JPH0975739A - Waste gas purification material and method for purifying waste gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently reduce and remove NOx from waste combustion gas contg. NOx and a larger amt. of oxygen than the amt. of oxygen reacting theoretically with unburnt components such as CO, hydrogen and hydrocarbons. SOLUTION: This waste gas purification material is made of a catalyst obtd. by carrying 0.2-15wt.% (expressed in terms of silver) silver and/or one or more kinds of silver compds. and <=1wt.% (expressed in terms of iron) iron compd. on a porous inorg. oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purifying material capable of effectively reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and excess oxygen, and a purification method using the same.

[0002]

2. Description of the Related Art Excessive combustion exhaust gas emitted from internal combustion engines such as automobile engines, combustion equipment installed in factories, household fan heaters, and the like is excessive. It contains nitrogen oxides such as nitric oxide and nitrogen dioxide together with oxygen. Here, "containing excess oxygen" means that the exhaust gas contains more oxygen than the theoretical amount of oxygen necessary to burn unburned components such as carbon monoxide, hydrogen, and hydrocarbons. I do. In the following, nitrogen oxide refers to nitric oxide and / or nitrogen dioxide.

[0003] This nitrogen oxide is one of the causes of acid rain and is a major environmental problem. Therefore, various methods for removing nitrogen oxides in exhaust gas discharged from various combustion equipments are being studied.

[0004] As a method for removing nitrogen oxides from a combustion exhaust gas containing excess oxygen, a selective catalytic reduction method using ammonia is used particularly for a large-scale fixed combustion device (a large-scale combustor in a factory or the like). Has been put to practical use.

However, in this method, ammonia used as a reducing agent for nitrogen oxides is expensive, and ammonia is toxic. Therefore, the nitrogen oxides in the exhaust gas must be removed so that unreacted ammonia is not discharged. There are problems that the amount of injected ammonia must be controlled while measuring the concentration, and that the apparatus generally becomes large.

Therefore, many methods have been proposed for removing nitrogen oxides by using a catalyst in which a transition metal is supported on zeolite or alumina and adding a reducing agent having a theoretical reaction amount or less with oxygen in exhaust gas. However, in these methods, the nitrogen oxide removal rate is not sufficient, and in the case of exhaust gas from a vehicle or the like which contains moisture and sulfur oxides and the exhaust gas temperature greatly changes depending on operating conditions, the nitrogen oxide removal rate is remarkably large. descend.

Accordingly, it is an object of the present invention to provide a method for producing nitrogen oxides, carbon monoxide, hydrogen, hydrocarbons, and the like, such as combustion exhaust gas from a fixed combustion device and a gasoline engine, a diesel engine, or the like, which burns under oxygen excess conditions. An object of the present invention is to provide an exhaust gas purifying material and an exhaust gas purifying method which can efficiently reduce and remove nitrogen oxides from a combustion exhaust gas containing oxygen at a theoretical reaction amount or more with respect to an unburned portion and containing water.

[0008]

Means for Solving the Problems In view of the above problems, as a result of intensive studies, the present inventor has used an exhaust gas purifying material comprising a catalyst supporting a silver component and an iron component, and contained hydrocarbons and carbon atoms of 2 in the exhaust gas. By adding any one of the above oxygenated organic compounds or a fuel containing them, and contacting the exhaust gas with the above-mentioned purifying material, it has been found that nitrogen oxides can be effectively removed in a wide temperature range, and the present invention completed.

That is, the exhaust gas purifying material of the present invention for reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen which is larger than the theoretical reaction amount of coexisting unburned components is used as a porous inorganic oxide. One or more elements and / or compounds 0.2 to 1 selected from the group consisting of silver and silver compounds
It is characterized by comprising a catalyst supporting 5% by weight (converted to metal element) and 1% by weight or less of iron compound (converted to metal element).

[0010] A method of purifying exhaust gas of the present invention for reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen in excess of the theoretical reaction amount of coexisting unburned components uses the above exhaust gas purifying material. The exhaust gas purifying material is installed in the middle of an exhaust gas conduit, and the exhaust gas to which hydrocarbons and / or oxygen-containing organic compounds are added upstream of the purifying material is
The method is characterized in that the nitrogen oxide is removed by contacting the purification material at 50 to 650 ° C. with a hydrocarbon and / or an oxygen-containing organic compound in the exhaust gas.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. [1] Exhaust gas purifying material The exhaust gas purifying material of the present invention carries one or more elements and / or compounds selected from the group consisting of silver and silver compounds as a catalytically active species on a porous inorganic oxide and an iron compound. And acts to remove nitrogen oxides over a wide temperature range. As the porous inorganic oxide, alumina alone, or titania, silica, zirconia, zinc oxide, tin oxide,
It is preferable to use a composite or mixed oxide of alumina and at least one of magnesium oxide and zeolite.
As zeolite, ferrierite, mortenite, Z
Various zeolites such as SM-5 can be used.
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 a porous inorganic oxide such as alumina is preferably 10 m ² / g or more. When the specific surface area is less than 10 m ² / g, the dispersion of the catalytically active species is reduced, and good removal of nitrogen oxides cannot be performed. More preferred specific surface area of the porous inorganic oxide is 30 m ² / g or more.

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 preferably at least one of silver oxide, silver chloride and silver sulfate. And more preferably silver oxide and / or silver chloride. The supported amount of the silver component is 0.2 to 15% by weight (in terms of silver element) based on 100% by weight of the porous inorganic oxide. If the amount is less than 0.2% by weight, the removal rate of nitrogen oxides decreases. If the silver component is carried in an amount exceeding 15% by weight, the combustion of the hydrocarbon and / or the oxygen-containing organic compound itself tends to occur, and the nitrogen oxide removal rate is rather lowered. A preferable loading amount of the silver component is 0.5 to 12% by weight.
It is.

The iron compound is at least one selected from the group consisting of iron oxide, iron halide, iron sulfate, iron phosphate and the like, and is preferably iron oxide. The carrying amount of the iron component is 1% by weight or less (in terms of iron element) with respect to 100% by weight of the porous inorganic oxide. 1% by weight of iron component supported
Is exceeded, the removal characteristics of nitrogen oxides deteriorate. The preferable loading amount of the iron component is 0.001 to 0.8% by weight.

As a method for supporting a silver component and an iron component on an inorganic oxide such as alumina, a known impregnation method, precipitation method, or the like can be used. When using the impregnation method, a porous inorganic oxide is immersed in an aqueous solution of silver, iron nitrate, chloride, sulfate, carbonate or the like. When a halide or a sulfate is supported, the porous inorganic oxide is immersed in an aqueous nitrate solution, dried, and then immersed again in an aqueous solution of ammonium chloride or ammonium sulfate. To prepare a halide by a precipitation method, a nitrate is reacted with an ammonium halide to precipitate on the porous inorganic oxide as a halide. After drying this at 50 to 150 ° C, especially about 70 ° C,
It is preferable that the temperature is raised stepwise at 00 ° C. and firing is performed. The calcination is preferably performed in air, under a stream of nitrogen containing oxygen or under a stream of hydrogen gas. When calcination is performed under a nitrogen gas stream or a hydrogen gas stream, it is preferable to perform an oxidation treatment at 300 to 650 ° C. at last. In carrying silver on alumina, an alumina-based mixed or composite oxide, it is effective to use alumina hydrate such as boehmite as a starting material. Note that 65
Some silver and iron compounds are partially oxidatively decomposed during the firing process up to 0 ° C. However, for unknown reasons, high nitrogen oxide removal properties are obtained by using these compounds as starting materials.

[2] Form of Exhaust Gas Purifying Material A first preferred embodiment of the exhaust gas purifying material of the present invention is a purifying material obtained by coating the above-mentioned catalyst on a purifying material base. As the ceramic material forming the base of the purifying material, cordierite, mullite, alumina and a composite thereof are preferably used. In addition, a known metal material can be used for the base of the exhaust gas purifying material.

The shape and size of the substrate of the exhaust gas purifying material are as follows:
Various changes can be made according to the purpose. Also, as its structure,
Examples include a honeycomb structure type, a foam type, a three-dimensional network structure type made of a fibrous refractory, a granular form, a pellet form, and the like. The catalyst may be coated on the substrate using a wash coat method, a powder method, or the like, or a wash coat method, a sol
After the porous inorganic oxide is coated on the substrate using a gel method or the like, the catalytically active species can be supported using a known impregnation method, an ion exchange method, or the like.

The second preferred form of the exhaust gas purifying material of the present invention is a catalyst comprising a porous inorganic oxide in the form of pellets, granules, powders, honeycombs or plates carrying a catalytically active species, or a catalyst. Is formed into a honeycomb, foam, plate, pellet, or granule.

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

Further, the amount of the catalyst provided on the surface of the purifying material base is preferably 20 to 300 g / liter of the purifying material base. 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 purifying material base is 50 to 200 g / liter of the purifying material base.

If the purifying material having the above structure is used, 100
In a wide temperature range of up to 500 ° C., good removal of nitrogen oxides can be performed even with exhaust gas containing about 10% of moisture and sulfur oxides.

[3] Exhaust gas purification method Next, the method of the present invention will be described. First, the exhaust gas purifying material of the present invention is installed in the middle of an exhaust gas conduit.

The exhaust gas contains ethylene, propylene, etc. to a certain extent as residual hydrocarbons. However, since the amount is generally not sufficient to reduce NOx in the exhaust gas, hydrocarbons and / or oxygen-containing organic compounds are supplied from outside. Preferably, an oxygen-containing organic compound or a reducing agent obtained by mixing the compound with a hydrocarbon fuel is introduced into the exhaust gas. The position where the reducing agent is introduced is upstream of the position where the purifying material is installed.

As the hydrocarbon introduced from the outside, gaseous or liquid alkanes, alkenes and / or alkynes can be used under standard conditions. In particular, alkanes preferably have 2 or more carbon atoms. Specific examples of the hydrocarbon in a liquid state in a standard state include hydrocarbons such as light oil, cetane, heptane, kerosene, and gasoline. Among them, boiling point 5
Hydrocarbons at 0-350 ° C are particularly preferred. As the oxygen-containing organic compound introduced from the outside, alcohols such as ethanol and isopropyl alcohol having 2 or more carbon atoms, or a fuel containing them can be used.

The amount of the hydrocarbon and / or oxygen-containing organic compound introduced from the outside is determined by the weight ratio (weight of the reducing agent added / weight of the reducing agent /
(Weight of nitrogen oxides in the exhaust gas) is preferably 0.1 to 5. If the weight ratio is less than 0.1, the removal rate of nitrogen oxides does not increase. On the other hand, if it exceeds 5, fuel efficiency will be degraded.

When a fuel containing a hydrocarbon or an oxygen-containing organic compound is added, it is preferable to use gasoline, light oil, kerosene or the like as the fuel. In this case, the amount of the reducing agent is set such that the weight ratio (the weight of the reducing agent to be added / the weight of the nitrogen oxide in the exhaust gas) is 0.1 to 5 in the same manner as described above.

In the present invention, the space velocity is 500,000 h ^-1 or less, preferably 300,0 h or less, in order to efficiently promote the reduction and removal of nitrogen oxides by oxygen-containing organic compounds and hydrocarbons.
00h ^-1 or less.

Further, in the present invention, the temperature of the exhaust gas at the purification material installation site where the hydrocarbon and / or the oxygen-containing organic compound reacts with the nitrogen oxide is set at 150 to 650 ° C.
To keep. If the temperature of the exhaust gas is lower than 150 ° C., the reaction between the reducing agent and the nitrogen oxide does not proceed, and it is not possible to remove the nitrogen oxide satisfactorily. On the other hand, if the temperature exceeds 650 ° C., combustion of the hydrocarbon and / or the oxygen-containing organic compound itself starts, and reduction and removal of nitrogen oxides cannot be performed. The preferred exhaust gas temperature is from 200 to 600 ° C, more preferably from 250 to 550 ° C.

[0029]

The present invention will be described in more detail with reference to the following specific examples. Example 1 Commercially available powdered silica-alumina (SiO ₂ content: 5% by weight, average particle size 0.05 mm, specific surface area 350 m ² /
g) was immersed in an aqueous solution of silver nitrate, and an aqueous solution of ammonium chloride was added to precipitate silver chloride on silica-alumina.
After drying at 0 ° C., the temperature was increased stepwise from 100 ° C. to 600 ° C. in the air, and finally calcined at 600 ° C. for 3 hours. And 4% by weight of silver chloride based on silica-alumina powder
A catalyst supporting (silver element conversion value) and 0.01% by weight of iron (iron element conversion value) was obtained.

After slurrying 0.52 g of this catalyst,
A commercially available cordierite honeycomb molded body (400 cells /
Inch ² , diameter 20 mm, length 16.6 mm) by a wash coat method. This was dried in air at 80 ° C. for 3 hours, heated stepwise from 100 ° C. to 600 ° C., and finally baked at 600 ° C. for 3 hours to produce a silver- and iron-based exhaust gas purifying material.

The exhaust gas purifying material was set in a reaction tube. Next, gases having the composition shown in Table 1 (nitrogen monoxide, oxygen,
Ethanol, sulfur dioxide, nitrogen and water) at 3.4
At a flow rate of 8 liters (standard state) (the apparent space velocity of the purifying material is about 40,000 h ^-1 ), the temperature of the exhaust gas in the reaction tube is kept in the range of 300 to 550 ° C., and ethanol and nitrogen oxides are removed. Was reacted.

The concentration of nitrogen oxides in the gas after passing through the reaction tube was measured with a chemiluminescent nitrogen oxide analyzer to determine the nitrogen oxide removal rate. Table 2 shows the results.

Table 1 Concentrations of components (dry basis) Nitric oxide 800 ppm Oxygen 10% by volume Ethanol 1560 ppm (3 times the mass of nitric oxide) Sulfur dioxide 30 ppm Nitrogen Residual moisture 10% by volume (to the total volume of the above components) for)

Example 2 A commercially available powdery γ-alumina (average particle size: 0.05 mm, specific surface area: 200 m ² / g) was treated in the same manner as in Example 1 with 4% by weight of silver chloride (in terms of silver element) and 0% of iron. Example 1 containing 0.52 g of a silver and iron-based catalyst carrying 0.055% by weight (converted to iron element).
A slurry was prepared in the same manner as described above, and a commercially available cordierite honeycomb-shaped formed body (diameter 20 mm, length 16.6 mm, 400
Cells / inch < ² >), dried and baked stepwise to 600 [deg.] C. to prepare a silver / iron-based exhaust gas purifying material.

An exhaust gas purifying material was set in the reaction tube. Evaluation was performed using the gas having the composition shown in Table 1 under the same reaction conditions as in Example 1 (the apparent space velocity of the purification material was about 40,000 h ^-1 ). Table 2 shows the results.

Example 3 Example 1 was performed using an aqueous solution of silver nitrate and an aqueous solution of ferric nitrate.
Powdered silica-alumina (SiO ₂
Content: 5% by weight, average particle size 0.05 mm, specific surface area 3
Catalyst 0.5 supporting 4% by weight of silver (converted to elemental silver) and 0.05% by weight of iron (converted to elemental iron) on 50 m ² / g)
After slurrying 2 g, a commercially available honeycomb shaped body made of cordierite (diameter 20 mm, length 16.6 mm, 40
0 cells / inch ² ), dried and baked stepwise to 600 ° C. to prepare an exhaust gas purifying material.

An exhaust gas purifying material was set in the reaction tube. Evaluation was performed using the gas having the composition shown in Table 1 under the same reaction conditions as in Example 1 (the apparent space velocity of the purification material was about 40,000 h ^-1 ). Table 2 shows the results.

Comparative Example 1 γ-alumina powder (average particle size: 0.05 mm, specific surface area: 200 m ^{2) was} prepared in the same manner as in Example 1 using an aqueous silver nitrate solution.
/ G) carrying 4% by weight of silver (in terms of silver element) to prepare a silver-based catalyst. 0.52 g of this catalyst was used as a commercially available cordierite honeycomb-shaped formed body (diameter 20 mm, length 16.6).
mm, 400 cells / inch ² ) was coated in the same manner as in Example 1, dried, and fired stepwise to 600 ° C. to prepare an exhaust gas purifying material.

An exhaust gas purifying material was set in the reaction tube. Evaluation was performed using the gas having the composition shown in Table 1 under the same reaction conditions as in Example 1 (the apparent space velocity of the purification material was about 40,000 h ^-1 ). Table 2 shows the results.

Table 2 Nitrogen oxide removal rate (%) temperature Example 1 Example 2 Example 3 Comparative Example 1 300 ° C. 68.7 65.3 65.3 25.2 350 ° C. 70.3 75.6 76 .2 41.8 400 ° C. 85.6 86.3 87.8 52.6 450 ° C. 79.4 83.7 84.3 60.2 500 ° C. 65.6 70.5 70.2 50.5 550 ° C. 54 .8 57.3 52.3 35.8

Example 4 The exhaust gas purifying material of Example 1 was set in a reaction tube. Next, a gas having the composition shown in Table 3 (nitrogen monoxide, oxygen, propylene, nitrogen and moisture) was flowed at a flow rate of 3.48 liters per minute (standard state) (the apparent space velocity of the purification material was about 4
0,000h ^-1), the exhaust gas temperature in the reaction tube 30
While maintaining the temperature in the range of 0 to 500 ° C., propylene was reacted with nitrogen oxide.

The concentration of nitrogen oxides in the gas after passing through the reaction tube was measured by a chemiluminescent nitrogen oxide analyzer to determine the nitrogen oxide removal rate. Table 4 shows the results.

Table 3 Component Concentrations Nitric Oxide 800 ppm (dry basis) Oxygen 10% by volume (dry basis) Propylene 1714 ppm (dry basis) Nitrogen Balance (balance) Moisture 10% by volume ( based on the total volume of the above components)

Example 5 The exhaust gas purifying material of Example 2 was set in a reaction tube. The same reaction conditions as in Example 4 (the apparent space velocity of the purifying material was about 4
(Equivalent to 3,000 h ⁻¹ )), and was evaluated using a gas having a composition shown in Table 3. Table 4 shows the results.

Example 6 Commercially available powdery γ-alumina (average particle size: 0.05 mm, specific surface area: 200 m ² / g) and stannic oxide powder (average particle size: 0.1 mm or less, specific surface area: 71 m ² / g) And 95: 5
In the same manner as in Example 1, 4% by weight of silver chloride (in terms of silver element) and 0.05% by weight of iron (in terms of iron element) are supported on the powder mixed at a weight ratio of 1%. 52 g was slurried in the same manner as in Example 1, and a commercially available cordierite honeycomb-shaped formed body (diameter 20 mm, length 16.6 mm, 40
0 cells / inch ² ), dried and baked stepwise to 600 ° C. to prepare a silver- and iron-based exhaust gas purifying material.

An exhaust gas purifying material was set in the reaction tube. Evaluation was performed using the gas having the composition shown in Table 3 under the same reaction conditions as in Example 1 (the apparent space velocity of the purifying material was about 40,000 h ^-1 ). Table 4 shows the results.

Comparative Example 2 The exhaust gas purifying material of Comparative Example 1 was set in a reaction tube. The same reaction conditions as in Example 4 (the apparent space velocity of the purifying material was about 4
(Equivalent to 3,000 h ⁻¹ )), and was evaluated using a gas having a composition shown in Table 3. Table 4 shows the results.

Table 4 Nitrogen oxide removal rate (%) temperature Example 4 Example 5 Example 6 Comparative Example 2 300 ° C. 19.5 24.3 25.1 15.6 350 ° C. 26.7 30.4 31 .4 22.5 400 ° C. 64.7 67.4 65.4 59.6 450 ° C. 60.4 64.7 64.0 54.5 500 ° C. 35.9 40.4 38.2 24.6

As can be seen from Tables 2 and 4, as compared with Comparative Examples 1 and 2 using a purifying material composed of a silver-based catalyst, Examples 1 to 6 using the silver and iron purifying materials of the present invention were wider. Good removal of nitrogen oxides was observed in the exhaust gas temperature range.

[0050]

As described above in detail, the use of the exhaust gas purifying material of the present invention makes it possible to efficiently remove nitrogen oxides in exhaust gas containing excess oxygen in a wide temperature range. INDUSTRIAL APPLICABILITY The exhaust gas purifying material and the purification method of the present invention can be widely used for purifying exhaust gas of various types of combustors, automobiles and the like.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B01J 27/10 B01D 53/36 ZAB 27/18 102B 102H

Claims (6)

[Claims] 1. An exhaust gas purifying material for reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen in an amount larger than a theoretical reaction amount for coexisting unburned components, wherein silver and silver are used as porous inorganic oxides. 0.2 to 15% by weight of one or more elements selected from the group consisting of compounds and / or compounds
An exhaust gas purifying material comprising a catalyst supporting (a metal element conversion value) and 1% by weight or less of an iron compound (a metal element conversion value). 2. The exhaust gas purifying material according to claim 1, wherein the silver compound is at least one selected from the group consisting of an oxide of silver, silver halide, silver sulfate and silver phosphate, and the iron compound is An exhaust gas purifying material, which is at least one selected from the group consisting of iron oxide, iron halide, iron sulfate and iron phosphate. 3. The exhaust gas purifying material according to claim 1, wherein the porous inorganic oxide is composed of alumina alone or a mixture of alumina and any one or more of titania, silica, zirconia, ZnO, MgO, and tin oxide. An exhaust gas purifying material characterized by being a composite or mixed oxide. 4. The exhaust gas purifying material according to claim 1, wherein the catalyst is coated on a surface of a ceramic or metal substrate. 5. The exhaust gas purifying material according to claim 1, wherein the catalyst is formed into a pellet, a granule, a honeycomb, a foam, or a plate. 6. An exhaust gas purifying material according to claim 1, wherein nitrogen oxide is reduced from a combustion exhaust gas containing nitrogen oxide and oxygen in an amount larger than a theoretical reaction amount for a coexisting unburned component. In the exhaust gas purifying method for removing, the exhaust gas purifying material is provided in the middle of an exhaust gas conduit, and the exhaust gas to which a hydrocarbon and / or an oxygen-containing organic compound is added at an upstream side of the purifying material is subjected to the purifying material at 150 to 650 ° C. Exhaust gas purifying method, wherein the nitrogen oxides are removed by contact with a hydrocarbon and / or an oxygen-containing organic compound in the exhaust gas.