GB467209A - Improvements in or relating to the manufacture of caustic soda - Google Patents

Abstract

Alkali metal hydroxides or solutions thereof are obtained by reacting an alkali metal chloride with barium hydroxide in an aqueous medium at a temperature above 40 DEG C. preferably between 50 and 100 DEG C., to form solid basic barium chloride which is removed from the reaction mixture. The reaction may be effected in an aqueous alcoholic medium, e.g. a methanol-water mixture, or in an aqueous ammoniacal medium. The lower part of the temperature range is most suitable for the production of sodium hydroxide and the upper part for the production of potassium hydroxide. The mother liquor after the removal of the basic salt may be cooled and/or evaporated to remove unreacted barium hydroxide with or without some alkali metal chloride for return to the process. The evaporation may be accompanied by carbonation or sulphation. Evaporation and cooling may be effected simultaneously by a sudden reduction of pressure of the heated liquor, if desired in two or more stages with intermediate removal of solids. If the carbonation is effected prior to the evaporation, barium carbonate is precipitated and returned to the process after calcination, the alkali metal chloride being returned separately. At least a portion of the basic barium chloride also obtained in the reaction may be converted into oxide or hydroxide for return to the process. This conversion may be effected by treatment with water or aqueous ammonia whereby a solid phase of barium hydroxide separates followed by carbonation of the residual liquor (preferably by means of ammonium carbonate) whereby the residual barium is precipitated as the carbonate and is returned to the process after calcination. Specification 464,834 is referred to in the Provisional Specifications.