ZIF-90 film and preparation method thereof

Abstract

The invention provides a ZIF-90 film and a preparation method thereof. The preparation method comprises the following steps: S1, sequentially coating the surface of a carrier with ZIF-90 nano-powder and a precursor solution; and S2, heating the carrier coated with the ZIF-90 nano powder and the precursor solution in the step S1, and cooling to obtain the ZIF-90 film. According to the method, the ZIF-90 film is prepared on the large-aperture (0.5-10 microns) carrier for the first time, and the method has the advantages of being easy to operate, high in repeatability and wide in universality. The ZIF-90 membrane prepared by the preparation method provided by the invention has excellent propylene permeability and better propylene / propane separation selectivity.

Description

Technical Field

[0001] The present invention relates to the field of membrane technology separation, and more particularly, to a ZIF-90 membrane and a preparation method thereof. Background Art

[0002] Gas separation is one of the core technologies in modern industry, energy production, and environmental protection. Membrane separation technology realizes gas separation through a selective permeation membrane, which has technical advantages such as low energy consumption, simple operation, and environmental friendliness compared with traditional methods (such as cryogenic distillation, adsorption, and absorption). High-performance membrane materials are the core of membrane separation technology.

[0003] Zeolitic-imidazolate frameworks (ZIFs) materials are composed of transition metal atoms (Zn and Co) connected with imidazole / imidazole derivatives, and have excellent thermal stability and chemical stability. As gas separation membrane materials, ZIFs materials have attracted much attention in recent years due to their unique structures and properties. ZIF-90 (zeolitic-imidazolate framework-90) is a ZIFs material formed by zinc ions (Zn 2+ ) and imidazole-2-carboxaldehyde (ICA) ligands through coordination bonds. Traditional solvothermal synthesis methods (such as solvothermal method, vapor conversion method) can prepare highly crystalline ZIF-90 materials by regulating solvents, temperature, and ligand / metal ratio. Currently, most preparation technologies of ZIF-90 membranes are mainly applicable to carriers with nanoscale pore sizes (5 - 100 nanometers). When it comes to carriers with micron-scale pore sizes (0.5 - 10 microns), it is relatively difficult to directly synthesize an effective separation membrane. The core of this problem lies in that larger pore sizes are not conducive to the nucleation and growth of crystals, thus restricting the direct formation of ZIF-90 membranes on these carriers. Summary of the Invention

[0004] The technical problem to be solved by the present invention is how to nucleate on a macroporous commercial carrier.

[0005] To solve the above problems, the first aspect of the present invention provides a preparation method of a ZIF-90 membrane, including the following steps: S1: Coating ZIF-90 nanometer powder and a precursor solution on the surface of a carrier in sequence; S2: Heating the carrier coated with ZIF-90 nanometer powder and the precursor solution in step S1, and cooling to obtain a ZIF-90 membrane.

[0006] The present invention first coats a layer of ZIF-90 nanometer powder on the surface of the carrier. This nanometer powder can directly serve as the crystal nucleus for subsequent crystals, facilitating the growth of subsequent crystals. At the same time, the incorporation of ZIF-90 can artificially reduce the pore size of the carrier, which is beneficial to the formation of the ZIF-90 membrane layer.

[0007] Preferably, in the step S1, in terms of molar parts, the precursor solution includes 1 part of metal salt, 1-8 parts of organic ligand, and 50-500 parts of solvent.

[0008] Preferably, the metal salt is zinc nitrate hexahydrate or zinc acetate dihydrate, the organic ligand is imidazole-2-carboxaldehyde, and the solvent is one or two of methanol, water, N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc).

[0009] Preferably, in the step S1, the particle size of the ZIF-90 nanometer powder is 20-200 nanometers.

[0010] Preferably, in the step S1, the carrier is one of a tubular α-Al2O3 carrier, a tubular γ-Al2O3 carrier, a tubular SiO2 carrier, and a tubular PVDF carrier, and the pore diameter of the carrier is 0.5-10 microns.

[0011] Preferably, in the step S2, the heating temperature is 50-200 °C and the time is 5-120 min.

[0012] In the second aspect of the present invention, a ZIF-90 membrane is provided, and the ZIF-90 membrane is prepared by the preparation method described in the first aspect.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention first prepares a high-quality ZIF-90 membrane on a large-pore diameter carrier. First, a layer of ZIF-90 nanoparticles is coated on the large-pore diameter carrier. These nanoparticles can effectively reduce the pore diameter of the carrier. At the same time, the ZIF-90 nanoparticles can directly serve as the crystal nuclei for subsequent crystals, facilitating crystal growth. Then, by coating the precursor solution and heating operations, a high-quality ZIF-90 membrane is formed. The preparation method of the ZIF-90 membrane provided by the present invention has the advantages of simple operation, high repeatability, and wide versatility. The ZIF-90 membrane prepared by the preparation method provided by the present invention has excellent propylene permeability and good propylene / propane separation selectivity. Description of the Drawings

[0014] Figure 1 It is the SEM characterization result of the hollow carrier in Example 1 of the present invention; Figure 2 It is the XRD characterization result of the product M2 prepared in Example 1 of the present invention; Figure 3 It is the SEM characterization result of the product M2 prepared in Example 1 of the present invention; Figure 4 It is the XRD characterization result of the product M5 in Comparative Example 1 of the present invention; Figure 5 SEM characterization results of product M5 in Comparative Example 1 of the present invention. Specific embodiments

[0015] The technical solutions of the present invention will be described clearly and completely below. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0016] As described in the background art, to solve the technical problem that a large-pore carrier cannot directly synthesize a ZIF-90 membrane in the prior art, the specific embodiments of the present invention provide a method for preparing a ZIF-90 membrane on a large-pore (0.5 - 10 microns) carrier, which specifically includes the following steps: S1: Coat ZIF-90 nanopowder and a precursor solution on the surface of the carrier in sequence; S2: Heat the carrier coated with ZIF-90 nanopowder and the precursor solution in step S1, and a ZIF-90 membrane is obtained after cooling.

[0017] In the above embodiment, in step S1, ZIF-90 nanopowder is first coated on the surface of the large-pore carrier. This nanopowder can serve as crystal nuclei, facilitating the growth of subsequent crystals. At the same time, this nanopowder can also play a role in reducing the pore size of the carrier, providing conditions for the formation of the membrane layer during the subsequent preparation of the ZIF-90 membrane.

[0018] In step S1 of the above embodiment, in terms of molar parts, the precursor solution includes 1 part of metal salt, 1 - 8 parts of organic ligand, and 50 - 500 parts of solvent.

[0019] More specifically, the metal salt is zinc nitrate hexahydrate or zinc acetate dihydrate, the organic ligand is imidazole-2-carboxaldehyde, and the solvent is one or two of methanol, water, N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc).

[0020] In step S1 of the above embodiment, the particle size of the ZIF-90 nanopowder is 20 - 200 nanometers.

[0021] In step S1 of the above embodiment, the carrier is one of a tubular α-Al2O3 carrier, a tubular γ-Al2O3 carrier, a tubular SiO2 carrier, and a tubular PVDF carrier, and the pore size of the carrier is 0.5 - 10 microns.

[0022] In step S2 of the above embodiment, the heating temperature is 50 - 200 °C, and the time is 5 - 120 min.

[0023] The above technical solution of the present invention will be further described below in conjunction with the accompanying drawings, examples and specific data.

[0024] Unless otherwise specified, the separation selectivity of the binary mixed gas mentioned in the present invention refers to the ratio of the gas permeabilities of two gases; the gas permeability is the amount of substance (mol) of the gas passing through a unit membrane area (m 2 ) per unit time (s) and unit pressure (Pa). Both of the above two parameters in this specification are measured according to the method in J. Membr. Sci. (2010, 354, 48 - 54.).

[0025] Example 1 Preparation of ZIF-90 Membrane First, imidazole-2-carboxaldehyde was dissolved in methanol to form a ligand solution. Subsequently, zinc acetate dihydrate was slowly added to the ligand solution, and the mixture was stirred at room temperature (25 °C) until the solution became clear to obtain a precursor solution. The molar ratio of Zn, imidazole-2-carboxaldehyde, and methanol in the precursor solution was 1:2:124.

[0026] Three identical α-Al2O3 alumina tubular supports (with an effective pore size of 2 μm) were uniformly coated with 50 nm of ZIF-90 powder on the surface, then immersed in the precursor solution for 30 s, and then quickly transferred to a 50 °C forced-air oven and heated for 30 minutes, and then naturally cooled to room temperature. ZIF-90 tubular membranes were obtained, denoted as M1, M2, and M3 respectively.

[0027] The empty support, M1, M2, and M3 were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the separation selectivity and permeability of the binary gas were measured. The SEM characterization of the empty support is as Figure 1 shown, and the XRD results of the empty support and the M2 membrane are as Figure 2 shown, and the SEM characterization of the M2 membrane is as Figure 3 shown. From Figure 2 and Figure 3 the XRD and SEM characterization results of M2, it can be seen that the ZIF-90 tubular membrane was successfully prepared. The permeability and separation selectivity results of the ZIF-90 tubular membranes M1, M2, and M3 for the equimolar propylene / propane mixed gas are shown in Table 1.

[0028] Table 1

[0029] It can be seen from the detection results in Table 1 that the ZIF-90 tubular membranes M1, M2, and M3 all have good propylene permeability and good propylene / propane separation selectivity.

[0030] Comparative Example 1 Using the method of the Chinese invention patent with the publication number CN116531972A in the prior art, a ZIF-90 membrane was prepared on an α-Al2O3 alumina tubular support with an effective pore size of 2 μm. The specific steps are as follows: First, imidazole-2-carboxaldehyde was dissolved in methanol to form a ligand solution. Subsequently, zinc acetate dihydrate was slowly added to the ligand solution, and the mixture was stirred at room temperature (25 °C) until the solution became clear to obtain a precursor solution. The molar ratio of Zn, imidazole-2-carboxaldehyde, and methanol in the precursor solution was 1:2:124.

[0031] Three identical α-Al2O3 alumina tubular supports (with an effective pore size of 2 μm) were immersed in the precursor solution for 30 s, and then quickly transferred to a 50 °C forced-air oven and heated for 30 minutes, followed by natural cooling to room temperature. Thin films were obtained and denoted as A1, A2, and A3, respectively.

[0032] A1, A2, and A3 were immersed in a DMF solution, and then quickly transferred to a reaction kettle containing 15 ml of DMF solution and heated in an 80 °C forced-air oven for 12 hours, followed by natural cooling to room temperature. Tubular membranes were obtained after methanol activation and denoted as M4, M5, and M6, respectively.

[0033] The permeability and separation selectivity results of the tubular membranes M4, M5, and M6 for an equimolar propylene / propane gas mixture are shown in Table 2.

[0034] Table 2

[0035] XRD (X-ray diffraction) and SEM (scanning electron microscopy) characterizations were performed on M4, M5, and M6, and the separation selectivity and permeability for binary-component gases were measured. The XRD results of the M5 membrane are as Figure 4 shown, and the SEM characterization of the M5 membrane is as Figure 5 shown. Combining the results in Table 2, Figure 4 and Figure 5 it can be seen that in Comparative Example 1, a ZIF-90 membrane was not successfully prepared on a support with an effective pore size of 2 μm.

[0036] From the above examples and comparative examples, it can be seen that the present invention successfully prepared a ZIF-90 membrane on a large-pore support, and the ZIF-90 membrane has excellent propylene permeability and good propylene / propane separation selectivity.

[0037] Although the present disclosure is disclosed as above, the protection scope of the present disclosure is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present disclosure, and these changes and modifications will all fall within the protection scope of the present invention.

Claims

1. A method for preparing a ZIF-90 membrane, characterized in that: The following steps are involved: S1: coating ZIF-90 nanopowder and precursor solution on the carrier surface in sequence; S2: heating the carrier coated with the ZIF-90 nanopowder and the precursor solution in step S1, and obtaining a ZIF-90 film after cooling.

2. The preparation method according to claim 1, characterized in that In the step S1, the precursor solution includes 1 part of metal salt, 1 to 8 parts of organic ligand and 50 to 500 parts of solvent by mole.

3. The preparation method according to claim 2, characterized in that: The metal salt is zinc nitrate hexahydrate or zinc acetate dihydrate, the organic ligand is imidazole-2-carboxaldehyde, and the solvent is one or two of methanol, water, N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc).

4. The preparation method according to claim 1, characterized in that: In the step S1, the particle size of the ZIF-90 nanopowder is 20 to 200 nanometers.

5. The preparation method according to claim 1, characterized in that: In the step S1, the carrier is one of a tubular α-Al2O3 carrier, a tubular γ-Al2O3 carrier, a tubular SiO2 carrier, and a tubular PVDF carrier, and the pore size of the carrier is 0.5 to 10 microns.

6. The preparation method according to claim 1, characterized in that: In step S2, the heating temperature is 50-200° C. and the heating time is 5-120 min.

7. A ZIF-90 membrane, characterized in that The ZIF-90 membrane is prepared by the preparation method described in any one of claims 1 to 6.

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