JPH04334527A - Removal of nitrogen oxide - Google Patents

Abstract

PURPOSE:To remove a nitrogen oxide. CONSTITUTION:Org. matter or carbon monoxide is added to exhaust gas containing nitrogen oxide and this exhaust gas is brought into contact with a catalyst prepared by adding copper to crystalline silicate having composition represented by (1.0+ or -0.6) R2O.[a.M2O3.b.Al2O3].ySiO2 wherein M is an ion of one or more kinds of an element selected from an element of the Group VIII, a rare earth element, titanium, vanadium, chromium, niobium, antimony and gallium, a+b=1, a>=0, b>=0 and y>12 expressed in terms of molar ratio of oxide at 250-800 deg.C to remove nitrogen oxide.

Description

Detailed Description of the Invention [0001] [Industrial Application Field] The present invention relates to nitrogen oxides (hereinafter referred to as NOx
(abbreviated as ). [0002] Methods for removing NOx from exhaust gas and contaminated air include adsorption methods, oxidation absorption methods, and catalytic reduction methods.
The catalytic reduction method, which does not require post-treatment, is considered to be economically and technically advantageous. NOx in boiler exhaust gas in catalytic reduction method
The mainstream is the selective reduction method that adds a reducing gas such as ammonia, and the removal of NOx from automobile exhaust gas is performed using the coexisting H2
, CO, and hydrocarbons using reducing gases are mainstream. On the other hand, in recent years, research on direct decomposition catalysts for nitrogen oxides has been intensively carried out, and Pt/Al2 O3
, LaSrCoOx (perovskite structure), Ag-
Catalysts such as Co3 O4 and Cu-ZSM-5 have been reported. However, with both catalysts, the reaction rate is slow and H2O
, O2 and other coexisting gases cause the activity to decrease. [0004] The present inventors have also created a crystalline silicate which has a composition expressed by the following formula 1 in terms of the molar ratio of oxides, and whose crystal structure has a diffraction pattern shown in Table 1 below in X-ray diffraction. (1±0.6)R2 O・[aM2 O3 ・
bAl2O3]・y...(1) [In the above formula,
M: one or more element ions selected from the group consisting of Group VIII elements, rare earth elements, titanium, vanadium, chromium, niobium, antimony, and gallium, a+b=1, a≧0
, b≧0, y>12] [Table 1] It has been found that a catalyst containing copper has high activity in the direct separation reaction of nitrogen oxides.
No. 96) does not necessarily reflect the actual exhaust gas conditions (high SV, H2O
It is difficult to say that it has denitrification activity suitable for oxidation (containing a large amount of O2). Problem to be Solved by the Invention: N in boiler exhaust gas
The catalyst used for Ox removal is usually a V-W/TiO2 system, and ammonia is used as a reducing agent, but it is expensive and requires careful attention to safety, so an alternative reducing agent is desired. ing. Additionally, when removing NOx from automobile exhaust gas, NOx is usually removed using a three-way catalyst (Pt-Rh/Al2O3 system) only at an air-fuel ratio of around 14.6. In high O2 concentration exhaust gas, NO is removed by a three-way catalyst.
x removal is not possible. [0006] Furthermore, as a method for removing diluted NOx in public places such as underground tunnels and parking lots, it has been proposed to adsorb and concentrate diluted NOx using the PSA method, and then directly decompose the concentrated NOx using a catalyst. , O2, and H2O, a problem arises in that a large amount of catalyst is required to remove NOx. [0007] In view of the above-mentioned state of the art, the present invention aims to provide a method for removing NOx without the problems encountered in conventional methods. [Means for Solving the Problems] As a result of intensive studies on the effective use of the copper-containing crystalline silicate catalyst described above, we found that boiler exhaust gas (NO: about 500 ppm
, O2: approx. 10%, H2 O: approx. 10%)
It has been found that organic matter or carbon monoxide acts as an effective reducing agent instead of ammonia using the catalyst for removal. [0009] Furthermore, lean burn engine exhaust gas (O2
It has also become clear that the catalyst effectively acts to remove NOx in the exhaust gas (concentration 1 to 10%), and organic matter and carbon monoxide in the exhaust gas act effectively as reducing agents. Furthermore, when organic matter and carbon monoxide in the exhaust gas are low, it is possible to achieve the desired NOx removal performance by continuously supplying organic matter and carbon monoxide in a stationary engine and depending on the concentration of reducing agent in a mobile engine. There was found. The present invention was completed based on the above findings, and consists of: (1) adding organic matter or carbon monoxide to exhaust gas containing nitrogen oxides, and at a temperature of 250 to 800°C; 1. A method for removing nitrogen oxides from exhaust gas, which comprises contacting a catalyst containing copper in crystalline silicate having a composition expressed by the following formula in terms of molar ratio of oxides. (1.0±0.6)R2 O・[a・M2 O3 ・b
Al2O3 ]・ySiO2 [In the above formula, M: ion of one or more elements selected from the group consisting of group VIII elements, rare earth elements, titanium, vanadium, chromium, niobium, antimony, and gallium,
a+b=1, a≧0, b≧0, y>12]0011
(2) The organic substances to be added are paraffins such as ethane, propane, butane, pentane and hexane, olefins such as ethylene, propylene and butene, dienes such as acetylene and butadiene, alcohols such as methanol, ethanol, propanol and butanol, benzene and toluene. , aromatics of xylene, acetone, ketones of methyl ethyl ketone, dimethyl ether, ethers of diethyl ether, carboxylic acids of acetic acid, formic acid, formaldehyde, aldehydes of acetaldehyde, and methyl formate. Or gasoline, kerosene,
The above (1) characterized in that it is a mixture fuel such as light oil.
) Method for removing nitrogen oxides from exhaust gas. It is. [Function] The crystalline silicate used here is represented by the chemical composition shown in Formula 1 above, has a molecular sieving action, exhibits the X-ray diffraction pattern shown in Table 1 above, and has a unique pentasil type structure. It is. The method of containing copper is ion exchange method,
Both the impregnation method and the salt used include copper acetate, copper chloride, and copper nitrate. The organic substances added before the catalyst include paraffins such as ethane, propane, butane, pentane and hexane, olefins such as ethylene, propylene and butene, dienes such as acetylene and butadiene, methanol, ethanol, Alcohols such as propanol and butanol, aromatics such as benzene, toluene and xylene, ketones such as acetone and methyl ethyl ketone, ethers such as dimethyl ether and diethyl ether, carboxylic acids such as acetic acid and formic acid, aldehydes such as formaldehyde and acetaldehyde. It is also possible to use at least one substance selected from esters such as methyl formate, etc., or a mixture fuel such as gasoline (naphthas), kerosene, light oil, etc. Furthermore, carbon monoxide also acts as an effective reducing agent. [0014] The crystalline silicate catalyst containing copper was
When used for x removal, direct decomposition of NOx (2NO→N2
+O2) works effectively in the reaction, but if organic matter is present, the organic matter is activated by O2 present in the system,
It is believed that active organic compounds are formed. Taking the hydrocarbon C3 H6 as an example, the reaction formula is considered to be as follows. C3 H6 + 3/2O2 → 3CH2O
・(Assuming this is an active organic compound) (a) CH2
O・+O2 → CO2 +H2 O...
・・・・・・・・・ (b) CH2 O・+2N
O→ N2 +CO2 +H2 O ・・・・・・
... (c) [0016] However, CH2O. has not been confirmed at present and is thought to be a partially oxidized reaction intermediate, and this reaction intermediate is the
It is thought that the reaction proceeds competitively between O and O2. Examples (Example 1) (Catalyst Preparation) The crystalline silicate used in the present invention is Na2O.0.5Al2O3.0.5 in a dehydrated state.
A material represented by Fe2 O3 .25SiO2 and having a crystal structure shown in Table 1 was used. Note that this crystalline silicate was prepared as follows. [0018] Water glass No. 3 is dissolved in water to prepare solution A. Further, a solution B is prepared by dissolving ferric sulfate and aluminum sulfate in water. In addition, the number of moles charged in solution A and solution B is 36
Na2 O・[0.5Fe2 O3 ・0.5Al2
O3].25SiO2.1600H2O is prepared as follows, and equal amounts of solution A and solution B are dropped into separate containers to form a gel. An appropriate amount of sulfuric acid is added to the slurry gel produced by neutralization to adjust the pH of the gel to 9. Then, as an organic nitrogen compound, tetrapropylammonium bromide was added 10 times the total number of moles of Fe2O3 and Al2O3, mixed well with the above slurry, and
Place in a liter stainless steel autoclave. While stirring this slurry at 300 rpm,
It was allowed to react for several days. After cooling, the solid content is filtered and the washing water is
The product was thoroughly washed with water until H became 7, dried at 110°C for 12 hours, and calcined at 550°C for 3 hours to obtain crystalline silicate A. The crystalline silicate was subjected to copper ion exchange with a 0.04 molar acetic acid aqueous solution at 20° C. for 48 hours continuously, and after the ion exchange, it was washed with water and dried to prepare powder catalyst A. Carrying C
The u amount was 0.70 mmol. Alumina sol, silica sol, and water were added as binders to this powdered catalyst A, and the mixture was mixed and stirred to prepare a slurry for wash coating. A cordierite monolith base material was immersed in this slurry, and excess slurry was blown off to prepare honeycomb catalyst A. (Activity Evaluation) An activity evaluation test was carried out using the following simulated gas as a diesel exhaust gas denitrification test using Honeycomb Catalyst A. Temperature: 350℃, 450℃ GHSV: 30000h-1 Gas composition: NO: 400ppm, O2: 8%, CO2
: 10%, H2 O: 10%, balance N2 [0020] C2 H4 was uniformly supplied at 1000 ppm (2000 ppm in terms of C1) to the above simulated gas as a reducing agent upstream of the catalyst to carry out a denitrification reaction. The activity evaluation results are shown in Table 2. (Example 2) Using honeycomb catalyst A, the following hydrocarbon was added as a reducing agent, and the activity was evaluated under the same conditions as in Example 1. Reducing agents include ethane, propane, butane, pentane, hexane, propylene, butene, acetylene,
butadiene, methanol, 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, and carbon monoxide were each added at 2000 ppm in terms of C1. The activity evaluation results are shown in Table 2. (Comparative Example 1) Table 2 also shows the activity evaluation results when honeycomb catalyst A was used under the same conditions as Example 1, but no reducing agent was added. [Table 2] (Example 3) When preparing crystalline silicate, cobalt chloride, ruthenium chloride, rhodium chloride, lanthanum chloride, cerium chloride, titanium chloride, vanadium chloride, chromium chloride,
Crystalline silicates B, C, D, E, F, and G were obtained by repeating the same operation as for crystalline silicate A, except that niobium chloride, antimony chloride, and gallium chloride were each added in the same number of moles as Fe2O3 in terms of oxides. ,H,I,J,K,
L was prepared. The composition of these crystalline silicates excluding organic matter is the molar ratio of oxides (in dehydrated form) (H
,Na)2O・(0.5Al2O3 ・0.5M2
O3 )・25SiO2 (here M: Co, Ru, Rh, La, Ce, Ti, V
, Cr, Nb, Sb, Ga...crystalline silicate B to L). [0024] This crystalline silicate was converted into a honeycomb catalyst in the same manner as in Example 1 to prepare honeycomb catalysts B to L. As the activity evaluation conditions for these honeycomb catalysts as described above, C2 H4 was used as a catalyst reducing agent at 1
000 ppm (2000 ppm in terms of C1) was supplied to the front stage of the catalyst, and a denitrification reaction test was carried out. The activity evaluation results are shown in Table 3. [Table 3] [Effects of the Invention] According to the present invention, NOx can be efficiently removed by using a specific crystalline silicate catalyst containing copper and using a specific organic substance and carbon monoxide as a reducing agent. .

Claims (2)

[Claims] Claim 1: Adding organic matter or carbon monoxide to exhaust gas containing nitrogen oxides and producing a crystalline silicate having the composition of the following formula in terms of the molar ratio of oxides at a temperature of 250 to 800°C. A method for removing nitrogen oxides from exhaust gas, the method comprising bringing nitrogen oxides into contact with a catalyst containing copper. (1.0±0.6)R2 O・[a・M2 O3 ・b
Al2O3 ]・ySiO2 [In the above formula, M: ion of one or more elements selected from the group consisting of group VIII elements, rare earth elements, titanium, vanadium, chromium, niobium, antimony, and gallium,
a+b=1, a≧0, b≧0, y>12] [Claim 2]
The organic substances to be added are paraffins such as ethane, propane, butane, pentane and hexane, olefins such as ethylene, propylene and butene, dienes such as acetylene and butadiene, alcohols such as methanol, ethanol, propanol and butanol, benzene, toluene and xylene. Aromatics, ketones such as acetone and methyl ethyl ketone, ethers such as dimethyl ether and diethyl ether,
2. The fuel according to claim 1, characterized in that the fuel is at least one substance selected from the group consisting of acetic acid, carboxylic acids such as formic acid, formaldehyde, aldehydes such as acetaldehyde, and methyl formate, or a mixture fuel such as gasoline, kerosene, and light oil. Method for removing nitrogen oxides from exhaust gas.