Columnar denitration catalyst as well as preparation method and application thereof

Abstract

The invention discloses a columnar denitration catalyst as well as a preparation method and application thereof, and belongs to the technical field of catalysts. The columnar denitration catalyst containing Fe, Pr, Zr, Ti and Si elements is prepared through a precipitation method, the columnar denitration catalyst is simple in forming process, the main active component of the columnar denitration catalyst is iron oxide, the Pr element can improve the oxygen vacancy of the catalyst and can promote oxidation circulation in the reaction process of the catalyst, the Zr element provides an acid site, the ammonia gas adsorption capacity of the catalyst is improved, and the denitration efficiency of the columnar denitration catalyst is improved. The two synergistically improve the activity of the catalyst; ti and Si elements not only can be used as catalyst carriers, but also form a gel network structure to improve the strength of the catalyst. The final removal rate of nitric oxide can reach 95% or above, the average compressive strength of the catalyst reaches 60 N / grain or above, and the catalyst can be applied to removal of nitric oxide in middle-high pressure gas such as tail gas of a nitric acid plant.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a columnar denitrification catalyst, its preparation method, and its application. Background Technology

[0002] Nitrogen oxides (NO) x NO is a common air pollutant. NO and NO2 can react with water in the air to produce nitric acid and nitrite, leading to acid rain, which damages soil, vegetation, and river systems, and corrodes buildings and equipment. In addition, NO in vehicle exhaust... x When exposed to ultraviolet light, hydrocarbons undergo a series of reactions to form toxic photochemical smog, which not only reduces atmospheric visibility but also irritates human mucous membranes, causing headaches, respiratory disorders, and abnormal lung function in children, resulting in significant damage to human health.

[0003] Iron-based denitration catalysts are inexpensive and environmentally friendly, but their catalytic activity is poor due to insufficient oxidation performance and acidity sites, necessitating improvements in their acidity and oxidation properties. To improve oxidation performance, doping with elements such as Pr (purine terephthalic acid) that readily generate oxygen vacancies can enhance it. Praseodymium oxide can adsorb oxygen from the reactants, promoting the oxidation cycle in the catalytic process. Adding Zr can increase the acidity sites on the catalyst; ZrO2 can adsorb ammonia from the reactants, increasing the amount of active components adsorbed. The synergistic effect of Pr and Zr can significantly improve the activity of iron-based denitration catalysts.

[0004] Current research on denitrification catalysts mainly focuses on powder catalysts. Although powder catalysts exhibit good activity in experiments, their high bed resistance and poor mechanical properties make them difficult to apply in practical industrial environments. Therefore, further industrial molding of powder catalysts is needed to create monolithic catalysts. To achieve applications in high-pressure tail gas or flue gas fields such as nitric acid plants, high-strength molding of the catalyst is required to reduce the impact of excessive gas resistance drop caused by catalyst pulverization, and to minimize the impact of pulverized catalyst on downstream equipment. Catalyst molding requires the use of binders and pore-forming agents. Silicon and aluminum elements readily form gel networks and possess adhesive properties, making them suitable as binders in the molding process. Titanium-silicon composite sols readily form gel network structures, making them suitable for preparing high-strength denitrification catalysts. Furthermore, titanium-silicon oxides can serve as catalyst supports, improving the dispersion and utilization rate of active components, which is beneficial for enhancing catalyst activity.

[0005] The prior art discloses a denitrification catalyst and its forming method. The catalyst powder is a mixture of silicon-aluminum molecular sieve and copper, or silicon-aluminum molecular sieve and copper-containing compound. The chemical binder includes silica sol or aluminum sol. After mixing and kneading, the catalyst is extruded through a perforated plate of a certain shape under the extrusion action of a screw. The extruded material is cut into a columnar support catalyst of a certain length under the action of slicing. After drying and calcination, the support catalyst is immersed in a slurry of active components containing copper compounds. After filtration, drying and calcination, the formed catalyst is obtained. Summary of the Invention

[0006] In view of the above-mentioned prior art, the present invention provides a columnar denitrification catalyst, its preparation method and application, to solve the technical problems of low strength and poor catalytic activity of existing denitrification catalysts.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is to provide a method for preparing a columnar denitrification catalyst, comprising the following steps: S1: Iron salt, praseodymium salt, zirconium salt, silicate and titanium salt are co-dissolved in water to obtain a mixed solution; then an alkaline solution is added to the obtained mixed solution, and the mixture is stirred to precipitate; the precipitate is then collected, washed and dried to obtain the catalyst precursor; S2: Add pore-forming agent and extrusion aid to the catalyst precursor, mix evenly, and then extrude the mixture into columnar catalyst; S3: Calcine the columnar catalyst obtained in S2 to obtain the columnar denitration catalyst.

[0008] Based on the above technical solution, the present invention can be further improved as follows.

[0009] Furthermore, the amounts of iron salt, praseodymium salt, zirconium salt, silicate and titanium salt are based on the following: iron content of 1-8 wt%, Pr content of 0.5-5 wt%, Zr content of 0.5-5 wt%, Ti content of 20-40 wt%, and Si content of 10-30 wt% in the obtained catalyst precursor.

[0010] Furthermore, the amounts of iron salt, praseodymium salt, zirconium salt, silicate and titanium salt are based on the following: iron content of 4-6 wt%, Pr content of 1.5 wt%, Zr content of 3 wt%, Ti content of 30-31 wt%, and Si content of 25-26 wt% in the obtained catalyst precursor.

[0011] Furthermore, the iron salt is ferric nitrate, the praseodymium salt is praseodymium nitrate, the zirconium salt is zirconium nitrate, and the titanium salt is titanium oxysulfate; the alkaline solution is ammonia water.

[0012] Furthermore, the drying temperature in S1 is 100℃, and the drying time is 6 hours.

[0013] Furthermore, the pore-forming agent is methylcellulose or polyethylene glycol, and the amount of pore-forming agent added is 1-5% of the mass of the catalyst precursor; the extrusion aid is graphite or carbon black, and the amount of extrusion aid added is 1-6% of the mass of the catalyst precursor.

[0014] Furthermore, the diameter of the columnar catalyst is 1~6 mm and the length is 1~10 mm.

[0015] Furthermore, the calcination temperature in S3 is 400~600℃, and the calcination time is 1~3h.

[0016] The present invention also discloses a columnar denitrification catalyst prepared by the above preparation method.

[0017] The present invention also discloses the application of the above-mentioned columnar denitrification catalyst in the removal of nitrogen oxides from high-pressure tail gas or flue gas.

[0018] The beneficial effects of this invention are: 1. The columnar denitrification catalyst of the present invention has a simple molding process, short preparation cycle and low production cost, which is conducive to large-scale industrial production. The size of the catalyst is adjustable and the resulting catalyst has high strength, which can reach more than 60 N / particle.

[0019] 2. The columnar denitrification catalyst of this invention contains Fe, Pr, Zr, Ti, and Si elements. The forming process of this columnar denitrification catalyst is simple, and the main active component is iron oxide. Pr element can increase oxygen vacancies in the catalyst, promoting the oxidation cycle during the catalyst reaction. Zr element provides acidic sites, enhancing the catalyst's ability to adsorb ammonia. Both elements synergistically enhance the catalyst activity. Ti and Si elements not only serve as catalyst supports but also form a gelled network structure, improving catalyst strength. The final nitrogen oxide removal rate can reach over 95%, and the average compressive strength of the catalyst reaches over 60 N / particle, making it suitable for nitrogen oxide removal from medium- and high-pressure gases such as nitric acid plant tail gas. Attached Figure Description

[0020] Figure 1 This is a comparison chart of the denitrification effects of different denitrification catalysts. Detailed Implementation

[0021] The invention will be further described below with reference to the accompanying drawings and specific embodiments to enable those skilled in the art to better understand the invention, including but not limited to the following examples. Those skilled in the art should understand that, based on the content and concept of the invention, the raw materials, parameters, etc., in the examples can be replaced, combined, modified, and transformed, and these all fall within the protection scope of the invention.

[0022] Example 1 A columnar denitration catalyst is prepared by the following steps: (1) Ferric nitrate, praseodymium nitrate, zirconium nitrate, silicic acid, and titanium oxysulfate are dissolved in water to obtain a mixed solution; then ammonia is added to the obtained mixed solution, with the amount of ammonia added being twice the molar amount of NH3 compared to the anions of the dissolved substances; after stirring for 2 hours, precipitation is carried out; the precipitate is collected by filtration and washed three times with deionized water, and dried at 100°C for 6 hours to obtain the catalyst precursor; the amounts of ferric nitrate, praseodymium nitrate, zirconium nitrate, silicic acid, and titanium oxysulfate are based on the following amounts in the obtained catalyst precursor: iron content 6 wt%, Pr content 1.5 wt%, Zr content 3 wt%, Ti content 30 wt%, and Si content 25 wt%; (2) Add methylcellulose (pore-forming agent) and graphite (extrusion aid) to the catalyst precursor. The amount of pore-forming agent added is 3% of the mass of the catalyst precursor, and the amount of extrusion aid added is 1% of the mass of the catalyst precursor. After mixing evenly, the mixture is extruded into columnar catalyst with a length of 3.8 mm and a diameter of 5 mm by a fully automatic tablet press. (3) The columnar catalyst obtained in step (2) is calcined at 500°C for 2 hours to obtain the columnar denitration catalyst.

[0023] Example 2 A columnar denitration catalyst is prepared by the following steps: (1) Ferric nitrate, praseodymium nitrate, zirconium nitrate, silicic acid, and titanium oxysulfate are dissolved in water to obtain a mixed solution; then ammonia is added to the obtained mixed solution, with the amount of ammonia added being twice the molar amount of NH3 compared to the anions of the dissolved substances; after stirring for 2 hours, precipitation is carried out; the precipitate is collected by filtration and washed three times with deionized water, and dried at 100°C for 6 hours to obtain the catalyst precursor; the amounts of ferric nitrate, praseodymium nitrate, zirconium nitrate, silicic acid, and titanium oxysulfate are based on the following amounts in the obtained catalyst precursor: iron content 4wt%, Pr content 1.5wt%, Zr content 3wt%, Ti content 31wt%, and Si content 26wt%; (2) Add methylcellulose (pore-forming agent) and graphite (extrusion aid) to the catalyst precursor. The amount of pore-forming agent added is 3% of the mass of the catalyst precursor, and the amount of extrusion aid added is 1% of the mass of the catalyst precursor. After mixing evenly, the mixture is extruded into columnar catalyst with a length of 3.8 mm and a diameter of 5 mm by a fully automatic tablet press. (3) The columnar catalyst obtained in step (2) is calcined at 500°C for 2 hours to obtain the columnar denitration catalyst.

[0024] Example 3 A columnar denitration catalyst is prepared by the following steps: (1) Ferric nitrate, praseodymium nitrate, zirconium nitrate, silicic acid, and titanium oxysulfate are dissolved in water to obtain a mixed solution; then ammonia is added to the obtained mixed solution, with the amount of ammonia added being twice the molar amount of NH3 compared to the anions of the dissolved substances; after stirring for 2 hours, precipitation is carried out; the precipitate is collected by filtration and washed three times with deionized water, and dried at 100°C for 6 hours to obtain the catalyst precursor; the amounts of ferric nitrate, praseodymium nitrate, zirconium nitrate, silicic acid, and titanium oxysulfate are based on the following amounts in the obtained catalyst precursor: iron content 1 wt%, Pr content 5 wt%, Zr content 0.5 wt%, Ti content 40 wt%, and Si content 10 wt%; (2) Polyethylene glycol (pore-forming agent) and carbon black (extrusion aid) are added to the catalyst precursor. The amount of pore-forming agent added is 5% of the mass of the catalyst precursor, and the amount of extrusion aid added is 6% of the mass of the catalyst precursor. After mixing evenly, the mixture is extruded into columnar catalyst with a length of 1 mm and a diameter of 1 mm by a fully automatic tablet press. (3) The columnar catalyst obtained in step (2) is calcined at 400°C for 3 hours to obtain the columnar denitration catalyst.

[0025] Example 4 A columnar denitration catalyst is prepared by the following steps: (1) Ferric nitrate, praseodymium nitrate, zirconium nitrate, silicic acid, and titanium oxysulfate are dissolved in water to obtain a mixed solution; then ammonia is added to the obtained mixed solution, with the amount of ammonia added being twice the molar amount of NH3 compared to the anions of the dissolved substances; after stirring for 2 hours, precipitation is carried out; the precipitate is collected by filtration and washed three times with deionized water, and dried at 100°C for 6 hours to obtain the catalyst precursor; the amounts of ferric nitrate, praseodymium nitrate, zirconium nitrate, silicic acid, and titanium oxysulfate are based on the following amounts in the obtained catalyst precursor: iron content of 8wt%, Pr content of 0.5wt%, Zr content of 5wt%, Ti content of 20wt%, and Si content of 30wt%; (2) Polyethylene glycol (pore-forming agent) and carbon black (extrusion aid) are added to the catalyst precursor. The amount of pore-forming agent added is 1% of the mass of the catalyst precursor, and the amount of extrusion aid added is 1% of the mass of the catalyst precursor. After mixing evenly, the mixture is extruded into a columnar catalyst with a length of 6 mm and a diameter of 10 mm by a fully automatic tablet press. (3) Calcine the columnar catalyst obtained in step (2) at 600°C for 1 hour to obtain the columnar denitration catalyst.

[0026] Comparative Example 1 A columnar denitration catalyst is prepared by the following steps: (1) Ferric nitrate, praseodymium nitrate, zirconium nitrate, and aluminum nitrate were dissolved in water to obtain a mixed solution. Then, ammonia was added to the mixed solution, with the amount of ammonia added being twice the molar amount of NH3 compared to the anions of the dissolved substances. After stirring for 2 hours, precipitation was carried out. The precipitate was collected by filtration and washed three times with deionized water. It was then dried at 100°C for 6 hours to obtain the catalyst precursor. The amounts of ferric nitrate, praseodymium nitrate, zirconium nitrate, zirconium nitrate, and aluminum nitrate were based on the following: iron content of 5 wt%, Pr content of 1.5 wt%, Zr content of 3 wt%, and Al content of 46 wt% in the obtained catalyst precursor. (2) Add methylcellulose (pore-forming agent) and graphite (extrusion aid) to the catalyst precursor. The amount of pore-forming agent added is 3% of the mass of the catalyst precursor, and the amount of extrusion aid added is 1% of the mass of the catalyst precursor. After mixing evenly, the mixture is extruded into columnar catalyst with a length of 3.8 mm and a diameter of 5 mm by a fully automatic tablet press. (3) The columnar catalyst obtained in step (2) is calcined at 500°C for 2 hours to obtain the columnar denitration catalyst.

[0027] Comparative Example 2 A columnar denitration catalyst is prepared by the following steps: (1) Ferric nitrate, silicic acid, and titanium oxysulfate are dissolved in water to obtain a mixed solution; then ammonia is added to the obtained mixed solution, with the amount of ammonia added being twice the molar amount of NH3 compared to the anions of the dissolved substances; after stirring for 2 hours, precipitation is carried out; the precipitate is collected by filtration, washed three times with deionized water, and dried at 100°C for 6 hours to obtain the catalyst precursor; the amounts of ferric nitrate, praseodymium nitrate, zirconium nitrate, silicic acid, and titanium oxysulfate are based on the following: iron content of 5 wt%, Ti content of 32 wt%, and Si content of 27 wt% in the obtained catalyst precursor; (2) Add methylcellulose (pore-forming agent) and graphite (extrusion aid) to the catalyst precursor. The amount of pore-forming agent added is 3% of the mass of the catalyst precursor, and the amount of extrusion aid added is 1% of the mass of the catalyst precursor. After mixing evenly, the mixture is extruded into columnar catalyst with a length of 3.8 mm and a diameter of 5 mm by a fully automatic tablet press. (3) The columnar catalyst obtained in step (2) is calcined at 500°C for 2 hours to obtain the columnar denitration catalyst.

[0028] Experimental Example I. Strength Test of Columnar Denitrification Catalyst Tables 1, 2, and 3 show the strength distribution of the columnar denitrification catalysts prepared in Examples 1, 2, and Comparative Example 1, respectively. The strength was measured using a strength meter, and 40 particles of the same catalyst were randomly selected for testing. From Tables 1-3, it can be seen that the catalysts in Examples 1 and 2 have better strength, with average strengths reaching 75 N / particle and 70 N / particle, respectively. However, the catalyst prepared in Comparative Example 1 has poor strength, only 40 N / particle. This indicates that high-strength iron-based denitrification catalysts can be prepared using titanium-silicon composite oxide as a support, while catalysts prepared using alumina as a support have poorer strength. This is mainly because titanium and silicon easily form a gelled network structure during precipitation, which forms a high-strength structure after calcination, thereby improving the overall catalyst strength.

[0029] Table 1. Strength test results of the columnar denitrification catalyst prepared in Example 1 Table 2. Strength test results of the columnar denitrification catalyst prepared in Example 2 Table 3. Strength test results of the columnar denitrification catalyst prepared in Comparative Example 1 II. NO Conversion Rate Test of Columnar Denitrification Catalyst The NO conversion rate test method for column-shaped denitrification catalysts is as follows: 10 mL of columnar denitration catalyst was loaded into a quartz tube, and feed gas was introduced, with the reaction pressure controlled at 0.7 MPa. The feed gas contained 500 ppm NO, 500 ppm NH3, 5% O2, and the remainder was N2, with a volume hourly space velocity (GHSV) of 5000 h⁻¹. -1 The inlet and outlet concentrations of NO at different reaction temperatures were measured using a flue gas analyzer, thereby calculating the NO conversion rate of the catalyst.

[0030] The NO conversion rate test results of the columnar denitrification catalysts prepared in Examples 1, 2, and Comparative Example 2, as well as the commercial V2O5-WO3-TiO2 catalyst, are as follows: Figure 1 As shown. From Figure 1As can be seen, the columnar denitrification catalysts prepared in Examples 1 and 2 exhibit better denitrification catalytic effects than those prepared in Comparative Example 2. This indicates that Pr and Zr elements can enhance the catalyst activity. The main reason is that praseodymium oxide readily generates oxygen vacancies, promoting oxidation cycles during the catalyst reaction, while zirconium oxide provides certain acidic sites, enhancing the catalyst's ability to adsorb ammonia. Both elements synergistically improve the catalyst activity. Furthermore, compared to commercial V₂O₅-WO₃-TiO₂ catalysts, the catalyst developed in this invention has a wider activity temperature range (225–400 °C) and a higher denitrification rate (over 99%). This demonstrates that the columnar denitrification catalyst of this invention has superior denitrification performance compared to commercial catalysts.

[0031] The above results indicate that only titanium-silicon composite sol can both enhance the strength of the molded catalyst and ensure its high activity.

[0032] Although specific embodiments of the present invention have been described in detail with reference to examples, they should not be construed as limiting the scope of protection of this patent. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims are still within the scope of protection of this patent.

Claims

1. A method for producing a columnar denitration catalyst, characterized by, It comprises the following steps: S1: co-dissolve iron salt, praseodymium salt, zirconium salt, silicic acid and titanium salt in water to obtain a mixed solution; then add alkali liquor to the obtained mixed solution, stir and then precipitate; collect the precipitate and wash and dry to obtain a catalyst precursor; S2: add a pore-forming agent and an extrusion aid to the catalyst precursor, mix uniformly, and then extrude the mixture into a columnar catalyst; S3: calcine the columnar catalyst obtained in S2 to obtain a columnar denitration catalyst.

2. The method of claim 1, wherein: The amount of the iron salt, praseodymium salt, zirconium salt, silicic acid and titanium salt is determined according to the content of iron element in the obtained catalyst precursor, which is 1-8wt%, the content of Pr element is 0.5-5wt%, the content of Zr element is 0.5-5wt%, the content of Ti element is 20-40wt%, and the content of Si element is 10-30wt%.

3. The method of claim 2, wherein: The amount of the iron salt, praseodymium salt, zirconium salt, silicic acid and titanium salt is determined according to the content of iron element in the obtained catalyst precursor, which is 4-6wt%, the content of Pr element is 1.5wt%, the content of Zr element is 3wt%, the content of Ti element is 30-31wt%, and the content of Si element is 25-26wt%.

4. The method of any one of claims 1 to 3, wherein: The iron salt is ferric nitrate, the praseodymium salt is praseodymium nitrate, the zirconium salt is zirconium nitrate, and the titanium salt is titanyl sulfate; the alkali liquor is ammonia water.

5. The method of claim 1, wherein: The temperature of drying in S1 is 100℃, and the drying time is 6h.

6. The method of claim 1, wherein: The pore-forming agent is methyl cellulose or polyethylene glycol, and the addition amount of the pore-forming agent is 1-5% of the mass of the catalyst precursor; the extrusion aid is graphite or carbon black, and the addition amount of the extrusion aid is 1-6% of the mass of the catalyst precursor.

7. The method of claim 1, wherein: The diameter of the columnar catalyst is 1-6mm, and the length is 1-10mm.

8. The method of claim 1, wherein: The calcination temperature in S3 is 400-600℃, and the calcination time is 1-3h.

9. The columnar denitration catalyst prepared by the preparation method of any one of claims 1-8.

10. The application of the columnar denitration catalyst of claim 9 in removing nitrogen oxides in high-pressure tail gas or flue gas.

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