(7.4)-任务3（3.1）硫含量测定方法概述

Task3(3.1)OverviewofsulfurcontentdeterminationmethodsI.Determinationofthesignificanceofsulfurcontent1.HarmofSulfurandItsCompoundsInthestraight-runfraction,alkylsulfide(alcohol)ismore;Inthethermalcrackingfraction,aromaticsulfide(alcohol)ismore.Thehazardsofsulfuranditscompoundstopetroleumrefining,oilqualityanditsapplicationsareasfollows.(1)Corrodingoilrefiningdevices.Duringcrudeoilrefining,H2Scanbepartiallyformedbythedecompositionofvarioussulfur-containingorganiccompounds.Onceexposedtowater,H2Swillseverelycorrodemetaldevices.(2)Contaminatingcatalysts.Asulfur-containingsubstancewillformsulfideswiththemetalinthecatalyst,leadingtocatalystpoisoning.Ifcatalyticreformingfeedstock,thesulfurcontentmustbelessthan1.5mg/kg.(3)Influencingoilquality.Sulfurwillaffectpeople'ssensoryperformanceaswellasthestabilityofoilproducts,causingcorrosionofoilstoragecontainersorrelatedequipment.(4)Pollutingtheenvironmentseriously.SulfurandsulphurcompoundsinfueloilproductswillbeconvertedtoSO2orSO3afterburning,whichareoneofthemaincomponentstoformacidrainintheatmosphere.Facingtheworseningecologicalenvironment,Chinahasputforwardtheideaofconstructingacommunitywithasharedfutureformankind,advocatingthatwemustkeeptothemoralbottomlineandinternationalrulesinthetermofecologicalprotectionbothinresponsetonaturaldisastersandepidemicdiseaseoutbreak,ormaintainingeconomicorderandpoliticalsecuritybasedontheprincipleofreciprocityofrightsandobligationssoastoshouldertheresponsibilityofmaintainingworldpeaceanddevelopment.2.MeaningofdeterminationSulfurcontentsrefertothepresenceofSulfurandhydrogensulfide,mercaptan,anddisulfideinoilproducts,usuallyexpressedasamassfraction.Thesignificanceofthemeasurementisasfollows:(1)Lowsulfurcrudeoilhasamassfractionofsulfurcontentlowerthan0.5%.Sulfur-containingcrudeoilhasamassfractionofsulfurcontentbetween0.5%and2%.Highsulfurcrudeoilhasamassfractionofsulfurcontentabove2%.Crudeoilwithdifferentsulfurcontentsisalsodifferentinrefiningprocess.(2)Oilqualitycontrolindex.AccordingtoDomesticNo.3jetfuelqualityindex,thetotalsulfurcontentsarenotmorethan0.2%,andthecontentsofmercaptansulfurarenotmorethan0.002%.Atpresent,thedomesticautomobilegasolinequalityindexstipulatesthatsulfurcontentsarenotmorethan0.015%.QualityindexesofsulfurcontentsinsomeoilproductsandtestingmethodsareshowninTable7-3.EuropeanStandardforGasolineandDieselOilAsairpollutantssuchasnitrogenoxides(NOx),carbonmonoxide(CO),hydrocarbons(HC)andparticulatematter(PM)inautomobileexhaustareincreasinglyharmfultotheenvironment,countriesandregionsaroundtheworldhavesuccessivelyformulatedlimitstandardsforautomobileexhaustemissions.Amongthem,theEuropeanstandardisareferencestandardimplementedbymostcountriesandregions.SinceJanuary1,2009,theEuropeanVemissionstandardhasbeenimplemented,atpresent,theEuropeanVIemissionstandardhasbeenformulated.ThegasolineanddieselstandardrequirementsthatmeettheEuropeanVemissionstandardareasfollows.Gasoline:sulfurcontent≤10mg/kg,benzenecontent(volumefraction)≤1.0%,aromatichydrocarboncontent(volumefraction)≤35%,olefincontent,(volumefraction)≤18%,leadcontent≤5mg/L;Dieseloil:cetanenumber≥51,cetanenumberindex≥46,sulfurcontent≤10mg/kg,polycyclicaromatichydrocarbons(massfraction)≤8%,thedensityis820~845kg/m3.Knowledgeexpansion2.Overviewofsulfurcontentdeterminationmethods1.DoctortestSH/T0174-1992(2000)"QualitativeTestMethodforAromaticHydrocarbonsandLightPetroleumProductsMercaptan(DoctoralTestMethod)"ismainlyapplicabletoqualitativedetectionofmotorgasolineandmotorethanolgasoline(E10)andthethiolsulfurinlightpetroleumproductssuchasNo.3jetfuelandaromaticscanalsobedetectedforhydrogensulfide.Thepreparationmethodofthedoctor'sreagentissodiumlead(Na2PbO2)solutionisasfollows:(CH3COO)2Pb+2NaOH——→Na2PbO2+2CH3COOHAradicalprinciple:Sodiumplumbitesolutionreactswiththemercaptaninasampleandgeneratesleadthiol.Leadthiolfurtherreactswithsulfurelementstoformdarkerleadthiolsoastoqualitativelydetecttheexistenceofmercaptaninthesample.Themeasurementprocedureis:"Preliminarytest"iscarriedoutwithdoctoralreagent.Ifmercaptanispresentinthesample,thefollowingreactionoccurs:Na2PbO2+2RSH——→(RS)2Pb+2NaOHLeadmercaptanexistsinthetestsolutioninadissolvedstate,andthecolorisusuallynotobviousorthetestsolutionisslightlyyellowduetothedifferenceintherelativemolecularmassofmercaptan.The"finaltest"iscarriedoutwiththedoctoralreagent,thatis,asmallamountofsulfurpowderisaddedtotheabovesolution.Whenleadmercaptanencounterssulfurpowder,adarkprecipitateofleadsulfideisgenerated.Thereactionisasfollows:(RS)2Pb+S——→PbS↓+RSSRTheresultingleadsulfideprecipitatewilldarkerthecoloroftheliquidinterfacebetweenthedoctor'sreagentandthesample(oil)(theinterfacealsocontainsasulfurpowderlayer)(orange,brown,orevenblack).Ifthecolorofthesulfurpowderlayerparticipatinginthereactionisnotsignificantlydarker,itmeansthatthesampledoesnotcontainmercaptansulfur.Ifthecompositionofthesulfur-containingcomponentsinthesampleisrelativelycomplex,itisnecessarytopassthepreliminarytestresults(seeTable7-4)andcontinuethetest,andfurtherdeterminethepresenceofmercaptansulfuraftereliminatinginterference.Ifitisconfirmedthathydrogensulfideispresentinthesample,thesampleshallUsecadmiumchloridepretreatmenttoremovetheinterferenceofhydrogensulfide,andthenconductafinaltest;Ifonlyitisdeterminedthattheremaybeperoxides,anothertestisrequiredtofurtherconfirm,ifthesampledoesexist,thestandardtestmethodcannotbeusedtodetectthepresenceorabsenceofmercaptansulfurinthesample.Themainteststepsofthedoctoraltestmethodareasfollows:(1)Afteraddingsodiumleadsolutiontothepreliminarytestandshakingit,judgewhether(orpossible)hydrogensulfide,peroxide,thepresenceofmercaptansandelementalsulfur(onlymercaptansandelementalsulfurcanbedirectlyconcluded).Takeanothersampleforfurthertesting.Oneistoeliminatetheinterferenceofhydrogensulfide(drivenbyCdCl2),andthefinaltestcanbecontinued;Theotheristousepotassiumiodide-starchacidicsolutionfortesting,ifthetestsolutionturnsblue,itmeansthatthesamplecontainsperoxideandthereisnoneedtoconductafinaltest(becausethecorrectresultcannotbeobtained).(2)Thefinaltestaddssulfurpowdertoconfirmthepresenceofmercaptan.2.Ammonia-coppersulfatemethodGB/T505-1965(1990)"DeterminationofMercaptanSulfurContentinEngineFuel(Ammonia-CopperSulfateMethod)"iscurrentlyonlyusedasNo.2jetfuel[GB1788-1978(1988)]methodfordeterminationofmercaptansulfurcontent.Aradicalprinciple:Ammonia-coppersulfatesolutionwhichisdarkbluewhenammoniaisoverdosed,interactswithmercaptaninthesampletoformamercaptancompoundofcopper.Thedarkbluesolutionwillquicklyfade.Withthegradualdrippingofammonia-coppersulfatesolution,thesolutionappearslightbluewhenthereactionapproachesthestoichiometricpoint.Ifthecolordoesnotdisappearaftershaking,itreachesthetitrationendpoint.Thereactionprocessisasfollows:AddammoniawatertothecoppersulfateaqueoussolutiontogeneratealightgreenbasicsaltCu2(OH)2SO4precipitation:2CuSO4+2NH3•H2O——→Cu2(OH)2SO4↓+(NH4)2SO4Addexcessiveammoniawater,therewillbedarkblue[Cu(NH3)4]2generated:Cu2(OH)2SO4+8NH3•H2O→[Cu(NH3)4]SO4+[Cu(NH3)4](OH)2+8H20Theproduct[Cu(NH3)4]2generatedbytheaboveammonia-coppersulfatesolutionreactswiththemercaptanpresentinthesample,sothatthetitrantitself(darkblue)drippedintothetestsolutionquicklyfades:[Cu(NH3)4](OH)2+2C2H5SH→(C2H5S)2Cu+4NH3+2H2O[Cu(NH3)4SO4+2C2H5SH→(C2H5S)2Cu+4NH3+H2SO4Afterdroppingthetestsolutionwithaslightlyexcessiveamountofammonia-coppersulfatesolution(self-indicator),themixedsolutionwillpresentcoppertetramminecomplex[Cu(NH3)4]2lowconcentrationcolor(lightblue),reachingthetitrationendpoint.Themainteststepsforthedeterminationofmercaptansulfurcontentinenginefuelbytheammonia-coppersulfatemethodareasfollows.Takeacertainamountofsample(canbedeterminedaccordingtothepredictedmassfractionofmercaptansulfurinthesample,below0.01%,take100mL;0.01%~0.02%,take50mL;Above0.02%,take25mL)inaseparatoryfunnelandtitratewithammonia-coppersulfatesolution.Afterdroppingtheammonia-coppersulfatesolutiononebyone,theseparatoryfunnelcontainingthesampleshouldbeshakensharplyeachtimetomakethebluecolorinthewaterphaselighteruntilitdisappears.Whenthelightbluetitratedtotheaqueousphasedoesnotdisappearafterviolentshakingfor5min,itisconsideredtoreachthestoichiometricpointandcanbeusedasthetitrationendpoint.3.LampmethodGB/T380-1977(1988)StandardTestMethodforDeterminationofSulfurContentinPetroleumProducts(BurningLampMethod)ismainlyapplicabletothedeterminationoflightpetroleumproducts(suchasgasoline,kerosene,diesel,etc.)sulfurcontent,theburnersulfurcontenttesterisshowninFigure7-2.Aradicalprinciple:Putthesampleintoaspecificlampandcombustitcompletely,Convertsulfurcompoundsinthesampleintosulfurdioxide,Usesodiumcarbonatesolutiontoabsorbsulfurdioxide.Titratewithhydrochloricacidsolutionofknownconcentration.Fromthelostvolumeofhydrochloricacidsolutionduringthetitrationcalculatethesulfurcontentinthesample.Thesulfur-containingcompoundinthesampleiscompletelyburnedinthelamptoproducesulfurdioxide:Sulfide+O2--→SO2↑Aftersulfurdioxideisabsorbedby10mlofsodiumcarbonatesolutionwithamassconcentrationof0.3%(excess),sodiumsulfiteisgenerated:SO2+Na2CO3——→Na2SO3+CO2↑Theremainingsodiumcarbonateisthentitratedbackwithahydrochloricacidsolutionofaknownconcentration,andthesulfurcontentinthesamplecanbecalculatedfromthevolumeoftheconsumedhydrochloricacidsolution:Na2CO3+2HCl——→2NaCl+H2O+CO2↑Themassfractionofsulfurinthesampleiscalculatedaccordingtothefollowingformula:（7-5）0.0008g/mLinEq.(7-5),thetitrationdegreeofthe0.05mol/LHClsolutionusedforsulfur,whichcanbecalculatedfromthequantitativechemicalreactionrelationshipbetweenthesubstancesintheprincipleofdetermination.By

S∽SO2∽Na2CO3∽2HClThereareS∽HCl

Whentheconcentrationofthesubstanceofthehydrochloricacidsolutionusedis0.05mol/L,thetitrationdegreeisThenitstitrationtosulfurcanbecalculatedfromthefollowingratioasthen

T=0.0008g/mL4.TubefurnacemethodGB/T387-1990StandardTestMethodforDeterminationofSulfurContentinDarkPetroleumProducts(TubeFurnaceMethod)ismainlyapplicabletothedeterminationofdarkpetroleumproductswithsulfurcontentgreaterthan0.1%inthesample,themaininstrumentsandequipmentusedinthetestaretubularresistancefurnaces(asshowninFigure7-3).Principleofdetermination:Putthesampleintoatuberesistancefurnace,completelycombustitintheairflowatspecifiedvelocity.Useperoxide-sulfuricacidsolutiontoabsorbgeneratedSulfurdioxideandsulfurtrioxide,Sulfurdioxideisalsooxidizedtosulfuricacid.Titratewithsodiumhydroxidesolutionofknownconcentrationabsorbthenativeandnewlyformedsulfuricacidinthesolution.Accordingtothelostvolumeofsodiumhydroxidesolutionduringtitration,afterdeductingtheblankvalue,thesulfurcontentinthesamplecanbecalculated.Whenmeasuring,thesulfur-containingcompoundinthesampleiscompletelyburnedinatubularresistancefurnacetoproducesulfurdioxideandsulfurtrioxide:Sulfide

+O2——→SO2↑+SO3↑Sulfurtrioxideisabsorbedbythewaterinthereceivingsolutiontoformsulfuricacid:SO3+H2O——→H2SO4Sulfurdioxideisoxidizedbythehydrogenperoxideinthereceivingsolution,whichalsoproducessulfuricacid:SO2+H2O2——→H2SO4Thenthesulfuricacidintheaccepted(absorbing)solutionistitratedbackwithsodiumhydroxidesolution,andthesulfurcontentinthespecimencanbecalculatedbythevolumeofsodiumhydroxidesolutionconsumed.H2SO4+2NaOH——→Na2SO4+2H2OThemassfractionofsulfurinthespecimeniscalculatedbythefollowingequation:（7-6）5.Potentiometrictitrationmethod

GB/T1792-1988"Determinationofthiolsulfurindistillatefuels(potentiometrictitrationmethod)"isapplicabletothedeterminationofthiolsulfuringasoline,jetfuelandkerosenewithouthydrogensulfideintherangeof0.0003%~0.01%(Table7-3).Ifthefreesulfurmassfractionisgreaterthan0.0005%,thereissomeinterferenceinthedetermination.Thethiolsulfurcontentdeterminationdeviceisthesameasthepotentiometrictitrationdeviceforacidvaluedeterminationofpetroleumproductsandlubricants(Figure7-1).Itisdissolvedinsodiumacetateisopropanolsolventwithouthydrogensulfidespecimen,potentiometrictitrationwithsilvernitrateisopropanolstandardtitrationsolution,theendpointoftitrationisindicatedbythepotentialburstbetweentheglassreferenceelectrodeandsilver-silversulfideindicatorelectrode.Duringthetitration,thiolsulfideisprecipitatedassilverthiol,andthereactionisRSH+AgNO3

——→RSAg↓+HNO3Inthespecimen,themassfractionofthiolsulfuriscalculatedaccordingtoequation(7-7)（7-7）Inordertobetterdissolvesilvernitrateinthesampleandreducetheadsorptionofsilvernitratebysilvermercaptanprecipitation,alargeamountofisopropanolwasusedassolventintheexperiment.III.MainFactorsAffectingthedetermination1.Doctortest(1).Requirementsforreagents.Theprepareddoctorreagentsshouldbekeptinaclosedcontainer,inacolorlessandtransparentstate.Iftheyareunclean,pleasefilterthembeforeuse.(2)SulphurpowderanditsdosageThesublimationsulfurforuseshouldbepureanddrypowderedsulfur.Theamountaddedeachtimeshouldensurethatthereisathinsulfurlayerattheliquid-bondedinterfacebetweenthesampleandsodiumplumbitesolution.Itisabout35~40mg.Don'taddtoomuchortoolittle,whichmayaffectresultobservation.

(3)Makesurethatthereactioniscomplete.Inordertocompletethereactionwithinthespecifiedtime,thesampleshouldbeshakenforcefullyaftermixedwithdoctorreagent,andbeobservedoil-waterphasesandcolorchangesofthesulfurpowerlayerinspecifiedtime.(4)Eliminateinterferenceofhydrogensulfide.Ifthesamplecontainshydrogensulfide,PbSblackprecipitatewillappearwhenshakingbeforeaddingsulfurpowder.Anewsampleshouldbetakenandshakentogetherwithcadmiumchloridesolution,repeatedflushingandseparationwillremovehydrogensulfide(CdCl2+H2S--→cds↓+2HCl),otherwise,thefinaltestwillbedifficulttojudgewhetherthereismercaptansulfur.2.Ammonia-coppersulfatemethod(1)Theinfluenceofiodinevolatilizationandlossontestingresults.Coolthetestsolutionto20℃±5℃beforeaddingpotassiumiodidetoavoidiodinevolatilizationandloss(2)Samplepretreatment.Ifhydrogensulfideexists,cadmiumchloridesolutionshouldbeusedbeforethetesttoeliminatehydrogensulfide.

(3)Titrationendpointjudgment.Thetitrationoperationshouldbecarriedoutcarefully.Thoroughlyshakethesampleaccordingtothestandardtoavoidexcessiveamountofammonia-coppersulfatesolution,leadingtoahigherresult.Inordertomakethetitrationendpointeasytobeobserved,whenthevolumeofcolorlesswaterphasereaches4~5ml,dischargefromthelowerpartoftheseparatingfunnel.Ifthecolorchangeoftheaqueousphaseisdifficulttoobserveclearlyintheseparatoryfunnel,whenthetitrationendpointisexpectedtobereached,thetestsolutiontitratedtonearlycolorlesscanalsobereleasedfromtheseparatoryfunnel1~3dropsinthewhiteporcelainevaporatingdish(ordripplate)forcolorobservation.3.Lampmethod(1)Completecombustiondegreeofthesample.Blacksmokeduringcombustionorvolatilizationwithoutburningwillcauselowerresultofthetest.(2)Testmaterialsandenvironmentalconditions.Donotusematchesorothersulfur-containingigniters.Ifthelostvolumeofhydrochloricacidsolutioncausedbytitrationandsodiumcarbonatesolutionwithamassconcentrationof0.3%is0.05mlmorethanthatofthesameamountofblanktest,itisconsideredthattheexperimentalenvironmenthasbeencontaminatedwithsulfurcompounds.Thoroughventilationisneededforfurthertesting.(3)Absorptionliquiddosage.Ifthesodiumcarbonatesolutionintheabsorberisinjectedinaccuratelyorlostduringtheoperation,resultdeviationoftheblanktestwillbecaused.(4)Endpointjudgment.Stirtheabsorptionsolutionwhiletitrating.Comparethecolorwithitscounterpartoftheblanktestwhenitreachestheendpoint4.Tubefurnacemethod(1)Combustiontemperaturecontrol.Thetemperatureofthefurnacehearthmustbeabove900℃duringthetest.Otherwise,thetestingresultwillbelower.

(2)Requirementsforcombustion-supportin