Characterization-of-lignin-precipitated-from-the-s

AJSTDVol.21Issue157AJSTDVol.21Issue1pp.57-67(2004)CHARACTERIZATIONOFLIGNINPRECIPITATEDFROMTHESODABLACKLIQUOROFOILPALMEMPTYFRUITBUNCHFIBERSBYVARIOUSMINERALACIDSM.N.MohamadIbrahim*,S.B.ChuahSchoolofChemicalSciencesUniversitiSainsMalaysia,11800Minden,PulauPinang,MalaysiaW.D.WanRosliSchoolofIndustrialTechnology,UniversitiSainsMalaysia,11800Minden,PulauPinang,MalaysiaReceived28May2003,Accepted22September2003ABSTRACTSodaligninfromoilpalmemptyfruitbunchwasdirectlyisolatedbyvariousmineralacidsi.e.sulfuricacid,hydrochloricacid,phosphoricacidandnitricacidatthreelevelsofconcentration(20%v/v,60%v/vandconcentrated).Acomparisonstudywasperformedthroughphysico-chemicalpropertiesandstructuralfeaturesusingFT-IR,UV,13C-NMRandnitrobenzeneoxidation.TheFT-IRresultsshowedthatthereisnosignificantdifferencebetweenthemainstructuresoftheligninisolatedbyvariousacids.However,lowconcentrationofphosphoricacidispreferablebecauseofitshighestyield.TheS:V:Hratioof7-15:6-11:1asevaluatedbythenitrobenzeneoxidationproceduresuggeststhatsodalignincanbeclassifiedasbelongingtoeitherthecerealstrawongrasstype.TheUVresultsindicatethatphosphoricacidconsistentlygavethehighestabsorbancevalueamongthefouracidstestedinthisstudyregardlessofitsconcentrationlevel.TheC13-FTNMRspectra,suggestthattheligninstructureisindependentofthetypeofacidusedforprecipitation.1.INTRODUCTIONOilpalm(Elaeisguineensis)isanativeofWestAfrica.Itwasintroducedtovariouspartsofthetropicsforitsoil-producingfruit.InMalaysia,itisestimatedthat2.28millionhaoflandisbeingcultivatedwithoilpalmtrees1.Besidesproducingpalmoil,theindustryalsogeneratesmassiveamountsoflignocellulosicresiduessuchastrunks,frondsandemptyfruitbunches(EFB).Papergradepulpsfromthesefibreshavesincebeenestablished2,3,4.HowevertheligninextractedduringCorrespondingauthore-mail:[e-mail]ionofLigninPrecipitatedfromtheSodaBlackLiquorthepulpingprocesshassofarnotbeinginvestigatedforitsusefulness.Beforeitsapplicationscanbeconsidered,knowledgeofitsstructuralcharacterizationisrequired;thisstudypresentssuchaneffort.Ligninisanamorphouspolyphenolicmaterialarisingfromanenzyme-mediateddehydrogenatespolymerizationofthreemajorphenylpropanoidmonomers,whichareconiferyl,sinapylandp-coumarylalcohol5.Theligninstructuralelementsarelinkedbycarbon-carbonandetherbondstoformtri-dimensionalnetworkassociatedwiththehemicellulosespolysaccharidesinsidethecellwall6.Ligninisusuallyinsolubleinallsolventsandcanonlybedegradedbyphysicalorchemicaltreatments7.Duringthechemicalpulpingprocessathigh-temperatureandhigh-pressure,degradationofligninoccursanddissolvesintothespentliquor.Thedelignificationreactionsinvolvedthecleavageofnon-phenolicβ-O-4linkage,phenolicα-O-4linkageandreleasingfromtheassociatedbythepolysaccharide8,9.ThestructureofligninobtainedfromtheEFBfiberismorecomplexthenthestructureofligninextractedfromwoodduetoacomplexarrangementofsyringyl-andguaiacyl-propaneunitstogetherwithp-hydroxy-propaneunitintheEFBfiber.TheEFBfibercontainsabout17.2%lignin,whichisrelativelylowcomparetohardwoodandsoftwoodmaterials10.Theobjectiveofthisinvestigationistogainabetterunderstandingontheeffectsofdifferentmineralacidsusedinrecoveringsodalignin.EFBligninwasisolatedfromthesodablackliquorbyvarioustypeofmineralacidsi.e.sulfuricacid,hydrochloricacid,phosphoricacidandnitricacidatthreelevelsofconcentration(concentrated,60%v/vand20%v/v).Theobtainedligninwascharacterizedbothusingdestructivetechniquesuchasnitrobenzeneoxidationandnon-destructivemethodssuchasinfra-red(IR),ultraviolet(UV),nuclearmagneticresonance(FT-NMR)spectroscopyandgelpermeationchromatography(GPC).2.EXPERIMENTAL2.1MaterialTheemptyfruitbunch(EFB)rawmaterialusedinthisstudywassuppliedbySabutek(M)Sdn.Bhd.,alocalcompanyspecializinginrecyclingofEFB.Thefiberswerewashedwithwaterpriortopulping.2.2PulpingconditionsTheEFBfiberwaspulpedina20Lstainlesssteelrotarydigesterunitwith25%NaOH(cookingliquor)for3hoursatamaximumcookingtemperatureof170˚C,withacookingliquortoEFBratioof10:1.ThepHoftheobtainedblackliquorwas12.45anditsdensity1.02g/ml.ThesodaligninwasthenprecipitatedfromtheconcentratedblackliquorbyacidifyingittopH2usingvariousmineralacidsatthreelevelsofconcentrationi.e.20%,60%andconcentrated.TheacidsusedAJSTDVol.21Issue159inthisstudyweresulfuricacid,hydrochloricacid,phosphoricacidandnitricacid.TheprecipitatedligninwasthenfilteredandwashedwithwaterthatwasadjustedtopH2usingthecorrespondingacidusedintheearlierstep.Thesodaligninwasthendriedinavacuumovenat55˚Cfor24hourspriortofurtheranalysis.2.3AnalysisofligninNitrobenzeneoxidationwascarriedoutbyadding50mgdrysodaligninintoamixtureof7mlof2MNaOHand4mlofnitrobenzeneina15mlsteelautoclave.TheautoclavewassealedtightlywithascrewcapfittedwithTeflongasketandheatedto165˚Cfor3hoursinapreheatedthermostatoilbath.Aftertheheatingperiod,theautoclavewascooledwithicewater.Themixturewasthentransferredtoaliquid-liquidextractorforcontinuousextractionwithchloroform(5x20ml)toremoveanynitrobenzenereductionproductandexcessofnitrobenzene.TheoxidationmixturewasacidifiedbyconcentratedHC