Preparation and application of an alkyl chain-modified covalent organic framework membrane
By modifying COF membranes with alkyl chains to control pore size and surface properties, the selectivity problem of COFs in the separation of small gas molecules was solved, achieving efficient H2/CO2 separation with excellent mechanical strength and flexibility.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HUNAN UNIV
- Filing Date
- 2024-05-21
- Publication Date
- 2026-06-30
AI Technical Summary
Existing COFs have low selectivity when separating small gas molecules, making it difficult to achieve efficient H2/CO2 separation.
By introducing alkyl chains of different lengths and types to modify COF membranes, the pore size and surface chemical properties of the membrane can be precisely controlled, achieving steric hindrance effect and kinetic sieving within the membrane pores. The preparation method is simple and controllable.
It achieves efficient separation of H2/CO2, improves the selectivity and stability of the membrane, and has broad application prospects.
Smart Images
Figure CN118512932B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the preparation and application of an alkyl chain-modified covalent organic framework membrane, belonging to the field of gas membrane separation technology. Background Technology
[0002] Against the backdrop of global warming and continued environmental degradation, reducing carbon emissions and promoting the use of clean energy have become urgent priorities. Hydrogen, with its high energy conversion efficiency and zero-carbon emission environmental characteristics, has become one of the most promising and valuable alternative energy sources. Currently, methane steam reforming and its subsequent water-gas shift reaction dominate hydrogen production technology; however, this process generates a large amount of carbon dioxide as a major byproduct. To obtain high-purity hydrogen, it is necessary to find an effective hydrogen and carbon dioxide separation process to achieve pre-combustion capture. Compared to traditional separation technologies such as distillation, adsorption, and absorption, membrane separation technology has advantages such as low energy consumption and small footprint, meeting the needs of new processes for sustainable industrial development. Therefore, utilizing membrane separation technology to purify hydrogen and capture carbon dioxide is a highly promising approach.
[0003] Covalent organic frameworks (COFs) are 2D or 3D open networks precisely woven from organic connecting units via covalent bonds. COFs possess pre-designed topologies and tunable pore structures, representing a new class of crystalline porous polymers. Benefiting from their ordered and tunable pore structures, large specific surface areas, easily customizable functions, excellent thermal stability, and specific adsorption affinities, COFs hold great promise for applications in many fields, including catalysis, energy storage, and separation. However, most COFs have relatively large pore sizes (>6 Å), making it difficult to guarantee high selectivity when preparing COF membranes for separating small gas molecules (<4 Å). Summary of the Invention
[0004] To address the shortcomings of existing technologies, this invention achieves efficient H2 / CO2 separation using alkyl chain-modified COF membranes. By introducing alkyl chains of different lengths and types to precisely control the pore size and surface chemical properties of the COF membrane, multiple mechanisms, including steric hindrance and kinetic sieving, are synergistically controlled, ultimately achieving efficient H2 / CO2 separation. This technology has broad application prospects in energy, chemical engineering, and environmental protection. Currently, there are no reports in the literature regarding the use of alkyl chain-modified COF membranes for H2 / CO2 separation. The preparation method of this invention is simple and controllable, and the prepared membrane exhibits high separation performance and operational stability for H2 / CO2 separation.
[0005] This invention is achieved through the following technical solution: an alkyl chain-modified covalent organic framework membrane, its preparation method, and its application. The membrane material is composed of alkyl chain-modified covalent organic framework nanosheets. The preparation method consists of a two-step process: ultrasonic dispersion and uniform assembly, and vacuum-assisted self-assembly. The preparation method is simple and controllable. The resulting membrane has a thickness of approximately 200 nm.
[0006] The alkyl chain-modified covalent organic framework membrane of the present invention, wherein the COF nanosheets are DhaTGcl-CO or DhaTGcl-C 1-10% DhaTGcl-C 1-50% DhaTGcl-C 2-10% and DhaTGcl-C 2-50% The COF nanosheets are prepared by oil-water-oil three-phase interfacial polymerization; the alkyl chains are 2,5-dihexyloxy-terephthalaldehyde and 2,5-dihexyloxy-terephthalaldehyde.
[0007] Step 1) Preparation of alkyl chain modified covalent organic framework nanosheet dispersion: 2,5-dihydroxyterephthalaldehyde and a certain proportion of 2,5-dihexyloxyterephthalaldehyde or 2,5-dihexyloxyterephthalaldehyde monomers were dissolved in dichloromethane solution to prepare a 0.15 mmol aldehyde monomer solution, which was then ultrasonically dispersed and denoted as solution A; a 3 M acetic acid aqueous solution was prepared and denoted as solution B; a 0.1 mmol ammonium monomer solution was prepared by dissolving triaminoguanidine salt in N,N-dimethylformamide solution and ultrasonically dispersed and denoted as solution C; solution A was added to the bottom of a beaker in sequence, followed by the middle layer solution B, and finally solution C was added as the top solution. The mixture was allowed to stand at room temperature for 7 days to obtain a deep yellow solution. Dialysis was performed using a 30000 Da dialysis bag for 2 days to obtain a uniformly dispersed deep yellow colloidal solution, which is the alkyl chain modified covalent organic framework nanosheet dispersion.
[0008] Step 2) Dilution of alkyl chain-modified covalent organic framework nanosheets: The dispersion obtained in step 1) was diluted with deionized water to obtain a concentration of 0.1 mg / mL. -1 alkyl chain modified covalent organic framework nanosheet dispersion.
[0009] Step 3) Preparation of alkyl chain modified covalent organic framework membrane: The dispersion obtained in step 2) was filtered onto the surface of a polyacrylonitrile porous membrane by vacuum-assisted self-assembly, and then dried at 30°C for 24 hours to obtain an alkyl chain modified covalent organic framework membrane with a thickness of 200 nm.
[0010] When the alkyl chain-modified covalent organic framework membrane prepared above was used for H2 / CO2 separation, the H2 permeation rate was 354-475 GPU and the H2 / CO2 selectivity was 12-65 under the conditions of operating temperature of 25℃ and pressure of 1 bar.
[0011] Compared with the prior art, the advantages of the present invention are as follows:
[0012] Introducing alkyl chains into the COF framework or pores creates a steric hindrance effect, preventing larger CO2 molecules from passing through the membrane pores while allowing smaller H2 molecules to pass through. By optimizing the length and type of the alkyl chains, the H2 / CO2 separation performance can be controlled. Furthermore, the flexibility of the alkyl chains improves the foldability, ductility, and mechanical strength of the membrane structure. This technology has broad application prospects in energy, chemical, and environmental protection fields.
[0013] In this invention, the membrane preparation process is simple and controllable, the membrane structure is stable, and it can be extended to other covalent organic framework materials with different topologies, exhibiting strong versatility. When the membrane prepared in this invention is applied to an H2 / CO2 separation system, it demonstrates high permeability and high selectivity. Attached Figure Description
[0014] Figure 1 The DhaTGcl-C prepared in Example 1 of this invention 1-10% Scanning electron microscope image of nanosheets;
[0015] Figure 2 This is an electron microscope image of the surface of film 1 prepared in Example 1 of the present invention;
[0016] Figure 3 This is a cross-sectional electron microscope image of membrane 1 prepared in Example 1 of the present invention;
[0017] Figure 4 The DhaTGcl-C prepared in Example 2 of this invention 1-50% Scanning electron microscope image of nanosheets;
[0018] Figure 5 This is an electron microscope image of the surface of the film 2 prepared in Example 2 of the present invention;
[0019] Figure 6 This is a cross-sectional electron microscope image of the membrane 2 prepared in Example 2 of the present invention;
[0020] Figure 7 The DhaTGcl-C prepared in Example 3 of this invention 2-10% Scanning electron microscope image of nanosheets;
[0021] Figure 8 This is an electron microscope image of the surface of the film 3 prepared in Example 3 of the present invention;
[0022] Figure 9 This is a cross-sectional electron microscope image of the membrane 3 prepared in Example 3 of the present invention;
[0023] Figure 10The DhaTGcl-C prepared in Example 4 of this invention 2-50% Scanning electron microscope image of nanosheets;
[0024] Figure 11 This is an electron microscope image of the surface of the film 4 prepared in Example 4 of the present invention;
[0025] Figure 12 This is a cross-sectional electron microscope image of the membrane 4 prepared in Example 4 of the present invention;
[0026] Figure 13 This is a scanning electron microscope image of the DhaTGcl-CO nanosheets prepared in the comparative example of this invention;
[0027] Figure 14 This is an electron microscope image of the surface of the film 5 prepared in Comparative Example 1 of the present invention;
[0028] Figure 15 This is a cross-sectional electron microscope image of the membrane 5 prepared in Comparative Example 1 of the present invention.
[0029] Figure 16 This is a comparison chart of the H2 permeation rate and H2 / CO2 selectivity of membranes 1-4 of the present invention and comparative membrane 5.
[0030] Figure 17 This is a schematic diagram of the structure and gas sieving of a covalent organic framework modified with an alkyl chain. Detailed Implementation
[0031] This invention provides a method for preparing alkyl chain-modified covalent organic framework membranes for H2 / CO2 separation. The invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0032] The alkyl chain-modified covalent organic framework membrane of the present invention, wherein the COF nanosheets are DhaTGcl-CO or DhaTGcl-C 1-10% DhaTGcl-C 1-50% DhaTGcl-C 2-10% and DhaTGcl-C 2-50% The COF nanosheets are prepared by Schiff base reaction through oil-water-oil three-phase interfacial polymerization; the alkyl chains are 2,5-dihexyloxy-terephthalaldehyde and 2,5-dihexyloxy-terephthalaldehyde.
[0033] Example 1: Preparation of an alkyl chain-modified covalent organic framework membrane, the steps of which are as follows:
[0034] Step 1) Preparation of alkyl chain modified covalent organic framework nanosheet dispersion: Weigh 2,5-dihydroxyterephthalaldehyde (22.3 mg) and 2,5-dihexyloxyterephthalaldehyde (3 mg) aldehyde monomers and dissolve them in dichloromethane solution to prepare a 0.15 mmol aldehyde monomer solution, which is then ultrasonically dispersed and denoted as solution A. The alkyl chain 2,5-dihexyloxyterephthalaldehyde has a molar percentage of 10%. Prepare a 3 M acetic acid aqueous solution and denoted as solution B. Weigh triaminoguanidine salt (14 mg) and dissolve it in N,N-dimethylformamide solution to prepare a 0.1 mmol ammonium monomer solution, which is then ultrasonically dispersed and denoted as solution C. Add solution A to the bottom of the beaker in sequence, then add the middle layer solution B, and finally add solution C as the top solution. Let the reaction stand at room temperature for 7 days to obtain a deep yellow solution, named DhaTGcl-C. 1-10% Dialysis was performed for 2 days using a 30000 Da dialysis bag to obtain a uniformly dispersed, deep yellow colloidal solution of alkyl chain-modified covalent organic framework nanosheets.
[0035] Step 2) Preparation of a covalent organic framework dispersion modified with an alkyl chain: Dilute 1 mL of the covalent organic framework dispersion obtained in Step 1 to 10 mL to prepare a solution with a concentration of 0.1 mg / mL. -1 A dispersion of covalent organic framework nanosheets modified with alkyl chains; wherein DhaTGcl-C 1-10% Scanning electron microscope image of nanosheets as follows Figure 1 As shown.
[0036] Step 3) Preparation of an alkyl chain modified covalent organic framework membrane: The dispersion obtained in step 2 is deposited on the surface of a porous polyacrylonitrile by vacuum-assisted self-assembly to form an alkyl chain modified covalent organic framework membrane. After drying at 30°C for 24 hours, a covalent organic framework membrane with a thickness of 200 nm is obtained, which is denoted as membrane 1. Figure 2 It is the surface of membrane 1. Figure 3 This is a cross-sectional scanning electron microscope image of membrane 1.
[0037] The alkyl chain-modified covalent organic framework membrane (membrane 1) prepared in this invention was used for H2 / CO2 separation. Under the conditions of operating temperature of 25°C and pressure of 1 bar, the H2 permeation rate was 403 GPU and the H2 / CO2 selectivity was 15.9.
[0038] Example 2: Preparation of an alkyl chain-modified covalent organic framework membrane, the steps of which are as follows:
[0039] Step 1) Preparation of a dispersion of alkyl-chain covalent organic framework nanosheets: The preparation process is basically the same as in Example 1, except that: the aldehyde monomers 2,5-dihydroxyterephthalaldehyde (12.4 mg) and 2,5-dihexyloxyterephthalaldehyde (16.6 mg) weighed in Step 1) were dissolved in dichloromethane solution to prepare a 0.15 mmol aldehyde monomer solution and ultrasonically dispersed, wherein the alkyl chain 2,5-dihexyloxyterephthalaldehyde accounted for 50% of the total molar amount. The resulting yellow colloidal dispersion was named DhaTGcl-C. 1-50% .
[0040] Step 2) Preparation of a covalent organic framework dispersion modified with an alkyl chain: Dilute 1 mL of the covalent organic framework dispersion obtained in Step 1 to 10 mL to prepare a solution with a concentration of 0.1 mg / mL. -1 A dispersion of alkyl chain-modified covalent organic framework nanosheets; a scanning electron microscope image of the alkyl chain-modified covalent organic framework nanosheets is shown below. Figure 4 As shown.
[0041] Step 3) Preparation of an alkyl chain modified covalent organic framework membrane: The dispersion obtained in step 2 is deposited on the surface of porous polyacrylonitrile by vacuum-assisted self-assembly to form an alkyl chain modified covalent organic framework membrane. After drying at 30°C for 24 hours, a covalent organic framework membrane with a thickness of 200 nm is obtained, denoted as membrane 2. Figure 5 This is a scanning electron microscope image of the surface of membrane 2. Figure 6 This is a cross-sectional scanning electron microscope image of membrane 2.
[0042] The alkyl chain-modified covalent organic framework membrane (membrane 2) prepared in this invention was used for H2 / CO2 separation. Under the conditions of operating temperature of 25°C and pressure of 1 bar, the H2 permeation rate was 414 GPU and the H2 / CO2 selectivity was 18.
[0043] Example 3: Preparation of an alkyl chain-modified covalent organic framework membrane: The steps are as follows:
[0044] Step 1) Preparation of a dispersion of alkyl-chain covalent organic framework nanosheets: The preparation process is basically the same as in Example 1, except that: 2,5-dihydroxyterephthalaldehyde (22.3 mg) and 2,5-dihexyloxyterephthalaldehyde (5 mg) aldehyde monomers were weighed in step 1) and dissolved in dichloromethane solution to prepare a 0.15 mmol aldehyde monomer solution, which was then ultrasonically dispersed and denoted as solution A. The alkyl chain 2,5-dihexyloxyterephthalaldehyde accounted for 10% of the total molar amount. A deep yellow solution was obtained and named DhaTGcl-C. 2-10% .
[0045] Step 2) Preparation of a covalent organic framework dispersion modified with an alkyl chain: Dilute 1 mL of the covalent organic framework dispersion obtained in Step 1 to 10 mL to prepare a solution with a concentration of 0.1 mg / mL. -1 A dispersion of alkyl chain-modified covalent organic framework nanosheets; a scanning electron microscope image of the alkyl chain-modified covalent organic framework nanosheets is shown below. Figure 7 As shown.
[0046] Step 3) Preparation of an alkyl chain modified covalent organic framework membrane: The dispersion obtained in step 2 is deposited on the surface of a porous polyacrylonitrile by vacuum-assisted self-assembly to form an alkyl chain modified covalent organic framework membrane. After drying at 30°C for 24 hours, a covalent organic framework membrane with a thickness of 200 nm is obtained, denoted as membrane 3. Figure 8 This is a scanning electron microscope image of the surface of membrane 3. Figure 9 This is a cross-sectional scanning electron microscope image of membrane 3.
[0047] When the alkyl chain-modified covalent organic framework membrane (membrane 3) prepared in this invention was used for H2 / CO2 separation, the H2 permeation rate was 357 GPU and the H2 / CO2 selectivity was 65 under the conditions of operating temperature of 25°C and pressure of 1 bar.
[0048] Example 4: Preparation of an alkyl chain-modified covalent organic framework membrane: The steps are as follows:
[0049] Step 1) Preparation of a dispersion of alkyl-chain covalent organic framework nanosheets: The preparation process is basically the same as in Example 1, except that: 2,5-dihydroxyterephthalaldehyde (12.4 mg) and 2,5-dihexyloxyterephthalaldehyde (25 mg) aldehyde monomers were weighed in step 1) and dissolved in dichloromethane solution to prepare a 0.15 mmol aldehyde monomer solution, which was then ultrasonically dispersed and denoted as solution A. The alkyl chain 2,5-dihexyloxyterephthalaldehyde accounted for 50% of the total molar concentration. A deep yellow solution was obtained and named DhaTGcl-C. 2-50% .
[0050] Step 2) Preparation of a covalent organic framework dispersion modified with an alkyl chain: Dilute 1 mL of the covalent organic framework dispersion obtained in Step 1 to 10 mL to prepare a solution with a concentration of 0.1 mg / mL. -1 A dispersion of alkyl chain-modified covalent organic framework nanosheets; a scanning electron microscope image of the alkyl chain-modified covalent organic framework nanosheets is shown below. Figure 10 As shown.
[0051] Step 3) Preparation of an alkyl chain modified covalent organic framework membrane: The dispersion obtained in step 2 is deposited on the surface of a porous polyacrylonitrile by vacuum-assisted self-assembly to form an alkyl chain modified covalent organic framework membrane. After drying at 30°C for 24 hours, a covalent organic framework membrane with a thickness of 200 nm is obtained, denoted as membrane 4. Figure 11 This is an electron microscope image of the surface of film 4. Figure 12 This is a cross-sectional scanning electron microscope image of membrane 4.
[0052] The alkyl chain-modified covalent organic framework membrane (membrane 4) prepared in this invention was used for H2 / CO2 separation. Under the conditions of operating temperature of 25°C and pressure of 1 bar, the H2 permeation rate was 354 GPU and the H2 / CO2 selectivity was 38.
[0053] Comparative Example 1: Preparation of covalent organic framework membranes, including the preparation of DhaTGcl-CO nanosheet dispersion and the preparation of COF membranes, as follows:
[0054] Step 1) Preparation of covalent organic framework nanosheet dispersion: Weigh 2,5-dihydroxyterephthalaldehyde (24.9 mg) aldehyde monomer, dissolve it in dichloromethane solution to prepare a 0.15 mmol aldehyde monomer solution, and sonicate it; this is denoted as solution A. 3 M acetic acid aqueous solution is denoted as solution B. Weigh triaminoguanidine salt (14 mg), dissolve it in N,N-dimethylformamide solution to prepare a 0.1 mmol ammonium monomer solution, and sonicate it; this is denoted as solution C. Add solution A to the bottom of the beaker in sequence, then add the middle layer solution B, and finally add solution C as the top solution. Let the reaction stand at room temperature for 7 days to obtain a deep yellow solution, named DhaTGcl-CO. Dialyze the solution using a 30000 Da dialysis bag for 2 days to obtain a uniformly dispersed deep yellow covalent organic framework nanosheet colloidal solution.
[0055] Step 2) Preparation of covalent organic framework dispersion: Dilute 1 mL of the covalent organic framework dispersion obtained in Step 1 to 10 mL to prepare a solution with a concentration of 0.1 mg / mL. -1 A dispersion of covalent organic framework nanosheets; wherein the scanning electron microscope image of the covalent organic framework nanosheets is shown below. Figure 13 As shown.
[0056] Step 3) Preparation of covalent organic framework membrane: The dispersion obtained in step 2 is deposited on the surface of porous polyacrylonitrile through vacuum-assisted self-assembly to form a covalent organic framework membrane. After drying at 30°C for 24 hours, a covalent organic framework membrane with a thickness of 200 nm is obtained, which is denoted as membrane 5. Figure 14 This is a scanning electron microscope image of the surface of film 5. Figure 15 This is a cross-sectional scanning electron microscope image of membrane 5.
[0057] When the covalent organic framework membrane (membrane 5) prepared by the present invention was used for H2 / CO2 separation, the H2 permeation rate was 475 GPU and the H2 / CO2 selectivity was 12 under the conditions of operating temperature of 25°C and pressure of 1 bar.
[0058] Comparative examples and comparative cases demonstrate that the present invention significantly improves separation performance through an alkyl-chain-modified covalent organic framework membrane. In summary, the alkyl-modified COF membrane achieves highly efficient H2 / CO2 separation through the combined effects of multiple mechanisms, including pore size regulation, altered surface chemistry, steric hindrance, and kinetic sieving. Compared to the original COF membrane, the alkyl-chain-modified COF membrane exhibits effectively reduced pore size, stronger interaction between the alkyl chains and hydrogen gas within the pores, and a faster diffusion rate of hydrogen molecules within the membrane, thereby improving the selectivity for H2 / CO2. Furthermore, the alkyl-chain-modified COF membrane possesses superior mechanical strength and flexibility. It also partially repairs stacking defects within the membrane structure, thus eliminating obvious pinholes and accumulation depressions on the membrane surface and cross-section. Figure 16 This is a comparison chart of the H2 permeation flux and H2 / CO2 selectivity of membranes 1-4 and the control membranes. The prepared alkyl chain-modified covalent organic framework membranes achieve a breakthrough in separation performance and have good application prospects in the field of hydrogen separation.
[0059] Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many modifications under the guidance of the present invention without departing from the spirit of the present invention, and these modifications are all within the protection scope of the present invention.
Claims
1. A method for preparing an alkyl chain-modified covalent organic framework membrane, characterized in that, Includes the following steps: (1) Preparation of alkyl chain modified covalent organic framework nanosheet colloidal solution: 2,5-dihydroxyterephthalaldehyde and a certain proportion of 2,5-dihexyloxyterephthalaldehyde were dissolved in dichloromethane as solution A; the intermediate layer was composed of 3 M acetic acid aqueous solution as solution B; triaminoguanidine hydrochloride monomer was dissolved in N,N-dimethylformamide as solution C; solution A was first added to the beaker as the bottom solution, then solution B was slowly added as the intermediate buffer layer solution, and finally the top solution C was added. After simple sealing, the reaction was allowed to stand at room temperature for 7 days to obtain alkyl chain modified covalent organic framework nanosheet colloidal solution. (2) Preparation of alkyl chain modified covalent organic framework membrane by vacuum-assisted self-assembly: Alkyl chain modified covalent organic framework nanosheet colloidal solution was deposited onto the surface of porous support membrane by vacuum-assisted self-assembly. The alkyl chain-modified covalent organic framework membrane is used for H2 / CO2 separation.
2. The method for preparing the alkyl chain-modified covalent organic framework membrane according to claim 1, characterized in that, The nanosheet colloid solution obtained in step (1) was dispersed in a certain volume of deionized water, and the final concentration was 0.1 mg·mL -1 Step (2) was then performed.
3. The method for preparing the alkyl chain-modified covalent organic framework membrane according to claim 1 or 2, characterized in that, The porous support membrane is any one of polyacrylonitrile, polyethersulfone, polypropylene, and polytetrafluoroethylene.
4. An alkyl chain-modified covalent organic framework membrane, characterized in that: It is prepared according to any one of claims 1-3.
5. The application of the alkyl chain-modified covalent organic framework membrane according to claim 4 in H2 / CO2 separation, characterized in that, At 25°C and 1 bar, the H2 permeation rate of the prepared alkyl chain-modified covalent organic framework membrane was measured to be 354-475 GPUs (1 GPU = 1 × 10⁻⁶). -6 cm 3 (STP) cm -2 s -1 cmHg -1 The H2 / CO2 selectivity is 12-65.