The preparation of trichlorosilane ($SiHCl_3$, TCS)from the cupric chloride-catalyzed reaction of silicon and hydrogen chloride was studied. With the objective of finding the optimum conditions for obtaining the high yield of TCS, the effects of several variables in the reaction were studied. They were; (1) effect of catalysts, namely $CaCl_2$, $ZnCl_2$ and $CuCl_2$ (2) effect of concentration of $CuCl_2$ (3) effects of reaction temperature between 200℃ and 650℃, and (4) effect of flow rate of hydrogen chloride. The final product was confirmed by NMR mainly to be TCS, and its purity determined by gas chromatography was mainly contaminated by other higher silicon halides.
It was found that the product yield of TCS was decreased in the presence of $CaCl_2$ and $ZnCl_2$, whereas $CuCl_2$ proves to be an excellent catalyst. For example at 310℃, the product of TCS was increased by factor of 5.6 as compared to reaction with no catalyst. The product of TCS was increased when the concentration of $CuCl_2$ increase. Using $CuCl_2$ catalyst at 10% (weight) concentration, the optimum temperature for the reaction was found to be between 385℃ and 420℃.
In this temperature range, 90% (weight percent) of the total product was TCS. A small amount of $SiH_2Cl_2$ was found in the product. At higher reaction temperature, tetrachlorosilane($SiCl_4$, TET) content of the product was high and at 650℃, 90% of the total product was TET, and only 9% was TCS. The increase of TET content was especially rapid in the temperature range of 520-550℃.
The product of TCS was increased as the flow rate of HCI was increased with the catalyst of $CuCl_2$ at 10% and the temperature 400℃, the TCS yield is 82-83% at the flow rate of 200300cc/min and 90% at 400-600cc/min. Therefore, the yield of TCS was determined to be highest when $CuCl_2$ was used at 10% concentration with the HCl flow rate of 400-600cc/min at a temperature range of 385-420℃.
