Process for producing chlorine with low bromine content

Abstract

Chlorine with a low bromine content is produced by electrolyzing brine to produce gaseous chlorine, alkali metal hydroxide and hydrogen, separating the gaseous chlorine from the electrolyte (anolyte in the case of the membrane process), directing electrolyte to a primary dechlorination step using hydrochloric acid to remove gaseous chlorine therefrom, optionally directing depleted electrolyte (anolyte in the case of the membrane process) from the primary dechlorination step to a secondary dechlorination step using a reducing agent for chlorine and oxychlorine species, and recycling dechlorinated depleted electrolyte (anolyte in the case of the membrane process) to salt dissolvers to prepare brine for electrolysis. At least part of the gaseous chlorine generated in the primary dechlorination step is not combined with gaseous chlorine generated in the electrolysis step.

1 . A method of producing chlorine with low bromine content, which comprises:
 (a) electrolyzing brine to produce gaseous chlorine, alkali metal hydroxide and hydrogen,   (b) separating gaseous chlorine from the electrolyte (anolyte in the case of the membrane process),   (c) directing depleted electrolyte to a primary dechlorination step using hydrochloric acid to remove gaseous chlorine therefrom,   (d) optionally directing the depleted electrolyte (anolyte in the case of the membrane process) from the primary dechlorination step to a secondary dechlorination step using a reducing agent for chlorine and oxychlorine species,   (e) recycling dechlorinated depleted electrolyte (anolyte in the case of the membrane process) to salt dissolvers to prepare brine for electrolysis,   
       wherein at least part of the gaseous chlorine generated in step (c) is not combined with gaseous chlorine generated in steps (a) and (b). 
     
     
         2 . The process of  claim 1  wherein none of the gaseous chlorine generated in step (c) is combined with gaseous chlorine generated in steps (a) and (b). 
     
     
         3 . The process of  claim 1  wherein the chlorine generated in step (c) is utilized to generate hydrochloric acid. 
     
     
         4 . The process of  claim 1  wherein the chlorine generated in step (c) is utilized to generate alkali metal hypochlorite. 
     
     
         5 . The process of  claim 1  wherein the electrolysis step (a) is carried out at a pH of about 3.1 to about 5.5. 
     
     
         6 . The process of  claim 5  wherein the pH is about 3.5 to about 5.5. 
     
     
         7 . The process of  claim 5  wherein the pH is about 3.9 to about 5.5. 
     
     
         8 . The process of  claim 1  wherein step (a) is effected at a temperature of about 80° to about 90° C. 
     
     
         9 . The process of  claim 1  wherein depleted brine is subjected to further purification step. 
     
     
         10 . The process of  claim 1  wherein gaseous chlorine formed in processing of depleted brine is not mixed with the gaseous chlorine formed in steps (a) and (b).