JP2001220358A - Method for photolyzing organochlorine compound and photolyzing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an economical, safe and stable method for photolyzing an organochlorine compound. SOLUTION: This method for photolyzing the organochlorine compound comprises a first step for irradiating the gas containing the organochlorine compound to be decomposed with 150-280 nm ultraviolet rays, and a second step for irradiating the ultraviolet-irradiated gas with near ultraviolet rays or the light in the short wave length part of the visible light, having 300-500 nm wavelength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for decomposing an organic chlorine compound and a decomposition apparatus used for the method.

[0002]

2. Description of the Related Art With the development of industrial technology to date, organochlorine compounds (eg, chlorinated ethylene, chlorinated methane, etc.) have been used enormously, and disposal thereof has become a serious problem. In addition, these gases used have caused environmental problems such as polluting the natural environment, and great efforts have been made to solve them.

A specific treatment method is described below. For example, as a method for decomposing chlorinated ethylene using an oxidizing agent or a catalyst, a method of decomposing with ozone (JP-A-3-38297) or a method in which hydrogen chloride is used (Japanese Patent Application Laid-Open No. 63-218293) is known. It has also been suggested to use sodium hypochlorite as an oxidizing agent (US Pat. No. 5,525,008,
U.S. Patent No. 5611642). A method of combining sodium hypochlorite with ultraviolet irradiation has also been proposed (US Pat. No. 5,582,741). Furthermore, a method is known in which a photocatalyst composed of oxide semiconductor fine particles such as titanium oxide and liquid chlorinated ethylene are suspended under alkaline conditions and decomposed by light irradiation (Japanese Patent Application Laid-Open No. 7-141373).

In addition to the above, Japanese Patent Application Laid-Open No. 09-234338
A photodecomposition method of irradiating ultraviolet rays in a gas phase without using an oxidizing agent as disclosed in Japanese Patent Application Laid-Open Publication No. H11-15064 has already been attempted. Also, a method in which an exhaust gas containing an organic halogen compound is irradiated with ultraviolet rays to form an acidic decomposition gas, and then washed with alkali to render it harmless (Japanese Patent Application Laid-Open No. Sho 62-191025), contains an organic halide. A device has been proposed in which wastewater to be aerated is subjected to aeration treatment, and the discharged gas is irradiated with ultraviolet rays and then washed with alkali (Japanese Patent Application Laid-Open No. 62-191095). Also, as an example presumed to be reductive decomposition, decomposition of chlorinated ethylene by iron powder is known (Japanese Patent Laid-Open No. 8-2).
No. 57570). Regarding the decomposition of tetrachloroethylene (PCE) using silicon fine particles, reductive decomposition has also been reported.

[0005]

However, none of the above methods can be said to be sufficiently practical in terms of the decomposition efficiency and the device configuration required for the treatment, etc. There is a need for a method for decomposing chlorine compounds.

According to the present invention, a gas containing an organic chlorine compound is irradiated with ultraviolet rays, followed by irradiation with long-wavelength light in a reaction tank to efficiently decompose the gas and to enable treatment in a simple reaction tank. An object of the present invention is to provide a method and an apparatus for decomposing chlorine compounds.

[0007]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, a gas containing an organic chlorine compound is irradiated with ultraviolet rays at the first stage of the reaction to cause a decomposition reaction. The present inventors have found that in the subsequent reaction, sufficient decomposition can be obtained only by irradiation with light having a long wavelength, and the present invention has been completed based on this finding.

That is, the present invention provides a first step of irradiating a gas containing an organic chlorine compound with ultraviolet rays, and a method of irradiating the gas containing an organic chlorine compound after irradiation with the ultraviolet rays with a short-wavelength portion of near ultraviolet light or visible light. A photodecomposition method for an organic chlorine compound, comprising a second step of irradiating light.

The wavelength of the ultraviolet light in the first step is 15
0 nm to 280 nm, and the wavelength of light in the short wavelength portion of near ultraviolet light or visible light in the second step is 300 nm.
Preferably it is ~ 500 nm. The irradiation amount of light in the second step ^{10μW / cm 2 ~10mW / cm 2} , it is desirable preferably ^{50μW / cm 2 ~5mW / cm 2} . Further, a part of the organic chlorine compound is decomposed by irradiation of ultraviolet rays in the first step to generate chlorine gas,
The concentration of chlorine gas generated in the first step is 5 ppm to 10 ppm.
Preferably it is 00 ppm.

It is preferable that a gas containing an organic chlorine compound to be decomposed is directly added to the gas containing an organic chlorine compound after the irradiation of the ultraviolet rays in the second step.

Further, the present invention provides a means for irradiating a gas containing an organic chlorine compound with ultraviolet light having a wavelength of 150 nm to 280 nm in a closed space, a reaction tank containing the gas after irradiation with the ultraviolet light, An apparatus for decomposing an organochlorine compound, comprising: means for irradiating near-ultraviolet light having a wavelength of 300 nm to 500 nm or light having a short wavelength portion of visible light to a gas contained in a tank.

The volume of the closed space exposed to the ultraviolet light having a wavelength of 150 nm to 280 nm is 300 nm to 50 nm.
The volume is preferably in the range of 1/5 to 1/100 of the volume of the reaction tank exposed to near-ultraviolet light of 0 nm or light of a short wavelength portion of visible light. Further, the gas after the irradiation of the ultraviolet rays contains chlorine gas generated by partially decomposing the organic chlorine compound by the irradiation of the ultraviolet rays. Further, it is preferable that the reactor is provided with means for directly supplying a gas containing an organic chlorine compound which is a gas to be decomposed to the reaction tank.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The method for photodecomposition of an organochlorine compound of the present invention comprises a first step of irradiating a gas containing the organochlorine compound with ultraviolet light to trigger the decomposition of the organochlorine compound, and a gas containing the organochlorine compound after the treatment. It is characterized by having a second step of irradiating a short wavelength part of near ultraviolet light or visible light.

The apparatus for decomposing an organochlorine compound of the present invention, means for irradiating an ultraviolet ray having a wavelength of 150 nm to 280 nm to a gas containing an organochlorine compound in a closed space, a reaction tank, and a gas after the irradiation of the ultraviolet ray may be used. Means for supplying to the reaction vessel,
It is characterized in that a means for irradiating near-ultraviolet light of 300 nm to 500 nm or light of a short wavelength portion of visible light to a reaction tank containing the gas is provided.

First, in the method for decomposing a gaseous organochlorine compound according to one embodiment of the present invention, the gas containing the organochlorine compound to be decomposed in the first step is irradiated with ultraviolet rays (wavelength 15).
0 to 280 nm), and the subsequent step includes a step of irradiating the gas after irradiation with the ultraviolet light (150 to 280 nm) with near ultraviolet light of 300 nm to 500 nm or light in the short wavelength part of visible light. It has one feature.

Such a disassembly method will be described with reference to FIG. 1 showing one embodiment of a disassembly apparatus according to the present invention. In FIG. 1, 1 is a means for supplying a gas to be decomposed, 2 is a means for irradiating ultraviolet rays having a wavelength of 150 nm to 280 nm, and 3 is a trigger column. The gas from the trigger column 3 is guided to the reaction tank 5, and the gas is irradiated with near-ultraviolet light or short-wavelength light of visible light of 300 to 500 nm for a predetermined time by the light irradiation means 4 to decompose the gas to be decomposed. You. The decomposed gas is discharged from the exhaust pipe 6.

The photodecomposition method of the present invention comprises a first step of generating chlorine from a decomposition target, and a second step of performing a main decomposition reaction with light sufficient to excite the chlorine. First, in a first step, a gas containing an organic chlorine compound is irradiated with ultraviolet rays. The gas containing an organic chlorine compound in the trigger column of FIG.
Ultraviolet light of 0 nm is irradiated. Since the ultraviolet light has sufficient energy to break the carbon-chlorine bond of the organic chlorine compound, the carbon-chlorine bond is broken when the organic chlorine compound is irradiated with ultraviolet light. Here, chlorine molecules are generated from the cleaved chlorine radicals. That is, in the first step, chlorine is generated from the decomposition target substance in this manner.

In the subsequent second step, the chlorine produced in the first step is used to decompose organic chlorine compounds such as trichloroethylene and tetrachloroethylene. That is, in FIG. 1, the gas from the trigger column 3 contains the generated chlorine gas, and the gas containing the decomposition target substance and the chlorine gas is led to the reaction tank 5. A gas containing chlorine gas is irradiated with near-ultraviolet light of 300 nm to 500 nm or light of a short wavelength portion of visible light for a predetermined time to decompose the decomposition target gas.

A chlorine molecule has a maximum absorption peak at a wavelength of about 330 nm, and the wavelength of light required for forming chlorine radicals is about 485 nm or less from its binding energy. That is, light of a wavelength such as 254 nm is not required for radicalization. 300-500nm for radicalization of chlorine molecules
Light is enough. The chlorine radical radicalized by such light attacks and decomposes unreacted trichlorethylene and tetrachloroethylene. At this time, chlorine is generated from unreacted trichlorethylene,
It is radicalized by light of ５００500 nm, and the decomposition reaction proceeds in a chain.

FIG. 2 is a schematic view of an apparatus for decomposing an organic chlorine compound according to another embodiment of the present invention. In FIG. 2, the reaction tanks 5 are connected in series so that unreacted organic chlorine compounds such as trichlorethylene and tetrachloroethylene are in contact with chlorine gas for a longer time, and the first reaction tank 5-1 is connected.
Decomposed substances not decomposed in the reaction vessel 5-
By further irradiating light at 2, it is possible to achieve more complete decomposition. The number of reaction vessels to be connected can be appropriately selected depending on the concentration of the substance to be decomposed, the ease of decomposition, and the like.

The photodecomposition method of the present invention can be applied to a gas containing an organic chlorine compound. The target organic chlorine compound is not particularly limited, but the method of the present invention is suitable for the decomposition of an aliphatic chlorine compound, and examples thereof include chlorinated ethylene and chlorinated methane. Specifically, examples of the chlorinated ethylene include 1 to 4 chlorine-substituted products of ethylene, that is, chloroethylene, dichloroethylene, trichloroethylene, and tetrachloroethylene. Furthermore, examples of dichloroethylene include 1,1-dichloroethylene (vinylidene chloride), cis-1,2-dichloroethylene, and tras-1,2-dichloroethylene. Examples of the chlorinated methane include chlorine-substituted methanes such as chloromethane, dichloromethane, and trichloromethane. Chlorinated aromatic compounds to be decomposed include, for example, chlorobenzene.

There is no particular limitation on the gas containing the target organochlorine compound, and the gas is generated when exhaust gas from a coating plant, exhaust gas from a dry cleaning plant, a vacuum extraction gas from contaminated soil, or air stripping of groundwater. The present invention can be applied to a gas or the like. The photodecomposition method of the present invention is particularly suitable for treating a gas obtained by extracting an organic chlorine compound from soil or groundwater. Pollution by soil and groundwater with organochlorine compounds is often mainly caused by trichloroethylene or tetrachloroethylene. When the contamination is soil, the organic chlorine compound is mainly taken out by vacuum extraction method, and in the case of groundwater, the organic chlorine compound is taken out in a state of being once mixed with air by pumping and aeration method.

(Light and Light Irradiation Conditions) The light to be irradiated in the first step is, for example, at a wavelength of 150 to 280 nm, particularly 2 nm.
Light having a wavelength of 20 to 260 nm is particularly preferable in terms of the decomposition efficiency. Examples of the light source include a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, a xenon lamp, a deuterium lamp, and a metal halide lamp.
In particular, a mode using a germicidal lamp that efficiently emits ultraviolet light having a wavelength of 254 nm is desirable.

The light irradiated in the second step includes, for example,
Light having a wavelength of 300 to 500 nm, particularly 350 to 450 nm, is particularly preferred in terms of decomposition efficiency. The light irradiation intensity is from 10 μW / cm ² to from the viewpoint of decomposition efficiency.
10 mW / cm ² , especially 50 μW / cm ^{2 to 5} mW / c
A range of m ² is preferred. For example, in a light source having a peak at a wavelength of 365 nm, several hundred μW / cm ² (300 nm to 400
(measured between nm), practically sufficient decomposition proceeds. As a light source of such light, natural light (for example, sunlight) or artificial light (mercury lamp, black light, color fluorescent lamp (blue), etc.) can be used.

The irradiation of light may be performed directly from inside the reaction tank, or may be performed from outside the reaction tank via a reaction tank container. The shape of the reaction tank may be any form, for example,
A transparent tube such as a glass tube may spirally cover a cylindrical light source, and a reaction vessel may be used in which a mixed gas of a decomposition target gas and chlorine passes. As the light used in the second step, there is no need to use ultraviolet light having a wavelength of about 250 nm or less, which has a large effect on the human body, and glass or plastic can be used as the reaction tank.

In order to generate chlorine used in the main reaction (second step), an ultraviolet light source having a wavelength of about 250 nm is used in the first step. However, since the main reaction is a chain reaction by chlorine, a slight amount is used in the first step. It is sufficient if an amount of chlorine is obtained and the first step can be in very small form. For example,
The volume of the first step which is irradiated with ultraviolet light having a wavelength of 150 nm to 280 nm is 1/5 to 1/100 of the volume of the reaction tank which is irradiated with light having a wavelength of 300 nm to 500 nm or near ultraviolet light or a short wavelength portion of visible light. , Preferably 1/10 to 1
/ 50 is desirable.

In Japanese Patent Application Laid-Open Nos. 9-299753 and 10-180040, all of the plurality of reaction vessels are irradiated with the ultraviolet light. For decomposition. On the other hand, in the configuration of the present invention, it is possible to use a light source with low energy and excellent safety in the main reaction (second step), and therefore, it is possible to use a material such as glass, Compared with a conventional decomposer using a light source having light having a wavelength of about 250 nm, the whole system can realize a cheap and safe configuration.

[0028]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention.

Example 1 An experiment on the decomposition of trichlorethylene was carried out using air containing about 500 ppm of trichloroethylene. FIG.
Is a reaction tank used in this example. Trigger column 3
Is a 5 cm diameter with a 2 cm diameter quartz tube 7 inside,
This is a Pyrex glass internal irradiation type cylindrical container with a length of 18 cm.
Means 2 for irradiating ultraviolet rays of m to 280 nm [Toshiba Corporation
GL4 (4W)].

Air containing trichlorethylene is introduced into the trigger column 3 at a rate of 1 liter per minute from the supply means 1 for the gas to be decomposed, and the reaction gas irradiated with ultraviolet rays in the trigger column 3 is led to the reaction tank 5. At this time, the concentration of trichlorethylene was about 170 to 220 ppm, and the chlorine concentration was more than 50 ppm when measured with a detector tube.

The reaction gas introduced into the reaction tank 5 is supplied with a black light fluorescent lamp (manufactured by Toshiba, FL
20S ・ BLB, 20W) to the gas 300n wavelength
Light of m to 500 nm was irradiated. Light irradiation amount is 0.7 ~
It was 1.2 mW / cm ² . The decomposed gas is discharged from the exhaust pipe 6. Sampling the discharged gas,
When the trichlorethylene concentration was measured by a gas chromatograph equipped with an FID detector, it was found to be 98% or more decomposed.
The capacity of the reaction tank 5 was set to be 20 times that of the trigger column 3.

Example 2 A decomposition experiment was carried out using air containing about 500 ppm of trichloroethylene in the same manner as in Example 1 except that the apparatus shown in FIG. 2 was used, and it was found that decomposition was 99.5% or more.
In addition, the total capacity of the reaction tanks 5-1 and 5-2 was 50 times the trigger column 3.

Example 3 About 300 pp of trichloroethylene was used as a decomposition target gas.
When a decomposition experiment was performed in the same manner as in Example 2 except that air containing m 2, about 300 ppm of tetrachloroethylene and 100 ppm of dichloromethane was used, all of trichloroethylene, tetrachloroethylene, and dichloromethane were decomposed by 99.5% or more.

Embodiment 4 An example in which the present invention is applied to a contaminated soil remediation apparatus will be described. FIG. 3 is a schematic diagram of a contaminated soil remediation apparatus 10 according to one embodiment of the present invention. Contaminated soil repair device 1 of the present embodiment
On a wall surrounding the opening of the vertical shaft 11, a vacuum pump 12 for sucking air in the vertical shaft 11 is provided. further,
The vacuum pump 12 is connected to a processing tank 14 through a blower 13.
Is connected to the lower part. The air sucked by the vacuum pump 12 is blown into the processing tank 14 by the blower 13.

In the processing tank 14, reference numeral 3 denotes a trigger column having a capacity of about 5 liters. The germicidal lamp 2 (GL15, 15W, manufactured by Toshiba) is inserted into the quartz tube 7 therein, and efficiently emits light having a wavelength of 245 nm. Reference numerals 5-1 and 5-2 denote reaction vessels in which contaminated gas irradiated with ultraviolet rays in the trigger column 3 is led. Reaction tank 5-
The relaxation of the volume of 1,5-2 is about 200 liters, and the inside is irradiated with light from the black light fluorescent lamps 4-1 and 4-2. The effect of the contaminated soil remediation device of the present invention was confirmed at a site contaminated with trichloroethylene (TCE) and tetrachloroethylene (PCE).

When soil suction (vacuum extraction method) was performed from the soil contaminated with TCE and PCE according to a known method, the initial concentration of TCE was 200 to 600 ppm, and
Was from 100 to 400 ppm. This contaminated air is blown into the processing tank 14 at a flow rate of 6 m ³ / h,
Decomposition of TCE and PCE existing in gaseous state in air
Removal was performed. Light irradiation was performed with a black light fluorescent lamp. The black light has an irradiation wavelength peak near 360 nm, and efficiently emits light of 300 nm to 500 nm. The irradiation energy between 300 nm and 500 nm was approximately 0.2-0.6 mW / cm ² . The concentration of TCE and PCE in the discharged gas is determined by gas chromatography with FID detector (trade name: GC-14
B: Shimadzu Corporation, column is J & W DB-
624). As a result, the concentrations of TCE and PCE in the exhaust gas in the exhaust pipe 6 were 5 ppm or less.

Example 5 A decomposition experiment was carried out using air containing about 500 ppm of trichloroethylene in the same manner as in Example 1 except that the apparatus shown in FIG. 4 was used. In FIG. 4, a bypass pipe 15 is provided to supply a part (20% in this embodiment) of the decomposition target gas to the trigger column 3 and supply the rest directly to the reaction tank 5. The reaction gas containing chlorine irradiated with ultraviolet rays in the trigger column 3 and the decomposition target gas directly supplied from the bypass pipe 15 come into contact with each other in the reaction tank 5. (FL20S / BLB, 20W, manufactured by Toshiba), and the decomposition reaction proceeds.

In this configuration, the residence time in the trigger column can be increased by reducing the amount of the target gas passing through the trigger column. Although small, it is excellent in that chlorine can be reliably produced.

[0039]

As described above, according to the present invention, the effect of economically, safely and stably decomposing organic chlorine compounds at normal temperature and normal pressure can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view of an apparatus for decomposing an organic chlorine compound according to an embodiment of the present invention.

FIG. 2 is a schematic view of an apparatus for decomposing an organic chlorine compound according to another embodiment of the present invention.

FIG. 3 is a schematic diagram of an apparatus for decomposing an organic chlorine compound according to another embodiment of the present invention.

FIG. 4 is a schematic view of an apparatus for decomposing an organic chlorine compound according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Decomposition target gas supply means 2 Ultraviolet irradiation means 3 Trigger column 4, 4-1 and 4-2 Light irradiation means 5, 5-1 and 5-2 Reaction tank 6 Exhaust pipe 7 Quartz tube 10 Contaminated soil restoration device 11 Longitudinal resistance 12 vacuum pump 13 blower 14 processing tank 15 bypass pipe

Continued on the front page F-term (reference) 2E191 BA12 BB00 BB01 BD17 4D004 AA41 AB06 AC07 CA43 CB50 DA03 4G075 AA37 AA42 AA62 BA01 BA04 BA05 CA32 CA33 CA65 DA02 DA13 DA18 EA01 EA02 EB21 EB32 EC26 ED01 EE36 CB06 A04 AC04 BD84

Claims (12)

[Claims] 1. A first step of irradiating a gas containing an organic chlorine compound with ultraviolet rays, and irradiating the gas containing an organic chlorine compound after irradiation with the ultraviolet rays with near-ultraviolet light or short-wavelength light of visible light. A method for photodecomposing an organic chlorine compound, comprising a second step. 2. The method according to claim 1, wherein the wavelength of the ultraviolet light in the first step is one.
The photodecomposition method for an organic chlorine compound according to claim 1, wherein the wavelength is from 50 nm to 280 nm. 3. The wavelength of light in a short wavelength portion of near ultraviolet light or visible light in the second step is 300 nm to 500 nm.
The method for photodecomposing an organic chlorine compound according to claim 1, wherein 4. The method according to claim 3, wherein the irradiation amount of light in the second step is 10 μW / cm ² to 10 mW / cm ² in the wavelength region. 5. The irradiation amount of light in the second step is 50.
The photodecomposition method for an organochlorine compound according to claim 4, wherein the power is from μW / cm ^{2 to 5} mW / cm ² . 6. The method for photodecomposing an organic chlorine compound according to claim 1, wherein a part of the organic chlorine compound is decomposed by irradiation of ultraviolet rays in the first step to generate chlorine gas. 7. The method for photodecomposing an organic chlorine compound according to claim 6, wherein the concentration of chlorine gas generated in the first step is 5 ppm to 1000 ppm. 8. The organic chlorine compound according to claim 1, wherein a gas containing the organic chlorine compound as a decomposition target gas is directly added to the gas containing the organic chlorine compound after the ultraviolet irradiation in the second step. Photolysis method. 9. A means for irradiating an ultraviolet ray having a wavelength of 150 nm to 280 nm to a gas containing an organic chlorine compound in a closed space, a reaction tank containing the gas after the irradiation of the ultraviolet ray,
The wavelength of the gas contained in the reaction tank is 300 nm to 5 nm.
An apparatus for decomposing an organic chlorine compound, comprising: means for irradiating near-ultraviolet light of 00 nm or light of a short wavelength portion of visible light. 10. The volume of a closed space which is irradiated with ultraviolet light having a wavelength of 150 nm to 280 nm is 300 nm to 300 nm.
The apparatus for decomposing an organochlorine compound according to claim 9, wherein the apparatus is in a range of 1/5 to 1/100 of the volume of the reaction tank which is irradiated with light of a short wavelength portion of 500 nm near-ultraviolet light or visible light. 11. The apparatus for decomposing an organic chlorine compound according to claim 9, wherein the gas after the irradiation of the ultraviolet light contains chlorine gas generated by partially decomposing the organic chlorine compound by the irradiation of the ultraviolet light. 12. An apparatus for decomposing an organochlorine compound according to claim 9, further comprising means for directly supplying a gas containing an organochlorine compound as a gas to be decomposed to said reaction tank.