A method for removing potassium from activated carbon by alkali based on copolymer gel

Abstract

This invention discloses a method for potassium removal from alkaline activated carbon based on copolymer gel, belonging to the field of activated carbon technology. First, alkaline activated carbon and copolymer gel are mixed, and a surfactant is added for ultrasonic treatment to obtain a pretreated solution. The pretreated solution is then reacted at 20-30°C for 1.5-2.5 hours, followed by a reaction at 30-40°C for 45-65 minutes. Finally, CO2 is introduced until the pH reaches 7-7.5, and the system temperature is raised to 45-50°C for desorption. After desorption, CO2 is stopped, and the system is allowed to stand at 8-12°C to separate the precipitate. The precipitate is then washed and dried to obtain potassium-removed activated carbon. This invention creatively designs a copolymer gel that integrates crown ether and cycloene recognition sites and possesses temperature- and pH-responsive properties, enabling deep and selective removal of residual potassium ions from alkaline activated carbon under mild conditions, while avoiding damage to the carbon skeleton caused by strong acids and high temperatures.

Description

Technical Field

[0001] This invention belongs to the field of activated carbon technology, specifically relating to an alkaline activated carbon depotassium removal method based on copolymer gel. Background Technology

[0002] Alkaline activated carbon refers to a class of high-performance porous carbon materials prepared through high-temperature activation and etching processes using potassium hydroxide or sodium hydroxide as activators. This process can efficiently create a well-developed pore structure, especially an ultra-high specific surface area and abundant micropores, giving it irreplaceable advantages in supercapacitors, hydrogen storage, catalyst supports, and high-end adsorption fields. However, this superior performance is accompanied by an inherent process challenge: potassium residue. During the activation process, excess KOH not only acts as a pore-forming agent, but some of its potassium ions are retained in the carbon framework in various forms. These forms include KOH physically adsorbed in deep pores, exchangeable potassium bound to oxygen-containing functional groups (such as carboxyl groups and phenolic hydroxyl groups) on the carbon surface through ion exchange, and chemical potassium formed by reaction with the carbon matrix at high temperatures. This residual potassium will continue to be released in subsequent applications, leading to a series of serious problems: in electrochemical applications, potassium ion migration will reduce the cycle stability and coulombic efficiency of electrode materials; in catalysis or precision adsorption processes, potassium dissolution will contaminate the reaction system or products and may poison the active sites of catalysts; in addition, residual alkaline substances will also affect the surface chemical stability of activated carbon.

[0003] Currently, the mainstream methods for potassium removal from alkaline activated carbon in industrial and research processes still focus on two traditional pathways: physical cleaning and chemical replacement. However, both have inherent drawbacks that are difficult to overcome. The most common method is repeated washing with hot water or acids (such as hydrochloric acid and nitric acid). Although water washing is simple to operate and low in cost, it relies on the diffusion of potassium ions from the micropores into the aqueous phase due to the concentration gradient. This method is extremely inefficient for removing potassium from deep pores and strongly bound potassium, often requiring very long washing times and huge water consumption. Furthermore, the final residual potassium content is difficult to reduce to below 1%, failing to meet the requirements of high-end applications. Acid washing utilizes H₂... + Replacement K + While alkaline methods can improve the removal depth, the strong acid environment severely corrodes the oxygen-containing functional groups and part of the carbon skeleton on the surface of activated carbon, leading to a decrease in specific surface area and collapse of the pore structure, seriously damaging its performance. Simultaneously, it generates a large amount of potassium-containing acidic wastewater, causing serious environmental disposal problems and wasting potassium resources. Therefore, it is essential to propose a new alkaline activated carbon depotassium removal method. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide an alkaline activated carbon depotassium removal method based on copolymer gel.

[0005] The first aspect of this invention is to provide a method for potassium removal from alkaline activated carbon based on copolymer gel, comprising the following steps: S1: Alkali activated carbon and copolymer gel are mixed, surfactant is added and ultrasonic treatment is performed to obtain a pretreatment solution; S2: First, place the pretreatment solution at 20-30℃ for 1.5-2.5h, then place it at 30-40℃ for 45-65min. S3: Introduce CO2 into the S2 reaction system until the pH is 7-7.5, raise the system temperature to 45-50°C for desorption, after desorption is completed, stop the CO2 supply and let it stand at 8-12°C to separate the precipitate, wash and dry it to obtain potassium-degraded activated carbon. The copolymer gel is synthesized from 4-vinylbenzo-15-crown-5, N-cycloalkenylacrylamide and acrylic acid in a mass ratio of 1.8-2.2:2.5-3.5:0.7-0.75.

[0006] In step S2, the pH is between 10.5 and 11, and no additional reagents are needed for adjustment.

[0007] In some embodiments, the mass ratio of alkaline activated carbon to copolymer gel is 4-6:1-2; the surfactant is an aqueous solution containing 0.4-0.6% Tween-20; and the mass of the surfactant is 2.5-3.5 times the sum of the masses of alkaline activated carbon and copolymer gel.

[0008] In some embodiments, in S1, the ultrasonic treatment is performed at 35-45 kHz, 180-240 W, and 40-50 °C for 25-35 min; in S3, the CO2 flow rate is 0.1-0.3 L / min, the desorption time is 30-60 min, and the settling time is 8-12 min.

[0009] In some embodiments, the copolymer gel is prepared by the following steps: (1) Benzo-15-crown-5 and sodium hydride in a mass ratio of 5:1-1.3 were dispersed in solvent I under inert gas protection. Chloromethyl vinyl ether containing the polymerization inhibitor was added dropwise under ice bath conditions. After the addition was completed, the reaction was carried out. (2) Filtration step (1) The reaction system was quenched, extracted, dried organic phase, rotary evaporated and purified to obtain 4-vinylbenzo-15-crown-5; (3) Disperse N-isopropylacrylamide and tetraazacyclododecane in solvent II at a mass ratio of 5:3.5-4, add the mixed solution dropwise under ice bath conditions, and then carry out the reaction; (4) Filter the reaction system of step (3), wash the filtrate, dry the organic phase, rotary evaporate and purify to obtain N-cycloalkenylacrylamide; (5) Dissolve 4-vinylbenzo-15-crown-5, N-cycloalkenylacrylamide and acrylic acid in deionized water. After purging with nitrogen to remove oxygen, add a crosslinking agent and stir to obtain a reaction solution. (6) Under ice-water bath conditions, add an initiator and N,N,N',N'-tetramethylethylenediamine to the reaction solution. (7) Transfer the reaction system in step (6) to a mold and carry out a polymerization reaction. After the reaction is completed, wash and dry to obtain the copolymer gel.

[0010] It should be noted that in the present invention, first, benzo-15-crown-5 is used as the starting material. Its phenolic hydroxyl group forms a phenoxide anion under the action of a strong base (sodium hydride), and as a strong nucleophile, it attacks the chloromethyl carbon of chloromethyl vinyl ether, and an SN2 nucleophilic substitution reaction occurs to generate 4-vinylbenzo-15-crown-5. Through a stable ether bond, the crown ether cavity with potassium ion recognition ability is covalently connected to the vinyl ether group that can be free-radically polymerized, realizing the precise targeted capture of K + and avoiding unnecessary interactions with other functional groups on the surface of activated carbon.

[0011] In addition, in the present invention, N-cycloalkenylacrylamide is also generated from N-isopropylacrylamide NIPAM and cycloalkene as raw materials. Acryloyl chloride reacts with a secondary amine nitrogen of cycloalkene to generate N-acryloylcycloalkene, introducing a strong coordination group and a polymerization site. Subsequently, this intermediate combines with NIPAM derivatives (or through copolymerization), so that both N-isopropylacrylamide and cycloalkene units are retained in the final monomer molecule. Among them, the N-isopropylacrylamide segment undergoes a reversible volume phase change above and below its lower critical solution temperature LCST. At low temperature (<LCST), it swells, and the gel network expands, which is beneficial for penetration and capture; at high temperature (>LCST), it shrinks, generating a mechanical extrusion force and changing the local hydrophobicity, promoting the release of K + and the separation from activated carbon. The rigid macrocycle composed of four nitrogen atoms of the cycloalkene unit can form a stable chelation structure with a high coordination constant with potassium ions, thereby firmly locking the K + captured by the crown ether in the gel network and achieving low-residue desorption.

[0012] Finally, the present invention takes the above two functional monomers as the core, and in an aqueous solution with acrylic acid and a crosslinking agent, forms a three-dimensional network gel through free-radical copolymerization. The carboxyl group in the acrylic acid unit first dissociates into -COO - under alkaline conditions, and assists in adsorbing positively charged K + through electrostatic interaction; then, under a weakly acidic environment caused by introducing CO2, the carboxyl group is protonated into -COOH, and the electrostatic interaction disappears, releasing the adsorbed K + , thereby realizing the desorption of K + .

[0013] In some embodiments, solvent I is selected from at least one of anhydrous tetrahydrofuran and anhydrous acetonitrile, and the mass of solvent I is 9-11 times the sum of the mass of benzo-15-crown-5 and sodium hydride; solvent II is selected from at least one of anhydrous dichloromethane and anhydrous acetonitrile, and the mass of solvent II is 10-12 times the sum of the mass of N-isopropylacrylamide and tetraazacyclododecane; the polymerization inhibitor is selected from at least one of hydroquinone and 2,6-di-tert-butyl-p-cresol, and the mass of the polymerization inhibitor is 0.8-1.2% of the mass of chloromethyl vinyl ether; the mass ratio of chloromethyl vinyl ether to benzo-15-crown-5 is 2-3:5.

[0014] In some embodiments, the mixed solution is composed of 3.8-4.2 g of acryloyl chloride and 6-6.3 mL of triethylamine, wherein the mass ratio of acryloyl chloride to N-isopropylacrylamide is 3.5-4.5:4.8-5.2.

[0015] In some embodiments, the crosslinking agent is N,N'-methylenebisacrylamide, and the mass ratio of the crosslinking agent to acrylic acid is 1-2:7-7.5; the initiator is ammonium persulfate, and the mass ratio of the initiator to acrylic acid is 0.3-0.8:7-7.5.

[0016] In some embodiments, the mass of deionized water is 5-6 times the sum of the masses of 4-vinylbenzo-15-crown-5, N-cycloalkenylacrylamide and acrylic acid; and the volume of N,N,N',N'-tetramethylethylenediamine is 0.1-0.2% of the volume of deionized water.

[0017] In some embodiments, in step (1), the dropping time is 25-35 min and the reaction is carried out at room temperature for 10-14 h; in step (3), the dropping time is 50-65 min and the reaction is carried out at room temperature for 22-26 h.

[0018] In some embodiments, in step (5), the nitrogen deoxygenation time is 25-35 min; in step (7), the polymerization reaction is carried out at 35-45°C for 5-7 h.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention creatively designs a gel remover that integrates crown ether and cycloene recognition sites and possesses temperature- and pH-responsive properties. It enables deep and selective removal of residual potassium ions from alkaline activated carbon under mild conditions. The unique swelling-shrinkage behavior of the gel achieves separation from the activated carbon, and the removal of potassium ions is achieved through coupling with CO2. + Desorption avoids the damage to the carbon skeleton and surface functional groups caused by strong acids and high temperatures.

[0020] 2. The alkaline activated carbon depotassium removal method based on copolymer gel provided by this invention can deeply remove residual potassium from activated carbon, solving the problem of easy residue in traditional methods. No strong acid or strong alkali wastewater is generated during the depotassium removal process, exhibiting certain environmental friendliness. First, the poly(N-isopropylacrylamide) segments swell at low temperature, and the gel network expands, carrying surfactants to penetrate into the hydrophobic micropores of the activated carbon. Subsequently, the 4-vinylbenzo-15-crown-5 monomer recognizes and captures potassium through the crown ether cavity. + Meanwhile, the carboxyl groups of the polyacrylic acid segments ionize into -COO under alkaline conditions. - K adsorbed through electrostatic interaction + Subsequently, the cycloene unit exerts a strong chelating effect, binding with the captured K+. + A stable coordination structure is formed. When desorption is required, CO2 is introduced to slightly acidify the environment, causing the carboxyl group to protonate and releasing K+ when electrostatic interaction decreases. + The protonation of the nitrogen atom in the cycloene weakens the coordination bond, while the heating triggers the contraction of the temperature-sensitive chain segment, generating mechanical extrusion force and changing the gel density; finally, the cooling causes the gel to swell and the density to decrease, thereby achieving gravity separation from the high-density activated carbon and completing the removal. Detailed Implementation

[0021] The present invention will now be described in further detail with reference to specific embodiments.

[0022] Example 1 A method for potassium removal from activated carbon based on copolymer gels includes the following steps: S1: Alkali activated carbon and copolymer gel were mixed in a mass ratio of 5:1.5, and an aqueous solution containing 0.5% Tween-20 was added. The mixture was treated at 40 kHz, 200 W and 45 °C for 30 min to obtain a pretreated solution. The mass of the aqueous solution containing 0.5% Tween-20 was three times the sum of the mass of the alkaline activated carbon and copolymer gel. S2: The pretreatment solution is first placed at 25°C for 2 hours and then placed at 35°C for 50 minutes. S3: Introduce CO2 at a flow rate of 0.2 L / min into the S2 reaction system until the pH reaches 7.2. Raise the system temperature to 48°C for desorption for 45 min. After desorption, stop the CO2 flow and let it stand at 10°C for 10 min. Separate the precipitate, wash and dry it to obtain potassium-degraded activated carbon. The copolymer gel is prepared by the following steps: (1) Under inert gas protection, benzo-15-crown-5 and sodium hydride in a mass ratio of 5:1.2 were dispersed in anhydrous tetrahydrofuran. Chloromethyl vinyl ether containing hydroquinone was added dropwise under ice bath conditions for 30 min. After the addition was completed, the reaction was carried out at room temperature for 12 h. The mass of anhydrous tetrahydrofuran was 10 times the sum of the masses of benzo-15-crown-5 and sodium hydride. The mass of hydroquinone was 1% of the mass of chloromethyl vinyl ether. The mass ratio of chloromethyl vinyl ether to benzo-15-crown-5 was 2.5:5. (2) Filtration step (1) reaction system, the filtrate was quenched with saturated ammonium chloride aqueous solution, extracted with ethyl acetate, then the organic phase was dried with anhydrous sodium sulfate, the solvent was removed by rotary evaporation, and 4-vinylbenzo-15-crown-5 was purified by column chromatography. (3) N-isopropylacrylamide and tetraazacyclododecane in a mass ratio of 5:3.8 were dispersed in anhydrous dichloromethane. The mixed solution was added dropwise under ice bath conditions for 55 min. Then the reaction was carried out at room temperature for 24 h. The mass of anhydrous dichloromethane was 11 times the sum of the masses of N-isopropylacrylamide and tetraazacyclododecane. The mixed solution was made by mixing 4 g of acryloyl chloride and 6.2 mL of triethylamine. The mass ratio of acryloyl chloride to N-isopropylacrylamide was 4:5. (4) Filter the reaction system of step (3), wash the filtrate with 1M HCl, then wash with saturated NaHCO3, dry the organic phase with anhydrous magnesium sulfate, and rotary evaporate to obtain a pale yellow viscous liquid. Column chromatography is used to purify N-cycloalkenylacrylamide. (5) Dissolve 4-vinylbenzo-15-crown-5, N-cycloalkenylacrylamide and acrylic acid in deionized water at a mass ratio of 2:3:0.72, remove oxygen by purging with nitrogen for 30 min, and then add N,N'-methylenebisacrylamide and stir to obtain a reaction solution; wherein, the mass ratio of N,N'-methylenebisacrylamide and acrylic acid is 1.5:7.2, and the mass of deionized water used is 5.5 times the sum of the mass of 4-vinylbenzo-15-crown-5, N-cycloalkenylacrylamide and acrylic acid; (6) Under ice-water bath conditions, ammonium persulfate and N,N,N',N'-tetramethylethylenediamine were added to the reaction solution; wherein the mass ratio of ammonium persulfate to acrylic acid was 0.5:7.2, and the volume of N,N,N',N'-tetramethylethylenediamine was 0.15% of the volume of deionized water; (7) Transfer the reaction system of step (6) into a mold and polymerize at 40°C for 6 hours. After the reaction is completed, wash and dry to obtain copolymer gel.

[0023] Example 2 A method for potassium removal from activated carbon based on copolymer gels includes the following steps: S1: Alkali activated carbon and copolymer gel were mixed in a mass ratio of 6:2, and an aqueous solution containing 0.6% Tween-20 was added. The mixture was treated at 45 kHz, 240 W and 50 °C for 25 min to obtain a pretreated solution. The mass of the aqueous solution containing 0.6% Tween-20 was 3.5 times the sum of the mass of the alkaline activated carbon and copolymer gel. S2: The pretreatment solution is first placed at 30℃ for 2.5h, and then placed at 40℃ for 45min. S3: Introduce CO2 at a flow rate of 0.3 L / min into the S2 reaction system until the pH reaches 7.5. Raise the system temperature to 50°C for desorption for 60 min. After desorption, stop the CO2 flow and let it stand at 12°C for 8 min. Separate the precipitate, wash and dry it to obtain potassium-degraded activated carbon. The copolymer gel is prepared by the following steps: (1) Benzo-15-crown-5 and sodium hydride in a mass ratio of 5:1.3 were dispersed in anhydrous acetonitrile under an inert gas protection. Chloromethyl vinyl ether containing 2,6-di-tert-butyl-p-cresol was added dropwise under ice bath conditions for 35 min. After the addition was completed, the reaction was carried out at room temperature for 14 h. The mass of anhydrous acetonitrile was 11 times the sum of the masses of benzo-15-crown-5 and sodium hydride. The mass of 2,6-di-tert-butyl-p-cresol was 1.2% of the mass of chloromethyl vinyl ether. The mass ratio of chloromethyl vinyl ether to benzo-15-crown-5 was 3:5. (2) Filtration step (1) reaction system, the filtrate was quenched with saturated ammonium chloride aqueous solution, extracted with ethyl acetate, then the organic phase was dried with anhydrous sodium sulfate, the solvent was removed by rotary evaporation, and 4-vinylbenzo-15-crown-5 was purified by column chromatography. (3) N-isopropylacrylamide and tetraazacyclododecane in a mass ratio of 5:4 were dispersed in anhydrous acetonitrile. The mixed solution was added dropwise under ice bath conditions for 65 min. Then the reaction was carried out at room temperature for 26 h. The mass of anhydrous acetonitrile was 12 times the sum of the masses of N-isopropylacrylamide and tetraazacyclododecane. The mixed solution was made by mixing 4.2 g of acryloyl chloride and 6.3 mL of triethylamine. The mass ratio of acryloyl chloride to N-isopropylacrylamide was 4.5:5.2. (4) Filter the reaction system of step (3), wash the filtrate with 1M HCl, then wash with saturated NaHCO3, dry the organic phase with anhydrous magnesium sulfate, and rotary evaporate to obtain a pale yellow viscous liquid. Column chromatography is used to purify N-cycloalkenylacrylamide. (5) Dissolve 4-vinylbenzo-15-crown-5, N-cycloalkenylacrylamide and acrylic acid in deionized water at a mass ratio of 2.2:3.5:0.75, remove oxygen by purging with nitrogen for 35 min, and then add N,N'-methylenebisacrylamide and stir to obtain a reaction solution; wherein, the mass ratio of N,N'-methylenebisacrylamide and acrylic acid is 2:7.5, and the mass of deionized water used is 6 times the sum of the mass of 4-vinylbenzo-15-crown-5, N-cycloalkenylacrylamide and acrylic acid; (6) Under ice-water bath conditions, ammonium persulfate and N,N,N',N'-tetramethylethylenediamine were added to the reaction solution; wherein the mass ratio of ammonium persulfate to acrylic acid was 0.8:7.5, and the volume of N,N,N',N'-tetramethylethylenediamine was 0.2% of the volume of deionized water; (7) Transfer the reaction system of step (6) into a mold and polymerize at 45°C for 7 hours. After the reaction is completed, wash and dry to obtain copolymer gel.

[0024] Example 3 A method for potassium removal from activated carbon based on copolymer gels includes the following steps: S1: Alkali activated carbon and copolymer gel were mixed in a mass ratio of 4:1, and an aqueous solution containing 0.4% Tween-20 was added. The mixture was treated at 35 kHz, 180 W and 40 °C for 25 min to obtain a pretreated solution. The mass of the aqueous solution containing 0.4% Tween-20 was 2.5 times the sum of the mass of the alkaline activated carbon and copolymer gel. S2: The pretreatment solution is first placed at 20℃ for 1.5h, and then placed at 30℃ for 65min. S3: Introduce CO2 at a flow rate of 0.1 L / min into the S2 reaction system until the pH reaches 7. Raise the system temperature to 45°C for desorption for 60 min. After desorption, stop the CO2 flow and let it stand at 8°C for 12 min. Separate the precipitate, wash and dry it to obtain potassium-degraded activated carbon. The copolymer gel is prepared by the following steps: (1) Under inert gas protection, benzo-15-crown-5 and sodium hydride in a mass ratio of 5:1 were dispersed in anhydrous tetrahydrofuran. Chloromethyl vinyl ether containing hydroquinone was added dropwise under ice bath conditions for 25 min. After the addition was completed, the reaction was carried out at room temperature for 10 h. The mass of anhydrous tetrahydrofuran was 9 times the sum of the masses of benzo-15-crown-5 and sodium hydride. The mass of hydroquinone was 0.8% of the mass of chloromethyl vinyl ether. The mass ratio of chloromethyl vinyl ether to benzo-15-crown-5 was 2:5. (2) Filtration step (1) reaction system, the filtrate was quenched with saturated ammonium chloride aqueous solution, extracted with ethyl acetate, then the organic phase was dried with anhydrous sodium sulfate, the solvent was removed by rotary evaporation, and 4-vinylbenzo-15-crown-5 was purified by column chromatography. (3) N-isopropylacrylamide and tetraazacyclododecane in a mass ratio of 5:3.5 were dispersed in anhydrous dichloromethane. The mixed solution was added dropwise under ice bath conditions for 50 min. Then the reaction was carried out at room temperature for 22 h. The mass of anhydrous dichloromethane was 10 times the sum of the masses of N-isopropylacrylamide and tetraazacyclododecane. The mixed solution was made by mixing 3.8 g of acryloyl chloride and 6 mL of triethylamine. The mass ratio of acryloyl chloride to N-isopropylacrylamide was 3.5:4.8. (4) Filter the reaction system of step (3), wash the filtrate with 1M HCl, then wash with saturated NaHCO3, dry the organic phase with anhydrous magnesium sulfate, and rotary evaporate to obtain a pale yellow viscous liquid. Column chromatography is used to purify N-cycloalkenylacrylamide. (5) Dissolve 4-vinylbenzo-15-crown-5, N-cycloalkenylacrylamide and acrylic acid in deionized water at a mass ratio of 1.8:2.5:0.7, remove oxygen by purging with nitrogen for 25 min, and then add N,N'-methylenebisacrylamide and stir to obtain a reaction solution; wherein, the mass ratio of N,N'-methylenebisacrylamide and acrylic acid is 1:7, and the mass of deionized water used is 5 times the sum of the mass of 4-vinylbenzo-15-crown-5, N-cycloalkenylacrylamide and acrylic acid; (6) Under ice-water bath conditions, ammonium persulfate and N,N,N',N'-tetramethylethylenediamine were added to the reaction solution; wherein the mass ratio of ammonium persulfate to acrylic acid was 0.3:7, and the volume of N,N,N',N'-tetramethylethylenediamine was 0.1% of the volume of deionized water; (7) Transfer the reaction system of step (6) into a mold and polymerize at 35°C for 5 hours. After the reaction is complete, wash and dry to obtain copolymer gel.

[0025] Example 4 A method for potassium removal from activated carbon based on copolymer gels includes the following steps: S1: Alkali activated carbon and copolymer gel were mixed in a mass ratio of 4.5:1.5, and an aqueous solution containing 0.5% Tween-20 was added. The mixture was treated at 40 kHz, 190 W and 50 °C for 35 min to obtain a pretreated solution. The mass of the aqueous solution containing 0.5% Tween-20 was 3.5 times the sum of the mass of the alkaline activated carbon and copolymer gel. S2: The pretreatment solution is first placed at 25°C for 2 hours and then placed at 35°C for 50 minutes. S3: Introduce CO2 at a flow rate of 0.25 L / min into the S2 reaction system until the pH reaches 7.4. Raise the system temperature to 48°C for desorption for 40 min. After desorption, stop the CO2 flow and let it stand at 10°C for 9 min. Separate the precipitate, wash and dry it to obtain potassium-degraded activated carbon. The copolymer gel is prepared by the following steps: (1) Benzo-15-crown-5 and sodium hydride in a mass ratio of 5:1.1 were dispersed in anhydrous acetonitrile under an inert gas protection. Chloromethyl vinyl ether containing 2,6-di-tert-butyl-p-cresol was added dropwise under ice bath conditions for 30 min. After the addition was completed, the reaction was carried out at room temperature for 11 h. The mass of anhydrous acetonitrile was 10 times the sum of the masses of benzo-15-crown-5 and sodium hydride. The mass of 2,6-di-tert-butyl-p-cresol was 0.9% of the mass of chloromethyl vinyl ether. The mass ratio of chloromethyl vinyl ether to benzo-15-crown-5 was 2.5:5. (2) Filtration step (1) reaction system, the filtrate was quenched with saturated ammonium chloride aqueous solution, extracted with ethyl acetate, then the organic phase was dried with anhydrous sodium sulfate, the solvent was removed by rotary evaporation, and 4-vinylbenzo-15-crown-5 was purified by column chromatography. (3) N-isopropylacrylamide and tetraazacyclododecane in a mass ratio of 5:3.6 were dispersed in anhydrous acetonitrile, and the mixed solution was added dropwise under ice bath conditions for 60 min. Then the reaction was carried out at room temperature for 23 h. The mass of anhydrous acetonitrile was 11 times the sum of the masses of N-isopropylacrylamide and tetraazacyclododecane. The mixed solution was made by mixing 4 g of acryloyl chloride and 6.1 mL of triethylamine. The mass ratio of acryloyl chloride to N-isopropylacrylamide was 4:4.8. (4) Filter the reaction system of step (3), wash the filtrate with 1M HCl, then wash with saturated NaHCO3, dry the organic phase with anhydrous magnesium sulfate, and rotary evaporate to obtain a pale yellow viscous liquid. Column chromatography is used to purify N-cycloalkenylacrylamide. (5) Dissolve 4-vinylbenzo-15-crown-5, N-cycloalkenylacrylamide and acrylic acid in deionized water at a mass ratio of 1.9:2.8:0.73, remove oxygen by purging with nitrogen for 28 min, and then add N,N'-methylenebisacrylamide and stir to obtain a reaction solution; wherein, the mass ratio of N,N'-methylenebisacrylamide and acrylic acid is 1.8:7.3, and the mass of deionized water used is 4.5 times the sum of the mass of 4-vinylbenzo-15-crown-5, N-cycloalkenylacrylamide and acrylic acid; (6) Under ice-water bath conditions, ammonium persulfate and N,N,N',N'-tetramethylethylenediamine were added to the reaction solution; wherein the mass ratio of ammonium persulfate to acrylic acid was 0.4:7.3, and the volume of N,N,N',N'-tetramethylethylenediamine was 0.2% of the volume of deionized water; (7) Transfer the reaction system of step (6) into a mold and polymerize at 40°C for 6 hours. After the reaction is completed, wash and dry to obtain copolymer gel.

[0026] Example 5 A method for potassium removal from activated carbon based on copolymer gels includes the following steps: S1: Alkali activated carbon and copolymer gel were mixed in a mass ratio of 5:1.5, and an aqueous solution containing 0.55% Tween-20 was added. The mixture was treated at 45 kHz, 220 W, and 45 °C for 30 min to obtain a pretreated solution. The mass of the aqueous solution containing 0.55% Tween-20 was three times the sum of the mass of the alkaline activated carbon and copolymer gel. S2: The pretreatment solution is first placed at 25°C for 2.5 hours and then at 35°C for 65 minutes. S3: Introduce CO2 at a flow rate of 0.15 L / min into the S2 reaction system until the pH reaches 7.1. Raise the system temperature to 50°C for desorption for 50 min. After desorption, stop the CO2 flow and let it stand at 11°C for 10 min. Separate the precipitate, wash and dry it to obtain potassium-degraded activated carbon. The copolymer gel is prepared by the following steps: (1) Benzo-15-crown-5 and sodium hydride in a mass ratio of 5:1.2 were dispersed in anhydrous tetrahydrofuran under an inert gas protection. Chloromethyl vinyl ether containing 2,6-di-tert-butyl-p-cresol was added dropwise under ice bath conditions for 30 min. After the addition was completed, the reaction was carried out at room temperature for 13 h. The mass of anhydrous tetrahydrofuran was 10 times the sum of the masses of benzo-15-crown-5 and sodium hydride. The mass of 2,6-di-tert-butyl-p-cresol was 1.1% of the mass of chloromethyl vinyl ether. The mass ratio of chloromethyl vinyl ether to benzo-15-crown-5 was 2.8:5. (2) Filtration step (1) reaction system, the filtrate was quenched with saturated ammonium chloride aqueous solution, extracted with ethyl acetate, then the organic phase was dried with anhydrous sodium sulfate, the solvent was removed by rotary evaporation, and 4-vinylbenzo-15-crown-5 was purified by column chromatography. (3) N-isopropylacrylamide and tetraazacyclododecane in a mass ratio of 5:3.8 were dispersed in anhydrous dichloromethane. The mixed solution was added dropwise under ice bath conditions for 55 min. Then the reaction was carried out at room temperature for 25 h. The mass of anhydrous dichloromethane was 10 times the sum of the masses of N-isopropylacrylamide and tetraazacyclododecane. The mixed solution was made by mixing 4.1 g of acryloyl chloride and 6.3 mL of triethylamine. The mass ratio of acryloyl chloride to N-isopropylacrylamide was 4.2:5.1. (4) Filter the reaction system of step (3), wash the filtrate with 1M HCl, then wash with saturated NaHCO3, dry the organic phase with anhydrous magnesium sulfate, and rotary evaporate to obtain a pale yellow viscous liquid. Column chromatography is used to purify N-cycloalkenylacrylamide. (5) Dissolve 4-vinylbenzo-15-crown-5, N-cycloalkenylacrylamide and acrylic acid in deionized water at a mass ratio of 2.1:3.2:0.74, remove oxygen by purging with nitrogen for 35 min, and then add N,N'-methylenebisacrylamide and stir to obtain a reaction solution; wherein, the mass ratio of N,N'-methylenebisacrylamide and acrylic acid is 1.8:7.1, and the mass of deionized water used is 6 times the sum of the mass of 4-vinylbenzo-15-crown-5, N-cycloalkenylacrylamide and acrylic acid; (6) Under ice-water bath conditions, ammonium persulfate and N,N,N',N'-tetramethylethylenediamine were added to the reaction solution; wherein the mass ratio of ammonium persulfate to acrylic acid was 0.7:7.4, and the volume of N,N,N',N'-tetramethylethylenediamine was 0.18% of the volume of deionized water; (7) Transfer the reaction system of step (6) into a mold and polymerize at 45°C for 7 hours. After the reaction is completed, wash and dry to obtain copolymer gel.

[0027] Comparative Example 1 The results are basically the same as in Example 1, except that the copolymer gel is produced by physical mixing, that is, the same amount of 4-vinylbenzo-15-crown-5, N-cycloalkenylacrylamide and acrylic acid are physically mixed as in Example 1.

[0028] Comparative Example 2 It is basically the same as Example 1, except that 4-vinylbenzo-15-crown-5 is not added, that is, steps (1) and (2) are omitted.

[0029] Comparative Example 3 It is basically the same as Example 1, except that N-cycloalkenylacrylamide is not added, that is, steps (3) and (4) are omitted.

[0030] Comparative Example 4 It is basically the same as Example 1, except that CO2 is not introduced in step S3.

[0031] Comparative Example 5 The process is basically the same as in Example 1, except that the heating operation is not performed in step S3. That is, after adjusting the pH to 7.2, the CO2 flow is stopped and the mixture is allowed to stand.

[0032] The potassium-depotassium activated carbon obtained by the alkaline activated carbon depotassium removal method in Examples 1-5 and Comparative Examples 1-5, as well as the prepared copolymer gel, were tested, and the data results are shown in Table 1.

[0033] Test method: The original alkaline activated carbon had a potassium content of 2.5% and a sodium content of 0.5%. All examples and comparative examples were carried out under the same conditions of reaction time, temperature, and material ratio.

[0034] Potassium removal depth test: Activated carbon samples before and after treatment were microwave digested with aqua regia (HCl:HNO3 = 3:1), and tested after volume adjustment. Potassium residue rate (%) = (original activated carbon potassium content - treated activated carbon potassium content) / original activated carbon potassium content × 100%; Potassium removal rate = (1 - potassium residue rate / original potassium content) × 100%. K + Selectivity test: Prepare K at a known concentration + / Na + A mixed solution was used to simulate an alkaline environment to test the adsorption performance of the copolymer gel; the selectivity coefficient α(K) was measured. + / Na + )= (Qe_K + / Ce_K + ) / (Qe_Na + / Ce_Na + ), where Qe is the equilibrium adsorption amount and Ce is the equilibrium concentration.

[0035] Table 1 As shown in Table 1, the activated carbon treated for potassium removal in Examples 1-5 exhibits a low residual valence rate and a high removal rate, effectively removing potassium. + The selectivity is relatively strong. Looking at the comparative examples, it can be seen that Comparative Example 1 uses physical mixing. Physically mixed molecules cannot form a stable three-dimensional network. In a stirred and liquid-phase environment, functional small molecules (crown ether derivatives, cycloene derivatives, etc.) easily dissolve and leach from the activated carbon surface, failing to effectively enrich and function, leading to a decrease in all data. Comparative Example 2 lacks 4-vinylbenzo-15-crown-5, causing the gel to mainly rely on the chelating effect of cycloenes and the electrostatic interaction of carboxyl groups to adsorb ions. These two effects are less effective for K... + and Na +Limited distinguishing ability; Comparative Example 3 lacks N-cycloalkenylacrylamide, K + It is easily replaced or eluted, resulting in a high final residue rate; in Comparative Example 4, because CO2 was not introduced, the pH of the system could not be lowered, and the carboxyl groups remained in an ionized state (-COO). - Electrostatic attraction persists; the cycloene remains in a deprotonated state, affecting K. + The strong coordinate bonds were not weakened, and the vast majority of K + The K+ remains trapped within the gel and cannot be released into the liquid phase, leading to removal failure and making it impossible to measure the K+ in the final solution. + To infer the exact amount of K adsorbed by the gel, we can use the concentration. + (Qe); Comparative Example 5 was not subjected to heating treatment, allowing the gel network to remain in a swollen state at low temperature, with open pores and rich in water, weakening the K+. + The diffusion path from the network interior to the external liquid phase is long and has high resistance, resulting in a slow and incomplete desorption process. Consequently, the removal rate is far lower than in the example, and a large amount of K... + The ions are still distributed in an unknown and uneven state in the gel network and activated carbon pores. At this time, the measured solution ion concentration cannot represent the effective adsorption equilibrium concentration, so Qe and α are not comparable.

[0036] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A method for potassium removal from alkaline activated carbon based on copolymer gel, characterized in that, Includes the following steps: S1: Alkali activated carbon and copolymer gel are mixed, surfactant is added and ultrasonic treatment is performed to obtain a pretreatment solution; S2: The pretreatment solution is first placed at 20-30℃ for 1.5-2.5h, and then placed at 30-40℃ for 45-65min; S3: Introduce CO2 into the S2 reaction system until the pH is 7-7.5, raise the system temperature to 45-50°C for desorption, after desorption is completed, stop the CO2 supply and let it stand at 8-12°C to separate the precipitate, wash and dry it to obtain potassium-degraded activated carbon. The copolymer gel is synthesized from 4-vinylbenzo-15-crown-5, N-cycloalkenylacrylamide and acrylic acid in a mass ratio of 1.8-2.2:2.5-3.5:0.7-0.

75.

2. The alkaline activated carbon depotassium removal method based on copolymer gel according to claim 1, characterized in that, The mass ratio of alkaline activated carbon to copolymer gel is 4-6:1-2; the surfactant is an aqueous solution containing 0.4-0.6% Tween-20; the mass amount of the surfactant is 2.5-3.5 times the sum of the masses of alkaline activated carbon and copolymer gel.

3. The alkaline activated carbon depotassium removal method based on copolymer gel according to claim 1, characterized in that, In step S1, the ultrasonic treatment is performed at 35-45 kHz, 180-240 W, and 40-50 °C for 25-35 min; in step S3, the CO2 flow rate is 0.1-0.3 L / min, the desorption time is 30-60 min, and the settling time is 8-12 min.

4. The alkaline activated carbon depotassium removal method based on copolymer gel according to claim 1, characterized in that, The copolymer gel was prepared by the following steps: (1) Benzo-15-crown-5 and sodium hydride in a mass ratio of 5:1-1.3 were dispersed in solvent I under inert gas protection. Chloromethyl vinyl ether containing the polymerization inhibitor was added dropwise under ice bath conditions. After the addition was completed, the reaction was carried out. (2) Filtration step (1) reaction system, quench the filtrate, extract, dry the organic phase, rotary evaporate and purify to obtain 4-vinylbenzo-15-crown-5; (3) Disperse N-isopropylacrylamide and tetraazacyclododecane in solvent II at a mass ratio of 5:3.5-4, add the mixed solution dropwise under ice bath conditions, and then carry out the reaction; (4) Filter the reaction system of step (3), wash the filtrate, dry the organic phase, rotary evaporate and purify to obtain N-cycloalkenylacrylamide; (5) Dissolve the 4-vinylbenzo-15-crown-5, the N-cycloalkenylacrylamide and acrylic acid in deionized water, remove oxygen by purging with nitrogen, add crosslinking agent and stir to obtain a reaction solution; (6) Under ice-water bath conditions, an initiator and N,N,N',N'-tetramethylethylenediamine were added to the reaction solution; (7) Transfer the reaction system from step (6) into a mold and carry out the polymerization reaction. After the reaction is completed, wash and dry to obtain the copolymer gel.

5. The alkaline activated carbon depotassium removal method based on copolymer gel according to claim 4, characterized in that, Solvent I is selected from at least one of anhydrous tetrahydrofuran and anhydrous acetonitrile, and the mass of solvent I is 9-11 times the sum of the mass of benzo-15-crown-5 and sodium hydride; solvent II is selected from at least one of anhydrous dichloromethane and anhydrous acetonitrile, and the mass of solvent II is 10-12 times the sum of the mass of N-isopropylacrylamide and tetraazacyclododecane; the polymerization inhibitor is selected from at least one of hydroquinone and 2,6-di-tert-butyl-p-cresol, and the mass of the polymerization inhibitor is 0.8-1.2% of the mass of chloromethyl vinyl ether; the mass ratio of chloromethyl vinyl ether to benzo-15-crown-5 is 2-3:

5.

6. The alkaline activated carbon depotassium removal method based on copolymer gel according to claim 4, characterized in that, The mixed solution is composed of 3.8-4.2 g of acryloyl chloride and 6-6.3 mL of triethylamine, wherein the mass ratio of acryloyl chloride to N-isopropylacrylamide is 3.5-4.5:4.8-5.

2.

7. The alkaline activated carbon depotassium removal method based on copolymer gel according to claim 4, characterized in that, The crosslinking agent is N,N'-methylenebisacrylamide, and the mass ratio of the crosslinking agent to the acrylic acid is 1-2:7-7.5; the initiator is ammonium persulfate, and the mass ratio of the initiator to the acrylic acid is 0.3-0.8:7-7.

5.

8. The alkaline activated carbon depotassium removal method based on copolymer gel according to claim 4, characterized in that, The mass of the deionized water is 5-6 times the sum of the masses of the 4-vinylbenzo-15-crown-5, N-cycloalkenylacrylamide and acrylic acid; the volume of the N,N,N',N'-tetramethylethylenediamine is 0.1-0.2% of the volume of the deionized water.

9. The alkaline activated carbon depotassium removal method based on copolymer gel according to claim 4, characterized in that, In step (1), the dropping time is 25-35 min, and the reaction is carried out at room temperature for 10-14 h; in step (3), the dropping time is 50-65 min, and the reaction is carried out at room temperature for 22-26 h.

10. The alkaline activated carbon depotassium removal method based on copolymer gel according to claim 4, characterized in that, In step (5), the nitrogen deoxygenation time is 25-35 min; in step (7), the polymerization reaction is carried out at 35-45℃ for 5-7 h.

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