JPH08103654A - Catalyst for removal of nox inhibited in oxidation of sulfur dioxide and its production - Google Patents

Abstract

PURPOSE: To produce a denitration catalyst having superior denitration activity and controlled SO2 oxidation activity. CONSTITUTION: A V compd. and a W compd. or an Mo compd. as active components and water are added to a titania or titanium hydroxide carrier and they are mixed, dried and fired to prepare a 1st constituent component. A W compd. or an Mo compd. as an active component and water are added to a titania or titanium hydroxide carrier and they are mixed, dried and fired to prepare a 2nd constituent component. The 1st and 2nd components are pulverized, kneaded with water, dried and fired.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitrogen oxide removing catalyst which suppresses oxidation of sulfur dioxide and a method for producing the same, and more particularly to an exhaust gas denitration catalyst and a method for producing the same.
The present invention relates to a catalyst for nitrogen oxide removal, which suppresses the oxidation activity of sulfur dioxide (SO ₂ ) by utilizing the heterogeneity of catalyst components, and can suppress the by-product of SO ₃ to a very small extent, and suppresses the oxidation of sulfur dioxide, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally used combustion exhaust gas
Monia denitration equipment uses ammonia (NH ₃) And nitrogen oxides
(NO_x) Reaction rate and reaction rate
It uses a denitration catalyst. The denitration catalyst manufacturing method is generally
In addition, a high specific surface area (about 100 m²/ G or more) Oxidation
Oxidation that becomes an active ingredient in materials, especially titanium oxide (titania)
After the material is supported, it is fired.
At this time, by uniformly dispersing the active ingredient in the carrier,
Therefore, a catalyst with higher activity can be obtained. So, for example, five
For vanadium oxide, dissolve vanadate in oxalic acid.
And then mixed with titania slurry containing sulfate.
Better dispersibility. But with this method,
Simultaneously with the denitration reaction, sulfur dioxide (SO₂) Triacid
Sulfurized (SO ₃) Is also generated and injected as a reducing agent.
NH₃Unreacted NH₃And SO ₃By reaction with
Ammonium sulfate ((NH_Four)₂SO_Four) And denitration equipment
Problem of accumulation on the air preheater on the downstream side of the
was there.

Therefore, the inventors of the present invention invented a method for suppressing SO ₂ oxidation activity by making the catalyst components non-homogeneous, and proposed a method for producing a catalyst using the same (Japanese Patent Application No. 3-2).
No. 60839 and Japanese Patent Application No. 5-312211).
This method is an excellent method that can obtain a catalyst formed body while keeping the catalytically active component and the titanium oxide component in a non-homogeneous state and can reduce the SO ₂ oxidation rate. On the other hand, 200
A method has been proposed in which the SO ₃ oxidation activity is improved by mixing a coarse-grained active ingredient prepared to ˜350 mesh with a carrier (Japanese Patent Laid-Open No. 58-210849). This method was also an excellent method for lowering the SO ₂ oxidation rate. However, although these prior arts were effective in suppressing the SO ₂ oxidation rate, they did not sufficiently consider the initial denitration activity or the decrease in activity over time during use, and there are many points that should be improved as a practical catalyst. It was

[0004]

Among the above-mentioned prior arts, Japanese Patent Laid-Open No. 58-210849 discloses that SO is obtained by making catalyst component 1 and titania 2 exist inhomogeneously as shown in FIG.
_{2 It} suppresses the oxidation rate, but as shown in Fig. 5, it is homogenized by thermal diffusion of the catalyst components during the catalyst production process and during use, and
There is a problem that the O ₂ oxidation rate gradually increases.

[0005] On the other hand, Japanese Patent Application No. 3-260839 makes a high concentration of V-supported titania and M _O or W-supported titania non-uniformly present. In this case, the denitrification activity is mainly due to the V-supported titania catalyst. I will be responsible. In general, V-supported titania catalysts are known to produce degradation and readily compound component such as sodium contained in the dust in the exhaust gas (N _a), potassium (K). Therefore, this catalyst has not been improved in its properties and has a problem that although it has a low SO ₂ oxidation rate, it is greatly deteriorated by the alkali metal contained in the SO _x -containing gas. By further Japanese Patent Application No. Hei 5-312211 is fired mixed with titania titania catalyst carrying M _o or W and V, a catalyst preparation method attempts to improve the drawbacks of the catalyst, but the catalyst Although it is not deteriorated by the alkali metal as described above, there is a problem that V is partially thermally diffused similarly to _Mo and W, and the SO ₂ oxidation rate is lower than that of the catalyst.

The object of the present invention is to improve the SO ₂ oxidation rate over time, which is a problem of the above-mentioned prior art, or to have a low denitrification activity, and to reduce the depletion with time. (EN) Provided are a denitration catalyst having the above-mentioned properties and capable of suppressing SO ₂ oxidation activity, and a method for producing the same.

[0007]

The invention claimed in this application to achieve the above object is as follows. (1) In a denitration catalyst for catalytically reducing nitrogen oxides in exhaust gas containing sulfur dioxide with ammonia, molybdenum (M _o ) and vanadium (V), or oxides of tungsten (W) and vanadium (V), respectively. And a first component composed of titanium oxide and molybdenum (M
_O ) or tungsten (W) oxide and a second constituent component consisting of titanium oxide, both of which are molded while maintaining a physically mixed state, thereby suppressing the oxidation of sulfur dioxide. DeNOx catalyst. (2) In a method for producing a denitration catalyst in which nitrogen oxides in exhaust gas containing sulfur dioxide are catalytically reduced with ammonia, an active component composed of a vanadium compound and a tungsten compound or a molybdenum compound is supported on a carrier composed of titania or titanium hydroxide. First obtained by pre-firing
Oxidation of sulfur dioxide, characterized in that the constituents and a second constituent obtained by carrying out preliminary calcination by supporting an active ingredient composed of a tungsten compound or molybdenum compound on a carrier composed of titania or titanium hydroxide are calcined after mixing. A method for producing a denitration catalyst that suppresses the above.

(3) In a method for producing a denitration catalyst in which nitrogen oxides in exhaust gas containing sulfur dioxide are catalytically reduced with ammonia, a tungsten compound or molybdenum compound and a concentration not more than a concentration at which it can be adsorbed on a carrier made of titania or titanium hydroxide. No. 1 component obtained by carrying out an active ingredient comprising a vanadium compound and then pre-baked, and a second component obtained by carrying a tungsten compound or molybdenum compound on a carrier made of titania or titanium hydroxide and then pre-baking A method for producing a denitration catalyst which suppresses the oxidation of sulfur dioxide, which comprises mixing the components with each other and then calcining the mixture. (4) The method for producing a denitration catalyst which suppresses the oxidation of sulfur dioxide according to claim 3, wherein the amount of the tungsten or molybdenum compound supported on the carrier when obtaining the second component is not less than the adsorbable concentration. .

[0009]

[Function] The inventors of the present invention applied the SO of Japanese Patent Application No. 5-312211.
₃A detailed study of the process of increasing the oxidation rate over time revealed that
It has been clarified that the mechanism proceeds like this. (1) V₂O_Five/ M_OO₃/ T_iO₂(T_iO₂Up M_O
O₃And V₂O_FiveCarrying T) and T_iO₂On the contact surface of
First M_OO₃Is T_iO₂Move to V₂O_Five/ M _OO₃
/ T_iO₂M_OO₃Concentration decreases, T_iO₂And V₂O
_Five/ M_OO₃/ T _iO₂Near the interface of V₂O_Five/ T_iO
₂(T_iO₂Up V₂O_FiveCarrying the)). (2) As a result, V₂O_Five/ T_iO₂And M_O
O₃/ T_iO₂(T_iO₂Up M_OO₃Carrying one)
Becomes a mixed catalyst of N, and as described above, N_a, V by K₂
O_Five/ T_iO₂A decrease in catalyst activity occurs.

The point of the present invention is that V ₂ O ₅ / M _O O ₃
The first step of thermal diffusion of / T _i O ₂ is to suppress migration of M _O O ₃ , and for this purpose, V ₂ O ₅ / M _O
It is necessary to combine O ₃ / T _i O ₂ and M _O O ₃ / T _i O ₂ . Here, by using M _O O ₃ / T _i O ₂ instead of conventional T _i O ₂ , V ₂ O ₅ / M
Since the _{O O 3} / T _{i O 2} can suppress the diffusion of the M _O O ₃ to T _i O _2, as in the prior art N _a, reduction in denitration activity by K hardly occurs. Further, inventors have achieved a experimental fact that the vanadium pentoxide is hardly thermally diffuses on titania molybdenum oxide is supported, by adding a _{M O O 3 / T i O} 2 carrying the pre-oxidized molybdenum If, it is possible to diffuse the suppression of the T _i O ₂ of the V ₂ O ₅ as compared with the case of adding T _i O ₂ of the prior art, the reduction with time in sO ₂ oxidation properties change and alkali metals by active suppression The obtained catalyst can be obtained. Note that W also has the same action as M _o .

The above object of the present invention is to provide a first component in which titania supports one of molybdenum oxide and tungsten oxide and vanadium pentoxide, and a first component in which titania supports one of molybdenum oxide and tungsten oxide. This can be achieved by molding the two components while leaving the non-uniformity and firing as necessary. Here, the first component can be obtained by carrying out preliminary calcination by supporting an active component composed of a compound of molybdenum or tungsten and a compound of vanadium using titania or titanium hydroxide as a carrier. At this time, it is necessary that all of the components to be carried have a concentration not higher than the concentration capable of being adsorbed on the carrier. If excess vanadium compound is present in the first component, the second
When mixed with the component, since the vanadium compound can move to the surface of the second component, the vanadium compound is homogenized, which hinders suppression of SO ₂ oxidation activity.

The second component can be obtained by carrying out pre-baking with a compound of molybdenum or tungsten supported by titania or titanium hydroxide as a carrier. At this time, if the concentration of the compound of molybdenum or tungsten is lower than the concentration that can be adsorbed on the carrier, the vanadium compound is adsorbed on the first component when mixed with the first component, and the vanadium compound is homogeneously dispersed. , SO ₂
It hinders suppression of oxidative activity. The amount of molybdenum, tungsten, and vanadium adsorbed on the carrier is proportional to the specific surface area of the carrier, so that it is possible to prepare a catalyst having an arbitrary active ingredient concentration by suppressing the specific surface area of the carrier.

Furthermore, in order to mold the first component and the second component while leaving inhomogeneity, the first component and the second component must not dissolve in the solvent (water) during the mixing process, that is, both are insoluble. It is important that the particles are mixed as secondary particles.

[0014]

EXAMPLES Next, the present invention will be described in more detail by way of examples. Denitration catalyst of this example, molybdenum (M _o),
An oxide of tungsten (W) and vanadium (V) or a compound that forms each oxide by heating is used as a raw material of an active ingredient, and titania or a precursor thereof is used as a raw material of a carrier.

The manufacturing process of the catalyst according to this embodiment is as shown in FIG. First, a vanadium compound and a molybdenum or tungsten compound are supported on a carrier raw material and then pre-baked to obtain a first component. The molybdenum or tungsten compound is supported on the carrier raw material and preliminarily calcined. The second component is added to the first component, sufficiently mixed, and then calcined. Here, the vanadium compound concentration contained in the first component must be equal to or lower than the concentration capable of being adsorbed by the carrier raw material. The titania slurry used in this experiment adsorbs 10 mol% of ammonium vanadate (NH ₄ VO ₃ ) in terms of vanadium pentoxide.

In the present embodiment, the pre-fired first component is used.
And 2nd component total 20kg, Al₂O ₃・ S_iO₂Inorganic
Knead 3 kg of fiber and 10 kg of water with a kneader for 1 hour
Clay-like, 0.2 mm thick SUS304 metal lath base
The surface is roughened by spraying aluminum onto the plate
Applied to the plate to make a plate-like catalyst with a thickness of about 0.9 mm, and then air-dry
Firing was performed. This allows easy evaluation of catalytic activity
This is because the shape when used as a catalyst is other shape.
It may be (pellet, honeycomb, powder).

Example 1 Ammonium metavanadate powder, ammonium molybdate and titania slurry (titania content 30 wt%, SO ₃ content 6 wt%) were used as raw materials for the first component. The respective mixing ratios were weighed so that the V / M _o / T _i atomic ratio was 2/8/90, water was added, and the mixture was mixed for 2 hours. Then, it was dried and pre-baked at 450 ° C. for 2 hours, and after baking, it was ground with a hammer mill. On the other hand, the second component, the titania slurry and molybdate ammonium dried after kneaded mixture with water at a ratio of M _o / T _i ratio = 8/92, and 2 hours pre-baking at 450 ° C., calcined After that, it was crushed in the same manner. First component and second
The weight ratio of the components is 1/1 and the firing temperature is 500 ° C.

Examples 2 to 4 Catalyzing was carried out under the same conditions as in Example 1 except for the pre-calcination temperature and the calcination temperature. The pre-baking temperature was 300 ° C., the baking temperature was 350 ° C., the pre-baking temperature was 450 ° C., the baking temperature was 500 ° C., and the pre-baking temperature was 550 ° C., the baking temperature was 600 ° C. Example 5 Catalyzing was carried out under the same conditions as in Example 1 except that ammonium paratungstate was used instead of ammonium molybdate.

Comparative Example 1 The composition of the first component was V / M _o / T _i without adding the second component.
A catalyst was prepared under the same conditions as in Example 1 except that the atomic ratio was adjusted to 1/8/91. Comparative Examples 2 to 3 Catalyzing was carried out under the same conditions as in Example 1 except for the pre-calcination temperature and the calcination temperature. The conditions were such that when the preliminary firing temperature was 250 ° C., the firing temperature was 300 ° C., and when the preliminary firing temperature was 600 ° C., the firing was performed at 650 ° C.

Comparative Example 4 A molybdenum compound was not added to the second component and only titania was used, and the composition of the first component was 2/16 in V / M _o / T _i atomic ratio.
The catalyst was prepared under the same conditions as in Example 1 in the subsequent steps. Comparative Example 5 The composition of the first component was prepared without adding a molybdenum compound so that the V / T _i atomic ratio was 2/98, and the second component was M _o.
A catalyst was prepared under the same conditions as in Example 1 except that the ratio was adjusted to / T _i ratio = 16/84.

The measurement of the activity was carried out under simulated combustion exhaust gas conditions. The composition of the gas is S when measuring the SO ₂ oxidation rate.
O ₂ : 500 ppm, O ₂ concentration: 3.0%, the rest is nitrogen gas, gas flow velocity is area velocity 6 (m / h), measurement temperature 380
It was carried out at ° C. On the other hand, the denitration rate is NO _x concentration: 200 ppm
, NH ₃ concentration: 240 (ppm), CO ₂ concentration: 12%,
H ₂ O concentration: 12%, O ₂ concentration: 3.0%, the rest is nitrogen gas, measurement temperature is 350 ° C., gas velocity is 51 m in area velocity.
It was carried out under the condition of / h.

Table 1 shows the measurement results of the examples and comparative examples.
You. According to the initial activity measurement result, it is the first embodiment according to the present invention.
5 and Comparative Example 4 according to the related art only have high denitration activity and low
SO ₂Shows oxidative activity.

[0023]

[Table 1] Furthermore, the change with time in the combustion exhaust gas was measured for the catalysts of Example 1, Comparative Example 4 and Comparative Example 5. In a combustion device that uses heavy oil A as fuel, the ambient temperature is 35
Exposed to combustion exhaust gas at 0 ° C. for 100, 500 and 1000 hours. The measurement was performed under the same conditions as above. The results are shown in FIG. 2 for the denitration rate and in FIG. 3 for the SO ₂ oxidation rate. In Example 1, there is no change in the characteristics, but in Comparative Example 5, the denitration rate is clearly lowered. On the other hand, in Comparative Example 4, the SO ₂ oxidation rate is gradually increasing.

From the above results, the activity of both denitration and SO ₂ oxidation is stable at a more desirable level as compared with the prior art. In addition, the correlation between the conventional technique including an unknown technique and the present invention is schematically shown in FIG.

[0025]

Industrial Applicability According to the present invention, a catalyst having an activity equivalent to that of a conventional highly active catalyst and a lower SO ₂ oxidation rate can be obtained, so that ammonium sulfate can be produced in a low temperature region by SO ₃ and unreacted NH _3. It can be suppressed and the problem of metal corrosion at low temperature can be solved.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of a manufacturing process according to the present invention.

FIG. 2 is a graph showing changes with time in denitration rates due to combustion exhaust gas in Examples of the present invention and Comparative Examples.

FIG. 3 is a graph showing an S content of combustion exhaust gas according to an example of the present invention and a comparative example.
Shows the time course of O ₂ oxidation rate.

FIG. 4 is a schematic diagram showing a mechanism of reducing the SO ₂ oxidation rate of a catalyst according to a conventional technique.

FIG. 5 is a schematic diagram showing a mechanism of increasing the SO ₂ oxidation rate of a catalyst according to a conventional technique.

FIG. 6 is a schematic diagram showing a correlation between a conventional technique and the present invention.

[Explanation of symbols]

 1 ... Catalyst component, 2 ... Titania.

Claims (4)

[Claims] 1. A denitration catalyst for catalytically reducing nitrogen oxides in exhaust gas containing sulfur dioxide with ammonia, wherein each of molybdenum (M _o ) and vanadium (V) or tungsten (W) and vanadium (V) is contained. while maintaining the first component consisting of an oxide of titanium oxide, made of molybdenum (M _o) or oxide and a second component consisting of titanium oxide, tungsten (W), both the physical mixing conditions A denitration catalyst that suppresses the oxidation of sulfur dioxide, which is formed. 2. A method for producing a NOx removal catalyst in which nitrogen oxides in exhaust gas containing sulfur dioxide are catalytically reduced with ammonia, in a carrier comprising titania or titanium hydroxide, an active ingredient comprising vanadium compound and tungsten compound or molybdenum compound. After mixing the first constituent component obtained by carrying and pre-calcining and the second constituent component obtained by carrying the active ingredient composed of a tungsten compound or molybdenum compound on a carrier composed of titania or titanium hydroxide and pre-calcined. A method for producing a denitration catalyst which suppresses the oxidation of sulfur dioxide, which comprises calcination. 3. A method for producing a NOx removal catalyst in which nitrogen oxides in exhaust gas containing sulfur dioxide are catalytically reduced with ammonia, wherein a tungsten compound or molybdenum compound and a concentration not more than that which can be adsorbed on a carrier made of titania or titanium hydroxide are used. A first constituent component obtained by carrying an active ingredient composed of a vanadium compound and then pre-calcined, and a second constituent component obtained by carrying a tungsten compound or molybdenum compound on a carrier made of titania or titanium hydroxide and then pre-calcined. A method for producing a denitration catalyst which suppresses the oxidation of sulfur dioxide, comprising: 4. The denitration catalyst according to claim 3, wherein the amount of the tungsten or molybdenum compound supported on the carrier when the second component is obtained is larger than the adsorbable concentration. Manufacturing method.