Janus PVDF oil-water separation membrane and application thereof in oil-water separation

Abstract

The invention relates to the technical field of food industry, in particular to a Janus PVDF oil-water separation membrane and application thereof in oil-water separation. The invention provides an oil-water separation membrane. The oil-water separation membrane comprises asymmetric acylation modified zein and a base membrane. The asymmetric modified zein-based Janus PVDF membrane obtained by the invention is used as an oil-water separation membrane, has excellent reuse performance while ensuring excellent separation flux, and is a novel green and efficient oil-water separation membrane.

Description

Technical Field

[0001] The invention relates to the technical field of food industry, and in particular to a Janus PVDF oil-water separation membrane and application thereof in oil-water separation. Background Art

[0002] In the existing technology, membrane separation has important advantages in the treatment of oily wastewater, such as high efficiency in removing oil pollution, no secondary pollution, strong system stability, etc. Although traditional oil-water separation membranes are widely used in the food industry, the preparation and deposition materials of the membranes are polluting, the oil-water separation efficiency is low, and the number of uses is limited. Therefore, it is of great significance to develop green, pollution-free, high separation efficiency, and reusable oil-water separation membranes.

[0003] In recent years, Janus PVDF oil-water separation membrane is considered to be the most promising material for treating oily wastewater. The preparation of existing Janus membranes is mainly through the unilateral deposition of opposite wettability materials on a single wettability base membrane, but there are problems such as low separation flux, poor environmental friendliness of the deposited materials, and the inability to reuse the membranes. For example, document CN201210144571.3 discloses an oil-water separation mesh membrane with super hydrophobic properties, which is a chitosan-based polymer coating layer with a micron thickness coated on the mesh of a 100-400 mesh fabric mesh. The oil-water separation mesh membrane uses chitosan as the membrane deposition material, and has the characteristics of salt resistance, environmental friendliness, bioaffinity, low cost and fast speed. However, chitosan is a hydrophilic polymer, and the combination with the hydrophobic membrane is not strong enough, resulting in poor durability of the oil-water separation mesh membrane.

[0004] Therefore, how to provide an oil-water separation membrane with a simple preparation method, good anti-pollution properties and excellent oil-water separation effect, and can be reused multiple times, so as to solve the technical problems of the oil-water separation membrane preparation method in the prior art being complex, not environmentally friendly, and having poor durability, is a problem that technical personnel in this field urgently need to solve. Summary of the invention

[0005] The purpose of the present invention is to provide an asymmetrically modified zein protein particle, the preparation method of the protein particle is simple, the protein is close to a semi-modified state, has the best amphiphilicity, and can achieve the best stabilizing effect at the oil-water interface.

[0006] Another object of the present invention is to provide a method for preparing a novel Janus PVDF membrane. The oil-water separation membrane preparation method is simple, the process is environmentally friendly, has good anti-pollution properties and excellent oil-water separation effect, and can be reused multiple times to achieve effective separation of various complex oil-water mixtures, showing great application value in the separation application of oily wastewater.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The invention provides an oil-water separation membrane, comprising: asymmetrically acylated modified zein and a basement membrane.

[0009] Preferably, the base membrane is a Janus PVDF membrane;

[0010] Preferably, the acylation degree of the asymmetrically acylated zein is 4-10%.

[0011] Preferably, the method for preparing the asymmetrically acylated zein comprises the following steps:

[0012] (1) using molten paraffin as a dispersed phase and a zein solution as a continuous phase, adding a surfactant, and mixing to form an emulsion;

[0013] (2) adjusting the pH of the emulsion and adding an acylating agent to carry out an acylation reaction;

[0014] (3) After the reaction is completed, the solid part is collected and washed with water, the washing liquid is ultrafiltered, the retentate is collected, and the asymmetrically acylated zein is obtained after freeze-drying.

[0015] Preferably, the volume ratio of the molten paraffin to the zein solution in step (1) is 1:2-4;

[0016] Preferably, the surfactant is Tween-20;

[0017] Preferably, the concentration of the surfactant is 40-60 mg / L.

[0018] Preferably, the pH in step (2) is adjusted to 9.5 to 10.5;

[0019] Preferably, the acylating agent is succinic anhydride.

[0020] The present invention also provides a method for preparing the oil-water separation membrane, comprising the following steps:

[0021] 1) mixing the asymmetrically acylated zein with a glutaraldehyde solution to obtain an asymmetrically acylated zein solution;

[0022] 2) Dropping the asymmetrically acylated zein solution on the surface of the basement membrane and letting it stand.

[0023] Preferably, the concentration of the asymmetrically acylated zein solution is 6 to 12 mg / mL;

[0024] Preferably, the mass fraction of the glutaraldehyde solution is 1.5-2.5%.

[0025] Preferably, the standing time in step 2) is 10 to 18 hours.

[0026] Preferably, during the preparation of the oil-water separation membrane, the ambient temperature is maintained at 25-45°C.

[0027] The present invention also provides the use of the oil-water separation membrane or the oil-water separation membrane prepared by the preparation method of the oil-water separation membrane in oil-water separation. The oil-water separation membrane is used for separating oil-water mixtures or oil-water emulsions.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present invention provides a method for preparing a novel Janus PVDF oil-water separation membrane using asymmetric modified zein particles as deposition materials. The present invention constructs asymmetric modified zein particles by a Pickering emulsion method, and then uses an evaporation induction method to orient the modified protein particles, and achieves the construction of Janus oil-water separation by tightly adsorbing them in the pores of the PVDF membrane through hydrophobic interactions. The amphiphilic asymmetric modified zein is tightly adsorbed in the pores, providing a significant directional Laplace pressure difference for the liquid on both sides of the Janus membrane, so that it has an ultra-high oil-water separation flux at a low driving pressure, while showing good anti-pollution and excellent reusability. The oil-water separation membrane not only has an efficient oil-water separation effect, but also has the advantages of being green, pollution-free, long-lasting and durable, and has broad application prospects in the field of food industry.

[0030] The present invention uses asymmetric modified zein particles as the deposition material for the oil-water separation membrane for the first time. The prepared Janus PVDF oil-water separation membrane is green and pollution-free and has excellent separation efficiency. It has excellent reuse performance while ensuring excellent separation flux. It is a new type of green and efficient oil-water separation membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0032] Figure 1 The interfacial tension curves of asymmetrically modified zein with different acylation degrees; different Tween-20 concentrations (left); different amounts of succinic anhydride added (right).

[0033] Figure 2TEM images of zein; unmodified zein (left); asymmetrically modified zein (right).

[0034] Figure 3 The contact angles of the hydrophilic and hydrophobic sides of protein-based membranes with different acylation degrees change with time; different amounts of succinic anhydride added (left); different Tween-20 concentrations (middle); and the oil contact angle on the hydrophilic side (right).

[0035] Figure 4 The SEM image of the unmodified membrane (only the base membrane) (left); the SEM image of the asymmetrically modified zein base membrane (right).

[0036] Figure 5 are the contact angles of oil and water on the hydrophilic side (upper figure) and the hydrophobic side (lower figure) of the membrane.

[0037] Figure 6 The flux and oil retention of Janus PVDF membranes with different acylation degrees (left); the flux and oil retention of Janus PVDF membranes with different Tween-20 concentrations (right).

[0038] Figure 7 The flux and oil retention of Janus PVDF membrane at different protein concentrations (left); the flux and oil retention of Janus PVDF membrane at different temperatures (right).

[0039] Figure 8 The reusability test of Janus PVDF membrane. DETAILED DESCRIPTION

[0040] The invention provides an oil-water separation membrane, comprising: asymmetrically acylated modified zein and a basement membrane.

[0041] In the present invention, the base membrane is a Janus PVDF membrane;

[0042] In the present invention, the acylation degree of the asymmetrically acylated zein is 4-10%, preferably 5-9%, more preferably 6-8%, and more preferably 7%.

[0043] In the present invention, the method for preparing the asymmetrically acylated zein comprises the following steps:

[0044] (1) using molten paraffin as a dispersed phase and a zein solution as a continuous phase, adding a surfactant, and mixing to form an emulsion;

[0045] (2) adjusting the pH of the emulsion and adding an acylating agent to carry out an acylation reaction;

[0046] (3) After the reaction is completed, the solid part is collected and washed with water, the washing liquid is ultrafiltered, the retentate is collected, and the asymmetrically acylated zein is obtained after freeze-drying.

[0047] In the present invention, the volume ratio of the molten paraffin to the zein solution in step (1) is 1:2-4, preferably 1:3.

[0048] In the present invention, the surfactant is Tween-20;

[0049] In the present invention, the concentration of the surfactant is 40 to 60 mg / L, preferably 44 to 56 mg / L, more preferably 48 to 52 mg / L, and more preferably 50 mg / L.

[0050] In the present invention, the pH value of step (2) is adjusted to 9.5 to 10.5; preferably 9.7 to 10.3; more preferably 9.9 to 10.1; and more preferably 10.

[0051] In the present invention, the acylating agent is succinic anhydride.

[0052] The present invention also provides a method for preparing the oil-water separation membrane, comprising the following steps:

[0053] 1) mixing the asymmetrically acylated zein with a glutaraldehyde solution to obtain an asymmetrically acylated zein solution;

[0054] 2) Dropping the asymmetrically acylated zein solution on the surface of the basement membrane and letting it stand.

[0055] In the present invention, the concentration of the asymmetrically acylated zein solution is 6 to 12 mg / mL; preferably 7 to 11 mg / mL; more preferably 8 to 10 mg / mL; and more preferably 9 mg / mL.

[0056] In the present invention, the mass fraction of the glutaraldehyde solution is 1.5-2.5%; preferably 1.7-2.3%; more preferably 1.9-2.1%; and more preferably 2%.

[0057] In the present invention, the standing time in step 2) is 10 to 18 hours, preferably 11 to 17 hours, more preferably 12 to 16 hours, and more preferably 14 hours.

[0058] In the present invention, during the preparation of the water separation membrane, the ambient temperature is maintained at 25-45°C; preferably 30-40°C; more preferably 34-36°C; and more preferably 35°C.

[0059] The present invention also provides the use of the oil-water separation membrane or the oil-water separation membrane prepared by the preparation method of the oil-water separation membrane in oil-water separation. The oil-water separation membrane is used for separating oil-water mixtures or oil-water emulsions; preferably oil-water mixtures.

[0060] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0061] Example 1

[0062] A method for preparing an asymmetric modified zein-based Janus PVDF membrane comprises the following steps:

[0063] (1) Preparation of asymmetrically modified zein

[0064] 10 mL of 60 mg / mL zein (Sigma-Aldrich Corp; St. Louis, MO, USA) ethanol aqueous solution (ethanol concentration of 80%) was added dropwise into 50 mL of ultrapure water with a pH of 8.5 through a constant flow pump (10 r / min), and the ultrapure water was always kept in a stirring state (speed 900 rpm) and the pH was always kept at about 8.5. After the solution was dripped, stirring was continued for 30 minutes. Then, a rotary evaporator (45° C.) was used to remove the ethanol and part of the water in the solution, and then centrifuged (speed 1000 rpm, 10 minutes) to remove the protein particles with larger particle size, and the zein antisolvent particles with a concentration of 2% were obtained.

[0065] Heat the zein antisolvent particle solution at 60°C for 15 minutes. Pour in molten paraffin (paraffin: zein antisolvent particle solution = volume ratio 1:3), add Tween-20 with a final concentration of 55 mg / L, and then use a high-speed disperser to disperse at 20,000 rpm for 3 minutes, then immerse in an ice-water mixture and cool rapidly. Centrifuge to remove protein particles and aqueous solution not fixed on the paraffin surface, and then add an equal volume of ultrapure water with a pH of 8.5.

[0066] The overall pH of the mixture was adjusted to 10, and succinic anhydride with a mass fraction of 13% (relative to the amount of protein) was added in small amounts several times, and the pH of the solution was maintained at about 10 with 1M NaOH. After the pH no longer showed a downward trend, the reaction was completed, and the upper layer of paraffin was taken by centrifugation at 3000rpm for 10min, and an appropriate amount of ultrapure water was added to rinse the surface of the paraffin. The solid paraffin in the solution was initially filtered out using a Buchner funnel, and then filtered twice using a water-based microporous filter membrane with a pore size of 0.8μm. Finally, the asymmetric modified zein particles were obtained by freeze drying at -72℃ for 48h.

[0067] (2) Preparation of asymmetric modified zein-based Janus PVDF membrane

[0068] First, a 2% glutaraldehyde solution was prepared, and the asymmetrically modified zein (to a final concentration of 10 mg / mL) was dissolved in the solution, and vortexed and ultrasonicated until the protein was completely dissolved (no suspended matter in the solution). Then, under constant temperature (30°C) and constant humidity conditions, 0.4 mL of the protein solution was dropped on the surface of a PVDF membrane (regular hemispherical shape, 50 mm in diameter, 0.45 μm in pore size), and left overnight for 12 hours.

[0069] Experimental Example 1 Preparation of asymmetric zein-based films with different acylation degrees

[0070] ① Preparation of asymmetrically modified zein with different acylation degrees

[0071] The other methods are the same as in Example 1, except that the final concentrations of Tween-20 in step (1) are set to 45 mg / L, 50 mg / L, 55 mg / L, and 60 mg / L, respectively.

[0072] ② Preparation of asymmetrically modified zein with different amounts of succinic anhydride added

[0073] The other methods are the same as those of Example 1, except that the mass fractions of succinic anhydride in step (1) are set to 12%, 12.5%, 13%, 13.5%, and 14%, respectively.

[0074] The dynamic interfacial tension of the asymmetric modified zein with different Tween-20 concentrations and different succinic anhydride additions prepared in this example was detected and analyzed. The asymmetric modified zein was fully dissolved in ultrapure water at a mass fraction of 0.5% (w / v), and the interfacial tension value of the protein droplet was measured in real time by the hanging drop method (the volume of the protein solution was 10 μL). The lower the oil-water interfacial tension value, the stronger the stability of the particles to the oil-water interface and the better the amphiphilic properties.

[0075] Asymmetric modified zein was prepared using the Tween-20 concentration and succinic anhydride addition amount corresponding to the protein with the best amphiphilic properties in the above results as conditions, the modified protein particles were fully dissolved in water, positively charged polystyrene microspheres were slowly added while stirring, and stirring was continued for 30 minutes to allow the microspheres to fully combine with the hydrophilic groups on the surface of the asymmetric modified particles. The mixture was then dried on a copper grid and placed in a transmission electron microscope (TEM) for photography.

[0076] The dynamic interfacial tension curves of asymmetrically modified zein with different Tween-20 concentrations in this example are shown in Figure 2. Figure 1As shown in the left figure, the interfacial tension of the protein particles gradually decreases with the increase of Tween-20 concentration, reaching the lowest point at a concentration of 55 mg / L. Continuing to increase the concentration will cause the particle interfacial tension to increase, even exceeding the interfacial tension of the unmodified zein antisolvent particles. This can be attributed to the fact that with the increase of Tween-20 concentration, the hydrophilic region of the protein expands and stabilizes at the oil-water interface. When the concentration is too high, the hydrophilic region in the water phase dominates, reducing the stability of the oil-water interface. This shows that the asymmetric modified zein has the best amphiphilic properties under the condition of 55 mg / L Tween-20 concentration.

[0077] The dynamic interfacial tension curves of asymmetrically modified zein with different amounts of succinic anhydride added in this example are shown in FIG. Figure 1 As shown in the figure on the right, the interfacial tension of the protein particles decreases with the increase of the amount of succinic anhydride, reaching a minimum value at an addition of 13%. Beyond this point, further increase of succinic anhydride will lead to higher interfacial tension. This may be due to the fact that the excessive hydrophilic groups on the surface of the protein interact more strongly with water than with the hydrophobic groups of the oil, thereby reducing the stability of the oil-water interface. This shows that the amphiphilic properties of asymmetrically modified zein are best when 13% succinic anhydride is added.

[0078] In this example, asymmetric modified zein was prepared under the conditions of 55 mg / L Tween-20 concentration and 13% succinic anhydride addition. The modification of the hydrophilic groups on the surface of zein was observed as follows: Figure 2 As shown, there is no polystyrene microsphere adsorption on the surface of unmodified zein ( Figure 2 Left), the surface of asymmetrically modified zein particles shows a state of local adsorption of microspheres ( Figure 2 Right), demonstrating the successful local modification of zein antisolvent particles.

[0079] In summary, the asymmetric modified zein prepared at a Tween-20 concentration of 55 mg / L and a succinic anhydride addition amount of 13% has the lowest dynamic interfacial tension, the protein is close to a semi-modified state, has the best amphiphilicity, and can achieve the best stabilization effect at the oil-water interface.

[0080] Experimental Example 2 Preparation of asymmetrically modified zein-based films with different acylation degrees

[0081] ① Preparation of asymmetrically modified zein-based membranes with different Tween-20 concentrations

[0082] The other methods are the same as in Example 1, except that the final concentrations of Tween-20 in step (1) are set to 50 mg / L, 55 mg / L, and 60 mg / L, respectively.

[0083] ② Preparation of asymmetrically modified zein-based membranes with different amounts of succinic anhydride added

[0084] The other methods are the same as those of Example 1, except that the mass fractions of succinic anhydride in step (1) are set to 12%, 13%, and 14%, respectively.

[0085] The hydrophilicity and hydrophobicity on both sides of the asymmetric modified zein-based membranes prepared in this example with different Tween-20 concentrations and succinic anhydride addition amounts were measured and analyzed. The hydrophilicity and hydrophobicity on both sides of the membrane were measured by a contact angle meter (SDC-100S) using the hanging drop method (the droplet volume was set to 5 μL) and the droplet collapse speed was characterized based on the change in the droplet contact angle at different times. A fast collapse speed indicates that the water droplet can penetrate the membrane at a faster speed.

[0086] An asymmetric modified zein-based membrane was prepared using the Tween-20 concentration and succinic anhydride addition amount corresponding to the membrane with the fastest droplet collapse rate in the above results. The membrane's surface morphology and hydrophilicity were characterized using a field emission scanning electron microscope (SEM) and a contact angle meter.

[0087] The collapse speed of the water droplet on the hydrophobic side of the asymmetrically modified zein-based membrane with different acylation degrees and the change of the contact angle of the oil droplet on the hydrophilic side with time are shown in the following figure. Figure 3 As shown in the figure, on the hydrophobic side of the membrane modified with protein particles with different amounts of succinic anhydride added, the water droplets collapsed to varying degrees around 30 seconds ( Figure 3 Left), and the collapse effect was most significant when the acylation degree was 8.7%; on the hydrophobic side of the membrane modified with protein particles at different Tween-20 concentrations, the water droplets collapsed to varying degrees around 40s ( Figure 3 The collapse effect was most significant when the Tween-20 concentration was 55 mg / L; Figure 3 As shown in the right figure, the oil contact angle of the hydrophilic side of the asymmetric modified zein-based membrane remained stable within 60 seconds without collapse, indicating that the hydrophilic layer of the membrane can effectively block the penetration of oil droplets. It can be seen that when the acylation degree of asymmetric modified zein is 8.7% and the Tween-20 concentration is 55 mg / L, the droplet collapse speed is the fastest, indicating that the membrane prepared under this condition has the fastest unidirectional liquid guide speed and has a good interception effect on oil droplets.

[0088] In this embodiment, the asymmetric modified zein modified PVDF membrane was prepared with an acylation degree of 8.7% and a Tween-20 concentration of 55 mg / L. The membrane morphology was observed as follows: Figure 4 As shown in the left figure and the right figure of 4, the SEM images show that the inner wall of the native PVDF pore is smooth; after protein modification, obvious granular protrusions are observed in the pore, which provides preliminary evidence for the successful incorporation of asymmetrically modified zein into the PVDF pore.

[0089] In this embodiment, the PVDF membrane is modified with an asymmetric modified zein with an acylation degree of 8.7% and a Tween-20 concentration of 55 mg / L. The hydrophilic and hydrophobic properties of the asymmetric modified zein-based PVDF membrane are as follows: Figure 5 As shown in Figure 2, the contact angle of the protein-modified side is 55.257°, ​​and the contact angle of the non-protein-modified side is 122.387°, indicating that one side of the membrane is hydrophilic and the other side is hydrophobic. Figure 4 The corresponding conclusions were quantitatively verified.

[0090] In summary, the asymmetric modified zein prepared at a Tween-20 concentration of 55 mg / L and a protein acylation degree of 8.7% was successfully modified in the pores to prepare a Janus PVDF membrane with asymmetric wettability.

[0091] Experimental Example 3 Application of asymmetric modified zein-based membrane in oil-water separation under different conditions

[0092] (1) Preparation of asymmetric modified zein-based Janus PVDF membranes under different conditions

[0093] ① Preparation of Janus PVDF membranes with different acylation degrees

[0094] The other methods are the same as those in Example 1, except that a 2% glutaraldehyde solution is prepared, and asymmetric modified zein (protein concentration of 10 mg / mL) prepared under different acylation degrees (4.1%, 5.0%, 8.4%, 8.7%) is dissolved in the solution, and vortexed and ultrasonicated until the protein is completely dissolved. Then, under constant temperature (30° C.) and constant humidity conditions, 0.4 mL of the protein solution is dropped on the surface of the PVDF membrane and left to stand overnight for 12 hours.

[0095] ② Preparation of Janus PVDF membrane with different Tween-20 concentrations

[0096] The other methods are the same as in Example 1, except that a 2% glutaraldehyde solution is prepared, and the asymmetric modified zein (protein concentration is 10 mg / mL) prepared under different Tween-20 concentrations (40 mg / L, 45 mg / L, 50 mg / L, 55 mg / L, 60 mg / L) is dissolved in the solution, and vortexed and ultrasonicated until the protein is completely dissolved. Then, under constant temperature (30°C) and constant humidity conditions, 0.4 mL of the protein solution is dropped on the surface of the PVDF membrane and left to stand overnight for 12 hours.

[0097] ③ Preparation of Janus PVDF membranes with different protein concentrations

[0098] The other methods are the same as in Example 1, except that a 2% glutaraldehyde solution is prepared, and asymmetric modified zein with different protein concentrations (6 mg / L, 7 mg / L, 8 mg / L, 9 mg / L, 10 mg / L, 11 mg / L) is dissolved in the solution, and vortexed and ultrasonicated until the protein is completely dissolved. Then, under constant temperature (30°C) and constant humidity conditions, 0.4 mL of the protein solution is dropped on the surface of the PVDF membrane and left to stand overnight for 12 hours.

[0099] ④ Preparation of Janus PVDF membranes at different temperatures

[0100] The other methods were the same as in Example 1, except that a 2% mass fraction glutaraldehyde solution was prepared, asymmetric modified zein (10 mg / mL) was dissolved in the solution, and vortexed and ultrasonicated until the protein was completely dissolved. Then, under different ambient temperature conditions (25°C, 35°C, 45°C), 0.4 mL of the protein solution was dropped on the surface of the PVDF membrane and left to stand overnight for 12 hours.

[0101] (2) Application of Janus PVDF membranes in oil-water separation under different conditions

[0102] 2μL ultrapure water and 5μL soybean oil were dripped into the hydrophobic side of the Janus PVDF membrane under different conditions, and the contact angle values ​​were recorded every 5s. The hydrophilicity and hydrophobicity on both sides of the membrane were measured by the contact angle meter using the hanging drop method. The soybean oil was dyed with Nile red and mixed with water containing 20mg / L Tween-80 at a ratio of 1:50. The mixed solution was then dispersed at high speed (20000rpm, 3min) to obtain a stable water-in-oil emulsion. The emulsion was separated using a membrane and a sand core suction pump (0.4bar), and the completion time of the corresponding volume of oil-water separation was recorded.

[0103] The calculation formula of oil-water separation flux (J) is as follows:

[0104] (1)

[0105] △V is the volume of filtered oil-in-water emulsion; S is the effective filtration area of ​​the membrane; t is the oil-water separation time; P is the transmembrane pressure.

[0106] The absorbance value at a wavelength of 580nm before and after the separation of the water-in-oil emulsion was measured by an ultraviolet spectrophotometer to calculate the oil-water separation efficiency of the membrane. The calculation formula is as follows:

[0107] (2)

[0108] C0 is the absorbance value before separation of the oil-in-water emulsion; C is the absorbance value after separation of the oil-in-water emulsion; R is the oil-water separation efficiency

[0109] The oil-water separation performance of the asymmetric modified zein-based membrane with different acylation degrees and Tween-20 concentrations in this embodiment is shown in FIG. Figure 6 As shown in Figure 2, when the acylation degree was 8.4% and the Tween-20 concentration was 55 mg / L, the membrane achieved a maximum separation flux of 20524.47 Lm -2 h -1 bar -1 , with a separation efficiency of 97.91%. This can be attributed to the optimal amphiphilicity of the modified zein under these conditions, which enables it to have strong hydrophilicity while maintaining tight binding to the PVDF membrane.

[0110] Specifically, the hydrophobic side of the modified zein interacts with the PVDF membrane surface through hydrophobic interactions, while the hydrophilic side generates capillary forces in the pores, promoting the efficient separation of oil-water emulsions. Further increases in Tween-20 concentration and succinic anhydride addition led to a significant decrease in the oil-water separation performance of the membrane. This may be due to the excessive hydrophilicity of the particle surface weakening its binding affinity with the membrane, resulting in the shedding of nanoparticles during the separation process. It shows that the PVDF membrane has the highest separation flux and the best separation efficiency when the degree of acylation is 8.4% and the Tween-20 concentration is 55 mg / L.

[0111] The oil-water separation performance of the asymmetric modified zein-based membrane prepared under different protein concentrations and temperature conditions in this embodiment is as follows: Figure 7 As shown. The membrane fluxes prepared with different protein concentrations are quite different ( Figure 7 Left figure), as the protein concentration increases, the membrane flux also increases, reaching a peak at a concentration of 10 mg / mL. This can be attributed to the enhanced capillary forces within the pores of the PVDF membrane at higher protein concentrations, resulting in improved separation efficiency. At a concentration of 10 mg / mL, the protein adsorption sites on the membrane surface are saturated, and further increasing the protein concentration will lead to pore blockage. In addition, excess protein may lead to incomplete dissolution, thereby destroying the evaporation-induced self-assembly process. Temperature is another key factor affecting evaporation-induced self-assembly, and the optimal temperature promotes the formation of ordered and stable self-assembled structures. Excessively high temperatures will cause the solvent to evaporate rapidly, leaving the solute molecules or nanoparticles with insufficient time for proper ordered self-assembly. The membrane flux effects under different temperature conditions are shown in Figure 2. Figure 7 As shown in the figure on the right, the highest membrane flux was achieved at 35°C. This shows that the separation flux of the PVDF membrane is the highest and the separation efficiency is the best when the protein concentration is 10 mg / mL and the temperature is 35°C.

[0112] (3) Durability evaluation of asymmetric modified zein-based Janus PVDF membrane

[0113] The durability of the membrane is a key factor in evaluating the performance of the oil-water separation membrane, so the durability of the Janus PVDF membrane prepared by the method of Example 1 was evaluated. First, the water-in-oil emulsion was prepared. The soybean oil was dyed with Nile red, and the dyed soybean oil was mixed with water containing 20 mg / L Tween80 at a ratio of 1:50. The mixed solution was then dispersed at high speed (20000 rpm, 3 min) to obtain a stable water-in-oil emulsion. The emulsion was separated using a membrane and a sand core suction pump (0.4 bar), and the completion time of the corresponding volume of oil-water separation was recorded. The above operation was repeated many times.

[0114] This example tests the reusability of the membrane through multiple oil-water separation experiments. Figure 8 As shown in the figure, the prepared Janus PVDF membrane can perform about 30 cycles of oil-water separation experiments while maintaining a good oil-water separation efficiency, and the separation flux is not significantly reduced. However, the existing Janus membrane can only achieve 10 to 20 oil-water separation experiments.

[0115] In summary, according to the preparation method of Example 1, the specific condition parameters are set to 8.4% protein acylation degree, 55 mg / L Tween-20 concentration, and 9 mg / L protein concentration. The prepared Janus PVDF oil-water separation membrane has a thermal conductivity of 20524.47 Lm at a temperature of 35°C. -2 h -1 bar -1 The ultra-high flux of Janus PVDF membrane is 97.91%. At the same time, the Janus PVDF membrane maintains long-term stability and the separation flux is always maintained at 20,000 Lm -2 h -1 bar -1 about.

[0116] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An oil-water separation membrane, characterized in that: include: Asymmetrically acylated zein and basal membrane.

2. The oil-water separation membrane according to claim 1, characterized in that: The base membrane is a Janus PVDF membrane; the acylation degree of the asymmetrically acylated zein is 4-10%.

3. The oil-water separation membrane according to claim 1, characterized in that: The method for preparing the asymmetrically acylated zein comprises the following steps: (1) using molten paraffin as a dispersed phase and a zein solution as a continuous phase, adding a surfactant, and mixing to form an emulsion; (2) adjusting the pH of the emulsion and adding an acylating agent to carry out an acylation reaction; (3) After the reaction is completed, the solid part is collected and washed with water, the washing liquid is ultrafiltered, the retentate is collected, and the asymmetrically acylated zein is obtained after freeze-drying.

4. The oil-water separation membrane according to claim 3, characterized in that: In step (1), the volume ratio of the molten paraffin to the zein solution is 1:2-4; the surfactant is Tween-20; and the concentration of the surfactant is 40-60 mg / L.

5. The oil-water separation membrane according to claim 3, characterized in that: In step (2), the pH is adjusted to 9.5-10.5; and the acylating agent is succinic anhydride.

6. The method for preparing an oil-water separation membrane according to any one of claims 1 to 5, characterized in that: The steps include: 1) mixing the asymmetrically acylated zein with a glutaraldehyde solution to obtain an asymmetrically acylated zein solution; 2) Dropping the asymmetrically acylated zein solution on the surface of the basement membrane and letting it stand.

7. The preparation method according to claim 6, characterized in that: Step 1) The concentration of the asymmetrically acylated zein solution is 6-12 mg / mL; the mass fraction of the glutaraldehyde solution is 1.5-2.5%.

8. The preparation method according to claim 6, characterized in that: The standing time in step 2) is 10 to 18 hours.

9. The preparation method according to claim 6, characterized in that: During the preparation of the oil-water separation membrane, the ambient temperature is maintained at 25-45°C.

10. Use of an oil-water separation membrane according to any one of claims 1 to 5 or an oil-water separation membrane prepared by the method for preparing an oil-water separation membrane according to any one of claims 6 to 9 in oil-water separation, characterized in that: The oil-water separation membrane is used for separation of oil-water mixture or oil-water emulsion.

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