JPH01143630A - Method for treating fluorocarbon - Google Patents

Abstract

PURPOSE:To treat fluorocarbon efficiently by introducing a gas containing fluorocarbon to the surfaces of a photocatalyst such as a semiconductor irradiat ed by a light. CONSTITUTION:A gas containing fluorocarbon is introduced into a photocatalytic reactor 2 through an inlet 1 and decomposed by a photocatalyzing material 4, which is irradiated by an ultraviolet ray lamp 5, etc., and made to form electric fields by electrodes. A photocatalyzing matter 4 such as TiO2, Co3O4, Ag2O, Fe2O3 and NiO is fixed on Ti electrode plates to which voltages are applied so as to form electric fields. A treated gas is ejected out of an outlet 3.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a treatment method for detoxifying fluorocarbons, and particularly to a treatment method for detoxifying fluorocarbons to such an extent that only an extremely low concentration remains. .

(Prior art) Freon (chlorofluorocarbon) used as a working medium in compression refrigerators
Because chlorofluorocarbons (chlorofluorocarbons) destroy the ozone layer in the atmospheric stratosphere, there have been recent efforts to internationally regulate their use.

The ozone layer absorbs light of 290 to 370 nm that is harmful to living things, and if the chlorine Cl contained in CFC decomposes and destroys ozone, the harmful light will reach the earth's surface, so the ozone layer There are discussions about how to prevent the destruction of Freon-22, which is most commonly used as Freon for refrigerators, contains hydrogen atoms in its molecules and is therefore unstable, and is thought to have a high possibility of decomposing before reaching the stratosphere. However, freon-
Some countries, such as Canada, have argued that all halogenated chlorofluoroalkanes should be regulated, since there is no proof that 22 has no effect on ozone layer depletion.

If all halogenated chlorofluoroalkanes were regulated, all of the major refrigerants currently used in refrigerators, such as CFC-113, CFC-11, CFC-114, CFC-12, and CFC-22, would be regulated. It will be regulated.

However, it is thought to be extremely difficult to convert fluorocarbons, which have particularly excellent properties as a working medium for refrigerators, into other media, so in the future, the production of fluorocarbons will be allowed in the necessary quantities, but its release into the atmosphere will be regulated. I think it will happen. In fact, the regulatory method established in September 1986 was to limit the amount of fluorocarbons produced.

In order to prevent the release of fluorocarbons into the atmosphere, it is first important to prevent the release of fluorocarbons, especially when the refrigerator is disposed of. It is relatively easy to recover fluorocarbons used in centrifugal refrigerators, such as R-11 and R-113, which remain solid at room temperature, and recycling is still being carried out today. However, R-12 and R-22, which are used in car coolers, room coolers, refrigerators, etc., are gases at room temperature, and
Due to the small amount of filling per unit, no collection is currently taking place.

In addition, the thermal decomposition method and catalytic method conventionally considered for processing the recovered fluorocarbons are only capable of processing a high concentration of fluorocarbons to a relatively low concentration.

(Problem to be solved by the invention) Although the amount of fluorocarbons filled per car cooler, room cooler, refrigerator, etc. is small, the total number of units is large, so fluorocarbons are released from the car coolers, etc. that are discarded. The amount of fluorocarbons is also considerable, and preventing the release of fluorocarbons from them is an urgent issue to address the ozone depletion problem. However, since it is difficult to collect them from one vehicle to the next, the method of collection is as described above. The space where car coolers etc. filled with fluorocarbons are gathered, dismantled and scrapped is made into a sealed structure, the fluorocarbons are released into the space, and the fluorocarbons are collected by pressurizing and condensing or cooling and condensing. One possible method is to then release the air from which the fluorocarbons have been removed into the atmosphere. However, with this method, the concentration of fluorocarbons in the space is low, so a huge amount of energy is required to condense the fluorocarbons from the air, and the recovery equipment is a batch system, making the mechanism complicated. It has drawbacks such as:

Therefore, a method that can process fluorocarbons continuously and efficiently at low cost instead of the condensation method is desired, but the thermal decomposition method and catalytic method described above can only treat high concentrations of fluorocarbons. It has the disadvantage that it can only remove up to a target low concentration, is inefficient, and has unstable performance.

For this reason, it is desired to develop a treatment method that can treat low-concentration fluorocarbons and can also remove extremely small amounts.

The present invention solves the above-mentioned problems, and aims to provide a method for treating fluorocarbons that can decompose fluorocarbons of various concentration levels to low concentrations and that can operate stably and continuously for a long period of time. It is.

(Structure of the Invention) The present invention is a method for decomposing fluorocarbons by passing a fluorocarbon-containing gas over a photocatalyst that is irradiated with light.

In the present invention, the photocatalyst is converted into a natural substance by being irradiated with light, and decomposes the fluorocarbon when it comes into contact with the fluorocarbon.

Therefore, any photocatalyst may be used as long as it is excited by light irradiation and promotes the decomposition action.

Generally, it is preferable to use semiconductor materials because they are effective, easily available, and have good processability.

From the viewpoint of effectiveness and economy, ≠Se, Ge, St, Ti, Z
n, Cu, Al, Sn, Ga, In.

P, As, Sb, C, Cd, S, Te, Ni5Fe, C
o, ,Ag, Mo, Sr, ,W, Cr5Ba.

Any one of Pb, a compound, or an alloy thereof is preferable, and these are used alone or in combination of two or more types.

For example, the elements include Si, Ge, and Se, and the compounds include AIP, A1As, GaP, 1eSb, and GaA.
s, InP, GaSb, InSb.

Cd5, CdSe, ZnS, MoS2, WTe, Cr
2Te, , MoTe, Cu, S, WSz, oxides include Tioz, Bizo:+, CuO1Cu.

0, ZnO,, MOO:l, I no3, Ag, 01P
bo, 5rTiO,, BaTiO2, CO3O4, Fe
There are 2O3 and NiO.

The photocatalyst can be used by itself, but since it only needs to be present in the portion that contacts the fluorocarbon, it can be used supported by another carrier. As the carrier, metal members such as Ti plates, ceramics such as alumina and silica, glass, etc. can be used. As a method for fixing the photocatalyst to the support, known methods such as sintering, vapor deposition, and sputtering can be used as appropriate.

The shape of the photocatalyst is preferably such that a fluorocarbon-containing gas can pass therethrough, and it may be in the form of a lattice, a plate, a granule, a pleat, a mesh, etc. depending on the type of device. If it is supported on a carrier and used, it is easy to form it into a specific shape.

Since light irradiation is used to excite the photocatalyst, it is necessary to use light that can sufficiently excite the photocatalyst.Although ordinary visible light excites it to some extent, ultraviolet rays are used because the degree of excitation is large. most preferred. For ultraviolet rays, a lamp that emits wavelengths in the light absorption region determined by the type of photocatalyst may be selected. When the photocatalyst is TiO□, for example, the light absorption is in the near ultraviolet range, so a lamp that emits light with a wavelength in the near ultraviolet range is used.

Light sources used for light irradiation include mercury lamps, hydrogen discharge tubes,
A xenon discharge tube, a Lyman discharge tube, etc. can be used as appropriate, and the efficiency is higher as the amount of light emitted is larger.

The light source may be placed inside the photocatalytic reactor, but
The photocatalyst may be placed on the other side outside the reactor, and the photocatalyst may be irradiated with ultraviolet light using a reflective surface or through a dense irradiation.

Although a gas containing a high concentration of fluorocarbons can be used as the fluorocarbon-containing gas, a gas containing a medium concentration of fluorocarbons of several percent can be well treated, and the present invention can be used to treat a gas containing fluorocarbons with an extremely low concentration. can be removed to the extent that it is only discharged. According to the present invention, a gas containing about several percent of fluorocarbons can be treated to 0. It can be emitted as a gas containing less than 1% CFC. In view of operability and efficiency, it is preferable to dilute fluorocarbons with a high concentration to about 1 to several 10% before treatment.

Any temperature from room temperature to 350° C. can be adopted as the temperature at which the fluorocarbon treatment is performed.

Further, in carrying out the present invention, if an electric field is formed around the photocatalyst and the treatment is performed in the electric field, the treatment effect will be further enhanced. A well-known method can be used as appropriate for forming the electric field. Most conveniently, when the photocatalyst is supported on a metal member such as a metal plate, the metal member may be used as one electrode and the other electrode may be provided separately.

The material and structure of the electrode may be those used in ordinary electric field generating equipment. For example, as the electrode material, stainless steel, copper, or tungsten is appropriately used in a linear, mesh, or plate shape.

These materials are designed in consideration of deterioration caused by light irradiation and fluorocarbons.
Heat treatment in air, chemical treatment, metal thin film deposition, Ti
By coating the surface with a stable semiconductor such as 0z, it is possible to make the material stable over a long period of time.

The voltage applied as an electric field is 50V to 30KV, preferably 0. The voltage is 1 to 20 KV, and the voltage can be determined by preliminary tests as appropriate based on the type of device, the material and structure of the electrodes used, or efficiency and economical efficiency.

The ability of the photocatalyst to decompose and remove fluorocarbons is improved by forming an electric field on the photocatalyst, and the fluorocarbons are decomposed and removed to a low concentration. This is thought to be because the photocatalyst surface becomes active against fluorocarbons by placing it in a photocatalytic laminated field, so that the decomposition of fluorocarbons by the photocatalyst is significantly improved. The choice of whether or not to use an electric field in fluorocarbon treatment depends on the type, scale, economics, and
Laws can be imposed as appropriate depending on the effect, etc.

Furthermore, the effects of the present invention can be further improved by combining other fluorocarbon treatment methods. Other fluorocarbon treatment methods that can be combined with the present invention include conventionally known treatment methods, such as thermal decomposition methods, catalytic methods, and methods using scavengers. As this other method for treating fluorocarbons, any method may be used as long as a high concentration of fluorocarbons can be reduced to a relatively low concentration, and catalytic methods and thermal decomposition methods are preferable from the viewpoint of treatment effect, cost, operational efficiency, equipment scale, etc.

Whether to use the method of the present invention alone or in combination with a treatment method other than the method of the present invention as a treatment method for fluorocarbons depends on the type, scale, coexisting components, economic efficiency, operability, and effectiveness of the fluorocarbon source. Laws can be enacted as appropriate based on the following.

Next, the present invention will be explained based on the drawings.

FIG. 1 shows an example of application to an apparatus for treating fluorocarbon-containing gas emitted from a machine filled with fluorocarbons using a photocatalyst that is irradiated with light in an electric field at room temperature.

The symbol 1 is an inlet of air containing fluorocarbons that is discharged when a machine filled with fluorocarbons is scrapped. CFCs with a medium concentration are decomposed in the photocatalytic reactor 2 that forms an electric field and is irradiated with light, resulting in a low concentration (0.1% or less).
and is discharged from outlet 3.

The photocatalytic reactor 2 includes a photocatalytic material 4 (4-1 to 4-6), an ultraviolet lamp 5, and an electrode (FIG. 2, described later) for forming an electric field on the surface of the photocatalytic material.

The photocatalytic material 4 is irradiated with ultraviolet light by the ultraviolet lamp 5, and an electric field is formed around the photocatalytic material by the electrodes.

FIG. 2 shows an example of electric field formation. The photocatalytic material 4 is
It is fixed on a Ti plate electrode 6, and an electric field is created by applying a voltage between the temporary Ti electrode 6 and another electrode (tungsten) 7. In FIG. 2, 8 indicates an inlet gas flow, and 9 indicates an outlet gas flow.

Next, a case in which the treatment of fluorocarbons by the method of the present invention and the treatment of fluorocarbons by another method are performed in combination will be explained with reference to the drawings.

In FIG. 3, the symbol lO is the inlet of fluorocarbons discharged from a space (not shown) in which a machine filled with fluorocarbons is scrapped. The target is decomposed to a low concentration, and then decomposed in the photocatalyst section 12 in which an electric field is formed, resulting in a low concentration (0
, 1% or less) and is discharged from the outlet 13.

The catalyst filling section 11 is a reactor filled with a catalyst. As a catalyst, usually MnOz, Co oxide-added MnO2,
Metal oxide catalysts such as Fe01NiO, Ag, Pt, P
A catalyst in which a noble metal catalyst such as d is supported on 5i02 or T-alumina is used. The fluorocarbon decomposition rate in the catalyst filling section 11 is processed as follows.

12 is a photocatalytic reactor in which an electric field is formed, and this reactor is the same as that described in FIGS. 1 and 2 above. In the photocatalytic reactor 12, the fluorocarbons (concentration of several percent) discharged without being able to be treated by the catalyst filling unit 11 are passed over the photocatalyst that is irradiated with light in an electric field, thereby being decomposed and removed to an extremely low concentration.

(Example) Hereinafter, the present invention will be specifically explained with reference to Examples.

The present invention is not limited only to these examples.

Air containing 5% of fluorocarbons was flowed through with a meteor flow of 0.1 n/min, and the outlet fluorocarbon concentration was measured. The results are shown in Table 1.

Conditions for fluorocarbon treatment equipment Formation of electric field: As shown in Figure 2, a photocatalytic Ti plate (negative electrode)
2. The photocatalyst surface and the tungsten electrode (positive electrode) were fixed at a distance of 1.5 mm. Apply OKV Freon source: Cylinder ultraviolet lamp: Mercury lamp 20W Equipment size: 50 x 100 x 200 cylinders Table 1 Table 2 also shows the results (outlet fluorocarbon concentrations) of TiO2, CO3O, and photocatalyst materials after continuous operation for about one month. show.

Table 2: As a comparative example, results were obtained without applying an electric field to the photocatalyst.
It was 0.5%.

Example 2 In the same manner as in Example 1, 50% of the fluorocarbons were discharged from the fluorocarbon source, and the fluorocarbons were fed into the treatment equipment as shown in Fig. 3 at 0.31/min.
The outlet fluorocarbon concentration was measured in the same manner. The results are shown in Table 3.

Processing equipment conditions Catalyst: MnO with 10% by weight of CO oxide added.

Catalyst temperature: 150℃ Photocatalyst: TiO□, Ag2O Ultraviolet lamp: Mercury lamp 20W Equipment size: 80 (Fir)xtoo (t!Ii)X
300mm Table 3 Table 4 shows the results of continuous operation for about one month (outlet fluorocarbon concentration) for TiO□ and Ag2O photocatalyst materials.

Table 4 (Effects of the Invention) (1) According to the present invention: 1. Freon could be treated stably with high efficiency over a long period of time.

ii. The concentration of discharged fluorocarbons could be significantly lowered.

(2) In the present invention, by forming an electric field at or around the photocatalyst, i. the fluorocarbon decomposition effect by the photocatalyst was significantly improved.

ii. Freon could be treated stably with high efficiency over a long period of time.

iii. The concentration of fluorocarbons emitted from FJF could be reduced to a virtually negligible concentration (extremely low concentration).

iv, continuous use, and intermittent use have similar effects.

(3) In the present invention, by using in combination with another fluorocarbon treatment method, it was possible to: i. deal with a wide variety of sources;

11. We were able to create a practical method that takes advantage of the features (advantages) of both methods.

iii. We were also able to deal with high concentrations of fluorocarbons.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an outline of a photocatalytic reactor for explaining the method of the present invention, Fig. 2 is a diagram showing an example of an electrode for forming an electric field, and Fig. 3 is a diagram showing an example of a photocatalytic reactor for explaining the method of the present invention. FIG. 3 is a schematic diagram for explaining a case where processing methods are combined. 4.4-1 to 4-6... Photocatalyst material, UV lamp, 6... Ti plate electrode, 7... Tungsten electrode,
11... Catalyst filling part, 12... Photocatalyst reactor. Representative Patent Attorney (8107) Kiyoshi Sasaki ′ (and 3 others) ″ Figure 1, Part 3

Claims (8)

[Claims] (1) A method for treating fluorocarbons, which comprises passing a fluorocarbon-containing gas over a photocatalyst that is irradiated with light. (2) The method for treating fluorocarbons according to claim 1, wherein the photocatalyst is a semiconductor. (3) Photocatalyst is Se, Ge, Si, Ti, Zn, Cu,
Sn, Al, Ga, In, P, As, Sb, C, Cd,
A patent claim consisting of a composite of one or more selected from S, Te, Ni, Fe, Co, Ag, Mo, Sr, W, Cr, Ba, Pb, or a compound or alloy thereof. A method for treating fluorocarbons as described in Scope 2. (4) A method for treating fluorocarbons according to any one of claims 1 to 3, wherein the treatment is carried out in an electric field. (5) The method for treating fluorocarbons according to claim 4, wherein the voltage of the electric field is within the range of 50V to 30KV. (6) The method for treating fluorocarbons according to any one of claims 1 to 5, wherein the treatment is carried out at a temperature of room temperature to 350°C. (7) The fluorocarbon treatment method according to claim 1, which is performed in combination with another fluorocarbon treatment method. (8) The method for treating fluorocarbons according to claim 7, which uses at least one of a thermal decomposition method, a catalytic method, and a method using a fluorocarbon scavenger as another method for treating fluorocarbons.