Reaction principle and reaction equation for the production of polysilicon using the modified Siemens method

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The production methods and reaction principles for the main processes of the project are as follows: H2 preparation and purification – Hydrogen is produced by electrolyzing deionized water in an electrolyzer. Electrolysis of H2O → H2 + O2; HCl synthesis: In the hydrogen chloride synthesis furnace, a mixture of hydrogen and chlorine gases undergoes a combustion reaction to produce hydrogen chloride gas. After passing through an air cooler, a water cooler, a deep cooler, and a mist separator, this gas is sent on to the trichlorosilane synthesis process. H2 + Cl2 → 2HCl. Synthesis of SiHCl3: In the SiHCl3 synthesis furnace, silicon powder reacts with HCl at a temperature of 280–300°C to produce silicon trichloride and silicon tetrachloride. At the same time, as a side reaction of the formation of high-chloride silicon compounds, polysiloxanes of the SinCl2n+2 series and derivatives of the SinHmCl(2n+2)-m type are formed. Main reactions: Si + 3HCl → SiHCl3 + H2; Si + 4HCl → SiCl4 + 2H2. Side reactions: 2SiHCl3 → SiH2Cl2 + SiCl4; 2Si + 6HCl → Si2Cl6 + 3H2; 2Si + 5HCl → Si2HCl5 + 2H2. The synthesis gas is separated by dry methods – a dry dust removal system consisting of three-stage cyclone dust collectors is used to remove some of the silicon powder. Subsequently, the gas is washed with liquid chlorosilane at low temperature, resulting in the separation of liquid chlorosilane, hydrogen, and hydrogen chloride gases, which are then recycled back to the system for use. Separation and purification of chlorosilanes: The separation and purification of chlorosilanes are achieved based on the principle of pressure distillation, through the use of energy-efficient processes. This process can ensure the production of high-purity trichlorosilane and silicon tetrachloride for polysilicon manufacturing (for hydrogenation). SiHCl3 hydrogen reduction deposits polycrystalline silicon on the original silicon rod. High-purity H2 and refined SiHCl3 enter the reduction furnace, where they react on the surface of the silicon-core heating element at 1050°C. 5SiHCl3 + H2 → 2Si + 2SiCl4 + 5HCl + SiH2Cl2. Dry separation of reduction off-gases: The principle and process of dry separation of reduction off-gases are similar to those of the dry separation process for silicon oxyhydrogen synthesis gas. SiCl4 hydrogenation: Silicon tetrachloride is produced during the hydrogen reduction of trichlorosilane; after condensing silicon tetrachloride and removing trichlorosilane, thermal hydrogenation is carried out to convert it back into trichlorosilane. Silicon tetrachloride is fed into the hydrogenation reactor, where it undergoes a conversion reaction at a temperature of 400–500°C and a pressure of 1.3–1.5 Mpa. The main reaction is SiCl4 + H2 → SiHCl3 + HCl; the side reaction is 2SiHCl3 → SiH2Cl2 + SiCl4. Dry separation of the hydrogenated gas: The hydrogenated gas obtained from the silicon tetrachloride hydrogenation process is separated in this step into silane liquid, hydrogen gas, and hydrogen chloride gas, which are then recycled back to the system for use. The principle and process of dry separation of hydrogenated gas are similar to those of the dry separation process for silicon trichloride synthesis gas. This post was last edited by LHY8771 on 2009-3-2 16:12]