JP2005161216A - Purification of gas containing harmful organic substances by electron beam irradiation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for purifying a gas containing harmful organic substances by utilizing high-density active species and ozone generated by electron beam EB irradiation and improving energy use efficiency as compared with conventional methods. To do.
A method for purifying a gas containing a toxic organic substance comprising irradiating an oxygen-containing gas containing a toxic organic substance with an electron beam, and oxidizing and decomposing the toxic organic substance in the irradiation gas by a high-density active species generated; From the ozone generated by irradiation of the unreacted active species or electron beam in the irradiation gas while allowing the irradiation gas to flow through the solid catalyst filling tank and adhering and concentrating undecomposed harmful organic substances or decomposition products on the surface of the solid catalyst. A method comprising combining the step of oxidatively decomposing the undecomposed harmful organic substance or decomposition product on the catalyst surface with dissociated oxygen atoms.
[Selection] Figure 1

Description

  The present invention relates to a method for oxidative decomposition and detoxification by electron beam irradiation of organic substances harmful to a human body contained in a gas.

  As a method of purifying gas containing harmful organic substances, conventionally, a gas containing harmful organic substances is irradiated with an electron beam (hereinafter also referred to as “EB”), and the high density active species generated from the gas components in the gas. There is a method to oxidize and decompose harmful organic substances.

  In the above conventional method, as the concentration of the harmful organic substance decreases after EB irradiation, the reaction between the active species or between the active species and the base gas component becomes relatively faster as compared with the oxidative decomposition. The components resulting from these reactions are often active species with relatively low reactivity, and since the reactivity with harmful organic substances is small in the gas, the concentration of harmful organic substances per unit energy input is oxidatively decomposed. It falls (for example, refer nonpatent literature 1 and 2).

  In addition, as decomposition products generated from harmful organic substances, non-volatile organic substances or particulate substances composed of non-volatile organic substances may be generated, and these substances easily adhere to the irradiation container or the inner surface of the pipe and are in the gas phase. (See, for example, Non-Patent Document 3). For this reason, even if active species are present in the gas, these products cannot be oxidatively decomposed.

Furthermore, since ozone generated from the base gas component with EB irradiation has a very low reactivity with harmful organic substances, a decomposition technique that actively utilizes ozone in the gas has not been developed so far.
K. Hirota and three others, “Dechlorination of chlorobenzene in air with electron beam”, Radiation Physic and Chemistry, The Netherlands, Elsevier, 2000, 57, p. 63-73 K. Hirota and two others, “Electron-Beam Decomposition of Carbon Tetrachloride in Air / Nitrogen”, Bulletin of the Chemical Society of Japan, The Chemical Society of Japan 2000, 73, p. 2719-2724 Miki Takahashi, “Basics of Aerosolology”, Aerosol Society of Japan, 2003, p. 46-71

  Therefore, in the present invention, a method for purifying a gas containing harmful organic matter, which has improved energy utilization efficiency as compared with the conventional method by utilizing high-density active species and ozone generated by electron beam irradiation, is provided. Is an issue.

  As a result of earnest research to solve the above problems, the present inventors have attempted to improve the energy utilization efficiency by combining the oxidation reaction by EB irradiation and the oxidation reaction on a solid catalyst or in water. The present invention has been completed.

That is, the present invention is a method for purifying a gas containing harmful organic substances,
Irradiating an oxygen-containing gas containing a harmful organic substance with an electron beam, and oxidizing and decomposing the harmful organic substance in the irradiation gas by the generated high-density active species;
From the ozone generated by irradiation of the unreacted active species or electron beam in the irradiation gas while allowing the irradiation gas to flow through the solid catalyst filling tank and adhering and concentrating undecomposed harmful organic substances or decomposition products on the surface of the solid catalyst. It is characterized by combining with a step of oxidatively decomposing the undecomposed harmful organic substance or decomposition product on the catalyst surface by the dissociated oxygen atoms.

Further, the present invention is a method for purifying a gas containing harmful organic substances,
Irradiating an oxygen-containing gas containing a harmful organic substance with an electron beam, and oxidizing and decomposing the harmful organic substance in the irradiation gas by the generated high-density active species;
Circulating the irradiation gas into water, dissolving the components in the irradiation gas, dissolving dissolved undecomposed harmful organic substances or decomposition products, dissolving dissolved unreacted active species or ozone generated by electron beam irradiation And the step of oxidatively decomposing the undecomposed harmful organic substance or decomposition product with the water-soluble active species generated in this manner.

  Furthermore, the present invention is characterized in that in the above method, water containing hydrogen peroxide is used instead of water.

  According to the purification method of the present invention, the oxidative decomposition rate of harmful organic substances per unit energy input and the complete oxidative decomposition rate up to inorganic substances are improved, and pollutant gas can be rendered harmless with high energy efficiency.

  Active species generated by the reaction of active species or active species produced by EB irradiation, or active species and base gas (oxygen-containing gas such as air containing harmful organic substances) components have low reactivity with harmful organic substances, but solid catalysts Sufficient ability to oxidize and activate. Moreover, these active species can oxidatively decompose high-concentration organic substances concentrated in water or water containing hydrogen peroxide.

A conceptual diagram of the purification method of the present invention is shown in FIG.
In the oxidative decomposition reaction process of harmful organic substances in the gas in the EB irradiation field, first, nonvolatile gaseous substances are formed from the organic substances, and part of them is condensed to form particulate substances. These materials are then oxidatively decomposed to produce inorganic substances. Such a non-volatile or particulate substance generally has a property of being easily attached to a solid catalyst having a large surface area and being easily dissolved in water. Therefore, in the present invention, these substances are deposited on a solid catalyst or concentrated while being dissolved in water or water containing hydrogen peroxide, so that the above active species or the active species and the base gas component are mixed. Oxidative decomposition is efficiently carried out by active species resulting from the reaction, which have relatively low reactivity and a relatively long lifetime.

  Furthermore, ozone contained in the irradiation gas is dissociated on the solid catalyst or in water, and as a result, oxygen atoms that can oxidatively decompose organic substances are liberated. Further, in water containing hydrogen peroxide, hydroxyl radicals that are highly reactive are generated from the reaction with hydrogen peroxide. By using these oxygen atoms or hydroxyl radicals, it is possible to oxidize and decompose harmful organic substances and non-volatile or particulate substances that could not be decomposed in an EB irradiation field in a very short time.

  A gas containing harmful organic substances is circulated through the solid catalyst, water, or hydrogen peroxide-containing water immediately after EB irradiation to effectively utilize active species that are less reactive on the catalyst surface or in water, etc. The decomposition product can be concentrated and oxidatively decomposed, and further activated by ozone dissociation.

  Here, the `` hazardous organic substance '' as used in the present invention is a general term for organic substances that may cause carcinogenesis, a decrease in immune function, or a harmful effect on the human body such as sick house syndrome, In particular, substances designated by the Air Pollution Control Law, organic solvent poisoning prevention regulations and specific chemical substances, etc., and organic substances that are subject to the regulation of obstacle prevention, as well as polychlorinated biphenyls (PCB), dioxins and many Ring aromatic organic substances and the like.

In addition, the “active species” in the present invention is free radicals, ions, electrons, and the like generated from gas molecules by electrons having an energy number of eV to several MeV.
The “solid catalyst” in the present invention is, for example, a catalyst that can be activated by heat, a so-called thermal catalyst, a photocatalyst that can be activated by ultraviolet light or visible light, and the like. Examples of the thermal catalyst include a three-way catalyst containing rhodium, palladium, or platinum, and the thermal catalyst is used while being kept at a temperature of about room temperature to 500 ° C. These shapes are preferably a honeycomb shape or a spherical shape. On the other hand, photocatalysts include titanium dioxide, gallium phosphate, zirconium oxide, thallium oxide, cadmium sulfide, potassium thallium oxide, cadmium selenide, titanium strontium oxide, niobium oxide, zinc oxide, molybdenum sulfide, iron oxide, bismuth oxide, oxidation Examples thereof include a carrier containing tungsten or tin oxide added with a transition metal such as platinum, gold, silver, tungsten, molybdenum, vanadium, chromium, copper, or cobalt. In addition, there is no restriction | limiting by the crystal structure of a support | carrier, For example, in the case of the titanium dioxide widely utilized as a photocatalyst, any of anatase, a rutile, or brookite may be sufficient. Furthermore, the shape of the catalyst is preferably a shape filled with a spherical catalyst, a honeycomb shape, a fiber shape, or the like, and the use temperature is preferably from room temperature to a maximum of about 500 ° C.

Furthermore, the “water containing hydrogen peroxide” in the present invention is an aqueous solution having a hydrogen peroxide concentration of 30% by weight at the maximum.
A first embodiment of the purification method of the present invention is shown in FIG.

  In FIG. 2, first, a gas 6 containing harmful organic substances is circulated through the irradiation container. Next, the electron beam 2 generated from the electron beam generator 1 passes through the irradiation window foil 4 of the irradiation container 3 and is incident on the gas. At that time, the active species react with harmful organic substances in the electron beam irradiation field 4 in the irradiation container. Subsequently, irradiation gas is distribute | circulated in the solid catalyst 8 installed in the back | latter stage of the electron beam irradiation field. Here, the solid catalyst is heated by the heater 9 as necessary. The surface of the solid catalyst is activated by the remaining active species, and unreacted harmful organic substances and decomposition products are oxidized on the surface of the solid catalyst. As a result, the purified gas 10 is obtained.

  Here, the “EB generator” as used in the present invention means that electrons generated from a metal surface are accelerated by an electric field by heating a metal filament in a vacuum or applying a strong electric field to a metal electrode or the like. This is an apparatus for extracting accelerated electrons into an atmospheric pressure gas by passing through a thin diaphragm made of an inorganic material or an organic material such as a metal. The beam generated by the EB generator may be either continuous or pulsed.

A second embodiment of the purification method of the present invention is shown in FIG.
In FIG. 3, similarly to the first aspect described above, after reacting the active species with harmful organic substances in the electron beam irradiation field 14 in the irradiation container, water 18 and Mix with irradiation gas. At this time, unreacted harmful organic substances and decomposition products are oxidized in water by the remaining active species activated in water, and as a result, purified gas 20 is obtained.

A third embodiment of the purification method of the present invention is shown in FIG.
In FIG. 4, in the second embodiment described above, hydrogen peroxide mixed water 28 is used instead of water 18.

  As a method of dissolving the irradiation gas component in water or water containing hydrogen peroxide, a method of aeration of the irradiation gas in the water or aqueous solution, or a method of circulating the irradiation gas in a pipe sprayed with water or an aqueous solution Furthermore, there is a method in which irradiation gas is circulated in a tube filled with a metal filling or the like and flowing through this wall while water or an aqueous solution is transmitted.

  The following examples illustrate the invention in more detail.

(Example 1)
Pure air containing 1100 ppmv of benzene (carbon dioxide concentration of 0.5 ppmv or less) was irradiated with EB of acceleration energy lMeV at an absorbed dose of 5 kGy (hereinafter referred to as “basic experimental system”).

  The resulting gas contained about 60 ppmv benzene, about 30 ppmv carbon dioxide and about 20 ppmv ozone. Therefore, the oxidative decomposition rate of benzene (= decreased benzene concentration / pre-irradiation benzene concentration × 100) is about 40%, and the complete oxidative decomposition rate (= generated carbon dioxide concentration / (pre-irradiation benzene concentration × 6) × 100). Was about 5%.

  In the basic experimental system, a container filled with a solid catalyst was introduced immediately after the irradiation container. The container filled with the solid catalyst was covered with a shielding lead plate so that EB and accompanying braking X-rays were not directly irradiated. In this experimental system, pure air containing 100 ppmv of benzene was irradiated with EB so that the absorbed dose was 5 kGy, and the irradiation gas was put into a container filled with spherical (diameter 5 mm) anatase-type titanium dioxide pellets as a solid catalyst. lead. As a result, the obtained gas contained about 50 ppmv benzene, about 50 ppmv carbon dioxide and about 10 ppmv ozone. The oxidative degradation rate and complete oxidative degradation rate of benzene were about 50% and about 8.3%, both higher than the results of the basic experimental system.

(Example 2)
In the basic experimental system shown in Example 1, a washing bottle containing ultrapure water was installed immediately after the irradiation container. The air-cleaning bottle containing the ultrapure water was covered with a shielding lead plate so that EB and accompanying braking X-rays were not directly irradiated. In this experimental system, pure air containing 100 ppmv of benzene was EB-irradiated so that the absorbed dose was 5 kGy, and the irradiation gas was guided to a washing bottle containing ultrapure water. The benzene concentration in the gas after passing through the washing bottle decreased to about 50 ppmv immediately after the irradiation gas was introduced, but became constant at about 60 ppmv after about 30 minutes. Further, the gas passing through the washing bottle contained about 50 ppmv of carbon dioxide. The oxidative degradation rate of benzene was the same as that in the basic experimental system, but the complete oxidative degradation rate was about 8.3%, which was larger than the value obtained in the basic experimental system. Further, almost no ozone was detected in the gas passing through the washing bottle.

(Example 3)
In the basic experimental system shown in Example 1, a washing bottle containing ultrapure water containing 10% hydrogen peroxide (hereinafter simply referred to as “hydrogen peroxide solution”) is installed immediately after the irradiation container. did. The washing bottle containing hydrogen peroxide was covered with a shielding lead plate so that EB and the accompanying braking x-rays were not directly irradiated. In this experimental system, pure air containing 100 ppmv of benzene was irradiated with EB so that the absorbed dose was 5 kGy, and the irradiation gas was guided to a washing bottle. The concentrations of benzene and carbon dioxide in the gas after passing through the washing bottle were about 45 ppmv and 60 ppmv, respectively, and no ozone was detected. The oxidative degradation rate and complete oxidative degradation rate of benzene were about 55% and about 10%, respectively, which were higher than the results of the basic experimental system.

FIG. 1 is a conceptual diagram of the purification method of the present invention. FIG. 2 is a conceptual diagram showing a first embodiment of the purification method of the present invention. FIG. 3 is a conceptual diagram showing a second embodiment of the purification method of the present invention. FIG. 4 is a conceptual diagram showing a third aspect of the purification method of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electron beam generator 2 Electron beam 3 Irradiation container 4 Electron beam irradiation field 5 Irradiation window stay 6 Gas containing harmful organic substance 7 Solid catalyst filling tank 8 Solid catalyst 9 Heater 10 Purifying gas 11 Electron beam generator 12 Electron beam 13 Irradiation Container 14 Electron beam irradiation field 15 Irradiation window night 16 Gas containing harmful organic substances 17 Water tank 18 Water tank 19 Spray water 20 Purified gas 21 Electron beam generator 22 Electron beam 23 Irradiation container 24 Electron beam irradiation field 25 Irradiation window night 26 Harmful Gas containing organic matter 27 Storage water tank 28 Mixed water tank 29 Spray mixed water 30 Purified gas

Claims (3)

A purification method for gases containing harmful organic substances,
Irradiating an oxygen-containing gas containing a harmful organic substance with an electron beam, and oxidizing and decomposing the harmful organic substance in the irradiation gas by the generated high-density active species;
From the ozone generated by irradiation of the unreacted active species or electron beam in the irradiation gas while allowing the irradiation gas to flow through the solid catalyst filling tank and adhering and concentrating undecomposed harmful organic substances or decomposition products on the surface of the solid catalyst. A method comprising combining the step of oxidatively decomposing the undecomposed harmful organic substance or decomposition product on the catalyst surface with dissociated oxygen atoms. A purification method for gases containing harmful organic substances,
Irradiating an oxygen-containing gas containing a harmful organic substance with an electron beam, and oxidizing and decomposing the harmful organic substance in the irradiation gas by the generated high-density active species;
Circulating the irradiation gas into water, dissolving the components in the irradiation gas, dissolving dissolved undecomposed harmful organic substances or decomposition products, dissolving dissolved unreacted active species or ozone generated by electron beam irradiation And a step of oxidatively decomposing the undecomposed harmful organic substance or decomposition product with the water-soluble active species generated as described above. A purification method for gases containing harmful organic substances,
Irradiating an oxygen-containing gas containing a harmful organic substance with an electron beam, and oxidizing and decomposing the harmful organic substance in the irradiation gas by the generated high-density active species;
The irradiation gas is circulated in water containing hydrogen peroxide to dissolve the components in the irradiation gas, and the dissolved undecomposed harmful organic substance or decomposition product is dissolved into the unreacted active species or electron beam irradiated. And a step of oxidatively decomposing the undecomposed harmful organic substance or decomposition product with a water-soluble active species generated by dissolving ozone generated by the process.

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