JPH07144117A - Decomposing method of chlorinated organic compound - Google Patents

Abstract

PURPOSE:To efficiently decompose a chlorinated org. compd. in a combustion waste gas and tp prevent the generation of dioxin, etc., by using a vanadium oxide catalyst at a specified temp., condition and oxygen concn. CONSTITUTION:The combustion waste gas containing the chlorinated org. compd. is brought into contact with the vanadium oxide catalyst at 170-500 deg.C under the presence of 0.5-21vol.% oxygen and under the absence of ammonia. The catalyst in which vanadium pentoxide is deposited on an alumina or a titania carrier is used. The decomposition of monochlorobenzene, that is a dechlorination reaction, is caused, therefore, prevention of the generation of dioxin, etc., particularly in the combustion waste gas is possible at relatively low temp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for decomposing chlorinated organic compounds, and more specifically, chlorinated organic compounds such as dioxins generated by incineration of municipal waste, industrial waste, etc., or exhaust gas treatment. The present invention relates to a method for preventing the emission of chlorinated organic compounds to the outside of the system by decomposing and reducing or removing them.

[0002]

2. Description of the Related Art It has been reported that flue gas such as municipal waste and industrial waste contains chlorinated organic compounds such as aromatic chlorinated compounds which are considered to be dioxins and their precursors. Even if a small amount of dioxin adversely affects the ecosystem of plants and animals, it is necessary to reduce the content in exhaust gas as much as possible. Therefore, it is desirable to decompose dioxin in exhaust gas.

Recently, it has been reported that dioxin is rendered harmless by a thermal decomposition treatment, but the treatment condition is 50
In addition to requiring a high temperature of 0 ° C. or higher, the problem of volatilization of heavy metals occurs. In addition, a catalytic cracking method using a platinum or palladium catalyst has been reported, but the catalyst is expensive, and it is poisoned by sulfur oxides and nitrogen oxides contained in the combustion exhaust gas and cannot be used for a long time. Is not enough.

[0004]

DISCLOSURE OF THE INVENTION In view of the above situation, the present invention provides an inexpensive chlorinated organic compound in combustion exhaust gas such as municipal waste and industrial waste in the presence of a catalyst having durability against impurities, It is intended to provide a method for disassembling.

[0005]

The inventors of the present invention have conducted extensive studies to achieve the above-mentioned object, and as a result, by using a specific solid catalyst at a specific temperature and an oxygen concentration, chlorine in combustion exhaust gas can be obtained. The present invention has been completed by discovering that organic compounds are decomposed efficiently. That is, the gist of the present invention is to provide a combustion exhaust gas containing a chlorinated organic compound at 170 to 50
At a temperature of 0 ° C. in the presence of 0.5-21% oxygen,
In addition, the method for decomposing a chlorinated organic compound is characterized by contacting with a vanadium oxide catalyst in the absence of ammonia.

The structure of the present invention will be described in detail below. Examples of the exhaust gas targeted by the present invention include combustion exhaust gas such as municipal waste and industrial waste. Usually, dioxins represented by 2,3,7,8-tetrachlorodibenzodioxin and 2,3,4,7,8-pentachlorodibenzofuran are contained in these exhaust gases in an amount of 10 to 10.
40 mg / Nm ³ is also contained, and monochlorobenzene (hereinafter abbreviated as MCB) which is a precursor of these dioxins, dichlorobenzene, or chlorinated organic compounds such as O-chlorophenol and chlorobenzofuran are also contained.

The solid catalyst used in the present invention is preferably vanadium pentoxide, which is usually used by supporting it on a carrier. As the carrier, generally known silica, silica-alumina, diatomaceous earth and the like can be used, but alumina and titania are preferable in the exhaust gas. Titania is particularly preferred when sulfur compounds are present. The vanadium oxide content is preferably 1 to 20 wt% as vanadium pentoxide, and more preferably 2 to 10 wt%.

The shape of the catalyst may be cylindrical, spherical, honeycomb or plate-like. The size and shape of the catalyst are determined by the raw material properties, the presence or absence of dust, the amount of gas, the size of the reactor, and the like. The catalyst is usually prepared by dissolving (1) vanadium pentoxide in an oxalic acid aqueous solution, (2) impregnating the shaped carrier in the aqueous solution for 3 to 10 hours at room temperature, (3) draining, and (4). 3 at 60-110 ° C
After drying for 50 hours, (V) in air flow, (space velocity) SV
Baking is performed under the conditions of 100 to 2,000 h ⁻¹ and temperature of 450 to 650 ° C.

The catalyst thus prepared is used under the following conditions to decompose chlorinated organic compounds. Temperature 170
~ 500 ° C, preferably 200-400 ° C, SV100
To 50,000 h ^-1 , preferably 1,000 to 20,0
00h ^-1 , oxygen concentration 0.5 to 21%, preferably 1 to 1
Exhaust gas is contacted with the catalyst in the absence of 5% ammonia.
If the temperature is less than 170, decomposition is difficult, and if it exceeds 500 ° C., the decomposition proceeds, but the heat consumption is high, and the durability of the catalyst also becomes problematic.

As the reaction system, a fixed bed system is usually used.
To treat chlorinated organic compounds with this catalyst, exhaust gas discharged from a combustion furnace is usually passed through a bag filter to remove dust and the like, and then chlorine organic compounds are decomposed in the catalyst bed, and then acidic gas is absorbed through an alkali washing tower to remove atmospheric air. discharge. If the amount of dust and heavy metals is small, a catalyst bed can be installed in front of the bag filter.

[0011]

EXAMPLES Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to the description of the examples unless it exceeds the gist.

[Example 1] (Preparation of catalyst) 218.5 g of oxalic acid and 95 g of V ₂ O ₅ were dissolved in demineralized water at room temperature to make 1 liter, and 4 parts of this aqueous solution were prepared.
500 ml of spherical TiO ₂ carrier having a diameter of ˜6 mm was immersed and left for 5 hours. After that, the liquid was drained by a centrifugal filter and dried at 110 ° C. for 12 hours by a hot air dryer. Next, this is passed through a tube furnace at SV2, 200 hr ^-1 while passing air through it to 500
Firing at 3 ° C. for 3 hours prepared 3 wt% V ₂ O ₅ / TiO ₂ .

(Treatment of Exhaust Gas) A make-up gas shown in Table 1 was added to the atmospheric pressure fixed bed flow reactor filled with 30 ml of the solid catalyst prepared as described above at SV 20,000 h ^-1 and temperature 2
It was made to pass at each temperature of 00, 250, 300, 350, and 400 ° C. Monochlorobenzene (MCB) was put into a vaporizer whose temperature was controlled at 0 ° C., and the vaporized MCB was entrained in the make-up gas and passed through the catalyst bed. In the analysis, a part of the gas discharged from the catalyst bed was sampled, and the decomposition rate of MCB was measured by gas chromatography. The results are shown in Table 2.

[Example 2] The same procedure as in Example 1 was carried out except that SV was 5,000 h ^-1 . The results are shown in Table 2. [Example 3] The same procedure as in Example 1 was carried out except that the oxygen concentration in the gas was set to 1%. The results are shown in Table 2.

[Example 4] The same procedure as in Example 1 was repeated except that the oxygen concentration in the gas was changed to 15%. Comparative Example 1 Except that oxygen is not introduced into the gas,
The same procedure as in Example 1 was performed. MCB was hardly decomposed.

[Comparative Example 2] NH ₃ in a gas of 100 pp
The same procedure as in Example 1 was performed except that m was introduced. The results are shown in Table 2.
However, it was found that the MCB decomposition rate was the same as in Example 1 and it was not necessary to intentionally introduce NH ₃ . In addition,
It was found that NO was partially decomposed when NH ₃ was introduced.

Comparative Example 3 The procedure of Example 1 was repeated except that the catalyst bed temperature was 150 ° C. MCB was hardly decomposed.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

According to the present invention, it is clear from the examples that monochlorobenzene decomposes, that is, a dechlorination reaction occurs. From this, it can be presumed that not only it is possible to prevent the generation of dioxin, which is a particular problem, in combustion exhaust gas, but also it is possible to effectively decompose it.

Claims (2)

[Claims] 1. A combustion exhaust gas containing a chlorinated organic compound at a temperature of 170 to 500 ° C. for 0.5 to 21 vo.
A method for decomposing a chlorinated organic compound, which comprises contacting with a vanadium oxide catalyst in the presence of 1% oxygen and in the absence of ammonia. 2. The method according to claim 1, wherein the vanadium oxide catalyst is loaded on an alumina or titania carrier in an amount of 0.5 to 20 wt%.