JP6132498B2 - Titanium / silicon / tungsten oxide, denitration catalyst using the same, method for preparing the oxide, and denitration method - Google Patents

Description

The present invention relates to an oxide of titanium, silicon and tungsten, a denitration catalyst using the oxide, a method for preparing the oxide, and a denitration method. In particular, oil-fired boilers and coal-fired boiler, gas-fired boilers, gas turbines, gas engines, diesel engines, thermal power plants, nitrogen oxides contained in exhaust gas discharged from waste incinerators and various industrial processes (NO _X) The present invention relates to a denitration catalyst that is excellent in removing water, a preparation method thereof, and a denitration method.

  As a method for removing nitrogen oxides in exhaust gas that is currently in practical use, a selective catalyst that catalytically reduces nitrogen oxides in exhaust gas using a reducing agent such as ammonia or urea and decomposes it into nitrogen and water. The reduction method (SCR method) is common. In recent years, as environmental pollution caused by nitrogen oxides has become serious worldwide, as represented by acid rain, a high-performance catalyst has been demanded.

  As a prior art relating to a denitration catalyst, for example, an exhaust gas treatment catalyst comprising titanium dioxide and / or a titanium composite oxide is disclosed as an effective catalyst for removing nitrogen oxides (Patent Document 1), but sufficient treatment performance is disclosed. Could not be said to have.

  Many exhaust gas treatment catalysts using a composite oxide of titanium oxide and silicon oxide as a catalyst component have been proposed (Patent Document 2), but further improvement in activity is desired.

The reasons why these catalysts do not work effectively include heavy oil-fired boilers, coal-fired boilers, gas-fired boilers, gas turbines, gas engines, diesel engines, thermal power plants, waste incinerators, and various industries. Due to the difference in exhaust gas discharged from the process, the target of treatment depends on the existence of catalyst poison, the presence of water vapor, the space velocity between the gas to be treated and the catalyst, the concentration of nitrogen oxides (NO _x ), etc. The nitrogen oxide (NO _x ) that is formed cannot be efficiently processed.

Japanese Patent Laid-Open No. 2004-943

  The present invention aims to improve the activity of the catalyst. In particular, it aims to develop an effective catalyst for the treatment of exhaust gas generated from gas-fired boilers and gas turbines.

  In order to solve the above-mentioned problems, the present inventors have intensively studied and found the following technique to complete the invention. That is, when the pore diameter is measured at 0.003 to 40 μm, it has peaks at 1 to 20 μm (A peak) and 0.006 to 0.06 μm (B peak), and at least one of the A peak or the B peak. Is an oxide of titanium / silicon / tungsten (hereinafter also referred to as “Ti—Si—W oxide”) characterized by showing the first size within the range in which the pore diameter is measured. A denitration catalyst using an oxide, a method for producing the oxide, and a denitration method using the catalyst.

The Ti—Si—W oxide according to the present invention is a substance having a peak of pore diameter at a special position, and by using it as a catalyst for flue gas denitration, nitrogen oxide (NO _X ) in exhaust gas can be efficiently used. In particular, it effectively acts on the treatment of exhaust gas generated from a gas-fired boiler or gas turbine.

FIG. 1 shows a Ti-Si-W oxide related to Example 1 which is the present invention, which is subjected to pore measurement and differentially displayed. The horizontal axis is the pore diameter, and the vertical axis is an arbitrary value indicating the strength. The pore volume can be calculated from the peak area in a specific range of pore diameters. FIG. 2 shows a Ti-Si-W oxide related to Example 2 which is the present invention, which is subjected to pore measurement and differentially displayed. The explanation of the horizontal and vertical axes is the same as in FIG. FIG. 3 shows pores of a mixed oxide of titanium and tungsten (hereinafter also referred to as “Ti—W mixed oxide”) related to Comparative Example 1 and differentially displayed. The explanation of the horizontal and vertical axes is the same as in FIG.

When the pore diameter is measured at 0.003 to 40 μm, the first invention has peaks at 1 to 20 μm (A peak) and 0.006 to 0.06 μm (B peak), and A peak or B peak least an oxide of titanium-silicon-tungsten where one also, characterized in that it presents one th size within the range of measuring the pore diameter (hereinafter, also referred to as "Ti-Si-W oxide") and It is the manufacturing method of the catalyst for nitrogen oxide removal characterized by using . Preferably, when the pore volume of the pore diameter at 0.003 to 40 μm (referred to as “total pore volume”) is 1, the pore volume of the A peak is 0.3 to 0.6 (A / total The pore volume of the B peak is 0.3 to 0.6 (B / total pore volume), and the pore volume ratio of the A peak to the B peak is 0.9. -2.0 (B / A), titanium 40-98 mass% (TiO ₂ conversion), silicon 1-30 mass% (SiO ₂ conversion) and tungsten 1-30 mass% (WO ₃ conversion) ) Is a method for producing a nitrogen oxide removing catalyst using a Ti—Si—W oxide .

The titanium / silicon / tungsten compound is neutralized and mixed with a mixed aqueous solution of ammonia water, a silicon source and a tungsten source, and the sulfuric acid aqueous solution of titanyl sulfate is adjusted to pH 3 to 10 to generate a precipitate as a hydroxide, This is a method for producing a catalyst for removing nitrogen oxides using a titanium / silicon / tungsten oxide obtained by a coprecipitation method in which a precipitate slurry is filtered, washed with water, dried and fired after precipitation.

The second invention is a denitration method characterized in that exhaust gas containing nitrogen oxides is treated in the presence of ammonia using the catalyst obtained by the production method of the first invention .

(First invention)
When the pore diameter is measured at 0.003 to 40 μm, the first invention has peaks at 1 to 20 μm (A peak) and 0.006 to 0.06 μm (B peak), and A peak or B peak At least one of the oxides of titanium, silicon, and tungsten is characterized by showing the first size within the range in which the pore diameter is measured.

  The A peak is a group of pores having a peak at a pore diameter of 1 to 20 μm. The pore volume of the A peak is 0.3 to 0.6 (A / total pore volume) when the pore volume having a pore diameter at 0.003 to 40 μm (referred to as “total pore volume”) is 1. Preferably 0.3 to 0.5 (A / total pore volume). If it is less than 0.3, the denitration performance is lowered, which is not preferable. If it exceeds 0.6, the denitration performance is not improved so much, but the mechanical strength of the catalyst is lowered and the wear resistance strength is lowered. This is because harmful effects may occur.

  The B peak is a group of pores having a peak at a pore diameter of 0.006 to 0.06 μm. The pore volume of the B peak is 0.3 to 0.6 (B / total pore volume), preferably 0.3 to 0.5 (B / total pore) when the total pore volume is 1. Volume). If it is less than 0.3, the denitration performance is lowered, which is not preferable. If it exceeds 0.6, the denitration performance is not improved so much, but the mechanical strength of the catalyst is lowered and the wear resistance strength is lowered. This is because harmful effects may occur.

  The pore volume ratio between the A peak and the B peak is preferably 0.9 to 2.0 (B / A), more preferably 0.9 to 1.7. If it is less than 0.9, the denitration performance is low, which is not preferable. If it exceeds 2.0, the denitration performance is not improved so much, but the mechanical strength of the catalyst is lowered and the wear resistance strength is lowered. This is because there is a risk of harmful effects.

  A peak or B peak is in the range of pore diameters in the range of 0.003 to 40 μm, at least one shows the size of the first peak, and both may have the same peak size, One shows the first size and the other shows the second size. The first size refers to a group of pores having a maximum peak in the pore volume in a range of pore diameters in which the pore diameter is a peak when the pore diameter is 0.003 to 40 μm. Similarly, the second size refers to a group of pores having a second peak in pore volume.

  The pore diameter and pore volume can be measured by a commonly used mercury intrusion porosimeter. The peak is a peak generated when the pore diameter measurement result is displayed in a differential form with the pore diameter as the horizontal axis and the pore volume as the vertical axis.

Ti-Si-W oxides are titanium 40-98 mass% (TiO ₂ conversion), silicon 1-30 mass% (SiO ₂ conversion) and tungsten 1-30 mass% (WO ₃ conversion). Is preferred. More preferably, titanium is 60 to 98% by mass (in terms of TiO ₂ ), silicon is in the range of 1 to 20% by mass (in terms of SiO ₂ ), and tungsten is in the range of 1 to 20% by mass (in terms of WO ₃ ). Most preferably, titanium is 70%. 98 wt% (TiO ₂ equivalent), a silicon 1 to 20 mass% (SiO ₂ equivalent) and tungsten 1 to 10 mass% (WO ₃ conversion). If titanium is less than 40% by mass, the denitration performance is low, which is not preferable. If it exceeds 98% by mass, the heat resistance of the catalyst is low, which is not preferable. If silicon is less than 1% by mass, the moldability of the catalyst is not preferable. This is because when the amount exceeds 30% by mass, the denitration performance becomes low and is not preferable. When the content of tungsten is less than 1% by mass, the denitration performance decreases and is not preferable, and when it exceeds 30% by mass, This is because the additive effect cannot be sufficiently obtained and the denitration performance may be lowered.

  The Ti-Si-W oxide not only exhibits a pore distribution with a specific peak of pore diameter, but also exhibits an effect on oxidation and reduction reactions, and particularly exhibits an excellent effect on removal of nitrogen oxides. It is.

  In addition, the Ti—Si—W oxide only needs to have the pore diameter peak, and the oxides do not need to be complexed. Furthermore, there is no problem even if other compounds are contained as long as the pore peak is maintained. For example, oxides such as vanadium, molybdenum, iron, manganese, nickel, barium, strontium, silver, cesium, and magnesium can be used. 0.1-20 mass% can be added with respect to Ti-Si-W oxide.

(Production method of Ti-Si-W oxide)
The preparation method of Ti-Si-W oxide is the third invention, and as a method, (1) neutralize a sulfuric acid aqueous solution of titanyl sulfate to a mixed aqueous solution of ammonia water, a silicon source, and a tungsten source, and mix thoroughly; pH adjustment of pH 3 to 10, preferably pH 4 to 8 to generate precipitates mainly as hydroxides, and after sufficient precipitation, the precipitate slurry is filtered, washed with water, dried and fired, (2 ) An impregnation method in which one oxide is impregnated with the other aqueous solution and dried and fired; (3) a kneading method in which each precursor is mixed with water and kneaded into a slurry, dried, and fired; (4) There is a solid phase reaction method in which the respective oxide precursors are sufficiently mixed and fired, but a coprecipitation method is preferred.

Moreover, when manufacturing the said oxide, although a commercially available raw material can also be used as it is, Preferably it is adjusting and using for the liquid of a predetermined density | concentration. For example, 20 to 400 g (TiO ₂ basis) with respect to L of liquid (L) in the case of the titanium source is preferably 50 to 100 g (TiO ₂ equivalent). In the case of a silicon source, it is 0.5 to 200 g (SiO ₂ equivalent), preferably 1 to 100 g (SiO ₂ equivalent) per liter of liquid. In the case of tungsten source 50 to 500 g (WO ₃ conversion) with respect to L of liquid, preferably 100 to 400 g (WO ₃ conversion). When these amounts are exceeded, the reaction proceeds locally before mixing uniformly and it is difficult to produce uniform hydroxides, and this is not preferred. If the amount is less than these amounts, the pH of the solution is unlikely to fall within a predetermined range. This is not preferable. In any case, it may be difficult to produce a target oxide.

(Second invention)
The second invention is a catalyst for removing nitrogen oxides containing Ti—Si—W oxides. Any material may be used as long as it contains a Ti—Si—W oxide, and it exhibits a function in a form usually used as a catalyst. The denitration catalyst is preferably one selected from the group consisting of Ti-Si-W oxide and vanadium, tungsten, molybdenum, iron, manganese, nickel, barium, strontium, silver, cesium and magnesium as active components. It can be obtained by adding the above elements or compounds thereof. In particular, those containing one or more elements selected from the group consisting of vanadium, tungsten and molybdenum or compounds thereof as active ingredients are preferred. The content of the active ingredient is 0.1 to 20% by mass (as oxide) when the catalyst is 100% by mass, preferably 0.2 to 15% by mass (as oxide), more preferably 0.4. -10% by mass (as oxide). This is because if the amount is less than 0.1% by mass (as oxide), the denitration performance is lowered, which is not preferable. If the amount exceeds 20% by mass (as oxide), the addition effect cannot be sufficiently obtained and the denitration performance is deteriorated. Because there is a case to do.

  The catalyst component may be formed into a clay shape by adding water, a molding aid, and the like, and may be formed into a shape suitable for the intended use, for example, a honeycomb shape, a pellet shape, or a powder shape. In the case of a honeycomb, it is preferable that the corner has a side of 50 to 200 mm, the opening has a side of 1 to 10 mm, the rib thickness is 0.1 to 1.5 mm, and the length is 200 to 2000 mm.

(Denitration method)
Fourth invention for removing a gas containing nitrogen oxides (NO _X). The target gas may be any gas as long as it contains nitrogen oxides, but is preferably exhaust gas generated from a gas-fired boiler or a gas turbine. The concentration of nitrogen oxides (NO _X ) is 10 to 2000 ppm (NO _X conversion), preferably 20 to 500 ppm (NO _X conversion), more preferably 40 to 100 ppm (NO _X conversion). These gases can be treated even if they contain water, SO _x , dust or the like.

At the time of denitration, ammonia or urea can be added to the exhaust gas. The addition amount is 0.2 to 2.0 mol, preferably 0.5 to 1.0 mol in terms of ammonia (1/2 mol in the case of urea) with respect to 1 mol of nitrogen oxide (NO _X conversion). It is.

  Processing temperature is 150-500 degreeC, Preferably it is 200-450 degreeC, More preferably, it is 250-400 degreeC.

The space velocity is 1000 to 100000 hr ⁻¹ (STP), preferably 2000 to 50000 hr ⁻¹ (STP), more preferably 3000 to 30000 hr ⁻¹ (STP).

  Although the above-mentioned components can be added in the following examples, the invention will be described in detail by the following examples and comparative examples as representative examples. The present invention is not limited to the following examples as long as the effects of the present invention are achieved.

Example 1
<Preparation of Compound A (Ti-Si-W Oxide)>
1.4 kg of ammonium paratungstate (containing 90 wt% as WO ₃ ) and 0.6 kg of monoethanolamine were mixed and dissolved in 10 L of water (containing 120 g / L as WO ₃ ) to prepare a uniform solution. This tungsten-containing solution and silica sol (containing 30 wt% as SiO ₂ ) 3.4 kg, 10 wt% ammonia water 240 L mixed solution (SiO ₂ containing 4 g / L), sulfuric acid solution of titanyl sulfate (70 g as TiO ₂ ) / L content, sulfuric acid concentration 290 g / L) 260 L was gradually added dropwise with good stirring to form a precipitate, and then an appropriate amount of 25 mass% aqueous ammonia was added to adjust the pH to 7. The slurry was left to mature for 40 hours, then filtered, washed and dried at 150 ° C. for 20 hours. This was calcined at 500 ° C. for 5 hours in an air atmosphere, and further pulverized using a hammer mill to obtain Compound A (Ti—Si—W oxide).

The composition of Compound A was 89/ ₅ /6% by mass (as oxide) of TiO ₂ / SiO ₂ / WO ₃ .

(Example 2)
<Preparation of Compound B (Ti-Si-W Oxide)>
1.4 kg of ammonium paratungstate (containing 90 wt% as WO ₃ ) and 0.6 kg of monoethanolamine were mixed and dissolved in 10 L of water (containing 120 g / L as WO ₃ ) to prepare a uniform solution. This tungsten-containing solution and silica sol (containing 30 wt% as SiO ₂ ) 3.4 kg, 10 wt% ammonia water 240 L mixed solution (SiO ₂ containing 4 g / L), sulfuric acid solution of titanyl sulfate (70 g as TiO ₂ ) / L containing, sulfuric acid concentration 290 g / L) 260 L was gradually added dropwise with good stirring to form a precipitate, and then an appropriate amount of 25 mass% aqueous ammonia was added to adjust the pH to 5. The slurry was left to mature for 40 hours, then filtered, washed and dried at 150 ° C. for 20 hours. This was calcined at 500 ° C. for 5 hours in an air atmosphere, and further pulverized using a hammer mill to obtain Compound B (Ti—Si—W oxide).

The composition of Compound B was 89/5/6 mass% in terms of mass ratio (as oxide) of TiO ₂ / SiO ₂ / WO ₃ .

(Comparative Example 1)
DT-52 (trade name) manufactured by Cristal Global, which is a commercially available mixed oxide of titanium and tungsten (hereinafter referred to as “Ti—W mixed oxide”) was used as the mixture a.

The composition of the mixture a was 90/10% by mass in terms of TiO ₂ / WO ₃ (as oxide).

(Measurement of pore diameter and pore volume)
The pore diameter and pore volume of the compounds A and B obtained in Examples 1 and 2 and the mixture a obtained in Comparative Example 1 were measured with a mercury intrusion porosimeter.

  Value of pore volume ratio (A / total pore volume) between A peak (1-20 μm) and total pore volume (0.003-40 μm), B peak (0.006-0.06 μm) and total pore Value of pore volume ratio (B / total pore volume) of volume (0.003 to 40 μm) and pore volume ratio of A peak (1.0 to 20 μm) and B peak (0.006 to 0.06 μm) The value of (B / A) is shown in Table 1. As can be seen from Table 1, the compounds A and B (Examples 1 and 2) were compared with the mixture a (Comparative Example 1) as follows: A / total pore volume value, B / total pore volume value, B / A It can be seen that the value of is high.

  The results of pore size distribution in which the pore diameter is plotted on the horizontal axis, the pore volume is plotted on the vertical axis, and differential type are displayed are shown in FIG. 1 for Compound A (Example 1) and FIG. 2 for Compound B (Example 2). a (Comparative Example 1) is shown in FIG. As can be seen from FIGS. 1 to 3, the compounds A and B (Examples 1 and 2) are the first and second peaks of the A peak and the B peak as compared to the mixture a (Comparative Example 1), and the B peak ( It can be seen that the peak area of 0.006 to 0.06 μm is large. On the other hand, it can also be seen that the mixture a has the largest peak in the pore system of 0.2 to 0.6 μm. In the following, a catalyst is prepared using these compounds.

(Example 3)
<Preparation of catalyst A>
20 kg of the Ti—Si—W oxide powder (compound A) obtained in Example 1 was added 1.5 kg of ammonium metavanadate (containing 78 wt% as V ₂ O ₅ ), 2.1 kg of oxalic acid, monoethanolamine 0 A homogeneous solution in which 5 kg is mixed and dissolved in 3 L of water, 0.9 kg of ammonium paratungstate (containing 90 wt% as WO ₃ ), and a uniform solution in which 0.4 kg of monoethanolamine is mixed and dissolved in 2 L of water are molded. The mixture was added together with an auxiliary agent and an appropriate amount of water, kneaded with a kneader, and then molded into a honeycomb shape having an external shape of 80 mm square, a length of 500 mm, an aperture of 2.9 mm, and a wall thickness of 0.4 mm. This was dried at 80 ° C. and then calcined at 450 ° C. for 5 hours in an air atmosphere to obtain Catalyst A.

The composition of catalyst A was 91/ ₅ /4% by mass in terms of the mass ratio of compound A / V ₂ O ₅ / WO ₃ (as oxide).

Example 4
<Preparation of catalyst B>
20 kg of the Ti—Si—W oxide powder (compound B) obtained in Example 2 was added to 1.5 kg of ammonium metavanadate (containing 78 wt% as V ₂ O ₅ ), 2.1 kg of oxalic acid, monoethanolamine 0 A homogeneous solution in which 5 kg is mixed and dissolved in 3 L of water, 0.9 kg of ammonium paratungstate (containing 90 wt% as WO ₃ ), and a uniform solution in which 0.4 kg of monoethanolamine is mixed and dissolved in 2 L of water are molded. The mixture was added together with an auxiliary agent and an appropriate amount of water, kneaded with a kneader, and then molded into a honeycomb shape having an external shape of 80 mm square, a length of 500 mm, an aperture of 2.9 mm, and a wall thickness of 0.4 mm. This was dried at 80 ° C. and then calcined at 450 ° C. for 5 hours in an air atmosphere to obtain Catalyst B.

The composition of the catalyst B was 91/ ₅ /4% by mass in terms of mass ratio of compound B / V ₂ O ₅ / WO ₃ (as oxide).

(Comparative Example 2)
<Preparation of catalyst a>
20 kg of the Ti—W mixed oxide powder (mixture a) obtained in Comparative Example 1, 1.5 kg of ammonium metavanadate (containing 78 wt% as V ₂ O ₅ ), 2.1 kg of oxalic acid, 0.1% of monoethanolamine A uniform solution in which 5 kg is mixed and dissolved in 3 L of water, 0.9 kg of ammonium paratungstate (containing 90 wt% as WO ₃ ), and a uniform solution in which 0.4 kg of monoethanolamine is mixed and dissolved in 2 L of water It was added together with an agent and an appropriate amount of water, kneaded with a kneader, and then formed into a honeycomb shape having an external shape of 80 mm square, a length of 500 mm, an opening of 2.9 mm, and a wall thickness of 0.4 mm by an extruder. This was dried at 80 ° C. and then calcined at 450 ° C. for 5 hours in an air atmosphere to obtain catalyst a.

The composition of the catalyst a was 91/ ₅ /4% by mass in terms of the mass ratio of the mixture a / V ₂ O ₅ / WO ₃ (as oxide).

(Catalyst evaluation)
Catalysts A and B obtained in Examples 3 and 4 and catalyst a obtained in Comparative Example 2 were filled in a stainless steel reaction tube immersed in a molten salt bath, and synthesis gas having the following composition was charged under the following conditions. It was introduced into the layer and the denitration rate was measured.

The NOx removal rate was determined according to the following equation by measuring the NO _X concentration at the reaction tube inlet and the reaction tube outlet with a NO _X meter (chemiluminescence type, MODEL 5100 manufactured by Nippon Thermo Co., Ltd.). The obtained denitration rate is shown in Table 2. As can be seen from Table 2, the catalysts A and B (Examples 3 and 4) have a higher denitration rate than the catalyst a (Comparative Example 2).

<Reaction conditions>
Gas temperature: 350 ° C
Space velocity (STP): 26000 hr ⁻¹
<Syngas composition>
NO _X : 100 ppm, dry
NH ₃ : 100 ppm, dry,
O ₂ : 15%, dry
H ₂ O: 10%, wet
N ₂ : balance

  The present invention is a technique effective in the field of exhaust gas treatment, particularly in the treatment of exhaust gas containing nitrogen oxides.

Claims (6)

When the pore diameter was measured at 0.003 to 40 μm, it had peaks at 1 to 20 μm (A peak) and 0.006 to 0.06 μm (B peak), and at least one of the A peak or the B peak was the fine particle. A method for producing a catalyst for removing nitrogen oxide, characterized by using an oxide of titanium, silicon, and tungsten, wherein the oxide of titanium, silicon, and tungsten is used. The oxide of titanium / silicon / tungsten according to claim 1 has a pore volume (referred to as “total pore volume”) having a pore diameter at 0.003 to 40 μm as 1. The pore volume of the A peak is 0.3 to 0.6 (A / total pore volume) and the pore volume of the B peak according to claim 1 is 0.3 to 0.6 (B / total fine volume). The method for producing a catalyst for removing nitrogen oxides according to claim 1, wherein the pore volume is a pore volume. The titanium / silicon / tungsten oxide according to claim 1 has a pore volume ratio of A peak to B peak according to claim 1 of 0.9 to 2.0 (B / A). A method for producing a catalyst for removing nitrogen oxides according to claim 1. The oxide of titanium, silicon, and tungsten according to claim 1 is 40 to 98% by mass of titanium (in terms of TiO2), 1 to 30% by mass of silicon (in terms of SiO2), and 1 to 30% by mass of tungsten (in terms of WO3). The method for producing a catalyst for removing nitrogen oxides according to claim 1, wherein 5. The titanium / silicon / tungsten oxide according to claim 1 is mixed with an aqueous solution of ammonia water, a silicon source, and a tungsten source after neutralizing a sulfuric acid aqueous solution of titanyl sulfate to a pH of 3 to 10. It is obtained by a coprecipitation method in which a precipitate is produced as a hydroxide by adjusting and precipitated, and then the precipitate slurry is filtered, washed with water, dried and fired. The manufacturing method of the catalyst for nitrogen oxide removal of any one of Claims 1. A denitration method comprising treating an exhaust gas containing nitrogen oxides in the presence of ammonia using the catalyst for removing nitrogen oxides obtained by the method according to any one of claims 1 to 5.

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