JPH0338256A - Manufacture of plate-shaped catalyst for removing nitrogen oxide - Google Patents

Abstract

PURPOSE:To improve the strength of the end parts of a plate-shaped catalyst liable to damage and thereby obtain the catalyst high in strength and wear resistance by impregnating or coating the end faces of the catalyst in the form of a plate with the silica sol having a size not larger than a predetermined diameter. CONSTITUTION:An inorg. fiber-woven fabric is impregnated with inorg. oxide particles contg. silica sol and then dried. After drying, this inorg. fiber-woven fabric is thereafter coated with the catalytic composition contg. preconditioned titanium oxide and formed into a predetermined shape and size, followed by drying and then baking so as to be formed into a plate-shaped catalyst body. Moreover, the end faces of this plate-shaped catalyst body are impregnated or coated with the silica sol having a size of at most 20mum in diameter and then dried. Since the catalyst thus formed has the gaps between the fibers in the inorg. fiber-woven fabric filled with the inorg. oxide particles and the end faces reinforced, this catalyst provides a long lifetime due to a high strength and wear resistance.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing a plate-shaped catalyst for removing nitrogen oxides,
In particular, the present invention relates to a method for producing a plate-shaped catalyst for removing nitrogen oxides, which is suitable for preventing crushing of the ends.

[Conventional technology]

In general, catalysts that remove nitrogen oxides from exhaust gas (hereinafter simply referred to as catalysts) include titanium oxide (Ti0.), molybdenum (Mo), tungsten (W), and vanadium (V).
Catalyst compositions made of oxides such as catalytic converters and the like are used in the form of particles, plates, honeycombs, etc. -In particular, in the case of boiler exhaust gas fueled by heavy oil or coal, gas containing large amounts of soot and ash needs to be treated with low pressure loss, so it is necessary to treat the gas with a combination of plate catalysts and large aperture ratios. A catalyst having passages parallel to the gas flow direction, such as a honeycomb catalyst, is used. Examples of such catalysts include those in which a catalyst component is coated on a metal substrate (Japanese Patent Publication No. 61-28377), catalyst components extruded into a honeycomb shape (Japanese Patent Publication No. 60-3856, etc.), ceramic fiber matrix, etc.
Many products are known and have already been put into practical use, such as those in which a honeycomb or paper is formed into a honeycomb shape and then coated with a catalyst precursor material (Japanese Patent Publication No. 5B-11253, etc.).

[Problem to be solved by the invention]

Among the conventional technologies mentioned above, those in which a catalyst is coated on a metal substrate have many flat plate parts, so the pressure drop is small, ash does not easily accumulate, and the abrasion resistance is excellent, but it is heavy and requires special The problem was that the metal substrate was oxidized under these conditions.

In addition, inorganic fibers, paper, etc. whose surfaces are coated with catalyst components are strong against impact forces, but have low mechanical strength and suffer from wear due to ash particles contained in exhaust gas.

In order to solve these problems, ceramic or glass fiber woven cloth is impregnated with inorganic oxide fine particles to strengthen it, and then a catalyst composition mainly composed of titanium oxide and cotton-like inorganic fibers are added to water. The present inventors have proposed a catalyst that is coated with a melted and mixed paste or slurry, compacted using a roller press or the like, then dried and calcined, and an application is pending (unpublished).

However, the edges of plate-shaped catalysts based on screen materials such as ceramic woven cloth are thin and can be damaged during handling, especially in denitrification equipment for boilers that use coal as the main fuel. The major problem remained that they were easily worn out or damaged by the large amount of soot and dust contained in the exhaust gas.

An object of the present invention is to eliminate the problems of the above-mentioned techniques, and to provide a plate-shaped catalyst for removing nitrogen oxides, which is subjected to edge treatment suitable for preventing crushing of the edges of a plate-shaped catalyst based on a ceramic screen or the like. The purpose is to provide a manufacturing method.

[Means to solve the problem]

The above object is a method for producing a plate-shaped catalyst for removing nitrogen oxides in which a catalyst composition is supported on an inorganic fiber woven fabric, which includes a step of impregnating the inorganic fiber woven fabric with inorganic oxide fine particles containing silica sol and then drying it; A step of applying a pre-prepared catalyst composition containing titanium oxide to the dried inorganic fiber woven fabric, a step of forming the bottom of this into a molded rod having a predetermined shape and dimensions, and drying and baking this molded rod. A plate for removing nitrogen oxides, comprising the steps of: forming a plate-shaped catalyst body by impregnating or coating the end face of the plate-shaped catalyst body with silica sol having a particle size of 20 μm or less and drying the same. This is achieved by a method for producing a shaped catalyst.

[Effect]

The catalyst in the present invention is a slurry or paste catalyst obtained by adding water to an inorganic fiber woven fabric containing oxide particles, mixing catalyst particles and cotton-like inorganic fibers, and kneading the mixture while heating. By coating, appropriately rolling, and then drying and baking, a catalyst body consisting of a catalyst layer coated on an inorganic fiber woven fabric with fiber gaps filled with oxide fine particles is obtained.

The inorganic fiber woven fabric used in the present invention is, for example, a yarn diameter of 3 to
20 μm inorganic fibers are bundled into 200 to 800 fibers using a sizing agent such as starch or plastic emulsion, and these are further sewn together in the vertical and horizontal directions using about 5 to 10 fibers. Therefore, a cloth made of yarn made of a large number of twisted inorganic fibers has extremely high strength, and since it is an inorganic material, it has excellent heat resistance. However, fibers are weak against friction, and if single fibers are in direct contact with each other, the strength may be reduced. In cases where the sizing agent is exposed to high temperatures of 300'C or higher in actual equipment, such as catalysts used in the powder processing, the above-mentioned sizing agent thermally decomposes and contacts between fibers occur, causing the single fibers to have heat resistance. However, the strength of the woven fabric decreases. In the catalyst of the present invention, the oxide fine particles fill the gaps between the fibers constituting the woven fabric, and the single fibers do not come into contact with each other even when exposed to such high temperatures. In the examples of the present invention described later, 5iOt is used as the main component:
52-56%, Alz 03: 12-16%, C
aO: 12-25%, MgO: 0-6%, B! 01=8
~13% E glass fiber (wire diameter 9am), 5i
Impregnated with Oz sol (particle size 7-9X10-”am)
Those fired at 0°C/2 h are used, and f after firing is
fi amount ratio (inorganic oxide fine particles/glass fiber) is approximately 0.1
It was 2.

In the fibers used in the present invention, the gaps between them are filled with fine particles of oxide, making it difficult for single fibers to come into direct contact with each other.

Moreover, the fine particles of oxide are scattered between the fibers and do not restrict the movement of the fibers themselves. Under such conditions, the strength of the woven fabric fibers is high even at high temperatures. Furthermore, the fibers are loosely constrained, allowing for elongation and flexibility. Therefore, a catalyst using fibers impregnated with oxide fine particles has both strength and elasticity.

A fiber containing oxide fine particles coated with a catalyst layer as in the present invention has excellent bending strength and elasticity.

In the structure of the present invention, the particles of the catalyst component layer are intertwined with the cotton-like inorganic fibers while coagulating and bonding with each other, forming an extremely dense and strong structure that is entangled with the fibrous fabric. As a result, the catalyst body obtained as a structure has the combined strength of the catalyst component layer and the woven fabric in addition to the strength of the fibrous fabric and the catalyst layer, and as shown above, the catalyst and cotton-like Rolled inorganic fiber mixtures, ceramic sheets etc. coated with catalyst components,
It has significantly higher strength than a ceramic sheet simply impregnated with a catalyst component solution.

Furthermore, in the present invention, after impregnating an inorganic fiber woven fabric with oxide fine particles and drying it, a catalyst component paste is applied, dried, and fired, and then silica sol is impregnated and supported on the end of this fired product, and then the silica sol is impregnated and supported on the end of the fired product. Since it is used after drying, the silica sol can be infiltrated into the porous catalyst, and a denitrification catalyst having strong end portions can be obtained. The particle size of the silica sol used in this case is preferably 20 μm or less, and the supported amount is preferably 50 to 250 g/rrf. If the particle size of the silica sol exceeds 20 μm, the bending strength decreases.

〔Example〕

The manufacturing process of the catalyst of this example is shown in FIG.

Further, Table 1 shows the composition of the glass fiber woven fabric used in the present invention.

Table (1) Preparation of catalyst paste To 60 kg of metatitanium slurry prepared by the sulfuric acid method containing 30% by weight of titanium oxide (TiO2), 0.62 kg of ammonium metavanadate (NHs VOs) and ammonium molybdate ((N ) 1.) AMo, O,...
4.51 kg of 4 HtO) was added and kneaded while evaporating water using a kneader heated to 140°C. The resulting paste-like material with a water content of 38% by weight was formed into a columnar shape with a diameter of 3M using an extrusion granulator, and then dried using a fluidized bed dryer. The dried granules were calcined at 560° C. for 2 hours while flowing air, and then ground using a hammer mill to a particle size of 90% by weight or less of 20 μm or less to obtain catalyst fine particles.

Add 3 kg of water to a mixture of 7.9 kg of the above catalyst powder and 2.1 kg of cotton-like inorganic fibers, and knead with a kneader for 30 minutes.
A 23% by weight catalyst paste was obtained.

(2) Reinforced glass fiber woven fabric made of inorganic fiber woven fabric (E glass, 10 pieces/inch
, 460°C/2 h heat cleaning material) with a particle concentration of 20% by weight (particle size 7 to 9 x 10-
3 μm) and then dried at 120°C.

(3) Molding and firing of catalyst The inorganic fiber woven fabric cut into 500-square pieces was heated with the catalyst paste at a pressure of 1.4 tons and a speed of 7.5 m/min.
After applying the paste to the woven fabric, which was rolled with a rotating roller at a speed of 100 min, the woven fabric was sandwiched between two perforated metal molds made of 5US304 metal lath and dried at 180°C for 1 hour.

Thereafter, the mold was removed and the catalyst was fired in air at 550° C. for 2 hours to obtain a catalyst molded body as shown in FIG.

Specific examples are shown in Table 2, including an example in which the above-mentioned inorganic fiber woven fabric was impregnated with a reinforcing agent and then coated with a catalyst. As shown in Table 2, it is preferable that the ratio of the inorganic fiber fine particle diameter to the inorganic fiber diameter is 0.2 or less, and the ratio of the inorganic oxide fine particle weight to the inorganic fiber woven fabric weight is about 0.05 to 0.8. .

Margin below (4) Catalyst end reinforcement Each brand of silica sol stock solution having the average particle system and concentration shown in Table 3 can be used as it is or diluted with water.
Prepare a silica sol solution with a concentration of
Impregnated with silica sol by dipping or coating, 180″
After drying at C for 1 hour, it was fired at 550'C for 2 hours. The impregnated portion was taken as a test piece and the bending strength was measured. The results are shown in FIG. 5. For all brands, the bending strength was improved compared to the one not impregnated with silica sol.

In addition, Figure 6 shows the bending strength of the catalyst molded body described above, which was dried at room temperature without being fired, immersed in the same silica sol solution, dried and fired under the same conditions. To improve the strength, it is best to impregnate the catalyst after it has been fired.

FIG. 2 shows the change in the bending strength of the impregnated catalyst depending on the particle size of the silica sol. Silica sol with a particle size of 20 t1m or less is particularly effective in improving strength.

FIG. 7 shows the improvement in the tensile strength of the catalyst when impregnated with silica sol and alumina sol at a concentration of 8% by weight. Moreover, FIG. 3 shows the relationship between the amount of silica sol impregnated per unit area and the bending strength.

There are some variations in the test results, but the loading amount is 50%.
g/rd or more, it is possible to ensure a bending strength of 400 kg/c4 or more. Note that even if the amount of impregnated support is increased beyond 150 g/rrf, the bending strength does not improve.

Figure 8 shows the CataffoidS shown in Table 3.
The relationship between bending strength and treatment temperature is shown when a catalyst calcined body is impregnated once with 5I-350 silica sol having a solid content of 15% by weight and treated in an oxidizing atmosphere at 180 to 550°C. If the final calcination temperature is in the range of 180 to 550"C, the strength of the catalyst will hardly change. Therefore, if it is dried at about 180"C after impregnation and used in exhaust gas at 300 to 400"C, It can be seen that the final firing at a high temperature of 500 to 550°C is not necessary.

FIG. 9 shows a mixed slurry of catalyst particles and silica sol in which the ratio of catalyst and silica sol is 10:90.30:70.
Impregnation with mixed slurry is not only effective in improving strength, but is also superior to impregnation with only silica sol in terms of catalyst activity. Indicates a high value.

In addition, when comparing the impregnation of silica sol with the same loading amount,
Higher strength is obtained by lowering the solid content concentration and increasing the number of impregnations.

Blank space below [Effects of the Invention] The catalyst of the present invention has an inorganic fiber woven fabric support inorganic oxide particles to fill the gaps between the fibers constituting the woven fabric, so that when used at high temperatures, the single fibers do not interact with each other. The strength does not decrease due to contact, and the strength of the edges of the plate-shaped catalyst, which are easily damaged when handling the catalyst or when used in denitrification equipment, has been improved, resulting in high strength and wear resistance. It is durable and has a long lifespan.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the plate-shaped catalyst and end treatment according to the present invention, Figure 2 is a relationship between the particle size of silica sol and bending strength in end treatment, and Figure 3 is a diagram of the relationship between the silica sol particle size and bending strength in the end treatment. Figure 4 is a diagram showing the relationship between supported amount and bending strength. Figure 4 is a systematic diagram of the catalyst manufacturing process in the present invention. Figures 5 and 6 are diagrams showing the bending of the catalyst when the catalyst is impregnated with silica sol after and without firing. Figure 7 shows the tensile strength when impregnated with 8% by weight silica sol and alumina sol once or twice. Figure 8 shows the final firing temperature and catalyst bending strength after silica sol impregnation. FIG. 9 is a diagram showing the improvement in bending strength due to impregnation with a mixed slurry of catalyst and silica sol. l... Plate-shaped denitrification catalyst, 2... End treatment section, 3...
Impregnation range, 4...exhaust gas flow path.

Claims (2)

[Claims] (1) A method for manufacturing a plate-shaped catalyst for removing nitrogen oxides in which a catalyst composition is supported on an inorganic fiber woven fabric, which includes a step of impregnating an inorganic fibrous woven fabric with inorganic oxide fine particles containing silica sol and then drying it; a step of applying the prepared catalyst composition containing titanium oxide to the dried inorganic fiber woven fabric;
A process of forming this into a molded body of a predetermined shape and size, a process of drying and firing this molded body to form a plate-shaped catalyst body, and a process of forming a particle size of 20 μm or less on the end surface of this plate-shaped catalyst body. 1. A method for producing a plate-shaped catalyst for removing nitrogen oxides, comprising the steps of impregnating or applying silica sol and drying. (2) In claim (1), the supported amount of silica sol to be impregnated or applied on the end surface of the plate-shaped catalyst body is 50 to 250 g.
/m^2. A method for producing a plate-shaped catalyst for removing nitrogen oxides.