Method for preparing polyquaternary ammonium nanofiltration membrane based on Portland reaction interfacial polymerization and application of polyquaternary ammonium nanofiltration membrane

Abstract

The invention discloses a method for preparing a polyquaternary ammonium nanofiltration membrane on the basis of Porschitramine reaction interfacial polymerization. The method comprises the following steps: dissolving a surfactant in a tris (2-dimethylaminoethyl) aqueous solution to prepare an aqueous-phase monomer solution; taking a 1, 3, 5-tri (bromomethyl) benzene n-heptane solution as an oil-phase monomer solution; the water-phase monomer solution and the oil-phase monomer solution are subjected to a Portland reaction at an oil-water interface, rapid crosslinking is performed to form a polymer network, and an ultrathin polyquaternary ammonium separation layer is constructed on the surface of a bottom membrane to prepare the polyquaternary ammonium nanofiltration membrane. The polyquaternary ammonium nanofiltration membrane has narrow pore size distribution and high-density positive electricity, so that the size screening effect and the Dooth effect can be synergistically enhanced, and excellent water flux and divalent cation rejection rate are realized. In addition, the polyquaternary ammonium nanofiltration membrane does not contain groups easy to hydrolyze and has good acid-base stability. The polyquaternary ammonium nanofiltration membrane can be applied to nanofiltration treatment of salt lake water and lithium battery positive electrode material lixivium, double-source lithium extraction is achieved, the preparation process is simple, and industrial large-scale preparation is easy.

Description

Technical Field

[0001] The present invention relates to the technical field of nanofiltration membrane separation, and in particular to a preparation method and application of a positively charged nanofiltration membrane based on the Menshutkin reaction. Background Art

[0002] With the transformation of transportation to electric, the continuous increase of consumer electronics, the growing demand for renewable energy, and the positive drive of carbon neutrality and carbon peak, the demand for lithium-ion batteries has increased rapidly, intensifying the supply pressure of lithium resources. Salt lake brine accounts for about 70% of the global lithium reserves, but the technical problem of magnesium / lithium separation makes the development of salt lake brine difficult. At the same time, the rapid expansion of lithium battery applications has led to a large number of waste batteries being generated every year, bringing double challenges of environmental pollution and resource depletion. During the treatment of waste batteries, the positive electrode material needs to be treated with strong acid to obtain an acidic solution containing lithium ions and divalent cations such as cobalt, manganese, and nickel.

[0003] Nanofiltration membranes can achieve efficient ion separation by synergistically using the Donnan effect and size sieving. Their positive charge and appropriate pore size are crucial for the separation of monovalent and divalent cations. In addition, the weakly alkaline salt lake brine and the strongly acidic leaching solution of lithium battery positive electrode materials pose higher requirements for the acid-base stability of nanofiltration membranes. The surface positive charge of traditional polyamide nanofiltration membrane materials depends on the protonation of amino groups, is greatly affected by the environmental acidity and alkalinity, and the residual acyl chloride groups are prone to hydrolysis, which will also bring surface negative charge. Moreover, the amide groups are prone to hydrolysis in acidic and alkaline environments, resulting in structural damage, and their application in lithium extraction from salt lakes and the recycling of waste lithium batteries is limited.

[0004] The Menshutkin reaction is a nucleophilic substitution reaction between a tertiary amine and a halogenated hydrocarbon, which can generate a quaternary ammonium salt. Interface polymerization based on the Menshutkin reaction can form a cross-linked network with a high density of positive charge and does not contain easily hydrolyzed groups, and has great development potential in the application of separating monovalent and divalent cations under acidic and alkaline conditions. Summary of the Invention

[0005] In view of the above-mentioned prior art, the present invention provides a method for preparing a polyquaternary ammonium nanofiltration membrane by interfacial polymerization based on the Menshutkin reaction. This preparation method performs interfacial polymerization with the tripod symmetric monomer tris(2-dimethylaminoethyl)amine and 1,3,5-tris(bromomethyl)benzene, in order to obtain a nanofiltration membrane with both a high divalent cation rejection rate, a high water permeation flux, and excellent stability in acidic and alkaline environments.

[0006] To solve the above technical problems, the present invention provides a method for preparing a polyquaternary ammonium nanofiltration membrane by interfacial polymerization based on the Menschutkin reaction. Using sodium dodecyl sulfate as a surfactant, the surfactant is dissolved in an aqueous solution of tris(2-dimethylaminoethyl)amine to obtain an aqueous monomer solution; a heptane solution of 1,3,5-tris(bromomethyl)benzene is used as the oil-phase monomer solution; with the assistance of the surfactant, the aqueous monomer and the oil-phase monomer undergo a Menschutkin reaction and rapid crosslinking at the oil-water interface to form a polymer network, and an ultrathin polyquaternary ammonium separation layer is constructed on the surface of the polyacrylonitrile substrate membrane, thereby preparing a polyquaternary ammonium nanofiltration membrane. The specific steps are as follows:

[0007] Step 1) Prepare an aqueous solution of tris(2-dimethylaminoethyl)amine with a mass fraction of 2.5-10%, and add sodium dodecyl sulfate to the 2.5-10% aqueous solution of tris(2-dimethylaminoethyl)amine according to a mass fraction of 0.01%, and ultrasonicate for 10-20 min to obtain an aqueous monomer solution;

[0008] Step 2) Prepare a heptane solution of 1,3,5-tris(bromomethyl)benzene with a mass fraction of 0.6%, and ultrasonicate for 20-30 min to obtain an oil-phase monomer solution;

[0009] Step 3) Fix the polyacrylonitrile membrane in a plastic mold, add the aqueous monomer solution prepared in Step 1 to the mold, and seal the mold. The dosage of the aqueous monomer solution is in a ratio of 0.2 mL / cm 2 to the exposed area of the membrane. After soaking and reacting for 30 min, take out the membrane and remove the residual liquid on the membrane surface;

[0010] Step 4) Fix the membrane treated in Step 3 in a plastic mold, add the oil-phase monomer solution prepared in Step 2 to the mold, and seal the mold. The dosage of the oil-phase monomer solution is in a ratio of 0.2 mL / cm 2 to the exposed area of the membrane. After soaking and reacting for 4 h, take out the membrane, wash it with n-heptane, and put it in an oven for thermal crosslinking reaction to obtain a polyquaternary ammonium nanofiltration membrane.

[0011] Furthermore, in the preparation method of the present invention:

[0012] In Step 1), the mass fraction of the aqueous solution of tris(2-dimethylaminoethyl)amine is 5%. The ultrasonication time is 10 min; in Step 2), the ultrasonication time is 20 min.

[0013] In Step 3), the molecular weight cut-off of the polyacrylonitrile substrate membrane is 15 kDa.

[0014] In Step 4), the temperature of the oven is 60 °C, and the thermal crosslinking reaction time is 10 min.

[0015] In steps 3) and 4), the temperature of the immersion reaction is 20 - 30 °C.

[0016] Compared with the prior art, the advantages of the present invention are as follows:

[0017] In the preparation method of the present invention, tri(2-dimethylaminoethyl)amine, a tertiary amine monomer, is used as the aqueous phase monomer, and 1,3,5-tris(bromomethyl)benzene is used as the oil phase monomer. A Menschutkin reaction occurs at the oil-water interface to generate quaternary ammonium groups. Both monomers in the two phases have a three-legged symmetric structure, which is easy to crosslink to form a dense polymer network containing sub-nanopores. Relying on the high-density surface positive charge and narrow pore size distribution, the Donnan effect and size sieving effect are fully exerted to achieve efficient retention of divalent cations; at the same time, high water permeability is achieved by virtue of the ultra-thin separation layer and strong hydrophilicity; in addition, the positive charge of the prepared polyquaternary ammonium nanofiltration membrane does not depend on protonation, and its structure does not contain easily hydrolyzable groups, and it has high charge stability and structural stability in acidic and alkaline environments. The prepared nanofiltration membrane is used in the process of extracting lithium from salt lakes and recycling waste lithium batteries, efficiently retaining divalent cations in the feed liquid and allowing lithium ions to pass through, realizing the efficient extraction and utilization of lithium resources; the materials used are easily available, and the preparation process is simple, which is easy for industrial scale preparation.

[0018] The pure water flux of the polyquaternary ammonium nanofiltration membrane prepared by the preparation method of the present invention is 29 - 33 L m -2 h -1 bar -1 , the rejection rate of Mg 2+ is 98.9 - 99.5%, and the rejection rates of Mn 2+ , Co 2+ and Ni 2+ are all greater than 98%, and the rejection rate of Li + is 45.1 - 54.1%; after the polyquaternary ammonium nanofiltration membrane is immersed in an acidic solution with pH = 0 or an alkaline solution with pH = 12 for 60 days, the rejection rate of Mg 2+ only decreases by 1.0 - 1.2%, and the water flux only decreases by 0.6 - 2.7 L m -2 h -1 bar -1 , and the performance is basically stable, as shown in Figure 9 , Figure 10 and Table 2; applying the polyquaternary ammonium nanofiltration membrane prepared by the present invention to nanofiltration treatment of salt lake water and the leaching solution of the cathode material of lithium batteries realizes lithium extraction from two sources, including using the polyquaternary ammonium nanofiltration membrane to perform nanofiltration treatment on the pretreated clarified salt lake water to obtain a lithium ion solution, realizing lithium extraction from salt lakes; using the nanofiltration membrane to perform nanofiltration treatment on the leaching solution obtained after acid-leaching the waste lithium battery cathode material to obtain a lithium ion solution, realizing the efficient extraction and utilization of lithium resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It shows a schematic diagram of the preparation of a polyquaternary ammonium nanofiltration membrane by interfacial polymerization based on the Menschutkin reaction of the present invention;

[0020] Figure 2 It is the Fourier transform infrared spectrum of the nanofiltration membrane and the polyacrylonitrile substrate membrane in Example 2;

[0021] Figure 3 It is the X-ray photoelectron spectrum of the surface of the nanofiltration membrane prepared in Example 2;

[0022] Figure 4 a and b of are the scanning electron microscope photos of the polyacrylonitrile substrate membrane and the nanofiltration membrane prepared in Example 2 respectively;

[0023] Figure 5 It is the separation layer thickness of the nanofiltration membrane prepared in Example 2;

[0024] Figure 6 It is the static water contact angle diagram of the surface of the nanofiltration membrane prepared in Example 2;

[0025] Figure 7 It is the change of the Zeta potential of the surfaces of the nanofiltration membrane and the polyacrylonitrile substrate membrane prepared in Example 2 with pH;

[0026] Figure 8 It is the rejection rate diagram of the nanofiltration membrane prepared in Example 2 for different divalent and monovalent cations;

[0027] Figure 9 It is the influence of the concentration of tris(2-dimethylaminoethyl)amine on the MgCl retention performance of the nanofiltration membrane in the preparation method of the present invention 2 ;

[0028] Figure 10 It is the influence of the concentration of 1,3,5-tris(bromomethyl)benzene on the MgCl retention performance of the nanofiltration membrane in the preparation method of the present invention 2 ; Detailed implementation mode

[0029] The design concept of the method for preparing a polyquaternary ammonium nanofiltration membrane based on the Menschutkin reaction proposed by the present invention is that the tertiary amine group of the aqueous monomer and the halogenated hydrocarbon undergo a Menschutkin reaction at the oil-water interface to form a polymer network rich in quaternary ammonium. Using tris(2-dimethylaminoethyl)amine as the aqueous monomer and 1,3,5-tris(bromomethyl)benzene as the oil-phase monomer, both of which have a three-legged symmetric structure, using an aqueous solution of tris(2-dimethylaminoethyl)amine as the aqueous monomer solution and a 1,3,5-tris(bromomethyl)benzene n-heptane solution as the oil-phase monomer solution, and using sodium dodecyl sulfate as the surfactant. With the assistance of the surfactant, the aqueous monomer and the oil-phase monomer undergo a Menschutkin reaction at the oil-water interface, quickly crosslinking to form a polymer network, and constructing an ultra-thin polyquaternary separation layer on the surface of the polyacrylonitrile substrate membrane, thereby preparing a polyquaternary ammonium nanofiltration membrane.

[0030] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. However, the following embodiments are by no means any limitation to the present invention.

[0031] Example 1

[0032] A polyquaternary ammonium nanofiltration membrane was prepared by an in-situ interfacial polymerization method based on the Menschutkin reaction, as shown in a of Figure 1 . The preparation steps of the nanofiltration membrane are as follows:

[0033] Step 1: Weigh 0.125 g of tris(2-dimethylaminoethyl)amine, add 4.875 g of pure water thereto, and then add 0.005 g of sodium dodecyl sulfate. Ultrasonic for 20 min to obtain an aqueous monomer solution with a mass fraction of tris(2-dimethylaminoethyl)amine of 2.5%.

[0034] Step 2: Weigh 0.03 g of 1,3,5-tris(bromomethyl)benzene, add 4.97 g of n-heptane thereto, and ultrasonic for 20 min to obtain an oil-phase monomer solution with a mass fraction of 1,3,5-tris(bromomethyl)benzene of 0.6%.

[0035] Step 3: Wash the polyacrylonitrile substrate membrane three times with pure water and then fix it in a plastic mold. Add an appropriate amount of the aqueous monomer solution to the mold so that the ratio of the solution volume to the exposed substrate membrane area is 0.2 mL / cm 2 . After soaking the substrate membrane for 30 min, disassemble the mold and use a rubber roller to remove the residual liquid on the surface to ensure that there are no visible liquid droplets on the membrane surface.

[0036] Step 4: After assembling the mold in Step 3, continue to add an appropriate amount of the oil-phase monomer solution and seal the mold so that the ratio of the solution volume to the exposed substrate membrane area is 0.2 mL / cm 2 . After reacting for 4 h, take out the treated substrate membrane.

[0037] Step 5: Wash the treated substrate membrane three times with n-heptane and then put it into an oven for thermal crosslinking for 10 min to obtain a polyquaternary ammonium nanofiltration membrane, denoted as PQA-2.5-0.6 membrane.

[0038] The separation performance of the prepared PQA-2.5-0.6 membrane was evaluated using a cross-flow device, and two characteristic parameters, salt rejection rate and water flux, were used as the main evaluation indicators:

[0039] Calculation formula for rejection rate: R = (1 - C p / C f ) × 100%, where R represents the rejection rate, and C p and C f are the concentrations of salt (ppm) in the permeate and the feed solution, respectively. When not specifically indicated, the salt concentration used is 1000 ppm.

[0040] Water flux (L m- 2 h -1 bar -1 ) is defined as: under certain operating pressure conditions, the volume of water permeating through a unit effective membrane area per unit pressure and per unit time, and the test pressure is 4 bar.

[0041] Example 2

[0042] A polyquaternary ammonium nanofiltration membrane was prepared by in-situ interfacial polymerization based on the Menschutkin reaction. The preparation process of Example 2 was basically the same as that of Example 1, except that: in Step 1, the mass of tris(2-dimethylaminoethyl)amine was changed from 0.125 g to 0.250 g, and the mass of pure water was changed from 4.875 g to 4.750 g, to obtain an aqueous monomer solution with a tris(2-dimethylaminoethyl)amine mass fraction of 5%; the finally prepared nanofiltration membrane was denoted as PQA-5-0.6 membrane.

[0043] Example 3

[0044] A polyquaternary ammonium nanofiltration membrane was prepared by in-situ interfacial polymerization based on the Menschutkin reaction. The preparation process of Example 3 was basically the same as that of Example 1, except that: in Step 1, the mass of tris(2-dimethylaminoethyl)amine was changed from 0.125 g to 0.375 g, and the mass of pure water was changed from 4.875 g to 4.625 g, to obtain an aqueous monomer solution with a tris(2-dimethylaminoethyl)amine mass fraction of 7.5%; the finally prepared nanofiltration membrane was denoted as PQA-7.5-0.6 membrane.

[0045] Example 4

[0046] A polyquaternary ammonium nanofiltration membrane was prepared by in-situ interfacial polymerization based on the Menschutkin reaction. The preparation process of Example 4 was basically the same as that of Example 1, except that: in Step 1, the mass of tris(2-dimethylaminoethyl)amine was changed from 0.125 g to 0.500 g, and the mass of pure water was changed from 4.875 g to 4.500 g, to obtain an aqueous monomer solution with a tris(2-dimethylaminoethyl)amine mass fraction of 10%; the finally prepared nanofiltration membrane was denoted as PQA-10-0.6 membrane.

[0047] Example 5

[0048] A polyquaternary ammonium nanofiltration membrane was prepared by in-situ interfacial polymerization based on the Menschutkin reaction. The preparation process of Example 5 was basically the same as that of Example 2, except that: in Step 2, the mass of 1,3,5-tris(bromomethyl)benzene was changed from 0.03 g to 0.01 g, and the mass of n-heptane was changed from 4.97 g to 4.99 g, to obtain an oil-phase monomer solution with a 1,3,5-tris(bromomethyl)benzene mass fraction of 0.2%; the finally prepared nanofiltration membrane was denoted as PQA-5-0.2 membrane.

[0049] Example 6

[0050] A polyquaternary ammonium nanofiltration membrane was prepared by in-situ interfacial polymerization based on the Menschutkin reaction. The preparation process of Example 6 was basically the same as that of Example 2, except that: in Step 2, the mass of 1,3,5-tris(bromomethyl)benzene was changed from 0.03 g to 0.02 g, and the mass of n-heptane was changed from 4.97 g to 4.98 g, obtaining an oil-phase monomer solution with a mass fraction of 1,3,5-tris(bromomethyl)benzene of 0.4%. The finally prepared nanofiltration membrane was denoted as PQA-5-0.4 membrane.

[0051] Example 7

[0052] A polyquaternary ammonium nanofiltration membrane was prepared by in-situ interfacial polymerization based on the Menschutkin reaction. The preparation process of Example 7 was basically the same as that of Example 2, except that: in Step 2, the mass of 1,3,5-tris(bromomethyl)benzene was changed from 0.03 g to 0.04 g, and the mass of n-heptane was changed from 4.97 g to 4.96 g, obtaining an oil-phase monomer solution with a mass fraction of 1,3,5-tris(bromomethyl)benzene of 0.8%. The finally prepared nanofiltration membrane was denoted as PQA-5-0.8 membrane.

[0053] Example 8

[0054] A polyquaternary ammonium nanofiltration membrane was prepared by in-situ interfacial polymerization based on the Menschutkin reaction. The nanofiltration membrane prepared in Example 2 was immersed in a hydrochloric acid solution with pH = 0 for 60 days and then taken out and rinsed with water 5 times. The obtained nanofiltration membrane was denoted as PQA acid-leached membrane.

[0055] Example 9

[0056] A polyquaternary ammonium nanofiltration membrane was prepared by in-situ interfacial polymerization based on the Menschutkin reaction. The nanofiltration membrane prepared in Example 2 was immersed in a sodium hydroxide solution with pH = 12 for 60 days and then taken out and rinsed with water 5 times. The obtained nanofiltration membrane was denoted as PQA alkali-leached membrane.

[0057] Comparative Example 1

[0058] A polyquaternary ammonium nanofiltration membrane was prepared by in-situ interfacial polymerization based on the Menschutkin reaction. The preparation process of Comparative Example 1 was basically the same as that of Example 2, except that in Step 1, the aqueous-phase monomer was changed from tris(2-dimethylaminoethyl)amine to 1,1,4,7,10,10-hexamethyltriethylenetetramine, obtaining an aqueous-phase monomer solution with a mass of 1,1,4,7,10,10-hexamethyltriethylenetetramine of 5%. The finally prepared nanofiltration membrane was denoted as PQA-H membrane.

[0059] The formulations of the aqueous monomer solutions and the oil-phase monomer solutions in the above Examples 1-9 and Comparative Example 1 are shown in Table 1. Among them, the aqueous monomers in Examples 1-9 are all tris(2-dimethylaminoethyl), and the aqueous monomer in Comparative Example 1 is 1,1,4,7,10,10-hexamethyltriethylenetetramine. The test results of the ion separation performance of the nanofiltration membranes prepared in the above Examples 1-9 and Comparative Example 1 are shown in Figure 9 , Figure 10 and Table 2.

[0060] Table 1

[0061]

[0062] Table 2

[0063]

[0064]

[0065] Next, the structures and properties of the polyquaternary ammonium nanofiltration membranes prepared in the examples and comparative examples were evaluated through characterization and testing.

[0066] (1) The polyquaternary ammonium nanofiltration membrane and the polyacrylonitrile substrate membrane prepared in Example 2 were characterized by infrared spectroscopy, and the results are as Figure 2 shown.

[0067] Fourier transform infrared spectroscopy (FT-IR) was used to prove the successful occurrence of the Menschutkin reaction. The FT-IR spectra of the prepared membrane PQA-5-0.6 membrane and the polyacrylonitrile substrate membrane are as Figure 2 shown. The comparison results show that the PQA-5-0.6 membrane shows peaks at 3400 (O-H stretching), 3022 (crosslinked C-N + ) and 1383 cm -1 (unreacted C-N); these peaks were not observed in the PAN spectrum. The FT-IR test results prove the successful occurrence of the Menschutkin reaction and the successful preparation of the polyquaternary ammonium separation layer, containing unreacted tertiary amines and crosslinked quaternary ammonium groups conjugated with OH- counteranions.

[0068] (2) The polyquaternary ammonium nanofiltration membrane and the polyacrylonitrile substrate membrane prepared in Example 2 were tested by X-ray photoelectron spectroscopy (XPS), and the results are as Figure 3 shown.

[0069] X-ray photoelectron spectroscopy (XPS) was used to characterize the chemical composition and content of the membrane surface. The high-resolution N 1s XPS spectrum of the polyquaternary ammonium membrane shows two peaks at 402 and 399 eV, representing crosslinked quaternary ammonium groups (C-N + ) and unreacted tertiary amines (C-N), respectively, according to their C-N +The percentage estimation of the XPS peak area shows that the near-surface crosslinking degree of the PQA separation layer is approximately ≈70%, confirming its high crosslinked structure and high density of quaternary ammonium groups near the surface.

[0070] (III) The surface morphologies of the polyquaternary ammonium nanofiltration membrane and the polyacrylonitrile substrate membrane prepared in Example 2 were observed by scanning electron microscopy, and the results are as Figure 4 a and Figure 4 b shown.

[0071] Scanning electron microscopy (SEM) was used to observe the surface morphology of the membrane. As can be seen from Figure 4 a, many pores (10 - 50 nm) are randomly distributed on the polyacrylonitrile substrate membrane. As can be seen from Figure 4 b, the surface of the prepared PQA-5-0.6 membrane is very dense, no obvious pores can be seen, and the overall membrane surface is relatively smooth, confirming the successful synthesis of the dense polyquaternary ammonium separation layer on the surface of the polyacrylonitrile substrate membrane.

[0072] (IV) The cross-section of the polyquaternary ammonium nanofiltration membrane prepared in Example 2 was observed by transmission electron microscopy, and the results are as Figure 5 shown.

[0073] Transmission electron microscopy (TEM) was used to observe the thickness of the separation layer of the membrane. As can be seen from Figure 5 , the thickness of the separation layer of the PQA-5-0.6 membrane is only 12.4 nm, and its ultra-thin separation layer is beneficial to achieving high water permeability.

[0074] (V) The static water contact angle test was carried out on the polyquaternary ammonium nanofiltration membrane prepared in Example 2, and the results are as Figure 6 shown.

[0075] The static water contact angle at the moment when the water droplet contacts the membrane surface was used to evaluate the hydrophilicity of the membrane. As can be seen from Figure 6 , the water contact angle of the PQA-5-0.6 membrane is very small, only 23°, confirming that the prepared polyquaternary ammonium nanofiltration membrane has good hydrophilicity.

[0076] (VI) The Zeta potential test was carried out on the polyquaternary ammonium nanofiltration membrane and the polyacrylonitrile substrate membrane prepared in Example 2, and the results are as Figure 7 shown.

[0077] With the increase of pH, the zeta potential of the polyacrylonitrile substrate membrane drops sharply and remains negative throughout the pH range (3 - 10), while the potential of the PQA-5-0.6 membrane drops gently when the pH value increases and still maintains a positive surface charge at pH = 10, confirming the high density of positive charges on the membrane surface and its stability in the acid-base environment.

[0078] (7) The polyquaternary ammonium nanofiltration membrane prepared in Example 2 was tested for its separation performance of different ions, as Figure 8 shown.

[0079] The PQA-5-0.6 membrane has a relatively high rejection rate of divalent cations (Mn 2+ , Zn 2+ , Mg 2+ , Co 2+ , Cu 2+ , Ca 2+ and Ni 2+ ) with different hydration radii, about 97%, while the rejection rate of monovalent ions (Li + , Na + , K + and Cs + ) is relatively low, about 55%. This further confirms that the surface of the prepared polyquaternary ammonium membrane is positively charged with a high density, and the repulsive force on divalent ions is greater than that on monovalent ions, resulting in a higher rejection rate of divalent ions. Among them, the rejection rates of Mg 2+ , Mn 2+ , Co 2+ and Ni 2+ are all greater than 98%, indicating that the prepared polyquaternary ammonium nanofiltration membrane can efficiently remove divalent cations in the brine of salt lakes and the leachate of the positive electrodes of waste lithium batteries.

[0080] Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can make many improvements and changes without departing from the purpose of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A method for preparing a polyquaternary ammonium nanofiltration membrane based on interfacial polymerization of the Menschuttekin reaction, characterized in that: Sodium dodecyl sulfate is used as a surfactant, and the surfactant is dissolved in a tris(2-dimethylaminoethyl) aqueous solution to prepare an aqueous monomer solution; 1,3,5-tri(bromomethyl)benzene n-heptane solution is used as the oil phase monomer solution; with the assistance of surfactant, the water phase monomer and the oil phase monomer undergo Menschuttekin reaction at the oil-water interface and quickly cross-link to form a polymer network, and an ultra-thin polyquaternary ammonium separation layer is constructed on the surface of the polyacrylonitrile base membrane, thereby preparing a polyquaternary ammonium nanofiltration membrane.

2. The method for preparing a polyquaternary ammonium nanofiltration membrane according to claim 1, characterized in that: The following steps are involved: Step 1) preparing a tris(2-dimethylaminoethyl) / water solution with a mass fraction of 2.5-10%, adding sodium dodecyl sulfate to the tris(2-dimethylaminoethyl) / water solution with a mass fraction of 0.1%, and ultrasonicating for 10-20 minutes to obtain an aqueous monomer solution; Step 2) preparing a 1,3,5-tri(bromomethyl)benzene / n-heptane solution with a mass fraction of 0.2-0.8%, and ultrasonicating for 20-30 minutes to obtain an oil phase monomer solution; Step 3) Fix the polyacrylonitrile membrane in a plastic mold, add the aqueous monomer solution prepared in step 1) into the mold, and seal the mold. The ratio of the amount of the aqueous monomer solution to the exposed area of ​​the membrane is 0.2 mL / cm 2 After soaking and reacting for 30 minutes, the membrane was taken out and the residual liquid on the membrane surface was removed; Step 4) Fix the film treated in step 3) in a plastic mold, add the oil phase monomer solution prepared in step 2) into the mold, and seal the mold. The ratio of the amount of the oil phase monomer solution to the exposed area of ​​the film is 0.2 mL / cm 2 , soak and react for 4 hours, take out the membrane and wash it with n-heptane, put it into an oven for thermal cross-linking reaction to obtain a polyquaternary ammonium nanofiltration membrane.

3. The preparation method according to claim 2, characterized in that: In step 1), the mass fraction of tris(2-dimethylaminoethyl) is 5%.

4. The method for preparing a polyquaternary ammonium nanofiltration membrane according to claim 2, characterized in that: In step 2), the mass fraction of 1,3,5-tri(bromomethyl)benzene is 0.6%.

5. The method for preparing a polyquaternary ammonium nanofiltration membrane according to claim 2, wherein: In step 1), the ultrasonic time is 10 min; in step 2), the ultrasonic time is 20 min.

6. The method for preparing a polyquaternary ammonium nanofiltration membrane according to claim 2, characterized in that: In step 3), the molecular weight cutoff of the polyacrylonitrile bottom membrane is 15 kDa.

7. The method for preparing a polyquaternary ammonium nanofiltration membrane according to claim 2, characterized in that: In step 4), the temperature of the oven is 60° C. and the thermal crosslinking reaction time is 10 min.

8. The method for preparing a polyquaternary ammonium nanofiltration membrane according to claim 2, characterized in that: In step 3) and step 4), the temperature of the soaking reaction is 20-30°C.

9. An application of a polyquaternary amine nanofiltration membrane, characterized in that: The pure water flux of the polyquaternary ammonium nanofiltration membrane prepared by the method for preparing a polyquaternary ammonium nanofiltration membrane according to any one of claims 1 to 7 is 29 to 33 L m - 2h -1 bar -1 ,Mg 2+ Retention rate 98.9~99.5%, Mn 2+ 、Co 2+ and Ni 2+ The retention rates of Li + The retention rate is 45.1-54.1%; After the polyquaternary ammonium nanofiltration membrane was immersed in an acidic solution of pH=0 or an alkaline solution of pH=12 for 60 days, the Mg 2+ The interception rate only decreased by 1.0-1.2%, and the water flux only decreased by 0.6-2.7 L m -2 h -1 bar -1 , the performance is basically stable; The polyquaternary ammonium nanofiltration membrane is used to carry out nanofiltration treatment of salt lake water and lithium battery positive electrode material leachate to achieve dual-source lithium extraction.

10. The use of the polyquaternary amine nanofiltration membrane according to claim 8, characterized in that: The pre-treated clarified salt lake water is subjected to nanofiltration treatment using the polyquaternary amine nanofiltration membrane, or the leaching liquid obtained after acid dissolution of the waste lithium battery positive electrode material is subjected to nanofiltration treatment using the nanofiltration membrane, both of which can obtain a lithium ion solution.

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