OZONE GENERATION METHOD AND OZONE GENERATION DEVICE

Abstract

An ozone generation method comprising: Supplying a crude feed gas comprising oxygen and methane Performing a catalytic oxidation of methane from the crude feed gas to obtain a treated feed gas Generating ozone from the treated feed gas.

Claims

1. An ozone generation method comprising: Supplying a crude feed gas comprising oxygen and methane Performing a catalytic oxidation of methane from the crude feed gas to obtain a treated feed gas Generating ozone from the treated feed gas.

2. The ozone generation method according to claim 1, comprising the additional step of heating the crude feed gas to a temperature of at least 150° C. and at most 700° C. before and/or during performing the catalytic oxidation of methane from the crude feed gas to obtain a treated feed gas.

3. The ozone generation method according to claim 2, further comprising the additional steps of: Recovering at least a part of the heat from the treated feed gas Heating the crude feed gas with the recovered heat before and/or during the heating of the crude feed gas to a temperature of at least 150° C. and at most 700° C.

4. The ozone generation method according to claim 1, wherein the catalytic oxidation is performed with a catalyst chosen among palladium, platinum and platinum-palladium.

5. The ozone generation method according to claim 1, comprising the additional step of drying the treated feed gas to remove at least some water before generating ozone from the treated feed gas.

6. The ozone generation method according to claim 1, comprising the additional step of cooling the treated feed gas before generating ozone from the treated feed gas.

7. The ozone generation method according to claim 1, comprising the additional step of cooling the ozone generator with a cooling liquid.

8. The ozone generation method according to claim 6, wherein the step of cooling the treated feed gas is performed with at least part of the cooling liquid outputted from the ozone generator.

9. An ozone generation device, comprising: A supply of a crude feed gas comprising oxygen and methane A catalytic unit adapted to perform a catalytic oxidation of methane from the crude feed gas to obtain a treated feed gas An ozone generator adapted to be fed by the treated feed gas.

10. The ozone generation device according to claim 9, further comprising a heating unit adapted to heat the crude feed gas and/or the catalytic unit to at least 150° C. and at most 700° C.

11. The ozone generation device according to claim 10, further comprising a heat exchanger adapted to recover at least part of the heat from the treated feed gas and to heat the crude feed gas and/or the catalytic unit with the recovered heat.

12. The ozone generation device according to claim 9, further comprising a drying unit adapted to remove at least some water from the treated feed gas.

13. The ozone generation device according to claim 9, further comprising a cooling unit adapted to cool the treated feed gas.

14. The ozone generation device according to claim 9, wherein the ozone generator is adapted to be cooled by a cooling liquid.

15. The ozone generation device according to claim 9, further comprising circulation means adapted to circulate toward the cooling unit at least part of the cooling liquid outputted from the ozone generator.

16. The ozone generation device according to claim 9, wherein the catalytic unit comprises a catalyst chosen among platinum-palladium and platinum-palladium.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Further advantages and preferred embodiments of the present invention will become apparent from the following detailed description and drawing, in which:

[0050] FIG. 1 is a schematic view of an ozone generation device according to the present invention

[0051] FIG. 2 shows a graph of a value of peak absorption (Y-axis) of the methane at 3020-3010 cm.sup.−1 in the treated feed gas, as a function of the temperature of the crude feed gas during the step of catalytic oxidation (X-axis).

[0052] FIG. 3 shows an IR transmission spectrum of the treated feed bas, at different temperatures of the crude feed gas during catalytic oxidation.

DETAILED DESCRIPTION

[0053] The present ozone generation method and ozone generation device are intended to be used in all places and for all applications requiring ozone. For example, ozone can be used for disinfecting, deodorizing, sanitizing, cleaning, killing insects or parasites or as a raw material for the chemical industry. The present ozone generation device can be installed in a fixed location, for example as part of a dedicated industrial facility, such as a water treatment plant. Alternatively, the present ozone generation device can be mobile, for example as a mobile agricultural treatment unit or into a cruising ship for laundry cleaning and/or swimming pool sanitation.

Ozone Generation Device

[0054] Now referring to FIG. 1, the ozone generation device according to the present invention comprises a crude feed gas input A as a supply, a catalytic device 10, an ozone generator 20 and an ozone output B.

[0055] The catalytic device 10 may comprise a heat exchanger 11, a heating unit 12 and comprises a catalytic unit 13. In addition, the catalytic device 10 may further comprise a cooling unit 14.

[0056] Downstream the catalytic device 10, a mixer 30 and a drying unit 40 can be placed upstream the ozone generator 20.

Ozone Generation Method

[0057] A crude feed gas can be produced by a conventional method and consists essentially of oxygen, for example more than 99.9% v/v of oxygen. The crude feed gas may be contaminated by a tiny amount of methane, for example less than 0.1% v/v of methane and usually 10 to 100 ppm. Non-reactive gas such as nitrogen and/or argon may also be present into the crude feed gas for example below 10% v/v.

[0058] Such a crude feed gas is fed into the gas circuit of the ozone generator by the crude feed gas input A at a relative pressure of 0.1 to 1.5 MPa and preferably 0.2 to 1.0 MPa and is then treated by the catalytic device 10.

[0059] The crude feed gas can be heated in an optional preheating step into the heat exchanger 11 and then in an optional but preferred heating step in the heating unit 12. The crude feed gas can be brought to room temperature if it is colder and preferably to a temperature of at least 150° C., preferably at least 200° C., again preferably at least 220° C. and at most preferably 300° C. or 340° C. In order to save costs and to preserve the environment, the crude feed gas temperature is at most 700° C., preferably at most 530° C. and again preferably at most 440° C.

[0060] The heated crude feed gas is then treated into the catalytic unit and a catalytic oxidation of methane can occur according to the following equation:

CH.sub.4+O.sub.2.fwdarw.CO.sub.2+H.sub.2O

[0061] Due to the catalysis performed into the catalytic unit and the important proportion of oxygen in view of methane, a very quick oxidation reaction can occur, thus removing or decreasing the proportion of methane into the treated feed gas in view of the crude feed gas.

[0062] After treatment into the catalytic unit 13, the treated feed gas is optionally introduced again into the heat exchanger 11 in order to recover heat from the treated feed gas and to perform the optional preheating step of the crude feed gas, thus increasing the global energetic efficiency of the catalytic device.

[0063] The treated feed gas may then be cooled into the cooling unit 14. The cooling unit 14 can be either part of the catalytic device 10 as shown in FIG. 1 or be outside the catalytic device 10. After cooling, the treated feed gas has a temperature of room temperature to 70° C., preferably room temperature to 50° C.

[0064] The cooled treated feed gas may then be introduced into a mixer 30 comprising a gas input C in order to introduce air or nitrogen into the treated feed gas.

[0065] The mixed treated feed gas can then be dried into the drying unit 40, in order to remove at least some and preferably most or all the water contained into the treated feed gas. This water may come from the catalytic oxidation of methane and/or from the air or nitrogen introduced by the mixer 30.

[0066] The dried treated feed gas, outputted from the drying unit 40 can then be introduced into the ozone generator 20 in order to produce ozone, outputted by ozone output B to any ozone application.

[0067] The ozone generator can be cooled by a cooling liquid such a water, fed by cooling liquid input D. Preferably, the cooling liquid may also be used as a cooling liquid for the cooling unit 14, as shown in FIG. 1, in order to limit the flow of wasted cooling liquid.

Catalytic Unit

[0068] The catalytic unit 13 is preferably an inflow cartridge, for example made of stainless steel and partially filled with a catalyst adapted to catalyse oxidation of methane.

[0069] Generally speaking, the catalyst can be selected from platinum, palladium, ruthenium, rhodium, rhenium, chromium, cobalt, copper, gold, under pure form or as oxide, and their combinations.

[0070] The catalyst may be supported on an appropriate support such as alumina or carbon, and preferably a ceramic support such as alumina. Ceramic support other than alumina includes ZnAl.sub.2O.sub.4 spinel, silica and silicate.

[0071] Examples of catalyst comprise lanthanum and ruthenium oxide, such as La.sub.3.5Ru.sub.4.0O.sub.13 supported on alumina, platinum, palladium, platinum palladium or rhenium supported on alumina, gold, cobalt oxide such as Co.sub.3O.sub.4 supported on alumina, chromium oxide such as ZnCrO.sub.4, CuCrO.sub.4, PbCrO.sub.4 or Cr.sub.2O.sub.3 supported on alumina, copper oxide supported on alumina and manganese oxide such as La.sub.0.6Sr.sub.0.4MnO.sub.3.

[0072] A preferred catalyst consists of palladium supported on alumina or palladium-platinum supported on alumina. The catalyst may be placed as a bulk powder, as a granular material or as a honeycomb structure into the catalytic unit.

[0073] The catalytic unit may be heated for example by an electrical resistor to at least 150° C., preferably at least 200° C., again preferably at least 220° C. and at most preferably 300° C. or 340° C. In order to save costs and to preserve the environment, the crude feed gas temperature is at most 700° C., preferably at most 530° C. and again preferably at most 440° C.

[0074] The catalytic unit 13 may be dimensioned according to the flow rate of crude feed gas, the amount of methane into the feed gas and the selected catalyst.

Cooling Unit, Heating Unit and Heat Exchanger

[0075] The heat exchanger 11 may be tubular and may use heat recovered from the treated feed gas. Alternatively, the heat exchanger 11 may be replaced by a simple heater based on power supply, on an external hot fluid or on a liquid fuel.

[0076] The heating unit 12 may use power such as an electrical resistor, an external hot fluid or a liquid fuel. For example, the heating unit 12 may be a heat exchanger of the same kind as the heat exchanger 11. Alternatively or in combination, the heating unit 12 may be integrated to the catalytic unit 13. Alternatively or in combination, the heat exchanger 11 and the heating unit 12 may be the same unit performing both heat recovery from the treated heat gas and heating the crude feed gas by additional heating means.

[0077] Finally, the cooling unit may comprise a tubular liquid-gas heat exchanger using as a cooling liquid: cold water, tap water or any cooling liquid outputted from the ozone generator such as water. Preferably, the cooling unit decreases the temperature of the feed gas to 100° C. or less, preferably 75° C. or less and again preferably 50° C. or less, or even to room temperature.

Drying Unit

[0078] The drying unit 40 is intended to remove at least part of the water contained in the treated feed gas and may be based on the capture of water molecules into or on a specific material, for example by sorption. For example, the dry material could be an adsorbent such as zeolites, molecular sieves, alumina, silica gel or activated carbon.

[0079] In this case, a regeneration system 41 comprising an air input E, a compressor and a heater could be used for periodic regeneration of the drying unit 40.

[0080] Alternatively, water removal could be performed by condensing water under low temperature for example in a condensing unit adapted to decrease temperature of the feed gas. This condensing unit could be the same unit as the above cooling unit.

Ozone Generator

[0081] Ozone generator 20 may be based on any ozone generation method and preferably on corona discharge. Other kinds of ozone generation methods comprise ultraviolet light and cold plasma, all of them providing advantageous results as part of the present invention.

[0082] Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitations, the scope of the present invention being limited only by the terms of the appended claims.

[0083] In particular, it is clear that the ozone generation device of FIG. 1 comprises all required valves, controllers and sensors, as known by the skilled person. It is also clear that the required safety equipment linked with the feed gas, the ozone produced or the heating temperature may be added to the present ozone generating device.

EXAMPLES

[0084] In a first example, a 500 cubic centimetre (cc) cartridge filled with platinum supported on alumina achieved 100% methane oxidation of 250 cc/s crude feed gas comprising up to 100 ppm methane at a temperature of 400° C. The residence time of the feed gas into the cartridge, i.e. the time required for the feed gas to pass through the cartridge is at most 10 s, preferably at most 3 s and again preferably 1 or 2 s.

[0085] The same catalytic unit achieved 75 to 80% of methane oxidation in a similar experiment performed with a crude feed gas at room temperature.

[0086] In a second example, a crude feed gas comprising oxygen and 40 to 70 ppm of methane was injected in a catalytic unit at a pressure of 5.5 Bar-g and a flow rate of 750 N dm.sup.3/s. The catalytic unit consisted in a cylindrical vertical pipe of a diameter of 41.8 mm (DN40) and a volume of 150 ml. Catalyst under the form of 2-4 mm alumina spheres loaded with Palladium was introduced in the catalytic unit. The residence time of the crude feed gas into the catalytic unit was 1.8 s. The crude feed gas was heated to temperatures of 60° C., 130° C., 200° C., 220° C., 280° C., 340° C. and 410° C.

[0087] The proportion of methane into the treated feed gas was followed thanks to an infrared spectrometer and the absorption of methane was monitored at a wavenumber of 3020-3010 cm.sup.−1 (wavelength of 3311 to 3322 nm).

[0088] As visible in FIG. 2 showing values of the peak absorption of methane at 3020-3010 cm.sup.−1 in the treated feed gas, according to various temperature of the crude feed gas, the absorption of methane, initially at 3% below 200° C. progressively decreases from 200° C. to reach almost 0% (no absorption) at 340° C. and above.

[0089] In addition, a scaled tanh curve has been fit to the measured values (dashed line), showing the tendency of the reduction of methane in the treated feed gas and such a reduction is significant at a temperature of at least 220° C. and very significant at a temperature of at least 300° C. The oxidation of methane is almost completed at a temperature of 340° C. and fully completed at a temperature of 410° C.

[0090] In FIG. 3, the absorption peak of methane at a wavenumber of 3020-3010 cm.sup.−1 in the treated feed gas after catalytic oxidation at 350° C., 440 and 530° C. is directly plotted at the same scale versus the absorption peak of the crude feed gas. Before treatment, the crude feed gas shows an important absorption peak and the area of the peak is very significantly reduced at catalytic oxidation temperature of 350° C. At temperatures of 440° C. and 530° C., methane absorption is not visible anymore and the treated feed gas is thus free of methane.