Separation nanofiltration membrane as well as preparation method and application thereof

Abstract

The invention discloses a separation nanofiltration membrane and a preparation method and application thereof.According to the preparation method, sulfonyl chloride is added into an organic phase of an interfacial polymerization reaction, and the interfacial polymerization reaction is interfered through the sulfonyl chloride, so that the positive charge density of the surface of the nanofiltration membrane is improved; inorganic base is adopted as a water-phase buffering agent, so that a relatively large membrane pore originally caused by competition of organic-phase monomers is shrunk; in order to compensate adverse effects caused by addition of sodium carbonate, membrane pores can be further reduced and the positive charge density on the surface of the membrane can be improved by subsequently adopting secondary grafting of polyamine monomers, so that mineral ion interception and improvement of lithium-magnesium separation characteristics are realized. In conclusion, the preparation method disclosed by the invention adopts a synergistic mechanism of water-phase buffering, organic-phase sulfonyl chloride and secondary grafting of the polyamine monomer, so that the effective pore diameter and the surface charge density of the membrane are well balanced, and the prepared nanofiltration membrane shows good positive electricity effect, water permeability and lithium-magnesium separation performance; the method has the potential of being applied to the field of lithium resource extraction.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanofiltration membranes, and in particular relates to a separation nanofiltration membrane and a preparation method and application thereof. Background Art

[0002] With the surge in demand for lithium resources, extracting lithium from salt lake brines has become an important method. Currently, lithium extraction from salt lake brines accounts for over 60% of the global lithium supply. However, lithium in brines often coexists with high concentrations of magnesium, resulting in a very low lithium content, with the magnesium-to-lithium ratio in brines typically ranging from 10 to 50. Common traditional methods for extracting lithium from salt lakes include precipitation, adsorption, and electrodialysis, but their widespread adoption is limited by low efficiency, high pollution, and high costs. Nanofiltration membrane separation, due to its low energy consumption and ease of operation, has become one of the most promising solutions.

[0003] Traditional nanofiltration membranes are prepared based on the interfacial polymerization (IP) reaction of piperazine (PIP) and trimesoyl chloride (TMC). However, these nanofiltration membranes have two technical drawbacks: first, the pore size distribution of the nanofiltration membrane is wide (0.5-1.0 nm), which cannot match the difference in hydration radius between lithium ions (0.382 nm) and magnesium ions (0.428 nm). Second, the nanofiltration membrane surface has a high negative charge density (Zeta potential <-40 mV), and due to the hydrolysis of carboxyl groups, magnesium ions are electrostatically attracted, which in turn reduces selectivity. Therefore, an ideal nanofiltration membrane surface should have a sufficiently high positive charge density (or a low negative charge density) and an appropriate pore size to promote its widespread application in lithium-magnesium separation technology.

[0004] In recent years, research on high-efficiency lithium-magnesium separation nanofiltration membranes has made great progress. The introduction of other aqueous monomers such as crown ethers can significantly improve the lithium-magnesium separation performance, but the synthesis of such monomers is complex and will reduce the mechanical strength of the nanofiltration membrane. Secondary interfacial polymerization can also improve the lithium-magnesium separation performance, but it usually significantly reduces the water flux. In order to achieve higher Mg 2+ In order to achieve a high retention rate and a higher lithium-magnesium separation effect, it is necessary to develop a nanofiltration membrane with both suitable pore size distribution and high positive charge density. Summary of the Invention

[0005] To overcome the problems of the prior art, one object of the present invention is to provide a method for preparing a separation nanofiltration membrane. A second object of the present invention is to provide a separation nanofiltration membrane produced by the above-mentioned preparation method. A third object of the present invention is to provide applications of the above-mentioned separation nanofiltration membrane.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] The first aspect of the present invention provides a method for preparing a separation nanofiltration membrane, comprising the following steps:

[0008] S1. coating an aqueous solution on a porous support layer, removing excess water, and then coating an organic solution, and performing an interfacial polymerization reaction to obtain a primary nanofiltration membrane;

[0009] The aqueous phase solution includes a polyamine 1, an inorganic base and water; the polyamine 1 is a polyamine containing two or more amino functional groups; the organic phase solvent includes a polyacyl chloride, a sulfonyl chloride and an organic solvent; the polyacyl chloride is a polyacyl chloride containing two or more acyl chloride functional groups;

[0010] S2. Immersing the primary nanofiltration membrane in an aqueous solution containing polyamine 2 to perform a secondary grafting reaction, and heat-curing the obtained primary nanofiltration membrane to obtain the separation nanofiltration membrane; the polyamine 2 is a polyamine containing 3 or more amino functional groups.

[0011] The present invention adds sulfonyl chloride to the organic phase of the interfacial polymerization reaction, and increases the positive charge density on the surface of the nanofiltration membrane by interfering with the interfacial polymerization reaction through the sulfonyl chloride; and uses an inorganic base as an aqueous phase buffer. The inorganic base can promote the occurrence of the interfacial polymerization reaction by neutralizing protons, thereby reducing the larger membrane pores originally caused by competition between organic phase monomers; in order to compensate for the adverse effects caused by the increase in negative charge density on the membrane surface caused by the addition of sodium carbonate to the piperazine aqueous phase, subsequent secondary grafting of polyamine monomers can further reduce the membrane pores and increase the positive charge density on the membrane surface, thereby achieving improved mineral ion retention and lithium-magnesium separation properties.

[0012] Preferably, the material of the porous support layer is at least one selected from polysulfone, polyethersulfone, polyacrylonitrile, polyvinylidene fluoride, polytetrafluoroethylene, and polyethylene.

[0013] Preferably, the coating method is dipping.

[0014] More preferably, step S1 specifically comprises: immersing the porous support layer in an aqueous solution for 10 seconds to 5 minutes, removing excess water, and then immersing the porous support layer in an organic solution for 10 seconds to 3 minutes, and performing an interfacial polymerization reaction to obtain a primary nanofiltration membrane.

[0015] Further preferably, the porous supporting layer is immersed in the aqueous solution for 10 seconds to 3 minutes.

[0016] More preferably, the mixture is immersed in the organic phase solution for 10 seconds to 1.5 minutes.

[0017] Preferably, the method of removing excess moisture is drying.

[0018] Preferably, the inorganic base is selected from at least one of sodium carbonate, sodium bicarbonate, potassium carbonate and potassium bicarbonate.

[0019] The aqueous phase buffer of the present invention adopts a carbonate strong alkali salt as the aqueous phase buffer, which can improve the pH buffering capacity of the polyamine solution more than other inorganic bases.

[0020] Preferably, the mass concentration of the inorganic base in the aqueous solution is 0.2 wt% to 2 wt%.

[0021] More preferably, the mass concentration of the inorganic base in the aqueous solution is 0.2 wt% to 1.5 wt%.

[0022] More preferably, the mass concentration of the inorganic base in the aqueous solution is 0.5 wt % to 1 wt %.

[0023] Preferably, the polyamine 1 includes aromatic polyamines and / or aliphatic polyamines; the aromatic polyamines include one or more of m-phenylenediamine, p-phenylenediamine, iso-phenylenediamine, diaminobenzoic acid and diaminobenzenesulfonic acid; the aliphatic polyamines include one or more of piperazine, piperazinecarboxylic acid, piperazine carboxylate, ethylenediamine, propylenediamine, butanediamine and pentamethylenediamine.

[0024] Preferably, the mass concentration of the polyamine 1 in the aqueous solution is 0.05 wt % to 5 wt %.

[0025] More preferably, the mass concentration of the polyamine 1 in the aqueous solution is 1 wt% to 4 wt%.

[0026] Preferably, the polyacyl chloride includes at least one of trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride and phthaloyl chloride.

[0027] Preferably, the mass concentration of the polyacyl chloride in the organic phase solution is 0.05 wt % to 5 wt %.

[0028] More preferably, the mass concentration of the polyacyl chloride in the organic phase solution is 0.05 wt % to 1 wt %.

[0029] Further preferably, the mass concentration of the polyacyl chloride in the organic phase solution is 0.05 wt % to 0.5 wt %.

[0030] Preferably, the mass concentration of the sulfonyl chloride in the organic phase solution is 0.05 wt% to 5 wt%.

[0031] More preferably, the mass concentration of the sulfonyl chloride in the organic phase solution is 0.05 wt% to 0.5 wt%.

[0032] More preferably, the mass concentration of the sulfonyl chloride in the organic phase solution is 0.05 wt% to 0.2 wt%.

[0033] Preferably, the polyamine 2 is selected from at least one of polyetherimide, polyethylene polyamine, and tris(2-aminoethyl)amine.

[0034] Preferably, the mass concentration of the polyamine 2 in the aqueous solution containing the polyamine 2 is 0.05 wt % to 5 wt %.

[0035] More preferably, the mass concentration of the polyamine 2 in the aqueous solution containing the polyamine 2 is 0.05 wt % to 1 wt %.

[0036] Preferably, the temperature of the heat curing treatment is 50-80° C., and the time is 2-10 minutes.

[0037] More preferably, the temperature of the heat curing treatment is 60-70° C., and the time is 2-6 minutes.

[0038] The second aspect of the present invention provides a nanofiltration membrane prepared by the preparation method described in the first aspect.

[0039] The third aspect of the present invention provides the use of the nanofiltration membrane prepared in the second aspect in the field of lithium-magnesium separation.

[0040] Preferably, the lithium-magnesium separation is specifically the separation of magnesium ions and sodium ions.

[0041] The beneficial effects of the present invention are:

[0042] The present invention provides a method for preparing a separation nanofiltration membrane. Compared with the traditional nanofiltration membrane preparation method, the preparation method of the present invention adds sulfonyl chloride to the organic phase of the interfacial polymerization reaction, and the positive charge density on the surface of the nanofiltration membrane is increased by interfering the interfacial polymerization reaction with sulfonyl chloride; and an inorganic base is used as an aqueous phase buffer. The inorganic base can promote the occurrence of the interfacial polymerization reaction by neutralizing protons, so that the larger membrane pores originally caused by the competition of the organic phase monomers are reduced; in order to compensate for the adverse effects caused by the increase in the negative charge density on the membrane surface caused by the addition of sodium carbonate to the piperazine aqueous phase, the subsequent secondary grafting of polyamine monomers can further reduce the membrane pores and increase the positive charge density on the membrane surface, thereby achieving the improvement of mineral ion retention and lithium-magnesium separation characteristics. In summary, the preparation method of the present invention adopts the synergistic mechanism of "aqueous phase buffering + organic phase sulfonyl chloride + polyamine monomer secondary grafting" compared to the traditional nanofiltration membrane, so that the effective pore size and surface charge density of the membrane are well balanced. The prepared nanofiltration membrane shows good positive electric effect, water permeability and lithium-magnesium separation performance, and has the potential to be applied in the field of lithium resource extraction. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The water permeability coefficients and the retention rates of xylose, MgCl2, NaCl, and Na2SO4 of the separation nanofiltration membranes of Comparative Example 1, Comparative Example 7, and Comparative Example 8 are shown;

[0044] Figure 2 The water contact angle and zeta potential of the separation nanofiltration membranes of Comparative Example 1, Comparative Example 7 and Comparative Example 8;

[0045] Figure 3 The water permeability coefficient, pore size, and retention rate of xylose, MgCl2, NaCl, and Na2SO4 of the separation nanofiltration membranes of Comparative Example 1 and Examples 1-4 are shown;

[0046] Figure 4 The water contact angle and zeta potential of the separation nanofiltration membranes of Comparative Example 1 and Examples 1-4;

[0047] Figure 5 The water permeability coefficients of the separation nanofiltration membranes of Comparative Examples 2-4 and the retention rates of xylose, MgCl2, NaCl, and Na2SO4;

[0048] Figure 6 The water permeability coefficients of the separation nanofiltration membranes of Comparative Example 1 and Comparative Examples 5-6, as well as the retention rates of xylose, MgCl2, NaCl, and Na2SO4;

[0049] Figure 7 The lithium-magnesium separation performance of the separation nanofiltration membrane of Example 1;

[0050] Figure 8 This is the lithium-magnesium separation performance of the separation nanofiltration membrane of Example 4. DETAILED DESCRIPTION

[0051] The present invention is further described in detail below through specific examples. Unless otherwise specified, the raw materials used in the following examples can be obtained from conventional commercial sources or prepared and isolated by simple synthesis; unless otherwise specified, the processes used are conventional processes in the art.

[0052] Example 1

[0053] This embodiment provides a separation nanofiltration membrane, and the steps for preparing the separation nanofiltration membrane are as follows:

[0054] The polysulfone-based membrane was immersed in an aqueous solution containing 2.0 wt% piperazine and 0.5 wt% sodium carbonate for 2 minutes to remove excess surface moisture; then it was reacted in a n-hexane solution containing 0.05 wt% sulfonyl chloride and 0.1 wt% trimesoyl chloride for 1 minute; then a 0.2 wt% aqueous solution of tris(2-aminoethyl)amine was added and reacted for 1 minute; then it was taken out and thermally cured at 65°C for 4 minutes; finally, the prepared nanofiltration membrane was rinsed with deionized water and the filtration performance was tested.

[0055] Example 2

[0056] This embodiment provides a separation nanofiltration membrane, and the steps for preparing the separation nanofiltration membrane are as follows:

[0057] The polysulfone-based membrane was immersed in an aqueous solution containing 2.0 wt% piperazine and 0.5 wt% sodium carbonate for 2 minutes to remove excess surface moisture; then it was reacted in an n-hexane solution containing 0.05 wt% sulfonyl chloride and 0.1 wt% trimesoyl chloride for 1 minute; then a 0.5 wt% aqueous solution of tris(2-aminoethyl)amine was added and reacted for 1 minute; then it was taken out and heat-cured at 65°C for 4 minutes; finally, the prepared nanofiltration membrane was rinsed with deionized water and the filtration performance was tested.

[0058] Example 3

[0059] This embodiment provides a separation nanofiltration membrane, and the steps for preparing the separation nanofiltration membrane are as follows:

[0060] The polysulfone-based membrane was immersed in an aqueous solution containing 2.0 wt% piperazine and 1.0 wt% sodium carbonate for 2 minutes to remove excess surface moisture; then it was reacted in an n-hexane solution containing 0.05 wt% sulfonyl chloride and 0.1 wt% trimesoyl chloride for 1 minute; then a 0.2 wt% aqueous solution of tris(2-aminoethyl)amine was added and reacted for 1 minute; then it was taken out and thermally cured at 65°C for 4 minutes; finally, the prepared nanofiltration membrane was rinsed with deionized water and the filtration performance was tested.

[0061] Example 4

[0062] This embodiment provides a separation nanofiltration membrane, and the steps for preparing the separation nanofiltration membrane are as follows:

[0063] The polysulfone-based membrane was immersed in an aqueous solution containing 2.0 wt% piperazine and 1.0 wt% sodium carbonate for 2 minutes to remove excess surface moisture; then it was reacted in an n-hexane solution containing 0.05 wt% sulfonyl chloride and 0.1 wt% trimesoyl chloride for 1 minute; then a 0.5 wt% aqueous solution of tris(2-aminoethyl)amine was added and reacted for 1 minute; then it was taken out and heat-cured at 65°C for 4 minutes; finally, the prepared nanofiltration membrane was rinsed with deionized water and the filtration performance was tested.

[0064] Comparative Example 1

[0065] This comparative example provides a separation nanofiltration membrane, and the preparation steps of the separation nanofiltration membrane are as follows:

[0066] The polysulfone-based membrane was immersed in a 2.0 wt% piperazine aqueous solution for 2 minutes to remove excess surface moisture; then, it was reacted in a hexane solution containing 0.05 wt% sulfonyl chloride and 0.1 wt% trimesoyl chloride for 1 minute; then, it was taken out and thermally cured at 65°C for 4 minutes; finally, the prepared nanofiltration membrane was rinsed with deionized water and the filtration performance was tested.

[0067] Comparative Example 2

[0068] This comparative example provides a separation nanofiltration membrane, and the preparation steps of the separation nanofiltration membrane are as follows:

[0069] The polysulfone-based membrane was immersed in a 0.2wt% piperazine aqueous solution for 2 minutes to remove excess surface moisture; then it was reacted in a 0.15wt% trimesoyl chloride n-hexane solution for 1 minute; then it was taken out and heat-cured at 65°C for 4 minutes; finally, the prepared nanofiltration membrane was rinsed with deionized water and the filtration performance was tested.

[0070] Comparative Example 3

[0071] This comparative example provides a separation nanofiltration membrane, and the preparation steps of the separation nanofiltration membrane are as follows:

[0072] The polysulfone-based membrane was immersed in an aqueous solution containing 0.2wt% piperazine and 0.15wt% sodium carbonate for 2 minutes to remove excess surface moisture; then it was reacted in a 0.15wt% hexane solution of trimesoyl chloride for 1 minute; then it was taken out and thermally cured at 65°C for 4 minutes; finally, the prepared nanofiltration membrane was rinsed with deionized water and the filtration performance was tested.

[0073] Comparative Example 4

[0074] This comparative example provides a separation nanofiltration membrane, and the preparation steps of the separation nanofiltration membrane are as follows:

[0075] The polysulfone-based membrane was immersed in an aqueous solution containing 0.2wt% piperazine and 0.5wt% sodium carbonate for 2 minutes to remove excess surface moisture; then it was reacted in a 0.15wt% hexane solution of trimesoyl chloride for 1 minute; then it was taken out and thermally cured at 65°C for 4 minutes; finally, the prepared nanofiltration membrane was rinsed with deionized water and the filtration performance was tested.

[0076] Comparative Example 5

[0077] This comparative example provides a separation nanofiltration membrane, and the preparation steps of the separation nanofiltration membrane are as follows:

[0078] The polysulfone-based membrane was immersed in a 2.0 wt% piperazine aqueous solution for 2 minutes to remove excess surface moisture; then it was reacted in a 0.05 wt% sulfonyl chloride and 0.1 wt% trimesoyl chloride n-hexane solution for 1 minute; then a 0.2 wt% tris(2-aminoethyl) aqueous solution was added and reacted for 1 minute; then it was taken out and thermally cured at 65°C for 4 minutes; finally, the prepared nanofiltration membrane was rinsed with deionized water and the filtration performance was tested.

[0079] Comparative Example 6

[0080] This comparative example provides a separation nanofiltration membrane, and the preparation steps of the separation nanofiltration membrane are as follows:

[0081] The polysulfone-based membrane was immersed in a 2.0 wt% piperazine aqueous solution for 2 minutes to remove excess surface moisture; then it was reacted in a n-hexane solution containing 0.05 wt% sulfonyl chloride and 0.1 wt% trimesoyl chloride for 1 minute; then a 0.5 wt% tris(2-aminoethyl) aqueous solution was added and reacted for 1 minute; then it was taken out and thermally cured at 65°C for 4 minutes; finally, the prepared nanofiltration membrane was rinsed with deionized water and the filtration performance was tested.

[0082] Comparative Example 7

[0083] This comparative example provides a separation nanofiltration membrane, and the preparation steps of the separation nanofiltration membrane are as follows:

[0084] The polysulfone-based membrane was immersed in an aqueous solution containing 0.2wt% piperazine and 0.5wt% sodium carbonate for 2 minutes to remove excess surface moisture; then it was reacted in a 0.15wt% hexane solution of trimesoyl chloride for 1 minute; then it was taken out and thermally cured at 65°C for 4 minutes; finally, the prepared nanofiltration membrane was rinsed with deionized water and the filtration performance was tested.

[0085] Comparative Example 8

[0086] This comparative example provides a separation nanofiltration membrane, and the preparation steps of the separation nanofiltration membrane are as follows:

[0087] The polysulfone-based membrane was immersed in an aqueous solution containing 0.2 wt% piperazine and 1.0 wt% sodium carbonate for 2 minutes to remove excess surface moisture; then it was reacted in a 0.15 wt% hexane solution of trimesoyl chloride for 1 minute; then it was taken out and thermally cured at 65°C for 4 minutes; finally, the prepared nanofiltration membrane was rinsed with deionized water and the filtration performance was tested.

[0088] The differences between Examples 1-4 and Comparative Examples 1-8 are shown in Table 1:

[0089] Table 1 Substance concentrations of aqueous solution, organic solution and secondary grafting solution in Examples 1-4 and Comparative Examples 1-8

[0090]

[0091]

[0092] Experimental analysis of nanofiltration membrane pore size and lithium-magnesium separation performance

[0093] 1. Test method

[0094] All nanofiltration membranes were tested using a laboratory-scale cross-flow filtration system with three parallel filtration units. Each filtration unit had an effective area of ​​20.6 cm 2 . Three independent membrane pieces cut from the same membrane were used in parallel experiments. Before sampling, the membrane must be pre-compressed at 0.8 MPa for at least 50 minutes to ensure its stability. Subsequent tests were carried out under cross-flow conditions with an operating pressure of 0.5 MPa and a water temperature of 20°C. The ionic strength of the inorganic salt solutions used in the tests was 10 mmol / L, and the concentrations of the single solute solutions of glycerol, xylose, glucose, and sucrose were all 100 mg / L (their retention rates were used to calculate the cut-off molecular weight of the composite nanofiltration membrane), as well as 5 different Mg 2+ / Li + A mixed raw material solution of MgCl2 and LiCl with a ratio of 1:1.

[0095] 2. Experimental results

[0096] Figure 1The permeability coefficients and retention rates of xylose, MgCl2, NaCl, and Na2SO4 for Comparative Examples 1, 7, and 8 are shown. At an operating pressure of 0.5 MPa, Comparative Example 1 exhibits an extremely high magnesium chloride retention rate and a relatively low sodium sulfate retention rate of 91.0% and 42.0%, respectively, which are typical characteristics of positively charged membranes. The disadvantage of Comparative Example 1 is that it is relatively loose, with a xylose retention rate of only 38.0%, corresponding to a pore size of 0.442 nm. The membrane structure is primarily composed of linear polyamide segments, so electrostatic effects play a dominant role in the retention of magnesium chloride and sodium sulfate. By adding 0.5 wt% sodium carbonate to the piperazine aqueous phase, the effective pore size of the prepared membrane (Comparative Example 7) is significantly reduced to 0.395 nm (xylose retention rate of 50.0%). Increasing the sodium carbonate concentration to 1.0 wt% further reduces the effective pore size of the membrane (Comparative Example 8) to 0.384 nm (xylose retention rate of 59.0%). The reduction in effective pore size is in line with expectations, as the addition of sodium carbonate to the aqueous phase significantly increases the pH buffering capacity of the solution. The reduction in membrane effective pore size leads to a decrease in membrane water permeability, which is 12.0, 10.5, and 9.6 L / m for Comparative Examples 1, 7, and 8, respectively. 2 / h / bar.

[0097] At the same time, adding sodium carbonate to the piperazine solution also changed the retention characteristics of the nanofiltration membrane. Figure 1 The retention rates of xylose, MgCl2, NaCl, and Na2SO4 in Comparative Examples 1, 7, and 8 are also mentioned; Figure 2 The water contact angles and zeta potentials of Comparative Examples 1, 7, and 8 are shown. Compared to Comparative Example 1, Comparative Example 7 exhibits a slightly higher magnesium chloride rejection rate of 95.0%, while its sodium sulfate rejection rate is significantly higher, reaching 71.0%. Comparative Example 8 exhibits a slightly lower magnesium chloride rejection rate of 85.0%, but a higher sodium sulfate rejection rate of 78.0%. However, for all three membranes, sodium sulfate rejection is consistently lower than that of magnesium chloride. In contrast, sodium chloride rejection rates vary only slightly, fluctuating within a narrow range of 51% to 54%. The addition of sodium carbonate to the aqueous phase alters the single-salt retention characteristics of nanofiltration membranes, which is partly due to a narrowing of the effective pore size and partly due to changes in the membrane surface charge. The surface zeta potential of the membranes of Comparative Examples 1, 7, and 8 was measured in a 1 mmol / L KCl solution at pH 6.8. The results showed that although all membranes had a higher rejection rate for magnesium chloride than sodium sulfate, a negative Zeta potential was measured on the top surface of each membrane. In addition, increasing the concentration of sodium carbonate in the piperazine aqueous solution used to prepare the membrane would increase the negative charge density on the membrane surface, which is not conducive to the effective separation of Li+ / Mg 2+ Therefore, due to the large number of negatively charged carboxyl groups on the membrane surface, the surface hydrophilicity of the membrane is improved.

[0098] To compensate for the negative surface charge density of the membrane caused by the addition of sodium carbonate to the piperazine aqueous phase, a secondary grafting process was employed. This process grafted tris(2-aminoethyl)amine monomer onto the nascent polyamide active layer by reacting with residual acyl chloride groups. Although tris(2-aminoethyl)amine was dissolved in water as the aqueous phase, it is generally believed to be more reactive and more active than water molecules when reacting with residual acyl chloride groups. Figure 4 The water contact angle and Zeta potential of Comparative Example 1 and Examples 1-4 are shown. The experimental results show that tris(2-aminoethyl)amine was successfully grafted onto the active layer, which was confirmed by the gradual decrease in the absolute value of the Zeta potential of Examples 1-4. It was observed that when the concentration of tris(2-aminoethyl)amine was high enough (for example, 0.5wt%), the Zeta potential values ​​of the two treated membranes, Example 1 and Example 4, were similar to that of Comparative Example 1. The change in the water contact angle on the surface of the tris(2-aminoethyl)amine treated membrane was small, indicating that the grafting of tris(2-aminoethyl)amine had limited effect on hydrophilicity. In addition, due to the introduction of tris(2-aminoethyl)amine, Figure 3 The permeability coefficient, pore size and retention rate of xylose, MgCl2, NaCl and Na2SO4 of the separation nanofiltration membranes of Comparative Example 1 and Examples 1-4 are shown in the figure. As can be seen from the figure, the pore size of Examples 1-4 is further reduced, the retention rate of magnesium chloride is improved, and the water flux is slightly decreased. However, due to the increase in positive charge, the retention rate of sodium sulfate is also decreased.

[0099] For comparison, when no sulfonyl chloride was added to the organic phase, the increase in the sodium carbonate concentration in the aqueous phase not only reduced the effective pore size of the membrane but also increased the negative charge density on the membrane surface. Figure 5 The water permeability coefficients and the retention rates of xylose, MgCl2, NaCl, and Na2SO4 of Comparative Examples 2-4 are as follows: the xylose retention rate / magnesium chloride retention rate of Comparative Example 2, Comparative Example 3, and Comparative Example 4 are 54.0% / 60.0%, 62.0% / 52.0%, and 67.0% / 28.0%, respectively. Figure 6 The water permeability coefficients of Comparative Examples 1 and 5-6, as well as the retention rates of xylose, MgCl2, NaCl, and Na2SO4, are shown. In addition, when sodium carbonate is not added to the aqueous phase, the grafted tri(2-aminoethyl)amine (Comparative Example 5 and Comparative Example 6) has less effect on the retention performance than Comparative Example 3 and Comparative Example 4.

[0100] Figure 7 This is a lithium-magnesium separation performance diagram of Example 1; Figure 8The lithium-magnesium separation performance of Example 4 is shown in FIG1 . The results show that Examples 1 and 4 perform well in lithium-magnesium separation, and their lithium-magnesium separation coefficients are both above 40. Compared with Example 4, Example 1 performs better, with not only a higher separation factor but also better water permeability. This may be because the effective pore size and surface charge density of the membrane have reached a good balance.

[0101] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing a separation nanofiltration membrane, characterized in that: The steps include: S1. coating an aqueous solution on a porous support layer, removing excess water, and then coating an organic solution, and performing an interfacial polymerization reaction to obtain a primary nanofiltration membrane; The aqueous phase solution includes a polyamine 1, an inorganic base and water; the polyamine 1 is a polyamine containing two or more amino functional groups; the organic phase solvent includes a polyacyl chloride, a sulfonyl chloride and an organic solvent; the polyacyl chloride is a polyacyl chloride containing two or more acyl chloride functional groups; S2. Immersing the primary nanofiltration membrane in an aqueous solution containing polyamine 2 to perform a secondary grafting reaction, and heat-curing the obtained primary nanofiltration membrane to obtain the separation nanofiltration membrane; the polyamine 2 is a polyamine containing 3 or more amino functional groups.

2. The method for preparing a separation nanofiltration membrane according to claim 1, wherein: The material of the porous support layer is selected from at least one of polysulfone, polyethersulfone, polyacrylonitrile, polyvinylidene fluoride, polytetrafluoroethylene, and polyethylene.

3. The method for preparing a separation nanofiltration membrane according to claim 1, wherein: The coating method is dip coating; Preferably, step S1 specifically comprises: immersing the porous support layer in an aqueous solution for 10 seconds to 5 minutes, removing excess water, and then immersing the porous support layer in an organic solution for 10 seconds to 3 minutes to perform an interfacial polymerization reaction to obtain a primary nanofiltration membrane.

4. The method for preparing a separation nanofiltration membrane according to claim 1, wherein: The inorganic base is selected from at least one of sodium carbonate, sodium bicarbonate, potassium carbonate and potassium bicarbonate; And / or, the mass concentration of the inorganic base in the aqueous solution is 0.2 wt% to 2 wt%.

5. The method for preparing a separation nanofiltration membrane according to claim 1, wherein: The polyamine 1 includes aromatic polyamines and / or aliphatic polyamines; the aromatic polyamines include one or more of m-phenylenediamine, p-phenylenediamine, mesitylenetriamine, diaminobenzoic acid and diaminobenzenesulfonic acid; the aliphatic polyamines include one or more of piperazine, piperazinecarboxylic acid, piperazine carboxylate, ethylenediamine, propylenediamine, butanediamine and pentamethylenediamine; And / or, the mass concentration of the polyamine 1 in the aqueous solution is 0.05 wt % to 5 wt %.

6. The method for preparing a separation nanofiltration membrane according to claim 1, wherein: The polyvalent acyl chloride monomer includes at least one of trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride, and phthaloyl chloride; And / or, the mass concentration of the polyacyl chloride in the organic phase solution is 0.05wt% to 5wt%; And / or, the mass concentration of the sulfonyl chloride in the organic phase solution is 0.05 wt % to 5 wt %.

7. The method for preparing a separation nanofiltration membrane according to claim 1, wherein: The polyamine 2 is selected from at least one of polyetherimide, polyethylene polyamine, and tris(2-aminoethyl)amine; And / or, the mass concentration of the polyamine 2 in the aqueous solution containing the polyamine 2 is 0.05 wt % to 5 wt %.

8. The method for preparing a separation nanofiltration membrane according to claim 1, wherein: The temperature of the heat curing treatment is 50-80° C., and the time is 2-10 minutes.

9. A separation nanofiltration membrane obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the separation nanofiltration membrane according to claim 9 in the field of lithium-magnesium separation.

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