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A comparative study on chemical conversion of cellulose between the batch-type and

Cellulose 9: 301–311, 2002.

©2002KluwerAcademicPublishers.PrintedintheNetherlands.

301

Acomparativestudyonchemicalconversionofcellulosebetweenthebatch-typeand?ow-typesystemsinsupercriticalwaterN

KatsunobuEharaandShiroSaka*

DepartmentofSocio-EnvironmentalEnergyScience,GraduateSchoolofEnergyScience,KyotoUniversity,606-8501Sakyo-ku,Kyoto,Japan;*Authorforcorrespondence(e-mail:saka@energy.kyoto-u.ac.jp;phone:+81-75-753-4738;fax:+81-75-753-4738)

Received29October2001;acceptedinrevisedform4March2002

Keywords:Chemicalconversion,Hydrolysis,Sacchari?cation,SupercriticalwaterAbstract

Microcrystallinecellulose(avicel)wastreatedinsupercriticalwaterusingbatch-typeand?ow-typesystems.The?ow-typesystemmadeitpossibletoshortentheheating,treatingandcoolingtimes,comparedwiththebatch-typesystem.Asaresult,the?ow-typesystemwasabletoliquefyavicelwithoutproducinganysupercriticalwater-insolubleresidue.Althoughhydrolyzedproductssuchasglucoseandfructose,andpyrolyzedproductssuchaslevoglucosan,5-hydroxymethylfurfural,erythrose,methylglyoxal,glycolaldehydeanddihydroxyacetonewerefoundincommonfromthewater-solubleportiontreatedbybothsystems,the?ow-typesystemgaveawater-solubleportionwithmorehydrolyzedandlesspyrolyzedproducts,togetherwithwater-solubleoligosaccharidesconsistingofcellobiosetocellododecaoseandtheirdecomposedproductsattheirreducingendofglucose,suchas[?-D-glucopyranosyl]1–11?-D-levoglucosan,[?-D-glucopyranosyl]1–11?-D-erythroseand[?-D-glucopyrano-syl]1–11?-D-glycolaldehyde.Inaddition,theprecipitatesofpolysaccharideswererecoveredafter12hsettingofthewater-solubleportion.Theseresultsindicatedthatthe?ow-typesystemcanhydrolyzecellulosewithmini-mizingpyrolyzedproducts.Ontheotherhand,thebatch-typesystemresultedinahigheryieldofthepyrolyzedproductsduetothelongertreatment,butahigheryieldofglucoseduepossiblytothehigherpressureandcon-comitantlyhigherionicproductofwater.Basedontheselinesofevidence,theprocesstoincreasetheyieldofthesugarisdiscussedundersupercriticalwatertreatment.Introduction

Fossilresources,whichincreasethecarbondioxideemissionintheenvironmentsthroughtheircombus-tion,areconsideredtobecomeexhaustedsoonerorlater.Therefore,biomassresourceswillbecomemoreimportantinthefutureasalternativestothefossilre-sources.Fortheconversionofbiomassresourcesintousefulchemicalsandbiomass-energy,sacchari?cationofcellulosicresourcesfollowedbyfermentationisoneofthedirections.Furthermore,glucosewhichcanbeconvertedtochemicalssuchasethanol,ethyleneand5-hydroxymethylfurfural(5-HMF)isakeyprod-Presentedatthe8thAnnualMeetingoftheCellu-loseSocietyofJapanwhichwasheldonJuly12–13,2001.

A comparative study on chemical conversion of cellulose between the batch-type and

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uct.Forthispurpose,twomajormethodsexistforhydrolysisofcarbohydrates,byacidcatalyst(Parisi1989)andenzymaticsacchari?cation(ChangandHoltzapple2000).Althoughtheseprocesseshavebeenre?nedandconsiderablydeveloped,theyhaveatleastthefollowingdrawbacks;theformerhasacorrosionproblemofthereactorbyacid,whilethelatterinvolvestheuseofenzymeexpensiveforitspreparation(Goldstein1980).

Forchemicalconversionofcellulose,ontheotherhand,anewapproachhasbeendevelopedrecentlywithnon-catalyticsubcritical(Sakakietal.1996a,1996b;Walsumetal.1996)orsupercriticalwater(>374°C,>22.1MPa)treatment(Sakakietal.1996b;Sasakietal.1998).Inourlaboratory,itwasconse-quentlyreportedthatwoodybiomassresourcescanbe

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