JPH05123571A - Adsorbent of nitrogen oxide and removal of nitrogen oxide using the same - Google Patents

Abstract

PURPOSE:To obtain a deodorant efficiently removing nitrogen oxide, especially, nitrogen dioxide by compounding alumina, manganese oxide and alkali metal oxide and/or alkaline earth metal oxide in a specific ratio as the adsorbent of nitrogen oxide. CONSTITUTION:Alumina of 10-99wt.%, 70-0.5wt.% of manganese oxide and 20-0.5wt.% of alkali metal oxide and/or alkaline earth metal oxide are compounded to be formed into a desired shape. The specific surface area (BET surface area) of this adsorbent is 50m<2>/g or more and the pore volume thereof is set to 0.3cc/g or more. Since this adsorbent is effective for adsorbing and removing nitrogen oxide, especially, nitrogen dioxide, nitrogen monoxide may be preliminarily oxidized to nitrogen dioxide before brought into contact with the adsorbent.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Regarding the method of removing nitrogen oxides from a fixed type nitrogen oxides generation source such as a boiler, conventionally, ammonia has been used as a reducing agent to selectively reduce the nitrogen oxides to produce harmless nitrogen oxides. The catalytic reduction method of converting into water is widely used as the most economical method.

By the way, the concentration of nitrogen oxides contained in ventilation gas or atmosphere in road tunnels, sheltered roads, deep underground spaces, road intersections, etc., and gases discharged from combustion equipment used at home is 5,
It is about ppm, which is extremely lower than the nitrogen oxide concentration in the boiler exhaust gas, the gas temperature is room temperature, and the amount of gas is enormous. Therefore, for example, in order to efficiently remove nitrogen oxides by applying the above catalytic reduction method to the ventilation gas of a road tunnel, the temperature of this ventilation gas is set to 300 ° C.
Since it is necessary to do the above, and as a result, a large amount of energy is required, there is an economical problem in applying the above catalytic reduction method as it is.

Under these circumstances, a gas having a low concentration of nitrogen oxides, such as the ventilation gas for the road tunnel as described above, for example, about 5 ppm or less (in the present invention, these ventilation gases, the atmosphere, etc. are referred to as "exhaust gas"). It is desired to remove nitrogen oxides efficiently.

As an adsorbent / removal agent 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 the study by the present inventors, it has been found that this adsorbent is easily affected by the water content in the exhaust gas, and the nitrogen oxide adsorption capacity is significantly reduced when the humidity of the exhaust gas is high.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an adsorbent having an excellent adsorbing ability for a low concentration of nitrogen oxide contained in exhaust gas.

Another object of the present invention is to provide an adsorbent having an excellent ability to adsorb a particularly low concentration of nitrogen dioxide in the exhaust gas without being affected by the humidity of 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 by using an adsorbent.

[0009]

According to the studies by the present inventors, an adsorbent containing alumina, manganese oxide, and an alkali metal oxide and / or an alkaline earth metal oxide in a specific ratio is used. The inventors have found that the above-mentioned objects can be achieved by doing so, and completed the invention.

One aspect of the present invention is to add (A) alumina to 10
99% by weight, 70 to 0.5% by weight of (B) manganese oxide, and 20 to 0.5% by weight of (C) alkali metal oxide and / or alkaline earth metal oxide It is an adsorbent for nitrogen oxides.

Another aspect of the present invention is to use (A) alumina in an amount of 10 to 99.
% By weight, 70 to 0.5% by weight of (B) manganese oxide,
And (C) an exhaust gas is brought into contact with an adsorbent containing 20 to 0.5% by weight of an alkali metal oxide and / or an alkaline earth metal oxide to adsorb and remove nitrogen oxides. This is a method for removing nitrogen oxides.

[0012] Preferably, a method of removing nitrogen oxides by previously oxidizing nitrogen monoxide in the exhaust gas into nitrogen dioxide and then contacting it with an adsorbent. Hereinafter, the present invention will be described in detail.

The adsorbent of the present invention comprises alumina as the component (A), manganese oxide as the component (B), and an alkali metal oxide and / or an alkali metal oxide as the component (C). The proportion of the component (A) is 15 to 99% by weight, preferably 20 to 98% by weight, and the proportion of the component (B) is 70 to 0.5% by weight, preferably 60 to 1% by weight. The proportion of the component (C) is 20 to 0.5% by weight, preferably 15 to 1% by weight.

When the ratio of the component (A) is less than 15% by weight, the nitrogen oxide adsorption capacity is lowered, and when it exceeds 99% by weight, the nitrogen oxide adsorption capacity is similarly decreased. descend. When the proportion of the component (B) exceeds 70% by weight, the raw material cost of the adsorbent increases, and the nitrogen oxide adsorption capacity also decreases, while when it is less than 0.5% by weight, the nitrogen oxide adsorption capacity rapidly increases. It is not preferable because If the ratio of the component (C) is less than 0.5% by weight, the effect of attachment is hardly recognized, and if it exceeds 20% by weight, the nitrogen oxide adsorption capacity is lowered, which is not preferable.

The starting materials for the above components are oxides, hydroxides, ammonium salts, nitrates, sulfates of the respective metals,
It is appropriately selected from acetate, oxalate, halide and the like.

The method for preparing the adsorbent of the present invention will be exemplified below, but the method for preparing the adsorbent according to the present invention can be appropriately changed depending on the starting materials of the respective components, and the present invention is limited to these methods. It is not something that will be done.

(1) An aqueous solution containing manganese as the component (B) and an alkali metal and / or an alkaline earth metal as the component (C) is impregnated with the alumina powder (A), evaporated and dried. After that, bake at 300 to 800 ° C,
Then, a method of molding into a desired shape. It is also possible to preform the alumina powder and impregnate this compact with an aqueous solution containing the components (A) and (C).

(2) After adding an aqueous solution containing manganese as the component (B) and (C) an alkali metal and / or an alkaline earth metal to an aqueous solution of aluminum nitrate, aluminum sulfate, etc., a uniform solution is obtained. Then, an alkaline solution such as ammonia or sodium hydroxide was added thereto to coprecipitate, and the resulting precipitate was washed and dried, and then 3
A method of firing at 00 to 800 ° C. and then molding into a desired shape.

(3) Alumina powder is added to an aqueous solution containing manganese as the component (B) and (C) an alkali metal and / or an alkaline earth metal to form a slurry, and then ammonia, An alkaline solution such as sodium hydroxide is added to deposit the components (B) and (C) on the alumina powder, which are washed and dried,
A method of firing at 300 to 800 ° C. and then molding into a desired shape.

The shape of the adsorbent is not particularly limited, and can be appropriately selected from a columnar shape, a cylindrical shape, a spherical shape, a plate shape, a honeycomb shape, and other integrally molded shapes.
The specific surface area (BET surface area) of the adsorbent is 50 m ² / g or more, preferably 80 m ² / g or more, and the pore volume is 0.3 cc / g or more, preferably 0.4 cc / g or more. ..

The method of contacting the adsorbent with the exhaust gas in the method for removing nitrogen oxides of the present invention is not particularly limited, and the exhaust gas is usually introduced into the layer composed of the adsorbent. Further, the treatment conditions at this time cannot be unconditionally specified because it depends on the properties of the exhaust gas, but the temperature of the supplied gas is usually 0 to 100 ° C., particularly 0 to 5 ° C.
The range of 0 ° C is preferred. The space velocity (SV) of the supplied gas is usually 500 to 50000 hr ~ ¹ (ST
P), especially 1000 to 20000 hr to ¹ (ST
The range of P) is preferable.

The adsorbent of the present invention is particularly effective in adsorbing and removing nitrogen dioxide among nitrogen oxides. Therefore, when removing the nitrogen oxides in the exhaust gas, the nitrogen oxides in the exhaust gas can be removed even more effectively if the nitric oxide is pre-oxidized and converted to nitrogen dioxide and then contacted with an adsorbent. You can Of course, the exhaust gas may be directly contacted with the adsorbent of the present invention to adsorb and remove mainly nitrogen dioxide among nitrogen oxides.

In order to convert the nitric oxide into nitrogen dioxide, for example, ozone generated by an ozonizer may be added to oxidize nitric oxide. Alternatively, the exhaust gas may be brought into contact with an oxidation catalyst to remove nitrogen monoxide. It is also possible to oxidize nitric oxide.

[0024]

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

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

The nitrogen oxides in the exhaust gas can be removed more effectively by contacting the exhaust gas with the adsorbent of the present invention after the nitric oxide in the exhaust gas is previously oxidized to convert it to nitrogen dioxide. ..

[0027]

EXAMPLES The present invention will be described in more detail below with reference to examples.

(Example 1) Manganese nitrate [Mn (N
O _{3) 2} · 6H ₂ O] 495g and aluminum nitrate _{[Al 2 (NO 3) 3 ·} 9H 2 O ] 1196g and calcium acetate _{Ca (CH 3 COO) 2 ·} H 2 O ] was 79g water 6
It was dissolved in liter (hereinafter referred to as L) to obtain a uniform aqueous solution. A 10% sodium hydroxide aqueous solution was gradually added dropwise to this aqueous solution while stirring well, and the solution was added until the pH reached 7, and then allowed to stand for aging for 2 hours.

The coprecipitate thus obtained was separated by filtration, washed well with water, dried at 120 ° C. for 10 hours, and then calcined at 550 ° C. for 5 hours to give Al ₂ O ₃ -M.
An nO ₂ —CaO powder was obtained.

An appropriate amount of water was added to this powder, which was well mixed with a kneader, and then an extruder was used to obtain a diameter of 4 mm and a length of 5 m.
m was molded into pellets. These pellets at 100 ℃
After being dried for 10 hours at 550 ° C., it was baked at 550 ° C. for 5 hours in an air atmosphere.

The composition of the adsorbent thus obtained is
Al ₂ O ₃ : MnO ₂ : CaO in a weight ratio as an oxide
= 65: 30: 5. The specific surface area of this adsorbent is 180 m ² / g, and the pore volume is 0.48 c.
It was c / g.

(Example 2) γ- manufactured by Sumitomo Chemical Co., Ltd.
Alumina powder (trade name A-11) aqueous solution 500g and which is dissolved manganese nitrate _{[Mn (NO 3) 2 · 6H} 2 O ] 762g and calcium acetate _{[Ca (CH 3 COO) 2 ·} H 2 O ] 121g Add to 1 liter to make a slurry. After evaporating the water on a warm bath, this is heated to 100 ° C.
At 10 ° C for 10 hours and then at 500 ° C for 3 hours.
to obtain a l ₂ O ₃ -MnO ₂ -CaO powder.

Then, the above powder was treated in the same manner as in Example 1 to obtain an adsorbent. The composition of this adsorbent is Al ₂ O ₃ : MnO ₂ : CaO = 6 by weight ratio as an oxide.
5: 30: 5 and its specific surface area is 110 m ² /
g, the pore volume was 0.45 cc / g.

Examples 3 to 7 An adsorbent was obtained in the same manner as in Example 1 except that magnesium acetate and barium acetate were used instead of calcium acetate. Further, an adsorbent in which the contents of calcium oxide, magnesium oxide and barium oxide in the adsorbent were changed was prepared by the same method as in Example 1. The composition (weight ratio as an oxide), specific surface area, and pore volume of these adsorbents are as shown in Table 1.

[0035]

[Table 1]

Examples 8 to 11 An adsorbent was obtained in the same manner as in Example 2 except that sodium nitrate and potassium nitrate were used instead of calcium acetate. Further, an adsorbent in which the contents of sodium oxide and potassium oxide in the adsorbent were changed was prepared by the same method as in Example 2. The composition (weight ratio as an oxide), specific surface area and pore volume of these adsorbents are as shown in Table 2.

[0037]

[Table 2]

Example 12 With respect to the adsorbents obtained in Examples 1 to 11, the nitrogen oxide adsorption performance (NOx removal rate) was evaluated by the following method.

72 mL of the adsorbent was filled in a glass reaction tube having an inner diameter of 30 mm. After ozone generated by an ozonizer was added to the synthesis gas having the following composition to convert nitric oxide into nitrogen dioxide, the synthesis gas was introduced into the adsorbent layer under the following conditions.

Synthetic gas composition Nitric oxide (NO): 5 ppm, H ₂ O: 2.5% by volume, remainder: Air treatment conditions Gas amount: 6 NL / min, treatment temperature: 25 ° C., space velocity (SV): 5000 hr ~ ¹ (STP), gas humidity: 85
% RH After 10 hours and 20 hours have passed since the synthesis gas was introduced, the nitrogen dioxide (NO ₂ ) concentration in the synthesis gas at the inlet and the outlet of the adsorbent layer was measured by a chemiluminescence type NOx meter, and The NOx removal rate was calculated in accordance with.

NOx removal rate (%) = [(inlet NO ₂ concentration−outlet NO ₂ concentration) / (inlet NO ₂ concentration)] × 100 The obtained results are shown in Table 3.

[0042]

[Table 3]

According to the methods of Examples 1 and 2, adsorbents having different manganese oxide contents in the adsorbent were prepared. For these adsorbents, the NOx removal rate after 20 hours was obtained in the same manner as in Example 12, and the results are shown in Table 4.

[0044]

[Table 4]

From the results shown in Tables 3 and 4, it is understood that the adsorbent of the present invention is excellent in the adsorption performance of nitrogen oxides and is suitable for the adsorption removal of low concentration nitrogen oxides in exhaust gas.

Claims (4)

[Claims] 1. (A) 10 to 99% by weight of alumina,
Nitrogen oxidation characterized by containing (B) manganese oxide in an amount of 70 to 0.5% by weight and (C) an alkali metal oxide and / or alkaline earth metal oxide in an amount of 20 to 0.5% by weight. Adsorbent for things. 2. A specific surface area (BET surface area) of 50 m ² /
The nitrogen oxide adsorbent according to claim 1, which has a pore volume of 0.3 g / g or more and a pore volume of 0.3 cc / g or more. 3. (A) 10 to 99% by weight of alumina,
Exhaust gas is contacted with an adsorbent containing 70 to 0.5 wt% of (B) manganese oxide and 20 to 0.5 wt% of (C) alkali metal oxide and / or alkaline earth metal oxide. And removing the nitrogen oxides by adsorption. 4. The removal method according to claim 3, wherein the nitric oxide in the exhaust gas is previously oxidized to nitrogen dioxide and then contacted with the adsorbent.