book

Chemical Reaction Engineering

by L.K. Doraiswamy, Deniz Uner

July 2013

Intermediate to advanced

578 pages

14h 38m

English

CRC Press

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ObjectivesIntroductionThe essential minimum of chemical reaction engineeringThe skill developmentGetting startedWarm-up questionsQualitativeQuantitative
Chapter objectivesIntroductionReaction ratesDifferent definitions of the rateBasic rate equationStoichiometry of the rate equationBasic relationshipsConversion–concentration relationshipsVariable-density reactionsReactorsBatch reactorReactions without volume changeReactions with volume changeNonisothermal operationOptimal operating policiesPlug-flow reactorsBasic PFR equationDesign equationsNonisothermal operationPerfectly mixed flow reactor (MFR)Basic CSTR equationNonisothermal operationMultiple steady statesMSS in a CSTRAdiabatic CSTRStability of the steady statesComparison of BR, PFR, and MFRExplore yourselfReferencesBibliography

Chapter objectivesIntroductionReduction of complex reactionsStoichiometry of simple and complex reactionsMathematical representation of simple and complex reactionsIndependent reactionsRate equationsThe concept of extent of reactionDetermination of the individual rates in a complex reactionSelectivity and yieldDefinitionsAnalytical solutionsMaximizing selectivity in a complex reaction: Important considerationsMultistep reactionsDefinitionsYield versus number of stepsReactor design for complex reactionsBatch reactor design based on number of componentsUse of extent of reaction or reaction coordinatesPlug-flow reactorContinuous stirred tank reactorReactor choice for maximizing yields/selectivitiesParallel reactions (nonreacting products)The general caseEffect of reaction orderOne of the reactants undergoes a second reactionParallel–consecutive reactionsPlug-flow reactor with recycleThe basic design equationOptimal design of RFRUse of RFR to resolve a selectivity dilemmaSemibatch reactorsConstant-volume reactions with constant rates of addition and removal: Scheme 1Variable-volume reactor with constant rate of inflow: Scheme 2Variable-volume reactor with constant rate of outflow of one of the products: Scheme 3General expression for an SBR for multiple reactions with inflow of liquid and outflow of liquid and vapor: Scheme 4Nonisothermal operationOptimum temperatures/temperature profiles for maximizing yields/selectivitiesOptimum temperaturesOptimum temperature and concentration profiles in a PFRParallel reactions Consecutive reactionsExtension to a batch reactorExplore yourselfReferencesBibliography
Reactive distillationMembrane reactorsInorganic membranes for organic reactions/synthesisPotentially exploitable features of membranesEquilibrium shift in membrane reactorsControlled addition of reactantsPreventing excess reactant “slip” in reactions requiring strict stoichiometric feedsMimicking trickle-bed operation with improved performanceCoupling of reactionsHybridizationPhase transfer catalysisReferences
Chapter objectivesIntroductionTwo limits of the ideal reactorPlug-flow reactors with recycleTanks-in-series modelNonidealities defined with respect to the ideal reactorsNonidealities in tubular reactorsAxial dispersion modelNonidealities in MFRResidence time distributionTheoryTypes of distributionConcept of mixingRegions of mixingFully segregated flowMicromixing policyModels for partial mixingAxial dispersion modelTanks-in-series modelModels for partial micromixingDegree of segregation defined by the age of the fluid at a pointTurbulent mixing modelsCharacteristic timescalesEngulfment-deformation diffusion modelInteraction by exchange with a meanZone modelJoint PDFPractical implications of mixing in chemical synthesisGeneral considerationsDramatic illustration of the role of addition sequence of reagentsExplore yourselfReferencesBibliography
Limits of mean field theoryThe predator–prey problem or surface mixingMixing problem addressedShort contact time reactorsMicrofluidic reactorsPassive devices for mixing and pumpingKnudsen pumpMixingSlug flow as a mixerDean flow as a static mixerElastic turbulenceReferences
IntroductionThe different tools of the tradeRelationship between thermodynamics and chemical reaction engineeringRelationship between transport phenomena and chemical reaction engineeringRelationship between chemical reaction engineering and kineticsChemical reaction engineering as an experimental and theoretical science
Chapter objectivesIntroductionBasic thermodynamic relationships and propertiesBasic relationshipsHeats of reaction, formation, and combustionImplications of liquid phase reactionsFree energy change and equilibrium constantStandard free energy change and equilibrium constantEquilibrium compositions in gas phase reactionsAccounting for condensed phase(s)Complex equilibriaSimultaneous solution of equilibrium equationsExtension to a nonideal systemMinimization of free energyThermodynamics of reactions in solutionPartial molar propertiesMedium and substituent effects on standard free energy change, equilibrium constant, and activity coefficientGeneral considerationsSolvent and solute operatorsCommentsExtrathermodynamic approachBasic principlesGroup contributions or additivity principleExtrathermodynamic relationships between rate and equilibrium parametersPolanyi and Brønsted relationsHammett relationship for dissociation constantsExtrathermodynamic approach to selectivityTheoretical analysisThermodynamics of adsorptionHenry’s lawLangmuir isothermInhomogeneities expressed in terms of a site-energy distributionTwo-dimensional equations of state and their corresponding adsorption isothermsAppendixDerivation of chemical equilibrium relationships for simple reactionsReactions in gas phaseReactions in liquid phaseExplore yourselfReferencesBibliography
Reactor design for thermodynamically limited reactionsKineticsOptimization of temperatures and pressuresReferences
Chapter objectivesChemical kineticsCollision theoryTransition state theoryProposing a kinetic modelBrief excursion for the classification of surface reaction mechanismsLangmuir–Hinshelwood–Hougen–Watson modelsLangmuir isothermRate-determining stepBasic procedureEley–Rideal mechanismMars–van Krevelen mechanismMichelis–Menten mechanismInfluence of surface nonidealityParadox of heterogeneous kineticsMicrokinetic analysisPostulate a mechanismDetermine the kinetic parametersSimplify the mechanismCompare the model predictions with the kinetic dataExplore yourselfReferencesBibliography
Chapter objectivesIntroductionDiffusivityDiffusivities in gasesDiffusivities in liquidsEffective diffusivityTransport between phasesGeneral remarksFilm theoryPenetration theorySurface renewal theoryCharacteristic times for diffusion, reaction, and mass transferTwo-film theory of mass and heat transfer for fluid–fluid reactions in generalMass transferHeat transferMass transfer across interfaces: FundamentalsSolid catalyzed fluid reactionsOverall schemeRole of diffusion in pellets: Catalyst effectivenessFirst-order isothermal reaction in a spherical catalystWeisz modulus: Practical useful quantityNonisothermal effectiveness factorsMulticomponent diffusionMiscellaneous effectsExtension to complex reactionsNoncatalytic gas–solid reactionsGas–liquid reactions in a slabTwo-film theorySlow reactionsInstantaneous reactionsEffect of external mass and heat transferExternal effectiveness factorCombined effects of internal and external diffusionRelative roles of mass and heat transfer in internal and external diffusionGas phase reactantsLiquid phase reactantsRegimes of controlExplore yourselfReferences
Chapter objectivesChemical reaction tests in a laboratoryA perspective on statistical experimental designBatch laboratory reactorsRate parameters from batch reactor dataFrom concentration dataFrom pressure dataFlow reactors for testing gas–solid catalytic reactionsDifferential versus integral reactorsEliminating or accounting for transport disguisesEliminating the film mass transfer resistanceEliminating the pore diffusion resistancesEliminating axial dispersion effectsKoros–Nowak criterionCatalyst dilution for temperature uniformityGradientless reactorsTransport disguises in perspectiveGuidelines for eliminating or accounting for transport disguisesAnalyzing the dataModeling of solid catalyzed reactionsThe overall schemeLHHW modelsSelection of the most plausible modelInfluence of surface nonidealityExplore yourselfReferences
ObjectivesIntroductionThe different tools of the tradeProcess intensificationMicrofluidicsMembrane reactorsCombo reactorsHomogeneous catalysisPhase-transfer catalysisReferences
Chapter objectivesIntroductionEffect of catalyst packing in a tubular reactorFixed-bed reactorNonisothermal, nonadiabatic, and adiabatic reactorsDesign methodologies for NINA-PBRQuasi-continuum modelsCell modelModels based on the pseudo-homogeneous assumptionHomogeneous, pseudo-homogeneous, and heterogeneous models1D pseudo-homogeneous nonisothermal, nonadiabatic flowReduction to isothermal operationMomentum balanceThe basic model: 2D pseudo-homogeneous nonisothermal, nonadiabatic with no axial diffusionExtension to nonideal models with and without heterogeneityAdiabatic reactorThe approachA unique conversion–temperature relationshipSingle-bed reactorMultiple-bed reactorA simple graphical procedureStrategies for heat exchangeChoice between NINA-PBR and A-PBRSome practical considerationsBackmixing or axial dispersionNonuniform catalyst distributions between tubesScale-up considerationsAlternative fixed-bed designsRadial-flow reactorsMaterial, momentum, and energy balancesMaterial balanceMass balanceMomentum balanceSome important observationsCatalytic wire-gauze reactorsExplore yourselfReferencesBibliography
Chapter objectivesGeneral commentsFluidization: Some basicsMinimum fluidization velocityTwo-phase theory of fluidizationGeldart’s classificationClassification of fluidized-bed reactorsVelocity limits of a bubbling bedFluid mechanical models of the bubbling bedComplete modeling of the fluidized-bed reactorBubbling bed model of fluidized-bed reactorsBubbling bedBubble rise velocityMain featuresMass transfer between bubble and emulsionSolids distributionEstimation of bed propertiesHeat transferCalculation of conversionEnd region modelsDilute bed regionGrid or jet regionPractical considerationsRecommended scale-up procedureStrategies to improve fluid-bed reactor performancePacked fluidized-bed reactorsReactor model for packed fluidized bedsStaging of catalystExtension to other regimes of fluidization types of reactorsTurbulent bed reactorFast fluidized-bed reactorTransport (or pneumatic) reactorCirculation systemsDeactivation controlHeat transfer controlledReactor choice for a deactivating catalystBasic equationFixed-bed reactorFluidized-bed reactorMoving bed reactorSome practical considerationsSluggingDefluidization of bed: Sudden deathGulf streamingEffects of finesStart-upFluidized-bed versus fixed-bed reactorsExplore yourselfReferences
Chapter objectivesIntroductionModeling of gas–solid reactionsShrinking core modelVolume reaction modelZone modelsThe particle–pellet or grain modelsOther modelsExtensions to the basic modelsBulk-flow or volume-change effectsEffect of temperature changeModels that account for structural variationsEffect of reactionEffect of sinteringA general model that can be reduced to specific onesGas–solid noncatalytic reactorsFixed-bed reactorsMoving-bed reactorsFluidized-bed reactorsReferences
Chapter objectivesIntroductionDiffusion accompanied by an irreversible reaction of general orderDiffusion and reaction in series with no reaction in film: Regimes 1 and 2 (very slow and slow reactions), and regimes between 1 and 2Regimes 1 and 2: Very slow and slow reactionsRegimes between 1 and 2Diffusion and reaction in film, followed by negligible or finite reaction in the bulk: Regime 3 (fast reaction), and regime covering 1, 2, and 3Reaction entirely in filmReactions both in film and bulk (regimes 1–2–3)Measurement of mass transfer coefficientsMicrofluidic devicesReactor designA generalized form of equation for all regimesRegime 1: Very slow reactionRegime 2 and regime between 1 and 2: Diffusion in film without and with reaction in the bulkRegime 3: Fast reactionRegime between 2 and 3Regime 4: Instantaneous reactionClassification of gas–liquid contactorsClassification-1 (based on manner of phase contact)Classification-2 (based on the manner of energy delivery)Mass transfer coefficients and interfacial areas of some common contactorsRole of backmixing in different contactorsReactor design for gas–liquid reactionsThe overall strategyCalculation of reactor volumeCase 1: Plug gas, plug liquid, and countercurrent steady stateCase 2: Same as case 1 but with cocurrent flowCase 3: Plug gas, mixed liquid, and steady stateCase 4: Mixed gas, mixed liquid, and steady stateCase 5: Mixed gas, batch liquid, and unsteady stateCommentsReactor choiceThe criteriaVolume minimization criterionGeneral discussionLimitations of volume minimizationSteps in volume minimizationEnergy minimization criteriaCriterion 2(a): Homogeneous regime (regime 1)Criterion 2(b): Heterogeneous regime (regimes 2–4)Comparison of criteriaLiquid–liquid contactorsClassification of liquid–liquid reactorsValues of mass transfer coefficients and interfacial areas for different contactorsCalculation of reactor volume/reaction timeStirred tank reactor: Some practical considerationsReferences
Chapter objectivesIntroductionDesign of three-phase catalytic reactorsThe approachSemibatch reactors: Design equations for (1,0)- and (1,1)-order reactionsContinuous reactorsTypes of three-phase reactorsMechanically agitated slurry reactorsMass transferMinimum speed for complete suspensionGas holdupControlling regimes in an MASRBubble column slurry reactorsRegimes of flowMass transferMinimum velocity for complete solids suspensionGas holdupLoop slurry reactorsTypes of loop reactorsMass transferTrickle bed reactors (TBRs)Regimes of flowMass transferControlling regimes in TBRsCollection and interpretation of laboratory data for three-phase catalytic reactionsExperimental methodsEffect of temperatureInterpretation of dataThree-phase noncatalytic reactionsSolid slightly solubleNegligible dissolution of solid in the gas–liquid filmSignificant dissolution of solid in the gas–liquid filmSolid insolubleReferencesBibliography
IntroductionGeneral considerationsMajor types of membrane reactorsModeling of membrane reactorsPacked-bed inert selective membrane reactor with packed catalyst (IMR-P)Model equationsExtension to consecutive reactionsFluidized-bed inert selective membrane reactor (IMR-F)Catalytic selective membrane reactor (CMR-E)Main features of the CMR-EPacked-bed catalytic selective membrane reactor (CMR-P)Catalytic nonselective membrane reactor (CNMR-E)Catalytic nonselective hollow membrane reactor for multiphase reactions (CNHMR-MR)Immobilized enzyme membrane reactorOperational featuresCombining exothermic and endothermic reactionsControlled addition of one of the reactants in a bimolecular reaction using an IMR-PEffect of tube and shell side flow conditionsComparison of reactorsEffect (1)Effect (2)Combined effectExamples of the use of membrane reactors in organic technology/synthesisSmall- and medium-volume chemicalsVitamin KLinalool (a fragrance)Membrane reactors for economic processes (including energy integration)References
Distillation column reactorEnhancing role of distillation: Basic principleBatch reactor with continuous removal of productCase 1: Accumulation of SCase 2: S is not completely vaporizedPacked DCROverall effectiveness factor in a packed DCRResidue curve map (RCM)Design methodologyGenerating residual curve mapsDistillation–reactionDissociation–extractive distillationBasic principleTheoryReferences
IntroductionGeneralFormalisms in transition metal catalysisUniqueness of transition metalsOxidation state of a metalCoordinative unsaturation, coordination number, and coordination geometryLigands and their role in transition metal catalysisElectron rules (“electron bookkeeping”)18-electron rule16–18-electron ruleOperational scheme of homogeneous catalysisBasic reactions of homogeneous catalysisReactions of ligands (mainly replacement)Elementary reactions (or activation steps)Coordination reactionsAddition reactionsMain reactionsInsertionEliminationMain features of transition metal catalysis in organic synthesis: A summaryA typical class of industrial reactions: HydrogenationHydrogenation by Wilkinson’s catalystWilkinson’s catalystThe catalytic cycleKinetics and modelingA general hydrogenation modelGeneral kinetic analysisIntrinsic kineticsMultistep controlRole of diffusionComplex kinetics—Main issueReactions involving one gas and one liquidRegimes 1 and 2Regime between 1 and 2 (reaction in bulk)Regime 3 (reaction in film)Two gases and a liquidReferences
IntroductionWhat is PTC?Fundamentals of PTCClassification of PTC systemsPhase-transfer catalystsMechanism of PTCLiquid–liquid PTCSolid–liquid PTCSolid-supported PTC or triphase catalysis (TPC)Modeling of PTC reactionsLLPTC modelsSLPTC modelsInterpretation of the role of diffusion: A cautionary noteSupported PTC (TPC)Kinetic mechanism of TPC systemsMethodology for modeling solid-supported PTC reactionsSupported PTC with LHHW kinetics“Cascade engineered” PTC processReferences
ObjectiveIntroductionResource economyCarbon and hydrogenBio-renewablesEnergy economyHeat integration in microreactorsSonochemical reaction triggeringPhotochemical or photocatalytic systemsElectrochemical techniquesMicrowavesChemical reaction engineer in the twenty-first centuryIn Closing

Content preview from Chemical Reaction Engineering

Chapter 13 Membrane-assisted reactor engineering

Introduction

We commenced our treatment with an introduction to the exploitable features of membrane reactors (without attempting to describe membrane synthesis) earlier in this book. We gave a brief introduction for the membrane reactors in Interlude I following Chapter 2. In this chapter, we describe the main variations in design and mode of operation of these reactors, develop performance equations for the more important designs, and compare the performances of some important designs with those of the traditional mixed and plug-flow reactors. Finally, we present a summary of the applications of membrane reactors in enhancing the rates of organic reactions.