A beaded-structured nanofiltration membrane with high permeability selectivity, its preparation method and application

Abstract

The present invention discloses a bead-shaped structure nanofiltration membrane with high permeation selectivity, its preparation method and application, belonging to the technical field of membrane separation. The preparation method includes: (1) preparing an aqueous solution by using an aqueous monomer and a non-ionic surfactant, wherein the aqueous monomer is a polyamine monomer, and the non-ionic surfactant is a polyoxyethylene-type non-ionic surfactant, selected from fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ether or fatty amine polyoxyethylene ether; (2) carrying out an interfacial polymerization reaction on a microfiltration substrate membrane by using the aqueous solution prepared in step (1) and an acyl chloride monomer oil phase solution to prepare the bead-shaped structure nanofiltration membrane with high permeation selectivity. This method has simple process and low equipment requirements. The prepared bead-shaped structure nanofiltration membrane has strong separation ability for single and multivalent salts while maintaining high permeability, and has good application prospects in the field of water treatment.

Description

Technical Field

[0001] The present invention relates to the field of membrane separation technology, and particularly relates to a bead-shaped nanofiltration membrane with high permeation selectivity, a preparation method thereof, and an application thereof. Background Art

[0002] Water resources are the material basis for all production and life in human society. With the progress of human society and the development of the economy, the increase in human activities has led to the overexploitation and pollution of water resources, and the problem of water resource shortage has become increasingly obvious. Relying on renewable water resources to achieve the recycling of water resources can not only effectively solve the problem of water resource shortage, but also reduce the pressure on the natural water cycle system and protect the ecological environment. The technology of selective separation of monovalent and multivalent salts has good application prospects in water treatment, resource recovery and utilization, etc. Among them, the nanofiltration membrane technology based on polyamide materials has attracted attention due to its simple preparation process, low energy consumption, simple operation and other advantages. Nanofiltration membrane technology is a separation technology between ultrafiltration and reverse osmosis. Under the combined action of mechanisms such as pore size screening, Donnan effect, and dielectric exclusion, nanofiltration membranes can effectively separate monovalent and multivalent salts and are widely used in fields such as hard water softening and food processing.

[0003] Currently, the interfacial polymerization method is usually used to prepare polyamide nanofiltration membranes. This method has a fast reaction speed and unstable interface, resulting in defects in the prepared membranes and unable to achieve the ideal separation ability. For example, Chinese patent document with publication number CN110756056A discloses a method for preparing a polyamide nanofiltration membrane by interfacial polymerization. In this invention, a polysulfone ultrafiltration membrane is immersed in an aqueous solution of p-phenylenediamine, and soaked to make its surface saturated with adsorbed p-phenylenediamine molecules; after taking it out, the excess liquid is removed so that there are no obvious droplets on the surface of the PSF ultrafiltration membrane; the solution of trimesoyl chloride is poured on the surface of the PSF ultrafiltration membrane, and after the reaction, the oil-phase solution is removed to obtain a polyamide nanofiltration membrane; the polyamide nanofiltration membrane is placed in an oven at 40-90 °C for heat treatment to promote the subsequent polymerization reaction; after the reaction is completed, the nanofiltration membrane is immersed in a NaHSO3 solution for standby. Although the selection of the aqueous monomer p-phenylenediamine can improve the tolerance of the nanofiltration membrane to chlorine-containing cleaning agents, its flux is low and the separation ability of monovalent and multivalent salts is not strong. Chinese patent document with publication number CN116617879A discloses a new method for preparing a polyamide nanofiltration membrane by interfacial polymerization of active ester-amine. This invention uses an active ester monomer to replace the traditional acyl chloride monomer for interfacial polymerization reaction, reduces the reaction activity, and the prepared nanofiltration membrane has a high flux and can be used for the separation of salts and dyes, etc., but cannot be used for the separation of monovalent and multivalent salts.

[0004] In order to improve the separation ability of polyamide nanofiltration membranes for monovalent and multivalent salts, many methods such as substrate membrane modification, introduction of an intermediate layer, development of new monomers, and membrane surface modification have been developed by researchers. However, these methods have problems such as complex operation and high development costs, which are not conducive to large-scale preparation. Summary of the Invention

[0005] The present invention provides a method for preparing a beaded-structured nanofiltration membrane with high permeability and selectivity. The process is simple and requires low equipment. It can construct a beaded-structured nanofiltration membrane different from existing small vesicles, tubes, and craters. The beaded-structured nanofiltration membrane has strong separation ability for single and multivalent salts while maintaining high permeability, and has good application prospects in the field of water treatment.

[0006] The specific technical solution adopted is as follows:

[0007] A method for preparing a beaded-structured nanofiltration membrane with high permeability and selectivity, comprising the following steps:

[0008] (1) Prepare an aqueous solution using an aqueous monomer and a nonionic surfactant. The aqueous monomer is a polyamine monomer, and the nonionic surfactant is a polyoxyethylene-type nonionic surfactant, selected from fatty alcohol polyoxyethylene ethers, fatty acid polyoxyethylene ethers, or fatty amine polyoxyethylene ethers;

[0009] (2) Perform an interfacial polymerization reaction on a microfiltration substrate membrane using the aqueous solution prepared in step (1) and an oil-phase solution of an acyl chloride monomer to prepare the beaded-structured nanofiltration membrane with high permeability and selectivity.

[0010] The present invention introduces a nonionic surfactant into the interfacial polymerization reaction system. A nonionic surfactant is added to the aqueous solution, and then the aqueous solution is used to react with the oil-phase solution of the acyl chloride monomer to form a membrane. Based on the hydrophilic-hydrophobic interaction, the nonionic surfactant can self-assemble into stable micelle microspheres in the aqueous solution and move to the interface as a template for the formation of the polyamide membrane structure, ultimately forming a polyamide membrane with a beaded structure at the interface. The polyamide membrane with a beaded structure has a larger specific surface area, resulting in an increase in permeability. At the same time, the nonionic surfactant promotes the migration of polyamine monomers at the interface, enriching more charges on the membrane surface, thereby leading to an increase in the selectivity of single and multivalent salts. If other additives such as Na3PO4 are also included in the aqueous solution, it will affect the formation of the beaded structure and further affect the permeability and single / multivalent salt selectivity of the prepared polyamide membrane.

[0011] Preferably, the nonionic surfactant is a fatty alcohol polyoxyethylene ether. The repeating unit number of the polyoxyethylene group in the fatty alcohol polyoxyethylene ether is 1-20, further 1-10, and the average molecular weight is 200-1200. Using the oxygen-containing functional group of the fatty alcohol polyoxyethylene ether molecule and the hydrogen bond interaction between monomers can change the monomer diffusion at the interface.

[0012] Specifically, the polyamine monomer is at least one of piperazine, m-phenylenediamine, p-phenylenediamine, polyethyleneimine, 1,2-ethylenediamine, 1,6-hexanediamine, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, spermine or melamine.

[0013] Preferably, in the aqueous solution, the concentration of the polyamine monomer is 500 - 10000 ppm (mass concentration), and the concentration of the non-ionic surfactant is 100 - 1000 ppm (mass concentration), further preferably 200 - 500 ppm.

[0014] Specifically, the acyl chloride monomer includes trimesoyl chloride. In the oil phase solution, the concentration of the acyl chloride monomer is 500 - 10000 ppm (mass concentration), and the solvent of the oil phase solution is at least one of Isopar G, n-hexane, n-heptane or cyclohexane.

[0015] The microfiltration substrate membrane is selected from polysulfone microfiltration membranes, polyethersulfone microfiltration membranes or polyacrylonitrile microfiltration membranes, etc. The cut-off molecular weight of the microfiltration substrate membrane is 1 kDa - 200 kDa.

[0016] Specifically, the process of the interfacial polymerization reaction is as follows: Pour the aqueous solution prepared in step (1) onto the surface of the microfiltration substrate membrane, let it stand for 1 - 10 min, pour out the aqueous solution to remove excess water; then pour the acyl chloride monomer oil phase solution onto the microfiltration substrate membrane treated with the above aqueous solution, let it stand for 1 - 5 min, pour out the acyl chloride monomer oil phase solution and transfer it to be treated at 50 - 90 °C for 5 - 20 min.

[0017] The present invention also provides a high-permeability and selective bead-shaped structure nanofiltration membrane prepared by the preparation method of the high-permeability and selective bead-shaped structure nanofiltration membrane described above.

[0018] The present invention also provides the application of the high-permeability and selective bead-shaped structure nanofiltration membrane in the selective separation of mono- and multivalent salts.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] (1) The preparation method of the high-permeability and selective bead-shaped structure nanofiltration membrane provided by the present invention has a simple process, low cost, easy access to equipment, mild operating conditions. By adding an appropriate amount of non-ionic surfactant to the aqueous solution, the mono- and multivalent salt selectivity of the nanofiltration membrane can be significantly improved, while maintaining high permeability and high flux, which is convenient for industrial application.

[0021] (2) The method of the present invention utilizes the self-aggregation and interfacial migration phenomena of non-ionic surfactants to make them act as templates. Moreover, the hydrogen bond interaction between the oxygen-containing functional groups in the non-ionic surfactants and the interfacial polymerization monomers can change the monomer diffusion at the interface, constructing a bead-like structure. The surfactant micelle layer is stable on the membrane surface structure, which can significantly increase the effective permeation area and surface charge density of the membrane. While maintaining high permeability, the selectivity for mono- and multi-valent salts is increased by 20 - 50 times, showing broad application prospects in the field of selective separation of mono- and multi-valent salts. Description of the Drawings

[0022] Figure 1 SEM images of the polyamide nanofiltration membrane (PA membrane) prepared in Comparative Example 1, where (a) has a magnification of 10,000 times and (b) has a magnification of 50,000 times.

[0023] Figure 2 SEM images of the bead-like structure nanofiltration membrane (PA-NS membrane) with high permeability and selectivity prepared in Example 1, where (a) has a magnification of 10,000 times and (b) has a magnification of 50,000 times.

[0024] Figure 3 SEM images of the polyamide nanofiltration membrane (PA-IS membrane) prepared in Comparative Example 2, where (a) has a magnification of 10,000 times and (b) has a magnification of 50,000 times. Detailed Embodiments

[0025] The present invention will be further illustrated below in conjunction with the embodiments and the drawings. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The operation methods without specific conditions noted in the following embodiments are generally carried out under conventional conditions or according to the conditions recommended by the manufacturers. The content not described in detail in this specification belongs to the prior art well-known to those skilled in the art. The experimental materials used in the following embodiments can be obtained from conventional biochemical reagent companies without special instructions.

[0026] Example 1

[0027] Piperazine and fatty alcohol polyoxyethylene ether AEO-9 (the number of repeating units of the polyoxyethylene group is 9 and the average molecular weight is 590) were dissolved in deionized water to prepare an aqueous solution. In the aqueous solution, the concentration of piperazine was 2000 ppm and the concentration of AEO-9 was 500 ppm; trimellitic acid chloride was dissolved in n-hexane to prepare an oil phase solution. In the oil phase solution, the concentration of trimellitic acid chloride was 3000 ppm. A polysulfone microfiltration membrane with a cut-off molecular weight of 2 kDa was fixed in a non-reactive plate-frame assembly. The aqueous solution was poured onto the surface of the bottom membrane and maintained for 5 min, then the aqueous solution was poured out, and the excess water was removed with a rubber roller. Then the oil phase solution was poured onto the surface of the bottom membrane and maintained for 2 min, and then the oil phase solution was poured out. The plate-frame assembly containing the bottom membrane was placed in an oven at 80 °C for 10 min. After taking it out and cooling at room temperature, the prepared nanofiltration membrane with a bead-like structure having high permeation selectivity was stored in deionized water.

[0028] SEM pictures of the nanofiltration membrane with a bead-like structure having high permeation selectivity (PA-NS membrane) are as Figure 2 shown in (a) and (b) in

[0029] Example 2

[0030] In this example, the preparation method of the nanofiltration membrane with a bead-like structure having high permeation selectivity is only different from that of Example 1 in that the non-ionic surfactant used is fatty alcohol polyoxyethylene ether AEO-3, and the number of repeating units of the polyoxyethylene group of AEO-3 is 3 and the average molecular weight is 315.

[0031] Example 3

[0032] In this example, the preparation method of the nanofiltration membrane with a bead-like structure having high permeation selectivity is only different from that of Example 1 in that the non-ionic surfactant used is fatty alcohol polyoxyethylene ether AEO-7, and the number of repeating units of the polyoxyethylene group of AEO-7 is 7 and the average molecular weight is 480.

[0033] Example 4

[0034] In this example, the preparation method of the nanofiltration membrane with a bead-like structure having high permeation selectivity is only different from that of Example 1 in that in the aqueous solution, the concentration of fatty alcohol polyoxyethylene ether AEO-9 is 400 ppm.

[0035] Example 5

[0036] In this example, the preparation method of the nanofiltration membrane with a bead-like structure having high permeation selectivity is only different from that of Example 1 in that in the aqueous solution, the concentration of fatty alcohol polyoxyethylene ether AEO-9 is 300 ppm.

[0037] Example 6

[0038] In this example, the preparation method of the bead-shaped structure nanofiltration membrane with high permeability selectivity is only different from that of Example 1 in that the concentration of fatty alcohol polyoxyethylene ether AEO-9 in the aqueous solution is 200 ppm.

[0039] Comparative Example 1

[0040] In this comparative example, the difference from Example 1 is only that fatty alcohol polyoxyethylene ether AEO-9 is not added.

[0041] The SEM images of the polyamide nanofiltration membrane (PA membrane) are as shown in Figure 1 (a) and (b) therein. It can be seen that the typical vesicular structure of the polyamide nanofiltration membrane is smoother on the membrane surface and has less effective permeation area compared with the membrane prepared in Example 1.

[0042] Comparative Example 2

[0043] In this comparative example, the preparation method of the polyamide nanofiltration membrane is only different from that of Example 1 in that an aqueous solution is prepared using aqueous monomer piperazine and ionic surfactant sodium dodecyl sulfate. In the aqueous solution, the concentration of piperazine is 2000 ppm and the concentration of sodium dodecyl sulfate is 500 ppm; other process flows and parameters are the same as those in Example 1.

[0044] The SEM images of the polyamide nanofiltration membrane (PA-IS membrane) are as shown in Figure 3 (a) and (b) therein. When the type of surfactant changes, a PA membrane with a striped structure is obtained and the bead-shaped structure disappears.

[0045] Sample Analysis

[0046] The polyamide nanofiltration membranes prepared in Comparative Examples 1-2 and Examples 1-6 were subjected to separation tests of a mixed salt of 2000 ppm sodium chloride and 2000 ppm sodium sulfate. The test pressure was 0.6 MPa, and pre-pressurization was carried out for 60 min before the test. The flux and selectivity of the membrane can be calculated by equations (1-1) and (1-2):

[0047]

[0048] Among them, △m is the mass of the permeate collected during this time interval, △t is the duration, S m is the effective membrane area, ρ w is the solution density, and △P is the transmembrane pressure.

[0049]

[0050] Among them, (C Cl ) pis the osmotic concentration of Cl - ions, (C SO4 ) p is the osmotic concentration of SO4 2- ions, (C Cl ) f is the feed concentration of Cl - ions, (C SO4 ) f is the feed concentration of SO4 2- ions, S Cl / SO4 is Cl - / SO4 2- selective separation factor.

[0051] The pure water fluxes and the selectivity of mono- and multi-valent salts (NaCl / Na2SO4) of the polyamide nanofiltration membranes of Comparative Examples 1-2 and Examples 1-6 are shown in Table 1. The results show that the polyamide nanofiltration membrane prepared by the method of the present invention can significantly improve the selectivity of mono- and multi-valent salts of the nanofiltration membrane while maintaining a high permeation flux, and the selectivity of mono- and multi-valent salts is increased by 20-50 times compared with that of Comparative Example 1 without adding non-ionic surfactants. This is because the non-ionic surfactant self-assembles on the surface of the nanofiltration membrane to form micellar aggregates, increasing the effective charge on the membrane surface, while the micellar structure is destroyed in Comparative Example 2, and the (Cl - / SO4 2- ) selectivity is poor.

[0052] Table 1 Selectivity of mono- and multi-valent salts (NaCl / Na2SO4) of nanofiltration membranes in comparative examples and examples

[0053] <![CDATA[Flux (L / m 2 h bar)]]> Selective Comparative Example 1 7.4 2.1 Comparative Example 2 19.1 1.1 Example 1 18.7 56 Example 2 16.2 73 Example 3 16.5 45 Example 4 18.6 48 Example 5 18.3 62 Example 6 18.4 53

[0054] The above-described embodiments have described the technical solutions of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, supplements or similar replacements made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A preparation method of a bead-shaped structure nanofiltration membrane with high permeability and selectivity, characterized in that, It includes the following steps: (1) Prepare an aqueous solution using an aqueous monomer and a non-ionic surfactant. The aqueous monomer is a polyamine monomer, and the non-ionic surfactant is a fatty alcohol polyoxyethylene ether. The number of repeating units of the polyoxyethylene group in the fatty alcohol polyoxyethylene ether is 1 - 20, and the average molecular weight is 200 - 1200; (2) Conduct an interfacial polymerization reaction on a microfiltration substrate membrane using the aqueous solution prepared in step (1) and an acyl chloride monomer oil phase solution to prepare the high-permeability and selective bead-shaped structure nanofiltration membrane; In the aqueous solution, the concentration of the polyamine monomer is 500 - 10000 ppm, and the concentration of the non-ionic surfactant is 100 - 1000 ppm; The microfiltration substrate membrane is selected from a polysulfone microfiltration membrane or a polyethersulfone microfiltration membrane; The process of the interfacial polymerization reaction is as follows: Pour the aqueous solution prepared in step (1) onto the surface of the microfiltration substrate membrane, let it stand for 1 - 10 min, pour out the aqueous solution, and remove the excess water; Then pour the acyl chloride monomer oil phase solution onto the microfiltration substrate membrane treated with the above aqueous solution, let it stand for 1 - 5 min, pour out the acyl chloride monomer oil phase solution, and transfer it to be treated at 50 - 90 °C for 5 - 20 min.

2. The preparation method of the bead-shaped structure nanofiltration membrane with high permeability and selectivity according to claim 1, characterized in that, The polyamine monomer is at least one of piperazine, m-phenylenediamine, p-phenylenediamine, polyethyleneimine, 1,2-ethylenediamine, 1,6-hexanediamine, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, spermine, or melamine.

3. The preparation method of the bead-shaped structure nanofiltration membrane with high permeability selectivity according to claim 1, characterized in that, The acyl chloride monomer includes trimesoyl chloride. In the oil phase solution, the concentration of the acyl chloride monomer is 500 - 10000 ppm, and the solvent of the oil phase solution is at least one of IsoparG, n-hexane, n-heptane, or cyclohexane.

4. A high-permeability and selective bead-shaped structure nanofiltration membrane prepared by the preparation method of the high-permeability and selective bead-shaped structure nanofiltration membrane according to any one of claims 1 - 3.

5. Application of the high-permeability and selective bead-shaped structure nanofiltration membrane according to claim 4 in the selective separation of mono- and polyvalent salts.

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