金属离子对离子液体中竹子酸解的影响

Effectsofmetalionsonthehydrolysisofbamboobiomass

in1-butyl-3-methylimidazoliumchloridewithdiluteacidas

catalyst

NanWanga,JieZhanga,HonghuiWanga,QiangLib,Sun’anWeia,DanWanga,?

ab

DepartmentofChemicalEngineering,SchoolofChemistryandChemicalEngineering,ChongqingUniversity,Chongqing400044,PRChinaNationalKeyLaboratoryofBiochemicalEngineering,InstituteofProcessEngineering,ChineseAcademyofSciences,Beijing100190,PRChina

highlights

??MetalionswasusedinacidichydrolysisofbamboobiomassinILs.??Themechanismofthehydrolysissystemwasinvestigated.

??Thereactiontimewassigni?cantlydecreasedalongwiththeincreasedTRSyield.??ThemosteffectiveionisCu

2+

ionandthemaximalTRSyieldof67.1%wasachieved.

articleinfoabstract

Inthisstudy,theeffectsofsixmetalionsincludingNa+,K+,Mg2+,Ca2+,Cu2+andFe3+onhydrolysisofbamboobiomassbydilutedhydrochlorideacid(HCl)inionicliquid[C4mim]Clundermildconditionswasinvestigated.Thesemetalionsasco-catalystsexhibitedsigni?canteffectsonacceleratingthehydro-lysisprocessandimprovingtheyieldoftotalreducingsugarcomparedtosingledilutedhydrochlorideacidhydrolysisin[C4mim]Clatthesameconditions.ThemosteffectiveionwasCu2+andthetotalreduc-ingsugaryieldof67.1%wasachievedat100°CwithCuCl2asco-catalystafter4-hreaction.Thetotalreducingsugaryieldwasincreasedbyabout7%andthereactiontimewasdecreasedby3h.Thekineticmodelwasalsoinvestigatedtogiveaninsightintothemechanismofhydrolysisprocess.

ó2014ElsevierLtd.Allrightsreserved.

Articlehistory:

Received29June2014

Receivedinrevisedform23September2014

Accepted24September2014Availableonline2October2014Keywords:

BamboobiomassIonicliquidsMetalionsHydrolysis

Dilutehydrochlorideacid

1.Introduction

Lignocellulosicbiomasshasshownpromiseasanef?cientrenewablecleanenergyresourcethatcanbeconvertedtofuelsandhigh-valuedchemicals.Extensiveresearchanddevelopmentprogramshavebeeninitiatedworldwidetotransformthelignocel-lulosicbiomassintovariousvaluableproductsthroughbiore?nery,inwhichliberationofreducingsugarsfromlignocelluloseisthe?rstkeystep(Ragauskasetal.,2006;J?gerandBüchs,2012).Unfortunately,lignocellulosicbiomassconfersanotoriousresis-tancetohydrolysisduetoitscomplexhetero-matrixstructure(Himmeletal.,2007).

Uptonow,hydrolysisoflignocelluloseorcellulosetoitscomponentmonomericsugarshasbeenwidelyinvestigated.Correspondingauthorat:P.O.Box94,174ShazhengStreet,ShapingbaDistrict,DepartmentofChemicalEngineering,SchoolofChemistryandChemicalEngineer-ing,ChongqingUniversity,Chongqing400044,PRChina.Tel./fax:+862365111179.

E-mailaddress:dwang@cqu.edu.cn(D.Wang).

http://dx.doi.org/10.1016/j.biortech.2014.09.1250960-8524/ó2014ElsevierLtd.Allrightsreserved.

Amongallthehydrolysistechnologies,enzymesandacidcata-lystsarethemostpromisinghydrolysiscatalysts(Lenihanetal.,2010;Wangetal.,1996).However,thesecommonhydrolysismethodsexhibitcertaindisadvantagesandarenotcost-effectiveforlarge-scaleapplications.Forexample,enzy-matichydrolysissuffersarelativelylowhydrolysisrateandenzymesareusuallyexpensiveanddif?culttorecycle(Mora-Paleetal.,2011).Thetraditionaldilutedacidhydrolysisprocessrequiresharshconditionsandresultsinthedecompo-sitionofmonosaccharide(Mora-Paleetal.,2011).Whatismore,pretreatment,asahighcostprocess,isusuallyrequiredtodecomposetheruggedconstructionoflignocelluloseinthathydrolysisabove.Concentratedacidssuchassulfuricacidandhydrochloricacidhavealsobeenusedtotreatlignocellulose(Heinonenetal.,2012).Thoughtheyarepowerfulagentsforcellulosehydrolysis,concentratedacidsaretoxic,hazardousandrequirecorrosion-resistantreactors(SunandCheng,2002).Andtheconcentratedacidwillbecomeenvironmentalpollutantwithoutthoroughrecycling.Therefore,hydrolysisof

400N.Wangetal./BioresourceTechnology173(2014)399–405

lignocelluloseviaaneconomicalandenvironmentallyfriendlyapproachremainsachallenge.

Theveryhighsolvatingpropertyofionicliquids(ILs)wasexploitedinthedissolutionofcellulosebyRogersetal.in2002(Swatloskietal.,2002).Sincethen,researchontreatmentofligno-celluloseinILshasgainedmuchmoreattention.IthasalreadybeenshownthatILscandissolvealargenumberofbiomass,suchascornstalk,wheatstraw,ricestrawandwood(daCostaLopesetal.,2013;WeerachanchaiandLee,2013;Sunetal.,2009).AndILscanpresentahighef?ciencyinthepretreatmentofbiomass(Vielletal.,2013;Bianetal.,2014).Furthermore,sinceLiandZhao(2007)?rstlyfoundthatmineralacidscouldfacilitatethehydrolysisofcelluloseintheionicliquid1-butyl-3-methylimida-zoliumchloride,muchmoreattentionhasbeenpaidonthehydro-lysisofbiomassinILswithacidcatalystsdirectly(Rinaldietal.,2008;Sieversetal.,2009;Vanoyeetal.,2009).Lietal.(2008)reportedbiomasshydrolysisinILswithdifferentinorganicacidsascatalystsandamaximum81%liberationofthetotalreducingsugarswasachieved.AmarasekaraandOwereh(2009)usedBr?nstedacidILs,whichactasboththesolventandcatalyst,todis-solveandhydrolyzecelluloseandobtainedatotalreducingsugaryieldof62%.Withoutenzymehydrolysissubsequently,combinedILdissolutionandacidcatalysismayprovideaneconomicalapproachtoreleasereducingsugarsfrombiomass.

Inrecentyears,additionofmetalionsintraditionaldiluteacidpretreatmentorhydrolysishasbecomearesearchhighlight,sincemetalionscanincreasethedecompositionrateofcelluloseandhemicelluloseandreducetheseverityofhydrolysisconditions(Kamireddyetal.,2013).Monavarietal.(2011)foundthatadditionofsmallamountofferroussulfateindilute-acidpretreatmentresultedinaslightlyincreasedoverallglucoseyield.Weietal.(2011)reportedthatduringdiluteacidandferrousionco-catalystpretreatment,solubilizedsugarsincreasedinthehydrolysatecon-comitantlywithanincreaseofreducingsugarsinthebiomassres-idues.Yanetal.(1996)reportedthatahighyieldofsugarcouldbeobtainedfromhydrolysisofpeatwithferricchlorideandhydrogenchlorideascatalysts.Zhaoetal.(2013)investigatedtheacidhydro-lysisofcornstoverundermicrowaveradiationbyaddingvariousmetalsaltsindividuallyasco-catalystsandfoundthatFeSO4hadexhibitedabettercatalyticeffect.

Thoughsomeworkshavebeenexecutedtoexaminetheeffec-tivenessoftheadditionofacidascatalystinILsforlignocellulosehydrolysisandthesupplementationofmetalionsfortheacidichydrolysisrespectively,thereisseldominformationontheacidichydrolysisoflignocellulosicbiomassinILswithmetalionsaddedasco-catalyst.ThepurposeofthisstudyistoinvestigatetheeffectsofmetalionadditionsonthediluteacidhydrolysiswithILsasreactionmediumandprovideaninsightontheselectivityofmetalionsthatcanyieldhighreducingsugars.Inordertoreducetheenergyconsumptionandtheproductsdegradation,thehydrolysiswereconductedatlowseverityconditions.Inthiswork,dilutedhydrochlorideacidcatalyzedhydrolysisofbamboopowderin1-butyl-3-methylimidazoliumchloride([C4mim]Cl)wereper-formedwithsixkindsofmetalchlorides(NaCl,KCl,MgCl2,CaCl2,CuCl2,FeCl3)addedrespectivelyasco-catalyst.Thepossibledecompositionmechanismoflignocellulosein[C4mim]Clwithhydrochlorideacid(HCl)andCuCl2wasproposed.

2.Methods2.1.Materials

ThefeedstockmaterialwasobtainedfreelyfromabamboogroveinChongqingCity,China.Bamboowasmilledtopassthroughan80meshsieve.Themainchemicalcompositionof

rawbambooexpressedintheweightpercentofthedrymatterisasfollows:40.1%glucan,20.3%xylan,22.3%lignin.Thecontentofeachcompositionwasdeterminedusingatwo-stepacidhydro-lysismethoddevelopedbytheNationalRenewableEnergyLabora-tory(NRTL)(Sluiteretal.,2011).

ILsusedinthedegradation,namely1-butyl-3-methyl-imidazo-liumchloride([C4mim]Cl),waspreparedaccordingtothemethodreportedbyWebbetal.(2003).1-Butyl-3-methyl-imidazoliumchlorideexistsinitsliquidformattemperaturesbetween60°Cand70°C.

2.2.Hydrolysisofbamboo

Experimentswerecarriedoutinamicro-glassround-bottom?ask.4gof[C4mim]Clwasplacedinthereactorandheatedto100°C.0.2gbamboowasthenadded,followedbytheadditionofanappropriateamountofmetalchloridesanddifferentconcen-trationsofHCl.Themixturewasstirredat20rpmunderatmo-sphericpressurefor7h.Atdifferenttimeintervals,samples(0.1mL)werewithdrawn,quenchedimmediatelywithcoldwaterandthenweighedandrecordedasMS.Thesampleswereneutral-izedwithanappropriateamountof0.05MNaOH,centrifugedat10,000rpmfor5minandsubjectedtosugaranalysis.ThevolumemeasuredwasrecordedasV1.2.3.Sugaranalysis

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