Two-Step Process for the Synthesis of Dimethyldichlorosilane Using Copper Aluminate Catalysts

The present study relates to the development of a new generation of copper aluminate-type spinel catalysts for the production of dimethyldichlorosilane ((CH3)2SiCl2) from silicon tetrachloride (SiCl4) in a two-step reaction process. The first step is the reaction of SiCl4 with H2 over the spinel catalysts at high temperature (∼650 °C) to produce a copper–silicon-rich solid (copper silicide) by silicon deposition. In the second step, the silicon component of this solid reacts with CH3Cl at 300 °C to form (CH3)2SiCl2. Copper aluminates (CuAl2O4) were found to exhibit superior activity over other conventional copper catalysts and held better particle integrity in laboratory-scale fixed bed and fluid bed reactors. Their activity was maintained even at a 240 °C reaction temperature with CH3Cl, producing high selectivity toward (CH3)2SiCl2. Maximum production of (CH3)2SiCl2 was achieved right from the beginning of the reaction with CH3Cl without requiring any “activation period”. In contrast, the conventional Cu-supported catalysts required “an activation period” of several initial cycles to obtain maximum steady state activity. The high rate of methylchlorosilanes production on spinel catalysts is attributed to the smaller particle sizes of copper and the in situ formation of a reactive copper silicide (Cu3.17Si) phase as a result of the reaction with SiCl4/H2. The copper aluminate catalyst was tested in 45 experiments in time on stream and showed stable selectivity toward (CH3)2SiCl2 in a laboratory-scale fixed bed reactor. It demonstrated superior and acceptable attrition resistance and copper retention, whereas conventional supported copper catalysts did not retain the copper during piloting in a fluidized process. Overall, we developed a low cost, efficient, and scalable process to produce dimethyldichlorosilane ((CH3)2SiCl2).