Three electrode electrolytic cell and method for making hypochlorous acid

1. A method comprising:

electrolyzing a source liquid in an electrolytic device comprising:

a first cathode in a cathode chamber; and

an anode and a second, auxiliary cathode in an anode chamber, wherein the anode chamber and cathode chamber are separated by a barrier and the anode and the auxiliary cathode are separated by a gap that lacks a barrier, the anode being positioned between the barrier and the second, auxiliary cathode; and

during the step of electrolyzing, adjusting a level of current applied to the auxiliary cathode by a control circuit in response to pH of an anolyte liquid produced from the source liquid by the anode chamber, the control circuit energizing the electrolytic device.

2. The method of claim 1 , further comprising:

measuring the pH of the anolyte liquid with a pH sensor along a liquid flow path downstream of the anode chamber.

3. The method of claim 1 , wherein the step of adjusting comprises adjusting the level of current applied to the auxiliary cathode by a control circuit within a closed process control loop with respect to the pH of the anolyte liquid.

4. The method of claim 1 , wherein the step of adjusting comprises adjusting the level of current applied to the auxiliary cathode by a control circuit within an open process control loop with respect to the pH of the anolyte liquid.

5. The method of claim 1 , wherein energizing electrolyzing comprises applying current to the first cathode, the auxiliary cathode and the anode simultaneously.

6. The method of claim 1 , wherein adjusting comprises:

measuring the pH of the anolyte liquid; and

adjusting the current applied to the auxiliary cathode so as to maintain the pH within a desired pH range.

7. The method of claim 6 , wherein adjusting comprises:

if the pH is less than a desired low pH threshold, increasing the level of current applied to the auxiliary cathode; and

if the pH is greater than a desired high pH threshold, decreasing the level of current applied to the auxiliary cathode.

8. The method of claim 1 , wherein the level of current applied to the auxiliary cathode is greater than a level of current applied to the first cathode during the steps of electrolyzing and adjusting.

9. The method of claim 1 , wherein:

electrolyzing comprises applying a substantially constant total current to the electrolytic cell; and

adjusting comprises adjusting a portion of the total current applied to the auxiliary cathode relative to a portion of the total current applied to the first cathode such that the total current applied to the electrolytic cell remains substantially constant.

10. The method of claim 1 , wherein adjusting comprises:

holding a level of current applied to the first cathode substantially constant during the step of electrolyzing; and

adjusting the level of current applied to the auxiliary cathode in response to the pH of the anolyte liquid.

11. The method of claim 10 , further comprising:

adjusting a concentration of salt in the source liquid to maintain a desired range of concentration of free chlorine in the anolyte liquid, in response to changes in the level of current applied to the auxiliary cathode.

12. A system for generating hypochlorous acid, the system comprising:

an electrolytic cell configured to receive a source liquid and comprising:

a first cathode in a cathode chamber; and

an anode and a second, auxiliary cathode in an anode chamber, wherein the anode chamber and cathode chamber are separated by a barrier and the anode and the auxiliary cathode are separated by a gap that lacks a barrier, the anode being positioned between the barrier and the second, auxiliary cathode; and

a control circuit comprising a pH control input and being configured to energize the electrolytic cell to produce an anolyte liquid from the source liquid in the anode chamber, the control circuit further being configured to adjust a level of current applied to the auxiliary cathode in response to the pH control input.

13. The system of claim 12 , further comprising:

a pH sensor, which is positioned to measure pH the anolyte liquid.

14. The system of claim 13 , wherein the control circuit comprises:

a closed-process control loop, which adjusts the level of current applied to the auxiliary cathode in response to pH measurements received by the pH control input from the pH sensor.

15. The system of claim 13 , wherein the control circuit comprises:

an open loop, which adjusts the level of current applied to the auxiliary cathode in response to control signals applied to the pH control input.

16. The system of claim 12 , wherein the control circuit is configured to apply current to the first cathode, the auxiliary cathode and the anode simultaneously.

17. The system of claim 12 , wherein the control circuit is configured to adjust the current applied to the auxiliary cathode so as to maintain pH of the anolyte liquid within a desired pH range.

18. The system of claim 17 , wherein the control circuit comprises circuitry configured to:

increase the level of current applied to the auxiliary cathode, if the pH is less than a desired low pH threshold; and

decrease the level of current applied to the auxiliary cathode, if the pH is greater than a desired high pH threshold.

19. The system of claim 12 , wherein the control circuit is configured to apply a greater level of current to the auxiliary cathode than to the first cathode while energizing the electrolytic cell and adjusting the level of current applied to the auxiliary cathode.

20. The system of claim 12 , wherein the control circuit comprises:

a constant current source, configured to apply a substantially constant total current to the electrolytic cell; and

a current proportioning circuit, which adjusts a portion of the total current applied to the auxiliary cathode in response to the pH control input, relative to a portion of the total current applied to the first cathode such that the total current applied to the electrolytic cell remains substantially constant.

21. The system of claim 12 , wherein the control circuit comprises:

a first current source configured to apply a substantially constant level of current to the first cathode; and

a second current source configured to adjust the level of current applied to the auxiliary cathode in response to the pH control input, while the level of current applied to the first cathode remains substantially constant.

22. The system of claim 21 , further comprising:

a water line configured to receive water;

a first brine line configured to receive a first brine solution;

a pump configured to move the first brine solution through the first brine line, wherein the pump is controlled by the control circuit based on the level of current applied to the auxiliary cathode; and

a mixing location configured to receive the water and the first brine solution from the water line and the first brine line, and to output a mixture of the water and the first brine solution as the source liquid.

23. The system of claim 12 , wherein the barrier is formed of a hydrophilic microporous material that conducts electrical current between the anode chamber and the cathode chamber and does not act as an ion exchange membrane.