Hollow gas separation membrane as well as preparation method and application thereof
By using imidazolium cationic liquid intercalation and modified polyimide in hollow fiber membranes, the problem of two-dimensional material agglomeration in polymers was solved, improving gas separation selectivity and permeability, and extending membrane lifespan.
Patent Information
- Application Number
- CN202511863894.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-11
- Publication Date
- 2026-02-10
AI Technical Summary
Traditional hollow fiber membranes tend to agglomerate during the manufacture of mixed matrix membranes, leading to increased transport resistance and reduced gas permeability. Furthermore, existing technologies struggle to effectively improve gas separation selectivity and permeability.
By intercalating an ionic liquid containing imidazolium cationic groups into a two-dimensional material, a gas separation membrane is formed through intercalation-induced pore expansion, dual adsorption sites, and lubrication effects, combined with modified polyimide and a specific pore structure. This solves the problem of aggregation of two-dimensional materials in polymers and enhances the gas separation selectivity and permeability.
It effectively reduces transmission resistance, improves the permeability and selectivity of the gas separation membrane, and extends the membrane's service life, achieving high-efficiency gas separation performance.
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Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of gas separation, and particularly relates to a hollow gas separation membrane and a preparation method and application thereof. BACKGROUND
[0002] Traditional gas separation membranes mainly include flat membranes, roll membranes and hollow fiber membranes. Flat membranes are considered to be a common form of gas separation membranes due to their special properties, including: extremely small thickness, good compatibility with polymers, high thermal conductivity, good dispersibility in polymers, good compatibility with polymers, high thermal conductivity, and high dispersibility in solvents such as dimethylformamide. However, the main problem in the manufacture of mixed matrix membranes is that two-dimensional materials are prone to agglomeration in the polymer matrix. This results in a high area-volume ratio of two-dimensional materials that loses its advantage, thereby increasing the transmission resistance and reducing the permeability of the gas in the polymer matrix. Compared with flat membranes, hollow fiber membranes have higher packing density per unit volume, larger filtration area, self-mechanical support, good flexibility and easy operation of component preparation, and thus hollow fiber membranes are expected to become a more excellent gas separation membrane.
[0003] Therefore, how to provide a hollow fiber membrane with good gas separation performance and high selectivity has become a problem to be solved. SUMMARY
[0004] In view of the deficiencies of the prior art, the purpose of the present application is to provide a hollow gas separation membrane and a preparation method and application thereof. The product provided by the present application solves the problem of agglomeration of two-dimensional materials in the polymer matrix during the manufacture of mixed matrix membranes, thereby reducing the transmission resistance and increasing the gas permeability of the separation membrane. The ionic liquid is intercalated in the two-dimensional material, and the separation selectivity and permeability are simultaneously improved through intercalation hole expansion, double adsorption sites and lubrication effect.
[0005] To achieve the purpose of the present application, the following technical solutions are adopted:
[0006] In a first aspect, the present application provides a hollow gas separation membrane, which comprises a first non-porous dense separation layer, a support layer and a second non-porous dense separation layer, the first dense separation layer and the second dense separation layer comprise a polymer, and the support layer comprises a two-dimensional material and an ionic liquid.
[0007] The ion liquid contains imidazolium cation groups in the molecular structure, and the content of the imidazolium cation groups is 0.01%-0.5% (for example, 0.01%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45% or 0.5%, etc., but not limited to the above listed values, and other values not listed in the above value range are also applicable).
[0008] In the present application, the ion liquid containing a specific content of imidazolium cation groups is used, the imidazolium cation forms specific adsorption with CO2 molecules through the π electrons of the five-membered nitrogen heterocycle, and at the same time, the alkyl substituent chain forms a synergistic interfacial effect with the polymer and the two-dimensional material, thereby improving the selectivity and permeability of the hollow gas separation membrane; if the content of the imidazolium cation group is too high, the interaction between the polymer molecular chains will be weakened, which will significantly reduce the mechanical strength of the hollow gas separation membrane and affect its structural stability and durability.
[0009] In the present application, the ion liquid is intercalated in the two-dimensional material, and the ion liquid and the two-dimensional material play a synergistic role in the gas separation membrane. The two-dimensional material provides a screening channel with a rigid skeleton, and the dynamic functional groups of the ion liquid strengthen the dissolution and interfacial bonding. They are uniformly distributed in the hollow gas separation membrane, solving the problem of agglomeration of two-dimensional materials in polymers, reducing the transmission resistance, and not being easily washed away by high-pressure gas flow or liquid. The selectivity and permeability of the gas separation are simultaneously improved through intercalation, double adsorption sites and lubrication effect.
[0010] Preferably, the molecular structure of the ion liquid further comprises an imine anion group.
[0011] In the present application, the ion liquid containing an imine anion group is also used, which has excellent chemical stability and hydrophobic properties, can reduce the erosion of water vapor and acidic impurities on the hollow gas separation membrane, optimize the interfacial compatibility of the ion liquid with the polymer and the two-dimensional material, avoid agglomeration and loss, improve the gas permeation rate, and prolong the stability and service life of the hollow gas separation membrane during long-term operation.
[0012] Preferably, the ion liquid comprises any one of 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide, 1-ethyl-3-methylimidazolium bis(pentafluoroethylsulfonyl) imide, 1-methyl-3-propylimidazolium bis(septadecafluoropropylsulfonyl) imide, 1-ethyl-3-butylimidazolium bis(nonadecafluorobutylsulfonyl) imide or 1-ethyl-3-methylimidazolium thiocyanate or a combination of at least two thereof.
[0013] Preferably, the support layer includes a first support layer, a transition layer, and a second support layer. The first support layer is located between the first non-porous dense separation layer and the transition layer and has micron-sized pores. The transition layer includes interpenetrating micron-sized pores and nano-sized pores. The second support layer is located between the transition layer and the second non-porous dense separation layer and has nano-sized pores.
[0014] Preferably, the pore size of the micropores in the first support layer is 0.5-3 μm (e.g., 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm or 3 μm, etc.), and the pore size of the nanopores in the second support layer is 10-100 nm (e.g., 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm, etc.).
[0015] In this invention, ionic liquid is intercalated into the layered structure of a two-dimensional material. The layered structure is easily dispersed in the casting solution to form a "physical template". Through the non-solvent phase separation (NIPS) process, a continuous hierarchical pore structure can be formed. That is, the support layer contains a hierarchical pore structure from micron pores to mixed pore transition layer and then to nanopores. The two sides also include a first non-porous dense separation layer and a second non-porous dense separation layer. This allows the gas separation membrane in the air to significantly reduce the gas mass transfer resistance and better balance high gas permeability and high gas selectivity.
[0016] Preferably, the polymer comprises any one or a combination of at least two of polyethersulfone, polyimide, polyethylene glycol, polyacrylonitrile, polyvinylidene fluoride, polyetherimide, polydimethylsiloxane, or polyether block amide, with polyimide being the most preferred.
[0017] Preferably, the polyimide comprises a modified polyimide.
[0018] This invention improves the plasticization resistance and stability of polyimide by modifying it, thereby increasing the service life of the gas separation membrane and enhancing its gas permeability.
[0019] Preferably, the modified polyimide is prepared by a method comprising the following steps:
[0020] The modified polyimide is obtained by mixing polyimide with a crosslinking agent, followed by pre-crosslinking, main crosslinking, and curing.
[0021] The above-mentioned specific modification process is simple to operate and can effectively improve the performance of the modified polyimide.
[0022] The polyimide is mixed with a solvent (e.g., NMP) to form a solution before being mixed with the crosslinking agent, in order to avoid excessively high local concentrations caused by direct solid feeding, which could lead to agglomeration or uneven crosslinking.
[0023] Preferably, the crosslinking agent comprises any one or a combination of at least two of 1,3-cyclohexanediamine, isophoronediamine, p-phenylenediamine, or 4,4'-diaminodiphenylmethane.
[0024] Preferably, the molar ratio of the anhydride end of the polyimide to the crosslinking agent is 1:(1.1-1.5), such as 1:1.1, 1:1.15, 1:1.2, 1:1.25, 1:1.3, 1:1.35, 1:1.4, 1:1.45 or 1:1.5, but is not limited to the values listed above. Other unlisted values within the above range are also applicable, with 1:(1.2-1.3) being the preferred value.
[0025] Preferably, the pre-crosslinking temperature is 55-65℃ and the time is 1-3 h. The temperature can be 55℃, 56℃, 57℃, 58℃, 59℃, 60℃, 61℃, 62℃, 63℃, 64℃ or 65℃, etc., and the time can be 1 h, 1.5 h, 2 h, 2.5 h or 3 h, etc., but is not limited to the values listed above. Other unlisted values within the above range are also applicable.
[0026] Preferably, the temperature for the main crosslinking is 110-130℃ and the time is 5-7 h. The temperature can be 110℃, 115℃, 120℃, 125℃ or 130℃, etc., and the time can be 5 h, 5.5 h, 6 h, 6.5 h or 7 h, etc., but is not limited to the values listed above. Other unlisted values within the above range are also applicable.
[0027] In this invention, a pre-crosslinking process is adopted, in which the diamine groups react slowly with the anhydride ends of polyimide under a relatively low temperature environment to form uniformly distributed initial crosslinking points. Then, the main crosslinking is performed, and the crosslinking reaction is deepened by high temperature. Based on the initial sites formed by pre-crosslinking, a three-dimensional network is constructed to ensure uniform crosslinking density, strengthen the crosslinking structure, and improve crosslinking uniformity. When applied in gas separation membranes, this can improve gas permeability and extend the service life of the gas separation membrane.
[0028] Preferably, the curing temperature is 140-160℃ and the time is 0.5-1.5 h. The temperature can be 140℃, 145℃, 150℃, 155℃ or 160℃, etc., but is not limited to the values listed above. Other values not listed in the above range are also applicable.
[0029] Preferably, the crosslinking process is carried out under an inert atmosphere.
[0030] It should be noted that the inert atmosphere can be any available inert gas, such as nitrogen, and is not specifically limited here.
[0031] Preferably, the two-dimensional material includes any one or a combination of at least two of hexagonal boron nitride, molybdenum disulfide, titanium dioxide, graphene oxide, layered double hydroxides, or black phosphorus, and more preferably any one or a combination of at least two of hexagonal boron nitride, molybdenum disulfide, or layered double hydroxides.
[0032] The two-dimensional material selected in this invention is a two-dimensional layered structure. By controlling the interlayer spacing with an ionic liquid containing imidazolium cationic groups, the molecular size differences of the gases to be separated can be matched more precisely, thereby achieving efficient size sieving.
[0033] Secondly, the present invention provides a method for preparing the air-gas separation membrane as described above, the method comprising the following steps:
[0034] The polymer is mixed with the first solvent, then a two-dimensional material and an ionic liquid are added, stirred, and ultrasonically treated to obtain a casting solution.
[0035] The second solvent is mixed with water to obtain the core fluid;
[0036] The casting solution and the core solution are simultaneously spun, soaked, and dried through a spinneret to obtain the air separation membrane.
[0037] This invention directly adds ionic liquids to the casting solution. Compared with the conventional method of first spinning to form a film and then attaching the ionic liquid, the preparation process is simpler and allows the ionic liquid to be uniformly distributed inside the film. Ionic liquid molecules can insert between the layers of the two-dimensional material, expanding and fixing the interlayer spacing, creating a more stable and rapid gas transport channel. Furthermore, in conventional techniques, ionic liquids have difficulty penetrating into the interior of the already formed two-dimensional material stack structure, resulting in poor performance. In terms of long-term stability, the ionic liquid directly added to the casting solution in this invention is "locked" in the polymer network, making it less prone to loss.
[0038] Preferably, based on the mass of the casting solution as 100%, the raw materials for preparing the casting solution include 10-40% polymer, 50-85% first solvent, 0.5-5% two-dimensional material and 0.5-5% ionic liquid.
[0039] The polymer can be 10%, 15%, 20%, 25%, 30%, 35%, or 40%, etc.; the first solvent can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, or 85%, etc.; the two-dimensional material can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, etc.; and the ionic liquid can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, etc., but is not limited to the values listed above. Other unlisted values within the above range are also applicable.
[0040] Preferably, based on the mass of the casting solution as 100%, the air separation membrane comprises, by mass, 15-25% polymer, 70-84% solvent, 0.5-2.5% two-dimensional material and 0.5-1.5% ionic liquid.
[0041] It should be noted that the optimal range can maximize the synergistic effect of polymers, two-dimensional materials and ionic liquids, thereby improving the selectivity and permeability of gas separation.
[0042] Preferably, based on the mass of the casting solution as 100%, the raw materials for preparing the casting solution also include 0.1-1% of a dispersant (e.g., 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%).
[0043] It should be noted that this application does not specifically limit the type of dispersant. For example, the dispersant can be a nonionic surfactant, including any one or a combination of at least two of Tween 85, Tween 80, Tween 60 or Tween 40.
[0044] Preferably, the first solvent includes any one or a combination of at least two of water, N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone.
[0045] Preferably, the second solvent includes any one or a combination of at least two of N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone.
[0046] Preferably, the temperatures of the casting solution, core solution, and spinneret are independently 25-70°C, such as 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, or 70°C, but not limited to the values listed above. The above values are also applicable, with 40-60°C being the preferred temperature.
[0047] Preferably, during the spinning process, the height of the air section is 10-80 cm, such as 10 cm, 20 cm, 30 cm, 40 cm, 50 cm, 60 cm, 70 cm or 80 cm, but not limited to the values listed above. Other unlisted values within the above range are also applicable, with 20-60 cm being the preferred value.
[0048] Preferably, during the spinning process, the coagulation bath temperature is 20-70℃, such as 20℃, 30℃, 40℃, 50℃, 60℃ or 70℃, but not limited to the values listed above. Other values not listed above are also applicable, with 30-60℃ being the preferred temperature.
[0049] Preferably, the coagulation bath during the spinning process is water.
[0050] Preferably, the drying time is 30-60 min, such as 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min, but not limited to the values listed above. Other values not listed in the above range are also applicable.
[0051] Thirdly, the present invention also provides the application of the gas separation membrane described above in the preparation of gas separation mixing matrix membranes.
[0052] Compared with the prior art, the present invention has the following beneficial effects:
[0053] This invention provides a gas separation membrane for gas separation. By employing an ionic liquid with a specific structure and intercalating the ionic liquid into a two-dimensional material, the ionic liquid and the two-dimensional material work synergistically in the gas separation membrane. The rigid framework of the two-dimensional material provides sieving channels, while the dynamic functional groups of the ionic liquid enhance dissolution and interfacial bonding. The membrane is homogeneously distributed within the gas separation membrane, solving the problem of aggregation of two-dimensional materials in polymers, reducing transport resistance, and making it less susceptible to being carried away by high-pressure gas flow or liquid rinsing, thus preventing loss. Furthermore, the intercalation expands the pores, creates dual adsorption sites, and provides a lubrication effect, simultaneously improving the gas separation selectivity and permeability. Detailed Implementation
[0054] To further illustrate the technical means and effects of the present invention, the following describes the technical solution of the present invention in conjunction with preferred embodiments of the present invention. However, the present invention is not limited to the scope of the embodiments.
[0055] In the following example, the polyimide was purchased from Shandong Huaxia Shenzhou New Material Co., Ltd., and the model number was FPI-02;
[0056] The polyethersulfone was purchased from Solvay, model Udel® P-3500 LCD MB;
[0057] The graphene oxide was purchased from Suzhou Juxu Graphene Technology Co., Ltd., model number JCNANO-GO-W-20;
[0058] The hexagonal boron nitride was purchased from Suzhou Napu New Materials Technology Co., Ltd., model number NP-hBN-100;
[0059] Molybdenum disulfide was purchased from Sigma-Aldrich (Sigma), model number 698608;
[0060] 1-Ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imine salt was purchased from BASF, model number Basionics® HP 01;
[0061] 1-Butyl-3-methylimidazolium tetrafluoroborate was purchased from Sigma-Aldrich (Sigma), model number 790823;
[0062] The Twain 85 was purchased from Sigma-Aldrich (Sigma), model number P8561.
[0063] Preparation Example 1
[0064] This preparation example provides a modified polyimide, prepared by the following method:
[0065] Polyimide (PI) was dissolved in N-methylpyrrolidone (NMP) at a concentration of 15 wt% and stirred at 80°C for 12 h; the viscosity of the solution was controlled between 2000-4000 cP (25°C).
[0066] 1,3-cyclohexanediamine was dissolved in N-methylpyrrolidone (5 wt%) at a molar ratio of 1.2:1 to the anhydride end of polyimide, and then added dropwise to the above polyimide solution. The mixture was stirred for 2 h under nitrogen protection.
[0067] The mixture was first heated at 60°C for 2 h for pre-crosslinking, then heated to 120°C for 6 h for main crosslinking, then heated to 150°C for curing for 1 h, and finally immersed in methanol for 1 h to replace residual N-methylpyrrolidone. The mixture was then dried at 20°C for 24 h to obtain the modified polyimide.
[0068] Preparation Example 2
[0069] This preparation example provides a modified polyimide, prepared by the following method:
[0070] Polyimide (PI) was dissolved in N-methylpyrrolidone at a concentration of 15 wt% and stirred at 80°C for 12 h. The viscosity of the solution was controlled between 2000 and 4000 cP (at 25°C).
[0071] Isophorone diamine was dissolved in N-methylpyrrolidone (5 wt%) at a molar ratio of 1.5:1 to the anhydride end of polyimide, and then added dropwise to the above polyimide solution. The mixture was stirred for 2 h under nitrogen protection.
[0072] The mixture was first heated at 55°C for 3 h for pre-crosslinking, then heated to 110°C for 7 h for main crosslinking, then heated to 160°C for curing for 0.5 h, and finally immersed in methanol for 1 h to replace residual N-methylpyrrolidone, and dried at 20°C for 24 h to obtain the modified polyimide.
[0073] Preparation Example 3
[0074] This preparation example provides a modified polyimide, prepared by the following method:
[0075] Polyimide (PI) was dissolved in N-methylpyrrolidone at a concentration of 15 wt% and stirred at 80°C for 12 h. The viscosity of the solution was controlled between 2000 and 4000 cP (at 25°C).
[0076] p-Phenylenediamine was dissolved in N-methylpyrrolidone (5 wt%) at a molar ratio of 1.1:1 to the anhydride end of polyimide, and then added dropwise to the above polyimide solution. The mixture was stirred for 2 h under nitrogen protection.
[0077] The mixture was first heated at 65°C for 1 h for pre-crosslinking, then heated to 130°C for 5 h for main crosslinking, then heated to 140°C for curing for 1.5 h, and finally immersed in methanol for 1 h to replace residual N-methylpyrrolidone, and dried at 20°C for 24 h to obtain the modified polyimide.
[0078] Preparation Example 4
[0079] This preparation example provides a modified polyimide, prepared by the following method:
[0080] Dissolve 15 g of polyimide (PI) in 85 g of N-methylpyrrolidone (NMP) and stir at 80 °C for 12 h; control the viscosity of the solution between 2000-4000 cP (25 °C). Add 5 g of sodium hydroxide to prepare a homogeneous solution, and then react in a sealed environment at 120 °C for 5 h; add hydrochloric acid to adjust the pH to between 1 and 3, and then remove the water by rotary evaporation.
[0081] Ethylenediamine was dissolved in N-methylpyrrolidone (5 wt%) at a molar ratio of 1.2:1 to the anhydride end of polyimide, and then added dropwise to the above polyimide solution. The mixture was stirred at 20°C for 3 hours under nitrogen protection to obtain the modified polyimide.
[0082] Example 1
[0083] This embodiment provides a medium-air gas separation membrane, prepared from the following raw materials (by mass percentage):
[0084] The preparation method is as follows:
[0085] 1. Preparation of precursor: The modified polyimide material provided in Preparation Example 1 was dried in a vacuum oven at 60°C for 24 hours and then placed in a desiccator for 2 hours. The dried modified polyimide material was added to N,N-dimethylacetamide to dissolve and obtain the precursor. The mixture was stirred with a magnetic stirrer at 60°C and 200 rpm for 6 hours.
[0086] 2. Preparation of casting solution: Hexagonal boron nitride, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and Tween 85 were added to the precursor and dispersed in a water bath ultrasonic bath at a power of 250W and a frequency of 50kHz for 50 minutes to obtain the casting solution (modified polyimide 20%, hexagonal boron nitride 2%, 1.5% 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 0.5% Tween 85, and the remainder being solvent N,N-dimethylformamide). The solution was then degassed under vacuum for 12 hours before use.
[0087] 3. Preparation of core solution: Add N,N-dimethylformamide to deionized water (to form a 50% aqueous solution), stir evenly, and let stand for 6 hours to remove bubbles before use.
[0088] 4. Spinning: The casting solution and core solution are separately fed into the spinneret, and spinning is carried out using hollow fiber spinning equipment (Dalian Kona DKN-2). The temperature of the casting solution, core solution, and spinneret is 50℃, the air section height is 40cm, the coagulation bath temperature is 25℃, and the coagulation bath is water. The product is collected after washing with water.
[0089] 5. Drying: Dry at 80℃ for 6 hours until the membrane fibers are completely dry to obtain the air separation membrane.
[0090] Example 2
[0091] This embodiment provides a medium-air gas separation membrane, which is the same as that in Example 1, except that the composition of the casting solution obtained in step 2 is as follows.
[0092] The modified polyimide provided in Preparation Example 1 consisted of 15% hexagonal boron nitride, 2% 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide salt, 0.5% Tween 85, and the remainder was the solvent N,N-dimethylformamide.
[0093] The preparation method is the same as in Example 1 (the ultrasonic time is changed to 30 min).
[0094] Example 3
[0095] This embodiment provides a medium-air gas separation membrane, which is the same as that in Example 1, except that the composition of the casting solution obtained in step 2 is as follows.
[0096] The modified polyimide provided in Preparation Example 1 consisted of 25% hexagonal boron nitride, 2% 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide salt, 0.5% Tween 85, and the remainder was the solvent N,N-dimethylformamide.
[0097] The preparation method is the same as in Example 1 (the ultrasonic time is changed to 30 min).
[0098] Example 4
[0099] This embodiment provides a medium-air gas separation membrane, which is the same as that in Example 1, except that the composition of the casting solution obtained in step 2 is as follows.
[0100] The modified polyimide provided in Preparation Example 2 consisted of 10% hexagonal boron nitride, 0.5% 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide salt, 0.1% Tween 85, and the remainder was the solvent N,N-dimethylformamide.
[0101] The preparation method is the same as in Example 1 (the ultrasonic time is changed to 30 min).
[0102] Example 5
[0103] This embodiment provides a medium-air gas separation membrane, prepared from the following raw materials (by mass percentage):
[0104] The modified polyimide provided in Preparation Example 3 consisted of 40% hexagonal boron nitride, 5% 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide salt, 1% Tween 85, and the remainder was the solvent N,N-dimethylacetamide.
[0105] The preparation method is the same as in Example 1 (the ultrasonic time is changed to 60 min).
[0106] Example 6
[0107] This embodiment provides a medium-air gas separation membrane. The raw materials used in its preparation are the same as those in Example 1, except that the modified polyimide provided in Preparation Example 1 is replaced with an equal amount of polyimide.
[0108] Example 7
[0109] This embodiment provides a medium-air gas separation membrane. The raw materials used in its preparation are the same as those in Example 1, except that the modified polyimide provided in Preparation Example 1 is replaced with an equal amount of polyethersulfone.
[0110] Example 8
[0111] This embodiment provides a medium-air gas separation membrane. Except for replacing the modified polyimide provided in Preparation Example 1 with an equal amount of the modified polyimide provided in Preparation Example 4, the raw materials are the same as in Example 1.
[0112] Example 9
[0113] This embodiment provides a medium-air gas separation membrane. Except for replacing the hexagonal boron nitride provided in Preparation Example 1 with molybdenum disulfide, the raw materials are the same as in Example 1.
[0114] Example 10
[0115] This embodiment provides a medium-air gas separation membrane. Except for replacing the hexagonal boron nitride provided in Preparation Example 1 with graphene oxide, the raw materials are the same as in Example 1.
[0116] Example 11
[0117] This embodiment provides a medium-air gas separation membrane. The raw materials used in its preparation are the same as in Example 1, except that the 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt provided in Preparation Example 1 is replaced with 1-butyl-3-methylimidazolium tetrafluoroborate.
[0118] Example 12
[0119] This embodiment provides a medium-air gas separation membrane, and the raw materials used in its preparation are the same as those in Example 1.
[0120] The preparation method is as follows:
[0121] 1. Preparation of precursor: The modified polyimide material provided in Preparation Example 1 was dried in a vacuum oven at 60°C for 24 hours and then placed in a desiccator for 2 hours. The dried modified polyimide material was added to N,N-dimethylacetamide to dissolve and obtain the precursor. The mixture was stirred with a magnetic stirrer at 60°C and 200 rpm for 6 hours.
[0122] 2. Preparation of casting solution: Hexagonal boron nitride and Tween 85 were added to the precursor and dispersed in a water bath ultrasonic instrument at a power of 250W and a frequency of 50kHz for 50 minutes to obtain the casting solution (modified polyimide 20%, hexagonal boron nitride 2%, Tween 85 0.5%, and the remainder being solvent N,N-dimethylformamide). The solution was then degassed under vacuum for 12 hours before use.
[0123] 3. Preparation of core solution: Add N,N-dimethylformamide to deionized water (to form a 50% aqueous solution), stir evenly, and let stand for 6 hours to remove bubbles before use.
[0124] 4. Spinning: The casting solution and core solution are separately fed into the spinneret, and spinning is carried out through hollow fiber spinning equipment. The temperature of the casting solution, core solution, and spinneret is 50℃, the air section height is 40cm, the coagulation bath temperature is 25℃, and the coagulation bath is water. The product is collected after washing with water.
[0125] 5. Drying: Dry at 80℃ for 6 hours until the film fibers are completely dry.
[0126] 6. Post-treatment: The dried hollow fiber membrane is immersed in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imine salt ionic liquid, and the ionic liquid is heated to 60°C for 2 hours.
[0127] 7. Finally, the post-treated hollow fiber membrane is immersed in isopropanol (3 times, 30 min each time) to remove residual NMP inside, and the hollow gas separation membrane is obtained.
[0128] Comparative Example 1
[0129] This comparative example provides a medium-air gas separation membrane, which is the same as that in Example 1 except that the composition of the casting solution obtained in step 2 is as follows.
[0130] The modified polyimide provided in Preparation Example 1 contains 20% Tween 85, 0.5% Tween 85, and the remainder is the solvent N,N-dimethylformamide.
[0131] The preparation method is the same as in Example 1.
[0132] Comparative Example 2
[0133] This comparative example provides a medium-air gas separation membrane, which is the same as that in Example 1 except that the composition of the casting solution obtained in step 2 is as follows.
[0134] The modified polyimide provided in Preparation Example 1 consisted of 20% hexagonal boron nitride, 2% Tween 85, and the remainder was the solvent N,N-dimethylformamide.
[0135] The preparation method is the same as in Example 1.
[0136] Comparative Example 3
[0137] This comparative example provides a medium-air gas separation membrane, which is the same as that in Example 1 except that the composition of the casting solution obtained in step 2 is as follows.
[0138] The modified polyimide provided in Preparation Example 1 consisted of 20% 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide salt, 1.5% Tween 85, and the remainder was the solvent N,N-dimethylformamide.
[0139] Effect test:
[0140] The products provided in Examples 1-12 and Comparative Examples 1-3 were subjected to permeability, selectivity, and service life tests, and the test methods are as follows:
[0141] 1. CO2 Permeability (GPU) Test
[0142] Test standard: Refer to GB / T 40260-2021 "Test method for permeation performance of gas separation membrane".
[0143] Test equipment: Constant volume gas permeation apparatus (model: VAC-V2, Beijing Jingwei Gaobo Instrument Co., Ltd.).
[0144] Test conditions:
[0145] Test gases: high-purity CO2 (purity ≥ 99.99%), high-purity CH4 (purity ≥ 99.99%).
[0146] Test temperature: 25℃ (simulating normal industrial operating conditions);
[0147] Test pressure: 0.5 MPa (compliant with the normal pressure range for natural gas purification and industrial waste gas treatment);
[0148] Effective test area of membrane: 10 cm² 2 The sealing method is a rubber ring seal to prevent gas leakage.
[0149] Test steps:
[0150] Hollow fiber membranes were cut into 5 cm long filaments, sealed at both ends, and then placed into a permeation tank. Vacuum degassing was performed for 2 hours to remove residual gas from the membrane.
[0151] Introduce the test gas (CO2 first, then CH4), maintain the test pressure for 30 minutes, and record the change in downstream gas volume after the permeation flux reaches equilibrium.
[0152] The permeability is calculated using the formula: P = VL / (AΔPt), where P is the permeability (in GPU, 1 GPU = 1 × 10⁻⁶). -6 cm 3 ·cm / (cm 2 ·s·cmHg), V is the permeate gas volume, L is the membrane thickness, A is the effective area, ΔP is the pressure difference across the membrane, and t is the test time.
[0153] Parallel sample requirements: Three parallel samples are tested for each sample, and the average value is taken as the final result. The relative standard deviation (RSD) is ≤5%.
[0154] 2. CO2 / CH4 Selectivity Test
[0155] Test logic: The separation coefficient is calculated based on the permeability of a single gas. The selectivity calculation formula is as follows:
[0156]
[0157] in CO2 penetration rate, CH4 permeability.
[0158] Test conditions: consistent with single gas permeability test (temperature 25℃, pressure 0.5 MPa) to avoid errors caused by changes in conditions.
[0159] Data validity: The calculated selectivity results are valid only if the RSD of both sets of single gas permeability tests is ≤5%.
[0160] 3. Service life test
[0161] Test simulation conditions: Simulate an industrial natural gas purification scenario. The test gas is simulated natural gas (CO2 volume fraction 15%, CH4 volume fraction 85%), pressure 1.0 MPa, temperature 40℃ (including a certain humidity, relative humidity 60%).
[0162] Test equipment: Continuous gas separation membrane evaluation device (model: SEP-G100, Jiangsu Sujing Group), equipped with an online gas chromatograph (GC-2030, Shimadzu) to monitor the gas composition on the permeate side in real time.
[0163] Test steps:
[0164] Hollow fiber membranes were assembled into small membrane modules (effective area 0.1 m²). 2 ), connected to the evaluation device, and simulated natural gas was introduced for stable operation for 24 hours;
[0165] Sampling was conducted every 200 hours to analyze CO2 permeability and CO2 / CH4 selectivity, and performance changes were recorded.
[0166] The test is stopped when the CO2 permeability drops to 80% of the initial value, or the CO2 / CH4 selectivity drops to 75% of the initial value. The cumulative running time is the service life.
[0167] Stability assessment: If the performance degradation does not reach the above threshold after 3000 hours of continuous operation, the service life shall be calculated as 3000 hours.
[0168] The results are as follows:
[0169]
[0170] The data above shows that the product provided by this invention has the advantages of good gas separation permeability and selectivity, and long service life. Comparative Examples 1-8 show that this invention, by using a specific method to modify polyimide, can further improve the product's performance compared to other modification methods and other polymers. Comparative Examples 1-3 show that this invention, by limiting the proportions of polymer, ionic liquid, and two-dimensional material, achieves the best synergistic effect in gas separation selectivity and permeability. Comparative Examples 1, 12, and Comparative Examples 1-3 show that this invention, by directly adding ionic liquid to the casting solution, can intercalate the ionic liquid into the two-dimensional material. The ionic liquid and the two-dimensional material work synergistically in the gas separation membrane, solving the aggregation problem of the two-dimensional material in the polymer, reducing transmission resistance, making it less susceptible to being washed away by high-pressure gas flow or liquid, less prone to loss, and having a long service life. Furthermore, it simultaneously improves gas separation selectivity and permeability through intercalation pore expansion, dual adsorption sites, and lubrication effects. Comparative Examples 1, 9-11 show that this invention, by selecting specific raw materials, can effectively improve the product's performance. Example 9 uses molybdenum disulfide with a layer spacing of (0.62). The permeability (nm) is greater than that of hexagonal boron nitride, resulting in lower gas transport resistance and a permeability of 580 GPU (higher than the hexagonal boron nitride system), but a selectivity of 55 (slightly lower than the 62 of hexagonal boron nitride). Example 10 uses graphene oxide, which has the narrowest interlayer spacing (0.3-0.6 nm), and a stronger size sieving effect than hexagonal boron nitride, with a selectivity of 70 (second highest), but it is prone to interlayer aggregation, resulting in a permeability of only 380 GPU. In contrast, Example 1 uses hexagonal boron nitride (h-BN), which combines "high permeability + high selectivity", has the best dispersibility in its layered structure, and the best synergistic effect with ionic liquids, making it the preferred filler.
[0171] It should be noted that a hybrid matrix membrane refers to a composite gas separation membrane that combines the excellent properties of inorganic fillers with the good processability of polymer matrices.
[0172] The above specific embodiments are for further introduction of the present invention. It is understood that the above solutions are also applicable to the separation and extraction of other gases such as H2, N2 and CH4, and the performance can be improved to varying degrees.
[0173] The applicant declares that the present invention is illustrated through the above embodiments to demonstrate the air-gas separation membrane, its preparation method, and its application. However, the present invention is not limited to the above embodiments, meaning that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials for the product of the present invention, addition of auxiliary components, and selection of specific methods, etc., all fall within the protection and disclosure scope of the present invention.
[0174] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.
[0175] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.
Claims
1. A gas separation membrane for air separation, characterized in that, The air separation membrane comprises a first non-porous dense separation layer, a support layer, and a second non-porous dense separation layer. The first and second dense separation layers comprise polymers, and the support layer comprises a two-dimensional material and an ionic liquid. The ionic liquid contains imidazolium cationic groups in its molecular structure, and the content of imidazolium cationic groups is 0.01%-0.5% based on 100% of the mass of the hollow fiber membrane.
2. The air-gas separation membrane according to claim 1, characterized in that, The molecular structure of the ionic liquid also includes imine anionic groups; Preferably, the ionic liquid comprises any one or a combination of at least two of the following: 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imine, 1-ethyl-3-methylimidazolium bis(pentafluoroethylsulfonyl)imine, 1-methyl-3-propylimidazolium bis(heptafluoropropylsulfonyl)imine, 1-ethyl-3-butylimidazolium bis(nonafluorobutylsulfonyl)imine, or 1-ethyl-3-methylimidazolium thiocyanate.
3. The air-gas separation membrane according to claim 1 or 2, characterized in that, The support layer includes a first support layer, a transition layer, and a second support layer. The first support layer is located between a first non-porous dense separation layer and a transition layer and has micron-sized pores. The transition layer includes interpenetrating micron-sized pores and nano-sized pores. The second support layer is located between the transition layer and the second non-porous dense separation layer and has nano-sized pores.
4. The air-gas separation membrane according to claim 1, characterized in that, The polymer includes any one or a combination of at least two of polyethersulfone, polyimide, polyethylene glycol, polyacrylonitrile, polyvinylidene fluoride, polyetherimide, polydimethylsiloxane, or polyether block amide, preferably polyimide.
5. The air-gas separation membrane according to claim 4, characterized in that, The polyimide includes modified polyimide.
6. The air-gas separation membrane according to claim 5, characterized in that, The modified polyimide is prepared by a method comprising the following steps: The modified polyimide is obtained by mixing polyimide with a crosslinking agent, followed by pre-crosslinking, main crosslinking, and curing. Preferably, the crosslinking agent comprises any one or a combination of at least two of 1,3-cyclohexanediamine, isophoronediamine, p-phenylenediamine, or 4,4'-diaminodiphenylmethane; Preferably, the molar ratio of the anhydride end of the polyimide to the crosslinking agent is 1:(1.1-1.5), more preferably 1:(1.2-1.3); Preferably, the pre-crosslinking temperature is 55-65℃ and the time is 1-3 h; Preferably, the temperature for the primary crosslinking is 110-130℃, and the time is 5-7 h; Preferably, the curing temperature is 140-160℃ and the time is 0.5-1.5 h; Preferably, the crosslinking process is carried out under an inert atmosphere.
7. The air-gas separation membrane according to any one of claims 1-6, characterized in that, The two-dimensional material includes any one or a combination of at least two of hexagonal boron nitride, molybdenum disulfide, titanium dioxide, graphene oxide, layered double hydroxides, or black phosphorus, preferably any one or a combination of at least two of hexagonal boron nitride, molybdenum disulfide, or layered double hydroxides.
8. A method for preparing a gas separation membrane in the air according to any one of claims 1-7, characterized in that, The preparation method includes the following steps: The polymer is mixed with the first solvent, then a two-dimensional material and an ionic liquid are added, stirred, and ultrasonically treated to obtain a casting solution. The second solvent is mixed with water to obtain the core fluid; The casting solution and the core solution are simultaneously spun, soaked, and dried through a spinneret to obtain the air separation membrane.
9. The preparation method according to claim 8, characterized in that, Based on the casting solution by mass of 100%, the raw materials for preparing the casting solution include 10-40% polymer, 50-85% first solvent, 0.5-5% two-dimensional material, and 0.5-5% ionic liquid; Preferably, based on the casting solution by weight of 100%, the raw materials for preparing the casting solution further include 0.1-1% dispersant; Preferably, the first solvent includes any one or a combination of at least two of water, N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone; Preferably, the second solvent comprises any one or a combination of at least two of N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone; Preferably, the temperatures of the casting solution, core solution, and spinneret are independently 25-70°C, more preferably 40-60°C; Preferably, during the spinning process, the height of the air section is 10-80 cm, more preferably 20-60 cm; Preferably, during the spinning process, the coagulation bath temperature is 20-70℃, more preferably 30-60℃; Preferably, during the spinning process, the coagulation bath is water; Preferably, the drying time is 30-60 minutes.
10. The application of a gas separation membrane according to any one of claims 1-7 in the preparation of a gas separation mixed matrix membrane.