JPH08309149A - Decomposition method for chlorinated organic compound - Google Patents

Abstract

PURPOSE: To efficiently remove harmful substances such as chlorinated organic compounds including dioxin in combustion exhaust gas by specifying heating temperature and oxygen concentration respectively in a method in which gas containing chlorinated organic compounds is contacted with a vanadium oxide catalyst containing gold with heating and in the presence of oxygen. CONSTITUTION: In the decomposition of chlorinated organic compounds including dioxin which is generated in the combustion of urban waste and industrial waste, gas containing chlorinated organic compounds is brought into contact with a vanadium oxide catalyst containing gold at 100-500 deg.C and in the presence of 0.5-25vol.% of oxygen. Usually the vanadium oxide catalyst containing gold is supported on a carrier to be used; silica, alumina, titania, diatomaceous earth, etc., can be used as the carrier. Among them, titania (TiO2 ) is used preferably. The amounts of gold and vanadium oxide supported on titania are 0.001 20wt.% and 0.5-50wt.%, respectively.

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 particularly, it relates to a method for decomposing chlorinated organic compounds such as dioxins generated by combustion of municipal waste or industrial waste into gold. The present invention relates to a method of decomposing by contacting with a vanadium oxide catalyst containing.

[0002]

2. Description of the Related Art Combustion exhaust gas from municipal solid waste and industrial waste contains chlorinated organic compounds such as aromatic chlorine compounds, which are generally considered to be dioxins and their precursors. In general, chlorinated organic compounds are highly toxic, but dioxin is a serious poison that causes teratogenic effects such as teratogenic effects on plants and animals, and the content in flue gas can be reduced as much as possible. is necessary. Therefore, various methods of removing chlorinated organic compounds such as dioxins have been proposed, such as an activated carbon adsorption method, a thermal decomposition method, or a catalytic decomposition method. Among them, the catalytic cracking method is 500
It is an excellent method that can be performed under the condition of ℃ or less.

[0003]

However, the catalyst in the catalytic cracking method proposed hitherto lacks durability against impurities such as nitrogen oxides, sulfur oxides, and heavy metal fumes contained in combustion exhaust gas. There is a problem to say. Further, conventional catalysts using platinum or palladium are expensive.

Further, even in the catalytic cracking method, if the treating temperature is relatively high, dioxin may be regenerated from the decomposed product after the treating. The present invention has been made in view of the above circumstances, and an object thereof is to decompose an economically advantageous chlorinated organic compound using a catalyst that is resistant to impurities and is relatively inexpensive. Another object of the present invention is to provide a chlorinated organic compound using a catalyst having a high activity even at a relatively low temperature such as 150 to 350 ° C., which is less likely to regenerate dioxin. It is to provide a method for decomposing a compound.

[0005]

That is, the gist of the present invention is to use a gas containing a chlorinated organic compound in an amount of 100 to 500.
A method for decomposing a chlorinated organic compound is characterized in that it is brought into contact with a vanadium oxide catalyst containing gold in the presence of 0.5 to 25 vol% oxygen at a temperature of ° C.

The structure of the present invention will be described in detail below. Examples of the exhaust gas to be treated in the present invention include combustion exhaust gas such as municipal waste and industrial waste. Such flue gas usually contains 2, 3, 7, 8
-Tetrachlorodibenzodioxin, 2,3,4
Dioxins represented by 7,8-pentachlorodibenzofuran are contained in an amount of 10 to 40 ng / Nm ³ . Further, monochlorobenzene, dichlorobenzene or o-chlorophenol, which is a precursor of these dioxins,
It also contains chlorinated organic compounds such as chlorobenzofuran.

In the present invention, a vanadium oxide catalyst containing gold is used as a decomposition catalyst for chlorinated organic compounds. Such a catalyst is usually used by supporting it on a carrier, and as the carrier, silica, alumina, titania, diatomaceous earth or the like can be used. Above all, it is preferable to use titania (TiO ₂ ). In particular, when sulfur oxide is contained in the combustion exhaust gas, it is preferable to use titania.

The supported amount of vanadium oxide is
It is usually 0.5 to 50 wt%, preferably 2 to 40 wt%. The amount of gold supported is usually 0.001 with respect to the carrier.
-20 wt%, preferably 0.01-10 wt%. Further, the content of gold with respect to vanadium oxide is usually 0.001 to 0.2 times by weight.

The size and shape of the catalyst are generally determined by the properties of the raw materials, the presence or absence of dust, the amount of gas, the size of the reactor and the like. Examples of the shape of the catalyst include a cylindrical shape, a spherical shape, a honeycomb shape, and a plate shape.

When a columnar or spherical supported catalyst is prepared, for example, I) vanadium pentoxide (V ₂ ) is added to an aqueous solution of oxalic acid.
O ₅ ) is dissolved, II) this aqueous solution is impregnated with, for example, a cylindrical or spherical shaped carrier for 3 to 10 hours, III) drained, and IV) dried at 40 to 150 ° C. for 3 to 50 hours, and then V ) Air velocity, space velocity (hereinafter abbreviated as SV) 100 to 2
The vanadium oxide-supporting carrier is calcined under the conditions of 000 h ⁻¹ and a temperature of 450 to 650 ° C., and then VI) the vanadium oxide-supporting carrier prepared as described above in an aqueous solution of chloroauric acid for 3 to 10 hours. Impregnate, VII) Drain, VIII) 4
After drying at 0 to 150 ° C for 3 to 50 hours, IX) in an air stream,
Space velocity (hereinafter referred to as SV) 100 to 2000
A method of firing under conditions of h ⁻¹ and temperature of 450 to 650 ° C. can be used.

When preparing a honeycomb-shaped or plate-shaped supported catalyst, a carrier component is first coated on a substrate having a desired shape, and then the catalyst component is supported on this carrier component in the same manner as described above. Can be used. FIG. 1 illustrates a method for preparing a honeycomb catalyst using titania as a carrier.

The material of the base material is not particularly limited, but cordierite or the like is used for an extrusion molded product such as a lattice, and inorganic fiber such as alumina or silica is used for a corrugated product. When the titania to be coated is used as a slurry, it is preferable to use a slurry in which a titania sol having a caking property is dispersed together with a titania powder.

The source of vanadium oxide is not particularly limited, but vanadium pentoxide (V ₂ O ₅ ) powder is preferably used. This is dissolved in an aqueous solution of oxalic acid to obtain a vanadium-supporting liquid. Although the raw material of the gold supporting liquid is not particularly limited, chloroauric acid tetrahydrate (HAuCl
₄ · 4H ₂ O) is preferred, which was dissolved in water or the like and carrying a liquid gold. These supporting liquids may be mixed and used.

As a supporting method when the vanadium-supporting liquid and the gold-supporting liquid are used separately, first, for example, the vanadium-supporting liquid is impregnated with the carrier, dried, and fired to obtain V _2. A method of preparing an O ₅ -supported catalyst, then impregnating the above-mentioned V ₂ O ₅ -supported catalyst in a gold supporting liquid, drying and calcining it can be employed. In addition, a method of first supporting gold on a carrier and then supporting vanadium oxide or a method of mixing the above two supporting liquids as described above to prepare a mixed supporting liquid and simultaneously supporting gold and vanadium oxide. The method can also be adopted.

In a catalyst using a base material such as a honeycomb catalyst, the total amount of the carrier component and the catalyst component is 5 to 70 wt%, preferably 10 to 50 wt% of the weight of the produced catalyst.

When a catalyst having a shape such as a honeycomb catalyst is manufactured, a carrier component such as titania and gold and vanadium oxide or its raw material are kneaded together with a molding aid, and then extruded or the like. It may be shaped by a molding method. However, if the supported amount of gold is extremely small, such as less than 1%, uneven distribution due to gold precipitation may occur or gold may be taken into the catalyst and stop working as an active ingredient. Therefore, as described above, it is preferable to form the carrier in advance and then carry these components.

In the present invention, the catalyst prepared as described above is used, and the temperature is 100 to 500 ° C., preferably 1
0.5 to 25 vol at a temperature of 50 to 350 ° C
%, Preferably 1 to 15 vol% oxygen in the presence of decomposing chlorinated organic compounds. If the temperature is less than 100 ° C, the decomposition reaction is difficult to occur, and if it exceeds 500 ° C, the decomposition proceeds, but the heat consumption is large, the durability of the catalyst is impaired, and dioxin is regenerated from the decomposition product. The possibility of

The pressure at the time of decomposition is usually 0 to 9 k in gauge pressure.
It is g / cm ² , preferably 0.01 to 5 kg / cm ² . Moreover, SV is normally 100～50000H ^-1, preferably 1000~20000h ^-1. The method of the present invention is 0.05 to 500 ng / Nm in terms of dioxin (2,3,7,8-tetrachlorodibenzodioxin).
It is suitable for treating a gas containing a chlorinated organic compound at a concentration of about ³ and is highly effective when applied to the treatment of combustion exhaust gas such as the aforementioned municipal solid waste and industrial waste.

When ammonia gas is introduced into the gas before the catalytic decomposition, the chlorinated compound can be removed and the nitrogen compound can be decomposed at the same time. Furthermore, even if the gas to be treated contains a small amount of water, it does not affect the decomposition of the chlorinated product. Therefore, from this point as well, the catalyst of the present invention is practically preferable. The treatment of the above chlorinated organic compound is usually performed after removing dust and the like by passing the combustion exhaust gas through a bag filter, and the exhaust gas after the decomposition treatment, after removing the acidic gas by an alkali washing tower, Release to atmosphere. However, in the case of combustion exhaust gas containing little dust and heavy metals, pretreatment with a bag filter can be omitted.

[0020]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. Example 1 <Catalyst preparation> 20.7 parts by weight of titania powder, 32.7 parts by weight of titania sol and 150 parts by weight of 1.0 wt% nitric acid aqueous solution were placed in a ball mill and treated at 100 rpm for 24 hours to obtain a solid content concentration of 16. A 2 wt% titania slurry was prepared. In this titania slurry, as a base material,
A ceramic fibrous honeycomb (manufactured by Nichias) having an effective surface area of 20.5 cm ² / cm ³ , a porosity of 73%, a cell number of 205 cells / inch ² , and a volume of 30 ml was immersed, and then air blowing was performed. Then, this immersion and air blowing were repeated three times to coat the above honeycomb substrate with titania. Then, after drying overnight at 150 ℃, 700 ℃
A titania carrier was produced by firing at 3 hours.

The titania carrier obtained by the above coating was immersed in an aqueous solution in which 20 g of vanadium pentoxide and 46 g of oxalic acid were dissolved in 60 ml of water at room temperature for 3 hours.
Dry at 5 ° C for 5 hours and 120 ° C overnight, then 5
It was baked at 00 ° C. for 3 hours. Further, this was immersed in an aqueous solution of 2.5 g of chloroauric acid tetrahydrate dissolved in 60 ml of water at room temperature for 3 hours, drained, dried at 60 ° C. for 5 hours and at 120 ° C. overnight, and further dried at 500 ° C. The mixture was calcined for 3 hours to prepare a supported catalyst.

The composition of the catalyst (catalyst A) thus prepared was V ₂ O ₅ 8.5 wt%, Au 0.5 wt%, Ti
O _{2 was} 37.2 wt%, and the balance was a honeycomb substrate.

<Activity test> The above catalyst was placed in a glass reactor.
30cc filled, activity test in atmospheric pressure fixed bed flow reactor
Was done. The size of the fixed catalyst bed is 26 mm in height and 26 m in width.
The height was 44 mm. Source gas composition is monochrome
Robenzene (MCB) is 100ppm, O ₂Is 10 vo
1%, the rest is N₂Met. This raw material gas is SV500
0h^-1The temperature is raised while passing through and kept at 250 ° C for 1 hour.
After that, the gas passing through the reactor is sampled with a microsyringe.
Ring and analyzed by gas chromatography. analysis
The method was the absolute calibration curve method. The results are shown in Table 1. What
The meaning of each symbol in Table-1 is as shown in Table-2.
It

Example 2 A catalyst activity test was conducted in the same manner as in Example 1 except that the activity test temperature was 200 ° C. Table of results
It is shown in FIG.

Comparative Example 1 In Example 1, the vanadium aqueous solution was used alone,
A catalyst (catalyst B) was prepared in the same manner as in Example 1. The composition of the obtained catalyst was V ₂ O ₅ 8.8 wt%, TiO ₂
It was 37.1 wt%. A catalyst activity test was conducted on this catalyst in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 2 A catalyst activity test was conducted in the same manner as in Comparative Example 1 except that the temperature of the activity test was 200 ° C. The results are shown in Table 1.

[0027]

[Table 1]

[0028]

Table 2 (Table 2) A: V ₂ O ₅ 8.5 wt%, Au 0.5 wt% TiO ₂ 37.2 wt% B: V ₂ O ₅ 8.8 wt%, TiO ₂ 37.1 wt% MCB: Mono Chlorobenzene

As is clear from the above examples, it is understood that the decomposition reaction (dechlorination reaction) of monochlorobenzene occurs with the vanadium oxide catalyst containing gold. Therefore,
This catalyst can also decompose chlorinated organic compounds such as dioxins.

[0030]

Industrial Applicability As described above, according to the present invention, by using a vanadium oxide catalyst containing gold, which is durable against impurities, it is possible to remove socially problematic municipal solid waste or industrial waste. Provided is an effective method for removing harmful substances such as chlorinated organic compounds such as dioxins in combustion exhaust gas.

[Brief description of drawings]

FIG. 1 is a flowchart showing an example of a process for preparing a titania-supported catalyst.

Claims (3)

[Claims] 1. A gas containing a chlorinated organic compound is added to 10
A method for decomposing a chlorinated organic compound, which comprises contacting with a vanadium oxide catalyst containing gold in the presence of 0.5 to 25 vol% oxygen at a temperature of 0 to 500 ° C. 2. A vanadium oxide catalyst containing gold is supported on titania, and the supported amounts of gold and vanadium oxide on titania are 0.001 to 20 wt% and 0.5 to respectively.
The decomposition method according to claim 1, which is 50 wt%. 3. A vanadium oxide catalyst containing gold is (1)
A method of supporting vanadium oxide first on a carrier and then gold, (2) a method of simultaneously supporting vanadium oxide and gold on a carrier, (3) first supporting gold and then vanadium oxide on a carrier The method for decomposing according to claim 1 or 2, which is obtained by any one of the following methods.