JPH06106028A - Treatment of nitrous oxide containing gas - Google Patents

Abstract

PURPOSE:To effectively decompose nitrous oxide in waste gas by bringing nitrous oxide contg. gas in the presence of materials poisoning a catalyst unto contact with a multicomponent catalyst contg. Rh2O3, Co2O3, cerium compounds, alkali metal compounds, alkaline earth metal compounds, etc., at a specified temperature CONSTITUTION:Nitrous oxide contg. gas in the presence of one or more of materials poisoning a catalyst, moisture, sulfur compounds and halogenated compounds, is brought into contact with a multicomponent catalyst contg. as effective components one or more of group A compounds consisting of Rh2O3 or Co2O3, or their mixture, group B compounds consisting of cerium compounds (example: CeO2) and group C compounds consisting of alkali metal compounds (example: K2CO3) or alkaline earth metal compounds or their mixture each at a temperature of 100-600 deg.C. Thus, nitrous oxide in waste gas is effectively decomposed into oxygen and nitrogen at a relatively low temperature without requiring a reducing agent, such as ammonia.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating a nitrous oxide-containing gas for decomposing and removing nitrous oxide contained in various industrial exhaust gases.

[0002]

2. Description of the Related Art Regarding the release of various industrial exhaust gases such as combustion exhaust gases and exhaust gases from chemical plants into the atmosphere, various regulatory measures have been taken from the viewpoint of pollution prevention and environmental protection. In particular, nitrogen oxides are strictly regulated to be released into the atmosphere as photochemical smog, acid rain, and other causative substances. Conventionally, the nitrogen oxides that have been subject to emission regulations are nitric oxide (NO) and nitrogen dioxide (NO ₂ ), and denitration technology has also been studied for these substances, using reducing substances such as ammonia. The catalytic reduction method and the method of decomposing it into nitrogen and oxygen using a catalyst such as a metal catalyst have been developed.

Among nitrogen oxides, nitrous oxide was considered to be stable and harmless as compared with other nitrogen oxides. However, in recent years, it has become clear that this nitrous oxide decomposes in the stratosphere to produce nitric oxide, and it also shows a high greenhouse effect, and its half-life is as long as about 150 years, which contributes to global warming. It is becoming a problem, with some implications. The amount of nitrous oxide contained in various exhaust gases has not yet been elucidated in detail, but it varies depending on the type of fuel, combustion conditions, etc.
It has been reported that nitrous oxide is contained at about 0 ppm. This nitrous oxide is completely decomposed by the denitration method described above,
In the case of denitrification method using ammonia as a reducing agent, nitrous oxide is produced by the reaction of nitric oxide, nitrogen dioxide and ammonia depending on the operating conditions of the denitrification equipment, and the concentration increases. It has become clear that there is.

Under these circumstances, various methods for decomposing and removing nitrous oxide contained in various exhaust gases have been studied and proposed. Conventionally, the main method proposed as a method for decomposing nitrous oxide in exhaust gas is a catalytic decomposition method of decomposing by contacting with a metal catalyst at a high temperature (Japanese Patent Laid-Open No. Sho 6-62).
No. 3-7826), a catalytic reduction method in which a catalyst is brought into contact with a reducing gas such as ammonia or hydrogen to perform reductive decomposition (Japanese Patent Publication No. 55-47933, JP-A-2-6812).
No. 0) or a method of decomposing by light or radiation (Japanese Patent Laid-Open Nos. 63-111927 and 63-11).
1929 publication). In these methods, the treatment temperature is high, and 0.01 to 0.15% of sulfur oxides, 5 to 20% of water, and 0.5 to 100 ppm of halogen substances are contained in ordinary combustion exhaust gas. Since these substances are contained, there are many problems such as poisoning of the catalyst due to these substances to lower the decomposition activity and the need for a special device, and the fact is that they have not been put into practical use.

Among the above-mentioned conventional techniques, the catalytic cracking method is considered to be the simplest and most practical, but this method generally requires treatment at a high temperature. JP-A-63-782
In the method described in Japanese Patent No. 6, a nitrous oxide-containing gas is contacted with a catalyst containing a metal of group Ib or VIII of the periodic table of elements or an oxide or complex oxide of the metal. However, in order to obtain a denitrification rate of 50% or more, a high temperature of 350 ° C. or more is required except for the noble metal catalyst. Further, according to the experiments by the present inventors, the NiO and Fe described here are
There is a problem that catalysts such as ₂ O ₃ , CoO and CuO are deactivated in a short time when the exhaust gas to be treated contains water or sulfur oxides, and the decomposition activity of nitrous oxide is reduced. There was found.

The present inventors have conducted extensive studies on a method for decomposing and removing nitrous oxide which does not have the above-mentioned problems, and as a result, Rh ₂ O ₃
Alternatively, Co ₂ O ₃ , especially a catalyst containing these mixtures as an active ingredient has a high nitrous oxide decomposition activity even at a relatively low temperature, and the activity decrease due to poisoning such as water and sulfur oxides is very small, and the activity is maintained for a long time. It was found that a stable and high decomposition performance of nitrous oxide can be maintained, and the application was filed previously (Japanese Patent Application No. 3-140629).

[0007]

However, the above-mentioned Rh ₂
The O ₃ -Co ₂ O ₃ -based catalyst has a characteristic that the resistance to poisoning substances is remarkably large as compared with the conventionally used catalysts.
Under the condition that a halogenated substance such as hydrogen fluoride coexists, the catalytic activity greatly decreases, and there is still a problem in using it for a long time. The object of the present invention is to solve the problems in the conventional catalytic cracking method, to enable treatment at a relatively low temperature, and to contain nitrous oxide containing water and catalyst poisoning substances such as sulfur oxides and halogen substances. An object of the present invention is to provide a method for treating a nitrous oxide-containing gas capable of treating exhaust gas.

[0008]

According to the present invention, a nitrous oxide-containing gas is used as a group A compound composed of Rh ₂ O ₃ or Co ₂ O ₃ or a mixture thereof, and a compound B composed of a cerium compound.
A multi-component catalyst containing, as an active ingredient, one or more each of a group C compound and an alkali metal compound, an alkaline earth metal compound, or a mixture thereof, and a group C compound,
Method for treating a nitrous oxide-containing gas, which comprises contacting at a temperature of 100 to 600 ° C. to decompose nitrous oxide, and one or more catalyst poisonous substances among water, sulfur oxides and halogen substances The nitrous oxide-containing gas that coexists with
Rh ₂ O ₃ or Co ₂ O ₃ or a group A compound composed of a mixture thereof, a group B compound composed of a cerium compound, and an alkali metal compound or an alkaline earth metal compound, or a group C compound composed of a mixture thereof, respectively, each being one or more kinds. A multi-way catalyst containing as an active ingredient, 100 to 6
A method for treating a nitrous oxide-containing gas, which comprises contacting at a temperature of 00 ° C. to decompose nitrous oxide.

The catalyst used in the process of the present invention is R
h ₂ O ₃ or Co ₂ O ₃ or a group A compound consisting of a mixture thereof, a group B compound consisting of a cerium compound and an alkali metal compound or an alkaline earth metal compound or a group C compound consisting of a mixture thereof, respectively It is a multi-way catalyst containing a mixture of as an active ingredient.
These catalysts are used by granulating each active ingredient together with a binder component such as colloidal silica having SiO ₂ as a main component, or by supporting it on a carrier such as titania, alumina, silica / alumina, or magnesia. Is convenient. In addition, the shape and size of the catalyst depends on the purpose of use,
It may be appropriately selected according to the usage situation, etc.
A spherical shape, a ring shape, a cylindrical shape, a plate shape, a honeycomb shape, or the like can be used, but a honeycomb shape, a plate shape, or the like is particularly preferable in terms of contact efficiency with gas, pressure loss, and the like.

The method for producing the multi-way catalyst used in the present invention is not particularly limited, but the following examples are mentioned as preferred methods. That is, powdered Rh ₂ O ₃
Alternatively, a cerium compound is added to Co ₂ O ₃ or a mixed powder obtained by mixing these at an arbitrary ratio, and an alkali metal compound, an alkaline earth metal compound, or a mixture thereof is added as a raw material, together with an appropriate binder component. A method of kneading with water, adding a carrier component as necessary, mixing and molding into an appropriate size, then pulverizing the dried product to adjust the particle size, kneading with water together with a binder component and a carrier component and molding into an arbitrary shape A method of post-drying, a method of mixing with a binder component with water to form a slurry, and adhering it to a carrier having an arbitrary shape and drying can be employed. Here, when a compound other than an oxide is used as the cerium compound, the alkali metal compound or the alkaline earth metal compound, heat treatment is performed in an oxidizing atmosphere at a temperature of 300 ° C. or higher, preferably 400 to 800 ° C. The portion is used by changing it to an oxide form. It should be noted that since the oxidation gradually progresses during use depending on the use conditions, it is possible to omit the previous oxidation treatment. It is not clear in what manner the cerium compound, alkali metal compound or alkaline earth metal compound acts effectively in the thus prepared multi-way catalyst, but most of them exist in the form of oxides. It is estimated to be.

The cerium compound used for producing the multi-way catalyst is not particularly limited as long as it can be converted into CeO ₂ or Ce ₂ O ₃ by oxidation, and Ce ₂ (NO ₃ ) ₃ , C
Although e ₂ (CO ₃ ) ₃ and CeCl ₃ can be used, it is particularly preferable to use them in the form of CeO ₂ or Ce (CH ₃ COO) ₃ . Further, as the alkali metal compound or the alkaline earth metal compound, K ₂ CO ₃ , KN
O ₃ , KOH, K ₂ SO ₄ , Na ₂ CO ₃ , MgC
O ₃ , CaCO ₃ or the like can be used. Rh ₂
As a method for mixing the cerium compound, the alkali metal compound, the alkaline earth metal compound or the like with the powder of O ₃ or Co ₂ O ₃ , a method of mixing in a powder form or a method of dissolving in water and adding and mixing can be adopted. it can.

The content ratio of the active ingredient in the catalyst is from a supported catalyst in which individual active ingredients or a mixture thereof are supported on various carriers to a content rate of 98% by weight or more formed with a small amount of a binder component. It can be arbitrarily set within a wide range according to the processing conditions such as the property of the processing gas, the processing apparatus, the processing temperature, or the required decomposition rate of nitrous oxide. When the metal oxide is supported on the carrier, it is preferable that the amount of the metal oxide supported is in the range of 0.1 to 30% by weight. If it is less than 0.1% by weight, the catalytic activity is low, and if it exceeds 30% by weight, the reinforcing effect by the carrier becomes small.

The mixing ratio of the A, B and C group compounds contained in the catalytically active component is 10% by weight.
~ 90%, Group B compounds 5 to 45% and Group C compounds 5 to 4
5%.

Nitrogen oxide can be decomposed into oxygen and nitrogen by filling the reaction tank with the catalyst thus prepared and reacting it with a gas containing nitrous oxide.
The reaction temperature and the space velocity (SV) of the gas vary depending on the concentration of nitrous oxide in the gas, the form and amount of the catalyst used, the shape of the reactor, etc., but the reaction temperature is in the range of 100 to 600 ° C.
Particularly, the range of 150 to 600 ° C. is preferable, and the space velocity is
The range of 3000 to 20000 (hr ^-1 ) is preferable. If the temperature is lower than 100 ° C, the decomposition of nitrous oxide is difficult to proceed, and if it exceeds 600 ° C, the catalyst is severely deteriorated, which is not preferable. When the space velocity is less than 3000 (hr ⁻¹ ), there is no change in the decomposition rate of nitrous oxide, but the gas processing capacity becomes small and it is not practical.
When it exceeds (hr ⁻¹ ), the decomposition rate of nitrous oxide is lowered, which is not preferable.

According to the method of the present invention, nitrous oxide in exhaust gas can be decomposed into oxygen and nitrogen without using a reducing agent such as ammonia or hydrogen. Moreover, the catalyst used in the present invention is highly active even at a relatively low temperature, and the activity reduction due to poisoning of water, sulfur oxides, halogen substances, etc. is very small, and especially for sulfur oxides and halogen substances having a large poisoning action. It is possible to maintain a stable and high denitrification rate for a long time even under the condition that water coexists.

[0016]

EXAMPLES The method of the present invention will be described in more detail with reference to the following examples. (Preparation of catalyst) Commercially available Co ₂ O ₃ (purity 99.5%),
Rh ₂ O ₃ (purity 99.0%), Ce (CH ₃ COO)
_A catalyst was prepared according to the following procedure using ₃ (purity 99.5%), KOH (purity 99.5%) and Na ₂ CO ₃ (purity 99.5%). (1) Co ₂ O ₃ or Rh ₂ O ₃ PLAIN catalyst Co ₂ O ₃ or Rh ₂ O ₃ with respect to 100 parts by weight of the binder (a molding aid) colloidal silica was added 3 parts by weight SiO ₂ as a water Kneaded This kneaded material has a diameter of about 3
Molded into a 0 mm spherical shape, 24 at 120 ℃ in air atmosphere
What was dried for a period of time was crushed to obtain a granular catalyst of 1 to 3 mm. These catalysts are (Co ₂ O ₃ ) and (R
h ₂ O ₃ ) is displayed.

(2) Mixed catalyst of Co ₂ O ₃ and potassium compound To 100 parts by weight of Co ₂ O ₃ and 5 parts by weight of KOH, 3 parts by weight of colloidal silica as SiO ₂ was added and kneaded with water. This kneaded material was molded into a spherical shape having a diameter of about 30 mm, dried in an air atmosphere at 120 ° C. for 24 hours, and further heat-treated in an air atmosphere at 500 ° C. for 1 hour to be crushed,
A granular catalyst of 1 to 3 mm was obtained. This catalyst is (Co ₂ O ₃
-K) is displayed. (3) Mixed catalyst of Co ₂ O ₃ and cerium compound Co ₂ O ₃ 100 parts by weight and 5 parts by weight of Ce (CH ₃ C
3 parts by weight of colloidal silica as SiO ₂ was added to OO) ₃ and kneaded with water. This kneaded material was molded into a spherical shape having a diameter of about 30 mm, dried in an air atmosphere at 120 ° C. for 24 hours, and further heat-treated in an air atmosphere at 500 ° C. for 1 hour to be crushed to obtain a granular catalyst of 1 to 3 mm. Obtained. Show this catalyst and (Co ₂ O ₃ -Ce).

(4) Catalyst prepared by adding potassium compound or sodium compound to mixture of Co ₂ O ₃ and cerium compound 100 parts by weight of Co ₂ O ₃ and 5 parts by weight of Ce (CH ₃ C
₃ parts by weight of colloidal silica as SiO ₂ was added to a mixture obtained by adding 5 parts by weight of KOH or Na ₂ CO ₃ to OO) ₃ and kneaded with water. This kneaded material was molded into a spherical shape having a diameter of about 30 mm, dried in an air atmosphere at 120 ° C. for 24 hours, and further heat-treated in an air atmosphere at 500 ° C. for 1 hour to be crushed to obtain a granular catalyst of 1 to 3 mm. Obtained. These catalysts (Co ₂ O ₃ -Ce-K) and (Co ₂ O _3-
Ce-Na) is displayed. (5) A catalyst prepared by adding a potassium compound or a sodium compound to a mixture of Co ₂ O ₃ , Rh ₂ O ₃ and a cerium compound Co ₂ O ₃ and Rh ₂ O ₃ are 98/2 or 50, respectively.
₃ parts by weight of colloidal silica as SiO ₂ was added to a mixture of 100 parts by weight of a mixture of 100 parts by weight, 5 parts by weight of Ce (CH ₃ COO) ₃ and 5 parts by weight of KOH, and kneaded with water. This kneaded material was molded into a spherical shape having a diameter of about 30 mm, dried in an air atmosphere at 120 ° C. for 24 hours, and further heat-treated in an air atmosphere at 500 ° C. for 1 hour to be crushed to obtain a granular catalyst of 1 to 3 mm. Obtained. To view these catalysts and _{(Co 2 O 3 -Rh 2 O} 3 -Ce-K-2/98) and _{(Co 2 O 3 -Rh 2 O} 3 -Ce-K-50/50).

(6) Titania-supported catalyst using Co ₂ O ₃ and Rh ₂ O ₃ To a mixture of 10 parts by weight of Co ₂ O _{3 and} 10 parts by weight of Rh ₂ O ₃ was added 3 parts by weight of colloidal silica as SiO _2. Further, 100 parts by weight of γ-titania heat-treated at 500 ° C. for 5 hours in a nitrogen atmosphere was added and kneaded with water. This kneaded material was molded into a spherical shape having a diameter of about 30 mm, dried in an air atmosphere at 120 ° C. for 24 hours, further heat-treated in an air atmosphere at 500 ° C. for 1 hour, and then crushed to give 1 to 3 m.
m granular catalyst was obtained. This catalyst was converted to (Co ₂ O ₃ -Rh ₂
It is displayed as O ₃ / TiO ₂ .

(7) Co₂O₃, Rh₂O₃And Seriu
Titania with the addition of potassium compounds to a mixture of magnesium compounds
Supported catalyst γ-tita heat-treated at 500 ° C. for 5 hours in a nitrogen atmosphere
Near 100 parts by weight Co₂O₃10 parts by weight, Rh₂O₃
10 parts by weight, 2 parts by weight Ce (CH₃COO) ₃And K
S colloidal silica was added to the mixture containing 2 parts by weight of OH.
iO₂Was mixed with 3 parts by weight and kneaded with water. This kneaded product
Molded into a spherical shape with a diameter of about 30 mm, and 120 in an air atmosphere.
Dry at ℃ for 24 hours, and further in air atmosphere at 500 ℃
What was heat-treated for 1 hour was crushed and granulated into 1 to 3 mm
A catalyst was obtained. This catalyst is₂O₃-Rh₂O₃-C
e-K / TiO₂) Is displayed.

(Nitrous oxide decomposition and removal test) 25 ml of each of the catalysts prepared as described above was filled in a test device composed of a quartz tube having an inner diameter of 20 mm, and a gas having a predetermined composition was passed under a predetermined temperature condition. The concentration of nitrous oxide in the gas at the inlet and outlet of the reaction tube was measured. From that value,
The decomposition rate of nitrous oxide was calculated and the activity of the catalyst was compared.

Example 1 The temperature of the catalyst layer was set as shown in Table 1, and air containing 150 ppm of N ₂ O was added to
It was passed through at a space velocity of 6000 hr ^-1 , and the decomposition rate of N ₂ O was measured. The results are shown in Table 1. The catalyst used in the present invention exhibits a high nitrous oxide decomposition activity even at a relatively low temperature, and in particular, a remarkable synergistic effect is recognized in the catalyst group containing Co ₂ O ₃ and Rh ₂ O ₃ .

[0023]

[Table 1]

Example 2 The temperature of the catalyst layer was set as shown in Table 2, 150 ppm N ₂ O and 50 ppm SO were added.
Air containing ₂ and 14% water is used for 5000 hr ^-1
At a space velocity of 100 N after 100 hours from the start of the reaction.
The decomposition rate of ₂ O was measured. The results are shown in Table 2.

[0025]

[Table 2]

(Example 3) The temperature of the catalyst layer was set as shown in Table 3, and 150 ppm of N ₂ O and 35 ppm of HC were set.
1 hr and air containing 14% of water for 5000 hr ^-1
At a space velocity of 100 N after 100 hours from the start of the reaction.
The decomposition rate of ₂ O was measured. The results are shown in Table 3.

[0027]

[Table 3]

Example 4 The temperature of the catalyst layer was set as shown in Table 4, 150 ppm of N ₂ O and 50 ppm of SO were added.
Air containing ₂ , 35 ppm of HCl and 14% of water was passed through at a space velocity of 5000 hr ⁻¹ , and the decomposition rate of N ₂ O 100 hours after the start of the reaction was measured. The results are shown in Table 4.

[0029]

[Table 4]

From the results shown in Tables 2 to 4, when the catalyst of the present invention was used, the degree of deactivation was extremely small, and high nitrous oxide decomposition activity was exhibited even at a relatively low temperature.
₂ O ₃ , Rh ₂ O ₃ , Ce (CH ₃ COO) ₃ and KO
With the catalyst that uses H together, about 50% at 200 ° C, 250 ° C
It can be seen that the high decomposition rate is maintained at about 90% and at 300 to 400 ° C. of 99% or more.

[0031]

According to the method of the present invention, nitrous oxide in exhaust gas can be efficiently decomposed into oxygen and nitrogen without using a reducing agent such as ammonia or hydrogen. Moreover, the catalyst used in the present invention has a high activity even at a relatively low temperature, has a very small activity reduction due to poisoning of catalyst poisoning substances such as water and sulfur oxides, and can maintain a stable high denitration rate for a long time. Therefore, it is extremely effective in treating various exhaust gases containing nitrous oxide, which often contain water, sulfur oxides, halogen substances and the like.

Front page continuation (72) Masatoshi Adachi Inventor Masatoshi Adachi 1-3 Kyōchi-cho, Wakamatsu-ku, Kitakyushu, Mitsui Mining Co., Ltd. Kyushu Research Center

Claims (2)

[Claims] 1. A gas containing nitrous oxide is rhodium trioxide (Rh ₂ O ₃ ) or cobalt trioxide (Co ₂ O).
₃ ) or a multi-component compound containing, as an active ingredient, one or more each of a group A compound consisting of a mixture thereof, a group B compound consisting of a cerium compound, and an alkali metal compound or an alkaline earth metal compound or a group C compound consisting of a mixture thereof. Contact with a catalyst at a temperature of 100 to 600 ° C.,
A method for treating a nitrous oxide-containing gas, which comprises decomposing nitrous oxide. 2. A nitrous oxide-containing gas in which one or more kinds of catalyst poisoning substances among water, sulfur oxides and halogen substances coexist is rhodium sesquioxide (Rh ₂ O ₃ ) or cobalt sesquioxide (Co _2). O ₃ ) or a group A compound consisting of a mixture thereof, a group B compound consisting of a cerium compound, and an alkali metal compound or an alkaline earth metal compound, or a group C compound consisting of a mixture thereof, each as an active ingredient. Multi-way catalyst, 100-600
A method for treating a nitrous oxide-containing gas, which comprises contacting at a temperature of ° C to decompose nitrous oxide.