Oxidative/extractive Desulfurization Process In Deep Eutectic Solvents With Heteropolyacids-based Catalysts

The sulfur oxides?SO_x?produced by combustion of fuels has resulted in increasingly serious environmental pollution,economic wastage and threat to people's health.So,strict limitations of sulfur content in fuels have been carried out worldwide.Hydrodesulfurization?HDS?plays role of the most commonly used method which needs to be carried out under rigorous conditions.The poor efficiency of aromatic sulfides removal resulted in difficulty in achieving deep desulfurization.Consequently,it is urgently needed to explore alternative technologies.Oxidative desulfurization?ODS?combined with extractive desulfurization?EDS?has become one of the most popular desulfurization technologies for simple operation,mild reaction conditions,ideal desulfurization efficiency and so on.Ionic liquids?ILs?have gradually replaced traditional extractants while expensive cost,difficulty in biodegradation and other defects have hindered its industrialization.Deep eutectic solvents?DESs?own analogous physical and chemical properties to ILs which are considered to be new green solvents and can replace ILs for their cheap materials,simple synthesis method and biodegradable.Firstly,neutral,acidic and alkaline choline chloride-based DESs were synthesized and used as extractants during research process.Then,the catalytic system was established to explore catalytic oxidative desulfurization efficiency of thiophenic sulfides in fuel,which applied commercial grade tungsten compounds as catalysts and combined with DESs.Influence of different desulfurization systems,types and dosage of catalysts,temperature and time on desulfurization was investigated.The results showed that neutral DES ChCl/2PEG owned the highest activity and the removal of DBT in model oil could reach up to 99.1% under the optimum conditions.The activity of ChCl/2PEG had no significant reduce after 4 cycles.The structure of ChCl/2PEG had been proved to have no change before and after reaction by1 HNMR.In addition,the desulfurization efficiency of ChCl/2PEG on removal of different sulfides from high to low was DBT,4-MDBT,4,6-DMDBT,3-MBT,BT.Finally,the oxidation products of DBT were confirmed as corresponding sulfoxides DBTO and sulfones DBTO₂ by GC-MS analysis.Quaternary phosphonium polyoxometalates catalysts were synthesized according to different molar ratios in order to further explore the catalytic activity of polyoxometalates during desulfurization process.The extractive/catalytic oxidative desulfurization system?ECODS?wasestablished with above catalysts,DESs and H₂O₂.The structures of catalysts and inmiscible character of DESs with oil were confirmed by FT-IR.Experiments about effect of catalyst types and dosage,oxidants,interfering substances on desulfurization efficiency were carried out.It was showed that deep desulfurization could be obtained under 50 oC within 120 min with 0.051 g[TTPh]₃PMo₁₂O₄₀,O/S molar ratio to 4 and V?ChCl/2Ac?: V?model oil?to 2.5:5.BT was easier to be removed than DBT under the same conditions.In addition,it was found that the presence of cyclohexene had a serious influence on desulfurization efficiency according to the study of inhibiting compounds.Combining the researches above,it was found that acidic conditions own better desulfurization efficiency relatively.So,quaternary ammonium-based,pyridine-based and imidazole-based phosphotungstates were synthesized according to literatures.The successful synthesis of catalysts was characterized by1 HNMR,FT-IR and MS.Influence of catalysts especially the acidity and cationic types on desulfurization efficiency was investigated during research process.The results showed that the order of catalysts was [PSTEtA]₃PW₁₂O₄₀ >[PSPy]3PW₁₂O₄₀ > [PSim]₃PW₁₂O₄₀ > [TBAC]3PW₁₂O₄₀ > [Bmim]₃PW₁₂O₄₀.The desulfurization selectivity of sulfides above followed DBT > 3-MBT > 4-MDBT >4,6-DMDBT > BT.According to FT-IR characterization of sulfone DBTO2 which belongs to oxidation product of DBT,the possible desulfurization mechanism was put forward combining kinetic curves about oxidation of DBT under different dosage of H₂O₂ and temperature.