Nanofiltration composite membrane with interspersed rigid and flexible structures as well as preparation method and application of nanofiltration composite membrane

Abstract

The invention discloses a nanofiltration composite membrane with interspersed rigid and flexible structures as well as a preparation method and application of the nanofiltration composite membrane. The thickness of the film is 1-500 nm; the polymer is obtained by in-situ polymerization of polybasic organic amine and rigid biguanide monomers on a porous support layer; a biguanide monomer with a rigid structure, high positive charge density and a low interface mass transfer energy barrier is embedded and expands a flexible and tightly-wound polyamide network, a continuous semi-permanent microcavity with rigidity and softness, high positive charge density is constructed in a functional layer, and a transmission channel of water molecules is expanded. The membrane has higher water permeability and magnesium-lithium selectivity, the preparation process is simple and easy to operate, and large-scale production and application are facilitated.

Description

TECHNICAL FIELD

[0001] The application relates to a nanofiltration composite membrane with rigid-flexible structure and a preparation method and application thereof, and belongs to the field of membrane separation. BACKGROUND

[0002] In recent years, with the rapid rise of new energy electric vehicles, consumer electronics and energy storage industries, the demand for lithium-based batteries has shown explosive growth. It is estimated that the lithium consumption in 2025 will be three times that in 2018, leading to a global shortage of lithium resources. At present, more than 70 percent of exploitable lithium resources are stored in salt lake brine, so extracting lithium resources from salt lake brine is an effective way to solve the problem. However, the problem of high magnesium-lithium ratio exists in natural salt lake brine, and due to the similar ion hydration radius and chemical properties of lithium ions and magnesium ions, it is difficult to effectively separate the two.

[0003] Polyamide nanofiltration membranes have broad application prospects in lithium extraction from salt lake brine with high magnesium-lithium ratio due to their ability to effectively separate monovalent / multivalent ions. Among them, magnesium-lithium selectivity is one of the main indicators to measure the performance of nanofiltration membranes, and increasing the positive charge density or preparing positively charged nanofiltration membranes is the key to improving magnesium-lithium selectivity. In recent years, researchers have improved the positive charge density or prepared positively charged nanofiltration membranes by introducing high positive charge density water phase reaction monomers, grafting modified monomers with positive charges, and constructing intermediate layers with positive charges during the interfacial polymerization process, thereby improving the separation selectivity of monovalent / multivalent cations. It is worth noting that polyethyleneimine-based polyamide membranes prepared by using polyethyleneimine and trimesoyl chloride have attracted widespread attention in the field of salt lake magnesium-lithium separation, because they contain a large number of unreacted positively charged amino groups, which are beneficial to the separation of magnesium ions and lithium ions which are both cations.

[0004] However, there is a trade-off between the water permeability and magnesium-lithium selectivity of polyamide nanofiltration membranes, which seriously hinders the improvement of the comprehensive performance of nanofiltration membranes and is one of the main obstacles limiting the large-scale application of nanofiltration membranes in the field of salt lake lithium extraction. Unfortunately, the branched polyethyleneimine and trimesoyl chloride form a flexible, tightly twisted polyamide network, which narrows the transmission channel of water molecules; polyethyleneimine also has a large molecular volume and a locally high positive charge density, resulting in a large number of "defects" in the functional layer, which exacerbates the trade-off between selectivity and permeability. SUMMARY

[0005] In view of the trade-off between selectivity and permeability of polyamide nanofiltration membranes, the present application intends to embed and expand the rigid structure and high positive charge density of the biguanide monomer in the flexible and tightly wound polyamide network, to build a "rigid and flexible" high positive charge density and continuous semi-permanent microcavity in the functional layer, to expand the transmission channel of water molecules; the rigid monomer will preferentially embed in the large pore defects, enhance the positive charge density nearby, improve the pore size separation and Donnan effect, realize the synergistic regulation of pore structure and charge density, and is expected to simultaneously improve the water permeability and magnesium-lithium selectivity, and improve the trade-off between permeability and selectivity of the nanofiltration membrane.

[0006] According to one aspect of the present application, a nanofiltration composite membrane with rigid and flexible structure interpenetration is provided, the thickness of the nanofiltration composite membrane is 1-500 nm;

[0007] Optionally, the thickness of the nanofiltration composite membrane is 10-100 nm.

[0008] Optionally, the thickness of the nanofiltration composite membrane is any value or a range value between any two values of 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm.

[0009] The nanofiltration composite membrane is obtained by in-situ polymerization of a polybasic organic amine and a rigid biguanide monomer on a porous support layer;

[0010] The polybasic organic amine is selected from at least one of polyethyleneimine, tetraethylenepentamine, triethylenetetramine, diethylenetriamine, 2,2',2"-triaminotriethylamine, polyamide-amine, piperazine, m-phenylenediamine, p-phenylenediamine, 1,2-ethylenediamine, 1,6-hexanediamine, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, spermine or melamine;

[0011] The rigid biguanide monomer is selected from at least one of the compounds having the structure shown in Formula I;

[0012]

[0013] wherein R1, R2 are independently selected from at least one of benzene ring, naphthalene and imidazolium rigid structure.

[0014] Wherein, the benzene ring, naphthalene and imidazolium rigid structure can also contain substituents, which can contain substituents including amino, nitro, carboxyl, methyl and the like.

[0015] According to another aspect of the present application, a preparation method of the above-mentioned nanofiltration composite membrane with rigid and flexible structure interpenetration is provided, comprising the following steps:

[0016] immersing a porous support layer in an aqueous solution containing a polybasic organic amine and a rigid bisguanide monomer to obtain an infiltrated porous support layer, placing an organic solvent solution containing a polybasic acid chloride on the infiltrated porous support layer, polymerizing, and drying to obtain the nanofiltration composite membrane with rigid-flexible structure interpenetration.

[0017] The porous support layer is selected from a non-woven fabric;

[0018] Optionally, the non-woven fabric is compounded with a polymer;

[0019] The polymer is selected from at least one of polysulfone, polyethersulfone, polyimide, polyacrylonitrile, polypropylene, and polyether ether ketone.

[0020] The concentration of the polybasic organic amine in the aqueous solution containing a polybasic organic amine and a rigid bisguanide monomer is 0.01-5wt%;

[0021] Optionally, the concentration of the polybasic organic amine in the aqueous solution containing a polybasic organic amine and a rigid bisguanide monomer is 0.05-2wt%;

[0022] Optionally, the concentration of the polybasic organic amine in the aqueous solution containing a polybasic organic amine and a rigid bisguanide monomer is any value selected from 0.05wt%, 0.2wt%, 0.5wt%, 0.75wt%, 1wt%, 1.5wt%, 2wt%, or a range value between any two of them.

[0023] The concentration of the rigid bisguanide monomer in the aqueous solution containing a polybasic organic amine and a rigid bisguanide monomer is 0.01-5.00wt%.

[0024] Optionally, the concentration of the rigid bisguanide monomer in the aqueous solution containing a polybasic organic amine and a rigid bisguanide monomer is selected from any value selected from 0.01wt%, 0.05wt%, 0.1wt%, 0.2wt%, 0.25wt%, 0.5wt%, 1wt%, 1.25wt%, 1.5wt%, 1.75wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, or a range value between any two of them.

[0025] The immersion time is 10s-10min;

[0026] Optionally, the immersion time is 1-6min.

[0027] Optionally, the immersion time is any value selected from 10s, 1min, 2min, 3min, 4min, 5min, 6min, 7min, 8min, 9min, 10min, or a range value between any two of them.

[0028] the polybasic acid chloride is selected from at least one of trimesoyl chloride, isophthaloyl chloride, terephthaloyl chloride, pyromellitic acid chloride, adipoyl chloride;

[0029] the organic solvent is selected from at least one of n-hexane, cyclohexane, n-heptane, n-octane, isopentane, Isopar-G, Isopar-E, Isopar-L or acetone;

[0030] the concentration of the organic solvent solution containing polybasic acid chloride is 0.01-5.00wt%.

[0031] Optionally, the concentration of the polybasic acid chloride in the organic solvent solution containing polybasic acid chloride is selected from any value of 0.01wt%, 0.15wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 3wt%, 4wt%, 5wt% or a range value between any two of them.

[0032] the polymerization time is 1s-5min;

[0033] Optionally, the polymerization time is 5s-1min.

[0034] Optionally, the polymerization time is any value of 1s, 5s, 30s, 45s, 1min, 2min, 3min, 4min, 5min or a range value between any two of them.

[0035] the drying temperature is 50-150℃;

[0036] Optionally, the drying temperature is any value of 50℃, 75℃, 100℃, 125℃, 150℃ or a range value between any two of them.

[0037] the drying time is 1-20min.

[0038] Optionally, the drying time is selected from any value of 1min, 5min, 10min, 15min, 20min or a range value between any two of them.

[0039] the aqueous solution containing organic amine and rigidly positively charged monomer further contains a buffer;

[0040] the buffer is selected from any one of trisodium phosphate / hydrochloric acid, triethylamine / camphorsulfonic acid, sodium hydroxide / hydrochloric acid.

[0041] the pH of the aqueous solution containing organic amine and rigidly positively charged monomer ranges from 7 to 12.

[0042] According to another aspect of the present application, there is provided an application of the above-mentioned nanofiltration composite membrane with rigid-flexible structure interpenetrating, characterized in that;

[0043] application in single / multivalent ion separation, water treatment or lithium extraction from salt lake (magnesium-lithium separation).

[0044] The beneficial effects that can be produced by the present application include:

[0045] 1) The preparation method of the nanofiltration composite membrane provided by the present application embeds and expands the rigid structure, high positive charge density and low interfacial mass transfer energy barrier of the biguanide monomer in the flexible and tightly wound polyamide network, thereby constructing a "rigid-flexible" high positive charge density continuous semi-permanent microcavity in the functional layer, and expanding the transmission channel of water molecules.

[0046] 2) The preparation method of the nanofiltration composite membrane provided by the present application is based on the fact that the diffusion speed of the rigid biguanide monomer is faster than that of the high molecular weight polybasic organic amine, which preferentially diffuses to the surface of the initial membrane and reacts with excess polybasic acid chloride to form a new polyamide layer, thereby repairing the defects of the functional layer and increasing the charge density in the pore.

[0047] 3) The nanofiltration composite membrane provided by the present application has higher water permeability and magnesium-lithium selectivity, and the preparation process is simple and easy to operate, which is conducive to large-scale production and application. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 The infrared spectra of the composite membranes prepared in Comparative Example 1 and Example 3 of the present application and the PSf porous support membrane;

[0049] Figure 2 The water flux, magnesium chloride and lithium chloride rejection rates of the composite membranes prepared in Examples 1 to 4 of the present application;

[0050] Figure 3 Atomic force microscope images of the surface of the polyamide nanofiltration composite membranes prepared in Comparative Example 1 and Example 3 of the present application, wherein a is the AFM image of the TFC membrane, and b is the AFM image of the PBG-0.40 membrane.

[0051] Figure 4 Thickness measurement of the polyamide nanofiltration composite membranes prepared in Comparative Example 1 and Example 3 of the present application, wherein a is the AFM image of the TFC membrane, and b is the thickness measurement image of the PBG-0.40 membrane. DETAILED DESCRIPTION

[0052] The present application will be described in detail below with reference to the examples, but the present application is not limited to these examples.

[0053] Unless otherwise specified, the raw materials in the examples of the present application are purchased through commercial channels.

[0054] The analysis method in the embodiments of the present application is as follows:

[0055] The infrared spectra of the composite membranes prepared in Comparative Example 1 and Example 3 and the PSf porous support membranes were obtained by using an infrared spectrometer at room temperature;

[0056] The atomic force microscope pictures of the surfaces of the polyamide nanofiltration composite membranes prepared in Comparative Example 1 and Example 3 were obtained by using an atomic force microscope at room temperature.

[0057] The calculation of water flux and solute rejection rate in the embodiments of the present application is as follows:

[0058] The formula for calculating the flux is formula (1):

[0059]

[0060] wherein J w (L / (m 2 ·h)) is the water flux, V represents the volume of the permeate, S (m 2 ) is the test area of the membrane, and Δt (h) is the test time.

[0061] The formula for calculating the solute rejection rate is formula (2):

[0062]

[0063] wherein C p (g / L) and C f (g / L) represent the salt concentrations of the permeate and the material liquid, respectively. The salt concentration is measured by a DDSJ-308A conductivity meter (Shanghai, China).

[0064] Comparative Example 1

[0065] The prepared nanofiltration composite membrane comprises an ultrathin separation polyamide layer, a porous polysulfone ultrafiltration support layer, and a non-woven fabric. First, a water phase solution with a concentration of 0.2wt% polyethyleneimine and 1wt% trisodium phosphate is prepared, and the pH is adjusted to 10 using hydrochloric acid; a solution of 0.15wt% trimesoyl chloride in n-hexane is prepared. During the interfacial polymerization membrane preparation process, the water phase solution is first poured on the surface of the polysulfone ultrafiltration membrane, and after 5 minutes of immersion, the residual solution is poured off, and the membrane surface is blown dry with a nitrogen or air knife; then the n-hexane solution is poured on the membrane surface, and after 30 seconds of polymerization reaction, the excess n-hexane solution is poured off. Dry in a blast oven at 50 degrees Celsius for 10 minutes, and finally store the prepared nanofiltration composite membrane in deionized water for standby, marked as TFC membrane.

[0066] Example 1

[0067] The prepared nanofiltration composite membrane comprises an ultra-thin separation polyamide layer, a porous polysulfone ultrafiltration support layer and a non-woven fabric. First, a water phase solution with a concentration of 0.2wt% polyethyleneimine, 0.2wt% phenylbiguanide and 1wt% trisodium phosphate is prepared, and hydrochloric acid is used to adjust the pH to 10; a n-hexane solution with a concentration of 0.15wt% trimesoyl chloride is prepared. In the interfacial polymerization membrane preparation process, the water phase solution is first poured on the surface of the polysulfone ultrafiltration membrane, and after 5 minutes of immersion, the residual solution is poured off, and the membrane surface is blown dry with a nitrogen or air knife; then the n-hexane solution is poured on the membrane surface, and after 30 seconds of polymerization reaction, the excess n-hexane solution is poured off. Dry in a blast oven at 50 degrees Celsius for 10 minutes, and finally store the prepared nanofiltration composite membrane in deionized water for standby, marked as PBG-0.20 membrane.

[0068] Example 2

[0069] The experimental operation steps and conditions are the same as those of Example 1, except that the concentration of phenylbiguanide in the water phase is selected as 0.30wt%, and the membrane is marked as PBG-0.30 membrane.

[0070] Example 3

[0071] The experimental operation steps and conditions are the same as those of Example 1, except that the concentration of phenylbiguanide in the water phase is selected as 0.40wt%, and the membrane is marked as PBG-0.40 membrane.

[0072] Example 4

[0073] The experimental operation steps and conditions are the same as those of Example 1, except that the concentration of phenylbiguanide in the water phase is selected as 0.50wt%, and the membrane is marked as PBG-0.50 membrane.

[0074] According to Figure 1 It can be seen that, compared with the polysulfone support layer (PSf membrane) and the TFC membrane, the PBG-0.40 membrane has an amide I band at 1636cm -1 , which proves that a polyamide layer is successfully formed on the polysulfone base membrane.

[0075] Test Example

[0076] The performance of the nanofiltration composite membrane is evaluated by measuring the water flux and solute rejection rate. The test conditions are: 6bar, 20℃, 3L / min, respectively testing pure water, magnesium chloride solution and lithium chloride solution system, and the salt concentration is 1g / L, and the test results are as follows Figure 2 .

[0077] By Figure 2It can be seen that the water flux of the nanofiltration composite membrane is higher than that of the composite membrane of Comparative Example 1 when phenylbiguanide is added in the water phase compared to Comparative Example 1 without adding phenylbiguanide. With the increase of the concentration of phenylbiguanide from 0.10% to 0.50%, the rejection rate of the new nanofiltration membrane to magnesium chloride increases from 91.74% to 96.24%, and the rejection rate to lithium chloride increases from 40.48% to 53.38%, which is better than the rejection rate of TFC membrane to magnesium chloride and lithium chloride of 87.28% and 61.89%. The pure water flux increases from 21.12 Lm - 2 h -1 to 36.45 Lm -2 h -1 , which is better than the pure water flux of 6.99 Lm -2 h -1 of the TFC membrane.

[0078] Figure 3 are AFM images of TFC and PBG-0.40 membranes. Compared with the traditional interfacial polymerization prepared TFC membrane, it can be found that the surface morphology of PBG-0.40 membrane is smoother.

[0079] Figure 4 are thicknesses of TFC and PBG-0.40 membranes. Compared with the thickness of 31.8 nm of TFC membrane, the thickness of PBG-0.40 membrane increases to 37.4 nm.

[0080] The above is only a few embodiments of the present application, and does not limit the present application in any form. Although the preferred embodiments are disclosed as above, they are not intended to limit the present application. Any skilled person in the art can make some changes or modifications to the above disclosed technical content without departing from the scope of the technical solution of the present application, which are equivalent to equivalent embodiments and belong to the scope of the technical solution.

Claims

1. A nanofiltration composite membrane with rigid-flexible structure interpenetration, characterized in that, the thickness of the nanofiltration composite membrane is 1-500 nm; the nanofiltration composite membrane is obtained by in-situ polymerization of a polybasic organic amine and a rigid biguanide monomer on a porous support layer; the polybasic organic amine is selected from at least one of polyethyleneimine, tetraethylenepentamine, triethylenetetramine, diethylenetriamine, 2, 2', 2''-triaminotriethylamine, polyamide-amine, piperazine, m-phenylenediamine, p-phenylenediamine, 1, 2-ethylenediamine, 1, 6-hexanediamine, 1, 3-cyclohexanediamine, 1, 4-cyclohexanediamine, spermine or melamine; the rigid biguanide monomer is selected from at least one of compounds with the structure shown in formula I; wherein R 1, R 2 are independently selected from at least one of benzene ring, naphthalene and imidazolium rigid structure. 2.The nanofiltration composite membrane according to claim 1, characterized in that, the benzene ring, naphthalene and imidazolium rigid structure further contains a substituent; the substituent is selected from at least one of amino, nitro, carboxyl and methyl. 3.The nanofiltration composite membrane according to claim 1, characterized in that, the thickness of the nanofiltration composite membrane is 10-100 nm. 4.A preparation method of the nanofiltration composite membrane with rigid-flexible structure interpenetration according to any one of claims 1-3, characterized in that, comprising the following steps: immersing a porous support layer in an aqueous solution containing a polybasic organic amine and a rigid biguanide monomer to obtain an infiltrated porous support layer, placing an organic solvent solution containing a polybasic acid chloride on the infiltrated porous support layer, polymerizing, drying to obtain the nanofiltration composite membrane with rigid-flexible structure interpenetration. 5.The preparation method according to claim 4, characterized in that, the porous support layer is selected from non-woven fabric; preferably, the non-woven fabric is compounded with a polymer; the polymer is selected from at least one of polysulfone, polyethersulfone, polyimide, polyacrylonitrile, polypropylene and polyether ether ketone. 6.The preparation method according to claim 4, characterized in that, the concentration of the polybasic organic amine in the aqueous solution containing the polybasic organic amine and the rigid biguanide monomer is 0.01-5 wt%; preferably, the concentration of the polybasic organic amine in the aqueous solution containing the polybasic organic amine and the rigid biguanide monomer is 0.05-2 wt%; the concentration of the rigid biguanide monomer in the aqueous solution containing the polybasic organic amine and the rigid biguanide monomer is 0.01-5.00 wt%. 7.The preparation method according to claim 4, characterized in that, the immersion time is 10 s-10 min; preferably, the immersion time is 1-6 min. 8.The preparation method according to claim 4, characterized in that, the polybasic acid chloride is selected from at least one of trimesic acid chloride, isophthalic acid chloride, terephthalic acid chloride, pyromellitic acid chloride and adipoyl chloride; the organic solvent is selected from at least one of n-hexane, cyclohexane, n-heptane, n-octane, isopentane, Isopar-G, Isopar-E, Isopar-L and acetone; the concentration of the organic solvent solution containing the polybasic acid chloride is 0.01-5.00 wt%. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 9. The preparation method according to claim 4, characterized in that, the polymerization time is 1s-5min; preferably, the polymerization time is 5s-1min; the drying temperature is 50-150℃; the drying time is 1-20min.

10. Use of the nanofiltration composite membrane having rigid-flexible structure interpenetrated according to any one of claims 1 to 3, characterized in that ； application in single / multivalent ion separation, water treatment or lithium extraction from salt lake.

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