(book)The Engineering Of Chemical Reactions L. D. Schmidt OXFORD UNIVERSITY PRESS (pdf document) download at fliiby.com

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Gubbins, Cornell University Associate Editors Mark A. Barteau, University of Delaware Edward L. Cussler, University of Minnesota Douglas A. Lauffenburger, University of Illinois Manfred Morari, ETH W. Harmon Ray, University of Wisconsin William B. Russel, Princeton University Receptors: Models for Binding, Trafficking, and Signalling D. Lauffenburger and J. Linderman Process Dynamics, Modeling, and Control B. Ogunnaike and W. H. Ray Microstructures in Elastic Media N. Phan-Thien and S. Kim Optical Rheometry of Complex Fluids G. Fuller Nonlinear and Mixed Integer Optimization: Fundamentals and Applications C. A. Floudas Mathematical Methods in Chemical Engineering A. Varma and M. Morbidelli The Engineering of Chemical Reactions L. D. Schmidt Analysis of Transport Phenomena W. M. Deen THE ENGINEER,NG OF CHEAilCAL REAC’TIONS LANNY D. SCHMIDT University of Minnesota New York 1998 Oxford OXFORD UNIVERSITY PRESS OXFORD UNIVERSITY PRESS Oxford New York Athens Auckland Bangkok Bogota Bombay Buenos Aires Calcutta Cape Town Dar es Salaam Delhi Florence Hong Kong Istanbul Karachi Kuala Lumpur Madras Madrid Melbourne Mexico City Nairobi Paris Singapore Taipei Tokyo Toronto Warsaw and associated companies in Berlin Ibadan Copyright 0 1998 by Oxford University Press, Inc. Published by Oxford University Press, Inc., 198 Madison Avenue, New York, New York, 10016 Oxford is a registered trademark of Oxford University Press All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior permission of Oxford University Press, Library of Congress Cataloging-in-Publication Data Schmidt, Lanny D., 1938The engineering of chemical reactions / Lanny D. Schmidt. p, cm.-(Topics in chemical engineering) Includes bibliographical references and index. ISBN O-19-510588-5 (cloth) 1. Chemical reactors. I. Title. II. Series: Topics in chemical engineering (Oxford University Press) TP157.S32 1 9 9 7 97-39965 66o--dc2 1 CIP Cover Photos: The upper-photo shows a view across the Mississippi River of the Exxon refinery in Baton Rouge, Louisiana. This is one of the largest refineries in the world, converting over 400,000 barrels per day of crude oil into gasoline and diesel fuel. This refinery also produces petrochemicals for products such as polymers and plastics. The lower photo shows three new types of products made by chemical engineers. These are foods (Cheerios), pharmaceuticals (aspirin), and microelectronics (memory chips). The skills which have been developed in petroleum and petrochemicals have enabled chemical engineers to expand into new processes such as these. 9816543 Printed in the United States of America on acid-free paper CONTENTS PREFACE xi PART I: FUNDAMENTALS 1 INTRODUCTION Chemical 3 Reactors 3 4 5 Chemical Reaction Engineering What Do We Need To Know? Industrial Processes 7 Modeling Sources 72 10 References 14 2 REACTION RATES, THE BATCH REACTOR, AND THE REAL WORLD Chemical Multiple Reaction Rate Reactions Reactions Rates 26 29 31 34 30 27 25 21 Approximate Reactions Coefficients Elementary Reactions Stoichiometry 32 Reactor Mass Balances The Batch Reactor 378 Reaction Rates Near Equilibrium 37 V vi Contents Variable Chemical Density Reactors 47 57 53 53 Thermodynamics and Reactors Adiabatic Reactor Temperature Chemical Equilibrium 57 Petroleum Refining 60 Polyester from Refinery Products and Natural Gas Reaction-Rate Summary 80 Data 74 ’ 68 “What Should I Do When I Don’t Have Reaction Rates?” 73 3 SINGLE REACTIONS IN CONTINUOUS ISOTHERMAL REACTORS Continuous Reactors 86 86 89 94 97 The Continuous Stirred Tank Reactor Conversion in a Constant-Density CSTR The Plug-Flow Tubular Reactor 92 Conversion in a Constant-Density PFTR The l/r Plot Variable-Density 99 700 707 707 109 712 715 776 719 Reactors 86 Comparison between Batch, CSTR, and PFTR Semibatch Reactors Space Velocity and Space Time Chemical Reactors in Series Autocatalytic Reactions Reversible Reactions Transients in Continuous Reactors Synthesis Gas Reactions 779 Some Important Single-Reaction Processes: Alkane Activation Staged Reactors 726 The Major Chemical Companies Reactor Design for a Single Reaction Notation 134 127 134 4 MULTIPLE REACTIONS IN CONTINUOUS REACTORS The Petrochemical industry Olefins 749 151 752 156 Mass Balances 146 146 Conversion, Selectivity, and Yield Complex Reaction Networks Series Reactions Parallel Reactions 757 768 Multiple Reactions with Variable Density Real Reaction Systems and Modeling 776 187 180 Approximate Rate Expressions for Multiple-Reaction Systems Contents Simplified Reaction Reactions Mechanisms 182 189 192 795 vii Collision Theory of Bimolecular Reactions Activated Complex Theory 793 Designing Reactors for Multiple Reactions 5 NONISOTHERMAL REACTORS Heat Generation and Removal Energy Balance in a CSTR Energy Balance in a PFTR Equations To Be Solved Adiabatic Reactors 218 207 208 271 212 214 216 Heat Removal or Addition to Maintain a Reactor Isothermal Trajectories and Phase-Plane Plots Trajectories of Wall-Cooled Reactors Other Tubular Reactor Configurations The Temperature Profiles in a Packed Bed 229 231 233 234 238 Exothermic versus Endothermic Reactions 6 MULTIPLE STEADY STATES AND TRANSIENTS Heat Generation and Removal in a CSTR Adiabatic CSTR 248 250 Stability of Steady States in a CSTR 245 245 Observation of Multiple Steady States 253 Transients in the CSTR with Multiple Steady States Other Reactions in a CSTR 257 260 261 Variable Coolant Temperature in a CSTR Designing Reactors for Energy Management 256 7 CATALYTIC REACTORS AND MASS TRANSFER Catalytic Reactions 268 273 Catalytic Reactors 270 Surface and Enzyme Reaction Rates Porous Catalysts 274 276 280 Transport and Reaction Mass Transfer Coefficients External Mass Transfer 268 283 290 Pore Diffusion 284 Temperature Dependence of Catalytic Reaction Rates The Automotive Catalytic Converter The Catalytic Wall Reactor Langmuir-Hinshelwood 295 298 310 Kinetics 291 A Summary of Surface Reaction Kinetics Designing Catalytic Reactors 311 VIII . Contents Electrochemical Bioreactors Reactors 375 376 312 314 Real Catalytic Reactors The Human Reactor PART II: APPLICATIONS Designing a Chemical Reactor and Introduction To Applications Stages of Design 327 325 8 NONIDEAL REACTORS, BIOREACTORS, AND ENVIRONMENTAL MODELING 330 The “Complete” Equations Residence Time Distribution Laminar Flow Tubular Reactors Dispersion in Tubular Reactors Recycle Reactors CSTRs in Series 344 347 349 355 330 333 339 347 335 Reactor Mass and Energy Balances 347 Diagnosing Reactors Modeling the Environment Summary 360 Cell Cultures and Ecological Modeling 9 REACTIONS OF SOLIDS 367 367 368 Reactions Involving Solids Solids Reactors 371 Reaction Rates of Solids Chemical Vapor Deposition and Reactive Etching 372 377 Films, Spheres, and Cylinders 373 Macroscopic and Microscopic Solids Dissolving and Growing Films Dissolving and Growing Spheres Diffusion through Solid Films Transformation of Spheres Electrical Analogy Summary 393 391 386 378 382 389 10 CHAIN REACTIONS, COMBUSTION REACTORS, AND SAFETY Chain Reactions 399 406 408 417 Characteristics of Chain Reactions Autooxidation and Lab Safety Combustion 474 Chemical Synthesis by Autooxidation 399 Contents Hydrogen Alkane Oxidation 414 iX Chain Branching Reactions Oxidation 416 418 422 Thermal Ignition 420 Thermal and Chemical Autocatalysis Premixed Flames Diffusion Flames Energy Generation 422 424 425 426 437 433 Combustion of Liquids and Solids Solid and Liquid Explosives Explosions and Detonations Reactor Safety Summary 434 436 11 POLYMERIZATION REACTIONS AND REACTORS Ideal Addition Polymerization 443 445 454 Polyolefins Free-Radical Catalytic Condensation Polymerization 452 Polymerization Polymerization 457 460 465 Polymerization Reactors Fisher Tropsch Polymerization 467 469 Forming Polymers Crystallization 468 469 Integrated Polymer Processing 12 MULTIPHASE REACTORS Mass Transfer Reactors Mass Balance Equations lnterfacial Surface Area 476 476 478 478 481 481 Types of Multiphase Reactors Mass Transfer between Phases Multiphase Reactor Equations Equilibrium between Phases Membrane Reactors Falling Film Reactor Bubble Column Reactors Trickle Bed Reactor 483 484 484 488 493 499 Falling Film Catalytic Wall Reactor 501 Multiphase Reactors with Catalysts 502 506 507 Other Multiphase Reactors Reactor-Separation Catalytic Distillation Integration 503 Analysis of Multiphase Reactors 508 X Contents Chromatographic Iron Ore Refining Summary Reactors 572 513 509 The Petroleum Refinery 515 Appendix A Integrating Differential Equations Appendix B Notation 524 528 527 Appendix C Conversion Factors Index 531 PREFACE I learned about chemical reactors at the knees of Rutherford Aris and Neal Amundson, when, as a surface chemist, I taught recitation sections and then lectures in the Reaction Engineering undergraduate course at Minnesota. The text was Aris’ Elementary Chemical Reaction Analysis, a book that was obviously elegant but at first did not seem at all elementary. It described porous pellet diffusion effects in chemical reactors and the intricacies of nonisothermal reactors in a very logical way, but to many students it seemed to be an exercise in applied mathematics with dimensionless variables rather than a description of chemical reactors. We later used Octave Levenspiel’s book Chemical Reaction Engineering, which was written with a delightful style and had many interesting figures and problems that made teaching from it easy. Levenspiel had chapters on reactions of solids and on complex reactors such as fluidized beds, topics to which all chemical engineering students should be introduced. However, the book had a notation in which all problems were worked in terms of the molar feed rate of one reactant F~~ and the fractional conversion of this reactant X. The “fundamental equations” for the PFTR and CSTR given by Levenspiel were V = FAN 1 dX/rA (X) and V = FA,Xf r-A(X), respectively. Since the energy balance is conventionally written in terms of spatial variations of properties (as is the general species balance), there was no logical way to solve mass and energy balance equations simultaneously, as we must do to consider nonisothermal and nonideal reactors. This notation also prohibits the correct handling of multiple reaction systems because there is no obvious X or r,J with multiple reactions, and Levenspiel could only describe selectivity and yield qualitatively. In that notation, reactors other than the perfect plug flow and the perfectly stirred reactor could not be handled because it did not allow consideration of properties versus position in the reactor. However, Levenspiel’s books describe complex multiphase reactors much more thoroughly and readably than any of its successors, certainly more than will be attempted here. xi xii Preface We next used the texts of Hill and then Fogler in our chemical reactors course. These books are adapted from Levenspiel, as they used the same notation and organization, although they reduced or omitted reactions of solids and complex reactors, and their notation required fairly qualitative consideration of nonisothermal reactors. It was our opinion that these texts actually made diffusion in porous pellets and heat effects seem more complicated than they need be because they were not sufficiently logically or mathematically based. These texts also had an unnecessary affinity for the variable density reactor such as A + 3 B with ideal gases where the solutions require dealing with high-order polynomials and partial fractions. In contrast, the assumption-of constant density (any liquid-phase reactor or gases with diluent) generates easily solved problems. At the same time, as a chemist I was disappointed at the lack of serious chemistry and kinetics in reaction engineering texts. All beat A + B to death without much mention that irreversible isomerization reactions are very uncommon and never very interesting. Levenspiel and its progeny do not handle the series reactions A + B + C or parallel reactions A --f B, A + C sufficiently to show students that these are really the prototypes of all multiple reaction systems. It is typical to introduce rates and kinetics in a reaction engineering course with a section on analysis of data in which log-log and Arrhenius plots are emphasized with the only purpose being the determination of rate expressions for single reactions from batch reactor data. It is typically assumed that any chemistry and most kinetics come from previous physical chemistry courses. Up until the 1950s there were many courses and texts in chemical engineering on “Industrial Chemistry” that were basically descriptions of the industrial processes of those times. These texts were nearly devoid of mathematics, but they summarized the reactions, process conditions, separation methods, and operating characteristics of chemical synthesis processes. These courses in the chemical engineering curriculum were all replaced in the 1950s by more analytical courses that organized chemical engineering through “principles” rather than descriptions because it was felt that students needed to be able to understand the principles of operation of chemical equipment rather than just memorize pictures of them. Only in the Process Design course does there remain much discussion of the processes by which chemicals are made. While the introduction of principles of chemical engineering into the curriculum undoubtedly prepared students to understand the underlying equations behind processes, succeeding generations of students rapidly became illiterate regarding these processes and even the names and uses of the chemicals that were being produced. We became so involved in understanding the principles of chemical engineering that we lost interest in and the capability of dealing with processes. In order to develop the processes of tomorrow, there seems to be a need to combine principles and mathematical analysis along with applications and synthesis of these principles to describe processes. This is especially true in today’s changing market for chemical engineers, where employers no longer are searching for specialists to analyze larger and larger equipment but rather are searching for engineers to devise new processes to refurbish and replace or retrofit old, dirty, and unsafe ones. We suggest that an understanding of how and why things were done in the past present is essential in devising new processes. Students need to be aware of the following facts about chemical reactors. 1. The definition of a chemical engineer is one who handles the engineering of chemical reactions. Separations, fluid flow, and transport are details (admittedly sometimes very Preface XIII ‘.’ important) in that task. Process design is basically reactor design, because the chemical reactors control the sizes and functions of other units. 2. The most important reactor by far in twentieth century technology is the fluidized catalytic cracker. It processes more chemicals than any other reactor (except the automotive catalytic converter), the products it creates are the raw materials for most of chemical technology, and this reactor is undoubtedly the largest and most complex piece of equipment in our business. Yet it is very possible that a student can receive a B.S. degree in chemical engineering without ever hearing of it. 3. Most industrial processes use catalysts. Homogeneous single reaction systems are fairly rare and unimportant. The most important homogeneous reaction systems in fact involve free radical chains, which are very complex and highly nonlinear. 4. Energy management in chemical reactors is essential in reactor design. 5. Most industrial reactors involve multiple phases, and mass transfer steps between phases are essential and usually control the overall rates of process. 6. Polymers and their monomers are the major commodity and fine chemicals we deal with; yet they are considered mostly in elective polymer chemistry and polymer properties courses for undergraduates. 7. Chemical engineering is rapidly changing such that petroleum processing and commodity chemical industries are no longer the dominant employers of chemical engineers. Polymers, bioprocesses, microelectronics, foods, films, and environmental concerns are now the growth industries needing chemical engineers to handle essential chemical processing steps. 8. The greatest safety hazard in chemical engineering operations is without question caused by uncontrolled chemical reactions, either within the chemical reactor or when flammable chemicals escape from storage vessels or pipes. Many undergraduate students are never exposed to the extremely nonlinear and potentially hazardous characteristics of exothermic free radical processes. It is our belief that a course in chemical reaction engineering should introduce all undergraduate students to all these topics. This is an ambitious task for a one-semester course, and it is therefore essential to focus caref..."

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