Preparation method of oriented molecular sieve membrane for hydrogen separation
By using a nano-molecular sieve seed layer and the Van de Drift growth theory, an oriented molecular sieve membrane with a consistent crystal orientation was prepared, which solved the problem of intercrystalline defects in the molecular sieve membrane growth process, achieved efficient hydrogen separation, and improved separation performance.
Patent Information
- Application Number
- CN202511380793.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-25
- Publication Date
- 2025-12-26
AI Technical Summary
Existing molecular sieve membranes suffer from intergranular defects and grain boundary problems during growth, which leads to reduced gas separation efficiency and selectivity. Traditional methods make it difficult to prepare oriented molecular sieve membranes that combine high permeability and high selectivity.
By employing a seed layer of nanomolecular sieves and using the Van de Drift growth theory to regulate crystal growth kinetics, an oriented molecular sieve membrane with a consistent crystal orientation is formed. The high inductive activity and high density arrangement of the nanomolecular sieves reduce self-nucleation and promote crystal growth along a specific direction.
High permeability and high separation selectivity of hydrogen gas separation were achieved, intercrystalline defects were reduced, accessibility of target channels was optimized, and separation performance of H2/CO2 and H2/CH4 was improved.
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Figure CN121198073A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of oriented molecular sieve membrane preparation, in particular to a preparation method of an oriented molecular sieve membrane for hydrogen separation, and belongs to the technical field of molecular sieve membrane separation. BACKGROUND
[0002] With the rapid development of hydrogen energy and carbon capture technology, H2 separation plays a key role in syngas purification, natural gas purification and carbon neutralization industry. Molecular sieve membranes show excellent gas separation potential due to their regular pore structure, high hydrothermal stability and molecular size sieving effect. The small pores of the molecular sieve membrane can realize molecular level separation according to the size, shape and difference of gas molecules, and it is an important separation membrane material for the separation of small molecule gas such as H2. Although a variety of functional molecular sieve membranes have been reported to be widely used in various separation fields, the preparation of molecular sieve membranes for efficient small molecule gas separation is still a great challenge.
[0003] Due to the high Al content in the molecular sieve, the strong electronegativity will cause a large number of defects in the growth process of the zeolite membrane, i.e. intercrystalline defects and interface defects, which will cause the gas to pass through the molecular sieve membrane mainly through non-selective paths. In addition, the traditional molecular sieve membrane is a membrane with randomly arranged crystals, and the arrangement direction of the crystals in the membrane layer is different, which causes the gas to frequently encounter crystal boundaries during diffusion, thereby causing high diffusion resistance, which seriously restricts the separation efficiency and selectivity of the membrane. In addition to promoting the growth of ordered crystals, adjusting the orientation of the molecular sieve membrane to be consistent with the anisotropic pore structure can optimize the accessibility of the target pore channel and inhibit the generation of undesirable grain boundary defects. The arrangement and connection of the pores in different crystal face directions are different, which will cause obvious differences in the gas diffusion rate, and the orientation arrangement of the crystal has a significant influence on the separation performance of the molecular sieve membrane.
[0004] There are still many challenges in preparing highly oriented zeolite membranes with high permeance and high selectivity. For example, in traditional hydrothermal synthesis, there is a phenomenon of self-nucleation of crystals in the bulk solution, which will interfere with the seed-induced growth. The method of oriented seed plane epitaxial growth is not suitable for the preparation of all oriented zeolite membranes; a key limitation is that there are technical challenges in orderly depositing oriented seeds on a porous substrate to form a highly oriented monolayer seed layer (Angew. Chem. Int. Ed., 52 (2013) 8693-8698). In addition, in the process of controlled plane-out secondary growth, it is still a major challenge to effectively suppress the growth of undesirable twin crystals (Adv. Mater., 27 (2015) 3243-3249). Evolutionary growth follows Van der Drift's selection principle, that is, through competitive epitaxial growth, the fastest growth direction ultimately determines the main orientation of the membrane, which is considered as a universal strategy for preparing oriented membranes (Chem.-Eur. J., 30 (2024) e202304162; Adv. Funct. Mater., 34 (2024) 2404643). By precisely controlling the nucleation and growth parameters to promote the growth of crystals in the expected direction, the preparation of oriented zeolite membranes is achieved. For example, by chemically modifying the substrate to enhance its adhesion to crystals in a specific orientation, Huang et al. used APTES and other reagents to modify the substrate, successfully preparing oriented LTA membranes (J. Membr. Sci., 437 (2013) 57-64; J. Membr. Sci., 350 (2010) 5-9).
[0005] The chemical modification method has certain limitations in application: (i) the chemical modification process is extremely sensitive to synthesis conditions; (ii) different substrates usually have specific adaptability requirements, which together limit its universal application on various porous substrates. In order to overcome this limitation, the present application introduces a layer of nanometer molecular sieve seeds to prepare oriented zeolite membranes in a clear solution synthesis system: nanometer molecular sieves have undefined crystal plane directions to induce anisotropic growth of crystals; small size, high specific surface area, and high density arrangement provide abundant active sites for crystal growth, and make it very easy for adjacent crystals to "contact" and compete for growth, meeting the conditions for triggering Van der Drift's evolutionary mechanism to grow oriented membranes. SUMMARY
[0006] In order to overcome the problem of the reduction of separation selectivity caused by intercrystalline defects and the low permeation and diffusion efficiency caused by complex grain boundary route in the preparation of conventional molecular sieve membrane, the application provides a preparation method of oriented molecular sieve membrane for hydrogen separation.
[0007] In order to achieve the above-mentioned purpose, the technical scheme of the application is as follows:
[0008] A preparation method of oriented molecular sieve membrane for hydrogen separation, comprising the following steps:
[0009] (1) Preparation of nanocrystal seed layer: 0.05g of nanomolecular sieve is dispersed in 10g of deionized water, ultrasonic dispersion is carried out for 1h to obtain a nanomolecular sieve seed dispersion liquid, and then the supernatant is taken after standing at room temperature for 12h to obtain a uniformly dispersed nanomolecular sieve seed aqueous solution. A clean Al2O3 substrate (front side upward) is horizontally immersed in the molecular sieve aqueous solution, taken out horizontally after standing for 10s, and dried in a 100℃ oven for 30min, and the step is repeated for 3 times.
[0010] (2) Preparation of secondary growth solution: Si source and Al source synthesis solutions are prepared according to the proportion of the molecular sieve growth gel, the two solutions are uniformly mixed, and then aging treatment is carried out for a period of time to obtain a uniform transparent secondary growth solution. The substrate with the seed layer immersed and coated is horizontally placed at the bottom of a hydrothermal kettle, and the prepared growth gel is added, and crystallization is carried out in an oven for a period of time.
[0011] Preferably, the type of the above-mentioned molecular sieve is one of LTA, SOD, FAU, MFI and CHA.
[0012] Preferably, the aging treatment time of the above-mentioned synthesis solution is one of 0-48h.
[0013] Preferably, the crystallization time of the above-mentioned molecular sieve membrane growth gel is one of 1-48h.
[0014] The oriented LTA molecular sieve membrane provided by the application is applied to the separation and purification of H2 in H2 / CO2 and H2 / CH4.
[0015] The application has the following advantages compared with the conventional small-pore molecular sieve membrane currently studied:
[0016] 1. The oriented molecular sieve membrane is prepared by using a non-oriented seed layer, high induction activity of nanometer molecular sieve and high density arrangement of nanometer molecular sieve seeds. The nanometer molecular sieve has high surface energy, so that it can be easily adsorbed on the surface of the substrate, and the crystal growth induced by the randomly oriented and densely arranged nanometer seed layer meets the condition of triggering the Van der Drift evolution mechanism. The nanometer molecular sieve seeds are universally applicable to various types of molecular sieve membranes, which provides a new idea for the preparation of oriented molecular sieve membranes.
[0017] 2. The application utilizes the characteristics of nanometer molecular sieve that can induce crystal growth on the molecular sieve seeds, and can reduce the self-nucleation phenomenon in the bulk phase solution to a certain extent.
[0018] 3. The oriented LTA molecular sieve membrane prepared by the application reduces irregular grain boundary routes, optimizes the accessibility of target channels, is beneficial to reducing the diffusion resistance of gas molecules, and has a higher gas permeation amount in H2 / CO2, H2 / CH4 H2 separation and purification. In addition, since the intergrowth crystals in the membrane layer are arranged in a consistent direction, this can effectively reduce the invisible intergranular defects in the membrane, ultimately leading to the LTA membrane having a super-high permeation amount while having a higher H2 selectivity in H2 / CO2, H2 / CH4 H2 separation and purification.
[0019] The oriented molecular sieve membrane provided by the application can be widely used in various fields such as environment, chemical industry, medicine, etc. BRIEF DESCRIPTION OF DRAWINGS
[0020] Figure 1 : Uniform LTA nanometer seed layer prepared by the method
[0021] Figure 2 : Surface image of the oriented LTA molecular sieve membrane prepared by the method
[0022] Figure 3 : Cross-sectional image of the oriented LTA molecular sieve membrane prepared by the method
[0023] Figure 4 : XRD image of the oriented LTA molecular sieve membrane prepared by the method
[0024] Figure 5 : H2 / CO2, H2 / CH4 separation performance image of the oriented LTA molecular sieve membrane DETAILED DESCRIPTION
[0025] The technical solutions of the application will be described in detail below with specific embodiments, but the application is not limited to the following embodiments. Any modification within the concept and scope of the application is within the protection scope of the application.
[0026] Materials and reagents required in the preparation of the molecular sieve membrane:
[0027] The porous Al2O3 substrate was purchased from Foshan Yirun Fine Ceramic New Material Co., Ltd., sodium silicate (Na2SiO3), 325 mesh Al powder was purchased from Alfa Aesar Company, sodium hydroxide (NaOH) was purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd., LTA nanomolecular sieve was self-made in the laboratory, and deionized water was self-made in the laboratory.
[0028] The related test conditions and methods involved in the present application are as follows:
[0029] Scanning electron microscope (SEM) test: the scanning electron microscope (SEM, JSM-7900F) was used to analyze the microstructure and thickness of the molecular sieve membrane; X-ray diffraction (XRD) test: the X-ray diffraction (XRD, Bruker, D8 Advance) was used to analyze the crystalline structure of the molecular sieve membrane.
[0030] Gas separation performance test: the Wicke-Kallenbach device was used to evaluate the single-component and mixed-component separation performance of the oriented LTA membrane. The LTA membrane was placed in a stainless steel cell and permeated to a steady state. The measured membrane area was 0.785cm 2 . Under the same preparation conditions, three membranes prepared under the same conditions were selected for parallel experiment permeation test. For single-component gas separation test, the volume flow rate of raw gas (H2, CO2 or CH4) was set to 100mL min -1 . For binary gas separation test, the total volume flow rate of the two raw gases was kept at 100mL min -1 (50mL min -1 each). The permeation side was initially purged with argon at a speed of 40ml min -1 . The transmembrane pressure difference and temperature were maintained at 1bar and 25℃ respectively. The gas chromatography method (456-GC, Scion) was used to determine the permeation gas concentration.
[0031] Example 1:
[0032] Preparation of nanocrystal seed layer: 0.05g of LTA nanomolecular sieve was dispersed in 10g of deionized water, ultrasonic dispersion was carried out for 1h to obtain a nanomolecular sieve seed dispersion liquid, and then the supernatant was taken after standing at room temperature for 12h to obtain a uniformly dispersed nanomolecular sieve seed aqueous solution. A clean Al2O3 substrate (front side upward) was horizontally immersed in the molecular sieve aqueous solution, horizontally pulled out after standing for 10s, and placed in a 100℃ oven for drying for 30min, and this step was repeated for 3 times.
[0033] Preparation of the secondary growth solution: Si source and Al source synthesis solutions were prepared according to the molecular sieve growth gel ratio (50Na2O: 1Al2O3: 5SiO2: 1000H2O), and the prepared Al source synthesis solution was added dropwise into the Si source synthesis solution. After mixing uniformly, the mixture was subjected to aging treatment for 20 h to obtain a transparent and uniform secondary growth solution. The substrate with the seed layer prepared by immersion coating was vertically placed at the bottom of an autoclave, and the prepared secondary growth solution was added. Crystallization was performed in an oven at 60°C for 24 h. The molecular sieve membrane after crystallization was washed to neutral with deionized water and dried in an oven at 60°C.
[0034] Example 2:
[0035] Preparation of the nanoseed layer: 0.05 g of SOD nanomolecular sieve was dispersed in 10 g of deionized water, and ultrasonic dispersion was performed for 1 h to obtain a nanomolecular sieve seed dispersion liquid. Then, the mixture was left to stand at room temperature for 12 h, and the supernatant was taken to obtain a uniformly dispersed nanomolecular sieve aqueous solution. A clean Al2O3 substrate (with the front face upward) was horizontally immersed in the molecular sieve aqueous solution, and after being left to stand for 10 s, the substrate was horizontally pulled out and dried in an oven at 100°C for 30 min. This step was repeated three times.
[0036] Preparation of the secondary growth solution: Si source and Al source synthesis solutions were prepared according to the molecular sieve growth gel ratio (50Na2O: 1Al2O3: 5SiO2: 1000H2O), and the prepared Al source synthesis solution was added dropwise into the Si source synthesis solution. After mixing uniformly, the mixture was subjected to aging treatment for 20 h to obtain a transparent and uniform secondary growth solution. The substrate with the seed layer prepared by immersion coating was vertically placed at the bottom of an autoclave, and the prepared secondary growth solution was added. Crystallization was performed in an oven at 60°C for 24 h. The molecular sieve membrane after crystallization was washed to neutral with deionized water and dried in an oven at 60°C.
[0037] Example 3:
[0038] Preparation of the nanoseed layer: 0.05 g of SOD nanomolecular sieve was dispersed in 10 g of deionized water, and ultrasonic dispersion was performed for 1 h to obtain a nanomolecular sieve seed dispersion liquid. Then, the mixture was left to stand at room temperature for 12 h, and the supernatant was taken to obtain a uniformly dispersed nanomolecular sieve aqueous solution. A clean Al2O3 substrate (with the front face upward) was horizontally immersed in the molecular sieve aqueous solution, and after being left to stand for 10 s, the substrate was horizontally pulled out and dried in an oven at 100°C for 30 min. This step was repeated three times.
[0039] Preparation of secondary growth solution: According to the ratio of the molecular sieve growth gel (70Na2O: 1Al2O3: 20SiO2: 2000H2O), the synthesis solution was prepared respectively, stirred for 24h, and the aging treatment of the secondary growth solution was completed to obtain a transparent and uniform secondary growth solution. The substrate with the seed layer prepared by immersion coating was vertically placed at the bottom of the hydrothermal kettle, and the secondary growth solution was added. Crystallization was carried out in a 75°C oven for 20h. The crystallized molecular sieve membrane was washed with deionized water to neutral and dried in a 60°C oven.
[0040] Example 4:
[0041] After the drying of the LTA molecular sieve membrane was completed, the membrane was activated in a vacuum drying oven at 80°C for 12h, and then fixed in the membrane module with aluminum foil paper. The test area was 0.785cm 2 . Ar was used as the purge gas, and the flow rate was set to 40mL min -1 . The LTA membrane was placed in the membrane module and permeated to the steady state. Single-component gas permeation tests of H2, CO2 and CH4 were carried out, and the flow rate was set to 100mL min -1 . Double-component gas permeation tests of H2, CO2 and CH4 were carried out, and the flow rate was set to 50mL min -1 . The transmembrane pressure difference and temperature were maintained at 1bar and 25°C, respectively. The concentration of the permeated gas was determined by gas chromatography (456-GC, Scion).
[0042] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.
Claims
1. A method for preparing an oriented molecular sieve membrane for hydrogen separation, comprising the following steps: (1) obtaining a homogeneous molecular sieve aqueous solution by taking the supernatant of a nanometer molecular sieve dispersion liquid after standing for 12 hours; (2) immersing a clean Al2O3 substrate (with the front side facing upwards) horizontally into the above-mentioned homogeneous molecular sieve aqueous solution for 10 seconds, and then drying in a 100°C oven, repeating the process for 3 times; (3) preparing a transparent and uniform secondary growth solution of the molecular sieve membrane according to the proportioning of the molecular sieve synthesis solution, aging the secondary growth solution, and then vertically placing the substrate with the seed layer obtained by the above-mentioned immersion coating at the bottom of a hydrothermal kettle, and adding the prepared molecular sieve synthesis solution to perform crystallization treatment in a heating oven.
2. The method for preparing an oriented molecular sieve membrane for hydrogen separation according to claim 1, characterized in that, In step (1), the nanometer molecular sieve crystal has a grain size of 50-150 nm.
3. The method for preparing an oriented molecular sieve membrane for hydrogen separation according to claim 1, characterized in that, In step (1), the average grain size of the uniform nanometer molecular sieve dispersion liquid is 100 nm.
4. The method for preparing an oriented molecular sieve membrane for hydrogen separation according to claim 1, characterized in that, In step (2), the Al2O3 substrate is a flat and porous ceramic substrate.
5. The method for preparing an oriented molecular sieve membrane for hydrogen separation according to claim 1, characterized in that, In step (3), the secondary growth synthesis solution is a transparent and uniform clear solution.
6. The method for preparing an oriented molecular sieve membrane for hydrogen separation according to claim 1, characterized in that, In step (3), the secondary growth crystallization time is one of 1-48 hours.
7. The method for preparing an oriented molecular sieve membrane for hydrogen separation according to claim 1, characterized in that The crystal in the oriented molecular sieve membrane has a highly ordered and consistent arrangement in a specific crystal face direction.
8. The method for preparing an oriented molecular sieve membrane for hydrogen separation according to claim 1, characterized in that The ultrathin and dense molecular sieve membrane is one of LTA, SOD, FAU, MFI and CHA.
9. Compared with the prior art, the present application has the following beneficial effects: (1) The oriented molecular sieve membrane is prepared by using non-oriented seeds through a hydrothermal growth method, which utilizes the high induction activity of nanometer molecular sieve seeds, promotes the crystal to grow faster in a certain direction based on the Van de Drift growth theory, and is suitable for various types of molecular sieve membranes, which provides a new idea for the preparation of oriented molecular sieve membranes; (2) Different from the method of using oriented seeds as growth sources in the traditional growth process, the present application uses high-activity nanometer molecular sieve as seeds, which to some extent makes up for the limitation of being difficult to prepare a single-layer oriented seed layer; (3) The oriented LTA molecular sieve membrane prepared by the present application reduces the irregular grain boundary route, optimizes the accessibility of the target channel, is beneficial to reducing the diffusion resistance of gas molecules, has a higher gas permeation amount in H2 / CO2 and H2 / CH4 H2 separation and purification, and in addition, the intergrowth crystals in the membrane layer are arranged in a consistent direction, which effectively reduces the invisible intercrystalline defects in the membrane, ultimately resulting in that the LTA membrane has an ultrahigh permeation amount and a high H2 selectivity in H2 / CO2 and H2 / CH4 H2 separation and purification.