由乙烯焦油制备锂离子电池负极材料用碳质前驱体的氧化反应机理与反应动力学.pdf

Cite this:NewCarbonMaterials,2024,39(2):354-366DOI:10.1016/S1872-5805(22)60597-3The oxidation reaction mechanism and its kinetics for a carbonaceousprecursor prepared from ethylene tar for use as ananode material for lithium-ion batteriesGUOTian-rui,CHENRong-qi,GAOWei,WANGYan-li,ZHANLiang*（State Key Laboratory of Chemical Engineering,East China University of Science and Technology,Shanghai 200237,China）Abstract：TheoxidationreactionmechanismanditskineticsforethylenetarwereinvestigatedinordertoobtainasuitableanodematerialforLi-ionbatteries.Theoxidationofethylenetarwasdividedinto3stages(350550,550700and700900K)accordingtothethermogravimetriccurve.Torevealtheoxidationreactionmechanism,thecomponentsofthegasesevolvedatdifferentstageswereanalyzedbymassspectrometryandinfraredtechnology.Basedontheseresultsthereactionwasdividedinto4stages(323400,400605,605750and750860K)toperformsimulationcalculationsofthekinetics.Usingtheiso-conversionmethod(Coats-Red-fern)toanalyzethelinearregressionrates(R2)between17commonreactionkineticsmodelsandexperimentaldata,anoptimumre-actionkineticsmodelforexpressingtheoxidationofethylenetarwasdeterminedandtheresultswereasfollows.(1)Duringoxida-tion,thesidechainsofaromaticcompoundsfirstreactwithoxygentoformalcoholsandaldehydes,leavingperoxy-radicalsonaro-maticrings.Subsequently,thearomaticcompoundswithperoxy-radicalsundergopolymerization/condensationreactionstoformlar-germolecules.(2)Afourth-orderreactionmodelwasusedtodescribethefirst3stagesintheoxidationprocess,andtheactivationenergiesare47.33,18.69and9.00kJmol1at323400,400605,605750K,respectively.Athree-dimensionaldiffusionmodelwasappliedtothefourthstageoftheoxidationprocess,andtheactivationenergyis88.37kJmol1at750860K.Ahighsofteningpointpitchwasalsoproducedforuseasacoatingofthegraphiteanode,andafterithadbeenappliedthecapacityretentionafter300cyclesincreasedfrom51.54%to79.07%.Key words:Ethylenetar；Oxidationreactionmechanism；Reactionkinetics；Carbonaceousprecursor；Lithium-ionbatteries1IntroductionFunctionalcarbonmaterialshavebeenplayinganimportantroleinelectricalapplications,thermalman-agement(e.g.,heat conduction and insulation),en-ergystorage(e.g.,electrodematerials),environmentalprotection(e.g.,gas capture),and various otherfields14.Itiswellknownthathigh-softening-pointpetroleumpitchisanimportantcarbonaceousprecurs-or5.Forexample,petroleumpitchwithahighsoften-ingpointcanbeappliedasthecoatingmaterialtotheanodematerialsoflithium-ionbatteries,rawmateri-alsforpitch-basedcarbonfiberandpitch-basedspher-icalactivatedcarbon68.Amongthese,ethylene tar is an important re-sourceforpreparinghighsofteningpointpetroleumpitches910.Therawmaterialforethyleneproductionismainlynaphtha(atmosphericcrudeoilfractionwithaninitialdistillationpointof200C).TheCHbondandCCbondofnaphthaarebrokenathightemperatures(600800C)toproduceethyleneandpropylene.Meanwhile,olefins can also polymerizeandcyclizetoproducearomatichydrocarbons.There-fore,themaincomponentsofethylenetararemono-cyclic,polycyclic aromatic hydrocarbons and heavyaromaticdistillates,whicharevaluableresourcesrichinaromatichydrocarbons.Asthebyproductofhydro-carbonscrackinginethyleneproduction(ca.15%inyield),ethylenetarisproducedinlargeamountseveryyearwiththeincreasingdemandforethylene.Thus,itisregardedasanidealmaterialforproducinghigh-qualitypitch.Toincreasethesofteningpointandcarbonyieldofsyntheticpitch1114,theairoxidationmethodhasbeenwidelyappliedtopreparehigh-qualitypitch1518.Several researchers11,13,19 have reported that the airoxidationmethodcancausepolymerization/Received date：2021-08-30；Revised date：2021-11-04Corresponding author：ZHANLiang,Professor.E-mail:Author introduction：GUOTian-rui.E-mail:guo_Homepage:http:/ and emission of water2224.Nevertheless,themechanismoftheairoxidationreactionseemstoberelated to the experimental conditions25 and thechemicalpropertiesoftherawmaterials11,13.Mostofthecurrentstudiesfocusontheoxida-tionmechanismandkineticsofstandardmixtures2628.Yamaguchietal.28reportedthattheal-kyl-andbridgedalkyl-aromaticswerethemostreact-iveforlightaromatichydrocarbonspolymerizedwithairat330C,2.1MPa.Meanwhile,basedonfurtheranalysisoftheresultsandproducts,aseriesofoxida-tionmechanismsrelatedtothegrowthofmolecularmass were suggested.In addition,the interactionbetween hydrocarbons was observed while standardcompoundswereoxidizedbyair27.Theoxidationre-actionmechanismandkineticsofindustrialmixturescomposedofaromatichydrocarbons,suchasethylenetar(ET),havebeenlessinvestigateddespitetheeco-nomyandsimplicityoftheprocessandthelowcostoftherawmaterials.Toacquireanexcellentcarbonaceousprecursor,wetriedtorevealtheoxidationprocessofethylenetar.Thereactionextentofethylenetarwasanalyzedbytheweightoftheresidues,whilethereactionpro-cess of ethylene tar was monitored by a combinedTG-MS-FTIRtechnique.BasedontheCoats-Redfernmethod,thebasicdynamicparameterswereattained,whichprovided technical guidance for the prepara-tionofcarbonaceousprecursor.Finally,weproduceda high-softening-point petroleum pitch to coat ongraphitetoimprovetheelectrochemicalpropertiesofanodeinlithium-ionbatteries.2Materialsandmethods 2.1 Raw material and pretreatmentTheoriginalethylenetarprovidedbyPetroChi-naJilin Petrochemical Company Co.,Ltd was pre-treatedbyatmosphericdistillationat230C.Afterre-movingthelightfractions,theheavyresidue(ET-HR)wasusedforsubsequentexperimentsandcharacteriz-ation.Naturalgraphite(NG)wassuppliedbyShang-haiShanshanTechCo.,Ltd.2.2 Experimental proceduresAbout800gET-HRwasplacedina2Lstain-lesssteelreactorandheatedat2Cmin1to310C.Thetemperaturewasheldat310Cfor10h,whilethewholeprocesswasinairatmospherewithaflowrate of 2 Lmin1.The oxidized product cooled toroomtemperaturenaturallywaslabeledasETP.Tocoatgraphite,ETPwasdissolvedinthetet-rahydrofuran solution with NG.The mass ratio ofETPtographitewas1:10.Aftersufficientstirringfor24h,thesolutionwasevaporatedinathermostaticwaterbath.Theobtainedsolidwasthencarbonizedat1000Cfor2hinN2atmosphere.Finally,ETPNGwasacquired.Thehalf-cellwasassembledintheargon-filledgloveboxwiththeelectrolyteof1molL1LiPF6inethylene carbonate(EC)/diethyl carbonate(DMC)/ethylmethylcarbonate(EMC)(111byvolume).Poly(vinylidenefluoride)(PVDF)wasservedasthebinder,while super C was the conductive agent.ETPNG,binder,and conductive agent were dis-persed in N-methyl-2-pyrrolidone(NMP)at a massratioof9253,whichwasthencoatedoncopperfoilanddriedtoserveasanode.CR2016wasusedinthe electrochemical tests with the counter electrode(lithiumfoil)andtheporousseparator(Celgard2500).2.3 CharacterizationTheoxidationprocessofET-HRwasevaluatedby a synchronous thermal analyzer(STA-8000,PerkinElmer,America).Thesampleweightof15mg,aheatingrateof5Kmin1from300to900K,andanairflowrateof20mLmin1werechosenastheex-perimentalconditions.Anelementalanalyzer(VARIOEL,Germany)wasusedtoanalyzetheelementalcompositionofET-HR.Thefourcompon-entsofpitchweremeasuredbythin-layerchromato-graphy(TLC)withflameionizationdetection(FID),whichenhanced our understanding of the composi-第2期GUOTian-ruietal:Theoxidationreactionmechanismanditskineticsforacarbonaceous355tionanddistributionofethylenetar.Agaschromato-graphy-massspectrometry(GCMS-QP2010Plus,Shi-madzu,Japan)wasadoptedtoseparateandidentifythe chemical composition of ET-HR.Based on theprobabilitymatching method(PBM)and the com-poundspectrumdataofNIST08andNIST08Slibrary,thestructureofthecomponentswasdeterminedac-cordingtotheconfidenceorsimilarity29.Themolecularmassdistributionwasanalyzedbyamatrix-assistedlaserdesorption/ionizationtime-of-flightmassspectrometryanalyzer(4800PlusMALDITOF/TOF,AB SCIEX,America).A simultaneousthermalanalyzer(STA-8000,PerkinElmer,America)was used to obtain simultaneous weight signal andheatflowsignalatanairflowrateof20mLmin1andheatingrateof5Cmin1.TheTG-MS-FTIRinstru-mentincludesathermogravimetricanalyzer(SETSVSEvolution16/18,SETARAM,France),amassspec-trumanalyzer(OMNIstar,Pfeiffer,Germany),andaFourier transform infrared spectrometer(Tensor27,Bruker,Germany)30.Thetestconditionsweresettothefollowing:thesampleweightof15mg,anairflowrateof20mLmin1,andaheatingrateof5Cmin1from300to900K.TheevolvedgasesofTGAweredetectedbythemassspectrometerinaheliumatmo-sphereat280C.ThethermogravimetricanalysiswasconnectedwiththeFouriertransforminfraredspectro-meterthroughathermalinsulationpipe,andthetem-perature of the connecting pipe was maintained at280Ctopreventthecondensationoftheproducts.Theinfraredspectrumhadascanningrangeof4000600 cm1 and a resolution of 4 cm1.The scanningelectronmicroscope(SEM,JEOL-7100F,Japan)wasusedtoobservethemorphologyofthesamples.TheX-ray diffraction(XRD,Bruker D8 Advance,Germany)with Cu-Ka radiation(=0.15406 nm)wastodetectthecrystallinestructure.Thescatteringangles(2)werefrom10to80withascanrateof5min1.Thecycleperformanceofthehalf-cellwastestedon LAND CT2001A(China)by galvanostaticcharge/discharge.Thevoltagerangewas02V(vs.Li/Li+).Theratewas0.2Cforthefirst5cycles,afterwhichitkeptat0.5Cuntilthe300thcycle.2.4 Kinetics theoryThepyrolysisofthesolidcanbeexpressedasthefollowingreactionprocess31:A(solid)B(solid)+C(gas)d/dtkf()Inthenon-isothermalexperimentsimulatedbyathermogravimetricanalyzer,theweightofthesamplewasmeasuredasafunctionoftemperature.Therateofconversion,isalinearfunctionofatemper-ature-independentrateconstant andatemperature-independentfunctionofconversion:d/dt=kf()(1)twhere istheconversiondegree,and istime.isexpressedas:=mimtmim(2)mimtt mwhereistheinitialweightofthesample,istheweightofthesampleattime,isthefinalweightofthesampleinthereaction.kThereactionrateconstant,hasbeendescribedbytheArrheniusexpression:k=Aexp(EaRT)(3)AEaRTwhere isthepre-exponentialfactor,istheactiva-tionenergy,isthegasconstant,and istheabso-lutetemperature.ThecombinationofEqs.(1)and(3)gives:d/dt=Aexp(EaRT)f()(4)=dT/dtIfthetemperatureofthesampleischangedbyacontrolledandconstantheatingrate,there-arrangementofEq.(4)gives:d/dT=Aexp(EaRT)f()(5)Theintegrated form of Eq.(5)is further ex-pressedas:G()=w0df()=AwTT0exp(EaRT)dT(6)T0whereistheinitialtemperature.As one of the most popular iso-conversionalmethods,Coats-Redfernapproximationwasadopted,expressedas32:wexp(EaRT)dT=(RT2Ea)exp(EaRT)(7)BycombiningEq.(6)andEq.(7),thenewequa-356新型炭材料（中英文）第39卷tionwasexpressedas:ln(G()T2)=lnAREa(12RTEa)EaRT(8)2RT/EaBecause the expression,is much lessthan1,Eq.(8)couldbesimplifiedas:ln(G()T2)=ln(AREa)EaRT(9)G()ln(G()/T2)1/TA series of reaction models defining aresummarizedinTable13334.Iftheoptimalreactionmodelisselected,thefunctionimageofwithrespecttoshouldbeastraightline.Throughtheslopeandintercept,theactivationenergyandpre-exponentialfactorcanbeobtained.3Resultsanddiscussion 3.1 Characterization of ET-HR3.1.1ThefundamentalpropertiesofET-HRAsshowninTable2,afteratmosphericdistilla-tionat230C,thesaturatedfractionofethylenetarwascompletelyremoved,andtheratioofcarbontohydrogenwas increased to 1.13.In addition,it re-mainedsolubleintolueneevenwhenthecarbonyieldofET-HRreachedthevalueof14.1%.3.1.2GC-MSandLDITOF/MSofET-HRGC-MSwasadoptedtoseparateandidentifythechemical composition of ET-HR.The characteristicpeaks of various compounds were recorded inFig.1(a),andthepossiblesubstancescorrespondingtothesepeaksweresummarizedinTable3.ThedatarevealsthatET-HRisanextremelycomplexmixturecomposedofaromatichydrocarbonswithvarioussidechains.The organic compounds with lower boilingpointscanbeseparatedandconfirmedwellbyGC-MS.Nevertheless,itisdifficulttodistinguishaccur-atelyforsomelargermolecules.Tosolvethisprob-lem,we tried to further analyze ET-HR by LDITOF/MS.TheresultshowninFig.1(b)suggeststhatalargenumberofwell-definedpeaksarenotdisplayedinGC-MS.Inaddition,thesepeaksarecontinuouslydistributedinthemolecularmassrangeof100800,indicatingthatET-HRcontainslotsofpolycyclicaro-matichydrocarbons.3.2 Oxidation mechanism of ET-HR3.2.1DSC-TGAofET-HRAsshowninFig.2(b),DTGcurvereveals3sig-nificantmasslossstages,andthemasslossdataatdif-ferentstagesisshowninFig.2(a).Thefirststageoc-cursbetween300and520K,andthepeakappearsat399K.Thefirststage,showingmasslossof42.7%,iscausedbythevolatilizationoflightcomponents,to-gether with oxidation and polymerization/condensa-Table 1 A series of frequently-used mechanism models defining G()33-34MechanismsSymbolf()G()OrderofreactionFirstorderF11ln(1)SecondorderF2(1)2(1)11ThirdorderF3(1)3(1)21/2FourthorderF4(1)4(1)31/3DiffusionOne-waytransportD10.52Two-waytransportD2ln(1)1+(1)ln(1)Three-waytransportD31.5(1)2/31(1)1/311(1)1/32ContractinggeometryContractingcylinderR22(1)1/21(1)1/2ContractingsphereR33(1)2/31(1)1/3RandomnucleationandnucleigrowthAvrami-ErofeevA3/21.5(1)ln(1)1/3ln(1)3/2Avrami-ErofeevA22(1)ln(1)1/2ln(1)1/2Avrami-ErofeevA33(1)ln(1)2/3ln(1)1/3Avrami-ErofeevA44(1)ln(1)3/4ln(1)1/4ExponentialnucleationPowerlawP3/22/31/22/3PowerlawP221/21/2PowerlawP332/31/3PowerlawP443/41/4第2期GUOTian-ruietal:Theoxidationreactionmechanismanditskineticsforacarbonaceous357tion of aromatic compounds.Volatilization of lightcomponentsisanendothermicprocess,whileoxida-tion and polymerization/condensation of aromaticcompoundsareexothermicprocesses.TheDSCcurveshowsthatthewholeprocessisendothermicfrom300to400K,indicatingthatthevolatilization of light components plays a dominantrole.After 400 K,the endothermic state graduallychangestoanexothermicstate,indicatingthatthevo-latilization of light components gradually decreasesandexothermicreactionssuchasoxidationandcon-densationpolymerizationofaromaticcompoundsaregraduallyenhanced.From520to719K,thepeakofthesecondstageappearsat619K.Inthisstage,theoxidationandpolymerization/condensationofaromat-iccompoundsplayanimportantrole,whichcausesamasslossof31.3%.Inthethirdstage,between719and900K,thereisamasslossof26.1%.Thepeakofthethirdstageappearsat820K.TheDSCcurvesug-gests that there is a great exothermic peak at thisstage,indicatingthataviolentexothermicreactionoc-curs.Itisinferredthatthisprocessmaybeaviolentthermaloxidativedecompositionoffusedringaromat-iccompounds.3.2.2Evolvedgasesanalysisoftheoxidationpro-cessofET-HRBasedonGC-MS,somesubstancesthatmayap-pearintheevolvedgasescanbedetermined.Astherepresentative of oxidation products,mass units ofthese compounds are recorded in Table 4 and sub-sequentlyanalyzedbymassspectrometer.AsshowninFig.3(a),thepeakofthefirststageappearsat450K,whichisslightlyhigherthanthatoftheDTGcurve.Thethermogravimetryanalyzerandmassspectromet-erareconnectedbypipeline,whichcausesthedelay.Twoamuisallocatedtohydrogenasanimport-antfeatureofpolymerization/condensation.Withtheoccurrenceofpolymerization/condensation,theratioofcarbontohydrogenincreaseswhileHleavesintheform of hydrogen or other small molecules.In thecurve,thereare2peaksofpolymerization/condensa-tion,respectively appearing at 450 and 650 K.De-pendingonthesizeofthemolecule,thedifficultyofthereactionisdifferent.Thelargerthemoleculeis,the more difficult polymerization/condensation willbe.Taking 2,6-dimethylnaphthalene as an example,thepossiblereactionisshowninFig.4.16amumaybethepeakofmethane.BasedonGC-MS,weknowthatlotsofalkylsidechainsarepresentinET-HR,soitisverylikelytoproducegasesTable 2 The fundamental properties of ethylene tar and ET-HRElementa