High-flux polypiperazine amide nanofiltration membrane and preparation method thereof

Abstract

The invention relates to the technical field of water treatment membranes, and particularly discloses a high-flux polypiperazine amide nanofiltration membrane and a preparation method thereof.The high-flux polypiperazine amide nanofiltration membrane comprises a polysulfone base membrane and a polypiperazine amide functional layer located on the polysulfone base membrane, and the functional layer is formed by an interfacial polymerization reaction of a water phase solution and an organic phase solution; the aqueous phase solution comprises piperazine (PI P), polyvinyl alcohol (PVA) and triethylamine hydrochloride (TEA.HCl); the organic phase solution contains trimesoyl chloride (TMC) and a cyclohexane solvent; according to the invention, polyvinyl alcohol is introduced into a water-phase solution as an additive and has a synergistic effect with a catalyst triethylamine hydrochloride, so that an interfacial polymerization process is effectively regulated and controlled, a polyamide functional layer with better permeation selectivity is formed, and the technical bottleneck that flux and rejection rate are difficult to obtain at the same time in a traditional nanofiltration membrane is broken through; and effective consideration of the two performances is realized.

Description

Technical Field

[0001] This invention belongs to the field of water treatment membrane technology, specifically relating to a high-flux polypiperazine amide nanofiltration membrane and its preparation method. Background Technology

[0002] Nanofiltration (NF) technology is one of the mainstream technologies for municipal water treatment, and its core component is a polypiperazine amide composite membrane.

[0003] The polypiperazine amide nanofiltration membrane prepared by the traditional interfacial polymerization method has a trade-off between flux and rejection rate. That is, a high rejection rate is often accompanied by a low flux, and vice versa. Therefore, how to optimize the concentration ratio of aqueous monomer PIP, additive PVA, catalyst TEA·HCl and organic monomer TMC is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] The purpose of this invention is to provide a high-flux polypiperazine amide nanofiltration membrane and its preparation method, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A high-flux polypiperazine amide nanofiltration membrane includes a polysulfone-based membrane and a polypiperazine amide functional layer thereon, the functional layer being formed by an interfacial polymerization reaction between an aqueous phase solution and an organic phase solution;

[0007] The aqueous solution contains piperazine (PIP), polyvinyl alcohol (PVA), and triethylamine hydrochloride (TEA·HCl);

[0008] The organic phase solution contains trimesoyl chloride (TMC) and cyclohexane solvent.

[0009] Preferably, the mass-volume concentrations of each component in the aqueous solution are: PIP: 0.4%, PVA: 0.02%–0.1%, TEA·HCl: 0.8%.

[0010] Preferably, the mass-volume concentration of TMC in the organic phase solution is 0.14%.

[0011] A method for preparing a high-flux polypiperazine amide nanofiltration membrane as described in any of the above claims, comprising the following steps:

[0012] S1. Base membrane pretreatment: Immerse the polysulfone base membrane in pure water, remove it, fix it, and dehydrate it;

[0013] S2. Preparation of aqueous solution: Dissolve PIP, PVA and TEA·HCl in deionized water;

[0014] S3. Preparation of organic phase solution: Dissolve TMC in cyclohexane;

[0015] S4. Interfacial polymerization: Pour the aqueous solution onto the surface of the base film, let it stand for 60 seconds, and then remove it; then pour the organic solution, let it stand for 30 seconds, and then remove it.

[0016] S5. Thermal crosslinking treatment: Place the obtained composite film in a 30℃ oven and dry for 8–10 minutes.

[0017] Preferably, in step S1, the polysulfone-based membrane is fixed to the polytetrafluoroethylene frame by a pressure-sensitive adhesive and dehydrated using an air knife.

[0018] Preferably, in step S4, both the aqueous solution and the organic solution completely immerse the surface of the base film.

[0019] Preferably, in step S5, the thermal crosslinking temperature is 30±0.5℃ and the time is 8–10 minutes.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] (1) By introducing polyvinyl alcohol as an additive into the aqueous solution and working synergistically with the catalyst triethylamine hydrochloride, the interfacial polymerization process was effectively controlled, forming a polyamide functional layer with better permeation selectivity. This broke through the technical bottleneck of traditional nanofiltration membranes in achieving both flux and rejection rate, and effectively balanced the performance of both.

[0022] (2) The preparation method has mild process conditions, simple operation, good repeatability, no need for complicated post-processing or expensive equipment, and is easy to achieve large-scale production. The nanofiltration membranes produced exhibit excellent water permeability and moderate desalination rate. Attached Figure Description

[0023] Figure 1 This is a comparison chart of desalination rate and water flux in Examples 1-6 of the present invention;

[0024] Figure 2 These are scanning electron microscope (SEM) images of the film surfaces in Examples 1-6 of the present invention;

[0025] Figure 3 The images shown are scanning electron microscope (SEM) images of the membrane cross-sections of Examples 1-6 of the present invention. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1:

[0028] Please see Figures 1-3 As shown, this embodiment provides a method for preparing a high-flux polypiperazine amide nanofiltration membrane (named NF-1), the specific steps of which are as follows:

[0029] S1. Base membrane pretreatment: Take a polysulfone (PSF) ultrafiltration base membrane and immerse it in deionized water for at least 30 minutes to remove surface impurities and protective agents; then, take out the moistened base membrane and use pressure-sensitive adhesive to fix it flat on a 24cm×36cm polytetrafluoroethylene frame; use an air knife-assisted drying system to blow on both sides of the base membrane with uniform air force to remove excess moisture from the surface, so that the base membrane surface is in a state of being moist but without water accumulation;

[0030] S2. Preparation of aqueous solution: Weigh 0.4 g of piperazine (PIP) and 0.8 g of triethylamine hydrochloride (TEA·HCl) and place them in a beaker; add an appropriate amount of deionized water and stir until completely dissolved. Transfer the solution to a 100 mL volumetric flask, dilute to the mark with deionized water, and shake well to obtain an aqueous solution containing 0.4% (w / v) PIP and 0.8% (w / v) TEA·HCl.

[0031] S3. Preparation of organic phase solution: Weigh 0.14 g of trimesoyl chloride (TMC), place it in a dry beaker, add cyclohexane solvent, stir until TMC is completely dissolved, transfer the solution to a 100 mL volumetric flask, dilute to the mark with cyclohexane, shake well, and obtain a 0.14% (w / v) TMC cyclohexane solution.

[0032] S4. Interfacial Polymerization: Place the fixed base membrane horizontally. Pour the aqueous solution prepared in step S2 onto the base membrane surface at a constant speed, ensuring the solution completely submerges and covers the entire membrane surface. Allow the reaction to proceed for 60 seconds. After the reaction, tilt the base membrane frame at approximately a 45-degree angle, allowing gravity to allow excess aqueous solution to flow down naturally until no obvious droplets flow down the membrane surface. Immediately pour the organic solution prepared in step S3 onto the aqueous-treated base membrane surface at a constant speed, ensuring the TMC solution completely covers the membrane surface. Allow the reaction to proceed for 30 seconds to carry out the interfacial polymerization reaction. After the reaction, use gravity to completely remove excess organic solution.

[0033] S5. Thermal crosslinking treatment: The composite membrane that has undergone interfacial polymerization, together with the polytetrafluoroethylene frame, is placed in a forced-air drying oven preheated to 30±0.5℃ and heat-treated for 8 minutes. After the treatment is completed, it is removed to obtain the desired polypiperazine amide nanofiltration membrane (NF-1).

[0034] Example 2:

[0035] This embodiment provides a method for preparing a high-flux polypiperazine amide nanofiltration membrane (named NF-2). Compared with Example 1 (NF-1), this embodiment adds polyvinyl alcohol (PVA) as an additive in the aqueous phase to regulate the functional layer structure and improve water flux. The specific steps are as follows:

[0036] S1. Base Membrane Pretreatment: Take a polysulfone (PSF) ultrafiltration base membrane and immerse it in deionized water for at least 30 minutes to remove surface impurities and preservatives. Then, remove the moistened base membrane and use a pressure-sensitive adhesive to fix it flat onto a 24cm × 36cm polytetrafluoroethylene frame. Use an air knife-assisted drying system to blow evenly on both sides of the base membrane to remove excess moisture, leaving the base membrane surface in a moist but water-free state.

[0037] S2. Preparation of aqueous solution: Weigh 0.4 g of piperazine (PIP), 0.02 g of polyvinyl alcohol (PVA), and 0.8 g of triethylamine hydrochloride (TEA·HCl), place them in a beaker, add an appropriate amount of deionized water, and stir until all solutes are completely dissolved (PVA needs to be slightly heated or stirred for a long time to promote dissolution). Transfer the solution to a 100 mL volumetric flask, dilute to the mark with deionized water, and shake well to obtain an aqueous solution containing 0.4% (w / v) PIP, 0.02% (w / v) PVA, and 0.8% (w / v) TEA·HCl.

[0038] S3. Preparation of organic phase solution: Weigh 0.14 g of trimesoyl chloride (TMC), place it in a dry beaker, add cyclohexane solvent, stir until TMC is completely dissolved, transfer the solution to a 100 mL volumetric flask, dilute to the mark with cyclohexane, shake well, and obtain a 0.14% (w / v) TMC cyclohexane solution.

[0039] S4. Interfacial Polymerization: Place the fixed base membrane horizontally, and pour the aqueous solution prepared in step S2 onto the base membrane surface at a constant speed, ensuring that the solution completely submerges and covers the entire membrane surface. Let it stand for 60 seconds. After the reaction, tilt the base membrane frame at an angle of about 45 degrees, allowing the excess aqueous solution to flow down naturally under gravity until no obvious droplets flow down the membrane surface. Immediately pour the organic solution prepared in step S3 onto the surface of the aqueous-treated base membrane at a constant speed, ensuring that the TMC solution completely covers the membrane surface. Let it stand for 30 seconds to carry out the interfacial polymerization reaction. After the reaction, use gravity self-drainage to completely remove the excess organic solution.

[0040] S5. Thermal crosslinking treatment: The composite membrane that has undergone interfacial polymerization, together with the polytetrafluoroethylene frame, is placed in a forced-air drying oven preheated to 30±0.5℃ and heat-treated for 8 minutes. After the treatment is completed, it is removed to obtain the desired polypiperazine amide nanofiltration membrane (NF-2).

[0041] Example 3:

[0042] This embodiment provides a method for preparing a high-flux polypiperazine amide nanofiltration membrane (named NF-3). This embodiment aims to further explore the effect of polyvinyl alcohol (PVA) concentration in the aqueous phase on membrane performance. Based on Example 2, the amount of PVA added is increased. The specific steps are as follows:

[0043] S1. Base Membrane Pretreatment: Take a polysulfone (PSF) ultrafiltration base membrane and immerse it in deionized water for at least 30 minutes to remove surface impurities and preservatives. Then, remove the moistened base membrane and use a pressure-sensitive adhesive to fix it flat onto a 24cm × 36cm polytetrafluoroethylene frame. Use an air knife-assisted drying system to blow evenly on both sides of the base membrane to remove excess moisture, leaving the base membrane surface in a moist but water-free state.

[0044] S2. Preparation of aqueous solution: Weigh 0.4 g of piperazine (PIP), 0.04 g of polyvinyl alcohol (PVA), and 0.8 g of triethylamine hydrochloride (TEA·HCl), place them in a beaker, add an appropriate amount of deionized water, and stir until all solutes are completely dissolved (PVA needs to be slightly heated or stirred for a long time to promote dissolution). Transfer the solution to a 100 mL volumetric flask, dilute to the mark with deionized water, and shake well to obtain an aqueous solution containing 0.4% (w / v) PIP, 0.04% (w / v) PVA, and 0.8% (w / v) TEA·HCl.

[0045] S3. Preparation of organic phase solution: Weigh 0.14 g of trimesoyl chloride (TMC) and place it in a dry beaker. Add cyclohexane solvent and stir until the TMC is completely dissolved. Transfer the solution to a 100 mL volumetric flask and dilute to the mark with cyclohexane. Shake well to obtain a 0.14% (w / v) TMC cyclohexane solution.

[0046] S4. Interfacial Polymerization: Place the fixed base membrane horizontally. Pour the aqueous solution prepared in step S2 onto the base membrane surface at a uniform speed, ensuring the solution completely submerges and covers the entire membrane surface. Let it stand for 60 seconds. After the reaction, tilt the base membrane frame at approximately a 45-degree angle, allowing gravity to allow excess aqueous solution to flow down naturally until no obvious droplets flow down the membrane surface. Immediately pour the organic solution prepared in step S3 onto the aqueous-treated base membrane surface at a uniform speed, ensuring the TMC solution completely covers the membrane surface. Let it stand for 30 seconds to carry out the interfacial polymerization reaction. After the reaction, use gravity to completely remove excess organic solution.

[0047] S5. Thermal crosslinking treatment: The composite membrane that has undergone interfacial polymerization, together with the polytetrafluoroethylene frame, is placed in a forced-air drying oven preheated to 30±0.5℃ and heat-treated for 8 minutes. After the treatment is completed, it is removed to obtain the desired polypiperazine amide nanofiltration membrane (NF-3).

[0048] Example 4:

[0049] This embodiment provides a method for preparing a high-flux polypiperazine amide nanofiltration membrane (named NF-4). This embodiment further investigates the effect of polyvinyl alcohol (PVA) concentration in the aqueous phase on membrane performance, and further increases the amount of PVA added based on Example 3. The specific steps are as follows:

[0050] S1. Base Membrane Pretreatment: Take a polysulfone (PSF) ultrafiltration base membrane and immerse it in deionized water for at least 30 minutes to remove surface impurities and preservatives. Then, remove the moistened base membrane and use a pressure-sensitive adhesive to fix it flat onto a 24cm×36cm polytetrafluoroethylene frame. Use an air knife-assisted drying system to blow evenly on both sides of the base membrane to remove excess moisture, so that the base membrane surface is moist but free of standing water.

[0051] S2. Preparation of aqueous solution: Weigh 0.4 g of piperazine (PIP), 0.06 g of polyvinyl alcohol (PVA), and 0.8 g of triethylamine hydrochloride (TEA·HCl), place them in a beaker, add an appropriate amount of deionized water, and stir until all solutes are completely dissolved (PVA needs to be slightly heated or stirred for a long time to promote dissolution). Transfer the solution to a 100 mL volumetric flask, dilute to the mark with deionized water, and shake well to obtain an aqueous solution containing 0.4% (w / v) PIP, 0.06% (w / v) PVA, and 0.8% (w / v) TEA·HCl.

[0052] S3. Preparation of organic phase solution: Weigh 0.14 g of trimesoyl chloride (TMC) and place it in a dry beaker. Add cyclohexane solvent and stir until the TMC is completely dissolved. Transfer the solution to a 100 mL volumetric flask and dilute to the mark with cyclohexane. Shake well to obtain a 0.14% (w / v) TMC cyclohexane solution.

[0053] S4. Interfacial Polymerization: Place the fixed base membrane horizontally. Pour the aqueous solution prepared in step S2 onto the base membrane surface at a uniform speed, ensuring the solution completely submerges and covers the entire membrane surface. Let it stand for 60 seconds. After the reaction, tilt the base membrane frame at approximately a 45-degree angle, allowing gravity to allow excess aqueous solution to flow down naturally until no obvious droplets flow down the membrane surface. Immediately pour the organic solution prepared in step S3 onto the aqueous-treated base membrane surface at a uniform speed, ensuring the TMC solution completely covers the membrane surface. Let it stand for 30 seconds to carry out the interfacial polymerization reaction. After the reaction, use gravity to completely remove excess organic solution.

[0054] S5. Thermal crosslinking treatment: The composite membrane that has undergone interfacial polymerization, together with the polytetrafluoroethylene frame, is placed in a forced-air drying oven preheated to 30±0.5℃ and heat-treated for 8 minutes. After the treatment is completed, it is removed to obtain the desired polypiperazine amide nanofiltration membrane (NF-4).

[0055] Example 5:

[0056] This embodiment provides a method for preparing a high-flux polypiperazine amide nanofiltration membrane (named NF-5). This embodiment further systematically studies the regulatory effect of polyvinyl alcohol (PVA) concentration in the aqueous phase on membrane performance. Based on Example 4, the amount of PVA added is further increased to approach the optimal range of flux performance. The specific steps are as follows:

[0057] S1. Base Membrane Pretreatment: Take a polysulfone (PSF) ultrafiltration base membrane and immerse it in deionized water for at least 30 minutes to remove surface impurities and preservatives. Then, remove the moistened base membrane and use a pressure-sensitive adhesive to fix it flat onto a 24cm × 36cm polytetrafluoroethylene frame. Use an air knife-assisted drying system to blow evenly on both sides of the base membrane to remove excess moisture, leaving the base membrane surface in a moist but water-free state.

[0058] S2. Preparation of aqueous solution: Weigh 0.4 g of piperazine (PIP), 0.08 g of polyvinyl alcohol (PVA), and 0.8 g of triethylamine hydrochloride (TEA·HCl), place them in a beaker, add an appropriate amount of deionized water, and stir until all solutes are completely dissolved (PVA needs to be slightly heated or stirred for a long time to promote dissolution). Transfer the solution to a 100 mL volumetric flask, dilute to the mark with deionized water, and shake well to obtain an aqueous solution containing 0.4% (w / v) PIP, 0.08% (w / v) PVA, and 0.8% (w / v) TEA·HCl.

[0059] S3. Preparation of organic phase solution: Weigh 0.14 g of trimesoyl chloride (TMC) and place it in a dry beaker. Add cyclohexane solvent and stir until the TMC is completely dissolved. Transfer the solution to a 100 mL volumetric flask and dilute to the mark with cyclohexane. Shake well to obtain a 0.14% (w / v) TMC cyclohexane solution.

[0060] S4. Interfacial Polymerization: Place the fixed base membrane horizontally. Pour the aqueous solution prepared in step S2 onto the base membrane surface at a uniform speed, ensuring the solution completely submerges and covers the entire membrane surface. Let it stand for 60 seconds. After the reaction, tilt the base membrane frame at approximately a 45-degree angle, allowing gravity to allow excess aqueous solution to flow down naturally until no obvious droplets flow down the membrane surface. Immediately pour the organic solution prepared in step S3 onto the aqueous-treated base membrane surface at a uniform speed, ensuring the TMC solution completely covers the membrane surface. Let it stand for 30 seconds to carry out the interfacial polymerization reaction. After the reaction, use gravity to completely remove excess organic solution.

[0061] S5. Thermal crosslinking treatment: The composite membrane that has undergone interfacial polymerization, together with the polytetrafluoroethylene frame, is placed in a forced-air drying oven preheated to 30±0.5℃ and heat-treated for 8 minutes. After the treatment is completed, it is removed to obtain the desired polypiperazine amide nanofiltration membrane (NF-5).

[0062] Example 6:

[0063] This embodiment provides a method for preparing a high-flux polypiperazine amide nanofiltration membrane (named NF-6). This embodiment uses the upper limit of the preferred concentration of polyvinyl alcohol (PVA) in the aqueous phase formulation to systematically demonstrate the highest water flux performance achievable by the technical solution of this invention. The specific steps are as follows:

[0064] S1. Base membrane pretreatment: Take a polysulfone (PSF) ultrafiltration base membrane and immerse it in deionized water for at least 30 minutes to remove surface impurities and protective agents. Then, take out the wet base membrane and use pressure-sensitive adhesive to fix it flat on a 24cm×36cm polytetrafluoroethylene frame. Use an air knife-assisted drying system to blow on both sides of the base membrane with uniform air force to remove excess moisture from the surface, so that the base membrane surface is in a state of being moist but without water accumulation.

[0065] S2. Preparation of aqueous solution: Weigh 0.4g of piperazine (PIP), 0.10g of polyvinyl alcohol (PVA), and 0.8g of triethylamine hydrochloride (TEA·HCl), place them in a beaker, add an appropriate amount of deionized water, and stir until all solutes are completely dissolved (PVA needs to be slightly heated or stirred for a long time to promote dissolution). Transfer the solution to a 100mL volumetric flask, dilute to the mark with deionized water, and shake well to obtain an aqueous solution containing 0.4% (w / v) PIP, 0.10% (w / v) PVA (i.e., the upper limit of the scope of the claims of this invention), and 0.8% (w / v) TEA·HCl.

[0066] S3. Preparation of organic phase solution: Weigh 0.14 g of trimesoyl chloride (TMC) and place it in a dry beaker. Add cyclohexane solvent and stir until the TMC is completely dissolved. Transfer the solution to a 100 mL volumetric flask and dilute to the mark with cyclohexane. Shake well to obtain a 0.14% (w / v) TMC cyclohexane solution.

[0067] S4. Interfacial Polymerization: Place the fixed base membrane horizontally. Pour the aqueous solution prepared in step S2 onto the base membrane surface at a constant speed, ensuring the solution completely submerges and covers the entire membrane surface. Allow the reaction to proceed at a stand time for 60 seconds. After the reaction, tilt the base membrane frame at approximately a 45-degree angle, allowing gravity to allow excess aqueous solution to flow down naturally until no obvious droplets flow down the membrane surface. Immediately pour the organic solution prepared in step S3 onto the aqueous-treated base membrane surface at a constant speed, ensuring the TMC solution completely covers the membrane surface. Allow the reaction to proceed at a stand time for 30 seconds to carry out the interfacial polymerization reaction. After the reaction, use gravity to completely remove excess organic solution.

[0068] S5. Thermal crosslinking treatment: The composite membrane that has undergone interfacial polymerization, together with the polytetrafluoroethylene frame, is placed in a forced-air drying oven preheated to 30±0.5℃ and heat-treated for 8 minutes. After the treatment is completed, it is removed to obtain the desired polypiperazine amide nanofiltration membrane (NF-6).

[0069] Performance test example:

[0070] To verify the performance of the polypiperazine amide nanofiltration membrane prepared in this invention, standardized separation performance tests were performed on the membrane samples prepared in all examples (NF-1 to NF-6). The test indicators were water flux (J) and sodium chloride rejection (R).

[0071] 1. Test conditions and environment

[0072] Testing apparatus: This test uses a standard flat-sheet membrane evaluation system (effective membrane area: 28 cm²). 2 );

[0073] Test temperature: 25.0±0.5℃ (controlled by a constant temperature circulating water bath);

[0074] Operating pressure: 0.5 MPa (controlled by a high-pressure nitrogen cylinder and a back pressure valve);

[0075] Test solution: 500 mg / L sodium chloride (NaCl) aqueous solution (prepared with deionized water);

[0076] 2. Test Procedure

[0077] The membrane to be tested is placed in the test cell and pre-pressed with deionized water at 0.5 MPa for 30 minutes until the water flux is stable, so as to ensure that the membrane performance is in a stable state.

[0078] Replace the feed solution from deionized water with a 500 mg / L NaCl solution;

[0079] Continue operating the system under the same pressure (0.5 MPa) and temperature (25°C) conditions until the throughput stabilizes again (usually about 20-30 minutes);

[0080] After the system stabilizes, formal data acquisition begins. An electronic balance (accuracy 0.01g) is used to continuously collect the permeate over a certain period of time (t) and record its mass (converted to volume V). At the same time, a portable conductivity meter is used to measure the conductivity of the feed liquid (Cf) and the permeate (Cp).

[0081] To ensure data accuracy, at least three parallel measurements were performed on each membrane sample, and the average value was taken as the final result.

[0082] 3. Calculation Method

[0083] Water flux (J) is calculated according to formula (1):

[0084]

[0085] In the formula: J is the water flux (L·m -2 ·h -1 V is the volume of permeate (L); S is the effective area of ​​the membrane (m²). 2 ); t is the sampling time (h);

[0086] The sodium chloride retention rate (R) is calculated according to formula (2):

[0087]

[0088] In the formula: R is the retention rate (%); C p Permeate conductivity (μS / cm); C f The conductivity of the feed liquid (μS / cm);

[0089] Note: In the low concentration range, the concentration of NaCl solution has a good linear proportional relationship with its conductivity, so the retention rate can be directly calculated using the conductivity ratio.

[0090] 4. Test Results

[0091] The following table summarizes the performance test results of the membranes (NF-1 to NF-6) of various embodiments of the present invention:

[0092] Membrane sample number PVA concentration (% w / v) Water flux (LMH) NaCl retention rate (%) NF-1 0.00 17.52 42.2 NF-2 0.02 37.92 34.3 NF-3 0.04 39.60 33.7 NF-4 0.06 42.72 32.8 NF-5 0.08 43.68 30.8 NF-6 0.10 48.00 30.4

[0093] Test results show that as the PVA concentration increases from 0% to 0.10%, the water flux of the membrane shows a significant upward trend (from 17.52 LMH to 48.00 LMH), while maintaining a moderate NaCl rejection rate of over 30%. In particular, the membranes prepared by Examples NF-2 to NF-6 fully meet and exceed the expected technical indicators of this invention (water flux ≥ 37 LMH, NaCl rejection rate ≥ 30%), proving the effectiveness and superiority of the preparation method of this invention.

[0094] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-flux polypiperazine amide nanofiltration membrane, characterized in that, It includes a polysulfone-based membrane and a polypiperazine amide functional layer thereon, the functional layer being formed by an interfacial polymerization reaction between an aqueous solution and an organic solution; The aqueous solution contains piperazine (PIP), polyvinyl alcohol (PVA), and triethylamine hydrochloride (TEA·HCl); The organic phase solution contains trimesoyl chloride (TMC) and cyclohexane solvent.

2. The high-flux polypiperazine amide nanofiltration membrane according to claim 1, characterized in that: The mass-volume concentrations of each component in the aqueous solution are: PIP: 0.4%, PVA: 0.02%–0.1%, TEA·HCl: 0.8%.

3. The high-flux polypiperazine amide nanofiltration membrane according to claim 1, characterized in that: The mass-volume concentration of TMC in the organic phase solution is 0.14%.

4. A method for preparing a high-flux polypiperazine amide nanofiltration membrane as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Base membrane pretreatment: Immerse the polysulfone base membrane in pure water, remove it, fix it, and dehydrate it; S2. Preparation of aqueous solution: Dissolve PIP, PVA and TEA·HCl in deionized water; S3. Preparation of organic phase solution: Dissolve TMC in cyclohexane; S4. Interfacial polymerization: Pour the aqueous solution onto the surface of the base film, let it stand for 60 seconds, and then remove it; then pour the organic solution, let it stand for 30 seconds, and then remove it. S5. Thermal crosslinking treatment: Place the obtained composite film in a 30℃ oven and dry for 8–10 minutes.

5. The method for preparing a high-flux polypiperazine amide nanofiltration membrane according to claim 4, characterized in that: In step S1, the polysulfone-based membrane is fixed to the polytetrafluoroethylene frame with a pressure-sensitive adhesive and dehydrated using an air knife.

6. The method for preparing a high-flux polypiperazine amide nanofiltration membrane according to claim 4, characterized in that: In step S4, both the aqueous solution and the organic solution completely immerse the surface of the base film.

7. The method for preparing a high-flux polypiperazine amide nanofiltration membrane according to claim 4, characterized in that: In step S5, the thermal crosslinking temperature is 30±0.5℃ and the time is 8–10 minutes.

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