JPH08192056A - Denitration method - Google Patents

Abstract

(57) Abstract: In denitration method so as to contact reacting Objective denitrating agent and NO _X containing gas in the presence of a reducing agent, denitration efficiency of the NO _x containing gas in a reaction vessel at elevated temperatures of a wide range from low The purpose is to increase. [Configuration] In the denitration method so as to contact the reaction zeolite denitration agent 4 obtained by supporting an active metal and a NO _X containing gas in the presence of a reducing agent, as the denitration agent 4, copper as the active metal And a zeolite carrying cobalt as an active metal are simultaneously adopted, and an ammonium acetate aqueous solution is adopted as a reducing agent, and the reaction temperature in the reaction tank 1 is 250 ° C to 450 ° C.
And maintained in the range of ℃ provides a denitration method to perform denitration of the NO _X containing gas. As this denitration agent, zeolite in which copper and cobalt are separately supported is used in combination at a volume ratio of 1: 1.

Description

Detailed Description of the Invention

[0001]

The present invention relates to relates to a denitration process for removing nitrogen oxides contained in the exhaust gas of an internal combustion engine or the like (NO _X).

[0002]

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

Generally, the above-mentioned NO _X treatment method has been put into practical use as a flue gas denitration technique. This flue gas denitration technology is roughly classified into a dry method and a wet method. At present, the selective catalytic reduction method, which is one of the dry methods, has been technically preceded, and is attracting attention as an effective denitration method.

The main reaction of the selective catalytic reduction method is as follows.

4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O ... (1) In this reaction, ammonia, hydrocarbon and carbon monoxide are used as reducing agents. Since NO _X is selectively removed even when oxygen coexists, it is effective when used to remove NO _X contained in the exhaust gas of a diesel engine or the like. In this reaction, a noble metal such as platinum or various metal oxides supported on alumina, titanium oxide (TiO ₂ ) or the like is used as a catalyst.

Further, in Japanese Patent Laid-Open No. 63-283727, a zeolite containing various metals is added to N in the presence of hydrocarbons.
Method of contacting a gas containing O _x is disclosed.

[0007]

The above-mentioned selective catalytic reduction method can treat NO _x with a simple system and can obtain a high denitrification rate, and can convert NO _x into harmless N ₂ gas and H ₂ O. On the other hand, it has the advantage of eliminating the need for waste liquid treatment by decomposing, but on the other hand, due to the use of harmful ammonia gas, great care must be taken in handling the ammonia gas, and the reduction catalyst is There is a problem that it is necessary to replace the catalyst because it may be deteriorated by components other than NO _x . Particularly expensive precious metal-based catalysts cannot be used in many cases from an economical point of view.

[0008] Further, there is a problem that the sintering of the catalyst component proceeds at high temperature, and conversely, at low temperature, ammonium reacts with water or SO _x to form a salt such as ammonium sulfate on the catalyst surface. Therefore, there is a problem that the denitration rate is lowered. Therefore, the operating temperature range is 320 ° C to 45 ° C.
Currently, the temperature is limited to 0 ° C.

As another denitration method, a direct decomposition method has also been studied. For example, in recent years, catalysts such as Cu-ZSM-5 zeolite and perovskite type complex compounds have been found, but the most highly active Cu-ZSM-5 is found. Even with zeolite, the catalytic performance may deteriorate due to SO _X or O ₂ in the exhaust gas, which is an obstacle to practical use.

The present invention was made in view of the above, denitrification process that may especially reactor temperature increases the denitration effects of the NO _x containing gas such as the exhaust gases within a wide range from a low temperature of the hot It is intended to provide.

[0011]

In order to solve the above problems SUMMARY OF THE INVENTION The denitration method so as to contact reacting a denitrating agent and NO _X containing gas obtained by supporting an active metal on the zeolite in the presence of a reducing agent In the above, as the denitration agent, a zeolite carrying copper as an active metal and a zeolite carrying cobalt as an active metal are simultaneously adopted, and an ammonium acetate aqueous solution is adopted as a reducing agent, and the reaction temperature in the reaction tank is and maintained in the range of 250 ° C. to 450 ° C. to provide a denitration method to perform denitration of the NO _X containing gas.

The denitration agent is a zeolite in which copper and cobalt as active metals are separately supported and the volume ratio is 1:
1 is used in combination with ammonium acetate having a concentration of 6 (mol / l) as the reducing agent and 2 (m
It is injected into the reaction tank at a flow rate of 1 / h).

[0013]

According to such a denitration method, the zeolite supporting copper as an active metal and the zeolite supporting cobalt as the active metal are simultaneously brought into contact with the NO _x -containing gas so that the concentration of ammonium acetate as the reducing agent is 6 (mol).
/ L), the reaction temperature is 25 when the flow rate is 2 (ml / h)
A high denitration rate with high characteristics can be obtained in the range of 0 ° C to 450 ° C. This is based on the operating characteristics that the catalyst supporting copper has a high denitrification property at the low temperature side, and the catalyst supporting cobalt has a high denitrification property at the high temperature side.

The coexistence of ammonium acetate as a reducing agent suppresses the deterioration of the denitration agent due to SO _X in the exhaust gas, etc., and has the effect of increasing the denitration rate and extending the life of the denitration agent.

[0015]

EXAMPLES Specific examples of the denitration agent according to the present invention will be described below. In this example, a zeolite supporting copper and a zeolite supporting cobalt were simultaneously adopted as the catalyst for the denitration agent, and by using an aqueous solution of ammonium acetate as the reducing agent, the denitration effect was obtained in a wide range of the reaction temperature of 250 to 450 ° C. It is based on the finding that it exhibits high activity. Specifically, the catalyst supporting copper has a high denitration characteristic on the low temperature side, and the catalyst supporting cobalt has a high denitration characteristic on the high temperature side. First, the catalyst shown in FIG. The denitration efficiency was calculated when an ammonium acetate aqueous solution as a reducing agent was added to the denitration agent used. In the figure, 1 is a reaction tank, 2 is a gas introduction pipe, a denitration agent holder 3 is arranged in the center of the reaction tank 1, and in this denitration agent holder 3 a zeolite carrying copper and a zeolite carrying cobalt Is filled with the denitration agent 4 formed in a honeycomb shape. The denitration agent holder 3 and the denitration agent 4 are held at a predetermined temperature by a heater 5. In addition, the gas introduction pipe 2 adjacent to the reaction tank 1
Also, a heater 6 is provided.

Reference numeral 7 is a tank filled with a reducing agent solution, 8 is a pump for feeding the reducing agent into the reaction tank 1, and 9 is a nozzle for injecting the reducing agent solution into the reaction tank 1.

Model gas M supplied to the gas introduction pipe 2
In order to prepare, a NO gas cylinder 10, an SO ₂ gas cylinder 11, an O ₂ gas cylinder 12, and an N ₂ gas cylinder 13 are prepared, and the mass flow controllers 14, 15, 16, 1 are respectively provided.
A mixed gas of NO gas, SO ₂ gas, O ₂ gas and N ₂ gas was created by No. 7, and the model gas was flown into the gas introduction pipe 2 via the flow rate control valve 18.

Reference numeral 19 is a temperature control board for the heaters 5 and 2
0 recorder, 21 NO _X · O ₂ analyzer 22 is a gas chromatography. The model gas M before and after flowing into the reaction tank 1 is sent to the NO _x O ₂ analyzer 21 and the gas chromatograph 22 by the switching action of each flow rate switching valve provided in the pipeline, and measurement is performed. It is performed, and the result is recorded in the recorder 20.

The actual denitration operation using the apparatus of FIG. 1 and the result thereof will be described below. In the present example, as the denitration agent 4, a powder having a composition of NaY-type zeolite which is Na-containing Y-type zeolite and H-type mordenite is formed and processed into a honeycomb shape is used as a catalyst base material, and the activity to be carried by the catalyst base material is used. As metals, copper (Cu) and cobalt (C
o) was adopted, and those separately supported were used in combination at a volume ratio of 1: 1. Further, a 6 (mol / l) ammonium acetate aqueous solution was used as the reducing agent.

As a method of supporting copper as an active metal,
The above honeycomb-shaped catalyst base material was added to a 0.05M copper nitrate aqueous solution to obtain 2
After impregnating for an hour, wash with ion-exchanged water and keep at 150 ° C for 8 hours.
Dried for hours. As a result, copper as an active metal diffuses into the pores of the zeolite, and the water contained in the zeolite is removed by drying. By contacting the aqueous copper nitrate solution and the zeolite in this way, ion exchange occurs and copper, which is an active metal, is supported on the zeolite. As a method of supporting cobalt as an active metal, the same operation was performed below using an aqueous solution of cobalt nitrate instead of the above aqueous solution of copper nitrate.

Then, the denitration agent 4 thus obtained is used as a denitration agent holder 3.
It is filled with 263 (cm ³ ) and the reaction temperature is set to 250 ° C., 300 ° C., 350 ° C., 400 ° C. by driving the heater 5.
A flow rate of 2 (ml / h) of ammonium acetate aqueous solution as a reducing agent is supplied from the tank 7 by driving the pump 8 while setting the temperature at 450 ° C. and flowing the mixed gas as the model gas M by 1.8 (l / min). While maintaining the above, the mixture was injected from the nozzle 9 to the bottom of the reaction tank 1.

Next, the model gas M and the reaction tank 1 which have passed through the reaction tank 1 as shown by the arrow in FIG.
The NO _x concentration and oxygen concentration of the model gas M that did not pass through the chamber, that is, the model gas M before and after the reaction were measured by the NO _x · O ₂ analyzer 21. And N of the model gas M before the reaction
The O _X concentration is C ₀ (ppm), and the NO _X concentration after the reaction is C ₁
The denitration rate was calculated as (ppm) by the following formula.

Denitration rate (%) = {C ₀ (ppm) −C ₁ (ppm)} / {C ₀ (ppm)} × 100 (2) Table 1 shows the above reaction temperatures. The denitration rate is shown.

[0024]

[Table 1]

According to Table 1, the concentration of ammonium acetate as a reducing agent is 6 (mol / l) and the flow rate is 2 (ml / h).
The denitration rate at a reaction temperature of 250 ° C is 90%,
The denitration rate at 0 ° C is 92%, and the denitration rate at 350 ° C is 93%.
%, The denitration rate at 400 ° C. was 99%, and the denitration rate at 450 ° C. was 99%, and extremely high denitration rate was obtained from low temperature to high temperature. This shows the results based on the finding that the catalyst supporting copper has high denitration characteristics at low temperatures and the catalyst supporting cobalt has high denitration characteristics at high temperatures.

The ammonium acetate concentration is 1.0 (mo
1 / l) or less, the reaction between ammonium acetate and NO is hindered due to the large amount of H ₂ O component, and conversely, the ammonium acetate concentration is 10.0 (mol / l) or more. When it is high, the redox reaction between ammonium acetate and O ₂ gas proceeds and the amount of ammonium acetate that has not reacted with NO increases. This was supported by the fact that the higher the ammonium acetate concentration, the lower the oxygen concentration of the gas in the process gas.

Further, when the catalytically active zeolite-supported zeolite and the NO _x containing gas are subjected to a catalytic reaction, ammonium acetate as a reducing agent is allowed to coexist to deteriorate the denitration agent due to SO _x in the exhaust gas. And the like, the denitration rate is increased, and the life of the denitration agent is extended.

[0028]

As described in detail above, the present invention provides a denitration method in which a zeolite carrying copper as an active metal and a zeolite carrying cobalt are simultaneously reacted with a NO _x containing gas. The concentration of ammonium acetate as a reducing agent is 6 (mol / l),
When the flow rate is 2 (ml / h), the reaction temperature is 250 ° C ~
It is possible to obtain a high-performance denitration rate in a wide range of 450 ° C.

In the denitration method to which the present invention is applied, when catalytically reacting zeolite supporting an active metal serving as a catalyst and a NO _x containing gas, ammonium acetate as a reducing agent is allowed to coexist with the exhaust gas. It is sO _X or the like suppressing deterioration of the denitration agent due in, has the effect of improved life of the denitrating agent with NOx removal efficiency is high, denitration ratio is preferably maintained by regulating the concentration of reducing agent The effect is obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the configuration of an experimental apparatus that carries out a denitration method according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reaction tank 2 ... Gas introduction pipe 3 ... Denitration agent holder 4 ... Denitration agent 5, 6 ... Heater 7 ... (For reducing agent) tank 8 ... Pump 9 ... Nozzle 10 ... NO gas cylinder 11 ... SO ₂ gas cylinder 12 ... O ₂ Gas cylinder 13 ... N ₂ gas cylinder 14, 15, 16, 17 ... Mass flow controller 18 ... Flow rate control valve 19 ... Temperature control panel 20 ... Recorder 21 ... NO _X O ₂ analyzer 22 ... Gas chromatography

Claims (3)

[Claims] 1. A denitration method so as to contact reacting a denitrating agent and NO _X containing gas obtained by supporting an active metal on the zeolite in the presence of a reducing agent, as the denitration agent, copper as the active metal And a zeolite carrying cobalt as an active metal are simultaneously adopted, and an aqueous solution of ammonium acetate is adopted as a reducing agent, and the reaction temperature in the reaction tank is 250.
° C. denitration method characterized by retaining in the range of to 450 ° C. performing denitration of the NO _X containing gas. 2. The denitration method according to claim 1, wherein the denitration agent is a combination of zeolite in which copper and cobalt as active metals are separately supported at a volume ratio of 1: 1. 3. The reducing agent has a concentration of 6 (mol /
The denitration method according to claim 1, wherein the ammonium acetate of 1) is used and injected into the reaction tank at a flow rate of 2 (ml / h).