Preparation Of Silica Gel Supported Ionic Liquid Catalyst And Its Application In Synthesizing Polyoxymethylene Dimethyl Ethers

Polyoxymethylene dimethyl ethers(DMMn) is a new kind of oxygenous and green fuel, its physical and chemical properties are similar to diesel. DMMn is added to diesel as fuel without changing the structure of engine, it can not only improve combustion performance of diesel fuel and increase the cetane number of diesel and effectively improve the thermal efficiency of the diesel engine, but also greatly reducing the emissions of NOx and solid particles. Ionic liquids as new green catalysts are chemically stable, less volatile, mild catalytic condition and high catalytic activity. However, high cost and difficult separation from the catalytic products limit their industrial application.This paper firstly studied four kinds of imidazolium ionic liquids catalysts to synthetize DMMn from methanol and trioxymethylene(TOX), the results showed that the [SO3H-(CH2)3-HIM][HSO4] catalyst had the highest catalytic activity, the conversion of trioxymethylene and selectivity of DMM3-8 were 95.34% and 49.45% and the optimal conditions of synthesis DMMn were the ionic liquid dosage 2.0 wt%, methanol /trioxymethylene molar radio 6/3, reaction temperature 100℃, reaction time 3h and reaction pressure 1.0 MPa.Due to ionic liquids were difficult to separate from products and could not be reused, in order to solve the problems, [SO3H-(CH2)3-HIM][HSO4] was supported by silica gel directly through the sol-gel method. FT-IR, TG, BET and elemental analysis were used to investigate the structure, thermostability and channel property of the prepared catalyst. The conversion of TOX and selectivity of DMM3-8 were 95.46% and 49.10% under the optimal conditions of synthesis DMMn and the ionic liquid supported amount was 14.30%. The catalyst had higher catalytic activity after using four times and the catalytic products were easy to separate from the catalyst. However, silica gel directly immobilized the ionic liquid by sol-gel method was not stable enough and easy to lose in the process of synthesizing DMMn.To solve the problems of silica gel directly immobilized ionic liquid by the sol-gel method, on the basis of the sol-gel method, [SO3H-(CH2)3-HIM] [H SO4] was grafted to the silica gel with(3-chloropropyl) trimethoxysilane agent by chemical bond. FT-IR, TG, BET and elemental analysis showed that the silanized ionic liquid had been successfully grafted to the silica gel. Under the optimal reaction conditions and the ionic liquid supported amount was 15.81%, the conversion of trioxymethylene and the selectivity of DMMn were 95.37% and 48.49%. Supported ionic liquid amount, conversion of TOX and selectivity of DMM3-8 were 14.53%, 94.29% and 45.04% after using four times. Chemical graft was effective method and the process of preparation catalyst was simple, The silica gel supported silanized ionic liquid catalyst was stable, had high catalytic activity and had better reusable efficiency.