Preparation method of nanofiltration membrane with high pollution resistance

Abstract

The invention discloses a preparation method of a nanofiltration membrane with high pollution resistance, a polyethersulfone membrane is used as a support layer, and chitosan quaternary ammonium salt and trimesoyl chloride are used for interfacial polymerization. A hydrophilic functional group of the chitosan quaternary ammonium salt enhances the interaction between water molecules and the surface of the membrane and relieves the adsorption and deposition of pollutants on the surface of the membrane, so that the organic pollution resistance of the membrane is enhanced. In addition, positive charges carried by the chitosan quaternary ammonium salt can destroy bacterial cell membranes to cause bacterial death, so that the biological pollution resistance of the membrane is enhanced. The nanofiltration membrane prepared by the invention has excellent organic pollution and biological pollution resistance under the condition of keeping good water flux and separation performance, and has a better application prospect.

Description

Technical Field

[0001] The invention belongs to the field of nanofiltration membranes, and in particular relates to a method for preparing a nanofiltration membrane with high pollution resistance. Background Art

[0002] With the increasing global water shortage and water quality safety issues, the development of water treatment technologies that are both efficient and sustainable has become a core issue in the field of environmental engineering. In this context, membrane separation technology has become an important way to solve the water crisis with its advantages such as low energy consumption and high selectivity. However, a major challenge facing membrane technology is membrane fouling, including inorganic pollution, colloidal pollution, organic pollution and biological pollution. Among them, organic pollution and biological pollution of membranes are two common types of pollution in the membrane separation process. Organic pollution refers to the adsorption or deposition of organic matter in water on the membrane surface or in the membrane pores, and the interaction with the membrane through physical adsorption or chemical adsorption to form an organic pollution layer. Biological pollution refers to the growth and reproduction of microorganisms on the membrane surface or in the membrane pores to form a biofilm. Biological pollution and organic pollution can occur simultaneously and interact with each other, thus forming a complex composite pollution phenomenon. After the microorganisms form a biofilm on the membrane surface, they promote the adsorption or deposition of organic matter on the membrane. The organic matter provides a rich nutrient source for the microorganisms, which is conducive to the growth and reproduction of microorganisms, thereby aggravating membrane pollution, and ultimately leading to membrane flux attenuation and deterioration of effluent water quality. Therefore, it is of great significance to prepare membrane materials that are resistant to both organic and biological pollution.

[0003] Semi-aromatic polyamide nanofiltration membrane is a common separation membrane material, which is formed by interfacial polymerization of two monomers, aromatic polyamine (such as piperazine) and aromatic polyacyl chloride (such as trimesoyl chloride) on a porous support layer. The above-mentioned membrane material can effectively remove harmful substances such as salt, hardness ions, heavy metal ions, organic matter, etc. in water, produce high-quality pure water or treated water that meets specific water quality requirements, and is widely used in seawater desalination, brackish water desalination, industrial pure water preparation and other fields. However, membrane pollution is still an important factor limiting its long-term stable operation. Existing studies have attempted to change the polymerization monomer to improve the performance of the membrane, but it is a common problem that anti-pollution and separation efficiency are difficult to improve synergistically. The present invention innovatively uses chitosan quaternary ammonium salt (CQAS) as a water phase functional monomer, and constructs a new polyamide separation layer through interfacial polymerization reaction with trimesoyl chloride (TMC). The hydrophilicity of chitosan quaternary ammonium salt can promote the rapid transmission of water molecules, thereby improving the water flux of the membrane. On the other hand, chitosan quaternary ammonium salt has positively charged quaternary ammonium groups, which can destroy bacterial cell membranes through electrostatic adsorption, thereby improving the membrane's ability to resist biological pollution; 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 improving the membrane's ability to resist organic pollution.

[0004] The present invention uses polyethersulfone membrane as a carrier, chitosan quaternary ammonium salt and organic acid chloride as water phase and oil phase monomers respectively, and adopts interfacial polymerization to prepare a novel nanofiltration membrane. The nanofiltration membrane prepared by the present invention has excellent resistance to organic and biological pollution without affecting or even improving water flux and separation performance. Summary of the invention

[0005] In view of the existing problems, the present invention provides a method for preparing a nanofiltration membrane with high pollution resistance.

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

[0007] A method for preparing a nanofiltration membrane with high anti-pollution performance, using a polyethersulfone membrane as a carrier, specifically comprising:

[0008] providing an acetic acid solution containing a quaternary ammonium salt of chitosan;

[0009] providing an organic solvent solution containing an organic acid chloride;

[0010] providing sodium hydroxide solution;

[0011] Providing a carrier polyethersulfone membrane;

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

[0013] The excess acetic acid solution containing chitosan quaternary ammonium salt on the surface of the composite membrane was removed, dried for 1 min, and then immersed in sodium hydroxide solution for 2 h;

[0014] The excess sodium hydroxide solution on the surface of the carrier polyethersulfone membrane was removed, dried for 1 min, and then immersed in an organic solution containing organic acid chloride for 10 min;

[0015] The composite film was placed in an oven and heated at 55-65°C 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 acid chloride is selected from one or more of terephthaloyl chloride, isophthaloyl chloride, adipoyl chloride, phthaloyl chloride, trimesoyl chloride, cyclohexanetricarboxylic acid chloride, pyromellitoyl chloride, cyclobutanetetracarboxylic acid chloride and cyclopentanetetracarboxylic acid 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 acid chloride in the organic solution is 0.5 wt %.

[0022] The beneficial effects of the present invention are:

[0023] The present invention provides a method for preparing a nanofiltration membrane with high pollution resistance. A novel polyamide separation layer is constructed by using chitosan quaternary ammonium salt as a water phase functional monomer and trimesoyl chloride through interfacial polymerization reaction. The organic pollution resistance and biological pollution resistance of the composite membrane can be significantly improved, and good water flux and separation performance can be maintained. The composite membrane is a composite membrane with great development potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The SEM and AFM images of the embodiments of the present invention and the comparative examples are shown in FIG.

[0025] Figure 2 The water flux attenuation of the embodiments of the present invention and the comparative example before and after being polluted;

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

[0027] Figure 4 The water flux attenuation of the examples of the present invention and the comparative examples after being contaminated by organisms. ((a) is Escherichia coli, (b) is Staphylococcus aureus) DETAILED DESCRIPTION

[0028] In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with Examples and Comparative Examples. The materials, reagents or devices used in the Examples and Comparative Examples, if not otherwise specified, can all be obtained from conventional commercial sources, or can be obtained by prior art methods. Unless otherwise specified, the test or test method is a conventional method in the art. It should be understood that the following Examples and Comparative Examples are only used as specific illustrations, and do not limit the scope of protection of the present invention, and the obvious changes and modifications made by those skilled in the art according to the present invention are also included in the scope of the present invention.

[0029] Example

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

[0031] (2) Weigh 1 g of chitosan quaternary ammonium salt and dissolve it in 99 g of acetic acid solution (1:100). After the front side of the membrane obtained in step (1) is in contact with the acetic acid solution of chitosan quaternary ammonium salt for 15 minutes, the excess acetic acid solution of chitosan quaternary ammonium salt on the membrane surface is removed and the membrane is air-dried for 1 minute.

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

[0033] (4) Weigh 0.75 g of trimesoyl chloride and dissolve it in 149.25 g of n-hexane. After the front side of the membrane obtained in step (2) is in contact with the trimesoyl chloride solution for 1 min, the excess trimesoyl chloride solution on the membrane surface is removed and the membrane is air-dried for 1 min.

[0034] (5) The film obtained in step (4) was placed in an oven at 60°C and heated for curing for 30 minutes.

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

[0036] The nanofiltration membrane prepared in this 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-pressure 2 h, and the influent solution was 1 g / L sodium sulfate solution. The experimental results were: water permeability: 16.39 L·m -2 ·h -1 bar -1 , interception rate: 94.53%.

[0037] Comparison example

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

[0039] (2) A polyethersulfone membrane was used as a support layer. 0.5 g of piperazine was weighed and dissolved in 99.5 g of deionized water. The front side of the polyethersulfone membrane was in contact with the piperazine solution for 2 minutes. The excess piperazine solution on the membrane surface was removed and the membrane was air-dried for 1 minute.

[0040] (3) Weigh 0.15 g of trimesoyl chloride and dissolve it in 149.85 g of n-hexane. After the front side of the membrane obtained in step (2) is in contact with the trimesoyl chloride solution for 15 seconds, the excess trimesoyl chloride solution on the membrane surface is removed and the membrane is air-dried for 1 minute.

[0041] (4) The membrane obtained in step (3) was immersed in deionized water at 60° C. and heated in a water bath for 5 min.

[0042] (5) The membrane obtained in step (4) was soaked 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-pressure 2 h, and the influent solution was 1 g / L sodium sulfate solution. The experimental results were: water permeability: 12.69 L·m -2 ·h -1 bar -1 , interception rate: 99.19%.

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

[0044] 1. SEM and AFM images of 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 has a nodular structure and a dense surface, which is a characteristic of semi-aromatic polyamide membranes prepared by interfacial polymerization. In contrast, the CT membrane shows a significantly different number of nodules on its surface, which can be demonstrated by its significantly reduced roughness (7.9nm, while 21.9nm for the PT membrane), indicating that the surface of the new nanofiltration membrane constructed by interfacial polymerization of chitosan quaternary ammonium salt as a water-phase functional monomer and trimesoyl chloride is smoother.

[0046] 2. Water flux attenuation of nanofiltration membrane before and after contamination

[0047] The anti-organic fouling performance of nanofiltration membranes was studied using 600 mg / L dodecyltrimethylammonium bromide (DTAB) (a cationic surfactant), 600 mg / L bovine serum albumin (BSA) (negatively charged organic matter), and 600 mg / L sodium dodecyl sulfate (SDS) (an anionic surfactant). The normalized water flux (i.e., the ratio of instantaneous water flux to initial water flux) was used to compare the water flux attenuation of the nanofiltration membrane before and after fouling. The results are shown in Figure 2. Figure 2 The anti-fouling performance of the nanofiltration membrane was quantitatively analyzed by the flux decline rate (FDR) and flux recovery rate (FRR), and the results are shown in Table 1.

[0048] Table 1 Flux reduction rate and flux recovery rate of PT and CT after being contaminated by different pollutants

[0049]

[0050] like Figure 2As shown in (a), after adding DTAB, PT and CT were immediately contaminated, and the water flux decreased significantly. As time went by, the water flux finally reached a stable state. Compared with PT, CT has better anti-pollution performance. Figure 2 As shown in (b and c), after adding BSA and SDS, PT and CT were only slightly polluted, and the water flux decreased slightly. With the increase of time, the water flux gradually reached a stable state. Compared with PT, although CT did not show a more significant anti-pollution effect on BSA and SDS, it had a significant advantage in anti-pollution performance on DTAB. In general, CT has better anti-organic pollution performance 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 h, and the antibacterial adhesion properties of the composite membrane were tested. Figure 3 As shown. Taking PT as the standard, the antibacterial rate of CT against Escherichia coli is about 82%, and the antibacterial rate against Staphylococcus aureus is about 89%. CT shows better antibacterial performance than PT.

[0053] 4. Water flux attenuation of nanofiltration membrane after biological contamination

[0054] In order to study the antibacterial effect of the composite membrane in actual operation, Escherichia coli and Staphylococcus aureus were added to the feed liquid to simulate biological contamination. Figure 4 The attenuation of water flux of PT and CT after biofouling is shown. Figure 4 (a) shows that the DR of PT after being contaminated by E. coli t is 42%, while the DR of CT t Only 17%. Figure 4 (b) shows the DR of PT after contamination by Staphylococcus aureus. t is 55%, while the DR of CT t The above experimental results show that CT still has good antibacterial performance during actual operation.

[0055] The above tests are only based on the nanofiltration membrane prepared in the embodiment as an example, and the nanofiltration membranes prepared in other embodiments have similar effects to the embodiment, which will not be repeated here. In summary, the nanofiltration membrane prepared in the present invention exhibits excellent anti-pollution performance and has good water production efficiency and separation performance.

Claims

1. A method for preparing a nanofiltration membrane with high pollution resistance, characterized in that: The method comprises the following steps: (1) Cut a polyethersulfone membrane of appropriate size and soak it in deionized water for 24 hours to remove the preservatives and impurities on its surface; (2) contacting the front side of the polyethersulfone membrane with the aqueous monomer solution for 20 minutes, then removing excess aqueous monomer solution from the membrane surface, drying it for 1 minute, and setting it aside; The aqueous phase monomer is selected from one or more of o-phenylenediamine, m-phenylenediamine, chitosan quaternary ammonium salt, p-phenylenediamine, piperazine, ethylenediamine, diethylenetriamine and polyethyleneimine; (3) placing the side of the membrane obtained in step (2) in contact with the aqueous monomer solution in a sodium hydroxide solution with a pH of 8-13 for 2 hours, then removing excess sodium hydroxide solution from the membrane surface, drying it in the air for 1 minute, and setting it aside; (4) contacting the side of the membrane obtained in step (3) that contacts the sodium hydroxide solution with the organic phase monomer solution for 1 minute, then removing excess organic phase monomer solution from the membrane surface, drying it in the air for 1 minute, and setting it aside; The organic phase monomer is selected from one or more of terephthaloyl chloride, isophthaloyl chloride, adipoyl chloride, phthaloyl chloride, trimesoyl chloride, cyclohexanetricarboxylic acid chloride, pyromellitoyl chloride, cyclobutanetetracarboxylic acid chloride and cyclopentanetetracarboxylic acid chloride; (5) The film obtained in step (4) was placed in an oven and heated for curing for 30 minutes, then taken out and placed in deionized water and stored at 4°C.

2. A method for preparing a nanofiltration membrane with high pollution resistance as claimed in claim 1, characterized in that: In step (2), the mass fraction of the aqueous monomer solution is 1.0 wt %, and the solvent is an aqueous solution containing 1.0 wt % of acetic acid.

3. A method for preparing a polyamide composite membrane with high anti-pollution properties as claimed in claim 1, characterized in that: In step (3), the pH of the sodium hydroxide solution is 12.

4. A method for preparing a nanofiltration membrane with high pollution resistance as claimed in claim 1, characterized in that: In step (4), the mass fraction of the organic phase monomer solution is 0.5 wt %, and the solvent is n-hexane.

5. A method for preparing a nanofiltration membrane with high pollution resistance as claimed in claim 1, characterized in that: The oven is heated to a temperature of 55-65°C.

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