JP4922651B2 - Method for producing wear-resistant catalyst molded body - Google Patents

Description

The present invention relates to a method for producing a catalyst molded body for denitration or oxidative decomposition treatment of dioxins having excellent wear resistance.

  At present, boilers and engines are widely used as power sources in various industrial fields including commercial power generation facilities, and coal, oil, gas, etc. are generally used as fuels to operate these. However, a large amount of combustion gas generated when burning fossil fuel contains nitrogen oxides that cause air pollution. In order to discharge the burned gas into the atmosphere, the environmental impact, Considering the health hazards to residents, it is necessary to remove nitrogen oxides in the exhaust gas with a flue gas denitration treatment device and make it harmless, and then discharge it to the atmosphere. Examples of the flue gas denitration treatment apparatus for nitrogen oxides in these exhaust gases include, for example, a plate-like or honeycomb-like denitration catalyst containing a composite oxide composed of titanium and silicon or a titanium compound such as titanium dioxide as an exhaust gas flue. Denitration treatment equipment installed in the exhaust flue of the denitration catalyst, adding reducing gas such as ammonia and urea into the exhaust gas, and then passing through the denitration catalyst to make nitrogen oxides harmless to water and nitrogen Is generally used. Further, in the treatment of exhaust gas from incinerated waste, a catalyst for removing dioxins and organic compounds, denitration, and deodorization is often used.

  However, for example, in coal-fired boilers that use coal as the fuel, dust components such as fly ash are contained in the exhaust gas that is generated at a high concentration. Therefore, when the exhaust gas passes through the catalyst, the dust component and the catalyst come into contact with each other. It is widely known that the catalyst wears off, that is, a so-called wear phenomenon occurs, and the catalyst wear is particularly large at the exhaust gas inlet side end face where the collision with dust is severe.

  As a countermeasure against such catalyst wear due to dust in the exhaust gas, a method of coating the catalyst surface with glass such as water glass or soot has been proposed (Patent Document 1). However, in the method of coating the catalyst surface layer using glassy material such as water glass, the coating layer is destroyed by water vapor generated by heat treatment after the glassy coating, and when the coating layer is thickened to improve the strength, it is coated during heating. Problems such as thermal contraction / expansion of the layers occur and strain is destroyed. In addition, when these glassy coating-treated catalysts are exposed under high-concentration dust conditions, if the exposure is continued for a while, the vitreous coating layer is abraded by the dust and untreated parts are exposed, and then the exposed parts are mainly localized. Since abrasion occurred, sufficient abrasion resistance strength could not be obtained.

  As an improved method of the above method, there has been proposed a method in which a metal oxide is previously supported on a catalyst and the reaction between the vitreous such as sodium silicate and the catalyst to be coated later and the catalyst is suppressed (Patent Document 2). However, this method is not suitable as a mass production technique because the manufacturing process becomes more complicated.

  Further, as a method for improving the wear resistance strength, a coating method using a water-soluble colloidal solution such as silica gel has been proposed. In this method, since the inorganic fine particles in the colloidal solution penetrate into the inner surface of the catalyst pores and coat the pore surfaces, local wear phenomenon is less likely to occur compared to the vitreous coating method. However, if the amount of inorganic fine particles that enter the catalyst pores and cover the surface of the fine pores is small, the desired effect cannot be obtained. Therefore, in order to increase the amount of inorganic fine particles, treatment is performed with a colloidal solution containing silica or other high concentrations. However, a certain amount or more of the inorganic fine particles cannot be coated on the pore surface and remain on the catalyst surface, which may cause peeling of the coating layer or unevenness of the coating layer, resulting in a decrease in wear resistance.

Japanese Patent Publication No.57-26820 JP-A-11-57489

An object of the present invention is to provide a method for producing a wear-resistant catalyst which is excellent in wear resistance and is suitable for use in, for example, denitration treatment of exhaust gas containing dust.

According to the studies by the present inventors, it has been found that the above problems can be solved by the following invention.
(1) After forming a catalyst composition for denitration treatment or oxidative decomposition treatment of dioxins, the catalyst composition has pores having a pore diameter ranging from 0.01 to 100 μm, and is obtained by drying and firing, and gas flow In a porous catalyst molded body having through-holes in the direction, the gas inlet portion is a silica dispersion prepared using Snowtex (trade name) within a range of 15% of the total length of the molded body from the gas inlet end portion. When the immersion or impregnation treatment is performed, the pore occlusion ratio is 1.19 to 4.29%, and the pore occlusion volume in the pore diameter range of 0.01 to 0.1 μm is 10 to 29 of the total pore occlusion volume. % . A method for producing a wear-resistant catalyst molded body characterized by comprising:
(2) The method for producing a wear-resistant catalyst molded article according to the above (1), wherein the catalyst composition contains titanium-silicon composite oxide or titanium oxide as a main component and contains a catalytically active component.

  The wear-resistant catalyst molded body of the present invention is excellent in wear resistance, and is suitably used for, for example, denitration treatment of exhaust gas containing dust.

  The wear-resistant catalyst molded body of the present invention is a catalyst molded body used for various treatments such as denitration treatment of exhaust gas, oxidative decomposition treatment of dioxins, deodorization treatment, organic compound decomposition treatment, at least on the gas inlet side The part is made wear resistant. Typical examples include denitration treatment of exhaust gas and oxidative decomposition treatment of dioxins, especially wear phenomenon caused by dust in the exhaust gas, which makes the gas inlet side part of the catalyst molded body used for denitration treatment of exhaust gas wear resistant. Things can be mentioned.

  There is no restriction | limiting in particular about the said catalyst molded object, All can be used if it is a porous catalyst molded object which has a through-hole in the gas flow direction generally used for the said various processes. Specifically, for example, titanium-silicon composite oxide or titanium oxide such as titanium dioxide, which is generally used for denitration treatment of exhaust gas, contains oxides such as molybdenum, vanadium, and tungsten. The catalyst molded body is obtained by molding the catalyst composition to be formed into a honeycomb shape as shown in FIG. 1 or a plate shape as shown in FIG. 2. The wear-resistant catalyst molded body of the present invention is obtained from this catalyst molded body. At least the gas inlet side is subjected to wear resistance treatment. In addition, the said porous catalyst molded object has the pore of the range whose pore diameter is 0.01-100 micrometers normally.

  The wear-resistant catalyst molded body of the present invention has a pore blocking ratio of 1 to 35% and a pore diameter of 0.01 to 0.00 at the gas inlet side portion of the porous catalyst molded body having through holes in the gas flow direction. Silica is supported so that the closed volume of pores in the 1 μm range is 6 to 50% of the closed volume of all pores.

The blocking rate of the pores is 1 to 35%, preferably 3 to 30%. Here, the “blocking rate” is defined as follows. The pore volume is measured by mercury porosimetry.
Occlusion rate (%) = (total pore volume before abrasion resistance treatment−total pore volume after abrasion resistance treatment) / (total pore volume before abrasion resistance treatment) (× 100)
If the clogging rate is less than 1%, sufficient wear resistance strength cannot be obtained. On the other hand, if it exceeds 35%, the unevenness of the silica used in the wear resistance treatment occurs, and the wear resistance strength decreases.

  In the wear-resistant catalyst molded body of the present invention, among the pores having a pore diameter in the range of 0.01 to 100 μm of the catalyst molded body, pores having a pore diameter in the range of 0.01 to 0.1 μm (the present invention Then, it is preferable that at least a part of the pores having a pore diameter in the range of 0.01 to 0.1 μm is closed so that the blocking rate is in the range of 1 to 35%. That is, the wear resistance can be improved more effectively by closing at least a part of the pores having a minute pore diameter of 0.01 to 0.1 μm.

Further, in the wear-resistant catalyst molded body of the present invention, the pores having the pore diameters in the range of 0.01 to 0.1 μm are blocked so that the closed volume is 6 to 50% of the total pore closed volume. . That is, the numerical value calculated by the following formula (hereinafter referred to as the pore clogging rate in the range of pore diameter of 0.01 to 0.1 μm) is set to 6 to 50%.
Pore blockage rate (%) in the range of 0.01 to 0.1 μm
(Pore volume in the range of 0.01 to 0.1 μm before the wear resistance treatment−pore volume in the range of 0.01 to 0.1 μm after the wear resistance treatment) / (total before the abrasion resistance treatment) Pore volume-total pore volume after anti-abrasion treatment) (× 100)
The pore volume in the pore diameter range of 0.01 to 0.1 μm was measured by mercury porosimetry. In the pore volume measurement by the mercury intrusion method, mercury is injected while being gradually pressurized from a low pressure to a high pressure, and measurement is performed in the order of pores having a large pore diameter to a small pore diameter. At this time, since the pore diameter measured at each measurement pressure is constant, the pore volume ranging from 0.01 to 0.1 μm to the pore volume ranging from 0.01 to 0.1 μm pore diameter is measured. Asked.

  When the pore clogging ratio in the pore diameter range of 0.01 to 0.1 μm is less than 6%, the wear resistance of the catalyst molded body cannot be sufficiently improved.

The wear-resistant catalyst molded body of the present invention can be obtained by treating at least the gas inlet side with a solution or dispersion containing a silicon compound, followed by drying and firing. The treatment with the solution or dispersion may be performed so that the elemental compound sufficiently penetrates into the pores. For example, if a solution or dispersion containing a silicon compound is impregnated on at least the gas inlet side of the catalyst molded body. Good. For example, silica sol (for example, Snowtex (trade name)) can be used. Silica sol is practical because it has low oxidation performance of SO ₂ contained in exhaust gas (high SO ₂ oxidation performance generates SO ₃ and causes problems such as pipe corrosion and pipe clogging with sulfur compounds).
The treatment with the dispersion is performed using silica sol, and the pore clogging rate in the range of 0.01 to 0.1 μm is 6 to 50%. As the sol, those having an average particle diameter in the range of 5 to 20 μm are used.

  Although the entire catalyst molded body may be subjected to wear resistance treatment, it is usually sufficient to perform the wear resistance treatment on the gas inlet side portion (inlet side end portion) of the catalyst molded body. Specifically, for example, a range of 1 to 15% of the length of the catalyst molded body from the gas inlet side may be processed.

  The catalyst molded body is dried and fired after the treatment with the elemental compound solution or dispersion, and the firing is preferably performed at 50 to 650 ° C, preferably 100 to 500 ° C. If the calcination temperature is too low, the wear resistance strength is not sufficiently improved, while if it is too high, the catalyst may be thermally deteriorated or the wear strength may be reduced due to a change in crystal structure. In addition, it is thought that the said elemental compound is converted into forms, such as an oxide, by baking.

Hereinafter, the present invention will be described more specifically with reference to examples.
Example 1
As the catalyst molded body, a honeycomb-shaped catalyst molded body having a wall thickness of 1 mm and a length of 1 m, comprising a composite oxide composed of titania and silica as a main component and vanadium and tungsten added thereto, was used.

  A portion in a range of 50 mm from the end face of the catalyst molded body was impregnated with a colloidal solution having a silica content of 7% by mass prepared using Snowtex (trade name, manufactured by Nissan Chemical Co., Ltd.), and room temperature at room temperature. And then left to stand at 450 ° C. for 2 hours. As a result, a catalyst (1) in which the end face part (treatment part) was coated with silica was obtained.

When the pore volume of this catalyst (1) was measured by mercury porosimetry, the pore volume was 0.415 cc / g in the treated part and 0.42 cc / g in the untreated part. The pore volume in the range of 0.01 to 0.1 μm in pore diameter was 0.3245 cc / g in the treated part and 0.3250 cc / g in the untreated part. The blockage rate and the pore blockage rate in the range of 0.01 to 0.1 μm are shown in Table 1.
(Example 2)
A colloidal solution having a silica content of 7% by mass prepared using Snowtex (trade name, manufactured by Nissan Chemical Co., Ltd.) is applied to a portion in the range of 50 mm from the end face of the same catalyst molded body as used in Example 1. It was impregnated and allowed to stand at room temperature for 8 hours (impregnation-drying step: 4 times) and then calcined at 450 ° C. for 2 hours. As a result, a catalyst (2) in which the end face part (treatment part) was coated with silica was obtained.

When the pore volume of this catalyst (2) was measured by mercury porosimetry, the pore volume was 0.402 cc / g in the treated part and 0.42 cc / g in the untreated part. In addition, the pore volume in the pore diameter range of 0.01 to 0.1 μm was 0.3198 cc / g in the treated part and 0.3250 cc / g in the untreated part. The blockage rate and the pore blockage rate in the range of 0.01 to 0.1 μm are shown in Table 1.
(Comparative Example 1)
The same catalyst molded body as used in Example 1 was dried in a box-type dryer at 120 ° C. for 3 hours, and further calcined at 450 ° C. for 2 hours.

The pore volume of the catalyst (3) thus obtained was measured by mercury porosimetry, and the pore volume was 0.42 cc / g. Moreover, the pore volume in the pore diameter range of 0.01 to 0.1 μm was 0.3250 cc / g. The blockage rate and the pore blockage rate in the range of 0.01 to 0.1 μm are shown in Table 1.
(Comparative Example 2)
A colloidal solution having a silica content of 1% by mass prepared using Snowtex (trade name, manufactured by Nissan Chemical Co., Ltd.) is applied to a portion within a range of 50 mm from the end face of the same catalyst molded body used in Example 1. It was impregnated and allowed to stand at room temperature for 8 hours and then calcined at 450 ° C. for 2 hours. As a result, a catalyst (4) in which the end surface portion (treatment portion) was coated with silica was obtained.

When the pore volume of this catalyst (4) was measured by the mercury intrusion method, the pore volume was 0.418 cc / g in the treated part and 0.42 cc / g in the untreated part. The pore volume in the range of 0.01 to 0.1 μm in pore diameter was 0.3249 cc / g in the treated part and 0.3250 cc / g in the untreated part. The blockage rate and the pore blockage rate in the range of 0.01 to 0.1 μm are shown in Table 1.
(Example 3)
Each of the catalysts (1) to (4) was cut at a distance of 100 mm from the end face, and installed in the wind tunnel so that the catalyst opening was perpendicular to the gas flow direction and the treatment part was on the gas inlet side.

Silica sand-containing air containing 50 g / Nm ³ of silica sand having an average particle diameter of about 40 μm was passed through the catalyst at a speed of 30 m / sec for 60 minutes. The weight of the catalyst before the passage of the silica sand-containing air (before the test) and the weight of the catalyst after the passage (after the test) were measured, and the wear rate was determined according to the following formula.
Abrasion rate (%) = (catalyst weight before test−catalyst weight after test) / (catalyst weight before test) (× 100)
The results are shown in Table 1.

It is the perspective view and cross-sectional view of a honeycomb-shaped catalyst. It is the perspective view and cross-sectional view of a plate-shaped catalyst.

Claims (2)

After forming a catalyst composition for denitration treatment or oxidative decomposition treatment of dioxins, it is obtained by drying and firing, and has pores with a pore diameter in the range of 0.01 to 100 μm and penetrates in the gas flow direction. In a porous catalyst molded body having a mouth, the gas inlet portion is immersed or impregnated with a silica dispersion prepared using Snowtex (trade name) within a range of 15% of the total length of the molded body from the gas inlet end. By performing the treatment, the clogging rate of the pores is 1.19 to 4.29%, and the clogging volume of the pores in the pore diameter range of 0.01 to 0.1 μm is 10 to 29% of the total pore clogging volume. A method for producing a wear-resistant catalyst molded body characterized by the above. 2. The method for producing a wear-resistant catalyst molded body according to claim 1, wherein the catalyst composition contains titanium-silicon composite oxide or titanium oxide as a main component and additionally contains a catalytically active component.

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