Method for preparing ZIF-62 / BTESE composite membrane on tubular alumina carrier

Abstract

The invention belongs to the technical field of membrane separation, and provides a method for preparing a ZIF-62 / BTESE composite membrane on a tubular alumina carrier, and the method specifically comprises the following steps: firstly preparing a ZIF-62 crystal required by the composite membrane, introducing the crystal to the surface of the carrier in a vacuum filtration manner, and preparing a ZIF-62 / BTESE composite membrane on the tubular alumina carrier; then, BTESE is introduced into the ZIF-62 crystal layer through a dipping-pulling method and a wiping method to be used for filling gaps and repairing intergranular defects, and the prepared compact and defect-free ZIF-62 / BTESE composite film has good separation performance on H2 / CO2 gas.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane separation, and relates to a technique for preparing a metal-organic framework thin film on a tubular Al 2 O 3 carrier, and provides a method for preparing a film by compounding crystals with an organic-inorganic hybrid BTESE material. Background Art

[0002] Membrane separation technology uses a selective permeable membrane. Under the driving force of pressure or temperature gradient, according to the different permeation rates of each component of the mixture, the purpose of separation is achieved. It is a potential new separation technology, with the advantages of low energy consumption, no secondary pollution, small floor area, high separation efficiency, etc., and has been widely used in the field of gas separation or liquid separation.

[0003] Metal-Organic Frameworks (MOFs) materials are a class of crystalline materials formed by self-assembly of inorganic metal ions or metal-oxide clusters (secondary structural units) and monodentate or polydentate organic ligands rich in multi-functional groups through coordination bonds, which have the advantages of adjustable pore size and shape, large specific surface area, and easy functionalization of pores.

[0004] ZIF-62 is a Zn-based MOF with high chemical and thermal stability. It forms a three-dimensional porous structure by zinc ions and two organic ligands (imidazole and benzimidazole) through coordination bonds, and has a topological network similar to zeolite. However, the flexibility of the ligands makes its structure more adjustable. The actual pore size is It has good application value for the adsorption of small molecule gases and the separation of mixed gases. At present, there are many studies on ZIF-62 membranes, but basically they are concentrated on the preparation on sheet carriers. There are very few reports on the preparation of ZIF-62 membranes on tubular carriers. In an article titled 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) by Dana M stone et al., a continuous ZIF-62 polycrystalline film was synthesized inside a tubular carrier by a homologous metal induction method. Although its gas separation performance was not mentioned, it can be recognized from the electron microscope images that the membrane surface is not dense and there are a small number of cracks. Therefore, it can be found that it is very difficult to prepare a high-quality polycrystalline ZIF-62 membrane on a tubular carrier.

[0005] BTESE (Bis(triethoxysilyl)ethane) is an organic-inorganic hybrid material prepared by the sol-gel method using a bifunctional silyl precursor. In this material, the ethyl group serves as an organic bridging group, connecting the siloxane network to form a stable hybrid structure. The combination of ZIF-62 crystals and BTESE can effectively improve the crack problem existing in polycrystalline ZIF-62 membranes. The filling of the microporous network structure of BTESE repairs the intercrystalline defects, significantly enhancing the gas separation ability of the composite membrane.

[0006] Therefore, the present invention proposes a method for introducing BTESE into ZIF-62 crystals, enabling the preparation of a continuous, dense, flat, and defect-free ZIF-62 / BTESE composite membrane on the surface of a tubular support. Summary of the Invention

[0007] The object of the present invention is to provide a method for preparing a ZIF-62 / BTESE composite membrane on a tubular alumina support and its application. The prepared membrane has potential applications in the field of gas separation.

[0008] The inventive concept involved in the present invention: There are defects such as cracks on the surface of the polycrystalline ZIF-62 membrane prepared on a tubular alumina support, 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. The membrane layer is smooth and flat, with almost no defects on the surface, achieving a significant improvement in gas separation performance.

[0009] The technical solution of the present invention:

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

[0011] (1) Prepare a ZIF-62 crystal layer

[0012] Disperse the crystals in absolute ethanol to obtain a crystal solution; preheat the tubular alumina support at 50 - 80 °C for 2 - 5 h, then coat the crystal solution on the surface of the tubular alumina support by vacuum crystal coating method, and cure at 100 - 175 °C for 1 - 5 h to obtain a uniform, dense, and defect-free crystal layer;

[0013] (2) Prepare a BTESE sol

[0014] Add BTESE, H 2 O, and HCl to EtOH, stir at 20 - 45 °C for 2 - 5 h to form a stable original BTESE sol, and then dilute it with EtOH to obtain the required BTESE sol;

[0015] In the original BTESE sol, the molar ratio of each component is: EtOH:BTESE = 260 - 300; EtOH:H 2 O = 4 - 6; H 2 O:HCl = 500 - 700;

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

[0017] Using the BTESE sol obtained in step (2) as the coating solution, evenly coat it on the surface of the tubular alumina support coated with the crystal layer in step (1), and then calcine it at a temperature of 200 - 300 °C for 10 - 30 min; among them, after repeating the above operation 2 - 5 times, the ZIF-62 / BTESE composite membrane is obtained.

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

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

[0020] The length of the tubular alumina support is 4 - 6 cm, the outer surface area is 15 - 25 cm 2 , and the pore diameter is 0.02 - 10 μm.

[0021] The ZIF-62 / BTESE composite membrane obtained in step (3) is subjected to single-component gas permeation testing using a gas permeation testing device to evaluate the denseness and gas separation performance of the prepared ZIF-62 / BTESE composite membrane. The specific operation is as follows: Seal the ZIF-62 / BTESE composite membrane in a tubular membrane module using an O-ring rubber seal. One end of the ZIF-62 / BTESE composite membrane is sealed, and the other end is connected to a soap bubble tube. The pressure on the feed side is controlled by a back pressure valve, and the pressure is controlled at 0.1 Mpa. After the permeate side is connected to the soap bubble tube, it is in communication with the atmosphere. Use a stopwatch and a soap bubble flowmeter to obtain the time taken for a certain volume of gas to pass through the membrane. The testing is carried out at room temperature.

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

[0023]

[0024] Advantages of the present invention:

[0025] (1) The present invention has successfully prepared a dense ZIF-62 / BTESE composite membrane on a tubular alumina support tube. The surface of the ZIF-62 polycrystalline membrane reported in the existing literature is not dense, and there are defects such as cracks. By combining ZIF-62 crystals with BTESE, defects such as cracks that are prone to appear in the membrane layer can be effectively reduced, and the continuity and flatness of the prepared membrane can be improved.

[0026] (2) The dense and defect-free ZIF-62 / BTESE composite membrane prepared on the tubular support has good separation performance for H 2 / CO 2 gas. The filling and repair of the microporous network structure of the BTESE material mends the intercrystalline defects, and at the same time strengthens the continuity and denseness of the membrane layer, which can significantly improve the gas separation ability of the composite membrane for hydrogen and carbon dioxide. Description of the Drawings

[0027] Figure 1 is the scanning electron microscope (SEM) image of ZIF-62 crystals;

[0028] Figure 2 is the X-ray diffraction (XRD) pattern of ZIF-62 crystals;

[0029] Figure 3 is the scanning electron microscope (SEM) image of the ZIF-62 membrane synthesized by the homologous metal induction method, (a) surface, (b) cross-section;

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

[0031] Figure 5 is the scanning electron microscope (SEM) image of the ZIF-62 / BTESE composite membrane, (a) surface, (b) cross-section;

[0032] Figure 6 is the gas separation performance test diagram of the prepared ZIF-62 membrane and ZIF-62 / BTESE composite membrane, (a) permeability, (b) ideal selectivity. Detailed Embodiments

[0033] The following further describes the detailed embodiments of the present invention in conjunction with the 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, add ZIF-62 crystals to an anhydrous ethanol solution and then ultrasonically disperse them to prepare a crystal solution with a mass concentration of 0.02%. Seal one end of the carrier with a polytetrafluoroethylene stopper, connect the other end to a vacuum pump, immerse the carrier in the crystal solution, and vacuum filter 30 ml to obtain a ZIF-62 crystal layer on the surface of the carrier. Place it in an oven at 175 °C for drying for 2 h, take it out and let it cool naturally to room temperature. Finally, place the carrier tube with the introduced ZIF-62 crystal layer in a desiccator for standby.

[0038] (2) Preparation of BTESE sol

[0039] First, prepare a BTESE sol with a mass concentration of 5%. The specific molar ratio of the sol is BTESE:H 2 O:HCl:EtOH = 1:60:0.1:284. Weigh a quantitative amount of BTESE sol in a 50 ml beaker, transfer it to a water bath at 35 °C, add EtOH while stirring. After the solution is evenly mixed, gradually add a dilute HCl solution mixed with H 2 O. Stir and react for 3 h to obtain a 5% BTESE sol. Then add an equal mass of EtOH to dilute it to 2.5%.

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

[0041] Seal both ends of the carrier with the ZIF-62 crystal layer using polytetrafluoroethylene stoppers. At room temperature, use the dip-coating method to introduce the BTESE sol into the ZIF-62 crystal layer to fix the ZIF-62 crystal layer. The dipping time is controlled at 3 s, and then place it in a muffle furnace at 280 °C for high-temperature calcination for 20 min. Take it out and transfer it to an oven at 175 °C to cool down for 20 min. Subsequently, use the rubbing method to introduce BTESE. Wet the gauze with the BTESE sol, quickly and evenly rub the surface of the carrier in a circle, and then place the carrier in a muffle furnace at 280 °C for high-temperature calcination for 20 min. Take it out and transfer it to an oven at 175 °C to cool down for 20 min. Repeat this process three times to obtain the ZIF-62 / BTESE composite membrane. The obtained membrane is placed in a desiccator for single-component gas permeation testing.

[0042] Example 2

[0043] On the basis of Example 1, in step (1), change the mass concentration of the crystal solution to 0.04% to prepare the ZIF-62 / BTESE composite membrane.

[0044] Example 3

[0045] On the basis of Example 1, in step (2), change the concentration of the BTESE sol to 2% to prepare the ZIF-62 / BTESE composite membrane.

[0046] Example 4

[0047] On the basis of Example 1, the number of times of repeated rubbing and calcination in step (3) was changed to five times, and the ZIF-62 / BTESE composite membrane was prepared.

[0048] Comparative Example 1

[0049] Preparation of ZIF-62 membrane by homologous metal induction method:

[0050] (1) Preparation of ZnO sol

[0051] The specific reaction conditions for preparing ZnO sol are as follows: Weigh 8.4 g of zinc acetate (ZnAC 2 ) and add it to 48 ml of ethylene glycol methyl ether (EMEG) solution. Transfer it to a pre-prepared water bath at 70 °C and stir. After the suspension is heated up, add 2.4 ml of ethanolamine drop by drop, and continue to stir for 4 h to obtain a light yellow clear sol. Then cool it to room temperature and age for 24 h to obtain ZnO sol.

[0052] (2) Carrier pretreatment

[0053] The outer diameter of the tube is 12 mm, the inner diameter of the tube is 8 mm, the average pore diameter is greater than 1 μm, and the porosity is about 30-40%. The carrier pretreatment is divided into the following steps: First step, polish the outer surface of the carrier tube with 800-mesh, 1500-mesh, and 3000-mesh sandpapers in sequence, and cut it into short tubes of 5 cm; Second step, ultrasonically clean with deionized water, ultrasonically clean with 1 mol / L HCl solution, ultrasonically clean with deionized water until neutral, ultrasonically clean with 1 mol / L NaOH solution, and ultrasonically clean with deionized water until neutral. Each cleaning lasts for 30 min. The cleaned carrier tube is placed in an oven at 80 °C and dried overnight; Third step, calcine at 550 °C for 360 min, and the heating and cooling rates are both 1 °C / min. After calcination, store it at room temperature in a desiccator and wait for subsequent use.

[0054] (3) Introduction of ZnO layer

[0055] At room temperature, the zinc oxide layer was introduced by the dip-coating method. The specific steps are as follows: Seal both ends of the carrier tube with PTFE plugs, immerse it in the ZnO sol for 3 s, then place it in an oven at 100 °C and dry for 40 min. After taking it out and cooling, immerse it in the ZnO sol again for 3 s, and then still place it in an oven at 100 °C and dry for 30 min. Take it out and transfer the carrier to a muffle furnace, heat it up to 400 °C at a rate of 1 °C / min and calcine for 180 min. In the temperature range of 200-300 °C, the heating rate is changed to 0.5 °C / min. After cooling to room temperature at 1 °C / min, the carrier tube with a zinc oxide layer attached is obtained, and it is sealed in a sample bag and stored in a desiccator.

[0056] (4) Preparation of ZnO nanorods

[0057] The introduced ZnO layer provides insufficient metal source and has poor fixing ability. Therefore, a layer of ZnO nanorods needs to be obtained on the ZnO layer to increase the metal source concentration on the carrier surface. The specific process of ZnO nanorods is as follows: 1.265 g of Zn(NO 3 ) 2 ·6H 2 O and 0.591 g of C 6 H 12 N 4 are dissolved in 60 ml of H 2 O solvent, stirred and ultrasonicated for 30 min respectively to obtain a synthesis solution. The two ends of the carrier introducing the ZnO layer are sealed with polytetrafluoroethylene stoppers, placed in the inner liner of the autoclave, and then the synthesis solution is added. After sealing, it is placed in an oven for reaction. The reaction time is set to 6.5 h, and the reaction temperature is 100 °C. After the reaction, it is naturally cooled to room temperature. After taking out, the carrier is rinsed with a large amount of deionized water, vacuum dried at 80 °C overnight, and placed in a desiccator after being fully dried.

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

[0059] The two ends of the carrier introducing ZnO nanorods are sealed with polytetrafluoroethylene stoppers, placed in the inner liner of the autoclave, and then synthesized by homologous metal induction after adding the synthesis solution. The specific method is as follows: 1.981 g of Im and 0.384 g of BIm are dissolved in 24 ml of DMF solvent, ultrasonicated for 30 min, then added to the inner liner of the autoclave. After sealing, it is placed in an oven for reaction. The reaction time is set to 20 h, and the reaction temperature is 120 °C. After the reaction, it is naturally cooled to room temperature. After taking out, it is soaked and washed with anhydrous methanol reagent for three days, and the solvent is changed twice during this period. It is vacuum dried at 100 °C overnight and placed in a desiccator for single-component gas permeation testing after being fully dried.

[0060] Single-component gas permeation tests are carried out 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 are carried out on the ZIF-62 membrane and ZIF-62 / BTESE composite membrane prepared by the homologous metal induction method. The tests are carried out using a self-made gas permeation test device in the laboratory to evaluate the denseness and gas separation performance of the prepared membranes. The specific operation is as follows: The membrane is sealed in a tubular membrane module using an O-ring. One end of the membrane is sealed, and the other end is connected to a soap bubble tube. The pressure on the feed side is controlled by a back-pressure valve and controlled at 0.1 Mpa. After the permeate side is connected to the soap bubble tube, it is communicated with the atmosphere. The time taken for a certain volume of gas to pass through the membrane is obtained using a stopwatch and a soap bubble flowmeter. The tests are all carried out at room temperature.

[0062] As Figure 3As shown, obvious cracks exist on the surface of the ZIF-62 membrane prepared by the homologous metal-induced method, and its H 2 / CO 2 、H 2 / N 2 、H 2 / CH 4 The ideal selectivities of are only 12.1, 3.1, and 2.7 respectively, and the ideal selectivities of H 2 / N 2 and H 2 / CH 4 are less than the Knudsen diffusion selectivity (3.7 and 2.8). The ZIF-62 / BTESE composite membrane is continuous and dense, without obvious defects such as cracks or pinholes, and the membrane thickness is about 3.3 μm (see Figure 5 ). The test results of the ZIF-62 / BTESE composite membrane are as follows: The permeation flux of H 2 is 7.12×10 -8 mol·m -2 ·s -1 ·pa -1 , and the ideal selectivities for H 2 / CO 2 、H 2 / N 2 、H 2 / CH 4 reach 35.9, 3.8, and 3.1 respectively, all of which are greater than their Knudsen diffusion selectivities (4.7, 3.7, and 2.8), proving that the obtained ZIF-62 / BTESE composite membrane has no intercrystalline defects and the feasibility of this method. Among them, the ideal selectivity of H 2 / CO 2 reaches 35.9, indicating that the membrane obtained by this method has a certain gas separation ability.

Claims

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

2. The method for preparing a 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, the particle size of which is 0.6 to 3 μm, and the mass fraction of the crystal liquid is 0.01 to 0.06%.

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

4. The method for preparing a ZIF-62 / BTESE composite membrane on a tubular alumina support according to claim 1, characterized in that: In step (2), the mass ratio of the 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 to 4, characterized in that: The length of the tubular alumina carrier is 4 to 6 cm, and the surface area is 15 to 25 cm 2 , the pore size is 0.02~10μm.

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