Types of Chemical Reactors and Chemical Processes

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Q1. Chemical reactors are the most vital parts of many chemical, biochemical, polymer, and petroleum processes because they transform raw materials into valuable chemicals. A vast variety of useful and essential products are generated via reactions that convert reactants into products. A significant fraction of our transportation fuel (gasoline, diesel, and jet fuel) is produced within process units of a petroleum refinery that involve reactions. Reforming reactions are used to convert cyclical saturated Naphthenes into aromatics, which have higher octane numbers.

(i) Discuss any three types of chemical reactors employed in the petroleum/oil and gas industry with suitable design equation and a sketch.

(ii) Explain the unique characteristics, advantages, and disadvantages of each reactor type.


Note :

The answer will be

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  • the answer will be at least 10 pages or more
  • Provide Some figures/ pictures with reference
  • Harvard Referencing should be followed for both in-text and listing references.
  • refer to the attached books and other books form the internet related to Chemical reactions

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Elements of Chemical Reaction Engineering Fifth Edition Prentice Hall International Series in the Physical and Chemical Engineering Sciences Visit informit.com/ph/physandchem for a complete list of available publications. The Prentice Hall International Series in the Physical and Chemical Engineering Sciences had its auspicious beginning in 1956 under the direction of Neal R. Amundsen. The series comprises the most widely adopted college textbooks and supplements for chemical engineering education. Books in this series are written by the foremost educators and researchers in the field of chemical engineering. Make sure to connect with us! informit.com/socialconnect Elements of Chemical Reaction Engineering Fifth Edition H. SCOTT FOGLER Ame and Catherine Vennema Professor of Chemical Engineering and the Arthur F. Thurnau Professor The University of Michigan, Ann Arbor Boston • Columbus • Indianapolis • New York • San Francisco • Amsterdam • Cape Town Dubai • London • Madrid • Milan • Munich • Paris • Montreal • Toronto • Delhi • Mexico City São Paulo • Sidney • Hong Kong • Seoul • Singapore • Taipei • Tokyo Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this book, and the publisher was aware of a trademark claim, the designations have been printed with initial capital letters or in all capitals. The author and publisher have taken care in the preparation of this book, but make no expressed or implied warranty of any kind and assume no responsibility for errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of the use of the information or programs contained herein. For information about buying this title in bulk quantities, or for special sales opportunities (which may include electronic versions; custom cover designs; and content particular to your business, training goals, marketing focus, or branding interests), please contact our corporate sales department at corpsales@pearsoned.com or (800) 382-3419. For government sales inquiries, please contact governmentsales@pearsoned.com. For questions about sales outside the United States, please contact international@pearsoned.com. Visit us on the Web: informit.com/ph Library of Congress Cataloging-in-Publication Data Fogler, H. Scott, author. Elements of chemical reaction engineering / H. Scott Fogler.—Fifth edition. pages cm Includes index. ISBN 978-0-13-388751-8 (hardcover : alk. paper) 1. Chemical reactors. I. Title. TP157.F65 2016 660'.2832—dc23 2015032892 Copyright © 2016 Pearson Education, Inc. All rights reserved. Printed in the United States of America. This publication is protected by copyright, and permission must be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or likewise. For information regarding permissions, request forms and the appropriate contacts within the Pearson Education Global Rights & Permissions Department, please visit www.pearsoned.com/permissions/. ISBN-13: 978-0-13-388751-8 ISBN-10: 0-13-388751-0 Text printed in the United States on recycled paper at RR Donnelley in Kendallville, Indiana. First printing, January 2016 Dedicated to Janet Meadors Fogler For her companionship, encouragement, sense of humor, love, and support throughout the years This page intentionally left blank Contents PREFACE xvii ABOUT THE AUTHOR CHAPTER 1 1.1 1.2 1.3 1.4 1.5 CHAPTER 2 2.1 2.2 2.3 2.4 2.5 xxxiii MOLE BALANCES 1 The Rate of Reaction, –rA 4 The General Mole Balance Equation 8 Batch Reactors (BRs) 10 Continuous-Flow Reactors 12 1.4.1 Continuous-Stirred Tank Reactor (CSTR) 1.4.2 Tubular Reactor 14 1.4.3 Packed-Bed Reactor (PBR) 18 Industrial Reactors 22 12 CONVERSION AND REACTOR SIZING Definition of Conversion 32 Batch Reactor Design Equations 32 Design Equations for Flow Reactors 35 2.3.1 CSTR (Also Known as a Backmix Reactor or a Vat) 36 2.3.2 Tubular Flow Reactor (PFR) 36 2.3.3 Packed-Bed Reactor (PBR) 37 Sizing Continuous-Flow Reactors 38 Reactors in Series 47 2.5.1 CSTRs in Series 48 2.5.2 PFRs in Series 52 2.5.3 Combinations of CSTRs and PFRs in Series 53 2.5.4 Comparing the CSTR and PFR Reactor Volumes and Reactor Sequencing 57 vii 31 viii Contents 2.6 CHAPTER 3 3.1 3.2 3.3 3.4 CHAPTER 4 4.1 4.2 4.3 CHAPTER 5 5.1 5.2 5.3 5.4 5.5 5.6 Some Further Definitions 58 2.6.1 Space Time 58 2.6.2 Space Velocity 60 RATE LAWS 69 Basic Definitions 70 3.1.1 Relative Rates of Reaction 71 The Reaction Order and the Rate Law 72 3.2.1 Power Law Models and Elementary Rate Laws 72 3.2.2 Nonelementary Rate Laws 76 3.2.3 Reversible Reactions 80 Rates and the Reaction Rate Constant 83 3.3.1 The Rate Constant k 83 3.3.2 The Arrhenius Plot 90 Present Status of Our Approach to Reactor Sizing and Design 93 STOICHIOMETRY Batch Systems 107 4.1.1 Batch Concentrations for the Generic Reaction, Equation (2-2) 109 Flow Systems 113 4.2.1 Equations for Concentrations in Flow Systems 4.2.2 Liquid-Phase Concentrations 114 4.2.3 Gas-Phase Concentrations 115 Reversible Reactions and Equilibrium Conversion 126 105 114 ISOTHERMAL REACTOR DESIGN: CONVERSION Design Structure for Isothermal Reactors 140 Batch Reactors (BRs) 144 5.2.1 Batch Reaction Times 145 Continuous-Stirred Tank Reactors (CSTRs) 152 5.3.1 A Single CSTR 152 5.3.2 CSTRs in Series 155 Tubular Reactors 162 Pressure Drop in Reactors 169 5.5.1 Pressure Drop and the Rate Law 169 5.5.2 Flow Through a Packed Bed 170 5.5.3 Pressure Drop in Pipes 174 5.5.4 Analytical Solution for Reaction with Pressure Drop 5.5.5 Robert the Worrier Wonders: What If… 181 Synthesizing the Design of a Chemical Plant 190 139 177 ix Contents CHAPTER 6 ISOTHERMAL REACTOR DESIGN: MOLES AND MOLAR FLOW RATES 6.1 6.2 6.3 6.4 6.5 6.6 CHAPTER 7 7.1 7.2 7.3 7.4 7.5 7.6 7.7 CHAPTER 8 8.1 8.2 8.3 8.4 The Molar Flow Rate Balance Algorithm 208 Mole Balances on CSTRs, PFRs, PBRs, and Batch Reactors 6.2.1 Liquid Phase 208 6.2.2 Gas Phase 210 Application of the PFR Molar Flow Rate Algorithm to a Microreactor 212 Membrane Reactors 217 Unsteady-State Operation of Stirred Reactors 225 Semibatch Reactors 227 6.6.1 Motivation for Using a Semibatch Reactor 227 6.6.2 Semibatch Reactor Mole Balances 227 207 208 COLLECTION AND ANALYSIS OF RATE DATA 243 The Algorithm for Data Analysis 244 Determining the Reaction Order for Each of Two Reactants Using the Method of Excess 246 Integral Method 247 Differential Method of Analysis 251 7.4.1 Graphical Differentiation Method 252 7.4.2 Numerical Method 252 7.4.3 Finding the Rate-Law Parameters 253 Nonlinear Regression 258 Reaction-Rate Data from Differential Reactors 264 Experimental Planning 271 MULTIPLE REACTIONS Definitions 280 8.1.1 Types of Reactions 280 8.1.2 Selectivity 281 8.1.3 Yield 282 Algorithm for Multiple Reactions 282 8.2.1 Modifications to the Chapter 6 CRE Algorithm for Multiple Reactions 284 Parallel Reactions 285 8.3.1 Selectivity 285 8.3.2 Maximizing the Desired Product for One Reactant 285 8.3.3 Reactor Selection and Operating Conditions 291 Reactions in Series 294 279 x Contents 8.5 8.6 8.7 8.8 CHAPTER 9 Complex Reactions 304 8.5.1 Complex Gas-Phase Reactions in a PBR 304 8.5.2 Complex Liquid-Phase Reactions in a CSTR 307 8.5.3 Complex Liquid-Phase Reactions in a Semibatch Reactor 310 Membrane Reactors to Improve Selectivity in Multiple Reactions 312 Sorting It All Out 317 The Fun Part 317 REACTION MECHANISMS, PATHWAYS, BIOREACTIONS, AND BIOREACTORS 9.1 9.2 9.3 9.4 CHAPTER 10 10.1 10.2 333 Active Intermediates and Nonelementary Rate Laws 334 9.1.1 Pseudo-Steady-State Hypothesis (PSSH) 335 9.1.2 Why Is the Rate Law First Order? 338 9.1.3 Searching for a Mechanism 339 9.1.4 Chain Reactions 343 Enzymatic Reaction Fundamentals 343 9.2.1 Enzyme–Substrate Complex 344 9.2.2 Mechanisms 346 9.2.3 Michaelis–Menten Equation 348 9.2.4 Batch-Reactor Calculations for Enzyme Reactions 354 Inhibition of Enzyme Reactions 356 9.3.1 Competitive Inhibition 357 9.3.2 Uncompetitive Inhibition 359 9.3.3 Noncompetitive Inhibition (Mixed Inhibition) 361 9.3.4 Substrate Inhibition 363 Bioreactors and Biosynthesis 364 9.4.1 Cell Growth 368 9.4.2 Rate Laws 369 9.4.3 Stoichiometry 371 9.4.4 Mass Balances 377 9.4.5 Chemostats 381 9.4.6 CSTR Bioreactor Operation 381 9.4.7 Wash-Out 383 CATALYSIS AND CATALYTIC REACTORS Catalysts 399 10.1.1 Definitions 400 10.1.2 Catalyst Properties 401 10.1.3 Catalytic Gas-Solid Interactions 403 10.1.4 Classification of Catalysts 404 Steps in a Catalytic Reaction 405 10.2.1 Step 1 Overview: Diffusion from the Bulk to the External Surface of the Catalyst 408 10.2.2 Step 2 Overview: Internal Diffusion 409 399 xi Contents 10.3 10.4 10.5 10.6 10.7 CHAPTER 11 11.1 11.2 11.3 11.4 10.2.3 Adsorption Isotherms 410 10.2.4 Surface Reaction 416 10.2.5 Desorption 418 10.2.6 The Rate-Limiting Step 419 Synthesizing a Rate Law, Mechanism, and Rate-Limiting Step 421 10.3.1 Is the Adsorption of Cumene Rate-Limiting? 424 10.3.2 Is the Surface Reaction Rate-Limiting? 427 10.3.3 Is the Desorption of Benzene Rate-Limiting? 429 10.3.4 Summary of the Cumene Decomposition 430 10.3.5 Reforming Catalysts 431 10.3.6 Rate Laws Derived from the Pseudo-SteadyState Hypothesis (PSSH) 435 10.3.7 Temperature Dependence of the Rate Law 436 Heterogeneous Data Analysis for Reactor Design 436 10.4.1 Deducing a Rate Law from the Experimental Data 438 10.4.2 Finding a Mechanism Consistent with Experimental Observations 439 10.4.3 Evaluation of the Rate-Law Parameters 440 10.4.4 Reactor Design 443 Reaction Engineering in Microelectronic Fabrication 446 10.5.1 Overview 446 10.5.2 Chemical Vapor Deposition 448 Model Discrimination 451 Catalyst Deactivation 454 10.7.1 Types of Catalyst Deactivation 456 10.7.2 Reactors That Can Be Used to Help Offset Catalyst Decay 465 10.7.3 Temperature–Time Trajectories 465 10.7.4 Moving-Bed Reactors 467 10.7.5 Straight-Through Transport Reactors (STTR) 472 NONISOTHERMAL REACTOR DESIGN–THE STEADYSTATE ENERGY BALANCE AND ADIABATIC PFR APPLICATIONS Rationale 494 The Energy Balance 495 11.2.1 First Law of Thermodynamics 495 11.2.2 Evaluating the Work Term 496 11.2.3 Overview of Energy Balances 498 The User-Friendly Energy Balance Equations 502 11.3.1 Dissecting the Steady-State Molar Flow Rates to Obtain the Heat of Reaction 502 11.3.2 Dissecting the Enthalpies 504 11.3.3 Relating H Rx (T), HRx (T R), and C P 505 Adiabatic Operation 508 11.4.1 Adiabatic Energy Balance 508 11.4.2 Adiabatic Tubular Reactor 509 493 xii Contents 11.5 11.6 11.7 CHAPTER 12 Adiabatic Equilibrium Conversion 518 11.5.1 Equilibrium Conversion 518 Reactor Staging 522 11.6.1 Reactor Staging with Interstage Cooling or Heating 11.6.2 Exothermic Reactions 523 11.6.3 Endothermic Reactions 523 Optimum Feed Temperature 526 522 STEADY-STATE NONISOTHERMAL REACTOR DESIGN—FLOW REACTORS WITH HEAT EXCHANGE 12.1 12.2 12.3 12.4 12.5 12.6 12.7 12.8 CHAPTER 13 13.1 13.2 539 Steady-State Tubular Reactor with Heat Exchange 540 12.1.1 Deriving the Energy Balance for a PFR 540 12.1.2 Applying the Algorithm to Flow Reactors with Heat Exchange 542 Balance on the Heat-Transfer Fluid 543 12.2.1 Co-current Flow 543 12.2.2 Countercurrent Flow 544 Algorithm for PFR/PBR Design with Heat Effects 545 12.3.1 Applying the Algorithm to an Exothermic Reaction 548 12.3.2 Applying the Algorithm to an Endothermic Reaction 555 CSTR with Heat Effects 564 12.4.1 Heat Added to the Reactor, Q̇ 564 Multiple Steady States (MSS) 574 12.5.1 Heat-Removed Term, R(T ) 575 12.5.2 Heat-Generated Term, G(T ) 576 12.5.3 Ignition-Extinction Curve 578 Nonisothermal Multiple Chemical Reactions 581 12.6.1 Energy Balance for Multiple Reactions in Plug-Flow Reactors 581 12.6.2 Parallel Reactions in a PFR 582 12.6.3 Energy Balance for Multiple Reactions in a CSTR 585 12.6.4 Series Reactions in a CSTR 585 12.6.5 Complex Reactions in a PFR 588 Radial and Axial Variations in a Tubular Reactor 595 12.7.1 Molar Flux 596 12.7.2 Energy Flux 597 12.7.3 Energy Balance 598 Safety 603 UNSTEADY-STATE NONISOTHERMAL REACTOR DESIGN Unsteady-State Energy Balance 630 Energy Balance on Batch Reactors 632 13.2.1 Adiabatic Operation of a Batch Reactor 633 13.2.2 Case History of a Batch Reactor with Interrupted Isothermal Operation Causing a Runaway Reaction 640 629 xiii Contents 13.3 13.4 13.5 CHAPTER 14 14.1 14.2 14.3 14.4 14.5 CHAPTER 15 15.1 15.2 15.3 15.4 15.5 15.6 Semibatch Reactors with a Heat Exchanger Unsteady Operation of a CSTR 651 13.4.1 Startup 651 Nonisothermal Multiple Reactions 656 646 MASS TRANSFER LIMITATIONS IN REACTING SYSTEMS 679 Diffusion Fundamentals 680 14.1.1 Definitions 681 14.1.2 Molar Flux 682 14.1.3 Fick’s First Law 683 Binary Diffusion 684 14.2.1 Evaluating the Molar Flux 684 14.2.2 Diffusion and Convective Transport 685 14.2.3 Boundary Conditions 685 14.2.4 Temperature and Pressure Dependence of DAB 686 14.2.5 Steps in Modeling Diffusion without Reaction 687 14.2.6 Modeling Diffusion with Chemical Reaction 687 Diffusion Through a Stagnant Film 688 The Mass Transfer Coefficient 690 14.4.1 Correlations for the Mass Transfer Coefficient 690 14.4.2 Mass Transfer to a Single Particle 693 14.4.3 Mass Transfer–Limited Reactions in Packed Beds 697 14.4.4 Robert the Worrier 700 What If . . . ? (Parameter Sensitivity) 705 DIFFUSION AND REACTION Diffusion and Reactions in Homogeneous Systems 720 Diffusion and Reactions in Spherical Catalyst Pellets 720 15.2.1 Effective Diffusivity 721 15.2.2 Derivation of the Differential Equation Describing Diffusion and Reaction in a Single Catalyst Pellet 723 15.2.3 Writing the Diffusion with the Catalytic Reaction Equation in Dimensionless Form 726 15.2.4 Solution to the Differential Equation for a First-Order Reaction 729 The Internal Effectiveness Factor 730 15.3.1 Isothermal First-Order Catalytic Reactions 730 15.3.2 Effectiveness Factors with Volume Change with Reaction 733 15.3.3 Isothermal Reactors Other Than First Order 733 15.3.4 Weisz–Prater Criterion for Internal Diffusion 734 Falsified Kinetics 737 Overall Effectiveness Factor 739 Estimation of Diffusion- and Reaction-Limited Regimes 743 15.6.1 Mears Criterion for External Diffusion Limitations 743 719 xiv Contents 15.7 15.8 15.9 Mass Transfer and Reaction in a Packed Bed 744 Determination of Limiting Situations from Reaction-Rate Data Multiphase Reactors in the Professional Reference Shelf 751 15.9.1 Slurry Reactors 752 15.9.2 Trickle Bed Reactors 752 15.10 Fluidized Bed Reactors 753 15.11 Chemical Vapor Deposition (CVD) 753 CHAPTER 16 RESIDENCE TIME DISTRIBUTIONS OF CHEMICAL REACTORS 16.1 16.2 16.3 16.4 16.5 16.6 CHAPTER 17 750 General Considerations 767 16.1.1 Residence Time Distribution (RTD) Function 769 Measurement of the RTD 770 16.2.1 Pulse Input Experiment 770 16.2.2 Step Tracer Experiment 775 Characteristics of the RTD 777 16.3.1 Integral Relationships 777 16.3.2 Mean Residence Time 778 16.3.3 Other Moments of the RTD 778 16.3.4 Normalized RTD Function, E() 782 16.3.5 Internal-Age Distribution, I() 783 RTD in Ideal Reactors 784 16.4.1 RTDs in Batch and Plug-Flow Reactors 784 16.4.2 Single-CSTR RTD 785 16.4.3 Laminar-Flow Reactor (LFR) 786 PFR/CSTR Series RTD 789 Diagnostics and Troubleshooting 793 16.6.1 General Comments 793 16.6.2 Simple Diagnostics and Troubleshooting Using the RTD for Ideal Reactors 794 PREDICTING CONVERSION DIRECTLY FROM THE RESIDENCE TIME DISTRIBUTION 17.1 17.2 17.3 17.4 767 Modeling Nonideal Reactors Using the RTD 808 17.1.1 Modeling and Mixing Overview 808 17.1.2 Mixing 808 Zero-Adjustable-Parameter Models 810 17.2.1 Segregation Model 810 17.2.2 Maximum Mixedness Model 820 Using Software Packages 827 17.3.1 Comparing Segregation and Maximum Mixedness Predictions 829 RTD and Multiple Reactions 830 17.4.1 Segregation Model 830 17.4.2 Maximum Mixedness 831 807 xv Contents CHAPTER 18 MODELS FOR NONIDEAL REACTORS 845 18.1 Some Guidelines for Developing Models 846 18.1.1 One-Parameter Models 847 18.1.2 Two-Parameter Models 848 18.2 The Tanks-in-Series (T-I-S) One-Parameter Model 848 18.2.1 Developing the E-Curve for the T-I-S Model 849 18.2.2 Calculating Conversion for the T-I-S Model 851 18.2.3 Tanks-in-Series versus Segregation for a First-Order Reaction 852 18.3 Dispersion One-Parameter Model 852 18.4 Flow, Reaction, and Dispersion 854 18.4.1 Balance Equations 854 18.4.2 Boundary Conditions 855 18.4.3 Finding Da and the Peclet Number 858 18.4.4 Dispersion in a Tubular Reactor with Laminar Flow 858 18.4.5 Correlations for Da 860 18.4.6 Experimental Determination of Da 862 18.5 Tanks-in-Series Model versus Dispersion Model 869 18.6 Numerical Solutions to Flows with Dispersion and Reaction 870 18.7 Two-Parameter Models—Modeling Real Reactors with Combinations of Ideal Reactors 871 18.7.1 Real CSTR Modeled Using Bypassing and Dead Space 872 18.7.2 Real CSTR Modeled as Two CSTRs with Interchange 878 18.8 Use of Software Packages to Determine the Model Parameters 880 18.9 Other Models of Nonideal Reactors Using CSTRs and PFRs 882 18.10 Applications to Pharmacokinetic Modeling 883 APPENDIX A A.1 A.2 A.3 A.4 A.5 A.6 NUMERICAL TECHNIQUES Useful Integrals in Reactor Design 897 Equal-Area Graphical Differentiation 898 Solutions to Differential Equations 900 A.3.A First-Order Ordinary Differential Equations A.3.B Coupled Differential Equations 900 A.3.C Second-Order Ordinary Differential Equations Numerical Evaluation of Integrals 901 Semilog Graphs 903 Software Packages 903 897 900 901 APPENDIX B IDEAL GAS CONSTANT AND CONVERSION FACTORS 905 APPENDIX C THERMODYNAMIC RELATIONSHIPS INVOLVING THE EQUILIBRIUM CONSTANT 909 xvi Contents APPENDIX D SOFTWARE PACKAGES D.1 915 Polymath 915 D.1.A About Polymath 915 D.1.B Polymath Tutorials 916 MATLAB 916 Aspen 916 COMSOL Multiphysics 917 D.2 D.3 D.4 APPENDIX E RATE LAW DATA 919 APPENDIX F NOMENCLATURE 921 APPENDIX G OPEN-ENDED PROBLEMS 925 G.1 G.2 G.3 G.4 G.5 G.6 G.7 G.8 G.9 G.10 APPENDIX H APPENDIX I I.1 I.2 I.3 INDEX Design of Reaction Engineering Experiment Effective Lubricant Design 925 Peach Bottom Nuclear Reactor 925 Underground Wet Oxidation 926 Hydrodesulfurization Reactor Design 926 Continuous Bioprocessing 926 Methanol Synthesis 926 Cajun Seafood Gumbo 926 Alcohol Metabolism 927 Methanol Poisoning 928 925 USE OF COMPUTATIONAL CHEMISTRY SOFTWARE PACKAGES 929 HOW TO USE THE CRE WEB RESOURCES 931 CRE Web Resources Components 931 How the Web Can Help Your Learning Style 933 I.2.1 Global vs. Sequential Learners 933 I.2.2 Active vs. Reflective Learners 934 Navigation 934 937 Preface The man who has ceased to learn ought not to be allowed to wander around loose in these dangerous days. M. M. Coady A. Who Is the Intended Audience? This book and interactive Web site is intended for use as both an undergraduate-level and a graduate-level text in chemical reaction engineering. The level will depend on the choice of chapters, the Professional Reference Shelf (PRS) material (from the companion Web site) to be covered, and the type and degree of difficulty of problems assigned. It was written with today’s students in mind. It provides instantaneous access to information; does not waste time on extraneous details; cuts right to the point; uses more bullets to make information easier to access; and includes new, novel problems on chemical reaction engineering (e.g., solar energy). It gives more emphasis to chemical reactor safety (Chapters 12 and 13) and alternative energy sources—solar (Chapters 3, 8, and 10) and biofuel production (Chapter 9). The graduate material on topics such as effectiveness factors, non-ideal reactors, and residence time distribution is in Chapters 14–18 and now includes the software solutions for maximum mixedness and segregation models. A draft version of this book was class tested at the University of Michigan and other leading universities; then the text was further revised, taking into account the suggestions of more than 100 students. Much of the material was revised and reworked based on that feedback. B. What Are the Goals of This Book? B.1 To Have Fun Learning Chemical Reaction Engineering (CRE) Chemical reaction engineering (CRE) is one of two core courses that is unique to chemical engineering and that separates the chemical engineer from other xvii xviii Preface engineers. CRE is a great subject that is fun to learn and is the heart of chemical engineering. I have tried to provide a little Michigan humor as we go. Take a look at the humorous YouTube videos (e.g., “Black Widow” or “Chemical Engineering Gone Wrong”) that illustrate certain principles in the text. These videos were made by chemical engineering students at the universities of Alabama and Michigan. In addition, I have found that students very much enjoy the Interactive Computer Games (ICGs) that, along with the videos, are linked from the CRE homepage (http://www.umich.edu/~elements/5e). B.2 To Develop a Fundamental Understanding of Reaction Engineering The second goal of this book is to help the reader clearly understand the fundamentals of CRE. This goal is achieved by presenting a structure that allows the reader to solve reaction engineering problems through reasoning rather than through memorization and recall of numerous equations and the restrictions and conditions under which each equation applies. The algorithms presented in the text for reactor design provide this framework, and the homework problems give the reader practice using the algorithms described in Figures P-1 and P-2, shown in Section C. The conventional homework problems at the end of each chapter are designed to reinforce the principles in the chapter. These problems are about equally divided between those that can be solved with a calculator and those that require a personal computer with a numerical software package, such as Polymath, AspenTech, or COMSOL. To give a reference point as to the level of understanding of CRE required in the profession, a number of reaction engineering problems from the California Board of Registration for Civil and Professional Engineers—Chemical Engineering Examinations (PECEE) are included in the text.1 Typically, these problems should each require approximately 30 minutes to solve. Finally, the companion Web site should greatly facilitate learning the fundamentals of CRE because it includes Summary Notes of the material in each chapter, PowerPoint slides of class lecture notes, additional examples, expanded derivations, and self-tests. A complete description of these learning resources is in Appendix I. B.3. To Enhance Thinking Skills A third goal of this text is to enhance critical thinking skills and creative thinking skills. How does the book help enhance your critical and creative thinking skills? We discuss ways to achieve this enhancement in Section I of the Preface. 1 The permission for use of these problems—which, incidentally, may be obtained from the Documents Section, California Board of Registration for Civil and Professional Engineers—Chemical Engineering, 1004 6th Street, Sacramento, CA 95814, is gratefully acknowledged. (Note: These problems have been copyrighted by the California Board of Registration and may not be reproduced without its permission.) xix Preface C. What Is the Structure of CRE? C.1 What Are the Concepts that Form the Foundation of CRE? The strategy behind the presentation of material is to build continually on a few basic ideas in CRE to solve a wide variety of problems. These ideas, referred to as the Pillars of Chemical Reaction Engineering (Figure P-1), are the foundation on which different applications rest. They represent not only components of chemical reaction analysis, but also the physical phenomena of diffusion and contacting that affect chemical reactor design. Figure P-2 shows the first building blocks of CRE and the primary algorithm that allows us to solve CRE problems through logic rather than memorization. We start with the Mole Balance Building Block (Chapter 1) and then place the other blocks one at a time on top of the others until we reach the Evaluate Block (Chapter 5), by which time we can solve a multitude of isothermal CRE problems. As we study each block we need to make sure we understand everything in that block and don’t leave anything out so we don’t wind up with a cylindrical block. A tower containing cylindrical blocks would be unstable and would fall apart as we study later chapters. See the end of Chapter 1 lecture notes on the CRE Web site to see the tower of CRE fall if you have blocks with rounded edges. MULTIPLE REACTIONS MASS TRANSFER OPERATIONS NONISOTHERMAL OPERATION, MULTIPLE STEADY STATES MODELING REAL REACTORS, RTD, DISPERSION, SEGREGATION ANALYSIS OF RATE DATA, LABORATORY REACTORS, LEAST-SQUARES ANALYSIS DESIGN OF CHEMICAL REACTORS, PFR, CSTR, BATCH, SEMIBATCH, PACKED BEDS M O L E R A T E B A L A N C E S L A W S Figure P-1 S T O I C H I O M E T R Y E N E R G Y B A L A N C E S D I F F U S I O N C O N T A C T I N G Pillars of Chemical Reaction Engineering. Evaluate Combine Stoichiometry Rate Law Mole Balance Figure P-2 Building blocks. From these pillars and building blocks, we construct our CRE algorithm: Mole Balance + Rate Laws + Stoichiometry + Energy Balance + Combine → Solution With a few restrictions, the contents of this book can be studied in virtually any order after students have mastered the first six chapters. A flow diagram showing the possible paths is shown in Figure P-3. The reader will observe that although metric units are used primarily in this text (e.g., kmol/m3, J/mol), English units are also employed (e.g., lbm/ft3, Btu). This choice is intentional! We believe that whereas most papers published today use the metric system, a significant amount of reaction engineering data exists in the older literature in English units. Because engineers will be faced with extracting information and reaction rate data from older literature as well as from the current literature, they should be equally at ease with both English and metric units. xx Preface Ch. 1 Mole Balances Ch. 2 Conversion and Reactor Sizing Ch. 10 Catalysis and Catalytic Reactors Ch. 3 Rate Laws Ch. 4 Stoichiometry Ch. 9 Reaction Mechanisms, Pathways, Bioreactions, and Bioreactors Ch. 14 Mass Transfer Limitations in Reacting Systems Ch. 12 Steady-state Nonisothermal Reactor Design─ Flow Reactors with Heat Exchange Ch. 13 Unsteady-State Nonisothermal Reactor Design Figure P-3 C.2 Ch. 6 Isothermal Reactor Design: Moles and Molar Flow Rates Ch. 7 Collection and Analysis of Rate Data Ch. 8 Multiple Reactions Ch. 11 Nonisothermal Reactor Design─ The Steady-State Energy Balance and Adiabatic PFR Applications Ch. 15 Diffusion and Reaction Ch. 5 Isothermal Reactor Design: Conversion Ch. 16 Residence Time Distributions of Chemical Reactors Ch. 17 Predicting Conversion Directly from the Residence Time Distribution Ch. 18 Models for Nonideal Reactors Sequences for study using this text. What Is the Sequence of Topics in which This Book Can Be Used? Table P-1 shows examples of topics that can be converged in a graduate course and an undergraduate course. In a four-hour undergraduate course at the University of Michigan, approximately thirteen chapters are covered in the following order: Chapters 1 through 7 (Exam 1); Chapters 8, 11, and 12 (Exam 2); and Chapter 13 and parts of Chapters 9 and 10 (Exam 3). There are notes in the margins, which are meant to serve two purposes. First, they act as guides or commentary as one reads through the material. Second, they identify key equations and relationships that are used to solve CRE problems. D. What Are the Components of the CRE Web Site? The companion, interactive Web site material is an updated version of the CRE Web site and is a novel and unique part of this book. The main purposes of the Web site are to serve as an enrichment resource and as a “professional reference shelf.” The home page for the CRE Web site (http://www.umich.edu/~elements/5e/index.html) is shown in Figure P-4. For discussion of how to use the Web site and text interactively, see Appendix I. xxi Preface TABLE P-1 UNDERGRADUATE/GRADUATE COVERAGE Undergraduate Material/Course Mole Balances (Ch. 1) Smog in Los Angeles Basin (PRS Ch. 1) Reactor Staging (Ch. 2) Hippopotamus Stomach (PRS Ch. 2) Rate Laws (Ch. 3) Stoichiometry (Ch. 4) Reactors (Ch. 5): Batch, PFR, CSTR, PBR Reactors (Ch. 6): Semibatch, Membrane Data Analysis: Regression (Ch. 7) Multiple Reactions (Ch. 8) Bioreaction Engineering (Ch. 9) Adiabatic Reactor (Ch. 11) Steady-State Heat Effects (Ch. 12): PFR and CSTR with and without a Heat Exchanger Multiple Steady States Unsteady-State Heat Effects (Ch. 13) Reactor Safety Catalysis (Ch. 10) OF CRE Graduate Material/Course Short Review (Ch. 1–8, 11–12) Collision Theory (PRS Ch. 3) Transition State Theory (PRS Ch. 3) Molecular Dynamics (PRS Ch. 3) Aerosol Reactors (PRS Ch. 4) Multiple Reactions (Ch. 8): Fed Membrane Reactors Bioreactions and Reactors (Ch. 9, PRS 9.3–9.5) Polymerization (PRS Ch. 9) Co- and Countercurrent Heat Exchange (Ch. 12) Radial and Axial Gradients in a PFR COMSOL (Ch. 12) Reactor Stability and Safety (Ch. 12, 13, PRS 12.3) Runaway Reactions (PRS, Ch. 12) Catalyst Deactivation (Ch. 10) Residence Time Distribution (Ch. 16, 17) Models of Real Reactors (Ch. 18) Applications (PRS): Multiphase Reactors, CVD Reactors, Bioreactors Figure P-4 Screen shot of the book’s companion Web site (http://www.umich.edu/~elements/ 5e/index.html). The objectives of the Web site are fourfold: (1) To facilitate the learning of CRE by using the companion Web site to actively address the Felder/Solomon Inventory of Learning Styles 7 discussed in Web Appendix I (2) To provide additional technical material xxii Preface (3) To provide tutorial information and self-assessment exercises (4) To make the learning of CRE fun through the use of interactive games The following sections (D.1 through D.4) are listed at the end of most chapters and can be accessed from each chapter in the companion Web site.2 D.1 Expanded Material The expanded material consists of material that was removed from the printed text and moved to the Web site to reduce the size and weight of the physical textbook. Reducing the weight makes it easier for the students to carry the book with them at all times, such as while on the campus shuttle or while eating at the cafeteria or the student union. The expanded material includes derivations, examples, and novel applications of CRE principles. D.2 Learning Resources The Learning Resources give an overview of the material in each chapter and provide extra explanations, examples, and applications to reinforce the basic concepts of CRE; the Learning Resources are described in Appendix I. The CRE Web site includes the following additional resources: 1. Summary Notes and PowerPoint Slides The Summary Notes give an overview of each chapter and provide on-demand additional examples, derivations, and audio comments, as well as self-tests to assess each reader’s understanding of the material. Copies of the PowerPoint slides are available from this course taught at the University of Michigan as well as those from Professor Mary Kraft’s class at the University of Illinois. 2. What Entertainment Is on the Web Site? 2.A. YouTube Videos We have included links to humorous YouTube Videos made by students in Professor Alan Lane’s 2008 chemical reaction engineering class at the University of Alabama, as well as videos from the University of Michigan 2011 class. Specifically, check out “The Black Widow Murder Mystery” (Chapter 3), “CRF Reactor,” and “Diet Coke and Mentos” (Chapter 4); learn a new dance and song (“CSTR” to the tune of “YMCA”); hear a rap song (“Find Your Rhythm,” an “Ice Ice Baby” remix (Chapter 5)); and watch University of Michigan videos, including the ever-popular chemical engineering classic, “Reaction Engineering Gone Wrong.” 2.B. Interactive Computer Games (ICGs) Students have found the Interactive Computer Games to be both fun and extremely useful to review the important chapter concepts and then apply them to real problems in a unique and 2 http://www.ncsu.edu/felder-public/ILSdir/styles.htm xxiii Preface entertaining fashion. The following ICGs are available on the Web site: • • • • • • Quiz Show I (Ch. 1) Reactor Staging (Ch. 2) Quiz Show II (Ch. 4) Murder Mystery (Ch. 5) Tic Tac (Ch. 5) Ecology (Ch. 7) • • • • • The Great Race (Ch. 8) Enzyme Man (Ch. 9) Catalysis (Ch. 10) Heat Effects I (Ch. 12) Heat Effects II (Ch. 12) As you play these interactive games, you will be asked a number of questions related to the corresponding material in the textbook. The ICG keeps track of all the correct answers and at the end of the game displays a coded performance number that reflects how well you mastered the material in the text. Instructors have a manual to decode the performance number. 2.C. Web Modules The Web Modules are a number of examples that apply key CRE concepts to both standard and nonstandard reaction engineering problems (e.g., glow sticks, the use of wetlands to degrade toxic chemicals, and pharmacokinetics of death from a cobra bite). The Web Modules can be loaded directly from the CRE Web site (http://www.umich.edu/~elements/5e/web_mod/ index.html). 3. Solved Problems A number of solved problems are presented along with problem-solving heuristics. Problem-solving strategies and additional worked example problems are available in the Problem Solving section of the CRE Web site. D.3 Professional Reference Shelf This section of the CRE Web site contains 1. Material from the fifth edition of Elements of Chemical Reaction Engineering that is not included in the printed textbook. 2. Material that is important to the practicing engineer, such as details of the industrial reactor design for the oxidation of SO2 and design of spherical reactors and other material that is typically not included in the majority of chemical reaction engineering courses but is included here. E. Why Do We Assign Homework Problems? The working of homework problems facilitates a true understanding of CRE. After reading a chapter the student may feel they have an understanding of the material. However, when attempting a new or slightly different application of CRE in a homework problem, students sometimes need to go back and re-read xxiv Preface different parts of the chapter to get the level of understanding needed to eventually solve the homework problem. The end-of-chapter problems numbered “2” (e.g., P3-2A, P11-2B) ask questions about the example problems in that chapter. These example problems are a key resource. These number-2-level problems should be worked before tackling the more challenging homework problems in a given chapter. The subscript letter (A, B, C, or D) after each problem number denotes the difficulty of the problem (i.e., A = easy; D = difficult). F. What Is a Living Example Problem (LEP)? The example problems that use an Ordinary Differential Equation (ODE) solver (e.g., Polymath) are referred to as “Living Example Problems” or “LEPs” because students can load the Polymath program directly onto their own computers in order to study the problem. Students are encouraged to change parameter values and to “play with” the key variables and assumptions. Using the LEPs to explore the problem and asking “what if…?” questions provide students with the opportunity to practice critical and creative thinking skills. G. What Software Is Available to Solve the LEPs? Polymath. Polymath was developed by Professors Michael Cutlip and Mordechai Shacham. The Polymath software includes an ordinary differential equation (ODE) solver, a nonlinear equation solver, and nonlinear regression. As with previous editions of this book, Polymath is used to explore the example problems and to solve the homework problems. Polymath tutorials with screen shots are given on the CRE Web site Summary Notes in Chapter 1 and can also be accessed from the Home Page by going to Living Example Problems (LEPs) and then clicking on Polymath. Most chemical engineering departments in the United States have site licenses for Polymath. If your department does not have a site license and would like one, have your instructor e-mail the CACHE Corporation at cache@uts.cc.utexas.edu to learn how to obtain one. The LEPs need to be copied from the CRE Web site and pasted into the Polymath software. The Polymath software used in the examples in the text is available in most department computer labs in the United States. If you want to have Polymath on your personal laptop computer, you will need to purchase the program. An educational version of the software has been made available by Professors Cutlip and Shacham to students for $20 for a 4-month license, $30 for a 12-month license, or for $39 for a perpetual-use license. Polymath 6.1 is compatible with Windows XP, Windows Vista, Windows 7, and Windows 8. See the Polymath Web site (http://www.polymath-software.com) to obtain the laptop version. A special Polymath Web site (http://www.polymath-software.com/fogler) has been set up for this book by Polymath authors Professors Cutlip and Shacham. AspenTech. AspenTech is a process flow sheet simulator used in most senior chemical engineering design courses. It is now routinely introduced in earlier chemical engineering courses, such as thermodynamics, separations, and now in CRE. See the AspenTech Web site (http://www.aspentech.com) for more xxv Preface information. Like Polymath, AspenTech site licenses are available in most chemical engineering departments in the United States. Four AspenTech simulation examples specific to CRE are provided on the CRE Web site with step-by-step tutorial screen shots. As with Polymath programs, the input parameters in AspenTech can be varied to learn how they change the temperature and concentration profiles. Further details are given in Appendix D. COMSOL Multiphysics. The COMSOL Multiphysics software is a partial differential equation solver that is used with Chapters 12 and 18 to view both axial and radial temperature and concentration profiles. For users of this text, COMSOL has provided a special Web site that includes a step-by-step tutorial, along with examples. See http://www.comsol.com/ecre. Further details are given in Appendix D. Further details of these three software packages can be found in Appendix D. H. Are There Other Web Site Resources? FAQs. The Frequently Asked Questions (FAQs) page on the CRE Web site contains a compilation of questions collected over the years from undergraduate students taking reaction engineering. Visual Encyclopedia of Equipment (http://encyclopedia.che.engin.umich.edu). This section was developed by Dr. Susan Montgomery at the University of Michigan. Here, a wealth of photographs and descriptions of real and ideal reactors are given. Students with visual, active, sensing, and intuitive learning styles of the Felder/Solomon Index will particularly benefit from this section. Reactor Lab (http://www.ReactorLab.net). Developed by Professor Richard Herz at the University of California at San Diego, this interactive tool will allow students not only to test their comprehension of the CRE material, but also to explore different situations and combinations of reaction orders and types of reactions. CRE Web Site. The CRE Web site (http://www.umich.edu/~elements/5e/ index.html) will be used to update the text and identify typographical and other errors in the first and later printings of this text—available under Updates and FAQs on the CRE Web site home page. Additional material may also be added to include more solved problems, as well as additional Web Modules, which will also be found under Updates and FAQs. xxvi Preface I. How Can Critical Thinking and Creative Thinking Skills Be Enhanced? I.1. Enhance Critical Thinking Skills A third goal of this book is to enhance critical thinking skills. How does one enhance their critical thinking skills? Answer by learning how to ask the critical thinking questions in Table P-2 and carry out the actions in Table P-3. A number of homework problems have been included that are designed for this purpose. Socratic questioning is at the heart of critical thinking, and a number of homework problems draw from R. W. Paul’s six types of Socratic questions,3 shown in Table P-2 and given in the expanded material on the Web site. TABLE P-2 SIX TYPES OF SOCRATIC QUESTIONS USED IN CRITICAL THINKING (1) Questions for clarification: Why do you say that? How does this relate to our discussion? “Are you going to include diffusion in your mole balance equations?” (2) Questions that probe assumptions: What could we assume instead? How can you verify or disprove that assumption? “Why are you neglecting radial diffusion and including only axial diffusion?” (3) Questions that probe reasons and evidence: What would be an example? “Do you think that diffusion is responsible for the lower conversion?” (4) Questions about viewpoints and perspectives: What would be an alternative? “With all the bends in the pipe, from an industrial/practical perspective, do you think diffusion and dispersion will be large enough to affect the conversion?” (5) Questions that probe implications and consequences: What generalizations can you make? What are the consequences of that assumption? “How would the results be affected if you neglected diffusion?” (6) Questions about the question: What was the point of this question? Why do you think I asked this question? “Why do you think diffusion is important?” It is important to know these six types and be able to apply them when investigating a problem such as “Is there a chance the reactor will run away and explode?” or “Why did the reactor explode?” Critical thinking skills are like any skill, they must be practiced. Scheffer and Rubenfeld4,5 describe how to practice critical thinking skills using the activities, statements, and questions shown in Table P-3. The reader should try to practice using some or all of these actions every day, as well as asking the critical thinking questions in Table P-1 and on the Web site. 3 R. W. Paul, Critical Thinking (Santa Rosa, CA: Foundation for Critical Thinking, 1992). 4 Courtesy of B. K. Scheffer and M. G. Rubenfeld, “A Consensus Statement on Critical Thinking in Nursing,” Journal of Nursing Education, 39, 352–359 (2000). 5 Courtesy of B. K. Scheffer and M. G. Rubenfeld, “Critical Thinking: What Is It and How Do We Teach It?” Current Issues in Nursing (2001). xxvii Preface TABLE P-3 CRITICAL THINKING ACTIONS6 Analyzing: separating or breaking a whole into parts to discover their nature, function, and relationships “I studied it piece by piece.” “I sorted things out.” Applying Standards: judging according to established personal, professional, or social rules or criteria “I judged it according to….” Discriminating: recognizing differences and similarities among things or situations and distinguishing carefully as to category or rank “I rank ordered the various….” “I grouped things together.” Information Seeking: searching for evidence, facts, or knowledge by identifying relevant sources and gathering objective, subjective, historical, and current data from those sources “I knew I needed to look up/study….” “I kept searching for data.” Logical Reasoning: drawing inferences or conclusions that are supported in or justified by evidence “I deduced from the information that….” “My rationale for the conclusion was….” Predicting: envisioning a plan and its consequences “I envisioned the outcome would be….” “I was prepared for….” Transforming Knowledge: changing or converting the condition, nature, form, or function of concepts among contexts “I improved on the basics by….” “I wondered if that would fit the situation of ….” I have found that the best way to develop and practice critical thinking skills is to use Tables P-2 and P-3 to help students write a question on any assigned homework problem and then to explain why the question involves critical thinking.6 More information on critical thinking can be found on the CRE Web site in the section on Problem Solving (http://www.umich.edu/~elements/5e/probsolv/index.htm). I.2 Enhance Creative Thinking Skills The fourth goal of this book is to help enhance creative thinking skills. This goal is achieved by using a number of problems that are open-ended to various degrees. With these, students can practice their creative skills by exploring the example problems, as outlined at the beginning of the home problems of each chapter, and by making up and solving an original problem. Problem P5-1 in the text gives some guidelines for developing original problems. A number of techniques that can aid students in practicing and enhancing their creativity 6 R. W. Paul, Critical Thinking (Santa Rosa, CA: Foundation for Critical Thinking, 1992); B. K. Scheffer and M. G. Rubenfeld, “A Consensus Statement on Critical Thinking in Nursing,” Journal of Nursing Education, 39, 352–359 (2000). xxviii Preface can be found in Fogler, LeBlanc, and Rizzo7 (and its companion Web site), Strategies for Creative Problem Solving, Third Edition. The Web site for that book can be accessed from the CRE Web site home page. We use these techniques, such as Osborn’s checklist and de Bono’s lateral thinking (which involves considering other people’s views and responding to random stimulation) to answer add-on questions such as those in Table P-4. TABLE P-4 PRACTICING CREATIVE THINKING (1) Brainstorm ideas to ask another question or suggest another calculation that can be made for this homework problem. (2) Brainstorm ways you could work this homework problem incorrectly. (3) Brainstorm ways to make this problem easier or more difficult or more exciting. (4) Brainstorm a list of things you learned from working this homework problem and what you think the point of the problem is. (5) Brainstorm the reasons why your calculations overpredicted the conversion that was measured when the reactor was put on stream. Assume you made no numerical errors in your calculations. (6) “What if…” questions: The “What if…” questions are particularly effective when used with the Living Example Problems, where one varies the parameters to explore the problem and to carry out a sensitivity analysis. For example, what if someone suggested that you should double the catalyst particle diameter, what would you say? One of the major goals at the undergraduate level is to bring students to the point where they can solve complex reaction problems, such as multiple reactions with heat effects, and then ask “What if . . . ?” questions and look for optimum operating conditions and unsafe operating conditions. The solution to one problem exemplifies this goal: the Manufacture of Styrene (Chapter 12, Problem P12-26C). This problem is particularly interesting because two reactions are endothermic and one is exothermic. (1) Ethylbenzene → Styrene + Hydrogen: Endothermic (2) Ethylbenzene → Benzene + Ethylene: Endothermic (3) Ethylbenzene + Hydrogen → Toluene + Methane: Exothermic The student could get further practice in critical and creative thinking skills by adding any of the following exercises (x), (y), and (z) to any of the end-of-chapter homework problems. (x) How could you make this problem easier? More difficult? (y) Critique your answer by writing a critical thinking question. (z) Describe two ways you could work this problem incorrectly. To summarize, it is this author’s experience that both critical and creative thinking skills can be enhanced by using Tables P-2, P-3, and P-4 to extend any of the homework problems at the end of each chapter. 7 H. S. Fogler, S. E. LeBlanc, with B. Rizzo, Strategies for Creative Problem Solving, 3rd Ed. (Upper Saddle River, N.J.: Prentice Hall, 2014). xxix Preface J. What’s New in This Edition? J.1 Pedagogy This book maintains all the strengths of the fourth edition of Elements of Chemical Reaction Engineering by using algorithms that allow students to learn chemical reaction engineering through logic rather than memorization. It has the added strength of breaking down the material into smaller bites, as there are now 18 chapters to cover the same concepts as the 14 chapters in the fourth edition. At the same time, this edition provides new resources that allow students to go beyond solving equations in order to get an intuitive feel and understanding of how reactors behave under different situations. This understanding is achieved through more than 80 interactive simulations (LEPs) provided on the Web site. The Web site has been greatly expanded to address the Felder/Solomon Inventory of Different Learning Styles8 through interactive Summary Notes and new and updated Interactive Computer Games (ICGs). For example, as discussed in Appendix I the Global Learner can get an overview of the chapter material from the Summary Notes; the Sequential Learner can use all the hot buttons; and the active learner can interact with the ICGs and use the hot buttons in the Summary Notes. A new pedagogical concept is introduced in this text through expanded emphasis on the example problems. Here, the students simply load the Living Example Problems (LEPs) onto their computers and then explore the problems to obtain a deeper understanding of the implications and generalizations before working the homework problems for that chapter. This exploration helps students get an innate feel for reactor behavior and operation, as well as develop and practice their creative thinking skills. To develop critical thinking skills, instructors can assign one of the new homework problems on troubleshooting, as well as ask the students to expand homework problems by asking a related question that involves critical thinking using Tables P-2 and P-3. Creative thinking skills can be enhanced by exploring the example problems and asking “What if . . . ?” questions, by using one or more of the brainstorming exercises in Table P-4 to extend any of the homework problems, and by solving the open-ended problems. For example, in the case study on safety, students can use the LEP on the CRE Web site to carry out a postmortem analysis on the nitroaniline explosion in Example 13-2 to learn what would have happened if the cooling had failed for five minutes instead of ten minutes. To this end, a new feature in the text is an Analysis paragraph at the end of each example problem. Significant effort has been devoted to developing example and homework problems that foster critical and creative thinking. 8 http://www.ncsu.edu/felder-public/ILSdir/styles.htm xxx Preface J.2 Content The following areas have an increased emphasis in this new edition over previous CRE editions by including thorough example problems and homework problems: 1. Safety: Three industrial explosions are discussed and modeled. a. Ammonium Nitrate CSTR Explosion (Chapters 12 and 13) b. Nitroaniline Batch Reactor Runaway (Chapter 13) c. T2 Laboratories Batch Reactor Runaway (Chapter 13) d. Resources from SAChE and CCPS (Chapter 12) 2. Solar Energy: Three examples of solar energy conversion are discussed. a. Solar Chemical Reactions (Chapter 3) b. Solar Thermal Reactors (Chapter 8) c. Solar Catalytic Water Splitting (Chapter 10) 3. Alternative Fuels: a. Production of Algae for Biomass (Chapter 9) 4. AspenTech: An AspenTech tutorial for chemical reaction engineering and four example problems are provided on the CRE Web site. The example problems are a. Production of Ethylene from Ethane b. The Pyrolysis of Benzene c. Adiabatic Liquid Phase Isomerization of Normal Butane d. Adiabatic Production of Acetic Anhydride However, all intensive laws tend often to have exceptions. Very important concepts take orderly, responsible statements. Virtually all laws intrinsically are natural thoughts. General observations become laws under experimentation. K. How Do I Say Thank You? There are so many colleagues and students who contributed to this book that it would require another chapter to thank them all in an appropriate manner. I again acknowledge all my friends, students, and colleagues for their contributions to the fifth edition of Elements of Chemical Reaction Engineering. I would like to give special recognition as follows. First of all, I am indebted to Ame and Catherine Vennema, whose gift of an endowed chair greatly facilitated the completion of this project. My colleague Dr. Nihat Gürmen coauthored the original Web site during the writing of the fourth edition of this book. He has been a wonderful colleague to work with. I also would like to thank University of Michigan undergraduate students Arthur Shih, Maria Quigley, and Brendan Kirchner, who worked on earlier versions of the Web site. Their hard work and suggestions are greatly appreciated. Ben Griessmann was instrumental in making everything come together for the Web site for the fifth edition, including converting the fourth edition’s physical CD-ROM to online-only content for this new edition. Preface xxxi The many stimulating discussions on activation energy with Professor Michael Stamatakis in the Chemical Engineering Department at University College London are greatly appreciated. Michael B. Cutlip, coauthor of Polymath, not only gave suggestions and a critical reading of many sections, but also, most importantly, provided continuous support and encouragement throughout the course of this project. Professor Chau-Chyun Chen provided two AspenTech examples. Ed Fontes at COMSOL Mutiphysic not only provided encouragement, but also provided a COMSOL Web site containing a tutorial with CRE examples. Bernard Goodwin and Laura Lewin, editors at Prentice Hall, were extremely encouraging, helpful, and supportive throughout. Julie Nahil, full-service production manager at Prentice Hall, was fantastic throughout. She provided encouragement, attention to detail, and a great sense of humor, which were greatly appreciated. Indian Institute of Technology (IIT) students Darshan Shah, Anamika Singh, and Sravya Jangareddy, along with Fan Zhang, a University of Michigan student, and Keyvan Edrisi from Swedish Royal Institute of Technology, not only participated in the preparation of the solutions manual, but along with Maithri Venkat worked on the Web site to place many of the LEPs in Wolfram. Richa Motwani from IIT Guwahati, and Gunish Handa and Prafful Bhansali from IIT Bombay, did an extraordinary job in proofreading the galley proofs of the manuscript and making helpful suggestions for changes as well as putting the solution manual in final form. Thank you to students Krittin Binabdullah, Apirak Hanpan, and Thanaphoom Khrutphisit from Chulalongkorn University in Bangkok, along with Ph.D. candidate Cláudio Vilas Bôas Fávero for help in meeting the final deadline for this manuscript. I very much appreciated the patience of all my Ph.D. students during the period in which this book was written, Michael Senra, Zhenyu Huang, Michael Hoepfner, Nasim Haji Akbari Balou, Claudio Vilas Boas Favero, and Mark Sheng Zheng. Mark helped proofread a number of chapters of the page proofs; Professor Michael Senra class-tested the draft version of the fifth edition, and he and his students gave many valuable suggestions to this edition. There are others I would like to thank for a variety of different reasons: David Bogle, Lee Brown, Brice Carnahan, John Chen, Stu Churchill, Rane Curl, Jim Duderstadt, Tom Edgar, John Falconer, Rich Felder, Asterios Gavriilidis, Joe Goddard, Jay Jorgenson, Costas Kravaris, Steve LeBlanc, Joe Martin, Susan Montgomery, Max Peters, Phil Savage, Johannes Schwank, Mordechai Shacham, Klaus Timmerhaus, Ron West, Jim Wilkes, June Wispelwey, Max, Joe (aka “Jofo”), Sophia, Nicolas, and to the Starbucks staff at Plymouth Road Mall, where most of my final editing of this book was accomplished. Laura Bracken is very much a part of this book. I appreciate her excellent deciphering of equations and scribbles, her organization, her discovery of mistakes and inconsistencies, and her attention to detail in working with the galleys and proofs. Through all this was her ever-present wonderful disposition. Thanks, Radar!! Finally, to my wife Janet, love and thanks. Not only did she type the first edition of this book—on a Royal Select typewriter!—she also was a sounding board for so many things in this edition. She was always willing to help with xxxii Preface the wording and sentence structure. For example, I often asked her, “Is this the correct phrase or word to use here?” or “Should I mention Jofostan here?” Jan also helped me learn that creativity also involves knowing what to leave out. Without her enormous help and support the project would never have been possible. HSF Ann Arbor, Michigan November 2015 For updates and new and exciting applications, go to the Web site: http://www.umich.edu/~elements/5e/index.html For typographical errors, click on Updates & FAQ on the Home page to find http://www.umich.edu/~elements/5e/updates/index.html About the Author H. Scott Fogler is the Ame and Catherine Vennema professor of chemical engineering and the Arthur F. Thurnau professor at the University of Michigan in Ann Arbor, and was the 2009 National President of the American Institute of Chemical Engineers, a 50,000-member organization. He received his B.S. from the University of Illinois and his M.S. and Ph.D. from the University of Colorado. He is also the author of the Essentials of Chemical Reaction Engineering and co-author, with Steven LeBlanc and Benjamin Rizzo, of Strategies for Creative Problem Solving, Third Edition. Professor Fogler’s research interests include flow and reaction in porous media, wax and asphaltene deposition, asphaltene flocculation kinetics, gellation kinetics, colloidal phenomena, and catalyzed dissolution. He has been research advisor to more than forty-five Ph.D. students and has more than two hundred thirty-five refereed publications in these areas. Fogler has chaired ASEE’s Chemical Engineering Division, served as director of the American Institute of Chemical Engineers, and earned the Warren K. Lewis Award from AIChE for contributions to chemical engineering education. He also received the Chemical Manufacturers Association’s National Catalyst Award and the 2010 Malcom E. Pruitt Award from the Council for Chemical Research (CCR). He is the recipient of 11 named lectureships and is associate editor of Energy & Fuels. xxxiii This page intentionally left blank Mole Balances 1 The first step to knowledge is to know that we are ignorant. —Socrates (470–399 B.C.) How is a chemical engineer different from other engineers? The Wide Wild World of Chemical Reaction Engineering Chemical kinetics is the study of chemical reaction rates and reaction mechanisms. The study of chemical reaction engineering (CRE) combines the study of chemical kinetics with the reactors in which the reactions occur. Chemical kinetics and reactor design are at the heart of producing almost all industrial chemicals, such as the manufacture of phthalic anhydride shown in Figure 1-1. It is primarily a knowledge of chemical kinetics and reactor design that distinguishes the chemical engineer from other engineers. The selection of a reaction system that operates in the safest and most efficient manner can be the key to the economic success or failure of a chemical plant. For example, if a reaction system produces a large amount of undesirable product, subsequent purification and separation of the desired product could make the entire process economically unfeasible. 1 2 Mole Balances Figure 1-1 Chapter 1 Manufacture of phthalic anhydride. The chemical reaction engineering (CRE) principles learned here can also be applied in many areas, such as waste treatment, microelectronics, nanoparticles, and living systems, in addition to the more traditional areas of the manufacture of chemicals and pharmaceuticals. Some of the examples that illustrate the wide application of CRE principles in this book are shown in Figure 1-2. These examples include modeling smog in the Los Angeles (L.A.) basin (Chapter 1), the digestive system of a hippopotamus (Chapter 2 on the CRE Web site, www.umich.edu/~elements/5e/index.html), and molecular CRE (Chapter 3). Also shown are the manufacture of ethylene glycol (antifreeze), where three of the most common types of industrial reactors are used (Chapters 5 and 6), and the use of wetlands to degrade toxic chemicals (Chapter 7 on the CRE Web site). Other examples shown are the solid-liquid kinetics of acid-rock interactions to improve oil recovery (Chapter 7); pharmacokinetics of cobra bites (Chapter 8 Web Module); free-radical scavengers used in the design of motor oils (Chapter 9); enzyme kinetics (Chapter 9) and drug delivery pharmacokinetics (Chapter 9 on the CRE Web site); heat effects, runaway reactions, and plant safety (Chapters 11 through 13); and increasing the octane number of gasoline and the manufacture of computer chips (Chapter 10). 3 Mole Balances Section Hippo Digestion (Ch. 2) Smog (Ch. 1) H 2, C 2H 4 C2H6 1 C2H6 O2, C2H4, N2, C2H4O 5 C2H4 + Separator C2H4O H2O Transition State (dashed lines show transition state electron delocalization) C2H6 C 2H 4 O Ag 1 O CH2 CH2 2 2 Separator 4-Pentenal 2 C2H4 + H2 V = 81 ft3 X = 0.8 6 Vinyl Allyl Ether (arrows indicate electron movement) W = 45,440 lb X = 0.60 8 7 3 Molecular CRE (Ch. 3) H2O 0.9 wt % H2SO4 4 Air Waste water Absorber C2H4O(aq) V = 197 ft X = 0.80 C2H4O + H2O Cat. CH2 OH CH2 OH Chemical Plant for Ethylene Glycol (Ch. 5) Marsh Wetlands Remediation of Pollutants (Ch. 7 on the CRE Web site) Pulmonary OIL WELL ~~ ~~ ACID Oil Recovery (Ch. 7) Evaporation 200 million lb EG/year 9 3 Go Blue Motor Oil Heart Muscle Effective Lubricant Design Scavenging Free Radicals Lubricant Design (Ch. 9) Pharmacokinetics of Cobra Bites Multiple Reactions in a Batch (Body) Reactor Cobra Bites (Ch. 8 on the CRE Web site) Nitroanaline Plant Explosion Exothermic Reactions That Run Away Plant Safety (Ch.11 to Ch.13) Liver Intestines Pharmacokinetics (Ch. 9 on the CRE Web site) Etch and Then Remove Photoresist Microelectronic Fabrication Steps (Ch. 10) Figure 1-2 The wide world of CRE applications. 4 Mole Balances Chapter 1 Overview—Chapter 1. This chapter develops the first building block of chemical reaction engineering, mole balances, which will be used continually throughout the text. After completing this chapter, the reader will be able to: • • • Describe and define the rate of reaction Derive the general mole balance equation Apply the general mole balance equation to the four most common types of industrial reactors Before entering into discussions of the conditions that affect chemical reaction rate mechanisms and reactor design, it is necessary to account for the various chemical species entering and leaving a reaction system. This accounting process is achieved through overall mole balances on individual species in the reacting system. In this chapter, we develop a general mole balance that can be applied to any species (usually a chemical compound) entering, leaving, and/or remaining within the reaction system volume. After defining the rate of reaction, –rA, we show how the general balance equation may be used to develop a preliminary form of the design equations of the most common industrial reactors: • • • • Batch Reactor (BR) Continuous-Stirred Tank Reactor (CSTR) Plug-Flow Reactor (PFR) Packed-Bed Reactor (PBR) In developing these equations, the assumptions pertaining to the modeling of each type of reactor are delineated. Finally, a brief summary and series of short review questions are given at the end of the chapter. 1.1 The Rate of Reaction, –rA CH3 CH3 p-xylene The rate of reaction tells us how fast a number of moles of one chemical species are being consumed to form another chemical species. The term chemical species refers to any chemical component or element with a given identity. The identity of a chemical species is determined by the kind, number, and configuration of that species’ atoms. For example, the species para-xylene is made up of a fixed number of specific atoms in a definite molecular arrangement or configuration. The structure shown illustrates the kind, number, and configuration of atoms on a molecular level. Even though two chemical compounds have exactly the same kind and number of atoms of each element, they could still be different species because of different configurations. For example, 2-butene has four carbon atoms and eight hydrogen atoms; however, the atoms in this compound can form two different arrangements. H — C —C CH3 CH3 H cis-2-butene CH3 — C —C CH3 H H and trans-2-butene Section 1.1 5 The Rate of Reaction Reaction, –r –rA A When has a chemical reaction taken place? As a consequence of the different configurations, these two isomers display different chemical and physical properties. Therefore, we consider them as two different species, even though each has the same number of atoms of each element. We say that a chemical reaction has taken place when a detectable number of molecules of one or more species have lost their identity and assumed a new form by a change in the kind or number of atoms in the compound and/or by a change in structure or configuration of these atoms. In this classical approach to chemical change, it is assumed that the total mass is neither created nor destroyed when a chemical reaction occurs. The mass referred to is the total collective mass of all the different species in the system. However, when considering the individual species involved in a particular reaction, we do speak of the rate of disappearance of mass of a particular species. The rate of disappearance of a species, say species A, is the number of A molecules that lose their chemical identity per unit time per unit volume through the breaking and subsequent re-forming of chemical bonds during the course of the reaction. In order for a particular species to “appear” in the system, some prescribed fraction of another species must lose its chemical identity. There are three basic ways a species may lose its chemical identity: decomposition, combination, and isomerization. In decomposition, the molecule loses its identity by being broken down into smaller molecules, atoms, or atom fragments. For example, if benzene and propylene are formed from a cumene molecule, CH(CH3)2 A species can lose its identity by • Decomposition • Combination • Isomerization + C3 H6 cumene benzene propylene the cumene molecule has lost its identity (i.e., disappeared) by breaking its bonds to form these molecules. A second way that a molecule may lose its chemical identity is through combination with another molecule or atom. In the above reaction, the propylene molecule would lose its chemical identity if the reaction were carried out in the reverse direction, so that it combined with benzene to form cumene. The third way a species may lose its chemical identity is through isomerization, such as the reaction CH3 CH2— —C—CH2CH3 CH3 CH3C— — CHCH3 Here, although the molecule neither adds other molecules to itself nor breaks into smaller molecules, it still loses its identity through a change in configuration. 6 Mole Balances Chapter 1 To summarize this point, we say that a given number of molecules (i.e., moles) of a particular chemical species have reacted or disappeared when the molecules have lost their chemical identity. The rate at which a given chemical reaction proceeds can be expressed in several ways. To illustrate, consider the reaction of chlorobenzene and chloral to produce the banned insecticide DDT (dichlorodiphenyl-trichloroethane) in the presence of fuming sulfuric acid. CCl3CHO + 2C6H5Cl ⎯→ (C6H4Cl)2CHCCl3 + H2O Letting the symbol A represent chloral, B be chlorobenzene, C be DDT, and D be H2O, we obtain A + 2B ⎯→ C + D The numerical value of the rate of disappearance of reactant A, –rA, is a positive number. What is –rA? The rate of reaction, –rA, is the number of moles of A (e.g., chloral) reacting (disappearing) per unit time per unit volume (mol/dm3⋅s). Example 1–1 Chloral is being consumed at a rate of 10 moles per second per m3 when reacting with chlorobenzene to form DDT and water in the reaction described above. In symbol form, the reaction is written as A + 2B ⎯→ C + D Write the rates of disappearance and formation (i.e., generation) for each species in this reaction. Solution (a) Chloral[A]: The rate of reaction of chloral [A] (–rA) is given as 10 mol/m3·s Rate of disappearance of A = –rA = 10 mol/m3·s Rate of formation of A = rA = –10 mol/m3·s (b) Chlorobenzene[B]: For every mole of chloral that disappears, two moles of chlorobenzene [B] also disappear. Rate of disappearance of B = –rB = 20 mol/m3·s Rate of formation of B = rB = –20 mol/m3·s (c) DDT[C]: For every mole of chloral that disappears, one mole of DDT[C] appears. Rate of formation of C = rC = 10 mol/m3·s Rate of disappearance of C = –rC = –10 mol/m3·s (d) Water[D]: Same relationship to chloral as the relationship to DDT Rate of formation of D = rD = 10 mol/m3·s Rate of disappearance of D = –rD = –10 mol/m3·s Section 1.1 7 The Rate of Reaction Reaction, –r –rA A Analysis: The purpose of this example is to better understand the convention for the rate of reaction. The symbol rj is the rate of formation (generation) of species j. If species j is a reactant, the numerical value of rj will be a negative number. If species j is a product, then rj will be a positive number. The rate of reaction, –rA, is the rate of disappearance of reactant A and must be a positive number. A mnemonic relationship to help remember how to obtain relative rates of reaction of A to B, etc., is given by Equation (3-1) on page 71. A + 2B → C + D The convention –rA = 10 mol A/m3⋅s rA = –10 mol A/m3⋅s –rB = 20 mol B/m3⋅s rB = –20 mol B/m3⋅s rC = 10 mol C/m3⋅s What is –r A′ ? Definition of rj In Chapter 3, we will delineate the prescribed relationship between the rate of formation of one species, rj (e.g., DDT [C]), and the rate of disappearance of another species, – ri (e.g., chlorobenzene [B]), in a chemical reaction. Heterogeneous reactions involve more than one phase. In heterogeneous reaction systems, the rate of reaction is usually expressed in measures other than volume, such as reaction surface area or catalyst weight. For a gas-solid catalytic reaction, the gas molecules must interact with the solid catalyst surface for the reaction to take place, as described in Chapter 10. The dimensions of this heterogeneous reaction rate, –r A′ (prime), are the number of moles of A reacting per unit time per unit mass of catalyst (mol/s⋅g catalyst). Most of the introductory discussions on chemical reaction engineering in this book focus on homogeneous systems, in which case we simply say that rj is the rate of formation of species j per unit volume. It is the number of moles of species j generated per unit volume per unit time. We can say four things about the reaction rate rj. The reaction rate law for rj is • • • The rate law does not depend on the type of reactor used!! • What is –rA a function of? The rate of formation of species j (mole/time/volume) An algebraic equation Independent of the type of reactor (e.g., batch or continuous flow) in which the reaction is carried out Solely a function of the properties of the reacting materials and reaction conditions (e.g., species concentration, temperature, pressure, or type of catalyst, if any) at a point in the system However, because the properties and reaction conditions of the reacting materials may vary with position in a chemical reactor, rj can in turn be a function of position and can vary from point to point in the system. The chemical reaction rate law is essentially an algebraic equation involving concentration, not a differential equation. 1 For example, the algebraic form of the rate law for –rA for the reaction A ⎯→ products may be a linear function of concentration, –r A = kC A (1-1) or, as shown in Chapter 3, it may be some other algebraic function of concentration, such as 1 For further elaboration on this point, see Chem. Eng. Sci., 25, 337 (1970); B. L. Crynes and H. S. Fogler, eds., AIChE Modular Instruction Series E: Kinetics, 1, 1 (New York: AIChE, 1981); and R. L. Kabel, “Rates,” Chem. Eng. Commun., 9, 15 (1981). 8 Mole Balances Chapter 1 2 –r A = kC A (1-2) or k1C A –r A = ------------------1 + k2C A The rate law is an algebraic equation. The convention For a given reaction, the particular concentration dependence that the rate law 2 follows (i.e., –r A = kC A or –r A = kC A or …) must be determined from experimental observation. Equation (1-2) states that the rate of disappearance of A is equal to a rate constant k (which is a function of temperature) times the square of the concentration of A. As noted earlier, by convention, rA is the rate of formation of A; consequently, –rA is the rate of disappearance of A. Throughout this book, the phrase rate of generation means exactly the same as the phrase rate of formation, and these phrases are used interchangeably. 1.2 The General Mole Balance Equation To perform a mole balance on any system, the system boundaries must first be specified. The volume enclosed by these boundaries is referred to as the system volume. We shall perform a mole balance on species j in a system volume, where species j represents the particular chemical species of interest, such as water or NaOH (Figure 1-3). Figure 1-3 Mole balance on species j in a system volume, V. A mole balance on species j at any instant in time, t, yields the following equation: Rate of flow Rate of flow of j into – of j out of + the system the system (moles/time) (moles/time) Mole balance Rate of Rate of generation accumulation of j by chemical = of j within reaction within the system the system (moles/time) (moles/time) In – Out + Generation F j0 – Fj + Gj = Accumulation dN j --------= (1-3) dt Section 1.2 9 The General Mole Balance Equation In this equation, Nj represents the number of moles of species j in the system at time t. If all the system variables (e.g., temperature, catalytic activity, and concentration of the chemical species) are spatially uniform throughout the system volume, the rate of generation of species j, Gj , is just the product of the reaction volume, V, and the rate of formation of species j, rj . Gj = rj⋅V moles moles -------------- = ------------------------------ ⋅ volume time time ⋅ volume Now suppose that the rate of formation of species j for the reaction varies with position in the system volume. That is, it has a value r j1 at location 1, which is surrounded by a small volume, ΔV 1 , within which the rate is uniform; similarly, the reaction rate has a value r j2 at location 2 and an associated volume, ΔV 2 , and so on (Figure 1-4). Figure 1-4 Dividing up the system volume, V. The rate of generation, ΔG j1 , in terms of r j1 and subvolume ΔV 1 , is ΔG j1 = r j1 ΔV 1 Similar expressions can be written for ΔG j2 and the other system subvolumes, ΔV i . The total rate of generation within the system volume is the sum of all the rates of generation in each of the subvolumes. If the total system volume is divided into M subvolumes, the total rate of generation is M M i=1 i=1 G j = ∑ ΔG ji = ∑ r ji ΔV i 10 Mole Balances Chapter 1 By taking the appropriate limits (i.e., let M → ∞ and ΔV → 0 ) and making use of the definition of an integral, we can rewrite the foregoing equation in the form V Gj = ∫ r j dV From this equation, we see that rj will be an indirect function of position, since the properties of the reacting materials and reaction conditions (e.g., concentration, temperature) can have different values at different locations in the reactor volume. We now replace Gj in Equation (1-3) dN Fj0 – Fj + G j = ----------j dt (1-3) by its integral form to yield a form of the general mole balance equation for any chemical species j that is entering, leaving, reacting, and/or accumulating within any system volume V. This is a basic equation for chemical reaction engineering. F j0 – F j + ∫ V dN r j dV = ---------j dt (1-4) From this general mole balance equation, we can develop the design equations for the various types of industrial reactors: batch, semibatch, and continuous-flow. Upon evaluation of these equations, we can determine the time (batch) or reactor volume (continuous-flow) necessary to convert a specified amount of the reactants into products. 1.3 Batch Reactors (BRs) When is a batch reactor used? A batch reactor is used for small-scale operation, for testing new processes that have not been fully developed, for the manufacture of expensive products, and for processes that are difficult to convert to continuous operations. The reactor can be charged (i.e., filled) through the holes at the top (see Figure 1-5(a)). The batch reactor has the advantage of high conversions that can be obtained by leaving the reactant in the reactor for long periods of time, but it also has the disadvantages of high labor costs per batch, the variability of products from batch to batch, and the difficulty of large-scale production (see Industrial Reactor Photos in Professional Reference Shelf [PRS] on the CRE Web site, www.umich.edu/~elements/ 5e/index.html). Section 1.3 11 Batch Reactors (BRs) Figure 1-5(b) Batch reactor mixing patterns. Further descriptions and photos of the batch reactors can be found in both the Visual Encyclopedia of Equipment and in the Professional Reference Shelf on the CRE Web site. Figure 1-5(a) Simple batch homogeneous batch reactor (BR). [Excerpted by special permission from Chem. Eng., 63(10), 211 (Oct. 1956). Copyright 1956 by McGraw-Hill, Inc., New York, NY 10020.] A batch reactor has neither inflow nor outflow of reactants or products while the reaction is being carried out: Fj0 = Fj = 0. The resulting general mole balance on species j is dN ---------j = dt V ∫ r j dV If the reaction mixture is perfectly mixed (Figure 1-5(b)) so that there is no variation in the rate of reaction throughout the reactor volume, we can take rj out of the integral, integrate, and write the mole balance in the form Perfect mixing dN j --------- = r jV dt (1-5) Let’s consider the isomerization of species A in a batch reactor ⎯→ B A⎯ dNA dt = rAV Batch Reactor As the reaction proceeds, the number of moles of A decreases and the number of moles of B increases, as shown in Figure 1-6. 12 Mole Balances Chapter 1 NA0 NB1 NB NA NA1 0 t1 Figure 1-6 t 0 t1 t Mole-time trajectories. We might ask what time, t1, is necessary to reduce the initial number of moles from NA0 to a final desired number NA1. Applying Equation (1-5) to the isomerization dN A ---------- = r AV dt rearranging, dN dt = ---------Ar AV and integrating with limits that at t = 0, then NA = NA0, and at t = t1, then NA = NA1, we obtain t1 = ∫ N A0 N A1 dN A -----------–r A V (1-6) This equation is the integral form of the mole balance on a batch reactor. It gives the time, t1, necessary to reduce the number of moles from NA0 to NA1 and also to form NB1 moles of B. 1.4 Continuous-Flow Reactors Continuous-flow reactors are almost always operated at steady state. We will consider three types: the continuous-stirred tank reactor (CSTR), the plug-flow reactor (PFR), and the packed-bed reactor (PBR). Detailed physical descriptions of these reactors can be found in both the Professional Reference Shelf (PRS) for Chapter 1 and in the Visual Encyclopedia of Equipment, encyclopedia.che.engin.umich.edu, and on the CRE Web site. 1.4.1 Continuous-Stirred Tank Reactor (CSTR) What is a CSTR used for? A type of reactor commonly used in industrial processing is the stirred tank operated continuously (Figure 1-7). It is referred to as the continuous-stirred tank reactor (CSTR) or vat, or backmix reactor, and is primarily used for Section 1.4 13 Continuous-Flow Reactors Fj 0 Fj Figure 1-7(a) CSTR/batch reactor. (Photo courtesy of Pfaudler, Inc.) Figure 1-7(b) CSTR mixing patterns. Also see the Visual Encyclopedia of Equipment on the CRE Web site. liquid-phase reactions. It is normally operated at steady state and is assumed to be perfectly mixed; consequently, there is no time dependence or position dependence of the temperature, concentration, or reaction rate inside the CSTR. That is, every variable is the same at every point inside the reactor. Because the temperature and concentration are identical everywhere within the reaction vessel, they are the same at the exit point as they are elsewhere in the tank. Thus, the temperature and concentration in the exit stream are modeled as being the same as those inside the reactor. In systems where mixing is highly nonideal, the well-mixed model is inadequate, and we must resort to other modeling techniques, such as residence time distributions, to obtain meaningful results. This topic of nonideal mixing is discussed in Chapters 16, 17, and 18 on nonideal reactors. When the general mole balance equation F j0 – F j + ∫ V dN r j dV = ---------j dt (1-4) is applied to a CSTR operated at steady state (i.e., conditions do not change with time), dN j --------- = 0 dt 14 Mole Balances Chapter 1 in which there are no spatial variations in the rate of reaction (i.e., perfect mixing), The ideal CSTR is assumed to be perfectly mixed. V ∫ r j dV = V r j it takes the familiar form known as the design equation for a CSTR A FA0 F j0 – F j V = ---------------–r j FAO – FA – rA CSTR V= FA (1-7) The CSTR design equation gives the reactor volume V necessary to reduce the entering flow rate of species j from Fj0 to the exit flow rate Fj , when species j is disappearing at a rate of –rj. We note that the CSTR is modeled such that the conditions in the exit stream (e.g., concentration and temperature) are identical to those in the tank. The molar flow rate Fj is just the product of the concentration of species j and the volumetric flow rate v Fj = C j ⋅ v moles moles- volume -------------- = ----------------⋅ -----------------time volume time (1-8) Similarly, for the entrance molar flow rate we have Fj0 = Cj0 · v0. Consequently, we can substitute for Fj0 and Fj into Equation (1-7) to write a balance on species A as v0C A0 – vC A V = ---------------------------–r A (1-9) The ideal CSTR mole balance equation is an algebraic equation, not a differential equation. 1.4.2 Tubular Reactor When is a tubular reactor most often used? In addition to the CSTR and batch reactors, another type of reactor commonly used in industry is the tubular reactor. It consists of a cylindrical pipe and is normally operated at steady state, as is the CSTR. Tubular reactors are used most often for gas-phase reactions. A schematic and a photograph of industrial tubular reactors are shown in Figure 1-8. In the tubular reactor, the reactants are continually consumed as they flow down the length of the reactor. In modeling the tubular reactor, we assume that the concentration varies continuously in the axial direction through the reactor. Consequently, the reaction rate, which is a function of concentration for all but zero-order reactions, will also vary axially. For the purposes of the material presented here, we consider systems in which the flow field may be modeled by that of a plug-flow profile (e.g., uniform velocity as Section 1.4 15 Continuous-Flow Reactors Figure 1-8(a) Tubular reactor schematic. Longitudinal tubular reactor. [Excerpted by special permission from Chem. Eng., 63(10), 211 (Oct. 1956). Copyright 1956 by McGraw-Hill, Inc., New York, NY 10020.] Figure 1-8(b) Tubular reactor photo. Tubular reactor for production of Dimersol G. (Photo courtesy of Editions Techniq Institut français du pétrole.) in turbulent flow), as shown in Figure 1-9. That is, there is no radial variation in reaction rate, and the reactor is referred to as a plug-flow reactor (PFR). (The laminar-flow reactor is discussed in Chapters 16 through 18 on nonideal reactors.) Plug flow–no radial variations in velocity, concentration, temperature, or reaction rate Also see PRS and Visual Encyclopedia of Equipment. Figure 1-9 Plug-flow tubular reactor. The general mole balance equation is given by Equation (1-4) F j0 – F j + ∫ V dN r j dV = ---------j dt (1-4) The equation we will use to design PFRs at steady state can be developed in two ways: (1) directly from Equation (1-4) by differentiating with respect to volume V, and then rearranging the result or (2) from a mole balance on species j in a differential segment of the reactor volume ΔV . Let’s choose the second way to arrive at the differential form of the PFR mole balance. The differential volume, ΔV , shown in Figure 1-10, will be chosen sufficiently small such that there are no spatial variations in reaction rate within this volume. Thus the generation term, ΔG j , is ΔG j = ΔV ∫ r j dV = r j ΔV 16 Mole Balances Chapter 1 DV Fj0 Fj DGj V Figure 1-10 Fj V + DV Mole balance on species j in volume ΔV . Molar rate of Molar rate of Molar flow Molar flow Accumulation Generation rate of species j – rate of species j + = of species j of species j Out at ( V + ΔV ) In at V within ΔV within ΔV moles/time moles/time moles/time moles/time In Fj V – Out + Generation = Accumulation – Fj + V + ΔV r jΔV = 0 (1-10) Dividing by ΔV and rearranging –Fj Fj V + ΔV V ------------------------------- = rj ΔV the term in brackets resembles the definition of a derivative f (x + Δx) – f ( x ) df lim ------------------------------------- = ----Δx dx Δx → 0 Taking the limit as ΔV approaches zero, we obtain the differential form of steady state mole balance on a PFR dF j -------- = r j dV (1-11) We could have made the cylindrical reactor on which we carried out our mole balance an irregularly shaped reactor, such as the one shown in Figure 1-11 for reactant species A. However, we see that by applying Equation (1-10), the result would yield the same equation (i.e., Equation (1-11)). For species A, the mole balance is dF ---------A- = r A dV (1-12) Section 1.4 17 Continuous-Flow Reactors , Picasso’s reactor FA (V + ⌬V) FA (V) ⌬V Figure 1-11 Pablo Picasso’s reactor. Consequently, we see that Equation (1-11) applies equally well to our model of tubular reactors of variable and constant cross-sectional area, although it is doubtful that one would find a reactor of the shape shown in 1-11 unless it were designed by Pablo Picasso. The conclusion drawn from the application of the design equation to Picasso’s reactor is an important one: the degree of completion of a reaction achieved in an ideal plug-flow reactor (PFR) does not depend on its shape, only on its total volume. Again consider the isomerization A → B, this time in a PFR. As the reactants proceed down the reactor, A is consumed by chemical reaction and B is produced. Consequently, the molar flow rate FA decreases, while FB increases as the reactor volume V increases, as shown in Figure 1-12. FA0 V= F A0 ∫ FA dF A ---------–r A FA FB F B1 FA1 0 V1 0 V Figure 1-12 V1 V Profiles of molar flow rates in a PFR. We now ask what is the reactor volume V1 necessary to reduce the entering molar flow rate of A from FA0 to FA1. Rearranging Equation (1-12) in the form dF dV = ---------ArA and integrating with limits at V = 0, then FA = FA0, and at V = V1, then FA = FA1 V1 = ∫ FA1 F A0 dF A ---------- = rA ∫ FA0 F A1 dF ---------A–r A (1-13) 18 Mole Balances Chapter 1 V1 is the volume necessary to reduce the entering molar flow rate FA0 to some specified value FA1 and also the volume necessary to produce a molar flow rate of B of FB1. 1.4.3 Packed-Bed Reactor (PBR) The principal difference between reactor design calculations involving homogeneous reactions and those involving fluid-solid heterogeneous reactions is that for the latter, the reaction takes place on the surface of the catalyst (see Chapter 10). The greater the mass of a given catalyst, the greater the reactive surface area. Consequently, the reaction rate is based on mass of solid catalyst, W, rather than on reactor volume, V. For a fluid–solid heterogeneous system, the rate of reaction of a species A is defined as – r A′ = mol A reacted/(time x mass of catalyst) The mass of solid catalyst is used because the amount of catalyst is what is important to the rate of product formation. We note that by multiplying the mass ⎞ - , we heterogeneous reaction rate, – r A′ , by the bulk catalyst density, ρb ⎛⎝ ----------------volume⎠ can obtain the homogeneous reaction rate, –rA –rA = ρb (– r A′ ) mol-⎞ g ⎞ ⎛ -------mol ⎞ ⎛ --------⎛ -------------= ⎝ dm3 ⋅ s⎠ ⎝ dm3⎠ ⎝ g ⋅ s ⎠ The reactor volume that contains the catalyst is of secondary significance. Figure 1-13 shows a schematic of an industrial catalytic reactor with vertical tubes packed with solid catalyst. Figure 1-13 Longitudinal catalytic packed-bed reactor. [From Cropley, American Institute of Chemical Engineers, 86(2), 34 (1990). Reproduced with permission of the American Institute of Chemical Engineers, Copyright © 1990 AIChE. All rights reserved.] Section 1.4 19 Continuous-Flow Reactors PBR Mole Balance In the three idealized types of reactors just discussed (the perfectly mixed batch reactor, the plug-flow tubular reactor [PFR]), and the perfectly mixed continuous-stirred tank reactor [CSTR]), the design equations (i.e., mole balances) were developed based on reactor volume. The derivation of the design equation for a packed-bed catalytic reactor (PBR) will be carried out in a manner analogous to the development of the tubular design equation. To accomplish this derivation, we simply replace the volume coordinate in Equation (1-10) with the catalyst mass (i.e., weight) coordinate W (Figure 1-14). FA0 FA W FA(W + ΔW) FA(W) Figure 1-14 Packed-bed reactor schematic. As with the PFR, the PBR is assumed to have no radial gradients in concentration, temperature, or reaction rate. The generalized mole balance on species A over catalyst weight ΔW results in the equation In – FA W – Out + F A ( W + ΔW ) Generation = + r A′ ΔW Accumulation = 0 (1-14) The dimensions of the generation term in Equation (1-14) are moles A moles A ( r′A ) ΔW ≡ --------------------------------------------------------- ⋅ (mass of catalyst) ≡ ------------------(time)(mass of catalyst) time Use the differential form of design equation for catalyst decay and pressure drop. which are, as expected, the same dimensions of the molar flow rate FA . After dividing by ΔW and taking the limit as ΔW → 0, we arrive at the differential form of the mole balance for a packed-bed reactor dF ---------A- = r′A dW (1-15) When pressure drop through the reactor (see Section 5.5) and catalyst decay (see Section 10.7 on the CRE Web site Chapter 10) are neglected, the integral form of the packed-catalyst-bed design equation can be used to calculate the catalyst weight You can use the integral form only when there is no ΔP and no catalyst decay. FA W= ∫ F A0 dF A --------- = rA′ F A0 ∫ FA dF A --------–rA′ (1-16) W is the catalyst weight necessary to reduce the entering molar flow rate of species A, FA0, down to a flow rate FA. 20 Mole Balances Chapter 1 For some insight into things to come, consider the following example of how one can use the tubular reactor design in Equation (1-11). Example 1–2 How Large Is It? Consider the liquid phase cis – trans isomerization of 2–butene which we will write symbolically as A ⎯⎯→ B The reaction is first order in A (–rA = kCA) and is carried out in a tubular reactor in which the volumetric flow rate, v, is constant, i.e., v = v0 . CA0 v0 A→B V V=0 CA = 0.1CA0 v V1 1. Sketch the concentration profile. 2. Derive an equation relating the reactor volume to the entering and exiting concentrations of A, the rate constant k, and the volumetric flow rate v0 . 3. Determine the reactor volume, V1, necessary to reduce the exiting concentration to 10% of the entering concentration, i.e., CA = 0.1CA0, when the volumetric flow rate is 10 dm3/min (i.e., liters/min) and the specific reaction rate, –1 k, is 0.23 min . Solution 1. Sketch CA as a function of V. Species A is consumed as we move down the reactor, and as a result, both the molar flow rate of A and the concentration of A will decrease as we move. Because the volumetric flow rate is constant, v = v0 , one can use Equation (1-8) to obtain the concentration of A, CA = FA/ v0 , and then by comparison with the Figure 1-12 plot, obtain the concentration of A as a function of reactor volume, as shown in Figure E1-2.1. CA0 CA 0.1CA0 0 Figure E1-2.1 V1 V Concentration profile. Section 1.4 21 Continuous-Flow Reactors 2. Derive an equation relating V, v0, k, CA0, and CA. For a tubular reactor, the mole balance on species A (j = A) was shown to be given by Equation (1-11). Then for species A (j = A) dF ---------A- = r A dV Mole Balance: (1-12) For a first-order reaction, the rate law (discussed in Chapter 3) is Rate Law: Reactor sizing –r A = kC A (E1-2.1) Because the volumetric flow rate, v , is constant ( v = v0), as it is for most all liquid-phase reactions, dF A d (C Av ) d ( C A v0 ) dC ---------- = ------------------ = -------------------- = v0 ---------A- = r A dV dV dV dV (E1-2.2) Multiplying both sides of Equation (E1-2.2) by minus one and then substituting Equation (E1-2.1) yields Combine: v0 dC A - = –r A = kC A – --------------dV (E1-2.3) Separating the variables and rearranging gives v ⎛ dC ⎞ – ----0- ⎜ ---------A-⎟ = dV k ⎝ CA ⎠ Using the conditions at the entrance of the reactor that when V = 0, then CA = CA0 V v CA dC – ----0- ∫ ---------A- = ∫ dV k CA0 C A 0 (E1-2.4) Carrying out the integration of Equation (E1-2.4) gives v C A0 V = ----0- ln -------k CA Solve: (E1-2.5) We can also rearrange Equation (E1-2.5) to solve for the concentration of A as a function of reactor volume to obtain Concentration Profile C A= C A0exp ( –k V ⁄ v0) B A CA V 22 Mole Balances Chapter 1 1 3. Calculate V. We want to find the volume, V1, at which C A = ------ C A0 10 –1 3 for k = 0.23 min and v 0 = 10 dm /min. Evaluate: Substituting CA0 , CA , v 0 , and k in Equation (E1-2.5), we have C A0 10 dm3 10 dm3 /min- ---------------ln = ----------------- ln10 = 100 dm3 (i.e., 100 L; 0.1 m3 ) V = --------------------------–1 0.1C 0.23 A0 0.23 min Let’s calculate the volume to reduce the entering concentration to CA = 0.01 CA0. Again using Equation (E1-2.5) C A0 10 dm3 10 dm3 /min- ------------------= ----------------- ln 100 = 200 dm3 ln V = --------------------------–1 0.01C A0 0.23 0.23 min Note: We see that a larger reactor (200 dm3) is needed to reduce the exit concentration to a smaller fraction of the entering concentration (e.g., CA = 0.01 CA0). We see that a reactor volume of 0.1 m3 is necessary to convert 90% of species A entering into product B for the parameters given. Analysis: For this irreversible liquid-phase first order reaction (i.e., –rA = kCA) being carried out in a PFR, the concentration of the reactant decreases exponentially down the length (i.e., volume V) of the reactor. The more species A consumed and converted to product B, the larger must be the reactor volume V. The purpose of the example was to give a vision of the types of calculations we will be carrying out as we study chemical reaction engineering (CRE). 1.5 Industrial Reactors 2 Be sure to view the actual photographs of industrial reactors on the CRE Web site. There are also links to view reactors on different Web sites. The CRE Web site also includes a portion of the Visual Encyclopedia of Equipment, encyclopedia.che.engin.umich.edu, “Chemical Reactors” developed by Dr. Susan Montgomery and her students at the University of Michigan. Also see Professional Reference Shelf on the CRE Web site for “Reactors for Liquid-Phase and Gas-Phase Reactions,” along with photos of industrial reactors, and Expanded Material on the CRE Web site. In this chapter, and on the CRE Web site, we’ve introduced each of the major types of industrial reactors: batch, stirred tank, tubular, and fixed bed (packed bed). Many variations and modifications of these commercial reactors (e.g., semibatch, fluidized bed) are in current use; for further elaboration, refer to the detailed discussion of industrial reactors given by Walas. 3 2 Chem. Eng., 63(10), 211 (1956). See also AIChE Modular Instruction Series E, 5 (1984). 3 S. M. Walas, Reaction Kinetics for Chemical Engineers (New York: McGraw-Hill, 1959), Chapter 11. Chapter 1 23 Summary The CRE Web site describes industrial reactors, along with typical feed and operating conditions. In addition, two solved example problems for Chapter 1 can be found on the CRE Web site. Closure. The goal of this text is to weave the fundamentals of chemical reaction engineering into a structure or algorithm that is easy to use and apply to a variety of problems. We have just finished the first building block of this algorithm: mole balances. Mole Balance This algorithm and its corresponding building blocks will be developed and discussed in the following chapters: • • • • • • Mole Balance, Chapters 1 and 2 Rate Law, Chapter 3 Stoichiometry, Chapter 4 Combine, Chapter 5 Evaluate, Chapter 5 Energy Balance, Chapters 11 through 13 With this algorithm, one can approach and solve chemical reaction engineering problems through logic rather than memorization. SUMMARY Each chapter summary gives the key points of the chapter that need to be remembered and carried into succeeding chapters. 1. A mole balance on species j, which enters, leaves, reacts, and accumulates in a system volume V, is V F j0 – F j + ∫ r j dV = dN ---------j dt (S1-1) If, and only if, the contents of the reactor are well mixed will the mole balance (Equation (S1-1)) on species A give dN FA0 – FA + r AV = ----------A dt (S1-2) 2. The kinetic rate law for rj is • The rate of formation of species j per unit volume (e.g., mol/s⋅dm3) • Solely a function of the properties of reacting materials and reaction conditions (e.g., concentration [activities], temperature, pressure, catalyst, or solvent [if any]) and does not depend on reactor type • ...
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Chemical reactors in chemical processes 1

Chemical reactors in chemical processes
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Chemical reactors in chemical processes 2
For a chemical reaction to take place, there must be system information of a vessel or a container
where the reaction takes place. These vessels or tanks may commonly be known as reactors.
They are, in most cases, enclosed to prevent the contamination of the reactants. The reactors are
in simple terms, the vessels where the chemical reaction can take place (Penry, 1987). The
reactors can vary in sizes from those with few cubic centimeters to those with thousands of tons
depending on the volume of the reactants they have been designed to handle. Although several
factors can determine the design of chemical reactors, there are mainly two critical factors
including thermodynamic and kinetics of the chemical reaction being carried out
During the chemical reaction, heat can be emitted or absorbed. The measure of the energy in the
form of heat is called enthalpy. The chemical reaction can be endothermic or exothermic denoted
by a positive and negative sign in their enthalpy changes. When the enthalpy decreases with the
increase in the entropy, the reaction is said to be thermodynamically favorable. On the other
hand, chemical reaction to occur, there are many processes which may occur chemically with the
example being oxidation, hydrogenation, reduction, hydrolysis, halogenation just to numerate
few (Bailey, 1974). All these chemical processes occur at a different rate depending on how
faster or slow the particles will collide with one another to change from reactants to products. To
study all those chemical processes with their rate of reaction is what is referred to as chemical
kinetics. In conjunction to petroleum industry where crude oil is refined to its final products like
paraffin, petrol, diesel, alkanes, and alkenes, all those processes of converting the crude oil into
end products entail chemical reactions. The industry not only involved in the refining but also it
can be involved in transporting their ends products to the market
With that introduction in place, there can be many varieties of reactors used in these industries
ranging from nuclear reactors, moving bed reactors, chemical reactors among many others

Chemical reactors in chemical processes 3
though the discussion will majorly deal with chemical reactor which can be used in the
petroleum and gas industries
Chemical reactors
The chemical reactors can broadly be categoriz...


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