JPH02187147A - Denitration catalyst with ceramic paper utilized therefor - Google Patents

Abstract

PURPOSE:To thin the thickness of the title catalyst and to enhance strength thereof by impregnating ceramic paper with a mixture of titania sol and silica sol and thereafter drying and calcining this ceramic paper and then carrying vanadium oxide thereon and forming the denitration catalyst. CONSTITUTION:Silica/alumina-based or alumina-based ceramic fiber is manufactured to sheets and thereby ceramic paper is obtained. This ceramic paper is impregnated with a mixture of titania sol and silica sol and then dried and calcined. A denitration catalyst is formed by carrying vanadium oxide on the obtained ceramic paper with solid held thereon. As the mixing ratio of the mixture of titania sol and silica sol, the value of (SiO2/(TiO2+SiO2))X100 SiO2 mixing degree is regulated to <=80wt.% ordinarily 5-16wt.% preferably 7-13wt.%. The thickness of the obtained catalyst can be remarkably thinned and also mechanical strength is drastically enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a denitrification catalyst for selective reduction of nitrogen oxides (NOX) in exhaust gas with ammonia (NH3). Regarding catalysts.

Prior art and its problems It has been known that a catalyst in which a metal oxide such as ■20° is supported on anatase type titania (T102) exhibits excellent performance as an NH3 reduction selective denitrification catalyst. This catalyst can be prepared by adding an appropriate inorganic binder and water to the powdered catalyst components, kneading the mixture well, and granulating the mixed material into a granular catalyst of an appropriate particle size, or by preparing a monolithic catalyst (a granular catalyst of an appropriate size). It is manufactured by extrusion molding (see Figure 2). In the selective reduction denitrification method using NH3, a monolithic catalyst is said to be more advantageous than a granular catalyst in consideration of gas flow resistance in the catalyst bed and clogging of the catalyst bed due to dust.

However, anatase-type TiO2 lacks thermal stability, and even at relatively low temperatures, such as 500 to 600° C., the specific surface area decreases due to sintering and transition to catalytically inactive rutile-type crystals occurs. Therefore, sintering after extrusion cannot be performed sufficiently, and the mechanical strength of the monolithic catalyst is extremely low. Therefore, in the monolithic catalyst shown in FIG. 2, the wall thickness (2) is generally 1 + u +
It is said that it is difficult to make the wall thickness (2) less than 0.5 mm even for a catalyst for low flow rate which requires the above-mentioned opening (1) and has a small opening (1).

Furthermore, this catalyst requires careful handling and has the problem of impeding efficiency in the catalyst filling operation.

In order to overcome the above-mentioned drawbacks, plate-shaped catalysts reinforced with metal in the form of wire mesh or metal lath have also been proposed. However, this has a thick plate thickness of about 11 mm and is expensive to manufacture, so its advantage over a monolithic catalyst formed by extrusion molding is questionable. Furthermore, in order to improve the mechanical strength of this catalyst, it is necessary to form the catalyst as an extremely dense oxide, which impairs the diffusivity of gases such as N0xSNH3 within the catalyst pores, resulting in V2O5/TiO2 There is a tendency that the original performance of the catalyst system is not being demonstrated.

In order to solve the above-mentioned problems, the present inventors previously proposed a denitrification catalyst characterized by dispersing and retaining TiO2 fine powder in a glass fiber aggregate (preform) (Japanese Patent Application Laid-open No. Publication No. 55-155744 and Special Publication No. 58-
(See Publication No. 1976). However, although high activity can be obtained with this catalyst, the following new problems have arisen. That is, (1) it is necessary to use a metal support plate to impart rigidity to the glass fiber aggregate, (2) the plate thickness of the catalyst is as thick as 1ffi [5 to 2], and (
3) Catalyst powder flakes off little by little due to severe mechanical impact and scatters.

Therefore, the present inventors also proposed a denitrification catalyst with a novel structure using ceramic paper as a catalyst that can overcome all of the above-mentioned problems of the prior art. This catalyst is made by impregnating ceramic paper with titania sol, drying and firing, and supporting vanadium oxide on the titania-retaining paper obtained. This catalyst is thin and light, and has high mechanical strength. Also, the binder effect of T i 02 hardens the paper, giving rigidity to the catalyst and increasing its bending strength, resulting in less powder falling due to mechanical impact. Furthermore, the interfiber voids ensure the diffusivity of the reaction gas inside the catalyst and exhibit excellent activity.

In the manufacturing process of this catalyst, the ceramic paper is heated in a low-oxygen atmosphere as a pretreatment, and then fired after impregnation, so that all the organic binder is burned out and decomposed. Therefore, the strength of the catalyst after the binder is burnt off depends mostly on the binder effect of T i 02. However, TiO2 obtained by drying the sol has relatively low strength and low adhesion to fibers, so it does not exhibit a very strong binder effect.

If firing is performed at a temperature of 500 to 600°C, the strength of TiO2 will increase and the binder effect will improve, but anatase-type TiO2 lacks thermal stability and its specific surface area decreases even when heated at a relatively low temperature as described above. Inactivation of the catalyst occurs due to the transition to rutile-type crystals. The purpose of this invention is to
The object of the present invention is to provide a thinner (and lighter) denitrification catalyst that maintains the excellent properties of the ceramic paper-based catalyst described above, further increases the strength of the catalyst, and is thinner (and lighter).

Means for Solving the Problems In order to achieve the above objectives, the denitrification catalyst according to the present invention has the following features:
Ceramic paper produced by silica-alumina or alumina ceramic fiber papermaking is impregnated with a mixture of titania sol and silica sol, dried and fired, and the resulting solid-retaining paper supports vanadium oxide. It is characterized by

(1) In the denitration catalyst of the present invention, a mixture of titania sol and silica sol is used as the sol for impregnating ceramic paper.

A catalyst obtained by impregnating ceramic paper with a mixture of titania sol and silica sol, drying and firing, and supporting vanadium oxide on the obtained solid-retaining paper is different from a catalyst obtained by using only titania sol as the impregnating sol. In comparison, it is significantly superior in terms of vibration resistance, as shown in the vibration resistance test of Examples to be described later, and is comparable in terms of vibration resistance, as shown in the bending strength test of Examples to be described later. This is because when the sol dries and solidifies within the ceramic paper, the mixed silica sol forms solids relatively uniformly on the surface of the paper, and solids with excessive particle sizes become localized on the surface. This is thought to be due to the fact that it has the effect of preventing

The denitrification activity of the catalyst tends to decrease with the inclusion of 5LO2, as is clear from the activity test results of Examples described later.
2/(Ti02+SiO2 mixing rate [SiO2)]X1O
If O is 80% by weight or less, the SiO2 contamination rate [SiO
There is almost no effect due to the contamination of 2. The mixing ratio of titania sol and silica sol is set so that the SiO2 mixing ratio [SiO2 mixing ratio is usually 5 to 16% by weight, preferably 7 to 13% by weight.

(2) Catalyst powder is dispersed and held in the fiber preform.

v205/TiO2 due to sintering action without impairing catalytic activity
Since it is impossible in principle to improve the strength of the plate-shaped catalyst and/or monolithic catalyst in the system, it is necessary to consider reinforcement with some kind of fibrous material. In this case, two methods are considered: a method of kneading catalyst powder and fibers and producing a monolithic catalyst by extrusion molding (mixing wire method), and a method of dispersing and retaining catalyst powder in a fiber aggregate, that is, a fiber preform (fiber preform method). It will be done. For plate-shaped catalysts, the crosstalk method is excellent for increasing the amount of catalyst per plate area, but
In the kneading method, the diffusivity of the reaction gas inside the catalyst is low, and the catalyst's original performance cannot be demonstrated. Also, due to the extrusion moldability of the paste made by kneading the fibers, the board thickness was set to 0°50! ffl
It is difficult to do the following:

In the case of the fiber preform method, for example, the reaction temperature is 200°C.
If it is above, the catalyst powder may be 100 g/m2 or less, and the plate thickness is determined by the thickness of the fiber preform, and is 0.1
It can be freely set as long as it is 5 mm or more. Therefore, catalysts using the fiber preform method are advantageous.

(3) Ceramic paper is used as the fiber preform.

Glass fiber paper and ceramic paper are examples of fiber preform bodies in which fibers are accumulated as thinly as possible at a high density, and the fibers themselves can be expected to have a certain degree of rigidity.

Glass fiber paper generally has a low binder effect of an inorganic binder and its strength as a paper is lower than that of ceramic paper, so it is desirable to use ceramic paper.

In order to mold inorganic fibers into paper, it is necessary to add a binder to the fibers. As a binder, it is generally preferable to use an inorganic binder, since organic binders decompose and/or burn under the conditions in which the catalyst is used and lose their effectiveness.

(4) A sol impregnation method is applied to hold TiO2 powder or catalyst powder containing the same in inorganic fiber paper.

Methods for retaining catalyst powder in inorganic fiber paper include a method of impregnating TiO2 colloidal sol (sol impregnation method), and a method of impregnating TiO2 colloidal sol with TiO2 powder or V
A method of straining catalyst powder carrying 206 (catalyst powder straining method) is considered. When TiO2 is retained by the sol impregnation method, ceramic fibers have better contact with TlO2 than the adhesion between glass fibers and TiO2, and the amount of catalyst powder falling off is lower than when glass fiber paper is used. Shows characteristics with less.

When using ceramic paper, if T i O2 is retained by the sol impregnation method, the retained T i O
No. 2 exhibits an effect as a binder and improves the rigidity, especially the bending strength, of a plate-shaped catalyst, so it is advantageous compared to the catalyst powder immersion method.

The catalyst produced in this way has high activity due to the high diffusivity of the reaction components inside the catalyst and the ability of the catalyst powder to exhibit its original performance, compared to conventional monolithic catalysts produced by extrusion molding. Further, the thickness of the catalyst can be reduced to about 0.1 cm.

Therefore, when the catalyst surface density per volume is constant, this catalyst exhibits characteristics of higher porosity and lower gas flow resistance than conventional V2O6/TiO2-based monolithic catalysts.

(5) It is preferable to heat-treat the ceramic vapor in a low oxygen atmosphere in advance.

In order to increase the rigidity of the catalyst, it is necessary to use a high-density ceramic paper.

High-density ceramic paper is generally made using a combination of an organic binder and an inorganic binder. When applying the sol impregnation method to such paper, the mixing rate of T i 02 and SiO2 [in order to improve the compatibility between SiO2 and the fibers, the paper is heated in a low oxygen atmosphere before impregnating with the sol, and the fibers are It is preferable to carbonize and remove the organic binder on the surface. In this case, if 5% or more of oxygen is present, the organic binder is completely removed and the strength of the paper is significantly reduced. Furthermore, if no oxygen is present, a large amount of carbon remains on the fiber surface, making it impossible to improve adhesion. Therefore, it is desirable to heat the ceramic paper at an oxygen concentration of 1 to 5%. Heating conditions are 3
00~500℃ for 0.5~4 hours, preferably 350~
The temperature is 400°C for 2 to 3 hours.

As T i 02, anatase type T i 02 formed by hydrolysis of titanium salts such as titanium sulfate, titanium tetrachloride, and tetrapropyl titanate is preferable. Since the T i 02 thus formed has many large pores of 1000 Å or more, the diffusion rate of the reaction gas within the powder is high.

Titanium content is TiO per 1 m2 of ceramic vapor surface.
2 is contained in an amount of 20 to 300 g, preferably 30 to 200 g.

Commercially available silica sol can be used.

Vanadium oxide is supported on ceramic paper, for example, by impregnating ceramic paper with an ammonium metavanadate solution, drying and firing. The vanadium oxide precursor is not limited to those mentioned above.

Effects of the Invention The denitrification catalyst according to the present invention is made by impregnating ceramic paper with a mixture of titania sol and silica sol to retain TiO2 and SiO2, and allowing the resulting solid-retaining vapor to support vanadium oxide. Therefore, by using ceramic paper, the thickness of the catalyst can be significantly reduced, and the mechanical strength can be greatly increased. Further, by using a mixture of titania sol and silica sol, TiO2 can be firmly attached to the fibers of ceramic paper. Therefore, the binder effect of TiO2 can harden the vapor, impart rigidity to the catalyst, and increase bending strength. As a result, powder falling due to mechanical impact can be minimized. Furthermore, the interfiber voids in the fibers constituting the ceramic paper ensure the diffusivity of the reaction gas inside the catalyst, allowing it to exhibit higher activity than the conventional V2O5/TiO2-based denitrification catalyst mentioned at the beginning of this book.

Example Next, examples of the present invention will be shown together with comparative examples.

Example a, catalyst preparation Three types of ceramic papers (A) with specifications shown in Table 1
(13) Calcining (C) at 400°C for 2 hours in a mixed gas of 3% oxygen and residual N2 1. Ta. Next, titania sol (T i 02 min-333 Juumaru,
pH-3~4) and silica sol (Si02min-20% by weight)
, pH-6 to 7), dried at 120°C, and fired at 300°C for 3 hours. In this way, ceramic paper nitride TiO2
and SiO2 mixing rate [SiO2 solids were retained. The amount of solid matter retained was adjusted by diluting the mixed solution with pure water.

Next, the ceramic paper holding the TlO2 and SiO2 mixing ratio [SiO2] was immersed in a saturated solution of ammonium metavanadate at room temperature for 8 hours, dried at 120°C, and fired at 300°C for 3 hours. Thus, 98 shown in Table 2
A similar V20S/T i 02 type catalyst was obtained.

b. Vibration properties For each of the catalysts prepared as described above, the amount of catalyst powder falling off due to vibration was measured using the vibration resistance tester shown in FIG. The testing machine consists of a box body (3), a stainless steel diaphragm (4) with a thickness of 0.81 placed horizontally on the box body (3), and a 60Hz vibration exciter (5) installed on the top surface of the box body (3). The test catalyst (6) is fixed to the lower surface of the diaphragm (4) with double-sided adhesive tape.

Table 2 shows the Δ11 constant results of the cumulative amount of powder falling. As is clear from the same table, the catalyst obtained using a mixture of titania sol and silica sol as the impregnating sol shows significantly less powder falling off even when subjected to severe vibration, compared to the catalyst obtained using only titania sol. , which is extremely superior in terms of vibration resistance.

(Leaving space below) Table 1 Table 2 C1 Bending strength Using the ceramic papers (A) and (B) in Table 1 above and following the method described above, various catalysts with different retention amounts of T i 02 and SiO2 mixing ratio [SiO2 mixing Person rate 1
Various types of catalysts with different solid content retention amounts were prepared at 0% by weight. For these catalysts, the distance between fulcrums is 20 mm.
A three-point bending test was conducted, and the bending strength was measured according to the following formula.

Bending strength (kgl/m++m) - [3X breaking load Ck
gf )×distance between fulcrums (IIIll)]/[2×test piece width (nm)×test piece thickness (■)] The relationship between solids retention and bending strength is shown in the graph of FIG. As is clear from the same graph, the catalyst obtained using a mixture of titania sol and silica sol as the impregnating sol is comparable in terms of vibration resistance to the catalyst obtained using only titania sol.

d. SiO2 mixing rate [SiO2 mixing rate and catalytic activity Using the ceramic paper (B) in Table 1 above and according to the method described above, SiO2 mixing rate [SiO2 mixing rate and various types of catalysts with different solid content retention] were determined. Each was prepared. Activity tests were conducted on each of these catalysts using a stainless steel flow-through reaction tube with an inner diameter of 1 inch.

That is, the catalyst is filled and fixed in the reaction tube, and then the reaction temperature is controlled to a predetermined value, and the inlet NNOx-5 is
A prepared exhaust gas for testing having a composition of 0pp, -15% oxygen, and -10% water vapor was flowed into the reaction tube. Area velocity (A-V)
In other words, the gas flow rate per geometric surface area (m2) of the catalyst (
8m3/hour) to 43m/hour, * f: NH3 ratio (inlet NH3a degrees ppm / outlet NH31 degrees ppm
) was set to 1.2, and the inlet NH3 concentration was set to 60 ppm.

For each catalyst, the temperature was 150°C, 200°C and 300°C.
Denitrification rate at °C - [(Input NOx concentration ppm = Output N
Ox concentration 1) I) 11) / Inlet NOx concentration pl) m
]X100 was calculated. Table 3 shows the obtained denitrification rates. In addition, the relationship between the SiO2 mixing rate and the catalyst activity is shown in the graph of Fig. 4.
The relationship between 2/(Ti02 +S 102) x 100 and catalyst activity is shown in the graph of FIG.

(Margins below) Table As is clear from the above table and graph, the denitrification activity of the catalyst tends to decrease depending on the SiO2 contamination rate [SiO2 contamination rate];
If the temperature is less than 0, the SiO2 contamination rate [SiO2 contamination has almost no effect.

[Brief explanation of the drawing]

Figure 1 is a vertical cross-sectional view of a vibration resistance tester, Figure 2 is a partial perspective view of a conventional monolithic catalyst, Figure 3 is a graph showing the relationship between solids retention and bending strength, and Figure 4 is a graph showing the relationship between SiO2 mixture. Figure 5 is a graph showing the relationship between the amount of retained solids and the denitrification rate. Applicant for the above patents: Hitachi Zosen Corporation Figure 1 Figure 2 Figure 4 Figure 4 "fL (9/m2) Figure 3 Cl/m2 Figure 5

Claims (2)

[Claims] (1) Ceramic paper produced by silica-alumina-based or alumina-based ceramic fiber papermaking is impregnated with a mixture of titania sol and silica sol, dried and fired, and the resulting solid-retaining paper supports vanadium oxide. A denitrification catalyst using ceramic paper, which is characterized by the following: (2) Change the mixing ratio of titania sol and silica sol to SiO_
2 mixing rate [SiO_2/(TiO_2+SiO_2)]
The denitration catalyst according to claim 1, characterized in that x100 is set to 80% by weight or less, usually 5 to 16% by weight, preferably 7 to 13% by weight.