Modeling of Chemical Kinetics and Reactor Design

1126 Pages·2001·15.419 MB·English

by  A. Kayode Coker PhD

Modeling of
Chemical Kinetics
and
Reactor Design

Modeling of
Chemical Kinetics
and
Reactor Design
A. Kayode Coker, Ph.D.
Lecturerer and Consultant, AKC Technology
Boston Oxford Johannesburg Melbourne New Delhi Singapore
Dedication
To my wife Victoria and the boys Akin and Ebun,
love and thanks.
Modeling of
CHEMICAL KINETICS AND
REACTOR DESIGN
Copyright © 2001 by Gulf Publishing Company, Houston, Texas. All rights
reserved. Printed in the United States of America. This book, or parts thereof,
may not be reproduced in any form without permission of the publisher.
Gulf Publishing Company
Book Division
P.O. Box 2608, Houston, Texas 77252-2608
Library of Congress Cataloging-in-Publication Data
(To come)
ISBN 0-88415-481-5
Printed in the United States of America.
Printed on acid-free paper (∞).
iv
Acknowledgments
I wish to express my gratitude to the following for giving their time
in proofreading various sections of the text: Drs. A. A. Adesina,
L. M. Rose, C. J. Mumford, and J. D. Jenkins. I am indebted to
Emeritus Professor Octave Levenspiel for his encouragement and
advice in some chapters of the text, and to Drs. Waldram and Singh
for their comments, suggestions on safety in reaction engineering, and
the inclusion of HEL safety photographs in the text. I would also like
to thank Mr. Ed Steve for his comments and suggestions on scale-up
of reactors, and Mr. Joseph Rivera for some of the figures in the text. I
wish to express my gratitude to Drs. A. Bakker, J. B. Fasano, and V. V.
Ranade for contributing to Chapter 10 (Computational Fluid Dynamics
and Computational Fluid Mixing). I would like to acknowl-edge the
following companies for the use of their materials: Arthur D. Little,
HEL, M. W. Kellogg Ltd., Stone & Webster, Fauske & Associates, Inc.,
Simulation Sciences Inc., Chemineer, PROCEDE, and Absoft Corporation.
I would like to express my gratitude to the following institutions
for permission to reproduce their materials: Institution of Chemical
Engineers (U.K.), the American Institute of Chemical Engineers and
Chemical Engineering—a publication of Chemical Week Associates.
I am also indebted to those whose work was drawn.
I thank Dr. E. L. Smith for his comments and suggestions during
the preparation of some of the chapters in the text and wish him a
happy retirement. It has been a pleasure to have learned so much from
him during his tenure at Aston University.
Sincere gratitude to Tim Calk of Gulf Publishing Company for his
direction and editing of the book, to Danette DeCristofaro and Jerry
Hayes of ExecuStaff for their excellent production of the book, to Mr.
Phil Carmical and Ms. Jennifer Plumley of Butterworth-Heinemann for
the production of the CD-ROM.
v
My thanks to Ahmed Mutawa of Saudi Aramco Shell Refinery
(SASREF), an excellent student in the short course program for
developing conversion table software for the book.
In gratitude to the Almighty father, the Omnipotence, Omniscience,
and Omnipresence.
A. Kayode Coker, Ph.D.
Nippon Petroleum FCC Unit—Japan. (Courtesy M. W. Kellogg Ltd.)
vi
Contents
Preface................................................................................................. xiii
Introduction........................................................................................xvii
CHAPTER ONE
Reaction Mechanisms and Rate Expressions ................................11
Introduction 1
Typical Reaction Mechanisms 5
Reaction Mechanisms 8
Elementary and Non-Elementary Reactions 9
Types of Intermediate 10
The Arrhenius Equation and the Collision Theory 12
Transition State Theory 15
Chain Reactions 16
Catalytic Reactions 21
Guidelines to Formulating Reaction Mechanism 32
Testing Kinetic Models 34
Chain Length 37
References 58
CHAPTER TWO
Thermodynamics of Chemical Reactions .......................................59
Introduction 59
Chemical Equilibrium 60
Criteria for Equilibrium 63
Reaction Equilibrium 64
Ideal Gas Mixtures 65
Real Gases—Ideal Gaseous Solutions 65
Real Gases 67
Liquid State 69
Determining the Fugacity and the Fugacity Coefficient 70
Partial Molar Quantities 72
Effect of Temperature on the Equilibrium Constant 74
vii
Heats of Reaction 75
Heat Capacities of Gases 80
Heats of Formation 80
References 93
Appendix 94
CHAPTER THREE
Reaction Rate Expression................................................................109
Introduction 109
Reaction Rate Equation 110
Reaction Orders 114
Determining the Order of Reactions 116
Empirical Rate Equations of the nth Order 129
Method of Half-Life t 130
1/2
Parallel Reactions 134
Homogeneous Catalyzed Reactions 137
Autocatalytic Reactions 138
Irreversible Reactions in Series 140
First Order Reversible Reactions 146
Second Order Reversible Reactions 150
General Reversible Reactions 151
Simultaneous Irreversible Side Reaction 152
Pseudo-Order Reaction 154
Practical Measurements of Reaction Rates 155
Regression Analysis 171
Weighted Least Squares Analysis 173
Problems and Errors in Fitting Rate Models 175
References 216
CHAPTER FOUR
Industrial and Laboratory Reactors.............................................218
Introduction 218
Batch Isothermal Perfectly Stirred Reactor 220
Semi-Batch Reactors 222
Continuous Flow Isothermal Perfectly Stirred Tank Reactor 226
Continuous Isothermal Plug Flow Tubular Reactor 227
Continuous Multiphase Reactors 230
Fluidized Bed System 232
Fluid Catalytic Cracking (FCC) Unit 234
Deep Catalytic Cracking Unit 235
Determining Laboratory Reactors 243
Guidelines for Selecting Batch Processes 254
viii
Guidelines for Selecting Batch Processes 254
References 259
CHAPTER FIVE
Introduction to Reactor Design Fundamentals
for Ideal Systems...............................................................................260
Introduction 260
A General Approach 262
Ideal Isothermal Reactors 264
Numerical Methods for Reactor Systems Design 279
Reversible Series Reactions 287
The Semibatch Reactor 306
Continuous Flow Stirred Tank Reactor (CFSTR) 312
Multi-Stage Continuous Flow Stirred Tank Reactor 327
Equal Size CFSTR In Series 334
Space Time (ST) and Space Velocity (SV) 349
Fractional Conversion, Yield, and Selectivity in Reactors 351
Relationship Between Conversion, Selectivity, and Yield 353
Plug Flow Reactor 362
Heterogeneous Tubular Reactor 371
Design Equation for Systems of Variable Density 372
Design Equations for Heterogeneous Reactions 375
Comparison of Ideal Reactors 387
CFSTR and Plug Flow Systems 396
Dynamic Behavior of Ideal Systems 400
Flow Recycle Reactor 410
References 423
CHAPTER SIX
Non-Isothermal Reactors.................................................................424
Introduction 424
Operating Temperature, Reaction Types, and Temperature 425
Effect of Operating Parameters on Equilibrium Conversion 429
Energy Balance and Heat of Reaction 429
Energy Transferred between the System and Surroundings 434
Batch Reactor 457
Plug Flow Reactor 472
Autothermal Reactors 477
Conversion in Ammonia Synthesis 478
Two-Dimensional Tubular (Plug Flow) Reactor 492
Pressure Drop (∆P) in Tubular (Plug Flow) Reactors 494
Thermal Behaviors in Flow Systems 500
ix
Exothermic Reactions in CFSTRs 504
Thermal Behavior of a Tubular Flow Reactor 507
Variable Coolant Temperature in a CFSTR 515
Optimal Design of Non-Isothermal Reactors 518
Mimimum Reactor Volume at the Optimum Temperature
Progression (OTP) of a Single CFSTR with a Reversible
Exothermic Reaction 543
Optimum Reactor Size 546
References 551
CHAPTER SEVEN
Fluid Mixing in Reactors ................................................................552
Introduction 552
Mixing and Agitation of Fluids 553
Similarity 570
Mixing Time Correlation 578
Scale-up of Mixing Systems 584
Static Mixers 597
Heat Transfer in Agitated Vessels 615
Liquid-Solid Agitation 634
Batch Heating and Cooling of Fluids 636
Design of Mixing Systems 656
References 659
CHAPTER EIGHT
Residence Time Distributions in Flow Reactors.........................663
Introduction 663
The Residence Time Distribution Functions and
their Relationships 664
Determining RTD from Experimental Tracer Curves 680
Analysis of RTD from Pulse Input 688
Residence Time Distribution for a Laminar
Flow Tubular Reactor 708
E- and F-Curves for a Series of Stirred Tank Reactors 713
RTD Functions for CSTRs Where N Is Not an Integer 721
The Dispersion Model 723
Comparison of Tank In Series (TIS) and Dispersion
Plug Flow (DPF) Models 746
Residence Time Distribution in a Static Mixer 747
Glossary 756
References 760
x