Selective hydrobromination of metallurgical-grade silicon in a flow reactor system

Reactions of metallurgical-grade silicon (MG-Si) with gaseous hydrogen bromide (HBr) has been monitored by means of online gas chromatography in a flow reactor system. The formation of tri-bromosilane started to occur at 380 °C, accompanied by the consumption of HBr. The conversion of HBr into bromosilanes increased with an increase in reaction temperature and reached a maximum at 440 °C. An increase of the HBr concentration in a HBr-N₂ mixed gas led to an increase in the consumption of MG-Si, while it reduced the selectivity of the tri-bromosilane formation. An increase in total flow rate of the reaction gas caused a dramatic decrease in the HBr conversion and enhanced the selectivity of the tri-bromosilane formation. The rate constant for overall bromination reaction at 400 °C was measured to be 0.46 s⁻¹. Concentrations of impurities in the product were much less than those in MG-Si. Moreover, kerf loss silicon was subjected to the bromination reaction under the optimized conditions.