Composite nanofiltration membrane and preparation method thereof

Abstract

The invention discloses a composite nanofiltration membrane and a preparation method thereof, based on a polysulfone resin composite nanofiltration membrane, a high-flux anti-pollution composite nanofiltration membrane is designed by introducing a metal ion-carboxyl coordination interlayer polymer between a support layer and a separation layer. Compared with a conventional composite nanofiltration membrane, the technology selects the same base membrane material, the preparation process is simple, the cost of lipoic acid and metal ions in the middle layer is low, and the technology is suitable for large-scale production. Lipoic acid is a natural biomass small molecule, is wide in source and easy to obtain, can be subjected to ring opening polymerization under mild conditions, and not only can be coordinated with metal ions to enhance the mechanical strength, but also can enhance the antifouling and antibacterial capabilities in the presence of disulfide bonds and hydrophilic carboxyl groups. The composite nanofiltration membrane prepared by the invention has the advantages of being capable of keeping high flux, high salt rejection rate and stable operation under organic pollution, and the preparation method is simple to operate, short in treatment time, low in raw material cost, rapid in reaction and capable of being applied to industrial production and application.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nanofiltration membrane preparation, and particularly relates to a composite nanofiltration membrane and a preparation method thereof. BACKGROUND

[0002] With the rapid development of domestic manufacturing industry, a large amount of wastewater needs to be treated, so that the membrane separation technology becomes a crucial means. However, in the wastewater treatment process, pollutants are easy to be adsorbed, grown and deposited on the membrane surface, thereby causing the blockage of the membrane holes, reducing the permeation flux of the membrane and seriously restricting the development of the separation membrane technology. The composite nanofiltration membrane separation technology has the characteristics of low operating pressure, low operation cost and high selectivity, and is widely applied in the treatment of salt-containing organic wastewater and the like. Therefore, development of a high-performance composite nanofiltration membrane with anti-pollution ability can comprehensively utilize the advantages of the nanofiltration membrane and improve the anti-pollution ability, which has a significant advantage in wastewater treatment and recycling.

[0003] The patent document with the publication number CN111974231A proposes a photocatalytic antibacterial and anti-pollution composite nanofiltration membrane. The patent preparation method is to introduce a liquid phase with a catechol group on the surface of the polyamide layer after the interfacial polymerization of the conventional composite nanofiltration membrane, so as to improve the hydrophilicity of the nanofiltration membrane surface, and mix the liquid phase with functional nanoparticles to directly coat the surface to prepare the photocatalytic antibacterial and anti-pollution composite nanofiltration membrane.

[0004] The patent document with the publication number CN110052179A designs a preparation technology of a composite nanofiltration membrane with reduced number of residual carboxyl groups on the surface and anti-pollution. First, the polysulfone ultrafiltration membrane is soaked in a conventional aqueous solution, dried, immersed in an oil phase to undergo the first interfacial polymerization, without post-treatment, dried, and then immersed in a second aqueous solution (piperazine and non-ionic hydrophilic polymer) to undergo the second interfacial polymerization, and then obtained through subsequent heat treatment and water washing. The composite nanofiltration membrane prepared by the method has a magnesium sulfate rejection rate of more than 97% and a pure water flux decay rate of about 13%.

[0005] The patent document with the publication number CN111495217A coats triethylamine and cross-linked polyvinyl alcohol on the surface of the conventional composite nanofiltration membrane, and changes the hydrophilicity and nanometer roughness of the membrane surface through infrared heating and curing cross-linking. The prepared nanofiltration membrane has excellent anti-pollution performance, and the application COD range condition is improved, and the magnesium sulfate rejection rate is also more than 95%.

[0006] The patent document with the publication number CN112742215A replaces the current inorganic strong base with an organic weak acid-organic weak base buffer system; the buffer system uses organic amine as the alkaline substance to maintain the stability of the solution PH value, which can increase the reaction rate and promote the formation of a separation layer with more uniform thickness and smaller resistance. Taurine is used as the acidic counterpart, which is a natural organic acid with the advantages of low cost, easy availability and non-toxicity. Polyethyleneimine is used as the aqueous amine monomer, which will leave part of the amino functional groups after reacting with trimesoyl chloride, so that the membrane surface presents a positive charge.

[0007] Currently, the preparation techniques for improving the anti-fouling performance of composite nanofiltration membranes mainly fall into three categories. The first category is to introduce a liquid phase that can be mixed with functional nanoparticles on the surface of conventional polyamide, such as the patent CN111974231A which introduces photocatalytic antibacterial nanoparticles in a hydrophilic liquid phase. This type of solution requires harsh synthesis conditions, involving the use of reaction kettles and freeze-drying machines, making it difficult to achieve large-scale application. Moreover, the dispersion of nanoparticles and the firm combination with the liquid phase are also urgent problems to be solved.

[0008] The second category is to reduce the number of residual carboxyl groups on the membrane surface and increase the hydrophilic substances, such as the patent CN110052179A which performs a secondary interfacial polymerization based on conventional interfacial polymerization to react away excess carboxyl groups and adds non-ionic hydrophilic polymer. This type of solution has the risk of hydrolysis of acyl chloride groups on the surface during secondary interfacial polymerization, and is limited by the cross-linked network of polyamide in practical application, with low water phase diffusion efficiency and reaction speed, making it difficult to fully remove the residual carboxyl groups on the surface.

[0009] The third category is to directly coat hydrophilic substances on the surface of conventional polyamide, such as the patent CN111495217A which directly coats cross-linked polyvinyl alcohol on the surface of nanofiltration membrane. This type of solution requires the use of infrared heating, which is harmful to human skin and cannot be applied to long-term continuous industrial production. SUMMARY

[0010] To solve the above technical problems, the present application provides a composite nanofiltration membrane and a preparation method thereof.

[0011] The present application is achieved by the following technical solutions.

[0012] The present application provides a preparation method of a composite nanofiltration membrane, comprising the following steps:

[0013] S1: After pre-processing the polysulfone resin base film, immerse it in a metal ion solution to obtain material A;

[0014] S2: Immerse material A in solution A, take out the base film and remove the surface solvent;

[0015] S3: Then immerse it in amine solution and acyl chloride solution in sequence and then take it out;

[0016] S4: After drying, the membrane is wound up to complete the preparation of the composite nanofiltration membrane.

[0017] Preferably, in step S1, a polymer porous support layer is prepared on a polysulfone resin base film by liquid-solid phase conversion method, and the immersion time in the metal ion solution is 30-70s. After removal, the surface ethanol solvent is dried.

[0018] Preferably, in step S1, the concentration of the metal ion solution is 0.001 g / mL to 0.5 g / mL, and the metal ions include, but are not limited to, Fe. 3+ Cu 2+ Zn 2+ Al 3+ Zr 4+ One or more of them.

[0019] Preferably, in step S2, solution A is a thioctic acid solution with a concentration of 0.05 g / mL to 1 g / mL, and the immersion time is 80-120 seconds.

[0020] Preferably, in step S3, the amine solution is an aqueous solution of amine monomers with a concentration of 0.1wt%-5wt%, and the amine monomers include aromatic amines and aliphatic amines, including one or more of cyclohexanediamine, piperazine, ethylene glycolamine, ethylenediamine, propylenediamine, butylenediamine, hexanediamine, ethanolamine, polyethyleneimine, and triethylamine.

[0021] Preferably, in step S3, the acyl chloride solution is an acyl chloride monomer solution with a concentration of 0.01wt%-3wt%, and the solvent includes cyclohexane or similar organic solvents. The acyl chloride monomer includes one or more of the following: trimesoyl chloride, isophthaloyl chloride, biphenyl dimethyl chloride, and terephthaloyl chloride.

[0022] Preferably, in step S3, the substrate is immersed in an acyl chloride solution for 80-120 seconds, and after the water droplets on the substrate surface are dried, it is then immersed in an acyl chloride oil phase solution for 150-250 seconds.

[0023] Preferably, in step S4, before drying, the polysulfone resin base film treated in step S3 is first dried in solvent at 40-90°C, preferably 60-80°C, then immersed in hot water at 80°C-100°C for 7-13 minutes, then immersed in glycerol at a concentration of 8wt%-13wt% for 11-18 minutes, and finally dried in hot air at 65°C-80°C for 25-40 seconds.

[0024] A composite nanofiltration membrane prepared by the above preparation method.

[0025] The beneficial effects of this invention are as follows:

[0026] This invention, based on traditional polysulfone resin composite nanofiltration membranes, designs a high-flux, antifouling composite nanofiltration membrane by introducing a metal ion-carboxyl (lipoic acid) coordination intermediate polymer between the support layer and the separation layer. The metal ions include, but are not limited to, Fe. 3+ Cu 2+ Zn 2+ Al 3+ Zr 4+ This technology uses the same base membrane material as conventional composite nanofiltration membranes, has a simple preparation process, and the intermediate lipoic acid and metal ions are low-cost, making it suitable for large-scale production. Lipoic acid is a natural biomass small molecule with wide availability and can undergo ring-opening polymerization under mild conditions. It not only coordinates with metal ions to enhance mechanical strength, but the presence of disulfide bonds and hydrophilic carboxyl groups also enhances antifouling and antibacterial capabilities. The composite nanofiltration membrane prepared by this invention has the advantage of maintaining stable operation with high flux and high desalination rate under organic pollution conditions. The preparation method is simple to operate, has a short processing time, low raw material cost, and rapid reaction, making it suitable for industrial production and application. Attached Figure Description

[0027] Figure 1 This is a process flow diagram of the present invention; Detailed Implementation

[0028] The technical solution of the present invention is further described below, but the scope of protection is not limited to what is described.

[0029] Example 1:

[0030] like Figure 1 As shown, a method for preparing a composite nanofiltration membrane includes the following steps:

[0031] S1: After pre-processing the polysulfone resin-based film, it is immersed in a metal ion solution to obtain a film with an anti-fouling intermediate layer.

[0032] S2: Immerse the membrane in solution A, remove the base membrane and remove the surface solvent;

[0033] S3: Then immerse it in amine solution and acyl chloride solution in sequence and then take it out;

[0034] S4: After drying, the membrane is wound up to complete the preparation of the composite nanofiltration membrane.

[0035] In step S1, a polymer porous support layer is prepared on a polysulfone resin base film by liquid-solid phase conversion method. The immersion time in the metal ion solution is 30s, and the surface ethanol solvent is dried after removal.

[0036] In step S1, the metal ion solution is a metal chloride solution with a concentration of 0.5 g / mL, and the metal ion is Cu. 2+Zn 2 + .

[0037] In step S2, solution A is a lipoic acid solution with a concentration of 0.05 g / mL, and the person is immersed in solution A for 80 seconds.

[0038] In step S3, the amine solution is an aqueous solution of an amine monomer with a concentration of 0.1 wt%, and the amine monomer is ethylene glycol amine.

[0039] In step S3, the acyl chloride solution is a 0.01 wt% acyl chloride monomer solution, the solvent is cyclohexane, and the acyl chloride monomer is isophthaloyl chloride.

[0040] In step S3, the substrate is immersed in an acyl chloride solution for 80 seconds, and after the water droplets on the surface of the base film are dried, it is then immersed in an acyl chloride oil phase solution for 150 seconds to form a polyamide separation layer.

[0041] In step S4, before drying, the polysulfone resin base film treated in step S3 is first dried at 40°C to remove the solvent, then immersed in hot water at 80°C for 7 minutes, then immersed in glycerol at a concentration of 8wt% for 11 minutes, and finally dried with hot air at 65°C for 25 seconds.

[0042] Example 2:

[0043] like Figure 1 As shown, a method for preparing a composite nanofiltration membrane includes the following steps:

[0044] S1: After pre-processing the polysulfone resin-based film, it is immersed in a metal ion solution to obtain a film with an anti-fouling intermediate layer.

[0045] S2: Immerse the membrane in solution A, remove the base membrane and remove the surface solvent;

[0046] S3: Then immerse it in amine solution and acyl chloride solution in sequence and then take it out;

[0047] S4: After drying, the membrane is wound up to complete the preparation of the composite nanofiltration membrane.

[0048] In step S1, a polymer porous support layer is prepared on a polysulfone resin base film by liquid-solid phase conversion method. The immersion time in the metal ion solution is 70s, and the surface ethanol solvent is dried after removal.

[0049] In step S1, the metal ion solution is a metal chloride solution with a concentration of 0.5 g / mL, and the metal ion is Fe. 3+ Al 3 + Zr 4+ .

[0050] In step S2, solution A is a thioctic acid solution with a concentration of 1 g / mL, and the person is immersed in solution A for 120 seconds.

[0051] In step S3, the amine solution is an aqueous solution of an amine monomer with a concentration of 5 wt%, and the amine monomer is ethylenediamine.

[0052] In step S3, the acyl chloride solution is a 3 wt% acyl chloride monomer solution, the solvent is cyclohexane, and the acyl chloride monomer is biphenyl dicarboxylate chloride.

[0053] In step S3, the substrate is immersed in an acyl chloride solution for 120 seconds, and after the water droplets on the surface of the base film are dried, it is then immersed in an acyl chloride oil phase solution for 250 seconds to form a polyamide separation layer.

[0054] In step S4, before drying, the polysulfone resin base film treated in step S3 is first dried in solvent at 90°C, then immersed in hot water at 100°C for 13 minutes, then immersed in glycerol with a concentration of 13wt% for 18 minutes, and finally dried with hot air at 80°C for 40 seconds.

[0055] Example 3:

[0056] like Figure 1 As shown, a method for preparing a composite nanofiltration membrane includes the following steps:

[0057] S1: After pre-processing the polysulfone resin-based film, it is immersed in a metal ion solution to obtain a film with an anti-fouling intermediate layer.

[0058] S2: Immerse the membrane in solution A, remove the base membrane and remove the surface solvent;

[0059] S3: Then immerse it in amine solution and acyl chloride solution in sequence and then take it out;

[0060] S4: After drying, the membrane is wound up to complete the preparation of the composite nanofiltration membrane.

[0061] In step S1, a polymer porous support layer is prepared on a polysulfone resin base film by liquid-solid phase conversion method. The immersion time in the metal ion solution is 50s, and the surface ethanol solvent is dried after removal.

[0062] In step S1, the metal ion solution is a metal chloride solution with a concentration of 0.1 g / mL, and the metal ion is Fe. 3+ .

[0063] In step S2, solution A is a lipoic acid solution with a concentration of 0.03 g / mL, and the person is immersed in solution A for 100 seconds.

[0064] In step S3, the amine solution is a 5 wt% aqueous solution of an amine monomer, and the amine monomer is piperazine.

[0065] In step S3, the acyl chloride solution is a 2wt% acyl chloride monomer solution, the solvent is cyclohexane, and the acyl chloride monomer is trimesoyl chloride.

[0066] In step S3, the substrate is immersed in an acyl chloride solution for 100 seconds, and after the water droplets on the surface of the substrate are dried, it is then immersed in an acyl chloride oil phase solution for 200 seconds to form a polyamide separation layer.

[0067] In step S4, before drying, the polysulfone resin base film treated in step S3 is first dried in solvent at 65°C, then immersed in hot water at 90°C for 10 minutes, then immersed in glycerol with a concentration of 10wt% for 15 minutes, and finally dried with hot air at 70°C for 30 seconds.

[0068] Comparative Example 1:

[0069] The preparation method is basically the same as in Example 1, except that it is not immersed in a metal ion solution.

[0070] Performance testing:

[0071] The composite nanofiltration membranes prepared in Examples 1-3 and Comparative Example 1 were compared in terms of membrane performance. The membrane performance testing steps included testing the desalination rate, flux, and flux decay of the composite nanofiltration membranes in a 2000 ppm MgSO4 aqueous solution at an operating pressure of 100 psi (concentrate circulation). The test results are shown in Table 1.

[0072] Table 1. Test Results of MgSO4 Solution (Concentrate Circulation)

[0073]

[0074] As shown in Table 1, the composite nanofiltration membranes prepared in Examples 1-3 after introducing the antifouling intermediate layer of the present invention have better performance than the composite nanofiltration membrane of Comparative Example 1. Compared with Comparative Example 1, when running in MgSO4 solution, the flux and desalination rate of the composite nanofiltration membranes prepared in Examples 1-3 can remain stable for a longer period of time, and the decline in pure water flux remains at a low level. Among them, Example 3 is the best example, with the desalination rate only decreasing from 98.3% to 98.1%, and it can operate stably for a long time.

[0075] The composite nanofiltration membranes prepared in Examples 1-3 and Comparative Example 1 were immersed in Staphylococcus aureus culture medium (CFU = 300 / mL) and cultured at 37°C for 24 h. The percentage reduction in the number of bacteria was calculated to determine the antibacterial performance of the membrane. The antibacterial test results are shown in Table 2.

[0076] Table 2. Results of Antibacterial Test

[0077]

[0078] As can be seen from Table 2, the composite nanofiltration membrane with the addition of the intermediate layer has a superior antibacterial effect compared to the membrane without the intermediate layer.

Claims

1. A method for preparing a composite nanofiltration membrane, characterized in that, Includes the following steps: S1: After pre-processing the polysulfone resin base film, it is immersed in a metal ion solution to obtain material A; S2: Immerse material A in solution A, remove the base film and remove the surface solvent; S3: Then immerse it in amine solution and acyl chloride solution in sequence and then take it out; S4: After drying, the membrane is wound up to complete the preparation of the composite nanofiltration membrane.

2. The method for preparing a composite nanofiltration membrane as described in claim 1, characterized in that: In step S1, a polymer porous support layer is prepared on a polysulfone resin base film by liquid-solid phase conversion method. The immersion time in the metal ion solution is 30-70s, and the surface ethanol solvent is dried after removal.

3. The method for preparing a composite nanofiltration membrane as described in claim 1, characterized in that: In step S1, the concentration of the metal ion solution is 0.001 g / mL to 0.5 g / mL, and the metal ions include, but are not limited to, Fe. 3+ Cu 2+ Zn 2+ Al 3+ Zr 4+ One or more of them.

4. The method for preparing a composite nanofiltration membrane as described in claim 1, characterized in that: In step S2, solution A is a thioctic acid solution with a concentration of 0.05 g / mL to 1 g / mL, and the immersion time is 80-120 seconds.

5. The method for preparing a composite nanofiltration membrane as described in claim 1, characterized in that: In step S3, the amine solution is an aqueous solution of amine monomers with a concentration of 0.1wt%-5wt%. The amine monomers include aromatic amines and aliphatic amines, including one or more of the following: cyclohexanediamine, piperazine, ethylene glycolamine, ethylenediamine, propylenediamine, butylenediamine, hexanediamine, ethanolamine, polyethyleneimine, and triethylamine.

6. The method for preparing a composite nanofiltration membrane as described in claim 1, characterized in that: In step S3, the acyl chloride solution is a 0.01wt%-3wt% acyl chloride monomer solution, and the solvent includes cyclohexane or similar organic solvents. The acyl chloride monomer includes one or more of the following: trimesoyl chloride, isophthaloyl chloride, biphenyl dimethyl chloride, and terephthaloyl chloride.

7. The method for preparing a composite nanofiltration membrane as described in claim 1, characterized in that: In step S3, the substrate is immersed in an acyl chloride solution for 80-120 seconds, and after the water droplets on the substrate surface are dried, it is then immersed in an acyl chloride oil phase solution for 150-250 seconds.

8. The method for preparing a composite nanofiltration membrane as described in claim 1, characterized in that: In step S4, before drying, the polysulfone resin base film treated in step S3 is first dried in solvent at 40-90°C, preferably 60-80°C, then immersed in hot water at 80°C-100°C for 7-13 minutes, then immersed in glycerol at a concentration of 8wt%-13wt% for 11-18 minutes, and finally dried in hot air at 65°C-80°C for 25-40 seconds.

9. A composite nanofiltration membrane prepared by the preparation method according to any one of claims 1-8.

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