A method for plasma-enhanced chemical vapor deposition of hollow fiber gas separation membranes and applications thereof

Abstract

The application discloses a kind of plasma enhanced hollow fiber gas separation membrane chemical vapor deposition method and application.The hollow fiber gas separation membrane material is polymer, specifically selected from any one of polysulfone (PSf), polyethersulfone (PES), polyimide (PI), polybenzimidazole (PBI), cellulose acetate (CA), polyetherimide (PEI), polyamideimide.The dry jet / wet spinning process is used to prepare hollow fiber membrane, and the surface skin layer is functionally modified using plasma enhanced chemical vapor deposition technology, and the gas source is selected from one or more of H2, CH4, Ar, N2, CF4, O2 and NH3.The technology can control the pore structure and channel chemical properties of the skin layer of hollow fiber membrane, form a dense, ultra-thin, uniform and controllable atomic level selection layer, and significantly improve the gas separation performance.Meanwhile, the plasma treatment process is simple, low in cost and controllable, and suitable for large-scale industrial treatment.The obtained plasma enhanced chemical vapor deposition hollow fiber membrane also has excellent mechanical properties and plasticization stability, and has wide prospects in practical gas separation applications.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas separation membrane, and particularly relates to a method for plasma-enhanced chemical vapor deposition of hollow fiber gas separation membrane and application. BACKGROUND

[0002] Gas separation membrane technology is a pressure-driven gas separation process without phase change. Due to its advantages of high energy efficiency, low cost, simple maintenance, small footprint, green and pollution-free, etc., it has become an ideal choice to replace traditional separation methods (such as pressure swing adsorption and low-temperature distillation) and has shown good application prospects in pre-combustion CO2 capture, post-combustion CO2 capture, hydrogen separation and recovery, air separation, helium extraction from natural gas and decarburization of natural gas.

[0003] In the past few decades, microporous polymers have been used to prepare various membrane forms, including hollow fibers, plate-and-frame and spiral-wound, due to their low cost and easy processing. Among them, asymmetric hollow fiber membranes (HFMs) are widely used in industrial gas separation due to their unique structural characteristics, the combination of dense skin layer and porous sublayer, and high surface-to-volume ratio, self-supporting, flexibility and easy scale-up production.

[0004] The main challenge of gas separation membrane is that the gas separation performance of membrane material is limited by trade-off, and it is difficult to break through the upper limit of gas separation of permeability and selectivity. Existing commercial hollow fiber membrane materials, such as 5218, P84, CA, PESf, etc., have low selectivity due to wide polymer pore size distribution, and separation performance needs to be improved.

[0005] Plasma enhanced chemical vapor deposition (PECVD) is a post-processing method that excites specific gas sources into highly reactive free electrons, ions and other substances under the action of an electric field, allowing them to react with the sample surface in situ and at the atomic level. It has the advantages of in-situ reaction, controllable reaction, low cost, and large batch processing, and is expected to realize the modification of polymer microporous structure and break through the upper limit of gas separation. Chinese patent CN 118320629 A provides a plasma modification method for self-polymerization microporous polymer gas separation membrane. By adjusting the microporous structure of the membrane material, a high-efficiency gas selective transmission channel is constructed, thereby significantly improving the oxygen / nitrogen diffusion selectivity of the gas separation membrane. However, due to the high cost of synthesizing self-polymerization microporous polymer materials, the large-scale preparation of polymers is difficult, and it is impossible to realize the large-scale and application of gas separation membranes. Chinese patent CN106102885 A discloses a method for treating the surface of a polymer membrane using plasma. By treating part of the surface of the polymer membrane with plasma, active substances are introduced to improve the gas separation performance of the membrane material. However, this method is difficult to achieve uniform treatment on a large area, and thus it is difficult to effectively control the overall membrane pore structure. Bombarding the membrane surface may also affect the service life of the membrane. In addition, although the above two patents indicate that the polymer membrane can be selected from hollow fiber membranes, there is no description of the specific preparation method of the hollow fiber membrane.

[0006] The present application needs to provide a method for plasma enhanced chemical vapor deposition of hollow fiber gas separation membrane and a preparation process of the hollow fiber gas separation membrane. By plasma treatment, the surface skin layer of the hollow fiber membrane is functionally modified to regulate the skin layer microporous structure and pore chemical properties, forming a dense, ultra-thin, uniform and controllable atomic level selection layer to improve the gas separation performance. SUMMARY

[0007] The purpose of the present application is to provide a method for plasma enhanced chemical vapor deposition of hollow fiber gas separation membrane and its application, to obtain a hollow fiber membrane with high gas separation performance, excellent mechanical properties and plasticization stability, and to apply it to industrial gas separation scenarios.

[0008] To achieve this purpose, the present application adopts the following technical solutions:

[0009] In the first aspect, the gas separation membrane material is a polymer, specifically selected from any one of polysulfone (PSf), polyether sulfone (PES), polyimide (PI), polybenzimidazole (PBI), cellulose acetate (CA), polyetherimide (PEI), and polyamideimide.

[0010] Preferably, the gas separation membrane is an asymmetric hollow fiber membrane prepared by dry jet / wet spinning process.

[0011] In a second aspect, the present application provides a method for preparing a hollow fiber gas separation membrane, comprising the following steps:

[0012] (1) In a reaction kettle equipped with a mechanical stirrer, a certain weight ratio of polymer, solvents A and B, non-solvents C and D are added, the mixture is stirred for 1-7 days, and after complete dissolution, degassing is performed for 12-48 hours to obtain a spinning solution;

[0013] (2) The solvent A and the non-solvent C are prepared into a core solution according to a certain weight ratio;

[0014] (3) The spinning solution and the core solution are co-extruded through a spinneret into a coagulation bath for phase separation to prepare a nascent fiber, which is then drawn onto a spinning wheel for further solidification;

[0015] (4) The nascent fiber is removed from the spinning wheel, soaked in water for 1-5 days, and the water is replaced every 12 hours during the soaking. Then, the fiber is soaked in solvents E and F alternately for solvent exchange, and the solvents are replaced every 0.5-3 hours, for a total soaking time of 3-24 hours. The fiber is hung and dried in a fume hood for 30 minutes, and then baked in a vacuum drying oven at 120-180°C for 12-48 hours to remove any residual solvents, to obtain the final fiber;

[0016] (5) A 2-10 wt% solution of polydimethylsiloxane (PDMS) is prepared in solvent G, and the fiber is post-treated. After heating the solution at 80-120°C for 2-12 hours, the fiber is immersed in the solution for 1-30 minutes, and then excess solution is drained. The fiber is hung and dried in a fume hood for 8-24 hours, and then cured in a vacuum drying oven at 80-120°C for 2-12 hours. The final hollow fiber gas separation membrane is obtained.

[0017] The temperature of the reaction kettle in step (1) is 25-55°C;

[0018] Preferably, the weight ratio in step (1) is: polymer 10-40 wt%, solvent A 30-90 wt%, solvent B 0-35 wt%, non-solvent C 0-25 wt%, and non-solvent D 0-5 wt%;

[0019] Preferably, the sum of the weight ratios in step (1) is 100%;

[0020] Preferably, the polymer in step (1) is selected from any one of polysulfone (PSf), polyethersulfone (PES), polyimide (PI), polybenzimidazole (PBI), cellulose acetate (CA), polyetherimide (PEI), and polyamideimide;

[0021] Preferably, the solvent A in step (1) is selected from one or more of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP) and dimethyl sulfoxide (DMSO); the solvent B is selected from one or more of tetrahydrofuran (THF), dichloromethane (CH2Cl2) and trichloromethane (CHCl3); the non-solvent C is selected from one or more of methanol, ethanol and water; and the non-solvent D is selected from one or more of lithium chloride (LiCl), lithium nitrate (LiNO3), lithium perchlorate (LiClO4) and lithium sulfate (Li2SO4).

[0022] The weight ratio in step (2) is 0-95wt% of solvent A, 5-100wt% of non-solvent C.

[0023] Preferably, the sum of the weight ratio in step (2) is 100%.

[0024] The spinning nozzle aperture in step (3) is 0.2-0.7mm, and the temperature is 25-75℃; the spinning solution extrusion speed is 3-18mL / min -1 ; the core liquid flow rate is 1-6mL / min -1 ; the distance between the spinning nozzle and the coagulation bath, i.e. the air gap, is 2.5-30cm; the coagulation bath uses deionized water, and the temperature is 25-55℃; the rotating speed of the bobbin is 5-30m / min -1 ;

[0025] Preferably, the ratio of the spinning solution extrusion speed to the core liquid flow rate in step (3) is 3:1.

[0026] The solvent E in step (4) is selected from one or both of methanol and ethanol; and the solvent F is selected from one or both of n-hexane and n-heptane.

[0027] The solvent G in step (5) is selected from one or more of n-hexane, n-heptane and n-pentane.

[0028] In a third aspect, the present application provides a method for plasma-enhanced chemical vapor deposition of a hollow fiber gas separation membrane, comprising the following steps:

[0029] (1) placing the hollow fiber gas separation membrane in the reaction chamber of a plasma-enhanced chemical vapor deposition (PECVD) device, performing vacuum treatment on the reaction chamber for 30min to reach a certain vacuum degree;

[0030] (2) introducing a specific gas source into the reaction chamber to maintain a certain pressure in the reaction chamber;

[0031] (3) The gas source is excited into plasma by electric field, and the plasma is reacted with the hollow fiber membrane at a certain power and temperature for a certain time to obtain a plasma-assisted surface functionalized hollow fiber gas separation membrane.

[0032] The plasma enhanced chemical vapor deposition (PECVD) device in step (1) uses a radio frequency (RF) generator, and the reaction chamber is a quartz tube with a size of Φ150*1500mm;

[0033] Preferably, the hollow fiber gas separation membrane in step (1) is placed at a distance of 0-20cm from the RF coil directly below the reaction chamber;

[0034] Preferably, the vacuum degree after the vacuum treatment in step (1) reaches 0.1-1Pa.

[0035] The gas source in step (2) is selected from one or more of H2, CH4, Ar, N2, CF4, O2 and NH3;

[0036] Preferably, the gas source in step (2) is an ultra-high purity (UHP) gas;

[0037] Preferably, the pressure in the reaction chamber in step (2) is maintained at 5-200Pa.

[0038] The power of the gas source in step (3) is 10-300W, the reaction temperature is 0-100℃, and the reaction time is 0.5-30 minutes.

[0039] In a fourth aspect, the application provides a use of plasma enhanced hollow fiber gas separation membrane chemical vapor deposition, and the plasma enhanced chemical vapor deposition hollow fiber membrane is used for any one of pre-combustion CO2 capture, post-combustion CO2 capture, hydrogen separation and recovery, air separation, natural gas helium extraction and natural gas decarburization.

[0040] Compared with the prior art, the application has the following beneficial effects:

[0041] The polymer material described in the present application is selected from any one of polysulfone (PSf), polyethersulfone (PES), polyimide (PI), polybenzimidazole (PBI), cellulose acetate (CA), polyetherimide (PEI), and polyamide-imide, which is easy to obtain and convenient to process. The present application uses a dry jet / wet spinning process to prepare hollow fiber membranes, and uses plasma enhanced chemical vapor deposition technology to functionalize the surface skin layer, and the gas source is selected from one or more of H2, CH4, Ar, N2, CF4, O2 and NH3. This technology can regulate the pore structure and channel chemical properties of the skin layer of the hollow fiber membrane, form a dense, ultra-thin, uniform and controllable atomic level selection layer, and significantly improve the gas separation performance. At the same time, the plasma treatment process is simple, low in cost and controllable in reaction, and is suitable for large-scale industrial treatment. The plasma enhanced chemical vapor deposition hollow fiber membrane obtained by the present application also has excellent mechanical properties and plasticization resistance stability, and has a broad prospect in actual gas separation applications. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 is a schematic diagram of the plasma enhanced chemical vapor deposition (PECVD) device of the present application.

[0043] Figure 2 is a transmission electron microscope (TEM) morphology diagram of the cross section of the hollow fiber membrane before and after CF4 plasma treatment in Example 1 of the present application.

[0044] Figure 3 is a mechanical modulus diagram of the surface of the hollow fiber membrane before and after CF4 plasma treatment in Example 1 of the present application.

[0045] Figure 4 is a pore size distribution diagram of the hollow fiber membrane before and after O2 plasma treatment in Example 4 of the present application.

[0046] Figure 5 is the He / CH4 separation performance of the hollow fiber membrane under different gas source treatments in Examples 1-7 of the present application.

[0047] Figure 6 is the O2 / N2 separation performance of the hollow fiber membrane under different gas source treatments in Examples 1-7 of the present application. DETAILED DESCRIPTION

[0048] The technical solutions of the present application will be further described below in combination with the drawings and through specific embodiments.

[0049] Example 1

[0050] This embodiment provides CF4 plasma enhanced chemical vapor deposition 5218 Preparation method of hollow fiber gas separation membrane:

[0051] (1) In a 25℃ reaction kettle equipped with a mechanical stirrer, add 5218 polymer 500 g, solvent N-methyl pyrrolidone (NMP) 1130 g and non-solvent ethanol (EtOH) 285 g, weight ratio of 5 / 13 / 3, and stir for 4 days until completely dissolved, then degas for 24 hours to obtain a spinning solution; 5218 polymer 26.2 wt%, NMP 58.9 wt%, EtOH 14.9 wt%, stir the mixture for 4 days until completely dissolved, then degas for 24 hours to obtain a spinning solution;

[0052] (2) Prepare the core liquid by mixing solvent N-methyl pyrrolidone (NMP) 950 g and non-solvent water 50 g in a weight ratio of 95 / 5 wt%;

[0053] (3) Co-extrude the spinning solution and the core liquid through the spinneret into the coagulation bath for phase separation to produce a nascent fiber, and then further solidify on the spinning wheel. The spinneret hole diameter is 0.4 mm, the temperature is 25℃; the spinning solution extrusion speed is 6 mL min -1 ; the core liquid flow rate is 2 mL min -1 ; the distance between the spinneret and the coagulation bath, i.e. the air gap, is 10 cm; the coagulation bath uses deionized water, the temperature is 25℃; the spinning wheel speed is 20 m min -1 ;

[0054] (4) Take the nascent fiber off the spinning wheel, soak it in water for 3 days, and change the water every 12 hours. Then, soak the fiber in methanol and n-hexane alternately for solvent exchange, change the solvent every 0.5 hours, and soak for 3 hours. Hang and dry the fiber in a fume hood for 30 minutes, and then bake the fiber in a vacuum drying oven at 180℃ for 12 hours to remove any residual solvent, to obtain the final fiber;

[0055] (5) Prepare a 2 wt% polydimethylsiloxane (PDMS) solution in n-heptane for post-treatment of the fiber. Heat the solution at 100℃ for 6 hours, then immerse the fiber for 30 minutes, and then drain the excess solution. Hang and dry the fiber in a fume hood for 24 hours, and then solidify the fiber in a vacuum drying oven at 80℃ for 2 hours. Obtain the final hollow fiber gas separation membrane;

[0056] (6) Place the hollow fiber gas separation membrane in the reaction chamber of a radio frequency (RF) plasma enhanced chemical vapor deposition (PECVD) device, directly below the RF coil, and vacuumize the reaction chamber to a vacuum degree of 0.1 Pa;

[0057] (7) Introduce ultra-high purity (UHP) grade CF4 into the reaction chamber to maintain the reaction chamber pressure at 65 Pa;

[0058] (8) CF4 was excited into plasma by electric field, the exciting power was 50 W, and reacted with the membrane surface at 25℃ for 3 min to obtain a plasma enhanced chemical vapor deposition hollow fiber gas separation membrane, named as Matri-CF4-50W-65Pa-3min.

[0059] Example 2

[0060] This example provides a preparation method of a CF4 plasma enhanced chemical vapor deposition hollow fiber gas separation membrane 5218 Hollow fiber gas separation membrane preparation method, CF4 plasma treatment 5218 Hollow fiber gas separation membrane preparation method refers to Example 1, except that the plasma treatment temperature is changed from 25℃ to 50℃, and the treatment time is changed from 3 min to 10 min, and the obtained plasma enhanced chemical vapor deposition hollow fiber gas separation membrane is named as Matri-CF4-50W-65Pa-10min.

[0061] Example 3

[0062] This example provides a preparation method of a O2 plasma enhanced chemical vapor deposition polyether sulfone (PES) hollow fiber gas separation membrane:

[0063] (1) In a 25℃ reaction kettle equipped with a mechanical stirrer, add 500g of polyether sulfone (PES) polymer, 1078g of solvent N-methyl pyrrolidone (NMP) and 128g of non-solvent water (H2O), the weight ratio is polyether sulfone (PES) polymer 29.4wt%, NMP 63.1wt%, H2O 7.5wt%, stir the mixture for 4 days, and degas for 24 hours after complete dissolution, to obtain a spinning solution;

[0064] (2) Prepare the core liquid by mixing 500g of non-solvent ethanol and 500g of water according to a weight ratio of 50 / 50wt%;

[0065] (3) The spinning solution and the core liquid are co-extruded through a spinneret into a coagulation bath for phase separation to prepare a nascent fiber, and then drawn to a spinning wheel for further solidification. The spinneret hole diameter is 0.7mm, and the temperature is 25℃; the spinning solution extrusion speed is 3mL min -1 ; the core liquid flow rate is 1mL min -1 ; the distance between the spinneret and the coagulation bath, i.e. the air gap, is 10cm; the coagulation bath uses deionized water, and the temperature is 25℃; the spinning wheel speed is 5m min -1 ;

[0066] (4) The nascent fiber was removed from the spinning reel and soaked in water for 3 days, with water changed every 12 hours. After that, the fiber was soaked in methanol and n-hexane for solvent exchange, with solvent changed every 0.5 hour for 3 hours. The fiber was hung and dried in the fume hood for 30 minutes, and then baked in a vacuum drying oven at 180°C for 12 hours to remove any residual solvent, to obtain the final fiber;

[0067] (5) A 2wt% solution of polydimethylsiloxane (PDMS) was prepared in n-heptane, and the fiber was post-treated. After the solution was heated at 80°C for 2 hours, the fiber was immersed, with soaking time of 1 minute, and then excess solution was drained. The fiber was hung and dried in the fume hood for 8 hours, and then cured in a vacuum drying oven at 80°C for 2 hours. The final hollow fiber gas separation membrane was obtained;

[0068] (6) The hollow fiber gas separation membrane was placed in the reaction chamber of a radio frequency (RF) plasma enhanced chemical vapor deposition (PECVD) device, right below the RF coil, and the reaction chamber was vacuumized to a vacuum degree of 0.1 Pa;

[0069] (7) UHP grade O2 was introduced into the reaction chamber, with the pressure of the reaction chamber maintained at 13 Pa;

[0070] (8) The O2 was excited into plasma by electric field, with excitation power of 50 W, and reacted with the membrane surface at 25°C for 2 minutes, to obtain a plasma enhanced chemical vapor deposition hollow fiber gas separation membrane, named as PES-O2-50W-13Pa-2min.

[0071] Example 4

[0072] This example provides a method for preparing an O2 plasma enhanced chemical vapor deposition polyether sulfone (PES) hollow fiber gas separation membrane. The method for preparing the O2 plasma treated polyether sulfone (PES) hollow fiber gas separation membrane refers to Example 3, except that the pressure of the reaction chamber was maintained at 5 Pa. The obtained plasma enhanced chemical vapor deposition hollow fiber gas separation membrane was named as PES-O2-50W-5Pa-2min.

[0073] Example 5

[0074] This example provides a method for preparing an H2 plasma enhanced chemical vapor deposition cellulose acetate (CA) hollow fiber gas separation membrane:

[0075] (1) In a 50 °C reaction kettle equipped with a mechanical stirrer, add cellulose acetate (CA) polymer 500 g, solvent (N-methyl pyrrolidone (NMP) 1355 g and tetrahydrofuran (THF) 218 g) and non-solvent ethanol (EtOH) 109 g, the weight ratio is cellulose acetate (CTA) polymer 23 wt%, NMP 62 wt%, THF 10 wt%, EtOH 5 wt%, stir the mixture for 1 d, after complete dissolution, degas for 24 h, to obtain a spinning solution;

[0076] (2) Non-solvent water 1000 g as core liquid;

[0077] (3) Co-extrude the spinning solution and the core liquid through the spinneret into the coagulation bath for phase separation to prepare the as-spun fiber, and then further solidify on the spinning wheel. The spinneret hole diameter is 0.4 mm, and the temperature is 25 °C; the spinning solution extrusion speed is 3 mL min -1 ; the core liquid flow rate is 1 mL min -1 ; the distance between the spinneret and the coagulation bath, i.e. the air gap, is 20 cm; the coagulation bath uses deionized water, and the temperature is 30 °C; the spinning wheel speed is 20 m min -1 ;

[0078] (4) Take the as-spun fiber off the spinning wheel, soak it in water for 3 days, and change the water every 12 hours. Then, soak the fiber in methanol and n-hexane alternately for solvent exchange, and change the solvent every 0.5 hour for a total of 3 hours. Hang and dry the fiber in a fume hood for 30 minutes, and then bake the fiber in a vacuum drying oven at 180 °C for 12 hours to remove any residual solvent, to obtain the final fiber;

[0079] (5) Prepare a 5 wt% polydimethylsiloxane (PDMS) solution in n-hexane for post-treatment of the fiber. After heating the solution at 80 °C for 2 hours, immerse the fiber for 1 minute, and then drain the excess solution. Hang and dry the fiber in a fume hood for 24 hours, and then solidify the fiber in a vacuum drying oven at 80 °C for 2 hours. Obtain the final hollow fiber gas separation membrane;

[0080] (6) Place the hollow fiber gas separation membrane in the reaction chamber of a radio frequency (RF) plasma enhanced chemical vapor deposition (PECVD) device, 10 cm below the RF coil, and vacuumize the reaction chamber to a vacuum degree of 0.1 Pa;

[0081] (7) Introduce ultra-high purity (UHP) grade H2 into the reaction chamber to maintain the reaction chamber pressure at 3 Pa;

[0082] (8) H2 was excited into plasma by electric field, the excitation power was 150 W, and reacted with the membrane surface at 25℃ for 3 min to obtain a plasma-enhanced chemical vapor deposition hollow fiber gas separation membrane, named CTA-H2-150W-3Pa-3min.

[0083] Example 6

[0084] The present embodiment provides a preparation method of CH4 plasma-enhanced chemical vapor deposition polyetherimide (PEI) hollow fiber gas separation membrane:

[0085] (1) In a 25℃ reaction kettle equipped with a mechanical stirrer, polyetherimide (PEI) polymer 500 g, solvent (N-methyl pyrrolidone (NMP) 578 g and tetrahydrofuran (THF) 576 g) and non-solvent lithium nitrate (LiNO3) 16.8 g were added, the weight ratio was polyetherimide (PEI) polymer 30wt%, NMP 34.5wt%, THF 34.5wt%, LiNO3 1wt%, the mixture was stirred for 2 days, after complete dissolution, degassing for 24 hours to obtain a spinning solution;

[0086] (2) The solvent N-methyl pyrrolidone (NMP) 950 g and the non-solvent water 50 g were prepared into a core liquid according to the weight ratio of 95 / 5wt%;

[0087] (3) The spinning solution and the core liquid were co-extruded through the spinneret into the coagulation bath for phase separation to prepare the as-spun fiber, and then were further solidified on the spinning wheel. The spinneret aperture was 0.2 mm, and the temperature was 25℃; the spinning solution extrusion speed was 4.5 mL min -1 ; the core liquid flow rate was 1.5 mL min -1 ; the distance between the spinneret and the coagulation bath, i.e. the air gap, was 10 cm; the coagulation bath used deionized water, and the temperature was 25℃; the spinning wheel rotation speed was 22 m min -1 ;

[0088] (4) The as-spun fiber was taken off from the spinning wheel, soaked in water for 3 days, and the water was replaced every 12 hours. Then, the fiber was soaked in methanol and n-hexane alternately for solvent exchange, and the solvent was replaced every 1 hour, for a total of 6 hours. The fiber was hung and dried in a fume hood for 30 minutes, and then was baked in a vacuum drying oven at 180℃ for 12 hours to remove any residual solvent, to obtain the final fiber;

[0089] (5) The post-treatment of the fiber was performed by preparing a 2wt% polydimethylsiloxane (PDMS) solution in n-hexane. After heating the solution at 80°C for 2 hours, the fiber was immersed in the solution for 1 minute, and then the excess solution was drained. The fiber was hung and dried in a fume hood for 12 hours, and then cured in a vacuum oven at 80°C for 2 hours. The final hollow fiber gas separation membrane was obtained;

[0090] (6) The hollow fiber gas separation membrane was placed in the reaction chamber of a radio frequency (RF) plasma enhanced chemical vapor deposition (PECVD) device at a position 20 cm below the RF coil. The reaction chamber was vacuumized to a vacuum degree of 0.1 Pa;

[0091] (7) Ultra-high purity (UHP) CH4was introduced into the reaction chamber, and the pressure of the reaction chamber was maintained at 10 Pa;

[0092] (8) CH4was excited into plasma by an electric field with an excitation power of 250 W, and reacted with the membrane surface at 45°C for 3 minutes. A plasma enhanced chemical vapor deposition hollow fiber gas separation membrane was obtained, which was named PEI-CH4-250W-10Pa-3min.

[0093] Example 7

[0094] The present example provides a method for preparing an NH3 plasma enhanced chemical vapor deposition polysulfone (PSf) hollow fiber gas separation membrane:

[0095] (1) In a 25°C reaction kettle equipped with a mechanical stirrer, 500 g of polysulfone (PSf) polymer, 1104 g of solvent N-methyl pyrrolidone (NMP), and 68.5 g of non-solvent water (H2O) were added, with a weight ratio of 30wt% polysulfone (PSf) polymer, 65.9wt% NMP, and 4.1wt% H2O. The mixture was stirred for 2 days until completely dissolved, and then degassed for 24 hours to obtain a spinning solution;

[0096] (2) The solvent N-methyl pyrrolidone (NMP) 600 g and the non-solvent water 400 g were prepared into a core solution according to a weight ratio of 60 / 40wt%;

[0097] (3) The spinning solution and the core solution were co-extruded through a spinneret into a coagulation bath for phase separation to prepare a nascent fiber, which was then further solidified on a spinning wheel. The spinneret had a pore diameter of 0.7 mm and a temperature of 25°C; the spinning solution had an extrusion speed of 9 mL min -1 ; the core solution had a flow rate of 3 mL min -1 ; the distance between the spinneret and the coagulation bath, i.e. the air gap, was 5 cm; the coagulation bath used deionized water with a temperature of 25°C; and the spinning wheel had a rotation speed of 5 m min -1 ;

[0098] (4) The nascent fiber was removed from the spinning reel and soaked in water for 5 days, with water changed every 12 hours. After that, the fiber was soaked in methanol and n-hexane in turn for solvent exchange, with solvent changed every 1 hour for 6 hours. The fiber was hung and dried in the fume hood for 30 minutes, and then baked in a vacuum drying oven at 180℃ for 12 hours to remove any residual solvent, to obtain the final fiber;

[0099] (5) A 3wt% solution of polydimethylsiloxane (PDMS) was prepared in n-pentane, and the fiber was post-treated. After the solution was heated at 80℃ for 2 hours, the fiber was immersed, with an immersion time of 5 minutes, and then excess solution was drained. The fiber was hung and dried in the fume hood for 12 hours, and then cured in a vacuum drying oven at 80℃ for 2 hours. The final hollow fiber gas separation membrane was obtained;

[0100] (6) The hollow fiber gas separation membrane was placed in the reaction chamber of a radio frequency (RF) plasma enhanced chemical vapor deposition (PECVD) device, directly below the RF coil, and the reaction chamber was vacuumized to a vacuum degree of 0.1 Pa;

[0101] (7) UHP grade NH3 was introduced into the reaction chamber, and the pressure of the reaction chamber was maintained at 78 Pa;

[0102] (8) NH3 was excited into plasma by an electric field, with an excitation power of 50 W, and reacted with the membrane surface at 25℃ for 5 minutes, to obtain a plasma enhanced chemical vapor deposition hollow fiber gas separation membrane, designated as PSf-NH3-50W-78Pa-5min.

[0103] Application Example 1

[0104] In this application example, the cross-sectional morphology of the hollow fiber membrane before and after CF4 plasma treatment in Example 1 was characterized by transmission electron microscopy (TEM).

[0105] The results are shown in Figure 2 Compared with before treatment, a dense, ultrathin and uniform fluorinated selective layer of about 5 nm was formed on the surface of the plasma treated hollow fiber gas separation membrane. It is proved that the method provided by the application can realize uniform treatment of the membrane surface, which will be conducive to improving the gas separation selectivity.

[0106] Application Example 2

[0107] In this application example, the nanoscale mechanical properties of the hollow fiber membrane before and after CF4 plasma treatment in Example 1 were characterized by atomic force microscopy (AFM).

[0108] The results are shown in Figure 3As shown, the mechanical modulus of the surface of the hollow fiber gas separation membrane in the plasma treatment increased to 15.47 MPa compared with before the treatment (2.70 MPa). It is proved that the method provided by the application can make the membrane have excellent mechanical properties.

[0109] Application Example 3

[0110] In this application example, CO2 physical adsorption was used to study the pore size distribution of the hollow fiber membranes before and after O2 plasma treatment in Example 3.

[0111] As shown in the results, Figure 4 after O2 plasma treatment, the micropore and ultramicropore distributions of the hollow fiber membranes were both shifted to a smaller pore size region. It is proved that the method provided by the application can modify the pore structure of the membrane material.

[0112] Application Example 4

[0113] In this application example, the He, H2, CO2, O2, N2 and CH4 pure gas permeabilities of the plasma enhanced chemical vapor deposition hollow fiber gas separation membranes prepared in Examples 1-7 were tested at 35℃ and 2 bar, and the selectivities of H2 / N2, H2 / CH4, He / N2, He / CH4( Figure 5 ), CO2 / CH4 and O2 / N2( Figure 6 ) were calculated. The test results are shown in Table 1.

[0114] Table 1 Gas permeability and selectivity of plasma enhanced chemical vapor deposition hollow fiber gas separation membranes

[0115]

[0116] As shown in Table 1, Figure 5 and Figure 6 different plasma enhanced chemical vapor deposition hollow fiber gas separation membranes all showed excellent gas separation performance. With the increase of CF4 plasma treatment time, the permeability increased and the selectivity decreased due to etching. With the decrease of the O2 gas source pressure in the reaction chamber, the treatment degree increased, the permeability decreased, and the selectivity increased. In summary, the method provided by the application can make the gas separation performance of the membrane material break through the upper limit of gas separation, and has good application prospect in various separation scenarios.

Claims

1. A method of plasma enhanced hollow fiber gas separation membrane chemical vapor deposition, characterized by, The gas separation membrane is an asymmetric hollow fiber membrane prepared by a dry-jet / wet-spinning process; The method comprises the following steps: (1) In a reaction kettle equipped with a mechanical stirrer, add a polymer, a solvent A, optionally a solvent B, a non-solvent C, and optionally a non-solvent D, stir the mixture for 1-7 days, and after complete dissolution, degas for 12-48 hours to obtain a spinning solution; (2) Prepare a core liquid from the solvent A and the non-solvent C; (3) Co-extrude the spinning solution obtained in step (1) and the core liquid obtained in step (2) through a spinneret into a coagulation bath for phase separation to prepare a nascent fiber, and then draw it onto a spinning wheel for solidification; (4) The nascent fiber is removed from the spinning wheel and soaked in water for 1-5 days, with water changed every 12 hours. Thereafter, the fiber is soaked in solvent E and solvent F alternately for solvent exchange, with solvent changed every 0.5 hour, for 3-24 hours. The fiber is hung and dried in a fume hood for 30 minutes, and then dried in a vacuum oven at 120-180 o C for 12-48 hours to obtain the final fiber. (5) preparing a 2-10 wt% solution of polydimethylsiloxane in solvent G, post-treating the final fiber; heating the solution at 80-120 o C for 2-12 hours, immersing the final fiber, soaking for 1-30 minutes, draining the solution; hanging and drying the final fiber in a fume hood for 8-24 hours, and curing the final fiber in a vacuum drying oven at 80-120 o C for 2-12 hours; obtaining a final hollow fiber gas separation membrane; (6) Place the hollow fiber gas separation membrane in the reaction chamber of a plasma-enhanced chemical vapor deposition device, and perform vacuum treatment on the reaction chamber for 30 minutes to make the vacuum degree reach 0.1-1 Pa; (7) Introduce a gas source into the reaction chamber to maintain the pressure of the reaction chamber at 5-200 Pa; (8) The gas source is excited into plasma by electric field, the power of the gas source excitation is 10-300 W, the reaction temperature is 0-100 o C and the hollow fiber membrane for 0.5-30 minutes to obtain plasma-assisted surface functionalized hollow fiber gas separation membrane; The solvent E in step (4) is selected from methanol, and the solvent F is selected from n-hexane; The gas separation membrane material is a polymer, specifically selected from any one of polysulfone, polyethersulfone, polyimide, polybenzimidazole, cellulose acetate, polyetherimide, and polyamide-imide.

2. The method of claim 1, wherein, Step (1) the reactor temperature is 25-55 o C.

3. The method of claim 1, wherein, The weight ratio of the polymer, the solvent A, the optional solvent B, the non-solvent C, and the optional non-solvent D in step (1) is: polymer 10-40 wt%, solvent A 30-90 wt%, solvent B 0-35 wt%, non-solvent C 0-25 wt%, and non-solvent D 0-5 wt%. The sum of the weight ratios is 100%.

4. The method of claim 1, wherein, The solvent A in step (1) is selected from one or more of N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, or dimethyl sulfoxide; The solvent B is selected from one or more of tetrahydrofuran, dichloromethane, or trichloromethane; The non-solvent C is selected from one or more of methanol, ethanol, or water; The non-solvent D is selected from one or more of lithium chloride, lithium nitrate, lithium perchlorate, and lithium sulfate.

5. The method of claim 1, wherein, The weight ratio of the solvent A and the non-solvent C in step (2) is: solvent A 0-95 wt%, and non-solvent C 5-100 wt%. The sum of the weight ratios in step (2) is 100%.

6. The method of claim 1, wherein, The spinning nozzle aperture is 0.2-0.7 mm, and the temperature is 25-75 o C; the spinning dope extrusion speed is 3-18 mL / min -1 ; the core liquid flow rate is 1-6 mL / min -1 ; the distance between the spinning nozzle and the coagulation bath, i.e. the air gap, is 2.5-30 cm; the coagulation bath uses deionized water, and the temperature is 25-55 o C; the spinning wheel rotation speed is 5-30 m / min -1 .

7. The method of claim 1, wherein, The ratio of the spinning solution extrusion speed to the core liquid flow rate in step (3) is 3:

1.

8. The method of claim 1, wherein, The solvent G in step (5) is selected from one or more of n-hexane, n-heptane, or n-pentane.

9. The method of claim 1, wherein, The plasma-enhanced chemical vapor deposition device in step (6) uses a radio frequency generator, and the reaction chamber is a quartz tube with a size of Φ150*1500 mm.

10. The method of claim 1, wherein, In step (6), the hollow fiber gas separation membrane is placed at a distance of 0-20 cm from the radio frequency coil directly below the reaction chamber.

11. The method of claim 1, wherein, The gas source in step (7) is selected from one or more of H2, CH4, Ar, N2, CF4, O2, and NH3.

12. The method of claim 1, wherein, The gas source in step (7) is an ultra-high purity gas.

13. Use of the plasma-assisted surface functionalized hollow fiber gas separation membrane prepared according to the method of claim 1, characterized in that, The plasma-treated hollow fiber gas separation membrane is used for any one of pre-combustion CO2 capture, post-combustion CO2 capture, hydrogen separation and recovery, air separation, natural gas helium extraction, and natural gas decarburization.

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