JP3384464B2 - Method for treating volatile organic chlorine compounds - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the treatment of volatile organic chlorine compounds, and in particular, to the decomposition of volatile organic chlorine compounds such as trichloroethylene and tetrachloroethylene in the gas phase. How to do it. [0002] Environmental pollution due to volatile organic chlorine compounds, particularly soil pollution, groundwater and drinking water pollution, has been reported and has become a serious social problem. It is said that the contamination source is mainly caused by dry cleaning and leakage of a degreasing cleaning agent in the metal industry and the electronics industry. In general, these volatile organic chlorine compounds contained in water are expelled into the gas phase by a stripping method in which air is blown into the liquid and aerated, and this is made harmless by an adsorbent. It is also well known that a well is installed in the soil, the inside of the well is depressurized by a vacuum pump, and the volatile organic chlorine compound extracted into the gas is treated with an adsorbent. [0003] The gas adsorption treatment is a relatively reliable method, but when the concentration of the target component is low, the saturated adsorption amount of the adsorbent is as small as several% (WT) or less, and the disposable or factory take-back is regenerated. In that case, a large amount of adsorbent is required, and equipment and running costs are also high.
It was a problem. Even with used adsorbents, there is a risk that the environment will be polluted again even if the waste is disposed of or recycled at the factory of the adsorbent manufacturer. Therefore, a method has been developed in which the adsorbent is regenerated in situ and used repeatedly. In this method, an adsorbed component is desorbed by a regeneration gas or water vapor, subsequently recovered by a condenser (condenser), and a volatile organic chlorine compound is concentrated and disposed. When the concentrated and recovered volatile organic chlorine compounds are disposed of as industrial waste, there is a concern that they may cause environmental pollution again, and it is hard to say that this is a complete and safe processing method. [0005] Therefore, a method of decomposing and detoxifying volatile organic chlorine compounds using ultraviolet rays has been studied. For example,
A method of irradiating a gas containing a dilute volatile organic chlorine compound (stripping gas, etc.) with ultraviolet light. After adsorbing the organic chlorine compound in the gas to the adsorbent, the adsorbent is regenerated by heated air, and the regenerated exhaust gas A method of irradiating the volatile organic chlorine compound therein with ultraviolet rays for decomposition. However, there is a problem that these conventional ultraviolet decomposition methods cannot sufficiently decompose. SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and provides a method for efficiently and safely treating volatile organic chlorine compounds which can be sufficiently decomposed even by an ultraviolet ray decomposition method.
The task is to provide a law . [0007] In order to solve the above problems, the present invention provides an exhaust gas containing a volatile organic chlorine compound.
Adsorbed on activated carbon, from the activated carbon by steam or hot air
After desorption, the desorbed gas is condensed and liquefied to form volatile organic chlorine compounds.
Separate the solution containing
Transferring the chlorine compound into the gas phase, adding water vapor to the gas phase, and then exposing the gas phase to ultraviolet rays to decompose the volatile organic chlorine compound in the gas phase. This is a method for treating an organic chlorine compound . [0008] In the processing method, it is possible to <br/> the hydrogen source is used a gas containing water vapor. Further, in the present invention, the hydrogen source addition device for adding a gas containing water <br/> vapor in the gas phase containing the volatile organic chlorine compounds, volatile organic chlorine compounds are added to the hydrogen source an ultraviolet irradiation device which irradiates ultraviolet rays to the gas containing it is possible to use processing apparatus volatile organic chlorinated compounds with. Further, in the present invention, it is preferable that the above-mentioned processing apparatus is provided with a wet neutralization apparatus for processing the gas after the irradiation of the ultraviolet rays with an alkali agent. As described above, the present invention blows air into a volatile organic chlorine compound which is concentrated and recovered from a dilute gas and liquefied, or a volatile organic chlorine compound which has been used and must be disposed of. After irradiating the volatile high-concentration gas with ultraviolet rays in the presence of a hydrogen source to decompose volatile organic chlorine compounds in the gas into hydrogen chloride, carbon dioxide and water,
Further, the present invention provides a method for treating volatile organic chlorine compounds in which the gas is wet-neutralized with an alkaline agent such as caustic soda, passed through an adsorbent as a security filter, and then released to the atmosphere. [0010] It is effective to use ultraviolet rays having a short wavelength. When a mercury lamp is used, a wavelength of 253.7 nm, which is a resonance line of mercury, is compared with 184.9 nm.
4.9 nm is more effective. Therefore, the light source should be a low-pressure mercury lamp that efficiently generates this wavelength and that is made of a material (synthetic quartz) that transmits this wavelength. In addition, trichlorethylene (TCE)
It is considered that the chemical reaction formula for decomposing tetrachloroethylene is as shown below. [0011] trichlorethylene _{C 2 HCl 3 + 3 / 2O} 2 + H 2 O → 2CO 2 + 3HCl tetrachlorethylene _{C 2 Cl 4 + O 2 +} 2H 2 O → 2CO 2 + 4HCl organochlorine compounds in this manner is decomposed, with water The chlorine in the organic chlorine compound is fixed as hydrogen chloride by the reaction. The volatile organic chlorine compound concentration in the gas phase to be irradiated is 100 ppm to 50,000 ppm in the case of TCE.
The degree is effective. Further, for stable decomposition of a volatile organic chlorine compound by ultraviolet rays, a hydrogen source is required as shown in the above reaction formula according to the concentration of the substance, particularly the amount of chlorine atoms therein. The point of the present invention is to supply the hydrogen source to secure a required amount. For example, the decomposition of 1 mol of TCE requires 2 mol of hydrogen atoms, which is 1 m for water molecules.
ol. Water vapor in the atmosphere fluctuates depending on the weather. At a temperature of 10 ° C. and a relative humidity of 30%, the water vapor concentration is 900 ppm. The maximum concentration of trichlorethylene that can be decomposed with water vapor at this concentration is 900 ppm. Therefore, in order to stably decomposing TCE of high concentration, it is necessary to stably supply steam to the source of hydrogen. The operation of the present invention will be described with reference to FIG. 1 showing an example of the present invention. In FIG. 1, raw water 1 containing volatile organic chlorine compounds such as trichloroethylene and tetrachloroethylene is guided to a stripping device 2 and is sprayed on a packing 3 from above, and stripping gas (air) blown by a blower 4 from below. 5)
As a result, the volatile organic chlorine compounds in the water are removed, and the treated water 6 flows out. On the other hand, the exhaust gas 7 exhausted from the stripping device 2 contains a volatile organic chlorine compound expelled from the water, and this exhaust gas 7 is introduced into an adsorption device 9 filled with an adsorbent 8 to be adsorbed. When the organic chlorine compound is brought into contact with the agent 8, the organic chlorine compound in the exhaust gas 7 is adsorbed by the adsorbent 8, and is discharged as a detoxified processing gas 10. Adsorption conditions may be room temperature and normal pressure. Under such adsorption conditions, the adsorbent 8 loses its adsorbing ability due to the progress of adsorption, but before reaching breakthrough, the exhaust gas is stopped from being vented or switched to a pre-adsorption device, and the adsorbent component of the adsorbent 8 is adsorbed. It is only necessary to carry out desorption and regeneration. For desorption and regeneration, for example, steam 12 generated in the boiler 11 is supplied to the adsorbent layer after being further heated by the heater 13, passed through the adsorbent layer, and the volatile organic chlorine compound adsorbed by the adsorbent 8 is desorbed. I do. A high-temperature gas such as air can be used for desorption in addition to steam. The discharged vapor 14 containing a volatile organic chlorine compound is led to a condenser 15 where it is condensed and recovered. The condensed and recovered liquid is guided to a separation tank 16, where it is separated into a volatile organic chlorine compound liquid 17 and water 18, and the water 18 is mixed with the raw water 1 and subjected to stripping or the like again. On the other hand, volatile organic chlorine compounds 17
Is led to the waste liquid tank 19. A part of the air generated from an air source 20 such as a compressor is passed through the volatile organic chlorine compound liquid 17 in the waste liquid tank 19 to generate a gas 21 containing a high concentration of the volatile organic chlorine compound. . The gas is mixed with humidified air 23 containing water vapor, which is a hydrogen source, by a hydrogen source adding device, that is, a humidifying tank 22, so as to adjust to a constant concentration and air volume. Subsequently, the gas 24 containing the volatile organic chlorine compound and water vapor is allowed to flow for a predetermined time into a UV reactor 26 having a built-in low-pressure ultraviolet lamp 25 to decompose the organic chlorine compound in the gas by ultraviolet rays. The exposure time to ultraviolet rays is appropriately selected according to the intensity of the ultraviolet lamp and the gas flow rate. The gas 27 containing hydrogen chloride generated by the decomposition is guided to a neutralization tank 28, where it is neutralized and rendered harmless. Finally, it passes through a security filter 29 filled with activated carbon and is discharged to the atmosphere as a detoxified processing gas 30. . The neutralization tank may be of a scrubber type. EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto. Example 1 Using the apparatus shown in FIG. 1, a volatile organochlorine compound was treated according to the present invention under the following conditions. Treatment conditions (stripping apparatus 2) Method: Terralet packed tower (5 m packed) Aeration (air) / water flow: 30 Water flow speed: 60 m / h Trichlorethylene in raw water of raw water: 0.3 to 0.6 mg / Trichlorethylene in liter treated water: <0.03 mg / liter [Adsorption device 8] Method: Adsorption of fibrous activated carbon (steam regeneration) Adsorbent ventilation SV: 5000 liter / h Regenerated steam flow rate: 30 kg / h Inlet (exhaust gas) trichloroethylene : 2 to 4 ppm Outlet (processing gas) trichlorethylene: <0.33 ppm Regeneration frequency: Every 8 hours Regeneration time: 30 minutes (UV reactor 26) Ultraviolet lamp: Low-pressure mercury lamp (110w) Raw gas flow: 0.5 ~ 3.8 liter / min UV irradiation time: 1 ~ 8min UV reactor Capacity: 3.8 liter Raw gas trichlorethylene concentration: 18500 ppm Raw gas steam concentration: 25000 ppm Treatment gas trichlorethylene concentration: 0.5 ppm or less (Neutralization tank 28) Neutralizer: 1 N caustic soda solution (security filter 29) Filling Agent: granular activated carbon SV: 1000 (liter / hr) As described above, it was found that trichlorethylene was decomposed almost 100% by ultraviolet irradiation. At this time, the raw gas contained a sufficient amount of water vapor. FIG. 2 shows the results of analyzing the concentrations of carbon dioxide and carbon monoxide in the UV reactor processing gas. At a residence time of 8 minutes, carbon monoxide almost disappeared and the carbon dioxide concentration was 3750.
It became 0 ppm. From this result, it was found that carbon contained in the raw gas trichloroethylene was oxidatively decomposed into almost 100% carbon dioxide gas. Example 2 A volatile organic chlorine compound was adsorbed to and desorbed from an adsorbent by the same operation as in Example 1, and air was blown into the condensed liquid to be gasified, followed by treatment with a UV reactor. However, the trichlorethylene concentration was set to be about 5000 ppm. (UV reactor 26) Ultraviolet lamp: low-pressure mercury lamp (110 w) Raw gas flow rate: 1.0 to 7.6 liter / min Ultraviolet irradiation time: 0.5 to 4 min UV reactor volume: 3.8 liter Raw gas trichlorethylene concentration: 4900 ppm Raw gas water vapor concentration: 30,000 ppm Processed gas trichlorethylene concentration: 0.5 ppm or less (Neutralization tank 28) Neutralizer: 1 N caustic soda solution (security filter 29) Filler: Granular activated carbon SV: 1000 liter / h
r As described above, it was found that trichloroethylene was decomposed almost 100% by irradiation with ultraviolet rays. At this time, the raw gas contained a sufficient amount of water vapor. FIG. 3 shows the results of analyzing the concentrations of carbon dioxide and carbon monoxide in the UV reactor outlet gas. At a residence time of 4 minutes, carbon monoxide almost disappeared and the carbon dioxide concentration was 1010
It became 0 ppm. From this result, it was found that carbon contained in the raw gas trichloroethylene was oxidatively decomposed into almost 100% carbon dioxide gas. As described above, according to the present invention, volatile organic chlorine compounds can be effectively rendered harmless, and environmental pollution can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process diagram showing an example of an apparatus used for a processing method of the present invention. FIG. 2 is a graph showing gas concentrations of CO ₂ and CO in a UV reactor outlet gas. FIG. 3 is a graph showing gas concentrations of CO ₂ and CO in a UV reactor outlet gas. [Explanation of Signs] 1: Raw water, 2: Stripping device, 3: Packed material, 4:
Blower, 5: aerated gas, 6: treated water, 7: exhaust gas,
8: adsorbent, 9: adsorption device, 10: adsorption treatment gas, 1
1: boiler, 12: steam, 13: heater, 14:
Desorption steam, 15: condenser, 16: separation tank, 17:
Volatile organic chlorine compound liquid, 18: water, 19: waste liquid tank, 20: compressor, 21: gas containing high concentration of volatile organic chlorine compound, 22: humidifier, 23: humidified air, 2
4: gas to be treated, 25: low-pressure ultraviolet lamp, 26: UV
Reactor, 27: decomposition gas containing hydrogen chloride, 28: neutralization tank, 29: security filter, 30: detoxified processing gas

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Takashi Iwaizumi 4-2-1 Motofujisawa, Fujisawa-shi, Kanagawa Inside Ebara Research Institute Co., Ltd. (72) Inventor Yasuhiro Mitsui 1-6-127 Konan, Minato-ku, Tokyo (56) References JP-A-62-191095 (JP, A) JP-A-61-200836 (JP, A) JP-A-52-68859 (JP, A) JP-A-4-200715 (JP, A) Japanese Utility Model Hei 4-70126 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) B01D 53/70 B09C 1/06 C02F 1/20

Claims (1)

(57) [Claims] 1. An exhaust gas containing a volatile organic chlorine compound is adsorbed on activated carbon, desorbed from the activated carbon by steam or hot air, and the desorbed gas is condensed and liquefied to form a volatile organic chlorine compound. Is separated, the separated solution is aerated, and the volatile organic chlorine compound is transferred into the gas phase, and after adding water vapor to the gas phase , the gas phase is exposed to ultraviolet rays, and A method for treating a volatile organic chlorine compound, comprising decomposing the volatile organic chlorine compound.