A polyamide composite nanofiltration membrane modified by a multi-reactive group ionic liquid, a preparation method and application thereof

Abstract

This invention belongs to the field of membrane separation technology and discloses a polyamide composite nanofiltration membrane modified with a multi-reactive ionic liquid, its preparation method, and its applications. This invention prepares a polyamide nanofiltration membrane with high antibacterial properties, chlorine resistance, charge controllability, high flux, and high rejection rate through interfacial polymerization by adding an ionic liquid with multi-reactive groups (amino or hydroxyl) to an aqueous monomer. The polyamide nanofiltration membrane prepared by this invention has good flow retention performance, high water flux, and multifunctionality, and has broad application prospects in seawater desalination, wastewater treatment, and other fields.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to a polyamide composite nanofiltration membrane modified with a multi-reactive-group ionic liquid, its preparation method, and its application. Background Technology

[0002] Membrane separation technology has become the most widely used and effective method for solving problems such as desalination of brackish water, water pollution treatment and resource extraction due to its advantages such as convenient operation, high separation efficiency and no subsequent pollution.

[0003] Nanofiltration membrane technology is one of the most promising technologies for seawater desalination and wastewater treatment, characterized by low cost, high speed, strong selectivity, and flexible integration with other processes. Mainstream nanofiltration membranes have a thin-layer composite structure consisting of a porous substrate and an ultrathin, dense separation layer. This ultrathin, dense separation layer is typically prepared using interfacial polymerization. In interfacial polymerization, reactive monomers (usually diamines and polyacrylamide chlorides) are dissolved in two insoluble phases (such as water and n-hexane), and the two monomers undergo interfacial condensation polymerization on the surface of the porous support. The result is a dense, ultrathin active layer formed on the porous support, which plays a major role in selectivity. Therefore, how to control the interfacial polymerization reaction to design and prepare a high-performance polyamide skin is one of the most important aspects of the thin-layer composite nanofiltration / reverse osmosis membrane preparation process.

[0004] Ionic liquids (room-temperature ionic liquids, abbreviated as RTILs) have become an ideal alternative to traditional solvents due to their advantages such as low vapor pressure and no environmental pollution, attracting increasing attention and being hailed as "green solvents." Furthermore, ionic liquids typically possess many unique properties, such as low melting points, tunable Lewis acidity, good conductivity, wide electrochemical windows, negligible vapor pressure, wide operating temperatures, and special solubility, making them applicable in fields such as organic synthesis, catalysis, and batteries. A recent study (Angewandte Chemie International Edition, 2021, 60, 14636-14643) reported the use of non-reactive ionic liquids as solvents to replace the traditional aqueous phase. Utilizing the strong solvation capabilities of ionic liquids, the selection range of amine monomers was broadened, leading to the synthesis of polyamide nanofilms with ultra-low thickness and high cross-linking degree, achieving precise tuning of the pore size of the polyamide nanofilms at the angstrom scale. However, the polyamide skin prepared by the interfacial polymerization of acyl chloride and amine in this novel ionic liquid-alkane solvent system has a negatively charged surface, a narrow range of charge control, and the thin-layer composite membrane lacks antibacterial properties. Ionic liquids possess designable chemical structures, and their physicochemical properties can be altered by different substituent structures of anions / cations. Based on practical applications, ionic liquids with reactive functional groups and specific application functions can be designed and synthesized as monomers for novel interfacial polymerization reactions to prepare multifunctional polyamide thin-layer composite nanofiltration membranes with high retention capacity and high flux. Summary of the Invention

[0005] To address the problems of extremely fast interfacial polymerization reaction rates and poor controllability in existing technologies, the first objective of this invention is to provide a method for preparing a polyamide composite nanofiltration membrane modified with a multi-reactive-group ionic liquid, in which a diamino or dihydroxy ionic liquid is used as a reactive monomer in the aqueous phase to participate in the reaction.

[0006] The present invention adopts the following technical solution:

[0007] Step (1): Dissolve piperazine or m-phenylenediamine and a multi-reactive-group ionic liquid in water as the aqueous phase, and dissolve trimesoyl chloride (TMC) in n-hexane as the organic phase; the multi-reactive-group ionic liquid is one of diamino imidazole salt ionic liquid, monoamino imidazole salt glycine ionic liquid, or monoamino quaternary ammonium salt glycine ionic liquid, and the concentration of the multi-reactive-group ionic liquid is 0.5–1 wt%.

[0008] Preferably, the multi-reactive-group ionic liquid is one of 1-aminoethyl-3-methylimidazolium glycinate, 1-aminopropyl-3-methylimidazolium glycinate, diaminoethylimidazolium bis(trifluoromethanesulfonyl)imide, diaminopropylimidazolium bis(trifluoromethanesulfonyl)imide, and 1,1,1-trimethylhydrazine iodide.

[0009] Step (2): Fix the bottom membrane in a specific polymerization device, add an aqueous phase to wet the surface of the bottom membrane for a period of time, remove the excess aqueous phase, add an organic phase to polymerize; after the reaction is complete, pour out the organic phase, dry and solidify it, soak it in deionized water at room temperature, take it out and dry it to obtain the polyamide composite nanofiltration membrane modified with multi-reactive group ionic liquid; wherein, the bottom membrane is a polyethersulfone (PES) membrane.

[0010] Preferably, the concentration of piperazine or m-phenylenediamine in step (1) is 0.5-1 wt%, and the concentration of pyromellitic methyl chloride is 0.15-0.2 wt%.

[0011] Preferably, the wetting time after adding the aqueous phase in step (2) is 2 to 3 minutes, and the polymerization time after adding the organic phase is 1 to 2 minutes;

[0012] Preferably, the drying temperature in step (2) is 65-80°C and the curing time is 5-10 min;

[0013] Preferably, the soaking time in step (2) is 1 to 3 days.

[0014] The second objective of this invention is to provide a polyamide composite nanofiltration membrane modified with a multi-reactive-group ionic liquid prepared by the above method, which has the characteristics of high cross-linking degree, adjustable charge, antibacterial and oxidation resistance, high water flux and high retention performance for divalent and monovalent ions.

[0015] The third objective of this invention is to provide applications of the polyamide composite nanofiltration membrane modified with multi-reactive-group ionic liquids in seawater desalination, lithium extraction from salt lakes, and wastewater treatment.

[0016] Compared with existing technologies, the present invention has the following advantages:

[0017] (1) The nanofiltration membrane prepared by this invention has a high degree of cross-linking when used for ion separation, and is effective against Mg. 2+ / Ca 2+ / Ba 2+ Plasma has good interception rate and high water flux, and has good application prospects in the fields of seawater desalination and wastewater treatment.

[0018] (2) When the nanofiltration membrane prepared by the present invention is used for ion separation, it has a high reusability and strong anti-fouling ability. Moreover, the repeated use has little impact on the interception rate and water flux, making it suitable for large-scale industrial production.

[0019] (3) When the nanofiltration membrane prepared by the present invention is used for ion separation, it has the characteristic of adjustable charge. Since the added ionic liquid is charged, while the traditional polyamide nanofiltration membrane is negatively charged, the surface charge of the nanofiltration membrane can be controlled by adjusting the content of the ionic liquid. Thin-layer composite polyamide membranes with positive charge on the surface can be prepared for special applications such as lithium extraction from salt lakes that require the separation membrane material to have a positive charge on the surface.

[0020] (4) When the nanofiltration membrane prepared by the present invention is used for ion separation, it has the characteristic of antibacterial properties because the added ionic liquid has imidazole groups and quaternary ammonium salt groups, which have good antibacterial effects. Attached Figure Description

[0021] Figure 1 This is the structural formula of the ionic liquid used in this invention.

[0022] Figure 2 The flow rejection ratio of the nanofiltration membrane in a 1000 mg / L salt solution is given. M0 represents the nanofiltration membrane without added ionic liquid as a monomer, and M1 represents the nanofiltration membrane with added ionic liquid as a monomer. (Test conditions: Temperature = 25℃, Pressure = 0.6 MPa, Flow rate = 30 L / h)

[0023] Figure 3 This study tested the long-term stability of the nanofiltration membrane of the present invention in a 1000 mg / L sodium sulfate aqueous solution. (Test conditions: temperature = 25°C, pressure = 0.6 MPa, flow rate = 30 L / h)

[0024] Figure 4 The diagram shows the antibacterial performance characterization of the nanofiltration membrane of the present invention. In the diagram, A represents the antibacterial result of the nanofiltration membrane (M0) without added ionic liquid as a monomer against *Escherichia coli*, B represents the antibacterial result of the nanofiltration membrane (M1) with added ionic liquid as a monomer against *Escherichia coli*, C represents the antibacterial result of the nanofiltration membrane (M0) without added ionic liquid as a monomer against *Staphylococcus aureus*, and D represents the antibacterial result of the nanofiltration membrane (M1) with added ionic liquid as a monomer against *Staphylococcus aureus*.

[0025] Figure 5 This is a Zeta potential characterization diagram of the nanofiltration membrane of the present invention. M0 represents the nanofiltration membrane without the addition of ionic liquid as a monomer, and M1 represents the nanofiltration membrane with the addition of ionic liquid as a monomer. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0027] This invention provides a method for preparing a polyamide composite nanofiltration membrane modified with a multi-reactive-group ionic liquid, the specific implementation of which is as follows:

[0028] Step (1): Dissolve piperazine or m-phenylenediamine with a concentration of 0.5-1 wt% and a multi-reactive-group ionic liquid with a concentration of 0.5-1 wt% in water as the aqueous phase, and dissolve trimesoyl chloride (TMC) with a concentration of 0.15-0.2 wt% in n-hexane as the organic phase; the multi-reactive-group ionic liquid is one of 1-aminoethyl-3-methylimidazolium glycinate, 1-aminopropyl-3-methylimidazolium glycinate, diaminoethylimidazolium bis(trifluoromethanesulfonyl)imide, diaminopropylimidazolium bis(trifluoromethanesulfonyl)imide, and 1,1,1-trimethylhydrazine iodide.

[0029] Step (2): Fix the PES substrate membrane in a specific polymerization device, add an aqueous phase to wet the substrate membrane surface for 2-3 minutes, remove the excess aqueous phase, add an organic phase to polymerize for 1-2 minutes; after the reaction is complete, pour out the organic phase, dry and cure at 65-80℃ for 5-10 minutes, soak in deionized water at room temperature for 1-3 days, take it out and dry to obtain the polyamide composite nanofiltration membrane modified with multi-reactive group ionic liquid.

[0030] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0031] The PES membrane described below was purchased from Zhongke Ruiyang Membrane Technology Co., Ltd.; the pore size of the PES membrane is 0.05-0.1μm.

[0032] Example 1: Preparation of polyamide composite nanofiltration membrane modified with multi-reactive ionic liquid

[0033] (1) Dissolve 1 wt% piperazine and 0.5 wt% bis(aminoethyl)imidazolium bis(trifluoromethanesulfonyl)imide salt ionic liquid in water as the aqueous phase, and dissolve 0.2 wt% TMC in n-hexane as the organic phase.

[0034] (2) Fix the PES substrate in a specific polymerization device, add 5 ml of aqueous phase, let stand for 2 min and then pour out the aqueous phase, then add 5 ml of organic phase and perform polymerization reaction for 1 min and then pour out the organic phase, put it in a 70℃ oven to cure for 5 min and then take it out, soak it in deionized water for 1 day, and after drying, obtain a polyamide composite nanofiltration membrane modified with multi-reactive group ionic liquid.

[0035] Example 2: Preparation of polyamide composite nanofiltration membrane modified with multi-reactive group ionic liquid

[0036] (1) Dissolve 0.5 wt% piperazine and 1 wt% monoamino imidazole salt glycine ionic liquid in water as the aqueous phase, and dissolve 0.15 wt% TMC in n-hexane as the organic phase.

[0037] (2) Fix the membrane in a specific polymerization device, add 5 ml of aqueous phase, let stand for 2 min and then pour out the aqueous phase, then add 5 ml of organic phase and carry out polymerization reaction for 1 min and then pour out the organic phase, put it in a 65℃ oven to cure for 10 min and then take it out, soak it in deionized water for 2 days, and after drying, obtain a polyamide composite nanofiltration membrane modified with multi-reactive group ionic liquid.

[0038] Example 3: Preparation of polyamide composite nanofiltration membrane modified with multi-reactive group ionic liquid

[0039] (1) Dissolve 1 wt% piperazine and 0.5 wt% mono-amino quaternary ammonium salt glycine ionic liquid in water as the aqueous phase, and dissolve 0.2 wt% TMC in n-hexane as the organic phase.

[0040] (2) Fix the membrane in a specific polymerization device, add 5 ml of aqueous phase, let stand for 3 min and then pour out the aqueous phase, then add 5 ml of organic phase for polymerization reaction for 2 min and pour out the organic phase, put it in an 80℃ oven to cure for 5 min and then take it out, soak it in deionized water for 3 days, and after drying, obtain a polyamide composite nanofiltration membrane modified with multi-reactive group ionic liquid.

[0041] Test Example 1: Interception Performance Test

[0042] The retention rate can be used to represent the membrane's retention performance for a certain solute, as shown in equation (1):

[0043] R = (C f -C p ) / C f ×100% (1)

[0044] Among them, C f (mg / L) represents the concentration of the solute in the feed solution, C p (mg / L) indicates the concentration of the solute in the permeate.

[0045] The prepared polyamide nanofiltration membrane was placed in a cross-flow apparatus. Na₂SO₄, MgSO₄, and MgCl₂ salt solutions (all at a concentration of 1000 mg / L) were added to the feed side. The filtrate after nanofiltration was collected, and its conductivity was measured using a conductivity meter. The cutoff rate is as follows: Figure 1 As shown.

[0046] The nanofiltration membrane with an ionic liquid polyamide coating showed a rejection rate of 95.5% for Na2SO4, 93.8% for MgSO4, and 76.6% for MgCl2.

[0047] The nanofiltration membrane with a polyamide coating without the addition of a multifunctional ionic liquid was subjected to the above tests. The measured rejection rates were 98.0% for Na2SO4, 95.2% for MgSO4, and 71.8% for MgCl2.

[0048] Test Example 2: Water Flux Test

[0049] Water flux represents the volume of water flowing through a unit membrane area per unit time under a certain pressure, and is specifically calculated according to formula (2):

[0050] J=V / (A*T) (2)

[0051] Where V(L) represents the volume of filtrate, and A(m 2 ) represents the test area of ​​the sample, and T(h) represents the time taken to collect filtrate of volume V.

[0052] The water flux measured by the nanofiltration membrane with the ionic liquid polyamide coating was between 21 and 23 L·h. -1 ·m -2 ·bar -1 Within the range.

[0053] The nanofiltration membrane with a polyamide coating without the addition of a multifunctional ionic liquid was subjected to the above tests, and the water flux was measured to be between 18 and 20 L·h. -1 ·m -2 ·bar -1 Within the range.

[0054] Test Example 3: Long-term operational stability test

[0055] The nanofiltration membrane was placed in a cross-flow testing device, using a 1000 mg / L Na₂SO₄ aqueous solution as the feed solution. Under test conditions of 0.6 MPa, 30℃, and a cross-flow rate of 30 L / h, the nanofiltration performance was tested over time during continuous operation. Specifically, after a 30-minute pre-pressurization period, the water flux and Na₂SO₄ rejection rate were measured at the first time point. Subsequently, the nanofiltration performance was measured every 12 hours for a total of over 100 hours. The test results are as follows: Figure 2 As shown.

[0056] Test Example 4: Antibacterial Performance Test

[0057] The *E. coli* bacterial suspension was diluted to 10⁵ CFU / mL with PBS. 100 μL of the diluted suspension was added to the surface of each corresponding numbered sample. The samples were incubated at 37°C for 24 hours. After incubation, the samples were rinsed with 10 mL of sterile PBS, sonicated for 5 min, and then the co-culture solution was serially diluted 10-fold with sterile PBS. 100 μL of each diluted solution was evenly spread onto LB agar plates. The samples were incubated at 37°C for 18 hours, and then photographed and the colony count was recorded. The test results are as follows: Figure 3 As shown.

[0058] Test Example 5: Membrane Surface Potential Test

[0059] The membrane surface potential was measured by a surface analyzer using the flow potential method to analyze the charge on the membrane surface. The specific test procedure is as follows: First, the sample was precisely cut into two 1×2cm rectangles, and then firmly attached to the two sample stages with the test face facing outwards. The distance between the sample stages was adjusted to 100μm. A 1mM KCl solution was used as the test environment solution, and the pH of the solution was adjusted using hydrochloric acid and sodium hydroxide. The zeta potential values ​​of the sample surface were measured under different pH conditions. The test results are shown below. Figure 4 As shown.

[0060] The above embodiments are preferred embodiments of the present invention, but the technical embodiments of the present invention are not limited to the above embodiments. Any simplifications, changes, substitutions, modifications, or combinations made that deviate from the principles and spirit of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a polyamide composite nanofiltration membrane modified with a multi-reactive-group ionic liquid, characterized in that, The preparation method includes the following steps: Step (1): Dissolve piperazine or m-phenylenediamine and a multi-reactive-group ionic liquid in water as the aqueous phase, and dissolve trimesoyl chloride (TMC) in n-hexane as the organic phase; wherein, the multi-reactive-group ionic liquid is one of a diamino imidazolium salt ionic liquid, a monoamino imidazolium salt glycine ionic liquid, or a monoamino quaternary ammonium salt glycine ionic liquid, and the concentration of the multi-reactive-group ionic liquid is 0.5–1 wt%. Step (2): Fix the bottom membrane in a specific polymerization device, add an aqueous phase to wet the surface of the bottom membrane for a period of time, remove the excess aqueous phase, add an organic phase to polymerize; after the reaction is complete, remove the organic phase, dry and solidify, soak in deionized water at room temperature, take out and dry to obtain the polyamide composite nanofiltration membrane modified with multi-reactive group ionic liquid; wherein, the bottom membrane is a polyethersulfone membrane.

2. The method for preparing a polyamide composite nanofiltration membrane modified with a multi-reactive-group ionic liquid according to claim 1, characterized in that, The concentration of piperazine or m-phenylenediamine in step (1) is 0.5-1 wt%, and the concentration of pyromellitic acid chloride is 0.15-0.2 wt%.

3. The method for preparing a polyamide composite nanofiltration membrane modified with a multi-reactive-group ionic liquid according to claim 1, characterized in that, In step (2), the wetting time is 2 to 3 minutes and the polymerization time is 1 to 2 minutes.

4. The method for preparing a polyamide composite nanofiltration membrane modified with a multi-reactive-group ionic liquid according to claim 1, characterized in that, In step (2), the drying temperature is 65-80℃ and the curing time is 5-10 min.

5. The method for preparing a polyamide composite nanofiltration membrane modified with a multi-reactive-group ionic liquid according to claim 1, characterized in that, The soaking time in step (2) is 1 to 3 days.

6. A polyamide composite nanofiltration membrane modified with a multi-reactive-group ionic liquid, characterized in that, It is prepared by the method described in any one of claims 1-5.

7. The application of the polyamide composite nanofiltration membrane modified with multi-reactive-group ionic liquid as described in claim 6 in the fields of seawater desalination, lithium extraction from salt lakes, and wastewater treatment.

Images