CHEMICAL REACTION ENGINEERING A Story of Continuing Fascination

L. K. DoRAISWAMY Iowa State University Ames, IA 50011 ciples, one can only conceive of different disciplines of CRE. The areas mentioned above are precisely hemical engineering in its most general sense that. If all of them are to come under a single um­ is broadly centered on two aspects of chemical brella, then CRE, already interdisciplinary, would Cprocessing: transformation engineering and be truly ubiquitous. separation engineering. Transformation engineering Over the years, chemical reaction engineering has addresses the engineering of physical and chemical progressed along two rather different paths. In Eu­ change, while separation engineering deals with the rope the emphasis has been more on the application principles and tools by which the products of trans­ of new and exciting concepts to conventional tech­ formation can be obtained at stated levels of purity. nologies, including the "bread and butter" conven­ The engineering of chemical change constitutes the tions. On the other hand, in the United States core of chemical reaction engineering. Given the cen­ conventional technologies have not normally held trality of chemical change in any chemical process, it much attraction for academia, except perhaps in is surprising that the principles and practices of some areas such as catalysis. There is much to be chemical change did not coalesce into a well-defined said in favor of both approaches, but what is likely to area until the late 1950s. It was called "applied ki­ emerge as we move into the 21st Century is a bal­ netics" before that time. Part 3 of Chemical Process anced synthesis of the two paths. Principles, by Hougen and Watson,111 was perhaps the first book to attempt a coherent educational pre­ UNDERGRADUATE PROGRAMS IN CRE sentation of the principles of reactor design. Concepts of CRE are taught in different courses. The subsequent development of chemical reaction The emphasis in undergraduate curricula usually engineering (CRE) was rapid, almost dramatic, in tends to be on homogeneous reactions, catalytic re­ the 1960s and 1970s. The increasing use of sophisti­ actions, and occasionally on multiphase reactions cated methods, so aptly and appropriately discussed involving two or more reactive phases. It is impor­ by Aris,t21 provides a reflective backdrop to the con­ tant that students get a broad exposure to various tinuing research in this area. The field has expanded areas and systems covered by CRE in the junior so vastly and so heterogeneously, through the export year-in addition to a more rigorous course involv­ of its basic theme (interaction between chemical and ing a few selected systems (depending on the inter­ physical factors) to other areas of chemical transfor­ est and expertise of the instructor). It is not uncom­ mation, that its own scope-if one can conceive of a mon in today's world to find a graduating student scope for this "moving boundary problem"-is who has had little or no exposure to the emerging now being increasingly linked ("confined" is not areas of a subject, including CRE. This is a situation the right word) to chemical and petrochemical pro­ that must be addressed immediately. Students must cesses. Among these are biochemical reaction be given a firmer grounding in order to cope with the engineering, microelectronic reaction engineering, challenges of the next century. polymer reaction engineering, and electrochemical L. K. Doraiswamy received his BS from Ma­ reaction engineering. dras University and his MS and PhD from the In the author's opinion, this is an irreversible change University of Wisconsin. He is presently the Herbert L. Stiles professor at Iowa State Univer­ (perhaps in the right direction), and chemical reac­ sity, where he came after retiring as director of tion engineering will continue to grow vertically within India 's National Chemical Laboratory. His re­ search has spanned several areas of chemical its own province, but always overlapping interac­ reaction engineering: gas-solid (catalytic and tively with the boundaries of its progeny. In any case, noncatalytic) reactions, stochastic analysis, and surface science approach to catalytic reactor considering the quick dispersal of knowledge that is design. evident today and the commonality of many prin- © Copyright ChE Division of ASEE 1992 184 Chemical Engineering Education It is not uncommon in today's world to find a graduating student who has had little or no exposure to the emerging areas of a subject, including CRE. This is a situation that must be addressed immediately. Students must be given a firmer grounding in order to cope with the challenges of the next century.

Another concept that should be implemented is a It should also be mentioned that a regular gradu­ scaled-down version of the think-tank concept in ate course in CRE should involve a problem where which the student is given a design problem and the student is required to design a reactor for a makes no a priori assumption as to the type of reac­ selected reaction, starting from the base level-a tor to be used. This is beautifully brought out in a literature search for getting the correct rate equa­ Danckwerts Memorial Lecture by 0. Levenspiel13J tion. (This is slightly different from Levenspiel's where he illustrates the concept with a specific ex­ concept where the reaction is new and no infor­ ample. This approach stimulates thinking and analy­ mation is available.) Rase's Chemical Reactor De­ sis, and every effort should be made to provide a sign for Process Plantsrs1 contains such examples in course, or some kind of an individualized or tutorial its second volume. In today's context, however, these mechanism, to foster an "educational think tank" of examples should have a higher content of analysis the type proposed. and modeling.

COMPLEMENTARY ROLES MORE CHEMISTRY IN CRE OF ANALYSIS AND APPLICATION And-let's face it-the basis of all chemical engi­ All too often, at the end of a course the student has neering is, after all, chemistry, and the average learned most of the principles but has no clue as to chemical engineering student's knowledge of chem­ the systems (existing or potential) where they might istry is less than it should be. Either during a course be used. Sharma and Doraiswamy141 addressed this in CRE or by additional coursework in chemistry, problem in their book, where many examples are students must be required to gain a firmer feel for given which illustrate principles or design situa­ chemistry-definitely for inorganic and organic chem­ tions. Furthermore, the student should acquire a istry, and biochemistry and polymer chemistry in feel for numbers, e.g., What is a "slow" reaction? special cases. Here, students of biochemical engi­ What is the range of effective thermal conductivities neering or polymer reaction engineering are at an of common catalysts? What is the range of liquid­ advantage since they enjoy greater exposure to the side mass transfer coefficients in some real systems? chemistry aspects of the subject than do students in The argument that these concepts can be acquired a regular CRE course in chemical engineering. Such later is moot and less than comforting. exposure at an early stage enhances the student's ability not only to deal with everyday problems sub­ This brings us to the pedagogic problem of analy­ sequently encountered on the job, but also in later sis vs. application. Many books, including Bird, years to formulate exciting problems of current or 5 Stewart, and Lightfoot's Transport Phenomena,L 1 potential relevance. The need for more chemistry in tend to be analysis oriented. There is great merit in chemical engineering was stressed by the author in that approach- it was certainly the correct approach a lecture (delivered at Wisconsin some years ago111) at a time when there was an overdose of empiricism which included a number of examples to strengthen and when descriptive and "experience" aspects of the argument. process technology held sway. But it is increasingly evident that analysis and application must comple­ SOME RESEARCH AREAS ment each other. In CRE courses, for example, one In a field that covers such a large mix of possibili­ can talk of controlling regimes and can present ties, it would be presumptuous to list areas for con­ detailed analytical methods for discerning the tinued or future attention. Even so, there are certain controlling regimes, but it should be supplemented areas which have the potential for significant im­ with industrial (or even laboratory) examples of pact on the chemical industry (used in its broadest reactions conforming to those regimes. Thus, if sense). The following suggestions are perceptions one is considering the mass transfer regime, it not uncolored by the author's personal fancy or evalu­ would be instructive to illustrate with examples ation, and should therefore be viewed in that light. such as dehydrogenation of cyclohexane, decom­ position of hydrogen peroxide, and hydrogenation Catalysis and Catalytic Reaction Engineering of phenol (to name a few). In an age where there is an increasing tendency to Fall 1992 185 frown on conventional topics, catalysis is a refresh­ methanol. It is here that early exposure to inorganic ing exception. It is among the oldest areas in chem­ chemistry would be most useful. It would also be istry, and yet it continues to be new. Perhaps its useful in catalyst preparation technology, and it is main driving forces are the omnipotence of catalysis in this area that our ignorance coefficient is woefully and the intriguing fact that, in spite of its long run, high. Impregnation and drying of catalysts are still it is just beginning to emerge from the shadows of almost entirely empirical operations. The analysis of empiricism. We are still a long way from answering Varma and collaborators in a series of ten papers the question "Can one design a catalyst for a given (see, for example, Part 9 which contains all previous requirement?"-this could be the main reason for referencest141 and Part 10, to appear soon) shows that the unrelenting research in this area. With the help an optimum catalyst profile in the pellet can in­ of sophisticated instruments, we are now looking at crease catalyst activity and selectivity in many reac­ catalysis at its most fundamental level, particularly tions. This underscores the need for a more rigorous with the objectives of identifying the participating espousal of catalyst manufacturing science. sites, mapping their energy levels, and understand­ Solid State Reaction Engineering ing the basis of selectivity. Iowa State University has a strong school of research in these areas. Today, research in solid state materials is a fron­ tier of enquiry. Solid-solid reactions were first men­ From the point of view of catalytic reaction engi­ tioned in the mid-80s141 as an area of interest in neering and starting with the early publications of chemical reaction engineering. With the increasing Amundson,rs1 we seem to have almost reached the participation of chemical engineers in materials end of the line where steady-state analysis is con­ development, this interest has grown to an astonish­ cerned, and the state-of-the-art has been fully cov­ ing level today. Materials of interest include struc­ ered by Arisr91 (also see Levenspielr101 and Froment tural composites, ceramic materials, new metal and BischofltUJ). That is not so, however, with re­ compositions, and microelectronic materials. The spect to unsteady state analysis (including multi­ engineering science analysis of the reactions in­ plicity), for which some new mathematical tools have volved in these preparations has been late in com­ been developed. [12J The role of adsorption and the use ing, but it now appears to have taken root. There is of nonideal isotherms has all but evaded the atten­ little doubt that this interest will rise exponentially tion of reaction engineers, and only recently have in the years ahead. Take microelectronics as an ex­ we started to look at adsorption, catalysis, and reac­ ample of the role of CRE in these materials; here we tor design in their totality.t1a1 This is presently an have processes such as deposition, etching, diffu­ active area ofresearch at Iowa State University, and sion, and implantation, in which different types of a recent conference in Poland addressed the prob­ reactors are employed to carry out both homoge­ lem, perhaps for the first time in an international neous and heterogeneous reactions. CRE inputs are forum. Another approach that is gaining ground in just beginning to flow into the analysis of these catalytic processes is the simultaneous consideration operations. There is a need to introduce electronic of feedstock, catalyst, reactor, selectivity, and sepa­ materials concepts at the undergraduate level, per­ ration. I believe that these trends will continue well haps as an elective. into the 21st Century. Plasma-enhanced chemical vapor deposition using An area of catalytic reactor design that will gain a variety of techniques is an important method of momentum is gas phase polymerization in fluidized preparing solid state materials, particularly cata­ bed reactors. Following the first flush of success lytic materials. A strong school of research as Iowa of fluidized beds in the petroleum and petro­ State University is exploring the preparation, char­ chemical industries, interest in the area waned acterization, and use of such materials. when it was found that fluidization was no panacea for reactor evils. It began to wax again when coal Reaction-Cum-Separation conversion processes revived attention-but with a (or the reactor-separator combo) difference: fluidization of large particles. Perhaps One way to cut capital costs (and increase conver­ the stage is now set for another revival-in the area sion and selectivity in some cases) is to carry out the of polymerization. reaction and separation steps in a single piece of In addition to heterogeneous catalysis, we have equipment, or to devise technologies where useful homogeneous catalysis, where innovative coordina­ side-products are formed. The earliest example of tion chemistry and catalyst recovery play vital roles. the first kind is the well-known Solvay tower in An exciting example is reductive carbonylation of which a number of operations occur simultaneously 186 Chemical Engineering Education to ultimately produce soda ash. Indeed, the Solvay Microphase Reaction Engineering tower is a veritable combo of multiple operations. Reaction of a component from a liquid phase (which Although this reactor combo is no longer a complete we will call Phase 1) with another reactant of lim­ black box, many aspects of it still are. But that is ited solubility diffusing from a second phase can be only one major example. A number of other, less hastened if a small quantity of a microphase can be complicated, examples of reaction-cum-recovery can added to the system. If the particle size of the be cited: the removal/recovery of acid gases such as micro phase is smaller than the diffusion scale of the CO2, H2S, SO2, recovery of valuable products from reactant, then these particles can get inside the liq­ waste or dilute streams, or reaction-cum-crystalliza­ uid film and transport more of the reactant from tion in the manufacture of such important products Phase 2 intoPhase 1. From two excellent reviews on as citric and adipic acids. the subject,[16,111 it seems clear that the use of a There is increasing interest , particularly in schools microphase (which may be a simple adsorbent like outside the United States, in the analysis of combo active carbon, a catalyst, or a liquid dispersed as a reactors. The type of research involved here is colloid) can in some cases enhance the reaction rate usually concerned with the application of new by almost an order of magnitude. and innovative ideas in the so-called conventional Extension of this concept to include (1) sparingly manufacturing processes. At Iowa State, research soluble solute in Phase 1 itself, (2) a precipitated in crystallization has been in progress since the product with particles small enough to enter the 1950s, and more recently the problem of reaction­ liquid film (or the fluid element in the language of cum-crystallization has been added to this continu­ the penetration theory), capture more of the reac­ ing program. tant from the neighborhood of the second phase and In the removal of oxygen present in levels below discharge it into the bulk of Phase 1, and (3) micellar 2% in gases like CO2, it would be desirable to de­ catalysis, has shown interesting possibilities. Par­ velop absorbents with the ability to mimic hemoglo­ ticularly in cases like the production of citric acid bin-type regenerative action. Some manganese com­ (where each of the two major steps involved contains pounds probably have such an ability. In the separa­ a precipitating product phase), control of conditions tion of p- and m-xylenes the difference in reactivity to reduce particle size to microphase levels can lead of the two can be successfully exploited. Thus, one to remarkable enhancements in the precipitation can selectively alkylate m-xylene (with the para iso­ rate. This is obviously a kind of precipitate-induced mer untouched) using acetaldehyde to give autocatalysis and offers much challenge both for the dixylylethane (DXE).1151 DXE, when cracked, gives theoretician and the experimentalist. half the amount of the meta isomer back along with the industrially useful side-product dimethylstyrene. Organic Synthesis Engineering Innumerable other instances can be quoted involv­ (selectivity engineering?) ing reactive extraction, dissociation extraction re­ Much of the progress in CRE has been in areas action, and dissociation extraction crystallization relating to the production of high tonnage chemicals. to buttress the contention that this is indeed an It is only in the last ten to fifteen years that another exciting area of research with unlimited scope for focus has emerged: reaction engineering of small the use of novel concepts. volume chemicals. It is surprising that most of the hundreds of reactions involved in organic synthesis This area of research can serve as an example to have remained outside the pale of CRE. Indeed, strengthen the point made earlier that there should one is hard put to think of more than a few impor­ be more chemistry in CRE education and research. tant organic name reactions that have been sub­ In a lecture the author heard some years ago, the jected to rigorous analysis. Examples are: Henkel point was made that many companies do not expect reaction by Doraiswamy and collaboratorspa. 1s1 significant chemistry input from chemical engineers. Grignard reagent preparation by Hammerschmidt It would seem that chemistry input of the kind men­ and Richarz,(201 and Kolbe-Schmitt reaction by tioned here must come primarily from reaction engi­ Phadtare and Doraiswamy.c211 neers exposed to a lot of chemistry. (Here, chemistry means the chemistry ofrelatively large and complex With the increasing importance of small-volume molecules encountered in, say, drugs and pesticides chemicals, particularly in the field of drugs and drug manufacture.) It is significant that one sees a greater intermediates, one would be greatly surprised if re­ degree of chemistry orientation in biotechnology and action engineers do not, almost as a natural course, polymer science and engineering. extend their domain to include this area as a formal Fall 1992 187 part ofCRE research. One sees considerable activity lyzed reactions, meaning operating under condi­ in Europe (particularly in Bourne's school) and in tions where the diffusion and kinetic effects are some industrial research and development centers balanced to maximum advantage in Europe and the USA, but a more pronounced • increased attention to forced cycling involvement of CRE groups in academia is desirable. • use of appropriate solvents (for liquid phase reac­ Several ways of improving selectivity have been tions) such as dimethylsulfoxide to increase reac­ tivity used by chemists,r22 1 some of which are being pur­ sued vigorously by chemical engineers. Phase trans­ • use of ion exchange resins to replace liquid phase fer catalysis is an outstanding example of the former acid/base catalysts in which some reaction engineering groups are evinc­ • control strategies in multistep synthesis of phar­ ing keen interest. Other means of increasing selec­ maceuticals (including computerized optimization tivity are through the use of micelles, microphases, of the synthetic route) catalysts like zeolites and molecularly engineered • use of aqueous-aqueous extraction in reactive sepa­ layered structures, and controlled levels of ration micromixing. The last is particularly attractive from • reaction-cum-separation strategies for recovery of an engineering science point of view, as attested to valuable products from dilute solutions, or removal by the extensive publications of Bourne and collabo­ of polluting components therefrom rators (for example, Baldyga and Bourner2a1). An­ • hazard analysis and prevention other rewarding line of approach is the use of ultra­ Many of the areas listed are not "new topics," but sonics. The finding by Luche and Damieror2 41 that certainly all of them thrive on the use of innovative ultrasonification can enhance yields in the Barbier concepts. Areas such as recovery of valuable prod­ reaction augers well for the increasing role of ultra­ ucts from dilute solutions are replete with examples sonics in synthesis engineering. of the use of reaction as a tool for separation and A field of research in organic synthesis with great recovery. A general strategy of intensification in potential for enhanced selectivity and ease of opera­ which isolated studies have been reported, and which tion is the possibility of extending the concept of has the potential for treatment as an area of re­ supported liquid-phase catalysts to include supported search, is the role of dilution in process technology. reagents-with all the attendant advantages. The An attempt was made by the author some years edited book of Hodge and Sherringtonr2s1 provides agol 7J to put together the various aspects of intensifi­ clear evidence of the favorable role of the solid sup­ cation by dilution, i.e., dilution of the gas and solid port. With the extensive knowledge we now have of phases in catalytic reactions, dilution of solid in gas­ fluid-solid (catalytic and noncatalytic) reactions, this solid reactions, and "natural intensification" due to field offers great scope for innovative approaches to, dilution in biological systems. Increased effort in among other things, the reaction-diffusion problems this area could be very rewarding. inherent in such systems. Use of photochemistry and enzymes in organic synthesis can also greatly CONCLUSION enhance specificity. These are well-known areas to Education in CRE must explore new possibilities, the chemist and biochemist, but there is a definite some of which have been described in this article. need for increased CRE input. Among these are a mini think-tank, a broad expo­ Other Areas sure to the reaction engineering of a variety of sys­ There are many other areas that merit attention tems to supplement the prevailing practice of en­ and where there is bound to be continuing interest. larging on a few, and initiation of electives in some Among these are emerging areas such as solid-state reaction engi­ neering and interface engineering. • interfacial engineering, an area that covers a mul­ titude of systems, including catalysis, colloids, and The overview presented here with respect to re­ micellar action search is indicative of the areas of present/potential • multiphase reactions (which involve at least one relevance. The element of challenge will continue, liquid phase) extensively used in the manufacture whether the areas are new or traditional. While of fine chemicals the researcher in CRE, like his counterparts in • gas-solid noncatalytic reactions, so common in pol­ many other areas, must continue to vigorously ex­ lution abatement, preservation of monuments, ore plore new and emerging fields, let us not throw the processing, and catalyst regeneration conventional areas overboard. Recovery of value­ • analysis of operation "at the edge" in solid cata- added products from dilute solutions (or waste 188 Chemical Engineering Education streams) is an outstanding example of applying new Multiphase Reactions," Proc. Indian Natnl. Sci. Acad., 57A, concepts to old problems. Whether or not they at­ No. 1, 99 (1991) 17. Mehra, A., "Intensification of Multiphase Reactions Through tract one's fancy, their importance will continue the Use of a Microphase: 1, Theoretical," Chem. Eng. Sci., undiminished. So the educator, the researcher, and 43, 899 (1988) the funding agencies must look at new concepts in 18. Gokhale, M.V., A.T. Naik, and L.K. Doraiswamy, "An Un­ traditional areas with almost the same enthusiasm usual Observation in the Disproportionation of Potassium Benzoate to Terephthalate," Chem. Eng. Sci., 28, 401 (1975) as at the emerging areas. Nucleation and growth 19. Revankar, V.V.S., and L.K. Doraiswamy, "Kinetics of Ther­ must remain simultaneous. mal Conversion of Potassium Salts of Benzene (di- and tri-) The chemical industry, notwithstanding the strains Carboxylic Acids to Terephthalic Acid," Ind. Eng. Chem. Res., 31, 781 (1992) and vicissitudes imposed by a fluctuating economy 20. Hammerschmidt, W .W., and W. Richarz, "Influence of Mass and an increasing appreciation of environmental con­ Transfer and Chemical Reaction on the Kinetics ofGrignard cerns, permeates practically every facet of our lives Reagent-Formation for the Example of the Reaction of Bromocyclopentane with a Rotating Disk of Magnesium," and depends for its continued development on inven­ Ind. Eng. Chem. Res., 30, 82 (1991) tion as well as innovation. Invention is getting a 21. Phadtare, P .G. , and L.K. Doraiswamy, "Kolbe-Schmitt Car­ novel idea which works; innovation is overcoming all bonation of 2-naphthol," Ind. Eng. Chem. I Proc. Des. & Dev., hurdles to its economic use.1 261 There is scope for both 8, 165 (1969) 22. Sharma, M.M., Lecture: "Selectivity Engineering," published in CRE. To ensure continued dominance, academic by the Council of Scientific and Industrial Research, New research must become increasingly bold, industrial Delhi, India (1990) research must be supported rather than managed, 23. Baldyga, J ., and J .R. Bourne, "A Fluid Mechanical Ap­ and both must be more accommodative of shifts in proach to Turbulent Mixing and Chemical Reaction," Chem. Eng. Commun., 28, 231 (1984) approach and the delays they entail. 24. Luche, J.L., and J.C. Damiero, "Ultrasonics in Organic Syn­ thesis: 1, Effect on the Formation of Lithium Organometal­ REFERENCES lic Reagents," J. Am. Chem. Soc., 102, 7926 (1980) 1. Hougen, O.A., and KM. Watson, Chemical Process Prin­ 25. Hodge, P., and D.C. Sherrington, eds., Polymer Supported ciples, Part 3, Kinetics and Catalysis, Wiley, NY (1947) Reactions in Organic Synthesis, Wiley, NY (1980) 2. Aris, R., "Is Sophistication Really Necessary?" Ind. Eng. 26. Brown, A.V., "Invention and Innovation- Who and How," Chem., 58, 32(9) (1966) Chemtech (Dec), 709 (1973) 0 3. Levenspiel, 0 ., "Chemical Engineering's Grand Adventure," P.V. Danckwerts Memorial Lecture, Chem. Eng. Sci., 43, 1427 (1988) REVIEW: Design Project 4. Doraiswamy, L.K., and M .M. Sharma, Heterogeneous Reac­ Continued from page 174. tions: Analysis, Examples, and Reactor Design, Vols. 1, 2, ever, the authors do provide some insight into haz­ Wiley, NY (1984) 5. Bird, R.B., W.E. Stewart, and E.N. Lightfoot, Transport ardous operations analysis and general safety con­ Phenomena, Wiley, NY (1960) siderations. 6. Rase, H.F., Chemical Reactor Design for Process Plants, Vols. 1,2, Wiley, NY (1977) The nitric acid process selected is the traditional 7. Doraiswamy, L.K., "Across Millenia: Some Thoughts on An­ one without the more modern modification of reac­ cient and Contemporary Science and Engineering," Hougen tion gas compression. Surprisingly little is said about Lecture Series, Dept. of Chem. Engineering, University of the need for cleanup of the tail gases from the ab­ Wisconsin, Madison, WI (1987) 8. Aris, R., and A. Varma, eds., The Mathematical Under­ sorber. The authors have provided a relatively simple standing of Chemical Engineering Systems: Selected Papers process with a great deal of supporting data. This of Neal R. Amundson, Pergamon Press, NY (1980) should have appeal to faculty members who under­ 9. Aris, R., The Mathematical Theory of Diffusion and Reac­ stand quite well that it is an onerous chore to dig up tion in Permeable Catalysts, Vols 1,2, Oxford Univ. Press, London, UK (1975) (The reference here is to Vol. 1) all the supporting information for a realistic case 10. Levenspiel, 0 ., Chemical Reaction Engineering, Wiley, NY study. (1972) The use of this text in the design course should 11. Froment, G.F., and KB. Bischoff, Chemical Reactor Analy­ sis and Design, Wiley, NY (1990) follow an introductory design course which treats 12. Luss, D., "Steady State Multiplicity Features of Chemically such matters as equipment cost estimating, profit­ Reacting Systems," Chem. Eng. Ed., 20, 12 (1986) ability studies, profit and loss statements, and the 13. Doraiswamy, L.K., "Chemical Reactions and Reactors: A like. The authors point this out in the introductory Surface Science Approach," Prag. Surf Sci., 4, Nos. 1-4, 1- 277 (1991) material. If only one semester is allocated to design, 14. Gavriilidis, A. , and A. Varma, "Optimum Catalyst Activity it is the opinion of this reviewer that adoption of this Profiles in Pellets: 9. Study of Ethylene Oxidation," AJChE book would be a mistake. On the other hand, if a J ., 38, 291 (1992) second semester (or quarter) is available, material 15. Sharma, M.M., "Separations Through Reaction," J . Separ. Proc. Tech., 6, 9 (1985) in the book can support one or more worthwhile case 16. Sharma, M.M., "The Fascinating Role of Microphases in study projects. 0 Fall 1992 189