A method for continuously and rapidly preparing a molecular sieve membrane and application of the molecular sieve membrane

Abstract

This invention discloses a method for continuous ultra-fast preparation of molecular sieve membranes and their applications. The process involves rapidly heating both the synthetic sol and the carrier to high temperatures without contact between the synthetic sol and the porous carrier with a seed layer on its surface. The synthetic sol is then introduced into the reaction zone containing the carrier, allowing it to flow continuously along the carrier surface and contact the seed layer. The reaction proceeds rapidly under conditions exceeding the gas-phase equilibrium pressure and without sol circulation. After the reaction, the membrane is cooled, washed, dried, and calcined. Compared to traditional batch hydrothermal synthesis, this invention utilizes a high-concentration OSDA sol and high-temperature conditions to accelerate the nucleation and crystallization processes, and decouples the preheating process from the contact reaction process. Rapid membrane formation is achieved under conditions exceeding the gas-phase equilibrium pressure and with continuous flow. Multiple ultrathin and dense molecular sieve membranes can be continuously prepared within 1-25 minutes, which helps maintain the initial orientation and structural integrity of the seed layer and reduces membrane defects. The resulting molecular sieve membranes exhibit excellent gas separation performance, and this method has the potential for large-scale application.

Description

Technical Field

[0001] This invention relates to a method for continuous ultrafast preparation of molecular sieve membranes and the application of molecular sieve membranes, belonging to the field of molecular sieve membrane preparation technology. Background Technology

[0002] Membrane separation technology has advantages such as low energy consumption, simple operation, and small footprint, and has become one of the important technical pathways for process intensification and energy conservation and emission reduction in the fields of energy and environment (Nature, 2016, 532, 435-437). Taking molecular sieve membranes as an example, they have angstrom-scale (Å) regular pore structure and excellent hydrothermal stability, which can achieve efficient sieving of gas mixtures with similar molecular sizes under harsh operating conditions. Therefore, they have received widespread attention and research in the past decade.

[0003] Taking high-silica MFI and CHA molecular sieve membranes as examples, these membranes not only possess excellent molecular sieving capabilities but also typically exhibit good moisture resistance and hydrothermal stability, making them promising for applications in various gas separation scenarios. For instance, Wang et al. (J. Membrane. Sci., 2017, 540, 50-59) prepared a highly h0h-oriented MFI molecular sieve membrane at 413 K for 30 hours. This membrane showed a butane permeability of 3.1 × 10⁻⁶ at 333 K. -7 mol / (m 2 The separation factor for n- and isobutane was 29. Although this work has verified the advantages of molecular sieve membranes in terms of performance and stability, their preparation still mainly relies on the traditional route of batch hydrothermal secondary growth. It generally suffers from problems such as long synthesis cycle, difficulty in precise control of membrane microstructure and defects, and difficulty in achieving continuous production, resulting in low preparation efficiency, high synthesis cost and low reproducibility, which makes it difficult to meet the needs of industrial-scale preparation.

[0004] Currently, traditional batch hydrothermal synthesis is mostly carried out under static conditions, and the synthesis sol is prone to sedimentation, which limits the uniformity of film growth. At the same time, in the long-term alkaline sol and high-temperature environment, the seed layer and the newly grown film may undergo a "dissolution-recrystallization" process (Chinese. J. Catal., 2014, 35, 1800-1810), which will generate grain boundary defects and non-selective channels, further affecting the compactness and separation performance of the film.

[0005] To shorten the synthesis cycle, existing literature reports reducing membrane synthesis time to 2-4 hours, for example, by using oil bath heating or microwave heating to reduce thermal hysteresis and improve nucleation and crystallization rates (Int. J. Hydrogen. Energ., 2019, 44, 23107-23119). However, these methods still rely on batch-process synthesis, which cannot fundamentally meet the requirements for non-circulating, continuous production of molecular sieve membranes. The key limitation is that nucleation and crystallization often occur coupled during batch synthesis. Sol-phase nucleation and epitaxial crystal growth occur simultaneously, and several hours are still needed to "fill" defects, making it difficult to control nucleation uniformity and membrane microstructure, thus limiting further improvements in membrane quality and separation performance. Furthermore, the system pressure inside the closed high-pressure reactor is usually determined by the self-generated pressure of the heated solvent and is close to the gas-phase equilibrium pressure at the set temperature. During this process, localized vaporization easily occurs, forming bubbles, which can induce non-uniform growth and non-selective defects on the membrane surface. Therefore, there is an urgent need to propose a synthesis process for continuous molecular sieve membrane preparation, which can improve film uniformity and reduce defects while shortening the synthesis time, thereby meeting the needs of large-scale preparation. Summary of the Invention

[0006] The purpose of this invention is to provide a method for the continuous ultra-fast preparation of molecular sieve membranes and the application of the prepared molecular sieve membranes in gas separation. This method utilizes a high-concentration OSDA synthesis sol in synergy with high-temperature conditions, significantly improving nucleation and crystallization kinetics. By separating the preheating process from the contact reaction process, continuous and rapid reactions are achieved under conditions above the gas-phase equilibrium pressure and with the sol in a non-circulating state. During the preheating stage, isolated from the support, the sol rapidly forms a large number of crystal nuclei, which then contact the pre-coated seed layer in the reaction zone and directly participate in the reaction, forming multiple dense molecular sieve membranes within 1-25 minutes. Under conditions above the gas-phase equilibrium pressure, the formation of bubbles in the sol is suppressed, improving film uniformity. Compared with traditional batch hydrothermal synthesis, this invention significantly shortens the synthesis cycle, improves preparation efficiency, and enables non-circulating continuous preparation of molecular sieve membranes. Simultaneously, the minute-level preparation effectively reduces defects caused by "dissolution-recrystallization" during long-term hydrothermal processes, maintaining the initial orientation and structural integrity of the seed layer, thereby improving membrane quality and gas separation performance.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for continuous ultrafast preparation of molecular sieve membranes, characterized by comprising the following steps:

[0009] (1) Prepare a synthetic sol containing a high concentration of organic structure directing agent OSDA at room temperature, wherein the molar ratio of OSDA to SiO2 in the synthetic sol is 0.1-1:1;

[0010] (2) Introduce the synthetic sol into the preheating pipeline; install multiple porous carriers with molecular sieve seed layers on their surfaces in series in the reaction pipeline, and inject deionized water into the reaction pipeline to fill the reaction pipeline and the inner cavity of the carrier, thereby preventing the synthetic sol from entering the reaction zone and preventing the synthetic sol from contacting and reacting with the carrier during the preheating stage; under the condition that the synthetic sol and the porous carrier are isolated and not in contact, introduce inert gas into the system to raise the system pressure to a gas-liquid equilibrium pressure higher than the set temperature, and preheat the synthetic sol in the preheating pipeline and the porous carrier in the reaction pipeline at high temperature, so that they are heated to 460-485 K within 0.1-10 min;

[0011] (3) After preheating, the synthetic sol is introduced into the reaction zone of the porous carrier of the seed layer, so that the synthetic sol flows continuously along the surface of the carrier and contacts the molecular sieve seed layer. Under conditions of higher than the gas phase equilibrium pressure and non-circulation of the sol, it reacts rapidly to form a molecular sieve membrane. The contact time between the synthetic sol and the seed layer is 1-25 min.

[0012] (4) After the reaction is completed, the resulting membrane is rapidly cooled to terminate the reaction. Then, the cooled membrane is washed, dried and calcined to remove OSDA, and a molecular sieve membrane is obtained.

[0013] Preferably, the preparation method of the synthetic sol is as follows: mixing and stirring the silicon source, aluminum source, organic structure directing agent OSDA, alkali source and solvent, and aging at room temperature for 1-3 days.

[0014] Preferably, the molar composition of the synthetic sol, based on SiO2, is as follows: Al2O3:SiO2=(0-0.2):1; OSDA:SiO2=(0.1-1):1; Alkali source:SiO2=(0-0.8):1; H2O:SiO2=(10-100):1.

[0015] Preferably, the silicon source is selected from at least one of tetraethyl orthosilicate, tetramethyl orthosilicate, sodium silicate, water glass, or silicon powder; the aluminum source is selected from at least one of aluminum hydroxide, sodium aluminate, aluminum foil, aluminum isopropoxide, aluminum n-butoxide, aluminum foil, aluminum powder, or alumina; the organic structure directing agent is selected from one or more of organic amines or quaternary ammonium salt cations; and the alkali source is selected from at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, or cesium hydroxide.

[0016] Preferably, the carrier is one of a tubular single-channel carrier, a multi-channel porous carrier, or a hollow fiber carrier, and its material is at least one of alumina, zirconium oxide, titanium oxide, mullite, silicon carbide, and silicon oxide.

[0017] Preferably, the molecular sieve seed crystals are selected from MFI type, CHA type, LTA type, FAU type, AEI type, DDR type, RHO type, MEL type, and BEA type molecular sieves.

[0018] Preferably, during the preheating and continuous rapid reaction processes, the system is pressurized to above the gas phase equilibrium pressure using an inert gas, with a pressure of 1-3 MPa.

[0019] Preferably, the flow rate of the synthetic sol is adjusted by a back pressure valve or a needle valve, and the sol linear velocity is 2-100 cm / min.

[0020] Preferably, the synthetic sol and the seed-supported carrier are dynamically reacted at a high temperature of 460-485 K for 1-25 min.

[0021] Preferably, the multiple carriers are arranged in series, and the total length of the series connection is 0.1-100 m; the effective flow path length of the synthetic sol in the reactor is 0.1-10 m.

[0022] Molecular sieve membranes prepared by any of the methods described.

[0023] Application of molecular sieve membranes prepared by any of the methods in gas separation.

[0024] An apparatus for the continuous preparation of molecular sieve membranes, comprising:

[0025] A feeding device for supplying synthetic sol to the preparation device;

[0026] A preheating unit in fluid communication with the feeding device, the preheating unit comprising at least one preheating pipe;

[0027] A tubular reactor fluidly connected to the outlet of the preheating unit, wherein at least one porous carrier with a molecular sieve seed layer loaded on its surface is installed inside the tubular reactor, so that the synthetic sol flows along the axial direction of the carrier and reacts with the seed layer to form a molecular sieve membrane.

[0028] A heating device for heating the preheating unit and the tubular reactor;

[0029] A compressed gas bypass line connected to the pipeline of the preparation device is used to supply compressed gas to the system to pressurize the system and / or drive the synthetic sol to flow within the device;

[0030] The discharge pipeline is connected to the outlet of the tubular reactor.

[0031] The tubular reactor is equipped with multiple carriers with surface-loaded seed layers, and the multiple carriers are arranged in series so that the synthesis liquid or synthesis sol flows through each carrier in sequence.

[0032] A fluid control component is installed on the discharge pipeline. The fluid control component is used to adjust the system pressure and / or adjust the flow rate of the synthetic liquid or synthetic sol. It includes a back pressure valve and a flow control valve. The flow control valve is a needle valve.

[0033] A buffer tank is installed between the outlet of the tubular reactor and the discharge pipeline. The buffer tank is used to cool the synthetic sol after the reaction.

[0034] The compressed gas is an inert gas, selected from nitrogen, argon, or helium. The compressed gas is supplied through a bypass pipeline to suppress bubble generation during subsequent heating, allowing the reaction to proceed rapidly under conditions higher than the gas phase equilibrium pressure and without sol circulation.

[0035] The preparation apparatus also includes a dead-end bypass pipeline, which is equipped with a pressure relief valve to release liquid expansion and / or abnormal high pressure during the heating process, and a gas buffer volume is provided inside the pipeline.

[0036] The heating device includes an oil bath heating device, and the preheating tube and the tubular reactor are configured to be placed as a whole in the oil bath for heating.

[0037] The beneficial effects of this invention are as follows:

[0038] Its core technical solution is:

[0039] 1. The sol and the support for seed crystals are rapidly heated to high temperatures without contact or isolation, decoupling the nucleation of the sol from the crystallization of the support surface film. Then, the sol rich in ordered crystal nuclei is introduced into the reaction zone and flows continuously along the axial direction to contact and react with the seed layer.

[0040] 2. The use of high-concentration OSDA combined with high temperature significantly improves the nucleation and reaction rate of the sol, ensuring that a continuous film can be constructed in just minutes of contact time.

[0041] 3. Multiple molecular sieve membranes were continuously prepared under conditions higher than the gas phase equilibrium pressure and non-circulating continuous flow, which suppressed the formation of bubbles at high temperatures, while the high pressure also improved the nucleation and crystallization rates.

[0042] Specifically, by employing a high-concentration OSDA sol synthesis combined with high-temperature conditions, the nucleation and crystallization kinetics of the reaction system are significantly enhanced. Combined with a continuous-flow film-forming method, the film-forming time of molecular sieve membranes is significantly shortened from hours or even days in traditional batch hydrothermal synthesis to minutes, thereby significantly improving membrane preparation efficiency and reducing production costs. This invention separates the preheating process from the contact reaction process, allowing the sol to rapidly form a large number of crystal nuclei before reaching the reaction temperature. After preheating, the sol is introduced into the reaction zone to contact the pre-coated seed layer, promoting the direct participation of the crystal nuclei in the rapid epitaxial growth of the seed layer, thus forming a continuous and dense film layer more quickly. This process is beneficial for improving the film-forming rate and the controllability of film growth, which is difficult to achieve in traditional batch hydrothermal synthesis. Furthermore, this invention conducts a continuous, non-cyclic reaction under conditions higher than the gas-phase equilibrium pressure, effectively suppressing sol vaporization and bubble generation during the heating and reaction process, reducing localized non-uniform growth and non-selective defects caused by bubbles, thereby improving film uniformity and film quality. Meanwhile, the minute-level rapid preparation significantly reduces the formation of defects caused by the "dissolution-recrystallization" cycle that easily occurs in traditional long-duration hydrothermal processes, which is beneficial for maintaining the initial orientation and structural integrity of the seed layer, thereby improving the separation performance and stability of the membrane. The continuous flow of the sol inhibits sedimentation, making the contact between the sol and the support surface more uniform, which helps to improve the reproducibility of the membrane synthesis process. This strategy is applicable to the preparation of molecular sieve membranes with different framework types and different orientation requirements, and has good versatility and industrial scale-up prospects. In some embodiments, the prepared oriented MFI membranes used for n / isobutane separation and the SSZ-13 membrane used for CO2 / N2 separation both exhibited high separation selectivity and permeation rate, demonstrating the advantages of this continuous ultra-fast preparation method in gas separation applications. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of an ultrafast continuous synthesis device for molecular sieve membranes.

[0044] 1. Feed pump; 2. Preheating pipe; 3. Tubular reactor; 4. Buffer tank; 5. Back pressure valve; 6. Heating unit;

[0045] Figure 2 The image shows a scanning electron microscope (SEM) image (ad surface, eh cross section) of the four randomly oriented MFI molecular sieve membranes synthesized in Example 1 of this invention.

[0046] Figure 3 The image shows the X-ray diffraction (XRD) pattern of the randomly oriented MFI molecular sieve membrane synthesized in Example 1 of this invention.

[0047] Figure 4 SEM images (ad surface, eh cross section) of the four b-axis oriented MFI molecular sieve membrane synthesized in Example 2 of the present invention.

[0048] Figure 5 The image shows the XRD pattern of the b-axis oriented MFI molecular sieve membrane synthesized in Example 2 of this invention.

[0049] Figure 6 SEM images (ad surface, eh cross section) of the four SSZ-13 molecular sieve membranes synthesized in Example 3 of this invention.

[0050] Figure 7 The image shows the XRD pattern of the SSZ-13 molecular sieve membrane synthesized in Example 3 of this invention.

[0051] Figure 8 This is a SEM image of the MFI molecular sieve membrane synthesized in Example 4 of the present invention;

[0052] Figure 9 This is a SEM image of the MFI molecular sieve membrane synthesized in Example 5 of the present invention;

[0053] Figure 10 This is a SEM image of the MFI molecular sieve membrane synthesized in Example 6 of the present invention;

[0054] Figure 11 This is a SEM image of the MFI molecular sieve membrane synthesized in Example 7 of the present invention;

[0055] Figure 12 This is a SEM image of the MFI molecular sieve membrane synthesized in Example 8 of the present invention;

[0056] Figure 13 This is a SEM image of the MFI molecular sieve membrane synthesized in Example 9 of the present invention;

[0057] Figure 14 This is a SEM image of the MFI molecular sieve membrane synthesized in Comparative Example 1 of this invention.

[0058] Figure 15 This is a SEM image of the MFI molecular sieve membrane synthesized in Comparative Example 2 of this invention.

[0059] Figure 16 This is a SEM image of the MFI molecular sieve membrane synthesized in Comparative Example 3 of this invention. Detailed Implementation

[0060] This application proposes a method for the continuous ultra-rapid preparation of molecular sieve membranes by optimizing synthesis parameters and reactor design. This strategy employs a high-concentration OSDA synthetic sol in synergy with high temperature to enhance the nucleation and crystallization rates of the reaction system. Simultaneously, by separating the preheating process from the contact reaction process, the synthetic sol rapidly forms a large number of crystal nuclei and active species during the preheating stage. Once the reaction temperature is reached, it is introduced into the reaction zone to contact the seed layer, achieving rapid epitaxial growth of the seed layer. This accelerates the formation of a dense membrane layer and reduces the "dissolution-recrystallization" that occurs between the seed layer and the newly grown membrane layer under prolonged alkaline high-temperature conditions. Furthermore, this application conducts the continuous reaction under gas-phase equilibrium pressure conditions above the set temperature, effectively suppressing sol vaporization and bubble generation, and improving the uniformity and controllability of membrane synthesis. When using an oriented seed layer, oriented molecular sieve membranes can be rapidly prepared by maintaining the orientation of the seed layer. This innovative process significantly improves the controllability of the synthesis process while effectively reducing energy consumption and total product cost. To make the technical solution, innovative features, and beneficial effects of this invention clearer, detailed descriptions are provided below with reference to specific embodiments. However, the scope of protection of this invention is not limited to the following embodiments.

[0061] The continuous ultrafast preparation strategy described in this invention is not limited to the molecular sieve membrane types exemplified in the embodiments. The core of this invention lies in: pre-constructing a molecular sieve seed layer on the support surface; decoupling the nucleation and crystallization processes during the preheating stage; and, after preheating, allowing the synthetic sol to flow continuously along the support surface, reacting rapidly under conditions higher than the gas-phase equilibrium pressure and without sol circulation, thereby achieving rapid film formation. This strategy helps maintain the initial orientation and structural integrity of the seed layer and enables rapid growth of ultrathin films, thus making it applicable to the preparation of different types of molecular sieve membranes and different crystal orientations. As an example, but not limited to, the molecular sieve seed can be selected from MFI, CHA, LTA, FAU, AEI, DDR, RHO, MEL, and BEA type molecular sieves; those skilled in the art can select the appropriate seed system and film formation route according to the target separation system, required pore size / topology, and orientation requirements.

[0062] Furthermore, this invention is not limited to any specific synthetic liquid or synthetic sol formulation used in the embodiments. The synthetic sol can be obtained by mixing and stirring a silicon source, an aluminum source, an organic structure directing agent OSDA, an alkali source, and a solvent, and then aging it at room temperature for 1-3 days; its molar composition, based on SiO2, can be adjusted within the following ranges: Al2O3:SiO2=(0-0.2):1, OSDA:SiO2=(0.1-1):1, alkali source:SiO2=(0-0.8):1, H2O:SiO2=(10-100):1. To adapt to different molecular sieve frameworks and film-forming kinetics, the proportions of the above components can be selected and combined within the stated range. The silicon source, aluminum source, OSDA, and alkali source can also be replaced from the publicly available candidates. For example, the silicon source can be selected from tetraethyl orthosilicate, tetramethyl orthosilicate, sodium silicate, water glass, or silicon powder, etc.; the aluminum source can be selected from aluminum hydroxide, sodium aluminate, bauxite, aluminum isopropoxide, aluminum n-butoxide, aluminum foil, aluminum powder, or alumina, etc.; the OSDA can be selected from one or more organic amines or quaternary ammonium salt cations; and the alkali source can be selected from lithium hydroxide, sodium hydroxide, potassium hydroxide, or cesium hydroxide, etc.

[0063] Furthermore, the present invention is not limited to the carrier form and device scale shown in the embodiments. The carrier can be a tubular single-channel or multi-channel porous carrier, and its material can be selected from at least one of alumina, zirconium oxide, titanium oxide, mullite, silicon carbide and silicon oxide; multiple carriers can be arranged in series to achieve continuous scale-up, the total length of series connection can be 0.1-100m, and the effective flow path length can be 0.1-10m. Regarding process parameters, the sol and the pre-coated seed crystal carrier are rapidly preheated at a high temperature of 460-485 K for 0.1-10 min. The contact reaction can be carried out at 460-485 K, with a sol linear velocity of 2-100 cm / min and an effective contact time between the sol and the seed crystal layer of 1-25 min. The flow rate can be adjusted by a back pressure valve or a needle valve. During preheating and the reaction, the system can maintain a pressure of 1-3 MPa using an inert gas to remove air bubbles from the sol and provide driving force for the sol flow, allowing the reaction to proceed under conditions higher than the gas phase equilibrium pressure and without sol circulation. For post-treatment, the membrane activation conditions can also be selected within the publicly available range, such as calcination at 150-500 °C for 5-72 h in an air, oxygen, or ozone atmosphere, with a controlled heating rate of 0.2-5 °C / min. The above parameters and material selections can be matched and optimized according to the target membrane system, equipment size and production needs, but do not deviate from the technical concept of continuous flow contact reaction of the present invention.

[0064] The carrier configuration described in this invention is not limited to the single-channel tubular carrier used in the embodiments, but can also be a multi-channel porous carrier or a hollow fiber carrier, etc. For example, two or more parallel axial flow channels (multi-channel ceramic carrier) can be formed within the same carrier body, and the inner surface of each channel can serve as a substrate for seed layer loading and film growth. After preheating, the synthetic sol can simultaneously enter multiple channels under pressure and flow continuously along the channel axis, thereby achieving synchronous film formation on the inner surface of each channel. In terms of dimensional parameters, the outer dimensions, channel dimensions, and length of the carrier can be selected according to the device scale, target film area, and pressure requirements, and are not limited to the point values ​​of the embodiments. Taking a single-channel tubular carrier as an example, its outer diameter, inner diameter, and length can be adjusted around the dimensions of commercial carriers used in the embodiments: for example, the outer diameter can be about 5-30 mm, the inner diameter can be about 3-20 mm, and the length of a single carrier can be about 2-100 cm; the average pore size of the carrier can be selected according to the selected seed size, for example, about 50-500 nm. For multi-channel carriers, their overall dimensions can be on the same order of magnitude as single-channel carriers for ease of assembly. The diameter of each channel can be set according to flow distribution (e.g., approximately 1-15 mm), the channel wall thickness can be selected according to mechanical strength requirements (e.g., approximately 0.3-3 mm), and the carrier length can also be selected within the aforementioned range for a single carrier. Furthermore, the effective film area and throughput can be increased by connecting multiple carriers in series. In a multi-channel configuration, as long as the synthesized sol can flow continuously along the axial direction of each channel after preheating and fully contact the seed layer on the inner surface of the channel, a continuous and rapid film formation effect similar to that of a single-channel carrier can be achieved.

[0065] The molecular sieve membrane prepared by this invention is not only applicable to the gas separation process shown in the examples, but can also be used in various other gas separation and purification scenarios. Due to the regular microporous structure and molecular sieving / adsorption selectivity of the molecular sieve membrane, differentiated separation of different gas components in terms of diffusion rate and adsorption affinity can be achieved based on the selected molecular sieve framework type, membrane thickness, orientation, and intergranular defect control. Therefore, the molecular sieve membrane of this invention can be used to enrich target components, remove impurities, or purify gases from multi-component gases, and can be coupled with existing membrane separation devices, pressure swing adsorption, cryogenic separation, and other processes to improve separation efficiency and reduce energy consumption. As an example, but not limited to, the molecular sieve membrane of the present invention can be used for: hydrogen-related separation, such as hydrogen purification and recovery in systems like H2 / CO2, H2 / CH4, H2 / N2, and H2 / CO; carbon dioxide capture and natural gas purification, such as decarbonization and enrichment in systems like CO2 / CH4, CO2 / N2, and CO2 / H2; air separation and oxygen / nitrogen enrichment, such as O2 / N2 separation; separation of hydrocarbons and light gases, such as separation and purification of olefin / alkane systems like CH4 / N2, C2H4 / C2H6, and C3H6 / C3H8; and purification of gases containing sulfur / water impurities, such as removing H2S, H2O, or other trace polar impurities from natural gas, syngas, and refinery gas. For different gas systems, by selecting appropriate molecular sieve membrane types, such as different framework pore sizes and topologies, optimizing operating temperature and feed pressure, and controlling membrane defects and orientation, permeate flux and selectivity that meet the target separation requirements can be obtained. Furthermore, the molecular sieve membrane prepared by this invention can also be used for gas separation and process enhancement applications in high-temperature or corrosive environments. For example, it can achieve reaction-separation coupling in membrane reactors, such as removing reaction-generated water or CO2, or selectively permeating H2 to drive equilibrium conversion. It can also be used in scenarios such as chemical production tail gas treatment, refining gas recovery, and electronic-grade gas purification to achieve continuous and modular separation unit configurations. The above applications are merely illustrative examples, and the applicable gas separation range of the molecular sieve membrane of this invention is not limited to the above examples.

[0066] The specific implementation method is as follows:

[0067] Example 1: A method for continuous ultrafast preparation of randomly oriented MFI molecular sieve membranes and evaluation of their separation performance.

[0068] (1) Preparation of spherical MFI seeds and seed layers

[0069] Tetrapropylammonium hydroxide, deionized water, and tetraethyl orthosilicate were mixed in a molar ratio of 5 TPAOH:25 TEOS:480 H2O and stirred at room temperature for 6 h to form a homogeneous sol. The sol was transferred to a stainless steel reactor and hydrothermally synthesized at 413 K for 48 hours. The product was collected by centrifugation and dried overnight at 373 K. To remove the organic structure-directing agent, the resulting crystals were calcined in a muffle furnace at 773 K for 6 h, with a heating and cooling rate of 3 K / min. The calcined crystals were dispersed in ethanol to prepare a 0.1 wt% seed suspension, which was then sonicated for at least 1 h for later use.

[0070] A commercially available single-channel tubular α-Al₂O₃ support (outer diameter 10 mm, inner diameter 7 mm, average pore size 200 nm) was cut into 6 cm lengths. Both ends of the support were sealed with Duncan IN1001 ceramic glaze and sintered at 1223 K, with heating and cooling rates of 3 K / min. To prevent seed crystals from adhering to the outer wall of the tube, the outer surface was wrapped with polytetrafluoroethylene heat-shrink tubing. Subsequently, the support was immersed in the aforementioned seed crystal suspension for 40 s, removed, and dried at 373 K for 2 h to obtain a support loaded with a randomly oriented MFI seed layer.

[0071] (2) Continuous ultrafast synthesis of randomly oriented MFI molecular sieve membranes

[0072] use Figure 1 The self-made continuous ultrafast synthesis apparatus shown mainly includes a feed pump, a preheating unit, a tubular reactor, a buffer tank, a back pressure valve, and two bypass lines. Four seed-supported supports are connected in series in the tubular reactor, with a total length of 25 cm and an inner diameter of 1.4 cm. Before synthesis, the reactor is filled with deionized water to prevent the sol from prematurely contacting the supports during the preheating stage.

[0073] Tetrapropylammonium hydroxide, deionized water, and tetraethyl orthosilicate were mixed in a specific ratio and stirred at room temperature for 24 hours to form a homogeneous synthetic sol. The molar ratio was 1 TEOS:0.22 TPAOH:50 H2O. The sol was pumped (MP1006C) into a preheating tube (approximately 70 cm long, 1.4 cm inner diameter) located at the front of a tubular reactor. One end of the tubular reactor, filled with water, was carefully connected to the preheating tube filled with the sol to prevent air from entering. The other end of the tubular reactor was connected to a stainless steel buffer tank for cooling and circulating the reaction sol. Finally, the buffer tank was connected to a back pressure regulator and a high-precision needle valve for adjusting the flow rate (typically set to 2 ml / min).

[0074] After completing the installation and filling the preheating tubes with sol, shut off the feed pump. Open the high-pressure nitrogen bypass to raise the system pressure to 2 MPa to suppress bubble formation during subsequent heating. Another dead-end bypass line contains 3.2 ml of air and is equipped with a pressure relief valve to release liquid expansion during heating and abnormally high pressure due to operational errors. Immerse the reactor and preheating tubes entirely in a preheated oil bath, close the back pressure valve and needle valve, and heat statically for 5 minutes until the system temperature reaches 473 K, at which point the system pressure is approximately 2.5 MPa. After preheating, adjust the back pressure valve and needle valve to allow the sol to flow at a linear flow rate of approximately 4 cm / min (corresponding to a volumetric flow rate of 2 ml / min) through the four pre-coated seed carriers connected in series.

[0075] The total sol flow time was 15 min. The first 0.5 min was used to displace the pre-existing water in the carrier gaps. Subsequently, the sol flowed sequentially through each carrier, with effective contact times as follows: 14.5-13 min for the first carrier, 13-11.5 min for the second, 11.5-10 min for the third, and 10-8.5 min for the fourth. Based on this, the synthesis times (actual contact time between the sol and the carrier) for the four membranes were recorded as 14.5 min, 13 min, 11.5 min, and 10 min, corresponding to sample numbers M1, M2, M3, and M4.

[0076] After the reaction was complete, the oil bath was quickly switched to a cooling water bath to cool the system to below 333 K within 2 minutes. The membrane tube was removed, thoroughly washed with deionized water, and dried at 333 K for at least 12 hours. Finally, it was calcined at 473 K in an ozone atmosphere for 3 days to remove OSDA, thus obtaining the randomly oriented MFI molecular sieve membrane.

[0077] Figure 2 The middle (ad) region shows the surface SEM image of the randomly oriented MFI molecular sieve membrane, and (eh) shows the cross-sectional SEM image. Figure 2 It can be seen that the MFI molecular sieve membrane prepared by continuous ultra-fast process is continuous and dense with no obvious defects, and the membrane thickness is about 800 nm. Figure 3 The XRD pattern of the prepared MFI molecular sieve membrane shows that the prepared membrane is a pure MFI phase with random orientation of the membrane layers.

[0078] Example 2

[0079] (1) Preparation of MFI nanosheet seeds and seed layers

[0080] The procedure is basically the same as step (1) in Example 1, except that MFI nanosheets are used as seed crystals. MFI nanosheets are synthesized using a sol with a molar composition of 0.1 TPAOH:1 SiO2:30 H2O:0.8 NH4F. Specific steps: 15.6 g TEOS, 6.0 g TPAOH, and 17.5 g H2O are mixed and stirred at room temperature for 6 hours. The resulting sol is then transferred to a water bath maintained at 363 K and stirred for 12 hours to promote nucleation. Subsequently, 2.2 g NH4F and 18.0 g H2O are added, and the mixture continues to react at 363 K for 12 hours. The pre-crystallized sol is then transferred to a stainless steel autoclave and crystallized at 453 K for 72 hours. The resulting crystals are calcined in a muffle furnace at 773 K for 6 hours, with a heating and cooling rate of 3 K / min. The calcined crystals are dispersed in ethanol to prepare a 0.1 wt% seed crystal suspension, and ultrasonically treated for at least 1 hour for later use. b-axis oriented MFI nanosheet seed layers were prepared by coating seed crystals onto a carrier using the dip-coating method.

[0081] (2) As in step (2) of Example 1, MFI molecular sieve membranes are synthesized continuously and ultrafastly, except that the prepared membranes are b-axis oriented MFI molecular sieve membranes, and the corresponding membrane numbers are M5, M6, M7, and M8. Figure 4 As shown, the prepared b-axis oriented MFI molecular sieve membrane is continuous and dense with a uniform thickness of approximately 600 nm. Figure 5 The XRD pattern of the b-axis oriented MFI molecular sieve membrane shows that the prepared membrane is a pure MFI phase with a high b-axis orientation.

[0082] Example 3

[0083] (1) Preparation of SSZ-13 seed crystals and seed layers

[0084] The procedure is essentially the same as step (1) in Example 1, except that SSZ-13 molecular sieve is used as the seed crystal. SSZ-13 nanocrystals are synthesized from a sol with a molar ratio of 1SiO2:0.025Al2O3:0.4TMAdaOH:0.2NaOH:44H2O and crystallized at 433K for 96 hours. The solid product is collected by centrifugation and dried overnight at 373K. Before preparing the seed crystal suspension, OSDA is removed by calcination at 773K for 6 hours in a muffle furnace (both heating and cooling rates are 3K / min). The resulting crystals are dispersed in ethanol to form a 0.1wt% colloidal suspension and sonicated for at least 1 hour. The seed crystals are coated onto a carrier by dip-coating to prepare an SSZ-13 seed crystal layer.

[0085] (2) SSZ-13 molecular sieve membranes were synthesized continuously and ultrafastly as in step (2) of Example 1, except that the seed crystals used were the aforementioned SSZ-13 molecular sieve, and the molar ratio of the membrane synthesis sol was: 1SiO2:0.01Al2O3:0.6TMAdaOH:0.2NaOH:44H2O. The sol was aged at room temperature for 3 days and then used for membrane synthesis. The prepared membranes were SSZ-13 molecular sieve membranes, and the corresponding membrane numbers were M9, M10, M11, and M12. Figure 6 As shown, the prepared SSZ-13 molecular sieve membrane is continuous and dense with a uniform thickness of approximately 1000 nm. Figure 7 The XRD pattern of the prepared SSZ-13 molecular sieve membrane shows that the prepared membrane is a pure phase of SSZ-13.

[0086] Example 4

[0087] The process is essentially the same as in Example 1, except that the preheating and synthesis temperature is 413 K, and the resulting membrane is designated M13. Figure 8 As shown, the prepared MFI molecular sieve membrane has a large number of defects and the membrane layer is discontinuous.

[0088] Example 5

[0089] The process was essentially the same as in Example 1, except that the preheating and synthesis temperature was 413 K, the sol flow rate was 2 cm / min, the sol contact time was 20-25 min, and the resulting membrane was designated M14. Figure 9 As shown, the prepared MFI molecular sieve membrane still has a large number of defects and the membrane layer is discontinuous.

[0090] Example 6

[0091] The process is essentially the same as in Example 1, except that the molar composition of the membrane synthesis sol is 1.0 TEOS: 0.12 TPAOH: 60 H2O, and the resulting membrane is designated M15. Figure 10 As shown, the prepared MFI molecular sieve membrane crystals coexist with each other, and the membrane thickness is approximately 600 nm.

[0092] Example 7

[0093] The process is essentially the same as in Example 1, except that the molar composition of the membrane synthesis sol is 1.0 TEOS: 0.15 TPAOH: 165 H2O, and the resulting membrane is designated M16. Figure 11 As shown, the prepared MFI molecular sieve membrane has a large number of defects, and the membrane layer has not yet formed a continuous crystal layer.

[0094] Example 8

[0095] The process is essentially the same as in Example 1, except that MFI nanosheets were used as seed crystals, the sol flow rate was 12 ml / min, the sol contact time was 1-5 min, and the resulting film was designated M17. Figure 12 As shown, the MFI nanosheets have not yet grown into a continuous film.

[0096] Example 9

[0097] The process is essentially the same as in Example 1, except that MFI nanosheets were used as seed crystals, the sol flow rate was 1 ml / min, the sol contact time was 55-60 min, and the resulting film is designated M18. Figure 13 As shown, MFI crystals coexist, but the film orientation is poor.

[0098] Comparative Example 1

[0099] MFI molecular sieve membranes were synthesized using a conventional static method. The seed crystals and seed layer used were the same as in step (1) of Example 1, except for the composition of the membrane synthesis sol and the membrane synthesis steps. Tetrapropylammonium hydroxide, deionized water, and tetraethyl orthosilicate were mixed and aged at room temperature for 6 h to prepare a homogeneous sol with a molar ratio of 1.0 TEOS:0.15 TPAOH:165 H2O. The sol and the pre-coated seed crystal support were transferred to a stainless steel reactor and placed in an oven at 413 K for 24 h. The synthesized MFI molecular sieve membrane was designated M19. Figure 14 As shown, the crystals coexist with each other, the film is continuous and dense, and the film thickness is 1.5 μm.

[0100] Comparative Example 2

[0101] It is basically the same as Example 1, except that the synthetic carrier is a bare carrier and the resulting membrane is designated as M20.

[0102] Comparative Example 3

[0103] The process is basically the same as in Example 1, except that in step (2), the system temperature is set to 473 K. After the pipeline installation is completed, there is no preheating process. The back pressure valve and needle valve are directly opened and adjusted so that the sol flows through the series-connected carriers at a linear flow rate of about 4 cm / min. At this time, the sol flow and heating / nucleation occur simultaneously, and the resulting membrane is M21. Figure 16 As shown, the crystal layer has not yet formed a continuous film.

[0104] The gas separation performance of molecular sieve membranes was tested using equimolar amounts of n- / isobutane mixed gas (MFI molecular sieve membrane) or equimolar amounts of CO2 / N2 mixed gas (SSZ-13 molecular sieve membrane), and expressed as two parameters: gas permeation rate P and separation selectivity. The gas permeation rate P is expressed as the amount of gas permeating through a unit membrane area per unit time under unit pressure, P = N / (A × ∆P ×t), with units of mol / (m²). 2 S (Pa); Separation selectivity is the ratio of the permeation rate of the gas preferentially permeating the membrane to the permeation rate of the gas subsequently permeating the membrane, S=P A / P B It is worth noting that due to the high flux of CO2 through the SSZ-13 membrane, a significant concentration gradient exists between the feed and permeate sides. Gas composition on the feed, permeate, and permeate sides was continuously monitored using online gas chromatography (GC). The gas permeation rate was calculated as the logarithmic mean partial pressure (ΔP). ln,i Normalized flux (kPa), , where p f,i p r,i , and p p,i These represent the partial pressures of component i on the feed side, effluent side, and permeate side, respectively. The separation performance of the MFI membrane for the n-butane / isobutane mixture was evaluated using a permeate-side vacuum mode. Since the butane flux of the MFI membrane is relatively low, the change in gas concentration between the feed and effluent sides can be ignored. Therefore, the pressure difference was taken as the arithmetic difference of the transmembrane partial pressures (kPa). The prepared MFI membrane was tested for gas separation performance in a n / isobutane system. The test conditions were: 30℃, feed pressure 125 kPa, feed flow rate 400 ml / min, and molar composition 50 / 50%. The prepared SSZ-13 membrane was tested for gas separation performance in a CO2 / N2 system. The test conditions were: 30℃, feed pressure 200 kPa, feed flow rate 4000 ml / min, and molar composition 50 / 50%. The gas flow rate on the permeate side was measured by a soap bubble flow meter, and the gas composition on the permeate side was analyzed by a gas chromatograph (Shimadzu, GC2014). The test results are shown in Table 1.

[0105] Table 1. Separation performance of MFI molecular sieve membrane for n- / isobutane mixed gas

[0106]

[0107] A comparison of Example 1 and Comparative Example 3 reveals that, from a synthetic method perspective, this patent involves short-term high-temperature preheating under conditions where the sol and carrier are not in contact / isolated. Combined with high-concentration OSDA and high temperature synergy, this allows the sol to form a large number of ordered nuclei / highly active precursors within a few minutes of preheating. This ensures that the sol entering the reaction section remains in a highly active state rich in nuclei / nutrients. Subsequently, the sol flows continuously along the axial direction, rapidly and directionally transporting these nuclei and nutrients to the reaction section, where they contact the carrier seed layer and undergo epitaxial growth, achieving rapid closure and densification of the inner film layer within minutes. This process, which involves preheating and nucleation followed by transporting the nuclei to the carrier surface and then epitaxially growing on the surface, solves the fundamental problem of the "slow nucleation / crystallization while the sol flows within the reaction section" model, achieving ultra-fast synthesis.

[0108] In summary, the continuous ultrafast method for preparing molecular sieve membranes proposed in this application overcomes the key limitations of traditional batch synthesis of molecular sieve membranes. By synergistically enhancing nucleation and crystallization kinetics through high-concentration OSDA synthesis sol and high-temperature conditions, and by decoupling the preheating and contact reaction processes, the sol rapidly forms a large number of crystal nuclei during the preheating stage isolated from the support. Subsequently, rapid epitaxial growth occurs in the reaction zone and the pre-coated seed layer, thereby constructing a dense membrane layer within a short residence time. Simultaneously, continuous flow reaction under gas-phase equilibrium pressure conditions above the set temperature effectively suppresses vaporization and bubble formation, improves film uniformity, and reduces the risk of non-selective defect formation. The minute-level preparation also significantly reduces defect formation caused by the "dissolution-recrystallization" process in traditional long-term synthesis, which is beneficial for maintaining the initial orientation and structural integrity of the seed layer and improving membrane quality. The non-circulating continuous flow method in this patent enables the sol and the carrier to complete film formation with only one contact in the reaction section, and the continuous production and scale-up of molecular sieve membranes can be achieved through the series connection of carriers. If the circulating flow method is used, the membrane defect repair and continuous membrane formation can only be achieved gradually through long-term crystallization. The membrane is always in a reaction state of repeated contact with the sol. If the synthesis time is extended too much, dissolution-recrystallization will occur, increasing the risk of defect formation and making the film formation dependent on long-term contact reaction. Although the sol is in a dynamic flow state, it is still essentially a batch production process.

[0109] Overall, this strategy improves film formation rate while maintaining process controllability and scalability, providing a new process path for the continuous manufacturing of high-performance molecular sieve membranes and their large-scale application in gas separation.

Claims

1. A method for continuous ultrafast preparation of molecular sieve membranes, characterized in that, Includes the following steps: (1) Prepare a synthetic sol containing a high concentration of organic structure directing agent OSDA at room temperature, wherein the molar ratio of OSDA to SiO2 in the synthetic sol is 0.1-1:1; (2) Introduce the synthetic sol into the preheating pipeline; install multiple porous carriers with molecular sieve seed layers on their surfaces in series in the reaction pipeline, and inject deionized water into the reaction pipeline to fill the reaction pipeline and the inner cavity of the carrier, thereby preventing the synthetic sol from entering the reaction zone during the preheating stage and preventing the synthetic sol from contacting and reacting with the carrier; in the state where the synthetic sol and the porous carrier are isolated and not in contact, introduce inert gas into the system to raise the system pressure to a level higher than the gas phase equilibrium pressure at the set temperature, and preheat the synthetic sol in the preheating pipeline and the porous carrier in the reaction pipeline at high temperature, so that they are heated to 460-485 K within 0.1-10 min; (3) After preheating, the synthetic sol is introduced into the reaction zone of the porous carrier of the seed layer, so that the synthetic sol flows continuously along the surface of the carrier and contacts the molecular sieve seed layer. Under conditions of higher than the gas phase equilibrium pressure and non-circulation of the sol, it reacts rapidly to form a molecular sieve membrane. The contact time between the synthetic sol and the seed layer is 1-30 min. (4) After the reaction is completed, the resulting membrane is rapidly cooled to terminate the reaction. Then, the cooled membrane is washed, dried and calcined to remove OSDA, and a molecular sieve membrane is obtained.

2. The method for continuous ultrafast preparation of molecular sieve membranes according to claim 1, characterized in that, The preparation method of the synthetic sol is as follows: a silicon source, an aluminum source, an organic structure directing agent OSDA, an alkali source, and a solvent are mixed and stirred, and aged at room temperature for 1-3 days; the molar composition of the synthetic sol, based on SiO2, is: Al2O3:SiO2=(0-0.2):1; OSDA:SiO2=(0.1-1):1; alkali source:SiO2=(0-0.8):1; H2O:SiO2=(10-100):1; The silicon source is selected from at least one of tetraethyl orthosilicate, tetramethyl orthosilicate, sodium silicate, water glass, or silicon powder; the aluminum source is selected from at least one of aluminum hydroxide, sodium aluminate, aluminum foil, aluminum isopropoxide, aluminum n-butoxide, aluminum foil, aluminum powder, or alumina; the organic structure directing agent is selected from one or more of organic amines or quaternary ammonium salt cations; and the alkali source is selected from at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, or cesium hydroxide.

3. The method for continuous ultrafast preparation of molecular sieve membranes according to claim 1, characterized in that, The carrier is one of a tubular single-channel carrier, a multi-channel porous carrier, or a hollow fiber carrier, and its material is at least one of alumina, zirconium oxide, titanium oxide, mullite, silicon carbide, and silicon oxide; The molecular sieve seed crystals are selected from MFI, CHA, LTA, FAU, AEI, DDR, RHO, MEL, and BEA type molecular sieves; During the preheating and continuous rapid reaction processes, the system is pressurized to above the gas phase equilibrium pressure using an inert gas, with a pressure of 1-3 MPa.

4. The method for continuous ultrafast preparation of molecular sieve membranes according to claim 1, characterized in that, The flow rate of the synthesized sol in step (3) is adjusted by a back pressure valve or a needle valve, and the linear velocity of the sol is 2-100 cm / min; The synthetic sol described in step (3) is dynamically reacted with the seeded carrier at a high temperature of 460-485 K for 1-25 min; In step (3), multiple seed crystal layers are provided on the carrier, which are arranged in series and have a total length of 0.1-100 m. The flow path length of the synthetic sol in the reactor is 0.1-10 m.

5. The method for continuous ultrafast preparation of molecular sieve membranes according to claim 1, characterized in that, After the reaction in step (4) is completed, the resulting film is rapidly cooled to terminate the crystallization reaction; the calcination atmosphere is air, oxygen or ozone, the calcination temperature is 150-500 ℃, the calcination time is 5-72 h, and the heating rate is 0.2-5 ℃ / min.

6. The molecular sieve membrane prepared by the method according to any one of claims 1-5.

7. A method for gas separation using the molecular sieve membrane as described in claim 6.

8. An apparatus for the continuous preparation of molecular sieve membranes, characterized in that, include: A feeding device for supplying synthetic sol to the preparation device; A preheating unit in fluid communication with the feeding device, the preheating unit comprising at least one preheating pipe; A tubular reactor is in fluid communication with the outlet of the preheating unit. At least one porous carrier with a molecular sieve seed layer loaded on its surface is installed inside the tubular reactor, so that the synthetic sol flows along the axial direction of the carrier and reacts with the seed layer to form a molecular sieve membrane. A heating device for heating the preheating unit and the tubular reactor; A compressed gas bypass line connected to the pipeline of the preparation device is used to supply compressed gas to the system to pressurize the system and / or drive the synthetic sol to flow within the device; The discharge pipeline is connected to the outlet of the tubular reactor.

9. The apparatus for continuously preparing molecular sieve membranes according to claim 8, characterized in that, The tubular reactor is equipped with multiple carriers with surface-loaded seed layers, and the multiple carriers are arranged in series so that the synthesis liquid or synthesis sol flows through each carrier in sequence. A fluid control component is installed on the discharge pipeline. The fluid control component is used to adjust the system pressure and / or adjust the flow rate of the synthetic liquid or synthetic sol. It includes a back pressure valve and a flow control valve. The flow control valve is a needle valve. A buffer tank is provided between the outlet of the tubular reactor and the discharge pipeline. The buffer tank is used to cool the synthetic sol after the reaction. The compressed gas is an inert gas, selected from nitrogen, argon, or helium. The compressed gas is supplied through a bypass pipeline to suppress bubble generation during subsequent heating, allowing the reaction to proceed rapidly under conditions higher than the gas phase equilibrium pressure and without sol circulation.

10. The apparatus for continuously preparing molecular sieve membranes according to claim 8, characterized in that, The preparation apparatus also includes a dead-end bypass pipeline, which is equipped with a pressure relief valve to release liquid expansion and / or abnormal high pressure during the heating process, and a gas buffer volume is provided inside the pipeline. The heating device includes an oil bath heating device, and the preheating tube and the tubular reactor are configured to be placed as a whole in the oil bath for heating.

Images