JP3236031B2 - Method for decomposing and removing nitrous oxide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Various control measures have been taken with respect to emission of various industrial exhaust gases such as combustion exhaust gases and exhaust gases from chemical factories into the atmosphere from the viewpoints of pollution prevention and environmental conservation. In particular, emission of nitrogen oxides into the atmosphere as a causative substance such as photochemical smog and acid rain is strictly regulated. Conventionally, nitrogen oxides that have been subject to emission control are nitric oxide (NO) and nitrogen dioxide (NO ₂ ), and denitrification technology has also been studied for these substances, and reducing substances such as ammonia have been used. A catalytic reduction method and a method of decomposing into nitrogen and oxygen using a catalyst such as a metal catalyst have been developed. However, in recent years, nitrous oxide, which is contained in trace amounts in these exhaust gases but is said to be stable and harmless compared to other nitrogen oxides, can decompose in the stratosphere to produce nitric oxide. It has become a problem, for example, showing a high greenhouse effect and a long half-life of about 150 years, suggesting an effect on global warming. However, nitrous oxide cannot be decomposed and removed at all by the above-mentioned denitration method. Further, in the denitration method using ammonia as a reducing agent, depending on the operating conditions of the denitration apparatus, nitric oxide, nitrogen dioxide, ammonia, etc. It has even become clear that nitrous oxide may be produced in relatively high concentrations by the reaction of

Therefore, various methods for decomposing and removing nitrous oxide contained in various exhaust gases have been studied and proposed. Conventionally, a major method proposed as a method for decomposing nitrous oxide in exhaust gas is a catalytic cracking method in which a catalyst is decomposed by contact with a metal catalyst at a high temperature (JP-A-63-763).
No. 826, etc.), and a catalytic reduction method in which the catalyst is brought into contact with a catalyst together with a reducing gas such as ammonia or hydrogen to undergo reductive decomposition (JP-B-55-47933, JP-A-2-68120, etc.)
Alternatively, a method of decomposing by light or radiation (Japanese Unexamined Patent Publication No.
In these methods, the catalyst is covered by the high processing temperature, oxygen, sulfur oxides, moisture, etc. present in the exhaust gas. Poisons and decomposes,
There are many problems such as the necessity of a special device, and the fact is that it has not yet been put to practical use.

[0004]

Among the above prior arts, the catalytic cracking method is considered to be the simplest and practical one, but this method generally requires a treatment at a high temperature. The method described in JP-A-63-7826 discloses that a gas containing nitrous oxide is treated with a metal of Group Ib or Group VIII of the periodic table of the element or an oxide or composite oxide of the metal. In this method, a high temperature of 350 ° C. or more is required except for the noble metal catalyst, in order to obtain a denitration rate of 50% or more in view of Examples. In addition, according to experiments performed by the present inventors, catalysts such as NiO, Fe ₂ O ₃ , CoO, and CuO described here are short if the exhaust gas to be treated contains moisture or sulfur oxides. It has been found that there is a problem that it is deactivated in a short time and the decomposition activity of nitrous oxide is reduced. An object of the present invention is to solve the problems of the conventional catalytic cracking method, to perform treatment at a relatively low temperature, and to treat a nitrous oxide-containing exhaust gas in which moisture and sulfur oxides coexist. An object of the present invention is to provide a method for decomposing and removing nitric oxide.

[0005]

DISCLOSURE OF THE INVENTION The present inventors have searched for a catalyst for decomposing nitrous oxide and found that Rh ₂ O ₃ and Co
A metal oxide catalyst containing ₂ O ₃ as an active component has a very small activity decrease due to poisoning of moisture and sulfur oxides in exhaust gas, and has a high activity even at a relatively low temperature and decomposes nitrous oxide into oxygen and nitrogen. We have found that we can do this and completed the present invention.
That is, according to the present invention, the nitrous oxide-containing gas is converted to rhodium trioxide (Rh ₂ O ₃ ), cobalt trioxide (Co ₂ O ₃ ).
₃ ) A method for decomposing and removing nitrous oxide, which comprises contacting a catalyst containing any of these or any of these as an active ingredient at a temperature of 100 to 600 ° C. to decompose nitrous oxide, and water and / or sulfur. A nitrous oxide-containing gas in which an oxide coexists with a catalyst containing rhodium trioxide (Rh ₂ O ₃ ), cobalt sesquioxide (Co ₂ O ₃ ) or a mixture thereof as an active component at 100 to 600 ° C. This is a method for decomposing and removing nitrous oxide, which comprises contacting at a temperature to decompose nitrous oxide.

The catalyst used in the process of the present invention is R
one of _{h 2 O 3, Co 2 O} 3 , or mixtures thereof are those containing as an active ingredient. These catalysts
Each active ingredient is granulated together with a binder component such as colloidal silica containing SiO ₂ as a main component, or titania,
It is convenient to use it in a form supported on a carrier such as alumina, silica / alumina, or magnesia. Further, the shape, size, etc. of the catalyst may be appropriately selected according to the purpose of use, use conditions, etc., and shapes such as granules, bales, spheres, rings, columns, plates, and honeycombs can be used. In particular, a honeycomb shape, a plate shape, and the like are preferable in terms of gas contact efficiency and pressure loss.

The method for producing the catalyst is not particularly limited, but powdered Rh ₂ O ₃ or Co ₂ O ₃ or a mixed powder obtained by mixing these at an arbitrary ratio is used as a raw material, and water is added together with a binder component to water. Kneading, if necessary, adding a carrier component, mixing and molding to an appropriate size, and then drying and pulverizing the dried product; adjusting the particle size; kneading with water together with a binder component and a carrier component to form an arbitrary shape; Any method such as a method of drying, a method of mixing with water together with a binder component to form a slurry, and attaching the mixture to a carrier having an arbitrary shape and drying the mixture can be employed. The content ratio of the active ingredient in the catalyst ranges from a supported catalyst in which each active ingredient or a mixture thereof is supported on various supports, to a content of 98% by weight or more molded 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 properties of the processing gas, the processing apparatus and the processing temperature, or the required decomposition rate of nitrous oxide. When supported on a carrier, the supported amount is 0.1 to 3 as a metal oxide.
It is preferred that the content be in the range of 0% by weight. 0.1
If it is less than 30% by weight, the catalytic activity is low, and if it exceeds 30% by weight, the reinforcing effect of the carrier is small.

[0008] The catalyst thus prepared is charged into a reaction tank, and the reaction is performed through a gas containing nitrous oxide, whereby the nitrous oxide can be decomposed into oxygen and nitrogen.
The reaction temperature and the space velocity of the gas (SV) vary depending on the concentration of nitrous oxide in the gas, the form and amount of the catalyst used, the shape of the reactor, and the like.
In particular, 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., decomposition of nitrous oxide hardly proceeds, and if it is higher than 600 ° C., deterioration of the catalyst becomes severe, which is not preferable. When the space velocity is less than 3000 (hr ^-1 ), the decomposition rate of nitrous oxide does not change, but the gas processing capacity is reduced and it is not practical.
If it exceeds (hr ^-1 ), the decomposition rate of nitrous oxide decreases, 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 requiring 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 decrease in the activity due to poisoning by moisture or sulfur oxides, and can maintain a stable and high denitration rate for a long time. That is, in the conventional CoO and RhO-based catalysts, the influence of moisture and sulfur oxides is great, and no decomposition activity of nitrous oxide is observed at 250 ° C. or lower, but the Co ₂ O ₃ and Rh ₂ O ₃ -based catalysts of the present invention are not observed. With a catalyst, especially a mixed catalyst of both, a decomposition rate of 10% or more can be obtained at a temperature around 150 ° C. even under the condition that 20% by volume or less of moisture or 10% by volume or less of sulfur oxides coexist. At such a low temperature, a catalyst showing the activity of decomposing nitrous oxide in the coexistence of moisture or sulfur oxide has not hitherto been known.

[0010]

EXAMPLES The method of the present invention will be described more specifically 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%), CoO (purity 99.5%)
%) And RhO (purity 99.0%), and the catalyst was prepared according to the following operation. (1) Co ₂ O ₃ or Rh ₂ O ₃ plain catalyst and Co ₂
O ₃ and mixed catalyst Co of Rh ₂ O _{3 2} O ₃ or Rh ₂ O ₃ 100 parts by weight or Co ₂
O ₃ and Rh ₂ O ₃ and each 98/2 or 50/50
100 parts by weight of the mixture mixed in the ratio of
3 parts by weight of colloidal silica as SiO ₂ was added as a (molding aid) and kneaded with water. This kneaded material is about 30
It was formed into a spherical shape having a diameter of 1 mm and dried in an air atmosphere at 120 ° C. for 24 hours, and then crushed to obtain a granular catalyst having a size of 1 to 3 mm. These catalysts are referred to as (Co ₂ O ₃ ), (Rh ₂
O _3), indicated as _{(Co 2 O 3 -Rh 2 O} 3, 98/2) and _{(Co 2 O 3 -Rh 2 O} 3, 50/50). (2) Alumina-supported catalyst using Co ₂ O ₃ and Rh ₂ O ₃ 20 parts each of Co ₂ O ₃ or Rh ₂ O ₃ was added to 100 parts by weight of γ-alumina heated at 600 ° C. for 5 hours in a nitrogen atmosphere. The mixture was mixed with 3 parts by weight of colloidal silica as SiO _{2 and} kneaded with water. This kneaded material is formed into a sphere having a diameter of about 30 mm,
The product dried at 24 ° C for 24 hours was crushed to obtain a granular catalyst of 1 to 3 mm. Each of these catalysts was (Co ₂ O ₃ /
Al ₂ O ₃₎ and _{(Rh 2 O 3 / Al 2} O 3) to be displayed.

[0011] (3) Co ₂ O ₃ and Rh ₂ O ₃ colloidal silica 3 parts by weight was added as SiO ₂ in the mixture of titania supported catalyst Co ₂ O ₃ 50 parts by weight of Rh ₂ O ₃ 50 parts by weight Using Then, 100 parts by weight of titania (anatase type) was added and water-kneaded. This kneaded product was formed into a spherical shape having a diameter of about 30 mm, and dried at 120 ° C. for 24 hours in an air atmosphere, and crushed to obtain a granular catalyst of 1 to 3 mm. Show this catalyst and _{(Co 2 O 3 -Rh 2 O} 3 / TiO 2). (4) Alumina-supported catalyst using CoO and RhO 100 parts by weight of γ-alumina heat-treated at 600 ° C for 5 hours in a nitrogen atmosphere is immersed in an aqueous solution of cobalt nitrate or rhodium nitrate to form CoO or RhO, respectively.
The catalyst was prepared by adsorbing parts by weight, drying at 110 ° C. for 24 hours in an air atmosphere, and calcining at 600 ° C. for 5 hours in a nitrogen atmosphere. Each of these catalysts (CoO /
Al ₂ O ₃₎ and (RhO / Al ₂ O ₃₎ to be displayed. (Nitrous oxide decomposition removal test) 25 ml of each of the catalysts prepared as described above were filled in a test apparatus consisting 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, and a reaction tube was passed. The concentration of nitrous oxide in the gas at the inlet and outlet was measured. From the 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 60 ppm N ₂ O
At a space velocity of 000 hr ^-1 , the decomposition rate of N ₂ O was measured. The results are as shown in Table 1, the catalyst for use in the present invention exhibit proteolytic activity higher than the conventional CoO or RhO based catalysts nitrous oxide, in particular Co ₂ O ₃
A remarkable synergistic effect was recognized in the catalyst in which the catalyst was mixed with Rh ₂ O _3, and it was found that a decomposition rate of about 20% was obtained even at a low temperature of 150 ° C. Incidentally, N ₂ O concentration 1000p was subjected to the same test by changing the concentration of N ₂ O
Approximately the same decomposition rate was obtained up to about pm.

[0013]

[Table 1]

Example 2 The temperature of the catalyst layer was set as shown in Table 2, and air containing 150 ppm of N ₂ O and 14% of moisture was passed at a space velocity of 5000 hr ^-1 to start the reaction. 100 hours later, the decomposition rate of N ₂ O was measured. The results are as shown in Table 2 and show that the conventional CoO
Alternatively, RhO-based catalysts are highly deactivated and even at 400 ° C.
While only a decomposition rate of about 0% can be obtained, when the catalyst of the present invention is used, deactivation is small, and even a simple catalyst has a deactivation rate of 30%.
The catalyst exhibits a decomposition rate of about 40 to 60% at 0 ° C. and about 75 to 80% at 400 ° C. For a catalyst using both Co ₂ O ₃ and Rh ₂ O ₃ , about 10% at 150 ° C. and about 200% at 200 ° C. 40%, 2
It can be seen that high decomposition rates of about 80% at 50 ° C., about 90% at 300 ° C., and 99% or more at 400 ° C. are maintained.

[0015]

[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 50 ppm of S
Air containing O ₂ was passed at a space velocity of 5000 hr ⁻¹ , and the decomposition rate of N ₂ O was measured 100 hours after the start of the reaction. The results are as shown in Table 3 and show that the conventional C
While the oO or RhO-based catalyst is highly deactivated and can only obtain a decomposition rate of about 20 to 40% even at 400 ° C.,
When the catalyst of the present invention was used, the deactivation was small and Co ₂
About 40-45% at 300 ° C, 400 ° C even with O ₃ plain catalyst
Shows a decomposition rate of about 90%, and Co ₂ O ₃ and Rh ₂ O ₃
About 20% at 150 ° C, 200 ° C
About 50% at 250 ° C, about 90% at 300-400 ° C
As a result, it can be seen that a high decomposition rate of 99% or more is maintained.

[0017]

[Table 3]

[0018]

According to the method of the present invention, nitrous oxide in exhaust gas can be efficiently decomposed into oxygen and nitrogen without requiring 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, a very small decrease in the activity due to poisoning such as moisture and sulfur oxides, and a stable high denitration rate can be maintained over a long period of time. It is extremely effective in treating various exhaust gases containing nitrous oxide, which often contains moisture and sulfur oxides.

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁷ identification code FI B01J 23/74 311A (58) Field surveyed (Int.Cl. ⁷ , DB name) B01J 21/00-38/00 B01D 53 / 94

Claims (2)

(57) [Claims] 1. A catalyst comprising, as an active ingredient, one of rhodium trioxide (Rh ₂ O ₃ ), cobalt trioxide (Co ₂ O ₃ ), or a mixture thereof, comprising a nitrous oxide-containing gas.
A method for decomposing and removing nitrous oxide, comprising contacting at a temperature of 00 to 600 ° C. to decompose nitrous oxide. 2. Nitrous oxide-containing gas in which water and / or sulfur oxides coexist is converted to rhodium trioxide (Rh).
A catalyst containing any one of active ingredients, such as ₂ O ₃ ), cobalt trioxide (Co ₂ O ₃ ) or a mixture thereof;
A method for decomposing and removing nitrous oxide, comprising contacting at a temperature of 00 ° C. to decompose nitrous oxide.