Preparation method of hollow fiber gas separation membrane for decarburization of oilfield associated gas

Abstract

The invention relates to a preparation method of a hollow fiber gas separation membrane for decarburization of oilfield associated gas, and belongs to the technical field of separation membranes, and the preparation method specifically comprises the following steps: mixing 4, 4 '-diaminodiphenyl sulfone with diamine under the protection of argon, and then adding a solvent N, N-dimethylacetamide; after diamine is completely dissolved, dianhydride is added in batches until a polyamide acid prepolymer solution is obtained through stirring; adding a dehydrating agent and a catalyst into the polyamide acid prepolymer solution to generate a polyimide solution; the preparation method comprises the following steps: mixing dianhydride with sulfuryl-containing diamine, then adding the sulfuryl-containing diamine into a reaction solution, then pouring the reaction solution into a precipitant methanol to separate out a polymer, washing and drying to obtain a polyimide solid, then preparing the polyimide solid into a membrane casting solution, and carrying out a spinning process to obtain the hollow fiber gas separation membrane. And the hollow fiber gas separation membrane is prepared by spinning, so that the molecular chain structure is optimized, and the comprehensive performance of the material is improved.

Description

Technical Field

[0001] This invention relates to a method for preparing a hollow fiber gas separation membrane for decarbonization of associated gas in oil fields, belonging to the field of separation membrane technology. Background Technology

[0002] Natural gas is an important clean energy source for achieving China's dual-carbon development goals. Associated gas from oil fields refers to natural gas produced simultaneously with crude oil during oil extraction and is part of the oil and gas reservoir. Associated gas contains hydrocarbon gases such as methane and ethane, as well as small amounts of non-hydrocarbon gases such as carbon dioxide, hydrogen sulfide, and nitrogen. However, high carbon dioxide content reduces the heat released during combustion and can even cause flame retardancy issues, affecting its efficiency and value as a fuel. Decarbonization can improve the calorific value of associated gas, making it more suitable for energy utilization standards and better suited for industrial or residential fuel, thus achieving efficient resource utilization.

[0003] To improve the quality of associated gas in oil fields and thus increase economic benefits, carbon dioxide removal from natural gas is essential. There are many methods for associated gas decarbonization, which can be broadly categorized into chemical solvent methods, physical solvent methods, and membrane separation methods. Chemical solvent methods involve contacting an alkaline solution with the acidic components in the associated gas, primarily H2S and CO2, to react and form a compound. The alkaline solution, having absorbed the acidic components, can be regenerated to release these components from the compound. The most representative method in this process is the amine method, which is the most commonly used associated gas decarbonization method and is further subdivided into monoethanolamine (MEA), diethanolamine (DEA), diethylene glycolamine (DGA), diisopropanolamine (DIPA), and methyldiethanolamine (MDEA) methods. Amine solutions are mainly composed of alkanolamines and water. Physical solvent methods utilize the significant difference in solubility between certain solvents and hydrocarbons, such as H2S and CO2, to remove the acidic components. Because physical solvents have a high solubility for heavy hydrocarbons in associated gas, they are not suitable for associated gas with high heavy hydrocarbon content. Commonly used physical solvent methods include the polyethylene glycol dimethyl ether method, the propylene carbonate method, and the cold methanol method. Physical absorption methods utilize multi-stage flash evaporation technology to regenerate the solvent, requiring no additional heating; the associated gas dehydration occurs simultaneously during the reaction. Membrane separation technology evolved from industrial processes such as liquid separation to gas separation. Its principle is that the components in a gas mixture pass through the separation membrane at different rates under pressure. The filtered gas passes through the membrane module through different diffusion mechanisms, including microporous diffusion and dissolution diffusion. Membrane separation is a physical filtration technology developed and applied at the end of the last century. It removes H2S and CO2 from associated gas through selective permeation of the membrane during the separation process, making it more energy-efficient and lower in consumption.

[0004] However, the membrane materials currently in use (especially polymer membranes) have free volume between polymer chain segments. After gas molecules (such as CO, H2, and heavy hydrocarbons) dissolve, they will insert into the intersegment gaps, causing the polymer network to expand, which leads to swelling of the membrane material, reduced selectivity, and changes in the physical properties of the solution such as viscosity and surface tension. Summary of the Invention

[0005] To address the technical problems existing in the prior art, this invention provides a method for preparing a hollow fiber gas separation membrane for associated gas decarbonization in oil fields. The method involves the synergistic effect of mixing dianhydrides with sulfone-containing diamines and other diamines, followed by spinning to obtain a hollow fiber gas separation membrane. This optimizes the molecular chain structure and improves the overall performance of the material.

[0006] To achieve the above objectives, the technical solution adopted in this invention is a method for preparing a hollow fiber gas separation membrane for associated gas decarbonization in oil fields, which is carried out according to the following steps: S1. Under argon protection, 4,4'-diaminodiphenyl sulfone and diamine are mixed, and then N,N-dimethylacetamide is added as solvent, controlling the solid content to be 15%-35%; S2. After the diamine is completely dissolved, the temperature of the reaction system is lowered to 5 ℃. The dianhydride is added in batches, and the total number of moles of dianhydride and diamine is the same. The mixture is stirred until it is completely dissolved and the solution viscosity is stable, resulting in a uniform and transparent polyamic acid solution. The reaction is continued to be stirred to obtain a polyamic acid prepolymer solution. S3. Add a dehydrating agent and a catalyst to the polyamic acid prepolymer solution to react and generate a polyimide solution; S4. The reaction solution is then poured into methanol as a precipitant to precipitate the polymer. After washing and drying, polyimide solid is obtained. The polyimide solid is then formulated into a casting solution, and hollow fiber gas separation membrane is obtained through a spinning process.

[0007] Preferably, in step S2, the diamine is one or more of m-phenylenediamine, p-phenylenediamine, and 4,4'-diaminodiphenyl ether, and the molar ratio of 4,4'-diaminodiphenyl sulfone to the diamine is 1:19-3:7.

[0008] Preferably, the dianhydride is hexafluorodianhydride and biphenyltetracarboxylic dianhydride, and the molar ratio of hexafluorodianhydride to biphenyltetracarboxylic dianhydride is 1:9-9:1.

[0009] Preferably, in step S3, the dehydrating agent is acetic anhydride and the catalyst is 3-methylpyridine.

[0010] Compared with existing technologies, this invention has the following technical advantages: This invention prepares polyimide films by mixing dianhydrides and sulfone-containing diamines. Through molecular design, it achieves multi-dimensional optimization of thermal stability, mechanical strength, dielectric properties, and processability, breaking through the performance bottleneck of single-system materials. Its core advantage lies in its ability to flexibly match the needs of different application scenarios (such as the flexibility of flexible electronics, the high-temperature resistance of aerospace, and the low dielectric properties in the communications field) through component control, while also considering cost and environmental adaptability. This represents an important development direction for high-performance polymer film materials. Attached Figure Description

[0011] Figure 1 This is a cross-sectional scanning electron microscope (SEM) image of the separation membrane of the present invention. Detailed Implementation

[0012] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention. Example 1

[0013] 1) Under argon protection, 0.25 g of DDS and 2.05 g of MPD (DDS to MPD molar ratio of 1:19) were added to a dry, clean flask, followed by 38.7 mL of DMAC solvent and stirred thoroughly. After the diamine was completely dissolved, the reaction temperature was lowered to 5°C, and 7.99 g of 6FDA and 1.04 g of BPADA (6FDA to BPADA molar ratio of 9:1) were added in portions. Then, 1.65 mL of DMAc was added and dissolved thoroughly, controlling the solid content to approximately 15%. The reaction was stirred for 8 h to form a homogeneous polyamic acid solution.

[0014] 2) After the reaction was complete, 9.45 mL of acetic anhydride and 1.61 mL of 3-methylpyridine were added and reacted for 4 h. After the reaction was complete, the solution was poured into methanol to precipitate, filtered, and then dried under vacuum at 60 °C for 12 h to obtain 6FDA-BPADA-DDS-MPD polyimide solid.

[0015] 3) Weigh 10g of the synthesized polymer and add it to a three-necked flask equipped with a stirrer. Then add 2g of polyethylene glycol, 5mL of isopropanol, 3mL of tetrahydrofuran, 0.5g of sodium dodecylbenzenesulfonate and 40mL of DMF in sequence. Heat to 50℃ and stir to dissolve and prepare a casting solution.

[0016] 4) After the prepared casting solution is allowed to stand and kept at a constant temperature, and then degassed under vacuum for 12 hours, it is injected into the spinneret at a rate of 50 mL / h using a gear pump. The solution is then extruded through the spinneret into a phase inversion tank with water as the coagulation bath to obtain a hollow fiber membrane. The spinning conditions are as follows: the proportion of DMF in the spinneret core solution is 80% in water, the core solution flow rate is 50 mL / h, the coagulation bath temperature is 30℃, the washing tank temperature is 50℃, the distance between the spinneret and the coagulant is 20 cm, and the take-up rate is 20 m / min.

[0017] 5) The prepared hollow fiber membrane was tested for separation performance under simulated oilfield associated gas conditions. Its CO2 permeability coefficient was 85 Barrer and its CO2 / CH4 selectivity was 42. Example 2

[0018] 1) In a pre-dried three-necked flask under argon protection, add 0.66 g of DDS and 2.73 g of PPD (DDS to PPD molar ratio 2:8), and add 28.5 mL of DMAC and stir to dissolve. After the diamine is completely dissolved, lower the reaction temperature to 5°C, and add 6FDA and BPADA in portions: 5.99 g of 6FDA and 3.49 g of BPADA (6FDA to BPADA molar ratio 5:5). Add 26.3 mL of DMAc to dissolve completely, controlling the solid content to approximately 25%. Stir the reaction for 8 hours to form a polyamic acid solution.

[0019] 2) After the reaction was complete, 7.5 mL of acetic anhydride and 1.3 mL of 3-methylpyridine were added and reacted for 4 h. After the reaction was complete, the solution was poured into methanol to precipitate, filtered, and then dried under vacuum at 60 °C for 12 h to obtain 6FDA-BPADA-DDS-PPD polyimide solid.

[0020] 3) Weigh 10g of the synthesized polymer and add it to a three-necked flask with a stirrer. Then add 2g of polyethylene glycol, 5mL of isopropanol, 3mL of tetrahydrofuran, 0.5g of sodium dodecylbenzenesulfonate and 40mL of DMF in sequence. Stir to dissolve and prepare a casting solution.

[0021] 4) The prepared casting solution is kept at a constant temperature and allowed to stand under vacuum to remove bubbles. It is then injected into the spinneret at a rate of 50 mL / h using a gear pump. The solution is extruded through the spinneret into a phase inversion tank with water as the coagulation bath to obtain a hollow fiber membrane. The spinning conditions are as follows: DMF content in the spinneret core solution is 80% in water; core solution flow rate is 50 mL / h; coagulation bath temperature is 30℃; washing tank temperature is 50℃; distance between the spinneret and the coagulant is 20 cm; and take-up rate is 20 m / min.

[0022] 5) The prepared hollow fiber membrane was tested for separation performance under simulated oilfield associated gas conditions. Its CO2 permeability coefficient was 72 Barrer and its CO2 / CH4 selectivity was 48. Example 3

[0023] 1) In a pre-dried three-necked flask under argon protection, add 1.49 g of DDS (4,4'-diaminodiphenyl sulfone) and 3.36 g of ODA (DDS to ODA molar ratio of 3:7), and add 18.2 mL of DMAC and stir to dissolve. After the diamine is completely dissolved, lower the reaction temperature to 5°C, and add 6FDA and BPADA (6FDA to BPADA molar ratio of 1:9) in batches. Add 1.79 g of 6FDA and 8.33 g of BPADA, and add 27.3 mL of DMAc to dissolve completely, controlling the solid content to approximately 35%. Stir the reaction for 8 hours to form a polyamic acid precursor solution.

[0024] 2) After the reaction was complete, acetic anhydride (9.45 mL) and 3-methylpyridine (1.94 mL) were added and reacted for 4 h. After the reaction was complete, the solution was poured into methanol to precipitate, filtered, and then dried under vacuum at 60 °C for 12 h to obtain 6FDA-BPADA-DDS-ODA polyimide solid.

[0025] 3) Weigh 10g of the synthesized polymer and add it to a three-necked flask with a stirrer. Then add 2g of polyethylene glycol, 5mL of isopropanol, 3mL of tetrahydrofuran, 0.5g of sodium dodecylbenzenesulfonate and 40mL of DMF in sequence. Stir to dissolve and prepare a casting solution.

[0026] 4) The prepared casting solution is kept at a constant temperature and allowed to stand under vacuum to remove bubbles. It is then injected into the spinneret at a rate of 50 mL / h using a gear pump. The solution is extruded through the spinneret into a phase inversion tank with water as the coagulation bath to obtain a hollow fiber membrane. The spinning conditions are as follows: DMF content in the spinneret core solution is 80% in water; core solution flow rate is 50 mL / h; coagulation bath temperature is 30℃; washing tank temperature is 50℃; distance between the spinneret and the coagulant is 20 cm; and take-up rate is 20 m / min.

[0027] 5) The prepared hollow fiber membrane was tested for separation performance under simulated oilfield associated gas conditions. Its CO2 permeability coefficient was 68 Barrer and its CO2 / CH4 selectivity was 52. Example 4

[0028] 1) In a pre-dried three-necked flask under argon protection, add 0.33 g of DDS, 1.03 g of MPD, and 0.36 g of PPD (the molar ratio of DDS to the MPD+PPD mixed diamine is 1:9). Add 35.6 mL of DMAC and stir to dissolve. After the diamine is completely dissolved, lower the reaction temperature to 5°C. Add 6FDA and BPADA in portions (6FDA to BPADA molar ratio is 7:3), adding 7.02 g of 6FDA and 4.72 g of BPADA. Add 36 mL of DMAc to dissolve completely, controlling the solid content to approximately 20%. Stir the reaction for 8 hours to form a polyamic acid solution.

[0029] 2) After the reaction was complete, acetic anhydride (8.8 mL) and 3-methylpyridine (1.5 mL) were added and reacted for 4 h. After the reaction was complete, the solution was poured into methanol to precipitate, filtered, and then dried under vacuum at 60 °C for 12 h to obtain 6FDA-BPADA-DDS-MPD-PPD polyimide solid.

[0030] 3) Weigh 10g of the synthesized polymer and add it to a three-necked flask with a stirrer. Then add 2g of polyethylene glycol, 5mL of isopropanol, 3mL of tetrahydrofuran, 0.5g of sodium dodecylbenzenesulfonate and 40mL of DMF in sequence. Stir to dissolve and prepare a casting solution.

[0031] 4) The prepared casting solution is kept at a constant temperature and allowed to stand under vacuum to remove bubbles. It is then injected into the spinneret at a rate of 50 mL / h using a gear pump. The solution is extruded through the spinneret into a phase inversion tank with water as the coagulation bath to obtain a hollow fiber membrane. The spinning conditions are as follows: DMF content in the spinneret core solution is 80% in water; core solution flow rate is 50 mL / h; coagulation bath temperature is 30℃; washing tank temperature is 50℃; distance between the spinneret and the coagulant is 20 cm; and take-up rate is 20 m / min.

[0032] 5) The prepared hollow fiber membrane was tested for separation performance under simulated oilfield associated gas conditions. Its CO2 permeability coefficient was 78 Barrer and its CO2 / CH4 selectivity was 45.

[0033] Comparative Example 1 (compared to Example 1) 1) Under argon protection, 0.23 g DDS and 2.23 g MPD (DDS to MPD molar ratio of 1:20) were added to a dry and clean flask, followed by 38.7 mL of DMAC solvent and stirred thoroughly. After the diamine was completely dissolved, the reaction temperature was lowered to 5 °C, and 7.99 g 6FDA and 1.04 g BPADA (6FDA to BPADA molar ratio of 9:1) were added in portions, followed by 1.65 mL DMAc4 to dissolve completely, controlling the solid content to approximately 15%. The reaction was stirred for 8 h to form a homogeneous polyamic acid solution.

[0034] 2) After the reaction was complete, acetic anhydride (9.45 mL) and 3-methylpyridine (1.61 mL) were added and reacted for 4 h. After the reaction was complete, the solution was poured into methanol to precipitate, filtered, and then dried under vacuum at 60 °C for 12 h to obtain 6FDA-BPADA-DDS-MPD polyimide solid.

[0035] 3) Weigh 10g of the synthesized polymer and add it to a three-necked flask equipped with a stirrer. Then add 2g of polyethylene glycol, 5mL of isopropanol, 3mL of tetrahydrofuran, 0.5g of sodium dodecylbenzenesulfonate and 40mL of DMF in sequence. Heat to 50℃ and stir to dissolve and prepare a casting solution.

[0036] 4) After the prepared casting solution is allowed to stand and kept at a constant temperature, and then degassed under vacuum for 12 hours, it is injected into the spinneret at a rate of 50 mL / h using a gear pump. The solution is then extruded through the spinneret into a phase inversion tank with water as the coagulation bath to obtain a hollow fiber membrane. The spinning conditions are as follows: the proportion of DMF in the spinneret core solution is 80% in water, the core solution flow rate is 50 mL / h, the coagulation bath temperature is 30℃, the washing tank temperature is 50℃, the distance between the spinneret and the coagulant is 20 cm, and the take-up rate is 20 m / min.

[0037] 5) The prepared hollow fiber membrane was tested for separation performance under simulated oilfield associated gas conditions. The DDS content was insufficient, the sulfone group enhancement effect was weakened, the CO2 permeability coefficient was 62 Barrer, and the CO2 / CH4 selectivity was 31.

[0038] Comparative Example 2 (compared to Example 3) 1) In a pre-dried three-necked flask under argon protection, add 1.98 g of DDS (4,4'-diaminodiphenyl sulfone) and 2.88 g of ODA (DDS to ODA molar ratio of 4:6), and add 18.2 mL of DMAC and stir to dissolve. After the diamine is completely dissolved, lower the reaction temperature to 5°C, and add 6FDA and BPADA (6FDA to BPADA molar ratio of 1:9) in portions. Add 1.79 g of 6FDA and 8.33 g of BPADA, and add 27.3 mL of DMAc to dissolve completely, controlling the solid content to approximately 35%. Stir the reaction for 8 hours to form a polyamic acid precursor solution.

[0039] 2) After the reaction was complete, acetic anhydride (9.45 mL) and 3-methylpyridine (1.94 mL) were added and reacted for 4 h. After the reaction was complete, the solution was poured into methanol to precipitate, filtered, and then dried under vacuum at 60 °C for 12 h to obtain 6FDA-BPADA-DDS-ODA polyimide solid.

[0040] 3) Weigh 10g of the synthesized polymer and add it to a three-necked flask with a stirrer. Then add 2g of polyethylene glycol, 5mL of isopropanol, 3mL of tetrahydrofuran, 0.5g of sodium dodecylbenzenesulfonate and 40mL of DMF in sequence. Stir to dissolve and prepare a casting solution.

[0041] 4) The prepared casting solution is kept at a constant temperature and allowed to stand under vacuum to remove bubbles. It is then injected into the spinneret at a rate of 50 mL / h using a gear pump. The solution is extruded through the spinneret into a phase inversion tank with water as the coagulation bath to obtain a hollow fiber membrane. The spinning conditions are as follows: DMF content in the spinneret core solution is 80% in water; core solution flow rate is 50 mL / h; coagulation bath temperature is 30℃; washing tank temperature is 50℃; distance between the spinneret and the coagulant is 20 cm; and take-up rate is 20 m / min.

[0042] 5) The prepared hollow fiber membrane was tested for separation performance under simulated oilfield associated gas conditions. Excessive DDS content led to increased molecular chain crystallinity, and its CO2 permeability coefficient was 45 Barrer, while the CO2 / CH4 selectivity was 40.

[0043] Comparative Example 3 (compared to Example 1) 1) Under argon protection, 0.25 g DDS and 2.05 g MPD (DDS to MPD molar ratio of 1:19) were added to a dry and clean flask, followed by 38.7 mL of DMAC solvent and stirred thoroughly. After the diamine was completely dissolved, the reaction temperature was lowered to 5 °C, and 8.88 g of 6FDA (6FDA to BPADA molar ratio of 10:0) was added, followed by 41.65 mL of DMAc to dissolve it completely, controlling the solid content to approximately 15%. The reaction was stirred for 8 h to form a homogeneous polyamic acid solution.

[0044] 2) After the reaction was complete, acetic anhydride (9.45 mL) and 3-methylpyridine (1.61 mL) were added and reacted for 4 h. After the reaction was complete, the solution was poured into methanol to precipitate, filtered, and then dried under vacuum at 60 °C for 12 h to obtain 6FDA-DDS-MPD polyimide solid.

[0045] 3) Weigh 10g of the synthesized polymer and add it to a three-necked flask equipped with a stirrer. Then add 2g of polyethylene glycol, 5mL of isopropanol, 3mL of tetrahydrofuran, 0.5g of sodium dodecylbenzenesulfonate and 40mL of DMF in sequence. Heat to 50℃ and stir to dissolve and prepare a casting solution.

[0046] 4) After the prepared casting solution is allowed to stand and kept at a constant temperature, and then degassed under vacuum for 12 hours, it is injected into the spinneret at a rate of 50 mL / h using a gear pump. The solution is then extruded through the spinneret into a phase inversion tank with water as the coagulation bath to obtain a hollow fiber membrane. The spinning conditions are as follows: the proportion of DMF in the spinneret core solution is 80% in water, the core solution flow rate is 50 mL / h, the coagulation bath temperature is 30℃, the washing tank temperature is 50℃, the distance between the spinneret and the coagulant is 20 cm, and the take-up rate is 20 m / min.

[0047] 5) The prepared hollow fiber membrane was tested for separation performance under simulated oilfield associated gas conditions. Due to the lack of flexible segments of BPADA, the solubility decreased, and its CO2 permeability coefficient was 58 Barrer and the CO2 / CH4 selectivity was 38.

[0048] Comparative Example 4 (compared to Example 3) 1) In a pre-dried three-necked flask under argon protection, add 1.49 g of DDS (4,4'-diaminodiphenyl sulfone) and 3.36 g of ODA (with a molar ratio of DDS to ODA of 3:7), and add 18.2 mL of DMAC and stir to dissolve. After the diamine is completely dissolved, lower the temperature of the reaction system to 5°C, and add 6FDA and BPADA (with a molar ratio of 6FDA to BPADA of 1:10) in batches. Add 0.89 g of 6FDA and 10.41 g of BPADA, and add 27.3 mL of DMAc to dissolve completely, controlling the solid content to approximately 35%. Stir the reaction for 8 hours to form a polyamic acid precursor solution.

[0049] 2) After the reaction was complete, acetic anhydride (9.45 mL) and 3-methylpyridine (1.94 mL) were added and reacted for 4 h. After the reaction was complete, the solution was poured into methanol to precipitate, filtered, and then dried under vacuum at 60 °C for 12 h to obtain 6FDA-BPADA-DDS-ODA polyimide solid.

[0050] 3) Weigh 10g of the synthesized polymer and add it to a three-necked flask with a stirrer. Then add 2g of polyethylene glycol, 5mL of isopropanol, 3mL of tetrahydrofuran, 0.5g of sodium dodecylbenzenesulfonate and 40mL of DMF in sequence. Stir to dissolve and prepare a casting solution.

[0051] 4) The prepared casting solution is kept at a constant temperature and allowed to stand under vacuum to remove bubbles. It is then injected into the spinneret at a rate of 50 mL / h using a gear pump. The solution is extruded through the spinneret into a phase inversion tank with water as the coagulation bath to obtain a hollow fiber membrane. The spinning conditions are as follows: DMF content in the spinneret core solution is 80% in water; core solution flow rate is 50 mL / h; coagulation bath temperature is 30℃; washing tank temperature is 50℃; distance between the spinneret and the coagulant is 20 cm; and take-up rate is 20 m / min.

[0052] 5) The prepared hollow fiber membrane was tested for separation performance under simulated oilfield associated gas conditions. Excessive BPADA led to a decrease in heat resistance. Its CO2 permeability coefficient was 55 Barrer and its CO2 / CH4 selectivity was 35.

[0053] Comparative Example 5 (compared to Example 2) 1) In a pre-dried three-necked flask under argon protection, add 0.66 g DDS and 2.73 g PPD (DDS to PPD molar ratio of 2:8), and add 28.5 mL of DMAC and stir to dissolve. After the diamine is completely dissolved, lower the reaction temperature to 5°C, and add 6FDA and BPADA in portions: 5.99 g of 6FDA and 3.49 g of BPADA (6FDA to BPADA molar ratio of 5:5). Add 100.2 mL of DMAc to dissolve completely, controlling the solid content to approximately 10%. Stir the reaction for 8 hours to form a polyamic acid solution.

[0054] 2) After the reaction was complete, acetic anhydride (7.5 mL) and 3-methylpyridine (1.3 mL) were added and reacted for 4 h. After the reaction was complete, the solution was poured into methanol to precipitate, filtered, and then dried under vacuum at 60 °C for 12 h to obtain 6FDA-BPADA-DDS-PPD polyimide solid.

[0055] 3) Weigh 10g of the synthesized polymer and add it to a three-necked flask with a stirrer. Then add 2g of polyethylene glycol, 5mL of isopropanol, 3mL of tetrahydrofuran, 0.5g of sodium dodecylbenzenesulfonate and 40mL of DMF in sequence. Stir to dissolve and prepare a casting solution.

[0056] 4) The prepared casting solution is kept at a constant temperature and allowed to stand under vacuum to remove bubbles. It is then injected into the spinneret at a rate of 50 mL / h using a gear pump. The solution is extruded through the spinneret into a phase inversion tank with water as the coagulation bath to obtain a hollow fiber membrane. The spinning conditions are as follows: DMF content in the spinneret core solution is 80% in water; core solution flow rate is 50 mL / h; coagulation bath temperature is 30℃; washing tank temperature is 50℃; distance between the spinneret and the coagulant is 20 cm; and take-up rate is 20 m / min.

[0057] 5) The prepared hollow fiber membrane was tested for separation performance under simulated oilfield associated gas conditions. The system was too dilute, which hindered molecular chain growth. Its CO2 permeability coefficient was 48 Barrer and its CO2 / CH4 selectivity was 33.

[0058] Comparative Example 6 (compared to Example 3) 1) In a pre-dried three-necked flask under argon protection, add 1.49 g of DDS (4,4'-diaminodiphenyl sulfone) and 3.36 g of ODA (DDS to ODA molar ratio of 3:7), and add 18.2 mL of DMAC and stir to dissolve. After the diamine is completely dissolved, lower the reaction temperature to 5°C, and add 6FDA and BPADA (6FDA to BPADA molar ratio of 1:9) in portions. Add 1.79 g of 6FDA and 8.33 g of BPADA, and add 21.6 mL of DMAc to dissolve completely, controlling the solid content to approximately 40%. Stir the reaction for 8 hours to form a polyamic acid precursor solution.

[0059] 2) After the reaction was complete, acetic anhydride (9.45 mL) and 3-methylpyridine (1.94 mL) were added and reacted for 4 h. After the reaction was complete, the solution was poured into methanol to precipitate, filtered, and then dried under vacuum at 60 °C for 12 h to obtain 6FDA-BPADA-DDS-ODA polyimide solid.

[0060] 3) Weigh 10g of the synthesized polymer and add it to a three-necked flask with a stirrer. Then add 2g of polyethylene glycol, 5mL of isopropanol, 3mL of tetrahydrofuran, 0.5g of sodium dodecylbenzenesulfonate and 40mL of DMF in sequence. Stir to dissolve and prepare a casting solution.

[0061] 4) The prepared casting solution is kept at a constant temperature and allowed to stand under vacuum to remove bubbles. It is then injected into the spinneret at a rate of 50 mL / h using a gear pump. The solution is extruded through the spinneret into a phase inversion tank with water as the coagulation bath to obtain a hollow fiber membrane. The spinning conditions are as follows: DMF content in the spinneret core solution is 80% in water; core solution flow rate is 50 mL / h; coagulation bath temperature is 30℃; washing tank temperature is 50℃; distance between the spinneret and the coagulant is 20 cm; and take-up rate is 20 m / min.

[0062] 5) The prepared hollow fiber membrane was tested for separation performance under simulated oilfield associated gas conditions. The system viscosity was too high and the mixing was uneven. Its CO2 permeability coefficient was 38 Barrer and the CO2 / CH4 selectivity was 30.

[0063] Comparative Example 7 (compared to Example 1) 1) Under argon protection, 2.30 g of MPD was added to a dry, clean flask, followed by 38.7 mL of DMAC solvent and stirred thoroughly. After the diamine was completely dissolved, the reaction temperature was lowered to 5 °C, and 7.99 g of 6FDA and 1.04 g of BPADA (6FDA to BPADA molar ratio of 9:1) were added in portions. Then, 41.65 mL of DMAc was added and dissolved thoroughly, controlling the solid content to approximately 15%. The reaction was stirred for 8 h to form a homogeneous polyamic acid solution.

[0064] 2) After the reaction was complete, acetic anhydride (9.45 mL) and 3-methylpyridine (1.61 mL) were added and reacted for 4 h. After the reaction was complete, the solution was poured into methanol to precipitate, filtered, and then dried under vacuum at 60 °C for 12 h to obtain 6FDA-BPADA-MPD polyimide solid.

[0065] 3) Weigh 10g of the synthesized polymer and add it to a three-necked flask equipped with a stirrer. Then add 2g of polyethylene glycol, 5mL of isopropanol, 3mL of tetrahydrofuran, 0.5g of sodium dodecylbenzenesulfonate and 40mL of DMF in sequence. Heat to 50℃ and stir to dissolve and prepare a casting solution.

[0066] 4) After the prepared casting solution is allowed to stand and kept at a constant temperature, and then degassed under vacuum for 12 hours, it is injected into the spinneret at a rate of 50 mL / h using a gear pump. The solution is then extruded through the spinneret into a phase inversion tank with water as the coagulation bath to obtain a hollow fiber membrane. The spinning conditions are as follows: the proportion of DMF in the spinneret core solution is 80% in water, the core solution flow rate is 50 mL / h, the coagulation bath temperature is 30℃, the washing tank temperature is 50℃, the distance between the spinneret and the coagulant is 20 cm, and the take-up rate is 20 m / min.

[0067] 5) The prepared hollow fiber membrane was tested for separation performance under simulated oilfield associated gas conditions. Without the introduction of sulfone groups, the mechanical properties and selectivity of the separation membrane were reduced. Its CO2 permeability coefficient was 40 Barrer and its CO2 / CH4 selectivity was 22.

[0068] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the scope of the present invention.

Claims

1. A method for preparing a hollow fiber gas separation membrane for decarbonization of associated gas in oil fields, characterized in that: Follow these steps: S1. Under argon protection, 4,4'-diaminodiphenyl sulfone and diamine are mixed, and then N,N-dimethylacetamide is added as solvent, controlling the solid content to be 15%-35%; S2. After the diamine is completely dissolved, the temperature of the reaction system is lowered to 5 ℃. The dianhydride is added in batches, and the total number of moles of dianhydride and diamine is the same. The mixture is stirred until it is completely dissolved and the solution viscosity is stable, resulting in a uniform and transparent polyamic acid solution. The reaction is continued to be stirred to obtain a polyamic acid prepolymer solution. S3. Add a dehydrating agent and a catalyst to the polyamic acid prepolymer solution to react and generate a polyimide solution; S4. The reaction solution is then poured into methanol as a precipitant to precipitate the polymer. After washing and drying, polyimide solid is obtained. The polyimide solid is then formulated into a casting solution, and hollow fiber gas separation membrane is obtained through a spinning process.

2. The method for preparing a hollow fiber gas separation membrane for associated gas decarbonization in oilfields according to claim 1, characterized in that: In step S2, the diamine is one or more of m-phenylenediamine, p-phenylenediamine, and 4,4'-diaminodiphenyl ether, and the molar ratio of 4,4'-diaminodiphenyl sulfone to the diamine is 1:19-3:

7.

3. The method for preparing a hollow fiber gas separation membrane for associated gas decarbonization in oilfields according to claim 1, characterized in that: The dianhydride is hexafluorodianhydride and biphenyltetracarboxylic dianhydride, and the molar ratio of hexafluorodianhydride to biphenyltetracarboxylic dianhydride is 1:9-9:

1.

4. The method for preparing a hollow fiber gas separation membrane for associated gas decarbonization in oilfields according to claim 1, characterized in that: In step S3, the dehydrating agent is acetic anhydride and the catalyst is 3-methylpyridine.

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