Development of Direct Synthesis of Alkoxysilanes from Silica by Gas-Solid Reactions

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In the reaction of silica with dimethyl carbonate to give tetramethoxysilane, the effect of physical properties of silica on the reaction rate of the silica was examined. The silica, which was obtained by drying colloidal silica at 150ﾟC,Was calcined at various temperatures. The silica sample, on which potassium hydroxide as a catalyst was supported by 5wt.%, was loaded in a fixed-bed flow reactor. After heated at 260ﾟC for 1 h under a helium stream, the sample was subjected to contact with dimethyl carbonate vapor at 260ﾟC.For the calcination temperatures of 400-600ﾟC,the rate was greater at the higher calcination temperatures, while it was smaller for the 700-900ﾟC calcinations. The reaction rate was not controlled by the pore distribution or surface area of silica sample. Generation of new reactive silica surface with the reaction proceeding was a determining factor of the rate. Silica was found to react also with diethyl carbonate to give tetraethoxysilane. The effect of reaction variables on the rate of silica consumption was examined.Hydrous titanium oxide was found to react with diethyl carbonate to yield tetraethoxytitanium. thus, using potassium hydroxide (5wt.%) as a catalyst, a 93% yield of tetraethoxytitanium was obtained at 230ﾟC in an autoclave.The effect of reaction temperature and the temperature of calcining the hydrous titanium oxide on the tetraethoxytitanium yield was examined.