JPS637826A - Removing method for nitrous oxide in gas mixture - Google Patents

Abstract

PURPOSE:To separate and remove N2O effectively by contacting a mixed gas containing N2O with a catalyst containing a metal of Ib group or VIII group of the periodic table, an oxide or a composite oxide thereof. CONSTITUTION:A metal of group Ib or a metal of group VIII, of the periodic table such as Pd, Cu, Co, Ni, Fe or the like, or an oxide or a composite oxide thereof is carried on a carrier such as Al2O3, TiO2 and the like and filled in a catalyst filling layer as catalyst. After denitrated in a denitration device, generated N2O is contacted with the catalysts of the catalyst filling layer 4 at a temperature in the range of 250-600 deg.C, and N2O is decomposed into harmless N2 and O2 to be exhausted out of a stack 6 through a fan 5.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for removing nitrogen oxides, in particular nitrous oxide, from gas mixtures. In particular, a method for removing nitrous oxide from exhaust gas containing trace amounts of nitrous oxide, suitable for use as part of the removal process of nitrogen X [compounds] in industrial exhaust gases and automobile exhaust gases in various industries and automobiles. It is related to.

Conventional Technologies and Problems Conventionally, legal and other regulatory measures have been taken to prevent the release of exhaust gas from various industries and automobiles into the atmosphere from the perspective of pollution prevention. As a cause of rain and photochemical smog, its emissions are strictly restricted.

By the way, nitrogen oxide vlJ (NOx) in exhaust gas, which has traditionally been subject to emission regulations, is mainly composed of nitrogen monoxide (NOx).
) and nitrogen dioxide (NO2), therefore conventional exhaust gas denitrification techniques are also mainly aimed at removing nitrogen monoxide and nitrogen dioxide, such as reduction methods by adding ammonia, reduction methods using catalysts, radiation irradiation. Laws, etc. have been proposed.

-On the other hand, nitrous oxide (N20) in exhaust gas is, of course, NO.
Nitrogen, like NO2 and NO2, belongs to chemical substances, but until now there has been no legal emission regulation value, and the Japanese Industrial Standards (J
Official measurements such as IS) have not been established, and the reality is that they have been virtually ignored in the evaluation of denitrification equipment. This was because the N20d degree in the atmosphere remained constant compared to the No + NO2 concentration, and was said to be stable as it did not convert into other substances, and the physical properties of N20 were not fully understood. ◇ However, in the denitrification method according to the conventional technology as described above, Id
It has been recognized that N20 is produced at a relatively high rate through the reaction of NO, NO2, NH, etc., and in recent years,
N20 decomposes in the stratosphere and becomes N.

It has become clear that N20 produces
The issue of N20 emissions is also attracting attention. Under these circumstances, various exhaust gases that are the source of N200 in the atmosphere, especially exhaust gas after NOx removal generated from the Hakashi denitrification equipment currently used to remove nitric oxides from exhaust gas. A need has arisen for N20 removal.

Means for solving the problem 2 Functions and effects The present invention aims at removing nitrous oxide from among the nitrogen oxides contained in gas mixtures, especially various exhaust gases.

According to the invention, a gas mixture containing nitrous oxide is brought into contact with a catalyst comprising a metal of Group Htb or Group 1 of the Periodic Table of the Elements or an oxide agglomerate or composite oxide of said metal. A method for removing nitrous oxide in a gas mixture is provided, which comprises decomposing and removing nitrous oxide.

According to the method of the present invention, the nitrous oxide contained therein can be decomposed into nitrogen and oxygen and rendered harmless by simply contacting a gas mixture containing nitrous oxide, particularly exhaust gas, with the above catalyst. .

Particularly in the case of exhaust gases, the reaction products can therefore be released into the atmosphere without concern for further treatment.

Particularly preferred catalysts for use in the practice of the present invention are those containing palladium, nickel, iron, cobalt or copper, or oxides or composite oxides of these metals, as active ingredients. It is convenient to use the catalyst in the form of a supported catalyst, usually carried on a support. As a carrier, it has appropriate pores that allow the active ingredient to exhibit its catalytic action, and is an exhaust gas component.

For example, any material can be used as long as it does not react with sulfur oxides (SOx) and has excellent heat resistance, but porous ceramics are preferably used.

The porous ceramics used as the catalyst carrier is made of silica sand + At20s t at CI TjN as the raw material.
It can be manufactured by suitably combining one or more of H513N4 +TiO2, etc., according to a well-known manufacturing method.

The supporting of the catalytic active component on the carrier, that is, the production of the supported catalyst, can be carried out by any conventional method; however, for boat fishing, the carrier is impregnated with an aqueous solution of a bath salt of the catalytic metal, and then calcined. be able to.

For example, when Pd is supported on At20s, δ is rejected (Pd
/At20. Catalyst manufacturing method) #:j, 60 in nitrogen atmosphere
γ-At20s heated at 0'C for 5 hours was immersed in a palladium nitrate water bath solution to adsorb palladium nitrate,
This consists of drying in an air atmosphere at 110'C for 24 hours, and then firing in a nitrogen atmosphere at a temperature of 600'C for 5 hours.

As another example, method 8 (Pd/
[Method for producing TiO2 catalyst] is to immerse anatase-type TiO2 heated at 300°C in an indoor atmosphere for 5 hours in a palladium nitrate aqueous solution to adsorb palladium nitrate, and then dry and calcinate it in the same manner as above. Consisting of

The amount of catalytically active component supported is not particularly critical, but generally ranges from 2 to 30 parts by weight, based on the carrier used and calculated as metal.

As mentioned above, the method of the present invention can be applied to any gas mixture containing nitrous oxide, in particular to gas mixtures containing traces of nitrous oxide, in particular to exhaust gases, and thus to exhaust gases in a wide range of industrial and other industries as well as motor vehicle exhaust gases and K. The present invention can be applied to exhaust gases that have been partially purified, such as denitrification and desulfurization.

In accordance with an exemplary embodiment of the present invention, the method of the present invention comprises supplying a gas mixture stream containing nitrous oxide to
This is achieved by passing a Group B or Group 1 metal or an oxide or composite oxide of the metal to a packed bed of a catalyst supported on a carrier.

Such a gas phase catalytic reaction method using a fixed catalyst bed is of a type well known to those skilled in the art, and depends on the type and shape of the catalyst suitable for each particular treatment, the shape of the catalyst packed bed, and the reaction conditions, e.g. Gas hourly space velocities, catalyst bed temperatures, etc. can be readily determined by those skilled in the art by simple experimentation, if necessary.

Typical examples of the shape of the catalyst include a spherical shape, a ring shape, a columnar shape, a plate shape, a honeycomb shape, etc., and the shape of the catalyst packed bed includes a package shape of a plate catalyst, a package shape of a honeycomb catalyst, etc. An example is a catalyst bed in which a granular catalyst is packed in a stacked body or a wire mesh in a cylindrical shape. It shall be used selectively.

The temperature of the catalyst packed bed depends on the type and amount of catalyst used.

It varies depending on effectiveness, economy, etc., but - 250~ for boat fishing.
Any temperature range within the range of 600°C can be used, e.g. for a Pd/A 120g catalyst a range of 250-450°C is preferred.

Space velocity of the gas to be treated to the catalyst bed [SV (hr-'
): 1 also varies depending on the type, effect, economy, etc. of the catalyst, but generally the space velocity is 3,000 (hr) or more,
s,oo.

(hr-1) or more, preferably 8,000 (hr-'
) That's it.

Next, FIG. 1 shows a conceptual diagram of a specific example in which the method of the present invention is applied to the treatment of N20 generated from a conventional denitrification device for heavy oil combustion exhaust gas generated from a heavy oil combustion furnace.

Exhaust gas discharged from the heavy oil combustion furnace 1 with an average NOx (total of NO and NO2) concentration of 250 ppm is first treated with a normal denitrification device 2 to remove NOx, and then the N20 produced here is transferred to the catalyst packed bed 4. After decomposition, the detoxified exhaust gas is discharged from the chimney 6 via the fan 5.

Denitrification in the denitrification device 2 is carried out using ammonia (NHs) with a stoichiometric value of 0.7 to 00 g equivalent to the NOx concentration in the exhaust gas.
) is carried out by adding 3.

The NOx concentration in the exhaust gas downstream of the denitrification system [2] is 50pp
However, part of the NOx is converted to N209, and the N20J% degree here is 45 ppm.

If the denitrification rate is calculated here, the denitrification rate will be 80% (25oX100) when focusing only on the NOx concentration at the inlet and outlet of the denitrification equipment as in the conventional case. Next, look at KN20 and convert the N20 concentration to NOx concentration: 45 ppm
N20 corresponds to 90 ppm No], and the denitrification rate when NOx from N20 is added as the NOx concentration.

The catalyst packed bed 4 is a reactor filled with a catalyst for decomposing N20, which is a feature of the present invention.

The catalyst packed bed 4 in the embodiment shown in FIG. 1 is installed separately downstream of a normal denitrification device 2, but it is also possible to integrate the normal denitrification device 2 and the catalyst packed bed 4. It goes without saying that it can be done. Practically speaking, integration is preferable from the economical point of view (the entire device becomes smaller).

As is clear from the above examples, according to the present invention, N20
In particular, by installing the decomposition catalyst in the exhaust gas passage, the following effects (1) and (2) can be achieved.

That is, (1) N20 in the exhaust gas was decomposed into harmless and stable N2 and 02.

■ N20 was decomposed and the denitrification rate was substantially improved.

In other words, the conventional denitrification rate is determined by comparing the NOx concentration at the inlet of the denitrification equipment and the NOx concentration at the exit.
The rlt degree was not considered, but the N20 concentration was considered (
The denitrification rate (regarded as NOx) was reduced by the N20 concentration.

Example Next, the present invention will be further explained by examples.

Example 1 - i γ-Alumina heated at 600°C for 5 hours in an elementary atmosphere was immersed in a palladium nitrate water bath solution to adsorb palladium nitrate, then dried at 110°C for 24 hours in an air atmosphere, and further A reduced catalyst was prepared by firing in a nitrogen atmosphere at a temperature of 600'C for 5 hours.

The catalyst thus obtained is abbreviated as Pd/At2es.

The catalysts obtained by using a solution were each
At20s + Fe/Al2O5+ Co/At20
It is abbreviated as s and Cu/At20s.

The obtained catalyst has oxides of the respective metals supported on an alumina carrier.

The crystal form and jk (% by weight) of the oxide are as shown in Table 1.

The crystal form is -X#! This was identified by diffraction analysis.

Crystal type of oxide and t These catalysts 25- were each filled in a quartz tube with an inner diameter of 40.0 mm, and 60 ppm N20/air balance (preparation gas) was passed through. At a given reaction temperature (temperature of the catalyst packed part in the quartz tube), N20 downstream of the catalyst packed part was measured to examine the reaction rate.

Results Table 2 shows the reaction temperature and N20 reaction rate of each catalyst at a space velocity of 6.000 (hr-')K.

Note that the N20 reaction rate was calculated using the following formula.

As shown in Table 2, space velocity (SV) t 6,000 (
When the relationship between the reaction rate of N20 and the reaction temperature is plotted on orthogonal coordinates, it is as shown in FIG. 2.

Example 2 The same heating as in Example 1 was applied to anatase titanium dioxide (T
i02), and the respective water bath liquids were immersed and adsorbed in the same manner, dried in the air, and then fired in a vacuum, and tested in the same manner.

As a result, the same effect as in Experimental Example 1 was obtained.

The results for Pd/TiO2 are shown in FIG.

Example 3 The catalyst shown in Example 1 was filled into the exhaust port of a vehicle equipped with a catalyst, and the reaction rate of N20 was examined.

Note that the car was running at a constant speed of 45 km/hour.

When the present catalyst was not filled, the N20m degree was 26 ppm (average value).

The temperature of the melting medium filling part is 350℃ or 400'C rumored SV is 5
．． 000 (hr"). The reaction rate was calculated in the same manner as in Example 1, and the results are shown in Table 3.

[Brief explanation of the drawing]

FIG. 1 is a schematic flow sheet of a specific example in which the method of the present invention is applied to the treatment of N20-containing exhaust gas generated from a conventional denitrification device for exhaust gas generated from a heavy oil combustion furnace, and FIG. 2 is a schematic flow sheet of Example 1. It is a graph in which the relationship between the reaction rate of N20 and the reaction temperature is plotted on orthogonal coordinates for each operation of No. 2 and No. 2. In FIG. 1, 1-... Heavy oil combustion furnace, 2... Conventional denitration equipment, 3... Ammonia tank, 4... Catalyst packed bed of the present invention, 5... F/, 6...・It is a chimney.

Claims (1)

[Claims] 1. Contacting a gas mixture containing nitrous oxide with a catalyst containing a metal of Group Ib or Group VIII of the Periodic Table of Elements, or an oxide or composite oxide of the metal. 1. A method for removing nitrous oxide in a gas mixture, comprising decomposing and removing nitrous oxide by allowing the nitrous oxide to evaporate. 2. The method according to claim 1, wherein the metal of the active component of the catalyst is one or more selected from palladium, nickel, iron, cobalt and copper. 3. The method according to claim 1 or 2, wherein the catalyst is used in the form of a supported catalyst held on a carrier. 4. The method according to claim 3, wherein the carrier is a porous ceramic. 5. The method according to claim 3 or 4, wherein the amount of catalyst supported is 2 to 30% by weight as metal based on the carrier. 6. Transfer the gas mixture to the packed bed of supported catalyst at 3000 [SV (
hr^-^1)] The method according to any one of claims 1 to 5, wherein the method is carried out at a space velocity of at least hr^-^1)]. 7. The method according to any one of claims 1 to 6, wherein the contact between the gas mixture and the catalyst is carried out at a temperature of 250 to 600°C. 8. The method according to any one of claims 1 to 7, wherein the gas mixture is an exhaust gas containing trace amounts of nitrous oxide.