A deep eutectic solvent-induced furanic bio-based composite polyamide nanofiltration membrane

Abstract

The application belongs to the technical field of nanofiltration membranes, and discloses a eutectic solvent-induced furan bio-based composite polyamide nanofiltration membrane, and a preparation method thereof, which comprises four steps of synthesis of difuran dimethylamine monomers, pretreatment of an ultrafiltration membrane, preparation of an aqueous phase / organic phase solution, and interfacial polymerization to form a membrane; the interfacial polymerization aqueous phase is a mixed solvent of a eutectic solvent-water, the difuran dimethylamine is a monomer, and the organic phase is a polyacyl chloride solution.The difuran dimethylamine with a biomass source is used as the monomer, and dependence on petroleum-based raw materials is eliminated; the eutectic solvent is used to solve the bottleneck of poor water solubility of the furan monomer, the monomer diffusion kinetics is controlled through high viscosity of the eutectic solvent, excessive cross-linking is inhibited, a uniform and dense polyamide separation layer is formed, the trade-off effect between traditional membrane permeability and selectivity is broken, and the synergistic improvement of high water flux and ultra-high Mg 2+ / Li + separation selectivity is realized, the prepared nanofiltration membrane has excellent permeability and magnesium-lithium separation efficiency, and can be widely applied in the fields of water treatment and lithium extraction from salt lakes.

Description

Technical Field

[0001] This invention belongs to the field of nanofiltration membrane technology, specifically relating to a furan bio-based composite polyamide nanofiltration membrane induced by a eutectic solvent. Background Technology

[0002] Lithium, a key mineral resource known as "white oil," is experiencing a surge in demand in fields such as power batteries and energy storage devices. Among these, salt lake lithium resources represent a core potential area for lithium resource development. However, salt lake brines have long suffered from a high magnesium-to-lithium ratio, a characteristic that has become a core bottleneck restricting the efficient extraction of lithium from salt lakes—Mg... 2+ With Li + Because the hydration radii and physicochemical properties of lithium are similar, conventional separation techniques are insufficient to achieve efficient separation of the two, resulting in low efficiency and high cost in the development of lithium from salt lakes, which makes it difficult to meet the needs of industrial production.

[0003] Nanofiltration technology, with its outstanding advantages of low energy consumption, environmental friendliness, and ease of operation, has become a highly promising solution for lithium extraction from high magnesium-to-lithium ratio salt lakes. Its separation mechanism mainly relies on the size sieving effect and the Dornan electrostatic repulsion effect, and can specifically target Mg with similar hydration radii. 2+ With Li + Precise screening is crucial. However, current commercial nanofiltration membranes still face significant technical limitations: existing membrane materials are mostly based on petroleum-based polymers (such as polyethersulfone and aromatic polyamide), which have inherent defects in their chemical and microstructures, making it difficult to simultaneously achieve high permeability and high selectivity. This often results in a contradiction: "high flux but poor selectivity, and good selectivity but low flux." Furthermore, under high-pressure operation and in complex brine environments (high salinity and high hardness), these membrane materials are prone to membrane fouling, flux decay, and reduced selectivity, further limiting their large-scale application in lithium extraction from salt lakes. Therefore, developing membranes with both high water flux and high Mg content is essential. 2+ / Li + New nanofiltration membrane materials with selective separation and excellent environmental stability have become key to breaking through the current bottlenecks in lithium extraction technology from salt lakes and promoting the efficient development of lithium resources in salt lakes.

[0004] Addressing the limitations of traditional petroleum-based nanofiltration membranes, furan-based bio-based polyamide nanofiltration membranes offer a new pathway for the development of high-performance nanofiltration membranes due to their unique structural advantages. The furan ring possesses a rigid and electron-rich structural characteristic; polyamide nanofiltration membranes prepared based on this ring can construct a more regular and dense separation layer, theoretically significantly improving the separation efficiency of Mg2+. 2+ / Li +The separation selectivity of bio-based membranes is high, and the use of bio-based raw materials can reduce dependence on non-renewable petroleum-based raw materials. However, such bio-based membranes face a core technical bottleneck in mainstream interfacial polymerization processes that is difficult to overcome: their key monomers (such as 2,5-furandimethylamine) have extremely poor solubility in traditional aqueous solvents, making it impossible to prepare high-concentration monomer solutions that meet the requirements of interfacial polymerization. This severely limits the effective diffusion and full reaction of monomers at the oil-water interface, resulting in incomplete, loosely structured, and defective polyamide separation layers formed by polymerization. Consequently, they cannot realize their theoretical performance advantages, ultimately hindering the transition of such high-performance bio-based nanofiltration membranes from laboratory theoretical research to industrial practical applications.

[0005] In summary, the current field of lithium extraction from high magnesium-to-lithium ratio salt lakes faces dual technical bottlenecks: the difficulty in balancing the permeability and selectivity of nanofiltration membrane materials and the insufficient solubility of monomers in bio-based membranes. A feasible technical approach is urgently needed to solve these problems. Summary of the Invention

[0006] Addressing the technical bottlenecks of traditional petroleum-based polyamide nanofiltration membranes—namely, the non-renewable nature of the raw materials, high energy consumption during preparation, insufficient selectivity for separating high magnesium-to-lithium ratio brines, and the poor solubility of key monomers in bio-based furan polyamide nanofiltration membranes, making it difficult to prepare high-performance separation layers—the core objective of this invention is to provide a furan-based bio-based composite polyamide nanofiltration membrane induced by a low eutectic solvent. This solution addresses the challenge of efficient magnesium-to-lithium separation in high-salt, high-hardness brines, meeting the demand for high-performance, environmentally friendly separation membranes in lithium extraction from salt lakes.

[0007] The core idea of ​​this invention is to use difurandimethylamine derived from biomass as a monomer and employ a eutectic solvent-assisted interfacial polymerization process to construct a structurally regular and defect-free polyamide separation layer. By leveraging the characteristics of the eutectic solvent, the poor solubility of bio-based monomers and the challenges of interfacial polymerization kinetics control are simultaneously addressed, achieving nanofiltration membrane permeability comparable to that of Mg2+. 2+ / Li + The synergistic improvement in separation selectivity ultimately led to the preparation of a high-performance bio-based nanofiltration membrane suitable for lithium extraction from salt lakes.

[0008] Through in-depth research, this invention has discovered that eutectic solvents (DES), as green functional media formed by a specific combination of hydrogen bond acceptors and hydrogen bond donors, belong to the category of ionic liquid analogs. Their unique properties can specifically address the bottlenecks in the preparation of bio-based nanofiltration membranes. Specifically, compared to traditional aqueous solvents, DES exhibits a significantly higher solubility for the poorly soluble difuran dimethylamine monomer, effectively solving the core problem of its poor solubility. Simultaneously, its high viscosity allows it to act as a "diffusion regulator," precisely slowing the diffusion rate of the aqueous monomer to the organic phase. This enables precise control of the diffusion-reaction kinetics during interfacial polymerization, facilitating the formation of a polyamide separation layer with a reasonable crosslinking density and uniform nanopore structure. This discovery provides a feasible and efficient technical path for overcoming the bottlenecks in the preparation of bio-based furan polyamide nanofiltration membranes and improving membrane separation performance, and is one of the core innovations of this invention.

[0009] To achieve its objectives, the present invention employs the following technical solution: This invention first provides a method for preparing a furan-based bio-based composite polyamide nanofiltration membrane induced by a eutectic solvent, comprising the following steps: Step 1: Synthesis of difuran dimethylamine monomer. The specific operation is as follows: under low temperature conditions of -10℃ to 10℃, concentrated hydrochloric acid and furfurylamine are added to the reactor sequentially to form a salt; then levulinic acid is added dropwise, and the temperature is raised to 40~50℃ for 8~16 hours; after the reaction is completed, an alcohol solvent is added and the mixture is slurried, and the crude product is obtained by solid-liquid separation; the crude product is dissolved in an alkaline aqueous solution, extracted with an organic solvent, and the aqueous phase is acidified with hydrochloric acid to pH<2 to precipitate the product, which is then filtered after standing; the obtained solid is washed and dried to obtain difuran dimethylamine monomer.

[0010] Further, the molar ratio of furfurylamine, levulinic acid, and concentrated hydrochloric acid is 1.6~3:0.6~1.2:2.8~3.5; the alcohol solvent is at least one of methanol, ethanol, and isopropanol; and the organic solvent used for extraction is at least one of n-hexane, cyclohexane, dichloromethane, toluene, and ethyl acetate.

[0011] Step 2: Pretreatment of the ultrafiltration membrane. The specific operation is as follows: Immerse the ultrafiltration membrane in an alcohol solvent for 30-60 minutes, and then rinse it repeatedly with deionized water 3-5 times.

[0012] Furthermore, the ultrafiltration membrane is at least one of polyethersulfone membrane, polyvinyl chloride membrane, cellulose triacetate membrane, or polyvinylidene fluoride ultrafiltration membrane; the alcohol solvent is at least one of methanol, ethanol, and isopropanol.

[0013] Step 3, Preparation of aqueous and organic phase solutions: The difuran dimethylamine monomer prepared in step 1 is dissolved in a eutectic solvent composed of hydrogen bond acceptors and hydrogen bond donors, and then mixed with an alkaline aqueous solution to obtain an aqueous phase solution; polyacrylamide chloride is mixed with an organic phase solvent to obtain an organic phase solution.

[0014] Further, in the aqueous solution: the mass of the difurandimethylamine monomer accounts for 0.5 wt% to 1.5 wt% of the total mass of the aqueous solution; the base in the alkaline aqueous solution is at least one of sodium hydroxide, calcium hydroxide, and potassium hydroxide, and the molar ratio of the base to the difurandimethylamine monomer is 2 to 4:1; the hydrogen bond acceptor in the eutectic solvent is at least one of choline chloride, choline levulinate, betaine, hydrated zinc chloride, and amino acids, and the hydrogen bond donor is at least one of glycerol, ethylene glycol, citric acid, and lactic acid, and the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 5 to 7:1, and the mass of the eutectic solvent accounts for 30 wt% to 50 wt% of the total mass of the aqueous solution.

[0015] Further, in the organic phase solution: the polyacryl chloride includes at least one of pyromellitic tricarboxylic acid chloride, 3,4′,5-biphenyltricarboxylic acid chloride, 3,3′,5,5′-biphenyltetramethyl chloride, isophthaloyl chloride, 5-isocyanate isophthaloyl chloride, and 5-oxoformyl chloride isophthaloyl chloride, and the concentration of the polyacryl chloride in the organic phase solution is 0.10~0.30 wt%.

[0016] Step 4: Interfacial polymerization to prepare furan-based bio-based composite polyamide nanofiltration membrane. The specific operation is as follows: the pretreated ultrafiltration membrane is immersed in an aqueous solution for 10-20 min, and then excess solvent is removed to obtain an ultrafiltration membrane loaded with difuran dimethylamine in an aqueous phase; the obtained ultrafiltration membrane is placed in an organic phase solution and reacted for 1-5 min to complete the interfacial polymerization, and then subjected to thermosetting treatment to obtain a eutectic solvent-induced furan-based bio-based composite polyamide nanofiltration membrane.

[0017] Furthermore, the temperature of the thermosetting treatment is 60~80℃, and the time is 5~10 min.

[0018] The present invention also provides a furan bio-based composite polyamide nanofiltration membrane induced by a eutectic solvent prepared by the above preparation method, which has the following characteristics: the difuran dimethylamine monomer is derived from biomass, which can reduce the dependence on petroleum-based raw materials; the eutectic solvent can effectively solve the problem that the difuran dimethylamine monomer is difficult to dissolve in water, and its own viscosity can regulate the diffusion rate of the aqueous monomer, improve the permeability of the nanofiltration membrane, and enable the nanofiltration membrane to have high permeability-selectivity and effectively achieve magnesium-lithium separation.

[0019] Furthermore, the pure water flux of the nanofiltration membrane is 40 LMH bar. -1The above results show a MgCl2 rejection rate of 95.5% and a LiCl rejection rate of 31.5%, making it widely applicable in water treatment or lithium extraction from salt lakes.

[0020] Compared with the prior art, the beneficial effects of the present invention are reflected in: 1. Introducing DES to Solve the Problem of Solubility and Film Formation of Bio-based Monomers: This invention is the first to propose using a green eutectic solvent (DES) as an aqueous medium, innovatively solving the key technical bottleneck of poor solubility of high-performance bio-based bis(furan)dimethylamine monomers (such as 2,5-furandimethylamine) in traditional aqueous solvents. The high efficiency of DES allows for the preparation of high-concentration monomer solutions, ensuring the full progress of the interfacial polymerization reaction, thereby successfully preparing a complete, uniform, and defect-free furan polyamide separation layer, achieving an effective leap from molecular design to high-performance membrane preparation of bio-based materials.

[0021] 2. Precise Control of Interfacial Polymerization Kinetics Using DES Properties: This invention cleverly utilizes the high viscosity of DES as a "diffusion regulator" in the interfacial polymerization process. DES effectively slows down the diffusion rate of aqueous monomers to the organic phase, thereby precisely controlling the local monomer molar ratio and reaction kinetics at the reaction interface. This controlled polymerization process inhibits excessive crosslinking caused by overly rapid reactions, which is conducive to the formation of a polyamide network with a more reasonable crosslinking density and a more uniform nanoporous structure, laying the foundation for simultaneously improving membrane performance.

[0022] 3. Preparation of a high-performance magnesium-lithium separation membrane that overcomes the "trade-off" effect: The furan bio-based composite polyamide nanofiltration membrane prepared in this invention successfully overcomes the "trade-off" bottleneck of mutual constraint between permeability and selectivity in traditional membrane materials. This membrane exhibits excellent performance with synergistic improvement in permeability and selectivity, not only significantly increasing water flux but also achieving improved separation of Mg... 2+ / Li + The invention provides a new generation of core membrane materials and a feasible preparation scheme for the efficient and energy-saving extraction of lithium resources from brine in salt lakes with a high magnesium-to-lithium ratio. This invention achieves ultra-high separation selectivity. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the synthetic route of the difuran dimethylamine monomer in an embodiment of the present invention.

[0025] Figure 2 The image shows the 1H NMR spectrum of the difuran dimethylamine monomer prepared in Example 1.

[0026] Figure 3 Images (a) through (d) are scanning electron microscope (SEM) images of the nanofiltration membranes prepared in Example 1 and Comparative Examples 1, 3, and 4 of this invention, respectively.

[0027] Figure 4 This is a comparison chart showing the separation performance of nanofiltration membranes prepared in Example 1 and Comparative Examples 1-4 of the present invention. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1 This embodiment provides a method for preparing a furan-based bio-based composite polyamide nanofiltration membrane induced by a eutectic solvent, the specific steps of which are as follows: Step 1: Synthesis of difurandimethylamine monomer: At -5℃, 600 mL of concentrated hydrochloric acid was added to a three-necked flask, and then furfurylamine was slowly added dropwise using a constant pressure burette. As the reaction was exothermic, the temperature was controlled at around 0℃ and stirred for 30 min. Then, levulinic acid was added dropwise, with a molar ratio of furfurylamine, levulinic acid and hydrochloric acid of 2:1:3.2. The temperature was raised to 40℃ and the reaction was carried out for 12 h. After the reaction was completed, 600 mL of methanol solvent was added and stirred for 30 min. The solid and liquid phases were separated by centrifugation for 30 min to obtain the crude product. 2M sodium hydroxide aqueous solution was added to the crude product to adjust the pH to >11, and the mixture was stirred for 30 min to completely dissolve the product in water. The product was extracted three times with dichloromethane to separate the organic phase. Then, concentrated hydrochloric acid was added to the aqueous phase until a solid product precipitated (at which point the pH <2). The mixture was left at room temperature overnight to allow the product to completely precipitate as salt. The product was filtered to obtain a light brown solid, which was then dried in a vacuum drying oven at 50℃ to obtain the difurandimethylamine monomer.

[0030] Step 2, Pretreatment of ultrafiltration membrane: Immerse the polyethersulfone ultrafiltration membrane in ethanol for 60 min, then rinse it repeatedly with deionized water 3 times for later use.

[0031] Step 3: Preparation of the aqueous and organic phase solutions: 0.2 g (0.598 mmol) of the difurandimethylamine monomer prepared in Step 1 was dissolved in 8 g of a eutectic solvent composed of choline chloride (hydrogen bond acceptor) and ethylene glycol (hydrogen bond donor) (molar ratio of choline chloride to ethylene glycol: 1:6) to obtain a eutectic solvent containing difurandimethylamine; 1.794 mmol of sodium hydroxide was dissolved in deionized water to obtain 12 g of sodium hydroxide aqueous solution; the eutectic solvent containing difurandimethylamine was mixed with the sodium hydroxide aqueous solution to prepare an aqueous phase solution with a total mass of 20 g. Simultaneously, pyromellitic acid chloride was dissolved in n-hexane to prepare an organic phase solution with a concentration of 0.20 wt%.

[0032] Step 4: Interfacial polymerization to prepare nanofiltration membrane: The pretreated polyethersulfone ultrafiltration membrane is immersed in the above aqueous solution for 15 min. After removing the excess aqueous solvent from the membrane surface and wiping the surface water stains, it is then placed in the organic solution to react for 5 min to complete the interfacial polymerization. After removing the excess organic solvent from the membrane surface, it is placed in a 60℃ water bath for heat curing treatment for 10 min to obtain the eutectic solvent-induced furan bio-based composite polyamide nanofiltration membrane.

[0033] Example 2 In this embodiment, a furan-based bio-based composite polyamide nanofiltration membrane induced by a eutectic solvent was prepared using the same method as in Example 1, except that the molar ratio of furfurylamine, levulinic acid, and hydrochloric acid in step 1 was replaced with 3:1:3.

[0034] Example 3 In this embodiment, a furan-based bio-based nanofiltration membrane induced by a eutectic solvent was prepared using the same method as in Example 1, except that the polyethersulfone ultrafiltration membrane in step 2 was replaced with a polyvinylidene fluoride ultrafiltration membrane.

[0035] Example 4 In this embodiment, a furan-based bio-based composite polyamide nanofiltration membrane induced by a eutectic solvent was prepared using the same method as in Example 1, except that the mass fraction of the difuran dimethylamine monomer in the entire aqueous phase in step 3 was adjusted to 2%.

[0036] Example 5 In this embodiment, a furan bio-based composite polyamide nanofiltration membrane induced by a eutectic solvent was prepared using the same method as in Example 1, except that the mass fraction of the eutectic solvent in the entire aqueous phase in step 3 was adjusted to 50%.

[0037] Example 6 In this embodiment, a furan bio-based composite polyamide nanofiltration membrane induced by a eutectic solvent was prepared using the same method as in Example 1, except that the molar ratio of choline chloride and ethylene glycol in the eutectic solvent in step 3 was adjusted to 1:5.

[0038] Example 7 In this embodiment, a furan-based bio-based composite polyamide nanofiltration membrane induced by a eutectic solvent was prepared using the same method as in Example 1, except that the mass fraction of pyromellitic trimethylol chloride in the organic solvent in step 3 was adjusted to 0.30 wt%.

[0039] Example 8 In this embodiment, a furan-based bio-based composite polyamide nanofiltration membrane induced by a eutectic solvent was prepared using the same method as in Example 1, with the only difference being that the thermosetting temperature in step 4 was adjusted to 80°C and the thermosetting time was adjusted to 5 min.

[0040] Comparative Example 1 This comparative example prepared a furan bio-based composite polyamide nanofiltration membrane induced by a eutectic solvent using the same method as in Example 1, except that the hydrogen bond donor and hydrogen bond acceptor in the eutectic solvent of step 3 were replaced with oxalic acid and choline chloride, respectively.

[0041] Comparative Example 2 This comparative example prepared a furan bio-based composite polyamide nanofiltration membrane induced by a eutectic solvent using the same method as in Example 1, except that the hydrogen bond donor and hydrogen bond acceptor in the eutectic solvent of step 3 were replaced with urea and choline chloride, respectively.

[0042] Comparative Example 3 This comparative example prepared a furan-based bio-based polyamide nanofiltration membrane using the same method as in Example 1, except that the eutectic solvent in step 3 was replaced with pure water.

[0043] Comparative Example 4 This comparative example prepared a polyamide nanofiltration membrane using the same method as in Example 1, except that the aqueous solution in step 3 was replaced with a pure aqueous solution of anhydrous piperazine with a mass concentration of 0.35 wt%.

[0044] The polyamide nanofiltration membranes obtained in Examples 1-8 and Comparative Examples 1-4 were tested using the following specific test methods: (1) By nuclear magnetic resonance hydrogen spectrum ( 1 The structure of furan monomers was characterized by H NMR. Figure 2 The image shows the 1H NMR spectrum of the difuran dimethylamine monomer prepared in Example 1. Figure 2 As shown, the characteristic chemical shifts of ¹H NMR (400 MHz, deuterated dimethyl sulfoxide DMSO-d6, 25 °C) are: δ 12.01 ppm (-COOH), 8.61 ppm (-NH2), 6.47 / 6.21 ppm (-CH=). These characteristic peaks are in complete agreement with the theoretical structure of the target difuran dimethylamine monomer, proving that the monomer was successfully synthesized.

[0045] (2) The surface morphology and cross-sectional thickness of the nanofiltration membrane were characterized using a scanning electron microscope (Hitachi S4800) under the following test conditions: voltage 4 kV and current 7 μA. Figure 3 Images (a) to (d) are SEM images of the nanofiltration membranes prepared in Example 1 and Comparative Examples 1, 3, and 4. Figure 3 As shown, the nanofiltration membrane of Example 1 exhibits a uniformly distributed raised nodular structure on its surface. Compared with the membrane surface morphology of Comparative Examples 1, 3, and 4, it has a higher roughness and a larger effective permeable surface area. This structural feature is beneficial for increasing the contact area between the membrane and water, reducing water mass transfer resistance, and thus improving the membrane's pure water permeability.

[0046] (3) The hydrophilicity of the membrane surface was characterized using a German Dataphysics DCAT21 surface tension / dynamic contact angle measuring instrument. The method was as follows: 3 μL of water was dropped freely onto the membrane surface, the initial contact angle of the membrane was observed, and the dynamic change process of the contact angle was recorded by video. Each set of data was measured at least 5 times, and the average value was taken as the final result.

[0047] (4) Nanofiltration membrane flux: Nanofiltration membrane flux refers to the volume of permeate passing through a unit area of ​​membrane per unit time under a certain pressure. Pure water permeability J (Unit: L m) -2 h -1 bar -1 LMH bar -1 ) and water flux F (Unit: L m) -2 h -1 Calculate according to equations (1) and (2) respectively: (1) (2) In the formula, V The volume of permeate during the test, in liters (L). P The operating pressure of the device during the test, in bar; A Effective membrane area, in m² 2 ; The test time is in hours (h).

[0048] The test used a cross-flow filtration device with an effective membrane area of ​​7.068 cm². 2 (The radius of the permeate tank is 1.5 cm). Pre-pressurize at 25℃ and 6.0 bar for 30 min until the pressure stabilizes. Control the cross-flow velocity at 45 LPH. Record the permeate volume every 10 min and take the average value of multiple measurements.

[0049] (5) Retention rate of nanofiltration membrane: The rejection rate reflects the ability of a nanofiltration membrane to retain a certain solute. R The calculation formula is shown in equation (3): (3) In the formula, C f This refers to the ion concentration of the feed liquid. C p The ion concentration of the permeate is given. The conductivity of the feed solution and permeate was measured using a conductivity meter. The conductivity was used to characterize the ion concentration and calculate the rejection rate. A 2000 ppm MgCl2 and LiCl solution was used as the feed solution. The solution was pre-compressed at 25℃ and 6.0 bar for 30 min, with a cross-flow rate of 45 LPH. Conductivity was measured every 30 min, and multiple measurements were taken to obtain the average value.

[0050] Experimental results are as follows Figure 4 As shown in Table 1: Table 1 Test results of each embodiment and comparative example

[0051] Examples 1-8 are furan-based bio-based polyamide nanofiltration membranes prepared by DES-assisted interfacial polymerization using a choline chloride-ethylene glycol system; Comparative Example 1 is a furan-based bio-based polyamide nanofiltration membrane prepared by DES using a choline chloride-oxalic acid system; Comparative Example 2 is a furan-based bio-based polyamide nanofiltration membrane prepared by DES using a choline chloride-urea system; Comparative Example 3 is a furan-based bio-based polyamide nanofiltration membrane prepared using pure water as a solvent without the addition of DES; Comparative Example 4 is a conventional polyamide nanofiltration membrane prepared using pure water as a solvent and anhydrous piperazine as an aqueous monomer.

[0052] The data in the table clearly show that Example 1 exhibits excellent permeability and high magnesium-lithium separation performance. The furan-based polyamide nanofiltration membrane prepared in this invention achieves a synergistic improvement in high-purity water permeability and high magnesium-lithium separation selectivity. Its core mechanism stems from the precise control of the interfacial polymerization process and the membrane microstructure: First, DES, as a highly efficient solvent and diffusion regulator, can inhibit excessively fast interfacial polymerization reaction rates and over-crosslinking, promoting the formation of a polyamide network with moderate crosslinking density and a more loose and uniform structure, significantly reducing the mass transfer resistance of water within the membrane, thereby greatly improving the membrane's water permeability. Second, this controllable reaction process can construct nanopores with narrower pore size distribution and more ideal charge properties. Combined with the precise sieving effect brought about by the rigid structure of the furan ring, it can efficiently distinguish Mg with slight differences in hydration radius. 2+ and Li + Meanwhile, the differentiated interactions between specific chemical groups and different ions in the polyamide network further enhance the retention of magnesium ions, ultimately achieving ultra-high separation selectivity while maintaining high throughput.

[0053] A comparison of Example 1 with Comparative Examples 1 and 2 reveals that the key advantage of the choline chloride / ethylene glycol DES system lies in its moderate viscosity and reactivity. This system not only efficiently dissolves bio-based monomers but also serves as an ideal polymerization kinetic modifier, promoting the formation of a more uniform and porous polyamide network structure. The resulting membrane exhibits stronger hydrophilicity and a more optimized pore structure, thus demonstrating higher water flux while maintaining a high rejection rate, significantly reducing the operating energy consumption in actual separation processes.

[0054] Compared to Comparative Examples 3-4, DES plays a crucial dual role in this invention: firstly, it can efficiently dissolve the rigid, poorly soluble bio-based difuran dimethylamine monomer, fundamentally solving the technical problem of its extremely low solubility in pure water; secondly, its high viscosity precisely slows down the diffusion rate of the monomer from the aqueous phase to the organic phase, inhibiting runaway reaction and excessive cross-linking. These effects synergistically optimize the polyamide network structure, enabling the membrane to maintain high separation selectivity while constructing more efficient water transport channels, thereby significantly improving water permeability and achieving a substantial improvement in the overall membrane performance.

[0055] In summary, this invention presents a method for preparing furan-based bio-based composite polyamide nanofiltration membranes using eutectic solvent-assisted interfacial polymerization. The resulting membrane exhibits both excellent permeability and high magnesium-lithium separation selectivity. This invention innovatively introduces a green eutectic solvent (DES) into the interfacial polymerization system, solving for the first time the core technical challenge of poor solubility of bio-based difurandimethylamine monomers. Simultaneously, by utilizing the high viscosity of DES, the kinetics of monomer diffusion and interfacial polymerization reactions are precisely controlled, inhibiting excessive crosslinking and forming a uniform and stable polyamide separation layer. The resulting bio-based nanofiltration membrane successfully overcomes the "trade-off" effect that traditionally restricts permeability and selectivity in nanofiltration membranes, achieving high water flux and ultra-high magnesium-lithium separation selectivity. 2+ / Li + The synergistic improvement in separation selectivity provides a new generation of efficient and energy-saving membrane materials and preparation solutions for lithium extraction from salt lakes.

[0056] The present invention has been described above by way of example. It should be noted that, without departing from the core of the present invention, any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort fall within the protection scope of the present invention.

Claims

1. A method for preparing a furan-based bio-based composite polyamide nanofiltration membrane induced by a eutectic solvent, characterized in that, Includes the following steps: Step 1: Using furfurylamine and levulinic acid as raw materials, difuran dimethylamine monomer is synthesized under acidic conditions through salt formation and addition reactions; Step 2: Pre-treat the ultrafiltration membrane by soaking it in an alcohol solvent and rinsing it with deionized water; Step 3: Dissolve the difuran dimethylamine monomer prepared in Step 1 in a eutectic solvent composed of hydrogen bond acceptors and hydrogen bond donors, and then mix it with an alkaline aqueous solution to obtain an aqueous solution; mix the polyacrylamide chloride with an organic solvent to obtain an organic solution. Step 4: The pretreated ultrafiltration membrane is sequentially immersed in the aqueous phase solution and the organic phase solution to carry out interfacial polymerization reaction, and then subjected to thermosetting treatment to obtain a furan bio-based composite polyamide nanofiltration membrane induced by eutectic solvent.

2. The preparation method according to claim 1, characterized in that, The specific operation of step 1 is as follows: under low temperature conditions of -10℃ to 10℃, concentrated hydrochloric acid and furfurylamine are added to the reactor in sequence to form salt; then levulinic acid is added dropwise, and the temperature is raised to 40~50℃ for 8~16 hours; after the reaction is completed, an alcohol solvent is added to slurry, and the crude product is obtained by solid-liquid separation; the crude product is dissolved in an alkaline aqueous solution, extracted with an organic solvent, and the aqueous phase is acidified with hydrochloric acid to pH<2 to precipitate the product, which is then filtered after standing; the obtained solid is washed and dried to obtain the difuran dimethylamine monomer.

3. The preparation method according to claim 2, characterized in that: The molar ratio of furfurylamine, levulinic acid, and concentrated hydrochloric acid is 1.6~3:0.6~1.2:2.8~3.5; the alcohol solvent is at least one of methanol, ethanol, and isopropanol; and the organic solvent used for extraction is at least one of n-hexane, cyclohexane, dichloromethane, toluene, and ethyl acetate.

4. The preparation method according to claim 1, characterized in that, Step 2 involves immersing the ultrafiltration membrane in an alcohol solvent for 30-60 minutes, and then rinsing it repeatedly with deionized water 3-5 times.

5. The preparation method according to claim 1 or 4, characterized in that: The ultrafiltration membrane is a polyethersulfone membrane, a polyvinyl chloride membrane, a cellulose triacetate membrane, or a polyvinylidene fluoride ultrafiltration membrane, and the alcohol solvent is at least one or a combination of methanol, ethanol, and isopropanol.

6. The preparation method according to claim 1, characterized in that, In the aqueous solution described in step 3: the mass of the difurandimethylamine monomer accounts for 0.5 wt% to 1.5 wt% of the total mass of the aqueous solution; the base in the alkaline aqueous solution is at least one of sodium hydroxide, calcium hydroxide, and potassium hydroxide, and the molar ratio of the base to the difurandimethylamine monomer is 2 to 4:1; the hydrogen bond acceptor in the eutectic solvent is at least one of choline chloride, choline levulinate, betaine, hydrated zinc chloride, and amino acids, and the hydrogen bond donor is at least one of glycerol, ethylene glycol, citric acid, and lactic acid, and the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 5 to 7:1, and the mass of the eutectic solvent accounts for 30 wt% to 50 wt% of the total mass of the aqueous solution.

7. The preparation method according to claim 1, characterized in that, In the organic phase solution of step 3: the polyacryl chloride includes at least one of pyromellitic tricarboxylic acid chloride, 3,4′,5-biphenyltricarboxylic acid chloride, 3,3′,5,5′-biphenyltetramethyl chloride, isophthaloyl chloride, 5-isocyanate isophthaloyl chloride, and 5-oxoformyl chloride isophthaloyl chloride, and the concentration of the polyacryl chloride in the organic phase solution is 0.10~0.30 wt%.

8. The preparation method according to claim 1, characterized in that, The specific operation of step 4 is as follows: the pretreated ultrafiltration membrane is immersed in an aqueous solution for 10-20 min, and then the excess solvent is removed to obtain an ultrafiltration membrane loaded with difuran dimethylamine in an aqueous phase; the obtained ultrafiltration membrane is placed in an organic phase solution and reacted for 1-5 min to complete the interfacial polymerization, and then subjected to thermal curing treatment to obtain a furan bio-based composite polyamide nanofiltration membrane induced by eutectic solvent.

9. The preparation method according to claim 8, characterized in that, The thermosetting treatment is performed at a temperature of 60-80℃ for 5-10 minutes.

10. A furan-based bio-based composite polyamide nanofiltration membrane induced by a eutectic solvent, characterized in that, It is prepared by any one of claims 1-9.

Images