新MultiphaseReactionEngineering

1、Multiphase Reaction EBuidling 10-2009, 87951620DefinitionPropertiesClassificationMultiphase Reaction Engineering2DefinitionPropertiesClassification3Multiphase Reaction EngineeringTentative Schedule12/3/1412/8/1412/1/1411/26/1412/10/144Kinetics of Fluid-Fluid ReactionsIntroduction & CatalystsKinetics

2、 of Solid Catalyzed ReactionsKinetics of Solid Catalyzed ReactionsExternal Diffusion and DiffusionTextbooks and MaterialsChemical Reaction Engineering by Octave Levenspiel 12Elements of Chemical Reaction Engineering by H. Scott Fogler5Multiphase Reaction Engineering Complication of rate expressionCo

3、mplication of contacting patterns Other thoughts on flow modelingMovement of material from phase to phaseIncorporate mass transfer terms into chemical kinetics termReal flow deviates from ideal flow patternsA simple reasonable model is much betterIntroduction to Multiphase Reactions6Complication of

4、the Rate EquationTell how many rate steps are involved. The kinetics is given byand ignore the possible formation of CO. 22COOC7Tell how many rate steps are involved when air bubbles through a tank of liquid which contains dispersed microbes and is taken up by the microbes to produce product materia

5、l.Complication of the Rate Equation8Complication of the Rate Equation9Complication of the Rate EquationIf the steps are in series, as in Examples 17.1 and 17.2If they are in parallel10Dilute A diffuses through a stagnant liquid film onto a plane surface consisting of B, reacts there to produce R whi

6、ch diffuseback into the mainstream. Develop the overall rate expression for the L/S reaction which takes place on this flat surface.)()()(lRsBlAComplication of the Rate Equation11Complication of the Rate Equation12Complication of the Rate Equation13Complication of the Rate Equation14Complication of

7、the Contacting Patterns15Final Thoughts on Flow ModelingSimple reasonable model nonrepresentative modelKnowledge of flow pattern changes with scale-up16Catalysts17History over 2000 years1835Berzelius small amounts great effect 1894Ostwald catalysts accelerate without.1996 sales of process catalysts

8、$1 billion in US 2005 catalytic process 900 billion worldwide2007sales of process catalysts $3.5 billion in USCatalystsDefinitionPropertiesClassificationAdsorptionDeactivationRegeneration18Catalysts DefinitionDefinitionPropertiesClassificationreactioncatalystDecomposition of hydrogen peroxidemangane

9、se(IV) oxide, MnO2Nitration of benzeneconcentrated sulphuric acidManufacture of ammonia by the Haber ProcessironConversion of SO2 into SO3 during the Contact Process to make sulphuric acidvanadium(V) oxide, V2O5Hydrogenation of a C=C double bondnickelSubstance which affects reaction ratebut is chemi

10、cally unchanged at the end of the reaction 19Catalysts DefinitionDefinitionPropertiesClassification20Catalysts DefinitionDefinitionPropertiesClassification21Catalysts DefinitionDefinitionPropertiesClassification22Catalysts DefinitionDefinitionPropertiesClassification23Catalysts Properties24high cata

11、lytic activitygood selectivityCatalysts Properties25high catalytic activity4000/45500exp/ /32500exp/(/50032(/455000245183451832 RTRTkkCatalystasImolCalECOCHCHOCHCatalystNomolCalECOCHCHOCHcatACIAC）Catalysts Properties26good selectivityOHCHCHCHCHOHHCOHOHCOHHCOHHCOHHCHCHOCHOHHCCOCrZnOCPOHCOAlCCu2225004

12、60,522252140,52242360350,5223250200,522)(324332Catalysts Propertiesgood selectivity for desired products1high activity for desired reaction2stable performance for long periods3good accessibility of participants to surface427Desired Characteristics of a Good Commercial CatalystCatalysts PropertiesFlu

13、idized bed, 20 to 200 microns1Fixed bed, 4 to 8 mesh,1 to 20mm2Moving bed, 4 to 8 mesh,1 to 20mm3Slurry, powders of 400 mesh or so428Physical Properties of Granular Catalyst ： SIZE Catalysts Propertiesspecific surface1particle diameter2porosity3pore diameter429Physical Properties of Granular Catalys

14、t Sg=aVmN0/VSg=4.25Vm m2/g catalystdpmean=2Vp/Sgp=pVgCatalysts ClassificationDefinitionPropertiesClassification30Catalysts ClassificationDefinitionPropertiesClassification31nature of species responsible for catalytic activity Molecular catalysis Surface catalysis Enzyme catalysis Autocatalysis Homog

15、eneous catalysis Heterogeneous catalysisCatalysts ClassificationDefinitionPropertiesClassification32Typical catalytic materialsProton acidMultifunctional solidsTransition metalsLate transition metalsCatalysts ClassificationDefinitionPropertiesClassification33Alkylation and Dealkylation ReactionsIsom

16、erization ReactionsHydrogenation and Dehydrogenation Reactions Oxidation ReactionsHydration and Dehydration ReactionsHalogenation and Dehalogenation Reactions Catalysts ClassificationDefinitionPropertiesClassification34Alkylation and Dealkylation Reactions Friedel-Crafts catalystsAlCl3 along with a

17、trace of HClSilica-alumina, silica-magnesia, a clay ( montmorillonite ) Catalysts ClassificationAcid-promoted Al2O3Acid sites and hydrogenation sites such as Pt on Al2O335Isomerization Reactions Catalysts ClassificationCo, Ni, Rh, Ru, Os, Pd, Ir, and Pt.V, Cr, Mo, Ta, and W.36Hydrogenation and Dehyd

18、rogenation Reactions possible catalysts: calcium nickel phosphate, Cr2O3, etc.Catalysts ClassificationAg, Cu, Pt, Fe, Ni, and their oxidesV2O5 and MnO237Oxidation Reactions Catalysts ClassificationAlumina, silica-alumina gels, clays, phosphoric acid, and phosphoric acid salts.38Hydration and Dehydra

19、tion Reactions Catalysts ClassificationSelectivity of the desired product is lowA lower temperature is necessary39Halogenation and Dehalogenation Reactions Silver halidesSupported copperCatalysts Adsorption PHYSICAL ADSORPTION PhysisorptionCHEMICALADSORPTIONChemisorption40AdsorbateAdsorbentDefinitio

20、nPropertiesClassificationCatalysts Adsorption41Oxygen molecules (red) adsorb on a bimetallic surface of platinum (purple) and cobalt (green).DefinitionPropertiesClassificationCatalysts Adsorption42vander Waals forcesvalence forcesheat of adsorption1-15 kcal/mol.heat of adsorption10-100 kcal/molNo co

21、mpound formationSurface compounds formed.reversible processirreversible processNo activation energy requiredactivation energy requireddecreases with increase of Tfirst increases with increase of T not specific in naturespecific in natureadsorbed amount related to no such correlationmultimolecular la

22、yerunimolecular layerDefinitionPropertiesClassificationCatalysts Adsorption43Ethylidyne as chemisorbed on platinumDefinitionPropertiesClassificationCatalysts Adsorption44DefinitionPropertiesClassificationCatalysts Adsorption45adsorption rate of A or B?Equation of FreundlichTempkin equationBET(Brunau

23、er-Emmett-Teller) isothermLangmuir isotherm DefinitionPropertiesClassificationCatalysts Adsorption46Equation of Freundlichpurely empiricalapply to liquid and gas phasesat moderate pressuresAAnAAAddAAaaPnbbPkrPkrln1lnln1+=n, n1, b=(ka /kd)1/nDefinitionPropertiesClassificationCatalysts Adsorption47Tem

24、pkin equationsemi theoretical backgroundapply to production of ammonia and sulfuric acid)ln(1AAhddgAaaaPfekrePkrAAg+h=fa=ka /kdDefinitionPropertiesClassificationCatalysts Adsorption48A(g) + S AS A(g) + AS A2S A(g) + A2S A3S and so on00) 1(1)(CPVPCCVPPVPmmBET(Brunauer-Emmett-Teller) isothermTrue pict

25、ure of physical AdsorptionDefinitionPropertiesClassificationCatalysts Adsorption49Langmuir isotherm (red) and BET isotherm=(green)condition of high pressure and low temperatureDefinitionPropertiesClassificationCatalysts Adsorption50Langmuir isothermSurface of the adsorbent is uniform Adsorbed molecu

26、les do not interact.All adsorption occurs through the same mechanismA monolayer is formedFour assumptionsAADefinitionPropertiesClassificationCatalysts Adsorption51ra=kaPA(1-A) rd=kdA ra=rd A=KAPA/(1+KAPA)KA=ka/kdLangmuir isothermAADefinitionPropertiesClassificationCatalysts Adsorption52Extension of

27、the Langmuir EquationAAAAAAAPKPK1AA222AAAAAPKPK1AABB1VBABBAAVVBBBVAAAPKPKPKPK11AA222BBVBBBVAAABBAAVPKPKPKPK111VBAAA333BBCCVCCCVBBBVAAACCBBAAVPKPKPKPKPKPK33111VCBADefinitionPropertiesClassificationCatalysts Adsorption53Nondissociated adsorption OR dissociative adsorption ?COCOOCCO 2AAAAAAAPKPK1BAAB 2

28、AABBCOAVVCOAABABAaVCOaPKPKkPk2112DefinitionPropertiesClassificationCatalysts Deactivation54sintering or agingfouling or cokingpoisoningTypes of Catalyst Deactivationflow of the solid porous catalyst supportCatalysts Deactivation55Deactivation by Sintering (Aging)pore closureCatalysts Deactivation56D

29、eactivation by Sintering (Aging) atomic migration agglomeration of small metal siteslarger siteinterior atoms not accessible DefinitionPropertiesClassificationCatalysts Deactivation57Deactivation by Coking or Fouling 2000 to 3000 kPa hydrogen-rich streamsburning off the carbonDefinitionPropertiesCla

30、ssificationCatalysts Deactivation58Deactivation by Poisoningpoisoning molecules irreversibly chemisorbed to active sites a reactant and/or a product an impurity in the feed streamtrace impurities too costly to remove DefinitionPropertiesClassificationCatalysts Deactivation59Three methods to handle d

31、ecaying catalystSlow decay - Temperature-Time Trajectories Moderate decay - Moving-Bed Reactors Rapid decay - Straight-Through Transport Reactors DefinitionPropertiesClassificationCatalysts Deactivation60Catalysts Deactivation61DefinitionPropertiesClassificationCatalysts Deactivation62Straight-Throu

32、gh Transport ReactorsDefinitionPropertiesClassificationCatalysts Regeneration63Increasing gas-phase oxygen concentration and temperature006CADRteCCCDefinitionPropertiesClassificationMultiphase Catalytic Reaction Kinetics64 Surface Kinetics Pore Diffusion Resistance Particle T Film T Film Diffusion R

33、esistancekinetic rate equationsMultiphase Catalytic Reaction Kinetics65123gas/porous catalyst systems slow reactions gas/porous catalyst systems faster reactions liquid /porous catalyst systems slow reactions /, , Multiphase Catalytic Reaction Kinetics66Rate Equation for Surface KineticsPore Diffusi

34、on ResistanceHeat Effects during ReactionDetermine Resistance and RatesSelectivity for Multiple ReactionsMultiphase Catalytic Reaction Kinetics67REACTIONDESORPTIONADSORPTIONA molecule is adsorbed onto the surface and is attached to an active site.It reacts with another moleculeOr decomposes Products

35、 are desorbed from the surfaceand free the site.Rate Equation For Surface Kinetics68Rate Equation For Surface Kinetics69SRBASSRRSRBABBstepgcontrollinAASSRRBBBSRBrSRBSRAPKPKPKPPPKKKKKPPPPkr1)/(akk SRBArKKKKKK/Rate Equation For Surface Kinetics70SSRRstepgcontrollinSRBABBAASRBA2)(1)/(SSRRBBAASRBAPKPKPK

36、PKKPPPPkrBArKKkk SRBArKKKKKK/Rate Equation For Surface Kinetics71SSstepgcontrollinRRSRBABBAASSSBASBArBBAARSBAPKPPPKKKKPKPKKPPPPkr1)/(SBArRKKKKkk/SRBArKKKKKK/Rate Equation For Surface Kinetics72SSRRSRBABBstepgcontrollinAA2/12/12222)(1)/(SSRRBBBSRBSRBSRAPKPKPKPPPKrKKKKPPPPkrakk SRBArKKKKKK/Rate Equati

37、on For Surface Kinetics73Hougen and Watson (1947) Corrigan (1954, 1955) Walas (1959)Pore Diffusion Resistance 74Single Cylindrical Pore, First-Order ReactionRepresentation of a cylindrical catalyst porePore Diffusion Resistance 75Setting up the material balance for the elementary slice of catalyst p

38、orePore Diffusion Resistance 76Pore Diffusion Resistance 77Pore Diffusion Resistance 78MT =mL Thiele modulus.Pore Diffusion Resistance 79Distribution and average value of reactant concentration within a catalyst pore as a function of the parameter mLPore Diffusion Resistance 80= CA/CAs for first-ord

39、er reactions Pore Diffusion Resistance 81The effectiveness factor as a function of the parameter Thiele modulus mL or MTPore Diffusion Resistance 82MT or mL 4, = l/mL negligible pore diffusion resistancestrong pore resistancePore Diffusion Resistance 83Proper measure of particle sizecharacteristic s

40、ize of particle LPore Diffusion Resistance 84Pore Diffusion Resistance 85 with MT for the various particle shapesPore Diffusion Resistance 86Effectiveness factor versus MT for porous particles of various shapes87Finding pore resistance effects from experimentWagner-Weisz-Wheeler modulus Wagner modul

41、us Mw Pore resistance limitsMT 0.4 or Mw 4 or Mw 4Pore Diffusion Resistance 88Pore resistance limitslimits for negligible and for strong pore diffusion resistancePore Diffusion Resistance 89Pore Diffusion Resistance Particles of Different Sizesdiffusion-free regimestrong diffusion resistance90Pore D

42、iffusion Resistance ExtensionsMixture of Particles of Various Shapes and SizesMolar Volume Change91Pore Diffusion Resistance Arbitrary Reaction KineticsExtensionsfirst-order reversible reactionsfor nth-order irreversible reactions92Pore Diffusion Resistance In regime of strong pore resistance0 order

43、 becomes1/2 order1st order remains 1st order2nd order becomes 1.5 order3rd order becomes 2nd order93Pore Diffusion Resistance In regime of strong pore resistance94Pore Diffusion Resistance Summary-Diffusion Resistance in Pores95Pore Diffusion Resistance Fine solidsSummary-Diffusion Resistance in Por

44、esfree of pore diffusion resistancelarge pdifficult to useLarge particlesstrong pore diffusionsmall pinterior unusedlargest particle size still free of diffusional resistanceHeat Effects During Reaction96exothermic reactionParticles hotter than surrounding fluid Nonisothermal rate isothermal rate en

45、dothermic reactionsParticles cooler than surrounding fluidNonisothermal rate isothermal rateENCOURAGE nonisothermal behavior in EXOTHERMIC reactionsOR ?DEPRESS nonisothermal behavior for ENDOTHERMIC reactionssintering of drop in Heat Effects During Reaction97Film Twithin-particle THeat Effects Durin

46、g Reaction98Nonisothermal effectiveness factor curve for temperature variation within the particle.Determine Controlling Resistance and Rates99Criterion for film resistance / external diffusionactual reaction rate versus diffusion ratekobsVp kgSexfilm resistance affects the ratekobsVp kgSexfilm resi

47、stance controlling 100Determine Controlling Resistance and RatesMears Criterion for film resistance / external diffusionn = reaction orderR = catalyst particle radiusb = bulk density of catalyst bedkc = mass transfer coefficientCAb = bulk concentrationh = heat transfer coefficientRg = gas constantHR

48、x = heat of reactionE = activation energy101Determine Controlling Resistance and RatesCriterion for pore resistance / internal diffusionCalculation if De is knownComparing rates for different pellet sizestemperature activation energy? reaction order?102Determine Controlling Resistance and RatesDeter

49、mination of Limiting Situations from Reaction DataSelectivity for Multiple Reactions103unwantedWSRdesiredCBAkk21ssskCCCakr)(00111Ckakrsexternal diffusionSelectivity MT1MT2, 1k2 01102221)(1)1)(1)(1RAsARsCkakCkakrrS（104Selectivity for Multiple ReactionsunwantedSAdesiredRAkk212121aASaARCkrCkra1=a2 sele

50、ctivity S a1a2 selectivity S 105Selectivity for Multiple ReactionsSdesiredRA)(106Fluid-Fluid ReactionKineticsproduct of reaction desired materialremoval of unwanted component107Fluid-Fluid ReactionKinetics Overall Rate ExpressionEquilibrium SolubilityContacting Schememass transfer chemical ratesreac

51、tion in one or both phasesgas-liquid systemsliquid-liquid systemssemibatch countercurrentmixed flowbatchcountercurrent concurrent108Fluid-Fluid ReactionKinetics109Fluid-Fluid ReactionKineticsThe Two-film Theory110Fluid-Fluid ReactionKineticsRate Equation for Straight Mass Transfer (Absorption) of A1

52、11Fluid-Fluid ReactionKineticsRate Equation for Straight Mass Transfer (Absorption) of A112Fluid-Fluid Reaction KineticsHenrys law pAi=HACAiRate Equation for Straight Mass Transfer (Absorption) of A113Fluid-Fluid ReactionKinetics114Fluid-Fluid ReactionKineticsRate Equation for Mass Transfer and ReactionCase A: Instantaneous reaction with low CBCase B: Instantaneous reaction with high CBCase C: Fast reaction in liquid film, with low CBCase D: Fast reaction in liquid film, with high CB Case E and F: Intermediate rate with reaction in the film and in the main body of the l