JPH06319954A - Denitration - Google Patents

Abstract

PURPOSE:To efficiently denitrate NOx-containing gas by a method wherein a catalytic reaction is made between the denitration agent having a matal supported on zeolite and the NOx containing gas in the presence of carboxylic acid, etc. CONSTITUTION:When active matals such as V, Cr, etc., are supported on a carrier such as zeolite, etc., an active site occurs and denitration action is obtained. When a catalytic reaction is made between the denitrating agent thus obtained and NOx gas, carboxylic acid and/or carboxylic acid ammonium is made present as a reducing agent. Then SOx gas reacts preferentially with hydrocarbon and is restrained from covering the zeolite surfice. By this method, the denitration rate becomes high and the life of the denitrating agent can also be extended. Particularly by using cobalt as the active matal, the SOx poisoning can be suppressed.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an elimination technology NO _x, relates to a technique for especially removing NO _x from the NO _x containing gas such as flue gas of the internal combustion 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 of a diesel generator or the like is harmful to the human body and causes generation of 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 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.

[0007]

However, in the denitration method using the above zeolite, various metals contained in the zeolite as a catalyst component are sulfur oxides (SO _x ) in the exhaust gas.
It will be poisoned by the above and the catalytic activity will decrease.

Further, since the hydrocarbon used as the reducing agent in this denitration method is easily combusted in the high temperature exhaust gas, the amount of the hydrocarbon effectively acting as the reducing agent on the catalyst is small.

[0009] The present invention has been made under the above circumstances, and an object thereof to perform denitration of the NO _x containing gas such as the exhaust gas efficiently.

[0010]

In order to solve the above-mentioned problems, the invention according to claim 1 uses a denitration agent obtained by supporting a metal on zeolite and a NO _x -containing gas as a carboxylic acid and / or a carboxylic acid. Provided is a denitration method characterized by carrying out a contact reaction in the presence of ammonium acid.
The invention according to claim 2 provides the denitration method according to claim 1, wherein the NO _x -containing gas contains O ₂ . The invention according to claim 3 provides the denitration method according to claim 1 or 2, wherein a zeolite carrying cobalt is used as the denitration agent.

A fourth aspect of the present invention provides the denitration method according to the third aspect, wherein the NO _x- containing gas contains SO _x .

The fifth aspect of the present invention provides the denitration method according to any one of the first to fourth aspects, wherein acetic acid is used as the carboxylic acid.

The invention according to claim 6 provides the denitration method according to any one of claims 1 to 6, characterized in that ammonium acetate is used as the ammonium carboxylate.

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 an organic acid, for example, a carboxylic acid such as acetic acid or a salt of a carboxylic acid coexists as a reducing agent during the contact reaction between the NO _x gas and the denitration agent, the SO _x gas is preferentially mixed with hydrocarbon. As a result, the SO _x gas is prevented from coating the surface of the zeolite, and thereby the carrier such as zeolite or alumina is also prevented from reacting with the active metal.

It is known that when denitration is carried out in the presence of an organic acid, the denitration reaction is promoted in the presence of O ₂ .

Particularly, in the denitration agent using Co as an active metal, it was confirmed that the poisoning by SO _x is almost completely suppressed when the denitration is carried out in the coexistence of O ₂ and an organic acid, especially acetic acid. Was done. Further, in the denitration agent using V as an active metal, poisoning by SO _x is relatively small.

[0021] Although the denitrating agent to the metal of the active metal other than Co to varying slightly the degree of, contrast reduction in denitrification rate due to poisoning of the SO _x is seen by the Co and active metal It is possible to almost completely avoid such a decrease in the denitration rate.

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 zeolite used in each of the above inventions, it is preferable to use an alkali metal type zeolite, in particular, an X type zeolite containing Na, a Y type zeolite containing Na, a mordenite containing Na, and (K, It is preferable to use an A-type zeolite containing at least one of Na and Ca).

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

[0027]

Example In this example, denitration was carried out by contacting an exhaust gas containing excess oxygen with a catalyst obtained by impregnating an alkali metal type zeolite with cobalt by ion exchange in the presence of a reducing agent. As the reducing agent at this time, a mixed aqueous solution of ammonium acetate and acetic acid (Examples 1 and 2), an aqueous solution of ammonium acetate (Example 3), and acetic acid (Example 4) were used.

Further, V, Cu, Fe, Mo,
Using a denitration agent supporting Co, Cr, and Mn, acetic acid as a reducing agent was used to measure the denitration rate under various conditions (Example 5).

The details will be described below.

Example 1 First, 30% (by weight) 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. processed.

After drying this honeycomb for one day in the sun,
After being dried at 50 ° C. for 10 hours and at 100 ° C. for 5 hours in a dryer, it was further 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 formed body was immersed in this aqueous cobalt solution for 2 hours to obtain a cobalt-containing zeolite 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 the honeycomb was dried at 150 ° C. for 8 hours to obtain a zeolite denitration agent.

The NOx removal 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. A heater 9 keeps the vicinity of the denitration agent holder 7 and the honeycomb-shaped denitration agent 8 at a predetermined temperature.

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 tube 1, a mass spectrometer 11 and N
Process gas discharge pipe 1 for introducing process gas into the O _x analyzer 12
0 is inserted.

In the above apparatus, the NO _x containing gas flowing in from the gas introducing pipe 2 flows into the denitration pipe 1 through the gas introducing 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 for denitration. At this time, the reaction temperature was kept at about 400 ° C. by the heater 9.

After the NO _x- containing gas is denitrated, it is treated as a treatment gas through a treatment gas discharge pipe 10 to a mass spectrometer (AQA-360 manufactured by Nichiden Anelva) 11 and a NO _x analyzer (NOA-307DX manufactured by Shimadzu Corporation) 12. In this configuration, the NO _x removal rate is measured.

NO standard gas (including SO _x 100 (ppm) and O ₂ 13 (%)) having an inlet concentration of 820 (ppm) was flown into the above-mentioned denitration apparatus, and denitration was performed every 1000 seconds while spraying a reducing agent. went. The reducing agent was prepared by mixing 1 (N) acetic acid aqueous solution with 1 (mol / l) ammonium acetate aqueous solution.

FIG. 2 is a graph showing the correlation of NO concentration with respect to time around a (s) to (a + 1000) (s). Further, the correlation between the temperature and the oxygen concentration with respect to the time of denitration is shown in FIG. 2 together with the B line and the C line.

In this figure, as shown by line A, N
When the reducing agent is sprayed, the concentration of O becomes low, but the concentration increases eventually. At point a in the figure, the density is 1
It is 28 (ppm). If the reducing agent is sprayed at this point, NO
The concentration drops to 2 (ppm). The NO concentration will change around 2 (ppm) for a while after spraying, but will gradually increase.

Then, by spraying the reducing agent again at the time of (a + 1000) seconds, the NO concentration is again 2 (ppm).
Fall to.

As described above, the NO concentration becomes extremely low by spraying the reducing agent, and the reducing agent is sprayed again after the reducing agent is consumed, so that the NO concentration becomes 2 (pp) again.
It can be as low as m). This NO removal rate is
It has reached 99.8 (%).

As shown by the lines B and C in FIG. 2, the oxygen concentration was 13% and the temperature was stable at 400 ° C.

From the above experimental results, it can be seen that the NOx removal rate is greatly improved by spraying the reducing agent on the NO standard gas.

Example 2 In Example 2, denitration was carried out under the same conditions as in Example 1 except that the exhaust gas of the actual machine was used in place of the standard gas and the reducing agent was sprayed once every 1200 seconds.

As the exhaust gas of the actual machine, the exhaust gas of a 40 kw class diesel generator (ZX-40PBS manufactured by Meidensha) was used. The initial NO concentration was 780 (ppm).

FIG. 3 is a graph showing the correlation of NO concentration with time before and after d (s) to (d + 1200) (s). Further, the correlation of temperature and oxygen concentration with respect to the time of denitration is also shown in FIG.

In this figure, as shown by the line D, N
When the reducing agent is sprayed, the concentration of O becomes low, but the concentration increases eventually. The density is 6 at point d in the figure.
It is about 00 (ppm). If the reducing agent is sprayed at this point, the NO concentration drops to about 4 (ppm). The NO concentration will change around 4 (ppm) for a while after spraying, but will gradually increase.

Then, by spraying the reducing agent again at the time of (d + 1200) seconds, the NO concentration is again 4 (ppm).
Fall to. As described above, the NO concentration becomes extremely low by spraying the reducing agent, and the NO concentration is reduced again by spraying the reducing agent again after the reducing agent is consumed.
It can be as low as (ppm).

This NO removal rate reaches 99.4 (%). Further, as indicated by the lines E and F in FIG. 3, the oxygen concentration was 12.8 (%) and the temperature was 400 (° C.), which were stable.

Example 3 In Example 3, 1 to 10 (mol / l) ammonium acetate aqueous solution (manufactured by Kokusan Kagaku Co., Ltd., first grade) was used as a reducing agent, and denitration was performed under the same conditions as in Example 1. It was

As a result, as shown in Table 1, the NO gas having an inlet concentration of 820 (ppm) was reduced to 100 (ppm) by intermittently spraying the reducing agent once every 1000 seconds, to 87.8 (ppm). %) Removal rate was obtained.

[0058]

[Table 1]

Therefore, it can be seen that even if this reducing agent is used, denitration is sufficiently performed.

Example 4 In Example 4, denitration was performed under the same conditions as in Example 1 except that acetic acid of 1 to 10% was used as a reducing agent.

As a result, as shown in Table 2, NO gas having an inlet concentration of 820 (ppm) was reduced to 100 (ppm) by spraying the reducing agent, and a removal rate of 87.8% was obtained. It was

[0062]

[Table 2]

Example 5 In Example 5, V, Cu, Fe, Mo, Co, Cr and M were used.
A denitration agent carrying n was manufactured, and the denitration rates for standard gases A, B, and C having the compositions shown in Tables 3, 4, and 5 were measured.

[0064]

[Table 3]

[0065]

[Table 4]

[0066]

[Table 5]

In this example, the Co-supporting zeolite was produced in the same manner as in Example 1, and the zeolite supporting other metals such as V and Cu was replaced with the cobalt nitrate used in Example 1. Zeolite carrying each metal was produced according to Example 1 except that salts of these metals were used appropriately.

Further, in measuring the denitration rate, Example 1 was used.
The denitration apparatus used in 1. was used, and the measurement method was also in accordance with Example 1.

Table 6 shows the measurement results of the denitration rate using each of the above test gases A to C.

[0070]

[Table 6]

As shown in this table, in the test gas C containing no SO _x , a high denitration rate of about 90% was obtained with any supported metal.

On the other hand, test gas A containing SO _x
In most of the denitration agents, only about 60% of the denitration rate was obtained, and poisoning by SO _x is confirmed. However, in the denitration agent 1 using V as the supporting metal, 78
(%), A relatively high denitration rate was obtained, and in the denitration agent 5 using Co as the supporting metal, a very high denitration rate of 99.8 (%) was obtained.

Further, in the test gas B containing no O ₂ , the denitration rate was low by about 15 to 20 (%), and in the denitration agents 1 and 5 which had a high denitration rate in the test gas A, 25 ( %) And a denitration rate of about 30 (%) could only be obtained. Therefore, it is desirable to coexist with O ₂ when performing denitration.

Next, using the denitration agent 5 (cobalt-supporting zeolite) that gave the best results in the above test, the denitration rate for the actual exhaust gas was measured. The composition of this exhaust gas is shown in Table 7. It should be noted that dust particles in this exhaust gas are 45
(mg / Nm ³ ) included.

[0075]

[Table 7]

Table 8 shows the measurement results of the denitration rate for the above exhaust gas.

[0077]

[Table 8]

As shown in this table, in the denitration agent 5 carrying Co, 99.6 is obtained even when the actual exhaust gas is used.
A high NO _x removal rate of (%) is obtained, which shows that it has a very excellent denitration performance.

From this point, it is very suitable as a denitration agent for exhaust gas having a large amount of residual oxygen in the exhaust gas of gas engines, diesel engines and the like.

In each of the above examples, the volume and gas flow rate of the honeycomb were 700 (cm ² ), 3 (liter / mi).
n), and the temperature during denitration was kept constant at 400 ° C. by a heater.

The spraying amount of the reducing agent is variable in the range of 0.1 to 1.0 (cc / sec), but this spraying amount can be appropriately adjusted depending on the use conditions.

In each of the above examples, the reaction temperature of the zeolite denitration agent is preferably 300 to 600 (° C). The reaction pressure is not particularly limited, and the reaction is effective.

The space velocity (SV value: the velocity at which the exhaust gas is introduced into the catalyst layer) varies depending on the conditions such as the reaction temperature and the required NO _x removal rate, and is not particularly limited, but preferably about 5
00-1000 (1 / hr), more preferably 1000-
10000 (1 / hr).

Further, the acetic acid, ammonium acetate and the like used in this example can be stored as a solution, so that they are highly safe and easy to store and handle.

[0085]

INDUSTRIAL APPLICABILITY According to the present invention, when a zeolite supporting an active metal serving as a catalyst and a NO _x containing gas are catalytically reacted with each other, a carboxylic acid (or a salt thereof) is allowed to coexist, whereby SO _x in exhaust gas is Deterioration of the denitration agent due to the above is suppressed.

Therefore, the denitration rate is increased and the life of the denitration agent is greatly improved.

In particular, by using cobalt as the active metal, SO _x poisoning can be substantially suppressed and a high denitration rate can be obtained.

[Brief description of drawings]

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

FIG. 2 is a graph showing the correlation of NO concentration with time.

FIG. 3 is a graph showing the correlation of NO concentration with time.

[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 discharge pipe 11 ... Mass spectrometer 12 ... NO _x analyzer

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kaoru Kitayoseki 2-1-1 Osaki, Shinagawa-ku, Tokyo Inside the Meidensha Co., Ltd. No. Stock Company Shameidensha

Claims (6)

[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 carboxylic acid and / or ammonium carboxylate. 2. The denitration method according to claim 1, wherein the NO _x containing gas contains O ₂ . 3. The denitration method according to claim 1, wherein a zeolite carrying cobalt is used as the denitration agent. 4. The denitration method according to claim 3, wherein the NO _x- containing gas contains SO _x . 5. The denitration method according to any one of claims 1 to 4, wherein acetic acid is used as the carboxylic acid. 6. The denitration method according to any one of claims 1 to 5, wherein ammonium acetate is used as the ammonium carboxylate.