Diagramm TCS Synthesis

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TCS Synthesis

The Direct Silicon Chlorination unit is producing trichlorosilane SiHCl3 for further processing. The process uses HCl to chlorinate metallurgical silicon in a fluid bed reactor. 
 
HCl enters the bottom of the reactor through a robust blow pipe system. This blow pipe system and the silicon bed distribute the HCl across the cross section. Charge material metallurgical silicon is fed to the silicon bed of the reactor. An additional catalyst is not necessary. 
 
The reaction occurs at pressure range of 3 to 7 bar and temperature range of 250 to 350 °C.  Trichlorosilane synthesis is an exothermic process so the fluid bed reactor has to be chilled carefully. 
 
The main reaction is: Si + 3 HCl → SiHCl3 + H2 
 
The fraction of Trichlorosilane coming out of this reaction reaches about 85 %.
 
A competing reaction is: Si + 4 HCl → SiHCl4 + 2H2 
 
Dust separators like cyclones removes silicon dust from the product stream before raw Trichlorosilane is directly condensed and sent to the Rectification Unit. Silicon chlorination is a proven technology used by quite a number of traditional polysilicon suppliers.