A tannic acid modified MOF based mixed matrix hollow fiber carbon molecular sieve membrane, a preparation method and application thereof

Abstract

This invention relates to a tannic acid-modified MOF-based hybrid matrix hollow fiber carbon molecular sieve membrane, its preparation method, and its application. The method includes the following steps: S1, preparing tannic acid-modified MOF particles; S2, preparing spinning solution; S3, preparing a hybrid matrix precursor membrane; S4, carbonization. This invention is the first to design and successfully prepare a MOF-based hybrid matrix hollow fiber carbon molecular sieve membrane. By innovatively utilizing a tannic acid modification strategy, the interfacial compatibility between MOF particles and the cellulose matrix is ​​significantly improved, effectively enhancing the dispersion uniformity of MOF particles in the membrane matrix. This results in a hybrid matrix hollow fiber carbon molecular sieve membrane with uniform pore structure and excellent interconnectivity, achieving highly selective separation of the ethylene / ethane system. This provides a fundamental and innovative approach for the development of high-performance gas separation membranes. This invention achieves superior interfacial bonding and gas separation selectivity that are difficult to achieve with traditional hybrid matrix membranes.

Description

Technical Field

[0001] This invention relates to the field of mixed matrix membrane materials technology. In particular, it relates to a mixed matrix hollow fiber carbon molecular sieve membrane based on tannic acid-modified MOF, its preparation method, and its applications. Background Technology

[0002] In core industrial sectors such as petrochemicals and energy chemicals, the efficient separation of alkanes and olefins is a crucial link restricting the upgrading of the industrial chain and achieving energy conservation and emission reduction. It is also a core separation problem recognized by the industry as influencing the global chemical industry development landscape. Traditional separation methods (such as cryogenic distillation and adsorption separation) generally suffer from significant drawbacks such as high energy consumption, complex operation, and large equipment investment, making them unsuitable for the development demands of energy conservation, emission reduction, and efficient separation in industrial sectors. To address this challenge, hybrid matrix membrane strategies have been widely explored and applied. The core of these strategies is to combine functional nanoparticles (such as MOFs) with polymer matrices, aiming to synergistically improve the gas permeability and molecular sieving selectivity of the membrane, compensating for the performance shortcomings of single-matrix membranes. However, existing hybrid matrix membranes still face core technological bottlenecks: poor interfacial compatibility between nanoparticles and polymer matrices, leading to easy aggregation and resulting in membrane structural defects and uneven pore size distribution, making it difficult to achieve precise sieving of alkanes and olefins. High-temperature pyrolysis can promote the carbonization and reconstruction of polymer matrix by directional pyrolysis of mixed matrix precursors, and form a uniform microporous structure that is tightly bound to nanoparticles. This effectively solves the problems of interface defects and pore size disorder, and provides a feasible path for efficient separation.

[0003] However, the preparation of existing mixed-matrix carbon molecular sieve membranes faces insurmountable technical bottlenecks: poor interfacial compatibility between MOF particles and polymer precursors leads to easy aggregation in the spinning solution, resulting in disordered pore structure and widened pore size distribution during subsequent pyrolysis, hindering precise ethylene / ethane separation. Furthermore, traditional MOF doping systems do not specifically modify the MOF particles, resulting in significant interfacial defects between the MOF and polymer matrix. During pyrolysis, MOF particle detachment and pore collapse are common, further contributing to low membrane separation selectivity and unstable permeation flux. This makes it difficult to balance permeability and selectivity, failing to meet the industrial application requirements for ethylene / ethane separation.

[0004] Therefore, the key to overcoming existing technological bottlenecks lies in developing a modification strategy that can improve the interfacial compatibility between MOF particles and the polymer matrix, achieve uniform dispersion of MOF particles, and combine this strategy with dry-jet wet spinning to prepare high-performance hybrid matrix hollow fiber carbon molecular sieve membranes. This would solve problems such as MOF agglomeration, interfacial defects, and disordered pore structure, achieving efficient separation of ethylene / ethane. Currently, no publicly disclosed technical solution uses modified MOFs combined with polymer precursors to prepare hybrid matrix hollow fiber carbon molecular sieve membranes through a high-temperature carbonization process to solve the aforementioned technical challenges. Summary of the Invention

[0005] The technical problem to be solved by this invention is to address the problems of MOF particle agglomeration, poor interfacial compatibility, disordered pore structure, poor separation performance, and difficulty in achieving both permeability and selectivity in the existing mixed matrix membranes for ethylene / ethane separation. This invention provides a method for preparing a mixed matrix hollow fiber carbon molecular sieve membrane based on tannic acid modified MOF, and also provides the carbon molecular sieve membrane prepared by this method and its applications.

[0006] The innovation of this invention lies in the first-time combination of tannic acid-modified MOF with cellulose precursor, and the preparation of a mixed matrix hollow fiber carbon molecular sieve membrane through a dry-jet wet spinning-high-temperature carbonization process. Tannic acid modification not only solves the technical problems of MOF particle aggregation and poor interfacial compatibility, but also guides the directional reconstruction of the carbon matrix during the carbonization process, further optimizing the pore structure. This overcomes the dilemma of traditional mixed matrix membranes that are difficult to balance selectivity and permeability. Moreover, the preparation process is simple, highly controllable, and easy to scale up industrially, providing a high-efficiency and energy-saving membrane material and preparation scheme for ethylene / ethane separation.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In its first aspect, the present invention provides a method for preparing a hollow fiber carbon molecular sieve membrane based on a tannic acid-modified MOF mixed matrix, comprising the following steps: S1. MOF particles are soaked in tannic acid solution to prepare tannic acid modified MOF particles; S2. Using tannic acid-modified MOF particles as one of the raw materials to prepare spinning solution; S3. A mixed matrix precursor membrane is prepared by dry-jet wet spinning process using the spinning solution; S4. Carbonize the mixed matrix precursor membrane to obtain the mixed matrix hollow fiber carbon molecular sieve membrane based on tannic acid modified MOF.

[0008] Preferably, step S1 specifically includes: MOF particles were soaked in a tannic acid solution with a concentration of 2-5 g / L for 8-15 min, centrifuged, washed, and vacuum dried to obtain tannic acid modified MOF particles.

[0009] Preferably, the MOF particles mentioned in step S1 are selected from at least one of ZIF-8, ZIF-67, and MOF-5.

[0010] Preferably, step S2 specifically includes: S21. Add tannic acid-modified MOF particles to dimethyl sulfoxide and disperse by ultrasonication to obtain MOF dispersion; S22. Under stirring conditions, microcrystalline cellulose is added to the above MOF dispersion in multiple portions, followed by the addition of 1-ethyl-3-methylimidazolium acetate, and the mixture is heated and mixed to obtain the initial spinning solution. S23. Vacuum the initial spinning solution to remove bubbles, and obtain the spinning solution.

[0011] Preferably, the mass percentage of tannic acid-modified MOF particles added in step S2 is 8-15% of the mass of microcrystalline cellulose.

[0012] Preferably, step S2 specifically includes: S21. Add the tannic acid-modified MOF particles obtained in step S1 to 150-300g of dimethyl sulfoxide and ultrasonically disperse for 30-6 min to obtain MOF dispersion. S22. Under stirring conditions, 27.27 g to 54.54 g of microcrystalline cellulose was added to the above MOF dispersion in multiple portions, followed by 50 to 100 g of 1-ethyl-3-methylimidazolium acetate. The mixture was then stirred at 50 to 80 °C for 12 to 24 h to obtain the initial spinning solution. S23. The initial spinning solution is vacuumed at 50-60℃ for 12 h to remove air bubbles and obtain the spinning solution.

[0013] Preferably, the method for preparing the hollow fiber carbon molecular sieve membrane based on tannic acid-modified MOF includes the following steps: S1. Preparation of tannic acid-modified MOF particles: MOF particles were soaked in a 2-5 g / L tannic acid methanol aqueous solution for 8-15 min, then centrifuged and washed with ethanol 3-5 times at a centrifugation speed of 11000-14000 rpm. After washing, the particles were vacuum dried at room temperature for 12-24 h to obtain tannic acid modified MOF particles. S2. Preparation of spinning solution: S21. Add the tannic acid-modified MOF particles obtained in step S1 to 150-300g of dimethyl sulfoxide and ultrasonically disperse for 30-6 min to obtain MOF dispersion. S22. Under stirring conditions, 27.27 g to 54.54 g of microcrystalline cellulose was added to the above MOF dispersion in multiple portions, followed by 50 to 100 g of 1-ethyl-3-methylimidazolium acetate. The mixture was then stirred at 50 to 80 °C for 12 to 24 h to obtain the initial spinning solution. S23. Vacuum the initial spinning solution at 50-60℃ for 12 h to remove air bubbles from the initial spinning solution and obtain the spinning solution. S3. Preparation of mixed matrix precursor membrane: The spinning solution obtained in step S2 is spun into a hollow fiber membrane using a dry-jet wet spinning process. After spinning, the hollow fiber membrane is soaked in deionized water for 2-4 days, and the deionized water is replaced every 6-24 hours. After soaking, the mixed matrix precursor membrane is obtained. The parameters of the dry-jet wet spinning process are as follows: the core solution is deionized water; the core solution temperature, spinning solution temperature, and coagulation bath temperature are all 20-30℃; the spinning solution flow rate is 4-6 mL / min; the core solution flow rate is 1.0-1.5 mL / min; the height of the spinning head from the water surface is 2-3 cm; the drawing rate is 5.6-7.8 m / min; and the winding rate is 6.0-8.0 m / min. S4. Carbonize the mixed matrix precursor membrane: Place the mixed matrix precursor membrane in an argon atmosphere and heat it to 100-150℃ at a heating rate of 2-10℃ / min, and hold it at this temperature for 6-240 min; then heat it to 300-400℃ at a heating rate of 5-20℃ / min, and hold it for 30-120 min; finally heat it to 600-800℃ at a heating rate of 2-10℃ / min, and hold it for 60-240 min. After cooling, the mixed matrix hollow fiber carbon molecular sieve membrane based on tannic acid modified MOF is obtained.

[0014] In a second aspect, the present invention provides a hollow fiber carbon molecular sieve membrane based on a tannic acid-modified MOF, which is prepared by the preparation method described above.

[0015] A third aspect of the present invention provides the application of the tannic acid-modified MOF-based hollow fiber carbon molecular sieve membrane, as described above, in the separation of ethylene and ethane.

[0016] In a fourth aspect, the present invention provides a membrane module comprising a tannic acid-modified MOF-based mixed matrix hollow fiber carbon molecular sieve membrane as described above, the membrane module being used for the separation of ethylene and ethane.

[0017] The beneficial effects of this invention are: (1) This invention is the first to combine tannic acid modified MOF with cellulose matrix mixed matrix membrane system, breaking through the core technical bottleneck of MOF particle agglomeration and poor interfacial compatibility in traditional mixed matrix membrane, realizing the uniform dispersion of MOF particles in the matrix, and solving the problem of poor separation performance caused by interfacial defects in the prior art. It is a principle-based technical innovation. (2) This invention innovatively combines modified MOF with hollow fiber structure, taking into account the advantages of high specific surface area, high packing density and excellent separation performance of membrane. At the same time, the preparation process is simple and controllable, with low energy consumption and easy industrial scale-up. Compared with traditional separation methods and existing membrane materials, it significantly reduces the energy consumption and cost of ethylene / ethane separation and has significant industrial application value. (4) The modification strategy and preparation process of the present invention are universal and can be applied to the preparation of separation membranes of other MOF materials and other alkane / olefin systems, providing a new technical idea and technical path for the development of high-performance gas separation membranes and promoting the technological progress in the field of gas separation membrane materials. Attached Figure Description

[0018] Figure 1 TEM image of tannic acid-modified ZIF-8 prepared in Example 1; Figure 2 The images show the tannic acid-modified ZIF-8 prepared in Example 1 and the ZIF-8 prepared in Comparative Example 2 after being dispersed in DMSO solvent. Figure 3 The low-field NMR spectra of the precursor films prepared in Example 1, Comparative Example 1, and Comparative Example 2 are shown. Figure 4 SEM images of the hollow fiber carbon molecular sieve membranes prepared in Example 1 and Comparative Example 2; Figure 5 The X-ray diffraction patterns are those of the hollow fiber carbon molecular sieve membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2. Detailed Implementation

[0019] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples are commercially available. For examples where specific conditions are not specified, conventional conditions or conditions recommended by the manufacturer are followed. For reagents or instruments whose manufacturers are not specified, they are all commercially available products.

[0021] This invention provides a hollow fiber carbon molecular sieve membrane based on tannic acid-modified MOF and its preparation method, which includes the following steps: S1. Preparation of tannic acid-modified MOF particles: MOF particles were soaked in a 2-5 g / L tannic acid methanol aqueous solution for 8-15 min, then centrifuged and washed with ethanol 3-5 times at a centrifugation speed of 11000-14000 rpm. After washing, the particles were vacuum dried at room temperature for 12-24 h to obtain tannic acid modified MOF particles. S2. Preparation of spinning solution: S21. Add the tannic acid-modified MOF particles obtained in step S1 to 150-300g of dimethyl sulfoxide and ultrasonically disperse for 30-6 min to obtain MOF dispersion. S22. Under stirring conditions, 27.27 g to 54.54 g of microcrystalline cellulose was added to the above MOF dispersion in multiple portions, followed by 50 to 100 g of 1-ethyl-3-methylimidazolium acetate. The mixture was then stirred at 50 to 80 °C for 12 to 24 h to obtain the initial spinning solution. S23. Vacuum the initial spinning solution at 50-60℃ for 12 h to remove air bubbles and obtain the spinning solution. S3. Preparation of mixed matrix precursor membrane: The spinning solution obtained in step S2 is spun into a hollow fiber membrane using a dry-jet wet spinning process. After spinning, the hollow fiber membrane is soaked in deionized water for 2-4 days, and the deionized water is replaced every 6-24 hours. After soaking, the mixed matrix precursor membrane is obtained. The parameters for the dry-jet wet spinning process are as follows: the core solution uses deionized water; the core solution temperature, spinning solution temperature, and coagulation bath temperature are all 20-30℃; the spinning solution flow rate is 4-6 mL / min; the core solution flow rate is 1.0-1.5 mL / min; the height of the spinning head from the water surface is 2-3 cm; the drawing rate is 5.6-7.8 m / min; and the winding rate is 6.0-8.0 m / min. S4. Carbonize the mixed matrix precursor membrane: Place the mixed matrix precursor membrane in an argon atmosphere and heat it to 100-150℃ at a heating rate of 2-10℃ / min, and hold it at this temperature for 6-240 min; then heat it to 300-400℃ at a heating rate of 5-20℃ / min, and hold it for 30-120 min; finally heat it to 600-800℃ at a heating rate of 2-10℃ / min, and hold it for 60-240 min. After cooling, a mixed matrix hollow fiber carbon molecular sieve membrane based on tannic acid modified MOF is obtained.

[0022] The present invention also provides the application of the above-mentioned hollow fiber carbon molecular sieve membrane based on tannic acid modified MOF in the separation of ethylene and ethane.

[0023] The present invention also provides a membrane module comprising a tannic acid-modified MOF-based mixed matrix hollow fiber carbon molecular sieve membrane as described above, the membrane module being used for the separation of ethylene and ethane.

[0024] For example, in a preferred embodiment, the membrane module is assembled as follows: A hollow fiber carbon molecular sieve membrane sample based on a tannic acid-modified MOF mixed matrix with no obvious surface defects (macroscopic defects such as surface cracks or obvious bending) was selected and assembled into a membrane module. The two ends of the membrane sample were fixed to the shell with epoxy resin to form a sealed isolation between the feed side and the permeate side; a permeate side outlet was set on the shell. One working process of the membrane module is as follows: the mixed gas to be separated (taking a C2H4 / C2H6 mixed gas as an example) enters from one end of the membrane sample (feed side), C2H4 permeates through the membrane wall of the membrane sample and exits through the permeate side, and the remaining gas after separation exits from the other end of the membrane sample (feed side).

[0025] The above is the general concept of the present invention. Based on this, detailed embodiments and comparative examples are provided below to further illustrate the present invention.

[0026] The performance testing methods involved in the following examples and comparative examples are as follows: a single gas permeation test was conducted on the treated carbon molecular sieve membrane using the constant permeation volume method, with a feed pressure of 2 bar and a temperature of 25°C. The separation performance of the treated carbon molecular sieve membrane was evaluated and compared by calculating the membrane's permeability and selectivity.

[0027] The relevant performance evaluation methods involved in the following embodiments and comparative examples are as follows: (1) The formula for calculating gas permeability is as follows: In the formula, P is the single gas permeability (unit: GPU, 1 GPU = 1 × 10⁻⁶). -6 cm 3 (STP) cm -2 s -1 cmHg -1 = 3.35 × 10 -10 mol s -1 m -2 Pa -1 V (cm) 3 ( ) represents the volume of gas measured by osmosis, T (K) represents the experimental temperature, and A (cm²) represents the volume of gas measured by osmosis. 2 ) is the effective membrane area of ​​the carbon molecular sieve membrane. p and p (bar) are the pressures on the feed side and the permeation side, respectively; p1 and p2 represent the start and end pressures of the test, respectively.

[0028] (2) The formula for calculating gas separation selectivity is as follows: In the formula, This indicates the ideal selectivity of the membrane for gases a and b. This represents the permeability (Barrer) of gas a. This represents the permeability (Barrer) of gas b.

[0029] Example 1 A mixed matrix hollow fiber carbon molecular sieve membrane based on tannic acid-modified MOF, specifically a mixed matrix hollow fiber carbon molecular sieve membrane based on tannic acid-modified ZIF-8, is prepared by the following steps: S1, ZIF-8 modification: ZIF-8 particles (150 nm, dodecahedral structure) were added to a 5 g / L tannic acid methanol aqueous solution (methanol:water volume ratio of 3:1) and soaked for 10 min. Then, the particles were centrifuged and washed with ethanol 5 times at a centrifugation speed of 14000 rpm. After washing, the particles were vacuum dried at room temperature for 24 h to obtain tannic acid modified ZIF-8 particles.

[0030] S2. Preparation of spinning solution: 5.454 g of tannic acid modified ZIF-8 particles obtained in step S1 were added to 300 g of dimethyl sulfoxide and ultrasonically dispersed for 30 min to obtain tannic acid modified ZIF-8 dispersion. Under stirring conditions, 54.54 g of microcrystalline cellulose (Sigma-Aldrich, Avicel PH-101, particle size: 50 μm, the other examples and comparative examples are the same) were added to the above ZIF-8 dispersion in multiple portions, followed by 100 g of 1-ethyl-3-methylimidazolium acetate. The above solution was then placed in a mixer and mixed at 60 °C for 24 h to obtain the initial spinning solution. The initial spinning solution was vacuumed at 50-60 °C for 12 h to remove air bubbles and obtain the spinning solution.

[0031] S3. Preparation of mixed matrix precursor membrane: The spinning solution obtained in step S2 is spun into a hollow fiber membrane using a dry-jet wet spinning process. After spinning, the hollow fiber membrane is soaked in deionized water for 4 days, and the deionized water is replaced every 12 hours. After soaking, the mixed matrix precursor membrane is obtained. The parameters for the dry-jet wet spinning process are as follows: the core solution is deionized water, and the core solution temperature, spinning solution temperature, and coagulation bath temperature are all 25℃; the spinning solution flow rate is 6 mL / min, the core solution flow rate is 1.5 mL / min, the height of the spinning head from the water surface is 3 cm, the drawing rate is 7.8 m / min, and the winding rate is 8.0 m / min.

[0032] Step S4: Preparation of mixed matrix carbon molecular sieve membrane: The mixed matrix precursor membrane was placed in an argon atmosphere and heated to 120°C at a heating rate of 5°C / min, and held at this temperature for 120 min; then heated to 340°C at a heating rate of 10°C / min and held for 60 min; finally heated to 700°C at a heating rate of 5°C / min and held for 120 min. After cooling, a mixed matrix hollow fiber carbon molecular sieve membrane based on tannic acid modified ZIF-8 was obtained.

[0033] Example 2 A mixed matrix hollow fiber carbon molecular sieve membrane based on tannic acid-modified MOF, specifically another mixed matrix hollow fiber carbon molecular sieve membrane based on tannic acid-modified ZIF-8, is prepared by the following steps: S1, ZIF-8 modification: ZIF-8 particles were added to a 5 g / L tannic acid methanol aqueous solution and soaked for 10 min. Then, the particles were centrifuged and washed with ethanol 5 times at a centrifugation speed of 14000 rpm. After washing, the particles were vacuum dried at room temperature for 24 h to obtain tannic acid modified ZIF-8 particles.

[0034] S2. Preparation of spinning solution: 8.181 g of tannic acid modified ZIF-8 particles obtained in step S1 were added to 300 g of dimethyl sulfoxide and ultrasonically dispersed for 60 min to obtain a tannic acid modified ZIF-8 dispersion. Under stirring conditions, 54.54 g of microcrystalline cellulose was added to the above ZIF-8 dispersion in multiple portions, followed by 100 g of 1-ethyl-3-methylimidazolium acetate. The solution was then placed in a mixer and mixed at 60°C for 24 h to obtain the initial spinning solution. The initial spinning solution was vacuumed at 50-60°C for 12 h to remove air bubbles and obtain the spinning solution.

[0035] S3. Preparation of mixed matrix precursor membrane: The spinning solution obtained in step S2 is spun into a hollow fiber membrane using a dry-jet wet spinning process. After spinning, the hollow fiber membrane is soaked in deionized water for 4 days, and the deionized water is replaced every 12 hours. After soaking, the mixed matrix precursor membrane is obtained. The parameters of the dry-jet wet spinning process are as follows: the core liquid is deionized water, and the core liquid temperature, spinning solution temperature, and coagulation bath temperature are all 25℃; the spinning solution flow rate is 6 mL / min, the core liquid flow rate is 1.5 mL / min, the height of the spinning head from the water surface is 3 cm, the drawing rate is 7.8 m / min, and the winding rate is 8.0 m / min.

[0036] Step S4: Preparation of mixed matrix carbon molecular sieve membrane: The mixed matrix precursor membrane is placed in an argon atmosphere and heated to 120°C at a heating rate of 5°C / min, and held at this temperature for 120 min; then heated to 340°C at a heating rate of 10°C / min and held for 60 min; finally heated to 700°C at a heating rate of 5°C / min and held for 120 min, and after cooling, the mixed matrix hollow fiber carbon molecular sieve membrane based on tannic acid modified ZIF-8 is obtained.

[0037] Example 3 A mixed matrix hollow fiber carbon molecular sieve membrane based on tannic acid-modified MOF, specifically a mixed matrix hollow fiber carbon molecular sieve membrane based on tannic acid-modified ZIF-67, is prepared by the following steps: S1, ZIF-67 modification: ZIF-67 particles were added to a 5 g / L tannic acid methanol aqueous solution and soaked for 10 min. Then, the particles were centrifuged and washed 5 times with ethanol at a centrifugation speed of 14000 rpm. After washing, the particles were vacuum dried at room temperature for 24 h to obtain tannic acid modified ZIF-67 particles.

[0038] S2. Preparation of spinning solution: 5.454 g of tannic acid modified ZIF-67 particles obtained in step S1 were added to 300 g of dimethyl sulfoxide and ultrasonically dispersed for 60 min to obtain a tannic acid modified ZIF-67 dispersion. Under stirring conditions, 54.54 g of microcrystalline cellulose was added to the above ZIF-67 dispersion in multiple portions, followed by 100 g of 1-ethyl-3-methylimidazolium acetate. The solution was then placed in a mixer and mixed at 60 °C for 24 h to obtain the initial spinning solution. The initial spinning solution was vacuumed at 50-60 °C for 12 h to remove air bubbles and obtain the spinning solution.

[0039] S3. Preparation of mixed matrix precursor membrane: The spinning solution obtained in step S2 is spun into a hollow fiber membrane using a dry-jet wet spinning process. After spinning, the hollow fiber membrane is soaked in deionized water for 4 days, and the deionized water is replaced every 12 hours. After soaking, the mixed matrix precursor membrane is obtained. The parameters of the dry-jet wet spinning process are as follows: the core liquid is deionized water, and the core liquid temperature, spinning solution temperature, and coagulation bath temperature are all 25℃; the spinning solution flow rate is 6 mL / min, the core liquid flow rate is 1.5 mL / min, the height of the spinning head from the water surface is 3 cm, the drawing rate is 7.8 m / min, and the winding rate is 8.0 m / min.

[0040] Step S4: Preparation of mixed matrix carbon molecular sieve membrane: The mixed matrix precursor membrane is placed in an argon atmosphere and heated to 120°C at a heating rate of 5°C / min, and held at this temperature for 120 min; then heated to 340°C at a heating rate of 10°C / min and held for 60 min; finally heated to 700°C at a heating rate of 5°C / min and held for 120 min, and after cooling, the mixed matrix hollow fiber carbon molecular sieve membrane based on tannic acid modified ZIF-67 is obtained.

[0041] Example 4 A mixed matrix hollow fiber carbon molecular sieve membrane based on tannic acid-modified MOF, specifically a mixed matrix hollow fiber carbon molecular sieve membrane based on tannic acid-modified ZIF-5, is prepared by the following steps: S1, MOF-5 modification: 5.454g of MOF-5 particles were added to a 5 g / L tannic acid methanol aqueous solution and soaked for 10 min. Then, the particles were centrifuged and washed 5 times with ethanol at a centrifugation speed of 14000 rpm. After washing, the particles were vacuum dried at room temperature for 24 h to obtain tannic acid modified MOF-5 particles.

[0042] S2. Preparation of spinning solution: The tannic acid modified MOF-5 particles obtained in step S1 were added to 300 g of dimethyl sulfoxide and ultrasonically dispersed for 60 min to obtain a tannic acid modified MOF-5 dispersion. Under stirring conditions, 54.54 g of microcrystalline cellulose was added to the above MOF-5 dispersion in multiple portions, followed by 100 g of 1-ethyl-3-methylimidazolium acetate. The solution was then placed in a mixer and mixed at 60°C for 24 h to obtain the initial spinning solution. The initial spinning solution was vacuumed at 50-60°C for 12 h to remove air bubbles and obtain the spinning solution.

[0043] S3. Preparation of mixed matrix precursor membrane: The spinning solution obtained in step S2 is spun into a hollow fiber membrane using a dry-jet wet spinning process. After spinning, the hollow fiber membrane is soaked in deionized water for 4 days, and the deionized water is replaced every 12 hours. After soaking, the mixed matrix precursor membrane is obtained. The parameters of the dry-jet wet spinning process are as follows: the core liquid is deionized water, and the core liquid temperature, spinning solution temperature, and coagulation bath temperature are all 25℃; the spinning solution flow rate is 6 mL / min, the core liquid flow rate is 1.5 mL / min, the height of the spinning head from the water surface is 3 cm, the drawing rate is 7.8 m / min, and the winding rate is 8.0 m / min.

[0044] Step S4: Preparation of mixed matrix carbon molecular sieve membrane: The mixed matrix precursor membrane is placed in an argon atmosphere and heated to 120°C at a heating rate of 5°C / min, and held at this temperature for 120 min; then heated to 340°C at a heating rate of 10°C / min and held for 60 min; finally heated to 700°C at a heating rate of 5°C / min and held for 120 min, and after cooling, the mixed matrix hollow fiber carbon molecular sieve membrane based on tannic acid modified MOF-5 is obtained.

[0045] Comparative Example 1 A cellulose-derived hollow fiber carbon molecular sieve membrane, the preparation method of which includes the following steps: S1. Preparation of spinning solution: 54.54 g of microcrystalline cellulose was added to 300 g of dimethyl sulfoxide in multiple portions, followed by 100 g of 1-ethyl-3-methylimidazolium acetate. The solution was then placed in a mixer and mixed at 60°C for 24 h to obtain the initial spinning solution. The initial spinning solution was then vacuumed at 50-60°C for 12 h to remove air bubbles, thus obtaining the spinning solution.

[0046] S3. Preparation of cellulose precursor membrane: The spinning solution obtained in step S2 is spun into a hollow fiber membrane using a dry-jet wet spinning process. After spinning, the hollow fiber membrane is soaked in deionized water for 4 days, and the deionized water is replaced every 12 hours. After soaking, the cellulose precursor membrane is obtained. The parameters of the dry-jet wet spinning process are as follows: the core liquid is deionized water, and the core liquid temperature, spinning solution temperature, and coagulation bath temperature are all 25℃; the spinning solution flow rate is 6 mL / min, the core liquid flow rate is 1.5 mL / min, the height of the spinning head from the water surface is 3 cm, the drawing rate is 7.8 m / min, and the winding rate is 8.0 m / min.

[0047] Step S4: Preparation of cellulose-derived hollow fiber carbon molecular sieve membrane: The cellulose precursor membrane is placed in an argon atmosphere and heated to 120°C at a heating rate of 5°C / min, and held at this temperature for 120 min; then heated to 340°C at a heating rate of 10°C / min and held for 60 min; finally heated to 700°C at a heating rate of 5°C / min and held for 120 min, and after cooling, the cellulose-derived hollow fiber carbon molecular sieve membrane is obtained.

[0048] Comparative Example 2 A ZIF-8-based hollow fiber carbon molecular sieve membrane is prepared by the following steps: S1. Preparation of spinning solution: 5.454 g of ZIF-8 particles were added to 300 g of dimethyl sulfoxide and ultrasonically dispersed for 60 min to obtain ZIF-8 dispersion; under stirring conditions, 54.54 g of microcrystalline cellulose was added to the above ZIF-8 dispersion in multiple portions, followed by 100 g of 1-ethyl-3-methylimidazolium acetate. The solution was then placed in a mixer and mixed at 60 °C for 24 h to obtain the initial spinning solution; the initial spinning solution was vacuumed at 50-60 °C for 12 h to remove air bubbles, thus obtaining the spinning solution.

[0049] S3. Preparation of mixed matrix precursor membrane: The spinning solution obtained in step S2 is spun into a hollow fiber membrane using a dry-jet wet spinning process. After spinning, the hollow fiber membrane is soaked in deionized water for 4 days, and the deionized water is replaced every 12 hours. After soaking, the mixed matrix precursor membrane is obtained. The parameters of the dry-jet wet spinning process are as follows: the core liquid is deionized water, and the core liquid temperature, spinning solution temperature, and coagulation bath temperature are all 25℃; the spinning solution flow rate is 6 mL / min, the core liquid flow rate is 1.5 mL / min, the height of the spinning head from the water surface is 3 cm, the drawing rate is 7.8 m / min, and the winding rate is 8.0 m / min.

[0050] Step S4: Preparation of mixed matrix carbon molecular sieve membrane: The mixed matrix precursor membrane is placed in an argon atmosphere and heated to 120°C at a heating rate of 5°C / min, and held at this temperature for 120 min; then heated to 340°C at a heating rate of 10°C / min and held for 60 min; finally heated to 700°C at a heating rate of 5°C / min and held for 120 min, and after cooling, the ZIF-8-based mixed matrix hollow fiber carbon molecular sieve membrane is obtained.

[0051] Performance characterization and testing: Reference Figure 1 The image shows a TEM image of the tannic acid-modified ZIF-8 prepared in Example 1.

[0052] Reference Figure 2 The images show the tannic acid-modified ZIF-8 prepared in Example 1 and the ZIF-8 prepared in Comparative Example 2 after dispersion in DMSO solvent. It can be seen that the tannic acid-modified ZIF-8 is more stable in dispersion in the solvent and is less prone to sedimentation.

[0053] Reference Figure 3 The images show the low-field NMR spectra of the precursor membranes prepared in Example 1, Comparative Examples 1 and 2. The original base membrane, the unmodified ZIF mixed matrix membrane, and the modified ZIF mixed matrix membrane are labeled as Pristine, MMMs, and pMMMs, respectively, demonstrating that the hydrogen bonding between tannic acid and the precursor cellulose is enhanced after modification.

[0054] Figure 4 The images show SEM images of the hollow fiber carbon molecular sieve membranes prepared in Example 1 (right) and Comparative Example 2 (left), demonstrating that the tannic acid-modified ZIF-8 is more uniformly dispersed in the carbon molecular sieve membrane and no obvious defects are generated.

[0055] Figure 5 The X-ray diffraction patterns are of the hollow fiber carbon molecular sieve membranes prepared in Example 1 and Comparative Examples 1 and 2, respectively. The carbon molecular sieve membranes prepared in Example 1 and Comparative Examples 1 and 2 are labeled as pMMCMs, Pristine, and MMCMs, respectively, demonstrating the reduction in interlayer spacing of the carbon molecular sieve membranes after tannic acid modification of ZIF-8.

[0056] The gas separation performance test data of Examples 1, 2, 3, and 4 and Comparative Examples 1 and 2 are shown in Table 1 below: Table 1 According to the test results in Table 1: Comparison between the examples and the comparative examples: The gas permeation performance and selectivity of the examples are significantly better than those of the comparative examples. The hollow fiber carbon molecular sieve membrane obtained by doping with ZIF-8 (Comparative Example 2) has improved gas flux but reduced selectivity compared with the hollow fiber carbon molecular sieve membrane obtained without ZIF-8 (Comparative Example 1). However, when ZIF-8 is modified with tannic acid (Example 1), the gas flux and selectivity of the hollow fiber carbon molecular sieve membrane are greatly improved, showing a significantly superior effect. Comparison between examples: A comparison of Examples 1 and 2 with Examples 3 and 4 shows that the selection of different MOF particles has a significant impact on the gas flux of the obtained hollow fiber carbon molecular sieve membrane, and also has a certain impact on the gas selectivity. Overall, using ZIF-8 as the MOF particle can achieve the best results. The comparison between Examples 1 and 2 shows that, within a certain range, increasing the doping concentration of tannic acid modified ZIF-8 particles can increase the gas flux, but will reduce the selectivity. Therefore, it is necessary to strictly control the doping concentration of tannic acid modified ZIF-8 particles.

[0057] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a hollow fiber carbon molecular sieve membrane based on a tannic acid-modified MOF hybrid matrix, characterized in that, Includes the following steps: S1. MOF particles are soaked in tannic acid solution to prepare tannic acid modified MOF particles; S2. Using tannic acid-modified MOF particles as one of the raw materials to prepare spinning solution; S3. A mixed matrix precursor membrane is prepared by dry-jet wet spinning process using the spinning solution; S4. Carbonize the mixed matrix precursor membrane to obtain the mixed matrix hollow fiber carbon molecular sieve membrane based on tannic acid modified MOF.

2. The preparation method according to claim 1, characterized in that, Step S1 is as follows: MOF particles were soaked in a tannic acid solution with a concentration of 2-5 g / L for 8-15 min, centrifuged, washed, and vacuum dried to obtain tannic acid modified MOF particles.

3. The preparation method according to claim 2, characterized in that, The MOF particles mentioned in step S1 are selected from at least one of ZIF-8, ZIF-67, and MOF-5.

4. The preparation method according to claim 1, characterized in that, Step S2 is as follows: S21. Add tannic acid-modified MOF particles to dimethyl sulfoxide and disperse by ultrasonication to obtain MOF dispersion; S22. Under stirring conditions, microcrystalline cellulose is added to the above MOF dispersion in multiple portions, followed by the addition of 1-ethyl-3-methylimidazolium acetate, and the mixture is heated and mixed to obtain the initial spinning solution. S23. Vacuum the initial spinning solution to remove bubbles, and obtain the spinning solution.

5. The preparation method according to claim 4, characterized in that, The mass percentage of tannic acid-modified MOF particles added in step S2 is 8-15% of the mass of microcrystalline cellulose.

6. The preparation method according to claim 5, characterized in that, Step S2 is as follows: S21. Add the tannic acid-modified MOF particles obtained in step S1 to 150-300g of dimethyl sulfoxide and ultrasonically disperse for 30-6min to obtain MOF dispersion. S22. Under stirring conditions, 27.27 g to 54.54 g of microcrystalline cellulose was added to the above MOF dispersion in multiple portions, followed by 50 to 100 g of 1-ethyl-3-methylimidazolium acetate. The mixture was then stirred at 50 to 80 °C for 12 to 24 h to obtain the initial spinning solution. S23. The initial spinning solution is vacuumed at 50-60℃ for 12 h to remove air bubbles and obtain the spinning solution.

7. The preparation method according to claim 1, characterized in that, It includes the following steps: S1. Preparation of tannic acid-modified MOF particles: MOF particles were soaked in a 2-5 g / L tannic acid methanol aqueous solution for 8-15 min, then centrifuged and washed with ethanol 3-5 times at a centrifugation speed of 11000-14000 rpm. After washing, the particles were vacuum dried at room temperature for 12-24 h to obtain tannic acid modified MOF particles. S2. Preparation of spinning solution: S21. Add the tannic acid-modified MOF particles obtained in step S1 to 150-300g of dimethyl sulfoxide and ultrasonically disperse for 30-6min to obtain MOF dispersion. S22. Under stirring conditions, 27.27 g to 54.54 g of microcrystalline cellulose was added to the above MOF dispersion in multiple portions, followed by 50 to 100 g of 1-ethyl-3-methylimidazolium acetate. The mixture was then stirred at 50 to 80 °C for 12 to 24 h to obtain the initial spinning solution. S23. Vacuum the initial spinning solution at 50-60℃ for 12 h to remove air bubbles from the initial spinning solution and obtain the spinning solution. S3. Preparation of mixed matrix precursor membrane: The spinning solution obtained in step S2 is spun into a hollow fiber membrane using a dry-jet wet spinning process. After spinning, the hollow fiber membrane is soaked in deionized water for 2-4 days, and the deionized water is replaced every 6-24 hours. After soaking, the mixed matrix precursor membrane is obtained. The parameters of the dry-jet wet spinning process are as follows: the core solution is deionized water; the core solution temperature, spinning solution temperature, and coagulation bath temperature are all 20-30℃; the spinning solution flow rate is 4-6 mL / min; the core solution flow rate is 1.0-1.5 mL / min; the height of the spinning head from the water surface is 2-3 cm; the drawing rate is 5.6-7.8 m / min; and the winding rate is 6.0-8.0 m / min. S4. Carbonize the mixed matrix precursor membrane: Place the mixed matrix precursor membrane in an argon atmosphere and heat it to 100-150℃ at a heating rate of 2-10℃ / min, and hold it at this temperature for 6-240 min; then heat it to 300-400℃ at a heating rate of 5-20℃ / min, and hold it for 30-120 min; finally heat it to 600-800℃ at a heating rate of 2-10℃ / min, and hold it for 60-240 min. After cooling, the mixed matrix hollow fiber carbon molecular sieve membrane based on tannic acid modified MOF is obtained.

8. A hollow fiber carbon molecular sieve membrane based on a tannic acid-modified MOF hybrid matrix, characterized in that, It is prepared by the preparation method described in any one of claims 1-7.

9. The application of the hollow fiber carbon molecular sieve membrane based on tannic acid modified MOF as described in claim 8 in the separation of ethylene and ethane.

10. A membrane module, characterized in that, It includes the tannic acid-modified MOF-based hybrid matrix hollow fiber carbon molecular sieve membrane as described in claim 8, the membrane module being used for the separation of ethylene and ethane.

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