JPH08117557A - Decomposition of organochlorine compound - Google Patents

Abstract

PURPOSE: To decompose an organochlorine compd. in an economically advantageous manner by using a relatively inexpensive catalyst having durability against impurities and low temp. activity. CONSTITUTION: Gas containing an organochlorine compd. is brought into contact with a mixed oxide catalyst containing vanadium and molybdenum at 100-500 deg.C in the presence of 0.5-25vol.% of oxygen.

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 to vanadium-containing chlorinated organic compounds such as dioxins generated by combustion of municipal solid waste or industrial waste. And a method of decomposing by contacting with an oxide catalyst containing molybdenum.

[0002]

2. Description of the Related Art Combustion exhaust gas such as municipal waste and industrial waste contains chlorinated organic compounds such as dioxins and aromatic chlorine compounds which are considered to be precursors thereof. In general, chlorinated organic compounds are more or less toxic, but dioxin is a very toxic substance that has a significant adverse effect on animals and plants, such as teratogenicity, and its content in flue gas should be reduced as much as possible. is required. Therefore, various methods for removing chlorinated organic compounds such as dioxin have been proposed, for example, an activated carbon adsorption method, a thermal decomposition method, or a catalytic decomposition method. Among them, the catalytic cracking method is 500
This is an excellent method that can perform the treatment under the condition of not more than ℃.

[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.

The present invention has been made in view of the above circumstances, and an object thereof is an economically advantageous chlorinated organic substance using a catalyst which is resistant to impurities and is relatively inexpensive. 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 an oxide catalyst containing vanadium and molybdenum in the presence of 0.5 to 25 vol% oxygen at a temperature of ° C.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION 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,
Dioxins represented by 3,4,7,8-pentachlorodibenzofuran are contained in an amount of 10 to 40 ng / Nm ³ . Further, chlorinated organic compounds such as monochlorobenzene, dichlorobenzene or o-chlorophenol, chlorobenzofuran which are precursors of these dioxins are also included.

In the present invention, an oxide catalyst containing vanadium and molybdenum is used as a decomposition catalyst for chlorinated organic compounds. Such an oxide catalyst is particularly excellent in poisoning resistance to sulfur oxides. The oxide catalyst is usually used by being supported on a carrier.
Silica, alumina, diatomaceous earth and the like can be used, but titania (TiO ₂ ) is preferably used. In particular, it is preferable to use titania when the combustion exhaust gas contains sulfur oxides.

The amount of vanadium oxide supported on the carrier is
It is usually 0.5 to 50 wt%, preferably 2 to 40 wt%. The amount of molybdenum oxide supported on the carrier is
Usually 0.1 to 50 wt%, preferably 0.3 to 40 wt
%. Further, the content of molybdenum oxide relative to vanadium oxide is usually 0.1 to 1 times by weight, preferably 0.1 to 0.7 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 columnar shape, a spherical shape, a honeycomb shape, and a plate shape. When preparing a columnar or spherical supported catalyst, for example, I) vanadium pentoxide (V ₂ O ₅ ) and ammonium paramolybdate ((NH ₄ ) ₆ [Mo ₇ O ₂₄ ] .22H are added to an oxalic acid aqueous solution.
₂ O) is dissolved, II) this mixed aqueous solution is impregnated with, for example, a cylindrical or spherical shaped carrier for 3 to 10 hours, III) drained, and IV) after drying at 40 to 150 ° C. for 3 to 50 hours, V)
Space velocity (hereinafter abbreviated as SV) 100-in air flow
It is possible to use a method of firing under the conditions of 2000 h ⁻¹ and a temperature of 450 to 650 ° C.

When preparing a honeycomb-shaped or plate-shaped supported catalyst, a carrier having a desired shape is first coated with a carrier component, and then the carrier component is coated with the catalyst component in the same manner as described above. A supporting method 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 fibers such as alumina and silica are 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. However, when the supported amount is small, only a slurry in which titania powder is dispersed in an aqueous solution may be used.

The raw material 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 molybdenum oxide is not particularly limited, ammonium paramolybdate is preferable, and this is dissolved in hot water or an oxalic acid aqueous solution to prepare a molybdenum-supporting liquid. The supporting liquid may be prepared by mixing the raw materials, or may be used by mixing the prepared supporting liquid, as long as there is no inconvenience such as precipitation formation or reaction.

When the vanadium-carrying liquid and the molybdenum-carrying liquid are used separately, the supporting method is as follows. First, for example, the vanadium-carrying liquid is impregnated with the carrier, dried and calcined to carry the V ₂ O ₅ -supported catalyst It is possible to employ a method in which the above-mentioned V ₂ O ₅ -supported catalyst is impregnated in a molybdenum-supporting liquid, dried and calcined. In the case of producing a catalyst having a shape such as a honeycomb catalyst, in addition to the method of supporting the carrier component such as titania and the catalyst component on the substrate constituting the honeycomb as described above, the carrier component and the catalyst component or the raw material thereof. After kneading and with a molding aid, they may be shaped into a desired shape such as a honeycomb shape by a molding method such as an extrusion molding method.

In a catalyst using a base material such as a honeycomb catalyst, in addition to titania as a carrier component, silica (S
iO ₂ ) or alumina (Al ₂ O ₃ ) may be used in combination, but the amount of titania at that time is 3 in the catalyst weight after production.
It is preferable to set it to 0 wt% or more. Further, the total amount of the carrier component and the catalyst component is 5 to 70 wt% of the weight of the catalyst after production,
It is preferably 10 to 50 wt%.

In the present invention, the catalyst prepared as described above is used at 100 to 500 ° C., preferably 1
0.5 to 25 vol at a temperature of 50 to 400 ° C
%, Preferably 1 to 15 vol% oxygen in the presence of decomposing chlorinated organic compounds. If the temperature is lower than 100 ° C, the decomposition reaction is hard to occur, and if it exceeds 500 ° C, the decomposition proceeds, but the heat consumption is large and the durability of the catalyst is likely to be hindered.

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. When ammonia gas is introduced into the gas before the above catalytic decomposition, it is possible to remove the chlorinated compound and simultaneously decompose the nitrogen compound. Furthermore, even if a small amount of water is contained in the gas to be treated, it does not affect the decomposition of the chlorinated product. Therefore, from such a point, the catalyst of the present invention is practically preferable.

The treatment of the chlorinated organic compound is usually carried out after the combustion exhaust gas is passed through a bag filter to remove dust and the like, and the exhaust gas after the decomposition treatment is subjected to an alkali washing tower to remove acid gas and then to the atmosphere. discharge. However, in the case of a combustion exhaust gas containing little dust and heavy metals, the pretreatment by the bag filter can be omitted.

[0017]

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 dipping and air blowing were repeated 3 times to coat the above honeycomb substrate with titania to manufacture a titania carrier. Then 150 ° C
After drying overnight at 70 ° C., it was baked at 700 ° C. for 3 hours.

20 g of vanadium pentoxide in 100 ml of water,
Ammonium paramolybdate 4.9g and oxalic acid 46g
The titania carrier obtained by the above coating was immersed in an aqueous solution (solution for supporting) in which the above was dissolved at room temperature for 3 hours, and after draining, 6
Dry at 0 ° C for 5 hours and 120 ° C overnight, then
It was baked at 00 ° C. for 3 hours. The composition of the catalyst thus prepared (catalyst A) was V ₂ O ₅ 6.9 wt%, MoO ₃
1.4 wt%, TiO ₂ 34.0 wt%, and the balance was a honeycomb substrate.

<Activity test> A glass reactor was filled with 30 cc of the above catalyst, and an activity test was carried out in an atmospheric fixed bed flow reactor. The size of the fixed catalyst bed is 26 mm in height and 26 m in width.
The height was 44 mm. The composition of the source gas is monochlorobenzene (MCB) 100 ppm, nitric oxide (N
O) was 100 ppm, O _{2 was} 10 vol%, and the balance was N ₂ . The temperature is raised while passing this raw material gas at SV5000h ^-1 to 200 ° C, 250 ° C, 300 ° C, 350 ° C, 40 ° C.
After holding each temperature of 0 ° C. for 1 hour, the gas passed through the reactor was sampled with a microsyringe and analyzed by a gas chromatography method. The analytical method was an absolute calibration curve method.
The results are shown in Table 1. The meaning of each symbol in Table-1 is as shown in Table-3.

Example 2 In Example 1, 100 pp of ammonia was used as a source gas.
A catalyst activity test was conducted in the same manner as in Example 1 except that m was added. The results are shown in Table 1. Example 3 In Example 1, a raw material gas having a water content of 12 vol% by replacing a part of N ₂ gas with water was used, and a test at 150 ° C. was performed before a test at a temperature of 200 ° C. A catalyst activity test was conducted in the same manner as in Example 1 except for the above. The results are shown in Table 1.

Example 4 A catalyst (catalyst B) was prepared in the same manner as in Example 1 except that the concentrations of vanadium and molybdenum in the liquid for supporting vanadium and molybdenum were changed. The composition of the obtained catalyst was V ₂ O ₅ 6.6 wt%,
MoO _{3 was} 5.2 wt% and TiO _{2 was} 32.9 wt%. Using this catalyst, an activity test of the catalyst was performed in the same manner as in Example 1 except that the test at 150 ° C. was performed before the test at the temperature of 200 ° C. The results are shown in Table 1.

Comparative Example 1 A catalyst containing no molybdenum (Catalyst C) was prepared in the same manner as in Example 1 except that ammonium paramolybdate was not used and vanadium pentoxide was used alone. The composition of the obtained catalyst was V ₂ O ₅ 8.8 wt.
%, And TiO _{2 was} 37.1 wt%. This catalyst was tested for activity 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 Example 1 except that the catalyst of Comparative Example 1 (Catalyst C) was used and 100 ppm of ammonia was added to the raw material gas. The results are shown in Table 1. Comparative Example 3 Example 1 was repeated except that the catalyst of Comparative Example 1 (Catalyst C) was used and a raw material gas having a water content of 12 vol% was used by replacing a part of N ₂ gas with water.
A catalyst activity test was conducted in the same manner as in. The results are shown in Table-1
Shown in

Example 5 The catalyst of Example 1 (Catalyst A) was used in a municipal waste incinerator.
An exhaust gas treatment test was conducted. As a test device,
Using the same activity test equipment as in No. 1, polychlorinated dibenzoda
Ioxins (PCDDs) 118.4 ng / Nm³,
Polychlorinated dibenzofurans (PCDFs) 902ng /
Nm³And nitrogen oxides (so-called NOX) 75ppm
The exhaust gas contained in a packed bed of catalyst A at a temperature of 200 ° C.
V3000h ^-1Chlorine in the gas is passed by
The organic compounds and NOX were decomposed continuously. processing
The subsequent analysis of exhaust gas was performed in the same manner as in Example 1.

Chlorinated organic compounds and N in exhaust gas after treatment
Table 2 shows the content with OX and the decomposition rate.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

(Table 3) (Table 3) A: V ₂ O ₅ 6.9 wt%, MoO ₃ 1.4 wt% TiO ₂ 34.0 wt% B: V ₂ O ₅ 6.6 wt%, MoO ₃ 5.2 wt% TiO ₂ 32.9 wt% C: V ₂ O ₅ 8.8 wt%, TiO ₂ 37.1 wt% MCB: monochlorobenzene

As is clear from Examples 1 to 4 above, the mixed oxide catalyst containing vanadium and molybdenum
It is understood that the decomposition reaction (dechlorination reaction) of monochlorobenzene occurs. Further, it can be seen from Example 5 that decomposition of chlorinated organic compounds such as dioxins, which is a particular problem in combustion exhaust gas, is efficiently performed. When ammonia is introduced, nitrogen oxides can be removed at the same time. The above effect is higher in the vanadium / molybdenum mixed oxide catalyst used in the method of the present invention than in the vanadium oxide catalyst alone.

[0030]

As described above, by using the mixed oxide catalyst containing vanadium and molybdenum, which is low in cost and resistant to impurities, according to the method of the present invention,
An effective method is provided for removing harmful chlorinated organic compounds such as dioxins in combustion exhaust gas such as municipal waste and industrial waste, which are socially problematic.

[Brief description of drawings]

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

Claims (2)

[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 an oxide catalyst containing vanadium and molybdenum in the presence of 0.5 to 25 vol% oxygen at a temperature of 0 to 500 ° C. 2. The oxide catalyst is supported on titania, and the supported amounts of vanadium oxide and molybdenum oxide on titania are 0.5 to 50 wt% and 0.1 to 5, respectively.
The decomposition method according to claim 1, which is 0 wt%.