JP3240316B2 - Methyl bromide decomposition catalyst and method for treating exhaust gas containing methyl bromide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a methyl bromide decomposition catalyst and a method for treating an exhaust gas containing methyl bromide by contacting the same with the decomposition catalyst.

[0002]

2. Description of the Related Art Methyl bromide is mainly used in fields such as pesticide treatment, fumigation and treatment of grains in silos and silos. At that time, the exhaust gas containing methyl bromide is diluted and discharged by a large amount of air, and at present, no other special treatment is performed. However, methyl bromide is toxic to the human body, is designated as a specified Class 2 substance, and has an allowable concentration of 15 ppm. Further, recently, reduction of emission as a substance causing ozone layer depletion and global warming has been desired. Therefore, merely reducing the concentration of methyl bromide and discharging it does not solve the fundamental problem, and requires more reliable treatment of methyl bromide.

As a method for removing methyl bromide in exhaust gas, an adsorption recovery method and a direct oxidation method can be considered. However, in the case of the adsorption method, the apparatus becomes large and the production cost becomes expensive, and the operation is complicated by two steps of adsorption and desorption.
There are many problems such as that the purity of the recovered methyl bromide is low and it is difficult to reuse. In the case of the direct oxidation method, 1000
A temperature of at least ℃ is required, which causes secondary pollution due to generation of thermal NOx. In addition, since methyl bromide is a flammable gas and cannot be directly exposed to a flame, an indirect heating method must be used, which is disadvantageous for gas heating and is not economical.

As a catalyst decomposition method, Japanese Patent Publication No. 54-22792 describes a catalyst in which a transition metal such as Co or Cu is ion-exchanged or supported on a Na-type zeolite.

[0005] However, the zeolites described in the above patents are X-type and Y-type zeolites and are weak in acid, and the crystals are easily destroyed even in the presence of a small amount of acid.
Since hydrogen bromide is generated in the decomposition reaction of methyl bromide, the crystal structure of the zeolite is destroyed, and the decomposition activity decreases with long-term use. Further, the above patent does not describe the treatment of carbon monoxide generated by the decomposition of methyl bromide, and is incomplete as a substantial treatment method.

[0006]

SUMMARY OF THE INVENTION The present inventors have studied a method for decomposing methyl bromide to meet the above-mentioned problems, and as a result, have found that a catalyst comprising copper bromide supported on an acidic zeolite can be used as a catalyst. By contacting an exhaust gas containing the same, methyl bromide in the exhaust gas was successfully removed, and the present invention was completed as a method for treating an exhaust gas containing methyl bromide.

[0007]

Means for Solving the Problems The present invention provides a catalyst for decomposing methyl bromide obtained by supporting copper bromide on an acidic zeolite, and contacting the catalyst with an exhaust gas containing methyl bromide.
The present invention relates to a method for removing methyl bromide, which comprises decomposing methyl bromide in exhaust gas. Hereinafter, the present invention will be described in detail.

[0008] The catalyst used in the present invention is obtained by carrying copper bromide on acidic zeolite. Zeolite is SiO ₄
It is composed of tetrahedron and AlO ₄ tetrahedron,
Many types are known due to the difference in the abundance ratio of i and Al and the binding mode of each tetrahedron. In addition, zeolite is 3
It has a three-dimensional skeletal structure and forms cavities (pores) in the lattice. The size and shape of the pores vary depending on the type of zeolite, and some have pore diameters of 3 to 12 angstroms and one-dimensional to three-dimensional pore shapes.

Further, zeolite has an ion-exchange ability, and usually has an alkali metal ion such as Na or K in its skeleton. However, zeolite can easily convert ions by contact with various cations. It can be exchanged, which is one of the characteristics of zeolites.

The zeolite used in the present invention includes faujasite type, mordenite type, L type, omega type, ZSM-
Any of type 5, ferrierite type, etc. may be used. In the present invention, the above-mentioned zeolite is used as an acidic zeolite.

One method for forming acidic zeolite is to convert zeolite into an aqueous ammonium ion solution (NH ₄ C).
1, an aqueous solution of NH ₄ NO ₃ or the like) to form ammonium ion type zeolite, and then calcining it at a temperature of 300 ° C. or more to remove ammonia to form H type zeolite. Another method is a method of contacting with a strong acid such as hydrochloric acid and directly ion-exchanging with H ions to obtain H-type zeolite. The H-type zeolite thus prepared is called an acidic zeolite because it exhibits acidity.

In the treatment method of the present invention, hydrogen bromide gas is generated as will be described later. Among the zeolites, those having a composition in which the molar ratio of Si to Al (Si / Al) is less than 5 constituting the zeolite are acid. The crystal is easily broken by hydrogen bromide gas and loses its function as a catalyst. Therefore, it is not preferable to use a zeolite having a low Si / Al molar ratio in the present invention, and it is preferable to use a zeolite having a ratio of 5 or more. Further, in the present invention, a zeolite having a Si / Al molar ratio of less than 5 may be subjected to a dealumination treatment to increase the Si / Al molar ratio to 5 or more to increase the acid resistance.

As one method of increasing the Si / Al molar ratio of zeolite, there is a method of heating ammonium ion type zeolite at a temperature of 400 ° C. or more in a steam atmosphere, and is usually used for removing Al from faujasite type zeolite. It is a way to be. In addition, there is a method in which SiCl ₄ is brought into contact with zeolite under the condition that water vapor is not present. This method is a method of replacing Si with Al, and has an advantage that lattice defects generated by Al atoms are not generated. Furthermore,
A method using a chelating agent such as ethylenediaminetetraacetic acid,
There is a method using an acid such as hydrochloric acid. In the present invention, S
Those having a high i / Al molar ratio and zeolites obtained by any of the above-mentioned methods are also applicable.

By using such a zeolite acetate supporting copper bromide as a catalyst, methyl bromide can be suitably treated. Here, metal species other than copper are unsuitable because they have low activity and also cause degradation of activity. In addition, with copper salts other than copper bromide, the initial activity of methyl bromide decomposition is low, and the activity gradually increases as the reaction proceeds. At this time, copper is gradually brominated, and the same conditions as when copper bromide is finally carried are reached. Therefore, by supporting copper bromide, it shows high activity from the initial activity.

The method for supporting copper bromide is not particularly limited. For example, there is a method in which an acidic zeolite is brought into contact with an aqueous solution containing copper bromide to remove water and then dry. here,
The supported amount of copper bromide is 0.1 to 30% by weight based on zeolite. When the supported amount of copper bromide is less than 0.1% by weight, decomposition of methyl bromide does not proceed so much, and even if it exceeds 30% by weight, the effect corresponding thereto cannot be obtained.

The use form of the zeolite used in the present invention is as follows.
It may be in the form of a powder, and may be a molded product molded by a usual method or a crushed product. In addition, the size when these are used differs depending on the scale of use, but the diameter of the granulated material when granulated is preferably 0.2 to 10 mm.

The method of contacting the exhaust gas containing methyl bromide with the zeolite according to the present invention generally involves introducing the gas into a layer filled with zeolite in the form of powder, granules or pellets, or a layer formed into a honeycomb. It is a target. The contact temperature at this time is preferably 200 ° C. or higher. Further, the amount of methyl bromide in the treatment gas introduced into the zeolite layer is preferably 20% or less, more preferably 5% or less.

In the present invention, the introduction rate (space velocity: SV) of the processing gas containing methyl bromide in the method of introducing the processing gas into the zeolite layer is preferably 100,000 / hr or less, more preferably 10,000 / hr or less. It is.

Further, in the present invention, an oxygen source needs to be present in the reaction system. The oxygen source is used to oxidize carbon, which is the composition of methyl bromide, to convert it to carbon monoxide and carbon dioxide. As the oxygen source, oxygen, water vapor, or the like can be used. The amount of the oxygen source to be present in the reaction system is preferably a stoichiometric amount or more that is sufficient to decompose methyl bromide to generate carbon dioxide.

In the present invention, hydrogen bromide is contained in the gas component after the treatment. However, the treatment of hydrogen bromide is easy,
It can be easily removed by contact with hydroxides such as sodium and potassium, and alkalis such as ammonia and amine.

Although carbon monoxide is contained in the gas component after the treatment, an oxidation catalyst for carbon monoxide, such as Pt-alumina, Pd-alumina, Pd-titania, Pt-titania, Pd-titania zirconia, etc. The carbon monoxide can be easily converted to carbon dioxide by mixing in the cracking catalyst or installing it after the catalyst cracking device.

[0022]

The present invention is a simple method, and its operation is simple, and it can be used not only as a large-scale apparatus for large-scale processing but also as a small apparatus for small-scale processing. In addition, due to the decomposition of methyl bromide, there are few decomposed products that are difficult to treat in subsequent steps and harmful by-products that are difficult to collect, and this method does not cause secondary environmental pollution.

[0023]

【Example】

(Example 1) H-type mordenite-type zeolite (trade name “HSZ-650HOA” Si / Al manufactured by Tosoh Corporation)
= 12.5) and impregnated with a 10 wt% aqueous solution of copper bromide while dropping it, and used a catalyst containing 15 wt% of copper bromide as a catalyst.
0.5 g of the mixture is filled into a quartz reaction tube having a diameter of 12 mm and a length of 150 mm, and a gas (other component: air) containing 1.0 vol% of methyl bromide and 3.0 vol% of steam is used as a gas to be treated in a volume of 200 ml.
The reaction was carried out at a temperature shown below.

Since the gas after the reaction contains carbon monoxide, the gas is oxidized by passing it through a carbon monoxide oxidation catalyst obtained by supporting 1 wt% of tetramine dichloropalladium as palladium metal using titania as a carrier. , Converted to carbon dioxide. The analysis of the processing gas was performed by gas chromatography. Further, carbon monoxide was not contained in the processing gas.

The decomposition rate of methyl bromide was determined from the following amount per unit time. A: Introduced methyl bromide amount B: Unreacted methyl bromide amount Methyl bromide decomposition rate = (AB) / A × 100 The results are shown below.

[0026]

(Example 2) H-type mordenite-type zeolite molded product (trade name "HSZ-650" manufactured by Tosoh Corporation)
HOD ", silica binder 20%) was impregnated with a 10% by weight aqueous solution of copper bromide while being dropped, and treated in the same manner as in Example 1 except that a catalyst containing 15% by weight of copper bromide was used as a catalyst. The results are shown below. The gas after the treatment did not contain carbon monoxide.

[0028]

Example 3 A treatment was carried out in the same manner as in Example 1 except that the zeolite used in Example 1 contained 10 wt% of copper bromide as a catalyst. The gas after the treatment did not contain carbon monoxide.

[0030]

Example 4 The same treatment as in Example 1 was carried out except that the zeolite used in Example 1 contained 25 wt% of copper bromide as a catalyst. The gas after the treatment did not contain carbon monoxide.

[0032]

Example 5 The reaction temperature in Example 1
The time change of the methyl bromide decomposition rate at 300 ° C was examined.

[0034]

(Comparative Example 1) The same procedure as in Example 1 was carried out except that no carbon monoxide decomposition catalyst was mixed. The generation ratio of carbon monoxide: carbon dioxide was 9: 1.

(Comparative Example 2) The procedure of Example 1 was repeated, except that copper nitrate was used instead of copper bromide.

[0037]

Comparative Example 3 The reaction temperature in Comparative Example 2
The time change of the methyl bromide decomposition rate at 300 ° C was examined.

[0039]

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Satoru Kobayashi 16-3 Onogawa Tsukuba City, Ibaraki Pref., National Institute of Advanced Industrial Science and Technology (72) Inventor Akira Kushiyama 16-3 Onogawa Tsukuba City, Ibaraki Pref. Within the Institute for Environmental Technology (72) Inventor Reiji Aizawa 16-3 Onogawa Tsukuba, Ibaraki Pref.Institute of Industrial Science and Technology (72) Inventor Hideo Ouchi 16-3 Onogawa Tsukuba, Ibaraki Pref. Inside the Research Institute of Technology (72) Inventor Yasushi Fujii 1-10 Dogencho, Shinnanyo-shi, Yamaguchi Prefecture (72) Inventor Masahiro Tajima 2-6-10, Miyamae, Shinnanyo-shi, Yamaguchi Prefecture (72) Inventor Takeo Mori Examiner Satoshi Sera, 1-7-9 Tomiokahigashi, Kanazawa-ku, Yokohama-shi, Kanagawa Prefecture (56) Reference JP-A-52-7370 (JP, A) JP-A-1-148 334 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 21/00-38/74 B01D 53/86 B01D 53/94 C07C 19/075

Claims (2)

(57) [Claims] 1. A catalyst for decomposing methyl bromide, comprising 0.1 to 30% by weight of copper bromide supported on an acidic zeolite having a Si / Al molar ratio of 5 or more. 2. An exhaust gas containing methyl bromide is brought into contact with the methyl bromide decomposition catalyst according to claim 1 at a temperature of 200 ° C. or higher to decompose methyl bromide in the exhaust gas and generate the decomposition gas. A method for treating exhaust gas containing methyl bromide, comprising oxidizing carbon monoxide to carbon dioxide with a carbon monoxide oxidation catalyst.