Treatment of by-product silicon tetrachloride – except in the production of trichlorosilane and polysilicon (combined post)

Currently, polysilicon production is moving toward the third-generation closed-loop process: after SiCl4 is hydrogenated to produce SiHCl3, polysilicon is produced again, which results in significant reductions in hydrogen consumption, chlorine consumption, silicon consumption, and electricity usage. However, China’s third-generation technology is still in the experimental stage, while foreign countries have already entered this phase. Therefore, I believe we should focus our efforts on the development and research of the third generation; the hydrogenation of SiCl4 represents a bottleneck in the development of polysilicon in China

I have a technology for treating the waste generated in the Siemens process for producing polysilicon – silicon tetrachloride treatment technology. If you are interested, we can discuss it together. Especially companies that produce polysilicon.

There are currently two best ways to handle silicon tetrachloride: 1. Use it directly to produce silica, or 2. Hydrochlorinate it to convert it into trichlorosilane

Silicon tetrachloride, as a by-product of polysilicon production, severely limits the output of polysilicon in terms of China’s polysilicon manufacturing technology. Theoretically, 12 tons of silicon tetrachloride are produced per ton of polysilicon, but in practice this amount is often more than 20 tons. The thermal hydrogenation process mentioned by the original poster is now being used at Xinguang, but its daily processing capacity is limited; it is far smaller than the by-product volume of polysilicon, and the one-way conversion rate is very low. Chlorohydration technology has always presented problems in medium-silicon applications, with several explosions occurring.

There are many problems with the four-stage hydrogenation of medium silicon. The problem has not been fundamentally solved yet. The key is to change the original approach and explore new methods. Foreign countries impose too strict restrictions on our access to technology. Another point is that this problem needs to be addressed through a multidisciplinary approach. We can’t just stick to the original approach right now. There are also a few reports on this topic abroad.

I only know that Jiangsu Zhongneng sells its SiCl4 directly to factories that produce vapor-phase silica, but as production volume is increasing, these downstream factories do not have enough capacity to take in all the supply, which has forced Jiangsu Zhongneng to accelerate the installation of hydrogenation facilities

New process for comprehensive utilization of silicon tetrachloride produced as a by-product of polysilicon. With the large-scale development and utilization of green energy in the form of solar power, polysilicon, which is used as a raw material for photovoltaic cells, is seeing an increasing range of applications and higher demand. In recent years, the polysilicon industry in China has developed rapidly. In 2007, more than a dozen polysilicon projects across the country announced that they would start construction or go into operation. The safety and environmental concerns associated with silicon tetrachloride, a by-product of polysilicon production, are becoming increasingly prominent. How to handle silicon tetrachloride safely has become a key issue determining whether the polysilicon industry can develop healthily. Silicon tetrachloride is the most abundant by-product in polysilicon production. Unprocessed and unrecovered silicon tetrachloride is a highly corrosive, toxic, and hazardous liquid that poses serious risks to safety and the environment. Industry experts predict that by 2010, if the polysilicon production reaches 12,500 tons, the production of silicon tetrachloride will exceed 100,000 tons. Guangzhou Jibisheng Technology Industry Co., Ltd. is the first company in China to master the technology for the recycling of silicon tetrachloride. This process uses silicon tetrachloride as a raw material to produce fumed silica; furthermore, the hydrogen obtained after separating the exhaust gases generated during production can also be used to manufacture fumed silica. Hydrogen chloride, a by-product generated during the synthesis of fumed silica by vapor-phase methods, can also be used to produce trichlorosilane, a raw material for polysilicon. Using by-products from the polysilicon industry as raw materials to produce fumed silica is a technological process that offers both economic and environmental benefits. It not only addresses the bottlenecks that hinder the development of the polysilicon industry and promotes its growth, but also facilitates the rapid development of the fumed silica industry, thereby driving the advancement of China’s new materials sector. This post was last edited by yzhms on 2008-5-6 12:27.]

Now SiCl4 costs several hundred yuan per ton, and it is mainly produced by polysilicon companies. The process used for producing vapor-phase silica is quite mature. However, in China, only Gibisi possesses this technology; all other companies are foreign-owned. Currently, Cabot, Tosoh Soda, and Wacker have all set up factories in China

The alcoholysis of SiCl4 yields silicates: SiCl4 + 4HO-R ---- Si(OR)4 + 4HCl. If the alcohol contains a small amount of water, polyesters are formed; whereas with anhydrous alcohols, orthosilicates are produced. Methyl orthosilicate and ethyl orthosilicate are particularly widely used, especially as cross-linking agents in room-temperature vulcanizing silicone rubber. Another use is in the production of MQ resin, which also has a wide range of applications, though the market for it is not large.

Currently, projects related to trichlorosilane and polysilicon are being launched across the country, but everyone faces a major practical issue: the treatment of silicon tetrachloride. Everyone can discuss together how to deal with this problem. This post was last edited by LHY8771 on 2009-1-12 at 15:38.]