A polyimide hollow fiber membrane for oxygen / nitrogen separation preparation method

Abstract

The present application relates to the technical field of gas separation membrane, and particularly relates to a polyimide hollow fiber membrane preparation method for oxygen-nitrogen separation; aromatic dianhydride and diamine are first polymerized at low temperature in N-methylpyrrolidone to prepare a polyamide acid solution, polyvinylpyrrolidone pore-forming additives and polyethylene glycol rheological modifiers are added, and the solution is stirred and vacuum degassed to obtain a spinning dope; then the dope is moved into a spinning kettle, extruded through a hollow spinneret, and simultaneously fed with a core liquid, and then drawn and washed to obtain a nascent hollow fiber membrane; then the nascent membrane is wound and collected, washed with deionized water, and dried at room temperature; the dried nascent membrane is heat treated to completely heat imidize the polyamide acid and form a stable polyimide structure; finally, the membrane is drawn, shaped, and wound to obtain a finished product; through the above method, the spinning solution, spinning process and heat imidization process can be controlled, structural defects of the membrane filament are avoided, the compactness of the polyimide structure is improved, and the application requirements are met.

Description

Technical Field

[0001] This invention relates to the field of gas separation membrane technology, and more particularly to a method for preparing oxygen and nitrogen separation using a polyimide hollow fiber membrane. Background Technology

[0002] Industrial oxygen and nitrogen separation often employs cryogenic distillation, pressure swing adsorption, and membrane separation technologies. Membrane separation offers significant advantages due to its low energy consumption, small footprint, and continuous operation. Polyimide (PI) is a preferred material for oxygen and nitrogen separation membranes due to its excellent temperature resistance, solvent resistance, and gas selectivity. Currently, the preparation of polyimide hollow fiber membranes mostly uses polyamic acid as a precursor, followed by spinning, phase separation, and thermal imidization to obtain the finished product.

[0003] However, in the existing technology, due to deficiencies in the control of spinning solution, spinning process parameters and thermal imidization process, structural defects in the membrane fibers and poor density of the polyimide structure can easily occur, resulting in large fluctuations in the oxygen and nitrogen separation performance of polyimide hollow fiber membranes, which cannot meet the requirements. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a polyimide hollow fiber membrane for oxygen and nitrogen separation. This method aims to solve the technical problems in the prior art, where deficiencies in the control of spinning solution, spinning process parameters, and thermal imidization process easily lead to structural defects in the membrane fibers and poor density of the polyimide structure, resulting in large fluctuations in the oxygen and nitrogen separation performance of the polyimide hollow fiber membrane and failing to meet the requirements.

[0005] To achieve the above objectives, the present invention employs a method for preparing oxygen and nitrogen separation using a polyimide hollow fiber membrane, comprising the following steps: Aromatic dianhydride and aromatic diamine are polymerized at low temperature in N-methylpyrrolidone solution to obtain polyamic acid solution. Polyvinylpyrrolidone is added as a pore-forming aid and polyethylene glycol as a rheology modifier. After stirring evenly, vacuum degassing is performed to obtain spinning solution. The spinning solution is transferred into the spinning kettle and the spinning pipeline is connected to the hollow spinneret. The spinning solution is extruded through the spinneret and the core liquid is introduced into the hollow fiber at the same time. After traction and washing, the nascent hollow fiber membrane is obtained. The nascent hollow fiber membrane is drawn out from the external coagulation bath, collected by a winding device, and the wound membrane fibers are thoroughly washed with deionized water to remove residual solvent and impurities, and then air-dried at room temperature. The dried nascent hollow fiber membrane is heat-treated to completely thermally imidize the polyamic acid and form a stable polyimide structure. After heat treatment, stretching and winding are performed to obtain an oxygen-nitrogen separated polyimide hollow fiber membrane.

[0006] In the step of low-temperature polymerization of aromatic dianhydride and aromatic diamine in N-methylpyrrolidone solution to obtain polyamic acid solution, adding polyvinylpyrrolidone as a pore-forming aid and polyethylene glycol as a rheology modifier, stirring evenly and then vacuum degassing to obtain spinning solution: In a closed reactor under nitrogen protection throughout the process, aromatic dianhydride and aromatic diamine are added to N-methylpyrrolidone solvent. The reaction temperature is 0~5℃, the stirring rate is adjusted to 300~500r / min, and the reaction is carried out for 6~12h to obtain a polyamic acid solution with a solid content of 8~18wt%. Maintain the reaction system temperature at 0~5℃ and the stirring speed at 200~300r / min. Slowly add 0.5~3.0% by mass of polyvinylpyrrolidone as a pore-forming aid and 0.3~2.0% by mass of polyethylene glycol as a rheology modifier to the polyamic acid solution. After the addition is complete, continue stirring at room temperature for 2~4h. The mixed polyamic acid solution was transferred to a vacuum degassing kettle, the kettle was closed and a vacuum was drawn, and the vacuum degree was controlled at ≤-0.09MPa. At the same time, a low-speed stirrer was turned on, with a stirring rate of 80~120r / min, and the vacuum degassing treatment was carried out for 2~5 hours. The deaerated mixture is pressure filtered through a filter element with a precision of 50~100μm, with the filtration pressure controlled at 0.1~0.3MPa, to remove trace amounts of insoluble impurities and gel particles from the mixture, resulting in a stable spinning solution with a viscosity of 10000~50000mPa・s, free of bubbles and impurities.

[0007] In the step of adding aromatic dianhydride and aromatic diamine to N-methylpyrrolidone solvent in a sealed reactor under nitrogen protection throughout the process, the reaction temperature is 0~5℃, the stirring rate is adjusted to 300~500 r / min, and the reaction is carried out for 6~12 h to obtain a polyamic acid solution with a solid content of 8~18 wt%: The molar ratio of aromatic dianhydride to aromatic diamine is 1:0.98~1.02.

[0008] In the steps of transferring the spinning solution into the spinning kettle, connecting the spinning pipeline to the hollow spinneret; extruding the spinning solution through the spinneret while simultaneously introducing core liquid into the hollow fiber; and obtaining the nascent hollow fiber membrane through traction and washing: The spinning solution is transferred into the spinning kettle under sealed conditions at room temperature. The spinning kettle and stainless steel spinning pipeline are preheated at a constant temperature of 25~45℃. The spinning pipeline is then sealed and connected to a hollow spinneret with an outer diameter of 0.3~0.8mm and an inner diameter of 0.15~0.4mm. Turn on the spinning metering pump and precisely control the extrusion speed of the spinning solution at 3~10mL / min. At the same time, the core liquid is introduced into the inner hole of the hollow spinneret through the core liquid metering pump. The core liquid is a mixture of N-methylpyrrolidone and deionized water at a volume ratio of 3:7~6:4. The ratio of the core liquid flow rate to the spinning solution flow rate is controlled at 0.4~1.2. After the spinning dope and core solution are extruded simultaneously through the hollow spinneret, the resulting filament bundles pass through an air layer of 2-15 cm in height. The filament bundles then enter the external coagulation bath vertically. The external coagulation bath is a deionized water or an aqueous solution of 5-20% ethanol by volume. The bath temperature is controlled at 15-30℃. The filament bundles remain in the coagulation bath for 1-3 minutes to complete phase separation and molding, forming a hollow fiber prototype with an asymmetric structure. The hollow fiber filaments in the coagulation bath are pulled by a traction roller at a constant speed of 5~25m / min, and the membrane filaments are introduced into a continuous water washing tank. They are continuously washed with room temperature deionized water for 3~10min, with the water washing flow rate controlled at 5~10L / min, to initially remove the residual solvent and core liquid on the surface of the membrane filaments, and obtain the nascent hollow fiber membrane.

[0009] In the process of simultaneously extruding the spinning dope and core solution through a hollow spinneret, the resulting filaments pass through an air layer of 2-15 cm in height and then vertically enter an external coagulation bath. The external coagulation bath is a deionized water or an aqueous solution of 5-20% by volume ethanol, with the bath temperature controlled at 15-30°C. The filaments remain in the coagulation bath for 1-3 minutes to complete phase separation and form a hollow fiber prototype with an asymmetric structure. The ambient temperature of the air layer is controlled at 25~35℃ and the relative humidity is 40%~60%.

[0010] In the steps of drawing the nascent hollow fiber membrane from the external coagulation bath, collecting it through a winding device, thoroughly washing the wound membrane fibers with deionized water to remove residual solvents and impurities, and then air-drying it at room temperature: The nascent hollow fiber membrane, after initial washing, is drawn out from the washing tank, combed neatly by guide rollers, and then fed into the winding device. The nascent membrane filaments are collected in an orderly manner on the porous polypropylene roll at a winding speed of 3~8m / min. During the winding process, the winding tension is controlled to be 5~15N. Place the roll with the nascent membrane fibers into a special washing tank, add room temperature deionized water, and soak and wash the membrane fibers to remove residual N-methylpyrrolidone, core liquid components and trace impurities inside and on the surface of the membrane fibers. Remove the washed membrane fiber rolls from the washing tank, drain off the surface water, and place them at room temperature to air dry. During this period, turn the membrane fibers over periodically to ensure that the membrane fibers are dried evenly inside and out, and the moisture content is reduced to ≤1%.

[0011] In the step of placing the roll with the nascent membrane fibers into a special washing tank, adding room temperature deionized water to completely immerse the membrane fibers in the water for soaking and washing to remove residual N-methylpyrrolidone, core liquid components, and trace impurities from the inside and surface of the membrane fibers: During the soaking and washing process, after the first soaking for 1-2 hours, the water is replaced with deionized water. The soaking and washing process is repeated 3-6 times, with each soaking time lasting 1-3 hours. After the last wash, the conductivity of the washing solution is measured until the conductivity is ≤5μS / cm.

[0012] In the step of heat-treating the dried nascent hollow fiber membrane to completely thermally imidize the polyamic acid and form a stable polyimide structure: After drying, place the nascent hollow fiber membrane into a temperature-controlled oven, slowly expel the air from the oven, and introduce nitrogen for atmosphere protection. The nitrogen flow rate is controlled at 0.5~1.0L / min. Start the program to raise the oven temperature to 80~120℃ at a rate of 2~5℃ / min. After reaching the set temperature, keep it at that temperature for 1~2 hours to remove any residual trace moisture inside the membrane fibers. After dehydration is complete, continue to raise the oven temperature to 150-200℃ at a heating rate of 2-5℃ / min. After reaching the set temperature, keep it at the temperature for 1-2 hours to start the imidization reaction of polyamic acid, so that the polyamic acid molecules gradually dehydrate and cyclize to form a preliminary polyimide structure. Keep the nitrogen atmosphere constant and continue to raise the oven temperature to 250-300℃ at a heating rate of 2-5℃ / min. After reaching the set temperature, keep it at the temperature for 1-4 hours to allow the polyamic acid to undergo a complete thermal imidization reaction and form a structurally stable polyimide molecule structure. After complete imidization, turn off the heating program, maintain a nitrogen atmosphere, and allow the oven to cool naturally at a rate of ≤5℃ / min. Cool the oven to room temperature, turn off the nitrogen atmosphere after cooling, and remove the hollow fiber membrane.

[0013] In the step of stretching, shaping, and winding after heat treatment to obtain an oxygen-nitrogen separated polyimide hollow fiber membrane: The polyimide hollow fiber membrane filaments are unwound from the roll and introduced into the hot stretching and shaping equipment. The temperature in the hot stretching zone is precisely controlled at 80~150℃, and the membrane filaments are subjected to low-ratio hot stretching of 1%~5%. During the stretching process, the tension is kept stable at 10~20N. After the hot stretching is completed, the membrane fiber is introduced into the shaping zone of the device, where the temperature of the shaping zone is the same as that of the hot stretching zone. The membrane fiber is kept at this temperature for 10 to 30 minutes to stabilize the polyimide molecular chains that have been oriented after stretching. The shaped membrane fibers are combed neatly by guide rollers and fed into the finished product winding device. They are wound at a constant winding speed of 2~10m / min and the winding tension is controlled at 8~15N to obtain a polyimide hollow fiber membrane with an outer diameter of 200~1000μm, an inner diameter of 100~600μm, and a skin thickness of 50~300nm. The finished film filaments after winding are sealed and packaged, and then stored in a dry, light-proof environment with a temperature of 20~25℃ and a relative humidity of ≤40%.

[0014] This invention discloses a method for preparing a polyimide hollow fiber membrane for oxygen and nitrogen separation, comprising the following steps: Aromatic dianhydride and aromatic diamine are polymerized at low temperature in an N-methylpyrrolidone solution to obtain a polyamic acid solution; polyvinylpyrrolidone is added as a pore-forming aid and polyethylene glycol as a rheology modifier; after stirring evenly, vacuum degassing is performed to obtain a spinning solution; the spinning solution is transferred to a spinning kettle, and a spinning pipeline is connected to a hollow spinneret; the spinning solution is extruded through the spinneret, while a core liquid is simultaneously introduced into the hollow fiber; after traction and washing, a nascent hollow fiber membrane is obtained; the nascent hollow fiber membrane is drawn out from an external coagulation bath. The nascent hollow fiber membranes are collected by a winding device and thoroughly washed with deionized water to remove residual solvents and impurities, then air-dried at room temperature. The dried membranes are then heat-treated to fully thermally imidize the polyamic acid, forming a stable polyimide structure. After heat treatment, the membranes are stretched, shaped, and wound to obtain an oxygen-nitrogen separation polyimide hollow fiber membrane. This process allows for control of the spinning solution, spinning process, and thermal imidization, preventing structural defects in the membrane fibers, improving the density of the polyimide structure, and ensuring stable oxygen-nitrogen separation performance, meeting application requirements. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a flowchart of the steps in the preparation method of oxygen and nitrogen separation using polyimide hollow fiber membrane of the present invention.

[0017] Figure 2 This is a flowchart of steps S100 of the present invention.

[0018] Figure 3 This is a flowchart of steps S200 of the present invention.

[0019] Figure 4 This is a flowchart of steps S300 of the present invention.

[0020] Figure 5 This is a flowchart of steps S400 of the present invention.

[0021] Figure 6 This is a flowchart of steps S500 of the present invention. Detailed Implementation

[0022] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application.

[0023] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0024] It should be understood that although the terms first, second, third, etc., may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0025] Please see Figures 1-6 This invention provides a method for preparing a polyimide hollow fiber membrane for oxygen and nitrogen separation, comprising the following steps: S100: Aromatic dianhydride and aromatic diamine are polymerized at low temperature in N-methylpyrrolidone solution to obtain polyamic acid solution. Polyvinylpyrrolidone is added as a pore-forming aid and polyethylene glycol is added as a rheology modifier. After stirring evenly, vacuum degassing is performed to obtain spinning solution.

[0026] In this embodiment, aromatic dianhydride and aromatic diamine are polymerized at low temperature in N-methylpyrrolidone solution to obtain polyamic acid solution. Polyvinylpyrrolidone is added as a pore-forming aid and polyethylene glycol as a rheology modifier. After stirring evenly, vacuum degassing is performed to obtain spinning solution. The specific process is as follows: S101: In a closed reactor under nitrogen protection, aromatic dianhydride and aromatic diamine are added to N-methylpyrrolidone solvent at a molar ratio of 1:0.98~1.02. The reaction temperature is 0~5℃, the stirring rate is adjusted to 300~500r / min, and the reaction is carried out for 6~12h to obtain a polyamic acid solution with a solid content of 8~18wt%. S102: Maintain the reaction system temperature at 0~5℃ and the stirring speed at 200~300r / min. Slowly add polyvinylpyrrolidone (0.5~3.0% by mass of the total mass of the polyamic acid solution) as a pore-forming aid and polyethylene glycol (0.3~2.0% by mass of the total mass of the polyamic acid solution) as a rheology modifier to the polyamic acid solution. After the addition is complete, continue stirring at room temperature for 2~4h. S103: Transfer the mixed polyamic acid mixture to a vacuum degassing kettle, close the kettle and evacuate the vacuum, control the vacuum degree to ≤-0.09MPa, and at the same time turn on the low-speed stirring at a stirring rate of 80~120r / min to perform vacuum degassing treatment for 2~5h; S104: The deaerated mixture is pressure filtered through a filter element with a precision of 50~100μm, and the filtration pressure is controlled at 0.1~0.3MPa to remove trace amounts of insoluble impurities and gel particles from the mixture, resulting in a stable spinning solution with a viscosity of 10000~50000mPa・s, free of bubbles and impurities.

[0027] In the above process, firstly, in a sealed reactor under nitrogen protection, aromatic dianhydride and aromatic diamine are added to N-methylpyrrolidone solvent at a molar ratio of 1:0.98~1.02. The reaction temperature is 0~5℃, the stirring rate is adjusted to 300~500 r / min, and the reaction is carried out for 6~12 h to obtain a polyamic acid solution with a solid content of 8~18 wt%. While maintaining the reaction system temperature at 0~5℃ and the stirring rate at 200~300 r / min, polyvinylpyrrolidone is slowly added to the polyamic acid solution at a mass fraction of 0.5~3.0% of the total mass of the polyamic acid solution as a pore-forming aid, and polyvinylpyrrolidone at a mass fraction of 0.3~2% of the total mass of the polyamic acid solution. 0% polyethylene glycol was added as a rheology modifier, and stirring was continued at room temperature for 2-4 hours after the addition was completed. Then, the mixed polyamic acid solution was transferred to a vacuum degassing kettle, the kettle was closed and a vacuum was drawn, and the vacuum degree was controlled at ≤-0.09MPa. At the same time, low-speed stirring was started at a stirring rate of 80-120r / min for vacuum degassing treatment for 2-5 hours. Subsequently, the degassed solution was pressure filtered through a filter element with a precision of 50-100μm, and the filtration pressure was controlled at 0.1-0.3MPa to remove trace insoluble impurities and gel particles from the solution, resulting in a stable spinning solution with a viscosity of 10000-50000mPa・s, free of bubbles and impurities.

[0028] S200: The spinning solution is transferred into the spinning kettle and the spinning pipeline is connected to the hollow spinneret; the spinning solution is extruded through the spinneret and the core liquid is introduced into the hollow fiber at the same time. After traction and washing, the nascent hollow fiber membrane is obtained.

[0029] In this embodiment, the spinning solution is transferred into the spinning kettle, and the spinning pipeline is connected to the hollow spinneret; the spinning solution is extruded through the spinneret, and a core solution is simultaneously introduced into the hollow fiber. After traction and washing, a nascent hollow fiber membrane is obtained. The specific process is as follows: S201: The spinning solution is transferred into the spinning kettle under normal temperature and sealed conditions. The spinning kettle and stainless steel spinning pipeline are preheated at a constant temperature, and the temperature is controlled at 25~45℃. The spinning pipeline is then sealed and connected to a hollow spinneret with an outer diameter of 0.3~0.8mm and an inner diameter of 0.15~0.4mm. S202: Turn on the spinning metering pump and precisely control the extrusion speed of the spinning solution at 3~10mL / min. At the same time, the core liquid is introduced into the inner hole of the hollow spinneret through the core liquid metering pump. The core liquid is a mixture of N-methylpyrrolidone and deionized water at a volume ratio of 3:7~6:4. The ratio of the core liquid flow rate to the spinning solution flow rate is controlled at 0.4~1.2. S203: After the spinning dope and core solution are simultaneously extruded through a hollow spinneret, the resulting filament bundles pass through an air layer of 2-15cm in height. The ambient temperature of the air layer is controlled at 25-35℃ and the relative humidity is 40%-60%. The filament bundles enter the external coagulation bath vertically. The external coagulation bath is a deionized water or an ethanol aqueous solution with a volume fraction of 5-20%. The bath temperature is controlled at 15-30℃. The filament bundles stay in the coagulation bath for 1-3 minutes to complete phase separation and molding, forming a hollow fiber prototype with an asymmetric structure. S204: The hollow fiber prototype in the coagulation bath is pulled by the traction roller at a constant speed of 5~25m / min, and the membrane fiber is introduced into the continuous water washing tank. It is continuously washed with room temperature deionized water for 3~10min, and the water washing flow rate is controlled at 5~10L / min to initially remove the residual solvent and core liquid on the surface of the membrane fiber, and obtain the nascent hollow fiber membrane.

[0030] In the above process, the spinning solution is first transferred into the spinning kettle under sealed conditions at room temperature. The spinning kettle and stainless steel spinning tubing are preheated at a constant temperature of 25-45℃. The spinning tubing is then sealed and connected to a hollow spinneret with an outer diameter of 0.3-0.8 mm and an inner diameter of 0.15-0.4 mm. The spinning metering pump is turned on, and the extrusion rate of the spinning solution is precisely controlled at 3-10 mL / min. Simultaneously, the core liquid is introduced into the inner hole of the hollow spinneret through the core liquid metering pump. The core liquid is a mixture of N-methylpyrrolidone and deionized water at a volume ratio of 3:7-6:4, and the flow rate of the core liquid is controlled to be 0.4-1.2 compared to the flow rate of the spinning solution. After the spinning solution and core liquid are simultaneously extruded through the hollow spinneret, the resulting filament bundle... The fibers pass through an air layer 2-15 cm high, with the ambient temperature controlled at 25-35℃ and relative humidity at 40%-60%. The fibers then vertically enter an external coagulation bath, which is either deionized water or an aqueous solution of 5-20% ethanol by volume, with the bath temperature controlled at 15-30℃. The fibers remain in the coagulation bath for 1-3 minutes to complete phase separation and form a hollow fiber prototype with an asymmetric structure. The hollow fiber prototype is then pulled in the coagulation bath at a constant speed of 5-25 m / min by a traction roller, and the membrane fibers are introduced into a continuous water washing tank. The membrane fibers are continuously washed with room temperature deionized water for 3-10 minutes, with the water flow rate controlled at 5-10 L / min, to initially remove residual solvent and core liquid from the surface of the membrane fibers, resulting in a nascent hollow fiber membrane.

[0031] S300: The nascent hollow fiber membrane is drawn out from the external coagulation bath, collected by the winding device, and thoroughly washed with deionized water to remove residual solvent and impurities, and then air-dried at room temperature.

[0032] In this embodiment, the nascent hollow fiber membrane is drawn out from the external coagulation bath, collected by a winding device, and thoroughly washed with deionized water to remove residual solvent and impurities. It is then air-dried at room temperature. The specific process is as follows: S301: The nascent hollow fiber membrane, after preliminary washing, is drawn out from the washing tank, combed neatly by guide rollers, and then fed into the winding device. The nascent membrane filaments are collected in an orderly manner on the porous polypropylene roll at a winding speed of 3~8m / min. During the winding process, the winding tension is controlled to be 5~15N. S302: Place the roll with the nascent membrane fibers into a special washing tank, add room temperature deionized water, and immerse the membrane fibers completely in the water for soaking and washing. After the first soaking for 1-2 hours, replace the deionized water and repeat the soaking and washing 3-6 times, with each soaking time being 1-3 hours. After the last washing, test the conductivity of the washing solution until the conductivity is ≤5μS / cm to remove N-methylpyrrolidone, core liquid components and trace impurities remaining inside and on the surface of the membrane fibers. S303: Remove the washed membrane yarn rolls from the washing tank, drain the surface water, and place them at room temperature to air dry. During this period, turn the membrane yarns over periodically to ensure that the membrane yarns are dried evenly inside and out, and the moisture content is reduced to ≤1%.

[0033] In the above process, the nascent hollow fiber membrane, after preliminary washing, is first drawn out from the washing tank, combed neatly by guide rollers, and then fed into the winding device. The nascent membrane filaments are orderly collected on a porous polypropylene roll at a winding speed of 3~8 m / min, and the winding tension is controlled at 5~15 N during the winding process. Then, the roll with the nascent membrane filaments is placed in a special washing tank, and room temperature deionized water is added to completely immerse the membrane filaments in the water for soaking and washing. After the first soaking for 1~2 hours, the deionized water is replaced, and the soaking and washing is repeated 3~6 times, with each soaking time being 1~3 hours. After the last washing, the conductivity of the washing solution is tested until the conductivity is ≤5μS / cm to remove residual N-methylpyrrolidone, core liquid components, and trace impurities inside and on the surface of the membrane filaments. Then, the washed membrane filament roll is taken out from the washing tank, drained of surface free water, and placed at room temperature to air dry. During this period, the membrane filaments are turned over periodically to ensure that the membrane filaments are dried evenly inside and out until the moisture content is reduced to ≤1%.

[0034] S400: The dried nascent hollow fiber membrane is heat-treated to completely thermally imidize the polyamic acid, forming a stable polyimide structure.

[0035] In this embodiment, the dried nascent hollow fiber membrane is heat-treated to completely thermally imidize the polyamic acid, forming a stable polyimide structure. The specific process is as follows: S401: Place the dried nascent hollow fiber membrane into a temperature-controlled oven, slowly expel the air from the oven, introduce nitrogen for atmosphere protection, control the nitrogen flow rate at 0.5~1.0L / min, start the program temperature rise, raise the oven temperature to 80~120℃ at a temperature rise rate of 2~5℃ / min, and hold at the set temperature for 1~2 hours to remove the trace amount of residual moisture inside the membrane fibers; S402: After dehydration is complete, continue to raise the oven temperature to 150-200℃ at a heating rate of 2-5℃ / min. After reaching the set temperature, keep it at the temperature for 1-2 hours to start the imidization reaction of polyamic acid, so that the polyamic acid molecules gradually dehydrate and cyclize to form a preliminary polyimide structure. S403: Keep the nitrogen atmosphere constant and continue to raise the oven temperature to 250-300℃ at a heating rate of 2-5℃ / min. After reaching the set temperature, keep it at the temperature for 1-4 hours to allow the polyamic acid to undergo a complete thermal imidization reaction and form a structurally stable polyimide molecule structure. S404: After complete imidization, turn off the heating program, maintain a nitrogen atmosphere, and allow the oven to cool naturally at a rate of ≤5℃ / min. Cool the oven to room temperature. After cooling is complete, turn off the nitrogen atmosphere and remove the hollow fiber membrane.

[0036] In the above process, the dried nascent hollow fiber membrane is first placed in a temperature-controlled oven. Air is slowly expelled from the oven, and nitrogen is introduced for atmosphere protection, with the nitrogen flow rate controlled at 0.5~1.0 L / min. The programmed temperature rise is then initiated, increasing the oven temperature to 80~120℃ at a rate of 2~5℃ / min. After reaching the set temperature, the temperature is maintained for 1~2 hours to remove any residual trace moisture inside the membrane fibers. After dehydration is complete, the oven temperature is further increased to 150~200℃ at a rate of 2~5℃ / min. After reaching the set temperature, the temperature is maintained for 1~2 hours, and polymerization is then started. The imidization reaction of ammonium acid causes the polyammonium acid molecules to gradually dehydrate and cyclize, forming a preliminary polyimide structure. While maintaining a constant nitrogen atmosphere, the oven temperature is raised to 250-300℃ at a heating rate of 2-5℃ / min. After reaching the set temperature, it is held for 1-4 hours to allow the polyammonium acid to undergo a complete thermal imidization reaction, forming a structurally stable polyimide molecule structure. After complete imidization, the temperature program is turned off, and while maintaining a nitrogen atmosphere, the oven is allowed to cool naturally at a rate of ≤5℃ / min, cooling to room temperature with the oven. After cooling is complete, the nitrogen atmosphere is turned off, and the hollow fiber membrane filaments are removed.

[0037] S500: After heat treatment, stretching and winding are performed to obtain an oxygen-nitrogen separated polyimide hollow fiber membrane.

[0038] In this embodiment, after heat treatment, stretching, shaping, and winding are performed to obtain an oxygen-nitrogen separated polyimide hollow fiber membrane. The specific process is as follows: S501: The polyimide hollow fiber membrane filaments are unwound from the roll and introduced into the hot stretching and shaping equipment. The temperature of the hot stretching zone is precisely controlled at 80~150℃. The membrane filaments are subjected to low-ratio hot stretching of 1%~5%, and the tension is kept stable at 10~20N during the stretching process. S502: After the hot stretching is completed, the membrane fiber is introduced into the shaping zone of the device. The temperature of the shaping zone is the same as that of the hot stretching zone. The membrane fiber is kept at this temperature for 10-30 minutes to stabilize the polyimide molecular chains that have been oriented after stretching. S503: The shaped membrane fibers are combed neatly by guide rollers and fed into the finished product winding device. They are wound at a constant winding speed of 2~10m / min and the winding tension is controlled at 8~15N to obtain a polyimide hollow fiber membrane with an outer diameter of 200~1000μm, an inner diameter of 100~600μm, and a skin thickness of 50~300nm. S504: Seal and package the finished film filaments after winding, and store them in a dry and light-proof environment with a temperature of 20~25℃ and a relative humidity of ≤40%.

[0039] In the above process, the polyimide hollow fiber membrane filaments are first unwound from the roll and introduced into a hot stretching and setting device. The temperature in the hot stretching zone is precisely controlled at 80~150℃, and the membrane filaments are subjected to a low-ratio hot stretch of 1%~5%, maintaining a stable tension of 10~20N during the stretching process. After the hot stretching is completed, the membrane filaments are introduced into the setting zone of the device, where the temperature is consistent with that of the hot stretching zone. The membrane filaments are then set at this temperature for 10~30 minutes, allowing the polyimide molecular chains that have been stretched to become oriented to form a stable shape. The membrane fibers are stabilized and formed; then, the shaped membrane fibers are combed neatly by guide rollers and fed into the finished product winding device, where they are wound at a constant winding speed of 2~10m / min and the winding tension is controlled at 8~15N to obtain a polyimide hollow fiber membrane with an outer diameter of 200~1000μm, an inner diameter of 100~600μm, and a skin thickness of 50~300nm; the finished membrane fibers are then sealed and packaged, and stored in a dry and light-proof environment with a temperature of 20~25℃ and a relative humidity of ≤40%.

[0040] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein.

[0041] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope.

Claims

1. A method for preparing oxygen and nitrogen separation using a polyimide hollow fiber membrane, characterized in that, Includes the following steps: Aromatic dianhydride and aromatic diamine are polymerized at low temperature in N-methylpyrrolidone solution to obtain polyamic acid solution. Polyvinylpyrrolidone is added as a pore-forming aid and polyethylene glycol as a rheology modifier. After stirring evenly, vacuum degassing is performed to obtain spinning solution. The spinning solution is transferred into the spinning kettle and the spinning pipeline is connected to the hollow spinneret. The spinning solution is extruded through the spinneret and the core liquid is introduced into the hollow fiber at the same time. After traction and washing, the nascent hollow fiber membrane is obtained. The nascent hollow fiber membrane is drawn out from the external coagulation bath, collected by a winding device, and thoroughly washed with deionized water to remove residual solvent and impurities. It is then air-dried at room temperature. The dried nascent hollow fiber membrane is heat-treated to completely thermally imidize the polyamic acid and form a stable polyimide structure. After heat treatment, stretching and winding are performed to obtain an oxygen-nitrogen separated polyimide hollow fiber membrane.

2. The method for preparing oxygen and nitrogen separation using the polyimide hollow fiber membrane as described in claim 1, characterized in that, In the step of low-temperature polymerization of aromatic dianhydride and aromatic diamine in N-methylpyrrolidone solution to obtain polyamic acid solution, polyvinylpyrrolidone as a pore-forming aid and polyethylene glycol as a rheology modifier are added, and after stirring evenly, vacuum degassing is performed to obtain spinning solution: In a closed reactor under nitrogen protection throughout the process, aromatic dianhydride and aromatic diamine are added to N-methylpyrrolidone solvent. The reaction temperature is 0~5℃, the stirring rate is adjusted to 300~500r / min, and the reaction is carried out for 6~12h to obtain a polyamic acid solution with a solid content of 8~18wt%. Maintain the reaction system temperature at 0~5℃ and the stirring speed at 200~300r / min. Slowly add 0.5~3.0% by mass of polyvinylpyrrolidone as a pore-forming aid and 0.3~2.0% by mass of polyethylene glycol as a rheology modifier to the polyamic acid solution. After the addition is complete, continue stirring at room temperature for 2~4h. The mixed polyamic acid solution was transferred to a vacuum degassing kettle, the kettle was closed and a vacuum was drawn, and the vacuum degree was controlled at ≤-0.09MPa. At the same time, a low-speed stirrer was turned on, with a stirring rate of 80~120r / min, and the vacuum degassing treatment was carried out for 2~5 hours. The deaerated mixture is pressure filtered through a filter element with a precision of 50~100μm, with the filtration pressure controlled at 0.1~0.3MPa, to remove trace amounts of insoluble impurities and gel particles from the mixture, resulting in a stable spinning solution with a viscosity of 10000~50000mPa・s, free of bubbles and impurities.

3. The method for preparing oxygen and nitrogen separation using the polyimide hollow fiber membrane as described in claim 2, characterized in that, In a closed reactor under nitrogen protection throughout the process, aromatic dianhydride and aromatic diamine are added to N-methylpyrrolidone solvent. The reaction temperature is maintained at 0-5℃, the stirring rate is adjusted to 300-500 r / min, and the reaction is carried out for 6-12 hours to obtain a polyamic acid solution with a solid content of 8-18 wt%. The molar ratio of aromatic dianhydride to aromatic diamine is 1:0.98~1.

02.

4. The method for preparing oxygen and nitrogen separation using the polyimide hollow fiber membrane as described in claim 1, characterized in that, In the steps of transferring the spinning solution into the spinning kettle, connecting the spinning pipeline to the hollow spinneret; extruding the spinning solution through the spinneret while simultaneously introducing core liquid into the hollow fiber; and obtaining the nascent hollow fiber membrane through traction and washing: The spinning solution is transferred into the spinning kettle under sealed conditions at room temperature. The spinning kettle and stainless steel spinning pipeline are preheated at a constant temperature of 25~45℃. The spinning pipeline is then sealed and connected to a hollow spinneret with an outer diameter of 0.3~0.8mm and an inner diameter of 0.15~0.4mm. Turn on the spinning metering pump and precisely control the extrusion speed of the spinning solution at 3~10mL / min. At the same time, the core liquid is introduced into the inner hole of the hollow spinneret through the core liquid metering pump. The core liquid is a mixture of N-methylpyrrolidone and deionized water at a volume ratio of 3:7~6:

4. The ratio of the core liquid flow rate to the spinning solution flow rate is controlled at 0.4~1.

2. After the spinning dope and core solution are extruded simultaneously through the hollow spinneret, the resulting filament bundles pass through an air layer of 2-15 cm in height. The filament bundles then enter the external coagulation bath vertically. The external coagulation bath is a deionized water or an aqueous solution of 5-20% ethanol by volume. The bath temperature is controlled at 15-30℃. The filament bundles remain in the coagulation bath for 1-3 minutes to complete phase separation and molding, forming a hollow fiber prototype with an asymmetric structure. The hollow fiber filaments in the coagulation bath are pulled by a traction roller at a constant speed of 5~25m / min, and the membrane filaments are introduced into a continuous water washing tank. They are continuously washed with room temperature deionized water for 3~10min, with the water washing flow rate controlled at 5~10L / min, to initially remove the residual solvent and core liquid on the surface of the membrane filaments, and obtain the nascent hollow fiber membrane.

5. The method for preparing oxygen and nitrogen separation using the polyimide hollow fiber membrane as described in claim 4, characterized in that, After the spinning dope and core solution are simultaneously extruded through a hollow spinneret, the resulting filaments pass through an air layer of 2-15 cm in height. The filaments then vertically enter an external coagulation bath, which is a deionized water or 5-20% (v / v) ethanol aqueous solution. The bath temperature is controlled at 15-30°C. The filaments remain in the coagulation bath for 1-3 minutes to complete phase separation and form a hollow fiber prototype with an asymmetric structure. The ambient temperature of the air layer is controlled at 25~35℃ and the relative humidity is 40%~60%.

6. The method for preparing oxygen and nitrogen separation using the polyimide hollow fiber membrane as described in claim 1, characterized in that, In the steps of drawing the nascent hollow fiber membrane from the external coagulation bath, collecting it through a winding device, thoroughly washing the wound membrane fibers with deionized water to remove residual solvents and impurities, and then air-drying it at room temperature: The nascent hollow fiber membrane, after initial washing, is drawn out from the washing tank, combed neatly by guide rollers, and then fed into the winding device. The nascent membrane filaments are collected in an orderly manner on the porous polypropylene roll at a winding speed of 3~8m / min. During the winding process, the winding tension is controlled to be 5~15N. Place the roll with the nascent membrane fibers into a special washing tank, add room temperature deionized water, and soak and wash the membrane fibers to remove residual N-methylpyrrolidone, core liquid components and trace impurities inside and on the surface of the membrane fibers. Remove the washed membrane fiber rolls from the washing tank, drain off the surface water, and place them at room temperature to air dry. During this period, turn the membrane fibers over periodically to ensure that the membrane fibers are dried evenly inside and out, and the moisture content is reduced to ≤1%.

7. The method for preparing oxygen and nitrogen separation using the polyimide hollow fiber membrane as described in claim 6, characterized in that, In the step of placing the roll with the nascent membrane fibers into a special washing tank, adding room temperature deionized water to completely immerse the membrane fibers in the water, and soaking and washing to remove residual N-methylpyrrolidone, core liquid components, and trace impurities from the inside and surface of the membrane fibers: During the soaking and washing process, after the first soaking for 1-2 hours, the water is replaced with deionized water. The soaking and washing process is repeated 3-6 times, with each soaking time lasting 1-3 hours. After the last wash, the conductivity of the washing solution is measured until the conductivity is ≤5μS / cm.

8. The method for preparing oxygen and nitrogen separation using the polyimide hollow fiber membrane as described in claim 1, characterized in that, In the step of heat-treating the dried nascent hollow fiber membrane to completely thermally imidize the polyamic acid and form a stable polyimide structure: After drying, place the nascent hollow fiber membrane into a temperature-controlled oven, slowly expel the air from the oven, and introduce nitrogen for atmosphere protection. The nitrogen flow rate is controlled at 0.5~1.0L / min. Start the program to raise the oven temperature to 80~120℃ at a rate of 2~5℃ / min. After reaching the set temperature, keep it at that temperature for 1~2 hours to remove any residual trace moisture inside the membrane fibers. After dehydration is complete, continue to raise the oven temperature to 150-200℃ at a heating rate of 2-5℃ / min. After reaching the set temperature, keep it at the temperature for 1-2 hours to start the imidization reaction of polyamic acid, so that the polyamic acid molecules gradually dehydrate and cyclize to form a preliminary polyimide structure. Keep the nitrogen atmosphere constant and continue to raise the oven temperature to 250-300℃ at a heating rate of 2-5℃ / min. After reaching the set temperature, keep it at the temperature for 1-4 hours to allow the polyamic acid to undergo a complete thermal imidization reaction and form a structurally stable polyimide molecule structure. After complete imidization, turn off the heating program, maintain a nitrogen atmosphere, and allow the oven to cool naturally at a rate of ≤5℃ / min. Cool the oven to room temperature, turn off the nitrogen atmosphere after cooling, and remove the hollow fiber membrane.

9. The method for preparing oxygen and nitrogen separation using the polyimide hollow fiber membrane as described in claim 1, characterized in that, In the steps following heat treatment, stretching, shaping, and winding are performed to obtain the oxygen-nitrogen separated polyimide hollow fiber membrane: The polyimide hollow fiber membrane filaments are unwound from the roll and introduced into the hot stretching and shaping equipment. The temperature in the hot stretching zone is precisely controlled at 80~150℃, and the membrane filaments are subjected to low-ratio hot stretching of 1%~5%. During the stretching process, the tension is kept stable at 10~20N. After the hot stretching is completed, the membrane fiber is introduced into the shaping zone of the device, where the temperature of the shaping zone is the same as that of the hot stretching zone. The membrane fiber is kept at this temperature for 10 to 30 minutes to stabilize the polyimide molecular chains that have been oriented after stretching. The shaped membrane fibers are combed neatly by guide rollers and fed into the finished product winding device. They are wound at a constant winding speed of 2~10m / min and the winding tension is controlled at 8~15N to obtain a polyimide hollow fiber membrane with an outer diameter of 200~1000μm, an inner diameter of 100~600μm, and a skin thickness of 50~300nm. The finished film filaments after winding are sealed and packaged, and then stored in a dry, light-proof environment with a temperature of 20~25℃ and a relative humidity of ≤40%.

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