CHEMISTRY OF CATALYTIC PROCESSES

B. C. GATES, J. R. KATZER, from the reduced coke formation on zeolite J. H. OLSON, and G. C. A. SCHUIT catalysts and must promote more complete coke Univ ersity of Delciivcire removal in regeneration. The reactor design may Newark, Dela,ware 19711 based on a simplified series-parallel reaction net­ work, on the assumption of a small deviations M OST INDUSTRIAL REACTIONS are cataly- from piston flow in the riser, and on a balance tic, and many prncess improvements result between the energy required for the endothermic from discovery of better chemical routes, usually cracking reactions and the energy produced in involving new catalysts. Because catalysis plays coke burn-off from catalyst particles in the re­ a central role in chemical engineering practice, generator. it is strongly represented in chemical engineering teaching and research at Delaware. A graduate course entitled "Chemistry of Catalytic Processes" is designed to present a cross section of applied There is no stronger evidence of the value catalysis within the framework of detailed con­ of integrating chemistry and chemical sideration of important industrial processes. The engineeri ng than the industrial course brings together the subjects of chemical success in catal ytic processing. bonding, organic reaction mechanism, solid-state inorganic chemistry, chemical kinetics, and re­ actor design and analysis. There is no strnnger The 11rocesses are introduced in an order leading evidence of the value of integrating chemistry ro ughl y from the s implest to the most complex chemical and chemical engineering than the industrial concepts and fro m the best und erstood to the least well successes in catalytic processing. understood catalytic che mistry (Table 1). Cracking is the fi rst s ubject precented because the zeolite catalysts have Five classes of industrial processes are con­ kn ow n crystalline structures and relatively well defined sidered in sequence: catalytic cracking, catalysis ac id centers; the crackin g reactions proceed v ia carbonium by transition metal complexes, reforming, partial ion interm ediates, giving well characterized product dis­ oxidation of hydrocarbons, and hydrodesulfuriza­ t ri butions. The second s ubject, catalysis by transition tion. Each class is introduced with a description metal complexes, also involves well defined species and is un ified by the id ea of the cis-insertion mechanism, of the processes, which is follovved by details of whic h is di scussed on the basis of ligand field theory and the catalytic chemistry and process analysis and exem11 lified in detail by Ziegler-Natta 1>0ly merization. reactor design. Reforming introduces metal catalysis, the con­ To the extent that each subject allows, ties are cept of bifunctional reaction mechanism and ties drawn between the reaction chemistry and process with acid catalysis. Theory of metal catalysis is design. For example, the new zeolite cracking incomplete although solid-state theory and catalysts are used primarily because they have molecular orbital calculations on small metal high selectivity for gasoline production, but they clusters pro vi de insight; a tie still remains to be also have such high activity compared to the drawn between catalysis by metal complexes and earlier generation of silica-alumina catalysts that catalysis by clusters of metal atoms. The con­ they must be used diluted in a silica-alumina cluding topics of partial oxidation and hydrode­ matrix to prevent overcracking. Their application sulfurization involve solid state and surface has required redesign of catalytic crackers to ac­ chemistry of transition metal oxide and sulfide commodate rapid reaction predominantly in the catalysts; there is a thorough understanding of a riser tube (located upstream of what was former­ few oxidation catalysts (for example, bismuth ly the fluidized-bed reactor) ; redesign must also molybdate catalyzing ammoxidation of propy­ accommodate a changed energy balance resulting lene) but for the most part the chemistry is not

172 CHEMICAL ENGINEERING EDUCATION well understood, and the ties between the (1, 2 )). The notes are based largely on primary chemistry and the process design cannot be well literature, and since t he literature of industrial developed. processes does not give a good representation of current practice, the interpretations may some­ times be out-of-date and erroneous. COHERENCE VIA CHEMICAL CONCEPTS Many improvements in the co urse have re­ THE COHERENCE of the course is provided sulted from criticisms given by practitioners, and by the chemical rather than by the engineer­ we have attempted to include students from in­ ing concepts, and the latter are interwoven as dustry in classes ·with first-and-second-year gradu­ dictated by their practical value to the various ate students. The course has been offered in the processes. For example, interphase mass transfer 4 :30 to 6 :00 P .M. time period, which is convenient is considered in analysis and design of the gas­ to many potential students who are employed liquid reactors used in the oxo, Wacker, and vinyl nearby. Response has been favorable enou gh t hat acetate processes, which involve homogeneous the course is also offered yearly as a one-week catalysis by transition metal complexes. Mass short course. Those attending have been pre­ transport in catalyst pores is important in hydro­ dominantly industrial chemical engineers and desulfurization (affecting rates of the desired re­ chemists (in about equal numbers), some travel­ actions and rates of reactions giving pore-blocking ing from as far as the west coast and Europe. [J deposits) ; the unique phenomena of mass trans­ REFERENCES port in the molecular-scale intracrystalline pores of zeolites are introduced with catalytic cracking 1. Schuit, G. C. A., "Catalytic Oxidation over Inorganic and form the basis for an introduction to shape­ Oxides as Catalysts," Memoires cle Zn Societe Royale selective catalysis. Analysis of reactor and des Sciences de Liege, Sfrcieme S e1 ·ie, T om I , 227, 1971. 2. Schuit, G. C. A., and Gates, B. C., "Chemistry and catalyst particle stability is central to the dis­ Engineering of Catalytic H ydrodesulfu1·ization," A TChE cussion of catalytic oxidation processes, for which Jmwrwl 1 !I, 417 ( 1973 ). catalysts are selected and reactors designed to TA BLE. 1 give high yields of valuable partial oxidation Course Outline products and low yields of CO2. I. ZEOLITE-CATA LYZED CR ACKING AND RELATED Instrumental methods of analysis essential to PROCESSES catalyst characterization are introduced as they A. Processes are appropriate to the process, giving a represen­ 1. Catalytic Cracking tation of the breadth of their usefulness. For a. Process Conditions b. Reactor Operation example, chemisorption measurements, electron c. Regenerator Operation microscopy and x-ray line broadening to deter­ 2. Hydrocacking and l somerization mine metal surface areas and crystallite sizes are B. Reactions and Chemistr y introduced in discussion of catalytic reforming, 1. Chemical Bond Theory which involves supported-metal bifunctional a. Atomic Orbitals and E nergy Levels b. Molecular Orbitals catalysts. Infrared spectroscopy is useful for i. Linear Combinations of Atomic Orbitals probing the detailed structures of transition metal ii. Symmetry Aspects complexes (for example, the rhodium complexes iii. The Secular Determinant used as oxo catalysts) and for indicating the struc­ c. Multiple Atom Systems tures of acidic centers on zeolite surfaces. Elec­ i. Hybridization Theory ii. Electron-Deficient, Delocalized Molecular tron spin resonance and magnetization studies Bonds have provided essential information about oxida­ 2. Carbonium Ions tion and hydrodesulfurization catalysts contain­ a. Electron Deficiency Properties ing transition metal ions. b. Classical and Non-Classical Carbonium Ions c. Reactivity and Characteristic Reactions The course is an attempted synthesis of 3. Cracking Reactions chemistry and chemical engineering ; the synthesis a. Thermal Cracking is traditional in practice, but not in teaching, and b. A cid-Catalyzed Cracking· there is a lack of appropriate secondary literature C. Catalysts sources. Consequently we have prepared a 1. A morphous Catalysts a. Preparation thorough set of typewritten notes (portions of b. Structure and Surface Chemistry which have been published as review articles c. Acidity: Measurement and Correlat i1:m

FALL 1974 173 George Schuit received his Ph.D. from Leiden and worked a·t chemical engineering, he has recently done research conc:ernil')g the Royal Dutch Shell Laboratory in Amsterdam before becoming analysis of fixed-bed catalytic reactors, fouling of chromi;,/ alumina Professor of Inorganic Chemistry at the University of Technology, catalysts, partial oxidation, and automotive emissions control. Eindhoven, The Netherlands. His research interests are primarily in Jim Katzer received a Ph.D. in Chemical Engineering from MIT solid state inorganic chemistry and catalysis, and his recent publica­ and has been at Delaware since 1969. His primary researeh in1erests tions are concerned with hydrodesulfurization and selective oxida­ are catalytic chemistry and mass 1ransport in catalysts. His recent tion of hydrocarbons. He has been on organizing committees for work has e mphasized applications of catalysis to pollution abate­ the Roermond Conferences and the Third International Congress on ment, particularly catalytic reduction of nitrogen oxides, supported Catalysis, is a member of the Royal Dutch Academy of Sciences and metal catalysis, catalyst poisoning mechanisms, and transport and is on the editorial board of the Journal of Catalysis. In 1972 he' was reaction in zeolites. National Lecturer of the Catalysis Society and Unidel Distinguished Bru ce Gates received his Ph.D. from the University of Washington. Visiting Professor at the University of Delaware; he now holds joint He did postdoctoral research with a Fulbright grant at the University appointments at Eindhoven and Delaware. of Munich and worked for Chevron Research Company before join­ Jon Olson obtained a Doctor of Engineering degree at Yale ing the Delaware faculty in 1969. His current research concerns and worked for E. I. duPont de Nemours and Company before hydrodesulfurization, catalysis by transition metal complexes and joining the faculty at Delaware. With wide ranging interests in design and evaluation of synthetic polymer catalysts.

2. Crystalline (Zeolite) Catalysts C. Catalysts a. Structure and Surface Chemistry 1. Wacker-Pd Chloride i. Primary and Secondary Structural Units 2. Hydroformylation-Co and Rh Carbonyls ii. Type Y Zeolite 3. Carbonylation-Rh-Phosphine Complexes iii. Mordenite 4. Ziegler-Natta Polymerization-Transition b. Acidity Metal Chlorides and Metal Alkyl i. Chemical Probes D. Reaction Mechanisms ii. Instrumental Probes 1. The General Cis-Insertion Mechanism iii. Explanation from Structural Considera­ a. Experimental Evidence tions b. Molecular Orbital Explanation iv. Active Sites and Activity Correlations 2. Detailed Mechanisms of Particular Reactions D. Reaction Mechanisms a. Ethylene Oxidation 1. Reaction Chemistry Related to Surface Structure b. Hydroformylation a. Amorphous Catalysts· c. Carbonylation b. Zeolite Catalysts ,d. S,tereospecific J_"olymedzation 2. Hydrogen-Transfer Activity of Zeolites E. Quantitative Process Design 3. Activity and Selectivity Comparison of Zeolites 1. · Design of Gas-Liquid Reactors; Mass Transfer and Amorphous Catalysts Influence 4. Reaction Network and Deactivation: Quantitative 2. Preparation and Characterization of Solid Models Catalysts . E. Influence of Catalytic Chemistry and Mass Trans­ a_. Transition Metal Complexes Bound to 0 port on Choice of Processing Conditions Inorganic Surfaces ' 1. Superactivity of Zeolites b. Complexes Bound to Organic Matrices 2. Mass Transport Effects in Zeolites; ' Shape­ HI. CATALYTIC REFORMING Selective Catalysis A. Process 3. Effect of Zeolite Cracking Chemistry on Reactor 1. Principal Chemical Reactions and Regenerator Design 2. Thermodynamics and Kinetics F. Quantitative Reactor Design 3. Supported Metal Catalysts 1. Riser-Tube Cracker Design 4. Process Conditions and Reactor Design 2. Regenerator Design 8. Jleactions .and Chemistry II. CATALYSIS BY TRANSITION:METAL 1. Mechanisms of Metal Catalyzed Reactions COMPLEXES a. Hydrogenation-Dehydrogenation and H-D A. Processes Exchange 1. Wacker Process b. Isomerizatfon and Hydrogenolysis a. Reactions, Product Distribution, and Kinetics c. Cyclization b. Processing Conditions d. Aromatization c. Reactor Design · 2. Chemical Bond TJ.i,~ory 2. Vinyl Acetate Synthesis a. <:,- and·7r-Bonds 3. Oxo Process (Hydrofotmylation) ':b1 Deloci1lized Bol\ds 4. Methanol Carbonylation to Acetic Acid 'C. :'Bands-tin Metals 5. Ziegler-Natta Polymerization: Transition from :d. d•orbitat Contribution t!) ·. Transition Metal Homogeneous to Heterog·erteous Catalysis • B~nds , . ,· .- 8. Chemical Bond Theory ,,_ 3. Met~J Catalysis · '' 9 1. Ligand Fieid Theory · ·a. ' Electrons and' Metal Borid Strength 2. CT and 7r-Bonding in Complexes b. Electrons and' Adsorption on Metals

174 CHEMICAL ENGINEERING EDUCATION r. Theoretical Calculation,; of Electronic Pro- f. Ag 1>erties and S urface Bond Strength 2. Oxidation Selectivity d. Catalytic Activity : S urface Com1>otmd a . Correlations Correlations i . Ox ygen Bond Stren !!,"t h e. Alloys ii. Metal Oxide S trudure i. Miscibility Gaps and S urface Conl]Josition b. Oxygen Interchange wit h Metal Oxides ii. Catalytic ActiYity: Lig·and and Geometric c. Microsco 1>ic Cons iderations, Acti,·e Sites E ffects D. Deta il ed Reaction Mechanis ms involving Olefins­ C. Dual-Functional S upported-J\'[etal Catalys ts Examples Based on Solid and Inte rmediate Com­ (Pt/Al,0) plex Structures I. The· Metal, Practica I Cons iderations 1. Solid Structures. Bismuth :'llol yhclate and a. !'reparation and Characterization U ranium .A n timony b. E ffects of Crys tallite Size on Activity 2. Surface Chemistry c. S intering and Poisoning 3. Reactant-S urface I nt eractions d . . \lloys -1. Reaction Mec hanis m 2. The A lumina Support E. Quantitative Reactor Desig·n- The Hot S pot Prob­ a. l're1rnration and Properties le m h. Structure 1. Influence of Catalytic Che mistry on Choice of t·. Development and Control of .Acidity Process in g- Conditions; 1 he Need for Selective D. Reaction Net works and Reaction Mechanisms Catalysts 1. Dual-Functional Nature of Catalyst 2. Fluidized Bed Reactors a. Reaction Steps and Relation ·10 Catalysl 3. Fixed Bed Reactors Functions .1. Heat and Mass Trans fer in Catalyst Particles h. Studies with Physically Separated Func­ 5. Ca talyst Particle Stability tions, Mass Transport Considerations V. HYDRODESULFU RIZ ATION c. Effect of Stq11>0rt A cidity on Reformin1r :\. Processes Reactions I. S ulfur-conta ining compounds in Petroleum and d. Poisons and Poisoning Studies Coal-Derived Liquids wit h Hydrogen 2. Cyclization Reaction Net.work and Reaction 2. Conq)()s itions of ('o ' Mo and N i }lo Catalysts Mechanism :3. Processin g- Conditions :~. Overall Net work a . Pet rule um Distillates E. Relation of Process in g· to Catalytic Chemistr y b. Petroleum Residua l. Balancing the S treng ths of the Catalyst c. Coal Functions •'- Reactor Desig·n: Fixed a nd F luidized Reel s 2. Mass Trans11ort Effects on Selectivity B. Reactions and Chemist ry :~. 011timum Desig·n of Dual-Functional Catalytic 1. Model Reactant Compounds Systems a. Desulfurization Reaction Networks of I. Regeneration Procedures Related to Catalyst Thio11hene a nd Benzothioprenes Structure and Stability h. Kinetics of H ydrodes ulfurization of :i. Lumping in Fixed Bed Reactor Desig·n for Thiophene and Benzothiophenes :\'Jany Reactions 2. Petroleum Feed Stocks IV. SELECTIVE OXIDATION OF HYDROCA RBON S a. Com pos ition of Feed Stocks CATALYZED BY METAL OXIDES h. Simplified kinetics for Petrole um Feed ..-\. Processes Stocks 1. Phthalic A nhydride C. Catalysts a. Reactions 1. Structure of Co balt Molybdate and Nickel b. Process Conditions 1"I olybcla te Ca ta lysts 2. Maleic A nhydride ·2. Texture :t Acrolein and .Ac rylonitrile 3. Interaction of Catalyst wit h the S up11or t -I. Ethylene Oxide -1. E ff ects of Promotor~ B. Reactions and Che mistry 'l. Catalytic S ites 1. Chemical Bond Th eory a. Mono layer Model a. Electrost atic Bonds .in Solid Oxides b. I nterca la tion Model b. Changes in Cation Oxidation State D. Reaction Mechanisms of i\'Iocl el Compounds 2. A llylic Intermediates E. Process JJesil!,"n :J. Mars -van Kre,·elen Mechanism 1. Relation of Process Des ign to Catalytic -I. Reaction Network for N aphthalene Oxidation Che mistry of Hydrudes ul fu rization a nd S ide C. Catalysts Reactions 1. Compos ition a nd S tructure 2. Influence of l ntnqrnrticle \'\lass '.l.' ra ns11ort on

a. V 0 0 0 and MoO"-V ~0 -, Catalyst E ff ectiveness h. Bi, 0 :, -MoO:: :3. Ca talyst .\ g in g-·: l'ore lllocking a nd Interst it ial

c. Fe0 0 3 -Mo0~ De1>0sition

cl. U00 -Sbp ~ -I. Hot S pots and Reaetor Stability; A na lysis of e. Cu ..0 Trickle Bed a nd S lurry Beel Reactor~

FALL 1974 175