A thermally crosslinked semi-penetrating helium separation membrane and a preparation method and application thereof

Abstract

The present application relates to a kind of heat crosslinking semi-interpenetrating helium separation membrane and its preparation method and application, belong to gas separation membrane field.The present application is synthesized by 2,2'-bis (trifluoromethyl) -4,4'-diamino diphenyl, hexafluoro dianhydride, acetic anhydride and pyridine reaction fluorine-containing polyimide, fluorine is introduced in polymer, can increase the affinity of polymer to helium, increase solubility selectivity, while the pore blocking effect caused by fluorine atom substitution can increase size sieving diffusion selectivity.Using 2,5-dimethyl-p-phenylenediamine monomer and 4,4'- (ethyne-1,2-diyl) di-phthalic anhydride synthesis can be used for heat crosslinking alkynyl polymer.Blending two different polymers can synergistically combine the advantages of different materials, the membrane has good selectivity and permeability, has good heat stability and long-term performance stability.

Description

Technical Field

[0001] This invention relates to a high-performance thermally cross-linked semi-interpenetrating helium separation membrane for separating helium, its preparation method, and its application, belonging to the field of gas separation. Background Technology

[0002] Helium's strong chemical inertness and low boiling point make it widely used in defense, semiconductor manufacturing, medical and health industries, and other technological sectors. The concentration of helium (He) in the air is only 5.2 ppm, making it difficult to achieve resource utilization. Therefore, extracting He from natural gas is currently the only way to utilize He as a resource. The distribution of natural Helium resources is uneven. The United States has the world's richest Helium resources, accounting for approximately 34% of global reserves and producing about 40% of global helium. my country's Helium resources account for only 0.1% of the world's reserves, with a concentration generally less than 0.2%, and its production accounts for only 2% of global helium production. Currently, my country's industrial development is rapidly increasing its demand for Helium resources, necessitating the development of advanced natural gas helium extraction technologies for application in the helium production process.

[0003] Currently, the main technologies for helium extraction from natural gas include cryogenic methods, pressure swing adsorption (PSA), absorption methods, and membrane permeation separation. Cryogenic methods are the primary method for helium extraction from natural gas. Although this technology can extract high-purity He from natural gas, the low He concentration in my country's natural gas makes the cost of extracting He from natural gas using cryogenic methods high, thus restricting the large-scale construction of helium extraction plants in my country. PSA is generally suitable for the refining of crude He with impurity content less than 10%. In recent years, with the development of membrane separation technology, membrane separation technology has shown great application potential in the field of helium enrichment due to its advantages such as high separation efficiency, low operating energy consumption, and high operational flexibility. Organic polymer membranes have advantages such as corrosion resistance, easy processing and molding, and high gas selectivity, making them the most commonly used method in the field of gas separation. However, current helium separation membranes suffer from poor selectivity, low separation efficiency, and easy aging. Currently, no gas separation membrane is used alone to separate helium and nitrogen. Industrially, it needs to be combined with pressure swing adsorption, cryogenic methods, etc., to achieve efficient helium extraction. These methods consume a lot of energy and are not economically efficient for natural gas helium extraction. Therefore, it is necessary to develop a helium separation membrane with high selectivity and high separation efficiency to achieve low energy consumption and high efficiency helium separation and concentration. Summary of the Invention

[0004] Currently, the extraction of helium from natural gas using membrane separation technology faces challenges such as low flux, poor selectivity, and susceptibility to aging. To address these challenges, this invention aims to provide a high-performance, aging-resistant thermally cross-linked semi-interpenetrating helium separation membrane, its preparation method, and its applications. The thermally cross-linked semi-interpenetrating helium separation membrane of this invention exhibits excellent selectivity, moderate permeation rate, and high purity of the separated helium when used for helium separation. It also possesses good aging resistance.

[0005] This invention synthesizes fluorinated polyimides through the reaction of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, hexafluorodianhydride, acetic anhydride, and pyridine. Introducing fluorine into the polymer increases its affinity for helium and improves solubility selectivity. Simultaneously, the pore-blocking effect caused by fluorine atom substitution increases size sieving diffusion selectivity. Alkynyl polymers suitable for thermal crosslinking are synthesized using 2,5-dimethyl-p-phenylenediamine monomer and 4,4′-(acetylene-1,2-diyl)phthalic anhydride. Blending two different polymers can synergistically combine the advantages of different materials, resulting in polymer blends that exhibit superior properties compared to their respective natural polymers. This invention incorporates fluorinated polyimides into alkynyl polymers, allowing the two different polymer networks to physically mix in the same spatial regions, forming a semi-interpenetrating polymer network. Meanwhile, the alkynyl group in the alkynyl polymer undergoes 1,4-addition with the conjugated diene on the benzene ring at 250℃ to generate a six-membered cyclic compound. The fully aromatic special network polymer formed by cross-linking can inhibit the creep relaxation of the polymer chain and inhibit the aging of the polymer. At the same time, chemical bonds are introduced into the semi-interpenetrating polymer network to fix the linear components in the semi-interpenetrating polymer network.

[0006] The technical solution of the present invention is as follows:

[0007] The thermally crosslinked semi-interpenetrating helium separation membrane of the present invention has the following structural formula for the alkynyl polymer:

[0008]

[0009] The structural formula of the fluorinated polyimide is:

[0010]

[0011] The number-average molecular weight of the alkynyl polymer is 20,000 to 30,000 g / mol; the n of the fluorinated polyimide is 40 to 60, and the number-average molecular weight of the fluorinated polyimide is 28,000 to 42,000 g / mol.

[0012] In one embodiment, the ratio of the alkynyl polymer to the fluorinated polyimide is (5-35):1.

[0013] In one embodiment, the ratio of the alkynyl polymer to the fluorinated polyimide is 32.33:1, 15.67:1, 10.11:1, or 7.33:1.

[0014] In one embodiment, the alkynyl polymer is prepared by reacting 2,5-dimethyl-p-phenylenediamine monomer with 4,4′-(acetylene-1,2-diyl)phthalic anhydride in a molar ratio of 0.5 to 4:1 to obtain an intermediate product, alkynyldiamine, and then reacting alkynyldiamine with dimethoxymethane in a molar ratio of 1:1 to 6 to obtain the alkynyl polymer.

[0015] In one embodiment, the method for preparing the alkynyl polymer includes the following steps:

[0016] Step 1: Add 2,5-dimethyl-1,4-phenylenediamine and 4,4-(acetylene-1,2-diyl)phthalic anhydride to a three-necked flask, add 250 ml of N-methylpyrrolidone, and heat to 50–100 °C after the monomers are completely dissolved. React for 6–18 h, then add 50–100 ml of toluene to the flask and heat to reflux at 120–170 °C for 4–12 h with water. After the toluene is released, cool down. After the reaction is complete, discharge the product into ice water, wash it 5 times with deionized water, and vacuum dry it for later use. Nitrogen gas is purged throughout the reaction.

[0017] Step 2: Add the alkynyl diamine monomer to a 250 ml three-necked flask under ice-water bath conditions, add dimethoxymethane, and add trifluoroacetic acid dropwise over 30 minutes. After reacting in an ice-water bath for 1-4 hours, remove the ice-water bath and react at room temperature for 12-48 hours. Nitrogen gas is not required during the reaction. Discharge the product into a 2.5% ammonia solution. After discharge, stir for a period of time to ensure that the trifluoroacetic acid in the product is completely neutralized by the ammonia water, but the time should not be too long, as prolonged reaction under alkaline conditions will cause degradation of the product. Filter the product and wash it 5 times with deionized water. Vacuum dry the product and dissolve it in N-methylpyrrolidone. Filter out the insoluble solids and discharge the solution back into deionized water. Wash and dry to obtain the alkynyl polymer.

[0018] In one embodiment, in step 2, the volume ratio of trifluoroacetic acid to dimethoxymethane is 1:12; the solvent includes N-methylpyrrolidone.

[0019] In one embodiment, the fluorinated polyimide is obtained by reacting 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, hexafluorodianhydride, acetic anhydride and pyridine in a molar ratio of 0.1-0.6:0.1-0.6:1-6:1-6.

[0020] In one embodiment, the method for preparing the fluorinated polyimide includes the following steps:

[0021] Step 2-1: Add 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl to a three-necked flask, and then add N,N-dimethylacetamide under ice-water bath conditions until it is completely dissolved. Then, slowly add hexafluorodianhydride in batches and react under ice-water bath conditions for 1-6 hours. After removing the ice-water bath, react at room temperature for 12-48 hours.

[0022] Step 2-2: After mixing acetic anhydride and pyridine, slowly add the mixture dropwise to the reaction system at room temperature over 2–8 hours. After the addition is complete, raise the temperature to 60–120°C and continue the reaction for 6–18 hours, with nitrogen gas purging throughout the reaction. After the reaction is complete, discharge the product into water, filter it, and wash the product with water 5–6 times at 60–120°C until the solvent is completely removed. After washing, dry the product in an oven to obtain the final product.

[0023] The second objective of this invention is to provide a method for preparing a thermally crosslinked semi-interpenetrating helium separation membrane. The method involves dissolving a certain amount of fluorinated polyimide in an organic solvent, then adding a certain amount of alkynyl polymer and heating and stirring to fully dissolve it in the organic solvent. Impurities are removed by filtration to obtain a casting solution, which is then allowed to stand to remove bubbles. The casting solution is then uniformly coated onto a glass plate using a coating machine. After the solvent has completely evaporated, a semi-interpenetrating alkynyl polymer membrane is obtained. The semi-interpenetrating alkynyl polymer membrane is heated to a target temperature under a nitrogen atmosphere to induce a crosslinking reaction, thereby obtaining the thermally crosslinked semi-interpenetrating helium separation membrane.

[0024] In one embodiment, the solid content of the casting solution is 9-15 wt%, wherein the amount of fluorinated polyimide added is 3-12%.

[0025] In one embodiment, the organic solvent includes at least one selected from N-methylpyrrolidone, 1,3-dimethyl-2-imidazolinone, N-ethylpyrrolidone, and N,N-dimethylformamide.

[0026] In one embodiment, the solvent is evaporated by drying in a vacuum oven at 60–100°C for 48–72 h, and then drying in a vacuum oven at 100–120°C for 6–12 h; the resulting alkynyl polymer film has an average thickness of 16–32 μm.

[0027] In one embodiment, the solvent is evaporated by drying in a vacuum oven at 60°C for 48 hours, and then drying in a vacuum oven at 120°C for 12 hours; the resulting acetylene polymer film has an average thickness of 20 μm.

[0028] In one embodiment, the target temperature is 250–350°C, and the crosslinking reaction time is 15–60 min.

[0029] A third objective of this invention is to provide a method for applying the above-described separation membrane or the separation membrane prepared by the above-described method for He / N2 separation.

[0030] The volume fraction of helium in natural gas is 1-60%, and the volume fraction of nitrogen is 0-30%. The thermally cross-linked semi-interpenetrating helium separation membrane of this invention is used for separation, and the selectivity for He / N2 is ≥130. After testing of the mixed gas, the volume fraction of helium after separation is 98.7%.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] 1. The preparation method of the present invention is scientific, reasonable, simple and easy to implement, and low in cost.

[0033] 2. The semi-interpenetrating alkynyl polymer membrane described in this invention has excellent He / N2 selectivity and moderate permeability, with a helium permeability coefficient ≥15 Barrer and a He / N2 selectivity coefficient ≥240.

[0034] 3. The thermally cross-linked semi-interpenetrating helium separation membrane described in this invention can further improve permeability by appropriately sacrificing selectivity, with a helium permeability coefficient ≥60 Barrer and a He / N2 selectivity coefficient ≥130.

[0035] 4. Introducing fluorine into polymers can increase their affinity for helium and improve solubility selectivity. Simultaneously, the pore-blocking effect caused by fluorine atom substitution can increase size sieving diffusion selectivity. Adding fluorinated polyimide to an alkynyl polymer allows the two different polymer networks to physically mix in the same spatial region, forming a semi-interpenetrating polymer network. Simultaneously, the alkynyl groups in the alkynyl polymer undergo 1,4-addition with the conjugated diene on the benzene ring at 250°C, generating a six-membered cyclic compound. The resulting fully aromatic special network polymer formed through crosslinking can inhibit polymer chain creep relaxation. Furthermore, introducing chemical bonds into the semi-interpenetrating polymer network fixes the linear components within the network, inhibiting polymer aging and improving membrane lifespan. Attached Figure Description

[0036] Figure 1 This is a gas permeability testing device.

[0037] Figure 2Optical photographs of alkynyl polymer membranes containing different amounts of fluorinated polyimide and thermally crosslinked semi-interpenetrating helium separation membranes are shown. A is a photograph of the pure alkynyl polymer membrane in Comparative Example 1; B is a photograph of the semi-interpenetrating polymer membrane-1 prepared in Example 1 with 3% fluorinated polymer; C is a photograph of the semi-interpenetrating polymer membrane-2 prepared in Example 2 with 6% fluorinated polymer; D is a photograph of the semi-interpenetrating polymer membrane-3 prepared in Example 3 with 9% fluorinated polymer; E is a photograph of the semi-interpenetrating polymer membrane-4 prepared in Example 4 with 12% fluorinated polymer; and F is a photograph of the thermally crosslinked semi-interpenetrating helium separation membrane-3 prepared in Example 7 with 9% fluorinated polymer and thermally crosslinked at 330°C for 30 minutes. Detailed Implementation

[0038] The present invention will be further illustrated below through implementation examples, but is not limited to these embodiments.

[0039] Unless otherwise specified, all raw materials used in the examples were commercially available.

[0040] The gas permeability of the membrane was measured using a constant volume pressure swing method with a gas permeability testing device. He and N2 were used as test gases. The specific operating steps of the gas permeability coefficient testing device for the membrane sample are as follows:

[0041] (1) Cut the completely dried membrane to fit the size of the membrane tank and put it into the membrane tank.

[0042] (2) Open all valves of the device, connect the gas to be tested to the inlet, and ventilate for 10 minutes to fill the entire device with the predicted gas. Close the inlet valve 1 and the outlet valve 7, and turn on the vacuum pump. Wait for 5 minutes, then close valve 4 first and then turn off the vacuum pump. Detect the airtightness of the device by observing the change in the vacuum gauge reading.

[0043] (3) Close valve 2, open valve 1 and the gas cylinder valve, and fill the pressure stabilizing tank with the gas to be tested to about 105 kPa. Then close valve 1 and the gas cylinder valve. Next, close valve 3 and valve 5, and open valve 2. Similarly, observe whether the reading of the vacuum pressure gauge changes to check whether there are any defects in the membrane sample. After the above checks are completed and no errors are found, close valve 2.

[0044] (4) Turn on the vacuum pump, then open valves 4, 3 and 5 in sequence to re-evacuate the entire device for 2 hours. Then close valve 4 and turn off the vacuum pump. Finally, close valves 3 and 5 and check the device error: record the change in the vacuum gauge reading per unit time.

[0045] (5) After the device error is detected, open valve 2 and start recording the rate of change of vacuum. The recording time for He and N2 is 1 hour.

[0046] (6) After the test is completed, the gas in the pressure tank should be completely discharged. For flammable and harmful gases, an exhaust gas treatment device needs to be installed. Turn off all power switches of the device, take out the membrane sample, and test the average thickness of the membrane.

[0047] Based on the dissolution-diffusion mechanism, the gas permeability coefficient of the membrane is calculated using the following formula:

[0048]

[0049] In the formula, P is the permeability coefficient, Barrer[1Barrer=10 -10 cm 3 (STP)cm / (cm 2 [·s·cmHg)];Q is the cumulative amount of gas permeation from the start of gas permeation to time t, in cm 3 A represents the effective permeation area of ​​the membrane, in cm². 2 l is the membrane thickness, in cm; Δp is the pressure difference between the feed measurement and the permeation measurement, in cmHg.

[0050] Adopting such Figure 1 The apparatus shown is used to test gas permeation performance.

[0051] Example 1: Preparation of a semi-interpenetrating alkynyl polymer film-1

[0052] 1. Preparation of alkynyl polymers

[0053] Step 1: Add 2,5-dimethyl-1,4-phenylenediamine and 4,4-(acetylene-1,2-diyl)phthalic anhydride to a three-necked flask, add 250 ml of NMP, and heat to 50°C after the monomers are completely dissolved. React for 6 hours, then add 50 ml of toluene to the flask and heat to reflux (approximately 120°C), reacting with water for 4 hours. After releasing the toluene, cool the flask. After the reaction is complete, discharge the product into ice water, wash five times with deionized water, and vacuum dry for later use. Nitrogen gas is purged throughout the reaction.

[0054] Step 2: The alkynyl diamine monomer was added to a 250 ml three-necked flask under ice-water bath conditions. Dimethoxymethane was added, and trifluoroacetic acid was added dropwise over 30 minutes. The reaction was continued under ice-water bath conditions for 1 hour, then the ice-water bath was removed, and the reaction was allowed to proceed at room temperature for 12 hours. Nitrogen gas was not required during the reaction. The product was discharged into a 2.5% ammonia solution. After discharge, the mixture was stirred for a period of time to ensure complete neutralization of the trifluoroacetic acid in the product by the ammonia water. However, the stirring time should not be too long, as prolonged exposure to alkaline conditions can lead to product degradation. The product was filtered and washed five times with deionized water, then vacuum dried. The product was dissolved in N-methylpyrrolidone, and the insoluble solids were filtered out. The solution was discharged again into deionized water, washed, and dried to obtain the alkynyl polymer. The yield was 96%, and the number average molecular weight was 2.89 × 10⁻⁶. 4g / mol.

[0055] The molar ratio of 2,5-dimethyl-p-phenylenediamine monomer to 4,4′-(acetylene-1,2-diyl)phthalic anhydride monomer is 0.5:1, and the molar ratio of alkynyl diamine to dimethoxymethane is 1:1.5.

[0056] The volume ratio of trifluoroacetic acid to dimethoxymethane is 1:12; the solvent includes N-methylpyrrolidone.

[0057] 2. Preparation of fluorinated polyimide

[0058] Step 1: Add 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl to a three-necked flask, and then add N,N-dimethylacetamide under ice-water bath conditions until it is completely dissolved. Then, slowly add hexafluorodianhydride in batches and react under ice-water bath conditions for 1 hour. After removing the ice-water bath, react at room temperature for 12 hours.

[0059] Step 2: After mixing acetic anhydride and pyridine, slowly add the mixture dropwise to the reaction system over 2 hours at room temperature. After the addition is complete, heat the system to 60°C and continue the reaction for 6 hours, with nitrogen gas purging throughout the process. After the reaction is complete, discharge the product into water, filter it, and wash the product with water 5-6 times at 60°C until the solvent is completely removed. After washing, dry the product in an oven to obtain the final product.

[0060] The reaction is carried out in a molar ratio of 0.1:0.1:1:1 with 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, hexafluorodianhydride, acetic anhydride and pyridine.

[0061] 3. Preparation of semi-interpenetrating alkynyl polymer films

[0062] The fluorinated polyimide was dissolved in N-methylpyrrolidone (NMP), and then an alkynyl polymer was added and stirred until fully dissolved. The solid content was 10 wt%, and the amount of fluorinated polyimide added was 3%, i.e., the ratio of alkynyl polymer to fluorinated polyimide was 32.33:1. After filtration and degassing, the film was coated onto a glass plate using a coating machine and dried in a vacuum oven at 60°C for 48 h, and then dried in a vacuum oven at 120°C for 12 h to obtain an alkynyl polymer film with a thickness of 17 μm.

[0063] The permeation coefficients and separation coefficients of He and N2 were tested using a semi-interpenetrating alkynyl polymer membrane-1. The separation performance data are shown in Table 1.

[0064] Example 2: Preparation of semi-interpenetrating alkynyl polymer film-2

[0065] 1. Preparation of alkynyl polymers

[0066] Step 1: Add 2,5-dimethyl-1,4-phenylenediamine and 4,4-(acetylene-1,2-diyl)phthalic anhydride to a three-necked flask, add 250 ml of NMP, and heat to 60°C after the monomers are completely dissolved. React for 8 hours. Then add 60 ml of toluene to the flask and heat to reflux (approximately 130°C), reacting with water for 6 hours. After releasing the toluene, cool the flask. After the reaction is complete, discharge the product into ice water, wash five times with deionized water, and vacuum dry for later use. Nitrogen gas is purged throughout the reaction.

[0067] Step 2: The alkynyl diamine monomer was added to a 250 ml three-necked flask under ice-water bath conditions. Dimethoxymethane was added, and trifluoroacetic acid was added dropwise over 30 minutes. The reaction was continued under ice-water bath conditions for 2 hours, then the ice-water bath was removed, and the reaction was allowed to proceed at room temperature for 16 hours. Nitrogen gas was not required during the reaction. The product was discharged into a 2.5% ammonia solution. After discharge, the mixture was stirred for a period of time to ensure complete neutralization of the trifluoroacetic acid in the product by the ammonia water. However, the stirring time should not be too long, as prolonged exposure to alkaline conditions can lead to product degradation. The product was filtered and washed five times with deionized water, then vacuum dried. The product was dissolved in NMP, and the insoluble solids were filtered out. The solution was then discharged again into deionized water, washed, and dried to obtain the alkynyl polymer. The yield was 96%, and the number average molecular weight was 2.89 × 10⁻⁶. 4 g / mol.

[0068] The molar ratio of 2,5-dimethyl-p-phenylenediamine monomer to 4,4′-(acetylene-1,2-diyl)phthalic anhydride monomer is 1.2:1, and the molar ratio of alkynyl diamine to dimethoxymethane is 1:1.5.

[0069] The volume ratio of trifluoroacetic acid to dimethoxymethane is 1:12; the solvent includes N-methylpyrrolidone.

[0070] 2. Preparation of fluorinated polyimide

[0071] Step 1: Add 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl to a three-necked flask, and then add N,N-dimethylacetamide under ice-water bath conditions until it is completely dissolved. Then, slowly add hexafluorodianhydride in batches and react under ice-water bath conditions for 1.5 hours. After removing the ice-water bath, react at room temperature for 13 hours.

[0072] Step 2: Acetic anhydride and pyridine are mixed and slowly added dropwise to the reaction system over 2.5 hours at room temperature. After the addition is complete, the system is heated to 75°C and the reaction continues for 8 hours under nitrogen protection. After the reaction is complete, the product is discharged into water, filtered, and then washed with water 5-6 times at 70°C until the solvent is completely removed. After washing, the product is dried in an oven to obtain the final product.

[0073] The fluorinated polyimide is obtained by reacting 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, hexafluorodianhydride, acetic anhydride and pyridine in a molar ratio of 0.15:0.15:1.5:1.5.

[0074] 3. Preparation of semi-interpenetrating alkynyl polymer films

[0075] The fluorinated polyimide was dissolved in N-methylpyrrolidone (NMP), and then an alkynyl polymer was added and stirred until fully dissolved. The solid content was 10 wt%, and the amount of fluorinated polyimide added was 6%, i.e., the ratio of alkynyl polymer to fluorinated polyimide was 15.67:1. After filtration and degassing, the film was coated onto a glass plate using a coating machine and dried in a vacuum oven at 60°C for 48 h, and then dried in a vacuum oven at 120°C for 12 h to obtain an alkynyl polymer film with a thickness of 17.8 μm.

[0076] The permeation coefficients and separation coefficients of He and N2 were tested using a semi-interpenetrating alkynyl polymer membrane-2. The separation performance data are shown in Table 1.

[0077] Example 3: Preparation of semi-interpenetrating alkynyl polymer film-3

[0078] 1. Preparation of alkynyl polymers

[0079] Step 1: Add 2,5-dimethyl-1,4-phenylenediamine and 4,4-(acetylene-1,2-diyl)phthalic anhydride to a three-necked flask, add 250 ml of NMP, and heat to 70°C after the monomers are completely dissolved. React for 10 hours, then add 70 ml of toluene to the flask and heat to reflux (approximately 140°C). React with water for 8 hours. After the toluene is released, cool the flask. After the reaction is complete, discharge the product into ice water, wash five times with deionized water, and vacuum dry for later use. Nitrogen gas is purged throughout the reaction.

[0080] Step 2: The alkynyl diamine monomer was added to a 250 ml three-necked flask under ice-water bath conditions. Dimethoxymethane was added, and trifluoroacetic acid was added dropwise over 30 minutes. The reaction was carried out under ice-water bath conditions for 3 hours, then the ice-water bath was removed, and the reaction was allowed to proceed at room temperature for 20 hours. Nitrogen gas was not required during the reaction. The product was discharged into a 2.5% ammonia solution. After discharge, the mixture was stirred for a period of time to ensure complete neutralization of the trifluoroacetic acid in the product by the ammonia water. However, the stirring time should not be too long, as prolonged exposure to alkaline conditions can lead to product degradation. The product was filtered and washed five times with deionized water, then vacuum dried. The product was dissolved in N-methylpyrrolidone, and the insoluble solids were filtered out. The solution was discharged again into deionized water, washed, and dried to obtain the alkynyl polymer. The yield was 96%, and the number average molecular weight was 2.89 × 10⁻⁶. 4 g / mol.

[0081] The molar ratio of 2,5-dimethyl-p-phenylenediamine monomer to 4,4′-(acetylene-1,2-diyl)phthalic anhydride monomer is 1.8:1, and the molar ratio of alkynyl diamine to dimethoxymethane is 1:2.2.

[0082] The volume ratio of trifluoroacetic acid to dimethoxymethane is 1:12; the solvent includes N-methylpyrrolidone.

[0083] 2. Preparation of fluorinated polyimide

[0084] Step 1: Add 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl to a three-necked flask, and then add N,N-dimethylacetamide under ice-water bath conditions until it is completely dissolved. Then, slowly add hexafluorodianhydride in batches and react under ice-water bath conditions for 3.5 hours. After removing the ice-water bath, react at room temperature for 18 hours.

[0085] Step 2: Acetic anhydride and pyridine are mixed and slowly added dropwise to the reaction system over 4 hours at room temperature. After the addition is complete, the system is heated to 90°C and the reaction continues for 14 hours under nitrogen protection throughout the process. After the reaction is complete, the product is discharged into water, filtered, and then washed with water 5-6 times at 90°C until the solvent is completely removed. After washing, the product is dried in an oven to obtain the final product.

[0086] The fluorinated polyimide is obtained by reacting 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, hexafluorodianhydride, acetic anhydride and pyridine in a molar ratio of 0.2:0.2:2:2.

[0087] 3. Preparation of semi-interpenetrating alkynyl polymer films

[0088] The fluorinated polyimide was dissolved in N-methylpyrrolidone (NMP), and then an alkynyl polymer was added and stirred until fully dissolved. The solid content was 10 wt%, and the amount of fluorinated polyimide added was 9%, i.e., the ratio of alkynyl polymer to fluorinated polyimide was 10.11:1. After filtration and degassing, the film was coated onto a glass plate using a coating machine and dried in a vacuum oven at 60°C for 48 h, and then dried in a vacuum oven at 120°C for 12 h to obtain an alkynyl polymer film with a thickness of 19 μm.

[0089] The permeation coefficients and separation coefficients of He and N2 were tested using a semi-interpenetrating alkynyl polymer membrane-3. The separation performance data are shown in Table 1.

[0090] Example 4: Preparation of semi-interpenetrating alkynyl polymer film-4

[0091] 1. Preparation of alkynyl polymers

[0092] Step 1: Add 2,5-dimethyl-1,4-phenylenediamine and 4,4-(acetylene-1,2-diyl)phthalic anhydride to a three-necked flask, add 250 ml of NMP, and heat to 80°C after the monomers are completely dissolved. React for 10 hours, then add 75 ml of toluene to the flask and heat to reflux (approximately 150°C). React with water for 8 hours. After the toluene is released, cool the flask. After the reaction is complete, discharge the product into ice water, wash five times with deionized water, and vacuum dry for later use. Nitrogen gas is purged throughout the reaction.

[0093] Step 2: The alkynyl diamine monomer was added to a 250 ml three-necked flask under ice-water bath conditions. Dimethoxymethane was added, and trifluoroacetic acid was added dropwise over 30 minutes. The reaction was carried out under ice-water bath conditions for 4 hours, then the ice-water bath was removed, and the reaction was allowed to proceed at room temperature for 20 hours. Nitrogen gas was not required during the reaction. The product was discharged into a 2.5% ammonia solution. After discharge, the mixture was stirred for a period of time to ensure complete neutralization of the trifluoroacetic acid in the product by the ammonia water. However, the stirring time should not be too long, as prolonged exposure to alkaline conditions can lead to product degradation. The product was filtered and washed five times with deionized water, then vacuum dried. The product was dissolved in N-methylpyrrolidone, and the insoluble solids were filtered out. The solution was discharged again into deionized water, washed, and dried to obtain the alkynyl polymer. The yield was 96%, and the number average molecular weight was 2.89 × 10⁻⁶. 4 g / mol.

[0094] The molar ratio of 2,5-dimethyl-p-phenylenediamine monomer to 4,4′-(acetylene-1,2-diyl)phthalic anhydride monomer is 2.1:1, and the molar ratio of alkynyl diamine to dimethoxymethane is 1:2.4.

[0095] The volume ratio of trifluoroacetic acid to dimethoxymethane is 1:12; the solvent includes N-methylpyrrolidone.

[0096] 2. Preparation of fluorinated polyimide

[0097] Step 1: Add 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl to a three-necked flask, and then add N,N-dimethylacetamide under ice-water bath conditions until it is completely dissolved. Then, slowly add hexafluorodianhydride in batches and react under ice-water bath conditions for 3.8 hours. After removing the ice-water bath, react at room temperature for 20 hours.

[0098] Step 2: Acetic anhydride and pyridine are mixed and slowly added dropwise to the reaction system over 5 hours at room temperature. After the addition is complete, the system is heated to 90°C and the reaction continues for 14 hours under nitrogen protection throughout the process. After the reaction is complete, the product is discharged into water, filtered, and then washed with water 5-6 times at 90°C until the solvent is completely removed. After washing, the product is dried in an oven to obtain the final product.

[0099] The fluorinated polyimide is obtained by reacting 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, hexafluorodianhydride, acetic anhydride and pyridine in a molar ratio of 0.24:0.24:2:2.

[0100] 3. Preparation of semi-interpenetrating alkynyl polymer films

[0101] The fluorinated polyimide was dissolved in N-methylpyrrolidone (NMP), and then an alkynyl polymer was added and stirred until fully dissolved. The solid content was 10 wt%, and the amount of fluorinated polyimide added was 12%, i.e., the ratio of alkynyl polymer to fluorinated polyimide was 7.33:1. After filtration and degassing, the film was coated onto a glass plate using a coating machine and dried in a vacuum oven at 60°C for 48 h, and then dried in a vacuum oven at 120°C for 12 h to obtain an alkynyl polymer film with a thickness of 19 μm.

[0102] The permeation coefficients and separation coefficients of He and N2 were tested using a semi-interpenetrating alkynyl polymer membrane-4. The separation performance data are shown in Table 1.

[0103] Example 5: Preparation of Thermally Crosslinked Semi-Interpenetrating Helium Separation Membrane-1

[0104] 1. Preparation of alkynyl polymers

[0105] Step 1: Add 2,5-dimethyl-1,4-phenylenediamine and 4,4-(acetylene-1,2-diyl)phthalic anhydride to a three-necked flask, add 250 ml of NMP, and heat to 80°C after the monomers are completely dissolved. React for 12 hours, then add 80 ml of toluene to the flask and heat to reflux (approximately 150°C). React with water for 10 hours. After the toluene is released, cool the flask. After the reaction is complete, discharge the product into ice water, wash five times with deionized water, and vacuum dry for later use. Nitrogen gas is purged throughout the reaction.

[0106] Step 2: The alkynyl diamine monomer was added to a 250 ml three-necked flask under ice-water bath conditions. Dimethoxymethane was added, and trifluoroacetic acid was added dropwise over 30 minutes. The reaction was carried out under ice-water bath conditions for 4 hours, then the ice-water bath was removed, and the reaction was allowed to proceed at room temperature for 28 hours. Nitrogen gas was not required during the reaction. The product was discharged into a 2.5% ammonia solution. After discharge, the mixture was stirred for a period of time to ensure complete neutralization of the trifluoroacetic acid in the product by the ammonia water. However, the stirring time should not be too long, as prolonged exposure to alkaline conditions can lead to product degradation. The product was filtered and washed five times with deionized water, then vacuum dried. The product was dissolved in N-methylpyrrolidone, and the insoluble solids were filtered out. The solution was discharged again into deionized water, washed, and dried to obtain the alkynyl polymer. The yield was 96%, and the number average molecular weight was 2.89 × 10⁻⁶. 4 g / mol.

[0107] The molar ratio of 2,5-dimethyl-p-phenylenediamine monomer to 4,4′-(acetylene-1,2-diyl)phthalic anhydride monomer is 2.8:1, and the molar ratio of alkynyl diamine to dimethoxymethane is 1:3.5.

[0108] The volume ratio of trifluoroacetic acid to dimethoxymethane is 1:12; the solvent includes N-methylpyrrolidone.

[0109] 2. Preparation of fluorinated polyimide

[0110] Step 1: Add 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl to a three-necked flask, and then add N,N-dimethylacetamide under ice-water bath conditions until it is completely dissolved. Then, slowly add hexafluorodianhydride in batches and react under ice-water bath conditions for 4 hours. After removing the ice-water bath, react at room temperature for 18 hours.

[0111] Step 2: Acetic anhydride and pyridine are mixed and slowly added dropwise to the reaction system over 4 hours at room temperature. After the addition is complete, the system is heated to 100°C and the reaction continues for 15 hours under nitrogen protection throughout the process. After the reaction is complete, the product is discharged into water, filtered, and then washed with water 5-6 times at 100°C until the solvent is completely removed. After washing, the product is dried in an oven to obtain the final product.

[0112] The fluorinated polyimide is obtained by reacting 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, hexafluorodianhydride, acetic anhydride and pyridine in a molar ratio of 0.25:0.25:2.5:2.5.

[0113] 3. Preparation of thermally cross-linked semi-interpenetrating helium separation membrane

[0114] The above-mentioned fluorinated polyimide was dissolved in N-methylpyrrolidone (NMP), and then an alkynyl polymer was added and stirred until fully dissolved, with a solid content of 10 wt% and an addition amount of 9% fluorinated polyimide. After filtration and degassing, the membrane was coated onto a glass plate using a coating machine and dried in a vacuum oven at 60°C for 48 h, followed by drying in a vacuum oven at 120°C for 12 h, to obtain a semi-interpenetrating polymer membrane with a thickness of 20 μm. The membrane was cut into 4 cm × 4 cm squares and placed in a tube furnace under nitrogen protection. The heating rate was set to 5°C / min, the target temperature was 250°C, and the temperature was held for 10 min to obtain a thermally crosslinked semi-interpenetrating helium separation membrane-1.

[0115] The permeation coefficients and separation coefficients of He and N2 were tested using a thermally cross-linked semi-interpenetrating helium separation membrane-1. The separation performance data are shown in Table 1.

[0116] Example 6: Preparation of Thermally Crosslinked Semi-Interpenetrating Helium Separation Membrane-2

[0117] 1. Preparation of alkynyl polymers

[0118] Step 1: Add 2,5-dimethyl-1,4-phenylenediamine and 4,4-(acetylene-1,2-diyl)phthalic anhydride to a three-necked flask, add 250 ml of NMP, and heat to 90°C after the monomers are completely dissolved. React for 14 hours, then add 90 ml of toluene to the flask and heat to reflux (approximately 150°C), reacting with water for 12 hours. After the toluene is released, cool the flask. After the reaction is complete, discharge the product into ice water, wash five times with deionized water, and vacuum dry for later use. Nitrogen gas is purged throughout the reaction.

[0119] Step 2: The alkynyl diamine monomer was added to a 250 ml three-necked flask under ice-water bath conditions, followed by dimethoxymethane. Trifluoroacetic acid was added dropwise over 30 minutes. The reaction was continued under ice-water bath conditions for 6 hours, then the ice-water bath was removed, and the reaction was allowed to proceed at room temperature for 32 hours. Nitrogen gas was not required during the reaction. The product was discharged into a 2.5% ammonia solution. After discharge, the mixture was stirred for a period of time to ensure complete neutralization of the trifluoroacetic acid by the ammonia water, but the stirring time should not be too long, as prolonged exposure to alkaline conditions can lead to product degradation. The product was filtered and washed five times with deionized water, then vacuum dried. The product was dissolved in N-methylpyrrolidone, and the insoluble solids were filtered out. The solution was then discharged again into deionized water, washed, and dried to obtain the alkynyl polymer. The yield was 96%, and the number average molecular weight was 2.89 × 10⁻⁶. 4 g / mol.

[0120] The molar ratio of 2,5-dimethyl-p-phenylenediamine monomer to 4,4′-(acetylene-1,2-diyl)phthalic anhydride monomer is 3:1, and the molar ratio of alkynyl diamine to dimethoxymethane is 1:3.8.

[0121] The volume ratio of trifluoroacetic acid to dimethoxymethane is 1:12; the solvent includes N-methylpyrrolidone.

[0122] 2. Preparation of fluorinated polyimide

[0123] Step 1: Add 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl to a three-necked flask, and then add N,N-dimethylacetamide under ice-water bath conditions until it is completely dissolved. Then, slowly add hexafluorodianhydride in batches and react for 6 hours under ice-water bath conditions. After removing the ice-water bath, react at room temperature for 20 hours.

[0124] Step 2: Acetic anhydride and pyridine are mixed and slowly added dropwise to the reaction system over 6 hours at room temperature. After the addition is complete, the system is heated to 110°C and the reaction continues for 16 hours under nitrogen protection throughout the process. After the reaction is complete, the product is discharged into water, filtered, and then washed with water 5-6 times at 110°C until the solvent is completely removed. After washing, the product is dried in an oven to obtain the final product.

[0125] The fluorinated polyimide is obtained by reacting 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, hexafluorodianhydride, acetic anhydride and pyridine in a molar ratio of 0.32:0.32:3.2:3.2.

[0126] 3. Preparation of thermally cross-linked semi-interpenetrating helium separation membrane

[0127] The fluorinated polyimide was dissolved in N-methylpyrrolidone (NMP), and then an alkynyl polymer was added and stirred until fully dissolved, with a solid content of 10 wt% and an addition amount of 9% fluorinated polyimide. After filtration and degassing, the membrane was coated onto a glass plate using a coating machine and dried in a vacuum oven at 60°C for 48 h, followed by drying in a vacuum oven at 120°C for 12 h, to obtain a 20 μm thick semi-interpenetrating polymer membrane. This membrane was cut into 4 cm × 4 cm squares and placed in a tube furnace under nitrogen protection. The heating rate was set to 5°C / min, the target temperature was 300°C, and the temperature was held for 10 min to obtain a thermally crosslinked semi-interpenetrating helium separation membrane-2.

[0128] The permeability and separation coefficient of He and N2 were tested using a thermally cross-linked semi-interpenetrating helium separation membrane-2. The separation performance data are shown in Table 1.

[0129] Example 7: Preparation of Thermally Crosslinked Semi-Interpenetrating Helium Separation Membrane-3

[0130] 1. Preparation of alkynyl polymers

[0131] Step 1: Add 2,5-dimethyl-1,4-phenylenediamine and 4,4-(acetylene-1,2-diyl)phthalic anhydride to a three-necked flask, add 250 ml of NMP, and heat to 100°C after the monomers are completely dissolved. React for 18 hours. Then add 100 ml of toluene to the flask and heat to reflux (approximately 160°C), reacting with water for 14 hours. After removing the toluene, cool the flask. After the reaction is complete, discharge the product into ice water, wash five times with deionized water, and vacuum dry for later use. Nitrogen gas is purged throughout the reaction.

[0132] Step 2: The alkynyl diamine monomer was added to a 250 ml three-necked flask under ice-water bath conditions, followed by dimethoxymethane. Trifluoroacetic acid was added dropwise over 30 minutes. The reaction was continued under ice-water bath conditions for 8 hours, then the ice-water bath was removed, and the reaction was allowed to proceed at room temperature for 34 hours. Nitrogen gas was not required during the reaction. The product was discharged into a 2.5% ammonia solution. After discharge, the mixture was stirred for a period of time to ensure complete neutralization of the trifluoroacetic acid by the ammonia water, but the stirring time should not be too long, as prolonged exposure to alkaline conditions can lead to product degradation. The product was filtered and washed five times with deionized water, then vacuum dried. The product was dissolved in N-methylpyrrolidone, and the insoluble solids were filtered out. The solution was then discharged again into deionized water, washed, and dried to obtain the alkynyl polymer. The yield was 96%, and the number average molecular weight was 2.89 × 10⁻⁶.4 g / mol.

[0133] The molar ratio of 2,5-dimethyl-p-phenylenediamine monomer to 4,4′-(acetylene-1,2-diyl)phthalic anhydride monomer is 3.5:1, and the molar ratio of alkynyl diamine to dimethoxymethane is 1:3.6.

[0134] The volume ratio of trifluoroacetic acid to dimethoxymethane is 1:12; the solvent includes N-methylpyrrolidone.

[0135] 2. Preparation of fluorinated polyimide

[0136] Step 1: Add 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl to a three-necked flask, and then add N,N-dimethylacetamide under ice-water bath conditions until it is completely dissolved. Then, slowly add hexafluorodianhydride in batches and react under ice-water bath conditions for 7 hours. After removing the ice-water bath, react at room temperature for 22 hours.

[0137] Step 2: Acetic anhydride and pyridine are mixed and slowly added dropwise to the reaction system over 8 hours at room temperature. After the addition is complete, the system is heated to 120°C and the reaction continues for 18 hours under nitrogen protection throughout the process. After the reaction is complete, the product is discharged into water, filtered, and then washed with water 5-6 times at 120°C until the solvent is completely removed. After washing, the product is dried in an oven to obtain the final product.

[0138] The fluorinated polyimide is obtained by reacting 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, hexafluorodianhydride, acetic anhydride and pyridine in a molar ratio of 0.36:0.36:3.6:3.6.

[0139] 3. Preparation of thermally cross-linked semi-interpenetrating helium separation membrane

[0140] The fluorinated polyimide was dissolved in N-methylpyrrolidone (NMP), and then an alkynyl polymer was added and stirred until fully dissolved, with a solid content of 10 wt% and an addition of 9% fluorinated polyimide. After filtration and degassing, the membrane was coated onto a glass plate using a coating machine and dried in a vacuum oven at 60°C for 48 h, followed by drying in a vacuum oven at 120°C for 12 h, to obtain a 20 μm thick semi-interpenetrating polymer membrane. This membrane was cut into 4 cm × 4 cm squares and placed in a tube furnace under nitrogen protection. The heating rate was set to 5°C / min, the target temperature was 330°C, and the temperature was held for 10 min to obtain a thermally crosslinked semi-interpenetrating helium separation membrane-3.

[0141] The permeability and separation coefficient of He and N2 were tested using a thermally cross-linked semi-interpenetrating helium separation membrane-3. The separation performance data are shown in Table 1.

[0142] Comparative Example 1: Preparation of Alkyne Polymer Membranes

[0143] In this example, the alkynyl polymer is polymerized from 2,5-dimethyl-p-phenylenediamine monomer and 4,4′-(acetylene-1,2-diyl)phthalic anhydride monomer.

[0144] The method for preparing the above-mentioned alkynyl polymer film is characterized by comprising the following specific steps:

[0145] 1. Preparation of the alkynyl polymer: 13.44 g of 2,5-dimethyl-p-phenylenediamine monomer and 31.82 g of 4,4′-(acetylene-1,2-diyl)phthalic anhydride monomer were added to a three-necked flask equipped with a mechanical stirrer. Then, 145 ml of trifluoroacetic acid was added dropwise over 30 minutes. The reaction was carried out in an ice-water bath for 1 hour, then the ice-water bath was removed, and the reaction was allowed to proceed at room temperature for 48 hours. Nitrogen gas was not required during the reaction. The product was discharged into a 2.5% ammonia solution. After discharge, the mixture was stirred for a period of time to ensure complete neutralization of the trifluoroacetic acid in the product by the ammonia water, but the stirring time should not be too long, as prolonged exposure to alkaline conditions can lead to product degradation. The product was filtered and washed five times with deionized water, then vacuum dried. The product was dissolved in NMP, and the insoluble solids were filtered out. The solids were then precipitated in a mixture of pure water and methanol. The collected solids were filtered multiple times with pure water and dried to obtain the alkynyl polymer with a yield of 96% and a number average molecular weight of 2.89 × 10⁻⁶. 4 g / mol.

[0146] 2. Alkyne polymer membrane: The above-mentioned alkynyl polymer was dissolved in N-methylpyrrolidone (NMP) to obtain a solution with a solid content of 10 wt%. After filtration and degassing, the solution was coated onto a glass plate using a coating machine and dried in a vacuum oven at 60°C for 48 h, and then dried in a vacuum oven at 120°C for 12 h to obtain an alkynyl polymer membrane with an average thickness of 20 μm.

[0147] The permeation coefficients and separation coefficients of He and N2 were tested using an alkynyl polymer membrane, and the separation performance data are shown in Table 1.

[0148] Depend on Figure 2It was observed that when the addition amount of fluorinated polyimide was between 0% and 9%, the prepared semi-interpenetrating alkynyl polymer membrane had a smooth and uniform surface, and no obvious phase separation phenomenon was observed in the casting solution during membrane formation. When the addition amount of fluorinated polyimide reached 12%, the two polymers could not be mixed uniformly, and phase separation occurred. This was also observed in optical photographs, showing uneven polymer aggregation on the membrane surface. Gas separation performance of semi-interpenetrating membranes with different fluorinated polyimide addition amounts was tested. It was found that as the fluorinated polyimide addition amount increased from 3% to 9%, the helium and nitrogen fluxes of the semi-interpenetrating membrane gradually decreased, but the He / N2 selectivity increased significantly, from 64.14 to 240.3. Previous research has shown that thermal crosslinking of alkynyl polymer membranes can effectively improve the helium flux. Therefore, in order to further improve the helium flux while maintaining high selectivity, this invention selects a semi-interpenetrating polymer membrane with an addition of 9% fluorinated polyimide and further heat-treats it to prepare a thermally crosslinked semi-interpenetrating helium separation membrane. Under heating conditions, the triple bonds of the alkynyl polymer in the polymer membrane network undergo 1,4-addition with the double bonds on its own benzene ring to form a conjugated diene. The pore size and free volume of the membrane are adjusted, and the gas separation performance of the thermally crosslinked semi-interpenetrating helium separation membrane is investigated.

[0149] The test data in Table 1 show that the semi-interpenetrating alkynyl polymer membrane for He has a permeability coefficient ≥15 and a He / N2 selectivity ≥240, while the thermally crosslinked semi-interpenetrating helium separation membrane for He has a permeability coefficient ≥60 and a He / N2 selectivity ≥130. These results demonstrate that the helium can overcome the trade-off effect, improving gas permeability while maintaining high selectivity. Mixed gas testing showed that the purity of the separated helium reached 98.56%. With increasing addition of fluorinated polyimide, the helium flux decreased, while the nitrogen flux decreased less significantly, resulting in a marked decrease in nitrogen flux and a significant improvement in He / N2 selectivity.

[0150] As can be seen from the test data in Table 2, during the 60-day aging test, the helium flux of the alkynyl polymer membrane decreased from 9.22 Barrer to 11.8 Barrer, a decrease of 16.91%, while the helium flux of the thermally crosslinked semi-interpenetrating helium separation membrane decreased from 62.42 Barrer to 61.86 Barrer, a decrease of 0.8%, demonstrating good stability.

[0151] Introducing fluorine atoms increases the polymer's affinity for helium and improves solubility selectivity. Simultaneously, the pore-blocking effect caused by fluorine substitution enhances size sieving diffusion selectivity. Thermal crosslinking of the fluorinated alkyne polymer membrane slightly increases nitrogen flux while significantly improving helium flux. The alkyne groups in the fluorinated alkyne polymer undergo 1,4-addition with the conjugated diene on the benzene ring at 250°C, forming a six-membered cyclic compound. The fully aromatic special network polymer formed through crosslinking increases the polymer's free volume, resulting in a significant increase in helium flux. Furthermore, the fluorinated polyimide and alkyne polymer physically mix in the same spatial region, forming a semi-interpenetrating polymer network. Thermal crosslinking introduces chemical bonds into this network to fix the linear components, inhibiting polymer aging and improving membrane lifespan.

[0152] Table 1: Permeability data of single-component gases

[0153]

[0154] Table 2: Aging Data

[0155]

[0156] Table 3: Permeability data of mixed gases

[0157]

Claims

1. A thermally cross-linked semi-interpenetrating helium separation membrane, characterized in that, The separation membrane is prepared by mixing an alkynyl polymer and a fluorinated polyimide and then thermally crosslinking it. The structural formula of the alkynyl polymer is shown in Formula 1, wherein n of the alkynyl polymer is 50 to 70; and the number average molecular weight of the alkynyl polymer is 20,000 to 30,000 g / mol. Formula 1 The fluorinated polyimide has the structural formula shown in Formula 2, wherein n of the fluorinated polyimide is 40~60, and the number average molecular weight of the fluorinated polyimide is 28000~42000 g / mol. Equation 2.

2. The thermally cross-linked semi-interpenetrating helium separation membrane according to claim 1, characterized in that, The ratio of the alkynyl polymer to the fluorinated polyimide is (5~35):

1.

3. A thermally cross-linked semi-interpenetrating helium separation membrane according to claim 1 or 2, characterized in that, The alkynyl polymer is prepared by reacting 2,5-dimethyl-p-phenylenediamine monomer with 4,4'-(acetylene-1,2-diyl)phthalic anhydride in a molar ratio of 0.5 to 6:1 to obtain alkynyl diamine, and the alkynyl polymer is obtained by reacting alkynyl diamine with dimethoxymethane in a molar ratio of 1:1.5 to 6.

4. A thermally cross-linked semi-interpenetrating helium separation membrane according to claim 1 or 2, characterized in that, The fluorinated polyimide is obtained by reacting 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, hexafluorodianhydride, acetic anhydride and pyridine in a molar ratio of (0.1~0.6):(0.1~0.6):(1~6):(1~6).

5. The thermally cross-linked semi-interpenetrating helium separation membrane according to claim 3, characterized in that, The method for preparing the alkynyl polymer includes the following steps: Step 1: After N-methylpyrrolidone is completely dissolved in 2,5-dimethyl-1,4-phenylenediamine and 4,4-(acetylene-1,2-diyl)phthalic anhydride, the mixture is heated to 50-100°C and reacted for 6-18 h. Toluene is then added and the mixture is heated under reflux and reacted with water for 4-12 h. After the toluene is released, the mixture is cooled and discharged into ice water. The alkynyldiamine is then separated and purified. Nitrogen gas is purged throughout the reaction. Step 2: Add dimethoxymethane to the alkynyl diamine monomer under ice-water bath conditions, add trifluoroacetic acid dropwise, and react for 1-4 h. Then remove the ice-water bath and react at room temperature for 12-48 h. Do not pass nitrogen gas during the reaction. Discharge the product into a 2.5% ammonia solution, neutralize the trifluoroacetic acid with ammonia water, separate and purify, dissolve the product in a solvent, filter out the insoluble solids, discharge the solution back into deionized water, wash and dry to obtain the alkynyl polymer.

6. The thermally cross-linked semi-interpenetrating helium separation membrane according to claim 4, characterized in that, The method for preparing the fluorinated polyimide includes the following steps: Step 2-1: Add 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl to a three-necked flask, add N,N-dimethylacetamide under ice-water bath conditions until it is completely dissolved, add hexafluorodianhydride in batches and react under ice-water bath conditions for 1-6 h, then remove the ice-water bath and react at room temperature for 12-48 h. Step 2-2: After mixing acetic anhydride and pyridine, slowly add them dropwise to the reaction system at room temperature over 2-8 hours. After the addition is complete, heat the system to 60-120°C and continue the reaction for 6-18 hours. Nitrogen gas is introduced for protection throughout the reaction. After the reaction is complete, discharge the product into water, filter it, and wash the product with water 5-6 times at 60-120°C until the solvent is completely removed. After washing, dry the product to obtain the fluorinated polyimide.

7. The thermally cross-linked semi-interpenetrating helium separation membrane according to claim 5, characterized in that, In step 2, the volume ratio of trifluoroacetic acid to dimethoxymethane is 1:12; the solvent includes N-methylpyrrolidone.

8. A method for preparing a thermally cross-linked semi-interpenetrating helium separation membrane according to any one of claims 1-7, characterized in that, The separation membrane is prepared by dissolving fluorinated polyimide in an organic solvent, then adding an alkynyl polymer, stirring to fully dissolve it, filtering to remove impurities to obtain a casting solution, allowing it to stand to degas, uniformly coating the casting solution onto a glass plate, and waiting for the solvent to evaporate to obtain a semi-interpenetrating alkynyl polymer membrane; the semi-interpenetrating alkynyl polymer membrane is then heated under a nitrogen atmosphere to undergo a crosslinking reaction to obtain the thermally crosslinked semi-interpenetrating helium separation membrane.

9. The method for preparing a thermally cross-linked semi-interpenetrating helium separation membrane according to claim 8, characterized in that, The solid content of the casting solution is 9-15 wt%, of which the amount of fluorinated polyimide added is 3-12%. The organic solvent includes at least one of N-methylpyrrolidone, 1,3-dimethyl-2-imidazolinone, N-ethylpyrrolidone, and N,N-dimethylformamide.

10. The method for preparing a thermally cross-linked semi-interpenetrating helium separation membrane according to claim 8, characterized in that, The solvent is evaporated by drying in a vacuum oven at 60-100°C for 48-72 h, and then drying in a vacuum oven at 100-120°C for 6-12 h; the target temperature for thermal crosslinking is 250-330°C, and the crosslinking reaction time is 15-60 min.

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