Method for preparing chlorine-resistant nanofiltration membrane, and chlorine-resistant nanofiltration membrane prepared therewith

Abstract

A chlorine-resistant nanofiltration membrane and a preparation method therefor. The preparation method comprises: preparing a base membrane; making the base membrane be sequentially contact with an aqueous phase solution comprising an amine monomer and an organic phase solution comprising an acid chloride monomer, wherein the amine monomer includes a piperazine substance and a pyrimidine substance having two or more amino groups, and the acid chloride monomer includes an acid chloride monomer having three or more acid chloride groups; placing the base membrane that has completed contact in an environment having a temperature of 10-30°C, and spraying an aqueous solution containing a dialdehyde crosslinking agent; placing the base membrane in an environment having a temperature of 40-80°C for treatment; and carrying out work-up to obtain a chlorine-resistant nanofiltration membrane.

Description

Preparation method of chlorine-resistant nanofiltration membrane and the chlorine-resistant nanofiltration membrane prepared therefrom

[0001] Cross-reference to related applications

[0002] This disclosure claims priority and benefit to Chinese Patent Application No. 202411599246.5, entitled "Preparation Method of Chlorine-Resistant Nanofiltration Membrane and Chlorine-Resistant Nanofiltration Membrane Prepared Therefrom," filed with the China National Intellectual Property Administration on November 11, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure pertains to the field of nanofiltration membranes, specifically relating to a method for preparing a chlorine-resistant nanofiltration membrane and the chlorine-resistant nanofiltration membrane prepared therefrom. Background Technology

[0004] Nanofiltration, as a precise membrane separation technology, has a high retention capacity for various organic substances. It can remove inorganic ions to a certain extent and retain essential trace elements for the human body. It is one of the home water purification technologies to achieve safe and healthy drinking water. However, as the operating time increases, pollutants such as microorganisms will attach to, grow and reproduce on the surface of the membrane. When it reaches a certain level, it will form a biofilm, which will seriously reduce the performance of the membrane.

[0005] Currently, to avoid microbial contamination, activated chlorine is typically added to the raw water to kill or limit the growth and reproduction of microorganisms on the membrane surface. However, it is important to note that the separation layer of nanofiltration membranes is usually composed of polyamide, whose chemical structure is extremely sensitive to activated chlorine. When it comes into contact with activated chlorine, it can cause changes in the chemical structure of the polyamide network or even chain breakage. Even contact with low concentrations of activated chlorine can still affect the polyamide layer, leading to a decrease in the performance of the nanofiltration membrane and an increase in the cost of using the membrane.

[0006] To avoid the degradation of membrane performance due to contact between active chlorine and the membrane surface, a dechlorination process is added to some membrane application sites, that is, to remove active chlorine before the raw water enters the membrane section.

[0007] Currently, there is considerable research on the chlorination mechanism in the reverse osmosis membrane field, which mainly relates to the NH bonds in polyamides, including reversible amide bond chlorination, irreversible Orton rearrangement, direct chlorination, and the competing mechanism of amide group hydrolysis. However, for nanofiltration membranes, the nanofiltration membranes currently on the market are mainly prepared by interfacial polymerization of piperazine and trimesoyl chloride as reactants. Their unique structure determines that polypiperazine amides do not have NH bonds. Therefore, their chlorination resistance mechanism is mainly considered to be due to the unreacted amine groups undergoing chlorination substitution or being oxidized to hydroxylamine groups and further dehydrated to form imine groups. These changes in unreacted amine groups lead to changes in the chemical and physical properties of the membrane surface, resulting in fluctuations in the membrane's permeation and retention performance.

[0008] Based on research into the chlorine resistance mechanism, several chlorine-resistant modification strategies have been developed, such as surface modification, PA layer modification, support layer modification, and novel separation layer construction. In Patent Document 1 (CN113797762B), carboxyl-terminated SMA is added to the base membrane and esterified with tannic acid to prepare a chlorine-resistant nanofiltration membrane, but it does not mention the membrane's desalination performance, achieving a 96wt% rejection rate for 100 mg / L Congo red. In Patent Document 2 (CN114887486B), mannitol is used as the aqueous monomer to prepare a polyester chlorine-resistant nanofiltration membrane via interfacial polymerization. In Patent Documents 3 (CN113230912B) and 4 (CN115646225A), both use polytetrafluoroethylene microporous membranes as the base membrane and respectively graft m-amino acid... A chlorine-resistant nanofiltration membrane was prepared by modifying acetanilide and using a mixture of 4-sulfonamide o-aminophenol and amine monomers, but the permeation performance of the nanofiltration membrane was not specifically disclosed. In patent document 5 (CN109821427B), graphene oxide quantum dots were grafted onto the surface of a polyamide membrane to prepare a chlorine-resistant aromatic polyamide composite nanofiltration membrane. In patent document 6 (CN111514769B), a chlorine-resistant nanofiltration membrane was prepared by constructing a surface modification layer on the surface of the nanofiltration membrane. The surface modification layer was formed by the reaction of thiourea dioxide and polyvinyl alcohol on the surface of the polypiperazine amide layer, but its stability under long-term operation was not verified. Summary of the Invention

[0009] The problem the invention aims to solve

[0010] Existing nanofiltration membranes can suffer from reduced performance due to biofilms formed by microbial contamination. The addition of active chlorine to the raw water to inhibit the growth and reproduction of microorganisms on the nanofiltration membrane surface can cause changes in the membrane's chemical structure, leading to a decrease in membrane performance. To eliminate the damage to the membrane's chemical structure caused by active chlorine, an additional dechlorination process is required, which increases operating costs and maintenance difficulty.

[0011] Existing research on chlorine-resistant nanofiltration membranes has only examined one aspect of their performance. Furthermore, polyester chlorine-resistant nanofiltration membranes prepared using mannitol as the aqueous monomer suffer from low inorganic salt rejection rates and are prone to hydrolysis during alkaline washing, leading to performance failure. Chlorine-resistant aromatic polyamide composite nanofiltration membranes prepared by grafting graphene oxide quantum dots suffer from long grafting reaction times and require the assistance of a shaking incubator.

[0012] Therefore, there is an urgent need to develop a method for preparing a chlorine-resistant nanofiltration membrane that is low in production cost, high in production efficiency, simple and easy to operate, and does not require modification of existing equipment. Furthermore, there is an urgent need to provide a chlorine-resistant nanofiltration membrane that is low in operating cost, easy to maintain, has excellent desalination performance, permeation performance and chlorine resistance, and excellent performance stability under long-term operation.

[0013] Solution for solving the problem

[0014] The inventors have conducted long-term and in-depth research on the above-mentioned problems and discovered that: in the interfacial polymerization reaction, by further introducing pyrimidine substances with two or more amino groups as amine monomers on the basis of using piperazine substances as amine monomers, a structure containing pyrimidine rings can be formed in the polyamide layer. The included m-diazine ring structure can form a conjugated structure with the amide groups in the polyamide layer, improving the stability of chemical bonds and thus reducing the adverse effects caused by the attack of active chlorine on the membrane during operation. After the base membrane is successively contacted with an aqueous phase solution containing amine monomers and an organic phase solution containing acyl chloride monomers, it is first placed at a relatively low temperature, then sprayed with an aqueous solution containing dialdehyde crosslinking agent, and then treated at a relatively high temperature. This can improve the crosslinking degree and density of the polyamide layer, which is beneficial to further reduce the adverse effects of active chlorine on the polyamide layer and further improve the overall performance of the chlorine-resistant nanofiltration membrane, thereby solving the above-mentioned problems.

[0015] Specifically, this disclosure provides a method for preparing a chlorine-resistant nanofiltration membrane, which includes the following steps:

[0016] Prepare a base film, which comprises a nonwoven fabric layer and a polymer layer from bottom to top;

[0017] The base film is sequentially contacted with an aqueous solution containing amine monomers and an organic solution containing acyl chloride monomers. The amine monomers include piperazines and pyrimidines having two or more amino groups, and the acyl chloride monomers include acyl chloride monomers having three or more acyl chloride groups.

[0018] After contact is completed, the base film is placed in an environment with a temperature of 10-30°C and sprayed with an aqueous solution containing a dialdehyde crosslinking agent.

[0019] The treatment is carried out in an environment with a temperature of 40–80℃.

[0020] After post-processing, a chlorine-resistant nanofiltration membrane is obtained.

[0021] The preparation method described in this disclosure, wherein the polymer is selected from one or more of bisphenol A type polysulfone, polyarylsulfone, polyethersulfone, sulfonated bisphenol A type polysulfone, sulfonated polyethersulfone, and polyphenylene sulfone; preferably, the polymer is bisphenol A type polysulfone.

[0022] The preparation method described in this disclosure includes forming an intermediate layer on the base film before contacting the base film with the aqueous solution; preferably, the intermediate layer comprises polyvinyl alcohol.

[0023] The preparation method described in this disclosure, wherein the piperazine is selected from one or more of piperazine, 2-methylpiperazine, N-aminoethylpiperazine, 1,4-bis(3-aminopropyl)piperazine, piperazine-2,6-dione, trans-2,5-dimethylpiperazine, 2,2-dimethylpiperazine, cis-2,6-dimethylpiperazine, and 5,5-dimethylpiperazine-2-one; preferably, the concentration of the piperazine is 0.1 to 10 wt% based on the total weight of the aqueous solution.

[0024] The preparation method described in this disclosure, wherein the pyrimidine substance having two or more amino groups is selected from 2,4,6-triaminopyrimidine, 4,5,6-triaminopyrimidine, 2,4,5-triaminopyrimidine, 2,4,5,6-tetraaminopyrimidine, 2,4,5,6-tetraaminopyrimidine sulfate, 4,6-diaminopyrimidine, 4,6-diamino-2-mercaptopyrimidine, 4,6-diaminopyrimidine-5-formonitrile, 4,6-diamino-5-hydroxypyrimidine, 2,4-diaminopyrimidine, 2,4-diamino-6-methoxypyrimidine, 2,4-diamino-6-chloropyrimidine, 2,4-diamino-6-hydroxypyrimidine, 2,4-diamino-6-hydroxy-5-nitrosopyrimidine, 2,4-diamino-6-ethoxypyrimidine, 2,4- One or more of the following: diamino-5-hydroxymethylpyrimidine, 2,4-diaminopyrimidine-5-carboxylic acid, 2,4-diamino-5-iodopyrimidine, 2,4-diaminopyrimidine-5-carboxaldehyde, 2,4-diamino-6-ethylpyrimidine, 2,5-diaminopyrimidine, 2,5-diamino-4,6-dihydroxypyrimidine, 3-bromo-2,5-diaminopyrimidine, 4,5-diaminopyrimidine, 2-chloro-4,5-diaminopyrimidine, 4,5-diamino-2-thiouracil, 2-mercapto-4-hydroxy-5,6-diaminopyrimidine, and 5,6-diaminouracil; preferably, based on the total concentration of the amine monomers, the concentration of the pyrimidine substance having two or more amino groups is 20% to 50%.

[0025] The preparation method described in this disclosure, wherein the acyl chloride monomer having three or more acyl chloride groups is selected from one or more of pyromellitic trimethylolpropane chloride, biphenyltetramethylolpropane chloride, succinic trimethylolpropane chloride, 1,3,6-naphthalenetrisulfonyl chloride, pentyltrimethylolpropane chloride, cyclohexanetrimethylolpropane chloride, and hexamethylenetrimethylolpropane chloride; preferably, the concentration of the acyl chloride monomer is 0.01 to 1 wt% based on the total weight of the organic phase solution; preferably, the organic phase solution further comprises a solvent, wherein the solvent is selected from one or more of Isopar E, n-hexane, n-heptane, cyclohexane, ethylcyclohexane, and n-pentane.

[0026] The preparation method described in this disclosure, wherein the dialdehyde crosslinking agent is one or more selected from glyoxal, malondialdehyde, succinaldehyde, glutaraldehyde, o-phthalaldehyde, guavadialdehyde, and polyethylene glycol dialdehyde; preferably, the concentration of the dialdehyde crosslinking agent is 0.01 to 0.5 wt% based on the total weight of the aqueous solution containing the dialdehyde crosslinking agent.

[0027] The preparation method described in this disclosure further comprises an acid-binding agent and a surfactant in the aqueous phase solution; preferably, the acid-binding agent is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, and triethylamine / camphor sulfonic acid composite system; preferably, the surfactant is selected from one or more of sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, sodium dodecylbenzene sulfate, triethanolamine lauryl sulfate, and ammonium dodecyl sulfate.

[0028] The preparation method described in this disclosure, wherein the treatment time in an environment with a temperature of 40–80°C is 0.5 minutes or more and less than 8 minutes, preferably 0.5 minutes or more and less than 7 minutes, more preferably, the treatment time in an environment with a temperature of 40–60°C is 0.5 minutes or more and less than 6 minutes, and the treatment time in an environment with a temperature exceeding 60°C and below 80°C is 0.5 minutes or more and less than 4 minutes; preferably, the post-treatment includes washing with water at a temperature of 60–80°C; preferably, the post-treatment further includes washing with water at a temperature of 20–30°C, treatment with an aqueous solution containing glycerol, and heat drying.

[0029] This disclosure also provides chlorine-resistant nanofiltration membranes obtained by the methods of this disclosure.

[0030] The effects of the invention

[0031] The method for preparing the chlorine-resistant nanofiltration membrane disclosed herein has low production cost, high production efficiency, simple and easy operation, and does not require modification of existing equipment. The chlorine-resistant nanofiltration membrane prepared by the method disclosed herein has low operating cost, is easy to maintain, has excellent desalination performance, permeation performance and chlorine resistance performance, and excellent performance stability under long-term operation.

[0032] The nanofiltration membrane prepared by the method disclosed herein can have a water flux of up to 60 GFD, a magnesium sulfate removal rate of over 98%, and exhibits better flux stability, better desalination rate stability, and excellent chlorine resistance in dynamic tests of 1000 mg / L sodium hypochlorite solution after 10 hours of static soaking and 10 mg / L sodium hypochlorite solution after 300 hours. Attached Figure Description

[0033] Figure 1 shows the dynamic chlorine resistance evaluation results of the nanofiltration membranes of Comparative Example 1 and Example 6. Detailed Implementation

[0034] Various exemplary embodiments, features, and aspects of this disclosure will be described in detail below. The term "exemplary" as used herein means "serving as an example, embodiment, or illustration." Any embodiment illustrated herein as "exemplary" is not necessarily to be construed as superior to or better than other embodiments.

[0035] Furthermore, to better illustrate this disclosure, numerous specific details are set forth in the following detailed description. Those skilled in the art will understand that this disclosure 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 main points of this disclosure.

[0036] Unless otherwise stated, all units used in this specification are international standard units, and all numerical values ​​and ranges appearing in this disclosure should be understood to include systematic errors that are unavoidable in industrial production.

[0037] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0038] 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.

[0039] 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.

[0040] This disclosure provides a method for preparing a chlorine-resistant nanofiltration membrane, which includes the following steps:

[0041] Prepare a base film, which comprises a nonwoven fabric layer and a polymer layer from bottom to top;

[0042] The base film is sequentially contacted with an aqueous solution containing amine monomers and an organic solution containing acyl chloride monomers. The amine monomers include piperazines and pyrimidines having two or more amino groups, and the acyl chloride monomers include acyl chloride monomers having three or more acyl chloride groups.

[0043] After contact is completed, the base film is placed in an environment with a temperature of 10-30°C and sprayed with an aqueous solution containing a dialdehyde crosslinking agent.

[0044] The treatment is carried out in an environment with a temperature of 40–80℃.

[0045] After post-processing, a chlorine-resistant nanofiltration membrane is obtained.

[0046] The base film can be formed by coating a polymer solution onto a nonwoven fabric. There are no particular restrictions on the material of the nonwoven fabric, such as polyester nonwoven fabric.

[0047] Preferably, the polymer is one or more selected from bisphenol A type polysulfone, polyarylsulfone, polyethersulfone, sulfonated bisphenol A type polysulfone, sulfonated polyethersulfone, and polyphenylene sulfone. More preferably, the polymer is bisphenol A type polysulfone. There is no particular limitation on the molecular weight of the polymer, which can be in the range of, for example, 60,000 to 100,000 Da.

[0048] There are no particular limitations on the thickness and pore size of the base film. For example, the thickness of the base film can be in the range of 5.0 to 5.5 mil, and the pore size of the base film can be in the range of 20 to 40 nm.

[0049] Preferably, an intermediate layer is formed before the base film comes into contact with the aqueous solution. Preferably, the intermediate layer comprises polyvinyl alcohol (PVA). The intermediate layer can be formed, for example, by coating the base film with an aqueous solution of PVA at a mass concentration of 5 wt%, to improve the diffusion of amine monomers in the aqueous solution. There is no particular limitation on the molecular weight of the PVA; it can be in the range of, for example, 30,000 to 50,000 Da.

[0050] Preferably, the piperazine is selected from one or more of piperazine, 2-methylpiperazine, N-aminoethylpiperazine, 1,4-bis(3-aminopropyl)piperazine, piperazine-2,6-dione, trans-2,5-dimethylpiperazine, 2,2-dimethylpiperazine, cis-2,6-dimethylpiperazine, and 5,5-dimethylpiperazine-2-one.

[0051] Preferably, the concentration of the piperazine substance is 0.1 to 10 wt% based on the total weight of the aqueous solution. If the concentration is less than 0.1 wt%, a complete polyamide layer cannot be formed through interfacial polymerization, resulting in poor desalination performance of the prepared membrane. If the concentration is greater than 10 wt%, the thickness of the polyamide layer formed through interfacial polymerization is too large, leading to increased water molecule permeation resistance, low flux of the resulting membrane, and poor practical application effect.

[0052] More preferably, the concentration of the piperazine is 0.1 to 7 wt%, and even more preferably, the concentration of the piperazine is 0.1 to 4 wt%.

[0053] Preferably, the pyrimidine substance having two or more amino groups is selected from 2,4,6-triaminopyrimidine, 4,5,6-triaminopyrimidine, 2,4,5-triaminopyrimidine, 2,4,5,6-tetraaminopyrimidine, 2,4,5,6-tetraaminopyrimidine sulfate, 4,6-diaminopyrimidine, 4,6-diamino-2-mercaptopyrimidine, 4,6-diaminopyrimidine-5-carboxynitrile, 4,6-diamino-5-hydroxypyrimidine, 2,4-diaminopyrimidine, 2,4-diamino-6-methoxypyrimidine, 2,4-diamino-6-chloropyrimidine, 2,4-diamino-6-hydroxypyrimidine, 2,4-diamino-6-hydroxy-5-nitrosopyrimidine, 2, One or more of the following: 4-diamino-6-ethoxypyrimidine, 2,4-diamino-5-hydroxymethylpyrimidine, 2,4-diaminopyrimidine-5-carboxylic acid, 2,4-diamino-5-iodopyrimidine, 2,4-diaminopyrimidine-5-carboxaldehyde, 2,4-diamino-6-ethylpyrimidine, 2,5-diaminopyrimidine, 2,5-diamino-4,6-dihydroxypyrimidine, 3-bromo-2,5-diaminopyrimidine, 4,5-diaminopyrimidine, 2-chloro-4,5-diaminopyrimidine, 4,5-diamino-2-thiouracil, 2-mercapto-4-hydroxy-5,6-diaminopyrimidine, and 5,6-diaminouracil.

[0054] Preferably, based on the total concentration of the amine monomers, the concentration of the pyrimidine substances having two or more amino groups is 20% to 50%. If the concentration is less than 20%, the prepared nanofiltration membrane will have insufficient chlorine resistance. If the concentration is greater than 50%, the desalination performance (i.e., desalination rate, retention rate) of the prepared nanofiltration membrane will decrease.

[0055] There are no particular limitations on the contact time and contact temperature between the base film and the aqueous solution containing amine monomers. For example, the contact time can be 10 to 60 seconds within a temperature range of 15 to 45°C, preferably 15 to 30°C.

[0056] The aqueous solution may also contain acid-binding agents and surfactants.

[0057] The function of the acid-binding agent is to absorb the hydrogen chloride produced during the interfacial polymerization process, thereby promoting the interfacial polymerization reaction.

[0058] Preferably, the acid-binding agent is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, and a triethylamine / camphor sulfonic acid composite system. The concentration of the acid-binding agent in the aqueous solution can be adjusted according to the specific type of acid-binding agent selected to adjust the pH value of the aqueous solution to the range of 10-12.

[0059] The surfactant is used to promote the diffusion of amine monomers in order to prepare a nanofiltration membrane with a defect-free membrane surface.

[0060] Preferably, the surfactant is selected from one or more of sodium dodecylbenzenesulfonate, sodium dodecyl sulfonate, sodium dodecyl sulfate, sodium dodecylbenzene sulfate, triethanolamine lauryl sulfate, and ammonium dodecyl sulfate. More preferably, the surfactant content is 0.1 to 1.0 wt% based on the total weight of the aqueous solution.

[0061] Preferably, the acyl chloride monomer having three or more acyl chloride groups is selected from one or more of pyromellitic trimethylolpropane chloride, biphenyltetramethylolpropane chloride, succinic trimethylolpropane chloride, 1,3,6-naphthalenetrisulfonyl chloride, pentyltrimethylolpropane chloride, cyclohexanetrimethylolpropane chloride, and hexamethylenetrimethylolpropane chloride. The acyl chloride monomer having three or more acyl chloride groups can be used to increase the proportion of nonlinear polyamide in the polyamide chain.

[0062] The organic phase solution may also contain acyl chloride monomers having two acyl chloride groups. Preferably, the acyl chloride monomers having two acyl chloride groups are selected from one or more of isophthaloyl chloride, terephthaloyl chloride, phthaloyl chloride, 2,6-naphthalenedilicate chloride, 2,6-naphthalenedisulfonyl chloride, oxaloyl chloride, malonyl chloride, adipyl chloride, and succinyl chloride.

[0063] Preferably, the concentration of the acyl chloride monomer is 0.01–1 wt% based on the total weight of the organic phase solution. When the concentration is below 0.01 wt%, a nanofiltration membrane with good removal performance for the substance to be removed cannot be prepared; when the concentration is above 1 wt%, the prepared nanofiltration membrane is relatively dense, resulting in low flux and poor practical application performance. More preferably, the concentration is 0.05–0.3 wt%.

[0064] Preferably, the organic phase solution further comprises a solvent, which is one or more selected from Isopar E, n-hexane, n-heptane, cyclohexane, ethylcyclohexane, and n-pentane. When these solvents are used, they have two advantages: first, they can dissolve acyl chloride monomers; second, after the solvent is adsorbed onto the base film, it can evaporate quickly at room temperature (e.g., 10–30°C) or with only a small amount of air blowing.

[0065] There are no particular limitations on the contact time and contact temperature between the base film and the organic phase solution containing acyl chloride monomers. For example, the contact time can be 10 to 60 seconds within a temperature range of 15 to 45°C, preferably 15 to 30°C.

[0066] After the base membrane is sequentially contacted with an aqueous solution containing amine monomers and an organic solution containing acyl chloride monomers, an interfacial polymerization reaction will occur between the amine monomers and acyl chloride monomers on the surface of the base membrane to form an initial polyamide layer. The base membrane after contact is placed in an environment with a temperature of 10-30°C. After the organic solution evaporates, an aqueous solution containing a dialdehyde crosslinking agent is sprayed onto the membrane surface.

[0067] Regarding the evaporation of the organic phase solution, the choice of whether to use an air-drying method on the membrane surface can be made based on the physical properties of the selected organic phase solvent itself. It should be noted that the air volume should not be too large at this time to avoid the generation of defects. Usually, it is only necessary to place it in a room temperature environment for 0.5 to 3 minutes before spraying an aqueous solution containing dialdehyde crosslinking agent onto the membrane surface.

[0068] In this process, firstly, since the aforementioned volatile solvent was selected, it can evaporate rapidly at room temperature (e.g., 10–30°C) in a short time, which helps to reduce the shrinkage phenomenon of the base membrane caused by the base membrane being in an anhydrous state for a long time and thus reduces the adverse effects on the permeation performance of the prepared nanofiltration membrane; secondly, after the organic solvent evaporates, a mist of an aqueous solution containing dialdehyde crosslinking agent is sprayed onto the membrane surface, mainly to promote the reaction between the groups on the membrane surface and reduce the proportion of linear polyamide in the polyamide chain.

[0069] Preferably, the dialdehyde crosslinking agent is selected from one or more of glyoxal, malondialdehyde, succinaldehyde, glutaraldehyde, o-phthalaldehyde, guavadialdehyde, and polyethylene glycol dialdehyde. Polyethylene glycol dialdehyde, also known as dialdehyde-based polyethylene glycol, has the following structure.

[0070] Preferably, the concentration of the dialdehyde crosslinking agent is 0.01–0.5 wt% based on the total weight of the aqueous solution containing the dialdehyde crosslinking agent. More preferably, the concentration is 0.02–0.25 wt%.

[0071] Applying an aqueous solution containing a dialdehyde crosslinking agent at a concentration of 0.01–0.5 wt% (i.e., a relatively low concentration) by spraying not only allows the appropriate amount of crosslinking agent to be applied more evenly to the membrane surface, resulting in a more uniform degree of crosslinking across the entire membrane surface, but also ensures that crosslinking mainly occurs on the surface layer of the membrane. This avoids crosslinking in the lower / bottom layer of the membrane, which would lead to an overly dense functional layer (desalination layer) and cause undesirable flux reduction.

[0072] Preferably, the aqueous solution containing the dialdehyde crosslinking agent has a pH of 4 to 6 to promote the crosslinking reaction. For example, an aqueous solution with a hydrochloric acid concentration of 1 mol / L can be used to adjust the pH.

[0073] Preferably, a high-speed water mist spraying device is used to perform a high-speed spraying process of an aqueous solution containing a dialdehyde crosslinking agent, and the spraying temperature is room temperature (e.g., 10–30°C). More preferably, the spraying rate is 0.05–0.5 L / m³. 2 .

[0074] Subsequently, the membrane is subjected to heat treatment at 40–80°C to promote the reaction between unreacted amino and acyl chloride groups on the membrane surface and to promote the reaction between groups in the polyamide layer by dialdehyde crosslinking agents. This reduces the proportion of linear polyamide and increases the degree of crosslinking of the polyamide layer, which is beneficial for preparing nanofiltration membranes with better performance.

[0075] There is no particular limitation on the heat treatment time in an environment of 40–80°C. Preferably, the treatment time in an environment of 40–80°C is 0.5 minutes or more and less than 8 minutes. More preferably, the time is 0.5 minutes or more and less than 7 minutes. More preferably, the treatment time in an environment of 40–60°C is 0.5 minutes or more and less than 6 minutes. The treatment time in an environment of more than 60°C and less than 80°C is 0.5 minutes or more and less than 4 minutes.

[0076] The specific heat treatment time can be adjusted appropriately according to the specific temperature used. For example, when heat treatment is carried out at 60℃, the heat treatment time should not exceed 5 minutes. When heat treatment is carried out at 80℃, the heat treatment time should not exceed 3 minutes. If the heat treatment time is too long or the temperature is too high, the polyamide layer on the membrane surface will become too dense, and the membrane permeation performance will decrease significantly.

[0077] Preferably, the product is then washed with pure water at a temperature of 60–80°C to remove unreacted amine monomers, acyl chloride monomers, and dialdehyde crosslinking agents. There is no particular limitation on the washing time; for example, it can be 1–10 minutes, preferably 3–8 minutes.

[0078] Preferably, pure water at a temperature of 20-30°C is used for rinsing. There is no particular limitation on the rinsing time, for example, it can be 3-10 minutes.

[0079] Preferably, the base film is immersed in an aqueous solution containing glycerol for pore retention treatment. The concentration of glycerol is not particularly limited and can be in the range of, for example, 8 to 15 wt%. More preferably, the treatment is carried out at a temperature of 20 to 30°C for 1 to 5 minutes.

[0080] Preferably, the membrane is further subjected to heat drying to obtain the final nanofiltration membrane. Preferably, the heat drying temperature range is 60–90°C, and the drying time is 3–10 minutes.

[0081] Example

[0082] The embodiments of this disclosure 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 this disclosure. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0083] Preparation of base film

[0084] Prepare a bisphenol A type polysulfone-based membrane containing a polyvinyl alcohol interlayer, with a pore size range of 20–30 nm and an overall thickness of 5.2–5.3 mil.

[0085] Solution preparation

[0086] Preparation of aqueous solutions

[0087] Take 10g of piperazine or a total of 10g of piperazine and a pyrimidine substance with two or more amino groups, and 3g of sodium dodecyl sulfate, dissolve them in 987g of pure water, and add 0.1mol / L sodium hydroxide solution to adjust the pH to 10-11 to prepare an aqueous solution.

[0088] Preparation of organic phase solutions

[0089] Prepare an organic phase solution by dissolving 1 g of pyromellitic chloride in 999 g of Isopar E solvent.

[0090] Preparation of aqueous solutions containing crosslinking agents

[0091] Dissolve 1g of glutaraldehyde in a 50% aqueous solution in 999g of pure water and stir well. Adjust the pH to 4-6.

[0092] Comparative Example

[0093] After rinsing the base membrane with pure water, it was placed in an aqueous solution (containing 1.0 wt% piperazine) for 30 seconds to adsorb piperazine monomers. After removal, excess solution was removed from the surface, and the membrane was immersed in an organic phase solution for 30 seconds to carry out interfacial polymerization to generate the initial polyamide layer. Subsequently, it was placed in an environment of 20–25°C for 1 minute, and a blower with an airflow of 3 m / s was applied to the membrane surface to assist in the evaporation of the solvent, thus obtaining the initial nanofiltration membrane. The membrane was then washed sequentially with pure water at 60–70°C for 5 minutes and then with pure water at 20–25°C for 5 minutes. After that, it was immersed in an aqueous solution containing 12 wt% glycerol at 20–25°C for 2 minutes to perform a pore-preserving operation. Finally, the membrane was placed in an oven at 70–80°C for 6 minutes to dry the moisture inside the membrane, thus obtaining the final nanofiltration membrane.

[0094] Comparative Example 1

[0095] After rinsing the base membrane with pure water, it was placed in an aqueous solution (containing 1.0 wt% piperazine) for 30 seconds to adsorb piperazine monomers. After removal, excess solution was removed from the surface, and the membrane was immersed in an organic phase solution for 30 seconds to undergo interfacial polymerization to generate the initial polyamide layer. Subsequently, it was placed in an environment of 20–25°C for 1 minute, and a blowing airflow of 3 m / s was applied to the membrane surface to assist solvent evaporation. Afterward, an aqueous solution containing a crosslinking agent was sprayed onto the membrane surface (spraying rate: 0.1 L / m). 2 Afterwards, it is quickly heated in an environment of 55-60℃ for 2 minutes to obtain the initial nanofiltration membrane. Then, it is washed sequentially with pure water at 60-70℃ for 5 minutes and then with pure water at 20-25℃ for 5 minutes. After that, it is immersed in an aqueous solution containing 12wt% glycerol at 20-25℃ for 2 minutes to perform a pore preservation operation. Finally, the membrane is placed in an oven at 70-80℃ for 6 minutes to dry the moisture inside the membrane to obtain the final nanofiltration membrane.

[0096] The difference between Comparative Example 1 and Comparative Example 2 is that after the organic phase solution evaporates, an aqueous solution containing a crosslinking agent is sprayed on it and heat-treated at 55–60°C.

[0097] Comparative Example 2

[0098] After rinsing the base membrane with pure water, it was placed in an aqueous solution (containing 0.6 wt% piperazine + 0.4 wt% 2,4,6-triaminopyrimidine) for 30 seconds to adsorb amine monomers. After removal, excess solution was removed from the surface, and the membrane was immersed in an organic phase solution for 30 seconds to carry out interfacial polymerization to generate the initial polyamide layer. Subsequently, it was placed in an environment of 20–25°C for 1 minute, and a blower with an airflow of 3 m / s was applied to the membrane surface to assist in the evaporation of the solvent. Afterward, it was quickly transferred to an environment of 55–60°C for 2 minutes to obtain the initial nanofiltration membrane. Then, it was washed sequentially with pure water at 60–70°C for 5 minutes and then with pure water at 20–25°C for 5 minutes. After that, it was immersed in an aqueous solution containing 12 wt% glycerol at 20–25°C for 2 minutes to perform pore preservation. Finally, the membrane was placed in an oven at 70–80°C for 6 minutes to dry the moisture inside the membrane to obtain the final nanofiltration membrane.

[0099] The difference between Comparative Example 2 and Comparative Example 3 is that Comparative Example 2 contains 2,4,6-triaminopyrimidine as an amine monomer and is heat-treated at 55–60°C after evaporation from the organic phase solution.

[0100] Example 1

[0101] After rinsing the base membrane with pure water, it was placed in an aqueous solution (containing 0.6 wt% piperazine + 0.4 wt% 2,4,6-triaminopyrimidine) for 30 seconds to adsorb amine monomers. After removal, excess solution was removed from the surface, and the membrane was immersed in an organic phase solution for 30 seconds to undergo interfacial polymerization to form the initial polyamide layer. Subsequently, it was placed in an environment of 20–25°C for 1 minute, and a blowing airflow of 3 m / s was applied to the membrane surface to assist solvent evaporation. Afterward, an aqueous solution containing a crosslinking agent (spraying rate of 0.1 L / m²) was sprayed onto the membrane surface. 2 Afterwards, it is quickly heated in an environment of 55-60℃ for 2 minutes to obtain the initial nanofiltration membrane. Then, it is washed sequentially with pure water at 60-70℃ for 5 minutes and then with pure water at 20-25℃ for 5 minutes. After that, it is immersed in an aqueous solution containing 12wt% glycerol at 20-25℃ for 2 minutes to perform a pore preservation operation. Finally, the membrane is placed in an oven at 70-80℃ for 6 minutes to dry the moisture inside the membrane to obtain the final nanofiltration membrane.

[0102] Example 2

[0103] Example 2 was carried out in the same manner as Example 1, except that the aqueous solution contained 0.6 wt% piperazine + 0.4 wt% 4,5,6-triaminopyrimidine.

[0104] Example 3

[0105] Example 3 was carried out in the same manner as Example 1, except that the aqueous solution contained 0.6 wt% piperazine + 0.4 wt% 4,6-diaminopyrimidine.

[0106] Example 4

[0107] Example 4 was carried out in the same manner as Example 1, except that the aqueous solution contained 0.6 wt% piperazine + 0.4 wt% 4,6-diamino-5-hydroxypyrimidine.

[0108] Example 5

[0109] Example 5 was carried out in the same manner as Example 1, except that the aqueous solution contained 0.6 wt% piperazine + 0.4 wt% 2,4-diaminopyrimidine.

[0110] Example 6

[0111] Example 6 was carried out in the same manner as Example 1, except that the aqueous solution contained 0.6 wt% piperazine + 0.4 wt% 2,4-diamino-6-hydroxypyrimidine.

[0112] Example 7

[0113] Example 7 was carried out in the same manner as Example 1, except that the aqueous solution contained 0.6 wt% piperazine + 0.4 wt% 2,4-diaminopyrimidine-5-carboxylic acid.

[0114] Example 8

[0115] Example 8 was carried out in the same manner as Example 1, except that the aqueous solution contained 0.6 wt% piperazine + 0.4 wt% 2,5-diaminopyrimidine.

[0116] Example 9

[0117] Example 9 was carried out in the same manner as Example 1, except that after spraying an aqueous solution containing a crosslinking agent onto the membrane surface, it was quickly transferred to an environment of 40-45°C for 4 minutes for heating treatment.

[0118] Example 10

[0119] Example 10 was carried out in the same manner as Example 1, except that after spraying an aqueous solution containing a crosslinking agent onto the membrane surface, it was quickly transferred to an environment of 75-80°C for 1 minute for heat treatment.

[0120] Example 11

[0121] Example 12 was carried out in the same manner as Example 1, except that the aqueous solution contained 0.8 wt% piperazine + 0.2 wt% 2,4,6-triaminopyrimidine.

[0122] Example 12

[0123] Example 12 was carried out in the same manner as Example 1, except that the aqueous solution contained 0.5 wt% piperazine + 0.5 wt% 2,4,6-triaminopyrimidine.

[0124] Comparative Example 3

[0125] Comparative Example 3 was carried out in the same manner as Example 1, except that after spraying an aqueous solution containing a crosslinking agent onto the membrane surface, it was quickly transferred to an environment of 55-60°C for 8 minutes for heating treatment.

[0126] Comparative Example 4

[0127] Comparative Example 4 was carried out in the same manner as Example 1, except that after spraying an aqueous solution containing a crosslinking agent onto the membrane surface, it was quickly transferred to a 95-100°C environment for 1 minute of heating treatment.

[0128] Performance testing

[0129] (1) Permeation separation performance test

[0130] To test the performance of the prepared nanofiltration membranes, nanofiltration membrane sheets obtained from comparative examples 1-4 and Examples 1-10 were tested on a cross-flow membrane testing bench. The test conditions were: 2000 mg / L magnesium sulfate solution, operating pressure 100 psi, temperature 25°C, and pH 7. The stabilization time was 30 minutes. The rejection rate (also known as desalination rate) and permeate flux were recorded.

[0131] Static chlorine resistance evaluation: At 25℃, each nanofiltration membrane was immersed in a 1000 mg / L NaClO solution (adjusted to pH=7) for 10 hours. The residual chlorine solution was replaced every hour. After removal, the membranes were gently rinsed and soaked with deionized water. After confirming the absence of sodium hypochlorite, cross-flow filtration tests were performed under the following conditions: 2000 mg / L magnesium sulfate solution, operating pressure 100 psi, temperature 25℃, and pH 7. The stabilization time was 30 minutes, and the rejection rate (also known as desalination rate) and permeate flux were recorded.

[0132] The test results are shown in Table 1.

[0133] Table 1

[0134] Comparing the results of Comparative Example and Comparative Example 1, it can be seen that in Comparative Example 1, because the base membrane was first exposed to a relatively low temperature after being sequentially contacted with an aqueous solution containing amine monomers and an organic solution containing acyl chloride monomers, followed by spraying with an aqueous solution containing dialdehyde crosslinking agents and then treatment at a relatively high temperature, both the initial desalination rate and the desalination rate after chlorine resistance were improved compared to the Comparative Example. However, both the initial flux and the flux after chlorine resistance decreased. Furthermore, compared to the nanofiltration membrane of the Comparative Example, the chlorine-resistant nanofiltration membrane of Comparative Example 1 showed a smaller decrease in desalination rate after chlorine resistance compared to the initial desalination rate (i.e., a decrease in desalination rate).

[0135] Comparing the results of Comparative Example 1 and Comparative Example 2, it can be seen that in Comparative Example 2, since the base membrane is first subjected to a relatively low temperature and then treated at a relatively high temperature after being contacted sequentially with an aqueous solution containing amine monomers (including pyrimidine monomers with more than two amino groups) and an organic solution containing acyl chloride monomers, the initial flux and the flux after chlorination resistance can be improved. The initial desalination rate is slightly reduced, and the reduction in the desalination rate after chlorination resistance relative to the initial desalination rate is further reduced.

[0136] Compared with Comparative Examples and Comparative Examples 1-2, in Examples 1-12, since the base film was first exposed to a relatively low temperature after being contacted sequentially with an aqueous solution containing amine monomers (including pyrimidine monomers having more than two amino groups) and an organic solution containing acyl chloride monomers, and then sprayed with an aqueous solution containing a relatively low concentration of dialdehyde crosslinking agent, and then treated at a relatively high temperature, not only were the initial flux and desalination rates maintained at a high level, but the flux and desalination rates after chlorination resistance were also maintained at a high level, and the decay of the desalination rate was further reduced.

[0137] In Examples 1, 9, and 10, by using appropriate processing times for different temperatures, the initial flux and desalination rate were kept at a high level, and the flux and desalination rate remained at a high level after chlorine tolerance, thus minimizing the decline in desalination rate.

[0138] In Comparative Example 3, the polyamide layer became too dense due to the prolonged treatment time at 55–60°C, resulting in a significant decrease in flux. However, the desalination rate of the nanofiltration membrane after chlorine resistance was only slightly reduced compared to the initial desalination rate, indicating good chlorine resistance.

[0139] In Comparative Example 4, the polyamide layer became too dense due to the excessively high processing temperature, resulting in a decrease in both throughput and desalination rate.

[0140] (2) Dynamic chlorine resistance performance evaluation

[0141] Nanofiltration membranes from the comparative example, Example 1, and Example 6 were tested. The chlorine resistance evaluation process involved continuous operation of the membranes with a sodium hypochlorite solution containing 10 ppm residual chlorine (pH adjusted to 6.5–7.5). After rinsing with pure water at specified intervals, magnesium sulfate aqueous solution was used as the test solution to evaluate membrane performance. The test conditions were: 2000 mg / L magnesium sulfate solution, operating pressure 100 psi, temperature 25°C, and pH 7. The stabilization time was 30 minutes. The membrane's water flux and rejection rate were recorded accordingly. The total experimental run time was 300 hours. Active chlorine solution was replenished every 12 hours during the run to maintain the active chlorine concentration in the solution. The evaluation results are shown in Figure 1.

[0142] As shown in Figure 1, compared with the nanofiltration membranes of the comparative example, the nanofiltration membranes of Examples 1 and 6 showed a lower increase in flux and a significantly smaller decrease in desalination rate. This indicates that during long-term operation in a solution containing active residual chlorine, the nanofiltration membranes prepared by the method of this disclosure have better flux stability, better desalination rate stability, and better chlorine resistance.

[0143] It should be noted that although the technical solutions of this disclosure have been described with specific examples, those skilled in the art will understand that this disclosure should not be limited thereto.

[0144] The various embodiments of this disclosure 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 method for preparing a chloride-resistant nanofiltration membrane, characterized in that, It includes the following steps: Prepare a base film, which comprises a nonwoven fabric layer and a polymer layer from bottom to top; The base film is sequentially contacted with an aqueous solution containing amine monomers and an organic solution containing acyl chloride monomers. The amine monomers include piperazines and pyrimidines having two or more amino groups, and the acyl chloride monomers include acyl chloride monomers having three or more acyl chloride groups. After contact is completed, the base film is placed in an environment with a temperature of 10-30°C and sprayed with an aqueous solution containing a dialdehyde crosslinking agent. The treatment is carried out in an environment with a temperature of 40–80℃. After post-processing, a chlorine-resistant nanofiltration membrane is obtained.

2. The preparation method according to claim 1, wherein the polymer is one or more selected from bisphenol A type polysulfone, polyarylsulfone, polyethersulfone, sulfonated bisphenol A type polysulfone, sulfonated polyethersulfone, and polyphenylene sulfone; preferably, the polymer is bisphenol A type polysulfone.

3. The preparation method according to claim 1 or 2, wherein an intermediate layer is formed on the base film before the base film is contacted with the aqueous solution; preferably, the intermediate layer comprises polyvinyl alcohol.

4. The preparation method according to claim 1 or 2, wherein the piperazine is selected from one or more of piperazine, 2-methylpiperazine, N-aminoethylpiperazine, 1,4-bis(3-aminopropyl)piperazine, piperazine-2,6-dione, trans-2,5-dimethylpiperazine, 2,2-dimethylpiperazine, cis-2,6-dimethylpiperazine, and 5,5-dimethylpiperazine-2-one; preferably, the concentration of the piperazine is 0.1 to 10 wt% based on the total weight of the aqueous solution.

5. The preparation method according to claim 1 or 2, wherein the pyrimidine substance having two or more amino groups is selected from 2,4,6-triaminopyrimidine, 4,5,6-triaminopyrimidine, 2,4,5-triaminopyrimidine, 2,4,5,6-tetraaminopyrimidine, 2,4,5,6-tetraaminopyrimidine sulfate, 4,6-diaminopyrimidine, 4,6-diamino-2-mercaptopyrimidine, 4,6-diaminopyrimidine-5-carboxynitrile, 4,6-diamino-5-hydroxypyrimidine, 2,4-diaminopyrimidine, 2,4-diamino-6-methoxypyrimidine, 2,4-diamino-6-chloropyrimidine, 2,4-diamino-6-hydroxypyrimidine, 2,4-diamino-6-hydroxy-5-nitrosopyrimidine, 2,4-diamino-6-ethoxypyrimidine, One or more of the following: 2,4-diamino-5-hydroxymethylpyrimidine, 2,4-diaminopyrimidine-5-carboxylic acid, 2,4-diamino-5-iodopyrimidine, 2,4-diaminopyrimidine-5-carboxaldehyde, 2,4-diamino-6-ethylpyrimidine, 2,5-diaminopyrimidine, 2,5-diamino-4,6-dihydroxypyrimidine, 3-bromo-2,5-diaminopyrimidine, 4,5-diaminopyrimidine, 2-chloro-4,5-diaminopyrimidine, 4,5-diamino-2-thiouracil, 2-mercapto-4-hydroxy-5,6-diaminopyrimidine, and 5,6-diaminouracil; preferably, based on the total concentration of the amine monomers, the concentration of the pyrimidine substance having two or more amino groups is 20% to 50%.

6. The preparation method according to claim 1 or 2, wherein the acyl chloride monomer having three or more acyl chloride groups is selected from one or more of pyromellitic trimethylolpropane chloride, biphenyltetramethylolpropane chloride, succinic trimethylolpropane chloride, 1,3,6-naphthalenetrisulfonyl chloride, pentyltrimethylolpropane chloride, cyclohexanetrimethylolpropane chloride, and hexamethylenetrimethylolpropane chloride; preferably, the concentration of the acyl chloride monomer is 0.01 to 1 wt% based on the total weight of the organic phase solution; preferably, the organic phase solution further comprises a solvent, wherein the solvent is selected from one or more of Isopar E, n-hexane, n-heptane, cyclohexane, ethylcyclohexane, and n-pentane.

7. The preparation method according to claim 1 or 2, wherein the dialdehyde crosslinking agent is one or more selected from glyoxal, malondialdehyde, succinaldehyde, glutaraldehyde, o-phthalaldehyde, guavadialdehyde, and polyethylene glycol dialdehyde; preferably, the concentration of the dialdehyde crosslinking agent is 0.01 to 0.5 wt% based on the total weight of the aqueous solution containing the dialdehyde crosslinking agent.

8. The preparation method according to claim 1 or 2, wherein the aqueous phase solution further comprises an acid-binding agent and a surfactant; preferably, the acid-binding agent is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, and triethylamine / camphor sulfonic acid composite system; preferably, the surfactant is selected from one or more of sodium dodecylbenzenesulfonate, sodium dodecyl sulfonate, sodium dodecyl sulfate, sodium dodecylbenzene sulfate, triethanolamine lauryl sulfate, and ammonium dodecyl sulfate.

9. The preparation method according to claim 1 or 2, wherein the treatment time in an environment with a temperature of 40-80°C is 0.5 minutes or more and less than 8 minutes, preferably, the time is 0.5 minutes or more and less than 7 minutes, more preferably, the treatment time in an environment with a temperature of 40-60°C is 0.5 minutes or more and less than 6 minutes, and the treatment time in an environment with a temperature of more than 60°C and less than 80°C is 0.5 minutes or more and less than 4 minutes; preferably, the post-treatment includes washing with water at a temperature of 60-80°C; preferably, the post-treatment further includes washing with water at a temperature of 20-30°C, treatment with an aqueous solution containing glycerol, and heat drying.

10. A chlorine-resistant nanofiltration membrane, prepared by the preparation method according to any one of claims 1-9.

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