Method of photocatalytic gas purification

FIELD: physical or chemical processes and apparatus.

SUBSTANCE: method comprises saturating the initial gas mixture that is comprises agents to be oxidized with vapors of hydrogen peroxide. The photocatalyst is made of pure titanium dioxide that contains one or several transition metals.

EFFECT: expanded functional capabilities and enhanced efficiency.

7 cl, 2 dwg, 1 tbl, 11 ex

 

The invention relates to the field of photocatalytic purification of gases, including air, various devices using the principle of oxidation of organic and inorganic substances adsorbed on the surface of the photocatalyst under ultraviolet light with wavelength less than 400 nm.

Photocatalytic purification of gases and, in particular, air is widely known. In the works of A. Fujishima, K. Hashimoto, T. Watanabe "TiO2Photocatalysis: Fundamentals and Application", Bkc, Inc. 1999, and D. F. Ollis, H. Al-Ekabi "Photocatalytic Purification and Treatment of Water and Air, Elsevier 1993 described the field of application of photocatalytic methods of purification of gases.

The main disadvantages photocatalytic methods of cleaning gases are: 1) relatively low speed of treatment compared with other methods (adsorption, incineration) and 2) a rapid decline in the activity of the photocatalyst in the degradation of aromatic and heteroatomic organic compounds.

Closest to the proposed method is a method for photocatalytic treatment of gas and air, by which the cleaning is carried out in the presence of the photocatalyst, which is a titanium dioxide of the anatase modification, deposited on a porous carrier, made in the form of tubes, plates, shells, etc. (U.S. Pat. RF 2151632, B 01 D 53/86, B 01 J 21/06, 27.06.2000).

The disadvantages of this method are: 1) relatively Neva is okay speed of treatment and 2) the rapid decline in the activity of the photocatalyst in the degradation of aromatic and heteroatomic organic compounds

The invention solves the problem of increasing the efficiency of the photocatalytic purification of gases, including air.

The problem is solved by the method of purification of gases, including air, oxidation using a photocatalyst, in which the source gas mixture containing oxidizable substances, saturated with vaporized hydrogen peroxide.

As the photocatalyst used pure titanium dioxide crystal structure of anatase or titanium dioxide, containing one or more transition metals.

As a photocatalyst is used, preferably, titanium dioxide crystal structure of anatase containing one or more transition metals. Transition metals contained in the photocatalyst, are preferably platinum or palladium, or any mixture.

The feeding of the gas to be purified pairs of hydrogen peroxide is carried out in a special unit. The unit can be made in the form of an open heated container filled with an aqueous solution of hydrogen peroxide, or in the form of parallel layers of fabric impregnated with an aqueous solution of hydrogen peroxide, located in the saturated flow of the source gas, or in the form of nozzles, spraying an aqueous solution of hydrogen peroxide in the saturated flow of the source gas.

Photocatalytic method for the oxidation of substances is based on the following principle. When the absorption of quanta of ultraviolet radiation with a wavelength less than 400 nm photocatalyst formed electron-hole pairs. The generated holes have a high oxidative potential of about +3. In respect to the standard hydrogen electrode. Holes can either directly oxidize the adsorbed molecules, or to interact with the adsorbed hydroxyl groups with the formation of the strong oxidant - hydroxyl radicals (OH), which, in turn, oxidizes the adsorbed molecules of organic substances. Thus, HE formed radicals are the main oxidizing agents.

It is also known that the number HE formed radicals is determined, including the intensity incident on the catalyst UV radiation. Since the power sources of UV radiation used in domestic and industrial air cleaning devices is limited, this leads to the fact that the rate of oxidation of organic matter also has its limit. In addition, the oxidation of aromatic and heteroatomic organic compounds are often formed prone intermediates that lead to a General drop in the rate of oxidation on the catalyst and its decontamination. Reactivation of the catalyst requires a large amount of time (tens of hours), during which p is the psi should work in clean air. This poses a technical problem and leads to excessive costs on the regeneration of the catalyst.

In the present invention is proposed to solve the problem by introducing into the reaction system, a powerful additional source HE radicals, such as hydrogen peroxide. Molecules of hydrogen peroxide can decompose on the surface of titanium dioxide under the action of UV light and spontaneously, leading to the formation of additional quantities HE radicals. This increases the rate of oxidation of organic substances and dramatically reduces the deactivation of the catalyst. The preferred photocatalyst when working in the presence of vapors of hydrogen peroxide is titanium dioxide, doped with transition metals, since these elements dramatically accelerate the process of destruction of hydrogen peroxide due to its interaction with d-orbitals, electron shells.

This invention allows to widen the application of photocatalytic air cleaning devices, because it allows to maintain the efficiency of such devices in a wider range of concentrations of pollutants.

It is known that the vapor pressure of hydrogen peroxide over 35% aqueous solution is about 1 mm Hg at room temperature. Thus, the introduction of vapor peroxidation in contaminated air mixture can be performed in the following way. In the stream of air directly in front of the photocatalytic unit air purifier include a unit dosage of hydrogen peroxide (see Figure 1, block 4). Block constructively can represent:

1. Wide flat open vessel type Petri dishes, which is continuously fed an aqueous solution of hydrogen peroxide from a special tank. The air flow continuously blows this capacity and saturated vapors of hydrogen peroxide. To speed up the evaporation process and, accordingly, increase the concentration of hydrogen peroxide at the entrance to the photocatalytic purifier unit air capacity can be heated up to the boiling point of hydrogen peroxide solution. The material from which made the capacity of the evaporator, should be inert to the reaction of decomposition of hydrogen peroxide. It can be various types of glass, quartz or Pyrex; Teflon or other plastics that are resistant to the action of hydrogen peroxide at elevated temperatures.

2. The cloth or fabric that is resistant to the action of hydrogen peroxide at an elevated temperature, and inert to the reaction of its decomposition. For example, different types of fabrics, special varieties of asbestos or polymer fabrics. Such fabric is impregnated with an aqueous solution of hydrogen peroxide, for example, by the action Capella the governmental forces or irrigation surface of the nozzle. The moistened fabric is placed either parallel to the air flow several layers, or perpendicular. Further, due to the evaporation occurs, the saturation of air passing over / through cloth, vaporized hydrogen peroxide. To intensify the process of evaporation cloth or passing the air can be heated. This method allows you to more effectively saturate the air with vaporized hydrogen peroxide through improved surface contact of air with the solution than in the previous case.

3. Nozzle, spray an aqueous solution of hydrogen peroxide in the flow of the passing air. The air can be heated to improve the evaporation of the droplets of the feed solution.

In many cases, water vapor, forming part of vapor hydrogen peroxide solution, also lead to some increase in the rate of photocatalytic oxidation due to the formation of additional hydroxyl cover the catalyst surface.

As the photocatalyst in the present invention use a pure titanium dioxide crystal structure of anatase or titanium dioxide, containing one or more transition metals, preferably titanium dioxide crystal structure of anatase containing one or more transition metals, transition metals contained in the photocatalyst, the site which are preferably platinum or palladium, or any mixture.

Titanium dioxide, as well as modified titanium dioxide have such a high activity for the decomposition of hydrogen peroxide, so that a pair of N2O2added to air mixture in a unit dosage vapor hydrogen peroxide, are completely decomposed in the photocatalytic unit and extending from the device, clean the air, completely free from the fumes of hydrogen peroxide.

Figure 1 presents an example of a possible design photocatalytic air purifier equipped with a dosing of hydrogen peroxide: 1 - fan 2 - heat; 3 - pump; 4 - dosing of hydrogen peroxide; 5 - ceramic substrates with a photocatalyst; 6 - UV lamp.

Presented Fig. the dosing of hydrogen peroxide is schematically depicted in the form of block 4 and constructively can be any of these options.

The principle of operation of this device consists in the following. Polluted air is supplied to a fan (1), passes through the heat exchanger (2) and is heated. Then he gets into the unit-dispenser (4) and saturated vapors of hydrogen peroxide. Then there is the air cleaning section including a ceramic honeycomb carrier of the photocatalyst (5) and UV lamps (6). When you go outside the purified air gives up some of the heat received from the UV lamps, the heat exchanger (2). Circulation talonite the I between the heat exchangers is carried out using a pump (3).

The invention is illustrated by the following examples.

The invention is illustrated by the example of oxidation vapor diethylsulfide C2H5SC2H5in a static reactor. The location and appearance of the equipment for this experiment are presented in figure 2.

In the reactor (7) with a volume of 400 cm3, thermostatted at a temperature close to the room, put the tablet photocatalyst (8). Mixing of the gas in the reactor is carried out using a propeller (9), driven in rotation from the magnetic stirrer (15). Lighting spend mercury lamp DRSH-1000 (12)mounted on the lifting table (14), the light from which is filtered by an interference filter (13) with maximum transmittance at 365 nm and is directed to the photocatalyst (8) with the help of a mirror (11). Sampling gas from the reactor (7) for the analysis carried out through the sampler (10).

Example 1. The reactor is placed a glass plate coated with a photocatalyst (0.2 wt.% Pt/TiO2with a specific surface area of > 300 m2/g, weight of catalyst (20 mg) and injected with 0.5 μl of diethylsulfide. After 15 minutes, begin to illuminate the sample and to periodically take a gas sample from the reactor for analysis of CO2using a chromatograph. The calculated rate of CO2for the first 45 min of flow of reactions which is 9.6· 10-9mol/min

Example 2. Similar to example 1, with the difference that on the bottom of the reactor install a small glass Cup, which is added 2 ml of water before the beginning of the experience. The calculated rate of CO2for the first 45 min of the reaction is 9.4·10-9mol/min

Example 3. Similar to example 2, with the difference that in the Cup before the start of the experiment, add 2 ml of 35% solution of hydrogen peroxide. The calculated rate of CO2for the first 45 min of the reaction in this example is 3.7·10-8mol/min

Example 4. Similar to example 1, with the difference that as a photocatalyst take pure titanium dioxide brand Hombikat UV 100 (Sachtleben Chemie, 100% anatase, specific surface area of 340 m2/g). The calculated rate of CO2for the first 45 min of the reaction in this case is 1.05·10-8mol/min

Example 5. Similar to example 4, with the difference that on the bottom of the reactor install a small glass Cup, which is added 2 ml of 35% solution of hydrogen peroxide before the beginning of the experience. The calculated rate of CO2for the first 45 min of the reaction is 1.3·10-8mol/min

Example 6. Similar to example 1, with the difference that as a photocatalyst take titanium dioxide coated with Pd inthe number of 0.2 wt.%. The calculated rate of CO2for the first 45 min of the reaction in this example is 7.8·10-9mol/min

Example 7. Similar to example 6, with the difference that on the bottom of the reactor install a small glass Cup, which is added 2 ml of 35% solution of hydrogen peroxide before the beginning of the experience. The calculated rate of CO2for the first 45 min of the reaction is 2.6·10-8mol/min

In the above examples, the rate of formation of CO2in fact proportional to the speed of decomposition of vapors of diethylsulfide. These data are presented in the Table, they show that in the presence of vapors of hydrogen peroxide photooxidation of diethylsulfide runs 4 times faster (examples 1 and 3) in the case of using the photocatalyst coated with platinum and 3 times faster (examples 6 and 7) in the case of using the photocatalyst coated with palladium. In the case of use of pure titanium dioxide or replacement of the hydrogen peroxide solution in distilled water, this effect is much weaker (examples 4 and 5).

Table
ExampleThe rate of emission of CO2, mol/min
19,6·10-9
29,4&x000B7; 10-9
33,7·10-8
41,05·10-8
51,3·10-8
67,8·10-9
72,6·10-8

The following examples show the results of tests of photocatalytic air purifier lamp (PCF) (Testimony of the Russian Federation for useful model No. 8634, B 01 J 19/10, 16.12.98). This device uses a traditional principle of operation of such devices without adding vapor hydrogen peroxide.

Example 8. In a sealed plastic chamber with a volume of 400 liters put the PCF, in which the photocatalyst is used 3 g of titanium dioxide containing 0.2 wt.% supported metal platinum. The camera is inserted 0.3 cm3and acetone at room temperature, observing the process of increasing the concentration of carbon dioxide (CO2)formed in the photocatalytic decomposition of vapors of acetone. Measured for 1 h, the rate of formation of CO2is 1,63·10-5mol/min

Examples 9-11 describe the application of the proposed method in the known device (Certificate of the Russian Federation for useful model No. 8634, B 01 J 19/10, 16.12.98).

Example 9. Similar to example 8, with the difference that in the camera set the Petri dish, to the Yu pour 10 ml of 35% aqueous hydrogen peroxide solution. During the whole experiment the Cup is heated to a temperature of ≈ 40°C. Measured for 1 h, the rate of formation of CO2is 3,68·10-5mol/min

Example 10. Similar to example 8, with the difference that in the camera set the plastic tray filled with 35% aqueous hydrogen peroxide solution, with cover. Cover the entire length made 4 parallel section, in which the inserted piece of cloth made of polypropylene. The bottom edges of all four pieces immersed in a solution of hydrogen peroxide, which under the action of capillary forces climbs the fibers of the fabric to a height of about 10 centimeters. Axial fan located in the camera, blows air along the parallel layers of fabric, and it is saturated with vaporized hydrogen peroxide.

Measured for 1 h, the rate of formation of CO2when the photocatalytic oxidation of vapors of acetone under these conditions is 3.2·10-5mol/min

Example 11. Similar to example 8, with the difference that in the camera set axial fan that generates an air flow of 100 m3/hour. Air flow set nozzle, which under pressure of 35% aqueous hydrogen peroxide solution with a speed of 0.1 cm3/min. At the exit of the nozzle is formed a suspension, which is caught by the air stream.

Measured for 1 h, the rate of formation of CO when the photocatalytic oxidation of vapors of acetone under these conditions is 3.0·10-5mol/min

Comparison of examples 8, 9, 10 and 11 shows that the addition of vapor hydrogen peroxide to purify the air more than 2 times increases the efficiency of the PCF in examples 9 and 10 and 1.8 times increases the efficiency of the PCF in example 11.

Thus, as seen from the above examples, the proposed method can significantly increase the efficiency of the photocatalytic purification of gases and can be used in existing devices, photocatalytic purification of gases, and in newly developed.

1. The method of purification of gases, including air, oxidation using photocatalyst based on titanium dioxide, characterized in that the source gas mixture containing oxidizable substances, saturated with vaporized hydrogen peroxide.

2. The method according to claim 1, characterized in that as the photocatalyst used pure titanium dioxide crystal structure of anatase or titanium dioxide, containing one or more transition metals.

3. The method according to claim 2, characterized in that the photocatalyst is used, preferably, titanium dioxide crystal structure of anatase containing one or more transition metals.

4. The method according to any of claim 2 and 3 characterized in that that transition metals contained in the photocatalyst, are preferably platinum or palladium, or any mixture.

5. The method according to claim 1, characterized in that the feeding of the gas to be purified pairs of hydrogen peroxide is carried out in the block.

6. The method according to claim 5, characterized in that the unit is made in the form of an open heated container filled with an aqueous solution of hydrogen peroxide.

7. The method according to claim 5, characterized in that the unit is made in the form of parallel layers of fabric impregnated with an aqueous solution of hydrogen peroxide, located in the saturated flow of the source gas.

8. The method according to claim 5, characterized in that the unit is made in the form of nozzles, spraying an aqueous solution of hydrogen peroxide in the saturated flow of the source gas.



 

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