JPS5926341B2 - Denitration catalyst with porous film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a long-lasting denitrification catalyst that is used in a reaction that selectively catalytically reduces nitrogen oxides (hereinafter referred to as NOx) in exhaust gas with NH3.

Many methods have already been proposed for treating NOx in flue gas, but one method uses NH3 as a reducing agent and operates at a predetermined temperature in the presence of a catalyst to remove NOx.
The so-called selective catalytic reduction denitrification method is said to be the most practical.

Many catalysts have been proposed for use in this method.

The present inventors have previously developed a denitrification catalyst that is activated by treating an unactivated metal material whose surface layer is aluminum alloyed with aluminum soluble solution to make the surface porous. We proposed a sustainable denitrification catalyst formed by forming a film of high-quality silica (patent application filed in 1973).
2-73464).

This catalyst has great mechanical strength and also has KCI
Because it does not cause activity deterioration due to catalyst poisons such as
It is excellent in that it has stable and continuous activity.

As a result of intensive research into improving the above catalyst, the present inventors have further improved the porosity of the silica film of the above catalyst to improve the permeability of the reaction gas through the film, and have also improved the silica coating by using the above catalyst as a carrier. By supporting active substances on
We have completed a denitrification catalyst that has even better activity and is also perfect in terms of strength.

That is, the present invention provides a catalyst for catalytic reduction of nitrogen oxides with ammonia, which comprises immersing a porous metal catalyst base in a film-forming solution containing acidic colloidal silica and an organic titanium compound and/or an organic tin compound. A denitrification catalyst having a porous film formed by drying or firing to form a porous film on the catalyst base, immersing the thus obtained carrier in an active metal compound-containing solution, and drying to support the active metal compound. .

Examples of porous metal catalyst bases that can be used include those formed by subjecting a metal material whose surface layer is aluminum alloyed to eluting aluminum with an aluminum-soluble solution, and those formed by etching the surface of a metal material to make it porous and rough.

Examples of metal materials include (ζ pure iron, iron-based alloys, steel, nickel, nickel-based alloys, copper-based alloys, etc.).

AI alloying treatment of metal materials +i, for example, AI on the surface
This is done by heat treating the coated metal material.

Elution treatment of AI can be carried out, for example, by immersing a metal material whose surface layer is alloyed with A1 in an A1-soluble solution;
1. This can be done by a method such as spraying a soluble solution.

As the A1-soluble solution, aqueous solutions of alkali metal hydroxides such as NaOH, alkali metal carbonates, alkaline earth metal hydroxides, mineral acids, and the like are often used.

This AI elution process makes the surface layer of the metal material porous.

The porous metal material is preferably subjected to an oxidation treatment and/or an S02 treatment.

In the oxidation treatment, the treatment temperature, treatment time, and oxygen concentration are not particularly limited.

Preferably, at around room temperature to 400°C, oxygen is 0.
The treatment is carried out for 0.1 to 20 hours in an atmosphere containing 1 to 20.8% by volume.

The S02 treatment is preferably performed at around room temperature to 400°C, in an atmosphere containing 1100 pp or more of S02, and at a concentration of 0.1 to 400°C.
It will be held for 20 hours.

The processing conditions λ are appropriately selected within the above range.

Colloidal silica is limited to acidic materials.

The reason for this is that when acidic colloidal silica is used, a higher denitrification activity can be obtained than when alkaline colloidal silica is used.

The preferred pH of the acidic colloid is 3-4.

The concentration and temperature of the film-forming solution, the time and number of immersions are appropriately selected so that the thickness of the film becomes a desired value.

The drying temperature is preferably 50 to 150°C. Preferred embodiment Q
′! , 10-30% by weight of 5i02 as film-forming solution
The catalyst base was immersed in this colloidal silica at around room temperature for about 10 minutes, and after taking out the base from the solution, it was dried at about 90°C for 1 hour.
Repeat ~6 times.

When a mixture of colloidal silica and polymer emulsion is used as a film-forming solution, a film is formed by dipping and drying in a catalyst base, and the same base is fired, the porosity of the film is greatly improved.

As the polymer emulsion, an acrylic emulsion is preferably used because it does not generate harmful gases during firing.

The content of the polymeric substance in the film-forming solution is appropriately selected depending on the desired mechanical strength of the film, the components and particle size of dust in the reaction gas, and the like.

Preferably, 10 to 50 parts by weight of a polymeric substance is mixed with 100 parts by weight of silica (Si02) in the colloid.

Firing is performed in air at a temperature of 450 to 700°C, preferably 50°C.
It is carried out at 0 to 650°C for 1 to 5 hours.

The polymeric organic components are removed by calcination.

Furthermore, when a mixture of colloidal silica, a polymer emulsion, and a titanium compound is used as the film-forming solution, the carrier performance is improved and the resulting catalyst exhibits excellent activity.

Furthermore, when a mixture of colloidal silica, a polymer emulsion, a titanium compound, and a tin compound is used as the film-forming solution, a catalyst with excellent sulfuric acid resistance can be obtained.

Examples of the titanium compound to be mixed include ammonium salts of dihydroxy bislavtiquaside titanate Ti(OH)2Cocn(cH3)COOH)2 and ammonium oxalate titanate Ti.
Water-soluble organic titanium such as (OC2(NH4)203)4 is preferably used, and as the tin compound, an organic tin compound such as dibutyltin laurate is preferably used.

The reason why these organometallic compounds are preferably used is that these substances have excellent solubility in acidic colloidal silica.

On the other hand, inorganic compounds such as titanium chloride and tin chloride tend to gel the acidic colloidal silica and are therefore not preferred.

These titanium compounds and tin compounds are thermally decomposed by firing to become TiO2 and Sn02, respectively.

The preferred content of TiO2 in the film is 5i02 by weight.
40 to 100 copies per 100 copies, and 5n02
The preferred content is 30 to 7 parts per 100 parts of 5iO2 by weight.
It is 0 copies.

In the immersion of the carrier, the active metal compound-containing solution includes a solution containing a vanadium compound such as vanadyl sulfate, vanadyl oxalate, and ammonium metavanadate, a solution containing a hydrolyzable titanate ester such as tetraisoglopyltitanate, iron, Solutions containing copper, antimony sulfates or halides, tungstates, chromic acid, etc. are used.

By this immersion, V compounds, Ti compounds, and Fe are added to the carrier.
compound, Cu compound, sb compound, W compound, and (
or) a Cr compound is supported.

Conditions such as concentration, temperature, and immersion time after immersion depend on the amount of active ingredient to be supported on the catalyst.

The preferred loading amount is 0.15 to 1.5% as V by weight;
0.15 to 1.5% as Ti, 0.16 to 1.5% as Fe
1.6%, 0.17-1.7% as Cu, 0.1-3.0% as sb, 0.15-1.5% as W, Cr
It is 0.2 to 2.0%.

All of the obtained catalysts have high denitrification activity.

In particular, a catalyst supporting a V compound and a Ti compound has higher activity and is also excellent in sulfuric acid resistance.

Since the denitrification catalyst having a porous film according to the present invention is constructed as described above, the following effects are achieved.

That is, since the film-forming solution contains acidic colloidal silica, the resulting catalyst exhibits superior denitrification activity compared to a catalyst using alkaline colloidal silica.

Furthermore, since the film forming solution contains an organometallic compound as a titanium compound and/or a tin compound, titanium and/or tin can be uniformly dissolved in the acidic colloidal silica, and there is no risk of gelation of the acidic colloidal silica.

Reference Example 1 Measurement of Porosity of Coating Colloidal silica containing 22% by weight of SiO□ (pH=
3.5) and three types of acrylic polymer emulsions a, b, and C shown in Table 1 were mixed in different proportions to form 11 types of film-forming solutions A, B...
... J and K were prepared (however, solution A does not contain an emulsion).

Each of these 11 types of solutions was
It was poured into a Petri dish-shaped stainless steel container of rIL to a depth of about 4 mm.

These solutions were heated at 90° C. for 1 hour to remove moisture, and the resulting solids were calcined in air at 500° C. for 1 hour.

The coating thus formed was peeled off from each container, and the porosity of the coating was measured using a high-pressure mercury porous needle.

The results are shown in Table 2. Also, solutions A, C, E, G and J
The relationship between the pore diameter and the total pore volume was determined for the coatings α, β, γ, δ, and ε formed using the method.

The results are shown in Figure 1.

As can be seen from the figure, the coating α formed from a solution that does not contain an emulsion tends to be slightly less porous.
Films β and γ formed from solutions containing polymer emulsions
, δ and ε have large porosity.

Furthermore, when emulsion a made of a polymeric substance with a low glass transition temperature is used, most of the pores in the coating have a pore size of 30 to 70 pores, as shown by the curve γ, and the coating 1000 Å suitable for the reaction gas to pass through the inside
There are almost no pores with a pore diameter of 1000 Å or more, but when emulsion b made of a polymer material with a high glass transition temperature is used, as shown by the curve δ, the coating has pores with a pore diameter of 1000 Å or more. It has a relatively large amount of gas and has excellent gas permeability.

Reference Example 2 a Preparation of carrier SUS 304 (J
IS) A steel plate was immersed in an AI melt bath at 680°C for 20 minutes.

The steel plate whose surface was coated with AI in this way was heat treated at 800°C for 1 hour in a nitrogen gas atmosphere, so that A
The surface layer of the steel sheet was made into an A1 alloy by diffusing I.

The steel plate was then immersed in 200 ml of a 10% by weight NaOH aqueous solution at 80° C. for 3 hours to elute the AI in the alloy and make the surface layer porous.

The steel plate was then washed with water and air-dried. Furthermore, the steel plate is
The porous surface layer was oxidized by contacting with nitrogen gas containing % by volume at 300° C. for 3 hours.

In this way, a porous steel catalyst base was formed.

Next, the catalyst base was immersed in Solution A of the film-forming solutions prepared in Reference Example 1 at room temperature for 10 minutes, and after being taken out from the solution, it was dried at 90° C. for 1 hour.

This dipping/drying operation was repeated three times to form a porous silica film with a thickness of 7 to 10 μm on the surface of the catalyst base.

The steel plate was then fired in air at 600° C. for 1 hour to remove high molecular weight organic components.

In this way, carrier a was obtained. Also, among the film forming solutions prepared in Reference Example 1, solutions C and D.

Perform the same operation as above using G and J to obtain carrier c
, d, g and j were obtained.

b Measurement of strength of carrier The obtained carrier a was placed in a stirring tank filled with 60 to 80 mesh pieces of crushed silica gel, and the silica gel was agitated to abrade the surface of carrier a.

Changes in the weight of the carrier were determined at predetermined intervals, and the average wear thickness of the carrier was calculated from the values.

carrier c. The same operation was performed for d2g and j.

In this way, the relationship between operation time and average wear thickness was determined.

The results are shown in Figure 2. Generally, as the porosity improves, the abrasion resistance, that is, the mechanical strength decreases, but as is clear from Figure 2, the carrier C obtained using the solution containing the emulsion
2d2g and j both have superior porosity and are comparable in strength to carrier a obtained using a solution containing no emulsion.

Example 1 a Production of catalyst The catalyst base material had a diameter of 21 mm and a height of 20 mm.
Six catalyst bases were formed by the same porous treatment as in Reference Example 2 using a steel Schissig ring.

In addition, a mixed solution of colloidal silica and polymer emulsion a used in Reference Example 1, and Ti(OH)2(
The ammonium salt of OCH(CH3)COOH)2, dibutyltin laurate and polymer emulsion a were mixed in different proportions to form four types of film forming solutions shown in Table 3, and M, N and O were mixed. Prepared.

Then, the six catalyst bases formed beforehand were immersed, one each in solutions N and M, and two each in solutions N and 0.

Thereafter, immersion and drying were repeated under the same conditions as in Reference Example 2, followed by firing to form a porous film on the surface of each base to obtain six carriers.

Then, among these carriers, 1 ([i
! The outer five were made to support TiO2 and/or V2O5.

To support TiO2, the support was immersed in liquid tetraisoglobil titanate for 10 minutes at room temperature, and after being taken out from the liquid, the support was left under saturated steam at room temperature for 12 hours to hydrolyze the titanate, and then This was done by drying at 100°C.

In order to support V2O5, the support was immersed at room temperature for 10 minutes in an immersion solution prepared by dissolving 1 mol of 15% by volume monoethanolamine aqueous solution 14'KNH4VO, and after being taken out of the solution, it was heated in air at 300°C. This was done by baking for 1 hour.

When supporting both TiO2 and V2O5, the former was supported first.

In this way, the five types of catalysts shown in Table 3 1. my 1. n
2 and Gl were obtained.

Further, a carrier not supporting any of these compounds is also shown as catalyst o2 in the same table.

b. Activity Test Next, each of these catalysts was subjected to an activity test using a flow-through reaction tube made of quartz.

First, Catalyst 1 was filled and fixed in the reaction tube, then the reaction temperature was controlled to a predetermined value, and a prepared exhaust gas for testing having the composition shown in Table 4 was flowed into the reaction tube.

The gas flow rate per geometric surface area of the catalyst is 15 m/h.

The denitrification rate was determined from the amount of NO concentration at the inlet and outlet of the reaction tube.

The same operation was repeated with various reaction temperatures, and the denitrification rate at each temperature was determined.

Catalyst m, n-1, n-2y O-1 and o2
The denitrification rate was determined in the same manner.

The results are shown in Figure 3. As you can see from the same figure, v205
All catalysts supported on V205 exhibit high activity, and in particular, a catalyst formed by forming a support using a film-forming solution containing a polymer emulsion and supporting v205 on this support has even higher activity.

In addition, each catalyst obtained in this example was heated to 4000 p of sulfuric acid vapor.
The catalysts were exposed to air containing pm at 400° C. for 2 hours, and then the denitrification rate of each catalyst was determined by the same operation as above.

The results are shown in Figure 4. As can be seen from the comparison between Figures 3 and 4, catalyst 1, m.

All of fil, n-2 and o2 exhibited a slight decrease in activity at temperatures below 350°C.

On the other hand, Catalyst 01 containing 5n02 in its coating does not cause a decrease in activity and has excellent sulfuric acid resistance.

Example 2 a Manufacture of catalyst Using the film forming solution O used in Example 1,
A number of catalyst bases were prepared, and each base was immersed in the solution and subsequently dried a different number of times.

Hereinafter, firing and v205 were performed in the same manner as in Example 1.
A large number of catalysts with different coating thicknesses were obtained by supporting the catalysts.

b. Relationship between coating thickness and NOx removal rate The NOx removal rates of these catalysts at 300°C were measured to determine the relationship between coating thickness and NOx removal rate.

The measurement conditions are the same as in Example 1.

The results are shown in FIG. 5 by curve t.

Further, as the catalyst base, a cordierite Raschig ring and an alumina Raschig ring having the same shape as the base used in Example 1 were used, and the relationship between the film thickness and the denitrification rate was determined by the same operation as above.

The results are shown in FIG. 5 by curves U and V.

As can be seen from the figure, as the coating thickness increases, the NOx removal rate also improves, but even if the thickness is increased to 20 μm or more, the NOx removal rate hardly improves.

Further, from a comparison of curve t and curves U and V, it can be seen that when a porous steel material is used as a catalyst base, the base itself has considerable denitrification activity.

Reference Example 3 a Manufacture of catalyst Ten catalyst bases were formed by the same operation as in Reference Example 2 (however, 5S41 (JIS) was used as the steel material.

) These catalyst bases were subjected to film forming treatment using the film forming solution prepared in Example 1 under the same conditions as in Reference Example 2 to obtain 10 supports.

One of these carriers was immersed in 2 ooml of a 2N oxalic acid solution of NH4VO3 (1.0 mol/l) at room temperature for 30 minutes, taken out from the solution, and then dried at 100°C for 1 hour.

In this way, a V-supported catalyst was obtained.

Another carrier was immersed in a n-butyl alcohol solution of tetra-n-butyl titanate (1.5 mol/7) under the same conditions as above and dried under the same conditions to obtain a Ti-supported catalyst.

Furthermore, the remaining eight supports were first subjected to Ti loading treatment in the same manner as above using the titanate solutions with various concentrations shown in Table 5, and then with the above metavanadate solutions with various concentrations shown in Table 5. Using the solution, V supporting treatment was performed in the same manner as above to obtain eight Ti+V supported catalysts.

b Activity Test For each catalyst, the denitrification rate at 350°C was determined by the same operation as in Example 1.

Further, in the same manner as in Example 1, the denitrification rate after treatment with sulfuric acid vapor was determined for each catalyst.

These results are shown in Table 5.

As can be seen from the table, catalysts that support both a Ti compound and a V compound exhibit higher activity than catalysts that support one of them, and also have excellent sulfuric acid resistance.

Example 3 a Production of catalyst Seven catalyst bases having a porous surface layer as shown in Reference Example 2 and 0 of the film forming solution prepared in Example 1 were used to produce seven supports in the same manner as in Reference Example 2. I got it.

The metal salt-containing solution A...
......G for 10 minutes at room temperature, each carrier taken out from the solution was dried at 100°C for 1 hour, and further calcined at 300°C for 1 hour.

In this way, Fe supported catalyst, Cu supported catalyst, sb supported catalyst,
A Sb+Fe supported catalyst, a W+Fe supported catalyst, and a Cr supported catalyst were obtained.

b Activity test For each catalyst, the same operation as in Example 1 was carried out (however, the amount of gas passed per geometric surface area of the catalyst was 24 m7 hours).
The denitrification rates at 300°C and 350°C were determined.

The results are shown in Table 6. As can be seen from the table, each catalyst has high activity, especially at high temperatures.

Example 4 a Production of catalyst Catalyst with porous surface layer formed in Reference Example 2]; Four bases and four types of film forming solutions 1, 2, and 2 shown in Table 7 prepared in the same manner as in Reference Example 2. Using 3 and 4,
Four carriers were obtained by the same operation as in Reference Example 2.

Table 7 shows the composition of the coating formed on each carrier.

Next, as ■, N is in the range of 50 to 10001n9/l.
Aqueous solutions containing H4VO3 at various concentrations were prepared, and the same active ingredient loading operation as in Example 4 was carried out using these solutions.

Then, the relationship between the V compound concentration of each solution and the amount of V supported per unit amount of adsorbed substance in the film was determined.

This is shown in FIG. As can be seen from the figure, the compound (1) is strongly adsorbed to the coating, and as the concentration (2) increases, the amount of V supported also increases.

b Activity test Using each catalyst, the denitrification rate at 300° C. was determined in the same manner as in Example 1, and the relationship between this and the amount of V supported per unit amount of adsorbed substance in the film was determined.

This is shown in FIG. As can be seen from the figure, the denitrification rate improves as the supported amount increases, with V per unit amount of the adsorbed substance increasing, and this value shows the highest value in the range of 0.01 to 0.02.

In this case, the amount of V supported is 0.15 to 1.5% by weight as V.
It is.

Comparative Example 1 Using alkaline (pH 9,5) colloidal silica, other operations were performed in the same manner as in Example 1 to prepare film forming solution In this way, catalyst X corresponding to catalyst 0-1 was obtained.

An activity test was conducted on this catalyst X using the same procedure as in the example.

As a result of the test, the activity of catalyst X was lower than that of the corresponding catalyst 01.
The activity is low compared to that of the catalyst, especially at temperatures of 300-400 °C.

It showed only about 80% of the activity of -1.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between pore diameter and total pore volume, Figure 2 is a graph showing the relationship between treatment time and average wear thickness, and Figures 3 and 4 are graphs showing the relationship between reaction temperature and denitrification rate. Graph, 5th
The figure is a graph showing the relationship between film thickness and denitrification rate, and Figure 6 is V
FIG. 7 is a graph showing the relationship between the compound concentration and the amount of V supported per unit amount of adsorbent, and FIG. 7 is a graph showing the relationship between the amount of V supported per unit amount of adsorbent and the denitrification rate.

Claims (1)

[Scope of Claims] 1. A catalyst for catalytic reduction of nitrogen oxides with ammonia, which is prepared by immersing a porous metal catalyst base in a film-forming solution containing acidic colloidal silica and an organic titanium compound, and drying or burning the catalyst. forming a porous coating on the base, immersing the support thus obtained in a solution containing an active metal compound;
A denitrification catalyst having a porous coating formed by drying and supporting an active metal compound. 2. The catalyst according to claim 1, wherein the porous catalyst base is formed by subjecting a metal material whose surface is aluminum-alloyed to an aluminum elution treatment with an aluminum-soluble solution. 3. The catalyst according to claim 1 or 2, wherein the film-forming solution further contains an acrylic polymer emulsion. 4. The catalyst according to any one of claims 1 to 3, wherein the film-forming solution further contains an organic tin compound. 5. The catalyst according to any one of claims 1 to 4, wherein the active metal compound is a vanadium compound. 6. The catalyst according to any one of claims 1 to 4, wherein the active metal compounds are a vanadium compound and a titanium compound. 7. Any one of claims 1 to 4, wherein the active metal compound is a compound selected from the group consisting of iron, copper KW salts, halides, tungstates, and chromates. catalyst.