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Essentials of Chemical Reaction Engineering Essentials of Chemical Reaction Engineering Second Edition This page intentionally left blank Essentials of Chemical Reaction Engineering Second Edition H. SCOTT FOGLER Ame and Catherine Vennema Professor of Chemical Engineering and the Arthur F. Thurnau Professor The University of Michigan, Ann Arbor Boston • Columbus • Indianapolis • New York • San Francisco • Amsterdam • Cape Town Dubai • London • Madrid • Milan • Munich • Paris • Montreal • Toronto • Delhi • Mexico City São Paulo • Sydney • Hong Kong • Seoul • Singapore • Taipei • Tokyo Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this book, and the publisher was aware of a trademark claim, the designations have been printed with initial capital letters or in all capitals. The author and publisher have taken care in the preparation of this book, but make no expressed or implied warranty of any kind and assume no responsibility for errors or omissions. No liability is assumed for inci- dental or consequential damages in connection with or arising out of the use of the information or programs contained herein. For information about buying this title in bulk quantities, or for special sales opportunities (which may include electronic versions; custom cover designs; and content particular to your business, training goals, marketing focus, or branding interests), please contact our corporate sales department at corpsales@pear- soned.com or (800) 382-3419. For government sales inquiries, please contact
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[email protected] http://informit.com http://www.pearsoned.com/permissions/ Dedicated to Janet Meadors Fogler For her companionship, encouragement, sense of humor, love, and support throughout the years This page intentionally left blank vii Contents PREFACE xv ABOUT THE AUTHOR xxxi CHAPTER 1 MOLE BALANCES 1 1.1 The Rate of Reaction, –rA 4 1.2 The General Mole Balance Equation 8 1.3 Batch Reactors (BRs) 10 1.4 Continuous-Flow Reactors 12 1.4.1 Continuous-Stirred Tank Reactor (CSTR) 12 1.4.2 Tubular Reactor 14 1.4.3 Packed-Bed Reactor (PBR) 18 1.5 Industrial Reactors 23 CHAPTER 2 CONVERSION AND REACTOR SIZING 33 2.1 Definition of Conversion 34 2.2 Batch Reactor Design Equations 34 2.3 Design Equations for Flow Reactors 37 2.3.1 CSTR (Also Known as a Backmix Reactor or a Vat) 38 2.3.2 Tubular Flow Reactor (PFR) 38 2.3.3 Packed-Bed Reactor (PBR) 39 2.4 Sizing Continuous-Flow Reactors 40 2.5 Reactors in Series 49 2.5.1 CSTRs in Series 50 2.5.2 PFRs in Series 54 2.5.3 Combinations of CSTRs and PFRs in Series 55 2.5.4 Comparing the CSTR and PFR Reactor Volumes and Reactor Sequencing 59 viii Contents 2.6 Some Further Definitions 60 2.6.1 Space Time 60 2.6.2 Space Velocity 62 CHAPTER 3 RATE LAWS 71 3.1 Basic Definitions 72 3.1.1 Relative Rates of Reaction 73 3.2 The Rate Law 74 3.2.1 Power Law Models and Elementary Rate Laws 75 3.2.2 Nonelementary Rate Laws 78 3.2.3 Reversible Reactions 82 3.3 The Reaction Rate Constant 85 3.3.1 The Rate Constant k and Its Temperature Dependence 85 3.3.2 Interpretation of the Activation Energy 86 3.3.3 The Arrhenius Plot 92 3.4 Molecular Simulations 95 3.4.1 Historical Perspective 95 3.4.2 Stochastic Modeling of Reactions 96 3.5 Present Status of Our Approach to Reactor Sizing and Design 99 CHAPTER 4 STOICHIOMETRY 111 4.1 Batch Systems 113 4.1.1 Batch Concentrations for the Generic Reaction, Equation (2-2) 115 4.2 Flow Systems 119 4.2.1 Equations for Concentrations in Flow Systems 120 4.2.2 Liquid-Phase Concentrations 120 4.2.3 Gas-Phase Concentrations 121 4.3 Reversible Reactions and Equilibrium Conversion 132 CHAPTER 5 ISOTHERMAL REACTOR DESIGN: CONVERSION 147 5.1 Design Structure for Isothermal Reactors 148 5.2 Batch Reactors (BRs) 152 5.2.1 Batch Reaction Times 153 5.3 Continuous-Stirred Tank Reactors (CSTRs) 160 5.3.1 A Single CSTR 160 5.3.2 CSTRs in Series 163 5.4 Tubular Reactors 170 5.4.1 Liquid-Phase Reactions in a PFR υ = υ0 171 5.4.2 Gas-Phase Reactions in a PFR υ = υ0 (1 + εX) (T/T0)(P0/P) 172 5.4.3 Effect of ε on Conversion 172 5.5 Pressure Drop in Reactors 177 5.5.1 Pressure Drop and the Rate Law 177 5.5.2 Flow Through a Packed Bed 178 5.5.3 Pressure Drop in Pipes 182 Contents ix 5.5.4 Analytical Solution for Reaction with Pressure Drop 185 5.5.5 Robert the Worrier Wonders: What If… 189 5.6 Synthesizing the Design of a Chemical Plant 199 CHAPTER 6 ISOTHERMAL REACTOR DESIGN: MOLES AND MOLAR FLOW RATES 217 6.1 The Molar Flow Rate Balance Algorithm 218 6.2 Mole Balances on CSTRs, PFRs, PBRs, and Batch Reactors 218 6.2.1 Liquid Phase 218 6.2.2 Gas Phase 220 6.3 Application of the PFR Molar Flow Rate Algorithm to a Microreactor 222 6.4 Membrane Reactors 227 6.5 Unsteady-State Operation of Stirred Reactors 236 6.6 Semibatch Reactors 237 6.6.1 Motivation for Using a Semibatch Reactor 237 6.6.2 Semibatch Reactor Mole Balances 237 6.6.3 Equilibrium Conversion 243 CHAPTER 7 COLLECTION AND ANALYSIS OF RATE DATA 255 7.1 The Algorithm for Data Analysis 256 7.2 Determining the Reaction Order for Each of Two Reactants Using the Method of Excess 258 7.3 Integral Method 259 7.4 Differential Method of Analysis 263 7.4.1 Graphical Differentiation Method 264 7.4.2 Numerical Method 264 7.4.3 Finding the Rate-Law Parameters 265 7.5 Nonlinear Regression 271 7.5.1 Concentration–Time Data 273 7.5.2 Model Discrimination 276 7.6 Reaction-Rate Data from Differential Reactors 276 7.7 Experimental Planning 283 CHAPTER 8 MULTIPLE REACTIONS 293 8.1 Definitions 294 8.1.1 Types of Reactions 294 8.1.2 Selectivity 295 8.1.3 Yield 296 8.1.4 Conversion 296 8.2 Algorithm for Multiple Reactions 297 8.2.1 Modifications to the Chapter 6 CRE Algorithm for Multiple Reactions 298 x Contents 8.3 Parallel Reactions 300 8.3.1 Selectivity 300 8.3.2 Maximizing the Desired Product for One Reactant 300 8.3.3 Reactor Selection and Operating Conditions 306 8.4 Reactions in Series 309 8.5 Complex Reactions 319 8.5.1 Complex Gas-Phase Reactions in a PBR 319 8.5.2 Complex Liquid-Phase Reactions in a CSTR 323 8.5.3 Complex Liquid-Phase Reactions in a Semibatch Reactor 325 8.6 Membrane Reactors to Improve Selectivity in Multiple Reactions 327 8.7 Sorting It All Out 332 8.8 The Fun Part 332 CHAPTER 9 REACTION MECHANISMS, PATHWAYS, BIOREACTIONS, AND BIOREACTORS 349 9.1 Active Intermediates and Nonelementary Rate Laws 350 9.1.1 Pseudo-Steady-State Hypothesis (PSSH) 351 9.1.2 If Two Molecules Must Collide, How Can the Rate Law Be First Order? 354 9.1.3 Searching for a Mechanism 355 9.1.4 Chain Reactions 359 9.2 Enzymatic Reaction Fundamentals 359 9.2.1 Enzyme–Substrate Complex 360 9.2.2 Mechanisms 361 9.2.3 Michaelis–Menten Equation 364 9.2.4 Batch-Reactor Calculations for Enzyme Reactions 370 9.3 Inhibition of Enzyme Reactions 372 9.3.1 Competitive Inhibition 373 9.3.2 Uncompetitive Inhibition 376 9.3.3 Noncompetitive Inhibition (Mixed Inhibition) 377 9.3.4 Substrate Inhibition 379 9.4 Bioreactors and Biosynthesis 380 9.4.1 Cell Growth 383 9.4.2 Rate Laws 385 9.4.3 Stoichiometry 388 9.4.4 Mass Balances 394 9.4.5 Chemostats 398 9.4.6 CSTR Bioreactor Operation 399 9.4.7 Wash-Out 400 CHAPTER 10 CATALYSIS AND CATALYTIC REACTORS 419 10.1 Catalysts 419 10.1.1 Definitions 420 10.1.2 Catalyst Properties 421 10.1.3 Catalytic Gas-Solid Interactions 423 10.1.4 Classification of Catalysts 424 Contents xi 10.2 Steps in a Catalytic Reaction 425 10.2.1 Mass Transfer Step 1: Diffusion from the Bulk to the External Surface of the Catalyst—An Overview 428 10.2.2 Mass Transfer Step 2: Internal Diffusion—An Overview 429 10.2.3 Adsorption Isotherms 430 10.2.4 Surface Reaction 436 10.2.5 Desorption 438 10.2.6 The Rate-Limiting Step 439 10.3 Synthesizing a Rate Law, Mechanism, and Rate-Limiting Step 441 10.3.1 Is the Adsorption of Cumene Rate-Limiting? 444 10.3.2 Is the Surface Reaction Rate-Limiting? 447 10.3.3 Is the Desorption of Benzene Rate-Limiting? 449 10.3.4 Summary of the Cumene Decomposition 450 10.3.5 Reforming Catalysts 452 10.3.6 Rate Laws Derived from the Pseudo-Steady- State Hypothesis (PSSH) 456 10.3.7 Temperature Dependence of the Rate Law 456 10.4 Heterogeneous Data Analysis for Reactor Design 457 10.4.1 Deducing a Rate Law from the Experimental Data 457 10.4.2 Finding a Mechanism Consistent with Experimental Observations 459 10.4.3 Evaluation of the Rate-Law Parameters 461 10.4.4 Reactor Design 463 10.5 Reaction Engineering in Microelectronic Fabrication 467 10.5.1 Overview 467 10.5.2 Chemical Vapor Deposition 469 10.6 Model Discrimination 472 10.7 Catalyst Deactivation 475 10.7.1 Types of Catalyst Deactivation 477 10.8 Reactors That Can Be Used to Help Offset Catalyst Decay 485 10.8.1 Temperature–Time Trajectories 486 10.8.2 Moving-Bed Reactors 488 10.8.3 Straight-Through Transport Reactors (STTR) 492 CHAPTER 11 NONISOTHERMAL REACTOR DESIGN–THE STEADY- STATE ENERGY BALANCE AND ADIABATIC PFR APPLICATIONS 515 11.1 Rationale 516 11.2 The Energy Balance 517 11.2.1 First Law of Thermodynamics 517 11.2.2 Evaluating the Work Term 518 11.2.3 Overview of Energy Balances 520 11.3 The User-Friendly Energy Balance Equations 525 11.3.1 Dissecting the Steady-State Molar Flow Rates to Obtain the Heat of Reaction 525 11.3.2 Dissecting the Enthalpies 527 11.3.3 Relating �H Rx (T), �H�Rx (T R), and �C P 528 xii Contents 11.4 Adiabatic Operation 531 11.4.1 Adiabatic Energy Balance 531 11.4.2 Adiabatic Tubular Reactor 532 11.5 Adiabatic Equilibrium Conversion 541 11.5.1 Equilibrium Conversion 541 11.6 Reactor Staging with Interstage Cooling or Heating 546 11.6.1 Exothermic Reactions 546 11.6.2 Endothermic Reactions 547 11.7 Optimum Feed Temperature 550 CHAPTER 12 STEADY-STATE NONISOTHERMAL REACTOR DESIGN—FLOW REACTORS WITH HEAT EXCHANGE 565 12.1 Steady-State Tubular Reactor with Heat Exchange 566 12.1.1 Deriving the Energy Balance for a PFR 566 12.1.2 Applying the Algorithm