Improved electrochemical systems for generating ozone (in gaseous form and/or dissolved in water) have been invented for use in disinfection and in industrial processes in which the unique, highly oxidizing chemical properties of ozone are needed. More accurately, these systems generate oxygen along with high (relative to prior systems) concentrations of ozone and, optionally, with hydrogen as a byproduct. These systems contain no pumps and very few moving or wearing components, and the only inputs needed to operate these systems are electric energy and water supplied at mild pressure. Moreover, these systems can readily be designed and constructed on any scale (e.g., from research laboratory to industrial) to suit a wide variety of applications.
A basic system of this type (see figure) includes a power supply, an ozone-generator/anode-reservoir unit, a cathode phase separator, and a gas-destruction unit. At the bottom of the anode reservoir lies the active part of the ozone generator, which preferably is an electrolytic cell that contains a proton-exchange membrane with a porous anode on its upper face and a porous cathode on its lower face. A catalyst on the anode promotes the electrolytic production of oxygen and ozone, some of which dissolves into the water in the anode reservoir. The anode reservoir also serves as part of a liquid/gas separator, wherein oxygen and ozone generated at the anode form into bubbles or diffuse from the water and rise to the top of the reservoir. The rest of this phase separator is a hydrophobic membrane at the top of the reservoir that allows the O2 and O3 gases, but not water, to pass through to the top side. The mixture of O2 and O3 gases can be fed either to an O3-consuming process or to the gas-destruction unit.
A tube connects the cathode with the cathode phase separator. A hydrophobic membrane in the cathode phase separator allows hydrogen gas, but not water, to pass through to the top side. Hydrogen gas from the dry (top) side of the membrane is either sent to the gas-destruction unit or discharged to a hydrogen-consuming external process. Preferably, water that has been transferred from the anode to the cathode by electroosmosis is returned from the bottom of the cathode phase separator to the input (top) end of the anode reservoir through the tube depicted as the longest in the figure.
The source of water is connected directly to the anode reservoir. The liquid/gas-separator membranes make it possible for the water from the source to displace any gases from anode reservoir and from the lower compartment of the anode phase separator. Once these gases have been displaced, the water comes into direct contact with these membranes and the transfer of water ceases as the pressures in the anode reservoir and cathode phase separator equalize with the pressure in the source of water. Provided that the pressure in the source equals or exceeds the pressure in the anode reservoir, the anode reservoir and the cathode phase separator remain full of water during all phases of operation.
Preferably, a cooling unit (e.g., comprising heat spreaders, thermoelectric devices, and a heat sink) is attached to the anode reservoir to remove waste heat and to chill the reservoir in order to reduce the rate of degradation of dissolved ozone and increase the solubility of ozone in the water. The output stream of ozonated water is taken from just above the anode at the bottom of the anode reservoir.
The gas-destruction unit includes a source of combustion air, a hydrogen/air-mixing region, a hydrogen-destruction zone that contains a hydrogen/air-combustion catalyst, an air/ozone-mixing region, and an ozone-destruction region that contains an ozone-destruction catalyst. The products of the gas-destruction unit are vented and/or drained.
This work was done by Oliver J. Murphy, Craig C. Andrews, and Thomas D. Rogers of Lynntech, Inc., for Johnson Space Center.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to
7610 Eastmark Drive
College Station, TX 77840
Tel. No: (409) 693-0017
Fax No: (409) 764-7479
Refer to MSC-23046, volume and number of this NASA Tech Briefs issue, and the page number.