KFI zeolite molecular sieve membrane, preparation method and application thereof

Abstract

This invention belongs to the field of molecular sieve membrane technology, and discloses a KFI zeolite molecular sieve membrane, its preparation method, and its applications. This invention improves upon the in-situ hydrothermal method by first loading the supporting solution onto a carrier surface via filtration, followed by hydrothermal synthesis, thus obtaining the KFI molecular sieve membrane in a single in-situ synthesis. Compared to conventional methods, this invention shortens the production cycle, eliminates the need for KFI seed crystals, simplifies the steps, reduces costs, and is more suitable for industrial-scale production. Experiments have confirmed that the KFI-type zeolite molecular sieve membrane of this invention exhibits excellent dehydration and separation performance for organic solvents such as acetic acid and ethanol.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve membrane technology, specifically to a KFI zeolite molecular sieve membrane, its preparation method, and its application. Background Technology

[0002] Acetic acid (CH3COOH) is one of the 50 most important chemicals in industry, with a wide range of crucial applications. In chemical synthesis, it is a core raw material for synthesizing various compounds such as polyvinyl acetate, vinyl acetate, acetate esters, and chloroacetic acid. These products play an irreplaceable role in industries such as plastics, coatings, and adhesives. Simultaneously, acetic acid also serves as an important industrial solvent and raw material, deeply involved in multiple production stages such as textile printing and dyeing, photographic pharmaceutical manufacturing, and the rubber industry, providing a fundamental guarantee for the smooth operation of these industries. Whether using the traditional methanol carbonyl synthesis method or the increasingly popular biomass fermentation method to produce acetic acid, the dehydration and purification of crude acetic acid is an indispensable unit process in the entire production process. Although water and acetic acid do not usually form an azeotrope, the tangential pinch point characteristic of acetic acid solutions necessitates multiple equilibrium stages in the distillation column and the use of high reflux ratios when using distillation for dehydration, which undoubtedly leads to a significant increase in energy consumption. Traditional acetic acid dehydration methods, while technically mature and widely used, also suffer from many drawbacks such as high energy consumption, large equipment investment, and potential secondary pollution. Therefore, developing new environmentally friendly and energy-saving acetic acid dehydration and separation technologies is of particular importance for reducing the cost of acetic acid production, reducing energy consumption, and alleviating environmental pressure.

[0003] Membrane separation technology is a highly efficient method for separating mixtures using selective membrane materials. With advantages such as no phase change, small footprint, high efficiency, energy saving, and environmental friendliness, it is widely used in water and gas separation. Its core principle is to separate substances based on molecular characteristics through the selective permeability of the membrane. The driving force is mostly pressure difference or concentration difference, requiring no phase change and consuming far less energy than traditional processes such as distillation. This technology includes microfiltration, ultrafiltration, nanofiltration, and reverse osmosis, suitable for different separation scenarios. Pervaporation, as an important branch, is driven by chemical potential difference and based on mechanisms such as "dissolution-diffusion," making it particularly suitable for azeotropic separation and playing a significant role in organic matter recovery and solvent dehydration. Membrane materials are key; the application and optimization of various materials continuously improve its separation performance and application potential.

[0004] Although acetic acid and water do not form an azeotrope, they have a tangential pinch point, resulting in similar boiling points and a low separation coefficient. Conventional distillation requires numerous equilibrium stages and high reflux ratios, which not only dramatically increases energy consumption but also prolongs the separation cycle. Furthermore, acetic acid's strong corrosiveness accelerates equipment wear and tear, increasing maintenance costs. Simultaneously, high temperatures may trigger acetic acid decomposition or side reactions, affecting product purity. Inorganic membranes, with their excellent acid resistance and tunable hydrophilicity, hold great potential for acetic acid dehydration.

[0005] Molecular sieves are made of TO4 - (T = Si, Al, Ge...) Zeolite molecular sieves are 3D crystalline compounds with a porous structure constructed from tetrahedra. Zeolite molecular sieves are granular or powdery crystals with microporous structures, primarily used for adsorption, catalysis, and ion exchange; while zeolite molecular sieve membranes are continuous thin films, mainly used for molecular-level separation. Zeolite molecular sieve membranes are continuous, dense films (typically 1-100 μm thick), formed by the directional growth of zeolite crystals on the surface of a porous support (such as alumina or silicon carbide). The pores of the membrane extend along the surface of the support, forming "continuous molecular sieving channels," and the membrane layer is tightly bonded to the support, exhibiting high mechanical strength.

[0006] Zeolite molecular sieve membranes are the largest family of inorganic pervaporation membrane materials. They have adjustable hydrophilicity and sub-nanometer molecular sieve pores, and provide strong preferential adsorption and rapid selective diffusion to achieve efficient molecular separation.

[0007] The silica-to-alumina ratio of the zeolite molecular sieve membrane framework is one of the important factors determining the hydrophilicity and acid resistance of the membrane material. Generally, as the silica-to-alumina ratio of the zeolite membrane framework increases, the hydrophilicity of the membrane decreases and the acid resistance increases. According to the different silica-to-alumina ratios of molecular sieves, molecular sieve membranes can be divided into three categories: (1) low silica-to-alumina ratio, with a silica-to-alumina ratio of 1.0~1.5, such as NaA, NaY, etc.; (2) medium silica-to-alumina ratio, with a silica-to-alumina ratio of 2.0~5.0, such as CHA, ERI and T-type zeolites, etc.; (3) high silica-to-alumina ratio, with a silica-to-alumina ratio greater than 5.0, such as MOR, MFI, etc. MFI and MOR type zeolite membranes with high silica-to-alumina ratios can maintain good stability under high concentration and high temperature acidic conditions. Therefore, research on the application of zeolite membranes in acetic acid dehydration mainly focuses on MFI and MOR type zeolite membranes. However, the high silica-to-alumina ratio of MFI and MOR type zeolite membranes also limits the hydrophilicity of the membrane. While MFI and MOR type zeolite membranes exhibit excellent separation selectivity and acid / hydrothermal stability, there is still room for improvement in permeate flux. KFI molecular sieves possess an eight-membered ring structure with a pore size of 0.39 × 0.39 nm, falling between that of water molecules (0.26 nm) and small organic molecules, enabling precise molecular-scale sieving. With a silica-alumina ratio of 1.2–5, they exhibit excellent hydrophilicity and stability, making them ideal materials for preparing organic solvent dehydration membranes, especially under acidic conditions, where they demonstrate excellent application potential.

[0008] There are some reports on the synthesis of KFI molecular sieves. For example, Chinese patent ZL 202111609554.8 discloses the preparation of high-silica KFI molecular sieve powder, which mainly uses a template agent for synthesis, and the template agent needs to be removed at high temperature after the synthesis. Chinese patent ZL 202210564879.7 discloses a method for rapid synthesis of high-silica KFI molecular sieves, which adopts a two-stage synthesis method and requires the use of KFI molecular sieve seeds. The steps are relatively complicated and the cost is high.

[0009] Currently, the main methods for synthesizing zeolite molecular sieve membranes include in-situ hydrothermal synthesis, secondary growth, and microwave synthesis. However, there are relatively few reports on the preparation of KFI zeolite molecular sieve membranes. Chinese patent applications 202510948230.9 and 202510176476.9 report methods for preparing KFI zeolite molecular sieve membranes that involve first seeding KFI molecular sieve crystals onto a support surface, followed by a secondary synthesis method. This process is quite complex and costly.

[0010] Furthermore, there are currently very few reports on the preparation of KFI-type zeolite molecular sieve membranes for dehydration and purification of organic solvents such as acetic acid. Summary of the Invention

[0011] The purpose of this invention is to address the above-mentioned problems by providing a KFI zeolite molecular sieve membrane, its preparation method, and its application.

[0012] To achieve its objective, the present invention employs the following technical solution: The first aspect of the present invention provides a method for preparing a KFI zeolite molecular sieve membrane, comprising the following steps: Step (1) Prepare the loading solution Preparation of Solution A: Add aluminum source and alkali source to deionized water and stir until clear; Preparation of solution B: Add the strontium source to deionized water and stir until homogeneous; Preparation of the loading solution: Add solution A and solution B to the silicon source, stir and mix thoroughly to obtain a stable loading solution system; the amount of each raw material used is based on the molar ratio of SiO2: K2O: Al2O3: SrO: H2O introduced by them being (0.9~1.1): (0.1~0.3): (0.05~0.5): (0.006~0.03): (10~60). Weigh out the silicon source, alkali source, aluminum source, strontium source and deionized water. Step (2): Load the loading liquid onto the porous carrier. Loading can be done in any of the following ways: ① Place the porous carrier in the vacuum filtration device, drop the load liquid onto the carrier so that the surface of the carrier is covered by the load liquid, turn on the vacuum filtration pump, and use negative pressure of 40~100 Kpa to vacuum filter so that the surface of the carrier is tightly bonded to the load liquid film layer; the preferred vacuum filtration time is 1~15 minutes. ② Preheat the porous carrier, immerse the surface of the carrier into the loading liquid at a speed of 100-1000 μm / s for 5-20 s, and then pull it up at a speed of 100-1000 μm / s. A carrier loaded with the feed liquid is obtained; Step (3): Prepare the synthesis solution The amount of each raw material used in the synthesis liquid system is based on the molar ratio of SiO2: K2O: Al2O3: SrO: H2O introduced as (0.9~1.1): (0.1~0.3): (0.05~0.5): (0.006~0.03): (10~200). Weigh out the silicon source, alkali source, aluminum source, strontium source, and deionized water. Step (4) Crystallization film formation After the treatment in step (2) is completed, place the carrier in the reaction vessel, add the synthesis liquid to the reaction vessel so that the synthesis liquid completely submerges the carrier, seal the vessel and crystallize it at 100~180℃ for 3~6 days; After the crystallization reaction is complete, the support is removed, washed with deionized water until neutral, and dried to obtain a KFI zeolite molecular sieve membrane loaded on the support.

[0013] Generally, the synthesis solution in step (3) can be directly the loading solution in step (1), which is the same as the synthesis solution, in order to further reduce the operation steps and simplify the preparation process. The loading solution and the synthesis solution can also use different raw material ratios, and the KFI zeolite molecular sieve membrane of the present invention can still be successfully prepared.

[0014] The aluminum source is selected from aluminum hydroxide, aluminum nitrate, aluminum isopropoxide, or aluminum sulfate; The alkali source is selected from potassium hydroxide or potassium carbonate; The strontium source is selected from strontium acetate, strontium nitrate, or strontium chloride; The silicon source is selected from silica sol, silica, or tetraethyl orthosilicate.

[0015] In step (1), after adding solutions A and B to the silicon source, stir at 200-800 rpm for 5-60 minutes to ensure thorough mixing. The amount of each raw material used is based on the molar ratio of SiO2:K2O:Al2O3:SrO:H2O introduced as (0.9-1.1):(0.1-0.25):(0.05-0.3):(0.006-0.02):(10-50). Weigh out the silicon source, alkali source, aluminum source, strontium source, and deionized water. Preferably, the molar ratio of SiO2:K2O:Al2O3:SrO:H2O is 1:(0.18-0.25):(0.08-0.15):(0.008-0.015):(10-40) or 1:(0.20-0.24). (0.08~0.12) :(0.008~0.012) : (13~35); In step (3), the preparation method of the synthesis solution is as follows: Preparation of solution C: Add aluminum source and alkali source to deionized water and stir until clear; Preparation of solution D: Add the strontium source to deionized water and stir until homogeneous; Preparation of the synthesis solution: Add solution C and solution D to the silicon source, stir and mix thoroughly to obtain a stable synthesis solution system; Preferably, the synthesis solution is prepared as follows: After adding solutions C and D to the silicon source, stir at 200-800 rpm for 5-60 minutes to ensure thorough mixing, with a preferred stirring time of 5-20 minutes. The amounts of each raw material used are based on the molar ratio of SiO2:K2O:Al2O3:SrO:H2O being (0.9-1.1):(0.1-0.25):(0.05-0.3):(0.006-0.02):(10-150). Weigh out the silicon source, alkali source, aluminum source, strontium source, and deionized water. Preferably, the molar ratio of SiO2:K2O:Al2O3:SrO:H2O is 1:(0.18-0.25):(0.08-0.15):(0.008-0.015). (10~120) or 1: (0.20~0.24): (0.08~0.12): (0.008~0.012): (13~60).

[0016] Preferably, in step (2), the porous carrier is selected from Al2O3 carrier, zirconium dioxide, mullite, porous stainless steel, and more preferably Al2O3 carrier.

[0017] Preferably, in step (2), the porous carrier is sheet-like, tubular, plate-like, or hollow fiber-like, and the pore size on the porous carrier is 20~1000nm; more preferably, the pore size is 100~200nm.

[0018] Preferably, in step (2), the porous carrier is sheet-like, with each porous carrier measuring 350~400 mm. 2 Add 3-5 g of the loaded liquid to the surface of the filter and filter for 4-8 minutes.

[0019] In step (4), after sealing the container, the crystallization reaction is carried out at 110~160℃ for 3~6 days, preferably at 115~155℃ for 3~6 days, or at 115~155℃ for 4~5 days, or at 125~145℃ for 4~5 days.

[0020] A second aspect of the present invention provides a KFI zeolite molecular sieve membrane, which is prepared by the method described in any of the above-mentioned methods.

[0021] A third aspect of the present invention provides the application of the above-described KFI zeolite molecular sieve membrane in pervaporation, steam permeation, or organic solvent dehydration separation.

[0022] Preferably, the organic solvent is selected from acetic acid, ethanol, ethyl acetate or isopropanol.

[0023] The beneficial effects of this invention are: (1) This invention provides a novel method for preparing KFI-type zeolite molecular sieve membranes. This preparation method does not require the use of expensive organic template agents or environmentally harmful inorganic fluoride ions, and is energy-efficient and environmentally friendly. (2) Compared to the conventional two-stage synthesis method for preparing KFI zeolite molecular sieve membranes, which requires the use of KFI seeds, the present invention optimizes process efficiency, simplifying the process from "seed solution preparation → seed preparation → seed loading → synthesis solution preparation → crystallization" to "loading solution preparation → loading → synthesis solution preparation → crystallization". Unlike conventional methods, the present invention improves upon the in-situ hydrothermal method by first loading the loading solution onto the carrier surface and then performing hydrothermal synthesis, thus obtaining the KFI molecular sieve membrane in a single in-situ synthesis. The method of the present invention optimizes the molecular sieve membrane synthesis process. By loading a layer of loading solution onto the carrier, the loading solution penetrates to a certain depth into the carrier surface through pore permeation, enhancing the bonding force between the carrier and the loading solution membrane layer, achieving a match between the carrier and the loading solution. During the subsequent crystallization process, this guides the crystals to synthesize on the carrier surface, thereby synthesizing a continuous and dense membrane layer.

[0024] Compared to conventional methods, the method of this invention shortens the production cycle, eliminates the need for KFI seed crystals, simplifies the hydrothermal preparation steps of seed crystals, reduces costs, and is more suitable for industrial-scale production.

[0025] (3) Breakthrough in application scenarios: KFI molecular sieve membranes are usually only used for the separation of ethanol-water systems. The KFI molecular sieve membrane of this invention can not only be used for ethanol-water systems, but also for the separation of acetic acid-water systems. It can be tested for stability in a 50% water-acetic acid system and has good acid resistance.

[0026] The KFI zeolite molecular sieves of this invention belong to the medium silica-alumina ratio category, exhibiting not only excellent acid resistance but also superior hydrophilicity. This allows them to achieve high permeability flux while also possessing good acid-resistant separation selectivity and stability, making them suitable for dehydration separation applications in various organic solvent systems. Experiments have confirmed that the KFI-type zeolite molecular sieve membranes of this invention exhibit excellent dehydration separation performance for organic solvents such as acetic acid and ethanol. Furthermore, while demonstrating high separation performance, they also exhibit good acid resistance and stability. Attached Figure Description

[0027] Figure 1 This is a scanning electron microscope image of the surface of the molecular sieve membrane KFI-A1.

[0028] Figure 2 This is a cross-sectional scanning electron microscope image of the KFI-A1 molecular sieve membrane.

[0029] Figure 3Comparison of XRD patterns of KFI-A1 molecular sieve membrane and powder in reactor with standard KFI molecular sieve patterns.

[0030] Figure 4 The graph shows the pervaporation performance of molecular sieve membrane KFI-A1 for 50 wt% acetic acid / water pervaporation at different operating temperatures.

[0031] Figure 5 The graph shows the pervaporation performance of molecular sieve membrane KFI-A1 at an operating temperature of 70℃ for pervaporation of different concentrations of acetic acid / water.

[0032] Figure 6 The figure shows the comparison of the pervaporation performance of KFI molecular sieve membranes with different synthesis days at an operating temperature of 70℃ in 50wt% acetic acid / water.

[0033] Figure 7 The figure shows the comparison of the pervaporation performance of KFI molecular sieve membranes synthesized at different temperatures under an operating temperature of 70°C in 50 wt% acetic acid / water.

[0034] Figure 8 The figure shows the comparison of the pervaporation performance of KFI molecular sieve membranes with different synthesis days at an operating temperature of 70℃ in 90wt% ethanol / water.

[0035] Figure 9 XRD patterns of KFI-G1 and KFI-G2 molecular sieve membranes prepared with different ratios of loading solution and synthesis solution. Detailed Implementation

[0036] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

[0037] The main raw materials / materials and their sources in the various embodiments of this invention are as follows: The porous support used in this embodiment of the invention is an Al2O3 sheet-like porous carrier with a diameter of 22 mm and a circular upper surface area of ​​380 mm². 2 It has a thickness of 2mm and a volume of 0.76 cm³. 3 The micropores on the carrier have a diameter of 100 nm.

[0038] Aluminum hydroxide (Al(OH)3), potassium hydroxide (KOH), and strontium acetate (C4H6O4Sr) are commercially available conventional chemicals with a purity of ≥99%.

[0039] Silica sol: A dispersion of nano-sized silica particles in water or a solvent. In the embodiments of this invention, the silica sol used is an aqueous dispersion of silica, wherein the mass fraction of SiO2 is 30%.

[0040] Example 1: KFI zeolite molecular sieve membrane of the present invention I. Preparation of the KFI zeolite molecular sieve membrane of the present invention The KFI zeolite molecular sieve membrane of the present invention is prepared by the following steps: Step (1) Prepare the loading solution Preparation of Solution A: Add aluminum source aluminum hydroxide and alkali source potassium hydroxide to deionized water and stir until clear; Preparation of solution B: Strontium source strontium acetate (C4H6O4Sr) was added to deionized water and stirred until homogeneous; Preparation of the loading solution: Add solution A and solution B to the silicon source silica sol, and stir magnetically at 400 rpm for 10 min to mix thoroughly and evenly; a stable loading solution system is formed, in which the molar ratio of SiO2: K2O: Al2O3: SrO: H2O in the loading solution system is 1: 0.222: 0.1: 0.0095: 15.55.

[0041] Step (2), Loading of the loading liquid on the carrier The process is carried out using a standard laboratory vacuum filtration apparatus, which includes a receiving bottle, a filter cup, and a vacuum pump. The filter cup is installed on the receiving bottle, and the vacuum nozzle on the receiving bottle is connected to the vacuum pump with a tube to perform vacuum filtration.

[0042] Install the filter cup onto the receiving bottle, connect the suction nozzle on the receiving bottle to the vacuum pump with a tube, place the Al2O3 sheet porous carrier (hereinafter referred to as sheet carrier) flat at the bottom of the filter cup, take 4g of the loaded liquid prepared in step (1) and drop it onto the sheet carrier so that the surface of the sheet carrier is covered by the loaded liquid, turn on the vacuum pump and filter for 5 minutes at a negative pressure of 50 kPa.

[0043] In the method of this invention, the porous support is not limited to sheet-like form; it can also be tubular, plate-like, or hollow fiber-like. During vacuum filtration, the loading solution only needs to cover the surface of the support; the loading solution can also be in excess. This invention innovatively achieves a uniform loading of the loading solution membrane layer on the support surface beforehand by pre-filtering the loading solution. This enhances the bonding force between the support and the loading solution membrane layer, guiding crystals to synthesize on the support surface during the subsequent crystallization reaction, thereby synthesizing a dense molecular sieve membrane layer.

[0044] Step (3) Preparation of Synthesis Solution In this embodiment, the synthesis solution is directly the loading solution obtained in step (1), and the synthesis solution and the loading solution are the same solution.

[0045] Step (4) Crystallization film formation After the filtration in step (2), the sheet-like porous carrier is placed in the reactor. The loading solution (synthesis solution) prepared in step (1) is added to the reactor so that the synthesis solution completely submerges the sheet-like porous carrier. After sealing the reactor, it is allowed to stand at 145°C for 5 days for crystallization reaction.

[0046] After the crystallization reaction was completed, the support was removed and washed with deionized water until neutral. It was then dried in a 60°C oven for 12 hours to obtain a stable zeolite molecular sieve membrane loaded on a sheet-like porous support, which was denoted as molecular sieve membrane KFI-A1.

[0047] Figure 1 The image shows a scanning electron microscope (SEM) image of the synthesized KFI-type zeolite molecular sieve membrane, revealing uniform crystal growth and a dense membrane surface.

[0048] Figure 2 The image shows a cross-sectional scanning electron microscope (SEM) image of the synthesized KFI-type zeolite molecular sieve membrane, indicating that the membrane thickness is approximately 2 μm and the membrane layer is relatively uniform.

[0049] The prepared zeolite molecular sieve membrane was subjected to X-ray diffraction, and the X-ray diffraction results are as follows: Figure 3 As shown. By Figure 3 It can be seen that the XRD pattern of the molecular sieve membrane prepared in this embodiment is consistent with the standard pattern of KFI molecular sieve, indicating that the molecular sieve membrane prepared in this embodiment is a KFI zeolite molecular sieve membrane. Figure 3 In the text, Sample-KFI membrane represents a molecular sieve membrane, Sample-KFI is the powder taken out after the crystallization reaction in the reactor, and Standard-KFI is the standard spectrum of KFI molecular sieve. By comparison, it can be seen that the powder in the reactor is KFI zeolite.

[0050] Comparative example: The KFI-A1 method was used, but step (2) was omitted. Instead of adding the loading solution to the surface of the sheet support and then filtering, the sheet support was directly placed in the reactor for the crystallization reaction in step (3). After the reaction, no molecular sieve membrane was found to have formed on the surface of the support.

[0051] II. Performance Testing (1) Test method The sheet-like porous support loaded with KFI zeolite molecular sieve membrane prepared above was subjected to pervaporation test. The test device was based on Chinese Patent Application 202411972696.4 (Publication No. CN 119746641 A). Figure 5 The device in question differs from that in CN 119746641 A Figure 5The molecular sieve membrane tube in the present invention is replaced with a sheet-like porous support (hereinafter referred to as molecular sieve membrane) loaded with KFI zeolite molecular sieve membrane.

[0052] Tubular membrane modules are a common type of device in this field. One end of the module is closed, and the other end is connected to a pervaporation device. The assembled molecular sieve membrane and membrane module are placed in a feed tank containing a feed solution (e.g., an acetic acid / water system). A vacuum is drawn inside the membrane module, and the feed solution flows over the outside of the molecular sieve membrane. The easily permeable components in the feed solution (e.g., water) are preferentially adsorbed onto the surface of the molecular sieve membrane. Driven by the partial pressure difference between the inside and outside of the molecular sieve membrane, they permeate through the membrane to the permeate side and are collected through a cold trap tube connected to the permeate side of the membrane module (this is the permeate, which refers to the components in the feed solution that can permeate the molecular sieve membrane; in this case, the permeate is mostly water). The components that cannot permeate the molecular sieve membrane (acetic acid) remain in the feed tank, thus achieving the separation of water and acetic acid.

[0053] Pervaporation tests were conducted using the methods described above to assess the pervaporation performance of the molecular sieve membranes. The feed solution was an acetic acid / water system. Flux was characterized for all molecular sieve membrane products during the experiment. The definitions and detection methods for permeation flux and selectivity were based on industry standard HG / T 5540-2019.

[0054] (2) Performance of KFI zeolite molecular sieve membrane for pervaporation of 50 wt% water / acetic acid in the temperature range of 40~80 ℃ The performance of the prepared KFI-A1 molecular sieve membrane for pervaporation of 50 wt% acetic acid / water solution was investigated within the temperature range of 40–80 °C. The operating temperature was tested in an ascending trend. After each operating temperature test, the water bath temperature was adjusted to reach the target temperature of the feed solution. A 20-minute pre-vaporization process was performed before testing at the target operating temperature. After the pre-vaporization, the permeate was collected for flux calculation and component analysis using chromatography to calculate the selectivity at this operating temperature.

[0055] The results are attached. Figure 4 As shown, during the pervaporation test, the operating temperatures were set at 40 ℃, 50 ℃, 60 ℃, 70 ℃, and 80 ℃. The total permeation flux of the molecular sieve membrane increased significantly with increasing pervaporation feed liquid temperature. When the temperature increased from 40 ℃ to 80 ℃, the pervaporation flux increased from 322.07 g·m³. -2 ·h -1 It increased to 1050.41 g·m -2 ·h -1The separation factor fluctuated between 209.8 and 2396.2. Optimal flux was achieved at 80℃ with a permeate water content greater than 99%. This conforms to the conventional law of molecular sieve membranes: membrane flux increases with increasing pervaporation temperature.

[0056] (3) Performance of KFI type zeolite molecular sieve membrane for pervaporation of 50~90 wt% acetic acid / water at 70℃ The performance of the prepared molecular sieve membrane KFI-A1 in pervaporation of 50–90 wt% acetic acid / water was investigated. After each feed concentration test, the feed concentration was adjusted to the target concentration, and a 20-minute pre-vaporization process was performed before testing at the target feed concentration. After the pre-vaporization, the permeate was collected for flux calculation and component analysis using chromatography to calculate the selectivity at this feed concentration.

[0057] The results are attached. Figure 5 As shown, during the pervaporation test, the water concentration of the feed liquid was set at 10 wt%, 20 wt%, 30 wt%, 40 wt%, and 50 wt%. The total permeation flux of the molecular sieve membrane increased with the increase of the water concentration of the pervaporation feed liquid. When the water concentration increased from 10 wt% to 50 wt%, the pervaporation flux increased from 141.28 gm³ / s. -2 h -1 Increased to 748.7 g·m -2 ·h -1 The separation factor fluctuated within the range of 73.28 to 314.96. This conforms to the conventional rule of molecular sieve membranes: the higher the concentration of water in the feed solution, the higher the membrane flux.

[0058] III. Effects of Different Crystallization Times or Temperatures on Molecular Sieve Membranes 1. The effect of different crystallization times This experiment investigated the effect of different crystallization times on molecular sieve membranes. The steps (1) and (2) of the molecular sieve membrane preparation method were exactly the same as those of KFI-A1, except that different crystallization reaction days (3, 4, 5, and 6 days) were set in step (3), and the crystallization reaction temperature was 145℃ for all steps. The prepared molecular sieve membranes were subjected to pervaporation tests at an operating temperature of 70℃ in 50wt% acetic acid / water. A 20-minute pre-vaporization process was performed before testing at the target operating temperature. After the pre-vaporization was completed, the pervaporated permeate was collected for flux calculation and component analysis using chromatography to calculate the selectivity.

[0059] The results are attached. Figure 6 As shown, the membrane synthesized in 3 days exhibited low performance, a short crystallization time, and failed to form a dense membrane. The membrane synthesized in 4 days showed the best performance, with a pervaporation flux of 1219.55 g·m³. -2 ·h-1 The separation factor was 1031.28. When the synthesis time was 6 days, defects appeared on the membrane surface, leading to decreased selectivity. A synthesis time of 4-5 days was optimal.

[0060] 2. The effect of different crystallization temperatures This experiment investigated the effect of different crystallization temperatures on molecular sieve membranes. The steps (1) to (3) of the molecular sieve membrane preparation method were exactly the same as those of KFI-A1, except that different crystallization temperatures (115℃, 125℃, 135℃, 145℃, 155℃) were set in step (4), and the crystallization reaction time was 5 days for all steps. The prepared membranes were subjected to pervaporation tests at an operating temperature of 70℃ in 50% acetic acid / water. A 20-minute pre-vaporization process was performed before testing at the target operating temperature. After the pre-vaporization was completed, the pervaporated permeate was collected for flux calculation and component analysis using chromatography to calculate the selectivity.

[0061] The results are attached. Figure 7 As shown, the low temperature of 115℃ resulted in a slow crystallization rate, failing to form a dense, defect-free membrane, exhibiting high flux but low selectivity. Temperatures of 125℃ and 135℃ were suitable, yielding optimal performance; the membrane synthesized at 125℃ had a pervaporation flux of 1277.7 g·m³. -2 ·h -1 The separation factor is 1364.48, indicating the best overall performance. However, a temperature of 155℃ is too high, leading to excessive crystal growth and reduced throughput.

[0062] In addition, an experiment was conducted to perform a crystallization reaction at 135°C for 4 days.

[0063] The molecular sieve membrane experimental group with a molar ratio of SiO2:K2O:Al2O3:SrO2:H2O of 1:0.222:0.1:0.0095:15.55 in the loaded solution (which also serves as the synthesis solution) is designated as group KFI-A. The experiments on molecular sieve membranes with different crystallization times or temperatures are summarized in Table 1. The numbering, crystallization conditions, and performance results of the molecular sieve membranes for different experimental groups are shown in Table 1. The pervaporation tests of each experimental group in Table 1 are the results of tests conducted at 70℃ on a 50% acetic acid / water system.

[0064] Table 1

[0065] Table 1 shows that the molecular sieve membrane prepared by crystallization at 125℃ for 5 days exhibited the best flux and selectivity. The molecular sieve membranes prepared by reaction at 145℃ for 4 days and 135℃ for 5 days also showed good flux and selectivity. However, the selectivity of the molecular sieve membrane decreased significantly after reaction at 145℃ for 3 days. Overall, the molecular sieve membranes in all experimental groups in Table 1 met the requirements for pervaporation separation of acetic acid and all showed promising application potential.

[0066] IV. Separation performance of molecular sieve membranes in ethanol-water systems Molecular sieve membranes prepared using different crystallization reaction days (3, 4, 5, 6 days) and a crystallization reaction temperature of 145℃ were subjected to pervaporation tests in 90wt% ethanol / water at an operating temperature of 70℃. A 20-minute pre-vaporization process was performed before testing at the target operating temperature. After the pre-vaporization, the permeate was collected for flux calculation and component analysis using chromatography to calculate the selectivity.

[0067] The results are attached. Figure 8 As shown, when the crystallization time is 4 days, the pervaporation flux of the molecular sieve membrane is 1690.04 g·m⁻¹. -2 ·h -1 With a separation factor of 505.31, the molecular sieve membrane exhibits the best overall performance, indicating that it can be used for ethanol-water separation.

[0068] Example 2: Effect of different raw material ratios on the performance of molecular sieve membranes Following the preparation method of KFI-A1 in Example 1, molecular sieve membranes with different raw material ratios were prepared. The differences are shown in Table 2, while the remaining steps are the same. The prepared molecular sieve membranes were subjected to pervaporation tests on a 50% acetic acid / water system at 70°C, and the results are shown in Table 2.

[0069] Table 2

[0070] Table 2 shows that molecular sieve membranes KFI-B and KFI-C have the best overall performance in terms of flux and selectivity. KFI-D, due to excess potassium, leads to an increase in OH content in the system. - Excessive concentration leads to over-dissolution of the silicon-aluminum source and uncontrolled crystal growth, resulting in decreased film crystallinity and the formation of impurities / amorphous phases. This, in turn, causes membrane leakage and excessive flux, indicating that the membrane is essentially non-selective and has no application prospects. The remaining experimental groups all exhibited acetic acid selectivity and separation capabilities. Both can be applied to the dehydration and separation of acetic acid.

[0071] Example 3: Effect of different ratios of loading solution and synthesis solution on the performance of molecular sieve membranes The loading solution was prepared using solutions A and B, while the synthesis solution was prepared using solutions C and D. The raw material ratios of the loading solution and the synthesis solution were different. The preparation method of the synthesis solution was as follows: Solution C was prepared by adding the aluminum source and alkali source to deionized water and stirring until clear; Solution D was prepared by adding the strontium source to deionized water and stirring until homogeneous. Solutions C and D were then added to the silicon source silica sol and magnetically stirred at 400 rpm for 10 minutes to ensure thorough mixing and a stable synthesis solution system.

[0072] The preparation method of KFI-A1 in Example 1 was followed, except that the ratio of the loading solution to the synthesis solution was different. The loading solution had a molar ratio of SiO2:K2O:Al2O3:SrO2:H2O of 1:0.222:0.1:0.0095:15.55; the synthesis solution had a molar ratio of SiO2:K2O:Al2O3:SrO2:H2O of 1:0.222:0.1:0.0095:60. After crystallization at 145 °C for 4 days, molecular sieve membrane KFI-G1 was obtained. Its pervaporation performance in a 90 wt.% ethanol-water system at 65 °C was: permeate flux of 851.37 g·m³. -2 ·h -1 The selectivity of water for ethanol was 998.56; its pervaporation performance in a 50 wt.% acetic acid-water system at 65 °C showed a permeation flux of 980.51 g·m³. -2 ·h -1 The selectivity of water for acetic acid is 1234.60.

[0073] The preparation method of KFI-A1 in Example 1 was followed, except that the ratio of the loading solution to the synthesis solution was different. The loading solution had a molar ratio of SiO2:K2O:Al2O3:SrO2:H2O of 1:0.222:0.1:0.0095:15.55; the synthesis solution had a molar ratio of SiO2:K2O:Al2O3:SrO2:H2O of 1:0.222:0.1:0.0095:120. After crystallization at 145 °C for 4 days, molecular sieve membrane KFI-G2 was obtained. Its pervaporation performance in a 90 wt.% ethanol-water system at 65 °C was: permeate flux of 1038.72 g·m³. -2 ·h -1 The selectivity of water for ethanol was 980.91; its pervaporation performance in a 50 wt.% acetic acid-water system at 65 °C showed a pervaporation flux of 1055.43 g·m³. -2 ·h -1 The selectivity of water for acetic acid is 1011.56.

[0074] Depend on Figure 9 It can be seen that the XRD pattern of the molecular sieve membrane prepared in this embodiment is consistent with the standard pattern of KFI molecular sieve, indicating that the molecular sieve membrane prepared in this embodiment is a KFI zeolite molecular sieve membrane.

Claims

1. A method for preparing a KFI zeolite molecular sieve membrane, characterized in that, Includes the following steps: Step (1) Prepare the loading solution Preparation of Solution A: Add aluminum source and alkali source to deionized water and stir until clear; Preparation of solution B: Add the strontium source to deionized water and stir until homogeneous; Preparation of the loading solution: Add solution A and solution B to the silicon source, stir and mix thoroughly to obtain a stable loading solution system; the amount of each raw material used is based on the molar ratio of SiO2: K2O: Al2O3: SrO: H2O introduced by them being (0.9~1.1): (0.1~0.3): (0.05~0.5): (0.006~0.03): (10~60). Weigh out the silicon source, alkali source, aluminum source, strontium source and deionized water. Step (2): Load the loading liquid onto the porous carrier. Loading can be done in any of the following ways: ① Place the porous carrier in the vacuum filtration device, drop the load liquid onto the carrier so that the surface of the carrier is covered by the load liquid, turn on the vacuum filtration pump, and use negative pressure of 40~100 Kpa to vacuum filter so that the surface of the carrier is tightly bonded to the load liquid film layer; the preferred vacuum filtration time is 1~15 minutes. ② Preheat the porous carrier, immerse the surface of the carrier into the loading liquid at a speed of 100-1000 μm / s for 5-20s, and then pull it up at a speed of 100-1000 μm / s. A carrier loaded with the feed liquid is obtained; Step (3): Prepare the synthesis solution The amount of each raw material used in the synthesis liquid system is based on the molar ratio of SiO2: K2O: Al2O3: SrO: H2O introduced as (0.9~1.1): (0.1~0.3): (0.05~0.5): (0.006~0.03): (10~200). Weigh out the silicon source, alkali source, aluminum source, strontium source, and deionized water. Step (4) Crystallization film formation After the treatment in step (2) is completed, place the carrier in the reaction vessel, add the synthesis liquid to the reaction vessel so that the synthesis liquid completely submerges the carrier, seal the vessel and crystallize it at 100~180℃ for 3~6 days; After the crystallization reaction is complete, the support is removed, washed with deionized water until neutral, and dried to obtain a KFI zeolite molecular sieve membrane loaded on the support.

2. The preparation method according to claim 1, characterized in that: The aluminum source is selected from aluminum hydroxide, aluminum nitrate, aluminum isopropoxide, or aluminum sulfate; The alkali source is selected from potassium hydroxide or potassium carbonate; The strontium source is selected from strontium acetate, strontium nitrate, or strontium chloride; The silicon source is selected from silica sol, silica, or tetraethyl orthosilicate.

3. The preparation method according to claim 1, characterized in that: In step (1), after adding solutions A and B to the silicon source, stir at 200-800 rpm for 5-60 minutes to ensure thorough mixing. The amount of each raw material used is based on the molar ratio of SiO2:K2O:Al2O3:SrO:H2O introduced as (0.9-1.1):(0.1-0.25):(0.05-0.3):(0.006-0.02):(10-50). Weigh out the silicon source, alkali source, aluminum source, strontium source, and deionized water. Preferably, the molar ratio of SiO2:K2O:Al2O3:SrO:H2O is 1:(0.18-0.25):(0.08-0.15):(0.008-0.015):(10-40) or 1:(0.20-0.24). : (0.08~0.12) : (0.008~0.012) : (13~35); In step (3), the preparation method of the synthesis solution is as follows: Preparation of solution C: Add aluminum source and alkali source to deionized water and stir until clear; Preparation of solution D: Add the strontium source to deionized water and stir until homogeneous; Preparation of the synthesis solution: Add solution C and solution D to the silicon source, stir and mix thoroughly to obtain a stable synthesis solution system; Preferably, after adding solutions C and D to the silicon source, stir at 200-800 rpm for 5-60 minutes to ensure thorough mixing, with a preferred stirring time of 5-20 minutes. The amounts of each raw material used are based on the molar ratio of SiO2:K2O:Al2O3:SrO:H2O being (0.9-1.1):(0.1-0.25):(0.05-0.3):(0.006-0.02):(10-150). Weigh out the silicon source, alkali source, aluminum source, strontium source, and deionized water. Preferably, the molar ratio of SiO2:K2O:Al2O3:SrO:H2O is 1:(0.18-0.25):(0.08-0.15):(0.008-0.015):(10-120) or 1: (0.20~0.24) : (0.08~0.12) : (0.008~0.012) : (13~60).

4. The preparation method according to claim 1, characterized in that: In step (2), the porous carrier is selected from Al2O3 carrier, zirconium dioxide, mullite, porous stainless steel, and preferably Al2O3 carrier.

5. The preparation method according to claim 1, characterized in that: In step (2), the porous carrier is in the form of sheet, tube, plate or hollow fiber, and the pore size on the porous carrier is 20~1000nm; preferably, the porous carrier has a pore size of 100~200nm.

6. The preparation method according to claim 5, characterized in that: In step (2), the porous carrier is in sheet form, with each porous carrier measuring 350~400 mm. 2 Add 3-5 g of the loaded liquid to the surface of the filter and filter for 4-8 minutes.

7. The preparation method according to claim 1, characterized in that: In step (4), after sealing the container, the crystallization reaction is carried out at 110~160℃ for 3~6 days, preferably at 115~155℃ for 3~6 days, or at 115~155℃ for 4~5 days, or at 125~145℃ for 4~5 days.

8. A KFI zeolite molecular sieve membrane, prepared by the method described in any one of claims 1 to 7.

9. The application of the KFI zeolite molecular sieve membrane according to claim 8 in pervaporation, steam permeation or organic solvent dehydration separation.

10. The application according to claim 9, characterized in that: The organic solvent is selected from acetic acid, ethanol, ethyl acetate or isopropanol.

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