Deactivation of CuSi and CuZnSnSi Due to Coke Formation during the Direct Synthesis of Methylchlorosilanes

Coke formation and the subsequent deactivation of silicon samples prepared using CuCl (CuSi) and CuCl copromoted with zinc and tin (CuZnSnSi) were studied during the direct reaction of silicon with methyl chloride to form methylchlorosilanes. Two types of coke, designated α and β, were identified when samples were subjected to post reaction analysis using temperature-programmed-oxidation and thermogravimetric analysis (TGA). Deactivation was correlated with the presence of β-coke. TGA results suggest that β-coke forms an overlayer on the surface, thereby blocking sites that are active for silicon gasification. The main effect of copromotion by zinc and tin was to decrease the amount of coke deposited; however, copromoted samples experienced more extensive deactivation than CuSi because coke that is formed is more likely to block active sites and result in deactivation. Incorporation of hydrogen into the feed stream suppressed coke formation and increased the stability of the samples for the direct reaction.