A method for preparing a crosslinked hollow fiber membrane and applications thereof
By employing a ternary synergistic strategy of side-linking, in-situ esterification, and interfacial crosslinking, a flexible covalent network polyimide hollow fiber membrane was constructed, which solved the problem of plasticization failure of traditional polyimide membranes under high pressure, achieving high throughput and good mechanical properties, and is suitable for industrial gas separation applications.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZHEJIANG QIANFENG NEW MATERIALS CO LTD
- Filing Date
- 2026-04-22
- Publication Date
- 2026-06-02
AI Technical Summary
Traditional polyimide films are prone to plasticization failure under high pressure, and the crosslinking strategy results in low throughput and poor mechanical properties, making it difficult to meet industrial requirements.
A ternary synergistic strategy of side-linking grafting-in-situ esterification-interfacial crosslinking is adopted to construct a flexible covalent network between polyimide molecular chains through diol grafting and acyl chloride crosslinking, forming a hollow fiber membrane with both large free volume and strong crosslinking structure.
It maintains high permeation flux and good mechanical properties under high pressure, solving the problem of plasticization failure of traditional membranes under high pressure and acidic environment, and is suitable for industrial fields such as natural gas decarbonization and hydrogen recovery.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of polymer membrane separation technology, and in particular to a method for preparing and applying a cross-linked hollow fiber membrane. Background Technology
[0002] In industrial applications such as natural gas decarbonization (CO2 / CH4 separation) and biogas purification, gas separation membranes may be exposed to high pressure (typically greater than 5 MPa) and high concentrations of acidic gases (such as CO2 and H2S). Polyimide (PI) has become the preferred material for commercial gas separation membranes due to its excellent thermal stability, mechanical strength, and gas selectivity.
[0003] However, traditional polyimide membranes face challenges in practical applications. First, there's the plasticization effect. Under high pressure, CO2 molecules can penetrate between polymer chains, increasing the free volume and fluidity of the chains, leading to a significant decrease in membrane selectivity and even separation failure. Second, there are limitations in crosslinking strategies. To suppress plasticization, existing technologies mostly employ thermal crosslinking or simple chemical crosslinking. While these methods improve membrane stability, they also result in drastically reduced flux and membrane fiber embrittlement. Traditional crosslinking reactions severely reduce the free volume of the gas, leading to low flux that is difficult to meet the demands of large-scale industrial applications. Moreover, crosslinking generally makes the membrane brittle, making it prone to breakage during assembly into membrane modules or high-pressure operation, thus lacking the value for large-scale applications.
[0004] Therefore, how to prepare a hollow fiber membrane that can resist high-pressure plasticization and has good mechanical properties without sacrificing permeation flux is a key issue that urgently needs to be addressed in the field of gas separation membranes. Summary of the Invention
[0005] Based on the above, this invention provides a polyimide hollow fiber membrane (i.e., a cross-linked hollow fiber membrane) that exhibits resistance to acidic gas plasticization, excellent mechanical properties, high pressure resistance, and outstanding separation performance. A flexible covalent network is constructed between the polyimide molecular chains through a ternary synergistic strategy of "side-linking grafting-in-situ esterification-interfacial cross-linking." Utilizing the reaction sites introduced by carboxyl diamines, the free volume of the polymer is effectively controlled through excess diol grafting. Furthermore, a cross-linked structure is formed on the membrane surface using acyl chloride cross-linking agents, significantly improving the structural stability of the hollow fiber under extremely high operating pressures. This completely solves the problem of plasticization failure that easily occurs in traditional gas separation membranes under high pressure and acidic environments, resulting in particularly excellent mechanical properties and outstanding separation performance. It has extremely high application potential and mechanical strength in industrial fields such as natural gas decarbonization and hydrogen recovery.
[0006] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of this invention is a method for preparing a cross-linked hollow fiber membrane, comprising the following steps: Step 1: Prepare polyamic acid by mixing diamine monomer and dianhydride monomer, and then dehydrate to prepare polyimide; Step 2: The polyimide is grafted with diol to obtain grafted modified polyimide; Step 3: The grafted modified polyimide is made into a hollow fiber membrane; Step 4: Immerse the hollow fiber membrane in an acyl chloride solution to carry out an interfacial crosslinking reaction to obtain the crosslinked hollow fiber membrane.
[0007] The second technical solution of the present invention is a cross-linked hollow fiber membrane prepared by the above-mentioned preparation method.
[0008] The third technical solution of the present invention is the application of the above-mentioned cross-linked hollow fiber membrane in gas separation.
[0009] Compared with the prior art, the present invention has the following beneficial effects: A flexible covalent network was constructed between polyimide molecular chains using a ternary synergistic strategy of "side grafting-in-situ esterification-interfacial crosslinking". The carboxyl groups on the AHPBA benzene ring were pre-esterified with excess diol to obtain flexible hydroxyl reaction sites. Subsequently, the flexible hydroxyl reaction sites and phenolic hydroxyl groups grafted onto the AHPBA benzene ring were crosslinked with acyl chlorides to obtain a synergistic chemical structure.
[0010] The cross-linked hollow fiber membrane prepared by the method of the present invention has high permeability, good mechanical properties, and can resist high pressure plasticization. Detailed Implementation
[0011] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.
[0012] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.
[0013] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.
[0014] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.
[0015] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.
[0016] The first aspect of this invention provides a method for preparing a cross-linked hollow fiber membrane, comprising the following steps: Step 1: Prepare polyamic acid by mixing diamine monomer and dianhydride monomer, and then dehydrate to prepare polyimide; Step 2: The polyimide is grafted with diol to obtain grafted modified polyimide; Step 3: The grafted modified polyimide is made into a hollow fiber membrane; Step 4: Immerse the hollow fiber membrane in an acyl chloride solution to carry out an interfacial crosslinking reaction to obtain the crosslinked hollow fiber membrane.
[0017] In a preferred embodiment of the present invention, in step 1, the diamine monomer includes phenolphthalein diamine (AHPBA); the dianhydride monomer includes 6FDA; and the molar ratio of the diamine monomer to the dianhydride monomer is 1:1.
[0018] In some embodiments of the present invention, the diamine monomer further includes other diamines commonly found in the art (such as p-phenylenediamine, 2,2'-bis(trifluoromethyl)benzidine (TFMB) and / or 3,5-diaminobenzoic acid (DABA)), and the amount of the other diamine added is 0 to 25 wt% of phenolphthalein diamine.
[0019] In this invention, AHPBA contains two active sites that react with acyl chlorides: one is the esterification of the carboxyl group on the AHPBA benzene ring by excess diol, resulting in a flexible hydroxyl reaction site; the other is a phenolic hydroxyl group. These two synergistically form a cross-linked structure with both large free volume and cross-linking strength, achieving high throughput and resistance to plasticization. When the content of other diamines is between 0 and 25 wt%, the aforementioned synergistic effect remains effective. When the content of other diamines is greater than 25 wt%, the aforementioned high throughput and resistance to plasticization significantly decrease.
[0020] In a preferred embodiment of the present invention, in step 1, the dehydration is carried out by azeotropic distillation.
[0021] In this invention, the purpose of using azeotropic distillation for dehydration instead of chemical imidization is to protect the phenolic hydroxyl groups from esterification.
[0022] In a preferred embodiment of the present invention, in step 2, the diol is ethylene glycol, propylene glycol, or 1,4-butanediol.
[0023] In a preferred embodiment of the present invention, in step 2, the amount of the diol used is 150-300 wt% of the mass of the polyimide.
[0024] In this invention, when the amount of glycol added is within the above-mentioned range, it can be ensured that the molar number of glycol is much greater than the molar number of carboxyl groups in the polymer. On the one hand, this can promote the degree of esterification reaction and allow the carboxyl groups to react as much as possible. On the other hand, an appropriate excess of glycol (equivalent to 4-10 times the molar number of carboxyl groups) can prevent the glycol from forming a cross-linked structure with the carboxyl groups in the polymer, thus avoiding the formation of gel.
[0025] In a preferred embodiment of the present invention, in step 2, the grafting modification temperature is 140-190℃ and the time is 1-4h.
[0026] In a preferred embodiment of the present invention, in step 4, the acyl chloride in the acyl chloride solution is at least one of trimesoyl chloride (TMC), isophthaloyl chloride (IPC), phthaloyl chloride, or adipic acid chloride; and the solvent of the acyl chloride solution is n-hexane.
[0027] This invention utilizes an acyl chloride solution with a functionality greater than two, which can undergo cross-linking reactions with flexible hydroxyl reaction sites and phenolic hydroxyl groups to generate a structure that combines large free volume and strong chemical cross-linking, ensuring that the separation membrane possesses both high throughput and resistance to plasticization. The reason for using n-hexane as the solvent is that, compared to commonly used alcohol solvents for cross-linking, n-hexane has a lower surface energy and superior pore-retention properties, thereby maintaining the high throughput of the separation membrane.
[0028] In a preferred embodiment of the present invention, in step 4, the concentration of the acyl chloride solution is 1~5wt%, and the interfacial crosslinking reaction time is 0.5~5min.
[0029] A second aspect of the present invention provides a cross-linked hollow fiber membrane prepared by the above-described preparation method.
[0030] A third aspect of the present invention provides the application of the above-described cross-linked hollow fiber membrane in gas separation.
[0031] The gas separation includes natural gas decarbonization, biogas purification, and carbon capture.
[0032] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.
[0033] The meanings of the abbreviations in this invention are as follows: 6FDA: Hexafluorodianhydride; TFMB: 2,2'-bis(trifluoromethyl)benzidine; DABA: 3,5-Diaminobenzoic acid; TMC: Trimethylbenzene chloride.
[0034] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.
[0035] The methods for preparing hollow fiber membranes, cross-linked dense membranes, and testing methods involved in the embodiments of the present invention are as follows: 1. Preparation of hollow fiber membranes Preparation of spinning solution: Grafted modified polyimide was dissolved in a mixed solvent of N-methylpyrrolidone (NMP), tetrahydrofuran (THF), and ethanol, with a solid content controlled at 25 wt%. The volume ratio of NMP, THF, and ethanol was 2:1:0.1. The mixture was stirred at room temperature for 24 hours. The casting solution was then transferred to a constant temperature (40℃) spinning tank and allowed to stand for degassing for 24 hours to obtain the spinning solution.
[0036] Core fluid preparation: an aqueous solution containing 10 wt% N-methylpyrrolidone.
[0037] The outer diameter of the spinning head is 0.8 mm, the inner diameter is 0.5 mm, the flow rate of the spinning solution is 3 mL / min, and the flow rate of the core solution is 1 mL / min. The spinning temperature is 40℃, the coagulation bath temperature is 50℃, the air gap is 5 cm, and the take-up speed is 30 m / min.
[0038] After the nascent membrane was gelled and cured in a coagulation bath (water), the hollow fiber gas separation membrane was washed in running water for 24 hours to remove residual solvent. The membrane was then carefully transferred to methanol and soaked for 30 minutes, repeated three times (with methanol replaced). The methanol was then replaced three times with n-hexane, 30 minutes each time. After drying the membrane at room temperature for 12 hours, the hollow fiber membrane was obtained.
[0039] 2. Preparation of cross-linked dense membranes Grafted polyimide was dissolved in DMF to prepare a 7% (w / w) solution. Then, impurities in the solution were filtered out using a 0.45 μm PTFE membrane. Finally, the filtered solution was poured into a smooth, flat petri dish. The petri dish was covered with aluminum foil to prevent dust from entering, and small holes were evenly punched into the foil using a needle. The petri dish was placed in a vacuum oven and heated at 60 °C for 12 hours. After the solvent had largely evaporated, the temperature was gradually increased to 120 °C and then 150 °C, and held at each temperature for 12 hours to ensure complete solvent evaporation. The resulting dense polymer film exhibited a smooth, flat, and uniform appearance, with a thickness of approximately 70 to 130 μm.
[0040] The aforementioned dense membrane was immersed in a solution containing TMC / n-hexane (5 g / 100 mL). After reacting for 3 minutes, the membrane was removed and dried at room temperature for 12 hours to obtain a cross-linked dense membrane. This cross-linked dense membrane was used to test the plasticization resistance of materials.
[0041] 3. Gas permeability test The CO2 flux, CO2 / N2, and CO2 / CH4 selectivity of cross-linked hollow fiber membranes were obtained using the following test method: Hollow fiber membrane elements with an effective length of 15 cm were fabricated using 30 cross-linked hollow fiber membranes, stainless steel straight-through sleeves, and epoxy resin-based adhesives. These membrane elements were inserted into a suitable stainless steel container for testing, with the temperature controlled at a constant 35°C. High-purity CO2 gas was introduced at a fixed pressure into the outside of the hollow fibers of the membrane element, with the gas outside the hollow fiber membrane element considered the upstream gas and the gas passing through the hollow fiber pores considered the downstream gas. The upstream gas pressure was kept constant at 0.5 MPa, and the rate of the downstream gas in the soap bubble flow meter was measured. The CO2 permeation flux was calculated using formulas. The CH4 and N2 permeation fluxes were tested in the same manner. The CO2 / CH4 and CO2 / N2 selectivity were compared to obtain the results.
[0042] 4. CO2 swelling resistance test The resistance of cross-linked dense membranes to CO2 swelling under different pressures was tested using a gas permeability testing device. The test pressure was gradually increased from 0.5 MPa to 6.0 MPa (specifically 1.0 MPa, 2.0 MPa, 3.0 MPa, 3.5 MPa, 4.5 MPa, 5.0 MPa, 5.5 MPa, and 6.0 MPa) to measure the permeability of the cross-linked dense membranes. The permeability (Barrer) at each pressure was calculated and recorded, and its relationship with pressure was analyzed. Based on this, anti-plasticization performance curves of the cross-linked dense membranes under different pressures were plotted. The pressure at which CO2 permeability began to increase was defined as the plasticizing pressure. If no increase in CO2 permeability was observed, it was considered that no plasticization occurred within the test pressure range.
[0043] Example 1 Step 1: First, nitrogen gas was bubbled into a three-necked flask, and phenolphthalein diamine (0.1 mol) and NMP were added and stirred until homogeneous. Then, 6 FDA (0.1 mol) was added in three batches to 150 mL of the NMP and diamine solution. NMP was added to adjust the solid content to 30 wt%. The reaction temperature was maintained at 0 °C, and the mixture was mechanically stirred for 24 hours (60 r / min) to obtain a polyamic acid solution. Next, 100 mL of toluene was added to the above polyamic acid solution, and azeotropic distillation was carried out at 150 °C for 6 hours, followed by cooling to room temperature. Finally, the polyimide solution was precipitated in methanol, pulverized, filtered, and dried in an empty oven at 130 °C for 16 hours to obtain polyimide A1.
[0044] Step 2: Add 30g of the above polyimide A1 to a three-necked flask, then add a mixed solution of NMP and toluene (NMP to toluene volume ratio 2:1), and stir until homogeneous. Add 60g of ethylene glycol. Continue adding the NMP and toluene mixed solution, adjusting the solid content to 15wt%, and stir until homogeneous. Reflux at 180℃ for 3 hours. Finally, precipitate the grafted polyimide solution in methanol, pulverize, filter, and dry in an empty oven at 150℃ for 16 hours. Grafted polyimide B1 is obtained.
[0045] Step 3: Use the above-mentioned grafted modified polyimide B1 to prepare hollow fiber membrane C1 according to the above-mentioned method "1. Preparation of hollow fiber membrane".
[0046] Step 4: Seal both ends of the hollow fiber membrane C1 with epoxy resin. Prepare a 2% (w / w) solution of trimesoyl chloride (TMC) in hexane. Immerse the hollow fiber membrane C1 with both ends sealed in the solution and react for 3 minutes. After removing it, dry the membrane at room temperature for 12 hours, then cut off the sealing resin at both ends to obtain the crosslinked hollow fiber membrane D1.
[0047] Example 2 The only difference from Example 1 is that the phrase "First, nitrogen gas is bubbled into a three-necked flask, phenolphthalein diamine (0.1 mol) and NMP are added, and the mixture is stirred until homogeneous. Then, 6FDA (0.1 mol) is added to the NMP and diamine solution in three batches" is changed to "First, nitrogen gas is bubbled into a three-necked flask, phenolphthalein diamine (0.1 mol), p-phenylenediamine (0.01 mol) and NMP are added, and the mixture is stirred until homogeneous. Then, 6FDA (0.11 mol) is added to the NMP and diamine solution in three batches." The resulting polyimide is designated A2. The resulting grafted modified polyimide is designated B2. The prepared hollow fiber membrane is designated C2. The resulting crosslinked hollow fiber membrane is designated D2.
[0048] Example 3 The only difference from Example 1 is that the phrase "First, nitrogen gas is bubbled into a three-necked flask, phenolphthalein diamine (0.1 mol) and NMP are added, and the mixture is stirred until homogeneous. Then, 6FDA (0.1 mol) is added to the NMP and diamine solution in three batches" is changed to "First, nitrogen gas is bubbled into a three-necked flask, phenolphthalein diamine (0.1 mol), p-phenylenediamine (0.02 mol) and NMP are added, and the mixture is stirred until homogeneous. Then, 6FDA (0.12 mol) is added to the NMP and diamine solution in three batches." The resulting polyimide is designated A3. The resulting grafted modified polyimide is designated B3. The prepared hollow fiber membrane is designated C3. The resulting crosslinked hollow fiber membrane is designated D3.
[0049] Example 4 The only difference from Example 1 is that the phrase "First, nitrogen gas is bubbled into a three-necked flask, phenolphthalein diamine (0.1 mol) and NMP are added, and the mixture is stirred until homogeneous. Then, 6FDA (0.1 mol) is added to the NMP and diamine solution in three batches" is changed to "First, nitrogen gas is bubbled into a three-necked flask, phenolphthalein diamine (0.1 mol), TFMB (0.01 mol), and NMP are added, and the mixture is stirred until homogeneous. Then, 6FDA (0.11 mol) is added to the NMP and diamine solution in three batches." The resulting polyimide is designated A4. The resulting grafted modified polyimide is designated B4. The prepared hollow fiber membrane is designated C4. The resulting crosslinked hollow fiber membrane is designated D4.
[0050] Example 5 The only difference from Example 1 is that the phrase "First, nitrogen gas is bubbled into a three-necked flask, phenolphthalein diamine (0.1 mol) and NMP are added, and the mixture is stirred until homogeneous. Then, 6FDA (0.1 mol) is added to the NMP and diamine solution in three batches" is changed to "First, nitrogen gas is bubbled into a three-necked flask, phenolphthalein diamine (0.1 mol), DABA (0.01 mol), and NMP are added, and the mixture is stirred until homogeneous. Then, 6FDA (0.11 mol) is added to the NMP and diamine solution in three batches." The resulting polyimide is designated A5. The resulting grafted modified polyimide is designated B5. The prepared hollow fiber membrane is designated C5. The resulting crosslinked hollow fiber membrane is designated D5.
[0051] Example 6 The only difference from Example 1 is that the ethylene glycol in step 2 is replaced with an equal mass of propylene glycol. The resulting polyimide is denoted as A1. The resulting grafted modified polyimide is denoted as B6. The prepared hollow fiber membrane is denoted as C6. The resulting crosslinked hollow fiber membrane is denoted as D6.
[0052] Example 7 The only difference from Example 1 is that the ethylene glycol in step 2 is replaced with an equal mass of 1,4-butanediol. The resulting polyimide is designated A1. The resulting grafted modified polyimide is designated B7. The prepared hollow fiber membrane is designated C7. The resulting crosslinked hollow fiber membrane is designated D7.
[0053] Example 8 The only difference from Example 1 is that in step 2, "adding 60g of ethylene glycol" is replaced with "adding 90g of ethylene glycol". The resulting polyimide is designated A1. The resulting grafted modified polyimide is designated B8. The prepared hollow fiber membrane is designated C8. The resulting crosslinked hollow fiber membrane is designated D8.
[0054] Example 9 The only difference from Example 1 is that in step 2, "adding 60g of ethylene glycol" is replaced with "adding 45g of ethylene glycol". The resulting polyimide is designated A1. The resulting grafted modified polyimide is designated B9. The prepared hollow fiber membrane is designated C9. The resulting crosslinked hollow fiber membrane is designated D9.
[0055] Example 10 The only difference from Example 1 is that in step 4, "preparing a 2% trimesoyl chloride (TMC) hexane solution" is replaced with "preparing a 2% isophthaloyl chloride (IPC) hexane solution". The resulting polyimide is denoted as A1. The resulting grafted modified polyimide is denoted as B1. The prepared hollow fiber membrane is denoted as C1. The resulting crosslinked hollow fiber membrane is denoted as D10.
[0056] Example 11 The only difference from Example 1 is that in step 4, "preparing a 2% trimesoyl chloride (TMC) hexane solution" is replaced with "preparing a 2% adipyl chloride hexane solution". The resulting polyimide is denoted as A1. The resulting grafted modified polyimide is denoted as B1. The prepared hollow fiber membrane is denoted as C1. The resulting crosslinked hollow fiber membrane is denoted as D11.
[0057] Example 12 The only difference from Example 1 is that the phrase "First, nitrogen gas is bubbled into a three-necked flask, phenolphthalein diamine (0.1 mol) and NMP are added, and the mixture is stirred until homogeneous. Then, 6FDA (0.1 mol) is added to the NMP and diamine solution in three batches" is changed to "First, nitrogen gas is bubbled into a three-necked flask, phenolphthalein diamine (0.1 mol), p-phenylenediamine (0.03 mol) and NMP are added, and the mixture is stirred until homogeneous. Then, 6FDA (0.13 mol) is added to the NMP and diamine solution in three batches." The resulting polyimide is designated A12. The resulting grafted modified polyimide is designated B12. The prepared hollow fiber membrane is designated C12. The resulting crosslinked hollow fiber membrane is designated D12.
[0058] Example 13 The only difference from Example 1 is that in step 2, "adding 60g of ethylene glycol" is replaced with "adding 48g of ethylene glycol". The resulting polyimide is denoted as A1. The resulting grafted modified polyimide is denoted as B13. The prepared hollow fiber membrane is denoted as C13. The resulting crosslinked hollow fiber membrane is denoted as D13.
[0059] Comparative Example 1 (too much p-phenylenediamine added) The only difference from Example 1 is that the phrase "First, nitrogen gas is bubbled into a three-necked flask, phenolphthalein diamine (0.1 mol) and NMP are added, and the mixture is stirred until homogeneous. Then, 6FDA (0.1 mol) is added to the NMP and diamine solution in three batches" is changed to "First, nitrogen gas is bubbled into a three-necked flask, phenolphthalein diamine (0.1 mol), p-phenylenediamine (0.04 mol) and NMP are added, and the mixture is stirred until homogeneous. Then, 6FDA (0.14 mol) is added to the NMP and diamine solution in three batches." The resulting polyimide is denoted as E1. The resulting grafted modified polyimide is denoted as F1. The prepared hollow fiber membrane is denoted as G1. The resulting crosslinked hollow fiber membrane is denoted as H1.
[0060] Comparative Example 2 (The alcohol used for modification is not difunctional, but trifunctional). The only difference from Example 1 is that in step 2, "adding 60g of ethylene glycol" is replaced with "adding 60g of glycerol". The resulting polyimide is denoted as E2. The resulting grafted modified polyimide is denoted as F2. The prepared hollow fiber membrane is denoted as G2. The resulting crosslinked hollow fiber membrane is denoted as H2.
[0061] Comparative Example 3 (too little diol was added) The only difference from Example 1 is that in step 2, "adding 60g of ethylene glycol" is replaced with "adding 24g of ethylene glycol". The resulting polyimide is designated E3. The resulting grafted modified polyimide is designated F3. The prepared hollow fiber membrane is designated G3. The resulting crosslinked hollow fiber membrane is designated H3.
[0062] Comparative Example 4 (dehydration did not use azeotropic distillation, i.e., no phenolic hydroxyl groups were used) Step 1: First, nitrogen gas was bubbled into a three-necked flask, and 0.1 mol of phenolphthalein diamine and NMP were added and stirred until homogeneous. Then, 0.1 mol of 6 FDA was added to the NMP and diamine solution in three batches. NMP was added to adjust the solid content to 30 wt%. The reaction temperature was maintained at 0 °C, and the mixture was mechanically stirred for 24 hours (60 r / min) to obtain a polyamic acid solution. Next, 0.3 mol of acid anhydride and 0.4 mol of pyridine were added to the above polyamic acid solution, and the reaction was carried out at room temperature for 20 hours. Finally, the polyimide solution was precipitated in methanol, pulverized, filtered, and dried in an empty oven at 130 °C for 16 hours to obtain polyimide A1.
[0063] Step 3: Use the above-mentioned grafted modified polyimide A1 to prepare hollow fiber membrane C14 according to the above-mentioned method "1. Preparation of hollow fiber membrane".
[0064] Step 4: The two ends of the hollow fiber membrane C1 are sealed with epoxy resin. A 2% trimesoyl chloride (TMC) solution in hexane is prepared. The hollow fiber membrane C1 with both ends sealed is immersed in the solution and reacted for 3 minutes. After being removed, the membrane is dried at room temperature for 12 hours. The sealing resin at both ends is then cut off to obtain the crosslinked hollow fiber membrane D14 (i.e., the only difference from Example 1 is that step 2 is omitted).
[0065] The performance test results of the cross-linked hollow fiber membranes prepared in the examples and comparative examples are shown in Table 1.
[0066] Table 1. Performance test results of crosslinked hollow fiber membranes prepared in the examples and comparative examples.
[0067] As can be seen from Table 1, the polyimide hollow fiber membranes crosslinked with acyl chloride all exhibit high CO2 flux and high CO2 / CH4 selectivity. The plasticizing pressure resistance of the examples is 45-68 bar, ensuring that they will not be plasticized by high-pressure CO2 in applications such as natural gas decarbonization, flue gas decarbonization, and associated gas decarbonization.
[0068] As can be seen from Examples 1, 12 and Comparative Example 1, when the content of p-phenylenediamine in the diamine increases, the flux of the cross-linked hollow fiber membrane decreases significantly, indicating that AHPBA can effectively ensure high flux.
[0069] In Comparative Example 2, a trifunctional alcohol was used instead of a difunctional alcohol during the grafting modification process. Although the amount of alcohol added was excessive, the trifunctional alcohol inevitably introduced cross-linking structures, which negatively affected the throughput.
[0070] In Comparative Example 3, the amount of alcohol added during the grafting modification process was relatively small. This resulted in insufficient grafting and partial cross-linking of the carboxyl groups through the diol. Consequently, the spinning processability decreased, the CO2 / CH4 selectivity was low, and the plasticizing resistance was reduced.
[0071] Comparative Example 4 used chemical imidization instead of azeotropic distillation in the dehydration process of polyamic acid. Chemical imidization reacts the phenolic hydroxyl groups to ester groups. In the subsequent crosslinking process of the hollow fiber membrane, the phenolic hydroxyl groups cannot react, and crosslinking only occurs at the flexible hydroxyl reaction sites. Therefore, the selectivity of this sample is not ideal.
[0072] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.
Claims
1. A method for preparing a cross-linked hollow fiber membrane, characterized in that, Includes the following steps: Step 1: Prepare polyamic acid by mixing diamine monomer and dianhydride monomer, and then dehydrate to prepare polyimide; Step 2: The polyimide is grafted with diol to obtain grafted modified polyimide; Step 3: The grafted modified polyimide is made into a hollow fiber membrane; Step 4: Immerse the hollow fiber membrane in an acyl chloride solution to carry out an interfacial crosslinking reaction to obtain the crosslinked hollow fiber membrane.
2. The preparation method according to claim 1, characterized in that, In step 1, the diamine monomer includes phenolphthalein diamine; the dianhydride monomer includes 6FDA; and the molar ratio of the diamine monomer to the dianhydride monomer is 1:
1.
3. The preparation method according to claim 1, characterized in that, In step 1, the dehydration is carried out by azeotropic distillation.
4. The preparation method according to claim 1, characterized in that, In step 2, the diol is ethylene glycol, propylene glycol, or 1,4-butanediol.
5. The preparation method according to claim 1, characterized in that, In step 2, the amount of the diol used is 150-300 wt% of the mass of the polyimide.
6. The preparation method according to claim 1, characterized in that, In step 2, the grafting modification temperature is 140-190℃ and the time is 1-4h.
7. The preparation method according to claim 1, characterized in that, In step 4, the acyl chloride in the acyl chloride solution is at least one of pyromellitic acyl chloride, isophthalic acyl chloride, phthalic acyl chloride, or adipoxy acyl chloride; the solvent of the acyl chloride solution is n-hexane.
8. The preparation method according to claim 1, characterized in that, In step 4, the concentration of the acyl chloride solution is 1~5wt%, and the interfacial crosslinking reaction time is 0.5~5min.
9. A cross-linked hollow fiber membrane prepared by the preparation method according to any one of claims 1 to 8.
10. The application of the cross-linked hollow fiber membrane as described in claim 9 in gas separation.