In-situ cyclic grafting modified polyamide nanofiltration membrane for extracting lithium from salt lake and preparation method of in-situ cyclic grafting modified polyamide nanofiltration membrane
A modified polyamide nanofiltration membrane with multi-scale mass transfer channels was constructed through dopamine bionic modification and in-situ cyclic grafting of a sandwich structure, which solved the problem of insufficient lithium ion selectivity of traditional nanofiltration membranes in salt lake brine with a high magnesium-lithium ratio, and achieved efficient separation and purification of lithium resources.
Patent Information
- Application Number
- CN202510903307.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-01
- Publication Date
- 2025-10-10
AI Technical Summary
Traditional nanofiltration membranes have difficulty in effectively separating lithium ions in salt lake brine with a high magnesium-to-lithium ratio. Their selectivity and chemical stability are insufficient and cannot meet the needs of efficient lithium extraction.
A modified polyamide nanofiltration membrane with multi-scale mass transfer channels was constructed by combining dopamine biomimetic modification with an in-situ cyclic grafting method of an organic phase/aqueous phase/organic phase sandwich structure to enhance the selective permeability of lithium ions and the chemical stability of the membrane.
It significantly improves the selectivity and separation efficiency of lithium ions, reduces operating costs, achieves efficient lithium resource recovery and purification, and adapts to complex salt lake environments.
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Figure CN120754723A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the field of membrane materials, and in particular relates to an in-situ circulating grafted modified polyamide nanofiltration membrane for lithium extraction from salt lakes and a preparation method thereof. Background Art
[0002] Lithium extraction from salt lakes is one of the important ways to develop lithium resources. More than 60% of the world's lithium resources are stored in salt lake brine. However, salt lake brine usually contains high concentrations of magnesium ions (Mg 2+ ), resulting in a magnesium-lithium ratio (Mg 2+ / Li + ) is high, which makes the selective separation of lithium ions a technical difficulty.
[0003] Traditional nanofiltration membranes are difficult to effectively separate Li+ / Mg in salt lake brine with high magnesium-lithium ratio 2+ , has limited performance in lithium ion selectivity, mainly due to the similar ion hydration radius (Mg 2+ :0.428nm / L : 0.382nm) and poor structural stability in extreme environments, making it difficult to meet the needs of efficient lithium extraction.
[0004] Therefore, developing a nanofiltration membrane material with high selectivity, excellent chemical stability and adaptability to complex environments can not only significantly improve the lithium recovery rate and purity, but also reduce energy consumption and operating costs, which is of great strategic significance for achieving efficient and green development of salt lake lithium resources. Summary of the Invention
[0005] To solve the above problems, the present invention provides an in-situ cyclic grafted modified polyamide nanofiltration membrane for lithium extraction from salt lakes and a preparation method thereof. The surface interface polymerization layer of the nanofiltration membrane has multi-scale mass transfer channels, which optimizes the mass transfer path and effectively enhances the selective permeability of the membrane material to lithium ions, especially in salt lake brine with a high magnesium-lithium ratio, which can effectively improve the magnesium-lithium separation coefficient.
[0006] The technical solution adopted in the present invention is as follows: A method for preparing an in-situ cyclic graft-modified polyamide nanofiltration membrane for lithium extraction from salt lakes comprises the following steps: (1) Basement membrane pretreatment Soak the substrate in deionized water and ultrasonically clean it for 10-15 minutes to remove surface contaminants. Then immerse the membrane in a 3% H2O2 solution at 50-60°C for 20-30 minutes to enhance the active groups (such as hydroxyl and carboxyl groups) on the membrane surface and enhance the adhesion of subsequent coatings.
[0007] (2) Dopamine modification
[0008] The membrane was modified by immersing it in a dopamine hydrochloride solution with a concentration of 2 mg / mL and a pH of 8 to 9 for 4 to 5 hours to introduce a biomimetic polydopamine layer to further improve the surface properties and coating adhesion of the membrane, and then dried at room temperature.
[0009] (3) Preparation of aqueous solution
[0010] Piperazine (PIP) and biodegradable sophorolipids were weighed, added to deionized water, and stirred until completely dissolved to form a uniform aqueous solution.
[0011] (4) Preparation of organic phase solution
[0012] Add sebacoyl chloride to an organic solvent (such as n-hexane) and stir until it is completely dissolved to form a sebacoyl chloride organic phase solution.
[0013] (5) In-situ modification of membrane surface
[0014] Using a cyclic grafting method, the dopamine-modified basement membrane is sequentially treated with an organic phase solution, an aqueous phase solution, and an organic phase solution to construct a sandwich structure. First, the pretreated and modified basement membrane is completely immersed in the organic phase solution for 5-10 minutes. Next, the membrane is carefully removed from the organic solution and the excess surface water is gently absorbed with filter paper, but not completely dried. The membrane is then quickly transferred to a uniform aqueous phase solution for 5-15 minutes, allowing the two liquids to react at the membrane surface to form a composite nanofilm. Finally, the membrane is removed again, excess water is absorbed, and the membrane is quickly immersed in the organic solution for 5-10 minutes to complete the construction of the sandwich structure. During the immersion process, the container can be gently shaken or the solution can be stirred to ensure a uniform reaction.
[0015] (6) Drying and curing
[0016] After removing the membrane, gently rinse the membrane surface with deionized water to remove unreacted reagents and impurities. It can be dried at 60-80°C for 20-30 minutes to stabilize and solidify the membrane.
[0017] Wherein, in the aqueous phase solution, the concentration of piperazine is 0.02-0.03 g / mL, and the concentration of sophorolipid is 6.5-15 mg / mL.
[0018] In the organic phase solution, the volume ratio of sebacic acid chloride to the organic solvent is 1-1.4:60.
[0019] The base membrane is any one of a polyamide membrane, a polyimide membrane, a polysulfone membrane and a polyethersulfone membrane.
[0020] The present invention also provides a modified polyamide nanofiltration membrane prepared by the above method.
[0021] The modified polyamide nanofiltration membrane prepared by the present invention is used for extracting lithium from salt lakes.
[0022] The present invention innovatively adopts dopamine biomimetic modification (2 mg / mL, pH 8.5, immersion for 4 hours) combined with organic phase / aqueous phase / organic phase sandwich structure in situ construction technology, enhances membrane surface activity by hydrogen peroxide, improves chemical stability by polydopamine layer, and forms a composite film with multi-scale mass transfer channels through reverse interfacial polymerization (organic phase-aqueous phase-organic phase). The membrane has high selectivity (Li+ / Mg 2+ ), has excellent chemical corrosion resistance and long-term reliable durability, providing an efficient and reliable membrane separation solution for lithium extraction from salt lakes.
[0023] The present invention has at least one of the following beneficial effects: (1) The present invention introduces biodegradable sophorolipids into the aqueous solution, which not only reduces the interfacial tension and promotes the uniform diffusion of the two-phase monomers, but also helps to form a more stable aqueous phase layer or interface layer on the membrane surface during the in situ cyclic grafting process, which is conducive to the formation of a thinner, more uniform, less defective and better-performing polyamide active separation layer.
[0024] (2) The present invention innovatively selects sebacyl chloride with a long fatty chain structure as the organic phase monomer, which gives the membrane material excellent flexibility, ductility, and brittleness resistance, significantly improving the mechanical properties of the membrane. At the same time, due to the reduction of the rigidity / crystallinity of the polymer, the water flux and separation performance are further improved.
[0025] (3) Through the interfacial polymerization reaction of aqueous and organic phase solutions, a composite film with multi-scale mass transfer channels is generated. By precisely controlling the intermolecular interactions, the film forms a multi-level pore structure from nanometer to micrometer scale, significantly optimizing the mass transfer path and greatly improving the permeation flux and separation efficiency. By loading the pores with adsorption sites, separation-enrichment-purification can be achieved simultaneously, effectively solving the problem of insufficient selectivity of traditional membranes under high magnesium-lithium ratio conditions, and providing a new solution for the efficient separation of lithium resources.
[0026] (4) By introducing the biomimetic polydopamine layer, the functionalized film and the polyamide-based membrane are more tightly bonded, significantly improving the interfacial stability. At the same time, the "sandwich structure" constructed by in-situ cyclic grafting further optimizes the multi-level cross-linked network of the membrane, allowing it to maintain excellent mechanical properties and chemical stability. This structural innovation not only enhances the durability of the membrane, but also significantly improves the separation efficiency by constructing multi-scale mass transfer channels. Through in-situ interfacial polymerization, the functionalized film is directly generated on the surface of the polyamide membrane, which is a simple process with low cost. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] Figure 1 This is a flow chart of the preparation process of modified composite polyamide nanofiltration membrane.
[0028] Figure 2 Schematic diagram of the device for membrane assembly for Mg / Li separation test. DETAILED DESCRIPTION
[0029] The embodiments of the present invention are further described below with reference to the accompanying drawings: The polyamide nanofiltration membrane used in the following examples of the present invention has a model number of NF3-PA (Zhongke Ruiyang, China), a molecular weight cut-off of 300-400 Da, and a pure water flux of 70 LMH.
[0030] Example 1
[0031] A preparation process of an in-situ cyclic grafted modified polyamide nanofiltration membrane for lithium extraction from salt lakes is as follows: Figure 1 As shown, the modification steps of the polyamide membrane are as follows: (1) Polyamide membrane pretreatment The polyamide membrane was immersed in deionized water and ultrasonically cleaned for 10-15 minutes; then the membrane was immersed in a 3% H2O2 solution at 60°C for 30 minutes.
[0032] (2) Dopamine modification
[0033] Prepare a dopamine hydrochloride solution with a concentration of 2 mg / mL and a pH of 8.5. Soak the pretreated polyamide membrane in the dopamine hydrochloride solution for 4 hours to modify the membrane and introduce a biomimetic polydopamine layer, then air-dry at room temperature.
[0034] (3) Preparation of aqueous solution
[0035] Weigh 0.6 g of piperazine (PIP) and 0.2 g of biodegradable sophorolipid into 30 mL of deionized water and stir until completely dissolved to form a uniform aqueous solution.
[0036] (4) Preparation of organic phase solution
[0037] Add 0.5 ml of sebacoyl chloride to 30 mL of n-hexane and stir evenly to form an organic phase solution.
[0038] (5) In-situ modification of membrane surface
[0039] Immerse the pretreated, dopamine-modified polyamide membrane completely in the organic phase solution for 10 minutes. Carefully remove the membrane and gently blot the excess surface water with filter paper, but do not allow it to completely dry. Quickly transfer the membrane to a uniform aqueous solution for 15 minutes to allow the two monomers to react at the membrane surface. Remove the membrane and blot the excess water. Then quickly immerse the membrane in the organic phase solution for another 10 minutes to complete the sandwich structure. During the immersion process, gently shake the container or stir the solution to ensure a uniform reaction.
[0040] (6) Drying and curing
[0041] After taking it out, gently rinse the membrane surface with deionized water to remove unreacted reagents and impurities; dry it at 60-80°C for 30 minutes to stabilize and solidify it.
[0042] Example 2
[0043] The difference between this embodiment and embodiment 1 is that the concentrations of the aqueous phase solution and the organic phase solution are different. The remaining steps are the same as those in embodiment 1; specifically, they are as follows: (1) Weigh 0.8 g of PIP and 0.2 g of sophorolipid, add them to 30 mL of deionized water, and stir until completely dissolved to prepare a uniform aqueous solution.
[0044] (2) Add 0.7 ml of sebacoyl chloride to 30 ml of mesitylene to obtain an organic phase solution.
[0045] Example 3
[0046] The difference between this embodiment and embodiment 1 is that the soaking time of the polyamide membrane is different, and the remaining steps are the same as those in embodiment 1; specifically, they are as follows: In-situ modification of the membrane surface: Immerse the pretreated, dopamine-modified polyamide membrane completely in an organic phase solution for 10 minutes. Carefully remove the membrane and gently blot the excess surface water with filter paper, but do not allow it to completely dry. Quickly transfer the membrane to a uniform aqueous phase solution for 5 minutes to allow the two monomers to react at the membrane surface. Remove the membrane and blot the excess water. Then quickly immerse the membrane in the organic phase solution for another 5 minutes to complete the sandwich structure. During the immersion process, gently shake the container or stir the solution to ensure a uniform reaction.
[0047] Example 4
[0048] The difference between this example and Example 1 is that the aqueous phase solution was prepared as follows: 0.6 g of piperazine (PIP) and biodegradable sophorolipid (0.4 g) were weighed, added to 30 mL of deionized water, and stirred until completely dissolved to form a uniform aqueous phase solution. The remaining steps were the same as in Example 1.
[0049] Comparative Example 1
[0050] The polyamide membrane was immersed in deionized water and ultrasonically cleaned for 15 minutes to remove surface contaminants. The membrane was then immersed in a 3% H2O2 solution (60°C, 30 minutes) and then dried at room temperature.
[0051] Comparative Example 2
[0052] The difference between this example and Example 1 is that the organic phase solution is prepared by weighing 0.5 g of trimesoyl chloride and adding it to 30 ml of n-hexane, stirring to form a uniform organic phase solution. The remaining steps are the same as in Example 1.
[0053] Comparative Example 3
[0054] The difference between this embodiment and embodiment 1 is that the interfacial polymerization method is different. The remaining steps are the same as embodiment 1. The specific interfacial polymerization method is as follows: the polyamide membrane modified with dopamine after pretreatment is completely immersed in a uniform aqueous solution for 15 minutes, taken out, and excess water is absorbed; then it is quickly transferred to an organic phase solution for 10 minutes to allow the two monomers to undergo an interfacial reaction on the membrane surface.
[0055] Performance test: Use Figure 2 The experimental device shown in the figure is used to test the membrane for brine (Mg 2+ / Li + = 20:1) and then the membrane was immersed in 2.5M H2SO4 and 2.5M NaOH solution for 30 days and then its performance was tested. Lithium ion flux J =
[0056] V: permeate flow rate; A: membrane effective area; t: time; : Transmembrane pressure difference
[0057] Magnesium-lithium separation coefficient: α Li / Mg =
[0058] Table 1 Comparison of test results between comparative examples and embodiments
[0059] Polyamide membranes modified by interfacial polymerization exhibit excellent lithium ion selectivity and chemical stability, making them suitable for lithium extraction from salt lake brines with high magnesium-to-lithium ratios. Optimizing reaction conditions can further enhance membrane performance. Unmodified polyamide membranes exhibit poor lithium ion selectivity and chemical stability, making them unsuitable for lithium extraction from salt lakes.
[0060] The above merely describes the preferred embodiments of the present application, and it should be pointed out that, for those skilled in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as falling within the protection scope of the present application.
Claims
1. A method for preparing an in-situ circulating graft-modified polyamide nanofiltration membrane for lithium extraction from salt lakes, characterized in that: The steps include: (1) Pre-treat the basement membrane by immersing it in 3% H2O2 solution; (2) Immersing the pretreated basement membrane in a dopamine hydrochloride solution to prepare a biomimetic polydopamine layer; (3) dissolving piperazine and sophorolipid in deionized water to obtain an aqueous solution; (4) Adding sebacoyl chloride to an organic solvent and stirring uniformly to obtain an organic phase solution; (5) In-situ modification of the membrane surface: the membrane material obtained in step (2) is sequentially treated with an organic phase solution, an aqueous phase solution, and an organic phase solution, and dried and solidified to obtain the modified polyamide nanofiltration membrane.
2. The method for preparing an in-situ circulating graft-modified polyamide nanofiltration membrane for lithium extraction from salt lakes according to claim 1, characterized in that: The pretreatment of step (1) is to soak at 50-60°C for 20-30 minutes.
3. The method for preparing an in-situ circulating graft-modified polyamide nanofiltration membrane for lithium extraction from salt lakes according to claim 1, characterized in that: The concentration of the dopamine hydrochloride solution in step (2) is 2 mg / mL, and the pH is 8-9; and / or the basement membrane is immersed in the dopamine hydrochloride solution for 4-5 hours.
4. The method for preparing an in-situ circulating graft-modified polyamide nanofiltration membrane for lithium extraction from salt lakes according to claim 1, characterized in that: In the aqueous solution, the concentration of piperazine is 0.02-0.03 g / mL, and the concentration of sophorolipid is 6.5-15 mg / mL.
5. The method for preparing an in-situ circulating graft-modified polyamide nanofiltration membrane for lithium extraction from salt lakes according to claim 1, characterized in that: In the organic phase solution, the volume ratio of sebacic acid chloride to the organic solvent is 1-1.4:
60.
6. The method for preparing an in-situ circulating graft-modified polyamide nanofiltration membrane for lithium extraction from salt lakes according to claim 1, characterized in that: The specific method of in-situ modification of the membrane surface in step (5) is as follows: the membrane material obtained in step (2) is completely immersed in the organic phase solution for 5 to 10 minutes, taken out, and excess liquid is removed; Transfer the membrane quickly to the aqueous solution for 5-15 minutes, remove it, and remove excess liquid; Transfer the membrane quickly into the organic phase solution for 5-10 minutes.
7. The method for preparing an in-situ circulating graft-modified polyamide nanofiltration membrane for lithium extraction from salt lakes according to claim 1, characterized in that: The drying and curing in step (5) is carried out by drying at a temperature of 60 to 80°C for 20 to 30 minutes.
8. The method for preparing an in-situ circulating graft-modified polyamide nanofiltration membrane for lithium extraction from salt lakes according to claim 1, characterized in that: The base membrane is any one of a polyamide membrane, a polyimide membrane, a polysulfone membrane and a polyethersulfone membrane; and the organic solvent is n-hexane.
9. The modified polyamide nanofiltration membrane prepared by the method according to any one of claims 1 to 8.
10. Use of the modified polyamide nanofiltration membrane according to claim 9 in lithium extraction from salt lakes.