JPH08229412A - Catalyst and method for removing nitrogen oxide - Google Patents

Abstract

PURPOSE: To reduce and remove nitrogen oxide in exhaust gas in the presence of ammonia by using a honeycomb catalyst for reducing and removing nitrogen oxide in exhaust gas in the presence of ammonia. CONSTITUTION: A nitrogen oxide removing catalyst has pores substantially consisting of two independent pore groups and is characterized by that pore vol. occupied by pore groups having a pore size of 0.01-0.03μm is 50-80% of total pore vol. and pare vol. occupied by pore groups having a poree size of 0.8-4μm is 10-30% of the total pore vol. Exhaust gas is brought into contact with this catalyst to reduce and remove nitrogen oxide in exhaust gas.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a catalyst for removing nitrogen oxides and a method for removing nitrogen oxides using the catalyst. More specifically, a honeycomb catalyst used for removing nitrogen oxides contained in exhaust gas discharged from a boiler, a heating furnace, a gas turbine, a diesel engine, various industrial processes, etc. Well about how to remove.

[0002]

2. Description of the Related Art Currently, as a method for removing nitrogen oxides in exhaust gas, nitrogen oxides can be selectively removed even in exhaust gas containing a high concentration of oxygen, and a reducing agent to be used is also used. The selective catalytic reduction method using ammonia as a reducing agent has become mainstream because it requires only a small amount and is economical.

Regarding the shape of the catalyst used in this selective catalytic reduction method, the honeycomb shape is effective because the dust in the exhaust gas is hard to deposit on the catalyst bed and the pressure loss of the catalyst bed is small. Nowadays, honeycomb catalysts are widely used. As a method for removing nitrogen oxides using a honeycomb catalyst, for example, Japanese Patent Publication No. 54-2941
No. 9 discloses the equivalent diameter of the through holes of the honeycomb-shaped catalyst to be 2 to
30 mm, aperture ratio 50 to 80%, gas flow rate 0.
It is disclosed that by specifying in the range of 5 to 60 m / sec, the through holes are not blocked by dust, the pressure loss is small, and a high nitrogen oxide removal rate (hereinafter referred to as "denitration rate") can be obtained. ing.

On the other hand, in recent years, as environmental pollution due to nitrogen oxides, such as acid rain, has become more serious in the world, high-performance and low-cost denitration technology is increasingly available as a measure to reduce nitrogen oxides. There is a strong demand.

However, in order to meet the above demand, the method described in Japanese Patent Publication No. 54-29419 is not sufficient, and the development of a catalyst for removing nitrogen oxides and a method for removing nitrogen oxides having higher denitration performance is strongly desired. Is desired.

[0006]

DISCLOSURE OF THE INVENTION The present invention is a honeycomb catalyst, which is excellent in denitration performance and has good durability, and a catalyst for nitrogen oxide removal using the catalyst, and efficient removal of nitrogen oxides using the catalyst. It is intended to provide a method.

[0007]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that the above object can be achieved by using a honeycomb catalyst having a specific pore distribution, and the present invention is based on this finding. It came to completion.

That is, the present invention is a honeycomb-shaped catalyst for catalytically reducing and removing nitrogen oxides in exhaust gas in the presence of ammonia, the pores being substantially composed of two independent pore groups. And the pore volume occupied by the group of pores having a pore diameter in the range of 0.01 to 0.03 μm is 50 to 80% of the total pore volume and has a pore diameter in the range of 0.8 to 4 μm. The pore volume occupied by the pore group is 10 to 30 of the total pore volume.
%, Relates to a catalyst for removing nitrogen oxides.

The present invention also relates to a method for removing nitrogen oxides, which comprises contacting exhaust gas with the above catalyst in the presence of ammonia to remove nitrogen oxides from the exhaust gas.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The honeycomb-shaped catalyst of the present invention has pores substantially composed of two independent pore groups, and the pore diameter of these pore groups is in the range of 0.01 to 0.03 μm. The first group of pores occupying 50-80% of the total pore volume,
The second group of pores having a pore size in the range of 0.8 to 4 μm accounts for 10 to 30% of the total pore volume. The total pore volume of the honeycomb catalyst of the present invention is 0.3 to 0.55c.
It is preferably in the range of c / g. The pore diameter, pore diameter distribution and pore volume in the present invention were measured using a mercury porosimetry porosimeter. The honeycomb-shaped catalyst of the present invention is characterized in that, as shown in FIG. 1, two groups of pores exist independently of each other, and that the pore size distribution is extremely sharp. On the other hand, as shown in FIG. 2, when the pores consist of a single pore group, or as shown in FIG. 3, the pores do not consist of two independent pore groups and The objects of the present invention cannot be achieved if they do not overlap with each other and do not have a uniform pore size.

In the honeycomb-shaped catalyst of the present invention, the extremely narrow pore size distribution of the pore groups means that the two pore groups are composed of pores having extremely uniform pore sizes. However, this is considered to be the reason why the honeycomb-shaped catalyst of the present invention exhibits excellent denitration activity. Although this mechanism is not clear, when the gas diffuses into the pores of the catalyst, the group of pores having a uniform pore size as in the present invention facilitates the diffusion of the gas into the pores. As a result, it is considered that the denitration activity is improved regardless of the cell wall thickness.

The honeycomb-shaped catalyst of the present invention is not particularly limited in the kind of its catalytically active component as long as it has the specific pore distribution as described above, and a honeycomb-shaped catalyst containing various catalytically active components is used. be able to. Specifically, for example, a catalyst containing titanium as a catalytically active component such as an oxide or a composite oxide containing titanium can be used. In particular, (A) a binary oxide containing titanium and silicon (hereinafter , Abbreviated as “TiO ₂ —SiO ₂ ”) 60 to 9
9.5 wt% and (B) vanadium, tungsten, copper,
A catalyst is preferably used because it contains 0.5 to 40% by weight of an oxide of at least one metal selected from manganese, cerium and tin.

In the catalyst composed of the components (A) and (B), the composition of TiO ₂ --SiO ₂ as the component (A) is 40 to 95% of titanium and 5 to 5% of silicon in atomic percentage.
It is preferably in the range of 60%. If the content of titanium is less than 40%, the denitration activity is lowered, and if it exceeds 95%, the SO ₂ oxidation activity is increased, which is not preferable. The component (B) is an oxide of one or more metals selected from vanadium, tungsten, copper, manganese, cerium and tin. The proportion of component (A) is 60 to 99.5% by weight, preferably 80 to 99% by weight, and the proportion of component B is 0.
It is 5 to 40% by weight, preferably 1 to 20% by weight. If the proportion of the component (A) is less than 60% by weight, the denitration activity cannot be expected to improve even though the raw material cost of the catalyst becomes high, and if it exceeds 99.5% by weight, the denitration activity is lowered, which is not preferable.

The method for preparing the honeycomb-shaped catalyst of the present invention is not particularly limited and can be prepared by various methods. Hereinafter, a typical preparation method of the catalyst composed of the components (A) and (B) will be described, but the present invention is not limited thereto.

In the preparation of TiO ₂ --SiO ₂ as the component (A), the titanium source is selected from inorganic titanium compounds such as titanium chloride and titanium sulfate, and organic titanium compounds such as titanium oxalate and tetraisopropyl titanate. Or two or more compounds, and as the silicon source, one or two selected from colloidal silica, fine particle silicic acid, water glass, inorganic silicon compounds such as silicon tetrachloride, and organic silicon compounds such as tetraethyl silicate. The above compounds can be used. The compounds of the titanium source and the silicon source are taken so that the atomic percentages of titanium and silicon are 40 to 95% and 5 to 60%, respectively, and titanium and silicon are converted into oxides in an acidic aqueous solution state or a sol state. 1-100g / L
The concentration is (liter, the same applies hereinafter) and kept at 10 to 100 ° C. Ammonia water was added dropwise thereto as a neutralizing agent under stirring,
A coprecipitated compound containing titanium and silicon is produced, filtered off, washed well, dried at 80 to 140 ° C. for 1 to 10 hours, and further calcined at 450 to 700 ° C. for 1 to 10 hours to form TiO ₂ −. SiO ₂ is obtained.

The starting material used for preparing the oxide of at least one metal selected from vanadium, tungsten, copper, manganese, cerium and tin as the component (B) is an oxide or hydroxide of each metal. , Ammonium salt, oxalate, halide and the like. Specifically, examples of the vanadium source include ammonium metavanadate, vanadyl sulfate, vanadyl oxalate, vanadium oxide, and the like, and examples of the tungsten source include tungsten oxide, ammonium paratungstate, and tungstic acid.

An aqueous solution of the starting material of the component (B) is added to the above component (A) together with a molding aid, mixed and kneaded, and molded into a honeycomb shape by an extrusion molding machine. The obtained molded product is
After drying at 50 to 120 ° C., 450 to 700 ° C., preferably 500 to 650 ° C. for 1 to 10 hours, preferably 2
The honeycomb catalyst of the present invention can be obtained by calcination in air for 6 hours. The specific surface area (BET surface area) of the honeycomb catalyst of the present invention is preferably 80 m ² / g or more.

The honeycomb-shaped catalyst of the present invention having a uniform pore diameter and having pores composed of two independent pore groups has the following features: (1) volatilization at the firing step during molding during the preparation of the honeycomb-shaped catalyst; A method of adding and mixing resins that decompose, organic polymers such as cellulose, and inorganic salts such as ammonia nitrate,
(2) Silica sand, α-alumina, cordierite, zirconia, and other powders may be added and mixed, and (3) the raw material powder may be appropriately adjusted in particle size.

Typical examples of the organic polymer which can be used in the above method (1) include polyethylene resin, acrylic resin, crystalline cellulose and the like. Further, as typical examples of the inorganic salts, ammonium nitrate, ammonium oxalate, ammonium carbonate and the like can be mentioned. The addition amount of these is preferably in the range of 5 to 30% by weight. The average particle size and the addition amount of the powder in the method (2) are 1 to 20 μm and 5 to 3, respectively.
The range of 0% is preferable. In the case of the method (3), the average particle size of the raw material powder is usually 2 to 30 μm, and if the particle size is too small, it is impossible to prepare a honeycomb-shaped catalyst having a desired pore distribution.

The opening ratio of the cross section of the honeycomb-shaped catalyst of the present invention is not particularly limited, but is preferably 80 to 90%. By setting the opening ratio of the cross section to 80% or more, it becomes possible to reduce the pressure loss of the catalyst bed,
Economical effects such as reduction of power consumption required for the fan can be obtained. If the aperture ratio of the cross section exceeds 90%, the cell wall thickness becomes very thin and the strength decreases, which is not practical. The thickness of the partition wall separating the through holes is not particularly limited, but is preferably 0.2 to 0.8 mm. If the thickness is less than 0.2 mm, the strength will be low,
On the other hand, if it exceeds 0.8 mm, the pressure loss increases, which is not preferable. The opening (diameter of the through hole) is 2 to 8 mm.
Is preferred.

The exhaust gas that can be treated by the honeycomb-shaped catalyst of the present invention is not particularly limited, and the honeycomb-shaped catalyst of the present invention is included in the exhaust gas discharged from boilers, heating furnaces, gas turbines, diesel engines and various industrial processes. It can be applied to the removal of nitrogen oxides.

Specifically, for example, sulfur oxide (SOx)
0 to 3,000 ppm, oxygen 1 to 20% by volume, carbon dioxide gas 1 to 15% by volume, water vapor 5 to 15% by volume, dust particles 0 to 30
g / Nm ³ and nitrogen oxides (NOx, mainly NO) 0 to
It can be applied to exhaust gas containing about 1,000 ppm. Normal boiler exhaust gas has a gas composition in the above range. The honeycomb-shaped catalyst of the present invention can also be used for treating special exhaust gas such as exhaust gas containing nitrogen oxides containing no sulfur oxides and exhaust gas containing nitrogen oxides containing halogen compounds.

The treatment conditions differ depending on the type and properties of the exhaust gas, but usually the amount of ammonia (NH ₃ ) added is preferably 0.5 to 3 parts by volume with respect to 1 part by volume of NOx. For example, in the case of boiler exhaust gas, most of NOx is NO, so it is preferable to set the molar ratio of NO to NH ₃ to around 1: 1. This is an excess of NH ₃
This is because it must be taken care that is not discharged as an unreacted material. Furthermore, when it is necessary to suppress the unreacted NH ₃ as much as possible, it is preferable to set the NH ₃ / NOx molar ratio to 1: 1 or less. It is preferable that the gas flow velocity be as low as possible in order to reduce pressure loss, but 1
If it is less than m / sec, the catalyst bed is clogged with dust particles or dust in the exhaust gas, which is not preferable. Therefore, in practice, it is preferable to appropriately select the gas flow rate within the range of 1 to 20 m / sec. The reaction temperature is usually 200 to 700 ° C.
And a range of 250 to 600 ° C. is particularly preferable. The space velocity is usually 1,000 to 100,000 hr ^-1 ,
Particularly, the range of 3,000 to 30,000 hr ^-1 is preferable. The pressure is not particularly limited, but 0.01 to 10
The range of kg / cm ² is preferred.

There are no particular restrictions on the type of reactor,
Conventional fixed bed, moving bed, fluidized bed and other reactors can be used.

[0025]

EXAMPLES The present invention will be described in more detail below with reference to examples.

Example 1 [Preparation of component A] An aqueous sulfuric acid solution of titanyl sulfate having the following composition was used as a titanium source.

TiOSO ₄ : 250 g / L (as TiO ₂ ) Total H ₂ SO ₄ : 1,100 g / L Separately, 400 L of water and ammonia water (NH ₃ , 25%) 2
86L was added, and Snowtex NCS-30 was added to this.
24 kg (containing about 30% by weight of silica sol manufactured by Nissan Kagaku Co., Ltd., SiO ₂ ) was added. To the resulting solution, 153 L of the above-mentioned sulfuric acid aqueous solution of titanyl sulfate was added to 300 L of water and diluted to slowly add a titanium-containing sulfuric acid aqueous solution under stirring,
A co-precipitated gel was produced. Let it stand for 15 hours as it is.
It was obtained iO ₂ -SiO ₂ gel. This gel was filtered, washed with water, and then dried at 200 ° C. for 10 hours. Then 600 ° C
The powder was calcined in an air atmosphere for 6 hours, ground with a hammer mill, and classified with a classifier to obtain a powder having an average particle diameter of 10 μm. The composition of the obtained powder (hereinafter referred to as “TS-1”) was Ti: Si = 4: 1 (atomic ratio), and BET
The surface area was 160 m ² / g.

[Preparation of Honeycomb-like Catalyst] 0.45 L of monoethanolamine was mixed with 4.5 L of water, 0.907 kg of ammonium paratungstate was added and dissolved therein, and then ammonium metavanadate 0.444 k
g was dissolved to form a uniform solution. This solution is
In addition to 10 kg of -1, add a proper amount of water with a kneader, mix well, knead, and then use an extrusion molding machine to obtain an outer shape of 50 m.
It was molded into a grid shape with an m-square, an aperture ratio of 84.6%, an opening of 6.9 mm, and a cell wall thickness of 0.5 mm. Then, after drying at 60 ° C., it was baked at 500 ° C. for 5 hours under air circulation.

The composition of the obtained honeycomb catalyst was TS-1: V ₂ O ₅ : WO ₃ = 87: in a weight ratio as an oxide.
It was 3: 7. Further, the pore volume of the first pore group and the second pore group having pore diameters in the range of 0.01 to 0.03 μm and 0.8 to 4 μm is 68% of the total pore volume, respectively.
% And 18%, total pore volume 0.44 cc / g
Met. The pore size distribution of the resulting honeycomb catalyst was measured by a mercury porosimetry porosimeter (manufactured by Shimadzu Corporation), and the results are shown in FIG. From FIG. 1, it can be seen that this honeycomb-shaped catalyst has pores composed of two independent pore groups.

[Evaluation of Performance of Honeycomb Catalyst] This honeycomb catalyst was filled in a reactor, the reaction temperature was 380 ° C., and the gas amount (AV) per gas contact area of the catalyst was 25 Nm ³ / m ² h.
, Gas flow rate per catalyst cross section 6m / sec (380 ° C)
The following simulated gas was supplied under the conditions of No. 1 and the denitration rate and pressure loss (pressure loss per 1 m) were measured. The denitration rate and pressure loss were measured as follows.

Denitration rate: The NOx concentration at the inlet and outlet of the catalyst layer was measured by a NOx meter (chemiluminescence type, manufactured by Yanagimoto Seisakusho) and determined according to the following equation.

Denitration rate (%) = [{(inlet NOx concentration) −
(Outlet NOx concentration)} / (Inlet NOx concentration)] × 100 Pressure loss: The pressure difference between the inlet and outlet of the catalyst layer was measured and calculated by converting it per 1 m of catalyst length. The results are shown in Table 1.

Simulated gas composition NO: 800 ppm O ₂ : 4% SO ₂ : 1,000 ppm H ₂ O: 10% NH ₃ : 800 ppm N ₂ : balance balance Examples 2 to 5 According to Example 1, the aperture ratio and the cell were measured. Honeycomb-shaped catalysts having different wall thicknesses were prepared, and the denitration rate and pressure loss thereof were measured in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 1 The TS-1 powder obtained in Example 1 was further pulverized by an air flow pulverizer to obtain a powder having an average particle diameter of 1 μm. Using this powder, according to Example 1, a honeycomb catalyst having an aperture ratio of 62.4%, a cell wall thickness of 1.0 mm, and an opening of 3.95 mm was prepared. The total pore volume of this honeycomb catalyst is 0.40c
c / g, and the pore distribution is 0.01 as shown in FIG.
It is composed of a single pore group having an inner diameter in the range of ˜0.03 μm, and the pore volume occupied by these pores is 90% of the total pore volume.
%Met. Using this honeycomb-shaped catalyst, the NOx removal rate and pressure loss were measured in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 2 In Comparative Example 1, titanium oxide (TiO ₂ ) having a specific surface area of 50 m ² / g was used as TS-1:
A honeycomb catalyst was prepared in the same manner as in Comparative Example 1 except that TiO ₂ was added at a ratio of 10: 2 (weight ratio) and molded. The total pore volume of the obtained honeycomb catalyst is 0.38c.
As shown in FIG. 3, the pore size distribution is c / g, and it can be seen that the two pore groups partially overlap with each other and the pore sizes are not uniform. Using this honeycomb-shaped catalyst, the denitration rate and the pressure loss were measured in the same manner as in Example 1,
The results are shown in Table 1.

[0036]

[Table 1]

From the results shown in Table 1, it is understood that the honeycomb catalyst of the present invention is excellent in denitration activity.

[0038]

The honeycomb-shaped catalyst of the present invention exhibits a high denitration activity because it has a specific pore size distribution. Also, it has good durability. As described above, since the honeycomb catalyst of the present invention has high denitration performance and good durability, it can be used to efficiently remove nitrogen oxides in exhaust gas.

[Brief description of drawings]

FIG. 1 shows the pore size distribution of the honeycomb-shaped catalyst obtained in Example 1.

FIG. 2 shows the pore size distribution of the honeycomb-shaped catalyst obtained in Comparative Example 1.

FIG. 3 shows the pore size distribution of the honeycomb-shaped catalyst obtained in Comparative Example 2.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 23/30 B01J 23/34 A 23/34 23/72 A 23/72 B01D 53/36 102C 102A (72) Inventor Akira Inoue 1 992 Nishikioki, Hamahama, Aboshi-ku, Himeji-shi, Hyogo Prefecture Nippon Shokubai Co., Ltd.

Claims (4)

[Claims] 1. A honeycomb catalyst for catalytically reducing and removing nitrogen oxides in exhaust gas in the presence of ammonia, which has pores substantially composed of two independent pore groups, The pore volume occupied by the pore group having a pore diameter in the range of 0.01 to 0.03 μm is 50 to 80% of the total pore volume, and the pore group having a pore diameter in the range of 0.8 to 4 μm occupies A catalyst for nitrogen oxide removal, which has a pore volume of 10 to 30% of the total pore volume. 2. The catalyst according to claim 1, which is an oxide or a composite oxide containing titanium. 3. A binary oxide containing titanium and silicon in an amount of 60 to 99.5% by weight and vanadium, tungsten,
The catalyst according to claim 1, containing a catalytically active component consisting of 0.5 to 40% by weight of an oxide of at least one metal selected from copper, manganese, cerium and tin. 4. A method for removing nitrogen oxides, which comprises contacting the exhaust gas with the catalyst according to claim 1, 2 or 3 in the presence of ammonia to remove the nitrogen oxides in the exhaust gas.