JPH02241543A - Preparation of catalyst for reducing nitrogen oxide - Google Patents

Abstract

PURPOSE:To obtain a high capacity denitration catalyst having high denitration capacity and a low SO2 oxidation rate by mixing hydrous titanium oxide and compounds of elements of the Groups IIa, IIIa of the Periodic table to bake the resulting mixture and supporting a catalytically active component by the baked mixture. CONSTITUTION:Hydrous titanium oxide such as a titania sol or metatitanic acid and element compounds such as sulfates or nitrates of elements of the Group IIa, IIIa of the Periodic Table are mixed and subsequently baked. A catalytically active component such as W or Mo is supported by the baked mixture to obtain a denitration catalyst. This catalyst has a large pore volume, high denitration capacity and a low SO2 oxidation rate and is excellent in mechanical strength, heat resistance, durability and moldability.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for producing a catalyst for reducing nitrogen oxides, which decomposes nitrogen oxides in exhaust gas into nitrogen and water in the coexistence of a reducing agent such as ammonia gas. .

More specifically, the present invention provides nitrogen oxide decomposition activity (
The present invention relates to a method for producing a catalyst for reducing nitrogen oxides, which has high denitrification activity (hereinafter referred to as denitrification activity), and has excellent moldability, mechanical strength, heat resistance, SOx oxidation resistance, and durability.

[Prior Art] Nitrogen oxide reduction catalysts (hereinafter referred to as denitrification catalysts), which are currently widely used industrially, contain vanadium on a carrier whose main component is titanium oxide.

It supports oxides of metals such as tungsten and molybdenum as active ingredients. Increasing the supporting wall of active components such as vanadium and tungsten is an effective means of increasing the denitrification activity of the catalyst, and increasing the amount of vanadium oxide is particularly effective.

However, increasing the content of these active ingredients
Not only does it increase the price of the catalyst, but it also increases the rate of oxidation of SOBA (sulfur dioxide gas, which is included in many combustion exhaust gases) into SO3, so it is not necessarily recommended. This corrodes various equipment and ducts located downstream of the denitrification equipment. In addition, SO□ reacts with ammonia, which is a reducing agent, to generate ammonium sulfate and ammonium bisulfate, but this ammonium sulfate and ammonium bisulfate adhere to the heat exchanger located downstream of the denitration equipment and reduce the heat exchange rate. In addition, it corrodes the heat exchanger. Therefore, it is not preferable to increase the content of active ingredients blindly.

As mentioned above, denitrification catalysts are required to have high denitrification activity and low SOx oxidation ability.5 In addition to mechanical strength, heat resistance, durability, etc., they also have excellent moldability. This is very important. For this reason, various techniques have been proposed to improve the formability and mechanical strength of denitrification catalysts. As a method for producing a carrier having sufficient mechanical strength,
The carrier raw material containing titanium hydroxide is first heated at 800°C or lower, preferably 200 to 700°C, and the first heated product is pulverized to a particle size suitable for molding, and then molded into the desired shape by a known method. .

In the method of secondary firing again at 800°C or lower, preferably 200 to 700°C, the carrier raw material to be primarily heated and the
It has been proposed that a metatitanic acid sol be present in the carrier raw material that has been pulverized after subsequent heating.

In addition, one method to improve the heat resistance and durability of denitrification catalysts is to increase the firing temperature of the titania raw material, which is the main base material of the catalyst, and to increase the firing time. Furthermore, it is known to raise the firing temperature of the catalyst to a level sufficiently higher than the operating temperature of the catalyst. However, this method has the disadvantage of reducing the denitrification activity of the catalyst and increasing the SOx oxidation ability.

Japanese Patent Publication No. 59-26331 proposes a denitrification catalyst that is durable at high temperatures. This catalyst is 600-750
It is obtained by firing at ℃, and the A component is titanium oxide, the B component is an oxide of at least one element selected from aluminum, zirconium, magnesium, calcium, and lanthanum, or silica or silica-alumina, and the C component. Contains tungsten oxide as a titanium atom, and the atomic ratio of the B component to one titanium atom is 0.05 to 0.7.
and the atomic ratio of tungsten is in the range of 0.01 to
It is in the range of 1.

[Purpose of the invention] Conventional denitrification catalysts, including those introduced above.

Among the various requirements required for this, most of them satisfied certain specific requirements, but were insufficient in other requirements. Rather, in industrial catalysts, it is common to improve other catalyst properties even if some catalyst properties are sacrificed. For example, even if some catalyst properties are sacrificed to some extent, mechanical strength Efforts are usually made to improve this.

The purpose of the present invention is to provide a method for producing a denitrification catalyst that satisfies all or most of the requirements that an industrial catalyst should have. It is an object of the present invention to provide a method for producing a denitrification catalyst that has a low oxidation rate, excellent mechanical strength, heat resistance, and durability, and excellent moldability.

[Structure of the Invention] The method for producing a denitrification catalyst according to the present invention includes mixing hydrous titanium oxide and a compound of at least one element selected from Groups IIa and IIa of the periodic table, and calcining the mixture. It is characterized by supporting a catalytically active component on the product.

The "hydrated titanium oxide" referred to in the present invention is a compound also known as titanium hydroxide or hydrated titanium oxide, and specifically includes titania sol, metatitanic acid, orthotitanic acid, and the like.

In the present invention, a titanium compound containing 50 wt% or more, preferably 80 wt% or more of hydrous titanium oxide can be used, and in particular, a hydrous titanium oxide slurry obtained as an intermediate product in the titanium oxide manufacturing process by the sulfuric acid method can be used. Those washed according to the conditions are suitable as starting materials for the present invention.

Compounds of elements selected from Groups Ila and IIa of the periodic table are sulfates, nitrates, and nitrates containing these elements.
Carbonates, acetates, oxalates, ammonium salts, chlorides, hydroxides, etc., especially Mg, Ba, La, Ce,
Of the above compounds containing at least one type of Y, water-soluble compounds are particularly preferred.

According to the method of the present invention, hydrous titanium oxide and periodic table I
A compound of at least one element selected from Group Ia and Group IIa is mixed. The amount of the compound mixed with hydrous titanium oxide is 1.0-10% by weight of the mixture in terms of oxide.
It is preferably in the range of 1.5 to 5.0% by weight, and more preferably in the range of 1.5 to 5.0% by weight.

At 1.0% by weight, satisfactory heat resistance and durability cannot be provided, and at more than 10% by weight, the moldability of the mixture deteriorates and the SOx oxidation ability of the catalyst increases.0Periodic Table 1
Among the compounds containing elements of groups Ia and IIIa, Mg, Ba, La.

Compounds containing at least one of Ce and Y are suitable for achieving the object of the present invention, but in particular, compounds containing Mg,
The use of a compound containing at least one of La, Co, and Y provides high denitrification performance.

It is particularly effective in obtaining a catalyst with low SOx oxidation ability and excellent durability.

To mix hydrous titanium oxide and the above compound, in order to improve the moldability of the powder obtained by firing the mixture, the above compound or its aqueous solution is added to an aqueous slurry of hydrous titanium oxide, and the mixed slurry is mixed. Adjust the pH to 6 or more, preferably in the range of 8 to 10, then 40 ° C or more,
Preferably, stirring is carried out at a temperature of 50 to 95°C for 0.5 to 5 hours.

The mixture thus obtained is then calcined at a temperature above 500°C, preferably from 550 to 700°C, for 1 to 7 hours. If the firing temperature is lower than 550°C, the powder obtained by firing will have poor fluidity and moldability.
It is not possible to impart sufficient heat resistance and durability to the denitrification catalyst obtained from this.

The denitrification catalyst of the present invention is prepared by supporting a catalytically active component by any method on the powder obtained from the above-mentioned calcination process. After being molded into a carrier, the carrier can be supported by any method. In addition, a denitrification catalyst is prepared by kneading a compound containing a catalytically active component and the above-mentioned calcined powder in the presence of water, then extruding it into a honeycomb shape, and drying and calcining it in a conventional manner. You can also.

During molding, molding aids, inorganic fibers, etc. can be added as necessary, and the molded product is usually fired at 500 to 700°C for about 1 to 10 hours.

Catalyst active components include W, Mo, V, Cu, Fe, M
At least one selected from the group consisting of n, Nb and Cr
Species of metals are used, among which W, Mo, and V are preferred catalytically active components.

The catalytically active component of the present invention is usually present in the catalyst in the form of an oxide, and its amount is in the range of 0.1 to 30% by weight of the catalyst in terms of oxide, similar to a normal denitrification catalyst.

The denitrification catalyst produced by the method of the present invention reduces and removes nitrogen oxides contained in exhaust gas from boilers, gas turbines, and combustion exhaust gas discharged from various industrial furnaces in the coexistence of a reducing agent such as ammonia. In this case, normal reaction conditions can be used.

[Example] Example 1 2.24 kg of lanthanum nitrate was added to 84 kg of metatitanic acid slurry with a concentration of 30% by weight as Ti0□, stirred in a can for 1 hour, and aqueous ammonia was added.P)! It was set at 7.0.

This was heated to 60°C and stirred for 2 hours. After cooling, the solids were separated by filtration, dried, and calcined at 620°C for 5 hours. The fired powder thus obtained contains lanthanum of La20. It contained 3.1% by weight.

To 5 kg of this calcined powder, 0.8 kg of an aqueous solution of ammonium metatungstate containing 50% tungsten as wO3, 96 g of vanadyl sulfate, and 2.0 kg of ion-exchanged water.
OQ, 65 g of polyvinyl alcohol, and 65 g of carboxymethyl cellulose were added and kneaded while heating for 1 hour. Next, after adjusting the moisture content, this mixture was extruded into a honeycomb shape, thoroughly dried, and then calcined at 620°C for 5 hours to obtain a honeycomb denitrification catalyst (pitch 7.4cm,
Wall thickness 1.4 Hozen).

Example 2 2.55 kg of cerium sulfate (C8(No, )3-68.O) was added to the same metatitanic acid slurry as in Example 1.
After stirring for 1 hour, ammonia water was added to adjust the pH to 8.
5, the temperature was raised to 60° C. and stirred for 2 hours. After cooling, the solid content was filtered off, dried, and further calcined at 550°C for 5 hours. The obtained fired powder contained 3.6% by weight of cerium as CeO2.

To 5 kg of this calcined powder, 0.81 kg of an aqueous solution of ammonium metatungstate containing 50% by weight of tungsten as vOl, 96 g of vanadyl sulfate, and 2.02 g of ion-exchanged water were added and kneaded, followed by 65 g of polyvinyl alcohol and 65 g of carboxymethyl cellulose. Add
The mixture was kneaded while heating for 1 hour. Thereafter, a honeycomb denitrification catalyst was obtained using the same method and conditions as in Example 1.

Example 3 Barium chloride (BaCl*2H*O) was added to 84 kg of hydrated titanium oxide slurry with a concentration of 15% by weight as Tie.
810g and lanthanum nitrate (La (NO-) 3.6
After adding 1-28 kg of H*0) and stirring for 1 hour, aqueous ammonia was added to adjust the pH to 9.0, and then to 80
The temperature was raised to ℃ and stirred for 1 hour. After cooling, the solid content was filtered off, dried, and calcined at 650°C for 5 hours. The obtained fired powder contained 3.5% by weight of lanthanum as La, 03 and 2.5% of heavy wall barium as BaO.

Add 4 kg of ammonium paratungstate to 5 kg of this fired powder.
63g, vanadyl sulfate 96g and ion exchange water 1.7Q
After adding and kneading, 65 g of polyvinyl alcohol and 86 g of carboxymethyl cellulose were further added and kneaded for 1 hour. Thereafter, a honeycomb denitrification catalyst was obtained using the same method and conditions as in Example 1.

Examples 4 to 7 Same as Example 1 except that barium chloride, yttrium nitrate, and magnesium chloride were used in place of lanthanum nitrate in Example 1, and the firing temperature to obtain the fired powder was changed to 580°C. By this method, a honeycomb denitrification catalyst shown in Table 4 was obtained.

Comparative Example I To 84 kg of hydrated titanium oxide slurry with a concentration of 30% by weight as Tie, lanthanum nitrate (La(NO3)3.6H
iO) 1.7 kg, then 10, 50% by weight
3.5 kg of ammonium metatungstate containing tungsten, 468 g of vanadyl sulfate, 317 g of polyvinyl alcohol and 317 g of carboxymethyl cellulose.
was added and heated and kneaded. After drying this mixed wire material, it was crushed and calcined at 620° C. for 5 hours.

To 5 kg of this calcined powder, 2.0 Q of ion-exchanged water and 65 g of carboxymethyl cellulose were added, kneaded for 5 hours to adjust the moisture content, and then extruded into a honeycomb shape in the same manner as in Example 1. A honeycomb-shaped catalyst was obtained by performing a drying and firing operation.

Comparative Example 2 To 15.4 kg of anatase-type titanium oxide with a specific surface area of 60 rrr/g obtained by firing at 580°C, an aqueous solution in which 2.3 kg of lanthanum nitrate Q, a(Now)i・6H□0) was dissolved was added. The mixture was heated to 50° C. and mixed for 3 hours with stirring at pH=7.0. After evaporating water to dryness, 620
It was baked at ℃ for 5 hours. The obtained fired powder contains lanthanum with La20. It contained 3.3% by weight.

A honeycomb-shaped catalyst was obtained in exactly the same manner as in Example 1, except that the above-mentioned calcined powder was used instead of the calcined powder obtained in Example 1.

[Evaluation of Catalyst] The catalyst performance of each of the catalysts obtained in each of the above Examples and Comparative Examples was evaluated by the following method.

(1) Denitration rate: Gas was denitrated using each catalyst under the conditions shown in Table 1, and the denitration rate was determined using the following formula.

Denitration rate = (2) SOx oxidation rate: Gas denitration treatment was performed under the conditions shown in Table 2, and the SOx oxidation rate was determined using the following formula.

-2: SOx Hi Snow gas temperature: 380°C SV: 2500hr-1 (3) Durability After contacting the catalyst with the gas having the composition shown in 2-3 for 2500 hours under the conditions shown in Table 1-3, the The same denitration treatment as in (1) above was carried out using a catalyst, the denitration rate was determined in the same manner, and the durability was evaluated.

Table-1: Rate evaluation gas temperature: 350°C SV: 10,000hr" Gas temperature = 430°C v: 80QOhr-' Balance The properties and performance evaluation of each catalyst are summarized in Table-4.
The pore volume of the catalyst was measured by mercury intrusion method, and the crushing strength was measured using a compressive strength testing machine.

[Effects of the Invention] As evidenced by the data shown in Table 4, the denitrification catalyst produced by the method of the present invention has high crushing strength despite having a large side hole volume. In addition, this catalyst has a high denitrification rate, excellent durability, and a low 5Oxl'iQ conversion rate. Therefore, the denitrification catalyst obtained by the method of the present invention exhibits excellent performance as an industrial catalyst.

Claims (1)

[Claims] 1. Nitrogen, characterized in that hydrous titanium oxide and a compound of at least one element selected from Groups IIa and IIIa of the Periodic Table are mixed and fired, and the fired product is made to support a catalytically active component. A method for producing an oxide reduction catalyst.