Composite nanofiltration membrane, method for preparing the same, and use thereof

Abstract

The application relates to the technical field of water treatment membrane materials, in particular to a composite nanofiltration membrane and a preparation method and application thereof. The preparation method of the composite nanofiltration membrane comprises the following steps: placing an aromatic or semi-aromatic nanofiltration membrane in a first organic solvent, the first organic solvent comprising sulfonyl chloride and a first alkane solvent, so that the amino group or the imino group on the surface of the nanofiltration membrane is subjected to an amidation reaction with the sulfonyl chloride; the aromatic or semi-aromatic nanofiltration membrane comprises a polymer base film and a separation layer formed on the surface of the polymer base film, and the polybasic acid chloride for forming the separation layer is an aromatic polybasic acid chloride. The composite nanofiltration membrane prepared by the above preparation method has a small membrane pore size, a large water permeation coefficient, a high surface sulfonic acid group concentration and a high negative electric effect.

Description

Technical Field

[0001] This application relates to the field of water treatment membrane materials technology, and in particular to a composite nanofiltration membrane, its preparation method, and its application. Background Technology

[0002] Organic micropollutants in slightly polluted water sources are often toxic, harmful, and difficult to remove, attracting increasing attention. These micropollutants pose potential risks, such as affecting drinking water safety. Therefore, growing focus is on how to efficiently remove organic micropollutants from raw water. Compared to conventional water treatment processes, emerging technologies have greater application potential. Nanofiltration, as an emerging water treatment technology, has shown broad application prospects in the field of advanced drinking water treatment. Nanofiltration is a membrane separation technology between ultrafiltration and reverse osmosis. The molecular weight cutoff of nanofiltration membranes is generally in the range of 200 Da to 1000 Da, corresponding to pore sizes generally below 1 nm. The lower the molecular weight cutoff and the smaller the pore size, the higher the retention rate of organic micropollutants; however, the lower the membrane permeability coefficient, and the greater the required operating pressure and energy consumption.

[0003] Nanofiltration membrane fouling is one of the most significant challenges facing nanofiltration processes. Nanofiltration membrane fouling includes organic fouling, biological fouling, inorganic fouling, and scaling fouling. Higher surface hydrophilicity generally helps reduce fouling. The nature and density of the membrane surface charge also significantly influence fouling. Higher negative charge density on the membrane surface is more conducive to reducing fouling caused by negatively charged substances in the water through electrostatic repulsion, but it may also increase fouling caused by the bridging effect of polyvalent cations such as calcium and aluminum. Compared to negatively charged carboxyl groups (-COOH) on the membrane surface, negatively charged sulfonic acid groups (-SO3H) are more beneficial for fouling control. Currently, the most common nanofiltration membrane with sulfonic acid groups is the sulfonated polysulfone membrane, generally prepared by phase inversion or coating methods. However, sulfonated polysulfone membranes have drawbacks such as a relatively large molecular weight cutoff (pore size) and a relatively low permeability coefficient.

[0004] Furthermore, nanofiltration membranes produced using conventional techniques, namely interfacial polymerization (IP), are effective against mineral ions (especially Ca2+). 2+ Mg 2+ Excessively high rejection rates of certain pollutants (such as micro-pollutants) lead to reduced chemical stability of the treated water, often necessitating remineralization and increasing investment and operating costs. From a practical application perspective, an ideal nanofiltration membrane should possess a sufficiently low molecular weight cutoff, a sufficiently high negative charge density on the membrane surface, the highest possible sulfonic acid groups, and the largest possible membrane permeability coefficient. This would enable improved rejection rates of micro-pollutants while reducing membrane fouling, mineral ion rejection rates, and the operating pressure required for filtration, thereby increasing treatment efficiency and reducing investment and operating costs. Summary of the Invention

[0005] Therefore, it is necessary to provide a composite nanofiltration membrane that can reduce membrane pore size, increase surface negative charge density, contain more sulfonic acid functional groups, and have a large membrane permeability coefficient, as well as its preparation method and application.

[0006] In a first aspect, this application provides a method for preparing a composite nanofiltration membrane, comprising the following steps:

[0007] An aromatic or semi-aromatic nanofiltration membrane is placed in a first organic solvent, the first organic solvent including sulfonyl chloride and a first alkane solvent, so that the amino or imino groups on the surface of the nanofiltration membrane undergo an amidation reaction with the sulfonyl chloride;

[0008] The aromatic or semi-aromatic nanofiltration membrane includes a polymer base membrane and a selective separation layer formed on the surface of the polymer base membrane.

[0009] In some embodiments, the sulfonyl chloride has a mass concentration of 0.05 wt% to 5 wt% in the first organic solvent.

[0010] In some embodiments, the method for preparing the aromatic or semi-aromatic nanofiltration membrane includes:

[0011] A polymer base film with a surface impregnated with polyamines is placed in a second organic solvent for interfacial polymerization; the second organic solvent includes aromatic polyacrylamide chlorides and second alkane solvents.

[0012] In some embodiments, the polyamine includes aromatic polyamines and / or aliphatic polyamines.

[0013] In some embodiments, the aromatic polyamine includes one or more of m-phenylenediamine, p-phenylenediamine, pyromellitic triamine, diaminobenzoic acid, and diaminobenzenesulfonic acid.

[0014] In some embodiments, the aliphatic polyamine includes one or more of piperazine, piperazine carboxylic acid, ethylenediamine, propylenediamine, butanediamine, and pentanediamine.

[0015] In some embodiments, the aromatic polyacrylamide chloride includes one or more of pyromellitic trimethylolpropionate chloride, terephthaloyl chloride, isophthaloyl chloride, and phthaloyl chloride.

[0016] In some embodiments, the aromatic polyacrylamide chloride has a mass concentration of 0.05 wt% to 5 wt% in the second organic solvent.

[0017] In some embodiments, the method of impregnating the polymer-based film with a polyamine includes:

[0018] The polymer-based film is immersed in a polyamine solution.

[0019] In some embodiments, the mass concentration of the polyamine in the polyamine solution is 0.05 wt% to 5 wt%.

[0020] In some embodiments, the first alkane solvent and the second alkane solvent are each independently selected from one or more of n-hexane, cyclohexane, n-heptane, petroleum ether, and isoalkanes.

[0021] In some embodiments, after the aromatic or semi-aromatic nanofiltration membrane is placed in a first organic solvent for interfacial polymerization, the method further includes a step of curing the obtained product to densify the polyamide layer on the surface of the composite nanofiltration membrane.

[0022] Secondly, this application also provides a composite nanofiltration membrane prepared by the preparation method described in the first aspect.

[0023] Thirdly, this application further provides an application of the composite nanofiltration membrane as described in the second aspect as a water treatment separation membrane.

[0024] The method for preparing the composite nanofiltration membrane provided in this application involves an amidation reaction (grafting or crosslinking reaction) of sulfonyl chloride with residual amino or imino groups in the selective separation layer of a nanofiltration membrane prepared by conventional interfacial polymerization (IP) reaction. The amidation reaction of sulfonyl chloride with amino or imino groups reduces the contribution of the amino or imino groups to the positive charge and hydrolyzes to produce sulfonic acid groups that are beneficial for membrane fouling control. Simultaneously, compared to other aromatic or aliphatic acyl chlorides (such as trimesoyl chloride and methanedisulfonyl chloride), sulfonyl chloride has a smaller molecular volume and moderate reactivity, ensuring that the secondary interfacial polymerization reaction has a suitable reaction rate and suitable reaction sites (such as the ability to diffuse deeper into the interior of the selective separation layer of the nanofiltration membrane). This allows for the increase of the negative charge density, especially the density of sulfonic acid functional groups, on the nanofiltration membrane surface while further reducing its pore size. By reducing the pore size of the composite nanofiltration membrane, the rejection rate of the nanofiltration membrane for micro-pollutants is improved. Increasing the negative charge density on the membrane surface significantly reduces the rejection rate of mineral ions such as calcium and magnesium. Furthermore, increasing the density of sulfonic acid groups on the membrane surface better controls membrane fouling. Thus, the composite nanofiltration membrane simultaneously achieves both selective rejection of mineral ions / micro-pollutants and anti-fouling properties. The composite nanofiltration membrane prepared by this method not only has a small pore size but also a sufficiently high water permeability coefficient, allowing it to operate at relatively low pressures. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 The graph shows the water permeability coefficient and the retention rate of inorganic mineral ions of the composite nanofiltration membranes prepared in Examples 1 and 2 and Comparative Examples 1 and 2.

[0027] Figure 2 The graph shows the molecular weight cutoff test results of the composite nanofiltration membranes prepared in Examples 1 and 2 and Comparative Examples 1 and 2.

[0028] Figure 3 The graph shows the test results of the micro-pollutant rejection rate of the composite nanofiltration membranes prepared in Example 1 and Comparative Examples 1 and 2.

[0029] Figure 4 The graph shows the test results of the water permeability coefficient and the rejection rate of inorganic mineral ions of the composite nanofiltration membranes prepared in Examples 3 and 4 and Comparative Examples 3 and 4. Detailed Implementation

[0030] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0032] Unless otherwise shown or indicated in the operational embodiments, all figures used to represent the amounts, physicochemical properties, etc., of ingredients in the specification and claims are to be understood to be adjusted by the term "about" in all cases. For example, therefore, unless stated to the contrary, the numerical parameters listed in the foregoing specification and appended claims are approximations, and those skilled in the art can appropriately modify these approximations to obtain the desired characteristics by utilizing the teachings disclosed herein. The use of numerical ranges indicated by endpoints includes all numbers within that range and any range within that range; for example, 1 to 5 includes 1, 1.1, 1.3, 1.5, 2, 2.75, 3, 3.80, 4, and 5, etc.

[0033] Traditional nanofiltration membranes either have large molecular weight cutoffs and pore sizes, low negative charge density on the membrane surface, or predominantly use carboxylic acid (-COOH) functional groups on the membrane surface. This results in high rejection rates for mineral ions but insufficient rejection of micro-pollutants, severe membrane fouling, or excessively high operating pressures. Therefore, this application provides a method for preparing a composite nanofiltration membrane to improve upon these problems.

[0034] In a first aspect, this application provides a method for preparing a composite nanofiltration membrane, comprising the following steps:

[0035] An aromatic or semi-aromatic nanofiltration membrane is placed in a first organic solvent, the first organic solvent including sulfonyl chloride and a first alkane solvent, so that the amino or imino groups on the surface of the nanofiltration membrane undergo an amidation reaction with the sulfonyl chloride;

[0036] The aromatic or semi-aromatic nanofiltration membrane includes a polymer base membrane and a selective separation layer formed on the surface of the polymer base membrane.

[0037] The method for preparing the composite nanofiltration membrane provided in this application involves a secondary interfacial polymerization reaction between sulfonyl chloride and residual amino or imino groups in the nanofiltration membrane. Compared to other aromatic or aliphatic acyl chlorides (such as trimesoyl chloride, phthaloyl chloride, oxaloyl chloride, malonyl chloride, etc.), sulfonyl chloride has a smaller molecular volume, moderate reactivity, and forms sulfonic acid functional groups on the selective separation layer of the membrane through amidation. This ensures that the secondary interfacial polymerization reaction has a suitable reaction rate and a suitable reaction location, allowing it to diffuse more deeply into the interior of the selective separation layer of the nanofiltration membrane. This increases the negative charge density on the nanofiltration membrane surface while further reducing its pore size and increasing the density of sulfonic acid groups on the membrane surface. By increasing the negative charge density, especially the density of sulfonic acid functional groups, on the surface of the composite nanofiltration membrane, its rejection rate for mineral ions such as calcium and magnesium can be significantly reduced, while its rejection rate for micro-pollutants can be increased. In other words, the composite nanofiltration membrane simultaneously achieves selective rejection of mineral ions / micro-pollutants and improves its anti-fouling performance. This composite nanofiltration membrane also has the advantages of small pore size and high water permeability.

[0038] It is understandable that sulfonyl chloride is an inorganic compound with the chemical formula SO2Cl2, and its structural formula is as follows.

[0039]

[0040] In some embodiments, the sulfonyl chloride concentration in the first organic solvent is 0.05 wt% to 5 wt%, for example, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, and 4.5 wt%. By controlling the sulfonyl chloride concentration within the above range, it can diffuse more easily into the interior of the polyamide active layer. Therefore, the sulfonyl chloride can react with residual amino or imino groups on the newly formed active layer from the outside in, thereby simultaneously achieving a stronger pore-shrinking effect, a lower mineral ion rejection rate, and higher membrane antifouling performance.

[0041] In some embodiments, the preparation method of the aromatic or semi-aromatic nanofiltration membrane includes:

[0042] A polymer-based film with a surface impregnated with polyamines is placed in a second organic solvent for interfacial polymerization.

[0043] The second organic solvent includes aromatic polyacrylamide chlorides and second alkane solvents.

[0044] It is understood that aromatic or semi-aromatic nanofiltration membranes specifically refer to nanofiltration membranes in which at least one of the polyacrylic chlorides in the raw materials is an aromatic polyacrylic chloride. Specifically, in this application, when at least one of the polyacrylic chlorides and at least one of the polyamines are aromatic compounds, the obtained nanofiltration membrane is an aromatic nanofiltration membrane; when at least one of the polyacrylic chlorides is an aromatic polyacrylic chloride and the polyamine is an aliphatic polyamine, the obtained nanofiltration membrane is a semi-aromatic nanofiltration membrane.

[0045] In this application, the selection of polyamines is not overly restricted; polyamines commonly used in the field of nanofiltration membrane preparation can be selected. In some embodiments, the polyamines include aromatic polyamines and / or aliphatic polyamines. Aromatic polyamines include one or more of m-phenylenediamine, p-phenylenediamine, pyromellitic triamine, diaminobenzoic acid, and diaminobenzenesulfonic acid; aliphatic polyamines include one or more of piperazine, piperazine carboxylic acid, ethylenediamine, propylenediamine, butanediamine, and pentanediamine.

[0046] In this application, the type of aromatic polyacrylamide chloride is not limited; any aromatic polyacrylamide chloride commonly used in the field of nanofiltration membrane preparation can be selected. In some embodiments, the aromatic polyacrylamide chloride includes one or more of pyromellitic trimethylolpropionate chloride, terephthaloyl chloride, isophthaloyl chloride, and phthaloyl chloride. The polyacrylamide chloride used in the first interfacial polymerization reaction is an aromatic polyacrylamide chloride, while the sulfonyl chloride used in the second interfacial polymerization reaction is a low molecular weight aliphatic polyacrylamide chloride. This allows the sulfonyl chloride to preemptively occupy the reaction sites of the aromatic polyacrylamide chloride, enabling it to react more quickly with unreacted amino or imino groups in the separation layer. This introduces sulfonyl chloride molecular chain segments onto the surface and interior of the separation layer, improving the hydrophilicity of the composite nanofiltration membrane, increasing the density of sulfonic acid groups, and reducing the membrane's molecular weight cutoff and pore size.

[0047] In some embodiments, the method of impregnating a polymer porous base membrane with a polyamine includes:

[0048] The polymer-based film was immersed in a polyamine solution.

[0049] In some embodiments, the solvent in the polyamine solution is water.

[0050] In this application, the mass concentrations of aromatic polyacrylamide chlorides and polyamines are not limited, as long as they can react with each other to form a separation layer. In some embodiments, the mass concentration of aromatic polyacrylamide chlorides in the second organic solvent is 0.05 wt% to 5 wt%, for example, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%. 4.5 wt%; In the polyamine solution, the mass concentration of the polyamine is 0.05 wt% to 5 wt%, for example, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%.

[0051] Preferably, in order to ensure that the polyamine produces excess amino or imino groups that can react with sulfonyl chloride, the mass concentration of the polyamine is higher than the mass concentration of the aromatic polyacryl chloride; more preferably, the mass concentration ratio of the polyamine to the aromatic polyacryl chloride is 1:(0.1 to 1).

[0052] In this application, the selection of the first alkane solvent and the second alkane solvent is based on the principle of not damaging the polymer base film and the separation layer and not reacting violently with aromatic polyacrylamide chlorides and sulfonyl chlorides. In some embodiments, the first alkane solvent and the second alkane solvent are each independently selected from one or more of n-hexane, cyclohexane, n-heptane, petroleum ether, and isoalkanes.

[0053] In this application, the material of the polymer-based membrane is not limited; any polymer-based membrane commonly used in nanofiltration membranes may be selected. In some embodiments, the polymer-based membrane is a polysulfone-based membrane, a polyethersulfone-based membrane, a polyvinylidene fluoride membrane, a polytetrafluoroethylene membrane, or a polyethylene-based membrane.

[0054] In some embodiments, after the polymer-based membrane with its surface wetted with polyamines undergoes interfacial polymerization in a second organic solvent, the process further includes rinsing the aromatic or semi-aromatic nanofiltration membrane with an alkane solvent. This rinsing removes unreacted aromatic polyacrylamide chlorides and a loose separation layer from the surface, reducing the overall thickness of the membrane's active layer and exposing more polyamines, i.e., residual amino or imino groups, thereby improving the water permeability of the composite nanofiltration membrane and the grafting effect of sulfonyl chlorides.

[0055] In some embodiments, after the aromatic or semi-aromatic nanofiltration membrane undergoes interfacial polymerization in a first organic solvent, a curing step is further included to give the composite nanofiltration membrane a stable structure. The curing method is not limited; for example, it can be thermosetting. Further, the thermosetting temperature can be 40°C to 120°C.

[0056] According to a specific implementation method, the preparation method of the composite nanofiltration membrane includes the following steps:

[0057] 1) Immerse the polymer base film in a polyamine solution to wet the surface of the polymer base film with polyamine;

[0058] 2) The polymer-based membrane with polyamine surface prepared in step 1) is placed in a second organic solvent for interfacial polymerization reaction. The second organic solvent includes aromatic polyacryl chloride and second alkane solvent, so that the polyamine reacts with the aromatic polyacryl chloride to form an aromatic or semi-aromatic nanofiltration membrane.

[0059] 3) Place the aromatic or semi-aromatic nanofiltration membrane obtained in step 2) in a first organic solvent, the first organic solvent including sulfonyl chloride and a first alkane solvent, so that the amino or imino groups on the surface of the nanofiltration membrane undergo an amidation reaction (grafting or cross-linking reaction) with the sulfonyl chloride.

[0060] 4) The nanofiltration membrane after the interfacial polymerization reaction in step 3) is thermally cured.

[0061] The preparation principle of composite nanofiltration membranes can be understood as follows:

[0062] After the polymer-based membrane is impregnated with polyamine, the polyamine diffuses into the first organic solvent, enabling it to react with aromatic polyacrylamide chlorides to form a new membrane (i.e., a selective separation layer, or active layer) on the surface of the polymer-based membrane. Excess polyamine (amino or imino groups) further undergoes an amidation reaction (i.e., grafting or cross-linking) with sulfonyl chlorides, allowing the sulfonyl chlorides to penetrate the separation layer, increasing the negative charge density on the composite nanofiltration membrane surface, particularly the density of sulfonic acid functional groups, and reducing the membrane pore size. Further thermosetting promotes the secondary interfacial polymerization reaction between the sulfonyl chlorides and the amino or imino groups in the polyamine, ensuring complete reaction and enhancing the chemical stability of the composite nanofiltration membrane.

[0063] Secondly, this application also provides a composite nanofiltration membrane prepared by the preparation method described in the first aspect.

[0064] The composite nanofiltration membrane provided in this application possesses excellent small pore size (pore size sieving effect), negative charge density (electrostatic effect), and sulfonic acid functional group density. While improving the rejection rate of micro-pollutants, it can reduce the rejection rate of mineral ions, thereby achieving water purification while ensuring the chemical stability of the water body and enhancing the membrane's antifouling performance. Furthermore, the average pore size of the composite nanofiltration membrane provided in this application can be as low as 0.30 nm, indicating that it has a very small pore size.

[0065] Thirdly, this application further provides an application of the composite nanofiltration membrane as described in the second aspect as a water treatment separation membrane.

[0066] The present application will be further described in detail below with reference to specific embodiments.

[0067] Example 1

[0068] 1) After immersing the polysulfone-based membrane in a piperazine solution for 2 min, the residual solution on the surface was removed; wherein the mass concentration of piperazine in the piperazine solution was 0.2 wt%. Subsequently, the polysulfone-based membrane was subjected to interfacial polymerization in a second organic solvent composed of trimesoyl chloride and n-hexane for 1 min, with the trimesoyl chloride having a mass concentration of 0.1 wt%, to obtain a semi-aromatic nanofiltration membrane. The semi-aromatic nanofiltration membrane was then rinsed with n-hexane for 10 s.

[0069] 2) The semi-aromatic nanofiltration membrane obtained in step 1) was placed in a first organic solvent for an amidation reaction (secondary interfacial polymerization reaction) for 30 s. The first organic solvent consisted of sulfonyl chloride and n-hexane, and the mass concentration of sulfonyl chloride was 0.1 wt%. Subsequently, it was heat-cured at 60 °C for 4 min and then rinsed with deionized water.

[0070] Example 2

[0071] The preparation method in this embodiment is basically the same as that in Example 1, except for the mass concentration of sulfonyl chloride. The specific steps are as follows:

[0072] 1) After immersing the polysulfone-based membrane in a piperazine solution for 2 min, the residual solution on the surface was removed; wherein the mass concentration of piperazine in the piperazine solution was 0.2 wt%. Subsequently, the polysulfone-based membrane was subjected to interfacial polymerization in a second organic solvent composed of trimesoyl chloride and n-hexane for 1 min, with the trimesoyl chloride having a mass concentration of 0.1 wt%, to obtain a semi-aromatic nanofiltration membrane. The semi-aromatic nanofiltration membrane was then rinsed with n-hexane for 10 s.

[0073] 2) The semi-aromatic nanofiltration membrane obtained in step 1) was placed in a first organic solvent for an amidation reaction (secondary interfacial polymerization reaction) for 30 s. The first organic solvent consisted of sulfonyl chloride and n-hexane, and the mass concentration of sulfonyl chloride was 0.2 wt%. Subsequently, it was heat-cured at 60 °C for 4 min and then rinsed with deionized water.

[0074] Example 3

[0075] The preparation method in this embodiment is basically the same as that in Example 1, except for the mass concentration of sulfonyl chloride. The specific steps are as follows:

[0076] 1) After immersing the polysulfone-based membrane in a piperazine solution for 2 min, the residual solution on the surface was removed; wherein the mass concentration of piperazine in the piperazine solution was 0.2 wt%. Subsequently, the polysulfone-based membrane was subjected to interfacial polymerization in a second organic solvent composed of trimesoyl chloride and n-hexane for 1 min, with the trimesoyl chloride having a mass concentration of 0.1 wt%, to obtain a semi-aromatic nanofiltration membrane. The semi-aromatic nanofiltration membrane was then rinsed with n-hexane for 10 s.

[0077] 2) The semi-aromatic nanofiltration membrane obtained in step 1) was placed in a first organic solvent for an amidation reaction (secondary interfacial polymerization reaction) for 30 s. The first organic solvent consisted of sulfonyl chloride and n-hexane, and the mass concentration of sulfonyl chloride was 0.4 wt%. Subsequently, it was heat-cured at 60 °C for 4 min and then rinsed with deionized water.

[0078] Example 4

[0079] The preparation method in this embodiment is basically the same as that in Example 1, except for the mass concentration of sulfonyl chloride. The specific steps are as follows:

[0080] 1) After immersing the polysulfone-based membrane in a piperazine solution for 2 min, the residual solution on the surface was removed; wherein the mass concentration of piperazine in the piperazine solution was 0.2 wt%. Subsequently, the polysulfone-based membrane was subjected to interfacial polymerization in a second organic solvent composed of trimesoyl chloride and n-hexane for 1 min, with the trimesoyl chloride having a mass concentration of 0.1 wt%, to obtain a semi-aromatic nanofiltration membrane. The semi-aromatic nanofiltration membrane was then rinsed with n-hexane for 10 s.

[0081] 2) The semi-aromatic nanofiltration membrane obtained in step 1) was placed in a first organic solvent for an amidation reaction (secondary interfacial polymerization reaction) for 30 s. The first organic solvent consisted of sulfonyl chloride and n-hexane, and the mass concentration of sulfonyl chloride was 1 wt%. Subsequently, it was heat-cured at 60 °C for 4 min and then rinsed with deionized water.

[0082] Comparative Example 1

[0083] The preparation method of this comparative example is basically the same as that of Example 1, except that the semi-aromatic nanofiltration membrane was not placed in the first organic solvent for secondary interfacial polymerization and was not rinsed with n-hexane solution. The specific steps are as follows:

[0084] A polysulfone-based membrane was immersed in a piperazine solution for 2 minutes, and the residual solution on the surface was removed. The piperazine concentration in the solution was 0.2 wt%. The polysulfone-based membrane was then subjected to interfacial polymerization in a second organic solvent composed of trimesoyl chloride and n-hexane for 1 minute, with the trimesoyl chloride concentration being 0.1 wt%. This yielded a semi-aromatic nanofiltration membrane. The membrane was then heat-cured at 60°C for 4 minutes and rinsed with deionized water.

[0085] Comparative Example 2

[0086] The preparation method of this comparative example is basically the same as that of Example 1, except that the semi-aromatic nanofiltration membrane was not placed in the first organic solvent for secondary interfacial polymerization and was not soaked in n-hexane solution. The specific steps are as follows:

[0087] A polysulfone-based membrane was immersed in a piperazine solution for 2 minutes, and the residual solution on the surface was removed. The piperazine concentration in the solution was 0.2 wt%. The polysulfone-based membrane was then subjected to interfacial polymerization in a second organic solvent consisting of trimesoyl chloride and n-hexane for 1 minute, with the trimesoyl chloride concentration being 0.1 wt%. This yielded a semi-aromatic nanofiltration membrane. The semi-aromatic nanofiltration membrane was then immersed in n-hexane for 40 seconds, followed by heat curing at 60°C for 4 minutes, and finally rinsed with deionized water.

[0088] Comparative Example 3

[0089] The preparation method of Comparative Example 3 is basically the same as that of Example 1, except that methylene disulfonyl dichloride is used instead of sulfonyl chloride. The specific steps are as follows:

[0090] 1) After immersing the polysulfone-based membrane in a piperazine solution for 2 min, the residual solution on the surface was removed; wherein the mass concentration of piperazine in the piperazine solution was 0.2 wt%. Subsequently, the polysulfone-based membrane was subjected to interfacial polymerization in a second organic solvent composed of trimesoyl chloride and n-hexane for 1 min, with the trimesoyl chloride having a mass concentration of 0.1 wt%, to obtain a semi-aromatic nanofiltration membrane. The semi-aromatic nanofiltration membrane was then rinsed with n-hexane for 10 s.

[0091] 2) The semi-aromatic nanofiltration membrane obtained in step 1) was placed in a first organic solvent for an amidation reaction (secondary interfacial polymerization reaction) for 30 s. The first organic solvent consisted of methylene disulfonyl dichloride and n-hexane, and the mass concentration of methylene disulfonyl dichloride was 0.1 wt%. Subsequently, it was heat-cured at 60 °C for 4 min and then rinsed with deionized water.

[0092] Comparative Example 4

[0093] The preparation method of Comparative Example 4 is basically the same as that of Example 1, except that methylene disulfonyl dichloride is used instead of sulfonyl chloride, and the mass concentration of methylene disulfonyl dichloride is 0.2 wt%. The specific steps are as follows:

[0094] 1) After immersing the polysulfone-based membrane in a piperazine solution for 2 min, the residual solution on the surface was removed; wherein the mass concentration of piperazine in the piperazine solution was 0.2 wt%. Subsequently, the polysulfone-based membrane was subjected to interfacial polymerization in a second organic solvent composed of trimesoyl chloride and n-hexane for 1 min, with the trimesoyl chloride having a mass concentration of 0.1 wt%, to obtain a semi-aromatic nanofiltration membrane. The semi-aromatic nanofiltration membrane was then rinsed with n-hexane for 10 s.

[0095] 2) The semi-aromatic nanofiltration membrane obtained in step 1) was placed in a first organic solvent for an amidation reaction (secondary interfacial polymerization reaction) for 30 s. The first organic solvent consisted of methylene disulfonyl dichloride and n-hexane, and the mass concentration of methylene disulfonyl dichloride was 0.2 wt%. Subsequently, it was heat-cured at 60 °C for 4 min and then rinsed with deionized water.

[0096] The raw materials and process parameters, such as proportions, used in the preparation methods of Examples 1-4 and Comparative Examples 1-4 are listed in Table 1 below:

[0097] Table 1

[0098]

[0099]

[0100] The composite nanofiltration membranes prepared in Examples 1-4 and Comparative Examples 1-4 were tested for filtration performance. The test results are shown in Table 2 below.

[0101] The filtering test conditions are as follows:

[0102] All nanofiltration membranes were tested using a laboratory-scale cross-flow filtration system. This system had three parallel filtration units. The effective area per cell was 20.6 cm². 2Three independent membrane sheets cut from the same membrane were used in parallel experiments. Before sampling, the membrane was pre-compressed at 8 bar for at least 50 minutes to ensure its stability. Subsequent tests were conducted under cross-flow conditions at an operating pressure of 0.5 MPa and a water temperature of 20 °C. The inorganic salt solutions used in the tests all had an ionic strength of 10 mmol / L, the single solute solutions of glycerol, xylose, glucose, and sucrose were all at a concentration of 100 mg / L (their rejection ratios were used to calculate the molecular weight cutoff of the composite nanofiltration membrane), and a mixed solution of five different organic micropollutants at a concentration of 50 μg / L: perfluorobutyric acid (PFBS), perfluorobutylsulfonic acid (PFHxA), perfluorohexanoic acid (PFHxA), perfluorohexylsulfonic acid (PFOA), and perfluorooctanoic acid (PFBA).

[0103] like Figure 1 As shown, under an operating pressure of 0.5 MPa, the composite nanofiltration membranes prepared in Examples 1 and 2, and Comparative Examples 1 and 2, exhibited magnesium chloride rejection rates of 42%, 55.1%, 32.7%, and 50.6%, respectively, and sodium chloride rejection rates of 51.6%, 48.8%, 55.4%, and 47.4%, respectively. Compared to the comparative examples, the composite nanofiltration membrane prepared in Example 1 exhibited a stronger surface negative charge effect due to the sulfonic acid groups generated from the hydrolysis of sulfonyl chloride, resulting in the lowest magnesium chloride rejection rate. However, due to the increased concentration of sulfonyl chloride, its pore-shrinking effect became more pronounced, weakening the surface negative charge effect of the composite nanofiltration membrane prepared in Example 2, leading to a magnesium chloride rejection rate higher than that of Comparative Example 1 but lower than that of Comparative Example 2. The initial increase followed by a decrease in the negative charge effect indicates that the preparation method provided in this application can achieve stepwise control of the negative charge effect. Figure 1 The composite nanofiltration membranes prepared in Examples 1 and 2 showed enhanced xylose retention rates compared to Comparative Examples 1 and 2, indicating that the preparation method provided in this application significantly improves the retention performance of the composite nanofiltration membrane. Furthermore, the water permeability coefficients of the composite nanofiltration membranes prepared in Examples 1 and 2 showed an increasing trend compared to Comparative Example 1, demonstrating that the preparation method provided in this application can maintain a high water permeability coefficient while improving the retention performance of the composite nanofiltration membrane.

[0104] Compared with Example 3, the nanofiltration membrane prepared in Example 2 has a slightly lower xylose rejection rate than that in Example 3, but the nanofiltration membrane prepared in Example 2 also has a lower magnesium chloride rejection rate than that in Example 3. Each has its own advantages and disadvantages. However, by further increasing the mass concentration of sulfonyl chloride (Example 4), the relevant performance of the nanofiltration membrane prepared is not much different from that in Example 3.

[0105] Figure 2 The cut-off molecular weights of the composite nanofiltration membranes prepared in Examples 1 and 2 and Comparative Examples 1 and 2; Figure 4 The results show the performance of the composite nanofiltration membranes prepared in Example 1 and Comparative Examples 1 and 2 in retaining micropollutants. Figure 2 and 4 It can be seen that the molecular weight cutoffs of the composite nanofiltration membranes prepared in Examples 1 and 2 and Comparative Examples 1 and 2 are 342 Da, 322 Da, 402 Da, and 472 Da, respectively. Compared with Comparative Example 1, the composite nanofiltration membranes prepared in Examples 1 and 2 show a significant enhancement in their retention performance of micropollutants, indicating that washing with alkane solvents can better expose the polyamines to the surface of the nanofiltration membrane, allowing sulfonyl chloride to have more sites for grafting reactions, thereby improving its water permeability coefficient.

[0106] Figure 4 The magnesium chloride, sodium chloride, and xylose rejection rates and permeability coefficients of the composite nanofiltration membranes prepared in Examples 3 and 4 and Comparative Examples 3 and 4 are shown. Compared with Example 1, the magnesium chloride and xylose rejection rates of Examples 3 and 4 show a significant upward trend. This indicates that the pore-shrinking effect is enhanced with increasing sulfonyl chloride concentration, leading to a significant decrease in the negative charge effect, thus affecting the membrane's retention performance. Compared with Example 1, although the MgCl2 rejection rate of Comparative Example 3 is similar, the xylose rejection rate of Comparative Example 3 is only 50.5%, far lower than the 61% of Example 1. Furthermore, after increasing the concentration of methylene disulfonyl dichloride, the xylose rejection rate of Comparative Example 4 is 56.1%, still lower than the xylose rejection rate of Example 1, and the magnesium chloride rejection rate of Comparative Example 4 is 55.2%, far higher than the 32.7% of Example 1. Therefore, the overall performance of the nanofiltration membranes prepared by replacing sulfonyl chloride with methylene disulfonyl dichloride is poor, indicating that this application can only use sulfonyl chloride.

[0107] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0108] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims, and the specification and drawings can be used to interpret the scope of the claims.

Claims

1. A method for preparing a composite nanofiltration membrane, characterized in that, Includes the following steps: An aromatic or semi-aromatic nanofiltration membrane is placed in a first organic solvent, the first organic solvent comprising sulfonyl chloride and a first alkane solvent, to induce an amidation reaction between the amino or imino groups on the surface and interior of the nanofiltration membrane and the sulfonyl chloride; the mass concentration of the sulfonyl chloride in the first organic solvent is 0.05 wt% to 4 wt%. The aromatic or semi-aromatic nanofiltration membrane includes a polymer base membrane and a selective separation layer formed on the surface of the polymer base membrane.

2. The method for preparing the composite nanofiltration membrane as described in claim 1, characterized in that, In the first organic solvent, the mass concentration of the sulfonyl chloride is 0.1 wt% to 1 wt%.

3. The method for preparing the composite nanofiltration membrane as described in claim 1, characterized in that, The method for preparing the aromatic or semi-aromatic nanofiltration membrane includes: A polymer base film with a surface impregnated with polyamines is placed in a second organic solvent for interfacial polymerization; the second organic solvent includes aromatic polyacrylamide chlorides and second alkane solvents.

4. The method for preparing the composite nanofiltration membrane as described in claim 3, characterized in that, The polyamines include aromatic polyamines and / or aliphatic polyamines.

5. The method for preparing the composite nanofiltration membrane as described in claim 4, characterized in that, The aromatic polyamines include one or more of m-phenylenediamine, p-phenylenediamine, pyromellitic triamine, diaminobenzoic acid, and diaminobenzenesulfonic acid.

6. The method for preparing the composite nanofiltration membrane as described in claim 4, characterized in that, The aliphatic polyamines include one or more of piperazine, piperazine carboxylic acid, ethylenediamine, propylenediamine, butanediamine, and pentanediamine.

7. The method for preparing the composite nanofiltration membrane as described in claim 3, characterized in that, The aromatic polyacrylic chlorides include one or more of pyromellitic trichloroisocyanurate, terephthaloyl chloride, isophthaloyl chloride, and phthaloyl chloride.

8. The method for preparing the composite nanofiltration membrane as described in claim 3, characterized in that, In the second organic solvent, the mass concentration of the aromatic polyacrylamide chloride is 0.05 wt% to 5 wt%.

9. The method for preparing the composite nanofiltration membrane as described in claim 3, characterized in that, The method of impregnating the polymer-based film with polyamine includes: The polymer-based film is immersed in a polyamine solution.

10. The method for preparing the composite nanofiltration membrane as described in claim 9, characterized in that, In the polyamine solution, the mass concentration of the polyamine is 0.05 wt% to 5 wt%.

11. The method for preparing the composite nanofiltration membrane according to any one of claims 3 to 10, characterized in that, The first alkane solvent and the second alkane solvent are each independently selected from one or more of n-hexane, cyclohexane, n-heptane, petroleum ether, and isoalkanes.

12. The method for preparing the composite nanofiltration membrane according to any one of claims 3 to 10, characterized in that, After the aromatic or semi-aromatic nanofiltration membrane is placed in a first organic solvent for amidation reaction, the method further includes a step of curing the obtained product to densify the polyamide layer on the surface of the composite nanofiltration membrane.

13. The composite nanofiltration membrane prepared by the preparation method according to any one of claims 1 to 12.

14. The application of the composite nanofiltration membrane as described in claim 13 as a water treatment separation membrane.

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