JP3154602B2 - Exhaust gas purification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nitrogen oxide (hereinafter referred to as NO
x), carbon monoxide (CO), hydrocarbons (hereinafter H
C) (hereinafter abbreviated as C).

[0002]

2. Description of the Related Art In the treatment of exhaust gas from automobiles and the like, it is general to purify NOx in a very narrow range near the stoichiometric air-fuel ratio using a catalyst by utilizing CO and HC in the exhaust gas. However, in the exhaust gas treatment of a lean burn gasoline engine or a diesel engine, since the exhaust gas contains excessive oxygen, the conventional catalysts do not show any denitration action. Recently, as a catalyst capable of purifying NOx in an oxygen-excess atmosphere, a crystalline silicate catalyst containing cobalt or copper has been spotlighted as a catalyst having high performance. However, these catalysts have a sufficient performance in the early stage of the reaction, but the deterioration of the catalyst due to heat, steam in the exhaust gas, or SO ₂ has occurred as a problem.

The inventors of the present invention have intensively studied catalysts that can overcome the above-mentioned problems, and have found that iridium-supported catalysts are highly durable and highly active catalysts (Japanese Patent Application No. Hei 10-26139). 5-26369, Japanese Patent Application 5-1
00698, Japanese Patent Application No. 5-228382, etc.). However, when purifying NOx exhausted from a diesel engine, a sufficient denitration rate has not yet been obtained even with the use of these catalysts because the HC concentration in the exhaust gas is low.

[0004]

Therefore, in order to overcome the above-mentioned problems, the present inventors have added light oil, kerosene and gasoline used as fuel to increase the hydrocarbon concentration in the exhaust gas and efficiently perform denitration. I found a way to do it. More preferably, denitration is performed with higher efficiency by adding the fuel to be added to a hydrocarbon containing a large amount of olefins or aromatics in which the catalyst effectively acts by thermal cracking or catalytic cracking. I found it.

The present invention has been completed based on the above findings, and the present invention includes the following first to third inventions. (1) A method for reducing nitrogen oxides into nitrogen by bringing the nitrogen oxides in the exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons into contact with a catalyst together with a reductant, wherein the catalyst has the general formula (1) ± 0.8) R ₂ O. (aM ₂ O ₃ .bM'O.cAl ₂ O ₃ ) .ySiO ₂ (where R is an alkali metal ion and / or hydrogen ion, and M is a group VIII element , A rare earth element, at least one element ion selected from the group consisting of titanium, vanadium, chromium, niobium, antimony and gallium, M 'is an alkaline earth metal ion of magnesium, calcium, strontium, barium, a ≧ 0 , 20
>B> 0 , a + c = 1, 3000>y> 11) is an iridium catalyst in which iridium is supported as an active metal on a support made of a crystalline silicate having an X-ray diffraction pattern shown in Table A, A method for purifying exhaust gas, wherein the reduced product is at least one hydrocarbon fuel oil selected from the group consisting of kerosene, light oil and gasoline. (First invention)

(2) The reduced product is kerosene, light oil or gasoline
At least one hydrocarbon fuel oil selected from the group consisting of
Rich in olefins and aromatic hydrocarbons obtained by thermal decomposition of
The exhaust gas purifying apparatus of (1), which is a gas.
Method. (2nd invention) (3) A group in which the reductant comprises kerosene, light oil and gasoline
Catalytically decomposes one or more hydrocarbon fuel oils selected from
Is a gas rich in olefins and aromatic hydrocarbons
(1) The method for purifying exhaust gas according to the above (1).
(Third invention)

The crystalline silicate according to the first invention is as follows:
It has the X-ray diffraction pattern shown in Table A.

[0008]

[Table 2]

In the first invention, the crystalline silicate is
As a method for supporting the indium, the crystalline silicate
Immersion in iridium salt solution, ion exchange method or impregnation method
Therefore, it can be carried. The supported iridium is
At 0.002 wt% or more, sufficient activity is exhibited, and
Has high activity at 0.02 wt% or more.

[0010] In the second invention , the method for pyrolyzing one or more hydrocarbon fuel oils selected from the group consisting of kerosene, light oil and gasoline comprises a tubular heating furnace in which these hydrocarbon fuel oils are maintained at about 800 ° C. At a residence time of 0.6 to 1.3 seconds. In addition, since the atmosphere becomes a reducing atmosphere, it is preferable to use an inert reaction tube, for example, a quartz tube. At this time, steam can be supplied at the same time to prevent by-products of coke.

In the third aspect of the present invention, the method for decomposing a hydrocarbon fuel oil may comprise the steps of:
Using a crystalline silicate loaded with 0 wt%, it can be carried out under the conditions of LHSV: 1 h -1 and residence time: about 500 ° C.

[0012]

Function: Using a catalyst supporting iridium, NOx,
The purification reaction formula for purifying the exhaust gas containing CO and HC is as follows.

[0013]

Embedded image * 1) C ₃ H ₆ is shown as a representative example of hydrocarbon (HC). * 2) CH ₂ O is shown as a representative example of the oxygen-containing hydrocarbon. In the above reaction formula, (1) indicates activation of HC, (2) indicates combustion of HC, (3) indicates denitration reaction, and (4) indicates combustion of CO.

The catalyst supporting iridium is C ₂ H ₄ , C
Olefins such as ₃ H ₆ and aromatics such as benzene and toluene efficiently form the above-mentioned CH ₂ O (oxygen-containing hydrocarbon), and have a function of selectively proceeding the denitration reaction (3). Therefore, rather than adding one or more hydrocarbon fuel oils selected from the group consisting of light oil, kerosene, and gasoline as a NOx reducing agent, they are converted into hydrocarbons having a high olefin content or aromatic content and added. Denitration can be performed more efficiently.

[0015]

EXAMPLES The present invention will be described below in detail with reference to Examples, but the present invention is not limited to the following Examples. (Example 1) の Preparation of catalyst 1 Water glass No. 1 (SiO ₂ : 30%): 5616 g of water:
The solution was dissolved in 5429 g, and this solution was designated as solution A. on the other hand,
Aluminum sulfate: 718.9 g, ferric chloride: 110 g, calcium acetate: 47.2 g, sodium chloride: 262 g, and concentrated hydrochloric acid: 2020 g are dissolved in water: 4175 g. Solution A and solution B are supplied at a constant rate to form a precipitate, and the mixture is sufficiently stirred to obtain a pH of 8.
Get a slurry of zero. This slurry was charged into a 20-liter autoclave, and 500 g of tetrapropylammonium bromide was further added. Hydrothermal synthesis was performed at 160 ° C. for 72 hours.
C. for 3 hours to obtain crystalline silicate 1. This crystalline silicate 1 has a molar ratio of oxides (the crystallization water is omitted).
The crystal structure is represented by the following composition formula, and the crystal structure is determined by X-ray diffraction.
It is displayed in. 0.5Na ₂ O.0.5H ₂ O [0.8Al ₂ O _3.
0.2Fe ₂ O ₃ .0.25 CaO] .25 SiO _{2 The} above crystalline silicate 1 was treated with a 4N NH ₄ Cl aqueous solution 40
The mixture was stirred at 3 ° C. for 3 hours to carry out NH ₄ ion exchange. After ion exchange washing and drying at 100 ° C. for 24 hours, 4
The resultant was fired at 00 ° C. for 3 hours to obtain H-type crystalline silicate 1.

(2) Catalysis Next, 3 parts of alumina sol and 3 parts of silica sol were used as binders for the above 100 parts of H-type crystalline silicate 1.
55 parts (SiO ₂ : 20%) and 200 parts of water were added and sufficiently stirred to obtain a slurry for wash coating. Next, a monolith base material for cordierite (a grid of 400 cells) was immersed in the slurry, taken out, and then sprayed with excess slurry and dried at 200 ° C. The coating amount is 200 g per 1 liter of the base material. Next, iridium chloride (IrCl _4.
H ₂ O: 2.88g / 200cc, it was immersed impregnated 1 hour the honeycomb coating material in H ₂ O), dried at 200 ° C. wiping the adhered liquid walls of the substrate. Then 50
A purging treatment was performed at 0 ° C. in a nitrogen atmosphere for 12 hours to obtain a honeycomb catalyst 1.

(2) Preparation of Catalysts 2 to 15 In the method for synthesizing the crystalline silicate 1 in the above preparation of the honeycomb catalyst 1, instead of ferric chloride, cobalt chloride, ruthenium chloride, rhodium chloride, lanthanum chloride, cerium chloride, chloride The same operation as that of crystalline silicate 1 was repeated except that titanium, vanadium chloride, chromium chloride, antimony chloride, gallium chloride, and niobium chloride were each added in the same mole number as Fe ₂ O _{3 in} terms of oxide. ~ 12 were prepared. The crystal structures of these crystalline silicates are shown in Table A above by X-ray diffraction, and their compositions are expressed in terms of the molar ratio of oxides (dehydrated form) to 0.5NaO ₂ .0.5H ₂ O ・ (0.2M ₂ O
₃・ 0.8Al ₂ O ₃・ 0.25CaO) ・ 25SiO
₂ Where M is Co, Ru, Rh, La, Ce,
Ti, V, Cr, Sb, Ga, Nb.

Further, in the method for synthesizing the crystalline silicate 1, magnesium acetate, strontium acetate, and barium acetate are used in place of calcium acetate in terms of oxides, respectively.
The same operation as that of the crystalline silicate 1 was repeated except that the same mole number as that of the aO was added, and the crystalline silicates 13 to 1 were added.
5 was prepared. The crystal structures of these crystalline silicates are shown in Table A above by X-ray diffraction, and their compositions are expressed in terms of a molar ratio of oxides (dehydrated form) of 0.5.
Na ₂ O · 0.5H ₂ O · (0.2Fe ₂ O ₃ · 0.8
Al ₂ O ₃ · 0.25MeO) · 25SiO ₂ .
Here, Me is Mg, Sr, and Ba.

Using the above crystalline silicates 2 to 15, the H-type crystalline silicate 2 is produced in the same manner as the honeycomb catalyst 1.
To 15 were obtained, and this silicate was further coated on a cordierite monolith substrate in the same step as in the preparation of the honeycomb catalyst 1 to obtain honeycomb coated products 2 to 15. Next, it was immersed in an iridium chloride aqueous solution, and honeycomb catalysts 2 to 15 were obtained in the same manner as the honeycomb catalyst 1. The above honeycomb catalyst 1
Table 15 below summarizes the properties of Nos. To 15.

[0020]

[Table 3]

[0021]

[0022]

Preparation of Fuel Decomposition Catalyst A 100 g of crystalline silicate and Zn (NO ₃ ) ₂ .6H ₂
O: 297.4 g was added to 5 liters of distilled water, and 70 ° C.
Then, the mixture was stirred for 24 hours to perform ion exchange. After ion exchange, filtration and washing were performed, followed by drying at 200 ° C. to prepare a crystalline silicate supporting Zn: 2.3 wt%. This catalyst was subjected to honeycomb treatment in the same manner as that for the honeycomb catalyst 1 to obtain a fuel decomposition catalyst A.

NOx Decomposition Test Using the honeycomb catalyst 1, a test for removing NOx from the simulated exhaust gas of a diesel engine was performed. The test conditions are as follows. Shape of honeycomb catalyst: 15 mm x 15 mm x 60 mm
(144 cells) 13.5 cc Gas amount 945 Nl / h, GHSV: 70,000 h ^-1 Temperature: 300, 400, 500 ° C Gas composition NO: 500 ppm, CO: 500 ppm, C ₂ H ₄ :
700 ppm (C ₁ terms: 1400ppm), CO _{2:
6%, H 2 O: 6} %, O 2: 10%, SO 2: 15pp
m The results of the denitration activity of the honeycomb catalyst 1 performed under the above test conditions (Run 1) are shown in Table C below.

Next, to vaporize diesel fuel used as a fuel, a C ₁ terms of the gas composition 3000 ppm (C ₂ H
₄ + gas oil: total C ₁ Convert 4400 ppm) performs the activity evaluation test of the honeycomb catalyst 1 was added (Run2), are also shown denitration activity at that time in the following Table C.

Further, the light oil was cracked using the fuel cracking catalyst A under the following conditions, and cracked hydrocarbons were supplied to the catalyst. Shape of fuel cracking catalyst A: 5 mm x 10 mm x 60 mm
(32 cells) 3 cc Light oil supply: 3 cc / h, LHSX: 1 h ^-1 Catalyst temperature: 500 ° C.

The hydrocarbon composition when gas oil is cracked under the above conditions is as follows. _{C 2 H 4: 15%,} C 3 H 6: 10%, C 4 H 8: 5
%, Benzene: 20%, toluene: 15%, xylene:
5%, other hydrocarbons: 30% When the above cracked gas was added to the honeycomb catalyst 1 (Run
The denitration activity result of 3) is also shown in Table C below.

(Example 2) 装置 Gas oil thermal cracking device Instead of using the fuel cracking catalyst A of Example 1, gas oil was cracked by a thermal cracking method. A quartz tube having an inner diameter of 6 mmφ is heated to 800 ° C. in an electric furnace. Light oil is supplied instantaneously in a heated quartz tube using a micropump so as to maintain a residence time of 1 second to perform thermal decomposition. The gas composition by the thermal decomposition is as follows. _{C 2 H 4: 25%,} C 3 H1: 20%, C 4 H 8: 5
% Benzene: 5%, toluene: 5%, other hydrocarbons: 40% Note, 3000ppm (C ₂ H ₄ + gas oil the pyrolysis gases with C ₁ converts the light oil in the same manner as in Example 1: Total C ₁ Conversion 44
(00 ppm) to the honeycomb catalyst 1 to perform an activity evaluation test (Run 4). The results of the denitration activity are also shown in Table C below.

[0029]

[Table 4]

(Example 3) In Catalysts 2 to 15 , the tests of Runs 1 to 4 shown in Examples 1 and 2 were carried out in the same manner as in Honeycomb Catalyst 1 to evaluate the denitration activity in the same manner as in Examples 1 and 2. did. Table D shows the denitration evaluation results at 400 ° C.

[0031]

[Table 5]

As shown in Examples 1, 2 and 3, the addition of hydrocarbon fuel to the catalyst containing iridium showed an improvement in the denitration activity. Further, the fuel was subjected to catalytic decomposition and thermal decomposition to produce olefins and olefins. It was confirmed that the conversion to a hydrocarbon containing a large amount of aromatics was added and the remarkable improvement in the denitration activity was achieved. Furthermore, when a 500-hour durability test was continuously performed by the above method, it was confirmed that there was no change in the catalyst performance and that stable performance could be maintained. In addition, the honeycomb catalyst 1 used in the present invention has CO, C
Since H can be removed by burning, there is no concern that the addition of fuel causes emission of unburned CH.

[0033]

As described above, the exhaust gas purifying method according to the present invention makes it possible to stably maintain high denitration performance, and to perform denitration in exhaust gas with high oxygen concentration and low hydrocarbon concentration such as diesel engine. It can be performed efficiently.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-245386 (JP, A) JP-A-51-35667 (JP, A) JP-A-5-192539 (JP, A) JP-A-5-92539 212246 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B01J 21/00-37/36

Claims (3)

(57) [Claims] 1. A method for reducing nitrogen oxides into nitrogen by bringing the nitrogen oxides in an exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons into contact with a catalyst together with a reductant, wherein the catalyst has a general formula (1 ± 0.8) R ₂ O. (aM ₂ O ₃ .bM'O.cAl ₂ O ₃ ) .ySiO ₂ (where R is an alkali metal ion and / or hydrogen ion, M is VIII Group element, rare earth element, at least one or more element ions selected from the group consisting of titanium, vanadium, chromium, niobium, antimony and gallium, M 'is an alkaline earth metal ion of magnesium, calcium, strontium, barium, a ≧ 0, 20
>B> 0 , a + c = 1, 3000>y> 11) is an iridium catalyst in which iridium is supported as an active metal on a support made of a crystalline silicate having an X-ray diffraction pattern shown in Table A, A method for purifying exhaust gas, wherein the reduced product is at least one hydrocarbon fuel oil selected from the group consisting of kerosene, light oil and gasoline. [Table 1] 2. The method according to claim 1, wherein the reduced product is kerosene, light oil or gasoline.
Heat at least one hydrocarbon fuel oil selected from the group consisting of
Decomposed olefins and aromatic hydrocarbon-rich gas
The exhaust gas purification according to claim 1, characterized in that:
Method. 3. The method according to claim 1, wherein the reduced product is kerosene, light oil or gasoline.
At least one hydrocarbon fuel oil selected from the group consisting of
Gases rich in olefins and aromatic hydrocarbons
The exhaust gas purification according to claim 1, wherein
Method.