Preparation method and application of polar-solvent-resistant nanofiltration membrane

Abstract

The invention provides a preparation method and application of a polar solvent resistant nanofiltration membrane, and belongs to the technical field of nanofiltration membrane preparation, the preparation method comprises the following steps: (a) a polyethylene membrane is oxidized and modified by potassium permanganate to obtain a modified polyethylene membrane; and (b) carrying out interfacial polymerization and thermocuring on phosphonitrilic chloride trimer and a polyphenol compound on the surface of the modified polyethylene film to form a polymer separation layer, and activating the polymer separation layer to obtain the polar solvent resistant nanofiltration membrane. The invention solves the technical problem of poor solvent resistance of the nanofiltration membrane in the prior art, and achieves the technical effects of effectively filtering and separating different components in the solution and having long-term stability.

Description

Technical Field

[0001] The invention relates to the technical field of nanofiltration membrane preparation, and in particular to a method for preparing a polar solvent-resistant nanofiltration membrane and application thereof. Background Art

[0002] At present, a large number of organic solvents are used in industrial production, such as methanol, ethanol, acetone, ethyl acetate, toluene, tetrahydrofuran, DMAC, DMF and NMP. On the one hand, most organic solvents are toxic substances, and the recovery of organic solvents is of great significance to resource conservation and environmental protection; on the other hand, in the production process, the extraction of products requires the removal of organic solvents, and the extraction method needs to take into account the influence of organic solvents. At present, the methods of organic solvent recovery and product extraction mainly include distillation, extraction, absorption and membrane separation. The distillation operation has a large processing scale, high operating temperature and energy consumption, which is suitable for the industrial production of ordinary compounds and difficult to handle heat-sensitive substances; extraction requires the introduction of new solvents as extractants, which consumes raw materials and increases costs, and the subsequent mixture needs secondary separation, which is not effective; the volatility of organic solvents is used to dissolve or react organic waste gas with absorbents to achieve the purpose of recovery, but the absorbent is generally also an organic solvent, which will cause secondary pollution. Therefore, in order to meet the requirements of green energy conservation and environmental protection, the treatment of related solvents through organic solvent separation membranes has received more and more attention.

[0003] Organic solvent nanofiltration (OSN) technology has shown great application potential in processes such as material separation, drug concentration and refining. Solvent-resistant nanofiltration membrane materials are the core of OSN technology. Nanofiltration membrane is a new type of membrane separation technology between reverse osmosis membrane and ultrafiltration membrane. Nanofiltration membrane has high filtration accuracy and flux, and can achieve separation, purification and concentration of substances at the molecular level. It is widely used in water treatment, chemical industry and medicine. However, traditional nanofiltration membranes are insufficient in solvent resistance. When in contact with organic solvents, they are easily corroded by solvents and swell and plasticize. When processing solutions containing organic solvents, problems such as decreased membrane flux and reduced filtration accuracy often occur. Therefore, it is of great practical significance to develop a nanofiltration membrane with high solvent resistance.

[0004] A Chinese invention patent application with publication number CN116078160A discloses a polyethylene-based solvent-resistant and acid-alkali-resistant reverse osmosis membrane and a method for preparing the same. The polyethylene membrane is placed in a polymer solution with a hydroxyl group for hydrophilic modification, and then the surface is coated with a PES-type polymer. Then, interfacial polymerization is performed on the PES coating to prepare the reverse osmosis membrane. This method immerses the polyethylene membrane in a hydrophilic agent for modification, and the binding between the hydrophilic agent and the polyethylene membrane is weak. At the same time, since a PES small-pore membrane layer is coated on the polyethylene surface, the advantage brought by the large-pore flux of the polyethylene will be reduced to a certain extent, and its separation layer is polyamide, which has limited tolerance to polar solvents.

[0005] The Chinese invention patent application with publication number CN103933881A discloses that an ultrafiltration membrane is used as a porous support layer, cyanuric chloride and / or hexachlorocyclotriphosphazene are selected as oil phase solutes to undergo polymerization reaction with amine water phase solutes at the interface between the two phases, the reaction temperature is controlled to activate various groups in the reaction monomers, and different active nucleophilic reagents are introduced step by step to connect specific groups, thereby synthesizing a loosely structured membrane selection layer on the surface of the porous support layer; however, the reagent used in the water phase of this method is amines, and it is prepared on an ultrafiltration membrane, resulting in a low flux of the obtained membrane product and limited solvent resistance. Summary of the invention

[0006] The object of the present invention is to provide a method for preparing a polar solvent-resistant nanofiltration membrane and its application, so as to solve at least one technical problem existing in the above-mentioned background technology.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: In one aspect, the present invention provides a method for preparing a polar solvent resistant nanofiltration membrane, comprising the following steps: (a) The polyethylene film is oxidized and modified by potassium permanganate to obtain a modified polyethylene film; (b) Hexachlorocyclotriphosphazene and polyphenol compounds are interfacially polymerized and thermally cured on the surface of the modified polyethylene membrane to form a polymer separation layer, and then the polymer separation layer is activated to obtain the polar solvent resistant nanofiltration membrane.

[0008] Furthermore, the polyethylene film is immersed in a potassium permanganate solution to obtain a modified polyethylene film.

[0009] Furthermore, the concentration of the potassium permanganate solution is 0.1-0.2 mol / L, the immersion temperature is 50-60° C., and the immersion time is 36-60 h.

[0010] Furthermore, the polyphenol compound is a mixture of one or more of 4,4'-dihydroxybiphenyl, 4,4'-dihydroxydiphenyl ether, 4,4'-dihydroxybenzophenone, bisphenol S, 4,4'-dihydroxydiphenyl disulfide, 4,4'-dihydroxydiphenyl propane or 3,5,4'-trihydroxystilbene, and derivatives thereof.

[0011] Furthermore, the thermal curing temperature is 70-80° C., and the thermal curing time is 20-30 hours.

[0012] Furthermore, the activation method includes immersing the separation layer in a polar solvent to activate the separation layer.

[0013] Furthermore, the polar solvent is a mixture of one or more of DMF, DMAC or DMSO.

[0014] Furthermore, the polar solvent soaks the separation layer for 5 to 8 minutes.

[0015] In a second aspect, the present invention provides a polar solvent resistant nanofiltration membrane prepared by the preparation method described in the first aspect.

[0016] In a third aspect, the present invention provides an application of the polar solvent resistant nanofiltration membrane as described in the second aspect in material separation, drug concentration and product purification.

[0017] The beneficial effects of the present invention are as follows: the technical problem of poor solvent resistance of nanofiltration membranes in the prior art is solved, and the technical effect of being able to effectively filter and separate different components in a solution and having long-term stability is achieved.

[0018] Additional aspects and advantages of the present invention will be given in part in the following description, which will become obvious from the following description, or may be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0020] Figure 1 This is a process flow chart of the method for preparing the polar solvent resistant nanofiltration membrane described in an embodiment of the present invention.

[0021] Figure 2 It is a reaction schematic diagram of the interfacial polymerization described in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below by the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be interpreted as limiting the present invention.

[0023] Those skilled in the art will understand that unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which this invention belongs.

[0024] It should also be understood that terms, such as those defined in commonly used dictionaries, should be understood to have a meaning consistent with that in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless as defined herein.

[0025] Those skilled in the art will appreciate that, unless otherwise stated, the singular forms "a", "an", "said" and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present invention refers to the presence of the features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements and / or groups thereof.

[0026] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples, unless they are contradictory.

[0027] To facilitate understanding of the present invention, the present invention is further explained below with reference to specific embodiments in conjunction with the accompanying drawings, and the specific embodiments do not constitute a limitation on the embodiments of the present invention.

[0028] Those skilled in the art should understand that the drawings are merely schematic diagrams of embodiments, and the components in the drawings are not necessarily necessary for implementing the present invention.

[0029] One of the purposes of the present invention is to provide a method for preparing a polar solvent-resistant nanofiltration membrane, which can solve the technical problem of poor solvent resistance of the nanofiltration membrane in the prior art.

[0030] The second object of the present invention is to provide a polar solvent resistant nanofiltration membrane, which can not only effectively filter and separate different components in a solution, but also has high solvent resistance and long-term stability, can work stably in a solvent for a long time, and maintain high separation performance and flux.

[0031] The third object of the present invention is to provide an application of a polar solvent-resistant nanofiltration membrane, which can avoid the problem of the nanofiltration membrane being easily corroded, swollen and plasticized when contacting an organic solvent, and can achieve outstanding application effects.

[0032] The first aspect of the present invention is a method for preparing a polar solvent resistant nanofiltration membrane, comprising the following steps: (a) The polyethylene film is oxidized and modified by potassium permanganate to obtain a modified polyethylene film; (b) Hexachlorocyclotriphosphazene and polyphenol compounds are interfacially polymerized and thermally cured on the surface of the modified polyethylene membrane to form a polymer separation layer, and the polymer separation layer is activated to obtain a polar solvent resistant nanofiltration membrane.

[0033] In the present invention, the polyethylene film is first oxidized by potassium permanganate, a strong oxidant, to improve its hydrophilicity, and then hexachlorocyclotriphosphazene and polyphenol compounds are subjected to interfacial polymerization reaction on the polyethylene film (substrate) to generate polyether compounds containing cyclotriphosphazene (cyclotriphosphazene derivatives) as a polymer separation layer. The molecular structure of the cyclotriphosphazene derivative contains phosphorus and nitrogen structures with single and double bonds arranged alternately, so it has excellent heat resistance, flame retardancy, solvent resistance and radiation resistance, which can greatly enhance the solvent resistance of the membrane product; then, the coating crosslinking density is increased by thermal curing, the coating stability and bonding strength are enhanced, and activation treatment is performed to improve the membrane performance, thereby obtaining a polar solvent resistant nanofiltration membrane.

[0034] The present invention provides a method for preparing a polar solvent resistant nanofiltration membrane, which uses a polyethylene membrane as a substrate. Compared with polysulfone as a substrate for a reverse osmosis / nanofiltration membrane, the polyethylene has a larger porosity and pore size, so the generated membrane product has a higher flux and is also more solvent resistant. Compared with directly using a polyethylene membrane or modifying it hydrophilically by dipping, or modifying the surface by coating a PES-type polymer, the present invention oxidizes the polyethylene membrane by using a strong oxidant, potassium permanganate, which can not only form carboxyl (-COOH), carbonyl (-C=O) and hydroxyl (-OH) groups on the membrane material to increase the hydrophilicity of the polyethylene membrane, but also the oxidation of potassium permanganate has an etching effect, which can remove the weak bonding layer on the surface of the polyethylene membrane, increase the surface roughness, and thus enhance the adhesion of subsequent interfacial polymerization and fiber layers. force; at the same time, the oxidation of potassium permanganate can deposit nano manganese dioxide particles on the polyethylene fibers, and the nano manganese dioxide particles can form hydrogen bonds with subsequent interfacial polymerization products, thereby enhancing the solvent resistance of the membrane; compared with the common polyamide layer, the present invention performs interfacial polymerization reaction on a polyethylene substrate with hexachlorocyclotriphosphazene and a polyphenol compound and thermally cures the reaction to generate a polyether polymer separation layer, and the polymer separation layer is more solvent-resistant; compared with direct film formation after interfacial polymerization, the present invention adds an activation treatment, for example, a polar solvent can be used for activation treatment, and the slight swelling effect of the polar solvent can be used to further improve the membrane flux without reducing the membrane desalination rate. At the same time, the polar solvent dissolves some small molecular fragments on the membrane and can repair some loose sites on the membrane surface.

[0035] In a preferred embodiment, the method for oxidative modification of the present invention comprises the following steps: The polyethylene film is immersed in a potassium permanganate solution to obtain a modified polyethylene film.

[0036] The polyethylene film is immersed in a potassium permanganate solution, the concentration of the potassium permanganate solution can be 0.1-0.2 mol / L, and its typical but non-limiting concentration is, for example, 0.1 mol / L, 0.12 mol / L, 0.14 mol / L, 0.16 mol / L, 0.18 mol / L, and 0.2 mol / L. The temperature of the potassium permanganate solution can be 50-60°C, and its typical but non-limiting temperature is, for example, 50°C, 52°C, 54°C, 56°C, 58°C, and 60°C; the polyethylene film can be immersed for 36-60 hours, and its typical but non-limiting time is, for example, 36 hours, 38 hours, 40 hours, 45 hours, 50 hours, 55 hours, and 60 hours; after immersion, the polyethylene film is taken out and rinsed with deionized water, and then dried at 70°C to obtain the modified polyethylene film. Under the action of potassium permanganate, the surface of the polyethylene fiber is oxidized to produce highly active oxygen-containing groups such as carboxyl (-COOH), carbonyl (-C=O) and hydroxyl (-OH), thereby increasing the hydrophilicity of the polyethylene film; in addition, potassium permanganate also has a certain etching effect due to its oxidizing property, which can remove the weak binding layer on the surface of the polyethylene, thereby increasing the surface roughness of the polyethylene fiber, thereby enhancing the adhesion between the subsequent interfacial polymerization and the fiber layer; at the same time, oxidation can also cause nano-manganese dioxide particles to be deposited on the polyethylene fiber. The existing nano-manganese dioxide particles can form hydrogen bonds with the subsequent interfacial polymerization products, thereby enhancing the solvent resistance of the film.

[0037] In a preferred embodiment, the polyphenol compounds include but are not limited to at least one of 4,4'-dihydroxybiphenyl, 4,4'-dihydroxydiphenyl ether, 4,4'-dihydroxybenzophenone, bisphenol S, 4,4'-dihydroxydiphenyl disulfide, 4,4'-dihydroxydiphenyl propane, 3,5,4'-trihydroxystilbene and their derivatives. Hexachlorocyclotriphosphazene reacts with the above polyphenol compounds to generate polyether compounds containing cyclotriphosphazene. The polyether polymer separation layer is more stable than conventional polyamide and more resistant to solvents.

[0038] In a preferred embodiment, the temperature of thermal curing can be 70-80°C, and typical but non-limiting temperatures are, for example, 70°C, 72°C, 74°C, 76°C, 78°C, and 80°C; the duration of thermal curing can be 20-30h, and typical but non-limiting durations are, for example, 20h, 22h, 24h, 26h, 28h, and 30h. The above-mentioned thermal curing temperature and duration are more conducive to further improving the crosslinking density of the coating, and are more conducive to further enhancing the stability and bonding strength of the coating.

[0039] In a preferred embodiment, the activation method includes but is not limited to immersing the separation layer in a polar solvent to activate the separation layer; wherein the polar solvent includes but is not limited to at least one of DMF, DMAC and DMSO.

[0040] In the present invention, the polar solvent may be used to soak the separation layer for 5 to 8 minutes, and a typical but non-limiting time period is, for example, 5 minutes, 6 minutes, 7 minutes, or 8 minutes, which is more conducive to further improving the activation effect.

[0041] The present invention uses a polar (mixed) solvent to activate the membrane layer after interfacial polymerization and thermal curing, and utilizes the slight swelling effect of the polar solvent to further increase the membrane flux without reducing the membrane desalination rate. At the same time, the polar (mixed) solvent dissolves some small molecular fragments on the membrane, and can repair some loose sites on the membrane surface.

[0042] A typical preparation method of a polar solvent resistant nanofiltration membrane, see Figure 1 , including the following steps: (1) Modification of base film: The polyethylene base film is immersed in potassium permanganate (KMnO 4 ) solution, the potassium permanganate concentration is 0.1-0.2 mol / L, the solution temperature is 55°C, after soaking for 2 days, the base film is rinsed with deionized water, and dried at 70°C to obtain a modified polyethylene base film; Under the action of potassium permanganate, the surface of polyethylene fiber is oxidized to produce highly active oxygen-containing groups such as carboxyl (-COOH), carbonyl (-C=O) and hydroxyl (-OH), which can increase the hydrophilicity of polyethylene; in addition, potassium permanganate also has a certain etching effect due to its oxidizing property, which can remove the weak binding layer on the surface of polyethylene, increase the roughness of the fiber surface, and thus enhance the adhesion between the subsequent interfacial polymerization product and the fiber layer; in addition, oxidation can cause nano-manganese dioxide particles to be deposited on polyethylene fibers, which can form hydrogen bonds with the subsequent interfacial polymerization products and enhance the solvent resistance of the film; (2) Aqueous phase preparation: preparing an aqueous phase solution by preparing aromatic phenol, aqueous phase additive and pure water; The aromatic phenol (polyphenol compound) may be at least one of 4,4'-dihydroxybiphenyl, 4,4'-dihydroxydiphenyl ether, 4,4'-dihydroxybenzophenone, bisphenol S, 4,4'-dihydroxydiphenyl disulfide, 4,4'-dihydroxydiphenyl propane, 3,5,4'-trihydroxystilbene, etc. or their derivatives; The aqueous phase additive may be at least one of NaOH, KOH and sodium carbonate (base), and at least one of sodium dodecyl sulfonate, sodium dodecyl sulfate and sodium dodecylbenzene sulfonate (surfactant); The concentration of aromatic phenol is 0.5~1mol / L. NaOH, KOH or sodium carbonate can deprotonate aromatic phenol and convert it into more reactive aryl sodium oxide (concentration 1.5~3mol / L). The mass fraction of surfactant is 0.03~5wt%; (3) Oil phase preparation: Hexachlorocyclotriphosphazene (HCCP), oil phase additive and solvent are prepared into an oil phase solution, with the HCCP concentration of 0.1~0.2 mol / L; The oil phase additive may be at least one of methyl trioctyl ammonium chloride and hexadecyl trimethyl ammonium bromide, with a concentration of 0.1-0.2 wt %; the solvent may be at least one of n-heptane, benzene, petroleum ether and dichloromethane; (4) Preparation of functional layer (interfacial polymerization IP, see Figure 2 ): The modified polyethylene-based film of step (1) is immersed in the aqueous phase solution of step (2), wherein the aqueous phase immersion time can be 5 to 10 minutes, and after being taken out, the excess phenol solution is removed with nitrogen or a rubber roller, and then immersed in the oil phase solution of step (3), wherein the oil phase immersion time can be 5 to 10 minutes, and then taken out; It should be noted that the modified polyethylene-based membrane can also be immersed in the oil phase solution first, and then immersed in the water phase solution; (5) Thermal curing treatment: The product after the interfacial polymerization in step (4) is sent to an oven for thermal curing treatment, wherein the thermal curing temperature can be 70° C. and the thermal curing time can be 24 hours to increase the crosslinking density of the coating and enhance the stability and bonding strength of the coating; (6) Solvent activation treatment: After the product after heat curing in step (5) is cooled to room temperature, the separation layer is immersed in a polar (mixed) solvent for activation treatment, and then the excess solvent is washed away with deionized water to obtain a polar solvent resistant nanofiltration membrane; The polar solvent may be at least one of DMF, DMAC and DMSO.

[0043] The preparation method provided by the present invention comprises the following steps: a polyethylene film is modified by a potassium permanganate oxidation method, and nano manganese dioxide particles are introduced while generating polar functional groups, so that the hydrophilicity can be enhanced and the solvent resistance can be improved; on the surface of the modified polyethylene film, an interfacial polymerization reaction is carried out by HCCP and a polyphenol compound, so that the problem of coating an ultrafiltration layer and affecting the membrane flux can be avoided, and cyclotriphosphazene is introduced into the separation layer, so that the solvent resistance of the prepared membrane layer is enhanced; and through a heat curing treatment, the crosslinking density is increased and the stability and the bonding force are enhanced; and a polar solvent is used for activation treatment, so that the membrane performance is effectively improved.

[0044] According to a second aspect of the present invention, there is provided a polar solvent resistant nanofiltration membrane prepared by any of the preparation methods described above.

[0045] The polar solvent resistant nanofiltration membrane provided by the present invention can not only effectively filter and separate different components in a solution, but also has high solvent resistance and long-term stability. The nanofiltration membrane can work stably in a solvent for a long time, maintain high separation performance and flux, and can avoid the phenomenon that the common polyamide and polyimide separation layers swell after long-term use in a solvent environment, resulting in a decrease in membrane separation performance.

[0046] According to a third aspect of the present invention, there is provided a use of the polar solvent resistant nanofiltration membrane described above in material separation, drug concentration and product purification.

[0047] The application of the polar solvent resistant nanofiltration membrane provided by the present invention can avoid the problem that the nanofiltration membrane is easily corroded and swells and plasticizes when it contacts with organic solvents, and the application effect is outstanding.

[0048] The present invention is further described below by way of examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or directly purchased from the market. Example 1

[0049] In this embodiment 1, a method for preparing a polar solvent resistant nanofiltration membrane is provided, comprising the following steps: S1: Purchase polyethylene battery separator on the market, with a thickness of 20 μm, a pore size of 0.1-0.2 μm, and a contact angle of 110°; S2: Modification of base film: The polyethylene membrane was immersed in a potassium permanganate solution with a concentration of 0.2 mol / L for 2 days at a temperature of 55°C, then taken out, rinsed, and dried at 70°C. The pore size of the membrane surface was about 0.15 μm, and the contact angle was 70°C, thereby obtaining a modified polyethylene base film; S3: aqueous phase preparation: 4,4'-dihydroxydiphenyl disulfide, NaOH, sodium dodecyl sulfate and pure water are prepared into an aqueous phase solution; Among them, the concentration of 4,4'-dihydroxydiphenyl disulfide is 0.5 mol / L, the concentration of NaOH is 2 mol / L, and the mass fraction of sodium dodecyl sulfate is 0.2 wt%; S4: Oil phase preparation: Hexachlorocyclotriphosphazene (HCCP), hexadecyltrimethylammonium bromide and toluene are prepared into an oil phase solution, wherein the concentration of HCCP is 0.1 mol / L and the concentration of hexadecyltrimethylammonium bromide is 0.1 wt%; S5: Preparation of functional layer (interfacial polymerization): The modified polyethylene-based membrane of step S2 is immersed in the aqueous solution of step S3 for 6 minutes and then taken out, and then the excess phenol solution is removed by nitrogen or a rubber roller, and then immersed in the oil phase solution of step S4 for 5 minutes and then taken out; S6: thermal curing treatment: sending the product after the interfacial polymerization in step S5 into an oven for thermal curing treatment, wherein the thermal curing temperature is 70° C. and the thermal curing time is 24 hours, so as to increase the crosslinking density of the coating and enhance the stability and bonding strength of the coating; S7: solvent activation treatment: After the product after heat curing in step S6 is cooled to room temperature, it is immersed in a mixed solution of DMAC and DMF, wherein the volume ratio of DMAC and DMF is 4:6, and the immersion time is 8 minutes. Then, the excess solvent is washed away with deionized water to obtain a polar solvent resistant nanofiltration membrane. Example 2

[0050] In this embodiment 2, a method for preparing a polar solvent resistant nanofiltration membrane is provided, comprising the following steps: S1: Purchase polyethylene battery separator on the market, with a thickness of 20 μm, a pore size of 0.1-0.2 μm, and a contact angle of 110°; S2: Modification of base film: The polyethylene membrane was immersed in a potassium permanganate solution with a concentration of 0.2 mol / L for 2 days at a temperature of 55°C, then taken out, rinsed, and dried at 70°C. The pore size of the membrane surface was about 0.15 μm, and the contact angle was 70°C, thereby obtaining a modified polyethylene base film; S3: aqueous phase preparation: 4,4'-dihydroxybenzophenone, KOH, sodium dodecylbenzene sulfonate and pure water are prepared into an aqueous phase solution; Among them, the concentration of 4,4'-dihydroxybenzophenone is 0.6 mol / L, the concentration of KOH is 2 mol / L, and the mass fraction of sodium dodecylbenzene sulfonate is 0.2 wt%; S4: Oil phase preparation: Hexachlorocyclotriphosphazene (HCCP), hexadecyltrimethylammonium bromide and toluene are prepared into an oil phase solution, with a HCCP concentration of 0.1 mol / L and a hexadecyltrimethylammonium bromide concentration of 0.1 wt%; S5: Preparation of functional layer (interfacial polymerization): The modified polyethylene-based membrane of step S2 is immersed in the aqueous solution of step S3 for 8 minutes and then taken out, and then the excess phenol solution is removed by nitrogen or a rubber roller, and then immersed in the oil phase solution of step S4 for 6 minutes and then taken out; S6: thermal curing treatment: sending the product after the interfacial polymerization in step S5 into an oven for thermal curing treatment, wherein the thermal curing temperature is 70° C. and the thermal curing time is 24 hours, so as to increase the crosslinking density of the coating and enhance the stability and bonding strength of the coating; S7: solvent activation treatment: after the product of the interfacial polymerization in step S5 is cooled to room temperature, it is immersed in a mixed solution of DMAC and DMF, wherein the volume ratio of DMAC and DMF is 1:1, and the immersion time is 5 minutes. Then, the excess solvent is washed away with deionized water to obtain a polar solvent resistant nanofiltration membrane. Example 3

[0051] The difference between this embodiment 3 and embodiment 1 is that in step S3, 4,4'-dihydroxybiphenyl is used in an equal amount to replace 4,4'-dihydroxydiphenyl disulfide, thereby configuring an aqueous phase solution; The remaining steps are the same as those in Example 1 to obtain a polar solvent-resistant nanofiltration membrane. Example 4

[0052] The difference between this embodiment 4 and embodiment 1 is that in step S3, bisphenol S is used in an equal amount to replace 4,4'-dihydroxydiphenyl disulfide, thereby configuring an aqueous phase solution; The remaining steps are the same as those in Example 1 to obtain a polar solvent-resistant nanofiltration membrane. Example 5

[0053] The difference between this embodiment 5 and embodiment 1 is that in step S3, 3,5,4'-trihydroxyphenylethylene is used to replace 4,4'-dihydroxydiphenyl disulfide in an equal amount, thereby configuring an aqueous phase solution; The remaining steps are the same as those in Example 1 to obtain a polar solvent-resistant nanofiltration membrane.

[0054] Comparative Example 1 The difference between this comparative example and Example 1 is that step S2 is to modify the base film by soaking in a hydroxyl-containing hydrophilic modifying agent, and the method is as follows:

[0055] S2: base film modification: soak the polyethylene membrane in a PVA (polyvinyl alcohol) modification solution, wherein the modification solution comprises: PVA concentration 1wt%, DMAC concentration 5wt%, and the rest water; soak for 15 minutes and then dry to obtain a modified polyethylene base film; The remaining steps are the same as those in Example 1 to obtain a nanofiltration membrane.

[0056] Comparative Example 2 The difference between this comparative example and Example 1 is that the solvent activation treatment in step S7 is not performed;

[0057] The remaining steps are the same as those in Example 1 to obtain a nanofiltration membrane.

[0058] Comparative Example 3

[0059] The difference between this comparative example and Example 1 is that a polysulfone ultrafiltration membrane is used, an aqueous solution of piperazine is used as an aqueous phase solution, trimesoyl chloride is used as an oil phase, and Isopar-G is used as a solvent, and a nanofiltration membrane is prepared by interfacial polymerization, and the method is as follows: S1: Polysulfone flat ultrafiltration membrane as the porous support layer; S2: Aqueous phase solution: The mass concentration of piperazine in the aqueous phase solution is 0.5%, and it also contains triethylamine and sodium dodecyl sulfate, and the mass fraction of sodium dodecyl sulfate is 0.1%; S3: Oil phase solution: The mass concentration of trimesoyl chloride in the oil phase solution is 3%; S4: immerse the polysulfone flat ultrafiltration membrane in the aqueous solution, let it stand for 10 minutes, then take it out, remove the excess solution with a rubber roller, and then introduce the oil phase solution to allow the two monomers to undergo interfacial polymerization reaction for 3 minutes; S5: Drying the membrane after interfacial polymerization to obtain a nanofiltration membrane.

[0060] Test example The nanofiltration membranes prepared in Examples 1-5 and Comparative Examples 1-3 were subjected to retention and flux tests, respectively; the test method was as follows: the operating pressure was 0.6 MPa, the test solution was 1 g / L magnesium sulfate solution, the solution temperature was 25°C, the pH was 6.5-7.5, and the water flux and desalination rate of the test membrane were measured after 30 minutes of operation; the test results are shown in Table 1.

[0061] The nanofiltration membranes prepared in Examples 1-5 and Comparative Examples 1-3 were subjected to solvent resistance tests, respectively, and the solvent was DMAC; the test method was: the membranes were immersed in the solvents, respectively, at room temperature for 20 days, and the flux of the membranes after immersion and the retention of 1 g / L magnesium sulfate were tested; the test results are shown in Table 2.

[0062] In Comparative Example 1, the hydrophilic additive was not firmly bonded to the polyethylene layer, so the desalination rate of the membrane was attenuated to a certain extent; in Comparative Example 3, the nanofiltration membrane had limited resistance to polar solvents. After being soaked in polar solvents, the desalination layer was damaged, the desalination rate decreased, and the flux increased.

[0063] Table 1 Nanofiltration membrane performance Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Comparative Example 3 Retention rate 97.50% 97.00% 98.00% 97.30% 97.00% 96.50% 96.80% 96.50% Flux (LMH) 24 25 23 25 26 26 20 30 Table 2 Nanofiltration membrane performance Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Comparative Example 3 Retention rate 97.00% 96.50% 97.60% 97.00% 96.70% 80.00% 96.00% 53.00% Flux (LMH) 26 27 24 26 28 28 23 41 In summary, the preparation method of polar solvent resistant nanofiltration membrane provided by the present invention uses polyethylene membrane as the substrate. Compared with polysulfone as the substrate of reverse osmosis / nanofiltration membrane, polyethylene has larger porosity and pore size, so the generated membrane product has higher flux and is also more solvent resistant; compared with directly using polyethylene membrane or modifying it by impregnation for hydrophilicity, or modifying the surface by coating PES polymer, the present invention oxidizes the polyethylene membrane by potassium permanganate, a strong oxidant, which can not only form carboxyl (-COOH), carbonyl (-C=O) and hydroxyl (-OH) groups on the membrane material to increase the hydrophilicity of the polyethylene membrane, but also the oxidation of potassium permanganate has an etching effect, which can remove the weak bonding layer on the surface of the polyethylene membrane, increase the surface roughness, and thus enhance the subsequent interfacial polymerization and fiber layer. Adhesion; at the same time, the oxidation of potassium permanganate can deposit nano manganese dioxide particles on the polyethylene fiber, and the nano manganese dioxide particles can form hydrogen bonds with the subsequent interfacial polymerization products, thereby enhancing the solvent resistance of the membrane; compared with the common polyamide layer, the present invention uses hexachlorocyclotriphosphazene and a polyphenol compound to carry out interfacial polymerization reaction on a polyethylene substrate and thermally cure to generate a polyether polymer separation layer, and the polymer separation layer is more solvent-resistant; compared with direct film formation after interfacial polymerization, the present invention adds an activation treatment, for example, a polar solvent can be used for activation treatment, and the slight swelling effect of the polar solvent can be used to further improve the membrane flux without reducing the membrane desalination rate. At the same time, the polar solvent dissolves some small molecular fragments on the membrane and can repair some loose sites on the membrane surface.

[0064] The polar solvent resistant nanofiltration membrane provided by the present invention can not only effectively filter and separate different components in a solution, but also has high solvent resistance and long-term stability. The nanofiltration membrane can work stably in a solvent for a long time, maintain high separation performance and flux, and can avoid the phenomenon that the common polyamide and polyimide separation layers swell after long-term use in a solvent environment, resulting in a decrease in membrane separation performance.

[0065] The application of the polar solvent resistant nanofiltration membrane provided by the present invention can avoid the problem that the nanofiltration membrane is easily corroded and swells and plasticizes when it contacts with organic solvents, and the application effect is outstanding.

[0066] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative work on the basis of the technical solution disclosed in the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a polar solvent resistant nanofiltration membrane, characterized in that: The following steps are involved: (a) The polyethylene film is oxidized and modified by potassium permanganate to obtain a modified polyethylene film; (b) Hexachlorocyclotriphosphazene and polyphenol compounds are interfacially polymerized and thermally cured on the surface of the modified polyethylene membrane to form a polymer separation layer, and then the polymer separation layer is activated to obtain the polar solvent resistant nanofiltration membrane.

2. The method for preparing a polar solvent resistant nanofiltration membrane according to claim 1, characterized in that: The polyethylene film is immersed in a potassium permanganate solution to obtain a modified polyethylene film.

3. The method for preparing a polar solvent resistant nanofiltration membrane according to claim 2, characterized in that: The concentration of the potassium permanganate solution is 0.1-0.2 mol / L, the soaking temperature is 50-60° C., and the soaking time is 36-60 h.

4. The method for preparing a polar solvent resistant nanofiltration membrane according to claim 1, characterized in that: The polyphenol compound is a mixture of one or more of 4,4'-dihydroxybiphenyl, 4,4'-dihydroxydiphenyl ether, 4,4'-dihydroxybenzophenone, bisphenol S, 4,4'-dihydroxydiphenyl disulfide, 4,4'-dihydroxydiphenyl propane or 3,5,4'-trihydroxystilbene.

5. The method for preparing a polar solvent resistant nanofiltration membrane according to claim 1, characterized in that: The polyphenol compound is a mixture of one or more of 4,4'-dihydroxybiphenyl derivatives, 4,4'-dihydroxydiphenyl ether derivatives, 4,4'-dihydroxybenzophenone derivatives, bisphenol S derivatives, 4,4'-dihydroxydiphenyl disulfide derivatives, 4,4'-dihydroxydiphenyl propane derivatives or 3,5,4'-trihydroxystilbene derivatives.

6. The method for preparing a polar solvent resistant nanofiltration membrane according to any one of claims 1 to 5, characterized in that: The thermal curing temperature is 70-80° C., and the thermal curing time is 20-30 hours.

7. The method for preparing a polar solvent resistant nanofiltration membrane according to any one of claims 1 to 5, characterized in that: The activation method includes immersing the separation layer in a polar solvent to activate the separation layer.

8. The method for preparing a polar solvent resistant nanofiltration membrane according to claim 7, characterized in that: The polar solvent is a mixture of one or more of DMF, DMAC or DMSO.

9. The method for preparing a polar solvent resistant nanofiltration membrane according to claim 7, characterized in that: The polar solvent soaks the separation layer for 5 to 8 minutes.

10. Use of a polar solvent resistant nanofiltration membrane prepared by the method for preparing a polar solvent resistant nanofiltration membrane according to any one of claims 1 to 9 in material separation, drug concentration and product purification.

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