GB537557A - Improvements in the manufacture of chlorine dioxide - Google Patents

Abstract

537,557. Chlorine dioxide. FAIRWEATHER, H. G. C. (Mathieson Alkali Works). Feb. 29, 1940, No. 3811. [Class 1 (ii)] Chlorine dioxide is obtained by reacting in aqueous solution a soluble inorganic chlorate and an inorganic acid in the presence of chloride ion, the proportion of water being 50-75 per cent. of the reaction mixture, the temperature being 15-60‹C., and an inert gas being passed through the reaction mixture. The invention provides a method of determining the ratios of chloride ions, chlorate ions and hydrogen ions so as to obtain maximum yield. This depends not only on the extent D of the decomposition of the chlorate/chloride mixture but also on the efficiency E of the decomposition in yielding chlorine dioxide rather than chlorine. In Fig. 2 the curve AB shows the relationship between efficiency E and the chloride/chlorate ion ratio. The theoretical ratio of chloride to chlorate ions entering into reaction is 5-4E and is shown by the curve CD. To the left of point P (ratio of 1.15) therefore the yield is low because the decomposition, though efficient, cannot proceed to full extent. The theoretical minimum hydrogen ion/chlorate ion ratio is 6-4E, and at least this amount should be used to obtain high yields. Excess of acid is not detrimental to efficiency unless hydrochloric acid is used, when excess acid will increase the chloride/chlorate ratio and reduce efficiency in accordance with curve AB. In practice it is convenient to use a 5 : 1 chlorite/chloride liquor obtained by the chlorination of lime. The efficiency in this case will be 81 per cent. and the amount of hydrochloric acid required is 2.75 mols. per mol. of chlorate. If sulphuric acid were used an efficiency of about 87 per cent. would be obtainable with a .minimum acid requirement of 2.55 mols. Specification 495,267 is referred to.