JPH03151023A - Photochemical treatment of gaseous harmful material - Google Patents

Abstract

PURPOSE:To photooxidize the harmful gas and to conveniently and efficiently treat the harmful gas by irradiating the harmful gas with vacuum UV rays in the presence of air or oxygen. CONSTITUTION:A gas contg. an organochlorine-based solvent such as trichloroethylene, dichloroethane, chloroform and carbon tetrachloride, fluorocarbons such as CFC-11 and CFC-113, benzene, methyl alcohol, diethyl ether, etc., is photooxidized and decomposed in the presence of gaseous oxygen, hydrogen peroxide or an aq. soln. of the peroxides such as periodate, perchlorate and chlorate. Synthetic quartz capable of transmitting the light of >= about 200nm wavelength is used as the material for the ordinary low-pressure mercury lamp as the vacuum UV source. Internal irradiation and external irradiation are used as the photoirradiation method. The irradiated acidic gas is passed through aq. alkali and removed. The harmful gas is conveniently and efficiently treated by this method.

Description

[Detailed Description of the Invention] [Prior Art] The present invention creates an unstable excited state by irradiating a gaseous harmful substance that is difficult to treat with vacuum ultraviolet light in the presence of air or oxygen, and at the same time, The present invention relates to a method for purifying contaminated air and treating harmful gases by generating ozone from coexisting oxygen and promoting the decomposition of harmful substances.

In factories, laboratories, and the like that use low-boiling-point compounds such as organic solvents and harmful gases, indoor air is contaminated by leaks of steam and gas. Many of these organic solvents and gases are highly toxic and difficult to treat. For example, organic chlorine solvents such as trichlorethylene, tetrachlorethylene, and 1,1.1-trichloroethane are known to be carcinogenic. Furthermore, the use of fluorocarbons used in refrigerants and sprays is regulated because they destroy the ozone layer.

In addition, various harmful organic solvents and gases that emit bad odors are known.

[Problems to be Solved by the Invention] Conventionally, these air pollutants have been removed by adsorption. However, this method requires expensive adsorbents;
It has disadvantages such as difficulty in processing after adsorption and contamination due to desorption. Furthermore, there are many harmful gases for which suitable adsorbents have not been found.

[Means for Solving the Problems] As a result of intensive research into a method for treating gaseous harmful substances that can overcome these drawbacks, the inventors of the present invention have found that, in the presence of air or oxygen, vacuum treatment with a wavelength of 200 nm or less A simple method that photooxidizes by irradiating it with ultraviolet light.
This led to the invention of a highly efficient method for treating harmful gases.

The vacuum ultraviolet light source used in the present invention uses synthetic quartz, which can transmit light with a wavelength of 200 nm or less, as the material of a normal low-pressure mercury lamp. The larger the capacity of the light source, the stronger the one resolution power, but a light source of about 100 W is sufficient for contaminated air from a workplace such as a normal factory.

This method is basically a photooxidative decomposition and requires the presence of oxygen at the same time as the light irradiation. Irradiation with vacuum ultraviolet light is sufficient to decompose dilute harmful substances present in the air. However, when the concentration of harmful substances increases, oxygen becomes insufficient and new substances with high molecular weight are often formed without being decomposed. In such cases, it is necessary to add oxygen in advance or to add oxygen during the process to ensure complete decomposition. The oxygen may be air, commercially available oxygen gas, or hydrogen peroxide. Also peroxide salts,
For example, periodates, perchlorates, chlorates can also be used. These peroxide salts are dissolved in water and used.
The concentration of the aqueous peroxide salt solution used in such a way that harmful gases pass through its upper surface varies depending on the amount of harmful gases, but is usually 1 to 10 normal.

In addition to the above-mentioned trichlorethylene, tetrachlorethylene, and 1,1.1-trichloroethane, gases that can be decomposed by this method include dichloroethane, dichloroethylene, tetrachloroethane, chloroform, organic chlorine solvents such as carbon tetrachloride, Freon 11, Freon 12, Freon such as Freon 113, Freon 114, and Freon 115, benzene, toluene, chlorobenzene, methyl alcohol, methyl alcohol, propyl alcohol, butyl alcohol, acetone,
Examples include diethyl ether, but are not limited thereto.

Light irradiation methods include both internal irradiation and external irradiation methods. Internal irradiation is a method in which a light source is installed inside a tube through which contaminated air passes and irradiates it directly. External irradiation is a method of irradiating light from outside the tube through the wall of the tube. For external irradiation, if the tube is made of quartz, a considerable amount of light in the vacuum ultraviolet region can pass through, but if synthetic quartz is used, there is less attenuation of the light. However, internal irradiation is preferable to external irradiation because there are fewer restrictions on tube material and light intensity.

The air after light irradiation contains organic halogen compounds such as hydrogen chloride and hydrogen fluoride, and nitrogen compounds and sulfur compounds such as nitric acid, nitrous acid, sulfuric acid, and sulfurous acid. These acidic gases can be removed by passing the light-irradiated gas through alkaline water.

[Example] Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Air containing 32,000 ppm of trichlorethylene was put into a 4.3 mfl quartz glass container, and a 70 W low-pressure mercury lamp with a pump tube made of synthetic quartz was heated to 10,20 mfl.
．． External irradiation was performed for 30 minutes. At this time, irradiation was performed while flowing nitrogen between the light source and the container. The gas in the container before and after light irradiation was analyzed using a gas chromatograph to measure the amount of decomposition. As a result, 84.94.98% for each irradiation time
was decomposing.

Example 2 In the same manner as in Example 1, air containing 5,200 ppm of 1,1,1-trichloroethane was placed in the same container as in Example 1, and irradiated with the same light source.

68% and 85% were degraded after 20 and 50 minutes of irradiation, respectively.

Example 3 Freon 11 248. 35% in air containing OOOppm
50 μQ of hydrogen peroxide solution was added, and irradiation was performed for 10, 20, and 30 minutes in the same manner as in Example 1.

93.97°98% of Freon 11 at each irradiation time
was decomposed. After irradiation for an additional 40 minutes, the amount of carbon dioxide gas was analyzed and it was found that 10-5 moles of carbon dioxide gas had been produced. This corresponds to the fact that the entire amount of Freon 11 added at the beginning was converted to carbon dioxide gas, indicating that the intermediate products were also completely decomposed.

Example 4 The container used in Example 1 was filled with oxygen, and 34.5% of Freon 113 was added. It was added so that it became OOOppm.

This was irradiated in the same manner as in Example 1. It was 51% after 10 minutes of irradiation, and decreased to 15% after 1 hour. 4 more
After irradiation for 0 minutes, this gas was introduced into a 0°1N aqueous sodium hydroxide solution, and as a result of anion analysis in the water, 3×10 −@mol of chlorine ions and fluorine ions were detected. This corresponds to the case where the entire amount of Freon 113 is decomposed and chlorine ions and fluorine ions are liberated.

Example 5 After filling the container with nitrogen in the same manner as in Example 1,
1 was added at a concentration of 28,800 ppm. This was irradiated in the same manner as in Example 1. 11% after 15 minutes of irradiation
However, almost no carbon dioxide gas was generated. This seems to indicate that Freon 11 was converted into other substances without being decomposed. Next, 100 μQ of 6N sodium perchlorate was added to the same sample and irradiated for 15 minutes in the same manner. Freon 11 is 5.4%, 2X10-
6 moles of carbon dioxide gas was generated. This indicates that approximately half of the total amount of fluorocarbons was converted to carbon dioxide gas.

Procedural Amendment 2 Kagiken No. 1532] 1. Indication of the case 1999 Patent Application No. 289280 2. Title of the invention Photochemical treatment method for gaseous hazardous substances 3. Person making the amendment Patent applicant related to the case Address: 1-3-1 Kasumigaseki, Chiyoda-ku, Tokyo Name (1
14) Director of the Agency of Industrial Science and Technology Ken Sugiyu 4, Designated Agent Slant Box 8, Contents of Amendment The following amendments will be made to the specification of this application.

(1) From page 4, line 16 to line 17, replace "...chlorobenzene, methyl alcohol, methyl alcohol, propyl alcohol, butyl alcohol,..." with "...chlorobenzene, methyl alcohol, propyl alcohol,..." Corrected to "butyl alcohol..."

Claims (3)

[Claims] (1) A method of decomposing harmful substances in the air using vacuum ultraviolet light. (2) A method of decomposing gaseous hazardous substances by mixing air or oxygen, or passing the hazardous gas over a hydrogen peroxide solution or an aqueous peroxide salt solution, and irradiating the substance with vacuum ultraviolet light. (3) A method in which the gas after photolysis treatment is passed through an alkaline aqueous solution to remove generated inorganic substances.