Composite nanofiltration membrane, method for preparing the same and use thereof

Abstract

The application relates to the field of membranes, and discloses a composite nanofiltration membrane and a preparation method and application thereof. The composite nanofiltration membrane comprises a bottom layer, a porous support layer and a polyamide separation layer in sequence. The polyamide separation layer is grafted with quaternary ammonium salt groups and / or quaternary phosphonium salt groups through N atoms. The quaternary ammonium salt groups have a structure shown in formula I. The quaternary phosphonium salt groups have a structure shown in formula II and / or formula III. The specific quaternary ammonium salt groups and / or quaternary phosphonium salt groups are grafted in the separation layer of the composite nanofiltration membrane, so that the composite nanofiltration membrane has a high magnesium-lithium separation coefficient while maintaining a high water flux, and is particularly suitable for the water treatment and separation field.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of membranes, in particular, to a composite nanofiltration membrane and a preparation method and application thereof. BACKGROUND

[0002] In recent years, with the wide application of new energy vehicles, the demand for lithium energy has gradually increased. In China, most of the lithium resources are contained in salt lake brine. In addition to lithium ions, salt lake water also contains a large amount of magnesium ions and sodium ions. Therefore, it is of high technical difficulty to extract pure lithium resources from salt lakes. Researchers have developed a series of methods and processes such as precipitation method, solar pond method, extraction method, calcination method, membrane separation method and adsorption method to obtain lithium resources. Among them, the membrane separation method and the adsorption method are the most widely studied.

[0003] The existing commercial nanofiltration membrane is not designed for magnesium-lithium separation, and its separation efficiency for magnesium ions and lithium ions is very low (magnesium-lithium separation coefficient is less than 5), which cannot be used for lithium extraction from salt lakes. In recent years, a large number of scientific researches have proved that increasing the positive charge density on the surface of the nanofiltration membrane separation layer can increase the retention rate of magnesium chloride through the Donnan effect, thereby improving the magnesium-lithium separation efficiency. Most of the researches are still in the laboratory stage, and the magnesium-lithium separation coefficient of the prepared nanofiltration membrane with positive charge on the surface is still less than 20. Therefore, how to use nanofiltration membrane to realize efficient magnesium-lithium separation still faces many challenges.

[0004] In addition, the positively charged nanofiltration membrane also has important application in the treatment of electroplating wastewater process. As a new process membrane material, the application of positively charged nanofiltration membrane will be more and more widely. SUMMARY

[0005] The purpose of the present application is to overcome the low magnesium-lithium separation efficiency of the existing nanofiltration membrane, and to provide a composite nanofiltration membrane with high magnesium-lithium separation coefficient, a preparation method and application thereof. The specific quaternary ammonium salt group and / or quaternary phosphonium salt group are grafted in the separation layer of the composite nanofiltration membrane, so that the composite nanofiltration membrane has high magnesium-lithium separation coefficient while maintaining high water flux, and is particularly suitable for water treatment separation field.

[0006] In order to achieve the above purpose, the first aspect of the present application provides a composite nanofiltration membrane, wherein the composite nanofiltration membrane comprises a bottom layer, a porous support layer and a polyamide separation layer in sequence.

[0007] The polyamide separation layer is grafted with a quaternary ammonium salt group and / or a quaternary phosphonium salt group through N atom; the quaternary ammonium salt group has a structure shown in formula I; the quaternary phosphonium salt group has a structure shown in formula II and / or formula III.

[0008]

[0009] wherein R1 is a C1-C9 substituted or unsubstituted alkylene; R2, R3 and R4 are each independently selected from C1-C3 alkyl or phenyl; R5 is a C1-C6 alkylene, phenyl or C7-C10 aralkyl; R6, R7 and R8 are each independently phenyl or C7-C10 aralkyl; R9, R 10 and R 11 are each independently phenyl or C7-C10 aralkyl, and n is an integer from 0 to 3;

[0010] X, X1 and X2 are each independently halogen.

[0011] The second aspect of the present application provides a preparation method of a composite nanofiltration membrane, wherein the preparation method comprises the following steps:

[0012] S1, under stirring, a first solution comprising a halogenated quaternary ammonium salt and / or a halogenated quaternary phosphonium salt, and a catalyst is added dropwise to a second solution containing a polyamine to react, to obtain a modified polyamine;

[0013] S2, a porous support layer is prepared on the bottom layer;

[0014] S3, after the surface of the porous support layer is subjected to a first contact with an aqueous phase containing the modified polyamine of step S1, and then subjected to a second contact with an organic phase containing a polyacyl chloride, and then subjected to a heat treatment, the composite nanofiltration membrane is obtained;

[0015] The halogenated quaternary ammonium salt has a structure shown in formula IV; the halogenated quaternary phosphonium salt has a structure shown in formula V or VI;

[0016]

[0017] wherein R1' is a C1-C9 substituted or unsubstituted alkylene; R2', R3' and R4' are each independently selected from C1-C3 alkyl or phenyl; R5' is a C1-C6 alkylene, phenyl or C7-C10 aralkyl; R6', R7' and R8' are each independently phenyl or C7-C10 aralkyl; n is an integer from 0 to 3; R9', R 10 ' and R 11 ' are each independently phenyl or C7-C10 aralkyl;

[0018] X1, X2, X3 and X are each independently halogen.

[0019] The third aspect of the present application provides a composite nanofiltration membrane prepared by the above preparation method.

[0020] The fourth aspect of the present application provides an application of the above composite nanofiltration membrane in the field of water treatment separation.

[0021] By the technical scheme, the composite nanofiltration membrane, the preparation method and the application thereof have the following beneficial effects:

[0022] The specific quaternary ammonium salt group and / or the specific quaternary phosphonium salt group are grafted in the separation layer of the composite nanofiltration membrane, so that the positive charge density of the composite nanofiltration membrane is significantly improved, the rejection effect of the composite nanofiltration membrane on magnesium ions is improved by using the repulsion effect between positive charges, and the magnesium-lithium separation efficiency of the composite nanofiltration membrane is improved while the high water flux of the composite nanofiltration membrane is maintained.

[0023] The specific quaternary ammonium salt group and / or the specific quaternary phosphonium salt group are grafted in the separation layer of the composite nanofiltration membrane, so that the positive charge density of the composite nanofiltration membrane is significantly improved, the rejection effect of the composite nanofiltration membrane on magnesium ions is improved by using the repulsion effect between positive charges, and the magnesium-lithium separation efficiency of the composite nanofiltration membrane is improved while the high water flux of the composite nanofiltration membrane is maintained. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 A schematic diagram of the reaction between 2-bromoethyl trimethyl ammonium bromide and the amino group (primary amine, secondary amine and tertiary amine) on the surface of the polyamide separation layer in Embodiment 1 of the present application;

[0025] Figure 2 An infrared spectrum of the membrane separation layer of the composite nanofiltration membrane in Embodiment 1 and Comparative Example 1;

[0026] Figure 3 An XPS spectrum of the membrane surface of the composite nanofiltration membrane in Embodiment 1;

[0027] Figure 4 An XPS spectrum of the membrane surface of the composite nanofiltration membrane in Comparative Example 1;

[0028] Figure 5 A schematic diagram of the reaction between bromopropyl triphenyl phosphonium bromide and the amino group (primary amine, secondary amine and tertiary amine) on the surface of the polyamide separation layer in Embodiment 7 of the present application;

[0029] Figure 6 An infrared spectrum of the composite nanofiltration membrane in Embodiment 7 and Comparative Example 1;

[0030] Figure 7 An XPS spectrum of the composite nanofiltration membrane in Embodiment 7. DETAILED DESCRIPTION

[0031] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not critical to the invention. Any numeric range recited is intended to include all values from the lower value to the upper value, inclusive of both values, and to sub-ranges falling within the specified range. In this context, a sub-range can be independently selected from the stated range.

[0032] The first aspect of the present application provides a composite nanofiltration membrane, wherein the composite nanofiltration membrane comprises a bottom layer, a porous support layer and a polyamide separation layer in sequence;

[0033] The polyamide separation layer is grafted with a quaternary ammonium salt group and / or a quaternary phosphonium salt group through N atoms.

[0034] The quaternary ammonium salt group has a structure shown in Formula I; and the quaternary phosphonium salt group has a structure shown in Formula II and / or Formula III.

[0035]

[0036] wherein R1 is a substituted or unsubstituted alkylene group with 1-9 carbon atoms; R2, R3 and R4 are each independently selected from an alkyl group with 1-3 carbon atoms or a phenyl group; R5 is an alkylene group with 1-6 carbon atoms, a phenyl group or an aralkyl group with 7-10 carbon atoms; R6, R7 and R8 are each independently a phenyl group or an aralkyl group with 7-10 carbon atoms; R9, R 10 and R 11 are each independently a phenyl group or an aralkyl group with 7-10 carbon atoms, and n is an integer from 0 to 3.

[0037] X, X1 and X2 are each independently a halogen.

[0038] In the present application, * refers to the position where the quaternary ammonium salt group or the quaternary phosphonium salt group is connected to the -NH-, of the polyamide separation layer.

[0039] In the present application, X1, X2, X3 and X are only used to distinguish different substituents and do not have a special meaning.

[0040] In the present application, the grafting of the specific quaternary ammonium salt group and / or the quaternary phosphonium salt group in the separation layer of the composite nanofiltration membrane makes the composite nanofiltration membrane have a high magnesium-lithium separation coefficient while maintaining a high water flux, and is particularly suitable for the field of water treatment separation.

[0041] In the present application, R1 can be a branched alkylene group or a linear alkylene group.

[0042] Further, R1 is a C1-C6 substituted or unsubstituted alkylene or phenyl, R2, R3 and R4 are each independently CH3; R5 is a C1-C3 alkylene, phenyl or C8-C9 aralkyl; R6, R7 and R8 are each independently phenyl; R9, R 10 and R 11 are each independently phenyl, and n is an integer of 0 to 3.

[0043] In one embodiment of the present application, R1 is a C1-C3 substituted alkylene, wherein the substituent is a hydroxyl group or a carboxyl group.

[0044] Further, X is Cl, Br or I, and X1 and X2 are each independently F, Cl, Br or I.

[0045] In one embodiment of the present application, in the formula I, R1 is ethylene, propylene, butylene, pentylene or hexylene; R2, R3 and R4 are methyl, ethyl or phenyl; and X is Cl, Br or I.

[0046] In one embodiment of the present application, in the formula II, R5 is propylene, ethylene, methylene or R6, R7 and R8 are phenyl; and X is Cl, Br or I.

[0047] According to the present application, the content of nitrogen atoms in the quaternary ammonium salt group in the composite nanofiltration membrane is 1 to 5 at. %.

[0048] In the present application, when the content of nitrogen atoms in the quaternary ammonium salt group in the composite nanofiltration membrane satisfies the above range, the composite nanofiltration membrane has a high surface electrode potential and a small average pore size, so that the composite nanofiltration membrane has a high magnesium-lithium separation coefficient.

[0049] Further, the content of nitrogen atoms in the composite nanofiltration membrane is 2 to 5 at. %.

[0050] According to the present application, the content of phosphorus atoms in the composite nanofiltration membrane is 0.4 to 3 at. %.

[0051] In the present application, when the content of phosphorus atoms in the composite nanofiltration membrane satisfies the above range, the composite nanofiltration membrane has a high surface electrode potential and a small average pore size, so that the composite nanofiltration membrane has a high magnesium-lithium separation coefficient.

[0052] Further, the content of phosphorus atoms in the composite nanofiltration membrane is 0.5 to 2 at. %.

[0053] According to the present application, the surface Zeta potential of the composite nanofiltration membrane is -5 mV to 15 mV.

[0054] In the present application, when the surface Zeta potential of the composite nanofiltration membrane meets the above range, it indicates that the composite nanofiltration membrane has a high surface electrode potential, and when it is used for magnesium-lithium separation, it can better repel divalent magnesium ions, so that the magnesium ions in the liquid are not easy to pass through the separation membrane, and at the same time, monovalent lithium ions can pass through as much as possible, thereby obtaining a higher magnesium-lithium separation efficiency.

[0055] In the present application, the surface Zeta potential of the composite nanofiltration membrane refers to the surface Zeta potential at pH=7.

[0056] Further, the surface Zeta potential of the composite nanofiltration membrane is 0 mV to 10 mV.

[0057] According to the present application, the average pore size of the composite nanofiltration membrane is 0.1-0.5nm.

[0058] In the present application, when the average pore size of the composite nanofiltration membrane meets the above range, it indicates that the composite nanofiltration membrane has high density, and when it is used for magnesium-lithium separation, it can better intercept divalent magnesium ions, so that the magnesium ions in the liquid are not easy to pass through the separation membrane, and at the same time, monovalent lithium ions can pass through as much as possible, thereby obtaining a higher magnesium-lithium separation efficiency.

[0059] Further, the average pore size of the composite nanofiltration membrane is 0.15-0.35nm.

[0060] According to the present application, the contact angle of the composite nanofiltration membrane is 30-80°.

[0061] In the present application, the composite nanofiltration membrane has a contact angle in the range described in the present application, which indicates that the composite nanofiltration membrane has excellent hydrophilicity, and can make the composite nanofiltration membrane have excellent water permeability.

[0062] Further, the contact angle of the composite nanofiltration membrane is 30-60°.

[0063] In the present application, the bottom layer and the porous support layer are not specifically limited and can be made of various existing materials having certain strength and capable of being used for nanofiltration and reverse osmosis membranes.

[0064] In the present application, the bottom layer is a non-woven fabric material, preferably polyester and / or polyethylene.

[0065] In the present application, the porous support layer material can be at least one of polyether sulfone, polysulfone, polyaromatic ether, polybenzimidazole, polyether ketone, polyether ether ketone, polyacrylonitrile, polyvinylidene fluoride and polyaryletherketone.

[0066] In the present application, the polyamide separation layer is generated by interfacial polymerization of a polyamine modified by a halogenated quaternary ammonium salt and / or a halogenated quaternary phosphonium salt and a polyacyl chloride.

[0067] In the present application, the polyamine is selected from at least one of polyethyleneimine, polyvinylamine, triethylenetetramine, tetraethylenepentamine, diethylenetriamine, polyethylene polyamine, piperazine, m-phenylenediamine and p-phenylenediamine, preferably polyethyleneimine and / or polyethylene polyamine.

[0068] In the present application, the polyacyl chloride is selected from at least one of 1,3,5-benzene tricarbonyl chloride, 1,2-benzene dicarbonyl chloride, 1,3-benzene dicarbonyl chloride, 1,4-benzene dicarbonyl chloride and adipoyl chloride, preferably 1,3,5-benzene tricarbonyl chloride and / or 1,4-benzene dicarbonyl chloride.

[0069] In the present application, the halogenated quaternary ammonium salt has the structure of formula IV;

[0070]

[0071] wherein R1' is a C1-C9 substituted or unsubstituted alkylene; R2', R3' and R4' are each independently selected from C1-C3 alkyl or phenyl; X1 and X are each independently halogen.

[0072] Further, R1' is a C1-C6 substituted or unsubstituted alkylene or phenyl; R2', R3' and R4' are each independently CH3; X is Cl, Br or I; X1 is F, Cl, Br or I.

[0073] In one specific embodiment of the present application, R1' is a C1-C3 substituted alkylene, wherein the substituent is hydroxyl or carboxyl, preferably hydroxyl.

[0074] In one specific embodiment of the present application, the halogenated quaternary ammonium salt is selected from at least one of 2-chloroethyltrimethylammonium chloride, 2-chloroethyltriethylammonium chloride, 2-chloroethyltriphenylammonium chloride, 3-chloro-2-hydroxypropyltrimethylammonium chloride, 3-chloropropyltrimethylammonium chloride, 4-chlorobutyltrimethylammonium chloride, 5-chloropentyltrimethylammonium chloride, 6-chlorohexyltrimethylammonium chloride, 2-bromoethyltrimethylammonium bromide, 3-bromopropyltrimethylammonium bromide, 4-bromobutyltrimethylammonium bromide, 5-bromopentyltrimethylammonium bromide, 6-bromohexyltrimethylammonium bromide, iodomethyltrimethylammonium iodide, 2-iodoethyltrimethylammonium iodide, 3-iodopropyltrimethylammonium iodide, 4-iodobutyltrimethylammonium iodide, 5-iodopentyltrimethylammonium iodide and 6-iodohexyltrimethylammonium iodide.

[0075] In the present application, the halogenated quaternary phosphonium salt has the structure of formula V or VI;

[0076]

[0077] wherein R5' is a C1-C6 alkylene, phenyl or C7-C10 aralkyl; R6', R7' and R8' are each independently phenyl or C7-C10 aralkyl; n is an integer from 0 to 3; R9' and R10' are each independently phenyl; X is CI, Br or I; X1, X2 and X3 are each independently F, CI, Br or I. 10 ' and R 11 ' are each independently phenyl; X is CI, Br or I; X1, X2 and X3 are each independently F, CI, Br or I.

[0078] X1, X2, X3 and X are each independently halogen.

[0079] Further, R5' is a C1-C3 alkylene, phenyl or C8-C9 aralkyl; R6', R7' and R8' are each independently phenyl; n is an integer from 0 to 3; R9' and R10' are each independently phenyl; X is CI, Br or I; X1, X2 and X3 are each independently F, CI, Br or I. 10 ' and R 11 ' are each independently phenyl; X is CI, Br or I; X1, X2 and X3 are each independently F, CI, Br or I.

[0080] In one embodiment of the present application, the halogenated quaternary phosphonium salt is at least one selected from the group consisting of 3-bromopropyltriphenylphosphonium bromide, 2-bromoethyltriphenylphosphonium bromide, 1-bromoethyltriphenylphosphonium bromide, bromomethyltriphenylphosphonium bromide, 3-chloropropyltriphenylphosphonium chloride, 2-chloroethyltriphenylphosphonium chloride, 1-chloroethyltriphenylphosphonium chloride, chloromethyltriphenylphosphonium chloride, 3-iodopropyltriphenylphosphonium iodide, 2-iodoethyltriphenylphosphonium iodide, 1-iodoethyltriphenylphosphonium iodide, iodomethyltriphenylphosphonium bromide, (3,3,3-trichloropropyl)triphenylphosphonium chloride, 4-bromomethylbenzyltriphenylphosphonium bromide (R5' is -CH2-phen-CH2-), (bromodifluoromethyl)triphenylphosphonium bromide (n = 0), 2-bromomethylbenzyltriphenylphosphonium bromide (R5' is -CH2-phen-CH2-), 3-bromomethylbenzyltriphenylphosphonium bromide (R5' is -CH2-phen-CH2-), 4-chloromethylbenzyltriphenylphosphonium chloride (R5' is -CH2-phen-CH2-), 2-chloromethylbenzyltriphenylphosphonium chloride (R5' is -CH2-phen-CH2-), 3-chloromethylbenzyltriphenylphosphonium chloride (R5' is -CH2-phen-CH2-), 4-iodomethylbenzyltriphenylphosphonium iodide (R5' is -CH2-phen-CH2-), 2-iodomethylbenzyltriphenylphosphonium iodide and 3-iodomethylbenzyltriphenylphosphonium iodide, preferably 3-bromopropyltriphenylphosphonium bromide and / or 4-bromomethylbenzyltriphenylphosphonium bromide.

[0081] According to the present application, the thickness of the bottom layer, the porous support layer and the polyamide separation layer is not particularly limited and can be a conventional selection in the art, but in order to enable the three layers to play a better synergistic role, so that the resulting composite nanofiltration membrane can better have excellent magnesium-lithium separation coefficient and higher water flux, preferably, the thickness of the bottom layer is 30-150 μm, preferably 50-120 μm; the thickness of the porous support layer is 10-100 μm, preferably 30-60 μm; the thickness of the polyamide separation layer is 10-500 nm, preferably 50-300 nm.

[0082] The second aspect of the present application provides a preparation method of a composite nanofiltration membrane, wherein the preparation method comprises the following steps:

[0083] S1, under stirring, adding a first solution containing a halogenated quaternary ammonium salt and / or a halogenated quaternary phosphonium salt and a catalyst to a second solution containing a polyamine to react to obtain a modified polyamine;

[0084] S2, preparing a porous support layer on the bottom layer;

[0085] S3, after the surface of the porous support layer is first contacted with an aqueous phase containing the modified polyamine of step S1 and then second contacted with an organic phase containing a polyacyl chloride, and after heat treatment, the composite nanofiltration membrane is obtained;

[0086] The halogenated quaternary ammonium salt has the structure shown in formula IV; the halogenated quaternary phosphonium salt has the structure shown in formula V or VI;

[0087]

[0088] wherein R1' is a substituted or unsubstituted alkylene group with 1-9 carbon atoms; R2', R3' and R4' are each independently selected from an alkyl group with 1-3 carbon atoms or a phenyl group; R5' is an alkylene group with 1-6 carbon atoms, a phenyl group or an aralkyl group with 7-10 carbon atoms; R6', R7' and R8' are each independently a phenyl group or an aralkyl group with 7-10 carbon atoms; n is an integer from 0 to 3; R9', R 10 ' and R 11 ' are each independently a phenyl group or an aralkyl group with 7-10 carbon atoms;

[0089] X1, X2, X3 and X are each independently a halogen.

[0090] In the present application, the halogenated quaternary ammonium salt and / or halogenated quaternary phosphonium salt is subjected to chemical reaction with a polyamine under the action of a basic catalyst to obtain a positive charge modified polyamine, and after interfacial polymerization, the surface positive charge density of the composite nanofiltration membrane is significantly improved, the rejection effect of the composite nanofiltration membrane on magnesium ions is improved by using the repulsion effect between positive charges, and then the magnesium-lithium separation efficiency of the composite nanofiltration membrane is improved while maintaining the high water flux of the composite nanofiltration membrane.

[0091] Further, R1' is a C1-C6 substituted or unsubstituted alkylene; R2', R3', and R4' are each independently CH3; R5' is a C1-C3 alkylene, phenyl, or C8-C9 aralkyl; R6', R7', and R8' are each independently phenyl; n is an integer from 0 to 3; R9', R 10 ' and R 11 ' are each independently phenyl.

[0092] Further, R1' is a C1-C3 substituted alkylene, wherein the substituent is a hydroxyl group or a carboxyl group, preferably a hydroxyl group.

[0093] Further, X is Cl, Br, or I.

[0094] Further, X1, X2, and X3 are each independently F, Cl, Br, or I.

[0095] According to the present application, the halogenated quaternary ammonium salt is selected from at least one of 2-chloroethyltrimethylammonium chloride, 2-chloroethyltriethylammonium chloride, 2-chloroethyltriphenylammonium chloride, 3-chloro-2-hydroxypropyltrimethylammonium chloride, 3-chloropropyltrimethylammonium chloride, 4-chlorobutyltrimethylammonium chloride, 5-chloropentyltrimethylammonium chloride, 6-chlorohexyltrimethylammonium chloride, 2-bromoethyltrimethylammonium bromide, 3-bromopropyltrimethylammonium bromide, 4-bromobutyltrimethylammonium bromide, 5-bromopentyltrimethylammonium bromide, 6-bromohexyltrimethylammonium bromide, iodomethyltrimethylammonium iodide, 2-iodoethyltrimethylammonium iodide, 3-iodopropyltrimethylammonium iodide, 4-iodobutyltrimethylammonium iodide, 5-iodopentyltrimethylammonium iodide, and 6-iodohexyltrimethylammonium iodide.

[0096] According to the present application, the halogenated quaternary phosphonium salt is selected from at least one of 3-bromopropyltriphenylphosphonium bromide, 2-bromoethyltriphenylphosphonium bromide, 1-bromoethyltriphenylphosphonium bromide, bromomethyltriphenylphosphonium bromide, 3-chloropropyltriphenylphosphonium chloride, 2-chloroethyltriphenylphosphonium chloride, 1-chloroethyltriphenylphosphonium chloride, chloromethyltriphenylphosphonium chloride, 3-iodopropyltriphenylphosphonium iodide, 2-iodoethyltriphenylphosphonium iodide, 1-iodoethyltriphenylphosphonium iodide, iodomethyltriphenylphosphonium bromide, (3,3,3-trichloropropyl)triphenylphosphonium chloride, 4-bromomethylbenzyltriphenylphosphonium bromide, (bromodifluoromethyl)triphenylphosphonium bromide, 2-bromomethylbenzyltriphenylphosphonium bromide, 3-bromomethylbenzyltriphenylphosphonium bromide), 4-chloromethylbenzyltriphenylphosphonium chloride, 2-chloromethylbenzyltriphenylphosphonium chloride, 3-chloromethylbenzyltriphenylphosphonium chloride, 4-iodomethylbenzyltriphenylphosphonium iodide, 2-iodomethylbenzyltriphenylphosphonium iodide, and 3-iodomethylbenzyltriphenylphosphonium iodide; preferably 3-bromopropyltriphenylphosphonium bromide and / or 4-bromomethylbenzyltriphenylphosphonium bromide.

[0097] According to the present application, the concentration of the halogenated quaternary ammonium salt and / or the halogenated quaternary phosphonium salt in the first solution is 0.5wt%-20wt%.

[0098] In the present application, when the concentration of the halogenated quaternary ammonium salt and / or the halogenated quaternary phosphonium salt in the first solution in the control step S1 meets the above range, it can be ensured that the halogenated quaternary ammonium salt and / or the halogenated quaternary phosphonium salt in the first solution can fully react with the polyamine in the second solution, more quaternary phosphonium salt and / or quaternary ammonium salt structures can be introduced into the polyamine, and the composite nanofiltration membrane can maintain a high water flux. Specifically, if the concentration of the halogenated quaternary ammonium salt and / or the halogenated quaternary phosphonium salt in the first solution is too low, when reacting with the polyamine, it is not possible to introduce enough quaternary ammonium salt structures and / or quaternary phosphonium salt structures on the polyamine, and if the concentration of the halogenated quaternary ammonium salt and / or the halogenated quaternary phosphonium salt in the first solution is too high, it will excessively consume the reactive amino groups in the polyamine, resulting in a decrease in the density of the polyamide separation layer and affecting the water flux of the composite nanofiltration membrane.

[0099] Further, the concentration of the halogenated quaternary ammonium salt and / or the halogenated quaternary phosphonium salt in the first solution is 1wt%-10wt%.

[0100] According to the present application, the catalyst is selected from at least one of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, sodium bicarbonate, potassium bicarbonate, disodium hydrogen phosphate, and dipotassium hydrogen phosphate, preferably potassium hydroxide.

[0101] According to the present application, the concentration of the catalyst in the first solution is 0.01wt%-5wt%.

[0102] In the present application, when the concentration of the catalyst in the first solution in the control step S1 meets the above range, it can ensure that the halogenated quaternary ammonium salt and / or halogenated quaternary phosphonium salt in the first solution can fully react with the polyamine in the second solution and has a high reaction rate, and the structure of the quaternary ammonium salt and / or quaternary phosphonium salt can be introduced into the molecular structure of the polyamine in a short time.

[0103] Further, the concentration of the catalyst in the first solution is 0.1wt%-1wt%.

[0104] According to the present application, in step S1, the polyamine is selected from at least one of polyethyleneimine, triethylenetetramine, tetraethylenepentamine, diethylenetriamine, polyethylene polyamine, piperazine, m-phenylenediamine and p-phenylenediamine; preferably polyethyleneimine and / or polyethylene polyamine.

[0105] According to the present application, the concentration of the polyamine in the second solution is 1wt%-20wt%, preferably 5wt%-10wt%.

[0106] According to the present application, the amount of the first solution and the second solution is such that the mass ratio of the polyamine, the halogenated quaternary ammonium salt and / or halogenated quaternary phosphonium salt, and the catalyst is 1-500:1-100:1.

[0107] In the present application, when the mass ratio of the polyamine, the halogenated quaternary ammonium salt and / or halogenated quaternary phosphonium salt, and the catalyst meets the above range, it can ensure that the halogenated quaternary ammonium salt and / or halogenated quaternary phosphonium salt in the first solution can fully react with the polyamine in the second solution, and the reaction rate and reaction efficiency are both high, and more quaternary phosphonium salt and / or quaternary ammonium salt structures can be introduced into the polyamine in a short time.

[0108] Further, the amount of the first solution and the second solution is such that the mass ratio of the polyamine, the halogenated quaternary ammonium salt and / or halogenated quaternary phosphonium salt, and the catalyst is 1-200:1-50:1.

[0109] According to the present application, in step S1, the reaction conditions include: the reaction temperature is 25-90℃; the reaction time is 1-48h.

[0110] In the present application, when the reaction conditions in step S1 meet the above range, it can ensure that the halogenated quaternary ammonium salt and / or halogenated quaternary phosphonium salt in the first solution can fully react with the polyamine in the second solution, and the reaction rate and reaction efficiency are both high, and more quaternary phosphonium salt and / or quaternary ammonium salt structures can be introduced into the polyamine in a short time.

[0111] Further, in step S1, the reaction conditions include: the reaction temperature is 40-60℃; the reaction time is 6-24h.

[0112] In a preferred embodiment of the present application, the first solution is added dropwise to the second solution containing the polyamine. By adding the first solution dropwise to the second solution containing the polyamine, the reaction rate can be controlled and the first solution and the second solution can be mixed sufficiently to ensure that the halogenated quaternary ammonium salt and / or halogenated quaternary phosphonium salt and the polyamine react sufficiently.

[0113] According to the present application, the speed of the dropwise addition is 0.5-5 mL / min, preferably 1-3 mL / min.

[0114] In the present application, the method for preparing the porous support layer in the base layer in step S2 is not particularly limited and can be prepared by a conventional method in the art, preferably by a phase inversion method, specifically, a polymer solution of the porous support layer material is coated on one surface of the base layer and a porous support layer is obtained through phase inversion.

[0115] In the present application, the phase inversion method can be preferably as follows: the support layer polymer material is dissolved in a solvent to obtain a polymer solution with a concentration of 10-20 wt%, and is defoamed at 20-40°C for 10-180 min; then the polymer solution is coated on the base layer to obtain an initial film, which is immediately immersed in water at a temperature of 10-30°C for 10-60 min to obtain the porous support layer polymer film through phase inversion.

[0116] The solvent can be N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, etc.

[0117] In the present application, the polyamide separation layer is generated by interfacial polymerization of the polyamine modified by the halogenated quaternary ammonium salt and / or halogenated quaternary phosphonium salt and the polyacid chloride.

[0118] According to the present application, the polyacid chloride is at least one selected from 1,3,5-benzene tricarbonyl chloride, 1,2-benzene dicarbonyl chloride, 1,3-benzene dicarbonyl chloride, 1,4-benzene dicarbonyl chloride and adipoyl chloride, preferably 1,3,5-benzene tricarbonyl chloride and / or 1,4-benzene dicarbonyl chloride.

[0119] According to the present application, the concentration of the modified polyamine in the aqueous phase is 0.1 wt%-5 wt%, preferably 0.5 wt%-2 wt%.

[0120] According to the present application, the concentration of the polyacid chloride in the organic phase is 0.01 wt%-1 wt%, preferably 0.1-0.5 wt%.

[0121] In the present application, the type of solvent of the organic phase is not particularly limited as long as it can dissolve the polyacyl chloride, preferably, the solvent of the organic phase is one or more of n-hexane, dodecane, n-heptane, and alkane solvent oil (Isopar E, Isopar G, Isopar H, Isopar L, and Isopar M).

[0122] In the present application, the conditions for the interfacial polymerization between the modified polyamine and the polyacyl chloride in step S3 are not particularly limited and can be performed according to the conventional conditions in the art, but in order to enable the three layers to play a better synergistic role, the resulting composite nanofiltration membrane can better have excellent magnesium-lithium separation coefficient and higher water flux, preferably, the first contact time is 5-100 s, preferably 10-60 s; the second contact time is 10-200 s, preferably 20-120 s; the heat treatment conditions include: the heat treatment temperature is 40-150℃, preferably 50-120℃; the heat treatment time is 0.5-10 min, preferably 1-5 min.

[0123] In the present application, in step S3, the volume ratio of the aqueous phase containing the modified polyamine to the membrane area of the porous support layer is 0.05-1 mL / cm 2 ; the volume ratio of the organic phase containing the polyacyl chloride to the membrane area of the porous support layer is 0.01-0.5 mL / cm 2 .

[0124] The third aspect of the present application provides a composite nanofiltration membrane prepared by the above preparation method.

[0125] The fourth aspect of the present application provides a use of the above composite nanofiltration membrane in the field of water treatment separation.

[0126] Other features and advantages of the present application will be described in detail in the following specific embodiments.

[0127] The present application will be described in detail below through examples.

[0128] In the following examples and comparative examples:

[0129] (1) The water flux of the composite nanofiltration membrane is tested by the following method: the separation membrane is loaded into a membrane cell, and the water permeation amount of the separation membrane within a certain time is measured under the conditions of 0.5 MPa and 25℃, and the water flux is calculated by the following formula:

[0130] J=Q / (A·t), wherein J is the water flux, Q is the water permeation amount (L), A is the effective membrane area of the separation membrane (m 2 ), and t is the time (h).

[0131] (2) The desalination rate of the composite nanofiltration membrane is tested by the following method: the composite separation membrane is installed in a membrane cell, the raw water solution is 2000 ppm magnesium chloride or 2000 ppm lithium chloride, and after being pre-pressed at 0.2 MPa for 0.5 h, the permeate is obtained at a pressure of 0.5 MPa, the concentrations of magnesium chloride and lithium chloride in the permeate are measured by a conductivity meter, and the desalination rate is calculated by the following formula:

[0132] R = (C p -C f ) / C p x 100%, wherein R is the desalination rate, C p is the concentration of magnesium chloride or lithium chloride in the raw solution (measured by a conductivity meter), and C f is the concentration of magnesium chloride or lithium chloride in the permeate (measured by a conductivity meter);

[0133] (3) The magnesium-lithium separation coefficient of the composite nanofiltration membrane is tested by the following method: the composite separation membrane is installed in a membrane cell, the raw water solution is a mixture of 2000 ppm magnesium chloride and 100 ppm lithium chloride, and after being pre-pressed at 0.2 MPa for 0.5 h, the permeate is obtained at a pressure of 0.5 MPa,

[0134] The magnesium-lithium separation coefficient is calculated by the following formula:

[0135] wherein S is the magnesium-lithium separation coefficient, C Li，p and C Li，f are the concentrations of lithium ions in the permeate and the raw material solution, respectively (measured by ion chromatography); and C Mg，p and C Mg，f are the concentrations of magnesium ions in the permeate and the raw material solution, respectively (measured by ion chromatography).

[0136] (4) Measurement of the surface contact angle of the composite nanofiltration membrane

[0137] The surface contact angle of the composite membrane sample is tested by a DSA100 type surface contact angle measuring instrument produced by KRUSS Company in Germany using the sessile drop method. Before testing, the sample is dried in a vacuum oven at 60°C for 30 min to remove the water on its surface and inside, and then the dried membrane is attached to a flat glass slide with double-sided tape. During testing, the volume of each water droplet is 2 μL, the water droplet is dropped on the membrane surface for 3 s, and then the contact angle is immediately tested. The final contact angle is determined by taking the average value of multiple measurements.

[0138] (5) Measurement of the content of nitrogen atoms and phosphorus atoms in the quaternary ammonium salt groups on the surface of the composite nanofiltration membrane:

[0139] The sample was dried to constant weight in an oven before measurement. The elemental composition of the surface of the composite membrane sample was determined using a Sigma Probe X-ray photoelectron spectrometer produced by the British Thermo VG company. For samples containing quaternary ammonium salt groups, the molar content of nitrogen atoms in the quaternary ammonium salt group was calculated by the ratio of the peak area of quaternary ammonium nitrogen in the fine spectrum of nitrogen atoms to the total peak area of nitrogen atoms, and the calculation formula is as follows; the content of phosphorus atoms can be directly measured by XPS spectrum.

[0140] where C N+ is the atomic percentage content (at.%) of quaternary amine nitrogen, C N is the total percentage content (at.%) of nitrogen atoms, S N+ is the peak area of quaternary amine nitrogen in the XPS spectrum, S N is the total peak area of nitrogen atoms in the XPS spectrum.

[0141] (6) Surface Attenuated Total Reflection Infrared Spectroscopy (ATR-FTIR) of the composite nanofiltration membrane

[0142] The sample was dried to constant weight in an oven before measurement. The elemental composition of the surface of the composite membrane sample was determined using a Sigma Probe X-ray photoelectron spectrometer produced by the British Thermo VG company. For samples containing quaternary ammonium salt groups, the molar content of nitrogen atoms in the quaternary ammonium salt group was calculated by the ratio of the peak area of quaternary ammonium nitrogen in the fine spectrum of nitrogen atoms to the total peak area of nitrogen atoms, and the calculation formula is as follows; the content of phosphorus atoms can be directly measured by XPS spectrum.

[0143] (7) Pore size test of the composite nanofiltration membrane: PEG solute transfer method was used to measure, and the detailed steps are as follows:

[0144] (i) Test the rejection rate of the composite membrane to PEG of different molecular sizes;

[0145] (ii) Linear fitting of PEG size and rejection rate in log-probability coordinate system, and the PEG size corresponding to 50% rejection rate is the average pore size of the composite membrane.

[0146] (8) Zeta potential test of the membrane surface: determined by Surpass electrokinetic analyzer (Anton Paar), and the circulating liquid is dilute aqueous solution of KCl, and the pH of the test solution is 7.

[0147] (9) The thickness of each layer in the composite nanofiltration membrane was measured by scanning electron microscope instrument, and the model of the scanning electron microscope was S-4800 of Hitachi company.

[0148] In addition, in the following examples and comparative examples:

[0149] Branched polyethyleneimine (weight average molecular weight of 25000 g / mol), 1,3,5-benzene tricarbonyl chloride, 2-chloroethyl trimethyl ammonium chloride, 2-bromoethyl trimethyl ammonium bromide, 3-bromopropyl trimethyl ammonium bromide, 3-bromopropyl triphenyl phosphonium bromide, chloromethyl triphenyl phosphonium chloride, iodomethyl triphenyl phosphonium iodide, and 4-bromomethyl benzyl triphenyl phosphonium bromide, and iodomethyl trimethyl ammonium iodide were purchased from Sigma-Aldrich. Other chemical reagents were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0150] The support layer was prepared by phase inversion method, and the specific steps were as follows:

[0151] A certain amount of polysulfone (number average molecular weight of 80000 g / mol) was dissolved in N, N-dimethylformamide to prepare a polysulfone solution with a concentration of 18% by weight, and the solution was degassed at 25°C for 120 min. Then, the polysulfone solution was coated on the polyester non-woven fabric (thickness of 75 μm) by using a doctor blade to obtain an initial film, and then the initial film was immersed in water at 25°C for 60 min, so that the polysulfone layer on the surface of the polyester non-woven fabric was phase-inverted into a porous membrane. Finally, the bottom-porous support layer with a total thickness of 115 μm was obtained after 3 times of water washing.

[0152] Example 1

[0153] (1) 5 g of polyethyleneimine was dissolved in 100 g of deionized water, and heated to 60°C under stirring; 10 g of an aqueous solution containing 5 wt% 2-bromoethyl trimethyl ammonium bromide (X and X1 are Br, R1' is ethylene, R2', R3', R4' are methyl) and 0.5 wt% potassium hydroxide was added dropwise into the solution at a rate of 1 mL / min, and after the addition was completed, the reaction was continued at 60°C for 24 h. The mass ratio of the polyamine, the halogenated quaternary ammonium salt and the catalyst was 100:10:1.

[0154] (2) The upper surface of the polysulfone support layer with an area of 400 cm 2 was contacted with 50 mL of an aqueous solution containing 0.5 wt% of the quaternary ammonium salt modified polyethyleneimine prepared above, and the liquid was discharged after being contacted at 25°C for 60 s; then, the upper surface of the support layer was contacted with 30 mL of an Isopar E solution containing 0.1 wt% of 1,3,5-benzene tricarbonyl chloride, and the liquid was discharged after being contacted at 25°C for 60 s; then, the membrane was placed in an oven and heated at 70°C for 3 min to obtain a composite nanofiltration membrane N1. The thickness of the bottom layer in the composite nanofiltration membrane N1 was 75 μm, the thickness of the porous support layer was 40 μm, and the thickness of the polyamide separation layer was 71 nm.

[0155] The Zeta potential, contact angle, nitrogen content, phosphorus content and average pore size of the surface of the composite nanofiltration membrane N1 are shown in Table 1.

[0156] The water flux, desalination rate of magnesium chloride and lithium chloride, and magnesium-lithium separation coefficient of the composite nanofiltration membrane N1 were tested, and the results are shown in Table 2.

[0157] Figure 1 A schematic diagram of the reaction of the primary amine, secondary amine and tertiary amine in the polyethyleneimine molecular chain with 2-bromoethyl trimethyl ammonium bromide is shown in Figure 1 Under the action of the catalyst KOH, 2-bromoethyl trimethyl ammonium bromide reacts with polyethyleneimine, and after the removal of HBr, the residue of 2-bromoethyl trimethyl ammonium bromide is connected to polyethyleneimine through N atoms.

[0158] Figure 2 The infrared absorption spectra of the composite nanofiltration membrane N1 and the composite nanofiltration membrane D1 are shown in Figure 2 It can be seen that the amino group characteristic peak of the composite nanofiltration membrane N1 at 3300 cm -1 is obviously weakened, and a characteristic absorption peak of quaternary ammonium salt group appears at 964 cm -1 . It is proved that 2-bromoethyl trimethyl ammonium bromide and polyethyleneimine react sufficiently, and the quaternary ammonium salt group is introduced into the polyamide separation layer of the composite nanofiltration membrane during the interfacial polymerization process.

[0159] Figure 3 The membrane surface XPS spectrum of the composite nanofiltration membrane N1 of Example 1 is shown in Figure 4 The membrane surface XPS spectrum of the composite nanofiltration membrane D1 of Comparative Example 1 is shown in Figure 3 and Figure 4 It can be seen that compared with the composite nanofiltration membrane D1, a new signal peak corresponding to the signal peak of the quaternary ammonium salt appears at the binding energy of 402.5 eV on the membrane surface of the composite nanofiltration membrane N1.

[0160] Example 2

[0161] (1) 10 g of polyethyleneimine was dissolved in 100 g of deionized water, and heated to 60°C under stirring; 5 g of an aqueous solution containing 1 wt% 2-bromoethyl trimethyl ammonium bromide and 0.1 wt% sodium hydroxide was added dropwise at a rate of 1 mL / min, and after the addition was completed, the reaction was continued at 60°C for 24 h. The mass ratio of the polyamine, the halogenated quaternary ammonium salt and the catalyst was 200:10:1.

[0162] (2) The same as Example 1, and the composite nanofiltration membrane N2 was obtained. The thickness of the bottom layer of the composite nanofiltration membrane N2 was 75 μm, the thickness of the porous support layer was 40 μm, and the thickness of the polyamide separation layer was 75 nm.

[0163] The Zeta potential, contact angle, nitrogen atom content, phosphorus atom content and average pore size of the surface of the composite nanofiltration membrane N2 are shown in Table 1.

[0164] The water flux, desalination rate for magnesium chloride and lithium chloride, and magnesium-lithium separation coefficient of the composite nanofiltration membrane N2 were tested, and the results are shown in Table 2.

[0165] Example 3

[0166] (1) 7.5 g of polyethyleneimine was dissolved in 100 g of deionized water, and heated to 60°C under stirring; 10 g of an aqueous solution containing 10 wt% 2-bromoethyltrimethylammonium bromide and 1 wt% potassium hydroxide was added dropwise to the solution at a rate of 1 mL / min, and after the dropwise addition was completed, the reaction was continued at 60°C for 24 h. The mass ratio of the polyamine, the halogenated quaternary ammonium salt, and the catalyst was 75:10:1.

[0167] (2) The same as in Example 1, to obtain the composite nanofiltration membrane N3. The thickness of the bottom layer in the composite nanofiltration membrane N3 was 75 μm, the thickness of the porous support layer was 40 μm, and the thickness of the polyamide separation layer was 68 nm.

[0168] The Zeta potential, contact angle, nitrogen atom content, phosphorus atom content, and average pore size of the surface of the composite nanofiltration membrane N3 are shown in Table 1.

[0169] The water flux, desalination rate for magnesium chloride and lithium chloride, and magnesium-lithium separation coefficient of the composite nanofiltration membrane N3 were tested, and the results are shown in Table 2.

[0170] Example 4

[0171] The same as in Example 1, except that 2-chloroethyltrimethylammonium chloride (X and X1 are Cl, R1’ is ethylene, and R2’, R3’, and R4’ are methyl) was used instead of 2-bromoethyltrimethylammonium bromide, to obtain the composite separation membrane N4. The thickness of the bottom layer in the composite nanofiltration membrane N4 was 75 μm, the thickness of the porous support layer was 40 μm, and the thickness of the polyamide separation layer was 82 nm.

[0172] The Zeta potential, contact angle, nitrogen atom content, phosphorus atom content, and average pore size of the surface of the composite nanofiltration membrane N4 are shown in Table 1.

[0173] The water flux, desalination rate for magnesium chloride and lithium chloride, and magnesium-lithium separation coefficient of the composite nanofiltration membrane N4 were tested, and the results are shown in Table 2.

[0174] Example 5

[0175] The preparation method is the same as that in Example 1, except that 3-bromopropyltrimethylammonium bromide (X and X1 are Br, R1' is propylene, and R2', R3', and R4' are methyl) is used instead of 2-bromoethyltrimethylammonium bromide to obtain a composite nanofiltration membrane N5. In the composite nanofiltration membrane N5, the thickness of the bottom layer is 75 μm, the thickness of the porous support layer is 40 μm, and the thickness of the polyamide separation layer is 72 nm.

[0176] The Zeta potential, contact angle, nitrogen content, phosphorus content, and average pore size of the surface of the composite nanofiltration membrane N5 are shown in Table 1.

[0177] The water flux, desalination rates for magnesium chloride and lithium chloride, and the magnesium-lithium separation coefficient of the composite nanofiltration membrane N5 are tested, and the results are shown in Table 2.

[0178] Example 6

[0179] The preparation method is the same as that in Example 1, except that iodomethyltrimethylammonium iodide (X and X1 are I, R1' is methylene, and R2', R3', and R4' are methyl) is used instead of 2-bromoethyltrimethylammonium bromide to obtain a composite nanofiltration membrane N6. In the composite nanofiltration membrane N6, the thickness of the bottom layer is 75 μm, the thickness of the porous support layer is 40 μm, and the thickness of the polyamide separation layer is 78 nm.

[0180] The Zeta potential, contact angle, nitrogen content, phosphorus content, and average pore size of the surface of the composite nanofiltration membrane N6 are shown in Table 1.

[0181] The water flux, desalination rates for magnesium chloride and lithium chloride, and the magnesium-lithium separation coefficient of the composite nanofiltration membrane N6 are tested, and the results are shown in Table 2.

[0182] Example 7

[0183] The preparation method is the same as that in Example 1, except that 3-bromopropyltriphenylphosphonium bromide (in Formula IV, R5' is propylene, R6', R7', and R8' are phenyl, and X1 and X are Br) is used instead of 2-bromoethyltrimethylammonium bromide to obtain a composite nanofiltration membrane N7. In the composite nanofiltration membrane N7, the thickness of the bottom layer is 75 μm, the thickness of the porous support layer is 40 μm, and the thickness of the polyamide separation layer is 85 nm.

[0184] The Zeta potential, contact angle, nitrogen content, phosphorus content, and average pore size of the surface of the composite nanofiltration membrane N7 are shown in Table 1.

[0185] The water flux, desalination rates for magnesium chloride and lithium chloride, and the magnesium-lithium separation coefficient of the composite nanofiltration membrane N7 are tested, and the results are shown in Table 2.

[0186] Figure 5The reaction scheme of the primary amine, secondary amine and tertiary amine in the polyethyleneimine molecular chain with 3-bromopropyltriphenylphosphonium bromide is shown in the following formula (II) : Figure 5 Under the action of catalyst KOH, 3-bromopropyltriphenylphosphonium bromide reacts with polyethyleneimine, and after removal of HBr, the residue of 3-bromopropyltriphenylphosphonium bromide is connected to polyethyleneimine through N atom.

[0187] Figure 6 The infrared spectrum of the composite nanofiltration membrane N7 and the composite nanofiltration membrane D1 is shown in the following figure: Figure 6 It can be seen from the figure that the composite nanofiltration membrane N7 has a C-P corresponding absorption peak at 1113 cm -1 , which proves that the quaternary phosphonium salt group exists in the polyamide separation layer.

[0188] Figure 7 The XPS spectrum of the surface of the composite nanofiltration membrane N7 is shown in the following figure. The signal peak at a binding energy of 132 eV corresponds to the quaternary phosphonium salt group in the polyamide separation layer.

[0189] Example 8

[0190] The preparation method is the same as that of Example 1, except that chloromethyltriphenylphosphonium chloride (in formula IV, R5' is methylene, n is 1, R6', R7', R8' are phenyl, X1 and X are Cl) is used instead of 2-bromoethyltrimethylammonium bromide, to obtain the composite nanofiltration membrane N8. Among them, the thickness of the bottom layer in the composite nanofiltration membrane N8 is 75 μm, the thickness of the porous support layer is 40 μm, and the thickness of the polyamide separation layer is 83 nm.

[0191] The Zeta potential, contact angle, nitrogen content, phosphorus content and average pore size of the surface of the composite nanofiltration membrane N8 are shown in Table 1.

[0192] The water flux, desalination rate of magnesium chloride and lithium chloride, and magnesium-lithium separation coefficient of the composite nanofiltration membrane N8 are tested, and the results are shown in Table 2.

[0193] Example 9

[0194] The preparation method is the same as that of Example 1, except that iodomethyltriphenylphosphonium iodide (in formula IV, R5' is methylene, n is 1, R6', R7', R8' are phenyl, X1 and X are I) is used instead of 2-bromoethyltrimethylammonium bromide, to obtain the composite nanofiltration membrane N9. Among them, the thickness of the bottom layer in the composite nanofiltration membrane N9 is 75 μm, the thickness of the porous support layer is 40 μm, and the thickness of the polyamide separation layer is 88 nm.

[0195] The Zeta potential, contact angle, nitrogen content, phosphorus content and average pore size of the surface of the composite nanofiltration membrane N9 are shown in Table 1.

[0196] The water flux, desalination rate of magnesium chloride and lithium chloride, and magnesium-lithium separation coefficient of the composite nanofiltration membrane N9 were tested, and the results are shown in Table 2.

[0197] Example 10

[0198] The preparation method is the same as in Example 1, except that 4-bromomethylbenzyltriphenylphosphine bromide (in Formula IV, R5' is...) is used. With n = 1, R6', R7', and R8' being phenyl groups, and X1 and X being Br, 2-bromoethyltrimethylammonium bromide was replaced to obtain the composite nanofiltration membrane N10. The composite nanofiltration membrane N10 has a bottom layer thickness of 75 μm, a porous support layer thickness of 40 μm, and a polyamide separation layer thickness of 92 nm.

[0199] The Zeta potential, contact angle, nitrogen atom content, phosphorus atom content, and average pore size of the N10 composite nanofiltration membrane surface are shown in Table 1.

[0200] The water flux, desalination rate of magnesium chloride and lithium chloride, and magnesium-lithium separation coefficient of the composite nanofiltration membrane N10 were tested, and the results are shown in Table 2.

[0201] Example 11

[0202] (1) Dissolve 5g of polyethyleneimine in 100g of deionized water and heat to 60℃ under stirring. Add 10g of an aqueous solution containing 2.5wt% 2-bromoethyltrimethylammonium bromide (X and X1 are Br, R1' is ethylene, R2', R3', and R4' are methyl) and 2.5wt% 3-bromopropyltriphenylphosphine bromide (in Formula IV, R5' is propylene, R6', R7', and R8' are phenyl, and X1 and X are Br) and 0.5wt% potassium hydroxide. After the addition is complete, continue the reaction at 60℃ for 24h. The mass ratio of polyamine, haloquaternary ammonium salt, haloquaternary phosphorus salt to catalyst is 100:5:5:1.

[0203] (2) Same as in Example 1, a composite nanofiltration membrane N11 was obtained. The thickness of the bottom layer of the composite nanofiltration membrane N11 is 75 μm, the thickness of the porous support layer is 40 μm, and the thickness of the polyamide separation layer is 79 nm.

[0204] The Zeta potential, contact angle, nitrogen atom content, phosphorus atom content, and average pore size of the N11 composite separation membrane surface are shown in Table 1.

[0205] The water flux, desalination rate of magnesium chloride and lithium chloride, and magnesium-lithium separation coefficient of the composite nanofiltration membrane N11 were tested, and the results are shown in Table 2.

[0206] Example 12

[0207] The preparation method was the same as that in Example 1, except that: in step (1), the mass ratio of the polyamine, the halogenated quaternary ammonium salt and the catalyst was 0.5:0.5:0.05 = 10:10:1, and the composite nanofiltration membrane N12 was obtained. The thickness of the bottom layer in the composite nanofiltration membrane N12 was 75 μm, the thickness of the porous support layer was 40 μm, and the thickness of the polyamide separation layer was 80 nm.

[0208] The Zeta potential, the contact angle, the nitrogen atom content, the phosphorus atom content and the average pore size of the surface of the composite nanofiltration membrane N12 are shown in Table 1.

[0209] The water flux, the desalination rates of magnesium chloride and lithium chloride, and the magnesium-lithium separation coefficient of the composite nanofiltration membrane N12 were tested, and the results are shown in Table 2.

[0210] Comparative Example 1

[0211] The upper surface of the above-mentioned polysulfone support layer was contacted with 50 mL of an aqueous solution containing 0.5% by weight of polyethyleneimine, and after 60 s of contact at 25°C, the liquid was drained. Then, the upper surface of the support layer was contacted with 30 mL of a solution of 1,3,5-benzene tricarbonyl chloride in Isopar E containing 0.1% by weight, and after 60 s of contact at 25°C, the liquid was drained. Then, the membrane was placed in an oven and heated at 70°C for 3 min to obtain the composite nanofiltration membrane D1. The thickness of the bottom layer in the composite nanofiltration membrane D1 was 75 μm, the thickness of the porous support layer was 40 μm, and the thickness of the polyamide separation layer was 85 nm.

[0212] The Zeta potential, the contact angle and the average pore size of the surface of the composite nanofiltration membrane D1 are shown in Table 1.

[0213] The water flux, the desalination rates of magnesium chloride and lithium chloride, and the magnesium-lithium separation coefficient of the composite nanofiltration membrane D1 were tested, and the results are shown in Table 2.

[0214] Table 1

[0215]

[0216]

[0217] Notes: a - the content of nitrogen atoms in the quaternary ammonium salt group; b - the content of phosphorus atoms in the composite nanofiltration membrane.

[0218] Table 2

[0219]

[0220] As can be seen from Table 1 and Table 2, compared with the composite nanofiltration membrane D1, the introduction of quaternary ammonium salt groups and / or quaternary phosphonium salt groups in the composite nanofiltration membranes N1-N12 prepared in the examples has a regulating effect on interfacial polymerization, making the interfacial polymerization more sufficient, resulting in a more dense separation layer of the composite nanofiltration membrane, a smaller pore size, and thus an improved rejection rate of magnesium chloride and an improved magnesium-lithium separation efficiency.

[0221] On the other hand, the halogenated quaternary ammonium salt and / or quaternary phosphonium salt reacts with the polyamine under the action of the basic catalyst to modify the quaternary ammonium salt group and / or quaternary phosphonium salt group with positive charge to the polyamine molecule, so that after interfacial polymerization, the surface positive charge density of the composite nanofiltration membrane is improved, the rejection effect of the composite nanofiltration membrane to magnesium ions is improved through the repulsion effect between positive charges, and thus the magnesium-lithium separation efficiency is improved.

[0222] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A composite nanofiltration membrane, characterized by, The composite nanofiltration membrane comprises a bottom layer, a porous support layer and a polyamide separation layer in sequence. The polyamide separation layer is grafted with quaternary phosphonium salt groups through N atoms. The quaternary phosphonium salt groups have structures shown in formula II and / or formula III. Formula II; Formula III; wherein R5is a C1-C6alkylene, phenyl or C7-C10aralkyl; R6, R7and R8are each independently phenyl or C7-C10aralkyl; R9, R 10 and R 11 are each independently phenyl or C7-C10aralkyl, and n is an integer from 0 to 3. X, X1 and X2 are each independently halogen.

2. The composite nanofiltration membrane according to claim 1, wherein, R5is C1-C3 alkylene, phenyl or C8-C9 aralkyl; R6, R7and R8are each independently phenyl; R9, R 10 and R 11 are each independently phenyl, and n is an integer from 0 to 3. X is Cl, Br or I; and X1 and X2 are each independently F, Cl, Br or I.

3. The composite nanofiltration membrane according to claim 1 or 2, wherein, The content of phosphorus atoms in the composite nanofiltration membrane is 0.4-3 at.%.

4. The composite nanofiltration membrane according to claim 3, wherein, The content of phosphorus atoms in the composite nanofiltration membrane is 0.5-2 at.%.

5. The composite nanofiltration membrane according to claim 1 or 2, wherein, The surface Zeta potential of the composite nanofiltration membrane is -5 mV to 15 mV.

6. The composite nanofiltration membrane according to claim 5, wherein, The surface Zeta potential of the composite nanofiltration membrane is 0 mV to 10 mV.

7. The composite nanofiltration membrane according to claim 1 or 2, wherein, The average pore size of the composite nanofiltration membrane is 0.1-0.5 nm.

8. The composite nanofiltration membrane according to claim 7, wherein, The average pore size of the composite nanofiltration membrane is 0.15-0.35 nm.

9. The composite nanofiltration membrane according to claim 1 or 2, wherein, The contact angle of the composite nanofiltration membrane is 30-80°.

10. The composite nanofiltration membrane according to claim 9, wherein, The contact angle of the composite nanofiltration membrane is 30-60°.

11. The composite nanofiltration membrane according to claim 1 or 2, wherein, The thickness of the bottom layer is 30-150 μm. The thickness of the porous support layer is 10-100 μm. The thickness of the polyamide separation layer is 10-500 nm.

12. The composite nanofiltration membrane according to claim 11, wherein, The thickness of the bottom layer is 50-120 μm. The thickness of the porous support layer is 30-60 μm. The thickness of the polyamide separation layer is 50-300 nm.

13. A method for producing the composite nanofiltration membrane according to any one of claims 1 to 12, characterized by, The preparation method comprises the following steps: S1, under stirring, adding a first solution comprising a halogenated quaternary phosphonium salt and a catalyst to a second solution containing a polyamine, and reacting to obtain a modified polyamine; S2, preparing a porous support layer on the bottom layer; S3, after the surface of the porous support layer is subjected to a first contact with an aqueous phase containing the modified polyamine of step S1 and a second contact with an organic phase containing a polyacyl chloride, and after heat treatment, the composite nanofiltration membrane is obtained; The halogenated quaternary phosphonium salt has structures shown in formula V or VI. Formula V; Formula VI; wherein R5' is C1-C6 alkylene, phenyl or C7-C10 aralkyl; R6', R7' and R8' are each independently phenyl or C7-C10 aralkyl; n is an integer from 0 to 3; R9', R 10 ' and R 11 ' are each independently phenyl or C7-C10 aralkyl; X1, X2, X3 and X are each independently halogen.

14. The production method according to claim 13, wherein R5' is C1-C3 alkylene, phenyl or C8-C9 aralkyl; R6', R7' and R8' are each independently phenyl; n is an integer from 0 to 3; R9', R 10 ' and R 11 ' are each independently phenyl; X is Cl, Br or I. X1, X2 and X3 are each independently F, Cl, Br or I.

15. The method of making according to claim 13, wherein, In step S1, the halogenated quaternary phosphonium salt is at least one of 3-bromopropyltriphenylphosphonium bromide, 2-bromoethyltriphenylphosphonium bromide, 1-bromoethyltriphenylphosphonium bromide, bromomethyltriphenylphosphonium bromide, 3-chloropropyltriphenylphosphonium chloride, 2-chloroethyltriphenylphosphonium chloride, 1-chloroethyltriphenylphosphonium chloride, chloromethyltriphenylphosphonium chloride, 3-iodopropyltriphenylphosphonium iodide, 2-iodoethyltriphenylphosphonium iodide, 1-iodoethyltriphenylphosphonium iodide, iodomethyltriphenylphosphonium bromide, (3,3,3-trichloropropyl)triphenylphosphonium chloride, 4-bromomethylbenzyltriphenylphosphonium bromide, (bromodifluoromethyl)triphenylphosphonium bromide, 2-bromomethylbenzyltriphenylphosphonium bromide, 3-bromomethylbenzyltriphenylphosphonium bromide, 4-chloromethylbenzyltriphenylphosphonium chloride, 2-chloromethylbenzyltriphenylphosphonium chloride, 3-chloromethylbenzyltriphenylphosphonium chloride, 4-iodomethylbenzyltriphenylphosphonium iodide, 2-iodomethylbenzyltriphenylphosphonium iodide, and 3-iodomethylbenzyltriphenylphosphonium iodide; And / or, the catalyst is at least one of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, sodium bicarbonate, potassium bicarbonate, disodium hydrogen phosphate, and dipotassium hydrogen phosphate; And / or, the concentration of the halogenated quaternary phosphonium salt in the first solution is 0.5wt%-20wt%; And / or, the concentration of the catalyst in the first solution is 0.01wt%-5wt%.

16. The method of making according to claim 15, wherein, In step S1, the halogenated quaternary phosphonium salt is 3-bromopropyltriphenylphosphonium bromide and / or 4-bromomethylbenzyltriphenylphosphonium bromide; And / or, the concentration of the halogenated quaternary phosphonium salt in the first solution is 1wt%-10wt%; And / or, the concentration of the catalyst in the first solution is 0.1wt%-1wt%.

17. The production method according to claim 13 or 14, wherein In step S1, the polyamine is at least one of polyethyleneimine, polyethylene polyamine, piperazine, m-phenylenediamine, and p-phenylenediamine; And / or, the concentration of the polyamine in the second solution is 1wt%-20wt%; And / or, the use amount of the first solution and the second solution is such that the mass ratio of the polyamine, the halogenated quaternary phosphonium salt, and the catalyst is 1-500:1-100:

1.

18. The method of making according to claim 17, wherein, In step S1, the polyamine is polyethyleneimine and / or polyethylene polyamine; And / or, the concentration of the polyamine in the second solution is 5wt%-10wt%.

19. The method of making according to claim 17, wherein, The polyethylene polyamine is at least one of triethylenetetramine, tetraethylenepentamine, and diethylenetriamine.

20. The production method according to claim 13 or 14, wherein The reaction conditions include: the reaction temperature is 25-90℃; and the reaction time is 1-48h; And / or, the first solution is added dropwise into the second solution containing the polyamine.

21. The method of making according to claim 20, wherein, The reaction conditions include: the reaction temperature is 40-60℃; and the reaction time is 6-24h; And / or, the speed of the dropwise addition is 0.5-5mL / min.

22. The method of making according to claim 13 or 14, wherein, In step S3, the first contact time is 5-100s; And / or, the second contact time is 10-200s; And / or, the heat treatment conditions include: the heat treatment temperature is 40-150℃; and the heat treatment time is 0.5-10min.

23. The method of making according to claim 22, wherein, In step S3, the first contact time is 10-60s; And / or, the second contact time is 20-120s; And / or, the heat treatment condition comprises: heat treatment temperature is 50-120℃; heat treatment time is 1-5min.

24. The production method according to claim 13 or 14, wherein In step S3, the polybasic acid chloride is selected from at least one of 1,3,5-benzene tricarboxylic chloride, 1,2-benzene dicarboxylic chloride, 1,3-benzene dicarboxylic chloride, 1,4-benzene dicarboxylic chloride and adipoyl chloride; And / or, the concentration of the modified polybasic amine in the aqueous phase is 0.1wt%-5wt%; And / or, the concentration of the polybasic acid chloride in the organic phase is 0.01wt%-1wt%.

25. The method of manufacturing according to claim 24, wherein, In step S3, the polybasic acid chloride is 1,3,5-benzene tricarboxylic chloride and / or 1,4-benzene dicarboxylic chloride; And / or, the concentration of the modified polybasic amine in the aqueous phase is 0.5wt%-2wt%; And / or, the concentration of the polybasic acid chloride in the organic phase is 0.1-0.5wt%.

26. The composite nanofiltration membrane prepared by the preparation method of any one of claims 13-25.

27. The use of the composite nanofiltration membrane of any one of claims 1-12 and 26 in the field of water treatment separation.

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