Regeneration method of SCR (Selective Catalytic Reduction) denitration catalyst

Abstract

The invention discloses an SCR (Selective Catalytic Reduction) denitration catalyst regeneration method which comprises the following steps: carrying out cleaning and arsenic removal on an arsenic-poisoned SCR denitration catalyst, and regenerating to obtain a regenerated catalyst; preparing a mixed impregnation liquid containing a water repellent agent, polypropylene carbonate and an organic solvent; adhering the mixed impregnation liquid to the surface of the regenerated catalyst and immersing the mixed impregnation liquid into channels of the regenerated catalyst by using a vacuum pressure impregnation process; drying to remove the organic solvent, and curing the poly (propylene carbonate) on the surface and in pores of the regenerated catalyst; a heat treatment is performed to remove the poly (propylene carbonate) and induce chemical grafting of the hydrophobing agent to the catalyst to form a hydrophobic network. The hydrophobic agent is introduced into the surface and pore channels of the arsenic-removed catalyst to construct a hydrophobic network, so that the hydrophobicity of the regenerated catalyst is improved.

Description

Technical Field

[0001] This invention relates to a method for regenerating an SCR denitrification catalyst, belonging to the field of catalyst regeneration technology. Background Technology

[0002] Selective catalytic reduction (SCR) technology, as the mainstream method for treating nitrogen oxides in flue gas denitrification, relies on the efficient operation of vanadium-tungsten-titanium (V2O5-WO3 / TiO2) catalysts. However, when treating flue gas from the combustion of arsenic-containing fuels, the catalyst faces a significant risk of failure.

[0003] Arsenic (As) exists primarily as gaseous As₂O₃ in high-temperature flue gas. With localized temperature fluctuations and increased diffusion resistance within the catalyst channels, gaseous arsenic condenses and deposits at the catalyst's active sites and microporous structure. This poisoning mechanism involves not only physical micropore blockage but also, more profoundly, chemical poisoning: arsenate or arsenite ions react with V₂O₃ on the support surface. 5+ The -OH bonds undergo irreversible binding, thus permanently occupying the active center, leading to a precipitous drop in denitrification efficiency.

[0004] Existing regeneration technologies use a combination of water washing, alkali washing, and acid washing to remove As and regenerate arsenic-poisoned SCR denitrification catalysts. However, the regenerated catalysts have poor hydrophobicity, which affects their resistance to water and sulfur. Summary of the Invention

[0005] The purpose of this invention is to provide a method for regenerating SCR denitrification catalysts, which improves the hydrophobicity of the regenerated catalyst by introducing a hydrophobic agent into the surface and pores of the catalyst after arsenic removal to construct a hydrophobic network.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for regenerating an SCR denitrification catalyst includes the following steps: The arsenic-poisoned SCR denitration catalyst was cleaned to remove arsenic and then regenerated to obtain a regenerated catalyst. Prepare a mixed impregnation solution containing a hydrophobic agent, polypropylene carbonate, and an organic solvent; Vacuum pressure impregnation process is used to make the mixed impregnation liquid adhere to the surface of the regenerated catalyst and penetrate into the pores of the regenerated catalyst. The organic solvent is removed by drying, and the polypropylene carbonate is cured on the surface and in the pores of the regenerated catalyst. Heat treatment is performed to remove polypropylene carbonate and induce chemical grafting of hydrophobic agents and catalysts to form a hydrophobic network.

[0007] Preferably, the arsenic removal process includes water washing, alkaline washing, and acid washing.

[0008] Preferably, the mixed impregnation solution is prepared by dissolving polypropylene carbonate in an organic solvent to form a clear solution, then adding a hydrophobic agent and stirring and mixing evenly at room temperature.

[0009] Preferably, the hydrophobic agent is phenyltrimethoxysilane, polymethylhydrosiloxane, or phenylphosphonic acid; the organic solvent is one or a mixture of several of dichloromethane, acetone, dimethyl carbonate, ethyl acetate, or tetrahydrofuran.

[0010] Preferably, the ratio of polypropylene carbonate to organic solvent is (50-150) g: 1000 mL; and the volume ratio of hydrophobic agent to organic solvent is (30-60) mL: 1000 mL.

[0011] Preferably, the mixing conditions are: mechanical stirring or magnetic stirring, speed 300-800 rpm, time 20-40 min.

[0012] Preferably, the vacuum pressure impregnation method is as follows: place the regenerated catalyst in the impregnation vessel, evacuate to below -0.08 MPa, use negative pressure to draw the mixed impregnation liquid into the vessel to immerse the catalyst, maintain the pressure for 5-10 minutes, and then slowly fill with nitrogen to atmospheric pressure for impregnation for 0.5-1 hours.

[0013] Preferably, the solid-liquid ratio of the regenerated catalyst to the mixed impregnation solution is 1 kg:(3-5) L.

[0014] Preferably, the conditions for drying and removing organic solvents are as follows: the impregnated regenerated catalyst is taken out, heated to 40-80°C at a rate of 5-8°C / min, and kept at that temperature for 2-4 hours.

[0015] Preferably, the heating procedure for heat treatment is as follows: heat to 200-220℃ at a rate of 1-2℃ / min, hold for 1-2 hours, then heat to 240-260℃ at a rate of 2-5℃ / min, and hold for 2-4 hours.

[0016] The beneficial effects of this invention are as follows: Traditional hydrophobic modification often employs physical coating (such as PTFE emulsion) or simple silane impregnation. The former easily forms a thick film that clogs micropores, leading to a significant decrease in denitrification activity; the latter, due to the "coffee ring effect" during solvent evaporation, causes the hydrophobic agent to migrate with the solvent to the outer surface of the catalyst or the pore openings, resulting in external hydrophobicity and internal hydrophilicity, and easily causing pore blockage.

[0017] This application utilizes polypropylene carbonate, which transforms from a liquid to a solid state during the drying process to remove organic solvents. This solidifies into a rigid polymer network on the catalyst surface (which is not a perfectly formed bonding plane and also contains pores) and within the pores. This process freezes the dispersed hydrophobic molecules in situ at various corners of the surface and pores, effectively preventing the hydrophobic agent from migrating to the pore openings or outer surfaces with solvent evaporation (i.e., suppressing the coffee ring effect). During heat treatment, the polypropylene carbonate decomposes and leaves the catalyst, allowing the hydrophobic agent to chemically bond with the pore walls in situ (utilizing the abundant Lewis and Brønsted acid sites on the regenerated SCR catalyst surface to induce an in-situ condensation reaction between the active functional groups in the hydrophobic agent and the hydroxyl groups on the catalyst surface during heat treatment). This forms a hydrophobic network on the catalyst surface and within the pores, achieving comprehensive hydrophobic protection without clogging the pores.

[0018] The hydrophobic network introduced by this method is anchored to the catalyst surface and pores through strong chemical bonds. This hydrophobic network not only significantly reduces water adsorption and capillary condensation, disrupting the medium environment for the formation of ammonium bisulfate (ABS), but also, through steric hindrance and low surface energy characteristics, prevents the small amount of ABS generated from adhering to the pore walls, making it easy to be discharged with the flue gas. This improves the resistance to water and sulfur and extends the life of the regenerated catalyst. Detailed Implementation

[0019] Example 1: This example provides a method for regenerating an SCR denitrification catalyst, including the following steps: Use 6 MPa, flow rate 1 m³ / h 3 The arsenic-poisoned SCR denitrification catalyst was purged with dry compressed air at a flow rate of 0.5 m / min for 15 min to remove surface dust. The catalyst was then placed in an ozone atmosphere and heated to 300°C at a flow rate of 3°C / min with an ozone flow rate of 0.5 m / min, and held at that temperature for 3 h.

[0020] The ozone-calcined catalyst was placed in an ultrasonic bath filled with water at 45°C and cleaned for 20 minutes under ultrasonic assistance at a bubbling pressure of 0.5 MPa to obtain a water-washed catalyst. The water-washed catalyst was then placed in an alkaline solution at a solid-liquid ratio of 1 g:10 mL and washed for 20 minutes. The alkaline solution consisted of 0.3 wt% NaOH, 6 wt% ammonia, 2 wt% EDTA, 1 wt% OP-10, with the remainder being water.

[0021] The alkaline-washed catalyst was then placed in an acid solution at a solid-liquid ratio of 1 g:10 mL and acid-washed for 20 min. The acid solution consisted of 5 wt% oxalic acid, 6 wt% citric acid, 1 wt% OP-10, and the balance being water. The acid-washed catalyst was then rinsed three times in water at 40 °C. Finally, it was dried at 100 °C for 3 h to obtain the arsenic-removed catalyst.

[0022] Next, the arsenic-removed catalyst was placed in an oxalic acid solution with an ammonium metavanadate content of 1wt% at a liquid-to-solid mass ratio of 10:1, impregnated at 70°C for 5 hours, filtered, dried at 120°C for 5 hours, and then calcined at 350°C for 3 hours to obtain the regenerated catalyst.

[0023] Dissolve 150g of polypropylene carbonate (Mw=30000g / mol) in 1000mL of acetone, then add 50mL of phenyltrimethoxysilane and stir mechanically at 800rpm for 30min to obtain a mixed impregnation solution.

[0024] The catalyst was placed in the impregnation vessel at a solid-liquid ratio of 1 kg: 5 L, and the vacuum was drawn to -0.1 MPa. Then, the mixed impregnation liquid was drawn into the impregnation vessel under negative pressure. After maintaining the pressure for 10 min, nitrogen was introduced to normal pressure and impregnated for 1 h.

[0025] After impregnation, the regenerated catalyst was removed, filtered, and heated to 60°C at a rate of 8°C / min and held for 3 hours. Then, the dried regenerated catalyst was heated to 200°C at a rate of 2°C / min and held for 2 hours, and then heated to 260°C at a rate of 2°C / min and held for 3 hours.

[0026] Example 2: This example provides a method for regenerating an SCR denitrification catalyst, including the following steps: Use 6 MPa, flow rate 1 m³ / h 3 The arsenic-poisoned SCR denitrification catalyst was purged with dry compressed air at a flow rate of 0.5 m / min for 15 min to remove surface dust. The catalyst was then placed in an ozone atmosphere and heated to 300°C at a flow rate of 3°C / min with an ozone flow rate of 0.5 m / min, and held at that temperature for 3 h.

[0027] The ozone-calcined catalyst was placed in an ultrasonic bath filled with water at 45°C and cleaned for 20 minutes under ultrasonic assistance at a bubbling pressure of 0.5 MPa to obtain a water-washed catalyst. The water-washed catalyst was then placed in an alkaline solution at a solid-liquid ratio of 1 g:10 mL and washed for 20 minutes. The alkaline solution consisted of 0.3 wt% NaOH, 6 wt% ammonia, 2 wt% EDTA, 1 wt% OP-10, with the remainder being water.

[0028] The alkaline-washed catalyst was then placed in an acid solution at a solid-liquid ratio of 1 g:10 mL and acid-washed for 20 min. The acid solution consisted of 5 wt% oxalic acid, 6 wt% citric acid, 1 wt% OP-10, and the balance being water. The acid-washed catalyst was then rinsed three times in water at 40 °C. Finally, it was dried at 100 °C for 3 h to obtain the arsenic-removed catalyst.

[0029] Next, the arsenic-removed catalyst was placed in an oxalic acid solution with an ammonium metavanadate content of 1wt% at a liquid-to-solid mass ratio of 10:1, impregnated at 70°C for 5 hours, filtered, dried at 120°C for 5 hours, and then calcined at 350°C for 3 hours to obtain the regenerated catalyst.

[0030] Dissolve 150g of polypropylene carbonate (Mw=30000g / mol) in 1000mL of acetone, then add 50mL of phenyltrimethoxysilane and stir mechanically at 800rpm for 30min to obtain a mixed impregnation solution.

[0031] The catalyst was placed in the impregnation vessel at a solid-liquid ratio of 1 kg: 5 L, and the vacuum was drawn to -0.1 MPa. Then, the mixed impregnation liquid was drawn into the impregnation vessel under negative pressure. After maintaining the pressure for 10 min, nitrogen was introduced to normal pressure and impregnated for 1 h.

[0032] After impregnation, the regenerated catalyst was removed, filtered, and heated to 40°C at a rate of 5°C / min and held for 3 hours. Then, the dried regenerated catalyst was heated to 200°C at a rate of 2°C / min and held for 2 hours, and then heated to 260°C at a rate of 2°C / min and held for 3 hours.

[0033] Comparative Example 1: It is basically the same as Example 1, except that no hydrophobic treatment was performed after the regenerated catalyst was obtained.

[0034] Comparative Example 2: Basically the same as Example 1, except that polypropylene carbonate was not added to the mixed impregnation solution.

[0035] Comparative Example 3: Basically the same as Example 1, except that 150g of polyethylene glycol (Mw=6000g / mol) was added to the mixed impregnation solution.

[0036] Comparative Example 4: It is basically the same as Example 1, except that the heat treatment conditions after impregnation of the regenerated catalyst are: heating to 180°C at a rate of 2°C / min and holding for 5 hours.

[0037] Catalytic activity testing: The denitrification effect of the catalyst after treatment was tested using simulated flue gas. The simulated flue gas composition was: NO: 500 ppm, NH3: 500 ppm, O2: 5%, N2 as the balance gas, and the space velocity was 30,000 h⁻¹. -1 The flue gas flow rate was 300 mL / min, the reaction temperature was 250℃, and the catalyst (30 mm × 30 mm × 200 mm) was placed in a fixed bed reactor. The catalyst denitrification efficiency was tested (10 h).

[0038] Catalyst water and sulfur stability test: The catalyst denitrification performance was tested using simulated flue gas. The simulated flue gas composition was: NO: 500ppm, NH3: 500ppm, O2: 5%, H2O: 3%, SO2: 100ppm, N2 as the balance gas, and the space velocity was 30,000 h⁻¹. -1 The flue gas flow rate was 300 mL / min, the reaction temperature was 250℃, and the catalyst (30 mm × 30 mm × 200 mm) was placed in a fixed bed reactor to test the catalyst denitrification efficiency (100 h).

[0039] The NO concentration at the reactor inlet and outlet was detected using a flue gas analyzer.

[0040] The formula for calculating denitrification efficiency is: , in, C in The NO concentration (ppm) at the inlet of the fixed-bed reactor. C out The NO concentration (ppm) at the outlet of the fixed-bed reactor.

[0041] The denitrification performance of the initial SCR denitrification catalyst (V2O5-WO3 / TiO2 catalyst) of the same specification, the SCR denitrification catalyst poisoned by arsenic after 800 days of use, the regenerated SCR denitrification catalysts obtained from Examples 1-2 and Comparative Examples 1-4 were tested, and the results are shown in Table 1.

[0042] Table 1: Denitrification performance of SCR denitrification catalysts

[0043] As can be seen from Table 1, the regenerated SCR denitrification catalyst without hydrophobic treatment (Comparative Example 1) showed better denitrification efficiency recovery. However, the denitrification efficiency of the regenerated SCR denitrification catalyst with hydrophobic treatment (Examples 1 and 2) was slightly lower than that of the regenerated SCR denitrification catalyst without hydrophobic treatment. This is because the formation of the hydrophobic network will mask some of the active sites to a certain extent.

[0044] In Example 2, the heating rate was slow, and the drying temperature (40°C) was within the glass transition region (near Tg) of polypropylene carbonate. At this temperature, the movement of polymer chain segments was restricted, and the free volume was insufficient, resulting in extremely low diffusion kinetics of the solvent acetone. Therefore, hydrophobic agent molecules had more time to undergo localized micro-aggregation, leading to excessive coverage of active sites and affecting denitrification efficiency to some extent. Simultaneously, the residual solvent, due to violent vaporization during subsequent rapid heating heat treatment, caused a scouring effect, which to some extent disrupted the microscopic continuity of the hydrophobic network. In contrast, Example 1 used a temperature higher than Tg, keeping polypropylene carbonate in a highly elastic state, ensuring smooth solvent drainage without affecting the hydrophobic network and preventing excessive coverage of active sites.

[0045] In Comparative Example 2, due to the more pronounced "coffee ring effect," a significant amount of hydrophobic agent accumulated at the pore openings, thus affecting the airflow into the pores and leading to a certain degree of decrease in denitrification efficiency. In Comparative Example 3, the polyethylene glycol remaining in the catalyst coked during heat treatment, causing pore blockage and affecting denitrification efficiency. In Comparative Example 4, because polypropylene carbonate could not be completely decomposed and vaporized, it covered certain active sites, resulting in a reduction in denitrification efficiency.

[0046] Since the denitrification efficiency of the regenerated SCR denitrification catalysts treated in Comparative Examples 3-4 was low, the above-mentioned catalyst water and sulfur resistance performance tests were only conducted on the regenerated SCR denitrification catalysts obtained in Examples 1-2 and Comparative Examples 1-2. The results are shown in Table 2.

[0047] Table 2: Water and sulfur resistance of SCR denitrification catalysts

[0048] As shown in Table 2, the regenerated SCR denitrification catalyst without hydrophobic treatment (Comparative Example 1) exhibits poor water and sulfur resistance, while the regenerated SCR denitrification catalysts with hydrophobic treatment (Examples 1 and 2) show superior denitrification efficiency and water and sulfur resistance compared to the untreated regenerated SCR denitrification catalyst. Due to the more pronounced "coffee ring effect" (Comparative Example 2), the hydrophobic agent tends to accumulate at the pore openings or on the surface. Although this can improve water and sulfur resistance to some extent, the hydrophobic effect within the pores is poor, affecting the water and sulfur resistance stability.

Claims

1. A method for regenerating an SCR denitrification catalyst, characterized in that, Includes the following steps: The arsenic-poisoned SCR denitration catalyst was cleaned to remove arsenic and then regenerated to obtain a regenerated catalyst. Prepare a mixed impregnation solution containing a hydrophobic agent, polypropylene carbonate, and an organic solvent; Vacuum pressure impregnation process is used to make the mixed impregnation liquid adhere to the surface of the regenerated catalyst or immerse it into the pores of the regenerated catalyst. The organic solvent is removed by drying, and the polypropylene carbonate is cured on the surface and in the pores of the regenerated catalyst. Heat treatment is performed to remove polypropylene carbonate and induce chemical grafting of hydrophobic agents and catalysts to form a hydrophobic network.

2. The SCR denitrification catalyst regeneration method according to claim 1, characterized in that, The cleaning process for removing arsenic includes water washing, alkaline washing, and acid washing.

3. The SCR denitrification catalyst regeneration method according to claim 1, characterized in that, The mixed impregnation solution is prepared by dissolving polypropylene carbonate in an organic solvent to form a clear solution, then adding a hydrophobic agent and stirring and mixing evenly at room temperature.

4. The SCR denitrification catalyst regeneration method according to claim 2, characterized in that, The hydrophobic agent is phenyltrimethoxysilane, polymethylhydrosiloxane, or phenylphosphonic acid; the organic solvent is one or a mixture of several of dichloromethane, acetone, dimethyl carbonate, ethyl acetate, or tetrahydrofuran.

5. The SCR denitrification catalyst regeneration method according to claim 2, characterized in that, The ratio of polypropylene carbonate to organic solvent is (50-150) g: 1000 mL; the volume ratio of hydrophobic agent to organic solvent is (30-60) mL: 1000 mL.

6. The SCR denitrification catalyst regeneration method according to claim 2, characterized in that, The mixing conditions are: mechanical or magnetic stirring, speed 300-800 rpm, time 20-40 min.

7. The SCR denitrification catalyst regeneration method according to claim 4, characterized in that, The vacuum pressure impregnation method is as follows: place the regenerated catalyst in the impregnation vessel, evacuate to below -0.08MPa, use negative pressure to draw the mixed impregnation liquid into the vessel to immerse the catalyst, maintain the pressure for 5-10 minutes, and then slowly fill with nitrogen to atmospheric pressure, impregnate for 0.5-1 hours.

8. The SCR denitrification catalyst regeneration method according to claim 6, characterized in that, The solid-liquid ratio of the regenerated catalyst to the mixed impregnation solution is 1 kg: (3-5) L.

9. The SCR denitrification catalyst regeneration method according to claim 6, characterized in that, The conditions for drying and removing organic solvents are as follows: take out the impregnated regenerated catalyst, heat it to 40-80℃ at a rate of 5-8℃ / min, and keep it at that temperature for 2-4 hours.

10. The SCR denitrification catalyst regeneration method according to claim 8, characterized in that, The heating procedure for heat treatment is as follows: heat to 200-220℃ at a rate of 1-2℃ / min, hold for 1-2 hours, then heat to 240-260℃ at a rate of 2-5℃ / min, and hold for 2-4 hours.

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