JPH05115751A - Method and catalyst for treating gas combustion exhaust gas - Google Patents

Abstract

PURPOSE:To simultaneously and efficiently remove nitrogen oxide, lower hydrocarbon and CO in exhaust gas with a single catalyst by catalytically reacting gas combustion exhaust gas generated under a condition wherein the ratio of raw material gas and air becomes the lean side of the raw material gas in the presence of a catalyst obtained by loading a metal such as Co or the like on a mordenite type zeolite carrier. CONSTITUTION:Gas combustion exhaust gas generated under such a condition that the ratio of raw material gas and air becomes the lean side of the raw material gas and containing nitrogen, oxygen, steam and CO2 as principal components and lower hydrocarbon, especially, methane, nitrogen oxide and CO as small amount components is catalytically reacted in the presence of a catalyst obtained by making a mordenite type zeolite carrier carry a metal selected from Co, Mn, Rh, platinum and Pd. As a result, a small amount of nitrogen oxide, lower hydrocarbon, especially, methane and CO contained in the gas combustion gas containing a relatively large amount of oxygen and steam at the same time in a gas engine can be simultaneously and efficiently removed using the single catalyst.

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 gas combustion exhaust gas and a catalyst used in the method.
The present invention relates to a method for purifying and treating exhaust gas from a gas engine, a gas turbine, etc., and a catalyst used in the method under the condition that the ratio of raw material gas to air is on the lean side of the raw material gas.

[0002]

2. Description of the Related Art Methane, ethane,
In gas engines, gas turbines, boilers, heating furnaces, etc. that use raw material gas consisting of propane, butane, etc., in order to improve combustion efficiency or thermal efficiency, the ratio of raw material gas to air is set to the lean side of raw material gas, that is, complete combustion of raw material gas. It is desirable to set the condition of 1.0 to 5.0 times, especially 1.0 to 3.0 times (hereinafter, referred to as air ratio) of the theoretical air amount required for the above. A large amount of oxygen and water vapor will coexist with hydrogen, especially methane, nitric oxide and carbon monoxide.

Conventionally, a selective reduction denitration method by addition of ammonia or a purification method by a three-way catalyst has been adopted as a method for purifying gas combustion exhaust gas by removing a small amount of the above-mentioned lower hydrocarbons, particularly methane, nitrogen oxides and carbon monoxide. However, there is a problem that the ammonia method is very toxic for handling ammonia, and the three-way catalyst method is effective only under conditions where there is almost no oxygen at an air ratio of around 1.0. Has been done.

For example, already, 66th CASJ Meeting Abstracts (66th
CATSJ Meeting Abstracts) N
o. 2L404, Vol. 32 No. 6 1990
Year, the pages 430 to 433, have been reported for the selective reduction of NO by hydrocarbons in the O ₂ and SO ₂ presence.

However, in the above report, in a gas engine or the like, a method for purifying gas combustion exhaust gas generated when the ratio of raw material gas to air is on the lean side of the raw material gas,
Specifically, there is nothing about a method for simultaneously and efficiently removing nitrogen oxides, lower hydrocarbons, especially methane, and carbon monoxide contained in the gas combustion exhaust gas in the presence of a relatively large amount of oxygen and water vapor. Not listed.

Japanese Unexamined Patent Publication No. 2-265649 discloses a method for purifying exhaust gas discharged from an automobile or the like, which is capable of efficiently purifying NOx, CO and hydrocarbons in an oxidizing atmosphere in which oxygen is excessively present. However, it is impossible to purify NOx at all with only an oxidation catalyst such as palladium, and in order to purify NOx, CO and hydrocarbons at the same time, a combination of a copper silicate catalyst and an oxidation catalyst such as palladium is used. It is only taught that it is necessary to use a different catalyst system. Moreover, the above hydrocarbon is not specifically described.

The present invention relates to a gas engine, a gas turbine,
In a gas boiler, heating furnace, gas stove, etc., it occurs when the ratio of raw material gas to air is set to the lean side of the raw material gas, and a small amount of gas contained in the gas combustion exhaust gas containing a relatively large amount of oxygen and water vapor at the same time. Nitrogen oxides, lower hydrocarbons, especially methane and carbon monoxide, can be efficiently removed at the same time by using a single catalyst, and a method for purifying and treating the above gas combustion exhaust gas, and high activity and excellent durability used in the method. The purpose is to provide a catalyst.

[0008]

[Means for Solving the Problems] That is, the present invention is
It is generated under the condition that the ratio of raw material gas to air is on the lean side of the raw material gas, contains nitrogen, oxygen, steam and carbon dioxide as major components, and contains lower hydrocarbons as minor components, especially methane, nitrogen oxides and monoxide. Gas combustion exhaust gas containing carbon, gas combustion exhaust gas characterized by catalytically reacting in the presence of a catalyst in which a metal selected from cobalt, manganese, rhodium, platinum or palladium is supported on a mordenite type zeolite carrier And a catalyst used in the method.

Examples of the raw material gas used in the method of the present invention include methane, natural gas; city gas containing methane, ethane, propane and butane; LPG such as propane and butane.

In the gas combustion engine, gas turbine, gas boiler, heating furnace, gas stove, etc., the gas combustion exhaust gas in the present invention has an air ratio of 1.0 when the ratio of the raw material gas to the air is the raw material gas lean side. ~ 5.
It means a gas generated under the condition of 0, preferably 1.0 to 3.0.

The lower hydrocarbon is a hydrocarbon having 1 to 16 carbon atoms, preferably methane, ethane, propane, butane, a mixture thereof, and a mixture containing ethane, propane, butane as a main component of methane, If the content is insufficient, it is preferably supplemented separately as needed.

The catalyst used in the method of the present invention comprises a metal selected from cobalt, manganese, rhodium, platinum or palladium supported on a mordenite type zeolite carrier.

The supported amount of the above metal is usually in the range of 0.1 to 40% by weight, preferably 0.5 to 20% by weight. If the supported amount is less than 0.1% by weight, the catalytic activity is not sufficient. It is not preferable, and if the supported amount exceeds 40% by weight, the effect of the mordenite type zeolite as the carrier decreases, which is not preferable.

Of the above metals, rhodium and platinum are
Particularly preferred are manganese, palladium and rhodium because of their high activity, and manganese, palladium and rhodium are particularly preferred because of their high activity of removing lower hydrocarbons, especially methane.

The mordenite-type zeolite used as a carrier for supporting the active component of the catalyst of the present invention has a molar ratio of SiO ₂ and Al ₂ O _{3 in} the zeolite (hereinafter referred to as “Cayvan ratio”) of 10 to 100, preferably 13 to 10. Fifty
It is in the range of. When the molar ratio is less than 10, it is not preferable because a stable mordenite crystal structure is difficult to form and heat resistance is poor, and when the molar ratio exceeds 100, the acid strength of the mordenite decreases and the catalytic activity decreases, which is not preferable. Specific examples of the mordenite type zeolite carrier include HSZ-650HOA (manufactured by Tosoh Corporation, trade name) and HSZ-640NAA (manufactured by Tosoh Corporation, trade name), and Na type mordenite and H type mordenite can be used. ..

The catalyst used in the method of the present invention is specifically prepared, for example, by preparing a solution of cobalt, manganese, rhodium, platinum or palladium nitrate, chloride, acetate, etc., and then impregnating them with an ion. It can be obtained by supporting it on the carrier by an exchange method, a kneading method, or the like, and then firing it. The catalyst thus obtained is used by being formed into a granular shape, a pellet shape, a spherical shape, a honeycomb or the like. For these moldings, for example, in the case of a honeycomb or the like, it is possible to adopt a method in which a mordenite-type zeolite is wash-coated with alumina on a cordurite substrate and then the active metal is supported.

The catalytic reaction in the method of the present invention is carried out at a reaction temperature of 200 to 900 ° C, preferably 300 to 600 ° C.

When the reaction temperature is lower than 200 ° C., sufficient activity is not exhibited, which is not preferable.

[0019]

According to the present invention, in a gas engine, a gas turbine, a gas boiler, a heating furnace, a gas stove, etc., this occurs when the ratio of raw material gas to air is set to the raw material gas lean side, and a relatively large amount occurs. Nitrogen oxides, lower hydrocarbons, especially methane and carbon monoxide, which are contained in a small amount in a gas combustion exhaust gas containing oxygen and water vapor at the same time, can be efficiently removed simultaneously by using a single catalyst. A purification / treatment method and a highly active and durable catalyst used in the method are provided.

[0020]

The present invention will be described in more detail with reference to Examples and Comparative Examples.

Example 1 As a raw material gas, for example, city gas (methane 88.5% by volume, ethane 4.6% by volume, propane 5.4% by volume and butane 1.5% by volume) was used, and the air ratio was 1. The gas combustion exhaust gas generated under the condition of the raw material gas corresponding to 7 is substantially equivalent to 82% by volume of nitrogen, 10% by volume of oxygen, 10% by volume of steam, 7% by volume of carbon dioxide,
Nitric oxide (NO) 200ppm, carbon monoxide 1000ppm
A mixed gas of 2700 ppm of methane and 2700 ppm of methane was prepared (hereinafter, may be abbreviated as “exhaust gas 1”) (all contents are dry base contents except steam).

Mordenite type zeolite (SiO ₂ / A
lO ₂ molar ratio = 15) (and sieved to the following mordenite and is sometimes abbreviated) to 20 to 42 mesh. The sized mordenite and cobalt nitrate were weighed so that metallic cobalt was 5% by weight ratio to mordenite (cobalt nitrate 4.939 g was weighed with respect to mordenite 20 g) and weighed nitric acid An aqueous solution was prepared by adding 100 ml of pure water to cobalt. Next, eggplant-shaped flask (500 ml) of rotary evaporator
The mordenite and the cobalt nitrate aqueous solution were transferred into the flask. While evacuating the inside of the flask to a reduced pressure with a vacuum pump, the flask was rotated in a hot water bath at 50 to 60 ° C. to evaporate and remove water in 120 minutes, leaving the flask as it is.
It was dried overnight in a dryer at 20 ° C, then placed in an electric furnace, heated to 500 ° C in 5 hours, calcined at 500 ° C for 3 hours, and cooled to room temperature in 3 hours to cool Co (5% by weight). ) / Mordenite catalyst (hereinafter sometimes referred to as catalyst 1) was obtained.

The exhaust gas 1 was passed through a microreactor (fixed bed flow reactor) filled with the Co (5% by weight) / mordenite catalyst, and the reaction temperature was 400 ° C. and SV was applied.
As a result of carrying out the catalytic reaction under the conditions of 40,000 h ⁻¹ and a reaction pressure of 0.4 kg / cm ² · G at the inlet of the catalyst layer, the removal rates of NOx, NO, CO and CH ₄ are as shown in Table 1, respectively. Met.

Example 2 Mn (5% by weight) / mordenite catalyst (hereinafter referred to as “catalyst 1”) obtained by the same method as that of catalyst 1 except that 4.462 g of manganese acetate was weighed instead of cobalt nitrate of catalyst 1 in Example 1. The same experiment as in Example 1 was carried out except that (Catalyst 2) was used. The results obtained are shown in Table 1.

Example 3 In place of the preparation of the catalyst 1 in Example 1, 19.5 g of mordenite whose particle size was adjusted to 20 to 42 mesh was placed in an eggplant type flask. On the other hand, 1 g of rhodium chloride was dissolved in pure water in a volumetric flask to make 100 ml of an aqueous solution, 50 ml of the rhodium chloride aqueous solution was taken with a Hall pipette, transferred to the eggplant-shaped flask, and the inside of the flask was evacuated to a reduced pressure with a vacuum pump. On the other hand, the flask was rotated in a hot water bath at 50 to 60 ° C to evaporate and remove water in 40 to 50 minutes, and the flask was dried in a dryer at 120 ° C overnight. Then, using an electric furnace, the temperature was raised to 500 ° C. in 6 hours, the firing was carried out at 500 ° C. for 3 hours, the temperature was lowered to room temperature in 3 hours, and Rh (1 wt%) / mordenite catalyst (hereinafter sometimes referred to as catalyst 3) Got The same experiment as in Example 1 was carried out except that the catalyst 3 thus obtained was used.
The results obtained are shown in Table 1.

Example 4 Catalyst 3 except that 1 g of palladium nitrate was used instead of rhodium chloride in Catalyst 3 and 18.9 g of mordenite was used.
Pd (1% by weight) / mordenite catalyst (hereinafter sometimes referred to as catalyst 4) in the same manner as in. The same experiment as in Example 1 was conducted except that the thus obtained catalyst 4 was used. The results obtained are shown in Table 1.

Example 5 Instead of 2700 ppm of methane in the exhaust gas 1 of Example 1, 13A gas (methane 88.5% by volume, ethane 4.6) was used.
A mixed gas (hereinafter, may be abbreviated as exhaust gas 2) containing 2800 ppm of C _{1 in} terms of C _{1 of a} mixed gas composed of vol.%, Propane 5.4 vol.% And butane 1.5 vol.% Was prepared. An experiment similar to that of Example 1 was performed, except that the above exhaust gas 2 was used instead of the exhaust gas 1 of Example 1.
The results obtained are shown in Table 1.

Example 6 A mixed gas containing 820 ppm of propylene instead of 2700 ppm of methane in the exhaust gas 1 of Example 1 (hereinafter sometimes referred to as exhaust gas 3) was prepared. Example 1
An experiment similar to that of Example 1 was performed, except that the exhaust gas 3 was used instead of the exhaust gas 1. The results obtained are shown in Table 1.

Example 7 An experiment similar to that of Example 5 was conducted, except that the catalyst 3 was used instead of the catalyst 1 of Example 5. The results obtained are shown in Table 1.

Example 8 A mixed gas (hereinafter sometimes abbreviated as exhaust gas 4) in which 7% by volume of carbon dioxide gas in the exhaust gas 1 of Example 1 was 4% by volume was prepared. Using the above exhaust gas 4, SV9000
An experiment similar to that of Example 1 was performed except that the condition of h ⁻¹ was used. The results obtained are shown in Table 1.

Example 9 The same experiment as in Example 8 was conducted except that the catalyst 3 was used in place of the catalyst 1 in Example 8. The results obtained are shown in Table 1.

Example 10 The same experiment as in Example 8 was conducted except that the catalyst 4 was used in place of the catalyst 1 of Example 8. The results obtained are shown in Table 1.

Examples 11 to 15 The same experiment as in Example 1 was conducted except that the catalysts shown in Table 1 were used. The results obtained are shown in Table 1.

Comparative Examples 1 to 11 The same experiment as in Example 1 was conducted except that the catalysts shown in Table 1 were used. The results obtained are shown in Table 1.

[0035]

[Table 1]

In Table 1, mordenite is SiO
A mordenite type zeolite carrier having a ₂ / AlO ₂ molar ratio of 210 is meant. In Table 1, mordenite is
A mordenite type zeolite carrier having a SiO ₂ / AlO ₂ molar ratio (Cayvan ratio) = 25) is meant. In Table 1, NOx and NO removal rates are defined by the following equations, respectively.

[0037]

[Equation 1] In Table 1, NOx specifically means the total amount of NO and NO ₂ measured by the chemiluminescence method (Chemilmi).

Claims (7)

[Claims] 1. A raw material gas is generated under the condition that the ratio of air to air is on the lean side of the raw material gas, contains nitrogen, oxygen, steam and carbon dioxide gas as main components and contains lower hydrocarbons, nitrogen oxides and Gas combustion exhaust gas containing carbon monoxide, a gas characterized by catalytically reacting in the presence of a catalyst in which a metal selected from cobalt, manganese, rhodium, platinum or palladium is supported on a mordenite type zeolite carrier. Combustion exhaust gas treatment method. 2. The treatment method according to claim 1, wherein 1.0 to 5.0 times the theoretical amount of air required for complete combustion of the raw material gas is used. 3. The processing method according to claim 1, wherein the contents of oxygen and water vapor in the gas combustion exhaust gas are in the ranges of 0.1 to 20% by volume of oxygen and 0.1 to 25% by volume of water vapor, respectively. 4. The processing method according to claim 1, wherein the lower hydrocarbon is methane or a mixture containing methane as a main component. 5. The reaction temperature of the catalytic reaction is 200 to 900.
The processing method according to claim 1, which is carried out under the condition of ° C. 6. A catalyst comprising a mordenite-type zeolite carrier carrying a metal selected from the group consisting of cobalt, manganese, rhodium, platinum and palladium, which is used in the treatment method according to any one of claims 1 to 5. 7. The mordenite-type zeolite carrier has a molar ratio of SiO ₂ and AlO _{2 in} the zeolite of 10 to 100.
The catalyst according to claim 6, which is in the range of.