A gas separation membrane, its preparation method and application

Abstract

This invention relates to a gas separation membrane, its preparation method, and its application, belonging to the field of gas separation membrane technology. The preparation method of this invention includes the following steps: (1) preparing a homogeneous spinning solution using polymer and MOF particles; the mass ratio of the polymer to MOF particles is 3-5:1-3; the polymer concentration is 30-50 wt%; (2) preparing a mixed matrix fiber membrane using an air jet; (3) roughening the surface of the mixed matrix fiber membrane to obtain a roughened mixed matrix fiber membrane; (4) attaching carbon nanotubes to the surface of the roughened mixed matrix fiber membrane using an air jet to prepare the gas separation membrane. The gas separation membrane of this invention has numerous pores and a highly disordered internal structure, increasing gas loading capacity while ensuring a certain strength and durability, and exhibiting excellent separation performance for both CO2 and CH4 gases.

Description

Technical Field

[0001] This invention belongs to the field of gas separation membrane technology, and particularly relates to a gas separation membrane, its preparation method and application. Background Technology

[0002] Membrane gas separation technology has attracted increasing attention due to its advantages such as simple process, low energy consumption, high separation efficiency, and no environmental pollution. Developing new materials with good gas permeability and simple, effective membrane fabrication processes will further advance the development of membrane gas separation technology. Based on existing products on the market, the better the gas permeability of a gas separation membrane, the worse its selectivity. Furthermore, inorganic membranes with good gas separation performance are hampered in industrial applications due to their high price and poor modeling. The applicability of gas separation membrane materials is also very important. Patent CN112354380A discloses a method for preparing an electrospun nanofiber gas separation membrane. The nanofiber gas separation membrane prepared by electrospinning has a relatively simple structure, a robust and durable internal framework, and a long gas transmission channel. Experiments have shown that this material prepared by electrospinning only has a relatively significant separation effect on CO2 gas, and the amount of gas that can pass through per unit time is very limited, resulting in a narrow application range. Patent CN 110404423A discloses a high-performance polyimide hollow fiber membrane and its preparation method and application. The polyimide hollow fiber membrane is prepared by dry-wet spinning. In this method, the nascent fiber membrane needs to be annealed at high temperature to near the glass transition temperature. The operation method is relatively complex and has high requirements for environmental equipment. Patent CN 108211679A discloses a mixed gas separation method based on liquid-containing carbon nanotube films. This method involves injecting an ionic solution into carbon nanotubes followed by end-capping, and controlling the stress of the carbon nanotube film under an electric field. This operation is complex, the product has high requirements for the working environment, and the production cost is high. Patent CN110270231A discloses MOF-derived gas separation membranes, their preparation methods, and applications. However, this method repeatedly uses toxic organic solvents such as NMP, requires a high-temperature environment when processing MOF materials, and utilizes ultrasonic stirring technology when mixing with polymer solutions. This results in high production costs, complex operation, and significant environmental pollution. To overcome the limitations of polymer membrane materials in terms of permeability and selectivity, mixed matrix membranes have been developed in recent years. These membranes incorporate inorganic particles as a dispersed phase into an organic matrix, allowing the two to complement each other's advantages and simultaneously possessing both good gas permeability and ease of processing and molding.

[0003] Although MOF materials have been introduced into membranes in existing technologies to improve gas permeability, most membrane fabrication methods still rely on electrospinning and wet spinning. This results in membrane materials with high inhomogeneity and poor permeability, particularly in the preparation of hollow fiber membranes for industrial applications. The required thinness and hollow structure of these membranes often lead to poor strength, limiting their applications. Furthermore, current membrane fabrication processes are relatively complex and primarily effective for separating hydrogen, with little effect on separating gases such as carbon dioxide and methane.

[0004] Carbon nanotubes, due to their light weight and excellent mechanical and electrochemical properties, have been widely used in the manufacture of electronic devices. A few patents have documented the use of carbon nanotubes as a dispersed phase in combination with polymers to prepare mixed matrix membranes, improving the compatibility between gas permeation and selectivity, and for gas separation. However, as a one-dimensional nanomaterial, carbon nanotubes themselves do not significantly improve membrane durability. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the problems of insufficient permeability, low selectivity, overly complex production process, and the generation of environmentally harmful or toxic byproducts in the production of products prepared by the prior art.

[0006] To address the aforementioned technical problems, this invention provides a gas separation membrane, its preparation method, and its application. A mixed matrix fiber membrane is prepared by blending a polymer as the continuous phase and pretreated MOFs as the dispersed phase, followed by air jetting. Carbon nanotubes are then attached to the surface of the roughened mixed matrix fiber membrane using a secondary spraying method to create a membrane suitable for separating CO2 and CH4 gases.

[0007] The first objective of this invention is to provide a method for preparing a gas separation membrane, comprising the following steps:

[0008] (1) The polymer and MOF particles are formulated into a uniform spinning solution; the mass ratio of the polymer to MOF particles is 3-5:1-3; the concentration of the polymer is 30-50 wt%.

[0009] (2) The spinning solution described in step (1) is made into a mixed matrix fiber membrane by means of air jet blowing;

[0010] (3) The surface of the mixed matrix fiber membrane described in step (2) is roughened to obtain a mixed matrix fiber membrane with a rough surface.

[0011] (4) Carbon nanotubes are attached to the surface of the rough mixed matrix fiber membrane described in step (3) by air jetting to form the gas separation membrane.

[0012] In one embodiment of the present invention, in step (1), the polymer is polyethylene terephthalate and / or polyamide; the MOF particles are MILs and / or ZIFs.

[0013] Furthermore, the polymer is polyethylene terephthalate.

[0014] Further, the ZIF is ZIF-67(Co); the ZIF-67(Co) is obtained by reacting Co(NO3)2·6H2O and 2-methylimidazole in a molar ratio of 1:4 to 1:32, the reaction temperature is 150℃-250℃, and the reaction time is 8h-64h.

[0015] In one embodiment of the present invention, in step (1), the MOFs particles are pretreated MOFs particles; the pretreated MOFs particles are MOFs particles activated in a vacuum environment of 140℃-300℃ for 8h-24h.

[0016] In one embodiment of the present invention, in step (1), the solvent of the spinning solution is water and / or polyvinylpyrrolidone.

[0017] In one embodiment of the present invention, in step (3), the surface roughening treatment is performed by immersing the mixed matrix fiber membrane in an etching solution for 15-45 minutes using a chemical etching method. The surface roughening treatment improves the surface roughness of the mixed matrix fiber membrane. When carbon nanotubes are blown onto the surface by airflow, the roughened mixed matrix fiber membrane can provide better adhesion conditions for carbon nanotubes compared to a smooth surface, thus improving the utilization rate of carbon nanotubes, reducing waste, and saving costs.

[0018] In one embodiment of the present invention, the etching solution is a sodium bicarbonate solution or a sodium hydroxide solution; the concentration of the etching solution is 10-30 wt%.

[0019] In one embodiment of the present invention, in steps (2) and (4), the conditions for the airflow blowing are: gas pressure of 0.1-2.0 MPa, spinning temperature of 20℃-90℃, receiving distance of 5-20 cm, and stretching ratio of 1-5 times.

[0020] In one embodiment of the present invention, in steps (2) and (4), the gas used for the airflow jet is helium or neon.

[0021] A second objective of this invention is to provide a gas separation membrane prepared by the aforementioned preparation method.

[0022] A third objective of this invention is to provide an application of the gas separation membrane described herein in the separation of CO2 and CH4.

[0023] The technical solution of the present invention has the following advantages compared with the prior art:

[0024] (1) The preparation method described in this invention employs air-jet spinning. Under the blowing of a high-speed airflow, the polymer material can be distributed randomly on the receiver, resulting in a membrane structure with numerous pores and high internal structural disorder. This increases the gas loading capacity while ensuring a certain strength and durability, and provides excellent separation for both CO2 and CH4 gases. In this structure, the organic ligands carried by the dispersed MOF particles improve their compatibility with the polymer. Furthermore, the co-spinning method of the polymer and pretreated MOF particles makes the MOFs more uniformly distributed in the membrane. When the target gas passes through, the screening effect of the gas separation membrane on the mixed gas is more uniform and intense, thereby improving the membrane's permeation separation performance. Meanwhile, in the prepared hybrid matrix fiber membrane, the MOF particles are three-dimensional structures with internal gaps and metal ions, which have a self-supporting function. Due to the presence of the air jet blowing process, the distribution of MOF particles with this special structure on the membrane is more uniform. While improving the mechanical properties of the hybrid fiber membrane, it does not produce anisotropy. In addition, when the product is used for gas separation, the internal space of the particles allows gas particles to pass through, thus increasing the packing density of the membrane material.

[0025] (2) The roughening treatment of the mixed matrix film described in this invention uses alkaline solution etching to form depressions of different shapes and sizes on the surface of the mixed matrix film, thereby increasing the surface roughness of the mixed matrix film and reducing the probability of carbon nanotubes falling off.

[0026] (3) In the gas separation membrane of the present invention, carbon nanotubes are attached to or embedded on the surface of the mixed matrix fiber membrane by airflow spraying, so that the carbon nanotubes are distributed on the surface of the membrane in a uniform and random manner. In addition, since the spraying airflow is a hot airflow, it can increase the viscosity of the mixed matrix membrane surface to a certain extent. At the same time, due to the roughening treatment, the contact area between the carbon nanotubes and the surface of the mixed matrix membrane is increased, making it easier for the carbon nanotubes to adhere to the surface of the mixed matrix membrane and less likely to fall off. The internal cavity structure of carbon nanotubes allows gas molecules to pass through, and since they have a certain selectivity for gases, they enhance the gas permeation and separation performance of the polymer membrane. A MOF mixed matrix fiber membrane containing carbon nanotubes with better gas permeability and selectivity is obtained for gas separation. Attached Figure Description

[0027] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein:

[0028] Figure 1 This is a schematic diagram of the process for preparing the hybrid matrix fiber membrane according to the present invention.

[0029] Figure 2 This is a schematic diagram of the gas separation membrane of the present invention.

[0030] Figure 3 This is a flowchart illustrating the preparation of the gas separation membrane according to the present invention.

[0031] Figure reference numerals: 1-spinning solution, 2-gas, 3-double-layer composite nozzle, 4-mixed matrix fiber membrane, 5-receiving device, 6-power supply, 7-carbon nanotube layer, 8-mixed matrix fiber membrane doped with MOF particles, 9-MOF particles. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0033] In this invention, unless otherwise stated, all materials used are commercially available.

[0034] In this invention, unless otherwise stated, experimental methods without specific conditions are generally performed under conventional conditions or according to the manufacturer's recommended usage conditions.

[0035] In this invention, unless otherwise stated, the polymer is polyethylene terephthalate, purchased from DuPont, model RE5231 BK533.

[0036] In this invention, unless otherwise stated, the CO2 / CH4 gas adsorption selectivity test shall refer to "Adsorption Phase Equilibrium and Selectivity of CH4 / CO2 on MIL-101". For a binary gas mixture, the gas adsorption selectivity S is defined by the formula: S = (x1 / y1) / (x2 / y2), where x1 is the mole fraction of CO2 in the adsorption phase, y1 is the mole fraction of CO2 in the mixed gas phase, x2 represents the mole fraction of CH4 in the adsorption phase, and y2 represents the mole fraction of CH4 in the mixed gas phase.

[0037] In this invention, unless otherwise stated, the gas permeability test is characterized by the permeability coefficient P, which, according to the standard GB / T 40260-2021 "Test Method for Gas Permeability of Polymer Membrane Materials", represents the volume of gas passing through a unit area of ​​sample per unit time under standard conditions when the gas is stably permeating, at a constant temperature and under a unit pressure difference.

[0038] In this invention, unless otherwise stated, such as Figure 1-2 As shown, a spinning solution 1 is prepared by mixing polymer and MOF particles. The spinning solution 1 is sprayed out from a channel located in the middle of the pipe, and gas 2 is sprayed simultaneously from channels on both sides. After passing through a double-layer composite nozzle 3, a mixed matrix fiber membrane 4 is formed and collected on a receiving device 5. With the power supply 6 turned on, the receiving device rotates at a certain speed to collect the nascent mixed matrix membrane. After surface roughening, carbon nanotubes are coated on the surface of the material by air jetting, resulting in a mixed matrix membrane 8 with a carbon nanotube layer 7 on the surface and MOF particles 9 as the matrix layer.

[0039] Example 1

[0040] Reference Figure 3 As shown, a gas separation membrane and its preparation method specifically include the following steps:

[0041] (1) Dissolve 2.1 mmol Co(NO3)2·6H2O and 8.40 mmol dimethylimidazole in 120 mL of water respectively. Then, stir and mix the two solutions evenly. Pour the mixed solution into a 300 mL high-pressure reactor lined with polytetrafluoroethylene and react in an oven at 180 °C for 48 h. After the reaction is completed, the system is naturally cooled to room temperature. After washing the obtained solid, it is vacuum dried at 110 °C for 12 h. The dried solid particles are activated at 200 °C for 14 h to obtain ZIF-67(Co).

[0042] (2) Add ZIF-67(Co) to the polymer solution with a polymer concentration of 32wt%, stir for 12h to obtain a uniformly mixed spinning solution. Let the spinning solution stand at room temperature for 8h and then filter the spinning solution.

[0043] (3) Using dry helium as the driving force, the spinning temperature is 90℃. The air jet spinning method is used to make the spinning solution squeezed out from the nozzle with an outer diameter of 0.80mm and an inner diameter of 0.40mm under a pressure of 0.5MPa. After passing through a receiving distance of 5.0cm and being stretched 2.0 times, a mixed matrix fiber membrane is formed and stored on the receiver.

[0044] (4) After cooling and forming, immerse the membrane in a 15wt% caustic soda solution for 30 minutes, then immerse it in water for 1 hour to remove the residual caustic soda solution on the membrane, and obtain a rough mixed matrix fiber membrane.

[0045] (5) After drying at room temperature, carbon nanotubes are sprayed onto the surface of a rough mixed matrix fiber membrane using dry helium as the driving force and air jet spinning at a pressure of 0.5 MPa and a receiving distance of 5.0 cm to obtain a gas separation membrane.

[0046] Example 2

[0047] A gas separation membrane and its preparation method, specifically including the following steps:

[0048] (1) Dissolve 2.1 mmol Co(NO3)2·6H2O and 8.40 mmol dimethylimidazole in 120 mL of water respectively. Then, stir and mix the two solutions evenly. Pour the mixed solution into a 300 mL high-pressure reactor lined with polytetrafluoroethylene and react in an oven at 180 °C for 48 h. After the reaction is completed, the system is naturally cooled to room temperature. After washing the obtained solid, it is vacuum dried at 110 °C for 12 h. The dried solid particles are activated at 200 °C for 14 h to obtain ZIF-67(Co).

[0049] (2) Add ZIF-67(Co) to the polymer solution with a polymer concentration of 32wt%, stir for 12h to obtain a uniformly mixed spinning solution. Let the spinning solution stand at room temperature for 8h and then filter the spinning solution.

[0050] (3) Using dry helium as the driving force, the spinning temperature is 90℃. The air jet spinning method is used to squeeze the spinning solution out from the nozzle with an outer diameter of 0.80mm and an inner diameter of 0.40mm under a pressure of 0.5MPa. After passing through a receiving distance of 20.0cm and being stretched 2.0 times, a mixed matrix fiber membrane is formed.

[0051] (4) After cooling and forming, immerse the membrane in a 15wt% caustic soda solution for 30 minutes, then immerse it in water for 1 hour to remove the residual caustic soda solution on the membrane, and obtain a rough mixed matrix fiber membrane.

[0052] (5) After drying at room temperature, dry helium gas is used as the driving force, and the spinning solution is extruded from a nozzle with an outer diameter of 0.80 mm and an inner diameter of 0.40 mm under a pressure of 0.5 MPa using the air jet spinning method. The carbon nanotubes are sprayed onto the surface of the rough mixed matrix fiber membrane through a receiving distance of 2.0 cm to obtain a gas separation membrane.

[0053] Example 3

[0054] A gas separation membrane and its preparation method, specifically including the following steps:

[0055] (1) Dissolve 2.1 mmol Co(NO3)2·6H2O and 8.40 mmol dimethylimidazole in 120 mL of water respectively. Then, stir and mix the two solutions evenly. Pour the mixed solution into a 300 mL high-pressure reactor lined with polytetrafluoroethylene and react in an oven at 180 °C for 48 h. After the reaction is completed, the system is naturally cooled to room temperature. After washing the obtained solid, it is vacuum dried at 110 °C for 12 h. The dried solid particles are activated at 200 °C for 14 h to obtain ZIF-67(Co).

[0056] (2) Add ZIF-67(Co) to the polymer solution with a polymer concentration of 32wt%, stir for 12h to obtain a uniformly mixed spinning solution. Let the spinning solution stand at room temperature for 8h and then filter the spinning solution.

[0057] (3) Using dry helium as the driving force, the spinning temperature is 90℃. The air jet spinning method is used to make the spinning solution squeezed out from the nozzle with an outer diameter of 0.80mm and an inner diameter of 0.40mm under a pressure of 0.5MPa. After passing through a receiving distance of 5.0cm and being stretched 2.0 times, a mixed matrix fiber membrane is formed and stored on the receiver.

[0058] (4) After cooling and forming, immerse the membrane in a 15wt% caustic soda solution for 30 minutes, then immerse it in water for 1 hour to remove the residual caustic soda solution on the membrane, and obtain a rough mixed matrix fiber membrane.

[0059] (5) After drying at room temperature, dry helium gas is used as the driving force, and the spinning solution is extruded from a nozzle with an outer diameter of 0.80 mm and an inner diameter of 0.40 mm at a pressure of 0.5 MPa using the air jet spinning method. The carbon nanotubes are sprayed onto the surface of the rough mixed matrix fiber membrane through a receiving distance of 10.0 cm to obtain a gas separation membrane.

[0060] Example 4

[0061] A gas separation membrane and its preparation method, specifically including the following steps:

[0062] (1) Dissolve 2.1 mmol Co(NO3)2·6H2O and 8.40 mmol dimethylimidazole in 120 mL of water respectively. Then, stir and mix the two solutions evenly. Pour the mixed solution into a 300 mL high-pressure reactor lined with polytetrafluoroethylene and react in an oven at 180 °C for 48 h. After the reaction is completed, the system is naturally cooled to room temperature. After washing the obtained solid, it is vacuum dried at 110 °C for 12 h. The dried solid particles are activated at 200 °C for 14 h to obtain ZIF-67(Co).

[0063] (2) Add ZIF-67(Co) to the polymer solution with a polymer concentration of 32wt%, stir for 12h to obtain a uniformly mixed spinning solution. Let the spinning solution stand at room temperature for 8h and then filter the spinning solution.

[0064] (3) Using dry helium as the driving force, the spinning temperature is 30℃. The air jet spinning method is used to make the spinning solution squeezed out from the nozzle with an outer diameter of 0.80mm and an inner diameter of 0.40mm under a pressure of 0.5MPa. After passing through a receiving distance of 5.0cm and being stretched 2.0 times, a mixed matrix fiber membrane is formed and stored on the receiver.

[0065] (4) After cooling and forming, immerse the membrane in a 15wt% caustic soda solution for 30 minutes, then immerse it in water for 1 hour to remove the residual caustic soda solution on the membrane, and obtain a rough mixed matrix fiber membrane.

[0066] (5) After drying at room temperature, carbon nanotubes are sprayed onto the surface of a rough mixed matrix fiber membrane using dry helium as the driving force and air jet spinning method at a pressure of 0.5 MPa and a receiving distance of 2.0 cm to obtain a gas separation membrane.

[0067] Example 5

[0068] A gas separation membrane and its preparation method, specifically including the following steps:

[0069] (1) Dissolve 2.1 mmol Co(NO3)2·6H2O and 8.40 mmol dimethylimidazole in 120 mL of water respectively. Then, stir and mix the two solutions evenly. Pour the mixed solution into a 300 mL high-pressure reactor lined with polytetrafluoroethylene and react in an oven at 180 °C for 48 h. After the reaction is completed, the system is naturally cooled to room temperature. After washing the obtained solid, it is vacuum dried at 110 °C for 12 h. The dried solid particles are activated at 200 °C for 14 h to obtain ZIF-67(Co).

[0070] (2) Add ZIF-67(Co) to the polymer solution with a polymer concentration of 50wt%, stir for 12h to obtain a uniformly mixed spinning solution. Let the spinning solution stand at room temperature for 8h and then filter the spinning solution.

[0071] (3) Using dry helium as the driving force, the spinning temperature is 90℃. The air jet spinning method is used to make the spinning solution squeezed out from the nozzle with an outer diameter of 0.80mm and an inner diameter of 0.40mm under a pressure of 0.5MPa. After passing through a receiving distance of 5.0cm and being stretched 2.0 times, a mixed matrix fiber membrane is formed and stored on the receiver.

[0072] (4) After cooling and forming, immerse the membrane in a 15wt% caustic soda solution for 30 minutes, then immerse it in water for 1 hour to remove the residual caustic soda solution on the membrane, and obtain a rough mixed matrix fiber membrane.

[0073] (5) After drying at room temperature, carbon nanotubes are sprayed onto the surface of a rough mixed matrix fiber membrane using dry helium as the driving force and air jet spinning at a pressure of 0.5 MPa and a receiving distance of 2.0 cm to obtain a gas separation membrane.

[0074] Example 6

[0075] A gas separation membrane and its preparation method, specifically including the following steps:

[0076] (1) 2.1 mmol Co(NO3)2·6H2O and 8.40 mmol dimethylimidazole were dissolved in 120 mL of polyvinylpyrrolidone solution, respectively. The two solutions were then stirred and mixed thoroughly. The mixed solution was poured into a 300 mL high-pressure reactor lined with polytetrafluoroethylene and reacted in an oven at 180 °C for 48 h. After the reaction was completed, the system was naturally cooled to room temperature. The resulting solid was washed and then vacuum dried at 110 °C for 12 h. The dried solid particles were then activated at 200 °C for 14 h to obtain ZIF-67(Co).

[0077] (2) Add ZIF-67(Co) to the polymer solution with a polymer concentration of 32wt%, stir for 12h to obtain a uniformly mixed spinning solution. Let the spinning solution stand at room temperature for 8h and then filter the spinning solution.

[0078] (3) Using dry helium as the driving force, the spinning temperature is 90℃. The air jet spinning method is used to make the spinning solution squeezed out from the nozzle with an outer diameter of 0.80mm and an inner diameter of 0.40mm under a pressure of 0.5MPa. After passing through a receiving distance of 5.0cm and being stretched 2.0 times, a mixed matrix fiber membrane is formed and stored on the receiver.

[0079] (4) After cooling and forming, immerse the membrane in a 15wt% caustic soda solution for 30 minutes, then immerse it in water for 1 hour to remove the residual caustic soda solution on the membrane, and obtain a rough mixed matrix fiber membrane.

[0080] (5) After drying at room temperature, carbon nanotubes are sprayed onto the surface of a rough mixed matrix fiber membrane using dry helium as the driving force and air jet spinning at a pressure of 0.5 MPa and a receiving distance of 2.0 cm to obtain a gas separation membrane.

[0081] Comparative Example 1

[0082] (1) Dissolve 2.1 mmol Co(NO3)2·6H2O and 8.40 mmol dimethylimidazole in 120 mL of water respectively. Then, stir and mix the two solutions evenly. Pour the mixed solution into a 300 mL high-pressure reactor lined with polytetrafluoroethylene and react in an oven at 180 °C for 48 h. After the reaction is completed, the system is naturally cooled to room temperature. After washing the obtained solid, it is vacuum dried at 110 °C for 12 h. The dried solid particles are activated at 200 °C for 14 h to obtain ZIF-67(Co).

[0083] (2) Add ZIF-67(Co) to the polymer solution with a polymer concentration of 32wt%, stir for 12h to obtain a uniformly mixed spinning solution. Let the spinning solution stand at room temperature for 8h and then filter the spinning solution.

[0084] (3) After drying at room temperature, the spinning temperature is 90℃. The fiber membrane is obtained by extruding it from a nozzle with an outer diameter of 0.80mm and an inner diameter of 0.40mm on an electrospinning machine.

[0085] (4) After cooling and forming, immerse the membrane in a 15wt% caustic soda solution for 30 minutes, then immerse it in water for 1 hour to remove the residual caustic soda solution on the membrane, thus obtaining a rough fiber membrane.

[0086] (5) After drying at room temperature, dry helium gas is used as the driving force, and the spinning solution is extruded from a nozzle with an outer diameter of 0.80 mm and an inner diameter of 0.40 mm under a pressure of 0.5 MPa using the air jet spinning method. The carbon nanotubes are sprayed onto the surface of the rough fiber membrane through a receiving distance of 2.0 cm to obtain a gas separation membrane.

[0087] Comparative Example 2

[0088] (1) Dissolve 2.1 mmol Co(NO3)2·6H2O and 8.40 mmol dimethylimidazole in 120 mL of water respectively. Then, stir and mix the two solutions evenly. Pour the mixed solution into a 300 mL high-pressure reactor lined with polytetrafluoroethylene and react in an oven at 180 °C for 48 h. After the reaction is completed, the system is naturally cooled to room temperature. After washing the obtained solid, it is vacuum dried at 110 °C for 12 h. The dried solid particles are activated at 200 °C for 14 h to obtain ZIF-67(Co).

[0089] (2) Add ZIF-67(Co) to the polymer solution with a polymer concentration of 32wt%, stir for 12h to obtain a uniformly mixed spinning solution. Let the spinning solution stand at room temperature for 8h and then filter the spinning solution.

[0090] (3) After drying at room temperature, the spinning solution is spun using a dry-wet spinning process. The spinning solution is extruded from a nozzle with an outer diameter of 0.80 mm and an inner diameter of 0.40 mm. A mixture of water and NMP is used as the core solution (mass ratio of 9:1). The solution is then treated in a water bath to remove residual solvent. The hollow fiber membrane is then dried in an oven at 100°C for 5 hours.

[0091] (4) After cooling and forming, immerse the membrane in a 15wt% caustic soda solution for 30 minutes, then roughen the surface. After that, immerse the membrane in water for 1 hour to remove the residual caustic soda solution and obtain a roughened hollow fiber membrane.

[0092] (5) After drying at room temperature, dry helium gas is used as the driving force, and the spinning solution is extruded from a nozzle with an outer diameter of 0.80 mm and an inner diameter of 0.40 mm under a pressure of 0.5 MPa using the air jet spinning method. The carbon nanotubes are sprayed onto the surface of the rough mixed matrix fiber membrane through a receiving distance of 2.0 cm to obtain a gas separation membrane.

[0093] Comparative Example 3

[0094] (1) 2.1 mmol Al(NO3)3·9H2O and 8.40 mmol 2-aminoterephthalic acid (NH2-H2BDC) were dissolved in 120 mL N,N-dimethylformamide (DMF), respectively. The two solutions were then stirred and mixed thoroughly. The mixed solution was poured into a 300 mL polytetrafluoroethylene-lined high-pressure reactor and reacted in an oven at 130 °C for 48 h. After the reaction was completed, the system was naturally cooled to room temperature. The resulting solid was washed and then vacuum dried at 110 °C for 12 h. The dried solid particles were then activated at 200 °C for 14 h to obtain MIL-88(Al).

[0095] (2) Add MIL-88(Al) to the polymer solution, the polymer concentration is 32wt%, stir for 12h to obtain a uniformly mixed spinning solution. Let the spinning solution stand at room temperature for 8h and filter the spinning solution.

[0096] (3) Using dry helium as the driving force, the spinning temperature is 90℃. The air jet spinning method is used to make the spinning solution squeezed out from the nozzle with an outer diameter of 0.80mm and an inner diameter of 0.40mm under a pressure of 0.5MPa. After passing through a receiving distance of 5.0cm and being stretched 2.0 times, a mixed matrix fiber membrane is formed and stored on the receiver.

[0097] (4) After cooling and forming, immerse the membrane in a 15wt% caustic soda solution for 30 minutes, then immerse it in water for 1 hour to remove the residual caustic soda solution on the membrane, and obtain a rough mixed matrix fiber membrane.

[0098] (5) After drying at room temperature, dry helium gas is used as the driving force, and the spinning solution is extruded from a nozzle with an outer diameter of 0.80 mm and an inner diameter of 0.40 mm under a pressure of 0.5 MPa using the air jet spinning method. The carbon nanotubes are sprayed onto the surface of the rough mixed matrix fiber membrane through a receiving distance of 2.0 cm to obtain a gas separation membrane.

[0099] Comparative Example 4

[0100] (1) Dissolve 2.1 mmol Co(NO3)2·6H2O and 8.40 mmol dimethylimidazole in 120 mL of water respectively. Then, stir and mix the two solutions evenly. Pour the mixed solution into a 300 mL high-pressure reactor lined with polytetrafluoroethylene and react in an oven at 180 °C for 48 h. After the reaction is completed, the system is naturally cooled to room temperature. After washing the obtained solid, it is vacuum dried at 110 °C for 12 h. The dried solid particles are activated at 200 °C for 14 h to obtain ZIF-67(Co).

[0101] (2) Add ZIF-67(Co) to the polymer solution with a polymer concentration of 32wt%, stir for 12h to obtain a uniformly mixed spinning solution. Let the spinning solution stand at room temperature for 8h and then filter the spinning solution.

[0102] (3) Using dry helium as the driving force, the spinning temperature is 90℃. The air jet spinning method is used to make the spinning solution squeezed out from the nozzle with an outer diameter of 0.80mm and an inner diameter of 0.40mm under a pressure of 0.5MPa. After passing through a receiving distance of 5.0cm and being stretched 2.0 times, a mixed matrix fiber membrane is formed and stored on the receiver.

[0103] (4) After cooling and molding, dry at room temperature, and then use dry helium as the driving force to spray carbon nanotubes onto the surface of the mixed matrix fiber membrane at a pressure of 0.5 MPa and a receiving distance of 2.0 cm to obtain a gas separation membrane.

[0104] Test Example 1

[0105] The CO2 / CH4 gas adsorption selectivity and permeability of the materials prepared in Examples 1-6 and Comparative Examples 1-4 were tested. The CO2 / CH4 mixed gas permeation and separation performance was tested at 35°C and 0.50 MPa. The gas separation performance of the membrane was expressed by the CO2 / CH4 selectivity S and the gas permeability coefficient P. The test results are shown in Table 1.

[0106] Table 1

[0107] Sample <![CDATA[CO2 / CH4 selectivity (S)]]> <![CDATA[Gas permeability coefficient P / m 3 / (m 2 ·s·Pa)]]> Example 1 107 <![CDATA[4.49×10 -7 ]]> Example 2 75 <![CDATA[2.09×10 -7 ]]> Example 3 78 <![CDATA[2.14×10 -7 ]]> Example 4 77 <![CDATA[2.54×10 -7 ]]> Example 5 71 <![CDATA[2.92×10 -7 ]]> Example 6 72 <![CDATA[2.44×10 -7 ]]> Comparative Example 1 45 <![CDATA[1.48×10 -7 ]]> Comparative Example 2 39 <![CDATA[1.66×10 -7 ]]> Comparative Example 3 41 <![CDATA[1.17×10 -7 ]]> Comparative Example 4 25 <![CDATA[1.61×10 -7 ]]>

[0108] As shown in Table 1, in terms of the strength of gas selectivity, the gas separation performance of the electrospinning process products shown in Comparative Example 1 and the dry-wet spinning process products shown in Comparative Example 2 is not as good as that of the air-jet spinning process provided in Example 1. The CO2 / CH4 selectivity coefficients S of the two are 45 and 39, respectively, which are much lower than the 107 shown in Example 1. This is because the amount of voids and the uniformity of macromolecular chain distribution inside the fiber material formed by dry-wet spinning are very low. While electrospinning is somewhat better than dry-wet spinning, due to its continuous process and the uniform effect of the electric field, the spatial structure formed inside is more compact, allowing far less gas molecules to pass through than the porous structure formed by air-jet spinning. In addition, Comparative Example 4 lacks the important step of surface roughening the mixed matrix membrane, so its gas permeability coefficient is much lower than that of Example 1. It can be seen that roughening has a great influence on the adhesion and detachment of carbon nanotubes. Changing the MOF material and not roughening the nascent membrane with carbon nanotubes will both reduce the gas separation performance of the product.

[0109] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a gas separation membrane, characterized by, Includes the following steps, (1) The polymer and MOF particles are prepared into a uniform spinning solution; the mass ratio of the polymer to MOF particles is 3-5:1-3; the concentration of the polymer is 30-50 wt%; the polymer is polyethylene terephthalate; the MOF particles are ZIF-67 (Co) or MIL-88 (Al); (2) The spinning solution described in step (1) is made into a mixed matrix fiber membrane by means of air jet blowing; (3) The surface of the mixed matrix fiber membrane described in step (2) is roughened to obtain a mixed matrix fiber membrane with a rough surface. (4) Carbon nanotubes are attached to the surface of the rough mixed matrix fiber membrane described in step (3) by air jetting to form the gas separation membrane.

2. The method for producing a gas separation membrane according to claim 1, characterized by, In step (1), the MOFs particles are pretreated MOFs particles; the pretreated MOFs particles are activated in a vacuum environment of 140℃-300℃ for 8h-24h.

3. The method for producing a gas separation membrane according to claim 1, characterized by, In step (1), the solvent of the spinning solution is water and / or polyvinylpyrrolidone.

4. The method for preparing the gas separation membrane according to claim 1, characterized in that, In step (3), the surface roughening treatment is performed by immersing the mixed matrix fiber membrane in an etching solution for 15 min to 45 min using a chemical etching method.

5. The method for preparing the gas separation membrane according to claim 4, characterized in that, The etching solution is a sodium bicarbonate solution or a sodium hydroxide solution; the concentration of the etching solution is 10-30 wt%.

6. The method for preparing the gas separation membrane according to claim 1, characterized in that, In steps (2) and (4), the conditions for the airflow blowing are: gas pressure of 0.1-2.0 MPa, spinning temperature of 20℃-90℃, receiving distance of 5-20 cm, and stretching ratio of 1-5 times.

7. The method for preparing the gas separation membrane according to claim 1, characterized in that, In steps (2) and (4), the gas used for the airflow jet is helium or neon.

8. The gas separation membrane prepared by the preparation method according to any one of claims 1-7.

9. The application of the gas separation membrane according to claim 8 in the separation of CO2 and CH4.

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