A method for preparing a polyamide-imide CO2 separation membrane and its application in flue gas carbon capture.

Abstract

This invention relates to a method for preparing a polyamide-imide CO2 separation membrane and its application in flue gas carbon capture, belonging to the field of separation membrane technology. The method uses diamine, dianhydride, and acyl chloride-modified monomers as raw materials, with a diamine to dianhydride molar ratio of 1:1; the total molar amount of dianhydride and acyl chloride monomers is 100%, with acyl chloride monomers accounting for 20%–40% and dianhydride monomers accounting for 60%–80%. First, diamine is dissolved in N-methylpyrrolidone, and dianhydride and acyl chloride monomers are added stepwise at an inert low temperature for polycondensation to obtain a modified polyamic acid solution. This solution is then chemically imidized to obtain a polyamide-imide substrate. The substrate is then dissolved, degassed, cast, dried, cured, and cooled before being peeled off to obtain a homogeneous and dense CO2 separation membrane. This invention regulates the molecular chain arrangement, increases the membrane free volume, enhances the preferential CO2 permeation performance, and takes into account the high strength, high stability, and flue gas corrosion resistance advantages of polyimide, significantly improving CO2 permeation flux and CO2 / N2 separation factor, thereby improving flue gas carbon capture efficiency and carbon dioxide purity.

Description

Technical Field

[0001] This invention relates to a method for preparing a polyamide-imide CO2 separation membrane and its application in flue gas carbon capture, belonging to the field of separation membrane technology. Background Technology

[0002] CO2 is a major greenhouse gas. Flue gas emitted from industrial coal-fired boilers, thermal power generation, chemical production, and steel smelting contains large amounts of CO2. Excessive greenhouse gas emissions have led to a series of problems, including global warming and ecological degradation. Therefore, industrial flue gas carbon capture and resource utilization have become key research directions in environmental protection and energy fields. Efficient, low-cost, and continuous flue gas decarbonization and CO2 capture technologies are core supports for achieving industrial energy conservation and emission reduction, and reaching low-carbon production goals. The demand for flue gas carbon capture technology has increased significantly across industries, while also placing more stringent requirements on capture efficiency, operating costs, equipment footprint, long-term stability, and secondary pollution control. Developing high-performance CO2 / N2 separation technologies and improving the overall benefits of industrial flue gas carbon capture has significant practical and social value.

[0003] Currently, mainstream industrial flue gas CO2 capture and separation technologies are mainly divided into three categories: chemical absorption, adsorption, and membrane separation. Chemical absorption offers high separation precision and is suitable for large-scale flue gas decarbonization. However, this process consumes large amounts of absorbent, suffers from severe equipment corrosion, high regeneration energy consumption, complex process flow, and easily generates secondary pollutants such as waste liquid and waste gas, resulting in high operation and maintenance costs. Adsorption equipment has a simple structure and is easy to operate, making it suitable for small to medium volume flue gas decarbonization scenarios. However, it suffers from problems such as easy saturation of adsorbent materials, short cycle life, and rapid decline in separation efficiency over long-term operation, failing to meet the requirements for long-term stable operation of industrial plants. Membrane separation, with its outstanding advantages such as low operating energy consumption, compact equipment size, simple operation, no secondary pollution, continuous and uninterrupted operation, and flexible modular assembly, perfectly adapts to the development needs of various industrial sites for flue gas carbon capture and distributed tail gas decarbonization, and is the core development direction of flue gas carbon capture technology at present and in the future.

[0004] Membrane materials are crucial in determining the effectiveness of carbon capture in membrane separation, directly impacting CO2 capture purity, recovery efficiency, membrane mechanical strength, and stability. Among numerous membrane materials, polyimide is considered an ideal substrate for CO2 gas separation membranes due to its excellent thermal stability, chemical resistance, mechanical properties, and resistance to trace impurities in flue gas. However, traditional polyimide molecules have a dense molecular chain arrangement and a low proportion of free volume within the membrane. This results in low CO2 permeation flux and insufficient CO2 / N2 separation selectivity during CO2 / N2 separation, making it impossible to simultaneously achieve high capture efficiency and high-purity CO2 recovery. Furthermore, relying solely on bulk structural modification using dianhydrides and diamine monomers limits the potential for modification and makes it difficult to fundamentally overcome the performance bottlenecks in flue gas carbon capture. Summary of the Invention

[0005] To address the technical problems existing in the prior art, this invention provides a method for preparing a polyamide-imide CO2 separation membrane and its application in flue gas carbon capture. This method reshapes the polymer molecular chain arrangement, increases the free volume within the membrane, and enhances the membrane material's preferential permeation capacity for CO2. While retaining the original high strength, high stability, and flue gas corrosion resistance of polyimide, it significantly improves the CO2 permeation flux and the CO2 / N2 separation factor, effectively enhancing flue gas carbon capture efficiency and CO2 product purity.

[0006] To achieve the above objectives, the technical solution adopted in this invention is a method for preparing a polyamide-imide CO2 separation membrane, comprising the following steps:

[0007] S1. Monomer Screening and Proportioning: Diamine monomer, dianhydride monomer, and acyl chloride-modified monomer are selected as polymerization raw materials, and the molar ratio of diamine monomer to dianhydride monomer is controlled at 1:1; based on the total molar number of dianhydride monomer and acyl chloride-modified monomer as 100%, the molar proportion of acyl chloride-modified monomer is 20% to 40%, and the molar proportion of dianhydride monomer is 60% to 80%.

[0008] S2. Preparation of polyamide-imide substrate: The diamine monomer of the specified amount is dissolved in N-methylpyrrolidone solvent. After it is fully dissolved, the corresponding proportions of dianhydride monomer and acyl chloride modified monomer are added stepwise. Polycondensation reaction is carried out under an inert protective atmosphere and low temperature environment to prepare a modified polyamic acid mixed solution. After chemical imidization, the polyamide-imide substrate is obtained.

[0009] S3. Casting and film forming process: The prepared polyamide-imide substrate is dissolved in N-methylpyrrolidone solvent. After sufficient degassing, it is formed by casting. Then, through drying, curing, cooling and peeling processes, a homogeneous and dense polyamide-imide CO2 separation membrane is obtained.

[0010] Preferably, the diamine monomer is one of 4,4'-diaminodiphenyl ether, p-triphenyl diether diamine, and meta-triphenyl diether diamine.

[0011] Preferably, the dianhydride monomer is one of hexafluorodianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and 3,3',4,4'-biphenyltetracarboxylic dianhydride.

[0012] Preferably, the acyl chloride modified monomer is one of 2,6-pyridine dicarbonyl chloride, 4,4'-oxobis(benzoyl chloride), and azobenzene-4,4'-dicarbonyl chloride.

[0013] Preferably, in step S2, the reaction temperature of the low-temperature polycondensation is 0°C, and the reaction time is 24 hours.

[0014] Compared with existing technologies, this invention has the following technical advantages: This invention modifies the molecular structure of polyimide using 2,6-pyridine dicarbonyl chloride, 4,4'-oxobis(benzoyl chloride), or azobenzene-4,4'-dicarbonyl chloride, introducing pyridine polar rings, ether-bonded flexible chains, and rigid azo sterically hindered groups into the molecular chain. This effectively increases the free volume within the membrane and the CO2 transport rate, achieving a synergistic improvement in CO2 permeation flux and CO2 / N2 separation selectivity. It can efficiently separate and enrich CO2 from industrial flue gas, obtaining high-purity CO2 products. The preparation process is mild and controllable, suitable for industrial-scale production. Compared with traditional polyimide separation membranes, the polyamide-imide separation membrane prepared by this invention has higher carbon capture efficiency, lower overall operating energy consumption, and a more compact supporting equipment structure. It also has excellent temperature resistance and resistance to corrosion from flue gas impurities, making it fully adaptable to flue gas carbon capture scenarios in various industries such as thermal power, steel, and chemical engineering. This provides a high-performance, low-cost new membrane separation technology route for the field of industrial carbon capture, with significant technical advantages and industrial application value. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the polyamide-imide film synthesized in this invention.

[0016] Figure 2 This is a cross-sectional SEM image of the polyamide-imide film in this invention. Detailed Implementation

[0017] 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.

[0018] Example 1

[0019] S1. Monomer selection and formulation: 6FDA was selected as the dianhydride monomer; ODA was selected as the diamine monomer; 2,6-pyridine dicarbonyl chloride was introduced as the modification unit; formulation control: the molar ratio of diamine monomer to dianhydride monomer was 1:1; the acyl chloride monomer accounted for 20% of the total molar amount of dianhydride and acyl chloride, and the dianhydride monomer accounted for 80%;

[0020] S2. Preparation of polyamide-imide substrate: 2.00 g ODA was dissolved in 44.31 mL NMP solvent (solid content 15%). After complete dissolution, 4.44 g 6FDA and 5.10 g 2,6-pyridine dicarbonyl chloride were added stepwise. The mixture was subjected to low-temperature polycondensation at 0 °C for 24 h under Ar atmosphere to obtain a modified polyamic acid solution. Subsequently, 6.0 mL acetic anhydride and 4.0 mL 3-methylpyridine were slowly added to the solution. After stirring for 24 h, the solution was poured into a methanol solution for precipitation. After washing and drying, the polyamide-imide film material was obtained.

[0021] S3. Casting and Film Formation Process: Weigh 5g of polyamide-imide membrane material and dissolve it in 19.42mL of NMP solvent (solid content 25%) to prepare a casting solution. After degassing for 2 hours, prepare a homogeneous and dense membrane using the casting method. After drying, curing, cooling and peeling, obtain the polyamide-imide CO2 separation membrane.

[0022] Tests: Polyamide-imide CO2 separation membranes were assembled into membrane modules for carbon capture in flue gas from small and medium-sized boilers. The measured CO2 permeation flux was 238.6 Barrer, and the CO2 / N2 separation factor was 36.8.

[0023] Example 2

[0024] S1. Monomer Screening and Proportioning: BTDA was selected as the dianhydride monomer; TPEQ was selected as the diamine monomer; and 4,4'-oxobis(benzoyl chloride) was introduced as the modifying unit. Proportioning control: The molar ratio of diamine monomer to dianhydride monomer was 1:1; the acyl chloride monomer accounted for 30% of the total molar amount of dianhydride and acyl chloride, and the dianhydride monomer accounted for 70%.

[0025] S2. Preparation of polyamide-imide substrate: 3.16 g TPEQ was dissolved in 47.57 mL NMP solvent (solid content 15%). After complete dissolution, 3.58 g BTDA and 1.405 g 4,4'-oxobis(benzoyl chloride) were added stepwise. The mixture was subjected to low-temperature polycondensation at 0 °C for 24 h under Ar atmosphere to obtain a modified polyamic acid solution. Subsequently, 6.0 mL acetic anhydride and 4.0 mL 3-methylpyridine were slowly added to the solution. After stirring for 24 h, the solution was poured into a methanol solution for precipitation. After washing and drying, the polyamide-imide film material was obtained.

[0026] S3. Casting and Film Formation Process: Weigh 5g of the above membrane material and dissolve it in 19.42mL of NMP solvent (solid content 25%) to prepare a casting solution. After degassing for 2 hours, prepare a homogeneous and dense membrane using the casting method. After drying, curing, cooling and peeling, obtain a polyamide-imide CO2 separation membrane.

[0027] Testing: The separation membrane was assembled into a membrane module for carbon capture in power plant flue gas. The measured CO2 permeation flux was 310.2 Barrer, and the CO2 / N2 separation factor was 37.2.

[0028] Example 3

[0029] S1. Monomer Screening and Proportioning: BPDA was selected as the dianhydride monomer; TPER was selected as the diamine monomer; azobenzene-4,4'-dicarbonyl chloride was introduced as the modifying unit. Proportioning Control: The molar ratio of diamine monomer to dianhydride monomer was 1:1; the acyl chloride monomer accounted for 40% of the total molar amount of dianhydride and acyl chloride, and the dianhydride monomer accounted for 60%.

[0030] S2. Preparation of polyamide-imide substrate: 3.48 g TPER was dissolved in 46.81 mL NMP solvent (solid content 15%). After complete dissolution, 2.94 g 6FDA and 1.355 g azobenzene-4,4'-dicarbonyl chloride were added stepwise. The mixture was subjected to low-temperature polycondensation at 0 °C for 24 h under Ar atmosphere to obtain a modified polyamic acid solution. Subsequently, 6.0 mL acetic anhydride and 4.0 mL 3-methylpyridine were slowly added to the solution. After stirring for 24 h, the solution was poured into a methanol solution for precipitation. After washing and drying, the polyamide-imide film material was obtained.

[0031] S3. Casting and Film Formation Process: Weigh 5g of the above membrane material and dissolve it in 19.42mL of NMP solvent (solid content 25%) to prepare a casting solution. After degassing for 2 hours, prepare a homogeneous and dense membrane using the casting method. After drying, curing, cooling and peeling, obtain a polyamide-imide CO2 separation membrane.

[0032] Testing: The separation membrane was assembled into a membrane module for flue gas carbon capture under operating conditions. The measured CO2 permeation flux was 312.5 Barrer, and the CO2 / N2 separation factor was 42.3.

[0033] Example 4

[0034] S1. Monomer Screening and Proportioning: 6FDA was selected as the dianhydride monomer; TPER was selected as the diamine monomer; and isophthaloyl chloride was introduced as the modification unit. Proportioning Control: The molar ratio of diamine monomer to dianhydride monomer was 1:1; the acyl chloride monomer accounted for 30% of the total molar amount of dianhydride and acyl chloride, and the dianhydride monomer accounted for 70%.

[0035] S2. Preparation of polyamide-imide substrate: 3.48 g of TPER was dissolved in 55.20 mL of NMP solvent (solid content 15%). After complete dissolution, 4.44 g of 6FDA and 12.693 g of 4,4'-oxobis(benzoyl chloride) were added stepwise. The mixture was subjected to low-temperature polycondensation at 0 °C for 24 h under Ar atmosphere to obtain a modified polyamic acid solution. Subsequently, 6.0 mL of acetic anhydride and 4.0 mL of 3-methylpyridine were slowly added to the solution. After stirring for 24 h, the solution was poured into a methanol solution for precipitation. After washing and drying, the polyamide-imide film material was obtained.

[0036] S3. Casting and Film Formation Process: Weigh 5g of the above membrane material and dissolve it in 19.42mL of NMP solvent (solid content 25%) to prepare a casting solution. After degassing for 2 hours, prepare a homogeneous and dense membrane using the casting method. After drying, curing, cooling and peeling, obtain a polyamide-imide CO2 separation membrane.

[0037] Testing: The separation membrane was assembled into a membrane module for large-scale carbon capture of flue gas in a large thermal power plant. The measured CO2 permeation flux was 323.3 Barrer, and the CO2 / N2 separation factor was 47.5.

[0038] 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 polyamide-imide CO2 separation membrane, characterized in that: Includes the following steps, S1. Monomer Screening and Proportioning: Diamine monomer, dianhydride monomer, and acyl chloride-modified monomer are selected as polymerization raw materials, and the molar ratio of diamine monomer to dianhydride monomer is controlled at 1:1; based on the total molar number of dianhydride monomer and acyl chloride-modified monomer as 100%, the molar proportion of acyl chloride-modified monomer is 20% to 40%, and the molar proportion of dianhydride monomer is 60% to 80%. S2. Preparation of polyamide-imide substrate: The diamine monomer of the specified amount is dissolved in N-methylpyrrolidone solvent. After it is fully dissolved, the corresponding proportions of dianhydride monomer and acyl chloride modified monomer are added stepwise. Polycondensation reaction is carried out under an inert protective atmosphere and low temperature environment to prepare a modified polyamic acid mixed solution. After chemical imidization, the polyamide-imide substrate is obtained. S3. Casting and film forming process: The prepared polyamide-imide substrate is dissolved in N-methylpyrrolidone solvent. After sufficient degassing, it is formed by casting. Then, through drying, curing, cooling and peeling processes, a homogeneous and dense polyamide-imide CO2 separation membrane is obtained.

2. The method for preparing a polyamide-imide CO2 separation membrane according to claim 1, characterized in that: The diamine monomer is one of 4,4'-diaminodiphenyl ether, p-triphenyl diether diamine, and meta-triphenyl diether diamine.

3. The method for preparing a polyamide-imide CO2 separation membrane according to claim 1, characterized in that: The dianhydride monomer is one of hexafluorodianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and 3,3',4,4'-biphenyltetracarboxylic dianhydride.

4. The method for preparing a polyamide-imide CO2 separation membrane according to claim 1, characterized in that: The acyl chloride modified monomer is one of 2,6-pyridine dicarbonyl chloride, 4,4'-oxobis(benzoyl chloride), and azobenzene-4,4'-dicarbonyl chloride.

5. The method for preparing a polyamide-imide CO2 separation membrane according to claim 1, characterized in that: In step S2, the reaction temperature for low-temperature polycondensation is 0°C, and the reaction time is 24 hours.

6. The CO2 separation membrane prepared by the method of any one of claims 1-5 is used in flue gas carbon capture.

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