o u r i r a j a n , S. J. A p p l . Polymer Sci. 1972, 16, 3185-3206.

25.

S o u r i r a j a n , S. "Reverse Osmosis"; Academic Press: New York, 1970; Chapter 2.

26.

Matsuura, T.; Pageau, L.; S o u r i r a j a n , S. J. A p p l . Polymer S c i . 1975, 19, 179-198.

27.

W i l k e , C.R.; Chang, P. AIChE J . 1955, 1, 264-270.

RECEIVED

December 4, 1980.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

19 Estimation of Interfacial Forces Governing the Reverse-Osmosis System: Nonionized Polar Organic Solute-Water-Cellulose Acetate Membrane TAKESHI MATSUURA, Y U T A K A TAKETANI, and S. SOURIRAJAN Division of Chemistry, National Research Council of Canada, Ottawa, Ontario K1A 0R9 Canada This extends the previous work (1) i n which the LennardJones type surface p o t e n t i a l f u n c t i o d th frictional f u n c t i o r e p r e s e n t i n g the interfacial molecule from the membran por and s o l v e n t t r a n s p o r t through a pore t o c a l c u l a t e data on membrane performance such as those on s o l u t e s e p a r a t i o n and the ratio of product r a t e to pure water permeation r a t e in reverse osmosis. I n the previous work (1) parameters i n v o l v e d in the Lennard-Jones type and frictional f u n c t i o n s were determined by a trial and e r r o r method so that the s o l u t i o n s in terms of s o l u t e s e p a r a t i o n and (product rate/pure water permeation r a t e ) ratio fit the experimental data. I n t h i s paper the potential f u n c t i o n is generated by using the experimental high performance liquid chromatography (HPLC) data in which the r e t e n t i o n time represents the a d s o r p t i o n and d e s o r p t i o n e q u i l i b r i u m of the s o l u t e a t the solvent-polymer i n t e r f a c e . The frictional f o r c e is expressed by a f u n c t i o n of the ratio of a d i s t a n c e a s s o c i a t e d w i t h steric r e p u l s i o n a t the i n t e r f a c e , to the pore r a d i u s . The frictional f u n c t i o n increases s t e e p l y w i t h increase in the latter ratio. The method of c a l c u l a t i n g reverse osmosis s e p a r a t i o n data by u s i n g the surface potential f u n c t i o n and the frictional f u n c t i o n so generated, i n c o n j u n c t i o n w i t h the t r a n s p o r t equation is illustrated by examples i n v o l v i n g c e l l u l o s e acetate membranes of different p o r o s i t i e s and 40 nonionized organic s o l u t e s in s i n g l e s o l u t e aqueous s o l u t i o n systems. Experimental HPLC Experiments. The l i q u i d chromatograph model ALC 202 of Waters A s s o c i a t e s f i t t e d w i t h a d i f f e r e n t i a l refractometer was used i n t h i s work. The method of column p r e p a r a t i o n and the general experimental technique used were the same as those reported e a r l i e r (2). A l l experiments were c a r r i e d out a t the l a b o r a t o r y temperature (23-25°C). The s o l v e n t (water) flow r a t e 0097-6156/81/0154-0315$06.00/0 © 1981 American Chemical Society

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UF

USES

3

through the column was f i x e d a t 0.27 cm /min. The pressure drop through the column was 1034kPa(=150psi)/ft. F o r t y s o l u t e s i n c l u d i n g a l c o h o l s , p o l y a l c o h o l s , phenols, ketones, e t h e r s , aldehydes, e s t e r s , amines, amides, n i t r i l e s and nitrocompounds were i n j e c t e d i n t o the column which was made from c e l l u l o s e acetate Eastman E-398 polymer. I O U L of sample s o l u t i o n ( s o l u t e c o n c e n t r a t i o n i n the range 1~10%) was i n j e c t e d i n t o the column, and the r e t e n t i o n time f o r each s o l u t e was determined. R a f f i n o s e whose r e t e n t i o n time was the l e a s t , was used as the unretained component to e s t a b l i s h the p o s i t i o n of s o l v e n t f r o n t . The r e t e n t i o n time measurements were d u p l i c a t e d and the average values obtained were used f o r computations; i n most cases, the r e s u l t s of d u p l i c a t e d measurements were i d e n t i c a l . I t was already e s t a b l i s h e d (2) that changes i n column l e n g t h , p a r t i c l e s i z e , packing d e n s i t y of column m a t e r i a l , s o l v e n t v e l o c i t y through the column, o p e r a t i n g pressure and sample s i z e d i d not a f f e c t the r e t e n t i o n tim otherwise i d e n t i c a l experimenta Reverse Osmosis Experiments. This work makes f u r t h e r use of reverse osmosis data a l r e a d y reported w i t h respect to membranes made from c e l l u l o s e acetate Eastman E-398 polymers (3,^,5^,60. Data on amides, n i t r i l e s and nitrocompounds were newly added i n t h i s work. The experimental d e t a i l s are b r i e f l y as f o l l o w s . Each membrane was subjected to an i n i t i a l pure water pressure of 2068kPa gauge(=300psig) f o r about 2h p r i o r to subsequent use i n reverse osmosis experiments a l l of which were c a r r i e d out a t 1724kPa gauge(=250psig) and a t l a b o r a t o r y temperature (23-25°C). For purposes of membrane s p e c i f i c a t i o n s i n terms of pure water p e r m e a b i l i t y constant A ( i n kg-mol of H^O/m »s«kPa) and s o l u t e t r a n s p o r t parameter (D^/KS) ( t r e a t e d as a s i n g l e q u a n t i t y , m/s), aqueous feed s o l u t i o n s c o n t a i n i n g 3500 ppm of NaCl were used ( 7 ) . Data on A and (D^/KS) thus obtained are l i s t e d i n Table I w i t h respect to a l l membranes used i n t h i s work together w i t h experimental reverse osmosis data of sodium c h l o r i d e s o l u t e . In a l l other experiments, the s o l u t e concentrations i n the aqueous feed s o l u t i o n s were so low (0.001 to 0.006 molal) that the osmotic pressures i n v o l v e d were n e g l i g i b l e compared to the o p e r a t i n g pressure. In each experiment, the f r a c t i o n s o l u t e s e p a r a t i o n defined as: 2

^ _ s o l u t e c o n c e n t r a t i o n i n f e e d - s o l u t e c o n c e n t r a t i o n i n product s o l u t e c o n c e n t r a t i o n i n feed membrane permeated product r a t e (PR) and pure water permeation r a t e (PWP) i n g/h f o r the e f f e c t i v e area of membrane surface used (=13.2 cm i n t h i s work) were determined a t the s p e c i f i e d o p e r a t i n g c o n d i t i o n s . A l l reverse osmosis experiments were f o r s i n g l e s o l u t e systems. The c o n c e n t r a t i o n s of sodium c h l o r i d e were determined using a c o n d u c t i v i t y b r i d g e ; the c o n c e n t r a t i o n s of organic s o l u t e s were determined by a Beckman t o t a l carbon 2

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

MATSUURA

19.

Interfacial Forces Governing the RO System

ET AL.

317

analyzer Model 915A. Data on s p e c i f i c a t i o n s and performances o f a l l f i l m s used i n t h i s work are given i n Table I . Theoretical In the e a r l i e r work (1) transport equations were developed on the b a s i s of surface force-pore flow model i n which a surface p o t e n t i a l f u n c t i o n and a f r i c t i o n a l f u n c t i o n are incorporated. The r e s u l t s can be b r i e f l y summarized as f o l l o w s : D e f i n i n g the f o l l o w i n g dimensionless q u a n t i t i e s , = r/R

P

(1)

CA(P)

= CA (P)/C

k c a l c u l a t e d by c

f

a

n

e

[exp(a(p))/i +

f' = 1 -

| e x p ( a ( p ) - l ) | | a(p)pdp

^

^

(7)

f a(p)pdp

The dimensionless r a d i a l v e l o c i t y p r o f i l e , expressed by a(p) i s obtained by s o l v i n g the d i f f e r e n t i a l equation 2

d a(p) dp

f

e

i

i

i

e

4 r^^( - "

l




C

)(

4




2

3

4 5

6 7

8

21.1 35.0

40.0 26.0

30.6 22.0

10 11

12 13

b b

b

39.5

33.5 b

52.47 50.57 41.43

40.6

14

9.39

7.48 8.61 Alcohols

7.36

2

60.2

74.0

75.0

85.8

82.8

92.2

82.9

93.5

83.2

94.4

66.2

81.3

60.6

75.5

Sodium c h l o r i d e c o n c e n t r a t i o n i n feed, 0.06 m o l a l .

G l y c e r o l feed c o n c e n t r a t i o n i n feed, 0.002 m o l a l , (PR)~(PWP),

C

39.5

45.0

b

83.3

94.3

82.7

91.9

59.5

73.0

40.0

62.0

b b b 20.49 43.84 66.64

8.57 7.20 7.54 9.42 10.09 Amides, N i t r i l e s , N i t r o compounds

75.6

85.6

Sodium c h l o r i d e c o n c e n t r a t i o n i n feed, 0.026 m o l a l unless otherwise s t a t e d ,

3

79.2

89.4

7.62 8.24 7.20 9.14 9.37 Ketones, E s t e r s , Ethers

82.5

93.4

21.1

62.81

25.48 22.64 50.70 76.51

23.0

9.833 2.195 2.877 26.81

20.40 18.90 34.40 42.20 28.18 34.34 22.23 49.09 46.67 36.00 21.53

b

25.45 22.77 43.57 51.38 30.14 37.06 23.91

22.6

2.515 2.772 10.15 25.75 3.302 6.759 2.230 18.36 25.13

k"

*

9

1.726 1.544 2.955 3.485 2.044 2.513 1.622 3.559 3.430 2.810 1.728 1.535 3.438 5,189

1

Operating pressure, 1724 kPa gauge (=250 p s i g ) Flow r a t e , 400 cm /min E f f e c t i v e membrane area, 13.2 cm .

0

NaCl > / (PWP), g/h NaCl experimental data (PR), g/h Solute s e p a r a t i o n , % Glycerol experimental d a t a Solute s e p a r a t i o n , % Pore r a d i u s , A Solutes s t u d i e d

k

( AM/ >NaCl m/s

7

F i l m No. A x l O , kg-mol/m . s.kPa

Table I . Experimental Reverse Osmosis D a t a f o r the System NaCl-H^O and Glycerol-H^O Using Porous C e l l u l o s e Acetate Membranes and Parameters C h a r a c t e r i z i n g Membranes

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

94.0

61.8

Solute s e p a r a t i o n , %

•

m / s

1 0 ?

•

data

m / s

Pore r a d i u s , A Solutes s t u d i e d

0

G l y c e r o l experimental Solute s e p a r a t i o n , %

1 0 6

NaCl *

9.98

8.35

78.3

87.3

31.64

61.43 45.0 63.96

17.50 31.4 38.24

29.63 44.1 57.78

8.66

9.47

58.0

9.24

63.9

7.30

83.1

93.8

21.58

22.80

21.0

8.31

78.6

87.8

31.69

33.48

28.2

7.199

2.271

23

Phenols, A n i l i n e s

10.04

41.8

61.0

77.2

74.8

84.6 74.3

60.53

36.15

54.51

44.65

47.16

37.1

13,09

2.371

1.546

4.338

2.593

3.917

3.198

22

21

20

19

18

P o l y a l c o h o l s , Carbohydrates

7.36

82.9

21.63

60.36

NaCl experimental (PR), g/h

X

/ k 6 )

^aCl

AM

43.3

33.78

23.05

62.86

(PWP), g/h

0

28.5

21.4

45.00

data

7.610

2.319

58.64

( D

2.291

1.564

17

4.263

A*10 , kg-mol/m r> &

In eq 13 and 14, D i s the d i s t a n c e between the polymer s u r f a c e and the s o l u t e mclecule a t which $(p) becomes very l a r g e , and E i s the f r i c t i o n a l f o r c e constant f o r the t r a n s p o r t of s o l u t e through the pore. As i t i s c l e a r from eq 14 the f r i c t i o n a l f o r c e i s a f u n c t i o n of D. Therefore, b and D a r e d i r e c t l y r e l a t e d . F u r t h e r , s i n c e the d i s t a n c e D i s a s s o c i a t e d w i t h s t e r i c r e p u l s i o n at the i n t e r f a c e , and s i n c e the l a t t e r d i r e c t l y p a r a l l e l s the e f f e c t i v e s i z e of the s o l u t e molecule concerned, i t i s reasonable to c o n s i d e r that D i s a f u n c t i o n of the e f f e c t i v e s i z e of the s o l u t e molecule. Therefore, both D and b can be r e l a t e d to the e f f e c t i v e s i z e of the s o l u t e molecule. For the purpose of mathematical a n a l y s i s , the l o c a t i o n of a molecule i n s i d e a pore may be considered as the l o c a t i o n of the center of the molecule, assuming s p h e r i c a l shape f o r the molecule. Therefore, the lowest l i m i t i n g d i s t a n c e D a t which s u r f a c e r e p u l s i o n f o r the molecule i s the h i g h e s t i s a c t u a l l y the r a d i u s of the molecule i t s e l f , since i t cannot be any c l o s e r to the membrane s u r f a c e . F u r t h e r , f o r n o n i o n i c s o l u t e s which are s u b j e c t to s h o r t range hydrogen bonding and/or d i s p e r s i o n f o r c e s of a t t r a c t i o n and r e p u l s i o n , the a c t u a l d i s t a n c e D cannot be too f a r d i f f e r e n t from the r a d i u s o f the molecule. Therefore, as a matter of p r a c t i c a l approximation the d i s t a n c e D i s considered i d e n t i c a l to an e f f e c t i v e r a d i u s of the molecule f o r purposes of a n a l y s i s i n t h i s work.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

19.

MATSUURA

Interfacial Forces Governing the RO System

ET AL.

321

I t has to be noted that f o r the s o l u t i o n of eq 7 and 8 together w i t h boundary c o n d i t i o n s given by eq 10 and 11, only pore r a d i u s , R, and parameters B, D and E are necessary. The other q u a n t i t i e s i n v o l v e d i n the above equations are a l l a v a i l able i n terms of the experimental c o n d i t i o n s used. In other words, the s o l u t e s e p a r a t i o n , f ' , which i s d e f i n e d on the b a s i s of the boundary c o n c e n t r a t i o n c ^ s t r i c t l y a function of v a r i a b l e s R, B, D and E under a given s e t of operating c o n d i t i o n s . In eq 7, s o l u t e s e p a r a t i o n was defined on the b a s i s o f boundary c o n c e n t r a t i o n c ^ > c —c f = (15) A2 i s

a s

A

2

A

3

C

In order to r e l a t e the above s o l u t e s e p a r a t i o n to that on the b a s i s o f feed c o n c e n t r a t i o

C

f =

C

Al" A3

A

1

A

C

J

(16)

A1

the f o l l o w i n g equation based on the b a s i c t r a n s p o r t e s t a b l i s h e d e a r l i e r (7) C

A2

=

C

+

A3

(

c

C

Ar A3

)

e

X

p

( 3

equation

17

lH

< >

can be employed using the f a c t that the molar d e n s i t y remains e s s e n t i a l l y constant f o r the present system. In eq 17, v i s the l i n e a r v e l o c i t y of the permeate s o l u t i o n through the membrane, which i s e s s e n t i a l l y the same as v ^ = A ( P ^ - P ) / c f o r d i l u t e s o l u t i o n s . Furthermore, from previous work the mass t r a n s f e r c o e f f i c i e n t k can be represented as a f u n c t i o n of pure water p e r m e a b i l i t y constant, A, as shown i n Figure 1 ( 8 ) . Combining eq 15, 16 and 17 we o b t a i n g

0

f f

(18)

+\ (1

which equation r e l a t e s f defined by eq 15 to f d e f i n e d by eq 16. A n a l y s i s of High Performance L i q u i d Chromatography (HPLC) Data On the b a s i s of a n a l y s i s of r e t e n t i o n time data obtained from l i q u i d chromatography experiments reported e a r l i e r (9) the existence o f i n t e r f a c i a l water i s assumed a t the s o l u t i o n polymer i n t e r f a c e and the e q u i l i b r i u m c o n c e n t r a t i o n of s o l u t e between s t a t i o n a r y - and mobile-phases i s regarded as that between

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

322

SYNTHETIC MEMBRANES: HF AND UF USES

i n t e r f a c i a l - and bulk-water phases. This model i s s c h e m a t i c a l l y described i n Figure 2. Expressing average concentration of s o l u t e i n the i n t e r f a c i a l r e g i o n as c ^ and the concentration of s o l u t e i n the b u l k s o l u t i o n phase c ^ , the e q u i l i b r i u m constant K can be w r i t t e n as K' = — Ab

(19)

C

I t i s f u r t h e r assumed that the e q u i l i b r i u m constant f o r is the same as that of o r d i n a r y water and i s u n i t y . Then, K' f o r other s o l u t e s can be c a l c u l a t e d from the r e l a t i o n (9) -

v'

[V]

-

R

[V]

Vmin

7

( 2 0

"Tv ! =17] Vwater Vmi L

L

s

where [VR] i s the experimental r e t e n t i o n volume, [v$}\jater ^ tv«] of D 0 and [vX] . i s [v£] of a reference s o l u t e , r a f f i n o s e . K L K mm K ' . i n t h i s p a r t i c u l a r system, which e x h i b i t s the lowest r e t e n t i o n volume among s o l u t e s i n j e c t e d ( 9 ) . From eq 20, values of K' f o r water and reference s o l u t e are one and zero, r e s p e c t i v e l y . Using the e q u i l i b r i u m constant defined by eq 20, r e t e n t i o n volume [v^] f o r any s o l u t e can be given by o

#

[ V

R

]

"

[ V

P

] m

-in

+

K

'

V

c

(

2

1

)

mm s where V represents the volume o f s t a t i o n a r y phase water and i s equal to the volume of the i n t e r f a c i a l water i n t h i s case. I n eq 20, the value o f K' may be equal t o , greater than o r l e s s than u n i t y depending on d e t a i l s of concentration gradient i n the i n t e r f a c i a l r e g i o n . Further, the i n t e r f a c i a l "water l a y e r t h i c k ness, t . i n Figure 2, evaluated i n the previous work (9) to be 9.5A f o r c e l l u l o s e acetate E-398 polymer m a t e r i a l , i s used i n t h i s work. Since membrane pore surface and the chromatography packing surface a r e both made out of the same polymer m a t e r i a l , i d e n t i c a l i n t e r f a c i a l forces have to govern both membrane t r a n s p o r t and chromatography e q u i l i b r i u m . The only d i f f e r e n c e between the two systems i s that i n the l a t t e r case, there i s no e f f e c t of s o l u t e movement ( k i n e t i c e f f e c t ) on the r e t e n t i o n volume data, and therefore the i n t e r f a c i a l f o r c e governing the chromatography e q u i l i b r i u m may be represented only by surface p o t e n t i a l working on the s o l u t e , which may be expressed by a Lennard-Jones type equation. The e q u i l i b r i u m constant, K', can be r e l a t e d to the LennardJones type p o t e n t i a l f u n c t i o n as f o l l o w s . The concentration p r o f i l e of the s o l u t e a t polymer-solution i n t e r f a c e may be described s c h e m a t i c a l l y as shown i n Figure 3a and 3b. K

K

g

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

19.

MATSUURA

ET

AL.

Interfacial Forces Governing the RO System

323

Figure 1. Effect of the PWP constant on the mass-transfer coefficient for sodium chloride

BULK SOLUTION

"A

'4. Figure 2. Equilibrium of solute between interfacial water and bulk solution

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

324

SYNTHETIC

MEMBRANES:

H F A N D U F USES

Using the p o t e n t i a l f u n c t i o n , cj>, as. a f u n c t i o n of the d i s t a n c e from the polymer s u r f a c e , 10RT

when dD

(dimensionless p o t e n t i a l f u n c t i o n eq 13 was d e r i v e d from eq 22), and Boltzmann's law, s o l u t e c o n c e n t r a t i o n i n the range 0. Supposing t h i s excessive amount of s o l u t e i s compressed i n the r e g i o n of i n t e r f a c i a l water, whose thickness i s t ^ (see Figure 3) and averaged out, the r e s u l t becomes, w a t e r

w a t e r

w a t e r

w a t e r

7

+C

A i " 77 Ab 1 / y

=

0% T D S

HYPE FILTRATION

110,00 18 2 % TDS

EVAPORATION

FILTRATE 90.000

36,40 5 5 % TDS

ME

73.600

L B S . / HR

LBS/HR

Figure 10. Energy requirement for water removal. Four-stage ME evaporation, A, compared with a combination of the four-stage ME evaporation and HF, B.

Features I n s t a l l a t i o n year S i z e s q . f t . membrane a r e a Configuration Product % TDS f e e d % TDS c o n c e n t r a t e Maximum feed r a t e GPM Max f i l t r a t i o n r a t e GPM Avg. f i l t r a t i o n r a t e a t max. f e e d Nominal power consumption approx. Kw. Nominal power concumption Kwh p e r 1000 l b s . f i l t r a t e No.of membrane r e p l a c e m e n t s

Toten

Reed

1976 4215 4 stage cont. N H 4 - S S L pH 2-2.5 6-10 12 88 44

1978 4817 4 stage cont. Ca-SSL pH 3-3.5 10 - 12 18 132 44

15

13

75

90

3.4 3

4.0 1

Figure 11. Features of the HF plants at Totel and Reed as of August 15, 1980

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

21.

CLAUSSEN

UF and

HF

in the Pulp and

Paper Industry

371

PRE-BLEACHED PULP

6000 TT? Effluent 40 tons Total Solids Total Chloride 7 tons 70 tons Color Pt 12 tons COD 4 tons BOD 3

Concentrate 250 m Solids 18 tons Chloride 1 ton Color Pt 63 tons COD 8 tons BOD 2 tons 3

5750 m 22 tons (12 tons org.) (10 tons NaCl) 6 tons Chloride 7 tons Color Pt 4 tons COD 2 tons BOO

Permeate Solids

Figure 12.

Ultrasep system for color removal. Materials balance for 600 tons of kraft pulp.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

SYNTHETIC MEMBRANES: HF AND

372

UF USES

F i g u r e 12 i s showing the d i s t r i b u t i o n of other e s s e n t i a l substance; f o r i n s t a n c e , BOD, COD, c h l o r i d e and TDS i n the two fractions. The o p e r a t i o n ran smoothly w i t h few major problems. Membrane c l e a n i n g frequency was, on average, once every three weeks. D i f f e r e n t membranes were used; the l a s t set was i n continuous o p e r a t i o n f o r more than 8,000 hours without s i g n i f i c a n t change i n performance. This process i s found to be competitive to e x i s t i n g c o l o r removal processes, both w i t h regard to economy and c o l o r removal efficiency. To which degree i t i s going to be u t i l i z e d i s depending on what k i n d of r e g u l a t i o n s there w i l l be w i t h regard to emmissions from b l e a c h p l a n t s . However, the f i r s t i n d u s t r i a l i n s t a l l a t i o n of i t s k i n d w i l l be made t h i s year i n Japan.

dustry.

ABSTRACT. Membrane filtration than five years on a commercial s c a l e in the pulp and paper inContinuous, m u l t i - s t a g e p l a t e and frame based systems are being used f o r purification, and molecular distribution c o n t r o l of l i g n o s u l f o n a t e from spent sulfite l i q u o r and preconc e n t r a t i o n of weak spent sulfite l i q u o r before evaporation. Larger s c a l e , long term pilot operations w i t h the s i m i l a r systems f o r s e p a r a t i o n of lignin from k r a f t b l a c k l i q u o r and c o l o r removal from bleach p l a n t e f f l u e n t s are going on successa d v i s i n g new and comprehensive a p p l i c a t i o n s f o r membrane filtration process in this i n d u s t r y . The aspect of saving fossile energy is a common f e a t u r e of most such operations as hyperfiltration i s typical low energy c o n c e n t r a t i o n method and the lignin products in many cases r e p l a c e petroleum based chemicals. Literature Cited 1.

2. 3.

4. 5. 6.

DDS Modules, U.S. Patent 3,872,015, GB patent 1,390,671, Italy patent 978,747, S w i t z e r l a n d patent 542,639, New Zealand patent 169,679. L. Janzen, P.H. Claussen, Norway patent 127,545, Swiss patent 560,289, P o r t u g a l , France, Brazil, Italy patents. K. F o r s s , A. Fuhrman, Karatex adhesive, F i n l a n d patent 167,647, U.S. patent 4,105,606. Patents GDR, A u s t r i a , GB, Hungary, e t c . J . Manson, EKA AB Sweden. Proceedings from I n t e r n a t i o n a l Pulp Bleaching Conference i n Toronto, June, 1979. P.H. Claussen, Pulp and Paper Canada, March, 1978. K. F o r s s , R. Kokkonen, H. Sirelius, P.E. Sagfors, Pulp and Paper Canada, December, 1979.

RECEIVED December 17,

1980.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

22 Pressure-Independent Ultrafiltration—Is It Gel Limited or Osmotic Pressure Limited? 1

D A N I E L R. T R E T T I N and M A H E N D R A R. D O S H I Environmental Sciences Division, The Institute of Paper Chemistry, Appleton, WI 54912

Ultrafiltration i n v o l v e s the p r e s s u r e - a c t i v a t e d s e p a r a t i o n of chemical species whic a membrane. Solute r e t e n t i o e x c l u s i o n , that is, a s i e v i n g - t y p e of mechanism and s o l v e n t passes through by pore flow. As an initially homogeneous solution is p r e s s u r i z e d over a s e l e c t i v e membrane, s o l v e n t permeates through w h i l e r e j e c t e d s o l u t e accumulates in the vicinity of the membrane. The net result is a l a y e r of s o l u t i o n adjacent to the membrane surface of substantially greater s o l u t e c o n c e n t r a t i o n than that of the bulk s o l u t i o n . This phenomenon of concentrat i o n polarization always operates to reduce the s o l v e n t permeat i o n r a t e which may become pressure independent in some cases. In the ultrafiltration of macromolecular s o l u t i o n s , a l a r g e number o f i n v e s t i g a t o r s have observed that as pressure is increased, permeate f l u x first increases and then remains more o r l e s s pressure independent. B l a t t , e t al. (1970), among o t h e r s , argued that one of the reasons f o r the observed pressure independence could be due to the formation of a g e l l a y e r on the membrane s u r f a c e . The permeate r a t e in t h i s case may be expressed as: I

I

AP - ATT

K\

N

,

( 1 )

p (R + R ) m g are the h y d r a u l i c r e s i s t a n c e s o f the membrane and

where R and R m g gel l a y e r r e s p e c t i v e l y , AP and ATT represent the a p p l i e d pressure and osmotic back pressure and y i s the permeate v i s c o s i t y . I n the case of pressure independent u l t r a f i l t r a t i o n of macromolecular s o l u t i o n s , i f the a p p l i e d pressure i s much greater than the osmotic pressure d i f f e r e n c e across the membrane, and s i n c e the gel r e s i s t a n c e i s g e n e r a l l y s u b s t a n t i a l l y greater than that of a membrane, Eq. (1) can be s i m p l i f i e d t o :

1

Current address: Union Camp Corporation, Franklin, VA 23851. 0097-6156/81/0154-0373$09.25/0 © 1981 American Chemical Society

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

374

SYNTHETIC

HF

AND

UF

USES

AP » ATT ' R » R g g Any i n c r e a s e i n pressure a f t e r the occurrence of g e l formation merely i n c r e a s e s g e l t h i c k n e s s and hence R^ so that the permeate v

w

AP " UR

MEMBRANES:

m

f l u x remains e s s e n t i a l l y independent of pressure. There could be other p o s s i b i l i t i e s f o r the observed pressure independence. We know t h a t , i n the absence of g e l formation, i n c r e a s e i n the a p p l i e d pressure r e s u l t s i n the i n c r e a s e i n s o l u t e c o n c e n t r a t i o n at the membrane s u r f a c e . I f osmotic pressure i s q u i t e s e n s i t i v e to the changes i n s o l u t e c o n c e n t r a t i o n , i t i s p o s s i b l e that an i n c r e a s e i n AP gives r i s e to p r o p o r t i o n a l i n c r e a s e i n Air so that the net d r i v i n g f o r c e , (AP - ATT) remains v i r t u a l l y constant. From Eq. ( 1 ) , then, the permeate r a t e i n the absence of g e l formatio due to osmotic pressure l i m i t a t i o n . Other phenomena, f o r example, solute-membrane i n t e r a c t i o n s may give r i s e to pressure independent permeate r a t e . Gel p o l a r i z e d u l t r a f i l t r a t i o n was r e c e n t l y analyzed f o r cross flow and u n s t i r r e d batch c e l l systems by T r e t t i n and Doshi (1980 a,b). We have shown i n these papers that the w i d e l y used f i l m theory does not p r e d i c t the l i m i t i n g f l u x a c c u r a t e l y . The o b j e c t i v e of t h i s paper i s to d e r i v e an e x p r e s s i o n f o r the permeate f l u x when the pressure independent u l t r a f i l t r a t i o n of macromolecular s o l u t i o n s i s osmotic pressure l i m i t e d . We w i l l a l s o attempt to d i s t i n g u i s h between g e l and osmotic pressure l i m i t e d u l t r a f i l t r a t i o n of macromolecular s o l u t i o n s . The e f f e c t of osmotic pressure i n macromolecular u l t r a f i l t r a t i o n has not been analyzed i n d e t a i l although many s i m i l a r i t i e s between t h i s process and reverse osmosis may be drawn. An e x c e l l e n t review of reverse osmosis research has been given by G i l l et a l . (1971). I t i s g e n e r a l l y found, however, that the simple l i n e a r osmotic p r e s s u r e - c o n c e n t r a t i o n r e l a t i o n s h i p used i n reverse osmosis s t u d i e s cannot be a p p l i e d to u l t r a f i l t r a t i o n where the c o n c e n t r a t i o n dependency of macromolecular s o l u t i o n s i s more complex. I t i s a l s o reasonable to assume t h a t v a r i a b l e v i s c o s i t y e f f e c t s may be more pronounced i n macromolecular u l t r a f i l t r a t i o n as opposed to reverse osmosis. S i m i l a r l y , because of the r e l a t i v e l y low d i f f u s i v i t y of macromolecules compared to t y p i c a l reverse osmosis s o l u t e s (by a f a c t o r of 100), conc e n t r a t i o n p o l a r i z a t i o n e f f e c t s are more severe i n u l t r a f i l t r a tion. An e a r l y work c o n s i d e r i n g osmotic pressure i n the u l t r a f i l t r a t i o n of macromolecular s o l u t i o n s was done by B l a t t , et a l . , (1970), who employed a theory which had been developed f o r cross flow reverse osmosis systems. They e s s e n t i a l l y suggested t h a t the f i l m theory r e l a t i o n s h i p given by Eq. (2) could be s o l v e d simultaneously w i t h Eq. (1) to p r e d i c t permeate r a t e s , where the

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

22.

TRETTIN

AND

Pressure-Independent UF

DOSHI

375

value of k was determined from a Leveque-type s o l u t i o n of the convective d i f f u s i o n equation n e g l e c t i n g t r a n s v e r s e v e l o c i t y .

|v | = k 1

1 w

ln

c - c cw - c p o p

(2)

Presented data were not analyzed i n terms of t h i s model, however, because i t was f e l t that macromolecular s o l u t i o n s g e n e r a l l y had very low osmotic p r e s s u r e s . Goldsmith (1971) p o i n t e d out that developed osmotic p r e s sures f o r macromolecular s o l u t i o n s were not n e c e s s a r i l y negl i g i b l e . The u l t r a f i l t r a t i o n of Carbowax 20M (polyethylene oxide) and various Dextrans was s t u d i e d i n t h i n channel and tube flow as w e l l as s t i r r e d batch c e l l h turbulen d lamina flo regimes were considered Eq. (2) and the phenomenologica p Eq (1) Rg = 0. From Eq. (1) i t was p o s s i b l e to c a l c u l a t e an average value of ATT where R , the membrane r e s i s t a n c e , AP, and e x p e r i mental f l u x Iv I were known. The average value of c could be w w e x t r a c t e d from a known osmotic pressure r e l a t i o n s h i p , and an experimental value of k_could f i n a l l y be found from Eq. ( 2 ) . Experimental values of k were compared to t h e o r e t i c a l values to estimate molecular d i f f u s i o n c o e f f i c i e n t . The d i f f e r e n c e between the experimental and the l i t e r a t u r e value of the d i f f u s i o n c o e f f i c i e n t was a t t r i b u t e d to the c o n c e n t r a t i o n dependency of v i s c o s i t y and d i f f u s i o n c o e f f i c i e n t . K o z i n s k i and L i g h t f o o t (1972) modeled the u l t r a f i l t r a t i o n of bovine serum albumin (BSA) through a r o t a t i n g d i s k . Concentrat i o n dependent v i s c o s i t y and d i f f u s i v i t y were assumed, and the one-dimensional convective d i f f u s i o n equation, which was coupled to the a p p r o p r i a t e Navier-Stokes equation, was s o l v e d n u m e r i c a l l y . Osmotic pressure data of Scachard et: a l . (1944) were used. Numerical p r e d i c t i o n of f l u x agreed very w e l l w i t h experimental r e s u l t s f o r the r o t a t i n g d i s k . T h e i r model was extended to other flow geometries, such as t u b u l a r and t h i n channel, where average values of v i s c o s i t y and d i f f u s i v i t y were used. The conv e c t i v e d i f f u s i o n equation i n t h i s case was s o l v e d through s i m i l a r i t y t r a n s f o r m a t i o n . The p u b l i s h e d data of B l a t t , _et a l . , (1970) were analyzed i n terms of the developed model but agreement was not good. M i t r a and Lundblad (1978) s t u d i e d the t h i n channel u l t r a f i l t r a t i o n of immune serum g l o b u l i n (ISG) and human serum albumin (HSA) . Data were i n t e r p r e t e d u s i n g the f i l m theory r e l a t i o n s h i p of: m

1

1

&

v

1

w

= A

In

v

(c /c ) w o

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

C3)

376

SYNTHETIC MEMBRANES: HF

AND

UF

USES

where m u l t i p l e r e g r e s s i o n techniques were employed to s o l v e f o r the value of the constants A, B, and c . The value of c was * ' w w assumed to equal the corresponding c o n c e n t r a t i o n at which the developed osmotic pressure approximately e q u a l l e d the a p p l i e d system pressure. Agreement of data w i t h the general model was not good, the c a l c u l a t e d value of A e x h i b i t i n g a 21% standard d e v i a t i o n . Large a x i a l pressure drops along the t h i n channel at the h i g h e r v e l o c i t i e s s t u d i e d may be a p a r t i a l e x p l a n a t i o n of the discrepancy. Leung and P r o b s t e i n (1979) s t u d i e d the u l t r a f i l t r a t i o n of macromolecular s o l u t i o n s i n steady s t a t e , laminar channel f l o w . The convective d i f f u s i o n equation was s o l v e d by an i n t e g r a l method. A p a r a b o l i c c o n c e n t r a t i o n p r o f i l e was assumed. The osmotic pressure r e l a t i o n s h i p of V i l k e r (1975) f o r 0.15M s a l i n e BSA s o l u t i o n s a t pH 4.5, and a e a r l y i n t e r p o l a t i n g th g e l and d i l u t e s o l u t i o n c o n c e n t r a t i o n l i m i t s were used. The determination of t h i s d i f f u s i v i t y r e l a t i o n s h i p has been o u t l i n e d i n a previous paper [ P r o b s t e i n , et a l . (1979)]. The i n t e g r a l s o l u t i o n was checked i n the l i m i t i n g case of a l i n e a r osmotic p r e s s u r e - c o n c e n t r a t i o n r e l a t i o n s h i p and constant d i f f u s i v i t y w i t h B r i a n ' s (1966) f i n i t e d i f f e r e n c e s o l u t i o n f o r reverse osmosis systems. Thin channel u l t r a f i l t r a t i o n data were acquired by Leung and P r o b s t e i n using BSA i n 0.10M acetate s o l u t i o n at pH 4.7. A discrepancy emerges i n the use of V i l k e r s osmotic p r e s sure r e l a t i o n s h i p , however. In an e a r l i e r paper, P r o b s t e i n , et a l . , (1979) determined the g e l l i n g ( s o l u b i l i t y l i m i t ) concent r a t i o n of BSA i n 0.10M acetate s o l u t i o n (pH 4.7) to be 34 g/100 cc. We have determined the value to be approximately 38.5 g/100 cc [ T r e t t i n and Doshi (1980b)]. I t i s c l e a r from F i g . 5 t h a t V i l k e r has determined osmotic pressures f o r BSA i n 0.15M s a l i n e s o l u t i o n s (pH 4.5) up to c o n c e n t r a t i o n s of 48 g/100 cc. This f i n d i n g suggests the e f f e c t of b u f f e r type i s s u b s t a n t i a l i n i n f l u e n c i n g s o l u t e s o l u b i l i t y l i m i t s and most probably s o l u t i o n osmotic pressure. Therefore, i t i s h a r d l y a d m i s s i b l e to use V i l k e r s s a l i n e b u f f e r osmotic pressure data to i n t e r p r e t the t h i n channel u l t r a f i l t r a t i o n data of BSA i n acetate b u f f e r without f u r t h e r c o n f i r m a t i o n of the e f f e c t of b u f f e r type. The preceding review has shown that although many advances have been made i n the understanding of macromolecular u l t r a f i l t r a t i o n , some very fundamental questions s t i l l remain unanswered. For i n s t a n c e , the establishment of when an u l t r a f i l t r a t i o n process i s osmotic pressure l i m i t e d or g e l l i m i t e d needs to be more c l e a r l y d e f i n e d . In macromolecular u l t r a f i l t r a t i o n s o l u t i o n osmotic pressure i s o f t e n a s t r o n g f u n c t i o n of moderate-to-high s o l u t e c o n c e n t r a t i o n (c ) due to the i n c r e a s e d importance of the second and t h i r d order v i r i a l terms i n the F l o r y equation [Brandup and Immergut (1967), B i l l m e y e r (1971)]. In t h i s event, the u l t r a f i l t r a t i o n f l u x may be l i m i t e d by the osmotic pressure and/or 1

1

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

22.

TRETTIN AND

DOSHI

311

Pressure-Independent UF

by the formation of a g e l l a y e r depending on the nature of the s o l u t e and o p e r a t i n g c o n d i t i o n s . The determination of a f l u x l i m i t i n g cause i s the primary concern of t h i s paper. T h e o r e t i c a l Development Consider the u n s t i r r e d batch c e l l geometry shown i n F i g . 1 where the general s o l u t e mass balance equation of

|£_

|v |

|£-

w

1

dt

1

2 /8y

9

D

2

W

c

dy

a p p l i e s . I t i s i m p l i c i t l y assumed i n the d e r i v a t i o n of Eq. (4) that the s o l u t i o n densit diffusio coefficien indepen dent of s o l u t e c o n c e n t r a t i o n The appropriate boundary and i n i t i a l c o n d i t i o n s are: at y = 0

(5)

;. c = c ( t ) w

f |

iv I c R = D -| w| w 9y' y -> °°, c = c

(6) w

y

=

0

(7)

for a l l t o

t

+

0 , c = C

q

for a l l y

(8)

where R = 1 - c /c p w The phenomenological equation of permeate v e l o c i t y i s | v j = MP

il-§);

A = ^-

(9) m

where ATT

=

TT

w

-

TT

(10)

p

I f osmotic pressure i s r e l a t e d to s o l u t e concentration by a cubic equation: TT = b c + b i c 0

2

+ b c

3

2

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

378

SYNTHETIC

MEMBRANES:

HF

AND

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

UF

USES

22.

TRETTIN AND DOSHI

Pressure-Independent UF

379

then ATT

B c

AP

w

[1 + a i c

+ a

w

c/]

2

where

B

= Mo

,

a i

b l - ^ R ^ b

=

n r

a 2

b

=

2

(3-3R R ) b

2

+

0

( 1 2 )

0

Our o b j e c t i v e i s to d e r i v e an e x p r e s s i o n f o r the permeate v e l o c i t y when u l t r a f i l t r a t i o n i s osmotic pressure l i m i t e d . We therefore, introduce equivalent w a l l concentration, ^ > f ° r

which the osmotic pressur the asymptotic case, as ATT approaches A P , the permeate v e l o c i t y w i l l approach zero, Eq. ( 9 ) , and from Eq. (11) we have:

1 = B c (1 + a i c + a wa wa

2

c *) wa

(13)

Equation (13) i s then the d e f i n i n g equation f o r c ^ . We w i l l use c as a c h a r a c t e r i s t i c c o n c e n t r a t i o n i n making l o c a l concentrawa t i o n dimensionless. Time, d i s t a n c e and v e l o c i t y are expressed i n dimensionless forms by a proper combination of a c h a r a c t e r i s t i c v e l o c i t y AAP and d i f f u s i o n c o e f f i c i e n t , D:

Eq. (4) may be transformed to 80 8T

80 3Z

W

(15)

Z

=

8 0 8^

where the boundary c o n d i t i o n s of Eq. (5)-(8) become "

R

w

e

w

=

all

d6)

n

z=0 e(t>0)

= 5£1 = C

17

e

W

wa

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

SYNTHETIC MEMBRANES: HF AND

380

UF USES

C

(0,z)

6

and Eq.

(9) may

0 (T,~)

=

= -°- = e c o wa

( 1 8 )

be r e w r i t t e n as

w = 1 - Be

9

wa

(1 + a i c 0 + a c wa w wa

2

2

w

I n t r o d u c i n g the s i m i l a r i t y

2

0 )

(19)

w

coordinate

1

x = Z/WT) /*

(20)

0(T,X)]

Equations (15)-(18) become [6(T,Z) =>

^

T

Z

8T

- 2 /T

0 (T,0)

U

W

R w 0

T ;

'

w

8X

8X2

- || | x=0

= 0 , 0 (T,»)

(22)

= 6

(23)

The s i m i l a r i t y t r a n s f o r m a t i o n , Eq. (20), used here i s gene r a l l y a p p l i e d to o b t a i n s m a l l time s o l u t i o n . However, i n the case of g e l p o l a r i z e d u l t r a f i l t r a t i o n , T r e t t i n and Doshi (1980 b) have used such s i m i l a r i t y t r a n s f o r m a t i o n to o b t a i n an expression f o r the l i m i t i n g permeate v e l o c i t y . We have, t h e r e f o r e , used s i m i l a r i t y t r a n s f o r m a t i o n to evaluate osmotic pressure l i m i t e d permeate v e l o c i t y . In the case of g e l p o l a r i z e d u l t r a f i l t r a t i o n , c^ = c = constant and consequently, Eq. (21) to (23) can be g

s o l v e d by c o n s i d e r i n g 0 as a f u n c t i o n of x only and by s e t t i n g w T as a constant. However, i n the osmotic pressure l i m i t i n g case considered here, c i s a f u n c t i o n of time. We can s o l v e Eq. w (21) to (23) i n the form of a power s e r i e s i n T ° * : 0 # 5

5

6 -- f ( x ) ++ fl

f

0

* f / ,+

fi(?)

2

f2(x) T

, f

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

(24)

22.

TRETTIN AND DOSHI

381

Pressure-Independent UF

then e

= i

w

^

+

i ^ >

+

...

+

(25)

where

lim

6

= f (O) = 1

(26)

0

W

->oo

T

Substituting for 0

i n Eq. (19) and r e a r r a n g i n g y i e l d s : (27)

w / T = Sifi(O) + I f y r + where 2

Bi = - (1 + B a i c + 2B a wa

2

c

3

) wa

C28)

The value of B remains to be determined. S u b s t i t u t i n g f o r 0 and w/~T i n Eq. (21) and c o n s i d e r i n g terms of c o e f f i c i e n t T° only gives 2

-2xf

! 0

- 2Bi f i ( 0 ) f

T 0

= fo"

(29)

where the boundary c o n d i t i o n s of Eq. (22)-(23) become T

-2R [ B i f i ( 0 ) ] f ( 0 ) = f o ( 0 )

(30)

0

3 1

f (°°) = 0 o

( )

f„(0) = 1

(32)

0

Equation

(29) may be i n t e g r a t e d to y i e l d 00

6 0

= 1 + Ii

2

2

exp [ 6 i f i ( 0 ) ]

/ Bl

2

exp (-5 ) d £

(33)

fi(0)

where 5 = x + 3! f!(0)

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

(34)

382

SYNTHETIC

MEMBRANES:

HF

AND

UF

USES

o r , more simply, 2(6 -l) o

/TT

where

V _w

C35)

72

Ii =

1

exp (^-^- ) e r f c

W

- . = Bi f i ( 0 ) 0

/rk

2 Considering the w a l l boundary c o n d i t i o n of Eq. (30), Eq. (35) becomes i-e

(36) R/r

1

T" '

2

In a s i m i l a r manner as p r e v i o u s l y , consider c o e f f i c i e n t s of only i n Eq. (21)

fi" +

2fi

?

(x + B i f i ( 0 ) ] + 2 f i (37)

2B

2

I i exp [-(x + 23i 2

1

fi(0)x)]

2

Considering the c o e f f i c i e n t s o f x"" / f o r the w a l l boundary cond i t i o n of Eq. (22) y i e l d s 2

-2R ( B i f i ( 0 ) + g ) = f!'(())

(38)

2

where Bl f i ( 0 ) = I /2R ; 2

f2(oo)

= o

(39)

The s o l u t i o n f o r f i i s : f i =[fi(0) + B

r I i /r? / e x p ( r ) e r f c ( r ) d r ~ ] 2

2

(40) exp

w 4

exp(-r )

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

22.

TRETTIN AND DOSHI

383

Pressure-Independent UF

where r = x + y-, and l i m f i = 0, r -> Evaluating

lim f

00

x ->

x

= fi(0) =

Ii 2R3i

x -> 0

(41)

oo

the f i r s t d e r i v a t i v e o f Eq. (40) at x = 0 gives

f (0)

= -26a f!*(()) + 32 I i A

f

exp

M*-J erfc^)

(42)

The w a l l boundary c o n d i t i o n o f Eq. (38) may be equated to Eq. (42) to y i e l d a r e l a t i o n s h i p f o r the value o f 3 namely 6

= B

2

(0)(l-R) (R-l) + 0

(43)

S u b s t i t u t i n g f o r 62 i n Eq. (27), n e g l e c t i n g T- / yields 1

w / r = 3i

fi(0)(R-D

fi(0)

/r[(R-l)+6

T

- 1

terms s m a l l e r

than

2

/

2

(44)

o

]

The dimensionless permeate v e l o c i t y w i l l be p r o p o r t i o n a l to when r:

>

y

fi(0)(R-l) [(R-D+e ] o

_

Ii(l-R) 2R 3 i [ ( R - i ) + e ]

(45)

Q

Equation (45) i s w r i t t e n i n dimensional form as

t

»

(A

D AP)

V (1-R) w [ ( R - l ) + QJ 7

2

|3i|

(46)

I f the c r i t e r i o n suggested i n Eq. (46) i s met, s o l u t e conc e n t r a t i o n at the membrane surface w i l l be approximately equal to the asymptotic v a l u e , c . The s o l u t e c o n c e n t r a t i o n d i s t r i b u t i o n wa can be d e s c r i b e d by a s i n g l e independent v a r i a b l e , x. The problem then becomes analogous to the g e l p o l a r i z e d u l t r a f i l t r a t i o n case s o l v e d i n T r e t t i n and Doshi (1980b). I n t h i s same paper, an i n t e g r a l method s o l u t i o n i s a l s o d e r i v e d . A p l o t of c a l c u l a t e d values o f V v s . 0o which s a t i s f y Eq. (36) i s g i v e n i n F i g . 2 f o r w —

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

384

SYNTHETIC

MEMBRANES:

HF

AND

UF

USES

v a r i o u s values of R. An unpublished work of V i l k e r (1975) has r e c e n t l y come to our a t t e n t i o n where a s i m i l a r concept i s p r e sented. An analogous treatment to the u n s t i r r e d batch c e l l may be performed f o r the t h i n channel system where

u ^ - | | |£ £ w' dy

D^f

-

v

1

(47)

8y2

3

and the boundary c o n d i t i o n s are at y = 0

c = c

(x)

(48)

|v | c W w y = 0 3

2-

, c> = c

C50)

for a l l x

o

0, c = c

51

for a l l y

A diagram of the t h i n channel system i s shown i n F i g . 3. Transforming Eq. (47) to dimensionless form, we f i n d

_ |9

t

z

_

w

w

3A

|i dz

=

14

(52)

3z2

where z

A Ap = — =

c / c

/ wa'

V

y

»

w

, X

=

=

| w| A~AP '

A

2

(A A P ) x D '

and assuming a J_inerarized

.

3D h A AP

axial velocity

p r o f i l e , namely,

3

The boundary c o n d i t i o n s of Eq. (48)-(51) become

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

53

< >

TRETTIN AND DOSHI

Pressure-Independent UF

Figure 3. Thin-channel crossflow system

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

385

386

SYNTHETIC

MEMBRANES:

HF AND U F

rets

C (x)

e (x,o) - *

( 5 6 )

- -

C

USES

W

wa (0,z)

=

eCA.co)

=

C

o

/

C

w

a

=

Q

^

q

Equation (19) remains unchanged except that 6 i s now a f u n c t i o n w of X i n s t e a d o f T . 2

2

w = 1 - Be 6 (1 + otic 6 + a c 0 ) wa w wa w wa * 2

I n t r o d u c i n g the s i m i l a r i t y batch c e l l problem, Eq. ( 2 0 ) ,

TT

(19)

, analogou

Equations (52), (55)-(57) become [0 (A z) => 0 (A,n)] *

i

3

n

3 A

0

-u

^ A

1

/

3

(n + w ( ^ - j

n

10

i

w " 8n

,

2

80

80

)

r t

- v Q

(59)

I

(60) n =o

0(A,O) = 0 The corresponding g e l p o l a r i z e d u l t r a f i l t r a t i o n problem, where c = c = constant, i s s o l v e d by T r e t t i n and Doshi (1980a) w g 0(A,°°) = 0 ) by c o n s i d e r i n g 0 as a f u n c t i o n o f r| o n l y . I n the osmotic p r e s sure l i m i t e d case, as we have done f o r the u n s t i r r e d batch c e l l , we expand 0 i n the f o l l o w i n g form: e =

g 0

( n )

+

w

( 6 1 )

Q

( 6 2

+

_

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

(63)

22.

TRETTIN AND DOSHI

e

= i

w

Pressure-Independent UF

^

+

^

+

+

...

387

(

6

4

)

where l i m 6 = g (0) = 1 X -> 00 S u b s t i t u t i n g f o r 0 i n Eq. (19) and rearranging y i e l d s w

w X

l / 3

0

= S i g i ( 0 ) + - j ^ y + ... 1

65

( >

66

< >

3

S u b s t i t u t i n g f o r 0 and w A / i n Eq. (59) and c o n s i d e r i n g terms of c o e f f i c i e n t A onl give 0

- n

2

go

1

-(f)

l/3

B i giCO)

T

go = go"

(67)

where the boundary c o n d i t i o n s of Eq. (60)-(62) become 1/3

-(f)

P i g i ( 0 ) go(0) R = go'(0)

g

( a 3 ) 0

= G

(68)

(69)

O

go(0)

?

= 1

( °)

Equation (67) may be i n t e g r a t e d using Eq. (69)-(70) to y i e l d

the boundary c o n d i t i o n s o f

0 - 1

T 1 1

2

"/ exp [- (\ n + W n)] d n 0 J w 3

tt

(71)

where f

- W R = g CO) = I i w

0

( 7 2

Considering the w a l l boundary c o n d i t i o n of Eq. ( 6 8 ) , Eq. (71) becomes

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

)

388

SYNTHETIC

MEMBRANES:

HF AND U F

USES

1 W =

0 0

w

R

(73)

J

exp [- (y n

3

+ w

n ) ] dn

w

0

-1/3

Without c o n s i d e r i n g c o e f f i c i e n t s of A ' , we may develope an approximate r e l a t i o n s h i p d e f i n i n g the parameters which i n fluence the rate at which an asymptotic w a l l concentration i s reached. From Eq. (64)

e =

...

w

for c y c , w ^ wa'

Therefore,

W or

( 7 4 )

3

simply,

x

D

»




w

,,

h(AAP)3

(76)

-[BTJ

;

From Eq. (76) i t can be seen that the membrane pure solvent f l u x (A AP) has a l a r g e e f f e c t i n determining the required chann e l length to reach an asymptotic w a l l concentration ( c ^ ^ a ^ * c

W

since

= ^

u

>

, i t may be seen that hydrodynamic shear at the

membrane surface i s a l s o an important f a c t o r and Eq. (76) becomes:

°

2

(77)

Y

'w 3 (A AP) When the c r i t e r i o n of Eq. (46) f o r the u n s t i r r e d batch c e l l , or Eq. (77) f o r the cross flow p a r a l l e l p l a t e system, i s s a t i s f i e d , i t i s p o s s i b l e to make the s i m p l i f y i n g assumption o f constant w a l l concentration (c c ). Consequently, Eq. (36) , w ^ wa becomes

y

3

7

(78)

where V = w /if w

= Iv I ( 4 t / D ) V w

2

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

(79)

22.

TRETTIN AND DOSHI

Pressure-Independent UF

389

f o r the u n s t i r r e d batch c e l l and Eq. (73) becomes 00

c —- c wa -^-f-

= w

/

w

exp [ - ( | n

3

+ w

C80)

n)] d n

w

where h x D

W = v w w 1

1/3

(81)

2

1

f o r the cross flow p a r a l l e l p l a t e system. An i n t e g r a l method s o l u t i o n of Eq. (78) has been d e r i v e d by T r e t t i n and Doshi (1980b) and may be represented as

w

c -c wa o c -c wa p

Ki

c -c wa p c -c o p

(82)

where K i = 2 m / ( n i + 1)

(83)

and

ni =

/c - c \ wa _p_] Ic - c V o p

//c - c \ 2 ^c -c [ ( wa p' + 8 wa p [C - c o p Vo °p

1/2 1

(84)

C

S i m i l a r l y , the s o l u t i o n of Eq. (80) f o r the p a r a l l e l p l a t e system has been d e r i v e d by T r e t t i n and Doshi (1980a) and i s represented as c -c wa o c -c wa p

w = w

K

2

c -c wa p c -c o P

1/3

(85)

where K

2

2

= 2n /(n 2

2

+ D O * + 2)

(86)

and 1/2 C

n

2

=

+ 24

C

wa p\ c - c ° P,

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

(87)

390

SYNTHETIC MEMBRANES:

HF AND U F

USES

In both i n t e g r a l method s o l u t i o n s the value o f D and s o l u t i o n density are assumed constant. A d d i t i o n a l l y , as shown i n T r e t t i n and Doshi (1980a, b ) , both i n t e g r a l method s o l u t i o n s agree very w e l l w i t h t h e i r corresponding exact s o l u t i o n s . Note that i f one wants to c a l c u l a t e o r W^, i n t e g r a l method r e s u l t s , Equations (82)-(87) a r e convenient w h i l e f o r the c a l c u l a t i o n o f the asymptotic w a l l c o n c e n t r a t i o n , > exact s o l u t i o n , Equations c

w a

(78)-(81) are convenient. In u n s t i r r e d batch c e l l u l t r a f i l t r a t i o n , the value o f |v | i s t y p i c a l l y very s m a l l and t h e r e f o r e d i f f i c u l t to measure i n s t a n t a n e o u s l y . I t i s p o s s i b l e , however, to a c c u r a t e l y measure eluded permeate volume (AV) as a f u n c t i o n o f time. Therefore, upon i n t e g r a t i o n , Eq. (79) becomes

AV

= 2

t

w

where A

= the t r a n s p o r t s u r f a c e area o f membrane

T = time of permeat c o l l e c t i o n T AV = / A o

t

|v^| dt = eluded permeate volume i n time T.

When accumulated permeate volume i s measured a t three consecutive times ( T i , T 2 , T ) , i t i s p o s s i b l e to w r i t e 3

A V A V

2 3

- A Vi - A Vi

1

=

2

T2 / T3 / 1

2

1

T1 / 1

- Ti /

2

.

(

2

^

J

I f sample times are s e l e c t e d such t h a t T2 = 2 T i , T3 = 4Ti an accuracy of data may be checked:

In a l l batch c e l l experiments, data a c c e p t a b i l i t y l i m i t s were e s t a b l i s h e d as ± 3% o f the 0.4142 v a l u e . Acquired data which were not w i t h i n these l i m i t s were d e l e t e d . As o u t l i n e d i n T r e t t i n and Doshi (1980b), a c o r r e c t i o n must be made to the e x p e r i m e n t a l l y measured value o f AV t o a d j u s t f o r the permeate c o l l e c t e d d u r i n g the i n i t i a l p e r i o d o f f i l t r a t i o n when c < c o r c . Although the d u r a t i o n o f t h i s r e g i o n i s w wa g s m a l l , i t occurs at a time when permeate f l u x i s g r e a t e s t and i s &

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

22.

TRETTIN AND DOSHI

Pressure-Independent UF

t h e r e f o r e necessary to c o r r e c t f o r . permeate may be adjusted as f o l l o w s

AV =

AV exp

391

Experimentally c o l l e c t e d

91

AV corr

C )

S u b s t i t u t i n g f o r AV i n Eq. (88) and r e a r r a n g i n g y i e l d s AV —iff =2A V (D/4) / + 1/ 2 t w R

1

2

1

(92)

2

AV (1/T / ) corr

or AV exp

172

_T

corr

Jlim

T By p l o t t i n g

AV T / 2 vs. 1/T / 1

2

T

and e x t r a p o l a t i n g t o i n f i n i t e

time

(T), we can minimize the e f f e c t s o f the i n i t i a l r e g i o n where c^ 1

2

i s not constant, and determine the t r u e value o f AV/T / [or ( A V / T / ] ^ ) as p r e d i c t e d by Eq. (88). 1

2

I t i s important to d i g r e s s momentarily t o d i s c u s s i n f u r t h e r AV d e t a i l the i n t e r p r e t a t i o n of the ? y ? v s . 1/T / p l o t . Since 1

2

T

both models presented i n T r e t t i n and Doshi (1980a, 1980b) were d e r i v e d e x p l i c i t l y f o r the constant w a l l c o n c e n t r a t i o n boundary c o n d i t i o n , and i n p a r t i c u l a r f o r g e l p o l a r i z a t i o n , the q u e s t i o n a r i s e s as to the d i f f e r e n c e between g e l p o l a r i z e d behavior and constant w a l l c o n c e n t r a t i o n (osmotic pressure e q u i v a l e n t ) behavi o r . The major s i m i l a r i t y between the two processes o f g e l p o l a r i z e d and osmotic pressure e q u i v a l e n t u l t r a f i l t r a t i o n i s that the s o l u t e c o n c e n t r a t i o n a t the membrane s u r f a c e i s constant w i t h respect to time, as i n the u n s t i r r e d batch c e l l case, o r a x i a l A V

ex

p o s i t i o n , as i n the cross flow case. Therefore, a p l o t o f • fy\ vs. w i l l be l i n e a r i n the u n s t i r r e d batch c e l l case. The major d i f f e r e n c e between the two processes i s t h a t i n g e l p o l a r i z e d u l t r a f i l t r a t i o n , not only i s the w a l l c o n c e n t r a t i o n constant but i t i s a l s o independent of a p p l i e d pressure. This i s n o t true of osmotic pressure e q u i v a l e n t u l t r a f i l t r a t i o n where w a l l concenAV T

e

t i o n i s pressure dependent.

Therefore, i n a

t

'1/S?

1

VS* 1/T /

p l o t , g e l p o l a r i z a t i o n i s i n d i c a t e d by an i n t e r s e c t i o n o f

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

2

392

SYNTHETIC

MEMBRANES:

HF AND U F

USES

AV exp, v a r i a b l e AP l i n e s (at constant c ) a t the same value o f o LT Ti / 2 J l i m . A process which i s osmotic pressure l i m i t e d w i l l i n t e r s e c t AV at a d i f f e r e n t value o f i / ^ f o r each a p p l i e d pressure t e s t e d . As can be seen, the u n s t i r r e d batch c e l l technique represents a unique method f o r c h a r a c t e r i z i n g macromolecular s o l u t i o n s as t o the pressure range i n which g e l p o l a r i z a t i o n occurs. One must be cautious i n using the batch c e l l technique, however, t o s e l e c t AP increments which are l a r g e enough to cause a d i s c e r n i b l e change i n the value o f c This i s p a r t i c u l a r l y t r u e i n cases wa where s o l u t i o n osmotic pressure i s a s t r o n g f u n c t i o n o f concentration. With the u l t r a f i l t r a t i o n o f macromolecular s o l u t i o n s i n cross flow systems suc u s u a l l y the procedure t s t a t e . Therefore, Eq. (81) may be i n t e g r a t e d to give A / z

X

T

2

D h L

= 1.5

1/3

1/3

2

D

s W

1.5 where

(94)

(95)

Iv wI *= average permeate f l u x Q = s L v = average v o l u m e t r i c permeate r a t e p w An analogous r e l a t i o n s h i p to Eq. (93) can be w r i t t e n t o account f o r i n i t i a l e f f e c t s where c ^ c : 1

and

1

l

1

w
0.01 g/cc). The l i t e r a t u r e contains numerous experimental determinations of the mutual d i f f u s i o n c o e f f i c i e n t of BSA i n v a r i o u s b u f f e r s o l u t i o n s [Creeth (1952), Charlwood (1953), K e l l e r , et a l . (1971), Doherty and Benedek (1974), P h i l l i e s , _et a l . (19 76)]. The range of reported d i f f u s i o n c o e f f i c i e n t at low c o n c e n t r a t i o n i s D = 5 . 5 — 7.Ox 10 cm /sec. However, values at h i g h e r concentrat i o n s show considerable s c a t t e r as p o i n t e d out by Shen and P r o b s t e i n (1977). P h i l l i e s , e t a l . (1976) have s t u d i e d BSA s o l u t i o n d i f f u s i v i t y i n 0.15M NaCl aqueous systems over the pH range of 4.3 — 7.6. Their data taken w i t h i n the h i g h e r pH and concent r a t i o n ranges have been i n t e r p r e t e d by P r o b s t e i n , e t a l . (1979) to y i e l d an average value of 6.7 x 10 cm /sec. Both Creeth (1952) and Charlwood (1953) have reported the d i f f u s i v i t y o f d i l u t e BSA_solutions to be w i t h i n the range of 6.6 x 10 cm /sec to 7.1 x 10 cm /sec at 25°C. T h e i r data a l s o show that the e f f e c t s of pH and b u f f e r type upon the d i f f u s i o n c o e f f i c i e n t are n e g l i g i b l e . The value of the d i f f u s i o n c o e f f i c i e n t f o r 0.15MNaCl BSA 7

2

7

2

7

7

2

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

2

394

SYNTHETIC

MEMBRANES:

HF AND U F

7

USES

2

s o l u t i o n (pH 7.4) was determined t o be 6.91 x 10 cm /sec from our u l t r a c e n t r i f u g e experiments a t 23.5°C. I t has been shown by T r e t t i n and Doshi (1980b) t h a t t h i s value i s reasonably constant over a wide range o f c o n c e n t r a t i o n i n the u l t r a f i l t r a t i o n of s a l i n e BSA s o l u t i o n s . Batch c e l l experiments were performed i n s t a i n l e s s s t e e l pressure c e l l s manufactured by the Gelman F i l t e r Company. The average membrane area e q u a l l e d 15.62 cm and the t o t a l c e l l volume was approximately 230 cm . The batch c e l l s were a f f i x e d to a support i n t e g r a l w i t h the b u i l d i n g s t r u c t u r e t o prevent extraneous v i b r a t i o n . The room temperature was c o n t r o l l e d w i t h i n the range of 21-24°C. T o t a l permeate volume was g r a v i m e t r i c a l l y measured as a f u n c t i o n of time f o r p e r i o d s as l o n g as 24 hours. C e l l p r e s sure was v a r i e d from 2.76 x 1 0 - 17.24 x 1 0 N/m (40 t o 250 psi). The m a j o r i t y of experiment t a t e membranes (5,000 — Systems. Several experiments were a d d i t i o n a l l y conducted u s i n g n o n c e l l u l o s i c (X-117) and p o l y s u l f o n e membranes a l s o from UOP. Both n o n c e l l u l o s i c membranes performed as w e l l as the c e l l u l o s e acetate membrane, y i e l d i n g s o l u t e r e j e c t i o n s g r e a t e r than 95%. 2

3

5

5

2

R e s u l t s and D i s c u s s i o n In T r e t t i n and Doshi (1980b), a p l o t o f 0.15M s a l i n e BSA s o l u t i o n data (pH 7.4) was presented showing that above 6.89 x 10 N/m a p p l i e d p r e s s u r e , a g e l l a y e r may have formed upon the membrane s u r f a c e . This graph has been reproduced i n F i g . 4 of t h i s paper w i t h a d d i t i o n a l data taken at 2.76 x 1 0 N/m and 4.14 x 1 0 N/m . At c e l l pressures o f 6.89 x 1 0 N/m o r g r e a t e r , the presence of g e l p o l a r i z a t i o n (pressure independence) i s i n d i c a t e d AV by the i n t e r s e c t i o n o f t / ? v s . 1/T / p l o t s as T -> f o r two 5

2

5

5

2

5

1

2

2

2

00

T

d i f f e r e n t pressures at constant b u l k s o l u t i o n c o n c e n t r a t i o n . When the data a t lower pressures are examined, they do not i n t e r s e c t AV

at the same value of L

as the h i g h e r pressure data.

It is

—I l i m

i n t e r e s t i n g to note, however, t h a t the lower pressure data p l o t s are l i n e a r , i n d i c a t i n g constant w a l l c o n c e n t r a t i o n . The w a l l c o n c e n t r a t i o n i n t h i s case corresponds approximately to the osmotic pressure e q u i v a l e n t (c ) of the a p p l i e d p r e s s u r e . Osmotic pressure l i m i t e d u l t r a f i l t r a t i o n data were analyzed by u s i n g Eq. (92) and the osmotic pressure data o f V i l k e r (1975) f o r 0.15M S a l i n e BSA s o l u t i o n s at pH 7.4. V i l k e r s data are reproduced i n F i g . 5 f o r BSA i n both 7.4 and 4.5 pH 0.15M s a l i n e s o l u t i o n . The comparison between theory and experiment i s q u i t e good as shown i n Table I where the value o f D was taken as 6.91 x 10 cm /sec. T

7

2

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

TRETTIN AND DOSHI

22.

A- 10.34*10 N/m O- 6 89x10 N/m •-4 14x10 N/m V-2.76x10 N/m 5

s

2

--'J C=1 03g/100cc

2

s

s

395

Pressure-Independent UF

Q

2

2

. - C=1.03g/100cc o

J7-

o

- '

1000 -f

----O-(c =2.17 0

___--o-

^

A-\ g __

/100cc

C=2 08 g/IOOcc ^ - — C=5 15g/100cc 7

0

0

- - - -O^ "

- - A- - -

_

C=5 10g/100cc 0

C ^5 08g/100cc 0

6 8 (1/T ) xio (sec-V ) 1/2

3

2

Figure 4.

Unstirred batch cell UF of 0.15M NaCl BSA solution (T = 21 °-24°C, pH 7.4) at various solute concentrations and applied pressures

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

396

SYNTHETIC

MEMBRANES:

HF AND U F

USES

Vincent L Vilker

Figure 5.

Solution osmotic pressure vs. solute concentration: 0.15M NaCl BSA solution (21)

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

22.

TRETTIN AND DOSHI

Pressure-Independent UF

397

TABLE I 0.15M SALIN

c

c

[N/m ]

c wa [g/lOOcc]

Experimental [AV/T / ] lim [mL-sec / J

AP x l O

o P [g/lOOcc] [g/lOOcc]

2

- 5

1

2

-1

2

Theoretical [AV/T / ],. lim [mL-sec / ] 1

2

-1

2

* R a

1.030

0.0033

2.76

40.45

0.1137

0.1127

0.989

1.030

0.0042

4.14

44.20

0.1248

0.1164

0.931

2.080

0.0058

2.76

40.45

0.0792

0.0752

0.949

2.140

0.7090

2.76

40.45

0.0897

0.0917

1.02

2.170

0.3472

4.14

44.20

0.0880

0.0847

0.964

5.080

0.0603

4.14

44.20

0.0455

0.0461

1.01

1

2

theoretical [AV/T / ! . 'lim experimental [ A V / T / ] . * lim 1

2

n

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

398

SYNTHETIC

MEMBRANES:

HF

AND

UF

USES

In order t o add i n s i g h t i n t o the time r e q u i r e d to reach an asymptotic w a l l c o n c e n t r a t i o n i n the batch c e l l , we can c a l c u l a t e the value o f t from Eq. (46).

t

V (1-R) w

» (A

AP)

2

(46)

I Si I[(R-i) + e ] o

where we have assumed the value of R t o equal 0.990. mate r e l a t i o n s h i p o f 4

2

1.42 x I O c - 8.96 x 1 0 c 25 £c< 40 g/100 cc

2

The approxi-

3

+ 17.74 c , (97)

2

where TT = [N/m ], c = [g/100 c c ] i s used to c a l c u l a t e | 3 i | Table I , we f i n d 6 = 2.5

,

0

The c a l c u l a t e d value o f 5.0 x 10

9

Fig

,

w

i s found to equal 4.20, and A =

i s specified.

Therefore,

N-sec t

»

(98)

0.264 seconds

which i s indeed a very short time p e r i o d t o reach the asymptotic w a l l c o n c e n t r a t i o n a t the membrane s u r f a c e . V i l k e r s pH 7.4 data were l i n e a r l y e x t r a p o l a t e d t o h i g h e r pressures where we have experienced g e l p o l a r i z a t i o n . At 6.89 x 1 0 N/m , the e x t r a p o l a t i o n i n d i c a t e s a value o f c equal t o 54 g/100 cc. This i s i n wa reasonable agreement w i t h our, and K o z i n s k i and L i g h t f o o t ' s (1972), determination of 58.5 g/100 cc ( g e l concentration) cons i d e r i n g the accuracy o f the e x t r a p o l a t e d value and the r e l a t i v e i n s e n s i t i v i t y of the model t o s m a l l changes i n c » The cross f l o w , t h i n channel data o f P r o b s t e i n , e t a l . , (1978) and M i t r a and Lundblad (1978) were analyzed i n terms o f the osmotic pressure e q u i v a l e n t model u s i n g V i l k e r s osmotic pressure data f o r 0.15M S a l i n e BSA s o l u t i o n s (pH 7.4). Although M i t r a and Lundblad d i d not study BSA d i r e c t l y , but r a t h e r human serum a l bumin (HSA), i t was f e l t that s u f f i c i e n t s i m i l a r i t y e x i s t e d between the two s o l u t e s that an approximate comparison u s i n g BSA parameters could be made [Scatchard, e t a l . (1944)]. Data were i n t e r p r e t e d t h e o r e t i c a l l y u s i n g the r e l a t i o n s h i p o f Eq. (94). I n the a n a l y s i s of P r o b s t e i n , e t a l . , data, the c i t e d values o f h = 0.19 cm (channel h a l f width) and L = 43 cm (channel length) were used. S i m i l a r l y , i n the a n a l y s i s o f M i t r a and Lundblad s 0.15M S a l i n e HSA s o l u t i o n (pH 6.9) data, the c i t e d values of h = 0.019 cm and L = 76 cm were used. The value o f D was taken to be 6.91 x 10 cm /sec i n a l l c a l c u l a t i o n s and s o l u t e r e j e c t i o n at the ?

5

2

wa

?

f

7

2

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

22.

TRETTIN AND

DOSHI

399

Pressure-Independent UF

membrane s u r f a c e was assumed to be complete. The i n t e r p r e t a t i o n of P r o b s t e i n , et a l . and M i t r a and Lundblad s data are shown i n Tables I I and I I I , r e s p e c t i v e l y . The data of M i t r a and Lundblad which were a c q u i r e d at a x i a l v e l o c i t i e s above 65.56 cm/sec were not considered due to h i g h pressure drops along the t h i n channel length. I t i s i n t e r e s t i n g to note i n Table I I t h a t , although theor e t i c a l p r e d i c t i o n of f l u x agrees w e l l w i t h experimental values at a p p l i e d pressures above 1.0 x 10 N/m , at lower pressures experimental f l u x i s s u b s t a n t i a l l y over p r e d i c t e d by theory. This o b s e r v a t i o n may be e x p l a i n e d i n terms of the approximate r e l a t i o n s h i p of T

5

D x

»

3(A

2

2

W

Y

w AP)

w

L*

3

(77)

w

At low pressures and h i g h a x i a l v e l o c i t i e s , the r a t i o of

—^p)T

i s l a r g e , and t h e r e f o r e longer a x i a l d i s t a n c e s are r e q u i r e d to reach an asymptotic w a l l c o n c e n t r a t i o n . When these i n i t i a l d i s tances, where c^ < c > are a p p r e c i a b l e , the osmotic pressure wa

e q u i v a l e n t model does not apply and the i n t e g r a l method or numeri c a l technique employed by Leung and P r o b s t e i n (1979) may have to be used. I t i s shown by the 0.689 x 10 N/m data i n Table I I that p r o g r e s s i v e l y b e t t e r agreement w i t h theory i s obtained as shear r a t e i s decreased. This o b s e r v a t i o n i s c o n s i s t e n t w i t h Eq. (77). In Table I I I , experimental f l u x i s c o n s i s t e n t l y o v e r p r e d i c t ed t h e o r e t i c a l l y by approximately 5%. This discrepancy may be due to the use of BSA s o l u t i o n parameters (D, TT) to i n t e r p r e t HSA s o l u t i o n data. Previous workers [Shen and P r o b s t e i n (1977, 1979), Probs t e i n , et a l . (1978, 1979)] have i n t e r p r e t e d g e l p o l a r i z a t i o n of BSA s o l u t i o n s to occur between 2.76 x 10 and 4.14 x 10 N/m app l i e d system pressure based upon f l u x _vs. pressure p l o t s . Our batch c e l l work has shown that g e l p o l a r i z a t i o n of s a l i n e BSA s o l u t i o n s does not occur at pressures below 6.89 x 10 N/m . This apparent discrepancy may be r e s o l v e d i n the f o l l o w i n g manner. In F i g . 6, we p l o t the value of W , which i s d i r e c t l y prow p o r t i o n a l to f l u x , vs_. AP, the a p p l i e d pressure. The value of W^ i s c a l c u l a t e d from Eq. (94) f o r the t h i n channel system u s i n g the a p p r o p r i a t e value of c ^ at each s p e c i f i c a p p l i e d pressure. 5

2

5

5

5

2

2

a

1

The value of c i s determined from V i l k e r s s a l i n e BSA s o l u t i o n wa data (pH 7.4). In F i g . 6 i t can be seen that at low AP, the d W w value of ~j~"j£p i s l a r g e and s h a r p l y decreases to a s m a l l value at

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

400

SYNTHETIC

MEMBRANES:

HF AND U F

USES

TABLE I I THIN CHANNEL UF OP (pH

7.4) -

0.15M

S A L I N E BSA

PROBSTEIN,

SOLUTIONS

e t a l . (1978)

Experimental c

100

o [g/100 c c ] 1.74

L*

[cm] 0.490

AP

xi0" 2

[N/m ] 2.76

?

c wa [g/100 40.34

cc]

4

|v

[cm/sec]

| xlO w [cm/sec]

34 5

6.38

1

1

theoretical

Iv

| xlO" w [cm,/ s e c ] 1

5 .87

R a 0.920

1,76 1.78

4.19

1.80 1.87

0.075

1. 74

2.13

2.07

3.67

4,.01

1.09

5,.8

3.04

3 .14

1.03

34 .5

6.10

5.68

0.931

1,76

23 .0

4.71

4 .93

1.05

1.80

11.5

3.67

3..88

1.06

5 ,8

3.04

3 .04

1.00

1 ,87

0.325

1. 74

6.53

1.38

37.33

1.10

11 .5

34..5

5.58

5..36

0.961

•!.. 76

23.0

4.56

4..66

1.02

1.78

17..3

4.06

4..22

1.04

1.80

11..5

3.60

3..66

1.02

5.1I

2.96

2..86

0.966

17.,3

3. 79

4.,08

1.08

11..5

3.33

3.,53

1.06

5 A]

3.04

2.,77

0.911

34.,5

3.60

4.,81

1.34

23..0

3.25

4.,18

1.29 1.20

L.87

1.00

1.78

6.82

1.03

32.83

30.50

1.80 1-87

2.15

i . 74

60.0

1.76

0.689

26.00

1.78

17..3

3.15

.i..78

1.80

11..5

2.90

3..28

1.13

5..8

2.40

2. 57

1.07

1.87

9.10

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

TRETTIN AND DOSHI

22.

Pressure-Independent UF

401

TABLE I I I THIN CHANNEL UF OF 0.15M SALINE HSA SOLUTIONS (pH 6.9)-MITRA AND LUNDBLAD (1978), AP =- 1.72 x l O N/m , c = 35.33 g/100 cc 5

c

2

Experimental 1 xlO

Theoretical | xlO"

4

o

g/100 cc]

[cm/sec J

3.83

33.70

6.25

6.95

1.11

A > 5

33.70

5.63

6.23

1.11

6.05

33.70

5.00

5.30

1.06

7.83

33.70

4.17

4.43

1.06

9.43

33.70

3.54

3.8 3

1.08

3.25

49.86

8.25

8.63

1.05

4.66

49.86

7.29

7.09

0.973

6.75

49.86

5.00

5.61

1.12

8.66

49.86

4.58

4.68

1.02

10.63

49.86

3.92

3.94

1.01

13.41

49.86

2.92

3.13

1.07

3.44

65.56

9.38

9.18

0.979

4.09

65.56

8.33

8.36

1.00

7.12

65.56

6.46

5.92

0.916

9.25

65.56

4.79

4.86

1.01 1.04 Av

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

402

SYNTHETIC

5

MEMBRANES:

HF AND U F

USES

2

values of AP above 3.0 x 1 0 N/m . This behavior i s c h a r a c t e r i s t i c o f a c t u a l experimental p l o t s . In f a c t , the d i f f e r e n c e i n p r e d i c t e d W between AP values of 2. 76 x 1 0 and 4.14 x 1 0 N/m w i s only 5%. I t i s our c o n t e n t i o n that a p l o t o f f l u x v s . AP does not n e c e s s a r i l y i n d i c a t e the presence o f g e l p o l a r i z a t i o n a t the p o i n t where f l u x appears t o become independent o f a p p l i e d p r e s sure. The s m a l l f l u x change behavior as a f u n c t i o n o f pressure may be due s o l e l y to the s o l u t i o n osmotic p r e s s u r e . The pressure range o f 2.76-4.14 x 1 0 N/m i s too narrow to y i e l d an accurate i n t e r p r e t a t i o n of g e l p o l a r i z a t i o n w i t h an average e r r o r l e s s than d W w 5%. Table IV gives the c a l c u l a t e d value o f as a f u n c t i o n of 5

5

5

2

2

AP f o r v a r i o u s values of C . The e x p e r i m e n t a l l y observed behavior q

of h i g h c o n c e n t r a t i o n s o l u t i o n s reaching a p l a t e a u r e g i o n a t s m a l l e r values o f AP a i s e x p l a i n e d by the f a c t t h a t the value o f ^ ^

decreases ( a t

constant AP) as the s o l u t i o n c o n c e n t r a t i o n i n c r e a s e s . Conclusions I t i s t h e o r e t i c a l l y shown f o r the u n s t i r r e d b a t c h c e l l t h a t , i n l i m i t i n g cases, the assumption o f constant w a l l (membrane) conc e n t r a t i o n w i t h respect to time may be made even i n the absence of g e l formation. Although the assumption of constant w a l l conc e n t r a t i o n i s s i m i l a r i n both g e l and osmotic pressure l i m i t e d u l t r a f i l t r a t i o n , i t i s important t o recognize that i n g e l p o l a r i z e d u l t r a f i l t r a t i o n , w a l l c o n c e n t r a t i o n i s a l s o pressure independent s i n c e i t corresponds t o the s o l u t e s o l u b i l i t y l i m i t . This i s not the case i n osmotic pressure l i m i t e d u l t r a f i l t r a t i o n where c^ i s approximately equal to the c o n c e n t r a t i o n a t which the developed osmotic pressure at the membrane s u r f a c e equals the a p p l i e d system p r e s s u r e . C r i t e r i a are presented — Eq. (46) f o r the u n s t i r r e d batch c e l l and Eq. (77) f o r the p a r a l l e l p l a t e system — to e s t a b l i s h the v a l i d i t y o f the constant w a l l concent r a t i o n (osmotic pressure e q u i v a l e n t ) assumption i n osmotic p r e s sure l i m i t e d u l t r a f i l t r a t i o n . When the assumption o f constant w a l l c o n c e n t r a t i o n i s j u s t i f i e d , data f o r the u n s t i r r e d batch c e l l and t h i n channel systems may be i n t e r p r e t e d using models presented i n T r e t t i n and Doshi (1980a, 1980b). Such an a n a l y s i s i s performed where agreement i s shown to be very good between theory and osmotic pressure l i m i t e d u l t r a f i l t r a t i o n experiments. I t i s f u r t h e r shown t h a t the c u r r e n t p r a c t i c e o f p l o t t i n g permeate f l u x vs. AP i n macromolecular c r o s s - f l o w u l t r a f i l t r a t i o n may l e a d to s e r i o u s m i s i n t e r p r e t a t i o n of g e l p o l a r i z a t i o n . I t i s t h e r e f o r e recommended that s o l u t i o n s be s t u d i e d i n the u n s t i r r e d

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

22.

TRETTIN AND DOSHI

403

Pressure-Independent UF

PRE-GEL REGION

GEL POLARIZATION REGION

C

0

=1.0g/KX) cc

Co =2.0g/KX) cc

C =4.0g/100cc o

,

—, 1.0

20

,

(

30

,

4.0 5.0 A P*10' (N/m ) 5

Figure 6.

W

w

, 6.0

7.0

2

vs. AP thin-channel crossflow system. Values of C from Figure 5 for various applied pressures.

w a

calculated

TABLE IV

J |-

VERSUS

AP ~ THIN CHANNEL SYSTEM (FROM FIG. 6)

AP x l 0 ~ [N/m ] 2

5

d AP (c = 1.0 g/100 cc.) o

d Ap (c = 2.0 g/100 cc) o

d A? (c = 4.0 g/100 cc) o

0.58

1.15

1.00

0.90

L.00

0.62

0.55

0.45

1.65

0.37

0.31

0.26

2 60

0.22

0.18

0.16

4.45

0.10

0.09

0.08

6.89

0.07

0.06

0.05

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

404

SYNTHETIC

MEMBRANES:

HF

AND

UF

USES

batch c e l l p r i o r to study i n c r o s s - f l o w systems i n order to determine the pressure at which g e l p o l a r i z a t i o n a c t u a l l y occurs. In previous work, pressure independent f l u x i s assumed to be due to the presence of g e l p o l a r i z a t i o n even at low p r e s s u r e s . Probably, the g e l p o l a r i z a t i o n i s the exception r a t h e r than the r u l e i n most i n d u s t r i a l - t y p e a p p l i c a t i o n s . Obviously, more care must be taken i n s o l u t e and s o l u t i o n c h a r a c t e r i z a t i o n w i t h regard to the i n t e r p r e t a t i o n of u l t r a f i l t r a t i o n data. Acknowled gment s The authors express t h e i r g r a t i t u d e to the member companies of The I n s t i t u t e of Paper Chemistry f o r t h e i r support of the graduate program. P o r t i o n s of t h i s work were used by one of the authors (DRT) as p a r t i a l f u l f i l l m e n t f th requirement f o th Ph.D degre at The I n s t i t u t e of Pape Nomenclat ure A A^, Bo b

= membrane c o e f f i c i e n t = — — u R

i— / \N-sec / ^ = membrane t r a n s p o r t s u r f a c e area (cm ) m

2

3

= constant as d e f i n e d by Eq. (13) (cm /g) = osmotic pressure constant as d e f i n e d by Eq. / N-cm \

(11)

bi

= osmotic pressure constant as d e f i n e d by Eq.

(11)

b2

= osmotic pressure constant as d e f i n e d by Eq. /N /fcm , \

3

(h

•

W ) 3N

*W c D d^ h I i , I2 Ki K2 k k L ni n2

= = = = = = = = = = = =

(11)

3

) 3

s o l u t e c o n c e n t r a t i o n (g/cm ) unless otherwise noted s o l u t e d i f f u s i o n c o e f f i c i e n t (cm /sec) h y d r a u l i c diameter (cm) channel h a l f h e i g h t (cm) constants of i n t e g r a t i o n dimensionless constant d e f i n e d by Eq. (92) dimensionless constant d e f i n e d by Eq. (95) mass t r a n s f e r c o e f f i c i e n t (cm/sec) average mass t r a n s f e r c o e f f i c i e n t (cm/sec) channel l e n g t h (cm) dimensionless constant d e f i n e d by Eq. (93) dimensionless constant d e f i n e d by Eq. (96) 2

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

22.

TRETTIN

Q

Pressure-Independent UF

DOSHI

405

= S L |V | = average v o l u m e t r i c permeate r a t e (cm /sec) W . w = x + —

P

w

r „ R

AND

_ theoretical flux = r a t i o of : ^ • -•, experimental f l u x

a

d^p R

= Reynolds number = e

y

R

= solute rejection

Sc 5

c o e f f i c i e n t = 1- c /c p w = Schmidt number = y/Dp = w i d t h of membrane (cm)

Sh

= average Sherwoo

t T u

|v^|

= = = = =

|v^|

= permeate v o l u m e t r i c f l u x (cm/sec)

V

w

= dimensionless p o s i t i v e f l u x constant f o r batch c e l l [Eq. (91)] = dimensionless p o s i t i v e permeate f l u x constant f o r t h i n channel [Eq. (94)] = dimensionless permeate f l u x d e f i n e d by Eq. (16)

x x y

= a x i a l d i s t a n c e coordinate (cm) = s i m i l a r i t y coordinate d e f i n e d by Eq. (22) = t r a n s v e r s e d i s t a n c e coordinate (cm)

z

= dimensionless t r a n s v e r s e d i s t a n c e d e f i n e d by Eq. (16)

J

kd

W

time (sec) time p e r i o d (sec) a x i a l v e l o c i t y (cm/sec) average a x i a l v e l o c i t y (cm/sec) average permeate v o l u m e t r i c f l u x (cm/sec)

Greek L e t t e r s oti, a 2

= osmotic pressure constants d e f i n e d by Eq. (13) cc

3i Ti> 6 5 ri 6

T2

(

2

cc

g constant d e f i n e d by Eq. (30) osmotic pressure v i r i a l c o e f f i c i e n t s w a l l shear r a t e (1/sec) mass boundary l a y e r t h i c k n e s s (cm) d e f i n e d by Eq. (36) s i m i l a r i t y coordinate f o r t h i n channel system d e f i n e d by Eq. (65) = dimensionless s o l u t e c o n c e n t r a t i o n d e f i n e d by Eq. (16)

= = = = = =

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

SYNTHETIC

406

MEMBRANES:

H F AND U F

USES

X

= dimensionless a x i a l d i s t a n c e coordinate d e f i n e d by Eq. (60)

y

= solution viscosity

TT p T (J) AP AV ATT

= = = = = = =

N—s ec o— 2

s o l u t i o n osmotic pressure (N/m ) s o l u t i o n d e n s i t y (g/cm ) dimensionless time as d e f i n e d by Eq. (16) dimensionless constant d e f i n e d by Eq. (60) a p p l i e d h y d r o s t a t i c pressure (N/m ) t o t a l permeate volume (cm ) TT - TT = s o l u t i o n osmotic pressure d i f f e r e n c e w p between w a l l c o n c e n t r a t i o n s o l u t i o n and permeate (N/m ) 3

2

3

2

Subscripts g m o p w wa 1, 2, 3 exp corr

= = = = = = = = =

of g e l o f membrane o f bulk s o l u t i o n o f permeate s o l u t i o n at w a l l p o s i t i o n of asymptotic s o l u t i o n a t measurement times e x p e r i m e n t a l l y measured correction

Abstract In macromolecular ultrafiltration, as pressure is i n c r e a s e d , permeate flux first i n c r e a s e s and then in a l a r g e number o f cases l e v e l s out and remains more o r l e s s pressure independent. This could be due to the i n c r e a s e in s o l u t e c o n c e n t r a t i o n a t the membrane s u r f a c e such that e i t h e r g e l formation occurs o r the corresponding osmotic pressure approaches the a p p l i e d p r e s s u r e . L i m i t i n g f l u x f o r the g e l p o l a r i z e d case was r e c e n t l y analyzed f o r cross flow and u n s t i r r e d batch cell systems by Trettin and Doshi (1980,a, b ) . In t h i s paper we have analyzed the osmotic pressure l i m i t e d ultrafiltration for the two systems. Our unstirred batch cell data and the literature cross flow data agree q u i t e w e l l w i t h the theory. We have f u r t h e r shown t h a t an unstirred batch cell system can be used t o determine whether p r e s sure independent ultrafiltration of macromolecular s o l u t i o n is gel or osmotic pressure limited. Other causes f o r the observed p r e s sure independence may be present but a r e not considered in t h i s paper.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

22.

TRETTIN AND DOSHI

Pressure-Independent UF

407

Literature Cited Blatt,

W. F., A. D r a v i d , A. S. M i c h a e l s , and L. Nelsen, " S o l u t e Polarization and Cake Formation in Membrane Ultrafiltration: Causes, Consequences, and C o n t r o l Techniques", in Membrane Science and Technology, J . E. Flinn, ed. p. 47, Plenum P r e s s , New York, N.Y. (1970).

B i l l m e y e r , F. W., Jr., "Textbook o f Polymer S c i e n c e " , Second E d i t i o n , I n t e r s c i e n c e , New York (1967). Brandrup, J., and E. H. Immergut, "Polymer Handbook," I n t e r s c i e n c e , New York (1967). B r i a n , P. L. T., in D e s a l i n a t i o n by Reverse Osmosis, U. Merten, editor, MIT P r e s s Cambridge Mass. p 161 (1966) Charlwood, P. A., " E s t i m a t i o Heterogeneity Measurements," J. Phys. Chem., 57, 125 (1953). Creeth, J . M., "The Use o f the Gouy D i f f u s i o m e t e r w i t h D i l u t e P r o t e i n S o l u t i o n s . An Assessment o f the Accuracy o f the Method," Biochem. J., 51, 10 (1952). Creeth, J . M., " S t u d i e s of Free D i f f u s i o n in L i q u i d s w i t h the Rayleigh Method," J. Am. Chem. Soc., 77, 6428 (1955). D e i s s l e r , R. G., " A n a l y s i s o f Turbulent Heat T r a n s f e r , Mass Transfer, and Friction i n Smooth Tubes a t High P r a n d t l and Schmidt Numbers," NACA Report No. 1210 (1955). Doherty, P., and G. B. Benedek, "The E f f e c t o f Electric Charge on the D i f f u s i o n of Macromolecules," J . Chem. Phys., 61, 5426 (1974). Gill,

W. N., L. J . Derzansky, and M. R. Doshi, "Convective D i f f u s i o n in Laminar and Turbulent Hyperfiltration (Reverse Osmosis) Systems," in Surface and Colloid Science, Volume 4, E. M a t i j e v i c , ed., p. 261, Wiley and Sons, New York, N.Y. (1971).

Goldsmith, R. L., "Macromolecular Ultrafiltration with Microporous Membranes," Ind. Eng. Chem., Fundam., Volume 10, No. 1, p. 113 (1971). Keller, K. H., E. R. Canales, and S. I . Yum, "Tracer and Mutual D i f f u s i o n C o e f f i c i e n t s o f P r o t e i n s , " J . Phys. Chem., 75, 379 (1971).

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

408

SYNTHETIC

MEMBRANES:

HF

AND U F

USES

K o z i n s k i , A. A., and E. N. L i g h t f o o t , " P r o t e i n Ultrafiltration: A General Example of Boundary Layer Filtration," AIChE J., Volume 18, No. 5, p. 1030 (1972). Leung, W. F., and R. F. P r o b s t e i n , "Low Polarization in Laminar Ultrafiltration of Macromolecular S o l u t i o n s , " Ind. Eng. Chem., Fundam., Volume 18, No. 3, p. 274 (1979). Longsworth, L. G., " D i f f u s i o n Measurement, a t 1°, o f Aqueous S o l u t i o n s o f Amino A c i d s , P e p t i d e s , and Sugars," J . Am. Chem. Soc., 74, 4155 (1952). M i c h a e l s , A. S., "New Separation Technique f o r the CPI," Chem. Eng. P r o g r e s s , Volume 64, No. 12, p. 31 (1968). M i t r a , F., and J. L. Lundblad G l o b u l i n and Human S t u d i e s , " Separatio No. 1, p. 89 (1978).

"Ultrafiltration

o f Immune Serum

Phillies, G. D. J., G. B. Benedek, and N. A. Mazer, " D i f f u s i o n in P r o t e i n S o l u t i o n s at High Concentrations: A Study o f Q u a s i e l a s t i c L i g h t S c a t t e r i n g Spectroscopy," J . Chem. Phys., 65, 1883 (1976). P o r t e r , M. C., "Concentration Polarization w i t h Membrane Ultrafiltration," Ind. Eng. Chem. Prod. Res. Develop., Volume 11, No. 3, p. 234 (1972). P r o b s t e i n , R. F., J. S. Shen, and W. F. Leung, "Ultrafiltration of Macromolecular S o l u t i o n s at High Polarization in Laminar Channel Flow," D e s a l i n a t i o n , Volume 24, p. 1 (1978). Scatchard, G., A. C. B a t c h e l d e r , and A. Brown, "Chemical, Clinical, and Immunological Studies on the Products o f Human Plasma F r a c t i o n a t i o n . V I . The Osmotic Pressure o f Plasma and of Serum Albumin," J o u r n a l of Clinical I n v e s t i g a t i o n , Volume 23, p. 458 (1944). Shen, J. S., and R. F. P r o b s t e i n , "On the P r e d i c t i o n o f L i m i t i n g F l u x in Laminar Ultrafiltration o f Macromolecular S o l u t i o n s , " Ind. Eng. Chem., Fundam., Volume 16, No. 4, p. 459 (1977). Shen, J. S., and R. F. P r o b s t e i n , "Turbulence Promotion and Hydrodynamic O p t i m i z a t i o n in and Ultrafiltration Process," Ind. Eng. Chem. Process Des. Dev., Volume 18, No. 3, p. 547 (1979).

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

22.

TRETTIN AND DOSHI

Pressure-Independent UF

409

T o s t e v i n , J. E., "The Hydrodynamic P r o p e r t i e s o f the Alditol O l i g o s a c c h a r i d e s , " Ph.D. D i s s e r t a t i o n , The Institute o f Paper Chemistry, 1966. Trettin, D. R., and M. R. Doshi, " L i m i t i n g F l u x in Ultrafiltration of Macromolecular S o l u t i o n s , " To be P u b l i s h e d , Chemical Engineering Communications (1980a). Trettin, D. R., and M. R. Doshi, "Ultrafiltration i n an U n s t i r r e d Batch Cell," To be P u b l i s h e d , Ind. Eng. Chem., Fundam. (1980b). Vilker,

V. L., Ph.D. T h e s i s , MIT, Dept. of Chemical E n g i n e e r i n g , Cambridge, Mass. (1975).

RECEIVED December 4, 1980.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

23 Polymer Solute Rejection by Ultrafiltration Membranes L E O S Z E M A N and M I C H A E L W A L E S Abcor, Inc., 850 Main Street, Wilmington, MA 01887

Ultrafiltration membranes are used, both on industrial s c a l e as w e l l as in l a b o r a t o r i e s s e p a r a t i o n and c o n c e n t r a t i o ble m a t e r i a l s . R e j e c t i o n o f the s o l u t e (or dispersed c o l l o i d ) is, together w i t h permeate flux, one of the two key performance parameters of any ultrafiltration membrane. The values of rejection coefficients are o f crucial importance in many a p p l i c a t i o n s of ultrafiltration. The o b j e c t i v e o f this c o n t r i b u t i o n is t o consider and analyze the i n d i v i d u a l f a c t o r s a f f e c t i n g rejection o f polymer s o l u t e s by ultrafiltration membranes. The f a c t o r s that will be considered i n c l u d e steric rejection ( s i e v i n g ) , s o l u t e velocity l a g and solute-membrane interaction. Our a n a l y s i s e x p l o i t s h e a v i l y a model concept of a s p h e r i c a l s o l u t e in a cylindrical capillary and we do not want t o dispute the simplicity o r inadequacy inherent i n this model. However, we want t o demonstrate that even w i t h i n the framework of this idealized model, u s e f u l p r e d i c t i o n s about the membrane rejection behavior can be made. We are not going t o d i s c u s s here the e f f e c t s of f o u l i n g (adsorption) o r of electrostatic charge, even if we have t o bear in mind that these may be overwhelmingly important in many situations. The d i s c u s s i o n will a l s o consider only a case of a preponderantly convective s o l u t e transport w i t h a negligible contribution due t o diffusion. Steric

Rejection

In h i s w e l l known d e r i v a t i o n of a formula f o r s t e r i c r e j e c t i o n , J . D. Ferry (1) a r r i v e d i n 1936 a t a simple r e l a t i o n between the s o l u t e r e j e c t i o n c o e f f i c i e n t , R 2 , and the s o l u t e t o pore diameter r a t i o , A, where R

2

3 0097-6156/81/0154-041l$06.00/0 © 1981 American Chemical Society

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

412

SYNTHETIC

R

2

= 1-4

/ o

MEMBRANES:

3

HF

AND

2

($-3 )dB = ( X ( 2 - X ) ) ; f o r X1

(lc)

These r e l a t i o n s can be used as rough estimates of s t e r i c r e j e c t i o n , i f the s o l u t e and membrane pore dimensions are known. The d e r i v a t i o n i s based on a s t r i c t l y model s i t u a t i o n (see Figure 1) and a long l i s t of necessary assumptions can be w r i t t e n . Apart from the s i m p l i f i e d geometry (hard sphere i n a c y l i n d r i c a l pore), i t was a l s o assumed that the s o l u t e t r a v e l s a t the same v e l o c i t y as the surrounding l i q u i d , that the s o l u t e c o n c e n t r a t i o n i n the a c c e s s i b l e p a r t s of the pore i s uniform and equal t o the c o n c e n t r a t i o n i n the feed l i q u i d i s Newtonian, d i f f u s i o n a port i s n e g l i g i b l e (pore P e c l e t number i s s u f f i c i e n t l y h i g h ) , c o n c e n t r a t i o n p o l a r i z a t i o n and membrane-solute i n t e r a c t i o n s are absent, e t c . Solute V e l o c i t y Lag In g e n e r a l , a sphere moving through a c y l i n d r i c a l pore does not move w i t h the same v e l o c i t y as the surrounding f l u i d . Consequently, the formula ( l b ) has t o be c o r r e c t e d f o r t h i s e f f e c t . I n 1975, Paine and Scherr (2) c a l c u l a t e d drag coeff i c i e n t s k , k i which weight the c o n t r i b u t i o n s of the sphere and f l u i d v e l o c i t i e s t o the drag f o r c e F: 2

F = -6TTTVL

(k v 2

2

- kivx)

(2)

The drag c o e f f i c i e n t s k]^ and k are both a f u n c t i o n of X and 3 (dimensionless d i s t a n c e of sphere's center from the pore's a x i s ) . The dependence of k]^ and k on 3 can be neglected without too much e r r o r (2) and the r a t i o of k i / k can be considered t o depend only on X. In a steady-state s i t u a t i o n , the drag f o r c e has to be zero and a constant s o l u t e v e l o c i t y l a g can be described by an equation: 2

2

2

vo k-. 2 — = i~ = exp (-0.7146X ) l 2 V

(3)

k

The right-hand s i d e of Equation (3) was obtained by a l e a s t square f i t of a f u n c t i o n (exp (-°cX) on the values of k]^ and k reported by Paine and Scherr (2) f o r d i f f e r e n t values of X. Paine and S c h e r r s values represent a r i g o r o u s t h e o r e t i c a l s o l u t i o n f o r a c e n t e r - l i n e motion of a r i g i d sphere i n s i d e a c y l i n d r i c a l tube. Applying t h i s c o r r e c t i o n , we can then w r i t e 2

2

f

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

23.

ZEMAN

Polymer Solute Rejection

AND WALES

413

for solute rejection: R

2

2

= 1 - ( 1 - ( A ( 2 - A ) ) ) exp (-0.7146A )

2

(4)

The magnitude of the s o l u t e v e l o c i t y l a g c o r r e c t i o n i s shown i n F i g u r e 2. As seen, f o r a r i g i d sphere i n a c y l i n d e r , t h i s c o r r e c t i o n i s not too l a r g e . N e v e r t h e l e s s , we w i l l keep c o n s i d e r i n g i t i n f u r t h e r d i s c u s s i o n s . The c o r r e c t i o n c a l c u l a t e d from Equation (16b) of Anderson and Quinn ( 7 ) , a p p l i c a b l e f o r A

! 3 j r

3

where N N

(23)

To i l l u s t r a t e t h i s e f f e c t o » o 3 = 40A and r ^ = 1000A (O.lu). The c a l c u l a t e d r e j e c t i o n curve (dashed l i n e ) i s shown i n Figure 5 and compared to that of a h o l e f r e e membrane ( f u l l l i n e ) . In the s o l u t e s i z e range of i n t e r e s t , the R = 1 p l a t e a u ( q u a n t i t a t i v e r e j e c t i o n of the s o l u t e ) i s never achieved. R e j e c t i o n curves of t h i s s o r t are very commonly encountered i n p r a c t i c e . r

2

Van der Waals A t t r a c t i v e Forces In the d e r i v a t i o n of J . D. F e r r y ' s formula, Equation ( l b ) , i t was assumed that the s o l u t e c o n c e n t r a t i o n w i t h i n the a c c e s s i b l e part of the membrane pore i s uniform and equal to C F . Obviously t h i s assumption cannot hold i f we are to acknowledge the presence of i n t e r a c t i v e forces between the s o l u t e and the pore w a l l (membrane) . Here we w i l l concentrate only on the e f f e c t of Van der Waals forces but analogous treatments could be developed f o r other i n t e r a c t i v e p o t e n t i a l s ( e l e c t r o s t a t i c , e t c . ) . We f i r s t consider an atom w i t h i n a c y l i n d r i c a l o r i f i c e i n the membrane (component 3) of r a d i u s r = 1 i n t e r a c t i n g w i t h a c y l i n d r i c a l volume element d V at a d i s t a n c e x (see Figure 6a). The p o t e n t i a l energy of i n t e r a c t i o n (Van der Waals a t t r a c t i o n ) i s -p N dV 2 >

3

3

f

atom-3

M 3

6 x

0

t

where

and 2

= (s sin

2

2

0 + 3 -23s sin0 s i n ( ) ) )

1/2

(28)

The c l u s t e r of constants i n Equation (27) can be s i m p l i f i e d by u s i n g the Hamaker constant, H 3 3 : P

N

17

3 a

2 •

H33 = ( - V - ) 2

2

-

(29)

and t h e r e f o r e * (B,A) =

H

3 3

' I (B X)

(30)

f

TT

The f a c t that the s o l u t e (component 2) and the membrane (component 3) a r e made from two d i f f e r e n t m a t e r i a l s separated by the solvent (component 1) w i l l be r e f l e c t e d by the use of a composite Hamaker constant. 1/2 H

213

=

( H

1/4 2 (H

11

- 22

V

>

(31)

The energy of i n t e r a c t i o n f o r a s p h e r i c a l s o l u t e of r a d i u s X i n a s o l v e n t - f i l l e d i n f i n i t e c y l i n d r i c a l pore w i t h a r a d i u s 3=1 and a t a r a d i a l p o s i t i o n 3 i s t h e r e f o r e

* (3'X) = ^

H

2 1 3

I (3'X)

(32)

TT

The s o l u t e c o n c e n t r a t i o n p r o f i l e w i t h i n the a c c e s s i b l e p a r t of the pore w i l l be determined by the Boltzmann d i s t r i b u t i o n law.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

422

SYNTHETIC

Figure 6b.

MEMBRANES:

HF

AND

UF

Schematic of a spherical solute within the pore

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

USES

23.

Polymer

Z E M A N AND WALES

C

Solute

Rejection

423

= C exp (-$/kT)

2

(33)

2

o -14 The value o f kT considered (25 C) i s 4.12 x 10 e r g . R a d i a l d i s t r i b u t i o n o f s o l u t e molecules i n the pore does not change the average s o l u t e c o n c e n t r a t i o n i n the pore and t h e r e f o r e ,2 Tr(l-A)

C

I"*

_

= C -2ir / exp

2 j F

2

-

$

(

dg,

(34)

wherefrom: _ c

(1-A)

C 2

=

"

2

(35)

* i=r

2

e x p ( " T j ) 6 dg

/

Equations (32), (33) an f u n c t i o n o f B and A f o r d i f f e r e n t values of H 3 (Hamaker con s t a n t ) . Due t o the complexity o f c a l c u l a t i o n ( e v a l u a t i o n o f two t r i p l e i n t e g r a l s ) , t h i s i s best done on a computer. T y p i c a l r e s u l t s of computer c a l c u l a t i o n s are shown i n F i g u r e 7. The e f f e c t of Van der Waals a t t r a c t i v e f o r c e s w i l l lead t o an accumulation of s o l u t e molecules near the w a l l s f o r s m a l l values of A but a t l a r g e values of A , the p o s i t i o n s c l o s e t o the pore a x i s s t a r t being preferred. The value o f H ^3 chosen i n our c a l c u l a t i o n i s r a t h e r l a r g e . The expected magnitude of Hamaker constants would be between 2 x 1 0 " - 5 x l O " ^ erg depending on the " h y d r o p h i l i c i t y " o f both the s o l u t e and the membrane. To c a l c u l a t e r e j e c t i o n c o e f f i c i e n t s , we use the formula 2

2

13

1

/

R

9 1

= 1 -£ C

1-A J

/ C (B-B ) dB

2,F o

9

(36)

1

that accounts f o r the presence of a c o n c e n t r a t i o n gradient w i t h i n the a c c e s s i b l e part o f the pore. R e j e c t i o n curves c a l c u l a t e d from Equations (32), (33), (35) and (36) are shown i n F i g u r e 8. I t i s seen t h a t the e f f e c t i s most pronounced below A = 0.7 and i t s magnitude depends on the value o f the r e s p e c t i v e Hamaker constant. The r e j e c t i o n c o e f f i c i e n t i s increased by the a t t r a c t i v e f o r c e s between the s o l u t e and the membrane. I t i s t o be expected that f o r l a r g e values o f H, a d s o r p t i o n a l s o occurs and the pore dimensions are changed correspondingly. The e f f e c t s of adsorbed s o l u t e l a y e r s may be very important, but these were not considered i n our a n a l y s i s o f the solute-membrane interaction effects.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

424

SYNTHETIC

Figure 7.

MEMBRANES

HF

AND

UF

USES

Example of calculated concentration profiles for the value of H i X 10~ erg and different values of A and f$

2 3

13

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

= 1.5

23.

ZEMAN

Polymer Solute Rejection

AND WALES

Concentration

425

Polarization

T y p i c a l r e s u l t s of an u l t r a f i l t r a t i o n experiment a l s o r e f l e c t the presence of c o n c e n t r a t i o n p o l a r i z a t i o n . This phenomenon, i . e . accumulation of s o l u t e i n f r o n t of the membrane, was described i n great d e t a i l by others (Refs. 3, 4 ) . A consequence of c o n c e n t r a t i o n p o l a r i z a t i o n i s a strong dependence of measured r e j e c t i o n c o e f f i c i e n t s on transmembrane f l u x e s . An i l l u s t r a t i o n of the e f f e c t i s presented i n Figure 9, which shows the measured "apparent" r e j e c t i o n c o e f f i c i e n t s (R ) as a f u n c t i o n of transmembrane f l u x f o r two water-soluble polymers (Tetronic 707 and Carbowax 4000). I t i s c l e a r from F i g u r e 9 that i f we want t o minimize the e f f e c t s of c o n c e n t r a t i o n p o l a r i z a t i o n , we have to conduct experiments at very low values of transmembrane f l u x . a

Theory of S t e r i c R e j e c t i o The experimental r e s u l t s are going to be presented i n d e t a i l elsewhere and only a b r i e f p r e s e n t a t i o n w i l l be given below. The p r e d i c t i v e power of Equation (4) was t e s t e d w i t h defined polymeric s o l u t e s and track-etched Nuclepore f i l t e r s . The polymers used were: l i n e a r polyethylene oxides, (Carbowaxes s u p p l i e d by Union Carbide C o r p o r a t i o n ) , and Dextran T f r a c t i o n s , (Pharmacia Fine Chemicals). For Carbowaxes, the s o l u t e r a d i i used i n c a l c u l a t i o n s were mean r a d i i of g y r a t i o n c a l c u l a t e d from molecular weights v i a the Flory-Fox equation and u s i n g the Mark-Houwink constants given i n reference (5). For n o n - l i n e a r dextrans, we used the Stokes r a d i i c a l c u l a t e d from molecular weights using the c o r r e l a t i o n of data reported by Granath and K v i s t (6). Both types of polymer have very narrow d i s t r i b u t i o n s of molecular weight. The s o l u t e r a d i i are summar i z e d i n Table I I I . Table I I I Solute R a d i i

Solute

M

w

(Daltons)

R a d i u s

(

Carbowax 4000

4,010

25.4

Carbowax 6000

7,000

34.6

Dextran T10

10,500

23.8

Dextran T40

39,500

44.4

Dextran T70

68,500

57.5

&

}

Mean r a d i u s of g y r a t i o n Stokes Radius

Nuclepore f i l t e r s used have s t r a i g h t - t h r o u g h pores w i t h diameters s p e c i f i e d by Nuclepore Corporation as 150, 300 and 500A. These are the s o - c a l l e d " r a t e d " pore diameters and they represent

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

426

SYNTHETIC MEMBRANES: HF AND UF USES

Figure 8. Effect of solute-membrane interaction on rejection. Rejection curves calculated for H = 0, H = 0.8 X IO' erg, and H = 2.0 X iO' erg. 13

13

213

213

1.0

213

THEORY

- = 1-R

K

— e (Brian's Model) 1(dalM tWons)Q(GPM)(cm/s) iR OTetronic 707 12000 3.5 6.4xl0' 0.97 ACarbowax 4000 3500 1.7 3.7xl0" 0.83 V Membrane: ABC0R HFM 100 a

Rl

k

R

O

3

3

0.5

-

0

100 200

300 400 500 600 700 800 FLUX (J), GFD

900 1000

Figure 9. Effect of concentration polarization. Theoretical curves calculated for the values of R i and k specified in the figure. Experimental data for Tetronic 707 (O) and Carbowax 4000 (A) ultraflltered through the ABCOR HFM 100 membrane.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

23.

ZEMAN

AND

WALES

Polymer Solute Rejection

All

the maximum v a l u e . According to Nuclepore l i t e r a t u r e , the a c t u a l pore s i z e s should not vary more than +0% to -20% from the r a t e d values. For each f i l t e r - s o l u t e combination, A was c a l c u l a t e d as a r a t i o of the s o l u t e r a d i u s to the " r a t e d " pore r a d i u s . The p r e d i c t e d value of the r e j e c t i o n c o e f f i c i e n t was then c a l c u l a t e d from Equation (4). The comparison between the p r e d i c t e d values and those a c t u a l l y measured w i t h Carbowaxes 4000 and 600 i s shown i n F i g u r e 10a and b, r e s p e c t i v e l y . The measurements were c a r r i e d out at s e v e r a l values of AP i n order to assess the importance of c o n t r i b u t i o n from c o n c e n t r a t i o n p o l a r i z a t i o n . Using the GPC a n a l y s i s of feed and permeate s o l u t i o n s (Figure 11 a,b), we a l s o c a l c u l a t e d a p a r t of the s o l u t e r e j e c t i o n curve for the given f i l t e r s . The example of such a curve i s a Carbowax r e j e c t i o n curve f o r Nuclepore 150% (diameter) f i l t e r (Figure 11c). The agreement between experimenta predictio Equation (4) ( s o l i d l i n e A s i m i l a r t e s t was performed w i t h Dextran T f r a c t i o n s and Nuclepore 150&, 300&, 500X (diameter) f i l t e r s . The r e s u l t s are summarized i n F i g u r e 12. The experimental p o i n t s were obtained both from s i n g l e s o l u t e measurements (+ - r e j e c t i o n of T10 and T70 by the 150& f i l t e r ) and from a n a l y s i s of the GPC t r a c e s ( F 1 ~ 500& f i l t e r , A-300& f i l t e r , o-1508 f i l t e r ) . The agreement between the experimental data and the p r e d i c t i o n of Equation (4) ( s o l i d l i n e ) i s again s u r p r i s i n g l y good, c o n s i d e r i n g the crudeness of assumptions i n v o l v e d i n i t s d e r i v a t i o n . Simultaneous R e j e c t i o n Measurements The GPC a n a l y s i s of feed and permeate s o l u t i o n i s i d e a l l y s u i t e d f o r r a p i d simultaneous r e j e c t i o n measurements. S i m u l t a eous r e j e c t i o n i s of great importance i n u l t r a f i l t r a t i o n p r a c t i c e . As an example, we show here a simultaneous measurement of r e j e c t i o n of p r o t e i n s and of l a c t o s e i n whey u l t r a f i l t r a t i o n (Figure 13). The membrane used was the ABCOR HFK membrane and the feed s o l u t i o n had a t y p i c a l composition of a p a r t i a l l y concentrated whey stream. The feed ( ) and the permeate (- - -) s o l u t i o n s were analyzed by GPC (Waters 1-125 columns) w i t h simultaneous monitoring of uv absorbance ( A 2 8 0 ) * °^ r e f r a c t i v e index d i f f e r e n c e (ARI). The a n a l y s i s shows a q u a n t i t a t i v e r e j e c t i o n (R=100%) of a l l whey p r o t e i n s and a very low r e j e c t i o n (R=8%) of l a c t o s e . anc

Conclusions According to our a n a l y s i s , the predominant e f f e c t c o n t r o l l i n g r e j e c t i o n of polymeric s o l u t e s by uncharged u l t r a f i l t r a t i o n membranes i s the s t e r i c f a c t o r determined by the v a l u e of parameter A. The c o n t r i b u t i o n s to r e j e c t i o n from hydrodynamic l a g , Van der Waals a t t r a c t i o n between the s o l u t e and the membrane can be r e garded as of r e l a t i v e l y minor importance.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

SYNTHETIC

428

MEMBRANES:

H F A N D U F USES

N150A

^ 10

20

30

AP(psi)

N500A

40

N150A

N300A

A N500A

10

"S

TT

4,

1

20

30

i

AP(psi)

40

L

Figure 10. R(%) as a function of A P for Nuclepore 150 A (Q), Nuclepore 300 A (A), and Nuclepore 500 A ([7]): (a) 0.1 Carbowax 4000; (b) 0.1 Carbowax 6000. Solid lines show theoretical predictions according to Equation 4.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

23.

ZEMAN

AND

Polymer Solute Rejection

WALES

429

R(%)

o o /

40

/

20

1

10

1 20

30

40

50

RADIUS OF G Y R A T I O N (A)

Figure 11. Measured apparent rejection of polyethylene oxide (Carbowax) at AP = 50 psi: (a) GPC trace of a blend solution containing 0.02% of each Carbowax 1000, 1400, 1540, 4000, and 6000; (b) GPC trace of a permeate obtained by UF at AP == 50 psi through Nuclepore 150 A membrane; (c) apparent rejection calculated from GPC traces shown in a and b, (Q), as a function of solute radius of gyration. The solid line shows theoretical prediction according to Equation 4.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

430

SYNTHETIC

MEMBRANES:

HF

AND

UF

USES

Figure 12. Measured apparent rejection of dextrans by Nuclepore filters calculated from GPC traces as a function of A. Points calculated from Nuclepore 150 A (O), 300 A (A), and 500 A ([J) traces. The solid line shows theoretical prediction according to Equation 4. Rejection coefficients measured for single dextran fractions (T10 and T70) and the Nuclepore 150 A filter are shown also (+).

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

23.

ZEMAN

AND

WALES

Polymer Solute Rejection

431

AR.I.

20 15 —ELUTION VOLUME, ML Figure 13. Simultaneous rejection measurement by GPC. The GPC profiles: ARI trace (upper,) and A o trace (lower) for whey feed and permeate obtained by UF through the ABCOR HFK membrane. The peak labelled IgG corresponds to whey immunoglobulines; peaks labelled oc and /3 correspond to oc -lactalbumin and /3-lactoglobulin, respectively. 28

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

432

SYNTHETIC

MEMBRANES:

HF AND U F

USES

The t y p i c a l u l t r a f i l t r a t i o n r e s u l t s w i l l r e f l e c t e f f e c t s of the r e s p e c t i v e s i z e d i s t r i b u t i o n s of both the s o l u t e and the membrane pores, as w e l l as o f c o n c e n t r a t i o n p o l a r i z a t i o n . A l l of these e f f e c t s should be expected to lower the membrane r e j e c t i o n coefficient. Acknowledgement We thank Mr. Michael Morin of ABCOR, INC. f o r i n v a l u a b l e help i n performing the computer c a l c u l a t i o n s . L i s t of Symbols 2 A

Membrane area, cm

A^

Coefficient

a

Constant i n Equation ( 7 ) , A d a l t o n

b

Constant i n Equation ( 7 ) , dimensionless -3

C^

Solute c o n c e n t r a t i o n i n the feed, g cm

F

C^ p f(M«)

-3 Solute c o n c e n t r a t i o n i n the permeate, g cm Solute d i f f e r e n t i a l molecular weight dalton'

distribution,

1

F

Viscous drag f o r c e , dyne

H

Hamaker constant, e r g

I

Integrals Solvent f l u x , cm s ^ -2 -1

J

Solute f l u x , g cm s

2

k

Mass t r a n s f e r c o e f f i c i e n t , cm s ^ (Figure 9)

k

Boltzmann constant, e r g °K

k^,k^

Drag c o e f f i c i e n t s , dimensionless o

1^

Pore l e n g t h , A

M^

Solute molecular weight, d a l t o n

M^

Number average s o l u t e molecular weight, d a l t o n

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

23.

ZEMAN

M

AND WALES

0

z,w

Polymer Solute Rejection

433

Weight average s o l u t e molecular weight, d a l t o n Membrane polymer molecular weight, d a l t o n -2 Number of pores per u n i t membrane area, cm -2

N » N

Number of holes per u n i t membrane area, cm

N^

Arogadro number, mole ^

r

D i s t a n c e , cm

r^

o Solvent molecule r a d i u s , A

r^

Solute r a d i u s

r^ R or R^

Membrane pore r a d i u s , A Solute r e j e c t i o n c o e f f i c i e n t , dimensionless

R

Apparent r e j e c t i o n c o e f f i c i e n t , dimensionless

a

s

D i s t a n c e , cm o

T

Absolute temperature,

K

vv^

Solvent v e l o c i t y , cm s ^ Solute v e l o c i t y , cm s ^

V

Volume, cm

W^

Solute hindrance c o e f f i c i e n t , dimensionless

x

D i s t a n c e , cm

y

D i s t a n c e , cm

3

Angle, r a d i a n

$

Van der Waals i n t e r a c t i o n energy, e r g

0)

Angle, r a d i a

Subscripts

1

Solvent

2

Solute

3

Membrane

Literature Cited 1.

F e r r y , J. D., Chem. Rev., 1936, 18, 373

2.

Paine, P. L.; Scherr, P., B i o p h y s i c a l J., 1975, 15, 1087

3.

B r i a n , L. T., " D e s a l i n a t i o n by Reverse Osmosis", Merten, U., Ed., The MIT P r e s s , Cambridge, Massachusetts, 1966, 101

4.

B l a t t , W. F.; David, A.; M i c h a e l s , A. S.; Nelsen, L., "Membrane Science and Technology", F l i n n , J . E., Ed., Plenum P u b l i s h i n g C o r p o r a t i o n , New York, 1970, 47

5.

Ring, W., Cantow, H. J., H o l t r u p , H., European Polymer J., 1966, 2, 151

6.

Granath, K. A.; K v i s t , B. A., J. Chromatogr., 1967, 28, 69-81

7.

Anderson, J. L.; Quinn, J. A., Biophys. J., 1974, 14, 130-150

RECEIVED

December

4,

1980.

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

24 Recent Applications of Dynamic Membranes C R A I G A . B R A N D O N — C A R R E , Inc., Seneca, SC 29678 J. L E O GADDIS—Department of Mechanical Engineering, Clemson University, Clemson, SC 29631 H . G A R T H SPENCER—Department of Chemistry, Clemson University, Clemson, SC 29631

The systematic i n v e s t i g a t i o n o f dynamically-formed membranes began w i t h t h e formatio the Oak Ridge N a t i o n a tion membrane most o f t e n used in subsequent a p p l i c a t i o n s has been prepared by s e q u e n t i a l d e p o s i t i o n s o f zirconium IV hydrous oxide f o l l o w e d by poly(acrylic acid) on a s u i t a b l e porous support under pressure and cross f l o w c o n d i t i o n s . Although not competitive w i t h t h e conventional hyperfiltration membranes f o r desalination, the resulting hyperfiltration (RO) membrane possesses p r o p e r t i e s d e s i r e d f o r some industrial a p p l i c a t i o n s . (2) It is s u i t a b l e f o r a p p l i c a t i o n s r e q u i r i n g high temperature during e i t h e r o p e r a t i o n , c l e a n i n g , or sterilization and for those in which a charged membrane is advantageous. Results from two s t u d i e s i n v o l v i n g high volume recovery of multicomponent process e f f l u e n t s are presented here as illustrat i o n s o f recent a p p l i c a t i o n s o f hyperfiltration membranes in a t u b u l a r c o n f i g u r a t i o n supported by porous s t a i n l e s s steel. The first is a l a b o r a t o r y s e p a r a t i o n o f dyes from a s a l i n e dye manufacturing process e f f l u e n t and t h e second a pilot renovation of wash water from a dye range f o r reuse. The general p r o p e r t i e s o f r e p r e s e n t a t i v e dynamically-formed membranes are provided in Table I . Separation o f Dye Manufacturing

Process E f f l u e n t

In a t y p i c a l dye s y n t h e s i s t h e dye i s s a l t e d - o u t o f t h e r e a c t i o n s o l u t i o n and captured on a f i l t e r press. The dye f i l t r a t e i s normally d i l u t e d w i t h f i l t e r washings and other water sources t o as much as (100:1) (water: dye f i l t r a t e ) , t r e a t e d , and discharged from t h e p l a n t . The authentic samples of dye f i l t r a t e used i n t h i s study were h i g h l y c o l o r e d , near n e u t r a l l i q u i d s w i t h high s a l t concentrations (5 t o 20 weight percent) and a t o t a l organic carbon (TOC) c o n c e n t r a t i o n o f about 0.5 percent.

0097-6156/81/0154-0435$05.00/0 © 1981 American Chemical Society

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

SYNTHETIC

436

Table I .

MEMBRANES:

H F A N D U F USES

CARRE, Inc. Membrane S p e c i f i c a t i o n s

Ultrafiltration ZOSS

Hyperfiltration ZOPA

Tubular

Tubular

Flow Geometry

(3l6£)

stainless steel (3l6£)

Membrane Support

stainless steel

Membrane M a t e r i a l

zirconium

Method o f Replacement

i

Prefiltration Requirement

hO mesh screen

1+0 mesh screen

Pressure

g r e a t e r than 1000 psig

greater than 1000 psig

greater than 100°C (212°F)

greater than 100°C (212°F)

Limitation

Temperature Limitation pH Range

oxide

zirconium oxide polyacrylate

solution

solution

U-ll

2-13

P e r m e a b i l i t y with Test S o l u t i o n @ 100°F

0 . 1 t o O.k

0.05

8 200°F

O.k t o 1 . 2

0.2

S a l t Rejection"^

5 - 20%

80 - 90%

-

-

0.07

0.3

Test S o l u t i o n 1000 mg/l o f NaNO^ i n water Flux equals P e r m e a b i l i t y times pressure Examples: ( l ) ZOSS Membrane at 1000 p s i g at 100°F F l u x = 0 . 2 5 x 1000 = 250 g a l l o n s / d a y / f t (2) ZOPA Membrane at 1000 p s i g at 200°F Flux = 0 . 2 5 x 1000 = 250 g a l l o n s / d a y / f t ^ Flux with wastewater must be measured. c

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

24.

BRANDON

ET AL.

Dynamic Membranes

437

F o u r f l u i d s were s t u d i e d : f i l t r a t e s f r o m t h e m a n u f a c t u r e o f (a) "basic y e l l o w C I U 8 0 5 ^ , i n d o l e t y p e ; (b) a c i d y e l l o w C I 1 3 9 0 6 , a z o - t y p e ; ( c ) a c i d b l u e CI 6 2 0 5 5 a n t h r a q u i n o n e t y p e ; a n d (d) an e q u a l m i x t u r e o f t h e a b o v e , t e r m e d " c o m p o s i t e " . T a b l e I I i d e n t i f i e s the s t r u c t u r e s o f the product dyes. Test f l u i d s r a n g i n g i n d i l u t i o n f r o m 2 : 3 t o 1 0 0 : 1 were u s e d . A need e x i s t s t o f r a c t i o n a t e t h e s o l u t e s i n t h e dye f i l t r a t e i n t o r e t a i n e d o r g a n i c and p a s s e d i n o r g a n i c s a l t f r a c t i o n s . The passage o f simple e l e c t r o l y t e s occurs through u l t r a f i l t r a t i o n membranes a n d i o n - e x c l u s i o n h y p e r f i l t r a t i o n membranes a t a h i g h salt concentration. B o t h t y p e s o f dynamic membranes were t e s t e d . The dynamic u l t r a f i l t e r had b e e n o b s e r v e d t o r e t a i n c o l o r i n s p e n t dye s o l u t i o n s , b u t i t s c o l o r r e t e n t i o n u s i n g t h e s e d i l u t e d dye f i l t r a t e s ( 1 0 0 : 1 ) was n e g l i g i b l e and no q u a n t i t a t i v e r e s u l t s are presented. A d e s c r i p t i o n o f the experiments and preliminary results usin basi yello U805^ d composit f i l t r a t e s has been p u b l i s h e d hyperfilter using aci yello f i l t r a t e s are d e s c r i b e d here. T h e p r o p e r t i e s o f t h e dye f i l t r a t e s are p r o v i d e d i n Table I I I . The e f f e c t s o f p e r t i n e n t o p e r a t i n g p a r a m e t e r s on t h e s e p a r a t i o n p r o c e s s were m e a s u r e d . Most e x p e r i m e n t s were p e r f o r m e d a t 5 . 2 MPa (750 p s i ) . D e l i b e r a t e e x c u r s i o n s i n t e m p e r a t u r e were made t o measure t h i s e f f e c t and p r o v i d e a means o f c o m p e n s a t i n g t h e f l u x d a t a f o r t e m p e r a t u r e and r e p o r t i n g a l l c o m p a r i s o n d a t a a t U5°C. The s e p a r a t i o n o f s o l u t e s was a n t i c i p a t e d t o depend on c o n c e n t r a t i o n and pH and t h e s e e f f e c t s were d e t e r m i n e d systematically. Two e x p e r i m e n t a l p r o c e d u r e s were c a r r i e d o u t . In the f i r s t , a 1 0 0 : 1 ( w a t e r and dye f i l t r a t e ) d i l u t i o n was c o n c e n t r a t e d t o o n e - t e n t h i t s i n i t i a l v o l u m e . R e j e c t i o n b a s e d on c o l o r a b s o r b ance {hlO nm) and e l e c t r i c a l c o n d u c t i v i t y , f l u x , p r e s s u r e , t e m p e r a t u r e , a n d c r o s s f l o w r a t e were m e a s u r e d a t i n t e r v a l s during the concentration experiment. I n the second, a s l i g h t l y d i l u t e d dye f i l t r a t e ( 2 : 3 ) was u s e d and t h e h y p e r f i l t r a t i o n a t s t e a d y s t a t e was e v a l u a t e d a s i n t h e f i r s t p r o c e d u r e . The t e s t was r e p e a t e d a t d i l u t i o n s r e a c h i n g ( 1 0 0 : 1 ) , w i t h pH and t e m p e r ature excursions a t a d i l u t i o n o f 3 : 1 . The v a r i a t i o n o f f l u x w i t h t e m p e r a t u r e f o r a l l t h e f l u i d s i s shown i n F i g u r e 1 . Each t r e n d i s reasonably c o r r e l a t e d b y 5

J

= J

q

exp[-2,500 ( i - i )] o

[1]

where J Q i s t h e f l u x a t T = 3l8K ( i +5°C). T h e v a r i a t i o n o f f l u x and r e j e c t i o n s w i t h pH i s shown i n F i g u r e s 2 a n d 3 f o r t h e t w o fluids. Q

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

438

SYNTHETIC

Table I I .

MEMBRANES:

H F A N D U F USES

S t r u c t u r e s o f Product Dyes

Product Dye

Structure

Basic Yellow, CI hQ05k

CH

3

O^NJ-CHIN-N—^>-0 I I C h U

C

H

3

Acid Yellow, CI 13906

S 0

2

N H

C O - N H - O

2

"

N a

f

A c i d Blue, CI 62055

0

N H

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

24.

BRANDON

ET AL.

Dynamic Membranes

439

Table I I I . P r o p e r t i e s o f Dye F i l t r a t e s Property

A c i d Y e l l o w , CI 13906

(mg/L)

A c i d B l u e , CI 62055

(mg/L)

CI"

116,000

12,600

TDS

217,000

111,000

COD

lU,200

Hl,900

6,l80

21,800

177,000

50,000

Alkalinity

E q u i v a l e n t NaCl

(by c o n d u c t i v i t y ) pH

9.1

9.3

Cr

0.3k

0.20

Cu

Q.kh

Ni

1.73

0.63

Zn

0.63

0.87

Hg

17.8

760.

13.8

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

SYNTHETIC

440

MEMBRANES:

HF

AND

UF

USES

3• 3

2- 9 103/T

Figure 1.

Effect of temperature on membraneflux:P = 5.2 MPa (750 psi)

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

24.

Dynamic Membranes

BRANDON E T A L .

H

1

.

1

1

441

A

I

•

A

•6 r .4

° .2

•

O

I

9

6° •

conductivity

I

L

i

i

I

i

_l

I

I

I

1

L_

0 2

1 0 5 Jo (m/s)

PH

Figure 2. Rejection (r) and flux (J ) dependence on pH for the acid yellow CI 13906 filtrate: solid points at conductivity (LJ = 0.026 S/cm and open points at L = 0.06 S/cm; P = 5.2 MPa (750 psi). 0

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

442

SYNTHETIC

•

MEMBRANES:

HF

AND

UF

USES

•

pH

Figure 3.

Rejection (r) and flux (J ) dependence on pH for the acid blue CI 62055 filtrate: conductivity (L) = 0.042 S/cm; P = 5.2 MPa (750 psi). 0

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

24.

BRANDON

ET AL.

443

Dynamic Membranes

The dependence of the r e j e c t i o n s on the concentration i s o f primary i n t e r e s t . The r e j e c t i o n s and f l u x dependence on concent r a t i o n (represented by the c o n d u c t i v i t y of the feed) i s shown i n Figures h and 5 f o r the two f l u i d s . The most s i g n i f i c a n t feature i s the d i f f e r e n c e i n r e j e c t i o n based on absorbance (A) and t h a t based on c o n d u c t i v i t y ( L ) , i . e . , the d i f f e r e n c e i n r e j e c t i o n o f the c o l o r e d organic dye s a l t s and the simple s a l t s (the major c o n t r i b u t o r t o the c o n d u c t i v i t y ) . The membrane e f f e c t i v e l y concentrates the c o l o r w i t h r e j e c t i o n , r ^ , g r e a t e r than 0.9 ^or most data w h i l e passing simple s a l t s w i t h r e j e c t i o n , r ^ , l e s s than O.k at high c o n c e n t r a t i o n . This r e s u l t suggests the dependence of the s e p a r a t i o n f a c t o r , ajjj, where L a'A l

[2]

on c o n c e n t r a t i o n d i f f e r s f o r the two f l u i d s . As shown i n Figure 6, increases w i t h concentration f o r the a c i d y e l l o w CI 13906 f i l t r a t e but remains n e a r l y constant f o r the a c i d blue CI 62055 f i l t r a t e . The r e j e c t i o n o f c o l o r i s coupled w i t h t h a t of cond u c t i v i t y i n the l a t t e r f i l t r a t e but not i n the former. These r e j e c t i o n s are uncoupled i n the b a s i c y e l l o w CI kQO^h f i l t r a t e . (3_) I n c r e a s i n g i o n i c s t r e n g t h decreases the i o n - e x c l u s i o n e f f e c t i v e n e s s of charged membranes. The r e s u l t s i n d i c a t e t h a t the c o l o r e d components of the a c i d blue f i l t r a t e behave as a simple e l e c t r o l y t e , w h i l e the l a c k of a r e d u c t i o n i n the c o l o r r e j e c t i o n of the other two f l u i d s suggests the c o l o r e d species are e i t h e r l a r g e r or aggregated so t h a t t h e i r r e j e c t i o n s are independent of i o n i c s t r e n g t h . The dye f i l t r a t e s contained c o l o r e d species i n a d d i t i o n t o the product dye. This was determined by s e p a r a t i n g the c o l o r e d species by l i q u i d chromatography and comparing the e l e c t r o n i c s p e c t r a of each c o l o r e d e l u t i o n band w i t h the p u r i f i e d product dyes. Thus conclusions f o r the d i f f e r e n c e i n behavior cannot be based on the product-dye s t r u c t u r e s . I n summary, the dynamically-formed u l t r a f i l t e r d i d not separate c o l o r e d compounds from the s a l t . The dynamicallyformed h y p e r f i l t e r e f f e c t i v e l y r e t a i n e d the c o l o r e d compounds w h i l e p r o v i d i n g low r e j e c t i o n of the s a l t . Because the s a l t r e j e c t i o n was low i n the concentrated s o l u t i o n s r e s u l t i n g i n low osmotic pressure d i f f e r e n c e s , the f i l t r a t i o n of concentrated s o l u t i o n s w i t h high i o n i c strengths could be accomplished at the r e l a t i v e l y low o p e r a t i n g pressure o f 5-2 MPa (750 p s i ) . Renovation of Dye Range Wash Water f o r Reuse A p r o j e c t i s i n progress t o demonstrate the c l o s e d - c y c l e operation of a production dye range. The cooperative agreement w i t h LaFrance I n d u s t r i e s i n v o l v e s the Environmental P r o t e c t i o n

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

444

SYNTHETIC MEMBRANES:

A

>

1

A

1

k

HF

AND U F

USES

A

a b s o r b a n c e

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o

O O

1

1

1

• •

•

•

•

•

i

0 0

.02

l .04 C o n d u c t i v i t y

Figure 4.

i .08

1

.0 6 (

.10

S/cm)

Rejection (v) and flux (J ) vs. conductivity for the acid yellow CI 13906 filtrate: P = 5.2 MPa (750 psi). 0

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

BRANDON

445

Dynamic Membranes

ET AL.

1.0

A .8 .6 r

O O

.4 .2

con ducti vity

I

l_

0 2

10° J

0

(m/s)

O

• o

0

.02

.04

.06

-08

(s/cm)

Conductivity

Figure 5. Rejection (r) and flux (J ) vs. conductivity for the acid blue CI 62055 filtrate:filledsymbols represent the concentration procedure; open symbols the dilution procedure; P = 5.2 MPa (750 psi). 0

30

I O

y e l l o w

A

blue

o

-

O

o

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A A i

D

Figure 6.

o

O

10

.1

I

.2

I

.3

Dependence of the separation factor « feed

L A

>4

on the conductivity (L) of the

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

In

Synthetic Symposium FLUX, GAL/FT

ACS /DAY

DIRECT ACRYLIC BLEACH DIRECT ACRYLIC DISPERSED DIRECT ACRYLIC DISPERSED DIRECT ACRYLIC ACRYLIC ACRYLIC DIRECT AUTOMOTIVE ACRYLIC DIRECT ACRYLIC DIRECT DIRECT DIRECT AUTOMOTIVE ACRYLIC DIRECT ACRYLIC BLEACH DCRECT DIRECT DIRECT DIRECT ACRYLIC DIRECT ACRYLIC DISPERSED DIRECT REACTTVE DIRECT

S3Sn 3fl QNV 3H :S3NVHaiA[3P\[ 3U3H1NAS

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In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

T Y P F