《反应工程基础：Chap3 Rate Laws and Stoichiometry》由会员分享，可在线阅读，更多相关《反应工程基础：Chap3 Rate Laws and Stoichiometry（75页珍藏版）》请在金锄头文库上搜索。
1、Chapter2-Summary1.TheconversionXisthemolesofAreactedpermoleofAfed.Forbatchsystems:Forflowsystems:ForreactorsinserieswithnosidestreamsBatchCSTRPFRPBR2. Mole balance equations in four common reactorsIntegralDifferentialIntegralDifferentialChapter 1Chapter 23.IfrA=f(X)isgiven,thefollowinggraphicaltechn
2、iquescanbeusedtosizeaCSTRandaplug-flowreactorPFRCSTRSpacetimeChapter3RateLawsandStoichiometrySuccess is measured not so much by the position one has reached in life, as by the obstacles one has overcome while trying to succeed.BookerT.WashingtonOverviewHowtoobtaintherateofreactionasafunctionofconver
3、sionStep1:(Part1)definetheratelaw,relatingtherateofreactiontotheconcentrationsofthereactingspeciesandtotemperatureStep2:(Part2)defineconcentrationsforflowandbatchsystemsanddevelopastoichiometrictablesothatonecanwriteconcentrationsasafunctionofconversionPart1RateLaws3.1BasicdefinitionsTypesofreaction
4、sMolecularityofareactionisthenumberofatoms,ions,ormoleculesinvolved(colliding)inareactionstepunimolecular,bimolecular,termolecularHomogeneousHeterogeneousIrreversibleReversibleExamples:UnimolecularreactionBimolecularreactionTermolecularreaction3.1.1RelativeratesofreactionRateofformationofC=(Rateofdi
5、sappearanceofA)Similarly: ReactionstoichiometryExample: 3.2 The reaction order and the rate lawRatelaworkineticexpression:algebraicequationthatrelatesrAtothespeciesconcentrationskA:rateconstant,orspecificrateofreaction3.2.1 Power law models and elementary rate lawsReactionorder:referstothepowers,e.g
6、.,Overallorderofthereaction,nA BAProductsReactionorder:nZero-order(n=0)First-order(n=1)Second-order(n=2)Third-order(n=3)Unit:Elementaryreaction:evolvesasinglestepThestoichiometriccoefficients:identicaltothepowersintheratelawFollows an elementary rate law, BUT, nonelementary reactionRatelaws,determin
7、edbyexperimentalobservationCollisiontheoryPathways3.2.2NonelementaryratelawsHomogeneousreactionsApparent reaction orders .Apparentfirstorder(N2O),overallfirstorderorderof-1(O2),firstorder(N2O),overall0orderHeterogeneousreactionsRatelawintermsofpracticalpressuresratherthanconcentrations(T)(B)Langmuir
8、-HinshelwoodkineticsAdsorptionconstants,kPa-1IdealgaslawComputationalfluiddynamics(CFD)withdetailedchemistry计算流体力学耦合基元反应动力学详细考察壁面导热、孔径、活性比表面积影响，指导催化剂设计、反应器设计、优化原料气体组成，等等。COCO2 2 + 2 H + 2 H2 2OOCHCH4 4 + 2 O + 2 O2 2CHCH4 4 + O + O2 2CO + 2 HCO + 2 H2 2CFDwithdetailedchemistryCFD表面机理3.2.3Reversibler
9、eactionsAllratelawsforreversiblereactionsmustreducetothethermodynamicrelationshipRelatingthereactingspeciesconcentrationsatequilibrium.Atequilibrium:Forwardandreversespecificreactionrateconstants,kBandk-BConcentrationequilibriumconstantwhere,Concentrationequilibriumconstantequilibriumconstant:decrea
10、seswithincreasingtemperatureforexothermicreactions;increaseswithincreasingtemperatureforendothermicreactions.k:toparticularspeciesAtequilibrium:Nochangeinthetotalnumberofmolesandtheheatcapacityterm,CP=0TKCEndothermicTKCExothermic3.3Thereactionrateconstantk:specificreactionrateortherateconstantalways
11、stronglydependentontemperature!catalysttotalpressureingas-phasereactionsionicstrength,solvent,etc.,inliquid-phaseArrheniusequationA:pre-exponentialfactororfrequencyfactorE:activationenergy,J/molorcal/molR:gasconstant,8.314J/molK=1.987cal/molKT:absolutetemperatureWhyisthereanactivation energyThemolec
12、ulesneedenergytodistortorstretchtheirbondssothattheybreakthemandthusformnewbondsThestericandelectronrepulsionforcesmustbeovercomeasthereactingmoleculescomeclosetogetherActivationenergy:abarriertoenergytransfer(fromkineticenergytopotentialenergy)betweenreactingmoleculesthatmustbeovercome.Potentialene
13、rgyreactantsproductsA+BCA-B-CAB+CEAB+EICEIA+EBCHRxEBEnergybarrierEA-B-CReactioncoordinateDetermination of the activation energyDataset:(T1,kA1),(T2,kA2),(T3,kA3),.(Tn,kAn)lnk1/TSlope=-(E/R)LowEHighEHow to experimentally determine the activation energy, EEvsk:Temperature sensitivityFromLevenspielsboo
14、kBatchCSTRPFRPBRDifferentialformAlgebraicformIntegralformDesign equationsBatchCSTRPFRPBRMole balance equations in four common reactorsIntegralDifferentialIntegralDifferentialChapter 1Chapter 2PresentstatusofourapproachtoreactorsizinganddesignRatelaw+Be able to design isothermal reactorsPart 2 Stoich
15、iometryGeneralreaction“PermoleofA”3.5BatchsystemsSpeciesInitially(mol)Change(mol)Remaining(mol)ABCDI(inerts)TotalsThechangeinthetotalnumberofmolespermoleofAreactedTodeterminethereactionrateasafunctionofconversionX,weneedtoknowtheconcentrationsofthereactingspeciesasafunctionofconversion.3.5.1Equation
16、sforbatchconcentrationsBatchconcentrationDefinetheparameterWeneedV(X)toobtainCj=hj(X)3.5.2Constant-volumebatchreactionsystemsNochangeinvolumeasthereactionprogressesConstant-volumeConstant-densityWater-gasshiftreactionGas-phasereactions:Liquid-phasereactions:Essentiallyaconstant-volumereactionprocess
17、Exception:polymerizationprocessesTosummarizeforliquid-phasereactions:Constant-volumebatchreactionsystemsExamples:p71,limitingreactant3.6FlowsystemsEnteringFA0FB0FC0FD0FI0LeavingFAFBFCFDFIStoichiometrictableforaflowsystemSpeciesFlowratetoreactor(mol/time)Changewithinreactor(mol/time)Effluentratefromr
18、eactor(mol/time)ABCDI(inerts)Totals3.6.1EquationsforconcentrationinflowsystemsDefinitionofconcentrationforaflowsystem3.6.2Liquid-phaseconcentrationsForliquids,volumechangewithreactionisnegligiblewhennophasechangesaretakingplace.3.6.3ChangeinthetotalnumberofmoleswithreactioninthegasphaseSynthesisofam
19、moniaExamples:.Batchreactorswithvariablevolumet =0:Seldom encounteredEquationofstateZ:compressibilityfactorValidforbothbatchandflowsystemsCompleteconversionX=1,NT=NTfVariable-volumebatchFlowreactorswithvariablevolumetricflowrateAtentrance:Gaslaw:ConcentrationintermsofconversionforgasflowsystemsandGa
20、s-phaseconcentrationasafunctionofconversionConcentrationsinavariable-volumegasflowsystemNotconstant!Examples, P77-83Closure.WritetheratelawintermsofconcentrationandtheArrheniustemperaturedependenceUsethestoichiometrictabletowritetheconcentrationsintermsofconversiontofinallyarriveatarelationshipbetwe
21、entherateofreactionandconversion.StoichiometryRateLawMoleBalanceChapter3Chapter3Chapter1Chapter4:combineandevaluateChapter8:energybalance(isothermal reactor design)Stoichiometry3.7MeasuresotherthanconversionIntermsofNA,NBorFA,FBTo be included in Chapter 4. 3.8ReactionwithcondensationPhase-changeGas-
22、phasereactionCVDprocess:thinfilmdepositiononsolidsurfaces.Ingeneral:Example:P86-87SummaryPartI1.RelativeratesofreactionforthegenericreactionTherelativeratesofreactioncanbewritteneitheras2.Reactionorderisdeterminedfromexperimentalobservation:3.Thetemperaturedependenceofaspecificreactionrateisgivenbyt
23、heArrheniusequationA:frequencyfactorE:activationenergyEquilibriumconstantSummaryPart24.ThestoichiometrictableforthereactionSpeciesFlowratetoreactor(mol/time)Changewithinreactor(mol/time)Effluentratefromreactor(mol/time)ABCDI(inerts)Totals5.Inthecaseofidealgases,Batchconstantvolume:Flowsystems:GasLiq
24、uid6.Forgas-phasereactions,7.ForincompressibleliquidsHoldforgas-phasereactionscarriedoutatconstantvolumeinbatchsystems8.Intermsofgas-phasemolarflowrates,theconcentrationofspecies i isForsilicontobeusedinthemanufactureofmicroelectronicdevices,itmustcontainlessthan150partspertrillionofimpurities.Thisu
25、ltrapuresiliconcanbeproducedbyreactingmetallurgicalsilicon(98%pure)andHCltoformtrichlorosilaneandotherproducts.Thismixtureisdistilledandthenthetrichlorosilaneisreactedwithhydrogenat1100Ctoformpolycrystallinesilicon,HCl,andothersilaneproductsinthefollowingreaction:Setupastoichiometrictableforthefollo
26、wingcase:x = 1 y = 2 z = 2 Thetotalpressuremaybetakentobe2atmandthefeedisstoichiometric.Sketchtheconcentrationsofeachspeciesasafunctionofconversion.Thefirststepinsettingupourstoichiometrictableistodeterminethestoichiometriccoefficients(a, b, c, d, & e).Aftermakingsuretheelementsarebalancedonbothside
27、softheaboveequation,thecompleteequationlookslike:Species Symbol Flow Rate In Change in Flow Rate Flow Rate Out SiHCl3 A FAo -FAoX FAo(1-X) H2 B FAo -FAoX FAo(1-X) Si C 0 0.5FAoX 0.5FAoX HCl D 0 2FAoX 2FAoX Si1H2Cl2 E 0 0.5FAoX 0.5FAoX KnowingthatCTo=CT.UnderconstanttemperatureandpressureWedonotinclu
28、decomponentCinthiscalculationbecauseitisasolid.Combiningtheaboveequations,theconcentrationofeachspeciescanbewrittenas:?第三代西门子法多晶硅工艺图产氢裂解气提氢系统 5MW高压整流电源 5MW等离子体反应器 新疆天业CokeCaC22300 CH2OCa(OH)2CaO900 CCOCaC2 method (90% of C2H2 production)CoalC2H2H2 (by-product)CO, CH4, C2H4C(un-pyrolyzed)H2Thermal pl
29、asma4000 CPlasma pyrolysisC2H2Coal“All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident.”ArthurSchopenhauer(1788-1860)Start by doing what is necessary; then do what is possible; and suddenly you are doing the impossible.St.FrancisofAssissi
