GB714234A - Manufacture of sodium chlorate - Google Patents

Abstract

<PICT:0714234/III/1> In the manufacture of sodium chlorate by electrolysis of sodium chloride solution, the solution is circulated in the interpolar space between cathode and anode at such a speed that the OH-ions from the cathode cannot reach the anode, the products of electrolysis NAOH + Cl2 thus being carried out of the p interpolar space and allowed to react to form sodium hypochlorite which is transformed to chlorate and chloride by chemical means. The solution, without separation of chlorate may be recycled until the desired conversion is attained. In the drawing sodium chloride solution from tank 13 is passed by pump 15 and line 14 to vat 16 from which is regulated quantities it is fed by line 17 to an inlet chamber 5 of the electrolysis cell. The solution passes up between graphite anode 2 and surrounding cylindrical cathode 1 at a speed correlated to the migration speed of the OH-ions to prevent them reaching the anode, and enters chamber 3. The caustic soda and chlorine unite to form sodium hypochlorite whilst hydrogen also from the electrolysis is withdrawn at 7. The hypochlorite solution leaves chamber 3 by pipe 8 and enters chamber 10 when the hypochlorite breaks down to chloride and chlorate. An equation relating the rate of hypochlorite-chlorate transformation to pH, temperature and concentration of hypochlorite ions is given. Temperature, not exceeding 50 DEG C. and pH between 5.5 and 7.5 are preferred and are obtained by adding hydrochloric acid, for example, at point 9 before the reactants enter tank 10. The solution then passes to tank 13 optionally through a heater 23, and the solution is recycled until the chlorate content is sufficient when it is withdrawn at 31 and new chloride introduced at 30. If desired several such installations may work in series, the pump 15 delivering solution from tank 13 of one to the vat 16 of the next. In an example the cathode anode assembly had a height of 64 cms., the interpolar distance was 1 cm. and the anode diameter 6 cms. The current was 36 amperes and the minimum electrolyte flow rate was 2 litres (but preferably 10) per hour. The electrolysis temperature was 40 DEG C. and the average pH 7.5.