A composite nanofiltration membrane with high permeation selectivity and anti-pollution performance and a preparation method thereof

Abstract

The application discloses a composite nanofiltration membrane with high permeation selectivity and anti-pollution performance and a preparation method thereof, and comprises the following steps: performing water solution treatment of a polyamine monomer on the surface of a porous ultrafiltration base film; after removing the excess water solution on the surface, performing surface treatment on the surface by using an organic solution of a polyacyl chloride monomer, generating an interface polymerization reaction, and generating a primary membrane with acyl chloride reaction functional groups on the surface; and performing surface treatment on the primary membrane by using a water solution of nitrogen-oxygen zwitterionic polyethyleneimine (ZPEI), and obtaining the composite nanofiltration membrane with high permeation selectivity and anti-pollution performance after heat treatment. The composite nanofiltration membrane prepared by the application has high rejection rates for multivalent anions and cations, and has the anti-pollution performance. The preparation method of the application is controllable and low in cost, and has great industrial application prospect.

Description

Technical fields:

[0001] This invention belongs to the field of nanofiltration membrane technology, and relates to a composite nanofiltration membrane with both high permeability selectivity and antifouling properties, and its preparation method. Background technology:

[0002] Pressure-driven nanofiltration membranes are widely used in water softening, wastewater resource recovery, and dye desalination due to their advantages such as no phase change during separation, small footprint, low cost, simple operation, and easy scale-up. However, low separation selectivity and membrane fouling still affect the separation efficiency and service life of nanofiltration membranes.

[0003] Interfacial polymerization is currently the main method for preparing commercially available composite nanofiltration membranes. Negatively charged nanofiltration membranes have high rejection rates for multivalent anions but low rejection rates for cations. To improve the selectivity of negatively charged nanofiltration membranes for anions and cations, common strategies include adding surfactants and polyvinyl alcohol to the aqueous phase to control the interfacial polymerization process and prepare composite nanofiltration membranes with low molecular weight cutoffs and narrow pore size distributions. However, these strategies have not improved the antifouling ability of nanofiltration membranes.

[0004] Hydrophilic surfaces typically enhance the antifouling ability of nanofiltration membranes. Surface grafting modification techniques can modify the surface of nanofiltration membranes with monomers or polymers containing functional groups through chemical bonding, thereby controlling the hydrophilicity, pore size, porosity, and surface charge density of the membrane. Zwitterionic polymers are electrically neutral at their isoelectric point and have strong interactions with water molecules, forming a thick hydration layer on the membrane surface. This strong hydration layer effectively prevents non-specific adhesion of pollutants to the membrane surface. Among these, nitrogen-oxygen zwitterionic materials with directly linked zwitterionic functional groups exhibit stronger hydrophilicity and excellent physicochemical stability. Therefore, optimizing the molecular structure and utilizing traditional nanofiltration membrane preparation methods to construct nanofiltration membranes that combine excellent separation selectivity with good antifouling properties has become a research focus. Summary of the Invention:

[0005] To address the shortcomings of the existing technology, the purpose of this invention is to provide a composite nanofiltration membrane with both high permeability selectivity and antifouling properties, and its preparation method, in order to solve the problems that negatively charged composite nanofiltration membranes are not suitable for efficient sieving of polyvalent anions and cations, and that it is difficult to achieve both separation performance and antifouling performance.

[0006] 1. To achieve the above objectives, the present invention provides a composite nanofiltration membrane with both high permeability selectivity and antifouling properties, and a method for preparing the same, comprising the following steps:

[0007] (1) Treat the surface of the porous ultrafiltration membrane with an aqueous solution of polyamine monomer (0.1-0.5 w / v%) for 10-300 s; after removing the excess aqueous solution from the surface, treat the surface with an organic solution of polyacryl chloride monomer (0.1-0.5 w / v%) for 10-120 s to induce interfacial polymerization and generate a native membrane with acryl chloride reactive functional groups on the surface.

[0008] (2) Under room temperature conditions, the original ecological membrane was cleaned with organic solvents and the surface of the original ecological membrane was treated with an aqueous solution of ZPEI with a mass-volume ratio of 0.05-0.2% for 10-300s.

[0009] (3) After heat treatment at 50-80℃ for 1-30 minutes, a composite nanofiltration membrane with both high permeability selectivity and antifouling properties is obtained.

[0010] 2. Preferably, the ultrafiltration base membrane is one or a mixture of several of the following: polysulfone, polyethersulfone, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, and polypropylene. More preferably, it is polyvinylidene fluoride.

[0011] 3. Preferably, the polyamine is one or a mixture of several selected from piperazine, piperazine derivatives, m-phenylenediamine, and polyethyleneimine. More preferably, it is piperazine, with an aqueous monomer concentration of 0.3% and a contact time of 60 s.

[0012] 4. Preferably, the polyacrylamide chloride monomer is one or a mixture of several of the following: trimesoyl chloride, isophthaloyl chloride, and phthaloyl chloride. More preferably, it is trimesoyl chloride, the concentration of the organic phase monomer is 0.3%, and the contact time is 60 s.

[0013] 5. Preferably, the solvent of the organic solution is one or a mixture of several solvents selected from ethyl acetate, n-hexane, cyclohexane, etc. Hexane is preferred.

[0014] 6. Preferably, the number average molecular weight of ZPEI is between 200 and 70,000, and the quaternary ammonia nitrogen of the nitrogen-oxygen zwitterion accounts for 10-40% of the nitrogen content in the ZPEI molecule. Preferably, the number average molecular weight is 1800, the zwitterion content is 24.8%, the ZPEI concentration is 0.15%, and the contact time is 30s.

[0015] 7. Preferably, the heat treatment temperature is 60°C and the heat treatment time is 10 min.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The composite nanofiltration membrane prepared by this invention exhibits excellent permeation selectivity and antifouling properties. The preparation method of this invention can control the surface charge and pore size of the membrane. Further optimization using interfacial polymerization-surface grafting conditions can achieve optimization of the structure and performance of the polyamide nanofiltration membrane. The preparation process is controllable, technologically mature, and low-cost, making it highly promising for industrial applications.

[0018] The optimized composite nanofiltration membrane has high water permeation flux and high rejection rates for both divalent anions and cations (Na2SO4: 96.6%, MgCl2: 91.3%), while also exhibiting good antifouling capabilities. This makes it a promising candidate for applications in industries such as seawater desalination pretreatment, water softening, and wastewater resource recovery. Attached image description:

[0019] Figure 1 The image shows an electron microscope image of the TFC membrane prepared by interfacial polymerization of piperazine as an aqueous monomer and pyromellitic trimethylol chloride as an organic monomer in Comparative Example 1 of this invention. The scale bar is 2 μm.

[0020] Figure 2 This is an electron microscope image of the ZPEI@TFC nanofiltration membrane prepared by grafting ZPEI onto the surface of a native TFC containing acyl chloride functional groups, as shown in Example 1 of the present invention. The scale bar is 2 μm.

[0021] Figure 3 Examples 1, 1, and 2 of this invention are used to test the antifouling performance of bovine serum albumin (BSA). Detailed implementation method:

[0022] To achieve the objectives of this invention, the experiment will be described in detail below with reference to specific embodiments, but the invention is not limited to the following embodiments.

[0023] This invention employs a cross-flow membrane permeation selective separation performance tester to test membrane separation performance. The effective area of ​​the membrane tank is 7.1 cm². 2 Throughout the experiment, the operating pressure was 6 bar, the feed temperature was maintained at 25 ± 0.5℃, and the feed solution was a 1000 ppm sodium sulfate (Na2SO4) and magnesium chloride (MgCl2) solution. The system was pre-pressurized for 1 hour before the test.

[0024] Formula for calculating permeation flux:

[0025]

[0026] Where V is the volume of the filtrate, in liters (L); and A is the effective filtration area, in meters (m²). 2 Δt is the time required for V volume of filtrate to pass through, in hours.

[0027] Formula for calculating the retention rate:

[0028]

[0029] Among them, C p C represents the conductivity of the permeate. f The conductivity of the feed liquid is expressed in μS·cm. -1 .

[0030] In the antifouling performance test, BSA (1 g·L⁻¹) was used. -1 The nanofiltration membrane was used as a model contaminant. First, the nanofiltration membrane was placed in the membrane tank and operated at a constant pressure of 6 bar using deionized water. Each test lasted 1 hour, and the filtrate was collected to calculate the permeate flux. After 3 hours of testing, the water in the cross-flow device was drained. Then, the simulated contaminant was dissolved in a prepared PBS buffer solution (NaCl: 8g, KCl: 0.2g, Na₂HPO₄: 2.88g, KH₂PO₄: 0.2g, diluted to 1L), stirred thoroughly, and operated at a constant pressure under the same conditions. Each test lasted 1 hour, and the filtrate was collected to calculate the permeate flux. After 7 hours of testing, the remaining solution in the device was drained, and the system was cleaned with deionized water at a pressure of 1 bar for 1 hour (this cleaning time was not included in the test time). Then, the contaminant solution was replaced with deionized water, and the pressure was slowly increased to 6 bar. Each test lasted 1 hour, and the filtrate was collected to calculate the permeate flux. The test ended after 3 hours.

[0031] The antifouling performance of nanofiltration membranes is calculated using the flux recovery rate (FRR) formula as follows:

[0032]

[0033] Among them, J W The flux is calculated using deionized water at a constant pressure for 2 hours; J R The flux is the result of simple rinsing with deionized water followed by stabilization at pressure for 2 hours.

[0034] Example 1:

[0035] A method for preparing a composite nanofiltration membrane with both high permeability selectivity and antifouling properties includes the following steps:

[0036] S1, pour a 0.3 w / v% piperazine aqueous solution onto the prepared hydrophilic polyvinylidene fluoride supported membrane surface, react for 60 s, and then remove the excess piperazine aqueous solution from the membrane surface. Next, pour a 0.3 w / v% trimesoyl chloride organic phase solution onto the membrane surface, react for 60 s, discard the excess organic phase solution, and rinse with n-hexane.

[0037] S2, a 0.05 w / v% ZPEI aqueous solution was poured onto the active TFC surface to initiate the grafting reaction. Excess solution was discarded after 30 seconds.

[0038] S3, after drying, place in a 60℃ oven for 10 minutes. After removing, place in water for later use.

[0039] Testing showed that the prepared composite nanofiltration membrane, which combines high permeability selectivity and antifouling properties, exhibited a Na₂SO₄ rejection rate of 96.6% and a MgCl₂ rejection rate of 91.3% at 6 bar, with a pure water permeation flux of 139.8 L·m⁻¹. -2 ·h -1 The FRR after the second cycle was 85%.

[0040] Example 2:

[0041] S1, pour a 0.3 w / v% piperazine aqueous solution onto the surface of the prepared hydrophilic polyvinylidene fluoride supported membrane, react for 180 s, and then remove the excess piperazine aqueous solution from the surface of the membrane. Next, pour a 0.3 w / v% trimesoyl chloride organic phase solution onto the membrane surface, react for 120 s, discard the excess organic phase solution, and rinse with n-hexane.

[0042] S2, a 0.15 w / v% ZPEI aqueous solution was poured onto the active TFC surface to initiate the grafting reaction. Excess solution was discarded after 180 s.

[0043] S3, after drying, place in a 60℃ oven for 10 minutes. After removing, place in water for later use.

[0044] Testing showed that the prepared composite nanofiltration membrane, which combines high permeability selectivity and antifouling properties, exhibited a Na₂SO₄ rejection rate of 96.3% at 6 bar and a pure water permeation flux of 135.6 L·m⁻¹. -2 ·h -1 .

[0045] Example 3:

[0046] S1, pour a 0.3 w / v% piperazine aqueous solution onto the prepared hydrophilic polyvinylidene fluoride supported membrane surface, react for 60 s, and then remove the excess piperazine aqueous solution from the membrane surface. Next, pour a 0.3 w / v% trimesoyl chloride organic phase solution onto the membrane surface, react for 120 s, discard the excess organic phase solution, and rinse with n-hexane.

[0047] S2, a 0.15 w / v% ZPEI aqueous solution was poured onto the active TFC surface to initiate the grafting reaction. Excess solution was discarded after 180 s.

[0048] S3, after drying, place in a 60℃ oven for 10 minutes. After removing, place in water for later use.

[0049] Testing showed that the prepared composite nanofiltration membrane, which combines high permeability selectivity and antifouling properties, exhibited a Na₂SO₄ rejection rate of 96.5% at 6 bar and a pure water permeation flux of 153 L·m⁻².-2 ·h -1 .

[0050] Example 4:

[0051] S1, pour a 0.3 w / v% piperazine aqueous solution onto the prepared hydrophilic polyvinylidene fluoride supported membrane surface, react for 60 s, and then remove the excess piperazine aqueous solution from the membrane surface. Next, pour a 0.3 w / v% trimesoyl chloride organic phase solution onto the membrane surface, react for 120 s, discard the excess organic phase solution, and rinse with n-hexane.

[0052] S2, a 0.15 w / v% ZPEI aqueous solution was poured onto the active TFC surface to initiate the grafting reaction. Excess solution was discarded after 180 s.

[0053] S3, after drying, place in a 60℃ oven for 10 minutes. After removing, place in water for later use.

[0054] Testing showed that the prepared composite nanofiltration membrane, which combines high permeability selectivity and antifouling properties, exhibited a Na₂SO₄ rejection rate of 96.2% at 6 bar and a pure water permeation flux of 145.2 L·m⁻². -2 ·h -1 .

[0055] Example 5:

[0056] S1, pour a 0.3 w / v% piperazine aqueous solution onto the prepared hydrophilic polyvinylidene fluoride supported membrane surface, react for 180 s, and then remove the excess piperazine aqueous solution from the membrane surface. Next, pour a 0.3 w / v% trimesoyl chloride organic phase solution onto the membrane surface, react for 60 s, discard the excess organic phase solution, and rinse with n-hexane.

[0057] S2, a 0.15 w / v% ZPEI aqueous solution was poured onto the active TFC surface to initiate the grafting reaction. Excess solution was discarded after 180 s.

[0058] S3, after drying, place in a 60℃ oven for 10 minutes. After removing, place in water for later use.

[0059] The prepared composite nanofiltration membrane, which combines high permeability selectivity and antifouling properties, was tested and found to have a Na2SO4 rejection rate of 96.2% at 6 bar and a pure water permeation flux of 145 L·m⁻¹. -2 ·h -1 .

[0060] Example 6:

[0061] S1, pour a 0.3 w / v% piperazine aqueous solution onto the prepared hydrophilic polyvinylidene fluoride supported membrane surface, react for 60 s, and then remove the excess piperazine aqueous solution from the membrane surface. Next, pour a 0.3 w / v% trimesoyl chloride organic phase solution onto the membrane surface, react for 60 s, discard the excess organic phase solution, and rinse with n-hexane.

[0062] S2, a 0.05 w / v% ZPEI aqueous solution was poured onto the active TFC surface to initiate the grafting reaction. Excess solution was discarded after 180 s.

[0063] S3, after drying, place in a 60℃ oven for 10 minutes. After removing, place in water for later use.

[0064] The prepared composite nanofiltration membrane, which combines high permeability selectivity and antifouling properties, was tested and found to have a Na2SO4 rejection rate of 92.2% at 6 bar and a pure water permeation flux of 183 L·m⁻¹. -2 ·h -1 .

[0065] Comparative Example 1:

[0066] S1, pour a 0.3 w / v% piperazine aqueous solution onto the prepared hydrophilic polyvinylidene fluoride supported membrane surface, react for 60 s, and then remove the excess piperazine aqueous solution from the membrane surface. Next, pour a 0.3 w / v% trimesoyl chloride organic phase solution onto the membrane surface, react for 60 s, discard the excess organic phase solution, and rinse with n-hexane.

[0067] S2, pour an aqueous solution without ZPEI onto the active TFC surface to initiate the grafting reaction. After 30 seconds, discard the excess solution.

[0068] S3, after drying, place in a 60℃ oven for 10 minutes. After removing, place in water for later use.

[0069] Testing showed that the prepared composite nanofiltration membrane, which combines high permeability selectivity and antifouling properties, exhibited a Na₂SO₄ rejection rate of 98.1% and a MgCl₂ rejection rate of 35.6% at 6 bar, with a pure water permeation flux of 152.4 L·m⁻¹. -2 ·h -1 The FRR after the second cycle was 45%.

[0070] Comparative Example 2:

[0071] S1, pour a 0.3 w / v% piperazine aqueous solution onto the prepared hydrophilic polyvinylidene fluoride supported membrane surface, react for 60 s, and then remove the excess piperazine aqueous solution from the membrane surface. Next, pour a 0.3 w / v% trimesoyl chloride organic phase solution onto the membrane surface, react for 60 s, discard the excess organic phase solution, and rinse with n-hexane.

[0072] S2, a 0.05 w / v% aqueous solution of polyethyleneimine (PEI) is poured onto the surface of the active TFC layer to initiate a grafting reaction. Excess solution is discarded after 30 seconds.

[0073] S3, after drying, place in a 60℃ oven for 10 minutes. After removing, place in water for later use.

[0074] Testing showed that the prepared composite nanofiltration membrane, which combines high permeability selectivity and antifouling properties, exhibited a Na₂SO₄ rejection rate of 87.8% and a MgCl₂ rejection rate of 94% at 6 bar, with a pure water permeation flux of 161.4 L·m⁻¹. -2 ·h -1 The FRR after the second cycle was 48%.

Claims

1. A method for preparing a composite nanofiltration membrane possessing both high permeability selectivity and antifouling properties, characterized in that: The composite nanofiltration membrane comprises an ultrafiltration substrate, a polyamide layer, and a nitrogen-oxygen zwitterionic polyethyleneimine (ZPEI) crosslinked layer, wherein the ZPEI structural formula is as follows: The preparation method includes the following steps: (1) Treat the surface of the porous ultrafiltration membrane with an aqueous solution of 0.1-0.5 w / v% polyamine monomer for 30-180 s; after removing the excess aqueous solution from the surface, treat the surface with an organic solution of 0.1-0.5 w / v% polyacryl chloride monomer for 10-120 s to generate an interfacial polymerization reaction and produce a primitive membrane with acryl chloride reactive functional groups on the surface. (2) Under room temperature conditions, the original ecological membrane was cleaned with organic solvents and the surface of the original ecological membrane was treated with an aqueous solution of ZPEI with a mass-volume ratio of 0.05-0.2% for 10-300s. (3) After heat treatment at 50-80℃ for 1-30 minutes, a composite nanofiltration membrane with both high permeability selectivity and antifouling properties is obtained.

2. The method for preparing a composite nanofiltration membrane with high permeation selectivity and anti-fouling performance according to claim 1, characterized in that: In step (1), the ultrafiltration membrane is one or a mixture of several of polysulfone, polyethersulfone, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile and polypropylene polymer.

3. The method for preparing a composite nanofiltration membrane with high permeation selectivity and anti-fouling performance according to claim 1, characterized in that: In step (1), the polyamine is one or a mixture of piperazine, piperazine derivatives, m-phenylenediamine, and polyethyleneimine.

4. The method for preparing a composite nanofiltration membrane with high permeation selectivity and anti-fouling performance according to claim 1, characterized in that: In step (1), the polyacrylamide chloride monomer is one or a mixture of several of the following: trimesoyl chloride, isophthaloyl chloride, and terephthaloyl chloride.

5. The method for preparing a composite nanofiltration membrane with high permeation selectivity and anti-fouling performance according to claim 1, characterized in that: In step (1), the solvent of the organic solution is one or a mixture of several of the solvents selected from ethyl acetate, n-hexane, and cyclohexane.

6. The method for preparing a composite nanofiltration membrane with high permeation selectivity and anti-fouling performance according to claim 1, characterized in that: In step (2), the number average molecular weight of ZPEI is between 200 and 70,000, and the quaternary ammonia nitrogen of the nitrogen-oxygen zwitterion in the ZPEI molecule accounts for 10 to 40% of the nitrogen content in the molecule.

7. A composite nanofiltration membrane with both high permeability selectivity and antifouling properties prepared by the method according to any one of claims 1 to 6.

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