JPH09155162A - Deinitration method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform the denitration of a gas containing NOx such as exhaust gas at a low temperature by allowing a denitrating agent consisting of a metal borne by zeolite to chemically react with a gas containing NOx through their mutual contact in the presence of ketone. SOLUTION: A denitrating agent 8 is obtained by depositing a metal such as V or Cr on a zeolite carrier. In addition, a gas guide-in pipe 2 and a bypass pipe 4 with a flow rate adjusting valve 3 are connected to a gas guide-in port 5, and a denitrating holder 7 is formed in the center part of a denitrating pipe 1 to support the honeycomb-like denitrating agent 8. Further, a heater 9 is disposed near the denitrating agent holder 7 and the honeycomb-like denitrating agent 8 to a specified temperature. Besides, a nozzle 6 for ejecting a reducing agent solution such as ketone is inserted into a space between the gas guide-in pipe 5 of the denitrating pipe 1 and the denitrating agent holder 7. Thus it is possible to denitrate the gas containing NOx in a comparatively lower temperature area in the presence of ketone as the reducing agent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology for removing NO _x , for example, a technology for removing NO _x contained in smoke emitted from an internal combustion engine such as a diesel engine.

[0002]

2. Description of the Related Art Conventionally, NO _x processing technology has been required in various fields. For example, NO _x present in exhaust gas from a diesel generator or the like is harmful to the human body and may cause acid rain. Therefore, it is desired to effectively treat NO _x in the exhaust gas.

Examples of such NO _x removal methods include a three-way catalyst method used in automobiles (gasoline vehicles) and a selective catalytic reduction method using ammonia.

However, in the above-mentioned three-way catalyst method, particularly when denitration of exhaust gas with excess oxygen is carried out, the deterioration of the catalyst progresses and the life of the catalyst is shortened.

Further, in the selective catalytic reduction method using ammonia, harmful and dangerous ammonia gas is used, so that it is necessary to handle it with caution. Furthermore, since the reduction catalyst is deteriorated by other components in the exhaust gas, it is necessary to replace the catalyst, which is economically disadvantageous when a particularly expensive noble metal-based catalyst is used.

Therefore, for example, Japanese Patent Laid-Open No. 63-283727.
As disclosed in the publication, a method of contacting a zeolite containing various metals with a gas containing NO _{x in} the presence of hydrocarbons has been studied and has already been put to practical use. The Japanese Patent Application No. 5-178670 filed by the present applicant also discloses a technique for denitration by contacting a catalyst supporting cobalt on zeolite with NO _x gas in the presence of a reducing agent such as carboxylic acid or its ammonium salt. It is shown.

[0007]

However, when the catalyst supporting cobalt on zeolite is brought into contact with NO _x gas in the presence of a reducing agent such as carboxylic acid or its ammonium salt, the optimum reaction temperature is 400 ° C. That is a relatively high temperature. Therefore, the installation location of such denitration equipment is
Limited by such high temperatures. Therefore, it is desired to shift the optimum reaction temperature to the low temperature side to expand the adaptability.

[0008] The present invention has been made under the above background, and to perform the denitration of the NO _x containing gas such as the exhaust gas at a low temperature and its problems.

[0009]

In order to solve the above problems SUMMARY OF THE INVENTION The present invention is characterized by contacting reacting denitrating agent and NO _x containing gas obtained by the metal is supported the zeolite in the presence of a ketone And

Acetone is preferably used as the ketone.

More preferably, the metal is cobalt and the contact temperature between the NO _x containing gas and the zeolite is about 250 ° C.

The present invention will be described in more detail below.

V, C on a carrier such as zeolite or alumina
When a metal (active metal) such as r, Cu, Fe, Mo, W, Mn, Mg, Ru, and Rh is supported, active points are expressed and a denitration action is obtained.

However, when the NOx removal agent in which a metal is supported on a carrier such as zeolite as described above is actually used for catalytic reaction with exhaust gas of a diesel engine to perform NOx removal, the NOx removal performance deteriorates.

The cause is S contained in the exhaust gas.
It can be mentioned that O _x gas (sulfur sulfide) coats the surface of zeolite and also reacts with the catalytically active metal to become a catalyst poison.

On the other hand, when a reducing agent is allowed to coexist during the contact reaction between the NO _x gas and the denitration agent, the SO _x gas preferentially reacts with the hydrocarbon. Therefore, the SO _x gas is suppressed from coating the surface of the zeolite, which also suppresses the reaction of the carrier such as zeolite or alumina with the active metal.

As described above, in the conventional method, carboxylic acid and ammonium carboxylate are used as reducing agents for the denitration agent. In contrast, in the present invention,
Acetone, which is a ketone, is used as the reducing agent.

As the catalyst, the same cobalt / zeolite system as the conventional one can be used. By using this reducing agent, it is possible to lower the conventional reaction temperature (optimum) of 400 ° C. to 250 ° C., and the denitration rate at 250 ° C. becomes close to 100%.

The main reason why this reaction temperature is possible is that
The ignitability of the reducing agent used, that is, the combustion temperature, is related to the carboxylic acid (eg, the boiling point of acetic acid is 117 ° C).
On the other hand, the boiling point of acetone can be inferred from the fact that it is 56.5 ° C. Since the NO _x reduction reaction proceeds at the same time as the combustion reaction, it is considered that the low temperature reaction is easy to vaporize the reducing agent. Therefore, it is preferable to use acetone having a low boiling point as the reducing agent, and among the acetones, acetone having a lower boiling point than the conventionally used carboxylic acid is preferably used.

Examples of the method of allowing the reducing agent to coexist during the contact reaction between the NO _x gas and the denitration agent include a method of spraying a solution of the reducing agent at the time of denitration.

As the above-mentioned zeolite, it is preferable to use an alkali metal-type zeolite, particularly Na-containing X-type zeolite, Na-containing Y-type zeolite, Na-containing mordenite, and (K, Na, C).
It is preferable to use type A zeolite containing at least one of a).

As the active metal supported on this zeolite, cobalt is preferably used. There are various methods for supporting the active metal, but preferably the zeolite is immersed in a metal salt solution having a predetermined concentration, and the active metal such as cobalt is sufficiently diffused in the pores of the zeolite. After checking, evaporate the metal salt solution as it is, or
Alternatively, the immersed zeolite is pulled out and taken out from the aqueous solution, and then the water contained in the zeolite is removed.

By thus bringing the metal salt and zeolite into contact with each other, ion exchange or the like occurs and the active metal is supported on the zeolite. In the present specification, the state in which the active metal and the zeolite are physically or chemically integrated is described as carrying, not limited to such ion exchange.

The active metal salt is not particularly limited as long as it does not inhibit denitration, and for example, nitrates, acetates and the like are used.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION In the present embodiment, a catalyst obtained by impregnating a Y-type zeolite containing Na with cobalt by ion exchange is brought into contact with exhaust gas containing excess oxygen in the presence of a reducing agent. Denitration was performed. Acetone was used as a reducing agent at this time. Acetone was used as an aqueous solution diluted with pure water to about 40% in consideration of safety in handling. The details are shown below.

First, 30% (%) of clay and glass fibers were mixed and kneaded with powder of Na-containing Y-type zeolite (NaY-type zeolite: HSZ-320NAA manufactured by Tosoh Corporation), and then formed into a honeycomb shape. .

This honeycomb was dried for one day in the sun, dried at 50 ° C. for 10 hours and 100 ° C. for 5 hours, and then calcined at 750 ° C. for 2 hours to obtain a catalyst base material.

Next, 500 (ml) of a 0.1 (N) acetic acid aqueous solution was added to 500 (ml) of a 0.6 (mol / l) ammonium acetate aqueous solution.
Was added to make 1 liter, and cobalt nitrate was added to this mixed aqueous solution to prepare a solution having a concentration of 0.1 (mol / l) (cobalt nitrate 0.05 mol impregnation).

The above honeycomb molded body was immersed in this aqueous cobalt solution for 2 hours to obtain a zeolite containing cobalt by ion exchange. At this time, the pH of the aqueous cobalt solution was about 4.4.

After that, the honeycomb was taken out, washed with pure water, immersed in pure water for 30 minutes to remove impurities, and dried at 150 ° C. for 8 hours to obtain a zeolite denitration agent.

The denitration efficiency when a reducing agent was added to this catalyst was determined using the apparatus shown in FIG.

In FIG. 1, reference numeral 1 is a denitration pipe having a gas introduction port 5, to which a gas introduction pipe 2 and a bypass pipe 4 having a flow rate adjusting valve 3 are connected. A denitration agent holder 7 is provided at the center of the denitration tube 1, and a honeycomb-shaped denitration agent 8 is supported thereby. These denitration agent holder 7 and honeycomb-shaped denitration agent 8
The vicinity is maintained at a predetermined temperature by the heater 9.

A nozzle 6 for injecting a reducing agent solution is inserted between the gas inlet 5 of the denitration tube 1 and the denitration agent holder 7. At the other end of the denitration pipe 1, a processing gas discharge pipe 10 for introducing a processing gas to the mass spectrometer 11 and the NO _x analyzer 12 is inserted.

In the above apparatus, the NO _x containing gas flowing in from the gas introduction pipe 2 flows into the denitration pipe 1 through the gas introduction port 5 after the flow rate is adjusted by the flow rate adjusting valve 3. At this time, the surplus gas is exhausted from the bypass pipe 4.

The NO _x containing gas flowing into the denitration pipe 1 is
After the reducing agent is sprayed by the nozzle 6, it is contacted with a honeycomb-shaped denitration agent to denitrate. At this time, the reaction temperature was kept at about 250 ° C. by the heater 9.

The denitration has been NO _x containing gas as the process gas, the mass spectrometer through the processing gas exhaust pipe 10 (Nichiden ANELVA Ltd., AQA-360) 11 and NO _x analyzer (manufactured by Shimadzu Corporation, NOA-307DX) 12 In this configuration, the NO _x removal rate is measured.

NO _x standard gas (NO / N ₂ :
While adjusting the concentration of NO 1000ppm) and O ₂ gas to 13%, 2 liters per minute are contacted. Table 1 shows the standard gas components.

[0038]

Table 1 NO _x 1000 (ppm) SO _x 100 (ppm) O ₂ 13 (%) H ₂ O 10 (%) Immediately before this catalyst, an aqueous acetone solution was added in an amount of 0.5 (cc / h). And denitration was performed. As shown in Table 2, N
Removal rate of O _x is very high and 99.6%, the denitration temperature 40
The result was comparable to that at 0 ° C.

[0039]

[Table 2] From this result, even if the denitration reaction temperature is lowered to 250 ° C. by using acetone as the reducing agent, it is as good as when the denitration temperature is 400 ° C. using another reducing agent such as acetic acid or ammonium acetate. It turned out that the result was obtained. Therefore, even if the reaction temperature is further lowered, it is possible to obtain a certain degree of high denitration rate. The volume of the honeycomb is 700 (c
m ² ).

Furthermore, since the acetone used in this example can be stored as a solution, it is highly safe and easy to store and handle.

[0041]

As described above, according to the present invention,
By using acetone as the reducing agent, denitration can be performed in a lower temperature range (about 250 ° C.) than before, and a high denitration rate can be obtained.

Moreover, since denitration in a low temperature range is possible,
It is easier to install than conventional denitration equipment, and its application range has expanded.

Furthermore, since the conventional honeycomb catalyst can be used, the reaction temperature can be lowered by only replacing the reducing agent, and the range of the reaction temperature range is widened.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a denitration device according to an embodiment of the present invention.

[Explanation of symbols]

1 ... Denitration pipe 2 ... Gas introduction pipe 3 ... Flow control valve 4 ... Bypass pipe 5 ... Gas introduction port 6 ... Nozzle 7 ... Denitration agent holder 8 ... Honeycomb denitration agent 9 ... Heater 10 ... Gas exhaust pipe 11 ... Mass spectrometer 12 ... NO _x analyzer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hoki Haba 2-1-117 Osaki, Shinagawa-ku, Tokyo Inside the Meidensha Co., Ltd.

Claims (3)

[Claims] 1. A denitration method comprising contacting a denitration agent obtained by supporting a metal on zeolite and a NO _x -containing gas in the presence of a ketone. 2. The denitration method according to claim 1, wherein acetone is used as the ketone. 3. The metal is cobalt and N
The denitration method according to claim 1 or 2, wherein the contact temperature between the O _x -containing gas and the zeolite is about 250 ° C or higher.