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Attrition

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AttritionAttrit

    Attrition

1288

    ;JournalofZhejiangUniversitySCIENCEA

    ;ISSN1673565X(Print);ISSN18621775(Online)

    ;wwwzjuedu.cn/jzus;wwwspringerlink.com

    ;Email:jZUS@ZjU.educn

    ;Teng/JZhejiangUnivSciA20089(9):12881295

    ;Attritionresistantcatalystfordimethylethersynthesis

    ;?n’l?’?’

    ;lntlUtdlZedbedreactor

    ;Li.huaTENG

    ;(InstituteofBiologyandEnvironmentalScience,ZhejiangWanliUniversity,Ningbo315100,China)

    ;Email:tlh98@163.corn

    ;ReceivedMar.3,2008;revisionacceptedMay12,2008

    ;Abstract:Fluidized.bedreactorisacandidatefordimethylether(DME1synthesisfromsyngasbecauseofitsexcellentheat

    ;removalcapability.Inordertoimprovetheattritionresistanceofcatalyst.anamountofsilicasolasbinderwasaddedtothe

    ;catalystcomposedofmethanolsynthesiscomponentCuO/ZnO/Al2OandmethanoldehydrationcomponentHZSM.5,which

    ;waspreparedbycoprecipitationandshapedbyspraydryingtogetsphericalparticles.Theeffectofsilicasolonthecatalytic

    ;activitywasinvestigatedinafixed.bedflowmicroreactor.Basedontheexperimentresults.silicasolintherangeof0-20wt%

    ;hadsmalleffectonthecatalyticactivity.Generally.theCOconversionandDMEyielddecreasedwiththeincreaseinconcen.

    ;trationofsilicaso1.whiletheattritionresistanceofcatalystsincreasedwithincreasingsilicaso1.indicatingthatitwasfeasibleto

    ;improvetheattritionresistancewithoutgreatlysacrificingtheactivityofcatalyst.Inaddition.thecharacterizationsofcatalysts

    ;werecarriedoutusingBrunauer.Emmett.Teller(BET),X.raypowderdiffraction(XRD)andtemperatureprogrammedreduction

    ;(TPR).

    ;Keywords:Dimethylether(DME),Attritionresistance,Catalyticactivity,Silicasol ;doi:10.1631/jzus.A0820155Documentcode:ACLCnumber:TQ426.63

    ;INTRODUCTION

    ;Dimethylether(DME1hasattractedwideatten.

    ;tionasausefulchemicalintermediatefortheprepa.

    ;rationofmanyimportantchemicals.suchasmethyl

    ;acetateandlowerolefins.Especially,DMEcanbe ;usedasafuelfordieselengineswiththerl’nale.

    ;cienciesequivalenttotraditionaldieselfue1.much ;lowerNOxemission.near.zerosmokeproductionand ;lessenginenoise.ThephysicalpropertiesOfDMEare ;similartotheseofliquefiedpetroleumgas(LPG),so ;DMEcanreplaceLPGasdomesticfue1.Inaddition. ;DMEisalsousedasanaerosolpropellanttosubsti. ;tuteforchlorofluorocarbonswhichharmtheozone ;layer(Takeguchieta1.,2000;Omataeta1.,2002; ;Luaneta1.,2007;Moradieta1.,2007a).Therefore, ;whenairpollutionandenergycrisisaretwoofthe ;mostseriOUSproblemsallovertheworld.thestudyon ;DMEasanalternativeandcleanfuelisagainem. ;phasized(Qieta1.,2001;Kimeta1.,2004;Suneta1., ;2004;FeiPfa1..2006;Semelsbergereta1..2006; ;Moradieta1..2007b).

    ;Sincethel980s.directsynthesisofDMEfrom ;syngashasbeencontinuingresearchfoCUSforits ;markedeconomicvaluesandtheoreticalsignificance ;(Gogateeta1.,1992;Pengeta1.,1999;Yaripoureta1., ;2005;Andreaseneta1.,2006;Wangeta1.,2006a). ;However,thethreereactions,i…emethanolsynthesis

    ;(CO+2H2CH3OH+90.4kJ),methanoldehydra- ;tion(2CHOHCHOCH+H2O+23.7kJ)and

    ;watergasshift(CO+H2OCO2+H2+40.9kJ)

    ;includedintheprocessofdirectDMEsynthesisfrom ;syngasareallhighlyexothermicreactions.Therefore, ;thereisneedforreactorstoeasilyremovereaction ;heat.Slurrybubblecolumnreactors(SBCRs)are ;attractivefortheirheatremovalcapability(Guoand ;Huang,1997;Liueta1.,2002).However,SBCRs ;

    ;Teng/JZhejiangUnivSciA20089(9):12881295

    ;encounterseriousmasstransferproblemduetothe ;introductionofinertliquidphasesuchaswaxyliquid ;forefficientheatremoval,whichbecomesthedraw

    ;backofindustrialproductionOfDME.XiaoandLu ;(2002)proposedtosynthesizeDMEinfluidizedbed

    ;reactor.Fluidized-b?edreactorsshowbetterheatre

    ;movalpropertybecauseofthemovementofcatalyst ;particlesinthebed.Ithasbeencalculatedthatthe ;coemcientofheattransferinfluidizedbedreactoris

    ;fivetimesasmuchasthatinSBCRs.Furthermore.it

    ;wasreportedfWangeta1.,2001)thatintheslurry ;reactortheCOconversionwasabout17%.theselec

    ;tivityOfDMEwas70%attheconditionsOf7260.C. ;P----4.0MPa,H2/CO=1.0(v/v),andgasspacevelocity ;of3000ml/(g.h.Underthesameconditions,inthe ;fluidized..bedreactorCOconversionandDMEselec.. ;tivitycanbeashighasupto48.5%and97.0%(Teng, ;2004),whileinafixedbedreactor,thecorresponding

    ;levelsare10.7%and91.9%(Lueta1..2002).Obvi

    ;ously.thefluidized-bedreactordemonstratacon

    ;siderableDMEproductivityimprovementoverboth ;thefixedbedandtheslurryreactor.Therefore,one ;canconcludethatamongdifferentreactorsthefluid

    ;ized-bedisthemostpromisingcandidateforcon

    ;ductingtheDMEsynthesisfromsyngas.

    ;However,catalystsusedinfluidized-bedreactor ;aresubjecttoattritionfromcollisionbetweencatalyst ;particlesandthereactorwallwhichcanresultinloss ;ofcatalystandpluggingoffilter(Rayeta1.,1987; ;PetukhovandKalman,2003).Soattritionresistance ;isoneofthecriticalparametersinthedevelopmentof ;catalysts.Theobjectiveofthisstudyistodevelopa ;kindofcatalystsuitableforfluidizedbedapplication

    ;withhighcatalyticperformanceandhighattrition ;resistance.ThecatalystpresentedinthisPaDeris ;basedonCubasecatalystandHZSM5.preparedbya

    ;conventionalcoprecipitationmethod(Ramoseta1., ;2005).Themethodtoimproveattritionresistanceis ;tointroducesilicasolasbindertotheactivecompo

    ;nents,followedbyspraydryingwhichyieldsspheri

    ;calparticlesfavorableforfluidizedbedreactoraD

    ;plication(Bukureta1..2005).However,improvement ;inattritionresistanceattheexpenseofactivityand ;selectivityofcatalystisundesirable.Todetermineif ;thesilicasolisfeasibleinimprovingtheattrition ;resistancewithoutsacrificingtheactivityofcatalyst, ;theeffectofsilicasolonthecatalyticperformance ;andattritionresistancewasstudied.

    ;EXPERIMENTS

    ;1289

    ;Catalystpreparation

    ;Thecatalystsusedinthisstudywerepreparedby ;aconventionalcoprecipitationmethodandshapedby ;spraydrying.Thesecatalystshadthesamecomposi

;tionOfCuO,ZnO,A12O3andHZSM5butwithdif-

    ;ferentconcentrationsofsilicaso1.Theprocessof ;catalystpreparationwasdescribedindetailasfollows. ;First.itwasprecipitatedfromanaqueoussolutionOf ;Cu03)2andZn(NO3)2bydropwiseadditionofa1 ;mol/LaqueoussolutionofNa2COat80.Ctoafinal ;PHvalueof7.Then.themixturewasthoroughly ;washedbydeionizedwatertoremovethesodiumion ;andthenAI(OH)powerwasaddedtotheprecipitate. ;Atthistimethecompositionofcatalystwas38 ;CuO/38ZnO/8A12O3byweight,whichwastheactive ;componentformethanolsynthesis.Itcontained9.5 ;partsbyweight(pbw)ofA1203.Followingthis,the ;aciddehydrogenationcomponentHZSM5wasthor-

    ;oughlymixedwiththeaboveprecipitate.Theratioof ;themethanolsynthesiscomponenttotheaciddehy

    ;drogenationcomponentis5:1byweight.Afterthat.

    5,lessthan0.05wt%ofsodium,25 ;silicasolfpH4;

    ;wt%ofsilica,providedbyQingdaoSeaChemical ;ResearchInstitute)ofdifferentpartsbyweightas ;binderwasaddedandblendedcompletely.Finally,the ;slurrywasspraydriedinaspraydrierwithdimen

    ;sionsOf1.8minsidediameterand6.8mtotalhighto ;obtainsphericalparticles.Thespraydriedcatalyst

    ;wascalcinedat350.Cfor3hinamumefurnace. ;Spraydryeroperatingconditionshavemuchef- ;fectontheparticlecharacteristics.Inordertoobtain ;thesuitableoperatingconditions,theef-fectofope

    ;atingconditionsontheparticlesizedistributionand ;morphologywasstudied.Basedontheexperimental ;resultsobrained,itwasdeterminedthattheappropriate ;parameterswerenozzlediameterOf0.91TlIn.pressure ;of2MPa.feedrateOf30L/h.theinlettemperatureof ;300.Candoutlettemperatureof140.C.Thedetail ;resultsweredescribedin(Teng,2004).

    ;Reactionstudies

    ;ThecatalyticpropertyofcatalystsforDME ;synthesisfromsyngaswastestedinalaboratoryscale

    ;high..pressureandhigh..temperaturestainlessfixed.. ;bedreactor.Thereactorhadasizeofl0mmx300 ;mmandcontained2.0gofpackedcatalysts(40;80

    ;

    ;1290Tong/JZhejiangUnivSciA20089(9):12881295

    ;meshes).Thesecatalystsweresupportedbetweentwo

    ;layersofquartz,theupperlayerofwhichwasusedto ;preheatthereactants.Athermocouplewaslocatedat ;thelevelofthecatalystsinthereactor.Gasflowrate ;wascontrolledbymassflowcontroller.Thereaction ;pressurewascontrolledbybackpressurevalve.The ;downstreamlinefromthereactorexittotheanalysis ;systemwascoatedbyheatingbelttoavoidthecon

     ;densationofwaterandmethanolformedduringreac

    ;tion.Beforethefeedgaswasintroduced.catalysts ;needtobereducedwithpureH,atthenormalpres

    ;sureandaflowrateof100ml/minaccordingtothe ;followingheatingprogram:heatingupfromroom ;temperatureto300.Cataheatingrateof1.C/min ;andthenkeepingfor3h.

    ;Followingcatalystreduction,thereactortem

    ;peraturewasdecreasedtoreactiontemperatureand ;H2flowwasstopped,followedbysyngasataspace ;velocityof3000ml/(g_h1.Thesyngaswasapremixed ;gasofCOandH2(H2/CO=1,v/v).Thereactorsystem ;wasthenpressurizedto3MPa.Afterachievingthe ;desiredprocessconditionof260.C,3MPa,3000 ;ml/(g_h),thesamplewasanalyzedeveryother0.5h ;tilltheactivityofcatalystreachedastablestate. ;Alltheproductsandfeedgaswereanalyzedby ;anonline7890Tgaschromatographmadeby ;ShanghaiTianmeiScientiticInstrumentFactoryin ;ChinathatwascoupledwithaCDMClEXintegrator

    ;Thedifrerentgasestobeanalyzedwereseparatedby ;acolumnfilledwithGDX101.Athermalconductiv

    ;itydetector(TCD1wasusedtodetectreactionprod

    ;ucts.TheCOconversionandDMEyieldwerede

    ;finedasfollows:

    ;ynME=2FoulYDME,.ut

    ;Y..

    ;×100%(mol/mo1),

    ;×100%(mol/mo1),

    ;whereFinisgasflowrateatinletofreactor(mol/min); ;Foutisgasflowrateatoutletofreactor(mol/min); ;Yco,in,Yco,out,YDME,outare

    ;inlet,outletandmolarof

    ;percentbymolarofCOat

    ;DMEatoutlet,respectively.

    ;Catalystcharacterization

    ;DetailedphysicalandchemicalcharacterizatiOn

;ofcatalystswascarriedoutusingthefollowingana

    ;lyticaltechniques.Morphologyinformationforeach ;samplewithdifferentbinderpartsbyweightwas ;achievedbyaJapaneseJSM6360LVfromJEOL

    ;scanningelectronmicroscopefSEM)atanacceler

    ;atingvoltageof15.0kV.Thesampleswerecoated ;withpalladiumbeforeSEMmeasurementstoavoid ;chargingproblems.

    ;Theattritionofthecatalystswasmeasuredusing ;testmethodASTMD575795inafluidizedbedtest

    ;systemwith26mm(diameter)x25001TIITI(height). ;Particlesizeslessthan20Bmareconsideredfines. ;Thefinecollectionwasweighedbeforeandafterthe ;test.Thesystemconsistsofaverticalattritiontube ;madefromstainlesssteelwith20001TIITIlongand26 ;mminsidediameter.Thereisanorificeplateattached ;tothebottomofthistube.Abovetheattritiontubeis ;thesettingchamberwitha1001TIITIinsidediameter. ;Thegasoutletofthesettingchamberisconnected ;withafilterinordertopreventfineparticlelOSS.The ;attritionlOSSiScalculatedfromthefineparticlesto ;givearelativeestimationoftheattritionresistanceof ;thecatalyst.TheattritionlOSSiSbasedonthefinelOSS ;after4h.Tofurtherillustratetheattritionresistanceof ;thecatalystprepared,akindofindustrializedcatalyst ;Cu/SiO,forfluidizedbedreactorwasusedforcom

    ;parison.TheattritionlOSSOfdifferentcatalystswas ;testedunderthesametestcondition.

    ;Particlesizedistribution(PSD)ofcatalystpar

    ;ticleswasanalyzedusinganAmericanLS(Ac

    ;cuSizerTM780)particlesizeanalyzerfromcompany ;ofParticleSizingSystems(PSS).Thissystemwas ;controlledwithacomputersystem,andtheoutput ;fromthecomputerprovidedaplotofvolumeper

    ;centageVSparticlesizeinterva1.Thesamplewas ;measuredbeforeandafterattritionmeasurement. ;TheBrunauerEmmett1ller(BET)specific

    ;surfaceareaofthecatalystswasdetermined,basedon ;N2physicsorptionatliquidnitrogentemperatureona ;micromeriticsASAP2010system.Thesampleswere ;degassedat393Kfor1hpriortoeachmeasurement. ;Xraypowderdiffraction(XRD)patternswere ;obtainedonaRigakuD/max255VB/PCXrayunit,

    ;andtheXRDpatternswererecordedfor20from5.

;tO75.usingCuKradiation.Analyseswerecon

    ;ductedusingacontinuousscanmodeatascanrateof ;8./min.

    ;Fordeterminationofthereductionbehaviorof ;thecatalysts,temperatureprogrammedreduction ;

    ;Tong/dZhefiangUnivSciA20089{9):1288-1295 ;(TPR)experimentswerecarriedoutonAutochemII ;2920system.Asampleofcloseto0.025gwasdried ;anddegassedunderArflowat400.Cfor1h.and ;followedbycoolingdowntoambienttemperature. ;ReductionwasperformedunderH2/Argasmixture ;(5/95.v/v).Thetotalgasflowwas50ml/minand ;temperatureprogramwas25-600.Cataheatingrate ;of5.C/min.

    ;RESUISANDDISCUSSION

    ;EffectOfbindersilicasoloncatalyticactivity ;Whencatalyticactivitywasinspectedinaflu. ;idized.bed.reactor.alotofgaswasneededandthe ;operationwascomplicated.Sincethemainpurposeof ;theevaluationofcatalyticactivitywastoinspectthe ;changeofthecatalyticactivityafteraddingbinder, ;namelytherelativevaluesoftheactivity.theevalua. ;tiononthecatalyticactivitymainlyinthefixed.bed ;micro.reactorwasconducted.

    ;Theefrectofbindersilicasolonthecatalytic ;activitywasshowninFig.1.Generally,theCOcon

    ;versionandDMEyielddecreasedwithanincreasein ;concentrationofbindersilicaso1.However,ascanbe ;seen,thecatalyticactivitywasnotremarkablyde. ;creasedintherangeOf0tO20wt%silicasol;beyond ;20wt%additionofsilicasolcatalyticactivityand ;DMEyielddecreasedsignificantly.Gaschromatog. ;raphyanalysisshowedthatthemainby.productwas ;methano1.Thecontentofmethanolincreasedwiththe ;increaseofthesilicaso1.Thisismainlyduetoexist

    ;ingapreferentia1amnitVofthemethanoldehydration ;componentforthesilicasol1eadingtosurface ;blockingprovedbythefollowingXRDpattems, ;whichinhibitedthereactionofmethanoltoDME.For ;Concentrationofsilicasol(wt%)

    ;Fig.1Effectofsilicasoloncatalyticactivity ;1291

    ;thecatalystwithoutsilicasol,C0conversionand

    ;DMEyieldwere66.8%and46.2%.respectively. ;When20wt%silicasolwasintroducedtothecatalyst. ;theCOconversiondecreasedto60.5%andtheyield ;ofDMEdecreasedto42%.indicatingthatitispos. ;sibletoimprovetheattritionresistancebyadditionof ;bindersilicasoltothecatalystcomponentsfollowed

     ;byspraydryingwithoutgreatlysacrificingtheactiv

    ;ityofcatalyst.

    ;Thecatalystcontaining20wt%silicasolwas ;evaluatedina1aboratory.scalefluidized.bedreactor. ;Theexperimentalresultsshowedthatthecatalysthad ;agoodactivityandselectivity.Thedetailresultswere ;describedin(Teng,2004).Then,themorphology ;information.PSDandothercharacteristicsofthe ;particleswerecharacterized.

    ;CatalystcharacterizatiOn

    ;Therewasagreatinfluenceofphysica1and

    ;chemicalpropertyofcatalystsonthecatalyticprop

    ;erty.Direntcharacterizationmethodswereusedto ;explainandidentifytheexperimentresults. ;1.BET

    ;TheBETspecificsurfacearea.porevolume. ;averageporediameterandattritionlossofcatalysts ;withbindersilicasolfrom0to30wt%werelistedin ;Table1.Theattritionlosswasbasedontheweightof ;thefineparticlesafter4h.Asshown,theattritionloss ;decreasedwithanincreaseinconcentrationofsilica ;sol,indicatingsilicasolisfavorablefortheim. ;provementofattritionresistance.TheBETspecific ;surfaceareaandporevolumeofcatalystsshowedthe ;maxima,whileaverageporediameterdecreasedwith ;increasingsilicaso1.Theresultsmaybeexplainedby ;matsilicasolenterstheporesoftheorigina1network ;ofthecatalysts,whichhelpstopreventacollapseof ;Table1Effectofsilicasolonphysicalpropertiesof ;catalysts

    ;一一

    ;

    ;1292Teng/JZhejiangUnivSciA20089(9):12881295

    ;porestructure.Ontheotherhand.thereareinter. ;1ockingforcescreatedbetweenthebindersilicasol ;andcatalystcomponents.Itwasalsofoundthatthe ;catalystswithdifferentcontentofbindersilicasolhad ;adensityofabout0.53-0.60g/cmfnotshownin

    ;Tablel1.indicatingthatforthedensitytherewasno ;significantchangewiththeadditionofbinder. ;2.XRD

    ;XRDOfthecatalystscontaining10wt%binder. ;20wt%binderandthecatalystwithoutsilicasolwere ;showninFig.2.Thepattemshadbeenplottedover20 ;valuerangingfrom5.to75..Theidenti?

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