一篇甲醇合成的外文文獻(xiàn)原文

1、 ANewLow-TemperatureSynthesisRouteofMethanol:CatalyticEffectoftheAlcoholicSolvent1.IntroductionGas-phasemethanolisbeingproducedindustriallyby30-40milliontonperyeararoundtheworld,fromCO/CO2/H2atatemperaturerangeof523-573Kandapressurerangeof50-100bar,usingcopper-zinc-basedoxidecatalyst.Undertheseextre

2、mereactionconditions,theefficiencyofmethanolsynthesisisseverelylimitedbythermodynamicsasmethanolsynthesisisanextremelyexothermicreaction1.,2Forexample,at573Kand50bar,itiscalculatedbythermodynamicsthattheoreticmaximumone-passCOconversionisaround20%forflow-typereactorwhenH2/CO=2.Alsoitisreportedthatth

3、eone-passCOconversionintheindustrialICIprocessisbetween15and25%,evenifH2-richgasisused(H2/CO=5,523-573K).3Therefore,developingalow-temperatureprocessformethanolsynthesis,whichwillgreatlyreducetheproductioncostandutilizethethermodynamicadvantageatlowtemperature,ischallengingandimportant.3Ifconversion

4、ishighenoughinmethanolsynthesis,recyclingoftheunreactedsyngascanbeomittedandaircanbeuseddirectlyinthereformer,insteadofpureoxygen.Generally,low-temperaturemethanolsynthesisisconductedintheliquidphase.TheBNLmethodfirstreportedbyBrookhavenNationalLaboratory(BNL),usingaverystrongbasecatalyst(mixtureofN

5、aH,acetate),realizedthiscontinuousliquid-phasesynthesisinasemi-batchreactorat373-403Kand10-50bar.However,aremarkabledrawbackofthisprocessisthatevenatraceamountofcarbondioxideandwaterinthefeedgasorreactionsystemwilldeactivatethestronglybasiccatalystsoon,4,5resultinginhighcostcomingfromthecompletepuri

6、ficationofthesyngasfromreformer,andreactivationofthedeactivatedcatalyst.Thisisthemainreasonstoppingthecommercializationofthislow-temperaturemethanolsynthesismethod.Liquid-phasemethanolsynthesisfrompureCOandH2viatheformationofmethylformatehasbeenwidelystudied,wherecarbonylationofmethanolandsuccessive

7、hydrogenationofmethylformatewereconsideredastwomainstepsofthereaction.6-13co+ch3oh-hcooch3HCOOCHj+2比皿叫ZCHOH匚0+2H2-CH3OHPalekaretal.usedapotassiummethoxide/copperchromitecatalystsystemtoconductthisliquid-phasereactioninasemi-batchreactorat373-453Kand30-65bar.6AlthoughthemechanismofBNLmethodisstillcon

8、troversial,alotofresearchersthinkthatitissimilartothemechanismabove.3However,similartothatintheBNLmethod,inthisprocessCO2andH2Oactaspoisonstothestrongbasecatalyst(RONa,ROK)aswellandmustbecompletelyremovedfromsyngas,makingcommercializationoflow-temperaturemethanolsynthesisdifficult.Tposedanewmethodof

9、low-temperaturesynthesisofmethanolfromCO2/H2onaCu-basedoxidecatalystusingethanolasakindof“catalyticsolvent”,bywhichmethanolwasproducedinabatchreactorat443Kand30bar.14Thisnewprocessconsistedofthreesteps:(1)formicacidsynthesisfromCO2andH2;(2)esterificationofformicacidbyethanoltoethylformate;and(3)hydr

10、ogenationofethylformatetomethanolandethanol.Consideringthatthewater-gasshiftreactionatlowertemperatureiseasilycon-ductedonCu/ZnOcatalyst,15-25anewrouteofmethanolsynthesisfromCO/H2containingCO2,asamorepracticalwayofmethanolsynthesis,isproposed.Itconsistsofthefollowingfundamentalsteps:(i)co+h2o=co2+h2

11、C02+H2+ROH=HCOOR十H20HCOOR十2H2=CH3OH十ROHCO十2H2=CHjOHAsformicacidwasnotdetectedintheproducts,wesuggestedthereactionpathasstep(2).Tsubakietal.investigatedthesynthesisreactionofmethanolfromCO/CO2/H2,usingethanolasreactionmediuminabatchreactorandfoundhighselectivityformethanolformationattemperatureaslowa

12、s423-443K.26Inthiscommunication,thecatalyticpromotingeffectsofdifferentalcoholsonthesynthesisofmethanolfromCO/CO2/H2onCu/ZnOcatalystwereinvestigated.Highyieldsofmethanolwererealizedwhilesomealcoholswereutilized.2.ExperimentalSectionThecatalystwaspreparedbytheconventionalcoprecipitationmethod.Anaqueo

13、ussolutioncontainingcopper,zincnitrates(Cu/Zninmolarratio=1),andanaqueoussolutionofsodiumcarbonatewereaddedsimultaneouslywithconstantstirringto300mLofwater.TheprecipitationtemperatureandpHvalueweremaintainedat338Kand8.3-8.5,respectively.Theresultingprecipitatewasfiltratedandwashedwithdistilledwater,

14、followedbydryingat383Kfor24handcalcinationat623Kfor1h.Thisprecursorwasthenreducedbyaflowof5%hydrogeninnitrogenat473Kfor13handsuccessivelypassivatedby2%oxygendilutedbyargon.TheBETsurfaceareaforthecatalystwas59.4m2/g.ThecatalysthereisdenotedasCu/ZnO(A).Intheexperimentsusingreactantgasofdifferentcompos

15、ition,acommerciallyavailableICIcatalyst(ICI51-2)wasalsousedthroughthesamereductionpretreatment,denotedhereasCu/ZnO(B).TheBETsurfaceareaforCu/ZnO(B)was20.1m2/g.Toconfirmtheinfluenceofthecatalystpassivation,atailor-madereactorwhereinsitureductionofthecatalystbeforeethanolintroductionwasavailable,wasus

16、edtoperformthecatalystreductionandreaction;butnodifferenceinreactionbehaviorwasobserved.Sousingpassivatedcatalystreducedseparatelyhadnoinfluence.Inthereaction,aclosedtypicalbatchreactorwithinnervolumeof80mLandastirrerwasused.Thestirringspeedofthepropeller-typestirrerwascarefullycheckedtoeliminatethe

17、diffusionresistancebetweengas,liquid,andsolidphases.Adesiredamountofsolventandcatalystwasaddedintothereactor.Thenthereactorwasclosedandtheairinsidethereactorwaspurgedbyreactantgas.ApressurizedmixturegasofCO(31.90%),CO2(5.08%),andH2(60.08%)wasintroducedandthenthereactiontookplaceatthedesiredtemperatu

18、re.Arof2.94%inthefeedgaswasusedasinnerstandard.Afterreaction,thereactorwascooledbyice-waterandthenthegasinsidethereactorwasreleasedveryslowlyandcollectedinagas-bagforanalysis.Thestandardreactionconditionswereasfollows:catalyst=1.0g;solvent=20mL;reactiontemperature=443K;initialpressure=30bar.Atthesta

19、ndardreactiontemperatureof443K,thepressurewascalculatedtobe55bar,includingthevaporpressureofabout10barfromethanol.27AllproductswereconfirmedonGC-MS(ShimadzuGCMS1600)andanalyzedbytwogaschromatographs(ShimadzuGC-8A/FIDforliquidproducts,andGLScienceGC-320/TCDforgasproducts).Conversionoryieldwascalculat

20、edonthebasisofallcarboninthefeedgas.Intheexperimentsusingreactantgasofdifferentcomposition,whereCu/ZnO(B)wasemployed,aconventionalmagneticallystirredbatchreactorwasused.Thereactionconditionswere:temperature=423K;initialpressure=30bar;reactiontime=2h;catalyst0.2g;alcohol(ethanol):5mL.3.ResultsandDisc

21、ussionTheanalysisresultsshowedthatonlyCOandCO2existedinthepostreactiongasandonlymethanolandthecorrespondingHCOORweretheobtainedliquidproducts.Table1listedtheresultsof13kindsofalcoholsusedasreactionsolventseparatelyunderthesamereactionconditionswhereCu/ZnO(A)wasemployed.Forcomparison,theresultsinthec

22、asesofnosolventandcyclohexanewerealsolistedinTable1.Thetotalconversionwasthesumoftheyieldsofbothmethanolandester.Fromthetable,noactivityappearedwhencyclohexanewasusedornosolventwasused.However,inmostreactions,whenalcoholwasused,highactivitywasobserved,suggestingthecatalyticpromotingeffectofalcoholat

23、lowtemperature.Thesealcoholsloweredthereactiontemperaturesignificantlyandacceleratedthereaction,butdidnotaffectstoichiometryoftheoverallreactionasinsteps(1)-(3)listedabove.Table1.EffectsofDifferentAlcoholsontheSynthesisofMethanolfromCO/COa/Hzsolventyieldofmethanol%)yieldofHCOOR(%)totalconversion(%)r

24、atioofROHtofeedgascarbon*(niol/niol)none0000cyclohexane0000ethanol10.221.1311.3512.811-propanol9.270.169.439.942-propanol13.1910.2723.469.811-butanol8.9708.978.162-butanol11.2610.2221.488.14iso-butanol8.1908.198.13f-butanol5.8305.837.961-pentanol7.7407.746.912-pentanol3.728.0911.816.91cyclopentaiiol

25、6.7106.717.081-hexanol7.1707.175.96ethyleneglycol00013.40benzylalcohol0007.225Temperature=443K;Initialpressure=30bar;reactiontime=2h;CtVZnO(A)=1.00g;alcohol20mL;feedgasCO/CO2/H2/Ar=31.90/5.08/60.08/2.94;stirringspeedofthepropeller-tpestirrer=1250rpm.bRatioofmolarnumberof20niLROHtototalmolarnumbersof

26、COandCO2inthefeedgasat293Iand30barbeforereaction.Forthesix1-alcoholsfromethanolthrough1-hexanoltobenzylalcohol,theconversionstomethanolandthecorrespondingester(HCOOR)decreasedwithincreasingcarbonnumberofalcoholmolecule.Noesterwasobservedforthesefirstalcoholswhentheircarbonnumberwasmorethanthree.This

27、isinaccordancewiththeratesequenceofdifferent1-alcoholsintheesterificationreaction,28providingtheevidencethatstep(2)wasrate-determining.Astheconcentrationofester,HCOOR,wassolow,step(3)wasbelievedtobequickerthanstep(2).Itshouldbenotedthat,forallalcohols,theyhadalargemolarratioofROHtothetotalcarboninth

28、efeedgas;thedifferencecomingfromtheinfluenceofmolarnumbersofdifferentalcoholicsolventscanbeignored.Concerningthealcoholswiththesamecarbonnumberbutdifferentstructure,thesecondalcoholhadhighestactivity,asshowninthereactionsin2-propanol,2-bu-tanol,and2-pentanolseparately.2-Propanolexhibitedhighestactiv

29、ityamongthesethree2-alcohols.Forexample,at443K,thetotalconversioninthesolventof2-propanolwashighupto23.46%,amongwhichmethanoland2-propylformateyieldsaccountedfor13.19%and10.27%,respectively.Foralcoholswithlargerspatialobstacle,thereactionhadloweractivity,asshowninthecasesofiso-butanol,tert-butylalco

30、hol,andcyclopentanol.Inaddition,forethyleneglycolandbenzylalcohol,noactivitywasobserved.Butthereasonisnotveryclearnow.Onthereasonsfordifferentbehaviorsofthealcoholswiththesamecarbonnumberbutdifferentstructure,itisconsideredthatdifferentalcoholtypeaffectedstep(2)byboththeelectroniceffectandspatialeff

31、ect.For1-butanol,theelectrondensityofoxygenatominROHislower.Asaresult,ROHattackedthecarbonatomofHCOOCu,theintermediateofstep(2),moreslowly.Butthespatialobstacleof1-butanolisthesmallestamongallbutanols,andthisisfavorabletothenucleophilicattackintheesterificationreaction.Ontheotherhand,iso-butanolhash

32、ighelectronicdensityinitsoxygenatomandthisshouldacceleratethereaction.Butitslargemolecularvolumebecameaseverespatialobstacleinthenucleophilicattack.Soitsesterificationratewaslow.Asabalancedeffectbetweenelectronicfactorandspatialfactor,2-butanolexhibitedhighestactivityamong4butanols,intherate-determi

33、ningstep(2).Astheoppositeexample,tert-butylalcoholgavetheyieldofmethanolaslowas5.83%here.Itshouldbepointedoutthattheaccumulatedester(HCOOR)canbeeasilytransferredtomethanolandROHunderhigherH2partialpressure.Twoexperimentswereconductedtodemonstratethis.Onewasthehydrogenationofethylformateinabatchreact

34、orandtheotherwasthehydrogenationof2-butylformateinaflow-typesemi-batchautoclavereactor.Forthefirstone,thereactionconditionsweresimilartothoseusedinthesynthesisreactionofmethanoldescribedabove.AmixturegasofH2andN2withatotalinitialpressureof30bar(20barH2and10barN2)wasusedasfeedgas.Ethylformate(1.5mL)a

35、nd18.5mLofcyclohexaneweremixedandpouredintothereactorinsteadof20mLofalcohol.After2hreaction,thetotalconversionofethylformatewas98.20%andtheyieldofmethanolwas83.69%.MethylformateandCOwerebyproducts.Methylformatemightcomefromthetransesterificationofethylformateandthemethanolproduced.COmightcomefromthe

36、decompositionofethylformate.Forthelatterexperiment,7.5mLof2-butylformate(5timesamountinvolumeofethylformateusedinthefirstexperiment)and12.5mLofcyclohexanewerepouredinthereactor.AflowofpureH2(20mL/min,30bar)wasusedasflowinggas.After8hcontinuousreactionat443K,96.23%of2-butylformatewastransferredtometh

37、anoland2-butanol.Thetotalconversionswerehighwhile2-alcoholswereutilized.Buttheyieldstoesterwerealsohigh,especiallyfor2-pentanol.Itisreferredthatstep(3)abovewasslowerif2-alcoholswereused.Inothercases,therateofstep(3)wasmuchfasterthanthatofstep(2),resultinginthedisappearanceorverylowyieldofthecorrespo

38、ndingesters.IfthewaterwasaddedtoethanolwiththesamemolaramountasthatofCO2inthefeedgasunderstandardconditions,andthesameexperimentwasconducted,similarresultswereobtained.Waterdidnotaffectthereactionbehavioratthesereactionconditions.Fromthereactionmechanismabove,waterwasonlyanintermediate,similartother

39、oleofCO2insteps(1)-(3).Table2.EffectofReactantGasCompositioninaMagneticallyStirredAutoclaveexpt=no.CO(bar)h2(bar)co2(bar)ethylformatevield(駒nietlianolvield3totalyield(%)110000002102000.3000.30腫9.6181.50.280.150.4347.5184.50.430.170.605050.400.953Temperature=423I;initialpressure=30bar;react

40、iontime=2h;Cii/ZnO(B)=0.2g;alcohol(etlianol):5niL.*Argonof0.9barisalsoincluded.InTable2,theinfluencefromvariousreactantgascompositionwasinvestigatedat423KwherecatalystCu/ZnO(B)wasused.ItisclearthatthetotalreactionrateincreasedwiththeincreasingofCO2contentinthesyngas.ThereactionofCO2+H2exhibitedthehi

41、ghestreactionrate.ItseemsthatmethanolsynthesisratewasfasterfromCO2+H2thanfromCO+H2,supportingthatstep(1)inthereactionmechanismwasreasonable.ItisinterestingthatpureCOdidnotreact,indicatingcarbonylationofalcoholtoesterimpossible.WhileusingpureCO+H2asreactantgas,ethylformateformedbutmethanolwasnotobtai

42、ned.ThereactionratewasratherlowerthanthatofCO2-containedsyngas.ItishardtodeterminethereactionrouteofpureCO+H2now,asCOinsertiontoethanoltoformanesterwasexcluded.Maybewatercontainedintheethanol(about100-150ppm)reactedwithCOtoformCO2andfulfilledsteps(1)and(2).4.ConclusionsTheuseofalcohol,especially2-al

43、cohols,asacatalyticsolventinthesynthesisofmethanolfromCO/CO2/H2,notonlyrealizedanewlow-temperaturemethanolsynthesismethod,butalsoovercamedrawbacksoftheBNLmethodandotherlow-temperaturemethanolsynthesismethods.Thiseffectfromaccompanyingalcoholicsolventdecreasedgreatlythetemperatureandpressureofthesynt

44、hesisreactiononCu/ZnOsolidcatalyst,viaanewreactionpath.Thismethodisverypromisingtobecomeanewtechnologyforlow-temperaturemethanolsynthesiswherepurificationofsyngasisnotnecessary.Sincethereactionemployedconventionalsolidcatalyst,verymildreactionconditions,andsyngascontainingCO2andH2O,itmightbeapromisi

45、ngpracticalmethodformethanolsynthesisatlowtemperature.Infact,whentheamount(weight)ofcatalystwasincreased,theconversionwasincreasedlinearlyinourexperiments.50-60%conversionwasrealizedinaflow-typesemi-batchreactor,aslow-temperaturemethanolsynthesishasnothermodynamiclimitation.Butinthehigh-temperaturer

46、eaction,eventhecatalystweightisenhanced,conversioncannotbeincreasedduetointrinsicthermodynamicslimitation.Inthefuture,abubble-columnreactorisconsideredforlarge-scalesynthesis.AcknowledgmentResearchforFutureProgramfromJapanSocietyforthePromotionofScience(JSPS)isgreatlyacknowledged(JSPS-RFTF98P01001).EF0100395References1Herman,R.G.;Simmons,G.W.;Klier,K.Stud.Surf.Sci.Catal.1981,7,475.2Graaf,G.H.;Sijtsema,P.;Stamhuis,E.J.;Oosten,G.Chem.Eng.Sci.1986,41,2883.3Marchionna,M.;Lami,M.;Galleti,A.CHEM