JPH07323225A - Catalyst for reductive-removing nitrogen oxides in waste combustion gas - Google Patents

Abstract

PURPOSE:To provide a reductive denitration catalyst for low temp. waste combustion gas without lowering the catalytic activity over a long period of time. CONSTITUTION:Vanadium compounds, vanadium compounds and one or more kind selected among compounds of molybdenum, tungsten and cerium, if necessary, further platinum group metal are deposited 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 for combustion exhaust gas, and more particularly to a catalyst for reducing and removing nitrogen oxides from exhaust gas at a relatively low temperature after wet desulfurization by ammonia reduction. It relates to a reduction removal catalyst.

[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. The NOx removal treatment for removing nitrogen oxides (NOx) from the combustion exhaust gas is usually desirably performed after removing the sulfur oxides (SOx) coexisting in the exhaust gas. However, the amount of flue gas after wet flue gas desulfurization treatment, which has been widely used to remove SOx from flue gas, is about 5
The temperature is as low as 0 ° C, and even if it is reheated with a gas-gas heater, the temperature can be raised up to about 100 ° C at most, and the reaction rate is slow even if a denitration reactor using a conventional denitration catalyst is installed. It was too practical. Therefore, development of a catalyst that can perform denitration treatment with a high denitration rate from low-temperature exhaust gas after wet flue gas desulfurization treatment has been demanded, and a catalyst having high denitration activity at low temperature has also been proposed. For example, in JP-A-49-39572,
A catalyst in which vanadium oxide is supported on activated carbon has been proposed as a denitration treatment catalyst for low-temperature exhaust gas.

[0003]

However, according to the inventors, although the above-mentioned proposed vanadium oxide-supported catalyst has a high denitration activity in the initial stage, the catalytic activity gradually decreases with the lapse of treatment time, and the catalyst is gradually removed for a long period of time. It was discovered that continuous denitration treatment has problems. Based on the above findings, the inventors have found that the catalyst activity does not decrease even in exhaust gas denitration treatment for a long period of time, and a low space temperature (SV ), And for the purpose of providing a catalyst capable of reducing and removing nitrogen oxides at a stable high denitration rate for a long period of time, the present invention was further studied by studying supported components and the like.

[0004]

According to the present invention, a carbonaceous material is loaded with a vanadium compound and at least one compound selected from molybdenum, tungsten and cerium compounds. A catalyst for reducing nitrogen oxides in exhaust gas is provided. The present invention also provides a catalyst for nitrogen oxide reduction and removal of combustion exhaust gas, which is obtained by further supporting a platinum group metal on the catalyst for nitrogen oxide reduction and removal.

[0005]

The present invention is configured as described above, and by supporting a vanadium compound and one or more kinds selected from molybdenum, tungsten and cerium compounds on a carbonaceous material, a conventional proposed reduction denitration catalyst can be obtained. On the contrary, it is possible to maintain stable reduction denitration performance for a long period in the denitration treatment at a low temperature. In addition, there are no nitrous oxide by-products that are suppressed in order to prevent global warming. Further, the activity can be improved by further supporting a platinum group metal as a catalyst component. The catalyst for nitrogen oxide reduction removal for combustion exhaust gas of the present invention is obtained by, for example, subjecting a low temperature exhaust gas at about 100 ° C. or lower after wet combustion desulfurization of combustion exhaust gas to contact treatment at high space velocity in the presence of ammonia. The nitrogen oxide can be reduced and removed stably with a high denitration rate for a long period of time.

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 it is less than the specified value, the desired catalytic activity cannot be obtained.

In the present invention, the vanadium (V) compound as the catalytically active component is a trivalent, tetravalent or pentavalent vanadium oxide, an inorganic acid salt or an organic acid salt,
It can be supported on the above carbonaceous material. Usually, ammonium metavanadate reduced with oxalic acid and vanadyl sulfate can be preferably used. As a loading 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 finally supported on the carrier,
Generally, it is presumed to take the form of oxide. In the catalyst of the present invention, the loading amount of V is 0.1 to V on the basis of V element.
It is 20% by weight, preferably 1 to 10% by weight. 0.1
If it is less than wt%, sufficient denitration performance cannot be obtained, and if it exceeds 20 wt%, the specific surface area of the carbonaceous material decreases, which is an adverse effect and is not preferable.

Among the molybdenum (Mo), tungsten (W) and cerium (Ce) compounds which are other catalytically active components of the present invention, the molybdenum (Mo) and tungsten (W) compounds are divalent and trivalent. A tetravalent, pentavalent, or hexavalent oxide, inorganic acid salt, or organic acid salt can be used to support the carbonaceous material. Normal,
Ammonium molybdate and ammonium paratungstate are preferably used. As the cerium (Ce) compound, any of a trivalent or tetravalent oxide, an inorganic acid salt, and an organic acid salt can be used for supporting. Normal,
Cerium nitrate can be preferably used. The carbonaceous material may be supported by any known method like the vanadium compound. For example, the carbonaceous material may be immersed in an aqueous solution of the Mo, W, and Ce compounds, and dried at room temperature to 200 ° C. Baking is performed at 200 to 600 ° C. in an inert gas stream such as nitrogen. It is presumed that the Mo, W, and / or Ce compound supported as described above generally takes the form of an oxide on the final support. In the catalyst of the present invention, the supported amount of the above Mo, W and Ce compounds is
The molar ratio is 0.1 to 2, and preferably 0.5 to 1.5 with respect to the amount of V supported. If this molar ratio is less than 0.1, sufficient denitration performance cannot be obtained, and even if the molar ratio exceeds 2, no further effect can be obtained.

In the present invention, in addition to the two catalyst components of the vanadium compound and any one or more of molybdenum (Mo), tungsten (W) and cerium (Ce) compounds, if necessary, a catalyst is further added. As a component, a platinum group metal compound, that is, ruthenium (Ru), rhodium (R
A compound of h), palladium (Pd), 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 a spray method, an impregnation method, a kneading method, or the like can be used. Usually, a spray method or an 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 200 to 200 ° C. in an inert gas stream such as nitrogen. A platinum group metal-supporting carbonaceous carrier can be obtained by firing at 600 ° C. 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 platinum group metal supported amount is 0.001 to 0.1% by weight, preferably 0.01 to 0.05% by weight, based on the platinum group metal element.
This is because if the amount is less than 0.001% by weight, the effect of supporting is hardly obtained, and if the amount exceeds 0.1% by weight, no further effect is obtained.

As described above, the catalyst for removing nitrogen oxides from flue gas according to the present invention preferably comprises a vanadium compound, a molybdenum (Mo), a tungsten (W) and a cerium (Ce). Two or more components of any one of the compounds can be supported and formed as a catalyst component. In addition, if necessary, in order to obtain higher activity, a platinum group metal compound can be further supported as a catalyst component in addition to the above two components to form the catalyst. 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 also possible to carry out the loading of the respective components in sequence and to perform drying and baking in common so as to form a single stage. Also,
In the spray method and the impregnation method, carrying is carried out under reduced pressure, so that the carried component can be carried uniformly on the carbonaceous material carrier, which is preferable.

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. The above-described nitrogen oxide reduction removal catalyst for combustion exhaust gas of the present invention is stable for a long period of time by contact treatment with low temperature combustion exhaust gas such as after wet desulfurization in the presence of ammonia at a large SV of about 1000 / hour or more. Nitrogen oxides in exhaust gas can be reduced and removed with a high denitration rate.

[0012]

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. After immersing the V-supported activated carbon obtained as described above in 100 ml of an ammonium molybdate aqueous solution containing 1 mol / liter of Mo under reduced pressure,
It separated by filtration. The Mo-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-Mo-supported activated carbon catalyst. The obtained V-Mo supported activated carbon catalyst had a V supported amount of 4.0% by weight and a Mo supported amount of 7.2% by weight.

212 ml of the V-Mo-supported activated carbon catalyst produced above was filled 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 an SV of 2,750 / hour, 500 ppm of nitric oxide (NO), 5% by volume of oxygen (O ₂ ), 12% by volume of carbon dioxide (CO ₂ ) and water (H ₂ O) 9. Ammonia (NH ₃ ) 500 ppm was added to the pseudo-combustion exhaust gas containing 5% by volume and the balance being nitrogen gas, and continuously flow-treated. The process gas composition in each processing times shown in Table 1 (strain) was measured by Shimadzu Corporation chemiluminescent NO _X meter, it was calculated NOx removal efficiency. Nitrous oxide (N ₂ O)
The production amount of 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 result is
The results are shown in Table 1. In addition, the concentration of produced N ₂ O in the table (pp
m) is a value throughout the processing time (hereinafter the same).

[0014]

[Table 1]

Examples 2 to 5 The concentration of the aqueous solution was adjusted so that the supported amounts of V and Mo of the catalyst components were the values shown in Table 1, and the same procedure as in Example 1 was carried out.
A V-Mo 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.

Examples 6 to 8 200 m of an aqueous ammonium paratungstate solution containing 0.05 mol / liter of W was added to V-supported activated carbon prepared in the same manner as in Example 1 except that the concentration of V was changed.
After immersing in 1 l and impregnating, it was dried under reduced pressure by an evaporator. The W-impregnated V-supported activated carbon obtained was further dried in a dryer at 100 ° C. for 12 hours. The W impregnation operation was adjusted to one, two or three times so that the W loading amount shown in Table 1 was obtained. After impregnating with a predetermined amount of W supported and dried, it was calcined in a nitrogen stream at 450 ° C. for 5 hours to obtain a VW supported activated carbon catalyst. 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.

Examples 9-11 100 m of mixed aqueous solution containing 0.5 mol / l of vanadyl sulfate and 0.25 mol / l of cerium nitrate.
A V-Ce supported activated carbon catalyst was prepared in the same manner as in Example 1 except that 1 was used. (Example 9) Further, the amount of Ce supported was changed by changing the cerium nitrate concentration to 0.51 mol / liter (Example 10) and 10.5 mol / liter (Example 11). A 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.

Examples 12 to 14 V-Mo-supporting activated carbon prepared in the same manner as in Example 1 was cooled to room temperature and then immersed in 100 ml of a 0.0001 mol / liter chloroplatinic acid aqueous solution under reduced pressure to obtain platinum ( Pt)
Was impregnated and filtered off. The activated carbon thus obtained was dried in a dryer at 110 ° C for 12 hours, and then dried in a nitrogen stream at 450 ° C for 5 hours.
It was calcined for an hour to obtain a V-Mo-Pt-supported activated carbon catalyst.
(Example 12) V-Mo-Pt was performed in exactly the same manner except that the concentration of chloroplatinic acid was changed to 0.001 mol / liter (Example 13) and 0.007 mol / liter (Example 14). 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.

Example 15 VW-supported activated carbon prepared in the same manner as in Example 7 was cooled to room temperature, then immersed in 100 ml of a 0.001 mol / liter chloroplatinic acid aqueous solution under reduced pressure, and separated by filtration. The obtained activated carbon was dried in a drier at 110 ° C. for 12 hours and then fired in a nitrogen stream at 450 ° C. for 5 hours to obtain V-W-Pt.
Supported activated carbon 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.

Example 16 V-Ce-supporting activated carbon prepared in the same manner as in Example 10 was cooled to room temperature, then immersed in 100 ml of a 0.001 mol / liter platinum chloride aqueous solution under reduced pressure, and separated by filtration.
The obtained activated carbon was dried in a drier at 110 ° C. for 12 hours and then calcined in a nitrogen stream at 450 ° C. for 5 hours to obtain V-Ce-
Pt-supported activated carbon 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.

Comparative Example 1 A V-supported activated carbon catalyst was obtained in the same manner as in Example. 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.

As is clear from the above Examples and Comparative Examples, each of the V-Mo, VW, and V-Ce supported activated carbon catalysts of the present invention has a higher denitration initial activity than the V supported activated carbon catalyst. However, it can be seen that the denitration treatment can be stably performed without lowering the activity even after long-term use. on the other hand,
It can be seen that the V-supported activated carbon catalyst has a high initial activity, but the activity decreases as it is used. Further, it can be seen that the V-Pt-Mo-supported activated carbon catalyst in which platinum is further supported on the V-Mo-supported activated carbon has high activity and sustains the activity. Further, it can be seen that the catalyst of the present invention is free of nitrous oxide by-product.

[0023]

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, nitrogen oxides can be stably reduced and removed from a low temperature gas such as a combustion exhaust gas after wet flue gas desulfurization at a large space velocity, that is, in a small reactor for a long time, which is extremely effective in preventing environmental pollution. High utility value. Further, by using the nitrogen oxide reduction removal catalyst for flue gas of the present invention, the flue gas is continuously put into practical use after the sulfur oxides of the air pollution are removed by the wet flue gas desulfurization which has already been put to practical use. It is industrially useful because it can be removed easily and smoothly with a very compact device.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location B01J 23/16 ZAB A B01D 53/36 102 H (72) Inventor Naoki Sonehara Tsurumi Ward, Yokohama City, Kanagawa Prefecture 2-12-1 Tsurumi Chuo Chiyoda Kakoh Construction Co., Ltd. (72) Inventor Takashi Kimura 2-12-1 Tsurumi Chuo 2-chome Tsurumi-ku, Yokohama, Kanagawa Prefecture Chiyoda Kakoh Construction Co., Ltd.

Claims (2)

[Claims] 1. A catalyst for reducing and removing nitrogen oxides from combustion exhaust gas, comprising a vanadium compound and one or more compounds selected from molybdenum, tungsten and cerium compounds supported on a carbonaceous material. 2. The catalyst for reducing nitrogen oxides in combustion exhaust gas according to claim 1, which further carries a platinum group metal.