JPH0751539A - Decomposition of organochlorine compound - Google Patents

Abstract

PURPOSE:To decompose an organochlorine compd. at a high flow rate with high efficiency by decomposing organochlorine compd.-containing gas at a medium or high temp. using an alumina catalyst. CONSTITUTION:A quartz column 1 is arranged in an electric heater 4 so as to be capable of being heated to a predetermined temp. The quartz column 1 is packed with an alumina catalyst and an air sending pipe 2 is connected to the column 1. The column 1 is heated to the predetermined temp. by the electric heater 4 and organochlorine-containing gas 3 is passed through the column 1 from the sending pipe 2 to be catalytically decomposed under heating. By this constitution, the organochlorine compd. is prefectly decomposed at a high speed at a relatively low temp. and the catalyst withstands long-time use.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to decomposition and purification of organic chlorine compounds in air or gas, or to adsorb organic chlorine compounds on activated carbon and desorb the adsorbed organic chlorine compounds again in air or gas. The present invention relates to decomposition and purification of organic chlorine compounds in the air or gas in the case of being allowed to do so.

[0002]

2. Description of the Related Art In recent years, environmental pollution due to volatile organic chlorine compounds such as trichloroethylene and tetrachloroethylene has become a problem, and it is said that the pollution source is caused by dry cleaning, cleaning wastewater in the metal industry, electronic industry and the like. Since a large amount of organic chlorine compounds are handled in dry cleaning, transfer of chlorine-based solvent to groundwater due to wastewater or wastewater leakage is a serious social problem. for that reason,
Regarding the tetrachlorethylene, the Environment Agency has established and managed provisional guidance guidelines to prevent the emission of these compounds into public water bodies.

On the other hand, volatile organochlorine compounds such as trichlorethylene and tetrachloroethylene contained in washing wastewater of the metal industry and the electronics industry do not have a high boiling point and have a poor affinity for water, so that air is blown into the water. As a result, the organochlorine compound can be transferred from the waste water into the air in a considerably efficient manner. Therefore, in these cases, by interposing a step of transferring the organic chlorine compound from the waste water into the air through a stripping device or the like, various other coexisting COD and BOD components and S
There is a method of treating wastewater by separating it from S and the like.

If the exhaust gas exhausted by stripping is released into the atmosphere without being treated, it will cause a new environmental pollution. However, since an organic chlorine compound can be adsorbed very efficiently by passing it through an activated carbon adsorption tower, it has been generally practiced to adsorb the exhaust gas with an adsorbent to render it harmless.

As described above, it is preferable to adsorb both the organic chlorine compound used in dry cleaning and the organic chlorine compound from the metal industry, the electronic industry, etc. with activated carbon or the like. As a method of treating the adsorbed activated carbon, the adsorbed activated carbon is treated with heated air or gas to desorb organic chlorine compounds from the activated carbon to obtain air or gas containing the organic chlorine compounds. Method for decomposing (Japanese Patent Publication No. 63-48573, Japanese Patent Publication No. 63-
(Japanese Patent No. 48574) has been proposed. However,
The method of decomposing the organic chlorine compound by irradiating the desorbed gas with ultraviolet rays also has a poor decomposition efficiency, and since the organic chlorine compound remains in the gas irradiated with the ultraviolet ray, there remains a problem that re-adsorption is required.

Further, conventionally, as a method of decomposing an organic chlorine compound contained in air or gas, a combustion method of decomposing at a temperature of 1000 ° C. or more is known. However, it is dangerous because it will not completely decompose unless heated to a high temperature.
In addition, because of the high temperature, corrosion of the device due to acid is likely to occur.
There is also a method of decomposing an organic chlorine compound by thermal decomposition using a noble metal catalyst. With this method, it is possible to decompose a high concentration of organic chlorine compounds at a relatively low temperature, but the durability time of the catalyst is extremely short due to the corrosive action of the noble metal catalyst by the acid.

[0007]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems, and makes it possible to decompose organic chlorine compounds in air or gas at relatively low temperature, at high speed, and more thoroughly. To provide the technology. Further, the present invention is
An object of the present invention is to provide a method for catalytic thermal decomposition of an organic chlorine compound using a catalyst that can be used for a long time.

[0008]

The above-mentioned problems are (1) a method for decomposing an organochlorine compound, which comprises decomposing an organochlorine compound-containing gas at an intermediate or high temperature using an alumina catalyst. Preferably, it can be solved by (2) a method of decomposing an organochlorine compound, which comprises decomposing an organic chlorine compound-containing gas with hydrogen and then decomposing it at an intermediate temperature or high temperature using an alumina catalyst. The above decomposition reaction is carried out by stripping the organochlorine compound when it is contained in water and transferring it to air or gas, and when it is contained in air or gas, the alumina catalyst is used as it is. Air or gas containing an organic chlorine compound may be passed through the packed column for decomposition.

As the alumina catalyst used in the present invention,
Alumina simple substance is preferable, but a substance containing a certain amount of silica or the like as an impurity may be used. And its crystal form is
It may be γ-Al ₂ O ₃ , ε-Al ₂ O ₃ , or α-Al ₂ O _{3, and} it does not depend on the type as long as it is an alumina catalyst.
The shape can be freely selected such as spherical shape or rod shape. A silica-alumina catalyst in which silicon atoms of silicon oxide are replaced by aluminum atoms and an alumina catalyst supported on palladium, which will be described later, are not suitable for the present invention in terms of effect and life.

Among the above-mentioned organic chlorine compounds, trichlorethylene, tetrachloroethylene and the like, which are generally used in a large amount, are particularly important as a treatment target. Further, the above-mentioned intermediate temperature to high temperature is 400 ° C. or higher, preferably 400 to 80.
It is 0 ° C. In the treatment method of the present invention, air or gas containing an organic chlorine compound is added to SV2000 to 10,000 hr.
Even if the treatment is performed at a high speed of ^-1 , the organic chlorine compounds in the air or gas can be decomposed sufficiently. When air or gas containing an organic chlorine compound is thermally decomposed, chlorine gas is produced as a by-product, but by adding hydrogen gas to the column in an amount sufficient for chlorine to react during thermal decomposition, it is easy to process. It can be hydrogen chloride.

[0011]

When the organic chlorine compound present in air or gas is heat-treated, chlorine is separated from the organic chlorine compound.
When an alumina catalyst is present in this atmosphere, the decomposition temperature can be lowered, and the organic chlorine compound present in air or gas can be sufficiently decomposed at moderate to high temperatures. When hydrogen coexists when the organic chlorine compound is thermally decomposed, the separated chlorine reacts with the coexisting hydrogen to form hydrogen chloride which is easy to process.

[0012]

EXAMPLES Hereinafter, using the apparatus shown in FIGS. 1 and 2,
An example of catalytic thermal decomposition of an organic chlorine compound will be shown by 1) an example of the decomposition method of the present invention using an alumina catalyst and 2) a comparative example by a conventional method. However, the embodiments of the present invention are not limited to the following description.

1. Apparatus An apparatus used in Examples and Comparative Examples of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 shows an apparatus for catalytic thermal decomposition of organic chlorine compounds. In FIG. 1, a quartz column 1 is installed in an electric heater 4 so that the temperature can be raised to a predetermined temperature.
An air supply pipe 2 is connected to the quartz column 1, a medium gas 3 containing an organic chlorine compound is passed through the air supply pipe 2, and these 3 are introduced to the quartz column 1 to catalytically decompose the organic chlorine compound. The gas after the reaction is discharged from the system through the gas outflow pipe 8. In the case of adding hydrogen to the medium gas 3 containing the organic chlorine compound, a branch pipe 5 is provided at the addition point A, and the branch pipe 5 is connected to the hydrogen gas cylinder 6. FIG. 2 shows a state in which the silica column 1 is filled with the catalyst 7.

2. Catalyst In the example of the present invention, an alumina catalyst (diameter: 2 m) was used as the catalyst 7.
m × 4 mm long rod-shaped body, surface area 225 m ² / g; Toyo CCI Co., Ltd., trade name CF331-4) was used.
In the comparative example, zeolite (particle size 3 mm), titania (particle size 3 mm) and palladium-supported alumina (particle size 3 mm) were used as the catalyst 7. The amount of catalyst is 20 cm
³ used. Organic Chlorine Compound In the examples and comparative examples of the present invention, tetrachlorethylene (PCE) and trichlorethylene (TCE) were used as the organic chlorine compound.

EXAMPLE Air was used as the medium gas, the initial concentration of TCE in this air was 2000 ppm, and the initial concentration of PCE was 100 ppm.
It is set to 0 ppm. The PC is connected to the air supply pipe 2 of the reactor shown in FIG.
Air 3 containing E or TCE (hereinafter referred to as a sample) was sent. In the case of adding hydrogen gas, before feeding to the quartz column 1, 10 times as much hydrogen gas as TCE or PCE was added from the hydrogen gas cylinder 6 to the air 3 containing the sample at the addition point A. The quartz column 1 is heated to a predetermined temperature by an electric heater 4, an alumina catalyst 7 is placed in the column 1, air 3 containing a sample is passed through the column 1, and the decomposed gas is discharged from a gas outflow pipe 8 to the outside of the system. The decomposition rate was obtained by analyzing the residual amount of TCE or PCE in the exhaust gas. Reaction conditions (aeration amount, reaction temperature, hydrogen gas addition amount),
The reaction results (decomposition rate) are shown in Table 1 together with the durability time of the catalyst.

Comparative Example Air was used as the medium gas 3, the initial concentration of TCE was 2000 ppm and the initial concentration of PCE was 1000 ppm in the air, and the air was fed to the air feeding pipe 2 of the reactor shown in FIG. When hydrogen gas is added, TCE or PC is added to the air 3 containing the sample at the addition point A before being fed to the quartz column 1.
Hydrogen gas in an amount 10 times that of E was added. A quartz column 1 is heated to a predetermined temperature by an electric heater 4, a zeolite, titania or palladium-supported alumina catalyst 7 is placed in the column 1, and an air 3 containing a sample is placed in the column 1.
The decomposed gas was discharged to the outside of the system through the gas outflow pipe 8, and the decomposition rate was obtained by analyzing the residual amount of TCE or PCE in the exhaust gas. The reaction conditions (aeration amount, reaction temperature, hydrogen gas addition amount) and reaction results (decomposition rate) are shown in Table 1 together with the catalyst durability time.

[0017]

[Table 1]

It can be seen from Table 1 that the catalytic pyrolysis of the organic chlorine compound by the treatment method of the present invention is superior to the catalytic pyrolysis of the organic chlorine compound using the conventional catalyst in the following points. Recognize.

That is, (1) the catalyst of zeolite, titania, and palladium-supported alumina, which has been conventionally used for the catalytic thermal decomposition treatment of organic chlorine compounds, is 300 to 500 ° C.
Although TCE can be decomposed at such a low temperature, the durability of the catalyst was extremely short because the catalyst was weak against acid. On the other hand, in the case of the present invention using an alumina catalyst,
Irrespective of whether hydrogen gas is added or not, if the temperature is raised to 600 ° C., both tetrachloroethylene (PCE) and trichlorethylene (TCE) are SV2000hr ⁻¹ 9
It could be decomposed by 8% or more. The durability of the alumina catalyst was 300 hours or more. When an alumina catalyst was used and hydrogen gas was added, the decomposition rate was 98% or more at 700 ° C. even at a high flow rate of SV10000 hr ⁻¹ .

[0020]

When the organic chlorine compound contained in air or gas is removed by catalytic thermal decomposition, the method for decomposing an organic chlorine compound of the present invention has the following effects. By using an alumina catalyst, a catalyst durability time of 300 hours or more can be obtained. SV10000 hr ^-1 can be processed even at a high flow rate, and the decomposition efficiency is extremely high. Since it can be decomposed even at an intermediate temperature of 500 ° C, it is less dangerous than in the case of non-contact decomposition. For various types of COD and BOD components, such as sewage and industrial wastewater, which also contain a large amount of SS, a stripping process that blows air into the treated water and transfers the organochlorine compounds to the treated water is also included. By using the present invention, PCE 0.1 mg / liter or less, TCE 0.3 mg or less for sewage or industrial wastewater using the present invention.
It is possible to reduce the content of organic chlorine compounds to the level of the strict treatment regulation of not more than 1 liter / liter.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an apparatus for catalytic pyrolysis of organochlorine compounds.

FIG. 2 is a schematic view of a column packed with a catalyst.

[Explanation of symbols]

 1 Quartz column 2 Air supply pipe 3 Medium gas + sample 4 Electric heater 5 Branch pipe 6 Hydrogen gas cylinder 7 Catalyst packed bed 8 Gas outflow pipe A Hydrogen gas addition point

Claims (2)

[Claims] 1. A method for decomposing an organochlorine compound, which comprises decomposing an organochlorine compound-containing gas using an alumina catalyst at moderate to high temperatures. 2. A method for decomposing an organochlorine compound, which comprises mixing hydrogen into a gas containing an organochlorine compound and then decomposing the mixture at a medium to high temperature using an alumina catalyst.