JP2003275583A - Nitrogen dioxide absorbent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitrogen dioxide adsorbent which exhibits excellent nitrogen dioxide absorption performance. <P>SOLUTION: At least one component selected from Ru, Pt, Rh, Ir, and Pd and at least one component selected from Mn, Fe, Cu, Co, Ni, Ce, and Ca are combined and are carried on a porous oxide carrier and further a basic amino acid and/or organic amine compound is carried thereon. The basic amino acid is preferably alginine and the organic amine compound guanidine. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in an exhaust gas purifying apparatus for absorbing or adsorbing nitrogen dioxide (NO ₂ ) from, for example, a road tunnel ventilation gas containing a low concentration of nitrogen oxides (NOx). It relates to nitrogen dioxide absorption or adsorbents.

[0002]

_2. Description of the Related Art The NO ₂ concentration in a road tunnel ventilation gas is as low as about 0.1 ppm. Such low concentration N
An absorption method or an adsorption method is effective for removing O ₂ .

NO ₂ is an acidic gas and easily reacts with alkaline substances. Therefore, the present inventors have found that in order to remove the low-concentration NO ₂ in the road tunnel ventilation gas as described above, nitrogen dioxide impregnated with an alkali metal hydroxide is carried on a Mn—Ti surface-modified titania carrier. Absorbent (see JP-A-10-211427), adsorbent comprising activated carbon carrying a Group IA or Group IIA metal (JP-A-11-11427).
No. 57463)) and the like.

Further, the inventors of the present invention proceeded with research and
A basic carrier is used for the porous carrier, which has higher performance than the absorbent.
Carrying mino acid and / or organic amine compound
NO _Two  Absorbent (see JP-A-11-192415)
), A basic amino acid and / or a complex oxide carrier
NO carrying organic amine compounds_Two  Absorbent (JP
No. 2001-187340).

The alkali metal-supported absorbent has a small NO ₂ absorption capacity and is easily affected by coexisting moisture. Since the absorbent is installed in a road underground tunnel, a small NO ₂ absorption capacity is not preferable because it increases the regeneration frequency of the absorbent. Further, the fact that the absorbent is easily affected by the coexisting moisture causes deterioration in performance when the moisture is high such as rain.

The activated carbon type absorbent has a large absorption capacity,
As the amount of NO ₂ absorbed increases, NO ₂ is discharged at the same time, which causes a problem that the NO concentration at the outlet becomes higher than the NO concentration at the inlet. Although there is no limitation on NO in the environmental standards, increasing NO emission is not preferable from the viewpoint of environmental protection.

[0007] Therefore, the present inventors have developed and proposed an absorbent in which a basic amino acid and an organic amine compound are supported on a porous carrier in order to solve the above problems of the absorbent.

In order to further improve durability, Mn and at least one substance selected from Fe, Cu, Co, Ni, Ce and Ca are combined and supported on a porous oxide to form a composite oxide. We proposed an absorbent in which a basic amino acid and an organic amine compound are supported on the carrier.

The present inventors have further added to these carriers R
It has been found that an absorbent having a basic amino acid and an organic amine compound carried on a carrier carrying at least one substance selected from u, Pt, Rh, Ir and Pd as an essential component improves absorption performance.

The above-mentioned Japanese Patent Laid-Open No. 11-
The invention of No. 192415 is a NO ₂ prepared by supporting a basic amino acid and / or an organic amine compound on a porous carrier.
Regarding absorbent. Adsorption of NOx using this absorbent is performed as follows.

Gas-phase NO ₂ is adsorbed on the active sites,
Therefore, a form that easily reacts with alkali (N ₂ O ₃ , N ₂
Change to O ₄ ).

This modified product reacts rapidly with the alkali in the vicinity of the active site, and is stably retained as a nitrate or nitrite. Since the catalyst active site is vacant, the adsorption-denaturation cycle can be repeated.

The produced nitrate and nitrite anions (NO ₃ and NO ₂ ) diffuse from the vicinity of the active site to the surroundings, and free alkali is regenerated in the vicinity to form a modified product on the active site. The reaction of is repeated.

Therefore, since a large amount of alkali exists near the active point at the beginning of NO ₂ absorption, the absorption rate is NO ₂
The rate of absorption to the active point becomes rate-determining, and the rate of diffusion to the periphery of the active point becomes rate-determining as the amount of NO ₂ absorbed increases.

The present inventors have previously proposed a porous carrier obtained by impregnating titania (TiO ₂ ) with a manganese (Mn) salt, followed by drying and firing, as the carrier having the NO ₂ modification catalytic action. (See Japanese Patent Application Laid-Open No. 8-192049). Further, a composite oxide carrier (see JP 2001-187340 A) in which manganese (Mn) is an essential component and a substance of at least one component selected from Fe, Cu, Co, Ni, Ce and Ca is combined with the manganese (Mn) is disclosed. Proposed.

The present inventors further promote the action of by supporting at least one component selected from Ru, Pt, Rh, Ir and Pd as an essential component on the above porous carrier and complex oxide carrier. I found that I can do it. Further, it has been found that a substance in which a basic amino acid, particularly arginine, and an organic amine compound, particularly guanidine, are carried as an alkali on the oxide carrier has a high NO ₂ absorption performance.

The NO ₂ absorbent having the above structure is sufficiently practical to absorb and remove NO ₂ contained in the ventilation gas of the road tunnel.

[0018]

The nitrogen dioxide absorbent according to the present invention comprises a porous oxide carrier, at least one component selected from Ru, Pt, Rh, Ir and Pd, and Mn, Fe, Cu, C.
At least one component selected from o, Ni, Ce and Ca is combined and supported, and further a basic amino acid and / or an organic amine compound is supported.
Arginine is preferred as the basic amino acid, and guanidine is preferred as the organic amine compound.

The nitrogen dioxide absorbent according to the present invention may further carry an alkali hydroxide. The alkali hydroxide is preferably a substance selected from the group consisting of lithium hydroxide, potassium hydroxide and sodium hydroxide, or a combination thereof.

The preferred porous oxide is a material selected from the group consisting of titania, alumina, silica, silica-alumina, zirconia and zeolite, or a combination thereof.

The porous oxide carrier may be a composite oxide carrier obtained by adding a necessary metal component to an amorphous oxide and calcining it.

The porous oxide may be retained in the spaces between the fibers of the plate-shaped or honeycomb-shaped preform.

Ru, Pt, Rh,
At least one component selected from Ir and Pd, and M
In order to support at least one component selected from n, Fe, Cu, Co, Ni, Ce and Ca in combination, an aqueous solution of an inorganic acid salt or an organic acid salt of these metals alone or in combination thereof other than sulfates. Are impregnated into the porous oxide simultaneously or sequentially. The concentration of the aqueous solution is Ru, P
0.1 to 100 g for t, Rh, Ir and Pd
Metal / liter, preferably 1-10 g metal / liter, 0.1-51 mol / liter for Mn, Fe, Cu, Co, Ni, Ce and Ca, preferably 0.
It is 5 to 3 mol / liter.

The specific surface area of the porous oxide is preferably 30
~ 500 m ² / g, more preferably 60-120 m
² / g.

The porous oxide may be retained in the spaces between the fibers of the plate-shaped or honeycomb-shaped preform.

The nitrogen dioxide absorbent according to the present invention may contain, for example, 0.1 to 3.0 mol / liter, preferably 0.3 to 1.5 mol / liter of basic amino acid and 0. It is produced by successively impregnating a porous oxide carrier with two aqueous solutions each containing 1 to 3.0 mol / liter, preferably 1.0 to 2.0 mol / liter of an organic amine compound. Also, this is 0.1 to 3.0 mol / liter, preferably 0.3.
-1.5 mol / l basic amino acid and / or 0.1-3.0 mol / l, preferably 1.0-
It is also prepared by impregnating a porous oxide support with one aqueous solution containing 2.0 mol / liter of an organic amine compound. After the above impregnation, the porous oxide carrier is heated to 150 ° C
Hereafter, it is preferably dried at 100 ° C or lower.

One example of a porous oxide support is a porous oxide with solid acidity. The porous oxide having solid acidity is alumina, silica-alumina, titania, zeolite, zirconia, or the like. These may be used alone or in combination of two or more.

The nitrogen dioxide absorbent having the above-mentioned structure is supplied with ventilation gas for road tunnels at a flow rate of 0.05 to 10.0 Nm /
It is preferably used for road tunnel ventilation gas purification, in which nitrogen dioxide in ventilation gas is absorbed and removed by passing through s (empty tower standard).

Hereinafter, the nitrogen dioxide absorbent according to the present invention will be described in more detail.

Amino acids generally have both an amino group (basic) and a carboxyl group (acidic). Amino groups help fix nitrogen dioxide, while carboxyl groups do not.
Further, both arginine and guanidine have HN = C (imido group), which reacts with a solid acid point similarly to the amino group to help immobilize arginine and guanidine on the carrier surface. Therefore, the number of free amino groups effective for nitrogen dioxide fixation is increased, and arginine and guanidine are less likely to evaporate than other organic amine compounds and exhibit a high nitrogen dioxide fixation ability.

However, the carboxyl group in arginine is located near the amino group due to its molecular structure, and not only is it not useful for fixing nitrogen dioxide, but also NO which propagates between the amino groups.
₃ -, NO ₂ - to spread such has also become a disincentive.

When a basic compound acts on the carboxyl group, the carboxyl group also effectively functions to immobilize nitrogen dioxide, and the absorption capacity of the absorbent increases. In particular, when guanidine is used as the basic compound, only amino groups effective for diffusion of nitrogen dioxide are present, and the factors inhibiting diffusion are reduced.

If the diffusion of nitrogen dioxide is facilitated, not only the absorption rate of nitrogen dioxide is improved, but also a wide area around the catalyst active point is effective for immobilizing nitrogen dioxide, leading to an increase in absorption capacity.

An increase in the supported amount of arginine and the like leads to an increase in the absorbed amount of nitrogen dioxide, but an excessive supported amount causes clogging of catalyst pores and burial of catalytic active sites due to arginine and the like, which lowers the absorption rate.

[0035]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing a nitrogen dioxide absorbent according to the present invention and its performance are specifically shown in Examples.

Example 1 a) Absorbent ceramic paper honeycomb (thickness 0.6 mm: manufactured by Nippon Inorganic Co., Ltd.) with a solid content concentration of 33% by weight of titania (TiO ₂₎
) After soaking in the sol solution, it was dried in air at 110 ° C. to hold the titania between the ceramic fibers constituting the paper. The ceramic paper honeycomb was dipped in a titania colloid solution and dried again to obtain a honeycomb in which anatase-type titania was dispersed and held.

The amount of titania retained in this honeycomb is 211
It was g / m ² . This was immersed in a 3 mol / liter manganese nitrate (Mn (NO ₃ ) ₂ ) aqueous solution for 30 minutes, dried at 120 ° C. in aeration, and then heated to 450 ° C. at a rate of 1.5 ° C./minute, Baked for 3 hours. In addition, 1.3 g-Ru / liter of ruthenium chloride (Ru
C1 ₃₎ were immersed for 30 minutes in an aqueous solution, dried at 120 ° C. in a ventilated, the temperature was raised to 250 ° C. at a 1.5 ° C. / minute rate, and baked for 30 minutes. The specific surface area of the Mn—Ru-added carrier thus obtained was 97 m ² / g.

This was immersed in a mixed aqueous solution of 0.5 mol / l L-arginine and 1.5 mol / l guanidine carbonate for 30 minutes, then dried in air at 90 ° C.
O ₂ absorbent (A) was obtained.

B) Evaluation of absorbent performance Honeycomb-shaped absorbent (A) (20 mm × 20 mm × 46)
mm ×, a honeycomb surface area of 900 m ² / m ³ ) was passed through a gas having the composition shown in Table 1 at a flow rate of 2.5 N liter / min to analyze the nitrogen dioxide concentration in the upstream and downstream of the absorbent. , NO ₂ breakthrough rate (NO ₂ breakthrough rate =
Outlet NO ₂ concentration / inlet NO ₂ concentration) was measured for a predetermined time.

Then, an acceleration gas containing a large amount of nitrogen dioxide shown in Table 2 was passed for a predetermined time, and the nitrogen dioxide absorption rate and the cumulative absorption amount at that time were measured.

From the beginning of absorption until the amount of NO ₂ absorbed reaches 4 Nl / m ² , the breakthrough rate shows almost 0, and then rises, and when the amount of absorbed reaches 8 Nl / m ² , the breakthrough rate increases. The rate was 0.14.

[0042]

[Table 1]

[0043]

[Table 2]

Example 2 As shown in Table 3, the same operation as in Example 1 was performed except that a mixed aqueous solution of manganese nitrate and various metal nitrates was used in place of the aqueous manganese nitrate solution, and the NO ₂ absorbent B was obtained. ~ G was obtained.

By the same operation as in Example 1, the initial breakthrough rate and the breakthrough rate after absorbing 8 Nl / m ² of these absorbents were measured. The results are also shown in Table 3.

Comparative Example 1 As shown in Table 3, the same operation as in Example 2 was carried out except that the step of adding Ru was omitted to obtain Ru non-loaded NO ₂ absorbents A ′ to G ′.

By the same operation as in Example 1, the initial breakthrough rate and the breakthrough rate after absorbing 8 Nl / m ² of these absorbents were measured. The results are also shown in Table 3.

[0048]

[Table 3]

As can be seen from Table 3, the performance improvement of the absorbent by supporting Ru is recognized.

Example 3 As shown in Table 4, NO ₂ absorbents H to K were obtained in the same manner as in Example 1 except that various noble metal chloride aqueous solutions were used instead of the ruthenium chloride aqueous solution.

By the same operation as in Example 1, the initial breakthrough rate and the breakthrough rate after absorbing 8 Nl / m ² of these absorbents were measured. The results are also shown in Table 4.

[0052]

[Table 4]

As can be seen from Table 4, even if the ruthenium chloride aqueous solution is changed to various kinds of noble metal chloride aqueous solutions, the noble metal supporting effect is similarly recognized.

Example 4 As shown in Table 5, NO ₂ absorbents L and M were obtained in the same manner as in Example 1 except that the concentration of the ruthenium chloride aqueous solution was changed.

By the same operation as in Example 1, the initial breakthrough rate and the breakthrough rate after absorbing 8 Nl / m ² of these absorbents were measured. The results are also shown in Table 5.

[0056]

[Table 5]

As can be seen from Table 5, even when the concentration of the ruthenium chloride aqueous solution is changed, the same supporting effect is recognized, and the effect is increased as the concentration is increased.

[0058]

The nitrogen dioxide absorbent according to the present invention comprises a porous oxide carrier and at least one component selected from Ru, Pt, Rh, Ir and Pd, and Mn, Fe, Cu and C.
Since at least one component selected from o, Ni, Ce and Ca is combined and carried, and further a basic amino acid and / or an organic amine compound is carried, it exhibits excellent nitrogen dioxide absorption performance.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Daisuke Fujita             1-89 Minami Kohoku 1-89, Suminoe-ku, Osaka             Standing Shipbuilding Co., Ltd. F-term (reference) 4D002 AA12 AC10 BA04 CA07 DA01                       DA02 DA03 DA12 DA19 DA21                       DA22 DA23 DA24 DA25 DA26                       DA31                 4G066 AA20C AA22C AA23C AA32A                       AA53A AA61C AB07B AB13B                       AD10B BA07 CA28 DA02                       FA12 FA22

Claims (5)

[Claims] 1. Ru, Pt, R on a porous oxide support
at least one component selected from h, Ir and Pd,
A nitrogen dioxide absorbent characterized by supporting at least one component selected from Mn, Fe, Cu, Co, Ni, Ce and Ca in combination, and further carrying a basic amino acid and / or an organic amine compound. 2. The nitrogen dioxide absorbent according to claim 1, further comprising an alkali hydroxide supported thereon. 3. The porous oxide is titania, alumina,
The nitrogen dioxide absorbent according to claim 1 or 2, which is a substance selected from the group consisting of silica, silica-alumina, zirconia, and zeolite, or a combination thereof. 4. The nitrogen dioxide absorbent according to claim 1, wherein the porous oxide is a composite oxide. 5. The nitrogen dioxide absorbent according to claim 1, wherein the porous oxide is retained in the gaps between the fibers of the plate-shaped or honeycomb-shaped preform. .