JPH04338233A - Adsorbent for nox and method for removing nox by using this adsorbent - Google Patents

Abstract

PURPOSE:To obtain the adsorbent which has the excellent capacity to adsorb the NOx and more particularly nitrogen dioxide in exhaust gases and is not affected by the moisture in the exhaust gases by incorporating an alumina component and metal oxide components, such as manganese and nickel, into this adsorbent. CONSTITUTION:This adsorbent contains 30 to 99.5wt.%, more preferably 40 to 99wt.% alumina as the component and 70 to 0.5wt.%, more preferably 60 to1wt.% metal oxides selected from the manganese, nickel, cobalt, and lanthanum as the components. The specific surface area is specified to >=50cm<2>/g, more preferably >=80m<2>/g and the pore volume to >=0.3cc/g, more preferably >=0.4cc/g. The resulted adsorbent has the excellent capacity to adsorb the NOx, and more particularly low-concn. nitrogen dioxide in the exhaust gases and removes these materials without being affected by the moisture in the exhaust gases.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adsorbent for nitrogen oxides and a method for removing nitrogen oxides using this adsorbent. More specifically, the present invention is directed to low concentration nitrogen oxides (NOx: nitrogen monoxide and nitrogen dioxide) contained in exhaust gas.
In particular, the present invention relates to an adsorbent suitable for removing nitrogen dioxide and a method for efficiently adsorbing and removing low concentration nitrogen oxides in exhaust gas, particularly nitrogen dioxide, using this adsorbent.

0002

[Prior Art] Conventionally, a method for removing nitrogen oxides from a fixed nitrogen oxide source such as a boiler uses ammonia as a reducing agent to selectively reduce nitrogen oxides to harmless nitrogen. The catalytic reduction method, which converts it into water, is widely used as the most economical method.

By the way, the concentration of nitrogen oxides contained in ventilation gas or the atmosphere in road tunnels, sheltered roads, deep underground spaces, road intersections, etc., and in gases emitted from combustion equipment used in homes, etc. , 5
The concentration of nitrogen oxides is about ppm, which is extremely low compared to the nitrogen oxide concentration in boiler exhaust gas, the gas temperature is room temperature, and the amount of gas is enormous. Therefore, in order to efficiently remove nitrogen oxides by applying the above catalytic reduction method to the ventilation gas of a road tunnel, for example, the temperature of this ventilation gas must be set at 300°C.
Since it is necessary to do the above, and as a result, a large amount of energy is required, it is economically problematic to apply the above catalytic reduction method as it is. Under these circumstances, gases with a low concentration of nitrogen oxides, for example, about 5 ppm or less, such as ventilation gas from road tunnels as mentioned above (in the present invention, these ventilation gases, atmospheric air, etc. are collectively referred to as "exhaust gas"). ) is desired to efficiently remove nitrogen oxides from

[0004] As an adsorbent and remover for low concentration nitrogen oxides, an adsorbent in which copper chloride is supported on zeolite is disclosed in JP-A-1-29.
It is disclosed in Japanese Patent No. 9642. However, according to studies conducted by the present inventors, it has been found that this adsorbent is easily affected by moisture in the exhaust gas, and its ability to adsorb nitrogen oxides is significantly reduced when the humidity of the exhaust gas is high.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide an adsorbent that has excellent ability to adsorb low concentration nitrogen oxides contained in exhaust gas.

Another object of the present invention is to provide an adsorbent that is not affected by the humidity of the exhaust gas and has excellent adsorption ability for particularly low concentration nitrogen dioxide in the exhaust gas.

Another object of the present invention is to provide a method for efficiently adsorbing and removing nitrogen oxides, particularly nitrogen dioxide, in exhaust gas using an adsorbent.

[0008]

[Means for Solving the Problems] According to the research conducted by the present inventors, an adsorbent containing alumina and an oxide of at least one metal selected from manganese, nickel, cobalt, and lanthanum in a specific ratio is used. It has been found that the above objective can be achieved by doing so.

One of the aspects of the present invention is that (A) alumina 30-9
9.5% by weight and (B) 70 to 0.5% by weight of an oxide of at least one metal selected from manganese, nickel, cobalt and lanthanum. Another invention comprises (A) 30-99.5% by weight alumina and (B) at least one selected from manganese, nickel, cobalt and lanthanum.
The present invention relates to a method for removing nitrogen oxides, which comprises bringing the exhaust gas into contact with an adsorbent containing 70 to 0.5% by weight of a metal oxide to adsorb and remove nitrogen oxides from the exhaust gas.

The present invention will be explained in detail below.

The adsorbent of the present invention comprises alumina as the component (A) and an oxide of at least one metal selected from manganese, nickel, cobalt and lanthanum as the component (B). The ratio of ingredients is 30-9
The proportion of component (B) is 9.5% by weight, preferably 40 to 99% by weight, and the proportion of component (B) is 70 to 0.5% by weight, preferably 60 to 1% by weight.

If the proportion of component (A) is less than 30% by weight, the raw material cost of the adsorbent will increase and the nitrogen oxide adsorption capacity will decrease, while if it exceeds 99.5% by weight, the nitrogen oxide adsorption capacity will decrease. It is not desirable because it decreases rapidly.

The methods for preparing the adsorbent of the present invention include the following methods, but the present invention is not limited to these methods.

The starting materials for each component used in this preparation are appropriately selected from oxides, hydroxides, ammonium salts, nitrates, sulfates, oxalates, halides, etc. of each metal.

(1) Alumina powder is impregnated in an aqueous solution containing at least one of manganese, nickel, cobalt and lanthanum as component (B), evaporated and dried, and then calcined at 300 to 800°C. How to mold. Note that the alumina powder may be molded in advance and this molded body may be impregnated.

(2) Add an aqueous solution containing at least one of manganese, nickel, cobalt, and lanthanum as component (B) to an aqueous solution of aluminum nitrate, aluminum sulfate, etc. to make a homogeneous solution, and then add ammonia, Co-precipitate by adding an alkaline solution such as sodium hydroxide, and wash and dry the obtained precipitate.
A method of firing at 0 to 800°C and then molding.

(3) After adding alumina powder to an aqueous solution containing at least one of manganese, nickel, cobalt, and lanthanum as component (B) to form a slurry, add ammonia, sodium hydroxide, etc. A method in which component (B) is deposited on alumina powder by adding an alkaline solution, washed and dried, then fired at 300 to 800°C, and then molded.

The shape of the adsorbent of the present invention is not particularly limited, and may be cylindrical, cylindrical, spherical, plate-like, honeycomb-like,
Other integrally molded ones can be selected as appropriate.

The specific surface area (BET surface area) of the adsorbent of the present invention is 50 m2/g or more, preferably 80 m2/g or more, and the pore volume is 0.3 cc/g or more, preferably 0.4 cc/g. g or more.

[0020] In the method for removing nitrogen oxides of the present invention, there is no particular restriction on the method of contacting the above-mentioned adsorbent with the exhaust gas, and the method is usually carried out by introducing the exhaust gas into a layer made of the above-mentioned adsorbent. In addition, the processing conditions at this time cannot be specified as they vary depending on the properties of the exhaust gas, but the temperature of the gas to be supplied is usually 0 to 100°C, especially 0 to 5°C.
A range of 0°C is preferred. In addition, the space velocity (SV) of the supplied gas is usually 500 to 50,000 hr￣1 (ST
P), especially from 1000 to 20000hr￣1 (ST
The range P) is preferred.

The adsorbent of the present invention is particularly effective in adsorbing and removing nitrogen dioxide among nitrogen oxides. Therefore, when removing nitrogen oxides from exhaust gas, if nitrogen monoxide is oxidized in advance and converted to nitrogen dioxide, and then brought into contact with the adsorbent of the present invention, nitrogen oxides from exhaust gas can be removed even more effectively. Can be removed. Of course, the exhaust gas may be directly brought into contact with the adsorbent of the present invention to adsorb and remove mainly nitrogen dioxide among nitrogen oxides.

[0022] In order to convert the above-mentioned nitrogen monoxide into nitrogen dioxide, for example, ozone generated by an ozonizer can be added to oxidize the nitrogen monoxide, or alternatively, the exhaust gas can be brought into contact with an oxidation catalyst to oxidize the nitrogen monoxide. Oxidation of nitrogen oxide can also be carried out.

[0023]

Effects of the Invention The adsorbent of the present invention has an excellent ability to adsorb nitrogen oxides in exhaust gas, especially nitrogen dioxide, and is not affected by moisture in exhaust gas.

[0024] When the adsorbent of the present invention is used, at room temperature,
It can efficiently remove low concentration nitrogen oxides, especially nitrogen dioxide, contained in exhaust gas, and can be used for a long period of time because it is not affected by the humidity of exhaust gas.

[0025] After nitrogen monoxide in the exhaust gas is oxidized in advance to convert it into nitrogen dioxide, the nitrogen oxides in the exhaust gas can be more effectively removed by contacting this exhaust gas with the adsorbent of the present invention. .

[0026]

[Examples] The present invention will be explained in more detail below with reference to Examples.

Example 1 Manganese nitrate (Mn(NO3)2.6H2O) 165g
and aluminum nitrate (Al2(NO3)3.9H2
O) 3310g to 6 liters of water (hereinafter expressed as L)
to make a homogeneous aqueous solution. 10% in this aqueous solution
An aqueous sodium hydroxide solution was gradually added dropwise while stirring well until the pH reached 7, and then left to mature for 2 hours.

The coprecipitate thus obtained was separated by filtration, thoroughly washed with water, dried at 120°C for 10 hours, and then calcined at 550°C for 5 hours to form Al2O3-
MnO2 powder was obtained.

[0029] After adding an appropriate amount of water to this powder and mixing it thoroughly with a kneader, it was molded into a shape with a diameter of 4 mm and a length of 5 m using an extrusion molding machine.
It was molded into a pellet shape of m. These pellets were heated to 100°C.
After drying at 550° C. for 10 hours, it was fired at 550° C. for 5 hours in an air atmosphere.

The composition of the adsorbent thus obtained is:
Weight ratio as oxide: Al2O3:MnO2=90
:10. In addition, the specific surface area of this adsorbent is 270
m2/g, and the pore volume was 0.51 cc/g.

Example 2 γ-Alumina powder manufactured by Sumitomo Chemical Co., Ltd. (trade name A-
11) 500 g was added to 1 L of an aqueous manganese nitrate solution containing 55.55 g of manganese dioxide (MnO2) to form a slurry. After evaporating water on a hot bath, this was dried at 100°C for 10 hours, and then calcined at 500°C for 3 hours to obtain Al2O3-MnO2 powder.

[0032] The above powder was then treated in the same manner as in Example 1 to obtain an adsorbent. The composition of this adsorbent is Al2O3:MnO2=90:10 in weight ratio as an oxide.
The specific surface area was 130 m2/g, and the pore volume was 0.50 cc/g.

Examples 3 to 5 Example 1 was repeated except that nickel nitrate (Example 3), cobalt nitrate (Example 4) and lanthanum nitrate (Example 5) were used instead of manganese nitrate. The adsorbent was obtained by the same method. The composition (weight ratio as oxide), specific surface area, and pore volume of these adsorbents were as follows.

[0034] Al2O3:NiO=90:10 Specific surface area: 260m2/g, pore volume: 0.49cc/gAl2
O3:CoO=90:10 Specific surface area: 253 m2/g, pore volume: 0.50 cc/
gAl2O3:La2O3=90:10 Specific surface area: 25
6 m2/g, pore volume: 0.48 cc/g Example 6 The nitrogen oxide adsorption performance (NOx removal rate) of the adsorbents obtained in Examples 1 to 5 was evaluated by the following method.

[0035] 72 mL of the adsorbent was filled into a glass reaction tube having an inner diameter of 30 mm. After adding ozone generated by an ozonizer to a synthesis gas having the composition shown below to convert nitrogen monoxide into nitrogen dioxide, this synthesis gas was introduced into the adsorbent layer under the following conditions.

Synthesis gas composition Nitric oxide (NO): 5pp
m, H2O: 2.5% by volume, remaining: air processing conditions Gas amount: 6NL/min, processing temperature: 25°C, space velocity (SV
): 5000hr￣1 (STP), gas humidity: 85%R
H After 10 and 20 hours have elapsed since the introduction of the above synthesis gas, the concentration of nitrogen dioxide (NO2) in the synthesis gas at the inlet and outlet of the adsorbent layer was measured using a chemical color NOx meter, and the NOx concentration was measured according to the following formula. The removal rate was calculated.

NOx removal rate (%) = [(Inlet NO2 concentration - Outlet NO2 concentration)/(Inlet NO2 concentration)] x 100 The obtained results are shown in Table 1.

[0038]

[Table 1]

Example 7 According to the method of Example 1, adsorbents were prepared in which the contents of manganese oxide, cobalt oxide, nickel oxide, and lanthanum oxide were varied.

[0040] Regarding these adsorbents, the NOx removal rates after 10 hours were determined in the same manner as in Example 6, and the results are shown in Table 2.
It was shown to.

[0041]

[Table 2]

From the results in Tables 1 and 2, it can be seen that the adsorbent of the present invention has excellent adsorption performance for nitrogen oxides and is suitable for adsorption and removal of low concentration nitrogen oxides in exhaust gas.

[0043]

Claims (4)

[Claims] Claim 1: (A) Alumina 30-99.5% by weight
and (B) oxide 70 of at least one metal selected from manganese, nickel, cobalt and lanthanum.
A nitrogen oxide adsorbent comprising 0.5% by weight. [Claim 2] Specific surface area (BET surface area) is 50 m2
The adsorbent for nitrogen oxides according to claim 1, which has a pore volume of 0.3 cc/g or more and a pore volume of 0.3 cc/g or more. Claim 3: (A) Alumina 30-99.5% by weight
and (B) oxide 70 of at least one metal selected from manganese, nickel, cobalt and lanthanum.
A method for removing nitrogen oxides, which comprises bringing the exhaust gas into contact with an adsorbent containing 0.5% by weight to adsorb and remove nitrogen oxides from the exhaust gas. 4. Claim 3, wherein the exhaust gas is brought into contact with the adsorbent after nitrogen monoxide in the exhaust gas is oxidized to nitrogen dioxide.
The method for removing nitrogen oxides described in .