水-乙醇中乳糖溶解度

FluidPhaseEquilibria173(2000)121–134Solid–liquidequilibriumofa-lactoseinethanol/waterJoséJ.B.Machadoa,JoãoA.Coutinhob,EugéniaA.Macedoa;aLaboratoryofSeparationandReactionEngineering,DepartamentodeEngenhariaQu´ımica,FaculdadedeEngenharia,RuadosBragas,4050-123Porto,PortugalbDepartamentodeQu´ımica,UniversidadedeAveiro,3810Aveiro,PortugalAccepted7June2000AbstractSolubilitiesofa-lactoseinwater–ethanolsolventmixtureswereobtainedusinganaccurateanalyticalmethod,at25,40and60Cinaconcentrationrangefrom0to100sugar-freewt.%ofwater.Thea-lactosesolubilityisastrongfunctionofthewaterconcentrationinthesolventmixture.Itincreasesmonotonicallywithtemperatureandwithwaterconcentration.TheexperimentaldatawerecorrelatedusingaUNIQUAC-basedmodelandwerepredictedusingtwodifferentUNIFAC-basedmodels.©2000ElsevierScienceB.V.Allrightsreserved.Keywords:a-Lactose;Data;ModifiedUNIQUAC;ModifiedUNIFAC1.IntroductionCarbohydratesolutionsareimportantinavarietyofareas,suchasbiologicalandfoodindustries.Theyareofteninvolvedincrystallizationprocesses.Anincreasedinterestinsystemscontainingthebiologicalmoleculesfoundincarbohydratesolutionshasmadeevidenttheneedforboth,experimentalinformationonthermodynamicpropertiesofmixturescontainingsugars,andproperthermodynamicmodelsabletorepresentthem.Inspiteofthewellrecognizedimportanceofsugar-containingsystems,asdemonstratedbythegrow-ingnumberofpublicationsonthesubject[1–7],thereisstillalackofexperimentalinformationonthesolid–liquidequilibriumofaqueousandnonaqueousmulticomponentsolventmixturescontainingcommonsugars.Thesesystemsarepresentinmanyprocessesinthefood,chemicalandpharmaceuticalindustries.Avarietyofapproachesareavailableformodelingthesehighlycomplexsystems.TheUNIQUACmodel[8]wasusedbyLeMaguer[9]todescribeonlytheexcessGibbsenergyandexcessenthalpyoffivebinaryaqueouscarbohydratesystems.Cattéetal.[10]appliedthemodifiedUNIQUACmodel[11]Correspondingauthor.Tel.:C351-222041653;fax:C351-222041674.E-mailaddress:[e-mail](E.A.Macedo).0378-3812/00/$20.00©2000ElsevierScienceB.V.Allrightsreserved.PII:S0378-3812(00)00388-5122J.J.B.Machadoetal./FluidPhaseEquilibria173(2000)121–134tocorrelateeightdifferentthermodynamicpropertiesofthreebinarywater/sugarsystemsandtopredicttheosmoticcoefficientandwateractivityoftwosugarsinaqueoussolutionsat25C.However,theuseoftheunsymmetricconventionbyCattéetal.[10]hinderstheapplicationoftheirmodelinthecaseofmixedsolvents.PeresandMacedo[12]proposedamodifiedUNIQUACmodelthatisabletocorrelateandpredictvapor–liquidandsolid–liquidequilibriaofaqueoussolutionscontainingmorethanonesugar.Thesolubilityofasinglesugarinmixedsolventshasbeenthefocusofsomecontributionstoo.Bockstanzetal.[3]usedaRedlich–Kisterequation,inapurelyempiricalway,tocorrelatethesolubilityofd-glucoseinwater–ethanolmixturesat35C.Basedontheirearlierwork[12],PeresandMacedo[6]proposedthreeUNIQUAC-basedmodelsforthesolubilityofsucroseandd-glucoseinmixedsolvents.Also,anumberofpredictivegroup-contributionmethodshavebeenproposedtodescribethiskindofsystems.Achardetal.[13],usedthemodifiedUNIFAC[11]modeltopredictwateractivities,boilingtemperaturesandfreezingpointsofoneormoresugarsinwater.BecausethismodelusestheoriginalUNIFACgroupdefinitions,itisnotcapabletorepresentsugarsolubilitiesaccuratelyenough.Therepre-sentationofsugarsolubilitiesataquantitativelevelrequiresthedefinitionofspecialgroupsforsugarmolecules(e.g.[14,15]).Abedetal.[14]andGabasandLaguérie[15],definednewgroupsfortheUNIFACmodel[16]andesti-matednewinteractionparametersfrombinaryandternarysolubilitydata.Theyusedtheseparameterstopredictsolid–liquidphaseequilibriainternarysystemsoftwosugarsinwateratafixedtemperature(25or70C).Cattéetal.[17],proposedanewmodelwhich,usingamodifiedUNIFACequation[11],makespos-sibletodiscriminatebetweencarbohydrateisomers.Theseauthorsusedthismodeltodescribesomether-modynamicpropertiesofsevenwater/sugarsystems.Thelimitationsofthisapproachhavebeendiscussedelsewhere[18].PeresandMacedo[18,19],proposedamodifiedUNIFACmodeltopredictthermodynamicpropertiesofsystemscontainingwaterand/ornon-aqueoussolvents,andoneormoresugars.Morere-cently,Spiliotisetal.[20]presented,withoutprovidinginformationonthevaluesoftheinteractionparam-eters,anewUNIFACapproachforthedescriptionofpartitioncoefficientsofsugarsinsolventmixtures.a-Lactoseisthemajorsugarinmilkandiswidelyusedinindustry.Thea-lactoseisusedasanalterna-tivesweeteningagentforsucrose.Itisalsousedasasolidsupportforactivesubstancesinpharmaceuticalformulations.Crystallizationofa-lactoseisapotentialroutefora-lactoseremovalfromfoodproductsspeciallyaimedtopeoplesufferingfromlactose-intolerance.Thereisalackofdataconcerningpropertiesofa-lactoseinasingleormixedsolventssolutions[1,21–24].Theoptimizationanddesignofnewpro-cessesintheindustryrequiresknowledgeofsolid–liquidandliquid–vaporequilibriaforthesemixtures.Inthisworksolid–liquidequilibriumdatafora-lactoseinmixturesofwaterandethanolat25,40and60Chavebeenobtained,usingasimpleandaccurateanalyticalapparatus.ThesesolubilityexperimentaldatawerecorrelatedwiththemodifiedUNIQUACmodelproposedbyPere