Kinetic study for hydrolysis of methyl lactate catalyzed by cation-exchange resin
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Kineticstudyforhydrolysisofmethyllactatecatalyzedbycation-exchangeresinShao-tongJiang*,MoLiu,Li-junPanSchoolofBiotechnologyandFoodEngineering,TheKeyLaboratoryforAgriculturalProductsProcessingofAnhuiProvince,HefeiUniversityofTechnology,Hefei230009,China
1.IntroductionLacticacid(2-hydroxypropionicacidor2-hydroxypropanoicacid),CH3-CHOHCOOH,isthemostwidelyexistingcarboxylic
acid,hasaprimepositionduetoitsversatileapplicationsinfood,pharmaceutical,textile,leather,andotherchemicalindustries(Yuetal.,2007).Intherecentyears,lacticacidhasattractedgrowingattentionasamonomerforthesynthesisofbiodegradableplastic—polylacticacid(Fukuzumietal.,2009),wherethehighpurityoflacticacidisrequired.Purificationoflacticacidfromfermentationbrothisconventionallyobtainedbycalciumsaltformationfollowedbyreleaseoftheacid(Joglekaretal.,2006),reactiveextraction(HaringtonandHossain,2008),adsorption(Aljundietal.,2005),ion-exchange(Caoetal.,2002),electrodial-ysis(Yietal.,2008)andesterification–hydrolysismethod(esterificationoflacticacidwithasuitablealcoholandsubse-quenthydrolysisofthepurifiedester)(Zhaoetal.,2009).Becauseofthelowvolatilityoflacticacid(1228Cat1661.73Pa),itsaffinitytowater,anditstendencytoself-polymerize,etc.,itishardtogethighpuritylacticacid.However,theesterification–hydrolysismethodiswidelyacceptedashighlyefficientwithhighpurity,andthisprocesscanbecarriedoutbyreactivedistillation(Kimetal.,2000;Maetal.,2005;RakeshKumaretal.,2006a,b;Seoetal.,1999).Reactivedistillationhasbeenproposedasapromisingtechniquefortherecoveryoflacticacidwithhighpurityandyield
fromfermentationbroth,itcanberealizedbytwodistillationcolumns(Kimetal.,2002)oronedistillationcolumn(ChoiandHong,1999).Forthecorrectdesignofreactivedistillationcolumn,kineticsstudyforesterificationoflacticacidwithalcoholandhydrolysisoflacticacidesterareveryimportant.Kineticsofesterificationhavebeenreportedbyseveralauthors,intheirresearch,sulfuricacid(TroupeandKobe,1950a,b)orcation-exchangeresins(Delgadoetal.,2007)wereusedascatalyst,theeffectsofreactiontemperature,catalystloading,initialreactantmolarratio,etc.,wereinvestigated,theexperimentaldatawerecorrelatedbyheterogeneous(Delgadoetal.,2007)orhomogeneous(SeoandHong,2000)model.Sanzetal.(2004)reportedthekineticstudyforthereactivesystemoflacticacidesterificationwithmethanol:methyllactatehydrolysisreaction,Amberlyst15wasusedascatalyst,threemodels,thequasi-homogeneous(Q-H),theLang-muir–Hinshelwood(L–H),andtheEley–Rideal(E–H)modelswerecompared,Q-HmodelwasfoundtorepresentthehydrolysisreactionsoverAmberlyst15fairlywell.Delgadoetal.(2007)reportedkineticstudyforesterificationoflacticacidwithethanolandhydrolysisofethyllactateusinganion-exchangeresincatalyst,L–Hmodelgavethebestagreementwiththekineticexperimentaldata.Inthiswork,hydrolysisofmethyllactateovercationexchangeresinD001hasbeeninvestigated.Severalexperimentshavebeencarriedouttoanalyzetheinfluenceofthestirrerspeed,catalystsize,catalystloading,initialreactantmolarratioandtemperatureonthereaction.Toprovideageneralkineticmodel,experimentaldatawerecorrelatedbypseudo-homoge-neousmodel.
JournaloftheTaiwanInstituteofChemicalEngineers41(2010)190–194ARTICLEINFOArticlehistory:Received23March2009Receivedinrevisedform19June2009Accepted22June2009Keywords:MethyllactateHydrolysisCation-exchangeresinPseudo-homogeneousmodelABSTRACTThekineticofmethyllactatehydrolysisovercationexchangeresinD001ispresentedinthiswork.Theinfluencesofcatalystloading,initialreactantmolarratio,andtemperatureonreactionwereinvestigated.Thereusabilityofcation-exchangeresinwasstudied,nosignofdeactivationwasobservedforthereusedcatalyst.Theexperimentaldatawerecorrelatedbypseudo-homogeneousmodel.Theactivationenergyofthereactionwasfoundtobe45.84kJ/molinthepresenceofD001.Theequilibriumconstantwasfoundtobeaweakfunctionofthetemperaturebecauseofthesmallvalueoftheheatofthereaction.Thepseudo-homogeneousmodelwasfoundtorepresentthehydrolysisreactionoverD001fairlywell.ß2009TaiwanInstituteofChemicalEngineers.PublishedbyElsevierB.V.Allrightsreserved.
*Correspondingauthor.Tel.:+865512901505/8224;fax:+865512901507.E-mailaddresses:jiangshaotong@yahoo.com.cn,liumo1985@gmail.com(S.-t.Jiang).
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1876-1070/$–seefrontmatterß2009TaiwanInstituteofChemicalEngineers.PublishedbyElsevierB.V.Allrightsreserved.doi:10.1016/j.jtice.2009.06.006