JPH06269673A - 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 Co (e.g., aqueous cobalt nitrate soln.) is brought into contact with Y-type zeolite containing Na to support Co on zeolite and this zeolite is baked to produce a denitration agent. This denitration agent and NOx-containing gas are brought into contact with each other 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 zeolites containing various metal in the presence of hydrocarbons is disclosed in JP Sho 63-283727.

However, this method has a problem that various metals contained as a catalyst component are poisoned by sulfur oxide (SO _x ) contained in the exhaust gas and the catalytic activity is lowered.

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

The invention according to claim 1 is characterized in that a solution containing cobalt and a Y-type zeolite containing Na are brought into contact with each other to support the cobalt on the zeolite, and then the zeolite is calcined. A method for manufacturing the same is provided.

Examples of the cobalt-containing solution include cobalt nitrate aqueous solution and cobalt acetate aqueous solution.

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

The invention according to claim 2 provides a denitration method, wherein the denitration agent of claim 1 and the NO _x containing gas are contacted in the presence of heavy fuel oil A to denitrate the NO _x gas. To do.

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 preferentially with A heavy oil. Therefore, SO _x gas does not cover the surface of the zeolite and does not react with the active metal 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.

There is no particular limitation on the method of coexisting the heavy oil A at the time of denitration, but, for example, cobalt-supported zeolite with N
Examples include a method of spraying A heavy oil when the O _x -containing gas is circulated.

[0021]

EXAMPLE In this example, a denitration agent (cobalt-supporting zeolite) was produced by ion-exchanging a part of the components of Y-type zeolite containing Na with cobalt, and the denitration agent and the NO _x -containing gas were mixed with each other. Denitration was performed by bringing them into contact with each other in the presence of A heavy oil. 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 capable of injecting a reducing agent solution at a rate 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 a NO _x analyzer (NOA-307DX manufactured by Shimadzu Corporation) 11 as a processing gas through a processing gas discharge pipe 10. .

Next, the zeolite carrying cobalt was subjected to pretreatment as a pretreatment to denitrate to produce a denitration agent, and its denitration rate was measured.

First, 30% of clay and glass fibers were mixed with the powder amount of Na-containing mordenite (Na mordenite: Tosoh, HSZ-320NAA), and the mixture was well kneaded to form a 65 × 65 × 65 (mm) square. Was formed into a honeycomb shape.

This honeycomb was dried in the sun for 1 day, then dried in a dryer at 50 ° C. for 10 hours and 100 ° C. for 5 hours, and further fired at 750 ° C. for 2 hours to form a supporting base material. Got

Next, the honeycomb body is washed with pure water,
The honeycomb body was immersed in 1 liter of an aqueous Co (NO ₃ ) ₂ (cobalt nitrate) solution (mol / l) at room temperature for 2 hours, washed with pure water, and dried at 120 (° C) for 5 hours. .

Further, before the denitration, a denitration agent 1 was produced by pre-treatment by firing at 500 (° C.) in the atmosphere 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.

A heavy oil is used as the reducing agent injected from the nozzle 6, and the injection amount is 0.25 (cc / sec) (1
Spraying for 2 seconds). The temperature during the reaction is 4 by the heater 9.
The temperature was maintained at about 00 (° C).

A blank test was conducted using the honeycomb body not carrying the above cobalt as the denitration agent 2.

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

[0039]

[Table 1]

As shown in this table, the NO removal rate is 1.0 (%) in the denitration agent 2 which does not carry cobalt, whereas it is 48.7 (%) in the denitration agent 1 which carries cobalt. It can be seen that a very high denitration rate is obtained.

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).

Particularly, in 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 48.7 (%) can be obtained as compared with the conventional denitration. It was

In the above embodiment, the denitration agent has a reaction temperature of 3
It works at 00 to 600 (° C.) and reacts effectively without being limited to the reaction pressure.

Next, the concentration of the cobalt solution was adjusted to 0-0.5 (mo
The result of measuring the denitration rate as (l / l) is shown in FIG.

As shown in this figure, when the concentration of the cobalt solution is 0.01 (mol / l), the denitration rate becomes the highest.
This is because when the concentration of the cobalt solution becomes 0.01 (mol / l) or more, the pH of the cobalt solution becomes low and the structure of zeolite is destroyed.

[0046]

INDUSTRIAL APPLICABILITY In the present invention, the NaY type zeolite immersed in the solution containing cobalt is fired as a pretreatment. By pretreatment in this way, it is possible to strengthen the bond between cobalt and zeolite,
It is possible to increase the denitration rate and prolong the catalyst life.

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 between the cobalt solution concentration and the NO _x removal rate.

[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 (2)

[Claims] 1. A method for producing a denitration agent, which comprises contacting a solution containing cobalt with a Y-type zeolite containing Na to support the cobalt on the zeolite and then calcining the zeolite. 2. A denitration method characterized by the denitrating agent according to claim 1, wherein and the NO _x containing gas is contacted in the presence of A heavy oil perform denitration of the NO _x gas.