JSC “Giredmet”, Moscow, Russia:

A. M. Chapygin, Leading Researcher
A. V. Belozerov, Laboratory Assistant
A. A. Gasanov, Division Manager of Particularly Pure Substances, Rare and Rare Earth Metals
V. V. Apanasenko, Laboratory Manager of Technology for Separation of Rare Earth Metals and Compounds, e-mail: VVApanasenko@giredmet.ru

The process of technical silicon tetrachloride purification from impurities has been developed with an optical quality product obtaining. The purification involves the chlorination of hard-removable impurity chlorosilanes followed by the silicon tetrachloride rectification in a quartz column with the removal of the main group of impurities, which are compounds of metals and non-metallic substances. For the development of SiCl₄ purification process, the conditions for the interaction of chlorosilanes contained in silicon tetrachloride with gaseous chlorine are determined. It has been established that the dichlorosilane and trichlorosilane chlorination proceeds already at room temperature during 15–24 hours and if the reaction mixture is illuminated by daylight, then from 1 to 5 hours, the residual content in SiCl₄ is less than 1·10^–4 % (wt.). Dichlorosilane and trichlorosilane are converted in this process into the main product, which is silicon tetrachloride and a number of other hydrogen-containing impurities from substances close in volatility to SiCl₄ is converted to the high-boiling compounds, which can be effectively separated by subsequent rectification. After treatment with chlorine and the necessary holding of the reaction mixture, it is separated by rectification in a quartz column with 35 trays into a light fraction, which is returned to chlorination, and the target fraction, which is a finished product. Gradually accumulating bottom, which is a high-boiling impurities mixture, is removed periodically from the rectification process and it is neutralized by 20% (wt.) aqueous solution of caustic soda. The combination of chlorination and rectification refinement allows to purify silicon tetrachloride to an optical quality product, removing a wide range of metal compounds and nonmetals to a residual content on the level of 1·10–6–1·10–8 % (wt.).
The work was carried out with the financial support of the Ministry of Education and Science of the Russian Federation within the fulfilment of the agreement 14.579.21.0138 from 03.10.2016 (unique ID: RFMEFI57916X0138).

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