Methods and systems for production of an aqueous hypochlorous acid solution

1. A method for making an aqueous hypochlorous acid (HClO) solution, the method comprising

electrolyzing a solution of sodium chloride to produce a solution of sodium hypochlorite in an electrolysis cell, wherein the electrolysis cell comprises a first chamber, at least one positive electrode disposed in the first chamber, and at least one negative electrode disposed in the first chamber, wherein the solution of sodium hypochlorite is produced in the chamber with the at least one positive electrode and the at least one negative electrode, wherein the solution of sodium hypochlorite after the electrolyzing has at least 500 ppm sodium hypochlorite; and

producing the aqueous hypochlorous acid solution by adjusting a pH of the solution of sodium hypochlorite to a value within a range of 3 to 8 by adding a selected weak acid to the solution of sodium hypochlorite to produce a buffer comprising the selected weak acid and a salt of the selected weak acid.

2. The method of claim 1 , wherein the aqueous hypochlorous acid solution has no more than 500 ppm hypochlorous acid.

3. The method of claim 1 , further comprising adding a basic salt or a base to the solution of sodium chloride.

4. The method of claim 3 , wherein the basic salt or the base is selected from sodium bicarbonate, sodium carbonate, or sodium hydroxide.

5. The method of claim 1 , wherein the selected weak acid is acetic acid and the buffer comprises a combination of acetic acid and sodium acetate.

6. The method of claim 5 , wherein the buffer in the aqueous hypochlorous acid solution has a molar ratio of acetic acid to sodium acetate in a range from 1:100 to 100:1.

7. The method of claim 1 , further comprising diluting the solution of sodium hypochlorite.

8. The method of claim 1 , wherein the solution of sodium hypochlorite after the electrolyzing has at least 1000 ppm sodium hypochlorite.

9. The method of claim 1 , wherein producing the aqueous hypochlorous acid solution comprises producing the aqueous hypochlorous acid solution by adjusting a pH of the solution of sodium hypochlorite to a value within a range of 4 to 6.

10. The method of claim 1 , wherein the electrolysis cell does not include a membrane or separator between the at least one positive electrode and the at least one negative electrode.

11. A method for making an aqueous hypochlorous acid (HClO) solution, the method comprising

electrolyzing a solution of sodium chloride to produce a solution of sodium hypochlorite in an electrolysis cell which comprises at least one positive electrode and at least one negative electrode;

producing the aqueous hypochlorous acid solution by adjusting a pH of the solution of sodium hypochlorite to a value within a range of 3 to 8 by adding a selected weak acid to the solution of sodium hypochlorite to produce a buffer comprising the selected weak acid and a salt of the selected weak acid; and

transferring the solution of sodium hypochlorite from the electrolysis cell after the electrolyzing and, after the transferring, receiving the selected weak acid in the electrolysis cell.

12. The method of claim 1 , further comprising generating, storing, or re-generating the solution of sodium hypochlorite in the electrolysis cell while the aqueous hypochlorous acid solution in a product tank is being consumed.

13. The method of claim 12 , further comprising regenerating the solution of sodium hypochlorite by re-electrolyzing the solution of sodium hypochlorite after storing for a predetermined time period, wherein the predetermined time period is at least twelve hours.

14. The method of claim 1 , further comprising

prior to the electrolyzing, directing a portion of the solution of sodium chloride from a NaCl tank to the electrolysis cell; and

after the electrolyzing, directing the solution of sodium hypochlorite into a product tank.

15. The method of claim 14 , wherein the NaCl tank, the electrolysis cell, and the product tank are all disposed in a housing.

16. A method for making an aqueous hypochlorous acid (HClO) solution, the method comprising

electrolyzing a solution of sodium chloride to produce a solution of sodium hypochlorite in an electrolysis cell, wherein the electrolysis cell comprises a first chamber, at least one positive electrode disposed in the first chamber, and at least one negative electrode disposed in the first chamber, wherein the solution of sodium hypochlorite is produced in the first chamber with the at least one positive electrode and the at least one negative electrode;

producing the aqueous hypochlorous acid solution by adjusting a pH of the solution of sodium hypochlorite to a value within a range of 3 to 8 by adding a selected weak acid to the solution of sodium hypochlorite to produce a buffer comprising the selected weak acid and a salt of the selected weak acid; and

using a level gauge to monitor a level of the aqueous hypochlorous acid solution in a product tank.

17. The method of claim 16 , further comprising repeating the electrolyzing and the producing in response to the level gauge.

18. The method of claim 16 , further comprising using a pH gauge to monitor a pH of the aqueous hypochlorous acid solution in the product tank.

19. The method of claim 11 , wherein the selected weak acid is acetic acid.

20. The method of claim 16 , wherein the solution of sodium hypochlorite after the electrolyzing has at least 500 ppm sodium hypochlorite.