A two-dimensional rub-18 zeolite membrane, its preparation method and application in gas separation

Abstract

The application provides a two-dimensional RUB-18 zeolite membrane and a preparation method and application thereof in gas separation, and belongs to the technical field of two-dimensional nanosheet membrane preparation and gas separation, and the preparation method of the two-dimensional RUB-18 zeolite membrane comprises the following steps: ball-milling stripping to obtain a two-dimensional RUB-18 zeolite nanosheet solution; and placing a porous substrate into the two-dimensional RUB-18 zeolite nanosheet solution to perform electrophoretic deposition. The application provides a mild method for preparing two-dimensional RUB-18 zeolite nanosheets by ball-milling stripping, and the two-dimensional RUB-18 zeolite membrane is prepared from the two-dimensional RUB-18 zeolite nanosheets, which is simple, efficient, low in cost, and a two-dimensional RUB-18 zeolite membrane with a thickness of 200-800 nm can be grown on the porous substrate in 5-50 minutes, and the two-dimensional RUB-18 zeolite membrane can be successfully used for gas separation, and the permeability and selectivity can be considered.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of two-dimensional nanosheet membrane preparation and gas separation, and particularly relates to a two-dimensional RUB-18 zeolite membrane and a preparation method thereof and application thereof in gas separation. BACKGROUND

[0002] Hydrogen is one of the cleanest and greenest fuels in the world, which can replace traditional fossil energy. However, the separation process is one of the processes with the largest energy consumption, accounting for 45% to 55% of the total energy consumption of the global industry. Therefore, it has become increasingly urgent to develop efficient separation processes to alleviate the heavy energy burden. Membrane separation is a relatively new concept, but it has developed rapidly due to its low energy consumption, high efficiency, sustainability and easy operation. However, traditional polymer separation membranes generally have a trade-off effect between permeability and selectivity, and both cannot be achieved simultaneously.

[0003] The unique feature of zeolite molecular sieves is that their framework structure is composed of shared oxygen tetrahedra TO4 and central T atoms (such as Si, Al or others), and traditional molecular sieve membranes contain three-dimensional (3D) framework topology. According to the literature [Varoon K, Zhang X, Elyassi B, et al. Dispersible exfoliated zeolite nanosheets and their application as a selective membrane [J]. Science, 2011, 334 (6052): 72-75], it has become a frontier research topic to construct high-performance molecular sieve membranes using two-dimensional nanosheets with atomic thickness. Compared with three-dimensional nanosheets, two-dimensional nanosheets have only one atomic thickness, which can minimize the transmission resistance and maximize the flux; in addition, they are more flexible in mechanics. They emphasize that guest molecules can penetrate into two-dimensional molecular sieve membranes and achieve precise molecular sieving by relying on the pores in the two-dimensional nanosheets or the interlayer channels between adjacent nanosheets, which provides us with unprecedented freedom to adjust their pore size and function. These advantages make two-dimensional molecular sieve membranes an excellent choice for high-performance separation membranes. However, it is difficult to obtain zeolite nanosheets suitable for separating mixed gases, and self-assembly into membranes is prone to defects. SUMMARY

[0004] To solve the above technical problems, the application provides a two-dimensional RUB-18 zeolite membrane and a preparation method thereof and application thereof in gas separation.

[0005] To achieve the above-mentioned purpose, the application provides the following technical solutions.

[0006] One of the technical solutions of the application is:

[0007] A method for preparing a two-dimensional RUB-18 zeolite membrane, comprising the following steps:

[0008] Ball-milling to obtain a two-dimensional RUB-18 zeolite nanosheet solution;

[0009] Putting a porous substrate into the two-dimensional RUB-18 zeolite nanosheet solution and performing electrophoretic deposition.

[0010] Further, the method for ball-milling to obtain a two-dimensional RUB-18 zeolite nanosheet solution is as follows:

[0011] Mixing RUB-18 zeolite powder with a mixed solution of methanol and water, ball-milling to obtain a two-dimensional RUB-18 zeolite nanosheet solution.

[0012] Further, the volume ratio of the methanol and water is (0.2-5) : 1.

[0013] Further, the ball-milling time is 5-24 h and the rotation speed is 50-500 rpm.

[0014] Further, the method for ball-milling to obtain a two-dimensional RUB-18 zeolite nanosheet solution is as follows: taking 5-50 mg of RUB-18 powder and adding it into a ball-milling tank containing a mixed solution of methanol and water in a volume ratio (mL) of 5:1-1:5 for ball-milling, thereby obtaining a two-dimensional RUB-18 zeolite nanosheet solution; the ball-milling time is 5-24 h and the rotation speed of the ball-milling machine is 50-500 rpm. The type and ratio of the solvent for wet ball-milling have an influence on the ball-milling effect. In order to achieve a good stripping effect (the nanosheets are as thin as possible), the ratio of the solvent is very important. The stripping effect is not obvious when a single solvent is used. In order to make the stripped nanosheets well dispersed in the solution, the selection of the solvent is also very important. If the nanosheets are not well dispersed in the solvent, they are prone to aggregate and are not easy to form a film. Further, the method for synthesizing RUB-18 zeolite powder is as follows: mixing raw materials SiO2, NaOH and H2O in a mass-volume ratio of (5-30) g:(0.5-5) g:(1-30) mL, magnetically stirring for 0.5-4 h, transferring into a reaction kettle and reacting at 70-150 ℃ for 5-20 days, and then drying in an oven after the reaction is completed, thereby obtaining RUB-18 zeolite powder.

[0015] Further, the porous substrate is polyvinylidene fluoride (PVDF), polyamide (PA), polyether sulfone (PES), sulfonated polyether sulfone (SPES), polysulfone (PSF), polytetrafluoroethylene (PTFE), sulfonated polysulfone (SPSF), polyethylene terephthalate (PET), or α-alumina, preferably PVDF, PET, PTFE, anodized aluminum, or α-alumina, and more preferably α-alumina. Different substrates have an impact on the performance of the film. If the pore size of the selected substrate is too large, the nanosheets will collapse when stacked; if the pore size is too small, it will affect the gas permeation amount; the selected substrate has a smooth surface, which helps to reduce defects during film formation; the surface of the α-alumina substrate is smoother, and the pore size is more uniform, so the substrate is preferably α-alumina.

[0016] Further, during electrophoretic deposition, the concentration of the two-dimensional RUB-18 zeolite nanosheet solution is 0.1-10 mg / mL, the voltage is 1-40 V, the current is 0.001-0.010 A, and the time is 5-50 min. The voltage, time, and solution concentration during electrophoretic deposition all affect the performance of the film. If the voltage is too small, the electric field will be too weak, the nanosheets will move and stack too little, the substrate will not be full, and defects will occur; if the voltage is too large, the nanosheets will aggregate, and defects will occur. Under normal circumstances, the longer the time, the more nanosheets stacked on the substrate, and the fewer defects produced, but the film thickness will increase, and the gas permeation amount will decrease. If the solution is too dilute, there will be too few nanosheets, and defects will occur easily; if the solution is too concentrated, the nanosheets will aggregate or have thick sheets on the substrate, and defects will occur easily. Therefore, the voltage, time, and solution concentration during electrophoretic deposition are limited.

[0017] Further, after electrophoretic deposition, the electrophoretic deposition product is dried to obtain a two-dimensional RUB-18 zeolite film.

[0018] Further, the drying method is not limited in the present application, and any drying method that can achieve the drying effect can be used, such as natural ventilation drying, normal temperature vacuum drying, or low temperature vacuum drying. The drying temperature is 25-80℃, and the drying time is 6-48 h.

[0019] The present application provides a mild method for preparing two-dimensional RUB-18 zeolite nanosheets by ball milling, which is simple and efficient when preparing two-dimensional RUB-18 zeolite films from two-dimensional RUB-18 zeolite nanosheets, has low cost, and can grow a two-dimensional RUB-18 zeolite film with a thickness of 200-800 nm on a porous substrate in 5-50 minutes. The two-dimensional RUB-18 zeolite film can be successfully used for gas separation, and can balance permeability and selectivity.

[0020] Technical solution two of the present application:

[0021] A two-dimensional RUB-18 zeolite membrane prepared according to the above method has a thickness of 200-800 nm. The application prepares a separation membrane based on a novel two-dimensional material, and since the size / physical and chemical properties of the assembly unit and the interlayer spacing can be regulated respectively, the permeability and selectivity can be optimized respectively, and the bottleneck limitation of the upper limit of traditional polymer membrane separation can be broken through.

[0022] The third technical solution of the application is:

[0023] The two-dimensional RUB-18 zeolite is applied to gas separation, and the gas is at least one of hydrogen, a gas with different kinetic diameters and characteristics from hydrogen.

[0024] Further, the gas is one or two of hydrogen (H2, 0.29 nm (diameter, same below)), carbon dioxide (CO2, 0.33 nm), nitrogen (N2, 0.36 nm), methane (CH4, 0.38 nm), ethylene (C2H4, 0.39 nm), propylene (C3H6, 0.40 nm), ethane (C2H6, 0.42 nm) and propane (C3H8, 0.43 nm), and especially exhibits high selectivity and good hydrothermal stability for H2 / CO2 separation; when the separated gas is two, the volume ratio of the separated gas is 1:1, and the total flow rate is 20-200 mL; the purge gas is one of argon (Ar), helium (He) and methane (CH4), and the total flow rate is 20-100 mL.

[0025] Compared with the prior art, the application has the following advantages and technical effects:

[0026] (1) The two-dimensional RUB-18 zeolite membrane with good gas separation selectivity, flux and stability is simply prepared by electrophoretic deposition technology, and the membrane thickness is very small (in the nanometer level, only 200-800 nm), which overcomes the defect that the membranes of the prior art are micrometer level in thickness, and the membrane of the application has good industrial amplification application prospect.

[0027] (2) The two-dimensional RUB-18 zeolite membrane is applied to gas separation for the first time.

[0028] (3) The RUB-18 nanosheet is successfully peeled off by the wet ball milling method.

[0029] (4) When the two-dimensional RUB-18 zeolite membrane prepared by the application is applied to gas separation, especially H2 / CO2 separation, it can exhibit good gas separation selectivity and flux, and has good water vapor and long-period stability (>100 h), and is very suitable for industrial large-scale production, and has good industrial amplification application potential in the field of gas separation. BRIEF DESCRIPTION OF DRAWINGS

[0030] The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate preferred embodiments of the present application and serve to explain the principles of the present application. In these drawings:

[0031] Figure 1 A scanning electron microscope (SEM) image of the two-dimensional RUB-18 zeolite nanosheets of Example 1;

[0032] Figure 2 A graph of the performance of the two-dimensional RUB-18 zeolite membrane of Example 1 in separating different gases. DETAILED DESCRIPTION

[0033] Various illustrative embodiments of the present application are described below in detail. The detailed description set forth below in connection with the appended drawings is intended as a description of the present application and is not intended to represent the only embodiments in which the present application can be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the present application. However, it will be apparent to those skilled in the art that the present application can be practiced without these specific details. In some instances, well-known structures and functions have not been described in detail in order to avoid obscuring the concept of the present application.

[0034] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. In addition, where particular ranges of values are given, it is meant to include every possible value within the range, as well as the range itself. Each smaller range that falls within the broader ranges is also a contemplated embodiment. The upper and lower limits of these smaller ranges can independently be included or excluded in the smaller ranges.

[0035] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, the preferred methods and materials are described. All patents, patent applications, publications, and descriptions mentioned herein are incorporated by reference to the extent allowed by law. Nothing herein is to be construed as an admission that the application is not entitled to antedate such disclosure by virtue of prior application.

[0036] Various modifications and changes can be made to the specific embodiments of the present application described herein without departing from the scope or spirit of the application. Other embodiments of the application will be apparent to those of ordinary skill in the art from the description and examples herein. The description and examples are illustrative of the application and are not intended to limit the scope of the application in any way.

[0037] As used herein, the terms "comprise", "comprising", "include", "including", "have", "having" or the like are open-ended and do not exclude additional, unrecited elements or method steps.

[0038] Each of the raw materials used in the embodiments of the present application is commercially available.

[0039] The technical solutions of the present application are further described below through examples.

[0040] Example 1

[0041] The preparation method of the two-dimensional RUB-18 zeolite membrane in this example is as follows:

[0042] (1) Hydrothermal synthesis of RUB-18 zeolite powder: the raw materials SiO2, NaOH and H2O were weighed and mixed in a mass-volume ratio of 15 g: 2.2 g: 10 mL, magnetically stirred for 2 h, transferred into a reaction kettle and reacted at 100℃ for 18 days. After the reaction was completed, it was placed in an oven for drying to obtain RUB-18 zeolite powder;

[0043] (2) Exfoliation to obtain a RUB-18 zeolite nanosheet solution: 30 mg of the RUB-18 zeolite powder synthesized in step (1) was added to a ball mill tank containing 20 mL of a mixed solution of methanol and water in a volume ratio of 1:1 for ball milling. The ball milling time was 18 h and the speed of the ball mill was 350 rpm, thereby obtaining a two-dimensional RUB-18 zeolite nanosheet solution. The scanning electron microscope (SEM) image of the two-dimensional RUB-18 zeolite nanosheets in this example is shown in Figure 1 . The specific method was to drop the solution containing zeolite nanosheets on a gold-sprayed anodic aluminum oxide (AAO), and after the solvent was volatilized, the two-dimensional RUB-18 zeolite nanosheets were observed under the electron microscope. Figure 1 The middle part similar to a square in Figure 1 indicates that the nanosheets were successfully obtained after ball milling, and the morphology of the nanosheets was well maintained and not damaged.

[0044] (3) The α-alumina was used as a porous substrate and was placed in a two-dimensional RUB-18 zeolite nanosheet solution with a concentration of 8 mg / mL for electrophoretic deposition. The voltage was 20 V, the current was 0.002 A, and the electrophoretic deposition time was 20 min. The concentration calculation method of this step was: the mass of the two-dimensional RUB-18 zeolite nanosheets divided by the volume of the solvent. The mass of the two-dimensional RUB-18 zeolite nanosheets was obtained by suction filtration onto a non-polar substrate and scraping down for weighing (the same below). The thickness of the membrane was observed to be 300 nm under a scanning electron microscope (SEM).

[0045] (4) The electrophoretic deposition product of step (3) was dried by low-temperature vacuum drying. The drying temperature was 60℃ and the drying time was 12 h, thereby obtaining a two-dimensional RUB-18 zeolite membrane.

[0046] The two-dimensional RUB-18 zeolite membrane prepared in this example was applied in gas separation:

[0047] The prepared two-dimensional RUB-18 zeolite membrane was assembled into a gas mold for gas separation test. Specifically, the dried two-dimensional RUB-18 zeolite membrane was placed in the mold, the single gas or mixed gas to be tested was connected to the upper part of the mold, the purge gas was connected to the lower part of the mold to drive the gas through the membrane continuously, and the other part was connected to the chromatograph to observe the chromatograph output. The types of raw gas were hydrogen (H2, 0.29 nm) and carbon dioxide (CO2, 0.33 nm), hydrogen (H2, 0.29 nm) and nitrogen (N2, 0.36 nm), hydrogen (H2, 0.29 nm) and methane (CH4, 0.38 nm), and hydrogen (H2, 0.29 nm) and propylene (C3H6, 0.40 nm), with a gas volume ratio of 1:1 and a total flow rate of 50 mL; the purge gas was argon (Ar) with a total flow rate of 25 mL. The gas separation performance was detected by Agilent gas chromatograph 7890A and calculated.

[0048] The gas flux in the experimental test parameters is represented by P, with the unit of GPU, 1 GPU = 3.35 x 10 -10 mol·m -2 ·s -1 ·pa -1 , the gas fluxes are P(H2) = 420 GPU, P(CO2) = 1.9 GPU, P(N2) = 1.8 GPU, P(CH4) = 1.6 GPU, and P(C3H6) = 0.9 GPU, and the gas selectivities corresponding to H2 / CO2, H2 / N2, H2 / CH4, and H2 / C3H6 are 221, 233, 263, and 467, respectively. The experimental results are shown in Figure 2

[0049] The two-dimensional RUB-18 zeolite membrane of the present embodiment was placed in a mold and mixed with hydrogen and carbon dioxide gas. First, continuous testing was performed for 5 days, then mixed with hydrogen and carbon dioxide gas containing 3% water vapor (wet gas) for 5 days, and then returned to dry gas. The hydrogen and carbon dioxide gas selectivity changed from 221 to 215, and the hydrogen permeation amount changed from 420 GPU to 434 GPU, both of which did not change significantly, indicating that the membrane can also separate gas normally in the presence of water vapor and has good stability.

[0050] Example 2

[0051] The preparation method of the two-dimensional RUB-18 zeolite membrane of the present embodiment is as follows:

[0052] (1) Hydrothermal synthesis of RUB-18 zeolite powder: raw materials SiO2, NaOH and H2O were weighed according to the mass-volume ratio of 6g:2g:13mL and mixed, then magnetically stirred for 0.5h, transferred into a reaction kettle and reacted at 70℃ for 20 days. After the reaction was completed, the reaction kettle was placed in an oven for drying to obtain RUB-18 zeolite powder; ​

[0053] (2) Peeling to obtain RUB-18 zeolite nanosheet solution: 50 mg of RUB-18 zeolite powder synthesized in step (1) was taken into a ball mill tank containing a mixed solution of methanol and water in a volume ratio of 5:1 at 20 mL, and ball milling was performed at a speed of 500 rpm for 5 h, thereby obtaining a two-dimensional RUB-18 zeolite nanosheet solution;

[0054] (3) PVDF was taken as a porous substrate and placed into a RUB-18 zeolite nanosheet solution with a concentration of 10 mg / mL, and electrophoretic deposition was performed at a voltage of 40 V and a current of 0.001 A for 5 min;

[0055] (4) The product of electrophoretic deposition in step (3) was dried by vacuum drying at room temperature, the drying temperature was 25 °C, and the drying time was 48 h, thereby obtaining a two-dimensional RUB-18 zeolite film.

[0056] The two-dimensional RUB-18 zeolite film prepared in this example was applied to gas separation:

[0057] The raw gas was hydrogen (H2) and carbon dioxide (CO2), the total flow rate of the raw gas was 50 mL, and the volume ratio was 1:1; the purge gas was argon (Ar), and the total flow rate was 25 mL. The gas separation performance was calculated after detection by Agilent gas chromatograph 7890A.

[0058] The gas fluxes tested in the experiment were P(H2) = 2092 GPU and P(CO2) = 308 GPU, and the H2 / CO2 gas selectivity was 6.8.

[0059] The two-dimensional RUB-18 zeolite film of this example was placed in a mold, and a mixed gas of hydrogen and carbon dioxide was introduced, and then continuous testing was performed for 5 days, and then a mixed gas of hydrogen and carbon dioxide containing 3% water vapor (moisture) was introduced for 5 days, and then dry gas was introduced again. The hydrogen and carbon dioxide mixed gas selectivity changed from 6.8 to 6, and the hydrogen permeation amount changed from 2092 GPU to 2100 GPU, and there was no obvious change, indicating that the film can also normally separate gas in the presence of water vapor and has good stability.

[0060] Example 3

[0061] The preparation method of the two-dimensional RUB-18 zeolite film of this example is as follows:

[0062] (1) Hydrothermal synthesis of RUB-18 powder: raw materials SiO2, NaOH and H2O were weighed and mixed in a mass-volume ratio of 30 g:5 g:18 mL, respectively, and magnetically stirred for 4 h, and then transferred into a reaction kettle and reacted at 150 °C for 5 days. After the reaction was completed, it was placed in an oven for drying, thereby obtaining RUB-18 zeolite powder;

[0063] (2) Peeling and obtaining RUB-18 zeolite nanosheet solution: 5 mg of RUB-18 zeolite powder synthesized in step (1) was taken into a ball mill tank containing a 20 mL mixed solution of methanol and water in a volume ratio of 1:5 for ball milling, the ball milling time was 24 h, and the rotation speed of the ball mill was 50 rpm, thereby obtaining a two-dimensional RUB-18 zeolite nanosheet solution;

[0064] (3) The PA was placed into the RUB-18 zeolite nanosheet solution with a concentration of 0.1 mg / mL as a porous substrate, electrophoretic deposition was performed at a voltage of 1 V and a current of 0.01 A for 50 min;

[0065] (4) The electrophoretically deposited product of step (3) was dried by natural ventilation drying at a temperature of 25°C for 24 h, thereby obtaining a two-dimensional RUB-18 zeolite film.

[0066] Application of the two-dimensional RUB-18 zeolite film prepared in this example in gas separation:

[0067] The raw gas was hydrogen (H2) and carbon dioxide (CO2), the total flow rate of the raw gas was 50 mL, the volume ratio was 1:1, the purge gas was argon (Ar), and the total flow rate was 25 mL. The gas separation performance was calculated after detection by Agilent gas chromatograph 7890A.

[0068] The gas fluxes tested in the experiment were P(H2) = 625 GPU and P(CO2) = 3.7 GPU, and the H2 / CO2 gas selectivity was 169.

[0069] The two-dimensional RUB-18 zeolite film of this example was placed in a mold, and a mixed gas of hydrogen and carbon dioxide was introduced. First, continuous testing was performed for 5 days, then a mixed gas of hydrogen and carbon dioxide containing 3% water vapor (moisture) was introduced for 5 days, and then dry gas was introduced again. The hydrogen / carbon dioxide mixed gas selectivity changed from 169 to 158, and the hydrogen permeation rate changed from 625 GPU to 600 GPU, both of which did not change significantly, indicating that the film can also separate gas normally in the presence of water vapor and has good stability.

[0070] Example 4

[0071] The preparation method of the two-dimensional RUB-18 zeolite film of this example is as follows:

[0072] (1) Hydrothermal synthesis of RUB-18 powder: SiO2, NaOH and H2O were weighed and mixed according to a mass / volume ratio of 25 g:4 g:12 mL, respectively, and then magnetically stirred for 3 h. The mixture was then transferred to a reaction kettle and reacted at 120°C for 16 days. After the reaction was completed, the reaction kettle was placed in an oven for drying, thereby obtaining RUB-18 zeolite powder;

[0073] (2) Peeling and obtaining RUB-18 zeolite nanosheet solution: 30 mg of RUB-18 zeolite powder synthesized in step (1) was taken into a ball mill tank containing a 20 mL mixed solution of methanol and water in a volume ratio of 1:1 for ball milling, the ball milling time was 15 h, and the rotation speed of the ball mill was 200 rpm, thereby obtaining a two-dimensional RUB-18 zeolite nanosheet solution;

[0074] (3) PET was taken as a porous substrate and was put into a two-dimensional RUB-18 zeolite nanosheet solution with a concentration of 8 mg / mL for electrophoretic deposition, the voltage was 30 V, the current was 0.005 A, and the electrophoretic deposition time was 20 min;

[0075] (4) The product of step (3) was dried by low-temperature vacuum drying, the drying temperature was 50°C, and the drying time was 18 h, thereby obtaining a two-dimensional RUB-18 zeolite film.

[0076] The two-dimensional RUB-18 zeolite film prepared in this example was used in gas separation:

[0077] The raw gas was hydrogen (H2) and carbon dioxide (CO2), the total flow rate of the raw gas was 50 mL, the volume ratio was 1:1, the sweeping gas was helium (He), and the total flow rate was 25 mL. The gas separation performance was detected by Agilent gas chromatograph 7890A and was calculated.

[0078] The gas fluxes tested in the experiment were P(H2) = 658 GPU and P(CO2) = 5.7 GPU, and the H2 / CO2 gas selectivity was 115.

[0079] The two-dimensional RUB-18 zeolite film of this example was put into a mold, and a mixed gas of hydrogen and carbon dioxide was introduced, which was continuously tested for 5 days, and then a mixed gas of hydrogen and carbon dioxide containing 3% water vapor (moisture) was introduced for 5 days, and then dry gas was introduced again. The hydrogen and carbon dioxide mixed gas selectivity changed from 115 to 105, and the hydrogen permeation changed from 658 GPU to 623 GPU, which did not change significantly, indicating that the film could also normally separate gas in the presence of water vapor and had good stability.

[0080] Example 5

[0081] The preparation method of the two-dimensional RUB-18 zeolite film of this example was as follows:

[0082] (1) Hydrothermal synthesis of RUB-18 zeolite powder: raw materials SiO2, NaOH and H2O were weighed and mixed in a mass-volume ratio of 10 g:3 g:20 mL, magnetically stirred for 2 h, transferred into a reaction kettle, and reacted at 100°C for 20 days. After the reaction, it was dried in an oven to obtain RUB-18 zeolite powder;

[0083] (2) Peeling to obtain RUB-18 zeolite nanosheet solution: 30 mg of RUB-18 zeolite powder synthesized in step (1) was taken into a ball mill tank containing 20 mL of a mixed solution of methanol and water in a volume ratio of 1:3, and ball milling was performed at a rotation speed of 400 rpm for 10 h, thereby obtaining a two-dimensional RUB-18 zeolite nanosheet solution;

[0084] (3) PTFE was taken as a porous substrate and placed into the RUB-18 zeolite nanosheet solution with a concentration of 8 mg / mL, and electrophoretic deposition was performed at a voltage of 10 V and a current of 0.008 A for 25 min.

[0085] (4) The product of electrophoretic deposition in step (3) was dried by low-temperature vacuum drying at a temperature of 40 °C for 40 h, thereby obtaining a two-dimensional RUB-18 zeolite film.

[0086] The two-dimensional RUB-18 zeolite film prepared in this example was used for gas separation:

[0087] The raw gas was hydrogen (H2) and carbon dioxide (CO2), and the total flow rate of the raw gas was 50 mL with a volume ratio of 1:1; the sweeping gas was methane (CH4) with a total flow rate of 25 mL. The gas separation performance was calculated after detection by Agilent gas chromatograph 7890A.

[0088] The gas fluxes tested in the experiment were P(H2) = 320 GPU and P(CO2) = 1.7 GPU, and the H2 / CO2 gas selectivity was 188.

[0089] The two-dimensional RUB-18 zeolite film of this example was placed in a mold and mixed with hydrogen and carbon dioxide, and then continuously tested for 5 days, and then mixed with hydrogen and carbon dioxide containing 3% water vapor (moisture) and tested for 5 days, and then returned to dry gas. The hydrogen and carbon dioxide mixed gas selectivity changed from 188 to 169, and the hydrogen permeation flux changed from 320 GPU to 298 GPU, which did not change significantly, indicating that the film can also normally separate gas in the presence of water vapor and has good stability.

[0090] Example 6

[0091] The same as example 1, except that step (3) was: α-alumina was taken as a porous substrate and placed into the two-dimensional RUB-18 zeolite nanosheet solution with a concentration of 8 mg / mL, and electrophoretic deposition was performed at a voltage of 20 V and a current of 0.002 A for 50 min.

[0092] The two-dimensional RUB-18 zeolite film prepared in this example was used for gas separation:

[0093] The raw gas is hydrogen (H2) and propane (C3H8), the total flow rate of the raw gas is 50 mL, and the volume ratio is 1:1; the purge gas is argon (Ar), and the total flow rate is 25 mL. The gas separation performance is calculated after detection by Agilent gas chromatograph 7890A.

[0094] The tested gas fluxes are P(H2) = 210 GPU and P(C3H8) = 0.628 GPU, and the H2 / C3H8 gas selectivity is 334.

[0095] The two-dimensional RUB-18 zeolite membrane of the embodiment is placed in a mold, and a mixed gas of hydrogen and propylene is introduced. First, continuous testing is performed for 5 days, then a mixed gas of hydrogen and propylene containing 3% water vapor (wet gas) is introduced for 5 days, and then dry gas is connected back. The hydrogen-propane mixed gas selectivity changes from 334 to 323, and the hydrogen permeation rate changes from 210 GPU to 205 GPU, both of which do not change significantly, indicating that the membrane can also normally separate gas in the presence of water vapor and has good stability.

[0096] Example 7

[0097] The same as example 1, except that step (3) is: the PET is placed into the two-dimensional RUB-18 zeolite nanosheet solution with a concentration of 8 mg / mL as a porous substrate, and electrophoretic deposition is performed at a voltage of 30 V, a current of 0.001 A, and an electrophoretic deposition time of 30 min.

[0098] The two-dimensional RUB-18 zeolite membrane prepared in this embodiment is used for gas separation:

[0099] The raw gas is hydrogen (H2) and ethylene (C2H4), the total flow rate of the raw gas is 20 mL, and the volume ratio is 1:1; the purge gas is argon (Ar), and the total flow rate is 20 mL. The gas separation performance is calculated after detection by Agilent gas chromatograph 7890A.

[0100] The tested gas fluxes are P(H2) = 362 GPU and P(C2H4) = 6.6 GPU, and the H2 / C2H4 gas selectivity is 55.

[0101] The two-dimensional RUB-18 zeolite membrane of the embodiment is placed in a mold, and a mixed gas of hydrogen and ethylene is introduced. First, continuous testing is performed for 5 days, then a mixed gas of hydrogen and ethylene containing 3% water vapor (wet gas) is introduced for 5 days, and then dry gas is connected back. The hydrogen-ethylene mixed gas selectivity changes from 55 to 53, and the hydrogen permeation rate changes from 362 GPU to 351 GPU, both of which do not change significantly, indicating that the membrane can also normally separate gas in the presence of water vapor and has good stability.

[0102] Example 8

[0103] The same as example 1, except that PTFE is used as the porous substrate in step (3).

[0104] The two-dimensional RUB-18 zeolite membrane prepared in this example is used for gas separation:

[0105] The raw gas is hydrogen (H2) and ethylene (C2H4), and the total flow rate of the raw gas is 100 mL with a volume ratio of 1:1; the purge gas is helium (He), and the total flow rate is 100 mL. The gas separation performance is calculated after detection by Agilent gas chromatograph 7890A.

[0106] The gas fluxes tested in the experiment are P(H2) = 1423 GPU and P(C2H4) = 54 GPU, and the H2 / C2H4 gas selectivity is 26.

[0107] The two-dimensional RUB-18 zeolite membrane of this example is placed in a mold, and a mixed gas of hydrogen and ethylene is introduced. First, it is continuously tested for 5 days, and then a mixed gas of hydrogen and ethylene containing 3% water vapor (wet gas) is introduced for 5 days. Then, the dry gas is returned, and the hydrogen-ethylene mixed gas selectivity changes from 26 to 23, and the hydrogen permeation rate changes from 1423 GPU to 1416 GPU, both of which do not change significantly, indicating that the membrane can also separate gas normally in the presence of water vapor and has good stability.

[0108] Comparative Example 1 (membrane prepared by ultrasonic exfoliation)

[0109] (1) Hydrothermal synthesis of RUB-18 zeolite powder: raw materials SiO2, NaOH and H2O are weighed according to a mass-volume ratio of 15g:2.2g:10mL and mixed, then magnetically stirred for 2h, and then transferred to a reaction kettle for reaction at 100℃ for 18 days. After the reaction is completed, it is placed in an oven for drying to obtain RUB-18 zeolite powder;

[0110] (2) Exfoliation to obtain RUB-18 zeolite nanosheet solution: 30mg of RUB-18 zeolite powder synthesized in step (1) is taken and added to a 20mL mixed solution containing methanol and water in a volume ratio of 1:1 in a ultrasonic machine, ultrasonic time is 5h, ultrasonic power is 200W, and temperature is maintained at about 30℃, thereby obtaining a two-dimensional RUB-18 zeolite nanosheet solution;

[0111] (3) Put α-alumina as a porous substrate into a two-dimensional RUB-18 zeolite nanosheet solution with a concentration of 8mg / mL, and perform electrophoretic deposition with a voltage of 20V and a current of 0.002A for 20min;

[0112] (4) The electrophoretically deposited product of step (3) is dried by low-temperature vacuum drying, the drying temperature is 60℃, and the drying time is 12h, to obtain a two-dimensional RUB-18 zeolite membrane.

[0113] The two-dimensional RUB-18 zeolite membrane prepared in the present comparative example was applied in gas separation: the gas separation test was the same as in Example 1.

[0114] The gas flux in the experimental test parameters is represented by P, with the unit of GPU, 1 GPU = 3.35 x 10 -10 mol·m -2 ·s -1 ·pa -1 , the gas fluxes are P(H2) = 2430 GPU, P(CO2) = 162 GPU, P(N2) = 405 GPU, P(CH4) = 270 GPU, and P(C3H6) = 105 GPU, respectively, and the gas selectivities corresponding to H2 / CO2, H2 / N2, H2 / CH4, and H2 / C3H6 are 15, 6, 9, and 23, respectively. It can be seen that the RUB-18 zeolite membrane prepared by the ultrasonic exfoliation method basically has no practical application performance, and therefore no stability test was performed.

[0115] Comparative Example 2

[0116] The same as in Example 1, except that in step (2), methanol was replaced by an equal amount of isopropanol during ball milling.

[0117] The nanosheets were not well dispersed in the solution of isopropanol and water, the nanosheets were massively aggregated, the membrane was not dense, and no gas separation performance was obtained.

[0118] Comparative Example 3

[0119] The same as in Example 1, except that in step (2), the volume ratio of methanol to water was 1:10 during ball milling.

[0120] Due to the excessive amount of water added in the present comparative example, the effect of ball milling exfoliation was reduced, there were many large blocks in the solution or aggregation, the film forming effect was poor, there were many defects, and no gas separation performance was obtained.

[0121] Comparative Example 4

[0122] The same as in Example 1, except that in step (3), the α-alumina was replaced by nylon.

[0123] Due to the excessively large pore size of the substrate in the present comparative example, the nanosheets were easy to collapse during stacking, the film forming had many defects, and had no practical application value, and therefore no subsequent performance test was performed.

[0124] Comparative Example 5

[0125] The same as in Example 1, except that in step (3), the α-alumina was replaced by small-pore AAO (average pore size of 50 nm).

[0126] Due to the too small pore size of the substrate in the present comparative example, the gas permeation amount is affected, which has no practical application value, so no subsequent performance test is carried out.

[0127] Comparative Example 6 (vacuum suction filtration film)

[0128] The same as Example 1, except that in step (3), the electrophoretic deposition film is changed to suction filtration film, and the specific method is as follows: pour the zeolite nanosheet solution with a concentration of 8 mg / mL into the suction filtration device, start suction filtration, and stop suction filtration after the solution is filtered out.

[0129] The two-dimensional RUB-18 zeolite film prepared in the present comparative example is used for gas separation:

[0130] The raw gas is hydrogen (H2) and carbon dioxide (CO2), the total flow rate of the raw gas is 50 mL, and the volume ratio is 1:1; the purge gas is methane (CH4), and the total flow rate is 25 mL. The gas separation performance is calculated after detection by Agilent gas chromatograph 7890A.

[0131] The gas fluxes tested in the experiment are P(H2) = 120 GPU and P(CO2) = 3.7 GPU, and the H2 / CO2 gas selectivity is 32.

[0132] Put the two-dimensional RUB-18 zeolite film of the present comparative example into the mold, and pass in the mixed gas of hydrogen and carbon dioxide, first continuously test for 5 days, then pass in the mixed gas of hydrogen and carbon dioxide containing 3% water vapor (moisture), test for 5 days, and then pass in the dry gas again. The hydrogen and carbon dioxide mixed gas selectivity changes from 32 to 16, the hydrogen permeation amount changes from 120 GPU to 352 GPU, and both the selectivity and the permeation amount change obviously, indicating that the film is difficult to separate gas in a water vapor environment for a long time, and the stability is general.

[0133] Comparative Example 7

[0134] The same as Example 1, except that in step (3), the film forming voltage is changed from 20 V to 50 V.

[0135] Due to the too high voltage in the present comparative example, the nanosheet rapidly settles in a short time, the film is not dense, and has no gas separation performance.

[0136] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any change or replacement easily thought of by those skilled in the art within the technical range disclosed in the present application should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. Use of a two-dimensional RUB-18 zeolite membrane in gas separation, characterized in that, The gas is at least one of hydrogen, a gas different from hydrogen in kinetic diameter and characteristics; The method for preparing the two-dimensional RUB-18 zeolite film comprises the following steps: Ball-milling peeling obtains a two-dimensional RUB-18 zeolite nanosheet solution, and the specific method is as follows: RUB-18 zeolite powder is mixed with a mixed solution of methanol and water, and then ball-milling is performed to obtain a two-dimensional RUB-18 zeolite nanosheet solution, wherein the volume ratio of the methanol and water is (0.2-5) : 1, the ball-milling time is 5-24 h, and the ball-milling speed is 50-500 rpm; The porous substrate is placed in the two-dimensional RUB-18 zeolite nanosheet solution, and electrophoretic deposition is performed, and the electrophoretic deposition product is dried to obtain a two-dimensional RUB-18 zeolite film; During the electrophoretic deposition, the concentration of the two-dimensional RUB-18 zeolite nanosheet solution is 0.1-10 mg / mL, the voltage is 1-40 V, the current is 0.001-0.010 A, and the time is 5-50 min; The thickness of the two-dimensional RUB-18 zeolite film is 200-800 nm.

2. Use according to claim 1, characterized in that, The porous substrate is polyvinylidene fluoride, polyamide, polyether sulfone, sulfonated polyether sulfone, polysulfone, sulfonated polysulfone, anodic aluminum oxide, terephthalate glycol or alpha-aluminum oxide.

3. Use according to claim 1, characterized in that, The type of the separated gas is one or two of hydrogen, carbon dioxide, nitrogen, methane, ethylene, propylene, ethane and propane; When the separated gas is two, the volume ratio of the separated gas is 1:1; the purge gas is one of argon, helium and methane.

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