A method for preparing a ZIF-62 / BTESE composite membrane on a tubular alumina support

Abstract

The application belongs to the field of membrane separation technology and provides a method for preparing a ZIF-62 / BTESE composite membrane on a tubular alumina carrier, specifically: first, ZIF-62 crystals required by the composite membrane are prepared, the crystals are introduced to the surface of the carrier by vacuum suction filtration, then BTESE is introduced into the ZIF-62 crystal layer by the immersion-pulling method and the rubbing coating method for filling gaps and repairing intergranular defects, and the prepared dense defect-free ZIF-62 / BTESE composite membrane has good separation performance for H2 / CO2 gas.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology and relates to the technology of preparing a metal-organic framework thin film on a tubular Al2O3 support. It provides a method for preparing a composite membrane of crystal and organic-inorganic hybrid BTESE material. Background Technology

[0002] Membrane separation technology utilizes selectively permeable membranes to achieve separation based on the different permeation rates of the components in a mixture under pressure or temperature gradient driving force. It is a promising new separation technology with advantages such as low energy consumption, no secondary pollution, small footprint, and high separation efficiency, and has been widely used in gas and liquid separation.

[0003] Metal-organic frameworks (MOFs) are a class of crystalline materials formed by the self-assembly of inorganic metal ions or metal-oxygen clusters (secondary structural units) and monodentate or polydentate organic ligands rich in multifunctional groups through coordination bonds, resulting in regular channels and periodic network structures. They have advantages such as adjustable channel size and shape, large specific surface area, and easy functionalization of channels.

[0004] ZIF-62 is a Zn-based MOF with high chemical and thermal stability. It consists of zinc ions and two organic ligands (imidazolium and benzimidazole) forming a three-dimensional porous structure through coordination bonds. It possesses a topological network similar to zeolites, but the flexibility of the ligands allows for greater structural tunability. The actual pore size is within [missing information]. ZIF-62 membranes have good application value for the adsorption of small molecule gases and the separation of mixed gases. Currently, there is considerable research on ZIF-62 membranes, but it mainly focuses on their preparation on sheet-like supports. Reports on the preparation of ZIF-62 membranes on tubular supports are very few. Dana M. Stone et al., in their paper entitled "Control of ZIF-62 and agZIF-62 Film Thickness within Asymmetric Tubular Supports through Pressure and Dose Time Variation of Atomic Layer Deposition" (small 2024, 2307202), synthesized a continuous ZIF-62 polycrystalline membrane inside a tubular support using a homologous metal-induced method. Although their gas separation performance was not mentioned, electron microscopy images revealed that the membrane surface was not dense and contained a small number of cracks. Therefore, it can be seen that preparing high-quality polycrystalline ZIF-62 membranes on tubular supports is extremely difficult.

[0005] BTESE (Bis(triethoxysilyl)ethane) is an organic-inorganic hybrid material prepared from a bifunctional silane precursor via a sol-gel method. The ethane group acts as an organic bridging group, connecting the siloxane network to form a stable hybrid structure. The combination of ZIF-62 crystals and BTESE effectively improves the cracking problem in polycrystalline ZIF-62 films. The microporous network structure of BTESE fills and repairs intergranular defects, significantly improving the gas separation capability of the composite membrane.

[0006] Therefore, this invention proposes a method for introducing BTESE into ZIF-62 crystals, which enables the preparation of continuous, dense, flat and defect-free ZIF-62 / BTESE composite films on the surface of tubular carriers. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing ZIF-62 / BTESE composite membranes on tubular alumina supports and their applications. The prepared membranes have potential applications in the field of gas separation.

[0008] The inventive concept involved in this invention is as follows: The surface of the polycrystalline ZIF-62 membrane prepared by the tubular alumina carrier has defects such as cracks, making it difficult to further improve the gas separation performance. Therefore, combining ZIF-62 crystals with BTESE to prepare a composite membrane can effectively reduce the formation of defects, resulting in a smooth and flat membrane with almost no defects on the surface, thus achieving a significant improvement in gas separation performance.

[0009] The technical solution of this invention:

[0010] A method for preparing ZIF-62 / BTESE composite membranes on tubular alumina supports, comprising the following steps:

[0011] (1) Preparation of ZIF-62 crystal layer

[0012] The crystals were dispersed in anhydrous ethanol to obtain a crystal liquid; the tubular alumina support was preheated at 50-80℃ for 2-5 hours, and the crystal liquid was coated on the surface of the tubular alumina support by vacuum coating method, and then cured at 100-175℃ for 1-5 hours to obtain a uniform, dense and defect-free crystal layer.

[0013] (2) Preparation of BTESE sol

[0014] BTESE, H2O, and HCl are added to EtOH and stirred at 20–45°C for 2–5 hours to form a stable original BTESE sol. The desired BTESE sol is then obtained by diluting it with EtOH.

[0015] In the original BTESE sol, the molar ratios of the components are: EtOH:BTESE = 260–300; EtOH:H2O = 4–6; H2O:HCl = 500–700.

[0016] (3) Preparation of ZIF-62 / BTESE composite membrane

[0017] Using the BTESE sol obtained in step (2) as a coating liquid, it is uniformly coated on the surface of the tubular alumina carrier coated with the crystal layer in step (1), and then calcined at a temperature of 200-300℃ for 10-30 minutes; wherein, the above operation is repeated 2-5 times to obtain the ZIF-62 / BTESE composite film.

[0018] In step (1), the crystal is ZIF-62 with a particle size of 0.6 to 3 μm and the mass fraction of the crystal liquid is 0.01 to 0.06%.

[0019] In step (2), the mass ratio of added EtOH to the original BTESE sol is 0.8 to 1.5.

[0020] The tubular alumina carrier has a length of 4–6 cm and an outer surface area of ​​15–25 cm². 2 The pore size is 0.02–10 μm.

[0021] The ZIF-62 / BTESE composite membrane obtained in step (3) was subjected to single-component gas permeation testing using a gas permeation testing device to evaluate the compactness and gas separation performance of the prepared ZIF-62 / BTESE composite membrane. The specific operation was as follows: The ZIF-62 / BTESE composite membrane was sealed in a tubular membrane module using an O-ring. One end of the ZIF-62 / BTESE composite membrane was sealed, and the other end was connected to a soap bubble tube. The pressure on the raw material side was controlled by a back pressure valve, maintaining the pressure at 0.1 MPa. The permeation side was connected to the soap bubble tube and then open to the atmosphere. The time taken for a certain volume of gas to pass through the membrane was obtained using a stopwatch and a soap bubble flow meter. All tests were conducted at room temperature.

[0022] The gas permeation rate is represented by P, and the unit is mol / (m²). 2 The ideal gas selectivity (α) is defined as the number of moles of gas flowing through a unit membrane area per unit time under a unit transmembrane pressure. It is also defined as the ratio of the permeation rates of two different gases.

[0023]

[0024] The beneficial effects of this invention are:

[0025] (1) This invention successfully prepared a dense ZIF-62 / BTESE composite film on a tubular alumina carrier tube. Existing literature reports that the ZIF-62 polycrystalline film surface is not dense and contains defects such as cracks. By combining ZIF-62 crystals with BTESE, defects such as cracks that are prone to occur in the film layer can be effectively reduced, improving the continuity and smoothness of the prepared film.

[0026] (2) The dense and defect-free ZIF-62 / BTESE composite membrane prepared on the tubular support has good separation performance for H2 / CO2 gases. The microporous network structure of BTESE material fills and repairs the intercrystalline defects, while also enhancing the continuity and density of the membrane layer, which can significantly improve the separation ability of the composite membrane for hydrogen and carbon dioxide gases. Attached Figure Description

[0027] Figure 1 The image shows a scanning electron microscope (SEM) image of the ZIF-62 crystal.

[0028] Figure 2 The X-ray diffraction (XRD) pattern of the ZIF-62 crystal is shown.

[0029] Figure 3 These are scanning electron microscope (SEM) images of the ZIF-62 film synthesized by the homologous metal induction method: (a) surface, (b) cross section.

[0030] Figure 4 This is the X-ray diffraction (XRD) pattern of the ZIF-62 film synthesized by the homologous metal-induced method;

[0031] Figure 5 These are scanning electron microscope (SEM) images of the ZIF-62 / BTESE composite film: (a) surface, (b) cross-section.

[0032] Figure 6 The graphs show the gas separation performance of the prepared ZIF-62 membrane and ZIF-62 / BTESE composite membrane, with (a) permeability and (b) ideal selectivity. Detailed Implementation

[0033] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0034] Example 1

[0035] Preparation of ZIF-62 / BTESE composite membrane:

[0036] (1) Preparation of ZIF-62 crystal layer

[0037] First, ZIF-62 crystals were added to anhydrous ethanol solution and then ultrasonically dispersed to obtain a crystal solution with a mass concentration of 0.02%. One end of the carrier was sealed with a polytetrafluoroethylene stopper, and the other end was connected to a vacuum pump. The carrier was immersed in the crystal solution and vacuum filtered for 30 ml, resulting in a ZIF-62 crystal layer on the surface of the carrier. The carrier was then dried in an oven at 175℃ for 2 hours, removed, and allowed to cool naturally to room temperature. Finally, the carrier tube with the ZIF-62 crystal layer was placed in a desiccator for later use.

[0038] (2) Preparation of BTESE sol

[0039] First, a 5% BTESE sol was prepared with a molar ratio of BTESE:H₂O:HCl:EtOH = 1:60:0.1:284. A measured amount of BTESE sol was weighed into a 50ml beaker and transferred to a 35℃ water bath. EtOH was added while stirring. After the solution was thoroughly mixed, a dilute HCl solution containing H₂O was added dropwise. The mixture was stirred and reacted for 3 hours to obtain a 5% BTESE sol. Then, an equal amount of EtOH was added to dilute the solution to 2.5%.

[0040] (3) Preparation of ZIF-62 / BTESE composite membrane

[0041] The carrier with the ZIF-62 crystal layer was sealed at both ends with PTFE stoppers. BTESE sol was introduced into the ZIF-62 crystal layer at room temperature using an impregnation-coating method to fix the ZIF-62 crystal layer. The impregnation time was controlled at 3 seconds. Then, it was placed in a muffle furnace at 280℃ for 20 minutes and then cooled in a 175℃ oven for 20 minutes. Subsequently, BTESE was introduced using a wiping method. Gauze was moistened with BTESE sol and quickly and evenly wiping a ring around the surface of the carrier. The carrier was then placed in a muffle furnace at 280℃ for 20 minutes and then cooled in a 175℃ oven for 20 minutes. This process was repeated three times to obtain the ZIF-62 / BTESE composite membrane. The obtained membrane was placed in a desiccator for single-component gas permeation testing.

[0042] Example 2

[0043] Based on Example 1, the mass concentration of the crystal liquid in step (1) was changed to 0.04%, and a ZIF-62 / BTESE composite membrane was prepared.

[0044] Example 3

[0045] Based on Example 1, the concentration of BTESE sol was changed to 2% in step (2) to prepare ZIF-62 / BTESE composite membrane.

[0046] Example 4

[0047] Based on Example 1, the number of repeated wiping and calcination in step (3) was changed to five times to prepare the ZIF-62 / BTESE composite membrane.

[0048] Comparative Example 1

[0049] Preparation of ZIF-62 membranes by homologous metal-induced method:

[0050] (1) Preparation of ZnO sol

[0051] The specific reaction conditions for preparing ZnO sol are as follows: Weigh 8.4g of zinc acetate (ZnAC2) and add it to 48ml of ethylene glycol methyl ether (EMEG) solution. Transfer it to a pre-prepared 70℃ water bath and stir. After the suspension is heated, add 2.4ml of ethanolamine dropwise and continue stirring for 4h to obtain a pale yellow clear sol. Then, cool it to room temperature and age it for 24h to obtain ZnO sol.

[0052] (2) Carrier pretreatment

[0053] The tube has an outer diameter of 12 mm, an inner diameter of 8 mm, an average pore size greater than 1 μm, and a porosity of approximately 30–40%. The carrier pretreatment consists of the following steps: First, the outer surface of the carrier tube is sequentially polished with 800-grit, 1500-grit, and 3000-grit sandpaper, and then cut into 5 cm short tubes. Second, the tubes are ultrasonically cleaned with deionized water, then with 1 mol / L HCl solution, then with deionized water until neutral, then with 1 mol / L NaOH solution, and finally with deionized water until neutral. Each cleaning lasts 30 minutes. After cleaning, the carrier tubes are placed in an 80℃ oven to dry overnight. Third, the tubes are calcined at 550℃ for 360 minutes, with a heating and cooling rate of 1℃ / min. After calcination, the tubes are stored at room temperature in a desiccator, awaiting subsequent use.

[0054] (3) Introduction of ZnO layer

[0055] The zinc oxide layer was introduced at room temperature using the dip-coating method. The specific steps are as follows: the two ends of the carrier tube were sealed with PTFE stoppers, immersed in ZnO sol for 3 seconds, and then dried in a 100℃ oven for 40 minutes. After cooling, it was immersed in ZnO sol again for 3 seconds, and then dried in a 100℃ oven for 30 minutes. The carrier was then transferred to a muffle furnace and heated to 400℃ at a rate of 1℃ / min for 180 minutes. The heating rate was changed to 0.5℃ / min within the temperature range of 200-300℃, and then cooled to room temperature at a rate of 1℃ / min to obtain the carrier tube with the zinc oxide layer. The sample bag was sealed and stored in a desiccator.

[0056] (4) Preparation of ZnO nanorods

[0057] The introduced ZnO layer provides insufficient metal source and has poor fixation ability. Therefore, it is necessary to obtain a ZnO nanorod layer on the ZnO layer to increase the metal source concentration on the support surface. The specific process for obtaining the ZnO nanorod is as follows: 1.265g Zn(NO3)2·6H2O and 0.591g C6H 12 The N4 was dissolved in 60 ml of H2O solvent, and the mixture was stirred and sonicated for 30 min each to obtain the synthesis solution. The two ends of the support with the introduced ZnO layer were sealed with PTFE stoppers, placed in the liner of the reactor, and the synthesis solution was added. After sealing, the reactor was placed in an oven for reaction at 100℃ for 6.5 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The support was then rinsed with plenty of deionized water, vacuum dried at 80℃ overnight, and then placed in a desiccator after thorough drying.

[0058] (5) Synthesis of ZIF-62 membrane

[0059] The ZnO nanorods were introduced onto a support sealed at both ends with PTFE stoppers and placed in a reactor liner. After adding the synthesis solution, synthesis was carried out via homologous metal induction. The specific method is as follows: 1.981 g of Im and 0.384 g of Bim were dissolved in 24 ml of DMF solvent, sonicated for 30 min, and then added to the reactor liner. The reactor was sealed and placed in an oven for reaction at 120 °C for 20 h. After the reaction, the mixture was allowed to cool naturally to room temperature. It was then removed and soaked in anhydrous methanol for three days, changing the solvent twice during this period. It was then vacuum dried overnight at 100 °C. After thorough drying, it was placed in a desiccator for single-component gas permeation testing.

[0060] Single-component gas permeation tests were performed on the ZIF-62 membrane obtained in Comparative Example 1 and the ZIF-62 / BTESE composite membrane obtained in Example 1:

[0061] Single-component gas permeation tests were conducted on ZIF-62 membranes and ZIF-62 / BTESE composite membranes prepared by the homologous metal-induced method. The tests were performed using a self-made gas permeation testing apparatus to evaluate the compactness and gas separation performance of the prepared membranes. The specific operation was as follows: The membrane was sealed in a tubular membrane module using O-rings. One end of the membrane was sealed, and the other end was connected to a soap bubble tube. The feed side pressure was controlled at 0.1 MPa using a back pressure valve. The permeate side was connected to the soap bubble tube and then open to the atmosphere. The time taken for a certain volume of gas to pass through the membrane was obtained using a stopwatch and a soap bubble flow meter. All tests were conducted at room temperature.

[0062] like Figure 3As shown, the ZIF-62 membrane prepared using the homologous metal-induced method exhibits obvious cracks on its surface, with ideal selectivities of only 12.1, 3.1, and 2.7 for H2 / CO2, H2 / N2, and H2 / CH4, respectively. The ideal selectivities for H2 / N2 and H2 / CH4 are lower than those for Knudsen diffusion (3.7 and 2.8). In contrast, the ZIF-62 / BTESE composite membrane is continuous and dense, without obvious cracks or pinholes, and has a thickness of approximately 3.3 μm (see...). Figure 5 The test results for the ZIF-62 / BTESE composite membrane are as follows: the H2 permeation flux is 7.12 × 10⁻⁶. -8 mol·m -2 ·s -1 ·pa -1 The ideal selectivity for H2 / CO2, H2 / N2, and H2 / CH4 reached 35.9, 3.8, and 3.1, respectively, all exceeding their Knudsen diffusion selectivity (4.7, 3.7, and 2.8), demonstrating the absence of intergranular defects in the obtained ZIF-62 / BTESE composite membrane and the feasibility of the method. The ideal selectivity of 35.9 for H2 / CO2 indicates that the membrane obtained by this method has a certain gas separation capability.

Claims

1. A method for preparing a ZIF-62 / BTESE composite membrane on a tubular alumina support, characterized in that, The steps are as follows: (1) Preparation of ZIF-62 crystal layer The crystals were dispersed in anhydrous ethanol to obtain a crystal liquid; the tubular alumina support was preheated at 50-80℃ for 2-5 hours, and the crystal liquid was coated on the surface of the tubular alumina support by vacuum coating method, and then cured at 100-175℃ for 1-5 hours to obtain a uniform, dense and defect-free crystal layer. (2) Preparation of BTESE sol BTESE, H2O, and HCl are added to EtOH and stirred at 20–45°C for 2–5 hours to form a stable original BTESE sol. The desired BTESE sol is then obtained by diluting it with EtOH. (3) Preparation of ZIF-62 / BTESE composite membrane Using the BTESE sol obtained in step (2) as a coating liquid, it is uniformly coated on the surface of the tubular alumina carrier coated with the crystal layer in step (1), and then calcined at a temperature of 200-300℃ for 10-30 minutes; wherein, the above operation is repeated 2-5 times to obtain the ZIF-62 / BTESE composite film.

2. The method for preparing ZIF-62 / BTESE composite membrane on a tubular alumina support according to claim 1, characterized in that, In step (1), the crystal is ZIF-62 with a particle size of 0.6 to 3 μm and the mass fraction of the crystal liquid is 0.01 to 0.06%.

3. The method for preparing ZIF-62 / BTESE composite membrane on a tubular alumina support according to claim 1, characterized in that, In step (2), the molar ratio of each component in the original BTESE sol is: EtOH:BTESE = 260-300; EtOH:H2O = 4-6; H2O:HCl = 500-700.

4. The method for preparing ZIF-62 / BTESE composite membrane on a tubular alumina support according to claim 1, characterized in that, In step (2), the mass ratio of added EtOH to the original BTESE sol is 0.8 to 1.

5.

5. The method for preparing a ZIF-62 / BTESE composite membrane on a tubular alumina support according to any one of claims 1-4, characterized in that, The tubular alumina carrier has a length of 4–6 cm and an outer surface area of ​​15–25 cm². 2 The pore size is 0.02–10 μm.

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