High-selectivity high-mechanical-strength hollow fiber oxygen-enriched membrane and preparation method and application thereof

Abstract

The application discloses a kind of high selectivity high mechanical strength hollow fiber oxygen-enriched membrane and its preparation method and application, belong to oxygen separation material technical field.The preparation method includes: pretreatment polyether sulfone and solvent;Preparation casting solution, including polyether sulfone, organic solvent and non-solvent;Synthesis bismuth-strontium co-doped titanium-based perovskite type nano composite oxide as filler;Filler is added to casting solution by dry-wet spinning, phase separation control is carried out in gradient temperature coagulation bath;Post-processing includes washing, drying and high-temperature annealing.The obtained hollow fiber membrane has multi-level pore structure, oxygen-nitrogen selectivity is as high as 7 or more, tensile strength reaches 35MPa or more, with high permeation flux and excellent mechanical strength, suitable for shipborne oxygen enrichment system or medical oxygen supply equipment.

Description

Technical Field

[0001] This invention belongs to the field of oxygen separation materials technology, specifically relating to a highly selective hollow fiber oxygen-enriched membrane, its preparation method, and its application. Background Technology

[0002] Oxygen, as an important energy raw material, is widely used in various fields such as medicine, metallurgy, and aerospace. Oxygen-enriched air with an oxygen volume fraction of more than 21% is widely used in large ships at sea, such as for medical support, cutting and welding during emergency maintenance, oxygen for crew breathing, improving engine performance, and increasing the efficiency of wastewater biological treatment.

[0003] The current method of supplying oxygen to ships using gas cylinders can no longer meet the oxygen enrichment needs of modern large ships. Enriching and concentrating oxygen using air as a raw material is a more feasible approach. Currently available separation methods mainly include cryogenic, pressure swing adsorption, and membrane separation. Among them, membrane separation technology, as an emerging high technology, has the characteristics of low process cost, simple equipment operation, and high gas enrichment efficiency. Therefore, it is considered an ideal choice for shipborne high-purity oxygen preparation technology.

[0004] However, existing oxygen-enriched membrane materials generally suffer from problems such as difficulty in balancing selectivity and permeation flux, and insufficient mechanical strength, especially prone to performance degradation under complex marine environmental conditions. For example, Chinese patent application CN98113914.0 discloses a method for preparing a polyimide asymmetric hollow fiber membrane, including casting solution preparation and filamentation process, (1) the casting solution formula is as follows (weight percentage): polyimide 15-35%, low boiling point organic solvent 25-45%, polar organic solvent 30-60%; (2) filamentation: after the casting solution is filamentized by a spinning nozzle, it is purged with nitrogen gas at a relative humidity of 30-80% for 0.5-15 seconds to evaporate the solvent; then a gel bath is performed to complete the phase inversion, the gel solution is water, and the water bath time is 12-84 hours. This invention is simple and easy to operate, low in cost, and the product made from it has high stability and stable performance.

[0005] For example, Chinese patent application CN201510455064.5 provides a modified polyimide hollow fiber gas separation membrane, a modification method, and its application. The method includes the following steps: irradiating the polyimide hollow fiber gas separation membrane with ionizing radiation to obtain the modified polyimide hollow fiber gas separation membrane. This invention also provides the modified polyimide hollow fiber gas separation membrane obtained by the modification method of the polyimide hollow fiber gas separation membrane and its application in removing CO2 from biogas. The modified polyimide hollow fiber gas separation membrane provided by this invention has excellent heat resistance, organic solvent resistance, and excellent mechanical properties; when used to remove CO2 from biogas, the modified polyimide hollow fiber gas separation membrane of this invention has a good separation effect on CO2 / CH4 mixed gases, that is, it has high selectivity and permeability, and can significantly improve the permeability coefficient of CO2 gas.

[0006] However, existing preparation methods still suffer from low gas separation performance and low membrane material strength, limiting their application in high-load continuous oxygen supply systems. Furthermore, polyimide materials are susceptible to humid heat aging during long-term operation, leading to a decrease in selectivity. Therefore, there is an urgent need to develop a hollow fiber oxygen-enriched membrane material that combines high oxygen selectivity, high permeation flux, and excellent mechanical strength. Summary of the Invention

[0007] This invention addresses the problems existing in the prior art by proposing a highly selective and mechanically strong hollow fiber oxygen-enriched membrane and its preparation method. By controlling the polymer blending ratio and phase transformation kinetics, the microstructure of the skin layer is optimized to improve oxygen / nitrogen selectivity. Simultaneously, a nano-reinforcing phase is introduced and uniformly dispersed in the support layer, significantly improving the membrane material's compressive and impact resistance. A gradient temperature coagulation bath is employed to control the phase separation process, achieving efficient optimization of the membrane's internal pore structure. Ultimately, this results in a synergistic improvement in the membrane material's mechanical stability and separation performance under high permeation flux.

[0008] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows: A method for preparing a highly selective and mechanically strong hollow fiber oxygen-enriched membrane includes the following preparation steps: (1) Pretreatment: Place the polyethersulfone particles in an oven at 120-150℃ and dry for 4-8 hours; place the organic solvent in a molecular sieve desiccator and let it stand for 12-16 hours to remove moisture. (2) Preparation of casting solution: Add the dried polyethersulfone to an organic solvent and stir in a water bath at 45-50℃ for 6-13 hours until completely dissolved to obtain a uniform and transparent solution; then add a non-solvent and continue stirring at 45-50℃ for 2-4 hours, let stand to degas for 6 hours, and finally prepare a casting solution with a polyethersulfone mass fraction of 15%-25%; (3) Preparation of bismuth-strontium co-doped titanium-based perovskite nanocomposite oxides: according to the stoichiometric ratio La 0.6 Sr 0.2 Bi 0.2 TiO3 was prepared by weighing lanthanum nitrate, strontium nitrate, bismuth nitrate, and tetrabutyl titanate. Lanthanum nitrate, strontium nitrate, and bismuth nitrate were dissolved in deionized water and stirred until a completely clear aqueous solution of the A-site source was obtained. Tetrabutyl titanate was dissolved in anhydrous ethanol and stirred until homogeneous to obtain an ethanol solution of the titanium source. Under vigorous stirring, the ethanol solution of the titanium source was slowly added dropwise to the aqueous solution of the A-site source to form a mixed precursor solution. Citric acid was added to the mixture as a complexing agent, and the molar ratio of citric acid to total metal ions was controlled. Prepare a solution with a ratio of (1.5-2.5):1; adjust the pH of the solution to 7-8 with ammonia to form a stable sol system; continuously stir the sol in a water bath at 70-85℃ to evaporate the water until a viscous gel is formed; subject the gel to a first-stage heat treatment at 400-500℃ for 1-2 hours, then at 800-900℃ for 4-6 hours, allow it to cool naturally, and grind it to obtain bismuth-strontium co-doped titanium-based perovskite nanocomposite oxide with uniform particle size; (4) Dry-wet spinning: Bismuth-strontium co-doped titanium-based perovskite nanocomposite oxide powder is added to the casting solution and ultrasonically dispersed for 10-12 hours to ensure uniform distribution of the filler. Then, the dry-wet spinning process is used, and the casting solution is extruded into the coagulation bath through the spinneret under a nitrogen atmosphere for gradient temperature coagulation treatment. (5) Post-treatment: Soak the obtained hollow fiber membrane in deionized water at room temperature for 12-24 hours to fully wash away the residual solvent. Then place it in a vacuum drying oven at 60-80℃ for 6-12 hours. After drying, the hollow fiber membrane is subjected to high-temperature annealing treatment and kept at 180-220℃ in an inert gas atmosphere for 1-2 hours, and then naturally cooled to room temperature.

[0009] Furthermore, the organic solvent is one or more of N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), or dimethyl sulfoxide (DMSO).

[0010] Furthermore, the non-solvent is one or more of methanol, ethanol, or isopropanol, and the amount added is 5%-15% of the total mass of the transparent solution.

[0011] Furthermore, in step (3), the mass concentration of the aqueous solution of the A-site source is 0.1-0.2 g / mL, the mass concentration of the ethanol solution of the titanium source is 0.05-0.15 g / mL, and the volume ratio of the ethanol solution of the titanium source to the aqueous solution of the A-site source is (1-1.5):1.

[0012] Furthermore, the mass concentration of nanocomposite oxide powder in the casting solution in step (4) is 20-30%.

[0013] Furthermore, the coagulation bath in step (4) is a mixture of water and organic solvent, wherein the organic solvent is N-methylpyrrolidone, and the volume fraction of N-methylpyrrolidone is 1-3%; the gradient temperature coagulation treatment is as follows: the first stage is 30-40℃, and the residence time is 10-15 min; the second stage is 40-50℃, and the residence time is 8-12 min; the third stage is 50-60℃, and the residence time is 5-8 min, so as to finally achieve phase separation control and form a film morphology with a uniform and penetrating finger-like pore structure and a dense selective layer working together.

[0014] A hollow fiber oxygen-enriched membrane prepared by a method for producing a high-selectivity, high-mechanical-strength hollow fiber oxygen-enriched membrane.

[0015] The application of the hollow fiber oxygen-enriching membrane in a shipboard oxygen enrichment system or medical oxygen supply equipment.

[0016] Beneficial effects: (1) This invention introduces bismuth-strontium co-doped titanium-based perovskite nanocomposite oxides. By performing high-temperature crystallization of the filler at 800-900℃ before film formation, a "pre-activated" filler with a complete perovskite crystal phase, high concentration of oxygen vacancies, and stable Bi-Sr synergistic effect is pre-constructed. Specifically, this invention creatively introduces Sr at the A-site of the perovskite. 2+ and B 3+ Sr 2+ As a "structure modifier," its introduction can create oxygen vacancies; while Bi 3+ As an "electronic structure modifier", its unique 6s 2 Lone pairs of electrons interact strongly with oxygen vacancies, stabilizing the vacancies and, more importantly, optimizing the migration path and energy barrier of oxygen ions between them. These two factors work synergistically to create efficient and stable oxygen ion-specific transport channels within the filler. When this filler is dispersed in a polyethersulfone matrix, it forms continuous, rapid oxygen ion channels, thereby further enhancing the oxygen and nitrogen selectivity of the composite membrane.

[0017] (2) Furthermore, this invention employs gradient temperature coagulation bath technology, controlling the temperature from low to high, successfully inducing the formation of an asymmetric hierarchical porous structure consisting of a dense surface layer, a middle layer of finger-like pores, and a bottom layer of sponge-like pores. The dense surface layer and the highly selective nanofiller together constitute the separation functional layer; the well-developed, interconnected finger-like pores inside greatly reduce gas transport resistance. This perfect combination of hierarchical structure and functional filler is the physical basis for achieving both high throughput and high selectivity.

[0018] (3) Finally, based on traditional post-processing, this invention introduces a high-temperature annealing process at 180-220℃. This temperature is higher than the glass transition temperature (Tg) of polyethersulfone, but much lower than its decomposition temperature. At this temperature, the molecular chain mobility of polyethersulfone is enhanced, enabling sufficient chain rearrangement and relaxation, effectively eliminating internal stress, and making the membrane structure more compact and stable. At the same time, this process can significantly enhance the interfacial interaction between the polymer chain and the nanofiller, forming a stronger interfacial bonding force, thereby enabling stress to be effectively transferred from the polymer matrix to the rigid nanofiller, greatly improving the tensile strength, modulus, and long-term structural stability of the membrane.

[0019] (4) In summary, the hollow fiber oxygen-enriched membrane prepared by the present invention has improved oxygen and nitrogen selectivity to above 7 and tensile strength to above 35 MPa, exhibiting excellent mechanical strength and oxygen and nitrogen selectivity. It is suitable for shipborne and medical oxygen environments under complex working conditions such as high pressure and high humidity, and has significant application prospects and industrialization value. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the hollow fiber membrane gas permeation testing device of the present invention; Figure 2 This is a schematic diagram of a gas permeation test membrane assembly. Figure 3 Electron micrograph of the membrane material in an embodiment of the present invention; Figure 4 The images shown are electron microscope images of the membrane materials obtained in Comparative Examples 4-9, where A is Comparative Example 4, B is Comparative Example 5, C is Comparative Example 6, D is Comparative Example 7, E is Comparative Example 8, and F is Comparative Example 9. Detailed Implementation

[0021] The technical solution of the present invention will be further described below with reference to specific embodiments, but it is not limited thereto.

[0022] Example 1 A method for preparing a highly selective and mechanically strong hollow fiber oxygen-enriched membrane includes the following preparation steps: (1) Pretreatment: Place the polyethersulfone particles in an oven at 120-150℃ and dry for 4 hours; place the organic solvent in a molecular sieve desiccator and let it stand for 12 hours to remove moisture. (2) Preparation of casting solution: The dried polyethersulfone is added to an organic solvent and stirred in a water bath at 45-50℃ for 6 hours until completely dissolved to obtain a uniform and transparent solution; then a non-solvent is added and stirred at 45-50℃ for 2 hours, and allowed to stand for 6 hours to remove bubbles, and finally a casting solution with a polyethersulfone mass fraction of 15% is prepared. (3) Preparation of bismuth-strontium co-doped titanium-based perovskite nanocomposite oxides: according to the stoichiometric ratio La 0.6 Sr0.2 Bi 0.2 TiO3 was prepared by weighing lanthanum nitrate, strontium nitrate, bismuth nitrate, and tetrabutyl titanate. Lanthanum nitrate, strontium nitrate, and bismuth nitrate were dissolved in deionized water and stirred until a completely clear aqueous solution of the A-site source was obtained. Tetrabutyl titanate was dissolved in anhydrous ethanol and stirred until homogeneous to obtain an ethanol solution of the titanium source. Under vigorous stirring, the ethanol solution of the titanium source was slowly added dropwise to the aqueous solution of the A-site source to form a mixed precursor solution. Citric acid was added to the mixture as a complexing agent, with the molar ratio of citric acid to total metal ions controlled at 1.5:1. The pH of the solution was adjusted to 7-8 with ammonia to form a stable sol system. The sol was continuously stirred in a water bath at 70-85℃ to evaporate water until a viscous gel was formed. The gel underwent a first-stage heat treatment at 400-500℃ for 1 hour, followed by a second heat treatment at 800-900℃ for 4 hours. After natural cooling, the gel was ground to obtain uniformly sized bismuth-strontium co-doped titanium-based perovskite nanocomposite oxides. (4) Dry-wet spinning: Bismuth-strontium co-doped titanium-based perovskite nanocomposite oxide powder is added to the casting solution and ultrasonically dispersed for 10 hours to ensure uniform distribution of the filler. Then, the dry-wet spinning process is used to extrude the casting solution into the coagulation bath through the spinneret under a nitrogen atmosphere for gradient temperature coagulation treatment. (5) Post-treatment: The obtained hollow fiber membrane was soaked in deionized water at room temperature for 12 hours to fully wash away the residual solvent. Then it was placed in a vacuum drying oven at 60-80℃ for 6 hours. After drying, the hollow fiber membrane was subjected to high-temperature annealing treatment and kept at 180-220℃ in an inert gas atmosphere for 1 hour, and then naturally cooled to room temperature.

[0023] The organic solvent is N-methylpyrrolidone (NMP).

[0024] The non-solvent is methanol, and the amount added is 5% of the total mass of the transparent solution.

[0025] In step (3), the mass concentration of the aqueous solution of the A-site source is 0.1 g / mL, the mass concentration of the ethanol solution of the titanium source is 0.05 g / mL, and the volume ratio of the ethanol solution of the titanium source to the aqueous solution of the A-site source is 1:1.

[0026] The mass concentration of nanocomposite oxide powder in the casting solution in step (4) is 20%.

[0027] The coagulation bath in step (4) is a mixture of water and organic solvent, wherein the organic solvent is N-methylpyrrolidone, and the volume fraction of N-methylpyrrolidone is 1%; the gradient temperature coagulation treatment is as follows: the first stage is 30-40℃, and the residence time is 10 min; the second stage is 40-50℃, and the residence time is 8 min; the third stage is 50-60℃, and the residence time is 5 min, so as to achieve phase separation control and form a uniform and penetrating finger-like pore structure and a dense selective layer synergistic membrane morphology.

[0028] Example 2 A method for preparing a highly selective and mechanically strong hollow fiber oxygen-enriched membrane includes the following preparation steps: (1) Pretreatment: Place the polyethersulfone particles in an oven at 120-150℃ and dry for 6 hours; place the organic solvent in a molecular sieve desiccator and let it stand for 14 hours to remove moisture. (2) Preparation of casting solution: The dried polyethersulfone is added to an organic solvent and stirred in a water bath at 45-50℃ for 10 hours until completely dissolved to obtain a uniform and transparent solution; then a non-solvent is added and stirred at 45-50℃ for 2 hours, and allowed to stand for 6 hours to remove bubbles, and finally a casting solution with a polyethersulfone mass fraction of 20% is prepared. (3) Preparation of bismuth-strontium co-doped titanium-based perovskite nanocomposite oxides: according to the stoichiometric ratio La 0.6 Sr 0.2 Bi 0.2 TiO3 was prepared by weighing lanthanum nitrate, strontium nitrate, bismuth nitrate, and tetrabutyl titanate. Lanthanum nitrate, strontium nitrate, and bismuth nitrate were dissolved in deionized water and stirred until a completely clear aqueous solution of the A-site source was obtained. Tetrabutyl titanate was dissolved in anhydrous ethanol and stirred until homogeneous to obtain an ethanol solution of the titanium source. Under vigorous stirring, the ethanol solution of the titanium source was slowly added dropwise to the aqueous solution of the A-site source to form a mixed precursor solution. Citric acid was added to the mixture as a complexing agent, with the molar ratio of citric acid to total metal ions controlled at 2:1. The pH of the solution was adjusted to 7-8 with ammonia to form a stable sol system. The sol was continuously stirred in a water bath at 70-85℃ to evaporate water until a viscous gel was formed. The gel underwent a first-stage heat treatment at 400-500℃ for 1 hour, followed by a second heat treatment at 800-900℃ for 5 hours. After natural cooling, the gel was ground to obtain uniformly sized bismuth-strontium co-doped titanium-based perovskite nanocomposite oxides. (4) Dry-wet spinning: Bismuth-strontium co-doped titanium-based perovskite nanocomposite oxide powder is added to the casting solution and ultrasonically dispersed for 10 hours to ensure uniform distribution of the filler. Then, the dry-wet spinning process is used to extrude the casting solution into the coagulation bath through the spinneret under a nitrogen atmosphere for gradient temperature coagulation treatment. (5) Post-treatment: The obtained hollow fiber membrane was soaked in deionized water at room temperature for 16 hours to fully wash away the residual solvent. Then it was placed in a vacuum drying oven at 60-80℃ for 10 hours. After drying, the hollow fiber membrane was subjected to high-temperature annealing treatment and kept at 180-220℃ in an inert gas atmosphere for 2 hours, and then naturally cooled to room temperature.

[0029] The organic solvent is dimethylacetamide (DMAc).

[0030] The non-solvent is ethanol, and the amount added is 10% of the total mass of the transparent solution.

[0031] In step (3), the mass concentration of the aqueous solution of the A-site source is 0.1 g / mL, the mass concentration of the ethanol solution of the titanium source is 0.1 g / mL, and the volume ratio of the ethanol solution of the titanium source to the aqueous solution of the A-site source is 1.2:1.

[0032] The mass concentration of nanocomposite oxide powder in the casting solution in step (4) is 25%.

[0033] The coagulation bath in step (4) is a mixture of water and organic solvent, wherein the organic solvent is N-methylpyrrolidone, and the volume fraction of N-methylpyrrolidone is 3%; the gradient temperature coagulation treatment is as follows: the first stage is 30-40℃, and the residence time is 10 min; the second stage is 40-50℃, and the residence time is 12 min; the third stage is 50-60℃, and the residence time is 5 min, so as to achieve phase separation control and form a uniform and penetrating finger-like pore structure and a dense selective layer synergistic membrane morphology.

[0034] Example 3 A method for preparing a highly selective and mechanically strong hollow fiber oxygen-enriched membrane includes the following preparation steps: (1) Pretreatment: Place the polyethersulfone particles in an oven at 120-150℃ and dry for 8 hours; place the organic solvent in a molecular sieve desiccator and let it stand for 16 hours to remove moisture. (2) Preparation of casting solution: The dried polyethersulfone is added to an organic solvent and stirred in a water bath at 45-50℃ for 13 hours until completely dissolved to obtain a uniform and transparent solution; then a non-solvent is added and stirred at 45-50℃ for 4 hours, and allowed to stand for 6 hours to remove bubbles, and finally a casting solution with a polyethersulfone mass fraction of 25% is prepared. (3) Preparation of bismuth-strontium co-doped titanium-based perovskite nanocomposite oxides: according to the stoichiometric ratio La 0.6 Sr 0.2 Bi 0.2TiO3 was prepared by weighing lanthanum nitrate, strontium nitrate, bismuth nitrate, and tetrabutyl titanate. Lanthanum nitrate, strontium nitrate, and bismuth nitrate were dissolved in deionized water and stirred until a completely clear aqueous solution of the A-site source was obtained. Tetrabutyl titanate was dissolved in anhydrous ethanol and stirred until homogeneous to obtain an ethanol solution of the titanium source. Under vigorous stirring, the ethanol solution of the titanium source was slowly added dropwise to the aqueous solution of the A-site source to form a mixed precursor solution. Citric acid was added to the mixture as a complexing agent, with the molar ratio of citric acid to total metal ions controlled at 2.5:1. The pH of the solution was adjusted to 7-8 with ammonia to form a stable sol system. The sol was continuously stirred in a water bath at 70-85℃ to evaporate water until a viscous gel was formed. The gel underwent a first-stage heat treatment at 400-500℃ for 2 hours, followed by a second heat treatment at 800-900℃ for 6 hours. After natural cooling, the gel was ground to obtain uniformly sized bismuth-strontium co-doped titanium-based perovskite nanocomposite oxides. (4) Dry-wet spinning: Bismuth-strontium co-doped titanium-based perovskite nanocomposite oxide powder is added to the casting solution and ultrasonically dispersed for 12 hours to ensure uniform distribution of the filler. Then, the dry-wet spinning process is used, and the casting solution is extruded into the coagulation bath through the spinneret under a nitrogen atmosphere for gradient temperature coagulation treatment. (5) Post-treatment: The obtained hollow fiber membrane is soaked in deionized water at room temperature for 12-24 hours to fully wash away the residual solvent. Then it is placed in a vacuum drying oven at 60-80℃ for 12 hours and then the dried hollow fiber membrane is subjected to high-temperature annealing treatment. It is kept at 180-220℃ in an inert gas atmosphere for 2 hours and then naturally cooled to room temperature.

[0035] The organic solvent is dimethyl sulfoxide (DMSO).

[0036] The non-solvent is isopropanol, and the amount added is 15% of the total mass of the transparent solution.

[0037] In step (3), the mass concentration of the aqueous solution of the A-site source is 0.2 g / mL, the mass concentration of the ethanol solution of the titanium source is 0.15 g / mL, and the volume ratio of the ethanol solution of the titanium source to the aqueous solution of the A-site source is 1.5:1.

[0038] The mass concentration of nanocomposite oxide powder in the casting solution in step (4) is 30%.

[0039] The coagulation bath in step (4) is a mixture of water and organic solvent, wherein the organic solvent is N-methylpyrrolidone, and the volume fraction of N-methylpyrrolidone is 3%; the gradient temperature coagulation treatment is as follows: the first stage is 30-40℃, and the residence time is 15min; the second stage is 40-50℃, and the residence time is 12min; the third stage is 50-60℃, and the residence time is 8min, so as to finally achieve phase separation control and form a uniform and penetrating finger-like pore structure and a dense selective layer synergistic membrane morphology.

[0040] Comparative Example 1 In this comparative example, except that no doping element was used in the preparation of the nanocomposite oxide, the raw materials and preparation process were the same as in Example 1. That is: A method for preparing a highly selective and mechanically strong hollow fiber oxygen-enriched membrane includes the following preparation steps: (1) Pretreatment: Place the polyethersulfone particles in an oven at 120-150℃ and dry for 4 hours; place the organic solvent in a molecular sieve desiccator and let it stand for 12 hours to remove moisture. (2) Preparation of casting solution: The dried polyethersulfone is added to an organic solvent and stirred in a water bath at 45-50℃ for 6 hours until completely dissolved to obtain a uniform and transparent solution; then a non-solvent is added and stirred at 45-50℃ for 2 hours, and allowed to stand for 6 hours to remove bubbles, and finally a casting solution with a polyethersulfone mass fraction of 15% is prepared. (3) Preparation of titanium-based perovskite nanocomposite oxides: According to the stoichiometric ratio of LaTiO3, weigh lanthanum nitrate and tetrabutyl titanate, dissolve lanthanum nitrate in deionized water, and stir until a completely clear aqueous solution of the A-site source is obtained; dissolve tetrabutyl titanate in anhydrous ethanol and stir evenly to obtain an ethanol solution of titanium source; under vigorous stirring, slowly add the ethanol solution of titanium source to the aqueous solution of A-site source to form a mixed precursor solution; add citric acid as a complexing agent to the mixture, and control the molar ratio of citric acid to total metal ions at 1.5:1; adjust the pH of the solution to 7-8 with ammonia water to form a stable sol system; continuously stir the sol in a water bath at 70-85℃ to evaporate the water until a viscous gel is formed; subject the gel to the first stage of heat treatment at 400-500℃ for 1 hour, then at 800-900℃ for 4 hours, cool naturally, and grind to obtain titanium-based perovskite nanocomposite oxides with uniform particle size; (4) Dry-wet spinning: Titanium-based perovskite nanocomposite oxide powder is added to the casting solution and ultrasonically dispersed for 10 hours to ensure uniform distribution of the filler. Then, the dry-wet spinning process is used to extrude the casting solution into the coagulation bath through the spinneret under a nitrogen atmosphere for gradient temperature coagulation treatment. (5) Post-treatment: The obtained hollow fiber membrane was soaked in deionized water at room temperature for 12 hours to fully wash away the residual solvent. Then it was placed in a vacuum drying oven at 60-80℃ for 6 hours. After drying, the hollow fiber membrane was subjected to high-temperature annealing treatment and kept at 180-220℃ in an inert gas atmosphere for 1 hour, and then naturally cooled to room temperature.

[0041] The organic solvent is N-methylpyrrolidone (NMP).

[0042] The non-solvent is methanol, and the amount added is 5% of the total mass of the transparent solution.

[0043] In step (3), the mass concentration of the aqueous solution of the A-site source is 0.1 g / mL, the mass concentration of the ethanol solution of the titanium source is 0.05 g / mL, and the volume ratio of the ethanol solution of the titanium source to the aqueous solution of the A-site source is 1:1.

[0044] The mass concentration of nanocomposite oxide powder in the casting solution in step (4) is 20%.

[0045] The coagulation bath in step (4) is a mixture of water and organic solvent, wherein the organic solvent is N-methylpyrrolidone and the volume fraction of N-methylpyrrolidone is 1%; the gradient temperature coagulation treatment is as follows: the first stage is 30-40℃ and the residence time is 10min; the second stage is 40-50℃ and the residence time is 8min; the third stage is 50-60℃ and the residence time is 5min.

[0046] Comparative Example 2 In this comparative example, except for the use of only the dopant element Bi in the preparation of the nanocomposite oxide, the raw materials and preparation process are the same as in Example 1. That is, in the preparation of the nanocomposite oxide: Preparation of bismuth-doped titanium-based perovskite nanocomposite oxides: according to the stoichiometric ratio of La 0.6 Bi 0.4 TiO3 was prepared by weighing lanthanum nitrate, bismuth nitrate, and tetrabutyl titanate. Lanthanum nitrate and bismuth nitrate were dissolved in deionized water and stirred until a completely clear aqueous solution of the A-site source was obtained. Tetrabutyl titanate was dissolved in anhydrous ethanol and stirred until homogeneous to obtain an ethanol solution of the titanium source. Under vigorous stirring, the ethanol solution of the titanium source was slowly added dropwise to the aqueous solution of the A-site source to form a mixed precursor solution. Citric acid was added to the mixture as a complexing agent, and the molar ratio of citric acid to total metal ions was controlled at 1.5:1. The pH of the solution was adjusted to 7-8 with ammonia to form a stable sol system. The sol was continuously stirred in a water bath at 70-85℃ to evaporate water until a viscous gel was formed. The gel was subjected to a first-stage heat treatment at 400-500℃ for 1 hour, followed by a second heat treatment at 800-900℃ for 4 hours. After natural cooling, the gel was ground to obtain bismuth-doped titanium-based perovskite nanocomposite oxide with uniform particle size.

[0047] Comparative Example 3 In this comparative example, except for the use of only the dopant element Sr in the preparation of the nanocomposite oxide, the raw materials and preparation process are the same as in Example 1. That is, in the preparation of the nanocomposite oxide: Preparation of strontium-doped titanium-based perovskite nanocomposite oxides: according to the stoichiometric ratio of La 0.6 Sr 0.4TiO3 was prepared by weighing lanthanum nitrate, strontium nitrate, and tetrabutyl titanate. Lanthanum nitrate and strontium nitrate were dissolved in deionized water and stirred until a completely clear aqueous solution of the A-site source was obtained. Tetrabutyl titanate was dissolved in anhydrous ethanol and stirred until homogeneous to obtain an ethanol solution of the titanium source. Under vigorous stirring, the ethanol solution of the titanium source was slowly added dropwise to the aqueous solution of the A-site source to form a mixed precursor solution. Citric acid was added to the mixture as a complexing agent, and the molar ratio of citric acid to total metal ions was controlled at 1.5:1. The pH of the solution was adjusted to 7-8 with ammonia to form a stable sol system. The sol was continuously stirred in a water bath at 70-85℃ to evaporate water until a viscous gel was formed. The gel was subjected to a first-stage heat treatment at 400-500℃ for 1 hour, followed by a second heat treatment at 800-900℃ for 4 hours. After natural cooling, the gel was ground to obtain strontium-doped titanium-based perovskite nanocomposite oxide with uniform particle size.

[0048] Comparative Example 4 In this comparative example, except for the use of a single-temperature coagulation bath, the raw materials and preparation process are the same as in Example 1. That is, the first stage is treated at 30-40℃ for 23 minutes. The coagulation bath in step (4) is a mixture of water and organic solvent, wherein the organic solvent is N-methylpyrrolidone, and the volume fraction of N-methylpyrrolidone is 1%; the coagulation bath treatment temperature and time are: 30-40℃, and the residence time is 23min.

[0049] Comparative Example 5 In this comparative example, except for the use of a single-temperature coagulation bath, the raw materials and preparation process are the same as in Example 1. Specifically, the treatment is carried out at 40-50°C for 23 minutes in the second stage. The coagulation bath in step (4) is a mixture of water and organic solvent, wherein the organic solvent is N-methylpyrrolidone, and the volume fraction of N-methylpyrrolidone is 1%; the coagulation bath treatment temperature and time are: 40-50℃, and the residence time is 23min.

[0050] Comparative Example 6 In this comparative example, except for the use of a single-temperature coagulation bath, the raw materials and preparation process are the same as in Example 1. Specifically, the treatment is carried out at 50-60°C for 23 minutes in the third stage. The coagulation bath in step (4) is a mixture of water and organic solvent, wherein the organic solvent is N-methylpyrrolidone, and the volume fraction of N-methylpyrrolidone is 1%; the coagulation bath treatment temperature and time are: 50-60℃, and the residence time is 23min.

[0051] Comparative Example 7 In this comparative example, except for the use of only a two-stage temperature coagulation bath treatment, the raw materials and preparation process are the same as in Example 1. That is: The coagulation bath in step (4) is a mixture of water and organic solvent, wherein the organic solvent is N-methylpyrrolidone and the volume fraction of N-methylpyrrolidone is 1%; the gradient temperature coagulation treatment is as follows: the first stage is 30-40℃ with a residence time of 13min; the second stage is 40-50℃ with a residence time of 10min.

[0052] Comparative Example 8 In this comparative example, except for the use of only a two-stage temperature coagulation bath treatment, the raw materials and preparation process are the same as in Example 1. That is: The coagulation bath in step (4) is a mixture of water and organic solvent, wherein the organic solvent is N-methylpyrrolidone and the volume fraction of N-methylpyrrolidone is 1%; the gradient temperature coagulation treatment is as follows: the first stage is 30-40℃ and the residence time is 13min; the second stage is 50-60℃ and the residence time is 10min.

[0053] Comparative Example 9 In this comparative example, except for the use of only a two-stage temperature coagulation bath treatment, the raw materials and preparation process are the same as in Example 1. That is: The coagulation bath in step (4) is a mixture of water and organic solvent, wherein the organic solvent is N-methylpyrrolidone and the volume fraction of N-methylpyrrolidone is 1%; the gradient temperature coagulation treatment is as follows: the first stage is 40-50℃ with a residence time of 13min; the second stage is 50-60℃ with a residence time of 10min.

[0054] Performance testing Morphology and Structure: To observe the microstructure of the polyethersulfone hollow fiber membrane, the cross-section of the membrane fibers was studied using a scanning electron microscope (SEM, JSM-7800F, Japan). The prepared membrane fibers were quenched in liquid nitrogen to expose their cross-sections. All samples were coated with a platinum film under vacuum conditions with a thickness of 0.2 nm.

[0055] Mechanical property testing: The mechanical properties of hollow fiber membranes were determined using a multifilament strength tester. The sample length was 20 cm, and the tensile rate was 200 mm / min when measuring the tensile strength. To ensure the accuracy of the test data, each sample was tested 5 times, and the average value was taken.

[0056] Gas permeability test: Hollow fiber membranes were tested in a pure gas system. A schematic diagram of the testing apparatus is shown below. Figure 1 As shown, each test group used 10 15 cm hollow fiber membranes inserted into an aluminum casting head, which was then sealed with epoxy resin to assemble a small membrane module (see schematic diagram of the membrane module). Figure 2The gas permeability of the membrane module was measured using a bubble flow meter at 25℃ and 0.5MPa. The gas flux (J) of the hollow fiber membrane was calculated using formula (1), and the separation coefficient was calculated using formula (2). ).

[0057] (1) (2) Where J is the gas flux of the hollow fiber, GPU[1GPU = 1×10 -6 cm 3 (STP) / (cm 2 [·s·cmHg)];Q is the permeability, cm 3 (STP) / s; Δp is the pressure difference between the feed side and the permeate side, cmHg; A is the membrane surface area, cm². 2 n represents the number of fibers within the module; D represents the outer diameter of the hollow fiber (cm); l represents the effective length of the hollow fiber (cm). The test results are shown in Table 1. Table 1 Performance Test Results The data in the table show that the hollow fiber oxygen-enriched membranes prepared in Examples 1 to 3 exhibit significant advantages in gas flux and O2 / N2 selectivity. Among them, Example 1 shows the highest O2 / N2 selectivity at 7.97, with a tensile strength of 40.1 MPa, demonstrating the best overall performance. In comparison, the selectivity of undoped Comparative Example 1 is significantly reduced to 2.95, while the selectivity improvement in Comparative Examples 2 and 3 (doped with a single element) is limited. Solidification treatment has a significant impact on the membrane structure. Comparison of solidification bath processes shows that Comparative Examples 4 to 6 (treated at a single temperature) result in a substantial decrease in mechanical properties. While Comparative Examples 7 to 9 (treated with two gradients) improve some performance, they are still inferior to the examples treated with three gradients. This indicates that by using Sr and Bi dual-element synergistic modification and a three-stage gradient solidification process, the membrane pore structure and surface dense layer can be effectively controlled, achieving a balance between high selectivity, high mechanical strength, and good gas permeability. The SEM images of the membrane cross-sections also show that Example 1 has uniform pore size, a distinct dense layer, and smooth, finger-like pore walls, which facilitates efficient gas transport. In contrast, Comparative Examples 4 to 9 have uneven pore size and relatively thin dense layers, which can affect gas selectivity and mechanical strength to some extent. Therefore, the synergistic effect of elemental doping and gradient solidification processes has a decisive influence on membrane performance, and neither can be neglected.

[0058] It should be noted that the above embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a highly selective, high-mechanical-strength hollow fiber oxygen-enriched membrane, characterized in that, The preparation steps include the following: (1) Pretreatment: Place the polyethersulfone particles in an oven at 120-150℃ and dry for 4-8 hours. Place the organic solvent in a molecular sieve desiccator and let it stand for 12-16 hours to remove moisture. (2) Preparation of casting solution: Add the dried polyethersulfone to an organic solvent and stir in a water bath at 45-50℃ for 6-13 hours until completely dissolved to obtain a uniform and transparent solution; then add a non-solvent and continue stirring at 45-50℃ for 2-4 hours, let stand to degas for 6 hours, and finally prepare a casting solution with a polyethersulfone mass fraction of 15%-25%; (3) Preparation of bismuth-strontium co-doped titanium-based perovskite nanocomposite oxides: according to the stoichiometric ratio La 0.6 Sr 0.2 Bi 0.2 TiO3 was prepared by weighing lanthanum nitrate, strontium nitrate, bismuth nitrate, and tetrabutyl titanate. Lanthanum nitrate, strontium nitrate, and bismuth nitrate were dissolved in deionized water and stirred until a completely clear aqueous solution of the A-site source was obtained. Tetrabutyl titanate was dissolved in anhydrous ethanol and stirred until homogeneous to obtain an ethanol solution of the titanium source. Under vigorous stirring, the ethanol solution of the titanium source was slowly added dropwise to the aqueous solution of the A-site source to form a mixed precursor solution. Citric acid was added to the mixture as a complexing agent, and the molar ratio of citric acid to total metal ions was controlled. Prepare a solution with a ratio of (1.5-2.5):1; adjust the pH of the solution to 7-8 with ammonia to form a stable sol system; continuously stir the sol in a water bath at 70-85℃ to evaporate the water until a viscous gel is formed; subject the gel to a first-stage heat treatment at 400-500℃ for 1-2 hours, then at 800-900℃ for 4-6 hours, allow it to cool naturally, and grind it to obtain bismuth-strontium co-doped titanium-based perovskite nanocomposite oxide with uniform particle size; (4) Dry-wet spinning: Bismuth-strontium co-doped titanium-based perovskite nanocomposite oxide powder is added to the casting solution and ultrasonically dispersed for 10-12 hours to ensure uniform distribution of the filler. Then, the dry-wet spinning process is used, and the casting solution is extruded into the coagulation bath through the spinneret under a nitrogen atmosphere for gradient temperature coagulation treatment. (5) Post-treatment: Soak the obtained hollow fiber membrane in deionized water at room temperature for 12-24 hours to fully wash away the residual solvent, then dry it in a vacuum drying oven at 60-80℃ for 6-12 hours, and then anneal the dried hollow fiber membrane at high temperature for 1-2 hours in an inert gas atmosphere at 180-220℃, and then cool it naturally to room temperature. The coagulation bath in step (4) is a mixture of water and organic solvent, wherein the organic solvent is N-methylpyrrolidone, and the volume fraction of N-methylpyrrolidone is 1%-3%; the gradient temperature coagulation treatment is as follows: the first stage is 30-40℃, and the residence time is 10-15 min; the second stage is 40-50℃, and the residence time is 8-12 min; the third stage is 50-60℃, and the residence time is 5-8 min, so as to finally achieve phase separation control and form a uniform and penetrating finger-like pore structure and a dense selective layer synergistic membrane morphology.

2. The method for preparing the highly selective and mechanically strong hollow fiber oxygen-enriched membrane according to claim 1, characterized in that, The organic solvent in step (2) is one or more of N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), or dimethyl sulfoxide (DMSO).

3. The method for preparing the highly selective and mechanically strong hollow fiber oxygen-enriched membrane according to claim 1, characterized in that, The non-solvent mentioned in step (2) is one or more of methanol, ethanol or isopropanol, and the amount added is 5%-15% of the total mass of the transparent solution.

4. The method for preparing a highly selective, high-mechanical-strength hollow fiber oxygen-enriched membrane according to claim 1, characterized in that, In step (3), the mass concentration of the aqueous solution of the A-site source is 0.1-0.2 g / mL, the mass concentration of the ethanol solution of the titanium source is 0.05-0.15 g / mL, and the volume ratio of the ethanol solution of the titanium source to the aqueous solution of the A-site source is (1-1.5):

1.

5. The method for preparing a highly selective, high-mechanical-strength hollow fiber oxygen-enriched membrane according to claim 1, characterized in that, The mass percentage of nanocomposite oxide powder in the casting solution in step (4) is 20%-30%.

6. A hollow fiber oxygen-enriched membrane prepared by the method of preparing a high-selectivity, high-mechanical-strength hollow fiber oxygen-enriched membrane according to any one of claims 1-5.

7. The application of the hollow fiber oxygen-enriching membrane according to claim 6 in a shipboard oxygen enrichment system or medical oxygen supply equipment.

Images