JP3324776B2 - Method for treating nitrogen oxide-containing gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a carbon dioxide CO ₂ coexistence relates to a process for the treatment of nitrogen oxide-containing gas to decompose and remove nitrogen oxides contained (hereinafter referred to as NOx).

[0002]

2. Description of the Related Art Exhaust gas from various combustors contains NOx together with a large amount of oxygen, and it is said that NOx not only causes photochemical smog but also causes damage to the respiratory system for the human body. Regarding the process of reducing NOx to harmless N ₂ ,
A so-called three-way catalyst system for converting NO into N ₂ using a reducing agent such as CO or various hydrocarbons (HC) has been established, and a process using ammonia as a reducing agent has been adopted as a method adopted in plants and the like. Established

[0003]

However, in the three-way catalyst system, it is necessary to prepare CO or hydrocarbon separately, which makes the apparatus complicated and increases the cost. on the other hand,
When ammonia is used, there is a problem that it may be contaminated and cannot be used in an indoor space. Although it has been conventionally desired to directly decompose NOx without using various reducing agents, none has been established at a practical level. Furthermore, recently, as a method of directly decomposing NOx, NOx is brought into contact with a perovskite-type compound,
It has been proposed to decompose this directly and render it harmless.
However, it has now been found that some perovskite compounds cannot exhibit their direct decomposition activity effectively in the presence of carbon dioxide CO ₂ . Carbon dioxide CO ₂ is a gas contained in a gas discharged from various combustors, for practical use carbon dioxide (CO ₂₎
It is essential that the direct decomposition activity is exhibited in the coexistence. Therefore, an object of the present invention is to provide a method for treating a nitrogen oxide-containing gas that can effectively treat NOx contained in the gas by direct decomposition even in the presence of carbon dioxide and CO ₂ .

[0004]

In order to achieve this object, a method of treating a nitrogen oxide-containing gas according to the present invention is characterized in that the nitrogen oxide-containing gas is treated with magnesium zirconate (Mg) at a temperature range of 750 ° C. or more. MgZrO _x (x is 1
3)) is to decompose and remove nitrogen oxides by contacting with a remover having a main component, and the actions and effects are as follows.

[0005]

[Action] That is, magnesium zirconate (MgZrO _x (x is 1-3)) as a direct decomposition / removal agent for nitric oxide
Is used, but this compound shows an effective decomposition activity even in the presence of carbon dioxide gas. Therefore, if this compound is disposed at a site where NOx is transferred, and this site is set at 750 ° C. or higher,
NOx is directly decomposed into nitrogen and oxygen, and the nitrogen oxide-containing gas can be rendered harmless.

[0006]

Accordingly, a method for treating a nitrogen oxide-containing gas can be obtained which can effectively treat NOx contained in the gas by direct decomposition even in the presence of carbon dioxide and CO ₂ . .

[0007]

In EXAMPLES removal of NOx in the NOx-containing gas, MgZrO _{x (x} = 1~3 in the gas flow path, a perovskite-type compound to form an oxygen deficiency at room temperature or higher,
(Hereinafter, this will be omitted.) And this arrangement | positioning part is kept warm at 750 degreeC or more. By doing so, NOx is removed and clean gas is sent out downstream of the portion where the gas flow path is provided. Below is MgZr
The decomposition activity of O _x for NOx will be described more specifically. Compound MgZrO _x formed into granules of 1-2 mm, reaction temperature 900 ° C NOx concentration 3000 ppm SV value 1000 h ^-1 CO ₂ concentration 12% Result NOx removal rate 10%

[Experimental Example] An experimental example relating to the present application will be described below. Here, the target is the general formula MZrO _x
(X = 1 to 3, M: Mg, Ba, Sr).
These are perovskite-type compounds, and it has been found that these compounds exhibit decomposition activity with respect to this gas when they are brought into contact with only NOx. It is thought that the reason why these compounds work effectively in the decomposition of NOx may be related to the fact that the oxygen contained in the structure is desorbed due to the heating operation and the number of oxygen defects increases. I have.

[0009] Now, the various exhaust gas, also CO ₂ as well as NOx is contained in a large amount. This CO ₂ acts as an inhibitor in the mechanism of direct decomposition of NOx, and may significantly reduce the direct resolution of NOx. We have C
Various experiments were conducted on the NOx direct decomposition catalyst in the presence of O ₂ gas, and the following results were obtained.

First, the state of change in the NOx resolving power of the above compound in the case of CO ₂ coexistence and of NOx alone will be described. [Result 1] NOx decomposition characteristics in the presence of CO ₂ Perovskite-type compounds having compositions of MgZrO _x , BaZrO _x , and SrZrO _x were each formed into granules having a size of 1 to 2 mm, the reaction temperature was 900 ° C, and the NOx concentration was 3000 ppm.
FIG. 1 shows the result of contact under the conditions of —CO ₂ (12%) and SV: 1000 h ⁻¹ . The vertical axis indicates the NOx removal rate, and the horizontal axis indicates the elapsed time. Here, MgZrO _x is
, And BaZrO _x is indicated by ●, and SrZrO _x is indicated by Δ. As a result, while MgZrO _x maintained a removal rate of about 10% even about 2 hours after the start of the experiment, BaZr
O ₃ and SrZrO ₃ showed almost no decomposition activity.

[Result 2] Decomposition characteristics of NOx alone FIG. 2 shows the removal rate of NOx without CO ₂ , corresponding to FIG. The experimental conditions, the results CO ₂ for one of the conditions
The only difference is that there is no gas. As a result, BaZrO _x is the highest, and the removal rate decreases in the order of SrZrO _x and MgZrO _x . Here, in result 1, Mg having the highest removal rate was used.
In the case of ZrO _x , in FIG. 1 as compared with FIG. 2, the removal rate is reduced by half, but is still maintained.

[Result 3] NOx removal rate depending on CO ₂ concentration in MgZrO _x FIG. 3 shows the results of NOx removal (decomposition) characteristics of MgZrO _x under different CO ₂ gas concentrations. Other conditions were as follows: reaction temperature: 900 ° C., SV value: 10
00h ^-1 , NOx concentration: 3000 ppm, which is the same as described above. ○ The one with a CO ₂ gas concentration of 12%
, And those of 500 ppm are indicated by ●. As a result, when the CO ₂ gas concentration is 12%, the removal rate is
pm, a removal performance of about 15% can be obtained.

[0013] [Results 4] The relationship diagram 4 the NOx removal rate and the reaction temperature in MgZrO _x are shown changes in the NOx removal rate for reaction temperatures of MgZrO _x. The experimental conditions were as follows: SV: 1000h
^-1 , CO ₂ concentration: 12%, NOx concentration: 3000 ppm
It is. As a result, in the temperature range of 750 ° C. or more, NOx
Effective removal was observed by direct decomposition of the compound. The removal rate increased as the temperature range was increased, and at about 900 ° C., a removal rate of about 10% was obtained.

[0014] [Results 5] The relationship diagram 5 of the NOx removal rate and the SV value in MgZrO _x are shown changes in the SV value and the NOx removal rate MgZrO _x. The experimental conditions were as follows: reaction temperature: 900 ° C., CO
₂ concentration: 12%, NOx concentration: 3000 ppm,
The values 2 hours after the start of the measurement are shown. As a result, the NOx removal rate decreases as the SV value increases,
^-1 indicates a value of about 10%, indicating data that can be sufficiently put into practical use.

[0015] [Another Embodiment] MgZrO _x only needs to satisfy the above conditions in use, in the synthesis process, the starting raw material is not limited in particular, solid-phase reaction method is also a method for synthesizing And a liquid phase reaction method, but the method is not particularly limited. Further, the compound is kept in a particulate state with N
It may be provided in a gas containing Ox or may be used after being formed into any shape such as a honeycomb shape.

In the claims, reference numerals are provided for convenience of comparison with the drawings, but the present invention is not limited to the configuration shown in the attached drawings.

[Brief description of the drawings]

FIG. 1 is a view showing the NOx removal rate of each compound in the presence of carbon dioxide.

FIG. 2. NO of each compound when carbon dioxide does not coexist
Diagram showing x removal rate

FIG. 3 is a graph showing the NOx removal rates of MgZrO _{x in} the presence of different concentrations of carbon dioxide gas.

FIG. 4 is a diagram showing the relationship between the NOx removal rate of MgZrO _x and the reaction temperature.

FIG. 5 is a diagram showing the relationship between the NOx removal rate of MgZrO _x and the SV value.

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Shigeru Morikawa 17 Nakamichi-ji Minamicho, Shimogyo-ku, Kyoto-shi Kyoto Prefecture Inside the Kansai New Technology Research Institute (72) Inventor Takashi Kobayashi 17 Nakamichi-ji Minamicho, Shimogyo-ku, Kyoto Kyoto (56) References JP-A-4-118050 (JP, A) JP-A-4-171016 (JP, A) JP-A-4-265154 (JP, A) (58) Fields investigated ( Int.Cl. ⁷ , DB name) B01D 53/94 B01J 21/00-38/74

Claims (1)

(57) [Claims] 1. A method for treating a nitrogen oxide-containing gas which decomposes and removes a nitrogen oxide contained in the presence of carbon dioxide CO ₂ , wherein the nitrogen oxide-containing gas is heated at a temperature of 750 ° C. or higher. With magnesium zirconate (MgZrO _x (x is 1 to
3) A method for treating a nitrogen oxide-containing gas, wherein the nitrogen oxide is decomposed / removed by contacting the same with a remover as a main component.