Polysilicon production

You must be referring to the hydrogenation of silicon tetrachloride technology, namely cold hydrogenation technology. This technique makes use of a reversible reaction: 3SiCl4 + 2H2 + Si → 4SiHCl3. Copper-based or iron-based catalysts are used, and under conditions of 400–800°C and 2–4 MPa, silicon tetrachloride is converted into trichlorosilane, which serves as a raw material for producing polysilicon, within a fluidized bed reactor. Hydrogen chloride gas can be added to the system to increase the yield of trichlorosilane. To optimize the reaction conditions, metal silicon particles with uniformly distributed iron silicide or copper silicide on their surface can be used as raw materials to react with silicon tetrachloride, hydrogen, and hydrogen chloride to produce trichlorosilane. Methods for producing such silicon particles include mixing the silicon particles with a measured amount of catalyst, melting the mixture, and then rapidly cooling it. This process places high demands on the equipment, mainly due to the extremely high pressure and temperature inside the reduction furnace. A few domestic polysilicon manufacturers purchased production equipment using this process from abroad, but abandoned its use for safety reasons. 　 Thermal hydrogenation technology: Thermal hydrogenation technology makes use of the reaction: SiCl4 + H2 → SiHCl3 + HCl to reduce silicon tetrachloride to trichlorosilane. In this process, graphite rods are used as heating materials in the reduction reactor; electric heating is employed to maintain the temperature inside the reactor at around 1250°C, while the pressure within the reactor remains within the range of 0.25–0.40 MPa. The ratio of hydrogen flow to silicon tetrachloride flow is (3–4):1; after thorough mixing, the temperature is raised to 200–300 °C, and the mixture is fed into the reactor for reaction. The one-pass conversion rate of silicon tetrachloride in this process, as well as the yield of silicon trichlorohydride, is around 20%. Based on energy calculations, using this process, 6–8 kWh of electricity is consumed per 1 kg of trichlorosilane produced. Since graphite is used as the heating material, at high temperatures it may react with silicon tetrachloride and hydrogen to produce chloroalkanes such as chloromethane and chloroform. These chloroalkanes end up mixed in the resulting trichlorosilane, and if they are not completely separated, it will affect the quality of the polysilicon product. Therefore, the temperature in the reactor cannot be too high. This is the main reason for the low one-way conversion rate of this process. Furthermore, at higher temperatures, silicon tetrachloride may react with hydrogen to produce a small amount of elemental silicon powder. This silicon powder covers the surface of the high-temperature graphite heating rods, forming a loose layer that can lead to spark discharge between the graphite rods and thus damage the equipment. This technology has been effectively utilized at Sichuan Leshan Xinguang Silicon Industry Co., Ltd. 　

You can search for this directly on Baidu and you’ll find the answer