Preferred orientation zeolite imidazole skeleton-8 self-supporting gas separation membrane and preparation method thereof

Abstract

The invention provides a preferred orientation zeolite imidazole skeleton-8 self-supporting gas separation membrane and a preparation method thereof.The method comprises the steps that zinc acetate dihydrate, 2-methylimidazole and hexadecyl trimethyl ammonium bromide are dissolved in deionized water, stirring, centrifugal treatment, filtering, growth solution standing, drying and other steps are conducted, and the preferred orientation zeolite imidazole skeleton-8 self-supporting gas separation membrane is obtained. And finally, the self-supporting gas separation membrane with preferred orientation and cubic morphology is formed. In the preparation process, parameters such as the proportion of all the components, stirring conditions, the temperature and humidity of a constant-temperature and constant-humidity chamber and the like are strictly controlled, so that uniform growth and good mechanical strength of the membrane are ensured. The preparation method is simple and efficient, and the obtained membrane has excellent gas separation performance and long-term stability.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of functional materials, and in particular to a preferentially oriented zeolite imidazole framework-8 self-supporting gas separation membrane and a preparation method thereof. Background Art

[0002] Membrane separation technology is a new type of environmentally friendly separation technology. Compared with traditional gas separation technologies such as cryogenic distillation and pressure swing adsorption, it has the advantages of low energy consumption, high efficiency and sustainability, simple operation and high efficiency. Zeolite imidazole framework-8 (ZIF-8) is one of the important members of metal-organic framework (MOF) materials and has shown great advantages in the field of gas separation. Its zeolite-like permanent porosity, easy synthesis, and excellent thermal and chemical stability have made it one of the most studied MOF materials in hydrocarbon separation in recent years. However, ZIF-8 is a discrete crystal, and it is difficult to independently form a continuous pure ZIF-8 membrane. It usually requires a support such as alumina and polymer membrane to provide strength for assembly into a membrane. In addition, the interaction between the ZIF-8 layer and the support layer is weak, and it is easy to fall off and produce non-selective defects. Summary of the invention

[0003] The embodiment of the present application provides a preferentially oriented zeolite imidazole framework-8 self-supporting gas separation membrane and a preparation method thereof, which are used to solve the technical problems existing in the above-mentioned background technology.

[0004] In the first aspect, the present application provides a preferentially oriented zeolite imidazole framework-8 self-supporting gas separation membrane and a preparation method thereof, comprising: step 1: dissolving zinc acetate dihydrate, 2-methylimidazole and hexadecyltrimethylammonium bromide in deionized water respectively, then adding the hexadecyltrimethylammonium bromide aqueous solution to the 2-methylimidazole aqueous solution, and then mixing and stirring with the zinc acetate dihydrate aqueous solution; step 2: dissolving zinc acetate dihydrate, 2-methylimidazole and hexadecyltrimethylammonium bromide in deionized water respectively, and then adding the hexadecyltrimethylammonium bromide aqueous solution to the 2-methylimidazole aqueous solution; The ammonium acetate aqueous solution is added to the 2-methylimidazole aqueous solution, and then mixed with the zinc acetate dihydrate aqueous solution and stirred. After centrifugal treatment, deionized water is added and stirred again; step 3: the solution obtained in step 1a and step 1b is added to a vacuum filtration system with porous anodized aluminum, and filtered by pressure; then, the zinc acetate dihydrate aqueous solution and the 2-methylimidazole / hexadecyltrimethylammonium bromide aqueous solution are used as growth liquids, left to stand at room temperature, filtered by suction, and finally placed in a constant temperature and humidity chamber for drying; and the gas separation membrane is peeled off from the porous anodized aluminum substrate to form the gas separation membrane.

[0005] Furthermore, in step 1, the masses of zinc acetate dihydrate, 2-methylimidazole and hexadecyltrimethylammonium bromide are 0.1-5g, 1-10g and 0.0010-0.1g respectively; the zinc acetate dihydrate, 2-methylimidazole and hexadecyltrimethylammonium bromide are dissolved in 1-20mL, 5-50mL and 5-50mL of deionized water respectively.

[0006] Furthermore, in step 2, the masses of zinc acetate dihydrate, 2-methylimidazole and hexadecyltrimethylammonium bromide are 0.1-5g, 1-10g and 0.0010-0.1g respectively; the zinc acetate dihydrate, 2-methylimidazole and hexadecyltrimethylammonium bromide are dissolved in 1-20mL, 5-50mL and 5-50mL of deionized water respectively; the hexadecyltrimethylammonium bromide aqueous solution in step 2 is added to 5-20mL of 2-methylimidazole aqueous solution, mixed with the zinc acetate dihydrate aqueous solution and stirred for 10-60min; after centrifugation at a speed of 500-10000r / min, 5-50mL of deionized water is added and stirred again for 5-60min, and the stirring speed is 100-600r / min.

[0007] Furthermore, in step 3, the standing time at room temperature is 10-60 minutes; after filtration, the mixture is placed in a constant temperature and humidity chamber for drying for 12-60 hours, wherein the temperature of the constant temperature and humidity chamber is controlled at 25-80° C., and the humidity is controlled at 20%-80% RH.

[0008] Furthermore, the pore size of the porous anodized aluminum in step 2 is 50-500 nm, and the thickness is 50-500 μm; the pressure of the pressure filtration in step 2 is 0.1-1.0 bar.

[0009] Furthermore, the temperature and humidity conditions of the constant temperature and humidity chamber in step 3 can promote the uniform growth of the self-supporting gas separation to form a dense and continuous structure.

[0010] Furthermore, the porosity of the porous anodized aluminum in step 3 is between 30% and 70% to ensure gas permeability while maintaining sufficient mechanical strength; the preparation process of the self-supporting gas separation membrane in step 3 also includes forming a dense layer on the porous anodized aluminum substrate, and the thickness of the dense layer is 0.1-5μm to improve the selectivity and stability of the membrane.

[0011] In the second aspect, an embodiment of the present application provides a preferentially oriented zeolite imidazole framework-8 self-supporting gas separation membrane. The preferential orientation and cubic morphology of the preferentially oriented zeolite imidazole framework-8 self-supporting gas separation membrane jointly achieve good coplanarity between crystals in the membrane and can be effectively used for gas separation.

[0012] Furthermore, the gas separation includes: separation of 1,3-butadiene / n-butene, 1,3-butadiene / isobutylene, 1,3-butadiene / n-butane, and 1,3-butadiene / isobutane.

[0013] The technical solution of the present invention to solve the material technical problem is to provide a self-supporting gas separation membrane of preferentially oriented zeolite imidazole framework-8 obtained according to the method, which is characterized in that the crystals of the material are well coplanar and the crystals grow preferentially.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] (1) The present invention uses hexadecyltrimethylammonium bromide cationic surfactant as a capping agent for ZIF-8, so that the morphology of ZIF-8 is adjusted from a characteristic rhombic dodecahedron to a cube, laying a foundation for good coplanarity between crystals.

[0016] (2) Hexadecyltrimethylammonium bromide, which has both polar hydrophilic groups and non-polar hydrophobic groups, is in a state where the hydrophobic end faces upward and the hydrophilic end faces downward in aqueous solution, and induces the 2-

[0017] The methylimidazole ligands are arranged regularly in water, and after zinc acetate dihydrate is added, a coordination reaction occurs to form a regular arrangement of ZIF-8 crystals.

[0018] (3) Under the pressure-driven and epitaxial growth preparation strategies, a pure ZIF-8 self-supporting film with preferential orientation is formed, which together with the cubic morphology reduces the intercrystalline defects after assembly.

[0019] (4) The preferentially oriented ZIF-8 self-supporting gas separation membrane of the present invention can be applied to the field of gas separation, providing a new preparation idea for the application of pure MOF membrane in the field of gas separation.

[0020] These and other aspects of the present application will become more clearly understood in the description of the following embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 A schematic diagram of the preparation mechanism of a self-supporting gas separation membrane of a preferentially oriented zeolite imidazole framework-8 provided by the present invention;

[0023] Figure 2(a) surface morphology and (b) cross-sectional morphology of a dense layer on the surface of a self-supporting gas separation membrane with a preferentially oriented zeolite imidazole framework-8 provided by the present invention;

[0024] Figure 3 (a) a physical image and (b) a general cross-sectional morphology image of a preferentially oriented zeolite imidazole framework-8 self-supporting gas separation membrane provided by the present invention;

[0025] Figure 4 A schematic diagram of the C4 hydrocarbon (a) single component gas permeability coefficient and (b) ideal selectivity of a preferentially oriented zeolite imidazole framework-8 self-supporting gas separation membrane provided by the present invention;

[0026] Figure 5 Schematic diagram of (a) C4 hydrocarbon mixed gas permeability coefficient and (b) mixed gas separation selectivity of a preferentially oriented ZIF-8 membrane according to an embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] Embodiment 1:

[0029] Step 1:

[0030] Material preparation: Weigh 0.1-5g zinc acetate dihydrate, 1-10g 2-methylimidazole and 0.0010-0.1g hexadecyltrimethylammonium bromide.

[0031] Dissolution: Dissolve zinc acetate dihydrate in 1-20 mL of deionized water, dissolve 2-methylimidazole in 5-50 mL of deionized water, and dissolve hexadecyltrimethylammonium bromide in 5-50 mL of deionized water.

[0032] Mixing: Add the hexadecyltrimethylammonium bromide aqueous solution to the 2-methylimidazole aqueous solution, then mix with the zinc acetate dihydrate aqueous solution and stir for 10-60 minutes.

[0033] Step 2:

[0034] Repeat step 1: Prepare the same solution again according to the method in step 1.

[0035] Centrifugation: The mixed solution in step 2 is centrifuged at a speed of 500-10000 r / min for 10-30 min.

[0036] Stir again: add 5-50 mL of deionized water and stir again for 5-60 min at a stirring speed of 100-600 r / min.

[0037] Step 3:

[0038] Filtration: Add the solutions obtained in step 1 and step 2 into a vacuum filtration system of porous anodized aluminum with a pore size of 50-500 nm and a thickness of 50-500 μm, and filter at a pressure of 0.1-1.0 bar.

[0039] Preparation of growth solution: Mix an aqueous solution of zinc acetate dihydrate and an aqueous solution of 2-methylimidazole / hexadecyltrimethylammonium bromide to prepare a growth solution.

[0040] Standing: Let the growth solution stand at room temperature for 10-60 minutes.

[0041] Filtration: Filter the liquid after it has stood still.

[0042] Drying: Place the filtered membrane in a constant temperature and humidity chamber at a temperature of 25-80°C and a humidity of 20%-80% RH and dry it for 12-60 hours.

[0043] Embodiment 2:

[0044] Step 1:

[0045] Follow step 1 in Example 1.

[0046] Step 2:

[0047] The operation was carried out according to step 2 of Example 1, but the stirring speed was adjusted to 200-400 r / min before stirring again after centrifugation.

[0048] Step 3:

[0049] Filtration: Use porous anodized aluminum with a porosity of 40%-60%.

[0050] Standing: Let the growth solution stand at room temperature for 30 minutes.

[0051] Filtration: Use appropriate filtration equipment for filtration.

[0052] Drying: Place the filtered membrane in a constant temperature and humidity chamber at 30-60°C and 40%-60%RH for 24 hours.

[0053] Stripping: The gas separation membrane is produced by stripping from a porous anodized aluminum substrate.

[0054] Formation of dense layer: A 0.5 μm thick dense layer was formed on the porous anodized aluminum substrate to improve the selectivity and stability of the membrane.

[0055] Embodiment three:

[0056] Samples: A plurality of ZIF-8 self-supporting gas separation membrane samples were prepared according to the method in Example 2, but the type and concentration of the surfactant were changed.

[0057] Performance test: Perform gas separation test on each sample and record its separation coefficient and permeation rate.

[0058] Structural characterization: Use SEM, XRD, TEM and other methods to analyze the microstructure of the membrane.

[0059] Result analysis: Compare the effects of different surfactants on membrane performance and determine the optimal surfactant type and concentration.

[0060] Performance Test:

[0061] Gas permeability test: Use a commercial gas permeability test system to measure the separation performance of 1,3-butadiene / n-butene, 1,3-butadiene / isobutylene, 1,3-butadiene / n-butane, and 1,3-butadiene / isobutane.

[0062] Stability test: Place the prepared membrane in a high temperature and high humidity environment and continuously monitor changes in its separation performance.

[0063] Structural characterization:

[0064] Scanning electron microscopy (SEM): observe the surface morphology of the membrane.

[0065] X-ray diffraction (XRD): Determine the crystal structure of the film.

[0066] Transmission electron microscopy (TEM): observe the internal structure of the membrane.

[0067] Pore ​​size distribution analysis: The pore size distribution of the membranes was determined using nitrogen adsorption / desorption isotherms.

[0068] Result analysis:

[0069] Data analysis: record the test results and analyze the performance differences of the membrane under different preparation conditions.

[0070] Performance evaluation: Evaluate the suitability of the membrane for different gas separation scenarios.

[0071] Embodiment 4:

[0072] Sample preparation: The sample was prepared according to the method in Example 1, but the stirring conditions in step 1, such as stirring speed, stirring time, etc., were changed.

[0073] The performance test, structural characterization and result analysis process described in Example 3 were used to record the test results, analyze the performance differences of the membrane under different stirring conditions, and evaluate the applicability of the membrane in different gas separation scenarios.

[0074] Sample preparation: The samples were prepared according to the method in Example 1, but the temperature and humidity conditions of the constant temperature and humidity chamber were changed in step 3.

[0075] Using the performance testing, structural characterization and result analysis process described in Example 3, the test results were recorded, the performance differences of the membrane under different temperature and humidity conditions were analyzed, and the applicability of the membrane in different gas separation scenarios was evaluated.

[0076] The above description is only a preferred embodiment of the present invention, and therefore cannot be used to limit the scope of the present invention. That is, equivalent changes and modifications made according to the patent scope of the present invention and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A method for preparing a preferentially oriented zeolite imidazole framework-8 self-supporting gas separation membrane, characterized in that: include: Step 1: Dissolve zinc acetate dihydrate, 2-methylimidazole and hexadecyltrimethylammonium bromide in deionized water respectively, then add the hexadecyltrimethylammonium bromide aqueous solution to the 2-methylimidazole aqueous solution, and then mix with the zinc acetate dihydrate aqueous solution and stir; Step 2: Dissolve zinc acetate dihydrate, 2-methylimidazole and cetyltrimethylammonium bromide in deionized water respectively, then add the cetyltrimethylammonium bromide aqueous solution to the 2-methylimidazole aqueous solution, mix with the zinc acetate dihydrate aqueous solution and stir, centrifuge, add deionized water and stir again; Step 3: Add the solution obtained in step 1a and step 1b into a vacuum filtration system with porous anodized aluminum and filter it under pressure; then, use an aqueous solution of zinc acetate dihydrate and an aqueous solution of 2-methylimidazole / hexadecyltrimethylammonium bromide as growth solutions, let them stand at room temperature, filter them by suction, and finally put them into a constant temperature and humidity chamber to dry; peel them off from the porous anodized aluminum substrate to form the gas separation membrane.

2. The preparation method according to claim 1, characterized in that: In step 1, the masses of zinc acetate dihydrate, 2-methylimidazole and hexadecyltrimethylammonium bromide are 0.1-5g, 1-10g and 0.0010-0.1g respectively; the zinc acetate dihydrate, 2-methylimidazole and hexadecyltrimethylammonium bromide are dissolved in 1-20mL, 5-50mL and 5-50mL of deionized water respectively.

3. The preparation method according to claim 1, characterized in that: In step 2, the masses of zinc acetate dihydrate, 2-methylimidazole and hexadecyltrimethylammonium bromide are 0.1-5g, 1-10g and 0.0010-0.1g respectively; the zinc acetate dihydrate, 2-methylimidazole and hexadecyltrimethylammonium bromide are dissolved in 1-20mL, 5-50mL and 5-50mL of deionized water respectively; The hexadecyltrimethylammonium bromide aqueous solution in step 2 is added to 5-20 mL of 2-methylimidazole aqueous solution, mixed with zinc acetate dihydrate aqueous solution and stirred for 10-60 min; after centrifugation at a speed of 500-10000 r / min, 5-50 mL of deionized water is added and stirred again for 5-60 min at a stirring speed of 100-600 r / min.

4. The preparation method according to claim 1, characterized in that: In step 3, the standing time at room temperature is 10-60 minutes; after filtration, the mixture is placed in a constant temperature and humidity chamber for drying for 12-60 hours, wherein the temperature of the constant temperature and humidity chamber is controlled at 25-80° C. and the humidity is controlled at 20%-80% RH.

5. The preparation method according to claim 1, characterized in that: The porous anodized aluminum in step 2 has a pore size of 50-500 nm and a thickness of 50-500 μm; The pressure of the pressure filtration in step 2 is 0.1-1.0 bar.

6. The preparation method according to claim 1, characterized in that: The temperature and humidity conditions of the constant temperature and humidity chamber in step 3 can promote the uniform growth of the self-supporting gas separation to form a dense and continuous structure.

7. The preparation method according to claim 1, characterized in that: The porosity of the porous anodized aluminum in step 3 is between 30% and 70% to ensure gas permeability while maintaining sufficient mechanical strength; The preparation process of the self-supporting gas separation membrane in step 3 also includes forming a dense layer on the porous anodized aluminum substrate, wherein the thickness of the dense layer is 0.1-5 μm, so as to improve the selectivity and stability of the membrane.

8. The preferentially oriented zeolite imidazole framework-8 self-supporting gas separation membrane obtained by the preparation method according to any one of claims 1 to 7, characterized in that: The preferred orientation and cubic morphology of the preferred oriented zeolite imidazole framework-8 self-supporting gas separation membrane together achieve good coplanarity between crystals in the membrane and can be effectively applied to gas separation.

9. The preferentially oriented zeolite imidazole framework-8 self-supporting gas separation membrane obtained by the preparation method according to any one of claims 1 to 7, characterized in that: The gas separation includes: separation of 1,3-butadiene / normal-butene, 1,3-butadiene / isobutene, 1,3-butadiene / normal-butane, and 1,3-butadiene / isobutane.

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