Extractive Oxidation Desulfurization Mechanism Of Tetrahydrothiophene Catalyzed By Imidazole Ionic Liquids

The demand for fossil fuels is increasing,and fuel specifications are becoming more stringent under environmental law.Heavy oil plays an important role in the world energy,but a large amount of organic sulfide in heavy oil reduces the quality of oil and poses a threat to the environment.In this study,using tetrahydrothiophene（THT）as model compound and imidazole ionic liquid as extractant and catalyst,the role of ionic liquid（ILS）in extraction-oxidation desulfurization and its mechanism were studied by molecular simulation.The action mode,charge distribution and energy change of different kinds of ionic liquids in the extraction process were investigated,and their catalytic mechanism in the oxidation process of THT by H₂O₂ was explored.Then supported ionic liquids were introduced to compare their roles in the extraction-oxidation desulfurization process.The main conclusions of this paper are as follows:1.The complexation between ionic liquid and THT is mainly due to the action of ionic liquid cations,and it increases with the length of side chain.The oxidation products of THT form a more stable complex with ionic liquid,and the complexation energy increases by more than 100%,easy to achieve the extraction process.2.When ionic liquid interacts with THT,charge transferres from THT to ILS,and local charge enrichment occurs in S atom,S-C bond becomes longer and bond energy weakens.Ionic liquids also activate H₂O₂,making its O-O bond significantly longer.3.The catalytic effects of different kinds of ionic liquids mainly effect in the first step of oxidation process,which is also a step of rate-limiting reaction.The energy barrier of rate-limiting reaction is reduced by more than 32%.According to the size of the reflected energy barrier,the catalytic performance is positively correlated with the length of cationic side chain:[HMIM][Al Cl₄]>[AMIM][Al Cl₄]>[BMIM][Al Cl₄]>[PMIM][Al Cl₄]>[EMIM][Al Cl₄].Different ionic liquids have different catalytic properties:[EMIM][Al Cl4]>[EMIM][HSO₄]>[EMIM]Cl>[EMIM]Br.4.The ionic liquid is loaded on the surface of the carrier in the adsorption modeη¹S.The optimal load fraction of[Emim][Al Cl₄]on MCM-41 was 17%.The carrier also catalyzed the oxidation of THT,the catalytic performance of the carrier could not be mutually promoted with that of the ionic liquid,but was somewhat inhibited.