Preparation method of nanofiltration membrane with high anti-pollution property

Abstract

The application discloses a preparation method of a nanofiltration membrane with high anti-pollution property, which uses polyethersulfone as a support layer and uses chitosan quaternary ammonium salt and trimesoyl chloride for interfacial polymerization. The hydrophilic functional groups of the chitosan quaternary ammonium salt enhance the interaction between water molecules and the membrane surface, relieve the adsorption and deposition of pollutants on the membrane surface, and thus enhance the anti-organic pollution property of the membrane. In addition, the positive charges carried by the chitosan quaternary ammonium salt can destroy the bacterial cell membrane and cause the death of bacteria, thus enhancing the anti-biological pollution property of the membrane. The nanofiltration membrane prepared by the application has excellent anti-organic pollution and anti-biological pollution abilities under the condition of maintaining good water flux and separation performance, and has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of nanofiltration membranes, specifically relating to a method for preparing a nanofiltration membrane with high antifouling properties. Background Technology

[0002] With the increasing global water scarcity and water quality safety issues, developing water treatment technologies that are both highly efficient and sustainable has become a core issue in the field of environmental engineering. Against this backdrop, membrane separation technology, with its advantages of low energy consumption and high selectivity, has become an important approach to solving the water crisis. However, a major challenge facing membrane technology is membrane fouling, including inorganic fouling, colloidal fouling, organic fouling, and biological fouling. Among these, organic fouling and biological fouling are two of the most common types of fouling in membrane separation processes. Organic fouling refers to the adsorption or deposition of organic matter in the water on the membrane surface or within the membrane pores, interacting with the membrane through physical or chemical adsorption to form an organic fouling layer. Biological fouling refers to the growth and reproduction of microorganisms on the membrane surface or within the membrane pores, forming a biofilm. Biological and organic fouling can occur simultaneously and interact, resulting in complex compound fouling phenomena. After microorganisms form a biofilm on the membrane surface, it promotes the adsorption or deposition of organic matter on the membrane. The organic matter, in turn, provides a rich nutrient source for microorganisms, which is conducive to their growth and reproduction, thus exacerbating membrane fouling and ultimately leading to membrane flux decline and effluent water quality deterioration. Therefore, it is of great significance to prepare membrane materials that are resistant to both organic and biological pollution.

[0003] Semi-aromatic polyamide nanofiltration membranes are a common type of separation membrane material, formed by the interfacial polymerization of two monomers: aromatic polyamines (such as piperazine) and aromatic polyacrylamide chlorides (such as trimesoyl chloride) on a porous support layer. These membrane materials can effectively remove harmful substances such as salt, hardness ions, heavy metal ions, and organic matter from water, producing high-quality pure water or treated water that meets specific water quality requirements. They are widely used in seawater desalination, brackish water desalination, and industrial pure water production. However, membrane fouling remains a significant factor limiting its long-term stable operation. Existing research attempts to improve membrane performance by modifying the polymerizing monomers; however, the difficulty in synergistically improving antifouling properties and separation efficiency is a common challenge. This invention innovatively uses chitosan quaternary ammonium salt (CQAS) as the aqueous phase functional monomer, and constructs a novel polyamide separation layer with trimesoyl chloride (TMC) through an interfacial polymerization reaction. The hydrophilicity of chitosan quaternary ammonium salt promotes the rapid transport of water molecules, thereby increasing the membrane's water flux. On the other hand, chitosan quaternary ammonium salt has positively charged quaternary ammonium groups, which can destroy bacterial cell membranes through electrostatic adsorption, thereby enhancing the membrane's resistance to biofouling; the hydroxyl and amino groups of chitosan quaternary ammonium salt form a dense hydration layer on the membrane surface, which can block the penetration of organic pollutants, thereby enhancing the membrane's resistance to organic pollution.

[0004] This invention uses a polyethersulfone membrane as a carrier and chitosan quaternary ammonium salt and organic acyl chloride as monomers in the aqueous and oil phases, respectively, to prepare a novel nanofiltration membrane via interfacial polymerization. The nanofiltration membrane prepared by this invention exhibits excellent resistance to organic and biological fouling without affecting, or even improving, water flux and separation performance. Summary of the Invention

[0005] To address the existing problems, this invention provides a method for preparing a nanofiltration membrane with high anti-fouling properties.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing a nanofiltration membrane with high antifouling properties, using a polyethersulfone membrane as a carrier, specifically includes:

[0008] Provide an acetic acid solution containing chitosan quaternary ammonium salt;

[0009] Provide organic solvent solutions containing organic acyl chlorides;

[0010] Provide sodium hydroxide solution;

[0011] Provide a carrier polyethersulfone membrane;

[0012] The carrier polyethersulfone membrane was immersed in an acetic acid solution containing chitosan quaternary ammonium salt for 15 min;

[0013] Remove excess acetic acid solution containing chitosan quaternary ammonium salt from the surface of the composite membrane, air dry for 1 minute, and then immerse in sodium hydroxide solution for 2 hours.

[0014] Remove excess sodium hydroxide solution from the surface of the carrier polyethersulfone membrane, air dry for 1 minute, and then immerse it in an organic solution containing organic acyl chloride for 10 minutes.

[0015] The composite film is placed in an oven and heated at 55-65℃ for 30 minutes for curing.

[0016] Preferably, the organic amine is selected from one or more of o-phenylenediamine, m-phenylenediamine, chitosan quaternary ammonium salt, p-phenylenediamine, piperazine, ethylenediamine, diethylenetriamine, and polyethyleneimine;

[0017] The organic acyl chloride is selected from one or more of terephthaloyl chloride, isophthaloyl chloride, adipyl chloride, phthaloyl chloride, trimesoyl chloride, cyclohexyl chloride, pyromellitic chloride, tetramethylpyroyl chloride, and cyclopentanetetramethyl chloride;

[0018] The organic solvent is selected from one or more of toluene, benzene, n-hexane, cyclohexane, and n-heptane.

[0019] Preferably, the organic amine is chitosan quaternary ammonium salt (CQAS); the organic acyl chloride is trimesoyl chloride (TMC); and the organic solvent is n-hexane.

[0020] Preferably, the organic amine concentration in the organic amine solution is 1.0 wt%.

[0021] Preferably, the concentration of organic acyl chloride in the organic solution is 0.5 wt%.

[0022] The beneficial effects of this invention are as follows:

[0023] This invention provides a method for preparing a nanofiltration membrane with high antifouling properties. A novel polyamide separation layer is constructed by interfacial polymerization of chitosan quaternary ammonium salt as an aqueous functional monomer and trimesoyl chloride. This method can significantly improve the composite membrane's resistance to organic and biofouling, while maintaining good water flux and separation performance. It is a composite membrane with great development potential. Attached Figure Description

[0024] Figure 1 SEM and AFM images of embodiments and comparative examples of the present invention;

[0025] Figure 2 This illustrates the water flux reduction before and after contamination in the embodiments and comparative examples of the present invention.

[0026] Figure 3 This is a comparison of the antibacterial properties of the embodiments and comparative examples of the present invention; ((a) and (b) are Escherichia coli, (c) and (d) are Staphylococcus aureus)

[0027] Figure 4 The figures show the water flux decline after biological contamination in the embodiments and comparative examples of the present invention. ((a) Escherichia coli, (b) Staphylococcus aureus) Detailed Implementation

[0028] To better understand the present invention, the following embodiments and comparative examples further illustrate its content. Unless otherwise specified, the materials, reagents, or apparatus used in the embodiments and comparative examples are readily available from conventional commercial sources or can be obtained through existing technical methods. Unless otherwise specified, the testing or experimental methods are conventional methods in the art. It should be understood that the following embodiments and comparative examples are merely illustrative and do not limit the scope of protection of the present invention. Furthermore, obvious changes and modifications made by those skilled in the art according to the present invention are also included within the scope of the present invention.

[0029] Example

[0030] (1) Cut a polyethersulfone film of appropriate size and soak it in deionized water for 24 hours to remove the surface preservatives and impurities.

[0031] (2) Weigh 1g of chitosan quaternary ammonium salt and dissolve it in 99g of acetic acid solution (1:100). After contacting the front side of the membrane obtained in step (1) with the acetic acid solution of chitosan quaternary ammonium salt for 15min, remove the excess acetic acid solution of chitosan quaternary ammonium salt from the membrane surface and air dry for 1min.

[0032] (3) Take an appropriate amount of sodium hydroxide solution with pH 12, and after contacting the front side of the membrane obtained in step (2) with the sodium hydroxide solution for 2 hours, remove the excess sodium hydroxide solution from the membrane surface and air dry for 1 minute.

[0033] (4) Weigh 0.75g of trimesoyl chloride and dissolve it in 149.25g of n-hexane. After contacting the front side of the membrane obtained in step (2) with the trimesoyl chloride solution for 1 minute, remove the excess trimesoyl chloride solution from the membrane surface and air dry for 1 minute.

[0034] (5) Place the film obtained in step (4) in an oven at 60°C and heat it for 30 minutes to cure.

[0035] (6) Immerse the membrane obtained in step (5) in deionized water and store it in a refrigerator at 4°C for later use.

[0036] The nanofiltration membrane prepared in this embodiment was placed in a membrane performance evaluation device. The experimental conditions were: pressure 10 bar, temperature 25 °C, flow rate 1 L / min, pre-pressure for 2 h, and the influent aqueous solution was 1 g / L sodium sulfate solution. The experimental results were: water permeability: 16.39 L·m -2 ·h -1 ·bar -1 Retention rate: 94.53%.

[0037] Comparison Example

[0038] (1) Cut a polyethersulfone film of appropriate size and soak it in deionized water for 24 hours to remove the surface preservatives and impurities.

[0039] (2) Take a polyethersulfone membrane as the support layer, weigh 0.5g piperazine and dissolve it in 99.5g deionized water. After contacting the front of the polyethersulfone membrane with the piperazine solution for 2 minutes, remove the excess piperazine solution from the membrane surface and let it air dry for 1 minute.

[0040] (3) Weigh 0.15g of trimesoyl chloride and dissolve it in 149.85g of n-hexane. After contacting the front side of the membrane obtained in step (2) with the trimesoyl chloride solution for 15s, remove the excess trimesoyl chloride solution from the membrane surface and air dry for 1min.

[0041] (4) Immerse the membrane obtained in step (3) in deionized water at 60°C and heat it in a water bath for 5 minutes.

[0042] (5) The membrane obtained in step (4) was immersed in deionized water and stored in a refrigerator at 4°C for later use. The nanofiltration membrane prepared in this comparative example was placed in a membrane performance evaluation device. The experimental conditions were: pressure 10 bar, temperature 25°C, flow rate 1 L / min, pre-pressurization for 2 h, and the influent aqueous solution was 1 g / L sodium sulfate solution. The experimental results were: water permeability: 12.69 L·m -2 ·h -1 ·bar -1 Retention rate: 99.19%.

[0043] The nanofiltration membrane prepared in the examples was named CQAS / TMC (hereinafter referred to as CT), and the nanofiltration membrane prepared in the control examples was named PIP / TMC (hereinafter referred to as PT). The CT prepared in the examples and the PT used as a control were tested:

[0044] 1. SEM and AFM images of the nanofiltration membrane

[0045] The surface morphology of the nanofiltration membrane was characterized by scanning electron microscopy (SEM), and the surface roughness was characterized by atomic force microscopy (AFM). Figure 1 As shown, the PT membrane exhibits a nodular structure and a dense surface, characteristic of semi-aromatic polyamide membranes prepared by interfacial polymerization. In contrast, the CT membrane displays a significantly different number of nodules on its surface, evidenced by its significantly reduced roughness (7.9 nm, compared to 21.9 nm for the PT membrane). This indicates that the novel nanofiltration membrane constructed by interfacial polymerization of chitosan quaternary ammonium salt as an aqueous functional monomer with trimesoyl chloride has a smoother surface.

[0046] 2. Water flux decline of nanofiltration membrane before and after fouling

[0047] The resistance of nanofiltration membranes to organic fouling was studied using 600 mg / L dodecyltrimethylammonium bromide (DTAB) (a cationic surfactant), 600 mg / L bovine serum albumin (BSA) (a negatively charged organic compound), and 600 mg / L sodium dodecyl sulfate (SDS) (an anionic surfactant). Normalized water flux (the ratio of instantaneous water flux to initial water flux) was used to compare the water flux decay of the nanofiltration membranes before and after fouling. The results are as follows: Figure 2 As shown in Table 1, the antifouling performance of nanofiltration membranes was quantitatively analyzed using flux decline rate (FDR) and flux recovery rate (FRR).

[0048] Table 1. Flux Decrease and Recovery Rates of PT and CT After Contamination by Different Pollutants

[0049]

[0050] like Figure 2As shown in (a), after the addition of DTAB, both PT and CT were immediately contaminated, resulting in a significant decrease in water flux. Over time, the water flux eventually stabilized. Compared to PT, CT exhibited better resistance to contamination. Figure 2 As shown in (b) and (c), after the addition of BSA and SDS, PT and CT were only slightly contaminated, with a slight decrease in water flux. Over time, the water flux gradually stabilized. Compared to PT, although CT did not show a more significant anti-fouling effect against BSA and SDS, it exhibited a significant advantage in anti-fouling performance against DTAB. Overall, CT demonstrated better resistance to organic contamination than PT.

[0051] 3. Comparison of antibacterial properties of nanofiltration membranes

[0052] Escherichia coli (Gram-negative bacteria) and Staphylococcus aureus (Gram-positive bacteria) were co-cultured with the composite membrane for 12 hours, and the antibacterial adhesion properties of the composite membrane were tested. The results are as follows: Figure 3 As shown, using PT as the standard, CT showed an antibacterial rate of approximately 82% against Escherichia coli and approximately 89% against Staphylococcus aureus. CT demonstrated better antibacterial performance than PT.

[0053] 4. Water flux decline of nanofiltration membranes after biofouling

[0054] To study the antibacterial effect of the composite membrane during actual operation, Escherichia coli and Staphylococcus aureus were added to the feed liquid to simulate biological contamination. Figure 4 The data shows the decline in water flux of PT and CT after biofouling. Figure 4 As shown in (a), after being contaminated with E. coli, PT's DR t It is 42%, while CT's DR t Only 17%. For example... Figure 4 As shown in (b), after being contaminated with Staphylococcus aureus, the DR of PT... t It is 55%, while CT's DR t The result is 19%. The above experimental results indicate that CT still possesses good antibacterial properties during actual operation.

[0055] The above tests are only examples of nanofiltration membranes prepared in the embodiments. Nanofiltration membranes prepared in other embodiments have similar effects to those in the embodiments, and will not be described in detail here. In summary, the nanofiltration membrane prepared by this invention exhibits excellent antifouling performance and has good water production efficiency and separation performance.

Claims

1. A method for preparing a nanofiltration membrane with high antifouling properties, characterized in that, The method includes the following steps: (1) Cut a polyethersulfone film of appropriate size and soak it in deionized water for 24 hours to remove the surface preservatives and impurities; (2) The front side of the polyethersulfone membrane is in contact with the aqueous monomer solution for 20 min, then the excess aqueous monomer solution on the membrane surface is removed, and the membrane is dried for 1 min for later use. The aqueous monomer is chitosan quaternary ammonium salt, the mass fraction of the aqueous monomer solution is 1.0 wt%, and the solvent is an aqueous solution containing 1.0 wt% acetic acid. (3) Contact the side of the membrane obtained in step (2) that is in contact with the aqueous monomer solution in a sodium hydroxide solution with a pH of 8-13 for 2 hours, then remove the excess sodium hydroxide solution from the membrane surface, and air dry for 1 minute for later use. (4) Contact the side of the membrane obtained in step (3) that is in contact with the sodium hydroxide solution with the organic phase monomer solution for 1 min, then remove the excess organic phase monomer solution from the membrane surface, air dry for 1 min, and set aside. The mass fraction of the organic phase monomer solution is 0.5 wt%, and the solvent is n-hexane. The organic phase monomer is selected from one or more of the following: terephthaloyl chloride, isophthaloyl chloride, adipyl chloride, phthaloyl chloride, trimesoyl chloride, cyclohexyl chloride, pyromellitic tetrachloroyl chloride, cyclobutanetetrachloroyl chloride, and cyclopentanetetrachloroyl chloride; (5) Place the film obtained in step (4) in an oven and heat it for 30 minutes. Then take it out and place it in deionized water and store it at 4°C.

2. The method for preparing a nanofiltration membrane with high antifouling properties as described in claim 1, characterized in that, In step (3), the pH of the sodium hydroxide solution is 12.

3. The method for preparing a nanofiltration membrane with high antifouling properties as described in claim 1, characterized in that, The oven is heated to a temperature of 55–65°C.

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