Silicon production by Siemens process: the ratio of hydrogen to trichlorosilane in the reduction gas mixture

The following answer comes from an article I read; thanks to the author! Not only the H2/TCS ratio, but also temperature and pressure need to be considered. Discussion: At a reaction temperature of 1373 K and a pressure of 0.1 MPa, with a feed H2/SiHCl3 ratio of 0.1 to 10 (1 kmol of SiHCl3), the amount of Cl2 required to achieve energy coupling in the system was calculated for feed compositions of SiHCl3+H2+Cl2 and SiHCl3+H2. The equilibrium composition of the system and the heat absorbed by the system were also determined. As shown in Figure 3, as the H2/SiHCl3 ratio increases, the amount of Cl2 needed to enable energy coupling in the reduction system gradually increases, and at equilibrium all of the Cl2 can be consumed in the reaction. The amount of SiHCl3 in the equilibrium composition increases gradually, mainly due to the reduction of the byproduct SiCl4 to form SiHCl3 ； When the H2/SiHCl3 ratio increased from 0.1 to 6.6, H2 was produced at equilibrium, and the main reaction occurring in the system was the decomposition of SiHCl3 ； When the H2/SiHCl3 ratio is greater than 6.6, it facilitates the reduction reaction of SiHCl3 ； As the H2/SiHCl3 ratio increases, the amount of polycrystalline silicon also increases. When the H2/SiHCl3 ratio rises from 0.1 to 10, the heat absorbed by the system at equilibrium in the SiHCl3 + H2 reaction increases by a factor of 1.05. Conclusion: For the SiHCl3 reduction reaction system, the appropriate operating temperature is 1323∼1473 K, with a pressure of 0.1 MPa. Under conditions of low temperature and low H2/SiHCl3 ratio, the decomposition reaction of SiHCl3 occurs primarily ； At temperatures above 1323 K and a H2/SiHCl3 ratio greater than 6.6, low pressure is favorable for the reduction of SiHCl3 to produce polycrystalline silicon. The amount of polycrystalline silicon in the equilibrium composition of the SiHCl3+H2+Cl2 energy-coupled system is lower than that in the equilibrium result of the SiHCl3+H2 system under corresponding conditions, while the amount of the by-product SiH2Cl2 in the equilibrium compositions of the two systems differs little.

I’m just skeptical about the pressure from upstairs! ! It shouldn’t be 0.1 MPa, right! ! !

There is no doubt regarding the pressure requirements on the 3rd floor; currently, reduction furnaces come in both atmospheric-pressure and pressurized types, with the majority of those used in China being atmospheric-pressure reduction furnaces.

According to literature reports, it is not higher than 8 bar