JP2001113170A - Method for manufacturing for denitration catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing for a denitration catalyst capable of removing NOx, excellent in durability and with the oxidation of sulfur dioxide to sulfur trioxide strictly inhibited. SOLUTION: The denitration catalyst containing the oxides of silicon, titanium, tungsten and vanadium for removing NOx in an exhaust gas is manufactured by the following method. Namely, a vanadium compound is added to a multiple oxide (WO3-SiO2) of tungsten and silicon prepared by previously depositing tungsten on the oxide of silicon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a denitration catalyst, that is, a catalyst for removing nitrogen oxides (NO _x ) in exhaust gas.

[0002]

2. Description of the Related Art As a method of removing nitrogen oxides from exhaust gas which has been put into practical use at present, harmless nitrogen is removed by catalytically reducing nitrogen oxides in exhaust gas on a denitration catalyst using a reducing agent such as ammonia or urea. The so-called SCR method for selective catalytic reduction to decompose into water and water is common. In recent years, as environmental pollution caused by nitrogen oxides, as represented by acid rain, has become more serious worldwide, it has been required to improve the efficiency of denitration technology.

[0003] In view of such circumstances, the present applicant has proposed that a binary oxide composed of titanium and silicon and / or a ternary oxide composed of titanium, zirconium and silicon be added to vanadium, tungsten, molybdenum, and uranium. , At least one element selected from the group consisting of copper, iron, chromium, manganese and cerium, or tin, zinc, titanium, zirconium, nickel, cobalt, niobium, tantalum, phosphorus, boron, bismuth, antimony, alkali A catalyst for purifying nitrogen oxides comprising at least one element selected from the group consisting of metals and alkaline earth metals (JP-B-57-3053)
No. 2) and sulfuric acid in at least one hydrated oxide selected from the group consisting of binary hydroxides composed of titanium and silicon and / or ternary hydroxides composed of titanium, zirconium and silicon. And / or an oxide of at least one element selected from the group consisting of vanadium oxide, tungsten, molybdenum, tin and cerium is added to the sulfur-containing composite oxide obtained by heat treatment in the presence of an ammonium sulfate compound. Catalyst that suppresses the oxidation reaction of sulfur dioxide to sulfur trioxide and has excellent durability in a nitrogen oxide purification catalyst comprising
Further, in a denitration catalyst containing a titanium oxide, a vanadium oxide and / or a tungsten oxide, a fine peak having a peak of a peak of a pore diameter distribution in a range of 0.01 to 0.05 μm. Hole group and 0.1 ~
A pore group having at least two pore groups with a pore group having a peak of a pore diameter distribution in a range of less than 0.8 μm, and a peak of a pore size distribution in a range of 0.01 to 0.05 μm. The ratio of the peak intensity of the pore size distribution of the pore group having the peak of the pore size distribution in the range of 0.1 to less than 0.8 μm with respect to the peak intensity of the pore size distribution of the pore group having the apex is 0.4 or more. Among certain catalysts, a denitration catalyst capable of efficiently removing lean nitrogen oxides in exhaust gas (Japanese Unexamined Patent Publication No.
No. 235206) has already been filed.

All of these catalysts have excellent nitrogen oxide removal performance, low sulfur oxide oxidation performance, and excellent durability, but have higher performance and higher durability. The appearance of a catalyst is preferred. JP-A-59-21342 discloses a method for preparing a denitration catalyst in which a ternary oxide of titanium, tungsten and silicon is formed, and then a vanadium compound is added to the oxide. It is described that the denitration catalyst prepared by this method has a high nitrogen oxide removal performance and a low sulfur oxide oxidation performance, but the oxidation performance of the sulfur oxide is not sufficiently low. There is still room for improvement from the viewpoint of durability.

[0005]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a denitration system which is more excellent in removing nitrogen oxides and more durable, and in which the oxidizing performance of sulfur dioxide to sulfur trioxide is extremely suppressed. It is to provide a method for producing a catalyst.

[0006]

Means for Solving the Problems As a result of intensive experiments, the present inventors have found that a composite oxide of tungsten and silicon (WO ₃ —SiO ₂ ) prepared in advance by supporting tungsten on a silicon oxide. The present inventors have found that the above object can be achieved by including a step of adding a vanadium compound to the present invention, and completed the present invention.

That is, a method for producing a denitration catalyst according to the present invention is a method for producing a denitration catalyst for removing nitrogen oxides in exhaust gas, comprising oxides of silicon, titanium, tungsten and vanadium. And a step of adding a vanadium compound to a composite oxide of tungsten and silicon (WO ₃ —SiO ₂ ), which is prepared by supporting tungsten on a silicon oxide in advance.

Further, a composite oxide of tungsten and silicon (WO ₃ —SiO ₂ ) prepared by previously supporting tungsten on a silicon oxide, and a composite oxide prepared by supporting titanium on a silicon oxide in advance. Further, a vanadium compound is added after mixing a composite oxide of titanium and silicon (TiO ₂ —SiO ₂ ).

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The denitration catalyst produced according to the present invention is a catalyst containing oxides of silicon, titanium, tungsten and vanadium. Silicon oxide is 10 to 50% by weight, titanium oxide is 10 to 90% by weight, tungsten oxide is 1 to 25% by weight, vanadium oxide is 0.1 to 1%.
Preferably it is 5% by weight.

As a supply source of the catalyst, a silicon source may be appropriately selected from colloidal silica, water glass, fine particle silicon, inorganic silicon compounds such as silicon tetrachloride and organic silicon compounds such as tetraethyl silicate. it can. As the titanium source, any inorganic or organic compound can be used as long as it produces a titanium oxide by firing.For example, inorganic titanium compounds such as titanium tetrachloride and titanium sulfate or titanium oxalate, tetraisopropyl An organic titanium compound such as titanate can be used. In addition, as for the tungsten source and the vanadium source, any of inorganic and organic compounds may be used as long as they generate an oxide by firing.
For example, hydroxide containing each metal, ammonium salt,
Oxalates, halides, sulfates, nitrates and the like can be used as appropriate.

In the present invention, first, tungsten is supported on a silicon oxide to prepare a composite oxide of tungsten and silicon (WO ₃ —SiO ₂ : hereinafter referred to as “tungsten-silica composite oxide”). By preparing tungsten-silica composite oxide by previously supporting tungsten on silicon oxide in this way, the tungsten is more densely packed on the carrier than in the case of preparing conventionally supported tungsten in a liquid. It is considered that the catalyst is excellent in activity and durability of the catalyst.

In the present invention, a catalyst is produced by adding a vanadium compound to the above-mentioned tungsten-silica composite oxide (WO ₃ —SiO ₂ ), and the method of adding titanium is not particularly limited. For example, the above-mentioned tungsten-silica composite oxide (WO ₃ —SiO ₂ ) and a titanium-silicon composite oxide (TiO ₂ —SiO ₂ : hereinafter referred to as “titania”) prepared by previously supporting titanium on a silicon oxide. -Referred to as "silica composite oxide")
A method of adding a vanadium compound, a method of mixing the above-mentioned tungsten-silica composite oxide (WO ₃ —SiO ₂ ) with titanium oxide, and then adding a vanadium compound may be mentioned. composite oxides (WO ₃ -SiO ₂₎ titania - after mixing silica composite oxide and (TiO ₂ -SiO _2), a method of adding a vanadium compound is particularly preferable.

The method for preparing the tungsten-silica composite oxide and the titania-silica composite oxide in the present invention is not particularly limited, but can be prepared by a coprecipitation method or the like. For example, a tungsten-silica composite oxide is prepared by adding an aqueous solution of ammonium metatungstate to a solution of silica sol to form a uniform solution, adding an acid such as nitric acid or sulfuric acid to form a precipitate, washing the precipitate slurry with water, and filtering. 50-150 ° C, preferably 60
To 120 ° C., and then fired at 200 to 500 ° C., preferably 250 to 400 ° C.
A silica composite oxide can be obtained.

The titania-silica composite oxide forms a precipitate by adding an aqueous solution of titanyl sulfate to a solution of the silica sol.
Drying at 150 ° C., preferably 60-120 ° C.,
The target titania-silica composite oxide can be obtained by firing at 300 to 650 ° C, preferably 400 to 550 ° C.

The tungsten-silica composite oxide obtained by the above-mentioned preparation method or a mixture of the tungsten-silica composite oxide and the powder of the titania-silica composite oxide are mixed with vanadium, for example, ammonium metavanadate. An aqueous solution containing vanadium dissolved in an aqueous oxalic acid solution is added together with a forming aid, mixed, kneaded, and formed into a honeycomb shape by an extruder. After drying the molded product preferably at 50 to 120 ° C., preferably at 300 to 650 ° C., more preferably at 3 to 60 ° C.
The desired catalyst can be obtained by calcining at 50 to 550 ° C in an air atmosphere for preferably 1 to 10 hours, more preferably 2 to 6 hours.

As another method, a tungsten-silica composite oxide or a mixture of the same and a titania-silica composite oxide is previously formed into a honeycomb shape and fired.
A method of impregnating and supporting an aqueous solution containing vanadium can also be adopted. The catalyst produced in this manner contains silicon, titanium, tungsten and vanadium oxides, uses silicon oxide as a carrier, and contains titanium oxide, tungsten oxide and vanadium oxide as active components. .

The shape of the catalyst is not limited to the honeycomb shape, but can be used by shaping into a desired shape such as a plate, a corrugated plate, a net, a column, or a cylinder. The denitration catalyst produced according to the present invention has excellent decomposition activity of nitrogen oxides discharged from boilers, incinerators, gas turbines, diesel engines and various industrial processes, and is suitably used for treating exhaust gas containing these nitrogen oxides. . Furthermore, these exhaust gases generally contain sulfur dioxide, and when the sulfur dioxide is oxidized to sulfur trioxide, problems such as corrosion of the device occur. As compared with a denitration catalyst obtained by forming a ternary oxide of titanium, tungsten and silicon and then adding a vanadium compound to the oxide as disclosed in JP-A-59-21342, It is more preferably used because of its low ability to oxidize sulfur dioxide to sulfur trioxide.

In order to carry out denitration using the denitration catalyst produced according to the present invention, the denitration catalyst is brought into contact with exhaust gas in the presence of a reducing agent such as ammonia or urea to reduce and remove nitrogen oxides in the exhaust gas. . The conditions at this time are not particularly limited, and the reaction can be carried out under conditions generally used for this type of reaction. Specifically, the type of exhaust gas,
It may be appropriately determined in consideration of the properties, the required nitrogen oxide decomposition rate, and the like.

The space velocity of the exhaust gas is usually 100
~ 100000Hr^-1(STP), preferably 2
00 ~ 50000Hr^-1(STP). 100hr
^-1If less, the processing equipment becomes too large and inefficient
And 100000Hr ^-1Above which the decomposition efficiency is low
Down.

[0020]

The present invention will be specifically described below with reference to examples. Example 1 First, 12 kg of ammonium metatungstate solution (manufactured by Nippon Inorganic Chemical Industry Co., Ltd., containing 50 wt.% In terms of WO ₃ ) and silica sol (Snowtex-30, manufactured by Nissan Chemical Co., Ltd., S
iO ₂ converted 30 wt.% containing) 46.7kg, further industrial aqueous ammonia (25wt.% NH ₃ content) 5.28 kg
And 7.92 liters of water were mixed to prepare a homogeneous solution.
To this solution, 3.88 kg of industrial concentrated sulfuric acid was gradually added dropwise with stirring to form a precipitate. At this time, the temperature of the solution was kept at 60 ° C. or lower. After the dropwise addition of concentrated sulfuric acid, it was confirmed that the pH of the coprecipitated slurry was between 4 and 6. If the pH was higher than 6, the pH was adjusted by further adding concentrated sulfuric acid. The thus obtained coprecipitated slurry was allowed to stand for about 12 hours, washed sufficiently with water, filtered, and then heated at 100 ° C. for 1 hour.
Let dry for hours. Further, at 350 ° C. in an air atmosphere,
Fired for hours. The tungsten thus prepared is
The composition of the silica powder is WO ₃ : SiO ₂ = 30: 70
(Weight ratio in terms of oxide). This composite oxide powder is designated as WS-1.

Next, silica sol (Snowtex-3)
0, manufactured by Nissan Chemical Industries, containing 30 wt.% In terms of SiO ₂ )
0.5 kg, 103 kg of industrial ammonia water (containing 25 wt.% NH ₃ ) and 73 l of water were mixed to prepare a uniform solution. The solution titanyl sulfate sulfuric acid solution (manufactured by Tayca Corporation, 70 g / liter as TiO _2, 287 g / liter containing a H ₂ SO ₄₎ to 240.6 liters, was gradually added dropwise with stirring, to produce a precipitate. After allowing this coprecipitated slurry to stand for about 40 hours, after sufficiently washing with water,
Filter and dry at 100 ° C. for 1 hour. Further, firing was performed at 550 ° C. for 4 hours in an air atmosphere. The composition of the titania-silica powder thus prepared is TiO ₂ : Si
O ₂ = 8: 2 (oxide molar ratio). This composite oxide powder is referred to as TS.

Next, 1.29 kg of ammonium metavanadate, 1.67 kg of oxalic acid and 0.4 kg of monoethanolamine were mixed and dissolved in 10.5 liter of water. 6.7 kg of the WS-1 powder and 12.3 kg of the TS powder prepared above are mixed, a vanadium-containing solution is added together with a molding aid, and the mixture is mixed well with a blender while adding an appropriate amount of water. Knead well, 80mm
It was extruded into a honeycomb shape having corners, openings of 4 mm, wall thickness of 1.0 mm, and length of 500 mm. The obtained molded product is
After drying at ° C, the mixture was calcined at 450 ° C for 5 hours under flowing air to obtain a target catalyst. The composition at this time is represented by weight ratio, WS-1:
TS: V ₂ O ₅ = 33.3: 61.7: 5 (TiO ₂ : SiO ₂ : WO ₃ : V ₂ O ₅ = 5 by weight in terms of oxide)
2: 33: 10: 5). Example 2 ammonium metatungstate solution (Nippon Inorganic Color & Chemical Co., Ltd., WO ₃ in terms of 50 wt.% Content) 20 kg silica sol (Snowtex -30, manufactured by Nissan Chemical Industries, Ltd., SiO ₂
Convert 30 wt.% Containing) 33.3 kg, and further mixed industrial aqueous ammonia (25 wt.% NH ₃ content) 4.28 kg of water 6.41 l, to prepare a uniform solution. To this solution, 3.14 kg of industrial concentrated sulfuric acid was gradually added dropwise with stirring to form a precipitate. At this time, the temperature of the solution was kept at 60 ° C. or lower. After the completion of the dropping of the concentrated sulfuric acid, it was confirmed that the pH of the coprecipitated slurry was between 4 and 6. When the pH was higher than 6, the pH was adjusted by further adding concentrated sulfuric acid. The coprecipitated slurry thus obtained was allowed to stand for about 12 hours, washed sufficiently with water, filtered, and dried at 100 ° C. for 1 hour. Further, firing was performed at 350 ° C. for 2 hours in an air atmosphere. The composition of the tungsten-silica powder thus prepared was WO ₃ : SiO ₂ = 50: 50 (weight ratio in terms of oxide). This composite oxide powder is WS-
Let it be 2.

Others were prepared in the same manner as in Example 1, and the composition in this case was WS-2: TS: V _{2 by} weight ratio.
O ₅ = 20: 75: 5 (weight ratio in terms of oxide, Ti
O ₂ : SiO ₂ : WO ₃ : V ₂ O ₅ = 63.2: 21.
8: 10: 5). Example 3 ammonium metatungstate solution (Nippon Inorganic Color & Chemical Co., Ltd., WO ₃ in terms of 50 wt.% Content) 28 kg silica sol (Snowtex -30, manufactured by Nissan Chemical Industries, Ltd., SiO ₂
Convert 30 wt.% Containing) 20 kg, further industrial aqueous ammonia (25wt.% NH ₃ content) 3.27Kg water 4.9
One liter was mixed to prepare a homogeneous solution. In this solution,
2.4 kg of industrial concentrated sulfuric acid was gradually added dropwise with stirring,
A precipitate formed. At this time, the temperature of the solution was kept at 60 ° C. or lower. After the dropwise addition of concentrated sulfuric acid, it was confirmed that the pH of the coprecipitated slurry was between 4 and 6. If the pH was higher than 6, the pH was adjusted by further adding concentrated sulfuric acid. After allowing the coprecipitated slurry thus obtained to stand for about 12 hours,
After sufficiently washing with water, the mixture was filtered and dried at 100 ° C. for 1 hour. Further, firing was performed at 350 ° C. for 2 hours in an air atmosphere. The composition of the tungsten-silica powder thus prepared was WO ₃ : SiO ₂ = 70: 30 (weight ratio in terms of oxide). This composite oxide powder is designated as WS-3.

Otherwise prepared in the same manner as in Example 1.
In this case, the composition is expressed in weight ratio, WS-3: TS: V_Two
O_Five= 14.3: 80.7: 5 (weight ratio in terms of oxide,
TiO _Two: SiO_Two: WO_Three: V_TwoO_Five= 68: 17:
10: 5). Example 4 Titania-silica powder (TS) and tungsten-silica
Example except that the mixing ratio of the powder (WS-3) was changed.
In the same manner as in Example 3, a catalyst was obtained. Composition in this case
Is the weight ratio, WS-3: TS: V_TwoO_Five= 28.6: 6
6.4: 5 (TiO2 weight ratio in terms of oxide)_Two: Si
O_Two: WO_Three: V_TwoO_Five= 56: 19: 20: 5)
Was. Example 5 Commercially available oxidation instead of titania-silica powder (TS)
Titanium powder (made by Millennium, trade name DT-51)
A catalyst was prepared in the same manner as in Example 1 except that
Was. The composition in this case is expressed by weight ratio, WS-1: TiO._Two:
V_TwoO_Five= 33.3: 61.7: 5 (weight ratio in terms of oxide)
And TiO_Two: SiO_Two: WO_Three: V_TwoO_Five= 61.
7: 23.3: 10: 5). Comparative Example 1 Ammonium metavanadate 1.2 in 4 liters of water
9 kg and oxalic acid 1.67 kg and monoethanolamine
0.4 kg were mixed and dissolved. Next, 4 liters
2.25kg of ammonium paratungstate in water
Mix and dissolve 0.9 kg of monoethanolamine
Was. Mix vanadium-containing and tungsten-containing solutions
Then, a homogeneous solution was prepared. Commercial TiO_TwoPowder (Milleni
Am Co., Ltd. DT-51)
Charge the mixed solution containing Na and Tungsten and
After mixing well with a blender while adding an amount of water,
Knead well with a heater, 80 mm square, 4 mm aperture, meat
Extruded into a 1.0mm thick, 500mm long honeycomb shape
Molded. After drying the obtained molded product at 60 ° C.,
The mixture was calcined at 450 ° C. for 5 hours to obtain a target catalyst. this
The composition at the time is by weight, TiO_Two: WO_Three: V_TwoO_Five= 8
5: 10: 5. Comparative Example 2 Commercial TiO_TwoInstead of powder, the T prepared in Example 1
Except using S powder, it prepared by exactly the same method.
The composition in this case is TS: V by weight._TwoO_Five= 85: 1
0: 5 (TiO 2 weight ratio in terms of oxide)_Two: SiO_Two: W
O_Three: V_TwoO_Five= 71.6: 13.4: 10: 5).
Was. Comparative Example 3 Ammonium metatungstate solution (Nippon Inorganic Chemical Co., Ltd.)
Industry company, WO_Three(Contains 50 wt.% In conversion)
Kasol (Snowtex-30, manufactured by Nissan Chemical Industries, Inc., SiO
_Two9.4kg, and 30% by weight
Monia water (25 wt.% NH_Three5.5 kg of water and 8.
3 liters were mixed to prepare a homogeneous solution. This solution
In addition, titanyl sulfate solution (manufactured by Teica, TiO_Twoage
70 g / l, H_TwoSO_Four287g / L
215 liters is gradually dropped while stirring.
To form a precipitate. The coprecipitated slurry thus obtained
After standing for about 40 hours, after sufficiently washing with water, filtration,
Dry at 100 ° C. for 1 hour. Furthermore, under air atmosphere,
It was baked at 550 ° C. for 2 hours. The thus prepared chip
The composition of the tania-silica-tungsten powder is Ti
O_Two: SiO_Two: WO_Three= 75.3: 14.2: 10.
5 (weight ratio in terms of oxide). This composite oxide powder
Is TSW.

Next, 1.29 kg of ammonium metavanadate, 1.67 kg of oxalic acid and 0.4 kg of monoethanolamine were mixed and dissolved in 10.5 liter of water. A vanadium-containing solution was added together with a molding aid to 19 kg of the previously prepared TSW powder, mixed well with a blender while adding an appropriate amount of water, and kneaded well with a continuous kneader to obtain a 80 mm square, 4 mm mesh, meat. 1.0mm thick,
It was extruded into a honeycomb shape having a length of 500 mm. The obtained molded product was dried at 60 ° C., and calcined at 450 ° C. for 5 hours under an air flow to obtain a target catalyst. The composition in this case is TSW: V ₂ O ₅ = 95: 5 by weight ratio (TiO ₂ : SiO ₂ : WO ₃ : V ₂ O ₅ = 71.5 in oxide conversion weight ratio).
6: 13.4: 10: 5). Example 6 Using the catalysts obtained in Examples 1 to 5 and Comparative Examples 1 to 3, a denitration performance test and measurement of an SO ₂ oxidation rate were performed under the following conditions.

NO_x: 200 ppm, SO_Two: 1000
ppm, NH_Three: 200 ppm, O _Two: 10%, H
_TwoO: 15%, N_Two: Balance, gas temperature: 250-4
00 ° C, space velocity: 30,000Hr^-1 The denitration rate and SO_TwoThe oxidation rate is calculated according to the following formula.
I asked. Denitration rate (%) = [(reactor inlet NO_xConcentration)-(Reactor
Exit NO_xConcentration)] ÷ (Reactor inlet NO_xConcentration) × 10
0 SO_TwoOxidation rate (%) = (SO at reactor outlet)_ThreeConcentration) ÷ (anti
Reactor entrance SO_TwoConcentration) × 100 Obtained denitration rate and SO_TwoThe oxidation rate is shown in Table 1.

[0027]

[Table 1]

Example 7 Using the catalysts obtained in Example 3 and Comparative Examples 1 and 2,
The gas having the composition shown in Example 6 was continuously supplied at a temperature of 350 ° C., and the durability of the catalyst was examined. Table 2 shows the change in the denitration rate with the lapse of time.

[0029]

[Table 2]

[0030]

The denitration catalyst produced according to the present invention has excellent denitration performance and maintains the catalyst performance for a long time, and at the same time, has an extremely high oxidation performance of sulfur dioxide coexisting in exhaust gas to sulfur trioxide. Since it is low, it is suitably used as a catalyst for removing nitrogen oxides.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Motonobu Kobayashi F-term (Reference) 4D048 AA06 AB03 BA06X BA06Y BA07X BA07Y BA23X BA23Y BA27X BA27Y BB01 4G069 AA03 AA08 BA02A BA02B BA02C BA04A BA04B BA04C BA27C BA37 BB04A BB04B BB06A BB06B BB10C BC50C BC54A BC54B BC54C BC60A BC60B BC60C BE17C CA02 CA03 CA10 CA13 FB09 FB30 FB77 FC09

Claims (2)

[Claims] 1. A method for producing a denitration catalyst for removing nitrogen oxides in an exhaust gas, comprising a silicon, titanium, tungsten and vanadium oxide, comprising the steps of: Composite oxide of tungsten and silicon (WO ₃ -Si
A method for producing a denitration catalyst, comprising a step of adding a vanadium compound to O ₂ ). 2. A composite oxide of tungsten and silicon (WO ₃ —SiO ₂ ) which is prepared by previously supporting tungsten on a silicon oxide, and prepared by previously supporting titanium on a silicon oxide. after mixing the composite oxide of titanium and silicon (TiO ₂ -SiO _2), the addition of a vanadium compound, method for producing a denitration catalyst according to claim 1, wherein.