JPH0747278A - Denitration agent and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a denitration agent with a high denitration efficiency and a wide temperature range in which a denitration activity is exhibited. CONSTITUTION:This denitration agent consists of chromium and cobalt carried by zeolite. The agent is manufactured by dipping zeolite into a chromium- containing solution and a cobalt-containing solution, so that zeolite carries chromium and cobalt.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to NO _x removal technology,
In particular, it relates to a technique for removing NO _x from a NO _x- containing gas such as exhaust gas from an 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. Since the selective catalytic reduction method can treat NO _x with a simple system, a high denitration rate can be obtained. Moreover, NO _x
Since it can be decomposed into harmless N ₂ and H ₂ O, there is an advantage that waste liquid treatment becomes unnecessary.

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

Further, at high temperatures, there arises inconveniences such as progress of sintering of the catalyst components, and at low temperatures ammonia reacts with water or SO _x , so that salts such as ammonium sulfate are formed on the catalyst surface and the denitration rate decreases. To do. Therefore, the operating temperature range is limited to 320 to 450 ° C.

As described above, since there are many problems in the method using ammonia, other denitration methods are currently being researched, and the direct decomposition method has been attracting attention.

This direct decomposition method is the most ideal method for removing NO _x , and in recent years, catalysts such as Cu-ZSM-5 zeolite and perovskite type complex compounds have been found.

[0008]

[0008] However, the denitration rate even the most highly active Cu-ZSM-5 as the catalyst, the catalyst performance is deteriorated by SO _x or of H ₂ O in the exhaust gas in the direct decomposition method Is decreased, and 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 provide a denitration agent having a high denitration rate and capable of maintaining the high denitration rate for a long period of time.

[0010]

In order to solve the above problems, the invention according to claim 1 provides a denitration agent characterized in that zeolite is loaded with chromium and cobalt.

According to the second aspect of the present invention, a zeolite is immersed in a solution containing chromium and a solution containing cobalt to support the chromium and the cobalt on the zeolite, thereby producing a denitration agent. Provide a way.

When the zeolite is immersed in a solution containing a metal having a catalytic activity, the components in the zeolite and the metal are partially ion-exchanged, and the metal is supported on the zeolite to obtain a denitration agent. Examples of the solution containing the metal include a salt solution of the metal.

Usually, in a denitration agent in which a metal having catalytic activity (catalytic metal) is carried on the zeolite, a single kind of metal is carried on the zeolite.

Further, for example, an alloy of a metal having high conductivity is
As shown in the example where the conductivity of each metal is lower than that of the original metal, it is generally said that by combining a plurality of metals, better characteristics can be obtained than when the original metals are used alone. However, the characteristics may be deteriorated.

However, in the present invention, it has been confirmed that by supporting a plurality of catalytic metals on zeolite, better characteristics can be obtained as compared with the case where a single metal is used.

Usually, the temperature range in which the catalytic activity is obtained depends on the catalytic metal species. For example, when Fe is used as a catalytic metal, high catalytic activity is obtained in a high temperature range of about 300 (° C.) or higher, but the catalytic activity is low in a low temperature range.

In the denitrification agent in which a plurality of catalytic metals are supported on zeolite as in the present invention, the catalytic activities of the respective metals are not offset, and conversely, the temperature range in which the catalytic activities are obtained is such that each metal is used alone. In the denitration agent obtained by supporting on zeolite, the temperature range is the sum where the catalytic activity is obtained.

Further, due to the synergistic effect of supporting a plurality of metals in this way, an unexpected effect that a higher denitrification rate can be obtained than a denitrification agent obtained by supporting each catalyst metal on zeolite alone. was gotten.

Preferred examples of the zeolite as the supporting base material include NaY-type zeolite, HY-type zeolite, Na-type mordenite, H-type mordenite, A-type zeolite, X-type zeolite, and the like. A denitration effect is obtained. In the present specification, the above various zeolites and other types of zeolites are collectively referred to as zeolites. Further, in the present specification, zeolite and metal are integrated (regardless of physical or chemical)
It is described as carrying.

Since the denitration efficiency increases with the contact area between NO _x and the denitration agent, it is desirable that the denitration agent has a large surface area, for example, a honeycomb structure.

There are various methods for supporting the metal on the zeolite, but it is preferable to use a solution containing the zeolite at a predetermined concentration (for example, a salt solution of the metal).
Immerse in, and evaporate the solution as it is after confirming that the above metal has sufficiently diffused into the pores of the zeolite, or pull out the immersed zeolite from the solution, then the water content in the zeolite The metal is supported by removing.

It is considered that the metal is carried by diffusion into the pores of the zeolite and is partially ion-exchanged so that it is supported. Therefore, when the zeolite is immersed in the solution containing the metal, the immersion time is set to the zeolite fineness. Any material may be used as long as the metal can be sufficiently diffused in the pores, and it is, for example, about 12 hours depending on the metal species.

At this time, if the diffusion of the metal is sufficient, it is possible to shorten the impregnation time. Further, even if the impregnation time is 12 hours or longer, there is no alteration of the zeolite, so that the impregnation time is 12 hours or longer. No problem.

The solution containing the above metal is not particularly limited as long as the above ion exchange is sufficiently carried out, but preferable examples include solutions of metal nitrates, sulfates, chlorides and the like.

[0025]

EXAMPLE In this example, a zeolite containing Na was impregnated with a salt solution of a metal to be supported, and the composition component of the zeolite was replaced with the metal salt to obtain a metal-supported zeolite.

By supporting the metal on the zeolite, the performance of separating the nitrogen oxide (NO _x ) contained in the zeolite into nitrogen (N ₂ ) and oxygen (O ₂ ) is improved.

In such a metal-supported zeolite, the temperature range in which the specific catalytic activity is exhibited varies depending on the supported metal salt aqueous solution at the time of impregnation.

Therefore, an attempt was made to prepare a catalyst capable of maintaining high denitration performance under a wide range of temperature conditions by supporting a plurality of metals on zeolite. At the same time, the denitrification performance was compared with the zeolite supporting a plurality of metals and the zeolite supporting each metal alone, and the synergistic effect of supporting a plurality of metals was examined.

In this example, the denitration rate of each denitration agent sample was measured using the denitration test apparatus shown in FIG.

In this figure, 1 is NO (1000 (pp
m)) / N ₂ gas supply part, 2 is an O ₂ gas (10%) supply part,
3 is a flow rate controller, 4 is a gas direction selector switch, 5 is a quartz tube (main body of denitration apparatus) 6, is a denitration agent, 7 is a heater, and 8 is N
_Ox concentration analyzer.

N supplied from the NO / N ₂ gas supply unit 1
O gas and O ₂ O ₂ gas inside diameter 42 mixed gas through the gas direction change-over switch 4 in the quartz tube inlet after being adjusted the flow rate by the flow regulator 3 supplied from the gas supply unit (mm) phi quartz It flows into the tube 5 and the NO _x concentration analyzer 8, respectively. The SV value of the mixed gas was 2000 (h ^-1 ).

A 70 (g) denitration agent 6 is installed in the quartz tube 5, and a heater 7 is provided on the outer circumference of the quartz tube 5 so that the temperature in the quartz tube can be kept constant. ing. In this embodiment, the temperature condition during denitration by the heater 7 was set to 200, 300, 400 (° C.).

The mixed gas flowing into the quartz tube 5 is denitration agent 6
After being denitrated, the gas flows into the NO _x concentration analyzer 8 at the quartz tube outlet through the gas direction changeover switch 4.

The NO _x concentration analyzer 8 measures the NO _x concentration before denitration and the NO _x after denitration supplied as described above. The denitration rate was measured from these values. The denitration rate was calculated by the following formula.

[0035]

[Equation 1] Denitration rate = 100 × (Inlet NO _x concentration−Outlet NO _x concentration) / Inlet N
Using O _x concentration above denitration testing device, we examined the denitration performance of the denitration agent obtained zeolite by supporting various metal in each example.

The shape of the structure-strengthening agent-containing zeolite used as the denitration agent is not particularly limited, but a shape having a large contact area with the NO _x -containing gas is preferable. In each example, a pellet type shape was used.

Example 1 (Denitration agent supporting cobalt and chromium) First, NaY type zeolite (HSZ-320NAA, manufactured by Tosoh Corporation) 100 (g) as a carrier zeolite was washed with pure water to a concentration of 0.1 (mol / mol After washing with sodium chloride (NaCl) solution (1), it was washed again with pure water and dried to remove impurities on the surface and inside of the zeolite.

This zeolite was immersed in 300 (cc) of an aqueous solution of chromium nitrate [Cr (NO ₃ ) ₃ ] having a concentration of 0.1 (mol / l) for 12 hours, and then thoroughly washed with pure water to 120 (° C.). Dry for 3 hours and allow to cool naturally.

Further, this zeolite was added to 0.1% by the same method.
(mol / l) cobalt nitrate [Co (NO ₃ ) ₂ ] aqueous solution 300 (cc)
Was immersed in water, washed with pure water, dried and naturally cooled to obtain a denitration agent. This denitration agent is referred to as Example 1.

Next, a denitrifying agent in which only chromium was supported on zeolite and a denitrifying agent in which only cobalt was supported on zeolite were manufactured.

First, as in Example 1, NaY type zeolite (HSZ-320, manufactured by Tosoh Corporation) was used as the carrier zeolite.
NAA) 100 (g) was washed with pure water, washed with an aqueous solution of sodium chloride (NaCl) with a concentration of 0.1 (mol / l), then washed again with pure water and dried to remove impurities on the surface and inside of the zeolite. Removed.

This zeolite was immersed in a chromium nitrate aqueous solution 300 (cc) having a concentration of 0.1 (mol / l) for 12 hours, thoroughly washed with pure water, dried at 120 (° C.) for 3 hours, and naturally cooled. Then, a denitration agent was obtained. This is Comparative Example 1.

Further, in Comparative Example 1, the concentration was 0.1 (mol / l)
Comparative Example 2 was manufactured in the same manner except that cobalt nitrate having a concentration of 0.1 (mol / l) was used instead of chromium nitrate.

With respect to each of the denitration agents of Example 1 and Comparative Examples 1 and 2, the denitration rate was measured by the denitration test apparatus of FIG. 1 under the temperature conditions of 200 (° C.), 300 (° C.) and 400 (° C.). The results are shown in Table 1 and FIG.

[0045]

[Table 1]

In FIG. 2, L1 shows the characteristics of Example 1, L2 shows the characteristics of Comparative Example 1, and L3 shows the characteristics of Comparative Example 2.

Assuming that the synergistic effect due to the support of chromium and cobalt on the zeolite cannot be obtained, the denitration rate takes the larger value of Comparative Examples 1 and 2. In this case, the denitration rate of the denitration agent of Example 1 was in agreement with the graph (L2) of Comparative Example 1 up to point A in the graph of FIG. Match.

However, as shown in Table 1 and FIG.
Denitration agent supporting chromium and cobalt (Example 1)
The denitrification rate is always higher than that of the denitrification agent (comparative examples 1 and 2) in which a single metal is supported on zeolite. Therefore, it can be seen that in the denitration agent of Example 1, a high denitration rate is obtained due to the synergistic effect of supporting both chromium and cobalt.

The temperature range in which the catalytic activity is obtained is C
The denitration agent in which chromium is solely supported by using an r (NO ₃ ) ₃ aqueous solution is 100 (° C.) to 300 (° C.), and the denitration agent in which cobalt is solely supported by using an Co (NO ₃ ) ₂ aqueous solution is 300-6
The catalyst activity is 00 (° C.), and the catalytic activity is obtained in a wide temperature range of 100 to 600 (° C.) even in the denitration agent that supports both chromium and cobalt.

As explained above, the metals supported on zeolite have different temperature characteristics and show catalytic activity at low or high temperatures. By supporting a plurality of such metals in combination, catalytic activity can be obtained in a wide temperature range, and a denitration agent having excellent denitration performance can be obtained.

In the above embodiment, two kinds of metal are supported on the zeolite, but three or more kinds of metals can be supported on the zeolite. It is also possible to obtain a denitration agent having the temperature characteristics required for the denitration agent.

It is also possible to properly adjust the denitration rate and the like by adjusting the metal concentration in the solution in which the zeolite is impregnated when supporting each catalytic metal.

[0053]

In the present invention, by supporting chromium cobalt with zeolite, it is possible to obtain a higher denitrification rate than the denitrifying agent in which the original metal alone is supported on zeolite.

Further, the temperature range in which the catalytic activity is obtained is the sum of the denitration agents in which the original metals are individually supported, and the denitration rate becomes high.

[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 denitration rate of each denitration agent.

[Explanation of symbols]

1 ... NO (1000 (ppm)) / N ₂ gas supply unit 2 ... O ₂ gas (10%) supply unit 3 ... Flow rate regulator 4 ... Gas direction selector switch 5 ... Quartz tube (denitration device body) 6 ... Denitration agent 7 ... Heater 8 ... NO _x concentration analyzer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01D 53/94 B01J 29/076 ZAB A 9343-4G 37/02 101 Z 8017-4G B01D 53/36 102 C

Claims (2)

[Claims] 1. A denitration agent characterized by supporting chromium and cobalt on zeolite. 2. A method for producing a denitration agent, characterized in that zeolite is immersed in a solution containing chromium and a solution containing cobalt to support the chromium and cobalt on the zeolite.