Patent ID: 8268159

Claim:
A method for producing a sodium hypochlorite solution, comprising: (a) obtaining an electrolytic cell comprising a sodium ion conductive ceramic membrane configured to selectively transport sodium ions, the ceramic membrane separating an anolyte compartment configured with an anode and a catholyte compartment configured with a cathode; (b) providing an impure sodium chloride solution containing calcium, magnesium, or other precipitable cations in the anolyte compartment of the cell; (c) providing water and sodium ions in the catholyte compartment of the electrolytic cell; (d) applying an electric current to the electrolytic cell thereby: i. oxidizing chlorine anions in the anolyte compartment according to the following reaction: 2Cl − →Cl 2 +2e − and forming hypochlorous acid according to the following reaction: Cl 2 +H 2 O→HOCl+HCl; ii. causing sodium ions to pass through the sodium ion conductive ceramic membrane from the anolyte compartment to the catholyte compartment; and iii. decomposing water in the presence of sodium ions in the catholyte compartment according to the following reaction: Na + +H 2 O+e − →NaOH+½H 2 ; (e) withdrawing and transporting sodium hydroxide solution from the catholyte compartment to the anolyte compartment in a controlled fashion to produce sodium hypochlorite in the anolyte compartment according to the following reaction: HOCl+HCl+2NaOH→NaOCl+NaCl+2H 2 O; (f) maintaining a pH of the impure sodium chloride solution within the anolyte compartment at a pH less than 8, wherein the pH of the impure sodium chloride solution within the anolyte compartment is also maintained at about 6 or greater; and (g) removing a solution comprising sodium hypochlorite from the anolyte compartment.