Hydrogel hydrophilic modified gradient pore oil-water separation membrane as well as preparation method and application thereof

Abstract

The invention provides a hydrogel hydrophilic modified gradient pore oil-water separation membrane as well as a preparation method and application thereof, and belongs to the technical field of separation membranes. The hydrogel hydrophilic modified gradient pore oil-water separation membrane comprises a base membrane with a porous structure and a hydrogel layer coated on a porous structure framework of the base membrane, and a gradient pore structure with a small pore diameter on one side and a large pore diameter on the other side is formed. The hydrogel hydrophilic modified gradient pore oil-water separation membrane prepared by the method has a super-hydrophilic and super-oleophobic surface and has excellent anti-fouling performance and oil interception performance, the gradually expanded pore diameter can provide large oil-water separation flux, emulsified oil with surface activity can be effectively treated, and the oil-water separation membrane has the advantages of high oil-water separation efficiency, high oil-water separation efficiency and the like. And excellent pollution resistance is maintained under different environmental conditions, and long-term stable operation is realized.

Description

Technical Field

[0001] This invention relates to the field of separation membranes, and more particularly to a hydrogel-modified gradient pore oil-water separation membrane, its preparation method, and its application. Background Technology

[0002] Oily wastewater is one of the major environmental pollutants, posing a significant threat to ecological security and human health. Traditional treatment processes for oily wastewater typically involve various physical, chemical, and biological methods, but all suffer from low efficiency, high cost, poor stability, and difficulty in meeting discharge standards.

[0003] Membrane separation technology, as a green, low-consumption, and efficient separation technology, is widely used in the treatment of various wastewaters. However, when applied to oil-water separation, irreversible membrane fouling often occurs due to the adhesion of oil droplets, leading to a decline in membrane separation performance and a sharp reduction in membrane lifespan. Summary of the Invention

[0004] In view of this, in order to at least partially solve the aforementioned technical problems, the present invention provides a hydrogel-modified gradient pore oil-water separation membrane, its preparation method, and its application.

[0005] According to one embodiment of the present invention, a hydrogel-modified gradient pore oil-water separation membrane is provided, comprising: a base membrane having a porous structure, and a hydrogel layer covering the porous structure framework of the base membrane, forming a gradient pore structure with small pore size on one side and large pore size on the other side.

[0006] According to another aspect of the present invention, a method for preparing a hydrogel-modified gradient pore oil-water separation membrane is provided, comprising: immersing a base membrane having a porous structure in a hydrogel precursor solution containing a first initiator; removing excess solution from the surface of the base membrane, subjecting it to a prepolymerization reaction under ultraviolet light to obtain a prepolymerized base membrane; coating the surface of the prepolymerized base membrane with a hydrogel precursor solution containing a second initiator, subjecting it to a polymerization reaction again under ultraviolet light, and washing it to obtain a hydrogel-modified gradient pore oil-water separation membrane.

[0007] According to another embodiment of the present invention, an application of the above-mentioned hydrogel hydrophilic modified gradient pore oil-water separation membrane is provided, wherein the hydrogel hydrophilic modified gradient pore oil-water separation membrane is used to separate oil-water mixtures; the particle size of stable oil droplets in the oil-water mixture is 0.05~20μm.

[0008] Based on the above technical solution, the hydrogel hydrophilic modified gradient pore oil-water separation membrane, its preparation method, and its application provided by the present invention have at least one of the following beneficial effects:

[0009] (1) The hydrogel-modified gradient pore oil-water separation membrane of the present invention is obtained by hydrogel-modifying the base membrane, giving it superhydrophilic and superoleophobic properties as well as good anti-oil properties. It can effectively treat emulsified oil containing surface activity, reduce membrane fouling, and extend service life.

[0010] (2) The hydrogel hydrophilic modified gradient pore oil-water separation membrane provided by the present invention has a gradient pore structure with a small pore size on one side and a large pore size on the other side. The hydrogel modification on the water inlet side forms small pores, which are more hydrophilic and can better block oil droplets from passing through, thus giving the hydrogel hydrophilic modified gradient pore oil-water separation membrane excellent antifouling and oil interception performance; the pore size increases in gradient along the thickness direction, and the larger pore size on the water production side provides a larger oil-water separation flux.

[0011] (3) The hydrogel hydrophilic modified gradient pore oil-water separation membrane provided by the present invention is prepared by a combination of physical and chemical methods. It is simple to operate, has low energy consumption, can be adapted to large-scale production, and has good practicality. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the hydrogel-modified gradient pore oil-water separation membrane in an embodiment of the present invention;

[0013] Figure 2 This is a schematic flowchart of the method for preparing hydrogel-modified gradient pore oil-water separation membrane in an embodiment of the present invention;

[0014] Figure 3 This is a scanning electron microscope image of the hydrogel-modified gradient pore oil-water separation membrane in Example 1 of the present invention;

[0015] Figure 4 The images are optical microscope images of the emulsion oil and water before and after filtration by the hydrogel hydrophilic modified gradient pore oil-water separation membrane in Example 1 of the present invention. The left side is the emulsion oil and water before filtration, and the right side is the filtered product water.

[0016] Figure 5 The separation process curves are for hydrogel-modified gradient pore oil-water separation membranes.

[0017] [Explanation of Labels in the Attached Image]

[0018] 1-Gradient aperture;

[0019] 2-Hydrogel layer;

[0020] 3-The skeletal structure of the base membrane. Detailed Implementation

[0021] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the invention. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the invention for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0022] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "comprising" as used herein indicates the presence of features, steps, or operations, but does not exclude the presence or addition of one or more other features.

[0023] In realizing the concept of this invention, it was discovered that while modifying the oil-water separation membrane and loading a strongly hydrophilic functional layer on its surface can effectively enhance the membrane's anti-fouling performance, the introduction of the hydrophilic functional layer inevitably reduces the membrane's oil-water separation flux, making it difficult to balance anti-fouling performance and separation flux. Related technologies disclose an antigen-oil-contaminated oil-water separation membrane, its preparation method, and its applications. This oil-water separation membrane undergoes a Michael addition reaction between dopamine and hydrophilic carbon dots with amino groups on their surface, and is co-deposited in one step on the surface of a substrate mesh or substrate membrane. The membrane surface simultaneously possesses hydrophilic groups such as hydroxyl, carboxyl, and amino groups, enabling it to form an aqueous film under the action of water, thus exhibiting excellent antigen-oil contamination resistance. This technology utilizes the hydrophilicity and strong adhesion of dopamine combined with the special structure and morphology of carbon dots to construct a superhydrophilic / underwater superoleophobic coating with micro / nano structures on the substrate surface, effectively solving the problem of membrane performance degradation and shortened service life due to contamination during oil-water separation, and exhibiting good antigen-oil contamination resistance. However, this method involves a complex preparation process, requires a high-temperature and high-pressure environment, and also generates chemical waste liquid.

[0024] Another related technology discloses a super-resistant oil-water separation membrane, its preparation method, and its application. This oil-water separation membrane is constructed in situ with a hydrophilic polymer hydrogel layer and surface-grafted with hydrophilic polymer brushes, forming a hierarchical spatial molecular structure modification layer. The membrane surface simultaneously possesses a composite microstructure of hydrophilic polymer brushes and a hydrogel layer, enabling the formation of a dense hydration layer underwater, thus exhibiting super-resistant resistance to oil contamination. Utilizing the synergistic effect of the hydrophilic polymer brushes and the hydrogel layer, a super-hydrophilic / underwater super-oleophobic modification layer with a hierarchical molecular structure is constructed on the substrate surface. This membrane effectively inhibits oil droplet adhesion and filter cake formation, achieving a water flux of 1000 L·m³ when treating hydrocarbon oils and volatile oil emulsions from traditional Chinese medicine. -2 ·h -1 ·bar -1 Approximately [number missing]. However, this method also suffers from a complex preparation process and difficulty in practical application.

[0025] To address the shortcomings of related technologies, the present invention aims to provide a hydrogel-modified gradient pore oil-water separation membrane that combines excellent antifouling performance and high water flux, while also possessing the advantages of simple preparation method and high practicality.

[0026] Specifically, according to one embodiment of the present invention, a hydrogel-modified gradient pore oil-water separation membrane is provided, comprising: a base membrane having a porous structure, and a hydrogel layer covering the porous structure framework of the base membrane, forming a gradient pore structure with small pore size on one side and large pore size on the other side.

[0027] Figure 1 This is a schematic diagram of the hydrogel-modified gradient pore oil-water separation membrane in an embodiment of the present invention.

[0028] According to embodiments of the present invention, such as Figure 1 As shown, a porous base membrane is hydrophilically modified with hydrogel, resulting in a hydrogel layer 2 coating the outer side of the base membrane's framework structure 3. This creates a gradient pore structure 1 with small pores on one side and large pores on the other, giving it superhydrophilic and superoleophobic properties. Water in emulsified oil can pass through the membrane pores, while oil droplets are blocked, thus enabling the processing of difficult-to-separate emulsified oils. Furthermore, the hydrogel-modified gradient pore oil-water separation membrane retains the "dot-fiber" network structure of the base membrane. After hydrogel modification, it forms a structure with small pores on the inlet side and large pores on the product side, with the pore size gradually increasing from the inlet side to the product side. Both the inlet and product sides are superhydrophilic and superoleophobic surfaces, but the inlet side exhibits stronger hydrophilic and oleophobic properties, resulting in excellent antifouling and oil-blocking performance. The larger pore size on the product side provides a higher oil-water separation flux, improving oil-water separation efficiency. This is because smaller pore sizes make it harder for oil droplets to pass through the membrane pores, resulting in a higher oil rejection rate; larger pore sizes result in lower separation pressure, thus providing a greater separation flux. This invention utilizes the excellent physical structure of the porous base membrane (a "dot-fiber" network structure) combined with hydrophilic modification using chemical methods, enabling the hydrogel-modified gradient pore oil-water separation membrane to maintain high flux and excellent antifouling performance under different environmental conditions, and to operate stably for a long time.

[0029] According to embodiments of the present invention, the inlet-side pore size of the hydrogel-modified gradient pore oil-water separator is 10~500nm, for example, 10nm, 50nm, 100nm, 200nm, 300nm, 400nm, or 500nm; the product-side pore size is 20~1000nm, for example, 20nm, 100nm, 300nm, 500nm, 700nm, 900nm, or 1000nm.

[0030] Figure 2This is a schematic flowchart of the method for preparing hydrogel-modified gradient pore oil-water separation membrane in an embodiment of the present invention.

[0031] According to another aspect of the present invention, a method for preparing a hydrogel-modified gradient pore oil-water separation membrane is provided, such as... Figure 2 As shown, it includes steps S1-S3.

[0032] Step S1: Immerse the base membrane with a porous structure in a hydrogel precursor solution containing the first initiator.

[0033] Step S2: Remove excess solution from the surface of the base film and place it under ultraviolet light for prepolymerization reaction to obtain a prepolymerized base film.

[0034] Step S3: Coat the surface of the prepolymerized base membrane with a hydrogel precursor solution containing a second initiator, place it under ultraviolet light again for polymerization reaction, and after cleaning, obtain a hydrogel hydrophilic modified gradient pore oil-water separation membrane.

[0035] According to embodiments of the present invention, removing excess solution from the surface of the base membrane before the prepolymerization reaction can reduce the clogging of the base membrane pores by the hydrogel, thus avoiding affecting the oil-water separation effect. Prepolymerization allows the base membrane to be initially coated with hydrogel, becoming more hydrophilic, which facilitates the hydrogel's entry into the interior of the base membrane during subsequent polymerization reactions, achieving complete modification of both the interior and surface of the base membrane; it also makes the coated hydrogel less prone to detachment, resulting in better modification effects. The gradient pores 1 of the hydrogel hydrophilic modified gradient pore oil-water separation membrane are formed based on the characteristic of UV light attenuating from top to bottom during UV photopolymerization. The attenuation of UV light leads to a decrease in initiator activity, thus reducing the amount of hydrogel adhering and resulting in larger pore sizes. Gradient pores 1 give the membrane better antifouling and oil-blocking properties and higher oil-water separation flux. The preparation method of the present invention is carried out without the need for high temperature and high pressure conditions, is simple to operate, and has low energy consumption, possessing the potential for large-scale production.

[0036] According to embodiments of the present invention, in step S1, the base membrane includes, but is not limited to, any one of polytetrafluoroethylene (PTFE) membrane, polyvinylidene fluoride (PVDF) membrane, polypropylene (PP) membrane, polysulfone (PSF) membrane, polyethersulfone (PES) membrane, cellulose acetate (CA) membrane, ceramic (CM) membrane, and stainless steel (SS) membrane. PTFE membrane is preferred because it possesses excellent physical and chemical stability and is widely used, facilitating industrial application. Furthermore, PTFE membrane has a unique "dot-fiber" structure, i.e., a spiderweb-like microporous structure of nodes (dots) + microfibers (fibers), which facilitates the loading of the hydrogel network and enables the prepared hydrogel-modified gradient pore oil-water separation membrane to also possess a "dot-fiber" structure, achieving its functions of water permeability, oil blocking, and high-efficiency filtration.

[0037] According to an embodiment of the present invention, in step S1, the pore size of the base membrane is 0.05~2μm, for example, it can be 0.05μm, 0.1μm, 0.5μm, 0.8μm, 1μm, 1.2μm, 1.5μm, 1.8μm, or 2μm, preferably 0.05~0.2μm. As the pore size of the membrane gradually decreases, the flux also decreases, while the oil rejection rate increases. If the pore size is too large (greater than 2μm), the oil rejection rate of the membrane will decrease, and the flux will increase; if the pore size is too small (less than 0.05μm), the flux will be too small. A relatively balanced flux and oil rejection rate can be obtained when the pore size is 0.05~2μm.

[0038] According to an embodiment of the present invention, before step S1, the base film must first be cleaned, including nitrogen purging and water rinsing. This removes impurities adhering to the base film to avoid affecting the subsequent coating of the base film by the hydrogel.

[0039] According to an embodiment of the present invention, the base film is pretreated before being immersed in a hydrogel precursor solution containing a first initiator. The pretreatment involves wetting the base film with a 50%–100% (v / v) ethanol solution for 0.5–6 hours. Ethanol is a polar organic solvent that can dissolve oil and organic residues, and rapidly disperse particulate matter such as dust, thus removing contaminants from the base film surface and improving the uniformity of modification. More importantly, the base film itself is a hydrophobic material, and hydrophilic hydrogel precursors are difficult to spread on the surface and inside the base film. Ethanol, however, has good compatibility with the hydrogel precursor, making it easier for it to spread and penetrate the base film surface, thereby improving the modification efficiency.

[0040] According to an embodiment of the present invention, in step S1, the base film is immersed in the hydrogel precursor solution containing the first initiator for 10 to 120 minutes, for example, 10 minutes, 20 minutes, 30 minutes, 60 minutes, or 120 minutes. The purpose of step S1 is to allow the hydrogel precursor to fully wet the "dot-fiber" structure of the base film, making it more hydrophilic.

[0041] According to an embodiment of the present invention, in step S2, after the base membrane is immersed in a hydrogel precursor solution containing the first initiator, excess solution needs to be removed from the surface of the base membrane, including: gently rolling the surface of the base membrane with a silicone roller. This step is to remove components adsorbed on the membrane surface to prevent them from adhering to the base membrane surface during subsequent polymerization reactions, thus preventing membrane pore blockage and reduced separation flux.

[0042] According to embodiments of the present invention, in steps S1 and S3, the mass fraction of the first initiator or the second initiator in the hydrogel precursor solution is 0.05% to 5%, for example, 0.05%, 0.1%, 0.5%, 1%, or 5%. The first and second initiators are each independently selected from any 1 to 3 of the following: benzoyl peroxide, dicumyl peroxide, azobisisobutyronitrile, cyclohexyl peroxide, tert-butyl peroxide, tert-butylperoxy-2-ethylhexyl, propylaminoanthraquinone, benzoyl peroxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, or diethylbenzene peroxide. For example, benzoyl peroxide can be used alone as an initiator, or azobisisobutyronitrile, cyclohexyl peroxide, and tert-butyl peroxide can be used in combination. Using multiple initiators in combination can broaden the reaction temperature range, improve reaction stability, and increase the hydrogel polymerization strength. Furthermore, since the main function of prepolymerization is to make the base membrane more hydrophilic, facilitating the entry of hydrogel into the base membrane during the second polymerization step, and achieving complete modification of both the interior and surface of the base membrane, prepolymerization can use only one initiator, while the second polymerization step can use a combination of multiple initiators. This avoids hydrogel clogging of membrane pores and reducing separation flux during the prepolymerization reaction, while ensuring the polymerization strength of the second polymerization step and achieving complete modification of the base membrane.

[0043] According to an embodiment of the present invention, in steps S1 and S3, the temperature of the hydrogel precursor solution is 20~50℃, for example, 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, or 50℃. Setting the temperature to 20~50℃ provides moderate activity of the hydrogel precursor molecular chains, uniform cross-linking, and the formation of a continuous and stable gel modification layer.

[0044] According to an embodiment of the present invention, in steps S1 and S3, the mass fraction of the hydrogel precursor in the hydrogel precursor solution is 5% to 50%, for example, 5%, 10%, 20%, 40%, or 50%. A suitable concentration (5% to 50%) of hydrogel precursor solution can form a modified layer of uniform thickness, which covers the surface of the base film without affecting the flow of pores.

[0045] According to embodiments of the present invention, in steps S1 and S3, the hydrogel precursor comprises any one or more of acrylic acids, acrylamides, or vinyl alcohols. Various hydrogel precursors possess different properties, such as varying hydrophilicity, mechanical strength, rigidity, and flexibility. By selecting and compounding multiple hydrogel precursors, functional complementarity between different types of hydrogel precursors can be achieved, improving overall performance, regulating the structure of the hydrogel-modified layer, optimizing membrane flux and retention rate, and enhancing the bonding stability between the hydrogel-modified layer and the base membrane.

[0046] According to embodiments of the present invention, in steps S1 and S3, acrylic acid precursors include acrylic acid, methacrylic acid, and acrylates; acrylamide precursors include methacrylamide and methyl acrylate; and vinyl alcohol precursors are polyvinyl alcohols with a molecular weight of 20,000 to 200,000, for example, 20,000, 40,000, 80,000, 100,000, or 200,000. Acrylic acid and acrylamide hydrogel precursors are small molecules capable of polymerization, and any one or more can be selected for blending. Polyvinyl alcohol, however, is a macromolecular polymer that can undergo chemical crosslinking with other monomers through ultraviolet light irradiation. Therefore, when using a vinyl alcohol hydrogel precursor, it is necessary to blend it with acrylic acid or acrylamide precursors.

[0047] For example, the preparation method of the hydrogel precursor solution may include: sequentially adding deionized water, an initiator, methacrylic acid, methacrylamide, and a 10% (w / w) polyvinyl alcohol solution with a molecular weight of 20,000, mixing and stirring continuously for 24 hours, followed by sonication for 1 hour. The total mass fraction of the above components can be 20%, wherein the mass ratio of initiator:polyvinyl alcohol:methacrylic acid:methacrylamide is 1:70:600:2. It should be noted that the polyvinyl alcohol solution needs to be preheated in an 85°C water bath for 10 hours to ensure complete dissolution and form a homogeneous and stable 10% (w / w) polyvinyl alcohol mother liquor.

[0048] The effective amount of hydrogel components coated on the base membrane is adjusted by modifying the concentration of the hydrogel precursor solution, soaking time, and coating solution volume. This prevents excessive coating from clogging membrane pores and reducing membrane flux, or insufficient coating from resulting in incomplete coverage and reduced separation performance.

[0049] According to an embodiment of the present invention, in steps S2 and S3, the ultraviolet light wavelength is 320~400nm, for example, 320nm, 365nm, 395nm, or 400nm; the ultraviolet irradiation time is 10s~300s, for example, 10s, 20s, 30s, 40s, 60s, 120s, 180s, or 300s; and the ultraviolet irradiation intensity is 5~1000μW / cm². 2 For example, it can be 5 μW / cm 2 20 μW / cm 2 100μW / cm 2 500 μW / cm 2 1000 μW / cm 2 The membrane ambient temperature during ultraviolet irradiation is 20~50℃, for example, 20℃, 30℃, 40℃, or 50℃. Controlling the ultraviolet irradiation time, ultraviolet light intensity, and ambient temperature is to obtain a hydrogel coating with a suitable degree of cross-linking and achieve better oil-water separation performance.

[0050] According to an embodiment of the present invention, in step S3, the coating method is roller coating, which achieves coating by contacting and pressing the roller with the base film. This method has the advantages of good uniformity and high efficiency, and also makes it easy to control the coating thickness.

[0051] According to an embodiment of the present invention, in step S3, after the polymerization reaction is completed, the hydrogel hydrophilic modified gradient pore oil-water separation membrane is cleaned with deionized water. It can be soaked in deionized water for 1 to 24 hours, for example, 1 hour, 2 hours, 3 hours, 6 hours, 9 hours, 12 hours, 18 hours, or 24 hours.

[0052] According to another aspect of the present invention, an application of the above-mentioned hydrogel hydrophilic modified gradient pore oil-water separation membrane is provided. The hydrogel hydrophilic modified gradient pore oil-water separation membrane is used to separate oil-water mixtures. The particle size of the stable oil droplets in the oil-water mixture is 0.05~20μm, for example, it can be 0.05μm, 1μm, 5μm, 10μm, or 20μm.

[0053] According to embodiments of the present invention, the hydrogel-modified gradient pore oil-water separation membrane provided by the present invention has a superhydrophilic and superoleophobic surface, exhibiting excellent antifouling and oil-blocking properties. Furthermore, the pore size on the inlet side is small, gradually increasing towards the product water side; this gradually enlarging pore size provides a large oil-water separation flux. The hydrogel-modified gradient pore oil-water separation membrane possesses good physical and chemical stability, effectively treats emulsified oils containing surface-active substances, and maintains high flux, excellent antifouling properties, and long-term stable operation under various environmental conditions.

[0054] For example, the hydrogel-modified gradient pore oil-water separation membrane provided by the present invention can maintain stable and reliable oil-water separation performance after being treated with an acidic solution with a pH of 1, an alkaline solution with a pH of 13, and after being continuously rinsed for 30 minutes under 0.3 bar hydraulic conditions and ultrasonically treated in an ultrasonic cleaner for 30 minutes.

[0055] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0056] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0057] Example 1

[0058] (1) The PTFE membrane with a porous structure (pore size of 0.2 μm) was pre-wetted with 50% ethanol solution for 30 min.

[0059] (2) The base film obtained in step (1) is immersed in a hydrogel precursor solution containing azobisisobutyronitrile for 30 min. The mass fraction of azobisisobutyronitrile is 1%; the mass fraction of hydrogel precursor in the hydrogel precursor solution is 20%; the composition and mass ratio of the hydrogel precursor are polyvinyl alcohol: hydroxyethyl acrylate: N,N'-bis(acryloyl)urea = 50:500:2; the solution temperature is kept stable at 40℃.

[0060] (3) After removing excess solution from the surface, the film is subjected to a prepolymerization reaction under ultraviolet irradiation to obtain a prepolymerized base film. The ultraviolet irradiation time is 30 s, the ultraviolet wavelength is 365 nm, and the ultraviolet irradiation intensity is 100 μW / cm². 2 The ambient temperature during ultraviolet irradiation is 20℃.

[0061] (4) The prepolymerized base film is coated with a hydrogel precursor solution containing the second initiator and then subjected to UV irradiation for polymerization. The second initiator is azobisisobutyronitrile and cyclohexyl benzoyl peroxide (molar ratio 1.34:1), with a mass fraction of 1%. The hydrogel precursor solution contains 20% hydrogel precursor by mass, and the composition and mass ratio of the hydrogel precursor are polyvinyl alcohol: hydroxyethyl acrylate: N,N'-bis(acryloyl)urea = 50:500:2. The UV irradiation time is 30 s, the UV wavelength is 365 nm, and the UV irradiation intensity is 100 μW / cm². 2 The ambient temperature during ultraviolet irradiation is 20℃.

[0062] (5) Soak the base membrane obtained in step (4) in deionized water for 24 hours to obtain a hydrogel hydrophilic modified gradient pore oil-water separation membrane.

[0063] The microstructure of the hydrogel-modified gradient pore oil-water separation membrane was scanned using scanning electron microscopy, and its scanning electron micrograph was obtained, as shown in the figure. Figure 3 As shown.

[0064] Figure 3 This is a scanning electron microscope image of the hydrogel-modified gradient pore oil-water separation membrane in Example 1 of the present invention.

[0065] according to Figure 3 It can be seen that the hydrogel-modified gradient pore oil-water separation membrane provided by the present invention has a "dot-fiber" network structure with obvious hydrogel coating.

[0066] Example 2

[0067] The preparation method of Example 2 is the same as that of Example 1, except that the soaking time of the base film in step (1) is 60 min and the mass fraction of the hydrogel precursor in step (2) is 40%.

[0068] Example 3

[0069] The preparation method of Example 3 is the same as that of Example 1, except that the initiator in step (2) is benzoyl peroxide, the ultraviolet wavelength in step (3) is 395 nm, and the initiator in step (4) is benzoyl peroxide and cyclohexyl peroxide with a molar ratio of 0.91:1.

[0070] Example 4

[0071] The preparation method of Example 4 is the same as that of Example 1, except that the pore size of the PTFE membrane is adjusted to 0.1 μm in step (1).

[0072] Example 5

[0073] The preparation method of Example 5 is the same as that of Example 1, except that the pore size of the PTFE membrane is adjusted to 0.3 μm in step (1).

[0074] Example 6

[0075] The preparation method of Example 6 is the same as that of Example 1, except that the pore size of the PTFE membrane is adjusted to 0.4 μm in step (1).

[0076] Example 7

[0077] The preparation method of Example 7 is the same as that of Example 1, except that the pore size of the PTFE membrane is adjusted to 0.5 μm in step (1).

[0078] Example 8

[0079] The preparation method of Example 8 is the same as that of Example 1, except that the ultraviolet irradiation time in step (3) is adjusted to 10s.

[0080] Example 9

[0081] The preparation method of Example 9 is the same as that of Example 1, except that the ultraviolet irradiation time in step (3) is adjusted to 50s.

[0082] Example 10

[0083] The preparation method of Example 10 is the same as that of Example 1, except that the ultraviolet irradiation time in steps (3) and (4) is adjusted to 70s.

[0084] Example 11

[0085] The preparation method of Example 11 is the same as that of Example 1, except that the ultraviolet irradiation time in step (4) is adjusted to 10s.

[0086] Example 12

[0087] The preparation method of Example 12 is the same as that of Example 1, except that the ultraviolet irradiation time in step (4) is adjusted to 50s.

[0088] Example 13

[0089] The preparation method of Example 13 is the same as that of Example 1, except that the ultraviolet irradiation time in steps (3) and (4) is adjusted to 70s.

[0090] Example 14

[0091] The preparation method of Example 14 is the same as that of Example 1, except that the ultraviolet irradiation time in steps (3) and (4) is adjusted to 80s.

[0092] Example 15

[0093] The preparation method of Example 15 is the same as that of Example 1, except that the initiator in step (2) is changed to benzoyl peroxide.

[0094] Example 16

[0095] The preparation method of Example 16 is the same as that of Example 1, except that the initiator in step (4) is adjusted to benzoyl peroxide and phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide, with a molar ratio of 1.73:1.

[0096] Example 17

[0097] The preparation method of Example 17 is the same as that of Example 1, except that the initiator in step (2) is adjusted to dicumyl peroxide and azobisisobutyronitrile, with a molar ratio of 0.61:1.

[0098] Example 18

[0099] The preparation method of Example 18 is the same as that of Example 1, except that the initiator in step (4) is adjusted to dicumyl peroxide, azobisisobutyronitrile, and cyclohexyl benzoyl peroxide, with a molar ratio of 0.61:1:0.75.

[0100] Example 19

[0101] The preparation method of Example 19 is the same as that of Example 1, except that the mass fraction of the hydrogel precursor is 5% in steps (2) and (4).

[0102] Example 20

[0103] The preparation method of Example 20 is the same as that of Example 1, except that the mass fraction of the hydrogel precursor is 40% in steps (2) and (4).

[0104] Example 21

[0105] The preparation method of Example 21 is the same as that of Example 1, except that the mass fraction of the initiator in steps (2) and (4) is 0.5%.

[0106] Example 22

[0107] The preparation method of Example 22 is the same as that of Example 1, except that the mass fraction of the initiator is 5% in steps (2) and (4).

[0108] Comparative Example 1

[0109] The preparation method of Comparative Example 1 is the same as that of Example 1, except that the coating in step (4) is replaced by soaking.

[0110] Comparative Example 2

[0111] The preparation method of Comparative Example 2 is the same as that of Example 1, except that the soaking in step (2) is replaced by coating.

[0112] Comparative Example 3

[0113] The preparation method of Comparative Example 3 is the same as that of Example 1, except that the step (3) to remove excess solution from the surface is omitted.

[0114] Performance testing

[0115] Preparation of oil-water emulsion: Take 1L of deionized water, mix 1g of soybean oil and 0.1g of sodium dodecylbenzenesulfonate as emulsifier, pour into an emulsifier and stir for 90min.

[0116] Emulsion oil-water separation test: The hydrogel hydrophilic modified gradient pore oil-water separation membrane was clamped in a self-made acrylic component. Water was continuously circulated along the tangential direction on one side, and a certain pressure was applied to drive the water through the oil-water separation membrane to the other side for recycling.

[0117] Evaluation Criterion 1: The chemical oxygen demand (COD) in the filtered liquid is used to indirectly determine the oil content in the water. The ratio of the difference in COD before and after filtration to the COD of the emulsion before filtration (i.e., separation efficiency or oil rejection rate) is used for evaluation. The higher the oil rejection rate, the better the separation performance of the membrane.

[0118] Evaluation Criterion 2: Perform 5 filtrations. The flux ratio between the first and last filtrations is the flux recovery rate. A higher flux recovery rate indicates better membrane stability and antifouling performance, and vice versa.

[0119] In addition, the hydrogel-modified gradient pore oil-water separation membrane prepared in Example 1 was used to separate the oil and water in the emulsion. The change in oil content during the separation process is as follows: Figure 4 As shown.

[0120] Figure 4 The images are optical microscope images of the emulsion oil and water before and after filtration by the hydrogel-modified gradient pore oil-water separation membrane in Example 1 of the present invention. The left side shows the emulsion oil and water before filtration, and the right side shows the filtered product water.

[0121] according to Figure 4 It is known that the hydrogel hydrophilic modified gradient pore oil-water separation membrane of the present invention can effectively filter out oil droplets in emulsion oil and water, thereby achieving water purification.

[0122] Oil-water separation was performed multiple times using the hydrogel-modified gradient pore oil-water separation membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2, and the separation process curves were obtained, as shown below. Figure 5 As shown.

[0123] Figure 5 The separation process curves are for hydrogel-modified gradient pore oil-water separation membranes.

[0124] according to Figure 5 It can be seen that Example 1 has a better oil-water separation effect, and still has a high separation throughput even after being reused three times. Its oil-water separation performance is significantly higher than that of Comparative Example 1 and Comparative Example 2.

[0125] The oil cut-off rate, oil-water separation flux, and flux recovery rate of each embodiment and comparative example are shown in Table 1.

[0126] Table 1

[0127]

[0128] A comprehensive analysis of Examples 1-22 shows that the hydrogel-modified gradient pore oil-water separation membrane provided by the present invention has excellent flux recovery rate for emulsified oil, with flux recovery rates all above 90%.

[0129] A comprehensive analysis of Examples 1 and 4-7 shows that as the pore size of the base membrane increases, the flux of the hydrogel-modified gradient pore oil-water separation membrane also increases significantly, but the oil rejection rate decreases accordingly; conversely, as the pore size of the base membrane decreases, the flux of the hydrogel-modified gradient pore oil-water separation membrane also decreases significantly, but the oil rejection rate increases.

[0130] A comprehensive analysis of Examples 1-2, 19-20, and 21-22 reveals that the concentrations of the hydrogel precursor and initiator directly affect the hydrogel loading. When the concentration of the hydrogel precursor or initiator is too low, the hydrogel coating on the membrane surface is insufficient, resulting in insufficient hydrophilicity, high oil-water separation flux, and low flux recovery rate. Conversely, when the concentration of the hydrogel precursor or initiator is too high, the hydrogel coating on the membrane surface is sufficient, but the effective membrane pores are blocked, resulting in low oil-water separation flux and high flux recovery rate.

[0131] A comprehensive analysis of Examples 1 and 15-18 shows that hydrogel hydrophilic modified gradient pore oil-water separation membranes prepared by different combinations of initiators all exhibit excellent oil interception performance and flux recovery rate for emulsified oil, but there may be slight differences in flux.

[0132] A comprehensive analysis of Example 1 and Comparative Example 1 shows that when the coating in step (4) is changed to immersion, the membrane as a whole can still have a certain degree of hydrophilicity, but it will lose the gradient pore structure and have the problem of low water flux.

[0133] A comprehensive analysis of Example 1 and Comparative Example 2 shows that when the soaking in step (2) is replaced by coating, the membrane as a whole can also have a certain degree of hydrophilicity. However, during the experiment, there will be problems of hydrogel shedding and incomplete coverage, which will result in a low water flux recovery rate of the membrane.

[0134] A comprehensive analysis of Example 1 and Comparative Example 3 shows that when excess hydrogel precursor solution is not removed from the surface of the base membrane, hydrogel will accumulate on the membrane surface, causing membrane pore blockage and thus reducing membrane flux.

[0135] In summary, the hydrogel-modified gradient pore oil-water separation membrane provided by this invention possesses superhydrophilic and superoleophobic properties, effectively handling emulsified oils containing surface-active components. Furthermore, it exhibits excellent physical and chemical stability, maintaining high throughput and superior antifouling performance under various environmental conditions while operating stably for extended periods. Additionally, the preparation method of this invention combines physical and chemical approaches, is simple to operate, requires no additional chemical reagents, is environmentally friendly, has low energy consumption, and possesses potential for large-scale production.

[0136] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A hydrogel hydrophilically modified gradient-pore oil-water separation membrane, characterized by, The application relates to a hydrogel hydrophilic modification gradient hole oil-water separation membrane.

2. The hydrogel hydrophilic modification gradient hole oil-water separation membrane according to claim 1, wherein: the membrane hole on the water inlet side of the hydrogel hydrophilic modification gradient hole oil-water separation membrane is 10-500 nm, and the membrane hole on the water outlet side is 20-1000 nm. The application relates to a hydrogel hydrophilic modification gradient hole oil-water separation membrane. The application relates to a hydrogel hydrophilic modification gradient hole oil-water separation membrane.

3. A method for preparing a hydrogel hydrophilically modified gradient-pore oil-water separation membrane according to claim 1 or 2, characterized by, The application relates to a hydrogel hydrophilic modification gradient hole oil-water separation membrane.

4. The preparation method according to claim 3, wherein: the base film is selected from any one of polytetrafluoroethylene film, polyvinylidene fluoride film, polypropylene film, polysulfone film, polyethersulfone film, cellulose acetate film, ceramic film and stainless steel film; the pore size of the base film is 0.05-2 mu m; the base film is pretreated by wetting the base film with an ethanol solution with a volume fraction of 50-100% before being soaked in the hydrogel precursor solution containing the first initiator, and the pretreatment time is 0.5-6 h; and the soaking time is 10-120 min.

5. The preparation method according to claim 3, wherein: the mass fraction of the first initiator or the second initiator in the hydrogel precursor solution is 0.05%-5%; the first initiator and the second initiator are independently selected from any 1-3 of benzoyl peroxide, dicumyl peroxide, azobisisobutyronitrile, cyclohexylbenzoyl peroxide, tert-butyl peroxide, tert-butyl peroxy-2-ethylhexyl, propyl amino anthraquinone, benzoyl peroxide, phenyl bis (2, 4, 6-trimethyl benzoyl) phosphine oxide and diethyl benzene peroxide.

6. The preparation method according to claim 3, wherein: the temperature of the hydrogel precursor solution is 20-50 DEG C; the mass fraction of the hydrogel precursor in the hydrogel precursor solution is 5%-50%; and the hydrogel precursor comprises any one or more of acrylic acid, methacrylic acid, acrylate, acrylamide and vinyl alcohol.

7. The preparation method according to claim 6, wherein: the acrylic acid comprises acrylic acid, methacrylic acid and acrylate; the acrylamide comprises methacrylamide and methyl acrylamide; and the vinyl alcohol is polyvinyl alcohol with a molecular weight of 20,000-200,000.

8. The preparation method according to claim 3, wherein: the removal of the excess solution on the surface of the base film comprises: using a silica gel roller to lightly roll the surface of the base film.

9. The preparation method according to claim 3, wherein: the pre-polymerization of the base film is carried out under ultraviolet light.

10. Application of the hydrogel hydrophilic modification gradient hole oil-water separation membrane according to claim 1 or 2, wherein: the hydrogel hydrophilic modification gradient hole oil-water separation membrane is used for separating an oil-water mixture. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The wavelength of the ultraviolet light is 320-400 nm; the ultraviolet irradiation time is 10-300 s; the ultraviolet irradiation light intensity is 5-1000 μW / cm 2 ; and the film environment temperature during ultraviolet irradiation is 20-50℃. ​ ​ The particle size of the stable oil droplets in the oil-water mixture is 0.05-20 μm.

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