Crosslinked thermally rearranged polybenzoxazole hollow fiber gas separation membranes, and methods of making and using the same

Abstract

The application provides a crosslinked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane and a preparation method and application thereof, and belongs to the technical field of polymer membrane separation. In the synthesis of the polymer, a phenolphthalein-based diamine monomer with a lactone ring is introduced, so that the phenolphthalein-based diamine monomer is polycondensed with a dianhydride to form a polyimide, and then the polyimide is prepared into a hollow fiber membrane precursor, and then crosslinking is performed at a lower temperature, and then the temperature is further increased to prepare a thermal rearrangement hollow fiber membrane. At this time, the polymer chains are crosslinked, the flowability is hindered, the thickening degree of the skin layer is greatly reduced, and the plasticization resistance is also improved.

Description

Technical Field

[0001] This invention relates to the field of polymer membrane separation technology, and in particular to a cross-linked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane, its preparation method, and its application. Background Technology

[0002] In recent years, with the rapid development of industry worldwide, the demand for energy has been increasing. To date, the energy used on a large scale in industry still primarily comes from traditional fossil fuels. The combustion of these fuels releases large amounts of carbon dioxide, gradually altering the global climate due to the greenhouse effect. Global warming continues, and reducing the amount of carbon dioxide in the atmosphere is one of the most significant challenges facing humanity today.

[0003] Although natural gas is also a fossil fuel, it emits significantly less carbon dioxide than coal and oil when burning the same amount of heat. Therefore, using natural gas is currently one of the important means of effectively controlling carbon dioxide emissions. However, during the extraction process, raw natural gas often contains high concentrations of carbon dioxide. This not only reduces the calorific value of the natural gas but also causes pipeline corrosion and increases transportation costs during transport. Therefore, it is necessary to separate and purify raw natural gas.

[0004] Compared to traditional separation technologies such as chemisorption and pressure swing adsorption, membrane separation technology offers advantages such as high efficiency, low energy consumption, low cost, and strong environmental sustainability. Common membrane types include flat-sheet membranes, spiral-wound membranes, and hollow fiber membranes, among which hollow fiber membranes have attracted widespread attention due to their high packing density and ease of large-scale integration. However, when used for natural gas separation, the membrane often becomes plasticized due to the action of highly condensable gases such as carbon dioxide and heavy hydrocarbons. Plasticization refers to the swelling of the polymer matrix as the upstream gas pressure increases, leading to increased molecular chain mobility and a rapid increase in the flux of the gas separation membrane, while the selectivity decreases sharply.

[0005] Thermal rearrangement polymers are polymers with heterocyclic structures formed by the reaction of the imine ring and its adjacent functional groups in polyimide. Common thermal rearrangement polymers include polybenzimidazole (PBI), polybenzoxazole (PBO), and polybenzothiazole (PBT). These polymers have rigid molecular chains, good thermal stability, and are microporous materials with high free volume fractions. However, these polymers are difficult to synthesize directly. High-temperature heat treatment to transform polyimide with adjacent functional groups is a relatively simple method. Membranes prepared by thermal rearrangement reactions exhibit high permeability and appropriate selectivity. If interchain thermal rearrangement occurs, a network structure can be formed, improving the membrane's resistance to swelling.

[0006] For asymmetric membrane precursors, during the thermal rearrangement membrane fabrication process at high temperatures, the porous sublayer collapses, causing skin thickening, which reduces membrane flux. Therefore, suppressing skin thickening during heat treatment is a pressing issue that needs to be addressed. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a cross-linked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane, its preparation method and application.

[0008] To minimize skin thickening during heat treatment, this invention introduces a phenolphthalein-based diamine monomer with a lactone ring into the polymer synthesis process, causing it to condense with dianhydride to form polyimide. The presence of the lactone ring not only improves the polymer's solubility but also allows it to degrade and generate free radicals during lower-temperature heat treatment, leading to cross-linking reactions between polymer chains. Utilizing this property of the lactone ring, the phenolphthalein-based polyimide is prepared as a hollow fiber membrane precursor, then cross-linked at a lower temperature, and further heated to prepare a thermally rearranged hollow fiber membrane. At this point, because the polymer chains are already cross-linked, their flowability is hindered, significantly reducing skin thickening and improving their resistance to plasticization.

[0009] To achieve the above objectives, the present invention provides the following technical solution: a cross-linked thermally rearranged polybenzoxazole hollow fiber gas separation membrane, having the structure shown in Formula I:

[0010]

[0011] Where m represents the mole fraction of 6FDA-DAP repeating units in a molecular chain, n represents the mole fraction of 6FDA-DAP repeating units in the same molecular chain, m1 and m2 represent the mole fraction of 6FDA-DAP repeating units in different molecular chains, and satisfy 0.1≤m≤0.9, 0.1≤n≤0.9, 0.1≤m1≤0.9, 0.1≤m2≤0.9, and m+n=1.

[0012] Preferably, the pore structure of the cross-linked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane consists of a dense skin layer and a porous sublayer; the skin layer has a thickness of 1-50000 nm, an inner diameter of 0.05 mm-0.5 mm, and an outer diameter of 0.1 mm-1 mm.

[0013] This invention also provides a method for preparing the crosslinked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane described in the above technical solution, comprising the following steps:

[0014] Step 1. Prepare the polyimide precursor casting solution;

[0015] Step 2. The precursor casting solution is spun by dry-jet wet spinning to prepare a polyimide hollow fiber membrane precursor containing acetate groups or hydroxyl groups at the ortho-position;

[0016] Step 3. The polyimide hollow fiber membrane precursor containing acetate or hydroxyl groups at the ortho position is subjected to heat treatment to obtain the crosslinked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane.

[0017] Preferably, the polyimide is obtained by polymerization of a dianhydride monomer and a diamine monomer; the dianhydride monomer is 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane; and the diamine monomer is 2,4,6-trimethyl-1,3-phenylenediamine and 3,3'-diaminophenolphthalein.

[0018] More preferably, the molar ratio of the diamine monomer to the dianhydride monomer is 1:1; in the diamine monomer, the proportion of 3,3'-diaminophenolphthalein in the total molar ratio of 2,4,6-trimethyl-1,3-phenylenediamine and 3,3'-diaminophenolphthalein diamine is 0 to 100 mol% and not 0; the proportion of 2,4,6-trimethyl-1,3-phenylenediamine in the total molar ratio of 2,4,6-trimethyl-1,3-phenylenediamine and 3,3'-diaminophenolphthalein diamine is 100 to 0 mol% and not 100 mol.

[0019] Preferably, the polyimide is prepared by a chemical imidization method or a one-step method.

[0020] Preferably, the precursor casting solution is obtained by uniformly mixing the polyimide with N-methylpyrrolidone, tetrahydrofuran, and ethanol; the mass fraction of polyimide in the casting solution precursor is 15-40%.

[0021] Preferably, the spinning process parameters for spinning the precursor casting solution by dry-jet wet spinning are: casting solution temperature of room temperature to 50°C, spinneret temperature of room temperature to 100°C, and air gap of 5 to 30 cm.

[0022] Preferably, the heat treatment involves raising the temperature from room temperature to 250-400°C for thermal crosslinking for 0.1-3 hours, and then further raising the temperature to 400-500°C and holding it for 0.1-3 hours to carry out a thermal rearrangement reaction.

[0023] Preferably, the heating rate during the heating process is 3-10℃ / min.

[0024] The present invention also provides the application of the cross-linked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane in gas separation.

[0025] Beneficial technical effects:

[0026] 1. This invention prepares a cross-linked thermally rearranged polybenzoxazole hollow fiber gas separation membrane by heat-treating polyimide with excellent film-forming properties. This solves the problem that polybenzoxazole is difficult to dissolve in common solvents and is difficult to prepare. The heat treatment process is simple and easy to operate.

[0027] 2. The cross-linked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane prepared by this invention has a cross-linked network structure, exhibiting high selectivity for CO2 / CH4, CO2 / N2, and O2 / N2, and excellent resistance to plasticization. It can operate stably in pure CO2 at a pressure of 30 atmospheres. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 The images shown are magnified partial skin layers of the cross-linked thermal rearrangement polybenzoxazole hollow fiber gas separation membranes obtained in Examples 1-4, where (a) is a magnified partial skin layer of Example 1, (b) is a magnified partial skin layer of Example 2, (c) is a magnified partial skin layer of Example 3, and (d) is a magnified partial skin layer of Example 4.

[0030] Figure 2 This is a magnified view of a local skin layer of the cross-linked thermally rearranged polybenzoxazole hollow fiber gas separation membrane obtained in Comparative Example 2.

[0031] Figure 3 The images show the overall morphology of the hollow fiber gas separation membrane obtained in Comparative Example 1 and a magnified view of a local cortex, where (a) is the overall morphology image and (b) is a magnified view of a local cortex.

[0032] Figure 4 The infrared spectrum of the cross-linked thermally rearranged polybenzoxazole hollow fiber gas separation membrane obtained in Example 1;

[0033] Figure 5 The diagrams show the anti-plasticization performance of the hollow fiber gas separation membranes in Example 3 and Comparative Examples 1 and 2, where (a) is the anti-plasticization performance diagram of Comparative Example 1, (b) is the anti-plasticization performance diagram of Comparative Example 2, and (c) is the anti-plasticization performance diagram of Example 3. Detailed Implementation

[0034] 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.

[0035] 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 within the scope of this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0036] 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 or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0037] 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 obvious to those skilled in the art. This specification and embodiments are merely exemplary.

[0038] 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.

[0039] This invention provides a cross-linked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane, having the structure shown in Formula I:

[0040]

[0041] Where m represents the mole fraction of 6FDA-DAP repeating units in a molecular chain, n represents the mole fraction of 6FDA-DAP repeating units in the same molecular chain, m1 and m2 represent the mole fraction of 6FDA-DAP repeating units in different molecular chains, and satisfy 0.1≤m≤0.9, 0.1≤n≤0.9, 0.1≤m1≤0.9, 0.1≤m2≤0.9, and m+n=1.

[0042] In some embodiments, the pore structure of the crosslinked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane consists of a dense skin layer and a porous sublayer; the thickness of the dense skin layer is preferably 1-50000 nm, more preferably 1-500 nm, the inner diameter is preferably 0.05 mm-0.5 mm, more preferably 0.1-0.2 mm, and the outer diameter is preferably 0.1 mm-1 mm, more preferably 0.2-0.4 mm.

[0043] The crosslinked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane provided by this invention has an asymmetric structure with a dense skin layer and a porous sublayer. It is synthesized by chemical imidization or a one-step method using 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) as the dianhydride monomer and 2,4,6-trimethyl-1,3-phenylenediamine (DAM) and 3,3'-diaminophenolphthalein (DAP) as diamine monomers. The synthesized polyimide is then used to prepare a hollow fiber membrane precursor, which is then heat-treated at high temperature.

[0044] Specifically, the following steps are included:

[0045] Step 1. Prepare the polyimide precursor casting solution;

[0046] Step 2. The precursor casting solution is spun by dry-jet wet spinning to prepare a polyimide hollow fiber membrane precursor containing acetate groups or hydroxyl groups at the ortho-position;

[0047] Step 3. The polyimide hollow fiber membrane precursor containing acetate or hydroxyl groups at the ortho position is subjected to heat treatment to obtain the crosslinked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane.

[0048] In this invention, polyimide is first prepared as a precursor casting solution.

[0049] In some embodiments, the polyimide is obtained by polymerization of a dianhydride monomer and a diamine monomer; the dianhydride monomer is 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane; and the diamine monomer is 2,4,6-trimethyl-1,3-phenylenediamine and 3,3'-diaminophenolphthalein. In this invention, the introduction of 2,4,6-trimethyl-1,3-phenylenediamine can, on the one hand, increase the molecular weight of the obtained polyimide, avoiding the problem of difficulty in spinning due to low viscosity of the casting solution during the subsequent preparation of hollow fiber membranes; on the other hand, it can also improve the flux of the hollow fiber membrane.

[0050] In some embodiments, the molar ratio of the diamine monomer to the dianhydride monomer is 1:1; in the diamine monomer, the proportion of 3,3'-diaminophenolphthalein in the total molar ratio of 2,4,6-trimethyl-1,3-phenylenediamine and 3,3'-diaminophenolphthalein diamine is 0 to 100 mol% and not 0, preferably 30 to 70 mol%, more preferably 50 to 70 mol%; the proportion of 2,4,6-trimethyl-1,3-phenylenediamine in the total molar ratio of 2,4,6-trimethyl-1,3-phenylenediamine and 3,3'-diaminophenolphthalein diamine is 100 to 0 mol% and not 100 mol%, preferably 70 to 30 mol%, more preferably 50 to 30 mol%.

[0051] In some embodiments, the weight-average molecular weight of the polyimide is preferably 10,000 to 2,000,000, more preferably 100,000 to 1,000,000.

[0052] In some embodiments, the polyimide is prepared by a chemical imidization method or a one-step method.

[0053] In other embodiments, when the polyimide is prepared by a chemical imidization method, the following steps are included:

[0054] (1) Under 0℃ conditions, first purge with N2 for about 15 minutes, then dissolve the diamine monomers 2,4,6-trimethyl-1,3-phenylenediamine (DAM) and 3,3'-diaminophenolphthalein (DAP) and the dianhydride monomer hexafluoropropane dianhydride (6FDA) in N-methylpyrrolidone (NMP). The molar ratio of the monomers is diamine monomer: dianhydride monomer = 1:1, and the solid content of the solution is 15-30wt%. Place it in an ice-water mixture and stir to dissolve for 2-24 hours.

[0055] (2) Chemical imidization was carried out using acetic anhydride as a dehydrating agent and pyridine as a catalyst for 2 to 24 hours. The resulting product was precipitated in methanol, filtered, and dried under vacuum at 50 to 250°C to obtain a polyimide polymer. The molar ratio of acetic anhydride to diamine monomer was 5:1, and the molar ratio of pyridine to diamine monomer was 2.5:1.

[0056] In other embodiments, when the polyimide is prepared by a one-step method, it includes the following steps:

[0057] Under nitrogen protection, 3,3'-diaminophenolphthalein (DAP), 2,4,6-trimethyl-1,3-phenylenediamine (DAM), and 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) were dissolved in m-cresol, and isoquinoline was added as a catalyst. The mixture was stirred at 180-220°C for 4-8 hours. The resulting polymer solution was precipitated in methanol, filtered, and then dried. The ratio of diamine to dianhydride was the same as in the chemical imidization method.

[0058] In some embodiments, the precursor casting solution is obtained by uniformly mixing the polyimide with N-methylpyrrolidone, tetrahydrofuran, and ethanol; the mass fraction of polyimide in the casting solution precursor is 15-40%.

[0059] In this invention, after obtaining the precursor casting solution, the precursor casting solution is spun using a dry-jet wet spinning method to prepare a polyimide hollow fiber membrane precursor containing acetate groups or hydroxyl groups at the ortho-position. The structural formula of the polyimide hollow fiber membrane precursor containing acetate groups or hydroxyl groups at the ortho-position is as follows:

[0060]

[0061] Where m and n represent the mole fractions of the corresponding repeating units, and satisfy 0.1≤m≤0.9, 0.1≤n≤0.9, and m+n=1;

[0062] R represents an acetate group (-OOCCH3) or a hydroxyl group (-OH). If polyimide is synthesized by chemical imidization, then R is -OOCCH3. If polyimide is synthesized by a one-step method, then R is -OH.

[0063] In some embodiments, the spinning process parameters for spinning the precursor casting solution by dry-jet wet spinning are as follows: the casting solution temperature is room temperature to 50°C, the spinneret temperature is room temperature to 100°C, and the air gap is 5 to 30 cm. A nascent fiber membrane is formed under the combined action of the external coagulation bath and the core solution. The external coagulation bath and the core solution can be one or a mixture of two or more of alcohol, water, N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

[0064] After obtaining the nascent fibrous membrane, the present invention further includes solvent exchange and drying steps; the solvent exchange involves soaking the nascent fibrous membrane in running water, methanol, and n-hexane to remove residual solvent. The present invention does not have special requirements for the drying method; methods well known to those skilled in the art can be used.

[0065] In this invention, after obtaining the polyimide hollow fiber membrane precursor, the polyimide hollow fiber membrane precursor containing acetate groups or hydroxyl groups at the ortho position is subjected to heat treatment to obtain the crosslinked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane.

[0066] In some embodiments, the heat treatment involves raising the temperature from room temperature to 250-400°C for thermal crosslinking for 0.1-3 hours, followed by further raising the temperature to 400-500°C and holding it for 0.1-3 hours to perform a thermal rearrangement reaction; the atmosphere during the heat treatment is nitrogen, helium, or argon. This invention first crosslinks the hollow fiber membrane at a lower temperature, increasing the glass transition temperature of the polymer and reducing the migration rate of the molecular chains. This significantly reduces the degree of skin collapse during the thermal rearrangement reaction at higher temperatures.

[0067] In some embodiments, the heating rate during the heating process is preferably 3-10°C / min.

[0068] This invention also provides the application of the cross-linked thermally rearranged polybenzoxazole hollow fiber gas separation membrane in gas separation. The cross-linked thermally rearranged polybenzoxazole hollow fiber gas separation membrane provided by this invention exhibits high CO2 / CH4, CO2 / N2, and O2 / N2 selectivity, high throughput, excellent thermal stability, and anti-plasticization properties, and can be used in fields such as carbon dioxide removal from natural gas and flue gas, as well as air separation.

[0069] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0070] Example 1

[0071] (1) Under 0℃ conditions, first purge under N2 atmosphere for about 15 minutes, then dissolve 36.05g of 2,4,6-trimethyl-1,3-phenylenediamine (DAM) and 41.76g of 3,3'-diaminophenolphthalein (DAP) (molar ratio of DAM to DAP 2:1) in 713.22g of N-methylpyrrolidone (NMP), place in an ice-water mixture and stir to dissolve. After dissolution, add 159.93g of hexafluoropropane dianhydride (6FDA) and continue stirring to dissolve.

[0072] (2) Stir the solution at room temperature for 24 hours to form a viscous polyamic acid solution; then add 183.76g acetic anhydride and 71.19g pyridine for imidization. After reacting at room temperature for 24 hours, allow the polymer to precipitate in methanol. After washing with methanol for 24 hours, place it in a vacuum oven at 100-250℃ and dry for 48 hours.

[0073] (3) The dried polyimide was mixed evenly with tetrahydrofuran, N-methylpyrrolidone and anhydrous ethanol at room temperature. After stirring for 8 hours, a precursor casting liquid with a polyimide content of 30wt.% was obtained. After ultrasonic degassing, it was poured into a liquid tank and degassed for another 12 hours.

[0074] (4) The precursor casting solution was spun by dry-jet wet spinning. Nitrogen gas at a pressure of 0.3 MPa was introduced into the feed tank. The feed temperature was 50 °C, the air gap was 7 cm, the core liquid flow rate was 1 ml / min, the feed liquid flow rate was 3 ml / min, the core liquid was a mixture of water and N-methylpyrrolidone (15 / 85 wt.%), the external coagulation was water at 50 °C, and the take-up speed was set to 50 m / min. The spun hollow fiber membrane was soaked in water for 24 hours, then transferred to methanol for 30 min, and repeated 3 times. It was then transferred to n-hexane for 30 min, and repeated 3 times. Finally, it was dried under vacuum at 120 °C to obtain a polyimide hollow fiber membrane precursor containing acetate groups at the ortho position.

[0075] (5) After placing the polyimide hollow fiber membrane precursor containing acetate groups at the ortho position into a tube furnace, nitrogen gas is introduced to purge the air in the furnace for 15 minutes at a flow rate of 400 ml / min. Under this atmosphere, the temperature is heated to 350°C at a heating rate of 5°C / min and held for 1 hour. The temperature is then increased to 450°C and held for 30 minutes. After the tube furnace cools down naturally, a cross-linked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane is obtained.

[0076] The infrared spectra of the obtained polyimide hollow fiber membrane precursor and the cross-linked thermally rearranged polybenzoxazole hollow fiber gas separation membrane are shown in the figure. Figure 4 As shown, 1558cm -1 1484cm -1 The absorption peak at that point is a characteristic absorption peak of the polybenzoxazole structure, which confirms its structure.

[0077] Example 2

[0078] (1) Weigh 36.05g of 2,4,6-trimethyl-1,3-phenylenediamine (DAM), 41.76g of 3,3'-diaminophenolphthalein (DAP), 159.93g of hexafluoropropane dianhydride (6FDA), 1343.58g of m-cresol, and 12ml of isoquinoline, add them to a three-necked flask, and stir and react at 190℃ for 8h in N2 atmosphere to obtain a high-viscosity polyimide solution. Pour the solution into methanol to allow the polymer to settle, wash with methanol for 24 hours, and then dry in a vacuum oven at 100-250℃ for 48 hours.

[0079] (2) The dried polyimide was mixed evenly with tetrahydrofuran, N-methylpyrrolidone and anhydrous ethanol at room temperature. After stirring for 8 hours, a precursor casting solution with a polyimide content of 30wt.% was obtained. After ultrasonic degassing, it was poured into a material tank and degassed for another 12 hours.

[0080] (3) The precursor casting solution was spun by dry-jet wet spinning. Nitrogen gas at a pressure of 0.3 MPa was introduced into the feed tank. The feed temperature was 50°C, the air gap was 7 cm, the core liquid flow rate was 1 ml / min, the feed liquid flow rate was 3 ml / min, the core liquid was a mixture of water and N-methylpyrrolidone (15 / 85 wt.%), the external coagulation was water at 50°C, and the take-up speed was set to 50 m / min. The spun hollow fiber membrane was soaked in water for 24 hours, then transferred to methanol for 30 min, repeated 3 times, then transferred to n-hexane for 30 min, repeated 3 times, and finally dried under vacuum at 120°C to obtain a polyimide hollow fiber membrane precursor containing hydroxyl groups at the ortho-position.

[0081] (4) After placing the polyimide hollow fiber membrane precursor containing hydroxyl groups at the ortho position into the tube furnace, nitrogen gas is introduced to purge the air in the furnace for 15 minutes at a flow rate of 400 ml / min. Under this atmosphere, the temperature is heated to 350°C at a heating rate of 5°C / min and held for 1 hour. The temperature is then increased to 450°C and held for 30 minutes. After the tube furnace cools down naturally, the cross-linked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane is obtained.

[0082] Example 3

[0083] (1) Same as step (1) in Example 1.

[0084] (2) Same as step (2) in Example 1.

[0085] (3) Same as step (3) in Example 1.

[0086] (4) Same as step (4) in Example 1.

[0087] (5) After placing the polyimide hollow fiber membrane precursor containing acetate groups at the ortho position into a tube furnace, nitrogen gas was purged for 15 min to remove air from the furnace at a flow rate of 400 ml / min. Under this atmosphere, the temperature was heated to 350°C at a heating rate of 5°C / min and held for 1 h. Then, the temperature was further increased to 475°C and held for 30 min. After the tube furnace cooled naturally, the crosslinked thermally rearranged polybenzoxazole hollow fiber gas separation membrane was obtained.

[0088] Example 4

[0089] (1) Same as step (1) in Example 1, except that the molar ratio of DAM and DAP is 1:1.

[0090] (2) Same as step (2) in Example 1.

[0091] (3) Same as step (3) in Example 1.

[0092] (4) Same as step (4) in Example 1.

[0093] (5) Same as step (5) in Example 1.

[0094] Comparative Example 1

[0095] Same as Example 1, except that step (5) of heat treatment of the polyimide hollow fiber membrane precursor containing acetate or hydroxyl groups at the adjacent position is omitted.

[0096] Comparative Example 2

[0097] (1) Same as step (1) in Example 1.

[0098] (2) Same as step (2) in Example 1.

[0099] (3) Same as step (3) in Example 1.

[0100] (4) Same as step (4) in Example 1.

[0101] (5) After placing the hollow fiber membrane into the tubular furnace, nitrogen gas is purged for 15 minutes to remove air from the furnace at a flow rate of 400 ml / min. Under this atmosphere, the temperature is directly heated to 475°C at a heating rate of 5°C / min and held for 30 minutes. After the tubular furnace cools naturally, the cross-linked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane is obtained.

[0102] The inner and outer diameters of the hollow fiber gas separation membranes prepared in Examples 1-4 and Comparative Examples 1-2 were measured using an optical microscope. Specific data are shown in Table 1.

[0103] Table 1. Comparison of inner and outer diameters of hollow fiber gas separation membranes prepared in the examples and comparative examples (unit: μm)

[0104]

[0105]

[0106] Electron micrographs of the precursor fibers and cross-linked thermally rearranged hollow fiber membranes obtained in the examples and comparative examples are shown below. Figure 1-3 As shown, the membrane cross-section has a fully sponge-like structure without finger-like pores. In Comparative Example 1, the original membrane skin thickness is within 1 μm. Observation of the hollow fiber cross-section after heat treatment reveals that the final skin thickness of the hollow fiber membranes of Examples 1, 2, 3, and 4, which underwent low-temperature pre-crosslinking, is between 1 and 2 μm, showing no significant increase compared to the original membrane (Comparative Example 1). However, the skin of Comparative Example 2, which did not undergo low-temperature crosslinking, shows a significant increase compared to the original membrane (Comparative Example 1), with a thickness of approximately 5 μm.

[0107] The pure gas separation performance of the crosslinked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane and polyimide hollow fiber membrane precursors obtained in the examples and comparative examples is shown in Table 2. The test pressure was 0.5 MPa and the test temperature was 35 °C.

[0108] Table 2 Comparison of pure gas separation performance of hollow fiber membranes in the examples and comparative examples

[0109]

[0110] The data in the table show that the membrane layer after low-temperature pre-crosslinking is thinner (Examples 1-4), resulting in higher flux. Examples 1 and 4 show that flux decreases with decreasing DAM content in the molecular structure. Examples 1 and 3 show that flux gradually increases with increasing thermal rearrangement temperature.

[0111] The anti-plasticization properties of the crosslinked thermal rearrangement polybenzoxazole hollow fiber membrane and polyimide hollow fiber membrane precursors obtained in Examples 3, 2, and 1 are as follows: Figure 5 As shown, the fiber membrane precursor was plasticized at a pressure of approximately 200 psi. The heat-treated hollow fiber membranes exhibited improved resistance to plasticization compared to the precursor fibers. In Example 3, the cross-linked thermal rearrangement hollow fiber membrane did not plasticize at a pressure of 450 psi. However, the hollow fiber membrane obtained in Comparative Example 2, which did not undergo low-temperature pre-crosslinking, showed increased CO2 permeability with increasing pressure after reaching 350 psi, indicating plasticization.

[0112] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A cross-linked thermally rearranged polybenzoxazole hollow fiber gas separation membrane, characterized in that, It has the structure shown in Equation I: Formula I; Where m represents the mole fraction of 6FDA-DAP repeating units in a molecular chain, n represents the mole fraction of 6FDA-DAP repeating units in the same molecular chain, m1 and m2 represent the mole fraction of 6FDA-DAP repeating units in different molecular chains, and satisfy 0.1≤m≤0.9, 0.1≤n≤0.9, 0.1≤m1≤0.9, 0.1≤m2≤0.9, and m+n=1; The cross-linked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane has a pore structure consisting of a dense skin layer and a porous sublayer; the skin layer has a thickness of 1-50000 nm, an inner diameter of 0.05 mm-0.5 mm, and an outer diameter of 0.1 mm-1 mm. The crosslinked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane is prepared by chemical imidization or a one-step method to synthesize polyimide polymers using 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride as the dianhydride monomer, 2,4,6-trimethyl-1,3-phenylenediamine and 3,3'-diaminophenolphthalein as diamine monomers. The synthesized polyimide is then used to prepare a hollow fiber membrane precursor, which is then heat-treated at high temperature.

2. The method for preparing the crosslinked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane according to claim 1, characterized in that, Includes the following steps: Step 1. Prepare the polyimide precursor casting solution; Step 2. The precursor casting solution is spun by dry-jet wet spinning to prepare a polyimide hollow fiber membrane precursor containing acetate groups or hydroxyl groups at the ortho-position; Step 3. The polyimide hollow fiber membrane precursor containing acetate or hydroxyl groups at the ortho position is subjected to heat treatment to obtain the crosslinked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane.

3. The preparation method according to claim 2, characterized in that, The polyimide is obtained by polymerization of dianhydride monomer and diamine monomer; the dianhydride monomer is 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane; the diamine monomer is 2,4,6-trimethyl-1,3-phenylenediamine and 3,3'-diaminophenolphthalein.

4. The preparation method according to claim 3, characterized in that, The molar ratio of the diamine monomer to the dianhydride monomer is 1:1; in the diamine monomer, the proportion of 3,3'-diaminophenolphthalein in the total molar ratio of 2,4,6-trimethyl-1,3-phenylenediamine and 3,3'-diaminophenolphthalein diamine is 0 to 100 mol% and is not 0; the proportion of 2,4,6-trimethyl-1,3-phenylenediamine in the total molar ratio of 2,4,6-trimethyl-1,3-phenylenediamine and 3,3'-diaminophenolphthalein diamine is 100 to 0 mol% and is not 100 mol.

5. The preparation method according to claim 2, characterized in that, The polyimide is prepared by a chemical imidization method or a one-step method.

6. The preparation method according to claim 2, characterized in that, The spinning process parameters for spinning the precursor casting solution by dry-jet wet spinning are as follows: casting solution temperature is room temperature to 50°C, spinneret temperature is room temperature to 100°C, and air gap is 5 to 30 cm.

7. The preparation method according to claim 2, characterized in that, The heat treatment involves raising the temperature from room temperature to 250-400℃ for thermal cross-linking for 0.1-3 hours, and then further raising the temperature to 400-500℃ and maintaining it for 0.1-3 hours to carry out a thermal rearrangement reaction.

8. The preparation method according to claim 7, characterized in that, The heating rate during the temperature increase is 3-10℃ / min.

9. The application of the cross-linked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane according to claim 1 in gas separation.

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