JPH0474532A - Exhaust gas denitrating catalyst and method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a catalyst for exhaust gas denitrification and a flue gas denitrification method. 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.

[Conventional technology]

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 N01NO□, 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. species are dispersed and entrained.

In particular, among these, SOx, dust, and heavy metals such as arsenic (As) reduce the activity of the catalyst in the catalytic reduction method, and are an obstacle to continuous and efficient exhaust gas denitrification treatment.

Therefore, in conventional flue gas denitrification methods, a distinction is made between so-called clean exhaust gas, which is combustion exhaust gas such as LNG-LPG, which contains almost no SOx or dust, and so-called dirty exhaust gas, which is combustion exhaust gas from heavy oil or coal fuel. Methods using different conditions have been proposed.

For clean exhaust gas, a catalyst mainly composed of 7-At□03 as described in Japanese Patent Publication No. 56-44778 is used, while for dirty exhaust gas, the above Ah (h photocatalyst is severely degraded by SOx, For example, special public service in 1983-
As described in Japanese Patent No. 48584, a catalyst containing titanium (Ti) as a main component is used, and in both cases about 250 to 400
It is common practice to process at a temperature range of ℃.

In addition, the dirty exhaust gas treatment method is mainly a combination of dust removal, denitrification, and desulfurization, but wet flue gas desulfurization lowers the exhaust gas temperature and requires reheating if denitration 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 the activity of the catalyst, it is necessary to 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 exhaust gas denitrification catalyst that is highly active, exhibits little deterioration, and uses a large pore size alumina as a carrier.

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 catalyst poisoning substances such as dust and SO, and contrary to the mainstream of conventional flue gas denitrification treatment methods, 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 employs a desulfurization treatment-denitration treatment method including a dust removal process.

[Means to solve the problem]

According to the present invention, an aluminum salt is added to an aluminum hydroxide-containing slurry maintained at a temperature of about 120 to 450 degrees Celsius and a pH of 6 to 11 and above 50 degrees Celsius, which is used for denitration treatment of exhaust gas with SOX of 150 ppm or less, in the presence of a reducing gas. One or more of vanadium, tungsten, molybdenum, and chromium as a catalyst component is added to the alumina support obtained by repeating the step of adjusting the pH to 5 or lower or 11 or higher by alternately adding a neutralizing agent and the step of returning the pH to 6 to 11 several times. Provided is a catalyst for exhaust gas denitrification characterized by supporting two or more types of catalyst components.

In addition, S
OX An aluminum salt, at least one of which substantially contains a sulfate group, and a neutralizing agent are added to an aluminum hydroxide-containing slurry, which is maintained at a temperature of 50°C or higher and has a pH of 8 to 11, which is used for denitrification treatment of exhaust gas with an aluminum molar ratio of OX 150 ppm or less. For exhaust gas denitration, characterized in that one or more catalyst components of vanadium, tungsten, molybdenum, and chromium are supported on an alumina carrier obtained by adding at a rate of 20 to 500%/hr. A catalyst is provided.

Furthermore, in the presence of each of the above catalysts and reducing gas, SOx after passing through a wet flue gas desulfurization process at a temperature of about 120 to 450°C.
A flue gas denitrification method is provided, which is characterized in that it treats flue gas having a concentration of 150 ppm or less.

The present invention will be explained in detail below.

The exhaust gas treated in the present invention has a SOx content of about 15
If the SOx contained in the exhaust gas to be treated is 150 ppm or more, it is necessary to remove the SOx to about 150 ppm or less in advance. 1 in exhaust gas
If 50 ppm or more of SOx is contained, it will react with alumina, which is 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 exhaust 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
With a high desulfurization rate of 0% or more, it can be removed stably over a long period of time, 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 an SOx concentration of approximately 150.
ppm or less, and the dust is also about 10 mg/Nm' or less, which is suitable for exhaust gas to be treated with the exhaust gas denitrification catalyst of the present invention.

The alumina carrier of the exhaust gas denitrification catalyst of the present invention can be prepared by a specific method, namely, the patent No. 1151078 (Japanese Patent Publication No. 1983-44605) and No. 1533358 (Japanese Patent Publication No. 1-16772) previously proposed by the applicant. An aluminum salt such as aluminum nitrate, aluminum chloride, aluminum sulfate, sodium aluminate, etc., and ammonia, sodium hydroxide, sodium aluminate, sulfuric acid,
Boehmite can be obtained by adding neutralizing agents such as nitric acid, hydrochloric acid, and aluminum sulfate alternately or simultaneously to rapidly grow boehmite crystals and control the pore volume and pore diameter.

The alumina carrier obtained by the above method has an average pore diameter of 100 Å, which is generally used for flue gas denitration of clean exhaust gas.
Compared to the following carriers, the average pore diameter is larger, for example, 100
Since the average pore diameter is adjusted to be larger than Å, preferably 150 to 300, reducing gas and N to be removed are
Having a large pore diameter is effective in facilitating the diffusion of Ox into the catalyst pores and in flue gas denitrification, which is the rate-limiting reaction for 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 of the remaining dust or residual SOx with reducing gas such as ammonia Even if the exhaust gas contains trace amounts of ammonium sulfate, aluminum sulfate, and other sulfates produced by the reaction between SOx and the catalyst, the carrier of the present invention, that is, the catalyst, has a large average pore diameter. This has the advantage that catalyst pores are less likely to be clogged by dust.

Furthermore, in the catalyst of the present invention, boehmite crystal particles are agglomerated and bonded with activated aluminum hydroxide during the manufacturing process of the carrier, so the mechanical strength of the obtained carrier is strong and there is less pulverization when used as a catalyst, which is 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 using the alumina carrier with a large pore size in the present invention has conventionally been mainly used for hydrodesulfurization of heavy hydrocarbons and hydrogenation treatment of hydrogenated membrane metals, etc. It has never been applied to smoke denitrification treatment, and this is the first time the inventors have attempted to apply it, and the present invention has also revealed for the first time that it has an excellent effect in flue gas denitrification treatment.

To prepare the catalyst of the present invention, an alumina carrier is prepared by the method described in the above 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 aluminum sulfate is added to the slurry while maintaining and stirring the slurry at a pH of 6 to 10 and a temperature of 50°C or higher. The resulting boehmite slurry is filtered, washed, molded, dried, and calcined by adding sodium aluminate in the same manner to maintain the pH at 6 to 9 several times. An alumina carrier can be obtained by

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.
An alumina carrier can be obtained by filtering, washing, molding, drying, and calcining a boehmite slurry obtained by simultaneously adding, for example, aluminum sulfate and sodium aluminate while stirring to maintain the pH at 8 to 11.

In preparing the above-mentioned catalyst carrier, 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. According to
The pore volume and average pore diameter of the resulting alumina support were adjusted, and both were made relatively large so that the average pore diameter was approximately 130 to 2.
00 has a pore distribution on the large pore diameter side and can be adjusted sharply.

Further, the molding method 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 spherical, cylindrical, prismatic, honeycomb, or
It may be cylindrical or may have an irregular shape such as a star shape, a rectangular tube shape, or a T-shape.

The catalyst component may be supported by any method such as an impregnation method, a spraying method, an ion exchange method, etc., and a suitable compound of the catalyst component, e.g. Aqueous solutions 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, brought to 1°C, 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 heated to 90° C. in the same manner as No. 11.

Next, in a stainless steel mixing container with a heat insulator, 0.71% of 90°C deionized water and 0.2% of the above aluminum chloride aqueous solution!
Add the above sodium hydroxide aqueous solution 0.21% while stirring.
was added. The pH of the resulting viscous slurry of seed aluminum hydroxide was 9.

Next, the resulting slurry was stirred and held for 3 minutes, and then, while stirring, the aluminum chloride aqueous solution was mixed with 0.2!
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 six times, and the resulting slurry was filtered, washed and filtered with deionized water to obtain a dehydrated boehmite cake.

The dehydrated boehmite cake was molded into a cylindrical shape using an extruder with a die having a diameter of 2 mm, dried at 120°C for 4 hours, and then fired at 600°C for 1 hour to obtain an alumina molded body.

The obtained molded body had an average pore diameter of 147 mm and a pore volume of 1.
It was 16 cc/g. The side crushing strength measured under load using a disk with a diameter of 5fi was 2.1 kg.

Next, the alumina molded body obtained above was immersed in an aqueous vanadyl oxalate solution, dried at room temperature, and then calcined at 500°C for 3 hours to obtain a catalyst in which 0.2% by weight of v205 was supported on the alumina support. I got an A.

Similarly, an aqueous solution of ammonium molybdate was used instead of an aqueous solution of vanadyl oxalate, and MoO
A catalyst B was obtained in which 0.2% by weight of 2 was supported.

Example 2 A120: l aluminum sulfate aqueous solution with a concentration of 80 g/l 0.051! , deionized water 10I! , added to 90
Heating and holding at ℃, A1□03 concentration 69 while stirring.
0.35 n of a sodium aluminate aqueous solution of 2 g/2 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 ℃, the Al
An aluminum sulfate aqueous solution with a 2O3 concentration of 8 g/ffi was fed at a rate of 0.291/hr, and a sodium aluminate aqueous solution with an AlO3 concentration of 69 g/l was simultaneously fed at a rate of 0.20 E/hr continuously for 3 hours using a constant rate injector. Added. The resulting slurry was filtered, washed and filtered with deionized water to obtain a dehydrated boehmite cake.

The dehydrated boehmite cake was molded into a cylinder using an extruder with a die having a diameter of 1.6 mm, dried at 120°C for 6 hours, and then fired at 500°C for 3 hours to obtain an alumina molded body. The obtained molded body had an average pore diameter of 180 mm, a pore volume of 1.01 cc/g, and a crushing strength of 2.9 kg.
It was 11.

Catalysts C1 and V were loaded with 2% by weight of VzOso in the same manner as in Example 1 using the above alumina molded body as a carrier.
A catalyst was obtained which supported 2% by weight of zOso and 1% by weight of CrzO,.

Example 3 11.6% by weight sulfuric acid aqueous solution 0.15I! , was added to deionized water 101, heated to 80°C, maintained, stirred, and then added 1□03 sodium aluminate aqueous solution 0.42 with a concentration of 69 g/l to hydroxylate the seeds of PHIO. An aluminum slurry was obtained.

The obtained slurry-like seed aluminum hydroxide was heated to a temperature of 80°C.
11.6% by weight sulfuric acid aqueous solution was added at 0.15 A/hr3 while stirring to maintain the pH at 9.5 to 10.
Then, an aqueous solution of sodium aluminate of 69 g# of A1403:A was added continuously for 9 hours in the same manner as in Example 2 at a rate of 0.2742/hr. The obtained slurry was treated in the same manner as in Example 2 to obtain an alumina molded body. The obtained molded body had an average pore diameter of 238 mm and a pore volume of 1.12 cc/
g, and the crushing strength was 2.7 kg.

v2 by dipping method using the obtained alumina molded body as a carrier.
o, 0.2% by weight, WOffo, 1% by weight, CrzO3
o.

Catalyst E carrying 1% by weight was obtained.

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 93% 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 CO2 concentration: 12 (volχ)HzO concentration: 8 (volχ)0□ Concentration:
6 (volχ)NoX concentration: 2
00 (ppm) SOx concentration: 101000 (p
P dust (fly ash): 5 0 0
(mg/Nm3) (2) Desulfurization treatment gas NoX concentration: 195 (ppm) SOx concentration:
70 (ppm) dust (fly 7 fl)
: 4 (mg/Nm3) (3) Added reducing gas: NH, concentration: 190 ppm (4) S, V,
(Gas amount N1./hour ÷ catalyst capacity! 5000 hr') (5) Processing gas (after 5 hr) Accordingly, all combustion exhaust gases can be subjected to exhaust gas denitrification treatment at a high denitrification rate.

Claims (5)

[Claims] (1) S
A step of alternately adding an aluminum salt and a neutralizing agent to an aluminum hydroxide-containing slurry maintained at 50°C or higher at a pH of 6 to 11 used for denitration treatment of exhaust gas with an Ox content of 150 ppm or less to make the pH 5 or less or 11 or more;
A catalyst for exhaust gas denitration, characterized in that one or more catalyst components of vanadium, tungsten, molybdenum, and chromium are supported on an alumina carrier obtained by repeating the step of returning to step 11 multiple times. (2) At a temperature of about 120 to 450°C and in the presence of reducing gas
An aluminum salt, at least one of which substantially contains a sulfate group, and a neutralizing agent are added to an aluminum hydroxide-containing slurry, which is maintained at a temperature of 50° C. or higher and has a pH of 8 to 11, which is used for denitration treatment of exhaust gas with an Ox content of 150 ppm or less, at an aluminum molar ratio. A catalyst for exhaust gas denitration, characterized in that one or more catalyst components of vanadium, tungsten, molybdenum, and chromium are supported on an alumina carrier obtained by adding at a rate of 20 to 500%/hr. . (3) Claim (1) or (1) wherein the exhaust gas has been subjected to wet desulfurization in advance in a gas-liquid-solid reaction treatment step using a jet bubbling reactor, and the amount of dust in the exhaust gas is 10 mg/Nm^2 or less. 2) The exhaust gas denitrification catalyst described above. (4) Exhaust gas with SOx 150ppm or less
5 at a temperature range of 450°C, reducing gas and pH 6-11.
An alumina carrier obtained by repeating the steps of alternatingly adding an aluminum salt and a neutralizing agent to an aluminum hydroxide-containing slurry kept at 0° C. or higher to make the pH 5 or less or 11 or more, and the step of returning the pH to 6 to 11 several times. One or two of vanadium, tungsten, molybdenum and chromium.
A flue gas denitrification method characterized by processing in the presence of a catalyst supporting more than one type of catalyst component. (5) Exhaust gas with SOx 150ppm or less, approximately 120~
5 at a temperature range of 450°C, reducing gas and pH 8-11.
An aluminum salt, at least one of which substantially contains a sulfate group, and a neutralizing agent are added to an aluminum hydroxide-containing slurry maintained at 0° C. or higher at an aluminum molar ratio of 20 to 500.
In the presence of a catalyst for exhaust gas denitrification, which is characterized in that one or more catalyst components of vanadium, tungsten, molybdenum, and chromium are supported on an alumina carrier obtained by adding at a rate of %/hr. A flue gas denitrification method characterized by processing with.