elements chenzicn 1 reaction - iut.ac.irivut.iut.ac.ir/content/129/chap1.pdf · in the physical and...

Elements of Chenzicn 1

Reaction Engineering

PRENTICE HALL PTR INTERNATIONAL SERIES IN THE PHYSICAL AND CHEMICAL ENGINEERING SCIENCES

NEAL R. AMUNDSON, SERIES EDITOR, University of Houston

ANDREAS AcRI\~OS, Stanford University JOHN DAALER, University of Minnesota H. SCOTT F%LER, University of Michigan

THOMAS J. H A N R A ~ , University of Illinois JOHN M. PRAUSNITZ. University of California

L. E. SCR~I~EN, University ofMinnewta

BALZHISER, SAMUEI-S, AND EWASSEN Chemical Engineering Thermodynamics BEQUETTE Process Controi: Modeling, Design, and Simulation BEQUETTE Process Dynamics BIEGLER, GROSSIWA?~~. AND WESTERBERG Systematic Methods of Chemical Process

Design RRosILow A N 5 JOSEPH Techniques of Model-based Control CQNSTAN~NXDES AND MOSTOUFI Numerical Methods for Chemical Engineers

with MATLAB Applications CROWL AND LOUVAR Chemical Process Safety: Fundamentals with Applications,

2nd edition CUTLIP AND SHACHAM Problem Solving in Chemical Engineering with Numerical

Methods DENY Process Fluid Mechanics ELLIOT AND LIRA Introductory Chemical Engineering Thermody narnics F~GLER Elements of Chemical Reaction Engineering, 4th edition HEMMELBLGU AND RIGGS Basic Principles and CalcuIations in Chemical

Engineering, 7th edition H J N E ~ AND MADDOX Mass Transfer: Fundamentals and Applications PRAUSNITZ, LICHTENTHALER, AND DE AZEVEDO Molecular Thermodynamics

of Fluid-Phase Equilibria, 3rd edition PRENTICE EIectrochernical Engineering Principles SHULER ASD KARGI Bioprocess Engineering, 2nd edition STEPHANOPOUU~S Chemical Process Control TESTER AND MODELL Thermodynamics and Its Applications, 3rd edition TURTON, BAILIE, WHITING. AND SHAEIWITZ Analysis, Synthesis, and Design

of Chemical Processes, 2nd edition WII.KES Fluid Mechanics for Chemical Engineers, 2nd edition

Elements of Chemical

Reaction Engineering

Fourth Edition

H. SCOTT FOGLER

Arne and Catherine Vennema Professor of Chemical Engineering

The University of Michigan, Ann Arbor

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Library of Congress Ca~aloging-in- Prtblication Data

FogIer. H. Scott. Elements of chemical reaction engineering I A. Scott Fogler4th ed.

p. cm. Includes bibliographical references and index. ISBN 23-13-047394-4 (alk. paper)

1. Chemical reactors. I. Title.

Copyright O 2006 Pearson Education, Inc.

All rights reserved. Printed in the United States of Amwics This publication is pmtected by copyright. and permission must k obtained from the publisher prior to any prohibited reproductiod, storage in a retrieval system. or transmission in any form or by any means, electronic, mechanical. photocopying, recording, or likewise. For information r~gard~ng permissions. write to:

Pearson Education, Inc. Rights and Contracts Department One Lake Street Upper Saddle River. NJ 07458

, ISBN 0-13-047394-4

Text printed in the United States on recycled paper at Courier in Westford. Massachusetts. First printing. August 1005

Dedicated fo rke tIrerno9 of

Professors

Gi useppe Parravano Joseph J. Martin Donald L, Katz

of the University of Michigan whose standards and lifelong achievements

serve to inspire us

PREFACE

1 .I The Rate of Reaction, 4 1.2 The Genera1 Mole Balance Equation 8 1.3 Batch Reactors 10 J .4 Continuous-Row Reactors 12

1.4. J Continuous-Stirwd Tank Reactor, 12 1.4.2 Tubular R~aclor 14 1.4.3 Packed-Bed Reacror 17

1.5 Industrial Reactors 21 Summary 25 CD-ROM Material 26 Questions and Problems 29 Supplementary Reading 35

Contents

2 CONVERSION AND REACTOR SIZING

2.1 Definition of Conversion 38 2.2 Batch Reactor Design Equations 38 2.3 Design Equations for Flow Reactors 48

2.3.1 CSTR (alsr~ known as a Backmix Reactor or Vat) 43

2.2.2 Tubular Flow R~QCIOP {PFR) 44 2.3.3 Packed-Bed Rearm 45

2.4 Applications of the Design Equations for Continuous-Flow Reactors 45

Contents

2.5 Reactors in Series 54 2.5.1 CSTRs in Series 5 5 2.5.2 PFRs i n Series 58 2.5.3 Cr~tnbinarions of CSTRs and PFRs in Series 60 2.5.4 Comparing rhe CSTR alid PFR Reuctor filrrmes ~mli

Reactor Seqitencitlg 64 2.6 Some Further Definitions 66

2.6.1 Spacelime 66 2.6.2 Space Vekocic 68 Summary 69 CD-ROM Materials 71 Questions and Problems 72 Supplementary Reading 77

PART 1 Rate Laws 80 3.1 Basic Definitions 80

3.1. I Relative Rates of Reaction 81 3.2 The Reaction Order and the Rate Law 82

3.2.1 Power Lnw Models nnd Elementnry Rate Ln~w 82 3.2.2 Nonelemenrav Rate Lnws 85 3-2.3 Reversible Reacrions 88

3.3 The Reaction Rate Constant 91 3.4 Present Status of Our Approach to Reactor Sizing

and Design 98 PART 2 Stoichiometry 99 3.5 Batch Systems 100

3.5. i Equations fur Batch Concentrations 102 3.5.2 Constant- Volcf me Bn fch Reaction Systems 103

3.6 Flaw Systems 106 3.6.1 Eqttations for Concenfrarions in Flow

Systems 107 3.6.2 Liquid-Phase Concmtmtions 108 3.6.3 Change in the Total Number of Moles with R~enction in

rhe Gas Phase 108 Summary 124 CD-ROM Material 126 Questions and Problems 131 Supplementary Reading 141

4 ISOTHERMAL REACTOR DESIGN

PART I Mole Balances in Terms of Conversion 144 4.1 Design Structure for Isorherma! Reactors 144 3.1 Scale-Up of Liquid-Phase Batch Reactor Data to the Design

of a CSTR 148 4.2.1 Batch Opemfion 148

4.3 Design of Contincous Stirred Tank Reactors (CSTRs) 156 4.3, J A Single CSTR 157 4.3.2 CSTRs in Series 158 4.3.3 CSTRs in PrrroIIeI 160 4.3.4 4 Second-Order Reoctiott irt n CSTR 162

4.4 Tubular Reactors 168 4.5 Pressure Drop in Reactors 175

4.5.1 Presslire Drop a~rd the Rate Law 175 4.5.2 Flow Throirgh a Packed Bed 177 4.5.3 Pressure Drop in Pipes 182 4.5.4 Analvfica! Solution for Reaction with

Presstire Drop 185 4.5.5 Spherical Packed-Bed Reactors 196

4.6 Synthesizing the Design of a Chemical Plant 196

PART 2 Mole Balances Written i n Terms of Concentration and Molar Flow Rate 198

4.7 Mole Balances on CSTRs, PFRs, PBRs. and Batch Reactors 200 4.7.1 Liquid Phase 300 4.7.2 Gas Pi~nse 200

4.8 Microreactors 201 4.9 Membrane Reactors 207 4.10 Unsteady-State Operation of Stirred Reactors 215

4.10.1 Startup of a CSTR 216 4.10.2 Sernibcrrct? Reactors 217 4.10.3 Writing the Semibatch Reactnr Equa [ions in Terms

qf Cancentrntions 21 9 4.10.4 Wriring the Semibnrch Reacror Equations in Terns

of Conversion 223 4.1 1 The Practical Side 226

Summary 227 ODE Solver Algorithm 230 CD-ROM Material 231 Questions and Problems 234 Some Thoughts on Critiquing What You read 249 Journal Critique Problems 249 Supplementary Reading 253

5 COLLECTION AND ANALYSIS OF RATE DATA

Contents

253

5.1 The Algorithm for Data Analysis 254 5.2 Batch Reactor Data 256

5.2.1 Differential Method ofAna!ysis 257 5.2.2 bztegral Mefhod 267 5.2.3 Nonlinear Regression 271

5.3 Method of Initial Rates 277 5.4 Method of Half-Lives 280 5.5 Differential Reactors 281 5.6 Experimental Planning 289 5.7 Evaluation of Laboratory Reactors 289

5.7. i Criteria 289 5.7.2 Types of Reacrors 290 57.3 Su171may qf Reactor Ratings 290 Summary 291 CD-ROM Material 293 Questions and Proble~ns 294 Journal Critique Problems 302 Supplementary Reading 303

Definitions 305 6. I . I Types ?f Renctio~u 305 Parallel Reactions 310 6.2.1 Moxilni: b g rhe Desired Product,for Oize

Renciant 311 6.2.2 Reartor Selection n11d Opemfing Corrdiflirfons 31 7 Maximizing the Desired Product in Series Reactions 320 Algorithm for Solution of Complex Reactions 327 6.4.1 Mole Boln~lces 327 6.4.2 Npt Rures ?f Reaction 329 6.4.3 Stnrclrinmerp: Co~~r~oerr~rurio~~s 334 Multiple Reactions in a PFWPBR 335 Multiple Reactions in a CSTR 343 Membrane Reactors to Improve Selectivity in Multiple Reactions 347 Complex Reactions of Ammonia Oxidation 351 Sorting Jt All Out 356 The Fun Part 356 Summary 357 CD-ROM Material 359 Questions and Problems 361 Journal Critique Problems 372 Supplementary Reading 375

Contents

7 R EA CTION MECHANISMS, PA TH WA YS, BIOREACTZONS, AND BIOREACTORS

7.1 Active Intermediates and Nonelementary Rate Laws 377 7.1.1 Pseudo-Sready-State Hypothesis (PSSH) 379 7.1.2 Searching for a Mechanism 383 7.1.3 Chain Reactions 386 7.1.4 Reaction Pathways 391

7.2 Enzymatic Reaction Fundamentals 394 7.2.1 Et~z~rneSuhsrrate Complex 395 7.2.2 Mechanisms 397 7.2.3 Micheelis-MentenEquation 399 7.2.4 Batch Reactor Calcularions for Enzyme

Reactions 404 7 .3 lnhibi tion of Enzyme Reactions 404

7.3.1 Comperirive Inhibirion 410 7.3.2 Uncomperitive Inhibition 412 7 3.3 Noncclmpetitive Inhibition (Mixed Inlzibi~ion) 41 4 7.3.4 Substrate Inhibition 416 7.3.5 Multiple Enzyme and Substrare Systen~s 417

7.4 Bioreactors 418 7.4.1 CelI Growth 422 7.4.2 Rare Laws 423 7.4.3 Stoichiometiy 426 7.4.4 Mass Balances 431. 7.4.5 Chemosrafs 434 7.4.6 Design Equations 435 7.4.7 Wash-out 436 7.4.8 0.rqgen-Limited Growth 438 7.4.9 Scale-up 439

7.5 Physiologically Based Pharmacokinetic (PBPK) Models 439 Summary 447 CD-ROM Material 449 Questions and Problems 454 Journal Critique Problems 468 Supplementary Reading 469

8 STEA DY-STA TE NONISOTHERMA L REACTOR DESIGN

8.1 Rationale 472 8.2 The Energy Balance 473

8.2.1 First Law of Tl~erpnodynamics 473 8.2.2 E\3aluarit~g the Work Tern 474 8.2.3 O\?en,ien4 of Ellel-gy BaIa~~ces 476 8.2.4 Dissecti?t,q the Stead!-Srate Molar Flow Riir~s

to Okrain !he Hear of Reaction 479 8.2.5 Dissec ring h e Enrhalpies 48 1 8.2.6 Relating AHR,IT 1, AHOR, (TR 1- and AC, 483

Adiabatic Operation 486 8.3.1 Adiabafic Energy B~lance 486 8.3.2 Adiabatic Tirbular Reactor 487 Steady-State Tubular Reactor with Heat Exchange 495 8.4.1 Deriving the Dtergv Balance for a PFR 495 8.4.2 Balance on tire CovInnt Heat Transfer Fl~rirl 499 Equilibrium Conversion 511 8.5.1 Adiabatic Temperature and Equilibrilam

Conversion 5 t 2 8.5.2 Optimum Feed Temperature 520 CSTR with Heat Effects 522 8.6.1 Hear Added to the Reactot; 6 522 Multiple Steady States 533 8.7.1 Heat-Removed Term, R(TI 534 8.7.2 Heat of Generation, G(T) 534 8.7.3 Ignition- Extinction Curve 536 8.7.4 Runaway Reactions in a CSTR 540 Nonisotherrnal Multiple Chemical Reactions 543 8.8.1 Energy Balance for Mulriple Reactiorls in

Plrcg-Flow Rencdors 544 8.8.2 Energy Balance for Multiple Reactions

in CSTR 548 Radial and Axial Variations in a Tubular Reactor 551 The Practical Side 561 Summary 563 CD-ROM Material 566 Questions and Problems 568 Journal Critique Problems 589 Supplementary Reading 589

9 UiVSTEAD Y-STR TE NOAXSOTHERMA L REA CTOR DESIGN

4.1 The Unsteady-State Energy Balance 591 9.2 Energy Balance on Batch Reactors 594

9.2.1 Adinbatic Operation of a Batch Reactor 594 9.2.2 Batch Reactor with Intermpred Isothermal

Operation 599 9.2.3 Reactor Safety: The Use ofthe ARSST ro Find AH,,, E

and to Size Pressure Relief Valves 605 9.3 Semibatch Reactors with a Heat Exchanger 614 9.4 Unsteady Operation of a CSTR 619

9.4.1 Startup 619 9.4.2 Falling Off the Steady State 623

9.5 Nonisothermal Multiple Reactions 625 9.6 Unsteady Operation of Plug-Flow Reactors 628

xiii

Summary 629 CD-ROM Material 630 Questions and Problems 633 Supplementary Reading 614

10.1 CataIysts 645 10.1.1 D.cjniri017s 646 10.1.2 Cnrctl.;st Properties 648 10. I . 3 CdassiJication of Crrml?r.sts 652

0 Steps in n Catalytic Reaction 455 10.2.1 Step I Overview: Difllsion fram t i le Btdk to the

External Transport 658 10.2.2 Step 2 Overview: Int~rnal Diffiision 660 10.2.3 Adsorption Isotherms 661 10.2.4 Surfnce Reection 646 10.2.5 Desorption 668 10.2.6 The Rate-Litniring Step 669

10.3 Synthesizing a Rate Law, Mechanism, and Me-Limiting Step 671 10.3. I Is the ddsorprion of Curn.me Rate-Limi~ing ? 674 10.3.2 Is the Scttface Reaction Rate-Limiting? 677 10.3.3 IS the De.wrprion of Benzene Rate- Limiting? 678 10.3.4 Summary of the C~rmene Decomposition 680 10.3.5 Reforming C~~taly ,~rs 681 10.3.6 Rate Lnws Derived from the Pseudo-Steady

S r ~ f e Hypothesis 684 10.3.7 Terrtperuture Dependence of the Rare Caw 687

10.4 Heterogeneous Data Analysis for Reactor Design 688 10.4.1 Dediicing a Rare h w f m r n the

E~perirnentul Dara 689 10.4.2 Finding n Mechanism Consistent with

Experimental Observations 691 10.4.3 Evnluation of the Rare Law Pammeters 692 10.4.4 Reactor Design 694

10.5 Reaction Engineering in Microelectronic Fabrication 698 IQ5.I Overview 698 10.5.2 Etching 700 10.5.3 Chemical Vapor Deposition 701

10.6 Model Discrimination 704 10.7 Catalyst Deactivation 707

10.7.1 Types of Catalyst Deactivation 709 10.7.2 Tenaperatlire-Erne Trajectories 721 10.7.3 Moving-Bed Reactors 722 10.7.4 sf might-TElmugh Tmnsporr Reactors (STTR) 728

Contents

Summary 733 ODE Solver Algorithm 736 CD-ROM Material 736 Questions and Problems 738 Journal Critique Problems 753 Supplementq Reading 755

11 EXTERNAL DIFFUSION EFFECTS ON HETEROGENEOUS REACTIOM 757

1 1.1 Diffusion Fundamentals 758 1 I . 1. I Defilitions 758 11.1.2 Molar Flux 759 11.1.3 Fick'sFirsrLaw 760

1 1.2 Binary Diffusion 761 J 1.2.1 Eiralrtatirag The Molar F l u 761 11.2.2 Boundary Corlditions 765 11.2.3 Modeling Difusion Withorcr Reaction 766 1 I . 2.4 Temperature art$ Pres.ture Depend~nce

of DAB 770 I J.2.S Modeling Difision with Chemical Reaction 771

11.3 External Resistance to Mass Transfer 771 1 1.3.1 TIne Mass Transfer Coeficient 771 11.3.2 Mass Transfer Coeficient 773 11.3.3 Correlario~~s for fhe Mass Transfer Co~firienr 774 11.3.4 Mass Transfer to a Single Particle 776 11.3.5 Mnss Transfer-Limited Reactions in

Packed Beds 780 11.3.6 Robert the Worrier 783

1 1.4 What If. . . ? (Parameter Sensitivity) 788 1 1.5 The Shrinking Core Model 792

1 1 -5.1 Cara!\.sr Regenerarion 793 11.5.2 Phanl~acokinetics-DissoIufinn qf Monodispers~d

SoIid Particles 798 Summary 800 CD-ROM Material 801 Questions and ProbIems 802 Supplementary Reading 810

12 DIFFUSION AND REACTION

12.1 Diffusion and Reaction in Spherical Catalyst Pellets 814 12.1. I Efccti~,e D~fif~rrsil'iry 814 12.1.2 Deri~nfion qf rhe D$fer@nrial Equatinn D~scribing

Diffusinrr artd R~ucrion 81 6 12.1.3 Wririrrg the Equarion in Dimensionless f i m n 819

Contents

12.1.4 Solution to the Dlferential Equation for a First-Order Reaction 822

12.2 Internal Effectiveness Factor 827 12.3 Falsified Kinetics 833 1 2,4 Overall Effectiveness Factor 835 12.5 Estimation of Diffusion- and Reaction-Limited

Regimes 838 12.5.1 wei.Ti-Prsate Crilerion for I~tterna! Diffusion 839 12.5.2 Mearx' Crirerion for External Difusion 841

12.6 Mass Transfer and Reaction in a Packed Bed 842 12.7 Determination of Limiting Siruations from

Reaction Data 848 12.8 Multiphase Reactors 849

12.8.1 SlurnRenctors 850 12.8.2 Trickk Bed Reactors 850

12.9 Fluidized Bed Reactors 851 1 2.10 Chemical Vapor Depwi tion (CVD) 851

Summary 853 CD-ROM Material 852 Questions and Problems 855 Journal Article Problems 863 Journal Cririque Problems 863 Supplementary Reading 865

13 DTSTRIBUTZOM OF RESIDENCE TIMES FOR CHEMICAL REACTORS 867

1 3.1 General CIlaracterislics 868

PART I Characterislics and Diagnostics 868 13. I . J Reside~rce-Tirne Didribulion (RTD) Functior? 870

13.2 Measurement of the RTD 871 13.2.1 Puhe Irrput E~prrit~ient 871 13.2.2 Step Tracer E.rl?erinzenr 876

13.3 Characteristics of the RTD 878 13.3. S Jniegr-a1 R~lnrir~tlshil~s 838 13.3.2 Mearr Residenre Tinw 879 13.3.3 Orher Mor~lerrts of the RTD 881 13,3.4 Not.rlla/ted RTD F~o~crion. E(O) 884 13.3.5 I~~re~nol-Age Di.~~rihuriorr, I(a) 885

13.3 RTD in Ideal Reactors 885 13.4.1 RTDs i ~ t Batch and Plug-Flow RPCICIOKT 885 13.4.2 Single-CSTR RTD 887 13.4.3 Lcrrlri~lc~r FICJM* Reocror ( L F R ) 888

13.5 Diagnoqtics and Troubleshnoting 891 13.5.1 Gniewl Cnn~rlrenrs 891 12.5.2 Si171plc Diog\~os~ic.~ o ~ d Tt~~~lhlesho(~fi t7g U S ~ I F R the

KTD for kIenl Rericrors 892 1.q.5.3 PFR/CSTRSeriesRTD 897

PART 2 Predicting Conversion and Exit Concentration 902 1 3.6 Reactor Modeling Using the RTD 902 3 3.7 Zero-Parameter Models 904

13.7. I Segr~gnrion M o d ~ l 904 13.7.2 bfLL~hum Mi.redne.7~ Mode/ 91 5 13.7.3 Comparirzg Segregarion and M o x i r n ~ / ~ ~ l iWi.xedness

Predictions 922 I 3.8 Using Software Packages 923

13.8 1 Heot Eflect.? 927 1 3.9 RTD and Multiple Reactions 927

13.9.1 Segregafion Model 927 13.9.2 Ma~itnurn bIixedizess 928 Summary 933 CD-ROM Material 934 Questions and Probkms 936 Supplementary Reading 944

14.1 Some Guidelines 946 14.1. I One- Pornmeter Models 947 14.1.2 Two- Parnmer~r Models 948

14.2 Tanks-in-Series (T-1-51 Model 948 14.3 Dispersion Model 955 14.4 Flow. Reaction, and Dispersion 957

14.4.1 Balance Eqlrnrinns 957 14.4.2 Bouadcd~ Conditions 958 14.4.3 Finding D, and the Pecler Number 962 14.4.4 Dispersion in a Ethular Reactor with

Laminar Florv 962 14.4.5 Correlations for D, 964 14.4.6 Experimental Determination of D, 966 14.4.7 Slopp?: Tracer Inputs 970

14.5 Tanks-in-Series Model Versus Dispersion Model 974 14.6 Numerical Solutions to Flows with Dispersion

and Reaction 975 14.7 TWO-Parameter Models-Modeling Real Reactors with

Combinations of Ideal Reactors 979 14- 7.1 Real CSTR Modeled Using Bypassing and

Deadspace 979 14.7.2 Real CSTR Modeled as Two CSTRJ with

Interchange 985 14.8 Use of Software Packages to Determine the

Model Parameters 988 14.9 Other Models of Nonideal Reactors Using CSTRs

and PFRs 990 14.10 AppIications to Pharmacokinetic Modeling 991

Contents xvii

Appendix A

Appendix B

Appendix C

Appendix D

Appendix E

Appendix F

Appendix G

Appendix H

Appendix I

Appendix J

Summary 993 CD-ROM ~Vnterial 994 Questions and Problems 996 Supplementary Reading 1005

NUMERICAL ECHIVIQ UES

IDEAL GAS CONSTANT AND COWERSION FA CTORS

THERMODYNAMIC R ELA TIOIVSHIPS Z W L VING THE EQUILIBRIUM CONSTANT

MEASUREMENT OF SLOPES ON SEMILOG PAPER

SOFTWARE PACKAGES

NOMENCLATURE

RATE LAW DATA

OPEN-ENDED PROBLEMS

HOW TO USE THE CD-ROM

USE OF COMPUTATIONAL CHEMISTRY SOFTWARE PA CKAG ES

INDEX

ABOUT THE CD-ROM

Preface

The man who has ceased to learn ought not to be allowed to wander around Ioose in these dangerous days.

M. M. Coady

A. The Audience

This book and interactive CD-ROM 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 and CD-ROM Prufessionaf R@ference Shelf (PRS) material to be covered and the type and degree of difficulty of problems assigned.

B. The Goals

B.4. To Develop a Fundamental Understanding of Reaction Engineering

The first goal of this book is to enable the reader to develop a clear understanding of the fundamentals of chemical reaction engineering (CRE). This goal will be 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 will git~e practice at using the algorithms. The conventional home problems at the end 05 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

XX Preface.

calculator and those that require a personal computer and a numerical snftware package such as Polymath, MATLAB, or FEMLAB.

To give a reference point as to the level of nnderst:inding of CRE required in the profession. a number of reaction engineering problems from the California Board of Registration for Civil and Professional Engineers-Chern- ical Engineering Examinations (PECEE) are included in the text.] Typically. these problems should each require nppmximately 30 minutes to solve.

Finally, the CD-ROM should greatly facilitate learning the fundamentals of CRE because i t includes summary notes of the chapters, added examples, expanded derivations, and self test>. A complete description of these knrnirrg resorrrces is given in the 'The Integration of the Text and the CD-ROM" section in this Preface.

8.2. To Develop Critical Thinking Skills

A second goal is to enhance critical thinking skills. A number of home problems have been included that are designed for this purpose. Smratic question- ing is at the h e m of critical thinking, and a number of homework problems draw from R. W. Paul's six types of Sacsatic questions2 shown in Table P-I.

1 4 1) Q~resticmsjbfirr ck~r$uatiun: Why do you fay that7 Hoic does th~q relake to our d i ~ u s s ~ o n ?

1 *'Are you going to include diffusion In )our mole balance equations?"

(2) Quasrionr rhnr pmhc nssrrmpnons: What could we assume instead? How can you verify or disprove that assumption?

"Why are you neglecting rddial diffusion and including only ~ ~ l a l diffu~ionT'

( ( 3 ) Q~trsrions rhar p m k reasons and evirleucu: What would be an example?

( "Do you think that diffusion is respnnsibIe For the Iower cnnvers~onr'

((4) Quesrions about viewpoinrs and perspctrl-e~: Whar would be an alternative?

"With all the bends in the pipe. from an industriallpracticaI <randpoint, do you think diffusion and dispersion will be large enough to affect the cunvcr~ion'~'

( 5 ) Qttesrton~ rhut p d r ~mplrcations lrnd rt~nseqiteiice.~: What peneralizattons can you make'! What are the consequences of that assumption?

1 "How would our resulrs be affected if wo neglected diffusion?"

(6) Q~deftinns uhnut the querrion: What was the point of thrc question9 Why do you think I asked th~s question?

"Why do you thlnk diffusion is important'?'

I The permission for use of these problems, which. incidentally, may be obtained from the Documents Section, California R o d of Regiaration For Civil and Professional Engineers-Chemical Engineering, 1004 6th Street, Sacramento, CA 95814, is grate- fully acknowtedged. (Note: These problems have been copynghred by the California Board of Registration and may not be reproduced without its permission).

2 R. W. Paul, Crirical Thinking (Santa Rosa, Calif.: Fbundation for Critical Thinking, 1992).

Sec. B The Goais X X ~

Scheffes and RubenfeId1'l expand nn the practice of cntical thinking skill, discussed by R. W. Paul by using the activities. statements, and question5 shown in Table P-2.

T ~ L E P-? C R ~ I C A L THIYKINC SKLI 5' ' Analyzing: separating or brcaking a whole into pnrts to discover their nature. function, and

atio ion ship^ "I ~tudied ir piece hy pirce." "'1 sorted thing% out." .

Applying Standards: judging nccatding to e\tablishcd pr.wnal. profc~rional. or rocid rules or criteria "I judged it according to. ..."

Discriminating: recognizing differences and similariries among things or situarirln\ and &tin- guishing sarcfully as to catepr): or n n k "I rank ordered rhe various. ..." "I grouped things together."

Enformation Seeking: searching for evidence. facts, or knowledge by idel~tifyinp relevant sources and gathering objectibe, subjcctire, historical, rind current data from those wurces " 1 knew I needed ro look uplstudy ...:' "I kept .searching for dntn."

Loplical Reasoning: drawing inferenits or conclusions that are supported in or ]ustitied by evidence "I deduced from the information that ... Y "My rdtionale fur the conclusion was.. .."

Predicting: envisioning a plan and its convqurnces "I envisioned the outcome would he.. ..+' "1 wns prepared for.. . ."

Transforming Knowledge: cb:~nging or convening the condition. nature. form. or fi~nction of concepts among calltexts "I improved on the bilbics by.. .:' "I wondered i f that would fit the siuuation or ...."

I have found the best way so develop and practice critical thinking akills is to use Tdbles P-I and P-2 to help students write a question on any assigtled homework problem and then to explain why the question involves critical thinking.

More information on critical thinking can be found on the CD-ROM in the section on ProbI~rn Solving.

8.3. To Develop Creative Thinking Skills

The third goal of this book is to help deveIop creative thinking skills. This goal will be achieved by using a number of probiems that are open-ended to various degrees. Here the students can practice their creative skills by exploring the example problems as outlined at the beginning of the home problems of each

Courtesy of B. K. Scheffer and M. G. Rubenfeld. "A Consensus Statement on Critical Thinking in Nursing." Jorrntnl 01Niirsing Ehcntion. 39, 352-9 (20001. Courtesy of B. K. Scbeffer and M. 6. Rubenfeld, "Critical Thinking: What b It and How Do We Teach It?" Ctirrenr Issltes in A11rK~it~g (200 1).

xxii Prefs-ce

chapter and by making up and solving an original problem. Problem P4-I gives some guidelines for developing original problems. A number of techniques that can aid the sntdents in practicing and enhancing their creativity can be found in FogIer and CeBlanc5 and in the Thoughts on Problem Solving section on the CD-ROM and on the web site wwu:engifiumich.edu/-ere. We will 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-3.

(1 ! Brainstorm ideas to a~k another question or suggest another calculation that can be made for this homework problem

(2) Bralnstorin ways you could work this homework problem incorrectly.

( 3 ) Brainslorn ways to maie this problem easier or more difficult or more exciting.

(4) Brainstorm a lisl of thlngs you learned from working this homework problem and what ynu thtnk the p i n t of the problem is.

(5) Brainstorm the reafons why your calculations overpredicted the conversion that was mea- rured when the reactor was put on slrearn. Assume you made no numerical errors on your calculat~ons.

(6) "What if...'' questions: The "What i f .. " questions are particularly effective when used with the Linng Emntple Problems where one varies the parameters to explore the problem and to carry out a sensitivtty analysis. For example, w11rrt i f s o r n ~ o n ~ suggcrrtd rltor vou shmrld douhle th t caraly.~! pnrriclc d~umtrerel; wltat w odd you s o j '

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 rac- tions with heat effects, and then ask "What if ...*' questions and look for optimum operating conditions. One problem whose solution exemplifies this goal is the Manufacture of Styrene, Problem P8-26. This problem is panicuIarly interesting because twa reactions are endothermic and one is exothermic.

{I ) Ethylbenzene 4 Styrene + Hydrogen: Endofhennic (2) Ethylbenzene 4 Benzene + Ethylene: Endothem~ic (3) Ethylbenzene + Hydrngen + Toluene + Methane: Exo~hermic

To summarize Section B. i t is the author's experience that both critical and cse- ative thinking skills can be enhanced by using Tables P-I, P-2. and P-3 to extend any of the homework problems at the end of every chapter.

C. The Structure

The strategy behind the presentation of materia1 is to build continually on a few basic ideas in chemical reaction engineering to solve a wide variety of problems. These ideas. referred to as rhe PiIlacr ~ ; l f Clze~nical R~action Engineeri~lg.

.-

W. S. Fogler and S. E. LeBlanc. S~rnregiesfi)r Creative Pmblem Sol\.ing (Upper Sad- dre River. N.J.: Prentice HaH, 1995).

Sec. C The St:ucfvre xxiii

are the foundation on which different applications rest. The pillars holding up the application of chemical reaction engineering are shown in Figure P- I .

Figure P-I Pillars of Chemical Reaction Engineering.

From there Pillars we construct our CRE algorithm:

Mole balance + Rate laws + Stoichiornetry + Energy balance + Combine

With a few restrictions, the contents of this book can be studied in virtually any order after students have mastered the first four chapters. A flow dia- gram showing the possible paths can be seen in Figure P-2.

] CH ~ - C $ V E ~ S I W T & N O I FIEllCTOR SUING

CH 3 - RATE LAWS AND

CW 7 -1 810RELCTQNS tAEc;:sM5 H STAT? +iE&T H cEki~15 H Re+ 1 EEFECTS CATALYTIC D t S T R I 0 ~ I O N

BIOREACTQPS fll htf OR5 yrl VMSTEACY TH-, EYEQNuL NONIDEAL

STATE HEAT DIFFUSbOV REKTORS EFFECTS EFFFC'S

MULTLPLE R E K ~ l O Y S WITH HEP

F F C C r - C

IN POROUS

" -- u Figure P-2 Sequences for \tidying the text

xxiv Preface

Table P-4 shows examples of topics that ran be covered i n n graduate course and an undergradua~e course, In a four-hour undergraduate course at [he University of Michigan. approximately eight chapters are covered in the following order: Chapter? 1, 2, 3. 4, and 6; Sections 5.1-5.3; and Chapters 7. 8, and parts of Chapter 10.

TAHLE P-4. U\IDERGRADCATHGRADL'ATE COVERAGE OF CRE

Uttdp.ryrndrmr~ .Marerinl/C~llrce Gmdul~re ,Wo!eri~~i/Co~t r w

Shon Re\-iew ICh. 1-4 . 6. 8) Mole Balances (Ch. I ) Collision Theory (PRS Ch. 3) Smog in LOF Angeles Basin IPRS Ch. 1) Tran~ition State Theory (PRS Ch. 3) Reactor Staging (Ch. 2)

Molecular Dynarn~cs IPRS Ch 3) Hippopotamus Stomach (PRS Ch. 2)

Aero~ol Rwctors CPRS Ch 4) Ralr L w s (Ch. 3) Multiple Reactrons (Ch 6): Stoichiometry ICh.31 Fed Membrane Rracton Rc~ctors (Cb. 4):

Batch. PFR. CSTR. PER. Binreaction% and reactors (Ch. 7. PRS 7.3. 7.4.

Sernibntch. Membrane 7.51

Dara Analysis: Regresalon (Ch 5 1 Pnlymeri7~tion (PRS Ch 7) Co- and Counter Current Heat

Multiple Reactions (Ch. 6) Blood Congulatron (SN Ch. 6) Exchange (Ch. 8)

Bioreaction Engineering (Ch. 7) Radial and Axial Gndientx In a PFR

Steady-State Heat Effects (Ch. 8): FEMLAB ICh. 8 )

PFR and CSTR with and without Reactor Stabil~ty and Safety tCh. 8. 9. PRS 9.3)

a Hear Exchanger Runaway Reactions IPRS Ch. 8 )

Multiple Steady Stetea Catalyst Deactivation [Ch. 10)

Unsteady-State Heat Effects (Ch. 9) Revdmce Time Distributron [Ch 13 1 Models of Real Reactorc [Ch. 14)

Reactor Safety Catnlysit (Ch. 10) Applications (FRS): Mult~phase Reactors.

CVD Reactors. Bioesctors

The reader will observe that although metric units are used primarily in this text (e.g., kmoVm3, Jlmol), a variety of other units are also employed (e.g.. Ib/ft3). This 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 the current literature, they should be equally at ease with both English and metric units.

The notes in the margins are meant to serve two purposes. First, they act as guides or as commentary as one reads through the material. Second, they identify key equations and relationships that are used to solve chemical reaction engineering problems.

D. The Components of the CD-ROM

The interactive CD-ROM is a novel and unique part of this book. The main purposes of the CD-ROM are to serve as an enrichment resource and as a professional reference shelf. The home page for the CD-ROM and the CRE web site (www.engin.umich.edu/-cre/fogler&gl4nen) is shown in Figure P-3.

Sec. D The Components of the CD-ROM XXV

Figure P-3 Screen shot of the home page of the CD-ROM.

The objectives of the CD-ROM are threefold: ( I) to facilitate the learning of CRE by interactive1 y addressing the Feld~r/Solornon Inventory nf Learning Sglesh i n the Summary Notes. the additional examples, the Interactive Com- puting Modules (ICMs), and the Web ,Modules; (2) to provide additional technical material for the professional reference sheIf; (3) to provide other tutorial information, examples, derivations, and self tests, such as additionai thoughts or1 probtem solving, the use of computational software in chemical reaction engineering, and representative course structures. The following components are listed at the end of masr chapters and can be accessed from each chapter in the CD-ROM.

Learning Resources The Learning Resources gwe an overview of the material in each chapter and provide: extm explanations. examples, and applications to reinforce the basic concepts of chemical reaction engineering. The learning resources on the CD-Rob1 include the following: I . Srrrnmap Notes

The Summary Notes give an overview of each chapter and provide on-demand additional examples, derivations, and audio comments as well as

Summary Notes self tests to assess each reader's understanding of the material. 2. Web Mod;rles

The Web Modules, which apply key concepts to both standard and nonstaod- ard reaction engineering problems (e.g., the use of wetlands to degrade toxic chemicals, cobra bites), can be loaded directly from the CD-ROM.

xxvi Preface

0 Computer Modules

Additional Web Modules are expected to be added to the web site (wwn~.engin.un~ich,edu/-rre) over the next several years.

3. Interactiiu Conlpufer Modules (ICMs) Students have found the Interactive Computer M d u l e s to be hoth f u n and extremely useful to review the important chaprer concepts and then apply them to real problems in a unique and entertain~ng fashion. In addition to updating all the ICMs from the last edition, two new modules. The Gwaf Rauc (Ch. 6) and Enzyme Mon (Ch. 7)- have been added. The complete set of 1 1 modules foll~ws:

- Quiz Show I (Ch. 1 ) The Great Race (Ch. 61 Reactor Staging (Ch. 7) Enzyme Man {Ch. 7) Quiz Show H (Ch. 3) Heat Effect\ 1 (Ch. 8) Murder Mystep (Ch. 4) Heat Effects 11 tCh. 8 ) TIC Tac (Ch. 4 ) CataIyslr (Ch. JO)

* Ecoloey (Ch 5 )

4 . Solved Probler~rs A number of solved problems are presented along with problem-solving heu- ristics. Problem-solving strategies and additional worked example problems

solved Problems are available in the Pt~lbletn Sollirlg section of the CD-ROM. Living Example Problems A copy of Polymath is provided on the CD-ROM for the students zo use to salve

Q the homework problems. The example problems that use en ODE salver (e g.. CL Polymath) are referred to a< "living example problems" because students can W A

:-2 ~5 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

L ~ v ~ n g Example Problem with" rhe key variables and assumptions. Using rhk Living Example Problems to explore the problem and asking "What if.. ." questions pro\ ide students with the opportunity to practice crttical and crea~ive thlnking skills. Professional Reference Shelf This section of the CD-ROM contains I. Matertal ahat was in previous editions .(e.g., polymer~zation, rlurry reactnn.

and chern~cal vapor disporition reactors) that har been omitted from the pr~nled version of the fourth edition

2. New topics such as coll~siori artd rrarrsition smte rltenr?: aerosol rroc!orq, Refzrence Shelf DFT. and r-urlmvo,v mcriorts, which are commonly found In graduate courses

3. Material that is important ro the practicing engineer, such as derails of the industrial reactor design for the oxidation of SO? and design of spllericnl reactors and other ~na~esial that is typically not included in rhe majority of chemical reaction engineering courses

= Software Toolbox on the CD-ROM P f ~ / ~ f n n f ! l . The Polymath software rncludes an ordinary drfferen~ial equation (ODE) ~olver, a nonlinear equation \nlver, and nonl~near regression. Ac with prejious ed~tions. Polymath is inchded with t h ~ s edition to explore the example problems and to sol\.e the home problems. A special Polymath web sile ( r r ~ ~ ~ r ~ : ~ ~ ~ I ~ n t ~ t I ~ - ~ n f i ~ ~ o ~ ' ~ . c o ~ ~ ~ f n ~ I ~ r har hcen sel up for this book by Polymath authar\ Ct~tlip and Shacham Thi5 weh site provides inlrrnarion an how to ohlain an updated \t.rsion of Polymath at a di<cou~~t.

Sec. E The Integration of the Ted and the CD-ROM X X V ~ ~

FEMLAB. The FEMLAB software inciudes a partial differential equation solver. This edition includes a specially prepared version of FEMLAB on itc; own CD-ROM. With m L A B the students can view both axial and radial temperature and concentration profiles. Five of rhe FEMLAB modules are:

* Isothermal operation Adiabatic operation Heat effects with constant heat exchange fluid temperature Heat effects with variabre heat exchanger temperature Dispersion with Reaction using the Danckwerts Boundary Conditions (two cases)

As with the Polymath programs, the input parameters can be varied to learn how they change the temperature and concentration profiles.

Instructions are included on how to use not only the software packages ei Poly- math. MATLAR, and FEMLAB. but also on how to apply ASPEN PLUS to solve CRE problems. Tutorials with detailed screen shots are provided for Poly- math and E M L A B .

= Other CD-ROM Resources FAQs. The Frequently Asked Questions (FAQs) are a compilation of questions collected over the years from undergraduate students taking reaction engineering.

Pmblem Sol~+ing. In this section, both critical thinking and creative thinking are discussed along with what TO do if you get "stuck" on a problem.

Viswul E~rc~clopedia r!f Equip~r~ctnr. This section was developed by Dr. S u w ~ Montgomery at the Universify of Michigan. Here a wealth of photographs and descriptions of real and idea1 reactors are given. The students with visual. actibe, sensing, and intuitive leamlng styles of the FelderlSolomon Index will pafticu- Early benefit from this section.

Rearlor Lob. Developed by Professor Richard Hem at the University of Califor- nia at San Dlego, this interactive tml will allow students not only to test their comprehension of CRE material but also to explore different situations and combinations of reaction orders and types of reactions.

p.c G r c ~ n L~~llgiileering Home Pml?lfnrs. Green engineering problems for virtually every chapter have k e n developed by Professor Roben Hesketh at Rowan Unl- xersity and Professor Martin Abraham at the University of Toledo and can be

1 i found at ~'~'~:mwa~l.~du/gwcnrngrr~cer!ng. These problems also accompany the hook by David Allen and David Shonnard. Green Chernicul Enginwring: En1.i- mnt~terrmlly Cart.sciatrs Design of CI~emicnl Process~s (Prentice HaII. 2002).

Green engineering

E. The Integration of the Text and the CD-ROM

E.I. The University Student

There are a number of ways one can use the CD-ROM in conjunction with the text. The CD-ROM provides enrichment resources for the reader in the form of interactive tutorials. Pathways on how to use the materials to learn chemical

xxviii Preface

reaction engineering are shown in Figure P-4. The keys to [the CRE learning Aow sheets include primary resources and enrichment resources:

= Primary resources CD = Enrichment resources 0 In developing a fundamental understanding of the material, students may

wish to use only the primary resources without using the CD-ROM line., using only the boxes shown in Figure P-4), or they may use a few or all of the interactive tutorials in the CD-ROM (i.e.. the circles 4hown in Figure P-4). How- ever, to practice the skills that enhance critical and creative thinking, students are strongly encourr~ged to use the Lii-irlg E . ~ t t n p i ~ Pivhletns and vary the model patarnetem to ask and answer "What if. .." questions.

Summary Notes

lnteracflve Computer

t Start

Homework = Text ~ectures Problems

4

Modules Problems

Figure P-4 A Student Path~ay 20 Integrate the Class. the Text. and'rhe CD.

Note that even though the author recommends studying the Living Example Problems before working home problems. they may be bypassed, as is the case with all the enrichment resources. if time is short. However. class testing of the enrichment resources reveals that they not only greatly aid i n learning the material but also serve to motivate students through the noveI use of CRE principles.

E.2. For the Practicing Engineer

A figure similar to Figure P-4 for the practicing engineer Is given in the CD-ROM Appendix.

Sec G Vhat's New X X ~ X

E The Web

The web site (wu,\r:er?gh.~~tnicI~.e~Ett/-cre) will be used to updare the text and the CD-ROM. I t will ~den t i fy typographical and other errors In the hrst and later printings of the fourth edition of the text. In the near future. additional matenal will be added to include more solved probIem5 as well as additiana1 Web Modules.

G. What's New

Pedagogy. The fourth edition of this book maintains all the strengths of the previous additions by using algorithms that allow students to Iearn chemical reaction engineering throueh logic rather than memorization. At the same time it 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 sixty interactive simulations provided an the CD-ROM that is shrink wrapped with the text. The CD-ROM has been greatly expanded to address the Fttlder/SoIornon Inventory of Different Learning Styles7 throush interactive Summary Notes and new and updated Interactive Computer Modules (ICMs). For example, the Global Learner can get an overview of the chanter material from the Summary Notes: the Sequential Learner can use all the hot buttons: and the Active h earner can interact with the ICM's arid use the

hot buttons in the Summazy Notes. ~i new pedagogical concept is introduced in this edition 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 home problems for that chapter. This exploration helps the srudents get an innate feel of 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 home problems on trouble- shooting, as weIl as ask the students to expand home problems by ashrig a reIated question that involves critical thinking using Tables P-1 and P-2. Creative thinking skills can be enhanced by exproring the example: problems and asking "what if. . ." questions, by using one or more of the brainstorming exercises in Table P-3 to extend any of the home problems, and by working the open-ended problems. For example, .in the case study on safety, studtats can use the CD-ROM to c m y out a post-mortem on the nitroanaline explosiod in Example 9-2 to learn what would have happened if the cooling had failed for five minutes instead of ten minutes. Significant effort has been devoted to developing example and home probIems that foster critical and creative thinking.

hr tp: /h tvw.n~.~1~, eddfeldcr-pu hlic/llSrlir/scies. hon

Sec. H Acknowledgments xxxi

contributions to the first, second. and third editions (see Introduction, CD-ROM). For the fourth edition, 1 give special recognition as follows.

First of all. I thank my colleague Dr. Nihat Giimen who coauthored the CD-ROM and web site. His creativity and energy had a great impact on this project and reaIly makes the fourth edition of this text and associated CD-ROM special. He has h e n a wonderful colleague to work with.

Professor Flavio F. de Moraes not only translated the third edition into Portuguese, in col~aboration with Professor Luismar M. Porto, but also gave suggestions, as well as assistance proofreading the fourth edition. Dr. Susan Montgomery provided the Msuul Et~cyclopedia of Equiprnenr for the CD-ROM. as well as support and encouragement. Professor Richard Herz provided she Reaoior Lab portion of the CD-ROM. Dr. Ed Fonres. Anna Gordon, and the folks at Comsol provided a special version of FEMLAB to be included with this book. Duc Kguyen. Yongzhong Liu, and Nihat Giirmen also helped develop the FEMLAB material and web modules. These contributions are greatly appreciated.

EIena Mansilla Diaz contributed to the blood coagulation model and, along with Kihat Gurmen. to the pharmacokinetics model of the envenomation of the Fer-de-Lance. Michael Breson and Nihat Giirmen contributed to the Russell's Viper envenomation model, and David Umulis and Nihat Giirmen contributed to the aicohol metabolism. Veerapat (Five) Tanla yakom contributed a number of the drawings. along with many other details. Senior web designers Nathan Cornstock, Andrea Sterling. and Brian Vicente worked tirelessly wltb Dr. Giirmen on the CD-ROM. as wtlI as with web designers Jiewei Cao and Lei He. Professor Michael Cutlip. along with Professor Mordechai Schacham, provided Polymath and a special Poiymarh web site for the text. Brian Vicente took major responsibili~y for the solution manual, while Massimiliano No15 provided solutions to Chapters 13 and 14. Sornbuddha Ghosh also helped with the manual's preparation and some web material.

1 would also like to thank colleagues at the University of Colorado. Pro- fessor Will Medlin coauthored the Molecular Reaction Engineering Web Mod- ules (Dm), Professor Kristi Anseth contributed to rhe Tissue Engineering Example. and Professor Dliirlakar Kornpnla contributed to the Profe~sionaI Reference Shelf R7.4 Mul~ipEe En7yme~lMvlul~iplc Substrates.

I also thank MI> Ph.D. graduate students-Rama Venkate5an. Duc Kugyen. Ann Piyarat Wattana. Kris Paso. Veerapat (Five) Tantayako~m, Ryan Hartman, Hyin Lee. Michael Senra. Lizzie Wany, Pr;~chan~ Singh. and Kriangkrai Kraiwa~tannwong-for their patience and understanding during the period while I was wriring t h i ~ hook. In i~ddition. he supporl prclr~rded by the staff and colleagues at the departments. of chemical ensineerinp at Univer- sity College London and the University uf Colr~rado while 1 finiched the final details of the Text ic greatly appreciated. Boll1 are very stimu1;iling and art _ereat places to work and €0 spend a rahbaticr~l.

The stimulating discussions with Pmfessors Roben Hesketh. Phil Savage. John Falconer. D. B. Rattacharia. Rich %lacel, Eric McFarland, Will Medlin. ;ind Krisii hnceth are greatly appreciated. t also appreciate the fr~endchip and insight? provided by Dr. Lec Brown on Chapters 13 and 11. Mike Cutiip not

xxxii Preface

only gave suggestions and a critical rending of many section'; but. most impor- tantly, provided continuous support and encouragement throughout the course of this project.

Don MacLaren (cornpositon) and Yvette Raven (CD-ROM user interface design) made large contributions to this new edition. Bernard Goodwin (Pub- lisher) of Prentice Hall was extremely helpful and supportive throughout.

There are three people who need special mention as they helped pull everything together as we rushed to meet the printing deadline. Julie Nahil, Full-Service Production Manager at Prentice Hall. provided encouragement. attention to detail, and a great sense of humor that was greatly apprecinred. Janet Peters was nor only a meticulous proofreader of the page proofs, but also added many valuable editorial and other comments and suggestions. Brian Vicente put out extra effort so help finish so many details with the CD-ROM and also provided a number of drawings in the text. Thanks Julie, Janet, and Brian for your added effort.

Laura Bracken is so much a part af this manuscript. I appreciate her excellent deciphering of equations and scribbles, her organization. and her attention to detail in working with the galley and copy edited proofs. Through all this was her ever-present wonderful disposition. Thanks, Radar!!

Finally, to my wife Janet, love and thanks. Without her enormous help and support the project would never have been possible.

HSF Ann Arbor

For updates on the CD, new and exciting appIicatiws, and typographical errors for this printing. see the web site:

www. engin, umich. edd-cre or

ww.engin.umich.edrJ-cre/fogEerdGgumen

Mole Balances

The first step to knowiedge is to know that we are ignorant.

Socrates (470-399 0.c.)

The Wide 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

HOW ir n chcrnrcal kinetics and reactor design are at the heart of producing almost all industrial engilleer different chemicals such as the manufacture of phtharic anhydride shown in Figure 1-1.

fmm other I t is primarily a knowledge of chemical kinetics and reactor design that distin- guishes 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 n chemical plant. For example, if a reaction system produces n large amount of undesirable product, subsequent purifica- tion and separation af the desired product could make the entire prwess eco- nomically unfeasible.

Mole Balances Chap. 1

F w d W e r Sham

Ftgurt 1-1 Manufacture of phthalic anhydride.

The Chemical Reaction Engineering {CRE) principles learned here can also he applied in areas such as waste trearment. microelectronics. nanoparti- cles and living syrtems in addition to the more traditional areas of the manufacture of chemicals and phamaceutica1s. Some of the exainples that illustrate the wide application of CRE principles are shown in Figure 1-2. These examples include modeling smog in the L.A. basin (Chapter I ) , the digestive system of a hippopotamus (Chapter 2), and molecular CRE (Chapter 3). Also shown is the ~nanufacture of ethylene glycol (antifreeze), where three of the most common types of industrial reactors are used (Chapter 4). The CD-ROM describes the use of wetlands to degrade toxic chemicals (Chapter 4). Other examples shown are the solid-liquid kinetics of acid-rock interactions to improve oiI recovery (Chapter 5 1: pharrnacokinetics of cobra bites and of drug delivery (Chanter 6): free radical scavengers used in the design of motor oils (Chapter 7), enzyme kinetics. and pharmacokinetics (Chapter 7): heat effects, runaway reactions, and plant safety (Chapters 8 and 9); increasing the octane number of gasoline (Chapter 10): and the manufacture of computer chips (Chapter 12).

Sec f .l The Rate of Reachon. -r,

Smog (Ch. 1, Ch. 7)

-

Chemical Plant for Ethylene GlycoI (Ch. 4)

Effecl~ve Lubrtcani Design Scavsnglng

ACID Free Rad~mls Oil Recovery (Ch. 5)

Pharmsmkmetics 01 Gobm B~tes

Mult~ple React~ons m a ~ a l c h

(Bodvl Reactor Cobra kltes (Ch. 6)

N~troanaltne Plant Explosron Exoiherm~c React~ons That

Run Away Ptant Safety (Ch.8, Ch.9)

Hippo Digestion (Ch. 2) Q 1

Vinyl Ally1 Ether 4-Pentenal (arrows ~ndicate

Transitron Stale (dashed llnes show transillon State eIeclron belocallzatlon)

Molecular CRE (Ch. 3)

a - 2

Wetlands Remediation of Pollutants (Ch. 4)

Pharmacokhetics (Ch. 7)

Mic~mlectronic Fabrication Steps (Ch. 10, Ch. 12)

Figure 1-2 The wide uorlcI uf applications of CRE


Overview-Chapter 1. This chapter develops the first building block of chemical reaction engineering, mole balances. that will be used continually throughout the text. After completing this chapter the reader will be able to describe and define the mte of reaction, derive the general mole balance equation, and apply the general mole balance equation to the four most common types of industrial reacrors.

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, and discussing the earlier difficulties of properly defining the chemical reaction rate. 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, continuous-stined tank (CSTR), tubular (PFR), and packed bed (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 shon review questions are given at the end of the chapter.

1 .I The Rate of Reaction, -b

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 chemrcnl species refers to any chemicnI component or element with a given identic. The identity of a chemical species is determined by the kincl, nirrnbet; and conjigit- rrrrinn of that species' atoms. For example. the species nicotine Ea bad tobacco

GH, alkaloid) is made up of a fixed number of specitic atoms in a definite rnolecu- 8 lar arrangement ar configuntioa. The stnicture shown iIlustmtes the kind,

Nicotine number. and configuration of atoms in the species nicotine (responsible for "nicotine fits") on a molecuiar level.

Even though two chemical compounds have exactly the same 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 eisht hydrogen atoms; however, the atoms in this compound can form two different arrangements.

H H H \ / \ /

CH3 ,C=C

\ and ,C=C \ CH, ' 3 3 CH, H

cis-2-butenc trii~ts-2-but ene

Sec 1 1 The Rate of R99ctl99 -5 5

When hac a chemical reaction

tnken pliice'?

A species r an low i ts identill, by

decomposition. combination,

ur isomcrizaIion.

As a consequence of the different configurations, these two isomers display different chemical and physrcal propertres. Therefore. we consider them as two different xpecie~ even thnuph each has the same number af atoms of ezch element.

We say that a chemical reactiort has tnken place when a detectable number of mulecufes 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 cre- ated nor destroyed when n chemicill reaction occurs. The mass refemd to is the totar collective mass of a11 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 ,artJ

nf disoppeorolzce of n species, say species A, i s the trtrntber ($A mnlrc~ries [hot lose their chemical i d tw t i~ per ~rtrir t i r l l ~ per ~rnir vc~iume fhrn~rgh fhe breaking and slrbreqiienr re-forming of ckentical bonds drrring the course of the rear- tion. 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 deconrposiriot~. the molecule lose4 its identity by being broken down into smaller molecuIes. atoms. or atom fragments. For example. if benzene and propylene are formed from n cumene molecule.

curnene benzene propylene

the cumene molecule has lost its identity [i.e., disappeared) by breaking its bonds to form these molecuies. A second way that a molecule may lose its species identity is through conlbinarion with another molecule or atom. In the example above. the propylene molecule would Lose its species identity if he reaction were carried out in the reverse direction so that i t combined with benzene to form curnene. The third way a species may lose its identity is through isorneri-ization, such as the reaction

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 Balanoes Chap. 1

What is -r,?

To summarize this point, we say that a given number of molecules (e.g., mole) 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 chIoraI to produce the insecticide DDT (dichlorodiphenyl-trichlomthane) in the pres- ence of fuming sulfuric acid.

Letting the symbol A represent chloral, B be chlorobenzcne, C be DDT, and D be H 2 0 we obtain

The numerical value of the rate of disappearance of reactant A, -r,. is a positive number (e.g., -r, = 4 mol Aldm3+s).

The rate of reaction, -r,, i s the number of moles of A (e.g.. chloral) reacting (disappearing) per unit time per unit volume (mol/dm3.s).

r~ = 4 rnol Aldm' F

-rs = 8 mol Bldrn' r r, = 4 mol B/dm3 a

A+ZB-+C+D The convention The symbol r j is the rate of formation (generation] of species j. If species j is

a reactant, the numerical value of r, will be a negative number (e.g.. r , = -4 moles Atdm3.s). If species j is a product. then r, will be a positive number (e.g.. rc = 4 moles C/dm"s), In Chapter 3. we will delineate the prescribed relationship between the rate of formation of one species. r, (e-g., DDT[C]), and the rate of disappearance of another species. -r, ( e . ~ . , chlorobenzene[B]), in a chemical reaction.

Heterogeneous reactions involve more than one phase. In heterogeneous reaction systems, the rate of reaction i s 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 qolid catalyst surface for the reaction to take place,

The dimensions o f this heterogeneous reaction rate, r ; (prime). are the What ir r ; ? nan~her of rnoic.7 of A rraciirig per eni, rims per enit rrlar.7 of carnlysi

(tnol/s+g catalyst). Most of the introductory di5cussions on chemical reaction engineering in

this hook focus on homogeneous'sy stems. The mathematical definition of a chemical reaction rate has been a source

of confusion in chernlcal and chemical engineering literature for many years. The origin of this confusion stems from laboratory bench-scale experiments tha~ were carried out to obtain chemical reaction raw data. These early txperi- ments were batch-type. in which the reaction vessel was closed and rigid: consequently, the ensuing reaction took place at constant volume. The reactants were mixed together at time t = O and the concentration of one of the reactants. CA, was measured at iarious rimes I. The r;tte of reactinn \+as deter-

See. 1.1 The Rats of Reaction, -r, 7

mined from the slope of a plot of C, as a function of time. Letting r-, be the rate of formation of A per unit volume (e.g., mol /s.dm", the investigators then defined and reported the chemical reaction rate as

dC* r* = - dl

Surnma:y Notes

The ~ i t c Inw doe5 nor depcnd on

the I> p of rescrur u\cd?!

However this "definition" is wrong! Ft is simply a mole balance that i s only valid for a constant volume batch system. Equation (1-1) will not apply to any continuous-flow reactor operated at steady srate. such as the lank (CSTR) reactor where the concentration does not vary from day to day (i.e.. the concentration is not a function of time). For amplification on this point, see the section "Ir Sodium Hydroxide Reacting?'iin the Summary Note!, for Chap- ter 1 on the CD-ROM or on the weh.

In conclusion. Equation ( 1 - 1 I is not the definition of the cheinical reaction rate. we shall simply say that I . is the rate #ff irrnul ir)~? of .sfwc.ifb j j w r .

aaii i?o!unir. i r is the number of rno/es of species j generated per unit volume per unit rime.

The rate equation (i.e., rate law) for rj i s an algebraic eqzlation that is solely a function of the properties of the reacting materials and reaction conditions (e.g., species concentration, temperature. pressure, ar type uf catalyst, if any) at a pnint in the system. The rate equation is independent of the type of reactor le.g., batch or continuous flow) in which the reaction is carried out. However, because the propertiec and reaction conditions of the reacting materials may vary with position i n a chemicaI reactor. r, can in [urn be a function of position and can vary from point to point in the system.

The chemical reaction rate law is esrentially an algebraic eq~~iitiun involving concentration, not a differential equation.[ For example. the alpe- hraic form of the rate law for -r, fur the reaction

may be a linear function of concentratinn,

or. as shown in Chapter 3. i t may he some other algebraic fi~nction of concenrration, such as

- - - - - . - ' For furllicr elaboration on his poinl. w e CIJPJPI G i c . .Tr.i., 2.T. 337 (19711): R. L.

C~)nc\ and H. S. Foplcr. crl5 . AIChE .Llrrdrrlrtr I r f \ ~ r l t r f i o r i 5l~r.ic.r E: XKuzc..r. 1 . I (New Yt11.k: AIChE. 1981 1. :tnd R . 1. Kahcf. "R;~te\." Cher~r. [ti<. Cr>tr~r~rroi . Y. I 5 (19x1 ).


The rate law is an k ,C , -r4 = - al~ebra~c equation. I +klCA

For a given reaction. the particufar co-xentrarion dependence that the rate law follows (i.e.. -r , = kc, or - rA = kc; or ... ) must be determined from exper- irnenral observation. Equation (1-2) states that the rate of disappearance of A i h

equal to a rate constant k (which is a function of temperature) times the square The convention of the concentration of A. By convention. r, is the rare of formation of A; con-

sequently. -,-, is the rate uf disappearance of A. Throughout this book. the phrase mte qf gerlerution means exact1 y the same as the phrase rntr qf'jiwmn- tion, 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 sTstern vo l~me . We shall perform a mole balance on species j in a system volume. where species j represents the particular chemical species of inrerest, such ax water or NaOH (Figure 1-3).

System J Vorurne

Figure 1-3 Balance on system volume.

A mole balance on species j at any instant i n time. t. yields the following equation:

of j wirhin

Rate of flow Rate of flow 1 of j in to 1-1 o f j o u t o f ] + the system the system

(moles1 time (molesftime) I the system 1

Mole balance In + Out + Generation = Accumulation

50 a Fi + G, - - 3 (1-3)

dt

- - Rate of generation

of reaction j by chemical within

the system (molesJtime) -

=

Sec. 1.2 The General Mole Balance Equation 9

where N, represents the number of moles of species j in the system at time t. I f all the system variable5 l e . ~ . , temperature. catalytic activity, concentration of she chemical species) are spatially uniform throughout the system volume, the rate of generation of specie? j, G,. i s jur t the product of the reaction volume. V. and the rate of formation of species j , r,.

Suppose now that the rate of formation of species j for the reaction varies with the position in the system volume. Thai is. i t has a value r,, at location I. which is surrounded by a small volume, A V l , within which the rate is uniform: similarly, the reaction rate has a value x,? at location 2 and an aswciated volume, AV, (Figure 1-4).

Figure 1-4 Dividing up the system volume, K

The rate of generation, AG,, , i n terms of r j l and subvolume A V t , is

AG,, = r j , hV1

Similar expressions can be written for AG,? and the other system subvolumes, AV, . The total rate of generation wirhin the system volume is the sum of all the rates of generation in each of the subvolurnes. If the total system volume is divided into rM subvoIumes, the total rate of generation is

10 Mole Balances Chap. 1

This i s a baxic equation for

chemical reac~ion engineeri~ig.

By taking the appropriate limits (i.e., let M + w and A V + 0 ) and making use of the definition of an integral, we can rewrite the foregoing equation in the form

From this equation we see that r, 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.

We now replace G, in Equation (1-3)

hy its integral form to y~eld a form of the general inole balance equation for any chemical species j that is entering, leaving, reacting. andlor accumulating within any system voluine 1!

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 equarions we can determine the time (batch) or reaclor volume (cominuous-flow) necessary to convert a specified amount of the reactants into products.

f .3 Batch Reactors

is a hatch A hatch reactor is used for small-scale operation. for testing new procesces that reactor u\rriq have not been fully de\elnped. for the manufacture of expensive products. and

for processes that are difficult 10 conImen to continuous operations. The reactor can he charged (i.e., filled) through the holes at the top (Figure 1 -S[al). The

/ @\ batch reactor has the advantngc of high convercions 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 vxiabiliry of products from

Reference Shelf batch to batch. and the difficulty of large-scale production (see Profecsional Reference Shelf [PRS]).

Sec. 1.3 Batch Reactors I I

Figure I-5(a) Simple batch homogeneous Figure 1-5(6) Batch reactor m~xing patrems. reactor. [Excerpted by special permission Further descr~ptionr and pho~os of the batch from Chem. Eng, (5.?(10), 2 1 I (Oct. 19561 reactors can be found in both the Vr~~rul Copyright 1856 by McGraw-Hill. Inc., New Ewc~clopcdra of Equrpnretrl and in the York, h'Y 10020.1 Pmfe~sinnrtl Rcf~rtr>rt Shelf on the CD-ROM

A batch reactor has neither inflow nor outflow of reactants or products while the reac~ion is being carried out: F,o = F, = 0. The resulting general mole balance on species j is

- If the reaction mixture is perfectly mixed (Figure 1 -5[b]) so that there is no variation in the rate af reaction throughout the reactor volume. we can take r, out of the integral, integrate. and write the mole balance in the form

Perfect mixing

Let's consider the isomerization of species A in a 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.

Mole Balances Chae. 1

0 ti t 0 '1

Figure 1-6 Mole-time rrajectories.

We might ask what time. t , , is necessary to reduce the initial number of moles from NAo to a final desired number NAI. Applying Equation (1-5) to the isomerization

rearranging.

and integrating with limits that at r = 0. then N, = N,,, and at t = I , , then NA = we obtain

This equation is the integral form of the mole balance on a batch reactor. It gives the time, r , . necessary to reduce the number of moles from /VAo to N,, and also to form rYB1 moles of B.

1.4 Continuous-Flow Reactors

Continuous flow reactors are almost always operated at steady state. We wiil consider three types: the continuous stirred tank reactor (CSTR), the plug flow reactor (PFR), and the packed bed reactor (PBR). Detailed descriptions of these reactors can be found in both the Professional Reference Shelf IPRS) for Chapter 1 and in the Visrral Encyciopeclin of Equiprnenr on the CD-ROM,

1.4-1 Continuous-Stirred Tank Reactor

A type of reactor used commonly in industrial processing is the stirred tank What is a CSTR operated continuously (Figure 1-7). It is referred to as the continuo~u-stirred

uxd tnrlk renrtor (CSTR) or vat, or backmix reactor; and i s used primarily for liquid

What reac~ion systems use a

CSTR?

The idtal CSTR i v assumed t r r ht.

perrec~ly mixed.

phase reactions. I t i s normafly operared a t steady state and I \ a\surned to be perfectly mixed: conrequenily, t hers is no ti me dependence or pokition dependence of the temperature. [he concentration, or the reaction rnte inside rile CSTR. That is, every variable i> the wme at every point inside the reactor. Becat~se the temperature md concenrration are identical everywhere u itliin the reaction vessel, they are the same at the exit point as they are elsewhere in the tank. Thus the temperature and concentralion in the exit stream are modeled a5

being the same as those jnside the reactor. In systems where mixing is highly nonideill, the weII-mixed model i* inadequate and we must resort to other modeling techniques, such ns rebidence-time distributions, to obtain meaning- ful results. This topic o f nonideal mixing is discussed in Chapters 13 and 14.

Figure 1-7(a) CSTRharch Figure I-71bk CSTR mixing patterns. reactor. [Courtesy of Pfnudlcr. Inc.1 Alw see the Vir~rnl Enr~cluped~n oJ

Eqwp~nent on the CD-ROM.

When the general mole balance equation

is applied to a CSTR operated at steady state (i.e., conditions do not change with time),


in which there are no spatial variations in the rate of reaction (i.e., perfect mixing),

it takes rhe familiar form known as the design eqrrarion for a CSTR: F~~ Al

The CSTR design equation gives the reactor volume I{ necessary to reduce the entering flow rate of species j, from Fj, to the exit flow rate F,, when species j i s disappearing at a rate of -rj. We note that the CSTR i s modeled such that the conditions in the exit stream (e.g.. concentration, temperature) are identical to those in the tank. The molar flow rate 6 is just the product of the concentralion of species j and the volumetric flow rate u :

Fl = Cj+ v

p& - moles volume time volume time I

Consequently. we could combine Equations (1-7) and ( 1-8) to write a balance on species A as

1.4.2 Tubular Reactor

In addition 10 the CSTR and batch reactors, another type of reactor commonly used in industry is the ruhlliar rmr.ror: It consists of a cylindrical pipe and is

When is normally operated at steady state, as i~ the CSTR. Tubular reactors are used reactor mnsi

u,ed? most often for gas-pha~e reactions. A schematic and a photograph of industrial tubular reactors are shown i n Figure 1-8.

In the tubular reactor, the reactants are continually consumed as they flow down the length of the reactor. In modeliny the tubular reactor. we assume that the concentration varies continuoucly in the axial direction through the reactor. Con~equcntly. 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 l e g . . uniform veIocity as in turbulent floa). as shewn rn Figure 1-9. Thar is. there i h no radial variation it1 reaction rate and the reactor is referred to as a plug-fiow rcactor [PFR). (The laminar flow renctor is diwurced in Chapter 13.)

Sec. l .d Contintlous-Flow Reactors 15

ee PRS and Enr~clopr- E q l t i p ~ ~ ~ ~ n t .

Figure 1-8(a) Tubular reoclrw wherna~ic Figurc 1-8(bl Tuhulw i-ellclur photo Longitudinal tubular reactor. [Excerpted b! Tubular reac~or for p~vductlon of Dlmerwl G. spctnl permission from CIINII. Ella, h3( 10). [Photo Colrnecy of Editions Technvq 2 1 1 (Oct. lq56). Copyright 1956 by Institute Frrrncois du Pc~rolj McCrau -Hill. Inc , Kcu York, Y 1' 10010.1

Plug tlr>ur-l~o radral iarinlionr in vclncity.

Reactants Products

Fiaure 1-9 Pluy-flow tu l l~~lar re;lctor.

The general moIe balance equation i s given by Equation ( 3 4 ) :

The equation we will use to design PFRs at steady <tare can be developed in two ways: ( I ) directly from Equation (1-4) by differentiating with respect to i,olume V, or ( 7 , ) froin a inole balance on species j in a differential segment of the reactor volume A\'. Let's choose the second way to arrive at the differential form of the PFR mole balance. The differential volume. A V , shnwn in Fig- ure 1-10. will be chosen sufficiently small such that there are no spatial variations in reaction rate within this volume. Thus the generation term. AG,, i s

Figure 1-14) Molc balance cm \pc.r~t=c j tn trrlutnc A \ ' .


Molar flow Molar flow , Generotinn

of species j within AV

of species j within A V

I n - Out +-g en era ti on = Accumulation

Dividing by A V and rearranging

the term in brackets resembles the definition of the derivative

Taking the limit as AV approaches zero, we obtain the differential form of steady state moIe balance on a PFR.

Tubular mador

We could have made the cylindrical reactor on which we carried out our mole balance an itregular shape reactor, such as the one shown in Figure 1-1 1 for reactant species A.

Picasso's reactor

Figure 1-11 Pablo Picasso's reactor.

However, we see that by applying Equation (1-10) the result would yield the same equation (i.e., Equation [I-1 I]). For species A, the mole balance is

Sec. 1.4 Continuovs-Flow Reactors 2 7

Consequently. we see that Equation ( I - I I ) applies equally well to our model o f tubular reactors of' variable and constant cross-sectional area, although ir is duubtful that one would hnd a reactor of the shape shown in Figure I-l l unIess it were designed by Pablo Picasso. The conclusion drawn from the applicarion 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 jsornerizntion A + B, this time in a PFR. As the reactants proceed down the reactor. A is consumed by chemical reaction and B is produced. Consequent!y, the molar Raw rate of A decreases and that of B increases, as shown i n Figure 1 - 1 2.

Figure 1-12 Profiles of molar flow rates in a PFR.

We now ask what is the reactor volume V , necessary to reduce the entering molar flow rare of A from FA, to FA!. Rearranging Equation ( I - 12) in the f o rrn

and integrating with limits at V = 0, then FA= FA,,, and at V = V,. then FA= FA,.

V, is the volume necessary to reduce the entering molar flow rate FA, to some specified value FA1 and also the volume necessary to produce a molar flow rate o f B of FBI.

1.4.3 Packed-Bed Reactor

The principal difference between reactor design calculations involving homogeneous reactions and those involving fluid-solid heterogeneous reactions is that for the: batter, the reaction takes place on the surface of the catalyst. Con- sequently, the reaction rate is based on mass of solid catalyst. W, rather than on

d 8 Mole Balances Chap. 1

reactor volume, K For a fluid-solid heterogeneous system, the rate of reaction of a substance A is defined as

-r; = mol A reacted/s.g catalyst

The mass of solid catalyst is used because the amount of the catalyst is what is important to the rate of product formation. The reactor volume that contains rhe catalyst is of secondary significance. Figure 1-1 3 shows a schematic of an industrial catalytic reactor with vertical tubes packed with catalyst.

Product gas

t

Feed gas

Figure 1-13 Longitudinal cataly~ic packed-bed reactor [From Cmpley, American Institute of Chemical Engineers. 8612). ?4 t I99U). Reproduced with perrnik~ion of the American In~titute of Chemical Enpinccrs. Copynpht O 1 9 0 AIChE. All right\ reserved ]

In the three idealized types of reactors just discussed (rhe perfectly mixed batch reactor. the plug-flow tubular reacror 1PFR). and the perfectly mixed continuous-stirred rank reactor (CSTR), the design equations (i.e.. mole balances)

PRR were developed based nn reactor volume. The derivation of the design equation

Mole B~~~~~~ For a packed-bed catalytic reacror (PRR) will be carried out in a manner analogous to the development of the tubular design equation. To accomplish this derivation, we simply replace the voFume coordinate in Equation (1-10) with the catalyst weight coordinate W (Figure 1-14),

Figure 1-14 Pncherl-lxcf reactor srhem;~tic.

Sec. 1.4 Continuous-Flow Reactors 19

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 AW results in the equation

In - Out + Generation = Accumulation

The dimensions of the generation term in Equation (1-14) are

( r L ) A W z !notes A moles A . (mass of catabsr) = - (time) (rnass of caraly.~r) ~ i r f ~ e

which are. as expected, the same dimensions of the molar flow rate FA. After dividing by AW and taking the limit as A W -+ 0. we arrive at the differential

Use differential form form of the mole balance for a packed-bed reactor: of d m g n equation

for cataIy<t decay and

pressure drop.

When pressure drop through the reactor (see Section 4.5) and catalyst decay (see Section 10.7) are neglected, the integral form af the packed-cata- Iyst-kd design equation can be used to calculate the catalyst weight.

Use integral fnrm only for no AP and

no catalyst decay.

W i s the catalyst weight necessary to reduce the entering molar flow rate of species A. F,,. to a flow rate FA.

For some insight into things to come, consider the following example of how one can use the tubular reactor design Equation ( 1 - 1 I ) .

Exumpk 1-1 How Large Is it?

Consider the liquid pha.re ris - rrrrrls isomerizafion of 3-burene

cis-2-butene runs-2-bu tene

which we will write symbolically as

1 A - R

The first order (-r, = kc,) reaction is carried nut in a rubular reactor in which the volulnezric flow mte, c, IF constanl. 1.e.. I? = E ) , ~ .

20 Mole Balances Chap. '

Reactor sizing

1. Sketch the concentration prof le. 2. Derive an equation relating the reactor volume to the entering and exitrng

concentrations of A , the rate constant R, and the volumetric Row rate v . 3. Determine the reactor volume necessary to reduce the exiting concentration t~

10% of the entering concentration when the volumetric ffow rate is I ( dm3/rnin (i.e., litenlrnin) and the specific reaction rate, k. is 0.23 mrrr-' .

1. Speciec 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 = v , , one can use Equation (1-8) to obtain the concentration of A, C, = F , ~ U ~ , and then by compariwn with Figure 1-12 plot the concenrration of A as a function of rertctor volume as shown in Figure El-1.1.

Figure EI-1.1 Concentration prufile.

2. Derive an equation relating Y v,, k, CAo, and CA.

For a tubular reactor, the mole balance on species A Cj = A) was shown to be given by Equation ( 1 - 1 1). Then for species A (j = A) results

For a fist-order reaction, the rate law (discussed in Chapter 3) is

Because the volumetric flow rate. u , is constant ( u = uo). as it is for most liquid- phase reactions,

Multiplying both sides of Equation (EI-1.2) by minus one and then substituting Equation (E 1-1. I ) yields

Sec r 5 Industriat Rsac!ors

I U ~ i n g the conditions a ihc entrance ef the reactor that when V = 0, Ben C , = C,,,, 1 A+B

I 3. We want to find the vo:olume. V , , at which C , = --C,,, for k = 0.23 min-I and c ,, = 10 dmJlmin. I0

V

C,= C,,,exp - ( k V / ~ * l

I Substituting C*,,, C,. y,. and k in Equation (El-1.5). we have

- 5f:d5 , J:( ,V k r C,

Carrying oul the integration of Equation (E I - 1.4) gives

We see that a reactor volume of 0. E rn' is neceshary to cnnven 904 of species A entering into product B for the parameters given.

In the remainder of this chapter we look at slightly more detailed drawings of some typical industrial reactors and point out a few of the advantages and diradvantages of each.'

1.5 Industrial Reactors

When is a batch Be sure to view actual photographs of industrial reactors on the CD-ROM and reactor ur~d ' ' on the Web site. These are also links to view reactors on different web sites.

The CD-ROM also includes a portion of the K.slml Ei~cyclopen'ia of Equip- ment-Chemical Reactors developed by Dr. Susan Montgomery and her students at University of Michigan.

d Links

[I] Liquid-Phase Reactions. Semibatch reactors and CSTRs are used primarily for liquid-phase: reactions. A semibatch reactor (Figure 1- 151 has essentially the same disadvantages as the batch reactor. However. it has the advanrages of temperature control by regulation of the feed rate and the capabifity of minimiz- ing unwanted side reactions through the maintenance of a Iow concentration of one of the reactants. The semibatch reactor is also used for two-phase reactions in which a gas usually is bubbled continuousty through the liquid.

Chern. Eng., 63(10), 2 l 1 ( 1956). See also AlChE MoritlEar hstn~crion Series E, 5 (1984).


Flus gas

t

and product

Reactant B

Heater or m l e r

, Naphtha and recycle gas

Compressed alr Furnace

Figure 1-15(s) Semibatch reactor. Figure I-15fi) Fluidized-bed catalytic reactor. [Excerpted by spec~al permis\ion rrom [Excerpted by ~pecial permiss~on from Chem. Chc~n. Errg., fi .?(lO~. 21 1 rocl. 19561. Grx., h3( 10). 21 1 (Oct. 1956). Copyright 1956 by Copyright 1956 by McGrau-H111. Inc., McCraw-Hirl. Inc., New York, NY 1 Ml2O.l Yew York. NY 10020.1

M'hat are the advanrages and

A CSTR is used when intense agitation is required. Figure I-71a) showed

disadvantaFer of a a cutaway view of a Pfaudler CSTRhatch reactor. Table 1-1 gwes the typicaI CSTR? sizes (along with that of the comparable size of a familiar object) and costs for

batch and CSTR reactors. All reactors are glass lined and the prices include heatinglcooling jacket, motor, mixer. and bafff eq. The reactors can be operated at temperalures between 20 and 450°F and at pressures up to 100 psi.

The CSTR can either be used by itceIf or. in the manner shown in Figure 1-16, as part of a series or battery of CSTRs. I t is relatively easy to mainrain good temperature conrrol with a CSTR because i t is well mixed. There is. however. the disadvantage that the cornersion of reactant per volume of reactor i s the smallest of the flow reactors. Consequen~ly. very large reactors are neces-

Iblurrn' Pljce

5 Gallnnr S19.01KI (was~eba~ket I

50 Gallonr S38.M) (yarhuge can 1

5()0 Gallon4 S70,W (Jacuzzi)

! ~ ) / I I I I I P Price

I CIUO Gallons 585.IKX1 12 Jacuzzis)

4000 GaI lom $150.000 (8 J~cuzz i r l

ROW G a l l o n ~ 5280.000 [pafnline lanker)

Sec. I 5 Industrial Reactors 23

sary to obtain high conversions. An industrial flow sheet for the manufacture of nitrobenzene from benzene using a cascade of CSTRs is shown and described in the Professional Reference Shelf for Chapter 1 on the CD-ROM.

Feed

cooling jackets

F

Product

Figure 1-16 Baltery of mrred tank< IExcerplcd by special permrssion from C l r ~ ~ n . Org.. 631 10). 21 I (Oct. 1956) Copyright 1956 by McGraw-HIII, Inc.. New York. NY 1010 1

If you are not able to afford to purchase a new reactor. it may be possible to find a used reactor thul may f i r your needs. Previously owned reactors are

Lrrkr much less expensive and can he purchased from equipment clearinghouses such ns Aaron Equipment Company ( ~ ~ w ~ : a u r n ~ ~ e q u i p n ~ c n f . c o ~ n ) or Loeb Equipment Supply ~ w ~ ~ ~ : l o e b e g ~ i p ~ ~ ~ e n f . c o ~ ~ ~ f l .

What are the /2J Gas-Phase Reactions. The tubular reactor (i.e.. plug-flow reactor [PFR]) a d l ~ n f a ~ e s and is relatively easy to maintain (no moving partc), and it usually produces thc

d~qadbantage< of a PFR? highest convesqion per reactor volume of any of the flow reactors. The disad-

vantage of the tubular reactor is that it i s difficult to control temperature within the reactor. and hat spots can occur when the reaction i s exothermic. The tubular reactor is commonly found either in the form of one long rube or as one of

CSTR: liquids a number of shorter reactors arranged in a tube hank as shown in Figures PFR, gnce\ I -R(a) and (h). Most homoyeneaus liquid-phase flow reacrors are CSTRr.

whcreoq moxt homogeneous pis-phase flow reactors are tubular. The cosrq of PFRs and PBRs (without catalyst) are similar to the costs of

heat exchangers and can be found in Planf Desipl and Erot~or~~ics~for Cl~rr?lr- cnl ErrgErreer.5. 5th cd.. by M. S. Peters and K. D. Timmerhaus (New York: McGraw-Hill, 2002). Frnln Figure 15-12 of the Peters and Tirnmerhaus book. one can get an estimate of the purchase cost per foot of $ 1 for a I -in. pipe and 52 per foot for a ?-in. pipe for single tube? and approximately 520 to $50 per square font of \usface area for fixed-tube sheet exchangers.

A packed-bed (also called a hxed-bed) reactor is essentially a tubular renctor that is packed w~rh solid satatyst panicles (Figure 1 - 1 3). Th~s Iieterogcneous reaction rystenl i\ moG1 often used to c;1(:11y~e gas 1.eactionx. This reactor has the same difiicultiec with temperature conlrol a\ nther tubular reactors: in addition. he c:~lab\! is 11rui1lly troubIc\i~ine 10 repl;~ce. On occasion. channeling of thc


gas flow occurs. resulting in ineffective use of piins of the reactor bed. The ad%antage of the packed-bed reactor i s that for most reactionr it give^ the high- e5t conversion per weight of catalyst of any catalytic reactor.

Another type of catalytic reactor in common use is the Ruidized-bed (Fig- ure I - 15[b]) reactor, which is analogous to the CSTR in that its contents. though heterogeneous, are well mixed. resulting in an even temperature distri- bution throughout the bed. The fluidized-bed reactor can only be approximately modeled as a CSTR (Example 10.3): for higher precision it requires a model of its own (Section PRS12.3). The temperature is relatively uniform throughout, thus avoiding hot spots. This type of reactor can handle large amounts of feed and solids and has good temperature control; consequently. i t is used in a large number of applications. The advantages of the ease of catalyst replacement or regeneration are sometimes offset by the high cost of the reactor and catalyst regneration equipment. A thorough discussion of a gas-phase industrial reactor and process can be fwnd on the Pmfessional Reference Shelf of the CD-ROM

Refe:enceChe1f for Chapter I . The process is the manufacture of paraffins from synthesis gas (CO and H1) in a straight-through transport reactor (see Chapter 10).

In this chapter. and on the CD-ROM, we've introduced each of the major types of industrial reactors: batch. semibatch, stirred tank, tubuIar, fixed bed (packed bed), and fluidized bed. Many variations and modifications of these commercial reactors are in current use; for further elaboration, refer to the detaiIed discussion of industrial reactors given by Walas.-'

The CD-ROM describes industrial reactors. along with typical feed and

sclu& Roblemr operating conditions. In addition, two solved example problems for Chapter 1 can be found on the CD.

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 ro a variety of problems. We have just finished the first building block of this algorithm: mole balances. This algorithm and its cone- sponding building blocks will be developed and discussed in the following chapters:

Mole BaIance, Chapter 1 Rate Law, Chapter 3 Stoichiometry, Chapter 3 Combine, Chapter 4 Evaluate, Chapter 4 - Energy Balance, Chapter 8

With this algorithm, one can approach and solve chemical reaction engineering probIems through logic rather than memorization.

3 S. M. Walas, Reaction Kinetics for CIzemical Engineers (New York: McGraw-Hill. 1959). Chapter I 1.

Chap. 1 Sun?mary 25

S U M M A R Y

Each chapter summary giles the Lcy points of the chapter that need to be remembered and carried into succeeding chnpters.

I. A more balance on species j. u h ~ c h enters. leaves, reacts. and accumuIntea in a system volume F: is

c d N F,"-F,+/ sfl==i (51-I)

dr

Ik nndon1.v iJ: the contents of the reactor are well mixed, then a mole balance (Equation S 1- 1 1 on specie? A grves

2. The kinetic rate law for r, is:

Solely a function of properties of reacting materials and mactirm cond~tions (a.g., concentration [activities], temperature, pressure, catalyst or solvent [if any11 The rate of formation of species j per unit volume (e.p., molls~dm'l An intensive quantity Ii.e.. it does not depend an the total amount) An algebraic equation. no? a differential equation (e.g., -rA = kc,. -rq = kc:)

For homogeneous catalytic systems. typical units of -5 may be gram moles per second per liter: for heterogeneous systems, typical units of $ may be gram moles per second per gram of catalyst, By convention, -rF, iis the n t e of disappearance of species A and r , is the rate of formation OF species A.

3. Mole balances on species A in four common reactors are as FoIlow~:

TABLE S-I SUM~~IARV OF REACTOR MOLE BALAYCES

Reacror Mole hrlunce Cornnwnr

Diflerenrrd firm A!srhrrrir f i r m Intqroi Fnrrlr

CSTR No spatid variations. - steady state

Steady state

PBR Steady state

26 Mole Batrnces Cclap. T

C D - R O M M A T E R I A L

Learning Resources 1 . S~irntlrar~ tdorrs 2 Web Miireriol

Summa. y Motes A. Problem-Solving Algnr~rhin B. G e t ~ ~ n p Unstuck on a Problen~

Thic \ire on the web and CD-ROM gives t i p on how to overcome mental krrriers in pmbleni snl'r In$.

C. Stnng in L.A. bacin

R. G~ttinr Unstuck C. Smog in L.A.

3. Ir~rerncrr~,c Co)~iprrrer. Morltilet A. Quiz Show I

Chap 1 CD-ROt! Material 27

4. Solved Pmhlerlw A. CDPI-AB Batch Reactor Calculations: A Hint of Things to Come B. PI-14, Modeling Smog in the L.A. Basin

FAQ [Frequently Asked Questions]-In VpdateslFAQ icon sectlon Professional Refemnee Shelf

L ~ v i n g Example Problem I . Photos of Real Reactors Smog in L A .

2 . Reactor Section of the Usual Er~cj*clopedia of Eqrripme~ri This sectlon of the CD-ROhI shows industria1 equipment and disct~sses its operation. The reactor portlon of thir encyclopedia i s ~ncluded on the CD-ROM accompanj ing this h o k

Reference 9 e l f

28 Mole Balances Chap. '

E~~implrs of 3. The productitm of nitrobenzene exnmple problem. Here thc procesh Ilo~r ~nrlu\tr~rtl reacr~ons rheet ir prven. don: with operating cr>ntl~tinris.

and reactors N~trobanzens

Vacuum Vapors

I ,- C

Crude I I I I I nrlrobenzerre

Recorrcenlraled 0c1d Condensare

Sulhr~c acid

Ntrrrc acid pump lank Steam

Makeup sulfune acrd I Figure PRS.A-I Flou~sbce~ For the rnanuhcture of nitrobenzene.

4. Fischer-Tropsch Reaction and Reactor Example. .4 Fischcr-Tropsch reaction carried out in o typ~caE straight-through trancppr reactor {Riser).

Figore PRS.B-I Thc reactor Ir 3.5 m in d~amcter irnd 38 m tnl[. [Schematic and phoro courtesy of SasollSastech FT Limirrd.]

Chaa. 1 Questions and Probl~rrrs 29

Here photograph\ and ichernatics of the equiprnenr along with the feed rate\. reactor sizes. and principal renotlons

are also discussed in the PRS.

CIUEST1ONS A N D P R O B L E M S

I wish I had an answer for that, because I'm getting tired of answering that question.

Yogi Berra. New York Yankees Spnrrs Illi~str(lterl, June 1 I, 1 984

The subscript to each af the problem numben ind~cates the level of difficulty: A, leaxt difficult: D. most dlfficulr.

In each of the questions and problems below, rather than just drawing a box around your enwer. write a sentence or two describing how you solved the problem, the assurnp- tions you made, the reasonableness of )our answer, what you learned, and any other facts that you want to include. You may wish no refer to W. /.trunk and E. 8. White. The El~ntenrs of SMe. 4th Ed. (New York: Macrnillan, 2000) and Joseph M. Williams, Stvke: Ten Lessons in Clarity & Gmcc, 6th Ed. (Glcnview, Ill.: Scott, Foresman, 1999) to enhance the quality of your sentences.

P_'- = Hint on the web

Refore solving PI-lA (a) Read through the Pmhcc. Write a paragraph describing buth the content the problems, smtr goals and the intellectual goals OF the course and text. Also describe

or <ketch qual~ta- what's on the CD and how the CD can be used with the text and course. tively the expected

re~ults ur trendq. (h) List the areas in Figure 1-1 you are most looking forward to studying. (c) Take n quick look at the weh modules and list the ones that you feel are

the most novel applicntions of CRE. (dl Visit the problem-solving web site, www.engin.umich.edid-cw/pmb-

solv/ciaserlkep.hrrn, to find way? to "Get Unstuck" on a problem and to review the "Pmblem-Soivtng Alpotithm." List four ways that might help yo11 in your solutions to the home problems.

(a) After reading each page or two ask yourself a question. Make a I~st ~f the four best questions for this chapter.

(b) Make a list of the five most imponant things you learned from this chapter.

Visit the web site on Critical and Creative Thinking, ~urvw.enpin.rimich.edu/ -ce/probsoIv/stmtegv/crit-11-cwat, hrm.

(a) Write 3 paragraph describing what "critical thinking" i s and how you can develop your critical thinkrng skills.

(b) Write a paragraph describing what "'creative thinking" i s and then list four things you will do during he next month that will, increase your creative thtnking skills.


(c) Write a question based on the material in this chapter that involves criti-

IC%f Quiz Shnw

PI-l*

cal thinking and explain why it involves cntical thinking. ( d ) Repeat (c) for creative thinking. (e) Brainstorm a Iist of ways you could work problems P-XX (to be speci-

fied by your instructor--e.g., Example El, or PI-15,) incorrectly. Surf the CD-ROM and the web (www.engin.umrch.edd-cw). Go on a scaven- ger hunt using the summary notes for Chapter E on the CD-ROM. (a) What Frequently Asked Question (FAQ) is not really frequently asked?

hot button leads to a picture of a cobra?

(c) What ISellTe;;/l hot button leads to r picture o f r rabbit?

(d) Whai 4101 buffnn leads to a picture of a hippo?

(e) Review the oblecrives for Chapter 1 in the Summary Notes on the CD-ROM. Write n paragraph in which you descr~he how well you feel you me1 these objec~ives. Diqcuss any difficulties you encountered and three ways (e.p.. meet with professor. claqsmarec) you plan to address removing these difficulties.

(f) Loub at the Chemical Reactor section of the Vi.rual E~lc?.rinl~rdin of Eyuiprnenr on the CD-ROM. Write a paragraph describing what you learned.

(g) View the photos and schematics on the CD-ROM under Elements of Chemical Reaction Englneerrng--Chapter 1. Look at the qulcktime vid- eos. Write a paragraph describing two or more of the reactors. What sim- ilarities and differences do you observe be~ween the reacton on the weh (e.g.. 1r~tr~n.Ir~ebeqrtipi71er1t.con~). on the CD-ROM. and in the text? How do the used reactor prices compare ai th those In Table 1 - I ?

Load the Interactive Computer Module (ICM) from the CD-ROM. Run the module and then record your performance number for the module which indi- cates your mastery of the material. ICM Kinetics Challenge 1 Performance # Example 1-1 Calculate the volume of a CSTR for the conditions used to figure the plug-lion reactor volume in Example E -1. Which volume i s larger. the PFR or the CSTR'? Explain why. Suggest two ways to work t h ~ s problem ~ncorrec~ly. Calculate the rime ra reduce the number of moles of A to 19 of its initial value in a constant-volume batch reactor for the reaction and data in Example 1 - 1 . \%'hat assumptions were made in the dcrivat~on of the design equation for: la) the batch reactor? (b) the CSTR? {c) the plug-Row reacior (PIT)? Id) thc packed-bed reactor IPBR)? (e) State in words the meanings of -r,. -r; . and rX . Is the reaction nte -r,

an extensive quantity'! Explain. Use the mole balance to derive an equation analogous to Equi~rion ( 1-7 1 for n fluid- ifrd CSTR contalnrnp catalyst particles in terms of the catalys~ we~ght. IV and other appropriate term\. Hirlr: Scc rnaq~n figure.

Chap. 1 Ouestions and Problems 31

PI-10, How can you conven the general mole balance equation for a given species, Equation { 1-4)- to a general mass balance equation for that species?

1 We are going to consider the cell as a reactor. The nutrient corn steep liquor enters the cell of the mrcroorganlsm Penirillfunl chnsngenum and is decom- posed to form such products as amino acids. RNA. and DNA. Write an unsteady mass balance an (a) the corn steep liquor. Ib) RNA. and (c) pencil- lin. Assume the cell is well mixed and that RNA remains inside the cell.

PI-12, The United States produced 32.59 af the world's chemical products in 2002 according to "Global Top 50." Cherniraf rtnd Engrrleerin~ Nen:~. July 28* 2003. Table PI-12.1 lists the 10 most produced chemicals in 2002.

TABLE PI-I? I . CHEUICAL PROI)L~~ICJ%

Reference: Clnentirrr I urrrl E r ~ g i ~ r t ~ r i t l p NPII,S. July 7 . ?Oi l?, htl/~://p11/7.~.(1~.~.0~fi/c't~~d

(a ) What were fhc I 0 rnoxt pmduced chemicals for the year that just ended7 Were there an\: sipnifica~lt chanfes from the 1995 qtatist~cs? (See Chapter I of 3rd edi~ion of El~rnents o j CRE.) The Fame issue of C&E Nm:r ranks chenircal companies as riven in Table PI - 12.2.

(b) What I0 companies were tops in <ales for the year jusr ended? Did any significant changes mcur cnmpared to the 2002 statist ~ c s ?

(c) Why do you think H,SO, is the mosl produced chemical? What are some of its wes?

(d3 What is the current annual production rate Ilblyr) of ethylene, ethylene oxide. and benzene?

(e\ Wh?. do you su\pect there are \r) few organic chcniicals rn the top 10?

Mole Balances Chap.

Dew Chemical Dupont ExxonMobil General Electnc Hunt~man Corp. PPG lndustrie~ Equistar Chemicals Chevron Phil lips Enstrnsn Cheti~lcal Prarair

Refemnres: Rank 1002. Chrmirul ortrl E~tprneerirrx N ~ I I ' s , May I? . 2003. Rank 2001 : CE~erniuul ~ t r d E t ~ , q [ r ~ c c r i n ~ Neam3, May 13, 2002. Rank 2000 Chctnrtnl r i r ~ d Errgrne~rirzg AVr~:ci's. May 7 , 200 1 . Rank 1994: Cl~emicfll ot~rl En#~nrcr i r~g Ncu.~, May I . ?W. Itttp //psbs.ncs-or.y/retd

P1-13', Referring to the text material and the additional references on comrnerciz reactors given at the end of this chapter. fill in Table P I - t 3.

TABLT PI. 1.1 COMPARISON OF REACTOR TYPES

kind.^ of ??pe qf Phuscs Reortor Chrrmct~risfics Prrvrnr Use Ar1rfl1~1rrgt.s Disodrctntugrs

Batch -- CSTR -- PFR -- PBR --

PI-14, Schematic diagrams of the: Lor; Angeles basin are shown In Figure P I - 14. Thr

Ucmbe- B basin R o o t covers approximately 300 square miles ( 2 x 10'"ff2) and is almos completely surrounded by mountain ranges. 1F one assumes an inversior height in fhe basin of 2000 ft. the corresponding volume of air in the basin i! 4x 1013ff3. We shall use this system volume to mode1 the accumulation anc depletion of air pollutants. As a very rough first approximation. we shall trea

Halt of Fame the Lus Angeles basin as a well-mixed container (analogous to a CSTR) i r which there are no spatial variations in pollutant concentrations.

Chap. 1 Ouestions and Problems

Q ~ ~ c a n t s manklim or hills

C.A. vo W l n d f m

SFde view

Figure PI-14 Schematic diagmrns or the Loc AngeIes basin.

living Efample Prob!em

We shall perform an unsteady-stale mole balance on CO as i t is depreted from the basin area by a Santa Ano wind. Snnta Ana winds nre hrgh-velocity winds that originate in the Mojave Desert just to the northeast of Lw Angeles. Load the Smog in Los Angeles Raslin Web Module. Use the data in the module to work part 1-14 (a) through (h) given in the module. Load the living example polymath code and explore the problem. Fur part (I), vary the parameters D,,, n, and b. and write a paragraph describing what you find.

There i s heavier traffic in the L.A. basin in the mornings and in the eve- nings as workers go to and from work in downtown L.A. ConscquentIy, the flow of CO into the L.A. basin might be better represented by the sine function over a 24-hour period.

PI-ISB The reaction

is to be carried out isothermnl!y in a continuous-flow reactor. Calculate both the CSTR and PFR reacmr volumes necessary to consume 99% of A (i.e.. C4 = O.OICA,) when the entering molar flow rate is 5 molfh, assuming the reaction rate -rA is:

mol (a) -r, = k with k = 0.05 - (Am.: V = 99 dm3) h . dm'

(b) -rA = LC, with k = 0.0001 s-I dm'

(c) -rA = kc: with k = 3 - (Ans.: r/csre = 66,000 dm") moE . h

The entering volumetric flow rate is TO ddlh. (Note: FA = C,u. For a constant volumetric flow rate v = v , , then FA = C,u,, . Also. C,,, = F,dv, = [5 rnol/hl/llQ drnJlhJ = 0.5 molldrnJ .) (d) Repeat (a). (hl, and Ic) tocalculate the time necessary to consume 99.9%

of species A in a 1000 dm3 constant volume batch reactor with CAo = 0.5 molldm3.

P1-16* Write a one-pangraph Pummary of a journal articIe on chemical kinetics or reaction engineering. The articIe must have heen published within the lasr five years. What did you Iem from this article? Why 2s the article important?


P1-17, (a) There are initially 5 0 0 rabbits fx) and 200 foxes (y) on F m e r Oat's property. Use Polymath or MATLAB to plot the concentration of foxes and rabbits as a function of time for a period of up to 500 days. The predator-prey relationships are given by the following set of coupled ordinar). differential equatims:

Constant for growth of rabbits k, = 0.02 day ' Constant for death of rabbits k2 = 0 aKX34/(day x no. of foxes) Constani for p m h of foxes after eating labbits k, = O.N04/(day x no. of rabbitq) Constant for death of foxes Ir, = 0.04 duj-' What do your results look like for the case of k , = 0.00004/(day x no. of rabbits) and r,,,, = 8I)O daysq A l ~ o plot the number of foxes versus the number of rabb~ts. Explain why the curves look the way they do. Vary the parameters k , , k z . k7, and k,. Discuss which parameters can or cannot be larger than others. Write a paragraph describing what you find.

(b) Use Polymath or MATLAB to solve the following set of nonlinear algebraic equations:

Polymath Tutorial

with initial guesses of x = 2. = 2. Try to become familiar with the edit keys in Polymath MATLAB. See the CD-ROM for instructions.

Screen shots on how to run Polymath are shown at the end of Summary Notes Summary Notes for Chapter 1 on the CD-ROM and on the web.

PI-18, What if: (a) the benzene feed stream in Example R1.3-1 in the PRS were not pre-

heated by the product stream'? What would be the consequences? (b) you needed the cast of a 6000-gallon and a 15.000-gallon Pfaudler reac-

tor? What ~eould they be7 {c) the exit concenrration of A in Example 1-1 were specified at 0.1% of the

entering concentration? (d) ot~ly one operator showed up to run the nitrobenzene plant. What would

be some of >our firs1 concemc? PI-19, Enrim Ferrni (1901-19541 Problems (EEP). Enrico Ferrni was an Ftalran

physicist who received the Nohel Prize for his work on nuclear processes. Fermi was famous for h ~ s "Back of the B~velope Order of Mqnltude Caicu- Intion" to obtain an estimate' of the answer through logic and making reason- able assumptions. He used a process to set bounds on the answer hy saying i t is probably larger than one number and smaller than another and amved at an answer lhat was aithin a factor of 10. hrtp://tnarhfon~t~~. 0r~/wurk~hop1/~~in~96/i~~t~rdi.rc~/s~~1~~2. h1m1 Enrico Fcrmi Problem IEFP) #l How many piano tuners are there In the city of Chicago? Show the steps in yonr reasoning. I. Populat~un 01' Chicago 1. Ntlrnber of people per hourchold

Chap. 1 Supplementary Reading

3. Numkr of households 4. Households wlth pianos 5 . Average number of tunes per year 6. Etc. An answer is given on the web under Summary Notes for Chapter 1.

PI-20, EFP #2. How many square meters of pizza were eaten by an unde~raduare student body population of 20,000 during the Fail term 2W?

PI-21, This problem will be used in each of the following chapters to help develop critical-thinking skill$. (a ) Write a question about this problem that involve critical thinking. (b) What generalizations can you make about the results of this problem? (c) Write a question that will expand this problem.

PI-22 New material for the 2nd printing the following changesladditions have been made to h e 2nd printing.

NOTE TO INSTRUCTORS: Add~tional problems (cf. those from the preceding ed~tions) can be found in the solurin~is manual and on the CD-ROM. These problems could he photocopied and used ro lielp reinforce the fundamental princrples discusred in [hi\ chapler.

CDPT-A, Calculate the time to consume 80% af species A in a constant-volume batch reactor for a first- and a second-order reaction. (Includes SoIution)

CDP143, Derive the differential mole balance equation for a foam reactor. [Znd Ed. PI-loB]

Lolved Problems

S U P P L E M E N T A R Y R E A D I N G

1 . For further elaboration of the development of the general balance equation. see not only the web site wnn~.e~;gin.utnich.~dul-cre hut also

FELDER, R. M., and R. W. ROUSSEALJ, El~nterltot? Prfnciplex of Clzcnr~col Pro- cesses, 3rd ed. New York: Wile>/, 2200, Chapter 4.

HIMMELBLAU. D. M,, and J . D. Riggs. Basic Prinripl~s and Calcirlariorts in Chen~icnl E~tgi?~eeriltg, 7th ed. Upper Saddle Rwer, N.J.: Prentice Hall. 2004. Chapters 2 and h.

SANDERS. R . 1. . The Alrafninx ofSkzing, Denver. CO: Golden Bell Press, 1974.

2. A detailed explanation of a number af topics in ?his chapter can be found in

CRY~ES, R. L.. and H. S. FOCLEH, eds.. AlCItE Mndulular I~t.~rrucriorl Serz~r E. K ~ I I E Y ~ T S . VOIS. 1 and 2. New York: AlChE, 1981.

3. An excellent description of the various types of commercial reactors used in industry is found in Chapter I I of

WAIAS. S. M., Rencfiotl Kinerfc.s for CCheicuI Brgil~eers. New Y d McGnw-HiU, 1959.

1. A discussion nf some of the most important industr~al processes i s presented by

MEYERS, R.A., Handbook of Chcnlicols Pmd~rcriott Processes. New York: McGraw-H111. 1986

See also

MCKETTA. J. 1.. ~ d . . Etrryrloprriiu oj" Cl~e~rricnl Pmrrsse.~ urld Design. New York: Marcel Dckker. 197h.

36 Mola Balances Chap.

.4 simiIar book. which describes a larger nuniber o f processes, i s

AL'STIY. C. T.. S l ~ r e ~ ~ e ' ~ Clirrnicnl PTOCF.TF Indrrstrirs. 5th ed. New Yorb McGraw-Hill, 1984.

5. The following journals may be useful in obtaining infomation on chemical reac tiun engineering: Internotional Jo~~rnul of CS~ernEcrlE Kinetics, Joltrnnl of Car~ilyxi~ Journal of Applied Catul~r.~is. AlChE Jolurr ma/. CEwmical Engineering Scie~ce Canadian Journal of Chemical Etigineering, Chemical Drgzr~eering Comrnunica tro~ls, Joi~rnnl of Physical C.hettiisrr?: and Jndusrrrol nnd Engit~cerirrg Chemisrc Reseami1.

d 6. The price of chemicals ern be found in such journals as the Ch~ttiicoi Marketin! LlnRr Reporter, Cherniml Weekly3 and Chemical Engrr~eering News and on the ACS wet

site hrrp://pubs. acs.or~/c~n.

Conversion 2 and Reactor Sizing

Be more concerned with your character than with your reputation, because character is what you redly are while reputation is merely what others think you are.

John Wooden, coach, UCLA Bruins

Overview. In the first chapter, the general mole balance equation was detived and then applied to the four most common types of industrial reactors. A balance equation was developed for each reactor type and these equations are summarized in TabIe S-I. In Chapter 2, we will evaluate these equations to size CSTRs and PFRs. To size these reactors we first define conversion, which is a measure of the reaction's progress toward completion, and then rewrite all the balance equations in terms of conversion. These equations are ofren referred to as the design equations. Next, we show how one may size a reactor line., determine the reactor volume necessary to achieve a specified conversion) once the relationship between the reaction rate, - r ~ , and conversion, X, is known. In addition to being abIe to size C S R s and PFRs once given -r, =Am, another goal of this chapter is to compare CSTRs and PFRs and the overall conversions far reactors arranged in series. It is also important to arrive at the best arrangement of reactors in series.

After completing this chapter you will be able to size CSTRs and PFRs given the rate of reaction as a function of conversion and to calculate the overall conversion and reactor volumes for reactors arranged in series.