JP3270084B2 - Catalyst for removing nitrogen oxides and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for removing nitrogen oxides and a method for producing the same, and more particularly to a catalyst for removing nitrogen oxides having high activity and excellent wear resistance and a method for producing the same.

[0002]

2. Description of the Related Art In general, a catalyst for removing nitrogen oxides in exhaust gas (hereinafter simply referred to as a catalyst) includes titanium oxide (T).
iO ₂ ), molybdenum (Mo), tungsten (W),
A catalyst composition comprising one or more oxides such as vanadium (V) is formed into a granule, plate, honeycomb, or the like. Above all, in the case of boiler exhaust gas using fuel such as heavy oil or coal, it is necessary to treat a gas containing a large amount of dust and ash with low pressure loss, and a combination of a plate-shaped catalyst (for example, Japanese Patent Publication No. 61-28377). And a catalyst having a passage parallel to the gas flow direction, such as a honeycomb catalyst having a large aperture ratio (Japanese Patent Publication No. 60-3856). In particular, for a boiler having a large amount of dust in exhaust gas, it is necessary to improve the abrasion resistance of the catalyst. Therefore, a method of increasing the strength by adding an inorganic binder such as silica sol (for example, JP-A-55-155740) Publication).

[0003]

The strengthening of the catalyst by the inorganic binder as described above makes the catalyst dense and hinders the diffusion of the reaction gas, or depending on the type of the inorganic binder, becomes a catalyst poison and reduces the denitration rate. There's a problem. In consideration of this, in order to satisfy a certain denitration performance, it is easy to think in advance of increasing the amount of the metal active component in anticipation of a decrease in the denitration rate due to the inorganic binder. there is a possibility that detrimental to the generated easily, on the downstream side device ammonium sulfate oxidation rate of SO ₂ becomes higher contained in.

An object of the present invention is to eliminate the above-mentioned problems of the prior art, to provide a catalyst for removing nitrogen oxides having a high abrasion resistance to dust in exhaust gas, a high denitration rate, and a low SO ₂ oxidation rate. It is to provide a manufacturing method thereof.

[0005]

According to a first aspect of the present invention, there is provided a catalyst for removing nitrogen oxides comprising titanium oxide mixed with at least one of molybdenum, vanadium and tungsten. , A titanium oxide to which at least one of molybdenum, vanadium, and tungsten is added, or a catalyst powder obtained by preliminarily sintering a raw material thereof, silica sol, and one of the active components.
The present invention relates to a catalyst for removing nitrogen oxides, which is obtained by molding, drying, and calcining a mixture of at least one kind.

According to a second aspect of the present invention, in the first aspect, the vanadium compound has a vanadium content of 2 atm% or less in the catalyst powder and an active component added later is 0.1 to 1.5 atm%. The present invention relates to a catalyst for removing nitrogen oxides. The third invention of the present application is directed to a method for producing a catalyst for removing nitrogen oxide in which titanium oxide is mixed with one or more oxides of molybdenum, vanadium, and tungsten. 450 to which one or more components of
After pre-firing at ℃ or more, finely pulverized into a catalyst powder,
The weight ratio of SiO _{2 to} the catalyst powder (SiO ₂
(Catalyst powder) of 0.08 to 0.18 and one or more of the above components are mixed to form a catalyst composition, which is formed into a predetermined shape, dried and calcined. The present invention relates to a method for producing a catalyst for removing matter.

A fourth invention of the present application relates to the method for producing a catalyst for removing nitrogen oxides according to the third invention, wherein the component added to the catalyst powder together with the silica sol is a vanadium compound.

[0008]

By performing the preliminary calcination at [action] high temperature, after decomposing compound of a metal active ingredient added in advance, TiO ₂
Sintering proceeds to produce a dense catalyst powder having a strong bonding strength. Therefore, the metal active component added later is
Since the catalyst cannot enter the inside of the catalyst powder and is attached to and supported on the outer surface of the catalyst powder or exists between the powders, the catalyst easily contacts the reaction gas, greatly contributes to the denitration reaction, and has a high denitration rate. The catalyst powders are strengthened by the filling effect of silica sol when viewed microscopically and crosslinked macroscopically by inorganic short fibers, so that cracks due to shrinkage during drying are prevented, and the catalyst has high abrasion resistance.

[0009]

【Example】

Example 1 Titanium oxide ammonium metavanadate metatitanic acid slurry by sulfuric acid method containing 30 wt% of _{(TiO 2) (NH 4 VO} 3) and ammonium molybdate _{((NH 4) 6 Mo 7} O 24 · 4H 2 O) In addition, 140
The mixture was kneaded while evaporating water using a kneader heated to ° C. The obtained paste-like substance having a water content of 38% was extruded into a 3 mmφ column by an extruder and then dried by a fluidized bed drier. The dried granules are allowed to flow for 55
After pre-firing at 0 ° C for 2 hours, 2 hours using a hammer mill.
A catalyst powder having a composition of Ti / Mo / V = 93/5/2 (atomic ratio) was obtained by pulverizing the particles having a particle size of 0 μm or less to have a particle size of 90% or more.

Next, ammonium metavanadate is added to the catalyst powder so that the atomic weight of vanadium is 0.1 to 0.5 atm%, and the mixture is dry-mixed.
nm acidic silica sol with SiO ₂ / catalyst powder = 0.0
A small amount of water was added at a ratio of 88 (weight ratio) together with a small amount of water, and then the inorganic short fibers were mixed at a ratio of 15% to the catalyst powder to obtain a catalyst composition. Example 2 The composition of the catalyst powder was Ti / Mo = 90/10 (atomic ratio), the pre-firing temperature was 480 ° C., and ammonium metavanadate was added after 1.0 and 1.5 atm% (mol number of V). Except for the above, a catalyst composition of Example 2 was prepared in the same manner as in Example 1. Comparative Example 1 The catalyst powder obtained in Example 1 was preliminarily calcined and then pulverized. The composition was Ti / Mo = 95/5, Ti / Mo / V.
= 93/5/2, Ti / Mo / V = 92/5/3, and Ti / Mo / V = 90.5 / 5 / 4.5, without post-addition of the metal active component, Thereafter, a catalyst composition was prepared in the same manner as in Example 1.

The catalyst compositions of the prepared Examples and Comparative Examples were formed into a molded catalyst by the following procedure, and the catalytic performance was compared. That is, the catalyst composition is sandwiched between two woven fabrics (E glass, 200 × 7 fibers, 10/1 inch mesh) made of inorganic fibers, and the catalyst composition is 7.5.
Roll coating was performed at a speed of m / min, and the mixture was heated and molded at a temperature of 200 ° C. with a roller and a press having a corrugated shape. .

The denitration rate and SO _{2 of the} obtained catalyst molded body
FIG. 1 summarizes the characteristics of the oxidation rate. The horizontal axis in the figure is
Indicates the amount of vanadium, which is the active component in the catalyst,
The characteristics are shown based on Comparative Example Catalyst 1 without vanadium addition. As can be seen from the upper diagram of FIG. 1, the catalyst of this example has a greater degree of improvement in the denitration ratio with respect to the amount of vanadium than the catalyst of the comparative example. In the catalyst of the comparative example, the active ingredient such as vanadium was uniformly contained in the catalyst powder, but the inside of the catalyst powder did not contribute to the denitration reaction, and thus it is considered that the denitration rate was lower than the amount of vanadium added. In the catalyst of the present embodiment, vanadium is post-added to the catalyst powder which has been compacted in advance by preliminary calcination.Therefore, vanadium exists on the surface of the catalyst powder and is effectively used for the denitration reaction. Nevertheless, it is considered that the denitration rate was high.

The lower part of FIG. 1 shows the SO ₂ oxidation rate. Similar to the denitration rate, the characteristics are shown based on the catalyst of Comparative Example 1 without vanadium added. The limit of the SO ₂ oxidation rate is estimated to be about three times the value of the reference catalyst from actual machine tests and the like.
It can be seen that the catalyst of this example can be used without any problem in actual equipment by setting the amount of vanadium contained in the catalyst powder in advance to 2 atm% or less and the amount of vanadium added later to 1.5 atm% or less.

From the results shown in FIG. 1, it can be said that the catalyst of this embodiment has a high denitration ratio and a low SO ₂ oxidation ratio. By making the amount of vanadium in the catalyst powder 3 atm% or more in the comparative example catalyst 1, it is possible to obtain a catalyst having a high denitration rate, but the SO ₂ oxidation rate also increases, and application to an actual machine is difficult. There is a risk of trouble. Next, the abrasion resistance of the molded catalyst is shown in FIG. Wear loss is 700μm in particle size
The catalyst weight was evaluated when 8 kg of the front and rear rigid grit was naturally dropped from a height of 0.5 m. The characteristics of each catalyst are shown on the basis of the abrasion loss of Comparative Example Catalyst 1 with silica sol added. It can be seen that the abrasion resistance is improved by adding the silica sol to any of the catalysts. The reason why the abrasion resistance of Example 2 is slightly lower than that of Catalyst 1 of the present invention is that the preliminary calcination temperature is low. FIG. 3 shows the effect of the calcination temperature on the abrasion resistance of the catalyst of the present example. It is a plot of abrasion loss and specific surface area. From this figure, it can be seen that the rate of change in any of the characteristics increases from around 450 ° C., and that the catalyst powder starts sintering around 450 ° C. Therefore, from the viewpoint of abrasion resistance, it is desirable that the preliminary calcination and the main calcination be performed at 450 ° C. or higher, and the optimum calcination condition is up to around 600 ° C. at which the catalytic performance starts to decrease.

[0015] relationship between physical properties and wear resistance of the silica sol used was as shown in FIG. 4, the particle size 20mm or less, SiO ₂
If the weight ratio is in the range of 0.08 to 0.18, the abrasion resistance is sufficiently exhibited. It is not known in detail about the mechanism of the development of wear resistance. However, by firing, Mo and V supported on TiO ₂ act like a binder, and partial sintering of the catalyst powder proceeds, and It is considered that the bond between the catalyst powders became a strong catalyst. In the catalyst of the present embodiment, the silica sol is further filled, whereby the catalyst is densified and the wear resistance is further improved.

As described above, it has been shown that the molded catalyst obtained by applying the composition of the catalyst of the present invention to a woven fabric composed of inorganic fibers is superior in terms of the denitration rate and the SO ₂ oxidation rate as compared with the comparative catalyst. However, a similar effect can be obtained also by separately applying to a thin metal plate and molding, or extruding and molding into a honeycomb shape.

[0017]

According to the present invention, a silica sol and a metal active component are mixed with a catalyst raw material mainly composed of TiO ₂ which has been subjected to high-temperature pre-calcination to form a catalyst composition. Abrasion-resistant catalysts having excellent denitration performance can be easily obtained by forming a plate-like catalyst having a base material of, or by forming a honeycomb-like catalyst by extrusion.

[Brief description of the drawings]

FIG. 1 is a diagram showing the denitration rate and SO ₂ oxidation rate of the catalyst of the present invention.

FIG. 2 is a view showing the wear resistance of the catalyst of the present invention.

FIG. 3 is a diagram showing the relationship between the calcination temperature, the specific surface area, and the abrasion loss in the catalyst of the present invention.

FIG. 4 is a diagram showing a relationship between physical properties of silica sol and abrasion resistance.

Claims (4)

(57) [Claims] 1. A nitrogen oxide removing catalyst comprising a titanium oxide mixed with one or more oxides of molybdenum, vanadium and tungsten, wherein one or more active components of molybdenum, vanadium and tungsten are added. A catalyst for removing nitrogen oxides, comprising: forming, drying and calcining a mixture of a catalyst powder, a silica sol, and one or more of the above-mentioned active ingredients, which is obtained by preliminarily calcining the titanium oxide or its raw material, and then pulverizing the powder. . 2. The catalyst according to claim 1, wherein the amount of vanadium in the catalyst powder is 2 atm% or less, and the amount of the active component added later is 0.1 atm.
A catalyst for removing nitrogen oxides, which is a vanadium compound of 1.5 to atm%. 3. A method for producing a catalyst for removing nitrogen oxide, comprising mixing one or more oxides of molybdenum, vanadium, and tungsten with titanium oxide, wherein the titanium oxide raw material comprises vanadium, molybdenum, and tungsten. the plus one or more components comminuted After prebaked at 450 ° C. or higher and the catalyst powder, which the weight ratio of SiO ₂ to the catalyst powder (SiO ₂ / catalyst powder) 0.0
A method for producing a catalyst for removing nitrogen oxides, comprising mixing a silica sol of from 8 to 0.18 with at least one of the above components to form a catalyst composition, forming the catalyst composition into a predetermined shape, drying and calcining the catalyst composition. . 4. The method for producing a catalyst for removing nitrogen oxides according to claim 2, wherein the component added to the catalyst powder together with the silica sol is a vanadium compound.