Low-temperature amino crosslinking modified self-polymerization microporous polymer gas separation membrane, preparation method and application

Abstract

The invention relates to a low-temperature amino cross-linked modified self-polymerized microporous polymer gas separation membrane, a preparation method and application, and belongs to the technical field of gas separation membranes, and the preparation method comprises the following steps: 1) synthesizing a cross-linked precursor polymer PIM-BM through a bromomethylation reaction; (2) preparing a membrane casting solution from the PIM-BM and a micromolecular amine cross-linking agent, casting, and volatilizing to form a membrane; and 3) carrying out heat treatment at 40-80 DEG C under a vacuum condition for 6-32 hours to form a cross-linked network structure, wherein the thickness of the film is 40-120 microns. According to the invention, a covalent cross-linked network is constructed through a low-temperature Hofmann alkylation reaction of an amine cross-linking agent so as to limit the movement of a polymer chain segment; the strong CO2 affinity of amido (-NH2) realizes dissolution selectivity compensation, and the diffusion selectivity synergistic effect of an inherent micropore channel of PIM-BM is combined, so that the tradeoff limitation of permeability-selectivity of a traditional gas separation membrane is broken through; the cross-linked structure can effectively improve the physical aging resistance of the PIM-BM film, and has good long-term continuous operation stability; the preparation process is low in low-temperature process energy consumption, easy to scale, suitable for the fields of coal-fired flue gas CO2 capture, natural gas purification and the like, and has industrial application potential.

Description

Technical Field

[0001] The present invention belongs to the technical field of microporous polymer separation membranes, and relates to a low-temperature amino-crosslinked modified self-polymerized microporous polymer gas separation membrane, a preparation method and an application thereof. The obtained crosslinked membrane can be used in, but is not limited to, a gas separation system. Background Art

[0002] As one of the most important clean energy sources of our time, natural gas plays a crucial role in human production and life, as well as in energy conservation and emission reduction. However, raw natural gas extracted directly from wells often cannot be used directly due to its presence of large amounts of acidic gases (CO2 and H2S) and inert components (N2). Acidic gases can corrode transmission pipelines and storage equipment, impacting gas compression and transportation capabilities and potentially causing safety issues. Furthermore, the presence of CO2 reduces the calorific value of natural gas, impacting economic efficiency. Therefore, developing new and efficient technologies for separating CO2 from natural gas is crucial.

[0003] Compared with traditional CO2 capture technologies such as cryogenic distillation, absorption, and adsorption, polymer gas separation membranes offer advantages such as low cost, small footprint, and environmental friendliness. As a new type of gas separation membrane material, self-polymerizing microporous polymers (PIMs) offer the advantages of high gas permeability, good thermal stability, simple preparation, ease of processing, and post-modification. Their application in CO2 and CH4 separation has been extensively studied. However, PIMs membranes have moderate selectivity and are subject to severe physical aging and plasticization. Plasticization refers to the phenomenon in which the permeability of condensable gases such as carbon dioxide and hydrocarbons increases with increasing pressure, while the permeability selectivity decreases. Aging refers to the phenomenon in which the physical properties of polymer membranes change over time, resulting in a decrease in gas permeability, without the influence of external conditions. This phenomenon seriously affects the gas separation performance of the membrane, reduces its stability, and significantly shortens its service life.

[0004] In order to improve the selectivity, anti-plasticization and anti-aging properties of PIMs membranes, the present invention intends to regulate the micropore distribution through a low-temperature amino cross-linking strategy, and at the same time introduce polar sites (-NH2) with strong CO2 affinity, significantly enhancing the solubility of PIMs membranes for CO2 molecules, so that the constructed cross-linked network maintains excellent CO2 transmission flux, while improving the ideal CO2 / CH4 selectivity. Summary of the Invention

[0005] In view of the problems of easy aging and poor plasticization resistance of existing self-polymerized microporous polymer gas separation membranes, the present invention provides a low-temperature amino-crosslinked modified self-polymerized microporous polymer gas separation membrane material and preparation method, which can solve the problems of micropore collapse and insufficient plasticization resistance caused by high-temperature crosslinking of traditional PIM membranes.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A low-temperature, amine-crosslinked, modified, self-polymerized microporous polymer gas separation membrane comprises a bromomethylated PIM-BM matrix and an amine-based small molecule crosslinker. The amine-based small molecule crosslinker is introduced into the PIM-BM membrane matrix via solution blending to form a pre-crosslinked structure, which is then crosslinked via heat treatment to yield a crosslinked membrane material. The strong CO2 affinity of the amine groups (-NH2) of the amine-based small molecule crosslinker in the crosslinked membrane material achieves solubility selectivity compensation. This, combined with the diffusion selectivity of the inherent microporous channels of the PIM-BM, results in a crosslinked membrane with high gas selectivity and excellent resistance to plasticization and aging.

[0008] A method for preparing a low-temperature amino-crosslinked modified self-polymerized microporous polymer gas separation membrane comprises the following steps:

[0009] Step (1) Preparation of bromomethylated polymer (PIM-BM):

[0010] Step 1.1) Preparation of monomer 3,3,3′,3′,4,4′-hexamethyl-2,2′,3,3′-tetrahydro-1,1′-spirobis[indene]-5,5′,6,6′-tetrol (TTSBI-M): 3-methylcatechol is dissolved in a mixture of glacial acetic acid and hydrobromic acid, acetone is added dropwise, and the mixture is reacted at a temperature of 110-150° C. for 8-24 hours. The reaction product is then poured into deionized water to precipitate brown flocs. Finally, the flocs are washed multiple times with glacial acetic acid, filtered, and vacuum-dried to obtain the white powder monomer TTSBI-M.

[0011] Step 1.2) Preparation of methylated PIM (PIM-M): Dissolve tetrafluoroterephthalonitrile, anhydrous potassium carbonate, and the monomer TTSBI-M prepared in step 1.1) in solvent A. Add toluene and react under nitrogen at a temperature of 100-170°C for 3-10 hours. The reaction product is then rinsed in deionized water, repeatedly rinsed several times, filtered, and vacuum-dried to obtain PIM-M.

[0012] Step 1.3) Preparation of bromomethylated PIM (PIM-BM): Dissolve the PIM-M prepared in step 1.2) in chlorobenzene, add N-bromosuccinimide and azobisisobutyronitrile, and react under nitrogen at 80-160°C for 2-6 hours. After cooling, the reaction product is washed in methanol, repeatedly washed and filtered 4-5 times, and then dried under vacuum to obtain PIM-BM as a yellow solid. The reaction mechanism of this step is as follows: Using azobisisobutyronitrile as a free radical initiator and N-bromosuccinimide as a bromine source, a nucleophilic substitution reaction between N-bromosuccinimide and PIM-M introduces a bromine atom at the benzyl position of PIM-M, thereby preparing the bromomethylated PIM (PIM-BM).

[0013] Furthermore, in the step 1.1), 20 to 70 mL of glacial acetic acid, 30 to 80 mL of hydrobromic acid, and 20 to 40 mL of acetone are added to every 20 g of 3-methylcatechol;

[0014] Furthermore, in step 1.1), the vacuum drying temperature is 60-90° C. and the time is 24-42 h;

[0015] Furthermore, in step 1.2), the solvent A is one or a mixture of two or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone;

[0016] Furthermore, in the step 1.2), 8 to 16 g of tetrafluoroterephthalonitrile, 15 to 30 g of anhydrous potassium carbonate, 30 to 60 mL of toluene, and 80 to 140 mL of solvent A are added to every 20 g of TTSBI-M;

[0017] Furthermore, in step 1.2), the vacuum drying temperature is 70-100° C. and the time is 18-32 h;

[0018] Furthermore, in the step 1.3), 150-300 mL of chlorobenzene, 1.78-5.89 g of N-bromosuccinimide, and 0.18-0.58 g of azobisisobutyronitrile were added to every 9.76 g of PIM-M;

[0019] Furthermore, in step 1.3), the vacuum drying temperature is 70-100° C. and the time is 18-32 h;

[0020] Step (2) Preparation of membrane material:

[0021] Step 2.1) Dissolve PIM-BM in solvent B at room temperature to form a PIM-BM solution. Stir for 5-24 hours, and then remove impurities from the PIM-BM solution using a syringe filter.

[0022] Step 2.2) At room temperature, dissolve an amine small molecule crosslinker in solvent B to form a crosslinker solution, and stir for 1 to 3 hours.

[0023] Step 2.3) Add the crosslinker solution dropwise to the PIM-BM solution at room temperature and stir to obtain a fully mixed casting solution;

[0024] Step 2.4) The mixed casting solution is poured into a quartz mold and allowed to stand at room temperature for degassing. After natural evaporation, a film without heat treatment is obtained, which is denoted as "c-PIM / X" film, where X represents a cross-linking agent.

[0025] Furthermore, in step 2.3), the concentration of the mixed casting solution is 2-4 w / w%, and the mass ratio of the amine small molecule cross-linking agent to the PIM-BM is 1:4-38.

[0026] Furthermore, in step 2.2), the amine small molecule cross-linking agent is at least one of ethylenediamine (EDA), diethylenetriamine (DETA), and tris(2-aminoethyl)amine (TAEA); preferably tris(2-aminoethyl)amine (TAEA).

[0027] Furthermore, in step (2), the solvent B is chloroform, tetrahydrofuran or N,N-dimethylformamide;

[0028] Furthermore, in step 2.3), the casting solution is stirred for 5 to 9 hours, allowed to stand for degassing for 2 to 12 hours, and allowed to volatilize naturally for 24 to 48 hours.

[0029] Step (3) Preparation of cross-linked PIM membrane:

[0030] The c-PIM / X membrane obtained in step (2) is heated under vacuum conditions to undergo a crosslinking reaction, thereby obtaining a low-temperature crosslinked modified PIM gas separation membrane; wherein the vacuum heat treatment conditions are: a crosslinking temperature of 20 to 80°C and a crosslinking time of 6 to 32 hours. The reaction mechanism of this step is as follows: PIM-BM and an amine-based small molecule crosslinker are pre-crosslinked through ionic interactions between the -CH2Br group of PIM-BM and the -NH2 group of the crosslinker, and are fully mixed in solvent B; finally, PIM-BM and the crosslinker form covalent chemical bonds (-CH2-NH-) at low temperatures through a Hoffman alkylation reaction, thereby constructing a crosslinked network in the microporous matrix. The introduced -NH2 enhances the solubility of the PIM membrane for CO2 and improves the CO2 / CH4 solubility selectivity, thereby achieving long-term stable and excellent CO2 / CH4 separation performance. This low-temperature crosslinking method is helpful for preparing anti-plasticization and anti-aging c-PIM / X crosslinked membrane materials, and can also be used to prepare other polymer crosslinked membranes.

[0031] Furthermore, in step (3), the cross-linking temperature is preferably 20 to 40° C., and the cross-linking time is 12 to 20 hours.

[0032] Furthermore, in step (3), the cross-linked PIM membrane is labeled as "c-PIM / XT", where X is the type of cross-linking agent and T is the cross-linking temperature.

[0033] Furthermore, in step (3), the thickness of the cross-linked PIM film is 40 to 120 microns.

[0034] The invention discloses an application of a low-temperature amino-crosslinked modified self-polymerized microporous polymer gas separation membrane for gas separation, salinity difference power generation, ion exchange and other systems.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The thermal crosslinking of polymers reported in the prior art tends to occur at high temperatures (T>200°C) to ensure a high degree of crosslinking. This process may involve uncontrolled degradation of the backbone structure. In contrast, the present invention establishes a method of constructing a crosslinking network in a PIM matrix by combining functionalized modified PIM with an amine small molecule crosslinker at low temperatures (20-80°C, preferably 20-40°C). By varying the content of the amine small molecule crosslinker and the crosslinking temperature, the pore size distribution is adjusted, thereby achieving effective regulation of the free volume within the polymer membrane.

[0037] (2) The present invention introduces the amine cross-linking agent into the PIM-BM membrane directly by solution blending with the PIM-BM to form a pre-cross-linked structure, and realizes the cross-linking of the membrane by low-temperature heat treatment under vacuum conditions, thereby restricting the movement of polymer chain segments, making the separation membrane have good anti-plasticization properties, and improving the plasticization pressure for the separation of acidic gases such as CO2.

[0038] (3) The present invention fully optimizes various parameters in the membrane making process, especially focusing on the effects of the concentration of the cross-linking agent in the mixed casting solution, the stirring time of the mixed casting solution, and the static degassing time on the membrane performance. The cross-linked membrane prepared can enhance the solubility of CO2. At the same time, the constructed cross-linked network can achieve an extremely high molecular sieving effect, which greatly improves the CO2 / CH4 separation selectivity coefficient of the membrane. The CO2 flux of the low-temperature amino-cross-linked modified self-polymerized microporous polymer gas separation membrane prepared by the present invention is not less than 500 Barrer, and the ideal CO2 / CH4 selectivity is not less than 300. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a scanning electron microscope image of the cross-linked membrane c-PIM / TAEA-20°C in Example 1.

[0040] Figure 2This is a scanning electron microscope image of the cross-linked membrane c-PIM / DETA-30℃ in Example 2.

[0041] Figure 3 This is a scanning electron microscope image of the cross-linked membrane c-PIM / EDA-80℃ in Example 3.

[0042] Figure 4 3. It is the Fourier transform infrared spectra of the c-PIM / EDA-80°C cross-linked film, EDA and PIM-BM in Example 3.

[0043] Figure 5 This is the CO2 plasticization resistance test of Example (1-3) (test conditions: CO2 pure gas, 35°C). DETAILED DESCRIPTION

[0044] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0045] Example 1: The method of the present invention comprises the following steps:

[0046] Step (1) Preparation of bromomethylated polymer (PIM-BM):

[0047] Step 1.1) Preparation of monomer 3,3,3′,3′,4,4′-hexamethyl-2,2′,3,3′-tetrahydro-1,1′-spirobis[indene]-5,5′,6,6′-tetrol (TTSBI-M): 20 g of 3-methylcatechol was dissolved in a mixture of 20 mL of glacial acetic acid and 30 mL of hydrobromic acid. 20 mL of acetone was added dropwise, and the mixture was reacted at 110°C for 24 h. The reaction product was then poured into deionized water to precipitate a brown flocculent substance. Finally, the flocculent substance was washed multiple times with glacial acetic acid, filtered, and dried under vacuum at 60°C for 42 h to obtain TTSBI-M as a white powder.

[0048] Step 1.2) Preparation of methylated PIM (PIM-M): Dissolve 8 g of tetrafluoroterephthalonitrile, 15 g of anhydrous potassium carbonate, and 20 g of TTSBI-M prepared in Step 1.1) in 80 mL of N,N-dimethylformamide (DMF). Add 30 mL of toluene and react at 100°C under nitrogen for 10 h. The reaction product is then rinsed in deionized water, repeatedly rinsed several times, filtered, and dried under vacuum at 70°C for 32 h to obtain PIM-M as a pale yellow solid.

[0049] Step 1.3) Preparation of bromomethylated PIM (PIM-BM): Dissolve 9.76 g of PIM-M prepared in step 1.2) in 150 mL of chlorobenzene, add 1.78 g of N-bromosuccinimide and 0.18 g of azobisisobutyronitrile, and react at 80°C under nitrogen for 6 h. After cooling, the reaction product is washed in methanol, repeatedly washed and filtered 4-5 times, and then dried under vacuum at 70°C for 32 h to obtain a yellow solid, PIM-BM. The reaction mechanism of this step is as follows: Using azobisisobutyronitrile as a free radical initiator and N-bromosuccinimide as a bromine source, a nucleophilic substitution reaction between N-bromosuccinimide and PIM-M introduces a bromine atom at the benzyl position of PIM-M, thereby preparing bromomethylated PIM (PIM-BM).

[0050] Step (2) Preparation of membrane material:

[0051] Step 2.1) Dissolve 1.0 g of PIM-BM in 24 g of chloroform at room temperature to prepare a 4 wt% PIM-BM solution. Stir for 5 h, and then remove impurities from the PIM-BM solution using a syringe filter.

[0052] Step 2.2) At room temperature, 0.263 g of tris(2-aminoethyl)amine (TAEA) was dissolved in 6.0 g of chloroform to form a crosslinker solution. The mass ratio of PIM-BM to TAEA was 1:3.8, and the stirring time was 1 h.

[0053] Step 2.3) Add the crosslinker solution dropwise to the PIM-BM solution at room temperature and stir for 5 h to obtain a fully mixed casting solution;

[0054] Step 2.4) The mixed casting solution was poured into a quartz mold and allowed to stand at room temperature for degassing for 2 h. After natural evaporation for 24 h, a film without heat treatment was obtained, which was recorded as a "c-PIM / TAEA" film.

[0055] Step (3) Preparation of cross-linked PIM membrane:

[0056] The c-PIM / TAEA membrane obtained in step (2) was heated at 20°C for 32 hours under vacuum conditions to undergo a cross-linking reaction, thereby obtaining a low-temperature cross-linked modified PIM gas separation membrane; labeled as c-PIM / TAEA-20°C, the membrane thickness was 40 μm.

[0057] In Example 1, TAEA was uniformly distributed in the PIM-BM matrix, and the c-PIM / TAEA-20°C cross-linked film exhibited a uniform and dense surface structure, indicating that the interaction between the bromomethyl group and the amino group promoted the formation of an interface without obvious defects.

[0058] Example 2: The method of the present invention comprises the following steps:

[0059] Step (1) Preparation of bromomethylated polymer (PIM-BM):

[0060] Step 1.1) Preparation of monomer 3,3,3′,3′,4,4′-hexamethyl-2,2′,3,3′-tetrahydro-1,1′-spirobis[indene]-5,5′,6,6′-tetrol (TTSBI-M): 20 g of 3-methylcatechol was dissolved in a mixture of 45 mL of glacial acetic acid and 55 mL of hydrobromic acid, 30 mL of acetone was added dropwise, and the mixture was refluxed at 130° C. for 16 h to obtain a brown solution. The solution was then poured into deionized water to precipitate brown flocs. Finally, the flocs were washed multiple times with glacial acetic acid, filtered, and dried in vacuo at 75° C. for 30 h to obtain the white powder monomer TTSBI-M.

[0061] Step 1.2) Preparation of methylated PIM (PIM-M): Dissolve 12 g of tetrafluoroterephthalonitrile, 22.5 g of anhydrous potassium carbonate, and 20 g of the monomer TTSBI-M prepared in 1.1) in 80 mL of N-methylpyrrolidone. Add 45 mL of toluene and react at 135°C under nitrogen for 6.5 hours. The reaction product is then rinsed in deionized water three times, filtered, and dried in a vacuum oven at 85°C for 25 hours to obtain PIM-M as a pale yellow solid.

[0062] Step 1.3) Preparation of bromomethylated PIM polymer (PIM-BM): Dissolve 9.76 g of PIM-M prepared in 1.2) in 225 mL of chlorobenzene, add 3.83 g of N-bromosuccinimide and 0.38 g of azobisisobutyronitrile, and react under nitrogen at 120°C for 4 h. After cooling, the reaction product is washed in methanol, repeatedly washed and filtered 4-5 times, and dried in a vacuum oven at 85°C for 25 h to obtain PIM-BM as a yellow solid.

[0063] Step (2) Preparation of membrane material:

[0064] Step 2.1) Dissolve 1.0 g of PIM-BM in 37 g of tetrahydrofuran at room temperature to prepare a 2.6 wt% PIM-BM solution. After stirring for 14.5 h, remove impurities from the PIM-BM solution using a syringe filter.

[0065] Step 2.2) At room temperature, 0.143 g of diethylenetriamine (DETA) was dissolved in 9 g of tetrahydrofuran to form a crosslinker solution with a mass ratio of PIM-BM to TAEA of 1:7. The mixture was stirred for 2 h.

[0066] Step 2.3) Add the crosslinker solution dropwise to the PIM-BM solution at room temperature and stir for 7 h to obtain a fully mixed casting solution;

[0067] Step 2.4) The mixed casting solution was poured into a quartz mold and allowed to stand at room temperature for degassing for 7 h. After natural evaporation for 36 h, a film without heat treatment was obtained, which was recorded as a "c-PIM / DETA" film.

[0068] Step (3) Preparation of cross-linked PIM membrane:

[0069] The c-PIM / DETA membrane obtained in step (2) was heated at 30°C for 16 hours under vacuum conditions to undergo a cross-linking reaction, thereby obtaining a low-temperature cross-linked modified PIM gas separation membrane; labeled as c-PIM / DETA-30°C, the membrane thickness was 120 μm.

[0070] In Example 2, DETA was uniformly distributed in the PIM-BM matrix, and the c-PIM / DETA-30°C cross-linked film exhibited a uniform and dense surface structure, indicating that the interaction between the bromomethyl group and the amino group promoted the formation of an interface without obvious defects.

[0071] Example 3:

[0072] The method of the present invention comprises the following steps:

[0073] Step (1) Preparation of bromomethylated polymer (PIM-BM):

[0074] Step 1.1) Preparation of monomer 3,3,3′,3′,4,4′-hexamethyl-2,2′,3,3′-tetrahydro-1,1′-spirobis[indene]-5,5′,6,6′-tetrol (TTSBI-M):

[0075] 20 g of 3-methylcatechol was dissolved in a mixture of 70 mL of glacial acetic acid and 80 mL of hydrobromic acid, 40 mL of acetone was added dropwise, and the mixture was refluxed at 150°C for 8 h to obtain a brown solution. The solution was then poured into deionized water to precipitate brown flocs. Finally, the flocs were washed multiple times with glacial acetic acid, filtered, and dried in vacuo at 90°C for 24 h to obtain the white powder monomer TTSBI-M.

[0076] Step 1.2) Preparation of methylated PIM (PIM-M): Dissolve 16 g of tetrafluoroterephthalonitrile, 30 g of anhydrous potassium carbonate, and 20 g of the monomer TTSBI-M prepared in 1.1) in 140 mL of N,N-dimethylacetamide (DMAc). Add 60 mL of toluene and react under nitrogen at 170°C for 3 h. The reaction product is then rinsed in deionized water three times, filtered, and dried in a vacuum oven at 100°C for 18 h to obtain PIM-M.

[0077] Step 1.3) Preparation of bromomethylated PIM polymer (PIM-BM): Dissolve 9.76 g of PIM-M prepared in 1.2) in 300 mL of chlorobenzene, add 5.89 g of N-bromosuccinimide and 0.58 g of azobisisobutyronitrile, and react under nitrogen at 160°C for 2 h. After cooling, the reaction product is washed in methanol, repeatedly washed and filtered 4-5 times, and dried in a vacuum oven at 100°C for 18 h to obtain PIM-BM as a yellow solid.

[0078] Step (2) Preparation of membrane material:

[0079] Step 2.1) Dissolve 1.0 g of PIM-BM in 49 g of N,N-dimethylformamide at room temperature to prepare a 2 wt% PIM-BM solution. Stir for 24 h, and then remove impurities from the PIM-BM solution using a syringe filter.

[0080] Step 2.2) At room temperature, dissolve 0.026 g of ethylenediamine (EDA) in 10 g of N,N-dimethylformamide to form a crosslinker solution with a mass ratio of PIM-BM to TAEA of 1:38. Stir for 3 h.

[0081] Step 2.3) Add the crosslinker solution dropwise to the PIM-BM solution at room temperature and stir for 9 h to obtain a fully mixed casting solution;

[0082] Step 2.4) The mixed casting solution was poured into a quartz mold and allowed to stand at room temperature for degassing for 12 h. After natural evaporation for 48 h, a film without heat treatment was obtained, which was recorded as a "c-PIM / EDA" film.

[0083] Step (3) Preparation of cross-linked PIM membrane:

[0084] The c-PIM / EDA membrane obtained in step (2) was heated at 80°C for 6 hours under vacuum conditions to undergo a cross-linking reaction, thereby obtaining a low-temperature cross-linked modified PIM gas separation membrane; the membrane was labeled c-PIM / EDA-80°C, and the membrane thickness was 80 μm.

[0085] In Example 3, EDA is uniformly distributed in the PIM-BM matrix, and the c-PIM / EDA-80°C cross-linked film exhibits a uniform and dense surface structure, indicating that the interaction between the bromomethyl group and the amino group promotes the formation of an interface without obvious defects.

[0086] In Example 3, c-PIM / EDA-80℃ is at 3100-3500cm -1 A new broad peak appeared in the range of 690 cm-1, which was attributed to the NH stretching vibration of the secondary amine group (-NH-). -1 The intensity of the C-Br characteristic peak near 1050 cm- 1, which indicates that PIM-BM and EDA generate covalent chemical bonds (-CH2-NH-) through Hoffman alkylation reaction at low temperature, thus constructing a cross-linked network in the microporous matrix.

[0087] The c-PIM / XT cross-linked membrane prepared in the above example was subjected to CO2 and CH4 flux tests, and the results are shown in the following table:

[0088] Table 1. Gas separation performance of examples

[0089]

[0090] As shown in Table 1, the c-PIM / XT cross-linked membranes (Examples 1-3) prepared at low temperatures (20-80°C) exhibit excellent gas separation performance. Their CO2 fluxes are all above 500 barrers, and their CO2 / CH4 selectivities are all above 300, significantly outperforming existing cross-linked PIM membrane technologies that require high temperatures (typically >200°C). This breakthrough performance stems from the key innovation of the present invention's low-temperature amine-based cross-linking strategy: a small molecule amine cross-linker containing primary amine groups (-NH2) efficiently reacts with the bromomethyl groups (-CH2Br) of the bromomethylated PIM (PIM-BM) polymer chains at mild, low temperatures (20-80°C), forming a highly dense and stable cross-linked network. This network provides excellent size-selectivity, effectively suppressing larger CH4 molecules and resulting in extremely low permeation flux. Furthermore, the primary amine groups (-NH2) in the small molecule amine cross-linker have a strong affinity for CO2 molecules, significantly improving the PIM membrane's selectivity for CO2. This solubility selectivity compensation effect brought about by the introduction of amine groups effectively offsets the loss of CO2 permeation flux that may be caused by the densification of the cross-linked network, thereby achieving efficient suppression of CH4 while maintaining excellent CO2 transmission flux. It is the synergistic effect of the dense screening network constructed at low temperature and high efficiency and the CO2 solubility selectivity compensation given by the amine groups that give the c-PIM / XT cross-linked membrane an ultra-high CO2 / CH4 separation selectivity. In addition, Figure 5 In the CO2 plasticization resistance test of the c-PIM / XT cross-linked membrane, the CO2 permeability in Examples 1-3 decreased with increasing inlet pressure, and no plasticization occurred even when exposed to CO2 at a pressure as high as 0.8 MPa. This shows that low-temperature amino cross-linking can significantly improve the plasticization resistance of the gas separation membrane.

[0091] The above embodiments are merely examples for clarity of explanation and are not intended to limit the embodiments. For those skilled in the art, other variations or modifications may be made based on the above description, and these variations or modifications are still within the scope of protection of the present invention.

Claims

1. A method for preparing a low-temperature amino-crosslinked modified self-polymerized microporous polymer gas separation membrane, characterized in that: The following steps are involved: Step (1), synthesizing a cross-linked precursor polymer PIM-BM by bromomethylation reaction; comprising: Step 1.1), preparing monomer 3,3,3′,3′,4,4′-hexamethyl-2,2′,3,3′-tetrahydro-1,1′-spirobi[indene]-5,5′,6,6′-tetrol TTSBI-M; Step 1.2), preparing methylated PIM, namely PIM-M; Step 1.3), preparing a bromomethylated polymer PIM, namely PIM-BM; Step (2), dissolving PIM-BM and an amine small molecule cross-linking agent to prepare a casting solution, and then casting and volatilizing to form a film; Step (3), heat-treating the membrane obtained in step (2) under low-temperature vacuum conditions to form a cross-linked network structure, the heat treatment temperature is 20-80°C, and the time is 6-32 hours, to obtain a low-temperature amino-cross-linked modified self-polymerized microporous polymer gas separation membrane.

2. The method for preparing a low-temperature amino-crosslinked modified self-polymerized microporous polymer gas separation membrane according to claim 1, characterized in that: The step (1) is specifically as follows: Step 1.1) Preparation of monomer 3,3,3′,3′,4,4′-hexamethyl-2,2′,3,3′-tetrahydro-1,1′-spirobis[indene]-5,5′,6,6′-tetrol TTSBI-M: 3-methylcatechol is dissolved in a mixture of glacial acetic acid and hydrobromic acid, acetone is added dropwise, and the mixture is reacted at a temperature of 110-150° C. for 8-24 hours. The product is then post-treated and vacuum-dried to obtain the monomer TTSBI-M as a white powder. Step 1.2) Preparation of methylated PIM: Dissolve tetrafluoroterephthalonitrile, anhydrous potassium carbonate, and monomer TTSBI-M in solvent A, add toluene, and react under nitrogen at a temperature of 100-170°C for 3-10 hours, then wash and vacuum dry to obtain PIM-M; Step 1.3) Preparation of bromomethylated polymer PIM: PIM-M was dissolved in chlorobenzene, and N-bromosuccinimide and azobisisobutyronitrile were added. The mixture was reacted under nitrogen at a temperature of 80-160° C. for 2-6 h, and then washed and vacuum-dried to obtain yellow solid PIM-BM.

3. The method for preparing a low-temperature amino-crosslinked modified self-polymerized microporous polymer gas separation membrane according to claim 2, characterized in that: In the step 1.1): For every 20g of 3-methylcatechol, add 20-70mL of glacial acetic acid, 30-80mL of hydrobromic acid, and 20-40mL of acetone; The vacuum drying temperature is 60-90°C and the time is 24-42 hours.

4. The method for preparing a low-temperature amino-crosslinked modified self-polymerized microporous polymer gas separation membrane according to claim 2, characterized in that: In the step 1.2): Solvent A is one or a mixture of two or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; For every 20g of TTSBI-M, add 8-16g of tetrafluoroterephthalonitrile, 15-30g of anhydrous potassium carbonate, 30-60mL of toluene, and 80-140mL of solvent A; The vacuum drying temperature is 70-100°C and the time is 18-32 hours.

5. The method for preparing a low-temperature amino-crosslinked modified self-polymerized microporous polymer gas separation membrane according to claim 2, characterized in that: In the step 1.3): For every 9.76 g of PIM-M, add 150-300 mL of chlorobenzene, 1.78-5.89 g of N-bromosuccinimide, and 0.18-0.58 g of azobisisobutyronitrile; The vacuum drying temperature is 70-100°C and the time is 18-32 hours.

6. The method for preparing a low-temperature amino-crosslinked modified self-polymerized microporous polymer gas separation membrane according to claim 1, characterized in that: The step (2) is specifically as follows: Step 2.1), dissolving PIM-BM in solvent B to form a PIM-BM solution, stirring for 5 to 24 hours, and then removing impurities in the PIM-BM solution using a syringe filter; In step 2.2), a small molecule amine crosslinker is dissolved in solvent B to form a crosslinker solution, and the stirring time is 1 to 3 hours; Step 2.3) adding the crosslinker solution dropwise to the PIM-BM solution and stirring to obtain a fully mixed mixed casting solution; the concentration of the mixed casting solution is 2 to 4 w / w%, and the mass ratio of the amine small molecule crosslinker to the PIM-BM is 1:4-38; In step 2.4), the mixed casting solution is allowed to stand at room temperature for degassing and natural evaporation to obtain a film without heat treatment, which is denoted as "c-PIM / X" film, where X represents a cross-linking agent.

7. The method for preparing a low-temperature amino-crosslinked modified self-polymerized microporous polymer gas separation membrane according to claim 6, characterized in that: The amine small molecule crosslinking agent is at least one of ethylenediamine EDA, diethylenetriamine DETA, and tris(2-aminoethyl)amine TAEA; the solvent B is chloroform, tetrahydrofuran, or N,N-dimethylformamide; the casting solution is stirred for 5 to 9 hours, the static degassing time is 2 to 12 hours, and the solvent naturally evaporates for 24 to 48 hours.

8. The method for preparing a low-temperature amino-crosslinked modified self-polymerized microporous polymer gas separation membrane according to claim 1, characterized in that: In the step (3), the heat treatment temperature is 20-40° C. and the time is 12-20 hours.

9. A low-temperature amino-crosslinked modified self-polymerized microporous polymer gas separation membrane prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The gas separation membrane includes a bromomethylated PIM-BM matrix and an amine small molecule cross-linking agent, wherein the amine small molecule cross-linking agent is introduced into the PIM-BM membrane matrix by solution blending to form a pre-cross-linked structure, and the cross-linked structure is formed by heat treatment to obtain a cross-linked membrane material; the thickness of the cross-linked membrane material is 40 to 120 microns.

10. An application of the low-temperature amino-crosslinked modified self-polymerizing microporous polymer gas separation membrane according to claim 9, characterized in that: The gas separation membrane is used for gas separation, salinity difference power generation, ion exchange or other systems.

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