JPH0474533A - Exhaust gas denitrating catalyst and method - Google Patents

Abstract

PURPOSE:To obtain a zirconia-containing alumina carrier having high activity, reduced in deterioration and having a large pore size by using the zirconia- containing active alumina carrier containing zirconia in a specific ratio and having a definite mean pore size or more. CONSTITUTION:A zirconia-containing alumina carrier containing 10 - 50 wt.% of zirconia on the basis of alumina and having a mean pore size of about 400Angstrom or more is used. Vanadium or tungsten is supported on this carrier as a catalytic component. When the catalyst thus obtained is used in the denitration treatment of exhaust gas with SOx content of 150 ppm or less at about 120 - 450 deg.C in the presence of reducing gas, the exhaust gas is denitrated in a high denitration rate because the catalyst has sufficient denitration activity even at relatively low treatment temp.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a catalyst for exhaust gas denitration and a method for exhaust gas denitration. More specifically, exhaust gas after removing sulfur oxides (hereinafter referred to as SOX) contained in various combustion exhaust gases, including exhaust gas from sulfur-containing fuel combustion equipment such as boilers, through wet desulfurization. Nitrogen oxides (hereinafter referred to as NOX) in
shall be. ) and a flue gas denitrification method using the same.

[Prior Art] Many proposals have already been made for exhaust gas denitrification treatment for selectively and efficiently converting NOx in exhaust gas into harmless nitrogen.

In addition to NOx such as N01NO2, the exhaust gas contains carbon dioxide, -carbon oxide, sOX, and moisture, and also contains dust such as hydrocarbons, halides, oil mist, heavy metals, and dust from the fuel or combustion equipment. is entrained by scattering.

In particular, among these, SOx, arsenic (As) and das) I
This reduces the activity of the catalyst in the catalytic reduction method, and is an obstacle to continuous and efficient operation of flue gas denitration treatment.

Therefore, in conventional flue gas denitrification methods, the so-called clean flue gas, which is the combustion flue gas of LNG-LPG, etc., containing almost no SOX or dust, and the so-called dirty flue gas, which is the flue gas of heavy oil or coal fuel, are distinguished, and the catalyst and the Methods using different conditions have been proposed.

For clean exhaust gas, a catalyst containing 7-AI□03 as the main component as described in, for example, Japanese Patent Publication No. 56-44778 is used, while for dirty exhaust gas, a 1□03-based catalyst described above is susceptible to deterioration due to SOX. Violently, for example, the Tokuko Sho 63
-Titanium (Ti) as described in Publication No. 48584
using a catalyst whose main component is about 200 to 40
It is common practice to process at a temperature range of 0°C.

In addition, the dirty exhaust gas treatment method is mainly a combination of dust removal equipment, denitrification equipment, and desulfurization equipment, but wet flue gas desulfurization treatment lowers the exhaust gas temperature and requires reheating when denitration treatment is performed afterwards. Therefore, from the viewpoint of economy, the denitrification-dust removal method is currently the mainstream.

[Problem to be solved by the invention]

However, in exhaust gas denitrification treatment by catalytic reduction treatment, the treatment method is selected depending on the amount of SOX and dust in the exhaust gas as mentioned above, and especially in the treatment of dirty exhaust gas, in order to prevent a decrease in catalyst activity, it is necessary to use carriers and catalyst metals. The selection of the exhaust gas is important, and preliminary tests depending on the properties of the exhaust gas to be treated may be required.

A first object of the present invention is to provide a novel catalyst for exhaust gas denitrification using a zirconia-containing alumina having a large pore diameter as a carrier, which has high activity and little deterioration.

The second purpose of the present invention is to focus on the fact that the exhaust gas after wet flue gas desulfurization treatment contains less dust and catalyst poisoning substances such as SOX, and to remove dust and It is an object of the present invention to provide a flue gas denitrification method using the novel flue gas denitrification catalyst of the present invention, which adopts a desulfurization treatment-denitration treatment method including steps.

[Means for Solving the Problems] According to the present invention, at a temperature of about 120 to 450°C in the presence of a reducing gas, 10 to 50% by weight of zirconia is added based on alumina used for denitration treatment of exhaust gas with SOX of 150 ppm or less. One or two of vanadium, tungsten, molybdenum, and chromium are added to the zirconia-containing activated alumina support having an average pore diameter of about 400 Å or more as a catalyst component.
A catalyst for exhaust gas denitration is provided, which is characterized in that it supports more than one type of catalyst component.

In addition, exhaust gas with SOX of 150 ppm or less is reduced to approximately 12
Vanadium, tungsten, molybdenum, and chromium as catalyst components are added to a zirconia-containing activated alumina support containing 10 to 50% by weight of zirconia based on reducing gas and alumina and having an average pore diameter of about 400 Å or more in a temperature range of 0 to 450°C. A flue gas denitrification method is provided, which is characterized in that the treatment is carried out in the presence of a flue gas denitrification catalyst, which is characterized in that it supports one or more kinds of catalyst components.

The present invention will be explained in detail below.

The exhaust gas treated in the present invention has a SOx content of approximately 1
If the SOX contained in the exhaust gas to be treated is 150 ppm or more, it is necessary to remove SO2 to about 150 ppm or less in advance. If 150 ppm or more of SOX is contained in the exhaust gas, it will react with alumina, which is a component of the catalyst carrier of the present invention, to generate sulfate, the catalyst activity will decrease, and the desired denitrification treatment will not be achieved.

In the present invention, when the flue gas to be treated contains SOX of 150 ppm or more, the method for desulfurizing SOX to 150 ppm or less may be any known flue gas desulfurization treatment, but in particular, the jet bubbling reactor developed by the applicant may be used. It is preferable to perform flue gas desulfurization treatment using a gas-liquid-solid reaction (Japanese Patent No. 1282007) using (JBR). This JBR
In flue gas desulfurization treatment using
It can stably remove sulfur over a long period of time with a high desulfurization rate of 5% or more, and when dealing with flue gas that contains a large amount of dust emitted from coal-fired boilers, it is extremely effective at removing sulfur and dust at the same time as desulfurization. Efficient flue gas desulfurization treatment is carried out, and the flue gas from the flue gas desulfurization process has a SOX concentration of approximately 150.
ppm or less, and the dust easily becomes less than about 30 μ/Nrrr, making it suitable for exhaust gas to be treated with the exhaust gas denitrification catalyst of the present invention. However, in the present invention, SO in the exhaust gas
X concentration is 150ppm or less, dust concentration is 30+ng/N
rrr or less, there is no need to precede the flue gas desulfurization treatment with the above JBR method or other wet flue gas desulfurization methods;
If the desulfurized exhaust gas after the flue gas desulfurization treatment other than R contains a large amount of dust, the flue gas denitrification treatment of the present invention may be applied after performing the dust removal treatment.

The zirconia-containing activated alumina carrier of the flue gas denitrification catalyst of the present invention is disclosed in, for example, Patent No. 11510 previously proposed by the applicant.
No. 78 (Special Publication No. 57-44605) and No. 15333
58 (Japanese Patent Publication No. 1-16772), that is, a slurry containing aluminum hydroxide is mixed with a predetermined p.
At the H value, aluminum salts such as aluminum nitrate, aluminum chloride, aluminum sulfate, and sodium aluminate, and neutralizing agents such as ammonia, sodium hydroxide, sodium aluminate, sulfuric acid, nitric acid, hydrochloric acid, and aluminum sulfate are used alternately or It is made of alumina and zirconia with an average pore diameter of 400 Å or more obtained by simultaneously adding boehmite to rapidly grow crystals and controlling the pore volume and pore diameter. Those described in publications can be used.

The alumina carrier obtained by the above method has an extremely large average pore diameter of 400 Å or more, compared to carriers with an average pore diameter of 100 Å or less, which are generally used for flue gas denitrification of clean exhaust gas, and is suitable for removing reducing gas in denitrification treatment. It is effective to have such a large pore diameter in the flue gas denitrification reaction, in which NOX easily diffuses into the catalyst pores and the rate-determining rate is determined by the diffusion of these reactants.

In addition, the present invention is particularly aimed at exhaust gas treatment after flue gas desulfurization, and although most of the dust is removed in the desulfurization process, the reaction between the dust that remains without being removed, or the residual SOX and reducing gas such as ammonia is The carrier of the present invention, that is, the catalyst, has a large average pore diameter even if the exhaust gas contains trace amounts of ammonium sulfate, etc. produced by the reaction of SOx, and aluminum sulfate and other sulfates produced by the reaction between SOx and the catalyst. This has the advantage that catalyst pores are less likely to be clogged by dust or the like.

Furthermore, in the catalyst of the present invention, when the activated alumina constituting the carrier is obtained, for example, by the above-mentioned manufacturing method, the boehmite crystal particles are coagulated and bonded by activated aluminum hydroxide during the manufacturing process, resulting in strong mechanical strength. In addition, the zirconia content is further increased to create a zirconia-containing activated alumina which has extremely high strength even if the average pore diameter is 400 Å or more due to the strength-enhancing effect of zirconia as described in the above-mentioned Japanese Patent Application Laid-Open No. 60-25545. Since it is used as a carrier, there is little powdering during denitrification treatment, which is extremely preferable.

In the present invention, the catalyst components are vanadium (V), tungsten (W), molybdenum (Mo) and chromium (C
r), and is supported on the carrier as an oxide of each component. The supported amount is 0.01 to 2.0% by weight, preferably 0.05 to 0.0% by weight as the oxide of each component.
It is in the range of 5% by weight.

The catalyst of the present invention using a zirconia-containing activated alumina carrier with a large average pore diameter has conventionally been mainly used for hydrodesulfurization of heavy hydrocarbons and hydrogenation treatment of hydrogenated membrane metals. , which has never been applied to flue gas denitrification treatment until now, is the first attempt by the inventors to apply it, and the present invention also reveals for the first time that it has an excellent effect in flue gas denitrification treatment. It is.

To prepare the steel catalyst of the present invention, activated alumina is first prepared by the method described in the above-mentioned patent publication. That is, for example, seed aluminum hydroxide is added to an aluminum sulfate aqueous solution with sodium aluminate to produce an aluminum hydroxide-containing slurry, and the slurry is brought to a pH of 6 to IO, and aluminum sulfate is added while stirring and maintaining the temperature at 50 ° C. or higher. Then that p
Activated alumina is obtained by filtering, washing, molding, drying, and sintering the boehmite slurry obtained by reducing the pH to 6 or less and then adding sodium aluminate in the same manner to maintain the pH at 6 to 9 several times. can be obtained.

In addition, the aluminum hydroxide-containing slurry produced as described above is maintained at a pH of 8 to 11 and a temperature of 50°C or higher.
While stirring, the boehmite slurry obtained by simultaneously adding, for example, aluminum sulfate and sodium aluminate so as to maintain p)I at 8 to 11, is filtered, washed, shaped,
Activated alumina can be obtained by drying and firing.

In preparing the above-mentioned activated alumina, the amount of aluminum salt such as aluminum sulfate added to the seed aluminum hydroxide and the neutralizing agent such as sodium aluminate, and the number of additions when they are added alternately, should be appropriately selected. By adjusting the pore volume and average pore diameter of the alumina support obtained, it is possible to adjust the pore distribution so that the average pore diameter is on the large pore diameter side of about 400 Å or more.

The carrier of the present invention can be obtained by adding zirconia to the activated alumina obtained as described above. The method of incorporating zirconia into activated alumina is as described in the above-mentioned Japanese Patent Application Laid-Open No. 60-25545. It can be carried out by an impregnation method, a deposition method, a coprecipitation method, etc. by adjusting the weight %.

Further, the method for molding the catalyst of the present invention may be arbitrary, and additives such as various molding aids may be added. The shape of the molded body is not particularly limited, and may be any shape such as spherical, cylindrical, prismatic, honeycomb, cylindrical, or irregular shapes such as star, prismatic cylinder, and T-shape.

The catalyst component may be supported by any method such as an impregnation method, a spraying method, or an ion exchange method. For example, an aqueous solution of inorganic acid salts such as nitrates and sulfates, organic acid salts, chlorides, metal salts, etc. can be used. The above compound may also be added to the washed boehmite cake obtained in the preparation of the alumina carrier.

The flue gas denitrification treatment method of the present invention is a selective reduction contact method in which the flue gas that has been subjected to the flue gas desulfurization treatment is brought into contact with a reducing gas such as ammonia using the catalyst described above, and NOX in the flue gas is reduced to nitrogen. Any known flue gas denitrification device can be applied within the reaction temperature range of 120 to 450°C.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to Examples.

However, the present invention is not limited to the following examples.

Example 1 350'g of aluminum chloride (hexahydrate) was dissolved in deionized water as 11 and heated and maintained at 90°C.

On the other hand, in a separate container, 180 g of sodium hydroxide was dissolved in deionized water and similarly heated and maintained at 90° C. as IP.

Next, in a stainless steel mixing container equipped with a heat insulator, 0.72% of 90°C deionized water and 0.2% of the above aluminum chloride aqueous solution were added.
IP, and add the above sodium hydroxide aqueous solution 0 while stirring.
．． 2n was added. The pH of the resulting viscous slurry of seed aluminum hydroxide was 9.

Next, the obtained slurry was stirred and held for 3 minutes, and then the aluminum chloride aqueous solution 0.21 g was added to the aluminum chloride aqueous solution while stirring.
was added and held for 1 minute, then the above sodium hydroxide aqueous solution 0
．． 21 was added and held for 1 minute. This operation was repeated 25 times, and the resulting slurry was filtered, washed and filtered with deionized water to obtain a dehydrated boehmite cake.

The above dehydrated hemite cake was molded into an extruder with a diameter of 1.1 mm.
After molding into a cylinder of mmφ and drying at 120°C overnight,
An alumina molded body was obtained by firing at 550°C for 2 hours. The obtained molded body had a diameter of 0.87 mm, an average pore diameter of 530 mm, and a pore volume of 1.27 cc/g. Also, the side crushing strength measured under load using a disk with a diameter of 5 mm was 0.
．． It weighed 11 kg.

Next, zirconia chloride (ZrOCj2 z ・88zO
) 30 g of the alumina molded body obtained above was immersed in 100 mjt of a solution prepared by dissolving 40 g of alumina in deionized water for 1 hour.
Thereafter, the aqueous solution was removed by filtration, dried at 120°C for 5 hours, and then calcined at 500°C for 3 hours. The obtained zirconia-containing alumina molded body contained 17.8% by weight of zirconia, 21.7% by weight based on alumina, and had an average pore diameter of 54%.
4 people, pore volume was 0.83 cc/g. Moreover, the crushing strength was 0.68 kg.

The zirconia-containing alumina molded body obtained above was
After being immersed in a 0.2% by weight vanadyl oxalate aqueous solution as O5, dried at room temperature, and then fired at 500°C for 3 hours to obtain v20. A catalyst A in which 0.2% by weight of was supported was obtained.

Similarly, a catalyst B in which 0.2% by weight of M2O3 was supported on a zirconia-containing alumina carrier was obtained by using an aqueous ammonium molybdate solution instead of an aqueous solution of vanadyl oxalate.

Example 2 41203 '114 degrees 80 g/j2 aluminum sulfate aqueous solution 0.051! Add 11 to 10ff of deionized water, heat to 90°C and hold, and add AIz while stirring.
03 Concentration 69 Concentration 69 A/l Sodium phosphate aqueous solution 0.35
fi was added to obtain a slurry of seed aluminum hydroxide with a pH of 10.

The obtained slurry-like seed aluminum hydroxide was heated to a temperature of 90°C.
While stirring at ℃, Al was maintained at pH 9~IO.
2O3 concentration 8g/! aluminum sulfate aqueous solution at 23A
/hr, and A]203 concentration 69g/I! , aqueous solution of sodium aluminate was simultaneously added at 2.7 e/hr continuously for 10 hours using a constant rate syringe. The resulting slurry was filtered, washed and filtered with deionized water to obtain a dehydrated hemi 1-cake.

The dehydrated boehmite cake was molded into a cylindrical shape using an extruder with a die having a diameter of 1.6 mm, and a zirconia-containing alumina molded body was obtained in the same manner as in Example 1.

The obtained zirconia-containing alumina molded body contained 27% by weight of zirconia based on alumina, and had an average pore diameter of 680.
The pore volume was 0.61 cc/g.

Moreover, the crushing strength was 0.82 kg.

Catalyst C1 supported 0.5% by weight of V2O4, 50.1% by weight of V2O, and 0.0.1% by weight of V2O in the same manner as in Example 1 using the above zirconia-containing alumina molded body as a carrier.
A catalyst supporting % by weight was obtained.

Example 3 0.15 ffi of a 11.6 wt% sulfuric acid aqueous solution was added to deionized water Ion, heated to 80"C and held, and while stirring, a 0.15 ffi aqueous solution of sodium aluminate with an Al2O3 concentration of 69 g/l was added. 41!, to obtain r))410 seed aluminum hydroxide slurry.

The obtained slurry-like seed aluminum hydroxide was heated to a temperature of 80°C.
11.6 wt % sulfuric acid aqueous solution was added at 6.12/hr to maintain the pH at 9.5 to 10 while stirring at a temperature of 6.12 g/hr, and the Al2O3 concentration was 69 g/I! An aqueous solution of sodium aluminate was added continuously for 12 hours in the same manner as in Example 2 at a rate of 11.11/hr. The obtained slurry was used in Example 2.
An alumina molded body was obtained in the same manner as above.

The obtained alumina molded body was made into a zirconia-containing alumina molded body in the same manner as in Example 1. The obtained zirconia-containing alumina molded body contained 14.7% by weight of zirconia based on alumina, had an average pore diameter of 480, and a pore volume of 0.
．． It was 90 cc/g. Also, the crushing strength is 0.61
It was kg.

Using the obtained zirconia-containing alumina molded body as a carrier,
Catalyst E supporting 3% by weight of vzoso and 0.02% by weight of WO3 was obtained by a dipping method.

Example 4 A flue gas denitrification test was conducted using catalysts A, B, C, D, and E obtained as described above.

In the flue gas denitrification test, first, the test simulated flue gas shown below was subjected to continuous desulfurization treatment at a desulfurization rate of 92% using JBR, which performs the gas, liquid, and solid reactions described above in the same equipment. did.

The denitrification test conditions and test results were as follows.

(1) Test simulated exhaust gas 0□ concentration 5 (volχ) NOX concentration
250 (ppm) SO, concentration 600
(p concave) Dust 200 (mg/Nm3) (2) Desulfurization treatment gas NOX concentration 235 (ppm) SOX concentration
48 (ppm) Dust 3
(mg/Nm') (3) Added reducing gas: NH, concentration 23
0 ppm (4) S, V, (Gas amount Nρ/hour ÷ Catalyst capacity 5000 hr' (5) Processing gas (after 50 hr) Exhaust gas denitrification is performed at relatively low processing temperature and has sufficient denitrification activity. Further, by using the catalyst of the present invention, all types of combustion exhaust gas can be subjected to exhaust gas denitrification treatment at a high denitrification rate.

Claims (3)

[Claims] (1) S
Contains 10 to 50% by weight of zirconia based on alumina used for denitration treatment of exhaust gas with Ox 150 ppm or less,
A catalyst for exhaust gas denitration, characterized in that one or more catalyst components of vanadium, tungsten, molybdenum, and chromium are supported on a zirconia-containing activated alumina carrier having an average pore diameter of about 400 Å or more. (2) The above flue gas has been subjected to wet flue gas desulfurization in advance,
The catalyst for exhaust gas denitration according to claim 1, wherein the amount of dust in the exhaust gas is 30 mg/Nm^2 or less. (3) Exhaust gas with SOx 150ppm or less, approximately 120~
In the temperature range of 450°C, it contains 10-50% by weight of zirconia based on reducing gas and alumina, and has an average pore diameter of about 40%.
Treatment in the presence of a catalyst for exhaust gas denitration, characterized in that one or more catalyst components of vanadium, tungsten, molybdenum, and chromium are supported on a zirconia-containing activated alumina carrier having a diameter of 0 Å or more. A flue gas denitrification method characterized by: