Surfactant Encapsulated Polyoxometalates And Its Oxidative Desulfurization Performance

Under the increasingly stringent environmental regulations, the upgrade and innovation of oil desulfurization technology have been promoted into a significant position. The oxidative desulfurization(ODS) is considered as a very promising ultra-deep desulfurization technology because of its mild reaction conditions, without hydrogen supply, less investments, and so on. P olyoxometalates(POMs) have been widely used as the novel catalysts in the oxidative desulfurization area since they possess diverse structures, pseudo-liquid phase behavior, strong acid and redox properties. However, there exist water-oil two phases, which limit the full mixture of reactants and the mass transfer rate in hydrogen peroxide ODS system. The novel surfactant encapsulated polyoxometalates(SEPs) composite materials could solve the above problems. So in this thesis, a series of the amphiphilic SEPs materials were prepared and used as the oxidative desulfurization catalysts.Firstly, Anderson-type Q3[CoMo6O24H6] and Sandwich-type Q12[WZn3(H2O)2(ZnW9 O34)2](Q = [C18H37(CH3)3N+, [C16H33(CH3)3N]+, [C12H25(CH3)3N]+) were successfully synthesized and characterized by XRD, IR, TG, and EA. The experimental results showed that the encapsulation of surfactants inhibited the aggregation of POM anion clusters; as the carbon chain of the quaternary ammonium cation rose, the distribution of POM anion clusters would be better; the anions in SEPs still kept the full Anderson-type structure and all of them were encapsulated by surfactant cations in situ assembly.Secondly, SEPs materials were applied to oxidative desulfurization of model oils to evaluate the catalytic oxidation activity. The results showed that SEPs materials not only overcame the reaction resistance from the water-oil phases and the difficult separation and recovery of catalysts, but also had superior oxidative desulfurization performance.Thirdly, this thesis investigated the effects of assembly methods, reaction conditions including reaction solvents, oxidants, the oxidant amounts, the catalyst amounts, reaction temperature and reaction time, and sulfur types. As a r esult, the Anderson-type and Sandwich-type SEPs could effectively remove the thiophenic sulfur compounds. With Anderson-type [OTAC]3[CoMo6O24H6] as the catalyst, the DBT conversion reached 99% under the premium conditions; the sequence for oxidation activity of different sulfides was 4,6-DMDBT > DBT > BT; with Sandwich-type SEPs as catalysts, it revealed that the desulfurization rate of DBT increased as the alkyl length of SEPs materials rose while the desulfurization rate of BT increased as the alkyl length of SEPs materials decreased.Finally, the oxidation desulfurization mechanism of amphiphilic catalysts was discussed based on t he obtained experimental findings. Amphiphilic SEPs material transferred the heterogeneous reaction system into the emulsion system. The carbon chain length of SEPs, the molecular size of oxidants and the steric hindrance of sulfides decided whether the stable and proper emulsion system could be formed.