Synthesis, Characterization And Catalytic Property Of Heteropolyanion-based Imidazolium Ionic Liquids

Sulfur compounds in transportation fuels has been recognized as a major source of sulfur oxides which contributes to air pollution, acid rain. In order to decrease the emission of sulfur dioxide from the utilization of sulfur-containing fuel oils, many stringent environment legislations have been issued to limit the sulfur content of fuels. Oxidative desulfurization (ODS) combined with extraction is one of the most promising desulfurization processes, which can be performed at very mild conditions as ambient temperature and atmospheric pressure. Developing much higher efficient catalysts for ODS is a significant project.First, five heteroplyanion-based ionic liquids [BMIM]₃PW₁₂O₄₀, [MIMPS]₃- PW₁₂O₄₀, [CMMIM]₃PW₁₂O₄₀, [MIMPS]₃PMo₁₂O₄₀ and [MIMPS]₄SiW₁₂O₄₀ were synthesized. Their structures were characterized by IR, 1H NMR, UV-Vis spectrum and XRD. As for as we know, [CMMIM]₃PW₁₂O₄₀ have not been reported.In the extractive-oxidative desulfurization systems using acetonitrile as extractant, several parameters, e.g., hydrogen peroxide quantity, catalyst dosage, temperature and reaction time were investigated in detail. Among these five catalysts, [MIMPS]₃PW₁₂O₄₀ showed the highest activity with DBT conversion of 99.9 % at 60oC for 1 h. Under the optimal conditions, sulfur removal selectivity for S-compounds followed the order of DBT > BT > T and sulfone species was confirmed by GC–MS analysis to be the only product from DBT oxidation. Moreover, the catalyst [MIMPS]₃PW₁₂O₄₀ is recoverable and can be recycled 7 times with only a slight reduction in activity.When using ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethane- sulfonyl)imide ([BMIM][Tf₂N]) as extractant instead of acetonitrile, [MIMPS]₃- PW₁₂O₄₀ showed the highest activity again compared with the other four catalysts. When model oil 5 mL, IL [BMIM][Tf₂N] 1 mL, n(Catal.)/n(DBT) = 0.01, O/S = 4, T = 30 oC and reaction time 2 h, DBT conversion can reach above 99.9 %. In addtion, the catalyst and ionic liquid [BMIM][Tf₂N] can be reused together in such catalytic system. Even after being recycled 6 times, it still showed relative high activity. Under the same exprimental conditions, sulfur removal selectivity for S-compounds followed the order of DBT > BT > T.Comparing these two catalytic systems with different extractants, the latter system with IL [BMIM][Tf₂N] as extractant is obviously superior to the first one with acetonitrile as extractant. The latter system can realize deep desulfuriztion under more mild experimental condition and the catalyst and the extractant can be recycled together.