TITLE OZONE PRODUCTION FROM COs FIELD OF THE INVENTION The present invention relates to the production of ozone using substantially pure carbon dioxide.

BACKGROUND OF THE INVENTION In the commercial production of ozone, oxygen or air of high purity is fed to an ozone generator. The atoms of the oxygen molecule dissociate under the influence of an energy source and recombine as ozone.

Ozone is produced in commercial quantities primarily by two processes: electronic (corona discharge) and photochemical (ultraviolet light). Other methods include high-density electrolysis of aqueous phosphate solution and irradiation of oxygen with (3-or y-rays from a nuclear reactor or from radioactive isotopes.

Zadok, et al have shown that oxygen atoms can be generated by treatment of carbon dioxide with microwave radiation. By generating the oxygen atoms in the presence of an olefin absorbed on silica gel, oxidation products of the olefin can be produced. See, Nouveau Journal de Chimie, 6,695 (1982). Willis and Bindner report the production of ozone from carbon dioxide by irradiation at high dose rates (1026-1027 eV g-1 s-1).

See, Can. J. Chem. 48,3463 (1970). Another study shows that a small amount of ozone is produced during operation of a transversely excited atmospheric COz laser. See, J. App. Phys. 62,1585 (1987).

Generation of ozone from air is problematic when the ozone is to be used in chemical applications. Some of the nitrogen in the air may be converted to nitrogen

oxides that can react with certain chemicals to form undesirable nitrated products. When high purity oxygen is converted to ozone, the conversion does not exceed 20 percent in even the most efficient ozone generators.

When the ozone-containing gas stream is used for a chemical application, the ozone is nearly totally consumed. This leaves behind an oxygen-containing gas mixture in contact with organic materials, which may create an explosion hazard. In contrast, because the present invention utilizes substantially pure carbon dioxide--rather than oxygen--a potentially explosive gas containing oxygen and organic materials cannot result after the ozone is consumed.

SUMMARY OF THE INVENTION The present invention is a process for the production of ozone by passing substantially pure carbon dioxide between at least one pair of electrodes, the at least one pair of electrodes having a voltage difference between them sufficient to cause a corona discharge across them.

DETAILED DESCRIPTION OF THE INVENTION The present invention is a process for the generation of ozone. In the present invention, substantially pure carbon dioxide, COs, can be fed to a commercially available ozone generator to produce ozone. Currently, two methods are used to produce ozone in commercial quantities: corona discharge and ultraviolet light. The present invention involves the use of corona discharge.

Corona discharge involves passing a gas between two electrodes having an alternating voltage applied across them. Commonly, the positive electrode consists

of glass [typically borosilicate glass] with a thin metal electrode [typically aluminum, Nichrome, or silver-plate] etched or otherwise placed on the glass surface. The negative ground electrode is typically a metal electrode such as stainless steel. Often a commercial corona discharge unit will contain multiple positive electrode and ground electrode pairs. If the gas passed between an electrode pair is carbon dioxide, the voltage applied to the electrode pair may be from about 5 to 20 kV at 50-3000 Hz. Low voltage has an advantage of simplicity and reliability. Higher voltage often provides greater power efficiency.

Commercial ozone generators may be single-or double- fluid-cooled generators. See, Ozone News 26 (5), 33 (1998), Kirk-Othmer Encyclopedia of Chemical Technology, vol. 17,970 (1996).

The term"substantially pure carbon dioxide,"as used herein, is meant to denote carbon dioxide having less than about 5% oxygen by weight. Other gases, such as argon and helium, also may be present. In general, the amount of oxygen in the carbon dioxide feedstock should be kept below the explosive limit for any system (reactor in which the ozone/oxygen mixture is reacted with chosen reactants, vapor space of the gas exiting the reactor, etc.).

Once the ozone is produced, it is important to react it quickly. In the case of water treatment, one method of reaction involves the use of a dispersing device to provide small bubbles of ozone into circulation water. Another method is injection of the ozone into a circulating side stream of the water.

Organic compounds such as cycloalkanes and cycloalkenes can be reacted with ozone to produce ketone and alcohol products. For example, cyclohexane

can be reacted with ozone to produce a mixture of cyclohexanone and cyclohexanol.

Diacids can be produced by reaction of cycloalkenes, cycloalkanones, or cycloalkanols with ozone. In particular, Cg-Cis cycloalkenes, cycloalkanones, or cycloalkanols are preferred.

Particularly preferred are the C6 and C12 compounds, because their reactions produce important nylon intermediates--adipic acid and dodecanedioic acid.

The invention is illustrated by the following nonlimiting examples.

EXAMPLES Example 1 Ozonolysis of Cyclododecene with Ozone Produced from Carbon Dioxide in an Ozone Generator.

This example illustrates the ozonolysis of cyclododecene with ozone produced in accordance with the present invention to an ozonide intermediate, its subsequent rearrangement to 12-oxo-dodecanoic acid and further oxidation to dodecanedioic acid, a valuable nylon intermediate.

Ozone was generated with a ClearWater Tech, Inc.

Corona Discharge ozone generator Model M-1500 (240 V, 50/60 Hz, and 1.0 amps). Carbon dioxide gas from a cylinder was fed to the ozone generator at 100 cubic centimeters per minute. The carbon dioxide was obtained from MG Industries, Malvern, PA. It analyzed 99.99% minimum CO2. After exiting the ozone generator, the gas stream was analyzed for ozone level with an Ozone Monitor Model HC-NEMA 12 manufactured by PCI Ozone & Control Systems, Inc., West Caldwell, NJ.

After the ozone concentration reached a steady state,

the stream was redirected to a reaction vessel. The reactor was a cylindrical vessel with a tube through which the ozone-containing gas stream was introduced that reached nearly to the bottom of the vessel. On the end of the tube was a cylindrical fritted glass gas dispersion tube. The gas exiting the reactor was directed to a gas-washing bottle with a cylindrical fritted glass gas dispersion tube. The gas-washing bottle contained a 2% solution of potassium iodide.

When the material being ozonized in the reaction vessel was consumed, ozone passed through to the washing bottle and oxidized iodide to iodine, imparting a yellow color to the solution. The gas stream was then redirected to the ozone monitor to re-check its concentration in the gas stream.

The reaction vessel was charged with 35 grams of acetic acid and 6.0 grams of cyclododecene, which analyzed 96.8% cyclododecene and 2.5% cyclododecane.

Gas from the ozone generator, as described above, was passed through the reactor. The temperature of the reactor was kept between 20 and 24°C during the run.

After 1020 minutes the solution of potassium iodide turned yellow, indicating that the ozone was no longer being totally consumed. The average ozone concentration, calculated as the average of the readings on the Ozone Monitor at the start and at the conclusion of the experiment, was 0.905%. The vessel containing the ozonolysis product was then heated to at 80°C while oxygen gas was passed through the cylindrical fritted glass gas dispersion tube for a period of 3 hours. This procedure was necessary to completely oxidize the ozonide and aldehyde intermediate products to acidic products. On cooling a solid precipitated out. The solid was separated by

filtration and dried in a vacuum oven at 80°C for 18 hours. The dried solid product contained 3.00 grams of dodecanedioic acid as determined by calibrated liquid chromatography. The liquid filtrate resulting from the separation of the solid product weighed 16.72 grams and contained 0.67 grams dodecanedioic acid by calibrated Gas Chromatographic analysis. The yield of dodecanedioic acid from cyclododecene was 45.6%.

Example 2 Comparative This example illustrates the ozonolysis of cyclododecene with ozone generated from carbon dioxide containing a substantial amount of oxygen, rather than ozone generated from substantially pure carbon dioxide, in a corona discharge ozone generator.

The reaction setup described in Example 1 was charged with 6.0 grams of cyclododecene, which analyzed 96.8% cyclododecene, the balance being mainly cyclododecane and 35 grams of acetic acid. The gas fed to the ozone generator was obtained from MG Industries, Malvern, PA. It analyzed 19.9% oxygen, the balance being C02. Gas from the ozone generator, as described above, was passed through the reactor. The temperature of the reactor was kept between 18 and 22°C during the run. After 263 minutes the solution of potassium iodide turned yellow indicating that the ozone was no longer being totally consumed. The average ozone concentration, calculated as the average of the readings on the Ozone Monitor at the start and at the conclusion of the experiment, was 3.57%. The ozonolysis product was then heated to at 80°C while oxygen gas was passed through the cylindrical fritted glass gas dispersion tube for a period of 3 hours. On

cooling a solid precipitate out. The solid was separated by filtration and dried in a vacuum oven at 80°C for 18 hours. The dried solid product contained 3.34 grams of dodecanedioic acid as determined by calibrated liquid chromatography. The liquid filtrate resulting from the separation of the solid product was found to contain an additional 1.07 grams of dodecanedioic acid. The yield of dodecanedioic acid from cyclododecene was 59.79%.

Example 3 Ozonolysis of Oleic Acid with Ozone Produced from Carbon Dioxide in an Ozone Generator.

This example illustrates the ozonolysis of oleic acid with ozone produced in accordance with the present invention to an ozonide intermediate and its subsequent rearrangement and further oxidation to nonanoic acid and azelaic acid. Azelaic acid is a valuable nylon intermediate that is commercially produced by conventional ozonolysis by Emery Industries of Cincinnati, Ohio.

The reaction setup and experimental procedure described in Example 1 were followed. The reactor was charged with 10.89 grams of oleic acid, which analyzed 89.99% oleic acid and 35 grams of acetic acid. Gas from the ozone generator was passed through the reactor for 1262 minutes. The average ozone concentration was calculated to be 0.89%. After the 3 hour oxygen oxidation at 80°C a clear solution was obtained which contained 0.15 grams of oleic acid, 3.85 grams nonanoic acid and 4.74 grams of azelaic acid, as determined by calibrated Gas Chromatographic analysis. The yield of azelaic acid from oleic acid was 73.18%.

Example 4 Comparative This example illustrates the ozonolysis of oleic acid with ozone generated from carbon dioxide containing a substantial amount of oxygen, rather than ozone generated from substantially pure carbon dioxide, in a corona discharge ozone generator.

The reaction setup and experimental procedure described in Example 1 were followed. The feed gas to the ozone generator contained 19.9% oxygen, as in Example 2. The reactor was charged with 10.89 grams of oleic acid, which analyzed 89.99% oleic acid and 35 grams of acetic acid. The gas stream from the ozone generator was passed through the reactor for 318 minutes. The average ozone concentration was calculated to be 3.47%. After the 3 hour oxygen oxidation at 80°C a clear solution was obtained which contained 0.16 grams of oleic acid, 4.07 grams nonanoic acid and 4.97 grams of azelaic acid, as determined by calibrated Gas Chromatographic analysis. The yield of azelaic acid from oleic acid was 76.42%.