学位论文汽车专业翻译p001360.docx

学位论文汽车专业翻译p001360.docx

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学位论文汽车专业翻译p001360

INTRODUCTION

Mostoftheoildailyextractedisconsumedintransportation（approximately66.6%inAmerica）.Oftheenergyusedinthissector,approximately65%isconsumedbygasoline-poweredvehicles.Diesel-poweredtransport（trains,merchantships,heavytrucks,etc.）consumesabout20%,andairtrafficconsumesmostoftheremaining15%.InItaly,civilmobilityaccountsforabout74%oftotalconsumption,halfofwhichcorrespondingtoabout30%ofthenationaltotalconsumptionontransportation,insideurbanandsuburbanzones.Intheseenvironmenttherefore,caremissionsrepresentsthemainpollutionsource.Hydrogencars,byeliminatingCO2emissions,coulddrasticallyreduceinshorttimespollution,especiallyinourlivingareas.Themainobstacle,hinderingtheintroductionintothemarketofhydrogencars,isrepresentedbythelowefficiencyofhydrogenstoragesystem.

Figure1.Energydensity,bothvolumetricandgravimetric,ofvarioussystemsforhydrogenstorage.The2010and2015DOEtargetscorrespondto6.0and9.0%wt.

Wecanassumethatafuelcellequippedcarwouldrunabout100kmperkgofhydrogenburned.Consequentlyastandardof400kmwouldbefulfilledby4kgofhydrogen.Fig.1showsvariousstoragesystemsdimensionedtodeliver4kgofhydrogen.

Amongthedifferentstoragesystems,thehydrolysisofhydrideseemsthebestpromisingone（Fig.2）.

Thereactioncanberepresentedas:

2MeHn+nH2O→Me2On+2nH2

（1）

Thehydrideshouldnecessarilyberegeneratedoff-board.

AmongthedifferentmetalhydrideNaBH4showsahydrogencontenthigherthan10%wt.Thehighhydrogencontentandthesimplicityofsynthesismakesthesaltaperfectcandidatetostorehydrogenformobileapplication.AsafuelNaBH4islessflammableandlessvolatilethangasoline.Itisrelativelyenvironmentallyfriendlybecauseitwillquicklydegradeintoinertsaltswhenreleasedintotheenvironment.

Figure2.Weightpercentofhydrogenevolvedfromhydrolysisofvariouscomplexmetalhydrides.Thehydrogenweightwasreferredonlytotheweightofthemetalhydrideanditdoesnottakeintoaccounttheweightofwaterusedforthehydrolysis.

Thehydrogenisgeneratedbycatalytichydrolysisofborohydride:

NaBH4+2H2O→NaBO2+4H2

（2）

Thesodiumboratecanbereverselyturnedintosodiumborohydridebywellknowmethods.Theweightpercentageofhydrogenoverthehydrideofthehydrolysisreactionisincrediblyhigh,20%.Thecompoundwasdiscoveredinthe1940'sbyH.I.Schlessinger,wholedateamthatdevelopedmetalborohydridesforwartimeapplications.In1939AntonB.H.BurgandH.C.BrownbecameresearchassistantstoProfessorSchlesinger.IntheFallof1940hewasrequestedtoundertakefortheNationalDefenseResearchCommitteeasearchfornewvolatilecompoundsofuraniumoflowmolecularweight.,withoutthecorrosivepropertiesofuraniumhexafluoride.ByusingdiboranethesynthesisofU（BH4）4,acompoundwithadequatevolatility,wassuccessful.Toeffectivelyconfirmtheresulttheywererequestedtosupplyrelativelylargeamountsofthematerial.Thebottle-neckwasthepreparationofdiborane.Bythistimetheywouldnotbeabletosupplysufficientdiboranesotheyattemptedtofindamorepracticalroute.Theydiscoveredthatthereactionoflithiumhydridewithborontrifluorideinethylethersolutionprovidedsucharoute.Unfortunately,lithiumhydridewasinveryshortsupplyandcouldnotbesparedforthissynthesis.Instead,therewasalargeamountofsodiumhydride.Unfortunately,withthesolventsthenavailable,thedirectuseofsodiumhydridewasnotsuccessful.However,anewcompound,sodiumtrimethoxyborohydride,readilysynthesizedfromsodiumhydrideandmethylborate,solvedtheproblem.Itprovedtobeveryactivetoandprovidedthedesiredtransformationspreviouslyachievedwithlithiumhydride.Thyalsodiscoveredthattheadditionofmethylboratetosodiumhydridemaintainedat250°providedamixtureofsodiumborohydrideandsodiummethoxide.Thisalsoprovidesthebasisforthepresentindustrialprocessforthemanufactureofsodiumborohydride.Atthisstagetheywereinformedthattheproblemsofhandlinguraniumhexafluoridehadbeenovercomeandtherewasnolongeranyneedforuraniumborohydride.TheywereonthepointofdisbandingthegroupwhentheArmySignalCorpsinformedthatthenewchemical,sodiumborohydrideappearedverypromisingforthegenerationofhydrogentoinflatesignalballoon.Atthattime,therewasnodoubtaboutthefactthatNaBH4shouldreactwithwatertoliberatehydrogen.Someconcernsremainedaboutthesafetyofthereaction.Whentheytryforthefirsttimetoliberatehydrogenbyhydrolysistheborohydridewasplacedinaflaskandtheentireassemblywasputbehindanexplosionscreensinceitwasnotknowhowviolentthereactioncouldbe.Incredibly,theborohydridedissolvedinthewaterwithoutexplosionandwithslowhydrogenevolution,anditwasdiscoveredthatsodiumborohydridepossessesanunusualstabilityinalkalinewater.Severalstudyhavebeenthenconductedonhydrolysisofsodiumborohydride.ItwasfoundthatitisveryfastatlowpHandthathighpHvalues,preventwaterhydrolysis.Inpresenceofcatalyser（cobalt,nichel,iron）thereactionisquitefastandcompletealsoathighpH.ArmySignalalsoproposedtostudythenewcompoundforrocketenginebuttheprojectwasstoppedfewyearslater.Atthatagetechnicianstoldthatsodiumborohydridewouldhaveapossibilityforciviluseattheendofthecentury.Morethan60yearhavebeenpassedandnowitcouldbetherighttimeforsodiumborohydride.Severalcarmakersannouncedtheirintentiontopowerhybridhydrogencarwithsodiumborohydride.DaymlerChryslerbuiltaprototypeapplyingthetechnologythatusethatsaltforfuellingafuelcell（theNatrium,overaChryslerTown&Countrymodel）.EvenPSA-Peugeotbuiltaprototypewithruteniumascatalyser,theH2Omodel.Aliquidsolutionhalfweightsodiumborohydridehalfweightwater,stabilizedwithsodiumhydroxide,delivershydrogen（throughaRucatalyser）withanenergeticratio,involume,similartogasoline.MillenniumCell（whichhaspatentsoncatalyserandsystems）builtdifferentprototypewithFORD.MillenniumCellannouncedthatithasbeenawardedaPhaseISmallBusinessInnovationResearchProgram（"SBIR"）contractbytheAirForceResearchLaboratory（"AFRL"）todevelopasodiumborohydridebasedfuelcartridgedesignthathastheflexibilitytooperatewitheitherready-to-use,premixedsolutionsofsodiumborohydride,oralternatively,withsolidfuelpacketsthatawarfightercancombinewithavailablefieldwaterorbodilyfluids.Theabilitytoshipcartridgescontainingdrysodiumborohydridefuelwhichcanbemixedwithanavailablewatersupplyatpointofusewouldresultinasignificantreductioninweighttobehandled.

EXPERIMENTAL

ThehydrolysisinthevaporphaseofsolidNaBH4wasconductedinaoven.About1.0gramofcatalyzedsolidNaBH4wasplacedintheoveninpresenceofwatercontainedinaseparatecontainer.TheNaBH4wascatalyzedwithvariousmetalsalts（Co,NiorFe）ataconcentrationofabout2%mol.Theoutletoftheovenwasconnectedtoagraduatecylinderfilledwithwater.Theevolutionofhydrogenwasfollowedbywaterdisplacement.Thetemperatureoftheovenwasraisedfromroomtemperatureupto95°C.afterTheproductofhydrolysiswascharacterizedbyX-raypowderdiffractionusingaMiniflexRigaku（Cuk-αradiation）.Cartridgeswerepreparedbyusingthesamemixture（NaBH4+catalyst）.Blottingpaperwasusedtopreparethecartridges.ThecartridgeswerefilledwithNaBH4withaweightrangingfrom30upto150g.Thecartridgewereinsertedinametallicreactor.Thereactorisa6cmdiameter6cmhighcylinder.Liquidorvaporizedwaterwasintroducedbypumpingitwithacontrolledpumpintoathermocontrolledheater.Theamountofwaterwasrecordedbyusingaliquidflowmeter.Thehydrogenevolvedwascollected,filteredtoremovewatervaporandmeasuredbyusingagasflowmeter.

ENEAACTIVITIES

ThenewhydrogenreleasingsystemdevelopinginENEAisbasedonsolidNaBH4whichishydrolyzedwithwaterorsteam.Tomakethereactionveryfastacatalystwasused.Figure3showtheamountofhydrogenevolvedwhen1.0gramofcatalyzedNaBH4isputinpresenceofwatervaporinequilibriumwithliquidwateratvarioustemperatures,rangingfrom40to95°C.

Figure3.Volumeofhydrogenevolvedasafunctionoftimefrom1.0gofNaBH4inpresenceofwatervaporatvarioustemperature.Thecatalystwasnickelacetate2%mol.

Thepresenceofcatalystissoeffectivethathydrolysiscanbeconductedalsoatroomtemperature.Byincreasingthetemperatureobviouslytherateofhydrogenproductionincreases,andthereactiontimedecreases.Independentlyfromtemperatureaboutthetheoreticalamountofhydrogenwasrecovered.Fortemperaturelowerthan70°Candfortimelowerthan100min,thereactionseemsindependentfromtemperature.Forlongertimesitisevidentaprogressiveincreaseofthekineticofthereactionasthetemperatureincreases.Asecondreactiontakesplaceandtheactivationenergyofthisreactionissohighthat,fortemperaturehigherthan70°C,thereactionbecomesthefasterone.Figure4showsthevolumeofhydrogenevolvedrelatedonlytothesecondreaction.Itwasobtainedbysubtractingfromthecurvesplottedinfigure3theconstantcontributeduetothefirstreaction.Inthesamefigureitisplottedthehalf-lifetimeasafunctionofthetemperature.Fromthesedataanewgraph（Figure5）wasobtainedbyplottingthenaturallogarithmoftheinverseofthehalf-lifetimeasafunctionofth