JPH0947661A - Process and catalyst for purifying exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst of low level price demonstrating little lowered activities when exhaust gas containing a halogenated compound such as chloroflurocarbon gas, trichloroethylene, methyl bromide, hydrogen chloride, chlorine, bromine or the like and a combustible material such as CO, hydrocarbon, organic acid, alcohol, ester, aldehyde, amine, ammonia or the like is oxidized and/or decomposition purified. SOLUTION: A catalyst is used for oxidizing and/or decomposition purified exhaust gas containing a halogenated compound and a combustible material and one kind or more out of Al2 O3 , SiO2 , TiO2 and ZrO2 are used as carriers, on which transition metal composed of one kind or more of Cu, Ni, Co, Fe, Mn and Sn and cerium are used in the form of an oxide and in the range of 5g/L-50g/L respectively in an exhaust gas purifying catalyst.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification method and a purification catalyst, and more particularly to a petrochemical factory, printing, paint,
Flammability of carbon monoxide, hydrocarbons, aldehydes, alcohols, organic acids, organic nitrogen compounds, NH ₃ , organic halogen compounds, etc. discharged from painting and cleaning plants, etc.
The present invention relates to a catalyst for purifying exhaust gas containing harmful and malodorous components and an exhaust gas purification method using the catalyst.

[0002]

2. Description of the Related Art Flammability of CO, hydrocarbons, organic acids, alcohols, esters, aldehydes, amines, ammonia, etc. in exhaust gas discharged from various industrial facilities and coating factories,
The catalytic combustion method, which is one of the technologies for making harmless and odorless (purification) by completely oxidizing or oxidatively decomposing harmful and malodorous components, enables highly efficient purification at low concentration, low oxygen, and low temperature. Therefore, there is an increasing demand for exhaust gas purification methods. On the other hand, halogen catalysts used in petrochemistry (for example, methyl bromide for terephthalic acid synthesis), and in recent years, organic halogen compounds such as CFCs and trichlorethylene have been widely used as solvents, refrigerants, blowing agents, etc. Is released into the atmosphere as exhaust gas and waste liquid, it destroys the ozone layer and promotes global warming,
It has become clear that it becomes a causative agent of pollution such as groundwater pollution, and its emission prevention technology and detoxification technology are required.

Highly active combustion catalysts for purification of exhaust gas are usually
A combustion catalyst in which a noble metal such as platinum, palladium, or rhodium or a transition metal such as copper, manganese, or cobalt is dispersed and supported as a catalytically active component (metal or oxide) on an inorganic carrier having alumina with a high specific surface area as a main component in use. However, noble metals are inferior in economic efficiency, transition metals have low activity, and in the case where halogen compounds are present in the exhaust gas, these catalysts often have significantly reduced catalytic activity.

On the other hand, as a technique for detoxifying an organic halogen compound, a method of directly burning under a temperature condition of 800 ° C. or more is known. However, since the direct combustion method requires a large amount of fuel, it is not economical, and has a problem that highly toxic halogen gas is generated or CO is generated depending on the combustion conditions. The method of catalytically decomposing these compounds into harmless substances is said to be the most economical. Japanese Patent Application Laid-Open No. 3-47516 discloses granular TiO ₂ −
5 wt% Cu ion to ZrO ₂ or TiO ₂ —ZrO ₂
There is disclosed a method in which 0.1% CFC 113 or trichloroethylene is reacted with air containing 0.4% moisture at a temperature of 500 ° C. using a catalyst supported by 100% to decompose them into hydrogen halide. Although this catalyst is considered to be halogen-resistant, it has high activity for oxidative decomposition of halogen compounds, but it is not intended for simultaneous removal of other compounds, that is, harmful components in the exhaust gas. No mention is made of oxidative and / or degradative activity.

Further, the fluorocarbon decomposition catalyst disclosed in Japanese Patent Laid-Open No. 4-313344 is TiO ₂ --ZrO ₂ and TiO _2.
It is described that a catalyst in which a transition metal is supported on _2- ZrO ₂ is also effective for treating an exhaust gas containing CFCs, which is one kind of organic halogen compound. However, using cerium and its effectiveness and effects Is not described at all. Further, in the same publication, when CO, which is a toxic substance or a flammable substance, is contained in the exhaust gas, a precious metal such as Pd or Pt is simultaneously supported on the catalyst in addition to the transition metal, or a CO oxidation catalyst (Pd / Nalmina, Pt / (Titania, etc.) is required to be mixed with the catalyst or to be installed after the catalyst, and complete oxidation activity for harmful components other than CFCs of the catalyst,
No mention is made of degradative activity.

[0006]

When a transition metal compound, which is more economical than noble metal, is used as an active ingredient, its activity per unit amount is lower than that of the noble metal, so that it is often supported in a large amount. When a catalyst is exposed to a high temperature, sintering generally occurs, the number of active sites decreases, and the activity decreases. In order to prevent this, aggregation of active sites must be suppressed.

When a halogen compound coexists in the exhaust gas, the cause of the catalyst deactivation is halogenation of the alumina carrier surface. Aluminum halide has a low boiling point (AlCl ₃ 183 ° C.) and sublimates (178
C.), the surface structure of the catalyst gradually changes in the normal temperature range of use of the catalyst, which causes the catalytic active sites to collapse, decrease, and eventually decrease in activity. Therefore, it is desired to use a carrier that has low reactivity with halogen and is easily regenerated into an oxide by oxygen in exhaust gas, that is, a halogen-resistant carrier. Needless to say, it is desirable to use a substance that is hardly halogenated as the catalytically active component.

An object of the present invention is to solve the above-mentioned problems of the prior art and to purify exhaust gas containing halogen compounds and combustible substances, with low activity decrease, and at low cost, and a catalyst for purifying exhaust gas. It is to provide the exhaust gas purification method.

[0009]

The invention claimed in this application to achieve the above object is as follows. (1) In a catalyst that oxidizes and / or decomposes and purifies exhaust gas containing a halogen compound and a combustible substance, A
l ₂ O ₃ , SiO ₂ , TiO ₂ , or ZrO ₂ is used as a carrier, and Cu, Ni, C is used as a carrier.
An exhaust gas-purifying catalyst, characterized in that a transition metal made of one or more of o, Fe, Mn, and Sn and cerium are supported in the form of an oxide. (2) An exhaust gas purifying catalyst as described in (1), wherein the catalyst is supported on a refractory three-dimensional structure. (3) In a catalyst for oxidizing and / or decomposing and purifying exhaust gas containing a halogen compound and a combustible substance, Z
It formed from two components of and rO ₂ and TiO _2, ZrO ₂
Of 10 to 90 wt% and TiO _{2 in} the range of 90 to 10 wt% as a carrier, and Cu, Cu,
A transition metal element composed of one or more of Ni, Co, Fe, Mn, and Sn as an oxide was supported in the range of 5 gr / L to 50 gr / L, and cerium was supported as CeO _{2 in} the range of 5 gr / L to 50 gr / L. A characteristic exhaust gas purifying catalyst. (4) In a method of oxidizing and / or decomposing and purifying exhaust gas containing a halogen compound and a combustible substance, A
l ₂ O ₃ , SiO ₂ , TiO ₂ , or ZrO ₂ is used as a carrier, and Cu, Ni, C is used as a carrier.
O, Fe, Mn, Sn in the presence of a catalyst carrying a transition metal element consisting of one or more and cerium in the form of an oxide, the exhaust gas in the temperature range of 200 ~ 1000 ℃ into air or oxygen and water A method for purifying exhaust gas, which comprises contacting and oxidizing and / or decomposing a halogen compound or a combustible substance in the exhaust gas. (5) In the exhaust gas purification method as described in (4), the catalyst of (3) is used to oxidize and / or decompose an organic halogen compound or a combustible substance in the exhaust gas. (6) In the exhaust gas purification method as described in (4), the halogen compound is an organic chlorine compound and / or an organic bromine compound, and the concentration thereof is 1000 ppm or less as a halogen atom.

Among the above-mentioned drawbacks of the prior art, the deterioration of the carrier and the active ingredient by halogen is such that it is difficult to form a halide by the reaction of the substance and the halogen, and the halide is not volatile, and the oxidizing atmosphere It can be prevented by using a catalyst constituent that easily returns to the metal oxide. In general, whether or not a metal (oxide) is hard to form a halide can be estimated by calculating a thermodynamic equilibrium constant as described below. K is the equilibrium constant, and ΔG is the change in free energy.

[0011]

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Pd, which is a noble metal as a catalytically active component, exists as an oxide on the catalyst in the normal catalytic action temperature region, but the equilibrium is largely biased toward the chloride formation side. On the other hand, most transition metal oxides tend to be difficult to halogenate. On the other hand, although metal oxides such as Al ₂ O ₃ as a carrier component also have low reactivity with halogens, halides such as Al ₂ O ₃ are sublimable (AlCl ₃ : 178 ° C.) and have a boiling point. If a low amount (AlCl ₃ : 183 ° C.) is produced on the surface of the carrier even in a small amount, the surface structure is destroyed (= active site structure is collapsed). However, since cerium oxide is not easily halogenated and the boiling point of the halide is high (1727 ° C.), there is no such concern. Further, even if it is an inappropriate metal oxide alone, it is possible to make the halide more difficult to produce or to make it less volatile by compositing two kinds of metal oxides. In addition, Al ₂
It is also possible to prevent the formation of sublimable AlCl ₃ by allowing CeO ₂ to coexist in the O ₃ carrier.

As a result of a number of experiments, the inventor of the present invention has found that
The carrier used is ZrO₂, TiO ₂Etc. single or two
Ingredient metal oxides, active ingredients CuO, Fe₂O_ThreeHistory
Transferred metal oxide and CeO₂The catalyst composed of
It has been found that it is suitable for exhibiting a certain effect.
The composition of these changes depending on the coexisting substances in the exhaust gas.
Heat resistance and halogen resistance.
It is possible to apply it as a catalyst.

The catalyst of the present invention is effective when formed into a shape such as a granular shape, a spherical shape, a cylindrical shape, or a honeycomb shape.
In particular, it is clear that a heat-resistant three-dimensional structure carrying the catalyst of the present invention has excellent mechanical strength and is economically advantageous. There is no particular limitation on the type of apparatus used for purifying exhaust gas containing a combustible substance, a halogen compound, etc. using the catalyst of the present invention, but usually the catalyst is used as a fixed bed and oxidation and / or A flow tube reactor is used in which an exhaust gas containing a substance to be decomposed, oxygen and water vapor is introduced into a catalyst layer. The catalytic reaction conditions must be selected so that harmful combustible components are oxidized and / or decomposed, organic halogen compounds are completely decomposed, and harmful CO and the like are not generated. As a result of a number of experiments, the present inventors have found that the preferable reaction temperature used in the present invention is 200 to 1000 ° C.
The appropriate space velocity is 10,000 to 100,000 h ^-1 , and the concentration of the halogen compound is 1000 pp.
We have found that it is desirable to be less than m (as halogen atom). If the reaction temperature is 200 ° C or lower, a sufficient reaction rate cannot be obtained, and if the reaction temperature is 1000 ° C or higher, the sintering of the catalyst occurs and the catalyst deteriorates. Organic halogen compounds and their decomposition products, halogens and hydrogen halides, reversibly adsorb on this catalyst, so that some of the active sites are poisoned at low temperatures. The poisoning amount depends on the halogen concentration in the exhaust gas.
At 500 ° C or higher, the halogen oxidation in exhaust gas does not have any effect on the complete oxidation activity of combustible and harmful components of this catalyst, so there is no need to limit the concentration of halogen compounds in the exhaust gas, but poisoning occurs at reaction conditions of 500 ° C or lower. Therefore, unless it is 1000 ppm or less, sufficient complete oxidation activity cannot be obtained.
The higher the space velocity, the greater the economic effects such as reduction of catalyst amount and downsizing of the equipment, but 100,000 h
^If it exceeds ^-1 , processing efficiency decreases.

The organic halogen compound is oxidatively decomposed by oxygen in the exhaust gas to produce halogen gas, hydrogen halide, C
It forms part or all of O ₂ , H ₂ O and H ₂ .
It is not easy to detoxify halogen gas before discharging it from the system, rather than hydrogen halide. Therefore, in order to suppress the generation of halogen gas and to convert all the halogen to hydrogen halide, it is preferable to cause water vapor to exist in the exhaust gas and hydrolyze it. For example, in the hydrolysis of methylene chloride, the equilibrium of the hydrochloric acid production reaction is largely biased to the production side (right side) of the following equation near 450 ° C., but it is difficult to produce chlorine gas by the hydrolysis. On the other hand, decomposition by oxygen is likely to proceed and chlorine gas is generated. The amount of chlorine gas produced and the amount of hydrochloric acid produced by water are very small.

Decomposition of other organic halogen compounds shows a similar tendency.

[0017]

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Therefore, it is desirable that the amount of water vapor that should coexist in the exhaust gas be equal to or larger than the stoichiometric amount required for the hydrolysis of the organohalogen compound present in the exhaust gas.
Hydrogen halide such as HF, HCl and HBr generated in the processing gas can be easily recovered and removed by absorption with pure water or an alkaline aqueous solution, and the subsequent processing gas can be released into the atmosphere as exhaust gas.

[0019]

The present invention will be described below with reference to examples and comparative examples. Example 1 Tens of heat-resistant metal oxide carriers were added to a cordierite honeycomb (200 cells / in ² , apparent volume 1 liter).
0 g was carried. The preparation method is as follows. TiO ₂
And each colloidal aqueous solution containing the ZrO ₂ component in a weight ratio of 1: 1 are mixed. The honeycomb is dip-coated with this mixed solution, dried at 70 ° C. and 120 ° C. for 5 hours each, and then baked at 800 ° C. for 2 hours. CuO and CeO ₂ which are catalytically active components are added to the honeycomb with the carrier at a rate of 30 g / each.
L supported. The preparation method is as follows. After the thermal decomposition, a mixed aqueous solution of each nitrate containing a predetermined amount of CuO and CeO ₂ was carried on the honeycomb by the impregnation method. This was dried at room temperature and 120 ° C for 5 hours each, and then 6
Firing was performed at 00 ° C. for 2 hours to obtain a honeycomb-shaped integrated catalyst. This catalyst is No. 1.

The performance of this catalyst was evaluated using a fixed-pressure fixed bed flow tube reactor. 20mm × 20mm × 2 in the reaction tube
A honeycomb type catalyst cut into a size of 0 mm was filled, and a CO combustion reaction was carried out under the following conditions, and the combustion rate of each was determined to be the initial activity. Space velocity: 30000 h ^-1 , catalyst layer inlet temperature: 35
0 ° C., CO concentration: 600 ppm, methyl bromide concentration: 100 ppm, water vapor concentration 500 ppm, balance:
After the initial activity measurement in air, each of the catalysts exposed to methyl bromide (100 ppm) at 450 ° C. for 500 hours was subjected to CO burning rate measurement again under the above conditions to determine durability.
The results are shown in Table 1 together with the results of the catalysts of other examples. Example 2 Instead of the amount of CuO supported in Example 1, 50 g / L
Example 1 using copper nitrate containing the corresponding CuO
A catalyst No. 2 prepared in the same manner as in (1) was obtained. Example 3 Instead of the amount of CuO supported in Example 1, 10 g / L
Example 1 using copper nitrate containing the corresponding CuO
A catalyst No. 3 prepared in the same manner as in (1) was obtained.

Example 4 Catalyst No. 4 prepared in the same manner as in Example 1 was obtained by using copper nitrate containing CuO in an amount of 5 g / L instead of the amount of CuO supported in Example 1. Example 5 Instead of the amount of CeO ₂ supported in Example 1, 50 g /
Catalyst No. 5 prepared in the same manner as in Example 1 was obtained using cerium nitrate containing CeO ₂ corresponding to L ₂ . Example 6 Instead of the amount of CeO ₂ supported in Example 1, 10 g /
A catalyst No. 6 prepared in the same manner as in Example 1 was obtained by using cerium nitrate containing CeO ₂ corresponding to L ₂ . Example 7 Instead of the amount of CeO ₂ supported in Example 1, 5 g / L
Using cerium nitrate containing the corresponding CeO ₂ ,
Catalyst No. 7 prepared in the same manner as in Example 1 was obtained. Comparative Example 1 Instead of CuO and CeO ₂ supported in Example 1,
Using an aqueous solution containing only copper nitrate, a catalyst No. 8 prepared in the same manner as in Example 1 was obtained. The results of the same activity measurement as in Example 1 are shown in Table 1 together with the results of the catalysts of other Examples.
It was shown to. Comparative Example 2 Instead of CuO and CeO ₂ supported in Example 1,
Example 1 using an aqueous solution containing only cerium nitrate
A catalyst No. 9 prepared in the same manner as in (1) was obtained. The results of the same activity measurement as in Example 1 are shown in Table 1 together with the results of the catalysts of other Examples.

[0022]

[Table 1] In Table 1, the oxidation rates of Examples 1 to 6 hardly decrease even in the presence of halogen. However, although the oxidation rate of Example 7 using a catalyst having a low CeO ₂ content was high at the initial stage, it was 50%.
After 0h, it drops significantly. Therefore, C as a catalyst component
The effectiveness of eO ₂ can be seen. From the results of Examples 1, 5, 6, and 7, it can be seen that the required amount of CeO ₂ is> 5 g / L. Since Comparative Example 1 does not contain CeO ₂ , it has high initial activity but does not have halogen resistance. Comparative Example 2 has almost no catalytic activity because it does not contain a transition metal component as a catalyst component.

Example 8 A catalyst No. 10 prepared in the same manner as in Example 1 was prepared by using an aqueous manganese nitrate solution containing Mn ₂ O ₃ corresponding to 30 g / L in place of the CuO supported in Example 1. Obtained. Example 9 A catalyst No. 11 prepared in the same manner as in Example 1 was obtained by using an aqueous cobalt nitrate solution containing Co ₃ O ₄ corresponding to 30 g / L instead of the supported CuO in Example 1. Example 10 In place of CuO supported in Example 1, an iron nitrate aqueous solution containing 30 g / L of Fe ₂ O ₃ was used,
Catalyst No. 12 prepared in the same manner as in Example 1 was obtained. Example 11 A catalyst No. 13 prepared in the same manner as in Example 1 was obtained by using an aqueous nickel nitrate solution containing NiO equivalent to 30 g / L in place of CuO supported in Example 1. Example 12 A catalyst No. 14 prepared in the same manner as in Example 1 was obtained using an aqueous tin nitrate solution containing SnO ₂ in an amount of 30 g / L instead of CuO supported in Example 1. Example 1
The results of the same activity measurement as in Example 2 are shown in Table 2 together with the results of the catalysts of other Examples.

[0024]

[Table 2] In Table 2, it can be seen that those having a transition metal oxide and CeO ₂ as a catalyst component are excellent in oxidation rate and durability. Example 13 A catalyst No. 15 prepared in the same manner as in Example 1 was obtained by using a colloidal aqueous solution of Al ₂ O ₃ instead of the mixed colloidal aqueous solution of TiO ₂ and ZrO ₂ used in Example 1. Example 14 A catalyst No. 16 prepared in the same manner as in Example 1 was obtained by using a colloidal aqueous solution of SiO ₂ instead of the mixed colloidal aqueous solution of TiO ₂ and ZrO ₂ used in Example 1. Example 15 A catalyst N prepared in the same manner as in Example 1 using an aqueous colloidal solution of Al ₂ O ₃ —ZrO ₂ instead of the mixed aqueous colloidal solution of TiO ₂ and ZrO ₂ used in Example 1.
o.17 was obtained. Example 16 A catalyst No. 18 prepared in the same manner as in Example 1 was prepared by using a mixed colloidal aqueous solution of Al ₂ O ₃ —SiO ₂ instead of the mixed colloidal aqueous solution of TiO ₂ and ZrO ₂ used in Example 1. Obtained. Example 17 A catalyst prepared in the same manner as in Example 1 using a mixed colloidal aqueous solution of TiO ₂ —SiO ₂ instead of the mixed colloidal aqueous solution of TiO ₂ and ZrO ₂ used in Example 1.
I got No. 19. Example 18 A catalyst prepared in the same manner as in Example 1 by using a mixed colloidal aqueous solution of SiO ₂ —ZrO ₂ instead of the mixed colloidal aqueous solution of TiO ₂ and ZrO ₂ used in Example 1.
I got No. 20. Comparative Example 3 Instead of the mixed colloidal aqueous solution of TiO ₂ and ZrO ₂ used in Comparative Example 1, a sol of Al ₂ O ₃ was used,
Catalyst No. 21 prepared in the same manner as in Comparative Example 1 was obtained. Comparative Example 4 A catalyst No. prepared in the same manner as in Comparative Example 1 was prepared by using a SiO ₂ sol instead of the mixed colloidal aqueous solution of TiO ₂ and ZrO ₂ used in Comparative Example 1. 22 was obtained.

[0025]

[Table 3] In Table 3, all the catalysts are highly active when halogen does not coexist. When halogen coexists, all the catalysts containing CeO ₂ are highly active and highly durable except Comparative Examples 3 and 4. It is clear that the effectiveness of CeO ₂ is clear.

[0026] In the above embodiments 1 to 12, as a heat-resistant metal oxide support, TiO ₂ and ZrO ₂ in a weight ratio of 1: was used that contained in 1, TiO ₂ is 1:90
The object of the present invention was achieved by using a combination of 0 wt% and ZrO ₂ in the range of 10 to 90 wt%.

[0027]

EFFECTS OF THE INVENTION According to the present invention, a purification treatment of a halogen compound-containing exhaust gas can be achieved in the presence of air and water with an exhaust gas purification catalyst having a high oxidation activity and a high halogen resistance.

Claims (6)

[Claims] 1. A catalyst for oxidizing and / or decomposing and purifying exhaust gas containing a halogen compound and a combustible substance, wherein one or more heat-resistant oxides selected from Al ₂ O ₃ , SiO ₂ , TiO ₂ , and ZrO ₂ are used. As a carrier, Cu,
An exhaust gas purifying catalyst, characterized in that a transition metal composed of one or more of Ni, Co, Fe, Mn, and Sn and cerium are supported in the form of an oxide. 2. The exhaust gas purifying catalyst according to claim 1, wherein the catalyst is supported on a refractory three-dimensional structure. 3. A catalyst for oxidizing and / or decomposing and purifying exhaust gas containing a halogen compound and a combustible substance, which is formed of two components of ZrO ₂ and TiO ₂ ,
ZrO ₂ is 10 to 90 wt%, TiO ₂ is 90 to 10 wt%.
5gr / L to 50gr as a support, and a transition metal element composed of one or more of Cu, Ni, Co, Fe, Mn, and Sn as an oxide.
/ L, cerium as CeO ₂ supported in the range of 5 gr / L to 50 gr / L, an exhaust gas purifying catalyst. 4. A method for oxidizing and / or decomposing and purifying an exhaust gas containing a halogen compound and a combustible substance, wherein one or more heat-resistant oxides selected from Al ₂ O ₃ , SiO ₂ , TiO ₂ and ZrO ₂ are used. As a carrier, Cu,
In the presence of a catalyst in which a transition metal element made of one or more of Ni, Co, Fe, Mn, and Sn and cerium are supported in the form of an oxide, the exhaust gas is mixed with air or oxygen in a temperature range of 200 to 1000 ° C. An exhaust gas purification method comprising contacting with water to oxidize and / or decompose a halogen compound or a combustible substance in the exhaust gas. 5. The exhaust gas purification method according to claim 4, wherein the catalyst according to claim 3 is used to oxidize and / or decompose an organic halogen compound or a combustible substance in the exhaust gas. 6. The exhaust gas purification method according to claim 4, wherein the halogen compound is an organic chlorine compound and / or an organic bromine compound, and the concentration thereof is 1000 ppm or less as a halogen atom.