What is the reaction mechanism for the formation of trichlorosilane from metal silicon and hydrogen chloride, and what catalysts are used?

Currently, catalysts are hardly used; the reaction takes place directly

Without a catalyst, at temperatures above 280 degrees, SI and HCl react directly to produce trichlorosilane and silicon tetrachloride

My company doesn’t use catalysts at the moment; I’ve never heard of it either. 1. Process principle: The synthesis of SiHCl3 involves a chlorohydridation reaction carried out in a \"boiling furnace\" reactor, using silicon powder with a purity of 95.99% at temperatures ranging from 290–330°C and pressures between 0.2 MPaG and 0.4 MPaG. At room temperature, silicon powder does not react much with dry HCl. Therefore, to synthesize SiHCl3, silicon powder must first be preheated to above 280°C (at least above 220°C). At the same time, since this is a preheating reaction, it is necessary to remove the heat generated promptly after the reaction begins, in order to ensure that the reaction proceeds properly at the required temperature. While the main reactions mentioned above are taking place, silicon powder also reacts with HCl to produce various substances such as SiCl4, SiH2Cl2, and polysiloxanes. The side reactions are as follows: These reactions are very sensitive to temperature; at higher temperatures, the reactions tend to produce SiCl4, while at lower temperatures they tend to produce SiH2Cl2. The reactions cease when the temperature drops below 260°C. Therefore, in the SiHCl3 synthesis process, precise control of the reaction temperature is the main means to ensure quality. During the chlorohydration reaction of silicon powder, the small amount of impurities present in it also react to form chlorides. Most of these substances are separated and removed in solid form during dust removal, while only a small amount enters the condenser along with the SiHCl3 vapor mixture and gets dissolved in the liquid mixture. These impurities, present in ppm levels, are then separated during the distillation process

Thank you, your reply was somewhat inspiring to me

Under normal circumstances, the reaction takes place directly without a catalyst. The documents also mention the use of metals such as copper and iron as catalysts. The synthesis of trichlorosilane focuses on controlling the reaction temperature as well as silicon powder filtration and pipeline blockage.

Do not use silicon powder that is too pure; metallurgical-grade silicon powder is sufficient. Too high purity can actually reduce the amount of trichlorosilane produced. Ordinary silicon powder contains impurities such as aluminum, iron, and copper, which act as catalysts (in my opinion), facilitating the reaction between silicon tetrachloride and hydrogen to produce trichlorosilane, thereby increasing the conversion rate.

Is it better to use a catalyst or not? So, what can be done to improve the conversion rate now?

Copper or copper oxide is generally used as a catalyst

Floor 7 is correct; no catalysts were seen being used in actual production

2Si + 7HCl ====== HSiCl3 + SiCl4 + 3H2; CuCl2 can be used as a catalyst, with the ratio Si:CuCl2 generally controlled at 100:(0.4–1)