JPH06106171A - Treatment of volatile organohalogen compound - Google Patents

Abstract

PURPOSE:To efficiently decompose a volatile organohalogen compd. contained in water, waste water or exhaust gas to make the same harmless without bringing about the corrosion of a device or side reaction. CONSTITUTION:A fluid containing a volatile organohalogen compd. is passed through a metal-supported catalyst bed 3 while a reducing agent is added to the fluid and subsequently passed through a heating oxidative decomposition device 5. Hydrogen halide formed by the catalytic reductive decomposition of the volatile organohalogen compd. is stable and not again reacted with the coexisting org. substance to form a side reaction product. Since reductive decomposition reaction is advanced under a low temp. condition in the vicinity of room temp., a problem of the corrosion of a device due to hydrogen halide is suppressed. Hydrocarbon formed by catalytic reductive decomposition can be decomposed into carbon dioxide and water by heating oxidative decomposition (e.g; catalytic thermal oxidative decomposition). In this case, since no acid is formed as a decomposition product, the corrosion of the device is not brought about even under a heating condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating volatile organic halogen compounds, and in particular, by combining the catalytic reduction decomposition method and the oxidative decomposition method, the volatile organic halogen compounds in water, waste water and exhaust gas are combined. The present invention relates to a method for efficiently detoxifying a product without causing problems such as equipment corrosion and by-products.

[0002]

2. Description of the Related Art Volatile organic halogen compounds are one of environmental pollutants such as groundwater, soil and air, and their treatment is necessary. Conventionally, many methods have been studied for treating volatile organic halogen compounds contained in water, waste water, and exhaust gas, and the following methods have been studied and put into practical use.

Activated carbon adsorption method Catalytic thermal decomposition method UV oxidation method Aeration method

[0004]

Of the above processing methods,
In the catalytic thermal decomposition method of 1) and the ultraviolet oxidation method of 1, the input energy cost required for the treatment is excessive, and it is also reported that a side reaction product is generated. Further, the method (1) has a problem that an acid such as hydrogen chloride is generated under high temperature conditions, so that a corrosion resistant material needs to be used and the equipment cost becomes high. Further, the method (1) has a problem of air pollution due to volatile gas. Although many methods are combined as countermeasures, the method (1) has a problem in post-treatment because an effective method for treating exhaust gas and waste liquid discharged during regeneration of the adsorbent has not been found.

The present invention solves the above-mentioned conventional problems and efficiently decomposes volatile organic halogen compounds contained in water, waste water and exhaust gas without causing problems such as equipment corrosion and by-products. An object of the present invention is to provide a method for treating a volatile organic halogen compound that can be treated to render it harmless.

[0006]

The method for treating a volatile organic halogen compound according to the present invention comprises adding a reducing agent to a fluid containing a volatile organic halogen compound, followed by reduction treatment in the presence of a metal-supported catalyst, and then heating. Characterized by oxidative decomposition treatment.

The present invention will be described in detail below.

Examples of the volatile organic halogen compound to be treated in the present invention include trichloroethylene, tetrachloroethylene, 1,1-dichloroethylene, cis-dichloroethylene, trans-dichloroethylene, 1,1,1-trichloroethane and carbon tetrachloride. , Chloroform, vinyl chloride and the like.

As the reducing agent, hydrogen (H ₂ ) gas,
Hydrazine, hydroxylamine and the like are used.

The metal-supported catalyst is a metal supported on a carrier, and examples of the metal include platinum, palladium, ruthenium, rhodium, iron, copper, iridium, nickel, and the like, and the carrier includes alumina, Examples include titania, activated carbon, zirconia, zeolite, silica, glass and ion exchange resins. The shape of these carriers is not particularly limited, and may be spherical, pellet, powder, granular, or the like. The amount of metal supported on such a metal-supported catalyst is usually about 0.1 to 10% by weight.

As the heating oxidative decomposition method, a simple heating method and a contact heating oxidative decomposition method by heating in the presence of a catalyst are exemplified. In the latter case, as the catalyst, the same catalyst as the above-mentioned metal-supported catalyst can be used with air being mixed therein if necessary. Further, the heating temperature for the catalytic heating oxidative decomposition is usually 400 to
It is set to about 500 ° C.

In the method of the present invention, the catalytic reduction treatment decomposes the volatile organic halogen compound into hydrogen halides and hydrocarbons, and among the hydrogen halides and hydrocarbons produced by this catalytic reduction treatment, hydrocarbons are It is decomposed into carbon dioxide and water in the subsequent oxidative decomposition treatment. On the other hand, as a method for removing hydrogen halide, absorption by an alkaline aqueous solution or water, or a contact removal method by an adsorbent holding sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate or the like can be used.

The present invention will be described in detail below with reference to FIGS. 1 and 2 showing an example of an apparatus suitable for carrying out the present invention.

In FIGS. 1 and 2, 1 is a raw water tank, 2 is a diffusion tower equipped with a blower B, 3 is a catalyst packed tower, 4 is a hydrogen halide gas removing device, 5 is a thermal oxidative decomposition device, P ₁ and P ₂
Are pumps 11 to 17 are pipes.

In the apparatus shown in FIG. 1, the volatile organic halogen compound in the raw water is first diffused and treated as a gas, and the raw water in the raw water tank 1 is diffused from a pipe 11 equipped with a pump P ₁ to a diffusion tower 2 The volatile organohalogen compound contained in and introduced into is discharged into a gaseous state. On the other hand, the water from which the volatile organic halogen compound has been diffused and removed is stored in the lower part of the stripping tower 2.

The volatile organohalogen compound gasified in the stripping tower 2 is fed to the catalyst packing tower 3 through the pipe 12, while a reducing agent such as hydrogen gas is added through the pipe 16 and together with the hydrogen gas. It is introduced into the catalyst packed tower 3. In the catalyst packed tower 3, the volatile organic halogen compound is subjected to catalytic reduction treatment and decomposed into hydrogen halide and hydrocarbon.

The fluid containing hydrogen halides and hydrocarbons from the catalyst packed column 3 is then introduced into the hydrogen halide removal device (for example, the adsorbent packed column described above) 4 from the pipe 13 to remove the hydrogen halides. After that, it is introduced from the pipe 14 into the thermal oxidative decomposition device (for example, the catalytic thermal oxidative decomposition column filled with the above-mentioned metal-supported catalyst) 5, the hydrocarbons are decomposed into carbon dioxide and water, which are supplied from the pipe 15. Dissipated into the atmosphere.

The apparatus shown in FIG. 2 directly reduces volatile organic halogen compounds in raw water in a liquid phase.
Raw water in the raw water tank 1 is introduced into the catalyst packed column 3 through a pipe 11 provided with a pump P ₁ together with a reducing agent such as hydrogen gas from the pipe 16, and the volatile organic halogen compound contained therein is carbonized with hydrogen halide and carbon. Catalytic reduction decomposition with hydrogen.

The effluent of the catalyst-packed tower 3 is fed to the stripping tower 2 through a pipe 17 equipped with a pump P _2, and a part of the contained hydrocarbons and hydrogen halides is vaporized into a gaseous state.

The fluid containing hydrogen halide and hydrocarbon gasified in the stripping tower 2 is treated in the same manner as above via the pipe 13, the hydrogen halide gas removing device 4, the pipe 14 and the thermal oxidative decomposition device 5. The processing gas is diffused into the atmosphere through the pipe 15.

On the other hand, since the rest of the hydrogen halide remains in the treated liquid after being diffused, it is neutralized if necessary, or is removed by an ion exchange resin and then discharged or reused.

Whether the volatile organic halogen compound is released before catalytic reduction treatment, or whether the catalytic reduction treatment is performed and then released is appropriately determined depending on the concentration of the volatile organic halogen compound in the raw water. To be done.

The apparatus shown in FIGS. 1 and 2 is a processing apparatus for a liquid containing a volatile organic halogen compound, but as for the gas containing a volatile organic halogen compound, the raw gas is directly sent to the catalyst packed column 3 in FIG. It can be easily processed by feeding.

When the volatile organic halogen compound is subjected to the catalytic reduction treatment in the gas phase, it is preferable to use a gaseous reducing agent such as hydrogen gas, but the volatile organic halogen compound is subjected to the catalytic reduction treatment in the liquid phase. In this case, a liquid reducing agent such as hydrazine may be used in addition to hydrogen gas.

The apparatus shown in FIGS. 1 and 2 is an example of an apparatus suitable for carrying out the present invention, the present invention is not limited to the illustrated method, and the raw water (or raw gas) There is no particular limitation on the distribution speed, the supply amount of the reducing agent, etc.
It is appropriately determined depending on the concentration of the volatile organic halogen compound in raw water (raw gas), the type of the volatile organic halogen compound, and the like.

[0026]

In the present invention, the volatile gas containing the volatile organic halogen compound and the exhaust gas containing the volatile organic halogen compound, or the volatile organic halogen compound, which has been transferred from the water, waste water or soil to the gas phase by aeration treatment or the like. A reducing agent such as hydrogen gas is added to the water and waste water containing, and the volatile organic halogen compound is catalytically reduced and decomposed in the presence of the metal-supported catalyst. Hydrogen halide produced by catalytic reduction decomposition of a volatile organic halogen compound is stable, and does not react with coexisting organic substances again to produce a side reaction product.

Further, since the reductive decomposition reaction proceeds under low temperature conditions near room temperature, the problem of equipment corrosion due to hydrogen halide is suppressed.

On the other hand, the hydrocarbon produced by catalytic reduction decomposition can be decomposed into carbon dioxide and water by thermal oxidative decomposition (for example, catalytic thermal oxidative decomposition). In this case, since no acid is generated as a decomposition product, the device does not corrode even under heating conditions.

In the method of the present invention, for example, the reaction formula for treating trichlorethylene is as follows.

[0030]

[Chemical 1]

[0031]

EXAMPLES The present invention will be described in more detail with reference to the following examples.

Example 1 Ground water containing 0.1 mg / l of trichlorethylene was treated with the apparatus shown in FIG.

First, this groundwater is introduced into a diffusion tower having an inner diameter of 1.7 m and a height of 7.5 m, and is sprinkled from the upper side at a flow rate of 9 m ³ / hr, and air is blown from the lower side at a flow rate of 300 Nm ³ / hr. Then, they were brought into countercurrent contact. The concentration of trichlorethylene in the treated water at the bottom of the stripping tower is about 2 μg / l,
The concentration of trichlorethylene in the volatilized gas discharged from the upper portion was about 0.5 volume ppm.

Hydrogen gas was added to this volatilized gas at 0.3 Nm ³ /
The mixture was added at a flow rate of hr and introduced into a catalyst packed column (inner diameter 1.2 m × height 0.8 m) packed with 750 kg of 0.5 wt% platinum-alumina catalyst (1/8 inch pellet). Trichlorethylene was not detected in the exhaust gas from the catalyst packed tower.

The exhaust gas from this catalyst packed tower was ventilated to a hydrogen chloride gas removing device provided with a hydrogen chloride gas absorption layer containing 300 liters of a 5% aqueous sodium hydroxide solution, and further charged with about 500 liters of a platinum catalyst. Aeration is carried out at a heating oxidative decomposition apparatus at SV = 600 hr ^-1 , and the temperature is 400-45.
It decomposed by heating at 0 ° C. In the exhaust gas of this thermal oxidative decomposition apparatus, not only trichloroethylene and hydrogen chloride but also hydrocarbons such as ethane and methane were not detected, and they could be released into the atmosphere as they were.

[0036]

As described above in detail, according to the method for treating a volatile organic halogen compound of the present invention, the volatile organic halogen compound contained in water, waste water or exhaust gas can be treated without special pretreatment. The detoxification treatment can be performed by efficiently decomposing hydrogen halide, carbon dioxide, and water without causing the problem of corrosion of the device and side reaction products.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example of an apparatus suitable for carrying out the method for treating a volatile organic halogen compound according to the present invention.

FIG. 2 is a system diagram showing another example of an apparatus suitable for carrying out the method for treating a volatile organic halogen compound according to the present invention.

[Explanation of symbols]

 1 Raw Water Tank 2 Emission Tower 3 Catalyst Packing Tower 4 Hydrogen Halide Gas Removal Device 5 Thermal Oxidation Decomposition Device

Front page continuation (72) Inventor Haruka Tsurumaru 3-4-7 Nishishinjuku, Shinjuku-ku, Tokyo Kurita Industry Co., Ltd.

Claims (1)

[Claims] 1. A reducing agent is added to a volatile organic halogen compound-containing fluid, and then reduction treatment is performed in the presence of a metal-supported catalyst.
Then, the method for treating a volatile organic halogen compound is characterized in that it is subjected to oxidative decomposition by heating.