JPH07323227A - Catalyst for reduction removing nitrogen oxides in waste combustion gas - Google Patents

Abstract

PURPOSE:To provide a denitration catalyst without lowering the catalytic activity over a long period of time and capable of reductive-removing nitrogen oxides from a low temp. waste combustion gas in the presence of ammonia. CONSTITUTION:This catalyst for reductive-removing nitrogen oxides in the waste combustion gas is obtained by depositing a vanadium compound, a bromine compound and at least one kind of a compound of a metal selected among iron, cobalt and rare earth metal, if necessary, further platinum group metal on a carbonaceous material. As the carbonaceous material, an activated carbon based carbonaceous material having >=10m<2>/g specific surface area is preferably used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for reducing and removing nitrogen oxides from combustion exhaust gas, and more specifically to a combustion device capable of reducing and removing nitrogen oxides from exhaust gas at a relatively low temperature after wet desulfurization in the presence of ammonia. The present invention relates to a catalyst for reducing nitrogen oxides in exhaust gas.

[0002]

2. Description of the Related Art In recent years, environmental pollution has become a problem on a global scale, and various measures for preventing pollution have been proposed.
Emission standards for wastewater and exhaust gas have also been reviewed and studied. Combustion exhaust gas, which is a source of air pollution, will be more strictly regulated. In view of these circumstances, the inventors previously proposed a denitration catalyst for exhaust gas in which a carbonaceous material carries a vanadium compound and a bromine compound in Japanese Patent Application No. 5-124007. This catalyst can reduce nitrogen oxides in exhaust gas at a low space and a high space velocity (SV), and further, without the byproduct of nitrous oxide which is said to significantly promote global warming, It is excellent as a reduction denitration catalyst for exhaust gas.

[0003]

However, as a result of further investigations by the inventors regarding the use of the above-mentioned catalyst, etc., when nitrogen oxide is reduced using this catalyst,
It was found that the catalytic activity gradually decreased with the lapse of operation time, and the denitration rate gradually decreased compared to the initial operation. The present invention, based on the above findings, does not decrease the catalytic activity even in a long-term exhaust gas denitration treatment,
An object of the present invention is to provide a catalyst capable of reducing and removing nitrogen oxides from low-temperature exhaust gas containing nitrogen oxides, for example, exhaust gas after wet flue gas desulfurization in the presence of ammonia with a stable denitration rate for a long time. In order to achieve the above object, the inventors have further studied supported metals and the like based on the knowledge obtained in the development of the proposed denitration catalyst, and have completed the present invention.

[0004]

According to the present invention, a vanadium compound, a bromine compound, and iron are added to a carbonaceous material.
Provided is a catalyst for reducing and removing nitrogen oxides from combustion exhaust gas, which comprises a compound of at least one metal selected from cobalt and rare earth metals. Further, the present invention provides a nitrogen oxide reduction removal catalyst for combustion exhaust gas, which is obtained by further supporting a platinum group metal on the nitrogen oxide reduction removal catalyst for combustion exhaust gas carrying at least three components.

[0005]

The present invention is constituted as described above, and carries at least three components of a vanadium compound and a bromine compound and a compound of at least one metal selected from iron, cobalt and a rare earth metal on a carbonaceous material. As a result, compared with the conventionally proposed reduction denitration catalyst, it is possible to suppress a decrease in catalytic activity at low temperatures, and to maintain stable reduction denitration performance for a long period of time without nitrous oxide byproduct. Further, the activity can be improved by further supporting a platinum group metal as a catalyst component. The method for treating combustion exhaust gas of the present invention is
By using the above catalyst, low temperature exhaust gas of about 100 ° C. or lower after wet desulfurization of combustion exhaust gas is treated at a high space velocity in the presence of ammonia to stably produce nitrogen oxides at a high denitration rate for a long period of time. It can be reduced and removed.

The present invention will be described in more detail below. Examples of the carbonaceous material that is the catalyst carrier used in the present invention include charcoal, coconut shell and other wood-based activated carbon, coal tar pitch and other coal-based activated carbon, petroleum pitch and other petroleum-based activated carbon, activated carbon, activated coke and activated carbon fiber. As long as the carbonaceous material has a specific surface area of 10 m ² / g or more, any of them can be appropriately selected and used according to various usage conditions. Preferably,
An activated carbon-based carbonaceous material having a specific surface area of 100 to 2000 m ² / g, and more preferably 500 to 1500 m ² / g can be used. Specific surface area of carbonaceous material is 10m ² / g
If so, the predetermined catalyst activity cannot be obtained.

In the present invention, the vanadium compound as the catalytically active component is supported on the carbonaceous material by using an oxide, inorganic acid salt or organic acid salt of trivalent, tetravalent or pentavalent vanadium. be able to. Usually, ammonium metavanadate reduced with oxalic acid and vanadyl sulfate can be preferably used. As the supporting method, any known method such as a spray method, a dipping impregnation method, a kneading method or the like can be used. Usually, a spray method or a dip impregnation method is used. For example, the vanadium compound is dissolved in a soluble solvent such as water, the carbonaceous material is immersed in the solution, dried at room temperature to 200 ° C., and then in an inert gas stream such as nitrogen at 200 to 600 ° C. Can be calcined to obtain a vanadium-supporting carbonaceous carrier. The vanadium compound supported as described above is generally, finally, on a carrier,
It is presumed to take the form of oxide. In the catalyst of the present invention, the supported amount of vanadium is 0.1 to 20% by weight, preferably 1 to 10% by weight, based on vanadium element. If it is less than 0.1% by weight, sufficient denitration performance cannot be obtained, and if it exceeds 20% by weight, the specific surface area of the carbonaceous material decreases, which is an adverse effect and is not preferable.

As the bromine compound as another catalytically active component of the present invention, alkali metal salts such as hydrobromic acid, ammonium bromide, sodium bromide, etc., alkali rare earth metal salts such as magnesium bromide, etc. are used. It can be supported on a carbonaceous material. Usually, hydrobromic acid or ammonium bromide is used. The carbonaceous material may be supported by any known method as in the case of the vanadium compound. For example, the carbonaceous material may be immersed in an aqueous solution of bromide or the like and impregnated at room temperature to 15 ° C.
Dry at 0 ° C. and load. Also, after drying, if necessary,
You may bake at 150-600 degreeC in inert gas streams, such as nitrogen. In the catalyst of the present invention, the amount of bromine supported is 0.1 to 20% by weight, preferably 2 to 15% by weight, based on the elemental bromine. If it is less than 0.1% by weight, sufficient denitration performance cannot be obtained, and if it exceeds 20% by weight, the specific surface area of the carbonaceous material decreases, which is not preferable.

As the iron compound which is another catalytically active component of the present invention, either a divalent or trivalent iron oxide, an inorganic acid salt or an organic acid salt is used and is supported on the carbonaceous material. You can Usually, iron nitrate or iron sulfate is preferably used. Further, as the cobalt compound which is another catalytically active component, any of a divalent oxide, an inorganic acid salt and an organic acid salt can be used for supporting. Usually, cobalt nitrate or cobalt sulfate is used. Further, as the rare earth metal of the other catalytically active component, neodymium (Nd) or samarium (Sm) is preferable, and any one of oxides, inorganic acid salts, and organic acid salts of these compounds is supported on the carbonaceous material. it can. Usually, neodymium chloride or samarium chloride is used. The carbonaceous material may be supported by any known method as in the case of the vanadium compound. In the present invention, the supported amount of iron, cobalt and rare earth metal is 0.1 to 2 in molar ratio with respect to vanadium,
It is preferably 0.5 to 1.5. This molar ratio is 0.1
When the amount is less than the above, sufficient denitration performance cannot be obtained, and even when more than 2 is supported, no further effect can be obtained.

In the present invention, the above vanadium compound,
In addition to the bromine compound and one or more at least three catalyst components from iron, cobalt and rare earth metals, optionally,
Further, as a catalyst component, a platinum group metal compound, that is, ruthenium (Ru), rhodium (Rh), palladium (Pd),
A compound of osmium (Os), iridium (Ir), or platinum (Pt) can be supported. The platinum group metal compound can be supported on the carbonaceous material using an oxide, an inorganic acid salt, or an organic acid salt. Usually, an inorganic acid salt can be preferably used. As a supporting method, any known method such as an impregnation method or a kneading method can be used. Usually, the impregnation method is used. For example, the platinum group metal compound is dissolved in a soluble solvent such as water, the carbonaceous material is immersed in the solution, dried at room temperature to 200 ° C., and then,
The platinum group metal-supporting carbonaceous carrier can be obtained by firing at 200 to 600 ° C. in an inert gas stream such as nitrogen. It is presumed that the platinum group metal compound supported as described above generally takes the form of a metal or a metal oxide on the final support. In the catalyst of the present invention, the loading amount of the platinum group metal is 0.0001 to 0.
It is 1% by weight, preferably 0.01 to 0.05% by weight. If it is less than 0.0001% by weight, the effect of supporting it is hardly obtained, and if it exceeds 0.1% by weight, no further effect can be obtained.

As described above, the catalyst for reducing nitrogen oxides for combustion exhaust gas of the present invention is preferably a vanadium compound and a bromine compound which are preferably activated carbon-based carbonaceous materials, and one or more of iron, cobalt and a rare earth metal. At least three components can be supported and formed as a catalyst component. In addition, if necessary, in order to obtain higher activity, in addition to the above three components,
Further, a platinum group metal compound can be supported and formed as a catalyst component. Each of the above catalyst components may be supported separately, or depending on the compound of each catalyst component used, for example, a dipping impregnation method, a mixed solution may be simultaneously supported. Further, in the case of the spray method, it is possible to carry out the loading of the respective components in sequence and to carry out the drying and firing in common to further improve the process. When loaded separately, preferably
1 from vanadium components, iron, cobalt and rare earth metals
More than one species, the metal component of the platinum group metal is first supported, then,
It is preferable to carry a bromine component. In addition, in the spray method or the impregnation method, it is preferable to carry out the loading under a reduced pressure because the loading component can be loaded uniformly on the carbonaceous material carrier. Further, as a bromine compound, it can be supported as a salt of vanadium, iron, cobalt, a rare earth metal and / or a platinum group metal. In this case, considering the supported amount,
The deficient amount can be carried separately.

The shape of the catalyst of the present invention is not particularly limited. For example, a powdery, granular, granular, spherical, cylindrical, or other shaped body can be appropriately selected according to the processing conditions. Nitrogen oxide reduction removal catalyst of the combustion exhaust gas of the present invention,
SV is contacted with low-temperature combustion exhaust gas after flue gas wet desulfurization at about 100 ° C. or less in the presence of ammonia at a high space velocity of 1000 / hour or more to stably produce nitrogen oxides at a high denitration rate for a long period of time. Can be reduced and removed.

[0013]

EXAMPLES The present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples. Example 1 100 m of an aqueous solution containing vanadium ion 1 mol / l prepared by reducing ammonium metavanadate with oxalic acid.
50 g of commercially available granular activated carbon (trade name: GX, manufactured by Takeda Yakuhin Kogyo Co., Ltd., specific surface area of about 1,000 m ² / g) was added to 1 l, and the mixture was immersed and impregnated under reduced pressure, and separated by filtration. Next, the obtained V-impregnated activated carbon was dried in a drier at 100 ° C. for 12 hours, then calcined in a nitrogen stream at 450 ° C. for 5 hours, and cooled to room temperature to obtain V-supporting activated carbon. The V-supported activated carbon obtained as described above was immersed under reduced pressure in 100 ml of an aqueous ferric nitrate solution containing 1 mol / liter of iron (Fe) (trivalent),
It separated by filtration. The Fe-impregnated V-supported activated carbon separated by filtration was dried in a drier at 100 ° C. for 12 hours and then calcined in a nitrogen stream at 450 ° C. for 5 hours to obtain a V-Fe-supported activated carbon catalyst. The obtained V-Fe-supporting activated carbon was subsequently immersed and impregnated in 100 ml of a 1 mol / liter aqueous solution of hydrobromic acid under reduced pressure, and separated by filtration. The hydrogen bromide-impregnated activated carbon separated by filtration is dried in a dryer at 110 ° C. for 12 hours,
A V-Fe-Br supported activated carbon catalyst was obtained. VF obtained
The e-Br supported activated carbon catalyst has a V supported amount of 4.0% by weight,
Fe loading 4.5% by weight, Br loading 6.1% by weight
Met.

212 ml of the V-Fe-Br-supported activated carbon catalyst produced above was packed in a glass denitration reaction tube having an inner diameter of 30 mmφ and a height of 500 mm to form a catalyst fixed bed.
In this reaction tube, at a temperature of 100 ° C. and SV of 2,750 / hour,
Nitrogen oxide (NO) 500 ppm, oxygen (O2) 5% by volume, carbon dioxide (CO2) 12% by volume, water (H2 O) 9.
500 ppm of ammonia (NH3) was added to the pseudo-combustion exhaust gas containing 5% by volume and the balance being nitrogen gas, and continuously flow-treated. The processing gas composition at each processing time shown in Table 1 is the chemiluminescence formula N manufactured by Shimadzu Corporation.
The denitration rate was calculated by measuring with an OX meter. Nitrous oxide (N
The amount of 2 O) produced was measured by filling a gas chromatography column with UniBeads C (manufactured by GL Sciences). As a result, each processing time was 1 ppm or less. The denitration rate (%) was calculated by (NO inlet concentration-NO outlet concentration) / NO inlet concentration x 100. The results are shown in Table 1. Also, the concentration of produced N2 O in the table (p
pm) is a value throughout the processing time (the same applies hereinafter).

Examples 2 to 5 V-Fe-Br was prepared in the same manner as in Example 1 by adjusting the concentration of the aqueous solution so that the supported amounts of V, Fe and Br of the catalyst components were the values shown in Table 1. A supported activated carbon catalyst was obtained. Further, using each of the obtained catalysts, the pseudo combustion exhaust gas was treated in the same manner as in Example 1. The results are shown in Table 1.

[0016]

[Table 1]

Examples 6-8 0.25 (Example 6), 0.5 (Example 7) and 1.0 (Example 8) were obtained by adding 50 g each of V-supported activated carbon prepared in the same manner as in Example 1. ) It was immersed in 100 ml of each mol / liter neodymium chloride aqueous solution under reduced pressure to impregnate Nd of a rare earth metal and then separated by filtration. The obtained Nd
The impregnated V-supported activated carbon was dried in a dryer at 100 ° C. for 12 hours, then calcined in a nitrogen stream at 450 ° C. for 5 hours, and then cooled to room temperature. The obtained V-Nd-supported activated carbon was immersed in 100 ml of a 1 mol / liter aqueous solution of hydrobromic acid under reduced pressure to impregnate Br, and then separated by filtration. The Br-impregnated V-Nd-supporting activated carbon thus obtained was dried in a dryer at 110 ° C. for 12 hours, and each component-supporting amount of V-Nd-Br shown in Table 1 was used.
A supported activated carbon catalyst was obtained. Using each of the obtained catalysts, the pseudo combustion exhaust gas was treated in the same manner as in Example 1. The results are shown in Table 1.
It was shown to.

Example 9 50 g of V-supported activated carbon prepared in the same manner as in Example 1
10 mol of 0.5 mol / liter samarium chloride aqueous solution
It was immersed in 0 ml under reduced pressure, impregnated with Sm, and then separated by filtration. The obtained Sm-impregnated V-supported activated carbon was dried in a drier at 100 ° C. for 12 hours, then calcined in a nitrogen stream at 450 ° C. for 5 hours, and cooled to room temperature. The obtained V-Sm-supported activated carbon was added to 100 ml of a 1 mol / liter hydrobromic acid aqueous solution.
It was immersed therein under reduced pressure, impregnated with Br, and separated by filtration. The obtained Br-impregnated V-Sm-supporting activated carbon was heated at 110 ° C.
Was dried for 12 hours in a drier to obtain a V-Sm-Br-supported activated carbon catalyst. The V-Sm-Br supported activated carbon catalyst thus obtained had a vanadium supported amount of 2.1% by weight, a samarium supported amount of 5.3% by weight, and a bromine supported amount of 6.1% by weight.
Using the obtained catalyst, the pseudo combustion exhaust gas was treated in the same manner as in Example 1. The results are shown in Table 1.

Examples 10-12 0.25 (Example 6), 0.5 (Example 7) and 1.0 (Example 8) were obtained using 50 g each of V-supported activated carbon prepared in the same manner as in Example 1. ) Each cobalt nitrate aqueous solution of 100 mol / liter was immersed under reduced pressure to impregnate cobalt (Co), and then separated by filtration. Obtained Co
The impregnated V-supported activated carbon was dried in a dryer at 100 ° C. for 12 hours, then calcined in a nitrogen stream at 450 ° C. for 5 hours, and then cooled to room temperature. The obtained V-Co-supported activated carbon was immersed in 100 ml of a 1 mol / liter hydrobromic acid aqueous solution under reduced pressure to impregnate Br, and then separated by filtration. The Br-impregnated V-Co-supported activated carbon thus obtained was dried in a dryer at 110 ° C. for 12 hours, and each component-supported amount of V-Co-Br shown in Table 1 was used.
A supported activated carbon catalyst was obtained. Using each of the obtained catalysts, the pseudo combustion exhaust gas was treated in the same manner as in Example 1. The results are shown in Table 1.
It was shown to.

Examples 13 to 15 50 g of each V-Fe-supporting activated carbon prepared in the same manner as in Example 1 was added to 0.0001 (Example 13) and 0.001.
(Example 14) and 0.007 (Example 15) Platinum (Pt) was impregnated by immersing in 100 ml of each mol / liter chloroplatinic acid aqueous solution to impregnate platinum (Pt), followed by separation by filtration. The obtained Pt-impregnated V-Fe-supporting activated carbon was heated at 110 ° C.
After drying for 12 hours in a drier, then in a nitrogen stream at 450 ° C
The mixture was baked for 5 hours at room temperature and cooled to room temperature to obtain V-Fe-Pt-supported activated carbon. Each of the obtained V-Fe-Pt-supported activated carbons was further immersed in 100 ml of a 1 mol / liter hydrobromic acid aqueous solution under reduced pressure, impregnated with Br, and separated by filtration. The Br-impregnated V-Fe-Pt-supported activated carbon thus obtained was dried in a drier at 110 ° C for 12 hours to obtain V-Fe-Pt-Br-supported activated carbon catalysts each having a component-supporting amount shown in Table 2. Using each of the obtained catalysts, the pseudo combustion exhaust gas was treated in the same manner as in Example 1. The results are shown in Table 2.

[0021]

[Table 2]

Examples 16 to 18 50 g of each of the V-Nd-supporting activated carbons prepared in the same manner as in Example 6 was added to 0.0001 (Example 16) and 0.001.
(Example 17) and 0.007 (Example 18) Platinum (Pt) was impregnated by immersing in 100 ml of each mol / liter chloroplatinic acid aqueous solution to impregnate platinum (Pt), followed by separation by filtration. The obtained Pt-impregnated V-Nd-supported activated carbon was heated at 110 ° C.
After drying for 12 hours in a drier, then in a nitrogen stream at 450 ° C
The mixture was calcined for 5 hours and cooled to room temperature to obtain V-Nd-Pt-supported activated carbon. Each of the obtained V-Nd-Pt-supported activated carbons was further immersed in 100 ml of a 1 mol / liter hydrobromic acid aqueous solution under reduced pressure, impregnated with Br, and separated by filtration. The Br-impregnated V-Nd-Pt-supported activated carbon thus obtained was dried in a drier at 110 ° C. for 12 hours to obtain V-Nd-Pt-Br-supported activated carbon catalysts having the respective component-supporting amounts shown in Table 2. Using each of the obtained catalysts, the pseudo combustion exhaust gas was treated in the same manner as in Example 1. The results are shown in Table 2.

Examples 19 to 21 50 g of each V-Co-supporting activated carbon prepared in the same manner as in Example 10 was added to 0.0001 (Example 19) and 0.005.
1 (Example 20) and 0.007 (Example 21) mol /
Each of them was immersed in 100 ml of each chloroplatinic acid aqueous solution under reduced pressure to impregnate platinum (Pt), and separated by filtration. The obtained Pt-impregnated V-Co-supported activated carbon was added to 110
After drying for 12 hours in a dryer at ℃, 450 in a nitrogen stream
The mixture was calcined at 5 ° C for 5 hours and cooled to room temperature to obtain V-Co-Pt-supported activated carbon. Each of the obtained V-Co-Pt-supported activated carbons was further immersed in 100 ml of a 1 mol / liter hydrobromic acid aqueous solution under reduced pressure, impregnated with Br, and separated by filtration. The Br-impregnated V-Co-Pt-supported activated carbon thus obtained was dried in a drier at 110 ° C for 12 hours to obtain V-Co-Pt-Br-supported activated carbon catalysts each having a component-supporting amount shown in Table 2. Using each of the obtained catalysts, the pseudo combustion exhaust gas was treated in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 1 50 g of V-supported activated carbon prepared in the same manner as in Example 1
Was immersed in 100 ml of a 1 mol / liter hydrobromic acid aqueous solution under reduced pressure, impregnated with Br, and separated by filtration.
The Br-impregnated V-supported activated carbon thus obtained was dried in a dryer at 110 ° C. for 12 hours, and V-Br having the respective amounts of each component shown in Table 2 was carried.
A supported activated carbon catalyst was obtained. The pseudo-combustion exhaust gas was treated in the same manner as in Example 1 by using the obtained V-Br-supported activated carbon catalyst having a vanadium supported amount of 4.1% by weight and a bromine supported amount of 6.0% by weight. The results are shown in Table 2.

As is clear from the above Examples and Comparative Examples, the V-Fe-Br supported, V-Co-Br supported, V-Nd-Br supported, V-Sm-Br supported activated carbon catalyst of the present invention is It can be seen that although the initial activity of denitration is not higher than that of the V-Br-supported activated carbon catalyst, the activity does not decrease even after long-term use and the denitration treatment can be performed stably. On the other hand, it can be seen that the V-Br-supported activated carbon catalyst has a high initial activity, but the denitration activity decreases as the treatment time elapses. Further, it can be seen that the V-Fe-Pt-Br-supported activated carbon catalyst in which platinum is further supported on each of the above-mentioned catalyst component-supported activated carbons has high activity and the activity is sustained. Further, it can be seen that the catalyst of the present invention is free of nitrous oxide by-product.

[0026]

INDUSTRIAL APPLICABILITY The catalyst for reducing nitrogen oxides in combustion exhaust gas according to the present invention can stably denitrate combustion exhaust gas at a relatively low temperature for a long period of time. Therefore, the flue gas at a relatively low temperature after wet flue gas desulfurization is treated at a large space velocity, that is, in a small reactor to stably reduce and remove the nitrogen oxides contained therein for a long time. Therefore, it is extremely useful in preventing environmental pollution. In addition, by using the catalyst for reducing nitrogen oxides in combustion exhaust gas of the present invention, the wet flue gas desulfurization apparatus already used for removing SOx from combustion exhaust gas containing SOx and NOx which are sources of air pollution. By treating the combustion exhaust gas that has become low temperature, nitrogen oxides can be continuously and easily removed with a compact apparatus, and it is industrially useful.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical indication location B01J 23/10 ZAB A 23/22 ZAB A 23/40 ZAB A 23/70 ZAB A B01D 53/36 102 H (72) Inventor Naoki Sonehara 2-12-1, Tsurumi Chuo, Tsurumi-ku, Yokohama-shi, Kanagawa Chiyoda Kako Construction Co., Ltd. (72) Inventor Takashi Kimura 2-12-1, Tsurumi-cho, Tsurumi-ku, Yokohama Chiyoda Kakoh Construction Co., Ltd.

Claims (2)

[Claims] 1. Nitrogen oxidation of combustion exhaust gas, characterized in that a carbonaceous material is loaded with a vanadium compound, a bromine compound, and a compound of at least one metal selected from iron, cobalt, and a rare earth metal. Material reduction removal catalyst. 2. The nitrogen oxide reduction removal catalyst for combustion exhaust gas according to claim 1, further comprising a platinum group metal supported thereon.