Hydrochlorination of silicon in a fluidized-bed reactor

Hydrochlorination of metallurgical grade silicon in fluidized-bed reactor was studied with a temperature controlled within +- 5/sup 0/C/ The hydrogen chloride gas velocity varies from 2 to 5 ..mu../..mu../sub mf/, temperature from 340/sup 0/C to 400/sup 0/c and silicon particle size from 124 ..mu..m to 297 ..mu..m. It was found that a reaction condition with low temperature and smaller particle size favored the production of trichlorosilane. A reaction mechanism was proposed starting with a surface reaction between hydrogen chloride and silicon to produce silicon dichloride, which was reacted with hydrogen chloride again to form trichlorosilane. Trichlorosilane could be reacted further with hydrogen chloride to produce silicon tetrachloride. The first reaction step was heterogeneous and was assumed to be mass transfer controlled. The second and third reaction steps were homogeneous and irreversible.