Methods For Producing Sodium Hypochlorite With a Three-Compartment Apparatus Containing an Acidic Anolyte

Abstract

An electrochemical method for the production of a chlorine-based oxidant product, such as sodium hypochlorite, is disclosed. The method may potentially be used to produce sodium hypochlorite from sea water or low purity un-softened or NaCl-based salt solutions. The method utilizes alkali cation-conductive ceramic membranes, such as membranes based on NaSICON-type materials, and organic polymer membranes in electrochemical cells to produce sodium hypochlorite. Generally, the electrochemical cell includes three compartments and the first compartment contains an anolyte having an acidic pH.

1 . An electrolytic cell, comprising:
 an anolyte compartment holding an anolyte, the anolyte compartment comprising an anode in contact with the anolyte;   a catholyte compartment containing a catholyte, the catholyte compartment comprising a cathode in contact with the catholyte;   a middle compartment holding an electrolyte, the middle compartment being in operative communication with the anolyte compartment and the catholyte compartment;   a polymeric anion-conducting membrane positioned between the anolyte compartment and the middle compartment; and   an alkali cation-conductive ceramic membrane selective to one type of cation, the cation-conductive membrane positioned between the middle compartment and the catholyte compartment, and   wherein the anolyte comprises an alkali halide solution of pH less than about 5.5, such that the electrolytic cell produces a halogen-based oxidant product.   
   
   
       2 . The electrolytic cell of  claim 1 , wherein the alkali cation-conductive ceramic membrane comprises a MSICON membrane selective to M +  ions, where M comprises one or more of lithium, sodium, and potassium. 
   
   
       3 . The electrolytic cell of  claim 2 , wherein the alkali cation-conductive ceramic membrane comprises a NaSICON membrane selective to sodium ions. 
   
   
       4 . The electrolytic cell of  claim 1 , wherein the electrolyte comprises a pH greater than about 5.5. 
   
   
       5 . The electrolytic cell of  claim 1 , wherein the halogen-based oxidant product comprises a mixture of alkali hypohalite, hypohalous acid and halogen gas. 
   
   
       6 . The electrolytic cell of  claim 1 , wherein the catholyte comprises and alkali hydroxide. 
   
   
       7 . A method for forming a chlorine-based oxidant product, the method comprising:
 providing an electrolytic cell comprising:
 an anolyte compartment for holding an anolyte, the anolyte compartment comprising an anode positioned to contact the anolyte; 
 a catholyte compartment for containing a catholyte, the catholyte compartment comprising a cathode positioned to contact the catholyte; 
 a middle compartment for holding an electrolyte, the middle compartment being in operative communication with the anolyte compartment and the catholyte compartment; 
 a polymeric anion-conducting membrane positioned between the anolyte compartment and the middle compartment; and 
 an alkali cation-conductive ceramic membrane selective to one type of material, the cation-conductive membrane positioned between the middle compartment and the catholyte compartment; 
   introducing a first feed stream comprising a sodium chloride solution into the electrolytic cell;   applying a current between the anode and the cathode;   maintaining a pH of the anolyte to be less than about 4; and   producing the chlorine-based oxidant product.   
   
   
       8 . The method of  claim 7 , further comprising maintaining the pH of the electrolyte in the middle compartment to be greater than about 5.5. 
   
   
       9 . The method of  claim 7 , wherein the chlorine-based oxidant product comprises a mixture of sodium hypochlorite, hypochlorous acid and chlorine. 
   
   
       10 . The method of  claim 7 , wherein the mixture of sodium hypochlorite, hypochlorous acid and chlorine is combined with sodium hydroxide. 
   
   
       11 . The method of  claim 10 , wherein the sodium hydroxide is derived from the catholyte. 
   
   
       12 . The method of  claim 7 , further comprising:
 introducing the first feed stream into the anolyte compartment and the middle compartment;   introducing a second feed stream into the catholyte compartment;   feeding an effluent from the catholyte compartment into the middle compartment to control the pH of the electrolyte in the middle compartment; and   mixing an effluent from the middle compartment with an effluent from the anolyte compartment to form the chlorine-based oxidant product.   
   
   
       13 . The method of  claim 12 , wherein the mixing the effluent from the middle compartment with the effluent from the anolyte compartment occurs outside of the electrolytic cell. 
   
   
       14 . The method of  claim 12 , wherein the first feed stream comprises an aqueous sodium chloride solution and the second feed stream comprises water. 
   
   
       15 . The method of  claim 7 , further comprising:
 introducing the first feed stream liquid into the middle compartment;   introducing a second feed stream into the anolyte compartment;   introducing a third feed stream into the catholyte compartment;   recycling the first feed stream through the middle compartment;   recycling the third feed stream through the catholyte compartment;   obtaining an effluent from the anolyte compartment, wherein the effluent from the anolyte compartment comprises a chemical selected from chlorine, hypochlorous acid, hydrochloric acid, and mixtures thereof.   
   
   
       16 . The method of  claim 7 , wherein producing the chlorine-based oxidant product comprises mixing the effluent from the anolyte compartment with an alkali hydroxide source to form the chlorine-based oxidant product. 
   
   
       17 . The method of  claim 16 , wherein the mixing occurs outside the electrolytic cell. 
   
   
       18 . The method of  claim 16 , wherein the mixing occurs in the catholyte compartment. 
   
   
       19 . The method of  claim 7 , further comprising:
 introducing the first feed stream into the middle compartment and the catholyte compartment;   introducing a second feed stream into anolyte compartment;   recycling the first feed stream through the middle compartment and the catholyte compartment; and   obtaining an effluent from the anolyte compartment, wherein the effluent from the anolyte compartment comprises a chemical selected from chlorine, hypochlorous acid, hydrochloric acid, and mixtures thereof.   
   
   
       20 . The method of  claim 19 , further comprising mixing the effluent from the anolyte compartment with an alkali hydroxide source to form the chlorine-based oxidant product, wherein the mixing occurs outside the electrolytic cell. 
   
   
       21 . The method of  claim 7 , further comprising:
 introducing the first feed stream into the middle compartment;   introducing a second feed stream into the catholyte compartment;   recycling the first feed stream through the middle compartment;   introducing a third feed stream into the anolyte compartment; and   mixing an effluent from the catholyte compartment with an effluent from the anolyte compartment to form the chlorine-based oxidant product, wherein the effluent from the anolyte compartment comprises a chemical selected from chlorine, hypochlorous acid, hydrochloric acid, and mixtures thereof.   
   
   
       22 . The method of  claim 7 , further comprising:
 introducing the first feed stream into the catholyte compartment;   introducing a second feed stream into the anolyte compartment;   feeding an effluent from the catholyte compartment into the middle compartment; and   mixing an effluent from the middle compartment with an effluent from the anolyte compartment to form the chlorine-based oxidant product.   
   
   
       23 . The method of  claim 7 , further comprising:
 introducing the first feed stream into the middle compartment;   recycling the first feed stream through the middle compartment;   introducing a second feed stream into the anolyte compartment;   introducing a third feed stream into the catholyte compartment; and   feeding an effluent from the anolyte compartment into the catholyte compartment to form the chlorine-based oxidant product.   
   
   
       24 . The method of  claim 7 , wherein the chlorine-based oxidant product comprises sodium hypochlorite present at a concentration between about 0.1 wt. % and about 30 wt. %. 
   
   
       25 . The method of  claim 7 , wherein the chlorine-based oxidant product comprises sodium hypochlorite present at a concentration between about 0.1 wt. % and about 15 wt. %. 
   
   
       26 . The method of  claim 7 , wherein the chlorine-based oxidant product comprises sodium hypochlorite present at a concentration between about 0.1 wt. % and about 5 wt. %. 
   
   
       27 . A method for producing sodium hypochlorite, the method comprising:
 providing an electrolytic cell comprising:
 an anolyte compartment for holding an anolyte, the anolyte compartment comprising an anode positioned to contact the anolyte; 
 a catholyte compartment for containing a catholyte, the catholyte compartment comprising a cathode positioned to contact the catholyte; 
 a middle compartment for holding an electrolyte, the middle compartment being in operative communication with the anolyte compartment and the catholyte compartment; 
 a polymeric anion-conducting membrane positioned between the anolyte compartment and the middle compartment; and 
 a NaSICON alkali cation-conductive ceramic membrane selective to sodium ions, the cation-conductive membrane positioned between the middle compartment and the catholyte compartment, 
   introducing a first feed stream comprising an aqueous solution of a chemical selected from sodium chloride, hydrochloric acid, and mixtures thereof, into the electrolytic cell;   applying a current between the anode and the cathode;   maintaining a pH of the anolyte to be less than about 4;   producing a chlorine-based oxidant product comprising at least one of sodium hypochlorite, hypochlorous acid, and chlorine gas;   treating the chlorine-based oxidant product with sodium hydroxide; and   producing sodium hypochlorite at a concentration between about 0.1 wt. % and about 30 wt. %.   
   
   
       28 . The method of  claim 27 , wherein the product comprises sodium hypochlorite present at a concentration between about 0.1 wt. % and about 15 wt. %. 
   
   
       29 . The method of  claim 27 , wherein the product comprises sodium hypochlorite present at a concentration between about 0.1 wt. % and about 5 wt. % 
   
   
       30 . The method of  claim 27 , further comprising maintaining a pH of the electrolyte at a pH above about 5.5. 
   
   
       31 . The method of  claim 27 , wherein the aqueous solution comprises between about 1 and about 26 wt % sodium chloride. 
   
   
       32 . A method for forming a chlorine-based oxidant product, the method comprising:
 providing an electrolytic cell comprising:
 an anolyte compartment for holding an anolyte, the anolyte compartment comprising an anode positioned to contact the anolyte; 
 a catholyte compartment for containing a catholyte, the catholyte compartment comprising a cathode positioned to contact the catholyte; 
 a middle compartment for holding an electrolyte, the middle compartment being in operative communication with the anolyte compartment and the catholyte compartment; 
 a polymeric anion-conducting membrane positioned between the anolyte compartment and the middle compartment; and 
 an alkali cation-conductive ceramic membrane selective to one type of material, the cation-conductive membrane positioned between the middle compartment and the catholyte compartment; 
   introducing a first feed stream comprising a sodium chloride solution into the electrolytic cell;   applying a current between the anode and the cathode;   maintaining a pH of the anolyte to be less than about 4;   maintaining the pH of the electrolyte in the middle compartment to be greater than about 5.5;   producing the chlorine-based oxidant product comprising a mixture of sodium hypochlorite, hypochlorous acid and chlorine; and   combining the mixture of sodium hypochlorite, hypochlorous acid and chlorine with sodium hydroxide.