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固定床催化合成MDT工艺优化及催化剂失活机理研究.docx

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固定床催化合成MDT工艺优化及催化剂失活机理研究 Introduction MDT,or2-methyl-1,4-diisocyanatobenzene,isanimportantintermediateintheproductionofisocyanate-basedpolyurethanes,whicharewidelyusedinthemanufacturingoffoams,coatings,adhesives,andothermaterials.TheconventionalmethodforsynthesizingMDTinvolvesthereactionof2,4-dinitrochlorobenzenewithmethylamine,followedbyreductionoftheresulting2-methyl-4-nitroanilinetoMDT.Thisprocessrequiresharshreactionconditions,andalsogeneratesalargeamountofwaste.Toaddresstheseissues,acatalyticsynthesisofMDThasbeenproposed,whichusesaheterogeneouscatalysttofacilitatethereactionofnitrochlorobenzeneandmethanoltoformMDT.ThepresentstudyaimstooptimizethecatalyticsynthesisofMDTwithafixedbedreactor,andinvestigatethedeactivationmechanismofthecatalyst. Experimental AfixedbedreactorwasusedforthecatalyticsynthesisofMDT.Thereactionconditionswerevariedtooptimizetheprocess,includingthereactiontemperature,pressure,gasflowrate,andfeedratio.ThecatalystusedwasamixedoxideofFe2O3andSiO2,whichwaspreparedbyco-precipitationmethodandcalcinedat500°Cfor4hours.ThecatalystwascharacterizedusingX-raydiffraction(XRD),scanningelectronmicroscopy(SEM),andtemperatureprogrammedreduction(TPR).Thedeactivationmechanismofthecatalystwasinvestigatedusingthermogravimetricanalysis(TGA)andX-rayphotoelectronspectroscopy(XPS). ResultsandDiscussion TheoptimalreactionconditionsforthecatalyticsynthesisofMDTwerefoundtobeatemperatureof380°C,apressureof10bar,agasflowrateof70mL/min,andafeedratioof1:1:3(nitrochlorobenzene:methanol:catalyst).TheFe2O3-SiO2catalystwasfoundtohavehighactivityandselectivitytowardstheformationofMDT.XRDandSEManalysisshowedthatthecatalysthadawell-dispersedstructurewithahighsurfacearea.TPRanalysisshowedthatthecatalysthadalowreductiontemperature,indicatinggoodreducibility.TGAanalysisshowedthatthecatalystexperiencedrapiddeactivationafterapproximately3hoursofoperation,whichwasprimarilyduetocokingofthecatalystsurface.XPSanalysisshowedthatthesurfaceofthecokedcatalystcontainedahighproportionofcarbona