Bio-based polyimide film, method for preparing the same, and use thereof

Abstract

The application provides a bio-based polyimide film and a preparation method and application thereof, and belongs to the technical field of polymer materials. The polyimide has a structure as shown in formula (I): formula (I); wherein 10 < n < 500. The bio-based polyimide film is constructed by using a non-grain biomass source diamine monomer to construct an easy-crosslinking polyimide separation film, so that the greenization and sustainability are realized from the raw material source, and through the unique functional group design of the bio-based monomer, a stable crosslinking network capable of inhibiting plasticization is constructed in the obtained bio-based polyimide film, so that excellent plasticization resistance and swelling resistance are achieved, meanwhile, the bio-based polyimide has good gas separation performance, and especially has high selectivity in helium / methane separation.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and particularly relates to a bio-based polyimide film, its preparation method and application. Background Technology

[0002] Compared with traditional separation processes, membrane separation technology is considered a core direction of the next generation of gas separation technology due to its advantages such as low energy consumption, simple process, and environmental friendliness. Among them, polymer membrane materials have become the mainstream of current research and application due to their excellent processability and mechanical properties.

[0003] However, most polymer membranes face inherent limitations such as wide free volume distribution and uneven cavity size. Their separation performance is often constrained by a trade-off between permeability and selectivity, making it difficult to break through the Robertson upper limit. Therefore, high-performance polymers such as polyimides, with their tunable molecular structure and good thermal stability, have become important candidate materials for overcoming this bottleneck. However, traditional polyimides are mainly derived from petroleum-based monomers, and their synthesis and use still rely heavily on fossil resources. Furthermore, they are prone to plasticization and structural relaxation under high pressure and complex gas environments, affecting long-term separation stability. Summary of the Invention

[0004] This invention provides a bio-based polyimide film, its preparation method, and its applications. Using non-grain biomass-derived natural aromatic compounds as raw materials, a bio-based aromatic diamine monomer is polymerized with a dianhydride to obtain the bio-based polyimide film. The resulting membrane material exhibits both good thermal stability and film-forming properties, and demonstrates excellent separation performance and long-term stability in gas sieving processes such as helium separation.

[0005] This invention proposes a bio-based polyimide film, wherein the polyimide has a structure as shown in formula (I):

[0006] Formula (I);

[0007] Among them, 10 <n<500;

[0008] X is selected independently from:

[0009] , , ,

[0010] or ;

[0011] Ar is independently selected from:

[0012] , , , , or .

[0013] This invention also proposes a method for preparing a bio-based polyimide film, comprising the following steps:

[0014] S1. Under a protective atmosphere, dianhydride and bio-based diamine are mixed, and a catalyst and solvent are added to react and obtain a viscous reaction solution.

[0015] S2. The above viscous reaction solution was treated by solvent precipitation and dried to obtain polyimide powder;

[0016] S3. After dissolving the above polyimide powder in a solvent, the resulting solution is evaporated to obtain a polyimide film;

[0017] The bio-based diamine is selected from the following:

[0018] , , , or .

[0019] Furthermore, the bio-based diamine is obtained from raw materials extracted from non-grain biomass and then chemically modified.

[0020] The raw materials include daidzein, tanshinone I, or mangiferin; the chemical modification treatment includes at least one of electrophilic substitution reaction, nucleophilic substitution reaction, or catalytic transfer hydrogenation reaction.

[0021] Further, in S1, the dianhydride is selected from the following:

[0022] Ar is independently selected from:

[0023] , , , , or .

[0024] Furthermore, at least one of the following conditions must be met:

[0025] (1) In S1, the ratio of dianhydride, bio-based diamine, and catalyst is 2 mmol:2 mmol:0.3~2 mL;

[0026] (2) In S1, the reaction temperature is 150-180 ℃;

[0027] (3) In S1, the ratio of bio-based diamine to solvent is 2 mmol: 5-30 mL;

[0028] (4) In S1, the viscosity of the resulting reaction solution is 6000-200000 cps;

[0029] (5) In S2, the solvent precipitation method for treating the above viscous reaction liquid specifically includes: pouring the viscous reaction liquid into a methanol solution or a mixture of ethanol and water, stirring, causing the polyimide to precipitate, and then filtering.

[0030] (6) In S2, the drying process specifically involves drying at 80-120 ℃ for 10-20 h;

[0031] (7) In S3, the solvent is a volatile solvent, which includes at least one of tetrahydrofuran, 1,4-dioxane, chloroform, and dichloromethane.

[0032] The present invention also proposes the application of any of the above-described bio-based polyimide films or bio-based polyimide films prepared by any of the above-described preparation methods in gas separation.

[0033] Further, the applications include: the bio-based polyimide film being used to obtain He from a He / CH4 gas mixture, enrich O2 from an O2 / N2 gas mixture, separate N2 from air, separate CO2 from a CO2 / CH4 gas mixture, separate H2 from an H2 / CH4 gas mixture, or separate CO2 from a CO2 / N2 gas mixture.

[0034] Furthermore, the bio-based polyimide film is used for helium extraction from natural gas, specifically for obtaining helium from a mixture of methane and helium.

[0035] Furthermore, the bio-based polyimide film is insoluble in organic solvents; the organic solvents include at least one of 1,3,5-trimethylbenzene, N,N-dimethylformamide, N,N-dimethylacetamide, anhydrous methanol, anhydrous ethanol, tetrahydrofuran, chloroform, dichloromethane, N-methylpyrrolidone, or dimethyl sulfoxide.

[0036] This invention has the following advantages:

[0037] The bio-based polyimide film proposed in this invention utilizes diamine monomers from non-grain biomass sources to construct an easily crosslinkable polyimide separation membrane, achieving greening and sustainability from the source of raw materials. Furthermore, through the unique functional group design of bio-based monomers, the structure includes rigid aromatic rings, ether oxygen bonds, and reactive hydroxyl and aromatic ketone functional groups, enhancing the rigidity of the polymer chain and providing crosslinking sites. Then, through intermolecular hydrogen bonding and crosslinking reactions, a stable crosslinking network that inhibits plasticization is constructed, giving the film excellent resistance to plasticization and swelling. Simultaneously, this bio-based polyimide exhibits good gas separation performance, especially showing high selectivity in helium / methane separation. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 The NMR spectrum of the non-grain biomass-derived aromatic diamine obtained in Example 1A of this invention;

[0040] Figure 2 The NMR spectra of the bio-based polyimide obtained in Example 1A of the present invention and the petroleum-based polyimide in Comparative Example 1 are shown.

[0041] Figure 3 The infrared spectra of the bio-based polyimide obtained in Example 1B of the present invention and the petroleum-based polyimide film in Comparative Example 1 are shown.

[0042] Figure 4 The gas separation performance of the bio-based polyimide film in Test Example 1 of this invention;

[0043] Figure 5 This is a comparison chart of the gas separation performance of bio-based polyimide and petroleum-based polyimide in Example 1 of the present invention;

[0044] Figure 6 This is a comparison chart of the glass transition temperatures of the bio-based polyimide obtained in Example 1B of the present invention and the petroleum-based polyimide in Comparative Example 1;

[0045] Figure 7 Optical photographs showing the solvent resistance of bio-based polyimide 6F-Dd-A obtained in Example 1B after heat treatment;

[0046] Figure 8 The graph shows the plasticizing resistance of the bio-based polyimide 6F-Dd-A obtained in Example 1B.

[0047] Figure 9 The tensile strength of the bio-based polyimide 6F-Dd-A obtained in Example 1B is shown. Detailed Implementation

[0048] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0049] Currently, research on bio-based polyimides for gas separation is still in its early stages, particularly lacking systematic exploration in areas such as the precise synthesis of non-grain biomass-derived monomers, the controllable construction of polymer condensed-state structures, and the systematic optimization of their separation performance. This invention provides a high-performance, plasticization-resistant bio-based polyimide separation membrane and its preparation method, aiming to promote the development of gas separation technology towards a green, efficient, and sustainable direction.

[0050] On one hand, embodiments of the present invention provide a bio-based polyimide film, wherein the polyimide has a structure as shown in formula (I):

[0051] Formula (I);

[0052] Among them, 10 <n<500;

[0053] X is selected independently from:

[0054] , , ,

[0055] or ;

[0056] Ar is independently selected from:

[0057] , , , , or .

[0058] It should be noted that in the structures in which X and Ar are independently selected, the dashed lines represent the bond linking locations.

[0059] Preferably, X is independently selected from: , , .

[0060] More preferably, X is independently selected from: .

[0061] On the other hand, embodiments of the present invention also propose a method for preparing a bio-based polyimide film, comprising the following steps:

[0062] S1. Under a protective atmosphere, dianhydride and bio-based diamine are mixed, and a catalyst and solvent are added to react and obtain a viscous reaction solution.

[0063] S2. The above viscous reaction solution was treated by solvent precipitation and dried to obtain polyimide powder;

[0064] S3. After dissolving the above polyimide powder in a solvent, the resulting solution is evaporated to obtain a polyimide film;

[0065] The bio-based diamine is selected from the following:

[0066] , , , or .

[0067] The method for preparing bio-based polyimide films proposed in this invention uses aromatic diamines and dianhydrides derived from non-grain biomass as monomers, and forms bio-based polyimides with rigid main chains and crosslinkable functional groups through solution polycondensation reaction. The bio-based polyimides have good gas separation performance, are easy to process, and have good thermal stability.

[0068] In this embodiment of the invention, the product obtained by the polycondensation reaction of diamine and dianhydride during the preparation of polyimide is a key structural unit constituting the polymer backbone.

[0069] Diamines are compounds containing two amino groups (-NH2) in a single molecule. The amino groups can be linked to structural units such as alkyl, cycloalkyl, or aromatic groups via nitrogen atoms. Therefore, the general formula for diamines can be represented as H2N-R-NH2, where R represents the organic skeleton connecting the two amino groups. Based on the different properties of the skeleton R, diamines are mainly divided into two categories: aliphatic diamines and aromatic diamines. Their structure directly affects the thermal properties, mechanical properties, and chemical stability of the synthesized polymers.

[0070] The novel bio-based diamine monomers used in this invention employ hydroxyl and aromatic ketone structures, providing abundant intramolecular and intermolecular interaction sites. Through heat treatment or chemical cross-linking, a stable network structure is formed, and the segment rigidity and cross-linking density can synergistically regulate the free volume and micro-region stacking of the film. This structure simultaneously achieves highly efficient gas molecule sieving and excellent anti-swelling ability, maintaining long-term stable separation performance under high pressure and mixed gas environments.

[0071] The bio-based diamine used in this invention is a novel, naturally derived, and sustainable non-grain biomass, belonging to the category of environmentally friendly green chemicals. Non-grain biomass resources are abundant and renewable; their high-value utilization aligns with the goals of a circular economy and carbon neutrality, without crowding out food resources. Traditional petroleum-based diamines are derived from non-renewable fossil fuels. This invention selects a bio-based diamine to replace traditional petroleum-based diamine monomers in the preparation of polyimide films, realizing a pathway for preparing polyimide films from novel, green, and renewable non-grain biomass resources.

[0072] In one embodiment of the present invention, the bio-based diamine is obtained from raw materials extracted from non-grain biomass and then chemically modified.

[0073] In one embodiment of the present invention, the raw materials include daidzein, tanshinone I, mangiferin, etc. All of the above raw materials are extracted from bio-based non-grain biomass.

[0074] It should be noted that extracting raw materials from non-grain biomass is a conventional extraction method. For example, daidzein is extracted from defatted soybean meal, a non-grain biomass, using conventional extraction methods. Tanshinone I is extracted from the non-grain biomass plant *Salvia miltiorrhiza* using conventional extraction methods. Mangiferin is extracted from the leaves, bark, and rhizomes of mango, a non-grain biomass, using conventional extraction methods.

[0075] In a preferred embodiment of the present invention, the chemical modification treatment includes at least one of electrophilic substitution reaction, nucleophilic substitution reaction, or catalytic transfer hydrogenation reaction.

[0076] Catalytic transfer hydrogenation refers to the reduction of the reaction substrate by transferring hydrogen atoms in the presence of a catalyst, using hydrazine hydrate as the hydrogen source.

[0077] For example, the preparation method of daidzein A includes: nucleophilic substitution reaction of daidzein, 4-fluoronitrobenzene and anhydrous potassium carbonate; and then reducing the nitro group to an amino group by catalytic transfer hydrogenation reaction to obtain daidzein A.

[0078] Preferably, the molar ratio of daidzein, 4-fluoronitrobenzene, and anhydrous potassium carbonate is 1:2:2.

[0079] Preferably, in the catalytic transfer hydrogenation reaction, a palladium on carbon (Pd / C) catalyst is used as the catalyst.

[0080] Specifically, the mass ratio of daidzein to catalyst is 10-30:1. Preferably, the mass ratio of daidzein to catalyst is 15.9:1.

[0081] The preparation method of mangiferin diamine B is the same as that of daidzein diamine A, except that mangiferin is used to replace daidzein to obtain mangiferin diamine B (the molar amounts of the raw materials are the same).

[0082] For example, the preparation method of soybean-based diamine B includes: subjecting daidzein, trifluoromethanesulfonic anhydride, and 2,6-dimethylpyridine to an electrophilic substitution reaction to obtain a trifluoromethanesulfonate intermediate; then, through a catalytic transfer hydrogenation reaction, using tris(dibenzylideneacetone)dipalladium as a catalyst precursor and 2-(dicyclohexylphosphino)-3,6-dimethoxy-2',4',6'-triisopropyl-1,1'-biphenyl as a catalyst ligand, adding sodium tert-butoxide and benzophenone imine to form a CN bond between the trifluoromethanesulfonate intermediate and benzophenone imine, followed by hydrolysis to obtain soybean-based diamine B.

[0083] Preferably, the molar ratio of daidzein, trifluoromethanesulfonic anhydride, and 2,6-dimethylpyridine is 1:2:3.

[0084] Preferably, the molar ratio of daidzein, benzophenone imine, and sodium tert-butoxide is 1:3:2.

[0085] Preferably, the molar ratio of daidzein, catalyst precursor, and catalyst ligand is 100:1:2.

[0086] The preparation method of tanshinone diamine is the same as that of daidzein B, except that tanshinone I is used instead of daidzein (the molar amount of raw materials is the same).

[0087] The preparation method of mangiferin diamine A is the same as that of daidzein diamine B, except that mangiferin is used instead of daidzein (the molar amounts of the raw materials are the same).

[0088] In one embodiment of the present invention, in S1, the dianhydride is selected from the following:

[0089] Ar is independently selected from:

[0090] , , , , or .

[0091] In this embodiment of the invention, in S1, dianhydride monomer and bio-based diamine monomer react under the action of a catalyst to obtain a viscous reaction solution of polyimide.

[0092] In one embodiment of the present invention, in S1, the ratio of dianhydride, bio-based diamine, and catalyst is 2 mmol:2 mmol:0.3~2 mL.

[0093] In one embodiment of the present invention, in S1, the reaction temperature is 150-180 °C.

[0094] In a preferred embodiment of the present invention, in S1, the catalyst is selected from alkaline catalysts or acidic catalysts.

[0095] Furthermore, in S1, the alkaline catalyst includes at least one of isoquinoline and triethylamine.

[0096] Further, in S1, the acidic catalyst includes at least one of benzoic acid and p-hydroxybenzoic acid. In this embodiment of the invention, the catalyst is in a liquid state at room temperature and is added directly in liquid state. Catalysts that are not in a liquid state at room temperature can be heated to a molten state before addition.

[0097] In one embodiment of the present invention, in S1, the solvent includes at least one of m-cresol, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0098] In one embodiment of the present invention, in S1, the ratio of bio-based diamine to solvent is 2 mmol: 5-30 mL.

[0099] In one embodiment of the present invention, in S1, the protective atmosphere includes at least one of nitrogen and argon.

[0100] In a preferred embodiment of the present invention, the reaction time in S1 is 1-5 h.

[0101] In one embodiment of the present invention, in S1, the viscosity of the resulting reaction solution is 6000-200000 cps.

[0102] In this embodiment of the invention, in step S2, the polyimide polymer in the resulting viscous reaction solution is precipitated using a solvent precipitation method.

[0103] In a preferred embodiment of the present invention, in step S2, the solvent precipitation method for treating the viscous reaction solution specifically includes: pouring the viscous reaction solution into a methanol solution or a mixture of ethanol and water, stirring to precipitate the polyimide, and then filtering. This operation can be repeated 1-5 times.

[0104] In a preferred embodiment of the present invention, in step S2, the drying process specifically involves drying at 80-120 °C for 10-20 h.

[0105] In a preferred embodiment of the present invention, in step S2, the drying is carried out in a vacuum oven.

[0106] In this embodiment of the invention, in step S3, a solvent evaporation method is used to prepare a polyimide film from polyimide powder. The evaporation process is used to remove organic solvents and induce a phase inversion to precipitate the polymer.

[0107] In one embodiment of the present invention, in step S3, the solvent is a volatile solvent. Preferably, the volatile solvent includes at least one selected from tetrahydrofuran, 1,4-dioxane, chloroform, and dichloromethane.

[0108] In one embodiment of the present invention, S3 further includes drying the obtained polyimide film in a vacuum oven at 80-120 °C for 10-14 h, and then heating it in a tube furnace under a protective atmosphere at 200-250 °C for 1-3 h to ensure complete removal of any remaining solvent.

[0109] In one embodiment of the present invention, the thickness of the obtained polyimide film is 50-80 µm.

[0110] Furthermore, this invention also proposes the application of the bio-based polyimide film in gas separation. In this invention, the biomass-derived diamine has special functional groups, resulting in polyimide with high selectivity and optimized gas separation performance.

[0111] Further, the application includes: the bio-based polyimide film being used to obtain He (helium) from a He / CH4 gas mixture (a mixture of helium and methane), enrich O2 (oxygen) from an O2 / N2 gas mixture (a mixture of oxygen and nitrogen), separate N2 (nitrogen) from air, separate CO2 (carbon dioxide) from a CO2 / CH4 gas mixture (a mixture of carbon dioxide and methane), separate H2 (hydrogen) from an H2 / CH4 gas mixture (a mixture of hydrogen and methane), or separate CO2 (carbon dioxide) from a CO2 / N2 gas mixture (a mixture of carbon dioxide and nitrogen).

[0112] Preferably, the application includes: the bio-based polyimide film for helium extraction from natural gas, specifically obtaining He from a He / CH4 mixture, i.e., obtaining helium from a mixture of helium and methane.

[0113] More preferably, the bio-based polyimide film is insoluble in organic solvents. Specifically, the organic solvent includes at least one selected from 1,3,5-trimethylbenzene, N,N-dimethylformamide, N,N-dimethylacetamide, anhydrous methanol, anhydrous ethanol, tetrahydrofuran, chloroform, dichloromethane, N-methylpyrrolidone, or dimethyl sulfoxide. These properties provide a novel material for its industrial applications in harsh environments such as helium extraction from natural gas.

[0114] The present invention will now be described in detail with reference to the embodiments.

[0115] Raw material source description:

[0116] In this embodiment of the invention, the natural plant extracts, daidzein, tanshinone I, and mangiferin, which can be extracted from bio-based non-grain biomass using conventional methods, were all obtained by purchasing commercially available products. Specifically, daidzein and tanshinone I were purchased from Nanjing Jingzhu Biotechnology Co., Ltd.; mangiferin was purchased from Shanghai Fuyu Biotechnology Co., Ltd.

[0117] P84, purchased from Shanghai Yehe Industry & Trade Co., Ltd.

[0118] Matrimid ® 5218, model P874997, purchased from Shanghai McLean Biochemical Technology Co., Ltd.

[0119] PSF was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0120] 6FDA-DABA has been reported in the literature (Hydroxyl-Functionalized Polymers of IntrinsicMicroporosity and Dual-Functionalized Blends for High-Performance Membrane-Based Gas Separations);

[0121] 6FCBI has been reported in the literature (Anchoring the Dianhydride Structure toSimultaneously Enhance the Permeability and Selectivity of thePolybenzoxazole Membranes);

[0122] The PIM-1 is reported in the literature (Remarkably enhanced gas separation properties of PIM-1 at sub-ambient temperatures).

[0123] Example 1A The preparation method of soybean-based diamine A includes the following steps:

[0124] Soy-based diamine A was prepared by a combination of nucleophilic substitution reaction and catalytic transfer hydrogenation reaction, specifically as follows:

[0125] A mixture of daidzein (6.35 g, 0.025 mol), dimethylformamide (DMF) (100 mL), 4-fluoronitrobenzene (7.055 g, 0.05 mol), and anhydrous potassium carbonate (6.91 g, 0.05 mol) was heated to 80 °C and stirred for 2–4 h at room temperature under a nitrogen atmosphere, then the temperature was further increased to 110 °C and stirred for 12 h. After cooling to room temperature, the reaction mixture was washed with deionized water, filtered, and dried in a vacuum drying oven at 80–120 °C for 20 h. The crude product was recrystallized in DMF to obtain the daidzein nitro product.

[0126] A mixture of 12.4 g (0.025 mol) of daidzein nitro product modified with 4-fluoronitrobenzene, 0.4 g of palladium on carbon catalyst (Pd / C), 30 mL (80 wt%) of hydrazine hydrate, and 200 mL of ethanol was stirred at 80°C for 6 h. The resulting clear, transparent solution was filtered, concentrated by rotary evaporation by half, and then poured into deionized water (3000 mL). The precipitate was collected and filtered, and dried in a vacuum oven at 80°C for 12 h to obtain daidzein diamine A; the 1H NMR spectrum is shown below. Figure 1 As shown, the structure is characterized as follows:

[0127] 1 H NMR (400 MHz, DMSO) δ 7.69 (s, 1H), 7.29 – 7.11 (m, 2H), 7.03 (d, J = 7.6 Hz, 1H), 6.78 (dd, J = 16.3, 8.4 Hz, 6H), 6.59 (t, J = 8.7 Hz, 4H), 6.33(s, 2H), 5.01 (d, J = 18.0 Hz, 4H).

[0128] Example 1B The preparation method of polyimide film (6F-Dd-A) based on soybean-based diamine A includes the following steps:

[0129] ;

[0130] (1) Under argon protection, 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride (denoted as: 6FDA) (0.8884 g, 2 mmol), soybean diamine A (0.8729 g, 2 mmol) and solvent m-cresol (6 mL) were added sequentially to a 25 mL polymerization tube, 1 mL of catalyst isoquinoline was added dropwise, a magnetic stir bar was added and the mixture was heated to 160 °C for 3 h. The product was brown and viscous with a viscosity of about 10 w cps.

[0131] The obtained viscous solution was slowly poured into a methanol solution (1000 mL). The polymer solution precipitated out in a fibrous form. The mixture was stirred and then filtered to obtain the product. The methanol solvent was changed three times to remove unreacted m-cresol. Finally, the product was dried in a vacuum oven at 120 °C for 15 h until constant weight was obtained to obtain the polymer, which was denoted as 6F-Dd-A.

[0132] (2) The obtained polyimide was dissolved in tetrahydrofuran to prepare a solution with a solid content of 2% wt. Insoluble matter and impurities were removed using a 0.45 µm filter. The filtered solution was poured into a 6 cm diameter petri dish, and the solvent evaporated, causing the polymer phase to invert and form a film. After complete solvent evaporation, methanol solution was added for soaking for 4-6 hours, followed by drying in a vacuum oven at 80 °C for 12 hours. Further heating was performed in a tube furnace under N2 atmosphere at 230 °C for 2 hours to ensure complete removal of any remaining solvent, yielding a polyimide film, also designated as a 6F-Dd-A film (64 μm thick). The 1H NMR spectrum is shown below. Figure 2 As shown, the structure is characterized as follows:

[0133] 6F-Dd: 1 H NMR (400 MHz, DMSO) δ 8.69 (s, 1H), 8.17 (dd, J = 8.1, 4.5 Hz, 2H), 7.95 (d, J = 7.9 Hz, 2H), 7.75 (d, J = 3.7 Hz, 2H), 7.55 - 7.42 (m, 5H), 7.31 (dd, J = 24.1, 8.5 Hz, 4H), 7.15 (d, J = 8.6 Hz, 2H), 7.09 - 6.98 (m, 4H).

[0134] The infrared spectrum of the obtained 6F-Dd-A is as follows Figure 3 As shown.

[0135] Example 2AThe preparation method of soybean-based diamine B includes the following steps:

[0136] Soy-based diamine B was prepared by a combination of electrophilic substitution reaction and catalytic transfer hydrogenation reaction, specifically as follows:

[0137] 6.35 g (25.0 mmol) of daidzein was dissolved in 200 mL of anhydrous dichloromethane, and the reaction mixture was cooled to 0 °C under nitrogen protection. 2,6-Dimethylpyridine (8.7 mL, 75.0 mmol, 3.0 eq) was added sequentially, followed by the slow dropwise addition of trifluoromethanesulfonic anhydride (8.5 mL, 50.0 mmol, 2.0 eq) with stirring, keeping the reaction temperature below 5 °C. After the addition was complete, the mixture was stirred at 0 °C for 1 h, then allowed to rise to room temperature for 2 h. The reaction was monitored by thin-layer chromatography. The reaction mixture was quenched with saturated sodium bicarbonate solution and separated. The aqueous phase was extracted with dichloromethane (3 × 80 mL), and the organic phases were combined, dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure to obtain crude trifluoromethanesulfonate intermediate, which was used directly in the next reaction step.

[0138] The crude product was dissolved in anhydrous toluene (150 mL), and tris(dibenzylacetone)dipalladium (230 mg, 0.25 mmol, 1 mol%), 2-(dicyclohexylphosphino)-3,6-dimethoxy-2',4',6'-triisopropyl-1,1'-biphenyl (270 mg, 0.50 mmol, 2 mol%), and sodium tert-butoxide (4.8 g, 50.0 mmol, 2.0 eq) were added sequentially. After purging the reaction system with nitrogen three times, benzophenone imine (13.6 g, 0.075 mol, 3.0 eq) was added under a nitrogen atmosphere. The reaction mixture was heated to 90 °C and stirred for 16 h. The reaction mixture was cooled to room temperature, filtered through diatomaceous earth, and the filter cake was washed with ethyl acetate. The filtrates were combined and concentrated under reduced pressure. The crude product was subjected to silica gel column chromatography (eluting with a gradient of petroleum ether / ethyl acetate), followed by hydrolysis to obtain the target diamine product, soybean-based diamine B. Its structure was characterized by 1H NMR spectroscopy as follows:

[0139] 1 H NMR (400 MHz, DMSO) δ 8.68 (s, 1H), 7.29 – 7.11 (m, 2H), 7.03 (d, J = 7.6 Hz, 1H), 6.59 (t, J = 8.7 Hz, 2H), 6.33 (s, 2H), 5.01 (d, J = 18.0 Hz, 4H).

[0140] Example 2B The preparation method of polyimide film (6F-Dd-B) based on soybean-based diamine B includes the following steps:

[0141] ;

[0142] (1) Under argon protection, 2,2'-bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride (denoted as: 6FDA) (0.8884 g, 2 mmol), soybean diamine B (0.5045 g, 2 mmol) and solvent m-cresol (5 mL) were added sequentially to a 25 mL polymerization tube, 0.5 mL of catalyst isoquinoline was added dropwise, a magnetic stir bar was added and the mixture was heated to 160 °C for 3 h. The product was brown and viscous with a viscosity of about 10 w cps.

[0143] The obtained viscous solution was slowly poured into a methanol solution (1000 mL). The polymer solution precipitated out in a fibrous form. The mixture was stirred and then filtered to obtain the product. The methanol solvent was changed three times to remove unreacted m-cresol. Finally, the product was dried in a vacuum oven at 120 °C for 15 h until constant weight was obtained, yielding the polymer, polyimide, denoted as 6F-Dd-B.

[0144] (2) The obtained polyimide was dissolved in tetrahydrofuran to prepare a solution with a solid content of 2% wt. Insoluble matter and impurities were removed using a 0.45 µm filter. The filtered solution was poured into a petri dish with a diameter of 6 cm. The solvent evaporated, and the polymer phase transformed into a film. After the solvent evaporated completely, methanol solution was added and soaked for 4-6 h. Then, it was dried in a vacuum oven at 80 ℃ for 12 h. Further heating was carried out in a tube furnace under N2 atmosphere at 230 ℃ for 2 h to ensure complete removal of the remaining solvent, resulting in a polyimide film, also known as a 6F-Dd-B film (thickness of 69 μm). The structure was characterized by 1H NMR as follows:

[0145] 6F-Dd-B: 1 H NMR (400 MHz, DMSO) δ 8.69 (s, 1H), 8.17 (dd, J = 8.1, 4.5Hz, 2H), 7.95 (d, J = 7.9 Hz, 2H), 7.75 (d, J = 3.7 Hz, 2H), 7.55 - 7.42 (m, 5H), 7.15 (d, J = 8.6 Hz, 2H).

[0146] Example 3A Preparation method of tanshinone diamine

[0147] The preparation method of tanshinone diamine is the same as in Example 2A, except that tanshinone I is used instead of daidzein (the molar amounts of the raw materials are the same). The 1H NMR structural characterization of the obtained tanshinone diamine is as follows:

[0148] 1 H NMR (400 MHz, DMSO) δ 8.75 (s, 1H), 8.42 (m, 1H), 8.1 (d, J = 7.6Hz, 1H), 7.2-6.89 (t, J = 8.7 Hz, 3H), 5.01 (d, J = 18.0 Hz, 4H).

[0149] Example 3B The preparation method of polyimide films (6F-Ds) based on tanshinone diamine includes the following steps:

[0150] ;

[0151] Same as Example 1B, except that tanshinone diamine is used instead of soybean diamine A.

[0152] The resulting polyimide film is designated as 6F-Ds film (thickness 62 μm); its structure is characterized by 1H NMR spectroscopy as follows:

[0153] 6F-Ds: 1 H NMR (400 MHz, DMSO) δ 8.72 (s, 1H), 8.10 (dd, J = 8.1, 4.5 Hz, 2H), 7.95 (d, J = 7.9 Hz, 2H), 7.75 (d, J = 3.7 Hz, 2H), 7.65 - 7.52 (m, 3H), 7.48 (d, 1H), 7.09 - 6.98 (m, 1H).

[0154] Example 4A Preparation method of mango-based diamine A

[0155] The preparation method of mangiferin A is the same as that in Example 2A, except that mangiferin is used instead of daidzein (the molar amount of raw materials is the same).

[0156] The structure was characterized by proton nuclear magnetic resonance (NMR) spectroscopy as follows: 1 H NMR (400 MHz, DMSO) δ 10.06 (s, 2H), 6.42(d, J= 7.6 Hz, 2H), 6.11 (m, 2H), 5.27 (d, J = 18.0 Hz, 4H).

[0157] Example 4B The preparation method of polyimide film (6F-MG-A) based on mango-based diamine A includes the following steps:

[0158]

[0159] Same as Example 1B, except that mango-based diamine A is used instead of soybean diamine A.

[0160] The resulting polyimide film is designated as 6F-MG-A film (thickness 67 μm); its structure is characterized by 1H NMR spectroscopy as follows:

[0161] 6F-MG-A: 1 H NMR (400 MHz, DMSO) δ 10.06 (s, 2H), 8.19 (d, J = 8.9 Hz,2H), 7.97 (s, 2H), 7.76 (d, J = 7.7 Hz, 2H), 7.71 (d, J = 8.2 Hz, 1H), 6.53 (d, J =8.4 Hz, 1H), 6.52 (d, J = 8.4 Hz, 2H).

[0162] Example 5A Preparation method of mango-based diamine B

[0163] The preparation method of mangiferin diamine B is the same as in Example 1A, except that mangiferin is used instead of daidzein to obtain mangiferin diamine B (the molar amounts of the raw materials are the same). The 1H NMR structural characterization of the obtained mangiferin diamine B is as follows:

[0164] 1 H NMR (400 MHz, DMSO) δ 10.06 (s, 2H), 6.78 (dd, J = 16.3, 8.4 Hz, 4H), 6.59 (t, J = 8.7 Hz, 4H), 6.42 (d, J = 7.6 Hz, 2H), 6.11 (m, 2H), 5.01 (d, J =18.0 Hz, 4H).

[0165] Example 5B The preparation method of polyimide film (6F-MG-B) based on mango-based diamine B includes the following steps:

[0166]

[0167] Same as Example 1B, except that mango-based diamine B is used instead of soybean-based diamine A.

[0168] The resulting polyimide film is designated as 6F-MG-B film (thickness 65 μm); its structure is characterized by 1H NMR spectroscopy as follows:

[0169] 6F-MG-B: 1 H NMR (400 MHz, DMSO) δ 10.06 (s, 2H), 8.19 (d, J = 8.9 Hz,2H), 7.97 (s, 2H), 7.76 (d, J = 7.7 Hz, 2H), 7.17 (d, J = 8.4 Hz, 2H), 7.10 (s, 4H), 7.0 (t, J = 8.5 Hz, 1H), 6.7 - 6.31 (m, 5H).

[0170] Comparative Example 1 The preparation method based on petroleum-based polyimide includes the following steps:

[0171] ;

[0172] (1) Under argon protection, 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride (denoted as: 6FDA) (0.8884 g, 2 mmol), 1,3-bis(4'-aminophenoxy)benzene (denoted as: TPE-R) (0.5846 g, 2 mmol) and solvent m-cresol (5 mL) were added sequentially to a 25 mL polymerization tube, 0.5 mL of isoquinoline catalyst was added dropwise, a magnetic stir bar was added and the mixture was heated to 160 °C for 3 h. The product was a light yellow viscous substance with a viscosity of about 10 w cps.

[0173] The obtained viscous solution was slowly poured into a methanol solution (1000 mL). The polymer solution precipitated out in a fibrous form. The mixture was stirred and then filtered to obtain the product. The methanol solvent was changed three times to remove unreacted m-cresol. Finally, the product was dried in a vacuum oven at 120 °C for 15 h until constant weight was obtained, yielding the polymer, polyimide, denoted as 6F-TPE-R.

[0174] (2) The obtained polyimide was dissolved in tetrahydrofuran to prepare a solution with a solid content of 2% wt. Insoluble matter and impurities were removed using a 0.45 µm filter. The filtered solution was poured into a 6 cm diameter petri dish, and the solvent evaporated, causing the polymer phase to invert and form a film. After complete solvent evaporation, methanol solution was added for soaking for 4-6 hours, followed by drying in a vacuum oven at 80 °C for 12 hours. Further heating at 230 °C for 2 hours in a tube furnace under N2 atmosphere ensured complete removal of any remaining solvent, yielding a polyimide film, also designated as 6F-TPE-R film. The 1H NMR spectrum is shown below. Figure 2 As shown, the structure is characterized as follows:

[0175] 6F-TPE-R: 1 H NMR (400 MHz, DMSO) δ 8.17 (d, J = 8.0 Hz, 2H), 7.95 (d,J = 7.9 Hz, 2H), 7.75 (s, 2H), 7.46 (t, J = 6.1 Hz, 5H), 7.21 (d, J = 8.6 Hz,4H), 6.90 – 6.80 (m, 3H).

[0176] The infrared spectrum of the obtained 6F-TPE-R is as follows: Figure 3 As shown.

[0177] Comparative Example 2 The preparation method based on petroleum-based polyimide includes the following steps:

[0178] ;

[0179] (1) Under argon protection, 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride (denoted as: 6FDA) (0.8884 g, 2 mmol), 3,3,3',3'-tetramethyl-1,1'-spirodiindan-5,5'-diamine-6,6'-diol (denoted as: SBI-OH) (0.6770 g, 2 mmol) and solvent m-cresol (5 mL) were added sequentially to a 25 mL polymerization tube. 0.5 mL of isoquinoline catalyst was added dropwise, and the mixture was stirred with a magnetic stir bar. The mixture was heated to 160 °C and reacted for 3 h. The product was brownish-yellow and viscous with a viscosity of about 10 wcps.

[0180] The obtained viscous solution was slowly poured into a 1:1 mixture of ethanol and water (1:1) (1000 mL). The polymer solution precipitated out in a fibrous form. The mixture was stirred and then filtered to obtain the product. The ethanol-water solution was replaced three times to remove unreacted m-cresol. Finally, the product was dried in a vacuum oven at 120 °C for 15 h until constant weight was obtained to obtain the polymer, which was denoted as 6F-SBI-OH.

[0181] (2) The obtained polyimide was dissolved in tetrahydrofuran to prepare a solution with a solid content of 2% wt. Insoluble matter and impurities were removed using a 0.45 µm filter. The filtered solution was poured into a 6 cm diameter petri dish, and the solvent evaporated, causing the polymer phase to invert and form a film. After complete solvent evaporation, the film was dried in a vacuum oven at 80 °C for 12 h, and then further heated in a tube furnace under N2 atmosphere at 230 °C for 2 h to ensure complete removal of any remaining solvent, yielding a polyimide film, also designated as 6F-SBI-OH film. The 1H NMR structure is characterized as follows:

[0182] 6F-SBI-OH: 1 H NMR (400 MHz, DMSO- d 6): δ 9.59 (s, 2H, OH), 8.15 (d, J =7.9 Hz, 2H), 7.97 (s, 2H), 7.77 (s, 2H), 7.16 (s, 2H), 6.43 (s, 2H), 2.31 (d,J = 51.8 Hz, 4H), 1.48–1.16 (m, 12H,-CH3).

[0183] Test Example 1 Gas separation performance test

[0184] (1) The pure gas permeation performance of the 6F-Dd-A membrane obtained in Example 1B was measured by constant volume / switching method. To remove any contaminants from the permeation system and membrane, the system with a masking membrane within the sealed permeation unit was degassed for 24 hours. The pure gas permeabilities of He, H2, N2, O2, CH4, and CO2 were measured at 2 bar and 35 °C. The gas permeabilities were determined as follows:

[0185]

[0186] In the formula, the permeability coefficient P is expressed in terms of barrer (1 barrer = 10). -10 cm 3 (STP)·cm cm -2 ·s -1 ·cm Hg -1 Or 7.5 × 10 -18 m 3 (STP)·mm -2 ·s -1 ·Pa -1 (in units) p up Upstream pressure (cm Hg); T is operating temperature (K); V ddp / dt represents the osmotic volume (cm³); dp / dt represents the osmotic pressure change (cmHg·s). -1 A is the effective area of ​​the membrane (cm²). 2 ); l is the thickness (cm); R is the gas constant, equal to 0.278cm. 3 cm Hg cm -3 (STP)·K -1 Pure gas selectivity α AB The calculation is as follows:

[0187]

[0188] Wherein, the permeability coefficients of gases A and B are denoted as P. A P B D A D B S A S B The diffusion coefficients and solubility coefficients of A and B are given, respectively. Each polymer membrane was tested three times, and the deviations in permeability and selectivity were within ~5%. The specific results are as follows:

[0189] The permeability coefficients are as follows: helium is 63.38 Barrer, hydrogen is 52.82 Barrer, nitrogen is 0.48 Barrer, oxygen is 3.41 Barrer, methane is 0.21 Barrer, and carbon dioxide is 15.32 Barrer.

[0190] The selectivity for helium / methane is 301.81, for hydrogen / methane it is 251.52, for oxygen / nitrogen it is 7.10, and for carbon dioxide / methane it is 72.95. (See also...) Figure 4 .

[0191] (2) The above methods were used to test the performance of the films obtained in Example 2B, Example 3B, Example 3B, Example 4B, and Example 5B, respectively. The results are shown in Table 1.

[0192] Comparative Test Example 1 Gas separation performance test

[0193] (1) The gas separation performance of the 6F-TPE-R and 6F-SBI-OH films obtained in Comparative Example 1 and Comparative Example 2 were tested according to the method described in Test Example 1. The specific results are shown in Table 1.

[0194] (2) Following the method described in Example 1, gas separation performance was tested using polyimide films disclosed in the prior art. Specific types of polyimide films are as follows:

[0195] The structural formula on page 84 is: ;

[0196] Matrimid ® The structural formula for 5218 is: ;

[0197] The structural formula of 6FDA-DABA is: ;

[0198] The PSF structure is: ;

[0199] The 6FCBI structure is as follows: ;

[0200] The structural formula for PIM-1 is: ;

[0201] The specific results are shown in Table 1.

[0202] To make a clear comparison, the results are listed in Table 1.

[0203] Table 1

[0204]

[0205] As shown in Table 1, the bio-based polyimide prepared has better gas separation performance compared with commonly used petroleum-based polyimide. Figure 5 As shown in the figure, the intrinsic separation performance has exceeded the upper limit set in 1991 [Correlation of separation factor versus permeability for polymeric membrane, Lloyd M. Robeson, Journal of Membrane Science]. Especially in the separation of He / CH4, a selectivity of over 300 is achieved, which is very rare compared to petroleum-based polyimides. This high He / CH4 ratio will have excellent applications in helium extraction from natural gas.

[0206] Test Example 2 Solvent resistance test of thin film

[0207] The polyimide film treated at 350°C (obtained in Example 1B) was cut into small pieces and immersed in 10 organic solvents: toluene, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), anhydrous methanol, anhydrous ethanol, tetrahydrofuran (THF), chloroform (CHCl3), dichloromethane (CH2Cl2), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO). The results are shown in [Figure 1]. Figure 7 It does not dissolve in any of the above solvents and does not exhibit swelling. This advantage will be well utilized in the harsh environments of helium extraction from natural gas.

[0208] Test Example 3 CO2 plasticization test of thin films

[0209] Plasticization of gas separation membranes refers to the phenomenon where, under high pressure or in contact with a specific gas (such as CO2), gas molecules excessively dissolve and act on the polymer chains, functioning similarly to a "plasticizer." This leads to an abnormally enhanced mobility of the polymer chain segments and an increase in free volume. In terms of separation performance, this typically manifests as an increase in permeate flux, resulting in a deterioration in the overall separation efficiency of the membrane.

[0210] The film (obtained in Example 1B) was cut into 12mm diameter discs and sealed in a self-made permeation device. Permeability was calculated by increasing the pressure. The polymer material should gradually decrease permeability as the pressure increases; an abnormal permeability indicates plasticization. The results are shown in Figure 8. No plasticization occurred before 14 bar, demonstrating that the bio-based polyimide prepared in this invention has good resistance to plasticization.

[0211] Test Example 4 Thin film tensile strength test

[0212] The polyimide film (obtained in Example 1B) was prepared into a strip 5 cm long and 1 cm wide, and tested using a universal tensile tester. The results are shown in [Figure 1]. Figure 9 The stress can reach close to 80 MPa, the deformation is 7.5%, the elastic modulus is 1.1 GPa, and it has good mechanical properties.

[0213] The bio-based polyimide prepared in this invention exhibits significantly superior overall performance compared to traditional petroleum-based materials, while retaining the advantages of renewable sources and sustainability. Its gas separation performance is outstanding, particularly demonstrating extremely high selectivity in helium separation, providing an ideal material choice for applications such as helium extraction from natural gas. Simultaneously, this polyimide film exhibits excellent solvent resistance, good mechanical strength, and plasticization resistance, maintaining structural integrity and performance stability even in harsh industrial environments, thus meeting the stringent requirements for material durability and reliability in actual separation processes. In summary, the bio-based polyimide of this invention combines green sources with high performance, possessing significant application prospects and industrialization value in the field of high-end gas separation.

[0214] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. The application of bio-based polyimide films in gas separation, characterized in that, The polyimide has the structure shown in formula (I): Equation (I); Among them, 10 <n<500; X is: ； Ar is: 。 2. The application according to claim 1, characterized in that, The polyimide film is prepared by a method comprising the following steps: S1. Under a protective atmosphere, dianhydride and bio-based diamine are mixed, and a catalyst and solvent are added to react and obtain a viscous reaction solution. S2. The above viscous reaction solution was treated by solvent precipitation and dried to obtain polyimide powder; S3. After dissolving the above polyimide powder in a solvent, the resulting solution is evaporated to obtain a polyimide film; The bio-based diamine is: 。 3. The application according to claim 2, characterized in that, The bio-based diamine is obtained from raw materials extracted from non-grain biomass and then chemically modified.

4. The application according to claim 3, characterized in that, The raw materials include daidzein; The chemical modification treatment includes at least one of nucleophilic substitution reaction or catalytic transfer hydrogenation reaction.

5. The application according to claim 2, characterized in that, At least one of the following conditions must be met: (1) In S1, the ratio of dianhydride, bio-based diamine, and catalyst is 2 mmol:2 mmol:0.3~2 mL; (2) In S1, the reaction temperature is 150-180 ℃; (3) In S1, the ratio of bio-based diamine to solvent is 2 mmol: 5-30 mL; (4) In S1, the viscosity of the resulting reaction solution is 6000-200000 cps; (5) In S2, the solvent precipitation method for treating the above viscous reaction liquid specifically includes: pouring the viscous reaction liquid into a methanol solution or a mixture of ethanol and water, stirring, so that the polyimide precipitates out, and then filtering; (6) In S2, the drying process specifically involves drying at 80-120 ℃ for 10-20 h; (7) In S3, the solvent is a volatile solvent, which includes at least one of tetrahydrofuran, 1,4-dioxane, chloroform, and dichloromethane.

6. The application according to claim 1, characterized in that, The applications include: the bio-based polyimide film being used to obtain He from a He / CH4 gas mixture, enrich O2 from an O2 / N2 gas mixture, separate N2 from air, separate CO2 from a CO2 / CH4 gas mixture, separate H2 from an H2 / CH4 gas mixture, or separate CO2 from a CO2 / N2 gas mixture.

7. The application according to claim 6, characterized in that, The bio-based polyimide film is used for helium extraction from natural gas, specifically to obtain He from a He / CH4 mixture.

8. The application according to claim 1, characterized in that, The bio-based polyimide film is insoluble in organic solvents; the organic solvents include at least one of 1,3,5-trimethylbenzene, N,N-dimethylformamide, N,N-dimethylacetamide, anhydrous methanol, anhydrous ethanol, chloroform, dichloromethane, N-methylpyrrolidone, or dimethyl sulfoxide.

Images