Study on the Process of Direct Synthesis of Triethoxysilane
|School||Qingdao University of Science and Technology|
|Keywords||direct synthesis non-chloride copper catalysts nanocomposite Copper-Cobalt catalyst Cu3Si|
Triethoxysilane is an important alkoxysilane for its good performance, and the process of direct synthesis of triethoxyilane has won more attention for the simple process and less pollution than the traditional process, recently.In this paper, nanosized copper catalysts such as copper（Ⅱ） hydroxide, copper （Ⅰ） and copper（Ⅱ） oxide are prepared by chemical precipitation. X-ray powder diffraction and Scanning electron microscope are used to characterize various copper compounds catalyst. The process for preparing triethoxysilane is studied systemically by reacting silicon metal with ethanol over cupric hydroxide catalyst in an inert medium of biphenyls and diphenyl ether. When the catalyst（56 wt% of silicon） and silicon metal （4474μm） are dispersed in an inert solvent（6.0 mL/gSi）, under the optimal flow rate of ethanol （0.45 mL/min）, the nano- cupric hydroxide catalyst exhibits the best catalytic performance, with 95.3% silicon conversion and 40.1% selectivity to triethoxysilane obtained at 215°C. To improve the yield of triethoxysiliane, cupric oxide and cuprous oxide are used as the additives. The yield of triethoxysiliane almostly increased by 12%25%, when m（CuO）:m（Cu（OH）2）=0.4 and m（Cu2O）: Cu（OH）2)=0.6.In addition, Nanocomposite Copper-Cobalt and Co3O4 catalysts are prepared using ammonia as precipitant. X-ray diffraction, Scanning electron microscope and N2 physical adsorption are used to characterize the crystal morphology and specific surface area of the catalysts, respectively. It is demonstrated that the composite catalyst has a smaller diameter than that of cupric hydroxide and the specific surface areas increased by 28%. When using the composite catalyst for the synthesis of triethoxysiliane, the reaction temperature decreased, the inducing time shortened, and the yield of triethoxysiliane increased by about 30%46%. The optimical reaction temperature is 205°C, the feeding rate of ethanol is 0.450.65 mL/min and the catalyst content is 4%5wt% of silicon. Besides, When using the cobalt oxide in the process of preparing triethoxysiliane with the suitable ratio of m （Co3O4）: m （Cu（OH）2） =0.7, the silicon conversation is 86.2% and the yield increased by about 25%.Lastly, the reaction mechanism of direct synthesis of triethoxysilane has been preliminary discussed, using the cuprous chloride as the catalyst. The mixture of silicon and catalyst are characterized before and after the reaction by the X-ray diffraction and Scanning electron microscope. It is demonstrated that Cu3Si as the reactive intermediate is present after the pretreatment, which triggeres the attack of ethoxy on the Si-Cu bond.