Gamma-cyclodextrin modification-based polyacrylonitrile nanofiltration membrane and application thereof in magnesium-lithium separation

Abstract

The invention belongs to the technical field of nanofiltration membrane preparation, and particularly relates to a gamma-cyclodextrin modification-based polyacrylonitrile nanofiltration membrane and application of the gamma-cyclodextrin modification-based polyacrylonitrile nanofiltration membrane in magnesium-lithium separation. Gamma-cyclodextrin is added to a polyacrylonitrile membrane to modify the polyacrylonitrile membrane, so that the membrane flux and the lithium-magnesium separation capacity are improved; the preparation method comprises the following steps: dipping and coating polyethyleneimine, 1, 3, 5-benzoyl chloride and gamma-cyclodextrin materials on the surface of a polyacrylonitrile nanofiltration membrane, and preparing the gamma-cyclodextrin modified polyacrylonitrile nanofiltration membrane through an in-situ deposition-interfacial polymerization-high-temperature crosslinking technology, so that efficient separation of lithium and magnesium and resource recovery of lithium are realized; the purposes of cyclically and stably utilizing the modified polyacrylonitrile nanofiltration membrane and efficiently separating lithium and magnesium are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of nanofiltration membrane preparation, and specifically relates to a polyacrylonitrile nanofiltration membrane modified based on gamma-cyclodextrin and its application in magnesium-lithium separation. Background Art

[0002] Lithium belongs to the IA group of elements, ranking first among alkali metals, and is known as "white oil". Lithium is widely used in glass, ceramics, medical and other fields. With the rapid development of lithium batteries, lithium has received great attention in the field of new energy materials. Salt lake brine has abundant lithium resources, and its lithium extraction process has the advantages of low energy consumption, high economy and environmental friendliness. Therefore, it is of great significance to the development of salt lake lithium resources. At present, the salt lake brine in Qinghai area has less lithium and more magnesium. The chemical properties of lithium and magnesium are similar, and it is difficult to separate them efficiently, which limits the resource utilization of lithium in salt lake brine.

[0003] Existing lithium-magnesium separation methods include calcination-leaching, adsorption, electrodialysis and multi-stage membrane separation, etc. They have their own advantages in efficiency and selectivity, thus promoting the development of resource recovery and industrial application. Nanofiltration membrane is a membrane between ultrafiltration membrane and reverse osmosis membrane, with the characteristics of high membrane flux and good interception effect. Nanofiltration membrane can effectively intercept high-valent ions and has a low interception rate for monovalent ions, which makes it show great potential in solving high-concentration ion interference (such as magnesium, sodium, potassium, and calcium) in salt lake brine. In the extraction of lithium from salt lake brine, the membrane separation method uses a selective nanofiltration membrane to gradually remove impurities in the brine and concentrate lithium resources under the application of external force, and finally precipitate lithium products. This method is suitable for lithium extraction from salt lake brine. It has the characteristics of low operating difficulty, low production cost, excellent lithium-magnesium separation effect and environmental friendliness. It has become one of the important technical means for lithium extraction from salt lakes.

[0004] However, the nanofiltration membranes for magnesium-lithium separation prepared by existing methods have problems such as low membrane flux, poor selectivity, uneven membrane pore size and poor chemical stability. Summary of the invention

[0005] In view of the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin and its application in magnesium-lithium separation. By adding γ-cyclodextrin to the polyacrylonitrile membrane to modify it, its membrane flux and lithium-magnesium separation ability are improved, and efficient separation of lithium and magnesium and resource recovery of lithium are achieved, so as to achieve the purpose of efficiently separating lithium and magnesium while cyclically and stably utilizing the modified polyacrylonitrile nanofiltration membrane.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A method for preparing a polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin comprises the following steps:

[0008] The polyethyleneimine is dissolved in water to form a polyethyleneimine aqueous phase solution, 1,3,5-benzenetricarboxylic acid chloride is dissolved in n-hexane to form a 1,3,5-benzenetricarboxylic acid chloride organic phase solution, and γ-cyclodextrin and sodium hydroxide are dissolved in water to obtain a γ-cyclodextrin modified solution.

[0009] The polyethyleneimine aqueous solution is coated on the surface of the polyacrylonitrile nanofiltration membrane, deposited in situ, and the base membrane is modified to obtain the polyacrylonitrile nanofiltration membrane containing polyethyleneimine.

[0010] The 1,3,5-benzenetricarboxylic acid chloride organic phase solution is coated on the surface of the polyacrylonitrile nanofiltration membrane containing polyethyleneimine, and in-situ deposition is performed to obtain the polyacrylonitrile nanofiltration membrane containing polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride.

[0011] The gamma-cyclodextrin modified solution is coated on the surface of a polyacrylonitrile nanofiltration membrane containing polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride, and interfacial polymerization is performed. The hydroxyl groups in the gamma-cyclodextrin react with the amino groups in the polyethyleneimine to generate amide groups, thereby obtaining a modified polyacrylonitrile nanofiltration membrane.

[0012] The modified polyacrylonitrile nanofiltration membrane is subjected to a high-temperature cross-linking reaction to obtain a polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin. The microstructure of the polyacrylonitrile membrane is optimized through the high-temperature cross-linking reaction, thereby improving the selectivity, chemical stability and separation ability of the membrane.

[0013] The invention modifies a polyacrylonitrile membrane by polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride to improve the pore size of the polyacrylonitrile membrane, then adds gamma-cyclodextrin to the polyacrylonitrile membrane to modify it, improves the membrane flux and the lithium-magnesium separation ability, adopts the method of impregnating and coating polyethyleneimine, 1,3,5-benzenetricarboxylic acid chloride and gamma-cyclodextrin materials on the surface of the polyacrylonitrile nanofiltration membrane, and obtains the gamma-cyclodextrin-modified polyacrylonitrile nanofiltration membrane through in-situ deposition-interfacial polymerization-high temperature cross-linking technology, realizes efficient separation of lithium and magnesium and resource recovery of lithium, and achieves the purpose of efficiently separating lithium and magnesium while cyclically and stably utilizing the modified polyacrylonitrile nanofiltration membrane.

[0014] In a preferred embodiment of the present invention, the mass ratio of polyethyleneimine to γ-cyclodextrin is 40:1-6.

[0015] In a preferred embodiment of the present invention, the mass ratio of 1,3,5-benzenetricarboxylic acid chloride to γ-cyclodextrin is 0.5-3:1.

[0016] In a preferred embodiment of the present invention, in the polyethyleneimine aqueous phase solution, the dosage ratio of polyethyleneimine to water is 0.1g~0.5g:50mL~100mL, in the 1,3,5-benzenetricarboxylic acid chloride organic phase solution, the dosage ratio of 1,3,5-benzenetricarboxylic acid chloride to n-hexane is 0.01g~0.05g:50mL~100mL, and in the γ-cyclodextrin modified solution, the dosage ratio of γ-cyclodextrin, sodium hydroxide and water is 0.01g~0.06g:0.2g~0.5g:50mL~100mL.

[0017] In a preferred embodiment of the present invention, the in-situ deposition time is 5 minutes to 10 minutes.

[0018] In a preferred embodiment of the present invention, the interfacial polymerization time is 5 minutes to 10 minutes.

[0019] In a preferred embodiment of the present invention, the high temperature cross-linking reaction temperature is 60° C. to 80° C., and the reaction time is 10 minutes to 15 minutes.

[0020] Another object of the present invention is to provide a polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin prepared by any of the preparation methods described above.

[0021] The third object of the present invention is to provide an application of the above-mentioned γ-cyclodextrin modified polyacrylonitrile nanofiltration membrane in magnesium-lithium separation, with an initial magnesium-lithium concentration ratio of 1:50.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The present invention first applies a polyethyleneimine aqueous solution to the surface of a polyacrylonitrile nanofiltration membrane, deposits it in situ, modifies the base membrane, and obtains a polyacrylonitrile nanofiltration membrane containing polyethyleneimine. Then, an organic phase solution of 1,3,5-benzenetricarboxylic acid chloride is applied to the surface of the polyacrylonitrile nanofiltration membrane containing polyethyleneimine, deposits it in situ, and obtains a polyacrylonitrile nanofiltration membrane containing polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride. Then, a γ-cyclodextrin modified solution is applied to the surface of the polyacrylonitrile nanofiltration membrane containing polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride, and interfacial polymerization is performed. The hydroxyl groups in γ-cyclodextrin react with the amino groups in polyethyleneimine to generate amide groups, and a modified polyacrylonitrile nanofiltration membrane is obtained. The modified polyacrylonitrile nanofiltration membrane is subjected to a high-temperature cross-linking reaction to obtain a polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin. The microstructure of the polyacrylonitrile membrane is optimized through the high-temperature cross-linking reaction, thereby improving the selectivity, chemical stability and separation ability of the membrane. The invention modifies a polyacrylonitrile membrane by polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride to improve the pore size of the polyacrylonitrile membrane, then adds gamma-cyclodextrin to the polyacrylonitrile membrane to modify it, improves the membrane flux and the lithium-magnesium separation ability, adopts the method of impregnating and coating polyethyleneimine, 1,3,5-benzenetricarboxylic acid chloride and gamma-cyclodextrin materials on the surface of the polyacrylonitrile nanofiltration membrane, and obtains the gamma-cyclodextrin-modified polyacrylonitrile nanofiltration membrane through in-situ deposition-interfacial polymerization-high temperature cross-linking technology, realizes efficient separation of lithium and magnesium and resource recovery of lithium, and achieves the purpose of efficiently separating lithium and magnesium while cyclically and stably utilizing the modified polyacrylonitrile nanofiltration membrane.

[0024] 2. The cyclodextrin used in the present invention is a green natural material composed of glucose units. The nanofiltration membrane modified by cyclodextrin not only improves the lithium-magnesium separation effect but also has a high lithium recovery rate, which is very friendly to the environment and ecology. In the extraction of lithium from salt lake brine, the membrane separation method gradually removes impurities in the brine and concentrates lithium ions under the application of external force through a selective nanofiltration membrane, and finally realizes lithium resource recovery, providing a solution for the further promotion and application of nanofiltration technology in the field of lithium extraction from salt lake brine. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A flow chart was prepared for the present invention.

[0026] Figure 2 Surface SEM scanning electron micrographs of the polyethyleneimine nanofiltration membrane prepared in (a) Comparative Example 1 and the polyethyleneimine nanofiltration membrane modified with γ-cyclodextrin prepared in (b) Example 1 of the present invention.

[0027] Figure 3 This is an AFM atomic force microscope image of the surface of the polyethyleneimine nanofiltration membrane of the present invention.

[0028] Figure 4This is an AFM atomic force microscope image of the surface of the polyethyleneimine nanofiltration membrane after cyclodextrin modification of the present invention.

[0029] Figure 5 It is the permeation / retention rate of lithium / magnesium ions under different addition amounts of polyethyleneimine of the present invention.

[0030] Figure 6 It is the permeation / retention rate of lithium / magnesium ions under the addition amount of 1,3,5-benzenetricarboxylic acid chloride of the present invention.

[0031] Figure 7 It is the permeability / retention rate of lithium / magnesium ions under different γ-cyclodextrin addition amounts of the present invention.

[0032] Figure 8 This is a cycle number-efficiency diagram for separating lithium and magnesium ions using the polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin of the present invention. DETAILED DESCRIPTION

[0033] The following is a detailed description of the technical solutions in the embodiments of the present invention in combination with the preferred embodiments and the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] It should be noted that all professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, various raw materials, reagents, instruments and equipment used in the following embodiments of the present invention can be purchased from the market or prepared by existing methods.

[0035] The preparation flow chart of the present invention is as follows Figure 1 As shown, firstly, a polyethyleneimine aqueous phase solution, a 1,3,5-benzenetricarboxylic acid chloride organic phase solution and a γ-cyclodextrin modified solution are prepared, and the polyethyleneimine aqueous phase solution is coated on the surface of a polyacrylonitrile nanofiltration membrane, and in-situ deposition is performed to obtain a polyacrylonitrile nanofiltration membrane containing polyethyleneimine; then, the 1,3,5-benzenetricarboxylic acid chloride organic phase solution is coated on the polyacrylonitrile nanofiltration membrane containing polyethyleneimine to obtain a polyacrylonitrile nanofiltration membrane containing polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride; then, a γ-cyclodextrin modified solution is coated on the surface of the polyacrylonitrile nanofiltration membrane containing polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride, and interfacial polymerization is performed to obtain a modified polyacrylonitrile nanofiltration membrane; finally, the modified polyacrylonitrile nanofiltration membrane is subjected to high temperature cross-linking to obtain a γ-cyclodextrin modified polyacrylonitrile nanofiltration membrane.

[0036] Example 1

[0037] A method for preparing a polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin comprises the following steps:

[0038] (1) Weigh 0.4 g of polyethyleneimine and dissolve it in 50 ml of deionized water to form a polyethyleneimine aqueous phase solution; weigh 0.03 g of 1,3,5-benzenetricarboxylic acid chloride and dissolve it in 50 ml of n-hexane to form a 1,3,5-benzenetricarboxylic acid chloride organic phase solution; weigh 0.03 g of γ-cyclodextrin and 0.2 g of sodium hydroxide and dissolve them in 50 ml of deionized water, and ultrasonically dissolve them to form a clear and transparent γ-cyclodextrin modified solution.

[0039] (2) The polyethyleneimine aqueous solution in step (1) is coated on the surface of the polyacrylonitrile nanofiltration membrane, and in-situ deposited for 8 minutes to make it evenly dispersed on the surface of the polyacrylonitrile nanofiltration membrane to obtain a polyacrylonitrile nanofiltration membrane containing polyethyleneimine, which is then poured out.

[0040] (3) The 1,3,5-benzenetricarboxylic acid chloride organic phase solution in step (1) is applied to the surface of the polyacrylonitrile nanofiltration membrane containing polyethyleneimine in step (2), and in-situ deposition is performed for 6 minutes to uniformly disperse the solution on the surface of the polyacrylonitrile nanofiltration membrane to obtain a polyacrylonitrile nanofiltration membrane containing polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride, which is then poured out.

[0041] (4) Use a rubber wheel to remove the residual aqueous phase and organic phase solution on the surface of the polyacrylonitrile nanofiltration membrane, and air-dry for 5 minutes to remove the residual solution on the surface of the polyacrylonitrile nanofiltration membrane.

[0042] (5) The γ-cyclodextrin modified solution in step (1) is coated on the surface of the polyacrylonitrile nanofiltration membrane containing polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride in step (4), and interfacial polymerization is performed for 5 minutes, and then the remaining γ-cyclodextrin modified solution is poured out.

[0043] (6) The modified polyacrylonitrile nanofiltration membrane in step (5) is placed in a 60° C. vacuum drying oven for high temperature cross-linking for 10 minutes to obtain a γ-cyclodextrin modified polyacrylonitrile nanofiltration membrane.

[0044] Example 2

[0045] A method for preparing a polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin comprises the following steps:

[0046] (1) Weigh 0.4 g of polyethyleneimine and dissolve it in 50 ml of deionized water to form a polyethyleneimine aqueous phase solution; weigh 0.03 g of 1,3,5-benzenetricarboxylic acid chloride and dissolve it in 50 ml of n-hexane to form a 1,3,5-benzenetricarboxylic acid chloride organic phase solution; weigh 0.01 g of γ-cyclodextrin and 0.2 g of sodium hydroxide and dissolve them in 50 ml of deionized water, and ultrasonically dissolve them to form a clear and transparent γ-cyclodextrin modified solution.

[0047] (2) The polyethyleneimine aqueous solution in step (1) is coated on the surface of the polyacrylonitrile nanofiltration membrane, and in-situ deposited for 8 minutes to make it evenly dispersed on the surface of the polyacrylonitrile nanofiltration membrane to obtain a polyacrylonitrile nanofiltration membrane containing polyethyleneimine, which is then poured out.

[0048] (3) The 1,3,5-benzenetricarboxylic acid chloride organic phase solution in step (1) is applied to the surface of the polyacrylonitrile nanofiltration membrane containing polyethyleneimine in step (2), and in-situ deposition is performed for 6 minutes to uniformly disperse the solution on the surface of the polyacrylonitrile nanofiltration membrane to obtain a polyacrylonitrile nanofiltration membrane containing polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride, which is then poured out.

[0049] (4) Use a rubber wheel to remove the residual aqueous phase and organic phase solution on the surface of the polyacrylonitrile nanofiltration membrane, and air-dry for 5 minutes to remove the residual solution on the surface of the polyacrylonitrile nanofiltration membrane.

[0050] (5) The γ-cyclodextrin modified solution in step (1) is coated on the surface of the polyacrylonitrile nanofiltration membrane containing polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride in step (4), and interfacial polymerization is performed for 5 minutes, and then the remaining γ-cyclodextrin modified solution is poured out.

[0051] (6) The modified polyacrylonitrile nanofiltration membrane in step (5) is placed in a 60° C. vacuum drying oven for high temperature cross-linking for 10 minutes to obtain a γ-cyclodextrin modified polyacrylonitrile nanofiltration membrane.

[0052] Example 3

[0053] A method for preparing a polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin comprises the following steps:

[0054] (1) Weigh 0.4 g of polyethyleneimine and dissolve it in 50 ml of deionized water to form a polyethyleneimine aqueous phase solution; weigh 0.03 g of 1,3,5-benzenetricarboxylic acid and dissolve it in 50 ml of n-hexane to form a 1,3,5-benzenetricarboxylic acid chloride organic phase solution; weigh 0.015 g of γ-cyclodextrin and 0.2 g of sodium hydroxide and dissolve them in 50 ml of deionized water, and ultrasonically dissolve them to form a clear and transparent γ-cyclodextrin modified solution.

[0055] (2) The polyethyleneimine aqueous solution in step (1) is coated on the surface of the polyacrylonitrile nanofiltration membrane, and in-situ deposited for 8 minutes to make it evenly dispersed on the surface of the polyacrylonitrile nanofiltration membrane to obtain a polyacrylonitrile nanofiltration membrane containing polyethyleneimine, which is then poured out.

[0056] (3) The 1,3,5-benzenetricarboxylic acid chloride organic phase solution in step (1) is applied to the surface of the polyacrylonitrile nanofiltration membrane containing polyethyleneimine in step (2), and in-situ deposition is performed for 6 minutes to uniformly disperse the solution on the surface of the polyacrylonitrile nanofiltration membrane to obtain a polyacrylonitrile nanofiltration membrane containing polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride, which is then poured out.

[0057] (4) Use a rubber wheel to remove the residual aqueous phase and organic phase solution on the surface of the polyacrylonitrile nanofiltration membrane, and air-dry for 5 minutes to remove the residual solution on the surface of the polyacrylonitrile nanofiltration membrane.

[0058] (5) The γ-cyclodextrin modified solution in step (1) is coated on the surface of the polyacrylonitrile nanofiltration membrane containing polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride in step (4), and interfacial polymerization is performed for 5 minutes, and then the remaining γ-cyclodextrin modified solution is poured out.

[0059] (6) The modified polyacrylonitrile nanofiltration membrane in step (5) is placed in a 60° C. vacuum drying oven for high temperature cross-linking for 10 minutes to obtain a γ-cyclodextrin modified polyacrylonitrile nanofiltration membrane.

[0060] Example 4

[0061] A method for preparing a polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin comprises the following steps:

[0062] (1) Weigh 0.4 g of polyethyleneimine and dissolve it in 50 ml of deionized water to form a polyethyleneimine aqueous phase solution; weigh 0.03 g of 1,3,5-benzenetricarboxylic acid chloride and dissolve it in 50 ml of n-hexane to form a 1,3,5-benzenetricarboxylic acid chloride organic phase solution; weigh 0.045 g of γ-cyclodextrin and 0.2 g of sodium hydroxide and dissolve them in 50 ml of deionized water, and ultrasonically dissolve them to form a clear and transparent γ-cyclodextrin modified solution.

[0063] (2) The polyethyleneimine aqueous solution in step (1) is coated on the surface of the polyacrylonitrile nanofiltration membrane, and in-situ deposited for 8 minutes to make it evenly dispersed on the surface of the polyacrylonitrile nanofiltration membrane to obtain a polyacrylonitrile nanofiltration membrane containing polyethyleneimine, which is then poured out.

[0064] (3) The 1,3,5-benzenetricarboxylic acid chloride organic phase solution in step (1) is applied to the surface of the polyacrylonitrile nanofiltration membrane containing polyethyleneimine in step (2), and in-situ deposition is performed for 6 minutes to uniformly disperse the solution on the surface of the polyacrylonitrile nanofiltration membrane to obtain a polyacrylonitrile nanofiltration membrane containing polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride, which is then poured out.

[0065] (4) Use a rubber wheel to remove the residual aqueous phase and organic phase solution on the surface of the polyacrylonitrile nanofiltration membrane, and air-dry for 5 minutes to remove the residual solution on the surface of the polyacrylonitrile nanofiltration membrane.

[0066] (5) The γ-cyclodextrin modified solution in step (1) is coated on the surface of the polyacrylonitrile nanofiltration membrane containing polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride in step (4), and interfacial polymerization is performed for 5 minutes, and then the remaining γ-cyclodextrin modified solution is poured out.

[0067] (6) The modified polyacrylonitrile nanofiltration membrane in step (5) is placed in a 60° C. vacuum drying oven for high temperature cross-linking for 10 minutes to obtain a γ-cyclodextrin modified polyacrylonitrile nanofiltration membrane.

[0068] Example 5

[0069] A method for preparing a polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin comprises the following steps:

[0070] (1) Weigh 0.4 g of polyethyleneimine and dissolve it in 50 ml of deionized water to form a polyethyleneimine aqueous phase solution; weigh 0.03 g of 1,3,5-benzenetricarboxylic acid chloride and dissolve it in 50 ml of n-hexane to form a 1,3,5-benzenetricarboxylic acid chloride organic phase solution; weigh 0.06 g of γ-cyclodextrin and 0.2 g of sodium hydroxide and dissolve them in 50 ml of deionized water, and ultrasonically dissolve them to form a clear and transparent γ-cyclodextrin modified solution.

[0071] (2) The polyethyleneimine aqueous solution in step (1) is coated on the surface of the polyacrylonitrile nanofiltration membrane, and in-situ deposited for 8 minutes to make it evenly dispersed on the surface of the polyacrylonitrile nanofiltration membrane to obtain a polyacrylonitrile nanofiltration membrane containing polyethyleneimine, which is then poured out.

[0072] (3) The 1,3,5-benzenetricarboxylic acid chloride organic phase solution in step (1) is applied to the surface of the polyacrylonitrile nanofiltration membrane containing polyethyleneimine in step (2), and in-situ deposition is performed for 6 minutes to uniformly disperse the solution on the surface of the polyacrylonitrile nanofiltration membrane to obtain a polyacrylonitrile nanofiltration membrane containing polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride, which is then poured out.

[0073] (4) Use a rubber wheel to remove the residual aqueous phase and organic phase solution on the surface of the polyacrylonitrile nanofiltration membrane, and air-dry for 5 minutes to remove the residual solution on the surface of the polyacrylonitrile nanofiltration membrane.

[0074] (5) The γ-cyclodextrin modified solution in step (1) is coated on the surface of the polyacrylonitrile nanofiltration membrane containing polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride in step (4), and interfacial polymerization is performed for 5 minutes, and then the remaining γ-cyclodextrin modified solution is poured out.

[0075] (7) The modified polyacrylonitrile nanofiltration membrane in step (6) is placed in a 60° C. vacuum drying oven for high temperature cross-linking for 10 minutes to obtain a γ-cyclodextrin modified polyacrylonitrile nanofiltration membrane.

[0076] Example 6

[0077] A method for preparing a polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin comprises the following steps:

[0078] (1) Weigh 0.4 g of polyethyleneimine and dissolve it in 80 ml of deionized water to form a polyethyleneimine aqueous phase solution; weigh 0.03 g of 1,3,5-benzenetricarboxylic acid chloride and dissolve it in 80 ml of n-hexane to form a 1,3,5-benzenetricarboxylic acid chloride organic phase solution; weigh 0.03 g of γ-cyclodextrin and 0.2 g of sodium hydroxide and dissolve them in 80 ml of deionized water, and dissolve them by ultrasonication to form a clear and transparent γ-cyclodextrin modified solution.

[0079] (2) The polyethyleneimine aqueous solution in step (1) is coated on the surface of the polyacrylonitrile nanofiltration membrane, and in-situ deposited for 8 minutes to make it evenly dispersed on the surface of the polyacrylonitrile nanofiltration membrane to obtain a polyacrylonitrile nanofiltration membrane containing polyethyleneimine, which is then poured out.

[0080] (3) The 1,3,5-benzenetricarboxylic acid chloride organic phase solution in step (1) is applied to the surface of the polyacrylonitrile nanofiltration membrane containing polyethyleneimine in step (2), and in-situ deposition is performed for 5 minutes to uniformly disperse the solution on the surface of the polyacrylonitrile nanofiltration membrane to obtain a polyacrylonitrile nanofiltration membrane containing polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride, which is then poured out.

[0081] (4) Use a rubber wheel to remove the residual aqueous phase and organic phase solution on the surface of the polyacrylonitrile nanofiltration membrane, and air-dry for 5 minutes to remove the residual solution on the surface of the polyacrylonitrile nanofiltration membrane.

[0082] (5) The γ-cyclodextrin modified solution in step (1) is coated on the surface of the polyacrylonitrile nanofiltration membrane containing polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride in step (4), and interfacial polymerization is performed for 8 minutes, and then the remaining γ-cyclodextrin modified solution is poured out.

[0083] (6) The modified polyacrylonitrile nanofiltration membrane in step (5) is placed in a 70° C. vacuum drying oven for high temperature cross-linking for 15 minutes to obtain a γ-cyclodextrin modified polyacrylonitrile nanofiltration membrane.

[0084] Example 7

[0085] A method for preparing a polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin comprises the following steps:

[0086] (1) Weigh 0.4 g of polyethyleneimine and dissolve it in 100 ml of deionized water to form a polyethyleneimine aqueous phase solution; weigh 0.03 g of 1,3,5-benzenetricarboxylic acid chloride and dissolve it in 100 ml of n-hexane to form a 1,3,5-benzenetricarboxylic acid chloride organic phase solution; weigh 0.03 g of γ-cyclodextrin and 0.2 g of sodium hydroxide and dissolve them in 100 ml of deionized water, and dissolve them by ultrasonication to form a clear and transparent γ-cyclodextrin modified solution.

[0087] (2) The polyethyleneimine aqueous solution in step (1) is coated on the surface of the polyacrylonitrile nanofiltration membrane, and in-situ deposited for 8 minutes to make it evenly dispersed on the surface of the polyacrylonitrile nanofiltration membrane to obtain a polyacrylonitrile nanofiltration membrane containing polyethyleneimine, which is then poured out.

[0088] (3) The 1,3,5-benzenetricarboxylic acid chloride organic phase solution in step (1) is applied to the surface of the polyacrylonitrile nanofiltration membrane containing polyethyleneimine in step (2), and in-situ deposition is performed for 10 minutes to uniformly disperse the solution on the surface of the polyacrylonitrile nanofiltration membrane to obtain a polyacrylonitrile nanofiltration membrane containing polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride, which is then poured out.

[0089] (4) Use a rubber wheel to remove the residual aqueous phase and organic phase solution on the surface of the polyacrylonitrile nanofiltration membrane, and air-dry for 5 minutes to remove the residual solution on the surface of the polyacrylonitrile nanofiltration membrane.

[0090] (5) The γ-cyclodextrin modified solution in step (1) is coated on the surface of the polyacrylonitrile nanofiltration membrane containing polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride in step (4), and interfacial polymerization is performed for 10 minutes, and then the remaining γ-cyclodextrin modified solution is poured out.

[0091] (6) The modified polyacrylonitrile nanofiltration membrane in step (5) is placed in a vacuum drying oven at 80° C. for 12 minutes for high-temperature crosslinking to obtain a γ-cyclodextrin-modified polyacrylonitrile nanofiltration membrane.

[0092] Comparative Example 1

[0093] A method for preparing a polyacrylonitrile nanofiltration membrane comprises the following steps:

[0094] (1) Weigh 0.4 g of polyethyleneimine and dissolve it in 50 ml of deionized water to form a polyethyleneimine aqueous phase solution; weigh 0.03 g of 1,3,5-benzenetricarboxylic acid chloride and dissolve it in 50 ml of n-hexane to form a 1,3,5-benzenetricarboxylic acid chloride organic phase solution.

[0095] (2) The polyethyleneimine aqueous solution in step (1) is coated on the surface of the polyacrylonitrile nanofiltration membrane, and in-situ deposited for 8 minutes to make it evenly dispersed on the surface of the polyacrylonitrile nanofiltration membrane to obtain a polyacrylonitrile nanofiltration membrane containing polyethyleneimine, which is then poured out.

[0096] (3) The 1,3,5-benzenetricarboxylic acid chloride organic phase solution in step (1) is applied to the surface of the polyacrylonitrile nanofiltration membrane containing polyethyleneimine in step (2), and in-situ deposition is performed for 6 minutes to uniformly disperse the solution on the surface of the polyacrylonitrile nanofiltration membrane to obtain a polyacrylonitrile nanofiltration membrane containing polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride, which is then poured out.

[0097] (4) Use a rubber wheel to remove the residual aqueous phase and organic phase solution on the surface of the polyacrylonitrile nanofiltration membrane, and air-dry for 5 minutes to remove the residual solution on the surface of the polyacrylonitrile nanofiltration membrane.

[0098] (5) placing the polyacrylonitrile nanofiltration membrane containing polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride treated in step (4) in a vacuum drying oven at 60 to 80° C. for high temperature crosslinking for 10 minutes to obtain a polyacrylonitrile nanofiltration membrane.

[0099] Application Example 1

[0100] The application of the γ-cyclodextrin modified polyacrylonitrile nanofiltration membrane prepared in Example 1 in the separation of magnesium and lithium solutions is specifically to load γ-cyclodextrin on the polyacrylonitrile nanofiltration membrane through interfacial polymerization reaction to achieve the separation of lithium and magnesium ions in laboratory-prepared brine, comprising the following steps:

[0101] The laboratory-prepared salt solution was used to test the cross-flow filtration device, and the concentration of the salt solution was 1500ppm, wherein the lithium-magnesium concentration ratio was 1:50. The γ-cyclodextrin-modified polyacrylonitrile nanofiltration membrane prepared in Example 1 was cut into a circular membrane with a diameter of d=4 cm and placed in a cross-flow filtration device for testing. The test conditions were 0.6MPa and 27°C. Deionized water was used to stabilize for one hour, and then the laboratory-prepared salt solution was introduced. The reaction time was four hours in total, and 2 ml of solution was taken at each time point of 30 minutes, 60 minutes, 120 minutes, 180 minutes and 240 minutes. All tests were performed at least twice to obtain the average value. The concentration of metal ions was determined using a flame atomic absorption spectrometer (FAAS, Agilent 240, USA), and the separation coefficient of lithium-magnesium ions in the permeate after separation by the γ-cyclodextrin-modified polyacrylonitrile nanofiltration membrane was calculated.

[0102] Cyclic test:

[0103] In order to investigate the stability of the polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin prepared by the present invention in a laboratory-prepared salt solution, the polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin is used for multiple cycles to separate lithium and magnesium ions in the laboratory-prepared salt solution. The specific steps are as follows:

[0104] Step 1: The γ-cyclodextrin modified polyacrylonitrile nanofiltration membrane was cut into a circular membrane piece with a diameter of d=4 cm, and a laboratory-prepared salt solution was used to perform the test using a cross-flow filtration device.

[0105] Step 2: Weigh 0.18 g lithium chloride and 12.33 g magnesium chloride, prepare the lithium-magnesium salt solution required for the experiment, adjust the volume to 1000 ml, the concentration of the salt solution is 1500 ppm, the lithium-magnesium concentration ratio is 1:50, and the test conditions are 0.6 MPa, 27 ° C.

[0106] Step 3: Use deionized water to stabilize for one hour before the experiment, and then pass the salt solution prepared in the laboratory for the test. The flow rate is 5 ml per hour.

[0107] Step 4: The effective duration of the experiment is 40 hours. After every 20 hours of operation, the salt solution is replaced with deionized water to rinse the nanofiltration membrane in step 1 for 2 hours. The above process is a cycle experiment, and the above experimental process is repeated twice.

[0108] Step 5: Samples were taken every 2 hours within 20 hours, and 2 ml of solution was taken from each location. After each cycle, the concentration of metal ions was measured using a flame atomic absorption spectrometer (FAAS, Agilent 240, USA), and the separation coefficient of lithium and magnesium ions in the permeate after separation by the γ-cyclodextrin-modified polyacrylonitrile nanofiltration membrane was calculated.

[0109] Figure 2 (a) shows the surface morphology of the polyethyleneimine nanofiltration membrane without the addition of cyclodextrin. It is observed that the surface has a dense porous structure, which may lead to the poor lithium-magnesium separation effect of the polyethyleneimine nanofiltration membrane without the addition of cyclodextrin. Figure 2 (b) shows the surface morphology of the polyethyleneimine nanofiltration membrane after adding cyclodextrin. It is observed that the porous structure of the membrane surface is reduced and the membrane surface becomes rough, which can provide a larger effective surface area for water transmission, thereby improving the lithium-magnesium separation ability. This change can be attributed to the presence of γ-cyclodextrin and the reaction between 1,3,5-benzenetricarboxylic acid chloride and γ-cyclodextrin, resulting in the formation of a polyester grid. Compared with the structure of the nanofiltration membrane without the addition of cyclodextrin, the polyester structure exhibits a more uniform and rougher surface. Figure 3 and Figure 4 The surface roughness of the polyethyleneimine nanofiltration membrane before and after the addition of cyclodextrin is shown. The surface roughness of the polyethyleneimine nanofiltration membrane without cyclodextrin is Ra = 11nm, but after the addition of cyclodextrin, the roughness increases to Ra = 22.5nm. The incorporation of a cyclodextrin layer into the polyethyleneimine nanofiltration membrane results in a reduction in the porous structure. This phenomenon is accompanied by a significant increase in the membrane surface roughness, which affects the lithium-magnesium separation effect.

[0110] Figure 5 and Figure 6 The permeability / retention rate of lithium / magnesium ions of the polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin and different ratios of polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride prepared in Example 1. Figure 5 and Figure 6It can be found that when the addition amount of polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride is 0.4g and 0.03g respectively, the lithium-magnesium separation effect is better, indicating that it has a strong interception capacity for magnesium chloride and has a good lithium chloride enrichment effect. When polyethyleneimine is excessive, the deposition on the surface of the modified membrane is too thick, which affects the permeability of the membrane to various ions, and the lithium-magnesium separation effect is poor. When the amount of 1,3,5-benzenetricarboxylic acid chloride is too small, the functional groups required for the reaction with polyethyleneimine are relatively small, the pore size of the modified membrane is relatively large, the interception capacity for magnesium chloride is poor, and the lithium-magnesium separation effect is not significant.

[0111] Figure 7 The permeability / retention rate of lithium / magnesium ions of polyacrylonitrile nanofiltration membrane modified with different γ-cyclodextrin addition amounts. Figure 7 It can be found that when the addition amount of γ-cyclodextrin is 0.01-0.03 g, the water flux increases significantly, which can be attributed to the strong hydrophilicity of γ-cyclodextrin. With the increase of the addition amount, the water flux gradually increases. After that, the water flux decreases slightly when the addition amount of γ-cyclodextrin continues to increase. It may be because the excess γ-cyclodextrin masks the effective channel of the membrane surface in contact with the salt solution, resulting in a decrease in the separation efficiency of lithium and magnesium. It can be obtained that when the addition amount of γ-cyclodextrin is 0.03 g, it is the best amount.

[0112] Figure 8 The cycle number-efficiency diagram of the γ-cyclodextrin modified polyacrylonitrile nanofiltration membrane prepared in Example 1 for separating lithium and magnesium ions in a laboratory salt solution is shown in FIG. Figure 8 As shown, after two cycles, the separation coefficient of the polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin for magnesium and lithium ions in the laboratory salt solution is less than 0.1, and the retention efficiency of magnesium ions is greater than 89%, which indicates that the polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin of the present invention can effectively separate lithium and magnesium ions and has good stability. It further indicates that the polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin synthesized by in situ deposition-interfacial polymerization-high temperature cross-linking technology is suitable for lithium extraction from salt lake brine with high magnesium ion content.

[0113] In summary, the present invention increases the hydrophilicity of the membrane, improves the interception rate of magnesium ions and the permeability of lithium ions, and realizes efficient separation of lithium and magnesium by modifying the surface structure of the polyacrylonitrile nanofiltration membrane with γ-cyclodextrin. The preparation method of the membrane used in the present invention is simple to operate and low in cost, and has high practical value and feasibility in the field of lithium and magnesium separation from salt lake brine. This method is of great significance to promoting the practical application of nanofiltration technology in lithium extraction from salt lake brine, and at the same time plays an important role in ensuring the resource utilization of lithium from salt lake brine in my country.

[0114] It should be noted that when the present invention involves a numerical range, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as those in the embodiments, in order to avoid redundancy, the present invention describes a preferred embodiment. Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the attached claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0115] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin, characterized in that: The following steps are involved: Dissolving polyethyleneimine in water to form a polyethyleneimine aqueous phase solution, dissolving 1,3,5-benzenetricarboxylic acid chloride in n-hexane to form a 1,3,5-benzenetricarboxylic acid chloride organic phase solution, and dissolving γ-cyclodextrin and sodium hydroxide in water to obtain a γ-cyclodextrin modified solution; The polyethyleneimine aqueous solution is applied to the surface of the polyacrylonitrile nanofiltration membrane for in-situ deposition to obtain a polyacrylonitrile nanofiltration membrane containing polyethyleneimine; The 1,3,5-benzenetricarboxylic acid chloride organic phase solution is coated on the surface of the polyacrylonitrile nanofiltration membrane containing polyethyleneimine, and in-situ deposition is performed to obtain a polyacrylonitrile nanofiltration membrane containing polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride; The γ-cyclodextrin modified solution is coated on the surface of a polyacrylonitrile nanofiltration membrane containing polyethyleneimine and 1,3,5-benzenetricarboxylic acid chloride to perform interfacial polymerization, and the hydroxyl groups in the γ-cyclodextrin react with the amino groups in the polyethyleneimine to generate amide groups, thereby obtaining a modified polyacrylonitrile nanofiltration membrane; The modified polyacrylonitrile nanofiltration membrane is subjected to a high temperature cross-linking reaction to obtain a polyacrylonitrile nanofiltration membrane modified based on gamma-cyclodextrin.

2. The method for preparing a polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin according to claim 1, characterized in that: The mass ratio of polyethyleneimine to gamma-cyclodextrin is 40:1-6.

3. The method for preparing a polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin according to claim 1, characterized in that: The mass ratio of 1,3,5-benzenetricarboxylic acid chloride to γ-cyclodextrin is 0.5-3:

1.

4. The method for preparing a polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin according to claim 1, characterized in that: In the polyethyleneimine aqueous phase solution, the dosage ratio of polyethyleneimine to water is 0.1g-0.5g:50mL-100mL, in the 1,3,5-benzenetricarboxylic acid chloride organic phase solution, the dosage ratio of 1,3,5-benzenetricarboxylic acid chloride to n-hexane is 0.01g-0.05g:50mL-100mL, and in the γ-cyclodextrin modified solution, the dosage ratio of γ-cyclodextrin, sodium hydroxide and water is 0.01g-0.06g:0.2g-0.5g:50mL-100mL.

5. The method for preparing a polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin according to claim 1, characterized in that: The in-situ deposition time is 5 to 10 minutes.

6. The method for preparing a polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin according to claim 1, characterized in that: The interfacial polymerization time is 5 to 10 minutes.

7. The method for preparing a polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin according to claim 1, characterized in that: The high temperature cross-linking reaction temperature is 60° C. to 80° C., and the reaction time is 10 minutes to 15 minutes.

8. A polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the polyacrylonitrile nanofiltration membrane modified with γ-cyclodextrin as claimed in claim 8 in magnesium and lithium separation.

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