JPH08323148A - Denitrating apparatus - Google Patents

Abstract

PURPOSE: To increase the rate of denitration by using a denitrating agent obtd. by carrying cobalt on a catalyst carrier formed by firing and honeycombing principal stock prepd. by mixing NaY type zeolite with H mordenite in a proper ratio. CONSTITUTION: In a denitrating apparatus in which NOx -contg. gas and a denitrating agent obtd. by carrying an active metal on zeolite are brought into a catalytic reaction under coexistence of a reducing agent, a denitrating agent obtd. by carrying cobalt on a catalyst carrier formed by firing and honeycombing principal stock prepd. by mixing NaY type zeolite with H mordenite in a proper ratio is used. The weight ratio between the zeolite and mordenite is regulated to 90:10 to 85:15 and an aq. soln. contg. 3mol/l acetic acid and 3mol/l ammonium acetate is used as the reducing agent. The rate of denitration is increased and the service life of the denitrating agent is prolonged.

Description

Detailed Description of the Invention

[0001]

The present invention relates to relates to a denitration apparatus 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 treatment technology has been required in various fields. For example, NO _X present in exhaust gas of diesel engines, etc. is harmful to the human body and, if released in the air, acid rain is generated. Therefore, it is desired to effectively treat NO _x in these exhaust gases.

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 other denitration methods, a direct decomposition method or a selective reduction denitration method using a hydrocarbon-based reducing agent has been studied,
For example, in recent years, Cu-ZSM-5 zeolite, perovskite-type composite compounds, and the like, on which a metal such as a transition metal or an alkaline earth metal is supported or ion-exchanged, is used as a catalyst to reduce NO _x to N ₂ using a reducing agent. However, since the reaction mechanism of this reaction has not been elucidated in detail, there is a problem that the activity greatly changes depending on the temperature, the combination of the catalyst (metal), the reducing agent and the like. Most also highly active Cu-ZSM-5 zeolite may catalyst performance deteriorates with SO _X or O ₂ in the exhaust gas, which is an obstacle in practical use.

The present invention has been made in view of the above, and an object of the present invention is to obtain an apparatus having an improved denitrification rate by optimally setting the composition ratio of zeolite used as a catalyst carrier. is there.

[0011]

SUMMARY OF THE INVENTION The present invention, in order to achieve the above object, into contact reacting a denitrating agent and NO _X containing gas obtained by the active metal is supported on the zeolite in the presence of a reducing agent In this denitration device, a denitration device using a denitration agent in which cobalt is carried on the catalyst carrier by firing and honeycomb forming a main raw material in which NaY-type zeolite and H mordenite are mixed at an appropriate ratio is provided. .

The mixing ratio of the NaY type zeolite and H mordenite is set to "90:10" or "85:15" (weight ratio), and 3M acetic acid / 3M ammonium acetate aqueous solution (M = mol / l) is used as the reducing agent. I am using.

[0013]

According to such a denitrification apparatus, the denitrification rate is increased by optimizing the composition ratio of the zeolite used as the catalyst carrier, and in particular, "NaY type zeolite: H mordenite = 90: 10". It was confirmed that the denitrification action of the exhaust gas becomes extremely good by setting the mixing ratio (weight ratio) of “85:15”.

Further, by coexisting ammonium acetate as a reducing agent, deterioration of the denitration agent due to SO _x in the exhaust gas is suppressed, the denitration rate is increased, and the life of the denitration agent is improved. To be

[0015]

EXAMPLES Specific examples of the denitration apparatus according to the present invention will be described below. In this example, in the reaction of reducing nitrogen oxides (NO _x ) to nitrogen gas (N ₂ ) using a catalyst and a reducing agent, the composition ratio of the zeolite used as the catalyst carrier is set to be high, The main purpose is to obtain a characteristic denitration device.

In this example, denitration agents were prepared by the following Comparative Examples 1 and 2 and Examples 1 to 4 in which the composition ratio of zeolite was changed, and the denitration rate was measured for each Comparative Example and Example.

Comparative Example 1 Using only NaY type zeolite as the main raw material, the main raw material was fired to form a honeycomb carrier to form a catalyst carrier, which was impregnated with a 0.05M aqueous cobalt nitrate solution for 2 hours. Was carried out and dried at 150 ° C. for 8 hours to prepare a denitration agent.

Comparative Example 2 Using only H mordenite as the main raw material, this main raw material was fired to form a honeycomb carrier into a catalyst carrier, which was impregnated with a 0.05 M aqueous cobalt nitrate solution for 2 hours to obtain cobalt. It was carried and dried at 150 ° C. for 8 hours to prepare a denitration agent.

Example 1 As a combination of NaY type zeolite and H mordenite, “NaY type zeolite:
H mordenite = 95: 5 ”(weight ratio), the main raw material having a mixing ratio of calcination is fired to form a honeycomb carrier into a catalyst carrier,
This was impregnated with a 0.05 M aqueous cobalt nitrate solution for 2 hours to carry cobalt, and dried at 150 ° C. for 8 hours to prepare a denitration agent.

According to the above operation, cobalt as the active metal diffuses into the pores of the zeolite, and the water contained in the zeolite is removed by drying. By contacting the aqueous cobalt nitrate solution and the zeolite in this way, ion exchange occurs, and cobalt, which is an active metal, is supported on the zeolite.

Example 2 As a combination of NaY type zeolite and H mordenite, “NaY type zeolite:
The main raw material having a mixing ratio of “H mordenite = 90: 10” was fired in the same manner as above to perform honeycomb forming to obtain a catalyst carrier, which was impregnated with a 0.05M aqueous solution of cobalt nitrate for 2 hours to support cobalt, A denitration agent was prepared by drying at 150 ° C. for 8 hours.

Example 3 As a combination of NaY type zeolite and H mordenite, “NaY type zeolite:
The main raw material having a mixing ratio of H mordenite = 85: 15 ”was fired in the same manner as above to perform honeycomb forming to obtain a catalyst carrier, which was impregnated with a 0.05M aqueous solution of cobalt nitrate for 2 hours to support cobalt, A denitration agent was prepared by drying at 150 ° C. for 8 hours.

Example 4 As a combination of NaY type zeolite and H mordenite, “NaY type zeolite:
The main raw material with a mixing ratio of H mordenite = 80: 20 ”was fired in the same manner as above to perform honeycomb forming to obtain a catalyst carrier, which was impregnated with a 0.05 M aqueous solution of cobalt nitrate for 2 hours to support cobalt, A denitration agent was prepared by drying at 150 ° C. for 8 hours.

Regarding the denitration agents of Comparative Examples 1 and 2 and Examples 1 to 4 obtained as described above, 3M acetic acid / 3 as a reducing agent
An M ammonium acetate aqueous solution (M = mol / l) was added, and the denitration efficiency was determined by the apparatus shown in FIG. 1 in the figure
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 the denitration agent holder 3 is filled with a honeycomb-shaped denitration agent 4. The denitration agent holder 3 and the denitration agent 4 are held at a predetermined temperature by a heater 5. A heater 6 is also provided in the gas introduction pipe 2 adjacent to the reaction tank 1.

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 panel for the heaters 5 and 6, and
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 experimental conditions are as follows.

(1) Reaction temperature: 400 ° C. (2) Sample gas: NO concentration 860 ppm, oxygen concentration 8.5%, SO ₂ concentration: 60 ppm Gas flow rate 1.75 (l / min) (3) Reducing agent: 3M Acetic acid / 3M aqueous ammonium acetate solution (M = mol / l) (4) Main raw material of catalyst carrier: NaY type zeolite and H mordenite (5) Metal supported on catalyst carrier: cobalt (Co) The apparatus of FIG. 1 is used below. The actual denitration operation and its result will be described. In this example, Comparative Examples 1 and 2 and Examples 1 to 4 are used.
The denitration agent 4 supporting cobalt by means of the denitration agent holder 3
It is filled with 263 (cm ³ ) and the reaction temperature is set to 400 ° C. by driving the heater 5 to allow 1.75 (l / min) of the mixed gas to flow as the model gas M, and the tank is driven by the pump 8. 7 to acetic acid / reducing agent
An ammonium acetate aqueous solution was injected from the nozzle 9 to the bottom of the reaction tank 1 while maintaining a flow rate of 0.5 to 2 (ml / h).

The injection amount of the reducing agent is 0.5 to 2 (ml /
The acetic acid gas concentration when acetic acid is vaporized in the gas in h) is calculated to be 643 to 2571 ppm. Therefore, the amount of acetic acid to be reacted is changed by changing the injection amount.

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 reducing agent concentrations of 640 to 640. FIG. 2 is a graph showing the correlation between the reducing agent (acetic acid) concentration and the denitration rate when the denitration rate was changed to 2560 ppm.

[0033]

[Table 1]

According to Table 1 and FIG. 2, the denitrification rates of Examples 1 to 4 were higher than those of Comparative Examples 1 and 2, regardless of the concentration of the reducing agent, and particularly, Example 2 was used. In the example of the mixing ratio of NaY-type zeolite: H mordenite = 90: 10 ”and the mixing ratio of“ NaY-type zeolite: H mordenite = 85: 15 ”in Example 3, the reducing agent concentration is 1280 ppm or more. The denitration rate reached almost 100%, confirming that the denitration effect was good.

In the denitration apparatus to which the present invention is applied, when the zeolite supporting cobalt serving as the catalyst and the NO _x containing gas are caused to react with each other, ammonium acetate as a reducing agent is allowed to coexist in the exhaust gas. that is such a deterioration of the denitration agent according sO _X or the like is suppressed, has the effect of improving also the 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.

[0036]

As described in detail above, according to the present invention, it is possible to increase the denitration rate by optimizing the composition ratio of the zeolite used as the carrier of the catalyst, and in particular, "NaY type zeolite: H mordenite = 90". : 10 "
Alternatively, by using the same mixing ratio (weight ratio) of “85:15”, a denitrifying agent having high characteristics can be obtained.

In particular, since an expensive noble metal-based catalyst is not used as a reducing catalyst, it is effective from an economical point of view, and no harmful ammonia gas is used as a reducing agent. Has the advantage that it is not required.

Further, the coexistence of ammonium acetate in the reducing agent suppresses the deterioration of the denitration agent due to SO _X in the exhaust gas, and the effect of increasing the denitration rate and extending the life of the denitration agent can be obtained. To be

[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.

FIG. 2 is a graph showing the correlation between the concentration of reducing agent (acetic acid) and the denitration rate in this example.

[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 denitrator zeolite denitration agent obtained by supporting an active metal and a NO _X containing gas so as to contact the reaction in the presence of a reducing agent, a suitable ratio of NaY-type zeolite and H-mordenite A denitration device characterized in that the main raw material mixed in step 1 is fired and honeycomb formed into a catalyst carrier, and a denitration agent carrying cobalt is used on the catalyst carrier. 2. The mixing ratio of the NaY zeolite and H mordenite is “90:10” or “85:15”.
The denitration apparatus according to claim 1, wherein the (weight ratio) is set. 3. The denitration apparatus according to claim 1, wherein 3M acetic acid / 3M ammonium acetate aqueous solution (M = mol / l) is used as the reducing agent.