INTRODUCTION TO CHEMICAL REACTION ENGINEERING AND KINETICS - Ronald W. Missen

INTRODUCTION TO CHEMICAL REACTION ENGINEERING AND KINETICS - Ronald W. Missen

(Parte 1 de 7)

Ronald W. Missen Charles A. Mims

Bradley A. Saville

Ronald W. Missen Charles A. Mims Bradley A. Saville

Department of Chemical Engineering and Applied Chemistry University of Toronto

John Wiley & Sons, Inc. New York l Chichester l Weinheim l Brisbane l Singapore l Toronto

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Library of Congress Cataloging-in-Publication Data:

Missen, Ronald W. (Ronald William), 192%

Introduction to chemical reaction engineering and kinetics / Ronald W. Missen, Charles A. Mims, Bradley A. Saville.

p. cm.

Includes bibliographical references and index. ISBN 0-471-16339-2 (cloth : alk. paper) 1. Chemical reactors.2. Chemical kinetics.I. Mims, Charles A.

I. Saville, Bradley A.II. Title. TP157.M538 1999 660’.2832-dc21 98-27267

CIP Printed in the United States of America

Introduction to Chemical Reaction Engineering and Kinetics is written primarily for a first course in chemical reaction engineering (CRE) for undergraduate students in chemical engineering. The purpose of the work is to provide students with a thorough introduction to the fundamental aspects of chemical reactor analysis and design. For this purpose, it is necessary to develop a knowledge of chemical kinetics, and therefore the work has been divided into two inter-related parts: chemical kinetics and CRE. Included with this book is a CD-ROM containing computer software that can be used for numerical solutions to many of the examples and problems within the book. The work is primarily based on material given to undergraduate students in the Department of Chemical Engineering and Applied Chemistry at the University of Toronto.

Scope and Organization of Material

The material in this book deals with kinetics and reactors. We realize that students in many institutions have an introduction to chemical kinetics in a course on physical chemistry. However, we strongly believe that for chemical engineering students, kinetics should be fully developed within the context of, and from the point of view of, CRE. Thus, the development given here differs in several important respects from that given in physical chemistry. Ideal-flow reactor models are introduced early in the book (Chapter 2) because of their use in kinetics investigations, and to get students accustomed to the concepts early. Furthermore, there is the additional purpose of drawing a distinction between a reaction model (network) or kinetics scheme, on the one hand, and a reactor model that incorporates a kinetics scheme, on the other. By a reaction model, we mean the development in chemical engineering kinetics of an appropriate (local or point) rate law, including, in the case of a multiphase system, the effects of rate processes other than chemical reaction itself. By contrast, a reactor model uses the rate law, together with considerations of residence-time and (if necessary) particle-size distributions, heat, mass, and momentum transfer, and fluid mixing and flow patterns, to establish the global behavior of a reacting system in a vessel. We deliberately separate the treatment of characterization of ideal flow (Chapter 13) and of nonideal flow (Chapter 19) from the treatment of reactors involving such flow. This is because (1) the characterization can be applied to situations other than those involving chemical reactors; and (2) it is useful to have the characterization complete in the two locations so that it can be drawn on for whatever reactor application ensues in Chapters 14-18 and 20-24. We also incorporate nonisothermal behavior in the discussion of each reactor type as it is introduced, rather than treat this behavior separately for various reactor types.

Our treatment of chemical kinetics in Chapters 2-10 is such that no previous knowledge on the part of the student is assumed. Following the introduction of simple reactor models, mass-balance equations and interpretation of rate of reaction in Chapter 2, and measurement of rate in Chapter 3, we consider the development of rate laws for single-phase simple systems in Chapter 4, and for complex systems in Chapter 5. This is vii viii Preface followed by a discussion of theories of reaction and reaction mechanisms in Chapters 6 and 7. Chapter 8 is devoted to catalysis of various types. Chapter 9 is devoted to reactions in multiphase systems. The treatment of chemical kinetics concludes in Chapter 10 with a discussion of enzyme kinetics in biochemical reactions. Our treatment of Chemical Reaction Engineering begins in Chapters 1 and 2 and continues in Chapters 1-24. After an introduction (Chapter 1) surveying the field, the next five Chapters (12-16) are devoted to performance and design characteristics of four ideal reactor models (batch, CSTR, plug-flow, and laminar-flow), and to the characteristics of various types of ideal flow involved in continuous-flow reactors. Chapter 17 deals with comparisons and combinations of ideal reactors. Chapter 18 deals with ideal reactors for complex (multireaction) systems. Chapters 19 and 20 treat nonideal flow and reactor considerations taking this into account. Chapters 21- 24 provide an introduction to reactors for multiphase systems, including fixed-bed catalytic reactors, fluidized-bed reactors, and reactors for gas-solid and gas-liquid reactions.

Ways to Use This Book in CRJ3 Courses

One way in which the material can be used is illustrated by the practice at the University of Toronto. Chapters 1-8 (sections 8.1-8.4) on chemical kinetics are used for a 40-lecture (3 per week) course in the fall term of the third year of a four-year program; the lectures are accompanied by weekly 2-hour tutorial (problem-solving) ses- sions. Chapters on CRE (l-15,17,18, and 21) together with particle-transport kinetics from section 8.5 are used for a similarly organized course in the spring term. There is more material than can be adequately treated in the two terms. In particular, it is not the practice to deal with all the aspects of nonideal flow and multiphase systems that are described. This approach allows both flexibility in choice of topics from year to year, and material for an elective fourth-year course (in support of our plant design course), drawn primarily from Chapters 9,19,20, and 2-24.

At another institution, the use of this material depends on the time available, the requirements of the students, and the interests of the instructor. The possibilities include:

(1)a basic one-semester course in CRE primarily for simple, homogeneous systems, using Chapters 1-4 (for kinetics, if required) and Chapters 1-17; (2) an extension of (1) to include complex, homogeneous systems, using Chapters 5 (for kinetics) and 18 in addition; (3) a further extension of (1) and (2) to include heterogeneous systems using Chapters 8 and 9 (for kinetics), and selected parts of Chapters 21-24; (4) a final extension to nonideal flow, using Chapters 19 and 20.

In addition, Chapters 6 and 7 could be reserved for the enrichment of the treatment of kinetics, and Chapter 10 can be used for an introduction to enzyme kinetics dealing with some of the problems in the reactor design chapters.

Reviewers have suggested that this book may be used both at the undergraduate level and at the beginning of a graduate course. The latter is not our intention or our practice, but we leave this to the discretion and judgement of individual instructors.

Problem Solving and Computer Tools

We place primary emphasis on developing the students’ abilities to establish the work- ing equations of an appropriate model for a particular reactor situation, and of course to interpret and appreciate the significance of quantitative results. In an introductory text in a field such as CRE, it is important to emphasize the development of principles,

Preface ix and to illustrate their application by means of relatively simple and idealized problem situations that can be solved with a calculator. However, with the availability of computer-based solution techniques, it is desirable to go beyond this approach for several reasons:

(1) Computer software allows the solution of more complex problems that require numerical, as opposed to analytical, techniques. Thus, a student can explore situations that more closely approximate real reactor designs and operating conditions. This includes studying the sensitivity of a calculated result to changing operating conditions. (2) The limitations of analytical solutions may also interfere with the illustration of important features of reactions and of reactors. The consequences of linear behavior, such as first-order kinetics, may be readily demonstrated in most cases by analytical techniques, but those of nonlinear behavior, such as second-order or Langmuir-Hinshelwood kinetics, generally require numerical techniques. (3) The development of mechanistic rate laws also benefits from computer simulations. All relevant elementary steps can be included, whereas, with analytical techniques, such an exploration is usually impossible.

(4)Computer-aided visual demonstrations in lectures and tutorials are desirable for topics that involve spatial and/or time-dependent aspects.

For these reasons, we include examples and problems that require numerical techniques for their solution together with suitable computer software (described below).

Computer Software: E-Z Solve: The Engineer’s Equation Solving and Analysis Tool

Accompanying this book is a CD-ROM containing the computer software E-Z Solve, developed by IntelliPro, Inc and distributed by John Wiley & Sons, Inc. It can be used for parameter estimation and equation solving, including solution of sets of both nonlinear algebraic equations and differential equations. It is extremely easy to learn and use. We have found that a single 2-hour tutorial is sufficient to instruct students in its application. We have also used it in research problems, such as modeling of transient behavior in kinetics investigations. Other computer software programs may be used, if appropriate, to solve most of the examples and problems in the text that are solved with the aid of E-Z Solve (indicated in the text by a computer icon shown in the margin above). The successful use of the text is not restricted to the use of E-Z Solve for software support, although we encourage its use because of its capabilities for nonlinear parameter estimation and solution of coupled differential and algebraic equations.

Appendix D provides examples illustrating the use of the software for these types of problems, along with the required syntax.

Web Site

A web site at w.wiley.com/college/missen is available for ongoing support of this book. It includes resources to assist students and instructors with the subject matter, such as sample files, demonstrations, and a description of the E-Z Solve software appearing on the CD-ROM that accompanies this book.

Acknowledgments

We acknowledge our indebtedness to those who have contributed to the literature on the topics presented here, and on whose work we have drawn. We are grateful for the x Preface contributions of S.T. Balke, W.H. Burgess, and M.J. Phillips, who have participated in the undergraduate courses, and for discussions with W.R. Smith. We very much appreciate the comments on the manuscript received from reviewers. CAM credits, in addition to his academic colleagues, his former coworkers in industry for a deep and continuing education into the subject matter. We are also grateful for the assistance given by Esther Oostdyk, who entered the manuscript; by Lanny Partaatmadja, who entered material for the “Instructor Resources”;and by Mark Eichhorn, Nick Palozzi, Chris Ho, Winnie Chiu and Lanny

Partaatmadja, who worked on graphics and on problems for the various chapters. We also thank Nigel Waithe, who produced copies of draft material for the students. We thank our students for their forbearance and comments, both written and oral, during the development of this book.

The development of the computer tools and their integration with the subject matter required strong support from Wayne Anderson and the late Cliff Robichaud at Wiley, and Philippe Marchal and his staff at Intellipro. Their assistance is gratefully acknowledged. We also thank the staff at Wiley and Larry Meyer and his staff at Hermitage Publishing Services for their fine work during the production phase.

Support for the development of the manuscript has been provided by the Department of Chemical Engineering and Applied Chemistry, the Faculty of Applied Science and Engineering, and the Office of the Provost, University of Toronto.

Ronald W. Missen Charles A. Mims

Bradley A. Saville Toronto, Ontario. May, 1998

Contents

1.INTRODUCTION 1 1.1 Nature and Scope of Chemical Kinetics1 1.2 Nature and Scope of Chemical Reaction Engineering 1.3 Kinetics and Chemical Reaction Engineering 2

1.4 Aspects of Kinetics 3

1.4.1 Rate of Reaction-Definition 3 1.4.2 Parameters Affecting Rate of Reaction: The Rate Law

1.4.3 Measurement of Rate of Reaction-Preliminary 5 1.4.4 Kinetics and Chemical Reaction Stoichiometry 6

1.4.5 Kinetics and Thermodynamics/Equilibrium 14 1.4.6 Kinetics and Transport Processes 15

1.5 Aspects of Chemical Reaction Engineering 15 1.5.1 Reactor Design and Analysis of Performance15

1.5.2 Parameters Affecting Reactor Performance 16 1.5.3 Balance Equations 16

1.5.4 An Example of an Industrial Reactor18

1.6 Dimensions and Units 19

1.7 Plan of Treatment in Following Chapters21

1.7.1 Organization of Topics 21 1.7.2 Use of Computer Software for Problem Solving21

(Parte 1 de 7)

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