JPH03217218A - Method for removing nitrogen oxide - Google Patents

Abstract

PURPOSE:To effectively remove nitrogen oxides, especially nitrogen monoxide, from combustion exhaust gas by treating the combustion exhaust gas incorporating oxygen at 200-500 deg.C in the coexistence of hydrocarbons and a zeolite catalyst carrying copper. CONSTITUTION:The zeolite catalyst carrying copper by at least about 0.5wt.% and preferably about 1.0wt.% is prepared by dispersing the zeolite in a copper solution and adding an alkline solution thereinto so as to control pH. Nitrogen oxides are removed from combustion exhaust gas incorporating, oxygen by treating this exhaust gas at 200-500 deg.C in the coexistence of hydrocarbons and the above-mentioned zeolite catalyst carrying copper. The hydrocarbons to be used are preferably selected from olefins, paraffins, naphthenes, etc., having 1-6C and the add amt. thereof is preferably 20-5000ppm to the combustion exhaust gas.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for efficiently removing nitrogen oxides from combustion exhaust gas containing oxygen. The present invention relates to a method for removing nitrogen oxides from oxygen-containing combustion exhaust gas at a constant temperature in the presence of hydrogen.

[Prior Art] From the perspective of environmental conservation, the removal of air pollutants is a major social issue. In particular, purification of combustion exhaust gas accompanying the expansion of industrial activities is a current urgent issue.

Nitrogen oxides contained in combustion exhaust gas emitted from factories, which are fixed sources, and automobiles, which are mobile sources, are said to be the cause of photochemical smog and are harmful to the human body, especially nitrogen monoxide (No. are difficult to remove and are the most important issue to consider.

Several methods have been proposed to remove nitrogen oxides from combustion exhaust gas. For example, a method called catalytic reduction method uses a reducing agent such as ammonia or hydrogen to remove No by converting it into N2 and H20 on a catalyst. However, since this method uses a reducing agent, measures must be taken to recover it and prevent leakage, and although it is effective for large-scale stationary sources, it is not suitable for sources such as automobiles.

On the other hand, many catalysts have been developed to purify the exhaust gas of gasoline engines, whose exhaust gas is a reducing gas.
Commonly used. However, these catalysts cannot be used in the coexistence of oxygen.

By the way, the catalytic decomposition of No, that is, the method of directly decomposing No into N2 and O2, requires only passing the exhaust gas through the catalyst layer, and is extremely simple, so it can be used in a wide range of applications. Various catalysts have been found for this purpose as well. Pt,
CuO, Co-based catalysts are effective in decomposing No, but both have the problem of being poisoned by the oxygen they produce.

Exhaust gases from diesel engines and exhaust gases from lean-burn gasoline engines usually contain oxygen, so conventional catalysts cannot handle this problem, so there is a need to develop a new method.

[Problems to be Solved by the Invention] Several catalysts have been proposed to solve the above problems. For example, JP-A-60-125250 discloses that a special zeolite containing copper is effective in decomposing NO in a system containing oxygen. Additionally, the effectiveness of copper-containing perovskites has also been shown in “rcHEMlsTRY”.
LETTER Magazine J, 1988, 1797-1800
It is said that these compounds can remove nitrogen monoxide even from exhaust gas containing oxygen, but their effectiveness is not clear, and there are reports that their activity is extremely low in the coexistence of oxygen.

An object of the present invention is to suppress a decrease in catalyst activity and to effectively remove nitrogen oxides, particularly nitrogen monoxide, from oxygen-containing combustion exhaust gas.

[Means for Solving the Problems] The present invention relates to a method for solving the above problems, in which combustion exhaust gas containing oxygen is made to coexist with hydrocarbons and treated at a specific temperature using a copper/zeolite catalyst. This is based on the discovery that nitrogen oxides, especially nitric oxide, can be efficiently removed by this method.

That is, the present invention provides a method for removing nitrogen oxides from combustion exhaust gas containing oxygen at 200 to 500°C in the coexistence of hydrocarbons using zeolite supported on copper as a catalyst. Regarding the removal method.

The zeolite supporting copper as used in the present invention is a zeolite containing a predetermined amount of copper.

In the present invention, the sulfur zeolite is a crystalline aluminosilicate, and its composition is represented by the following formula.

xM2 , O-AJ203 ・yS i02 ・z
H20 (n is the valence of the cation M, X is 0.8 to 2.0
(y is a number of 2.0 or more, 2 is a number of 0 or more) The basic structure of theolite is a regular three-dimensional combination of Si, AJ, and 0, and due to the difference in structural units, It takes on various crystal structures. There are many types of zeolites, which are characterized by X-ray diffraction and have different names depending on their crystal structure. For example, natural products include mordenite, erionite, and chabasite, and synthetic products include A type, X type, Y type, and ZSM-5.

The zeolite used in the present invention is not particularly limited. Either a natural product or a synthetic product may be used, but a synthetic product is preferably used because the former contains impurities and requires time and effort to purify.

Zeolite is synthesized by mixing a suitable silica source, alumina source, alkali source, or in some cases a metal compound (e.g. Fe, Ga, etc.) in place of the alumina source, and
It can be easily obtained by crystallization under hydrothermal conditions of about 50°C. There are also products obtained by hydrothermal synthesis by adding an organic substance called a template to the above-mentioned mixture. Zeolites are generally commercially available and may be used. The zeolite preferably used in the present invention is Y
type, mordenite type, metallosilicate, ZSM-5, etc., and ZSM-5 is more preferable.

In the present invention, the method of introducing copper into zeolite is not particularly limited. Examples include an ion exchange method in which cations in the zeolite are exchanged with the desired metal cations, and an impregnation method in which the zeolite is immersed in a solution containing the desired metal. Preferably, the zeolite is dispersed in a copper solution, and an alkaline solution is added therein to adjust the pH. The copper raw material compound used in the present invention can be used in any form as long as it is a water-soluble steel salt. Examples include sulfates, hydrochlorides, nitrates, organic acid salts, metal complex salts, and the like.

As the metal species, those that generate cations are preferred. In the present invention, the copper content of the zeolite is at least
0.5% by weight, preferably at least 1.0% by weight.

The catalyst used in the method of the present invention may be formed into a suitable shape such as a sphere, a column, a honeycomb, etc. using an inorganic oxide such as silica or alumina or clay as a binder after introducing copper into zeolite. Alternatively, before introducing copper into the theolite, a binder may be added and molded, and then copper may be introduced. In any case, it is not particularly limited.

The hydrocarbon used in the present invention is a compound composed of carbon and hydrogen, and includes commonly-called olefins, paraffins, cyclic compounds, and hydrocarbons containing these compounds. Preferably, it is volatile and gaseous at the processing temperature of the present invention. More preferably, it is at least one hydrocarbon selected from olefins, paraffins, and naphthenes having about 1 to 6 carbon atoms. The amount of hydrocarbon added is 10% to the combustion exhaust gas.
~10000 ppm, preferably 20-5000
It is ppm.

If the amount of hydrocarbon added is less than 10 ppm, there will be no effect, and if it exceeds 10,000 ppm, there will be an unfavorable effect on the catalyst.

Furthermore, the combustion exhaust gas referred to in the present invention is one that contains oxygen, and preferably contains 0.1% by volume or more of oxygen. This combustion exhaust gas is discharged from ordinary internal twist engines, boilers, etc. The present invention is particularly effective for exhaust gas containing a large amount of oxygen, such as combustion exhaust gas from diesel engines and lean-burn gasoline engines.

The processing temperature according to the invention is in the range 200-500°C, preferably 230-450°C. If this temperature is lower than 200°C, nitrogen monoxide cannot be removed, and if it is higher than 500°C, the coexisting hydrocarbons will burn, resulting in a low nitrogen monoxide removal rate.

Note that in the present invention, the contact time between the catalyst and the processing gas is not limited.

When carrying out the removal method of the present invention, combustion exhaust gas heated to a predetermined temperature using a cooler or the like is introduced into a reaction treatment section filled with a catalyst, and the specified hydrocarbons in a dedicated tank are pumped into the reaction treatment section or before it. Just add it to the appropriate line. If the combustion exhaust gas does not reach a predetermined temperature, the reaction treatment section may be heated.

In addition, when applying the removal method of the present invention to exhaust gas from an engine, a portion of fuel oil such as gasoline that has entered an existing fuel tank is used as hydrocarbons, and this is passed through a bypass line from the fuel tank to the reaction processing section. By passing through the engine, the engine may be bypassed, and the exhaust gas may be added directly to the reaction processing section provided on the exhaust gas outlet side.Alternatively, a reforming section may be provided in the bypass line, and a portion of fuel oil such as gasoline may be reformed. It can also be added to the reaction treatment section after performing the following steps.

[Effects of the Invention] According to the present invention, a decrease in catalyst activity was suppressed, and nitrogen oxides, particularly nitrogen monoxide, could be efficiently removed from oxygen-containing combustion exhaust gas.

[Example] Next, the present invention will be described in more detail with reference to Examples.

(Catalyst Preparation) 30.0 g of ZSM-5 zeolite of Si02/Ano2 o3 or about 50 was dispersed in a 2.0 g solution containing 4.0 g of copper nitrate, and diluted ammonia water was added dropwise little by little. The pH was adjusted to approximately 7. Thereafter, the zeolite was filtered and thoroughly washed with ion-exchanged water. The obtained zeolite was dried under reduced pressure to obtain a copper/zeolite catalyst.

Examples 1 to 3 Using the catalysts obtained in the above catalyst preparation, reactions were carried out at the predetermined reaction temperatures shown in Table 1 in a gas containing 1000 ppm of nitrogen monoxide and 1.0% by volume of oxygen.

About 1000 pp. of ethylene, pro/man, and propylene were used as hydrocarbons. added into the reaction gas.

Comparative Example 1 A reaction was carried out in the same manner as in Examples 1 to 3 except that no hydrocarbon was added.

Comparative Example 2 The reaction was carried out in exactly the same manner as in Example 1, except that the treatment temperature was outside the range of 200 to 500 °C specified in the present invention (150 °C and 550 °C). Examples 1 to 3 and comparison Table 1 shows the results of the No conversion rate at each temperature according to Examples 1 and 2.

As is clear from the results in Table 1, it was found that Examples 1 to 3 in which hydrocarbons were added had high decomposition activity in the treatment temperature range of 200 to 500°C.

On the other hand, in Comparative Example 1 in which no hydrocarbon was added, the treatment temperature was 4.
At 00°C, a removal rate of only a few percent could be obtained.

Furthermore, as shown in Comparative Example 2, even if hydrocarbons are added, there is almost no activity when the treatment temperature is less than 200°C, and 50°C
It can be seen that the activity decreases when the temperature exceeds 0°C.

Claims (1)

[Claims] 1. Nitrogen oxidation, characterized in that nitrogen oxides are removed from combustion exhaust gas containing oxygen at 200 to 500°C in the coexistence of hydrocarbons using zeolite supported on copper as a catalyst. How to remove things. 2. The hydrocarbon is at least one selected from olefins having 1 to 6 carbon atoms, paraffins, and naphthenes.
The removal method according to claim 1, which is a seed.