A method for preparing a polyamide composite membrane and the composite membrane application

Abstract

The application relates to the technical field of polyamide composite membrane preparation, and relates to a polyamide composite membrane preparation method and application of the composite membrane. A kind of polyamide composite membrane with good selectivity and permeability is prepared by synthesizing a kind of triamino quaternary ammonium salt monomer to participate in PEI / TMC interfacial polymerization process, which can efficiently separate magnesium ions and lithium ions in water. The novel polyamide composite nanofiltration membrane prepared by the application has a relatively dense and smooth surface morphology, and the PA layer has a small thickness. In a long-time filtration experiment, the membrane flux and retention rate are excellent and stable.

Description

Technical Field

[0001] This invention relates to the field of polyamide composite membrane preparation technology, and to a method for preparing a polyamide composite membrane and its applications, particularly in magnesium-lithium separation. Background Technology

[0002] Lithium (Li) is a strategically important non-renewable resource. As the lightest metal, it exhibits excellent properties such as high electrochemical activity, high specific heat capacity, high redox potential, and low thermal expansion, making it widely used in cutting-edge fields such as medicine, aerospace, and batteries. Furthermore, the explosive growth in demand for lithium-ion batteries from the electric vehicle and energy storage industries in recent years has led to a dramatic increase in Li consumption. The majority of recoverable Li is found in salt lakes, accounting for nearly 70% of the world's recoverable Li. To alleviate the shortage of Li resources, a multi-step separation process is needed to extract Li from salt lake brines containing a mixture of various ions. Among these, magnesium... and lithium Because ions have similar hydration radii, separation is difficult; therefore, magnesium lithium ions (Mg...) 2+ / Li + Separation has become a crucial step in obtaining high-purity Li resources. In summary, there is an urgent need for an advanced material to efficiently separate Mg. 2+ / Li + mixture.

[0003] Pressure-driven nanofiltration membrane technology has become a popular choice for Mg nanofiltration due to its advantages such as low energy consumption and high separation efficiency. 2+ / Li + The most promising technology for separation. Due to Mg 2+ and Li + The hydration radii are very similar, therefore the charge properties of nanofiltration membranes are very similar to those of Mg. 2+ / Li + Separation played a crucial role. In other words, the positively charged nanofiltration membrane facilitated the separation of Mg. 2+ / Li + The separation of Mg2+, therefore, the polyamide film composite membrane (TFCM) prepared by interfacial polymerization (IP) of polyethyleneimine (PEI) with a large number of positively charged amino groups, is effective against Mg2+. 2+ / Li + The separation exhibited relatively good selectivity, but there was still a problem of not being able to balance selectivity and permeability.

[0004] Chemical modification of the polyamide (PA) layer of TFCM can simultaneously improve membrane permeability and selectivity to a certain extent. Therefore, adding quaternary ammonium salt monomers during the interphase (IP) process adjusts the membrane's free volume, charge characteristics, and surface properties, thereby improving both permeability and selectivity. The participation of small-molecule quaternary ammonium salt monomers with amine groups in the IP process, along with the macromolecular polymer PEI, enhances interfacial reactivity, allowing for more complete reaction of the acyl chloride groups in TMC, resulting in a more compact, dense, and defect-free PA layer. This holds promise for further improving membrane selectivity and achieving high-efficiency extraction of high-purity Li. Summary of the Invention

[0005] The purpose of this invention is to overcome the technical problems mentioned in the background above, and to prepare a polyamide composite membrane with good selectivity and permeability by synthesizing a triamino quaternary ammonium salt monomer to participate in the PEI / TMC interfacial polymerization process, which can efficiently separate magnesium ions and lithium ions in water.

[0006] The first technical solution of this invention is the synthesis of a triaminoquaternary ammonium salt monomer, comprising the following steps:

[0007] (1) Mix 3,5-diamino-1,2,4-triazole (DAT) and 2-bromoethylamine in dimethylformamide at a molar ratio of 1:1-3.

[0008] (2) After stirring the reaction in a water bath at a constant temperature, a light green liquid was obtained. The liquid was then transferred and acetonitrile was added, resulting in the precipitation of a green oily substance.

[0009] (3) Using the supernatant, add DMF and dissolve completely. Then add acetonitrile to separate the white flocculent precipitate. After sonication and high-speed centrifugation, discard the supernatant and transfer the remaining white solid to vacuum dry to obtain triaminoquaternary ammonium salt monomer (DAT-NH2) powder, which is prepared by the following reaction:

[0010]

[0011] The second technical solution of the present invention is: the preparation of a polyamide composite film, comprising the following steps:

[0012] (1) Polyethyleneimine (PEI) with a mass concentration ratio of 5-10:1, DAT-NH2, sodium dodecyl sulfate (SDS), and Na2CO3 are added to a container containing deionized water in turn. The solution is sonicated until completely dissolved to obtain an aqueous solution for later use.

[0013] (2) Add 0.1-0.5 wt% of trimesoyl chloride (TMC) to a container containing n-hexane, and sonicate until completely dissolved to obtain an organic phase solution;

[0014] (3) Pour the aqueous solution into a container, and then put the polyethersulfone (PES) ultrafiltration membrane that has been soaked in deionized water for 12 hours into the container for 5 minutes after draining the water.

[0015] (4) After the PES membrane is removed, absorb the excess liquid.

[0016] (5) Then fix it on a customized interface polymerization mold, add an organic phase solution to react fully, and dry to obtain a DAT / PEI-TMC polyamide composite film.

[0017] Furthermore, in step (1), the mass concentration ratio of polyethyleneimine (PEI) to DAT-NH2 is 6-8:1.

[0018] Furthermore, the mass concentration of trimesoyl chloride (TMC) in step (2) is 0.3%.

[0019] The third technical solution of the present invention is: the use of the DAT / PEI-TMC polyamide composite membrane prepared by the above method for the efficient separation of magnesium ions and lithium ions in water.

[0020] Advantages of this invention:

[0021] This invention proposes a novel triaminoquaternary ammonium salt monomer to participate in the PEI / TMC interfacial polymerization process, preparing a polyamide composite membrane with good selectivity and permeability. Under an operating pressure of 6 bar, Mg... 2+ / Li + The separation factor reaches 40.3, and the permeation flux reaches 8.6 LMH / bar. Furthermore, it exhibits excellent long-term stability while maintaining superior separation performance. It demonstrates excellent application value for the efficient extraction of high-purity Li.

[0022] The novel polyamide composite nanofiltration membrane exhibits a relatively dense and smooth surface morphology, with a relatively thin PA layer. It demonstrates excellent and stable membrane flux and retention rate during long-term filtration experiments. Attached Figure Description

[0023] Figure 1 The image shows the morphology of the DAT / PEI-TMC composite membrane.

[0024] (a) SEM image of the membrane surface morphology;

[0025] (b) AFM image of the membrane surface morphology;

[0026] (c) TEM image of the membrane cross-section morphology.

[0027] Figure 2 The pure water flux of the DAT / PEI-TMC composite membrane under different operating pressures.

[0028] Figure 3 Membrane permeability and separation factor of DAT / PEI-TMC composite membrane for treating magnesium-lithium ion mixed solutions under different operating pressures.

[0029] Figure 4 The performance of the DAT / PEI-TMC composite membrane after 120 hours of long-term operation is shown.

[0030] Figure 5 This is a schematic diagram of the membrane structure and the separation process of Mg2+ / Li+. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] Example 1

[0033] (1) Add 8.4744g of 3,5-diamino-1,2,4-triazole (DAT), 17.5386g of 2-bromoethylamine, and 90mL of dimethylformamide (DMF) to a 150mL flask and mix.

[0034] (2) Place the flask in a water bath and stir at 500 r / min for 24 h at a constant temperature of 45°C to obtain a light green liquid. Transfer it to a 500 mL beaker and add 180 mL of acetonitrile to precipitate a green oily substance.

[0035] (3) Remove the beaker from the water bath, separate the upper suspension with a pipette, add 10 mL of DMF, dissolve completely, then add 180 mL of acetonitrile, separate the white flocculent precipitate, sonicate 3 times, then put it into a high-speed centrifuge to rotate, pour off the upper suspension, transfer the remaining white solid to a vacuum drying oven at 40 °C and dry for 2 h to obtain triaminoquaternary ammonium salt monomer (DAT-NH2) powder.

[0036] (4) Add 0.46wt% polyethyleneimine (PEI), 0.04wt% DAT-NH2, 0.1wt% sodium dodecyl sulfate (SDS), and 0.1wt% Na2CO3 to a blue bottle containing deionized water in sequence, sonicate until completely dissolved to obtain an aqueous solution, and wrap the bottle with tin foil for later use.

[0037] (5) Add 0.3 wt% trimesoyl chloride (TMC) to a blue-mouth bottle containing n-hexane, and sonicate until completely dissolved to obtain an organic phase solution;

[0038] (6) Pour the aqueous solution into a petri dish, and then drain the water from the polyethersulfone (PES) ultrafiltration membrane that has been soaked in deionized water for 12 hours and place it into the petri dish to soak for 5 minutes.

[0039] (7) After removing the PES membrane, cover it with two pieces of filter paper, lay it flat on a smooth glass plate, and gently roll the PES membrane with a roller to absorb excess liquid.

[0040] (8) Fix it on a custom interface polymerization (IP) mold, add an organic phase solution and react for 1 min, then put it in a 60℃ oven for a further reaction of 30 min to obtain a DAT / PEI-TMC composite membrane, soak it in deionized water for later use.

[0041] (9) The selectivity and permeability of the DAT / PEI-TMC polyamide composite membrane were evaluated using a cross-flow filtration device.

[0042] Example 2

[0043] (1) Add 8.4744g of 3,5-diamino-1,2,4-triazole (DAT), 17.5386g of 2-bromoethylamine, and 90mL of dimethylformamide (DMF) to a 150mL flask and mix.

[0044] (2) Place the flask in a water bath and stir at 500 r / min for 24 h at a constant temperature of 45°C to obtain a light green liquid. Transfer it to a 500 mL beaker and add 180 mL of acetonitrile to precipitate a green oily substance.

[0045] (3) Remove the beaker from the water bath, separate the upper suspension with a pipette, add 10 mL of DMF, dissolve completely, then add 180 mL of acetonitrile, separate the white flocculent precipitate, sonicate 3 times, then put it into a high-speed centrifuge to rotate, pour off the upper suspension, transfer the remaining white solid to a vacuum drying oven at 40 °C and dry for 2 h to obtain triaminoquaternary ammonium salt monomer (DAT-NH2) powder.

[0046] (4) Add 0.45wt% polyethyleneimine (PEI), 0.05wt% DAT-NH2, 0.1wt% sodium dodecyl sulfate (SDS), and 0.1wt% Na2CO3 to a blue bottle containing deionized water in sequence, sonicate until completely dissolved to obtain an aqueous solution, and wrap the bottle with tin foil for later use.

[0047] (5) Add 0.3 wt% trimesoyl chloride (TMC) to a blue-mouth bottle containing n-hexane, and sonicate until completely dissolved to obtain an organic phase solution;

[0048] (6) Pour the aqueous solution into a petri dish, and then drain the water from the polyethersulfone (PES) ultrafiltration membrane that has been soaked in deionized water for 12 hours and place it into the petri dish to soak for 5 minutes.

[0049] (7) After removing the PES membrane, cover it with two pieces of filter paper, lay it flat on a smooth glass plate, and gently roll the PES membrane with a roller to absorb excess liquid.

[0050] (8) Fix it on a custom interface polymerization (IP) mold, add an organic phase solution and react for 1 min, then put it in a 60℃ oven for a further reaction of 30 min to obtain a DAT / PEI-TMC composite membrane, soak it in deionized water for later use.

[0051] (9) The selectivity and permeability of the DAT / PEI-TMC polyamide composite membrane were evaluated using a cross-flow filtration device.

[0052] Example 3

[0053] (1) Add 8.4744g of 3,5-diamino-1,2,4-triazole (DAT), 17.5386g of 2-bromoethylamine, and 90mL of dimethylformamide (DMF) to a 150mL flask and mix.

[0054] (2) Place the flask in a water bath and stir at 500 r / min for 24 h at a constant temperature of 45°C to obtain a light green liquid. Transfer it to a 500 mL beaker and add 180 mL of acetonitrile to precipitate a green oily substance.

[0055] (3) Remove the beaker from the water bath, separate the upper suspension with a pipette, add 10 mL of DMF, dissolve completely, then add 180 mL of acetonitrile, separate the white flocculent precipitate, sonicate 3 times, then put it into a high-speed centrifuge to rotate, pour off the upper suspension, transfer the remaining white solid to a vacuum drying oven at 40 °C and dry for 2 h to obtain triaminoquaternary ammonium salt monomer (DAT-NH2) powder.

[0056] (4) Add 0.44wt% polyethyleneimine (PEI), 0.06wt% DAT-NH2, 0.1wt% sodium dodecyl sulfate (SDS), and 0.1wt% Na2CO3 to a blue bottle containing deionized water in sequence, sonicate until completely dissolved to obtain an aqueous solution, and wrap the bottle with tin foil for later use.

[0057] (5) Add 0.3 wt% trimesoyl chloride (TMC) to a blue-mouth bottle containing n-hexane, and sonicate until completely dissolved to obtain an organic phase solution;

[0058] (6) Pour the aqueous solution into a petri dish, and then drain the water from the polyethersulfone (PES) ultrafiltration membrane that has been soaked in deionized water for 12 hours and place it into the petri dish to soak for 5 minutes.

[0059] (7) After removing the PES membrane, cover it with two pieces of filter paper, lay it flat on a smooth glass plate, and gently roll the PES membrane with a roller to absorb excess liquid.

[0060] (8) Fix it on a custom interface polymerization (IP) mold, add an organic phase solution and react for 1 min, then put it in a 60℃ oven for a further reaction of 30 min to obtain a DAT / PEI-TMC composite membrane, soak it in deionized water for later use.

[0061] (9) The selectivity and permeability of the DAT / PEI-TMC polyamide composite membrane were evaluated using a cross-flow filtration device.

[0062] Example 4

[0063] (1) Add 8.4744g of 3,5-diamino-1,2,4-triazole (DAT), 17.5386g of 2-bromoethylamine, and 90mL of dimethylformamide (DMF) to a 150mL flask and mix.

[0064] (2) Place the flask in a water bath and stir at 500 r / min for 24 h at a constant temperature of 45°C to obtain a light green liquid. Transfer it to a 500 mL beaker and add 180 mL of acetonitrile to precipitate a green oily substance.

[0065] (3) Remove the beaker from the water bath, separate the upper suspension with a pipette, add 10 mL of DMF, dissolve completely, then add 180 mL of acetonitrile, separate the white flocculent precipitate, sonicate 3 times, then put it into a high-speed centrifuge to rotate, pour off the upper suspension, transfer the remaining white solid to a vacuum drying oven at 40 °C and dry for 2 h to obtain triaminoquaternary ammonium salt monomer (DAT-NH2) powder.

[0066] (4) Add 0.42wt% polyethyleneimine (PEI), 0.08wt% DAT-NH2, 0.1wt% sodium dodecyl sulfate (SDS), and 0.1wt% Na2CO3 to a blue bottle containing deionized water in sequence, sonicate until completely dissolved to obtain an aqueous solution, and wrap the bottle with tin foil for later use.

[0067] (5) Add 0.3 wt% trimesoyl chloride (TMC) to a blue-mouth bottle containing n-hexane, and sonicate until completely dissolved to obtain an organic phase solution;

[0068] (6) Pour the aqueous solution into a petri dish, and then drain the water from the polyethersulfone (PES) ultrafiltration membrane that has been soaked in deionized water for 12 hours and place it into the petri dish to soak for 5 minutes.

[0069] (7) After removing the PES membrane, cover it with two pieces of filter paper, lay it flat on a smooth glass plate, and gently roll the PES membrane with a roller to absorb excess liquid.

[0070] (8) Fix it on a custom interface polymerization (IP) mold, add an organic phase solution and react for 1 min, then put it in a 60℃ oven for a further reaction of 30 min to obtain a DAT / PEI-TMC composite membrane, soak it in deionized water for later use.

[0071] (9) The selectivity and permeability of the DAT / PEI-TMC polyamide composite membrane were evaluated using a cross-flow filtration device.

[0072] Example 5

[0073] (1) Add 8.4744g of 3,5-diamino-1,2,4-triazole (DAT), 17.5386g of 2-bromoethylamine, and 90mL of dimethylformamide (DMF) to a 150mL flask and mix.

[0074] (2) Place the flask in a water bath and stir at 500 r / min for 24 h at a constant temperature of 45°C to obtain a light green liquid. Transfer it to a 500 mL beaker and add 180 mL of acetonitrile to precipitate a green oily substance.

[0075] (3) Remove the beaker from the water bath, separate the upper suspension with a pipette, add 10 mL of DMF, dissolve completely, then add 180 mL of acetonitrile, separate the white flocculent precipitate, sonicate 3 times, then put it into a high-speed centrifuge to rotate, pour off the upper suspension, transfer the remaining white solid to a vacuum drying oven at 40 °C and dry for 2 h to obtain triaminoquaternary ammonium salt monomer (DAT-NH2) powder.

[0076] (4) Add 0.38wt% polyethyleneimine (PEI), 0.12wt% DAT-NH2, 0.1wt% sodium dodecyl sulfate (SDS), and 0.1wt% Na2CO3 to a blue bottle containing deionized water in sequence, sonicate until completely dissolved to obtain an aqueous solution, and wrap the bottle with tin foil for later use.

[0077] (5) Add 0.3 wt% trimesoyl chloride (TMC) to a blue-mouth bottle containing n-hexane, and sonicate until completely dissolved to obtain an organic phase solution;

[0078] (6) Pour the aqueous solution into a petri dish, and then drain the water from the polyethersulfone (PES) ultrafiltration membrane that has been soaked in deionized water for 12 hours and place it into the petri dish to soak for 5 minutes.

[0079] (7) After removing the PES membrane, cover it with two pieces of filter paper, lay it flat on a smooth glass plate, and gently roll the PES membrane with a roller to absorb excess liquid.

[0080] (8) Fix it on a custom interface polymerization (IP) mold, add an organic phase solution and react for 1 min, then put it in a 60℃ oven for a further reaction of 30 min to obtain a DAT / PEI-TMC composite membrane, soak it in deionized water for later use.

[0081] (9) The selectivity and permeability of the DAT / PEI-TMC polyamide composite membrane were evaluated using a cross-flow filtration device.

[0082]

[0083] In summary, as Figures 1 to 4 As shown, the novel polyamide composite nanofiltration membrane prepared in this study has a relatively dense and smooth surface morphology, and a relatively small PA layer thickness. It exhibits excellent and stable membrane flux and retention rate in long-term filtration experiments.

[0084] This demonstrates that the composite membrane prepared in this study meets industrial requirements and provides guidance and technical methods for the efficient extraction of high-purity Li. This invention is not limited to the specific embodiments described above; the specific embodiments are merely illustrative and not restrictive. Those skilled in the art, under the guidance of this invention, can make further modifications without departing from the spirit of this invention, and all such modifications are within the protection scope of this invention.

Claims

1. A method for synthesizing triaminoquaternary ammonium salt monomers, comprising the following steps: (1) Mix 3,5-diamino-1,2,4-triazole (DAT) and 2-bromoethylamine in dimethylformamide (DMF) at a molar ratio of 1:1-3. (2) After stirring the reaction in a water bath at a constant temperature, a light green liquid was obtained. The liquid was then transferred and acetonitrile was added, resulting in the precipitation of a green oily substance. (3) Using the supernatant, add DMF and dissolve it completely before adding acetonitrile. Separate the white flocculent precipitate, sonicate and centrifuge at high speed. Discard the supernatant and transfer the remaining white solid to vacuum dry to obtain triaminoquaternary ammonium salt monomer DAT-NH2 powder, which is prepared by the following reaction: 。 2. A method for preparing a polyamide composite film, characterized in that, Includes the following steps: (1) Polyethyleneimine (PEI) with a mass concentration ratio of 5-10:1, DAT-NH2, sodium dodecyl sulfate (SDS), and Na2CO3 are added to a container containing deionized water in sequence. The solution is sonicated until completely dissolved to obtain an aqueous solution for later use. The DAT-NH2 is prepared by the synthesis method according to claim 1; (2) Add 0.1-0.5 wt% of trimesoyl chloride (TMC) to a container containing n-hexane, and sonicate until completely dissolved to obtain an organic phase solution; (3) Pour the aqueous solution into a container, and then put the polyethersulfone (PES) ultrafiltration membrane that has been soaked in deionized water for 12 hours into the container for 5 minutes after draining the water. (4) After the PES membrane is removed, absorb the excess liquid. (5) Then fix it on a customized interface polymerization mold, add an organic phase solution to react fully, and dry to obtain a DAT / PEI-TMC polyamide composite film.

3. The preparation method according to claim 2, characterized in that, In step (1), the mass concentration ratio of polyethyleneimine (PEI) to DAT-NH2 is 6-8:

1.

4. The preparation method according to claim 2, characterized in that, In step (2), the mass concentration of trimesoyl chloride (TMC) is 0.3%.

5. A DAT / PEI-TMC polyamide composite membrane prepared by the method described in any one of claims 2-4, for efficient separation of magnesium ions and lithium ions in water.

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