Chlorination of trichlorosilane/chlorodimethylsilane using metal chlorides: experimental and mechanistic investigations

Removal of carbonaceous impurities from trichlorosilane (SiHCl(3)) reduces the carbon content of solar grade polysilicon produced with the improved Siemens method. The separation of chlorodimethylsilane (CH(3))(2)SiHCl from SiHCl(3) by distillation remains challenging due to the small difference in their boiling points. Herein, the chlorination of (CH(3))(2)SiHCl/SiHCl(3) with metal chlorides (WCl(6), MoCl(5)) were studied. The aim was to convert (CH(3))(2)SiHCl into (CH(3))(2)SiCl(2), increase the relative volatility of (CH(3))(2)SiHCl and SiHCl(3) and facilitate the distillation. The optimum reaction conditions were 60 °C, 60 min and n(WCl(6) or MoCl(5)): n(SiHCl(3) or (CH(3))(2)SiHCl) = 0.7 at 0.8 MPa. Under these conditions, and when WCl(6) and MoCl(5) were used as the chlorine sources, the extents of (CH(3))(2)SiHCl conversion were 22.7 and 18.5 times higher than those of SiHCl(3), respectively. In addition, a mechanistic study showed that the difference between the reactions of SiHCl(3) and (CH(3))(2)SiHCl resulted from the different energy barriers for the reactions of the [Image: see text] and (CH(3))(2)SiCl· radicals with WCl(x) or MoCl(x), and the barrier for the [Image: see text] reaction was higher than that for the (CH(3))(2)SiCl· reaction.