JPH06269674A - Production of denitration agent and denitration method - Google Patents

Abstract

PURPOSE:To denitrate NOx with high denitration efficiency by bringing a soln. containing Co into contact with Y-type zeolite containing Na to support Co on zeolite and baking Co supported zeolite to obtain a denitration agent and bringing this denitration agent into contact with NOx-containing gas in the coexistence of A-heavy oil. CONSTITUTION:A soln. containing a catalyst metal (e.g. Co) (e.g. cobalt nitrate soln. with a concn. of 0.005-0.05mol/l) and zeolite (e.g. mordenite containing Na) are brought into contact with each other to support the catalyst metal on zeolite and this metal supported zeolite is baked to produce a denitration agent. This denitration agent is brought into contact with NOx-containing gas in the coexistence of A-heavy oil. As a result, Nox in exhaust gas can be denitrated with high denitration efficiency.

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 treatment technology has been put to practical use as, for example, flue gas denitration technology. This flue gas denitration method is roughly classified into a dry method and a wet method, and the most advanced of these is the selective catalytic reduction method, which is a type of dry method. This main reaction is shown below.

4NO + 4NH ₄ + O ₂ → 6H ₂ O + 4N ₂ This reaction uses ammonia as a reducing agent as a reducing agent, and even if oxygen coexists, it selectively reacts with NO _x , so exhaust gas of a diesel engine, etc. Used to process. In this case, as a catalyst, a precious metal such as Pt or Al ₂ O ₃ ,
Various metal oxides supported on TiO ₂ or the like are used.
In the selective catalytic reduction method, NO _x can be treated with a simple system, a high denitration rate can be obtained, and NO _x can be decomposed into harmless N ₂ and H ₂ O, so that waste liquid treatment is unnecessary. It has advantages such as

However, in this method, since harmful and dangerous ammonia gas is used, it is necessary to handle it with caution, and the reduction catalyst is deteriorated by components other than NO _x in the exhaust gas, so catalyst replacement is required. Is required, which is economically disadvantageous especially when an expensive precious metal-based catalyst is used.

Further, at high temperatures, disadvantages such as progress of sintering of catalyst components occur, and at low temperatures, ammonia reacts with water or SO _x , so that salts such as ammonium sulfate are formed on the catalyst surface to denitrate. The rate drops. Therefore, the operating temperature range is limited to 320 to 450 ° C.

[0006] A three-way catalyst method is also used as a denitration method for exhaust gas from automobiles (gasoline vehicles). However, in exhaust gas with excess oxygen, the catalyst deteriorates faster and its life becomes shorter.

As described above, since there are many problems in the denitration method using ammonia and the three-way catalyst method, studies on other denitration methods have been conducted. At present, the denitration method based on the direct decomposition method is particularly attracting attention. This direct decomposition method is NO
_{This is} the most ideal removal method for _x , and has recently been adopted by Cu-ZSM-5.
Catalysts such as zeolites and perovskite-type composite compounds have been found.

[0008]

[SUMMARY OF THE INVENTION However, in the direct decomposition method, the most highly active Cu-ZSM-5 catalyst performance is deteriorated by SO _x or H ₂ O or the like in the exhaust gas as a catalyst denitration The rate drops. Therefore, it is very difficult to obtain a high denitration rate over a long period of time.

The present invention has been made in view of the above background, and an object thereof is to denitrate NO _x gas such as exhaust gas at a high denitration rate.

[0010]

[Means and Actions for Solving the Problems] In recent years, studies have been conducted on denitration agents in which a catalyst metal is supported on zeolite. Method of performing denitration in contact with NO _x containing gas and the zeolite containing the various metals coexist hydrocarbons is disclosed in JP Sho 63-283727.

However, in this method, it is desired to improve the denitration rate, and various metals contained as catalyst components are poisoned by sulfur oxide (SO _x ) contained in the exhaust gas and the catalytic activity is lowered. There was a problem that it would be done.

The present inventors have completed the present invention by earnestly researching under the above background.

According to the first aspect of the present invention, there is provided a method for producing a denitration agent, which comprises contacting a solution containing a catalytic metal with zeolite to support the catalytic metal on the zeolite and then calcining the zeolite. provide.

By calcining the zeolite as described above, the bond between the metal and the zeolite is strengthened.
The denitration rate can be increased.

As the above zeolite, it is preferable to use a zeolite containing an alkali metal.

Examples of such alkali metal-containing zeolite include Na-containing X-type zeolite, Na
Examples of the zeolite include Y-type zeolite containing Na, mordenite containing Na, and A-type zeolite containing at least one of (K, Na, Ca). In this specification, these zeolite species are simply referred to as zeolite.

The catalyst metal is not particularly limited, and examples thereof include those used in a conventional method, such as cobalt. As the solution containing the catalytic metal, for example, a solution of an appropriate salt of the catalytic metal can be used.

The invention according to claim 2 is the method for producing a denitration agent according to claim 1, characterized in that mordenite containing Na is used as the zeolite and cobalt is used as the catalyst metal. Production method.

Mordenite containing Na can be preferably used as a raw material for a denitration agent. Further, when cobalt is used as a catalyst metal, a high denitration rate can be obtained, and a cobalt solution can be easily obtained in the form of nitrate, acetate or the like.

The invention according to claim 3 is the invention according to claim 1 or 2.
In the method for producing a denitrifying agent according to the description, while using a cobalt nitrate solution as a solution containing the catalyst metal, the method for producing a denitrifying agent, characterized in that the concentration of cobalt nitrate is 0.005 to 0.05 (mol / l). I will provide a.

The cobalt nitrate solution can be preferably used as a solution of the above-mentioned catalyst metal and has a concentration of 0.00
A high denitration rate can be obtained by setting it to 5 to 0.05 (mol / l).

[0022] The invention of claim 4, wherein performs denitration of the NO _x gas is contacted in the presence of A heavy oil and denitrating agent and NO _x containing gas according to any one of claims 1 to 3 A denitration method characterized by the above is provided.

Normally, the NO _x -containing gas contains SO _{x and the} like, but when these components cover the surface of the denitration agent, the denitration rate becomes extremely low. Also, catalyst poisoning occurs.

As described above, when A heavy oil is coexistent as a reducing agent during denitration, SO _x gas reacts with A heavy oil preferentially. Therefore, SO _x gas does not cover the surface of zeolite and does not react with catalytic metals such as cobalt.

Further, the fuel oil A has an exhaust gas temperature (300 to 5).
Although it burns at 00 ° C., the soot contained in the exhaust gas is also burned at this time, so that poisoning of the catalyst due to the soot is also avoided, and therefore the catalyst life is greatly extended. In particular, since the heavy fuel oil A is used as a fuel for a diesel generator, it is not necessary to prepare a new reducing agent and it can be preferably used.

The method for coexisting the above-mentioned heavy oil A at the time of denitration is not particularly limited, and examples thereof include a method of spraying the heavy oil A when the NO _x -containing gas is passed through the denitration agent.

[0027]

Example In this example, a denitration agent (cobalt-supporting zeolite) was produced by ion-exchanging a part of the zeolite component with cobalt, and the denitration agent and the NO _x -containing gas were mixed in the presence of A heavy oil. Denitration was carried out by contact. At this time, denitration and NO _x concentration were measured using the denitration device shown in FIG.

In FIG. 1, reference numeral 1 denotes 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 honeycomb catalyst holder 7 is provided at the center of the denitration pipe 1, and the honeycomb catalyst 8 is supported thereby. A heater 9 keeps the catalyst holder 7 and the honeycomb catalyst 8 near the catalyst at a predetermined temperature.

A nozzle 6 for injecting a reducing agent solution in a range of 0.1 to 1 (cc) per minute (spraying for 1 second) is inserted between the gas inflow portion 5 of the denitration pipe 1 and the honeycomb catalyst 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 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. Excess 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 the honeycomb catalyst for denitration. At this time, the reaction temperature is heater 9
Therefore, the temperature is kept at about 400 ° C.

After the NO _x- containing gas is denitrated, the NO _x removal rate is measured by the NO _x analyzer (NOA-307DX manufactured by Shimadzu Corporation) 11 as the processing gas through the processing gas discharge pipe 10. .

Next, the denitration ratio of the denitration agent obtained by firing the zeolite carrying cobalt as a pretreatment was measured (Example 1). Further, the correlation between the concentration of the cobalt solution and the denitration rate when supporting cobalt was examined (Example 2).

Example 1 First, Na-containing mordenite (Na mordenite: manufactured by Tosoh, HSZ-640NAA) was used as zeolite.
Clay and glass fibers were mixed with this powder in an amount of 30 (%) and kneaded to form a honeycomb shape having 65 × 65 × 65 (mm) squares.

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, they were further fired at 750 ° C. for 2 hours to obtain a honeycomb body as a supporting base material.

Next, the honeycomb body is washed with pure water, and then 0.01
After immersing in 1 liter of Co (NO ₃ ) ₂ (cobalt nitrate) aqueous solution prepared to (mol / l) for 2 hours at room temperature, the above honeycomb body was washed with pure water and dried at 120 (° C) for 5 hours. did.

Further, before performing denitration, a denitration agent 1 was manufactured by pre-treatment by firing in air at 500 (° C.) for 3 hours. By performing the pretreatment in this way, the bond between cobalt and zeolite or the like can be strengthened.

Using this denitration agent 1, the denitration rate was measured by the denitration apparatus shown in FIG.

As the NO _x- containing gas, an actual exhaust gas from a diesel generator (40 kVA) was used, and 10 liters per minute was introduced into this denitration device.

Heavy oil A was used as the reducing agent injected from the nozzle 6, and the injection amount was 0.25 (cc / sec). The temperature during the reaction was kept at about 400 (° C.) by the heater 9.

A blank test was conducted under the same conditions as the denitration agent 2 except that the above-mentioned honeycomb body not carrying cobalt was used as the denitration agent.

Table 1 shows the measurement results of the denitration rate of the above denitration agents 1 and 2.

[0045]

[Table 1]

As shown in this table, the NO removal rate is 4.0 (%) in the denitration agent 2 which does not carry cobalt, whereas it is 57.0 (%) in the denitration agent 1 which carries cobalt. It can be seen that a very high denitration rate is obtained.

Example 2 In Example 2, the correlation between the concentration of the cobalt solution and the denitration rate when supporting cobalt was examined.

First, 30% of clay and glass fiber were mixed and kneaded with powder of Na-containing mordenite (Na mordenite: HSZ-640NAA, manufactured by Tosoh Corporation) to form a honeycomb shape.

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 drier, it was further fired at 750 ° C. for 2 hours to obtain a honeycomb body as a supporting base material.

Next, the honeycomb body is washed with pure water to obtain 0.005
It was immersed in 1 liter of Co (NO ₃ ) ₂ (cobalt nitrate) solution adjusted to (mol / l). This immersion needs to be performed until the pH of the aqueous cobalt nitrate solution changes from 3.0 to 5.5 and the progress of ion exchange is completed. In this example, the immersion time was set to 2 hours.

Therefore, the immersion time may be longer than the time when the ion exchange is completed, and can be appropriately adjusted according to the type of zeolite used, the shape of the honeycomb, and the like.

Ion exchange can be further promoted by immersing the honeycomb body in a fresh cobalt nitrate aqueous solution again.

The zeolite immersed in the cobalt nitrate solution was thoroughly washed until the red color on the zeolite surface (color of the aqueous cobalt nitrate solution) disappeared, and dried at 100 (° C.) for 2 hours. After that, as a further pretreatment, 2 at 500 (° C) in the atmosphere
Firing was performed for an hour to obtain a denitration agent. This denitration agent is referred to as denitration agent 4. By performing the pretreatment in this way, the bond between cobalt and zeolite or the like can be strengthened.

Next, in the method for producing the denitration agent 4, the concentration of the cobalt solution is 0.01 (mol / l), 0.05 (mol / l), 0.1 (mol / l)
Denitration agents 5, 6 and 7 were prepared as l). Also,
This honeycomb body on which cobalt was not carried was used as the denitration agent 3.

The denitration agents 3 to 7 were used as the denitration agents in the denitration apparatus, and the denitration rate of each denitration agent was measured. In addition, the exhaust gas from the diesel generator is used as the NO _x- containing gas, the heavy fuel oil A is used as the reducing agent injected from the nozzle 6, and the injection amount is 0.25.
(cc / sec). The temperature during the reaction was kept at about 400 (° C.) by the heater 9 and the SV value was kept constant at 2500.

The measurement results of the denitration rate are shown in Table 2 and FIG.

[0057]

[Table 2]

As shown in Table 2 and FIG. 2, it was found that a high denitration rate was obtained when the cobalt nitrate concentration was in the range of 0.005 to 0.05 (mol / l).
It can be seen that the denitration rate has a peak value of 57 (%) when it is (mol / l).

When the cobalt nitrate concentration is low, the amount of cobalt that is ion-exchanged is low, but when it exceeds 0.01 (mol / l), the pH of the cobalt nitrate solution is low and the acidity is high, and the zeolite crystal structure is May be destroyed.

Therefore, the pH of this cobalt solution is preferably about 4 to 7. Further, by using a buffer solution or the like which does not inhibit the carrying of cobalt and having a high cobalt concentration and a pH within the range of 4 to 7, destruction of the crystal structure can be prevented and the denitration rate can be increased.

Next, each of the above denitration agents 3 to
The actual cobalt content in 7 was measured. The results are shown in Table 3.

[0062]

[Table 3]

As shown in this table, the amount of supported cobalt itself becomes higher as the cobalt concentration in the cobalt solution becomes higher, and the amount of supported cobalt is changed in the present example in which the pH was not adjusted by the buffer solution or the like. 0.1
It can be seen that a high denitration rate can be obtained by setting it to about (wt%).

As described above, in this example, the cobalt-supported zeolite obtained by immersing the zeolite in the aqueous cobalt solution was pretreated to strengthen the bond between the cobalt and the zeolite, and to further support cobalt. A high denitrification rate can be obtained by setting the concentration of the cobalt nitrate solution of 0.01 to 0.01 (mol / l).

In particular, even in the actual denitration of exhaust gas of an actual diesel generator in which SO _x such as SO ₂ and excess oxygen exist, a very high denitration rate of 57% could be obtained as compared with the conventional case.

In each of the above examples, each denitration agent acts at a reaction temperature of 300 to 600 (° C.) and effectively reacts without being limited to the reaction pressure.

The space velocity (SV value: velocity of introducing exhaust gas into the catalyst layer) depends on conditions such as reaction temperature and required N.
It depends on the O _x removal rate and is not particularly limited, but is preferably about 500 to 1000 (1 / hr), more preferably 10
00 to 10,000 (1 / hr).

[0068]

In the present invention, the zeolite immersed in the cobalt solution is calcined as a pretreatment. By performing the pretreatment in this way, the bond between cobalt and zeolite or the like can be strengthened, the denitration rate can be increased, and the catalyst life can be extended.

Further, when denitration of the exhaust gas of a diesel engine is carried out, denitration can be carried out by spraying fuel A fuel oil as a reducing agent at the time of denitration. Therefore, a reducing agent storage tank and a cylinder are not required, and denitration can be performed compactly and economically.

[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 _x removal rate with cobalt nitrate concentration.

[Explanation of symbols]

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

Claims (4)

[Claims] 1. A method for producing a denitration agent, which comprises contacting a solution containing a catalytic metal with zeolite to support the catalyst on the zeolite, and then calcining the zeolite. 2. The method for producing a denitration agent according to claim 1, wherein mordenite containing Na is used as the zeolite, and cobalt is used as the catalyst metal. 3. The method for producing a denitration agent according to claim 1, wherein a cobalt nitrate solution is used as the solution containing the catalyst metal, and the cobalt nitrate concentration is 0.005 to 0.0.
A method for producing a denitration agent, which is characterized in that it is 5 (mol / l). 4. A denitration of the NO _x gas by contacting the denitration agent according to any one of claims 1 to 3 with a NO _x containing gas in the presence of heavy fuel oil A. Method.