大三下反应工程基础往届课件chap1

AboutreactionengineeringReactionengineeringisthedisciplinethatquantifiestheinteractionsoftransportphenomenaandkineticsinrelatingreactorperformancetooperatingconditionsandfeedvariables.

Thisquantificationrequiresathoroughunderstandingofthemicroscale(molecularlevelofscrutiny),mesoscale(transport-kineticeventsonacatalyst-particlelevel)andmacroscale(reactordesignincontextofprocessandplantdesign).

Itisthefieldthatdealswithchemicallyreactivesystemsofengineeringsignificance.Chemicalreactionengineeringresultsinageneralmethodologyusefulinapproachingavarietyofsystems(chemical,biochemical,biological,electrochemical)whereengineeringofreactionsisneeded;i.e.,wherethecause-and-effectrelationsimpartedbyreactionsandobservedinsmalllaboratoryvesselsneedtobe“scaledup”tocommercialproduction.ChemicalReactionEngineeringChemicalkinetics

chemicalreactionrates

reactionmechanisms

Chemicalreactionengineering

chemicalkinetics

reactordesignTheheartofproducingalmostallindustrialchemicalsSelectionofareactionsystem:SafeandEfficientEconomicallyfeasibleChemicalkineticsReactordesignThermodynamicsCatalystProcessconditionsExternalfieldReactortypeandstructureFluiddynamicsHeatandmasstransferEngineeringissues:e.g.,materialsScale-uporscale-downEfficiencyExamples:ReactorFeedstockAB(desired)CDProcessconditions:temperature,pressure,...

Example2CH3OH+NH3=HOCH2CN+H2O+3H22CH3OH+2NH3=NH2CH2CN+2H2O+3H24CH3OH+3NH3=NH(CH2CN)2+4H2O+6H22CH3OH+NH3=NH2CH2COOH+3H24CH3OH+NH3=NH(CH2COOH)2+6H2羟基乙腈氨基乙腈亚氨基二乙腈氨基乙酸亚氨基二乙酸InformationneededtopredictwhatareactorcandoReactorInputOutputPerformanceequationRelatesinputtooutputContactingpattern

orhowmaterialsflowthroughandcontacteachotherinthereactor

Kineticsorhowfastthingshappen.Ifveryfast,thenequilibriumtellswhatwillleavethereactor.Ifnotsofast,thentherateofchemicalreaction,andmaybeheatandmasstransfertoo,willdeterminewhatwillhappen.W.P.M.vanSwaaij,ChemEngJ,90(2002)25-45例：工业气固催化反应器的变迁W.P.M.vanSwaaij,ChemEngJ,90(2002)25-45通道内流型整体型催化剂反应器（Monolith）SoftwarePolymathMatlab

Femlab/COMSOLMathCAD

MathematicaAspenONE2006

HysysChapter1MoleBalances

Overview–Chapter1FirstbuildingblockofCREMolebalances

Chemicalspeciesenteringandleaving,and/orremainingwithinareactionsystemvolume

Beableto:describeanddefinetherateofreactionderivethegeneralmolebalanceequationapplythegeneralmolebalancetothefourmostcommontypesofindustrialreactorsFourmostcommontypesofreactorsBatchreactorContinuous-stirredtankreactor(CSTR)Tubularreactor(plugflowreactor,PFR)Packedbedreactor(PBR)BatchCSTRPBRPFR1.1Therateofreaction,-rAHowfastanumberofmolesofonechemicalspeciesarebeingconsumedtoformanotherchemicalspeciesChemicalspecies:anychemicalcomponentorelementwithagivenidentity

Identity:kind,numberandconfigurationWhenhasachemicalreactiontakenplaceWhenadetectablenumberofmoleculesofoneormorespecieshavelosttheiridentityandassumedanewformbyachangeinthekindofnumberofatomsTherateofdisappearanceofaspecies,sayspeciesA,isthenumberofAmoleculesthatlosetheirchemicalidentityperunittimeperunitvolumethroughthebreakingandsubsequentre-formingofchemicalbondsduringthecourseofthereaction.Threebasicwaysaspeciesmayloseitschemicalidentityposition:beingbrokenintosmallermolecules,atomsoratomfragmentsCombination:Isomerization:achangeinconfigurationExamples...Rateofreaction,-rAThenumberofAreacting(disappearing)perunittimeperunitvolume(mol/dm3·s)Example:Negative:reactantdisappearancePositive:productformation(/generation)HeterogeneousreactionsRateofreaction：ThenumberofmolesofAreactingperunittimeperunitmassofcatalyst(mol/s·gcatalyst)DefinitionofrjTherateequation(i.e.,ratelaw)forrjisanalgebraicequationthatissolelyafunctionofthepropertiesofthereactingmaterialsandreactionconditionsatapointinthesystem

(e.g.,speciesconcentration,T,P,ortypeofcatalyst,ifany)Therateequationisindependentofthetypeofreactor(e.g.,batchorcontinuousflow)inwhichthereactioniscarriedout.Wrongdefinition!!!OnlyvalidforaconstantvolumebatchsystemRateofformationofspeciesjperunitvolumeExample:Issodiumhydroxidereacting?NaOH+CH3COOC2H5

CH3COONa+C2H5OHSteadystatePerfectlymixed?Reacting!!!XAproductsTheratelawisanalgebraicequation.Byconvention:rA–rateofformationofA-rA–rateofdisappearanceofA(rateofgeneration)Example:1.2ThegeneralmolebalanceequationRateofflowofjintothesystem(moles/time)Rateofflowofjoutofthesystem(moles/time)Rateofgenerationofjbychemicalreactionwithinthesystem(moles/time)Rateofaccumulationofjwithinthesystem(moles/time)MolebalanceInOutGenerationAccumulation+-=-+=rj1rj2V1V2VAssumption:Allthesystemvariablesarespatiallyuniformthroughoutthesystemvolume.TherateofgenerationofspeciesjReactionratevarieswithpositioninthesystemBasicequation

forchemicalreactionengineeringDesignequations1.3BatchreactorsSmall-scaleoperation

fortestingnewprocesses

forthemanufactureofexpensiveproducts

for

processesdifficulttobeoperatedcontinuouslyHighlaborcostsperbatch,Variabilityofproductsfrombatchtobatch,

Difficultyoflarge-scaleproduction.BatchReactorStirringApparatusBatchreactor:hasneitherinflownoroutflowofreactantsorproductsGeneralmolebalanceonspeciesjPerfectmixing:Example:IsomerizationofspeciesANA0NANA10t1tNB10t1tNBABPConstantvolumebatchreactorConstantpressurebatchreactorMovableplug1.4Continuous-flowreactorsContinuousstirredtankreactor(CSTR)Plugflowreactor(PFR)Packedbedreactor(PBR)1.4.1Continuousstirredtankreactor(CSTR)

(orvat,orbackmixreactor)LiquidphasereactionsSteadystatePerfectlymixedNotimedependenceorpositiondependenceofthetemperature,theconcentration,orthereactionrateinsideEveryvariableisthesameateverypointinsidetheCSTR.IdenticaltemperatureandconcentrationeverywhereVariables:Exit=InsideCutawayViewofCSTR

GeneralmolebalanceequationDesignequationforaCSTRCSTRfeatures:(1)(2)1.4.2TubularreactorReactantsProductsPlugflow:noradialvariationsinvelocity,concentration,temperature,orreactionrateGeneralmolebalanceequationFj0ProductsVV+VVFjFjGjDifferentialvolumeVForspeciesA:In–Out+Generation=AccumulationDifferentialformofsteadystatemolebalanceFA0FAFA10V1VFB10V1VFBABExampleSomewordsonirregularshapereactorFA(V)VFA(V+V)Controlvolume:V(nospatialvariationsinreactionrate)高压聚乙烯：1000~2000atm，低密度，10万吨/年1.4.3Packed-bedreactorHeterogeneousreaction

Reactiontakesplaceonthesurfaceofthecatalyst.=molAreacted/s·gcatalystFA0WW+WWFA(W)FA(W+W)GjFAMolebalanceInOutGenerationAccumulation-+=DifferentialformIntegralformExample在一个反应流率恒定的管式反应器内进行一级不可逆液相反应，AB

(1)推导一个将反应器体积与A组分进出口浓度、反应速率常数k和体积流率关联的方程。

(2)当＝10L/min和反应速率常数k＝0.23min-1时，将出口浓度减少到入口浓度10％时所需的反应器体积。P12.1.5Industrialreactors[1]Liquid-phasereactionsSemibatchreactors

temperaturecontrolbyregulationofthefeedrate;

capabilityofminimizingunwantedsidereactionsthroughthemaintenanceofalowconcentrationofoneofthereactantsCSTRs

intenseagitation;

goodtemperaturecontrol;

smallestconversionofreactantpervolumeofreactor

[2]Gas-phasereactionsPFR:HighestconversionperreactorvolumeDifficulttocontroltemperaturewithinthereactor,hotspotswhenexothermicMosthomogeneousliquid-phaseflowreactorsareCSTRs;Mosthomogeneousgas-phaseflowreactorsaretubular.PBR:tubularreactorpackedwithsolidcatalystparticlesFluidizedbedMovingbedExample:Fischer-TropschReactionFischer-Tropschsynthesis(1923)SlurrybedTricklebedCFBFBRefertoDavis(2002),Dry(2002)Hightemperatureprocess(300-350

C)withiron-basedcatalystsisusedfortheproductionofgasolineandlinearlowmolecularmassolefins.

FB

CFB

FB:Sasol

Low-temperatureprocess(200-240

C)witheitherironorcobaltcatalystsisusedfortheproductionofhighmolecularmasslinearwax