Diagramm Fluid Bed Conversion

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STC-TCS Fluid Bed Conversion (Hydrochlorination)

The product of the fluid bed conversion is Trichlorosilane. Charge materials silicon tetrachloride (STC; SiCl4) and hydrogen (H2) are heated to a range of 550 to 650 °C before they fed to the fluid bed converter.
 
Charge material metallurgical silicon is mixed with copper catalyst and sent to the silicon bed of the reactor. SiCl4 and H2 enter the bottom of the reactor through a robust blow pipe system. This blow pipe system and the silicon bed distribute the superheated STC and H2 gas across the cross section. The fluid bed reactor (FBR) operates at a pressure of about 20 bar.
 
The net reaction is: 2H2 + 3 SiCl4 + Si ↔ 4 SiHCl3

This is a convenient way to summarize all the main reactions. It is a summary of the mechanisms and not a true reaction of its own. Conversion rate mainly depends on temperature, pressure and ratio H2/STC and may reaches the order of 20 to 30%.
 
The fluid bed reactor outlet gases are quenched and filtered. The carryover fines of silicon, metal chloride and some STC will be separated in the direct cooling system. Condensed mixture containing TCS, unreacted STC and other silanes are sent to the Rectification Unit. The gas H2 will be recycled to the fluid bed conversion by an oil-free reciprocating compressor.