Nanofiber membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of oil-water separation, and discloses a nanofiber membrane as well as a preparation method and application thereof. The nanofiber membrane is prepared through co-electrostatic spinning and comprises a first nanofiber and a second nanofiber which are wound with each other, the first nanofiber is polytetrafluoroethylene, and the second nanofiber is polyimide. The nanofiber membrane provided by the invention fundamentally avoids the formation of oil pollutants intercepted in the whole oil-water separation process, and has good tensile strength, thereby providing lasting and excellent anti-pollution performance for realizing super-stable long-term separation of the oil pollutants from oily wastewater.

Description

Technical Field

[0001] This invention relates to the field of oil-water separation technology, specifically to a nanofiber membrane, its preparation method, and its application. Background Technology

[0002] Oil extraction, transportation, and processing generate large amounts of oily wastewater, making the development of rapid and efficient oil-water separation materials a current focus of scientific research. The separation of emulsified oil and dissolved oil is currently the most challenging aspect. Traditional oil-water separation methods, including gravity separation, centrifugation, flotation, flocculation, and electrolysis, suffer from drawbacks such as low separation efficiency, high cost, potential secondary pollution, and low recycling rates when dealing with complex emulsified oil-water mixtures. Membrane separation technology, with its advantages of high selectivity, ease of operation, and recyclability, has become an emerging technological approach in the field of oil-water separation.

[0003] Current research on separation membranes typically aims for a uniform distribution of hydrophilic components on the membrane surface or pore walls, allowing water to pass through while oil is kept out of the membrane layer. However, emulsified oil isolated outside the membrane tends to accumulate on the surface of the membrane hydration layer, forming a demulsified oil film. Once a large amount of oil film forms on the membrane surface or blocks the pores, the water channels will be occupied or even closed, leading to a sharp decrease in water content per unit area.

[0004] Therefore, there is an urgent need to develop a nanofiber membrane that can fundamentally prevent the formation of oil contaminants trapped during the separation of emulsified oil-water mixtures, thereby providing long-lasting and excellent anti-fouling performance for the ultra-stable long-term separation of oil contaminants from oily wastewater. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of existing technologies, such as the formation of a large amount of oil film or blockage of pores on the membrane surface due to oil contaminants trapped during the separation of emulsified oil-water mixtures, which would occupy water channels and result in low antifouling performance, and the fact that polytetrafluoroethylene (PTFE) is almost insoluble in any solvent, making it difficult to process into nanofiber membranes. This invention provides a nanofiber membrane, its preparation method, and its applications. This technical solution allows water and oil to permeate through their respective channels, effectively preventing the intercepting phase from blocking the channels, enhancing the antifouling performance of the separation membrane, achieving ultra-stable separation of emulsified oil-water mixtures, and solving the problem of the difficulty in processing PTFE nanofiber membranes.

[0006] To achieve the above objectives, the first aspect of the present invention provides a nanofiber membrane, which is prepared by co-electrospinning and includes a first nanofiber and a second nanofiber entangled with each other, wherein the first nanofiber is polytetrafluoroethylene and the second nanofiber is polyimide.

[0007] Preferably, the pore size of the nanofiber membrane is 1-10 μm, and the porosity is 85%-95%.

[0008] Preferably, the diameter of the first nanofiber is 400-750 nm.

[0009] Preferably, the diameter of the second nanofiber is 50-310 nm.

[0010] Preferably, the mass ratio of the first nanofiber to the second nanofiber is (1.5-4):1.

[0011] A second aspect of the present invention provides a method for preparing a nanofiber membrane, the method comprising the following steps:

[0012] (1) Mix 4,4-diaminodiphenyl ether solution and pyromellitic dianhydride and carry out polycondensation reaction to obtain polyamic acid solution;

[0013] (2) Mix the polyvinyl alcohol solution and the polytetrafluoroethylene dispersion to obtain a mixed solution;

[0014] (3) Electrospinning the mixed solution and the polyamic acid solution together;

[0015] (4) The product obtained in step (3) is subjected to thermal imidization reaction and sintering.

[0016] Preferably, in step (1), the solvent of the 4,4-diaminodiphenyl ether solution is N,N-dimethylformamide.

[0017] Preferably, the concentration of the 4,4-diaminodiphenyl ether solution is 2-10 wt%.

[0018] Preferably, in step (1), the mass ratio of the amount of 4,4-diaminodiphenyl ether to the amount of pyromellitic dianhydride is 1:(0.8-1.2).

[0019] Preferably, in step (1), the polycondensation reaction is carried out under a protective gas, and the conditions for the polycondensation reaction include: a temperature of 0-5°C and a time of 5-8h.

[0020] Preferably, in step (2), the concentration of the polyvinyl alcohol solution is 8-12 wt%.

[0021] Preferably, the concentration of the polytetrafluoroethylene dispersion is 55-65 wt%.

[0022] Preferably, the mass ratio of the polyvinyl alcohol solution to the polytetrafluoroethylene dispersion is 1:(1-3).

[0023] Preferably, in step (2), the mixing conditions include: a temperature of 20-30°C and a time of 20-28h.

[0024] Preferably, the specific process of step (3) includes fixing the mixed solution and the polyamic acid solution on both sides of the electrostatic spinning receiving roller.

[0025] Preferably, the method further includes drying the product obtained in step (3) before carrying out the thermal imidization reaction.

[0026] Preferably, the drying conditions include a temperature of 70-90°C and a time of 10-16 hours.

[0027] Preferably, in step (4), the thermal imidization reaction process specifically includes: first heating to 95-105℃, reacting at 95-105℃ for 20-40 min, then heating to 195-205℃, reacting at 195-205℃ for 20-40 min, and finally heating to 295-305℃, reacting at 295-305℃ for 20-40 min.

[0028] Preferably, in step (4), the sintering conditions include: a temperature of 350-400℃ and a time of 4-8h.

[0029] A third aspect of the present invention provides a nanofiber membrane prepared by the method described above.

[0030] The fourth aspect of the present invention provides the application of the above-mentioned nanofiber membrane in emulsified oil-water separation.

[0031] Through the above technical solution, intertwined polytetrafluoroethylene (PTFE) nanofibers and polyimide nanofibers form dual channels through micro / nano spaces. These independent dual channels allow water and oil to be transported separately through the membrane, exhibiting high permeability and stability for surfactant-stabilized oil-in-water emulsions. The polyimide nanofibers form water channels, while the hydrophobic PTFE nanofibers act as aggregation sites and oil transport channels. Furthermore, emulsified oil droplets are deposited, migrated, coalesced, and removed between the intertwined PTFE and polyimide nanofibers. The nanofiber membrane described in this invention fundamentally avoids the formation of oil contaminants trapped during the entire oil-water separation process and possesses excellent tensile strength, thus providing durable and superior antifouling performance for achieving ultra-stable long-term separation of oil contaminants from oily wastewater. Attached Figure Description

[0032] Figure 1 and Figure 2 This is a scanning electron microscope image of the nanofiber membrane described in this invention. Detailed Implementation

[0033] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0034] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0035] The nanofiber membrane of this invention is prepared by co-electrospinning and comprises a first nanofiber and a second nanofiber entangled with each other. The first nanofiber is polytetrafluoroethylene (PTFE), and the second nanofiber is polyimide. In this nanofiber membrane, the entangled PTFE and polyimide nanofibers form dual channels through micro / nano spaces. Water and oil units can be transported separately through these independent dual channels, allowing water and oil to permeate through their respective channels. This effectively prevents channel blockage by intercepting phases and provides excellent tensile strength, achieving ultra-stable separation of emulsified oil-water mixtures.

[0036] In the nanofiber membrane of the present invention, in order to improve the efficiency of emulsified oil-water separation, the pore size of the nanofiber membrane is preferably 1-10 μm, more preferably 3-8 μm; the porosity is preferably 85%-95%, more preferably 87%-93%.

[0037] In the nanofiber membrane of the present invention, in order to improve the emulsified oil-water separation performance, the diameter of the first nanofiber is preferably 400-750 nm, more preferably 435-730 nm; the diameter of the second nanofiber is preferably 50-310 nm, more preferably 56-305 nm.

[0038] In the nanofiber membrane of the present invention, in order to ensure that the water and oil units are transported separately through independent dual channels, the mass ratio of the first nanofiber to the second nanofiber is preferably (1.5-4):1, more preferably (1.8-3):1.

[0039] In some embodiments, the nanofiber membrane of the present invention is prepared by co-electrospinning and comprises a first nanofiber and a second nanofiber entangled with each other, wherein the first nanofiber is polytetrafluoroethylene and the second nanofiber is polyimide, the pore size of the nanofiber membrane is 1-10 μm and the porosity is 85%-95%, the diameter of the first nanofiber is 400-750 nm and the diameter of the second nanofiber is 50-310 nm, and the mass ratio of the first nanofiber to the second nanofiber is (1.5-4):1.

[0040] This invention also provides a method for preparing a nanofiber membrane, the method comprising the following steps:

[0041] (1) Mix 4,4-diaminodiphenyl ether solution and pyromellitic dianhydride and carry out polycondensation reaction to obtain polyamic acid solution;

[0042] (2) Mix the polyvinyl alcohol solution and the polytetrafluoroethylene dispersion to obtain a mixed solution;

[0043] (3) Electrospinning the mixed solution and the polyamic acid solution together;

[0044] (4) The product obtained in step (3) is subjected to thermal imidization reaction and sintering.

[0045] According to the method described in this invention, polyvinyl alcohol is introduced as a framework, allowing nano-polytetrafluoroethylene (PTFE) to adhere to the framework surface. A polyamic acid solution is then formed through low-temperature solution condensation polymerization, followed by electrospinning to obtain a nanofiber membrane. Further thermal treatment involves thermal imidization and thermal decomposition of PTFE and polyimide nanofibers to form a nanofiber membrane in which PTFE and polyimide nanofibers are intertwined. This membrane forms dual channels through micro / nano spaces, exhibiting high permeability and stability to surfactant-stabilized oil-in-water emulsions. Moreover, this method solves the problem that PTFE is almost insoluble in any solvent, making it difficult to process into nanofiber membranes.

[0046] In the method described in this invention, the specific process of mixing in step (1) may include: slowly adding the pyromellitic dianhydride to the 4,4-diaminodiphenyl ether solution at a temperature of 0-5°C.

[0047] In the method described in this invention, in step (1), the solvent of the 4,4-diaminodiphenyl ether solution can be N,N-dimethylformamide. The concentration of the 4,4-diaminodiphenyl ether solution can be 2-10 wt%, preferably 2-8 wt%, specifically, for example, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, or 8 wt%.

[0048] In the method described in this invention, in order to ensure the formation of polyimide nanofibers, in step (1), the mass ratio of the amount of 4,4-diaminodiphenyl ether and the amount of pyromellitic dianhydride can be 1:(0.8-1.2), preferably 1:(0.9-1.1), and can be, for example, 1:0.9, 1:0.95, 1:1, 1:1.05 or 1:1.1.

[0049] In the method described in this invention, in step (1), the polycondensation reaction is carried out under a protective gas, which can be a conventional protective gas in the art. Preferably, to ensure the formation of the polyamic acid solution, the protective gas used is at least one of nitrogen, argon, and helium. More preferably, the purity of the nitrogen is 99 wt%-99.99 wt%. To ensure the formation of polyimide nanofibers, the polycondensation reaction is preferably carried out under stirring, and the conditions of the polycondensation reaction include: a temperature preferably 0-5°C, more preferably 0-3°C; a stirring rate preferably 500-1000 rpm, more preferably 600-800 rpm; and a time preferably 5-8 h, preferably 5-7 h.

[0050] In the method described in this invention, in step (2), the concentration of the polyvinyl alcohol solution can be 8-12 wt%, preferably 9-11 wt%. The preparation process of the polyvinyl alcohol solution can be carried out under stirring, and the conditions for preparing the polyvinyl alcohol solution include: the temperature can be 85-95℃, preferably 87-92℃; the stirring rate can be 1000-2000 rpm, preferably 1200-1500 rpm; and the time can be 5-8 h, preferably 5-7 h.

[0051] In the method described in this invention, the concentration of the polytetrafluoroethylene dispersion can be 55-65 wt%, preferably 57-62 wt%. The particle size of the polytetrafluoroethylene can be 180-220 nm. In a specific embodiment, the concentration of the polytetrafluoroethylene dispersion is 60 wt%, and the particle size of the polytetrafluoroethylene is 200 nm.

[0052] In the method described in this invention, to ensure the formation of polytetrafluoroethylene nanofiber films, the mass ratio of the polyvinyl alcohol solution to the polytetrafluoroethylene dispersion is preferably 1:(1-3), more preferably 1:(1-2). To facilitate the formation of polytetrafluoroethylene nanofiber films, polyvinyl alcohol is introduced as a framework, allowing the nano-polytetrafluoroethylene to adhere to the surface of the framework.

[0053] In the method described in this invention, in order to ensure the formation of polytetrafluoroethylene nanofiber film, in step (2), the mixing is preferably carried out under stirring, and the mixing conditions include: the temperature is preferably 20-30℃, more preferably 23-27℃; the stirring rate is preferably 2000-3000rpm, more preferably 2500-2800rpm; and the time is preferably 20-28h, more preferably 22-26h.

[0054] In the method described in this invention, to ensure the formation of polytetrafluoroethylene nanofibers and polyimide nanofibers, step (3) preferably includes fixing the mixed solution and the polyamic acid solution on both sides of the electrospinning receiving roller. In a specific embodiment, the electrospinning conditions include: a rotational speed of 70-90 rpm, preferably 75-85 rpm; a distance from the needle tip to the receiving device of 12-18 cm, preferably 14-16 cm; a translational speed of 100-140 mm / min, preferably 110-130 mm / min; and a translational distance of 250-300 mm, preferably 260-280 mm. By adjusting the voltage and spray speed of the electrospinning solution, nanofiber membranes with different fiber diameters and mass ratios can be obtained.

[0055] In the method described in this invention, the method may further include: drying the product obtained in step (3) before carrying out the thermal imidization reaction. The drying conditions include: a temperature of 70-90°C, preferably 75-85°C; a vacuum degree of -0.08 to -0.1 MPa, preferably -0.09 to -0.1 MPa; and a time of 10-16 h, preferably 10-14 h. The drying can be carried out in a vacuum drying oven. In this document, the vacuum degree is atmospheric pressure minus absolute pressure.

[0056] In the method described in this invention, to ensure the formation of polyimide nanofibers, the thermal imidization reaction in step (4) preferably includes: first heating to 95-105°C and reacting at 95-105°C for 20-40 minutes; then heating to 195-205°C and reacting at 195-205°C for 20-40 minutes; finally heating to 295-305°C and reacting at 295-305°C for 20-40 minutes. The thermal imidization reaction can be carried out in a vacuum drying oven. The vacuum level during the thermal imidization reaction is consistent with that during drying.

[0057] In the method described in this invention, to ensure complete volatilization of polyvinyl alcohol after thermal decomposition, the sintering conditions in step (4) include: a temperature preferably of 350-400℃, more preferably 380-400℃, and a time preferably of 4-8 hours, specifically for example, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, or 8 hours. The sintering can be carried out in a muffle furnace.

[0058] In some embodiments, the method for preparing the nanofiber membrane of the present invention includes the following steps:

[0059] (1) Under the condition of 0-5℃, pyromellitic dianhydride is slowly added to a 2-10wt% solution of 4,4-diaminodiphenyl ether, and stirred and polycondensed under the conditions of protective gas, stirring speed of 500-1000rpm and temperature of 0-5℃ for 5-8h to obtain a polyamic acid solution.

[0060] (2) Mix a polyvinyl alcohol solution with a concentration of 8-12 wt% and a polytetrafluoroethylene dispersion with a concentration of 55-65 wt% for 20-28 h at a stirring speed of 2000-3000 rpm and a temperature of 20-30℃ to obtain a mixed solution.

[0061] (3) Fix the mixed solution and the polyamic acid solution on both sides of the electrostatic spinning receiving roller, with a rotation speed of 70-90 rpm, a distance from the needle tip to the receiving device of 12-18 cm, a translation speed of 100-140 mm / min, and a translation distance of 250-300 mm.

[0062] (4) The product obtained in step (3) is dried at a temperature of 70-90℃ and a vacuum of -0.08 to -0.1MPa for 10-16h. Then, the temperature is adjusted and the original vacuum is maintained. The dried product is first heated to 95-105℃ and subjected to thermal imidization reaction at 95-105℃ for 20-40min. Then, the temperature is raised to 195-205℃ and subjected to thermal imidization reaction at 195-205℃ for 20-40min. Finally, the temperature is raised to 295-305℃ and subjected to thermal imidization reaction at 295-305℃ for 20-40min. Then, the product is sintered at 350-400℃ for 4-8h.

[0063] In other embodiments, the method for preparing the nanofiber membrane of the present invention includes the following steps:

[0064] (1) Under the condition of 0-3℃, pyromellitic dianhydride is slowly added to a 2-8wt% solution of 4,4-diaminodiphenyl ether, and stirred and polycondensed under the conditions of protective gas, stirring speed of 600-800rpm and temperature of 0-3℃ for 5-7h to obtain a polyamic acid solution.

[0065] (2) Polyvinyl alcohol and water are stirred and mixed for 5-8 hours at a stirring speed of 1200-1500 rpm and a temperature of 85-95℃ to prepare a polyvinyl alcohol solution with a concentration of 9-11 wt%. The polyvinyl alcohol solution and a polytetrafluoroethylene dispersion with a concentration of 57-62 wt% are mixed for 22-26 hours at a stirring speed of 2500-2800 rpm and a temperature of 23-27℃ to obtain a mixed solution.

[0066] (3) Fix the mixed solution and the polyamic acid solution on both sides of the electrostatic spinning receiving roller, with a rotation speed of 75-85 rpm, a distance from the needle tip to the receiving device of 14-16 cm, a translation speed of 110-130 mm / min, and a translation distance of 260-280 mm.

[0067] (4) The product obtained in step (3) is dried at a temperature of 75-85℃ and a vacuum of -0.09 to -0.1MPa for 10-14h. Then, the temperature is adjusted and the original vacuum is maintained. The dried product is first heated to 95-105℃ and subjected to thermal imidization reaction at 95-105℃ for 20-40min. Then, the temperature is raised to 195-205℃ and subjected to thermal imidization reaction at 195-205℃ for 20-40min. Finally, the temperature is raised to 295-305℃ and subjected to thermal imidization reaction at 295-305℃ for 20-40min. Then, the product is sintered at 380-400℃ for 4-8h.

[0068] This invention also provides a nanofiber membrane prepared by the above-described method. The nanofiber membrane of this invention exhibits high permeability and stability to surfactant-stabilized oil-in-water emulsions through the formation of dual channels. Water and oil units can be transported separately through independent dual channels, effectively preventing channel blockage by the intercepting phase. Furthermore, it possesses good tensile strength, achieving high-throughput, ultra-stable, long-term separation of emulsified oil-water mixtures.

[0069] This invention also provides the application of the aforementioned nanofiber membrane in emulsified oil-water separation. The nanofiber membrane described in this invention can be used to achieve high-flux, ultra-stable, long-term separation of emulsified oil-water mixtures, solving the problem of reduced flux and unstable use that cannot be addressed by existing technologies, and has broad application prospects in the field of oil-water separation.

[0070] The following examples further illustrate the nanofiber membrane, its preparation method, and its applications according to the present invention. These examples are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following examples.

[0071] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0072] In Examples 1-7 and Comparative Examples 1-4, polytetrafluoroethylene dispersion (concentration of 60 wt%, polytetrafluoroethylene particle size of 200 nm), polyvinyl alcohol, pyromellitic dianhydride, 4,4-diaminodiphenyl ether and sodium dodecyl sulfonate were purchased from Aladdin Biochemical Technology Co., Ltd., and N,N-dimethylformamide was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0073] Example 1

[0074] (1) Dissolve 10g of 4,4-diaminodiphenyl ether in N,N-dimethylformamide to prepare a 2wt% 4,4-diaminodiphenyl ether solution. Under the condition of 3℃, slowly add 10g of pyromellitic dianhydride to the 4,4-diaminodiphenyl ether solution and stir and polycondense for 6h under nitrogen atmosphere, stirring speed of 600rpm and temperature of 3℃ to obtain a polyamic acid solution.

[0075] (2) 10g of polyvinyl alcohol and 90g of water were stirred and mixed for 6h at a stirring speed of 1200rpm and a temperature of 90℃ to prepare a polyvinyl alcohol solution with a concentration of 10wt%. 10g of the polyvinyl alcohol solution and 10g of polytetrafluoroethylene dispersion with a concentration of 60wt% were mixed for 24h at a stirring speed of 2500rpm and a temperature of 25℃ to obtain a mixed solution.

[0076] (3) The mixed solution and the polyamic acid solution are fixed on both sides of the electrostatic spinning receiving roller, with a rotation speed of 80 rpm, a distance of 15 cm from the needle tip to the receiving device, a translation speed of 120 mm / min, and a translation distance of 270 mm; the spray speed of the mixed solution is 0.113 mm / min, and the voltage is +15.9 kV; the spray speed of the polyamic acid solution is 0.012 mm / min, and the voltage is -10.1 kV;

[0077] (4) Place the product obtained in step (3) flat into a vacuum drying oven and dry it for 12 hours at a temperature of 80°C and a vacuum of -0.1 MPa. Then adjust the temperature of the vacuum drying oven to maintain the original vacuum. First, raise the temperature of the dried product to 100°C and carry out a thermal imidization reaction for 30 minutes at a temperature of 100°C. Then raise the temperature to 200°C and carry out a thermal imidization reaction for 30 minutes at a temperature of 200°C. Finally, raise the temperature to 300°C and carry out a thermal imidization reaction for 30 minutes at a temperature of 300°C. Then place the product obtained after the thermal imidization reaction into a muffle furnace and sinter it at a temperature of 380°C for 4 hours.

[0078] Example 2

[0079] Nanofiber membranes were prepared according to the method of Example 1, except that 2 wt% of 4,4-diaminodiphenyl ether solution was replaced with 4 wt% of 4,4-diaminodiphenyl ether solution.

[0080] Example 3

[0081] Nanofiber membranes were prepared according to the method of Example 1, except that 2 wt% of 4,4-diaminodiphenyl ether solution was replaced with 8 wt% of 4,4-diaminodiphenyl ether solution.

[0082] Example 4

[0083] Nanofiber membranes were prepared according to the method in Example 3, except that 10g of polytetrafluoroethylene dispersion was replaced with 20g of polytetrafluoroethylene dispersion.

[0084] Example 5

[0085] The nanofiber membrane was prepared according to the method of Example 4, except that the spraying speed and voltage of the mixed solution and the polyamic acid solution were changed. Specifically, the spraying speed of the mixed solution was 0.113 mm / min and the voltage was +14 kV; the spraying speed of the polyamic acid solution was 0.022 mm / min and the voltage was -16.1 kV.

[0086] Example 6

[0087] The nanofiber membrane was prepared according to the method of Example 5, except that the spraying speed and voltage of the polyamic acid solution were changed. Specifically, the spraying speed of the polyamic acid solution was 0.062 mm / min and the voltage was -20.3 kV.

[0088] Example 7

[0089] Nanofiber membranes were prepared according to the method in Example 5, except that the sintering time was changed to 5 hours.

[0090] Example 8

[0091] Nanofiber membranes were prepared according to the method in Example 5, except that the sintering time was changed to 6 hours.

[0092] Example 9

[0093] Nanofiber membranes were prepared according to the method in Example 5, except that the sintering time was changed to 7 hours.

[0094] Example 10

[0095] Nanofiber membranes were prepared according to the method in Example 5, except that the sintering time was changed to 8 hours.

[0096] Example 11

[0097] (1) Dissolve 10g of 4,4-diaminodiphenyl ether in N,N-dimethylformamide to prepare a 2wt% 4,4-diaminodiphenyl ether solution. Under the condition of 0℃, slowly add 8g of pyromellitic dianhydride to the 4,4-diaminodiphenyl ether solution, and stir and polycondense for 5h under nitrogen atmosphere, stirring speed of 800rpm and temperature of 0℃ to obtain a polyamic acid solution.

[0098] (2) 8g of polyvinyl alcohol and 92g of water were stirred and mixed for 6h at a stirring speed of 1500rpm and a temperature of 85℃ to prepare a polyvinyl alcohol solution with a concentration of 8wt%. 10g of polyvinyl alcohol solution and 10g of polytetrafluoroethylene dispersion with a concentration of 60wt% were mixed for 20h at a stirring speed of 2800rpm and a temperature of 20℃ to obtain a mixed solution.

[0099] (3) The mixed solution and the polyamic acid solution are fixed on both sides of the electrostatic spinning receiving roller, with a rotation speed of 70 rpm, a distance from the needle tip to the receiving device of 12 cm, a translation speed of 100 mm / min, and a translation distance of 250 mm; the spraying speed of the mixed solution is 0.113 mm / min, and the voltage is +15.9 kV; the spraying speed of the polyamic acid solution is 0.012 mm / min, and the voltage is -10.1 kV;

[0100] (4) Place the product obtained in step (3) flat into a vacuum drying oven and dry it for 10 hours at a temperature of 70°C and a vacuum of -0.1 MPa. Then adjust the temperature of the vacuum drying oven to maintain the original vacuum. First, raise the temperature of the dried product to 95°C and carry out a thermal imidization reaction for 20 minutes at a temperature of 95°C. Then raise the temperature to 195°C and carry out a thermal imidization reaction for 20 minutes at a temperature of 195°C. Finally, raise the temperature to 295°C and carry out a thermal imidization reaction for 20 minutes at a temperature of 295°C. Then place the product obtained after the thermal imidization reaction into a muffle furnace and sinter it at a temperature of 350°C for 4 hours.

[0101] Example 12

[0102] (1) Dissolve 10g of 4,4-diaminodiphenyl ether in N,N-dimethylformamide to prepare a 4,4-diaminodiphenyl ether solution with a concentration of 8wt%. Under the condition of 5℃, slowly add 12g of pyromellitic dianhydride to the 4,4-diaminodiphenyl ether solution, and stir and polycondense for 8h under nitrogen atmosphere, stirring speed of 750rpm and temperature of 5℃ to obtain a polyamic acid solution.

[0103] (2) 12g of polyvinyl alcohol and 88g of water were stirred and mixed for 8h at a stirring speed of 1400rpm and a temperature of 95℃ to prepare a polyvinyl alcohol solution with a concentration of 12wt%. 10g of polyvinyl alcohol solution and 30g of polytetrafluoroethylene dispersion with a concentration of 60wt% were mixed for 28h at a stirring speed of 2700rpm and a temperature of 30℃ to obtain a mixed solution.

[0104] (3) The mixed solution and the polyamic acid solution are fixed on both sides of the electrostatic spinning receiving roller, with a rotation speed of 90 rpm, a distance from the needle tip to the receiving device of 18 cm, a translation speed of 140 mm / min, and a translation distance of 300 mm; the spray speed of the mixed solution is 0.113 mm / min, and the voltage is +15.9 kV; the spray speed of the polyamic acid solution is 0.012 mm / min, and the voltage is -10.1 kV;

[0105] (4) Place the product obtained in step (3) flat into a vacuum drying oven and dry it for 16 hours at a temperature of 90°C and a vacuum of -0.08 MPa. Then adjust the temperature of the vacuum drying oven to maintain the original vacuum. First, raise the temperature of the dried product to 105°C and carry out a thermal imidization reaction for 40 minutes at a temperature of 105°C. Then raise the temperature to 205°C and carry out a thermal imidization reaction for 40 minutes at a temperature of 205°C. Finally, raise the temperature to 305°C and carry out a thermal imidization reaction for 40 minutes at a temperature of 305°C. Then place the product obtained after the thermal imidization reaction into a muffle furnace and sinter it at a temperature of 400°C for 8 hours.

[0106] Comparative Example 1

[0107] (1) Dissolve 10g of 4,4-diaminodiphenyl ether in N,N-dimethylformamide to prepare a 2wt% 4,4-diaminodiphenyl ether solution. Under the condition of 3℃, slowly add 10g of pyromellitic dianhydride to the 4,4-diaminodiphenyl ether solution and stir and polycondense for 6h under nitrogen atmosphere, stirring speed of 500rpm and temperature of 3℃ to obtain a polyamic acid solution.

[0108] (2) The polyamic acid solution is fixed on the electrospinning receiving roller at a rotation speed of 80 rpm, a distance of 15 cm from the needle tip to the receiving device, a translation speed of 120 mm / min, and a translation distance of 270 mm; the spraying speed of the mixed solution is 0.113 mm / min, and the voltage is +15.9 kV;

[0109] (3) Place the product obtained in step (2) flat into a vacuum drying oven and dry it for 12 hours at a temperature of 80°C and a vacuum of -0.08 MPa. Then adjust the temperature of the vacuum drying oven to maintain the original vacuum. First, raise the temperature of the dried product to 100°C and carry out a thermal imidization reaction at 100°C for 30 minutes. Then raise the temperature to 200°C and carry out a thermal imidization reaction at 200°C for 30 minutes. Finally, raise the temperature to 300°C and carry out a thermal imidization reaction at 300°C for 30 minutes.

[0110] Comparative Example 2

[0111] (1) 10g of polyvinyl alcohol and 90g of water were stirred and mixed for 6h at a stirring speed of 1200rpm and a temperature of 90℃ to prepare a polyvinyl alcohol solution with a concentration of 10wt%. 10g of the polyvinyl alcohol solution and 10g of polytetrafluoroethylene dispersion with a concentration of 60wt% were mixed for 24h at a stirring speed of 2500rpm and a temperature of 25℃ to obtain a mixed solution.

[0112] (2) The mixed solution is fixed on the electrospinning receiving roller at a rotation speed of 80 rpm, a distance of 15 cm from the needle tip to the receiving device, a translation speed of 120 mm / min, and a translation distance of 270 mm; the spraying speed of the mixed solution is 0.113 mm / min, and the voltage is +10.9 kV;

[0113] (3) Place the product obtained in step (2) flat into a vacuum drying oven and dry it for 12 hours at a temperature of 80°C and a vacuum of -0.09MPa. Then place the dried product in a muffle furnace and sinter it at a temperature of 380°C for 4 hours.

[0114] Test Example 1

[0115] The pore size and porosity of the nanofiber membranes prepared according to Examples 1-12 and Comparative Examples 1 and 2 were tested and recorded in Table 1. The test method was in accordance with the national standard GB / T 42697-2023 "Test Method for Porosity of Nonwoven Fabrics".

[0116] Test Example 2

[0117] The separation efficiency of the nanofiber membranes prepared according to Examples 1-12 and Comparative Examples 1 and 2 in emulsified oil-water separation after 1 hour and 24 hours is tested and recorded in Table 2. The test method is as follows:

[0118] An emulsion with an oil content of 1% by volume was prepared by dissolving the anionic surfactant sodium dodecyl sulfate (SLS) in 2000 mL of deionized water to form a 0.1 g / L sodium dodecyl sulfate aqueous solution. Then, 20 mL of isooctane was added, and the mixture was ultrasonically stirred for 6 hours to obtain the final mixture. Emulsion separation experiments were performed using a cross-flow apparatus (purchased from Shandong Bona Biotechnology Group Co., Ltd.) (diameter 2.8 cm, height 1 cm), with an effective membrane area of ​​6.15 cm². 2 The pressure was 0.5 bar. Before separation, the nanofiber membrane was pre-wetted with a 10 wt% ethanol aqueous solution, then installed in a cross-flow apparatus. A peristaltic pump was used to perform emulsion separation of the resulting mixture under a certain pressure, yielding a layered aqueous and oil phase (cross-flow velocity 2.65 L / m). 2 / s). Continuous stirring during the separation process ensures the stability of the emulsion, and timely replenishment of the emulsion ensures a constant feed rate. The oil content in the aqueous phase (filtrate) is determined by infrared spectrophotometry, with specific methods referring to the national standard HJ637-2018 "Determination of Petroleum and Animal Oils in Water".

[0119] Separation efficiency is calculated using the following formula:

[0120]

[0121] C1 and C2 represent the oil content in the emulsion and aqueous phase (filtrate), respectively.

[0122] Test Example 3

[0123] The diameters of polytetrafluoroethylene nanofibers and polyimide nanofibers in the nanofiber membranes prepared according to Examples 1-12 and Comparative Examples 1 and 2 were measured and recorded in Table 1. The fiber membranes were tested using a scanning electron microscope with an accelerating voltage of 15 kV. The diameters of 100 fibers were measured using Nano Measurer software, and the average value was taken after three measurements at each location.

[0124] Test Example 4

[0125] The tensile strength of the nanofiber membranes prepared according to Examples 1-12 and Comparative Examples 1 and 2 was tested and recorded in Table 2. The tests were conducted using a tensile testing machine (Shanghai Xinxian Instrument Co., Ltd.) at a test speed of 300 mm / min.

[0126] The polyimide mass ratio M of the nanofiber membranes prepared in Examples 1-12 and Comparative Examples 1 and 2 was calculated using the following formula and recorded in Table 1:

[0127]

[0128] Q X =π·r n 2 ·v X ·t

[0129] Where ρ1 and ρ2 are the densities of the polyamic acid solution and the polytetrafluoroethylene solution, respectively, and m1 and m2 are the mass fractions of the polyamic acid solution and the polytetrafluoroethylene solution, respectively, r n v is the radius of the needle tip. x t represents the injection speed, and t represents the spinning time.

[0130] Table 1

[0131]

[0132] Table 2

[0133] serial number Tensile strength (MPa) Separation efficiency (%) after 1 hour Separation efficiency (%) after 24 hours Example 1 13.6 99.6 98.6 Example 2 15.6 99.1 97.6 Example 3 14.3 99.7 99.6 Example 4 18.6 98.6 99.3 Example 5 16.3 98.9 99.1 Example 6 15.6 99.7 98.6 Example 7 17.6 99.1 99.3 Example 8 21.6 99.6 98.8 Example 9 20.9 99.5 98.9 Example 10 21.9 99.3 99.4 Example 11 11.3 93.4 91.2 Example 12 11.9 91.4 90.3 Comparative Example 1 15.6 32.5 11.8 Comparative Example 2 13.4 45.7 23.5

[0134] As can be seen from the results in Tables 1 and 2, the embodiments using the nanofiber membrane described in this invention have high emulsification oil-water separation efficiency and high tensile strength, thereby achieving high-throughput, ultra-stable, long-term separation of emulsified oil-water mixtures.

[0135] according to Figure 1 and Figure 2It can be seen that the polytetrafluoroethylene nanofibers and polyimide nanofibers in the prepared nanofiber membrane are intertwined to form oil-water dual channels.

[0136] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A nanofiber membrane, characterized in that, The nanofiber membrane is prepared by co-electrospinning and includes a first nanofiber and a second nanofiber entangled with each other, wherein the first nanofiber is polytetrafluoroethylene and the second nanofiber is polyimide.

2. The nanofiber membrane of claim 1, wherein, The nanofiber membrane has a pore size of 1-10 μm and a porosity of 85%-95%.

3. The nanofiber membrane according to claim 1 or 2, characterized in that, The mass ratio of the first nanofiber to the second nanofiber is (1.5-4):

1.

4. The nanofiber membrane according to any one of claims 1-3, wherein, The diameter of the first nanofiber is 400-750 nm; And / or, the diameter of the second nanofiber is 50-310 nm.

5. A method for producing a nanofiber membrane, characterized by, The method includes the following steps: (1) Mix 4,4-diaminodiphenyl ether solution and pyromellitic dianhydride and carry out polycondensation reaction to obtain polyamic acid solution; (2) Mix the polyvinyl alcohol solution and the polytetrafluoroethylene dispersion to obtain a mixed solution; (3) Electrospinning the mixed solution and the polyamic acid solution together; (4) The product obtained in step (3) is subjected to thermal imidization reaction and sintering.

6. The method of claim 5, wherein, In step (1), the solvent of the 4,4-diaminodiphenyl ether solution is N,N-dimethylformamide; Preferably, the concentration of the 4,4-diaminodiphenyl ether solution is 2-10 wt%.

7. The method according to claim 5 or 6, characterized in that, In step (1), the mass ratio of the amount of 4,4-diaminodiphenyl ether to the amount of pyromellitic dianhydride is 1:(0.8-1.2).

8. The method according to any one of claims 5-7, characterized in that, In step (1), the polycondensation reaction is carried out under a protective gas, and the conditions for the polycondensation reaction include: a temperature of 0-5°C and a time of 5-8h.

9. The method according to any one of claims 5-8, characterized in that, In step (2), the concentration of the polyvinyl alcohol solution is 8-12 wt%. And / or, the concentration of the polytetrafluoroethylene dispersion is 55-65 wt%.

10. The method according to any one of claims 5-9, characterized in that, The mass ratio of the polyvinyl alcohol solution to the polytetrafluoroethylene dispersion is 1:(1-3).

11. The method according to any one of claims 5-10, characterized in that, In step (2), the mixing conditions include a temperature of 20-30°C and a time of 20-28h.

12. The method according to any one of claims 5-11, characterized in that, The specific process of step (3) includes fixing the mixed solution and the polyamic acid solution on both sides of the electrostatic spinning receiving roller.

13. The method according to any one of claims 5-12, characterized in that, The method further includes drying the product obtained in step (3) before carrying out the thermal imidization reaction; Preferably, the drying conditions include a temperature of 70-90°C and a time of 10-16 hours.

14. The method according to any one of claims 5-13, characterized in that, In step (4), the thermal imidization reaction process specifically includes: first heating to 95-105℃, reacting at 95-105℃ for 20-40 min, then heating to 195-205℃, reacting at 195-205℃ for 20-40 min, and finally heating to 295-305℃, reacting at 295-305℃ for 20-40 min.

15. The method according to any one of claims 5-14, characterized in that, In step (4), the sintering conditions include a temperature of 350-400℃ and a time of 4-8h.

16. A nanofiber membrane prepared by the method according to any one of claims 5-15.

17. The application of the nanofiber membrane according to any one of claims 1-4 and 16 in emulsified oil-water separation.

Images