Preparation method and application of monovalent cation selective membrane for efficient lithium-magnesium separation

Abstract

The invention discloses a preparation method and application of a monovalent cation selective membrane for efficient lithium-magnesium separation, and belongs to the technical field of preparation of cation selective membranes. The monovalent cation selective membrane is composed of a polyamide nanofiltration base membrane and a polyethyleneimine positive electricity layer, and the preparation method comprises the following steps: taking piperazine anhydrous as a water phase concentration and trimesoyl chloride as an oil phase monomer, reacting on a polyethersulfone ultrafiltration base membrane, and preparing the polyamide nanofiltration base membrane by utilizing an interfacial polymerization method; and anchoring on the surface of the polyamide nanofiltration base membrane by utilizing cross-linking of gallic acid and PEI with the molecular weight of about 70000 through a multi-layer deposition method to obtain the Gallic-PEI / polyamide composite membrane with the positively charged surface. The membrane can realize lithium-magnesium separation through pore size screening and electrostatic repulsion effect, and has high lithium-magnesium selectivity while maintaining large lithium ion flux in the application process of an electrodialysis system, so that the lithium-magnesium separation effect of salt lake brine is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of cation selective membrane preparation, and in particular relates to a method for preparing a monovalent cation selective membrane for efficient lithium-magnesium separation and its application. Background Art

[0002] Lithium compounds have excellent electrochemical activity and have great potential in commercial applications such as battery technology, ceramics and glass, grease, and polymer production. It is estimated that by 2100, the commercial demand for lithium will grow exponentially to 4.5 million tons per year. Therefore, the extraction of lithium is of great significance to meet the strong lithium market demand in the future. Salt lake brine is the main source of lithium, accounting for more than 70% of the total lithium reserves. Compared with traditional lithium extraction from ore, the extraction of lithium from salt lake brine has the advantages of low cost and relatively simple operation. Based on resource and cost advantages, most of the global lithium extraction uses salt lake brine as raw material, but how to effectively separate lithium ions (Li2O3) from salt lake brine remains a challenge. + ), magnesium ions (Mg 2+ ) is a difficult problem that needs to be solved urgently.

[0003] Due to time and demand constraints, traditional evaporation concentration methods are no longer economically viable. Progress has been made in a variety of brine concentration methods based on precipitation, ion exchange, solvent extraction, nanofiltration, electrodialysis, and electrochemical methods. Among them, the electrodialysis process has no phase change process, low energy consumption, greatly simplifies the process flow, and has good industrial application prospects. The key difficulty in using electrodialysis to extract lithium from salt lake brine is the interfering ions, especially Mg. 2+ The concentration is too high. 2+ He Li + The hydration radius of the ions is not much different, and the chemical reaction activity is also very similar. The traditional ion exchange membrane only has the selectivity between the counter ions and the common ions, and it is difficult to separate the two. The monovalent ion selective membrane has a considerable difference in the permeability between ions with the same charge but different valence states. Based on the characteristics of the monovalent ion selective membrane material with strong resistance to divalent ions and high permeability to monovalent ions, the monovalent ion selective membrane is used for electrodialysis to separate Li + From Mg 2+ It is entirely possible to separate it.

[0004] Polyethyleneimine (PEI) is a highly water-soluble polymer with a large number of amino groups. It is positively charged in water. Depositing it on the surface of a nanofiltration membrane can enhance the membrane's positive charge. However, the interaction between PEI and the membrane surface is weak, and the deposited layer formed is unstable.

[0005] Based on this, we proposed a method for preparing a monovalent cation selective membrane for efficient lithium-magnesium separation and its application, hoping to solve the shortcomings of the existing technology and provide a new method for the separation of Li-ion and magnesium from salt lake brine. +and Mg 2+ It provides theoretical basis and preliminary reference for the separation of Summary of the Invention

[0006] The purpose of the present invention is to address the existing problems and provide a method for preparing a monovalent cation selective membrane for efficient lithium-magnesium separation and its application.

[0007] The present invention is achieved through the following technical solutions:

[0008] A method for preparing a monovalent cation selective membrane for efficient lithium-magnesium separation is achieved by the following steps:

[0009] (1) Preparation of aqueous monomer solution:

[0010] dissolving anhydrous piperazine in ultrapure water to obtain an aqueous monomer solution;

[0011] (2) Preparation of oil phase monomer solution:

[0012] Dissolve trimesoyl chloride in n-hexane to obtain an oil phase monomer solution;

[0013] (3) Water phase load:

[0014] Fix the PES ultrafiltration base membrane to a polytetrafluoroethylene mold, inject the aqueous monomer solution, let it stand, then pour out the excess aqueous solution and wipe the membrane surface dry;

[0015] (4) Interface cross-linking:

[0016] Inject the oil phase monomer solution, let it stand for complete reaction, pour out the excess oil phase solution, and wipe the membrane surface dry;

[0017] (5) Post-processing:

[0018] The membrane is placed in an oven for drying and then taken out to obtain a polyamide nanofiltration base membrane;

[0019] (6) Multilayer deposition modification:

[0020] Pour the gallic acid solution evenly on the surface of the polyamide nanofiltration base membrane to deposit the gallic acid on the surface of the nanofiltration membrane;

[0021] Pour off the gallic acid solution on the membrane surface and wash with ultrapure water;

[0022] Then pour the polyethyleneimine solution on the membrane surface and heat it in a water bath to deposit the polyethyleneimine on the membrane surface;

[0023] Finally, a monovalent cation selective membrane for efficient lithium-magnesium separation was obtained.

[0024] Furthermore, the concentration of the aqueous monomer solution in step (1) is 0.5 to 0.7 wt%.

[0025] Furthermore, the concentration of the oil phase monomer solution in step (2) is 0.08-0.12 wt%.

[0026] Furthermore, the aqueous monomer solution in step (3) is allowed to stand on the membrane surface for 4 to 6 minutes.

[0027] Furthermore, the oil phase monomer solution in step (4) is allowed to stand for 1 to 3 minutes.

[0028] Furthermore, the drying temperature in step (5) is 55-65° C. and the drying time is 8-12 minutes.

[0029] Furthermore, the preparation method of the gallic acid solution in step (6) is as follows: dissolving gallic acid in a Tris buffer solution, then adding CuSO4 / H2O2 to accelerate self-polymerization, and fully mixing to obtain a gallic acid solution;

[0030] The concentration of the gallic acid solution is 1.3 to 1.7 wt %;

[0031] Tris buffer solution pH 8.8;

[0032] The concentration of CuSO4 is 5.1-5.5 mM, and that of H2O2 is 26-26.2 mM;

[0033] The deposition time of gallic acid solution on the membrane surface is 40 to 50 minutes;

[0034] Wash with ultrapure water three times.

[0035] Furthermore, the preparation method of the polyethyleneimine solution in step (6) is as follows: dissolving polyethyleneimine in ultrapure water and mixing thoroughly to obtain the polyethyleneimine solution;

[0036] The concentration of the polyethyleneimine solution is 1.3-1.7 wt %;

[0037] The molecular weight of polyethyleneimine is 70,000 Da;

[0038] The deposition time of polyethyleneimine solution on the membrane surface is 100 to 140 minutes.

[0039] Furthermore, the temperature of the water bath heating in step (6) is 55-65°C.

[0040] Application of a monovalent cation selective membrane in lithium-magnesium separation in salt lake brine.

[0041] Compared with the prior art, the present invention has the following advantages:

[0042] 1. The present invention uses anhydrous piperazine (PIP) as the aqueous phase concentration and trimesoyl chloride (TMC) as the oil phase monomer, reacts on a polyethersulfone (PES) ultrafiltration base membrane, and uses interfacial polymerization to prepare a polyamide nanofiltration base membrane. Then, through a multilayer deposition method, gallic acid (Gallic) and PEI with a molecular weight of about 70,000 are cross-linked and anchored on the surface of the polyamide nanofiltration base membrane to obtain a Gallic-PEI / polyamide composite membrane with a positive surface charge. This membrane can achieve lithium-magnesium separation through pore size screening and electrostatic repulsion. In the application process of the electrodialysis system, it has a high lithium-magnesium selectivity while maintaining a large lithium ion flux, thereby improving the effect of lithium-magnesium separation in salt lake brine.

[0043] 2. The gallic acid of the present invention can act as a "bio-glue layer" to undergo cross-linking reactions such as Michael addition / Schiff base reaction and amidation reaction with PEI, anchoring PEI on the surface of the nanofiltration membrane and improving the stability of the PEI positive layer, thereby obtaining a monovalent cation selective membrane with high selectivity and high lithium ion flux.

[0044] 3. The present invention prepares a monovalent cation selective membrane by depositing polyethyleneimine on the surface of a nanofiltration membrane. The membrane has the characteristics of high positive charge, high hydrophilicity and high lithium ion flux, and is very suitable for separation of lithium and magnesium in salt lake brine. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Schematic diagram of the process for preparing a monovalent cation selective membrane for efficient lithium-magnesium separation according to the present invention;

[0046] Figure 2 is a cross-sectional scanning electron micrograph of the monovalent cation selective membrane in Example 1;

[0047] Figure 3 1 is the electrochemical impedance spectroscopy of the monovalent cation selective membrane in Example 1 and Comparative Example 1;

[0048] Figure 4 The membrane and interface resistance fitting results of the monovalent cation selective membrane in Example 1 and Comparative Example 1;

[0049] Figure 5 is the ion flux of the monovalent cation selective membrane in Example 1 and Comparative Examples 1-3;

[0050] Figure 6 is the magnesium rejection rate and lithium-magnesium selectivity of the monovalent cation selective membrane in Example 1 and Comparative Examples 1-3;

[0051] Figure 7 It is the isoelectric point of the monovalent cation selective membrane in Example 1 and Comparative Examples 1-3. DETAILED DESCRIPTION

[0052] In order to further explain the present invention, it is described below with reference to the following specific embodiments.

[0053] Example 1

[0054] A method for preparing a monovalent cation selective membrane for efficient lithium-magnesium separation comprises the following steps:

[0055] (1) Preparation of aqueous monomer solution:

[0056] Anhydrous piperazine was dissolved in ultrapure water to obtain a solution concentration of 0.6 wt %;

[0057] (2) Preparation of oil phase monomer solution:

[0058] Take trimesoyl chloride and dissolve it in n-hexane to obtain a solution concentration of 0.1wt%;

[0059] (3) Water phase load:

[0060] Fix the PES ultrafiltration base membrane to a polytetrafluoroethylene mold, inject the aqueous monomer solution, and let it stand for 5 minutes to allow it to completely soak the membrane surface. Then pour out the excess aqueous solution and wipe the membrane surface dry.

[0061] (4) Interface cross-linking:

[0062] Inject the oil phase monomer solution and let it stand for 2 minutes to allow it to react completely. Pour out the excess oil phase solution and wipe the membrane surface dry.

[0063] (5) Post-processing:

[0064] The membrane was placed in an oven and heated at 60°C for 10 min, and then taken out to obtain a polyamide nanofiltration base membrane;

[0065] (6) Multilayer deposition modification:

[0066] Gallic acid was dissolved in a Tris buffer solution with a pH of 8.8, and CuSO4 (5.3 mM) / H2O2 (26.1 mM) was added to accelerate the self-polymerization, and the mixture was thoroughly mixed to obtain a gallic acid solution with a concentration of 1.5 wt%;

[0067] Pour the gallic acid solution evenly on the surface of the nanofiltration base membrane and leave it for 45 minutes to allow the gallic acid to deposit on the surface of the nanofiltration membrane;

[0068] Pour off the gallic acid solution on the membrane surface and wash with ultrapure water three times;

[0069] Dissolve polyethyleneimine with a molecular weight of 70,000 MW in ultrapure water and mix thoroughly to obtain a polyethyleneimine solution with a concentration of 1.5 wt%;

[0070] Then pour the polyethyleneimine solution on the membrane surface and heat it in a 60℃ water bath for 120min to deposit the polyethyleneimine on the membrane surface;

[0071] Finally, a monovalent cation selective membrane for efficient lithium-magnesium separation was obtained.

[0072] (7) The cross-sectional morphology, film and interface resistance of the prepared membrane were characterized. The results are as follows: Figure 2-Figure 4 As shown; the electrical properties, ion flux, magnesium retention rate and lithium-magnesium selectivity of the prepared membrane were tested, and the results are shown as follows Figure 5-Figure 7 shown.

[0073] Comparative Example 1

[0074] Comparative Example 1 shows a conventional nanofiltration membrane preparation method. Compared with Example 1, the main difference is that gallic acid and polyethyleneimine are not used for modification. The preparation process is as follows:

[0075] (1) Preparation of aqueous monomer solution:

[0076] Anhydrous piperazine was dissolved in ultrapure water to obtain a solution concentration of 0.6 wt %;

[0077] (2) Preparation of oil phase monomer solution:

[0078] Take trimesoyl chloride and dissolve it in n-hexane to obtain a solution concentration of 0.1wt%;

[0079] (3) Water phase load:

[0080] Fix the PES ultrafiltration base membrane to a polytetrafluoroethylene mold, inject the aqueous monomer solution, and let it stand for 5 minutes to allow it to completely soak the membrane surface. Then pour out the excess aqueous solution and wipe the membrane surface dry.

[0081] (4) Interface cross-linking:

[0082] Inject the oil phase monomer solution and let it stand for 2 minutes to allow it to react completely. Pour out the excess oil phase solution and wipe the membrane surface dry.

[0083] (5) Post-processing:

[0084] The membrane was placed in an oven and heated at 60°C for 10 min, and then taken out to obtain a polyamide nanofiltration membrane;

[0085] (6) The interfacial resistance of the prepared film was characterized, and the results were as follows: Figure 3-Figure 4 As shown; the electrical properties, ion flux, magnesium retention rate and lithium-magnesium selectivity of the prepared membrane were tested, and the results are shown as follows Figure 5-Figure 7 shown.

[0086] Comparative Example 2

[0087] Comparative Example 2 shows a method for preparing a monovalent cation selective membrane. Compared with Example 1, the main difference is that the molecular weight of the polyethyleneimine used is not 70,000 MW as specified in Example 1. The preparation process is as follows:

[0088] (1) Preparation of aqueous monomer solution:

[0089] Anhydrous piperazine was dissolved in ultrapure water to obtain a solution concentration of 0.6 wt %;

[0090] (2) Preparation of oil phase monomer solution:

[0091] Take trimesoyl chloride and dissolve it in n-hexane to obtain a solution concentration of 0.1wt%;

[0092] (3) Water phase load:

[0093] Fix the PES ultrafiltration base membrane to a polytetrafluoroethylene mold, inject the aqueous monomer solution, and let it stand for 5 minutes to allow it to completely soak the membrane surface. Then pour out the excess aqueous solution and wipe the membrane surface dry.

[0094] (4) Interface cross-linking:

[0095] Inject the oil phase monomer solution and let it stand for 2 minutes to allow it to react completely. Pour out the excess oil phase solution and wipe the membrane surface dry.

[0096] (5) Post-processing:

[0097] The membrane was placed in an oven and heated at 60°C for 10 min, and then taken out to obtain a polyamide nanofiltration base membrane;

[0098] (6) Multilayer deposition modification:

[0099] Gallic acid was dissolved in a Tris buffer solution with a pH of 8.8, and a certain amount of CuSO4 (5.3 mM) / H2O2 (26.1 mM) was added to accelerate the self-polymerization, and the mixture was thoroughly mixed to obtain a gallic acid solution with a concentration of 1.5 wt%;

[0100] Pour the gallic acid solution evenly on the surface of the nanofiltration base membrane and leave it for 45 minutes to allow the gallic acid to deposit on the surface of the nanofiltration membrane;

[0101] Pour off the gallic acid solution on the membrane surface and wash with ultrapure water three times;

[0102] Dissolve polyethyleneimine with a molecular weight of 25,000 MW in ultrapure water and mix thoroughly to obtain a polyethyleneimine solution with a concentration of 1.5 wt%;

[0103] Then pour the polyethyleneimine solution on the membrane surface and heat it in a 60℃ water bath for 120min to deposit the polyethyleneimine on the membrane surface;

[0104] Finally, a monovalent cation selective membrane for efficient lithium-magnesium separation was obtained.

[0105] (7) The electrical properties, ion flux, magnesium retention rate and lithium-magnesium selectivity of the prepared membrane were tested. The results are as follows: Figure 5-Figure 7 shown.

[0106] Comparative Example 3

[0107] Comparative Example 3 shows a method for preparing a monovalent cation selective membrane. Compared with Example 1, the main difference is that the molecular weight of the polyethyleneimine used is not 70,000 MW as specified in Example 1. The preparation process is as follows:

[0108] (1) Preparation of aqueous monomer solution:

[0109] Anhydrous piperazine was dissolved in ultrapure water to obtain a solution concentration of 0.6 wt %;

[0110] (2) Preparation of oil phase monomer solution:

[0111] Take trimesoyl chloride and dissolve it in n-hexane to obtain a solution concentration of 0.1wt%;

[0112] (3) Water phase load:

[0113] Fix the PES ultrafiltration base membrane to a polytetrafluoroethylene mold, inject the aqueous monomer solution, and let it stand for 5 minutes to allow it to completely soak the membrane surface. Then pour out the excess aqueous solution and wipe the membrane surface dry.

[0114] (4) Interface cross-linking:

[0115] Inject the oil phase monomer solution and let it stand for 2 minutes to allow it to react completely. Pour out the excess oil phase solution and wipe the membrane surface dry.

[0116] (5) Post-processing:

[0117] The membrane was placed in an oven and heated at 60°C for 10 min, and then taken out to obtain a polyamide nanofiltration base membrane;

[0118] (6) Multilayer deposition modification:

[0119] Gallic acid was dissolved in a Tris buffer solution with a pH of 8.8, and a certain amount of CuSO4 (5.3 mM) / H2O2 (26.1 mM) was added to accelerate the self-polymerization, and the mixture was thoroughly mixed to obtain a gallic acid solution with a concentration of 1.5 wt%;

[0120] Pour the gallic acid solution evenly on the surface of the nanofiltration base membrane and leave it for 45 minutes to allow the gallic acid to deposit on the surface of the nanofiltration membrane;

[0121] The gallic acid solution on the membrane surface was discarded and the membrane was washed three times with ultrapure water; polyethyleneimine with a molecular weight of 800 MW was dissolved in ultrapure water and mixed thoroughly to obtain a polyethyleneimine solution with a concentration of 1.5 wt%;

[0122] Then pour the polyethyleneimine solution on the membrane surface and heat it in a 60℃ water bath for 120min to deposit the polyethyleneimine on the membrane surface;

[0123] Finally, a monovalent cation selective membrane for efficient lithium-magnesium separation was obtained.

[0124] (7) The electrical properties, ion flux, magnesium retention rate and lithium-magnesium selectivity of the prepared membrane were tested. The results are as follows: Figure 5-Figure 7 shown.

[0125] Depend on Figure 3-Figure 4 It can be seen that compared with Comparative Example 1, the membrane and interface resistance of the monovalent cation selective membrane prepared according to the method of Example 1 are increased, which shows that it has a dense cross-linked layer structure. Figure 2 The cross-sectional scanning electron microscopy results correspond to those of the samples.

[0126] Depend on Figure 5-Figure 6 It can be seen that compared with Comparative Examples 1-3, the monovalent cation selective membrane prepared according to the method of Example 1 has a lower magnesium ion flux (0.10×10-8mol·cm-2·s-1), a higher magnesium retention rate (99.31%) and a higher lithium-magnesium selectivity (49.88), while maintaining a larger lithium ion flux.

[0127] Depend on Figure 7 It can be seen that Example 1 has higher surface electrical properties than Comparative Examples 1 to 3, indicating that the monovalent cation selective membrane prepared according to the method of Example 1 improves the lithium-magnesium separation effect through the combined effects of pore size screening and electrostatic repulsion.

[0128] In summary, the monovalent ion selective membrane prepared by the method of the present invention has the characteristics of high positive charge and high ion flux, has a higher retention rate for magnesium ions in salt lake brine, and can more efficiently separate Li + and Mg 2+ , while maintaining a high lithium ion flux.

[0129] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a monovalent cation selective membrane for efficient lithium-magnesium separation, characterized in that: This is achieved by following these steps: (1) Preparation of aqueous monomer solution: dissolving anhydrous piperazine in ultrapure water to obtain an aqueous monomer solution; (2) Preparation of oil phase monomer solution: Dissolve trimesoyl chloride in n-hexane to obtain an oil phase monomer solution; (3) Water phase load: Fix the PES ultrafiltration base membrane to a polytetrafluoroethylene mold, inject the aqueous monomer solution, let it stand, then pour out the excess aqueous solution and wipe the membrane surface dry; (4) Interface cross-linking: Inject the oil phase monomer solution, let it stand for complete reaction, pour out the excess oil phase solution, and wipe the membrane surface dry; (5) Post-processing: The membrane is placed in an oven for drying and then taken out to obtain a polyamide nanofiltration base membrane; (6) Multilayer deposition modification: Pour the gallic acid solution evenly on the surface of the polyamide nanofiltration base membrane to deposit the gallic acid on the surface of the nanofiltration membrane; Pour off the gallic acid solution on the membrane surface and wash with ultrapure water; Then pour the polyethyleneimine solution on the membrane surface and heat it in a water bath to deposit the polyethyleneimine on the membrane surface; Finally, a monovalent cation selective membrane for efficient lithium-magnesium separation was obtained.

2. The method for preparing a monovalent cation selective membrane for efficient lithium-magnesium separation according to claim 1, characterized in that: The concentration of the aqueous monomer solution in step (1) is 0.5-0.7 wt%.

3. The method for preparing a monovalent cation selective membrane for efficient lithium-magnesium separation according to claim 1, characterized in that: The concentration of the oil phase monomer solution in step (2) is 0.08-0.12 wt%.

4. The method for preparing a monovalent cation selective membrane for efficient lithium-magnesium separation according to claim 1, characterized in that: The aqueous monomer solution in step (3) is allowed to stand on the membrane surface for 4 to 6 minutes.

5. The method for preparing a monovalent cation selective membrane for efficient lithium-magnesium separation according to claim 1, characterized in that: The oil phase monomer solution in step (4) is allowed to stand for 1 to 3 minutes.

6. The method for preparing a monovalent cation selective membrane for efficient lithium-magnesium separation according to claim 1, characterized in that: The drying step (5) is performed at a temperature of 55 to 65° C. and for 8 to 12 minutes.

7. The method for preparing a monovalent cation selective membrane for efficient lithium-magnesium separation according to claim 1, characterized in that: The preparation method of the gallic acid solution in step (6) is as follows: dissolving gallic acid in a Tris buffer solution, then adding CuSO4 / H2O2 to accelerate autopolymerization, and fully mixing to obtain a gallic acid solution; The concentration of the gallic acid solution is 1.3 to 1.7 wt %; Tris buffer solution pH 8.8; The concentration of CuSO4 is 5.1-5.5 mM, and that of H2O2 is 26-26.2 mM; The deposition time of gallic acid solution on the membrane surface is 40 to 50 minutes; Wash with ultrapure water three times.

8. The method for preparing a monovalent cation selective membrane for efficient lithium-magnesium separation according to claim 1, characterized in that: The preparation method of the polyethyleneimine solution in step (6) is as follows: dissolving polyethyleneimine in ultrapure water and mixing thoroughly to obtain the polyethyleneimine solution; The concentration of the polyethyleneimine solution is 1.3-1.7 wt %; The molecular weight of polyethyleneimine is 70,000 Da; The deposition time of polyethyleneimine solution on the membrane surface is 100 to 140 minutes.

9. The method for preparing a monovalent cation selective membrane for efficient lithium-magnesium separation according to claim 1, characterized in that: The temperature of the water bath heating in step (6) is 55-65°C.

10. Use of the monovalent cation selective membrane according to any one of claims 1 to 9 in separating lithium and magnesium in salt lake brine.

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