【doc】氧化铝的真空碳热还原—氯化—歧化反应（英文）

【doc】氧化铝的真空碳热还原—氯化—歧化反应（英文） 氧化铝的真空碳热还原—氯化—歧化反应 (英文) Availableonlineatwww.sciencedirect.com . 一,, ? ? :,ScienceDirect PressTrans.NonferrousMet.Soc.China22(2012)215—221 Transactionsof NonfcrrousMetals SocietyofChina www.tnmse.ca Carbothermalreduction-chlorination.——disproportionationofaluminainvacuum FENGYue—bin一,YANGBin,DAIYong.nian 1.FacultyofScience,KunmingUniversityofScienceandTechnology,Kunming650500,Ch ina; 2.NationalEngineeringLaboratoryofVacuumMetallurgy,FacultyofMetallurgyandEnerg yEngineering, KunrningUniversityofScienceandTechnology,Ktmming650093,China Received4January2011;accepted8June2011 Abstract:Thecarbotherrnalreduction—chlorination— disproportionationofaluminainvacuumwasinvestigatedbvXRDand thermodynamicanalysis.Theexperimentsonaluminaandgraphiteat1643-1843Kinvacuu mwerecarriedout.Theresults demonstratethatA1C13(g)reactswithA120(g)orAl(g)generatedfromthecarbothermalred uctionofaluminatoformA1Cl(g),and theA1CI(g)disproportionatestoaluminumandA1C13(g)atalowertemperatureandthereac tionrateofA1Cl(g)reaches90%at980K and1OOPa.ThealuminumcanabsorbCOtocatalyzeitsdisproportionationtoCandC0,.andr eactbackwardwithC0toform A14C3,A1203,CandCO2,resultinginthealuminumproductcontainingC,A14C3andA1203.Theimpuritiesinthealuminumproduct decreaseastheA1Cl(g)disproportionationtemperaturedecreases.A1C1condensesatatem peratureapproximatedtotheroom temperature. Keywords:carbothermalreduction;A1,0:A1C1;vacuum:disproportionation 1Introduction Despitetheindus仃ia1supremacyofthe Hall—Heroultelectrolyticprocess.therehavebeen sustainedattemptstoproducealuminumbythe carbotherma1reductionofalumina.Theprocessescanbe dividedintotwogroups.Inthefirstapproach,aluminais directlyreducedtoaluminumusingcarbonasareducing agent.Theprocesshasbeenstudiedextensively【卜3]. However,itremainstobeaformidabletechnical challenge,duetothehightemperature,andtothe formationofaluminumcarbideandoxycarbidef41.In thesecondapproach,aluminumisproducedby carbothermalreductionwithsimultaneouschlorinationof alumina.Thepresentsituationoftheprocesswas describedinR『51.Recently,theresearchersin KunmingUniversityofScienceandTechnology,China havebeencarryingoutresearchanddevelopmentalwork onthelatterapproachtoproducealuminumby carbothermalreduction-chlorination-disproportionation ofaluminainvacuum,inwhichAICl(g)isgeneratedat hightemperaturesbythecarbotherma1reduction- chlorinationofaluminaanditwil1disproportionateinto AlandA1C13atlowtemperaturesf61.ItCallbe representedbythefollowingoverallreactions[6】: A1203(s)+3C(s)+A1C13(g)=3A1CI(g)+3CO(g)(1) 3A1Cl(g)=2Al(1,s)+A1C13(g)(2) Comparedwiththedirectcarbothermalreduction, thetemperaturesrequiredfortheprocessare considerablydecreased,andthealuminumproducts don'tneedtobeseparatedfromresiduesbecausethey areformedinthelowtemperaturezonebythe disproportionationofAICl(g),apanfromthe carbothermalreduction-chlorinationzone. WANGetal[6]provedthepracticalityofthe processthroughtheexperimentsontherawmaterialsof bauxiteandcoa1.YUANetal[7—10]investigatedthe processbyXRD,SEMandthermodynamicanalysis, therebyproposingthefollowingchlorinationreactions: A14C3(s)+A1203(s)+3A1C13(g)=9A1CI(g)+3CO(g), A1404C(s)+3C(s)+2AIC13(g)=6AICI(g)+4CO(g), A1404C(s)+A14C3(s)+AI203(s)+3C(s)+5AIC13(g)= 15A1CI(g)+7CO(g). Thepurposeofthisworkistoinvestigatethe mechanismoftheformationofAIthroughthe carbothermalreduction——chlorination——disproportionation Foundationitem:Project(u0837604)supportedbytheJointFundsoftheNationalNaturalSci enceFoundationofChinaandYunnanProvince Correspondingauthor:YANGBin;Tel/Fax:+86?871-5161583;E-mail:kgyb2005@126.c om DOI:10.1016/S1003-6326(11)61163-I 216FENGYue-bin,etal/Trans.NonferrousMet.Soc.China22(2012)215—221 ofaluminaatatemperaturerangedfrom1643to1843Kdeclineddownwardsintherangeof12 00—1900K. invacuum.Furthermore,vacuumisbeneficalforreaction(5) becauseitisavolumnexpansionreaction.Therefore, 2Thermodynamicanalysisreaction(5)canoccurunderconditionsstudied. 2.1Carbothermalreduction-ehlorinationofalumina ThecarbothermalreductionofaluminainAror vacuumwasfoundtoproceedthroughgasphase reactions,ratherthandirectsolid-solidreactions[11—13】 Therefore.A1Cl(g)shouldnotbeformedfromthedirect solid_solid-gasreactionsofalumina,carbonandA1C13, andbeformedfromthechlorinationreactionsofthe carbothernlalreductionproductswithA1C1. Thecarbothelmalreductionofaluminainvacuum formsA12O,AlandCO.Theoveral1reactionsare【13】: A12O3(s)+2C(s)=Al20(g)+2CO(g) Al2O3(s)+3C(s)=2Al(g)+3CO(g) (3) (4) Theinitialreactiontemperatureforreaction(3)is lowerthanthatforreaction(4)[14].However,theGibbs freeenergychangeofreaction(3)decreaseslesssharply thanthatofreaction(4),sothattheAG-Tcurvesof reactions(3)and(4)intersectattemepraturewhereAG ofreaction(3)equalsthatofreaction(4)[14].The intersectiontemperaturedecreaseswithdecreasingthe systempressure.asshowninFig.1.Themain A1一containingproductsofthecarbothermalreductionof aluminaareAlattheleftuppersideofthecalveand AI2Oattheright—lowersideofthecurve[14]. Pressure:/Pa Fig.1Temperatureatintersectionof?G_curvesofreactions (3)and(4)vssystempressure[14] ThechlorinationreactionofA120(g)toA1Cl(g)is postulated: 2A1C13(g)+3A120(g)=A1203(s)+6A1CI(g)(5) Basedonthedataofchemicalreactionand equilibriumofsoftware(HSC),theGibbsfreeenergy change(?G)ofreaction(5)wascalculatedandshown inFig.2.Ascanbeseen.Avaluesareallnegativeand j_一 0 g ? 司 Temperature/K Fig.2AGOofreaction(5)vstemperature ThechlorinationreactionofAl(g)toAICl(g)is 2Al(g)+AlCl3(g)=3AlCl(g)(6) BasedonthedataofHSC,theGibbsfreeenergy (AG)ofreaction(6)wascalculatedandshowninFig.3. Ascanbeseen.AGvaluesareallnegativeanddeclined downwardsintherangeof1200-1900K.Thesystem pressurehasnoinfluenceontheGibbsfreeenergy changeofreaction(6).Reaction(6)haseverbeenused toextractaluminumfromAlalloyf15,16]. , L o 基 0 司 Temperature/K Fig.3AG~ofreaction(6)vstemperature 2.2DisproportionationofAICl(g) A1CI(g)disproportionatesintoA1andA1C13(g) accordingtoEq.f2atlowtemperature.enthemole ratioofAICI(g)toAlCla(g)was0.5,therelationshipof Gibbsfreeenergychange(?G)ofreaction(2)and temperature(73wascalculatedbasedonthedataofHSC usingthemethodfromRef.[171,andshowninFig.4.As canbeseen,AGvalueofreaction(2)decreaseswith \2jBJQ暑 FENGYue-bin,etaYTrans.NonferrousMet.Soc.Chma22(2012)215—221217 decreasingthetemperatureandincreasingthesystem pressureintherangeof300—1900K.Therefore,the largerthesystempressureis,andthehigherthe temperatureis,themoreeasilytheA1CI(g) disproportionationisca~iedout. j. 0 g 司 Temperature/K Fig.4AGofreaction(2)VStemperatureatdifferentpressures (themoleratioofA1C1toA1C13is0.5) 3Experimental 3.1Apparatus Theexperimentswerecarriedoutinthefurnace designedbyourselves,asshowninFig.5[18]. 3.2Experimentalprocedure Alumina(analyticalgrade)andgraphite(fixed carboncontentof99.85%1withmolarratioof1:3were thoroughlymixedandpressedinacloseddieof20mm indiameterunder2/VIPatoproducecylindricalpellets 4 5 6 7 8 9 3 2 withmassofabout5g. 1)Carbothermalreductionofalumina(Experments A, TIlepelletswereheldinthegraphitecrucibleplaced inthevacuumfurnace,andheatedatacertain temperaturefor30min.Theresiduesandcondensates werethenanalyzedbyX-raydiffractiontechniqueusing aD/max-3Bdiffractometer(Japan)withCu radiation. Theexperimentswereconductedat1643.1693. 1743,1793and1843K,respectively.Thehighest pressureinthesystemreached150Pa.Thepresent conditionsweremainlyintherangeforproducingAI20 accordingtoFig.1,andtherebyaluminareactedwithC toformA120chieflyaccordingtoreaction(3). 2,Carbothermalreduction-chlorination-dispropor- tionationofalumina(ExperimentB, T}lepelletswereheldinthegraphitecrucibleplaced inthevacuumfurnace,andheatedinthepresenceof A1C13atacertaintemperaturefor30min.Theresidues andcondensateswerethenanalyzedbyX—raydiffraction techniqueusingaD/max一3Bdiffractometer(Japan)with CuKradiation. Theexperimentswereconductedat1643,1693, 1743,1793and1843K,respectively.Thehighest pressureinthesystemreached200Pa. 4ResuItsanddiscussion 4.1Phasecompositionofresidues Theresiduesafterheatingthepelletsintheabsence ofA1CI3(g)(ExperimentsA,consistedofA1203andCas thesameastherawmaterials,whichwasinagreement AlC1, Fig.5Schematicdiagramofvacuumfurnace:1— _AlCl3evaporator;2--Reactioncrucible;3--Graphitecondenser;4一VacuumPump; 5--Water-cooledcoveroffurnace;6--Thermalinsulatinglayer;7--Graphiteexothermicbod y;8--Exothermicbodybase; 9-一W.ater-cooledelectrode 218FENGYue-bin,etal/Trans.NonferrousMet.Soc.Chma22(2012)215-221 withtheearlierresultsthattheproductsofthereactions ofaluminaandcarboninvacuumwereallgases『13,141. Theresiduesafterheatingthepelletsinthepresence ofA1C13(g)(ExperimentsB,consistedofA1203andCas well,whichindicatedthatthereactionsoccurringwere thesameasthoseintheabsenceofA1C13(g).Therefore, A1C13(g)didnotparticipateinthereactionofalumina andgraphite.andAlClshouldbeformedbythereaction ofA1Cl3(g)andtheA1一containinggaseousproducts generatedfromthecarbotherma1reductionofalumina. ThemainA1.containinggaseousproductsshouldbeA120 becausethepresentconditionsweremainlyintherange forproducingA120accordingtoFig.1. 4.2Phasecompositionofeondensates Table1presentsthephasecompositionofthe condensatesformedintheexperiments. Table1Compositionofcondensates TheXRDpatternsofthecondensatesontheupper partofthereactioncrucibleformedbyheatingthepellets intheabsenceandthepresenceofA1C13(g)at1743Kfor 30minareshowninFig.6.Ascanbeseen,the condensatesformedinthecarbothermalreductionandin thecarbothermalreduction-chlorination-disproportiona- tionofaluminawereidenticalinphasecomposition.The condensatescouldbetheproductsoftheback-reactions OfAl,OandCOformedbycarbothermalreductionof alumina『13,14].HoweveLthediffractionpeakassigned t0CintheXRDpatternsofthecondensateformedinthe carbothermalreduction-chlorination-disproportionation wasconsiderablyweakerthanthatinthecarbothermal reduction.Theresultsupposedtheaboveconelusionthat A1C13(g)didnotpattieipateinthereactionofalumina andgraphite.andAlClshouldbeformedmainlybythe reactionofA1Cl3(g)andAl20(g),andthereactionof A120(g)andAIC13(g)occurredaccordingtoreaction(5) becauseAl203formedbyreaction(5)couldreactwith carbontoresultinareductionintheamountofcarbon. Fig.6XRDpatternsofcondensatesonupperpartofreaction crucible:(a)Carbothermalreduction;(b)Carbothermal reduction——chlorination-disproportionation TheXRDpatternsofthecondensatesonthebottom ofthecondenserformedbyheatingthepelletsinthe absenceandthepresenceofAIC13(g)at1743Kfor30 minareshowninFig.7.Ascanbeseen,boththe condensatesconsistedofA12O3andC.Thecondensates shouldbeformedmainlybytheback-reactionsofAl,0 andCO[13,14].However,thediffractionpeaksassigned tOAl20inthePatternsofthecondensateformedinthe carbothermalreduction—chlorination-disproportionation wereconsiderablymoreintensethanthoseinthe carbothermalreduction,andthediffractionpeaks assignedto.Al,Owerealsoobservedbesidesthose assignedtoa—Al201.Itwasfurtherindicatedthatthe chlorinationreactionofA120(g)occurredaccordingto reaction(5),becausereaction(5)couldgenerateA1203to resultinagrowthintheamountofA120.andthe condenserbosomtemperaturewaslowenoughtoavoid reactionofA12O3withcarbon. Forthecarbothermalreduction,thegaseous productsreactedbackwardstocondensateontheupper partofthereactioncrucibleandtheboRomofthe condenser.111egasfromcrucibleintothecondenser mainlyconsistedofCO,andconsequentlynocondensate formedinthecondenser.Forcarbothermalreduction- FENGYue-bin,etal/Trans.NonferrousMet.Soc.China22(2012)215-221 (a)',一 C .--AI203 ?? l一.』,一:,kI…一一. 20406O80 20/(.) Fig.7XRDpaRemsofcondensates chlorination-disproportionation 2l9 onbottomofcondenser:(a)Carbothermalreduction;Co)Carbothermalreduction- (b)? IL.妓己jL工上L...LL...20406080 20/(.) Fig.8XRDpatternsofcondensateson condensationplatesandtopofthecondenser: (a)lcondensationplate;(b)2condensation plate;(c)3condensationplate;(d)甜 condensationplate;(e)Topofthecondenser 220FENGYue-bin,etal/Trans.NonferrousMet.Soc.China22(2012)215—221 chlorination-disproportionation,besidesback-reactions thegaseousproductsreactedwithA1C13(g)toform A1CI(g),andconsequentlythegasfromcrucibleintothe condenserconsistedofCO,A1ClandAlC1unreacted. Thegascondensedcontinuouslywithdecreasing temperatureasitwentthroughthecondensationplates andthetopofthecondensertothecoverofthefurnace. TheXRDpattemsofthecondensatesonthe condensationplatesandonthetopofthecondenserin thepresenceofAIC13(g)at1743Kfor30minareshown inFig.8.A1Cl(g)intocondensershoulddisproportionate toformAlandA1CI3(g),andtherebythecondensates shouldconsistOfA1.Howeve~thecondensareson1撑 and2}}condensationplatescontainedC,Al4CandAl20 besidesA1.TheCshouldbeformedbythe disproportionationofCOaccordingtoreaction(7) becauseAlcouldabsorbCOtocatalyzeits disproportionationtoCandCO2. 2CO(g)C(s)+CO2(g)(7) TheA14C3andA1203shouldbeformedbythe back-reactionsofA1andCOaccordingtoreactions(8) and(9). 4Al(s)+6CO(g)=Al4C3(s)+3CO2(g)(8) 2AI(s)+3CO(g)=A1203(s)+3C(s)(9) FromFig.8,thediffractionpeaksassignedtoC, A14C3andA1203inthecondensatesgrewweakwith decreasingtemperature.Itwasindicatedthattheextent ofthedisproportionationofCOandthebackward reactionsofAIandCOdecreasedasthetemperature decreased. AIC13condensedonthewater-cooledcoverofthe furnacewherethetemperatureapproximatedtotheroom temperature,duetothelowsublimationtemperatureof A1C13invacuum[19]. 5Conclusions 1,A1CIinthecarbothermalreduction-chlorinatiOIr disproportionationofaluminainvacuumshouldbe formedbytwosuccessivereactionsteps.Inthefirststep, aluminareactswithcarbontogenerateA1EO(g)orAl(g). Inthesecondstep,theA120(g)orAl(g)reactswith A1C13(g)toformA1CI(g). 2)A1C1disproportionatestoaluminumandAIC13(g) atlowertemperatures.ThealuminumcanabsorbCOto catalyzeitsdisproportionationtoCandCO2,andreact backwardwimCOtoformA14C3,A12O3,CandCO2.The extentofthedisproportionationofCOandthebackward reactionsofAlandCOdecreasesastheA1CI(g) disproportionationtemperaturedecreases.AIC13 condensesatatemperatureapproximatedtotheroom temperature. References [1】BRUNOMJ.Aluminumcarbothermictechnology[RI. DOE/ID/13900.Pennsylvania:Alcoa,2004. 【2】GR0THEIMK,MOTZFELDTK,KVANDEH,SCHEIA. Carbothermalproductionofaluminium:Chemistryandtechnology [M】.Dusseldorf:Aluminium?Verlag,1989. 【3]MOTZFELDTK,SANBERGB.Chemicalinvestigationsconcerning carbothermicreductionofalumina【C]//PETERSONWS.Light Metals.Warrendale:TMS.1979:41l一428. [4]CHOATE,?'GREENJ.Technoeconomicassessmentofthe carbothermicreductionprocessforaluminumproduction【c]// GALLOWAYTJ.LightMetals2006,volume2,Aluminum ReductionTechnology.Warrendale:TMS,2006:445—450. 【5】FENGYue—bin,DAIYong-nian,WANGPing-yan.Researchofthe productionandrefiningofaluminumbydisproportionation[J1.Light Metals,2009(3):12—15.(inChinese) 【6]WANGPing-yan,LIUMou-sheng,DAIYong—nian.Vacuum metallurgyofAlfrombauxitebycarbothermicreaction—chloridation 【J].ChineseJournalofVacuumScienceandTechnology,2006,26(5): 377—380.(inChinese) 【7]YUANHal-bin,YANGBin,XUBao—qiang,YUQing—chun,FENG Yue—bin,DAIYong-nian.AluminumproductionbycarothelTnO- chlorinationreductionofaluminainvacuum[J].Transactionsof NonferrousMetalsSocietyofChina,2010,2O(8):1505—15lO. 【8】YUANHal—bin,Y_ANGBin,YuQing—chun,xu?