Modified polyethyleneimine composite nanofiltration membrane, preparation method and application thereof

Abstract

The application relates to a modified polyethylene imine composite nanofiltration membrane and a preparation method and application thereof, and belongs to the technical field of functional material membranes. A modified polyethylene imine layer is introduced on a base film, the modified polyethylene imine layer is formed through interfacial polymerization reaction of modified polyethylene imine and a polybasic acid chloride, the structure of the modified polyethylene imine composite nanofiltration membrane is loose and complete, the modified polyethylene imine composite nanofiltration membrane has high water flux, high dye rejection and low salt rejection capacity, and can realize high-selectivity separation of dye and salt solution.

Description

Technical Field

[0001] This invention belongs to the field of functional material membrane technology, and particularly relates to a modified polyethyleneimine composite nanofiltration membrane, its preparation method and application. Background Technology

[0002] In the textile and dyeing industries, the coexistence of dyes and salts in wastewater not only pollutes the environment but also wastes valuable resources. Dyes are among the toxic substances in textile wastewater, and many dyes are difficult to degrade, posing potential threats to water quality, ecosystems, and human health. Membrane separation technology can effectively remove dyes from wastewater, reducing negative environmental impacts. Salts in textile wastewater are important renewable resources; membrane separation technology enables salt recovery and reuse, reducing dependence on natural resources and decreasing wastewater discharge, thus alleviating the economic burden of wastewater treatment. With increasing global water scarcity, the sustainable use of water quality and resources has become particularly important; therefore, high-performance dye / salt membrane separation technology is of great significance to the textile and dyeing industries.

[0003] Currently, typical nanofiltration membranes employ a thin-film composite structure, comprising an ultrafiltration substrate and a polyamide selective layer. The selective layer, prepared by interfacial polymerization between polyamines and polyacrylamide chlorides, functions as a sieving layer. However, this reaction is difficult to control precisely, making it challenging to determine the selective performance of the selective layer. Traditional nanofiltration membranes typically exhibit similar retention characteristics for dyes and salts, and have low water flux, making selective separation of dyes and salts difficult. Therefore, optimizing the polymerization system and exploring new technologies to prepare porous nanofiltration membranes with high flux and selective separation of dyes and salts is of significant research importance. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a modified polyethyleneimine composite nanofiltration membrane, its preparation method, and its application. The modified polyethyleneimine composite nanofiltration membrane has a loose yet intact structure, exhibiting high water flux, high dye rejection rate, and low salt rejection rate, enabling highly selective separation of dyes and salt solutions.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] One of the technical solutions of the present invention:

[0007] The present invention provides a modified polyethyleneimine composite nanofiltration membrane, comprising a base membrane and a modified polyethyleneimine layer, wherein the modified polyethyleneimine is located on one side of the base membrane;

[0008] The modified polyethyleneimine layer is formed by interfacial polymerization of modified polyethyleneimine and polyacrylamide chloride.

[0009] Polyethyleneimine (PEI) is a synthetic polymer material with abundant amine functional groups. The amine groups of PEI can be easily chemically modified; by introducing different functional groups, its properties can be adjusted to meet various application requirements. Trimethylamine nitride zwitterionic monomer (TMAO) is a novel, highly efficient, and antifouling biomimetic material with superhydrophilic and antifouling properties. Based on this, this invention combines the advantages of both to prepare a modified polyethyleneimine composite nanofiltration membrane.

[0010] The second technical solution of the present invention:

[0011] This invention provides a method for preparing the modified polyethyleneimine composite nanofiltration membrane, comprising the following steps:

[0012] Dimethylaminopropylacrylamide (DMAPA) was dissolved in water to form solution A. The solution was placed in an oil bath, and hydrogen peroxide solution was added. The mixture was heated and stirred for 6-10 hours. After extraction with ethyl acetate and freeze-drying, the zwitterionic monomer (TMAO) was obtained. During the preparation of the zwitterionic monomer (TMAO), hydrogen peroxide acted as an oxidant, reacting with DMAPA in a redox reaction to form a stable zwitterionic group "N". + -O - "Amphoteric monomer (TMAO);

[0013] PEI and purified TMAO were dissolved in water to form solution B, which was heated and stirred in an oil bath for 10-14 hours. After extraction and purification with ethyl acetate, the polyamine TPEI was obtained by freeze drying. The carbon-carbon double bond in the zwitterionic monomer (TMAO) and the amino group of polyethyleneimine (PEI) undergo a Michael addition reaction to form the polyamine TPEI.

[0014] The polyamine TPEI was added to water and stirred until homogeneous to obtain an aqueous solution.

[0015] Polyacyl chlorides are dissolved in an organic solvent to prepare an oil phase solution;

[0016] The aqueous solution is poured onto the base membrane and kept for 8-15 minutes. Excess aqueous solution is then removed, followed by the addition of the oil phase solution. After the reaction, excess oil phase solution is removed, and the membrane is dried to obtain the modified polyethyleneimine composite nanofiltration membrane. Polyamine TPEI and polyacrylamide chloride undergo interfacial polymerization on a conventional macroporous support layer to form a polyamide layer.

[0017] Preferably, when preparing zwitterionic monomers:

[0018] The molar concentration of solution A is 0.2-2 mol / L, more preferably 0.5-1 mol / L;

[0019] The concentration of the hydrogen peroxide solution is 30 wt%.

[0020] The mass ratio of DMAPA to the hydrogen peroxide solution is 1:(1-2), more preferably 1:1.5;

[0021] The heating temperature is 60-70°C, more preferably 65°C;

[0022] The freeze-drying time is 24-60 hours, more preferably 48 hours;

[0023] The preferred heating and stirring time is 8 hours.

[0024] Preferably, when preparing the polyamine TPEI:

[0025] The molecular weight of the polyethyleneimine is 600 Da;

[0026] The mass ratio of PEI to TMAO is 1:(1-3), more preferably 2:3;

[0027] The mass ratio of PEI to water is 1:(4-10), more preferably 1:6;

[0028] The heating temperature is 80°C;

[0029] The freeze-drying time is 24-60 hours, more preferably 48 hours;

[0030] The preferred heating and stirring time is 12 hours.

[0031] Preferably, the mass concentration of the polyamine TPEI in the aqueous solution is 0.05-0.15%, more preferably 0.05-0.125%.

[0032] Preferably, the organic solvent is one of n-hexane, n-heptane, dodecane, and tetradecane;

[0033] The mass concentration of polyacrylamide chloride in the oil phase solution is 0.05-0.2%.

[0034] Preferably, the polyacrylamide chloride is pyromellitic trimethylolpropionate chloride.

[0035] Preferably, the base film is polysulfone (PSF), polyethersulfone (PES), polyethylene (PE), polyamide-imide (PAI), polypropylene (PP), or polyacrylonitrile (PAN).

[0036] Preferably, after pouring in the aqueous phase solution, the holding time is 10 minutes; after pouring in the oil phase solution, the reaction time is 5 minutes.

[0037] Preferably, the drying is carried out in an oven at a temperature of 60°C for a time of 5 minutes.

[0038] Preferably, before pouring the aqueous solution onto the base membrane, the base membrane is processed into a film sheet, wherein the film sheet is a circular film sheet with a diameter of 6 cm.

[0039] Preferably, the water used in the preparation process of this invention is ultrapure water.

[0040] This invention first dissolves DMAPA in ultrapure water, and then, under high temperature and aerobic conditions, reacts with hydrogen peroxide in a redox reaction to form a stable zwitterionic group "N". + -O - The zwitterionic monomer (TMAO) and polyethyleneimine (PEI), which provides an amino group, undergo a Michael addition reaction to form the polyamine TPEI. In this invention, the polyamine TPEI, compared to unmodified PEI, provides fewer amino reaction sites when reacting with polyacrylamide chlorides, resulting in a more porous modified polyethyleneimine layer after interfacial polymerization with polyacrylamide chlorides (significantly increasing water flux). Simultaneously, the TPEI structure contains zwitterionic "N" groups with equimolar oppositely charged groups. + -O - "It possesses strong hydration capabilities and superior antifouling properties. Furthermore, the composite nanofiltration membrane of this invention uses TPEI as the aqueous phase monomer, controlling the porosity of the polyamide layer, which not only improves the water flux of the nanofiltration membrane but also exhibits high selective separation performance for dyes / salts. Simultaneously, DMAPA and PEI are both inexpensive compounds, reducing the cost of preparing the composite nanofiltration membrane, making it applicable to the recycling of wastewater from the textile and dyeing industries."

[0041] The mass ratio of polyamine TPEI to polyacrylamide chloride in this invention is key to obtaining a thin-film composite nanofiltration membrane with both high flux and high dye and salt separation selectivity. The smaller the proportion of TPEI, the fewer amino reaction sites are provided, resulting in a more porous polyamide layer after reaction with polyacrylamide chloride, and thus a higher flux in the obtained nanofiltration membrane. However, if the proportion of TPEI is too small, the polyamide layer is prone to incompleteness, and the dye-blocking performance is greatly reduced. As the proportion of TPEI gradually increases, more amino reaction sites are provided, and a large number of amine monomers participate in interfacial polymerization, resulting in a denser polyamide layer. Although it has good dye-blocking ability, the dye / salt separation selectivity and flux are greatly reduced. This invention, by controlling a specific mass ratio of polyamine TPEI to polyacrylamide chloride, obtains a nanofiltration membrane with a complete and relatively porous polyamide layer, enabling the nanofiltration membrane to have both high flux and high dye and salt separation selectivity.

[0042] This invention yields a relatively porous modified polyethyleneimine composite nanofiltration membrane. This modified polyethyleneimine composite nanofiltration membrane exhibits high water flux, high dye rejection capacity, and low salt rejection capacity at lower pressures. When used in the treatment of wastewater containing dyes and salts, it can achieve highly selective separation of dyes and salt solutions.

[0043] The third technical solution of the present invention:

[0044] This invention provides the application of the modified polyethyleneimine composite nanofiltration membrane in wastewater treatment.

[0045] The present invention also provides the application of the modified polyethyleneimine composite nanofiltration membrane in the separation of dyes and salt solutions. The modified polyethyleneimine composite nanofiltration membrane of the present invention can achieve highly selective separation of dyes and salt solutions.

[0046] Compared with the prior art, the present invention has the following advantages and technical effects:

[0047] 1. This invention obtains a novel nanofiltration membrane by grafting the zwitterionic monomer TMAO onto polyethyleneimine (PEI) to obtain the polyamine TPEI, followed by interfacial polymerization. This membrane exhibits high dye rejection and very low salt rejection, enabling the separation of dyes and salts. Compared to traditional TFC membranes, this invention, by controlling the concentrations of the polyamine TPEI and polyacrylamide chlorides, produces a composite nanofiltration membrane with a complete and relatively loose polyamide layer, thus improving the water flux of the composite nanofiltration membrane while maintaining high selectivity for dye and salt separation.

[0048] 2. The composite nanofiltration membrane of the present invention contains zwitterionic "N" groups with equimolar oppositely charged groups in the TPEI polyamine structure. + -O - It has a strong hydration capacity, which gives the composite nanofiltration membrane excellent antifouling performance.

[0049] 3. The composite nanofiltration membrane of this invention not only retains dyes with molecular weights less than 1000 Da, but also increases water flux while maintaining a low retention rate for monovalent and divalent salt ions, achieving highly selective separation of dyes and salts. Furthermore, DMAPA and PEI are both inexpensive compounds, reducing the cost of membrane preparation and enabling its application in the recycling of wastewater from the textile and dyeing industries. Attached Figure Description

[0050] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0051] Figure 1 The image shows the retention results of the modified polyethyleneimine composite nanofiltration membrane of Example 1 for different dyes (Victoria Blue (VBB), Congo Red (CR), Coomassie Brilliant Blue R250 (CBB) and Evans Blue (EB)).

[0052] Figure 2The graph shows the retention results of the modified polyethyleneimine composite nanofiltration membrane of Example 1 and the composite nanofiltration membrane of Comparative Example 1 for different salt solutions (Na2SO4, MgSO4, MgCl2 and NaCl). The water flux (left Y-axis) represents the NF-PEI membrane. □ represents the water flux of the NF-TPEI membrane (left Y-axis), □ represents the retention of the NF-PEI membrane (right Y-axis), and ○ represents the retention of the NF-TPEI membrane (right Y-axis).

[0053] Figure 3 The graph shows the retention results of Congo Red (CR) dye by the four groups of modified polyethyleneimine composite nanofiltration membranes in Examples 1-2 and Examples 4-5.

[0054] Figure 4 The diagram shows the pure water flux of the four groups of modified polyethyleneimine composite nanofiltration membranes in Examples 1-2 and Examples 4-5.

[0055] Figure 5 The graph shows the antifouling performance of the modified polyethyleneimine composite nanofiltration membrane of Example 1 against different pollutants (bovine serum albumin (BSA), humic acid (HA) and sodium alginate (SA)).

[0056] Figure 6 The images show electron microscope (EM) images of the composite nanofiltration membranes of Example 1 and Comparative Example 1 (NF-TPEI is the composite nanofiltration membrane of Example 1, and NF-PEI is the composite nanofiltration membrane of Comparative Example 1). Detailed Implementation

[0057] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0058] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0059] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0060] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0061] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0062] All raw materials used in the embodiments of this invention were obtained through commercial purchase.

[0063] The CAS number for dimethylaminopropylacrylamide is 3845-76-9, and its structural formula is [insert structural formula here].

[0064]

[0065] The technical solution of the present invention will be further illustrated by the following embodiments.

[0066] Example 1

[0067] (1) Preparation of zwitterionic monomer (TMAO): 15.62 g DMAPA (dimethylaminopropylacrylamide) was dissolved in 100 mL of ultrapure water (1 mol / L), and 17 g of 30 wt% hydrogen peroxide solution (1.5 mol / L) was added dropwise in an oil bath at 65 °C. The mixture was heated and stirred for 8 h, then extracted with ethyl acetate and freeze-dried for 24 h to obtain purified TMAO.

[0068] (2) Preparation of polyamine TPEI: 3g PEI (MW=600Da) and 4.5g purified TMAO were dissolved in 18g ultrapure water and reacted at 80℃ for 12h. After extraction and purification with ethyl acetate, the mixture was freeze-dried for 48h to obtain polyamine TPEI.

[0069] (3) Preparation of aqueous solution: The polyamine TPEI was added to ultrapure water and stirred evenly to obtain an aqueous solution with a mass concentration of 0.075% of TPEI.

[0070] (4) Preparation of oil phase solution: Trimethylbenzene chloride (TMC) was dissolved in n-hexane and ultrasonically mixed to obtain an oil phase solution with a mass concentration of 0.15% of TMC in the oil phase solution.

[0071] (5) Interfacial polymerization reaction: The PES base membrane was cut into equal circular pieces (6 cm in diameter) and fixed with a polytetrafluoroethylene circular frame. The aqueous phase solution was poured onto the PES (polyethersulfone) base membrane. After 10 min, excess aqueous phase solution was removed using an air knife. Then, an oil phase solution was poured in, and after 5 min of contact, excess oil phase solution was removed. The membrane was then dried in a 60℃ oven for 5 min to obtain the modified polyethyleneimine composite nanofiltration membrane, denoted as NF-TPEI. The performance of the prepared composite nanofiltration membrane was tested under 0.4 MPa pressure with pure water and 2000 ppm MgCl2, respectively. The test results showed that the pure water permeability of the composite nanofiltration membrane was 203.0 μm. -2 h -1 bar -1 The rejection rate of MgCl2 aqueous solution is 2.0%.

[0072] Example 2

[0073] Same as Example 1, except that in step (3), the mass concentration of TPEI in the aqueous solution is 0.05%. The performance of the prepared composite nanofiltration membrane was tested with pure water and 2000 ppm MgCl2 at a pressure of 0.4 MPa. The test results showed that the pure water permeability of the composite nanofiltration membrane was 425.3 μm. -2 h -1 bar -1 The rejection rate of MgCl2 aqueous solution is 1.0%.

[0074] Example 3

[0075] Same as Example 1, except that in step (4), the mass concentration of TMC in the oil phase solution is 0.1%. The performance of the prepared composite nanofiltration membrane was tested with pure water and 2000 ppm MgCl2 at a pressure of 0.4 MPa. The test results showed that the pure water permeability of the composite nanofiltration membrane was 149.1 Lm. -2 h -1 bar -1 The rejection rate of MgCl2 aqueous solution was 2.8%.

[0076] Example 4

[0077] Same as Example 1, except that in step (3), the mass concentration of TPEI in the aqueous solution is 0.1%. The performance of the prepared composite nanofiltration membrane was tested at 0.4 MPa pressure using pure water and 2000 ppm MgCl2, respectively. The test results showed that the pure water permeability of the composite nanofiltration membrane was 145.6 μm. -2 h -1 bar -1 The rejection rate of MgCl2 aqueous solution was 5.1%.

[0078] Example 5

[0079] Same as Example 1, except that in step (3), the mass concentration of TPEI in the aqueous solution is 0.125%. The performance of the prepared composite nanofiltration membrane was tested with pure water and 2000 ppm MgCl2 at a pressure of 0.4 MPa. The test results showed that the pure water permeability of the composite nanofiltration membrane was 71.5 μm. -2 h -1 bar -1 The rejection rate of MgCl2 aqueous solution was 6.6%.

[0080] Example 6

[0081] (1) Preparation of TMAO: 34.05g DMAPA was dissolved in 100mL of ultrapure water (2mol / L), and 17g of 30wt% hydrogen peroxide solution was added dropwise in an oil bath at 60℃. The mixture was heated and stirred for 10h, then purified by extraction with ethyl acetate and freeze-dried for 60h to obtain purified TMAO.

[0082] (2) Preparation of polyamine TPEI: 3g PEI (MW=600Da) and 4.5g purified TMAO were dissolved in 18g ultrapure water and reacted at 80℃ for 14h. After extraction and purification with ethyl acetate, the mixture was freeze-dried for 24h to obtain polyamine TPEI.

[0083] (3) Preparation of aqueous solution: The polyamine TPEI was added to ultrapure water and stirred evenly to obtain an aqueous solution with a mass concentration of 0.05% of TPEI.

[0084] (4) Preparation of oil phase solution: TMC is dissolved in n-hexane and ultrasonically mixed to obtain an oil phase solution with a mass concentration of 0.2% of TMC in the oil phase solution;

[0085] (5) Interfacial polymerization reaction: Cut the PE base membrane into equal circular membrane pieces (6cm in diameter), fix them with a polytetrafluoroethylene circular frame, pour the aqueous solution onto the PE base membrane, remove the excess aqueous solution after 8 minutes, remove the aqueous solution with an air knife, then pour in the oil phase solution, contact for 5 minutes, remove the excess oil phase solution, and transfer to a 60℃ oven to dry for 5 minutes to obtain the modified polyethyleneimine composite nanofiltration membrane.

[0086] Example 7

[0087] (1) Preparation of TMAO: 34.05g DMAPA was dissolved in 100mL of ultrapure water (2mol / L), and 17g of 30wt% hydrogen peroxide solution was added dropwise in an oil bath at 60℃. The mixture was heated and stirred for 10h, then purified by extraction with ethyl acetate and freeze-dried for 60h to obtain purified TMAO.

[0088] (2) Preparation of polyamine TPEI: 3g PEI (MW=600Da) and 4.5g purified TMAO were dissolved in 18g ultrapure water and reacted at 80℃ for 14h. After extraction and purification with ethyl acetate, the mixture was freeze-dried for 24h to obtain polyamine TPEI.

[0089] (3) Preparation of aqueous solution: The polyamine TPEI was added to ultrapure water and stirred evenly to obtain an aqueous solution with a mass concentration of 0.15% of TPEI.

[0090] (4) Preparation of oil phase solution: TMC is dissolved in n-hexane and ultrasonically mixed to obtain an oil phase solution with a mass concentration of 0.05% of TMC in the oil phase solution;

[0091] (5) Interfacial polymerization reaction: The PSF base membrane was cut into equal circular membrane pieces (6 cm in diameter), fixed with a polytetrafluoroethylene circular frame, the aqueous phase solution was poured onto the PSF base membrane, and after 15 min, the excess aqueous phase solution was removed. The aqueous phase solution was removed with an air knife, and then the oil phase solution was poured in. After contacting for 5 min, the excess oil phase solution was removed, and the membrane was transferred to a 60℃ oven to dry for 5 min to obtain the modified polyethyleneimine composite nanofiltration membrane.

[0092] Example 8

[0093] (1) Preparation of TMAO: 3.405g DMAPA was dissolved in 100mL of ultrapure water (0.2mol / L), and 17g of 30wt% hydrogen peroxide solution was added dropwise in an oil bath at 60℃. The mixture was heated and stirred for 10h, then purified by extraction with ethyl acetate and freeze-dried for 40h to obtain purified TMAO.

[0094] (2) Preparation of polyamine TPEI: 3g PEI (MW=600Da) and 4.5g purified TMAO were dissolved in 18g ultrapure water and reacted at 80℃ for 12h. After extraction and purification with ethyl acetate, the mixture was freeze-dried for 60h to obtain polyamine TPEI.

[0095] (3) Preparation of aqueous solution: The polyamine TPEI was added to ultrapure water and stirred evenly to obtain an aqueous solution with a mass concentration of 0.1% of TPEI.

[0096] (4) Preparation of oil phase solution: TMC is dissolved in n-hexane and ultrasonically mixed to obtain an oil phase solution with a mass concentration of 0.1% of TMC in the oil phase solution;

[0097] (5) Interfacial polymerization reaction: The PAI base membrane was cut into equal circular membrane pieces (6 cm in diameter), fixed with a polytetrafluoroethylene circular frame, the aqueous phase solution was poured onto the PAI base membrane, and after 10 min, the excess aqueous phase solution was removed. The aqueous phase solution was removed with an air knife, and then the oil phase solution was poured in. After contacting for 5 min, the excess oil phase solution was removed, and the membrane was transferred to a 60℃ oven to dry for 5 min to obtain the modified polyethyleneimine composite nanofiltration membrane.

[0098] Example 9

[0099] Same as Example 1, except that:

[0100] In step (1), the concentration of the solution obtained by dissolving DMAPA in ultrapure water is 0.5 mol / L;

[0101] In step (3), the mass concentration of TPEI in the aqueous solution is 0.05%;

[0102] In step (4), the mass concentration of TMC in the oil phase solution is 0.1%;

[0103] The base film in step (5) is a PAN base film.

[0104] Example 10

[0105] Same as Example 1, except that:

[0106] In step (3), the mass concentration of TPEI in the aqueous solution is 0.05%;

[0107] In step (4), the mass concentration of TMC in the oil phase solution is 0.2%;

[0108] The base film in step (5) is a PP (polypropylene) base film.

[0109] Example 11

[0110] (1) Preparation of zwitterionic monomer (TMAO): 15.62 g DMAPA was dissolved in 100 mL of ultrapure water (1 mol / L), and 17 g of 30 wt% hydrogen peroxide solution (1.5 mol / L) was added dropwise in an oil bath at 65 °C. The mixture was heated and stirred for 8 h, then purified by extraction with ethyl acetate and freeze-dried for 24 h to obtain purified TMAO.

[0111] (2) Preparation of polyamine TPEI: 3g PEI (MW=600Da) and 6g purified TMAO were dissolved in 18g ultrapure water and reacted at 80℃ for 12h. After extraction and purification with ethyl acetate, the mixture was freeze-dried for 48h to obtain polyamine TPEI.

[0112] (3) Preparation of aqueous solution: The polyamine TPEI was added to ultrapure water and stirred evenly to obtain an aqueous solution with a mass concentration of 0.075% of TPEI.

[0113] (4) Preparation of oil phase solution: TMC is dissolved in n-hexane and ultrasonically mixed to obtain an oil phase solution with a mass concentration of 0.15% of TMC in the oil phase solution;

[0114] (5) Interfacial polymerization reaction: The PES base membrane was cut into equal circular membrane pieces (6 cm in diameter), fixed with a polytetrafluoroethylene circular frame, the aqueous phase solution was poured onto the PES base membrane, and after 10 min, the excess aqueous phase solution was removed. The aqueous phase solution was removed with an air knife, and then the oil phase solution was poured in. After contacting for 5 min, the excess oil phase solution was removed, and the membrane was transferred to a 60℃ oven to dry for 5 min to obtain the modified polyethyleneimine composite nanofiltration membrane.

[0115] Example 12

[0116] (1) Preparation of zwitterionic monomer (TMAO): 15.62 g DMAPA was dissolved in 100 mL of ultrapure water (1 mol / L), and 17 g of 30 wt% hydrogen peroxide solution (1.5 mol / L) was added dropwise in an oil bath at 65 °C. The mixture was heated and stirred for 8 h, then purified by extraction with ethyl acetate and freeze-dried for 24 h to obtain TMAO.

[0117] (2) Preparation of polyamine TPEI: 3g PEI (MW=600Da) and 4.5g purified TMAO were dissolved in 30g ultrapure water and reacted at 80℃ for 12h. After extraction and purification with ethyl acetate, the mixture was freeze-dried for 48h to obtain polyamine TPEI.

[0118] (3) Preparation of aqueous solution: The polyamine TPEI was added to ultrapure water and stirred evenly to obtain an aqueous solution with a mass concentration of 0.075% of TPEI.

[0119] (4) Preparation of oil phase solution: TMC is dissolved in n-hexane and ultrasonically mixed to obtain an oil phase solution with a mass concentration of 0.15% of TMC in the oil phase solution;

[0120] (5) Interfacial polymerization reaction: The PES base membrane was cut into equal circular membrane pieces (6 cm in diameter), fixed with a polytetrafluoroethylene circular frame, the aqueous phase solution was poured onto the PES base membrane, and after 10 min, the excess aqueous phase solution was removed. The aqueous phase solution was removed with an air knife, and then the oil phase solution was poured in. After contacting for 5 min, the excess oil phase solution was removed, and the membrane was transferred to a 60℃ oven to dry for 5 min to obtain the modified polyethyleneimine composite nanofiltration membrane.

[0121] Comparative Example 1

[0122] Same as Example 1, except that TMAO was not introduced into the composite nanofiltration membrane, that is, TMAO was not added in step (2), and the resulting composite nanofiltration membrane is denoted as NF-PEI.

[0123] Electron micrographs of the composite nanofiltration membranes of Example 1 and Comparative Example 1 are shown below. Figure 6 (NF-TPEI is the composite nanofiltration membrane of Example 1, and NF-PEI is the composite nanofiltration membrane of Comparative Example 1). It can be seen that PEI, with more amino reaction sites, reacts more vigorously with TMC, rapidly forming a dense network structure. This results in many uniformly distributed disk-shaped structures on the surface of the NF-PEI membrane, making the NF-PEI membrane rough and dense. In contrast, TPEI, compared to unmodified PEI, provides fewer amino reaction sites when reacting with polyacrylamide chlorides. Therefore, the interfacial polymerization reaction with polyacrylamide chlorides is milder, allowing more time to change the molecular arrangement to form a loose separation layer. Consequently, the NF-TPEI membrane is smooth and porous.

[0124] The performance of the prepared composite nanofiltration membrane was tested under a pressure of 0.4 MPa with pure water and 2000 ppm MgCl2, respectively. The test results showed that the pure water permeability of the composite nanofiltration membrane was 13.0 μm. -2 h -1 bar -1 The rejection rate of MgCl2 aqueous solution was 17.7%.

[0125] Comparative Example 2

[0126] Same as Example 1, except that:

[0127] In step (4), the mass concentration of TMC in the oil phase solution is 0.5%.

[0128] In this comparative example, the reduced proportion of TPEI resulted in an increased flux and decreased salt rejection rate in the composite nanofiltration membrane. This is because the reduced proportion of TPEI decreases the number of amino reaction sites provided, leading to a more porous polyamide layer obtained by reacting with polyacrylamide chlorides.

[0129] The performance of the prepared composite nanofiltration membrane was tested under a pressure of 0.4 MPa with pure water and 2000 ppm MgCl2, respectively. The test results showed that the pure water permeability of the composite nanofiltration membrane was 299.7 μm. -2 h -1 bar -1 The rejection rate of MgCl2 aqueous solution is 1.2%.

[0130] Comparative Example 3

[0131] Same as Example 1, except that:

[0132] In step (4), the mass concentration of TMC in the oil phase solution is 0.01%.

[0133] In this comparative example, the increased proportion of TPEI resulted in a higher flux and a lower salt rejection rate in the composite nanofiltration membrane. This is because the mass concentration of TMC was too low to react with polyacrylamide chlorides to obtain a complete polyamide layer.

[0134] The performance of the prepared composite nanofiltration membrane was tested under a pressure of 0.4 MPa with pure water and 2000 ppm MgCl2, respectively. The test results showed that the pure water permeability of the composite nanofiltration membrane was 780.2 μm. -2 h -1 bar -1 The rejection rate of MgCl2 aqueous solution is 0.4%.

[0135] Comparative Example 4

[0136] Same as Example 1, except that:

[0137] In step (4), the mass concentration of TMC in the oil phase solution is 0.05%.

[0138] In this comparative example, the increased proportion of TPEI resulted in a decrease in flux and an increase in salt rejection rate of the composite nanofiltration membrane. This is because the increased proportion of TPEI provides more amino reaction sites, leading to a denser polyamide layer obtained by reacting with polyacrylamide chlorides.

[0139] The performance of the prepared composite nanofiltration membrane was tested under a pressure of 0.4 MPa with pure water and 2000 ppm MgCl2, respectively. The test results showed that the pure water permeability of the composite nanofiltration membrane was 30.7 μm. -2 h -1 bar -1 The rejection rate of MgCl2 aqueous solution was 5.2%.

[0140] Comparative Example 5

[0141] Same as Example 1, except that:

[0142] In step (4), the mass concentration of TMC in the oil phase solution is 0.2%.

[0143] In this comparative example, the reduced proportion of TPEI resulted in a higher flux and lower salt rejection rate in the composite nanofiltration membrane. This is because the reduced proportion of TPEI decreases the number of amino reaction sites provided, leading to a more porous polyamide layer obtained by reacting with polyacrylamide chlorides.

[0144] The performance of the prepared composite nanofiltration membrane was tested under a pressure of 0.4 MPa with pure water and 2000 ppm MgCl2, respectively. The test results showed that the pure water permeability of the composite nanofiltration membrane was 259.7 μm. -2 h -1 bar -1 The rejection rate of MgCl2 aqueous solution is 1.4%.

[0145] Comparative Example 6

[0146] The preparation method is the same as in Example 1, except that pyromellitic chloromethyl chloride is replaced with phthaloyl chloride.

[0147] The performance of the prepared composite nanofiltration membrane was tested under a pressure of 0.4 MPa with pure water and 2000 ppm MgCl2, respectively. The test results showed that the pure water permeability of the composite nanofiltration membrane was 319.0 μm. -2 h -1 bar -1 The rejection rate of MgCl2 aqueous solution is 1.5%.

[0148] Comparative Example 7

[0149] The composite nanofiltration membrane was prepared according to the method of Example 5 in Patent 202211166482.9.

[0150] The performance of the prepared composite nanofiltration membrane was tested under a pressure of 0.4 MPa with pure water and 2000 ppm MgCl2, respectively. The test results showed that the pure water permeability of the composite nanofiltration membrane was 13.2 Lm. -2 h -1 bar -1 The rejection rate of MgCl2 aqueous solution was 98.3%.

[0151] Comparative Example 8

[0152] The preparation method is the same as in Example 1, except that the MW of PEI is 1800 Da.

[0153] The performance of the prepared composite nanofiltration membrane was tested under a pressure of 0.4 MPa with pure water and 2000 ppm MgCl2, respectively. The test results showed that the pure water permeability of the composite nanofiltration membrane was 126.4 μm. -2 h -1 bar -1 The rejection rate of MgCl2 aqueous solution was 6.2%.

[0154] Application examples

[0155] 1. The composite nanofiltration membrane prepared in Example 1 was placed on a laboratory cross-flow apparatus. Dye rejection performance tests were conducted using four dyes at a concentration of 50 ppm: Victoria Blue (VBB), Congo Red (CR), Coomassie Brilliant Blue R250 (CBB), and Evans Blue (EB). (Specific test procedure: The nanofiltration membrane was placed on the laboratory cross-flow apparatus. The dye rejection test was conducted at 0.2 MPa. Four dye solutions at a concentration of 50 ppm were used as feed for membrane filtration. Before measurement, the membrane sample was pressurized to achieve a stable permeate flux. Then, the solution permeate flux and the rejection rate of the four dyes were measured continuously at least three times, and the average value was taken.) The test results are as follows: Figure 1 As shown. (Through) Figure 1 It can be seen that the modified polyethyleneimine composite nanofiltration membrane of the present invention can effectively retain dyes with a molecular weight of less than 1000 Da, while also having good permeation flux.

[0156] 2. The composite nanofiltration membranes prepared in Example 1 and Comparative Example 1 were placed on a laboratory cross-flow apparatus. Salt rejection performance was tested using four salt solutions (Na₂SO₄, MgSO₄, MgCl₂, and NaCl) with a concentration of 2.0 g / L, respectively. (Specific test procedure: The nanofiltration membrane was placed on the laboratory cross-flow apparatus. The salt rejection test was conducted at 0.2 MPa. Four salt solutions with a concentration of 2.0 g / L (Na₂SO₄, MgSO₄, MgCl₂, and NaCl) were used as feed for membrane filtration. Before measurement, the membrane sample was pressurized to achieve a stable permeate flux. Then, the solution permeate flux and the rejection rate of the four salts were measured continuously at least three times, and the average value was taken.) The test results are as follows: Figure 2 As shown. (Through) Figure 2It can be seen that, compared with the composite nanofiltration membrane of polyethyleneimine, the modified polyethyleneimine composite nanofiltration membrane of the present invention allows salts to pass through more easily, with a rejection rate of <10% for all four salts, especially MgCl2, which has the highest pass rate, i.e., the MgCl2 rejection rate is the lowest (pass rate: magnesium chloride > magnesium sulfate > sodium chloride > sodium sulfate; solution permeation flux: sodium sulfate < magnesium sulfate < magnesium chloride < sodium chloride). Combined with the first item in the application examples, it can be seen that the modified polyethyleneimine composite nanofiltration membrane of the present invention has a high rejection rate for dyes and a high permeability for salts, thus facilitating the selective separation of dyes and salts.

[0157] 3. The four sets of modified polyethyleneimine composite nanofiltration membranes from Examples 1-2 and 4-5 were placed on a laboratory cross-flow apparatus. A 50 ppm Congo red (CR) dye was used to test the dye rejection performance (the test method was as follows: the nanofiltration membrane was placed on the laboratory cross-flow apparatus, the dye rejection test was conducted at 0.2 MPa, a 50 ppm Congo red (CR) dye solution was used as the feed for membrane filtration, the membrane sample was pressurized before measurement to achieve a stable permeation flux, and then the solution permeation flux and Congo red (CR) dye rejection rate were continuously measured at least three times and the average value was taken). The test results are as follows: Figure 3 As shown. (Through) Figure 3 It can be seen that as the TPEI concentration increases, the retention performance for Congo Red (CR) dye improves while the water flux gradually decreases. This is mainly because the increased TPEI concentration provides more amino sites for the TMC to react, resulting in a denser polyamide layer. Therefore, selecting an appropriate TPEI concentration can effectively improve the dye and salt separation selectivity of nanofiltration membranes without compromising the integrity of the polyamide layer.

[0158] 4. The pure water flux of the four groups of modified polyethyleneimine composite nanofiltration membranes in Examples 1-2 and 4-5 was tested. The specific method was as follows: the nanofiltration membranes were placed on a laboratory cross-flow apparatus, and the pure water flux test was conducted at 0.2 MPa. Pure water was used as the feed for membrane filtration. Before measurement, the membrane samples were pressurized to achieve a stable water flux. Then, the pure water flux was measured continuously at least three times, and the average value was taken. The results are as follows: Figure 4 As shown. (Through) Figure 4 It can be seen that as the TPEI mass concentration increases, the water permeability decreases. This can be attributed to the increasingly dense polyamide layer, which is not conducive to the transport of water molecules.

[0159] 5. The modified polyethyleneimine composite nanofiltration membrane prepared in Example 1 was placed on a laboratory cross-flow apparatus. The antifouling performance of the membrane was tested using representative pollutants from natural water sources: bovine serum albumin (BSA), humic acid (HA), and sodium alginate (SA). The pollutant concentration in the feed solution was 0.1 g / L. The BSA antifouling test was conducted at 0.2 MPa: First, the membrane sample was pressurized to achieve a stable water flux before measurement. Then, the pure water flux was continuously measured for 60 min, and the flux was recorded every 10 min. Afterward, the membrane was filtered again for 60 min using the BSA solution as feed. The permeate flux was also measured every 10 min and recorded. Afterward, the membrane after filtering the BSA solution was simply cleaned with deionized water for 30 min. Subsequently, the pure water flux was measured again and the data was re-recorded. The above steps were repeated for 3 cycles. The antifouling test procedure for HA and SA was the same as for BSA. Finally, the antifouling indices of the modified polyethyleneimine composite nanofiltration membrane for the above three pollutants were calculated: flux recovery rate (FRR), flux decline rate (Rt), reversible flux decline ratio (Rr), and irreversible flux decline ratio (Rir). The results are shown in [Figure number missing]. Figure 5 .pass Figure 5 It can be seen that the low Rir and high FRR of the modified polyethyleneimine composite nanofiltration membrane indicate that it has excellent antifouling performance.

[0160] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing a modified polyethyleneimine composite nanofiltration membrane, characterized in that, Includes the following steps: Dimethylaminopropylacrylamide was dissolved in water to form solution A. The solution was placed in an oil bath, and hydrogen peroxide solution was added. The mixture was heated and stirred for 6-10 hours. After extraction with ethyl acetate and freeze-drying, an amphoteric monomer was obtained. The molar concentration of solution A was 0.2-2 mol / L; the concentration of the hydrogen peroxide solution was 30 wt%; and the mass ratio of dimethylaminopropylacrylamide to the hydrogen peroxide solution was 1:(1-2). Polyethyleneimine and purified zwitterionic monomers were dissolved in water to form solution B. The solution was heated and stirred in an oil bath for 10-14 hours, purified by ethyl acetate extraction, and freeze-dried to obtain polyamine TPEI. The molecular weight of the polyethyleneimine was 600 Da. The mass ratio of polyethyleneimine to zwitterionic monomer was 1:(1-3), and the mass ratio of polyethyleneimine to water was 1:(4-10). The polyamine TPEI was added to water and stirred until homogeneous to obtain an aqueous solution, wherein the mass concentration of the polyamine TPEI in the aqueous solution was 0.05-0.125%. A polyacryl chloride is dissolved in an organic solvent to prepare an oil phase solution, wherein the mass concentration of the polyacryl chloride in the oil phase solution is 0.1-0.15%, and the polyacryl chloride is pyromellitic tricarboxylate chloride; The aqueous solution is poured onto the base membrane and kept for 8-15 minutes. Then, the excess aqueous solution is removed, followed by the addition of the oil solution. After the reaction, the excess oil solution is removed, and the membrane is dried to obtain the modified polyethyleneimine composite nanofiltration membrane.

2. The method for preparing the modified polyethyleneimine composite nanofiltration membrane according to claim 1, characterized in that, When preparing zwitterionic monomers: the heating temperature is 60-70℃; the freeze-drying time is 24-60h.

3. The method for preparing the modified polyethyleneimine composite nanofiltration membrane according to claim 1, characterized in that, When preparing the polyamine TPEI: the heating temperature is 80℃; the freeze-drying time is 24-60h.

4. The method for preparing the modified polyethyleneimine composite nanofiltration membrane according to claim 1, characterized in that, The organic solvent is one of n-hexane, n-heptane, dodecane, and tetradecane.

5. The method for preparing the modified polyethyleneimine composite nanofiltration membrane according to claim 1, characterized in that, The base film is made of polysulfone, polyethersulfone, polyethylene, polyamide imide, polypropylene, or polyacrylonitrile.

6. The method for preparing the modified polyethyleneimine composite nanofiltration membrane according to claim 1, characterized in that, After adding the aqueous phase solution, the holding time is 10 minutes; after adding the oil phase solution, the reaction time is 5 minutes.

7. A modified polyethyleneimine composite nanofiltration membrane, characterized in that, It is prepared according to any one of claims 1-6.

8. The application of the modified polyethyleneimine composite nanofiltration membrane according to claim 7 in wastewater treatment.

9. The application of the modified polyethyleneimine composite nanofiltration membrane according to claim 7 in the separation of dyes and salt solutions.

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