Research On Direct Conversion Of Methane In Ionic Liquid

Methane as a vast, low-cost and untapped energy sources has become more important inthe modern times. Methanol is clean starting point for many industrial processes, and isultimately incorporated into such products as plastics and paints. Additionally, it is easy tostore and carry. It is ideal way to make methane direct conversion to methanol, which hasbecome focus of attention for the world’s scientists. However, the stability of the C-H bondsin methane is generally unreactive, which results in needs of high temperature to make itactivated and methanol inclined to be deep oxidation. To improve the selectivity and yield ofmethane conversion to methanol, researchers have developed a great deal of new technics toproduce methanol. So far, there is no good way has been found to solve the industrializedproblem of methane transformed. Consequently, it is imperative to developing new chemicalprocess for direct conversion of methane.Recently, ionic liquids（ILs） have gained great focus for they are the needs of greenchemistry. Most of investigated ILs have the peculiar characters. Therefore, ILs as solventsand catalysts have been utilized widely in each field of chemical reaction. Jihong Cheng andhis co-workers have reported that the direct conversion of methane to methanol by ionicliquid dissolved platinum catalysts is available in2006, which is the first report on ILs beingutilized in the conversion of methane. However, there less report about ILs as catalysts in thereaction of methane directly translated into methanol derivatives.Molecular reaction become easier for ILs being liquid states and strong solvencies underambient temperature. Besides, structures of ILs are designable and ILs have ability ofcatalytic activity because the strong acid with Br nsted acid and Lewis acid, which make ussynthesize acidic ILs as catalysts. Furthermore, the conditions with conversion of methanegenerally are rigorous and strong acids as catalysts need exigent reactors. All the things aregoing to be improved along with acidic ILs as green catalysts and solvents being used in theprocedures of methane directly translated into methanol derivatives.In this letter, the properties and applications of the ionic liquids have been firstlydescribed and a series of acidic ionic liquids were synthesized. Secondly, the stabilities of ILs in the reaction of methane convert to methanol derivatives were studied. Then the conversionof methane to methanol derivatives could be carried out in the acidic ILs. The system of directconversion of methane with potassium peroxodisulfate as the oxidant, the acidic ionic liquidsas catalysts, the trifluoroacetic acid and trifluoroacetic anhydride as intermedias wasrespectively investigated under180℃and80℃. The reaction products were analyzed byGC-MS, FTIR and quantified by GC. The experiments confirmed that the ILs are stable in therigorous system. The system with80℃is better than with180℃. The[Hmim]⁺HSO₄^-ascatalyst is better than other acidic ILs that were used in the system. The yield of system with[Hmim]⁺HSO₄^-as catalyst is better than of system with HPA as catalyst （average yield andselectivity is26.9%and100%respectively）. At last, the possible mechanism was discussedabout the partial oxidation of methane to methanol by [Hmim]⁺HSO₄^-as catalysts.