Lithium ion sieve polymer composite membrane, and preparation method and application thereof

Abstract

This invention provides a lithium-ion sieve polymer composite membrane, its preparation method, and its application. The preparation method includes the following steps: mixing a lithium-ion sieve precursor, a hydrophobic polymer, a solvent, a hydrophilic monomer, and a photoinitiator to obtain a casting solution; casting the casting solution to obtain a wet film; photocuring the wet film, followed by drying and curing, and finally post-treatment to obtain the lithium-ion sieve polymer composite membrane. The preparation method of this invention introduces a hydrophilic monomer, integrating the polymerization and cross-linking process of the hydrophilic monomer into the cross-linking network of the hydrophobic polymer. This not only maintains the mechanical strength of the lithium-ion sieve polymer composite membrane but also improves the wettability of the membrane and exposes more active sites, thereby promoting rapid lithium adsorption. This results in a lithium-ion sieve polymer composite membrane with high mechanical strength, high adsorption capacity, high adsorption kinetics, and high selectivity.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion sieve technology, and relates to a lithium-ion sieve polymer composite membrane, its preparation method and application. Background Technology

[0002] With the rapid development of science and technology in recent years, lithium and its compounds play an extremely important role in chemical, glass, ceramic, metallurgical, pharmaceutical, lubricant, and nuclear energy fields, especially batteries. Currently, lithium resources are mainly stored in salt lake brines. However, due to the low lithium-ion concentration and relatively high impurity content in salt lake brines, there is a need to develop highly selective and efficient lithium extraction technologies from raw salt lake brine. The lithium-ion sieve adsorption method for lithium extraction from salt lakes has advantages such as simple process, low energy consumption, easy scalability, and applicability to low lithium concentration systems, thus possessing industrialization potential.

[0003] Ion sieve powders prepared in existing technologies are typically micron- or nano-sized, resulting in poor flowability and permeability when used directly, and causing significant pressure drops during column adsorption. Therefore, ion sieves need to be shaped before they can function in practical applications. Membrane molding is an emerging method for forming ion sieves, which typically involves dispersing the ion sieve in an organic solvent primarily composed of hydrophobic monomers, followed by solvent evaporation and solidification into a membrane. While ion sieve membranes produced by this method exhibit high mechanical strength and stability, they suffer from low adsorption capacity and slow kinetic performance.

[0004] Based on the above research, there is a need to provide a method for preparing lithium-ion sieves, which can rapidly prepare a lithium-ion sieve membrane with high mechanical strength, high adsorption capacity, high adsorption kinetics, and high selectivity. Summary of the Invention

[0005] The purpose of this invention is to provide a lithium-ion sieve polymer composite membrane, its preparation method, and its application. The preparation method involves introducing hydrophilic monomers, allowing the curing processes of the hydrophilic and hydrophobic monomers to proceed in steps, and integrating the polymerization and crosslinking process of the hydrophilic monomers into the crosslinking network of the hydrophobic polymer. This not only maintains the mechanical strength of the lithium-ion sieve polymer composite membrane but also improves the wettability of the membrane and exposes more active sites, thereby promoting the rapid adsorption of lithium. The resulting lithium-ion sieve polymer composite membrane possesses high mechanical strength, high adsorption capacity, high adsorption kinetics, and high selectivity.

[0006] To achieve this objective, the present invention employs the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a lithium-ion sieve polymer composite membrane, the method comprising the following steps:

[0008] (1) The lithium-ion sieve precursor, hydrophobic polymer, solvent, hydrophilic monomer and photoinitiator are mixed to obtain the casting solution;

[0009] (2) The casting solution described in step (1) is used to form a film to obtain a wet film;

[0010] (3) The wet film described in step (2) is first photocured, then dried and cured, and finally post-processed to obtain the lithium ion sieve polymer composite film.

[0011] This invention prepares a composite membrane using photo-initiated polymerization and solvent evaporation. Photocuring first polymerizes the hydrophilic monomers, followed by drying to evaporate the solvent and solidify the hydrophobic polymer. This allows the solidification processes of the hydrophilic monomers and the hydrophobic polymer to occur stepwise. Furthermore, during photocuring, the hydrophilic monomers polymerize within the cross-linked structure of the hydrophobic polymer, meaning the cross-linking polymerization of the hydrophilic monomers is integrated into the cross-linked network of the hydrophobic polymer. This not only maintains the mechanical strength of the lithium-ion sieve polymer composite membrane but also improves its wettability, creating a richer pore structure and exposing more active sites, thereby promoting rapid lithium adsorption. The result is a lithium-ion sieve polymer composite membrane with both high mechanical strength and stability, as well as high adsorption capacity and rapid kinetic performance.

[0012] Preferably, the mass ratio of the hydrophobic polymer to the hydrophilic monomer in step (1) is 1:(0.5-5), for example, it can be 1:0.5, 1:1, 1:2, 1:3, 1:4 or 1:5, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 1:(1-5).

[0013] The mass ratio of hydrophobic polymer to hydrophilic monomer in this invention affects the wettability and mechanical properties of the lithium-ion sieve polymer composite membrane. If the hydrophilic monomer is relatively small, its effectiveness will decrease. If the hydrophilic monomer is relatively large, the hydrophilic monomer will dissolve in the water, resulting in poor membrane stability, poor mechanical properties, and high swelling rate. This can easily cause the loss of ion sieve powder and affect the service life of the ion sieve composite membrane.

[0014] Preferably, the amount of hydrophilic monomer added in step (1) is 1-50 wt% of the total mass of the casting solution, for example, it can be 1 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, or 50 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 6.25-25 wt%.

[0015] Preferably, the hydrophilic monomer in step (1) is a hydrophilic monomer capable of photoinitiated free radical polymerization, including any one or a combination of at least two of polyvinyl monomers (polyethylene glycol diacrylate, polyethylene glycol acrylate), N-vinylpyrrolidone, acrylic acid, acrylic acid derivatives, methacrylic acid, methacrylic acid derivatives, acrylamide or acrylamide derivatives.

[0016] In the preferred hydrophilic monomers of this invention, the carbon-carbon double bonds in polyvinyl monomers (which can polymerize and can also be used as monomers) can undergo free radical polymerization, the carbon-carbon double bond groups in N-vinylpyrrolidone can undergo free radical polymerization, the carbon-carbon double bonds in polyethylene glycol acrylate (which can polymerize and can also be used as monomers) can undergo free radical polymerization, and the carbon-carbon double bonds in acrylamide can undergo free radical polymerization.

[0017] Preferably, the amount of hydrophobic polymer added in step (1) is 2-90 wt% of the total mass of the casting solution, for example, it can be 2 wt%, 5 wt%, 8 wt%, 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, or 90 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 5-10 wt%.

[0018] Preferably, the hydrophobic polymer in step (1) includes any one or a combination of at least two of polyvinyl chloride, polyacrylonitrile, or polyvinylidene fluoride (PVDF).

[0019] Preferably, the lithium-ion sieve precursor in step (1) includes a manganese-based lithium-ion sieve precursor and / or a titanium-based lithium-ion sieve precursor.

[0020] Preferably, in the lithium-ion sieve polymer composite membrane, the loading of the lithium-ion sieve precursor in step (1) is 20-150 wt%, for example, it can be 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, 90 wt%, 100 wt%, 110 wt%, 120 wt%, 130 wt%, 140 wt%, or 150 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] The loading of the lithium-ion sieve precursor in this invention refers to the percentage of the mass of the lithium-ion sieve precursor to the total mass of the dry film.

[0022] Preferably, the mixing in step (1) includes first mixing the lithium-ion sieve precursor, the hydrophobic polymer and the solvent to obtain a mixture, and then mixing the mixture with the hydrophilic monomer and the photoinitiator.

[0023] Preferably, the solvent in step (1) includes any one or a combination of at least two of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide.

[0024] Preferably, the mass ratio of the hydrophobic polymer to the solvent in step (1) is 1:(5-50), for example, it can be 1:5, 1:10, 1:20, 1:30, 1:40 or 1:50, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] Preferably, the mass ratio of the hydrophilic monomer to the photoinitiator in step (1) is 1:(0.005-0.02), for example, it can be 1:0.005, 1:0.01, 1:0.015 or 1:0.02, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] Preferably, the film-forming method in step (2) includes coating a casting solution onto a glass plate to form a film.

[0027] Preferably, the thickness of the wet film in step (2) is 200-300μm, for example, it can be 200μm, 225μm, 250μm, 275μm or 300μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] Preferably, ultraviolet light is used for the photocuring in step (3);

[0029] Preferably, the power of photocuring in step (3) is 120-280W, for example, 120W, 160W, 200W, 240W or 280W, and the time is 2-5min, for example, 2min, 3min, 4min or 5min, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] Preferably, the drying and curing temperature in step (3) is 50-70℃, for example, 50℃, 55℃, 60℃, 65℃ or 70℃, and the time is 1-5h, for example, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, the post-treatment in step (3) includes washing and acid soaking.

[0032] In a second aspect, the present invention provides a lithium-ion sieve polymer composite membrane, which is prepared by the preparation method described in the first aspect.

[0033] Thirdly, the present invention provides an application of the lithium-ion sieve polymer composite membrane as described in the second aspect, the application including lithium extraction from salt lakes.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The preparation method described in this invention uses hydrophobic polymer and hydrophilic monomer to prepare lithium ion screen polymer composite membrane, which not only ensures the mechanical strength of lithium ion screen composite membrane, but also ensures the contact area between composite membrane and brine, improves mass transfer rate, and can achieve efficient adsorption of lithium.

[0036] (2) The hydrophilic monomers described in this invention polymerize within the cross-linked structure of the hydrophobic polymer, thereby improving the wettability and hydrophilicity of the membrane, increasing the contact area between the lithium ion sieve and the brine, and thus improving the mass transfer rate and adsorption capacity. Furthermore, the adsorption effect and selectivity of the lithium ion sieve polymer composite membrane can be improved by selecting different hydrophilic monomers and controlling their concentration.

[0037] (3) The preparation method described in this invention uses photo-initiated polymerization and solvent evaporation to prepare lithium-ion sieve polymer composite membranes. The preparation process is simple and can be applied industrially. Attached Figure Description

[0038] Figure 1 This is a SEM image of the lithium-ion sieve polymer composite membrane described in Example 1 of the present invention. Detailed Implementation

[0039] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0040] Example 1

[0041] This embodiment provides a method for preparing a lithium-ion sieve polymer composite membrane, the method comprising the following steps:

[0042] (1) Add 3g of polyvinyl chloride powder and 6g of lithium ion sieve precursor Li2TiO3 to 48g of N,N-dimethylformamide solution. Under room temperature conditions, use ultrasonic dispersion technology to uniformly disperse the powder in the solution. Then use a mechanical stirrer to stir at room temperature for 12h to ensure that the mixture is completely uniform.

[0043] In step (1), the amount of polyvinyl chloride added is 5 wt% of the total mass of the casting solution, the loading of the lithium ion sieve precursor is 40 wt%, and the mass ratio of the polyvinyl chloride powder to N,N-dimethylformamide is 1:16.

[0044] (2) Add 6g of polyethylene glycol diacrylate (PEGDA600) and 60mg of photoinitiator 2959 to the above homogeneous mixture, and continue mechanical stirring at room temperature for 24h to ensure that all components are fully mixed and a homogeneous casting solution is formed.

[0045] The photoinitiator 2959 is 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone;

[0046] The mass ratio of polyvinyl chloride to polyethylene glycol diacrylate is 1:2;

[0047] The amount of polyethylene glycol diacrylate added is 10 wt% of the total mass of the casting solution;

[0048] The mass ratio of polyethylene glycol diacrylate to photoinitiator is 1:0.01;

[0049] (3) The prepared casting solution is evenly coated on a glass plate, the wet film thickness is controlled to be 300 μm, and the coated wet film is placed under a 150W ultraviolet lamp for 3 min of UV curing.

[0050] (4) Transfer the UV-cured wet film to an oven at 60°C and continue curing for 4 hours to ensure that the material is completely cured.

[0051] (5) After drying, the membrane is washed and acid-leached to obtain the lithium-ion sieve polymer composite membrane. The SEM image of the lithium-ion sieve polymer composite membrane is shown below. Figure 1 As shown.

[0052] Example 2

[0053] This embodiment provides a method for preparing a lithium-ion sieve polymer composite membrane, the method comprising the following steps:

[0054] (1) Add 3g of polyvinyl chloride powder and 60g of lithium ion sieve precursor Li2TiO3 to 60mL of N,N-dimethylformamide solution. At room temperature, use ultrasonic dispersion technology to uniformly disperse the powder in the solution. Then use a mechanical stirrer to stir at room temperature for 12h to ensure that the mixture is completely uniform.

[0055] In step (1), the amount of polyvinyl chloride added is 5 wt% of the total mass of the casting solution, the loading of the lithium ion sieve precursor is 70 wt%, and the mass ratio of the polyvinyl chloride powder to N,N-dimethylformamide is 1:20.

[0056] (2) Add 15g of polyethylene glycol diacrylate (PEGDA600) and 300mg of photoinitiator 2959 to the above homogeneous mixture, and continue mechanical stirring at room temperature for 24h to ensure that all components are fully mixed and a homogeneous casting solution is formed.

[0057] The photoinitiator 2959 is 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone;

[0058] The mass ratio of polyvinyl chloride to polyethylene glycol diacrylate is 1:5;

[0059] The amount of polyethylene glycol diacrylate added is 25 wt% of the total mass of the casting solution;

[0060] The mass ratio of polyethylene glycol diacrylate to photoinitiator is 1:0.02;

[0061] (3) The prepared casting solution is evenly coated on a glass plate, the wet film thickness is controlled to be 200μm, and the coated wet film is placed under a 280W ultraviolet lamp for 2min of UV curing.

[0062] (4) Transfer the UV-cured wet film to an oven at 70°C and continue curing for 3 hours to ensure that the material is completely cured.

[0063] (5) After drying, the membrane is washed and acid-soaked to obtain the lithium ion sieve polymer composite membrane.

[0064] Example 3

[0065] This embodiment provides a method for preparing a lithium-ion sieve polymer composite membrane, the method comprising the following steps:

[0066] (1) Add 3g of polyvinylidene fluoride powder (PVDF) and 6g of lithium ion sieve precursor Li2TiO3 to 36mL of N,N-dimethylformamide solution. At room temperature, use ultrasonic dispersion technology to uniformly disperse the powder in the solution. Then use a mechanical stirrer to stir at room temperature for 12h to ensure that the mixture is completely homogeneous.

[0067] The amount of polyvinylidene fluoride added in step (1) is 6.25 wt% of the total mass of the casting solution, the loading of the lithium ion sieve precursor is 40 wt%, and the mass ratio of the polyvinylidene fluoride powder to N,N-dimethylformamide is 1:12.

[0068] (2) Add 3g of polyethylene glycol diacrylate (PEGDA600) and 15mg of photoinitiator 2959 to the above homogeneous mixture, and continue mechanical stirring at room temperature for 24h to ensure that all components are fully mixed and a homogeneous casting solution is formed.

[0069] The photoinitiator 2959 is 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone;

[0070] The mass ratio of polyvinylidene fluoride to polyethylene glycol diacrylate is 1:1;

[0071] The amount of polyethylene glycol diacrylate added is 6.25 wt% of the total mass of the casting solution;

[0072] The mass ratio of polyethylene glycol diacrylate to photoinitiator is 1:0.005;

[0073] (3) The prepared casting solution is evenly coated on a glass plate, the wet film thickness is controlled to be 250 μm, and the coated wet film is placed under a 120W ultraviolet lamp for 5 min of UV curing.

[0074] (4) Transfer the UV-cured wet film to an oven at 50°C and continue curing for 5 hours to ensure that the material is completely cured.

[0075] (5) After drying, the membrane is washed and acid-soaked to obtain the lithium ion sieve polymer composite membrane.

[0076] Example 4

[0077] This embodiment provides a method for preparing a lithium-ion screen polymer composite membrane. The preparation method is the same as in Example 1, except that the mass ratio of polyvinyl chloride to polyethylene glycol diacrylate is 1:0.5 and the amount of hydrophilic monomer polyethylene glycol diacrylate added is reduced.

[0078] Example 5

[0079] This embodiment provides a method for preparing a lithium-ion screen polymer composite membrane. The preparation method is the same as in Example 1, except that the mass ratio of polyvinyl chloride to polyethylene glycol diacrylate is 1:7 and the amount of hydrophilic monomer polyethylene glycol diacrylate added is increased.

[0080] Example 6

[0081] This embodiment provides a method for preparing a lithium-ion screen polymer composite membrane. The preparation method is the same as in Example 1, except that polyethylene glycol diacrylate is replaced by N-vinylpyrrolidone.

[0082] Example 7

[0083] This embodiment provides a method for preparing a lithium-ion screen polymer composite membrane. The preparation method is the same as in Example 1, except that polyethylene glycol diacrylate is replaced with polyethylene glycol acrylate by mass.

[0084] Example 8

[0085] This embodiment provides a method for preparing a lithium-ion screen polymer composite membrane. The preparation method is the same as in Example 1, except that polyethylene glycol diacrylate is replaced by acrylamide.

[0086] Comparative Example 1

[0087] This comparative example provides a method for preparing a lithium-ion sieve polymer composite membrane. The preparation method is the same as that in Example 1 except that the UV curing described in steps (2) and (3) is not performed. That is, this comparative example does not add hydrophilic monomers and photoinitiators, nor does it perform UV curing.

[0088] The above examples and comparative examples tested the adsorption capacity of the lithium-ion sieve polymer composite membrane. The test method included: exposing the lithium-ion sieve polymer composite membrane to 50 mg·L⁻¹ water. -1 The LiCl solution (pH = 13) was prepared at 1 g·L⁻¹ -1 The lithium-ion sieve polymer composite membrane was mixed in a ratio (calculated based on the volume of the ion sieve) and kept fully agitated in the solution at room temperature. The uniformly agitated solution was sampled at specific time intervals to determine the Li concentration in the solution at this time. The adsorption capacity of the ion sieve membrane was calculated, and the adsorption capacity-time curve was plotted to obtain the adsorption equilibrium time and equilibrium concentration of the lithium-ion sieve membrane. The test results are shown in Table 1.

[0089] Table 1

[0090]

[0091]

[0092] As can be seen from Table 1:

[0093] As can be seen from Example 1 and Comparative Example 1, the preparation method of the present invention significantly improves the adsorption capacity of the lithium-ion sieve polymer composite membrane and reduces the adsorption equilibrium time by adding a hydrophilic monomer to the casting solution and polymerizing it in the cross-linked network of the hydrophobic polymer through photocuring. As can be seen from Example 1 and Examples 4-5, the amount of hydrophilic monomer added in the present invention affects the performance of the lithium-ion sieve polymer composite membrane. As can be seen from Example 1 and Examples 6-8, the performance of the lithium-ion sieve polymer composite membrane also changes when the type of hydrophilic monomer changes. Since PEGDA600 has a higher adsorption capacity and a faster equilibrium time, the preferred hydrophilic monomer of the present invention is PEGDA600.

[0094] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a lithium ion sieve polymer composite membrane, characterized by, The preparation method includes the following steps: (1) The lithium-ion sieve precursor, hydrophobic polymer, solvent, hydrophilic monomer and photoinitiator are mixed to obtain the casting solution; (2) The casting solution described in step (1) is used to form a film to obtain a wet film; (3) The wet film described in step (2) is first photocured, then dried and cured, and finally post-treated to obtain the lithium ion sieve polymer composite film. The mass ratio of the hydrophobic polymer to the hydrophilic monomer in step (1) is 1:(2-5); The hydrophilic monomer in step (1) is polyethylene glycol diacrylate and / or polyethylene glycol acrylate; The mixing in step (1) includes first mixing the lithium-ion sieve precursor, the hydrophobic polymer and the solvent to obtain a mixture, and then mixing the mixture with the hydrophilic monomer and the photoinitiator; The hydrophobic polymer in step (1) includes any one or a combination of at least two of polyvinyl chloride, polyacrylonitrile, or polyvinylidene fluoride; The lithium-ion sieve precursor in step (1) includes manganese-based lithium-ion sieve precursor and / or titanium-based lithium-ion sieve precursor. The post-treatment described in step (3) includes washing and acid leaching.

2. The production method according to claim 1, characterized by, The amount of hydrophilic monomer added in step (1) is 1-50 wt% of the total mass of the casting solution.

3. The preparation method according to claim 2, characterized in that, The amount of hydrophilic monomer added in step (1) is 6.25-25 wt% of the total mass of the casting solution.

4. The preparation method according to claim 1, characterized in that, The amount of hydrophobic polymer added in step (1) is 5-10 wt% of the total mass of the casting solution.

5. The preparation method according to claim 1, characterized in that, In the lithium-ion sieve polymer composite membrane, the loading of the lithium-ion sieve precursor in step (1) is 20-70 wt%.

6. The preparation method according to claim 1, characterized in that, The solvent in step (1) includes any one or a combination of at least two of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide.

7. The preparation method according to claim 1, characterized in that, The mass ratio of the hydrophobic polymer to the solvent in step (1) is 1:(5-50).

8. The preparation method according to claim 1, characterized in that, The mass ratio of the hydrophilic monomer to the photoinitiator in step (1) is 1:(0.005-0.02).

9. The preparation method according to claim 1, characterized in that, The method for forming a film in step (2) includes coating a casting solution onto a glass plate to form a film.

10. The preparation method according to claim 1, characterized in that, The thickness of the wet film in step (2) is 200-300 μm.

11. The preparation method according to claim 1, characterized in that, The photocuring in step (3) is performed using ultraviolet light.

12. The preparation method according to claim 1, characterized in that, The power of photocuring in step (3) is 120-280W, and the time is 2-5min.

13. The preparation method according to claim 1, characterized in that, The drying and curing temperature in step (3) is 50-70℃, and the time is 1-5h.

14. A lithium-ion sieve polymer composite membrane, characterized in that, The lithium-ion sieve polymer composite membrane is prepared by the preparation method described in any one of claims 1-13.

15. An application of the lithium-ion sieve polymer composite membrane as described in claim 14, characterized in that, The applications include lithium extraction from salt lakes.

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