Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Preparing nonmetal element
Patent
1994-12-30
1996-07-02
Niebling, John
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Preparing nonmetal element
204252, 204283, 204284, 204290R, 429 40, 429 42, C25B 100, C25B 1100
Patent
active
055318835
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a novel gas porous electrode, and in particular to an air or oxygen breathing cathode suitable for use in the generation of ozone.
BACKGROUND OF THE INVENTION
Ozone has a range of uses similar to that of chlorine, including the bleaching of clays and pulp and the treatment of drinking water swimming pool water, municipal secondary effluents, high quality water (eg for electronic component manufacturing) and odours. Because chlorine produces chlorinated organics, which present long term toxicity hazards at low concentrations in water, there is a large potential market for a less toxic replacement for chlorine. Ozone has the potential to take over from chlorine. In addition, ozone may be used in organic synthesis for the oxidation of the carbon-carbon double bond, medical therapy and serialization. Examples of chemical syntheses using ozone include the production of silver oxide, heliotropin, pelargonic acid, azelaic acid, peracetic acid, germicides, steroids, Nylon-9 precursor and the separation of cerium from other rare earths.
Ozone has a short half-life, and because of its highly reactive nature, tends to decompose in contact with most metals and oxides and is potentially explosive when concentrated either as a gas or liquid or when dissolved into solvents or absorbed into gels. Transportation therefore is not practical, and consequently it is desirable to generate ozone at the point of use. Currently, the major method of ozone generation adopted in industry and the utilities is corona discharge. In this process an alternating, very high voltage is discharged through a dry air or oxygen steam, producing a flow of gases containing up to approximately 2% ozone where an air stream is used, and up to approximately 4% ozone where oxygen is used. Corona discharge methods for ozone production have several disadvantages. In particular, the equipment required is capital intensive and bulky. In addition, the process requires the feed gas to be cleaned, compressed, cooled and dried before passing to the discharge tube. The use of oxygen rather than air where higher yields of ozone are required, adds significantly to the cost. The low ozone:oxygen ratios mean that dissolution of the ozone into water or other process medium is difficult, with low rates of transfer. An additional drawback is that appreciable amounts of nitrogen oxides are produced when an air feed is used, ultimately producing nitric acid if the output stream contacts water.
Another method of ozone generation is the electrolysis of water. In this process, water is electrolysed between an anode and a cathode. At the anode, oxygen and ozone are evolved as a mixture. The generation of ozone is most efficient at low temperatures. At the cathode, hydrogen may be evolved, or oxygen may be reduced at a gas porous air or oxygen depolarised cathode, reducing the overall voltage required to drive current through the cell.
Gas porous electrode technology is highly developed, and the general principals of gas porous electrode fabrication are well known to those skilled in the art [See Fuel Cell Handbook, A J. Appleby and F R Foulkes, Pub. Van Nostrand Reinhold, 1989: and references therein, EP 0357077A3, U.S. Pat. No. 4,564,427, U.S. Pat. No. 4,927,514]. In general terms, a gas porous electrode is an electronically conducting structure including a high-surface area body and a suitable catalyst. For example a catalyst layer and a hydrophobic support layer may be deposited on an electronically conducting substrate. Air or oxygen breathing cathodes are generally constructed so as to produce the maximum area of a three-phase interface, that is the maximum area of interface between the solid catalyst material, the electrolyte medium, and the gas phase (which in the case of ozone generation, is air or oxygen). This may be achieved by the admixture of the catalyst with a wet-proofing agent such as polytetrafluoroethylene (ptfe), or fluorinated ethylene propylene (fep), or a wax, etc. The partially wet-proofed catalyst
REFERENCES:
patent: 4927514 (1990-05-01), Solomon et al.
patent: 4980037 (1990-12-01), Hossain et al.
patent: 5300206 (1994-04-01), Allen et al.
patent: 5308465 (1994-05-01), Hillrichs et al.
Cameron Donald S.
Gascoyne John M.
Johnson Matthey Public Limited Company
Mayekar Kishor
Niebling John
LandOfFree
Electrode does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrode, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrode will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1503550