Polyamide nanofiltration membrane for magnesium-lithium separation and preparation method thereof

Abstract

The invention provides a magnesium-lithium separation polyamide nanofiltration membrane and a preparation method thereof. The polyamide nanofiltration membrane is doped with an aminated MXene two-dimensional material. The preparation method comprises the following steps: mixing the aminated MXene two-dimensional material, an amino monomer and water to obtain a water-phase membrane casting solution; mixing an acyl chloride monomer with a non-aqueous solvent to obtain an oil-phase membrane casting solution; sequentially soaking a base membrane in the water-phase membrane casting solution and the oil-phase membrane casting solution, and drying to obtain the magnesium-lithium separation polyamide nanofiltration membrane. The positive charge of the magnesium-lithium separation polyamide nanofiltration membrane is effectively enhanced, and the surface charge density is increased, so that the magnesium-lithium separation performance is enhanced.

Description

Technical Field

[0001] The invention belongs to the technical field of nanofiltration membrane development and relates to a magnesium-lithium separation polyamide nanofiltration membrane and a preparation method thereof. Background Art

[0002] Lithium resources are crucial to the development of industries such as new energy and aerospace. As the world's largest consumer of lithium resources, China is highly dependent on foreign suppliers, severely impacting national security and industrial development. Therefore, developing lithium resources found in salt lakes and oil and gas field brines is of strategic importance.

[0003] The core of lithium extraction technology from brine lies in the separation of magnesium and lithium, which currently mainly includes extraction, adsorption, membrane separation, electrochemical deintercalation, electrodialysis, etc. Among them, membrane separation technology based on nanofiltration membrane has the advantages of low cost, simple process, easy operation, and green environmental protection. It is an important development direction for the separation of magnesium and lithium from brine in the future. Nanofiltration membrane materials have nanoscale pores and carry charges on the surface. They can intercept Mg and Li under the combined action of pore size screening effect, Donnan effect, dielectric effect and other factors. 2+ Among various nanofiltration membranes, polyamide nanofiltration membranes, made from the polymerization of amine monomers and acyl chloride monomers, are the most widely used. However, commercial polyamide nanofiltration membranes are primarily negatively charged, making them unsuitable for separating magnesium and lithium from brine, and also struggle to balance permeability and selectivity.

[0004] The development of positively charged nanofiltration membranes by improving monomers and surface grafting modification is an important method for improving the magnesium-lithium separation performance of polyamide nanofiltration membranes. CN115738742B uses polyethyleneimine (PEI), cyclodextrin and carbonate as aqueous phase monomers to develop a positively charged membrane for lithium extraction from salt lakes. CN115105973B uses PEI and piperazine hexahydrate (PIP) as aqueous phase monomers to participate in interfacial polymerization, and then amino ionic liquid is modified to obtain a nanofiltration membrane for efficient magnesium-lithium separation. However, it is difficult to comprehensively improve the separation performance of the composite nanofiltration membrane after monomer improvement, and methods such as surface grafting modification are cumbersome and not conducive to large-scale production. Doping modification is an important way to improve the separation performance of polyamide composite nanofiltration membranes. CN116803474A uses boron nitride nanosheets and CN116531956A uses graphite carbon nitride, but these methods are difficult to effectively improve the magnesium-lithium separation performance. CN105597567B uses two-dimensional material MXene to fill PEI to prepare an organic-inorganic hybrid solvent-resistant nanofiltration composite membrane, but the simple MXene composite does not effectively improve the magnesium-lithium separation performance.

[0005] Therefore, it is necessary to develop a new method for preparing a composite polyamide nanofiltration membrane with both high magnesium-lithium separation performance and permeation flux. Summary of the Invention

[0006] In order to solve the above technical problems, the present application provides a magnesium-lithium separation polyamide nanofiltration membrane and a preparation method thereof. The magnesium-lithium separation polyamide nanofiltration membrane has effectively enhanced positive charge and increased surface charge density, thereby enhancing the magnesium-lithium separation performance.

[0007] In order to achieve the above technical effects, the present invention adopts the following technical solutions:

[0008] One of the objectives of the present invention is to provide a polyamide nanofiltration membrane for magnesium-lithium separation, wherein the polyamide nanofiltration membrane is doped with an amino-modified MXene two-dimensional material.

[0009] As a preferred technical solution of the present invention, the amino MXene two-dimensional material includes amino Ti3C2 and / or amino Ti2C.

[0010] A second object of the present invention is to provide a method for preparing a polyamide nanofiltration membrane for magnesium-lithium separation, the preparation method comprising:

[0011] Mixing the amino-modified MXene two-dimensional material, an amino monomer, and water to obtain an aqueous casting solution;

[0012] mixing the acyl chloride monomer with a non-aqueous solvent to obtain an oil-phase casting solution;

[0013] The base membrane is sequentially immersed in the aqueous phase casting solution and the oil phase casting solution, and then dried to obtain the magnesium-lithium separation polyamide nanofiltration membrane.

[0014] As a preferred technical solution of the present invention, the mass ratio of the amino monomer to the amino-modified MXene two-dimensional material is 100:2 to 5, such as 100:2, 100:2.5, 100:3, 100:3.5, 100:4, 100:4.5 or 100:5, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0015] As a preferred technical solution of the present invention, the concentration of the amino monomer in the aqueous casting solution is 0.02 to 0.2 wt%, such as 0.02 wt%, 0.05 wt%, 0.08 wt%, 0.1 wt%, 0.12 wt%, 0.15 wt%, 0.18 wt% or 0.2 wt%, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0016] As a preferred technical solution of the present invention, the concentration of the acyl chloride monomer in the oil phase casting solution is 0.1 to 0.3 wt%, such as 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt% or 0.3 wt%, etc., but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0017] As a preferred technical solution of the present invention, the amino monomer includes polyethyleneimine.

[0018] Preferably, the number average molecular weight of the polyethyleneimine is 5000 to 25000, such as 5000, 6000, 8000, 10000, 12000, 15000, 20000, 22000 or 25000, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0019] Preferably, the acyl chloride monomer comprises trimesoyl chloride.

[0020] Preferably, the non-aqueous solvent comprises cyclohexane.

[0021] As a preferred technical solution of the present invention, the time for the base membrane to be immersed in the aqueous casting liquid is 10 to 20 minutes, such as 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes or 20 minutes, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0022] Preferably, the base film is immersed in the oil phase casting liquid for 10 to 20 minutes, such as 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes or 20 minutes, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0023] As a preferred technical solution of the present invention, the base membrane is soaked in water for 10 to 20 minutes before being immersed in the aqueous casting liquid, such as 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes or 20 minutes, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] As a preferred technical solution of the present invention, the base membrane includes a polysulfone filter membrane or a polyethersulfone filter membrane.

[0025] Compared with the prior art, the present invention has at least the following beneficial effects:

[0026] (1) The present invention provides a polyamide nanofiltration membrane for separating magnesium and lithium and a preparation method thereof, wherein the polyamide nanofiltration membrane for separating magnesium and lithium effectively enhances positive charge and increases surface charge density, thereby enhancing magnesium and lithium separation performance;

[0027] (2) The present invention provides a magnesium-lithium separation polyamide nanofiltration membrane and a preparation method thereof. The magnesium-lithium separation polyamide nanofiltration membrane constructs a long-range continuous solvent molecule transmission channel inside the nanofiltration membrane, which is beneficial to improving the permeation flux of the composite separation membrane and improving the separation efficiency. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described below through specific implementation methods.

[0029] A specific embodiment of the present invention provides a polyamide nanofiltration membrane for magnesium-lithium separation, wherein the polyamide nanofiltration membrane is doped with an amino-modified MXene two-dimensional material.

[0030] In the present invention, the amino-modified MXene nanomaterial has a two-dimensional structure, strong hydrophilicity, and a large specific surface area. At the same time, the amino groups on the surface can effectively enhance the positive charge of the polyamide nanofiltration membrane layer, increase the surface charge density, and enhance the magnesium-lithium separation performance; at the same time, the two-dimensional MXene material constructs a long-range continuous solvent molecule transfer channel inside the nanofiltration membrane, which is beneficial to improving the permeation flux of the composite separation membrane and improving the separation efficiency.

[0031] A specific embodiment of the present invention provides a method for preparing a polyamide nanofiltration membrane for magnesium-lithium separation, the preparation method comprising:

[0032] Mixing the amino-modified MXene two-dimensional material, an amino monomer, and water to obtain an aqueous casting solution;

[0033] mixing the acyl chloride monomer with a non-aqueous solvent to obtain an oil-phase casting solution;

[0034] The base membrane is sequentially immersed in the aqueous phase casting solution and the oil phase casting solution, and then dried to obtain the magnesium-lithium separation polyamide nanofiltration membrane.

[0035] In one embodiment of the present invention, the amino-modified MXene two-dimensional material, the amino monomer, and water are ultrasonically mixed. The time and frequency of ultrasonic mixing can be specifically selected based on the amount of the amino-modified MXene two-dimensional material and the amino monomer used, and are not further limited herein. The ultrasonic mixing time can be 10 to 60 minutes, such as 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, or 60 minutes, but is not limited to the values ​​listed above. Other values ​​not listed within this numerical range are also applicable.

[0036] In one embodiment of the present invention, the base film is fixed in a mold before being soaked.

[0037] In a specific embodiment of the present invention, the size of the base film can be specifically selected according to product requirements and is not further limited herein. Specifically, it can be a square base film with a side length of 5 cm.

[0038] In one embodiment of the present invention, parameters such as the molecular cutoff and thickness of the basement membrane can also be specifically selected based on product requirements and are not further limited herein. Specifically, the molecular cutoff can be ≥10 kDa, such as 10 kDa, 15 kDa, 20 kDa, 25 kDa, 30 kDa, 35 kDa, 40 kDa, 45 kDa, or 50 kDa, and the thickness can be 0.1 to 0.5 mm, such as 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, or 0.5 mm, but are not limited to the values ​​listed above. Other values ​​not listed within the above ranges are also applicable.

[0039] In one embodiment of the present invention, the polyamide nanofiltration membrane is obtained by polymerizing an amino monomer and an acyl chloride monomer at the interface of the base membrane.

[0040] In a specific embodiment of the present invention, the thickness of the composite nanofiltration layer formed by interfacial polymerization can be 300 to 800 nm, such as 300 nm, 400 nm, 500 nm, 600 nm, 700 nm or 800 nm, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0041] In one embodiment of the present invention, the drying conditions may be drying at 20-30°C for 20-30 minutes, followed by drying at 50-70°C for 1-3 hours, specifically drying at 25°C for 25 minutes, followed by drying at 60°C for 2 hours.

[0042] For the convenience of understanding the present invention, the present invention is given below with examples. It should be understood by those skilled in the art that the examples are only for the purpose of helping to understand the present invention and should not be regarded as specific limitations of the present invention.

[0043] Example 1

[0044] This embodiment provides a method for preparing a polyamide nanofiltration membrane for magnesium-lithium separation, the preparation method comprising:

[0045] (1) A monolayer of amino-modified Ti3C2 MXene two-dimensional material and PEI were ultrasonically mixed in deionized water to form an aqueous casting solution, wherein the mass ratio of PEI to amino-modified MXene was 100:3, the molecular weight of PEI was 15000, the concentration was 0.1 wt.%, and the ultrasonic time was 30 min;

[0046] (2) dissolving trimesoyl chloride (TMC) in cyclohexane at a concentration of 0.2 wt.% to obtain an oil-phase casting solution;

[0047] (3) A 5 cm square polysulfone filter membrane base membrane with a molecular cutoff of 20 kDa and a thickness of 0.2 mm was fixed in a mold. Deionized water was added and soaked for 15 min, then the membrane was poured out. The aqueous casting solution was poured in until the membrane was completely covered. After 15 min, the excess aqueous casting solution was poured out. Then, the oil casting solution was poured in and poured out after 10 min to complete the interfacial polymerization process.

[0048] (4) The film after the interfacial polymerization was dried at 25°C for 25 min and then dried at 60°C for 2 h to obtain an amino-modified MXene-doped magnesium-lithium separation polyamide nanofiltration membrane.

[0049] The performance of the aminated MXene-doped polyamide nanofiltration membrane for magnesium-lithium separation was tested by cross-flow filtration. The feed solution was a mixed solution of magnesium chloride and lithium chloride, with a total salt concentration of 2 mg / mL and a magnesium-lithium ratio of 50. The cross-flow filtration test pressure was 0.5 MPa and the temperature was 30°C. The measured magnesium-lithium separation factor of the aminated MXene-doped polyamide nanofiltration membrane for magnesium-lithium separation was 22, and the membrane flux was 10.5 L / m 2 ·h·bar.

[0050] The calculation method of magnesium-lithium separation factor (S) is:

[0051] Among them, C f / mg and C f / Li with C p / mg and C p / Li are the concentrations of magnesium and lithium ions in the feed solution and permeate, respectively;

[0052] The calculation method of permeation flux (J) is:

[0053] Where J is the permeation flux, s is the effective area of ​​the membrane (cm 2 ), t is the operation time, and V is the volume of liquid that passes through during t time (L).

[0054] Example 2

[0055] This embodiment provides a method for preparing a polyamide nanofiltration membrane for magnesium-lithium separation, the preparation method comprising:

[0056] (1) A single-layer amino-modified Ti2C MXene two-dimensional material and PEI were ultrasonically mixed in deionized water to form an aqueous casting solution, wherein the mass ratio of PEI to amino-modified MXene was 100:2, the molecular weight of PEI was 25000, the concentration was 0.2 wt.%, and the ultrasonic time was 30 min.

[0057] (2) dissolving trimesoyl chloride (TMC) in cyclohexane at a concentration of 0.3 wt.% to obtain an oil-phase casting solution;

[0058] (3) A 5 cm square polysulfone filter base membrane with a molecular cutoff of 50 kDa and a thickness of 0.2 mm was fixed in a mold. Deionized water was added and soaked for 15 min, then the membrane was poured out. The aqueous casting solution was poured in until the membrane was completely covered. After 15 min, the excess aqueous casting solution was poured out. Then, the oil casting solution was poured in and poured out after 10 min to complete the interfacial polymerization process.

[0059] (4) Drying the film after the interfacial polymerization at 25°C for 25 minutes and then at 60°C for 2 hours to obtain an amino-modified MXene-doped polyamide nanofiltration membrane for magnesium-lithium separation;

[0060] The performance of the aminated MXene-doped polyamide nanofiltration membrane for magnesium-lithium separation was tested by cross-flow filtration. The feed solution was a mixed solution of magnesium chloride and lithium chloride, with a total salt concentration of 2 mg / mL and a magnesium-lithium ratio of 50. The cross-flow filtration test pressure was 0.5 MPa and the temperature was 30°C. The measured magnesium-lithium separation factor of the aminated MXene-doped polyamide nanofiltration membrane for magnesium-lithium separation was 26, and the membrane flux was 5.2 L / m 2 ·h·bar.

[0061] Example 3

[0062] This embodiment provides a method for preparing a polyamide nanofiltration membrane for magnesium-lithium separation, the preparation method comprising:

[0063] (1) A monolayer of amino-modified Ti3C2 MXene two-dimensional material and PEI were ultrasonically mixed in deionized water to form an aqueous casting solution, wherein the mass ratio of PEI to amino-modified MXene was 100:5, the molecular weight of PEI was 5000, the concentration was 0.05 wt.%, and the ultrasonic time was 30 min;

[0064] (2) dissolving trimesoyl chloride (TMC) in cyclohexane at a concentration of 0.1 wt.% to obtain an oil-phase casting solution;

[0065] (3) A 5 cm square polysulfone filter base membrane with a molecular cutoff of 10 kDa and a thickness of 0.2 mm was fixed in a mold. Deionized water was added and soaked for 15 min, then the membrane was poured out. The aqueous casting solution was poured in until the membrane was completely covered. After 15 min, the excess aqueous casting solution was poured out. Then, the oil casting solution was poured in and poured out after 10 min to complete the interfacial polymerization process.

[0066] (4) Drying the film after the interfacial polymerization at 25°C for 25 minutes and then at 60°C for 2 hours to obtain an amino-modified MXene-doped polyamide nanofiltration membrane for magnesium-lithium separation;

[0067] The performance of the aminated MXene-doped polyamide nanofiltration membrane for magnesium-lithium separation was tested by cross-flow filtration. The feed solution was a mixed solution of magnesium chloride and lithium chloride, with a total salt concentration of 2 mg / mL and a magnesium-lithium ratio of 50. The cross-flow filtration test pressure was 0.5 MPa and the temperature was 30°C. The measured magnesium-lithium separation factor of the aminated MXene-doped polyamide nanofiltration membrane for magnesium-lithium separation was 18, and the membrane flux was 14.6 L / m 2 ·h·bar.

[0068] Example 4

[0069] In this embodiment, except that the mass ratio of PEI to amino-modified MXene in step (1) is 100:5, the molecular weight of PEI is 25,000, and the concentration is 0.02 wt.%, the other conditions are the same as those in Example 1.

[0070] The performance of the aminated MXene-doped polyamide nanofiltration membrane for magnesium-lithium separation was tested by cross-flow filtration. The feed solution was a mixed solution of magnesium chloride and lithium chloride, with a total salt concentration of 2 mg / mL and a magnesium-lithium ratio of 50. The cross-flow filtration test pressure was 0.5 MPa and the temperature was 30°C. The measured magnesium-lithium separation factor of the aminated MXene-doped polyamide nanofiltration membrane for magnesium-lithium separation was 21, and the membrane flux was 11.3 L / m 2 ·h·bar.

[0071] Comparative Example 1

[0072] In this comparative example, except that the monolayer of amino-treated Ti3C2 MXene two-dimensional material is not added in step (1), the other conditions are the same as those in Example 1.

[0073] Under the same test conditions, due to the lack of MXene surface amino groups and solvent pathways constructed by two-dimensional nanosheets, the magnesium-lithium separation factor dropped to 18 and the membrane flux was 8.5 L / m 2 ·h·bar.

[0074] Comparative Example 2

[0075] In this comparative example, except that PEI is replaced by piperazine in step (1), the other conditions are the same as those in Example 1.

[0076] Under the same test conditions, the magnesium-lithium separation factor dropped to 5, and the membrane flux was 9.6 L / m 2 ·h·bar.

[0077] Comparative Example 3

[0078] In this comparative example, except that the mass ratio of PEI to amino-modified MXene in step (1) is 100:1, the other conditions are the same as those in Example 1.

[0079] Under the same test conditions, the magnesium-lithium separation factor dropped to 8, and the membrane flux was 18.5L / m 2 ·h·bar.

[0080] The applicant declares that the present invention uses the above-described embodiments to illustrate the detailed process equipment and process flow of the present invention. However, the present invention is not limited to the above-described detailed process equipment and process flow, and does not necessarily rely on the above-described detailed process equipment and process flow in order to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent replacements for the raw materials of the present invention's products, additions of auxiliary ingredients, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A polyamide nanofiltration membrane for separating magnesium and lithium, characterized in that: The polyamide nanofiltration membrane is doped with amino-modified MXene two-dimensional material.

2. The magnesium-lithium separation polyamide nanofiltration membrane according to claim 1, characterized in that The amino-modified MXene two-dimensional material includes amino-modified Ti3C2 and / or amino-modified Ti2C.

3. A method for preparing a polyamide nanofiltration membrane for magnesium-lithium separation according to claim 1 or 2, characterized in that: The preparation method comprises: Mixing the amino-modified MXene two-dimensional material, an amino monomer, and water to obtain an aqueous casting solution; mixing the acyl chloride monomer with a non-aqueous solvent to obtain an oil-phase casting solution; The base membrane is sequentially immersed in the aqueous phase casting solution and the oil phase casting solution, and then dried to obtain the magnesium-lithium separation polyamide nanofiltration membrane.

4. The preparation method according to claim 3, characterized in that The mass ratio of the amino monomer to the amino-modified MXene two-dimensional material is 100:2-5.

5. The preparation method according to claim 3 or 4, characterized in that The concentration of the amino monomer in the aqueous casting solution is 0.02-0.2 wt %.

6. The preparation method according to any one of claims 3 to 5, characterized in that The concentration of the acyl chloride monomer in the oil phase casting solution is 0.1-0.3 wt %.

7. The preparation method according to any one of claims 3 to 6, characterized in that The amino monomer includes polyethyleneimine; Preferably, the number average molecular weight of the polyethyleneimine is 5000 to 25000; Preferably, the acyl chloride monomer comprises trimesoyl chloride; Preferably, the non-aqueous solvent comprises cyclohexane.

8. The preparation method according to any one of claims 3 to 7, characterized in that The base film is immersed in the aqueous casting solution for 10 to 20 minutes; Preferably, the base film is immersed in the oil-phase casting solution for 10 to 20 minutes.

9. The preparation method according to any one of claims 3 to 8, characterized in that The base film is soaked in water for 10 to 20 minutes before being soaked in the aqueous casting solution.

10. The preparation method according to any one of claims 3 to 9, characterized in that: The base membrane includes a polysulfone filter membrane or a polyethersulfone filter membrane.