Butadiene separation copolymer-based carbon molecular sieve membrane and preparation method thereof

Abstract

The invention belongs to the technical field of membrane preparation and application, and discloses a butadiene separation copolymer-based carbon molecular sieve membrane and a preparation method thereof. Through the design of a carbon molecular sieve membrane precursor polymer material, a diamine monomer containing trifluoromethyl and ether bonds at the same time is introduced into a polymer structure,-CF3 releases gas in the pyrolysis process, and a rich porous structure is formed in the membrane. -O-enables the precursor polymer to be looser, and meanwhile, pore-forming sites are introduced, so that formation of a rich pore network is further promoted. The permeability of C4H6 is improved, and the carbon molecular sieve membrane for C4H6 separation, which has high selectivity and high permeability, is developed.

Description

A butadiene separation copolymer-based carbon molecular sieve membrane and its preparation method Technical Field

[0001] This invention belongs to the field of membrane preparation and application technology, and discloses a butadiene separation copolymer-based carbon molecular sieve membrane and its preparation method. Background Technology

[0002] 1,3-Butadiene (C4H6) is an important chemical raw material, widely used in the synthesis of rubber, resins, adiponitrile, and other products. It mainly originates from the C4 byproduct of ethylene production via steam cracking. This byproduct contains 30%-60% C4H6, as well as n-butene (n-C4H8), isobutene (i-C4H8), and n-butane (n-C4H8). 10 ), isobutane (i-C4H) 10 The C4 hydrocarbons contain components such as α, β, and γ. Because C4 hydrocarbons have similar boiling points and some form azeotropes, conventional low-temperature distillation separation is difficult and energy-intensive. While commonly used extractive distillation can separate them, solvent evaporation leads to energy consumption and environmental pollution. Developing efficient separation technologies can reduce the energy consumption, cost, and environmental impact of C4H6 purification. Membrane separation technology has advantages such as low energy consumption, environmental friendliness, small footprint, and ease of integration, and has great potential for application in gas separation.

[0003] Despite the advantages of membrane separation, research on membrane separation of C4H6 and other C4 hydrocarbons is limited, focusing primarily on polymer membranes, mixed matrix membranes (MMMs), and inorganic membranes. Polymer membranes are prone to plasticization or have low selectivity, MMMs have high permeability but insufficient selectivity, inorganic membranes such as ZIF-8 exhibit excellent separation performance, while metal-organic framework (MOF) membranes suffer from complex preparation and high cost. Ken-ichi Okamoto et al. (Olefin / Paraffin Separation through Carbonized Membranes Derived from an Asymmetric Polyimide Hollow Fiber Membrane, Ind. Eng. Chem. Res. 1999, 38, 4424-4432) prepared a hollow fiber CMS membrane based on BPDA-DDBT and evaluated its C4H6 / n-C ... 10 Separation performance. At 100℃ and 1 atm, the C4H6 permeability of this membrane is 80 GPU, and the C4H6 / n-C4H... 10 The selectivity is 50; the selective skin thickness of the hollow fiber carbon membrane is about 200 nm, and the intrinsic C4H6 permeability of the material is estimated to be about 16 Barrer, indicating that there is considerable room for improvement in the intrinsic permeability of the material. Summary of the Invention

[0004] For the separation of large volumes of C4 gas (C4H6: 4.31 Å, n-C4H) using existing carbon molecular sieve membranes... 10 4.69 Å, i-C4H 10 Addressing the low permeability of carbon molecular sieve membranes (i-C4H8: 4.84 Å, n-C4H8: 5.28 Å, i-C4H8: 4.46 Å, n-C4H8: 4.84 Å), this invention aims to improve the permeability of C4H6 by designing a precursor polymer material for carbon molecular sieve membranes. This involves introducing a diamine monomer containing both trifluoromethyl (-CF3) and ether bonds (-O-) into the polymer structure. During pyrolysis, -CF3 releases gas, forming a rich porous structure (micropores and ultramicropores) within the membrane. -O- makes the precursor polymer more porous and introduces pore-forming sites, further promoting the formation of a rich pore network. This enhances the permeability of C4H6 and develops carbon molecular sieve membranes for C4H6 separation that combine high selectivity and high permeability.

[0005] The technical solution of this invention: A butadiene separation copolymer-based carbon molecular sieve membrane, wherein the copolymer precursor comprises a dianhydride monomer, a diamine ①, and a diamine ②, and its structure is shown below: The dianhydride monomer is selected from one of the following structures: , , Diamine ① Choose one of the following monomers: , , Diamine ② can be selected from one of the following monomers: , , ; 0 < m : n < 5.

[0006] A method for preparing a butadiene separation copolymer-based carbon molecular sieve membrane, the steps are as follows: (1) Preparation of copolymer: At room temperature, first mix dried diamine ① and diamine ②, then add anhydrous N-methylpyrrolidone, stir to dissolve and pass dry nitrogen gas; after cooling to 0°C in an ice bath, add dianhydride monomer, stir and react in an ice bath for a period of time, and continue to react at room temperature for a certain time to obtain polyamic acid (PAA); then add catalyst B and dehydrating agent C, react at room temperature for a period of time, and PAA is converted into polyimide; after the reaction is completed, pour the reaction solution into methanol to obtain a white solid. After washing with methanol three times and drying under vacuum for a period of time, the target product is obtained; (2) Preparation of copolymer membrane: The polymer is dissolved in casting solvent A. After complete dissolution, it is filtered with a filter membrane and then evaporated into a membrane in an oven. Then it is transferred to a vacuum oven for drying to obtain a precursor polymer membrane; (3) Preparation of copolymer-based carbon molecular sieve membrane: The precursor polymer membrane obtained in step (2) is placed between two corundum plates and pyrolyzed under a nitrogen atmosphere according to the designed pyrolysis procedure to obtain a black and uniform butadiene separation copolymer-based carbon molecular sieve membrane.

[0007] The casting solvent A is one or a mixture of two or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

[0008] The catalyst B is one of pyridine, triethylamine, or 3-methylpyridine.

[0009] The dehydrating agent C is either acetic anhydride or triethylamine.

[0010] In step (1), the molar ratio of diamine ① to diamine ② is 3:1-1:3; in step (1), the molar amount of dianhydride monomer is the sum of the molar amounts of diamine ① and diamine ②; in step (1), the total concentration of diamine ①, diamine ② and dianhydride monomer in the reaction system is 10~30wt%; in step (1), the ice bath reaction time is 3-5h; in step (1), after the ice bath reaction is completed, the reaction is carried out at room temperature for 12-48h; in step (1), after the catalyst and dehydrating agent are added, the reaction is carried out at room temperature for 12-48h; in step (1), after the polymer is washed, the vacuum drying time is 12-24h.

[0011] In step (2), the mass fraction of the casting solution is 8-15 wt%.

[0012] In step (3), the pyrolysis time is 3-5 hours and the pyrolysis temperature is 500-900℃.

[0013] The beneficial effects of the present invention are as follows: In the method of the present invention, the -CF3 and -O- in the diamine monomer will form a rich porous structure (micropores and ultramicropores) in the membrane during the pyrolysis process. Compared with other carbon molecular sieve membranes used for C4H6, the copolymer carbon molecular sieve membrane of the present invention has high permeability and high selectivity, and can effectively separate C4H6. Attached Figure Description

[0014] Figure 1 is a comparison of the separation performance of the carbon membrane C4H6 / n-C4H8 prepared by the present invention with that of other C4H6 / n-C4H8 separation membranes.

[0015] Figure 2 is a comparison of the separation performance of the carbon membrane C4H6 / i-C4H8 prepared in this invention with that of other C4H6 / i-C4H8 separation membranes.

[0016] Figure 3 shows the carbon film C4H6 / n-C4H prepared according to the present invention. 10 Separation performance compared to other C4H6 / n-C4H 10 Comparison chart of separation membrane performance. Detailed Implementation

[0017] The specific embodiments of the present invention will be further described below in conjunction with the technical solutions and accompanying drawings.

[0018] Gas permeability test: The permeability test of the gas separation membrane in this invention is conducted using the constant volume change pressure method, with a test temperature of 35°C and a test pressure of 2 bar.

[0019] Example 16 Synthesis of FDA-DAM / 6FAPB (1:1): 2 mmol of dried DAM and 2 mmol of 6FAPB were added to a three-necked flask, followed by 9 mL of anhydrous NMP. The mixture was stirred at 200 rpm to dissolve and purged with dry nitrogen. After cooling to 0°C in an ice bath, 4 mmol of 6FDA and 3 mL of anhydrous NMP were added in a single batch. The mixture was stirred at 60 rpm and reacted in an ice bath for 3 h, followed by another 24 h at room temperature to obtain polyamic acid (PAA). Subsequently, 0.408 mL of pyridine and 3.6 mL of acetic anhydride were added, and the mixture was reacted at 110 rpm at room temperature for 24 h, converting PAA to polyimide. The reaction solution was poured into 200 mL of methanol to obtain a white solid. After washing three times with methanol, the solid was dried at 60°C for 12 h under forced air and then at 150°C under vacuum for 24 h to obtain the target product.

[0020] Preparation of copolymer polymer membrane: 0.2 g of polymer was dispersed in N,N-dimethylformamide (DMF) and stirred for 24 h. The casting solution was then filtered through a syringe equipped with a 0.45 μm filter membrane. The casting solution was dried at 60 °C for 12 h and then further vacuum dried in a vacuum oven at 120 °C for 12 h.

[0021] Preparation of copolymer polymer-based carbon molecular sieve membrane: The polymer membrane was sandwiched between corundum plates and placed in a tube furnace with a programmable controller. Nitrogen gas was purged for 1 hour before heat treatment. Then, heat treatment was performed according to the preset program, and the membrane was held at the target temperature of 550℃ for 2 hours. Finally, it was allowed to cool naturally to room temperature.

[0022] Example 26 Synthesis of FDA-DAM / 6FAPB (1:1): 2 mmol of dried DAM and 2 mmol of 6FAPB were added to a three-necked flask, followed by 9 mL of anhydrous NMP. The mixture was stirred at 200 rpm to dissolve and purged with dry nitrogen. After cooling to 0°C in an ice bath, 4 mmol of 6FDA and 3 mL of anhydrous NMP were added in a single batch. The mixture was stirred at 60 rpm and reacted in an ice bath for 3 h, followed by another 24 h at room temperature to obtain polyamic acid (PAA). Subsequently, 0.408 mL of pyridine and 3.6 mL of acetic anhydride were added, and the mixture was reacted at 110 rpm at room temperature for 24 h, converting PAA to polyimide. The reaction solution was poured into 200 mL of methanol to obtain a white solid. After washing three times with methanol, the solid was dried at 60°C for 12 h under forced air and then at 150°C under vacuum for 24 h to obtain the target product.

[0023] Copolymer membrane preparation: 0.2 g of polymer was dispersed in DMF and stirred for 24 h. The casting solution was then filtered through a syringe equipped with a 0.45 μm filter membrane. The casting solution was dried at 60 °C for 12 h and then further vacuum dried in a vacuum oven at 120 °C for 12 h.

[0024] Preparation of copolymer polymer-based carbon molecular sieve membrane: The polymer membrane was sandwiched between corundum plates and placed in a tube furnace with a programmable controller. Nitrogen gas was purged for 1 hour before heat treatment. Then, heat treatment was performed according to the preset program, holding at the target temperature of 650℃ for 2 hours, and finally naturally cooled to room temperature.

[0025] Example 36: Synthesis of FDA-DAM / 6FAPB (1:1): 2 mmol of dried DAM and 2 mmol of 6FAPB were added to a three-necked flask, followed by 9 mL of anhydrous NMP. The mixture was stirred at 200 rpm to dissolve and purged with dry nitrogen. After cooling to 0°C in an ice bath, 4 mmol of 6FDA and 3 mL of anhydrous NMP were added in a single batch. The mixture was stirred at 60 rpm and reacted in an ice bath for 3 h, followed by another 24 h at room temperature to obtain polyamic acid (PAA). Subsequently, 0.408 mL of pyridine and 3.6 mL of acetic anhydride were added, and the mixture was reacted at 110 rpm at room temperature for 24 h, converting PAA to polyimide. The reaction solution was poured into 200 mL of methanol to obtain a white solid. After washing three times with methanol, the solid was dried at 60°C for 12 h under forced air and then at 150°C under vacuum for 24 h to obtain the target product.

[0026] Copolymer membrane preparation: 0.2 g of polymer was dispersed in DMF and stirred for 24 h. The casting solution was then filtered through a syringe equipped with a 0.45 μm filter membrane. The casting solution was dried at 60 °C for 12 h and then further vacuum dried in a vacuum oven at 120 °C for 12 h.

[0027] Preparation of copolymer polymer-based carbon molecular sieve membrane: The polymer membrane was sandwiched between corundum plates and placed in a tube furnace with a programmable controller. Nitrogen gas was purged for 1 hour before heat treatment. Then, heat treatment was performed according to the preset program, holding at the target temperature of 700℃ for 2 hours, and finally naturally cooled to room temperature.

[0028] Example 46 Synthesis of FDA-DAM / 6FAPB (1:3): 2 mmol of dried DAM and 2 mmol of 6FAPB were added to a three-necked flask, followed by 9 mL of anhydrous NMP. The mixture was stirred at 200 rpm to dissolve and purged with dry nitrogen. After cooling to 0°C in an ice bath, 4 mmol of 6FDA and 3 mL of anhydrous NMP were added in one batch. The mixture was stirred at 60 rpm and reacted in an ice bath for 3 h, followed by another 24 h at room temperature to obtain polyamic acid (PAA). Subsequently, 0.408 mL of pyridine and 3.6 mL of acetic anhydride were added, and the mixture was reacted at 110 rpm at room temperature for 24 h, converting PAA to polyimide. The reaction solution was poured into 200 mL of methanol to obtain a white solid. After washing three times with methanol, the solid was dried at 60°C for 12 h under forced air and then at 150°C under vacuum for 24 h to obtain the target product.

[0029] Copolymer membrane preparation: 0.2 g of polymer was dispersed in DMF and stirred for 24 h. The casting solution was then filtered through a syringe equipped with a 0.45 μm filter membrane. The casting solution was dried at 60 °C for 12 h and then further vacuum dried in a vacuum oven at 120 °C for 12 h.

[0030] Preparation of copolymer polymer-based carbon molecular sieve membrane: The polymer membrane was sandwiched between corundum plates and placed in a tube furnace with a programmable controller. Nitrogen gas was purged for 1 hour before heat treatment. Then, heat treatment was performed according to the preset program, holding at the target temperature of 800℃ for 2 hours, and finally naturally cooled to room temperature.

[0031] Example 56 Synthesis of FDA-DAM / 6FAPB (1:3): 1 mmol of dried DAM and 3 mmol of 6FAPB were added to a three-necked flask, followed by 9 mL of anhydrous NMP. The mixture was stirred at 200 rpm to dissolve and purged with dry nitrogen. After cooling to 0°C in an ice bath, 4 mmol of 6FDA and 3 mL of anhydrous NMP were added in a single batch. The mixture was stirred at 60 rpm and reacted in an ice bath for 3 h, followed by another 24 h at room temperature to obtain polyamic acid (PAA). Subsequently, 0.408 mL of pyridine and 3.6 mL of acetic anhydride were added, and the mixture was reacted at 110 rpm at room temperature for 24 h, converting PAA to polyimide. The reaction solution was poured into 200 mL of methanol to obtain a white solid. After washing three times with methanol, the solid was dried at 60°C for 12 h under forced air and then at 150°C under vacuum for 24 h to obtain the target product.

[0032] Copolymer membrane preparation: 0.2 g of polymer was dispersed in DMF and stirred for 24 h. The casting solution was then filtered through a syringe equipped with a 0.45 μm filter membrane. The casting solution was dried at 60 °C for 12 h and then further vacuum dried in a vacuum oven at 120 °C for 12 h.

[0033] Preparation of copolymer polymer-based carbon molecular sieve membrane: The polymer membrane was sandwiched between corundum plates and placed in a tube furnace with a programmable controller. Nitrogen gas was purged for 1 hour before heat treatment. Then, heat treatment was performed according to the preset program, holding at the target temperature of 800℃ for 2 hours, and finally naturally cooled to room temperature.

[0034] Example 66 Synthesis of FDA-DAM / 6FAPB (2:3): 1.6 mmol of dried DAM and 2.4 mmol of 6FAPB were added to a three-necked flask, followed by 9 mL of anhydrous NMP. The mixture was stirred at 200 rpm to dissolve the DAM while purging with dry nitrogen. After cooling to 0°C in an ice bath, 4 mmol of 6FDA and 3 mL of anhydrous NMP were added in a single batch. The mixture was stirred at 60 rpm and reacted in an ice bath for 3 h, followed by another 24 h at room temperature to obtain polyamic acid (PAA). Subsequently, 0.408 mL of pyridine and 3.6 mL of acetic anhydride were added, and the mixture was reacted at 110 rpm at room temperature for 24 h, converting PAA to polyimide. The reaction solution was poured into 200 mL of methanol to obtain a white solid. After washing three times with methanol, the solid was dried at 60°C for 12 h under forced air and then at 150°C under vacuum for 24 h to obtain the target product.

[0035] Copolymer membrane preparation: 0.2 g of polymer was dispersed in DMF and stirred for 24 h. The casting solution was then filtered through a syringe equipped with a 0.45 μm filter membrane. The casting solution was dried at 60 °C for 12 h and then further vacuum dried in a vacuum oven at 120 °C for 12 h.

[0036] Preparation of copolymer polymer-based carbon molecular sieve membrane: The polymer membrane was sandwiched between corundum plates and placed in a tube furnace with a programmable controller. Nitrogen gas was purged for 1 hour before heat treatment. Then, heat treatment was performed according to the preset program, holding at the target temperature of 800℃ for 2 hours, and finally naturally cooled to room temperature.

[0037] Comparative Example 6: Synthesis of FDA-DAM: 4 mmol of dried DAM was first added to a three-necked flask, followed by 9 mL of anhydrous NMP. The mixture was stirred at 200 rpm to dissolve and purged with dry nitrogen. After cooling to 0°C in an ice bath, 4 mmol of 6-FDA and 3 mL of anhydrous NMP were added in one batch. The mixture was stirred at 60 rpm and reacted in an ice bath for 3 h, followed by a further reaction at room temperature for 24 h to obtain polyamic acid (PAA). Subsequently, 0.408 mL of pyridine and 3.6 mL of acetic anhydride were added, and the mixture was reacted at 110 rpm at room temperature for 24 h, converting PAA to polyimide. The reaction solution was poured into 200 mL of methanol to obtain a white solid. After washing three times with methanol, the solid was dried at 60°C for 12 h under forced air and then at 150°C under vacuum for 24 h to obtain the target product.

[0038] Polymer membrane preparation: 0.2 g of polymer was dispersed in DMF and stirred for 24 h. The casting solution was then filtered through a syringe equipped with a 0.45 μm filter membrane. The casting solution was dried at 60 °C for 12 h and then further vacuum dried in a vacuum oven at 120 °C for 12 h.

[0039] Preparation of copolymer polymer-based carbon molecular sieve membrane: The polymer membrane was sandwiched between corundum plates and placed in a tube furnace with a programmable controller. Nitrogen gas was purged for 1 hour before heat treatment. Then, heat treatment was performed according to the preset program, holding at the target temperature of 800℃ for 2 hours, and finally naturally cooled to room temperature.

[0040] As shown in Table 1, when the monomer ratio is fixed, the carbon membrane exhibits the best separation performance at a carbonization temperature of 800℃. Further comparison was conducted using a carbonization temperature of 800℃. Compared to the control example, all examples added 6FAPB diamine monomer containing both -CF3 and -O-. Performance results show that, at the same carbonization temperature, the addition of 6FAPB monomer improved both the permeability and selectivity of the C4H6 carbon membrane. Furthermore, the performance of the carbon membrane improved with increasing 6FAPB monomer content. This is because the -CF3 and -O- in the diamine monomer form abundant porous structures (micropores and ultramicropores) within the membrane during pyrolysis, contributing to improved permeability and selectivity. Figures 1, 2, and 3 compare the performance of the carbon membrane from this work with current C4H6 separation membranes. It can be seen that the performance of the carbon membrane from this work surpasses that of most current C4H6 separation membranes, demonstrating its excellent separation performance.

[0041] Table 1 shows the gas permeability and selectivity of the gas separation membranes prepared in the comparative and example cases.

Claims

1. A butadiene separation copolymer-based carbon molecular sieve membrane, characterized in that, The copolymer precursor of the butadiene separation copolymer-based carbon molecular sieve membrane comprises dianhydride monomer, diamine ①, and diamine ②, and its structure is shown below: The dianhydride monomer is selected from one of the following structures: 、 、 Diamine ① Choose one of the following monomers: 、 、 Diamine ② can be selected from one of the following monomers: 、 、 ;0<m:n<5。 2. A method for preparing a butadiene separation copolymer-based carbon molecular sieve membrane, characterized in that, The steps are as follows: (1) Preparation of copolymer: At room temperature, first mix the dried diamine ① and diamine ②, then add anhydrous N-methylpyrrolidone, stir to dissolve and pass dry nitrogen gas; after cooling to 0°C in an ice bath, add dianhydride monomer, stir and react in an ice bath for a period of time, and continue to react at room temperature for a certain period of time to obtain polyamic acid; then add catalyst B and dehydrating agent C, react at room temperature for a period of time, and PAA is converted into polyimide; after the reaction is completed, pour the reaction solution into methanol to obtain a white solid, wash with methanol three times, and vacuum dry for a period of time to obtain the target product; (2) Preparation of copolymer membrane: The polymer is dissolved in casting solvent A. After complete dissolution, it is filtered with a filter membrane and then evaporated into a membrane in an oven. The membrane is then transferred to a vacuum oven for drying to obtain a precursor polymer membrane. (3) Preparation of copolymer-based carbon molecular sieve membrane: The precursor polymer membrane obtained in step (2) is placed between two corundum plates and pyrolyzed under a nitrogen atmosphere according to the designed pyrolysis procedure to obtain a black and uniform butadiene separation copolymer-based carbon molecular sieve membrane.

3. The preparation method according to claim 2, characterized in that, In step (1), the casting solvent A is one or a mixture of two or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; the catalyst B is one of pyridine, triethylamine, and 3-methylpyridine; the dehydrating agent C is one of acetic anhydride and triethylamine; the molar ratio of diamine ① to diamine ② is 3:1-1:3; the molar amount of dianhydride monomer is the sum of the molar amounts of diamine ① and diamine ②; the total concentration of diamine ①, diamine ②, and dianhydride monomer in the reaction system is 10-30 wt%; the ice bath reaction time is 3-5 h; after the ice bath reaction, the reaction is carried out at room temperature for 12-48 h; after adding the catalyst and dehydrating agent, the reaction is carried out at room temperature for 12-48 h; after washing the polymer, the vacuum drying time is 12-24 h.

4. The preparation method according to claim 2, characterized in that, In step (2), the mass fraction of the casting solution is 8-15 wt%.

5. The preparation method according to claim 2, characterized in that, In step (3), the pyrolysis time is 3-5 hours and the pyrolysis temperature is 500-900℃.

Images