学位论文汽车专业翻译p001360Word文档格式.docx
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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