JPH0910556A - Removal of nitrogen oxide - Google Patents

Abstract

PURPOSE: To treat a low concentration of NOx efficiently using a compact device by adsorbing a nitrogen oxide using an adsorbent-denitrification catalyst layer until the adsorption volume of nitrogen oxide reaches the saturation point, then thermally desorbing the nitrogen oxide and at the same time, performing the reductive decomposition reaction by inducting an ammonia gas. CONSTITUTION: A three way cock 3 is closed for ammonia and opened for a gas containing NOx, and the gas containing NOx is guided into an NOx adsorbent-denitrification catalyst layer 4. In addition, the adsorption volume of NOx is continuously monitored using an NOx meter 7 and the gas is supplied until the adsorption volume of NOx reaches the saturation point. After that, the three way cock 3 is closed for the gas containing NOx and opened for ammonia. If the gas is heated using an NOx adsorbent-denitirification catalyst heating device 5, NOx is desorbed and is removed by decomposition under the NOx-NH3 , selective reduction reaction with a supplied ammonia.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently removing low-concentration nitrogen oxides contained in the atmosphere or various flue gas exhausts. More specifically, NOx in the exhaust gas of automobiles in highway tunnels and parking lots
Regarding removal method.

[0002]

2. Description of the Related Art NOx is a typical air pollutant,
Although many treatment technologies have been proposed so far, a large number of adsorbents such as activated carbon have been proposed particularly for treatment of low-concentration NOx. However, in any of these adsorbents, the period in which they exhibit adsorption capacity is finite, so it is necessary to replace or regenerate the adsorbent, which requires a lot of labor and cost for maintenance of the adsorption device. There was a problem saying that.

[0003]

SUMMARY OF THE INVENTION The present invention has been made to solve the above drawbacks, and an object of the present invention is to treat low-concentration NOx more efficiently than a compact device.

[0004]

In order to achieve the above object, the method according to the present invention is a nitrogen oxide adsorbent and a reductive decomposition to which a nitrogen oxide-containing gas introduction pipe is connected and which is provided with a heating means. In the device filled with the catalyst, the nitrogen oxide is first adsorbed until the saturated amount is reached, and the post-heating means is operated to desorb the adsorbed nitrogen oxide, and at the same time, ammonia gas is introduced to remove ammonia and nitrogen oxides. A method for removing nitrogen oxides, which is characterized in that a reducing component reaction is performed.

The NOx adsorbent and the NOx removal catalyst are each composed of a combination of at least one known component having an adsorption performance for NOx and an ammonia-NOx reduction activity. Examples of materials having adsorption performance for NOx include oxides of nickel, silver, copper, iron, cobalt, etc., and zeolite. Also, NO
NO of x which is difficult to be adsorbed is oxidized and easily adsorbed
_2. As an auxiliary agent for increasing the adsorption efficiency to the above oxides, oxides of manganese, particularly γ-manganese dioxide as filed by the inventors of the present invention on May 29, 1995, are also mentioned. You can This γ-manganese dioxide can be obtained by calcining commercially available manganese carbonate at 250 ° C. to 450 ° C. and acid-treating it, or by reacting manganese nitrate and potassium permanganate and washing with water to dry.

As the nitrogen oxide reduction decomposition catalyst according to the present invention, a known catalyst used as a catalyst for selective reduction using NH ₃ can be mentioned. More specifically, these are added to at least one carrier selected from oxides of titanium, aluminum, zirconium, silicon, etc., zeolites, etc. on the periodic table Ib, IIb, III.
a, IIIb, IVa, IVb, Va, VIa, VII
Ammonia SCR carrying at least one active species selected from oxides of a or VIII group elements
A use denitration _{catalyst, V 2 O 5 / TiO 2} , Fe 2 O 3 /
TiO ₂ , MnO ₂ / TiO ₂ , Cr ₂ O / TiO ₂ ,
_{CoO-TiO 2, CuO / TiO} 2, ZnO / TiO
₂ , NiO / TiO ₂ , WO ₃ / TiO ₂ , MoO / T
iO ₂ , SnO ₂ / TiO ₂ , V ₂ O ₅ / Al ₂ O ₃ ,
V ₂ O ₅ / ZrO ₂ , V ₂ O ₅ / SiO ₂ , V ₂ O ₅ /
Binary catalyst such as acid type zeolite and V ₂ O ₅ / WO ₃ /
TiO ₂ , Fe ₂ O ₃ / WO ₃ / TiO ₂ , MoO / W
Mention may be made of three-way catalysts such as O ₃ / TiO ₂ .

The above-mentioned known combination of components having adsorption ability for NOx and simultaneously ammonia-NOx reduction activity is NiO / V ₂ O ₅ / TiO ₂ , A.
g ₂ O / NiO / V ₂ O ₅ / TiO ₂ , NiO / V ₂ O
₅ / zeolite, Ag ₂ O / NiO / V ₂ O ₅ / zeolite and the like are more preferable.
NiO / γ-MnO ₂ / V ₂ O ₅ / TiO with O ₂ added
₂ , Ag ₂ O / NiO / γ-MnO ₂ / V ₂ O ₅ / Ti
O ₂ , NiO / γ-MnO ₂ / V ₂ O ₅ / zeolite,
Examples thereof include Ag ₂ O / NiO / γ-MnO ₂ / V ₂ O ₅ / zeolite.

In the NOx adsorbent layer-nitrogen oxide reduction decomposition catalyst layer heating means of the present invention, a heater may be installed in front of the NOx adsorbent layer and nitrogen oxide reduction decomposition catalyst layer, but as another method. Alternatively, these NOx adsorbent catalysts may be carried on a carrier that can be heated by energization. The carrier on which the adsorbent and the catalyst are carried needs to have the ability to generate heat in order to heat the adsorbent and the catalyst carried on the carrier. For example, a heat-generating base material which itself generates heat is used. Examples thereof include a base material to which a conductive material for heat generation is attached together with an adsorbent and a catalyst, and a honeycomb molded body to which a conductive material for heat generation is attached together with an adsorbent and a catalyst. In each of these base materials, a conductive wire is connected to both ends of the base material to conduct electricity, and the base material itself or the conductive material is heated. In this way, the term “heatable carrier” means that the carrier itself generates heat,
It also includes the case where the conductive material attached to the carrier generates heat.

Examples of the heat-generating base material include a breathable base material such as a thin wire net or a metal plate having a large number of pores (having a diameter of 30 μm or more). The metal plate having pores is, for example, a plate that has been perforated or lathed. They are,
It is possible to make a variety of structures, the most common of which is a honeycomb or corrugated metal carrier. The metal materials that can be used include
For example, metals such as iron, cobalt, molybdenum, titanium, zirconium, chromium, silver, gold, copper, nickel and tin, various iron alloys including stainless steel, copper alloys, nickel alloys, tin alloys, alloys such as chromium alloys. Is mentioned.

When a base material having a conductive material for heat generation attached thereto is used together with an adsorbent and a catalyst, the base material is, for example, a woven fabric made of organic fiber such as polyester, silica fiber or glass fiber, Further, non-woven fabrics such as polyester fiber, ceramic fiber and carbon fiber can be mentioned. It is preferable that these base materials have air permeability and have heat resistance of 100 ° C. or higher, particularly 150 ° C. or higher. Examples of the conductive material attached to the base material include graphite, carbon fiber, silicon carbide, silver, nickel chromium alloy, chromium aluminum alloy, and stainless steel. These conductive materials can be used in various shapes such as powder, whiskers, and short fibers. Further, it is preferable that the amount of the conductive material adhered to the base material is about 20 to 60%. If the amount of the conductive material is smaller than this, sufficient conductivity cannot be obtained and heat generation becomes insufficient. If it is too large, the contact between the adsorbent and the catalyst on the surface of the adsorbent and the catalyst may be hindered. As the adhesion method, in addition to a method of immersing the base material in a slurry containing an electrically conductive material together with an adsorbent and a catalyst, and in the case of a non-woven fabric base material, a method of adhering the catalyst and the conductive material at the time of its formation Etc. can be used.

When a honeycomb molded body having a conductive material for heat generation attached thereto together with an adsorbent and a catalyst is used, the adsorbent and the catalyst, the conductive material and the molding material are uniformly mixed and then extruded into a honeycomb shape. Alternatively, the adsorbent, the catalyst, and the conductive material are attached by dipping or the like after forming the honeycomb shape using only the forming material. The molded body can be used as it is, but if it is further fired to carbonize the molding material, the conductivity can be further improved. As the conductive material, the same conductive material as described above can be used. Examples of the molding material include methyl cellulose, polyvinyl chloride, polyethylene, polyamide and polyester. In addition, a reversible material such as clay may be added to the molding material in order to improve the extrudability. The content of the conductive material in the honeycomb formed body is about 30.
The content is preferably up to 70%, and if the content is less than this, sufficient heat generation cannot be obtained, and if it is more than this, the contact of ammonia with the adsorbent and catalyst on the adsorbent and catalyst surfaces is hindered. There is a risk.

By the heating means of the present invention, N
The temperature supplied to the Ox adsorbent-catalyst layer is 100 ° C to 40 ° C.
It is preferably in the range of 0 ° C. If the temperature is lower than the above range, desorption and regeneration of the adsorbent will be insufficient, which is not preferable. When the temperature is higher than the above range, the adsorbent-
The catalyst layer may be deteriorated and the adsorption performance and the denitration performance itself may be hindered, which is not preferable. Further, these heating means use ammonia-NO on the downstream side as described later.
Needless to say, it can be used as a means for supplying a heat source for the x reduction reaction.

In order to efficiently carry out the ammonia-NOx reduction reaction of the present invention, a heater or the above-mentioned N is used.
Ox adsorbent-Denitration catalyst heating device to adjust the gas temperature to 10
It is necessary to heat to 0 ° C to 400 ° C, preferably 150 ° C to 350 ° C. When the temperature is lower than the above range, the reaction is not sufficient, and when the temperature is higher than the above range, NOx may be generated due to the oxidation of ammonia, or the catalyst components may be deteriorated, which is not preferable. .

The catalyst or adsorbent according to the present invention can be formed into various shapes such as a honeycomb shape and a spherical shape by a conventionally known forming method. At the time of this molding, a molding aid, a molding reinforcement, an inorganic fiber, an organic binder and the like may be appropriately mixed. It is also possible to carry the coating on a preformed base material by a wash coating method or the like. Further, it is possible to use other conventionally known methods for preparing an adsorbent.

The present invention will be described in detail below based on examples. However, the present invention is not limited to the following examples. A. Preparation of NOx adsorption-denitration catalyst An aqueous solution of manganese nitrate prepared by dissolving 121.8 g of Wako Pure Chemical Industries special grade manganese nitrate in 20 ml of ion exchange water was dissolved in 2000 ml of ion exchange water of 40 g of Wako Pure Chemical Industries special grade potassium permanganate. The solution was added dropwise to an aqueous potassium manganate solution with stirring, the reaction was completed in about 30 minutes, and then filtered and washed with ion-exchanged water to obtain 61 g of a γ-MnO ₂ dried product. At this time, the specific surface area was 204 m ² / g. The X-ray diffraction intensity angle (2θ) showing the maximum intensity was 36.9 °. Next, 82 g of special grade nickel carbonate manufactured by Wako Pure Chemical Co., Ltd.
It was baked at 0 ° C. for 3 hours to obtain 60 g of nickel oxide. The specific surface area of the obtained NiO was 131.4 m ² / g. Further, 66.6 cc of an oxalic acid solution of ammonium metavanadate of 150 g / l as V ₂ O ₅ was added to 100 g of activated titanium dioxide having a specific surface area of 115 m ² / g, and an appropriate amount of water was added, and well mixed in a mortar. rear,
I dried up. After inviting this at 350 ° C. for 4 hours, it was crushed with a sample mill and V ₂ O ₅ / TiO
₂ (weight ratio 10/100) of powder was obtained. Next, 25 g of the above-mentioned γ-MnO _2, 25 g of NiO and V ₂ O ₅ / T.
Water and glass beads were added to 50 g of io ₂ (weight ratio 10/100) powder, and the mixture was stirred and mixed for 30 minutes to form a slurry. This slurry has a pitch of about 1.8 mm and a wall thickness of 0.4 m.
m of the conductive ceramic honeycomb was wash-coated and NiO / γ-MnO ₂ / V ₂ O ₅ / TiO ₂ (weight ratio 2
5/25 / 4.5 / 45.5). A NOx adsorbent-denitration catalyst that also functions as a heating device and was loaded with 22 g / cc was obtained.

B. Catalyst Evaluation Test The catalyst evaluation test was carried out using a test apparatus whose flow sheet is shown in FIG. In the figure, 1 is a NOx-containing gas, and 2 is an NH ₃ supply device. For the NOx-containing gas, the three-way cock 3 is closed with ammonia, the NOx-containing gas is opened, and N
It is introduced into the Ox adsorbent-desheathing catalyst layer 4, continuously monitored by the NOx meter 7, and the others are exhausted. The NOx-containing gas is supplied until NOx reaches saturation of adsorption. Then, the three-way cock is closed with NOx-containing gas and opened with ammonia, and heated by the NOx adsorbent-denitration catalyst heating device 5. The temperature at this time is appropriately adjusted while observing the resistance temperature detector 6. At the same time, ammonia is supplied from the ammonia supply device, and NOx desorbed by heating is NOx-NH
_3. Decomposition and removal by selective reduction reaction. The NOx concentration on the outlet side at this time was measured using a detector tube. (Test conditions) (1) NOx adsorption gas composition NOx 10ppm Air balance space velocity 10000Hr ^-1 temperature 25 ° C Humidity 45 ± 10% (2) Introduced ammonia gas gas composition NH ₃ 10ppm Air balance space velocity 10000Hr ^-1 temperature 25 ° C Humidity 45 ± 10% (3) NOx adsorbent-denitration catalyst layer heating temperature 100 ° C, 350 ° C

Example 1 In the catalyst evaluation test method described above, the ammonia-NOx adsorbent layer heating device was operated and the temperature was adjusted to 350 ° C. to carry out the reaction.

Example 2 In the catalyst evaluation test method described above, the ammonia-NOx adsorbent layer heating device was operated, and the temperature was adjusted to 150 ° C. to carry out the reaction.

Comparative Example 1 In the above-mentioned catalyst evaluation test method, NOx adsorbent-NOx adsorbent-without adsorbing NOx on the denitration catalyst layer in advance-
Activate the denitration catalyst heating device and set its temperature to 350 soil,
The NOx-containing gas having the above composition and ammonia are supplied to the denitration catalyst to be reacted. Space velocity at this time is 5000H
r ⁻¹ and 2500 Hr ⁻¹ . This assumes that the reactions in the examples are carried out in 2 series and 4 series, respectively.

The results are shown in Table 1.

[0021]

[Table 1]

[0022]

As shown in Table 1, the present invention provides low concentration NO.
x can be removed efficiently.

[0023]

[Brief description of the drawings]

 FIG. 1 is a flow sheet of a catalyst evaluation test. 1. NOx-containing gas 2. Ammonia supply device 3. Three-way cock 4. 4. NOx adsorbent-denitration catalyst layer 5. NOx adsorbent-denitration catalyst layer heating device 6. Resistance temperature detector 7. NOx meter

Claims (1)

[Claims] 1. A device in which a nitrogen oxide-containing gas introduction pipe and an ammonia gas introduction pipe are connected and which is equipped with a heating means and which is filled with a nitrogen oxide adsorbent and a reduction decomposition catalyst, the nitrogen oxide-containing gas is first added. Introduce it to adsorb nitrogen oxides until it reaches a saturated amount, and activate the post-heating means to desorb the adsorbed nitrogen oxides, and at the same time introduce ammonia gas to carry out the reductive decomposition reaction of ammonia and nitrogen oxides. A method for removing nitrogen oxides, which comprises: