Deep Catalytic Oxidation For Desulfurization Of Fuels Using Supported Ionic Liquids

In order to protect the human health and ecological environment, many stringent environmentalregulations that tend to limit the sulfur content of gasoline and diesel have been formulated in worldwide.However, aromatic sulfur-containing compounds, such as dibenzothiophene (DBT) and its derivatives,which account for a higher proportion of the total sulfur content in fuels, are hardly eliminated byhydrodesulfurization (HDS) because of their steric hindrance and low reactivity. Therefore, traditionalhydrodesulfurization processes face huge challenges. Catalytic oxidative desulfurization process has thegreatest potential to achieve deep desulfurization due to its high desulfurization rate, mild reactionconditions and easy operation. Both ionic liquid catalysts and supported ionic liquid catalysts wereprepared in this study. Then the performances of those catalysts for oxidative desulfurization of model oil(prepared by dissolving DBT in n-octane) were investigated in detail. The main experimental process andresults are as follws:(1) Four kinds of acidic ionic liquids, such as1-methylimidazolium hydrogen sulfate ([HMIM]HSO4),1-butyl-3-methylimidazolium hydrogen sulfate ([BMIM]HSO4),1-hexyl-3-methylimidazolium hydrogensulfate ([C6MIM]HSO4) and1-n-octyl-3-methylimidazolium hydrogen sulfate ([OMIM]HSO4), weresynthesized, characterized and applied in catalytic oxidative desulfurization process, respectively. Thestructures of those acidic ionic liquids were characterized by Fourier transformation infrared spectroscopy(FT-IR) and1H nuclear magnetic resonance spectrometer (1H NMR). The results of desulfurizationexperiment showed that the ionic liquid [BMIM]HSO4gave the best catalytic oxidative desulfurizationperformances. The DBT removal rate attained97.4%under conditions of molar ratio of O/S6:1, mass ratio of model oil/ionic liquid1.5:1, reaction time120.0min at60.0℃. This catalyst can be reused4timeswithout a significant decrease in activity.(2) The supported ionic liquid catalysts were prepared by immobilized acidic ionic liquid[BMIM]HSO4in silica gel through sol-gel method. The structures and characteristics of those catalystswere characterized by FT-IR, TG, XRD and SEM. Results showed that the [BMIM]HSO4had beensuccessfully immobilized in the silica-gel matrix. The catalytic oxidative desulfurization performances ofsupported ionic liquid catalysts were investigated systematiclly. Results suggested that the loaded amountsof [BMIM]HSO4immobilized in silica gel, mass ratio of model oil/catalyst, reaction temperature andmolar ratio of O/S play a key role in desulfurization process. It was found that the suitable loaded amountof [BMIM]HSO4was25.0%. The DBT removal rate of model oil can reach99.9%within5.0h under theconditions of reaction temperature at60.0°C, molar ratio of O/S10:1, mass ratio of model oil/catalyst3.5:1.(3) A polyoxometalate-based ionic liquid ([BMIM]3PW12O40) was synthesized and characterized byFT-IR, XRD, TG. The characterization results suggested that [BMIM]3PW12O40maintained the Kegginstructure of phosphotungstic acid essencially and exhibited a good thermal stability with little loss ofweight under400℃. The polyoxometalate-based ionic liquid [BMIM]3PW12O40was immobilized in silicagel through sol-gel method. The loaded amounts of [BMIM]3PW12O40in silica gel varied with the molarratio of SiO2/[BMIM]3PW12O40. The results of FT-IR and XRD showed the [BMIM]3PW12O40had beensuccessfully trapped in a silica-gel matrix.(4) The catalytic oxidative desulfurization performances of supported polyoxometalate-based ionicliquid (BPW/SiO2) were investigated. The effects of reaction temperature, reaction time and molar ratio ofO/S on the removal rate of DBT were studied by single factor experiments. To further optimize the reaction conditions of catalytic oxidative desulfurization process, an orthogonal experiment was carried out. Resultsindicate that the DBT removal rate of model oil can reach99.7%under optimal conditions of mass ratio ofmodel oil/catalyst35:6, molar ratio of O/S8:1, reaction temperature at70.0°C. The supported ionic liquidcatalyst can be reused7times without a significant decrease in activity.