Hollow fiber oxygen enriched membrane and method for preparing the same

Abstract

This invention belongs to the field of membrane separation and materials engineering technology, and particularly relates to a hollow fiber oxygen-enriched membrane and its preparation method. The oxygen-enriched membrane is composed of a porous base membrane layer and a selective permeation layer. The porous base membrane layer uses polysulfone, tetraethyl orthosilicate, nano-titanium dioxide, meta-aramid fiber micropowder, and chitosan-grafted graphene oxide as main raw materials, possessing excellent mechanical properties and structural stability. The selective permeation layer contains polyetherimide, nano-zirconia, chopped glass fibers, chitosan, and quaternary ammonium salt functionalized metal-organic framework materials, significantly improving the membrane's gas selectivity and antifouling ability. The oxygen-enriched membrane prepared by this invention through dry and wet spinning and composite impregnation processes possesses advantages such as high-efficiency separation, durable operation, and ease of industrial production, making it suitable for various applications in medical, industrial, and other fields.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation and materials engineering technology, and particularly relates to a hollow fiber oxygen-enriched membrane and its preparation method. Background Technology

[0002] Hollow fiber gas separation membranes, as a key representative of modern high-efficiency gas separation technology, are playing an increasingly important role in fields such as medical oxygen generation, household air purification, and industrial oxygen enrichment. Existing hollow fiber oxygen-enriching membranes are mostly made of polymer materials such as polysulfone and polyethersulfone, prepared through precision spinning and densification processes. However, in practical applications, these membrane materials generally face challenges such as performance degradation and limited lifespan. On the one hand, membrane materials are prone to aging and plasticization under long-term high pressure and complex gas environments, with microstructural expansion leading to a decline in separation performance. On the other hand, the membranes lack sufficient mechanical strength and fouling resistance, making them susceptible to contamination by impurities and particles during continuous operation, resulting in reduced flux and shortened lifespan. This is especially problematic in demanding applications such as medical or confined spaces, where safety and reliability are difficult to guarantee.

[0003] Furthermore, although some products attempt to improve mechanical strength and temperature resistance by incorporating inorganic nanoparticles or fiber reinforcement materials, poor dispersion and interfacial compatibility between different components often lead to uneven membrane structure and low yield rates during mass production. Existing dry and wet spinning and surface treatment processes have extremely stringent requirements for equipment and parameter control, and products are prone to problems such as uneven pore size distribution and delamination of the dense layer, which restricts the large-scale, low-cost production of hollow fiber oxygen-enriched membranes.

[0004] More significantly, the high-performance hollow fiber oxygen-enriched membrane market is currently dominated by foreign companies from Europe, America, and Japan. Domestically produced membranes still lag behind international advanced levels in areas such as high-temperature resistance, mechanical properties, anti-fouling capabilities, and customization. The high price and long delivery cycles of imported membranes severely hinder the independent control and widespread application of domestic oxygen production equipment. Faced with the ever-increasing demand for oxygen enrichment, breakthroughs are urgently needed in existing technologies, particularly in material systems, membrane structure innovation, and overall performance improvement. Therefore, developing a novel, high-performance hollow fiber oxygen-enriched membrane suitable for industrial production has become a crucial issue that the industry urgently needs to address. Summary of the Invention

[0005] The purpose of this invention is to provide a hollow fiber oxygen-enriched membrane and its preparation method, aiming to overcome the shortcomings of existing oxygen-enriched membranes in terms of high temperature resistance, mechanical strength, antifouling properties, and gas separation efficiency. Through innovative design of membrane structure and composition, this invention prepares a hollow fiber oxygen-enriched membrane with excellent performance, high stability, and suitability for industrial production, providing a more efficient and reliable solution for gas separation and oxygen enrichment applications.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] The first aspect of the present invention provides a hollow fiber oxygen-enriched membrane, the membrane being composed of two layers, an inner layer being a porous base membrane layer and an outer layer being a selectively permeable layer;

[0008] The raw materials for preparing the porous base film layer include, by weight, 80-120 parts of polysulfone, 8-16 parts of tetraethyl orthosilicate, 2-6 parts of nano-titanium dioxide, 0.5-2 parts of meta-aramid fiber micro powder, and 0.2-1 parts of chitosan-grafted graphene oxide.

[0009] The raw materials for preparing the selectively permeable layer, by weight, include: 8-15 parts of polyetherimide, 0.1-0.5 parts of nano-zirconia, 0.05-0.3 parts of chopped glass fiber, 0.05-0.3 parts of chitosan, and 0.05-0.5 parts of quaternary ammonium salt functionalized metal-organic framework materials (Q-MOFs).

[0010] Furthermore, the thickness of the porous base film layer is 60–120 μm, and the thickness of the selectively permeable layer is 0.2–1 μm.

[0011] Furthermore, the hollow fiber oxygen-enriched membrane has an outer diameter of 350–600 μm, an inner diameter of 200–350 μm, and a length of 20–60 cm.

[0012] Furthermore, the chitosan-grafted graphene oxide is prepared according to the following method:

[0013] (1) Graphene oxide (GO) and deionized water were mixed to obtain a GO dispersion. 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) were added to the GO dispersion and stirred to obtain an activated GO dispersion.

[0014] (2) Add the activated GO dispersion to the acetic acid solution of chitosan to obtain a mixture, adjust the pH of the mixture to 5-6, and stir the reaction.

[0015] (3) After the reaction is complete, the product is washed and dried to obtain chitosan-grafted graphene oxide.

[0016] Further, in step (1), the mass ratio of graphene oxide (GO) to deionized water is 1:(50-100), the mass ratio of EDC to GO is 1:(10-20), and the mass ratio of NHS to EDC is 1:(2-3).

[0017] Further, in step (2), the mass ratio of GO to chitosan is 1:(1-5); the stirring reaction time is 6-24 hours.

[0018] In this invention, the introduction of chitosan-grafted graphene oxide significantly enhances the overall performance of the hollow fiber oxygen-enriched membrane. From the perspective of material microstructure and interface regulation, GO itself possesses abundant oxygen-containing functional groups and a large specific surface area, providing excellent microscopic support and dispersion for membrane materials. However, bare GO often suffers from insufficient compatibility and agglomeration in polymer matrices, affecting the structural uniformity and long-term performance of the membrane. Through covalent grafting of chitosan molecules, a large number of amino and polysaccharide segments are introduced onto the surface of the GO sheets. This not only endows GO with higher hydrophilicity and polarity but also enables it to form strong interfacial forces with polymers such as polysulfone, greatly enhancing the dispersion and interfacial bonding of GO in the membrane, thereby improving the structural integrity and microscopic uniformity of the membrane material.

[0019] Furthermore, chitosan-grafted GO helps regulate the porous structure of the membrane during film formation, forming ordered or semi-ordered microporous channels, increasing the membrane's porosity and specific surface area. This provides a low-resistance diffusion path for the efficient permeation of small molecules such as oxygen, while simultaneously creating a molecular sieve effect for large molecules and impurity gases, thereby enhancing the membrane's gas separation selectivity and flux. The GO sheets themselves possess excellent mechanical properties, and the introduction of chitosan further strengthens the load transfer between the matrix and nanomaterials through molecular chain entanglement and interfacial bonding, effectively improving the strength and toughness of the membrane fibers. This allows the membrane to maintain a long lifespan and stability even under repeated pressure shocks and complex operating conditions.

[0020] In addition, chitosan has good natural hydrophilicity and antibacterial and antifouling properties. When it is uniformly grafted onto GO sheets, it can greatly improve the surface hydrophilicity of membrane materials, reduce the adsorption of organic pollutants and microorganisms, and extend the clean operation cycle of the membrane. It is very suitable for applications with high requirements for hygiene and stability, such as medical, drinking water and high-end oxygen supply.

[0021] Furthermore, the quaternary ammonium salt functionalized metal-organic framework material is prepared according to the following method:

[0022] (1) Dissolve zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and 2-methylimidazole (C4H6N2) in deionized water, stir, let stand, and a precipitate is formed. Collect the precipitate, wash and dry it to obtain ZIF-8 powder.

[0023] (2) Disperse ZIF-8 powder and trimethyl[3-(trimethoxysilyl)propyl]ammonium chloride in methanol, stir and react. After the reaction is complete, collect the solid product, wash and dry it to obtain quaternary ammonium salt functionalized metal-organic framework material.

[0024] Further, the molar ratio of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) to 2-methylimidazole (C4H6N2) in step (1) is 1:(1~2).

[0025] Further, the mass ratio of the ZIF-8 powder to trimethyl[3-(trimethoxysilyl)propyl]ammonium chloride in step (2) is 1:(0.05~0.5).

[0026] This invention introduces quaternary ammonium salt functional groups onto the surface of ZIF-8 materials, enhancing not only their dispersibility in polymer systems and interfacial compatibility with organic matrices, but also endowing the material with unique surface charges and antifouling capabilities. The cationic groups of the quaternary ammonium salt structure effectively inhibit the adsorption and deposition of negatively charged impurity molecules, improving the membrane's antifouling and anti-biofouling properties and extending the membrane's stable operating cycle under complex conditions. Simultaneously, the quaternary ammonium salt-modified MOF optimizes the molecular sieve pore environment at the microscopic level, facilitating the passage of oxygen molecules while creating stronger barriers against nitrogen and other gases or large molecular impurities, thereby further improving the selective permeation efficiency of oxygen.

[0027] Furthermore, the hydrophilicity and dispersibility of MOFs are enhanced after quaternary ammonium salt functionalization, enabling the formation of a more uniform and dense functional selective layer in the membrane material. This not only helps improve the gas separation accuracy and operational stability of the membrane, but also provides a guarantee for the large-scale preparation and long-term application of membrane modules.

[0028] A second aspect of this invention provides a method for preparing the aforementioned hollow fiber oxygen-enriched membrane, comprising the following steps:

[0029] (1) Polysulfone, tetraethyl orthosilicate, nano titanium dioxide, meta-aramid fiber powder, and chitosan-grafted graphene oxide were added to N-methylpyrrolidone, stirred, and allowed to stand to remove bubbles, thus preparing a porous membrane spinning solution.

[0030] (2) The porous base membrane spinning solution is extruded through a concentric nozzle, stretched in an air section, and then solidified in a deionized water coagulation bath at 5-15℃ to obtain hollow fiber filaments. After the filaments are formed, they are rinsed with deionized water and dried to obtain a porous hollow fiber base membrane.

[0031] (3) Dissolve polyetherimide, nano-zirconia, glass fiber chopped filaments, chitosan, and quaternary ammonium salt functionalized metal-organic framework material in N-methylpyrrolidone, stir, and obtain a composite solution; immerse the porous hollow fiber base membrane in the composite solution, remove it after immersion for 1 to 3 hours, allow it to stand and react, form a selective permeable layer, and obtain the composite membrane filaments;

[0032] (4) Wash and dry the composite membrane fibers to obtain a hollow fiber oxygen-enriched membrane.

[0033] Further, the mass of N-methylpyrrolidone in step (1) is 5 to 10 times the total mass of polysulfone, tetraethyl orthosilicate, nano titanium dioxide, meta-aramid fiber micro powder, and chitosan-grafted graphene oxide; the stirring time is 1 to 3 hours, and the standing time is 2 to 6 hours.

[0034] Further, in step (3), the mass of N-methylpyrrolidone is 10 to 30 times the total mass of polyetherimide, nano-zirconia, glass fiber chopped strands, chitosan and quaternary ammonium salt functionalized metal-organic framework material; the static reaction time is 1 to 3 hours.

[0035] The hollow fiber oxygen-enriched membrane of this invention achieves efficient and stable oxygen enrichment and separation through a unique multi-component synergistic design and a scientific two-layer composite structure. In the porous base membrane layer, polysulfone serves as the polymer backbone material, endowing the membrane with excellent film-forming properties and mechanical strength, and is the core support of the overall structure. Tetraethyl orthosilicate generates silica in situ through a sol-gel process, improving the membrane's structural density and peel strength, and enhancing the long-term stability of the base membrane. The addition of nano-titanium dioxide not only improves the mechanical properties and high-temperature resistance of the base membrane but also plays a positive role in improving the membrane's microstructure and gas permeability. Meta-aramid fiber micropowder, as a high-strength organic filler, further enhances the overall toughness and corrosion resistance of the membrane, ensuring its stability under complex operating conditions. The introduction of chitosan-grafted graphene oxide not only greatly improves the interfacial bonding and dispersion uniformity between nanomaterials and polymers but also enhances oxygen permeation rate and separation selectivity by regulating the microporous structure and strengthening the molecular sieve effect, while simultaneously endowing the base membrane with good hydrophilicity and antifouling properties, extending the membrane fiber lifespan.

[0036] In the selective permeation layer, polyetherimide serves as the framework for the high-performance separation membrane, exhibiting excellent chemical stability and dense film-forming properties. The addition of nano-zirconia and chopped glass fibers provides the selective layer with improved density, mechanical strength, and temperature resistance. Chitosan, as a natural antifouling agent, improves the membrane's hydrophilicity and resistance to biofouling, effectively preventing impurity blockage and biofilm fouling. Quaternary ammonium salt functionalized metal-organic framework materials further enhance molecular sieving precision and the membrane's surface antifouling ability, inhibiting impurity adsorption through interfacial charge modulation and optimizing the preferential oxygen permeation pathway at the microscopic level.

[0037] Regarding the preparation method, this invention combines dry and wet spinning with interfacial composite methods. The process is mild, the parameters are controllable, and it is easy to scale up for continuous production. The composite selective layer adopts impregnation and static reaction methods, which ensures that the film structure is dense and the interfacial bonding is strong, greatly improving product consistency and operability for industrial applications.

[0038] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0039] The hollow fiber oxygen-enriched membrane of this invention achieves significant innovation and improvement in structure, materials, and performance. The porous base membrane layer utilizes a synergistic combination of chitosan-grafted graphene oxide, aramid micropowder, and nano-titanium dioxide, effectively enhancing the membrane's mechanical strength, structural density, and durability, while optimizing the micropores to provide low-resistance channels for oxygen molecules and significantly improving gas separation selectivity. The quaternary ammonium salt functionalized metal-organic framework and nano-zirconia, specially introduced into the selective permeation layer, not only strengthen molecular sieving and interfacial charge regulation capabilities but also significantly improve the membrane surface's antifouling, anti-biofouling, and operational stability. Actual test results show that the oxygen / nitrogen selectivity, oxygen flux, mechanical properties, and antifouling ability of the membrane of this invention are superior to comparative examples and existing similar products, enabling long-term stable operation and maintaining high-efficiency separation performance. The preparation process parameters are controllable and suitable for large-scale production, providing a more reliable and efficient novel membrane material solution for high-end medical and industrial oxygen-enriched applications. Detailed Implementation

[0040] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Unless otherwise specified, all raw materials used in the embodiments are commercially available products. The following sources are illustrative examples.

[0042] The polysulfone was purchased from Ensinger Engineering Plastics (Shanghai) Co., Ltd., Udel® PSU.

[0043] The nano-titanium dioxide was purchased from Suzhou Youzir Nanomaterials Co., Ltd., with an average particle size of 20-30nm.

[0044] The meta-aramid fiber micron powder was purchased from DuPont, Kevlar® type micron powder.

[0045] The polyetherimide was purchased from DuPont, Aurum®.

[0046] The nano-zirconia was purchased from Suzhou Youzirconium Nanomaterials Co., Ltd., with an average particle size of 5-30 nm.

[0047] The chopped glass fiber filaments were purchased from China Jushi Co., Ltd., ECE R13-1200.

[0048] The graphene oxide was purchased from Changzhou Sixth Element Materials Technology Co., Ltd., with a sheet diameter of 0.5-5μm and a thickness of 1.2nm.

[0049] The polyethylene glycol was purchased from Jiangsu Haian Petrochemical Plant, PEG-4000.

[0050] Example 1

[0051] This embodiment provides a hollow fiber oxygen-enriched membrane, which consists of two layers: an inner layer is a porous base membrane layer, and an outer layer is a selectively permeable layer.

[0052] The raw materials for preparing the porous base film layer include, by weight: 100 parts polysulfone, 12 parts tetraethyl orthosilicate, 4 parts nano titanium dioxide, 1 part meta-aramid fiber micro powder, and 0.6 parts chitosan-grafted graphene oxide.

[0053] The raw materials for preparing the selectively permeable layer, by weight, include: 11 parts polyetherimide, 0.3 parts nano-zirconia, 0.1 parts chopped glass fiber, 0.15 parts chitosan, and 0.25 parts quaternary ammonium salt functionalized metal-organic framework material.

[0054] Chitosan-grafted graphene oxide was prepared by the following method:

[0055] (1) Weigh 1.0 g of graphene oxide (GO) dry powder and add it to 80 mL of deionized water. Disperse it for 30 minutes using an ultrasonic disperser to obtain a GO dispersion. Then, weigh 0.06 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and 0.02 g of N-hydroxysuccinimide (NHS). First, dissolve NHS in 5 mL of deionized water, and then slowly add it together with EDC to the GO dispersion. Stir at room temperature for 40 minutes to fully activate the carboxyl groups on the GO surface and obtain the activated GO dispersion.

[0056] (2) Weigh 2.0 g of chitosan and dissolve it in 100 mL of 1.0 wt% glacial acetic acid solution. Stir magnetically for 6 hours until all the chitosan is dissolved to obtain chitosan acetic acid solution. Slowly pour the activated GO dispersion into the chitosan acetic acid solution while stirring. Then, stir the mixture continuously at 25°C for 12 hours. During the reaction, adjust the pH of the mixture to 5.5 with 1 mol / L sodium hydroxide solution. Add the solution slowly in 3 portions, with an interval of 10 minutes between each addition. Detect the pH in real time with pH test paper to ensure that the pH is between 5 and 6.

[0057] (3) After the reaction is complete, the mixture is transferred to a centrifuge tube and placed in a refrigerated centrifuge. It is centrifuged at 8000 rpm for 15 minutes, the supernatant is discarded, and the mixture is resuspended in deionized water and centrifuged three times. Finally, it is washed twice with anhydrous ethanol. The precipitate after washing is spread out in a glass petri dish and dried in a vacuum drying oven at 40℃ for 16 hours to obtain chitosan-grafted graphene oxide.

[0058] Quaternary ammonium salt functionalized metal-organic framework materials are prepared by the following method:

[0059] (1) Dissolve 10 mmol of Zn(NO3)2·6H2O in 100 mL of deionized water to obtain solution A. Dissolve 15 mmol of C4H6N2 in 100 mL of deionized water to obtain solution B. Pour solution B into solution A and immediately stir with a magnetic stirrer at room temperature for 30 minutes. After stirring, let the reaction solution stand for 4 hours. The precipitate gradually forms. Centrifuge for 10 minutes to collect the precipitate. Resuspend the precipitate in deionized water and wash it three times by centrifugation. Then resuspend it in anhydrous methanol and wash it twice by centrifugation to remove impurities and unreacted substances. Spread the washed precipitate on a glass petri dish and dry it in a vacuum drying oven at 60℃ for 12 hours to obtain ZIF-8 powder.

[0060] (2) Weigh 1.0 g of dried ZIF-8 powder and add it to 50 mL of anhydrous methanol. Disperse it by ultrasonication for 15 minutes to ensure it is fully dispersed. Weigh 0.1 g of trimethyl[3-(trimethoxysilyl)propyl]ammonium chloride and add it to the dispersed ZIF-8 methanol suspension. Stir the reaction at room temperature for 12 hours. After the reaction is complete, centrifuge for 10 minutes to collect the product. Wash it three times with anhydrous methanol. Finally, spread the washed solid in a glass petri dish and dry it in a vacuum drying oven at 40 °C for 10 hours to obtain the quaternary ammonium salt functionalized metal-organic framework material.

[0061] Hollow fiber oxygen-enriched membranes are prepared as follows:

[0062] (1) Polysulfone, tetraethyl orthosilicate, nano titanium dioxide, meta-aramid fiber powder, and chitosan-grafted graphene oxide were added to N-methylpyrrolidone in sequence. The amount of NMP was 9 times the total mass of all solids. The mixture was stirred at 25°C for 2 hours. After stirring, the mixture was allowed to stand for 4 hours to degas until there were no obvious bubbles in the system, thus obtaining a porous base film spinning solution.

[0063] (2) The above spinning solution is loaded into a hollow fiber membrane spinning machine. A concentric nozzle is used. The outer layer is filled with spinning solution and the inner layer is filled with 10% polyethylene glycol aqueous solution. The core liquid flow rate is 0.4 mL / min and the spinning solution flow rate is 1.0 mL / min. The air section under the nozzle is 20 cm during spinning. After the spinning solution jet is stretched through the air section, it directly enters the 10℃ deionized water coagulation bath and the flow rate is kept constant. After the raw fiber stays in the coagulation bath for 40 minutes, it is carefully transferred to the flowing deionized water tank with non-woven fabric and rinsed continuously for 6 hours to ensure the removal of all NMP and low molecular weight impurities. The washed hollow fiber membrane is dried with non-woven fabric, spread evenly on a non-stick plate, and sent to a 60℃ vacuum drying oven to dry for 12 hours to obtain a porous hollow fiber base membrane.

[0064] (3) Add polyetherimide, nano-zirconia, glass fiber chopped filaments, chitosan, and quaternary ammonium salt functionalized metal-organic framework material to N-methylpyrrolidone. The amount of NMP is 20 times the total mass of all solid raw materials. Stir at room temperature for 2 hours to obtain a composite solution. Immerse the dried porous hollow fiber base membrane completely into the composite solution to ensure complete wetting. Keep it immersed at room temperature for 2 hours. Then, use a clamp to hold one end of the membrane fiber and slowly lift it out to allow the surface solution to drip dry naturally. Place it at 25°C and let it stand for 2 hours to form a dense and uniform selective permeable layer on the surface of the membrane fiber in situ.

[0065] (4) Rinse the composite membrane fibers three times in a beaker containing deionized water, changing the water each time. Stir gently for 10 minutes to remove excess solvent and unreacted components from the surface. After washing, lay the membrane fibers flat in a dust-free environment and dry them in a vacuum drying oven at 60°C for 10 hours. After taking them out, cut them into 30 cm membrane fibers with dust-free scissors. Measure the outer diameter as 500 μm, the inner diameter as 300 μm, the thickness of the base membrane layer as 100 μm, and the thickness of the selective permeation layer as 0.5 μm.

[0066] Example 2

[0067] This embodiment provides a hollow fiber oxygen-enriched membrane, which differs from Embodiment 1 in that: the raw materials for preparing the porous base membrane layer include, by weight, 110 parts of polysulfone, 10 parts of tetraethyl orthosilicate, 3 parts of nano titanium dioxide, 1.5 parts of meta-aramid fiber micro powder, and 0.4 parts of chitosan-grafted graphene oxide.

[0068] The raw materials for preparing the selectively permeable layer, by weight, include: 13 parts polyetherimide, 0.2 parts nano-zirconia, 0.3 parts chopped glass fiber, 0.1 parts chitosan, and 0.4 parts quaternary ammonium salt functionalized metal-organic framework material.

[0069] Comparative Example 1

[0070] This comparative example provides a hollow fiber oxygen-enriched membrane, which differs from Example 1 in that the raw materials for preparing the porous base membrane layer, by weight, include: 100 parts of polysulfone, 12 parts of tetraethyl orthosilicate, 4 parts of nano-titanium dioxide, 3 parts of meta-aramid fiber micro powder, and 0.1 parts of chitosan-grafted graphene oxide.

[0071] The raw materials for preparing the selectively permeable layer, by weight, include: 11 parts polyetherimide, 0.3 parts nano-zirconia, 0.1 parts chopped glass fiber, 0.15 parts chitosan, and 0.25 parts quaternary ammonium salt functionalized metal-organic framework material.

[0072] Comparative Example 2

[0073] This comparative example provides a hollow fiber oxygen-enriched membrane, which differs from Example 1 in that the raw materials for preparing the porous base membrane layer, by weight, include: 100 parts of polysulfone, 12 parts of tetraethyl orthosilicate, 4 parts of nano-titanium dioxide, 1 part of meta-aramid fiber micro powder, and 0.6 parts of chitosan-grafted graphene oxide.

[0074] The raw materials for preparing the selectively permeable layer, by weight, include: 11 parts polyetherimide, 0.01 parts nano-zirconia, 0.01 parts chopped glass fiber, 0.15 parts chitosan, and 1 part quaternary ammonium salt functionalized metal-organic framework material.

[0075] Comparative Example 3

[0076] This comparative example provides a hollow fiber oxygen-enriched membrane, which differs from Example 1 in that chitosan-grafted graphene oxide is replaced with polyethylene glycol.

[0077] Comparative Example 4

[0078] This comparative example provides a hollow fiber oxygen-enriched membrane, which differs from Example 1 in that the quaternary ammonium salt functionalized metal-organic framework material is replaced with lithium chloride.

[0079] Comparative Example 5

[0080] This comparative example provides a hollow fiber oxygen-enriched membrane, which differs from Example 1 in that:

[0081] In the preparation of hollow fiber oxygen-enriched membrane, step (3) is replaced by: adding polyetherimide, nano-zirconia, glass fiber chopped filaments, chitosan, and quaternary ammonium salt functionalized metal-organic framework material into N-methylpyrrolidone. The amount of NMP is 20 times the total mass of all solid raw materials. Stir at room temperature for 2 hours to obtain a composite solution. The dried porous hollow fiber base membrane is evenly spread on a dust-free plate. The composite solution is dipped in a fine brush and evenly coated on the outer surface of the hollow fiber base membrane so that the surface is evenly covered with a layer of composite solution. Immediately after coating, the membrane fibers are placed in a 25°C environment and left to stand for 2 hours to allow the solvent to evaporate. A selective permeable layer is gradually formed on the membrane surface.

[0082] Performance testing

[0083] The hollow fiber oxygen-enriched membranes prepared in Examples 1-2 and Comparative Examples 1-5 were subjected to performance tests, and the test methods are as follows:

[0084] Oxygen / nitrogen selectivity and oxygen permeation flux (GPU): Test method: The prepared membrane fibers are assembled into a single membrane test device. Under the conditions of 25°C and inlet pressure of 0.2 MPa, air is used as the feed gas to measure the permeation rate of oxygen and nitrogen through the membrane, and the selectivity and flux are calculated.

[0085] Oxygen / nitrogen selectivity = membrane permeation rate for oxygen / membrane permeation rate for nitrogen.

[0086] Tensile strength: Refer to GB / T 1040.3-2006. Test method: Cut 10 membrane filaments and stretch them at a rate of 50 mm / min using an electronic tensile testing machine until they break. Record the maximum tensile strength.

[0087] Antifouling performance: Test method: The membrane fibers were loaded into the gas separation membrane test device, and 100 mg / L bovine serum albumin (BSA) aqueous solution was used as the standard fouling solution. Air was introduced and the operating pressure was maintained at 0.2 MPa and temperature at 25℃ for 24 hours. The oxygen flux of the membrane before and after the test was recorded respectively. The flux retention rate = (flux after operation / initial flux) × 100% was used to evaluate the antifouling ability of the membrane.

[0088] The test results are shown in Table 1.

[0089] Table 1 Performance Test Results

[0090]

[0091] The above results show that the hollow fiber oxygen-enriched membranes prepared in Examples 1 and 2 both exhibit excellent separation performance, mechanical properties, and antifouling properties, indicating that the membranes have good long-term operational stability.

[0092] In Comparative Example 1, the excessive amount of meta-aramid fiber powder and the low content of chitosan-grafted graphene oxide resulted in a decrease in membrane density and hydrophilicity. The gas separation performance and mechanical properties were significantly lower than those of the Example, and the antifouling ability was insufficient.

[0093] In Comparative Example 2, the addition of nano-zirconia and glass fiber chopped strands was too low, while the content of quaternary ammonium salt functionalized metal-organic framework material was too high, resulting in uneven membrane structure and increased porosity. This manifested as a decrease in both selectivity and flux, as well as a decrease in flux retention.

[0094] In Comparative Example 3, when polyethylene glycol was used to replace chitosan-grafted graphene oxide, the overall interfacial bonding and structural uniformity of the membrane material deteriorated, the antifouling properties decreased, and the selectivity and flux were lower than those of the Example.

[0095] In Comparative Example 4, replacing the quaternary ammonium salt functionalized metal-organic framework material with lithium chloride weakened the molecular sieving effect and surface charge regulation ability of the membrane, reduced gas separation performance and flux, and also reduced the antifouling performance to some extent.

[0096] Comparative Example 5 used a coating method instead of in-situ composite, but the membrane layer bonding was weak and the density was insufficient, resulting in a significant reduction in mechanical properties and selectivity. The long-term operational stability and flux retention of the membrane also deteriorated.

[0097] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A hollow fiber oxygen-enriched membrane, the membrane body is composed of two layers, the inner layer being a porous base membrane layer and the outer layer being a selectively permeable layer; The raw materials for preparing the porous base film layer, by weight, include: Polysulfone 80-120 parts, tetraethyl orthosilicate 8-16 parts, nano titanium dioxide 2-6 parts, meta-aramid fiber micro powder 0.5-2 parts, chitosan grafted graphene oxide 0.2-1 parts; The raw materials for preparing the selectively permeable layer, by weight, include: 8-15 parts of polyetherimide, 0.1-0.5 parts of nano-zirconia, 0.05-0.3 parts of chopped glass fiber, 0.05-0.3 parts of chitosan, and 0.05-0.5 parts of quaternary ammonium salt functionalized metal-organic framework material; The preparation method of hollow fiber oxygen-enriched membrane includes the following steps: (1) Polysulfone, tetraethyl orthosilicate, nano titanium dioxide, meta-aramid fiber powder, and chitosan-grafted graphene oxide were added to N-methylpyrrolidone, stirred, and allowed to stand to remove bubbles, thus preparing a porous membrane spinning solution. (2) The porous base membrane spinning solution is extruded through a concentric nozzle, stretched in an air section, and then solidified in a 5-15℃ deionized water coagulation bath to obtain hollow fiber filaments. After the filaments are formed, they are rinsed with deionized water and dried to obtain a porous hollow fiber base membrane. (3) Dissolve polyetherimide, nano-zirconia, glass fiber chopped filaments, chitosan, and quaternary ammonium salt functionalized metal-organic framework material in N-methylpyrrolidone, stir, and obtain a composite solution; immerse the porous hollow fiber base membrane in the composite solution, remove it after immersion for 1 to 3 hours, allow it to stand and react to form a selective permeable layer, and obtain the composite membrane filaments; (4) Wash and dry the composite membrane fibers to obtain a hollow fiber oxygen-enriched membrane.

2. The hollow fiber oxygen-enriched membrane according to claim 1, characterized in that: The thickness of the porous base film layer is 60–120 μm, and the thickness of the selectively permeable layer is 0.2–1 μm.

3. The hollow fiber oxygen-enriched membrane according to claim 1, characterized in that: The hollow fiber oxygen-enriched membrane has an outer diameter of 350–600 μm, an inner diameter of 200–350 μm, and a length of 20–60 cm.

4. The hollow fiber oxygen-enriched membrane according to claim 1, characterized in that: The chitosan-grafted graphene oxide was prepared according to the following method: (1) Graphene oxide and deionized water were mixed to obtain a graphene oxide dispersion. 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide were added to the graphene oxide dispersion and stirred to obtain an activated graphene oxide dispersion. (2) Add the activated graphene oxide dispersion to the acetic acid solution of chitosan to obtain a mixture, adjust the pH of the mixture to 5-6, and stir the reaction. (3) After the reaction is complete, the product is washed and dried to obtain chitosan-grafted graphene oxide.

5. The hollow fiber oxygen-enriched membrane according to claim 4, characterized in that: In step (1), the mass ratio of graphene oxide to deionized water is 1:50 to 100, the mass ratio of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride to graphene oxide is 1:10 to 20, and the mass ratio of N-hydroxysuccinimide to 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride is 1:2 to 3; in step (2), the mass ratio of graphene oxide to chitosan is 1:1 to 5; and the stirring reaction time is 6 to 24 hours.

6. The hollow fiber oxygen-enriched membrane according to claim 1, characterized in that: The quaternary ammonium salt functionalized metal-organic framework material is prepared according to the following method: (1) Dissolve zinc nitrate hexahydrate and 2-methylimidazole in deionized water, stir, let stand, precipitate is generated, collect the precipitate, wash and dry to obtain ZIF-8 powder; (2) Disperse ZIF-8 powder and trimethyl[3-(trimethoxysilyl)propyl]ammonium chloride in methanol, stir and react. After the reaction is complete, collect the solid product, wash and dry it to obtain quaternary ammonium salt functionalized metal-organic framework material.

7. The hollow fiber oxygen-enriched membrane according to claim 6, characterized in that: The molar ratio of zinc nitrate hexahydrate to 2-methylimidazole in step (1) is 1:1 to 2; the mass ratio of ZIF-8 powder to trimethyl[3-(trimethoxysilyl)propyl]ammonium chloride in step (2) is 1:0.05 to 0.

5.

8. The hollow fiber oxygen-enriched membrane according to claim 6, characterized in that: The mass of N-methylpyrrolidone in step (1) is 5 to 10 times the total mass of polysulfone, tetraethyl orthosilicate, nano titanium dioxide, meta-aramid fiber powder, and chitosan-grafted graphene oxide; the stirring time is 1 to 3 hours, and the standing time is 2 to 6 hours.

9. The hollow fiber oxygen-enriched membrane according to claim 8, characterized in that: The mass of N-methylpyrrolidone in step (3) is 10 to 30 times the total mass of polyetherimide, nano-zirconia, glass fiber chopped strands, chitosan and quaternary ammonium salt functionalized metal-organic framework material; the static reaction time is 1 to 3 hours.

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