Ultrafiltration membrane device for waste alkali recovery

Abstract

This invention discloses an ultrafiltration membrane for waste alkali recovery, belonging to the field of ultrafiltration membrane technology. It includes several filtration units arranged in a decreasing concentration gradient. Each filtration unit includes a concentration chamber and a dilute chamber, with a cation exchange membrane disposed between the concentration and dilute chambers. The preparation method of the cation exchange membrane includes the following steps: ester hydrolysis of phenolphthalein and acidification to obtain carboxylated phenolphthalein; synthesis of hydrophilic polysulfone using 4,4'-dichlorodiphenyl sulfone, 4,4'-biphenylhydrazine, and carboxylated phenolphthalein as raw materials; acyl chloride modification of the carboxyl groups of the hydrophilic polysulfone to obtain acyl chloride polysulfone; reaction of the acyl chloride groups of the acyl chloride polysulfone with the amino group of trisodium 8-aminopyrene-1,3,6-trisulfonic acid to obtain modified polysulfone resin; and membrane preparation using the modified polysulfone resin, polyvinylpyrrolidone, and N-methylpyrrolidone to obtain the cation exchange membrane. This membrane is used to improve the hydrophilicity and antifouling ability of the polysulfone membrane, thereby improving separation efficiency and operational stability.

Description

Technical Field

[0001] This invention belongs to the field of ultrafiltration membrane technology, and specifically relates to an ultrafiltration membrane device for waste alkali recovery. Background Technology

[0002] During waste alkali recovery, when waste alkali and receiving liquid (tap water) are introduced to the two sides of the concentration chamber respectively, the waste alkali and its salts tend to migrate towards the dilute chamber due to the concentration gradient. Because the ultrafiltration membrane has selective permeability to cations, the cations (M...) on the waste alkali side... + The ions (OH-) migrate smoothly into the water side, and due to the requirement of electroneutrality, the anions also migrate into the water side simultaneously; - Ions have relatively small hydration radii and low charge numbers, while anions in salts (A...) - OH has a large hydration radius and a large number of charges, therefore OH - It will preferentially migrate across the membrane, A - The blockage allows the alkali in the waste liquid to be separated.

[0003] A search revealed that document CN202210367730.X discloses an apparatus for treating high-salt desulfurization wastewater. The apparatus continuously feeds ultrafiltration-treated wastewater into an electrodialysis unit for desalination, yielding a high-concentration salt solution and a low-concentration salt solution. The electrodialysis unit includes an electrodialysis chamber, a concentrate tank, and a desalination tank. The electrodialysis chamber contains opposing electrode plates, and between the electrode plates are several alternately arranged anion exchange membranes and cation exchange membranes. The anion exchange membranes and cation exchange membranes... The electrodialysis chamber is divided into alternating concentration and dilute chambers. The outlet of the concentration chamber is connected to the inlet of the concentrate tank, and the outlet of the dilute chamber is connected to the inlet of the dilute tank. The ultrafiltration membrane unit is connected to the inlet of the concentration chamber and the inlet of the dilute chamber via pipelines and a three-way valve. In step S500, the wastewater after ultrafiltration treatment is sent to the inlet of the concentration chamber and the inlet of the dilute chamber. Prior art document CN202180021608.0 discloses a cation exchange membrane that can be used to recover waste alkali by diffusion dialysis. Polysulfone (PSB) membranes are increasingly favored due to their excellent overall performance. However, the poor hydrophilicity of PSB membranes makes them prone to fouling during use, leading to reduced separation efficiency, shortened membrane lifespan, rapid flux decline, continuous decrease in separation efficiency, and a significant increase in cleaning frequency. Long-term operation can also cause membrane structural damage and deterioration of separation selectivity, significantly shortening membrane lifespan and increasing operating and maintenance costs. Therefore, developing a PSB-based ultrafiltration membrane for waste alkali recovery that exhibits excellent hydrophilicity, strong anti-fouling capabilities, high separation efficiency, and stable operation is of significant practical importance and application value for improving the resource utilization rate of industrial waste alkali, reducing environmental treatment costs, and promoting green and circular industrial development. Summary of the Invention

[0004] The purpose of this invention is to provide an ultrafiltration membrane device for waste alkali recovery, which improves the hydrophilicity and antifouling ability of polysulfone membranes, and enhances separation efficiency and operational stability.

[0005] The objective of this invention can be achieved through the following technical solutions: An ultrafiltration membrane device for waste alkali recovery includes a plurality of filtration units arranged in a decreasing concentration gradient. Each filtration unit includes a concentration chamber and a dilute chamber, and a cation exchange membrane is disposed between the concentration chamber and the dilute chamber. The preparation method of the cation exchange membrane includes the following steps: S1. Phenolphthalein is subjected to ester hydrolysis and acidification to obtain carboxylated phenolphthalein; S2. Hydrophilic polysulfone was synthesized using 4,4'-dichlorodiphenyl sulfone, 4,4'-biphenylhydrazine, and carboxylated phenolphthalein as raw materials. S3. The carboxyl group of the hydrophilic polysulfone is modified by acyl chloride to obtain acyl chloride polysulfone; S4. React the acyl chloride group of acyl chloride polysulfone with the amino group of trisodium 8-aminopyrene-1,3,6-trisulfonic acid to obtain modified polysulfone resin. S5. Using the modified polysulfone resin, polyvinylpyrrolidone and N-methylpyrrolidone as raw materials, a membrane is prepared to obtain the cation exchange membrane.

[0006] As a preferred technical solution of the present invention, step S1 specifically includes the following steps: take phenolphthalein, zinc powder, sodium hydroxide, anhydrous ethanol and deionized water, mix them, heat and reflux at 60-70°C for 10-12 hours, filter, take the liquid phase, adjust the pH to 5-6, precipitate acid, filter, collect the precipitate, wash and vacuum dry to obtain carboxylated phenolphthalein.

[0007] As a preferred embodiment of the present invention, the ratio of phenolphthalein, zinc powder, sodium hydroxide, anhydrous ethanol and deionized water is 5-6g: 15-16g: 17-18g: 40-50mL: 50mL.

[0008] As a preferred embodiment of the present invention, in step S2, the mass ratio of 4,4'-dichlorodiphenyl sulfone, 4,4'-biphenylhydrazine, and carboxylated phenolphthalein is 7-8:3.5-4.2:2-2.2.

[0009] As a preferred technical solution of the present invention, step S3 specifically includes the following steps: take the hydrophilic polysulfone and thionyl chloride and mix them, stir ultrasonically for 30-40 min, add N,N-dimethylformamide, heat to 65°C and stir for 8-12 h, filter, take the solid phase and wash with tetrahydrofuran, and vacuum dry to obtain acyl chloride polysulfone.

[0010] As a preferred embodiment of the present invention, the ratio of hydrophilic polysulfone, sulfoxide, and N,N-dimethylformamide is 1-1.2g: 20-40mL: 1-2mL.

[0011] As a preferred technical solution of the present invention, step S4 specifically includes the following steps: In a nitrogen atmosphere, the acyl chloride polysulfone, dimethyl sulfoxide, and N,N-dimethylformamide are mixed and stirred evenly, triethylamine is added, and 8-aminopyrene-1,3,6-trisulfonic acid trisodium salt is added in an ice-water bath in the dark. The mixture is heated to 20-25°C and stirred for 4-6 hours to obtain a mixture. The mixture is precipitated with anhydrous ethanol, centrifuged, and the solid phase is washed and vacuum dried to obtain modified polysulfone resin.

[0012] As a preferred embodiment of the present invention, the ratio of polysulfone chloride, dimethyl sulfoxide, N,N-dimethylformamide, triethylamine, and trisodium 8-aminopyrene-1,3,6-trisulfonic acid salt is 1-1.2g:40mL:40mL:0.2-0.4mL:4.1-4.3g.

[0013] In a preferred embodiment of the present invention, the mass ratio of the modified polysulfone resin, polyvinylpyrrolidone, and N-methylpyrrolidone is 8-10:5-6:30-40.

[0014] The beneficial effects of this invention are: The ultrafiltration membrane for waste alkali recovery disclosed in this invention is prepared by using a high-performance cation exchange membrane and double hydrophilic modification by carboxylated phenolphthalein copolymerization and pyrene trisulfonic acid grafting. It has ultra-high hydrophilicity, high pure water flux, excellent antifouling properties and good dimensional stability. Detailed Implementation

[0015] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with embodiments, is provided below. Example 1

[0016] An ultrafiltration membrane device for waste alkali recovery includes a plurality of filtration units arranged in a decreasing concentration gradient. Each filtration unit includes a concentration chamber and a dilute chamber, and a cation exchange membrane is disposed between the concentration chamber and the dilute chamber. The preparation method of the cation exchange membrane includes the following steps: S1. Mix phenolphthalein, zinc powder, sodium hydroxide, anhydrous ethanol and deionized water, heat and reflux at 60°C for 10 hours, filter, take the liquid phase, adjust the pH to 5, precipitate acid, filter, collect the precipitate, wash and vacuum dry to obtain carboxylated phenolphthalein; the ratio of phenolphthalein, zinc powder, sodium hydroxide, anhydrous ethanol and deionized water is 5g:15g:17g:40mL:50mL. S2. Under a nitrogen atmosphere, mix 4,4'-dichlorodiphenyl sulfone, 4,4'-biphenylhydrazine, carboxylated phenolphthalein, tetrahydrothiophene sulfone, and N-methyl-2-pyrrolidone. Heat to 80°C and stir at this temperature for 1 hour. Add anhydrous potassium carbonate and toluene, continue stirring, and heat to 140°C. Reflux at this temperature for 3 hours to remove water. During this time, monitor the water layer precipitation in real time using a water separator. Once no new water layer is added to the separator and no more water is generated in the system, start the distillation operation to completely distill off the toluene in the system. Continue heating to 175°C and stir at this temperature to carry out the nucleophilic aromatic substitution polycondensation reaction for 5 hours. During this period, sample the polymer every 1 hour for testing. The apparent viscosity of the solution was measured. When the apparent viscosity showed no significant increase and tended to stabilize after two consecutive tests, the polymerization reaction was considered to have reached its endpoint. Heating was stopped, and the reaction system was allowed to cool naturally to room temperature. The viscous reaction mixture was then slowly poured into deionized water under high-speed stirring to precipitate the precipitate. The precipitate was washed, boiled in boiling water three times for 30 minutes each time, and then vacuum dried to obtain hydrophilic polysulfone. The ratio of 4,4'-dichlorodiphenyl sulfone, 4,4'-biphenyl hydroquinone, carboxylated phenolphthalein, tetrahydrothiophene sulfone, N-methyl-2-pyrrolidone, anhydrous potassium carbonate, and toluene was 7g:3.5g:2g:40mL:40mL:4g:20mL. S3. Mix the hydrophilic polysulfone and thionyl chloride, sonicate for 30 min, add N,N-dimethylformamide, heat to 65℃ and stir for 8 h, filter, wash the solid phase with tetrahydrofuran, and vacuum dry to obtain acyl chloride polysulfone; the ratio of hydrophilic polysulfone, thionyl chloride and N,N-dimethylformamide is 1 g: 20 mL: 1 mL; S4. Under a nitrogen atmosphere, the acyl chloride polysulfone, dimethyl sulfoxide, and N,N-dimethylformamide were mixed and stirred until homogeneous. Triethylamine was added, and 8-aminopyrene-1,3,6-trisulfonic acid trisodium salt was added in an ice-water bath in the dark. The mixture was heated to 20°C and stirred for 4 hours to obtain a mixture. The mixture was precipitated with anhydrous ethanol, centrifuged, and the solid phase was washed and vacuum dried to obtain modified polysulfone resin. The ratio of the acyl chloride polysulfone, dimethyl sulfoxide, N,N-dimethylformamide, triethylamine, and 8-aminopyrene-1,3,6-trisulfonic acid trisodium salt was 1 g: 40 mL: 40 mL: 0.2 mL: 4.1 g. S5. Take the modified polysulfone resin, polyvinylpyrrolidone and N-methylpyrrolidone and mix them. Heat and stir at 120°C for 30 min until the polymer is completely dissolved and the casting solution is clear. Use a doctor blade to scrape the casting solution onto a glass plate to form a film layer with a thickness of 1200 μm. Then, let it stand at a constant temperature for 24 h to remove bubbles. Place it in a coagulation bath (the coagulation bath is water, and the temperature is room temperature) to remove the film. Soak it in deionized water for 30 h. Take it out and let it air dry at room temperature to obtain the cation exchange membrane. The mass ratio of the modified polysulfone resin, polyvinylpyrrolidone and N-methylpyrrolidone is 8:5:30. Example 2

[0017] An ultrafiltration membrane device for waste alkali recovery includes a plurality of filtration units arranged in a decreasing concentration gradient. Each filtration unit includes a concentration chamber and a dilute chamber, and a cation exchange membrane is disposed between the concentration chamber and the dilute chamber. The preparation method of the cation exchange membrane includes the following steps: S1. Mix phenolphthalein, zinc powder, sodium hydroxide, anhydrous ethanol, and deionized water, heat at 65°C, reflux and stir for 11 hours, filter, take the liquid phase, adjust the pH to 6, precipitate acid, filter, collect the precipitate, wash, and vacuum dry to obtain carboxylated phenolphthalein; the ratio of phenolphthalein, zinc powder, sodium hydroxide, anhydrous ethanol, and deionized water is 5.5g:15.5g:17.5g:45mL:50mL; S2. Under a nitrogen atmosphere, mix 4,4'-dichlorodiphenyl sulfone, 4,4'-biphenylhydrazine, carboxylated phenolphthalein, tetrahydrothiophene sulfone, and N-methyl-2-pyrrolidone. Heat to 80°C and stir at this temperature for 1.5 hours. Add anhydrous potassium carbonate and toluene, continue stirring, and heat to 140°C. Reflux at this temperature for 4 hours to remove water. Monitor the water layer precipitation in real time using a water separator. Once no new water layer is added to the separator and no more water is generated in the system, start the distillation operation to completely evaporate the toluene. Continue heating to 175°C and stir at this temperature to carry out the nucleophilic aromatic substitution polycondensation reaction for 8 hours. Sample the polymer solution every hour during this period. The apparent viscosity was measured, and when the apparent viscosity showed no significant increase and tended to stabilize after two consecutive tests, the polymerization reaction was considered to have reached its endpoint. Heating was stopped, and the reaction system was allowed to cool naturally to room temperature. The viscous reaction mixture was then slowly poured into deionized water under high-speed stirring to precipitate the precipitate. The precipitate was washed, boiled in boiling water three times for 30 minutes each time, and then vacuum dried to obtain hydrophilic polysulfone. The ratio of 4,4'-dichlorodiphenyl sulfone, 4,4'-biphenyl hydroquinone, carboxylated phenolphthalein, tetrahydrothiophene sulfone, N-methyl-2-pyrrolidone, anhydrous potassium carbonate, and toluene was 7.5g:3.9g:2.1g:40mL:40mL:4.5g:25mL. S3. Mix the hydrophilic polysulfone and thionyl chloride, sonicate for 35 min, add N,N-dimethylformamide, heat to 65℃ and stir for 10 h, filter, wash the solid phase with tetrahydrofuran, and vacuum dry to obtain acyl chloride polysulfone; the ratio of hydrophilic polysulfone, thionyl chloride and N,N-dimethylformamide is 1.1 g: 30 mL: 1.5 mL; S4. Under a nitrogen atmosphere, the acyl chloride polysulfone, dimethyl sulfoxide, and N,N-dimethylformamide were mixed and stirred until homogeneous. Triethylamine was added, and 8-aminopyrene-1,3,6-trisulfonic acid trisodium salt was added in an ice-water bath in the dark. The mixture was heated to 22°C and stirred for 5 hours to obtain a mixture. The mixture was precipitated with anhydrous ethanol, centrifuged, and the solid phase was washed and vacuum dried to obtain modified polysulfone resin. The ratio of acyl chloride polysulfone, dimethyl sulfoxide, N,N-dimethylformamide, triethylamine, and 8-aminopyrene-1,3,6-trisulfonic acid trisodium salt was 1.1 g: 40 mL: 40 mL: 0.3 mL: 4.2 g. S5. Take the modified polysulfone resin, polyvinylpyrrolidone and N-methylpyrrolidone and mix them. Heat and stir at 120°C for 35 min until the polymer is completely dissolved and the casting solution is clear. Use a doctor blade to scrape the casting solution onto a glass plate to form a film layer with a thickness of 1800 μm. Then, let it stand at a constant temperature for 24 h to remove bubbles. Place it in a coagulation bath (the coagulation bath is water at room temperature) to remove the film. Soak it in deionized water for 35 h. Take it out and let it air dry at room temperature to obtain the cation exchange membrane. The mass ratio of the modified polysulfone resin, polyvinylpyrrolidone and N-methylpyrrolidone is 9:5.5:35. Example 3

[0018] An ultrafiltration membrane device for waste alkali recovery includes a plurality of filtration units arranged in a decreasing concentration gradient. Each filtration unit includes a concentration chamber and a dilute chamber, and a cation exchange membrane is disposed between the concentration chamber and the dilute chamber. The preparation method of the cation exchange membrane includes the following steps: S1. Mix phenolphthalein, zinc powder, sodium hydroxide, anhydrous ethanol and deionized water, heat at 70°C, reflux and stir for 12 hours, filter, take the liquid phase, adjust the pH to 5, acid precipitate, filter, collect the precipitate, wash and vacuum dry to obtain carboxylated phenolphthalein; the ratio of phenolphthalein, zinc powder, sodium hydroxide, anhydrous ethanol and deionized water is 6g:16g:18g:50mL:50mL. S2. Under a nitrogen atmosphere, mix 4,4'-dichlorodiphenyl sulfone, 4,4'-biphenylhydrazine, carboxylated phenolphthalein, tetrahydrothiophene sulfone, and N-methyl-2-pyrrolidone. Heat to 80°C and stir at this temperature for 2 hours. Add anhydrous potassium carbonate and toluene, continue stirring, and heat to 140°C. Reflux at this temperature for 5 hours to remove water. During this time, monitor the water layer precipitation in real time using a water separator. Once no new water layer is added to the separator and no more water is generated in the system, start the distillation operation to completely distill off the toluene in the system. Continue heating to 175°C and stir at this temperature to carry out the nucleophilic aromatic substitution polycondensation reaction for 10 hours. During this time, samples are taken every 1 hour to test the polymer solubility. The apparent viscosity of the liquid was measured. When the apparent viscosity showed no significant increase and tended to stabilize after two consecutive tests, the polymerization reaction was considered to have reached its endpoint. Heating was stopped, and the reaction system was allowed to cool naturally to room temperature. The viscous reaction mixture was then slowly poured into deionized water under high-speed stirring to precipitate the precipitate. The precipitate was washed, boiled in boiling water three times for 30 minutes each time, and then vacuum dried to obtain hydrophilic polysulfone. The ratio of 4,4'-dichlorodiphenyl sulfone, 4,4'-biphenyl hydroquinone, carboxylated phenolphthalein, tetrahydrothiophene sulfone, N-methyl-2-pyrrolidone, anhydrous potassium carbonate, and toluene was 8 g: 4.2 g: 2.2 g: 40 mL: 40 mL: 5 g: 30 mL. S3. Mix the hydrophilic polysulfone and thionyl chloride, sonicate for 40 min, add N,N-dimethylformamide, heat to 65℃ and stir for 12 h, filter, wash the solid phase with tetrahydrofuran, and vacuum dry to obtain acyl chloride polysulfone; the ratio of hydrophilic polysulfone, thionyl chloride and N,N-dimethylformamide is 1.2 g: 40 mL: 2 mL; S4. Under a nitrogen atmosphere, the acyl chloride polysulfone, dimethyl sulfoxide, and N,N-dimethylformamide were mixed and stirred until homogeneous. Triethylamine was added, and 8-aminopyrene-1,3,6-trisulfonic acid trisodium salt was added in an ice-water bath in the dark. The mixture was heated to 25°C and stirred for 6 hours to obtain a mixture. The mixture was precipitated with anhydrous ethanol, centrifuged, and the solid phase was washed and vacuum dried to obtain modified polysulfone resin. The ratio of acyl chloride polysulfone, dimethyl sulfoxide, N,N-dimethylformamide, triethylamine, and 8-aminopyrene-1,3,6-trisulfonic acid trisodium salt was 1.2 g: 40 mL: 40 mL: 0.4 mL: 4.3 g. S5. Take the modified polysulfone resin, polyvinylpyrrolidone and N-methylpyrrolidone and mix them. Heat and stir at 120°C for 40 min until the polymer is completely dissolved and the casting solution is clear. Use a doctor blade to scrape the casting solution onto a glass plate to form a film layer with a thickness of 2400 μm. Then, let it stand at a constant temperature for 24 h to remove bubbles. Place it in a coagulation bath (the coagulation bath is water, and the temperature is room temperature) to remove the film. Soak it in deionized water for 40 h. Take it out and let it air dry at room temperature to obtain the cation exchange membrane. The mass ratio of the modified polysulfone resin, polyvinylpyrrolidone and N-methylpyrrolidone is 10:6:40.

[0019] Comparative Example 1 The difference from Example 2 is that the preparation method of the cation exchange membrane includes the following steps: S1. Mix phenolphthalein, zinc powder, sodium hydroxide, anhydrous ethanol, and deionized water, heat at 65°C, reflux and stir for 11 hours, filter, take the liquid phase, adjust the pH to 6, precipitate acid, filter, collect the precipitate, wash, and vacuum dry to obtain carboxylated phenolphthalein; the ratio of phenolphthalein, zinc powder, sodium hydroxide, anhydrous ethanol, and deionized water is 5.5g:15.5g:17.5g:45mL:50mL; S2. Under a nitrogen atmosphere, mix 4,4'-dichlorodiphenyl sulfone, 4,4'-biphenylhydrazine, carboxylated phenolphthalein, tetrahydrothiophene sulfone, and N-methyl-2-pyrrolidone. Heat to 80°C and stir at this temperature for 1.5 hours. Add anhydrous potassium carbonate and toluene, continue stirring, and heat to 140°C. Reflux at this temperature for 4 hours to remove water. Monitor the water layer precipitation in real time using a water separator. Once no new water layer is added to the separator and no more water is generated in the system, start the distillation operation to completely evaporate the toluene. Continue heating to 175°C and stir at this temperature to carry out the nucleophilic aromatic substitution polycondensation reaction for 8 hours. Sample the polymer solution every hour during this period. The apparent viscosity was measured, and when the apparent viscosity showed no significant increase and tended to stabilize after two consecutive tests, the polymerization reaction was considered to have reached its endpoint. Heating was stopped, and the reaction system was allowed to cool naturally to room temperature. The viscous reaction mixture was then slowly poured into deionized water under high-speed stirring to precipitate the precipitate. The precipitate was washed, boiled in boiling water three times for 30 minutes each time, and then vacuum dried to obtain hydrophilic polysulfone. The ratio of 4,4'-dichlorodiphenyl sulfone, 4,4'-biphenyl hydroquinone, carboxylated phenolphthalein, tetrahydrothiophene sulfone, N-methyl-2-pyrrolidone, anhydrous potassium carbonate, and toluene was 7.5g:3.9g:2.1g:40mL:40mL:4.5g:25mL. S3. Mix the hydrophilic polysulfone, polyvinylpyrrolidone, and N-methylpyrrolidone, heat and stir at 120°C for 35 minutes until the polymer is completely dissolved and the casting solution is clear. Use a doctor blade to scrape the casting solution onto a glass plate to form a film layer with a thickness of 1800 μm. Then, let it stand at a constant temperature for 24 hours to remove bubbles, place it in a coagulation bath (the coagulation bath is water, and the temperature is room temperature) to remove the film, soak it in deionized water for 35 hours, take it out and let it air dry at room temperature to obtain the cation exchange membrane. The mass ratio of the hydrophilic polysulfone, polyvinylpyrrolidone, and N-methylpyrrolidone is 9:5.5:35.

[0020] Comparative Example 2 The difference from Example 2 is that the preparation method of the cation exchange membrane includes the following steps: Commercially available polysulfone P-1700, polyvinylpyrrolidone, and N-methylpyrrolidone were mixed and heated and stirred at 120°C for 35 minutes until the polymer was completely dissolved and the casting solution was clear. The casting solution was then scraped onto a glass plate to form a film layer with a thickness of 1800 μm. The film was then allowed to stand at a constant temperature for 24 hours to remove bubbles. The film was then placed in a coagulation bath (water at room temperature) to remove the membrane. After soaking in deionized water for 35 hours, the membrane was removed and allowed to air dry at room temperature to obtain the cation exchange membrane. The mass ratio of polysulfone P-1700, polyvinylpyrrolidone, and N-methylpyrrolidone was 9:5.5:35.

[0021] Performance testing The cation exchange membranes prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to the following performance tests.

[0022] 1. Hydrophilicity test Using the seat drop method, ultrapure water was used as the test solution at room temperature (25℃). Five points were randomly selected on the membrane surface to test the contact angle, and the average value was taken.

[0023] 2. Pure water flux test Operating pressure: 0.1 MPa; temperature: 25℃; effective membrane area: 12.56 cm². 2 Pre-compress for 30 minutes until the flux stabilizes, record the permeate volume per unit time, and calculate using the formula: Pure water flux (L·m) -2 ·h -1 = Permeable liquid volume ÷ Effective area ÷ Time 3. Anti-pollution performance test Flux recovery rate (%) = (Fluid flow after cleaning ÷ Initial pure water flux) × 100% 4. Water absorption rate test Weigh the dry film (m1), soak it in deionized water at 25℃ for 24 hours until swelling equilibrium is reached, blot the surface free water with filter paper, and weigh it again (m2). Water absorption rate (%) = (m2 - m1) / m1 × 100% 5. Size swelling rate test Measure the dry film edge length (L1), and measure the wet film edge length (L2) after swelling equilibrium is reached: Swelling rate (%) = (L2 - L1) / L1 × 100% The test results are shown in Table 1: Table 1 As shown in Table 1, the cation exchange membranes prepared in Examples 1-3 of this invention, through carboxylated phenolphthalein copolymerization and pyrene trisulfonic acid grafting dual hydrophilic modification, possess ultra-high hydrophilicity, high pure water flux, excellent antifouling properties, and good dimensional stability. Their comprehensive performance is far superior to that of Comparative Example 1 without pyrene sulfonic acid grafting and Comparative Example 2 with pure polysulfone, thus meeting the requirements for long-term stable operation of the waste alkali recovery system.

[0024] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. An ultrafiltration membrane device for waste alkali recovery, comprising a plurality of filtration units arranged in a decreasing concentration gradient, each filtration unit comprising a concentration chamber and a dilute chamber, wherein a cation exchange membrane is disposed between the concentration chamber and the dilute chamber, characterized in that, The method for preparing the cation exchange membrane includes the following steps: S1. Phenolphthalein is subjected to ester hydrolysis and acidification to obtain carboxylated phenolphthalein; S2. Hydrophilic polysulfone was synthesized using 4,4'-dichlorodiphenyl sulfone, 4,4'-biphenylhydrazine, and carboxylated phenolphthalein as raw materials. S3. The carboxyl group of the hydrophilic polysulfone is modified by acyl chloride to obtain acyl chloride polysulfone; S4. React the acyl chloride group of acyl chloride polysulfone with the amino group of trisodium 8-aminopyrene-1,3,6-trisulfonic acid to obtain modified polysulfone resin. S5. Using the modified polysulfone resin, polyvinylpyrrolidone and N-methylpyrrolidone as raw materials, a membrane is prepared to obtain the cation exchange membrane.

2. The ultrafiltration membrane device for waste alkali recovery according to claim 1, characterized in that, Step S1 specifically includes the following steps: Take phenolphthalein, zinc powder, sodium hydroxide, anhydrous ethanol and deionized water, mix them, heat and reflux at 60-70℃ for 10-12 hours, filter, take the liquid phase, adjust the pH to 5-6, precipitate acid, filter, collect the precipitate, wash and vacuum dry to obtain carboxylated phenolphthalein.

3. The ultrafiltration membrane device for waste alkali recovery according to claim 2, characterized by The ratio of phenolphthalein, zinc powder, sodium hydroxide, anhydrous ethanol and deionized water is 5-6g: 15-16g: 17-18g: 40-50mL: 50mL.

4. The ultrafiltration membrane device for waste alkali recovery according to claim 1, characterized by In step S2, the mass ratio of 4,4'-dichlorodiphenyl sulfone, 4,4'-biphenylhydrazine, and carboxylated phenolphthalein is 7-8:3.5-4.2:2-2.

2.

5. The ultrafiltration membrane device for waste alkali recovery according to claim 1, characterized by Step S3 specifically includes the following steps: take the hydrophilic polysulfone and thionyl chloride, mix them, ultrasonically stir for 30-40 min, add N,N-dimethylformamide, heat to 65℃ and stir for 8-12 h, filter, take the solid phase, wash with tetrahydrofuran, and vacuum dry to obtain acyl chloride polysulfone.

6. The ultrafiltration membrane device for waste alkali recovery according to claim 5, characterized by The ratio of hydrophilic polysulfone, sulfoxide, and N,N-dimethylformamide is 1-1.2g: 20-40mL: 1-2mL.

7. The ultrafiltration membrane device for waste alkali recovery according to claim 1, characterized by Step S4 specifically includes the following steps: Under a nitrogen atmosphere, the acyl chloride polysulfone, dimethyl sulfoxide, and N,N-dimethylformamide are mixed and stirred evenly. Triethylamine is added, and 8-aminopyrene-1,3,6-trisulfonic acid trisodium salt is added in an ice-water bath in the dark. The mixture is heated to 20-25°C and stirred for 4-6 hours to obtain a mixture. The mixture is precipitated with anhydrous ethanol, centrifuged, and the solid phase is washed and vacuum dried to obtain modified polysulfone resin.

8. The ultrafiltration membrane device for waste alkali recovery according to claim 7, characterized by The ratio of polysulfone chloride, dimethyl sulfoxide, N,N-dimethylformamide, triethylamine, and trisodium 8-aminopyrene-1,3,6-trisulfonic acid is 1-1.2g:40mL:40mL:0.2-0.4mL:4.1-4.3g.

9. The ultrafiltration membrane for waste alkali recovery according to claim 1, characterized in that, In step S5, the mass ratio of the modified polysulfone resin, polyvinylpyrrolidone, and N-methylpyrrolidone is 8-10:5-6:30-40.

Images