JP3496964B2 - Catalyst for ammonia reduction of nitrogen oxides in exhaust gas and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to relates to a catalyst and a manufacturing method thereof for ammonia reduction of nitrogen oxides in the exhaust gas, in particular has a high pore volume, the nitrogen oxides contained in the exhaust gas (NO _X) The present invention relates to a catalyst having excellent activity for ammonia (NH ₃ ) reduction reaction and a method for producing the same.

[0002]

2. Description of the Related Art NO _{X in} smoke emitted from power plants, various factories, automobiles, etc. is a causative substance of photochemical smog and acid rain, and ammonia (NH ₃ ) is used as an effective removal method. Flue gas denitration method by selective catalytic reduction using a reducing agent is widely used mainly in thermal power plants. The catalyst, vanadium (V), molybdenum (M _O), or tungsten (W) and titanium oxide to the active ingredient (T _i
O ₂ ) -based catalysts are used, especially those containing vanadium as one of the active ingredients are not only highly active, they are also less deteriorated by impurities contained in the exhaust gas, and can be used at lower temperatures. Therefore, it has become the mainstream of the current denitration catalyst (Japanese Patent Laid-Open No. 50-128681). The catalyst is usually used by being formed into a honeycomb shape or a plate shape, and various manufacturing methods have been invented and devised.

When used in a boiler of a thermal power plant, the filling amount of the above-mentioned denitration catalyst becomes several hundred m ³ , and the catalyst life is as short as 2 years and as long as 10 years or more. In addition, exhaust gas containing acidic gas such as sulfur oxide (SO _x ), coal combustion ash, etc., as soot dust, dozens of mg /
Often included in m ³ . Therefore, not only the activity of the catalyst but also the strength of the structure and the strength such as abrasion resistance are required to be extremely high, and the research and development of a catalyst composition and a manufacturing method which are excellent for both of them have been advanced. Examples thereof include titanium oxide-based catalysts to which inorganic fibers are added to improve strength and at the same time make them porous to improve activity (JP-A-52-65191), titanium oxide-silica that is difficult to sinter, A catalyst with enhanced activity and strength using a zirconia-based amorphous carrier (JP-A-52-12)
2293), and a catalyst in which a high activity catalyst molded body is impregnated with a binder such as silica sol or aluminum sulfate to increase the strength (Japanese Patent Application No. 56-58723).

[0004]

3 and 4 are explanatory views showing a conventional method for producing a denitration catalyst. In the prior art shown in FIG. 3, the catalyst particles at the time of kneading to obtain a molding paste are heated. Due to the consolidation effect of kneading, the particles have extremely high density. Therefore, the molding paste becomes a paste having a low water content, and the catalyst obtained by molding this has a very small pore volume and a low activity. When the paste is prepared by increasing the water content in order to improve the activity, the distance between the catalyst particles is increased as shown in FIG. When water evaporates, the particles move with it, and only a dense catalyst can be obtained as shown in FIG. 5 (B).

Further, in the method of FIG. 4, titanium oxide or hydrous titanium oxide is not compacted by heating and kneading, so that it is porous, and a hard paste can be obtained in a state with a large amount of water as compared with the case of FIG. Since the pore volume of is large, it is easy to obtain a highly active catalyst. However, when high strength of the molded body is required, such as a honeycomb catalyst for denitration for coal or oil-fired boiler, a paste with low water content must be molded, but in normal kneading, a certain amount of water or more is required. It cannot be lowered and only low strength is obtained.
As described above, the titanium oxide-based denitration catalyst has a large difference in water content when a paste having a certain softness (viscosity) is obtained depending on whether the raw materials are heated and kneaded to be consolidated, and the water content is different from that produced in the production. The value is unique to the process and cannot be changed easily. Therefore, it has been extremely difficult to select manufacturing conditions that achieve both activity and strength that depend on paste moisture.

That is, the above-mentioned prior art does not consider independently controlling the pore volume of the catalyst, which is a major controlling factor of the activity, and the wet forming conditions for the honeycomb and the plate. There was a problem that it was extremely difficult to achieve both strength and strength. Figure 2 shows titanium (T
_i ), vanadium (V), and a tungsten-based catalyst in the case of forming a honeycomb, it is an example showing the relationship between the paste moisture and the penetration, which is a guideline for the softness of the paste. Generally, the relationship between paste water content and penetration is uniquely determined by the composition of the catalyst and the process of preparing the composition, and different compositions
The catalysts in the process show different relationships such as A, B, C, ....

On the other hand, the water content suitable for molding to obtain a high-strength catalyst with less distortion and defects requires that the softness of the paste represented by the penetration is within a certain range.
On the other hand, the catalytic activity is proportional to the pore volume, and since the pore volume is proportional to the water content of the paste, the more active it is, the higher the activity tends to be. Therefore, the composition
When the manufacturing process is determined, the optimum water content for catalyst molding is automatically determined, and it is not possible to freely select it in order to control the strength and activity. This is not only extremely inconvenient when it is necessary to individually control the activity and strength of the catalyst according to it, because it is used under various exhaust gases and conditions such as a flue gas denitration catalyst.
It was not possible to make full use of the catalyst performance, which was a big problem economically.

A first object of the present invention is to eliminate the above-mentioned problems of the prior art, provide a method of freely selecting the water content at the time of molding the catalyst, and make it possible to individually change the activity and the strength. Especially. The second object is to provide a high-strength, high-activity denitration catalyst based on the adoption of this method and a method for producing the same.

[0009]

In order to achieve the above object, the invention claimed in the present application is as follows. (1) Titanium oxide (T _i O _2), vanadium (V), molybdenum (M _o), tungsten (W), exhaust gas containing as active ingredient a compound of one or more elements of the iron (F _e) In the catalyst for ammonia reduction of nitrogen oxides, a kneaded product of a first component consisting of a dried or calcined powder of titanium oxide with the active component kneaded by heating and a second component consisting of hydrous titanium oxide powder. A catalyst for ammonia reduction of nitrogen oxides in exhaust gas, which is obtained by drying and firing a molded body.

(2) Containing, as an active ingredient, a compound of one or more elements of titanium oxide (T _i O ₂ ), vanadium (V), molybdenum (M _o ), tungsten (W) and iron (F _e ). In the method for producing a catalyst for ammonia reduction of nitrogen oxides in exhaust gas, the step of kneading titanium oxide and the active component while heating in the presence of water and simultaneously evaporating water to obtain a paste (heating kneading), A step of drying and / or firing the obtained paste, a step of pulverizing a dried or fired body to obtain a first component, a hydrous titanium oxide powder as a second component, and both components as a first component / a second component It is used at a weight ratio of 1/99 to 30/70, and has a step of adding water to this and kneading to obtain a paste, and a step of molding and drying and firing the obtained paste. In the exhaust gas Process for preparing a catalyst for ammonia reduction of iodine oxide.

(3) Containing, as an active ingredient, a compound of at least one element selected from titanium oxide (T _i O ₂ ), vanadium (V), molybdenum (M _o ), tungsten (W) and iron (F _e ). In the method for producing a catalyst for ammonia reduction of nitrogen oxides in exhaust gas, the step of kneading titanium oxide and the active ingredient while heating in the presence of water to obtain a paste, and drying and / or firing the paste Process,
A step of pulverizing the dried or fired body to a first component, and a hydrous titanium oxide powder as a second component, and both components as a first component /
The second component is used in a weight ratio of 1/99 to 30/70, and water and salts of the above-mentioned active ingredient are added and kneaded to obtain a paste, and the obtained paste is molded and then dried and baked. A method for producing a catalyst for ammonia reduction of nitrogen oxides in exhaust gas, the method comprising:

[0012]

In the method of the present invention, as shown in FIG. 1, the raw material which is heat-kneaded as the first component and the hydrous titanium oxide which has not undergone the heat-kneading step as the second component are used to knead both at a predetermined ratio. As shown in FIG. 6A, the catalyst particles are in a state of being dispersed in a hydrous titanium oxide hydroxide slurry having a high viscosity. In such a state, the hydrous titanium oxide particles hinder the movement of the particles, so that a hard paste can be obtained even with high water content, and the catalyst particles do not move and become densified during drying. It is possible to obtain a catalyst having a high pore volume such as

Further, the catalyst particles are connected by fine hydrous titanium oxide particles, and this bond is further strengthened by firing, so that high strength can be obtained despite the large pore volume. In addition to this, even though the oxides such as V, _Mo and W, which are active components, move on the particle surface during calcination to activate the surface of hydrous titanium oxide, the catalyst component is diluted with hydrous titanium oxide. It shows high activity. This, combined with the increase in pore volume described above, makes it possible to obtain a catalyst having high activity in spite of high strength.

The object of the present invention is to prepare titanium oxide in advance.
Vanadium (V), molybdenum (M _O),tungsten
(W), iron (F_e), Etc. that carry active ingredients
Alternatively, the calcined powder is used as the first component and the meta
Uses hydrous titanium oxide powders such as tartanic acid and orthotitanic acid
Mix both components in a weight ratio of 99/1 to 30/70.
Water, and if necessary, organic binder, inorganic fiber
By adding and kneading to prepare a molding paste
Can be achieved.

That is, instead of the conventional catalyst preparation method shown in FIGS. 3 and 4, in the present invention, a paste obtained by kneading the first component and the second component by the catalyst preparation method shown in FIG. 1 is used. It is characterized in that it is used to form a plate shape or a honeycomb shape.
In Figure 1, the first component, V to the slurry of hydrous titanium oxide powder or titanium oxide hydrate, M _o, W, by the addition of salts such as F _e to 50% or more of the slurry-like water, kneaded with a heating means Kneading with a machine (kneader) while evaporating water to make the water content 30-45%, then dry, if necessary 200 ° C
It is calcined at 600 ° C. Thereafter, the first component composition is pulverized with a hammer mill or the like to have an average particle size of 0.5 μm to 2 μm.

On the other hand, it is necessary that the hydrous titanium oxide powder used as the second component is not densified by heating and kneading in the manufacturing process. In other words, any material may be used as long as it has not been subjected to the consolidation step, but a surface area of 100 m ² / g or more and a sulfate group (SO ₄ ) content of 2% or less gives good results. After the first component and the second component are mixed in the above weight ratio, water, optionally a cellulosic organic binder such as methyl cellulose or an inorganic binder such as silica sol, and silica fiber, kaolin fiber, various glasses The mixture is kneaded with a kneader while adding inorganic fibers such as fibers and provided as a molding paste. Of course, it is also within the scope of the present invention to add an active ingredient such as V, _Mo or W when mixing the first component and the second component, and it is possible to improve the activity corresponding to the increase of the active ingredient content. Can be achieved.

For the molding, a known method such as honeycomb molding or a method of applying a metal substrate such as a metal lath or a mesh made of an inorganic fiber by using a roller is used, and the obtained molded product is dried to 300
Bake for several hours at ~ 600 ° C. Titanium oxide is generally used as a catalyst carrier, but when it is used as a catalyst for removing nitrogen oxides, it also has a catalytic activity function, so it is treated as one of the active components in the present invention.

[0018]

The present invention will be described in detail below with reference to examples.
It Examples 1-5 Slurry of metatitanate (T_iO₂Content: 30 wt%, S
O_FourContent: 8 wt%) 67 kg of paratungstic acid
MONMONIUM ((NH_Four)_TenH_Ten・ W₁₂O₄₆・ 6H ₂O)
With 3.59 kg and ammonium metavanadate 1.29 kg
Kneading (adding) while evaporating water using a heating kneader.
It was heat-kneaded to obtain a paste having a water content of about 36%. This is 3 ¢
After extruding into a columnar shape and granulating, dry in a fluidized bed dryer, then
It was baked in air at 550 ° C. for 2 hours. Hammer the resulting granules
-Mill so that the particle size of 1 μm or less becomes 60% or more.
It was crushed to obtain a denitration catalyst powder as the first component. Group at this time
Success is V / W / T_i= 4/5/91 (atomic ratio).

Apart from this, a specific surface area of 330 m ² / g, S
O ₄ content: 1.6 wt% hydrous titanium oxide powder (G5 manufactured by Rhone-Poulin) was prepared as the second component. First component and second component powders are 99 g / 1 g and 90 g / 10, respectively
g, 70g / 30g, 50g / 50g, 30g / 70g
The mixture was mixed at a ratio of 1, and water was added thereto, and the mixture was kneaded in a mortar to prepare a paste having a softness of about 80. The paste was molded into a columnar shape of 9.3 ¢ by a piston extruder, air-dried in the air, and further baked at 550 ° C for 2 hours.

Comparative Example 1 Using only the first component of Example 1, the same procedure as in the above Example was performed.
To prepare a catalyst molded body. Comparative example 2 The firing temperature during preparation of the first component of Comparative Example 1 was changed from 550 ° C. to 2
The temperature was changed to 50 ° C to obtain the first component powder. With this,
A catalyst molded body containing only the first component was obtained in the same manner as in Comparative Example 1. Comparative Example 3 Hydrous titanium oxide powder (T_iO₂Content: 86 wt%, S
O_FourContent: 1.6 wt%) Paratungs to 23.3 kg
Ammonium tenate ((NH_Four)_TenH_Ten・ W₁₂O ₄₆・ 6H
₂O) 3.59 kg and ammon metavanadate 1.
Add water to 29 kg to prepare a paste with a penetration of 80.
Molding, drying and firing were carried out in the same manner as in Example 1 to obtain a catalyst molded body.

[0021] Instead of the ammonium paratungstate in the preparation method of the first component of Example 6 Example 1, first using a 2.43kg of ammonium molybdate _{((NH 4) 6M o 7} O 24 · 4H 2 O) One component was prepared. This and the hydrous titanium oxide used in Example 1 as the second component were mixed at a ratio of 70 g / 30 g, and otherwise the same as in Example 1 to obtain a catalyst molded body. Comparative Example 4 Only the first component used in Example 6 was kneaded to obtain a catalyst molded body similar to that in Example 6. Example 7 3.2 kg of vanadyl sulfate (VOSO ₄ ) was added at the time of kneading the first component and the second component of Example 3, and a catalyst was similarly molded.

With respect to the catalyst molded bodies of Examples 1 to 7 and Comparative Examples 1 to 4, the pore volume and the crushing strength in the diameter direction were measured by a Kiya type tablet hardness meter. Also, after crushing the molded body, 10 to
The denitration activity was measured under the conditions shown in Table 1 using a 20-mesh-sized product.

[0023]

[Table 1] The obtained results are shown in Table 2, the weight ratio of the first component and the second component,
It is shown in comparison with the paste water content at the time of molding.

[0024]

[Table 2]

In each of the catalysts of Examples, the paste water content was the same as that of Comparative Examples 1, 2 and 4 which consisted only of the first component prepared through consolidation by heating and kneading (paste water content during molding). ) Is significantly increased, and accordingly, the pore volume is also significantly increased. Nevertheless, the strength of the molded body was hardly reduced.
Further, it can be seen that the catalytic activity shows high activity even though the first component containing the catalytically active component is diluted with the second component containing no active component.

On the other hand, in Comparative Example 3 in which a paste was prepared and molded without going through the heat-kneading step, the same moisture, and hence pore volume and activity at the time of molding as the present invention can be obtained. The strength is extremely low, which means that it is difficult to use as a practical catalyst. In particular, in the case where a structure having a certain strength is indispensable, such as in the case of being formed into a honeycomb shape or a cylindrical shape, the low strength is a fatal defect and cannot be put to practical use. On the other hand, although the catalyst of the present invention can be molded with the paste water content almost equal to that of Comparative Example 3, the strength is the same as that of Comparative Examples 1, 2 and 4 employing the consolidation process.

As described above, according to the method of the present invention, a hard paste can be obtained with high water content, the pore volume can be increased without lowering the strength, and a highly active catalyst can be obtained with a small amount of active ingredient. An excellent method. Further, according to the examples in Table 2, the mixing ratio of the first component and the second component is appropriately in the range of 99/1 to 30/70, and when the mixing ratio is small, the increase in the pore volume is small, and conversely it is too large. And strength,
It can be seen that this leads to a decrease in activity. Mixing ratio 90 /
Within the range of 10 to 50/50, a catalyst having excellent strength and activity can be obtained.

Further, by comparing Examples 7 and 3, by adding a vanadium salt which is an active component at the time of adding the second component and compensating for dilution by the second component of the catalyst component, It goes without saying that it is possible to make an extremely highly active catalyst that takes full advantage of the increase. Example 8 Ten 1400 twisted yarns of E glassy fiber having a fiber diameter of 9 μm were used.
Titania 40 on a plain weave mesh with a book / inch roughness
%, Silica sol 20% and polyvinyl alcohol 1% slurry were impregnated and dried at 150 ° C. to give rigidity to obtain a catalyst substrate.

Apart from this, the T _i / used in Example 6
M _o / V system first component 14kg and silica-alumina a hydrous titanium oxide which is the second component and 6kg inorganic fibers 5.3 kg,
40 kg of water was added and kneaded with a kneader to obtain a catalyst paste. The paste catalyst mixture prepared between the two base materials was placed and passed through a pressure roller to press-bond the catalyst between the meshes and the surface of the base material to obtain a plate-like catalyst having a thickness of about 1 mm. The obtained catalyst was dried at 180 ° C. for 2 hours and then calcined in the air at 550 ° C. for 2 hours.

The resulting catalyst has a pore volume of 0.37 ml / g
And 0.27 of those molded using only the first component
Significantly increased compared to ml / g. The catalyst strength was the same as that of the first component alone, and the denitration activity was increased by about 1.2 times. Further, when the catalyst was applied using the pressure roller, a phenomenon was observed in which the paste adhered to the roller when only the first component was used. It was found that there was almost no adhesion to the roller, and the workability could be greatly improved. Example 9 70 parts by weight of the first component used in Example 1, 30 parts by weight of the second component, 1 part by weight of calcium hydroxide, diameter 6 μm-6 mm length.
Water was added to 15 parts by weight of E glass fiber of (1) and methyl cellulose by weight and kneaded to prepare a paste having a water content of 28%. Using a screw extruder, this is a cell pitch of 4 mm,
It was formed into a square honeycomb shape having a cell wall thickness of 0.3 mm, air-dried and then fired at 550 ° C. for 2 hours.

Compared with the case where the same honeycomb was formed by using only this and the first component, the water content at the time of forming was 24% in the case of only the first component, while in the present embodiment, it was 2%.
It was revealed that a good molded product could be obtained at 8%.
This results in a pore volume of 0.24 ml / g to 0.2
It was revealed that the good results were obtained in which the activity was increased to 8 ml / g and the activity was increased to about 1.1 times.

[0032]

EFFECTS OF THE INVENTION According to the present invention, a hard paste can be obtained with a higher water content than in the conventional method, and it is possible to form a honeycomb shape or a plate shape with a high water content. This makes it possible to significantly increase the pore volume of the molded body and realize a highly active catalyst.

Further, the second component inhibits the movement of particles during drying and reduces the occurrence of cracks during drying, and since the catalyst particles are bonded to each other, a catalyst having a high pore volume and a high strength can be obtained. It will be possible to obtain. Further, the present invention corresponds to the use of an expensive catalyst component (first component) diluted with an inexpensive hydrous titanium oxide (second component), which can reduce the production cost of the catalyst.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram showing a method for preparing a catalyst of the present invention.

FIG. 2 is a diagram showing the relationship between the paste water content and the penetration of the paste, showing the problems of the prior art.

[Fig. 3]

FIG. 4 is a manufacturing process diagram of a conventional catalyst.

FIG. 5 is a schematic diagram showing a state of a catalyst paste according to a conventional method.

FIG. 6 is a schematic diagram showing the characteristics of the catalyst paste of the present invention.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI B01D 53/36 102H (56) References JP-A-53-26290 (JP, A) JP-A-5-96165 (JP, A) JP-A-2-198633 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 21/00-38/74 B01D 53/00-53/96

Claims (3)

(57) [Claims] 1. Titanium oxide (T_iO₂),vanadium
(V), molybdenum (M _o), Tungsten (W), iron
(F_e) A compound of one or more of the
For ammonia reduction of nitrogen oxides contained in exhaust gas
In the catalyst, titanium oxide is heated and kneaded with the active ingredient.
First component consisting of dry or calcined powder that is supported by
And kneaded with the second component consisting of hydrous titanium oxide powder
Nitrogen in exhaust gas characterized by dried and fired form
Catalyst for ammonia reduction of oxides. 2. Nitrogen in exhaust gas containing a compound of at least one element selected from titanium oxide (TiO ₂ ), vanadium (V), molybdenum (Mo), tungsten (W) and iron (Fe) as an active ingredient. In the method of producing a catalyst for ammonia reduction of oxides, a step of kneading titanium oxide and the active ingredient while heating in the presence of water and at the same time evaporating water to obtain a paste, and drying and / or drying the obtained paste. A step of firing, a step of obtaining a first component by drying or crushing the fired body, a hydrous titanium oxide powder as a second component, and both components in a first component / second component weight ratio of 1
Nitrogen oxidation in exhaust gas, characterized by using a ratio of / 99 to 30/70, adding water to this and kneading to obtain a paste, and molding and drying and baking the obtained paste. Method for producing a catalyst for ammonia reduction of a product. 3. Titanium oxide (T_iO₂),vanadium
(V), molybdenum (M _o), Tungsten (W), iron
(F_eA compound of one or more elements of
For ammonia reduction of nitrogen oxides contained in exhaust gas
In the method for producing a catalyst, titanium oxide and the active ingredient
To obtain a paste by kneading while heating in the presence of water
And a step of drying and / or firing the paste,
A step of pulverizing the dried or fired body to obtain the first component,
Titanium hydroxide powder as the second component, both components as the first component /
For the second component weight ratio of 1/99 to 30/70
Add the water and salts of the active ingredient to the mixture and knead
The process of obtaining the paste, and after molding the obtained paste, dry it.
In the exhaust gas, characterized by having a step of dry firing
A method for producing a catalyst for ammonia reduction of nitrogen oxides.