A crystalline porous polymer composite membrane for lithium-magnesium separation and a preparation method thereof

Abstract

The application discloses a kind of crystal porous polymer composite membranes for lithium-magnesium separation and preparation method thereof, and the composite membrane includes a porous substrate film playing a supporting role and a covalent organic framework porous polymer crystal film covered thereon, and the surface defects of the crystal film are covered and plugged by the ultra-thin polymer film generated by interface condensation.The application covers and plugs the gap defects by the interface condensation film means of two reaction monomers at the film defect position of grain gap and growth discontinuity, and the processing mode only needs to immerse the crystal film with defects in aqueous solution and oil phase solution containing reaction monomers in sequence to quickly complete the repair of surface defects, and the method is simple in operation, low in cost and strong in universality.

Description

Technical Field

[0001] This invention relates to the field of separation membrane technology, and in particular to a crystalline porous polymer composite membrane for lithium-magnesium separation and its preparation method. Background Technology

[0002] Two-dimensional covalent organic frameworks (COFs) are a class of crystalline porous polymer materials linked by covalent bonds. Due to their advantages such as low density, high porosity, regular pore structure, and functionalizability, they have become a highly sought-after membrane material. COF films with nanoscale regular pores show great promise for applications in molecular sieving, electronic devices, chemical sensors, and photocatalysts.

[0003] However, COFs, as crystalline separation membrane materials, face the challenge of being difficult to process into films. Previously, researchers conveniently prepared mixed matrix membranes by doping COFs into matrices such as polymers (Chem.Eur.J.,2016,22(14):4695-4699). Although this strategy can yield films containing COFs, it does not solve the fundamental problem of poor film-forming properties of COFs themselves, and the composite system cannot reflect the performance advantages of COFs materials. COFs films prepared using crystal growth methods can maintain the crystalline properties of COFs (Matter,4(2021)2027-2038), but there is a fatal problem that limits the practical application of this type of film, namely, there must be obvious grain gaps between the grains that make up the COFs film, and the size of these gaps (>10nm) is significantly larger than the pore size of COFs (0.5-5.0nm). For COFs films with nanoscale pores, these gaps are defects and weak points that are the first to break under stress. Furthermore, bending is inevitable during film preparation and application; this deformation is fatal to crystalline films, inevitably causing tearing at grain boundaries and leading to film failure, thus preventing the utilization of the advantages of nanopores. Currently, there are no measures to eliminate the performance impact of grain gaps in COFs films, thus limiting the large-scale application of COFs films. Summary of the Invention

[0004] This invention addresses the inherent defects in porous polymer crystalline membranes, such as intergranular gaps and growth discontinuities, which are common in existing technologies. The invention utilizes interfacial polycondensation of two reactive monomers to cover and seal these defects at their locations. This method involves rapidly repairing the surface defects by sequentially immersing the defective crystalline membrane in an aqueous solution and an oil solution containing the reactive monomers. The method is simple to operate, low in cost, and highly versatile.

[0005] To solve the above-mentioned technical problems, the present invention provides a crystalline porous polymer composite membrane for lithium-magnesium separation, comprising a porous substrate membrane that provides support and a covalent organic framework porous polymer crystalline thin film covering it. The covalent organic framework porous polymer crystalline thin film is defined as a crystalline thin film, and the surface defects of the crystalline thin film are covered and sealed by an ultrathin polymer thin film generated by interfacial condensation.

[0006] Furthermore, the ultrathin polymer films formed by interfacial polycondensation include aromatic polyamides or semi-aromatic polyamides.

[0007] Furthermore, the aromatic polyamide is formed by an interfacial polycondensation reaction between an aromatic binary or polyamine and an aromatic binary or polyacryl chloride.

[0008] The semi-aromatic polyamide is formed by interfacial polycondensation reaction of piperazine and its derivatives alicyclic or aliphatic binary or polyamines with binary or polyacyl chlorides.

[0009] The present invention also provides a method for preparing the crystalline porous polymer composite membrane for lithium-magnesium separation, wherein a reaction solution for preparing the crystalline thin film is prepared, and a base membrane is immersed in the reaction solution to grow a crystalline thin film on the surface of the base membrane; the crystalline thin film can be rapidly repaired by immersing it in an aqueous solution and an oil solution containing the reactive monomers.

[0010] Furthermore, the preparation method includes the following steps:

[0011] Step 1: Preparation of covalent organic framework porous polymer crystal thin films:

[0012] S1. Preparation of reaction solution: Dissolve 1,3,5-tris(4-aminophenyl)benzene in a mixed solvent of ethyl acetate and mesitylene, and sonicate until the monomer is completely dissolved; add 2,5-dimethoxybenzene-1,4-dicarboxaldehyde to the above solution, shake quickly and well to obtain the reaction solution for crystal film growth;

[0013] S2. Deposition and growth of crystalline thin film on the surface of the basement membrane: Place the basement membrane in a glass bottle, add the reaction solution to the glass bottle, shake slightly to ensure that the basement membrane is in full contact with the reaction solution, then add acetic acid as a catalyst, mix thoroughly, tighten the cap, and let the reaction stand at room temperature until a crystalline thin film grows on the surface of the basement membrane.

[0014] Step 2: Sealing surface defects in crystalline thin films using interfacial polycondensation of ultrathin polymer films:

[0015] The crystalline thin film obtained in step S2 is impregnated with an aqueous solution of m-phenylenediamine or piperazine to ensure that the defects of the crystalline thin film are fully impregnated with the aqueous solution. Then, the aqueous phase on the surface of the film is removed by blowing away with an air knife, and the film is then impregnated with an oil solution. Thus, a crystalline porous polymer composite film with interfacial condensation ultrathin polymer film covering the surface defects of the crystalline thin film is obtained.

[0016] More specifically, step S1 involves weighing 1.2-4.7 mg of 1,3,5-tris(4-aminophenyl)benzene and dissolving it in a 5.0 mL mixture of ethyl acetate and mesitylene, and sonicating until the monomer is completely dissolved; then adding 1.0-3.9 mg of 2,5-dimethoxybenzene-1,4-dicarboxaldehyde to the above solution, rapidly shaking and sonicating for 10 seconds to obtain the reaction mother liquor for crystal film growth, and denoting the monomer concentration in the reaction mother liquor as C0;

[0017] The volume ratio of ethyl acetate and mesitylene in the mixed solvent is 3:1.

[0018] Furthermore, a mixed solvent of ethyl acetate and mesitylene is added to the mother liquor to dilute its concentration to 0.10CO-1.0CO.

[0019] Furthermore, the base membrane in step S2 is a polyacrylonitrile porous base membrane. Step S2 specifically involves placing the base membrane in a 4.0 mL glass bottle. The base membrane has a size of 5 mm × 5 mm. 1.0 mL of reaction solution is added to the glass bottle. The bottle is shaken slightly to ensure that the base membrane is in full contact with the reaction solution. Then, 0.02 mL of acetic acid is added as a catalyst. After thorough mixing, the bottle cap is tightened and the mixture is allowed to stand at room temperature for 72 hours.

[0020] Further, step two specifically involves: immersing the crystalline thin film obtained in step S2 in a 2% (w / w) aqueous solution of m-phenylenediamine or piperazine for 2 minutes to ensure that the surface defects of the crystalline thin film are fully wetted by the aqueous solution; then removing the aqueous phase from the film surface by blowing it away with an air knife; and finally immersing the film surface in a 0.1% (w / w) solution of trimesoyl chloride and hexane for 30 seconds to obtain the crystalline porous polymer composite membrane.

[0021] The beneficial effects of this invention are:

[0022] This invention covers and seals gap defects such as grain gaps and growth discontinuities by using interfacial polycondensation of two reactive monomers to form a film. This treatment method only requires immersing the defective crystalline film in an aqueous solution and an oil solution containing reactive monomers to quickly repair the surface defects. This method is simple to operate, has low cost, and is highly universal.

[0023] In terms of effectiveness, it can both seal the porous surface of the substrate film without crystal growth (defect size of several to hundreds of micrometers) and seal the intergranular gaps (defect size of tens of nanometers), thereby obtaining a complete and continuous crystalline thin film, ensuring that the COF membrane material can truly exert the advantages of nanopores during use. The nanopores of COFs can provide channels for ion transport, and the appropriate internal chemical environment of the pores has selective permeability to specific ions.

[0024] On the other hand, applications such as ion transport have strict requirements for the uniformity of the pore size of the separation layer. Therefore, the separation layer cannot have defects larger than 10 nanometers. If large surface defects exist, a large number of ions will pass through the defect location rapidly without selectivity, resulting in no ion separation effect. Currently, the energy industry's huge demand for lithium batteries has spurred a lithium extraction boom. One of the major challenges in lithium extraction from salt lakes is separating lithium and magnesium ions from lake water. For lithium and magnesium ions with a size of less than 1 nanometer, the small size difference between them places even higher demands on the pore size precision of the separation membrane. The preparation method provided by this invention can lay the foundation for the practical application of COFs thin films and provide a solution for the selective separation of lithium and magnesium ions in salt lakes.

[0025] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the growth of a crystalline thin film from the base membrane in solution during step S2 of the present invention.

[0027] Figure 2 This is a schematic diagram of the diffusion dialysis testing device in step three of the present invention;

[0028] Figure 3 This is a schematic diagram of the surface of the crystal thin film of the present invention before it is sealed (photographed by scanning electron microscope (SEM));

[0029] Figure 4 This is a cross-sectional view of the composite membrane of the present invention (taken by scanning electron microscope (SEM));

[0030] Figure 5 This is a schematic diagram of the surface of the composite film of the present invention (taken by scanning electron microscope (SEM));

[0031] The labels for each figure are as follows:

[0032] 1. Reaction solution; 2. Base membrane; 3. Composite membrane; 4. Salt solution; 5. Ultrapure water; 6. Surface defects; 7. Crystalline thin film. Detailed Implementation

[0033] The following specific embodiments illustrate the detailed implementation of the present invention. Those skilled in the art can easily understand the advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented in other different ways, that is, different modifications and changes can be made without departing from the scope disclosed in the present invention.

[0034] Example: A crystalline porous polymer composite membrane for lithium-magnesium separation includes a porous base membrane that provides support and a covalent organic framework porous polymer crystalline thin film covering it. The covalent organic framework porous polymer crystalline thin film is defined as a crystalline thin film. The surface defects of the crystalline thin film (including grain gaps and size defects, but not limited to these) are covered and sealed by an ultrathin polymer thin film generated by interfacial polycondensation.

[0035] Ultrathin polymer films formed by interfacial polycondensation include aromatic polyamides or semi-aromatic polyamides.

[0036] Furthermore, the aromatic polyamide is formed by an interfacial polycondensation reaction between an aromatic binary or polyamine and an aromatic binary or polyacryl chloride.

[0037] The semi-aromatic polyamide is formed by interfacial polycondensation reaction of piperazine and its derivatives with alicyclic or aliphatic binary or polyamines and binary or polyacryl chlorides.

[0038] Example 1:

[0039] Step 1: Preparation of covalent organic framework porous polymer crystal thin films:

[0040] S1: Preparation of reaction solution: Weigh 4.7 mg of 1,3,5-tris(4-aminophenyl)benzene and dissolve it in a mixed solvent of 5.0 mL of ethyl acetate and mesitylene (volume ratio of 3:1), and sonicate until the monomer is completely dissolved; add 3.9 mg of 2,5-dimethoxybenzene-1,4-dicarboxaldehyde to the above solution, shake quickly and sonicate for 10 s. Use this solution as reaction solution 1 for the growth of covalent organic framework crystal films, and the concentration of this reaction solution is denoted as C0;

[0041] S2: Deposition and growth of crystalline thin film (COFs layer) on the surface of polyacrylonitrile porous substrate membrane: The substrate membrane used was a polyacrylonitrile ultrafiltration membrane (PAN-400) from Sepro, USA, with a molecular weight cutoff (MWCO) of 40,000 Da. The substrate membrane (5mm × 5mm) was placed in a 4.0mL glass bottle. 1.0mL of reaction solution was added to the bottle, and the mixture was gently shaken to ensure full contact between the substrate membrane and the reaction solution. Then, 0.02mL of acetic acid was added as a catalyst. After thorough mixing, the bottle was tightened and allowed to stand at room temperature for 72 hours. A COFs layer (i.e., a crystalline porous polymer film) was formed on the surface of the substrate membrane. The growth process is as follows: Figure 1 As shown, the surface morphology of the grown crystal film is as follows: Figure 3 As shown.

[0042] Step 2: Sealing Surface Defects in the Crystalline Thin Film with an Interfacial Polycondensation Ultrathin Polymer Film 6: The crystalline thin film (including the substrate film) obtained in step S2 is immersed in an aqueous solution containing 2% m-phenylenediamine for 2 minutes to ensure that the surface defects of the crystalline thin film are fully wetted by the aqueous phase solution. Then, the aqueous phase on the film surface is removed by blowing away with an air knife. The film surface is then immersed in a hexane solution containing 0.1% trimesoyl chloride for 30 seconds to obtain a continuous crystalline porous polymer composite film with defects repaired by an aromatic polyamide film. Figure 4 and Figure 5 As shown.

[0043] Step 3: Ion diffusion dialysis performance test of the composite membrane:

[0044] Ion diffusion dialysis performance evaluation device for composite membranes, such as Figure 2 As shown, the composite membrane is clamped between two glass diffusion cells. 7.0 mL of salt solution 4 is added to the front side of the membrane as the feed solution, and 7.0 mL of ultrapure water 5 is added to the other side. A magnetic stirrer is placed in both solutions for stirring. Due to the salt concentration difference between the two sides of the membrane, salt ions diffuse from the feed side (higher concentration) to the permeate side (lower concentration). The concentration of salt ions in the permeate after 1 hour of diffusion is detected by ion chromatography, allowing for the calculation of the transmembrane diffusion performance of various ions. The feed solution is a binary salt solution of LiCl and MgCl2 (both with a concentration of 0.1 mol / L).

[0045] In the diffusion dialysis experiment, the ion concentrations of the feed solution and permeate were determined using an LC-20A ion chromatograph (Shimadzu, Japan). 0.1 mL of permeate was taken from the permeate side of the diffusion cell, diluted 10-fold with ultrapure water, and then tested. Chromatographic column: Shodex IC YS-50 (4.6 mm ID × 125 mm).

[0046] In ion diffusion dialysis testing, the ion concentration in the permeate can be calculated by measuring the peak area of ​​cations in the permeate and then applying the linear equation described above. Standard curve determination: A series of LiCl (lithium chloride) or MgCl2 (magnesium chloride) standard solutions with varying concentration gradients are prepared. The peak area of ​​cations at each concentration is measured using an ion chromatograph. A standard curve is constructed based on the concentration-peak area relationship, and a linear equation is fitted.

[0047] Example 2:

[0048] Using the newly prepared reaction solution from Example 1 as the mother liquor, the above-mentioned mixed solvent was quickly added for dilution to obtain a reaction solution with a monomer concentration of 0.5CO. All other operations were the same as in Example 1.

[0049] Example 3:

[0050] Using the newly prepared reaction solution from Example 1 as the mother liquor, the above-mentioned mixed solvent was quickly added for dilution to obtain a reaction solution with a monomer concentration of 0.25CO. All other operations were the same as in Example 1.

[0051] Comparative Example 1:

[0052] Interfacial polycondensation was performed directly on the surface of a porous polyacrylonitrile substrate membrane to form a film, using the same materials and experimental conditions as in Example 1.

[0053] Comparative Example 2:

[0054] Same as Example 1, but without using interfacial polycondensation to seal defects in the crystal thin film.

[0055] The performance test data for the embodiments and comparative examples are shown in the table below.

[0056]

[0057]

[0058] Because the pore size of the aromatic polyamide film is smaller than that of the covalent organic framework film, its ion permeation rate is lower than that of the latter. This is demonstrated in Comparative Example 1, where the lithium-ion permeation rate is lower than that of Examples 1-3, and the permeation selectivity for lithium and magnesium ions is low. In Comparative Example 2, due to the large surface defects in the crystal separation layer, lithium and magnesium ions pass through the composite film rapidly and indiscriminately, thus there is no selectivity for the permeation of lithium and magnesium ions. Compared to Comparative Examples 1 and 2, Examples 1-3 all have higher lithium and magnesium permeation selectivity, indicating that the covalent organic framework film is selective for lithium and magnesium ions, and that the ultrathin polymer film formed by interfacial condensation can effectively block the large surface defects of the covalent organic framework film.

[0059] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structure made using the contents of the present invention specification and drawings, or directly or indirectly applied to other related technical fields, are similarly included within the patent protection scope of the present invention.

[0060] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structure made using the contents of the present invention specification and drawings, or directly or indirectly applied to other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A crystalline porous polymer composite membrane for lithium-magnesium separation, characterized in that: It includes a porous base membrane that provides support and a covalent organic framework porous polymer crystal film covering it. The surface defects of the crystal film are covered and sealed by an ultrathin polymer film generated by interfacial condensation. The preparation steps of the covalent organic framework porous polymer crystal film are as follows: S1. Preparation of reaction solution: Dissolve 1,3,5-tris(4-aminophenyl)benzene in a mixed solvent of ethyl acetate and mesitylene, and sonicate until the monomer is completely dissolved; add 2,5-dimethoxybenzene-1,4-dicarboxaldehyde to the above solution, shake quickly and well to obtain the reaction solution for crystal film growth; S2. Deposition and growth of crystalline thin film on the surface of the basement membrane: Place the basement membrane in a glass bottle, add the reaction solution to the glass bottle, shake slightly to ensure that the basement membrane is in full contact with the reaction solution, then add acetic acid as a catalyst, mix thoroughly, tighten the cap, and let the reaction stand at room temperature until a crystalline thin film grows on the surface of the basement membrane. Ultrathin polymer films formed by interfacial polycondensation include aromatic polyamides or semi-aromatic polyamides.

2. The crystalline porous polymer composite membrane for lithium-magnesium separation according to claim 1, characterized in that: The aromatic polyamide is formed by an interfacial polycondensation reaction between an aromatic binary or polyamine and an aromatic binary or polyacryl chloride. The semi-aromatic polyamide is formed by interfacial polycondensation reaction of piperazine and its derivatives alicyclic or aliphatic binary or polyamines with binary or polyacyl chlorides.

3. A method for preparing a crystalline porous polymer composite membrane for lithium-magnesium separation according to claim 1, characterized in that: The reaction solution for preparing crystalline thin films is used to immerse a base film in the reaction solution, allowing a crystalline thin film to grow on the surface of the base film. The crystalline thin film can be rapidly repaired by immersing it successively in an aqueous solution and an oil solution containing reactive monomers.

4. The method for preparing a crystalline porous polymer composite membrane for lithium-magnesium separation according to claim 3, characterized in that: The specific method for sealing surface defects in crystalline thin films using interfacial polycondensation ultrathin polymer films is as follows: The crystalline thin film obtained in step S2 is impregnated with an aqueous solution of m-phenylenediamine or piperazine to ensure that the defects of the crystalline thin film are fully impregnated with the aqueous solution. Then, the aqueous phase on the surface of the film is removed by blowing away with an air knife, and the film is then impregnated with an oil solution. Thus, a crystalline porous polymer composite film with interfacial condensation ultrathin polymer film covering the surface defects of the crystalline thin film is obtained.

5. The method for preparing a crystalline porous polymer composite membrane for lithium-magnesium separation according to claim 4, characterized in that: Step S1 specifically involves weighing 1.2-4.7 mg of 1,3,5-tris(4-aminophenyl)benzene and dissolving it in a 5.0 mL mixture of ethyl acetate and mesitylene, and sonicating until the monomer is completely dissolved; then adding 1.0-3.9 mg of 2,5-dimethoxybenzene-1,4-dicarboxaldehyde to the above solution, rapidly shaking and sonicating for 10 seconds to obtain the reaction mother liquor for crystal film growth, and denoting the monomer concentration in the reaction mother liquor as C0; The volume ratio of ethyl acetate and mesitylene in the mixed solvent is 3:

1.

6. The method for preparing a crystalline porous polymer composite membrane for lithium-magnesium separation according to claim 5, characterized in that: Add a mixed solvent of ethyl acetate and mesitylene to the reaction mother liquor to dilute the concentration of the reaction mother liquor to 0.10CO-1.0CO.

7. The method for preparing a crystalline porous polymer composite membrane for lithium-magnesium separation according to claim 6, characterized in that: The base membrane in step S2 is a polyacrylonitrile porous base membrane. Step S2 is specifically as follows: place the base membrane in a glass bottle with a volume of 4.0 mL. The base membrane has a size of 5 mm × 5 mm. Add 1.0 mL of reaction solution to the glass bottle, shake it slightly to ensure that the base membrane is in full contact with the reaction solution, and then add 0.02 mL of acetic acid as a catalyst. After mixing thoroughly, tighten the cap and let it stand at room temperature for 72 hours.

8. The method for preparing a crystalline porous polymer composite membrane for lithium-magnesium separation according to claim 4, characterized in that: The specific steps for sealing surface defects of crystalline thin films with interfacial polycondensation ultrathin polymer films are as follows: The crystalline thin film obtained in step S2 is immersed in a 2% (w / w) aqueous solution of m-phenylenediamine or piperazine for 2 minutes to ensure that the surface defects of the crystalline thin film are fully wetted by the aqueous phase solution. Then, the aqueous phase on the film surface is removed by blowing away with an air knife. Finally, the film surface is immersed in a 0.1% (w / w) solution of trimesoyl chloride and hexane for 30 seconds to obtain a porous crystalline polymer composite film.

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