Hollow fiber oxygen-enriched membrane and preparation method thereof

Abstract

The invention belongs to the technical field of membrane separation and material engineering, and particularly relates to a hollow fiber oxygen-enriched membrane and a preparation method thereof. The oxygen-enriched membrane is formed by compounding a porous base membrane layer and a selective permeable layer. The porous base membrane layer takes polysulfone, tetraethoxysilane, nano titanium dioxide, meta-aramid fiber micro powder and chitosan grafted graphene oxide as main raw materials, and has excellent mechanical properties and structural stability. The selective permeation layer contains polyetherimide, nano zirconium oxide, glass fiber chopped strands, chitosan and a quaternary ammonium salt functionalized metal organic framework material, so that the gas selectivity and the anti-pollution capacity of the membrane are remarkably improved. The oxygen-enriched membrane prepared through dry-wet spinning and a composite impregnation process has the advantages of efficient separation, durability in operation, easiness in industrial production and the like, and is suitable for various occasions such as medical occasions and industrial occasions.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane separation and material engineering, and in particular relates to a hollow fiber oxygen-enriched membrane and a preparation method thereof. Background Art

[0002] As an important representative of contemporary high-efficiency gas separation technology, hollow fiber gas separation membranes have played an increasingly important role in the fields of medical oxygen production, household air purification, industrial oxygen enrichment, etc. Existing hollow fiber oxygen-enriched membranes are mostly made of polymer materials such as polysulfone and polyethersulfone, and are prepared through precision spinning processes and densification treatments. However, in actual applications, such membrane materials generally face problems 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, and the expansion of the microstructure leads to a decrease in separation performance. On the other hand, the mechanical strength and pollution resistance of the membrane are insufficient, and it is easily contaminated by impurities and particles during continuous operation, resulting in reduced flux and shortened lifespan. Especially in high-demand occasions such as medical or confined spaces, safety and reliability are difficult to guarantee.

[0003] Furthermore, while some products attempt to enhance mechanical strength and heat resistance by incorporating inorganic nanoparticles or fiber reinforcements, poor dispersion and interfacial compatibility between the different components often lead to uneven membrane structures and low yields during mass production. Existing dry-wet spinning and surface treatment processes place extremely stringent requirements on equipment and parameter control, and products are prone to problems such as uneven pore size distribution and delamination of the dense layer, hindering the large-scale, low-cost production of hollow fiber oxygen-enriched membranes.

[0004] More significantly, the current market for high-performance hollow fiber oxygen-enriched membranes is dominated by foreign companies in Europe, the United States, and Japan. Domestically produced membranes still lag behind internationally advanced levels in terms of high-temperature resistance, mechanical properties, anti-pollution, and customization. Imported membranes are expensive and have long lead times, severely impacting the independent control and widespread application of domestic oxygen production equipment. Faced with the growing demand for oxygen enrichment, existing technologies urgently need breakthroughs in material systems, membrane structure innovation, and overall performance enhancement. Therefore, developing a hollow fiber oxygen-enriched membrane with a novel structure, superior performance, and suitability for industrial production has become a critical issue that the industry urgently needs to address. Summary of the Invention

[0005] The present invention aims to provide a hollow fiber oxygen-enriching membrane and its preparation method, aiming to address the deficiencies of existing oxygen-enriching membranes in terms of high-temperature resistance, mechanical strength, pollution resistance, and gas separation efficiency. Through innovative design of membrane structure and components, the present invention produces a hollow fiber oxygen-enriching membrane with excellent performance, strong stability, and suitability for industrial production, providing a more efficient and reliable solution for gas separation and oxygen enrichment applications.

[0006] In order to achieve the above object, the present invention provides the following technical solutions: The first aspect of the present invention provides a hollow fiber oxygen-enriched membrane, wherein the membrane body is composed of two layers, the inner layer is a porous base membrane layer, and the outer layer is a selective permeation layer; The raw materials for preparing the porous base membrane layer include, by weight, 80 to 120 parts of polysulfone, 8 to 16 parts of tetraethyl orthosilicate, 2 to 6 parts of nano-titanium dioxide, 0.5 to 2 parts of meta-aramid fiber powder, and 0.2 to 1 part of chitosan grafted graphene oxide; The raw materials for preparing the selective transmission layer include, by weight, 8 to 15 parts of polyetherimide, 0.1 to 0.5 parts of nano zirconium oxide, 0.05 to 0.3 parts of chopped glass fiber, 0.05 to 0.3 parts of chitosan, and 0.05 to 0.5 parts of quaternary ammonium salt functionalized metal organic framework materials (Q-MOFs).

[0007] Furthermore, the thickness of the porous base membrane layer is 60 to 120 μm, and the thickness of the selective transmission layer is 0.2 to 1 μm.

[0008] Furthermore, the outer diameter of the hollow fiber oxygen-enriched membrane is 350-600 μm, the inner diameter is 200-350 μm, and the length is 20-60 cm.

[0009] Furthermore, the chitosan-grafted graphene oxide is prepared according to the following method: (1) Graphene oxide (GO) and deionized water were mixed to obtain a GO dispersion, and 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; (2) Add the activated GO dispersion to the chitosan acetic acid solution to obtain a mixed solution, adjust the pH of the mixed solution to 5-6, and stir the reaction; (3) After the reaction is completed, the product is washed and dried to obtain chitosan-grafted graphene oxide.

[0010] Furthermore, 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).

[0011] Furthermore, in step (2), the mass ratio of GO to chitosan is 1:(1-5); and the stirring reaction time is 6-24 hours.

[0012] In the present invention, the introduction of chitosan grafted graphene oxide greatly improves the overall performance of the hollow fiber oxygen-enriched membrane. From the perspective of material microstructure and interface regulation, GO itself has rich oxygen-containing functional groups and a large specific surface area, which can provide good microscopic support and dispersion for the membrane material. However, bare GO often has problems such as insufficient compatibility and agglomeration in the polymer matrix, which affects the structural uniformity and long-term performance of the membrane. Through the covalent grafting of chitosan molecules, a large number of amino groups and polysaccharide chain segments are introduced to the surface of the GO layer, which not only gives GO higher hydrophilicity and polarity, but also forms a strong interfacial force with polymer materials such as polysulfone, greatly enhancing the dispersibility and interfacial bonding of GO in the membrane, thereby improving the structural integrity and microscopic uniformity of the membrane material.

[0013] Furthermore, chitosan-grafted GO helps regulate the membrane's porous structure during the membrane formation process, 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 also creating a molecular sieving effect for large molecules and impurity gases, thereby improving the membrane's gas separation selectivity and flux. While GO sheets themselves possess excellent mechanical properties, the introduction of chitosan further enhances the load transfer between the matrix and the nanomaterial through molecular chain entanglement and interfacial bonding, effectively improving the membrane's strength and toughness, enabling the membrane to maintain a long lifespan and stability despite repeated pressure shocks and complex operating conditions.

[0014] In addition, chitosan naturally has good hydrophilicity and antibacterial and anti-pollution properties. When it is evenly grafted onto the GO sheet, it can greatly improve the surface hydrophilicity of the membrane material, reduce the adsorption of organic pollutants and microorganisms, and extend the clean operation cycle of the membrane. It is very suitable for application fields with high requirements for hygiene and stability, such as medical, drinking water and high-end oxygen enrichment supply.

[0015] Furthermore, the quaternary ammonium salt functionalized metal organic framework material is prepared according to the following method: (1) Dissolve zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and 2-methylimidazole (C4H6N2) in deionized water, stir, and allow to stand to form a precipitate. Collect the precipitate, wash, and dry to obtain ZIF-8 powder. (2) Dispersing ZIF-8 powder and trimethyl[3-(trimethoxysilyl)propyl]ammonium chloride in methanol, stirring and reacting, collecting the solid product after the reaction, washing, and drying to obtain a quaternary ammonium salt functionalized metal organic framework material.

[0016] Furthermore, the molar ratio of the zinc nitrate hexahydrate (Zn(NO3)2·6H2O) to 2-methylimidazole (C4H6N2) in step (1) is 1:(1-2).

[0017] 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).

[0018] The present application introduces a quaternary ammonium salt functional group on the surface of the ZIF-8 material, which not only enhances the dispersibility of the material in the polymer system and the interfacial compatibility with the organic matrix, but also endows the material with unique surface charge and anti-pollution ability. The cationic group of the quaternary ammonium salt structure can effectively inhibit the adsorption and deposition of negatively charged impurity molecules, improve the anti-fouling and anti-biofouling performance of the membrane surface, and prolong the stable operation period of the membrane under complex working conditions. At the same time, the MOF modified by the quaternary ammonium salt optimizes the environment of the molecular sieve channel at the micro level, making oxygen molecules more easily pass through, while forming a stronger barrier to other gases such as nitrogen and macromolecular impurities, thereby further improving the selective permeation efficiency of oxygen.

[0019] In addition, after being functionalized by the quaternary ammonium salt, the hydrophilicity and dispersibility of the MOF are enhanced, and a more uniform and dense functional selective layer can be formed in the membrane material, which not only helps to improve the gas separation precision and working stability of the membrane, but also provides a guarantee for the large-scale preparation and long-term application of the membrane module.

[0020] The second aspect of the present application provides a preparation method of the hollow fiber oxygen-enriched membrane, comprising the following steps: (1) adding polysulfone, tetraethyl orthosilicate, nano titanium dioxide, meta-aramid fiber powder, and chitosan grafted graphene oxide into N-methyl pyrrolidone, stirring, and standing to degas, to prepare a porous base membrane spinning solution; (2) extruding the porous base membrane spinning solution through a concentric nozzle, stretching through an air section, and then entering a 5-15 DEG C deionized water coagulation bath for solidification to obtain a hollow fiber precursor, rinsing the precursor after forming, drying, and obtaining a porous hollow fiber base membrane; (3) dissolving polyetherimide, nano zirconium oxide, glass fiber short cut silk, chitosan, and quaternary ammonium salt functionalized metal organic framework material in N-methyl pyrrolidone, stirring to obtain a composite solution, immersing the porous hollow fiber base membrane in the composite solution, taking out after 1-3 hours of immersion, and standing to react to form a selective permeation layer, to obtain a composite membrane filament; (4) washing and drying the composite membrane filament to obtain a hollow fiber oxygen-enriched membrane.

[0021] Further, the mass of the N-methyl pyrrolidone in step (1) is 5-10 times the total mass of the polysulfone, tetraethyl orthosilicate, nano titanium dioxide, meta-aramid fiber powder, and chitosan grafted graphene oxide; the stirring time is 1-3 hours, and the standing time is 2-6 hours.

[0022] Furthermore, the mass of the N-methylpyrrolidone in step (3) is 10 to 30 times the total mass of the polyetherimide, nano-zirconium oxide, glass fiber chopped strands, chitosan and quaternary ammonium salt functionalized metal organic framework material; and the standing reaction time is 1 to 3 hours.

[0023] The hollow fiber oxygen-enriched membrane of the present invention achieves efficient and stable oxygen enrichment and separation effects through a unique multi-component collaborative design and a scientific two-layer composite structure. In the porous base membrane layer, polysulfone is a polymer skeleton material, which gives the membrane excellent film-forming properties and mechanical strength, and is the core support of the overall structure. Ethyl orthosilicate generates silicon dioxide in situ through a sol-gel process, which improves the structural density and peeling strength of the membrane and enhances 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 microscopic pore structure and gas permeability of the membrane. Meta-aramid fiber powder, as a high-strength organic filler, further enhances the overall toughness and corrosion resistance of the membrane, allowing the base membrane to remain stable under complex working conditions. The introduction of chitosan grafted graphene oxide not only greatly improves the interface bonding and dispersion uniformity between nanomaterials and polymers, but also improves the oxygen permeation rate and separation selectivity by regulating the microscopic porous structure and enhancing the molecular sieve effect, while giving the base membrane good hydrophilicity and anti-pollution properties, thereby extending the service life of the membrane filament.

[0024] In the selective permeation layer, polyetherimide serves as the backbone of the high-performance separation membrane, boasting excellent chemical stability and dense film-forming properties. The addition of nano-zirconium oxide and chopped glass fiber strands provides the selective layer with improved compactness, mechanical strength, and temperature resistance. Chitosan, a natural anti-fouling agent, improves the membrane's hydrophilicity and resistance to biofouling, effectively preventing impurity clogging and biofilm contamination. The quaternary ammonium salt-functionalized metal-organic framework further enhances molecular sieving accuracy and the membrane's surface anti-fouling capabilities. Through interfacial charge regulation, it inhibits impurity adsorption and optimizes the preferential permeation path for oxygen at the microscopic level.

[0025] In terms of preparation methods, this invention combines dry-wet spinning with interfacial bonding, resulting in a gentle process with controllable parameters, facilitating large-scale continuous production. The composite selective layer utilizes an impregnation and static reaction process, ensuring a dense membrane structure and strong interfacial bonding, significantly improving product consistency and operability for industrial applications.

[0026] Compared with the prior art, the advantages and beneficial effects of the present invention are: The hollow fiber oxygen-enriched membrane of the present invention has achieved significant innovation and improvement in structure, materials and performance. The porous base membrane layer adopts chitosan grafted graphene oxide in collaboration with aramid micropowder, nano-titanium dioxide and other components, which effectively enhances the mechanical strength, structural density and durability of the membrane body, optimizes the microscopic pores, provides a low-resistance channel for oxygen molecules, and greatly improves the selectivity of gas separation. The quaternary ammonium salt functionalized metal organic framework material and nano-zirconium oxide specially introduced in the selective permeation layer not only enhance the molecular sieving and interface charge regulation capabilities, but also significantly improves the anti-pollution, anti-biological contamination and operational stability of the membrane surface. Actual test results show that the oxygen / nitrogen selectivity, oxygen flux, mechanical properties and anti-pollution ability of the membrane of the present invention are better than those of the comparative example and existing similar products, and can operate stably for a long time and maintain high-efficiency separation performance. The preparation process parameters are controllable and suitable for large-scale production, providing a more reliable and efficient new membrane material solution for high-end medical and industrial oxygen-enriched applications. DETAILED DESCRIPTION

[0027] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0028] Unless otherwise specified, the raw materials used in the examples are common commercially available products, and the following sources are for illustrative purposes only.

[0029] Polysulfone was purchased from Ensinger Engineering Plastics (Shanghai) Co., Ltd., Udel® PSU.

[0030] Nano-titanium dioxide was purchased from Suzhou Youzi Nanomaterials Co., Ltd. with an average particle size of 20-30 nm.

[0031] Meta-aramid fiber powder was purchased from DuPont, Kevlar® type powder.

[0032] Polyetherimide was purchased from DuPont as Aurum®.

[0033] Nano-zirconia was purchased from Suzhou Youzi Nanomaterials Co., Ltd. with an average particle size of 5-30 nm.

[0034] Glass fiber chopped strands were purchased from China Jushi Co., Ltd., ECER13-1200.

[0035] Graphene oxide was purchased from Changzhou Sixth Element Material Technology, with a sheet diameter of 0.5-5 μm and a thickness of 1.2 nm.

[0036] Polyethylene glycol was purchased from Jiangsu Haian Petrochemical Plant, PEG-4000.

[0037] Embodiment 1 The embodiment provides a hollow fiber oxygen-enriched membrane, the membrane body is composed of an inner layer and an outer layer, the inner layer is a porous base membrane layer, and the outer layer is a selective permeation layer; The preparation raw materials of the porous base membrane layer include, in parts by weight: 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. The preparation raw materials of the selective permeation layer include, in parts by weight: 11 parts of polyetherimide, 0.3 parts of nano zirconium oxide, 0.1 parts of glass fiber short cut silk, 0.15 parts of chitosan and 0.25 parts of quaternary ammonium salt functionalized metal organic framework material.

[0038] The chitosan grafted graphene oxide is prepared by the following method: (1) 1.0 g of graphene oxide (GO) dry powder is weighed and added to 80 mL of deionized water, and an ultrasonic dispersing instrument is used for dispersion for 30 minutes to obtain a GO dispersion liquid, then 0.06 g of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and 0.02 g of N-hydroxysuccinimide (NHS) are weighed, the NHS is dissolved in 5 mL of deionized water, and then the EDC is slowly added to the GO dispersion liquid, and stirring is performed at room temperature for 40 minutes to fully activate the carboxyl groups on the surface of the GO, thereby obtaining an activated GO dispersion liquid.

[0039] (2) 2.0 g of chitosan is weighed and dissolved in 100 mL of 1.0 wt% glacial acetic acid solution, and magnetic stirring is performed for 6 hours until the chitosan is completely dissolved, thereby obtaining a chitosan acetic acid solution, the activated GO dispersion liquid is slowly poured into the chitosan acetic acid solution while stirring, then the mixed solution is continuously stirred at 25°C for 12 hours, during the reaction, the pH of the mixed solution is adjusted to 5.5 by using a 1 mol / L sodium hydroxide solution, and the solution is slowly added dropwise in three times with an interval of 10 minutes each time, and a pH test paper is used for real-time detection to ensure that the pH is between 5 and 6.

[0040] (3) After the reaction is completed, the mixed solution is transferred to a centrifuge tube and placed in a refrigerated centrifuge, and centrifugation is performed at 8000 rpm for 15 minutes, and the supernatant is discarded, and deionized water is repeatedly resuspended and centrifuged for three times, and finally the washed precipitate is spread on a glass culture dish and placed in a 40°C vacuum drying oven for drying for 16 hours, thereby obtaining the chitosan grafted graphene oxide.

[0041] The quaternary ammonium salt functionalized metal organic framework material is prepared by the following method: (1) Dissolve 10 mmol of Zn(NO3)2·6H2O in 100 mL of deionized water to obtain solution A, and dissolve 15 mmol of C4H6N2 in 100 mL of deionized water to obtain solution B. Pour solution B into solution A and immediately stir at room temperature for 30 minutes using a magnetic stirrer. After stirring, let the reaction solution stand for 4 hours. A precipitate gradually forms and is collected by centrifugation for 10 minutes. The precipitate is resuspended in deionized water and washed by centrifugation three times. It is then resuspended in anhydrous methanol and washed by centrifugation twice to remove impurities and unreacted products. The washed precipitate is spread on a glass culture dish and dried in a vacuum drying oven at 60°C for 12 hours to obtain ZIF-8 powder.

[0042] (2) Weigh 1.0 g of dried ZIF-8 powder and add it to 50 mL of anhydrous methanol. Ultrasonic dispersion is performed for 15 minutes to fully disperse it. Weigh 0.1 g of trimethyl[3-(trimethoxysilyl)propyl]ammonium chloride and add it to the dispersed ZIF-8 methanol suspension. Stir and react at room temperature for 12 hours. After the reaction is completed, centrifuge for 10 minutes to collect the product and wash it three times with anhydrous methanol. Finally, spread the washed solid in a glass culture dish and dry it in a vacuum drying oven at 40°C for 10 hours to obtain a quaternary ammonium salt functionalized metal-organic framework material.

[0043] The hollow fiber oxygen-enriched membrane was prepared as follows: (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 mixed system was stirred at 25°C for 2 hours. After stirring, the mixed solution was allowed to stand for 4 hours for degassing until there were no obvious bubbles in the system, thereby obtaining a porous base membrane spinning solution.

[0044] (2) The spinning solution was loaded into a hollow fiber membrane spinning machine using a concentric nozzle. The outer layer was fed with spinning solution and the inner layer was fed with 10% polyethylene glycol aqueous solution. The core liquid flow rate was 0.4 mL / min and the spinning solution flow rate was 1.0 mL / min. During spinning, the air section under the nozzle was 20 cm. After the spinning solution jet was stretched through the air section, it directly entered a 10°C deionized water coagulation bath and the flow rate was kept constant. After the raw silk stayed in the coagulation bath for 40 minutes, it was carefully moved to a flowing deionized water tank with a non-woven cloth and rinsed for 6 hours to ensure that all NMP and low molecular weight impurities were removed. The washed hollow fiber membrane was dried with a non-woven cloth on the surface, evenly spread on a non-stick plate, and sent to a 60°C vacuum drying oven for drying for 12 hours to obtain a porous hollow fiber base membrane.

[0045] (3) Add polyetherimide, nano-zirconium oxide, glass fiber chopped strands, chitosan, and quaternary ammonium salt functionalized metal organic framework materials into N-methylpyrrolidone, with the amount of NMP being 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-based membrane in the composite solution to ensure complete infiltration. Maintain immersion at room temperature for 2 hours, then clamp one end of the membrane fiber with a clamp 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 permeation layer on the surface of the membrane fiber.

[0046] (4) The composite membrane filaments were placed in a beaker of deionized water and rinsed three times, with fresh water replaced each time. The membrane filaments were gently stirred for 10 minutes to remove excess solvent and unreacted components on the surface. The washed membrane filaments were flattened in a dust-free environment and placed in a vacuum drying oven at 60°C for 10 hours. After being taken out, they were cut into 30 cm membrane filaments with dust-free scissors. The outer diameter was 500 μm, the inner diameter was 300 μm, the base membrane layer thickness was 100 μm, and the selective permeation layer thickness was 0.5 μm.

[0047] Example 2 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, in parts by weight, include: 110 parts of polysulfone, 10 parts of tetraethyl orthosilicate, 3 parts of nano-titanium dioxide, 1.5 parts of meta-aramid fiber powder, and 0.4 parts of chitosan-grafted graphene oxide; The raw materials for preparing the selective permeation layer include, by weight, 13 parts of polyetherimide, 0.2 parts of nano zirconium oxide, 0.3 parts of chopped glass fiber, 0.1 parts of chitosan, and 0.4 parts of quaternary ammonium salt functionalized metal organic framework material.

[0048] Comparative Example 1 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, in parts by weight, include: 100 parts of polysulfone, 12 parts of tetraethyl orthosilicate, 4 parts of nano-titanium dioxide, 3 parts of meta-aramid fiber powder, and 0.1 part of chitosan-grafted graphene oxide; The raw materials for preparing the selective transmission layer include, by weight, 11 parts of polyetherimide, 0.3 parts of nano zirconium oxide, 0.1 parts of chopped glass fiber, 0.15 parts of chitosan, and 0.25 parts of quaternary ammonium salt functionalized metal organic framework material.

[0049] Comparative Example 2 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, in parts by weight, include: 100 parts of polysulfone, 12 parts of tetraethyl orthosilicate, 4 parts of nano-titanium dioxide, 1 part of meta-aramid fiber powder, and 0.6 parts of chitosan-grafted graphene oxide; The raw materials for preparing the selective permeation layer include, by weight, 11 parts of polyetherimide, 0.01 parts of nano zirconium oxide, 0.01 parts of chopped glass fiber, 0.15 parts of chitosan, and 1 part of quaternary ammonium salt functionalized metal organic framework material.

[0050] Comparative Example 3 This comparative example provides a hollow fiber oxygen-enriched membrane, which differs from Example 1 in that chitosan-grafted graphene oxide is replaced by polyethylene glycol.

[0051] Comparative Example 4 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 by lithium chloride.

[0052] Comparative Example 5 This comparative example provides a hollow fiber oxygen-enriched membrane, which differs from Example 1 in that: In the preparation process of the hollow fiber oxygen-enriched membrane, step (3) is replaced by: adding polyetherimide, nano-zirconium oxide, glass fiber chopped strands, chitosan, and quaternary ammonium salt functionalized metal organic framework materials to N-methylpyrrolidone, with the amount of NMP being 20 times the total mass of all solid raw materials, stirring 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 board, and the composite solution is dipped with 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. After coating, the membrane fiber is immediately placed in an environment of 25°C and allowed to stand for 2 hours to allow the solvent to evaporate, and a selective permeation layer is gradually formed on the membrane surface.

[0053] Performance Testing The hollow fiber oxygen-enriched membranes prepared in Examples 1-2 and Comparative Examples 1-5 were subjected to performance tests using the following methods: Oxygen / nitrogen selectivity and oxygen permeation flux (GPU): Test method: Assemble the prepared membrane filaments into a single membrane test device. At 25°C and an inlet pressure of 0.2 MPa, using air as the raw gas, measure the membrane permeation rates for oxygen and nitrogen, respectively, and calculate the selectivity and flux.

[0054] Oxygen / nitrogen selectivity = membrane permeability to oxygen / membrane permeability to nitrogen.

[0055] Tensile strength: Refer to GB / T 1040.3-2006. Test method: Cut 10 membrane filaments and stretch them using an electronic tensile testing machine at a rate of 50 mm / min until they break. Record the maximum tensile strength.

[0056] Anti-fouling performance: Test method: The membrane fibers were installed in a gas separation membrane test device, and a 100 mg / L bovine serum albumin (BSA) aqueous solution was used as the standard contaminant liquid. Air was introduced, and the operating pressure was maintained at 0.2 MPa and the temperature was 25°C. The test was continued for 24 hours. The oxygen flux of the membrane was recorded before and after the test. The flux retention rate = (flux after operation / initial flux) × 100% was used to evaluate the anti-fouling ability of the membrane.

[0057] The test results are shown in Table 1.

[0058] Table 1 Performance test results The above results show that the hollow fiber oxygen-enriched membranes prepared in Example 1 and Example 2 both exhibit excellent separation performance, mechanical properties and anti-fouling performance, indicating that the membranes have good long-term operation stability.

[0059] In Comparative Example 1, the amount of meta-aramid fiber powder added is too high and the content of chitosan grafted graphene oxide is low, resulting in decreased density and hydrophilicity of the membrane, and the gas separation performance and mechanical properties are significantly lower than those in the embodiment, and the anti-pollution ability is insufficient.

[0060] In Comparative Example 2, the addition amount of nano-zirconium oxide and glass fiber chopped strands was too low, and the content of quaternary ammonium salt functionalized metal organic framework material was too high, resulting in uneven membrane structure and increased porosity, which was manifested as reduced selectivity and flux, and a decrease in flux retention rate.

[0061] In Comparative Example 3, polyethylene glycol was used instead of chitosan grafted graphene oxide, and the overall interface bonding strength and structural uniformity of the membrane material became worse, and the anti-pollution property decreased, resulting in lower selectivity and flux than the examples.

[0062] In Comparative Example 4, the quaternary ammonium salt functionalized metal organic framework material was replaced with lithium chloride. The molecular sieving effect and surface charge regulation ability of the membrane were weakened, the gas separation performance and flux were reduced, and the anti-pollution performance was also reduced to a certain extent.

[0063] Comparative Example 5 uses a coating method instead of in-situ compounding. The membrane layer is not firmly bonded and the density is insufficient. The mechanical properties and selectivity are significantly reduced. The long-term operation stability and flux retention rate of the membrane are also deteriorated.

[0064] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A hollow fiber oxygen-enriched membrane, the membrane body consists of two layers, the inner layer is a porous base membrane layer, and the outer layer is a selective permeation layer; The raw materials for preparing the porous base membrane 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 powder, and 0.2-1 part of chitosan grafted graphene oxide; The raw materials for preparing the selective transmission layer include, by weight, 8 to 15 parts of polyetherimide, 0.1 to 0.5 parts of nano zirconium oxide, 0.05 to 0.3 parts of chopped glass fiber, 0.05 to 0.3 parts of chitosan, and 0.05 to 0.5 parts of quaternary ammonium salt functionalized metal organic framework materials (Q-MOFs).

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

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

4. The hollow fiber oxygen-enriched membrane according to claim 1, characterized in that: The chitosan-grafted graphene oxide is prepared according to the following method: (1) Graphene oxide (GO) and deionized water were mixed to obtain a GO dispersion, and 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; (2) Add the activated GO dispersion to the chitosan acetic acid solution to obtain a mixed solution, adjust the pH of the mixed solution to 5-6, and stir the reaction; (3) After the reaction is completed, 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 (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); in step (2), the mass ratio of GO to chitosan is 1:(1-5); and the stirring reaction time is 6-24 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 (Zn(NO3)2·6H2O) and 2-methylimidazole (C4H6N2) in deionized water, stir, and allow to stand to form a precipitate. Collect the precipitate, wash, and dry to obtain ZIF-8 powder. (2) Dispersing ZIF-8 powder and trimethyl[3-(trimethoxysilyl)propyl]ammonium chloride in methanol, stirring and reacting, collecting the solid product after the reaction, washing, and drying to obtain a 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 the zinc nitrate hexahydrate (Zn(NO3)2·6H2O) to 2-methylimidazole (C4H6N2) in step (1) is 1:(1-2); the mass ratio of the ZIF-8 powder to trimethyl[3-(trimethoxysilyl)propyl]ammonium chloride in step (2) is 1:(0.05-0.5).

8. A method for preparing a hollow fiber oxygen-enriched membrane according to any one of claims 1 to 7, comprising the following steps: (1) Adding polysulfone, tetraethyl orthosilicate, nano-titanium dioxide, meta-aramid fiber powder, and chitosan grafted graphene oxide into N-methylpyrrolidone, stirring, and standing for degassing to prepare a porous base 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°C deionized water coagulation bath to obtain hollow fiber precursors. After the precursors are formed, they are rinsed with deionized water and dried to obtain a porous hollow fiber base membrane; (3) Dissolving polyetherimide, nano-zirconium oxide, chopped glass fiber, chitosan, and quaternary ammonium salt functionalized metal organic framework material in N-methylpyrrolidone and stirring to obtain a composite solution; immersing the porous hollow fiber-based membrane in the composite solution for 1 to 3 hours, then removing the porous hollow fiber-based membrane and allowing it to react to form a selective permeation layer, thereby obtaining a composite membrane fiber; (4) The composite membrane fibers are washed and dried to obtain hollow fiber oxygen-enriched membranes. Furthermore, the mass of the N-methylpyrrolidone in step (1) is 5 to 10 times the total mass of the 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 preparation method according to claim 8, characterized in that: In step (1), the mass of the N-methylpyrrolidone is 5 to 10 times the total mass of the 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.

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

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