Asymmetric double-layer polyamide composite membrane and its preparation method and application

Abstract

This invention provides an asymmetric bilayer polyamide composite membrane. The asymmetric bilayer polyamide composite membrane is obtained by sequentially introducing a polyacrylamide chloride organic monomer solution and a diamine aqueous monomer solution onto a base membrane using a one-step interfacial polymerization method. This invention also provides a method for preparing the aforementioned asymmetric bilayer polyamide composite membrane and its applications. Compared with existing technologies, this invention proposes to construct an oil-water-oil three-phase structure and achieve the preparation of an asymmetric bilayer polyamide separation layer using a one-step interfacial polymerization method. At the upper oil-water interface, due to the free interface polymerization, a thin, dense, and smooth polyamide layer is formed. At the lower oil-water interface, influenced by the base membrane, a thick and porous polyamide layer is formed. The upper and lower layers form an asymmetric bilayer polyamide separation layer during subsequent thermal crosslinking, thereby improving the flux and practicality of the polyamide composite membrane.

Description

Technical Field

[0001] This invention relates to the field of separation membrane technology for material separation, and more specifically, to an asymmetric bilayer polyamide composite membrane, its preparation method, and its application. Background Technology

[0002] Nanofiltration membranes play a crucial role in wastewater treatment, biological separation, and seawater desalination. Commercial nanofiltration membranes are typically composite membranes composed of a polyamide separation layer, an intermediate layer, and a porous polyester nonwoven support layer. The properties of the polyamide separation layer are critical to the water permeability, separation selectivity, and antifouling performance of the membrane composite. Interfacial polymerization technology is widely used in the preparation of the polyamide separation layer. First, a solution containing aqueous monomers (e.g., m-phenylenediamine or piperazine) is introduced onto the surface of the intermediate layer. After wetting for a certain period, excess aqueous phase is removed. Then, a solution containing oil-phase monomers (e.g., trimesoyl chloride) is introduced onto the membrane surface to undergo a polycondensation reaction, thereby forming a polyamide layer at the water-oil interface. Typically, polyamide layers prepared using traditional interfacial polymerization techniques have a thickness of 100-200 nm. Furthermore, due to the exothermic reaction and gas release during the reaction, the prepared polyamide separation layer has a relatively rough surface structure. The thickness of the polyamide separation layer is one of the key factors limiting membrane flux. In recent years, researchers have developed a variety of methods for preparing ultrathin polyamide separation layers (5-20 nm) to further improve the permeation flux of composite membranes.

[0003] In 2015, Professor Andrew G. Livingston's team at Imperial College London, UK, achieved the fabrication of ultrathin polyamide separation layers (<10 nm) by introducing a sacrificial layer of cadmium hydroxide nanowires onto the substrate surface. This strategy eliminated the influence of the substrate on interfacial polymerization and controlled the diffusion rate of aqueous amine monomers (Science, 2015, 348, 1347-1351). Compared to commercial membranes, the resulting polyamide composite membrane exhibited an approximately two-order-of-magnitude increase in water flux. In 2018, Professor Livingston's team further eliminated the influence of the substrate on the interfacial polymerization process through free-interfacial polymerization technology, enabling the fabrication of polyamide separation layers with thicknesses below 8 nm (Advanced Materials, 2018, 30, 1705973). In the same year, Professor Jeffrey R. McCutcheon's team at the University of Connecticut proposed using an electrostatic spraying technique similar to 3D printing to prepare a polyamide separation layer with a thickness of 4 nm (Science, 2018, 361, 682-686; US Patent 17610020). In 2020, Miao Jing et al. added cellulose nanocrystals as an intermediate layer to a microfiltration membrane with a large pore size, utilizing the superhydrophilicity and high porosity of cellulose nanocrystals to store and regulate the aqueous monomers, thus realizing the preparation of a high-flux polyamide composite nanofiltration membrane (Chinese Patent 202011499966.6).

[0004] While the aforementioned methods for preparing polyamide composite membranes offer advantages in controlling the thickness and roughness of the polyamide layer, they also suffer from problems such as complex interfacial polymerization processes, difficulties in transferring the polyamide separation layer, and poor membrane mechanical strength. Recently, Professor Enrique D. Gomez's team at Pennsylvania State University demonstrated through electron microscopy that thick and porous polyamide layers can provide high membrane flux (Science, 2021, 371, 72); however, high retention performance still requires a dense polyamide separation layer. Summary of the Invention

[0005] The purpose of this invention is to provide a double-layer asymmetric polyamide composite membrane that can solve the trade-off between separation layer thickness, flux and strength in the process of preparing polyamide separation layer by traditional interfacial polymerization technology.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: an asymmetric bilayer polyamide composite membrane, wherein the asymmetric bilayer polyamide composite membrane is obtained by sequentially introducing a polyacrylamide organic phase monomer solution and a diamine aqueous phase monomer solution onto a base membrane using a one-step interfacial polymerization method.

[0007] Preferably, the base film is a porous film with an intermediate layer deposited on its surface.

[0008] Preferably, the material of the intermediate layer is selected from one or more of carbon nanotubes, metal nanowires, metal oxide nanowires, cellulose nanocrystals, and covalent organic framework materials.

[0009] Preferably, the porous membrane is selected from one or more of polyvinylidene fluoride porous membranes, polyacrylonitrile porous membranes, polystyrene porous membranes, and polysulfone porous membranes.

[0010] Preferably, the porous membrane has a pore size of 0.1-2.0 μm. Using a porous membrane with the above characteristics allows the polyacrylamide chloride organic phase monomer solution to permeate through the membrane and components from bottom to top, forming an oil phase of a certain height.

[0011] A second objective of this invention is to provide a method for preparing an asymmetric bilayer polyamide composite film, the method specifically comprising the following steps:

[0012] S1. Dissolve diamine monomers in water to obtain an aqueous solution of diamine monomers;

[0013] S2. Dissolve the polyacryl chloride monomer in an organic solvent to obtain a polyacryl chloride organic phase monomer solution;

[0014] S3. Fix the base membrane in a component at the bottom that is permeable to the solution;

[0015] S4. Immerse the component with the base membrane fixed obtained in step S3 into a container containing a polyacryl chloride organic phase monomer solution, so that the polyacryl chloride organic phase monomer solution can pass through the base membrane from bottom to top to obtain a monolayer membrane.

[0016] S5. Introduce a diamine-based aqueous monomer solution onto the surface of the monolayer membrane obtained in step S4. After reacting for 0.5-5 minutes, remove and rinse the membrane. Finally, keep it warm to obtain an asymmetric bilayer polyamide composite membrane.

[0017] Preferably, in step S1, the diamine monomer is selected from one or more of piperazine, m-phenylenediamine, p-phenylenediamine, and o-phenylenediamine;

[0018] Preferably, the concentration of the diamine aqueous monomer solution is 0.01-2.0%.

[0019] Preferably, in step S2, the polyacryl chloride monomer is selected from one or more of isophthaloyl chloride, terephthaloyl chloride, trimesoyl chloride, phenyltetracarboxylate chloride, and cycloalkane polyacryl chloride;

[0020] Preferably, the concentration of the polyacrylamide chloride organic phase monomer solution is 0.01-2.0%.

[0021] Preferably, in step S4, the soaking time is 3-10 minutes.

[0022] Preferably, in step S5, the temperature for heat preservation is 60-70℃ and the heat preservation time is 5-15 minutes.

[0023] A third objective of this invention is to provide the application of the above-mentioned asymmetric bilayer polyamide composite membrane in reverse osmosis, nanofiltration, or forward osmosis.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] Firstly, this invention proposes to construct an oil-water-oil three-phase structure and achieve the preparation of an asymmetric bilayer polyamide separation layer through a one-step interfacial polymerization method. At the upper oil-water interface, interfacial polymerization occurs at a free interface, forming a thin, dense, and smooth polyamide layer. At the lower oil-water interface, a thick and porous polyamide layer is formed due to the influence of the base film. The upper and lower layers form an asymmetric bilayer polyamide separation layer during subsequent thermal crosslinking, thereby improving the flux and practicality of the polyamide composite membrane.

[0026] Secondly, the polyamide composite membrane prepared by the method of this invention eliminates the influence of the base membrane on the surface structure of the upper dense polyamide separation layer, and does not require a transfer process similar to that after preparing the polyamide separation layer at a free interface. Furthermore, although the polyamide separation layer prepared by this method is relatively thick, its asymmetrical bilayer structure improves the strength of the separation layer while ensuring its separation performance, making it more suitable for practical applications.

[0027] Thirdly, the present invention has the following two advantages: 1) By constructing an oil-water-oil three-phase structure, an asymmetric bilayer polyamide separation layer is prepared by one-step interfacial polymerization; 2) The bilayer polyamide film composite membrane includes a thin and dense smooth upper layer and a thick and loose lower layer. Attached Figure Description

[0028] Figure 1 This is a surface electron microscope (SEM) image of the polyvinylidene fluoride porous membrane with deposited carbon nanotubes used in Example 2 of the present invention.

[0029] Figure 2 This is a surface electron microscope (SEM) image of the polyacrylonitrile porous membrane used in Embodiment 4 of the present invention;

[0030] Figure 3 This is a surface electron microscope (SEM) image of the upper polyamide layer of the bilayer polyamide composite film prepared in Example 2 of the present invention;

[0031] Figure 4 This is a surface electron microscope (SEM) image of the lower polyamide layer of the bilayer polyamide composite film prepared in Example 2 of the present invention;

[0032] Figure 5This is a surface electron microscope (SEM) image of the cross-section of the bilayer polyamide composite film prepared in Example 3 of the present invention;

[0033] Figure 6 This is a surface electron microscope (SEM) image of the monolayer polyamide composite film prepared in Comparative Example 1 of this invention. Detailed Implementation

[0034] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0035] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0036] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This application specification and embodiments are merely exemplary.

[0037] This embodiment provides an asymmetric bilayer polyamide composite membrane. The asymmetric bilayer polyamide composite membrane is obtained by sequentially introducing a polyacrylamide organic phase monomer solution and a diamine aqueous phase monomer solution onto a base membrane using a one-step interfacial polymerization method. The base membrane is a porous membrane with an intermediate layer deposited on its surface. The material of the intermediate layer is selected from one or more of carbon nanotubes, metal nanowires, metal oxide nanowires, cellulose nanocrystals, and covalent organic framework materials. The porous membrane is selected from one or more of polyvinylidene fluoride porous membranes, polyacrylonitrile porous membranes, polystyrene porous membranes, and polysulfone porous membranes. The pore size of the porous membrane is 0.1-2.0 μm. By using a porous membrane with the above-mentioned characteristics, the polyacrylamide organic phase monomer solution can better permeate through the membrane and components from bottom to top to form an oil phase of a certain height.

[0038] This embodiment also provides a method for preparing an asymmetric bilayer polyamide composite film, which specifically includes the following steps:

[0039] S1. Dissolve diamine monomers in water to obtain a diamine aqueous monomer solution with a concentration of 0.01-2.0%, wherein the diamine monomers are selected from one or more of piperazine, m-phenylenediamine, p-phenylenediamine and o-phenylenediamine;

[0040] S2. Dissolve the polyacryl chloride monomer in an organic solvent to obtain a polyacryl chloride organic phase monomer solution with a concentration of 0.01-2.0%. The polyacryl chloride monomer is selected from one or more of isophthaloyl chloride, terephthaloyl chloride, trimesoyl chloride, phenyltetracarboxylate chloride, and cycloalkane polyacryl chloride.

[0041] S3. Fix the base membrane in a component at the bottom that is permeable to the solution;

[0042] S4. Immerse the component with the base membrane obtained in step S3 into a container containing a polyacryl chloride organic phase monomer solution for 3-10 minutes, so that the polyacryl chloride organic phase monomer solution can pass through the base membrane from bottom to top to obtain a monolayer membrane.

[0043] S5. Introduce a diamine-based aqueous monomer solution onto the surface of the monolayer membrane obtained in step S4. After reacting for 0.5-5 minutes, remove and rinse the membrane. Finally, keep it at a temperature of 60-70℃ for 5-15 minutes to obtain an asymmetric bilayer polyamide composite membrane.

[0044] This embodiment also provides the application of the above-mentioned asymmetric bilayer polyamide composite membrane in reverse osmosis, nanofiltration or forward osmosis.

[0045] The technical effects of the present invention will be described below with reference to specific embodiments.

[0046] Example 1:

[0047] S1. Dissolve piperazine monomer in water to prepare a 0.01% (w / w) aqueous solution of piperazine monomer;

[0048] S2. Dissolve the trimesoyl chloride monomer in n-hexane to prepare a trimesoyl chloride organic phase monomer solution with a mass concentration of 0.01%.

[0049] S3. Use a polystyrene porous membrane with silver nanowires deposited on its surface as a base membrane and fix it in a component whose bottom can be permeated by solution.

[0050] S4. Immerse the component with the base membrane obtained in step S3 into a container containing a solution of trimesoyl chloride organic phase monomer for 5 minutes, so that the trimesoyl chloride organic phase monomer solution can pass through the component and the base membrane from bottom to top to obtain a monolayer membrane.

[0051] S5. A piperazine aqueous monomer solution is introduced onto the surface of the monolayer membrane obtained in step S4. After reacting for 1 minute, the membrane is removed and rinsed. Finally, it is kept at 60°C for 5 minutes to obtain an asymmetric bilayer polyamide composite membrane.

[0052] The resulting polyamide composite membrane has a separation layer (i.e., the polyamide layer formed by the reaction) thickness of 68 nm (with the upper polyamide layer being 18 nm thick and the lower polyamide layer being 50 nm thick). Under cross-flow conditions and an applied pressure of 5 bar, it exhibits a retention capacity of 90.5 ± 1% for 1000 mg / L Na₂SO₄ solution, while its water permeation flux is 10⁵ L / m³. -2 h -1 .

[0053] Example 2

[0054] S1. Dissolve piperazine monomer in water to prepare a piperazine aqueous monomer solution with a mass concentration of 0.02%;

[0055] S2. Dissolve the trimesoyl chloride monomer in n-hexane to prepare a trimesoyl chloride organic phase monomer solution with a mass concentration of 0.02%.

[0056] S3, such as Figure 1 As shown, a polyvinylidene fluoride porous membrane with carbon nanotubes deposited on its surface is used as a base membrane and fixed in a component whose bottom can be permeated by solution.

[0057] S4. Immerse the component with the base membrane obtained in step S3 into a container containing a solution of trimesoyl chloride organic phase monomer for 5 minutes, so that the trimesoyl chloride organic phase monomer solution can pass through the component and the base membrane from bottom to top to obtain a monolayer membrane.

[0058] S5. A piperazine aqueous monomer solution is introduced onto the surface of the monolayer membrane obtained in step S4. After reacting for 1 minute, the membrane is removed and rinsed. Finally, it is kept at 60°C for 5 minutes to obtain an asymmetric bilayer polyamide composite membrane.

[0059] The separation layer (i.e., the polyamide layer formed by the reaction) of the resulting polyamide composite film has a thickness of 87 nm (of which the upper polyamide layer has a thickness of 22 nm and the lower polyamide layer has a thickness of 65 nm). Figure 3 As shown: the surface of the upper polyamide layer is smooth and flat, as... Figure 4 As shown: The lower polyamide layer has a rough surface with radial nanofolds and nanopores. Under cross-flow conditions and an applied pressure of 5 bar, it exhibits a retention capacity of 97.5 ± 1% for a 1000 mg / L Na₂SO₄ solution, while the water permeation flux is 90 L / m². -2 h -1 .

[0060] Example 3

[0061] S1. Dissolve the m-phenylenediamine monomer in water to prepare an aqueous m-phenylenediamine monomer solution with a mass concentration of 0.125%.

[0062] S2. Dissolve the isophthaloyl chloride monomer in n-hexane to prepare an isophthaloyl chloride organic phase monomer solution with a mass concentration of 0.1%;

[0063] S3. Use a polyvinyl chloride porous membrane with a covalent triazine framework material deposited on it as a base membrane and fix it in a component whose bottom can be permeated by solution.

[0064] S4. Immerse the component with the base membrane obtained in step S3 into a container containing an isophthalic chloride organic phase monomer solution for 10 minutes, so that the isophthalic chloride organic phase monomer solution can pass through the component and the base membrane from bottom to top to obtain a monolayer membrane.

[0065] S5. Introduce an aqueous m-phenylenediamine monomer solution onto the surface of the monolayer membrane obtained in step S4. After reacting for 40 seconds, remove and rinse the membrane. Finally, keep it at 60°C for 5 minutes to obtain an asymmetric bilayer polyamide composite membrane.

[0066] The separation layer (i.e., the polyamide layer formed by the reaction) of the obtained polyamide composite film has a thickness of 125 nm (of which the upper polyamide layer has a thickness of 58 nm and the lower polyamide layer has a thickness of 67 nm, as shown below). Figure 5 The surface electron microscope (SEM) image of the cross-section of the double polyamide layer shows that, under cross-flow conditions and an applied pressure of 5 bar, it exhibits a retention capacity of 96.1 ± 1% for a 1000 mg / L Na₂SO₄ solution, while the water permeation flux is 76 L m. -2 h -1 .

[0067] Example 4

[0068] S1. Dissolve piperazine monomer in water to prepare a 2.0% (w / w) aqueous solution of piperazine monomer;

[0069] S2. Dissolve terephthaloyl chloride monomer in n-hexane to prepare a 2.0% (w / w) organic phase monomer solution of terephthaloyl chloride.

[0070] S3, such as Figure 2 As shown, a polyacrylonitrile porous membrane with cadmium hydroxide nanowires deposited on its surface is used as a base membrane and fixed in a component whose bottom can be permeated by solution.

[0071] S4. Immerse the component with the base membrane obtained in step S3 into a container containing a terephthaloyl chloride organic phase monomer solution for 5 minutes, so that the terephthaloyl chloride organic phase monomer solution can pass through the component and the base membrane from bottom to top to obtain a monolayer membrane.

[0072] S5. A piperazine aqueous monomer solution is introduced onto the surface of the monolayer membrane obtained in step S4. After reacting for 0.5 min, the membrane is removed and rinsed. Finally, it is kept at 60℃ for 5 min to obtain an asymmetric bilayer polyamide composite membrane.

[0073] The resulting polyamide composite membrane has a separation layer (i.e., the polyamide layer formed during the reaction) thickness of 198 nm (with the upper polyamide layer being 83 nm thick and the lower polyamide layer being 115 nm thick). Under cross-flow conditions and an applied pressure of 5 bar, it exhibits a retention capacity of 97.5 ± 1% for a 1000 mg / L Na₂SO₄ solution, while maintaining a water permeation flux of 48 L / m³. -2 h -1 .

[0074] Example 5

[0075] S1. Dissolve p-phenylenediamine monomer in water to prepare a p-phenylenediamine aqueous monomer solution with a mass concentration of 0.02%;

[0076] S2. Dissolve the benzoyl chloride monomer in n-hexane to prepare a benzoyl chloride organic phase monomer solution with a mass concentration of 0.02%.

[0077] S3. A polysulfone porous membrane with cellulose nanocrystals deposited on its surface is used as a base membrane and fixed in a component whose bottom can be permeated by solution.

[0078] S4. Immerse the component with the base membrane obtained in step S3 into a container containing a benzoyl chloride organic phase monomer solution for 10 minutes, so that the benzoyl chloride organic phase monomer solution can pass through the component and the base membrane from bottom to top to obtain a monolayer membrane.

[0079] S5. Introduce an aqueous p-phenylenediamine monomer solution onto the surface of the monolayer membrane obtained in step S4. After reacting for 5 minutes, remove and rinse the membrane. Finally, keep it at 60°C for 5 minutes to obtain an asymmetric bilayer polyamide composite membrane.

[0080] The resulting polyamide composite membrane has a separation layer (i.e., the polyamide layer formed during the reaction) thickness of 132 nm (with the upper polyamide layer being 36 nm thick and the lower polyamide layer being 96 nm thick). Under cross-flow conditions and an applied pressure of 5 bar, it exhibits a retention capacity of 99.8 ± 1% for a 1000 mg / L Na₂SO₄ solution, while maintaining a water permeation flux of 22 L / m³. -2 h -1 .

[0081] Comparative Example 1

[0082] S1. Dissolve piperazine monomer in water to prepare an aqueous monomer solution of piperazine monomer with a mass concentration of 0.02%;

[0083] S2. Dissolve the trimesoyl chloride monomer in n-hexane to prepare a trimesoyl chloride organic phase monomer solution with a mass concentration of 0.02%.

[0084] S3. Use a porous polyvinylidene fluoride membrane with carbon nanotubes deposited on its surface as a base membrane and fix the base membrane on the sand chip.

[0085] S4. Pour the piperazine monomer aqueous phase monomer solution onto the surface of the base film, and then introduce the pyromellitic trimethylol chloride organic phase monomer solution and react for 1 min.

[0086] S5. Remove the unreacted solution, rinse the membrane surface with n-hexane, and keep it at 60°C for 5 minutes to obtain a single-layer polyamide film composite membrane.

[0087] The separation layer (i.e., the polyamide layer formed by the reaction) of the obtained monolayer polyamide composite film has a thickness of 24 nm, such as Figure 6 As shown, the surface of the monolayer polyamide is smooth, and the underlying carbon nanotubes are visible due to the ultrathin polyamide layer. Under cross-flow conditions and an applied pressure of 5 bar, the permeation flux to water is 210 L / m². -2 h -1 It has a retention capacity of 95.1±1% for 1000 mg / L Na2SO4, but it drops to 50% within 1 hour.

[0088] Comparative Example 2

[0089] S1. Dissolve piperazine monomer in water to prepare an aqueous monomer solution of piperazine monomer with a mass concentration of 0.02%;

[0090] S2. Dissolve the trimesoyl chloride monomer in n-hexane to prepare a trimesoyl chloride organic phase monomer solution with a mass concentration of 0.02%.

[0091] S3. Use the polyvinylidene fluoride porous membrane with deposited carbon nanotubes as the base membrane and fix the base membrane on the sand chip.

[0092] S4. Pour the piperazine monomer aqueous phase monomer solution onto the surface of the base film, and then introduce the pyromellitic trimethylol chloride organic phase monomer solution and react for 1 min.

[0093] S5. Remove unreacted solution, rinse the membrane surface with n-hexane, and then keep it at 60°C for 5 min.

[0094] S6. The film dried in step S5 is fixed on the sand chip as a base film. Steps S1-S5 are repeated to obtain the traditional double-layer polyamide film composite film.

[0095] The resulting bilayer polyamide composite membrane has a separation layer thickness of 83 nm and a water permeation flux of 35 L / m² under cross-flow conditions and an applied pressure of 5 bar.-2 h -1 It has a retention capacity of 96.7±1% for 1000 mg / L Na2SO4.

[0096] The method of this invention prepares a bilayer polyamide thin-film composite membrane, in which the thickness of the polyamide layer can be adjusted within the range of 80-200 nm. This eliminates the influence of the base film on the upper dense polyamide separation layer, enabling better control of the polyamide layer structure and morphology, improving the separation performance of the polyamide composite membrane, and solving the problem of lack of long-term operational stability in practical applications of ultrathin polyamide composite membranes. Figure 3 As shown, the surface roughness of the upper polyamide layer of the bilayer polyamide film composite film prepared by this invention is significantly reduced compared to polyamide composite films prepared by the traditional interface method, while the lower polyamide layer obtained by removing the upper layer is as follows: Figure 4 As shown, several radial nanofolds and nanopores can be observed on its surface, which is beneficial for increasing the water transport area and improving the membrane permeability. Specifically, 1) Traditional interfacial polymerization suffers from problems such as rough base film, low porosity, and poor surface wettability. This invention generates a polyamide layer through liquid-liquid interfacial polymerization, eliminating the uneven spreading of aqueous monomers on the membrane surface caused by uneven pore size distribution and hydrophobic surface properties of the base film in traditional interfacial polymerization. It optimizes monomer distribution, shortens the self-termination time, and generates a thinner polyamide layer; it also eliminates the increase in effective membrane thickness and resistance caused by physical blockage of base film pores. 2) This invention, as... Figure 3 , 4 As shown, the bilayer polyamide film composite membrane comprises a smooth, thin upper layer and a loose, thick lower layer. This shortens the mass transfer path, reduces water transport resistance, and increases the water transport area, all of which contribute to improved permeation selectivity. Simultaneously, the cross-linking of the upper and lower layers solves the problem of long-term operational stability in practical applications of ultrathin polyamide composite membranes without sacrificing permeation selectivity. 3) In this invention, the porous membrane serves as the base membrane. Due to its high porosity and hydrophobic properties, it allows the oil phase to rapidly permeate and form an oil layer of a certain height, while ensuring that the water phase does not diffuse into the base membrane after introduction. 4) The deposition of the intermediate layer in this invention enhances the mechanical strength of the polyamide composite membrane and improves its long-term operational stability in applications.

[0097] While the disclosure is as stated above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the protection scope of this invention.

Claims

1. An asymmetric bilayer polyamide composite film, characterized in that, The asymmetric bilayer polyamide composite membrane is obtained by sequentially introducing a polyacrylamide chloride organic monomer solution and a diamine aqueous monomer solution onto a base membrane using a one-step interfacial polymerization method. The specific preparation method of the asymmetric bilayer polyamide composite membrane includes the following steps: S1. Dissolve diamine monomers in water to obtain an aqueous solution of diamine monomers; S2. Dissolve the polyacryl chloride monomer in an organic solvent to obtain a polyacryl chloride organic phase monomer solution; S3. Fix the base membrane in a component at the bottom that is permeable to the solution; S4. Immerse the component with the base membrane fixed obtained in step S3 into a container containing a polyacryl chloride organic phase monomer solution, so that the polyacryl chloride organic phase monomer solution can pass through the base membrane from bottom to top to obtain a monolayer membrane. S5. Introduce a diamine-based aqueous monomer solution onto the surface of the monolayer membrane obtained in step S4. After reacting for 0.5-5 minutes, remove and rinse the membrane. Finally, keep it warm to obtain an asymmetric bilayer polyamide composite membrane.

2. The asymmetric bilayer polyamide composite film as described in claim 1, characterized in that, The base membrane is a porous membrane with an intermediate layer deposited on its surface.

3. The asymmetric bilayer polyamide composite film as described in claim 2, characterized in that, The material of the intermediate layer is selected from one or more of carbon nanotubes, metal nanowires, metal oxide nanowires, cellulose nanocrystals, and covalent organic framework materials.

4. The asymmetric bilayer polyamide composite film as described in claim 2, characterized in that, The porous membrane is selected from one or more of polyvinylidene fluoride porous membranes, polyacrylonitrile porous membranes, polystyrene porous membranes, and polysulfone porous membranes; and / or the pore size of the porous membrane is 0.1-2.0 μm.

5. A method for preparing an asymmetric bilayer polyamide composite film as described in any one of claims 1-4, characterized in that, The preparation method specifically includes the following steps: S1. Dissolve diamine monomers in water to obtain an aqueous solution of diamine monomers; S2. Dissolve the polyacryl chloride monomer in an organic solvent to obtain a polyacryl chloride organic phase monomer solution; S3. Fix the base membrane in a component at the bottom that is permeable to the solution; S4. Immerse the component with the base membrane fixed obtained in step S3 into a container containing a polyacryl chloride organic phase monomer solution, so that the polyacryl chloride organic phase monomer solution can pass through the base membrane from bottom to top to obtain a monolayer membrane. S5. Introduce a diamine-based aqueous monomer solution onto the surface of the monolayer membrane obtained in step S4. After reacting for 0.5-5 minutes, remove and rinse the membrane. Finally, keep it warm to obtain an asymmetric bilayer polyamide composite membrane.

6. The method for preparing the asymmetric bilayer polyamide composite film as described in claim 5, characterized in that, In step S1, the diamine monomer is selected from one or more of piperazine, m-phenylenediamine, p-phenylenediamine, and o-phenylenediamine; and / or, the concentration of the aqueous diamine monomer solution is 0.01-2.0%.

7. The method for preparing the asymmetric bilayer polyamide composite film as described in claim 5, characterized in that, In step S2, the polyacrylamide chloride monomer is selected from one or more of isophthaloyl chloride, terephthaloyl chloride, trimesoyl chloride, benzoyl chloride, and cycloalkane polyacrylamide chloride; and / or, the concentration of the polyacrylamide chloride organic phase monomer solution is 0.01-2.0%.

8. The method for preparing the asymmetric bilayer polyamide composite film as described in claim 5, characterized in that, In step S4, the soaking time is 3-10 minutes.

9. The method for preparing the asymmetric bilayer polyamide composite film as described in claim 5, characterized in that, In step S5, the temperature for heat preservation is 60-70℃, and the heat preservation time is 5-15 minutes.

10. The application of the asymmetric bilayer polyamide composite membrane according to any one of claims 1-4 in reverse osmosis, nanofiltration or forward osmosis.

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