JP2005081189A - Catalyst for denitrifying high temperature waste gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce a catalyst for denitrifying high temperature waste gas, which is suitable for reducing/removing nitrogen oxides contained in the high temperature gas discharged from a thermal power station, a high temperature boiler, or the like. <P>SOLUTION: This catalyst for denitrifying the nitrogen oxide-containing high temperature waste gas is obtained by depositing an oxide or a multiple oxide of at least one or more metals selected from the group consisting of vanadium, tungsten, molybdenum, iron, chromium, copper, manganese and cobalt on a carrier having ≤-11.35 acid strength Ho or ≥0.2 mmol/g solid acid content. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a denitration catalyst for high temperature exhaust gas and an exhaust gas denitration method. The present invention relates to a denitration catalyst.

High-temperature combustion exhaust gas discharged from thermal power plants and gas turbines is a gas containing nitrogen oxides, and it is necessary to remove nitrogen oxides in the exhaust gas to release it. Therefore, a denitration device is installed downstream of the combustion engine, a reducing agent is injected from the injection nozzle into the combustion exhaust gas, and is reacted reductively with nitrogen oxides (NO, NO ₂ ), harmless nitrogen (N ₂ ) Decompose into water (H ₂ O). At this time, in the method of removing nitrogen oxides from exhaust gas using a denitration catalyst, ammonia (NH ₃ ) or urea is usually added because it is necessary to cause a sufficient denitration reaction.

Conventionally, when nitrogen oxides in exhaust gas are reduced, when ammonia is added as a reducing agent and a denitration catalyst is used, the treatment is usually performed in a high temperature range of 400 ° C. or higher. The denitration reaction proceeds according to the following formula (1), and is decomposed into N ₂ and H ₂ O by a reaction of 1 mol of NO and 1 mol of NH ₃ .
4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ O (1)

However, a catalyst which has been used conventionally, in addition to the above expression becomes a high temperature of at least 450 ° C. (1), oxidation of NH ₃ itself by the following formula (2) will progress.
2NH ₃ + 5 / 2O ₂ → 2NO + 3H ₂ O (2)
Due to the reaction of the above formula (2), NH ₃ was not effectively used for the reduction of NO, and the denitration performance was lowered as the temperature increased. For this reason, for example, the conventional reduction treatment with addition of ammonia cannot be applied to the exhaust gas at 500 ° C. or more at the gas turbine outlet.

On the other hand, as a method for removing nitrogen oxides at a high temperature, a technique using titanium oxide containing heat-resistant inorganic fibers as a carrier has been reported (see Patent Document 1). However, a catalyst that simply supports tungsten on the support titanium oxide as an active ingredient has limitations in catalytic activity even if it is optimized based on the physical strength of inorganic fibers, etc. It was difficult to promote.
When a conventional tungsten-titanium-based denitration catalyst is used, ammonia as a reducing agent is decomposed at 450 ° C. or higher, so it is necessary to add a large amount (about 20% by weight) of tungsten oxide that suppresses ammonia decomposition. there were. The use of such a large amount of tungsten oxide has the disadvantage that the cost of the catalyst raw material is high because a large amount of expensive tungsten is added. In addition, this method has a problem that the running cost is increased because a large amount of ammonia as a reducing agent needs to be added.

JP-A-6-327944

In view of the above problems, the present inventors, in a method of denitrating high-temperature combustion exhaust gas using a reducing agent such as ammonia, efficiently act the reducing agent added to promote the denitration reaction, In order to develop an exhaust gas treatment method that reduces nitrogen oxides in exhaust gas, we have intensively studied.
As a result, the present inventors denitrated a small amount of a base metal oxide such as vanadium, tungsten, molybdenum or a rare earth oxide such as cerium or a composite oxide thereof supported on a carrier having a high acid strength or a carrier having a high acid amount. It has been found that such problems can be solved by performing exhaust gas treatment on the catalyst. The present invention has been completed from such a viewpoint.

That is, the present invention is a denitration catalyst for high-temperature exhaust gas containing nitrogen oxides, and has vanadium as an active ingredient on a carrier having an acid strength of Ho ≦ -11.35 or a carrier having a solid acid amount of 0.2 mmol / g or more. The present invention provides a denitration catalyst for high-temperature exhaust gas in which at least one oxide selected from the group consisting of tungsten, molybdenum, iron, chromium, copper, manganese and cobalt or a composite oxide thereof is supported.
As the support having the acid strength Ho ≦ -11.35, SO ₄ / TiO ₂ , SO ₄ / ZrO ₂ , SO ₄ / Al ₂ O ₃ , SO ₄ / TiO ₂ -ZrO ₂ and SO ₄ / TiO ₂ -Al ₂ At least one compound selected from the group consisting of O ₃ can be used. Incidentally, for example, a carrier having a currently known acid strength is known as a carrier having Ho = -16.04. However, the “carrier having an acid strength of Ho ≦ -11.35” in the present invention is not limited to this. It is meant to include all carriers with an acid strength of -11.35 or less. Examples of the carrier having a solid acid amount of 0.2 mmol / g or more include TiO ₂ -SiO ₂ , TiO ₂ -ZrO ₂ , SiO ₂ -Al ₂ O ₃ , TiO ₂ -P ₂ O ₅ , TiO ₂ -Al ₂ At least one compound selected from the group consisting of O ₃ , TiO ₂ —WO ₃ and TiO ₂ —CeO ₂ can be used.

  In the present invention, when tungsten oxide is supported as an oxide, the tungsten oxide concentration is usually 1.0% by weight or more and less than 20% by weight, preferably 2.0% by weight or more and 15% by weight, based on the total weight ratio of the catalyst including the support. Is less than. Further, when at least one oxide selected from the group consisting of vanadium, molybdenum, iron, chromium, copper, manganese and cobalt is supported as an oxide, the oxide concentration is the weight of the entire catalyst including the support. The ratio is usually 0.1% by weight or more and 1.0% by weight or less, preferably 0.15% by weight or more and 0.75% by weight or less. Further, when a composite oxide is supported as the active component, it is preferably at least one composite oxide selected from the group consisting of vanadium-tungsten, vanadium-molybdenum, and tungsten-cerium, for example.

  The denitration catalyst for high-temperature exhaust gas as described above can decompose and remove nitrogen oxides in the exhaust gas very effectively by circulating the exhaust gas at 400 ° C. or higher. The temperature range is usually preferably 400 ° C. or higher and 650 ° C. or lower. If it is less than 400 ° C., catalyst deterioration due to exhaust gas-containing components such as S may occur. When the temperature exceeds 650 ° C, catalyst deterioration is likely to occur due to high temperature. Examples of the reducing agent include ammonia and urea.

  According to the exhaust gas treatment method of the present invention, when a high temperature exhaust gas at 450 ° C. or higher is denitrated using a catalyst by the addition of a reducing agent, ammonia as a reducing agent is decomposed by increasing the amount of carrier acid or acid strength. The amount of the reducing agent added can be effectively acted on the catalyst while suppressing to a high temperature range. Therefore, it is possible to effectively reduce nitrogen oxides in the exhaust gas by promoting the denitration reaction of the exhaust gas. Moreover, since it is not necessary to use a large amount of expensive catalyst components in consideration of the ammonia decomposition reaction, the manufacturing cost of the catalyst itself is reduced. Furthermore, since the amount of ammonia added as a reducing agent for the denitration reaction is small, the running cost can be kept low.

  A specific form of the denitration catalyst for high temperature exhaust gas according to the present invention will be described. The present invention is not limited to the embodiments described below.

The denitration catalyst of the present invention is a denitration catalyst for high-temperature exhaust gas containing nitrogen oxides, and an active ingredient is supported on a carrier having an acid strength of Ho ≦ -11.35 or a carrier having a solid acid amount of 0.2 mmol / g or more. . In a carrier having an acid strength of Ho ≦ −11.35, the strong acid strength suppresses the auto-oxidative decomposition reaction of the reducing agent. On the other hand, when the amount of the solid acid is 0.2 mmol / g or more, the autooxidative decomposition reaction of the reducing agent is suppressed due to the acid sites present in large quantities.
Specific examples of the carrier having an acid strength of Ho ≦ −11.35 include, for example, SO ₄ / TiO ₂ , SO ₄ / ZrO ₂ , SO ₄ / Al ₂ O ₃ , SO ₄ / TiO ₂ —ZrO ₂ , SO ₄ / TiO ₂ —Al ₂ O _{3 and the} like can be mentioned, and these compounds can be used alone or in any combination as a carrier. Incidentally, for example, a carrier having a currently known acid strength is known as a carrier having Ho = -16.04. However, the “carrier having an acid strength of Ho ≦ -11.35” in the present invention is not limited to this. It is meant to include all carriers with an acid strength of -11.35 or less.
As a carrier having a solid acid amount of 0.2 mmol / g or more, specifically, for example, TiO ₂ -SiO ₂ , TiO ₂ -ZrO ₂ , SiO ₂ -Al ₂ O ₃ , TiO ₂ -P ₂ O ₅ , TiO _2- Al ₂ O ₃ , TiO ₂ —WO ₃ , TiO ₂ —CeO _{2 and the} like can be mentioned, and these compounds can be used alone or in any combination as a support.
By such an increase in the amount of solid acid or acid strength of the carrier, the decomposition reaction of ammonia as a reducing agent can be suppressed to a high temperature range.

In the denitration catalyst of the present invention, an oxide such as vanadium, tungsten, molybdenum, iron, chromium, copper, manganese, or cobalt or a composite oxide thereof is supported as an active component on any of the above carriers.
When tungsten oxide is supported as the oxide, the oxide concentration is usually 1.0% by weight or more and less than 20% by weight, preferably 2.0% by weight or more and less than 15% by weight, based on the total weight ratio of the catalyst including the support, particularly Preferably it is 3.0 weight% or more and less than 10 weight%. Even if the amount of tungsten oxide exceeds 20% by weight, the effect on the denitration performance is not increased and the cost is disadvantageous. Therefore, it is less than 20% by weight, preferably less than 15% by weight, particularly preferably less than 10% by weight. Is good.

  When at least one oxide selected from the group consisting of vanadium, molybdenum, iron, chromium, copper, manganese, and cobalt is supported as the oxide, the oxide concentration is usually the weight ratio of the entire catalyst including the support. It is 0.1 to 1.0% by weight, preferably 0.15 to 0.75% by weight. By suppressing the amount of these oxides to 1.0% by weight or less, preferably 0.75% by weight or less, the denitration performance can be promoted while suppressing the self-decomposition reaction of the reducing agent. If the amount of oxide is less than 0.1% by weight, the denitration reaction may not be sufficiently promoted, which is not preferable.

  Moreover, it is also possible to use complex oxide as an active component, for example, vanadium-tungsten (A component / B component), vanadium-molybdenum, cerium-tungsten, etc. are mentioned suitably. In this case, as the amount of active metal, the former A component / the latter B component is preferably in the range of 0.5 to 1: 5 to 10. This is because when the amount of component A is too large, the self-decomposition reaction of the reducing agent proceeds.

In the present invention, exhaust gas at 400 ° C. or higher is passed through the denitration catalyst to decompose and remove nitrogen oxides in the exhaust gas. The shape of the denitration catalyst is not particularly limited. For example, a honeycomb shape, or a stack of these or a catalyst filled with a granular catalyst can be used. Is preferred.
FIG. 1 shows an example of a honeycomb-shaped denitration catalyst used in the exhaust gas treatment method of the present invention. The size of the honeycomb-shaped catalyst can be arbitrarily determined depending on the exhaust gas properties, the flow rate, etc., and is not particularly limited. For example, the outer shape of the exhaust gas inlet is 50 to 200 mm square, and the length L is 100 to 100 mm. 1000mm ones can be used.

In the step of denitration treatment using the catalyst of the present invention, nitrogen oxides are removed by the following formula (1) using the denitration catalyst.
4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ O (1)
In the method for treating exhaust gas discharged from various combustion apparatuses, the exhaust gas discharged is sent to a denitration catalyst and a denitration process is performed. Ammonia or urea or the like is added as a reducing agent upstream of the denitration catalyst.

The exhaust gas that can be treated in the present invention is not particularly limited and can be applied to the treatment of exhaust gas containing nitrogen oxides. For example, boiler exhaust gas from a thermal power plant or factory that burns fuel such as coal or heavy oil, or metal Heating furnace exhaust gas from factories, oil refineries, petrochemical factories, etc., and particularly suitable for the treatment of gas discharged from thermal power plants and gas turbines.
EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not restrict | limited at all by these Examples.

(Preparation of catalyst)
Example 1
60 kg of metatitanic acid slurry (TiO ₂ content: 30% by weight) was mixed with 2.6 kg of zirconium oxychloride, neutralized with ammonia water, and then immersed in 1N sulfuric acid for 30 minutes.
The soaked powder was mixed with 280 g of cerium nitrate and a molding aid, and then kneaded while evaporating water using a heating kneader to obtain a catalyst paste. This was molded into a honeycomb shape having an outer shape of 75 mm square and a length of 500 mm with an extrusion molding machine. Next, after drying at 80 ° C., the catalyst (Example 1) was obtained by calcination at 600 ° C. in an air atmosphere for 5 hours.

Examples 2-8
In Example 1, instead of 280 g of cerium nitrate, 191 g of ammonium metavanadate (Example 2), 181 g of ammonium molybdate (Example 3), 450 g of iron nitrate (Example 4), 465 g of chromium nitrate (Example 5), The catalyst paste was mixed and kneaded in the same manner as in Example 1 except that 250 g of copper chloride (Example 6), 374 g of manganese nitrate (Example 7), or 362 g of cobalt nitrate (Example 8). Obtained and formed into a honeycomb, and then fired to obtain catalysts (Examples 2 to 8).

Examples 9-15
In Example 1, instead of 280 g of cerium nitrate, 51 g of ammonium metavanadate (Example 9), 49 g of ammonium molybdate (Example 10), 120 g of iron nitrate (Example 11), 124 g of chromium nitrate (Example 12), The catalyst paste was mixed and kneaded in the same manner as in Example 1 except that 67 g of copper chloride (Example 13), 100 g of manganese nitrate (Example 14), or 97 g of cobalt nitrate (Example 15). Obtained and formed into a honeycomb, and then fired to obtain catalysts (Examples 9 to 15).

Examples 16-19
In Example 1, instead of 280 g of cerium nitrate, 0.9 kg of ammonium paratungstate (Example 16), 1.8 kg (Example 17), 2.1 kg (Example 18), and 2.7 kg (Example 19) were used. Except for the above, mixing and kneading were carried out in the same manner as in Example 1 to obtain a catalyst paste, which was molded into a honeycomb shape and then fired to obtain catalysts (Examples 16 to 19).

Example 20
60 kg of metatitanic acid slurry (TiO ₂ content: 30% by weight) was immersed in 1N sulfuric acid for 30 minutes. The soaked powder was mixed with 1.8 kg of ammonium paratungstate and a molding aid, and then kneaded while evaporating water using a heating kneader to obtain a catalyst paste. Molded into. Next, after drying at 80 degreeC, it baked in the air atmosphere at 600 degreeC for 5 hours, and obtained the catalyst (Example 20).

Examples 21-23
In Example 20, instead of 60 kg of metatitanic acid slurry, 18 kg of zirconium hydroxide slurry (Example 21), 18 kg of aluminum hydroxide slurry (Example 22), or 18 kg of metatitanic acid / aluminum hydroxide slurry (Example 23) Except for the above, immersion, mixing, and kneading were performed in the same manner as in Example 20 to obtain a catalyst paste, which was molded into a honeycomb shape and then fired to obtain catalysts (Examples 21 to 23).

Example 24
A support was obtained by mixing 60 kg of a metatitanic acid slurry (TiO ₂ content: 30% by weight) and 22.5 kg of silica sol (SiO ₂ content: 20% by weight) and neutralizing with ammonia water.
The carrier powder was mixed with 1.8 kg of ammonium paratungstate and a molding aid, and then kneaded while evaporating water using a heating kneader to obtain a catalyst paste. Molded into. Next, after drying at 80 degreeC, it baked in the air atmosphere at 500 degreeC for 5 hours, and obtained the catalyst (Example 24).

Examples 25-29
In Example 24, instead of 60 kg of metatitanic acid slurry and 22.5 kg of silica sol,
60 kg of metatitanic acid slurry and 2.6 kg of zirconium oxychloride (Example 25),
22.5 kg of silica sol and 75 kg of aluminum nitrate (Example 26),
60 kg of metatitanic acid slurry and 5.2 kg of phosphoric acid (Example 27),
60 kg of metatitanic acid slurry and 19 kg of aluminum nitrate (Example 28), or 60 kg of metatitanic acid slurry and 8.6 kg of cerium nitrate (Example 29),
Except for the above, a carrier was prepared in the same manner as in Example 24, mixed and kneaded to obtain a catalyst paste, molded into a honeycomb shape, and calcined to obtain catalysts (Examples 25 to 29).

Comparative Example 1
In Example 24, instead of 60 kg of metatitanic acid slurry and 22.5 kg of silica sol,
Except that the carrier was prepared as 75 kg of metatitanic acid slurry, the carrier was prepared in the same manner as in Example 24, then mixed and kneaded to obtain a catalyst paste, molded into a honeycomb, and then fired to obtain a catalyst (Comparative Example 1 )

Example 30
60 kg of metatitanic acid slurry (TiO ₂ content: 30% by weight) was mixed with 2.6 kg of zirconium oxychloride, neutralized with ammonia water, and then immersed in 1N sulfuric acid for 30 minutes.
Thereafter, 0.2 kg of ammonium metavanadate and 1.8 kg of ammonium paratungstate were mixed in the soaked powder, mixed with a molding aid, and then kneaded while evaporating water using a heating kneader to obtain a catalyst paste, It was molded into a honeycomb shape in the same manner as in Example 1 with an extruder. Next, after drying at 80 degreeC, it baked in the air atmosphere at 600 degreeC for 5 hours, and obtained the catalyst (Example 30).

Examples 31-32
In Example 30, instead of 1.8 kg ammonium paratungstate,
1.9 kg of ammonium molybdate (Example 31), or
1.9 kg of ammonium molybdate and 280 g of cerium nitrate (Example 32),
The mixture was mixed with the carrier powder in the same manner as in Example 30 and then kneaded to obtain a catalyst paste, molded into a honeycomb shape, and then fired to obtain catalysts (Examples 31 to 32).

[Solid acid content measurement method]
A pyridine adsorption temperature programmed desorption (TPD) method was used to measure the solid acid amount of the catalyst. Table 1 shows the measurement conditions for the amount of solid acid. Under these measurement conditions, pyridine was saturated and adsorbed, and the amount of pyridine desorbed was defined as the acid amount.

[Acid strength measurement method]
The acid strength of the catalyst was measured by using p-nitrotoluene having a known pKa as an indicator to determine whether or not the color changed (O: changed, X: not changed). Table 2 shows the measurement conditions for acid strength.

[Exhaust gas treatment test]
The evaluation conditions for the denitration activity are as follows.
NOx: 65ppm
O ₂ : 15%, CO ₂ : 5%, H ₂ O: 7%, N ₂ : balance, GHSV: 24,000h ⁻¹ ,
Gas amount 220NL / h,
Catalyst layer temperature: 400, 500 ℃
The denitration rate is expressed by the following formula.
Denitration rate (%) = (1−Outlet NOx concentration / Inlet NOx concentration) × 100

  In Examples 1 to 23, Examples 30 to 32, and Comparative Example 1, acid strength was measured for each of the prepared catalysts. The results are shown in Tables 3 and 4. Subsequently, each exhaust gas containing nitrogen oxides at about 400 ° C. and about 500 ° C. was circulated, and the denitration rate (%) was measured. As a reducing agent, ammonia was continuously supplied. The obtained results are shown in Tables 3 and 4.

  In Examples 24-29 and Comparative Example 1, the amount of solid acid was measured for each of the prepared catalysts. The results are shown in Table 3. Next, exhaust gases at about 400 ° C. and about 500 ° C. were circulated in the same manner as described above, and the denitration rate (%) was measured. The results obtained are shown in Table 3.

  The catalyst of Comparative Example 1 did not have the acid strength of the present invention and did not have the solid acid amount of the present invention, and the denitration rate at each temperature was low. On the other hand, the catalyst supporting each active metal of Examples 1 to 23 having the acid strength of the present invention and the catalyst supporting each composite oxide of Examples 30 to 33 are both high in denitration. It was found to have a rate. It was also found that all the catalysts of Examples 24 to 29 having a solid acid amount of the present invention have a high denitration rate.

  The denitration catalyst of the present invention can promote a denitration reaction by efficiently acting a reducing agent added in a method of denitrating high-temperature combustion exhaust gas using a reducing agent such as ammonia. Therefore, it is not necessary to use a large amount of expensive catalyst components in consideration of the ammonia decomposition reaction, and the production cost of the catalyst itself is reduced. In addition, since the amount of ammonia added as a reducing agent for the denitration reaction is small, the running cost can be kept low, so it is particularly suitable for the treatment of gas discharged from thermal power plants and gas turbines. The above significance is extremely large.

It is a figure which shows an example of the external appearance of the honeycomb-shaped denitration catalyst used for the waste gas treatment of this invention.

Explanation of symbols

  1 Honeycomb-shaped denitration catalyst

Claims (7)

A denitration catalyst for high temperature exhaust gas containing nitrogen oxides,
On a carrier having an acid strength of Ho ≦ −11.35, or a carrier having a solid acid amount of 0.2 mmol / g or more,
A denitration catalyst for high-temperature exhaust gas, comprising at least one oxide selected from the group consisting of vanadium, tungsten, molybdenum, iron, chromium, copper, manganese and cobalt, or a composite oxide thereof. SO ₄ / TiO ₂ , SO ₄ / ZrO ₂ , SO ₄ / Al ₂ O ₃ , SO ₄ / TiO ₂ -ZrO ₂ and SO ₄ / TiO ₂ -Al ₂ O as the support having the acid strength Ho ≦ -11.35 _{2. The} denitration catalyst for high temperature exhaust gas according to claim 1, wherein at least one compound selected from the group consisting of ₃ is used. As a support having a solid acid amount of 0.2 mmol / g or more, TiO ₂ --SiO ₂ , TiO ₂ --ZrO ₂ , SiO ₂ --Al ₂ O ₃ , TiO ₂ --P ₂ O ₅ , TiO ₂ --Al ₂ O ₃ , hot exhaust gas denitration catalyst according to claim 1, characterized in that at least one compound selected from the group consisting of TiO ₂ -WO ₃ and TiO ₂ -CeO ₂ is used. The tungsten oxide is supported on the support as the oxide, and the oxide concentration is 1.0 wt% or more and less than 20 wt% in the weight ratio of the entire catalyst including the support. The denitration catalyst for high temperature exhaust gas according to any one of the above items. As the oxide, at least one oxide selected from the group consisting of vanadium, molybdenum, iron, chromium, copper, manganese and cobalt is supported on a support, and the oxide concentration is the weight of the entire catalyst including the support. The denitration catalyst for high temperature exhaust gas according to any one of claims 1 to 3, wherein the ratio is 0.1 wt% or more and 1.0 wt% or less. 4. The composite oxide according to claim 1, wherein the composite oxide is at least one composite oxide selected from the group consisting of vanadium-tungsten, vanadium-molybdenum, and cerium-tungsten. 5. Denitration catalyst for high temperature exhaust gas. An exhaust gas denitration method, wherein exhaust gas at 400 ° C or higher is circulated through the denitration catalyst for high temperature exhaust gas according to any one of claims 1 to 6 to decompose and remove nitrogen oxides in the exhaust gas.

Images