Electrolytic Process

Abstract

The invention relates to a process of producing alkali metal chlorate in an electrolytic cell comprising an anode and a cathode, wherein at least one chromium compound having a valence lower than +6 is added to the process, wherein said at least one chromium compound is oxidized to hexavalent chromium within said process, wherein substantially no hexavalent chromium is added to the process from an external source. The invention also relates to the use of an aqueous solution of chromium compounds as an additive to a chlorate process.

1 . Process of producing alkali metal chlorate in an electrolytic cell comprising an anode and a cathode, wherein at least one chromium compound having a valence lower than +6 is added to the process in an amount from 1 to 200 g chromium/ton produced chlorate, wherein said at least one chromium compound is oxidized to hexavalent chromium within said process, wherein substantially no hexavalent chromium is added to the process from an external source. 
     
     
         2 . The process according to  claim 1 , wherein the amount of hexavalent chromium added is less than about 30 molar percent based on the total amount of chromium added from an external source. 
     
     
         3 . The process according to  claim 1 , wherein no hexavalent chromium is added. 
     
     
         4 . The process according to  claim 1 , wherein a chromium(III) compound is added to the process. 
     
     
         5 . The process according to  claim 1 , wherein said at least one chromium compound having a valence lower than +6 is added to the scrubber liquid, to the cell line loop after the cells, or to the electrolyte going in to the cell. 
     
     
         6 . The process according to  claim 1 , wherein said at least one chromium compound having a valence lower than +6 is added to the electrolyzed solution prior to the reactor; to the process stream from the mother liquor scrubber; and/or to the reactor gas scrubber. 
     
     
         7 . The process according to  claim 1 , wherein said at least one chromium compound having a valence lower than +6 is added upstream of an electrolyte filter. 
     
     
         8 . The process according to  claim 1 , wherein said at least one chromium compound having a valence lower than +6 is added in an amount resulting in a chromium content from about 0.1 to about 20 g (calculated as sodium dichromate equivalents)/l electrolyte solution. 
     
     
         9 . The process according to  claim 1 , wherein the weight ratio of chromium derived from chromium compounds having a valence lower than +6 to hypochlorite ranges from about 1:30 to about 3:1. 
     
     
         10 . The process according to  claim 1 , wherein the amount of chromium compound(s) with a valence lower than +6 is added in an amount from about 1 to about 60 g chromium/ton produced chlorate. 
     
     
         11 . The process according to  claim 1 , wherein hexavalent chromium is formed from at least one chromium compound by means of oxidation in an aqueous solution which hexavalent chromium is subsequently transferred to the electrolytic cell. 
     
     
         12 . The process according to  claim 11 , wherein hexavalent chromium is formed in an aqueous solution in a medium separated from the process prior to transfer of said aqueous solution of hexavalent chromium to the process. 
     
     
         13 . The process according to  claim 1 , wherein substantially all hexavalent chromium within the process has been formed in-situ. 
     
     
         14 . A process for producing alkali metal chlorate in an electrolytic cell comprising an anode and a cathode, the process comprising adding an aqueous solution of chromium compounds to the chlorate process, said solution comprising chromium compounds, wherein the molar ratio of hexavalent chromium to chromium having a valence lower than +6 ranges from about 0:10000 to about 1:10000. 
     
     
         15 . A process for producing alkali metal chlorate in an electrolytic cell comprising an anode and a cathode, the process comprising adding an aqueous solution of chromium compounds to the chlorate process, said solution comprising at least one hexavalent chromium compound and at least one chromium compound having a valence lower than +6, wherein the molar ratio of hexavalent chromium to chromium having a valence lower than +6 ranges from about 1:10000 to about 3:10. 
     
     
         16 . The process according to  claim 2 , wherein a chromium(III) compound is added to the process. 
     
     
         17 . The process according to  claim 3 , wherein a chromium(III) compound is added to the process. 
     
     
         18 . The process according to  claim 14 , wherein the at least one chromium compound having a valence lower than +6 is a chromium(III) compound. 
     
     
         19 . The process according to  claim 15 , wherein the at least one chromium compound having a valence lower than +6 is a chromium(III) compound.