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

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