A non-uniform segmented hollow fiber membrane for high altitude train membrane separation oxygen production

Abstract

This invention discloses a non-uniform segmented hollow fiber membrane for oxygen generation in high-altitude trains. Specifically, the fiber membrane is divided into a front section and a rear section along the axial direction, and the front and rear sections are integrally formed. The front section uses a high-permeability material, while the rear section uses a low-permeability, high-selectivity material. The segmentation ratio, i.e., the percentage of the front section length to the total membrane length, is 30%-70%. This invention solves the problem of traditional homogeneous membranes being limited by the upper limit of the "permeability-selectivity" trade-off, achieving increased oxygen-enriched gas flow rate, concentration, and oxygen generation rate. It meets the synergistic requirements of high flow rate and high purity for oxygen supply systems in high-altitude trains, and can directly replace existing membrane modules, featuring low energy consumption and strong adaptability.

Description

Technical Field

[0001] This invention belongs to the field of gas separation membrane technology, and particularly relates to a non-uniform segmented hollow fiber membrane for oxygen generation by membrane separation on high-altitude trains. Background Technology

[0002] In high-altitude areas, the air is thin and the partial pressure of oxygen is low. Therefore, when trains operate in high-altitude environments, the low-oxygen environment inside the carriages can cause passengers to experience altitude sickness, such as dizziness and fatigue, seriously affecting their comfort and health safety. To meet the physiological needs of the human body, an onboard oxygen generation system is required to maintain the oxygen concentration in the carriages at 22.3%-25.5%. Membrane separation oxygen generation technology has become the mainstream technology for oxygen supply on high-altitude trains due to its advantages such as simple operation, low maintenance costs, and continuous oxygen supply.

[0003] The core of membrane separation oxygen generation is to achieve oxygen and nitrogen separation by utilizing the difference in solubility and diffusion rate of gases in the membrane material. Its separation performance depends on the permeability and selectivity of the membrane material, which respectively affect the flow rate and concentration of the generated oxygen gas. However, existing gas separation membranes have inherent technical bottlenecks. The permeability and selectivity of the membrane material are constrained by the "Robeson upper limit," exhibiting a trade-off relationship. Traditional homogeneous membranes cannot simultaneously achieve high oxygen-enriched flow rate and high oxygen-enriched concentration. In the oxygen generation scenario of high-altitude trains, this property of homogeneous membranes leads to lower separation performance of the oxygen generation system, failing to fully meet the dynamically changing oxygen supply demands in the high-altitude environment.

[0004] Existing research largely focuses on the development of novel membrane materials and the optimization of preparation processes, attempting to break through performance limits by improving the chemical structure of membrane materials. However, continuous innovation in materials makes it difficult to achieve higher performance levels. Currently, there is limited innovative research on membrane structure design, and no structural solution has been proposed that can effectively coordinate permeability and selectivity. Therefore, developing a high-performance membrane module based on structural innovation is of significant research value for optimizing membrane separation oxygen generation technology on high-altitude trains. Summary of the Invention

[0005] This invention aims to overcome the performance limitations of traditional homogeneous membranes, which are mutually restrictive in terms of permeability and selectivity, through innovative membrane structure. This allows for a synergistic improvement in oxygen enrichment flow rate and concentration, thereby enhancing the adaptability and economy of membrane modules. To this end, this invention provides a non-uniform segmented hollow fiber membrane for oxygen generation via membrane separation on high-altitude trains.

[0006] The present invention discloses a non-uniform segmented hollow fiber membrane for oxygen generation by membrane separation on plateau trains, specifically comprising: the fiber membrane being divided into a front section and a rear section along the axial direction, the front section and the rear section being an integrally formed structure; the front section using a high-permeability material and the rear section using a low-permeability, high-selectivity material; the segmentation ratio, i.e., the percentage of the front section length to the total membrane length, is 30%-70%.

[0007] Furthermore, in the highly permeable material at the front end, the permeability coefficients of oxygen and nitrogen are both twice that of the homogeneous membrane, and the selectivity remains at 4.07.

[0008] Furthermore, in the downstream low-permeability, high-selectivity material, the oxygen permeability coefficient is 50% of that of the homogeneous membrane, the nitrogen permeability coefficient is 30% of that of the homogeneous membrane, and the selectivity is improved to 6.78.

[0009] Furthermore, the segment ratio is 50%, meaning the length of the first segment is equal to the length of the second segment.

[0010] Furthermore, the hollow fiber membrane has a length of 1.6m, an inner diameter of 0.0003m, and 6000 hollow fibers. The effective membrane area is calculated based on the number of fibers.

[0011] Furthermore, the hollow fiber membrane adopts a counter-current flow method, with raw material air flowing axially into the hollow fiber cavity and oxygen-enriched gas permeating out from the outside of the membrane.

[0012] Operating conditions: The raw material gas air pressure is 0.9 MPa, the standard flow rate is 6.72 L / s, and the oxygen-enriched gas pressure is 0.1 MPa.

[0013] A method for preparing a non-uniform segmented hollow fiber membrane for oxygen generation via membrane separation on high-altitude trains includes the following steps:

[0014] Step 1: Prepare a reference hollow fiber membrane.

[0015] Using Matrimid polyimide as the base material, a spinning solution with a solid content of 18%-22% was prepared, with N-methylpyrrolidone as the solvent and anhydrous ethanol and polyvinylpyrrolidone as additives. A homogeneous reference hollow fiber membrane was prepared by dry and wet spinning process. The prepared reference hollow fiber membrane was soaked in deionized water and vacuum dried for later use.

[0016] Step 2: Post-coating selective modification.

[0017] Prepare a coating solution with a solid content of 2%-5%, using highly selective cross-linked polyimide as the coating material and a mixture of hexane and isopropanol as the solvent. Seal the reference hollow fiber membrane along the axial direction in sections, immersing only the pre-set section (30%-70% of the total length) into the coating solution, while keeping the front section sealed and not in contact with the coating solution. After the immersion coating is completed, pull the fiber membrane out of the coating solution at a constant rate to form an ultrathin selective skin layer on the surface of the rear section of the reference hollow fiber membrane.

[0018] Step 3: Post-treatment and curing.

[0019] After the hollow fiber membrane with dip coating is dried at room temperature, it is subjected to vacuum drying to completely evaporate the coating solvent. Then, it is subjected to thermal cross-linking treatment to enhance the adhesion between the coating and the substrate fiber. Finally, a non-uniform segmented hollow fiber membrane with a high permeability structure in the front section and a low permeability and high selectivity structure in the back section is obtained.

[0020] Furthermore, in step 1, the solid content of the spinning solution is 20%, and the oxygen permeability coefficient of the prepared benchmark homogeneous hollow fiber membrane is 3.72 × 10⁻⁶. -8 mol / (s·m 2 The nitrogen permeability coefficient is 0.92 × 10 Pa. -8 mol / (s·m 2 The oxygen-nitrogen separation selectivity was 4.07 (Pa).

[0021] Furthermore, in step 2, the dipping time is 10s-30s, the dipping temperature is 25℃, and the lifting speed is 5cm / min-10cm / min.

[0022] Furthermore, in step 3, the room temperature drying environment is a 25℃ dust-free environment, and the drying time is 30 minutes; the vacuum drying temperature is 60℃-80℃, and the drying time is 12h-24h; the thermal crosslinking treatment temperature is 180℃-200℃, and the treatment time is 2h-3h.

[0023] The beneficial technical effects of this invention compared to the prior art are as follows:

[0024] (1) Breaking through the trade-off between "permeability and selectivity" of homogeneous membranes: The high permeability of the front section rapidly increases the oxygen permeation, laying the foundation for oxygen production; the low permeability and high selectivity of the back section precisely suppress nitrogen permeation, intercept and separate the remaining oxygen, and finally achieve synergistic optimization of oxygen-enriched gas flow rate and purity.

[0025] (2) The oxygen-enriched gas flow rate is greatly increased: Under the optimized parameters, the oxygen-enriched gas flow rate of the segmented membrane is increased by more than 15% compared with that of the homogeneous membrane, and the high flow rate oxygen supply demand can be further met through parallel components.

[0026] (3) Slightly increased oxygen concentration: The oxygen concentration was increased from 43.40% of the homogeneous membrane to 43.64% of the segmented membrane, while meeting the oxygen concentration requirement of 35%-45% for plateau trains.

[0027] (4) Significantly optimized oxygen production rate: The segmented membrane design with optimized parameters increases the oxygen production rate from 36.47% to 43.45%, improves the utilization rate of high-pressure air, and reduces the energy consumption of the oxygen production system.

[0028] (5) Wide applicability: It can directly replace the homogenized membrane in the existing membrane separation oxygen generation system and be integrated into the oxygen generation system of plateau trains without modifying other hardware equipment, thus reducing the cost of modification. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a non-uniform segmented hollow fiber membrane structure for oxygen generation by membrane separation on plateau trains according to the present invention. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0031] The present invention provides a non-uniform segmented hollow fiber membrane structure for membrane separation oxygen production on high-altitude trains, as shown in the following figure. Figure 1 As shown, specifically:

[0032] (1) Membrane module structure:

[0033] Hollow fiber membranes, used for oxygen generation via membrane separation in high-altitude trains, are employed, with a counter-current flow pattern. Raw air flows axially into the hollow fiber cavity, while oxygen-enriched gas permeates out from the outside of the membrane. The hollow fiber membrane is divided into a front section and a rear section, which are integrally molded. The segment ratio, i.e., the percentage of the front section's length to the total membrane length, is 30%-70%.

[0034] (2) Non-uniform segmented membrane design with "high permeability at the front end and low permeability and high selectivity at the back end":

[0035] The front end uses highly permeable materials, preferably with oxygen and nitrogen permeability coefficients increased to twice that of homogeneous membranes, while maintaining selectivity at 4.07.

[0036] The downstream section uses low-permeability, high-selectivity materials, preferably reducing the oxygen permeability coefficient to 50% of that of the homogenized membrane and the nitrogen permeability coefficient to 30% of that of the homogenized membrane, thereby increasing the selectivity to 6.78 (the homogenized membrane selectivity is 4.07).

[0037] The segmentation ratio is adjustable, with a preferred ratio of 50%, meaning the lengths of the front and rear segments are equal. Simulation optimization is used to balance purity and yield.

[0038] (3) Performance basis:

[0039] A numerical model for gas membrane separation was established based on the gas dissolution-diffusion model. The pressure drop inside the membrane was described by the Hagen-Poiseuille equation, and the performance of the segmented membrane was verified. Simulation results show that the optimized design increases the oxygen-enriched gas flow rate by 18.51%, the oxygen concentration from 43.40% to 43.64%, and the oxygen production rate from 36.47% to 43.45%.

[0040] A method for preparing a non-uniform segmented hollow fiber membrane for oxygen generation via membrane separation on high-altitude trains includes the following steps:

[0041] Step 1: Prepare a reference hollow fiber membrane.

[0042] A benchmark homogeneous hollow fiber membrane was prepared using Matrimid polyimide as the substrate material, a spinning solution with a solid content of 20% was formulated, N-methylpyrrolidone as the solvent, and anhydrous ethanol and polyvinylpyrrolidone as additives. A wet-dry spinning process was employed. The oxygen permeability coefficient of the prepared benchmark homogeneous membrane was 3.72 × 10⁻⁶. -8 mol / (s·m 2 The nitrogen permeability coefficient is 0.92 × 10 Pa. -8 mol / (s·m 2 The oxygen-nitrogen separation selectivity was 4.07 (Pa). The prepared reference hollow fiber membrane was soaked in deionized water and vacuum dried before use.

[0043] Step 2: Post-coating selective modification.

[0044] The coating solution is prepared using highly selective cross-linked polyimide as the coating material and a mixed solvent of hexane and isopropanol, with a solid content of 2% to 5%. The reference hollow fiber membrane is axially segmented and sealed. A pre-defined section, comprising 30% to 70% of the total length, is immersed in the coating solution, while the preceding section remains sealed and does not come into contact with the solution. The immersion time is 10 to 30 seconds, and the immersion temperature is 25°C. After immersion, the fiber membrane is pulled out of the coating solution at a constant rate of 5 to 10 cm / min to ensure a uniform, defect-free, ultra-thin selective skin layer is formed on the surface of the latter section.

[0045] Step 3: Post-treatment and curing.

[0046] The coated hollow fiber membrane was air-dried at room temperature (25℃) for 30 minutes in a dust-free environment, then transferred to a vacuum drying oven at 60℃ to 80℃ for 12 to 24 hours to allow the coating solvent to completely evaporate. Following this, a thermal crosslinking treatment was performed. The thermal crosslinking temperature was 180℃ to 200℃, and the treatment time was 2 to 3 hours. This enhanced the adhesion between the coating and the substrate fibers, improving the membrane material's pressure resistance and vibration stability. The final product is a non-uniform segmented hollow fiber membrane with a high-permeability front section and a low-permeability, high-selectivity back section.

[0047] Example:

[0048] Non-uniform segmented membrane design

[0049] 1. Membrane structure parameters: Hollow fiber membrane length 1.6m, inner diameter 0.0003m, number of hollow fibers 6000, effective membrane area calculated based on the number of fibers; membrane structure parameters are consistent with those of homogeneous membrane.

[0050] 2. Segmented configuration: The segment ratio is 50%, that is, the front segment is 0.8m and the back segment is 0.8m; the oxygen permeability coefficient of the front segment is set to twice that of the homogeneous membrane, and the nitrogen permeability coefficient is set to twice that of the homogeneous membrane, so the selectivity is maintained at 4.07, which is higher than that of the homogeneous membrane; the oxygen permeability coefficient of the front segment is set to 50% of that of the homogeneous membrane, and the nitrogen permeability coefficient is set to 30% of that of the homogeneous membrane, so the selectivity is increased to 6.78, forming a low permeability and high selectivity characteristic.

[0051] 3. Operating conditions: The feed gas pressure is 0.9 MPa, the standard flow rate is 6.72 L / s, and the oxygen-enriched gas pressure is 0.1 MPa; a counter-current flow mode is adopted, with the feed air flowing in from the inner cavity of the hollow fiber and the oxygen-enriched gas collected from the outside of the membrane; the operating conditions are the same as those of the homogenized membrane.

[0052] Comparative example:

[0053] Traditional homogenizing membrane

[0054] 1. Membrane structure parameters: Hollow fiber membrane length 1.6m, inner diameter 0.0003m, number of hollow fibers 6000, effective membrane area calculated based on the number of fibers.

[0055] 2. Material properties: The oxygen permeability coefficient is 1.86×10-8 mol / (s•m2•Pa), the nitrogen permeability coefficient is 0.46×10-8 mol / (s•m2•Pa), and the selectivity is 4.07.

[0056] 3. Operating conditions: The raw material air pressure is 0.9 MPa, the flow rate under standard conditions is 6.72 L / s, and the oxygen-enriched gas pressure is 0.1 MPa; a counter-current flow mode is adopted, with the raw material air flowing in from the inner cavity of the hollow fiber and the oxygen-enriched gas collected from the outside of the membrane.

[0057] Performance comparison results:

[0058] Numerical model simulations show that the traditional homogeneous membrane produces an oxygen-enriched gas flow rate of 1.1801 L / s, an oxygen concentration of 43.40%, and an oxygen production rate of 36.47%. The non-uniform segmented hollow fiber membrane of this invention produces an oxygen-enriched gas flow rate of 1.3985 L / s, an oxygen concentration of 43.64%, and an oxygen production rate of 43.45%, all of which are superior to the homogeneous membrane.

Claims

1. A non-uniform segmented hollow fiber membrane for high altitude train membrane separation oxygen generation, characterized in that: The fiber membrane is divided into a front section and a rear section along the axial direction, and the front section and the rear section are integrally formed structures; the front section uses a high-permeability material, and the rear section uses a low-permeability, high-selectivity material; the segment ratio, that is, the percentage of the length of the front section to the total length of the membrane, is 30%-70%.

2. The non-uniform segmented hollow fiber membrane for high altitude train membrane separation oxygen generation according to claim 1, characterized in that: In the highly permeable material of the front end, the permeability coefficients of oxygen and nitrogen are both twice that of the homogeneous membrane, and the selectivity is maintained at 4.

07.

3. The non-uniform segmented hollow fiber membrane for high altitude train membrane separation oxygen generation according to claim 1, characterized in that: In the downstream low-permeability, high-selectivity material, the oxygen permeability coefficient is 50% of that of the homogeneous membrane, the nitrogen permeability coefficient is 30% of that of the homogeneous membrane, and the selectivity is increased to 6.

78.

4. The non-uniform segmented hollow fiber membrane for high altitude train membrane separation oxygen generation according to claim 1, characterized in that: The segmentation ratio is 50%, meaning the length of the first segment is equal to the length of the second segment.

5. The non-uniform segmented hollow fiber membrane for high altitude train membrane separation oxygen generation according to claim 1, characterized in that: The hollow fiber membrane has a length of 1.6m, an inner diameter of 0.0003m, and 6000 hollow fibers. The effective membrane area is calculated based on the number of fibers.

6. A non-uniform segmented hollow fiber membrane for oxygen generation by membrane separation on plateau trains according to claim 1, characterized in that: The hollow fiber membrane adopts a counter-current flow mode, with raw material air flowing axially into the hollow fiber cavity and oxygen-enriched gas permeating out from the outside of the membrane. Operating conditions: The raw material gas air pressure is 0.9 MPa, the standard flow rate is 6.72 L / s, and the oxygen-enriched gas pressure is 0.1 MPa.

7. The method for preparing a non-uniform segmented hollow fiber membrane for oxygen generation by membrane separation on plateau trains as described in any one of claims 1-6, characterized in that: Includes the following steps: Step 1: Prepare a reference hollow fiber membrane; Using Matrimid polyimide as the base material, a spinning solution with a solid content of 18%-22% was prepared, with N-methylpyrrolidone as the solvent and anhydrous ethanol and polyvinylpyrrolidone as additives. A homogeneous reference hollow fiber membrane was prepared by dry and wet spinning process. The prepared reference hollow fiber membrane was soaked in deionized water and vacuum dried for later use. Step 2: Post-coating selective modification; A coating solution with a solid content of 2%-5% is prepared. The coating material is a highly selective cross-linked polyimide, and the solvent is a mixture of hexane and isopropanol. The reference hollow fiber membrane is sealed in sections along the axial direction, with only the section that is pre-designated to be the rear section accounting for 30%-70% of the total length immersed in the coating solution, while the front section is kept sealed and does not come into contact with the coating solution. After the immersion coating is completed, the fiber membrane is pulled out of the coating solution at a constant rate, forming an ultrathin selective skin layer on the surface of the rear section of the reference hollow fiber membrane. Step 3: Post-treatment and curing; After the hollow fiber membrane with dip coating is dried at room temperature, it is subjected to vacuum drying to completely evaporate the coating solvent. Then, it is subjected to thermal cross-linking treatment to enhance the adhesion between the coating and the substrate fiber. Finally, a non-uniform segmented hollow fiber membrane with a high permeability structure in the front section and a low permeability and high selectivity structure in the back section is obtained.

8. The method for preparing a non-uniform segmented hollow fiber membrane for oxygen generation by membrane separation on plateau trains according to claim 7, characterized in that: The solid content of the spinning solution in the step 1 is 20%, and the oxygen permeation coefficient of the benchmark homogeneous hollow fiber membrane prepared is 3.72*10 -8 mol / (s*m 2 *Pa), the nitrogen permeation coefficient is 0.92*10 -8 mol / (s*m 2 *Pa), and the oxygen-nitrogen separation selectivity is 4.

07.

9. A method for preparing a non-uniform segmented hollow fiber membrane for oxygen generation by membrane separation on a plateau train according to claim 7, characterized in that: In step 2, the dipping time is 10s-30s, the dipping temperature is 25℃, and the lifting speed is 5cm / min-10cm / min.

10. A method for preparing a non-uniform segmented hollow fiber membrane for oxygen generation by membrane separation on a plateau train according to claim 7, characterized in that: In step 3, the room temperature drying environment is a dust-free environment at 25℃, and the drying time is 30 minutes; the vacuum drying temperature is 60℃-80℃, and the drying time is 12h-24h; the thermal crosslinking treatment temperature is 180℃-200℃, and the treatment time is 2h-3h.

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