JPH08215544A - Method for removing nitrogen oxide of diesel engine - Google Patents

Abstract

PURPOSE: To efficiently remove NOX and to prevent the discharge of ammonia by setting a denitration catalyst bed on the upstream side of a gas flow and a specified ammonia decomposing catalyst bed on the downstream side. CONSTITUTION: A denitration catalyst bed is set on the upstream side of a gas flow, and an ammonia decomposing catalyst bed capable of oxidizing and decomposing ammonia into nitrogen and NOX is set on the downstream side. The ammonia decomposing catalyst bed has a chemical composition (1±0.6)R2 O.[aM2 O3 .bAl2 O3 9147/28}.cMeO.ySiO2 when dehydrated (where R is alkali metal ion or hydrogen ion, M is >=1 kind selected from a group consisting of group VIII element, rare-earth element, titanium, vanadium, chromium, niobium, antimony and potassium, and Me is alkaline earth element), uses a crystalline silicate having an X-ray diffraction pattern as a carrier and contains at least one kind among platinum, palladium, ruthenium, iridium, and rhodium as an active metal.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for removing nitrogen oxides discharged from a diesel engine.

[0002]

2. Description of the Related Art As a method for removing nitrogen oxides contained in combustion exhaust gas from a boiler of a thermal power plant, a selective catalytic reduction method using ammonia as a reducing agent has been widely put into practical use. Ti with W and Mo as active ingredients
O ₂ type is mainly used.

On the other hand, in the case of a nitrogen oxide discharged from a mobile internal combustion engine of an automobile or the like, in the case of a gasoline automobile, a noble metal catalyst such as Pt or Rh is used in an exhaust gas in an extremely narrow range near the theoretical air-fuel ratio. Nitrogen oxides are removed using hydrocarbons and carbon monoxide. However, there is still no method for efficiently removing nitrogen oxides emitted from a diesel engine that has good fuel efficiency and high output.

[0004]

The composition of exhaust gas from a diesel engine has a higher oxygen concentration of 8 to 19% than that of a gasoline vehicle, and the content of hydrocarbons and carbon monoxide in the exhaust gas is low, and in addition, it is contained in light oil. Since the sulfur content is discharged as sulfur oxides, various catalytic studies have been conducted so far, but they have not yet been put to practical use.

For example, Cu / ZSM-5 catalyst (ZSM-
(5 catalysts with Cu supported), the NOx removal rate is 10% or less only with diesel engine exhaust gas, and even if diesel oil is added to the catalyst upper layer at a fuel consumption deterioration rate of 3%, the average NOx removal rate is at most It stays at about 25%, and significant catalyst deterioration is observed in about 100 hours.

Due to the above problems, the selective catalytic reduction method using ammonia as a reducing agent is currently the most efficient denitration method and is excellent in terms of the reducing agent consumption rate. For example, when a hydrocarbon is used as the reducing agent, 5 to 15 mol of hydrocarbon (hereinafter abbreviated as CH) is required to remove 1 mol of NO in the exhaust gas composition of a normal diesel engine, whereas When is used as a reducing agent, the consumption of ammonia is equimolar to NO.

However, in a mobile diesel engine such as a truck or a bus, the load changes remarkably, and when ammonia is used as a reducing agent, there is a problem that the leaking ammonia is directly discharged to the atmosphere.

In view of the above-mentioned state of the art, the present invention is to provide a method for purifying diesel engine exhaust gas which does not have the problems of the conventional method.

[0009]

That is, the present invention is
In a method of introducing the exhaust gas of a diesel engine containing nitrogen oxides into a reactor filled with a catalyst and catalytically removing ammonia or urea as a reducing agent, a denitration catalyst layer is installed on the upstream side of the gas flow, and the subsequent flow Has a function of oxidatively decomposing ammonia into nitrogen and nitrogen oxides (1 ± 0.6) R ₂ O · [aM ₂ O ₃ · bAl
₂ O ₃ ] .cMeO.ySiO ₂ (wherein R is an alkali metal ion and / or a hydrogen ion, M is selected from the group consisting of Group VIII elements, rare earth elements, titanium, vanadium, chromium, niobium, antimony, and gallium. One or more elements, Me is an alkaline earth element, a ≧ 0, b ≧ 0, c ≧
0, a + b = 1, y / c> 12, y> 12), and a crystalline silicate having an X-ray diffraction pattern shown in Table 1 below as a carrier, platinum as an active metal,
A method for removing nitrogen oxides from a diesel engine, characterized in that an ammonia decomposition catalyst layer containing at least one of palladium, ruthenium, iridium, and rhodium is installed to decompose and remove leak ammonia, and the exhaust gas in (1) above. A method for removing nitrogen oxides from a diesel engine, wherein the temperature at which ammonia or urea is added is 200 ° C. or higher.

[0010]

[Table 1] VS: Very strong M: Intermediate S: Strong W: Weak (X-ray source Cu)

[0011]

In the present invention, as the upper denitration catalyst, V,
A TiO ₂ -based catalyst containing W, Mo or the like as an active component can be used. Further, the ammonia decomposition catalyst on the lower side is (1 ± 0.6) R ₂ O. [a
M ₂ O ₃ · bAl ₂ O ₃ ] · cMeO · ySiO ₂ (wherein R is an alkali metal ion and / or a hydrogen ion, M
Is one or more elements selected from the group consisting of Group VIII elements, rare earth elements, titanium, vanadium, chromium, niobium, antimony, and gallium, Me is an alkaline earth element, and a ≧
0, b ≧ 0, c ≧ 0, a + b = 1, y / c> 12, y>
12) having the chemical composition and having the specific X shown in Table 1 above.
A catalyst containing at least one of platinum, palladium, ruthenium, iridium and rhodium as an active metal is used with a crystalline silicate having a line diffraction pattern as a carrier.

Normally, the operation modes of diesel engines such as trucks have operation patterns of 1 to 13 modes shown in Table 3 below depending on load conditions. Exhaust gas conditions between these modes are wide, exhaust gas temperature: 70 to 540 ° C., NOx concentration: 200 to 810 ppm, O ₂ concentration: 5 to 19%, C
O concentration: 100 to 300 ppm, HC concentration: 100 to 3
It is in the range of 00 ppm. Ammonia is preferable as the reducing agent, but since it is toxic, a nitrogen compound (for example, urea water) may be used. Since the temperature at which ammonia or urea water acts as a reducing agent for nitrogen oxides is about 200 ° C or higher, the reducing agent is supplied only when the exhaust gas temperature is about 200 ° C or higher. Furthermore, when ammonia leaks from the denitration catalyst in the previous stage due to a load change, etc., the ammonia decomposition catalyst can suppress the ammonia concentration to 0.1 ppm or less, and releases ammonia that is harmful to the atmosphere at a concentration as low as possible. be able to.

Both the denitration catalyst and the ammonia decomposition catalyst are 40
It can be supported as a coat type on a cordierite substrate of 0 cell / inch ² , and the capacity of the catalyst layer is 50
It is possible to reduce it to 10 liters or less with a 00cc truck.

As the reducing agent to be added, urea is more preferable.
It is preferable in terms of handling and danger, and the aqueous solution is used as exhaust gas.
By spraying into (CO)₂NH + 2H₂O →
NH ₃+ 2CO₂Ammonia is generated by the reaction of
Denitration can be performed in the same manner as in the conventional selective catalytic reduction method.
It

[0015]

EXAMPLES The effects of the present invention will be clarified below with reference to specific examples.

(Example 1) Preparation of ammonia decomposition catalyst Water glass No. 1 (SiO ₂ : 30%): 5616 g of water:
It was dissolved in 5429 g, and this solution was designated as solution A. on the other hand,
Water: 4175 g, aluminum sulfate: 718.9 g, ferric chloride: 110 g, calcium acetate: 47.2 g, sodium chloride: 262 g and concentrated hydrochloric acid: 2020 g were mixed and dissolved, and this solution was designated as solution B. Solution A and Solution B
Is supplied at a constant ratio to generate a precipitate, which is sufficiently stirred to p
A slurry of H: 8.0 was obtained. This slurry was charged into a 20 liter autoclave, 500 g of tetrapropylammonium bromide was further added, and hydrothermal synthesis was carried out at 160 ° C for 72 hours, followed by washing with water and drying, and further firing at 500 ° C for 3 hours to crystallize. A sex silicate 1 was obtained. This crystalline silicate 1 has a molar ratio of oxide (excluding water of crystallization) of 0.5Na ₂ O.0.5H ₂ O. [0.8A
l ₂ O ₃ · 0.2Fe ₂ O ₃ · 0.25CaO] · 25
It was represented by the composition formula of SiO ₂ , and the crystal structure was as shown in Table 1 above by X-ray diffraction.

The above crystalline silicate 1 was treated with 4N NH ₄ C.
1 aqueous solution was stirred at 40 ° C. for 3 hours to carry out NH ₄ ion exchange. It was washed after ion exchange, dried at 100 ° C. for 24 hours, and then calcined at 400 ° C. for 3 hours to obtain H-type crystalline silicate 1.

The H-type crystalline silicate was impregnated with an aqueous solution of chloroplatinic acid, an aqueous solution of palladium nitrate, an aqueous solution of ruthenium chloride, an aqueous solution of iridium chloride and an aqueous solution of rhodium chloride, evaporated to dryness, and then calcined at 500 ° C. for 3 hours to obtain a powder. A catalyst was obtained.

With respect to 100 g of the obtained powder catalyst, 3 g of alumina sol as a binder (Al ₂ O ₃ : 10)
%), Silica sol: 55 g (SiO ₂ : 20 wt%), and water: 200 g to make a slurry, and wash coat the cordierite honeycomb substrate (400 cells / inch ² ) to obtain a coating of 80 g / m ² per substrate surface area. Carried in quantity. The obtained catalysts were designated as ammonia decomposition catalysts 1 to 5. These ammonia decomposition catalysts 1 to 5 are Pt, respectively.
0.2 wt%, Pd 1 wt%, Ru 0.3 wt%
%, Ir was carried by 0.5 wt%, and Rh was carried by 0.2 wt%.

(Preparation of ammonia decomposition catalysts 6 to 19)
Note NH₃Crystalline silicate 1 in the preparation of cracking catalysts 1-5
In the synthetic method of
Gypsum, ruthenium chloride, rhodium chloride, lanthanum chloride, salt
Cerium chloride, titanium chloride, vanadium chloride, black chloride
Aluminum, antimony chloride, gallium chloride and niobium chloride
Fe as oxide₂O₃Since adding the same number of moles as
Crystals are obtained by repeating the same procedure as for crystalline silicate 1
Sex silicates 2-12 were prepared. These crystalline siri
The crystal structure of cate is shown in Table 1 by X-ray diffraction.
And its composition depends on the molar ratio of oxides (dehydrated form).
State), 0.5 Na₂O ・ 0.5H₂O
(0.2M₂O₃・ 0.8Al₂O ₃・ 0.25Ca
O) ・ 25SiO₂Is. Where M is Co, Ru, R
h, La, Ce, Ti, V, Cr, Sb, Ga, Nb
is there.

Further, in the method of synthesizing the crystalline silicate 1,
Instead of calcium acetate, magnesium acetate, vinegar
Cadmium strontium acid and barium acetate converted to oxides
Crystalline silicate except that the same number of moles as aO is added
By repeating the same operation as in 1, the crystalline silicate 13-
15 was prepared. The crystal structure of these crystalline silicates
Is shown in Table 1 above by X-ray diffraction, and the set
The composition is expressed by the molar ratio of oxides (dehydrated form), and
5Na₂O ・ 0.5H₂O ・ (0.2Fe₂O ₃・ 0.
8 Al₂O₃・ 0.25MeO) ・ 25SiO₂And
It Here, Me is Mg, Sr, or Ba.

Using the crystalline silicates 2 to 15 in the same manner as in the honeycomb catalyst 1, H-type crystalline silicate 2
~ 15 was obtained. Each of the H-type crystalline silicates was impregnated with a chloroplatinic acid aqueous solution, evaporated to dryness, and calcined at 500 ° C. for 3 hours to obtain a powder catalyst carrying 0.2 wt% of Pt.
These powder catalysts were coated on cordierite monolith substrates in the same manner as the ammonia decomposition catalysts 1 to 5 to obtain ammonia decomposition catalysts 6 to 19. Prepared NH ₃ decomposition catalysts 1-1
9 is shown in Table 2.

[0023]

[Table 2]

(Example 2) Preparation of denitration catalyst Vanadium pentoxide (V ₂ O) was added to a titania (TiO ₂ ) carrier.
₅ ) 4 wt% and tungsten trioxide (WO ₃ ) 8 w
Alumina sol and silica sol were added to the powder catalyst supported at t% in the same manner as the ammonia decomposition catalyst, and 400 cells to in
Ch ² cordierite honeycomb substrate (wall thickness: 0.2 m
m) was coated with 80 g / m ² (per surface area of the substrate) by the wash coating method. This catalyst was named denitration catalyst 1.

(Example 3) Denitration reaction test 1 190 mmφ × 179 mmL (= 5 liters) cylindrical denitration catalyst 1 was added in front of diesel engine exhaust gas to 19
A denitration reaction test was carried out by charging the columnar ammonia decomposition catalyst 1 of 0 mmφ × 108 mmL (= 3 liters) in series in the latter stage and adding urea under 13-mode conditions as the system 1. Table 3 shows the exhaust gas conditions in 13 modes.

[0026]

[Table 3]

In the 1, 2, 3, 4, 5, and 13 modes, the exhaust gas temperature is 200 ° C. or less, and the denitration catalyst 1 cannot operate, so urea is not sprayed in these modes. Mode 6-12 result of the addition of NOx discharged in the same amount of urea (= at N terms) in, showing the NOx concentration of the rear exhaust of the NH ₃ decomposing catalyst, the NH ₃ concentration in Table 4.

[0028]

[Table 4]

From these results, it was found that in Modes 6 to 12 in which urea was added in the same amount as the exhausted NOx amount, almost all of the NOx could be removed, and the outlet NH ₃ was all 0.1 ppm or less. In addition, it was confirmed that the hydrocarbons and carbon monoxide discharged would be oxidatively removed.

(Example 4) In Example 3, NH ₃ decomposition catalysts 2 to 19 were installed in place of the ammonia decomposition catalyst 1 to form systems 2 to 19 and urea was used in modes 6 to 12 as in Example 3.
And a 13-mode denitration reaction test was carried out. Thirteen
Table 5 shows the results of the mode average denitration rate and the average exhausted NH ₃ concentration.
Shown in

[0031]

[Table 5]

As shown in the results of Table 5, systems 1-1
No. 9 can denitrate at a high level, and leak NH ₃ can be almost eliminated.

(Comparative Example 1) As a comparative example, the denitration catalyst 1 was charged in place of the NH ₃ decomposition catalyst 1 in Example 3 (= denitration catalyst: 8 liters in total), and the denitration performance was the same as in Example 3 as the system 20. The test was conducted. The results are shown in Table 5.
Are also shown. System 2 as shown in the reaction results in Table 5
At 0, the average exhausted NH ₃ concentration is as high as 4 ppm, which is toxic N
It is not preferable because H ₃ is released into the atmosphere as it is.

[0034]

EFFECTS OF THE INVENTION According to the denitration method of the present invention, nitrogen oxides discharged from a diesel engine can be efficiently removed, and further, NH ₃ which serves as a reducing agent is discharged as little as possible. It is also possible to achieve stability and durability of 10,000 hours or more.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display area F01N 3/28 301 B01D 53/36 ZABE

Claims (2)

[Claims] 1. In a method of introducing exhaust gas of a diesel engine containing nitrogen oxides into a reactor filled with a catalyst to catalytically remove ammonia or urea as a reducing agent, a denitration catalyst layer is provided on the upstream side of the gas flow. It is installed and has a function of oxidatively decomposing ammonia into nitrogen and nitrogen oxides in the subsequent stream (1 ± 0.6) R ₂ O. [aM
₂ O ₃ · bAl ₂ O ₃ ] · cMeO · ySiO ₂ (wherein R is an alkali metal ion and / or a hydrogen ion, M is
Is one or more elements selected from the group consisting of Group VIII elements, rare earth elements, titanium, vanadium, chromium, niobium, antimony, and gallium, Me is an alkaline earth element, and a ≧
0, b ≧ 0, c ≧ 0, a + b = 1, y / c> 12, y>
Ammonia decomposition containing at least one of platinum, palladium, ruthenium, iridium and rhodium as an active metal, using as a carrier a crystalline silicate having a chemical composition of 12) and having an X-ray diffraction pattern described in detail herein. A method for removing nitrogen oxides in a diesel engine, which comprises disposing and removing leaked ammonia by installing a catalyst layer. 2. The method for removing nitrogen oxides from a diesel engine according to claim 1, wherein the temperature at which ammonia or urea is added to the exhaust gas is 200 ° C. or higher.