Effects-of-step-change-of-synthesis-temperature-on-synthesis-of-zeolite-4A-from-coal-fly-ash

Effectsofstep-changeofsynthesistemperatureonsynthesisofzeolite4AfromcoalflyashK.S.Hui,C.Y.H.Chao*DepartmentofMechanicalEngineering,TheHongKongUniversityofScienceandTechnology,ClearWaterBay,Kowloon190,HongKongReceived8December2004;receivedinrevisedform2September2005;accepted16September2005Availableonline2November2005AbstractPureform,singlephaseandhighcrystallinezeolite4Asamplesweresynthesizedbyapplyingstep-changeofsynthesistemperatureduringhydrothermaltreatmentofcoalflyashpreparedsolution.Theresultsindicatethatstep-changeofsynthesistemperatureduringhydrothermaltreatmentplaysanimportantroleinreducingtheoverallsynthesistimewhilemaintainingahighdegreeofcrystallinityforthesamples.Inordertoobtainsimilarqualityofzeolite4Asample,areductionbyhalfofthetotalsynthesistimecouldbeachievedbyapplyingstep-changeofsynthesistemperaturecomparedtousingconstanttemperaturethroughoutthesynthesisprocess.Generally,thecrystallinityofthesynthesizedzeolite4Asampleswasintherangeof75–87%.Theyielding(quantity)ofpurezeolite4Asamplesobtainedinalltheexperimentswasabout15–18%.Inaddition,crystalsofsmallerparticlesizeexistinginanarrowerparticlesizedis-tributionweresynthesized.�2005ElsevierInc.Allrightsreserved.Keywords:Coalflyash;Zeolite4A;Synthesis;Temperature1.IntroductionLargequantitiesofcoalflyashareproducedinelectricpowerplantsthroughouttheworldeveryyear.Theamountofcoalflyashformedisapproximately500milliontonsperyearandispredictedtoincrease.Efficientdisposalofcoalflyashhasbeenaworldwideissuebecauseofthemassiveamountofashproducedandharmfuleffectsonenviron-ment[1–3].Asatechniqueforrecyclingcoalflyash,synthe-sisofzeolitesfromcoalflyashhasreceivedextensiveattentionoverthelastdecade.Duetotheiruniformporesizesandlargesurfaceareas,zeolitesareveryusefulmateri-alsforawiderangeofapplicationssuchasionexchanger,molecularsieves,gasesadsorbentsandcatalysts.Manyresearchershaveinvestigatedthesynthesisofzeolitesfromcoalflyash[3–40].However,inmanyofthesestudies,thetotalconversiontimewasgenerallylong(24–72hormore)and