Concentration of xylose reaction liquor by nanofiltration for the production of xylitol sugar alcoho

Concentration of xylose reaction liquor by nanofiltration for the production of xylitol sugar alcohol

SeparationandPuri cationTechnology44(2005)

221–228

Concentrationofxylosereactionliquorbynano ltrationforthe

productionofxylitolsugaralcohol

G.S.Murthy,S.Sridhar ,M.ShyamSunder,B.Shankaraiah,M.Ramakrishna

MembraneSeparationsGroup,ChemicalEngineeringDivision,IndianInstituteofChemicalTechnology,Hyderabad500007,India

Received21June2004;receivedinrevisedform27December2004;accepted12January2005

Abstract

Xylitol,a ve-carbonsugaralcohol,isusedcommerciallyasanaturalsweetenerinseveralfoodproductsincludingsoftdrinksandconfectionery.Xylitolisproducedbycatalyticdehydrogenationofxylose,anintermediatesugarcompound,whichisextractedfromsugarcanebagasse,corncobsorricehusk.Thereactionliquorofxylosecontains1.5–2%ofd-xylosebesideswaterasthemajorconstituent.Thecurrentprocessofevaporationforconcentrationofxylosereactionliquorcanbeeffectivelyreplacedbythemoreeconomicalnano ltrationtechnique.Pilotscalenano ltration(NF)experimentswerecarriedoutusingapolyamide(PA)spiralmembranemodulehaving300molecularweightcut-off(MWCO)and1m2effectivearea.Atafeedpressureof20bar,xylosewasconcentratedfrom2to10%atareasonablyhighaverage uxof24l/(m2h)andrejectionof>99%whichindicatednegligiblelossesofthesugarinthepermeate.Theef ciencyofNFwascomparedwithanothermembranemethods,reverseosmosis(RO)forconcentrationofxylosereactionliquor.EffectoffoulingonNFmembraneperformanceandlifespanaswellasmethodsforcleaningthemembraneforrestoring uxandrejectionwereevaluated.Aneconomiccomparisonbetweennano ltrationandevaporationforafeedcapacityof1m3/hofxylosereactionliquorshowedthatNFcapitalinvestmentwas75%oftheevaporatorinstallationcost,whereastheoperatingcostforNFwasonly0.04timestheevaporationcost.©2005PublishedbyElsevierB.V.

Keywords:Nano ltration;Xylose;Xylitol;Polyamidemembrane;Economicestimate

1.Introduction

Xylitol,a ve-carbonsugaralcohol,isusedcommerciallyasanaturalsweetenerinseveralfoodproducts.Itisanidealsweetenerfordiabeticssinceitsmetabolismdoesnotrequireinsulin[1]andalsopreventsdentalcaries[2].Xylitolhasbeenshowntohaveapreventiveeffectagainstacuteotitisinchildrenbyimpairingthegrowthofotopathogenandreducestheadherenceofstreptococcuspneumoniaeandhaemaphilusin uenzaetothenasopharyngealcells.

Xylitolisfoundnaturallyinfruits[3]likestrawberries,plumsandpears,butinsmallquantities,whichmakesitsex-tractiondif cultanduneconomical.Xylitolcanbeproducedbybiologicalmeansfromxylose,anothersugar,byutiliz-ingyeastssuchasthespeciesbelongingtoCandidagenus

IICTCommunicationnumber:041225.

Correspondingauthor.Tel.:+914027193142;fax:+914027160757.E-mailaddress:sridhar11in@yahoo.com(S.Sridhar).

[4],fungisuchasPetromycesalbertensis[5]andalsobybacterialikeEnterobacterliquefaciens[6].Themostimpor-tantmethodutilizedinthesynthesisofxylitolinvolvesthechemicalreductionofxylose,whichinturnisobtainedbytheacidhydrolysisofxylanpresentinthehemicelluloseofbirchwood,beechwoodorthestructuralplanttissuessuchascorn-stalks,wheatstraw,cottonseed,peanuthulls,sugarcanebagasse,woodpulpand axstraw[7,8].Xyloseisalsoaversatilesugarcompoundandhasmanyapplicationssimilartothatofxylitol,suchas,sugarsourcefordiabeticpatients,non-nutritivesweetenerinpharmaceuticalindustry,additiveincolorphotography,brightenerinzincelectroplatingandethanolproductionduringfermentationprocess.Theproper-tiesofxyloseandxylitolarepresentedinTable1.

Inthepresentwork,xylosewasproducedbytheacidhy-drolysisofricehusk[9–12].Thehydrogenationofxylosegivesxylitol,whichisasugaralcoholsweeterthansucrose.However,presentseparationmethodsprovetobeexpensiveforconcentrationofxylosereactionliquorforsubsequent

1383-5866/$–seefrontmatter©2005PublishedbyElsevierB.V.doi:10.1016/j.seppur.2005.01.009