JPH04256420A - Method for reducing and removing nitrogen oxides - Google Patents

Abstract

PURPOSE:To effectively reduce and remove nitrogen oxide especially even at a low temp. by bringing the waste combustion gas incorporating nitrogen oxides, hydrocarbon and oxygen into contact with H-type ferrilite. CONSTITUTION:Exhausting combustion gas incorporating nitrogen oxides, hydrocarbons and oxygen are brought into contact with the H-type ferrilite. The H-type ferrilite is a zeolite having about 10-20mol. ratio of SiO2/Al2O3, and both of the natural or the synthetic ferrilite are usable. Also, the ferrilite may be usable so that the mol. ratio of SiO2/Al2O3 is increased by treating with mineral acid, etc., to remove aluminum. In the case of using this ferrilite as a catalyst, metallic cation therein is exchanged to hydrogen ion and converted to H-type. The treatment is preferable so that the space velocity (volumetric base)of the exhaust gas is 1000-50000hr<-1> and temp. is 100-700 deg.C. By this means the exhaust gas from the boiler, automobile engine, etc., are effectively purified to effectively reduce and remove nitrogen oxides especially even at a low temp. such as <=400 deg.C.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention relates to a method for treating exhaust gas containing nitrogen oxides emitted from boilers, automobile engines, etc., and more specifically, the present invention relates to a method for treating exhaust gas containing nitrogen oxides discharged from boilers, automobile engines, etc. This invention relates to a method for reducing and removing .

0002

[Prior Art] As a method for removing nitrogen oxides from exhaust gas emitted from boilers, automobile engines, etc., there is a selective catalytic reduction method in which the exhaust gas is treated with ammonia in the presence of a catalyst, and a selective catalytic reduction method in which exhaust gas is passed through a catalyst to remove nitrogen oxides. Non-selective catalytic reduction methods that reduce carbon monoxide and hydrocarbons by combustion have been put into practical use. Furthermore, for example, JP-A-60-125,250
The publication proposes a method using copper ion-exchanged zeolite as a catalyst that can directly catalytically decompose nitrogen oxides in the absence of a reducing agent.

[0003] In addition, a catalyst in which base metals such as Cu are contained in zeolite has been proposed as a catalyst that can selectively reduce nitrogen oxides using reducing components such as unburned carbon monoxide and hydrocarbons even in the presence of excess oxygen. (Unexamined Japanese Patent Publication No. 1983-10)
0,919, etc.). In addition, Hamada et al.
We have found that 5- and H-type mordenite are effective in reducing nitrogen oxides by unburned hydrocarbons even under oxygen excess (Applied Catalysis).
Catalysis), Volume 64 (1990) L
1-L4 pages).

However, even with these proposed methods using catalysts, the reduction and removal of nitrogen oxides is insufficient, and in particular, the removal ability at low temperatures required when a car is idling is insufficient. However, it has not been put into practical use yet.

[0005]

[Problems to be Solved by the Invention] An object of the present invention is to efficiently purify exhaust gas emitted from internal combustion engines such as boilers, automobile engines, etc., especially diesel engines, without using reducing agents such as ammonia. The present invention provides a method for reducing and removing nitrogen oxides that is particularly efficient even at low temperatures.

[0006]

[Means for Solving the Problems] The present inventor has completed the present invention as a result of intensive study on the above-mentioned problems. That is, the present invention provides a method for reducing and removing nitrogen oxides, which is characterized by bringing combustion exhaust gas containing nitrogen oxides, hydrocarbons, and oxygen into contact with H-type ferrierite.

The present invention will be explained in more detail below. The nitrogen oxide reduction and removal catalyst used in the method of the present invention must be H-type ferrierite. Ferrierite is "zeolite molecular sieves" (Z
EOLITE MOLECULAR SIEVES
), Donald W Breck (DONALD
W. BRECK), (1974) p. 146 Ta
ble2.31 and page 358 Table4.45
It is a zeolite described in SiO2 /Al
The zeolite usually has a 2 O3 molar ratio of 10 to 20. In the method of the present invention, both natural and synthetic ferrierite can be used. Further, it can be used by subjecting it to dealumination treatment using a mineral acid or the like to increase the SiO2/Al2O3 molar ratio.

[0008] Raw material ferrierite usually contains Na, K
Metal cations such as are present at ion exchange sites. In order to use it as a catalyst of the present invention, it is necessary to exchange these metal cations with H ions to form the H type. The method for exchanging H ions is not particularly limited, and a general method can be adopted, that is, treatment with a mineral acid and direct H ion exchange, or ammonium treatment followed by calcination.

[0009] Hydrochloric acid, sulfuric acid, nitric acid, carbonic acid, etc. can be used as the mineral acid, and methods such as mixing raw material ferrierite in an aqueous solution containing mineral acid, stirring, and washing are applied to treat with mineral acid. can. To treat with ammonium, raw ferrierite is mixed into an aqueous solution containing an ammonium compound,
Methods such as stirring and washing are applied. As the ammonium compound, ammonium chloride, ammonium nitrate, ammonium sulfate, ammonia water, etc. are used. After the ammonium treatment, H-type ferrierite can be obtained by firing at 500°C to 700°C.

The amount of mineral acid or ammonium compound added is preferably 0.5 to 10 equivalents to Al in the zeolite. If the amount is less than 0.5 times the equivalent amount, the amount of H ions introduced into the ion exchange site will be reduced, and if it is more than 10 times the amount, the corresponding effect will not be obtained. The concentration of zeolite slurry during mineral acid treatment and ammonium treatment is
It is preferably 1% to 50% by weight, which is usually adopted.

[0011] Furthermore, the processing conditions are 10 to 1, which is usually carried out.
Preferably, the temperature is 00°C and the time is 1 hour to 5 days. At a temperature of less than 10°C and a time of less than 1 hour, the amount of H ions introduced into the ion exchange site decreases, and the
If the temperature exceeds ℃ or the time exceeds 5 days, the corresponding effect will not be obtained. The ion exchange treatment can be repeated as necessary. The crystal structure of the catalyst used in the present invention is not essentially different before and after ion exchange.

The H-type ferrierite used in the present invention can also be used by mixing it with a binder such as a clay mineral and forming it into a cylindrical, spherical, or honeycomb shape. Alternatively, H-type ferrierite can be molded in advance and the molded product can be subjected to H ion exchange. As the binder used when molding H-type ferrierite, clay minerals such as kaolin, attabulgite, montmorillonite, bentonite, allophane, and sepiolite are preferred.

In the method of the present invention, it is essential to bring the combustion exhaust gas containing nitrogen oxides, hydrocarbons and oxygen into contact with H-type ferrierite. Nitrogen oxides include NO, NO2, N2O, N2O2, and the like. Although the type of hydrocarbon is not particularly limited, the effect of the method of the present invention is noticeable in combustion exhaust gas containing a large amount of hydrocarbons having 6 or less carbon atoms.

[0014] The concentration of these component gases in the combustion exhaust gas to be treated is not particularly limited, but usually 10 to 10,000 ppm for nitrogen oxides and 10 to 1 ppm for hydrocarbons.
0,000 ppm, and oxygen is 0.1-15%. In particular, nitrogen oxides can be efficiently removed even when exhaust gas contains oxygen in excess of the amount of oxygen required to completely oxidize reducing components such as hydrocarbons contained in the exhaust gas. Further, nitrogen oxides can be reduced and removed by further adding hydrocarbons to the exhaust gas. The space velocity and temperature of the exhaust gas during reduction and removal are not particularly limited, but
Space velocity (volume basis) 1,000-500,000hr
-1, the temperature is preferably 100°C to 700°C.

[0015]

Effects of the Invention According to the method for reducing and removing nitrogen oxides of the present invention, nitrogen oxides can be efficiently reduced and removed from combustion exhaust gas in which hydrocarbons and oxygen coexist.
The removal effect is high even at low temperatures below.

[Examples] The present invention will be explained in more detail with reference to Examples below. However, the present invention is not limited to these examples.

Example 1 SiO2/Al2O3 molar ratio of (Na,K) 12
Type Ferrierite 100g, 0.2mol/L
The mixture was added to 2 L of an aqueous ammonium nitrate solution and stirred at room temperature for a day and night, then washed and dried to obtain NH4 type ferrierite. Next, an activity test of the obtained catalyst was conducted.

[0017] The obtained catalyst was press-molded and then pulverized to a size of 12 to 20 mesh, and 0.5 g of the catalyst was placed in a flow reactor. The temperature was gradually raised under the flow of He gas, and then treatment was performed at 500° C. for 5 hours to obtain H-type ferrierite. After cooling, NO: 1,000ppm, C2H
He gas containing 250 ppm of O2 and 2% of O2 was flowed at a rate of 150 cc/min, and the steady-state purification activity at each temperature was measured. The space velocity at this time is 9,000h
It was r-1. Steady-state purification activity was evaluated as the conversion rate of NO to nitrogen after holding at each temperature for 2 hours.

The conversion rate to nitrogen is the conversion rate to N2=2×(N2)out/(NO)
in(N2)out: N2 concentration at the catalyst layer outlet (NO) in: NO concentration at the catalyst layer inlet. The results obtained are shown in Table 1.

[Table 1]

Comparative Example 1 Na-type ZSM with a SiO2/Al2O3 molar ratio of 23
-5 100g was added to 1L of 0.2mol/L ammonium nitrate aqueous solution, stirred at room temperature all day and night, washed and dried, and NH4 type ZSM-5 (comparative catalyst 1)
I got it.

Comparative Example 2 100 g of Na-type mordenite with a SiO2 /Al2 O3 molar ratio of 11 was added to 2 L of 0.2 mol/L ammonium nitrate aqueous solution, stirred all day and night at room temperature, washed and dried to obtain NH4-type mordenite ( Comparative catalyst 2) was obtained.

Comparative Example 3 (Na,K) with SiO2 /Al2O3 molar ratio of 12
type ferrierite 100g, 0.1mol/L
After adding to 2 L of copper acetate aqueous solution, ammonia water was added to adjust the pH to 7.5. After stirring at room temperature all day and night, the mixture was washed and dried to obtain Comparative Catalyst 3. The exchange rate of Cu is 1
It was 30%.

Comparative Example 4 In the same manner as in Example 1, an activity test was conducted on Comparative Catalysts 1 to 3 and the (Na, K) type ferrierite used in Example 1. The results obtained are shown in Table 2.

[Table 2]

As is clear from the Examples and Comparative Examples, according to the method for reducing and removing nitrogen oxides of the present invention, nitrogen oxides can be efficiently reduced and removed from combustion exhaust gas, especially at low temperatures of 400° C. or lower. Its removal effect is high.

Claims (3)

[Claims] 1. A method for reducing and removing nitrogen oxides, which comprises bringing combustion exhaust gas containing nitrogen oxides, hydrocarbons and oxygen into contact with H-type ferrierite. 2. H-type ferrierite is obtained by treating ferrierite with a mineral acid or ammonium compound in an amount of 0.5 to 10 times equivalent based on Al in the ferrierite.
The nitrogen oxide reduction and removal method described. [Claim 3] Combustion exhaust gas has a space velocity (volume basis)
1,000~50,000hr-1, temperature 100℃~7
The method for reducing and removing nitrogen oxides according to claim 1 or 2, wherein the method is brought into contact with H-type ferrierite at 00°C.