High-permeability-selectivity nanofiltration membrane with bead-like structure as well as preparation method and application of high-permeability-selectivity nanofiltration membrane

Abstract

The invention discloses a high-permeability-selectivity nanofiltration membrane with a bead-like structure and a preparation method and application thereof, and belongs to the technical field of membrane separation, the preparation method comprises the following steps: (1) preparing a water-phase solution by using a water-phase monomer and a nonionic surfactant, the nonionic surfactant is a polyoxyethylene type nonionic surfactant and is selected from fatty alcohol-polyoxyethylene ether, fatty acid polyoxyethylene ether or fatty amine polyoxyethylene ether; and (2) carrying out interfacial polymerization reaction on the water-phase solution prepared in the step (1) and the acyl chloride monomer oil-phase solution on a micro-filtration bottom membrane to prepare the high-permeability-selectivity bead-stringed structure nanofiltration membrane. The method is simple in process and low in equipment requirement, and the prepared nanofiltration membrane with the bead-like structure is high in univalent and multivalent salt separation capacity while keeping high permeability, and has a good application prospect in the field of water treatment.

Description

Technical Field

[0001] The invention relates to the technical field of membrane separation, and in particular to a beaded nanofiltration membrane with high permeability selectivity and a preparation method and application thereof. Background Art

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

[0003] At present, the interfacial polymerization method is usually used to prepare polyamide nanofiltration membranes. This method has a fast reaction speed and an unstable interface, which leads to defects in the prepared membrane and cannot achieve the ideal separation ability. For example, the Chinese patent document with the publication number CN110756056A discloses a method for preparing polyamide nanofiltration membranes by interfacial polymerization. The invention immerses the polysulfone ultrafiltration membrane in a p-phenylenediamine aqueous solution to saturate the surface with p-phenylenediamine molecules; removes excess liquid after taking it out, so that there are no obvious droplets on the surface of the PSF ultrafiltration membrane; pours a solution of trimesoyl chloride on the surface of the PSF ultrafiltration membrane, removes the oil phase solution after the reaction, and obtains a polyamide nanofiltration membrane; places the polyamide nanofiltration membrane in an oven at 40 to 90°C for heat treatment to promote subsequent polymerization reactions; after the reaction, immerses the nanofiltration membrane in a NaHSO3 solution for standby use. Although the selection of aqueous phase 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 single multivalent salts is not strong. A Chinese patent document with publication number CN116617879A discloses a new method for preparing polyamide nanofiltration membrane by active ester-amine interfacial polymerization. The invention uses active ester monomers instead of traditional acyl chloride monomers for interfacial polymerization, which reduces the reaction activity. The resulting 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 polyvalent salts.

[0004] In order to improve the monovalent and polyvalent salt separation ability of polyamide nanofiltration membranes, researchers have developed a variety of methods such as base membrane modification, introduction of intermediate layers, development of new monomers, and membrane surface modification. 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-structure nanofiltration membrane with high permeability selectivity. The process is simple and the equipment requirements are low. The beaded-structure nanofiltration membrane that is different from the existing vesicle, tubular and crater nanofiltration membranes can be constructed. The beaded-structure nanofiltration membrane has a strong ability to separate monovalent and polyvalent salts while maintaining high permeability, and has good application prospects in the field of water treatment.

[0006] The specific technical solutions adopted are as follows:

[0007] A method for preparing a beaded nanofiltration membrane with high permeability selectivity comprises the following steps:

[0008] (1) preparing an aqueous phase solution using an aqueous phase monomer and a nonionic surfactant, wherein the aqueous phase monomer is a polyamine monomer, and the nonionic surfactant is a polyoxyethylene nonionic surfactant selected from fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ether or fatty amine polyoxyethylene ether;

[0009] (2) The aqueous solution prepared in step (1) and the acyl chloride monomer oil solution are used to carry out an interfacial polymerization reaction on the microfiltration bottom membrane to prepare the highly permeable and selective beaded nanofiltration membrane.

[0010] The present invention introduces a nonionic surfactant into an interfacial polymerization reaction system, adds the nonionic surfactant to an aqueous solution, and then utilizes the aqueous solution and an acyl chloride monomer oil phase solution to undergo interfacial polymerization to form a film. Based on hydrophilic-hydrophobic interaction, the nonionic surfactant can self-assemble in an aqueous solution to form stable micelle microspheres, move to the interface as a template for the formation of a polyamide membrane structure, and finally form a polyamide membrane with a beaded structure at the interface. The polyamide membrane with the 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, and enriches more charges on the membrane surface, thereby resulting in an increase in the selectivity of a single multivalent salt. If other additives such as Na3PO4 are also included in the aqueous solution, the formation of the beaded structure will be affected, thereby affecting the permeability and the selectivity of a single multivalent salt of the obtained polyamide membrane.

[0011] Preferably, the nonionic surfactant is fatty alcohol polyoxyethylene ether, the number of repeating units of polyoxyethylene in the fatty alcohol polyoxyethylene ether is 1 to 20, further 1 to 10, and the average molecular weight is 200 to 1200. The monomer diffusion at the interface can be changed by utilizing the interaction between the oxygen-containing functional groups of the fatty alcohol polyoxyethylene ether molecules and the hydrogen bonds between the monomers.

[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 phase solution, the concentration of the polyamine monomer is 500-10000 ppm (mass concentration), and the concentration of the nonionic surfactant is 100-1000 ppm (mass concentration), and further 200-500 ppm.

[0014] Specifically, the acyl chloride monomer includes trimesoyl chloride, and 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 bottom membrane is selected from polysulfone microfiltration membrane, polyethersulfone microfiltration membrane or polyacrylonitrile microfiltration membrane, and the cut-off molecular weight of the microfiltration bottom membrane is 1kDa-200kDa.

[0016] Specifically, the process of the interfacial polymerization reaction is: pouring the aqueous solution prepared in step (1) onto the surface of the microfiltration bottom membrane, letting it stand for 1-10 minutes, pouring out the aqueous solution to remove excess water; then pouring the acyl chloride monomer oil phase solution onto the microfiltration bottom membrane treated with the aqueous solution, letting it stand for 1-5 minutes, pouring out the acyl chloride monomer oil phase solution and transferring to 50-90° C. for treatment for 5-20 minutes.

[0017] The present invention also provides a high permeability selectivity beaded structure nanofiltration membrane prepared by the preparation method of the high permeability selectivity beaded structure nanofiltration membrane.

[0018] The present invention also provides the application of the high permeability selectivity beaded structure nanofiltration membrane in the selective separation of monovalent and polyvalent salts.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The preparation method of the beaded nanofiltration membrane with high permeability selectivity provided by the present invention is simple in process, low in cost, easy to obtain equipment, and has mild operating conditions. By adding an appropriate amount of non-ionic surfactant to the aqueous solution, the mono- and polyvalent 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 interface migration phenomena of non-ionic surfactants to make them act as templates. 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 and construct a beaded structure. The surfactant micelle layer has a stable structure on the membrane surface, which can significantly increase the effective permeation area and surface charge density of the membrane. While maintaining high permeability, the selectivity for monovalent and polyvalent salts is increased by 20-50 times. It has broad application prospects in the field of selective separation of monovalent and polyvalent salts. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 These are SEM images of the polyamide nanofiltration membrane (PA membrane) prepared in Comparative Example 1, wherein (a) is magnified 10,000 times, and (b) is magnified 50,000 times.

[0023] Figure 2 These are SEM images of the highly permeable and selective beaded nanofiltration membrane (PA-NS membrane) prepared in Example 1, wherein (a) is magnified 10,000 times, and (b) is magnified 50,000 times.

[0024] Figure 3 These are SEM images of the polyamide nanofiltration membrane (PA-IS membrane) prepared in Comparative Example 2, where (a) is magnified 10,000 times, and (b) is magnified 50,000 times. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with the examples and accompanying drawings. It should be understood that these examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. The operating methods of the following examples that do not specify specific conditions are usually performed under normal conditions or under conditions recommended by the manufacturer. The content that is not described in detail in this specification sheet belongs to the prior art known to professionals in the field. The experimental materials used in the following examples, if not otherwise specified, can be purchased by conventional biochemical reagent companies.

[0026] Example 1

[0027] Piperazine and fatty alcohol polyoxyethylene ether AEO-9 (polyoxyethylene repeating unit number is 9, average molecular weight is 590) are dissolved in deionized water to prepare an aqueous solution, in which the concentration of piperazine is 2000ppm and the concentration of AEO-9 is 500ppm; trimesoyl chloride is dissolved in n-hexane to prepare an oil solution, in which the concentration of trimesoyl chloride is 3000ppm. A polysulfone microfiltration membrane with a cut-off molecular weight of 2kDa is fixed in a non-reactive plate-frame assembly, the aqueous solution is poured on the surface of the bottom membrane for 5 minutes, the aqueous solution is poured off, excess water is removed with a rubber roller, the oil solution is poured on the surface of the bottom membrane for 2 minutes, the oil solution is poured off, the plate-frame assembly containing the bottom membrane is placed in an 80°C oven for 10 minutes, taken out and cooled at room temperature, and the obtained high permeability selectivity beaded structure nanofiltration membrane is placed in deionized water for storage.

[0028] The SEM image of the highly permeable and selective beaded nanofiltration membrane (PA-NS membrane) is shown in Figure 2 As shown in (a) and (b), it can be observed that the nonionic surfactant self-organizes to form micelles, which serve as a template for the formation of the polyamide membrane, and finally a polyamide membrane with a beaded structure is obtained, and the effective permeation area of ​​the membrane is significantly increased.

[0029] Example 2

[0030] In this embodiment, the preparation method of the beaded nanofiltration membrane with high permeability selectivity is different from that of Example 1 only in that the non-ionic surfactant used is fatty alcohol polyoxyethylene ether AEO-3, 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 embodiment, the preparation method of the beaded nanofiltration membrane with high permeability selectivity is different from that of Example 1 only in that the non-ionic surfactant is fatty alcohol polyoxyethylene ether AEO-7, 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 embodiment, the preparation method of the beaded nanofiltration membrane with high permeability selectivity is different from that in Example 1 only in that the concentration of fatty alcohol polyoxyethylene ether AEO-9 in the aqueous solution is 400 ppm.

[0035] Example 5

[0036] In this embodiment, the preparation method of the beaded nanofiltration membrane with high permeability selectivity is different from that of Example 1 only in that the concentration of fatty alcohol polyoxyethylene ether AEO-9 in the aqueous solution is 300 ppm.

[0037] Example 6

[0038] In this embodiment, the preparation method of the beaded nanofiltration membrane with high permeability selectivity is different from that of Example 1 only 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 only difference from Example 1 is that no fatty alcohol polyoxyethylene ether AEO-9 is added.

[0041] The SEM image of the polyamide nanofiltration membrane (PA membrane) is shown in Figure 1 As shown in (a) and (b), the typical vesicle-like structure of the polyamide nanofiltration membrane can be seen. Compared with the membrane prepared in Example 1, the membrane surface is smoother and the effective permeation area is smaller.

[0042] Comparative Example 2

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

[0044] The SEM image of the polyamide nanofiltration membrane (PA-IS membrane) is shown in Figure 3 As shown in (a) and (b) in FIG, when the type of surfactant is changed, a PA film containing a stripe structure is obtained and the beaded 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 2000ppm sodium chloride and 2000ppm sodium sulfate mixed salts. The test pressure was 0.6MPa and the membranes were pre-pressed for 60min before the test. The flux and selectivity of the membranes can be calculated by equations (1-1) and (1-2):

[0047]

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

[0049]

[0050] Among them, (C Cl ) pCl - Osmotic concentration of ions (C SO4 ) p SO4 2- Osmotic concentration of ions (C Cl ) f Cl - The feed concentration of ions (C SO4 ) f SO4 2- Feed concentration of ions, S Cl / SO4 Cl - / SO4 2- Selective separation factor.

[0051] The pure water flux and monopolyvalent salt (NaCl / Na2SO4) selectivity 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 monopolyvalent salt selectivity of the nanofiltration membrane while maintaining a high permeation flux, and the monopolyvalent salt selectivity is increased by 20-50 times compared with the monopolyvalent salt selectivity of Comparative Example 1 without adding a nonionic surfactant. This is because the nonionic surfactant self-assembles on the surface of the nanofiltration membrane to form micelles, which increases the effective charge on the membrane surface, while the micelle structure in Comparative Example 2 is destroyed, (Cl - / SO4 2- ) has poor selectivity.

[0052] Table 1 Selectivity of nanofiltration membrane monopolyvalent salt (NaCl / Na2SO4) in comparative examples and examples

[0053] <![CDATA[Flux (L / m 2 h bar)]]> Selectivity 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 embodiments described above provide a detailed description of the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements or similar substitutions 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 method for preparing a beaded nanofiltration membrane with high permeability selectivity, characterized in that: The following steps are involved: (1) preparing an aqueous phase solution using an aqueous phase monomer and a nonionic surfactant, wherein the aqueous phase monomer is a polyamine monomer, and the nonionic surfactant is a polyoxyethylene nonionic surfactant selected from fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ether or fatty amine polyoxyethylene ether; (2) The aqueous solution prepared in step (1) and the acyl chloride monomer oil solution are used to carry out an interfacial polymerization reaction on the microfiltration bottom membrane to prepare the highly permeable and selective beaded nanofiltration membrane.

2. The method for preparing a beaded nanofiltration membrane with high permeability selectivity according to claim 1, characterized in that: The nonionic surfactant is fatty alcohol polyoxyethylene ether, the number of repeating units of polyoxyethylene in the fatty alcohol polyoxyethylene ether is 1-20, and the average molecular weight is 200-1200.

3. The method for preparing a beaded nanofiltration membrane with high permeability 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.

4. The method for preparing a beaded nanofiltration membrane with high permeability selectivity according to claim 1, characterized in that: In the aqueous phase solution, the concentration of the polyamine monomer is 500-10000 ppm, and the concentration of the nonionic surfactant is 100-1000 ppm.

5. The method for preparing a beaded 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. The solvent of the oil phase solution is at least one of Isopar G, n-hexane, n-heptane or cyclohexane.

6. The method for preparing a beaded nanofiltration membrane with high permeability selectivity according to claim 1, characterized in that: The microfiltration bottom membrane comprises a polysulfone microfiltration membrane, a polyethersulfone microfiltration membrane or a polyacrylonitrile microfiltration membrane.

7. The method for preparing a beaded nanofiltration membrane with high permeability selectivity according to claim 1, characterized in that: The process of the interfacial polymerization reaction is: pouring the aqueous phase solution prepared in step (1) onto the surface of the microfiltration bottom membrane, leaving it to stand for 1-10 minutes, pouring off the aqueous phase solution, and removing excess water; Then pour the acyl chloride monomer oil phase solution onto the microfiltration bottom membrane treated with the above aqueous phase solution, let it stand for 1-5 minutes, pour out the acyl chloride monomer oil phase solution and transfer to 50-90° C. for treatment for 5-20 minutes.

8. A highly permeable-selective beaded-structure nanofiltration membrane prepared according to the method for preparing a highly permeable-selective beaded-structure nanofiltration membrane according to any one of claims 1 to 7.

9. Use of the highly permeable and selective beaded nanofiltration membrane according to claim 8 in the selective separation of monovalent and polyvalent salts.

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