GB757761A - Preparation of alkali metal chlorates - Google Patents

Abstract

<PICT:0757761/III/1> In a process for producing alkali metal chlorates by electrolysis of a solution of the chloride, the chloride solution is circulated in the interelectrode space between an anode and a cathode at such a speed that the OH-ions formed at the cathode cannot on the average, reach the anode, and by allowing the electrolyzed solution to absorb the evolved chlorine to produce hypochlorite and thereafter allowing the hypochlorite solution obtained to rest for a time and at a temperature sufficient for it to be chemically transformed to chlorate, the transformation being effected in a reaction space outside the zone of electrolysis. Control of the migration of the OH-ions and the absorption of chlorine to form hypochlorite are effected by suitably correlating the speed of circulation of the chloride solution and the value of the electrolysis current. As shown in the Figure, chloride solution passes from vat 15 through line 16 to a vessel 4 beneath the electrolysis zone formed between a cathode 1 and an anode 2, through the interelectrode space to pass via pipe 7 to a vessel 9 where the chemical transformation of hypochlorite to chlorate occurs thence to a tank 12 from which the chloride solution now containing chlorate is recirculated through pump 14 and line 13 to the supply vat 15. Product chlorate solution is withdrawn from line 20. The electrolysis gases, other than chlorine, consisting almost entirely of hydrogen are removed through tube 6. In a process for producing sodium chlorate, the cathodeanode assembly had a height of 16 cms. and an interelectrode distance of 2 cms. with a graphite anode 6 cms. in diameter. Employing a current density of 10 amps per square decimeter, a minimum flow of electrolyte of 2.5 litres per hour was theoretically necessary to obtain the desired effect but to avoid disturbances due to gas evolution a flow of 10 litres per hour was employed. The hypochlorite solution at a pH of 8 passed from the electrolysis zone to the vessel 9 where the temperature was maintained at 60 DEG C. by heating means 10 and the pH reduced to 7.2 by acidification with hydrochloric acid. The solution after the transformation in vat 9 had a pH of 6.5. If desired the vat 9, instead of being separate from the electrolysis zone as shown may be adjacent to but distinct from the electrolysis zone proper. It is preferred to recycle the chloride solution containing the formed hypochlorite around the cycle until the chlorate concentration is sufficiently high or alternatively several plants may be arranged in series such that the pump 14 of one delivers the chloride/chlorate solution to the vat 15 of the next one. Fresh chloride solution is introduced into the system at a point 19. Specification 714,234 is referred to.