JP3293207B2 - Method for treating volatile organic halogen compound-containing gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a method for treating a gas containing a volatile organic halogen compound. More specifically, the present invention relates to a method for efficiently performing a gas phase decomposition treatment of a volatile organic halogen compound by suppressing the influence of moisture in a gas to be treated when performing a gas phase reduction decomposition treatment of a volatile organic halogen compound. Things.

[0002]

2. Description of the Related Art Volatile organic halogen compounds are one of environmental pollutants such as groundwater, soil and air, and it is necessary to remove the compounds. Various methods of treating wastewater, wastewater, groundwater, or soil bleed gas or exhaust gas have been studied.
As this treatment method, for example, (1) volatilization (aeration) treatment, (2) adsorption treatment, (3) oxidative decomposition treatment, (4) biological treatment, and (5) thermal decomposition treatment are known. However, each of these methods has some problems,
It is not always satisfactory. For example, the method (1) simply transfers volatile organic halogen compounds mixed in groundwater or soil to the atmosphere. Also,
The method (2) is a method for adsorbing and recovering a volatile organic halogen compound, and is often used in combination with the method (1). In this case, it is necessary to regenerate the adsorbent. During regeneration, regenerated effluent and exhaust gas containing a high concentration of the compound are discharged. Since these pollutants remain as they are, they cannot be a fundamental solution to environmental problems, and require a decomposition treatment technique capable of rendering the compounds harmless. As a method of decomposing a volatile organic halogen compound, the above-mentioned methods (3) to (5) have been studied. However, the method (3) is a method utilizing ultraviolet rays, ozone, hydrogen peroxide, etc., but requires a large amount of energy for ultraviolet irradiation, generation of ozone, heating, and the like.
It is inevitable that costs will increase. Although the processing methods (4) and (5) have been reported, there are not many examples. As described above, a practical method for efficiently detoxifying volatile organic halogen compounds has not been found yet.

[0003]

SUMMARY OF THE INVENTION Under such circumstances, the present invention can efficiently decompose a compound contained in a volatile organic halogen compound-containing gas to detoxify the compound, and can provide a long-term treatment. It is an object of the present invention to provide a method for treating a volatile organic halogen compound-containing gas capable of performing a stable treatment operation over a long period of time.

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, mixed a reducing gas with a volatile organic halogen compound-containing gas and passed the volatile gas through a catalyst layer. Focusing on the fact that the moisture contained in the gas to be treated has an effect on the performance of the reductive decomposition when the organic halogen compound is subjected to reductive decomposition, after reducing the relative humidity of the gas to be treated, It has been found that the object can be achieved by bringing the gas into contact with a reducing gas, and the present invention has been completed based on this finding. That is, the present invention provides a volatile organic compound comprising: bringing a gas containing a volatile organic halogen compound into contact with a reducing gas in the presence of a metal catalyst while reducing the relative humidity of the gas. An object of the present invention is to provide a method for treating a halogen compound-containing gas.

Hereinafter, the present invention will be described in detail. The volatile organic halogen compound-containing gas to be the object of the present invention is obtained by, for example, aeration treatment from volatile organic halogen compound-containing exhaust gas from various manufacturing processes, water or wastewater containing volatile organic halogen compounds, groundwater, and the like. Examples of the gas include gas obtained from soil containing a volatile organic halogen compound by bleeding or the like. From a liquid phase such as waste water, it can be easily obtained by aerating (aeration) a gas such as nitrogen gas or air in the liquid.
In the case of soil or the like, it can be obtained by piercing a plurality of pipes into the soil, drawing air in with a blower, and storing the air in a tank. In the case of a solid such as soil, the volatile organic halogen compound contained therein may be extracted with water or the like and contained in a liquid phase before aeration. The concentration of the organic halogen compound in the volatile organic halogen compound-containing gas is not particularly limited, but is 0.1 to 10,000 ppm by volume.
Of the degree can be used. The volatile organic halogen compound-containing gas thus obtained contains water, and this water has an adverse effect on the gas phase reductive decomposition treatment. Especially when aerated, the relative humidity of the gas is 100%
In order to achieve a high-speed and stable gas-phase reductive decomposition treatment of SV5000 hr ^-1 or more over a long period of time, effective measures against humidity (moisture) are necessary.

Therefore, in the present invention, measures are taken to reduce the relative humidity of the gas to be treated containing water and volatile organic halogen compounds before performing the gas phase reductive decomposition treatment. There is no particular limitation on the method for reducing the relative humidity. For example, (1) a method for reducing the relative humidity by heating the gas to be treated or the catalyst layer, and (2) a method for reducing the relative humidity by mixing dry air. (3) a method of reducing the relative humidity by dehumidification with an ion exchange resin,
Etc. can be used. The heating in the method (1) can be performed by using a heater, a heat pump, a roots blower, or the like, and the dry air in the method (2) can be obtained by using a dehumidified PSA (pressure swing adsorption method). it can. Further, as the ion exchange resin in the method (3), for example, a Na-type strong cation exchange resin or the like can be used. Further, in addition to these methods, a method using a membrane, a method using an industrial adsorbent, and the like can also be used.

The target relative humidity varies depending on the chemical properties and structure of the surface of the catalyst carrier and is appropriately selected. For example, when platinum / γ-alumina is used as the catalyst, the relative humidity is usually 60% or less, preferably 60% or less. By reducing the content to 40% or less, reductive decomposition treatment performance is greatly improved. The metal catalyst used in the reductive decomposition treatment in the method of the present invention is preferably a metal supported on a carrier, and examples of the metal include platinum, palladium, ruthenium, rhodium, iron, copper, iridium and nickel. However, among these, noble metals such as palladium, platinum, ruthenium, and rhodium are preferable, and palladium and platinum are particularly preferable. These noble metals are used in the form of metals, oxides, hydroxides and the like. Further, as the carrier, for example, alumina, silica, silica alumina, titania, activated carbon,
Examples thereof include zirconia, zeolite, glass, plastic, pellets, and ion exchange resins. Of these, alumina, zirconia and ion exchange resins are preferred. As the ion exchange resin, a weakly basic anion exchange resin having a styrene-divinylbenzene copolymer as a base is preferable. The loading amount of the metal is usually 0.1 to the carrier.
It is about 1 to 10% by weight. There is no particular limitation on the shape of the catalyst, such as spherical, pellet, powder, granular,
Any shape can be used, but it is preferable to fill a spherical or pellet-like or granular one into a column or the like and to continuously feed the gas to be treated. Even a powdery material can be packed in a column and operated in a fluidized bed state.

As the reducing gas used in the method of the present invention, in addition to hydrogen gas, for example, those generating hydrogen such as a hydrogen storage alloy and hydrogen obtained by electrolysis of water are used. In the method of the present invention, in the presence of the metal catalyst,
By bringing the volatile organic halogen compound-containing gas subjected to the relative humidity reduction treatment into contact with the reducing gas, the volatile organic halogen compound is reductively decomposed. The amount of the reducing gas to be added is usually selected in the range of the amount of hydrogen necessary for replacing the halogen of the halogen compound of the volatile organic halogen compound or more. As a method for treating the volatile organic halogen compound-containing gas in the method of the present invention, either a continuous method in which a metal catalyst is packed in a column and a gas to be treated and a reducing gas are passed through the column, or a batch method can be used. Although it is possible, the former continuous method is preferable. In the case of this continuous system, the flow rate of the gas to be treated is 100
It is preferably about 20,000 hr ^-1 . The volatile organic halogen compound to which the method of the present invention can be applied is generally a volatile organic compound having a boiling point of 150 ° C. or lower, preferably 80 ° C. or lower, such as trichloroethylene, tetrachloroethylene, trans-1, 2-dichloroethylene, cis-1,2-dichloroethylene, carbon tetrachloride, chloroethane, methylene chloride, chloroform, vinyl chloride, 1,1-dichloroethane, 1,2-dichloroethane, 1,2-dichloropropane, dichlorobromoethylene, , 1,1-trichloroethane, bromodichloromethane, chlorodibromomethane, bromoform, various fluorocarbons, and the like.

[0009]

Next, the present invention will be described in more detail by way of examples, which should not be construed as limiting the present invention. Example 1 Heating of Gas to be Treated (Catalyst Layer) The test was carried out using the apparatus shown in FIG. When trichlorethylene-containing water was introduced from the storage tank 1 to the stripping tower 2 and sprinkled from above, air was blown from below by the blower 3 and brought into countercurrent contact. As a result, a gas containing 0.5 ppm by volume of trichlorethylene (relative humidity 90%, 25% ° C). 0.5wt as catalyst
The trichloroethylene-containing gas was passed through the catalyst layer (inner diameter 30 mm, length 70 mm) 4 filled with about 50 g of% Pt / r-Al ₂ O ₃ together with hydrogen from the hydrogen generator 5 at SV 12,000 hr ^-1 . The concentration of trichlorethylene in the processing gas at the outlet of the catalyst layer was almost the same as the concentration of the inlet 8 hours after the start of hydrogenation. The gas phase decomposition treatment was continued for 7 days under the same conditions as described above, except that constant temperature water of about 40 ° C. was circulated from the constant temperature layer 7 to the jacket 6 of the catalyst layer and the catalyst layer was heated. The removal rate of trichlorethylene hardly changed with time, and was about 85%. The vapor pressure of water in the gas to be treated at a temperature of 25 ° C. and a relative humidity of 90% is 21.4 mmHg. When this is heated to 40 ° C., the relative humidity becomes about 39%.

Example 2 Dilution with dry air This was carried out using the apparatus shown in FIG. In the same manner as in Example 1, air containing 0.5 ppm by volume of trichloroethylene (relative humidity: 90%, 25 ° C.) was obtained, and dried air (relative humidity: almost 0%) from the PSA device 8 was added to the air at a volume ratio of 1: The mixture was mixed at a ratio of 1 and subjected to a gas phase decomposition treatment by ventilating the catalyst layer in the same manner as in Example 1. As a result, the removal rate of trichlorethylene was about 8%.
0-90% and duration was 7 days. In addition,
The PSA device 8 has a tower diameter of 40 mm, a height of 400 mm, and a volume of 0.4 mm.
5 liters of adsorption tower filled with synthetic zeolite 5A
Using a tower apparatus, adsorption pressure 9 kgf / cm ² , cycle time 10
Driven in minutes.

Example 3 Dehumidification by a cation exchange resin The measurement was carried out using the apparatus shown in FIG. In the same manner as in Example 1, air containing 0.5 ppm by volume of trichloroethylene (relative humidity 90%, 25 ° C.) was obtained, and this was packed with a column (30 mm in inner diameter, length 30 mm) packed with 500 ml of Na-type strong cation exchange resin (SK1B). SV 5,000 hr at 9)
Ventilated with ^-1 . The concentration of trichlorethylene in the outlet gas was almost the same as that of the inlet gas. Although trichlorethylene did not adsorb to the resin, the relative humidity of the outlet gas was 1% or less. When this dehumidified gas was passed through the catalyst layer 4 in the same manner as in Example 1 to conduct a gas phase decomposition treatment experiment, no trichlorethylene was detected in the treatment gas at the catalyst layer outlet. Duration was 30 hours. After 30 hours, the operation was stopped, and the ion exchange resin was heated to 150 ° C. for 1 hour to evaporate water. After that, when it was used again under the same conditions, it could be operated for 30 hours.

[0012]

According to the present invention, a treatment for reducing the relative humidity of a volatile organic halogen compound-containing gas is performed, and then the gas is brought into contact with hydrogen in the presence of a metal catalyst to thereby form the volatile organic halogen compound. Can be efficiently decomposed to make it harmless, and a stable processing operation can be performed for a long time.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an apparatus used in Example 1.

FIG. 2 is a schematic diagram of an apparatus used in Example 2.

FIG. 3 is a schematic diagram of an apparatus used in Example 3.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Storage tank 2 Stripping tower 3 Blower 4 Catalyst layer 5 Hydrogen generator 6 Jacket 7 Thermostat 8 PSA apparatus 9 Cation exchange resin packed column

Continuation of the front page (56) References JP-A-4-321634 (JP, A) JP-A-63-99413 (JP, A) JP-A-61-200836 (JP, A) JP-A-54-59233 (JP) U.S. Pat. No. 5,134,424 (US, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C07B 35/06 A62D 3/00 B01D 53/26 B01D 53/70 B01D 53/86 WPI (DIALOG)

Claims (1)

(57) [Claims] 1. A volatile organic halogen compound comprising: contacting a gas containing water and a volatile organic halogen compound with a reducing gas in the presence of a metal catalyst while reducing the relative humidity of the gas. A method for treating a compound-containing gas.