JP2012035208A - Metal substrate for catalyst and denitration catalyst using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal substrate which is hardly corroded even when being exposed for a long period of time in an actual usage environment of a catalyst and to provide a denitration catalyst which can maintain a low SOoxidation rate over the long term.SOLUTION: The substrate is characterized in that a phosphate is carried together with silica and titanium oxide in layers on the surface of the metal substrate. The substrate is produced by immersing the metal substrate into a treatment liquid slurried by adding the phosphate to a treatment liquid including colloidal silica, titanium oxide fine particle and polyvinyl alcohol, thereby, carrying the silica, titanium oxide, polyvinyl alcohol and phosphate on the metal substrate and, thereafter, drying and calcinating the treated metal substrate to form a corrosion-resistant film on the surface of the metal substrate.

Description

The present invention relates to a catalyst metal substrate, a denitration catalyst, and a production method thereof, and in particular, suppresses the oxidation activity from SO ₂ to SO _{3 of a} titanium oxide-based ammonia catalytic reduction denitration catalyst using a metal wire mesh or a lath plate. The present invention relates to a catalyst substrate and a denitration catalyst using the same.

  Ammonia reduction method denitration catalyst mainly composed of titanium oxide has high catalytic activity and excellent durability, so it is widely used for flue gas treatment of boilers and the like at home and abroad, and has become the mainstream of denitration catalyst (patent document) 1). These titanium oxide-based denitration catalysts are often used in honeycomb-like or plate-like catalysts in which a catalyst component is applied to a metal substrate, and the latter plate-like catalysts are particularly resistant to abrasion and accumulation due to soot and dust. Widely used for denitration of combustion exhaust gas. A number of methods for producing a plate catalyst have been proposed. Among them, a metal mesh lath obtained by cutting a slit (slit) with a predetermined pitch in a thin metal plate and applying a tensile force in a direction perpendicular to the slit is provided. Substrates have become the mainstream of plate catalysts in Japan and overseas because they can produce a catalyst with excellent mass productivity and high mechanical strength.

On the other hand, in recent years, energy demand has increased rapidly, and coal with a high sulfur content (high S coal) has come to be used as fuel. Along with this, a part of SO ₂ is SO ₃ due to the SO ₂ oxidation activity of the denitration catalyst. There are increasing troubles caused by SO ₃ , such as the generation of purple smoke due to SO ₃ in the chimney and the corrosion of the denitrator downstream. For this reason, the need for a catalyst with very low SO ₂ oxidation activity possessed by a denitration catalyst has increased, and a catalyst with a devised catalyst composition (Patent Document 2) or a catalyst with a distribution of catalyst component concentrations (Patent Document 3). It has been known.
JP 50-128681 JP-A-2-184342 JP 09-220468 A JP 52-14658 A Japanese Patent Laid-Open No. 06-246176

The prior art described above has the following two problems to be solved. One of them is that during the catalyst production process, the metal substrate is slightly corroded by SO ₄ in the catalyst raw material, which hinders the reduction of SO ₂ oxidation activity. As the titanium oxide-based denitration catalyst, titanium oxide by a sulfuric acid method is used which is inexpensive and provides high catalyst performance. In general, titanium oxide by the sulfuric acid method contains several wt% of sulfate radicals, and most of them remain in the catalyst component even after the steps of addition and firing of the catalyst component. For this reason, in the case of a catalyst using a catalyst substrate, when a paste or slurry of the catalyst component is coated or applied to the substrate by a wet method, the metal substrate is dissolved by residual sulfuric acid and the substrate component moves into the catalyst component. Among the suspension substrate components, elements such as iron (Fe), nickel (Ni), and chromium (Cr), when adsorbed on titanium oxide, can promote oxidation of SO ₂ more than V, which is a denitration catalyst component. It is known that a small amount of transition metal component dissolved during the catalyst production process hinders the reduction of SO ₂ oxidation activity.

The other is that the catalyst may be exposed to saturated steam at 50 to 60 ° C. when the boiler is started or stopped, or when the air heater is washed with water. In many coal-fired boilers, several percent of SO ₄ roots accumulate in the catalyst, and when it absorbs moisture, it may move into the catalyst and cause substrate corrosion, which may increase the SO ₂ oxidation rate.

As a method of preventing such corrosion of the metal substrate, a method of forming an inactivated film on the surface of the metal substrate has been proposed for the purpose of preventing contact between the metal substrate and the catalyst component (method of spraying metal aluminum) (Patent Document 4), a method of forming a film mainly composed of titanium oxide (Patent Document 5, etc.) Among them, the latter can form a dense and stable film with high adhesion on the surface of a metal substrate. It is highly effective because it can be done, but if it is exposed for a long time in the actual machine, a slight gap will be formed between the passivation film and the substrate, and SO ₄ root will accumulate in this slight gap and corrosion will occur. For this reason, it could not be said that corrosion was completely suppressed, and there was a point to be improved.
The object of the present invention is to solve the above-mentioned problems and to maintain a low SO ₂ oxidation rate over a long period of time by using a metal substrate that is not easily corroded even if it is exposed for a long time in the actual use environment of the catalyst. It is an object of the present invention to provide a denitration catalyst capable of

In order to achieve the above object, the invention claimed in the present application is as follows.
(1) A catalyst substrate characterized in that a phosphate is supported on a metal substrate surface in a layer together with silica and titanium oxide.
(2) The catalyst substrate according to (1), wherein the phosphate is one or more compounds selected from calcium phosphate, barium phosphate and zinc phosphate.
(3) The metal substrate is a metal lath, and a denitration catalyst component containing titanium oxide and an oxide of one or more elements selected from molybdenum, tungsten and vanadium is supported between the mesh and the surface of the catalyst substrate. A denitration catalyst characterized by that.
(4) A metal substrate is immersed in a slurry obtained by adding phosphate to a treatment liquid containing colloidal silica, finely divided titanium oxide and polyvinyl alcohol, and the silica, titanium oxide, polyvinyl alcohol and A method for producing a catalyst substrate, comprising supporting a phosphate, followed by drying and firing to form a corrosion-resistant film on the surface of the metal substrate.
(5) The catalyst substrate according to (4), wherein the phosphate is one or more compounds selected from calcium phosphate, barium phosphate and zinc phosphate.
(6) A metal lath is immersed as a metal substrate in a slurry obtained by adding phosphate to a treatment liquid containing colloidal silica, fine titanium oxide and polyvinyl alcohol, and the silica, titanium oxide, polyvinyl alcohol and After producing a catalyst substrate by supporting phosphate, drying and firing, oxides of one or more elements selected from titanium oxide, molybdenum, tungsten, and vanadium between the mesh and the surface of the catalyst substrate A method for producing a denitration catalyst comprising supporting a denitration catalyst component comprising:

According to the present invention, the metal substrate can be prevented from Fe generated by corrosion of the substrate in the denitration catalyst used in the carrier is moved to the catalyst, performance degradation resulting from it, in particular to prevent an increase in SO ₂ oxidation rate I can do it.

  In the present invention, it is important to form an inactive film containing a phosphate, particularly a phosphate insoluble or hardly soluble in water, on the surface of the metal substrate.

In a high-S coal boiler, a large amount of SO ₄ is adsorbed and accumulated in the catalyst, and this reacts with the metal substrate as shown in the following formulas (1) and (2) to produce iron sulfate.
Fe + SO ₄ ^2- → FeSO ₄ (1)
2Fe + 3SO ₄ ^2- → Fe ₂ (SO ₄ ) ₃ (2)

This iron sulfate dissolves when the catalyst is placed in a hygroscopic state, generates Fe ions, moves into the catalyst, and raises the SO ₂ oxidation rate. An inert film containing phosphate has the effect of suppressing SO ₄ from coming into contact with the metal substrate. However, since a slight gap is formed between the film and the substrate over time, it completely suppresses corrosion. I can't.

  On the other hand, in the present invention, the phosphate added to the inert film reacts with the sulfate and the following (3) to (8) on the contact surface with the lath substrate to insolubilize Fe.

Ca ₃ (PO ₄ ) ₂ + 3FeSO ₄ → Fe ₃ (PO ₄ ) ₂ + 3CaSO ₄ (3)
Ba ₃ (PO ₄ ) ₂ + 3FeSO ₄ → Fe ₃ (PO ₄ ) ₂ + 3BaSO ₄ (4)
Zn ₃ (PO ₄ ) ₂ + 3FeSO ₄ → Fe ₃ (PO ₄ ) ₂ + 3ZnSO ₄ (5)
Ca ₃ (PO ₄ ) ₂ + Fe ₂ (SO ₄ ) ₃ → 2FePO ₄ + 3CaSO ₄ (6)
Ba ₃ (PO ₄ ) ₂ + Fe ₂ (SO ₄ ) ₃ → 2FePO ₄ + 3BaSO ₄ (7)
Zn ₃ (PO ₄ ) ₂ + Fe ₂ (SO ₄ ) ₃ → 2FePO ₄ + 3ZnSO ₄ (8)

  As a component of the film to which phosphate is added, when supported on a metal substrate such as a lath or a metal mesh, it has good compatibility with metal, excellent liquid stability, and excellent adhesion to the substrate. Of these, silica and finely divided titanium oxide powder give good results. The method described in Patent Document 5 can be applied as a method for forming the film. That is, the lath-cut substrate is heated in a degreasing furnace to remove the adhering cutting oil, and the slurry is obtained by adding phosphate to a treatment liquid composed of polyvinyl alcohol, colloidal silica, and fine titanium oxide powder described in the patent. Then, the obtained lath plate is immersed to carry a film-forming component, and this is passed through a furnace at 120 to 200 ° C. to form a film.

Here, the phosphate is preferably an insoluble or hardly soluble phosphate. Use of phosphoric acid or a phosphate having high solubility (for example, aluminum phosphate) is not preferable because the catalyst is supported and then dissolved in a wet state and moved into the catalyst to reduce the activity. The addition amount of the phosphate, as long Fe ions and equimolar or more to produce a substrate corrosion, can not be said sweepingly because it varies depending on use conditions, in the range of 0.5g / m ² ~40g / m ² is Give good results. If it is less than this, the inhibitory effect is small, and if it is more than this, film formation becomes difficult. Further, the amount of the film supported is not particularly limited, but if it is too much, it is easy to peel off, and if it is too little, the anticorrosion is thinned, so the range of 30 to 150 g / m ² is preferable.

If the polyvinyl alcohol used in the treatment liquid to which the phosphate is added is too much, the viscosity becomes high and the operability becomes poor. Colloidal silica is sufficient to fill the gap between fine titanium oxide and phosphate, which are powder raw materials, and is selected to be 10 to 20 wt% with respect to the weight of fine titanium oxide and phosphate. Further, TiO ₂ titanium oxide is preferably produced by a chlorine method containing no sulfate radical, and a specific surface area of 10 m ² / g or less and an average particle size of 1 μm or less are preferable because of good dispersibility.

  The catalyst components supported on the metal substrate obtained by this method and the catalyst supporting method are generally known coating methods such as embedding a denitration catalyst paste made of oxides of Ti, W, Mo, and V in a metal lath mesh. A method of coating a slurry is suitable, but it goes without saying that the present invention is not limited by these methods.

Hereinafter, the present invention will be described in detail using specific examples.
[Example 1]
65 kg of colloidal silica (manufactured by Nissan Chemical Co., Ltd., trade name Snow Tech N (SiO ₂ content 20 wt%)) was obtained by dissolving 3 kg of polyvinyl alcohol (Kuraray PVA-117) in 47 kg of water. To the liquid, 35 kg of titania powder (CR-50 manufactured by Ishihara Sangyo Co., Ltd.) and 30 kg of calcium phosphate (first grade) were added and stirred well to prepare a slurry-like treatment liquid. A metal lath (SUS430, thickness 0.2mm) cut into 500mm x 500mm was immersed in this, and the liquid layer was drained by air blow to carry the above mixture on the lath surface, and then insolubilized at 140 ° C to form a coating layer. A substrate having was obtained. The film loading is about 70 g / m ² , of which the calcium phosphate loading is 21 g / m ² .

[Examples 2 and 3]
A substrate was obtained in the same manner as in Example 1 except that the calcium phosphate of Example 1 was changed to equimolar magnesium phosphate and zinc phosphate. The film loading was about 70 g / m ² , of which magnesium phosphate and zinc phosphate were 20 and 25 g / m ² , respectively.

[Example 4]
A substrate was obtained in the same manner as in Example 1 except that the amount of calcium phosphate added in Example 1 was 45 kg and the titanium oxide powder was 20 kg. The film loading amount is about 70 g / m ² , of which the calcium phosphate loading amount is 32 g / m ² .

[Comparative Example 1]
In Example 1, a substrate was obtained in the same manner as in Example 1 except that a lath substrate that did not form a film according to the present invention was used. The film loading is about 70 g / m ² .

[Comparative Example 2]
A substrate was obtained in the same manner as in Example 1 except that calcium phosphate was changed to titanium oxide having the same weight (CR-50 manufactured by Ishihara Sangyo Co., Ltd.). The film loading is about 70 g / m ² .

[Test Example 1]
In order to observe the effect of fixing Fe ions in the substrate by the phosphate addition of the present invention, the following simulation test was performed.
First, in order to simulate the state in which the substrate was corroded with sulfuric acid and iron sulfate was generated on the substrate surface, the substrates obtained in Examples 1 to 5 and Comparative Examples 1 and 2 were added to an aqueous solution containing 4 wt% as FeSO _4. After being immersed for 1 minute, it was air-dried at room temperature for 1 hour, and further dried at 120 ° C. for 2 hours. Hereinafter, this is simply referred to as iron sulfate treatment.

  Separately, titanium oxide, ammonium molybdate, and ammonium metavanadate are mixed at an atomic ratio of Ti: Mo: V = 93.5: 5: 1.5, and water, silica sol, silica-based ceramic fibers are added, and the kneader is mixed. And kneaded sufficiently to obtain a catalyst paste.

The lath plate subjected to the above-described iron sulfate treatment was passed through a pair of pressure rollers to apply the catalyst paste between the mesh of the substrate and the surface thereof. This was dried at 150 ° C. for 1 hour and then calcined at 500 ° C. for 2 hours to obtain a plate catalyst (coating amount 700 g / m ² ). The operation so far simulates the state in which the catalyst is supported on the surface of the corroded substrate.

[Test Example 3]
Using the same substrate as in Example 1, the same iron sulfate treatment as in Test Example 1 was performed.
Separately, titanium oxide, ammonium tungstate, and ammonium metavanadate are mixed at an atomic ratio of Ti: W: V = 93.5: 5: 1.5, and water, silica sol, silica-based ceramic fibers are added, and the kneader is mixed. And kneaded sufficiently to obtain a catalyst paste. The lath plate subjected to the iron sulfate treatment was passed through a pair of pressure rollers to apply the catalyst paste between the mesh of the substrate and the surface thereof. This was dried at 150 ° C. for 1 hour and then calcined at 500 ° C. for 2 hours to obtain a plate catalyst (coating amount 700 g / m ² ).

[Test Example 4]
After slicing the catalyst of Test Examples 1 and 2 to 100 mm x 100 mm in order to simulate the movement of the corrosion product iron sulfate generated on the substrate surface into the catalyst in a wet state with an actual machine etc. The mixture was allowed to stand for 1 hour in an airtight container with a relative humidity of 100%. This was taken out, dried at 120 ° C. for 2 hours, and calcined at 350 ° C. for 2 hours to obtain a test piece. This process is referred to as a moisture absorption process.

In order to examine the amount of Fe transferred from the substrate to the catalyst by the above moisture absorption treatment, the catalyst was peeled off from the obtained test piece and pulverized in a mortar, and the amount of Fe ₂ O ₃ in the catalyst powder was measured using a fluorescent X-ray measurement device. Measured.

Table 1 shows the amount of Fe ₂ O ₃ in the catalyst in the test pieces in which the catalyst is supported on the substrates of Examples 1 to 5 and Comparative Examples 1 and 2. From the results of Table 1, in the test pieces using the substrates of the examples, there is almost no difference in the amount of Fe ₂ O ₃ in the catalyst before and after the test, but in Comparative Example 1, Fe in the catalyst after the moisture absorption treatment. It can be seen that ₂ O ₃ is greatly increased. Further, in Comparative Example 2, although the amount of Fe ₂ O ₃ in the catalyst is smaller than that in Comparative Example 1, it is larger than that in Examples of the present invention. From this, in the catalyst of a comparative example, it can be said that the iron sulfate on the base material has moved into the catalyst because the catalyst is subsequently in a hygroscopic state. In contrast, in the catalyst of the example, the amount of Fe ₂ O _{3 in} the catalyst after the moisture absorption treatment is smaller than that in the comparative example. From this, it can be seen that the movement of Fe ions from the base material is prevented in the catalyst of the example.

[Test Example 5]
Catalyst loading and moisture absorption treatment were performed in the same manner except that the iron sulfate treatment of Test Example 1 was not performed.

[Test Example 6]
In order to see the effect of suppressing the increase in SO ₂ oxidation rate of the present invention, the following test was conducted.
The catalyst obtained in Test Examples 1 and 5 was cut to 100 × 20 mm and filled into a reaction tube in a flow system, and the SO ₂ oxidation rate of the catalyst was measured under the conditions shown in Table 2. The results are shown in Table 3. From the results of Table 3, in the catalyst using the base materials of Examples 1 to 4, a change was observed in the SO ₂ oxidation rate regardless of whether iron sulfate treatment was performed (Test Example 1) or not (Test Example 5). Although there is no catalyst, it can be seen that in the catalysts using the base materials of Comparative Examples 1 and 2, the SO ₂ oxidation rate is increased by the iron sulfate treatment (Test Example 1). From this, it can be seen that in the method of the present invention, an increase in the SO ₂ oxidation rate due to Fe migration is prevented.

Claims (6)

  A catalyst substrate, wherein a phosphate is supported on a metal substrate surface in a layer together with silica and titanium oxide.   The catalyst substrate according to claim 1, wherein the phosphate is one or more compounds selected from calcium phosphate, barium phosphate, and zinc phosphate.   The metal substrate is a metal lath, and a denitration catalyst component containing titanium oxide and an oxide of one or more elements selected from molybdenum, tungsten, and vanadium is supported between the mesh and the surface of the catalyst substrate. A denitration catalyst characterized by   A metal substrate is immersed in a slurry obtained by adding phosphate to a treatment liquid containing colloidal silica, fine titanium oxide and polyvinyl alcohol, and the silica, titanium oxide, polyvinyl alcohol and phosphate are immersed on the metal substrate. And then drying and baking to form a corrosion-resistant film on the surface of the metal substrate.   The catalyst substrate according to claim 4, wherein the phosphate is one or more compounds selected from calcium phosphate, barium phosphate, and zinc phosphate.   A metal lath is immersed as a metal substrate in a slurry obtained by adding phosphate to a treatment liquid containing colloidal silica, fine titanium oxide and polyvinyl alcohol, and the silica, titanium oxide, polyvinyl alcohol and phosphate are immersed in the metal lath. The catalyst substrate is manufactured by supporting and drying and firing, and then includes titanium oxide and an oxide of one or more elements selected from molybdenum, tungsten and vanadium on the mesh and on the surface of the catalyst substrate. A method for producing a denitration catalyst, comprising a denitration catalyst component.