大三下all反应工程基础往届课件chap6

回顾1－基本概念，解题思路－解题思路－基本环节：设计方程CSTRPFRBatch1级和2级反应恒容变容熟记、熟知、熟查2－膨胀因子膨胀率3－理想反应器：极端行为CSTRPFR实际反应器4－教学与学习A.科学概念、知识库B.技能：解决问题的能力（思路＋细节）实验解析数值(工具)iC.相关的数学0维：CSTR代数方程（组）1维：PFR常微分方程（组）2维：2D-PFR偏微分方程（组）直接求解迭代（试差）直接解析数值解（如Matlab）直接解析（如拉氏变换）数值解（如COMSOL）D.收获：知识，方法论，信心物理－建模－求解－应用Chapter6

MultipleReactionsOverviewMultiplereactions,somedesired,someundesiredEconomicsuccessofachemicalplant:minimizationofundesiredsidereactionsthatoccuralongwiththedesiredreactionReactorselectionfor:series,parallel,independent,andcomplexreactionsSelectivity&yield6.1Definitions6.1.1TypesofreactionsABCParallelk1k2SeriesABCk1k2ComplexA+BC+DA+CEIndependentreactionsAB+CDE+F(consecutive)examples...光气法合成异氰酸酯主要副反应釜式反应器生产工艺DesiredandundesiredreactionsReactorsystemADUSeparatorSelectivityHowoneproductisfavoredoveranotherInstantaneousselectivityofDOverallselectivityofDForabatch:(1)(2)EfficiencyofareactorsystemCostLowHighTotalcostReactorcostSeparatorcostExample:

OverallandinstantaneousselectivitiesforaCSTROverallandinstantaneousselectivitiesforaCSTR?ReactionyieldInstantaneousyieldOverallyieldBasedonmolesBasedonmolarflowrates(batchsystem)(flowsystem)Reactorperformance:Conversion,Selectivity,YieldCommentOverallselectivitiesandyields:importantindeterminingprofitsRate-basedselectivitiesgiveinsightsinchoosingreactorsandreactionschemesthatwillhelpmaximizetheprofitGreaterconversionMoreselectivity(oryield)转化率、选择性、收率的不同定义方式反应掉A的摩尔数投入A的摩尔数生成P时消耗A的摩尔数反应掉A的摩尔数生成P时消耗A的摩尔数投入A的摩尔数

转化率(Conversion)：选择性(Selectivity)：收率(Yield)：供参考6.2ParallelreactionsdesiredundesiredRatelawsReactionsSelectivityRateofdisappearanceofA6.2.1MaximizingthedesiredproductforonereactantCase1:

1>2Batchorplug-flow:betterchoiceCase2:

2>1CSTR:betterchoiceMakeCAaslargeaspossibleDilutethefeedstream,lowerCAGas-phase:noinerts,highpressureLiquid-phase:min.diluentsorarecyclereactor(productsrecycled)EffectoftemperatureCase3:ED>EUHightemperature:better!Case4:EU>EDLowtemperature:better!Example:Maximizingtheselectivity

(1)(2)(3)CAPFRorCSTR?EffectoftemperatureDiscussions:...Furtheroptimization:Howcanweincreasetheconversionandstillhaveahighselectivity?Given=0,CA,CX,CB,CY

andCAf(XA)SB/XYXACA0CAfC*ACSTRPFR6.2.2ReactorselectionandoperatingconditionsInstantaneousselectivityReactorselectionCriteria:Selectivity,Yield,Temperaturecontrol,Safety,CostSimultaneousreactionswithtworeactantsReactorselectionAB(a)CSTRAB(b)Tubularreactor(c)Batch(d)Semi-batchBPureAinitially(e)Semi-batchAPureBinitiallyAB(f)Amembranereactororatubularreactorwithsidestreams(g)AmembranereactororatubularreactorwithsidestreamsBAAB(h)SeriesofsmallCSTRsBA(i)TubularreactorwithrecycleAB(j)CSTRwithrecycleBADC(k)MembranereactorABCD(l)ReactivedistillationExampleCaseI:

1>2,1>2.Leta=1-2,b=1-2TubularreactorBatchreactorHighpressure(ifgasphase),andreduceinertsCaseII:

1>2,1<2.Leta=1-2,b=2-1Semibatchreactor,BfedslowlyMembranereactorortubularreactorwithsideBAseriesofsmallCSTRs:Atothefirst,BtoeachCaseIII:

1<2,1<2.Leta=2-1,b=2-1CSTRPFRwithalargerecycleratioDilutedfeedwithinertsLowpressure(ifgasphase)CaseIV:

1<2,1>2.Leta=2-1,b=1-2Semibatchreactor,AfedslowlyMembranereactorortubularreactorwithsideAAseriesofsmallCSTRs:freshAtoeach6.3MaximizingthedesiredproductinSeriesReactionsCjABC

example...tMolebalanceonARatelawStoichiometryCombiningLetIntegrating:atW=0,CA=CA0(1)MolebalanceonBRatelaw(net)StoichiometryCombiningIntegrating:(2)(3)OptimumyieldQuestion:k1=k2...?(4)MolebalanceonCEntrancecondition:’=0,CC=0FindingtheSelectivityinaCSTR.A.BalanceonSpeciesA

B.BalanceonSpeciesBC.BalanceonSpeciesCminimumvalueofVatwhichthereisanacceptablemolarflowrateofthedesiredproductBfromtheCSTR6.4Algorithmforsolutionofcomplexreactions6.4.1MolebalancesMolebalancesformultiplereactionsBatchCSTRPFR/PBRSemibatchBaddedtoAMolarquantities(GorL)Concentration(Liquid)6.4.2Netratesofreaction6.4.2AWritingthenetrateofformationforeachspeciesReaction1:...Reaction2:......Reactionq:...Netratesofreaction:i:reactionnumberj:species6.4.2BRatelawsj–speciesi–reactionnumberWeneedtodeterminetheratelawforatleastonespeciesineachreaction.6.4.2CStoichiometry:RelativeratesofreactionRelatetheratelawforaparticularreactionandspeciestootherspeciesparticipatinginthereaction6.4.2DCombineindividualratelawstofindthenetrateSummary:RatesRelativeratesRatelawsNetratesNeedexercise!6.4.3Stoichiometry:concentrationsLiquidphase:Gasphase:ForisothermalsystemswithnopressuredropIsothermalreactiondesignalgorithmformultiplereactionsReactions:numbereachreactionMolebalance:writemolebalanceoneachandeveryspeciesNetratelaws:writethenetrateofreactionforeachspecieswriteratelawforonespeciesineveryreactionIneachreactionrelatetheratesofreactionofeachspeciestooneanothercombinenetrates,ratelaws,andrelativeratestowritethenetratesintermsofconcentrationStoichiometry:forisothermalgas-phasereactions,writetheconcentrationsintermsofmolarflowrates;forliquid-phasereaction,justuseconcentrationsastheyarePressuredrop:writegas-phasepressuredroptermintermsofmolarflowratesCombine:UseanODEsolvertocombinestepsthroughtosolvefortheprofilesofmolarflowrates,concentration,andpressure,etc.6.5MultiplereactionsinaPFR/PBRCoupledODEsForconstant-pressurebatchsystems:simplysubstituteNiforFiExample,P2356.6MultiplereactionsinaCSTRAcoupledsetofalgebraicequations6.7Membranereactorstoimproveselectivity

inmultiplereactionsUseofmembranereactorstoenhanceselectivity(Chap