A preferentially oriented zeolite imidazolate framework-8 self-supporting gas separation membrane and a method of making the same

Abstract

The application provides a preferentially oriented zeolite imidazolate framework-8 self-supporting gas separation membrane and a preparation method thereof. The method comprises the following steps: dissolving zinc acetate dihydrate, 2-methyl imidazole and cetyl trimethyl ammonium bromide in deionized water, and finally forming a self-supporting gas separation membrane with preferential orientation and cubic morphology through stirring, centrifugal treatment, filtration, standing of the growth solution and drying. In the preparation process, the proportion of each component, stirring conditions, temperature and humidity of the constant temperature and humidity box and other parameters are strictly controlled to ensure uniform growth and good mechanical strength of the membrane. 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 embodiment of the present application relates to the technical field of functional materials, and particularly relates to a preferentially oriented zeolitic imidazolate framework-8 self-supporting gas separation membrane and a preparation method thereof. BACKGROUND

[0002] Membrane separation technology is a new type of environment-friendly separation technology. Compared with traditional gas separation technologies such as low-temperature distillation and pressure swing adsorption, the membrane separation technology has the advantages of low energy consumption, high efficiency, sustainability, simple operation and high efficiency. Zeolitic imidazolate framework-8 (ZIF-8) is an important member of metal-organic framework (MOF) materials and has shown great advantages in the field of gas separation. The permanent porosity similar to zeolite, easy synthesis and excellent thermal and chemical stability of ZIF-8 make it one of the most studied MOF materials in the field of hydrocarbon separation in recent years. However, ZIF-8 is a discrete crystal, and it is difficult to form a continuous pure ZIF-8 membrane independently. Usually, a support such as alumina or a polymer membrane is needed to provide strength to assemble the membrane. The interaction between the ZIF-8 layer and the support layer is weak, and the ZIF-8 layer is easy to fall off and produce defects without selectivity. SUMMARY

[0003] The embodiment of the present application provides a preferentially oriented zeolitic imidazolate framework-8 self-supporting gas separation membrane and a preparation method thereof to solve the technical problems in the background.

[0004] In the first aspect, the embodiment of the present application provides a preferentially oriented zeolitic imidazolate framework-8 self-supporting gas separation membrane and a preparation method thereof, which comprises the following steps: step 1: zinc acetate dihydrate, 2-methylimidazole and cetyltrimethylammonium bromide are respectively dissolved in deionized water, then the cetyltrimethylammonium bromide aqueous solution is added to the 2-methylimidazole aqueous solution, and then the zinc acetate dihydrate aqueous solution is mixed and stirred; step 2: zinc acetate dihydrate, 2-methylimidazole and cetyltrimethylammonium bromide are respectively dissolved in deionized water, then the cetyltrimethylammonium bromide aqueous solution is added to the 2-methylimidazole aqueous solution, and then the zinc acetate dihydrate aqueous solution is mixed and stirred, and then deionized water is added and stirred again after centrifugal treatment; step 3: the solutions obtained in steps 1a and 1b are added to a vacuum filtration system with porous anodic aluminum oxide, and pressure filtration is performed; then, the zinc acetate dihydrate aqueous solution and the 2-methylimidazole / cetyltrimethylammonium bromide aqueous solution are used as a growth solution, and are left to stand at room temperature, and then are subjected to suction filtration, and finally are dried in a constant temperature and humidity box; and the gas separation membrane is prepared by peeling off from the porous anodic aluminum oxide substrate.

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

[0006] Further, the mass of zinc acetate dihydrate, 2-methylimidazole and cetyltrimethylammonium bromide in step 2 is 0.1-5 g, 1-10 g and 0.0010-0.1 g respectively; the zinc acetate dihydrate, 2-methylimidazole and cetyltrimethylammonium bromide are dissolved in 1-20 mL, 5-50 mL and 5-50 mL of deionized water respectively; in step 2, the cetyltrimethylammonium bromide aqueous solution is added to 5-20 mL of 2-methylimidazole aqueous solution, mixed with the 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 speed of 100-600 r / min.

[0007] Further, the standing time at room temperature in step 3 is 10-60 min; after suction filtration, the product is placed in a constant temperature and humidity chamber for drying for 12-60 h, wherein the temperature of the constant temperature and humidity chamber is controlled at 25-80℃ and the humidity is controlled at 20%-80% RH.

[0008] Further, the pore size of the porous anodic aluminum oxide 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] Further, 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 membrane and form a dense and continuous structure.

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

[0011] In a second aspect, the embodiments of the present application provide a self-supporting gas separation membrane of preferentially oriented zeolitic imidazolate framework-8, which has preferential orientation and cubic morphology that together realize good co-planarity between crystals in the membrane and can be effectively applied to gas separation.

[0012] Further, the gas separation includes separation of 1,3-butadiene / n-butene, 1,3-butadiene / isobutene, 1,3-butadiene / n-butane, 1,3-butadiene / isobutane.

[0013] The technical scheme for solving the material technical problem of the present application is to provide a preferentially oriented zeolitic imidazolate framework-8 self-supporting gas separation membrane obtained according to the method.

[0014] Compared with the prior art, the present application has the beneficial effects that:

[0015] (1) The present application uses cetyltrimethylammonium bromide cationic surfactant as a capping agent for ZIF-8, so that the morphology of ZIF-8 is controlled from characteristic rhombohedron to cube, laying a foundation for good co-planarity between crystals.

[0016] (2) The cetyltrimethylammonium bromide with a polar hydrophilic group and a non-polar hydrophobic group simultaneously is in a state of hydrophobic end up and hydrophilic end down in an aqueous solution, and induces 2-methylimidazole ligands with a methyl polar group to arrange regularly in water.

[0017] The 2-methylimidazole ligands arrange regularly in water, and after adding zinc acetate dihydrate, a coordination reaction occurs to form regular arrangement of ZIF-8 crystals.

[0018] (3) Under the preparation strategy of pressure driving and epitaxial growth, a preferentially oriented pure ZIF-8 self-supporting membrane is formed, which together with the cube morphology reduces intercrystalline defects after assembly.

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

[0020] These aspects or other aspects of the present application will be more apparent in the following description of the embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0022] Figure 1 The present application provides a preferentially oriented zeolitic imidazolate framework-8 self-supporting gas separation membrane preparation mechanism schematic diagram.

[0023] Figure 2(a) surface topography and (b) cross-sectional topography of a dense layer on the surface of a preferentially oriented zeolitic imidazolate framework-8 self-supporting gas separation membrane according to the present invention;

[0024] Figure 3 (a) photograph and (b) overall cross-sectional topography of a preferentially oriented zeolitic imidazolate framework-8 self-supporting gas separation membrane according to the present invention;

[0025] Figure 4 (a) single component gas permeance and (b) ideal selectivity of C4 hydrocarbons of a preferentially oriented zeolitic imidazolate framework-8 self-supporting gas separation membrane according to the present invention.

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

[0027] In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be described below in connection with the drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of the present invention.

[0028] Embodiment 1

[0029] Step 1

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

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

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

[0033] Step 2

[0034] Repeat Step 1: according to the method of Step 1, prepare the same solution again.

[0035] Centrifugal treatment: centrifuge the mixed solution in Step 2 at a speed of 500-10000 r / min for 10-30 min.

[0036] Re-stirring: 5-50 mL of deionized water was added, and re-stirring was performed for 5-60 min at a stirring speed of 100-600 r / min.

[0037] Step 3:

[0038] Filtering: The solution obtained in Step 1 and Step 2 was filtered using a vacuum filtration system having a porous anodic aluminum oxide with a pore size of 50-500 nm and a thickness of 50-500 μm, using a pressure of 0.1-1.0 bar.

[0039] Preparation of growth solution: Zinc acetate dihydrate aqueous solution and 2-methylimidazole / cetyltrimethylammonium bromide aqueous solution were mixed to prepare a growth solution.

[0040] Standing: The growth solution was left to stand at room temperature for 10-60 min.

[0041] Suction filtration: The solution left to stand was subjected to suction filtration.

[0042] Drying: The membrane subjected to suction filtration was dried in a constant temperature and humidity chamber at a temperature of 25-80 °C and a humidity of 20-80% RH for 12-60 h.

[0043] Example 2:

[0044] Step 1:

[0045] The procedure of Step 1 in Example 1 was followed.

[0046] Step 2:

[0047] The procedure of Step 2 in Example 1 was followed, but after centrifugation, the stirring speed was adjusted to 200-400 r / min before re-stirring.

[0048] Step 3:

[0049] Filtering: A porous anodic aluminum oxide with a porosity of 40-60% was used.

[0050] Standing: The growth solution was left to stand at room temperature for 30 min.

[0051] Suction filtration: Suction filtration was performed using a suitable suction filtration device.

[0052] Drying: The membrane subjected to suction filtration was dried in a constant temperature and humidity chamber at a temperature of 30-60 °C and a humidity of 40-60% RH for 24 h.

[0053] Peeling: The gas separation membrane was peeled from the porous anodic aluminum oxide substrate.

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

[0055] Example Three:

[0056] Sample Preparation: Multiple ZIF-8 self-supporting gas separation membrane samples were prepared following the method in Example 2, but varying the type and concentration of surfactant.

[0057] Performance Testing: Gas separation tests were conducted on each sample, and the separation factor and permeation rate were recorded.

[0058] Structural Characterization: The microstructure of the membranes was analyzed using SEM, XRD, TEM, etc.

[0059] Result Analysis: The effects of different surfactants on membrane performance were compared to determine the optimal surfactant type and concentration.

[0060] Performance Testing:

[0061] Gas Permeation Rate Testing: Commercial gas permeation testing systems were used to measure the separation performance of 1,3-butadiene / n-butene, 1,3-butadiene / isobutene, 1,3-butadiene / n-butane, and 1,3-butadiene / isobutane.

[0062] Stability Testing: The prepared membranes were placed in a high temperature and high humidity environment, and the changes in their separation performance were continuously monitored.

[0063] Structural Characterization:

[0064] Scanning Electron Microscope (SEM): The surface morphology of the membranes was observed.

[0065] X-ray Diffraction (XRD): The crystal structure of the membranes was determined.

[0066] Transmission Electron Microscope (TEM): The internal structure of the membranes was observed.

[0067] Pore Size Distribution Analysis: Nitrogen adsorption / desorption isotherms were used to determine the pore size distribution of the membranes.

[0068] Result Analysis:

[0069] Data Analysis: Test results were recorded, and the performance differences of the membranes under different preparation conditions were analyzed.

[0070] Performance Evaluation: The applicability of the membranes in different gas separation scenarios was evaluated.

[0071] Example Four:

[0072] Sample Preparation: Samples were prepared following the method in Example 1, but varying the stirring conditions in Step 1, such as stirring speed, stirring time, etc.

[0073] Using the performance tests, structure characterization, and result analysis process described in Example 3, record the test results, analyze the performance differences of the membranes under different stirring conditions, and evaluate the applicability of the membranes in different gas separation scenarios.

[0074] Preparation of samples: 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 tests, structure characterization, and result analysis process described in Example 3, record the test results, analyze the performance differences of the membranes under different temperature and humidity conditions, and evaluate the applicability of the membranes in different gas separation scenarios.

[0076] The above description is only a preferred embodiment of the present application, and therefore cannot limit the scope of the present application. Any equivalent changes and modifications made in accordance with the scope and content of the present patent should still be within the scope of the present application.

Claims

1. A method for making a preferentially oriented zeolite imidazolate framework-8 self-supporting gas separation membrane, characterized in that, Comprising: Step 1: Dissolve zinc acetate dihydrate, 2-methylimidazole and cetyltrimethylammonium bromide in deionized water respectively, then add the cetyltrimethylammonium bromide aqueous solution into 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 into the 2-methylimidazole aqueous solution, and then mix with the zinc acetate dihydrate aqueous solution and stir, after centrifugal treatment, add deionized water and stir again; Step 3: Add the solutions obtained in steps 1a and 1b into a vacuum filtration system with porous anodic aluminum oxide, and use pressure filtration; then, use the zinc acetate dihydrate aqueous solution and the 2-methylimidazole / cetyltrimethylammonium bromide aqueous solution as a growth solution, stand at room temperature, perform suction filtration, and finally place in a constant temperature and humidity box for drying; peel off from the porous anodic aluminum oxide substrate to obtain the gas separation membrane; In step 1, the mass of zinc acetate dihydrate, 2-methylimidazole and cetyltrimethylammonium bromide is 0.1-5 g, 1-10 g and 0.0010-0.1 g respectively; the zinc acetate dihydrate, 2-methylimidazole and cetyltrimethylammonium bromide are dissolved in 1-20 mL, 5-50 mL and 5-50 mL of deionized water respectively; In step 2, the cetyltrimethylammonium bromide aqueous solution is added into 5-20 mL of 2-methylimidazole aqueous solution, mixed with the 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 for stirring again for 5-60 min at a stirring speed of 100-600 r / min; In step 3, the standing time at room temperature is 10-60 min; after suction filtration, place in a constant temperature and humidity box for drying for 12-60 h, wherein the temperature of the constant temperature and humidity box is controlled at 25-80℃ and the humidity is controlled at 20%-80%RH; In step 3, the pore size of the porous anodic aluminum oxide is 50-500 nm and the thickness is 50-500 μm; In step 2, the pressure of the pressure filtration is 0.1-1.0 bar.

2. The production method according to claim 1, characterized by, In step 2, the mass of zinc acetate dihydrate, 2-methylimidazole and cetyltrimethylammonium bromide is 0.1-5 g, 1-10 g and 0.0010-0.1 g respectively; the zinc acetate dihydrate, 2-methylimidazole and cetyltrimethylammonium bromide are dissolved in 1-20 mL, 5-50 mL and 5-50 mL of deionized water respectively.

3. The preparation method according to claim 1, wherein, In step 3, the temperature and humidity conditions of the constant temperature and humidity box can promote the uniform growth of the self-supporting gas separation, forming a dense and continuous structure.

4. The preparation method according to claim 1, wherein, The porosity of the porous anodic aluminum oxide in step 3 is between 30%-70% to ensure the gas permeation performance while maintaining sufficient mechanical strength; The preparation of the self-supporting gas separation membrane in step 3 further comprises forming a dense layer on the porous anodic aluminum oxide substrate, and the thickness of the dense layer is 0.1-5 μm to improve the selectivity and stability of the membrane.

5. The preferentially oriented zeolitic imidazolate framework-8 self-supported gas separation membrane prepared according to the method of any one of claims 1-4, characterized in that, The preferentially oriented zeolitic imidazolate framework-8 self-supporting gas separation membrane has preferential orientation and cubic morphology, which together realize good co-planarity between crystals in the membrane and can be effectively applied to gas separation.

6. The preferentially oriented zeolitic imidazolate framework-8 free-standing gas separation membrane prepared according to the method of any one of claims 1-4, characterized in that, The gas separation includes separation of 1,3-butadiene / n-butene, 1,3-butadiene / isobutene, 1,3-butadiene / n-butane and 1,3-butadiene / isobutane.

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