Phase Equilibria and Fluid Properties in the Chemical Industry Estimation and Correlation Truman S Storvick, EDITOR University of Missouri, Columbia Stanley I Sandler, EDITOR University of Delaware A symposium co-sponsored by the Engineering Foundation, the American Institute of Chemical Engineers, and the National Science Foundation at the Asilomar Conference Grounds Pacific Grove, CA, January 16-21, ACS 1977 SYMPOSIUM SERIES AMERICAN CHEMICAL SOCIETY WASHINGTON, D C 1977 In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 Library of Congress CIP Data Phase equilibria and fluid properties in the chemical industry (ACS symposium series; 60 ISS Includes bibliographical references and index Phase rule and equilibrium—Congresses Thermodynamics—Congresses Liquids—Congresses I Storvick, Truman S., 1928 II Sandler, Stanley I., 1940 III Engineering Foundation, New York IV Series: American Chemical Society ACS symposium series; 60 QD501.P384 ISBN 0-8412-0393-8 Copyright © 660.2'9'63 ACSMC8 60 1-537 77-13804 (1977) 1977 American Chemical Society A l l Rights Reserved N o part of this book may be reproduced or transmitted in any form or by any means—graphic, electronic, including photocopying, recording, taping, or information storage and retrieval systems—without written permission from the American Chemical Society The citation of trade names and/or names of manufacturers in this publication is not to be construed as an endorsement or as approval by ACS of the commercial products or services referenced herein; nor should the mere reference herein to any drawing, specification, chemical process, or other data be regarded as a license or as a conveyance of any right or permission, to the holder, reader, or any other person or corporation, to manufacture, reproduce, use, or sell any patented invention or copyrighted work that may in any way be related thereto PRINTED IN T H E UNITED STATES OF AMERICA In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 ACS Symposium Series Robert F Gould, Editor Advisory Board D o n a l d G Crosby Jeremiah P Freeman E Desmond G o d d a r d Robert A Hofstader J o h n L Margrave N i n a I M c C l e l l a n d J o h n B Pfeiffer Joseph V Rodricks A l a n C Sartorelli Raymond B Seymour R o y L Whistler Aaron W o l d In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 FOREWORD The A C S SYMPOSIUM SERIES was founded in 1974 to provide a medium for publishing symposia quickly in book form The format of the SERIES parallels that of the continuing ADVANCES IN CHEMISTRY SERIES except that in order to save time the papers are not typeset but are reproduced as they are submitted by the authors in camera-ready form As a further means of saving time, the papers are not edited or reviewed except by the symposium chairman, who becomes editor of the book Papers published in the A C S SYMPOSIUM SERIES are original contributions not published elsewhere in whole or major part and include reports of research as well as reviews since symposia may embrace both types of presentation In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 DEDICATION This work is dedicated to the memory of three men who contributed to our understanding of fluid properties Ping L Chueh Shell Development C o Houston, T X Geral M c G i l l University Montreal, Quebec, Canada Thomas M Reed University of Florida Gainesville, FL Illness and accident cut short their careers in 1976 and have left us with their last contribution In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 PREFACE We had two goals in organizing this conference T h e first was to * * provide a forum for state-of-the-art reviews of an area of chemical engineering often referred to as "thermodynamics and physical properties." T h e reviews should represent the work of both the academic researcher and the industrial practitioner This we thought was both necessary and timely because there were obvious dislocations between the current needs of the industrial chemical engineer and the research being done at universities, on the one hand, and the slow acceptance of new theoretical tools by the industria Our second objective was, through these reviews and the ensuing discussion, to develop a collection of research objectives for the next decade W e asked the session reporters to try to identify the important research problems that were suggested in the presentations and discussions of the sessions, as well as to set down their thoughts in this regard In this way, the major papers in this volume summarize the current state of research and industrial practice, while the reporter's summaries provide a listing of important questions and research areas that need attention now T h e conference was attended by 135 engineers and scientists from North America, Europe, Asia and Africa They represented, in almost equal numbers, the industrial and academic sectors Recognized authorities, presently active in physical properties work, were chosen to be speakers, panel members, session reporters and session chairmen T h e conference was held at the Asilomar Conference Grounds on the Monterey Penninsula of California, the beautiful setting matched by idyllic weather W e have tried to give an accurate account of the material presented at the conference sessions, but the printed word cannot reflect the friendships that were established nor the extent of the academioindustrial dialogue which was initiated Similarly, the unusual enthusiasm of the conference is not reflected here Indeed, this enthusiasm was so great that there were six ad-hoc sessions, continuations of scheduled sessions and meetings packed into the four sunny afternoons of the meeting Many important areas of work were identified as needing further attention during the next decade Several obvious to us (in no special order) are listed below: • It was generally agreed that nine out of 10 requests for data by xi In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 design engineers were for vapor-liquid equilbrium or mixture enthalpy data Reduction to field-level practice of either data banks or estimating procedures to supply this information would be very useful • Significant progress has been made on the group contribution methods for estimating phase equilibrium data Further development of these procedures is clearly justified • Perturbation methods based on theory from physics and chemistry, electronic computer simulation studies, and careful comparisons with real fluid behavior are moving quickly toward producing an effective equation of state for liquids These efforts are in the hands of the theoretician today, but further development and reduction to practice should be explored • F l u i d transport properties were not the primary concern at this conference, but progress between prediction and experiment for viscosities and thermal conductivities of gaseous mixtures was reported Clearly, much work needs to be done, especially for liquids • Real difficulties remain when attempts are made to predict, to extrapolate, or even to interpolate data for multicomponent mixtures containing hydrocarbons, alcohols, acids, etc Such systems were affection- ately identified as a "Krolikowski mess" at the conference Multicom- ponent mixtures of this kind may include more than one liquid and/or solid phase and with components that "commit chemistry" as well as physically distribute between the phases are commonly encountered in industrial practice from nightmare to T h e goal for the future is to reduce these problems headache proportions in industrial applications, though they may continue to remain an enigma for the theoretician • Cries for more experimental data were often heard Special needs include high pressure vapor-liquid equilibrium data; data on several properties for mixtures with very light, volatile components in heavy hydrocarbon mixtures; ionic solutions; acid gases in hydrocarbons; and certainly more emphasis on mixtures containing aromatic hydrocarbons Data with intrinsic value for design work and accurate enough for discriminating theoretical comparisons should have high priority Signifi- cantly, several conferees stated that their primary sources of new experimental data are rapidly shifting to laboratories outside the United States A n important measure of the success of a conference is its long-term impact It remains to be seen whether this conference results in any permanent interchange of ideas between academic and industrial engineers and whether the ideas expressed influence research in the coming years xii In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 A cknou/ledgments This volume is based on the Engineering Foundation Conference, "The Estimation and Correlation of Phase Equilibria and F l u i d Properties in the Chemical Industry," convened at the Asilomar Conference Grounds, Pacific Grove, C A , on Jan 16-21, 1977 T h e views presented here are not necessarily those of the Engineering Foundation, 345 East 47th St., New York, N.Y 10017 T h e advice, financial and moral support, and the concern for local arrangements, publicity, registration by Sandford Cole, Harold Commerer, Dean Benson and their staff permitted us to concentrate on the technical aspects of the meeting Manuscript typing was done by the University of Missouri, Stenographic Services Department Major funding for the conference by the National Science Foundation was a key ingredien for many American and have been otherwise unable to participate T h e interest and support of Marshall L i h and William Weigand of the National Science Foundation were especially appreciated The American Institute of Chemical Engineers made important contributions by co-sponsoring and publicizing the conference W e also thank the members of the Organizing Committee: Stanley Adler, Pullman-Kellogg Co.; Howard Hanley of the National Bureau of Standards; Robert Reid of the Massachusetts Institute of Technology; and L y m a n Yarborough of the Amoco Production C o They brought focus and structure to the general concept of the conference we brought to them Finally, and most important we thank the speakers, session reporters, and chairman who d i d their work diligently and in the best scientific tradition; and the conferees for their enthusiastic participation and important discussion contributions that made this conference special T S STORVICK STANLEY I SANDLER University of Missouri—Columbia University of Delaware June 1977 xiii In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 Origin of the Acentric Factor K E N N E T H S P I T Z E R University of California, Berkeley, Calif 94720 It was a pleasure t Sandler' invitatio this conference by reviewin which led m to propose the acentric factor in 1955 Although I had e followed s m of the work in which others have used the acentric oe factor, the preparation of this paper provided the incentive to review these applications more extensively, and I was most pleased to find that so much has been done I want to acknowledge at once m debt to John Prausnitz for suggestions in this review of recent y work as well as in m n discussions through the years ay Beginning in 1937, I had been very m c interested in the uh thermodynamic properties of various hydrocarbon molecules and hence of those substances in the ideal gas state This arose out of work with K m in 1936 on the entropy of ethane (1) which led to the ep determination of the potential barrier restricting internal rotation With the concept of restricted internal rotation and s m advances oe in the pertinent statistical mechanicsitbecame possible to calculate rather accurately the entropies of various light hydrocarbons (2) Fred Rossini and I collaborated in bringing together his heat of formation data and m entropy and enthalpy values to provide a y complete coverage of the thermodynamics of these hydrocarbons in the ideal gas state (3) As an aside I cite the recent paper of Scott (4) w o presents the best current results on this topic h But real industrial processes often involve liquids or gases at high pressures rather than ideal gases Hence it was a logical extension of this work on the ideal gases to seek methods of obtaining the differences in properties of real fluids from the respective ideal gases without extensive experimental studies of each substance M first step in this direction came in 1939 when I was able to y provide a rigorous theory of corresponding states (5) on the basis of intermolecular forces for the restricted group of substances, argon, kryptron, xenon, and in good approximation also methane This pattern of behavior c m to be called that of a simple fluid It is ae the reference pattern from which the acentric factor measures the departure Possibly w should recall the key ideas T e e h In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 PHASE EQUILIBRIA AND FLUID PROPERTIES IN CHEMICAL INDUSTRY i n t e r m o l e c u l a r p o t e n t i a l must be given by a u n i v e r s a l f u n c t i o n w i t h s c a l e f a c t o r s of energy and d i s t a n c e f o r each substance By then i t was well-known that the dominant a t t r a c t i v e f o r c e f o l l o w e d an i n v e r s e sixth-power p o t e n t i a l f o r a l l of these substances A l s o the r e p u l s i v e f o r c e s were known to be very sudden Thus the i n v e r s e s i x t h , power term w i l l dominate the shape of the p o t e n t i a l curve at longer d i s t a n c e s Even without d e t a i l e d t h e o r e t i c a l reasons f o r exact s i m i l a r i t y of shorter-range terms, one could expect that a u n i v e r s a l f u n c t i o n might be a good approximation I n a d d i t i o n one assumed s p h e r i c a l symmetry (approximate f o r methane), the v a l i d i t y of c l a s s i c a l s t a t i s t i c a l mechanics, and that the t o t a l energy was determined e n t i r e l y by the v a r i o u s i n t e r m o l e c u l a r d i s t a n c e s I should r e c a l l that i t was not f e a s i b l e i n 1939 to c a l c u l a t e the a c t u a l equation of s t a t e from t h i s model One could o n l y show that i t y i e l d e d correspondin s t a t e i n terms of the reduce pressure One could p o s t u l a t e other models which would y i e l d a c o r r e s ponding-states behavior but d i f f e r e n t from that of the simple f l u i d However, most such molecular models were s p e c i a l and d i d not y i e l d a s i n g l e f a m i l y of equations Rowlinson (6) found a somewhat more general case; he showed that f o r c e r t a i n types of a n g u l a r l y dependent a t t r a c t i v e f o r c e s the net e f f e c t was a temperature dependent change i n the r e p u l s i v e term From t h i s a s i n g l e f a m i l y of funct i o n s arose I had observed e m p i r i c a l l y , however, that the f a m i l y r e l a t i o n ship of equations of s t a t e was much broader even than would f o l l o w from R o w l i n s o n s model I t included g l o b u l a r and e f f e c t i v e l y s p h e r i c a l molecules such as tetramethylmethane (neopentane), where no a p p r e c i a b l e angular dependence was expected f o r the i n t e r m o l e c u l a r p o t e n t i a l , and f o r elongated molecules such as carbon d i o x i d e the angular dependence of the r e p u l s i v e f o r c e s seemed l i k e l y to be at l e a s t as important as that of the a t t r a c t i v e f o r c e s Thus the core model of K i h a r a (7) appealed to me; he assumed that the LennardJones 6-12 p o t e n t i a l a p p l i e d to the s h o r t e s t d i s t a n c e between cores i n s t e a d of the d i s t a n c e between molecular centers He was a b l e to c a l c u l a t e the second v i r i a l c o e f f i c i e n t f o r v a r i o u s shapes of core And I was a b l e to show that one obtained i n good approximation a s i n g l e f a m i l y of reduced second v i r i a l c o e f f i c i e n t f u n c t i o n s f o r cores of a l l reasonable shapes By a s i n g l e f a m i l y I mean that one a d d i t i o n a l parameter s u f f i c e d to d e f i n e the equation f o r any p a r t i c u l a r case While t h i s d i d not prove that a l l of the complete equations of s t a t e would f a l l i n t o a s i n g l e f a m i l y , i t gave me enough encouragement to go ahead w i t h the numerical w o r k — o r more a c c u r a t e l y to persuade s e v e r a l students to undertake the n u m e r i c a l work Let me emphasize the importance of f i t t i n g g l o b u l a r molecules i n t o the system I f these molecules are assumed to be s p h e r i c a l i n good approximation, they are easy to t r e a t t h e o r e t i c a l l y Why aren't they simple f l u i d s ? Many t h e o r e t i c a l papers ignore t h i s q u e s t i o n In f l u i d p r o p e r t i e s neopentane departs from the simple f l u i d p a t t e r n much more than propane and almost as much as n-butane But propane f In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 414 P H A S E EQUILIBRIA A N D F L U I D PROPERTIES IN C H E M I C A L INDUSTRY Very few r e f i n e r y operations operate about 800°F The c o a l g a s i f i c a t i o n processes, on the other hand, s t a r t a t about 1300°F and some operate up to n e a r l y 3000°F Many o f the new processes operate a t pressures of about 1000 p s i a R e l i a b l e zero pressure e n t h a l p i e s up to these temperatures a r e a v a i l a b l e f o r most of the m a t e r i a l s found i n g a s i f i e r s , but the mixing r u l e s and pressure c o r r e c t i o n s which the trade has been using f o r nonpolar mixtures are probably inadequate Another c o m p l i c a t i o n i s that the systems found i n g a s i f i e r s are r e a c t i n g systems a t high temperatures I n a d d i t i o n to the heterogeneous r e a c t i o n s , the homogeneous gas phase has many p o s s i b l e r e a c t i o n s such as: CO + H = C + H CH + H = C 2NH = N + 3H and these r e a c t i o n s a r e c a t a l y z e d by the ash components and a r e promoted by the l a r g e area s o l i d surfaces of the coke For some designs, i t may be necessary to p r e d i c t the chemical e q u i l i b r i a i n these systems V a p o r - l i q u i d e q u i l i b r i u m p r e d i c t i o n s i n these systems are p a r t i c u l a r l y i n t e r e s t i n g , and w i l l r e q u i r e some d i f f e r e n t techniques than the ones that the petroleum i n d u s t r y has used At the high pressures of the second generation g a s i f i e r s , water s t a r t s to condense as the gas i s cooled to about 500°F, and continues to condense down to the lowest temperature, probably around 100 F The condensate contains a p p r e c i a b l e q u a n t i t i e s of hydrogen s u l f i d e and carbon d i o x i d e , probably a l l of the ammonia, p o s s i b l y phenols and cyanides Depending on the type of g a s i f i e r , a hydrocarbon phase may a l s o c o n d e n s e , — r a n g i n g from t a r to benzene I n some u n l i k e l y circumstances, two hydrocarbon phases may separate, one l i g h t e r and one h e a v i e r than water The mutual s o l u b i l i t y of the phases i s a f f e c t e d by the d i s s o l v e d components, a l l of which a r e s o l u b l e i n a l l the phases And the e q u i l i b r i u m c a l c u l a t i o n s are f u r t h e r complicated by r e a c t i o n s i n the l i q u i d water phase, between the a c i d i c and b a s i c components The L u r g i gas cleanup system, shown i n Figures 2, 3, and 4, i s a good example of the problems i n v o l v e d Each of the f i v e counter-current exchangers represents a s e r i e s of complicated, simultaneous e q u i l i b r i u m and heat t r a n s f e r c a l c u l a t i o n s f o r a p o l a r mixture, w i t h a three- and p o s s i b l y four-phase system ( I f the s o l i d f i n e s are considered, the system i s f o u r , p o s s i b l y f i v e phases; but the s o l i d phase, which most l i k e l y stays w i t h the t a r , i s g e n e r a l l y neglected.) N e i t h e r the a v a i l a b l e enthalpy data, nor the a v a i l a b l e e q u i l i b r i u m c o r r e l a t i o n s , a r e r e a l l y adequate f o r such m i x t u r e s , and the problems would be worse i f the pressures were h i g h e r , as they may be i n the f u t u r e This i s not to say that In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 20 HIPKIN Thermodynamic Data Needs 415 L u r g i cannot design such a system; o b v i o u s l y they have, the p l a n t s so designed work E i t h e r L u r g i uses p r o p r i e t a r y data, o r they design from past experience; i n e i t h e r case, t h e i r techniques a r e not a v a i l a b l e to the t e c h n i c a l p u b l i c Nor i s i t known how much s a f e t y i s b u i l t i n t o t h e i r designs Cryogenic Region A t the low end of the temperature s c a l e , there are other data needs Here, the designer needs r e l i a b l e data f o r a s m a l l number o f simple systems And he needs data on s o l i d - l i q u i d phase r e l a t i o n s f o r a few m a t e r i a l s , notably carbon d i o x i d e , hydrogen s u l f i d e , and the higher hydrocarbons The c h i e f area where these data (or c o r r e l a t i o n s ) are r e q u i r e d has been f o r l i q u i f i e d n a t u r a l gas p l a n t s I t would appear t h a t the a v a i l a b l e data should be adequate s i n c e there i s a l o t o f i n f o r m a t i o n on the l i g h t hydrocarbons; w i l l be u n p l e a s a n t l y s u r p r i s e of methane gas a t low temperatures v a r i e s between v a r i o u s p r e d i c t i o n methods He w i l l a l s o f i n d that i t i s d i f f i c u l t to p r e d i c t where carbon d i o x i d e c r y s t a l l i z e s out of the l i q u i d hydrocarbon phase as n a t u r a l gas i s cooled Since deep r e f r i g e r a t i o n i s expensive, cryogenic p r o c e s s i n g r e q u i r e s accurate c o r r e l a t i o n s Exxon has r e c e n t l y p u b l i s h e d a paper on t h e i r new c a t a l y t i c g a s i f i c a t i o n process, i n which c o a l impregnated w i t h potassium carbonate i s g a s i f i e d w i t h steam and oxygen a t a low temperature (1200-1300°F) and a pressure of about 500 p s i ( ) Under these c o n d i t i o n s , the p r o d u c t i o n o f methane i s maximized, and the overa l l r e a c t i o n i s almost i s e n t h a l p i c The carbon d i o x i d e and methane are separated from the carbon monoxide and hydrogen, which are r e c y c l e d to the r e a c t o r The s e p a r a t i o n of methane from carbon monoxide and hydrogen i s cryogenic and, f o r good economy, r e q u i r e s r e l i a b l e enthalpy and e q u i l i b r i u m data Almost any cryogenic s e p a r a t i o n design becomes, a t some p o i n t , a balance between heat exchange costs and compression c o s t s And the optimum (minimum t o t a l cost) u s u a l l y occurs a t exchanger temperature d i f f e r e n c e s of only a few degrees, sometimes only a f r a c t i o n o f a degree To design exchangers to these c l o s e approaches r e q u i r e s very accurate e q u i l i b r i a data, and good e n t h a l py data I f the p l a n t uses a mixed r e f r i g e r a n t , the need i s more pronounced How Good Do the Data Need to Be? For the high temperature p o l a r mixtures a t h i g h p r e s s u r e s , the need i s p r i m a r i l y f o r p r e d i c t i o n methods that can be f a i r l y sloppy, but even more important i s some knowledge o f the degree of u n c e r t a i n t y i n the method The design engineer faced w i t h c a l c u l a t i n g the enthalpy o f a mixture o f CO, CO2, H , and CH4 w i t h 50% steam a t 1000 p s i a and 1500°F w i l l probably take the four gases at zero pressure and 1500°F, use some g e n e r a l i z e d pressure c o r r e c t i o n to r a i s e the mixture to 500 p s i a , and add the enthalpy o f In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 416 P H A S E EQUILIBRIA AND F L U I D PROPERTIES IN CHEMICAL INDUSTRY pure steam a t 500 p s i a and 1500°F Or, he may take a l l f i v e components at zero pressure (1 p s i a f o r the steam because he i s u s i n g steam t a b l e s ) and 1500°F, and use the g e n e r a l i z e d pressure c o r r e c t i o n to r a i s e the mixture to 1000 p s i a I f he does both, he w i l l have two d i f f e r e n t answers I f he uses d i f f e r e n t pressure c o r r e c t i o n s , he w i l l have more d i f f e r e n t answers I f he i s knowl e d g a b l e , he w i l l worry a l i t t l e about the f a c t that the pressure c o r r e c t i o n i s based on l i g h t hydrocarbons, or on a i r I f he checks, he w i l l f i n d t h a t the e f f e c t of pressure on the enthalpy of steam, from h i s steam t a b l e s , i s badly p r e d i c t e d by the genera l i z e d c o r r e l a t i o n What he needs i s some method which t e l l s him that h i s c a l c u l a t e d enthalpy has a reasonable p r o b a b i l i t y of being o f f by, say, + 10% Given that u n c e r t a i n t y , he can design enough s a f e t y f a c t o r i n t o the u n i t to take care of i t H i s problem occurs when he b e l i e v e o f f by 10% L a t e r , as the s y n f u e l i n d u s t r y becomes more s o p h i s t i c a t e d , b e t t e r accuracy w i l l be needed The heat flows around a l a r g e g a s i f i e r p l a n t are immense, and much of t h a t heat i s s u p p l i e d from expensive oxygen r e a c t i n g w i t h the c o a l A high-BTU syngas p l a n t producing 250 m i l l i o n standard c u b i c f e e t per day of gas a l s o produces about 15,000 tons per day of carbon d i o x i d e , e q u i v a l e n t to a heat of combustion of b i l l i o n BTU per hour To a v o i d l a r g e and expensive s a f e t y f a c t o r s i n the design of such p l a n t s , a c c u r ate enthalpy methods w i l l be needed For cryogenic s e p a r a t i o n s , i n d u s t r y already has the a p p r o x i mate methods What i s needed now i s accurate data and methods to reduce the cost of unnecessary s a f e t y f a c t o r s on expensive deep r e f r i g e r a t i o n The i n d u s t r y a l s o needs techniques to p r e d i c t s o l i d phase formation When Are the Data Needed? The petroleum i n d u s t r y and the n a t u r a l gas p r o c e s s i n g indust r y operated f o r about 40 years b e f o r e any r e a l attempt to develop data and c o r r e l a t i o n s was made They used crude approximations, such as Raoult's and Dalton's Laws, because they were good enough for the p r o c e s s i n g that the i n d u s t r y was doing a t t h a t time As p r o c e s s i n g became more complex, b e t t e r data were needed and were d e v e l o p e d , — a trend that s t i l l continues The s y n t h e t i c f u e l i n d u s t r y cannot undergo a comparable i n c u b a t i o n p e r i o d f o r i t s data requirements f o r two main reasons: The s y n t h e t i c f u e l s are intended to augment petroleum f u e l s that are p r e s e n t l y produced by s o p h i s t i c a t e d proc e s s i n g techniques based on adequate thermodynamic data S y n t h e t i c f u e l p l a n t s w i l l be horrendously expensive, and there i s a l a r g e economic i n c e n t i v e to provide data good enough to e l i m i n a t e expensive s a f e t y f a c t o r s from the design In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 20 HIPKIN Thermo dynamic Data Needs 417 Literature Cited Musser, William N., and John H Humphrey, "In-Situ Combustion of Michigan Oil Shale: Current Field Studies", Eleventh Intersociety Energy Conversion Engineering Conference, page 341 (1976) "Joint Application of Michigan-Wisconsin Pipeline Company and ANG Coal Gasification Company for Certificates of Public Convenience and Necessity", Docket No CP75-278 before the Federal Power Commission, Volume (1975) Crouch, W G., and R D Klapatch, "Solids Gasification for Gas Turbine Fuel: 100 and 300 BTU Gas", Eleventh Intersociety Energy Conversion Engineering Conference, page 268 (1976) Epperly, W R., an tion for SNG Production", Eleventh Intersociety Energy Conversion Engineering Conference, page 249 (1976) In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 Discussion C A ECKERT Two papers given i encountered by s c i e n t i s t under unusual c o n d i t i o n s Mike M o d e l l s paper s t r e s s e d the d i f f i c u l t i e s thermodynamicists have i n d e a l i n g w i t h multicomponent systems i n the c r i t i c a l r e g i o n He reviewed the c r i t e r i a f o r c r i t i c a l i t y i n multicomponent systems and developed the use of Legendre transformations to f i n d a s t a b l e p o i n t on the s p i n o d a l s u r f a c e Much of the d i s c u s s i o n f o l l o w i n g the paper centered about whether one could use the same type of approach to determine the b i n o d a l s u r f a c e — t h a t i s , i n a p r a c t i c a l sense, f i n d the compos i t i o n of c o e x i s t i n g phases Some comments on t h i s problem were as follows: H Ted Davis, U n i v e r s i t y of Minnesota, "The s p i n o d a l c o n d i t i o n s are u s e f u l i n c o n s t r u c t i n g the b i n a r y and ternary phase d i a grams M e i j e r i n g ( has used the s p i n o d a l e x t e n s i v e l y to l o c a t e _) c r i t i c a l p o i n t s f o r r e g u l a r s o l u t i o n s Once the c r i t i c a l p o i n t i s l o c a t e d , then a simple numerical technique can be used to march along a b i n o d a l to c o n s t r u c t the b i n o d a l curve Overlapping b i n o d a l s can then be used to l o c a t e three phases i n e q u i l i b r i u m , where such e x i s t Such a process i s being c a r r i e d out f o r l i q u i d phase diagrams by J e f f K o l s t a d working w i t h C E S c r i v e n and me at Minnesota." John S Rowlinson, U n i v e r s i t y of Oxford, United Kingdom, " I would l i k e to make two p o i n t s : I By c o n c e n t r a t i n g on the s p i n o d a l s u r f a c e , as Modell and Reid's elegant transformations do, one runs the r i s k of overl o o k i n g other kinds of behavior on c r i t i c a l s u r f a c e s For example, the s p i n o d a l curve may be o u t s i d e one of the b i n o d a l curves This does happen w i t h the ternary diagram f o r which G i s q u a d r a t i c i n composition, a system which was analyzed f u l l y by M e i j e r i n g (_1) Here, there a r e three t r i c r i t i c a l p o i n t s , and i t i s the presence of these, which a r e s i n g u l a r i t i e s not envisaged i n G i b b s treatment, which would i n v a l i d a t e the use of the s p i n o d a l alone as a s o l e c r i t e r i o n of c r i t i c a l behavior The Gibbs (and r e l a t e d ) treatments assume that the extenE f 418 In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 ECKERT 419 Discussion s i v e thermodynamic f u n c t i o n s form an a n a l y t i c s u r f a c e U = f(V,S,N^) around the c r i t i c a l p o i n t This assumption c o n f l i c t s w i t h the known e x i s t e n c e of "weak" s i n g u l a r i t i e s at t h i s p o i n t (e.g., Cy oo) In a mixture these s i n g u l a r i t i e s can g i v e r i s e to complic a t i o n s not, I t h i n k , encompassed i n M o d e l l s treatment Thus, R B G r i f f i t h s and Wheeler (_2) have suggested that there are "anomalies" on a g a s - l i q u i d c r i t i c a l curve f o r a b i n a r y mixture, not only at the c r i t i c a l azeotrope but a l s o at p o i n t s where the c r i t i c a l curve passes through the extremum w i t h respect to changes of pressure or temperature." The second paper of the evening given by Howard H i p k i n of B e c h t e l Corporation complimented the f i r s t i n that i t s t r e s s e d , from a much more p r a c t i c a l p o i n t of view, s p e c i f i c needs that w i l l be encountered i n the near f u t u r e by i n d u s t r i a l designers d e a l i n g w i t h methods f o r energy what s y n t h e t i c f u e l s migh what we know about such processes now p r e d i c t e d what they indeed might be He s t r e s s e d the need f o r heats of formation and Gibbs energies of formations at higher temperatures, e s p e c i a l l y f o r c o a l and o i l s h a l e ; f o r high temperature and pressure data e s p e c i a l l y for p o l a r mixtures; and the need f o r c a l c u l a t i o n a l methods f o r handling such data As one example he held f o r t h the spectre to an a n a l y s t of a five-phase system emerging from a L u r g i g a s i f i e r Rather extensive d i s c u s s i o n i n v o l v i n g a number of i n d i v i d u a l s f o l l o w e d d e a l i n g w i t h the imminent needs f o r new energy sources w i t h s m a l l l i k e l i h o o d of i t being s a t i s f i e d by n u c l e a r , s o l a r , or geothermal power However, severe problems e x i s t i n the u t i l i z a t i o n of c o a l or o i l shale i n terms of high c a p i t a l requirements coupled w i t h the environmental r e s t r i c t i o n s on emissions from such p l a n t s One q u i t e c o n s i d e r a b l e dilemma that becomes apparent i s that the production of energy from s y n t e h t i c f u e l s w i t h our current technology would only be p r a c t i c a l at c u r r e n t c a p i t a l c o s t s i f the s e l l i n g p r i c e of energy went up However, i t i s q u i t e evident that c a p i t a l costs are l i n k e d to energy c o s t s Thus, the consensus of the d i s c u s s i o n was that b e t t e r data are needed at higher temperatures and pressures, and i n the i n i t i a l stages, even r a t h e r "sloppy" data would be more u s e f u l than what i s now a v a i l a b l e This w i l l r e q u i r e b e t t e r m a t e r i a l s and may lead to new techniques such as, f o r example, s u p e r c r i t i c a l s e p a r a t i o n processes and higher temperature processes C e r t a i n l y the methods we now have f o r e s t i m a t i n g such p r o p e r t i e s w i l l prove inadequate, and new and b e t t e r methods w i l l c e r t a i n l y be r e q u i r e d As i l l u s t r a t e d so g r a p h i c a l l y by the f i r s t t a l k of the evening these w i l l undoubtedly be more d i f f i c u l t to develop and apply than current methods However, the general concensus was that i t i s q u i t e c l e a r that the energy c r i s i s w i l l soon be upon us i n a much more s e r i o u s sense than the general p u b l i c a p p r e c i a t e s , and we as s c i e n t i s t s and engineers must begin now to seek s o l u t i o n s i n terms of new data at more extreme c o n d i t i o n s and the thermodynamic framework w i t h i n which to apply them f In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 420 P H A S E EQUILIBRIA A N D F L U I D PROPERTIES IN C H E M I C A L INDUSTRY References Meijering, J L., Phillips Res Rep (1950) 5, 333; (1951) 6, 183 Griffiths, R B and Wheeler, J C Phys Rev (1970) 2, 1047 In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 21 A Group Contribution Molecular Model for Liquids and Solutions Composed of the Groups and CH , CH , OH, CO T NITTA, E A TUREK, R A GREENKORN, and K C CHAO Purdue University, West Lafayette, IN 47907 Group i n t e r a c t i o n model the d e s c r i p t i o n of a c t i v i t t i o n s Notable i n t h i s development are the p i o n e e r i n g work by P i e r o t t i , Deal and Derr (]L), Wilson and Deal (2), and subsequent c o n t r i b u t i o n s by S c h e l l e r (3), R a t c l i f f and Chao ( ) , Derr and Deal ( ) , and Fredenslund, Jones, and P r a u s n i t z ( ) N i t t a e t a l (7) extended the group i n t e r a c t i o n model to thermodynamic p r o p e r t i e s of pure p o l a r and non-polar l i q u i d s and t h e i r s o l u t i o n s , i n c l u d i n g energy of v a p o r i z a t i o n , pvT r e l a t i o n s , excess p r o p e r t i e s and a c t i v i t y c o e f f i c i e n t s The model i s based on the c e l l theory w i t h a c e l l p a r t i t i o n f u n c t i o n d e r i v e d from the C a r n a h a n - S t a r l i n g equation of s t a t e f o r hard spheres The l a t t i c e energy i s made up of group i n t e r a c t i o n c o n t r i b u t i o n s An important advantage of the model by N i t t a e t a l i s i t s a p p l i c a b i l i t y over a wide temperature range The same group parameters used i n the same equations have been found to g i v e good r e s u l t s at c o n d i t i o n s f o r which the c e l l model i s known to be a p p l i c a b l e — w h e r e the l i q u i d i s not "expanded", the reduced d e n s i t y i s g r e a t e r than two and the temperature i s not much above the normal b o i l i n g p o i n t I t i s not necessary to have d i f f e r e n t s e t s of group parameter values f o r d i f f e r e n t temperatures N i t t a e t a l (7) presented the p r o p e r t i e s of the groups CH3, CH2, OH, and CO and t h e i r i n t e r a c t i o n s Comparisons of the model and experimental data were made f o r a number of pure l i q u i d s and their solutions A d d i t i o n a l comparisons of s o l u t i o n p r o p e r t i e s w i t h the model c a l c u l a t e d values are presented here to cover the gamut of mixtures made up of the given groups from the non-polar/non-polar, through non-polar/polar, to p o l a r / p o l a r F i g u r e shows the p r e d i c t e d a c t i v i t y c o e f f i c i e n t s of n-hexane i n s o l u t i o n w i t h n-dodecane compared to experimental data by Broensted and Koefoed ( ) The same agreement i s obtained between our model and experimental data from the same source on the mixtures of other n-alkanes F i g u r e shows the p r e d i c t e d a c t i v i t y c o e f f i c i e n t s i n the system ethanol/n-octane at 75C i n comparison w i t h experimental 421 In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 422 P H A S E EQUILIBRIA A N D FLUID PROPERTIES IN C H E M I C A L INDUSTRY In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 21 NITTA E T A L Group Contribution Molecular Model 423 data by Boublikova and Lu ( ) The agreement i s the same as that p r e v i o u s l y reported by N i t t a e t a l (7) f o r the same system a t 45C w i t h data from the same source There i s a remarkable change i n a c t i v i t y c o e f f i c i e n t s i n t h i s system i n the temperature i n t e r v a l of 30C Thus the i n f i n i t e d i l u t i o n v a l u e of e t h a n o l i s reduced by a f a c t o r of about two w h i l e that of n-octane i s reduced by only about 10% w i t h t h i s temperature i n c r e a s e This remarkable change i s q u a n t i t a t i v e l y described by the model F i g u r e shows the p r e d i c t e d a c t i v i t y c o e f f i c i e n t s i n n-butanol/n-heptane a t 50C i n comparison w i t h the experimental data of A r i s t o v i c h e t a l (10) The agreement that i s obtained here f o r the h i g h a l c o h o l i s about the same as the p r e v i o u s l y reported r e s u l t s ( f o r the lower a l c o h o l s _) F i g u r e shows the p r e d i c t e d excess enthalpy of n-butanol/nheptane a t 15 and 55C i Nguyen and R a t c l i f f (11) and d e v i a t i o n s up to 30 cal/g-mole are observed f o r some compositions F i g u r e through show the a c t i v i t y c o e f f i c i e n t s i n the system n-hexane/2-propanone a t four temperatures 45, 20, -5, and -25C Experimental data are from Schaefer and R a i l (12) a t 45 and - C , and from R a i l and Schaefer (JL3) a t 20 and -25C The v a r i a t i o n of the a c t i v i t y c o e f f i c i e n t s w i t h temperature appears to be quant i t a t i v e l y d e s c r i b e d by our model The 45C isotherm was used i n the development of the p r o p e r t i e s of the CO group and the model i s t h e r e f o r e i n a sense f i t t e d to t h i s isotherm But the other isotherms were not used i n the development of the model, and the c a l c u l a t i o n s f o r them are of a p r e d i c t i v e nature F i g u r e shows the a c t i v i t y c o e f f i c i e n t s i n the system 2-propanal/n-hexanol (14) The molecular i n t e r a c t i o n s i n t h i s p o l a r / p o l a r mixture i s complex l e a d i n g to an apparent maximum i n the f i g u r e The e x i s t e n c e of the maximum i s c o r r e c t l y p r e d i c t e d by our model, but the c a l c u l a t e d v a l u e s seem to vary too r a p i d l y at s m a l l c o n c e n t r a t i o n s of acetone There a l s o seems to be c o n s i d e r a b l e u n c e r t a i n t y and s c a t t e r i n g of the experimental data i n the same range Acknowledgment This work was supported by N a t i o n a l Science Foundation through grants GK-16573 and ENG76-09190 D W Arnold a s s i s t e d i n the calculations Abstract The group contribution molecular model for liquids and solutions developed by Nitta et.al.is applied to properties of liquid solutions made up of the groups CH , CH , OH, and CO, and the results are compared with experimental data A wide range of molecular species in mixtures is included over a wide temperature range In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 424 P H A S E EQUILIBRIA A N D F L U I D PROPERTIES IN C H E M I C A L INDUSTRY In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 21 NITTA ET A L Group Contribution Molecular Model In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 425 426 P H A S E EQUILIBRIA A N D F L U I D PROPERTIES I N C H E M I C A L INDUSTRY M L FRRCTION N-HEXRNE OE Figure Activity coefficients in n-hexane-2-propanone at 5°C n r ~i r PE ITD R DC E cr C D _l Figure Activity coefficients in n-hexane—2-propanone at 20°C L _ M L FRRCTION N-HEXRNE OE In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 K O 21 NITTA E T AL Group Contribution Molecular Model Figure Activity coefficients in 2-propanone— n-hexanol at atm In Phase Equilibria and Fluid Properties in the Chemical Industry; 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Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 ... and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 4 PHASE EQUILIBRIA AND FLUID PROPERTIES IN CHEMICAL INDUSTRY. .. t In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 16 PHASE EQUILIBRIA AND FLUID PROPERTIES. .. at the beginning 1 In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977 12 PHASE EQUILIBRIA