DEACTIVATION OF CUSI AND CUZNSNSI DUE TO COKE FORMATION DURING THE DIRECT SYNTHESIS OF METHYLCHLOROSILANES

Coke formation and the subsequent deactivation of silicon samples prep ared using CuCl (CuSi) and CuCl copromoted with zinc and tin (CuZnSnSi ) were studied during the direct reaction of silicon with methyl chlor ide to form methylchlorosilanes. Two types of coke, designated alpha a nd beta, 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 beta- coke. TGA results suggest that beta-coke forms an overlayer on the sur face, thereby blocking sites that are active for silicon gasification. The main effect of copromotion by zinc and tin was to decrease the am ount of coke deposited; however, copromoted samples experienced more e xtensive deactivation than CuSi because coke that is formed is more li kely to block active sites and result in deactivation. Incorporation o f hydrogen into the feed stream suppressed coke formation and increase d the stability of the samples for the direct reaction. (C) 1996 Acade mic Press, Inc.