Synthesis And Catalytic Properties Of Silica-gel Supported Dendritic Metal Complexes For Catalytic Oxidative Desulfurization

Nowadays, as the environmental pollution aroused by the gases of SOX,which is formed by the combustion of sulfur-containing fuel, is becomingmore and more severe, governments all over the world constitute all kinds ofstringent regulations in order to reduce the content of sulfur in the fuel.The hydrodesulfurization (HDS) is a main method of the removal ofsulfur from petroleum distillates in a refinery, which is highly effective forthe removal of non-heterocycle containing sulfur such as mercaptan, sulphurether, disulfide etc. However, the traditional hydrodesulfurization (HDS)method is difficult for the remove of heterocyclic compounds such as DBTand its derivatives due to their steric hindrance. Therefore, the developmentof the alternative desulfurization processes, such as adsorption, oxidation,extraction and biodesulfurization is necessary. Among these methods,oxidative and adsorption desulfurization are one of the promisingapproaches due to the mild reaction condition, high desulfurizationefficiency, low operating costs and the simple process and other advantages.The preparation and adsorption desulfurization of CuY zeolite wereinvestigated in this thesis. Research showed that it was difficult for the Cu-Yzeolite to be a good desulfurization reagent due to the hugeconsume of the copper salt, harsh preparation condition and high energyconsumption. Compared with the process of adsorption desulfurization,oxidative desulfurization had the advantage of easier to continuousoperation. Therefore, silica gel for column chromatography was usedas a carrier and the dendritc PAMAM vanadium and molybdenumcomplexes were prepared as catalysts by solid phase synthesis, and theirstructures were fully prepared by IR, TGA, SEM, ICP, XPS, and BET etc.Dibenzothiophene (DBT)/n-octane solution (the content of DBT is500μg/g) was selected as the model diesel. Meanwhile, the oxidants were selected as oil-soluble tert-butylhydroperoxide (TBHP) and water-solubleH2O2, SGn-VVO2-[PAMAM-MSA](n=0,1,2,3) and SGn.5-COOH/MoO3(n=0,1,2,3) were used as a catalyst. The reaction time, the reactiontemperature, the amount of oxidant and different catalyst were examined onthe affect of desulfurization. Studies showed that the DBT conversion ratescan reach85.5%and97.6%, when using the TBHP as an oxidant and V andMo complex as catalyst, respectively. On the other hand, theDBT conversion rates were42.5%and84.6%when the H2O2as an oxidant.Furthermore, the oxidation activity was decreased little after the couplingsystem was recycled six times except the catalysts ofSGV0-[VO2-PAMAM-MSA] and MoO3/SG0.5-COOH.The catalytic oxidation mechanism and reaction kinetics of the DBTwere also investigated after the optimal desulfurization condition wasobtained. We speculated that the active metal formed metal peroxide interm-ediate state in the presence of oxidants, which scattered electron clouddensity on the peroxide and strengthened the electron affinity of theoxygen atoms, leading the oxidation of DBT. Meanwhile, the kinetic stagesof the two oxidation reactions were the first stage reaction andthe apparent activation energy was39.126kJ/mol and58.306kJ/mol, withSG2.0-[VVO2-PAMAM-MSA] and MoO3/SG1.5-COOH as catalysts,respectively.Although the DBT was oxidized into DBTO2in the above oxidationsystem, most of the DBTO2were leaved in the oil phase. In order to removeDBT and its oxidation products completely, several ionic liquids wereprepared and used to extract DBTO2from the oil phase. In this system, thethree different processes (catalyst/oxidation/extraction) were carried out inone step, Studies showed that the removal rate of DBT can reach95.0%when the oxidation temperature is90℃, time is60min, O/S is3:1, and thevolume ratio of [Omim]PF6to model oil is1:3, which is10%more than the system without ionic liquid. Moreover, the oxidation activity was decreasedlittle after the coupling system was recycled six times.