Anti-fouling composite nanofiltration membrane and method for preparing the same

Abstract

The present application relates to an anti-fouling composite nanofiltration membrane and a preparation method thereof, the composite nanofiltration membrane comprises, from bottom to top, a support material, a base film layer containing polysulfone and poly-p-phenyleneterephthalamide fibers, and a polyamide selection layer formed by polymerization of an amine monomer and an acyl chloride monomer, wherein the amine monomer contains an aminoguanidine salt. The anti-fouling composite nanofiltration membrane has excellent initial desalination rate and initial flux, maintains excellent desalination rate and low flux decay rate after being polluted by organic matters, has the ability to maintain relatively stable desalination rate and flux before and after being polluted, and the desalination rate and flux can be effectively recovered after being alkali washed for a period of time after being polluted, that is, the desalination rate is still excellent and the flux decay rate is low. The method provided by the present application does not need to modify the existing equipment, reduces the investment in equipment, improves the production efficiency, has low raw material cost, and has no pathogenic risk to the operating personnel.

Description

Technical Field

[0001] This invention relates to a composite nanofiltration membrane, and more specifically to the field of composite nanofiltration membranes that are resistant to fouling and have excellent desalination rate and flux. Background Technology

[0002] Industrial wastewater often contains large amounts of toxic and harmful substances, and untreated industrial wastewater poses a significant potential threat to the natural environment. Therefore, finding green and environmentally friendly water treatment methods and realizing the recycling of freshwater resources has become a crucial issue in today's technological development.

[0003] Membrane separation is a commonly used method in the field of water treatment technology today. Among membrane separation technologies, pressure-driven nanofiltration and reverse osmosis membrane separation technologies have attracted much attention due to their ability to directly convert seawater or brackish water into potable pure water.

[0004] Nanofiltration membranes are widely used not only in industrial and municipal wastewater treatment but also play a crucial role in fields such as lithium extraction from brackish water. However, during long-term use, nanofiltration membranes inevitably become contaminated by inorganic, organic, and biological pollutants. These pollutants not only cause a decline in membrane performance (desalination rate, water flux, etc.) but are also difficult to remove completely by conventional methods (such as acid washing and alkaline washing), resulting in irreversible degradation of membrane performance. To extend the service life of nanofiltration membranes and broaden their application scenarios, there is an urgent need to develop a high-performance nanofiltration membrane material that maintains excellent filtration performance and water flux while also possessing good anti-fouling capabilities.

[0005] Currently, the technologies for improving the antifouling performance of composite nanofiltration membranes can be mainly divided into three categories.

[0006] The first type involves introducing a sacrificial layer onto the surface of a conventional polyamide composite nanofiltration membrane. For example, CN117563429A discloses the introduction of a sacrificial layer formed by photocuring polyethylene glycol methyl ether methacrylate onto the polyamide selective layer. Such a sacrificial layer can be washed off under certain post-treatment conditions (such as acid washing, alkali washing, etc.), allowing the selective layer underneath to regain its filtration performance. Specifically, the patent document provides a fouling-resistant polyamide composite membrane and its preparation method. The disclosed method involves coating a fouling-resistant solution containing polyethylene glycol methyl ether methacrylate and a photoinitiator onto a polyamide separation layer formed by interfacial polymerization of a polyamine and a polyacrylamide chloride. The membrane is then irradiated under ultraviolet light to obtain an antifouling layer grown on the polyamide layer. Finally, heat treatment yields the fouling-resistant polyamide composite membrane. In this method, the polyamine used is m-phenylenediamine, and the polyacrylamide chloride is trimesoyl pyromellitic acid chloride. The composite membrane prepared by this method achieves a sodium chloride removal rate of over 99.34%, a water flux of 20.3 gfd to 31.4 gfd, and a water flux recovery rate of 89.9% to 97.9% after completing the fouling resistance test.

[0007] The second type involves introducing a hydrophilic modification layer, including a hydrophilic polymer layer and metal nanoparticles, into the nanofiltration membrane to improve its antifouling ability. This hydrophilic modification layer creates a surface layer with persistent hydrophilic groups on the nanofiltration membrane. Simultaneously, due to the presence of metal nanoparticles, the resulting nanofiltration membrane can enhance the rejection rate of hydrophobic organic micropollutants while reducing the adsorption of pollutants on the membrane surface and mitigating concentration polarization, thereby improving the sieving performance and antifouling properties of the nanofiltration membrane. For example, CN118320619A provides a method for preparing a hydrophilic charged modified nanofiltration membrane and its application in water treatment. The modified nanofiltration membrane disclosed includes an ultrafiltration membrane and a selective layer and a hydrophilic modification layer stacked on the surface of the ultrafiltration membrane. The selective layer is obtained by interfacial polymerization of an amine monomer and an acyl chloride. The hydrophilic modification layer includes a hydrophilic polymer layer and metal nanoparticles disposed on the surface of the hydrophilic polymer layer. The metal nanoparticles include Ag nanoparticles, Cu nanoparticles, and Au nanoparticles. One or more of the following, wherein the hydrophilic polymeric layer is composed of polydopamine or obtained by the polymerization reaction of dopamine and polyethyleneimine, the water contact angle test of the obtained membrane product shows that the hydrophilicity of the membrane surface is improved, the retention rate of Na2SO4 of the obtained membrane is above 95.7%, the retention rate of CaCl2 is increased from 35.5%~45.8% to 50.1%~80.5%, and the retention rate of NaCl is increased from 2.2%~14.7% to 13.6%~59.6%.

[0008] The third type utilizes the properties of special substances to reduce the number of unreacted acyl chloride groups on the selective layer surface and the number of carboxyl groups generated by the hydrolysis of acyl chloride groups. For example, CN118649566A discloses an antibacterial and antifouling nanofiltration membrane with surface-modified antimicrobial peptides and its preparation method. In this method, a polyamide layer is formed on a base membrane by interfacial polymerization of polyamines and polyacyl chlorides. Then, an aqueous solution of antimicrobial peptides is added dropwise. The antimicrobial peptide structure has one or more active amino groups that can react with the acyl chloride groups on the membrane surface, reducing the carboxyl content on the membrane surface and decreasing the adsorption of divalent cations such as calcium ions. The resulting membrane achieves a sodium sulfate rejection rate of over 99% and a magnesium sulfate rejection rate of approximately 96%. Antifouling performance tests using sodium alginate as a model pollutant show that the flux recovery rate increased from 74.99% to 92.16%. Summary of the Invention

[0009] The problem the invention aims to solve

[0010] The inventors of this invention have discovered that the above-mentioned methods used in the prior art still have some shortcomings.

[0011] In methods that use ultraviolet (UV) lamps to obtain an antifouling layer, prolonged exposure to UV light poses a risk of dermatitis, conjunctivitis, and keratitis to operators, making it unsuitable for large-scale safe production. In methods involving the introduction of metal nanoparticles, the uneven dispersion of these nanoparticles in the selective layer leads to a decrease in the water flux of the nanofiltration membrane material. In methods utilizing specialized substances such as antimicrobial peptides, the high cost of these substances increases the cost of large-scale production.

[0012] The purpose of this invention is to solve the problems existing in the prior art mentioned above, and to provide an anti-fouling composite nanofiltration membrane and its preparation method.

[0013] Solution for solving the problem

[0014] In order to solve the above-mentioned problems existing in the prior art, the inventors of this invention conducted in-depth research and discovered:

[0015] Using polysulfone as the polymer component in the casting solution and introducing poly(p-phenylene terephthalamide) fibers to prepare the base membrane, and utilizing aminoguanidine salts as the amine monomers in the aqueous solution, the base membrane layer prepared by blending polysulfone and poly(p-phenylene terephthalamide) fibers exhibits improved hydrophilicity, which is beneficial for improving membrane flux and antifouling properties. Furthermore, the hydrogen-bonding interaction between the molecular chains of poly(p-phenylene terephthalamide) fibers and the amine monomers can slow down the diffusion rate of the amine monomers during subsequent interfacial polymerization reactions with acyl chloride monomers. In addition, aminoguanidine salts exhibit higher reactivity and lower diffusion rates compared to other amine monomers (e.g., piperazine). Commonly used aqueous monomers in interfacial polymerization, due to their rapid diffusion rates, quickly enter the organic phase and react with oil-phase monomers to form a thin film, thus hindering further diffusion of subsequent aqueous monomers and leading to self-limitation of the reaction. The selective layer film thus formed has a ridge-valley structure, a surface morphology that facilitates the adhesion and deposition of contaminants. The high reactivity and low diffusion rate of aminoguanidine salt monomers weaken the "diffusion control" of the interfacial polymerization process and make it more "reaction control" to form a thinner, denser and smoother selective layer. This special selective layer structure reduces the attachment sites of pollutants. As a result, the polyamide selective layer obtained by the interfacial polymerization reaction of amine monomers and acyl chloride monomers has a strong ability to resist pollutant deposition, which significantly improves the antifouling performance of nanofiltration membrane materials.

[0016] Based on the above findings, the present invention provides a composite nanofiltration membrane, which comprises, from bottom to top:

[0017] Supporting materials;

[0018] The base film layer comprises polysulfone and poly(p-phenylene terephthalamide) fibers;

[0019] A polyamide selective layer, wherein the polyamide selective layer is formed by polymerization of amine monomers and acyl chloride monomers, wherein the amine monomers include aminoguanidine salts.

[0020] The composite nanofiltration membrane of the present invention, wherein the supporting material is a nonwoven fabric, and the polysulfone is at least one selected from bisphenol A type polysulfone, polyphenylene sulfone, and polyether sulfone. Preferably, the concentration of the polysulfone is 14wt% to 19wt% based on the total weight of the casting solution used to form the base membrane layer.

[0021] The composite nanofiltration membrane of the present invention, wherein the concentration of the poly(p-phenylene terephthalamide) fiber is greater than 0 wt% and less than 5 wt% based on the total weight of the casting solution used to form the base membrane layer.

[0022] The composite nanofiltration membrane of the present invention, wherein the aminoguanidine salt is at least one selected from aminoguanidine hydrochloride, aminoguanidine sulfate, aminoguanidine phosphate, and aminoguanidine nitrate, preferably, the concentration of the aminoguanidine salt is 1 wt% to 6 wt% based on the total weight of the aqueous solution containing amine monomers.

[0023] The composite nanofiltration membrane of the present invention, wherein the acyl chloride monomer is selected from at least one of pyromellitic phthaloyl chloride, isophthaloyl chloride, biphenyl phthaloyl chloride, and terephthaloyl chloride, preferably, the concentration of the acyl chloride monomer is 0.05wt% to 0.4wt% based on the total weight of the oil phase solution containing the acyl chloride monomer.

[0024] This invention also provides a method for preparing a composite nanofiltration membrane, which includes the following steps:

[0025] A casting solution is prepared, wherein the casting solution comprises polysulfone, poly(p-phenylene terephthalamide) fiber and solvent;

[0026] The casting solution is applied to a support material to form a base film layer;

[0027] The support material on which the base film layer is formed is sequentially contacted with an aqueous solution containing amine monomers and an oil solution containing acyl chloride monomers to form a polyamide selective layer, wherein the amine monomers include aminoguanidine salts;

[0028] Post-processing.

[0029] In the method of the present invention, the supporting material is a non-woven fabric, and the polysulfone is at least one selected from bisphenol A type polysulfone, polyphenylene sulfone, and polyether sulfone. Preferably, the concentration of the polysulfone is 14wt% to 19wt% based on the total weight of the casting solution.

[0030] In the method of the present invention, the concentration of the poly(p-phenylene terephthalamide) fiber is greater than 0 wt% and less than 5 wt% based on the total weight of the casting solution.

[0031] In the method of the present invention, the aminoguanidine salt is at least one selected from aminoguanidine hydrochloride, aminoguanidine sulfate, aminoguanidine phosphate, and aminoguanidine nitrate. Preferably, the concentration of the aminoguanidine salt is 1 wt% to 6 wt% based on the total weight of the aqueous solution containing the amine monomer.

[0032] In the method of the present invention, the acyl chloride monomer is selected from at least one of pyromellitic methyl methacrylate, isophthalic acid methyl methacrylate, biphenyl methyl methacrylate, and terephthalic acid methyl methacrylate. Preferably, the concentration of the acyl chloride monomer is 0.05wt% to 0.4wt% based on the total weight of the oil phase solution containing the acyl chloride monomer.

[0033] The effects of the invention

[0034] The antifouling composite nanofiltration membrane provided by this invention has excellent initial desalination rate and initial flux. Even after being contaminated by organic matter, it can still maintain an excellent desalination rate and a low flux decay rate. It also has the ability to maintain its own filtration performance (i.e., desalination rate) and flux relatively stable before and after contamination (i.e., small fluctuation range of desalination rate and flux). After being alkaline washed for a period of time after being contaminated, its desalination rate and flux can also be effectively restored, that is, it still maintains an excellent desalination rate and a low flux decay rate.

[0035] The method for preparing composite nanofiltration membranes with excellent antifouling properties, desalination rate, and flux provided by this invention does not require modification of existing equipment, reduces equipment investment, improves production efficiency, has low raw material costs, and poses no risk of illness to operators. Detailed Implementation

[0036] Various exemplary embodiments, features, and aspects of the present invention will be described in detail below. The term "exemplary" as used herein means "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as superior to or better than other embodiments.

[0037] Furthermore, to better illustrate the present invention, numerous specific details are set forth in the following detailed embodiments. Those skilled in the art should understand that the present invention can be practiced without certain specific details. In other instances, methods, means, apparatus, and steps well known to those skilled in the art have not been described in detail in order to highlight the spirit of the present invention.

[0038] Unless otherwise stated, all units used in this specification are international standard units, and all numerical values ​​and ranges appearing in this invention should be understood to include systematic errors that are unavoidable in industrial production.

[0039] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0040] In this specification, references to "some specific / preferred embodiments," "other specific / preferred embodiments," "implementation," etc., refer to specific elements (e.g., features, structures, properties, and / or characteristics) related to that embodiment, which are included in at least one of the embodiments described herein and may or may not be present in other embodiments. Furthermore, it should be understood that these elements may be combined in any suitable manner in various embodiments.

[0041] In this specification, the range of values ​​referred to as "value A to value B" refers to the range including the endpoint values ​​A and B.

[0042] The composite nanofiltration membrane of the present invention comprises, from bottom to top:

[0043] Supporting materials;

[0044] The base film layer comprises polysulfone and poly(p-phenylene terephthalamide) fibers;

[0045] A polyamide selective layer, wherein the polyamide selective layer is formed by polymerization of amine monomers and acyl chloride monomers, wherein the amine monomers include aminoguanidine salts.

[0046] The supporting material is non-woven fabric. There are no particular limitations on the material of the non-woven fabric; polyester PET, polypropylene PP, polyethylene PE, etc., can be used. Preferably, in this invention, polyester PET non-woven fabric is used as the supporting material.

[0047] Preferably, the polysulfone is selected from at least one of bisphenol A type polysulfone, polyphenylene sulfone, and polyether sulfone; more preferably, the polysulfone is bisphenol A type polysulfone.

[0048] There is no particular limitation on the molecular weight of polysulfone, but its weight-average molecular weight can be in the range of 75,000 to 85,000 Da, preferably in the range of 78,000 to 82,000 Da.

[0049] There are no particular limitations on the molecular weight distribution of polysulfone. The weight-average molecular weight / number-average molecular weight ratio (Mw / Mn) can be in the range of 1.8 to 2.2, preferably in the range of 1.8 to 2.0.

[0050] Preferably, the concentration of polysulfone is 14wt% to 19wt% based on the total weight of the casting solution used to form the base film layer.

[0051] The support material on which a base film layer is formed is also called a porous support layer.

[0052] There are no particular limitations on the solvent in the casting solution, as long as it can dissolve polysulfone. Examples include N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide. Preferably, this invention uses N,N-dimethylformamide as the solvent for dissolving polysulfone.

[0053] Preferably, the poly(p-phenylene terephthalamide) fiber is K29 type Kevlar fiber manufactured by DuPont, with a fiber fineness of 200 denier (200D).

[0054] Preferably, based on the total weight of the casting solution used to form the base film layer, the concentration of the poly(p-phenylene terephthalamide) fiber is greater than 0 wt% and less than 5 wt%, more preferably, the concentration is 1 wt% to 3 wt%.

[0055] Preferably, the aminoguanidine salt is at least one selected from aminoguanidine hydrochloride, aminoguanidine sulfate, aminoguanidine phosphate, and aminoguanidine nitrate; more preferably, the aminoguanidine salt is aminoguanidine nitrate.

[0056] Preferably, the concentration of the aminoguanidine salt is 1 wt% to 6 wt% based on the total weight of the aqueous solution containing the amine monomer, more preferably, the concentration is 3 wt% to 6 wt%.

[0057] Preferably, the acyl chloride monomer is selected from at least one of pyromellitic methyl methacrylate (PMMA), isophthaloyl chloride (IMMA), biphenyl methyl methacrylate (BMM), and terephthaloyl chloride (TTM).

[0058] Preferably, the concentration of the acyl chloride monomer is 0.05wt% to 0.4wt% based on the total weight of the oil phase solution containing the acyl chloride monomer, and more preferably, the concentration is 0.2wt% to 0.3wt%.

[0059] There are no particular limitations on the solvent used in the oil phase solution; examples include n-hexane, n-heptane, n-decane, methylcyclohexane, and ethylcyclohexane. Preferably, the present invention uses n-hexane as the solvent for the oil phase solution.

[0060] The method for preparing the composite nanofiltration membrane of the present invention includes the following steps:

[0061] A casting solution is prepared, wherein the casting solution comprises polysulfone, poly(p-phenylene terephthalamide) fiber and solvent;

[0062] The casting solution is applied to a support material to form a base film layer;

[0063] The support material on which the base film layer is formed is sequentially contacted with an aqueous solution containing amine monomers and an oil solution containing acyl chloride monomers to form a polyamide selective layer, wherein the amine monomers include aminoguanidine salts;

[0064] Post-processing.

[0065] The descriptions of the support material, polysulfone, poly(p-phenylene terephthalamide) fiber, aminoguanidine salt, and acyl chloride monomer are the same as those for the composite nanofiltration membrane described above.

[0066] There are no particular limitations on the contact time and temperature with the aqueous solution containing amine monomers; contact can be performed at a temperature of 20~40℃ for 20~40 s.

[0067] Preferably, after contact with an aqueous solution containing amine monomers, the sample is removed and dried by forced air until no water droplets remain on the surface.

[0068] There are no particular limitations on the contact time and temperature with oil-phase solutions containing acyl chloride monomers; contact can be performed for 10 to 60 seconds at a temperature of 20 to 30°C.

[0069] Preferably, after contact with an oil phase solution containing acyl chloride monomers, the sample is removed and subjected to forced-air drying until the organic solvent on the surface is removed.

[0070] Post-treatment includes, for example, hot water treatment at a temperature of 60-80°C, immersion in an aqueous solution containing glycerol, and drying at a temperature of 85-95°C. There is no particular limitation on the time for hot water treatment, which can be 3-5 minutes. There is no particular limitation on the concentration of glycerol, which can be 8wt%-20wt%. There is no particular limitation on the drying time, which can be 1-3 minutes.

[0071] Example

[0072] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0073] Example 1

[0074] A base membrane casting solution containing 18 wt% bisphenol A type polysulfone (Mn 80000 Da) and 1 wt% Kevlar fiber (K29 type, 200D) was prepared and applied to a PET nonwoven fabric. A polysulfone / Kevlar fiber porous support layer was prepared at 25°C using an impregnation-precipitation phase inversion method. The resulting support layer was immersed in an aqueous solution containing 3 wt% aminoguanidine nitrate at 25°C for 25 s, and then dried by air drying until no water droplets were visible on the surface. The resulting membrane was then immersed in a hexane solution containing 0.20 wt% trimesoyl chloride at 25°C for 50 s to allow interfacial polymerization to form a polyamide selective layer. After removing the membrane and removing the surface organic solvent by air drying, the resulting membrane was immersed in hot water at 80°C for 4 min, and then immersed in an aqueous solution containing 10 wt% glycerol for 2 min. Finally, the resulting membrane was dried by air drying at 90°C to obtain the composite nanofiltration membrane material of Example 1.

[0075] Example 2

[0076] A base membrane casting solution containing 17 wt% bisphenol A type polysulfone (Mn 80000 Da) and 2 wt% Kevlar fiber (K29 type, 200D) was prepared and applied to a PET nonwoven fabric. A polysulfone / Kevlar fiber porous support layer was prepared at 25°C using an impregnation-precipitation phase inversion method. The resulting support layer was immersed in an aqueous solution containing 3 wt% aminoguanidine nitrate at 25°C for 25 s, and then dried by air drying until no water droplets were visible on the surface. The resulting membrane was then immersed in a hexane solution containing 0.20 wt% trimesoyl chloride at 25°C for 50 s to allow interfacial polymerization to occur on the surface, forming a polyamide selective layer. After removing the membrane and removing the surface organic solvent by air drying, the resulting membrane was immersed in hot water at 80°C for 4 min, and then immersed in an aqueous solution containing 10 wt% glycerol for 2 min. Finally, the resulting membrane was dried by air drying at 90°C to obtain the composite nanofiltration membrane material of Example 2.

[0077] Example 3

[0078] A base membrane casting solution containing 16 wt% bisphenol A type polysulfone (Mn 80000 Da) and 3 wt% Kevlar fiber (K29 type, 200D) was prepared and applied to a PET nonwoven fabric. A polysulfone / Kevlar fiber porous support layer was prepared at 25°C using an impregnation-precipitation phase inversion method. The resulting support layer was immersed in an aqueous solution containing 3 wt% aminoguanidine nitrate at 25°C for 25 s, and then dried by air drying until no water droplets were visible on the surface. The resulting membrane was then immersed in a hexane solution containing 0.20 wt% trimesoyl chloride at 25°C for 50 s to allow interfacial polymerization to form a polyamide selective layer. After removing the membrane and removing the surface organic solvent by air drying, the resulting membrane was immersed in hot water at 80°C for 4 min, and then immersed in an aqueous solution containing 10 wt% glycerol for 2 min. Finally, the resulting membrane was dried by air drying at 90°C to obtain the composite nanofiltration membrane material of Example 3.

[0079] Example 4

[0080] A base membrane casting solution containing 16 wt% bisphenol A type polysulfone (Mn 80000 Da) and 3 wt% Kevlar fiber (K29 type, 200D) was prepared and applied to a PET nonwoven fabric. A polysulfone / Kevlar fiber porous support layer was prepared at 25°C using an impregnation-precipitation phase inversion method. The resulting support layer was immersed in an aqueous solution containing 4 wt% aminoguanidine nitrate at 25°C for 25 s, and then dried by air drying until no water droplets were visible on the surface. The resulting membrane was then immersed in a hexane solution containing 0.20 wt% trimesoyl chloride at 25°C for 50 s to allow interfacial polymerization to form a polyamide selective layer. After removing the membrane and removing the surface organic solvent by air drying, the resulting membrane was immersed in hot water at 80°C for 4 min, and then immersed in an aqueous solution containing 10 wt% glycerol for 2 min. Finally, the resulting membrane was dried by air drying at 90°C to obtain the composite nanofiltration membrane material of Example 4.

[0081] Example 5

[0082] A base membrane casting solution containing 16 wt% bisphenol A type polysulfone (Mn 80000 Da) and 3 wt% Kevlar fiber (K29 type, 200D) was prepared and applied to a PET nonwoven fabric. A polysulfone / Kevlar fiber porous support layer was prepared at 25°C using an impregnation-precipitation phase inversion method. The resulting support layer was immersed in an aqueous solution containing 5 wt% aminoguanidine nitrate at 25°C for 25 s, and then dried by air drying until no water droplets were visible on the surface. The resulting membrane was then immersed in a hexane solution containing 0.20 wt% trimesoyl chloride at 25°C for 50 s to allow interfacial polymerization to form a polyamide selective layer. After removing the membrane and removing the surface organic solvent by air drying, the resulting membrane was immersed in hot water at 80°C for 4 min, and then immersed in an aqueous solution containing 10 wt% glycerol for 2 min. Finally, the resulting membrane was dried by air drying at 90°C to obtain the composite nanofiltration membrane material of Example 5.

[0083] Example 6

[0084] A base membrane casting solution containing 16 wt% bisphenol A type polysulfone (Mn 80000 Da) and 3 wt% Kevlar fiber (K29 type, 200D) was prepared and applied to a PET nonwoven fabric. A polysulfone / Kevlar fiber porous support layer was prepared at 25°C using an impregnation-precipitation phase inversion method. The resulting support layer was immersed in an aqueous solution containing 6 wt% aminoguanidine nitrate at 25°C for 25 s, and then dried by air drying until no water droplets were visible on the surface. The resulting membrane was then immersed in a hexane solution containing 0.20 wt% trimesoyl chloride at 25°C for 50 s to allow interfacial polymerization to form a polyamide selective layer. After removing the membrane and removing the surface organic solvent by air drying, the resulting membrane was immersed in hot water at 80°C for 4 min, and then immersed in an aqueous solution containing 10 wt% glycerol for 2 min. Finally, the resulting membrane was dried by air drying at 90°C to obtain the composite nanofiltration membrane material of Example 5.

[0085] Example 7

[0086] A base membrane casting solution containing 16 wt% bisphenol A type polysulfone (Mn 80000 Da) and 3 wt% Kevlar fiber (K29 type, 200D) was prepared and applied to a PET nonwoven fabric. A polysulfone / Kevlar fiber porous support layer was prepared at 25°C using an impregnation-precipitation phase inversion method. The resulting support layer was immersed in an aqueous solution containing 5 wt% aminoguanidine nitrate at 25°C for 25 s, and then dried by air drying until no water droplets were visible on the surface. The resulting membrane was then immersed in a hexane solution containing 0.25 wt% trimesoyl chloride at 25°C for 50 s to allow interfacial polymerization to form a polyamide selective layer. After removing the membrane and removing the surface organic solvent by air drying, the resulting membrane was immersed in hot water at 80°C for 4 min, and then immersed in an aqueous solution containing 10 wt% glycerol for 2 min. Finally, the resulting membrane was dried by air drying at 90°C to obtain the composite nanofiltration membrane material of Example 6.

[0087] Example 8

[0088] A base membrane casting solution containing 16 wt% bisphenol A type polysulfone (Mn 80000 Da) and 3 wt% Kevlar fiber (K29 type, 200 Da) was prepared and applied to a PET nonwoven fabric. A polysulfone / Kevlar fiber porous support layer was prepared at 25°C using an impregnation-precipitation phase inversion method. The resulting support layer was immersed in an aqueous solution containing 5 wt% aminoguanidine nitrate at 25°C for 25 s, and then dried by air drying until no water droplets were visible on the surface. The resulting membrane was then immersed in a hexane solution containing 0.30 wt% trimesoyl chloride at 25°C for 50 s to allow interfacial polymerization to form a polyamide selective layer. After removing the membrane and removing the surface organic solvent by air drying, the resulting membrane was immersed in hot water at 80°C for 4 min, and then immersed in an aqueous solution containing 10 wt% glycerol for 2 min. Finally, the resulting membrane was dried by air drying at 90°C to obtain the composite nanofiltration membrane material of Example 8.

[0089] Comparative Example 1

[0090] A base membrane casting solution containing 19 wt% bisphenol A type polysulfone (Mn 80000 Da) and 0 wt% Kevlar fiber was prepared and applied to a PET nonwoven fabric. A polysulfone porous support layer was prepared at 25 °C using an impregnation-precipitation phase inversion method. The resulting support layer was immersed in an aqueous solution containing 5 wt% piperazine at 25 °C for 25 s, and then dried by air drying until no water droplets were visible on the surface. The resulting membrane was then immersed in a hexane solution containing 0.25 wt% trimesoyl chloride at 25 °C for 50 s to induce interfacial polymerization and form a polyamide selective layer. After removing the membrane and removing the surface organic solvent by air drying, the resulting membrane was immersed in hot water at 80 °C for 4 min, and then immersed in an aqueous solution containing 10 wt% glycerol for 2 min. Finally, the resulting membrane was dried by air drying at 90 °C to obtain the composite nanofiltration membrane material of Comparative Example 1.

[0091] Anti-fouling performance test:

[0092] The antifouling performance of the membranes in Comparative Example 1 and Examples 1-8 was compared.

[0093] The steps for testing the antifouling performance of the membrane are as follows:

[0094] A 2000 ppm MgSO4 aqueous solution was prepared as the raw water. Each group of membranes was continuously circulated at 100 psi for 20 min, while the raw water temperature was maintained at 20 ± 3 ℃. After the operation was completed, the desalination rate and flux data of each group of membranes were recorded as the initial performance of the membranes before contamination.

[0095] Subsequently, a mixed aqueous solution of 2000 ppm MgSO4 and 20 ppm bovine serum albumin (BSA) was prepared as the raw water and continuously circulated at 100 psi pressure for 24 hours. The raw water temperature was maintained at 20 ± 3℃.

[0096] Record the desalination rate and flux of each of the nine membrane groups after operation with BSA contamination, and calculate their respective rates of change relative to the initial desalination rate and initial flux.

[0097] The test results are shown in Table 1 below:

[0098] Table 1

[0099]

[0100] As can be seen from the test data of Examples 1 to 3 and Comparative Example 1 in Table 1, firstly, in each example, the initial desalination rate reached over 98.23%, and the desalination rate after contamination increased relative to the initial desalination rate. Secondly, as the Kevlar fiber content in the base membrane increased from 1wt% to 3wt%, the initial flux increased accordingly, and the flux decay decreased after contamination. In each example, the flux change rate was only -13.2%, -10.5%, and -8.7%, respectively, all of which were better than the flux change rate of Comparative Example 1 of -22.5%. Therefore, while maintaining excellent desalination rate and flux, it also showed better antifouling properties than Comparative Example 1.

[0101] The test data from Examples 3-6 and Comparative Example 1 show that, firstly, in each example, the initial desalination rate reached over 98.23%. The desalination rate increased after contamination compared to the initial rate. As the concentration of aminoguanidine nitrate in the aqueous solution increased during membrane synthesis, the membrane flux change rate showed a trend of first decreasing and then increasing, indicating that the antifouling performance first increased and then decreased. Specifically, after 24 hours of continuous circulation in a magnesium sulfate solution containing BSA contaminants, Example 5's flux only decreased from 36.69 GFD to 33.72 GFD, with a flux change rate of only -8.1%, far superior to the -22.5% flux change rate of Comparative Example 1. Therefore, in each example, while maintaining excellent desalination rate and flux, it also demonstrated superior antifouling performance compared to Comparative Example 1.

[0102] The initial desalination rates of all the above embodiments are better than those of Comparative Example 1, and the rate of change in desalination rate and flux after contamination are lower than those of Comparative Example 1, showing better stability. The above performance test results show that in this invention, the introduction of Kevlar fiber and aminoguanidine nitrate jointly promotes the antifouling performance of the composite nanofiltration membrane.

[0103] Recovery performance test after alkaline washing:

[0104] The membranes of Examples 1-8 and Comparative Example 1, which had undergone antifouling performance testing, were subjected to alkali washing, and their performance recovery after alkali washing was recorded.

[0105] The specific steps are as follows:

[0106] First, prepare a 2000 ppm sodium hydroxide aqueous solution as the raw water. Then, circulate each group of membranes under test at a pressure of 70 psi for 12 hours, while maintaining the raw water temperature at 20 ± 3℃. This process is called alkaline washing.

[0107] After alkaline washing, a 2000 ppm MgSO4 aqueous solution was prepared as the raw water. Each group of alkaline-washed membranes was continuously circulated at 100 psi for 20 min, with the raw water temperature maintained at 20 ± 3 ℃. After the operation, the desalination rate and flux data of each group of membranes were recorded as the post-alkaline-wash performance. By comparing the post-alkaline-wash performance with the initial performance, the alkaline-wash recovery rate of the membrane flux and desalination rate was calculated.

[0108] The test data is shown in Table 2 below:

[0109] Table 2

[0110]

[0111] As can be seen from the data in Table 2, after the introduction of Kevlar fiber and aminoguanidine nitrate, the membranes of Examples 1 to 8 can still maintain an excellent desalination rate of over 98.76% after fouling and alkaline washing, and the flux is also better than that of Comparative Example 1. In addition, the flux recovery rate is significantly better than that of Comparative Example 1.

[0112] As can be seen from the test data of the membranes in Examples 1-3, as the content of Kevlar fiber in the base membrane increases from 1wt% to 3wt%, the membrane flux recovery ability after alkali washing is significantly improved.

[0113] Among the membranes of the various embodiments, the membrane of Example 5 exhibits the best flux recovery capability after alkaline washing. After 12 hours of alkaline washing with sodium hydroxide aqueous solution, its flux recovered to 92.36% of the initial level, and the desalination rate for MgSO4 remained at a high level of 98.89%. Combined with the excellent contaminant resistance of Example 5 shown in Table 1 above (i.e., after 24 hours of BSA contamination, the flux decreased by only 8.1%, and the desalination rate changed by only 1.11%), the experimental results of this invention demonstrate that, among Examples 1 to 8 shown above, the polyamide composite nanofiltration membrane prepared under the process formulation conditions corresponding to Example 5 has the best antifouling performance.

[0114] It should be noted that although the technical solution of the present invention has been described with specific examples, those skilled in the art will understand that the present invention should not be limited thereto.

[0115] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A composite nanofiltration membrane, characterized in that, From bottom to top, they include: Supporting materials; The base film layer comprises polysulfone and poly(p-phenylene terephthalamide) fibers; A polyamide selective layer, wherein the polyamide selective layer is formed by polymerization of amine monomers and acyl chloride monomers, wherein the amine monomers include aminoguanidine salts.

2. The composite nanofiltration membrane according to claim 1, wherein the supporting material is a nonwoven fabric, and the polysulfone is at least one selected from bisphenol A type polysulfone, polyphenylene sulfone, and polyether sulfone.

3. The composite nanofiltration membrane according to claim 1 or 2, wherein the concentration of the polysulfone is 14wt% to 19wt% based on the total weight of the casting solution used to form the base membrane layer.

4. The composite nanofiltration membrane according to claim 1 or 2, wherein the concentration of the poly(p-phenylene terephthalamide) fiber is greater than 0 wt% and less than 5 wt% based on the total weight of the casting solution used to form the base membrane layer.

5. The composite nanofiltration membrane according to claim 1 or 2, wherein the aminoguanidine salt is at least one selected from aminoguanidine hydrochloride, aminoguanidine sulfate, aminoguanidine phosphate, and aminoguanidine nitrate.

6. The composite nanofiltration membrane according to claim 1 or 2, wherein the concentration of the aminoguanidine salt is 1 wt% to 6 wt% based on the total weight of the aqueous phase solution containing the amine monomer.

7. The composite nanofiltration membrane according to claim 1 or 2, wherein the acyl chloride monomer is at least one selected from trimesoyl chloride, isophthaloyl chloride, biphenyl chloride, and terephthaloyl chloride.

8. The composite nanofiltration membrane according to claim 1 or 2, wherein the concentration of the acyl chloride monomer is 0.05wt% to 0.4wt% based on the total weight of the oil phase solution containing the acyl chloride monomer.

9. A method for preparing a composite nanofiltration membrane according to any one of claims 1 to 8, characterized in that, Includes the following steps: A casting solution is prepared, wherein the casting solution comprises polysulfone, poly(p-phenylene terephthalamide) fiber and solvent; The casting solution is applied to a support material to form a base film layer; The support material on which the base film layer is formed is sequentially contacted with an aqueous solution containing amine monomers and an oil solution containing acyl chloride monomers to form a polyamide selective layer, wherein the amine monomers include aminoguanidine salts; Post-processing.

10. The method according to claim 9, wherein the support material is a nonwoven fabric, and the polysulfone is at least one selected from bisphenol A type polysulfone, polyphenylene sulfone, and polyether sulfone.

11. The method according to claim 9 or 10, wherein the concentration of polysulfone is 14wt% to 19wt% based on the total weight of the casting solution.

12. The method according to claim 9 or 10, wherein the concentration of the poly(p-phenylene terephthalamide) fiber is greater than 0 wt% and less than 5 wt% based on the total weight of the casting solution.

13. The method according to claim 9 or 10, wherein the aminoguanidine salt is at least one selected from aminoguanidine hydrochloride, aminoguanidine sulfate, aminoguanidine phosphate, and aminoguanidine nitrate.

14. The method according to claim 9 or 10, wherein the concentration of the aminoguanidine salt is 1 wt% to 6 wt% based on the total weight of the aqueous phase solution containing the amine monomer.

15. The method according to claim 9 or 10, wherein the acyl chloride monomer is at least one selected from pyromellitic methyl methacrylate, isophthaloyl chloride, biphenyl methyl methacrylate, and terephthaloyl chloride.

16. The method according to claim 9 or 10, wherein the concentration of the acyl chloride monomer is 0.05wt% to 0.4wt% based on the total weight of the oil phase solution containing the acyl chloride monomer.

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