Nanofiltration membrane, oil phase solution for preparing nanofiltration membrane and preparation method

Abstract

The invention relates to the technical field of permeable membranes, and discloses a nanofiltration membrane, which comprises: a base membrane layer comprising a non-woven fabric and a base membrane formed on the surface of the non-woven fabric; the separation layer is formed on the base film layer through in-situ polymerization, and the separation layer is provided with convex textures. A separation layer of the nanofiltration membrane is formed by an interfacial polymerization reaction of a water-phase monomer in a water-phase solution and an oil-phase monomer in an oil-phase solution, and the local growth rate of a polymerization reaction product is improved by controlling and accelerating the local polymerization reaction rate in the interfacial polymerization reaction process; according to the present invention, the non-uniform growth rate of the polymerization reaction product is utilized so as to self-assemble to form the convex texture structure, and the convex texture structure is similar to the leaf vein of the leaf, such that the uniformly polymerized surface morphology of the separation layer of the traditional nanofiltration membrane is changed, and the selective separation property of the monovalent ion and the divalent ion can be improved; the invention further discloses an oil phase solution for preparing the nanofiltration membrane and a preparation method of the nanofiltration membrane.

Description

Technical Field

[0001] The present application relates to the technical field of osmotic membranes, for example, to a nanofiltration membrane, an oil phase solution for preparing the same, and a preparation method. Background Art

[0002] Nanofiltration membrane is a relatively mature membrane technology for separation, with nanometer-scale pores, and is commonly used to separate small molecules and ions. Its application prospects in fields such as magnesium-lithium separation and printing and dyeing desalination have attracted much attention due to its unique properties. First of all, nanofiltration membranes can achieve selective permeability for different ion sizes and charges. Compared with other traditional separation methods (such as chemical precipitation or ion exchange), nanofiltration membrane separation technology requires less energy, has mild operating conditions, reduces the use of chemical reagents, and reduces environmental load, which is very consistent with the current development trend of green chemical industry. In addition, nanofiltration membrane systems usually have lower operating costs because their energy consumption is relatively low and they can be used for a long time under stable system operation.

[0003] Nanofiltration membranes are widely used in separation technologies, but they still face challenges in terms of selectivity and water flux. For example, there is a conflict between improving the selectivity of monovalent and divalent metal ions and increasing water flux, and it is impossible to achieve both.

[0004] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of this application, and therefore may include information that does not constitute prior art known to ordinary technicians in this field. Summary of the Invention

[0005] In order to provide a basic understanding of some aspects of the disclosed embodiments, a brief summary is given below. The summary is not an extensive review, nor is it intended to identify key / critical elements or delineate the scope of protection of these embodiments, but rather serves as a prelude to the detailed description that follows.

[0006] The embodiments of the present disclosure provide a nanofiltration membrane, an oil phase solution for preparing the same, and a preparation method to solve the technical problem of being unable to simultaneously improve the selective separation effect of monovalent and divalent metal ions of the nanofiltration membrane and improve the water flux.

[0007] In some embodiments, the nanofiltration membrane includes: a base membrane layer, including a supporting substrate and a base membrane formed on the surface of the supporting substrate; a separation layer, which is formed on the surface of the base membrane layer by in-situ polymerization, and the separation layer has a raised texture.

[0008] In some embodiments, the oil phase solution for preparing a nanofiltration membrane is used to prepare the aforementioned nanofiltration membrane; the oil phase solution comprises an acyl chloride monomer, an organic metal catalyst and an organic solvent, wherein the mass concentration of the organic metal catalyst is 0.01% to 1%.

[0009] In some embodiments, the method for preparing the nanofiltration membrane includes: preparing a base membrane layer, an aqueous solution and an oil solution, wherein the oil solution adopts the aforementioned oil solution; spreading the aqueous solution on the surface of the base membrane layer to obtain an aqueous-covered base membrane; bringing the oil solution into contact with the aqueous-covered layer of the aqueous-covered base membrane, and performing an interfacial reaction under the action of an organic metal catalyst in the oil solution, thereby forming a separation layer with a raised texture on the surface of the base membrane layer to obtain a composite membrane; and drying the composite membrane to obtain a nanofiltration membrane.

[0010] The nanofiltration membrane, the oil phase solution for preparing the nanofiltration membrane, and the preparation method provided in the embodiments of the present disclosure can achieve the following technical effects:

[0011] The separation layer of the nanofiltration membrane of the embodiment of the present disclosure is formed by the interfacial polymerization reaction of the aqueous phase monomer in the aqueous phase solution and the oil phase monomer in the oil phase solution. During the interfacial polymerization reaction, the local polymerization reaction rate is accelerated, the local growth rate of the polymerization reaction product is increased, and the uneven growth rate of the polymerization reaction product is utilized to self-assemble to form a raised texture structure. The raised texture structure is similar to the veins of leaves, thereby changing the uniformly polymerized surface morphology of the separation layer of the traditional nanofiltration membrane and being able to improve the selective separation of monovalent and divalent metal ions.

[0012] In the oil phase solution for preparing the nanofiltration membrane in the embodiment of the present disclosure, an organic metal catalyst is added to the oil phase monomer solution. The organic metal catalyst significantly accelerates the reaction rate between the aqueous phase monomer (e.g., amine monomer) in the aqueous phase solution and the oil phase monomer (e.g., acyl chloride monomer) in the oil phase solution by reducing the activation energy of the interfacial polymerization reaction during the interfacial polymerization process, so that the growth rate of the polyamide layer formed by polymerization is uneven in the local area, resulting in the gradual formation of a leaf vein-like self-assembled raised texture structure. It also changes the diffusion behavior of the aqueous phase monomer (e.g., amine monomer) and the oil phase monomer (e.g., acyl chloride monomer) at the interface, forming a difference in reaction rate in space, thereby inducing a complex leaf vein morphology, rather than a uniform structure in traditional interfacial polymerization.

[0013] The method for preparing the nanofiltration membrane of the embodiment of the present disclosure uses the aforementioned oil phase solution to prepare a nanofiltration membrane having a "vein-like" raised texture structure formed on the separation layer. The preparation method is simple, effective, and easy to operate.

[0014] The above general description and the following description are exemplary and explanatory only and are not intended to limit the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] One or more embodiments are exemplarily described by corresponding drawings. These exemplary descriptions and drawings do not limit the embodiments. Elements with the same reference numerals in the drawings are shown as similar elements. The drawings do not constitute a scale limitation. In addition,

[0016] Figure 1 Schematic diagram of the structure of a nanofiltration membrane provided by an embodiment of the present disclosure;

[0017] Figure 2 This is a flowchart of a method for preparing a nanofiltration membrane provided by an embodiment of the present disclosure;

[0018] Figure 3a This is a surface SEM photograph of the nanofiltration membrane I prepared in Example 1 provided in the embodiments of the present disclosure;

[0019] Figure 3b This is a cross-sectional SEM photograph of the nanofiltration membrane I prepared in Example 1 provided in the embodiments of the present disclosure;

[0020] Figure 4 This is a surface SEM photograph of the nanofiltration membrane II prepared in Example 2 provided in the embodiments of the present disclosure;

[0021] Figure 5 This is a cross-sectional SEM photograph of the nanofiltration membrane II prepared in Example 2 provided in the embodiments of the present disclosure;

[0022] Figure 6 This is a surface SEM photograph of the nanofiltration membrane III prepared in Example 3 provided in the embodiments of the present disclosure;

[0023] Figure 7 This is a cross-sectional SEM photograph of the nanofiltration membrane III prepared in Example 3 provided in the embodiments of the present disclosure;

[0024] Figure 8 This is a surface SEM photograph of the nanofiltration membrane IV prepared in Example 4 provided in the embodiments of the present disclosure;

[0025] Figure 9 This is a cross-sectional SEM photograph of the nanofiltration membrane IV prepared in Example 4 provided in the embodiments of the present disclosure;

[0026] Figure 10 This is a surface SEM photograph of the nanofiltration membrane V prepared in Example 5 provided in the embodiments of the present disclosure;

[0027] Figure 11 This is a cross-sectional SEM photograph of the nanofiltration membrane V prepared in Example 5 provided in the embodiments of the present disclosure;

[0028] Figure 12 This is a surface SEM photograph of the nanofiltration membrane VI prepared in Example 6 provided in the embodiments of the present disclosure;

[0029] Figure 13 This is a cross-sectional SEM photograph of the nanofiltration membrane VI prepared in Example 6 provided in the embodiments of the present disclosure;

[0030] Figure 14 This is a surface SEM photograph of the nanofiltration membrane VII prepared in Example 7 provided in the embodiments of the present disclosure;

[0031] Figure 15 This is a cross-sectional SEM photograph of the nanofiltration membrane VII prepared in Example 7 provided in the embodiments of the present disclosure;

[0032] Figure 16 This is a surface SEM photograph of the nanofiltration membrane VIII prepared in Example 8 provided in the examples of the present disclosure;

[0033] Figure 17 This is a cross-sectional SEM photograph of the nanofiltration membrane VIII prepared in Example 8 provided in the examples of the present disclosure;

[0034] Figure 18 This is a surface SEM photograph of the nanofiltration membrane comparison II prepared in Comparative Example 2 provided in the embodiments of the present disclosure;

[0035] Figure 19 This is a cross-sectional SEM photograph of the nanofiltration membrane comparison II prepared in comparative example 2 provided in the embodiments of the present disclosure.

[0036] Reference numerals:

[0037] 10. Base film layer; 11. Support substrate; 12. Base film; 20. Separation layer; 21. Raised texture. DETAILED DESCRIPTION

[0038] In order to be able to understand the features and technical content of the embodiments of the present disclosure in more detail, the implementation of the embodiments of the present disclosure is described in detail below in conjunction with the accompanying drawings. The accompanying drawings are for reference only and are not used to limit the embodiments of the present disclosure. In the following technical description, for the sake of convenience of explanation, a full understanding of the disclosed embodiments is provided through a number of details. However, one or more embodiments can still be implemented without these details. In other cases, to simplify the drawings, well-known structures, steps, and devices can be simplified for display.

[0039] In the description and claims of the embodiments of the present disclosure, as well as in the accompanying drawings, the terms "first," "second," and the like are used to distinguish similar items and are not necessarily used to describe a particular order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate to describe the embodiments of the present disclosure herein. In addition, the terms "including," "having," and any variations thereof are intended to cover non-exclusive inclusions.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs. The term "plurality" means two or more. In the disclosed embodiment, the character " / " indicates that the objects before and after are in an "or" relationship. For example, A / B means: A or B. The term "and / or" is a description of the association relationship between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or, three relationships of A and B.

[0041] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present disclosure can be combined with each other.

[0042] Those skilled in the art will understand that in the methods involved in the specification of this application and other parts, for example, in the methods of each embodiment or example, the writing order of each step does not mean a strict execution order and constitutes any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps A and B, which means that the method may include steps A and B performed sequentially, or steps B and A performed sequentially. For example, it is mentioned that the method may also include step C, which means that step C can be added to the method in any order. For example, the method may include steps A, B and C, or steps A, C and B, or steps C, A and B, etc.

[0043] In this application, open technical features or technical solutions described with words such as "contain," "include," and "includes" do not exclude additional members beyond the listed members unless otherwise specified, and can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions that include additional members beyond the listed members. For example, if A includes a1, a2, and a3, it may or may not include other members unless otherwise specified. This can be regarded as providing both the feature or solution of "A consists of a1, a2, and a3" and the feature or solution of "A includes not only a1, a2, and a3, but also other members."

[0044] The "ranges" disclosed in this application can be defined in the form of lower limits and upper limits. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. Ranges defined in this way can be inclusive or exclusive of the end values, any end value can be included or excluded independently, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4, and 5 are also listed, the following ranges are all expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" is an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to listing the parameter as, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and so on. For example, when a parameter is expressed as an integer selected from "2-10," this is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0045] In this application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0046] Combine Figure 1 As shown, an embodiment of the present disclosure discloses a nanofiltration membrane, comprising a base membrane layer 10 and a separation layer 20, wherein the base membrane layer 10 comprises a supporting substrate 11 and a base membrane 12 formed on the surface of the supporting substrate 11; the separation layer 20 is formed on the surface of the base membrane layer by in-situ polymerization, and the separation layer (surface) is formed with a raised texture 21.

[0047] In the nanofiltration membrane of the embodiment of the present disclosure, Figure 1 and Figure 3b As shown, the separation layer 20 is formed by the interfacial polymerization reaction of the aqueous phase monomers in the aqueous phase solution and the oil phase monomers in the oil phase solution. During the interfacial polymerization reaction, the local polymerization reaction rate is accelerated by controlling the local growth rate of the polymerization reaction product, and the uneven growth rate of the polymerization reaction product is utilized to self-assemble to form a raised texture 21 structure. The raised texture 21 structure is similar to the veins of leaves, thereby changing the uniformly polymerized flat morphology of the separation layer of the traditional nanofiltration membrane and improving the selective separation of monovalent and divalent metal ions. In addition, the raised texture 21 structure formed can increase the specific surface area of ​​the nanofiltration membrane, thereby enhancing the water flux.

[0048] In the nanofiltration membrane of the embodiment of the present disclosure, the supporting substrate 11 of the base membrane layer 10 plays a supporting role, and the specific material is not limited. Optionally, the supporting substrate 11 includes a non-woven fabric. The pore size of the non-woven fabric is generally above the micron scale, which will not affect the key membrane material properties such as the water flux and separation performance of the nanofiltration membrane. Therefore, it is suitable as a supporting substrate for the nanofiltration membrane. Optionally, the supporting substrate includes a polyethylene (PE) diaphragm for lithium batteries, a polyethylene terephthalate (PET) film, a polyacrylonitrile (PAN) film or a polytetrafluoroethylene (PTFE) film.

[0049] In some embodiments, in the basement membrane layer 10, the basement membrane 12 is porous (as shown in conjunction with FIG3 ). In this embodiment, the porous basement membrane can improve water flux. The porous basement membrane is combined with a separation layer having a "vein-like" raised texture structure to construct a composite nanofiltration membrane with a leaf-like structure, further improving the monovalent and divalent metal ion separation efficiency and water flux of the nanofiltration membrane. As shown in FIG3 , the pores in the porous basement membrane extend along the thickness direction of the basement membrane layer to form a pore structure. Therefore, the basement membrane can also be defined as a porous basement membrane or a porous basement membrane.

[0050] Optionally, in the porous base membrane (multi-porous base membrane), the pore size (pore size of the pore channel) is 0.1μm to 30μm. In this embodiment, the pore channels with a pore size of 0.1μm to 20μm account for more than 80%. Combined with the SEM image of the cross section of the nanofiltration membrane in the accompanying drawings, it can be seen that the large-pore channels are concentrated on the side of the base membrane layer away from the separation layer (this side is defined as the bottom side), forming a large-pore concentration layer; and the pore size in the large-pore concentration layer on the bottom side of the base membrane layer is 20μm to 30μm. And the thickness of the large-pore concentration layer is less than or equal to one-third of the thickness of the base membrane layer.

[0051] Optionally, the pore size of the pore channel close to the separation layer side is smaller than or equal to the pore size of the pore channel far from the separation layer side.

[0052] Optionally, the porous basement membrane includes a surface basement membrane and an inner basement membrane, wherein the surface basement membrane is the basement membrane adjacent to the separation layer; the pores in the surface basement membrane have a pore size of 0.1 μm to 10 μm, and the pores in the inner basement membrane have a pore size of 8 μm to 30 μm. In this embodiment, the porous basement membrane is divided into a surface basement membrane and an inner basement membrane based on the pore size to better understand the nanofiltration membrane structure of the disclosed embodiment.

[0053] Optionally, the pore size of the surface basement membrane pores in the range of 0.1 μm to 6 μm accounts for more than 50%.

[0054] Optionally, the pore size of the inner basement membrane pores is in the range of 8 μm to 20 μm, accounting for more than 80%.

[0055] In the embodiments of the present disclosure, the proportion of pores refers to the area proportion of pores on the cross-sectional SEM image of the nanofiltration membrane.

[0056] In some embodiments, the thickness of the base membrane layer is 100 micrometers to 400 micrometers. In this embodiment, the thickness of the base membrane layer is controlled to take into account both the supporting function of the base membrane layer and the water flux.

[0057] In some embodiments, the basement membrane layer has a thickness of 100 to 400 microns and is porous. This porous basement membrane, combined with a separation layer having a "vein-like" raised texture, creates a composite nanofiltration membrane with a leaf-like structure, further improving the nanofiltration membrane's monovalent and divalent metal ion separation efficiency and water flux. The pore size and distribution of the porous basement membrane in this embodiment are the same as those described above and will not be further elaborated here.

[0058] In some embodiments, in the presence of an organic metal catalyst, a separation layer is in situ polymerized on the base film layer, so that the separation layer forms a raised texture. During the interfacial polymerization process, the organic metal catalyst significantly accelerates the reaction rate between the aqueous phase monomer (e.g., amine monomer) in the aqueous phase solution and the oil phase monomer (e.g., acyl chloride monomer) in the oil phase solution by reducing the activation energy of the interfacial polymerization reaction, so that the growth rate of the polyamide layer formed by polymerization is uneven in the local area, resulting in the gradual formation of a leaf vein-like self-assembled raised texture structure. It will also change the diffusion behavior of the aqueous phase monomer (e.g., amine monomer) and the oil phase monomer (e.g., acyl chloride monomer) at the interface, forming a reaction rate difference in space, thereby inducing a complex leaf vein morphology, rather than a uniform structure in traditional interfacial polymerization. In addition, the organic metal of the organic metal catalyst can accelerate the polymerization of the aqueous phase monomer and the oil phase monomer to form a denser polymerization network structure, thereby enhancing the selective separation performance of monovalent and divalent metal ions.

[0059] Optionally, the separation layer of the nanofiltration membrane is formed by an interfacial polymerization reaction between aqueous monomers in an aqueous solution and oil-phase monomers in an oil-phase solution; an organometallic catalyst is added to the oil-phase solution. In this embodiment, the organometallic catalyst can be evenly dispersed in the oil-phase solution, allowing the raised texture to be more dispersed in the separation layer. The types of aqueous monomers and oil-phase monomers are not limited, as long as they can undergo interfacial polymerization.

[0060] It is understood that the oil phase solution also includes an oil phase monomer (eg, an acyl chloride monomer) and an organic solvent, and the amount of the organic metal catalyst added to the oil phase solution is determined according to actual conditions.

[0061] Optionally, the oil phase solution includes an acyl chloride monomer, an organic metal catalyst and an organic solvent, wherein the mass concentration of the organic metal catalyst is 0.01% to 2%.

[0062] Optionally, the mass concentration of the organometallic catalyst is 0.01% to 1%. Optionally, the mass concentration of the organometallic catalyst is 0.05% to 1%. Optionally, the mass concentration of the organometallic catalyst is 0.08% to 1%. Optionally, the mass concentration of the organometallic catalyst is 0.1% to 1%. Optionally, the mass concentration of the organometallic catalyst is 0.1% to 0.5%; or, the mass concentration of the organometallic catalyst is 0.5% to 1%.

[0063] Optionally, the mass concentration of the organometallic catalyst is 0.05%, 0.08%, 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, 0.25%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.5%, 2%, or any value in the range of 0.01% to 2%.

[0064] The mass concentration of the oil-phase monomer (e.g., acyl chloride monomer) in the oil-phase solution is not limited and is determined based on the specific oil-phase monomer type and actual needs. Optionally, the oil-phase monomer includes an acyl chloride monomer, and the mass concentration of the acyl chloride monomer is 0.1% to 5%. The type and concentration of the acyl chloride monomer are not limited, as long as it can react with the aqueous monomer in the aqueous solution to undergo polymerization.

[0065] Optionally, the acyl chloride monomer includes one or a mixture of trimesoyl chloride, pyromellitoyl chloride, cyclohexanedicarboxylic acid chloride, terephthaloyl chloride and succinoyl chloride.

[0066] Optionally, the mass concentration of the acyl chloride monomer is 0.1% to 5%. Optionally, the mass concentration of the acyl chloride monomer is 0.5% to 5%. Optionally, the mass concentration of the acyl chloride monomer is 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value between 0.1% and 10%.

[0067] In the embodiments of the present disclosure, the type of the organometallic catalyst is not limited, as long as it can reduce the activation energy of the interfacial polymerization reaction during the interfacial polymerization process.

[0068] Optionally, the metal element in the organometallic catalyst includes one or more of lithium, iron, nickel, titanium and rhodium.

[0069] Optionally, the organometallic catalyst includes one or more of n-butyllithium, tert-butyllithium, diisopropyl titanocene, nickel carbonyl, carbonyl ferrocene and rhodium carbonyl.

[0070] In some embodiments, the thickness of the separation layer is 50 nm to 200 nm. In this embodiment, controlling the thickness of the separation layer to 50 nm to 200 nm allows for the formation of a dense polymeric network structure, enhancing the selective separation of monovalent and divalent metal ions while ensuring water flux, making it suitable for industrial applications. The specific thickness of the separation layer can be achieved by controlling the interfacial polymerization time of the aqueous phase monomers and the oil phase monomers to achieve the desired thickness.

[0071] In some embodiments, the height of the raised texture is 10 nm to 30 nm. The height of the raised texture is controlled to be 10 nm to 30 nm, further improving the selectivity of the separation layer and obtaining a nanofiltration membrane with a high selectivity factor for monovalent and divalent metal ions.

[0072] In some embodiments, the protrusions of the separation layer are dispersed and formed on the surface of the separation layer. In this embodiment, the protrusions are dispersed and formed on the surface of the separation layer, which improves the density of the separation layer and the uniformity of the polymer network structure.

[0073] In some embodiments, the thickness of the separation layer is 50 nm to 200 nm, the protrusion height of the protrusion texture is 10 nm to 30 nm, and the protrusion texture of the separation layer is dispersedly formed on the surface of the separation layer.

[0074] In some embodiments, at a pressure of 0.2 bar, the pure water flux of the nanofiltration membrane is greater than or equal to 30 L / (m 2 ·h); and / or, after 30 days of continuous operation, the pure water flux is greater than or equal to 30L / (m 2 h); and / or, divalent metal ions (e.g., Mg 2+ or Ca 2+ ) has a rejection rate greater than or equal to 95%; and / or, monovalent metal ions (e.g., Li + or Na + ) has a rejection rate of less than or equal to 30%; and / or, a selectivity factor for monovalent and divalent metal ions is greater than or equal to 95. The ion selectivity and water flux of the nanofiltration membrane can meet industrial requirements.

[0075] Optionally, at a pressure of 0.2 bar, the pure water flux of the nanofiltration membrane can reach 34 L / (m 2 h) or more; and / or, the pure water flux can reach 34L / (m 2 h) or above; and / or, the rejection rate of divalent metal ions can reach 98% or above; and / or, the rejection rate of monovalent metal ions can reach 20% to 30%; and / or, the selectivity factor of monovalent and divalent metal ions can reach 100 or above. The ion selectivity and water flux of the nanofiltration membrane can meet industrial requirements.

[0076] The present disclosure discloses an oil phase solution for preparing a nanofiltration membrane, which is used to prepare the nanofiltration membrane of any of the aforementioned embodiments; wherein the oil phase solution includes an acyl chloride monomer, an organic metal catalyst and an organic solvent, wherein the mass concentration of the organic metal catalyst is 0.01% to 2%.

[0077] In the oil phase solution for preparing the nanofiltration membrane in the embodiment of the present disclosure, an organic metal catalyst is added to the oil phase monomer solution. The organic metal catalyst significantly accelerates the reaction rate between the aqueous phase monomer (e.g., amine monomer) in the aqueous phase solution and the oil phase monomer (e.g., acyl chloride monomer) in the oil phase solution by reducing the activation energy of the interfacial polymerization reaction during the interfacial polymerization process, so that the growth rate of the polyamide layer formed by polymerization is uneven in the local area, resulting in the gradual formation of a leaf vein-like self-assembled raised texture structure. It also changes the diffusion behavior of the aqueous phase monomer (e.g., amine monomer) and the oil phase monomer (e.g., acyl chloride monomer) at the interface, forming a difference in reaction rate in space, thereby inducing a complex leaf vein morphology, rather than a uniform structure in traditional interfacial polymerization.

[0078] Optionally, the mass concentration of the organometallic catalyst is 0.01% to 1%. Optionally, the mass concentration of the organometallic catalyst is 0.05% to 1%. Optionally, the mass concentration of the organometallic catalyst is 0.08% to 1%. Optionally, the mass concentration of the organometallic catalyst is 0.1% to 1%. Optionally, the mass concentration of the organometallic catalyst is 0.1% to 0.5%; or, the mass concentration of the organometallic catalyst is 0.5% to 1%.

[0079] Optionally, the mass concentration of the organometallic catalyst is 0.05%, 0.08%, 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, 0.25%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.5%, 2%, or any value in the range of 0.01% to 2%.

[0080] In the oil phase solution of the embodiments of the present disclosure, the type of the organometallic catalyst is not limited, as long as it can reduce the activation energy of the interfacial polymerization reaction during the interfacial polymerization process.

[0081] Optionally, the metal in the organometallic catalyst includes one or more of lithium, iron, nickel, titanium and rhodium.

[0082] Optionally, the organometallic catalyst includes one or more of n-butyllithium, tert-butyllithium, diisopropyl titanocene, nickel carbonyl, carbonyl ferrocene and rhodium carbonyl.

[0083] It is understandable that the oil phase solution of the embodiment of the present disclosure is an acyl chloride monomer solution with an organic metal catalyst added thereto. The type and concentration of the acyl chloride monomer are not limited as long as it can react with the aqueous monomer in the aqueous solution to undergo polymerization.

[0084] Optionally, the acyl chloride monomer includes one or a mixture of trimesoyl chloride, pyromellitoyl chloride, cyclohexanedicarboxylic acid chloride, terephthaloyl chloride and succinoyl chloride.

[0085] Optionally, the mass concentration of the acyl chloride monomer is 0.1% to 5%. Optionally, the mass concentration of the acyl chloride monomer is 0.5% to 5%. Optionally, the mass concentration of the acyl chloride monomer is 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value between 0.1% and 10%.

[0086] Combine Figure 2 As shown, the present disclosure also discloses a method for preparing a nanofiltration membrane, comprising the following steps:

[0087] S10, preparing a base film layer, an aqueous solution and an oily solution, wherein the oily solution is the oily solution of any of the aforementioned embodiments.

[0088] S20, spreading the aqueous solution on the surface of the base film layer to obtain an aqueous base film layer.

[0089] S30, bringing the oil phase solution into contact with the aqueous phase covering film of the aqueous phase covering base film layer, and performing an interfacial reaction under the action of an organic metal catalyst in the oil phase solution, thereby forming a separation layer with a raised texture on the surface of the base film layer to obtain a composite membrane.

[0090] S40, drying the composite membrane to obtain a nanofiltration membrane.

[0091] The method for preparing the nanofiltration membrane of the embodiment of the present disclosure adopts the oil phase solution of any of the aforementioned embodiments. The organic metal catalyst in the oil phase solution significantly accelerates the reaction rate between the aqueous phase monomer (e.g., amine monomer) in the aqueous phase solution and the oil phase monomer (e.g., acyl chloride monomer) in the oil phase solution by reducing the activation energy of the interfacial polymerization reaction during the interfacial polymerization process, so that the growth rate of the polyamide layer formed by polymerization is uneven in the local area, resulting in the gradual formation of a leaf vein-like self-assembled raised texture structure. It also changes the diffusion behavior of the aqueous phase monomer (e.g., amine monomer) and the oil phase monomer (e.g., acyl chloride monomer) at the interface, forming a reaction rate difference in space, thereby inducing a complex leaf vein morphology, rather than a uniform structure in traditional interfacial polymerization.

[0092] The method for preparing a nanofiltration membrane according to the disclosed embodiments involves preparing a base membrane layer (e.g., a porous base membrane layer) using phase inversion technology, constructing a functional layer containing amino groups on the surface of the base membrane layer (e.g., a porous base membrane layer), and then coating the membrane surface with a functional layer containing amide groups using surface coating technology. The nanofiltration membrane material is then dried and cleaned. The leaf-like composite nanofiltration membrane prepared according to the disclosed embodiments combines high monovalent and divalent metal ion separation efficiency with high water flux.

[0093] In step S10 of the preparation method of the embodiment of the present disclosure, the order of preparing the base film layer, the aqueous solution and the oily solution is not limited and they can be prepared simultaneously or determined according to actual conditions.

[0094] In some embodiments, in step S10, a base membrane layer is prepared, including: S11, spreading a membrane-forming liquid on a supporting substrate to form a membrane-forming liquid layer on the supporting substrate to obtain a membrane-forming supporting substrate; wherein the membrane-forming liquid includes a high molecular weight polymer, a pore-forming agent, and a first solvent. S12, soaking the membrane-forming supporting substrate in a solvent, and then drying it to obtain a base membrane layer. In this embodiment, a pore-forming agent is added to the membrane-forming liquid to make the obtained base membrane porous, thereby increasing water flux. The porous base membrane is combined with a separation layer having a "vein-like" raised texture structure to construct a composite nanofiltration membrane that imitates a leaf structure, further improving the monovalent and divalent metal ion separation efficiency and water flux of the nanofiltration membrane.

[0095] In step S11, the material of the support substrate is not limited and is determined according to actual conditions. Optionally, the support substrate includes non-woven fabric, polyethylene (PE) separator for lithium batteries, polyethylene terephthalate (PET) film, polyacrylonitrile (PAN) film or polytetrafluoroethylene (PTFE) film.

[0096] In step S11, the film-forming liquid is applied to the support substrate in any manner as long as the film-forming liquid adheres to the support substrate. Alternatively, the film-forming liquid is poured onto the support substrate (e.g., non-woven fabric) and formed into a film using a scraper.

[0097] Optionally, in the membrane-forming solution, the mass concentration of the high molecular weight polymer is 10% to 30%, and the mass concentration of the pore-forming agent is 0.1% to 10%.

[0098] Optionally, the high molecular polymer includes one or a mixture of polyethersulfone, polysulfone, cellulose acetate, polyetheretherketone, polyvinylidene fluoride and polyimide.

[0099] Optionally, the pore-forming agent includes one or a mixture of polyethylene glycol, ethylene glycol, polyvinyl pyrrolidone, sulfonated polystyrene, lithium chloride and ethanol. The pore-forming agent is not limited to the above-mentioned pore-forming agents, as long as they are soluble in both water and the first solvent.

[0100] Optionally, the first solvent includes one or a mixture of N,N-dimethylacetamide, N,N-dimethylformamide, methyl pyrrolidone, dimethyl sulfoxide, butyl acetate and methanesulfonic acid, which can be determined according to actual conditions.

[0101] Optionally, the mass concentration of the high molecular weight polymer is 10%, 12%, 15%, 18%, 20%, 25%, 30%, or any value between 10% and 30%.

[0102] Optionally, the mass concentration of the pore-forming agent is 0.1%, 0.2%, 0.5%, 0.8%, 1%, 3%, 4%, 5%, 8%, 10%, or any value between 0.1% and 10%.

[0103] In step S12 of this embodiment, the solvent used to soak the membrane support substrate is not limited, for example, water.

[0104] In some embodiments, in step S10, the aqueous phase solution includes: an amine monomer, an additive, and a second solvent, wherein the mass concentration of the amine monomer is 0.2% to 10%, and the mass concentration of the additive is 0.01% to 10%. In this embodiment, the additive includes a surfactant and / or a polymerization catalyst, but is certainly not limited to a surfactant and / or a polymerization catalyst, and may also be other conventionally selected auxiliary agents, without limitation. When the aqueous phase solution includes a polymerization catalyst, the polymerization catalyst can react with the hydrochloric acid byproduct formed during the polymerization reaction of the amine monomer and the acyl chloride to accelerate the reaction.

[0105] Optionally, the amine monomer includes one or a mixture of p-phenylenediamine, o-phenylenediamine, piperazine, hexamethylenediamine, 1,3,5-triaminobenzene and diaminomethylaniline.

[0106] Optionally, the surfactant includes one or a mixture of Tween 80, sodium lauryl sulfate, Span 80, polyvinyl alcohol, cetyltrimethylammonium bromide and nonylphenol polyoxyethylene ether.

[0107] Optionally, the polymerization catalyst includes one or a mixture of calcium hydride, phosphoric acid, sodium bicarbonate, diisopropylethylamine, triethylamine and pyridine.

[0108] Optionally, when the additive includes a surfactant, the mass concentration of the surfactant is 0.01% to 3%. Optionally, the mass concentration of the surfactant is 0.01%, 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.5%, 3%, or any value between 0.01% and 3%. In this embodiment, the aqueous phase solution includes an amine monomer, a surfactant, and a second solvent.

[0109] Optionally, when the additive includes a polymerization catalyst, the mass concentration of the polymerization catalyst is 0.1% to 5%. Optionally, the mass concentration of the polymerization catalyst is 0.2%, 0.3%, 0.5%, 0.8%, 1%, 0.3%, 0.5%, 0.8%, 1%, 1.5%, 2%, 3%, 4%, 5%, or any value between 0.2% and 5%. In this embodiment, the aqueous solution includes an amine monomer, a polymerization catalyst, and a second solvent.

[0110] Optionally, when the additive includes a surfactant and a polymerization catalyst, the total mass concentration of the surfactant and the polymerization catalyst is 0.2% to 8%, and the mass ratio of the surfactant to the polymerization catalyst is 1:0.25 to 1:100. In this embodiment, the aqueous solution includes an amine monomer, a surfactant, a polymerization catalyst, and a second solvent.

[0111] Optionally, the total mass concentration of the surfactant and the polymerization catalyst is 0.2%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or any value within the range of 0.2% to 8%.

[0112] Optionally, the mass ratio of surfactant to polymerization catalyst is 1:0.25, 1:0.3, 1:0.5, 1:1, 1:2, 1:5, 1:10, 1:30, 1:50, 1:80, 1:100, etc.

[0113] In the disclosed embodiment, in step S20, applying the aqueous solution to the surface of the base film to obtain the aqueous-applied base film includes: applying the base film to the aqueous solution, allowing the base film to contact the aqueous solution for a first predetermined time, and then drying the base film to obtain the aqueous-applied base film. Specifically, applying the base film to the aqueous solution is performed such that one side surface of the base film (the side surface being defined as the upper surface or first surface) contacts the surface of the aqueous solution. In this embodiment, the contact time between the base film and the aqueous solution is not limited and is determined based on actual needs.

[0114] Optionally, the first preset time for contacting the basement membrane with the aqueous solution is 1 to 15 minutes. Optionally, the first preset time is 1 to 12 minutes. Optionally, the first preset time is 1 to 10 minutes. Optionally, the first preset time is 1 minute, 2 minutes, 3 minutes, 5 minutes, 8 minutes, 10 minutes, 12 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, or any value within the range of 1 to 30 minutes.

[0115] In step S30 of the preparation method of the embodiment of the present disclosure, the oil phase solution is brought into contact with the surface of the aqueous phase covering base film to carry out an interfacial reaction, including: bringing one side surface of the aqueous phase covering base film (the first surface of the base film) into contact with the oil phase solution for a second preset time to carry out an interfacial reaction.

[0116] In some embodiments, in step S30, the contact time (defined as the second predetermined time) during which the oil phase solution contacts the surface of the aqueous phase-coated base membrane is 30 to 600 seconds. By controlling the contact time, the thickness of the separation layer can be controlled, ensuring selective separation of monovalent and divalent metal ions while achieving high water flux at low pressure.

[0117] Optionally, the contact time (second preset time) during which the oil phase solution contacts the surface of the aqueous phase coating base film is 30 to 500 seconds. Optionally, the second preset time is 60 to 500 seconds. Optionally, the second preset time is 120 to 300 seconds. Optionally, the second preset time is 30 seconds, 60 seconds, 90 seconds, 120 seconds, 150 seconds, 180 seconds, 240 seconds, 300 seconds, 360 seconds, 420 seconds, 450 seconds, 500 seconds, 540 seconds, 600 seconds, or any value within the range of 30 to 600 seconds.

[0118] In step S40 of the disclosed embodiment, the drying method is not limited and can be air-dried or air-dried, or can be performed at a certain temperature. During the drying process, the interfacial polymerization reaction can be accelerated, making the leaf-like structure of the prepared nanofiltration membrane more prominent. When drying at a certain temperature, heating can make the leaf-like structure more prominent, further promoting the effect.

[0119] In some embodiments, in step S40, the drying temperature for drying the composite film is room temperature to 80°C. Alternatively, the drying temperature is 25 to 85°C. Alternatively, the drying temperature is 25 to 60°C. Alternatively, the drying temperature is 30 to 60°C. Alternatively, the drying temperature is 40 to 60°C. Alternatively, the drying temperature is 45 to 55°C. Alternatively, the drying temperature is 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, or any value within the range of 25 to 60°C.

[0120] In some embodiments, in step S40, the composite membrane is dried for a time of 1 to 10 minutes. Alternatively, the drying time is 1 to 8 minutes. Alternatively, the drying time is 1 to 5 minutes. Alternatively, the drying time is 1 minute, 2 minutes, 3 minutes, 5 minutes, 8 minutes, 10 minutes, or any value within the range of 1 to 20 minutes. The drying time is determined based on actual conditions to ensure that the nanofiltration membrane does not crack after drying.

[0121] The following specific examples are provided to illustrate the nanofiltration membranes, oil-phase solutions, and preparation methods of the disclosed embodiments, to more clearly illustrate the technical problems, technical solutions, and beneficial effects addressed by the present application. It is apparent that the described embodiments are merely a portion of the embodiments of the present application, and are not intended to be exhaustive. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present application and its applications.

[0122] If no specific techniques or conditions are specified in the examples, the experiments were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. All reagents or instruments used without specifying the manufacturer are commercially available conventional products.

[0123] Example 1

[0124] A method for preparing nanofiltration membrane I comprises the following steps:

[0125] 1. Prepare the porous base membrane, aqueous solution and oil solution.

[0126] Preparation of porous base membrane: Add 12g of polyethersulfone (mass concentration of 12.5%) and 4g of polyethylene glycol (mass concentration of 4%) to 80g of N,N-dimethylacetamide and stir evenly to form a membrane-forming liquid, then pour it on the surface of the non-woven fabric and use a scraper to hang the membrane-forming liquid into a membrane, then put it into a solvent (e.g., water) for washing and soaking for 24 hours and then dry it to obtain a porous base membrane.

[0127] Preparation of aqueous solution: 0.5 g of p-phenylenediamine (mass concentration of 0.5%), 0.01 g of sodium lauryl sulfate (mass concentration of 0.01%), and 1 g of sodium bicarbonate (mass concentration of 1%) were added to 100 g of deionized water in sequence and stirred until uniformly mixed to obtain an aqueous solution.

[0128] Preparation of the oil phase solution: Add 0.5 g of trimesoyl chloride (mass concentration of 0.5%) and 1.0 g of n-butyl lithium (mass concentration of 1%) to 100 g of n-hexane, mix well, and fully dissolve to obtain an oil phase solution.

[0129] 2. Laying the first surface of the porous base membrane on the aqueous solution, allowing the porous base membrane to fully contact with the aqueous solution for 1 minute, removing excess water from the surface, and drying the porous base membrane to obtain an aqueous base membrane.

[0130] 3. The first surface of the aqueous-phase coated base membrane (on the same side as the first surface of the porous base membrane) was fully contacted with the oil phase solution for 10 minutes to carry out an interfacial reaction to obtain a composite membrane.

[0131] Fourth, the composite membrane was placed in an oven at 60° C. and dried for 1 minute, taken out, and stored in pure water to obtain a nanofiltration membrane I with a leaf-like structure.

[0132] like Figure 3a and Figure 3b The scanning electron microscope (SEM) photograph of the leaf-like nanofiltration membrane I obtained in Example 1 shows that the nanofiltration membrane I comprises a basement membrane layer and a separation layer. The basement membrane layer comprises a nonwoven fabric and a porous basement membrane formed on the surface of the nonwoven fabric. The separation layer is formed on the basement membrane layer by in-situ polymerization and has a "leaf vein-like" raised texture. Furthermore, the basement membrane layer comprises a surface basement membrane with smaller pores and an inner basement membrane with larger pores. The inner basement membrane has a concentrated large-pore layer on its underside, near the supporting substrate.

[0133] The membrane performance test data of the nanofiltration membrane I of this embodiment 1 is shown in Table 1.

[0134] Example 2

[0135] A method for preparing nanofiltration membrane II comprises the following steps:

[0136] 1. Prepare the porous base membrane, aqueous solution and oil solution.

[0137] Preparation of porous base membrane: Add 22g of polyvinylidene fluoride (mass concentration of 21.5%) and 0.5g of polyvinylpyrrolidone (mass concentration of 0.5%) to 80g of methanesulfonic acid and stir evenly to form a membrane-forming liquid, then pour it on the surface of the non-woven fabric and use a scraper to hang the membrane-forming liquid into a membrane, then put it into a solvent (e.g., water) for washing and soaking for 24 hours and then dry it to obtain a porous base membrane.

[0138] Preparation of aqueous solution: 5 g of piperazine (mass concentration of 5%), 0.1 g of Span 80 (mass concentration of 0.1%), and 0.1 g of triethylamine (mass concentration of 0.1%) were added to 100 g of deionized water in sequence and slowly stirred until uniformly mixed to obtain an aqueous solution.

[0139] Preparation of the oil phase solution: 3.0 g of cyclohexanedicarbonyl chloride (mass concentration: 3%) and 0.1 g of nickel carbonyl (mass concentration: 0.1%) were added to 100 g of n-hexane, mixed evenly, and fully dissolved to obtain an oil phase solution.

[0140] 2. Laying the first surface of the porous base membrane on the aqueous solution, allowing the porous base membrane to fully contact with the aqueous solution for 10 minutes, then removing excess water from the surface and drying it to obtain an aqueous base membrane.

[0141] 3. The first surface of the aqueous-phase coated base membrane (on the same side as the first surface of the porous base membrane) was fully contacted with the oil phase solution for 0.5 min to carry out interfacial reaction and obtain a composite membrane.

[0142] Fourth, the composite membrane was placed in an oven at 30°C and dried for 5 minutes, taken out, and stored in pure water to obtain the leaf-like nanofiltration membrane II.

[0143] like Figure 4 and Figure 5 The leaf-like nanofiltration membrane II obtained in Example 2 includes a basement membrane layer and a separation layer. The basement membrane layer comprises a nonwoven fabric and a porous basement membrane formed on the surface of the nonwoven fabric. The separation layer is formed on the basement membrane layer by in-situ polymerization and has a "leaf vein-like" raised texture. Furthermore, the basement membrane layer comprises a surface basement membrane with smaller pores and an inner basement membrane with larger pores. The inner basement membrane has a concentrated large-pore layer on its underside, near the supporting substrate.

[0144] The membrane performance test data of the nanofiltration membrane II of this embodiment 2 is shown in Table 1.

[0145] Example 3

[0146] A method for preparing nanofiltration membrane III comprises the following steps:

[0147] 1. Prepare the porous base membrane, aqueous solution and oil solution.

[0148] Preparation of porous base membrane: 17g of polyetheretherketone (mass concentration of 17%) and 2.0g of lithium chloride (mass concentration of 2%) are added to 80g of methylpyrrolidone and stirred evenly to form a membrane-forming liquid, which is then poured onto the surface of the non-woven fabric and the membrane-forming liquid is hung into a membrane using a scraper. The membrane is then placed in a solvent (e.g., water) for washing and soaking for 24 hours and then dried to obtain a porous base membrane.

[0149] Preparation of aqueous solution: 2.5 g of hexamethylenediamine (mass concentration of 2.5%), 0.5 g of Tween 80 (mass concentration of 0.5%), and 0.5 g of calcium hydride (mass concentration of 0.5%) were added to 100 g of deionized water in sequence, and slowly stirred until mixed uniformly to obtain an aqueous solution.

[0150] Preparation of the oil phase solution: 1.5 g of benzoyl chloride (mass concentration of 1.5%) and 0.55 g of carbonyl rhodium (mass concentration of 0.55%) were added to 100 g of n-hexane, mixed evenly, and fully dissolved to obtain an oil phase solution.

[0151] 2. Laying the first surface of the porous base membrane on the aqueous solution, allowing the porous base membrane to fully contact with the aqueous solution for 5 minutes, then removing excess water from the surface and drying it to obtain an aqueous base membrane.

[0152] 3. The first surface of the aqueous-phase coated base membrane (on the same side as the first surface of the porous base membrane) was fully contacted with the oil phase solution for 5 minutes to carry out an interfacial reaction to obtain a composite membrane.

[0153] Fourth, the composite membrane was placed in an oven at 45°C and dried for 2.5 minutes, taken out, and stored in pure water to obtain the leaf-like nanofiltration membrane III.

[0154] like Figure 6 and Figure 7 The leaf-like nanofiltration membrane III obtained in Example 3 includes a basement membrane layer and a separation layer. The basement membrane layer comprises a nonwoven fabric and a porous basement membrane formed on the surface of the nonwoven fabric. The separation layer is formed on the basement membrane layer by in-situ polymerization and has a "leaf vein-like" raised texture. Furthermore, the basement membrane layer comprises a surface basement membrane with smaller pores and an inner basement membrane with larger pores. The inner basement membrane has a concentrated large-pore layer on its underside, near the supporting substrate.

[0155] The membrane performance test data of the nanofiltration membrane III of this Example 2 is shown in Table 1.

[0156] Example 4

[0157] A method for preparing nanofiltration membrane IV comprises the following steps:

[0158] 1. Prepare the porous base membrane, aqueous solution and oil solution.

[0159] Preparation of porous base membrane: 14g of polyetheretherketone (mass concentration of 14.4%) and 3.5g of lithium chloride (mass concentration of 3.6%) are added to 80g of butyl acetate and stirred evenly to form a membrane-forming liquid, which is then poured onto the surface of the non-woven fabric and the membrane-forming liquid is hung with a scraper to form a membrane. The membrane is then placed in a solvent (e.g., water) for washing and soaking for 24 hours and then dried to obtain a porous base membrane.

[0160] Preparation of aqueous solution: 4.5 g of p-piperazine (mass concentration of 4.3%), 0.3 g of hexadecyltrimethylammonium bromide (mass concentration of 0.28%) and 0.75 g of phosphoric acid (mass concentration of 0.7%) were added sequentially to 100 g of deionized water to obtain an aqueous solution.

[0161] Preparation of the oil phase solution: 2 g of succinyl chloride and 0.3 g of diisopropyl titanocene were added to 100 g of n-hexane, mixed evenly, and fully dissolved to obtain an oil phase solution.

[0162] 2. Laying the first surface of the porous base membrane on the aqueous solution, allowing the porous base membrane to fully contact with the aqueous solution for 2.5 minutes, then removing excess water from the surface and drying it to obtain an aqueous base membrane.

[0163] 3. The first surface of the aqueous-phase coated base membrane (on the same side as the first surface of the porous base membrane) was fully contacted with the oil phase solution for 7.5 minutes to carry out an interfacial reaction and obtain a composite membrane.

[0164] Fourth, the composite membrane was placed in an oven at 40°C and dried for 4 minutes, taken out, and stored in pure water to obtain a nanofiltration membrane IV with a leaf-like structure.

[0165] like Figure 8 and Figure 9 The leaf-like nanofiltration membrane IV obtained in Example 4 includes a basement membrane layer and a separation layer. The basement membrane layer comprises a nonwoven fabric and a porous basement membrane formed on the surface of the nonwoven fabric. The separation layer is formed on the basement membrane layer by in-situ polymerization and has a "leaf vein-like" raised texture. Furthermore, the basement membrane layer comprises a surface basement membrane with smaller pores and an inner basement membrane with larger pores. The inner basement membrane has a concentrated large-pore layer on its underside, near the supporting substrate.

[0166] The membrane performance test data of the nanofiltration membrane IV of this Example 4 is shown in Table 1.

[0167] Example 5

[0168] A method for preparing a nanofiltration membrane V comprises the following steps:

[0169] 1. Prepare the porous base membrane, aqueous solution and oil solution.

[0170] Preparation of porous base membrane: 14g of polyetheretherketone (mass concentration of 14.4%) and 3.5g of lithium chloride (mass concentration of 3.6%) are added to 80g of butyl acetate and stirred evenly to form a membrane-forming liquid, which is then poured onto the surface of the non-woven fabric and the membrane-forming liquid is hung with a scraper to form a membrane. The membrane is then placed in a solvent (e.g., water) for washing and soaking for 24 hours and then dried to obtain a porous base membrane.

[0171] Preparation of aqueous solution: 1.7 g of 1,3,5-triaminobenzene (mass concentration of 1.7%), 0.8 g of nonylphenol polyoxyethylene ether (mass concentration of 0.8%), and 0.25 g of diisopropylethylamine (mass concentration of 0.25%) were added to 100 g of deionized water in sequence and stirred until uniformly mixed to obtain an aqueous solution.

[0172] Preparation of the oil phase solution: 1.4 g of succinyl chloride and 0.13 g of tert-butyl lithium were added to 100 g of n-hexane, mixed evenly, and fully dissolved to obtain an oil phase solution.

[0173] 2. Lay the first surface of the porous base membrane on the aqueous solution, allow the porous base membrane to fully contact with the aqueous solution for 1.2 minutes, then remove excess water from the surface and dry it to obtain an aqueous base membrane.

[0174] 3. The first surface of the aqueous-phase coated base membrane (on the same side as the first surface of the porous base membrane) was fully contacted with the oil phase solution for 4 minutes to carry out an interfacial reaction to obtain a composite membrane.

[0175] Fourth, the composite membrane was placed in an oven at 55°C and dried for 2.5 minutes, taken out, and stored in pure water to obtain the leaf-like nanofiltration membrane IV.

[0176] like Figure 10 and Figure 11 The leaf-like nanofiltration membrane V obtained in Example 5 includes a basement membrane layer and a separation layer. The basement membrane layer comprises a nonwoven fabric and a porous basement membrane formed on the surface of the nonwoven fabric. The separation layer is formed on the basement membrane layer by in-situ polymerization and has a "leaf vein-like" raised texture. Furthermore, the basement membrane layer comprises a surface basement membrane with smaller pores and an inner basement membrane with larger pores. The inner basement membrane has a concentrated large-pore layer on its underside, near the supporting substrate.

[0177] The membrane performance test data of the nanofiltration membrane V of this Example 5 is shown in Table 1.

[0178] Example 6

[0179] A method for preparing a nanofiltration membrane VI comprises the following steps:

[0180] 1. Prepare the porous base membrane, aqueous solution and oil solution.

[0181] Preparation of porous base membrane: 20g of cellulose acetate (mass concentration of 19.6%) and 2.0g of lithium chloride (mass concentration of 2%) are added to 80g of N,N-dimethylformamide and stirred evenly to form a membrane-forming liquid, which is then poured onto the surface of the non-woven fabric and the membrane-forming liquid is hung into a membrane using a scraper. The membrane is then placed in a solvent (e.g., water) for washing and soaking for 24 hours and then dried to obtain a porous base membrane.

[0182] Preparation of aqueous solution: 4.5 g of o-phenylenediamine (mass concentration of 4.3%), 0.6 g of nonylphenol polyoxyethylene ether (mass concentration of 0.57%) and 0.21 g of pyridine (mass concentration of 0.19%) were added to 100 g of deionized water in sequence and stirred until uniformly mixed to obtain an aqueous solution.

[0183] Preparation of the oil phase solution: 2.7 g of terephthaloyl chloride (mass concentration of 2.6%) and 0.47 g of carbonylferrocene (mass concentration of 0.46%) were added to 100 g of n-hexane, mixed evenly, and fully dissolved to obtain an oil phase solution.

[0184] 2. Lay the first surface of the porous base membrane on the aqueous solution, allow the porous base membrane to fully contact with the aqueous solution for 7.5 minutes, then remove excess water from the surface and dry it to obtain an aqueous base membrane.

[0185] 3. The first surface of the aqueous-phase coated base membrane (on the same side as the first surface of the porous base membrane) was fully contacted with the oil phase solution for 2.4 minutes to carry out an interfacial reaction and obtain a composite membrane.

[0186] Fourth, the composite membrane was placed in an oven at 50° C. and dried for 2 minutes, taken out, and stored in pure water to obtain a nanofiltration membrane VI with a leaf-like structure.

[0187] like Figure 12 and Figure 13 The leaf-like structure nanofiltration membrane VI obtained in Example 6 shown in the figure includes a base membrane layer and a separation layer, wherein the base membrane layer includes a non-woven fabric and a porous base membrane formed on the surface of the non-woven fabric; the separation layer is formed on the base membrane layer by in-situ polymerization, and the separation layer forms a "leaf vein-like" raised texture.

[0188] The membrane performance test data of the nanofiltration membrane VI of this Example 6 is shown in Table 1. In addition, the base membrane layer includes a surface base membrane with smaller pore diameters and an inner base membrane with larger pore diameters, and the inner base membrane has a large pore diameter concentrated layer on the bottom side close to the supporting substrate.

[0189] Example 7

[0190] The difference between Example 7 and Example 6 is that pyridine (polymerization catalyst) was not added during the preparation of the aqueous solution. The remaining steps and parameters were the same as those in Example 6.

[0191] like Figure 14 and Figure 15 The leaf-like nanofiltration membrane VII obtained in Example 7 includes a basement membrane layer and a separation layer. The basement membrane layer comprises a nonwoven fabric and a porous basement membrane formed on the surface of the nonwoven fabric. The separation layer is formed on the basement membrane layer by in-situ polymerization and has a "leaf vein-like" raised texture. Furthermore, the basement membrane layer comprises a surface basement membrane with smaller pores and an inner basement membrane with larger pores. The inner basement membrane has a concentrated large-pore layer on its underside, near the supporting substrate.

[0192] The membrane performance test data of the nanofiltration membrane VII of this Example 7 is shown in Table 1.

[0193] Example 8

[0194] The difference between Example 8 and Example 6 is that the amount of the organic metal catalyst carbonylferrocene added during the preparation of the oil phase solution is 2 g. The remaining steps and parameters are the same as those in Example 6.

[0195] like Figure 16 and Figure 17The leaf-like nanofiltration membrane VIII obtained in Example 8 includes a base membrane layer and a separation layer. The base membrane layer comprises a nonwoven fabric and a porous base membrane formed on the surface of the nonwoven fabric. The separation layer is formed on the base membrane layer by in-situ polymerization and has a "leaf vein-like" raised texture. Membrane performance test data for the nanofiltration membrane VIII in Example 8 are shown in Table 1.

[0196] Comparative Example 1

[0197] Compared with Example 1, this comparative example 1 is different in that the organic metal catalyst n-butyl lithium is not added during the preparation of the oil phase solution. The remaining steps and parameters are the same as those in Example 1.

[0198] The membrane performance test data of the nanofiltration membrane of Comparative Example 1 is shown in Table 1.

[0199] Comparative Example 2

[0200] Comparative Example 2 differs from Example 1 in that no polymerization catalyst, polyethylene glycol, was added during the preparation of the aqueous phase solution, and no organometallic catalyst, n-butyl lithium, was added during the preparation of the oil phase solution. The remaining steps and parameters were the same as in Example 1. No organometallic catalyst, n-butyl lithium, was added during the preparation of the oil phase solution. The remaining steps and parameters were the same as in Example 1.

[0201] The SEM photo of the nanofiltration membrane comparison II of this comparative example 2 is as follows Figure 17 and Figure 18 As shown, it can be seen that when no organic metal catalyst is added to the oil phase solution, the surface of the separation layer is uniform, the base membrane is dense, there are no large holes, and no leaf-like structure is formed.

[0202] The membrane performance test data of the nanofiltration membrane of Comparative Example 2 is shown in Table 1, where F0 is the pure water flux at the start of operation, F 30 is the pure water flux after 30 days of continuous operation, η is the selectivity factor of monovalent and divalent metal ions, and the pure water flux is.

[0203] Table 1

[0204]

[0205]

[0206] As can be seen from Table 1, nanofiltration membranes I to VIII of Examples 1 to 8 have high water flux at a pressure of 0.2 bar, and the drop in pure water flux after 30 days of continuous operation is very small, and they can maintain a good water flux. 2+ and Ca 2+ The interception rate of divalent metal ions such as Li + and Na +The retention rate of monovalent metal ions is 23% to 35%, and the selectivity factor for monovalent and divalent metal ions is 98 to 145, showing excellent ion selectivity. However, in the nanofiltration membrane of Comparative Example 1, Comparative I, the base membrane is porous and the separation layer is a polymeric homogeneous phase, resulting in a lower specific surface area and lower water flux. In the nanofiltration membrane of Comparative Example 2, the base membrane is not porous and the separation layer is a polymeric homogeneous phase, and the water flux is reduced by more than half, reaching a rate of decrease of 55% to 63%. Moreover, after 30 days of continuous operation, the pure water flux decreased by 16%, and the water flux stability deteriorated. The selectivity factor for monovalent and divalent ions decreased to 56, and the ion selectivity performance deteriorated.

[0207] In the examples disclosed herein, a cross-flow filtration system was used to characterize the water flux and separation performance of the prepared nanofiltration membrane material. Specifically, the following test steps were included:

[0208] First, place a nanofiltration membrane material of a certain size into the membrane pool of the membrane system. Use 1g / L of a divalent metal chloride aqueous solution (for example, magnesium chloride or calcium chloride) and 1g / L of a monovalent metal chloride aqueous solution (for example, lithium chloride or sodium chloride) as the stock solution. Test the water flux and retention rate of the nanofiltration membrane at a pressure of 0.4 bar:

[0209] The calculation formula of water flux is as follows: Where F is the water flux, V is the permeate volume, S is the effective membrane area, and t is the test time.

[0210] The retention rate is calculated as follows:

[0211]

[0212] Where R is the rejection rate, C0 is the salt concentration of the original solution, and C1 is the salt concentration of the permeate.

[0213] The calculation formula for the separation coefficient of monovalent and divalent metal ions is as follows: Wherein, η is the selectivity factor of monovalent and divalent metal ions (separation coefficient of monovalent and divalent metal ions), C M+,0 and C M+,1 are the concentrations of the original solution and permeate of the monovalent metal ion, C M2+,0 and C M2+,1 are the concentrations of the original solution and the permeate of the divalent metal ions, respectively. Specifically, the calculation formula for the magnesium-lithium separation coefficient is as follows:

[0214] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0215] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A nanofiltration membrane, characterized in that include: A base film layer, comprising a supporting substrate and a base film formed on a surface of the supporting substrate; The separation layer is formed on the surface of the base film layer by in-situ polymerization, and the separation layer has a convex texture.

2. The nanofiltration membrane according to claim 1, characterized in that In the basement membrane layer, the basement membrane is porous; and / or the thickness of the basement membrane layer is 100 μm to 400 μm; and / or the basement membrane is porous, and the pore size is 0.1 μm to 30 μm; Preferably, in the porous base membrane, the pore size of the pores close to the separation layer is smaller than or equal to the pore size of the pores away from the separation layer. Preferably, the porous basement membrane comprises a surface basement membrane and an inner basement membrane, wherein the surface basement membrane is the basement membrane close to the separation layer; the pore size of the pores in the surface basement membrane is 0.1 μm to 10 μm, and the pore size of the pores in the inner basement membrane is 8 μm to 30 μm; Preferably, the pore size of the surface basement membrane pores in the range of 0.1 μm to 6 μm accounts for more than 50%; Preferably, the pore size of the inner basement membrane pores is in the range of 8 μm to 20 μm, accounting for more than 80%.

3. The nanofiltration membrane according to claim 1, characterized in that In the presence of an organic metal catalyst, a separation layer is formed on the surface of the base film layer by in-situ polymerization, so that the separation layer has a raised texture; Preferably, the separation layer of the nanofiltration membrane is formed by an interfacial polymerization reaction between aqueous phase monomers in an aqueous phase solution and oil phase monomers in an oil phase solution; wherein an organic metal catalyst is added to the oil phase solution; Preferably, the oil phase solution comprises an acyl chloride monomer, an organic metal catalyst and an organic solvent, wherein the mass concentration of the organic metal catalyst is 0.01% to 2%; Preferably, the mass concentration of the organometallic catalyst is 0.01% to 1%; or, the mass concentration of the organometallic catalyst is 0.05% to 1%; or, the mass concentration of the organometallic catalyst is 0.1% to 1%; or, the mass concentration of the organometallic catalyst is 0.1% to 0.5%; or, the mass concentration of the organometallic catalyst is 0.5% to 1%; Preferably, the acyl chloride monomer comprises one or a mixture of trimesoyl chloride, pyromellitoyl chloride, cyclohexanedicarboxylic acid chloride, terephthaloyl chloride and succinoyl chloride; Preferably, the mass concentration of the acyl chloride monomer is 0.1% to 5%; or, the mass concentration of the acyl chloride monomer is 0.5% to 5%.

4. The nanofiltration membrane according to claim 3, characterized in that The metal element in the organometallic catalyst includes one or more of lithium, iron, nickel, titanium and rhodium; or, The organometallic catalyst includes one or more of n-butyllithium, tert-butyllithium, diisopropyl titanocene, nickel carbonyl, carbonyl ferrocene and rhodium carbonyl.

5. The nanofiltration membrane according to any one of claims 1 to 4, characterized in that The separation layer has a thickness of 50 nm to 200 nm; and / or The raised texture has a raised height of 10 nm to 30 nm; and / or The protrusion texture of the separation layer is dispersedly formed on the surface of the separation layer.

6. The nanofiltration membrane according to any one of claims 1 to 4, characterized in that At a pressure of 0.2 bar, the pure water flux of the nanofiltration membrane is greater than or equal to 30L / (m 2 ·h); and / or, after 30 days of continuous operation, the pure water flux is greater than or equal to 30L / (m 2 ·h); and / or, the retention rate of divalent metal ions is greater than or equal to 95%; and / or, the retention rate of monovalent metal ions is less than or equal to 30%; and / or, the selectivity factor of monovalent and divalent metal ions is greater than or equal to 95.

7. An oil phase solution for preparing a nanofiltration membrane, characterized in that: Used for preparing the nanofiltration membrane according to any one of claims 1 to 6; the oil phase solution comprises an acyl chloride monomer, an organic metal catalyst and an organic solvent, wherein the mass concentration of the organic metal catalyst is 0.01% to 2%.

8. The oil phase solution according to claim 7, characterized in that The mass concentration of the organometallic catalyst is 0.01% to 1%; or The mass concentration of the organometallic catalyst is 0.05% to 1%; or The mass concentration of the organometallic catalyst is 0.1% to 1%; or The mass concentration of the organometallic catalyst is 0.1% to 0.5%; or The mass concentration of the organic metal catalyst is 0.5% to 1%.

9. The oil phase solution according to claim 7 or 8, characterized in that: The metal element in the organometallic catalyst includes lithium, iron, nickel, titanium or rhodium; and / or, The organometallic catalyst includes one or a mixture of n-butyllithium, tert-butyllithium, diisopropyl titanocene, nickel carbonyl, carbonyl ferrocene and rhodium carbonyl.

10. The oil phase solution according to claim 7 or 8, characterized in that The mass concentration of the acyl chloride monomer is 0.1% to 5%; and / or, The acyl chloride monomer includes one or a mixture of trimesoyl chloride, pyromellitoyl chloride, cyclohexanedicarboxylic acid chloride, terephthaloyl chloride and succinoyl chloride; Preferably, the mass concentration of the acyl chloride monomer is 0.5% to 5%.

11. A method for preparing a nanofiltration membrane, characterized in that: include: Prepare a base film layer, an aqueous solution and an oily solution, wherein the oily solution is the oily solution according to any one of claims 7 to 10; Spreading the aqueous solution on the surface of the basement membrane layer to obtain an aqueous-phase-spreading basement membrane layer; The oil phase solution is brought into contact with the aqueous phase covering film of the aqueous phase covering base film layer, and an interfacial reaction is carried out under the action of an organic metal catalyst in the oil phase solution, thereby forming a separation layer with a raised texture on the surface of the base film layer to obtain a composite membrane; The composite membrane is dried to obtain a nanofiltration membrane.

12. The method for preparing a nanofiltration membrane according to claim 11, wherein: The contact time between the oil phase solution and the surface of the aqueous phase coating base film is 30 to 600 seconds; and / or the drying temperature of the composite film is room temperature to 80° C.; and / or the drying time of the composite film is 1 to 10 minutes; Preferably, the contact time between the oil phase solution and the surface of the aqueous phase coating base film is 60 to 500 seconds; and / or the drying temperature for drying the composite film is 30 to 60° C.; and / or the drying time for drying the composite film is 1 to 8 minutes; Preferably, the contact time between the oil phase solution and the surface of the aqueous phase coating base film is 120 to 300 seconds; and / or the drying temperature for drying the composite film is 45 to 55° C.; and / or the drying time for drying the composite film is 1 to 5 minutes.

13. The method for preparing a nanofiltration membrane according to claim 11 or 12, characterized in that: Preparing a base film layer includes: applying a film-forming liquid to a support substrate to form a film-forming liquid layer on the support substrate to obtain a film-forming support substrate; wherein the film-forming liquid includes a high molecular weight polymer, a pore-forming agent, and a first solvent; soaking the film-forming support substrate in the solvent and then drying it to obtain the base film layer; Preferably, in the membrane-forming solution, the mass concentration of the high molecular weight polymer is 10% to 30%; and / or the mass concentration of the pore-forming agent is 0.1% to 10%; Preferably, the high molecular polymer comprises one or a mixture of polyethersulfone, polysulfone, cellulose acetate, polyetheretherketone, polyvinylidene fluoride and polyimide; Preferably, the pore-forming agent comprises one or a mixture of polyethylene glycol, ethylene glycol, polyvinyl pyrrolidone, sulfonated polystyrene, lithium chloride and ethanol; Preferably, the first solvent comprises one or a mixture of N,N-dimethylacetamide, N,N-dimethylformamide, methylpyrrolidone, dimethyl sulfoxide, butyl acetate and methanesulfonic acid.

14. The method for preparing a nanofiltration membrane according to claim 11 or 12, characterized in that: An aqueous solution comprising: an amine monomer, an additive, and a second solvent, wherein the mass concentration of the amine monomer is 0.2% to 10%, and the mass concentration of the additive is 0.2% to 10%; wherein the additive comprises a surfactant and / or a polymerization catalyst; Preferably, the amine monomer includes one or a mixture of p-phenylenediamine, o-phenylenediamine, piperazine, hexamethylenediamine, 1,3,5-triaminobenzene and diaminomethylaniline; Preferably, the surfactant is selected from one or a mixture of Tween 80, sodium lauryl sulfate, Span 80, polyvinyl alcohol, cetyltrimethylammonium bromide and nonylphenol polyoxyethylene ether; Preferably, the polymerization catalyst comprises one or a mixture of calcium hydride, phosphoric acid, sodium bicarbonate, diisopropylethylamine, triethylamine and pyridine.

15. The method for preparing a nanofiltration membrane according to claim 14, characterized in that: In the case where the additive includes a surfactant, the mass concentration of the surfactant is 0.01% to 3%; In the case where the additive includes a polymerization catalyst, the mass concentration of the polymerization catalyst is 0.1% to 5%; When the additive includes a surfactant and a polymerization catalyst, the total mass concentration of the surfactant and the polymerization catalyst is 0.2% to 8%; and the mass ratio of the surfactant to the polymerization catalyst is 1:0.25 to 1:

100.

16. The method for preparing a nanofiltration membrane according to claim 11 or 12, characterized in that: Spreading the aqueous solution on the surface of the base film layer to obtain the aqueous base film layer; comprising: Laying the base film layer on the aqueous solution, allowing the base film layer to contact the aqueous solution for a first predetermined time, and then drying the base film layer to obtain an aqueous base film; Preferably, the first preset time is 1 to 15 minutes.

Images