A method for preparing a HEMA-PES composite nanofiltration membrane by one-step coating

Abstract

The present application relates to the preparation method of nanofiltration membrane, particularly to a kind of preparation method of HEMA-PES composite nanofiltration membrane of one-step coating, utilize one-step coating method to reduce coating thickness, further improve solidification efficiency, with acrylic resin as prepolymer, hydroxyethyl methacrylate as active diluent, TPO as photoinitiator, sodium p-styrenesulfonate as active monomer, composite nanofiltration membrane is prepared by ultraviolet light curing method, improve the hydrophilicity and mechanical strength of nanofiltration membrane, solve the problem that high rejection rate and high flux of nanofiltration membrane cannot be balanced, its heat resistance, acid and alkali resistance and other characteristics also perform well, can be applied to the treatment of wastewater generated in industry and the desalination and softening of wastewater.

Description

Technical Field

[0001] This invention relates to a method for preparing nanofiltration membranes, and in particular to a method for preparing HEMA-PES composite nanofiltration membranes by one-step coating. Background Technology

[0002] Membrane separation technology is widely used in pharmaceuticals, biotechnology, chemicals, textiles, food and wastewater treatment. Compared with traditional treatment processes such as chemical oxidation and physical adsorption, membrane separation technology has the advantages of simple technical route, large processing capacity per unit time, low energy consumption per unit processing capacity, and high coupling with other water treatment processes. It can effectively solve water pollution problems and realize water recycling.

[0003] Among various membrane separation technologies, nanofiltration membranes can retain nanoscale (0.001μm) substances. The molecular weight of organic matter they can retain is about 200-800, and the ability to retain dissolved salts is between 20% and 98%. Nanofiltration is generally used to remove organic matter and pigments from surface water and to remove dissolved salt ions. In food and pharmaceutical production, it can be used for the extraction and concentration of substances.

[0004] Nanofiltration membranes are generally prepared by thermal crosslinking and curing. During the thermal crosslinking process, most of the heat is used for crosslinking, but some heat is also lost to the environment. In addition, the curing process usually takes several hours or even days, so a lot of heat energy is required, which is not conducive to the preparation of nanofiltration membranes. At the same time, a large amount of solvent is generated during the curing process, which can easily cause environmental pollution.

[0005] Interfacial polymerization is also a commonly used method for preparing nanofiltration membranes. The nanofiltration membranes produced have the advantages of large permeate flux and good separation effect. However, the preparation process of interfacial polymerization is relatively complicated, and the production process requires large equipment investment and a large production room area, resulting in high production costs, which limits the preparation and promotion of nanofiltration membranes.

[0006] Ultraviolet (UV) curing is a simple and efficient method for preparing nanofiltration membranes. The method involves coating a base membrane with a coating material, followed by UV-induced curing to form a polymer coating. In practical applications, nanofiltration membranes prepared using this photocuring modification method not only exhibit good hydrophilicity but also allow for the control of the surface charge.

[0007] Compared to thermal crosslinking curing, UV curing takes only a few seconds to a few minutes from the start of the reaction to the end of curing, greatly reducing the time required for film formation and improving curing efficiency. UV curing also has a much higher energy utilization rate than traditional thermal curing methods. During UV curing, the energy emitted by the UV light is directly absorbed by the photoinitiator and active monomers, resulting in extremely high energy utilization. Furthermore, due to the shorter curing time, less energy is required for curing. In actual production, the use of UV curing can reduce equipment and plant space requirements, as well as other production costs, making it more suitable for large-scale production.

[0008] Although UV curing offers advantages such as high energy efficiency and fast processing speed, the varying water sources necessitate continuous improvement in the performance of the nanofiltration membranes to adapt to diverse water pollution problems. Besides requiring high permeation flux and separation efficiency, it also demands high antifouling properties against proteins and colloids, as well as resistance to acids, alkalis, and high temperatures. However, despite hydrophilic treatment during the preparation process to improve the hydrophilicity of the polymer coatings obtained by UV curing, the resulting nanofiltration membranes exhibit poor film-forming properties, large thickness, poor uniformity, and swelling upon contact with aqueous solutions. These issues not only affect the filtration efficiency and limit the application scenarios of the nanofiltration membranes but also reduce their lifespan.

[0009] Therefore, there is an urgent need for a UV curing method that can improve the film-forming properties and hydrophilicity of nanofiltration membranes. This method should not only improve the curing efficiency of nanofiltration membranes, but also increase the water flux and retention of inorganic salts, dyes, and other substances, while also improving the hydrophilicity and applicability of nanofiltration membranes. Summary of the Invention

[0010] The purpose of this invention is to provide a method for preparing composite nanofiltration membranes through one-step coating using ultraviolet light curing.

[0011] Another objective of this invention is to improve the water flux and retention rate of inorganic salts, dyes, and other substances in the composite nanofiltration membrane through a preferred embodiment, thereby enhancing the hydrophilicity of the nanofiltration membrane and extending its service life.

[0012] The technical solution adopted to achieve the purpose of this invention is:

[0013] UV-curable coating materials include: prepolymers containing unsaturated double bonds, photoinitiators, reactive monomer diluents, and other additives.

[0014] Furthermore, the prepolymer is selected from acrylic resin, the reactive diluent is selected from hydroxyethyl methacrylate (HEMA), the photoinitiator is selected from TPO, and the other additives are sodium p-styrene sulfonate (SSS).

[0015] Furthermore, the prepolymer is selected from methyl methacrylate.

[0016] Furthermore, the preparation method of the composite nanofiltration membrane includes the following steps:

[0017] Preparation of S1.PES-based film

[0018] The base membrane was a self-made polyethersulfone membrane, prepared by phase inversion method.

[0019] The casting solution was prepared according to the mass concentration ratio in Table 1 below. The casting solution was stirred at 60°C for 8 hours to ensure that the components in the casting solution were fully miscible. Then, it was degassed under vacuum for 30 minutes. The casting solution was then coated onto the surface of the base film using a 150μm doctor blade. After standing in the air for 30 to 60 seconds, it was immersed in pure water, and the PES liquid film was rapidly solidified into a film.

[0020] Table 1

[0021]

[0022] For the post-treatment of PES membranes, the solvent replacement method is used. The prepared membrane is placed in deionized water, and the water is changed every 6 to 8 hours. This process is repeated 4 times. Finally, the membrane is allowed to air dry at room temperature to obtain the PES base membrane for later use.

[0023] S2. Preparation of photocurable HEMA-PES composite nanofiltration membrane

[0024] (1) Preparation of casting solution: Methyl methacrylate, hydroxyethyl methacrylate and photoinitiator TPO are added to the container in sequence, and stirred on a magnetic stirrer for 30 min to 60 min. Then, the container is placed in a vacuum degassing device for 20 min to remove air bubbles from the solution to avoid uneven distribution of the cured coating.

[0025] Furthermore, the mass concentration of methyl methacrylate in the casting solution is 40%-52%;

[0026] Furthermore, the mass concentration of methyl methacrylate in the casting solution is 46%-49%.

[0027] Furthermore, the mass concentration of photoinitiator TPO in the casting solution is 1%-5%;

[0028] Furthermore, the mass concentration of photoinitiator TPO in the casting solution is 3%.

[0029] Furthermore, the mass concentration of hydroxyethyl methacrylate in the casting solution is 40%-52%;

[0030] Furthermore, the mass concentration of hydroxyethyl methacrylate in the casting solution is 49%.

[0031] (2) Photocuring method for film formation: First, place the PES base film on a clean and flat surface, pour the defoamed casting solution onto the surface of the base film, and scrape it once with a scraper to complete the first coating step.

[0032] Furthermore, the coating thickness achieved by the scraper is 2μm-8μm;

[0033] Furthermore, the coating thickness achieved by the scraper is 2 μm.

[0034] After the scraped membrane solution is cured under a UV lamp for 1 minute, it is then dried in an oven. The cured membrane is placed at the bottom of the reactor and fixed to obtain the HEMA-PES composite nanofiltration membrane.

[0035] Furthermore, the wavelength of the ultraviolet lamp is 365nm, and the distance between the ultraviolet lamp and the membrane liquid is controlled to be 7cm;

[0036] Furthermore, the oven temperature is set to 40℃-60℃, preferably 30℃.

[0037] To protect the activity of free radicals and ensure the smooth progress of the UV irradiation free radical polymerization reaction, the entire reaction is conducted in an inert gas environment.

[0038] Furthermore, the inert gas is N2.

[0039] Furthermore, to improve the water solubility of the HEMA-PES composite nanofiltration membrane and address the imbalance between high flux and high rejection rate in nanofiltration membranes, a HEMA-PES composite nanofiltration membrane containing sodium polystyrene sulfonate was prepared by adding sodium p-phenylene sulfonate as an active monomer. This membrane is called SSS@HEMA-PES composite nanofiltration membrane. A method for preparing the SSS@HEMA-PES composite nanofiltration membrane is also provided, as follows:

[0040] Weigh a certain amount of sodium p-styrene sulfonate, dissolve it in deionized water, add 5% TPO, stir until SSS is completely dissolved, and adjust the pH of the solution to 1.

[0041] Furthermore, the mass concentration of the sodium p-styrene sulfonate is 3%-7%;

[0042] Furthermore, the mass concentration of the sodium p-styrene sulfonate is 5%.

[0043] Pour the prepared sodium styrene sulfonate solution into the reactor, immerse the prepared HEMA-PES composite nanofiltration membrane in the SSS solution, and after 20 minutes until it is completely wetted, scrape off the excess liquid on its surface with a silicone flexible roller. Place the reactor under a UV lamp for crosslinking for 30 minutes, and obtain the composite nanofiltration membrane after complete curing.

[0044] The obtained composite membrane was immersed in a 5% Na2SO4 solution for 2 hours for ion exchange to saponify it. Then it was rinsed with deionized water and dried in an oven at 40°C. After drying, it was stored in a sealed bag for later use.

[0045] Compared with the prior art, the beneficial effects of the present invention are:

[0046] 1. The composite nanofiltration membrane prepared by one-step coating method has good retention effect on dyes under relatively low pressure (0.4-1.2 MPa) and good retention effect on inorganic salts such as 1000 ppm NaCl and Na2SO4. Moreover, the composite nanofiltration membrane also has the characteristics of strong antifouling ability, high separation efficiency and high flux. Its heat resistance and acid and alkali resistance are also good. It can be widely used in industrial wastewater treatment and wastewater desalination and softening.

[0047] 2. Using ultraviolet light curing, the curing time is shortened to just a few minutes or seconds. However, the thickness of the cured coating has a significant impact on the curing rate. One-step coating can reduce the coating thickness and further improve curing efficiency. Combined with ultraviolet light curing, there will be no residual solvent after curing and almost no by-products. The heat energy required in this process is also less, resulting in low production costs.

[0048] 3. To address the common challenge of balancing high flux and high rejection rate in nanofiltration membranes, a composite nanofiltration membrane with high rejection rate was prepared using hydroxyethyl methacrylate and sodium p-styrene sulfonate as active monomers, ensuring both high rejection rate and high flux of the nanofiltration membrane.

[0049] 4. The proportion of photoinitiator in the curing system directly determines whether the cured coating can be successfully cured under ultraviolet irradiation. The concentration of active monomer directly affects the curing time. Therefore, the concentration ratio of each substance in the curing system is particularly important. By obtaining a reasonable ratio through experiments, the curing efficiency can be improved and a nanofiltration membrane that meets the standards can be prepared. On this basis, adding sodium p-phenylethyl sulfonate as an active monomer can also improve the hydrophilicity, high temperature resistance, and acid and alkali resistance of the nanofiltration membrane. Attached Figure Description

[0050] Figure 1The determination of the molecular weight cutoff of the SSS@HEMA-PES and HEMA-PES composite nanofiltration membranes of this invention;

[0051] Figure 2 The rejection rate of the SSS@HEMA-PES composite nanofiltration membrane of this invention for different dyes;

[0052] Figure 3 This invention relates to the effect of continuous operating time of the SSS@HEMA-PES composite nanofiltration membrane on nanofiltration performance.

[0053] Figure 4 The effect of different coating thicknesses on flux and rejection rate of SSS@HEMA-PES composite nanofiltration membrane. Detailed Implementation

[0054] 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.

[0055] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0056] Example 1: Preparation of SSS@HEMA-PES composite nanofiltration membrane

[0057] Preparation of S1.PES-based film

[0058] The base membrane was a laboratory-made polyethersulfone (PES) membrane. First, a casting solution was prepared according to the mass ratios shown in the table below. The casting solution was stirred at 60°C for 8 hours to ensure complete miscibility of the components. After vacuum degassing for 30 minutes, the casting solution was applied to the base membrane surface using a 150 μm doctor blade. After standing in air for 30–60 seconds, it was immersed in pure water, and the PES liquid membrane rapidly solidified. After membrane formation, the prepared membrane was placed in deionized water, with the water changed every 6–8 hours, repeated four times. Finally, it was allowed to air dry at room temperature for later use.

[0059] Table 2

[0060]

[0061] S2. Preparation of photocurable HEMA-PES composite nanofiltration membrane

[0062] (1) Preparation of casting solution: Add 5.1g of methyl acrylate, 4.6g of hydroxyethyl methacrylate, and 0.3g of photoinitiator TPO to a beaker in sequence. To ensure that the solute is evenly dispersed in the solution, place it in an ultrasonic disperser and sonicate for 0.5h. Stir the solution magnetically and after stirring evenly, place it in a vacuum degasser for degassing.

[0063] (2) Photocuring method for film formation: After degassing, the solution is poured evenly onto the PES base film and scraped into a film with a thickness of 2μm in one go with a scraper. After the scraped film solution is placed under a UV lamp for 1 minute to cure, it is placed in an oven to dry. The cured film is then placed at the bottom of the reactor and fixed.

[0064] Preparation of S3.SSS@HEMA-PES composite nanofiltration membrane

[0065] Weigh out a certain mass of sodium styrene sulfonate (SSS), dissolve it in deionized water, add 5% aqueous photoinitiator, stir until the SSS is completely dissolved, prepare a 5% solution, and adjust the pH of the solution to 1.

[0066] Pour the prepared 5% sodium p-styrene sulfonate solution into the reactor. Immerse the prepared HEMA-PES composite nanofiltration membrane in the SSS solution for 20 minutes until it is completely wetted. Use a silicone flexible roller to scrape off the excess liquid on its surface. Place the reactor under a UV lamp for crosslinking for 30 minutes. After that, take out the membrane, wash it with pure water, and then put it in an oven to dry.

[0067] The obtained composite membrane was immersed in a 5% Na2SO4 solution for 2 hours for ion exchange to achieve saponification. After rinsing with deionized water, it was dried in an oven at 40°C and stored in a sealed bag for later use.

[0068] Example 2: Separation performance and stability test of SSS@HEMA-PES nanofiltration composite membrane

[0069] The separation performance of the composite nanofiltration membrane prepared in Example 1 was tested using a laboratory-made nanofiltration membrane separation performance testing device and a cross-flow filtration method.

[0070] The device mainly consists of a raw water tank, a high-pressure rotary pump, and a membrane chamber, among other components. The effective area of ​​the membrane sheet inside the membrane chamber is 21 cm². 2 A Nanjing Xianou XOYS-2006 uniform thermostatic control bath was used to maintain the feed solution temperature at 25℃, and the operating flow rate and operating pressure at 1.5 L / min and 4 bar, respectively. The feed concentration of the inorganic salt solution was 1000 ppm Na₂SO₄ and NaCl solution. After stabilization for 1 hour, samples were taken every 1 hour to record the exudate volume, and then the inorganic salt concentration was measured. Each membrane was sampled at least three times.

[0071] The permeation flux of the membrane is calculated using the formula:

[0072]

[0073] Where F represents the membrane permeation flux (L / m 2 •h); V represents the volume of permeate collected (L); A represents the effective membrane area (m²). 2 ); △p represents the operating pressure (bar); T represents the operating time for collecting permeate.

[0074] The retention rate of inorganic salts by nanofiltration membranes is calculated using the following formula:

[0075]

[0076] Where R represents the membrane rejection rate (%), and Cp and Cf represent the solute concentrations (ppm) of the permeate and feed liquid, respectively.

[0077] Calculations show that, under an operating pressure of 4 bar and an operating flow rate of 1.5 L / min, the SSS@HEMA-PES composite nanofiltration membrane has a pure water flux of 55.64 L / m²·h, a rejection rate of 92.31% for 1000 ppm Na₂SO₄ solution, and a rejection rate of 33.24% for 1000 ppm NaCl solution, demonstrating good separation performance.

[0078] Stability is a key characteristic for testing whether a membrane can be applied to industrial production. Therefore, long-term operation tests are conducted to verify the stability of the prepared composite membrane.

[0079] Long-term operation test results are as follows Figure 3 As shown, during the 50-hour nanofiltration process, the permeation flux of the SSS@HEMA-PES composite nanofiltration membrane remained stable at 13.37 L·m⁻¹. -2 ·h -1 ·bar -1 The rejection rate of Na2SO4 was approximately 92.34%, indicating that the composite nanofiltration membrane prepared by photocuring reaction has good stability.

[0080] Example 3: Determination of the molecular weight cutoff of the SSS@HEMA-PES nanofiltration composite membrane

[0081] The SSS@HEMA-PES composite nanofiltration membrane prepared in Example 1 was used to screen neutral organic molecules of different molecular weights, and the molecular weight cutoff (MWCO) of the nanofiltration membrane was determined based on the experimental results.

[0082] MWCO refers to the molecular weight at which the rejection rate of neutral organic molecules reaches 90%. The organic compounds used to determine the rejection rate are PEG200, PEG400, PEG600, and PEG800, with corresponding molecular weights of 200, 400, 600, and 800, respectively. The test method is to use the laboratory-made nanofiltration membrane separation performance testing device in Example 2. The solute is a single-component organic compound, and the feed concentration is 0.2 g / L.

[0083] Before and after the molecular weight cutoff test, the concentration of the solution was measured using a TOC-L CPH type TOC (total organic carbon) analyzer, and the MWCO of the SSS@HEMA / PES composite film was calculated using the fitted data.

[0084] Total organic carbon concentration was determined by combustion; the instrumental analysis method employed was combustion oxidation-nondispersive infrared absorption. Water samples were injected into quartz tubes and placed in a high-temperature furnace. Chromium trioxide was added as a catalyst at high temperature, causing the organic matter in the water to oxidize and decompose into carbon dioxide. The CO2 concentration was then measured using an infrared gas analyzer. Finally, the organic matter concentration in the permeate was calculated from the characterized carbon concentration. The results are as follows: Figure 1 As shown.

[0085] Example 4: Determination of dye rejection rate of SSS@HEMA-PES nanofiltration composite membrane

[0086] The dyes were filtered using the SSS@HEMA-PES composite nanofiltration membrane prepared in Example 1. The dye rejection rate was determined using the nanofiltration separation device in Example 2. The rejection rates of four dyes, namely methyl orange (MO), methylene blue (MB), Bengal rose red (RB), and reactive brilliance red X-3B, were determined using the prepared SSS@HEMA-PES composite nanofiltration membrane. The solute in the dye solution was a single-component dye with a feed concentration of 0.2 g / L.

[0087] The concentration of the dye solution before and after nanofiltration was determined using a UV-Vis spectrophotometer. The UV-Vis spectrophotometer was used for testing and analysis based on the Lambert-Beer law. Since different compounds have different absorbances at different absorption wavelengths, compounds, purity, and content were distinguished according to absorbance.

[0088] like Figure 2 The results show the retention performance of the SSS@HEMA-PES nanofiltration composite membrane for different types of dyes.

[0089] Among them, the rejection rates of nonionic dyes RB and X-3B were 99.13% and 98.11%, respectively. The molecular weights of RB and X-3B were approximately 973 and 615, respectively. RB has a larger Stokes radius, and size sieving plays a major role in separation, so the rejection rate of RB is slightly higher.

[0090] The rejection rates of ionic dyes MO and MB were 98.84% and 62.25%, respectively. MO is an anionic dye, while MB is a cationic dye. The synergistic effect of electrostatic repulsion and size sieving is the main mechanism by which the photocurable composite nanofiltration membrane separates these two ionic dyes. The surface of the photocurable composite nanofiltration membrane is negatively charged, thus exhibiting electrostatic repulsion for negatively charged substances. For the anionic dye MO, since it exhibits the same charge as the negatively charged membrane surface, the long-distance electrostatic repulsion caused by the Donnan effect results in a high rejection rate for MO. In addition, the solute is affected by steric hindrance on the membrane surface, thus the rejection rate of MO is much higher than that of MB.

[0091] Example 5: Effect of Coating Thickness on the Performance of Nanofiltration Composite Membranes

[0092] The thickness of the active layer of nanofiltration membranes prepared by ultraviolet light curing may be greater than that of traditional nanofiltration membranes. This is because the ultraviolet light curing method usually uses short-wavelength ultraviolet light for curing reaction. Its shorter wavelength can penetrate the active layer and generate a cross-linking reaction within the active layer. Therefore, the thickness of nanofiltration membranes prepared by the currently used ultraviolet light curing method is usually greater than 1 μm, and the stability of nanofiltration membranes can be improved by increasing the thickness of the active layer.

[0093] The thickness of the cured coating on the PES base membrane can be controlled by selecting a doctor blade with different slits, and repeated coating can also be used to increase the thickness of the nanofiltration membrane while ensuring the separation effect. Therefore, using the method of Example 1, by only changing the number of times the doctor blade is used in step S2, SSS@HEMA-PES nanofiltration composite membranes of different thicknesses can be prepared.

[0094] The number of times the doctor blade was applied in step S2 was changed to 2, 4, 6, and 8 times, respectively, resulting in membrane thicknesses of 2 μm, 4 μm, 6 μm, and 8 μm. The nanofiltration separation performance of the SSS@HEMA-PES nanofiltration composite membranes of different thicknesses for 1000 mg / L Na₂SO₄ and NaCl solutions was tested using the method in Example 2. The experimental results are as follows: Figure 4 As shown.

[0095] like Figure 4 The effect of different cured coating thicknesses on nanofiltration membrane permeation flux and inorganic salt rejection rate.

[0096] The results showed that the permeation flux of the nanofiltration membrane had a negative linear correlation with the thickness of the SSS@HEMA-PES cured coating, indicating that a thinner cured coating enhances the permeation flux of the nanofiltration membrane. The nanofiltration membrane prepared by one-step coating was only 1 μm thick. The thinner the nanofiltration membrane, the shorter the curing time and the faster the photocuring speed. The rapid film formation by photocuring can effectively reduce the penetration of casting solution into the base membrane and prevent the generation of other by-products. Figure 4 The results also show that when the thickness of the SSS@HEMA-PES nanofiltration membrane is thin, no defects will occur on the surface of the membrane. This is because the addition of sodium p-phenylenesulfonate improves the mechanical strength of the membrane to a certain extent, further ensuring the possibility of successfully preparing composite nanofiltration membranes by one-step coating method.

[0097] Example 6: Separation performance test of HEMA-PES composite nanofiltration membrane

[0098] The HEMA-PES composite nanofiltration membrane prepared by S1 and S2 in Example 1 was used to test the separation performance of the HEMA-PES composite nanofiltration membrane using the nanofiltration membrane separation performance testing device and method in Example 2. The calculation method of the test results was the same as that in Example 2.

[0099] The test results showed that, at an operating pressure of 4 bar and an operating flow rate of 1.5 L / min, the pure water flux of the HEMA-PES composite nanofiltration membrane was 18.08 L·m³. -2 ·h -1 ·bar -1 The rejection rate for Na2SO4 was 75.8%, and the rejection rate for NaCl was 16.8%.

[0100] Although the HEMA-PES composite nanofiltration membrane showed good water flux and retention effect, the pure water flux of the SSS@HEMA-PES composite nanofiltration membrane was significantly higher than that of the HEMA-PES composite nanofiltration membrane compared with the data measured in Example 2. Under the premise of high pure water flux, this is because a low concentration of sodium p-phenylenesulfonate was used in the preparation process, which not only increased the hydrophilicity of the membrane, but also made the nanofiltration membrane surface negatively charged by the addition of sodium styrenesulfonate, which changed the properties of the membrane surface and thus improved the membrane permeability and separation performance.

[0101] The SSS@HEMA-PES composite nanofiltration membrane also showed significantly higher rejection rates for Na2SO4 and NaCl than the HEMA-PES composite nanofiltration membrane, indicating that SSS@HEMA-PES has a better rejection effect on inorganic salts such as Na2SO4 and NaCl.

[0102] Example 7: Determination of the molecular weight cutoff of the HEMA-PES composite nanofiltration membrane

[0103] The HEMA-PES composite nanofiltration membrane prepared by S1 and S2 in Example 1 was used to screen neutral organic molecules of different molecular weights. The MWCO content in the nanofiltration membrane was detected by the experimental results. The specific experimental steps and methods were the same as in Example 3.

[0104] Experimental results are as follows Figure 1 As shown, the molecular weight cutoff (MWCO) of the SSS@HEMA-PES nanofiltration composite membrane is 260 Da, while that of the HEMA-PES composite nanofiltration membrane is 379 Da. The MWCO of the SSS@HEMA-PES composite nanofiltration membrane is significantly lower than that of the HEMA-PES composite nanofiltration membrane. This indicates that the introduction of the SSS monomer increases the crosslinking degree of the curing layer, thereby making the pore size of the composite membrane smaller, thus improving the filtration effect of the nanofiltration membrane and obtaining the best nanofiltration performance. This also solves the problem of the imbalance between high flux and high rejection rate that is common in nanofiltration membranes.

[0105] The above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an SSS@HEMA-PES composite nanofiltration membrane, characterized in that: Includes the following steps: Preparation of S1. PES Base Film: Using polyethersulfone (PES) film as the base film, a casting solution was prepared with polyvinylpyrrolidone (PVP), N,N-dimethylacetamide (NMA), and polyethylene glycol 400 (PEG 400). The casting solution was coated onto the surface of the base film, allowed to stand in air, then immersed in pure water to solidify into a film. The film was then placed in deionized water and finally removed and air-dried to obtain the PES base film. The PES base film had a PES concentration of 14.5% by mass; the casting solution contained 3% PES by mass, 79.5% NMA by mass, and 3% PEG 400 by mass. S2. Preparation of photocurable HEMA-PES composite nanofiltration membrane: Prepolymer methyl methacrylate, reactive diluent hydroxyethyl methacrylate, and photoinitiator TPO are sequentially added to a container, stirred evenly, and then degassed. The PES base membrane is placed on a flat surface, and casting solution is poured onto the base membrane surface. A single coating is applied using a doctor blade, with a coating thickness of 2μm-8μm. The coated membrane solution is cured under a UV lamp and then dried in an oven. The cured membrane is placed at the bottom of the reactor and fixed to obtain the HEMA-PES composite nanofiltration membrane. The photocuring process is carried out under inert gas protection. The mass concentration of methyl methacrylate is 40%-52%, the mass concentration of photoinitiator TPO is 1%-5%, and the mass concentration of hydroxyethyl methacrylate is 40%-52%. Finally, the HEMA-PES composite nanofiltration membrane prepared by S2 was immersed in sodium p-styrene sulfonate solution. After immersion for a certain period of time, the excess liquid on its surface was scraped off. The reactor was placed under ultraviolet light for cross-linking. After complete curing, it was immersed in Na2SO4 solution, then rinsed with deionized water and dried. After drying, it was stored in a sealed bag to obtain the SSS@HEMA-PES composite nanofiltration membrane.

2. The method for preparing an SSS@HEMA-PES composite nanofiltration membrane as described in claim 1, characterized in that: S1. Preparation of PES base film: The prepared casting solution was first stirred at 60℃ for 8 h and then vacuum degassed for 30 min. The casting solution was then coated onto the surface of polyethersulfone base film with a 150 μm doctor blade. After standing in the air for 30 s to 60 s, it was immersed in pure water to solidify into a film. Then it was placed in deionized water and the water was changed every 6 h to 8 h. This process was repeated 4 times. Finally, it was taken out and air-dried to obtain the PES base film. S2. Preparation of photocurable HEMA-PES composite nanofiltration membrane: Methyl methacrylate, hydroxyethyl methacrylate, and photoinitiator TPO were added sequentially to a container and stirred for 30-60 minutes. After stirring, the container was placed in a vacuum degassing machine for 20 minutes for vacuum degassing. The PES base membrane was placed on a flat surface, and the casting solution was poured onto the surface of the base membrane. The membrane was coated once with a doctor blade, with a coating thickness of 2-8 μm. The coated membrane solution was then placed under a UV lamp for 1 minute to cure. The UV lamp wavelength was 365 nm, the distance between the UV lamp and the membrane solution was 7 cm, and the oven temperature was set to 40℃-60℃. The photocuring process was carried out under N2 protection.

3. The method for preparing an SSS@HEMA-PES composite nanofiltration membrane as described in claim 2, characterized in that: In the preparation of the S2 photocurable HEMA-PES composite nanofiltration membrane: the thickness of the coating by the doctor blade is 2μm.

4. The method for preparing an SSS@HEMA-PES composite nanofiltration membrane as described in claim 1, characterized in that: In the preparation of S2 photocurable HEMA-PES composite nanofiltration membrane: the mass concentration of methyl methacrylate is 46%-49%, the mass concentration of photoinitiator TPO is 3%, and the mass concentration of hydroxyethyl methacrylate is 49%.

5. The method for preparing an SSS@HEMA-PES composite nanofiltration membrane as described in claim 1, characterized in that: The prepared HEMA-PES composite nanofiltration membrane was immersed in a sodium p-styrene sulfonate solution with a mass concentration of 3%-7%. The preparation method was as follows: sodium p-styrene sulfonate was dissolved in deionized water and 5% TPO was added. The mixture was stirred until the sodium p-styrene sulfonate was completely dissolved, and the pH of the solution was adjusted to 1.

6. The method for preparing an SSS@HEMA-PES composite nanofiltration membrane as described in claim 1, characterized in that: Pour the prepared sodium p-styrene sulfonate solution into the reactor, immerse the prepared HEMA-PES composite nanofiltration membrane in the sodium p-styrene sulfonate solution, and after 20 min until it is completely wetted, scrape off the excess liquid on its surface with a silicone flexible roller. Place the reactor under a UV lamp for crosslinking for 30 min. After complete curing, immerse it in a 5% Na2SO4 solution for 2 h, then rinse it with deionized water and dry it in an oven at 40℃. After drying, store it in a sealed bag to obtain the SSS@HEMA-PES composite nanofiltration membrane.

7. The SSS@HEMA-PES composite nanofiltration membrane prepared by any one of claims 1-6.

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