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 and (CH 3 ) 2 SiCl· radicals with WCl x or MoCl x , and the barrier for the reaction was higher than that for the (CH 3 ) 2 SiCl· reaction.