High-selectivity gas separation membrane based on micromolecule in-situ thermal crosslinking and preparation method of high-selectivity gas separation membrane

Abstract

The invention discloses a high-selectivity gas separation membrane based on micromolecule in-situ thermal crosslinking and a preparation method of the high-selectivity gas separation membrane, and belongs to the technical field of polymer functional materials and membrane separation. The gas separation membrane is formed by a linear polymer containing a Base structural unit and a micromolecular bifunctional or polyfunctional halogenated cross-linking agent through a thermally induced in-situ cross-linking reaction, and cross-linking agent molecules can be uniformly dispersed in a linear polymer matrix on the molecular scale. Carrying out heat treatment in an inert atmosphere to form a compact covalent network structure and sub-micropore aperture distribution; the free volume and the microporous structure of the gas separation membrane can be precisely regulated and controlled by regulating and controlling the crosslinking temperature, the crosslinking time and the dosage of the crosslinking agent, so that the molecular sieving effect on gas is improved, and the gas separation membrane shows excellent permeability and selectivity in separation systems such as H2 / N2, H2 / CH4, O2 / N2, CO2 / CH2 and the like, and has good plasticizing resistance and aging resistance.

Description

Technical Field

[0001] This invention belongs to the field of polymer functional materials and membrane separation technology, specifically relating to a highly selective gas separation membrane based on in-situ thermal crosslinking of small molecules and its preparation method. Background Technology

[0002] The efficient separation and purification of industrial gases, fine chemicals, and water is of great significance in the energy and environmental fields, involving key scenarios such as natural gas decarbonization, carbon capture and storage (CCS), high-purity hydrogen production, and air separation oxygen production. With the advancement of global carbon neutrality goals, the energy consumption of related separation processes is expected to double by 2050. Compared with traditional separation methods, membrane gas separation technology has advantages such as low energy consumption, simple operation, compact equipment, and ease of scalability, showing promising development prospects in hydrogen purification, oxygen enrichment, nitrogen enrichment, and carbon dioxide capture. However, existing polymer membrane materials still face two major bottlenecks.

[0003] First, traditional polymer membranes, such as those made of polyimide and polysulfone, are limited by the balance between permeability and selectivity. Their random pore structure, formed by the stacking of polymer segments, limits their gas molecule sieving capacity. According to Robeson's upper limit, gas permeability and selectivity are negatively correlated, making it difficult to simultaneously achieve high-flux and high-purity separation. Second, long-term operational stability is insufficient. Membrane materials are prone to plasticization under high pressure or in environments containing plasticizing gases (such as CO2), leading to increased free volume and decreased selectivity. Simultaneously, physical aging causes slow relaxation of polymer segments, collapse of the microporous structure, and a significant decrease in permeability over time, resulting in membrane performance degradation and severely restricting the industrial lifespan and economic viability of the membrane.

[0004] To address the aforementioned bottlenecks, crosslinking modification is considered an effective strategy. It can introduce covalent bonds to suppress chain segment movement and stabilize the pore structure, thereby improving the thermodynamic stability and separation performance of the membrane. Existing crosslinking methods include photocrosslinking and thermal crosslinking, each with its own advantages. However, they generally suffer from problems such as demanding reaction conditions, uneven membrane structure, or complex processes, making it difficult to simultaneously achieve performance improvement and industrial operability. Photocrosslinking methods have fast reaction rates, but limited ultraviolet penetration depth, easily leading to uneven crosslinking along the membrane thickness direction. Thermal crosslinking methods require high temperatures or specific functional groups, which may trigger side reactions or damage the inherent micropores of the polymer. Chemical crosslinking agents often use macromolecular crosslinking agents, which are prone to local aggregation due to uneven dispersion, reducing membrane uniformity.

[0005] Base (TB) polymers, as a novel type of self-porous polymer, exhibit excellent gas permeability due to their rigid tortuous skeleton and high free volume characteristics. The base exhibits relatively stable properties under high temperature, high pressure, and acidic conditions. Its NN-bridged structure can promote the bonding between phosphoric acid and the polymer, enhancing the selectivity for hydrogen / carbon dioxide, thus resulting in a highly efficient separation membrane material. However, its inherent defects hinder its practical application. First, the high molecular chain mobility and the tendency of flexible segments to undergo conformational changes lead to dynamic fluctuations in the pores, reducing sieving accuracy. Second, its weak resistance to plasticization means that highly adsorbent gases such as CO2 easily swell the polymer network, accelerating performance degradation. Furthermore, significant physical aging occurs; the high free volume structure tends towards thermodynamic steady state, micropores continuously shrink, and permeability decreases rapidly.

[0006] For example, Chinese patent publication number CN112275146A, filed on September 1, 2020, discloses a phosphoric acid-treated... Base polymer gas separation membrane, its preparation method and application, firstly utilizing... The rigid framework structure of the base is used to obtain a large free volume, thereby increasing the efficiency of gas transport. After phosphoric acid treatment, the interaction between nitrogen and phosphoric acid in the main chain is utilized to maintain the stability of phosphoric acid in the polymer and improve the selectivity of hydrogen for carbon dioxide. The selectivity can be adjusted by changing the acid treatment conditions of the polymer. However, this separation membrane relies on the acid-base interaction between phosphoric acid and nitrogen atoms in the TB framework. The bond energy is relatively weak and easily dissociated by environmental disturbances. Furthermore, phosphoric acid molecules are easily lost with gas permeation or condensate migration on the membrane surface, making it impossible to maintain the initial modification effect.

[0007] Chinese patent publication number CN117247515A, filed on September 22, 2023, discloses a patent containing... The method for preparing a gas separation membrane based on the base-based polyimide involves a multi-step reaction. First, an imide-containing diamine monomer is introduced into the diamine. Then, the synthesized diamine reacts with paraformaldehyde or dimethoxymethane to form TB units. Finally, the diamine containing the imide unit is linked together through the TB units to obtain TB-PIM-PI, where the main chain contains both imide and TB units. In other words, by adjusting the order of introducing the imide and TB units into the polymer, a high molecular weight PIM-PI separation membrane material is obtained. This gas separation membrane preparation method involves multiple steps, requiring the synthesis of an imide-containing diamine monomer followed by polycondensation with formaldehyde to construct TB units. This lengthy process makes the TB formation reaction prone to branching or cross-linking byproducts. Furthermore, while rigid imide groups improve anti-aging properties, excessive inhibition of chain segment movement leads to the solidification of free volume elements, making it impossible to dynamically control the pore size through cross-linking.

[0008] In summary, based on Based on the characteristics of base (TB) polymers and in-situ thermal crosslinking modification strategies, a gas separation membrane capable of precise pore size control and significantly improved selectivity and anti-plasticization properties was designed. This membrane has significant practical value and application prospects in industrial fields such as natural gas purification, carbon capture and storage (CCS), and high-purity gas preparation. Summary of the Invention

[0009] To address the problems existing in the prior art, this invention provides a highly selective gas separation membrane based on in-situ thermal crosslinking of small molecules and its preparation method. By controlling the crosslinking temperature, time, and amount of crosslinking agent, the free volume and microporous structure of the gas separation membrane can be precisely controlled, thereby enhancing the molecular sieving effect for gases. It exhibits excellent permeability and selectivity in separation systems such as H2 / N2, H2 / CH4, O2 / N2, and CO2 / CH2, and also possesses good anti-plasticization and anti-aging capabilities.

[0010] The technical solution of the present invention is as follows:

[0011] One objective of this invention is to provide a method for preparing a highly selective gas separation membrane based on in-situ thermal crosslinking of small molecules, wherein the gas separation membrane comprises... The linear polymer of the Base structural unit is formed by thermally induced in-situ crosslinking reaction with a difunctional or multifunctional small molecule halogenated crosslinking agent.

[0012] Furthermore, the aforementioned The linear polymer of the Base structural unit is any one or more of the following combinations: Trip-TB, Btrip-TB, Trip-PIM-TB, PIM-Trip-TB, SBI-TB, and EA-TB containing tripterene.

[0013] Furthermore, the functional group of the small molecule halogenated crosslinking agent is -CH2X, wherein X is selected from Cl, Br or I.

[0014] Furthermore, the small-molecule halogenated crosslinking agent is any one of 1,4-di(bromomethyl)benzene (BMB), 1,3-di(bromomethyl)benzene, 1,4-di(chloromethyl)benzene, 1,2,4,5-tetra(bromomethyl)benzene, and bis(bromomethyl)biphenyl.

[0015] Furthermore, it includes the following steps:

[0016] S1, containing The linear polymer with the base structure is dissolved in an organic solvent and stirred until a uniform casting solution is formed.

[0017] S2. Filter the casting solution obtained from S1, place it in a chloroform saturated atmosphere and let it stand to evaporate and form a film, slowly forming a precursor film.

[0018] S3. The precursor membrane is heat-treated under an inert atmosphere to complete the thermal crosslinking reaction and obtain the highly selective gas separation membrane.

[0019] Furthermore, the amount of small molecule halogenated crosslinking agent added in S1 is 0.1% to 20% of the mass of the linear polymer;

[0020] The organic solvent is any one of chloroform, dichloromethane, tetrahydrofuran, N-methylpyrrolidone (NMP) or N,N-dimethylformamide (DMF); the ratio of linear polymer to organic solvent is 1-100 mg / mL.

[0021] Furthermore, the ratio of the linear polymer to the organic solvent is 1-30 mg / mL.

[0022] Furthermore, the film-forming process temperature in S2 is 30-100℃.

[0023] Furthermore, the film-forming process temperature is 30-80℃.

[0024] Furthermore, the inert atmosphere in S3 is nitrogen or argon.

[0025] Furthermore, the heat treatment temperature in S3 is 100-500℃, and the heat treatment time is 1-20h.

[0026] Furthermore, the heat treatment temperature is 50-400℃, and the heat treatment time is 2-5h.

[0027] Furthermore, the oxygen content in the system is below 0.1 ppm during the heat treatment process.

[0028] The second objective of this invention is to provide a highly selective gas separation membrane based on in-situ thermal crosslinking of small molecules, wherein the gas separation membrane has a dense covalent network structure and a submicropore size distribution.

[0029] Furthermore, the oxygen (O2) permeability is 10-2000 Barrer, and the O2 / N2 selectivity is 3.6-8.9.

[0030] Furthermore, the CO2 permeability is 250-10000 Barrer, and the CO2 / CH4 selectivity is 10-100.

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

[0032] 1. This invention discloses for the first time a highly selective gas separation membrane based on in-situ thermal crosslinking of small molecules. Its core innovation lies in the design of the in-situ thermal crosslinking strategy for small molecules. Traditional... While base polymers possess high free volume, their active chain segment movement leads to dynamic fluctuations in pore size and poor resistance to plasticization. Existing crosslinking techniques, such as photocrosslinking or macromolecular crosslinking, easily cause structural inhomogeneity or damage to micropores. This invention innovatively selects small-molecule halogenated crosslinking agents containing difunctional or multifunctional groups. These agents can be uniformly dispersed within the TB polymer matrix, preventing phase separation. Then, under precise temperature control in an inert atmosphere, a thermally induced nucleophilic substitution reaction occurs, constructing a dense covalent network in situ. The covalent bonds compress the random macropores, refining the pore size and forming… The uniform submicropores enhance the molecular sieving effect, while the three-dimensional network controls the free volume and inhibits chain segment relaxation, effectively solving the problems of physical aging and plasticization.

[0033] 2. The high-selectivity gas separation membrane designed in this invention exhibits superior performance and stability in industrial gas separation. Firstly, the gas separation membrane demonstrates excellent permeability and selectivity: O2 permeability is 10-2000 Barrer, and O2 / N2 selectivity is 3.6-8.9; CO2 permeability is 250-10000 Barrer, and CO2 / CH4 selectivity is 10-100. The mixed gas separation performance exceeds the Robeson limit, achieving synergistic optimization of gas permeability and selectivity. Secondly, it possesses good resistance to plasticization and aging, making it suitable for six major industrial scenarios: O2 / N2 separation, CO2 / CH4 separation, natural gas decarbonization and purification, carbon capture and storage (CCS), high-purity hydrogen preparation or H2 / CH4 separation, industrial tail gas purification and recovery, and natural gas decarbonization.

[0034] 3. This invention also provides a method for preparing the aforementioned highly selective gas separation membrane. This process is simple, precise, and has industrialization potential. Not only does the preparation process require only two steps—solution casting and heat treatment—resulting in low raw material costs, but the heat treatment process can be directly integrated into a membrane production line. Furthermore, oxygen content control is achieved through standard inert gas circulation. Moreover, the free volume and micropore structure of the membrane can be precisely controlled by adjusting the crosslinking temperature, time, and crosslinking agent dosage. This improves the crosslinking rate and yield while ensuring uniform membrane thickness, overcoming the bottleneck of poor film-forming properties of traditional TB membranes. This achieves breakthroughs in gas separation membrane performance, lifespan, and cost, providing a reference solution for the further industrial development of gas separation membranes. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the BTB pretreated blend membrane described in Comparative Example 1 of the present invention;

[0036] Figure 2This is a schematic diagram of the gas separation BTB membrane after heat treatment and crosslinking according to Embodiment 1 of the present invention.

[0037] Figure 3 This is a scanning electron microscope (SEM) schematic diagram of the gas separation BTB membrane before and after heat treatment crosslinking in Embodiment 1 of the present invention;

[0038] Figure 4 These are TG-MS images of the membranes described in Comparative Example 1 and Comparative Example 3 of the present invention;

[0039] Figure 5 The above are DSC images of the gas separation BTB membranes described in Embodiments 2, 6 and Comparative Embodiment 3 of the present invention;

[0040] Figure 6 The BET diagrams are for comparative example 3 of the present invention and for gas separation BTB membranes prepared at different crosslinking temperatures. Detailed Implementation

[0041] The present invention will be further described below with reference to preferred embodiments. The endpoints and any values ​​of the ranges disclosed in the present invention are not limited to the precise ranges or values. These ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed herein.

[0042] Unless otherwise specified, the experimental methods in the following embodiments are conventional methods, performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions.

[0043] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0044] Comparative Example 1

[0045] This embodiment provides a method for preparing a BTB pretreated blend membrane, including the following steps:

[0046] S1. Dissolve 200 mg of TTB polymer obtained by copolymerization of 2,6-diamino-trimethene in 10 mL of chloroform, then add 20 mg of 1,4-bis(bromomethyl)benzene (BMB), and stir magnetically at room temperature until the system is completely clear and homogeneous;

[0047] S2. After filtering out insoluble matter, the system solution is added dropwise to a 60 mm diameter petri dish and placed under a chloroform-saturated atmosphere for 48 h to evaporate, thus obtaining a freshly formed BTB pretreated blend membrane with a membrane thickness of 70 μm.

[0048] Example 1

[0049] This embodiment provides a highly selective gas separation BTB membrane based on small molecule in-situ thermal crosslinking, the preparation method of which includes the following steps:

[0050] S1. Dissolve 200 mg of TB base polymer (TTB) obtained by copolymerizing 2,6-diamino-tripterene with dimethoxymethane in 10 mL of chloroform, then add 20 mg of 1,4-bis(bromomethyl)benzene (BMB), and stir magnetically at room temperature until the system is completely clear and homogeneous;

[0051] S2. After filtering out insoluble matter, the system solution is added dropwise to a 60 mm diameter petri dish and placed in a chloroform-saturated atmosphere at 65 °C for 48 h to evaporate, thus obtaining a freshly formed BTB pretreated blend membrane.

[0052] S3. The prepared BTB pretreated blend membrane was placed in a tube furnace and heat-treated for 2 hours at 270°C under argon protection in an environment with an oxygen content of less than 0.1 ppm to achieve crosslinking reaction, and finally a high-selectivity gas separation BTB membrane with a membrane thickness of 70 μm was obtained.

[0053] Example 2

[0054] This embodiment provides a highly selective gas separation BTB membrane based on small molecule in-situ thermal crosslinking, the preparation method of which includes the following steps:

[0055] S1. Dissolve 200 mg of TB base polymer (TTB) obtained by copolymerizing 2,6-diamino-tripterene with dimethoxymethane in 10 mL of chloroform, then add 20 mg of 1,4-bis(bromomethyl)benzene (BMB), and stir magnetically at room temperature until the system is completely clear and homogeneous;

[0056] S2. After filtering out insoluble matter, the system solution is added dropwise to a 60 mm diameter petri dish and placed in a chloroform-saturated atmosphere at 65 °C for 48 h to evaporate, thus obtaining a freshly formed BTB pretreated blend membrane.

[0057] S3. The prepared BTB pretreated blend membrane was placed in a tube furnace and heat-treated for 5 hours at 270°C under argon protection in an environment with an oxygen content of less than 0.1 ppm to achieve crosslinking reaction, and finally a high-selectivity gas separation BTB membrane with a membrane thickness of 70 μm was obtained.

[0058] Example 3

[0059] This embodiment provides a method for preparing a highly selective gas separation BTB membrane based on in-situ thermal crosslinking of small molecules, including the following steps:

[0060] S1. Dissolve 200 mg of TB base polymer (TTB) obtained by copolymerizing 2,6-diamino-tripterene with dimethoxymethane in 10 mL of chloroform, then add 20 mg of 1,4-bis(bromomethyl)benzene (BMB), and stir magnetically at room temperature until the system is completely clear and homogeneous;

[0061] S2. After filtering out insoluble matter, the system solution is added dropwise to a 60 mm diameter petri dish and placed in a chloroform-saturated atmosphere at 65 °C for 48 h to evaporate, thus obtaining a freshly formed BTB pretreated blend membrane.

[0062] S3. The prepared BTB pretreated blend membrane was placed in a tube furnace and heat-treated at 270°C for 10 hours under argon protection in an environment with an oxygen content of less than 0.1 ppm to achieve crosslinking reaction, and finally a high-selectivity gas separation BTB membrane with a membrane thickness of 70 μm was obtained.

[0063] Example 4

[0064] This embodiment provides a method for preparing a highly selective gas separation BTB membrane based on in-situ thermal crosslinking of small molecules, including the following steps:

[0065] S1. Dissolve 200 mg of TB base polymer (TTB) obtained by copolymerizing 2,6-diamino-tripterene with dimethoxymethane in 10 mL of chloroform, then add 10 mg of 1,4-bis(bromomethyl)benzene (BMB) and stir magnetically at room temperature until the system is completely clear and homogeneous.

[0066] S2. After filtering out insoluble matter, the system solution is added dropwise to a 60 mm diameter petri dish and placed in a chloroform-saturated atmosphere at 65 °C for 48 h to evaporate, thus obtaining a freshly formed BTB pretreated blend membrane.

[0067] S3. The prepared BTB pretreated blend membrane was placed in a tube furnace and heat-treated for 5 hours at 270°C under argon protection in an environment with an oxygen content of less than 0.1 ppm to achieve crosslinking reaction, and finally a high-selectivity gas separation BTB membrane with a membrane thickness of 70 μm was obtained.

[0068] Example 5

[0069] This embodiment provides a method for preparing a highly selective gas separation BTB membrane based on in-situ thermal crosslinking of small molecules, including the following steps:

[0070] S1. Dissolve 200 mg of TB base polymer (TTB) obtained by copolymerizing 2,6-diamino-tripterene with dimethoxymethane in 10 mL of chloroform, then add 30 mg of 1,4-bis(bromomethyl)benzene (BMB), and stir magnetically at room temperature until the system is completely clear and homogeneous;

[0071] S2. After filtering out insoluble matter, the system solution is added dropwise to a 60 mm diameter petri dish and placed in a chloroform-saturated atmosphere at 65 °C for 48 h to evaporate, thus obtaining a freshly formed BTB pretreated blend membrane.

[0072] S3. The prepared BTB pretreated blend membrane was placed in a tube furnace and heat-treated for 5 hours at 270°C under argon protection in an environment with an oxygen content of less than 0.1 ppm to achieve crosslinking reaction, and finally a high-selectivity gas separation BTB membrane with a membrane thickness of 70 μm was obtained.

[0073] Example 6

[0074] This embodiment provides a method for preparing a highly selective gas separation BTB membrane based on in-situ thermal crosslinking of small molecules, including the following steps:

[0075] S1. Dissolve 200 mg of TB base polymer (TTB) obtained by copolymerizing 2,6-diamino-tripterene with dimethoxymethane in 10 mL of chloroform, then add 20 mg of 1,4-bis(bromomethyl)benzene (BMB), and stir magnetically at room temperature until the system is completely clear and homogeneous;

[0076] S2. After filtering out insoluble matter, the system solution is added dropwise to a 60 mm diameter petri dish and placed in a chloroform-saturated atmosphere at 65 °C for 48 h to evaporate, thus obtaining a freshly formed BTB pretreated blend membrane.

[0077] S3. The prepared BTB pretreated blend membrane was placed in a tube furnace and heat-treated for 5 hours at 120°C under argon protection in an environment with an oxygen content of less than 0.1 ppm to achieve crosslinking reaction, and finally a high-selectivity gas separation BTB membrane with a membrane thickness of 70 μm was obtained.

[0078] Example 7

[0079] This embodiment provides a method for preparing a highly selective gas separation BTB membrane based on in-situ thermal crosslinking of small molecules, including the following steps:

[0080] S1. Dissolve 200 mg of TB base polymer (TTB) obtained by copolymerizing 2,6-diamino-tripterene with dimethoxymethane in 10 mL of chloroform, then add 20 mg of 1,4-bis(bromomethyl)benzene (BMB), and stir magnetically at room temperature until the system is completely clear and homogeneous;

[0081] S2. After filtering out insoluble matter, the system solution is added dropwise to a 60 mm diameter petri dish and placed in a chloroform-saturated atmosphere at 65 °C for 48 h to evaporate, thus obtaining a freshly formed BTB pretreated blend membrane.

[0082] S3. The prepared BTB pretreated blend membrane was placed in a tube furnace and heat-treated for 5 hours at 170°C under argon protection in an environment with an oxygen content of less than 0.1 ppm to achieve crosslinking reaction, and finally a high-selectivity gas separation BTB membrane with a membrane thickness of 70 μm was obtained.

[0083] Example 8

[0084] This embodiment provides a method for preparing a highly selective gas separation BTB membrane based on in-situ thermal crosslinking of small molecules, comprising the following steps:

[0085] S1. Dissolve 200 mg of TB base polymer (TTB) obtained by copolymerizing 2,6-diamino-tripterene with dimethoxymethane in 10 mL of chloroform, then add 20 mg of 1,4-bis(bromomethyl)benzene (BMB), and stir magnetically at room temperature until the system is completely clear and homogeneous;

[0086] S2. After filtering out insoluble matter, the system solution is added dropwise to a 60 mm diameter petri dish and placed in a chloroform-saturated atmosphere at 65 °C for 48 h to evaporate, thus obtaining a freshly formed BTB pretreated blend membrane.

[0087] S3. The prepared BTB pretreated blend membrane was placed in a tube furnace and heat-treated for 5 hours at 220°C under argon protection in an environment with an oxygen content of less than 0.1 ppm to achieve crosslinking reaction, and finally a high-selectivity gas separation BTB membrane with a membrane thickness of 70 μm was obtained.

[0088] Example 9

[0089] This embodiment provides a method for preparing a highly selective gas separation BTB membrane based on in-situ thermal crosslinking of small molecules, including the following steps:

[0090] S1. Dissolve 200 mg of TB base polymer (TTB) obtained by copolymerizing 2,6-diamino-tripterene with dimethoxymethane in 10 mL of chloroform, then add 20 mg of 1,4-bis(bromomethyl)benzene (BMB), and stir magnetically at room temperature until the system is completely clear and homogeneous;

[0091] S2. After filtering out insoluble matter, the system solution is added dropwise to a 60 mm diameter petri dish and placed in a chloroform-saturated atmosphere at 65 °C for 48 h to evaporate, thus obtaining a freshly formed BTB pretreated blend membrane.

[0092] S3. The prepared BTB pretreated blend membrane was placed in a tube furnace and heat-treated for 5 hours at 320°C under argon protection in an environment with an oxygen content of less than 0.1 ppm to achieve crosslinking reaction, and finally a high-selectivity gas separation BTB membrane with a membrane thickness of 70 μm was obtained.

[0093] Example 10

[0094] This embodiment provides a method for preparing a highly selective gas separation membrane based on in-situ thermal crosslinking of small molecules, including the following steps:

[0095] S1. Dissolve 200 mg of triphenylamine-triptene polymer obtained by copolymerizing 1,3,5-tris(4-formylphenyl)benzene and 2,6-diamino-triptene in 2 mL of dichloromethane, then add 0.2 mg of 1,3-di(bromomethyl)benzene and stir magnetically at room temperature until the system is completely clear and homogeneous;

[0096] S2. After filtering out insoluble matter, the system solution is added dropwise to a petri dish and placed in a chloroform-saturated atmosphere at 30°C for 48 hours to evaporate, thus obtaining a freshly formed pretreated blended membrane.

[0097] S3. The pretreated blend membrane is placed in a tube furnace and heat-treated for 20 hours at 100°C under nitrogen protection in an environment with an oxygen content of less than 0.1 ppm to achieve crosslinking reaction, and finally a highly selective gas separation membrane is obtained.

[0098] Example 11

[0099] This embodiment provides a method for preparing a highly selective gas separation membrane based on in-situ thermal crosslinking of small molecules, including the following steps:

[0100] S1. Dissolve 50 mg of benzimidazole-triphenylamine-triphenylene polymer obtained by copolymerizing 2,2',2”-(benzyl-1,3,5-triyl)tris(1H-benzi[d]imidazole) with 2,6-diamino-triphenylene in 50 mL of DMF, then add 40 mg of 1,2,4,5-tetra(bromomethyl)benzene and stir magnetically at room temperature until the system is completely clear and homogeneous;

[0101] S2. After filtering out insoluble matter, the system solution is added dropwise to a petri dish and placed under a chloroform-saturated atmosphere at 100°C for 48 hours to evaporate, thus obtaining a freshly formed pretreated blended membrane.

[0102] S3. The pretreated blended membrane is placed in a tube furnace and heat-treated at 500°C for 1 hour under nitrogen protection in an environment with an oxygen content of less than 0.1 ppm to achieve crosslinking reaction, and finally a highly selective gas separation membrane is obtained.

[0103] Comparative Example 2

[0104] Example 11 is the high-selectivity gas separation BTB membrane prepared in Example 2 after aging for one month under vacuum sealing conditions.

[0105] Comparative Example 3

[0106] S1. Dissolve 200 mg of TB base polymer (TTB) obtained by copolymerizing 2,6-diamino-triptene with dimethoxymethane in 10 mL of chloroform and stir magnetically at room temperature until the system is completely clear and homogeneous.

[0107] S2. After filtering out insoluble matter, the system solution is added dropwise to a 60 mm diameter petri dish and placed under a chloroform-saturated atmosphere for 48 h to evaporate, thus obtaining a freshly formed TTB membrane.

[0108] Comparative Example 4

[0109] Comparative Example 4 is the TTB original film prepared in Comparative Example 3 after aging under vacuum sealing conditions for one month.

[0110] Performance testing

[0111] 1. Pure gas permeability and selectivity test

[0112] The encapsulated membrane was placed in the constant volume pressure change test device. After the instrument was evacuated, the gas to be tested was introduced upstream at 0.2 MPa. The change in downstream pressure of the test membrane over time was used to obtain the amount of gas permeation per unit time, thereby obtaining its gas permeability. The test data are shown in Table 1.

[0113] Table 1. Test results of pure gas separation performance

[0114]

[0115] Note: Gas permeability and selectivity were measured at 35°C and 2 bar pressure, where 1 bar = 0.1 MPa.

[0116] Based on the test results of all the above embodiments, comparative embodiments, and Table 1, it can be seen that with the gradual increase of heat treatment temperature, heat treatment time, and crosslinking agent addition, the degree of crosslinking of the membrane material is significantly improved, thereby effectively controlling the microstructure of the membrane and the gas transport channels. On this basis, the gas separation performance of the membrane gradually improves, manifested in a continuous increase in the selectivity of gas pairs, and the trade-off between permeability and selectivity is optimized. Taking O2 / N2 separation as an example, compared with the uncrosslinked comparative embodiment 3, the membrane in embodiment 2, after the introduction of the crosslinking reaction, although the permeability of O2 decreased from 1170 Barrer to 613 Barrer, the selectivity of O2 / N2 significantly increased from 5.11 to 7.09, indicating that the crosslinking structure effectively enhances the sieving ability for small molecule gases.

[0117] Furthermore, the crosslinking treatment significantly improved the membrane's anti-aging properties. Comparing the performance changes between Example 9 and Comparative Example 4 revealed that the crosslinked membrane exhibited a significantly reduced decrease in gas permeability during long-term storage or use, while maintaining a high selectivity level. This further demonstrates that heat treatment crosslinking technology not only improves the initial separation performance of the membrane but also effectively enhances its operational stability and service life, providing crucial support for its widespread application in industrial gas separation.

[0118] This anti-trade-off effect is due to the following aspects: (i) First, the crosslinking reaction forms a stable covalent network between polymer chains, compressing or closing the original large-size, low-selectivity pores, while generating a large number of size-restricted, uniformly distributed submicropores. While these submicropores contribute to improved overall FFV, their smaller pore size and reduced connectivity lead to stronger steric hindrance during molecular migration, thus limiting molecular motion and reducing the effective diffusion rate. (ii) Secondly, the covalent network structure introduced by the crosslinking reaction locally stiffens the polymer backbone, restricting the mobility of chain segments and inhibiting large-scale structural rearrangement. This localized "freezing" effect of chain segments helps stabilize newly formed pores and prevent their collapse.

[0119] 2. Mixed gas permeability and selectivity test

[0120] The membrane packaged in Example 2 was installed in a cross-flow constant volume pressure swing test apparatus. First, the entire system was thoroughly evacuated to eliminate interference from residual gas within the system. Then, compressed air with a pressure range of 0.2–1.5 MPa was introduced upstream of the test apparatus as a gas supply source. The gas permeation rate per unit time was obtained by monitoring the pressure change in the downstream cavity of the membrane. To further determine the composition of the permeated gas, downstream gas samples were collected after stable permeation, and gas chromatography was used for component analysis to obtain the permeation performance of each gas component in the membrane material. The corresponding gas permeability test results are detailed in Table 2.

[0121] Table 2. Gas Separation Performance Test

[0122]

[0123] Note: The gas permeability and selectivity were measured at 35℃ and 2-15 bar, where 1 bar = 0.1 MPa.

[0124] Given that the membrane material prepared in Example 2 exhibited excellent permeability and selectivity in pure gas separation tests, further CO2 / CH4 mixed gas separation performance tests were conducted to evaluate its separation capacity and stability under practical application conditions. In the mixed gas permeation test, considering the significant competitive adsorption effect between CO2 and CH4, the permeability of both gases decreased to some extent with increasing upstream gas supply pressure.

[0125] For example, when the operating pressure increased from 2 bar to 15 bar, the CO2 permeability decreased from 2689 barrer to 2308 barrer, indicating that molecular competitive adsorption in the mixed gas state had a certain inhibitory effect on gas diffusion. However, despite the slight decrease in overall permeability, the selectivity of the membrane material for the CO2 / CH4 mixed gas remained above 22, demonstrating excellent molecular sieving ability.

[0126] More importantly, the membrane exhibits good pressure-dependent stability under different pressure conditions. Its CO2 / CH4 mixed gas separation performance is significantly better than the updated upper limit of CO2 / CH4 separation performance (Robeson upperbound) in 2018, and its overall performance surpasses that of advanced membrane materials reported in the current literature, demonstrating great potential for industrial application of stable and efficient separation of CO2 / CH4 under high pressure conditions.

[0127] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a highly selective gas separation membrane based on in-situ thermal crosslinking of small molecules, characterized in that, The gas separation membrane is composed of... The linear polymer of the Base structural unit is formed by thermally induced in-situ crosslinking reaction with a difunctional or multifunctional small molecule halogenated crosslinking agent.

2. The method for preparing a highly selective gas separation membrane based on in-situ thermal crosslinking of small molecules according to claim 1, characterized in that, The The linear polymer of the Base structural unit is any one or more of the following combinations: Trip-TB, Btrip-TB, Trip-PIM-TB, PIM-Trip-TB, SBI-TB, and EA-TB containing tripterene.

3. The method for preparing a highly selective gas separation membrane based on in-situ thermal crosslinking of small molecules according to claim 1, characterized in that, The functional group of the small molecule halogenated crosslinking agent is -CH2X, where X is selected from Cl, Br or I.

4. The method for preparing a highly selective gas separation membrane based on in-situ thermal crosslinking of small molecules according to claim 3, characterized in that, The small-molecule halogenated crosslinking agent is any one of 1,4-di(bromomethyl)benzene (BMB), 1,3-di(bromomethyl)benzene, 1,4-di(chloromethyl)benzene, 1,2,4,5-tetra(bromomethyl)benzene, and bis(bromomethyl)biphenyl.

5. The method for preparing a highly selective gas separation membrane based on in-situ thermal crosslinking of small molecules according to claim 1, characterized in that, Includes the following steps: S1, containing The linear polymer with the base structure is dissolved in an organic solvent and stirred until a uniform casting solution is formed. S2. Filter the casting solution obtained from S1, place it in a chloroform saturated atmosphere and let it stand to evaporate and form a film, slowly forming a precursor film. S3. The precursor membrane is heat-treated under an inert atmosphere to complete the thermal crosslinking reaction and obtain the highly selective gas separation membrane.

6. The method for preparing a highly selective gas separation membrane based on in-situ thermal crosslinking of small molecules according to claim 5, characterized in that, The amount of small molecule halogenated crosslinking agent added in S1 is 0.1% to 20% of the mass of the linear polymer; The organic solvent is any one of chloroform, dichloromethane, tetrahydrofuran, N-methylpyrrolidone (NMP) or N,N-dimethylformamide (DMF); the ratio of linear polymer to organic solvent is 1-100 mg / mL.

7. The method for preparing a highly selective gas separation membrane based on in-situ thermal crosslinking of small molecules according to claim 5, characterized in that, The film-forming process temperature in S2 is 30-100℃.

8. The method for preparing a highly selective gas separation membrane based on in-situ thermal crosslinking of small molecules according to claim 5, characterized in that, The inert atmosphere in S3 is nitrogen or argon.

9. The method for preparing a highly selective gas separation membrane based on in-situ thermal crosslinking of small molecules according to claim 5, characterized in that, The heat treatment temperature in S3 is 100-500℃, the heat treatment time is 1-20h, and the oxygen content of the system is less than 0.1ppm during the heat treatment process.

10. A highly selective gas separation membrane based on in-situ thermal crosslinking of small molecules, prepared by the production method according to any one of claims 1 to 9, characterized in that, The gas separation membrane has a dense covalent network structure and a submicropore size distribution; Oxygen (O2) permeability is 10-2000 Barrer, and O2 / N2 selectivity is 3.6-8.9; The CO2 permeability is 250-10000 Barrer, and the CO2 / CH4 selectivity is 10-100.

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