Efficient oxidation of p-xylene to terephthalic acid by using N,N-dihydroxypyromellitimide in conjunction with Co-benzenetricarb.pdf

Efficient oxidation of p-xylene to terephthalic acid by using N,N-dihydroxypyromellitimide in conjunction with Co-benzenetricarb.pdf

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AppliedCatalysisA,General599（2020）117569ContentslistsavailableatScienceDirectAppliedCatalysisA,GeneralELSEVIERjournalhomepage:

Efficientoxidationofp-xylenetoterephthalicacidbyusingN,NdihydroxypyromellitimideinconjunctionwithCo-benzenetricarboxylateLuoXuaDaweiChenaHaoranJiangaXiaYuana,b,.,aCollegeofChemicalEngineering,XiangtanUniversity,Xiangtan,411105,ChinabNational&LocalUnitedEngineeringResearchCentreforChemicalProcessSimulationandIntensification,Xiangtan,411105,ChinaARTICLEINFOABSTRACTKeywords:

p-XyleneoxidationTerephthalicacidCo-benzenetricarboxylateNDHPIMetal-0rganicframeworkTheMOFCo-BTC（BTC=benzenetricarboxylate）hasbeensynthesizedbyahydrothermalmethod,andcharacterizedbymeansofN2physicaladsorption,X-raydiffraction,scanningelectronmicroscope,thermogravimetricanalysis,andX-rayphotoelectronspectroscopy.Thematerialhasmultiplecrevices,asopposedtoaporestructure,andshowshighthermalstability,withCointhedivalentstate.IthasbeenusedinconjunctionwithN,N-dihydroxypyromellitimidetocatalyzetheoxidationofp-xylenetoterephthalicacid,thereactionconditionsforwhichhavebeeninvestigatedandoptimized.At150C,withacetonitrileassolventinsteadofaceticacidandintheabsenceofcorrosivebromine,theconversionofp-xylenereached100%andtheselectivityforterephthalicacidexceeded97%.Undertheoptimizedconditions,Co-BTCexhibitsstrongercatalyticactivitythancobalt（II）acetate,andmaintainsexcellentstabilityduringthereaction.Thereactionmechanismhasbeendeduced,andtherolesofN,N-dihydroxypyromellitimideandCo-BTCassynergisticcatalystsinthereactionhavebeenclarified.1.IntroductionInthepolyesterindustry,terephthalicacid（TA）isanimportantrawmaterialusedprimarilyinthemanufactureofnon-toxicpolyethyleneterephthalate（PET）,whichaccountsforabout20%ofthepolyestermarket.PETismainlyusedinmachineryparts,fibermaterials,andpackagingforfoodsandmedicines.Oxidationofp-xylene（PX）isthemainrouteforobtainingTA.ThisprocessisshowninScheme1,andisconsistentwithamechanismofhydrocarbonradicaloxidation.Ingeneral,thedifficultyofhydrocarbonoxidationliesmainlyintheinitiationstep,thatis,theformationofhydrocarbonradicalsbytheremovalofhydrogenfromalkylgroups1-4.However,intheoxidationofPX,p-methylbenzylradicalandpTAwillalsobepresent5,whichareresistanttooxidation.DuetothedifficultoxidationcharacteristicsofPX,currentindustrialproductionofTAmainlyreliesontheharshAmocoprocess,usingcobalt（II）acetate,manganese（II）acetate,andbromineascatalysts,andaceticacidassolvent,whichisconductedathightemperature（about200C）andhighpressure（1.5-3.0MPa）.TheselectivityforTAisover95%.Underthehigh-temperatureoperatingconditions,corrosivebromineactsasaco-catalyst,resultinginhighproductionandequipmentcosts.Therefore,thequestforanefficientandmildcatalyzedrouteforPXoxidation,leadingtoTAwithouttheneedforacidandbromine,hasbecomeahottopicofresearch.N-Hydroxyphthalimide（NHPI）anditsderivativesareeffectivecatalystsfortheoxidationoforganiccompoundsbymolecularoxygenundermildconditions6,andarewidelyusedasinitiatorsfortheoxidationofhydrocarbons.Tashiroetal.7usedNHPI/Co（OAc）z/Mn（OAc）zasacatalystandaceticacidasasolventtooxidizePXat100C.TheyieldofTAreached82%after14hofreaction;whenthetemperaturewasraisedto150C,theyieldofTAreached84%after3h.Koshinoetal.foundthatthePINOformedbythe-NO-HcleavageofNHPIismorelikelytocaptureaprotonfromthealkylgrouponthealkylaromatichydrocarboninacetonitrile（MeCN）thaninaceticacid;duringtheoxidationofPX,theeffectofN,N-dihydroxypyromellitimide（NDHPI）asaninitiatorissuperiortothatofNHPIbecauseitbearstwo-NOHgroups8.HeterogeneouscatalystshavealsobeenusedtocatalyzetheoxidationofPX9.Ratnasamyetal.loadedcobaltmanganeseoxideintoazeolitetocatalyzetheoxidationofPXathightemperature（473K）andanairpressureof550psi.TheconversionofPXwas100%,andtheselectivityforTAwasover98%,butcorrosivebrominewasstillneededasaco-catalysttocapturehydrogenfromthemethylgroup10.Dekaetal.preparedporousCe02asacatalysttocatalyzetheoxidationofPXtoTA.Usingonlywaterasasolventunderextremelymildconditions（70C,1bar02）,theconversionofPXreached100%andtheCorrespondingauthorat:

CollegeofChemicalEngineering,XiangtanUniversity,Xiangtan,411105,Hunan,China.E-mailaddress:

（X.Yuan）.https:

/doi.org/10.1016/j.apcata.2020.117569Received21December2019;Receivedinrevisedform6April2020;Accepted14April2020Availableonline07May20200926-860X/2020ElsevierB.V.Allrightsreserved.L.Xu,etaLp-toluladehyde（p-TALD）4-carbox）benzaldehyde（4-CBA）0.05Scheme1.OxidationofPXtoTA.0.5RelativePressure（P/Po）Fig.1.N2adsorption/desorptionofCo-BTC.101520-Fresh252Theta-Cycle13035Fig.2.XRDofCo-BTC.40I1.045selectivityforTAexceeded99%11.Guoetal.usedametalloporphyrin（T（p-Cl）PPMnCl）asacatalysttocatalyzetheoxidationofPXwithaceticacidasasolvent,althoughitsconcentrationwasashighas20%.Undertheseoperatingconditions（3.5h,180C,2.0MPa）,theconversionrateofPXwas41.8%,theselectivityforp-TAis82.1%,buttheselectivityforTAwasonly12.4%12.Porousmetal-organicframeworks（MOFs）,duetotheirvariablecombinationsofmetalsandorganicligands,offergreatdiversityintheirstructuresandproperties,makingthemsuitableforadsorbingdrugs13andharmfulsubstances14,15aswellasgasabsorption16-18andstorage19.Theyalsohavebroadprospectsandvaluein21009080;?

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.-008Cl-0.10-0.12-=-0.14L.-0.16100810200300400500600700800Temperature,Fig.3.TGAofCo-BTC.805800795Bindingenergy,eV790781.8785780Fig.4.XPSspectrumofCo-BTCwithpeakfittings.thefieldofcatalysis18,20,19,20,21,22,23.Todate,MOFshavebeenstudiedasheterogeneouscatalystsintheselectiveoxidationofsomehydrocarbons,suchascyclohexane24-27,cyclooctane28,olefins27,29-32,alcohols,27,33-35,andsoon.Wangetal.usedaCuMOFasacatalysttocatalyzetheoxidationofPXto4-hydroxymethylbenzoicacidunderamildconditions36.Tothebestofourknowledge,however,noMOFshavehithertobeenusedintheoxidationofPXtoTA.Inthisstudy,Co-BTC（BTC=benzenetricarboxylate）hasbeenusedasacatalystforthefirsttimeintheoxidationofPXtoTA.IthasbeenusedinconjunctionwithNDHPIinsteadofcorrosivebromineasaninitiatorforPXoxidationinthenon-acidicsolventMeCN.ThecatalyticpropertiesofCo-BTCandcobalt（II）acetatehavealsobeencompared.Throughsuitablydesignedexperiments,themodeofactionofNDHPIandCo-BTCinPXoxidationhasbeeninvestigated.Furthermore,thestabilityofCo-BTCintheoxidationofPXhasbeenstudied.2.Materialsandmethods2.1.MaterialsandreagentsMeCN（AR）,PX（AR）,Co（OAch-4H2O（AR）,Co（NO3h-6H2O（AR）,trimesicacid（H3BTC,AR）,NDHPI（AR）,dimethylsulfoxide（DMSO,AR）,andethanol（AR）werepurchasedfromMacklin.Waterwaspurifiedanddeionizedinourlaboratory.2.2.SyntheticprocedureCo-BTCwassynthesizedaccordingtoamethodintheliterature37,withsomemodifications.Thespecificprocesswasasfollows:

CoL.Xu,etaLAppliedCatalysisA,General599（2020）117569Fig.5.SEMimagesofCo-BTC.Table1Studyofcatalyticperformance.NDHPICo-BTCConversionSelectivity/%/g/g/%p-TALDp-TA4-CBATAla0.10000002a00.1000003a0.10.157.03.689.41.65.44b0.372093.50302.567.55b00.053.1973005b0.3720.0210002.51.396.270.37201000100.989.1aReactioncarriedoutat100Cfor12h,10gPX,20gMeCN,3.0MPa02bReactioncarriedoutat150Cfor12h,0.54gPX,25gMeCN,3.0MPa02cReactioncarriedoutat150Cfor12h,0.54gPX,25gMeCN,3.0MPa02;0.025gCo（0Acz-6H20wasadded.（N03h-6H20（4.8g）wasdissolvedindeionizedwater（20mL）,andH3BTC（2.0g）wasdissolvedinabsoluteethanol（130mL）.Whenthetwomaterialshadcompletelydissolved,thetwosolutionsweremixed,andthemixturewastransferredtoa200mLTefloncrystallizationvessel.Afteragitationinanultrasonicatorfor20min,themixturewastransferredtoanincubatorforcrystallizationbyprogrammedtemperaturecontrol.First,thetemperaturewasquicklyraisedto140Cwithin22minandmaintainedatthislevelfor24h;itwasthenuniformlyloweredto120Cin200min.After5h,thetemperaturewassteadilyreducedto100Coveraperiodof200minandmaintainedatthislevelfor5h.Finally,themixturewascooledtoroomtemperature.Thevesselwasremovedfromtheincubator,thesupernatantwasdecanted,andthesolidwascollectedbysuctionfiltrationandwashedwithabsoluteethanoluntilthewashingswerecolorlessandtransparent.Thereafter,thesolidwasplacedinavacuumovenat80Cfor24h.Thedark-bluesolidproductwasdesignatedasCo-BTC.2.3.CatalysisandproductanalysisAllreactionswerecarriedoutinanautoclaveequippedwitha100mLquartzvesselandoperatedatastirringspeedof1000rpm.Inarepresentativereactionprocess,combinedcatalyst（0.372gNDHPI,0.05gCo-BTC）,rawmaterial（0.54gPX）,andsolvent（25g3acetonitrile）werecombinedinthequartzvessel.Theautoclavewasthenclosed,andtheinsideofthereactorwasflushedtwicewithoxygenthroughavalve.Thereactorwasfinallysuppliedwithoxygen（3MPa,roomtemperature）,thenheatedto150C,andthereactionwasallowedtoproceedfor12h.Thereafter,theproductwastakenupinDMSOandanalyzedbyhigh-performanceliquidchromatography38.2.4.CharacterizationThespecificsurfaceareasandporestructuresofsamplesweremeasuredbyN2