Ultrahigh hydrophilic membrane for efficiently and stably separating oil-in-water emulsion

Abstract

A membrane technology based on a wettability material has the problem of membrane pollution and cannot efficiently and stably separate and purify oil-containing wastewater, so that a preparation method of a hydrophilic membrane with excellent hydrophilicity and an open pore channel is urgently needed. The invention discloses an ultrahigh hydrophilic membrane for efficiently and stably separating an oil-in-water emulsion, which is characterized in that magnetic nanoparticles (Fe3O4 MNPs) are wrapped in membrane fibers through electrostatic spinning and an in-situ growth method, and a hydrophilic polyaniline rough micro-nanosphere structure grows on the surface of the membrane fibers. Under the action of a magnetic field, the magnetic particles obtain magnetism, the generated magnetic interaction force pulls the nanofiber to optimize the membrane structure, and hydrophilic groups are further exposed while membrane holes are supported. The flux of the prepared three-dimensional hydrophilic membrane for separating n-hexane-in-water emulsion under the action of a 0.2 T magnetic field is up to 8957.9 Lm <-2 > h <-1 >, and the efficiency is up to 99.87%. The membrane shows optimal separation performance in short-term and long-term cycle tests, and is expected to be applied to actual oily wastewater purification scenes.

Description

Technical Field

[0001] The present invention belongs to the fields of water treatment, membrane technology and oil-water separation technology, and specifically relates to an ultra-high hydrophilic membrane that can efficiently and stably separate oil-in-water emulsions, and an ultra-high hydrophilic membrane with an optimized magnetically responsive three-dimensional structure that is ultimately obtained through emulsion separation performance testing. Technical Background

[0002] Agricultural water accounts for more than 60% of my country's total water consumption, and water shortage has become a serious problem. Using purified industrial wastewater and domestic sewage for agricultural irrigation is a feasible path. However, hydrocarbon organic matter in wastewater inhibits gas exchange in plant roots, posing a challenge to ecological security. Membrane technology based on wettability materials can effectively alleviate this problem, but most membranes are easily clogged by oil adhesion. Researchers have drawn inspiration from nature to create functional materials with special wettability to alleviate membrane fouling and ensure stable permeation flux. For example, materials such as zeolite imidazolate framework-L (ZIF-L), ZnO, Cu(OH)2 and acidic metal complexes are coated on the grid to construct a superhydrophilic-underwater superoleophobic surface. However, these hydrophilic surfaces constructed from one-dimensional and two-dimensional perspectives are often subjected to inevitable liquid washing and scratching / friction, resulting in the gradual damage of the superoleophobicity of the interface. Therefore, there is an urgent need for a preparation method for a superhydrophilic membrane with a stable rough structure for the efficient removal of emulsified oil in water.

[0003] In recent years, electrospinning has been recognized as a relatively new and versatile technology for fabricating complex or porous membranes. Its composition and structure are controllable. In particular, electrospun fiber membranes composed of continuously entangled fibers typically exhibit a three-dimensional (3D) porous network structure, which, along with the chemical composition, influences surface wettability. Therefore, it is expected that a 3D hydrophilic structure with fully exposed hydrophilic groups can be constructed, effectively separating oil and water. However, under long-term separation and filtration pressure, the membrane structure becomes compacted, the exposure of the hydrophilic groups decreases, and the collapsed membrane pore structure overlaps, resulting in reduced flux. Studies have shown that magnetic interaction forces derived from magnetic response can induce structural changes in materials. Manjua et al. used the mutual repulsion and attraction of superparamagnetic iron oxide nanoparticles in a magnetic field to induce macroscopic contraction and expansion of hydrogels. However, the changes in magnetically responsive materials are mostly surface morphology, and few studies have reported on the use of magnetic particles blended with nanofibers to modify membrane pore structure through intrafiber interactions.

[0004] In this work, we report a method for preparing a hydrophilic film with optimized three-dimensional structure on a PVDF-based membrane by a simple electrospinning method and in-situ growth of polyaniline (PANI). Polyethylene oxide (PEO) was selected as the precursor, and ferroferric oxide magnetic nanoparticles were used as the magnetic responsive material. Under specific conditions, aniline-induced micro-nanospheres gave the membrane fibers a three-dimensional rough superhydrophilic structure. At the same time, the addition of inorganic particles such as ferroferric oxide nanoparticles can enhance the rigidity of the membrane. The coercive force imparts a magnetic retention ability that enables the membrane to optimize the pore structure under the action of a magnetic field, further exposing the hydrophilic rough structure. The prepared superhydrophilic membrane has stable underwater superoleophobic properties and can separate various oil-in-water emulsions. Based on this, a simple continuous oil-water separation device was designed to test the flux and separation efficiency of multiple cycles of separation of small-sized oil-in-water emulsions, evaluate its anti-pollution and long-term separation capabilities, and provide new ideas for the efficient and stable removal of pollutant oil phases in water. Summary of the Invention

[0005] The present invention addresses the problems of insufficient membrane hydrophilicity and reduced flux and efficiency in long-term separation of oily wastewater. By constructing an ultra-high hydrophilic membrane with a unique three-dimensional rough structure, the hydrophilicity can be improved while optimizing the membrane structure under magnetic response, achieving efficient and stable oil-water separation flux and separation efficiency, and clarifying the mechanism of its excellent separation performance.

[0006] The present invention specifically achieves its purpose through the following technical solutions:

[0007] (1) Preparation of PVDF-based membranes that can provide growth sites by electrospinning and water etching

[0008] 10-15 wt% PVDF powder and 0-4 wt% PEO powder were weighed and added to 15 mL of DMF. The mixture was stirred in a 50°C waterbath until completely dissolved. The solution was removed and cooled to 40°C. Then, 3-5 wt% 200 nm Fe3O4 nanoparticles were added. The mixture was mechanically stirred continuously until a uniform, stable black solution was formed. The mixture was sealed during stirring. The solution was degassed in a 60°C vacuum drying oven for 1 hour. The spinning solution was directly electrospun using an electrospinning apparatus to produce a PVDF-PEO membrane. The spinning solution was loaded into a 10 mL syringe, attached to a syringe pump, and the electrospinning machine was turned on. The electrospinning parameters were: a feed rate of 1-2 mL / h, a 20G needle, a distance between the needle and the collector of 24-30 cm, a DC power supply voltage of 16-18 kV, a collector drum speed of 140 rpm, and aluminum foil collection. The relative humidity and temperature of the electrospinning environment were controlled at 45 ± 5% and 30 ± 5°C, respectively, for 6–8 hours. After spinning, the PVDF-PEO membrane was removed and dried in a vacuum drying oven at 25°C for 24 hours to allow the residual DMF solvent to evaporate.

[0009] (2) Preparation of ultra-high hydrophilic membranes by in situ growth method

[0010] Polyaniline-modified nanofibers were prepared using a chemical oxidative polymerization method. The prepared PVDF substrate was immersed in 100 mL of a 1.0-2.0 mol / L aniline-containing HCl solution (Solution A). A corresponding amount of ammonium persulfate (APS, ANI / APS molar ratio 1:1) was then added and dissolved in 100 mL of 1.0-2.0 mol / L hydrochloric acid (Solution B). Polymerization was allowed to proceed at 0°C for a specified time. After sufficient reaction, the fibers were washed several times with deionized water and vacuum-dried for 12 hours to obtain polyaniline-modified nanofibers.

[0011] (3) Characterization of oil-water separation performance of ultrahigh hydrophilic membranes with different aniline contents (400 μL, 600 μL, 800 μL) and different initiation times (Blue, Green, 3 h) under a 0.2 T magnetic field

[0012] Step 1:

[0013] Three surfactant-stabilized oil-in-water emulsions (n-hexane, 1,2-dichloroethane, and soybean oil) were prepared by mixing them with deionized water at a volume ratio of 1:99. 0.10 mg / mL of the surfactant Tween 80 was added. The emulsions were stirred at 1000 rpm for at least 4 hours to ensure stability in subsequent experiments. The resulting emulsions were stabilized for 24 hours.

[0014] Step 2:

[0015] Oil-water separation performance tests were conducted using a laboratory-built dead-end filtration device. First, the membrane material was placed between two transparent glass containers and secured with clamps. The prepared oil-in-water emulsion was then quickly poured into the glass tube, maintaining a height of 10 cm. The membrane was then subjected to its own gravity and an applied magnetic field, allowing the entire oil-water separation experiment to proceed.

[0016] The permeation flux of oil-water separation is calculated by recording the volume, time, effective membrane area and pressure of the liquid column on the membrane for the emulsion to completely permeate through the membrane. The calculation formula is as follows:

[0017]

[0018] Where J is the permeation flux (L m -2 h -1 ), V is the volume of the emulsion that permeates the membrane (L), A is the effective area of ​​the membrane, Δ t is the filtration time (h).

[0019] The oil-water separation efficiency is evaluated by measuring the total organic carbon (TOC) content in the filtrate using a multi N / C3100 Total Organic Carbon Analyzer. The calculation formula is as follows:

[0020]

[0021] Wherein, η0 is the separation efficiency (%), C0 and Cp are the water content (ppm) in the oil before and after emulsion filtration, respectively.

[0022] Preferably, in step 1, the oil products are categorized by light oil, heavy oil, and viscous oil, with n-hexane selected for light oil, 1,2-dichloroethane selected for heavy oil, and soybean oil selected for viscous oil. When preparing the surfactant-containing oil-water emulsion, Tween 80 is selected as the surfactant to prepare the oil-in-water emulsion.

[0023] Compared with existing emulsion processing technologies, the ultra-high hydrophilic membrane proposed in the present invention has the following advantages: The present invention targets extremely small particle size and highly stable emulsions. Through simple electrospinning and in-situ growth methods, magnetic nanoparticles (Fe3O4 MNPs) are wrapped inside the membrane fibers, and hydrophilic polyaniline rough micro-nanosphere structures are grown on the surface. Under the action of a magnetic field, the magnetic particles acquire magnetism, and the resulting magnetic interaction force pulls the nanofibers to optimize the membrane structure, supporting the membrane pores while further exposing the hydrophilic groups. The prepared ultra-high hydrophilic membrane 600PANI-Green has a flux of up to 8957.9 Lm2 for separating n-hexane emulsions in water under a 0.2T magnetic field. -2 h -1 The membrane has demonstrated optimal separation performance in both short-term and long-term cycle tests, achieving an efficiency of 99.87%. It is expected to be used in practical oily wastewater purification scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Preparation flow chart of ultra-high hydrophilic membrane and schematic diagram of separation mechanism.

[0025] Figure 2 Oil-water separation permeation flux and separation efficiency of multiple types of small-sized emulsions using ultra-high hydrophilic membranes with different PANI contents and initiation times at magnetic field intensities of 0T and 0.2T.

[0026] Figure 3 Digital photos and optical microscope images of 600PANI-Green membrane before and after separation of different types of oil-in-water emulsions at 0T and 0.2T magnetic field strengths.

[0027] Figure 4 Short-term cyclic permeation flux of n-hexane-in-water emulsion treated by ultrahighly hydrophilic membranes with different PANI contents and initiation times under magnetic field strengths of 0 T (a, c) and 0.2 T (b, d).

[0028] Figure 5600 Permeation flux and separation efficiency of PANI-Green membrane for long-term circulation separation of n-hexane-in-water emulsion. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further described below with reference to the accompanying drawings, but the scope of protection claimed in the present invention is not limited thereto.

[0030] Example 1

[0031] like Figure 1 As shown, first, polyvinylidene fluoride (PVDF) and polyethylene oxide (PEO) are blended in the organic solvent N,N-dimethylformamide (DMF) and spun by electrospinning under certain experimental conditions to obtain a uniform PVDF-PEO membrane. The PEO in the membrane fiber is dissolved in water by water etching, thereby forming a PVDF-based membrane with multiple protrusions. The PVDF-based membrane is then placed in an HCl solution containing a certain concentration of aniline. An HCl solution containing the oxidant ammonium persulfate (APS) is added, mixed evenly, and reacted at 0°C. After a certain period of time, polyaniline grows in situ on the surface of the membrane fiber. The unique micro-nano spherical rough structure grown is composed of the hydrophilic polymer polyaniline. Its morphology is inspired by the surface structure of broccoli for its wettability and has a certain influence on the contact morphology of water droplets. Finally, the mechanism by which the membrane maintains high flux and high separation efficiency during long-term separation processes is attributed to the optimization of the membrane structure under the action of the magnetic field. The pore structure supported by the magnetic force not only exposes the hydrophilic groups more fully, but also increases the degree of openness of the pore channels, which is more conducive to liquid penetration.

[0032] Example 2

[0033] Figure 2 (a) shows the pure water permeation flux of each ultra-high hydrophilic membrane in the presence or absence of a magnetic field. Due to the hydrophilic groups of polyaniline grown on the membrane fiber surface, water is captured after contacting the membrane surface, wets the entire membrane, and then permeates through the three-dimensional network structure inside the membrane. The experimental results show that at a concentration of 600 μL aniline, the pure water flux of the 600 PANI-Green membrane reaches a maximum of 8000 L m -2 h -1 The flux of the Blue and 3h stages decreased to varying degrees. This corresponds to the wetting properties of each membrane, showing a consistent change pattern. At the same time, under the action of a vertical magnetic field with a magnetic field strength of 0.2T, all membranes showed a trend of increasing flux, but the degree of increase was significantly different. Among them, the best-performing 600PANI-Green membrane flux increased by 11000L m -2 h -1Analysis of the confocal microscopy results above shows that different membranes respond differently to magnetic fields due to their structural characteristics, and naturally, the degree of membrane structural optimization also varies, leading to different degrees of membrane pore openness. For pure water permeation, the hydrophilicity of the membrane surface and the pore channels are key factors. For hydrophilic separation membranes, the pure water flux is positively correlated with the degree of pore channel openness. This conclusion can be verified by the relationship between the pure water flux and the confocal microscopy results.

[0034] Figure 2 (bd) show the permeation flux and separation efficiency of n-hexane-in-water emulsion, soybean oil-in-water emulsion, and 1,2-dichloroethane-in-water emulsion, respectively, at magnetic field intensities of 0 T and 0.2 T, respectively, for ultra-highly hydrophilic membranes with varying PANI contents and initiation times. The 600PANI-Green membrane exhibits excellent magnetic responsiveness, significantly improving permeation flux, particularly when separating n-hexane-in-water emulsion, where the flux increased by 40.84%. The separation efficiency also increased from 95.24% to 99.87%. Similarly, the membrane also showed significant improvements in permeation flux with increasing magnetic field strength for separating soybean oil-in-water emulsions and 1,2-dichloroethane-in-water emulsions. This improvement is attributed in part to the optimized structure of the membrane fibers due to the interaction with magnetic particles, resulting in open pore channels and low water permeation resistance. Furthermore, the "tangent point" contact between the three-dimensional rough microsphere structure and the oil droplets reduces membrane fouling. The hydrophilic surface also exposes numerous amino groups, increasing contact with water and promoting the formation of a hydration layer. Ultra-highly hydrophilic membranes prepared with aniline concentrations of 400 μL and 800 μL exhibited similar flux trends to pure water when separating different oil-in-water emulsions, with both permeation flux and separation efficiency lower than those of the 600PANI-Green membrane. The 800PANI-3h membrane, which had the worst separation performance, exhibited excessively low flux when separating 1,2-dichloroethane-in-water emulsions, and showed little improvement in magnetic field performance. Even after magnetic field optimization, its separation efficiency was less than 90%, demonstrating poor magnetic responsiveness and separation properties. Therefore, compared to ultra-highly hydrophilic membranes prepared with other aniline concentrations and induction times, the 600PANI-Green membrane exhibited significant separation performance advantages.

[0035] Example 3

[0036] The separation effect of 600PANI-Green membrane on various oil-in-water emulsions under different magnetic field strengths was further studied, such as Figure 3As shown in the figure. From the digital photos, the feed emulsions are all milky white and opaque, with a large number of oil droplets dispersed in the water. After membrane separation, each filtrate becomes clear and transparent. However, when using a higher-resolution optical microscope to observe the distribution of droplets in the emulsions before and after membrane separation, it was found that in the absence of a magnetic field, a small number of oil droplets were still distributed in the filtrate after separation, which would lead to a decrease in separation efficiency. After adding a magnetic field, all types of water-in-oil emulsions had almost no oil droplets in the filtrate after separation, and the separation efficiency was higher than 98%. Among them, the water-in-hexane emulsion with the best separation effect exceeded 99%. This shows that the 600PANI-Green membrane can respond instantly to the magnetic field and show excellent separation performance with the magnetic field gradient.

[0037] Example 4

[0038] Considering the complex oil-water system in the actual environment, membrane materials with good stability and anti-fouling properties are crucial to ensure efficient and stable purification of oily wastewater. Figure 4 Figures show the short-term cyclic permeation flux of water and water-in-hexane solutions treated with ultra-highly hydrophilic membranes with varying PANI contents and initiation times at 0 and 0.2 T. The results show that, compared with membranes with other initiation stages at aniline concentrations of 400 μL, 800 μL, and 600 μL, the 600 PANI-Green membrane maintains a high permeation flux for water after 10 consecutive separation cycles without a magnetic field, a 6.12% decrease compared to the initial separation flux. However, under a magnetic field of 0.2 T, the permeation flux of pure water decreases by 3.87% after 10 separation cycles, a lesser decrease than under the conditions without a magnetic field. This experimental result demonstrates that optimizing membrane structure under magnetic field conditions can, to a certain extent, alleviate the problem of membrane pore overlap, reduce liquid permeation resistance, and maintain flux stability.

[0039] It is also surprising that when a magnetic field is applied, the 600PANI-Green membrane also maintains a high and stable flux and a high separation efficiency when separating n-hexane-in-water emulsion ( Figure 4 (d) and Figure 4 (b)). This is not only due to the membrane's optimized pore structure opening in response to magnetic fields, enabling excellent liquid permeation, but also to the hydrophilic roughness of the membrane fiber surface, which effectively forms a hydration layer and mitigates membrane fouling. Compared to other horizontal gradient membranes, the 600PANI-Green membrane responds faster to magnetic fields and exhibits greater permeation flux and stable cycling performance.

[0040] Example 5

[0041] Due to the strong hydrophilicity of the membrane surface under magnetic field stimulation, the three-dimensional hydrophilic 600PhNI-Green membrane has broad application prospects in the field of efficient and stable separation of oil and water. In order to verify this feature, we used water-in-n-hexane emulsion as a model oily wastewater to evaluate the continuous separation performance of 600PANI-Green. Using a laboratory-scale circulating filtration device, the changes in membrane flux and efficiency in 5 cycles were monitored. Figure 5 As shown in the figure, under the action of a 0.2T magnetic field, the membrane flux decreased by only 17.41% in the first cycle, and the separation efficiency remained above 99%, indicating excellent membrane separation performance. After sufficient ethanol rinsing, the membrane flux was effectively restored, and the initial flux decline in the second cycle increased slightly but was still less than 20%. Subsequent cycles showed similar cyclic stability, and the initial separation performance was basically restored in each cycle. The working mechanism of efficient and stable separation involves the increase in hydrophilicity of the membrane surface under magnetic field stimulation. This is due to the full exposure of the hydrophilic groups of polyaniline and the further optimization of the pore structure of the membrane under the action of the magnetic field. These results show that the 600PANI-Green membrane has excellent separation and purification performance for water-in-oil emulsion systems.

[0042] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions that fall within the scope of protection of the present invention are within the scope of protection of the present invention. It should be noted that improvements and modifications that can be made by a person skilled in the art without departing from the principles of the present invention are also considered to be within the scope of protection of the present invention.

[0043] In summary, the present invention provides an ultra-high hydrophilic membrane for the efficient and stable separation of oil-in-water emulsions. Oil-water separation experiments show that the ultra-high hydrophilic membrane has excellent permeation flux and separation efficiency for various types of oil-in-water emulsions, especially after applying a magnetic field, the flux of n-hexane-in-water emulsion reaches nearly 9000 L / min. -2 h -1 The separation efficiency is 99.87%, and the short-term cycle separation reduction is only 3.87%. The long-term cycle experiment of oil-water separation proves that the ultra-high hydrophilic membrane has stable cycle performance and is a new and effective strategy in the actual separation process of oil-water system.

Claims

1. An ultra-high hydrophilic membrane for efficient and stable separation of oil-in-water emulsions, characterized by: A rough morphology of hydrophilic polyaniline (PANI) micro-nanospheres is uniformly grown on the surface of a nanofiber membrane embedded with magnetic particles (MNPs), forming a three-dimensional network structure with high porosity. Under the action of a magnetic field, the hydrophilic groups can be effectively exposed. The hydrophilic micro-nanospheres quickly capture water droplets to form a hydration layer to prevent membrane fouling, while optimizing the membrane pore structure and improving the separation flux and efficiency. The nanofiber membrane is formed by stacking polyvinylidene fluoride (PVDF) and polyethylene oxide (PEO) after electrospinning; the magnetic particles are ferroferric oxide magnetic nanoparticles (Fe3O4MNPs); and the unique rough structure is formed by the in-situ growth and polymerization of aniline to form hydrophilic polyaniline micro-nanospheres.

2. The ultra-high hydrophilic membrane for efficiently and stably separating oil-in-water emulsions according to claim 1, characterized in that: The following steps are involved: S1, preparing a PVDF base membrane providing growth sites; S2, soak the PVDF base membrane prepared in step S1 into 100 mL of 1.0-2.0 mol / L aniline-containing hydrochloric acid (HCl) solution, and added initiator ammonium persulfate (APS, ANI / APS molar ratio 1:1) to prepare an ultra-high hydrophilic membrane with a unique three-dimensional rough structure.

3. The method for preparing an ultra-high hydrophilic membrane for efficiently and stably separating oil-in-water emulsions according to claim 2, characterized in that: The step S1 comprises weighing 10-15wt% PVDF powder and 0-4wt% PEO powder, adding the mixture to 15mL N,N-dimethylformamide (DMF), and stirring the mixture in a water bath at 50-70°C until the mixture is completely dissolved; taking out the solution and cooling it to 40°C, then adding 3-5wt% 200nm Fe3O4MNPs, and continuously mechanically stirring the mixture until a uniform and stable black solution is formed. The mixture is sealed during the stirring process and degassed in a vacuum drying oven at 60°C for 1h; electrospinning the spinning solution directly to obtain a PVDF-PEO membrane using an electrospinning device; placing the spinning solution into a 10mL syringe, fixing the syringe on a syringe pump, and starting the electrospinning machine; and electrospinning parameter conditions are as follows: an electrospinning feed rate of 1-2mL / h, a 20G needle, a distance between the needle and the collector of 24-30cm, and a DC power supply with a working voltage of 16-18kV. The electrospinning process was carried out under pressure, with the rotating speed of the collecting drum being 140 rpm and the aluminum foil being collected; the relative humidity and temperature of the electrospinning environment were controlled at 45 ± 5% and 30 ± 5°C, respectively, and the entire electrospinning time was 6-8 hours; after the spinning was completed, the electrospun membrane was removed and placed in a vacuum drying oven at 25°C for 24 hours to facilitate the volatilization of the residual DMF solvent; the PVDF-PEO membrane was immersed in a water bath at 60°C for 1 hour to dissolve the PEO in the fiber in water, and then placed in a vacuum drying oven at 30°C for 24 hours to obtain a PVDF base membrane; in the step S2, the prepared membrane was immersed in 100 mL of water. A 1.0-2.0 mol / L aniline-containing HCl solution was used as solution A, and then a corresponding amount of ammonium persulfate (APS, ANI / APS molar ratio of 1:1) was added and dissolved in 100 mL of 1.0-2.0 mol / L hydrochloric acid as solution B. The polymerization reaction was carried out at 0°C for a certain time. After sufficient reaction, it was washed with deionized water several times and vacuum dried for 12 hours to obtain an ultra-high hydrophilic membrane.

4. Use of the ultra-high hydrophilic membrane according to claim 3 in the efficient and stable separation of oil-in-water emulsions; characterized in that: According to the different properties of oils, three surfactant-stabilized oil-in-water emulsions were prepared, including n-hexane-in-water emulsion, 1,2-dichloroethane-in-water emulsion, and soybean oil-in-water emulsion. Specifically, the three oils were mixed with deionized water at a volume ratio of 1:99, and the surfactant tween was added. 80, stirred at a speed of 1000 rpm for more than 4 hours to ensure its stability in subsequent experiments, and the obtained emulsion was stabilized for 24 hours; single gravity, short-term, and long-term cyclic separation tests were carried out under the action of a magnetic field. The single gravity test was carried out using a laboratory-made dead-end filtration device. The membrane material was placed between two transparent glass containers and fixed with a clamp; the prepared water-in-oil emulsion was then quickly poured into the glass tube, and the emulsion height was always maintained at 10 cm; in the short-term cyclic experiment, 10 mL of water-in-hexane emulsion was quickly poured into the dead-end device, and the volume of the filtrate that permeated within 1 minute was measured; after the filtration was completed, the membrane was immediately rinsed with ethanol solution to remove contaminants on the membrane surface, and then the membrane was used to carry out the next cycle of oil-water separation experiment, and the cycle was repeated 10 times; In the long-term circulation experiment, a water-in-hexane emulsion was used as the contamination system, and the changes in the membrane permeation flux and separation efficiency with filtration time in each cycle were recorded; after the emulsion was filtered, the membrane was fully rinsed with ethanol solution before the next round of filtration.

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