JPH1066833A - Removal of nitrogen oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently nitrogen oxide by reacting nitrogen oxide with residual hydrocarbon in exhaust gas by bringing exhaust gas into contact with a catalyst prepared by mixing a first specific catalyst and a second specific catalyst at a specific spatial speed or less. SOLUTION: Exhaust gas is brought into contact with a catalyst prepared by mixing a first catalyst obtained by supporting 0.5-15wt.% of silver or a silver compd. on porous inorg. oxide in terms of a silver element and a second catalyst obtained by supporting 0.01-5wt.% of one or more kind of an element selected from a group consisting of Pt, Pd, Ru, Rh, Ir and Au on porous inorg. oxide in terms of a metal element at a spatial speed of 150,000hr<-1> or less. By this method, by the reaction of nitrogen oxide and residual hydrocarbon in exhaust gas, nitrogen oxide can be efficiently removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for effectively removing nitrogen oxides from a flue gas containing nitrogen oxides and excess oxygen.

[0002]

2. Description of the Related Art Various combustion exhaust gases discharged from gas engines, gas turbines and the like for cogeneration systems contain nitrogen oxides such as nitric oxide and nitrogen dioxide together with excess oxygen. (Commonly referred to as NOx). Here, the term “nitrogen oxide” generally refers to nitrogen monoxide and / or nitrogen dioxide, and “containing excess oxygen” means that the exhaust gas does not contain carbon monoxide, hydrogen, hydrocarbons, or the like. It means containing oxygen in excess of the theoretical amount of oxygen required to burn the combustion components.

[0003] Such nitrogen oxides are considered to be one of the causes of acid rain and are a major environmental problem. Therefore, various methods for removing nitrogen oxides in exhaust gas discharged from combustion equipment have been studied. For example, using a catalyst in which a catalytically active species is supported on an inorganic oxide, a method of removing nitrogen oxides by adding a hydrocarbon, an oxygen-containing organic compound, or the like having a theoretical reaction amount or less with oxygen in exhaust gas as a reducing agent Was proposed.

[0004] However, a removal method using a partial combustion component containing residual hydrocarbons and / or oxygen-containing organic compounds in exhaust gas as a reducing agent has not yet been established. Further, as a problem specific to gas engines and gas turbines, if the pressure loss of exhaust gas by the nitrogen oxide removing device is large, the output of the engine itself is greatly affected, and the combustion efficiency is reduced. Furthermore, the temperature of the exhaust gas is mainly low at 400 ° C., and the removal rate is not sufficient with the conventional catalyst.

[0005] Accordingly, an object of the present invention is to provide a combustion exhaust gas from a gaseous fuel combustion device, which contains unburned nitrogen oxides, carbon monoxide, hydrocarbons, etc., and oxygen containing at least a theoretical reaction amount with respect to a partial combustion component. An object of the present invention is to provide a method capable of efficiently removing nitrogen oxides from exhaust gas by using residual hydrocarbons and / or oxygen-containing organic compounds in the exhaust gas as a reducing agent.

[0006]

As a result of intensive studies in view of the above problems, the present inventor has found that liquefied petroleum gas, city gas, liquefied petroleum gas, city gas,
By contacting exhaust gas from combustion equipment using liquefied natural gas or the like under predetermined conditions, nitrogen oxides can be effectively removed using residual hydrocarbons and / or oxygen-containing organic compounds in the exhaust gas as a reducing agent. Discovered and completed the present invention.

That is, the method of the present invention for removing nitrogen oxides contained in exhaust gas discharged from a lean burn device using a gas fuel is selected from the group consisting of silver and a silver compound as a porous inorganic oxide. A first catalyst supporting one or more elements and / or compounds in an amount of 0.5 to 15% by weight (in terms of silver element), and Pt, Pd, R
One or more elements and / or compounds selected from the group consisting of u, Rh, Ir and Au are mixed with a second catalyst supporting 0.01 to 5% by weight (in terms of metal element). By contacting the exhaust gas with a catalyst at a space velocity of 150,000 hr ^-1 or less, the nitrogen oxides are reacted with residual hydrocarbons and / or oxygen-containing organic compounds in the exhaust gas to remove the nitrogen oxides. Characterized by

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the present invention, liquefied petroleum gas, city gas, or liquefied natural gas is used to contact exhaust gas from a combustion device with a nitrogen oxide removing material, and to remove residual hydrocarbons and / or oxygen-containing organic compounds in the exhaust gas. The nitrogen oxides in the exhaust gas are reacted to remove the nitrogen oxides. The combustion device is either a lean-burn gas engine or a gas turbine.

[1] Nitrogen oxide removing material The nitrogen oxide removing material of the present invention comprises a porous inorganic oxide carrying one or more elements and / or compounds selected from the group consisting of silver and silver compounds. And a second catalyst comprising a porous inorganic oxide carrying one or more elements and / or compounds selected from the group consisting of Pt, Pd, Ru, Rh, Ir and Au. Are mixed.

The above-mentioned removing material is placed in an exhaust gas conduit, the exhaust gas is brought into contact with the removing material, and the remaining hydrocarbons and / or oxygen-containing organic compounds in the exhaust gas are reacted with nitrogen oxides to form nitrogen in the exhaust gas. The oxide is reduced and removed.

The following catalyst is formed on the nitrogen oxide removing material. (1) First catalyst The first catalyst comprises a porous inorganic oxide carrying one or more elements and / or compounds selected from the group consisting of silver and silver compounds, and is formed on the inflow side of exhaust gas. Acts on nitrogen oxide removal in a wide temperature range. The silver compound is at least one selected from the group consisting of silver oxide, silver halide, silver sulfate, silver phosphate, and the like, and is preferably one or more of silver oxide, silver chloride, and silver sulfate, More preferred are silver oxide and / or silver chloride. As the porous inorganic oxide, alumina, titania, silica,
Any one of zirconia, zinc oxide, tin oxide, and magnesium oxide, or a composite or mixed oxide of two or more thereof can be used. Preferably, alumina alone or a composite or mixed oxide of alumina and any one or more of titania, silica, zirconia, zinc oxide, tin oxide, and magnesium oxide is used. When a composite or mixed oxide of alumina is used, the content of alumina is preferably set to 50% by weight or more. The use of alumina or a composite or mixed oxide of alumina improves the heat resistance and durability of the catalyst. Here, the tin oxide includes tin oxide in various oxidation states, and examples of the main tin oxide include stannous oxide and stannic oxide.

The specific surface area of the porous inorganic oxide such as alumina used for the first catalyst is preferably 10 m ² / g or more. If the specific surface area is less than 10 m ² / g, the dispersion of the silver component is reduced, and good removal of nitrogen oxides cannot be performed.
More preferable specific surface area of the porous inorganic oxide is 30 m ² /
g or more.

In the first catalyst, the amount of the silver component supported as an active species on the inorganic oxide such as γ-alumina is 0.5 to 15% by weight (100% by weight of the inorganic oxide). (Element conversion value). If the content is less than 0.5% by weight, the removal rate of nitrogen oxides decreases. Further, when the silver component is carried in an amount exceeding 15% by weight, combustion of the hydrocarbon itself is likely to occur, and the nitrogen oxide removal rate is rather lowered. The preferred loading of the silver component is 0.5 to 12% by weight.

As a method for supporting silver on an inorganic oxide such as alumina, a known impregnation method, precipitation method, ion exchange method or the like can be used. When using the impregnation method, silver nitrate,
The porous inorganic oxide is immersed in an aqueous solution of chloride, sulfate, carbonate or the like or an aqueous ammonia solution. Alternatively, the porous inorganic oxide is immersed in an aqueous solution of silver nitrate, dried, and then immersed again in an aqueous solution of ammonium chloride or ammonium sulfate. To prepare silver halide by the precipitation method, silver nitrate and ammonium halide are reacted to precipitate silver halide on the porous inorganic oxide. After drying at 50 to 150 ° C., particularly at about 70 ° C., it is preferable to raise the temperature stepwise at 100 to 650 ° C. for firing. The calcination is preferably performed in air, under a stream of nitrogen containing oxygen or under a stream of hydrogen gas.
When performing under a hydrogen gas stream, 300 to 650
The oxidation treatment is preferably carried out at a temperature of ° C. Compounds may be oxidatively decomposed by firing up to 650 ° C., but when these compounds are used as starting materials, the removal rate of nitrogen oxides is improved. The reason is still unknown.

(2) Second Catalyst The second catalyst is a porous inorganic oxide which contains P as a catalytically active species.
It carries at least one element and / or compound selected from the group consisting of t, Pd, Ru, Rh, Ir and Au. By using a second catalyst, nitrite,
Along with being able to effectively reduce nitrogen oxides in the presence of nitrogen-containing compounds such as ammonia and by-products such as aldehydes,
Generation of carbon monoxide due to oxidation of hydrocarbons or the like can be suppressed. As the porous inorganic oxide, alumina,
Any one of titania, silica, zirconia, zinc oxide, tin oxide, and magnesium oxide, or a composite or mixed oxide of two or more thereof can be used. Preferably, any one of alumina, titania and silica, or a composite or mixed oxide of two or more thereof is used. When a composite or mixed oxide of alumina is used, the content of alumina should be 50
It is preferable that the content be not less than weight%. Like the first catalyst,
The specific surface area of the porous inorganic oxide is preferably 10 m ² / g or more.

Of Pt, Pd, Ru, Rh and Au,
In particular, it is preferable to use at least one of Pt, Pd, and Au. Assuming that the porous inorganic oxide is 100% by weight, the supported amount of the platinum-based component is 0.01 to 5% by weight (in terms of a metal element). The preferred loading amount of the platinum-based component is 0.01 to
3% by weight (value in terms of metal element).

The loading of the active species can be carried out by a known impregnation method, precipitation method,
An ion exchange method or the like can be used. When using the impregnation method, the porous inorganic oxide is immersed in an aqueous solution of a carbonate, nitrate, acetate, sulfate, halide, phosphate, hexachlorometal acid, dinitrodiamine metal compound, or the like of the catalytically active species element. After drying at 50 to 150 ° C., particularly 70 ° C., the temperature is increased stepwise at 100 to 650 ° C. for firing.
This firing is performed in an atmosphere such as a hydrogen stream, air, or a nitrogen stream containing oxygen. When zirconium oxide is supported, an aqueous solution of a salt compound such as nitrate of zirconium can be used.

In the present invention, the first catalyst and the second catalyst are used as a mixture. Weight ratio of first catalyst to second catalyst (ratio of total weight of porous inorganic oxide and catalytically active species)
Is preferably 1: 100 to 100: 1. More preferably, the weight ratio of the first catalyst to the second catalyst is 1:10 to 1
0: 1.

[2] Form of Nitrogen Oxide Removing Material A first preferred embodiment of the nitrogen oxide removing material of the present invention is a removing material obtained by coating the above-mentioned mixed catalyst on a removing material substrate. As the ceramic material forming the substrate of the removing material, cordierite, mullite, alumina, a composite thereof, or the like is preferably used. Further, a known metal material can be used for the substrate of the nitrogen oxide removing material.

The shape and size of the substrate of the nitrogen oxide removing material can be variously changed depending on the purpose. Examples of the structure include a honeycomb structure type, a foam type, a three-dimensional network structure type formed of a fibrous refractory, a granular shape, a pellet shape, and the like. After coating the above-mentioned substrate with a catalyst using a wash coat method, a powder method, or the like, or coating the substrate with a porous inorganic oxide using a wash coat method, a sol-gel method, or the like, the catalyst is impregnated with a known active species. It can also be supported using a method, an ion exchange method or the like.

The second preferred form of the nitrogen oxide removing material of the present invention is that a catalytically active species is supported on a pellet, granular or powdery porous inorganic oxide and then mixed, or the mixed catalyst is mixed. It is a removal material formed into a honeycomb, foam, plate, pellet, or granule.

In the present invention, it is particularly preferable to use the above-mentioned catalyst coated on the surface of a metal honeycomb substrate. Compared to ceramic honeycombs such as cordierite, which are conventionally used, metallic honeycombs can have thinner partitions, so they can increase the aperture ratio without reducing the contact area and lower the pressure loss of the nitrogen oxide removal device. Can be done. In addition, they are characterized by high mechanical strength against vibration and impact and long life. Further, there is an unexpected feature that the catalytic activity of the metal honeycomb is reduced less than the cordierite due to long-term use. It is considered that the reason for this is that the amount of oil ash deposited and the deposition rate were reduced by making the partition walls thinner.

As a method for coating a metal honeycomb with a catalyst, there is a method in which a powdery mixed catalyst is coated on the surface of a metal honeycomb substrate by a known method (for example, a wash coat method). The number of cells of the metal honeycomb is preferably 100 to 400 cells / square inch. If the number of cells of the metal honeycomb is less than 100 cells / square inch, the contact area is not sufficient, and the nitrogen oxide removal rate is not sufficient. On the other hand, when the number of cells exceeds 400 cells / square inch, the pressure loss of the removing device increases, and the combustion of the gas engine and the gas turbine is affected.

When the form of the removing material is the first preferred embodiment described above, the thickness of the catalyst provided on the removing material base is generally limited by the difference in thermal expansion characteristics between the base material and the catalyst. In many cases. It is preferable that the thickness of the catalyst provided on the removing material substrate is 300 μm or less. With such a thickness, it is possible to prevent the removal material from being damaged by a thermal shock or the like during use. The method for forming the catalyst on the surface of the removing material substrate is performed by a known wash coating method or the like.

The amount of the catalyst provided on the surface of the removing material substrate is preferably 20 to 300 g / liter of the removing material substrate. If the amount of the catalyst is less than 20 g / liter, good NOx removal cannot be performed. On the other hand, when the amount of the catalyst is 300 g /
If it exceeds 1 liter, the removal characteristics are not so improved, and the pressure loss increases. More preferably, the amount of the catalyst provided on the surface of the removing material substrate is 50 to 200 g / liter of the removing material substrate.

If the above-described removing material is used, 200
In a wide temperature range of up to 400 ° C., good removal of nitrogen oxides can be performed even with exhaust gas containing about 10% of water.

[3] Nitrogen oxide removal method In the present invention, the space velocity between the exhaust gas and the catalyst is 150,000 h in order to efficiently promote the reduction and removal of nitrogen oxides by residual hydrocarbons and / or oxygen-containing organic compounds. ^-1 or less, preferably 100,000 h ^-1 or less. Space velocity 150,000h
^If it exceeds ^-1 , the reduction reaction of nitrogen oxide does not sufficiently occur, and the nitrogen oxide removal rate decreases. Here, the oxygen-containing organic compound means a mixture of oxygen-containing organic compounds generated by partially burning gaseous fuel in a combustion device.

Further, in the present invention, the temperature of the exhaust gas at the removing material installation site is maintained at 200 to 450 ° C. When the temperature of the exhaust gas is lower than 200 ° C., the reaction between the reducing agent and the nitrogen oxide does not proceed, and good nitrogen oxide cannot be removed. The preferred exhaust gas temperature is from 250 to 450C, more preferably from 300 to 400C.

[0029]

The present invention will be described in more detail with reference to the following specific examples. Example 1 A commercially available γ-alumina powder (specific surface area: 200 m ² / g) was loaded with 3% by weight (in terms of silver element) of silver using an aqueous silver nitrate solution, dried at 80 ° C. for 3 hours, and dried in air for 100 hours. ℃ -6
The temperature was raised stepwise to 50 ° C. and calcined at 650 ° C. for 3 hours to prepare a silver-based catalyst (first catalyst).

Commercially available γ-alumina powder (specific surface area 200
m ² / g) using an aqueous solution of dinitrodiamineplatinum (II), dried at about 70 ° C., gradually heated to 650 ° C., calcined at 650 ° C. for 3 hours, and added 1 wt. % Of platinum (in terms of metal element), to prepare a platinum-based catalyst (second catalyst).

1.25 g of the first catalyst and 1.25 g of the second catalyst are mixed, an alumina binder is added and kneaded. After drying, the mixture is fired stepwise to 600 ° C.
The mixture was sized to 0 mm to prepare a nitrogen oxide removing material.

The above-mentioned nitrogen oxide removing material was filled in a reaction tube and set. Next, nitrogen oxides in the exhaust gas from the gas engine were removed. The gas engine is a 15 KW lean burn gas engine, and the space velocity of the exhaust gas with respect to the purifying material is 31,000 h ^-1 (however, the exhaust gas is branched and adjusted by pumping at the purifying material outlet side). Nitrogen oxide concentration at the purifying material inlet is 420-640p
pm (in terms of oxygen concentration of 0%), of which the content of nitrogen dioxide is 59% by volume. The operation of the engine was performed at a rated value, and the exhaust gas temperature at the inlet of the purifying material was 250 to 45.
It was 0 ° C. The nitrogen oxide concentration was calculated by the following equation: Nitrogen oxide equivalent concentration = Cs × (21−On) / (21−)
Os) where Cs is the concentration of nitrogen oxides in the exhaust gas.
n is the reduced oxygen concentration (here, 0%), and Os is the oxygen concentration in the exhaust gas.

The concentration of nitrogen oxides in the gas after passing through the removing device was measured by a chemiluminescent nitrogen oxide analyzer to determine the nitrogen oxide removal rate. The results are shown in FIG.

Example 2 A commercially available silica powder (specific surface area: 38
0 m ² / g) using an aqueous solution of dinitrodiamineplatinum (II), dried at about 70 ° C., gradually heated to 650 ° C., calcined at 650 ° C. for 3 hours, and 1% by weight of silica powder. Was carried to prepare a platinum-based catalyst (second catalyst).

1.5 g of the first catalyst of Example 1 and 1 g of the above second catalyst were mixed, an alumina binder was added and kneaded, dried and calcined stepwise to 600 ° C.
The grains were sized to 1.0 mm to prepare a nitrogen oxide removing material.

The nitrogen oxide removing material was filled and set in a reaction tube, and nitrogen oxide in the exhaust gas from the gas engine was removed in the same manner as in Example 1. The space velocity of the exhaust gas with respect to the purification material is 31,000 h ^-1 (however,
The exhaust gas was branched off and adjusted by pumping at the outlet of the purifying material. The concentration of nitrogen oxides in the gas after passing through the removing device was measured with a chemiluminescent nitrogen oxide analyzer to determine the nitrogen oxide removal rate. The results are shown in FIG.

COMPARATIVE EXAMPLE 1 Alumina binder was added to 2.5 g of the first catalyst of Example 1 and kneaded.
The mixture was sized to 0.5 to 1.0 mm to prepare a nitrogen oxide removing material.

The above-mentioned nitrogen oxide removing material was filled and set in a reaction tube, and nitrogen oxide in the exhaust gas from the gas engine was removed in the same manner as in Example 1. The space velocity of the exhaust gas with respect to the purification material is 31,000 h ^-1 (however,
The exhaust gas was branched off and adjusted by pumping at the outlet of the purifying material. The concentration of nitrogen oxides in the gas after passing through the removing device was measured with a chemiluminescent nitrogen oxide analyzer to determine the nitrogen oxide removal rate. The results are shown in FIG.

Comparative Example 2 An alumina binder was added to 2.5 g of the second catalyst of Example 1 and kneaded. After drying, the mixture was fired stepwise to 600 ° C.
The mixture was sized to 0.5 to 1.0 mm to prepare a nitrogen oxide removing material.

The nitrogen oxide removing material was filled and set in a reaction tube, and nitrogen oxide in the exhaust gas from the gas engine was removed in the same manner as in Example 1. The space velocity of the exhaust gas with respect to the purification material is 31,000 h ^-1 (however,
The exhaust gas was branched off and adjusted by pumping at the outlet of the purifying material. The concentration of nitrogen oxides in the gas after passing through the removing device was measured with a chemiluminescent nitrogen oxide analyzer to determine the nitrogen oxide removal rate. The results are shown in FIG.

As can be seen from FIG. 1, in Examples 1 and 2, effective removal of nitrogen oxides was observed over the entire temperature range. On the other hand, in Comparative Example 1, the removal rate of nitrogen oxides on the high temperature side was extremely small. In Comparative Example 2, the nitrogen oxide removal rate on the low temperature side decreased.

[0042]

As described above in detail, according to the method of the present invention, nitrogen oxides in exhaust gas can be efficiently removed in an exhaust gas temperature range of 400 ° C. or less. The nitrogen oxide removing method of the present invention can be widely used for removing nitrogen oxides contained in exhaust gas of gas engines, gas turbines, lean-burn gas engines, and the like.

[Brief description of the drawings]

FIG. 1 is a graph showing a change in a nitrogen oxide removal rate with respect to an exhaust gas temperature in Examples 1 and 2 and Comparative Examples 1 and 2.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication B01D 53/36 102A (72) Inventor Naoko Aoyama 4-1-1, Suehiro, Kumagaya-shi, Saitama (72) Inventor Hideyasu Yokota 4-7-7 Kaminagaya, Konan-ku, Yokohama, Kanagawa Prefecture (72) Inventor Masahiro Yahagi 1-28-306 Nishisugamo, Toshima-ku, Tokyo (72) Inventor Shigeo Satokawa 2-17-10-103 Higashiyukiya, Ota-ku, Tokyo (72) Inventor Kenichi Yamaseki 1-6-3 Mure, Mitaka-shi, Tokyo

Claims (4)

[Claims] 1. A method for removing nitrogen oxides contained in exhaust gas discharged from a lean burn device using a gaseous fuel, wherein the porous inorganic oxide comprises at least one member selected from the group consisting of silver and silver compounds. Element and / or compound 0.5
-15% by weight (in terms of silver element) and a porous inorganic oxide containing Pt, Pd, Ru, Rh,
One or more elements and / or compounds selected from the group consisting of Ir and Au 0.01 to 5% by weight (in terms of metal element)
By contacting the exhaust gas with a catalyst obtained by mixing a second catalyst carrying the above at a space velocity of 150,000 hr ^-1 or less, the nitrogen oxides and residual hydrocarbons in the exhaust gas and / or A nitrogen oxide removing method, comprising reacting an oxygen-containing organic compound to remove the nitrogen oxide. 2. The method according to claim 1, wherein said gaseous fuel is one of liquefied petroleum gas, city gas, and liquefied natural gas. 3. The method according to claim 1, wherein
The method according to claim 1, wherein the combustion equipment is either a gas engine or a gas turbine. 4. The method of claim 3, wherein the gas engine is a lean burn gas engine.