JPH09155185A - Nox absorbent, manufacture thereof and device using nox absorbent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an NOx absorbent capable of efficiently absorbing/removing a low concentration of NOx contained in a combustion exhaust gas by adding the oxide of one type of element selected from among iron, nickel, manganese, copper, cobalt, chromium and zinc to a porous alumina as a main component. SOLUTION: A lowly concentrated NOx absorbent is formed of a porous alumina as a main component and the oxide of element selected from iron, nickel, manganese and cobalt borne by the porous alumina. In this case, the average pore diameter or/and the peak pore diameter of the porous alumina are 0.2-10nm and the pore volume is 0.03cc/g. Further, this lowly concentrated NOx absorbent is caused to release the once absorbed NOx by heating the absorbent at 300-600 deg.C. Besides, the NOx absorbent is capable of maintaining the NOx removing rate at 80% or more in the air at a space velocity of 10.324h<-1> and a linear velocity of 39cm/s and under other atmospheric conditions such as NOx concentration of 3.0ppm, moisture concentration of 1.5% and temperature of 25 deg.C. This NOx removing rate should persist for 10 hours or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a granular, powdery, filmy or honeycomb structure using an alumina-based porous body which selectively absorbs and removes low-concentration NOx contained in combustion exhaust gas and mixed gas. The present invention relates to a NOx removal device including a structural body.

[0002]

2. Description of the Related Art Up to now, the presence of activated alumina along with titania, zeolite, etc. has been known as a NOx adsorbent. Each of them has a very large specific surface area and has fine pores. Therefore, it utilizes the phenomenon that water, NOx, SOx and other highly adsorptive substances are simultaneously adsorbed on the pore surface by physical adsorption force. It was done. Therefore, it is used as an adsorbent for NOx and SOx in combustion exhaust gas, but the selectivity and the amount of adsorption of NOx are extremely low.

On the other hand, recently, as a new NOx absorber,
Perovskite-type composite oxides such as yttrium-strontium-cobalt composite oxides have become known. These characteristics have a very high selectivity for NOx absorption, and the amount of absorption is generally as large as 0.1 mol or more per mol of the absorber compound. However, these composite oxides absorb a large amount of NOx, but simultaneously react with the water vapor to be absorbed, and form nitrite or nitrate groups to destroy the perovskite structure. It had the disadvantage that it could not be reused.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an excellent NOx absorber and a method for producing the same, in order to solve the above problems.

[0005]

In order to achieve the above object, the present invention has the following constitution.

"A porous alumina produced by the alkoxide method, which carries an oxide of at least one element selected from the group consisting of iron, nickel, manganese, copper, cobalt, chromium, and zinc. A low concentration NOx (x = 1 to 2) absorber characterized by the above. ”Now, NOx
In order to increase the absorption amount, it is necessary to support an appropriate pore size distribution of porous alumina and a metal that is active in NOx absorption. Although the average pore diameter and the pore peak diameter of the porous alumina have been described as 0.5 to 10 nm, it is necessary to adjust the pore diameter to an appropriate range in order to efficiently absorb NOx. is there. When the pore diameter is 0.5 nm or less, usually some NOx molecules aggregate to form clusters, and thus it is difficult for the NOx molecules to enter the pores. When the pore diameter is 10 nm or more, the pores become too wide and are not efficiently absorbed. For the above reason, the pore size is preferably 0.5 to 10 nm. Further, the larger the pore volume, the more preferable, but at least 0.03 cc / g or more, preferably 0.
It is preferably 1 cc / g or more, more preferably 0.25 cc / g or more. In the alkoxide method alumina controlled in this range, NOx is practically efficiently absorbed / released. Further, by supporting a metal active in NOx absorption in the pores, the adsorption rate is improved. As described above, by advancing the optimization of the conditions, it becomes possible to produce a NOx absorber having high performance even under severe evaluation conditions.

The metal is preferably iron, nickel, manganese, copper, cobalt or manganese. Of these, manganese is the most preferred, followed by nickel and then copper. Of course, a plurality of these metals may be mixed, or a metal other than these may be contained.

The form of metal supported is not particularly limited, and may be contained up to substantially the inside of the absorbent body of the present invention, or the surface of the powder or molded body (pellet body etc.) of the absorbent body. Alternatively, it may have a distribution such that it is supported on the cavity surface in the pores and is not contained inside, or the content is smaller than the surface. However, in order to exert the performance more effectively with a small metal content, it is preferable that the metal is localized on the surface.

The content of the metal oxide is preferably 0.1 to 90% by weight, more preferably 1 to 30% by weight, particularly when it is supported on the powder. However, when localized on the surface, it is preferably 0.1 to 0.5 wt%, more preferably 0.2 to 0.4 wt%.

Further, the absorbed NOx is 300-60.
It is released by heating at 0 ° C., but it is preferable that at least 90% or more of NOx is released up to 500 ° C. in view of energy efficiency. In the release process,
It is preferable to be in an atmosphere having a low NOx partial pressure, and examples thereof include a method of reducing the pressure or flowing a carrier gas.

On the other hand, regarding the method for producing the alkoxide method alumina, the general formula Al (-OR ¹ ) _x (-OH) _y (A) x + y = 3 x ≧ 1 R ¹ is a C 1-6 substituted or unsubstituted Of the lower aliphatic alcohol solution containing an aliphatic or alicyclic group, the step of calcination, the step of calcination, and the supporting of the substance having the oxide element of claim 1 are carried out. In the formula (A), it is preferable that x = 3.
The C number is preferably 2. More preferably x
= 3 and the C number is 2.

Next, a method for supporting the metal oxide will be described. The substance having a target metal oxide metal is supported on the alkoxide-method alumina produced as described above. The substance having a metal of a metal oxide refers to a substance other than the metal oxide, which can become the metal oxide by a firing step. It may be supported in the form of a metal oxide or a metal element in a metal state, but in the actual process, it is preferable to support in the form of a metal salt or the like because it is easy to handle. As a method of supporting the metal salt or the like, it is preferable to prepare and use a metal salt solution, and it is more preferable to immerse alumina in the solution. After soaking in the metal salt solution, drying and firing are performed. As the metal salt, salts of inorganic acids such as nitric acid and sulfuric acid,
Alternatively, salts of organic acids such as acetic acid and oxalic acid can be mentioned. The difference in the salt also affects the effect of the invention, as shown in Examples described later. The solvent of the metal salt solution prepared for the immersion is not particularly limited, and may be water or alcohol such as methanol or ethanol. The shape of alumina may be any of powder, granules such as pellets, and honeycomb, and the shape is not particularly limited. Therefore, the absorber may be supported with a metal in a powder state by a dipping method or the like,
Alternatively, the absorber may be sintered and once formed into a desired shape (pellet, honeycomb, etc.) and then supported.

By this method, low-concentration NOx in combustion exhaust gas or mixed gas is selectively and efficiently absorbed and easily
Provided is a NOx absorber that can be released and reused.
NOx concentration 3.0ppm, water concentration 1.5%, temperature 25
NO that keeps a removal rate of 80% or more for 10 hours or more in air at a temperature of ℃, space velocity of 10,324 h ^-1 , and linear velocity of 39 cm / s
It is preferably an x absorber. The NOx concentration, the water concentration, the temperature, the space velocity, the linear velocity, the duration, and the like only indicate the measurement conditions, and the present invention cannot be implemented only under these conditions. Preferably, the removal rate is 80% or more even in the NOx concentration range of 3.0 to 10.0 ppm, and more preferably the outlet NOx concentration is 0.3 p.
pm or less. Alternatively, the space velocity is preferably 6000 to 20000 h ^-1 , more preferably 8000.
˜11000 h ⁻¹ . The linear velocity is preferably 5 to 100 cm / sec, more preferably 20.
The effect of the present invention is remarkably high with respect to the conventionally known example of ˜50 cm / sec.

The details of the method for producing the NOx absorber of the present invention will be described below.

(Production Method) The compound represented by the general formula (A) is heated in an inert gas atmosphere to completely dissolve it, and then a lower aliphatic alcohol is preferably used to obtain 0.01 to A solution having a concentration of 2.0 mol / liter is prepared. Examples of the lower aliphatic alcohol include methanol, ethanol, propanol, and butanol, with propanol being particularly preferred.

When a powder is prepared, the above-prepared aluminum alkoxide solution is put in a container and left in a conditioned atmosphere as a simple method. After standing, hydrolysis proceeds due to moisture in the air, and gelation is completed within 1 to several days. After drying the gel in a dryer until it is apparently free of volatile components, the gel is dried in the temperature range of 400 to 1000 ° C. for 10 minutes to
Bake for about 3 hours. The firing is performed in an oxidizing atmosphere, preferably in the air.

In the case of producing pellets, a method of producing by compressing the powder obtained above or by producing by adding a binder and firing can be considered, but either method may be used, but it is preferable to add a binder. It is a method of making.

Further, a metal oxide is supported on this alumina. The alumina produced as described above is immersed as an oxide in an aqueous solution of a metal salt calculated to have a predetermined weight% and left for 1 minute to several days. After that, 100 ~
Firing is performed in the temperature range of 600 ° C. to obtain alumina having metal oxides supported in the pores or on the surface thereof.

By utilizing this NOx absorber, it becomes possible to design the NOx absorber and the NOx removing device for various purposes. That is, a NOx adsorption cylinder filled with a granular or powdery NOx absorber, a hollow fiber membrane-shaped, flat membrane-shaped, and honeycomb-shaped structure in which the adsorbent is laminated or applied in a film on the surface of a base material, It can be used as a NOx removing device for combustion exhaust gas and a denitration device.

As described above, according to the method of the present invention, a granular, powdery, filmy, pelletized or honeycomb structure can be obtained by a simple operation such as drying from an alkoxide solution and then firing, without any complicated treatment. -Like porous alumina can be obtained, and a metal oxide can be supported on it.

(Evaluation method) NOx obtained by the present invention
By using the absorber, it becomes possible to stably separate gas and liquid in a high temperature and high pressure region for a long period of time.

The pore size of the obtained inorganic membrane structure is evaluated by a gas adsorption method or a differential scanning calorimetry method.

In the case of the gas adsorption method, the water content of the sample and N
When measuring mesopores of 2 nm or more after sufficiently releasing Ox, nitrogen gas is adsorbed, and the Dolimore-
The pore size is determined by the Heal method. When measuring micropores of 2 nm or less, adsorb argon gas and
The pore size distribution and the pore volume are determined by the rvath-Kawazoe method.

[0024]

【Example】

Example 1 and Comparative Example 1 Aluminum ethoxide (Al (OC ₂ H ₅ ) ₃ ) was heated in an inert gas atmosphere to completely dissolve it, and isopropyl alcohol was used to adjust the concentration to 1.0 mol / liter. Prepared to be a solution.

The prepared aluminum isopropoxide solution is put in a glass petri dish and left in an atmosphere whose relative humidity is adjusted to 60% for 24 hours. After standing, hydrolysis proceeds with moisture in the atmosphere, and gelation is completed. The gel was dried in a dryer set at 60 ° C. until apparently free of water, and then baked at 800 ° C. for 2 hours in the atmosphere.

The pore size of the obtained inorganic membrane structure was evaluated by the gas adsorption method. When nitrogen gas was adsorbed and the pore diameter was determined by the DH method, the pore peak diameter was 6.2 nm. The total pore volume was 0.584 cc / g. (Comparative Example 1) 4.5 g of the alumina thus produced was immersed in 10 ml of an aqueous solution of manganese nitrate prepared as an oxide so as to be 10 wt%, and left for one day. Then, it was taken out and baked at 400 ° C. for 5 hours. The sample after firing is N
Ox concentration 3.0ppm, water concentration 1.5%, temperature 25
Evaluation was carried out in air at a temperature of 10 ° C., a space velocity of 10,324 h ^{−1, and a} linear velocity of 39 cm / s (each sample is a powder).

A NOx absorber was obtained by the same procedure as in Example 1 except that manganese acetate was used instead of nitrate (Example 2).

The results are shown in FIG.

Examples 3 to 6 Iron (Example 3), copper (Example 4), cobalt (Example 5), nickel (Example 6) prepared in such a manner that the amount of oxide was 10 wt% instead of manganese nitrate. The same operation as in Example 1 was carried out except that each nitrate of 1) was used to obtain a NOx absorber. (Each sample is a powder body).

The results are shown in FIG.

The nitrate had a high initial absorbency, and the acetate had a long-term absorbency and excellent stability.

Example 7, Comparative Example 2 A pellet was prepared by adding a binder to the alumina prepared by the method of Example 1. The pellet as oxide 1
It was immersed in an aqueous solution of manganese nitrate prepared so as to be 0 wt% and left for one day. Then, it was taken out and baked at 400 ° C. for 5 hours. (Example 7) Further, an alumina pellet sample was prepared in the same manner as in Example 7 except that the sample was not immersed in an aqueous solution of metal nitrate and did not carry a metal oxide (Comparative Example 2). The pellets obtained were evaluated by the same evaluation method as in Example 1.

The results are shown in FIG.

[0034]

EFFECTS OF THE INVENTION The present invention selectively and efficiently absorbs low-concentration NOx in combustion exhaust gas or mixed gas,
A NOx absorber that can be easily released and reused is provided, and it can be used in various shapes such as a filling cylinder and a hollow fiber membrane.

[Brief description of the drawings]

FIG. 1 shows the results of evaluation experiments of NOx absorbers of Comparative Example 1 and Examples 1 and 2.

FIG. 2 shows the results of evaluation experiments of NOx absorbers of Examples 1, 3 to 6.

FIG. 3 shows the results of evaluation experiments of NOx absorbers of Example 7 and Comparative Example 2.

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[Procedure amendment]

[Submission date] November 5, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction contents]

By this method, low-concentration NOx in combustion exhaust gas or mixed gas is selectively and efficiently absorbed and easily
Provided is a NOx absorber that can be released and reused.
NOx concentration 3.0ppm, water concentration 1.5%, temperature 25
NO that keeps a removal rate of 80% or more for 10 hours or more in air at a temperature of ℃, space velocity of 10,324 h ^-1 , and linear velocity of 39 cm / s
It is preferably an x absorber. The NOx concentration, the water concentration, the temperature, the space velocity, the linear velocity, the duration, and the like only indicate the measurement conditions, and the present invention cannot be implemented only under these conditions. Preferably, the removal rate is 80% or more even in the NOx concentration range of 3.0 to 10.0 ppm, and more preferably the outlet NOx concentration is 0.3 p.
pm or less. Alternatively, the space velocity is preferably 6000 to 20000 h ^-1 , more preferably 8000.
˜11000 h ⁻¹ . The linear velocity is preferably 5 to 100 cm / sec, more preferably 20.
When it is up to 50 cm / sec, the effect of the present invention is significantly higher than that of the conventional known examples.

[Procedure amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0025

[Correction method] Change

[Correction contents]

[0025] The aluminum eth Kishido solution prepared into a glass Petri dish and left for 24 hours in dampening the atmosphere adjusted to a relative humidity of 60%. After standing, hydrolysis proceeds with moisture in the atmosphere, and gelation is completed. After drying the gel in a dryer set at 60 ° C until there is no apparent water content,
Firing was performed at 00 ° C. for 2 hours in the air.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0032

[Correction method] Change

[Correction contents]

Example 7, Comparative Example 2 A pellet was prepared by adding a binder to the alumina prepared by the method of Example 1. The pellet as oxide 1
It was immersed in an aqueous solution of manganese nitrate prepared so as to be 0 wt% and left for one day. Then, it was taken out and baked at 400 ° C. for 5 hours (Example 7). Further, an alumina pellet sample was prepared in the same manner as in Example 7 except that the sample was not immersed in an aqueous solution of metal nitrate and did not carry a metal oxide (Comparative Example 2). The pellets obtained were evaluated by the same evaluation method as in Example 1.

Claims (16)

[Claims] 1. A method comprising, as a main component, porous alumina produced by an alkoxide method and containing iron, nickel, manganese,
A low-concentration NOx (x = 1 to 2) absorber containing an oxide of at least one element selected from the group consisting of copper, cobalt, chromium, and zinc. 2. A porous alumina having an average pore size or / and a peak pore size of 0.2 to 10 nm and a pore volume of at least 0.03 cc / g, and iron, nickel, manganese, copper, cobalt, A low concentration NOx (x = 1 to 2) absorber containing an oxide of at least one element selected from the group consisting of chromium and zinc. 3. The NOx absorber according to claim 1, wherein the absorbed NOx is released by heating at 300 to 600 ° C. 4. NOx is reversibly released by increasing / decreasing temperature.
The NOx absorber according to claim 1, which absorbs. 5. A NOx concentration of 3.0 ppm and a water concentration of 1.
The NOx absorber according to claim 1, wherein a removal rate of 80% or more is continued for 10 hours or more in air at 5%, a temperature of 25 ° C, a space velocity of 10,324 h ^-1 , and a linear velocity of 39 cm / s. 6. A general formula Al (—OR ¹ ) _x (—OH) _y (A) (wherein, x + y = 3 x ≧ 1 R ¹ is a substituted or unsubstituted aliphatic group having 1 to 6 C atoms). Or a step of hydrolyzing a lower aliphatic alcohol solution containing an alicyclic group), a step of firing, and at least one selected from the group consisting of iron, nickel, manganese, copper, cobalt, chromium, and zinc. 5. A method for producing a low-concentration NOx (x = 1 to 2) absorber, which comprises supporting an oxide of the element. 7. The NO according to claim 6, wherein the firing is performed in an oxidizing atmosphere at 500 to 1000 ° C.
A method of manufacturing an x absorber. 8. The metal oxide according to claim 1 is locally present on the surface of the porous alumina, and the content of the oxide is 0.1 to 30 wt%. Item 1
The described NOx absorber. 9. A container comprising the NOx absorber according to claim 1, which is in a granular or powder form.
Ox absorber. 10. The porous alumina is formed into granules and then loaded with an oxide of at least one element selected from the group consisting of iron, nickel, manganese, copper, cobalt, chromium and zinc. NOx according to claim 1.
Absorber manufacturing method. 11. A NOx absorber comprising a hollow fiber membrane-shaped, flat membrane-shaped or honeycomb-shaped structure, which is obtained by laminating or coating the NOx absorber according to claim 1 on the surface of a base material. . 12. A NOx absorber for combustion exhaust gas according to claim 9 and / or 11. 13. The NOx absorption device for air purification according to claim 9 and / or claim 11. 14. A denitration device using the NOx absorption device according to claim 9 and / or 11. 15. A denitration device using a NOx absorber according to claim 1, wherein a denitration catalyst is supported. 16. The method for producing a NOx absorber according to claim 1, wherein the porous alumina is immersed in a metal salt solution.