Control of ph kinetics in an electrolytic cell having an acid-intolerant alkali-conductive membrane

Abstract

Systems and methods for recovering chlorine gas or an alkali metal from an electrolytic cell having an acid-intolerant, alkali-ion-selective membrane are disclosed. In some cases, the cell has an anolyte compartment and a catholyte compartment with an acid-intolerant, alkali-ion selective membrane separating the two. While a cathode is disposed within a catholyte solution in the catholyte compartment, a chlorine-gas-evolving anode is typically disposed within an aqueous alkali-chloride solution in the anolyte compartment. As current passes between the anode and cathode, chlorine ions in the anolyte solution can be oxidized to form chlorine gas. In some cases, the cell is configured so the chlorine gas is rapidly removed from the cell to inhibit a chemical reaction between the chlorine gas and the anolyte solution. In some cases, a vacuum or a heating system is used to increase the rate at which chlorine gas exits the cell. Other implementations are also described.

1 . An electrochemical cell comprising:
 an anolyte compartment;   a gas-permeable, chlorine-gas-evolving anode disposed within the anolyte compartment;   an aqueous alkali-chloride anolyte solution disposed in the anolyte compartment;   a catholyte compartment comprising a cathode and a catholyte solution;   an acid-intolerant, water-impermeable, alkali-ion-selective membrane separating the anolyte compartment from the catholyte compartment; and   means for increasing a rate at which chlorine gas exits the anolyte compartment to inhibit a chemical reaction between the chlorine gas and the anolyte solution.   
     
     
         2 . The cell of  claim 1 , wherein the anolyte solution comprises a concentrated aqueous sodium chloride solution. 
     
     
         3 . The cell of  claim 1 , wherein the anolyte solution comprises a concentrated aqueous lithium chloride solution. 
     
     
         4 . The cell of  claim 1 , wherein the means for increasing the rate at which chlorine gas exits the anolyte compartment comprises a vacuum system. 
     
     
         5 . The cell of  claim 1 , wherein the means for increasing the rate at which chlorine gas exits the anolyte compartment comprises a heating system that provides heat to the anolyte solution. 
     
     
         6 . The cell of  claim 1 , wherein the anolyte compartment is disposed above the catholyte compartment in the cell, and wherein the anode is disposed in a substantially horizontal orientation within the anolyte compartment. 
     
     
         7 . The cell of  claim 1 , further comprising a hydrophobic membrane that is permeable to chlorine gas, wherein the hydrophobic membrane covers an opening of the anolyte compartment. 
     
     
         8 . The cell of  claim 1 , wherein the alkali-ion-selective membrane comprises a substance selected from a NaSICON-type material, sodium beta-alumina, a LiSICON-type material, lithium aluminum titanium phosphate (LATP), La x Li y TiO 3-x  type perovskite, Li 2 O—Al 2 O 3 —TiO 2 —P 2 O 5  glass, and Li 2 S—P 2 S 5  Thio-LiSICON type materials. 
     
     
         9 . A method for electrolyzing an alkali-chloride salt in an electrolytic cell comprising an acid-intolerant membrane, the method comprising:
 providing an electrochemical cell comprising:
 an anolyte compartment; 
 a chlorine-gas-evolving anode disposed in the anolyte compartment; 
 an aqueous alkali-chloride anolyte solution disposed in the anolyte compartment; 
 a catholyte compartment comprising a cathode and a catholyte solution; and 
 an acid-intolerant, water-impermeable, alkali-ion-selective membrane separating the anolyte compartment from the catholyte compartment; 
   passing current between the anode and the cathode; and   rapidly removing chlorine gas from the anolyte compartment to inhibit a chemical reaction between the chlorine gas and the anolyte solution.   
     
     
         10 . The method of  claim 9 , further comprising maintaining the anolyte solution at a temperature between about 40 and about 90 degrees Celsius. 
     
     
         11 . The method of  claim 9 , wherein the removing chlorine gas comprises using a vacuum to remove the chlorine gas from the anolyte compartment. 
     
     
         12 . The method of  claim 9 , wherein the anolyte solution comprises a concentrated aqueous sodium chloride solution. 
     
     
         13 . The method of  claim 9 , wherein the anolyte solution comprises a concentrated aqueous lithium chloride solution. 
     
     
         14 . The method of  claim 9 , wherein an alkali-chloride salt selected from sodium chloride and lithium chloride accounts for between about 10 and about 80%, by weight, of the alkali-chloride anolyte solution. 
     
     
         15 . The method of  claim 9 , wherein the alkali-ion-selective membrane is disposed horizontally within the cell, and wherein the anolyte compartment is disposed above the catholyte compartment. 
     
     
         16 . The method of  claim 15 , further comprising a hydrophobic membrane that is permeable to chlorine gas, wherein the hydrophobic membrane covers an opening of the anolyte compartment. 
     
     
         17 . A method for electrolyzing an alkali-chloride salt in an electrolytic cell comprising an acid-intolerant membrane, the method comprising:
 providing an electrochemical cell comprising:
 an anolyte compartment; 
 a chlorine-gas-evolving anode disposed in a substantially horizontal orientation within the anolyte compartment; 
 an aqueous anolyte solution disposed in the anolyte compartment, wherein the anolyte comprises an alkali-chloride salt selected from sodium chloride and lithium chloride; 
 a catholyte compartment comprising a cathode and a catholyte solution; 
 an alkali-ion-selective membrane separating the anolyte compartment from the catholyte compartment, wherein the alkali-ion-selective membrane comprises a substance selected from a NaSICON-type material, sodium beta-alumina, a LiSICON-type material, lithium aluminum titanium phosphate (LATP), La x Li y TiO 3-x  type perovskite, Li 2 O—Al 2 O 3 —TiO 2 —P 2 O 5  glass, and Li 2 S—P 2 S 5  Thio-LiSICON type materials; 
   passing current between the anode and the cathode; and   rapidly removing chlorine gas from the anolyte compartment through a process selected from heating the anolyte solution to a temperature between about 40 and about 90 degrees Celsius and applying a vacuum to the anolyte compartment.   
     
     
         18 . The method of  claim 17 , wherein the alkali-ion-selective membrane is disposed horizontally within the cell, and wherein the anolyte compartment is disposed above the catholyte compartment. 
     
     
         19 . The method of  claim 18 , further comprising a hydrophobic membrane that is permeable to chlorine gas, wherein the hydrophobic membrane covers an opening of the anolyte compartment. 
     
     
         20 . The method of  claim 17 , wherein the alkali-chloride salt accounts for between about 10 and about 40 percent, by weight, of the anolyte solution.