JPH02307532A - Catalyst for removing nitrogen oxides - Google Patents

Abstract

PURPOSE:To obtain a catalyst becoming a high strength large-scale structure suitable for a large capacity denitrification apparatus by supporting fine inorg. oxide particles in the fiber interstices of an inorg. fiber fabric and specifying the diameter ratio and wt. ratio of both of them. CONSTITUTION:Fine particles of inorg. oxide consisting of titanium oxide and oxide of one or more kind of an element selected from vanadium, molybdenum and tungsten are supported within the fiber interstices of an inorg. fiber fabric composed of a ceramic fiber or a glass fiber. The ratio of the diameter of fine particles of inorg oxide to that of the inorg. fiber of the inorg. fiber fabric is set to 0.2 or less and the ratio of the wt. of the fine particles of inorg. oxide to that of the inorg. fiber fabric is set to 0.05-0.8. By this method, a high strength denitrification catalyst having elasticity in itself and capable of holding a shape by itself and suitable for a large capacity denitrification apparatus can be formed.

Description

[Detailed Description of the Invention] (Industrial Application Field) [The present invention relates to a catalyst for removing nitrogen oxides, particularly a catalyst for removing nitrogen oxides that has high strength, has low ventilation loss, and is less likely to cause soot or ash accumulation. Regarding catalysts.

[Conventional technology]

In general, catalysts that remove nitrogen oxides from exhaust gas (hereinafter simply referred to as catalysts) have a catalyst composition consisting of titanium oxide (TiO) and oxides such as molybdenum (Mo), tungsten (W), and vanadium (V). Materials formed into granules, plates, honeycomb shapes, etc. are used.In particular, in the case of boiler exhaust gas that uses fuel such as heavy oil or coal, gas containing large amounts of soot and ash is treated with low pressure drop. Therefore, a combination of plate-shaped catalysts or a catalyst with passages parallel to the gas flow direction, such as a honeycomb-shaped catalyst with a large aperture ratio, is used.Such catalysts include a catalyst on a metal substrate. (Special Publication No. 61-28377), and one in which the catalyst component was extruded into a honeycomb shape (Special Publication No. 60-38)
56, etc.), or one in which ceramic fiber mat or paper is formed into a honeycomb shape and then coated with a catalyst precursor material (Japanese Patent Publication No. 58-11253, etc.) are known, and have already been put into practical use. There is.

[Problem to be solved by the invention]

Among the conventional techniques mentioned above, those in which a catalyst is coated on a metal substrate have many flat plate parts, so the pressure drop is small and ash is less likely to accumulate, which is an excellent method, but it is heavy and the metal substrate is oxidized. There was a problem.

In addition, when the catalyst component is molded into a honeycomb shape by extrusion molding, the molded body can reach 15 mm due to the limitations of the molding technology.
In order to fill a large-capacity device, which is limited to dimensions of approximately 0 square meters and requires several hundred yards, it was necessary to assemble a large number of these small-sized devices. Furthermore, there was a problem that the molded body was weak against impact force.

Furthermore, inorganic fiber cloth or paper whose surface is coated with a catalytic component has a problem in that although it is strong against impact forces, it has low mechanical strength and is abraded by ash particles contained in exhaust gas.

An object of the present invention is to provide a catalyst and a method for manufacturing the same that can eliminate such problems of the prior art and provide a high-strength, large-sized structure suitable for large-capacity denitrification equipment.

[Means to solve the problem]

The above purpose is to strengthen a ceramic or glass fiber woven cloth by impregnating it with inorganic oxide fine particles, and to prepare a paste made by mixing a catalyst composition mainly composed of titanium oxide and cotton-like inorganic fibers dissolved in water. Alternatively, this can be accomplished by coating with a slurry and compacting it using a roller press or the like.

[Effect]

As in the present invention, a catalyst in the form of a slurry or paste is applied to an inorganic fiber woven fabric containing oxide fine particles, which is appropriately rolled and then dried and fired. A catalyst body consisting of a catalyst layer coated on a fibrous fabric is obtained. Inorganic fiber fabric has a thread diameter of 3
Fibers of ~20 μm are bundled into 200 to 800 fibers using a sizing agent such as starch or plastic emulsion, and these are further sewn into approximately 5 to 10 fibers in the vertical and horizontal directions. Therefore, a cloth made of threads sewn from a large number of inorganic fibers has extremely high resilience, and since it is an inorganic material, it has excellent heat resistance. However, fibers are weak against friction, and the strength is low when single fibers are in direct contact with each other. In cases where the catalyst is exposed to high temperatures of 300°C or higher in actual equipment, such as catalysts used in powder-processing processes,
The above-mentioned sizing agent thermally decomposes, causing contact between the fibers, and even if the single fibers have heat resistance, the strength as a woven fabric decreases.In the catalyst of the present invention, the oxide fine particles constitute the woven fabric. Figure 1 shows an electron microscope image of the inside of an inorganic fiber woven fabric impregnated with oxide fine particles. The photo of 0 wires is an example of E glass fiber (wire diameter 9
μm, main component: SLOg 52-56%, /l! 03
12-16%, CaO12-25%, Mg0O-6%
, 81038-13%), SiOx sol (particle size 7-9
It was impregnated with X10-''μm) and fired at 550°C for 2 hours, and the weight ratio (inorganic oxide fine particles/glass fiber) after firing was about 0.12.

As is clear from this figure, the gaps between the fibers used in the present invention 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. In such a state, the strength of the woven 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. FIG. 8 shows the effect of the inorganic fiber woven fabric in the catalyst. (a) is a mixture of catalyst and cotton-like inorganic fiber (weight ratio 79
/21) was made into a paste state with a water content of 23%, rolled with rollers, and fired at 550°C/2 hours. On the other hand, in (b), the above-mentioned mixture paste of the catalyst and cotton-like inorganic fibers was applied to the inorganic fiber woven fabric containing the above-mentioned oxide fine particles while rolling it, and the same was fired. (
As is clear from the load-displacement curve of the catalyst without woven fiber fabric in a), the catalyst alone has bending strength but has a small amount of deformation, resulting in a so-called hard but brittle structure. on the other hand,(
As in Example hiI of the present invention in b), a fabric in which a fibrous fabric containing fine oxide particles is coated with a catalyst layer has excellent bending strength and elasticity. In the structure of the above embodiment of the present invention, the particles of the catalyst component layer are coagulated and bonded to each other, intertwined with the flocculent inorganic fibers, and are raked to form a dense and strong structure, and are entangled with the woven fiber fabric. There is. As a result, the strength of the catalyst body obtained as a structure is due to the composite reinforcement of the catalyst component layer and the woven fabric, in addition to the strength of the fibrous fabric and the catalyst layer, respectively. Those made by rolling a mixture of cotton-like inorganic fibers, or those coated with a catalyst component on the surface of ceramic sheets, etc.
This is significantly higher than when a ceramic sheet is simply impregnated with a catalyst component solution.In addition, in the examples of the present invention, after coating or impregnating an inorganic fiber woven fabric with a catalyst composition paste or slurry, the inorganic fiber woven fabric is Because the catalyst is dried as a structure containing cloth by being sandwiched between perforated sheet metal molds or roll-formed, the catalyst maintains its predetermined shape and becomes dense and strong. Therefore, it is possible to easily obtain a catalyst body of any shape and large size, and it is also possible to manufacture the above-mentioned plate-shaped catalyst body with less ash accumulation through a simple process.

〔Example〕

The present invention will be explained in detail using specific examples.

Example 1 The manufacturing process of the catalyst of the present invention is shown in FIG. Further, Table 2 shows the composition of the glass fiber woven fabric used in the present invention.

77 kg of metavanadate was added to 60 kg of metatitanic acid slurry prepared by the sulfuric acid method containing 30 W (%) of titanium oxide (TiO2).
Mon'y m(N HaV Os) 0.62
kg and ammonium molybdate ((NH,).

MO? 4.51 kg of Osm' 4 Hz O) was added and kneaded while evaporating water using a kneader heated to 140°C. The obtained paste-like material having a moisture content of 38% was formed into a columnar shape with an outer diameter of 3φ and a length of 10IrI[11] using an extrusion granulator, and then dried using a fluidized bed dryer.

After baking the dried granules at 560°C for 2 hours with air flowing through them, we used a hammer mill to produce more than 20J1m! The catalyst was pulverized to a particle size of 10% or more to obtain fine catalyst particles.

3 kg of water was added to a mixture of 7.9 kg of the above catalyst powder and 2.1 kg of cotton-like inorganic fibers, and the mixture was kneaded with a kneader for 30 minutes.
A catalyst paste with a moisture content of 23 wt% was obtained.

Next, glass fiber woven fabric (E glass, 10 pieces/1nch,
460℃/2h heat cleaning material), particle concentration 2
0wt% 5ift sol (particle size 7-9×1O-um)
After impregnation, it was dried at 120°C.

The inorganic fiber woven fabric was cut into 500 mm + square pieces,
Two porous sheet metals obtained by rolling the catalyst paste with a rotating roller at a pressure of 1.4 ton and a speed of 7.5 m/min, applying the paste to a woven fabric, and then processing the 5US304 metal lath. It was sandwiched between molds 2 as shown in Figure 4 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.

Example 2.3 In place of the Stow sol in Example 1, the particle size and concentration were (particle size lO~20X10-3 μm, concentration 20W
t%), (particle size 16-20 x 10-3 ~ 3 μm, concentration 4
A catalyst was produced using a SiO sol having a concentration of 0 wL%), but in the same manner as above.

Example 4.5 Instead of 5iOz in Example 1 (StOl /T
ich/PVA=14/84/2 (weight ratio), 6
0wt% slurry, SiO□: particle size 10-20X
IO-3 μm, S i O,: average particle size 0°5
Using μm5PVA (abbreviation for polyvinyl alcohol),
Each glass fiber woven fabric (E glass, IO pieces/1nc
Catalysts were produced in the same manner as above (E glass, 8 pieces/1 nch, 460°C/2h heat cleaning material).

Example 6 Instead of Sin in Example 1, the average particle size was 0.8
U m catalyst of Example 1 (calcined at 560°C/2 h)
was dissolved in water to prepare a 50 wt % slurry, and the slurry was impregnated into the glass fiber woven fabric. Two sheets of this were used and rolled with the catalyst paste sandwiched between them, but otherwise a catalyst was produced in the same manner.

Example 7 The catalyst of Example 6 with an average particle size of 0.8 μm was mixed with SiO! /Catalyst = 2/4 B (S i Ox is the same as in Example 2) was dissolved in water to prepare a catalyst slurry with a concentration of 50 wt %, and impregnated into an inorganic fiber woven fabric, and the rest were as in Example 2. A catalyst was produced in the same manner as in Example 6.

Comparative example 1 Inorganic fiber woven fabric (E glass, 10 pieces/1nch.

A catalyst was produced in the same manner as in Example 7 except that the molded woven fabric was not reinforced using a sizing agent (phenolic resin).

For each of the catalyst bodies of Examples 1 to 7, the weight change when the glass fiber woven fabric was impregnated with the inorganic oxide fine particles was limited, and the weight ratio was calculated using equation (1). At this time, particles adhering to the outer surface of the molding due to impregnation were blown away with a blower, and the weight of the oxide particles between the fibers was accurately measured.

Further, the diameter ratio was determined using equation (2).

In addition, when multi-component inorganic oxide fine particles were used, the average diameter of the coarsest particles was used.

Further, the glass fiber woven fabric and the catalyst body were cut into pieces of 15 mm in width and 50 mm in length as shown in FIG. 6, and the tensile strength at break was determined using a precision tensile tester. Width 2 more
It was cut into pieces of 0 mm and 30 In 11 in length, the bending strength under load was determined, and the amount of deformation was measured using a dial gauge (Figure 7).

The results obtained are summarized in Table 1. As is clear from these results, the example catalyst according to the present invention has excellent tensile strength and bending strength even though it uses the same catalyst composition as the comparative example catalyst.

This is because, according to the method of the present invention, the catalyst has the stretchability and elasticity properties of the glass fiber woven fabric, and also the catalyst particles are strong with each other or with the cotton-like inorganic fibers mixed in the paste together with the catalyst. This shows that the structure was formed to realize the high-strength catalyst shown in Table 1.

As shown in Table 1, the catalyst of the present invention has extremely high mechanical strength and also has appropriate elasticity. This is due to the combination of the properties of the glass fiber woven fabric and the catalyst, resulting in this strength-related effect. It is generally believed that glass fibers are weak against friction, and that their strength decreases when single fibers come into direct contact with each other. In particular, when the actual catalyst is placed in a harsh environment of 300°C or higher, the sizing agent such as starch that protects the fibers will thermally decompose and lose its effectiveness.
Therefore, a decrease in fiber strength is inevitable. However, as in the present invention, by filling the gaps between the fibers with a sufficient amount of inorganic oxide fine particles so that the fibers do not come into contact with each other and do not restrict their movement, the strength decreases even at such high temperatures. It can be suppressed. FIG. 9 shows the load-displacement curve of the catalyst of Example 3 of the present invention.

This example 3. The catalyst contains SiO□ fine particles in the glass fiber at the above weight ratio of 0.64, and does not have the strength brittleness of the catalyst of the comparative example, and the mechanical strength of the catalyst is improved by inorganic oxide. Glass fiber woven fabric containing fine particles is reinforced to give it elasticity. In addition, this example 6.7
By using catalyst particles as the jjj% i, IJ 1' compound particles, it is possible to improve the compatibility between the glass fibers and the paste catalyst and prevent the catalyst layer from peeling off after molding.

This is because after the paste is applied to the glass fibers, the catalyst particles scattered near the glass fiber surface dissolve into the paste.
This is because they mix at the interface, and by firing in this state, the bond between the catalyst in the glass fiber and the paste catalyst is frozen. In addition, as in the catalyst of Example 6, by compressing the catalyst paste by sandwiching it between multiple glass fibers containing catalyst particles, it is possible to prevent the catalyst layer from peeling off (prevent it from falling off) and improve its strength in a multiaxial stress field. can be achieved. This can withstand multiaxial stress by shifting the orientation of multiple fibers from each other. Furthermore, in this catalyst, even if the glass fibers are exposed on the catalyst surface, the gaps between the glass fibers are impregnated with catalyst particles, so the above characteristics can be improved without reducing the catalytic activity. In this way, by using a plurality of glass fibers containing catalyst particles, it is possible to improve the strength and prevent the catalyst from peeling off without reducing the catalyst activity.

(Effects of the Invention) According to the present invention, it is possible to easily obtain a high-strength denitrification catalyst in which the catalyst itself has elasticity and can maintain its shape by itself.For this reason, the catalyst is incorporated as in the example shown in Fig. 5. By doing so, it is possible to form a catalyst structure having a shape that causes less pressure loss and is less likely to accumulate dust.

Moreover, by changing the shape of the mold, it is possible to create any shape such as wavy or uneven, and the size is also free. Therefore, large catalyst structures exceeding 500W square can be made with various flow path shapes. As a result, it is possible to design an exhaust gas treatment device using a catalyst whose shape and activity match the exhaust gas properties.

Table 2

[Brief explanation of the drawing]

FIG. 1 is an enlarged internal photograph of the glass fiber woven fabric containing S10□ fine particles used in the examples of the present invention, FIG. 2 is a diagram showing the manufacturing process of the catalyst of the present invention, and FIG. FIG. 4 is a diagram showing an example of the catalyst molded article of the invention, FIG. 4 is a diagram showing a method of molding the catalyst of FIG. 3, FIG. 5 is a cross-sectional view of a catalyst structure using the catalyst of the invention, and FIG. The figure shows the shape of a tensile test piece. Fig. 7 is a diagram showing the conditions and method of the bending test, Fig. 8 is a diagram showing the effect of glass fiber in the catalyst on the bending direction, and Fig. 9 is a diagram showing the load-displacement curve of the catalyst of this example. FIG. 1... Catalyst, 2... Porous mold, 3... Holding frame. Applicant Babcock Hitachi Co., Ltd. Agent Patent Attorney Takeshi Kawakita Figure 3 Figure 4? Fig. 5: 15 mm (Number of fibers: 3 mm) 1 Glass fiber Measured using a catalyst molded body Load (9 mm) Displacement (mm) Catalyst displacement of Example 3 (mm) This example 3. Amendment to Catalyst Procedure July 25, 1989 1. Indication of Case 1999 Patent Application No. 126456 Address: 2-6-2 Otemachi, Chiyoda-ku, Tokyo Name:
(544) Babcock Hitachi Co., Ltd. Representative horizontal 1) -
Department 4, Agent 103 Address: 11-8-6, Kayabacho-chome, Nihonbashi, Chuo-ku, Tokyo Subject of amendment Column 7 for detailed explanation of the invention in the specification, Contents of amendment (1) Description cylinder 4 Add the following between lines 11 and 122 of the page. r That is, the present invention provides a catalyst for removing nitrogen oxides in which an inorganic fiber woven fabric is coated with a catalyst composition, in which inorganic oxide fine particles are supported in the fiber gaps of the inorganic fiber woven fabric, and the diameter of the inorganic oxide fine particles is It is characterized in that the ratio to the inorganic fiber diameter is 0.2 or less, and the ratio of the weight of the inorganic oxide fine particles to the weight of the inorganic fiber woven fabric is 0.05 to 0.8. When the ratio of the diameter of the inorganic oxide fine particles to the inorganic fiber diameter exceeds 0.2, the adhesion of the inorganic oxide fine particles is insufficient, and the ratio of the weight of the inorganic oxide fine particles to the weight of the inorganic fiber woven fabric is less than 0.05. If it exceeds 0.8, the wear resistance will be poor and the catalytic effect will be saturated. (2) "Heat cleaning material" on page 9, line 10 of the specification is changed to "heat cleaning material 1." (3) rlo-3-3um on page 1, line 5-6 of the specification.
Change J to r 10-'IJrrB. (4) '5iOz' on page 11, line 12 of the specification is rTi
Changed to o□1. (5) Lines 5-6 from the bottom and 4 from the bottom of page 1O of the specification
"Heat cleaning material" in each line is changed to "heat cleaning material j." (6) "Example 6" in line 11 on page 11 of the specification tube is changed to "Example 11." (7) Specification tube 11 Add the following between lines 11 and 122 of the page: rExample 8 (SfO□/T i Ot/PV
A = 14/84/2 (weight ratio) After drying the glass fiber woven fabric impregnated with 60 wt% slurry), 55 wt%
A catalyst slurry was deposited, dried and coated with 2% PVA. Using two sheets of this, they were rolled with a catalyst paste sandwiched between them, formed with a roller press, dried, and then placed in the air for 55 minutes.
The catalyst was calcined at 0'C for 2 hours to obtain a catalyst. 1 (8) "Example 7" in the 6th line from the bottom of page 11 of the specification.
This is changed to Example 11. (9) “Examples 1 to 7” on the 4th line from the bottom of No. 11 of the specification
be changed to Examples 1 to 81. (10) Table 1 on page 14 of the specification is revised as shown in the attached sheet. (11) Change ``Freeze 1'' on page 16, line 11 of the specification box to ``1 that occurs r''.
" has been changed to Example 6.8J. (13) On page 16 of the specification, lines 19-20, ``Catalyst particles are impregnated in the gaps'' is changed to 1, ``Catalyst particles are attached to r gaps or surfaces''. (14) In the second line of page 17 of the specification cylinder, "contains" was changed to "r impregnated and attached". that's all

Claims (3)

[Claims] (1) In a nitrogen oxide removal catalyst in which an inorganic fiber woven fabric containing glass is coated with a catalyst composition, inorganic oxide fine particles are supported in the fiber gaps of the inorganic fiber woven fabric, and the inorganic oxide fine particles have a diameter of The ratio to the fiber diameter is 0.2 or less,
A catalyst for removing nitrogen oxides, characterized in that the ratio of the weight of the inorganic oxide fine particles to the weight of the inorganic fiber woven fabric is 0.05 to 0.8. (2) The catalyst for removing nitrogen oxides according to claim (1), wherein the catalyst composition comprises titanium oxide and an oxide of one or more elements of vanadium, molybdenum, and tungsten. (3) The catalyst for removing nitrogen oxides according to claim (1) or (2), wherein the inorganic oxide fine particles are composed of a catalyst composition or a catalyst composition and SiO_2.