JPS5951339B2 - Honeycomb catalyst for nitrogen oxide removal - Google Patents

Description

[Detailed Description of the Invention] The present invention deals with sulfur oxides (hereinafter referred to as SOX) in exhaust gas.
Nitrogen oxides (N
At the same time, it removes S of SOx at a high rate.
The present invention relates to a honeycomb catalyst for removing nitrogen oxides that converts O2 into SO3 and has fewer harmful effects.

BACKGROUND OF THE INVENTION Combustion exhaust gases emitted from thermal power plants and various factories contain large amounts of NOx and SOX, which are the main cause of air pollution.

In order to remove NOx from these combustion exhaust gases, ammonia gas is injected into the combustion exhaust gases and a catalyst is used to remove NOx.
Recently, a method of selectively removing x by catalytic reduction has been attracting particular attention.

As a NOx removal catalyst using ammonia-based catalytic reduction method, it has a high NOx removal rate, is not poisoned by SOx in the exhaust gas, and has few harmful effects of converting SO3 of the SOx in the exhaust gas to SO3. is important, and there is a need for a catalyst that does not cause clogging due to dust in exhaust gas or increase pressure loss during use.

Conventionally, pellet-shaped catalysts and honeycomb-shaped catalysts are known as catalysts that selectively catalytically reduce and remove NOx in exhaust gas by adding ammonia.

However, the former has a large pressure loss in the catalyst layer,
The latter type of honeycomb-shaped catalyst has the disadvantage of not being able to obtain a large space velocity, requiring large-scale equipment, and of clogging the catalyst layer due to dust contained in the exhaust gas, which increases pressure loss. It has received particular attention recently.

This honeycomb-shaped catalyst is prepared by applying (1) on the surface of a honeycomb carrier made of cordierite, mullite, or the like.

Catalysts are known in which a mixture of catalytic metal oxides such as Fe, Cu, Mn, Mo, Co, W, etc. and titanium oxide or activated alumina is supported.

However, in such a honeycomb catalyst, the adhesion strength between the honeycomb antibody and the catalytic metal oxide is very weak, and during use, it may peel off due to external vibrations, shocks, or the wind pressure of the exhaust gas itself, and scatter to the outside, reducing the NOx removal effect. It has a fatal flaw that significantly reduces the

In order to improve these problems, it has been proposed that the honeycomb carrier itself be made of titanium oxide and impregnated with various catalyst metal oxides to increase the adhesion strength between the catalyst and the honeycomb carrier. The sintering strength of titanium oxide in this state is very low, and a practical catalyst has not yet been obtained.

On the other hand, conventional catalysts have a large effect of converting SO2 in exhaust gas into 803, and therefore, when ammonia gas is added dropwise, a large amount of ammonium sulfate is easily generated, causing clogging of the catalyst layer, or a larger amount of desulfurized ammonium sulfate is generated. A catalyst suitable for NOx removal has not yet been developed, as it requires equipment.

The honeycomb catalyst for removing nitrogen oxides of the present invention solves these conventional drawbacks and problems.

It is a honeycomb catalyst that is less susceptible to poisoning by SOX, can remove NOx at a high rate, and does not require permanent conversion of SO2 to SO3. It reduces and removes nitrogen oxides in exhaust gas by contacting it with the catalyst in the presence of ammonia. In the catalyst for removing nitrogen oxides, at least one or more oxides of vanadium, niobium, molybutine, tungsten, chromium, iron, copper, cobalt, nickel, and manganese.
0% by weight (the same applies hereinafter) and titanium oxide, which is the main component,
Glass component 2 or more containing 1% or more of at least one of phosphorus, antimony, arsenic, bismuth, germanium, and tin
This is a 20% homogeneously bonded honeycomb catalyst for removing nitrogen oxides.

In particular, the present invention uses titanium oxide as the main component to prevent poisoning by SOx in combustion exhaust gas, and specific catalytic metal oxides excellent in NOx removal such as vanadium, niobium, molybutin, tungsten, chromium,
A combination of at least one of the oxides of iron, copper, cobalt, nickel, and manganese, and 1% of any one of phosphorus, antimony, arsenic, bismuth, germanium, and tin that prevents the harmful effects of SO2 conversion to SO3. It is a honeycomb-shaped catalyst that is firmly and homogeneously bonded by the specific glass contained above.

Next, an example of the method for manufacturing the honeycomb catalyst of the present invention will be described. Preferably, anatase type titanium oxide and oxides of vanadium, niobium, molybdenum, tungsten, chromium, iron, copper, cobalt, nickel, manganese, etc. The glass component contains 1 to 20% of at least one kind, and 1% or more of at least one kind of phosphorus, antimony, arsenic, bismuth, germanium, and tin, and preferably has a softening point of 8.
Mix 1 to 20% of frit pulverized material (glass) at 00°C or less, add water and an organic plasticizer (for example, methyl cellulose, vinyl acetate, polyethylene oxide, etc.) to this mixture, and extrude it using a mixer to form it. A viscous composition with possible plasticity is sufficiently kneaded and the prepared mixture is molded into a honeycomb structure using a mold in which the cross-sectional shape of the through-holes of the extrudate is triangular, square, hexagonal, circular, etc. After extrusion into a body and then drying to remove moisture, it is heated in an oxidizing atmosphere at a temperature below 1000°C, preferably between 500°C and 90°C.
The catalyst of the present invention can be obtained by calcining at a temperature of 00°C.

As mentioned above, the glass component containing phosphorus, antimony, arsenic, bismuth, germanium, and tin (frits I/pulverized material) preferably has a softening point of 800°C or lower, such as pentavalent metal oxides such as P2O5, etc. Yohi SiO2
, TiO2, ZrO2, etc., one component or two or more components is 3 to 80 mol%, A1°03. B2O3,
0 to 55 mol% of one or more trivalent metal oxide components such as 5b203, pbo.

One or more divalent metal oxide components such as ZnO, Cab, MgO, BaO, etc. are 0 to 80 mol%, Na2
O, 20. A blended raw material containing 0 to 50 mol% of one or more monovalent metal oxidizing components such as Li2O is melted at 700°C to 1400°C, rapidly cooled in water, and then pulverized using a ball mill or the like. It can be easily obtained by doing.

Note that the finer the particle size of the frit pulverized product, the greater the strength increasing effect, and the average particle size is desirably 10 microns or less.

Next, the reasons for the limitations of the present invention are as follows: This is because if the amount added is less than 1%, the NOx removal effect of the catalyst is small, and if it exceeds 20%, the specific surface area of the catalyst is reduced, reducing the NOx removal effect.

The glass component content was set to 2% to 20%;
This is because the product will not have a strength that can withstand industrial use, and the NOx removal effect will decrease.

In addition, the glass components that contain 1% or more of phosphorus, antimony, arsenic, bismuth, germanium, and tin are limited to phosphorus, antimony, arsenic, bismuth, and tin in the glass components.
This is because if the content of germanium and tin is less than 1%, it will not be effective in preventing the conversion of SO2 in exhaust gas to SO3. The reason for this is that when phosphorus, antimony, arsenic, bismuth, germanium, and tin are added in the form of oxides, the same effect is produced initially, but during NOx removal, water in the exhaust gas This is because not only will the effect of preventing the reaction and conversion of S02 into 803 be lost, but also the catalyst life will be shortened.

Next, examples of the present invention will be described.

The raw materials are mixed to have the chemical composition (mol%) listed in Table 1, melted at a temperature of 1100°C to 1400°C, and then pulverized to produce 24 types of frits A-X listed in Table 1. I got it.

In addition, P in this frit. Sb, As, Bi,
The results of chemical analysis of Ge and Sn are shown in Table 1.

These 24 types of frit pulverized materials and 54 m2
Anatase-type titanium oxide powder having a specific surface area of /g and the catalyst component heavy metal oxide listed in Table 2 were mixed in the proportions listed in Table 2, and 100 parts by weight of this mixture was mixed with 55 parts by weight of water, 6 parts by weight of methylcellulose was added, thoroughly mixed in a kneader, and extruded into a honeycomb-shaped molded body with a hexagonal cross-section of through holes and a porosity of 65% using a vacuum extrusion molding machine.

After drying this molded body, it was fired at a firing temperature of 500°C to 900°C for 3 hours to produce the honeycomb catalysts A1 to I6 of the present invention.
1 and reference catalysts A112 to A156 were obtained.

For each honeycomb catalyst, the specific surface area by BET method, total pore volume by mercury intrusion porosimeter,
The axial crushing strength of the honeycomb was measured.

The results are shown in Table 2. Next, the results of measuring the NOx removal rate and SO2 conversion rate at 350°C for these 156 types of honeycomb catalysts are shown in Table 2.

The conditions for measuring the NOx removal rate were as follows.

Gas composition NO200ppm NH3200ppm5
0211000pp H2O 10% 2 02 3% CO2 12% N2 Residual gas space velocity 10,0001 /Hr NH3/NO ratio 1.0 The NOx removal rate and the conversion rate of SO2 to 803 were defined as below.

As is clear from the results in Table 2, as the glass content in the catalyst increases, the axial crushing strength of the honeycomb catalyst improves, and practical strength is obtained when the glass component content is 2% or more.

However, when the glass component content exceeds 20%, the specific surface area and pore volume of the honeycomb catalyst decrease, and the NOx removal rate decreases.

Furthermore, as is clear from the types of Fritz 1~, if the content of phosphorus, antimony, arsenic, bismuth, germanium, and tin in the glass component is less than 1%, the conversion rate of SO2 to SO3 will be high, making it unsuitable for practical use. It disappears.

Furthermore, if the amount of catalytic metal oxide exceeds 20%, the NOx removal rate will decrease and the conversion rate of SO2 to SO3 will increase, which is not preferred in practice.

As described above, the honeycomb catalyst for removing nitrogen oxides of the present invention contains titanium oxide, vanadium, niobium, and
Molybdenum, tungsten, chromium, iron, copper, cobal
- homogeneously bond 1 to 20% of at least one of the oxides of catalytic metals such as -, nickel, and manganese with 2 to 20% of a glass component containing 1% or more of phosphorus, antimony, arsenic, bismuth, germanium, and tin. Because it is a honeycomb-shaped catalyst, the crushing strength can be increased while maintaining a large specific surface area.Furthermore, there is no adverse effect of converting SO2 in exhaust gas to SO3, so there is less catalyst poisoning by SOX, and N
Since it is a catalyst that can remove Ox at a high rate and has almost no clogging phenomenon, it is extremely useful industrially as a catalyst for NOx in various combustion exhaust gases.

Claims (1)

[Claims] 1 In a nitrogen oxide removal catalyst that reduces and removes nitrogen oxides in exhaust gas by contacting the catalyst in the presence of ammonia, oxides of vanadium, niobium, molybdenum, tungsten, chromium, iron, copper, cobalt, nickel, and manganese are used. 1 to 20% by weight of at least one of the following, titanium oxide, which is the main component, and at least one of at least one of phosphorus, antimony, arsenic, bismuth, germanium, and tin.
A honeycomb catalyst for removing nitrogen oxides, characterized in that a glass component containing 2 to 20% by weight or more is homogeneously bonded.