FluidPhaseEquilibria246(2006)

131–136

Predictionofmethaneandcarbondioxidesolubilityinwater

inthepresenceofhydrate

ShahrzadHashemia,ArturoMacchia,SebastienBergeronb,PhillipServiob,

a

DepartmentofChemicalEngineering,UniversityofOttawa,CanadabDepartmentofChemicalEngineering,McGillUniversity,Canada

Received20September2005;receivedinrevisedform9March2006;accepted14May2006

Availableonline22May2006

Abstract

Mostproposedtechnologiestoformgashydratesusecontinuouslystirredtankreactorswheregasisbubbledintotheliquid.Fromareactormodelingpointofview,itisnecessarytodeterminethegassolubilityintheliquidwithandwithouthydratesasthiswilldictateinterphasemasstransferandaffectoverallconversion.ThisworkassembledamodeltopredictthesesolubilityvaluesusingtheTrebble–Bishnoiequationofstate,thevanderWaalsandPlatteeuwmodelandtheHoldermodel.Modelpredictions,aswellaspredictionsfromHenry’slaw,werecomparedtoavailableexperimentaldataofmethane–waterandcarbondioxide–watersystems.AlthoughHenry’slawcannotbeappliedunderhydrate–liquidwaterequilibrium,itsaccuracywasverygoodduetothesmalleffectofpressureonsolubilityinthatzone.Theaccuracyofthemodelinthisworkhasbeenimprovedbyre-adjustingitsparameterswithrecentvapor–liquidwaterandvapor–liquidwater–hydrateequilibriumdataofmethane–waterandcarbondioxide–watersystems.

©2006ElsevierB.V.Allrightsreserved.

Keywords:Gashydrate;Solubility;Hydrate–liquidwaterequilibrium;Methane;Carbondioxide

1.Introduction

Gashydratesarecrystallinesolidsthatformwhengasorvolatileliquidmoleculessuitableforhydrateformationareenclosedinacageconsistingofwatermolecules.ThepresenceofthehydrateforminggasmoleculesleadstostabilizationofthewaterlatticethroughphysicalbondingviavanderWaalsforces.Hydratecompoundsaremadenaturallywithinthepermafrostzoneandinsub-seasedimentattemperatureandpressurecon-ditionswithinthethermodynamicstabilityregion[1].Naturallyoccurringhydrates,containingmostlymethane,existinvastquantitiesandarebeinglookeduponasapotentialalternativeenergysource[1].Carbondioxidehydratesarealsoimportanthydrates.Theyarebeingconsideredasameanstosequestercarbondioxideinthedeepoceanthusreducingtheemissionofgreenhousegases[2].Carbondioxideisalsoacomponentofnat-uralgas(themajorcomponentbeingmethane)whichcanleadtohydrateformationinpipelinesresultinginpipelineblockage[3].

Correspondingauthor.Tel.:+15143981026;fax:+15143986678.E-mailaddress:phillip.servio@mcgill.ca(P.Servio).

Onesigni cantproposedtechnologyincorporatinggashydratesdealswithtransportationandstorageofgas.Hydratesarebeingregardedasanalternatemeansoftransportingnaturalgasoverothercurrentlyusedmethodssuchaslique ednaturalgas(LNG)orcompressednaturalgas(CNG)astheyeliminatethenecessityofverylowtemperatures( 160 C)andveryhighpressures(200atm).Thehydratecontainsabout160Sm3/m3ofhydrate,whichiscomparabletotheabovementionedtech-nologies(LNGandCNG)[4],atnearambienttemperature(0to 10 C)andpressures(10–1atm).

Attemptsatsynthesizinghydrateinanef cientmannerhaveusedacontinuouslystirredtankslurryreactorwherethehydrateforminggasisspargedintoacontinuouswaterphase[5].Gasdiffusesoutofthebubblesintotheliquidwaterwhereitiseven-tuallyconsumedatthesurfaceofsuspendedhydratecrystals.Thedrivingforcearoundthehydrateparticlecanbede nedasthedifferencebetweenthegashydrateformerconcentrationintheliquidbulkwateranditssolubilityatthehydrate–liquidinterface.Thepressureatthehydrateinterfacehastobeequaltotheexperimentalpressure[1],whiletheinterfacetempera-turecanbethethree-phase(H–Lw–V)ortwo-phase(H–Lw)temperaturedependingontheheattransferrate.Similarly,the

0378-3812/$–seefrontmatter©2006ElsevierB.V.Allrightsreserved.doi:10.1016/j. uid.2006.05.010