SU30268A1 - Method of separating hydrogen fluoride and silicon fluoride in the gas phase - Google Patents

Description

During the decomposition of fluorspar with sulfuric acid, along with hydrogen fluoride, silicon fluoride is released, which is formed due to the content of silicic acid in the spar and is a harmful impurity that contaminates the fluorine salts of fluorosilicate. In order to obtain pure fluorine salts, periodic purification is usually carried out by obtaining the absorption of gas with water, hydrofluoric acid from hydrofluoric acid, by precipitating with a last soda. The latter operation causes a large loss of hydrofluoric acid and creates extremely anti-hygienic conditions.

Continuous purification of the gas without prior absorption allows gas to be obtained with chemically pure hydrofluoric acid and pure fluorine salts by directly reacting the gas with solid reagents, for example, with soda.

The proposed gas purification cnoQo6 is based on the absorption of fluorine-silicon by solid sodium fluoride at elevated temperature. It is based on the property that solid sodium fluoride, when exposed to a mixture of hydrogen fluoride and silicon fluoride at a temperature above 250 ° C, is added

only hydrogen fluoride unites itself to form sodium silicofluoride. Note on the elasticity of dissociation of the latter is observed only at 400 °. Speed reaction

2NaF (solid) SiF (gas) Na2SiF6 (solid)

increases dramatically with increasing temperature, reaching a significant speed already at 300-350 °.

The method consists in the following: hydrofluoric gas is carried out over sodium fluoride, the reaction being carried out at a temperature above 200 °.

The method can be performed in this way. The gas is heated to a temperature of about 450 ° and passed through an apparatus of any type, for example, the type of saturating Gazenklever drums or shelving furnace, with countercurrent movement of solid sodium fluoride. The conversion of NaF to Na2SiF6 occurs almost completely - 95% sodium fluorosilicate is formed. Unabsorbed due to the conditions of kinetics and statics {elasticity and dissociation NagSiFo), the SiEj residue, the passage of the apparatus along with the rest of the gas, is cooled to 300-350 ° and absorbed quantitatively by sodium fluoride, which is introduced at the beginning of the apparatus.

The resulting mixture, containing about 40% NaoSiFii, is calcined at 600-700 ° in a rotating mechanical or muffle furnace. Sodium fluoride is returned to the treatment plant, and silicon fluoride is absorbed by water to produce hydrofluoric acid.

The subject matter of the invention.

A method of separating hydrogen fluoride and silicon fluoride in a gas phase, characterized in that gaseous silicon fluoride and hydrogen fluoride are passed, in order to release silicon fluoride, over solid sodium fluoride at a temperature of 200 to 500 °.