化学反应工程英文课件Chapter-5

化学反应工程Chapter5IdealReactorsforaSingleReactionInthischapterwedeveloptheperformanceequationforasinglefluidreactinginthethreeidealreactorsshowninFig.5.1.Wecallthesehomogeneousreactions.Inthebatchreactor,orBR,ofFig.5.1athereactantsareinitiallychargedintoacontainer,arewellmixed,andarelefttoreactforacertainperiod.Theresultantmixtureisthendischarged.Thisisanunsteady-stateoperationwherecompositionchangeswithtime;however,atanyinstantthecompositionthroughoutthereactorisuniform.化学反应工程BatchReactorMixedFlowReactor化学反应工程Thefirstofthetwoidealsteady-stateflowreactorsisvariouslyknownastheplugflow,slugflow,pistonflow,idealtubular,andunmixedflowreactor,anditisshowninFig.5.1b.Werefertoitastheplugflowreactor,orPFR,andtothispatternofflowasplugflow.Itischaracterizedbythefactthattheflowoffluidthroughthereactorisorderlywithnoelementoffluidovertakingormixingwithanyotherelementaheadorbehind.Actually,theremaybelateralmixingoffluidinaplugflowreactor;however,theremustbenomixingordiffusionalongtheflowpath.Thenecessaryandsufficientconditionforplugflowisfortheresidencetimeinthereactortobethesameforallelementoffluid.化学反应工程Theotheridealsteady-stateflowreactoriscalledthemixedreactor,thebackmixreactor,theidealstirredtankreactor,theC*(meaningC-star),CSTR,ortheCFSTR(constantflowstirredtankreactor)and,asitsnamessuggest,itisareactorinwhichthecontentsarewellstirredanduniformthroughout.Thus,theexitstreamfromthisreactorhasthesamecompositionasthefluidwithinthereactor.Werefertothistypeofflowasmixedflow,andthecorrespondingreactorthemixedflowreactor,orMFR.Thesethreeidealsarerelativelyeasytotreat.Inaddition,oneorotherusuallyrepresentsthebestwayofcontactingthereactants－nomatterwhattheoperation.Thesteadyandunsteadyoperation间歇操作(Batchreactor,BR)连续操作(MixedFlowReactor,MFR)连续操作(PlugFlowReactor,PFR)化学反应工程Forthesereasons,weoftentrytodesignrealreactorssothattheirflowsapproachtheseideals,andmuchofthedevelopmentinthisbookcentersaboutthem.InthetreatmenttofollowitshouldbeunderstoodthatthetermV,calledthereactorvolume,reallyreferstothevolumeoffluidinthereactor.Whenthisdiffersfromtheinternalvolumeofreactor,thenVr‘designates(指明,任命)theinternalvolumeofreactorwhileVdesignatesthevolumeofreactingfluid.Forexample,insolidcatalyzedreactorswithvoidage(空隙率)wehaveV=VrForhomogeneoussystems,however,weusuallyusethetermValone.化学反应工程5.1IDEALBATCHREACTORMakeamaterialbalanceforanycomponentA.Forsuchaaccountingweusuallyselectthelimitingcomponent.Inabatchreactor,sincethecompositionisuniformthroughoutatanyinstantoftime,wemaymaketheaccountingaboutthewholereactor.Notingthatnofluidentersorleavesthereactionmixtureduringreaction,Eq.4.1,whichwaswrittenforcomponentA,becomesinput=output+disappearance+accumulationorrateoflossofreactantArateofaccumudationwithinreactorduetoofreactantAchemicalreactionwithinthereactor(1)化学反应工程EvaluatingthetermsofEq.1,wefindAdisappearanceofAmolesAreactingbyreaction,(r)V(volumeoffluid)(time)(volumeoffluid)moles/timemoles/timeA,ofonaccumulatidtdXNdtXNddtdNAA0AA0A)]1([化学反应工程ByreplacingthesetwotermsinEq.1,weobtaindtdXNVrAA0A)((2)RearrangingandintegratingthengivesA0AAA0)(XVrdXNt(3)ThisisthegeneralequationshowingthetimerequiredtoachieveaconversionXAforeitherisothermalornonisothermaloperation.Thevolumeofreactingfluidandthereactionrateremainundertheintegralsign,foringeneraltheybothchangeasreactionproceed.化学反应工程Thisequationmaybesimplifiedforanumberofsituations.Ifthedensityofthefluidremainsconstant,weobtainAAA0AAA0A0AAfor0XCCdXdCtCrr(4)Forallreactionsinwhichthevolumeofreactingmixturechangesproportionatelywithconversion,suchasinsinglegas-phasereactionswithsignificantdensitychanges,Eq.3becomesAAXXAAA0A000A0AAAAAdXdXtNC(r)V(1X)(r)(1X)(5)化学反应工程Inoneformoranother,Eqs.2to5haveallbeenencounteredinChapter3.Theyareapplicabletobothisothermalandnonisothermaloperations.Forthelatterthevariationofratewithtemperature,andthevariationoftemperaturewithconversion,mustbeknownbeforesolutionispossible.Figure5.2isagraphicalrepresentationoftwooftheseequations.化学反应工程化学反应工程Space-TimeandSpace-VelocityJustasthereactiontimetisthenatureperformancemeasureforabatchreactor,soarethespace-timeandspace-velocitytheproperperformancemeasureofflowreactors.Thesetermsaredefinedasfollows:Space-time:timerequiredtoprocessone1reactorvolumeoffeedmeasured[time]satspecifiedconditions(6)化学反应工程Space-velocity:-1numberofreactorvolumesof1sfeedatspecifiedconditionswhich[time]canbetreatedinunittime(7)Thus,aspace-velocityof5hr-1meansthatfivereactorvolumesoffeedatspecifiedconditionsarebeingfedintothereactorperhour.Aspace-timeof2minmeansthatevery2minonereactorvolumeoffeedatspecifiedconditionsisbeingtreatedbythereactor.化学反应工程Nowwemayarbitrarilyselectthetemperature,pressure,andstate(gas,liquid,orsolid)atwhichwechoosetomeasurethevolumeofmaterialbeingfedtothereactor.Certainly,then,thevalueforspace-velocityorspace-timedependsontheconditionsselected.Iftheyareofthestreamenteringthereactor,therelationbetweensandandtheotherpertinent(有关的)variableisrate)feedc