GB663218A - Improvements in process for making chlorine dioxide - Google Patents

Abstract

Chlorine dioxide is prepared by reacting dry nitrogen peroxide with a solution of chloric acid in aqueous nitric acid containing not less than 35 per cent by weight HNO3 on the total of water and nitric acid. The chloric acid solution may be formed by dissolving an alkali or alkaline earth metal chlorate, e.g. of sodium, lithium, potassium, or calcium, in aqueous nitric acid. The reaction temperature should not exceed 50 DEG C. and is preferably 15-35 DEG C. The nitrogen peroxide may be diluted with say 85-90 per cent by volume of the total gas mixture of an inert gas such as air, nitrogen, or carbon dioxide. In a continuous process a nitrogen peroxide-air mixture is passed counter current to a saturated solution of sodium chlorate in nitric acid in a packed or baffled tower, and chlorine dioxide-air mixture is withdrawn. The sodium nitrate formed is removed from the tower as a slurry and passed, through a saturator where fresh sodium chlorate is added, to a separator where solid sodium nitrate is removed, while the chlorate solution is recycled to the tower. The sodium nitrate may be isolated or may be passed with additional material, if necessary, to a first generator where it is treated with sulphuric acid to form nitric acid and sodium sulphate or bisulphate. Some of the nitric acid is used in making up the chlorate-nitric acid mixture and the rest is passed to a second generator where it is treated with a mixture of sulphur dioxide and air at 20-35 DEG C. to produce both the nitrogen peroxide-air mixture and sulphuric acid for the first generator. The nitrogen peroxide may also be prepared by oxidizing ammonia or by direct combination of nitrogen and oxygen.