Preparation method of fluorine-containing Troger base carbon molecular sieve membrane with high gas separation performance

Abstract

The invention belongs to the technical field of membrane preparation and application, and discloses a preparation method of a fluorine-containing Telogen base carbon molecular sieve membrane with high gas separation performance. According to the fluorine-containing tro-base carbon molecular sieve membrane with the high gas separation performance, a tro-base polymer serves as a base material, a fluorine-containing diamine monomer is introduced during synthesis to obtain a fluorinated tro-base polymer, and then the carbon molecular sieve membrane is prepared through a further specific pyrolysis procedure. According to the invention, the fluorine-containing unit is added into the main chain of the basic polymer of the Telogen base, the carbon molecular sieve membrane with specific porosity is successfully prepared through pyrolysis, and the carbon molecular sieve membrane has remarkable hydrogen / helium reverse selectivity and high propylene / propane selectivity. The preparation method has a wide application prospect in the field of gas separation membranes.

Description

Technical Field

[0001] The invention belongs to the technical field of membrane preparation and application, and discloses a method for preparing a fluorine-containing Trog base carbon molecular sieve membrane with high gas separation performance. Background Art

[0002] Helium is the second most abundant element in the universe, with limited reserves on Earth. Due to its wide applications in military, scientific research, medicine, superconducting experiments and other fields, helium has become a rare strategic resource. Membrane technology has been used to separate helium and hydrogen from natural gas reservoirs, but the process remains very challenging because hydrogen and helium The kinetic diameter difference is less than The boiling point difference is less than 16K.

[0003] At the same time, light olefins are the basic synthetic raw materials of the petrochemical industry, and the separation and purification of their polymerization-grade products are key steps in the petrochemical production process. However, to date, existing technologies for propylene / propane separation, such as cryogenic distillation, consume a lot of energy and have high economic costs. Alleviating the severe energy consumption of propylene / propane separation has been identified as one of the seven major chemical separations that can change the global energy use pattern.

[0004] In recent years, membrane separation technology has received increasing attention in gas separation processes such as hydrogen recovery, oxygen enrichment, and carbon dioxide capture. Carbon molecular sieve (CMS) membranes are formed by pyrolysis of polymer membranes. Compared with polymer membranes, it has many advantages, including high thermal stability, excellent chemical resistance, and great potential for highly selective and cost-effective gas separation. The pyrolysis process involves the gradual decomposition, fragmentation, and aromatization of polymer chains to form "carbon chains" and "carbon plates", leading to the formation of ultra-micropores. The high carbon content and strong carbon-carbon (CC) bonds of the carbon molecular sieve membrane ensure excellent structural integrity and stability. The bimodal pore size distribution of the carbon molecular sieve membrane further improves the permeability and selectivity of the membrane. This is achieved through the micropores (7- ) in the fast gas diffusion and less than This is achieved by combining the ultra-micropores with the efficient screening function.

[0005] At present, in terms of helium / hydrogen separation, the selectivity of carbon molecular sieve membranes is generally in the range of 0.24-1.52 (Chong Yang Chuah, Tae-Hyun Bae, Polyimide-derived carbon molecular sieve membranes for advanced gas separation: From membrane development to pilot-scale operations [J]. Sep. Purif. Technol, 2023, 320, 124114). However, carbon molecular sieve membranes with a selectivity of 10.5 require complex and dangerous fluorine / nitrogen post-treatment processes (Qi Wu, Lu Liu, Yang Jiao, Zhenyuan Li, Ju Bai, Prof. Xiaohua Ma, Prof. Shuangjiang Luo, Prof. Suojiang Zhang, Precise Helium Sieving from Hydrogen Using Fluorine-Decorated Carbon Hollow Fiber Membranes, Angew. Chem. Int. Ed, 2024, 63 (33), e202400688). It is critical to develop reverse-selective helium-hydrogen separation membranes, where hydrogen with a larger kinetic diameter is more permeable than helium with a smaller kinetic diameter. Reverse-selective membranes offer several advantages over conventional helium-selective membranes. For example, hydrogen-selective membranes can significantly reduce separation costs because the unwanted hydrogen is more permeable and remains on the permeate side at very low pressure. However, the desired helium is retained on the high-pressure side, saving on helium compression costs, further reducing separation costs.

[0006] On the other hand, most of the carbon molecular sieve membrane materials used for propylene / propane separation are polyimides, and have shown promising propylene-propane separation performance, but the application of carbon molecular sieve membranes belonging to self-polymerized microporous polymers in propylene / propane separation has not been fully explored (Giuseppe Genduso, Wojciech Ogieglo, Yingge Wang, Ingo Pinnau [J], Carbon molecular sieve gas separation materials and membranes: A comprehensive review, J. Membr. Sci., 2024, 699, 122533).

[0007] Trog base polymer is a kind of self-polymerized microporous polymer. The carbon molecular sieve membrane pyrolyzed from it shows a hydrogen / helium selectivity of 2.37, but the hydrogen permeability is only 202.4 Barrer. In addition, the propylene / propane separation performance of Trog base carbon molecular sieve membrane has not been explored. This study intends to explore the propylene / propane intrinsic performance of Trog base carbon molecular sieve membrane, and further develop Trog base polymer carbon molecular sieve membrane with high hydrogen / helium and propylene / propane separation performance. Summary of the invention

[0008] In view of the shortcomings of existing carbon molecular sieve membranes, the present invention provides a method for preparing a fluorinated Trog base carbon molecular sieve membrane with high gas separation performance. To achieve the above purpose, the present invention provides a method for preparing a fluorinated Trog base carbon molecular sieve membrane, by introducing trifluoroisopropyl into the main chain of the Trog base polymer and pyrolyzing it, a carbon molecular sieve membrane with a specific micropore distribution, capable of efficiently separating hydrogen / helium and having both propylene / propane separation performance is customized.

[0009] The technical solution of the present invention:

[0010] A method for preparing a fluorine-containing Trog base carbon molecular sieve membrane with high hydrogen / helium separation performance comprises the following steps:

[0011] (1) Preparation of fluorinated trog base polymer: monomer A and monomer B are added to a dimethoxymethane solution; trifluoroacetic acid is slowly added dropwise to the system under an ice-water bath; the reaction mixture is stirred at 25° C., and aqueous ammonia is added to terminate the reaction. The obtained product is washed with solvent C for multiple times, re-dissolved with solvent D, re-precipitated with methanol, and filtered and dried to obtain a fluorinated trog base polymer;

[0012] (2) Preparation of fluoro-containing trog base precursor film: dissolving the fluoro-containing trog base polymer in chloroform, stirring and introducing the casting solution into a glass watch glass, and drying under vacuum conditions to obtain a polymer film after completely evaporating naturally;

[0013] (3) Preparation of fluorinated Trog base carbon molecular sieve membrane: Place the polymer membrane in a tubular furnace, introduce protective gas E, and carbonize it at 550°C-800°C. After maintaining the temperature for 1-3 hours, cool it to room temperature to obtain a fluorinated Trog base carbon molecular sieve membrane.

[0014] Furthermore, monomer A is 4,4'-diamino-3,3'-dimethylbiphenyl, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 4,4'-diaminooctafluorobiphenyl or 3,3-bis(trifluoromethyl)-[1,1-biphenyl]-4,4-diamine; monomer B is 4,4'-(hexafluoroisopropylidene)diphenylamine or 3,3',5,5'-tetramethylbenzidine; solvent C is water or methanol; solvent D is one or a mixture of two or more of chloroform, N-methylpyrrolidone and N,N-dimethylformamide; and protective gas E is nitrogen, argon or helium.

[0015] Furthermore, in step (1), the molar ratio of monomer A to monomer B is 1:0.2-0.5; the molar ratio of monomer A to dimethoxymethane is 1:4-6; the molar ratio of monomer A to trifluoroacetic acid is 1:20-30; the stirring time is 48-168h; and the volume ratio of ammonia water to trifluoroacetic acid is 5:1.

[0016] Furthermore, in step (2), the mass fraction of the casting liquid is 1.0-20.0wt.%; and the stirring time is 12-48h.

[0017] Beneficial effects of the present invention: The preparation method of the present invention forms a carbon molecular sieve membrane with a specific micropore distribution, high hydrogen permeability, and high hydrogen / helium selectivity by introducing trifluoroisopropyl into the main chain of the Trog base polymer and performing pyrolysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 BET spectra of fluorinated and non-fluorinated Trog base carbon molecular sieve membranes. DETAILED DESCRIPTION

[0019] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0020] The preparation method of the fluorinated Trog base carbon polymer membrane used in the present invention is as follows: 8.492g of 4,4'-diamino-3,3'-dimethylbiphenyl and 3.340g of 4,4'-(hexafluoroisopropylidene) diphenylamine are added to 20mL of dimethoxymethane solution, an ice-water bath is added to the system, and then 85mL of trifluoroacetic acid is slowly added to the system. The reaction mixture is stirred at 25°C for 96h, and 500mL of ammonia water is added to terminate the reaction. The obtained product is washed with an aqueous solution several times, redissolved in chloroform, reprecipitated with methanol, filtered, and vacuum dried at 80°C to obtain a fluorinated Trog base polymer.

[0021] Gas permeability test: The permeability test of the carbon molecular sieve gas separation membrane in the present invention adopts the constant volume variable pressure method, and the test temperature is 35°C.

[0022] Comparison example:

[0023] 10.615 g of 4,4'-diamino-3,3'-dimethylbiphenyl was added to 20 mL of dimethoxymethane solution, and an ice-water bath was added to the system. Then 85 mL of trifluoroacetic acid was slowly added to the system. The reaction mixture was stirred at 25 °C for 96 h, and 500 mL of ammonia water was added to terminate the reaction. The obtained product was washed with aqueous solution several times, redissolved in chloroform, reprecipitated with methanol, filtered, and vacuum dried at 80 °C to obtain a polymer without fluorotrog base.

[0024] 0.2 g of the obtained polymer was added into chloroform solvent to prepare a casting solution with a mass fraction of 2.0 wt.%. After stirring for 48 hours, the casting solution was introduced into a glass watch glass, and dried under vacuum conditions for 48 hours after natural evaporation for 24 hours.

[0025] The obtained film was taken to about 4 cm 2 Place it in a tubular furnace, introduce protective gas N2, raise the temperature to 550°C and maintain it for 2 hours, and then cool it naturally to room temperature to obtain the carbon molecular sieve membrane of Control Example 1.

[0026] Embodiment 1:

[0027] 8.492 g (40 mmol) of 4,4'-diamino-3,3'-dimethylbiphenyl and 3.340 g (10 mmol) of 4,4'-(hexafluoroisopropylidene)diphenylamine were added to 20 mL of dimethoxymethane solution, and 85 mL of trifluoroacetic acid was slowly added dropwise to the system under ice-water bath conditions. The synthesis and cleaning methods were consistent with those of Control Example 1.

[0028] 0.2 g of the obtained polymer was added into chloroform solvent to prepare a casting solution with a mass fraction of 2.0 wt.%. After stirring for 48 hours, the casting solution was introduced into a glass watch glass, and dried under vacuum conditions for 48 hours after natural evaporation for 24 hours.

[0029] The obtained film was taken to about 4 cm 2 The mixture was placed in a tubular furnace, and the protective gas N2 was introduced. The temperature was raised to 550°C and maintained for 2 hours. After the temperature was naturally cooled to room temperature, the carbon molecular sieve membrane of Example 1 was obtained.

[0030] Embodiment 2:

[0031] 6.369 g of 4,4'-diamino-3,3'-dimethylbiphenyl and 6.680 g of 4,4'-(hexafluoroisopropylidene)diphenylamine were added to 20 mL of dimethoxymethane solution, and 85 mL of trifluoroacetic acid was slowly added dropwise to the system under ice-water bath conditions. The synthesis and cleaning methods were consistent with those of Control Example 1.

[0032] 0.2 g of the obtained polymer was added into chloroform solvent to prepare a casting solution with a mass fraction of 2.0 wt.%. After stirring for 48 hours, the casting solution was introduced into a glass watch glass, and dried under vacuum conditions for 48 hours after natural evaporation for 24 hours.

[0033] The obtained film was taken to about 4 cm 2 The mixture was placed in a tubular furnace, and the protective gas N2 was introduced. The temperature was raised to 550°C and maintained for 2 hours. After the temperature was naturally cooled to room temperature, the carbon molecular sieve membrane of Example 2 was obtained.

[0034] Embodiment 3:

[0035] 5.308 g of 4,4'-diamino-3,3'-dimethylbiphenyl and 8.350 g of 4,4'-(hexafluoroisopropylidene)diphenylamine were added to 20 mL of dimethoxymethane solution, and 85 mL of trifluoroacetic acid was slowly added dropwise to the system under ice-water bath conditions. The synthesis and cleaning methods were consistent with those of Control Example 1.

[0036] 0.2 g of the obtained polymer was added into chloroform solvent to prepare a casting solution with a mass fraction of 2.0 wt.%. After stirring for 48 hours, the casting solution was introduced into a glass watch glass, and dried under vacuum conditions for 48 hours after natural evaporation for 24 hours.

[0037] The obtained film was taken to about 4 cm 2 The mixture was placed in a tubular furnace, and the protective gas N2 was introduced. The temperature was raised to 550°C and maintained for 2 hours. After the temperature was naturally cooled to room temperature, the carbon molecular sieve membrane of Example 3 was obtained.

[0038] Embodiment 4:

[0039] 0.2 g of the polymer obtained in Example 1 was added to chloroform solvent to prepare a casting solution with a mass fraction of 2.0 wt.%. After stirring for 48 hours, the casting solution was introduced into a glass watch glass, evaporated naturally for 24 hours, and then dried under vacuum conditions for 48 hours.

[0040] The obtained film was taken to about 4 cm 2 The mixture was placed in a tubular furnace, and the protective gas N2 was introduced. The temperature was raised to 700°C and maintained for 2 hours. After the temperature was naturally cooled to room temperature, the carbon molecular sieve membrane of Example 4 was obtained.

[0041] Embodiment 5:

[0042] 0.2 g of the polymer obtained in Example 1 was added to chloroform solvent to prepare a casting solution with a mass fraction of 2.0 wt.%. After stirring for 48 hours, the casting solution was introduced into a glass watch glass, evaporated naturally for 24 hours, and then dried under vacuum conditions for 48 hours.

[0043] The obtained film was taken to about 4 cm 2The mixture was placed in a tubular furnace, and the protective gas N2 was introduced. The temperature was raised to 800°C and maintained for 2 hours. After the temperature was naturally cooled to room temperature, the carbon molecular sieve membrane of Example 5 was obtained.

[0044] The hydrogen / helium separation performances of the control example and examples 1, 2, and 3 at 35°C and 2 Bar are shown in Table 1. By comparing the control example 1 and example 1, and example 2 and example 3, we can find that as the degree of fluorination increases, the hydrogen permeability and selectivity of the Trog base carbon molecular sieve membrane are simultaneously improved.

[0045] The hydrogen / helium separation performances of Examples 1, 4, and 5 at 35°C and 2 Bar are shown in Table 2. By comparing Example 1, Example 2, and Example 3, we can find that as the pyrolysis temperature increases, the hydrogen permeability of the Trog base carbon molecular sieve membrane decreases and the selectivity further improves.

[0046] The propylene / propane separation performance of the control example and examples 1, 2, and 3 at 35°C and 4 Bar is shown in Table 3. By comparing the control example 1 and example 1, and example 2 and example 3, we can find that as the pyrolysis temperature increases, as the degree of fluorination increases, the propylene permeability and selectivity of the Trog base carbon molecular sieve membrane increase simultaneously.

[0047] Table 1 shows the hydrogen / helium permeability and selectivity of the carbon molecular sieve membranes prepared in the control example and in Example 1, Example 2 and Example 3.

[0048]

[0049] Table 2 shows the hydrogen / helium permeability and selectivity of the carbon molecular sieve membranes prepared in the control example, Example 4 and Example 5.

[0050]

[0051] Table 3 shows the propylene / propane permeability and selectivity of the carbon molecular sieve membranes prepared in the control example, example 1, example 2 and example 3.

[0052]

Claims

1. A method for preparing a fluorine-containing Trog base carbon molecular sieve membrane with high gas separation performance, characterized in that: The following steps are involved: (1) Preparation of fluorinated trog base polymer: monomer A and monomer B are added to a dimethoxymethane solution; trifluoroacetic acid is slowly added dropwise to the system under an ice-water bath; the reaction mixture is stirred at 25° C., and aqueous ammonia is added to terminate the reaction. The obtained product is washed with solvent C for multiple times, re-dissolved with solvent D, re-precipitated with methanol, and filtered and dried to obtain a fluorinated trog base polymer; (2) Preparation of fluoro-containing trog base precursor film: dissolving the fluoro-containing trog base polymer in chloroform, stirring and introducing the casting solution into a glass watch glass, and drying under vacuum conditions to obtain a polymer film after completely evaporating naturally; (3) Preparation of fluorinated Trog base carbon molecular sieve membrane: Place the polymer membrane in a tubular furnace, introduce protective gas E, and carbonize it at 550°C-800°C. After maintaining the temperature for 1-3 hours, cool it to room temperature to obtain a fluorinated Trog base carbon molecular sieve membrane.

2. The method for preparing a fluorine-containing Trog base carbon molecular sieve membrane according to claim 1, characterized in that: The monomer A is 4,4'-diamino-3,3'-dimethylbiphenyl, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 4,4'-diaminooctafluorobiphenyl or 3,3-bis(trifluoromethyl)-[1,1-biphenyl]-4,4-diamine.

3. The method for preparing a fluorine-containing Trog base carbon molecular sieve membrane according to claim 1, characterized in that: The monomer B is 4,4'-(hexafluoroisopropylidene)diphenylamine or 3,3',5,5'-tetramethylbenzidine.

4. The method for preparing a fluorine-containing Trog base carbon molecular sieve membrane according to claim 1, characterized in that: The solvent C is water or methanol.

5. The method for preparing a fluorine-containing Trog base carbon molecular sieve membrane according to claim 1, characterized in that: The solvent D is one of chloroform, N-methylpyrrolidone, and N,N-dimethylformamide, or a mixture of two or more thereof.

6. The method for preparing a fluorine-containing Trog base carbon molecular sieve membrane according to claim 1, characterized in that: The protective gas E is nitrogen, argon or helium.

7. The method for preparing a fluorine-containing Trog base carbon molecular sieve membrane according to claim 1, characterized in that: In step (1), the molar ratio of monomer A to monomer B is 1:0.2-0.5; the molar ratio of monomer A to dimethoxymethane is 1:4-6; the molar ratio of monomer A to trifluoroacetic acid is 1:20-30; the stirring time is 48-168h; and the volume ratio of ammonia water to trifluoroacetic acid is 5:

1.

8. The method for preparing a fluorine-containing Trog base carbon molecular sieve membrane according to claim 1, characterized in that: In step (2), the mass fraction of the casting liquid is 1.0-20.0wt.%; and the stirring time is 12-48h.

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