A supercritical regeneration method for waste denitration catalyst and its product

Abstract

The present invention discloses a supercritical regeneration method of a waste denitration catalyst and a product thereof, comprising the steps of: (1) dissolving citric acid and hydrochloric acid in water to obtain a citric hydrochloric acid mixed acid solution; (2) mixing the waste denitration catalyst with the citric hydrochloric acid mixed acid solution to obtain a waste denitration catalyst pickling slurry; (3) introducing the waste denitration catalyst pickling slurry into a supercritical water generator for reaction to obtain an activated waste denitration catalyst pickling slurry; subjecting the activated waste denitration catalyst pickling slurry to solid-liquid separation to obtain an activated waste denitration catalyst mud; and (4) calcining the activated waste denitration catalyst mud to obtain a supercritical regenerated denitration catalyst. The present invention realizes the resource utilization of the waste denitration catalyst, which is a hazardous waste, through the supercritical regeneration of the waste denitration catalyst; the treatment method is simple, and the catalytic activity recovery index (k / k0) of the regenerated denitration catalyst can reach up to 1.24; compared with the existing harmless landfill technology, the present invention does not cause secondary pollution.

Description

Technical Field

[0001] The invention relates to resource utilization of hazardous wastes, and in particular to a supercritical regeneration method of a waste denitration catalyst and a product thereof. Background Art

[0002] At present, coal-fired power plants, chemical industry, metallurgy, cement and other industries are implementing ultra-low emission standards for flue gas pollutants (Technical Specifications for Ultra-low Emission Flue Gas Treatment Engineering of Coal-fired Power Plants (HJ2053-2018)), which not only makes the ultra-low emission technology transformation of large boilers necessary, but also makes the selective catalytic reduction (SCR) flue gas denitrification technology the preferred technical module for ultra-low emission of flue gas denitrification. SCR technology is mature and can achieve more than 90% denitrification effect. Its core is the catalyst (such as V2O5 / TiO2 and V2O5-WO3 / TiO2), and the physicochemical properties of the catalyst are directly related to the overall denitrification effect. At present, the denitrification reactor of the SCR system is mostly placed before the electrostatic precipitator (high dust arrangement), so the catalyst surface is easily blocked by a large number of solid particles carried by the flue gas, and is also easily poisoned by frequent contact with heavy metal pollutants in the flue gas. The denitrification catalyst in the denitrification system needs to be replaced every 3 to 5 years, and a large amount of waste denitrification catalyst is generated every year.

[0003] Waste denitration catalysts are hazardous wastes and are toxic. The cost of harmless disposal is as high as 2,000 to 3,000 yuan per ton. In addition, the current disposal method for waste denitration catalysts is single, mainly harmless landfill, which not only easily causes secondary pollution, but also wastes the useful precious metal resources in the catalyst. Summary of the invention

[0004] Purpose of the invention: In view of the above problems, the present invention proposes a supercritical regeneration method for a waste denitration catalyst. Another purpose of the present invention is to provide a supercritical regenerated denitration catalyst prepared based on the method. Through the supercritical regeneration of the waste denitration catalyst, the resource utilization of the waste denitration catalyst, which is a hazardous waste, is achieved, and the treatment method is simple and there is no secondary pollution.

[0005] Technical solution: The supercritical regeneration method of a spent denitration catalyst according to the present invention comprises the following steps:

[0006] (1) dissolving citric acid and hydrochloric acid in water to obtain a citric acid and hydrochloric acid mixed acid solution;

[0007] (2) mixing the waste denitration catalyst with a citric hydrochloric acid mixed acid solution, stirring evenly, and obtaining a waste denitration catalyst pickling slurry;

[0008] (3) introducing the waste denitration catalyst pickling slurry into a supercritical water generator through a high-pressure plunger pump for reaction to obtain activated waste denitration catalyst pickling slurry; performing solid-liquid separation on the activated waste denitration catalyst pickling slurry to obtain a solid portion as activated waste denitration catalyst mud;

[0009] (4) The activated spent denitration catalyst sludge is placed in a heating furnace for calcination to obtain a supercritical regenerated denitration catalyst.

[0010] Furthermore, in step (1), the concentration of hydrochloric acid is 0.25 to 4.25 mol / L; the molar ratio of citric acid to hydrochloric acid is 0.025 to 0.6:1, preferably 0.05 to 0.45:1.

[0011] Furthermore, in step (2), the solid-to-liquid ratio of the waste denitration catalyst to the citric hydrochloric acid mixed acid solution is 0.05-0.55:1 g / mL.

[0012] Furthermore, in step (3), the reaction time of the supercritical water generator is 0.3 to 3.25 h, preferably 0.5 to 2.5 h, the critical pressure is 22 to 48 MPa, and the critical temperature is 375 to 825°C.

[0013] Furthermore, in step (4), the calcination time is 1 to 5 hours, preferably 2 to 4 hours, and the calcination temperature is 300 to 600°C.

[0014] The invention also discloses a supercritical regeneration denitration catalyst prepared by the method.

[0015] During the reaction of the supercritical water generator, under the supercritical environment, hydrochloric acid, citric acid and water react to generate active free radical substances such as chlorine free radicals, hydroxyl free radicals, carbon dioxide free radicals, and hydrogen free radicals. In the supercritical water environment, the adhesion of particles, heavy metals, inorganic salts, etc. attached to the surface of the waste denitration catalyst is weakened and it is easier to fall off. At the same time, hydrochloric acid, citric acid and the generated active free radical substances in the supercritical environment can not only strengthen the surface purification process of the waste denitration catalyst through ion exchange, chelation reaction, and redox reaction, but also the generated active free radical substances can be adsorbed on the surface of the waste denitration catalyst and realize the surface activation and active site activation of the waste denitration catalyst through strong redox reaction. The activated waste denitration catalyst mud is calcined. During the calcination process, the residual chloride adsorbed on the surface of the activated waste denitration catalyst mud is volatilized by heat, and the volatilized chloride gas produces surface corrosion on the activated waste denitration catalyst, thereby improving the surface catalytic activity of the regenerated denitration catalyst. During the calcination process, the surface of the activated waste denitration catalyst mud adsorbs citric acid to undergo mineralization and decomposition, and the generated carbon monoxide and carbon dioxide gases can improve the surface catalytic activity of the regenerated denitration catalyst.

[0016] Beneficial effects: Compared with the prior art, the present invention completes the supercritical regeneration of the waste denitrification catalyst through the preparation of waste denitrification catalyst pickling slurry, supercritical activation, and high-temperature calcination steps, thereby realizing the resource utilization of the waste denitrification catalyst, a hazardous waste; the treatment method is simple, and the catalytic activity recovery index (k / k0) of the regenerated denitrification catalyst can reach up to 1.24; compared with the existing harmless landfill technology, the present invention will not cause secondary pollution, nor will it cause waste of useful precious metal resources in the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0018] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0019] Source of waste denitrification catalyst: The waste denitrification catalyst was taken from the flue gas SCR denitrification system of a waste incineration power plant in Suzhou. The waste denitrification catalyst was purged with compressed air and washed three times with clean water, and then dried for use.

[0020] Example 1

[0021] Effect of the molar ratio of citric acid to hydrochloric acid on the activity of the prepared supercritical regenerated denitrification catalyst

[0022] like Figure 1 As shown, citric acid and hydrochloric acid are dissolved in water to prepare a citric hydrochloric acid mixed acid solution, wherein the molar ratio of citric acid to hydrochloric acid is 0.025:1, 0.03:1, 0.04:1, 0.05:1, 0.25:1, 0.45:1, 0.5:1, 0.55:1, 0.6:1, and the concentration of hydrochloric acid is 0.25 mol / L. The waste denitration catalyst and the citric hydrochloric acid mixed acid solution are mixed at a solid-liquid ratio of 0.05:1 g / mL, stirred evenly, and the waste denitration catalyst pickling slurry is obtained. The waste denitration catalyst pickling slurry is introduced into a supercritical water generator through a high-pressure plunger pump for reaction for 0.5 hours to obtain an activated waste denitration catalyst pickling slurry, wherein the critical pressure of the supercritical water generator is 22 MPa, and the critical temperature of the supercritical water generator is 375°C. The activated waste denitration catalyst pickling slurry is subjected to solid-liquid separation, and the solid part obtained is the activated waste denitration catalyst mud. The activated waste denitration catalyst mud was placed in a heating furnace and calcined for 2 hours at a calcination temperature of 300° C. to obtain a supercritical regenerated denitration catalyst.

[0023] Catalyst activity test and calculation of catalyst catalytic activity recovery index (k / k0): The catalyst activity test and calculation of catalyst catalytic activity recovery index (k / k0) are carried out in accordance with the "Regeneration and Treatment Method of Deactivated Catalyst for Coal-fired Flue Gas Denitrification" (JB / T12129-2015). The catalyst activity test should intercept a catalyst sample block containing at least 4 channels and a length of not less than 200 mm, and at least four sample blocks should be selected for parallel testing. The results of this embodiment are shown in Table 1.

[0024] Table 1 Effect of the molar ratio of citric acid and hydrochloric acid on the activity of the prepared supercritical regenerated denitrification catalyst

[0025] Molar ratio of citric acid to hydrochloric acid <![CDATA[k / k0]]> Relative error 0.025:1 0.91 ±0.2％ 0.03:1 0.95 ±0.2％ 0.04:1 0.97 ±0.1％ 0.05:1 1.08 ±0.1％ 0.25:1 1.13 ±0.1％ 0.45:1 1.16 ±0.1％ 0.5:1 1.05 ±0.1％ 0.55:1 1.02 ±0.1％ 0.6:1 0.99 ±0.2％

[0026] As shown in Table 1, when the molar ratio of citric acid to hydrochloric acid is less than 0.05:1 (molar ratio of citric acid to hydrochloric acid = 0.04:1, 0.03:1, 0.025:1 and lower ratios not listed in Table 1), the amount of citric acid added is small, the surface purification effect of the waste denitration catalyst is poor, and the surface activity improvement effect during the calcination process is poor, resulting in a significant decrease in the catalyst catalytic activity recovery index as the molar ratio of citric acid to hydrochloric acid decreases. When the molar ratio of citric acid to hydrochloric acid is equal to 0.05-0.45:1 (molar ratio of citric acid to hydrochloric acid = 0.05:1, 0.25:1, 0.45:1), hydrochloric acid, citric acid and the generated active free radical substances in the supercritical environment can not only enhance the surface purification process of the waste denitration catalyst through ion exchange, chelation reaction, and redox reaction, but also the generated active free radical substances can be adsorbed on the surface of the waste denitration catalyst and realize the surface activation and active site activation of the waste denitration catalyst through strong redox reaction. The activated waste denitration catalyst mud is calcined. During the calcination process, the residual chloride adsorbed on the surface of the activated waste denitration catalyst mud is volatilized by heat, and the volatilized chloride gas produces surface corrosion on the activated waste denitration catalyst, thereby improving the surface catalytic activity of the regenerated denitration catalyst. During the calcination process, citric acid is adsorbed on the surface of the activated waste denitration catalyst mud for mineralization and decomposition, and the generated carbon monoxide and carbon dioxide gases can improve the surface catalytic activity of the regenerated denitration catalyst. Finally, the catalyst catalytic activity recovery index is greater than 1. When the molar ratio of citric acid to hydrochloric acid is greater than 0.45:1 (molar ratio of citric acid to hydrochloric acid = 0.5:1, 0.55:1, 0.6:1 and higher ratios not listed in Table 1), citric acid is added excessively, and there is too much residual carbon on the catalyst surface, resulting in a significant decrease in the catalyst catalytic activity recovery index as the molar ratio of citric acid to hydrochloric acid further increases. In general, considering the benefits and costs, when the molar ratio of citric acid to hydrochloric acid is equal to 0.05-0.45:1, it is most conducive to improving the activity of the prepared supercritical regenerated denitration catalyst. It should be noted that the performance requirement in the "Regeneration and Treatment Method of Deactivated Catalyst for Coal Flue Gas Denitrification" (JB / T12129-2015) is that the catalyst activity recovery index k / k0 should not be less than 0.9. In Table 1, when the molar ratio of citric acid to hydrochloric acid is 0.025-0.6:1, k / k0 is greater than 0.9, which can meet the industry standard requirements. In other words, when the molar ratio of citric acid to hydrochloric acid is in the range of 0.025-0.6:1, a supercritical regenerated denitrification catalyst that meets the requirements can be prepared, and the molar ratio of 0.05-0.45:1 is only a better selection range, and it does not limit the molar ratio to this range.

[0027] Example 2

[0028] Effect of supercritical water generator reaction time on the activity of prepared supercritical regenerated denitrification catalyst

[0029] Dissolve citric acid and hydrochloric acid in water to prepare a citric hydrochloric acid mixed acid solution, wherein the molar ratio of citric acid to hydrochloric acid is 0.45:1, and the concentration of hydrochloric acid is 2.25 mol / L. Mix the waste denitration catalyst and the citric hydrochloric acid mixed acid solution according to a solid-liquid ratio of 0.3:1 g / mL, stir evenly, and obtain a waste denitration catalyst pickling slurry. Introduce the waste denitration catalyst pickling slurry into a supercritical water generator through a high-pressure plunger pump and react for 0.25 hours, 0.3 hours, 0.4 hours, 0.5 hours, 1.5 hours, 2.5 hours, 2.75 hours, 3 hours, and 3.25 hours respectively to obtain an activated waste denitration catalyst pickling slurry, wherein the critical pressure of the supercritical water generator is 35 MPa, and the critical temperature of the supercritical water generator is 600°C. The activated waste denitration catalyst pickling slurry is subjected to solid-liquid separation, and the solid part obtained is the activated waste denitration catalyst mud. The activated waste denitration catalyst mud is placed in a heating furnace and calcined for 3 hours at a calcination temperature of 450°C to obtain a supercritical regenerated denitration catalyst.

[0030] The catalyst activity test and the calculation of the catalyst catalytic activity recovery index (k / k0) are the same as in Example 1. The results of this example are shown in Table 2.

[0031] Table 2 Effect of supercritical water generator reaction time on the activity of prepared supercritical regeneration denitrification catalyst

[0032] Supercritical water generator reaction time <![CDATA[k / k0]]> Relative error 0.25 hours 0.87 ±0.1％ 0.3 hours 0.94 ±0.2％ 0.4 hours 1.01 ±0.1％ 0.5 hours 1.12 ±0.1％ 1.5 hours 1.18 ±0.1％ 2.5 hours 1.21 ±0.1％ 2.75 hours 1.09 ±0.1％ 3 hours 1.04 ±0.2％ 3.25 hours 0.96 ±0.2％

[0033] As shown in Table 2, when the supercritical water generator reaction time is less than 0.5 hours (supercritical water generator reaction time = 0.4 hours, 0.3 hours, 0.25 hours and lower values ​​not listed in Table 2), the supercritical water generation time is short, the catalyst surface cleaning and activation are not sufficient, resulting in a significant decrease in the catalyst catalytic activity recovery index as the supercritical water generator reaction time decreases. When the supercritical water generator reaction time is equal to 0.5 to 2.5 hours (supercritical water generator reaction time = 0.5 hours, 1.5 hours, 2.5 hours), during the supercritical water generator reaction, hydrochloric acid, citric acid and water react in a supercritical environment to generate active free radical substances such as chlorine free radicals, hydroxyl free radicals, carbon dioxide free radicals, and hydrogen free radicals. In a supercritical water environment, the adhesion of particles, heavy metals, inorganic salts, etc. attached to the surface of the waste denitration catalyst is weakened and more likely to fall off. At the same time, hydrochloric acid, citric acid and the generated active free radical substances in the supercritical environment can not only strengthen the surface purification process of the waste denitration catalyst through ion exchange, chelation reaction and redox reaction, but also the generated active free radical substances can be adsorbed on the surface of the waste denitration catalyst and realize the surface activation and active site activation of the waste denitration catalyst through strong redox reaction. Finally, the catalyst catalytic activity recovery index is greater than 1.1. When the supercritical water generator reaction time is greater than 2.5 hours (supercritical water generator reaction time = 2.75 hours, 3 hours, 3.25 hours and higher values ​​not listed in Table 2), the supercritical water reaction time is too long, the catalyst surface collapses and passivates, resulting in the catalyst catalytic activity recovery index significantly decreasing with the further increase of the supercritical water reaction time. In general, combining benefits and costs, when the supercritical water generator reaction time is equal to 0.5 to 2.5 hours, it is most conducive to improving the activity of the prepared supercritical regeneration denitration catalyst. It should be noted that the performance requirement in the "Regeneration and Treatment Method of Denitrification Deactivated Catalyst for Coal-fired Flue Gas" (JB / T 12129-2015) is that the catalyst activity recovery index k / k0 should not be less than 0.9. In Table 2, when the supercritical water generator reaction time is 0.3 to 3.25 hours, k / k0 is greater than 0.9, which can meet the industry standard requirements. In other words, if the supercritical water generator reaction time is selected in the range of 0.3 to 3.25 hours, a supercritical regenerated denitrification catalyst that meets the requirements can be prepared, and the supercritical water generator reaction time of 0.5 to 2.5 is only a better selection range, and the reaction time is not limited to this range.

[0034] Example 3

[0035] Effect of calcination time on the activity of prepared supercritical regenerated denitrification catalyst

[0036] Dissolve citric acid and hydrochloric acid in water to prepare a citric hydrochloric acid mixed acid solution, wherein the molar ratio of citric acid to hydrochloric acid is 0.45:1, and the concentration of hydrochloric acid is 4.25 mol / L. Mix the waste denitration catalyst and the citric hydrochloric acid mixed acid solution according to a solid-liquid ratio of 0.55:1 g / mL, stir evenly, and obtain a waste denitration catalyst pickling slurry. The waste denitration catalyst pickling slurry is introduced into a supercritical water generator through a high-pressure plunger pump for reaction for 2.5 hours to obtain an activated waste denitration catalyst pickling slurry, wherein the critical pressure of the supercritical water generator is 48 MPa, and the critical temperature of the supercritical water generator is 825°C. The activated waste denitration catalyst pickling slurry is solid-liquid separated, and the solid part obtained is the activated waste denitration catalyst mud. The activated waste denitration catalyst mud is placed in a heating furnace and calcined for 0.5 hours, 1 hour, 1.5 hours, 2 hours, 3 hours, 4 hours, 4.5 hours, 5 hours, and 5.5 hours, respectively, and the calcination temperature is 600°C to obtain a supercritical regenerated denitration catalyst.

[0037] The catalyst activity test and the calculation of the catalyst catalytic activity recovery index (k / k0) are the same as in Example 1. The results of this example are shown in Table 3.

[0038] Table 3 Effect of calcination time on the activity of prepared supercritical regeneration denitrification catalyst

[0039] Calcination time <![CDATA[k / k0]]> Relative error 0.5 hours 0.84 ±0.1％ 1 hour 0.91 ±0.2％ 1.5 hours 0.99 ±0.1％ 2 hours 1.16 ±0.1％ 3 hours 1.22 ±0.1％ 4 hours 1.24 ±0.1％ 4.5 hours 1.17 ±0.1％ 5 hours 1.04 ±0.1％ 5.5 hours 0.79 ±0.2％

[0040] It can be seen from Table 3 that when the calcination time is less than 2 hours (calcination time = 1.5 hours, 1 hour, 0.5 hours and lower values ​​not listed in Table 3), the calcination time is short and the catalyst surface is insufficiently activated, resulting in a significant decrease in the catalyst catalytic activity recovery index as the calcination time decreases. When the calcination time is equal to 2 to 4 hours (calcination time = 2 hours, 3 hours, 4 hours), the residual chloride adsorbed on the surface of the activated waste denitration catalyst mud during the calcination process is volatilized by heat, and the volatilized chloride gas produces surface corrosion on the activated waste denitration catalyst, thereby improving the surface catalytic activity of the regenerated denitration catalyst. During the calcination process, citric acid adsorbed on the surface of the activated waste denitration catalyst mud undergoes mineralization and decomposition, and the generated carbon monoxide and carbon dioxide gases can improve the surface catalytic activity of the regenerated denitration catalyst. Finally, the catalyst catalytic activity recovery index is greater than 1.2. When the calcination time is less than 4 hours (calcination time = 4.5 hours, 5 hours, 5.5 hours and higher values ​​not listed in Table 3), the catalyst is over-burned and the surface is deactivated, resulting in a significant decrease in the catalyst catalytic activity recovery index as the calcination time further increases. In general, when the calcination time is equal to 2 to 4 hours, it is most conducive to improving the activity of the prepared supercritical regeneration denitration catalyst. It should be noted that the performance requirement in the "Regeneration and Treatment Method of Deactivated Catalyst for Coal-fired Flue Gas Denitration" (JB / T 12129-2015) is that the catalyst activity recovery index k / k0 should not be less than 0.9. In Table 3, when the calcination time is 1 to 5 hours, k / k0 is greater than 0.9, which can meet the industry standard requirements. In other words, the calcination time is selected in the range of 1 to 5 hours, and a supercritical regeneration denitration catalyst that meets the requirements can be prepared, and the calcination time of 2 to 4 is just a better selection range, and it is not limited to the calcination time. Only this range can be selected.

Claims

1. A supercritical regeneration method for a spent denitration catalyst, characterized in that: The following steps are involved: (1) dissolving citric acid and hydrochloric acid in water to obtain a citric acid-hydrochloric acid mixed acid solution; (2) mixing the spent denitration catalyst with a citric acid and hydrochloric acid mixed acid solution to obtain a spent denitration catalyst pickling slurry; (3) introducing the waste denitration catalyst pickling slurry into a supercritical water generator for reaction to obtain activated waste denitration catalyst pickling slurry; performing solid-liquid separation on the activated waste denitration catalyst pickling slurry to obtain activated waste denitration catalyst mud; (4) calcining the activated spent denitration catalyst sludge to obtain a supercritical regenerated denitration catalyst; In step (1), the molar ratio of citric acid to hydrochloric acid is 0.025-0.6:1, and the concentration of hydrochloric acid is 0.25-4.25 mol / L; In step (2), the solid-to-liquid ratio of the waste denitration catalyst to the citric hydrochloric acid mixed acid solution is 0.05-0.55:1 g / mL; In step (3), the supercritical water generator reaction time is 0.3-3.25 h, the critical pressure is 22-48 MPa, and the critical temperature is 375-825° C.; In the step (4), the calcination time is 1 to 5 hours, and the calcination temperature is 300 to 600°C.

2. The supercritical regeneration method of a spent denitration catalyst according to claim 1, characterized in that: In the step (1), the molar ratio of citric acid to hydrochloric acid is 0.05-0.45:

1.

3. The supercritical regeneration method of a spent denitration catalyst according to claim 1, characterized in that: The reaction time of the supercritical water generator in step (3) is 0.5 to 2.5 hours.

4. The supercritical regeneration method of a spent denitration catalyst according to claim 1, characterized in that: The calcination time in step (4) is 2 to 4 hours.

5. The supercritical regenerated denitration catalyst prepared by the method according to any one of claims 1 to 4.

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