JPH0631135A - Method for decomposing volatile organic halogen compound-containing gas in vapor phase - Google Patents

Abstract

PURPOSE:To efficiently decompose off an org. halogen compd. with the small input of energy by bringing a volatile org. halogen compd. -contg. gas into contact with a reducing agent in the presence of a metal carrying catalyst and then into contact with organisms capable of decomposing hydrocarbons. CONSTITUTION:Raw water is introduced into a stripping tower 1 and air is blown into the tower from a blower 4. The obtained aerated gas is discharged from the top of the tower 1, joined with hydrogen from an H2 cylinder 5 and introduced into a column 2 packed with a reduction catalyst (e.g. catalyst carrying Pd, etc., on the carrier of alumina, etc.) to reduce org. halogen compd. The gas is then introduced into a column 3 packed with a filler (e.g. activated carbon) carrying organisms (e.g. activated sludge) to biologically decompose the hydrocarbons formed by the reaction. Consequently, the org. halogen compd. transferred to a gaseous phase from waste water or soil by aeration, etc., is decomposed into gaseous CO2 and a treatable inorg. acid by passing it through the catalyst and biological bed without any pretreatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas phase decomposition treatment of volatile organic halogen compounds. More specifically, the present invention takes out a volatile organic halogen compound existing in a liquid or soil as a gas phase, reduces it with a reducing agent and a catalyst, and then decomposes the reduced product into carbon dioxide by biological treatment. It is about the method.

[0002]

Water containing a volatile organic halogen compound,
Examples of wastewater treatment methods include (1) aeration treatment,
Known are (2) adsorption treatment, (3) oxidative decomposition treatment, (4) biological treatment, (5) thermal decomposition treatment, and the like. However, each of these methods has some problems,
Not always satisfactory. For example, the method (1) simply transfers organic halogen compounds mixed in groundwater or soil to the atmosphere, and is not a drastic solution to environmental problems. The method (2) is a method of trapping and recovering an organic halogen compound, and is often used in combination with the method (1). In this case, the adsorbing ability of the adsorbent (such as activated carbon) is humidity. It is unavoidable that it will drop significantly under the influence of. In addition, the adsorption treatment method requires regeneration of the adsorbent, and in the case of performing steam regeneration or the like, regeneration waste liquid containing a high-concentration organic halogen compound is regenerated. For the purpose of radically solving environmental pollution, it is necessary to detoxify and decompose as described in (3) to (5) above. Among them, the oxidative decomposition method (3) has been extensively studied as a decomposition treatment method for organic halogen compounds, and many methods utilizing ultraviolet rays, ozone, hydrogen peroxide, etc. have been reported. Also, the decomposition treatment methods (4) and (5) have been reported, but not many. In the oxidative decomposition treatment method or the thermal decomposition treatment method, the amount of energy required for the generation of ultraviolet rays or ozone, or heating is large, and inevitably the cost is high, and halogen generated by decomposition coexists with an organic substance. It has a problem that it is easily re-reacted and a new organic halogen compound may be generated. Further, although the biological treatment method of (4) requires a small amount of input energy, a microorganism capable of efficiently decomposing has not been found yet, and thus cannot be said to be a practical method. On the other hand, a method of using iron powder as a reductive decomposition method has been reported, but it is not sufficiently satisfactory.

[0003]

DISCLOSURE OF THE INVENTION The present invention efficiently decomposes and removes organohalogen compounds in gas that has been transferred from the wastewater or soil into the gas phase by aeration treatment or the like with a small amount of energy, and a new The object of the present invention is to provide a method for treating a gas containing a volatile organic halogen compound without regenerating an organic halogen compound.

[0004]

Means for Solving the Problems The present inventors have paid attention to the fact that many organic halogen compounds contained in wastewater or soil to be removed are volatile, and once they are vaporized by aeration treatment or the like. If the organic halogen compound is reduced by a gas-phase catalytic reaction after being driven out, the organic halogen compound is efficiently decomposed into harmless hydrocarbons and hydrogen chloride, and the generated hydrogen chloride or other hydrogen halide is present in the organic substance. Not to re-react with and the biodegradation of the produced hydrocarbons
It was confirmed that it can be remarkably easily performed as compared with an organic halogen compound, and the present invention was completed based on this finding.

That is, the present invention is characterized in that a volatile organic halogen compound-containing gas is brought into contact with a reducing agent in the presence of a metal-supported catalyst, and then an organism having a hydrocarbon decomposing property is brought into contact with the volatile organic compound. The present invention provides a gas phase decomposition treatment method for a halogen compound-containing gas.

The present invention will be described in detail below. The volatile organic halogen compound-containing gas that is the subject of the present invention is an organic halogen compound-containing exhaust gas of various manufacturing processes or the air from the wastewater and the soil containing the volatile organic halogen compound,
A gas obtained by aeration operation treatment with nitrogen gas or the like is exemplified. The liquid phase such as drainage can be easily obtained by aerating (aeration) gas such as gas or air into the liquid. In the case of soil or the like, it can be obtained by piercing a plurality of pipes into the soil and drawing air with a blower to store it in a tank. Further, in the case of a solid such as soil, the volatile organic halogen compound contained therein may be extracted with water or the like to be contained in the liquid phase and then aerated.

The concentration of the organic halogen compound in the volatile organic halogen compound-containing gas is not particularly limited, but is 0.1
It is possible to use a material of about 10,000 volppm. Further, the volatile organic halogen compound to which the method of the present invention can be applied is usually a volatile one having a boiling point of 150 ° C. or lower, preferably 80 ° C. or lower, and examples thereof include 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 1,1,1-trichloroethane, bromodichloromethane, chlorodibromomethane,
Bromoform and the like can be mentioned.

The catalyst used in the method of the present invention is a metal supported on a carrier, and the metal is
For example, palladium, platinum, ruthenium, rhodium, copper,
Examples thereof include iron, iridium, and nickel. Among these, noble metals such as palladium, platinum, ruthenium, and rhodium are preferable, and palladium and platinum are particularly preferable. A metal, an oxide, a hydroxide or the like is used as the palladium. Examples of the carrier include alumina, titania, activated carbon, zirconia, zeolite, glass, silica, ion exchange resins and plastic pellets, and among these, alumina, zirconia and ion exchange resins are preferable. As the ion exchange resin, a weakly basic anion exchange resin having a styrene-divinylbenzene copolymer as a matrix is preferable. The amount of the metal supported is usually about 0.1 to 10% by weight with respect to the carrier.

The shape of the metal-supported catalyst is not particularly limited, and any shape such as powder, granules or pellets can be used. Granules or pellets are continuously packed in a column or the like. It is advisable to ventilate the gas to be treated. Even the powder form can be packed in a column and operated in a fluidized bed state. As the reducing agent used in the method of the present invention, in addition to hydrogen gas, for example, a hydrogen generating alloy such as a hydrogen storage alloy or the like, and hydrogen by electrolysis of water are used. In the method of the present invention, a volatile organic halogen compound is reductively decomposed using a metal-supported catalyst and a reducing agent. As an example, when the volatile organic halogen compound is trichlorethylene, decomposition is carried out according to the reaction formula shown below. It is supposed to happen. CHCl = CCl ₂ + 3H ₂ → CH ₂ = CH ₂ + 3HCl

That is, trichlorethylene is dechlorinated to produce ethylene and hydrogen chloride. Hydrogen chloride is stable and does not become a source of recontamination. In addition to ethylene, the production of methane and ethane is also recognized. In the method of the present invention, the addition amount of the reducing agent is usually selected in such a range as to replace the halogen of the volatile organic halogen compound with the halogen or more. As the treatment method of the volatile organic halogen compound-containing water in the method of the present invention, it is possible to use a continuous method in which a metal-supported catalyst is packed in a column, and a gas to be treated and a reducing agent are passed through the column, or a batch method. However, the former continuous method is preferable. In the case of this continuous system, the flow velocity of the gas to be treated is 50 to 50 in space velocity.
It is preferably about 000 hr ^-1 .

In order to treat the gas containing hydrocarbons such as ethylene produced by the reduction treatment, it is brought into contact with an organism having a hydrocarbon decomposing ability. Examples of such organisms include activated sludge and the like. Specific contact methods include a column method in which the above-mentioned organism-immobilized packing material is packed and a floating activated sludge treatment method. In the former case, the gas flow velocity is about 2.20 to 5000 hr ^{−1 in} space velocity. Examples of the filler include activity, plastics such as Styrofoam, peat, zeolite and the like. This packed bed is occasionally sprinkled with water as shown in the figure. On the other hand, in the floating state, gas may be supplied to a so-called activated activated sludge treatment device.

[0012]

EXAMPLES The present invention will be described in more detail by way of examples, which should not be construed as limiting the invention thereto.

Example 1 Raw water was introduced into the stripping tower 1 of FIG. 1, air was blown from a blower 4, and the obtained aeration gas was taken out from the upper portion of the stripping tower 1 and mixed with hydrogen to fill it with a reduction catalyst. It was introduced into a column 2 to reduce an organic halogen compound, and then introduced into a column 3 filled with a packing material carrying an organism, and a device for biodegrading hydrocarbons produced by the reduction was assembled.
90 m ^{3 of} raw water containing trichlene 100 mg / liter
Emission tower (1.7 with Net Ring TS-1 filled with Hr)
mφ × 7.5 mH), and air was aerated by aerating air from below at 3000 m ³ / Hr in terms of standard conditions. The trichlene concentration in the treated water was 2 mg / liter or less, and the trichlene concentration in the gas at the outlet of the stripping tower was 0.5 vol ppm.

90 g of hydrogen gas was added to the gas at the outlet of the stripping tower.
Add with Hr 0.5% platinum-alumina catalyst 3mφ x 3mL
Catalytic decomposition tower packed with 1500 kg of pellets (1.2
mφ × 1.5 mH). No trichlene was detected in the outlet gas of the catalytic decomposition tower. This catalyst decomposition tower outlet gas is sprinkled with sewage as it is and filled with peat to which bacteria are attached × 1000 mm × 7200 mmH (filling height 36
00 mmH) SV 3,000 led to biodegradation tower. Hydrocarbons such as ethylene and methane were not detected in the biodegradation tower outlet gas. In the apparatus shown in FIG. 1, the removal property of trichlene was examined under the same conditions except that the catalyst decomposition tower was excluded and hydrogen gas was not added. The results are shown below. The analysis was performed with a gas chromatograph.

Trichlorene, ethylene, at the outlet of the biodegradation tower,
Concentration of methane (Volume ppm) Example Comparative Example Tricethylene Ethylene Methane Triclen 10 hours ND ND ND 0.5 50 hours ND ND ND 0.6 100 hours ND ND ND 0.4 200 hours ND ND ND 0.5

[0016]

EFFECTS OF THE INVENTION According to the present invention, a volatile organic halogen compound in a gaseous state can be treated with a harmless carbon dioxide gas and a treatable inorganic acid (hydrogen chloride without passing through a catalyst and a biological layer without special pretreatment). (Halogen halide) and the pretreatment results in a compound that is easily biodegradable, which has the advantage of dramatically improving treatment efficiency. Also,
Contaminants such as volatile organic halogen compounds extracted from groundwater or soil by aeration or soil extraction can be detoxified in an energy-saving manner instead of being directly emitted to the atmosphere.

[Brief description of drawings]

FIG. 1 is a schematic view of an apparatus used in Example 2.

[Explanation of symbols]

1 stripping tower 2 catalyst tower 3 biological treatment column 4 blower 5 H ₂ generator (H ₂ cylinder)

Claims (1)

[Claims] 1. A volatile organohalogen compound-containing gas, which comprises contacting a volatile organohalogen compound-containing gas with a reducing agent in the presence of a metal-supported catalyst, and then contacting the organism with a hydrocarbon decomposing ability. Gas phase decomposition treatment method.