Crosslinked BPDA-based polyimide separation membrane for extracting helium from natural gas

Abstract

The invention relates to the technical field of gas separation membranes, in particular to a cross-linked BPDA-based polyimide separation membrane for extracting helium from natural gas, which is prepared by copolymerizing diamine with TPEQ and BPDA, carrying out thermal crosslinking to synthesize a plurality of cross-linked polyimides, carrying out imidization treatment to prepare a membrane casting solution, and carrying out vacuum drying on the membrane casting solution to obtain the cross-linked BPDA-based polyimide separation membrane for extracting helium from natural gas. The crosslinking type polyimide separation membrane for extracting helium from natural gas is prepared through the prepared membrane casting solution, adopted diamine comprises DABA, ppd and ODA, and three polyimide materials with different polarities and crosslinking densities are synthesized by precisely regulating and controlling the chemical structure and network form of crosslinking type polyimide. Preferential permeation of He is promoted by optimizing the structural advantages of diamine; in this way, the technical problems that in the prior art, a separation membrane material is difficult to meet the requirements of high permeation flux and high selectivity at the same time, and the stability is insufficient under complex working conditions are solved.

Description

Technical Field

[0001] This invention relates to the field of gas separation membrane technology, and more particularly to a cross-linked BPDA-based polyimide separation membrane for helium extraction from natural gas. Background Technology

[0002] Helium (He) and methane (CH4) are important components of natural gas. He is a scarce strategic resource with wide applications in aerospace, medical, and scientific research fields, while CH4 is a clean and efficient energy source. They often exist in a mixed state in natural gas. Currently, to meet the needs of clean energy supply and high-end industries, the efficient separation of He and CH4 from natural gas is of great significance.

[0003] The content of helium (He) in natural gas varies considerably. Conventional natural gas typically contains low levels of He, while in some helium-containing natural gas, the He content can reach 0.1%-3%, mostly found in specific geological structures. He is a non-renewable resource with limited global reserves, and the demand for high-purity He is increasing. Furthermore, the separation of He from CH4 faces numerous challenges.

[0004] Currently, the main methods for separating He and CH4 from natural gas include cryogenic distillation, pressure swing adsorption (PSA), and membrane separation. Membrane separation offers advantages such as simple process, low energy consumption, compact equipment, and ease of modular integration. It is suitable for natural gas fields of different sizes and distributed gas source processing scenarios, making it a separation technology with great development potential.

[0005] Natural gas contains CH4 with a large molecular weight and He with a small molecular weight, exhibiting significant differences in molecular size (He kinetic diameter 0.26 nm, CH4 approximately 0.38 nm) and physical properties. Existing separation membrane materials struggle to simultaneously meet the requirements of high permeation flux and high selectivity, and also suffer from insufficient stability under complex operating conditions. Summary of the Invention

[0006] The purpose of this invention is to provide a cross-linked BPDA-based polyimide separation membrane for helium extraction from natural gas, aiming to solve the technical problems that existing separation membrane materials cannot simultaneously meet the requirements of high permeation flux and high selectivity, and have insufficient stability under complex operating conditions.

[0007] To achieve the above objectives, the present invention employs a cross-linked BPDA-based polyimide separation membrane for helium extraction from natural gas. This membrane is prepared by copolymerizing diamine with TPEQ and BPDA, followed by thermal cross-linking to synthesize various cross-linked polyimides. After imidization treatment, a casting solution is prepared, and the cross-linked polyimide natural gas helium extraction separation membrane is then prepared using this casting solution.

[0008] The preparation method of the cross-linked BPDA-based polyimide separation membrane used for helium extraction from natural gas is as follows:

[0009] In a dried three-necked flask, diamine is added and, after dissolution, TPEQ is added. N,N-dimethylacetamide (DMAc) is used as the solvent, and the solid content is controlled at 15%-35%. After the diamine is completely dissolved, the temperature of the reaction system is lowered to 0-10℃, and BPDA is added, wherein the molar ratio of diamine to dianhydride is 1:1.02. The reaction is stirred for 6-8 hours to form a polyamic acid prepolymer solution.

[0010] The prepolymer solution is heated to 30-50℃ and the reaction continues for 12-18h to form a cross-linked polyimide precursor solution with a curable structure. The precursor solution is precipitated in methanol, filtered, and then vacuum dried at 60-80℃ for 12h to obtain cross-linked polyimide solid.

[0011] Cross-linked polyimide solids are placed in a muffle furnace for imidization treatment to form a stable cross-linked polyimide structure;

[0012] Take the imidized cross-linked polyimide, use N-methylpyrrolidone (NMP) as solvent, add polyvinylpyrrolidone (PVP, content 1%) as additive, control the polyimide concentration to 20%, stir and dissolve at 60℃ for 24h to form a uniform and transparent casting solution.

[0013] After the casting solution is allowed to stand for 12 hours to remove bubbles, it is evenly coated onto a clean glass plate and dried in a 50°C oven until constant weight, thus obtaining a cross-linked polyimide natural gas helium extraction separation membrane.

[0014] The amount of TPEQ added after the diamine is dissolved is 5%-15% of the total molar amount of the diamine.

[0015] The specific method for imidizing cross-linked polyimide solids in a muffle furnace to form a stable cross-linked polyimide structure is as follows:

[0016] The cross-linked polyimide solid was placed in a muffle furnace and heated to 300-350℃ at a rate of 5℃ / min. The temperature was kept constant for 3 hours to completely imidize the polyamic acid and form a stable cross-linked polyimide structure.

[0017] The diamines used include DABA, ppd, and ODA.

[0018] This invention discloses a cross-linked BPDA-based polyimide separation membrane for helium extraction from natural gas. It utilizes a diamine copolymerized with TPEQ and BPDA, followed by thermal cross-linking to synthesize various cross-linked polyimides. After imidization treatment, a casting solution is prepared, and the cross-linked polyimide natural gas helium extraction separation membrane is fabricated using this solution. The diamines used include DABA, ppd, and ODA. By precisely controlling the chemical structure and network morphology of the cross-linked polyimides, three polyimide materials with different polarities and cross-linking densities are synthesized. By optimizing the structural advantages of the diamine, preferential helium permeation is promoted. This approach solves the technical problem in existing separation membrane materials that struggle to simultaneously meet the requirements of high permeation flux and high selectivity, and that they suffer from insufficient stability under complex operating conditions. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art 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.

[0020] Figure 1 This is a schematic diagram of the performance test of the cross-linked BPDA-based polyimide separation membrane for helium extraction from natural gas prepared in Example 1 of the present invention.

[0021] Figure 2 This is a schematic diagram of the performance test of the cross-linked BPDA-based polyimide separation membrane for helium extraction from natural gas prepared in Example 2 of the present invention.

[0022] Figure 3 This is a schematic diagram of the performance test of the cross-linked BPDA-based polyimide separation membrane for helium extraction from natural gas prepared in Example 3 of the present invention. Detailed Implementation

[0023] The embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention.

[0024] This invention provides a cross-linked BPDA-based polyimide separation membrane for helium extraction from natural gas. It uses diamine copolymerized with TPEQ and BPDA, and synthesizes various cross-linked polyimides through thermal cross-linking. After imidization treatment, a casting solution is prepared, and the cross-linked polyimide natural gas helium extraction separation membrane is prepared using the prepared casting solution. The diamines used include DABA, ppd and ODA.

[0025] Example 1:

[0026] Please see Figure 1 , Figure 1 This is a schematic diagram of the performance test of the cross-linked BPDA-based polyimide separation membrane for helium extraction from natural gas prepared in Example 1 of the present invention.

[0027] In this embodiment, the cross-linked BPDA-based polyimide separation membrane for helium extraction from natural gas is prepared as follows:

[0028] S101. In a pre-dried three-necked flask, add 6.84 g of DABA and 118 ml of DMAc, stirring to dissolve and controlling the solid content to approximately 20%. After the DABA is completely dissolved, add 1.46 g of TPEQ (10% of the molar amount of DABA) to the solution. Lower the reaction temperature to 0–5 °C, add 14.7 g of BPDA (DABA to BPDA molar ratio of 1:1.02), and stir for 8 hours to form a polyamic acid prepolymer solution. Then, raise the temperature to 40 °C and continue the reaction for 12 hours to allow TPEQ to crosslink with the polyamic acid segments. After the reaction is complete, pour the solution into methanol to precipitate, filter, and then vacuum dry at 60 °C for 12 hours to obtain BPDA-DABA-TPEQ crosslinked polyimide solid.

[0029] S102. Place the BPDA-DABA-TPEQ cross-linked polyimide solid in a muffle furnace, heat it to 300℃ at a rate of 5℃ / min, and keep it at the temperature for 3h to completely imidize the polyamic acid and form a stable cross-linked polyimide structure.

[0030] S103. Weigh 25g of the imidized polymer and add 120ml of N-methylpyrrolidone (NMP). Using NMP as a solvent, add polyvinylpyrrolidone (PVP, 1% content) as an additive, controlling the polyimide concentration to 20%. Stir and dissolve at 60℃ for 24h to form a uniform and transparent casting solution. After allowing the casting solution to stand for 12h to remove bubbles, coat it evenly on a clean glass plate and dry it in a 50℃ oven to constant weight to obtain the BPDA-DABA-TPEQ crosslinked polyimide flat sheet film.

[0031] S104. The prepared flat sheet membrane was cut to the test size and its separation performance was tested under simulated natural gas conditions (He volume fraction 3%, CH4 volume fraction 97%). The results showed that the He permeability coefficient reached 850 Barrer and the He / CH4 selectivity reached 35, exhibiting good helium extraction performance.

[0032] Example 2:

[0033] Please see Figure 2 , Figure 2This is a schematic diagram of the performance test of the cross-linked BPDA-based polyimide separation membrane for helium extraction from natural gas prepared in Example 2 of the present invention.

[0034] In this embodiment, the cross-linked BPDA-based polyimide separation membrane for helium extraction from natural gas is prepared as follows:

[0035] S201. In a dry three-necked flask, add 9.01 g of ODA and 131 ml of DMAc, stirring to dissolve, controlling the solid content to approximately 20%. After the ODA is completely dissolved, add 1.46 g of TPEQ (10% of the molar amount of ODA) to the solution. After it is completely dissolved, lower the temperature of the reaction system to 0–5 °C, add 14.7 g of BPDA, and stir for 8 hours. Once a polyamic acid prepolymer solution is formed, raise the temperature to 45 °C and continue the reaction for 12 hours. After the reaction is complete, pour the solution into methanol to precipitate, filter, and then vacuum dry at 70 °C for 10 hours to obtain BPDA-ODA-TPEQ crosslinked polyimide solid.

[0036] S202. Place the BPDA-ODA-TPEQ cross-linked polyimide solid into a muffle furnace and heat it to 320°C at a rate of 5°C / min. Maintain the temperature for 3 hours to complete the imidization of polyamic acid and form a stable cross-linked polyimide structure.

[0037] S203. Take 30g of the imidized polymer, add 140ml of NMP, and use NMP as a solvent. Add polyvinylpyrrolidone (PVP, 1% content) as an additive, controlling the polyimide concentration to 20%. Stir and dissolve at 60℃ for 24h, and let stand for 12h to remove bubbles. Use a coating method to uniformly coat the casting solution onto a clean glass plate, and dry it in a 60℃ oven to constant weight to obtain the BPDA-ODA-TPEQ crosslinked polyimide flat sheet membrane.

[0038] S204. The gas separation performance of the prepared flat sheet membrane was tested. Under simulated helium-containing natural gas (He volume fraction 3%, CH4 volume fraction 97%), the He permeability coefficient was 780 Barrer, and the He / CH4 selectivity reached 38, achieving effective separation of helium and methane.

[0039] Example 2:

[0040] Please see Figure 3 , Figure 3 This is a schematic diagram of the performance test of the cross-linked BPDA-based polyimide separation membrane for helium extraction from natural gas prepared in Example 3 of the present invention.

[0041] In this embodiment, the cross-linked BPDA-based polyimide separation membrane for helium extraction from natural gas is prepared as follows:

[0042] S301. Add 4.8 g of ppd to a dry three-necked flask, add 110 ml of DMAc and stir to dissolve, controlling the solid content to be approximately 20%. After the ppd is completely dissolved, add 1.46 g of TPEQ (10% of the molar amount of ppd) to the solution, lower the reaction temperature to 8°C, add 14.7 g of BPDA, stir and react for 9 h. After forming a polyamic acid prepolymer solution, raise the temperature to 35°C and continue the reaction for 18 h. After the reaction is complete, pour the solution into methanol to precipitate, filter, and dry under vacuum at 60°C for 12 h to obtain BPDA-ppd-TPEQ crosslinked polyimide solid.

[0043] S302. Place the BPDA-ppd-TPEQ cross-linked polyimide solid in a muffle furnace and heat it to 350°C at a rate of 5°C / min. Maintain the temperature for 3 hours to fully imidize the polyamic acid and form a stable cross-linked polyimide structure.

[0044] S303. Weigh 28g of the imidized polymer and add it to a three-necked flask. Add 130ml of NMP. Using NMP as a solvent, add polyvinylpyrrolidone (PVP, 1% content) as an additive, controlling the polyimide concentration to 20%. Stir and dissolve at 60℃ for 24h, then allow to stand for 12h to degas. Coat the casting solution onto a glass plate using a coating method, and dry it in a 50℃ oven to constant weight to obtain a BPDA-ppd-TPEQ crosslinked polyimide flat sheet membrane.

[0045] S304. The membrane performance was tested under simulated helium-containing natural gas (He volume fraction 3%, CH4 volume fraction 97%). The results showed that the He permeability coefficient reached 820 Barrer and the He / CH4 selectivity reached 32, effectively verifying the applicability of the membrane for helium extraction from natural gas.

[0046] Using a cross-linked BPDA-based polyimide separation membrane for helium extraction from natural gas, as described in this invention, three polyimide materials with different polarities and cross-linking densities were synthesized by precisely controlling the chemical structure and network morphology of the cross-linked polyimide. By optimizing the diamine structure, preferential He permeation was promoted; simultaneously, by rationally controlling the polarity of the membrane material, utilizing the weak interaction between He and the membrane and the stable three-dimensional network of the cross-linked polyimide, the mechanical strength of the membrane was improved, and microscopic channels facilitating rapid He transport were constructed. The prepared cross-linked polyimide separation membrane not only achieves efficient separation of He and CH4, significantly improving the efficiency of natural gas helium extraction, but also effectively resists the influence of complex components through the enhanced cross-linking network, greatly improving the stability and service life of the membrane material, providing an efficient and reliable technical solution for natural gas helium extraction and CH4 concentration.

[0047] The above description discloses only one preferred embodiment of the present invention, and should not be construed as limiting the scope of the present invention. Those skilled in the art will understand that all or part of the processes of the above embodiments can be implemented, and equivalent changes made in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A cross-linked BPDA-based polyimide separation membrane for helium extraction from natural gas, characterized in that, A variety of cross-linked polyimides were synthesized by copolymerizing diamine with TPEQ and BPDA and then thermally cross-linking them. After imidization treatment, a casting solution was prepared, and a cross-linked polyimide natural gas helium extraction separation membrane was prepared using the prepared casting solution.

2. The cross-linked BPDA-based polyimide separation membrane for helium extraction from natural gas as described in claim 1, characterized in that, The preparation method of the cross-linked BPDA-based polyimide separation membrane for helium extraction from natural gas is as follows: In a dried three-necked flask, diamine is added and, after dissolution, TPEQ is added. N,N-dimethylacetamide (DMAc) is used as the solvent, and the solid content is controlled at 15%-35%. After the diamine is completely dissolved, the temperature of the reaction system is lowered to 0-10℃, and BPDA is added, wherein the molar ratio of diamine to dianhydride is 1:1.

02. The reaction is stirred for 6-8 hours to form a polyamic acid prepolymer solution. The prepolymer solution is heated to 30-50℃ and the reaction continues for 12-18h to form a cross-linked polyimide precursor solution with a curable structure. The precursor solution is precipitated in methanol, filtered, and then vacuum dried at 60-80℃ for 12h to obtain cross-linked polyimide solid. Cross-linked polyimide solids are placed in a muffle furnace for imidization treatment to form a stable cross-linked polyimide structure; Take the imidized cross-linked polyimide, use N-methylpyrrolidone (NMP) as solvent, add polyvinylpyrrolidone (PVP, content 1%) as additive, control the polyimide concentration to 20%, stir and dissolve at 60℃ for 24h to form a uniform and transparent casting solution. After the casting solution is allowed to stand for 12 hours to remove bubbles, it is evenly coated onto a clean glass plate and dried in a 50°C oven until constant weight, thus obtaining a cross-linked polyimide natural gas helium extraction separation membrane.

3. The cross-linked BPDA-based polyimide separation membrane for helium extraction from natural gas as described in claim 2, characterized in that, After the diamine has dissolved, the amount of TPEQ added should be 5%-15% of the total molar amount of the diamine.

4. The cross-linked BPDA-based polyimide separation membrane for helium extraction from natural gas as described in claim 3, characterized in that, The specific method for imidizing cross-linked polyimide solids in a muffle furnace to form a stable cross-linked polyimide structure is as follows: The cross-linked polyimide solid was placed in a muffle furnace and heated to 300-350℃ at a rate of 5℃ / min. The temperature was kept constant for 3 hours to completely imidize the polyamic acid and form a stable cross-linked polyimide structure.

5. The cross-linked BPDA-based polyimide separation membrane for helium extraction from natural gas as described in claim 4, characterized in that, The diamines used include DABA, ppd, and ODA.

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