GB886344A - Production of silicon halides - Google Patents

Abstract

Silicon halides (excluding silicon fluoride) are produced by reacting finely divided silica or silica-bearing materials in suspension in a molten alkali metal or alkaline earth metal halide with a halogen gas in the presence of an oxygen acceptor, preferably carbon or carbon monoxide. Phosgene may be used as oxygen acceptor and halogen. Silica, e.g. zircon or spent bauxite clay containing at least 25% wt. SiO2, and of particle size 76-1000m , is suspended in a molten halide bath in which the halide is preferably the same as the halogen gas employed. The carbon may be coke, graphite or anthracite having a particle size 50m to 2 inches and usually at least twice the average size of the silica employed. The reaction in the presence of carbon, which may be added before or during reaction with the halogen, is generally assisted by external heating, electric induction heating or by the heat produced by the addition of O2 to react with the carbon. Carbon monoxide, which may be added at the same time e.g. in admixture with, the halogen supplied to the melt, causes an exothenuic reaction and the process proceeds autothermally. Reaction temperatures below 1100 DEG C. e.g. 600 DEG -1000 DEG C. may be employed. In order to accelerate the reaction in the presence of carbon, boron or boron compounds e.g. boron halides or boron compounds which react with the halogen in situ to produce boron halides, for example, boron carbides, ferro-boron, anhydrous boric oxide or metal borides e.g. alkali metal or alkaline earth metal borates especially borax, may be incorporated as catalysts in the melt. Preferably such catalysts are halides of the same halogen as the halogen gas employed, are volatile e.g. Bcl3, and are added to the melt in the halogen gas. The boron halides may be recovered from the reaction products and recycled. Specification 864,538 is referred to.