A molecular sieve membrane with improved performance through ion exchange, its preparation method and application

Abstract

This invention discloses a molecular sieve membrane with improved performance through ion exchange, its preparation method, and its applications. The preparation method includes the following steps: S1: dissolving a metal salt in a solvent to prepare a metal ion solution; S2: contacting the molecular sieve membrane with the metal ion solution and performing ion exchange under microwave-assisted solvothermal conditions; S3: washing and drying the ion-exchanged molecular sieve membrane to obtain a molecular sieve membrane with improved performance after metal ion exchange. The improved molecular sieve membrane obtained by this invention exhibits significantly enhanced permeation flux and / or selectivity. It can be used not only for organic solvent dehydration and separation but also for gas separation (such as natural gas decarbonization, pre-combustion carbon capture, and ammonia collection in ammonia synthesis). The method is simple to operate, time-saving, and low-cost, making it suitable for large-scale industrial production.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of membrane separation technology, in particular to a molecular sieve membrane with improved performance by ion exchange, and a preparation method and application thereof. BACKGROUND

[0002] Anhydrous ethanol is an important organic solvent and chemical raw material, which has a wide range of applications in national defense industry, organic synthesis, food industry, medical and health care, and can also be used as biofuel or gasoline additive for internal combustion engine. The separation of ethanol and water is an important step for preparing anhydrous ethanol. However, it is difficult to meet the separation requirements by using traditional rectification due to the azeotropy of ethanol and water. The methods such as azeotropic rectification, molecular sieve adsorption and pressure swing adsorption can be used for further dehydration of ethanol, but the equipment investment is large, the process is complex and the energy consumption is high.

[0003] As a new type of separation technology with high efficiency, low energy consumption and simple process, membrane separation plays an increasingly important role in production and life. Membrane separation technology uses materials with selective separation function to realize the separation of different components in the feed liquid by using the selectivity of the membrane. Pervaporation (PV) is a kind of membrane separation technology, which is especially suitable for the separation of azeotropes. PV uses the chemical potential difference of certain components between the upstream and downstream of the membrane as the driving force for mass transfer, and uses the difference in affinity and mass transfer resistance of the membrane to different components in the feed liquid to achieve selectivity. The more commonly used aspects are: recovery of organic matter in water, separation of organic mixture system and dehydration of organic solvent.

[0004] Membrane material is the core of membrane separation. Molecular sieve membrane is a new type of membrane material that can realize molecular sieve separation, which has a pore size comparable to and uniform with the size of molecules, ion exchange performance, high temperature thermal stability, excellent shape-selective catalytic performance, easy modification and multiple types and structures for selection, and is an ideal membrane separation and membrane catalytic material. Molecular sieves have various types, which can be classified according to different characteristics: according to the structure type, molecular sieves can be divided into LTA type, FAU type, etc.; according to the different silicon aluminum ratio, molecular sieves can be generally divided into low-silicon zeolite molecular sieves (Si / Al<10, such as A type, X type, Y type, etc.), high-silicon zeolite molecular sieves (10<Si / Al<100, such as MOR type, FER type, ZSM-5, etc.), and full-silicon zeolite molecular sieves (Si / Al>100, such as MFI type, DDR type, etc.); according to the type of metal cation, molecular sieves can be divided into potassium type, sodium type, calcium type, etc.; according to the composition of the framework elements, molecular sieves can be divided into silicon-aluminum molecular sieves, phosphorus-aluminum molecular sieves, titanium-silicon molecular sieves, etc.; according to the shape of the carrier, molecular sieve membranes are also divided into single-channel molecular sieve membranes, multi-channel molecular sieve membranes, flat plate molecular sieve membranes, hollow fiber molecular sieve membranes, etc.

[0005] Zeolite molecular sieves are inorganic microporous materials with regular nanopores and cage structures, constructed using TO4 (T = Si, Al, P, etc.) tetrahedra as basic units and connected by bridging oxygen at common vertices. Their pore size is generally less than 2 nm. Typical LTA molecular sieve membranes possess a three-dimensional pore system with pore sizes at the nanoscale (0.3-0.5 nm), falling between water molecules (0.29 nm) and most organic molecules (>0.45 nm). They exhibit high chemical and thermal stability, and their regular pore structure enables precise molecular-scale sieving. Furthermore, due to their low silica-to-alumina ratio (only 1), LTA molecular sieve membranes display excellent hydrophilicity. Based on the adsorption-sieving mechanism, low silica-to-alumina ratio zeolite molecular sieve membranes exhibit excellent separation performance in organic solvent dehydration and have been the first to achieve industrial applications. To further enhance the pervaporation separation efficiency of molecular sieve membranes and broaden their industrial application fields, further optimization of molecular sieve membrane materials and processes is needed.

[0006] Molecular sieve membranes are typically grown on the surface of a porous support (common tubular molecular sieve membranes such as...). Figure 4 (As shown). Typical molecular sieve membrane tubes are usually installed in tubular membrane module devices. The inside of the membrane tube is evacuated (the inside of the membrane tube is the vacuum side, i.e., the permeate side). When the feed liquid flows through the outside of the membrane tube, the easily permeable components in the feed (such as water) are preferentially adsorbed on the surface of the molecular sieve membrane. Driven by the partial pressure difference between the inside and outside of the membrane tube, they permeate through the membrane layer and diffuse to the permeate side inside the membrane tube. The permeate enters the cold trap tube through the outlet connected to the permeate side of the membrane tube and is condensed and collected. Components that cannot permeate through the molecular sieve membrane are retained on the outside of the membrane tube and continue to circulate on the feed side until the separation requirements are met.

[0007] Ion exchange is an important method for optimizing the catalytic performance of molecular sieves or the separation performance of molecular sieve membranes. Unlike molecular sieve powders, molecular sieve membranes may experience the following issues during ion exchange: 1. The solid-liquid interface prioritizes contact area, resulting in a slower ion exchange rate and longer processing time; 2. Solvent water may damage the microstructure of low silica-to-alumina ratio molecular sieve membranes, reducing their crystallinity and stability, potentially leading to decreased or even lost separation performance; 3. Due to limited ion diffusion, ion exchange in molecular sieve membranes may be limited to the surface, resulting in insufficient exchange depth and limited performance improvement. To address these issues, researchers have explored various methods in recent years to improve ion exchange efficiency and enhance the overall membrane performance. Zhu Meihua et al. conducted ion exchange by immersing NaY-type molecular sieve membranes in solutions of different metal ions. Their research showed that different metal cations significantly affect the pervaporation performance of the molecular sieve membrane. Zhu Meihua et al. [Chinese Journal of Chemical Engineering, 2023, 59: 176-181.] immersed NaY-type molecular sieves in solutions of different metal ions (Ag... +, K + , Ca 2+ , Zn 2+ , Co 2+ , Mg 2+ ) aqueous solution at 50℃ for 2h, and compared the pervaporation performance before and after ion exchange. The results show that different metal cations have an important influence on the separation performance of NaY zeolite membrane. The selectivity of Y zeolite membrane exchanged by Zn(NO3)2 is improved by 230% in ethanol dehydration, but the total flux decreases by 45%, indicating that zinc ion exchange can significantly improve the selectivity, but may be accompanied by a decrease in flux.

[0008] On the other hand, NaA zeolite has a lower Si / Al ratio (1:1) and poor hydrothermal stability, and is more likely to be structurally damaged during ion exchange in water medium. Therefore, how to shorten the ion exchange time and optimize the ion exchange conditions to ensure the integrity of the microstructure and crystallinity of the zeolite membrane, while taking into account the improvement of permeation flux and selectivity, has become a focus of attention in academia and industry. This not only involves basic research in the field of materials science, but also has important significance for the practical application of zeolite membranes in industrial dehydration and separation. Unlike ion exchange of zeolite powder, ion exchange of zeolite membrane is limited by the small contact area of solid-liquid interface, so the treatment time of the membrane is longer.

[0009] Zhong et al. (Journal of Membrane Science, 2022, 643, 119998) used aqueous cation chloride solution (1.0 mol L -1 ) to continuously stir at 333K water bath for 48h, to exchange Na+ in the membrane into monovalent (H+, Li+, K+, Cs+) and divalent (Mg2+, Ca 2 +, Ba 2 +) cations. Among them, the H+-exchanged MOR membrane has the largest pore size and the highest water adsorption capacity, and when performing pervaporation on 90wt% acetic acid / water mixture at 348K, it shows a maximum permeation flux of 3.68kg m-2h-1 and a separation factor of 472. But the high water content and long ion exchange process are not suitable for NaA zeolite membrane with lower Si / Al ratio.

[0010] Huang Aiseng et al. (Chinese Chemical Letters, 2019, 30, 1204-1206) used 0.005 mol L -1 copper acetate (Cu(Ac)2) methanol solution, and after ion exchange at 50℃ for 5h, Cu-LTA zeolite membrane was obtained, but Cu 2+lower degree of ion exchange. Compared with the original Na-LTA membrane, the separation factor slightly decreased (Cu-LTA 3591, Na-LTA 4082) and the permeation flux increased by 113% (Cu-LTA 3.52 kg m-2h-1, Na-LTA 1.65 kg m-2h-1) in 90 wt.% ethanol aqueous solution at 75℃. Further attempts to increase the exchange ratio by high concentration of copper acetate (0.1 mol L -1 and 0.01, 0.005 mol L -1 methanol solution, but the LTA zeolite membrane was easily damaged with cracks under this condition.

[0011] In summary, the current molecular sieve membrane modification methods mainly have the following shortcomings: 1. long time-consuming; 2. the current ion exchange technology often needs a large amount of solution, which is high in cost; 3. the current ion exchange technology often cannot balance the flux and selectivity of the molecular sieve membrane. Whether the ion exchange time can be shortened, the ion exchange degree can be improved, and the microstructure of the membrane can be ensured to be complete and the crystallinity can be ensured to be high, while the permeation flux and selectivity of the molecular sieve membrane are improved, is the focus of the academic and industrial circles. There is no report on the application of microwave-assisted solvothermal method to ion exchange of molecular sieve membrane. SUMMARY

[0012] The purpose of the present application is to provide a molecular sieve membrane with improved performance by ion exchange and a preparation method and application thereof.

[0013] In order to achieve the purpose, the technical scheme adopted by the present application is:

[0014] The first aspect of the present application provides a method for preparing a high-performance molecular sieve membrane by ion exchange, comprising the following steps:

[0015] S1: dissolving a metal salt into a solvent to prepare a metal ion solution;

[0016] S2: contacting a molecular sieve membrane with the metal ion solution prepared in step S1, and performing ion exchange under the condition of microwave-assisted solvothermal method;

[0017] S3: washing and drying the molecular sieve membrane after ion exchange in step S2 to obtain a molecular sieve membrane with improved performance after metal ion exchange.

[0018] In step S1, the metal salt is selected from one or more of chloride, nitrate, sulfate and carbonate of neodymium ion, lanthanum ion, silver ion, copper ion, potassium ion, calcium ion, cesium ion or lithium ion;

[0019] The solvent in step S1 is deionized water, methanol, ethanol, isopropanol, n-propanol, ethylene glycol or a mixture of two or more thereof; the concentration of metal ions in the metal ion solution is 0.001-0.5 mol / L -1 .

[0020] Preferably, in step S1, the metal salt is selected from one or more of chloride, nitrate, sulfate and carbonate of neodymium ion, lanthanum ion and lithium ion; the solvent is preferably selected from deionized water, methanol, ethanol and isopropanol; the concentration of metal ions in the metal ion solution is 0.01-0.3 mol / L -1 or 0.03-0.1 mol / L -1 or 0.04-0.07 mol / L -1 .

[0021] The molecular sieve membrane comprises a carrier and a framework material loaded on the carrier; the carrier is in a form of a flat plate, a tube or a hollow fiber;

[0022] The carrier is selected from an alumina carrier, a titania carrier and a stainless steel mesh carrier, the alumina carrier comprises an α-Al2O3 carrier, a γ-Al2O3 carrier and an anodized aluminum carrier; the pore size of the micropores on the carrier is 5 nm-1 μm;

[0023] The framework material is selected from LTA, CHA, FAU, MOR, MFI and UFI molecular sieve membranes, and is preferably an LTA or CHA molecular sieve membrane.

[0024] Preferably, in step S2, the working temperature of the microwave-assisted solvothermal method is 30-150 ℃, and the processing time is 5-60 min.

[0025] Further preferably, the working temperature of the microwave-assisted solvothermal method is 50-130 ℃ or 50-120 ℃ or 90-105 ℃, and the processing time is 15-35 min or 20-30 min.

[0026] In step S3, the washing reagent used for washing the molecular sieve membrane is deionized water, methanol, ethanol, isopropanol or n-propanol, and the washing is performed until the eluate is close to neutral;

[0027] The drying condition is: drying at a temperature of 50-200 ℃ and a vacuum degree of 0-0.1 MPa for 0.5-24 h; preferably, drying at a temperature of 50-80 ℃ and a vacuum degree of 0-0.1 MPa for 8-16 h.

[0028] Preferably, in the above method, the molecular sieve membrane is compounded on the outer surface of a tubular porous carrier, and the object to be treated is a molecular sieve membrane tube.

[0029] In step S2, one end of the molecular sieve membrane tube is blocked with a plug, a metal ion solution is added into the molecular sieve membrane tube (preferably, the volume of the metal ion solution is 30% to 100% of the volume of the molecular sieve membrane tube), then the other end of the molecular sieve membrane tube is blocked with a plug with a pinhole, and the molecular sieve membrane tube with the ion exchange solution inside is placed in a microwave reaction kettle for microwave-assisted solvothermal reaction.

[0030] In step S3, after the microwave-assisted solvothermal reaction is completed, the molecular sieve membrane tube is taken out after the reaction system is cooled (preferably, when the temperature is below 50℃), the plug is removed, the molecular sieve membrane tube is washed until the eluate is close to neutral, and then the molecular sieve membrane tube is dried to obtain the product.

[0031] The second aspect of the present application provides a high-performance molecular sieve membrane prepared by any of the above methods.

[0032] The third aspect of the present application provides the use of the above molecular sieve membrane in pervaporation, vapor permeation or gas separation; preferably, the use in deep dehydration of organic solvents or dehydration of azeotropic or near-azeotropic systems of organic solvents / water.

[0033] The present application has the following advantages:

[0034] 1. Previous studies have shown that when water is used as the solvent of the ion solution, if the ion solution directly contacts the molecular sieve membrane, because the Si / Al ratio of NaA molecular sieve membrane (NaA is a common LTA type molecular sieve) is only 1, the hydrothermal stability is poor, and direct contact with the ion exchange solution with high water content (water is a strong polar solvent) may damage the structure of the molecular sieve membrane under heating conditions, and long-term high-temperature conditions may cause the collapse of the molecular sieve membrane framework and lose the separation performance. The present application has found that by treating the tubular LTA molecular sieve membrane by adding the ion exchange solution in the carrier side (i.e., the inside of the tube of the membrane tube), instead of directly contacting the ion exchange solution with the membrane side outside the membrane tube, the damage of the solvent to the membrane under heating conditions can be reduced.

[0035] 2. The present application uses microwave-assisted solvothermal method to perform ion exchange of the molecular sieve membrane, and the treatment process can perform fast and uniform ion exchange under mild reaction conditions; the ion exchange rate is fast, the operation process is simple, the treatment time can be effectively shortened, the heating uniformity is good, which helps to improve the uniformity of ion exchange; microwave heating can also accelerate the migration of ions, which helps to improve the ion exchange depth; by passing the ion exchange solution into the inside of the molecular sieve membrane tube for treatment, the amount of ion solution required can be greatly reduced, and the cost can be reduced; the method of the present application can realize batch-controlled preparation and be applied on a large scale in industry.

[0036] 3、The improved molecular sieve membrane of the method has obvious improvement in permeation flux and / or selectivity compared with the blank molecular sieve membrane without treatment, and the dehydration performance of the molecular sieve membrane is excellent when the operation parameters (temperature and concentration of raw liquid) in the pervaporation test are changed, and the molecular sieve membrane is suitable for dehydration of different solvents, especially for deep dehydration of organic solvents or dehydration of azeotropic or near-boiling system of organic solvents / water, thereby laying a foundation for further wide application of the molecular sieve membrane in pervaporation separation.

[0037] 4、The improved molecular sieve membrane of the application can not only be used for dehydration and separation of organic solvents, but also be used for gas separation (such as decarburization of natural gas, carbon capture before combustion, and collection of ammonia gas in synthetic ammonia) and the like. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 is a temperature gradient diagram of pervaporation of the blank control LTA membrane tube at different temperatures after microwave treatment (90℃, 20min) of the LTA membrane tube with a neodymium ion solution.

[0039] Figure 2 is a temperature gradient diagram of pervaporation of the blank control LTA membrane tube at different temperatures after microwave treatment (120℃, 20min) of the LTA membrane tube with a neodymium ion solution and a lanthanum ion solution.

[0040] Figure 3 is a concentration gradient diagram of pervaporation of the blank control LTA membrane tube at different concentrations after microwave treatment (90℃, 20min) of the LTA membrane tube with a neodymium ion solution.

[0041] Figure 4 is a conventional molecular sieve membrane tube.

[0042] Figure 5 is a performance detection device and flow process schematic diagram of the molecular sieve membrane tube. DETAILED DESCRIPTION

[0043] The application will be further described in combination with examples, but the application is not limited by the examples.

[0044] The experimental methods in the following examples are conventional methods, unless otherwise specified.

[0045] Glossary

[0046] Tubular molecular sieve membrane:

[0047] The tubular molecular sieve membrane (or molecular sieve membrane tube) used in the examples and comparative examples of the application is a commonly used membrane tube with Al2O3 porous ceramic base as the carrier (or support) and the membrane layer as the molecular sieve membrane (such as Figure 4The molecular sieve membrane is a thin film, and in the molecular sieve membrane tube, the molecular sieve membrane is compounded on the outer surface of the tubular porous carrier, which is installed into a tubular membrane assembly device for experiments during the experiment.

[0048] The molecular sieve membrane is grown on one side of the carrier, and is generally divided into a carrier side (for example, the inner side of the tubular carrier of the tubular molecular sieve membrane) and a membrane side (for example, the side of the membrane attached to the outer surface of the tubular carrier).

[0049] The tubular molecular sieve membrane used in the embodiments of the present application is of the LTA type (indicated using the international structure code), specifically, NaA type, which is commercially available; the length of the molecular sieve membrane tube is 50 mm, and the inner diameter is 8 mm.

[0050] Examples

[0051] The present application provides a preparation method of a molecular sieve membrane with improved performance by ion exchange, which is operated according to the following steps:

[0052] S1: 0.6265 g of neodymium chloride (NdCl3) powder is dissolved in a solvent (deionized water or alcohol) to 50 mL, and ultrasonic treatment is performed for 20 min to obtain a neodymium chloride solution with a concentration of 0.05 mol / L. -1

[0053] S2: The bottom of the tubular LTA molecular sieve membrane (hereinafter referred to as LTA molecular sieve membrane) is blocked with a polytetrafluoroethylene plug, 3.5 mL of the solution prepared in S1 is added into the tube of the LTA molecular sieve membrane to almost fill the metal ion solution in the tube, and then a polytetrafluoroethylene plug with a pinhole is used to block the top of the LTA molecular sieve membrane. The LTA molecular sieve membrane is transferred to a microwave reaction kettle, and the microwave parameters are set to be heated to 90℃ within 6 min, and then kept at 90℃ for 20 min, and then naturally cooled.

[0054] Since the temperature of microwave heating is close to the boiling point of the alcohol solvent, the vapor pressure is relatively large under the condition of sealing, and the plug is used to block the molecular sieve membrane tube to prevent the metal ion solution from flowing out from both ends of the membrane tube, so that there is always a small amount of metal ion solution in the membrane tube, and the metal ion solution passes through the micropores on the carrier from the inside of the membrane tube to the molecular sieve membrane loaded on the outer surface of the membrane tube for ion exchange. The plug at the top of the membrane tube has a pinhole to prevent the vapor pressure in the membrane tube from being too large to cause the plug to be knocked off.

[0055] ​In the previous experiment, we tried to use the metal ion solution and molecular sieve membrane directly contact with microwave heating assisted ion exchange, the microstructure of the molecular sieve membrane has no obvious change, but the repeatability of the membrane performance is not good. While using the membrane tube filled with metal ion solution, the molecular sieve membrane on the surface of the membrane tube is ion exchanged under the assistance of microwave heating, which can achieve sufficient ion exchange degree, while avoiding the solution and the membrane surface from a large number of contact, preventing the possible damage to the membrane structure.

[0056] S3: When the temperature of the reaction system is reduced to below 50°C, the LTA molecular sieve membrane is taken out, the upper and lower polytetrafluoroethylene plugs are removed, and the entire membrane tube is immersed in deionized water at room temperature for washing three times (at this time, the eluent after washing is close to neutral), and then transferred to a 60°C oven for 12h, to obtain the LTA molecular sieve membrane after ion exchange optimization under the assistance of microwave solvent.

[0057] The molecular sieve membranes of Examples 1-11 and Comparative Examples 1-2 were prepared according to the above method, except that the type and concentration of the selected metal salt, the solvent used to dissolve the metal salt, the heating treatment method (comparative examples do not use microwave heating, but use oven heating) and its operating parameters are different, and the specific experimental conditions are shown in Table 1:

[0058] Table 1 Molecular sieve membranes of examples and comparative examples

[0059]

[0060]

[0061] Comparative Examples

[0062] Different comparative examples were set up to compare the effects of different metal salts, solvents and heating treatment methods on the improvement of membrane performance, as shown in Table 1.

[0063] Performance Testing

[0064] The performance of the tubular molecular sieve membrane treated with metal salt solution prepared in the above examples and comparative examples was tested: the molecular sieve membrane treated with metal salt solution was installed into the tubular membrane module device for experiment (the detection schematic diagram is as shown in Figure 5The tubular membrane module device is a common module device in the current technical field, one end of which is closed and the other end is connected to the pervaporation device. The assembled membrane tube and membrane module are placed in a raw material tank containing raw liquid (90 wt.% ethanol / water system). The inside of the membrane tube is vacuumized (the inside of the membrane tube is the vacuum side, i.e. the permeation side), the raw liquid flows outside the membrane tube, and the easily permeable components (such as water) in the raw liquid are preferentially adsorbed on the surface of the molecular sieve membrane. Under the driving force of the pressure difference between the inside and outside of the membrane tube, the easily permeable components permeate through the molecular sieve membrane on the outer surface of the membrane tube into the permeation side inside the membrane tube, and are collected by the cold trap tube connected to the permeation side of the membrane tube (i.e. the permeate, which refers to the components in the raw liquid that can permeate through the molecular sieve membrane. In this case, the permeate is mostly water).

[0065] The pervaporation test is carried out according to the above method to detect the pervaporation performance of the molecular sieve membrane.

[0066] In the experiment, the flux of all molecular sieve membrane tube products is characterized, and the definition and detection method of permeation flux are referred to industry standard HG / T 5540-2019:

[0067] The permeation flux (J, kg m -2 h -1 ) and selectivity a 水 / 乙醇 are calculated by formulas (1) and (2) respectively:

[0068] J = M / (t x A) = (m1-m2) / (t x p x D x I) (1)

[0069] a (水 / 乙醇) = (y 水 / y 乙醇 ) / (x 水 / x 乙醇 ) = f x [(A 水，渗透液 / A 乙醇，渗透液 ) / (A 水，原料液 / A 乙醇，原料液 )] (2)

[0070] Where M is the mass of the permeate (kg); D is the outer diameter of the membrane tube (m), I is the effective membrane tube length (m), t is the test time (h), x 水 and x 乙醇 are the mass fractions of water and ethanol in the raw liquid, y 水 and y 乙醇 are the mass fractions of water and ethanol in the permeate, f is the relative correction factor, A 水，原料液 and A 乙醇，原料液 are the peak area percentages of water and ethanol in the raw liquid, A 水，渗透液 and A 乙醇，渗透液are the percentages of the peak area of the elution peak of water and ethanol in the permeate, respectively.

[0071] Test Results

[0072] The performance of the membrane tubes before (i.e. blank membrane tubes) and after treatment with metal ion solution was detected, and the raw material liquid was a 90wt.% ethanol / water system, and the temperature of the pervaporation was 60°C. The test results are shown in Table 2:

[0073] Table 2 Performance test results

[0074]

[0075] *Note: One example can have multiple repetitions, even if it is the same specification of the molecular sieve membrane tube, the initial performance of different blank membrane tubes can be different. In Table 2, Example 1-repetition 1, 2 and 3 refer to one of the multiple membrane tubes of the same specification of LTA molecular sieve membrane tube which is improved by the same treatment method. The performance of each membrane tube before and after treatment is detected.

[0076] The membrane tube of Comparative Example 1 was subjected to pervaporation at 60°C in a 90wt.% EtOH / H2O system, and the permeate flux was reduced from 1.46kg h -1 m -2 to 0.47kg h -1 m -2 , a decrease of 67.81%; the average water content in the permeate was reduced from 99.62% to 95.98%, a decrease of 3.66%; and the selectivity was reduced from 1936.48 to 180.39, a decrease of 90.68%. The flux of the membrane tube of Comparative Example 2 was reduced from 1.62kg h -1 m -2 to 1.45kg h -1 m -2 , the water content was reduced from 99.78% to 99.48%, and the selectivity was reduced from 3861.42 to 1686.21.

[0077] Figure 1 is a temperature gradient diagram of the pervaporation of the blank control LTA membrane tube at different temperatures after the neodymium ion solution was subjected to microwave treatment in the LTA membrane tube (90°C, 20min) (Example 1-repetition 2), and the raw material liquid was a 90wt.% ethanol / water system, and the temperature of the pervaporation was 60°C. Figure 1 As can be seen from the temperature gradient diagram, after the neodymium ion solution was subjected to microwave treatment in the LTA membrane tube, the water flux and the selectivity of the blank membrane tube at different temperatures were both improved. Especially at 60°C, the water content in the permeate was increased from 91.18% to 99.53%, and the corresponding selectivity (86.17→1746.84) was increased by 1927.20%, and the selectivity was significantly improved, and the reaction conditions were mild.

[0078] Figure 2 is the temperature gradient diagram of pervaporation of neodymium ion solution (Example 3) and lanthanum ion solution (Example 4) (solvent is water) in LTA membrane tube after microwave treatment (120℃, 20min) at different temperatures, and the feed liquid is 90wt.% ethanol / water system, and Figure 2 It can be seen that, at different temperatures, compared with neodymium ion exchange, the membrane tube after lanthanum ion exchange has better selectivity, and its selectivity performance is maintained at a high level.

[0079] Figure 3 is the concentration gradient diagram of pervaporation of neodymium ion solution (Example 1-Repeat 3) in LTA membrane tube after microwave treatment (90℃, 20min) and blank control LTA membrane tube at different ethanol / water system feed liquid concentrations (10, 15, 20, 25, 30wt% water concentration, corresponding to 90, 85, 80, 75, 70wt% ethanol concentration) at 60℃, and the membrane tube after neodymium ion exchange can maintain high selectivity in different feed liquid concentrations. The test results show that, for different concentrations of feed liquid, the Nd-LTA molecular sieve membrane after microwave-assisted ion exchange can maintain high separation performance, and has a wide range of applications. From the results of Examples 1-11 and Comparative Examples 1-2, it can be seen that when the heating method is oven heating, the flux and selectivity of the membrane tube are reduced, and the performance of the membrane tube cannot be improved but is decreased. When microwave heating is used, the flux and / or selectivity of the membrane tube can be improved. Compared with the use of water (Examples 1-4), the flux is reduced and the selectivity is improved. When alcohol is used as the solvent (Examples 5-11), the repeatability of the performance improvement of the membrane tube is better, and the flux and selectivity are improved. (Example 9) After the lanthanum ion solution is treated in the LTA membrane tube by microwave (50℃, 20min, and the solvent is isopropanol), in the feed liquid of 90wt.% ethanol / water system, the flux of pervaporation at 60℃ is 1.96kg h -1 m -2 , and the selectivity is 2719.61 (Table 2 data); when the test system is changed to 90wt.% methanol / water, the flux is 0.72kg h -1 m -2 , and the selectivity is 46.78; and when the system is changed to 90wt.% isopropanol / water, the flux increases to 1.82kg h -1 m -2 , and the selectivity increases to 222.64. The results show that the membrane after ion exchange optimization has a universal enhancement effect in many solvent dehydration.

[0080] Compared with the prior art, the method has the advantages of short time consumption, simple operation, low cost, small amount of ion exchange solution required, low cost, and can effectively improve the flux and / or selectivity of the membrane tube.

Claims

1. A method for preparing a high performance molecular sieve membrane by ion exchange, characterized by, The method comprises the following steps: S1: dissolving a metal salt into a solvent to prepare a metal ion solution; S2: the molecular sieve membrane comprises a carrier and a skeleton structure material loaded on the carrier; the carrier is tubular; the carrier is selected from an alumina carrier, a titania carrier, and a stainless steel mesh carrier; the alumina carrier comprises an α-Al2O3 carrier, a γ-Al2O3 carrier, and an anodic aluminum carrier; the pore size of the micropores on the carrier is 5 nm-1 µm; the skeleton structure material is selected from LTA, CHA, FAU, MOR, MFI, and UFI molecular sieve membranes; the molecular sieve membrane is compounded on the outer surface of the tubular porous carrier, and the object to be treated is a molecular sieve membrane tube; one end of the molecular sieve membrane tube is plugged with a plug, the metal ion solution prepared in step S1 is added into the molecular sieve membrane tube, then the other end of the molecular sieve membrane tube is plugged with a plug, and the molecular sieve membrane tube is placed in a microwave reaction kettle for microwave-assisted solvothermal reaction for ion exchange; S3: after the microwave-assisted solvothermal reaction is completed, the molecular sieve membrane tube is taken out after the reaction system is cooled, the plug is removed, and the molecular sieve membrane tube is washed until the eluent is close to neutral; Then the molecular sieve membrane tube is dried to obtain a molecular sieve membrane with improved performance after ion exchange of metal ions.

2. The method of claim 1, wherein: in step S1, the metal salt is selected from one or more of chloride, nitrate, sulfate, and carbonate of neodymium ions, lanthanum ions, silver ions, copper ions, potassium ions, calcium ions, cesium ions, and lithium ions; The solvent in step S1 is deionized water, methanol, ethanol, isopropanol, n-propanol, ethylene glycol or a mixed solvent of two or more thereof; the concentration of metal ions in the metal ion solution is 0.001-0.5 mol / L -1 .

3. The method of claim 2, wherein: in step S1, The metal salt is selected from one or more of chloride, nitrate, sulfate, carbonate of neodymium ion, lanthanum ion, lithium ion; the solvent is selected from deionized water, methanol, ethanol, isopropanol; the concentration of metal ion in the metal ion solution is 0.01-0.3 mol / L -1 .

4. The method of claim 1, wherein: the skeleton structure material is an LTA or CHA molecular sieve membrane.

5. The method of claim 1, wherein: in step S2, the working temperature of the microwave-assisted solvothermal method is 30-150 °C, and the treatment time is 5-60 min.

6. The method of claim 5, wherein: the working temperature of the microwave-assisted solvothermal method is 50-130 °C, and the treatment time is 15-35 min.

7. The method of claim 1, wherein: in step S3, the washing reagent used for washing the molecular sieve membrane is deionized water, methanol, ethanol, isopropanol, or n-propanol, and the washing is performed until the eluent is close to neutral; the drying conditions are as follows: drying at a temperature of 50-200 °C, a vacuum degree of 0-0.1 MPa, and for 0.5-24 h.

8. A high performance molecular sieve membrane characterized by: is prepared by the method of any one of claims 1-7.

9. The molecular sieve membrane of claim 8 for use in pervaporation, vapor permeation, or gas separation.

10. Use according to claim 9, characterized in that: the molecular sieve membrane for use in deep dehydration of an organic solvent or dehydration of an organic solvent / water azeotrope or near-azeotrope system.

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