Nanofiltration membranes and methods for making the same

Abstract

The present application relates to a kind of nanofiltration membrane and its preparation method.The preparation method of nanofiltration membrane includes the following steps: dissolving polysulfone in organic solvent, coating polysulfone solution on the surface of substrate, then immersed in coagulation bath, after polysulfone is completely solidified, polysulfone ultrafiltration membrane is obtained;Polysulfone ultrafiltration membrane is placed in polyphenol solution, after sufficient soaking, it is placed in iron salt solution, after sufficient reaction, the polysulfone ultrafiltration membrane with polyphenol and Fe 3+ Intermediate layer;And the polysulfone ultrafiltration membrane with polyphenol and Fe 3+ Intermediate layer is placed in oil phase solution, after sufficient soaking, the excess oil phase solution on the surface of membrane is removed, then it is placed in aqueous solution, after sufficient reaction, the excess aqueous solution on the surface of membrane is removed, and nanofiltration membrane is obtained.The preparation method of the above-mentioned nanofiltration membrane is combined with polyphenol and Fe 3+ Intermediate layer and reverse interface polymerization, while reducing the spatial size of membrane surface, the positive charge density of membrane surface is enhanced, which is conducive to improve the separation factor of Mg 2+ And Li + ​

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and in particular to a nanofiltration membrane and its preparation method. Background Technology

[0002] In recent years, lithium-ion batteries, as a novel energy storage material, have been widely used in smart electronic products and new energy vehicles, leading to a sharp increase in the demand for lithium resources. Currently, Li... + The supply mainly comes from brine lakes and seawater, but due to the presence of Li in seawater... + The low concentration of Mg makes lithium extraction from seawater challenging, thus existing research primarily focuses on lithium extraction from salt lake brines. Membrane separation technology, with its advantages of high separation accuracy, low energy consumption, good selectivity, and strong adaptability, has become one of the most effective technologies for lithium extraction from salt lakes. However, traditional nanofiltration membranes are less effective for Mg... 2+ / Li + The separation efficiency is still relatively low, which is not conducive to its widespread application. Summary of the Invention

[0003] Therefore, it is necessary to address how to improve Mg 2+ and Li + To address the separation factor problem, this paper provides a nanofiltration membrane and its preparation method.

[0004] A method for preparing a nanofiltration membrane includes the following steps:

[0005] Polysulfone is dissolved in an organic solvent to obtain a polysulfone solution. The polysulfone solution is coated on the surface of a substrate and then immersed in a coagulation bath. After the polysulfone is completely cured, a polysulfone ultrafiltration membrane is obtained.

[0006] The polysulfone ultrafiltration membrane was immersed in a polyphenol solution and then placed in an iron salt solution. After a complete reaction, a membrane containing polyphenols and iron was obtained. 3+ The middle layer is a polysulfone ultrafiltration membrane;

[0007] The polyphenol and Fe 3+ The polysulfone ultrafiltration membrane in the middle layer is placed in an oil phase solution and fully immersed. After removing the excess oil phase solution from the membrane surface, it is then placed in an aqueous phase solution and fully reacted. After removing the excess aqueous phase solution from the membrane surface, a nanofiltration membrane is obtained.

[0008] The nanofiltration membrane preparation method of this invention is simple. On the one hand, polyphenols and Fe... 3+ The introduction of the intermediate layer enhances the hydrophilicity of the membrane, Fe 3+ Through chelation with polyphenols, the spatial size of the membrane surface is reduced, while Fe... 3+ The introduction of [a specific technology / method] enhances the positive charge density on the membrane surface; on the other hand, reverse interfacial polymerization greatly increases the positive charge density on the nanofiltration membrane surface, thereby improving the [potential of Mg].2+ With Li + The separation factor. In summary, the nanofiltration membrane preparation method of the present invention involves polyphenols and Fe... 3+ The combination of intermediate layer and reverse interface polymerization reduces the surface space size of the film while enhancing the positive charge density on the film surface, which is beneficial for improving Mg content. 2+ With Li + The separation factor.

[0009] In one feasible implementation, the operation of dissolving polysulfone in an organic solvent is as follows: polysulfone is added to an organic solvent and stirred at a temperature of 75°C to 85°C for 10 to 24 hours.

[0010] In one feasible implementation, the organic solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone;

[0011] The polysulfone solution contains 17 wt% to 20 wt% of polysulfone.

[0012] The polysulfone solution is coated on the substrate surface with a thickness of 100 μm to 200 μm.

[0013] In one feasible implementation, the polyphenol solution contains a polyphenol mass fraction of 0.1 wt% to 2 wt%.

[0014] The polyphenols in the polyphenol solution are selected from at least one of resorcinol, pyrogallol, hydroquinone, and tannic acid.

[0015] In one feasible implementation, the operation of immersing the polysulfone ultrafiltration membrane in a polyphenol solution is as follows: the polysulfone ultrafiltration membrane is placed in a polyphenol solution, and then placed in a constant temperature shaker at 40℃~60℃ for 1h~5h. After the reaction is completed, it is thoroughly washed with deionized water.

[0016] In one feasible implementation, the iron salt solution contains Fe 3+ The concentration is 0.1 g / L to 2 g / L;

[0017] The iron salt in the iron salt solution is selected from at least one of ferric chloride and ferric sulfate.

[0018] In one feasible implementation, the oil phase solution comprises an oil phase monomer, and the concentration of the oil phase monomer in the oil phase solution is 0.1 wt% to 0.5 wt%.

[0019] The oil phase monomer is selected from at least one of 1,3-benzenedisulfonyl chloride, 1,3,5-benzenetrisulfonyl chloride, 1,3,6-naphthalenetrisulfonyl chloride, and pyromellitic acid trimethyl chloride.

[0020] In one feasible implementation, the aqueous solution comprises an aqueous monomer, and the concentration of the aqueous monomer in the aqueous solution is 0.01 wt% to 0.2 wt%.

[0021] The aqueous monomer is selected from at least one of m-phenylenediamine, p-phenylenediamine, ethylenediamine, butanediamine, polyethyleneimine, and piperazine.

[0022] In one feasible implementation, the aqueous solution further includes a promoter selected from at least one of sodium dodecyl sulfate and sodium dodecyl sulfonate;

[0023] After removing excess aqueous solution from the membrane surface, the following steps are also included: heat curing in an oven at 30℃~70℃ for 1min~10min.

[0024] A nanofiltration membrane is prepared using any of the nanofiltration membrane preparation methods described above.

[0025] The nanofiltration membrane of the present invention is prepared by the above-described preparation method, comprising a polysulfone ultrafiltration membrane, polyphenols, and Fe arranged sequentially from the inside out. 3+ The intermediate and functional layers, after experimental verification, can improve Mg 2+ With Li + The separation factor. Attached Figure Description

[0026] Figure 1 This is a flowchart of a method for preparing a nanofiltration membrane according to an embodiment of the present invention. Detailed Implementation

[0027] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0029] Through inventive research, the inventors of this invention discovered that traditional nanofiltration membranes employ a forward interfacial polymerization method, in which the substrate membrane first contacts an aqueous solution of amine monomers, followed by a solution of organic acyl chloride monomers, to form a PA structure. However, the excessive hydrolysis of acyl chloride groups on the surface of this structure results in a negatively charged membrane, which is detrimental to the removal of Mg from the brine. 2+ With Li + To address this issue, the present invention proposes a method for preparing a nanofiltration membrane, which can improve the separation of Mg. 2+ With Li + The separation factor is beneficial to the separation of Mg in the brine. 2+ With Li + The separation.

[0030] Please see Figure 1 The method for preparing a nanofiltration membrane according to an embodiment of the present invention includes the following steps:

[0031] S10. Dissolve polysulfone in an organic solvent to obtain a polysulfone solution. Coat the surface of the substrate with the polysulfone solution and then immerse it in a coagulation bath. After the polysulfone is completely cured, a polysulfone ultrafiltration membrane is obtained.

[0032] In step S10, the substrate can be non-woven fabric. A film of a certain thickness is scraped off using a doctor blade. The polysulfone film is placed in water and then a polysulfone ultrafiltration membrane is prepared by solvent-induced phase separation.

[0033] In step S10, the coagulation bath includes pure water; furthermore, the coagulation bath may also include an organic solvent. The organic solvent has a mass fraction of 0–20%, and includes one or a mixture of N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), and N-methylpyrrolidone (NMP).

[0034] In one feasible implementation, the process of dissolving polysulfone in an organic solvent involves adding polysulfone to the organic solvent and stirring at a temperature of 75°C to 85°C for 10 to 24 hours. In this case, the polysulfone dissolves relatively quickly in the organic solvent.

[0035] In one feasible implementation, the organic solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

[0036] In one feasible implementation, the mass fraction of polysulfone in the polysulfone solution is 17 wt% to 20 wt%. Further, the mass fraction of polysulfone in the polysulfone solution can be, but is not limited to, 17 wt%, 18 wt%, 19 wt%, or 20 wt%.

[0037] In one feasible implementation, the coating thickness of the polysulfone solution on the substrate surface is 100 μm to 200 μm. Further, the coating thickness of the polysulfone solution on the substrate surface can be, but is not limited to, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, or 200 μm.

[0038] The polysulfone ultrafiltration membrane prepared by step S10 can be stored in deionized water for later use.

[0039] S20. The polysulfone ultrafiltration membrane obtained in step S10 is placed in a polyphenol solution and fully immersed. Then it is placed in an iron salt solution and allowed to react fully to obtain a membrane containing polyphenols and iron. 3+ The middle layer is a polysulfone ultrafiltration membrane.

[0040] In one feasible implementation, the mass fraction of polyphenols in the polyphenol solution is 0.1 wt% to 2 wt%. Further, the mass fraction of polyphenols can be, but is not limited to, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, or 2 wt%.

[0041] In one feasible implementation, the polyphenols in the polyphenol solution are selected from at least one of resorcinol, pyrogallol, hydroquinone, and tannic acid.

[0042] In one feasible implementation, the procedure of thoroughly immersing the polysulfone ultrafiltration membrane in a polyphenol solution involves placing the polysulfone ultrafiltration membrane in the polyphenol solution, then reacting it in a constant-temperature shaker at 40℃ to 60℃ for 1 to 5 hours, followed by thorough rinsing with deionized water after the reaction. Furthermore, the temperature of the constant-temperature shaker can be, but is not limited to, 40℃, 45℃, 50℃, 55℃, or 60℃, and the reaction time can be, but is not limited to, 1 hour, 2 hours, 3 hours, 4 hours, or 5 hours.

[0043] In one feasible implementation, Fe in the iron salt solution 3+ The concentration is 0.1 g / L to 2 g / L. Furthermore, the Fe in the iron salt solution... 3+The concentration can be, but is not limited to, 0.1 g / L, 0.2 g / L, 0.3 g / L, 0.4 g / L, 0.5 g / L, 0.6 g / L, 0.7 g / L, 0.8 g / L, 0.9 g / L, 1.0 g / L, 1.1 g / L, 1.2 g / L, 1.3 g / L, 1.4 g / L, 1.5 g / L, 1.6 g / L, 1.7 g / L, 1.8 g / L, 1.9 g / L, or 2 g / L.

[0044] In one feasible implementation, the iron salt in the iron salt solution is selected from at least one of ferric chloride and ferric sulfate.

[0045] The reaction time in the iron salt solution is 10-30 minutes to obtain a product containing polyphenols and Fe. 3+ The polysulfone ultrafiltration membrane in the middle layer can be stored in deionized water for later use.

[0046] S30, The polyphenol and Fe obtained in step S20 3+ The polysulfone ultrafiltration membrane in the middle layer is placed in an oil phase solution and fully immersed. After removing the excess oil phase solution from the membrane surface, it is then placed in an aqueous phase solution and fully reacted. After removing the excess aqueous phase solution from the membrane surface, a nanofiltration membrane is obtained.

[0047] In step S30, a functional layer is prepared using a reverse interfacial polymerization method, that is, a layer containing polyphenols and Fe... 3+ The polysulfone ultrafiltration membrane in the middle layer is first placed in an oil phase solution, and then in an aqueous phase solution for interfacial polymerization. This reverse interfacial polymerization significantly increases the positive charge density on the nanofiltration membrane surface, thereby improving the Mg... 2+ With Li + The separation factor.

[0048] In one feasible implementation, the oil phase solution includes an oil phase monomer, and the concentration of the oil phase monomer in the oil phase solution is 0.1 wt% to 0.5 wt%. Further, the concentration of the oil phase monomer in the oil phase solution may be, but is not limited to, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, or 0.5 wt%.

[0049] In one feasible implementation, the oil phase monomer is selected from at least one of 1,3-benzenedisulfonyl chloride, 1,3,5-benzenetrisulfonyl chloride, 1,3,6-naphthalenetrisulfonyl chloride, and pyromellitic acid trimethyl chloride.

[0050] In one feasible implementation, the aqueous solution comprises an aqueous monomer, the concentration of which is 0.01 wt% to 0.2 wt%. Further, the concentration of the aqueous monomer in the aqueous solution may be, but is not limited to, 0.01 wt%, 0.02 wt%, 0.03 wt%, 0.04 wt%, 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt%, 0.1 wt%, 0.11 wt%, 0.12 wt%, 0.13 wt%, 0.14 wt%, 0.15 wt%, 0.16 wt%, 0.17 wt%, 0.18 wt%, 0.19 wt%, or 0.2 wt%.

[0051] In one feasible implementation, the aqueous monomer is selected from at least one of m-phenylenediamine, p-phenylenediamine, ethylenediamine, butanediamine, polyethyleneimine, and piperazine.

[0052] In one feasible implementation, the aqueous solution also includes a promoter selected from at least one of sodium dodecyl sulfate and sodium dodecyl sulfonate. The promoter facilitates the interfacial polymerization reaction between the oil-phase monomer and the aqueous-phase monomer.

[0053] In one feasible implementation, after removing excess aqueous solution from the membrane surface, the following step is included: heat curing in an oven at 30°C to 70°C for 1 to 10 minutes. Heat curing allows for a more complete reaction. Furthermore, the heat curing temperature can be, but is not limited to, 30°C, 40°C, 50°C, 60°C, or 70°C, and the heat curing time can be, but is not limited to, 1 minute, 2 minutes, 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, or 10 minutes.

[0054] The nanofiltration membrane preparation method of this invention is simple. On the one hand, polyphenols and Fe... 3+ The introduction of the intermediate layer enhances the hydrophilicity of the membrane, Fe 3+ Through chelation with polyphenols, the spatial size of the membrane surface is reduced, while Fe... 3+ The introduction of [a specific technology / method] enhances the positive charge density on the membrane surface; on the other hand, reverse interfacial polymerization greatly increases the positive charge density on the nanofiltration membrane surface, thereby improving the [potential of Mg]. 2+ With Li + The separation factor. In summary, the nanofiltration membrane preparation method of the present invention involves polyphenols and Fe... 3+ The combination of intermediate layer and reverse interface polymerization reduces the surface space size of the film while enhancing the positive charge density on the film surface, which is beneficial for improving Mg content. 2+ With Li + The separation factor.

[0055] The nanofiltration membrane of one embodiment is prepared using any of the nanofiltration membrane preparation methods described above.

[0056] The nanofiltration membrane of the present invention is prepared by the above-described preparation method, comprising a polysulfone ultrafiltration membrane, polyphenols, and Fe arranged sequentially from the inside out. 3+ The intermediate and functional layers, after experimental verification, can improve Mg 2+ With Li + The separation factor.

[0057] Referring to the above embodiments, in order to make the technical solution of the present invention more specific, clear and easy to understand, examples of the technical solution of the present invention are given below. However, it should be noted that the content to be protected by the present invention is not limited to the following embodiments.

[0058] Example 1

[0059] 18g of polysulfone was dissolved in 92g of N,N-dimethylformamide and stirred at 80℃ for 10h. After the polysulfone was completely dissolved, a polysulfone solution with a mass fraction of 18wt% was obtained. A 100μm thick film was scraped onto a nonwoven fabric using a film scraper and then placed in pure water at 25℃ for solvent exchange. When the film was formed in the coagulation bath, a polysulfone ultrafiltration membrane was obtained. The membrane was then rinsed with a large amount of pure water and set aside for use.

[0060] The scraped polysulfone ultrafiltration membrane was placed in a 0.1 wt% tannic acid solution and then placed in a shaker at 40°C for 2 hours. After thorough shaking, it was removed and rinsed with deionized water. The membrane was then placed in a 0.5 g / L ferric chloride solution for 10 minutes and rinsed with pure water to obtain a membrane containing polyphenols and Fe. 3+ The middle layer is a polysulfone ultrafiltration membrane.

[0061] 0.1 wt% trimesoyl chloride (TMC) was poured into the above-mentioned container containing polyphenols and Fe. 3+ The reaction was carried out on the polysulfone ultrafiltration membrane in the middle layer for 1 min. Then, a mixed solution of 2 wt% piperazine and 0.1 wt% sodium dodecyl sulfonate was poured onto the membrane surface and reacted for 2 min. After that, the excess solution on the membrane surface was poured off and the membrane was dried at room temperature. Then, the membrane was placed in a 60°C oven and dried for 5 min to obtain the nanofiltration membrane of Example 1.

[0062] Example 2

[0063] 18g of polysulfone was dissolved in 92g of N,N-dimethylformamide and stirred at 80℃ for 10h. After the polysulfone was completely dissolved, a polysulfone solution with a mass fraction of 18wt% was obtained. A 100μm thick film was scraped onto a nonwoven fabric using a film scraper and then placed in pure water at 25℃ for solvent exchange. When the film was formed in the coagulation bath, a polysulfone ultrafiltration membrane was obtained. The membrane was then rinsed with a large amount of pure water and set aside for use.

[0064] The scraped polysulfone ultrafiltration membrane was placed in a 0.3 wt% tannic acid solution and then placed in a shaker at 40°C for 2 hours. After thorough shaking, it was removed and rinsed with deionized water. The membrane was then placed in a 0.5 g / L ferric chloride solution for 10 minutes and rinsed with pure water to obtain a membrane containing polyphenols and Fe. 3+ The middle layer is a polysulfone ultrafiltration membrane.

[0065] 0.1 wt% trimesoyl chloride (TMC) was poured into the above-mentioned container containing polyphenols and Fe. 3+ The reaction was carried out on the polysulfone ultrafiltration membrane in the middle layer for 1 min. Then, a mixed solution of 2 wt% piperazine and 0.1 wt% sodium dodecyl sulfonate was poured onto the membrane surface and reacted for 2 min. After that, the excess solution on the membrane surface was poured off and the membrane was dried at room temperature. Then, the membrane was placed in a 60°C oven and dried for 5 min to obtain the nanofiltration membrane of Example 2.

[0066] Example 3

[0067] 18g of polysulfone was dissolved in 92g of N,N-dimethylformamide and stirred at 80℃ for 10h. After the polysulfone was completely dissolved, a polysulfone solution with a mass fraction of 18wt% was obtained. A 100μm thick film was scraped onto a nonwoven fabric using a film scraper and then placed in pure water at 25℃ for solvent exchange. When the film was formed in the coagulation bath, a polysulfone ultrafiltration membrane was obtained. The membrane was then rinsed with a large amount of pure water and set aside for use.

[0068] The scraped polysulfone ultrafiltration membrane was placed in a 0.3 wt% tannic acid solution and then placed in a shaker at 40°C for 2 hours. After thorough shaking, it was removed and rinsed with deionized water. The membrane was then reacted in a 1 g / L ferric chloride solution for 10 minutes and washed with pure water to obtain a membrane containing polyphenols and Fe. 3+ The middle layer is a polysulfone ultrafiltration membrane.

[0069] 0.1 wt% trimesoyl chloride (TMC) was poured into the above-mentioned container containing polyphenols and Fe. 3+ The reaction was carried out on the polysulfone ultrafiltration membrane in the middle layer for 1 min. Then, a mixed solution of 2 wt% piperazine and 0.1 wt% sodium dodecyl sulfonate was poured onto the membrane surface and reacted for 2 min. After that, the excess solution on the membrane surface was poured off and the membrane was dried at room temperature. Then, the membrane was placed in a 60°C oven and dried for 5 min to obtain the nanofiltration membrane of Example 3.

[0070] Example 4

[0071] 18g of polysulfone was dissolved in 92g of N,N-dimethylformamide and stirred at 80℃ for 10h. After the polysulfone was completely dissolved, a polysulfone solution with a mass fraction of 18wt% was obtained. A 100μm thick film was scraped onto a nonwoven fabric using a film scraper and then placed in pure water at 25℃ for solvent exchange. When the film was formed in the coagulation bath, a polysulfone ultrafiltration membrane was obtained. The membrane was then rinsed with a large amount of pure water and set aside for use.

[0072] The scraped polysulfone ultrafiltration membrane was placed in a 2 wt% tannic acid solution and then placed in a shaker at 40°C for 2 hours. After thorough shaking, it was removed and rinsed with deionized water. The membrane was then placed in a 1 g / L ferric chloride solution for 10 minutes and rinsed with pure water to obtain a membrane containing polyphenols and Fe. 3+ The middle layer is a polysulfone ultrafiltration membrane.

[0073] 0.1 wt% trimesoyl chloride (TMC) was poured into the above-mentioned container containing polyphenols and Fe. 3+ The reaction was carried out on the polysulfone ultrafiltration membrane in the middle layer for 1 min. Then, a mixed solution of 2 wt% piperazine and 0.1 wt% sodium dodecyl sulfonate was poured onto the membrane surface and reacted for 2 min. After that, the excess solution on the membrane surface was poured off and the membrane was dried at room temperature. Then, the membrane was placed in a 60°C oven and dried for 5 min to obtain the nanofiltration membrane of Example 4.

[0074] Comparative Example 1

[0075] This comparative example is a comparative example of Example 1, providing a nanofiltration membrane and its preparation method, the only difference being that forward interfacial polymerization is used. The preparation method of the nanofiltration membrane in this comparative example specifically includes the following steps:

[0076] 18g of polysulfone was dissolved in 92g of N,N-dimethylformamide and stirred at 80℃ for 10h. After the polysulfone was completely dissolved, a polysulfone solution with a mass fraction of 18wt% was obtained. A 100μm thick film was scraped onto a nonwoven fabric using a film scraper and then placed in pure water at 25℃ for solvent exchange. When the film was formed in the coagulation bath, a polysulfone ultrafiltration membrane was obtained. The membrane was then rinsed with a large amount of pure water and set aside for use.

[0077] The scraped polysulfone ultrafiltration membrane was placed in a 0.1 wt% tannic acid solution and then placed in a shaker at 40°C for 2 hours. After thorough shaking, it was removed and rinsed with deionized water. The membrane was then placed in a 0.5 g / L ferric chloride solution for 10 minutes and rinsed with pure water to obtain a membrane containing polyphenols and Fe. 3+ The middle layer is a polysulfone ultrafiltration membrane.

[0078] A mixed solution of 2 wt% piperazine and 0.1 wt% sodium dodecyl sulfate was poured onto the membrane surface and reacted for 2 min. Excess solution was poured off the membrane surface and the membrane was air-dried at room temperature. Then, 0.1 wt% trimesoyl chloride (TMC) was poured onto the membrane and reacted for 1 min. The membrane was then placed in a 60°C oven and dried for 5 min to obtain the nanofiltration membrane of Comparative Example 1.

[0079] Comparative Example 2

[0080] This comparative example is a comparative example of Example 3, providing a nanofiltration membrane and its preparation method, the only difference being that forward interfacial polymerization is used. The preparation method of the nanofiltration membrane in this comparative example specifically includes the following steps:

[0081] 18g of polysulfone was dissolved in 92g of N,N-dimethylformamide and stirred at 80℃ for 10h. After the polysulfone was completely dissolved, a polysulfone solution with a mass fraction of 18wt% was obtained. A 100μm thick film was scraped onto a nonwoven fabric using a film scraper and then placed in pure water at 25℃ for solvent exchange. When the film was formed in the coagulation bath, a polysulfone ultrafiltration membrane was obtained. The membrane was then rinsed with a large amount of pure water and set aside for use.

[0082] The scraped polysulfone ultrafiltration membrane was placed in a 0.3 wt% tannic acid solution and then placed in a shaker at 40°C for 2 hours. After thorough shaking, it was removed and rinsed with deionized water. The membrane was then reacted in a 1 g / L ferric chloride solution for 10 minutes and washed with pure water to obtain a membrane containing polyphenols and Fe. 3+ The middle layer is a polysulfone ultrafiltration membrane.

[0083] A mixed solution of 2 wt% piperazine and 0.1 wt% sodium dodecyl sulfate was poured onto the membrane surface and reacted for 2 min. Excess solution was poured off the membrane surface and the membrane was air-dried at room temperature. Then, 0.1 wt% trimesoyl chloride (TMC) was poured onto the membrane and reacted for 1 min. The membrane was then placed in a 60°C oven and dried for 5 min to obtain the nanofiltration membrane of Comparative Example 2.

[0084] Comparative Example 3

[0085] This comparative example is a comparative example of Examples 1 to 4, providing a nanofiltration membrane and its preparation method, the only difference being that polyphenols and Fe were not introduced. 3+ Intermediate layer. The preparation method of the nanofiltration membrane in this comparative example specifically includes the following steps:

[0086] 18g of polysulfone was dissolved in 92g of N,N-dimethylformamide and stirred at 80℃ for 10h. After the polysulfone was completely dissolved, a polysulfone solution with a mass fraction of 18wt% was obtained. A 100μm thick film was scraped onto a nonwoven fabric using a film scraper and then placed in pure water at 25℃ for solvent exchange. When the film was formed in the coagulation bath, a polysulfone ultrafiltration membrane was obtained. The membrane was then rinsed with a large amount of pure water and set aside for use.

[0087] 0.1 wt% trimesoyl chloride (TMC) was poured onto a polysulfone ultrafiltration membrane and reacted for 1 min. Then, a mixed solution of 2 wt% piperazine and 0.1 wt% sodium dodecyl sulfonate was poured onto the membrane surface and reacted for 2 min. After that, the excess solution on the membrane surface was poured off and the membrane was air-dried at room temperature. Then, the membrane was placed in a 60°C oven and dried for 5 min to obtain the nanofiltration membrane of Comparative Example 3.

[0088] Performance testing:

[0089] Membrane separation performance was tested using a cross-flow filtration device. First, the membrane was placed in the membrane tank and tested with a mixed solution of 2000 ppm MgCl2 and LiCl. Then, the separation factor was calculated according to the formula for calculating the separation factor.

[0090] The formula for calculating the separation factor is as follows:

[0091]

[0092] in, and C fLi + represent Mg in the feed liquid 2+ and Li + concentration, and C pLi + represent Mg in the permeate. 2+ and Li + concentration.

[0093] The test results are shown in Table 1.

[0094] Table 1. Performance test data of nanofiltration membranes in Examples 1-4 and Comparative Examples 1-3.

[0095]

[0096] The following conclusions can be drawn from Table 1:

[0097] (1) The nanofiltration membranes of Examples 1 to 4 of this invention have high separation factors, indicating that the separation is achieved through the reaction of polyphenols and Fe. 3+ The introduction of the intermediate layer and reverse interfacial polymerization improved Mg 2+ / Li + The separation factor;

[0098] (2) The nanofiltration membrane of Example 1 was compared with that of Comparative Example 1, and the nanofiltration membrane of Example 3 was compared with that of Comparative Example 2. Forward interfacial polymerization was used in Comparative Example 1 and Comparative Example 2, while reverse interfacial polymerization was used in the nanofiltration membranes of Example 1 and Example 3. The results showed that the separation factor of the nanofiltration membrane of Example 1 was greater than that of the nanofiltration membrane of Comparative Example 1, and the separation factor of the nanofiltration membrane of Example 3 was greater than that of the nanofiltration membrane of Comparative Example 2. This indicates that reverse interfacial polymerization can improve the separation factor of Mg. 2+ With Li + The separation factor;

[0099] (3) The nanofiltration membranes of Examples 1 to 4 were compared with the nanofiltration membrane of Comparative Example 3. No polyphenols and Fe were introduced into the nanofiltration membrane of Comparative Example 3. 3+ The intermediate layer exhibits a significantly lower separation factor than the nanofiltration membranes of Examples 1-4, indicating that the introduction of polyphenols and Fe... 3+ The intermediate layer can improve Mg 2+ / Li + The separation factor.

[0100] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0101] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a nanofiltration membrane, characterized in that, Includes the following steps: Polysulfone is dissolved in an organic solvent to obtain a polysulfone solution. The polysulfone solution is coated on the surface of a substrate and then immersed in a coagulation bath. After the polysulfone is completely cured, a polysulfone ultrafiltration membrane is obtained. The polysulfone ultrafiltration membrane was immersed in a polyphenol solution and then placed in an iron salt solution. After a complete reaction, a membrane containing polyphenols and iron was obtained. 3+ The middle layer is a polysulfone ultrafiltration membrane; The polyphenol and Fe 3+ The polysulfone ultrafiltration membrane in the middle layer is placed in an oil phase solution, fully immersed, and then excess oil phase solution is removed from the membrane surface. It is then placed in an aqueous phase solution, and after sufficient reaction, excess aqueous phase solution is removed from the membrane surface to obtain a nanofiltration membrane. The contact sequence between the oil phase solution and the aqueous phase solution is reverse interfacial polymerization, used to further increase the positive charge density on the membrane surface. The nanofiltration membrane is effective against Mg²⁺. + With Li + The separation factor is ≥6.

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2. The method for preparing a nanofiltration membrane according to claim 1, characterized in that, The procedure for dissolving polysulfone in an organic solvent is as follows: add polysulfone to an organic solvent and stir at a temperature of 75℃~85℃ for 10h~24h.

3. The method for preparing a nanofiltration membrane according to claim 1, characterized in that, The organic solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone; The polysulfone solution contains a polysulfone mass fraction of 17wt%~20wt%; The polysulfone solution is coated on the substrate surface with a thickness of 100μm to 200μm.

4. The method for preparing a nanofiltration membrane according to claim 1, characterized in that, The polyphenol solution contains polyphenols with a mass fraction of 0.1 wt% to 2 wt%. The polyphenols in the polyphenol solution are selected from at least one of resorcinol, pyrogallol, hydroquinone, and tannic acid.

5. The method for preparing a nanofiltration membrane according to claim 1, characterized in that, The procedure of immersing the polysulfone ultrafiltration membrane in a polyphenol solution is as follows: place the polysulfone ultrafiltration membrane in a polyphenol solution, then place it in a constant temperature shaker at 40℃~60℃ for 1h~5h, and after the reaction is completed, wash it thoroughly with deionized water.

6. The method for preparing a nanofiltration membrane according to claim 1, characterized in that, Fe in the iron salt solution 3+ The concentration is 0.1 g / L to 2 g / L; The iron salt in the iron salt solution is selected from at least one of ferric chloride and ferric sulfate.

7. The method for preparing a nanofiltration membrane according to claim 1, characterized in that, The oil phase solution comprises an oil phase monomer, and the concentration of the oil phase monomer in the oil phase monomer solution is 0.1 wt% to 0.5 wt%. The oil phase monomer is selected from at least one of 1,3-benzenedisulfonyl chloride, 1,3,5-benzenetrisulfonyl chloride, 1,3,6-naphthalenetrisulfonyl chloride, and pyromellitic acid trimethyl chloride.

8. The method for preparing a nanofiltration membrane according to claim 1, characterized in that, The aqueous solution comprises an aqueous monomer, and the concentration of the aqueous monomer in the aqueous solution is 0.01 wt% to 0.2 wt%. The aqueous monomer is selected from at least one of m-phenylenediamine, p-phenylenediamine, ethylenediamine, butanediamine, polyethyleneimine, and piperazine.

9. The method for preparing a nanofiltration membrane according to claim 1, characterized in that, The aqueous solution further includes a promoter, which is selected from at least one of sodium dodecyl sulfate and sodium dodecyl sulfonate; After removing excess aqueous solution from the membrane surface, the following steps are also included: heat curing in an oven at 30℃~70℃ for 1min~10min.

10. A nanofiltration membrane, characterized in that, The nanofiltration membrane is prepared by the method described in any one of claims 1 to 9, wherein the nanofiltration membrane comprises, from the inside out, a polysulfone ultrafiltration membrane, polyphenols, and Fe³⁺. + Intermediate layer and functional layer.

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