JP2000042409A - Catalyst for decomposing organochlorine compound and treatment of combustion exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the deterioration of the capacity of a catalyst with the elapse of time by specifying the content of molybdenum content, an average pore size and the vol. ratio of pores with a specific pore size. SOLUTION: A catalyst for decomposing an organochlorine compd. contains 0.1-20 wt.% of molybenum oxide formed by using a molybdenum raw material soln. prepared by dissolving ammonium paramolybdate or molybdenic acid in hot water. The mean pore size of this decomposition catalyst is set to 0.02-0.08 μm and the vol. of pores with a pore size of 0.02 μm or less thereof is set to 10% or less of the vol. of pores with a pore size of 0.006-2 μm. By this constitution, the deterioration of the catalyst by SOx in combustion exhaust gas with the elapse of time can be suppressed and an organochlorine compd. such as dioxins in combustion exhaust gas can be decomposed highly efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for decomposing chlorinated organic compounds and a method for treating combustion exhaust gas. More specifically, the present invention relates to dioxin in exhaust gas generated from combustion of municipal solid waste and industrial waste. TECHNICAL FIELD The present invention relates to a catalyst for decomposing chlorinated organic compounds such as chlorinated organic compounds and a method for treating combustion exhaust gas. Processing method of the catalyst and the combustion exhaust gas for the chlorinated organic compound decomposition of the invention, while suppressing temporal performance degradation of the catalyst by SO _x present in the flue gas, chlorinated organic compounds such as dioxin in the combustion exhaust gas Can be decomposed with high efficiency.

[0002]

2. Description of the Related Art Combustion exhaust gases such as municipal waste and industrial waste usually contain chlorinated organic compounds such as dioxin and its precursor, such as aromatic chlorine compounds. In general,
Chlorinated organic compounds in flue gas are more or less toxic. In particular, since dioxin is a very toxic substance that has a significant adverse effect on animals and plants, such as teratogenicity, it is strongly required to reduce the content of dioxin in combustion exhaust gas as much as possible.

[0003] As a method for removing chlorinated organic compounds such as dioxin in combustion exhaust gas, for example, an activated carbon adsorption method, a thermal decomposition method, a catalytic decomposition method and the like have been proposed. Among them, the catalytic cracking method is an excellent method for decomposing chlorinated organic compounds such as dioxin under the condition of 500 ° C. or less.

[0004] However, catalysts used in the conventional catalytic cracking method include nitrogen oxides contained in flue gas,
The resistance to sulfur oxides and heavy metal fumes is not sufficient. There is also a problem that a catalyst using platinum or palladium is expensive.

In general, in the catalytic cracking treatment of dioxin in combustion exhaust gas, nitrogen oxides are often removed at the same time. In this case, NO _x gas is nitrogen oxide components in the combustion exhaust gas is removed by reaction with ammonia into the incinerator in or denitration tower. However, if SO _x which is a sulfur oxide component is present in the combustion exhaust gas, acidic ammonium sulfate generated by the reaction between the introduced ammonia and SO _x adheres to the catalyst. When the compound is subjected to catalytic cracking, the performance of the catalyst significantly decreases.

On the other hand, when catalytic decomposition of a chlorinated organic compound is carried out at a temperature of about 300 ° C. or more, the decomposed dioxin is regenerated, so that catalytic decomposition of the chlorinated organic compound may be carried out at a temperature of 250 ° C. or less. Has been requested. However, when the catalytic cracking is performed at a temperature of 250 ° C. or less, it is not possible to avoid poisoning of the catalyst and deterioration of the performance due to the adhesion of the acidic ammonium sulfate.

[0007]

[SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and its object, while suppressing the temporal performance degradation of the catalyst by SO _x in the combustion exhaust gas,
A catalyst for decomposing chlorinated organic compounds that decomposes chlorinated organic compounds such as dioxin with high efficiency, and under conditions in which dioxin is not regenerated (for example, at a temperature of 100 to 250 ° C.)
An object of the present invention is to provide a method for treating flue gas, which decomposes chlorinated organic compounds in the flue gas with high efficiency.

[0008]

That is, the first aspect of the present invention is as follows.
The gist of the invention is that molybdenum oxide is contained in an amount of 0.1 to 20% by weight, the average pore diameter is 0.02 to 0.08 μm, and the volume of pores having a pore diameter of 0.02 μm or less is a small pore of 0.1 μm. 006
A catalyst for decomposing chlorinated organic compounds, which is 10% or less of the volume of pores of 2 μm.

Further, a second gist of the present invention resides in that a combustion exhaust gas containing a chlorinated organic compound is mixed with the above catalyst by 100 to 2 times.
A method for treating flue gas, comprising contacting at a temperature of 50 ° C. to decompose chlorinated organic compounds in the flue gas.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail. First, the catalyst for decomposing chlorinated organic compounds will be described. The decomposition catalyst for the chlorinated organic compound contains at least molybdenum oxide, and preferably contains molybdenum oxide, vanadium oxide and tungsten oxide. The content of molybdenum oxide is usually 0.1 to 2
0% by weight, preferably 0.3 to 10% by weight; the content of vanadium oxide is usually 0.5 to 50% by weight, preferably 0.7 to 40% by weight; Is usually 0.5 to 50% by weight, preferably 2 to 50% by weight.
40% by weight.

The cracking catalyst of the present invention has an average pore diameter of 0.0
2 to 0.08 μm, preferably 0.025 to 0.06 μm
m, and the volume of pores having a pore diameter of 0.02 μm or less is 10% or less, preferably 8% or less of the volume of pores having a pore diameter of 0.006 to 2 μm.

Usually, the above-mentioned catalyst for decomposing chlorinated organic compounds is used by being supported on a carrier. As the carrier, titania (TiO ₂ ), silica, alumina, diatomaceous earth and the like can be used. In particular, when treating a combustion exhaust gas containing a sulfur oxide, it is preferable to use titania having an effect of suppressing the reaction because vanadium oxide as an active component is sulfated.

When the amount of each component carried on the carrier is too small, the effect is not exhibited, and when the amount is too large, expensive metal is unnecessarily used. Therefore, it is preferable to set an appropriate amount. Specifically, it is as follows. That is, in the case of molybdenum oxide, usually 0.1 to 20
%, Preferably 0.3 to 10% by weight, and in the case of vanadium oxide, usually 0.5 to 50% by weight, preferably 0.7 to 40% by weight, and tungsten oxide is usually 0.5 to 0.5% by weight.
５０50% by weight, preferably 2-40% by weight.

Further, the ratio of molybdenum oxide to vanadium oxide is usually 0.01 to 5 times by weight, preferably 0.1 to 3 times by weight. When the proportion of molybdenum oxide is less than the above range, the effect of molybdenum oxide, that is, the effect of suppressing the deterioration of the decomposition rate over time is not exhibited. May drop.

The ratio of tungsten oxide to vanadium oxide is usually 0.1 to 30 times by weight, preferably 1 to 10 times by weight. When the proportion of the tungsten oxide is smaller than the above range, the effect of the tungsten oxide, that is, the effect of suppressing the deterioration of the decomposition rate over time due to thermal deterioration (sintering) is not exhibited, and is larger than the above range. In such a case, the effect of increasing the amount of use is insufficiently improved, which is not economical.

The shape and size of the cracking catalyst of the present invention are as follows:
It is appropriately selected depending on the properties of the raw material, the presence or absence of dust, the gas amount, the size of the reactor, and the like. Examples of the shape include a columnar shape, a spherical shape, a honeycomb shape, and a plate shape.

The raw material of the molybdenum oxide is not particularly limited, but may be ammonium paramolybdate or molybdic acid. These raw materials are dissolved in hot water or the like and used as a molybdenum raw material liquid.

The raw material of the vanadium oxide is not particularly limited, but may be vanadium pentoxide (V ₂ O ₅ ) or ammonium metavanadate. These raw materials are dissolved in an aqueous oxalic acid solution or an aqueous monoethanolamine solution and used as a vanadium raw material liquid. The material of the tungsten oxide is not particularly limited, and examples thereof include ammonium paratungstate or ammonium metatungstate. These raw materials are dissolved in hot water or the like and used as a raw material liquid for tungsten.

These raw material liquids may be prepared by mixing the raw materials, or may be used by mixing the prepared solutions, as long as there is no inconvenience of producing a precipitate or causing a reaction.

As a method for producing a honeycomb-shaped catalyst supported on a carrier, (a) a carrier component and a catalyst component or a raw material thereof are kneaded together with a molding aid, and then formed into a honeycomb shape by extrusion molding or the like. And (b) a method of impregnating and supporting a carrier component such as titania and a catalyst component on a honeycomb-shaped substrate. As an example of the above-mentioned manufacturing method (a), the following method is exemplified.

(1) Ammonium metavanadate and ammonium paratungstate are dissolved in an aqueous solution of about 10% monoethanolamine.

(2) Dissolve ammonium paramolybdate in water or an aqueous solution of about 10% monoethanolamine.

(3) Kneading the powdery titania and the aqueous solution prepared in the above (1) and (2) by a kneader.

(4) (i) Extruding the kneaded material, and
After drying at a temperature of 150 ° C. for 3 to 50 hours, a space velocity (hereinafter abbreviated as “SV”) 100 to 2000 (h−
Baking at a temperature of 450 to 650 ° C. in an air stream of 1), or (ii) kneading the kneaded product at a temperature of 50 to 150 ° C.
After drying for ５０50 hours, firing at a temperature of 450 to 650 ° C., and molding.

Further, as an example of the above-mentioned manufacturing method (b), the following method is exemplified. That is, cylindrical, spherical,
A carrier component is coated on a substrate having a desired shape such as a honeycomb shape or a plate shape, and the aqueous solution prepared in the above (1) or (2) is applied to impregnate the catalyst component.
Baking at a temperature of 50 ° C.

In the case of a catalyst formed on a base material, silica (SiO ₂ ), alumina (Al ₂ O ₃ ) or the like may be used in addition to titania as a carrier component. At that time, the amount of titania is preferably set to a high ratio particularly when treating a combustion exhaust gas containing a sulfur oxide in order to suppress sulfation of vanadium oxide as an active ingredient. Specifically, the amount of titania based on the total amount of the carrier component and the catalyst component is usually 30% by weight or more, preferably 40 to 97%.
% By weight. The total amount of the carrier component and the catalyst component is usually 5 to 70% by weight, preferably 10 to 50% by weight, based on the total amount of the base material, the carrier component and the catalyst component.

When the raw materials added as in the kneading / forming method are all catalyst components, the catalyst composition is estimated from the added amount on the assumption that the raw material components such as metal salts have changed into the corresponding metal oxides. . When the catalyst is manufactured by the impregnation method, the catalyst is treated with hydrofluoric acid, melted with ammonium sulfate, and subjected to plasma emission spectrometry (ICP-AES).
Analytical method) to determine the catalyst composition.

Next, the method for treating combustion exhaust gas of the present invention will be described. The flue gas containing a chlorinated organic compound and the catalyst for decomposing a chlorinated organic compound are usually mixed in the presence of 0.5 to 25% by volume, preferably 1 to 15% by volume of oxygen.
The chlorinated organic compound is decomposed by contact at a temperature of 0 to 250 ° C.

The combustion exhaust gas to be treated includes chlorinated organic compounds, usually 0.1 ppm or more of SO _x , usually 0.1 ppm.
exhaust gas containing the ppm or more NO _x, for example, exhaust gas or the like at the time of burning such as municipal waste and industrial waste and the like. Such combustion exhaust gas usually includes 2,3,7,8-
Tetrachlorodibenzodioxin, 2,3,4,7,
Dioxins represented by 8-pentachlorophenol dibenzofuran is included 10~40ng / Nm ^3. Furthermore,
Chlorinated organic compounds such as monochlorobenzene, dichlorobenzene, o-chlorophenol, and chlorobenzofuran, which are precursors of these dioxins, are also included.

The pressure during the contact treatment is usually a gauge pressure of -2.
９9 kg / cm ² , preferably −1 to 5 kg / cm ² . Moreover, SV is normally 100～50000H ^-1, preferably 1000~20000h ^-1.

The above-mentioned contact treatment with the chlorinated organic compound is usually carried out after removing dust and heavy metals by passing combustion exhaust gas through a bag filter. The exhaust gas after the contact treatment is discharged to the atmosphere after removing the acidic gas by passing it through an alkali washing tower or the like. In the case of a combustion exhaust gas having a small amount of dust and heavy metal, the pretreatment by the bag filter can be omitted.

The catalyst of the present invention comprises dioxin (2,3,
7,8-tetrachlorobenzodioxin).
05~500ng-TEQ / Nm ³ about the chlorinated organic compound concentration, 0.1 ppm or more of SO _x, 0.1 ppm
When the above-described combustion exhaust gas containing ammonia is treated at a temperature of 250 ° C. or lower, the chlorinated organic compound can be decomposed with high efficiency.

By introducing ammonia gas into the exhaust gas before the contact, the nitrogen compound (NO _x ) can be removed.

Further, even if the exhaust gas to be treated contains some water, it does not affect the decomposition of the chlorinated organic compound, and the catalyst of the present invention is practically preferable.

[0035]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist.

Example 1 <Preparation of Catalyst> A raw material liquid (1) was prepared by dissolving 386 g of ammonium metavanadate and 1089 g of ammonium paratungstate in 6000 g of a 10% by weight aqueous monoethanolamine solution heated to 80 ° C. Separately, a raw material liquid (2) was prepared by dissolving 73.6 g of ammonium paramolybdate in 600 g of water. The raw material liquid (1), the raw material liquid (2), 8700 g of titania powder, and 1000 g of a forming aid were kneaded with a double-arm kneader for 2 hours, and the obtained kneaded product was formed into a honeycomb structure having a diameter of 5 mm by an extruder.

The obtained molded product was dried at a temperature of 130 ° C. overnight (about 10 hours), and then SV 100 h ⁻¹ , temperature 6
The catalyst was calcined at 00 ° C. for 3 hours (hereinafter referred to as “catalyst A”
To be described). Table 1 shows the composition of the catalyst and its physical properties.

<Decomposition test of chlorinated organic compound>
30 mm x 30 mm x 500 mm
mm of catalyst A having a honeycomb structure. A treatment test of a model exhaust gas from a municipal garbage incinerator was conducted using an atmospheric pressure fixed bed flow reactor.

Dioxins having an average concentration of ³⁰ ng-TEQ / Nm ³ , SO ₂ having an average concentration of 20 ppm, and an average concentration of 1
A gas containing 00 ppm of NO _x was added while adding 75 ppm of ammonia, while SV 3000 h ⁻¹ , temperature 20
At 0 ° C., the mixture was passed through a normal pressure fixed bed flow reactor.
The analysis of exhaust gas after treatment is performed by gas chromatography mass spectrometry according to the "Manual for Standard Measurement and Analysis of Dioxins in Waste Disposal" (Environmental Maintenance Section, Water Environment Department, Ministry of Health and Welfare, Ministry of Health and Welfare) (February 1997). Was. The analysis was performed two weeks and six months after gas passage. Table 2 shows the evaluation results.

The adhesion amount of sulfur was measured using TSX-10 (halogen / sulfur analyzer, manufactured by Mitsubishi Chemical Corporation).
MS 500 ppm was used as a standard solution.

Comparative Example 1 A raw material liquid (3) was prepared in the same manner as in Example 1 except that 101.8 g of yttrium nitrate hexahydrate was used instead of ammonium paramolybdate. Using the obtained raw material liquid (3), 8730 g of titania powder, and 1000 g of a molding aid, a catalyst (catalyst B) was produced in the same manner as in Example 1. Table 3 shows the composition of the catalyst and its physical properties.

Using the catalyst B obtained, a decomposition test of chlorinated organic compounds was carried out in the same manner as in Example 1. Table 4 shows the evaluation results.

Comparative Example 2 Using the same raw materials as in Example 1, a molded article having a honeycomb structure was prepared in the same manner as in Example 1, molded, dried, and then dried.
It was calcined at a temperature of 70 ° C. for 5 hours to produce a catalyst (catalyst C). Table 5 shows the composition of the catalyst and its physical properties.

Using the obtained catalyst C, a decomposition test of chlorinated organic compounds was conducted in the same manner as in Example 1. Table 6 shows the evaluation results. In Tables 1, 3 and 5, "% by weight" of the composition is the weight% of the catalyst component excluding the molding aid.

[0045]

[Table 1]

[0046]

[Table 2]

[0047]

[Table 3]

[0048]

[Table 4]

[0049]

[Table 5]

[0050]

[Table 6]

[0051]

The catalyst for decomposing a chlorinated organic compound and the method for treating combustion exhaust gas of the present invention have a low adhesion rate of a sulfur compound, and the deterioration of the catalyst over time due to adhesion is suppressed.
Chlorinated organic compounds such as dioxin in flue gas can be decomposed with high efficiency, and chlorinated organic compounds in flue gas can be highly decomposed under conditions where dioxin is not regenerated (for example, at a temperature of 100 to 250 ° C). It can be decomposed with efficiency.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Ken Shirakami 1 Tohocho, Yokkaichi-shi, Mie Mitsubishi Chemical Corporation Yokkaichi Office (72) Inventor Kenichi Seino 1 Tohocho, Yokkaichi-shi, Mie Mitsubishi Chemical Corporation Yokkaichi Office

Claims (8)

[Claims] 1. A composition containing 0.1 to 20% by weight of molybdenum oxide, having an average pore diameter of 0.02 to 0.08 μm, and a volume of pores having a pore diameter of 0.02 μm or less having a pore diameter of 0.1 μm or less.
A catalyst for decomposing chlorinated organic compounds, which is 10% or less of the volume of pores of 006 to 2 μm. 2. The catalyst according to claim 1, which contains 0.5 to 50% by weight of each of vanadium oxide and tungsten oxide. 3. The amount of molybdenum oxide, vanadium oxide and tungsten oxide supported on the carrier and supported on the carrier is 0.1 to 20% by weight, 0.5 to 5% by weight, respectively.
The catalyst according to claim 2, which is 0% by weight and 0.5 to 50% by weight. 4. The catalyst according to claim 3, wherein the carrier is titania. 5. The catalyst according to claim 2, wherein the ratio of molybdenum oxide to vanadium oxide is 0.01 to 5 times by weight. 6. The weight ratio of tungsten oxide to vanadium oxide is 0.1 to 30 times by weight.
The catalyst according to any one of the above. 7. The combustion exhaust gas containing a chlorinated organic compound is treated with the catalyst according to claim 1 and 100 to 250.
A method for treating flue gas, comprising contacting at a temperature of ° C to decompose chlorinated organic compounds in the flue gas. 8. The combustion exhaust gas contains 0.5 to 25% by volume of oxygen, 0.1 ppm or more of sulfur oxide and 0.1 pp.
The treatment method according to claim 7, which contains m or more of ammonia.