JPH06226052A - Method for removing nox - Google Patents

Abstract

PURPOSE:To effectively remove NOx by adding org. matter to waste gases contg. the NOx and bringing the waste gases into contact with one kind of catalysts among specific catalyst groups under a condition of a prescribed temp. CONSTITUTION:The org. material is acted as a reducing agent in place of ammonia on the boiler waste gases and the catalysts consisting of a crystalline silicate catalyst, multiple oxide, zeolite and solid superstrong acid catalyst group are simultaneously brought into contact therewith as well, by which the NOx is removed. The chemical formula of the crystalline silicate catalyst is expressed by (+ or -0.6)R2O.[aM2O3.bAl2O3.cMeO].ySiO2 (R us an alkaline metal ion and/or hydrogen ion; M is >=1 kinds of the metals selected from a group consisting of group VIII metals, rare earth metals, titanium, vanadium, chromium, niobium, antimony and gallium; Me is an alkaline earth metal; a>=0, b>=0, c>=0, a+b=1, y/c>12, y>12). Metals, such as copper, cobalt, nickel, iron, chromium, zinc and manganese, are deposited in >=1 kinds thereon.

Description

Detailed Description of the Invention

[0001]

The present invention relates to nitrogen oxides (hereinafter referred to as NO
x) (abbreviated as x).

[0002]

2. Description of the Related Art As methods for removing NOx in exhaust gas and polluted air, there are adsorption method, oxidation absorption method, catalytic reduction method, etc.
The catalytic reduction method, which requires no post-treatment, is considered to be economically and technically advantageous. In the catalytic reduction method, NOx in the boiler exhaust gas is predominantly a selective reduction method in which a reducing gas such as ammonia is added, and NOx in the vehicle exhaust gas is coexistent with H ₂ and C ₂ .
The non-selective reduction method using reducing gas of O and hydrocarbon is the mainstream.

On the other hand, in recent years, research on a direct decomposition catalyst of nitrogen oxides has been earnestly conducted, and Pt / Al ₂ O ₃ ,
LaSrCoOx (perovskite structure), Al
Catalysts such as ₂ O ₃ and Cu-ZSM-5 have been reported.
However, the reaction rate of each of the catalysts is slow, and H ₂ O,
There is a problem that activity decreases due to coexisting gas such as O ₂ .

The present inventors have also reported that the crystalline silicate has a composition represented by the following formula 1 in terms of a molar ratio of oxides and has a crystal structure of X-ray diffraction having a diffraction pattern shown in the following Table A. It has been found that a catalyst supporting nickel, cobalt, iron, chromium, zinc and manganese has high activity, but it does not have a reaction rate until it is put to practical use. (1 ± 0.6) R ₂ O · [aM ₂ O ₃ · bAl ₂ O ₃ · cMeO] · ySiO ₂ (Equation 1) (wherein R is an alkali metal ion and / or a hydrogen ion, M is at least one metal selected from the group consisting of Group VIII metals, rare earth metals, titanium, vanadium, chromium, niobium, antimony and gallium, Me is an alkaline earth metal, a ≧ 0, b ≧ 0, c ≧ 0, a + b = 1, y / c> 1
2, y> 12)

[0005]

[Table 1] W: Weak M: Intermediate S: Strong VS: Very strong (X-ray source: Cu) I ₀ is the strongest peak intensity and I / I ₀ is the relative intensity

[0006]

[Problems to be Solved by the Invention] NO in boiler exhaust gas
The catalyst used for x removal is usually a V-W / TiO ₂ system, and ammonia is used as the reducing agent, but it is expensive and it is necessary to pay sufficient attention to safety, so an alternative reducing agent is desired. It is rare. In addition, in the removal of NOx from automobile exhaust gas, a Pt—Rh / Al ₂ O ₃ -based three-way catalyst (a catalyst that simultaneously removes hydrocarbons, carbon monoxide, and NOx in exhaust gas at the same time as an air-fuel ratio of 14 NOx only around 6
Although they are being removed, it is impossible to remove NOx with a three-way catalyst in exhaust gas with a high O ₂ concentration such as lean burn gasoline engine and diesel engine.

As a method for removing lean NOx in public places such as underground tunnels and parking lots, a method has been proposed in which lean NOx is adsorbed and concentrated by the PSA method, and further concentrated NOx is directly decomposed by a catalyst. , O ₂ and H ₂ O are present as coexisting gas, which causes a problem that a large amount of catalyst is required to remove NOx.

In view of the above-mentioned state of the art, the present invention intends to provide a method for removing NOx which does not have the problem of the conventional method.

[0009]

Means for Solving the Problems The present inventors have made the aforementioned conclusions.
Diligent study on effective utilization of crystalline silicate catalyst
As a result, boiler exhaust gas (NO: about 500 ppm, O₂:about
10%, H₂O: about 10%) for removing NOx in the catalyst
Instead of ammonia as an effective reducing agent using
It is confirmed that it works, and in the composition formula, Al
₂O₃, ZrO ₂, TiO₂Or SiO₂Oxidation like
Thing, Al₂O₃・ TiO₂, Al₂O₃・ ZrO₂, Z
rO₂・ TiO₂Or SiO₂・ Al₂O₃Like
Compound oxide, Y-type zeolite, mordenite, L-type Zeora
Ito, clinoptilolite, ferrierite, ZSM-
Zeoli, such as type 5 zeolite or type A zeolite
And further SO_Four/ ZrO₂, SO_Four/ ZrO₂・ A
l₂O₃, SO_Four/ ZrO₂・ TiO₂Or SO_Four/ T
iO₂Solid acid catalysts (solid super strong acid catalysts) such as
Effective in the presence of organic substances, similar to crystalline silicate catalysts
It was confirmed that nitrogen oxides could be purified.

Furthermore, as organic substances to be added, paraffins of ethane, propane, butane, pentane, hexane, olefins of ethylene, propylene, butene,
Acetylene, butadiene dienes, methanol, ethanol, propanol, butanol alcohols, benzene, toluene, xylene aromatics, acetone, methyl ethyl ketone ketones, dimethyl ether, diethyl ether ethers, acetic acid, formic acid carboxylic acids, At least one substance selected from the group consisting of formaldehyde, acetaldehyde aldehydes, and methyl formate or a mixed fuel such as gasoline, kerosene, and light oil is effective as a reducing agent in the nitrogen oxide purification reaction. It was confirmed.

The present invention has been completed based on the above findings. (1) An organic substance is added to exhaust gas containing nitrogen oxides,
A method for purifying nitrogen oxides in exhaust gas, which comprises contacting the catalyst with a catalyst of the following catalyst group under the condition of a temperature of 100 to 800 ° C. Expressed as a molar ratio of oxides in the dehydrated state, (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 a group VIII metal, a rare earth metal, titanium, vanadium, chromium, niobium, antimony, or gallium. One or more metals, Me is an alkaline earth metal, a ≧ 0, b ≧ 0, c ≧
0, a + b = 1, y / c> 12, y> 12), and copper, cobalt, nickel, a crystalline silicate having an X-ray pattern shown in Table A described in detail herein.
1 selected from the group consisting of iron, chromium, zinc and manganese
A catalyst supporting one or more metals. Al ₂ O ₃ , ZrO ₂ , TiO
₂ or SiO ₂ oxide and Al ₂ O ₃ TiO ₂ ,
Al ₂ O ₃ · ZrO ₂ , ZrO ₂ · TiO ₂ or SiO
1 selected from the group consisting of ₂ -Al ₂ O ₃ complex oxides
Catalyst composed of one or more kinds of oxides or composite oxides Y-type zeolite, mordenite, L-type zeolite,
Catalyst made of one or more kinds of zeolite selected from the group consisting of clinoptilolite, ferrierite, ZSM-5 type zeolite and A type zeolite SO ₄ / ZrO ₂ , SO ₄ / ZrO ₂ .Al
₂ O ₃ , SO ₄ / ZrO ₂ · TiO ₂ , SO ₄ / TiO
_A catalyst comprising one or more solid superacids selected from the group consisting of ₂ . (2) Organic substances added include ethane, propane, butane, pentane, hexane paraffins, ethylene, propylene, butene olefins, acetylene, butadiene dienes, methanol, ethanol, propanol, butanol alcohols, benzene, toluene. , At least one substance selected from the group consisting of xylene aromatics, acetone, methyl ethyl ketone ketones, dimethyl ether, diethyl ether ethers, acetic acid, formic acid carboxylic acids, formaldehyde, acetaldehyde aldehydes, and methyl formate. Alternatively, the method for purifying nitrogen oxides according to (1) above, which is a mixed fuel such as gasoline, kerosene, or light oil. Is.

[0012]

[Function] Lean burn engine exhaust gas (O ₂ concentration 1 to 1
It was also clarified that the catalyst effectively acts on the removal of NOx in (0%), and the organic matter in the exhaust gas acts effectively as a reducing agent. Further, it has been found that when the exhaust gas contains a small amount of organic matter, the stationary engine has continuous NOx removal performance if the organic engine is supplied continuously according to the concentration of the reducing agent. Also, it has been confirmed that the diesel engine has a predetermined NOx removal performance by adding an organic substance to the exhaust gas in accordance with the concentration of the reducing agent, as in the gasoline engine.

The temperature at which any catalyst and any reducing agent act is in a wide range of 100 to 800 ° C., and the influence of coexisting gases (SOx, H ₂ O, O ₂ etc.) is small.

When the above catalyst (crystalline silicate type, solid acid type) is used for removing NOx, the direct decomposition of NOx (2
Although it works effectively for the NO → N ₂ + O ₂ ) reaction, it is considered that when organic matter is present, the organic matter is activated by O ₂ present in the system to produce an active organic compound. Taking C ₃ H ₆ which is a hydrocarbon as an example, the reaction formula is considered to be as follows. C ₃ H ₆ + 3 / 2O ₂ → 3CH ₂ O · (this is assumed to be an active organic compound) (a) CH ₂ O · + O ₂ → CO ₂ + H ₂ O ··· (b) CH ₂ O・ + 2NO → N ₂ + CO ₂ + H ₂ O ・ ・ ・ ・ ・ ・ (c)

[0015]

【Example】

(Example 1) (Catalyst preparation) The crystalline silicate used in one example of the present invention is Na ₂ O · 0.5Al ₂ O ₃ · in a dehydrated state.
Represented by _{0.5Fe 2 O 3 · 0.1CaO · 25SiO} 2, were used those having a crystal structure shown in Table A. The crystalline silicate was prepared as follows.

Water glass No. 3 is dissolved in water to prepare a solution A.
Further, ferric sulfate, aluminum sulfate, and calcium acetate are dissolved in water to obtain solution B. The molar numbers of the solutions A and B charged were 36Na ₂ O. [0.5Fe ₂ O ₃ .0.
5Al ₂ O ₃ · 0.1CaO] · 25SiO ₂ · 160
It is prepared as 0H ₂ O, and the solution A and the solution B are dropped in equal amounts in different containers to form a gel. Add an appropriate amount of sulfuric acid to the above-mentioned slurry gel produced by neutralization, and adjust the pH of the gel.
To 9. Then, tetrapropylammonium bromide as an organic nitrogen compound was mixed with Fe ₂ O ₃ and Al.
Add 10 times the total number of moles of ₂ O _3, mix well with the above slurry, and place in a 3 liter stainless steel autoclave. While stirring this slurry at 300 rpm,
The reaction was carried out at 0 ° C for 3 days. After cooling, the solid content is filtered, washed thoroughly with water until the pH of the wash water reaches 7, dried at 110 ° C. for 12 hours, and calcined at 550 ° C. for 3 hours to obtain crystalline silicate 1.
Got The crystalline silicate was continuously subjected to copper ion exchange with a 0.04 molar aqueous solution of acetic acid at 20 ° C. for 48 hours, and after the ion exchange, was dripped and dried to prepare a powder catalyst 1. The amount of supported Cu was 0.70 mmol. Alumina sol, silica sol, and
Water was added and mixed and stirred to prepare a slurry for washcoat. A cordierite monolith substrate was dipped in this slurry and the excess slurry was blown off to prepare a honeycomb catalyst 1.

(Activity evaluation) Using the honeycomb catalyst 1, an activity evaluation test was carried out as a denitration test of diesel exhaust gas with the following simulated gas. ○ Temperature: 350 ℃, 450 ℃ ○ GHSV: 30000h ^-1 ○ Gas composition: NO: 400ppm, O ₂ : 8%, C
O ₂ : 10%, H ₂ O 10%, 1000 pp of C ₂ H ₅ OH as a reducing agent before the remaining N ₂ catalyst.
m (2000 ppm in terms of C ₁ ) was uniformly supplied to the above simulated gas to carry out the denitration reaction. The activity evaluation results are shown in Table B below.
Shown in.

(Example 2) In preparing a crystalline silicate, cobalt chloride, ruthenium chloride, rhodium chloride, lanthanum chloride, cerium chloride, titanium chloride, vanadium chloride and chloride were used instead of ferric sulfate in the same manner as in Example 1. The same operations as those for the crystalline silicate 1 were repeated except that chromium, niobium chloride, antimony chloride, and gallium chloride were added in the same mole number as Fe ₂ O _{3 in} terms of oxide. 5, 6, 7, 8, 9, 10,
11, 12 were prepared.

In the same manner as in Example 1, magnesium acetate, strontium acetate, and barium acetate were used as oxides instead of calcium acetate in the preparation of the crystalline silicate, respectively.
The same operations as those for the crystalline silicate 1 were repeated except that the same number of moles as aO was added, and the crystalline silicates 13, 1
4,15 were prepared.

These crystalline silicates were powder-catalyzed in the same manner as in Example 1 to obtain powder catalysts 2 to 15, and further honeycomb-catalyzed in the same manner as in Example 1 to prepare honeycomb catalysts 2 to 15.

The results of evaluation of the honeycomb catalysts 2 to 15 obtained in Example 2 under the same conditions as the activity evaluation conditions of Example 1 are also shown in Table B below.

(Example 3) Using crystalline silicate 1, ion exchange was carried out with 0.04 M aqueous solution of each of cobalt chloride, nickel chloride, ferric chloride, chromium nitrate, cuprous chloride and manganese chloride at 60 ° C for 48 hours. It was carried out continuously, after ion exchange, washed with water and dried to obtain powder catalysts 16 to 21. Further, in the same manner as in Example 1, the powder catalysts 16 to 21 were made into honeycomb to obtain honeycomb catalysts 16 to 21.

The results of evaluation of the honeycomb catalysts 16 to 21 obtained in Example 3 under the same conditions as the activity evaluation conditions of Example 1 are also shown in Table B below.

[0024]

[Table 2]

[0025]

[Table 3]

(Example 4) Al in the composition formula₂O₃(Γ type),
ZrO₂, TiO₂(Anatase type), SiO₂Oxidation of
Thing, Al₂O₃・ TiO₂, Al₂O₃・ ZrO₂, Z
rO₂・ TiO₂, SiO₂・ Al₂O₃Complex oxidation of
Thing, Y-type zeolite (SiO₂/ Al₂O₃: 6), Mo
Rudenite (SiO₂/ Al₂O₃: 15), L-type Zeo
Light (SiO₂/ Al₂O₃: 6), Clinoptilola
Ito (SiO₂/ Al₂O₃: 5), Ferrierite
(SiO₂/ Al₂O₃: 5), ZSM-5 type Zeoli
To (SiO₂/ Al₂O₃: 35), type A zeolite
(SiO₂/ Al₂O₃: 1) zeolite (all H
Type), and SO_Four/ ZrO₂, SO_Four/ ZrO₂・ A
l ₂O₃, SO_Four/ ZrO₂・ TiO₂, SO_Four/ Ti
O₂These catalysts were prepared as in Example 1 using the solid superacids of
Honeycombing was performed to obtain honeycomb catalysts 22 to 40.

The results of evaluation of the honeycomb catalysts 22 to 40 obtained in Example 4 under the same conditions as the activity evaluation conditions of Example 1 are also shown in Table C below.

From the results in Table C, it is possible to use the above catalyst.
C, even under high oxygen concentration₂H _FiveAdd OH
It was found that NOx can be efficiently purified by.

[0029]

[Table 4]

Example 5 Using honeycomb catalyst 1, the following hydrocarbon was added as a reducing agent and the same activity evaluation conditions as in Example 1 were used. The reducing agent is ethane, propane, butane, pentane, hexane, propylene, butene, acetylene,
Butadiene, methanol, ethylene, ethanol, propanol, butanol, benzene, toluene, xylene, acetone, methyl ethyl ketone, dimethyl ether, diethyl ether, acetic acid, formic acid, formaldehyde, acetaldehyde, methyl formate, gasoline, kerosene,
Light oil was further added at 2000 ppm in terms of C ₁ . The results of activity evaluation are shown in Table D.

As shown in Table D, it was found that NOx can be efficiently purified even under a high oxygen concentration by adding the reducing agent. It has been confirmed that the honeycomb catalysts 2 to 21 and 22 to 40 other than the honeycomb catalyst 1 can also efficiently purify NOx as with the honeycomb catalyst 1.

[0032]

[Table 5]

[0033]

EFFECTS OF THE INVENTION According to the present invention, it was found that nitrogen oxide in exhaust gas can be effectively purified by adding an organic substance to the exhaust gas containing nitrogen oxide and bringing it into contact with a catalyst as shown in Examples. It was

Claims (2)

[Claims] 1. An organic substance is added to an exhaust gas containing nitrogen oxides, and the organic substance is brought into contact with a catalyst of the following catalyst group under the condition of a temperature of 100 to 800 ° C. Purification method. Expressed as a molar ratio of oxides in the dehydrated state, (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 a group VIII metal, a rare earth metal, titanium, vanadium, chromium, niobium, antimony, or gallium. One or more metals, Me is an alkaline earth metal, a ≧ 0, b ≧ 0, c ≧
0, a + b = 1, y / c> 12, y> 12), and copper, cobalt, nickel, a crystalline silicate having an X-ray pattern shown in Table A described in detail herein.
1 selected from the group consisting of iron, chromium, zinc and manganese
A catalyst supporting one or more metals. Al ₂ O ₃ , ZrO ₂ , TiO
₂ or SiO ₂ oxide and Al ₂ O ₃ TiO ₂ ,
Al ₂ O ₃ · ZrO ₂ , ZrO ₂ · TiO ₂ or SiO
1 selected from the group consisting of ₂ -Al ₂ O ₃ complex oxides
Catalyst composed of one or more kinds of oxides or composite oxides Y-type zeolite, mordenite, L-type zeolite,
Catalyst made of one or more kinds of zeolite selected from the group consisting of clinoptilolite, ferrierite, ZSM-5 type zeolite and A type zeolite SO ₄ / ZrO ₂ , SO ₄ / ZrO ₂ .Al
₂ O ₃ , SO ₄ / ZrO ₂ · TiO ₂ , SO ₄ / TiO
_A catalyst comprising one or more solid superacids selected from the group consisting of ₂ . 2. The organic matter added is ethane, propane, butane, pentane, hexane paraffins, ethylene,
Propylene, butene olefins, acetylene, butadiene dienes, methanol, ethanol, propanol, butanol alcohols, benzene, toluene, xylene aromatics, acetone, methyl ethyl ketone ketones, dimethyl ether, diethyl ether ethers, The at least one substance selected from the group consisting of acetic acid, carboxylic acids of formic acid, formaldehyde, aldehydes of acetaldehyde, and methyl formate, or a mixed fuel of gasoline, kerosene, light oil, etc. Method for purifying nitrogen oxides.