JPH10118486A - Concentration of dilute nitrogen oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adsorb and remove gas containing dilute NOx with a low-cost adsorbent by dehydrating gas containing dilute nitrogen oxide and bringing the dehydrated gas into contact with an adsorbent consisting of manganese oxide borne by a carrier selected from crystalline silicate, alumina, titania, zirconia and silica, of a specific chemical composition. SOLUTION: When concentrating dilute nitrogen oxide (NOx ) contained in a gas polluted an a road or in a tunnel, the gas containing the dilute NOx is brought into contact, in a state in which the gas is dehydrated, with an adsorbent comprising manganese oxide borne by at least, one type of carrier selected from crystalline silicate, alumina, titania, zirconia and silica which have a chemical composition expressed by formula (1±0.8) R2 O.aM2 O3 .bAl2 O3 .cMeo.ySiO2 and also a specific X-ray diffraction pattern, and thereby, the nitrogen oxide is removed by adsorption at an ordinary temperature. In addition, the adsorbent is regenerated by supplying a hot air to the adsorbent into which the nitrogen oxide is adsorbed and desorbing the concentrated nitrogen oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is a dilute nitrogen oxides contained in contaminated gas, such as in road tunnels BACKGROUND OF THE INVENTION (hereinafter, referred to as lean No _x) it relates to a method of concentrating.

[0002]

2. Description of the Related Art Ventilation facilities in road tunnels are required to ensure a clear viewing distance mainly due to dust particles and to provide carbon monoxide (C).
O) and nitrogen oxides (NO _x ) are installed for the purpose of reducing harmful substances to below an allowable value. As the current ventilation system, a system is generally used in which fresh outside air is taken in from outside the tunnel, dust is removed as necessary, and then forced ventilation is performed outside the tunnel. However, this method only diffuses ventilation gas containing harmful substances into the atmosphere, and has not fundamentally improved the environment. Particularly in urban areas where air pollution due to automobile exhaust gas is becoming severe, the highly polluted area is expanded, which may hinder tunneling and shelter installation in road planning. Therefore, development of a new ventilation system that saves energy and does not affect the surrounding environment is desired.

However, tunnel ventilation gas at normal temperature and large capacity, concentration of NO _x is less and dilute 10 ppm, since the concentration of NO _x varies with traffic volume is particularity that intense already been put to practical use by the boiler flue gas It is impossible to directly apply the NO _x purification method using NH ₃ as a reducing agent. Therefore a low concentration _the NO _x purification methods, but a dry method and a wet method have been proposed, the wet method is difficult to put to practical use because it requires the waste water treatment apparatus, a tunnel ventilation gas as a dry method There is an adsorption method in which NO _x is adsorbed on an adsorbent, the temperature is changed and separation / concentration is performed, and then NH ₃ or the like is used as a reducing agent to make harmless nitrogen with a catalyst and removed.

However, as the adsorbents for lean NO _x which have been studied so far, there are noble metal adsorbents such as activated carbon and platinum. In the case of activated carbon, concentrated NO _x is desorbed by supplying heated air. In such a case, there is a risk of ignition, and in the case of a noble metal-based adsorbent, the adsorbent becomes expensive, so that there has been a problem in practical use. High performance, especially the possible removal of the lean NO _x by the dry method if it is possible to concentrate a dilute NO _x using dilute _the NO _x adsorbing agents that are not expensive, as mentioned above, sufficiently adsorbed lean NO _x The dry method has not yet been put to practical use because no adsorbent has been developed.

[0005]

[SUMMARY OF THE INVENTION The present invention has been made in view of the above prior art, provides a method that can concentrate in the high concentration NO _x containing gas using a relatively inexpensive adsorbent lean NO _x containing gas employed conventional NO by the selective catalytic reduction
_It makes _x harmless.

[0006]

The present invention SUMMARY OF] especially from adsorbent lean NO _x containing gas carrying the manganese oxide carrier N
N Of things O _x may efficiently adsorb and lean NO _x
O _{2 has} a higher polarity than NO and has been completed based on the finding that it is easily adsorbed by the adsorbent. That is, the present invention has the following structures (1) to (3).

(1) A gas containing a dilute nitrogen oxide is
In the dehydrated state, (1 ± 0.8) R _TwoO ・ [aM_TwoO
_Three・ BAl_TwoO_Three] ・ CMeO ・ ySiO_Two(Where R
Is an alkali metal ion and / or hydrogen ion, M is VIII
Group elements, rare earth elements, titanium, vanadium, chromium, d
1 selected from the group consisting of ob, antimony, and gallium
More than one kind of element, Me is an alkaline earth element, a ≧ 0, b ≧
0, c ≧ 0, a + b = 1, y / c> 12, y> 12)
X-ray diffraction pattern having a chemical composition and shown in Table A below
Crystalline silicate with alumina, alumina, titania,
At least one selected from the group consisting of zirconia and silica
Contact with adsorbent with manganese oxide supported on one type of carrier
To remove nitrogen oxides by adsorption at room temperature and remove nitrogen oxides.
Nitrogen oxidation concentrated by supplying heated air to the adsorbed adsorbent
Lean, characterized by desorbing substances and regenerating the adsorbent
A method for concentrating a nitrogen oxide-containing gas.

(2) The method for concentrating dilute nitrogen oxides as described in (1) above, wherein an adsorbent having an amount of manganese oxide carried on the carrier in the range of 0.5 to 30% by weight is used.

(3) The method for concentrating a dilute nitrogen oxide according to the above (1) or (2), wherein the dilute nitrogen oxide contains nitrogen dioxide as a main component.

[0010]

[Table 1] VS: Very strong M: Intermediate S: Strong W: Weak (X-ray source Cu)

[0011] (Function) adsorbent used in the present invention has an action of adsorbing efficiently lean NO _x containing air at ambient temperature, by supplying the heated air of about 400 ° C., adsorbed NO _x is It is completely desorbed. Thus the suction, by repeating the adsorption reaction, it is possible to concentrate the dilute NO _x laden air efficiently high concentration NO _x containing gas. The NO _x containing gas enriched to can be detoxified by applying a selective reduction denitration method of treating in the presence of a denitration catalyst by adding a reducing agent such as NH _3, which has been adopted conventionally.

Further, for example, the tunnel exhaust gas is lean NO _x containing gas contains dust, soot removal equipment is installed, such as an electrostatic precipitator. In the electric dust collector, when the applied voltage is increased, NO in NO _x is converted into NO ₂ , and the conversion ratio increases with the applied voltage. Therefore, when this phenomenon is utilized or ozone is added from outside the system to convert NO in NO _x into NO ₂ , as described above, since NO ₂ has a greater polarity than NO, the lean NO The adsorption and removal of _x is further promoted.

[0013]

EXAMPLES Hereinafter, the effects of the method of the present invention will be clarified by giving specific examples of the present invention. ○ Preparation of powder adsorbent 1 Water glass No. 1 (SiO ₂ : 30%): 5616 g of water:
The solution was dissolved in 5429 g, and this solution was designated as solution A. on the other hand,
A mixture was prepared by mixing and dissolving 718.9 g of aluminum sulfate, 110 g of ferric chloride, 47.2 g of calcium acetate, 262 g of sodium chloride and 2020 g of concentrated hydrochloric acid in 4175 g of water. Solution A and Solution B
Is supplied at a constant rate to produce a precipitate,
A slurry of H = 8.0 was obtained. This slurry was charged into a 20-liter autoclave, and 500 g of tetrapropylammonium bromide was further added.
Hydrothermal synthesis is performed for 2 hours, washed with water, dried, and calcined at 500 ° C. for 3 hours to obtain crystalline silicate 1. This crystalline silicate 1 has a composition formula of 0.5Na ₂ O · 0.5H ₂ O ·
[0.8Al ₂ O ₃ .0.2Fe ₂ O ₃ ] .0.25C
The crystal structure was represented by aO · 25SiO ₂ , and the crystal structure was represented by the above-mentioned Table A by X-ray diffraction.

The above crystalline silicate 1 is made of 4N NH ₄ C
The aqueous solution was stirred at 40 ° C. for 3 hours to carry out NH ₄ ion exchange. After washing after ion exchange and drying at 100 ° C. for 24 hours, it was calcined at 400 ° C. for 3 hours to obtain H-type crystalline silicate 1. An aqueous manganese chloride solution (MnCl ₂ : 18.3 g /
100 cc: water) and thoroughly kneaded.
And evaporated to dryness. Then at 500 ° C in air
A baking treatment was performed for 2 hours to obtain a powder adsorbent 1 supporting 7 wt% of MnO.

Preparation of powder adsorbents 2 to 15 In the method of synthesizing crystalline silicate 1 in the preparation of powder adsorbent 1 described above, instead of ferric chloride, cobalt chloride, ruthenium chloride, rhodium chloride, lanthanum chloride, chloride The same operation as that of crystalline silicate 1 was repeated except that cerium, titanium chloride, vanadium chloride, chromium chloride, antimony chloride, gallium chloride and niobium chloride were each added in the same mole number as Fe ₂ O _{3 in} terms of oxide. Functional silicates 2 to 12 were prepared. The crystal structures of these crystalline silicates are those shown in Table A above by X-ray diffraction,
Its composition is represented by the molar ratio of oxides (dehydrated state), and is 0.5Na ₂ O · 0.5H ₂ O · [0.2M ₂ O ₃
・ 0.8Al ₂ O ₃ ] ・ 0.25CaO ・ 25SiO ₂
It is. Where M is Co, Ru, Rh, La, Ce, T
i, V, Cr, Sb, Ga, Nb.

Further, in the method for synthesizing the crystalline silicate 1,
And instead of calcium acetate, magnesium acetate, vinegar
Strontium acid and barium acetate are converted to oxides, respectively.
crystalline silicate except that it is added in the same mole number as aO
The same operation as in Example 1 was repeated to obtain crystalline silicates 13-1.
5 was prepared. The crystalline structure of these crystalline silicates is
X-ray diffraction shown in Table A above and its composition
Represents the molar ratio of oxides (dehydrated form), and
5NaO_Two・ 0.5H_TwoO. [0.2Fe_TwoO _Three・ 0.
8Al_TwoO_Three] 0.25MeO.25SiO_TwoIn
You. Here, Me is Mg, Sr, and Ba.

Using the above crystalline silicates 2 to 15, the H-type crystalline silicates 2 to 2 are prepared in the same manner as the powder adsorbent 1.
No. 15 was obtained, and this silicate was impregnated with an aqueous manganese chloride solution to obtain powder adsorbents 2 to 15 in the same manner as powder adsorbent 1.

Alumina powder (γ-Al ₂ O ₃ manufactured by Sumitomo Chemical) titania powder (TiO ₂ manufactured by Ishihara Sangyo) is used as a carrier.
Mc-90), zirconia powder (Nikki Chemical's Zr)
O ₂ ) and silica powder (manufactured by Fuji Silysia Chemical Ltd.), MnO was supported at 7 wt% in the same manner as powder adsorbent 1, and powder adsorbents 16 to 19 were obtained.

Preparation of Slurry Silica sol (“Snowtex 0” manufactured by Nissan Chemical Co., silica content 20%) and alumina sol (Nissan Chemical Co., alumina content 10%) were used as binders. Then, 300 parts of water and 300 parts of water were added and mixed, and the pH was adjusted to 4 by adding nitric acid to prepare a slurry for washcoat.

Coating and Firing A monolithic honeycomb substrate made of cordierite (400 cells / inch ² ) is immersed in the above slurry, and after taking out, the excess slurry is blown off with compressed air, and is dried at 120 ° C. for about 30 minutes.
Dry for minutes. After drying, the honeycomb substrate is further immersed in the slurry, and by repeating these operations, a predetermined amount of adsorbent powder (about 60 g / m ³ substrate surface) is coated on the honeycomb substrate. The mixture was fired in an electric furnace for an hour to obtain honeycomb adsorbents 1 to 19.

Further, manganese oxide is added to the H-type crystalline silicate 1 carrier in the form of MnO of 0.5%, 2.0%, 10%,
Prototypes of powder adsorbents 20 to 23 carrying 30% were prepared. Further, as comparative examples, activated carbon powder (Shirasagi PHC-5 manufactured by Takeda Pharmaceutical Co., Ltd.) and activated alumina (Sumitomo Chemical) powder (100 mesh or less) were prepared.
25 was obtained. These powder adsorbents 20 to 25 were also formed into a honeycomb by the above method. Table B shows a number list of the honeycomb adsorbents 1 to 25.

[0022]

[Table 2]

[0023]

[Table 3]

Evaluation of Performance of Prototype Adsorbent Adsorption and desorption performance of the prototype adsorbent was evaluated by setting adsorption and desorption test conditions as shown in Table C below.

[0025]

[Table 4]

[0026] The second adsorption test results after implementation once desorption test and data, breakthrough time (time to be C / Co = 0.2, C: outlet concentration of NO _x, Co inlet concentration of NO _x) And the NO ₂ adsorption capacity up to the time when C / Co = 0.2 was determined. The test results are shown in Table D, and the breakthrough curves and desorption curves of each of the adsorbents (honeycomb adsorbents 1, 16, 24, and 25) are shown in FIGS. In each figure, (a) shows the NO ₂ adsorption breakthrough curve, and (b) shows the NO ₂ desorption curve.

[0027]

[Table 5]

Table D shows that the C / Co
If it does not reach 0.2, the breakthrough time is recorded as 60 minutes or more.
And NO_TwoThe adsorption capacity is the amount of adsorption up to 60 minutes.
I did. From Table D, it is found that the crystalline silica
And Al_TwoO_Three, TiO_Two, ZrO_Two, SiO_Twoof
The adsorbent (honeycomb numbers 1 to 23) has a long breakthrough time,
And NO_TwoLarge adsorption capacity. In contrast, activated carbon (C
No. 24) is NO _TwoHigh absorption capacity, but breakthrough
The time is extremely short and not practical. On the other hand, activated alumina
(Honeycomb number 25) is an adsorbent supporting manganese oxide
Than NO_TwoAdsorption capacity and breakthrough time are both inferior.
Call

Further, the following has been clarified from the honeycomb adsorbents 20 to 23 in which the amount of manganese oxide supported on the crystalline silicate was changed. That is, the smaller the amount of manganese oxide carried, the shorter the breakthrough start time, and the shorter the breakthrough time (the time when C / Co = 0.2), the shorter the breakthrough start time. The time is more than 60 minutes. On the other hand, the larger the supported amount, the better the adsorption performance. However, when the amount of oxide is 2 wt% or more, the adsorption performance is almost the same.

[0030]

_The NO _x adsorbing agent used in the present invention a method according to the present invention has been made to selectively adsorb and remove dilute NO _x in air at ambient temperature, the especially NO _2, being affected by moisture in the air NO ₂ can be efficiently adsorbed and removed, and as a result, the lean NO _x -containing gas can be concentrated to a high concentration NO _x -containing gas.

[Brief description of the drawings]

FIG. 1 is a chart showing a NO ₂ adsorption breakthrough curve and a NO ₂ desorption curve of a honeycomb adsorbent 1 used in an example of the present invention.

FIG. 2 is a chart showing a NO ₂ adsorption breakthrough curve and a NO ₂ desorption curve of the honeycomb adsorbent 16 used in the embodiment of the present invention.

FIG. 3 is a chart showing a NO ₂ adsorption breakthrough curve and a NO ₂ desorption curve of the honeycomb adsorbent 24 used in the embodiment of the present invention.

FIG. 4 is a chart showing a NO ₂ adsorption breakthrough curve and a NO ₂ desorption curve of the honeycomb adsorbent 25 used in the embodiment of the present invention.

Claims (3)

[Claims] 1. A gas containing a dilute nitrogen oxide is dehydrated to obtain (1 ± 0.8) R ₂ O · [aM ₂ O ₃
.BAl ₂ O ₃ ] .cMeO.ySiO ₂ , wherein R is an alkali metal ion and / or hydrogen ion, and M is a group consisting of a group VIII element, a rare earth element, titanium, vanadium, chromium, niobium, antimony, and gallium. One or more selected elements, Me is an alkaline earth element, a ≧ 0, b ≧
0, c ≧ 0, a + b = 1, y / c> 12, y> 12) and a crystal having an X-ray diffraction pattern shown in Table A described in the detailed description of the invention. Contacting at least one type of carrier selected from the group consisting of silicates, alumina, titania, zirconia and silica with an adsorbent carrying manganese oxide to adsorb and remove nitrogen oxides at room temperature and adsorb nitrogen oxides A method for concentrating a dilute nitrogen oxide-containing gas, comprising supplying heated air to the adsorbent and desorbing the concentrated nitrogen oxides to regenerate the adsorbent. 2. The amount of manganese oxide supported on a carrier is 0.
2. The method for concentrating dilute nitrogen oxides according to claim 1, wherein an adsorbent in a range of 5 to 30% by weight is used. 3. The method for concentrating a dilute nitrogen oxide according to claim 1, wherein the dilute nitrogen oxide contains nitrogen dioxide as a main component.