A method for preparing Janus hollow fiber membrane and the Janus hollow fiber membrane prepared therefrom

Abstract

This application discloses a method for preparing Janus hollow fiber membranes. The method involves co-extruding an inner and outer membrane-forming solution using a dual-channel nozzle with a spinning core solution to obtain a bilayer hollow fiber membrane. A modified monomer is then grafted onto the membrane to obtain the Janus hollow fiber membrane. The use of a dual-channel nozzle to prepare the bilayer separation membrane allows for flexible control of the thickness, transition mode, and structure of the hydrophilic and hydrophobic layers, achieving precise control of the Janus membrane structure. This effectively suppresses the delamination problem between the two layers. Utilizing the different chemical properties of the amphiphilic polymers in the two membrane-forming solutions, the hydrophilic-hydrophobic conversion of the Janus membrane can be achieved through a simple soaking grafting process. The method is simple to operate, allows for flexible control of the Janus membrane structure, and is more conducive to the large-scale production and industrial application of Janus hollow fiber membranes. It can be used in air flotation, ammonia stripping, and gas-liquid reactions. It can significantly enhance gas-liquid mass transfer and reduce equipment investment and operating costs.

Description

Technical Field

[0001] This application relates to a method for preparing a Janus hollow fiber membrane and the Janus hollow fiber membrane prepared therefrom, belonging to the field of Janus membrane preparation. Background Technology

[0002] Membrane separation processes are widely used as unit operations in chemical engineering. Membrane materials are the foundation and core of membrane separation technology, directly determining the efficiency and economy of the process. Developing novel membrane separation technologies is crucial for expanding the application areas and improving the efficiency of membrane separation. In recent years, Janus membranes, characterized by asymmetric morphological structures or wettability on both sides, have attracted widespread attention. The synergistic effect of the differences in microstructure and surface chemical properties on both sides of the Janus membrane provides an "intrinsic" driving force for the transport of gas and liquid within the membrane. This characteristic gives Janus membranes unique advantages over traditional separation membranes in unidirectional liquid transport, mist collection, directional oil-water separation, membrane distillation, and nanofiltration. Therefore, as an emerging membrane separation technology, in-depth research on Janus membranes, exploring their separation mechanisms and optimizing membrane fabrication methods, is of great significance for improving membrane separation efficiency and expanding the application range of Janus membranes.

[0003] The structure and chemical properties of Janus membranes play a decisive role in their separation performance. Based on their properties, Janus membranes are classified into three types: two-layered (layer A and layer B), with a significant difference in thickness between the two layers (A on B), two layers of similar thickness (AB), and one layer gradually transitioning to the other, i.e., a gradient transition of two symmetrical properties along the entire membrane thickness direction (A to B). The differences in the chemical properties of Janus membranes mainly include differences in wettability and charge. Wetting differences are determined by the microstructure and chemical composition of the membrane surface and are characterized by the contact angle (θ). Janus membranes with wettability differences have one side in a superphilic / liquiophilic state and the other side in a superphobic / liquiphobic state. Charged Janus membranes have opposite surface charges on both sides, enabling directional ion transport. Current research mainly focuses on the preparation and application of Janus membranes with differences in wettability on both sides.

[0004] Various membrane processes place different demands on the structure of Janus membranes. According to the Lapace equation,

[0005]

[0006] ΔP is the capillary force in the membrane pores, γ is the surface tension of the liquid, θ is the water contact angle on the membrane surface, and d is the pore size of the separation membrane.

[0007] As shown by the Lapace equation, the capillary force in the membrane pores is related to the wettability of the membrane material with gas or water and the membrane pore size. Therefore, in most Janus processes, only one side of the hydrophilic / hydrophobic layer plays a separation role, while the other side only serves a supporting function. Thus, preparing a Janus membrane with small pores (separation function) on one side and large pores (support function) on the other can effectively reduce the transmission resistance of gas and liquid within the Janus membrane. Therefore, an ideal Janus membrane requires not only a difference in wettability between the two layers but also a significant difference in pore size. Consequently, different membrane separation processes have specific requirements for the structure and chemical properties of the Janus membrane, making its preparation quite challenging.

[0008] Unlike traditional separation membranes that separate membranes based on pore size, Janus membranes separate membranes through differences in wettability on both sides, making their fabrication more complex. Janus membrane fabrication methods are divided into two types: asymmetric fabrication and asymmetric modification. Asymmetric fabrication is the simplest method, involving the separate preparation of each membrane layer followed by combination. Asymmetric modification involves fixing the membrane at the interface between two phases or on the surface of one phase, followed by selective modification of one or both sides. As discussed above, the membrane structure, the thickness of the hydrophilic / hydrophobic layer, and the transition mode significantly influence the performance of Janus membranes. Compared to traditional separation membrane fabrication technologies, Janus membrane fabrication is cumbersome, requires complex equipment, and is difficult to control in terms of membrane structure, making large-scale, continuous fabrication challenging. This is a key factor contributing to the current limited theoretical research and limited large-scale application of Janus membranes. Therefore, developing a simple, continuously operable, and universally applicable Janus membrane fabrication method is crucial for advancing both theoretical research and industrial applications of Janus membrane separation.

[0009] The non-solvent phase-separation method (NIPS) utilizes the exchange of solvents and non-solvents to form polymer-rich and polymer-poor phases, thereby completing the preparation of the separation membrane. The NIPS method features simple equipment and processes, is easy to operate, and has been successfully applied in the research and production of commercial separation membranes. However, the NIPS method requires the preparation of a membrane-forming solution with stable properties (polymer concentration and hydrophilicity / hydrophobicity). The surface segregation process has limited control over the membrane structure and performance, making it unsuitable for use alone in the preparation of Janus membranes with significant differences in pore size, hydrophilicity / hydrophobicity, and thickness between the two layers.

[0010] Since the 1970s, flat sheet and hollow fiber bilayer membranes prepared using bilayer coating and co-extrusion technologies have seen rapid development. Bilayer membranes utilize two different membrane-forming solutions to create a nascent flat sheet membrane and a hollow fiber membrane, then employ a one-step non-solvent-induced phase separation method to obtain the two-layer composite structure. Bilayer membrane fabrication technology is simple, allows for independent preparation of the two membrane-forming solutions, and preserves the properties of both membrane materials, making it an ideal technique for preparing Janus membranes. However, the delamination problem between the two membrane layers is a bottleneck restricting its application. Summary of the Invention

[0011] To address the above issues, this patent utilizes a bilayer membrane fabrication method, combined with polymer blending and chemical grafting techniques to develop a novel Janus membrane preparation strategy. The bilayer membrane technology is used to prepare a nascent membrane, with both the inner and outer layers containing hydrophilic amphiphilic polymers. One layer is a non-reactive amphiphilic polymer, and the other contains an active hydroxyl group. The bilayer membrane is prepared using a co-extrusion method, controlling the distribution of the hydroxyl-containing amphiphilic polymer within the membrane. The hydroxyl groups are then used as active sites for grafting with hydrophobic monomers containing silanol groups. Chemical grafting modification technology enables the grafting and growth of different hydrophilic / hydrophobic groups at specific active sites, thereby achieving the purpose of Janus membrane preparation.

[0012] Functional groups with similar hydrophilicity and hydrophobicity but different chemical reactivity are selected to formulate the bilayer membrane preparation solution. The distribution of functional groups (hydroxyl groups) in the membrane thickness direction is controlled, and then grafting modification technology is used to achieve grafting of different hydrophilic / hydrophobic groups onto the hydroxyl group, thereby achieving the purpose of Janus membrane preparation.

[0013] This invention first synthesizes two amphiphilic polymers (one of which contains hydroxyl groups). These two polymers are then dissolved in inner and outer film-forming solutions, respectively, and a bilayer membrane is prepared using a co-extrusion method. Since both the inner and outer film-forming solutions are hydrophilic, delamination does not occur between them. The resulting bilayer membrane is then immersed in a grafting modification solution containing hydrophobic monomers that react with hydroxyl groups, thereby transforming the hydroxyl-containing layer from hydrophilic to hydrophobic, thus forming a Janus hollow fiber membrane.

[0014] According to one aspect of this application, a method for preparing a Janus hollow fiber membrane is provided, comprising the following steps:

[0015] The inner and outer film-forming solutions are co-extruded using a dual-channel nozzle with a spinning core solution to obtain a double-layer hollow fiber membrane. Modified monomers are then grafted onto the membrane to obtain the Janus hollow fiber membrane.

[0016] The inner layer film-forming solution contains film-forming polymer A, inner layer additive, organic solvent A, and amphiphilic polymer A;

[0017] The outer film-forming solution contains film-forming polymer B, outer layer additive, organic solvent B, and amphiphilic polymer B;

[0018] The amphiphilic polymer A and the amphiphilic polymer B are independently selected from amphiphilic polymer I and amphiphilic polymer II;

[0019] The amphiphilic polymers described herein contain both hydrophilic and hydrophobic structures. One type of amphiphilic polymer contains hydroxyl groups and hydrophobic groups, and is named amphiphilic polymer I. The other type of amphiphilic polymer is named amphiphilic polymer II. The amphiphilic polymers are synthesized via free radical polymerization, selecting hydrophilic and hydrophobic monomers, with the monomers containing olefin structures.

[0020] The amphiphilic polymer I is obtained by polymerizing hydrophilic monomer I and hydrophobic monomer I;

[0021] The amphiphilic polymer II is obtained by polymerizing hydrophilic monomer II and hydrophobic monomer II;

[0022] The hydrophilic monomer I is selected from olefin monomers containing hydroxyl groups, specifically from at least one of allyl alcohol and butenol;

[0023] The hydrophilic monomer II is selected from at least one of polyethylene glycol acrylate and vinylpyrrolidone;

[0024] The hydrophobic monomer I and the hydrophobic monomer II are independently selected from at least one of styrene, methyl acrylate, acrylonitrile, and hexafluorobutyl acrylate;

[0025] The amphiphilic polymer A in the inner layer film-forming solution and the amphiphilic polymer B in the outer layer film-forming solution are different from each other.

[0026] The modified monomer is selected from at least one of hexafluorohexyltriethoxysilane and tridecafluorooctyltriethoxysilane.

[0027] The film-forming polymer A and film-forming polymer B are independently selected from at least one of polysulfone, polyethersulfone, polyvinylidene fluoride, polymethyl methacrylate, polyvinyl chloride, and polyacrylonitrile;

[0028] The inner layer additive is selected from at least one of polyethylene glycol, anhydrous lithium chloride, and polyvinylpyrrolidone.

[0029] The outer layer additive is selected from at least one of polyethylene glycol, anhydrous lithium chloride, and polyvinylpyrrolidone.

[0030] The organic solvent A and organic solvent B are independently selected from at least one of dimethylacetamide, dimethylformamide, N-methylpyrrolidone, and tetrahydrofuran;

[0031] The film-forming polymer A in the inner layer film-forming solution has a mass concentration of 10-25 wt%, the inner layer additive has a mass concentration of 5-20 wt%, and the amphiphilic polymer A has a mass concentration of 1-20 wt%.

[0032] Optionally, the mass concentration of film-forming polymer A in the inner layer film-forming solution is any value of 10wt%, 15wt%, 20wt%, 25wt%, or any range between two of these values; the mass concentration of the inner layer additive is any value of 5wt%, 10wt%, 15wt%, 20wt%, or any range between two of these values; and the mass concentration of amphiphilic polymer A is any value of 1wt%, 5wt%, 10wt%, 15wt%, 20wt%, or any range between two of these values.

[0033] The outer film-forming polymer B in the outer film-forming solution has a mass concentration of 10–25 wt%, the outer layer additive has a mass concentration of 5–20 wt%, and the amphiphilic polymer B has a mass concentration of 1–20 wt%.

[0034] Optionally, the mass concentration of film-forming polymer B in the outer film-forming solution is any value of 10wt%, 15wt%, 20wt%, 25wt%, or any range between two of these values; the mass concentration of the outer additive is any value of 5wt%, 10wt%, 15wt%, 20wt%, or any range between two of these values; and the mass concentration of amphiphilic polymer B is any value of 1wt%, 5wt%, 10wt%, 15wt%, 20wt%, or any range between two of these values.

[0035] The polymerization temperature is 50–80°C;

[0036] Optionally, the polymerization temperature is any value of 50°C, 60°C, 70°C, 80°C, or a range between any two.

[0037] The polymerization time is 40–600 min;

[0038] Optionally, the aggregation time is any value of 40 min, 600 min, or a range between both.

[0039] The polymerization involves a catalyst;

[0040] The catalyst is selected from at least one of azobisisobutyronitrile and benzoyl peroxide.

[0041] The grafted modified monomer includes the following steps:

[0042] The double-layer hollow fiber membrane is immersed in a solvent solution containing modified monomers;

[0043] The solvent is selected from at least one of n-hexane, cyclohexane, n-heptane, toluene, ethylbenzene, and ethyl acetate;

[0044] In the solvent solution containing the modified monomer, the mass ratio of the modified monomer to the solvent is 0.01 to 0.15:1.

[0045] Optionally, in the solvent solution containing the modified monomer, the mass ratio of the modified monomer to the solvent is any value among 0.01:1, 0.05:1, and 0.15:1, or any range between two of them.

[0046] The inner layer film-forming solution is stirred I;

[0047] The temperature of stirring I is 10–120°C;

[0048] Optionally, the temperature of the stirring I is any value or a range between 10℃, 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, and 120℃.

[0049] The stirring time for the first stirring step is 1 to 20 hours.

[0050] Optionally, the stirring time I is any value among 1h, 5h, 10h, 15h, and 20h, or a range between any two.

[0051] The outer film-forming solution is stirred (II);

[0052] The temperature of stirring II is 10–120°C;

[0053] Optionally, the temperature of the stirring II is any value or a range between 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, and 120°C.

[0054] The stirring time for the second stage is 1 to 20 hours.

[0055] Optionally, the stirring time II is any value among 1h, 5h, 10h, 15h, and 20h, or a range between any two.

[0056] The spinning core solution is selected from water or an aqueous solution containing ethanol, methanol, or an organic solvent;

[0057] The aqueous solution containing ethanol, methanol, or an organic solvent has a mass concentration of 10–80 wt%.

[0058] The total extrusion volume of the inner layer film-forming solution and the outer layer film-forming solution is 3-20 mL / min;

[0059] Optionally, the total extrusion volume of the inner layer film-forming solution and the outer layer film-forming solution is any value among 3 mL / min, 5 mL / min, 10 mL / min, 15 mL / min, and 20 mL / min, or a range between any two.

[0060] The ratio of the extrusion amount of the inner layer film-forming solution to the outer layer film-forming solution is 0.1 to 10:1.

[0061] Optionally, the ratio of the extrusion amount of the inner layer film-forming liquid to the outer layer film-forming liquid is any value among 0.1:1, 0.5:1, 1:1, 5:1, and 10:1, or any range between the two.

[0062] The double-layer hollow fiber membrane is gel-formed.

[0063] The solution used for gel molding is selected from water or an aqueous solution containing ethanol, methanol, or organic solvents.

[0064] The aqueous solution containing ethanol, methanol, or an organic solvent has a mass concentration of 10–80 wt%.

[0065] The Janus hollow fiber membrane undergoes washing, solvent exchange, and drying.

[0066] The washing is water washing;

[0067] The solvent exchange is a solvent exchange using ethanol and n-hexane as solvents;

[0068] The drying method is natural air drying or ethanol-n-hexane replacement air drying.

[0069] Janus hollow fiber membranes with different hydrophilic / hydrophobic layer thicknesses, hydrophilic / hydrophobic properties, and pore structures can be prepared by changing the composition, flow rate, core solution, and gel bath composition of the inner and outer membrane-forming solutions.

[0070] According to another aspect of this application, a Janus hollow fiber membrane is provided, which is prepared by the above-described preparation method.

[0071] According to another aspect of this application, an application of the above-mentioned Janus hollow fiber membrane is provided for processes such as CO2 absorption, air flotation, ammonia nitrogen stripping, and gas-liquid reaction.

[0072] The beneficial effects that this application can produce include:

[0073] 1) The preparation method provided in this application uses a dual-channel nozzle to prepare a bilayer separation membrane, which can flexibly control the thickness, transition mode and structure of the hydrophilic and hydrophobic layers, and achieve precise control of the Janus membrane structure.

[0074] 2) The preparation method provided in this application uses two membrane-forming solutions with similar hydrophilicity to prepare a bilayer membrane, which can effectively suppress the peeling problem between the two layers. In the post-processing stage, the different chemical properties of the amphiphilic polymers in the two membrane-forming solutions can be used to test the hydrophilic-hydrophobic conversion of the Janus membrane through a simple soaking and grafting process.

[0075] 3) The preparation method provided in this application is simple to operate and allows for flexible control of the structure of the Janus membrane, which is more conducive to the large-scale production and industrial application of Janus hollow fiber membranes.

[0076] 4) The Janus separation membrane developed in this application can be used in processes such as air flotation, ammonia nitrogen stripping, and gas-liquid reactions. It can significantly enhance gas-liquid mass transfer and reduce equipment investment and operating costs. Detailed Implementation

[0077] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0078] Unless otherwise specified, the raw materials and hydrophobic monomers used in the embodiments of this application were purchased commercially.

[0079] Example 1

[0080] Dissolve 8g of allyl alcohol and 2g of styrene in 415g of dimethylacetamide, add 0.1g of azobisisobutyronitrile, purge with nitrogen gas, and heat and stir at 50℃ for 40min to obtain a solution containing amphiphilic polymer I. Add 50g of PVDF and 25g of polyethylene glycol 400 to this solution to obtain the inner layer film-forming solution.

[0081] Take 20g of vinylpyrrolidone and 5g of styrene, dissolve them in 350g of dimethylacetamide, add 0.5g of azobisisobutyronitrile, and heat and stir at 60℃ for 80min to obtain a solution containing amphiphilic polymer II. Add 100g of PVDF and 25g of polyethylene glycol 400 to this solution to obtain the outer layer film-forming solution.

[0082] The inner and outer layer film-forming solutions were added to the inner and outer layer film-forming solution spinning tanks, respectively, and vacuum degassing was performed for 24 hours. The outer and inner layer film-forming solutions were then fed into a dual-channel nozzle, using ethanol as the core solution and deionized water as the outer gel bath, to spin a double-layer hollow fiber membrane. The flow rate of the outer layer film-forming solution was 5 ml / min, and the flow rate of the inner layer film-forming solution was 0.5 ml / min, resulting in a double-layer hollow fiber membrane. The obtained double-layer hollow fiber membrane was immersed in a grafting modification solution, and the grafting reaction was carried out for 24 hours. The grafting modification solution consisted of 1 g of hexafluorohexyltriethoxysilane and 100 g of n-hexane. The grafted double-layer membrane was rinsed in deionized water for 48 hours, and then dried using a successive ethanol-n-hexane displacement process to obtain a Janus hollow fiber membrane. This Janus membrane has a hydrophobic inner layer and a hydrophilic outer layer structure. The inner water contact angle is 125°, and the outer water contact angle is 38°.

[0083] The separation membrane was used in the bubbling method for CO2 absorption.

[0084] A N2 / CO2 mixture (85% N2, 15% CO2) and an absorbent (composed of 5% anhydrous piperazine, 38% N-methyl-diethanolamine, and 57% deionized water) were introduced into the Janus membrane module under pressure through the inlet. The mixture flowed from the outer surface of the Janus hollow fiber membrane into the membrane interior, combining with the absorbent to form microbubbles. The pressure of the mixed gas was 0.15 MPa, and the pressure of the absorbent was 0.02 MPa. The microbubbles combined with the absorbent inside the membrane module and in the subsequent absorption tubes. Gas-liquid separation was achieved through a gas-liquid separator. The gas after absorption was then introduced into a gas chromatograph to test the CO2 content in the mixed gas.

[0085] The test results are as follows: the average diameter of the microbubbles in the mixed gas is 30 μm, and the processing capacity of the mixed gas is 7 m³. 3 / m 2 The CO2 absorption rate in the mixed gas after absorption is 99.97%, and it can operate stably for a long time.

[0086] Example 2

[0087] Take 30g of butenol and 10g of methyl methacrylate, dissolve them in 350g of dimethylacetamide, add 0.1g of azobisisobutyronitrile, purge with nitrogen gas, and heat and stir at 70℃ for 200min to obtain a solution containing amphiphilic polymer I. Add 100g of polyethersulfone and 20g of anhydrous lithium chloride to this solution to obtain the outer layer film-forming solution.

[0088] 40g of polyethylene glycol acrylate and 10g of methyl acrylate were dissolved in 360g of dimethylacetamide. 0.5g of azobisisobutyronitrile was added, and the mixture was heated and stirred at 60℃ for 400min to obtain a solution containing amphiphilic polymer II. 70g of polyethersulfone and 20g of anhydrous lithium chloride were added to this solution to obtain the inner layer film-forming solution.

[0089] The inner and outer layer film-forming solutions were added to the inner and outer layer film-forming solution spinning tanks, respectively, and vacuum degassing was performed for 24 hours. The outer and inner layer film-forming solutions were then fed into a dual-channel nozzle, using water as the core solution and propanol as the outer gel bath, to spin a double-layer hollow fiber membrane. The flow rate of the outer layer film-forming solution was 1.5 ml / min, and that of the inner layer film-forming solution was 3.5 ml / min, resulting in a double-layer hollow fiber membrane. The obtained double-layer hollow fiber membrane was immersed in a grafting modification solution, and the grafting reaction was carried out for 24 hours. The grafting modification solution consisted of 5 g of hexafluorohexyltriethoxysilane and 95 g of toluene. The grafted double-layer membrane was rinsed in deionized water for 48 hours, and then dried using a successive ethanol-n-hexane displacement process to obtain a Janus hollow fiber membrane. This Janus membrane has a hydrophobic outer layer and a hydrophilic inner layer structure. The water contact angle between the inner and outer layers is 25°, and the water contact angle between the inner and outer layers is 130°.

[0090] The separation membrane was used in a direct contact membrane distillation process. The test water source was saline solution with a salt content of 3.5% and a temperature of 80°C. The saline solution flowed through the hydrophobic outer layer of the Janus membrane, while water vapor flowed through the hydrophilic inner layer of the Janus separation membrane. After condensation, desalinated water was obtained.

[0091] Water production rate is 80L / m 2 h, the desalination rate reached 99.8%.

[0092] Example 3

[0093] Take 45g of butenol and 15g of methyl methacrylate, dissolve them in 350g of dimethylformamide, add 0.3g of benzoyl peroxide, purge with nitrogen gas, and heat and stir at 80℃ for 500min to obtain a solution containing amphiphilic polymer I. Add 80g of polyvinyl chloride and 10g of polyvinylpyrrolidone to this solution to obtain the outer film-forming solution.

[0094] Take 60g of vinylpyrrolidone and 15g of hexafluorobutyl acrylate, dissolve them in 330g of dimethylformamide, add 0.4g of benzoyl peroxide, and heat and stir at 90℃ for 600min to obtain a solution containing amphiphilic polymer II. Add 75g of polyvinyl chloride and 20g of polyvinylpyrrolidone to this solution to obtain the inner layer film-forming solution.

[0095] The inner and outer layer film-forming solutions were added to the inner and outer layer film-forming solution spinning tanks, respectively, and vacuum degassing was performed for 24 hours. The outer and inner layer film-forming solutions were then fed into a dual-channel nozzle, using a 70% DMAC / 30% deionized water mixture as the core solution and deionized water as the outer gel bath to spin a bilayer hollow fiber membrane. The flow rate of the outer layer film-forming solution was 3 ml / min, and the flow rate of the inner layer film-forming solution was 7 ml / min, resulting in a bilayer hollow fiber membrane. The obtained bilayer hollow fiber membrane was immersed in a grafting modification solution, consisting of 10 g of hexafluorohexyltriethoxysilane and 90 g of n-hexane, for 24 hours. The grafted bilayer membrane was rinsed in deionized water for 48 hours, and then dried using a successive ethanol-n-hexane displacement process to obtain a Janus hollow fiber membrane. This Janus membrane has a hydrophobic outer layer and a hydrophilic inner layer structure. The inner water contact angle is 35°, and the outer water contact angle is 135°.

[0096] The separation membrane was used in a direct contact membrane distillation process. The test water source was saline solution with a salt content of 3.5% and a temperature of 80°C. The saline solution flowed through the hydrophobic outer layer of the Janus membrane, while water vapor flowed through the hydrophilic inner layer of the Janus separation membrane. After condensation, desalinated water was obtained.

[0097] Water production rate is 60L / m 2 h, the desalination rate reached 99.8%.

[0098] Comparative Example 1:

[0099] Take 60g of vinylpyrrolidone and 15g of hexafluorobutyl acrylate, dissolve them in 330g of dimethylformamide, add 0.4g of benzoyl peroxide, and heat and stir at 90℃ for 600min to obtain a solution containing amphiphilic polymers. Add 75g of polyvinyl chloride and 20g of polyvinylpyrrolidone to this solution to obtain a film-forming solution.

[0100] The film-forming solution was added to the spinning tank and vacuum degassed for 24 hours. The solution was then pumped into a single-channel nozzle, using a 70% DMAC / 30% deionized water mixture as the core solution and deionized water as the external gel bath to spin a double-layer hollow fiber membrane. The film-forming solution flow rate was 3 ml / min, resulting in a hydrophilic PVDF hollow fiber membrane with a water contact angle of 35°.

[0101] A N2 / CO2 mixture (85% N2, 15% CO2) and an absorbent (composed of 5% anhydrous piperazine, 38% N-methyl-diethanolamine, and 57% deionized water) were introduced into the PVDF membrane module under pressure through the inlet. The gas flowed from the outer surface of the PVDF membrane into the hollow fiber membrane, where it combined with the absorbent to form microbubbles. The pressure of the mixed gas was 0.15 MPa, and the pressure of the absorbent was 0.04 MPa. The microbubbles combined with the absorbent inside the membrane module and in the subsequent absorption tubes. Gas-liquid separation was achieved through a gas-liquid separator. The gas after absorption was then introduced into a gas chromatograph to test the CO2 content in the mixed gas.

[0102] After the test, the gas flux approached zero within 30 minutes, making operation impossible.

[0103] Comparative Example 2:

[0104] 40g of allyl alcohol and 10g of methyl acrylate were dissolved in 360g of dimethylacetamide, and 0.5g of azobisisobutyronitrile was added. The mixture was heated and stirred at 60℃ for 400min to obtain a solution containing amphiphilic polymers. 70g of polyethersulfone and 20g of anhydrous lithium chloride were added to this solution to obtain the inner layer film-forming solution. The film-forming solution was added to a spinning tank and vacuum degassed for 24h. The film-forming solution was fed into a single-channel nozzle, using water as the core liquid and propanol as the outer gel bath, to spin a hollow fiber membrane. The film-forming solution flow rate was 3.5ml / min, resulting in a hollow fiber membrane. The obtained hollow fiber membrane was immersed in a grafting modification solution, and the grafting reaction was carried out for 24h. The grafting modification solution consisted of 10g of hexafluorohexyltriethoxysilane and 90g of n-hexane. The grafted bilayer membrane was rinsed in deionized water for 48 hours, and dried by successive displacement of ethanol-n-hexane to obtain a hydrophobic hollow fiber membrane with a water contact angle of 135°.

[0105] The separation membrane was used in a direct contact membrane distillation process. The test water source was saline solution with a salt content of 3.5% and a temperature of 80°C. The saline solution flowed through the hydrophobic outer layer of the Janus membrane, while water vapor flowed through the hydrophilic inner layer of the Janus separation membrane. After condensation, desalinated water was obtained.

[0106] Water production rate is 20L / m 2 h, the desalination rate reached 99.8%.

[0107] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing a Janus hollow fiber membrane, characterized in that, Includes the following steps: The inner and outer film-forming solutions are co-extruded using a dual-channel nozzle with a spinning core solution to obtain a double-layer hollow fiber membrane. Modified monomers are then grafted onto the membrane to obtain the Janus hollow fiber membrane. The inner layer film-forming solution contains film-forming polymer A, inner layer additive, organic solvent A, and amphiphilic polymer A; The outer film-forming solution contains film-forming polymer B, outer layer additive, organic solvent B, and amphiphilic polymer B; The amphiphilic polymer A and the amphiphilic polymer B are independently selected from amphiphilic polymer I and amphiphilic polymer II; The amphiphilic polymer I is obtained by polymerizing hydrophilic monomer I and hydrophobic monomer I; The amphiphilic polymer II is obtained by polymerizing hydrophilic monomer II and hydrophobic monomer II; The hydrophilic monomer I is selected from at least one of allyl alcohol and butenol; The hydrophilic monomer II is selected from at least one of polyethylene glycol acrylate and vinylpyrrolidone; The hydrophobic monomer I and the hydrophobic monomer II are independently selected from at least one of styrene, methyl acrylate, acrylonitrile, and hexafluorobutyl acrylate; The amphiphilic polymer A in the inner layer film-forming solution and the amphiphilic polymer B in the outer layer film-forming solution are different from each other. The modified monomer is selected from at least one of hexafluorohexyltriethoxysilane and tridecafluorooctyltriethoxysilane.

2. The preparation method according to claim 1, characterized in that, The film-forming polymer A and film-forming polymer B are independently selected from at least one of polysulfone, polyethersulfone, polyvinylidene fluoride, polymethyl methacrylate, polyvinyl chloride, and polyacrylonitrile; The inner layer additive is selected from at least one of polyethylene glycol, anhydrous lithium chloride, and polyvinylpyrrolidone. The outer layer additive is selected from at least one of polyethylene glycol, anhydrous lithium chloride, and polyvinylpyrrolidone. The organic solvent A and organic solvent B are independently selected from at least one of dimethylacetamide, dimethylformamide, N-methylpyrrolidone, and tetrahydrofuran; The film-forming polymer A in the inner layer film-forming solution has a mass concentration of 10-25 wt%, the inner layer additive has a mass concentration of 5-20 wt%, and the amphiphilic polymer A has a mass concentration of 1-20 wt%. The outer film-forming polymer B in the outer film-forming solution has a mass concentration of 10–25 wt%, the outer layer additive has a mass concentration of 5–20 wt%, and the amphiphilic polymer B has a mass concentration of 1–20 wt%.

3. The preparation method according to claim 1, characterized in that, The polymerization temperature is 50–80°C; The polymerization time is 40–600 min; The polymerization involves a catalyst; The catalyst is selected from at least one of azobisisobutyronitrile and benzoyl peroxide.

4. The preparation method according to claim 1, characterized in that, The grafted modified monomer includes the following steps: The double-layer hollow fiber membrane is immersed in a solvent solution containing modified monomers; The solvent is selected from at least one of n-hexane, cyclohexane, n-heptane, toluene, ethylbenzene, and ethyl acetate; In the solvent solution containing the modified monomer, the mass ratio of the modified monomer to the solvent is 0.01 to 0.15:

1.

5. The preparation method according to claim 1, characterized in that, The inner layer film-forming solution is stirred I; The temperature of stirring I is 10–120°C; The stirring time for the first stirring step is 1 to 20 hours.

6. The preparation method according to claim 1, characterized in that, The outer film-forming solution is stirred (II); The temperature of stirring II is 10–120°C; The stirring time for the second stage is 1 to 20 hours.

7. The preparation method according to claim 1, characterized in that, The spinning core solution is selected from water or an aqueous solution containing ethanol, methanol, or an organic solvent; The aqueous solution containing ethanol, methanol, or an organic solvent has a mass concentration of 10–80 wt%.

8. The preparation method according to claim 1, characterized in that, The total extrusion volume of the inner layer film-forming solution and the outer layer film-forming solution is 3-20 mL / min; The ratio of the extrusion amount of the inner layer film-forming solution to the outer layer film-forming solution is 0.1 to 10:

1.

9. A Janus hollow fiber membrane, characterized in that, Prepared by the preparation method according to any one of claims 1 to 8.

10. An application of the Janus hollow fiber membrane according to claim 9, characterized in that, It is used in CO2 absorption, flotation, ammonia nitrogen stripping and gas-liquid reaction processes.

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