Catalyst loss and retention during alkali-catalysed carbon gasification

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1、CarbonVol.2Y.No.7,pp929-941.19910008-622319I$3.00+.11(1PrintedinGreatBritain.Copyright01991PergamonPressplcCATALYSTLOSSANDRETENTIONDURINGALKALI-CATALYSEDCARBONGASIFICATIONINCO2R.MEIJER,M.WEEDA,F.KAPTEIJN,andJ.A.MOULIJNDepartmentofChemicalEngineering,UniversityofAmsterdam,NieuweAchtergrach

2、t166,1018WVAmsterdam,TheNetherlands(Received2July1990;acceptedinrevisedform5November1990)Abstract-Characterizationofthecatalyst/carbonsamplesbyoutgassingyieldedreproducibleandcon-sistentresults,providedtheamountsofCO1andCOreleasedarerelatedtotheamountofalkalimetalactuallypresent.Thecataly

3、ticallyactiveclusterisanchoredtothecarbonbyphenolategroupsandiscapableofchemisorbingoneCO,moleculeperthreetofivealkalimetalatoms.BetweenKIC=0.02to0.04thealkaliclustersizeincreases,butthespecificgasificationrate,rK,remainsunaffected.DuringpotassiumcatalysedCO,gasificationinitially20%to40%o

4、fthepotassiumwaslost;therestremainedpresentthroughoutthegasificationprocess.TheamountofcatalystthatcanbestabilisedonthecarbonincreasesintheorderNa

5、ed.Thedifferencesbetweenthealkalimetalsarisefromtheirabilitytomigrateintothecarbonmatrixandtheirinteractionwithlatticeoxygenatwhichtheyaretrapped.ThismigrationofCsandKintothecarbonmatrixexplainstheburn-offprofilesofcatalyst/carbonsamplesafterTPDtreatment.Initiallyonlypartofthecatalystisac

6、tiveforgasification,butgraduallymorecatalystbecomesavailable,resultinginanincreasinggasificationrate.Thisbehaviourisabsentforsodium.KeyWords-Alkali-catalysed,carbongasification,carbonreactivity1.INTRODUCTIONcatalysedgasification.Itiswellknownthatadditionofalkalimetalstocar-co,+*+co+o-*(I)

7、bonaceousmaterialshasacatalyticeffectontheirgasi-Ification.Agenerallypostulatedmechanism[l-51forcatalyticgasificationconsistsofanoxidation-re-o-*+c,+C(0)+*(2)2ductioncycleinwhichoxygenistransferredtothecarbonmatrixthroughthecatalyticallyactivealkaliC(0)*co(3)species