A continuous directional ordering zif-l high performance membrane for alcohol water separation

Abstract

The patent relates to a method for improving the preparation of sodium alginate pervaporation membrane by using two-dimensional leaf-shaped zeolitic imidazolate framework (ZIF-L) material. The pervaporation mixed matrix membrane comprises a base film and a separation layer film, the base film adopts polyacrylonitrile (PAN) film, and the separation layer is composed of ZIF-L and sodium alginate. The application improves the distribution of ZIF-L in the membrane, forms directional arrangement, and improves the separation effect and selectivity of the composite membrane. By using a new process, the defect problem of ZIF-L-SA membrane is eliminated, a continuous ultrathin ZIF-L membrane is prepared by a secondary seed growth method, and the performance of the two-dimensional ZIF-L membrane is improved. The ZIF-L synthesis condition is mild, the method is simple, the hydrophilic modification of the membrane surface is realized, the internal water molecule transmission channel is constructed, and the separation factor and stability of the membrane are improved. The prepared high-flux pervaporation membrane has broad application prospect.

Description

TECHNICAL FIELD

[0001] The application relates to a continuous directional sequencing ZIF-L high-performance membrane for alcohol-water separation, and belongs to the technical field of separation membrane preparation. BACKGROUND

[0002] Pervaporation membrane technology is an advanced membrane separation technology that uses specially designed high polymer membranes to achieve efficient separation of components in liquid mixtures. This technology is based on the selective permeation and vaporization principle of membranes, and is an important development in the field of membrane science in the late 20th century and early 21st century. Pervaporation membrane technology is valued for its simple operation, strong adaptability, low energy consumption, high separation efficiency and environmental friendliness. It can achieve molecular-level separation and is not limited by traditional gas-liquid equilibrium, and is particularly suitable for processing systems that are high in cost or low in efficiency using conventional separation methods (such as distillation), such as separating azeotropes, close-boiling substances and heat-sensitive substances.

[0003] Sodium alginate, as a natural polysaccharide, has unique advantages and characteristics in the application of pervaporation membrane technology. Compared with some synthetic polymers, sodium alginate has relatively low cost and is widely available. Sodium alginate is easy to shape and can be prepared into a membrane through simple processes such as solution casting and coating, greatly reducing the difficulty of membrane preparation. Due to the presence of a large number of hydroxyl and carboxyl groups in the molecular chain of sodium alginate, it has strong hydrophilicity, which is beneficial to the permeation of water molecules and greatly enhances the permeation flux of the membrane. Sodium alginate can form a thermally irreversible gel when it encounters specific ions (such as calcium ions), which allows the pore structure and mechanical strength of the membrane to be adjusted through a simple cross-linking reaction during membrane preparation, which is important for improving the separation performance of the membrane.

[0004] However, sodium alginate membranes have strong hydrophilicity and poor water stability, and may swell in high humidity environments, affecting their structural stability and separation performance. Moreover, the mechanical strength is limited, and unmodified sodium alginate membranes have low mechanical strength and are easily broken, limiting their application in some harsh conditions. The selectivity is limited, although the separation performance can be improved through modification, but the natural sodium alginate membrane may not be as good as some specially designed synthetic polymer membranes in terms of selectivity.

[0005] Therefore, in order to improve the performance of the membrane, it is necessary to incorporate porous and non-porous fillers into the polymer matrix to regulate the synergistic effect between the polymer and the filler phase. ZIF-L has a zeolite-like topological structure, excellent thermal and chemical stability, permeability and suitable pore size, which is beneficial to promote molecular sieving and improve the stability and separation performance of sodium alginate membrane. However, the ZIF-L material synthesized in the current experiment has problems such as chaotic growth orientation and interface defects, which reduces the separation performance of the membrane. ZIF-L nanosheets with subtle interconnection and no interface defects help to form a continuous permeation path. For example, Chinese invention application 202310934028.1 discloses a preparation method of a high polymer supported vertical metal organic framework composite membrane, wherein the ZIF-L layer satisfies the directional growth, but the ZIF-L in the vertical direction has poor screening effect on ethanol and water. ZIF-L has a hexagonal window-like pore size on the horizontal orientation plane and a very small four-window ( Figure Five ), which is located between the kinetic diameters of water (2.68 Å) and ethanol (4.5 Å), and is expected to exhibit obvious screening effect on water / ethanol mixture. Studies have shown that the growth orientation of ZIF-L tends to be vertical over time, which is determined by the length-to-width ratio of the crystal. Therefore, it is necessary to artificially regulate the preparation of horizontally oriented continuous directional ordering ZIF-L layer to meet the needs of alcohol-water separation and purification. SUMMARY

[0006] The purpose of the present application is to address the current situation that the membrane flux and separation factor cannot be balanced and cannot well meet the requirements of membrane separation. A continuous directional ordering ZIF-L membrane for alcohol-water separation is prepared.

[0007] The method for preparing the hydrophilic modified sodium alginate membrane has the advantages of high flux, good separation factor and the like, is suitable for the membrane separation process, and can ensure excellent separation effect and long-term stable operation. In order to achieve the above purpose, the technical scheme adopted by the present application is as follows: a preparation method of a continuous directional ordering ZIF-L membrane for alcohol-water separation, the specific steps of which are as follows:

[0008] (1) Synthesis of two-dimensional leafy material ZIF-L: The substances involved in the synthesis steps of two-dimensional leafy material ZIF-L are composed of the following mass percentages: 31-69% of hexahydrate nitrate to dimethyl imidazole, and the hexahydrate nitrate is one or both of hexahydrate cobalt nitrate and hexahydrate zinc nitrate. Dissolve the hexahydrate nitrate and dimethyl imidazole in an appropriate amount of water at room temperature, respectively, pour the hexahydrate nitrate solution into the dimethyl imidazole solution quickly, and stir for 2-4 hours. Pour the solution into a centrifuge tube, centrifuge at a speed of 6000r-8000r per minute for 20 minutes, repeat three times, remove the supernatant and wash with the solution, and collect the lower layer material into a culture dish, dry at 60 degrees Celsius for 5-8 hours. Put into a mortar and grind into powder, and the two-dimensional leafy material ZIF-L is obtained.

[0009] (2) Preparation of continuously oriented and ordered ZIF-L layer: Take an appropriate amount of ZIF-L powder prepared in step (1), mix it in an appropriate concentration of a certain solution, and ultrasonic for a period of time to completely dissolve. Use a vacuum filter to filter it onto a PAN base film, and put the filtered PAN base film into the same proportion of stock solution as used in the previous synthesis of ZIF-L, and grow at an appropriate temperature for 30-60 minutes. Take out and rinse with deionized water, and dry at room temperature for 8-12 hours.

[0010] (3) Preparation of alcohol-water separation high-performance membrane: Take an appropriate amount of sodium alginate and add it to water, with a sodium alginate to water ratio of 2-3%, stir for 3-4 hours to obtain a transparent casting solution, and let it stand to degas. Pour the casting solution onto the ZIF-L layer prepared in step (2), spread it into a thin layer, and then put it into a spin coater for spinning. The casting solution spreads on the ZIF-L layer to form a thin layer. Treat the bubbles on the surface of the thin layer to make it defect-free, and then put the spun film into a drying rack to dry naturally, and the alcohol-water separation and purification high-performance membrane is obtained. Subsequently, different concentrations of ethanol can be used to test the performance.

[0011] Preferably, the solution used for washing after centrifugation in step (1) is one of water, ethanol, and acetone.

[0012] Preferably, the solution in which the powder is re-mixed in step (2) is one of PEI solution, PDA solution, and triethylamine solution.

[0013] Preferably, the mass concentration of the solution in which the powder is re-dissolved in step (2) is 1wt%-3wt%.

[0014] Preferably, the temperature at which the film is placed in the solution for growth after filtration in step (2) is 30°C-50°C.

[0015] Preferably, in step (3), the alcohol-water separation high-performance membrane is prepared by a spin coater at a speed of 1400r-1600r / min.

[0016] The present application improves the irregular and disordered ZIF-L structure prepared by previous experiments, and uses a secondary growth method to prepare a continuously directional ordered ZIF-L layer. The present study uses a PEI solution as an adhesive. By controlling the direction of the deposited seed layer, the deposition of the micron-sized ZIF-L nanosheet with PEI as the adhesive, followed by short secondary growth, can form a horizontally directional layer. When the ZIF-L crystal suspension is vacuum filtered, there is a normal force acting on the ZIF-L crystals near the carrier, i.e., the resistance under vacuum. The resistance causes the solution to be transported to the carrier and the ZIF-L crystals to be deposited on the surface. A large number of ZIF-L particles are well dispersed in the PEI matrix, and the PEI can form hydrogen bonds with the free hydroxyl groups on the ZIF-L crystals and the support surface, and also form Zn-N coordination bonds with the zinc cations on the crystal surface. Therefore, the addition of PEI in the seed crystal solution is crucial for ensuring that the seed crystals are firmly adhered to the support surface, and is the key to ensuring the horizontal growth of the seed crystals. The horizontally oriented ZIF-L layer can effectively fill the interstitial gaps between the ZIF-L crystals, improve the defect problems of the ZIF-L-SA membrane caused by previous blending, and improve the material performance. Advantages

[0017] The ordered arrangement and regular pore size of ZIF-L provide ordered water channels for the rapid transport of water molecules; the small pore size of 3.4 Å of ZIF-L is between the kinetic diameters of water (2.68 Å) and ethanol (4.5 Å), and the appropriate pore size of ZIF-L can produce a sieving effect between the kinetic diameters of water and ethanol. Due to the horizontal directional arrangement of ZIF-L, the interstitial gaps between the ZIF-L crystals can be effectively filled, the interface defects can be improved, and the separation layer can also produce a good sieving effect, greatly enhancing the separation performance of the membrane; the use of the adhesive in the process increases the hydrophilicity of the membrane; the coordination bond with the free hydroxyl groups on the ZIF-L crystals and the support surface also improves the stability of the membrane. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure One ZIF-L graph synthesized for Example 10

[0019] Figure Two ZIF-L graph synthesized for Example 2

[0020] Figure Three ZIF-L graph synthesized for Example 4

[0021] Figure Four Surface scanning electron microscope graph of the pervaporation membrane for Example 10

[0022] Figure Five Pore structure of ZIF-L in the horizontal direction DETAILED DESCRIPTION

[0023] The application will be further described in detail by specific embodiments. However, those skilled in the art will understand that the following examples are only used to illustrate the application and should not be regarded as limiting the scope of the application.

[0024] The continuous directional ordering ZIF-L membrane prepared by the application can be used for separating ethanol and water, and therefore the membrane permeation flux, the alcohol-water separation factor and the stability are three important parameters for evaluating the pervaporation.

[0025] The membrane permeation flux and the alcohol-water separation factor are tested under the following conditions: a pervaporation device, an ethanol concentration of 80-90%, a test temperature of 75°C and a test pressure of 300 Pa.

[0026] The membrane permeation flux (J) is defined as:

[0027] In the formula, Q represents the total mass of the permeate, g; A represents the effective membrane area, m 2 ; t represents the collection duration, h.

[0028] The alcohol-water separation factor (a) is defined as:

[0029] In the formula, X A and X B respectively represent the concentrations of ethanol and water in the raw material liquid, wt%; Y A and Y B respectively represent the concentrations of ethanol and water in the permeate, wt%.

[0030] Example 1:

[0031] (1) 0.59 g of Co(NO3)2·6H2O and 1.30 g of dimethylimidazole (Hmim) were respectively dissolved in 40 mL of water, after stirring and dissolving, the cobalt nitrate solution was quickly poured into the dimethylimidazole solution, and stirred at room temperature for 4 h. Centrifugation was repeated three times at a speed of 8000 r per minute for 20 minutes, and the two-dimensional ZIF-L crystals were collected and washed with deionized water for 3 times, dried at 60°C under vacuum and ground to obtain ZIF-L nanosheets.

[0032] (2) The ZIF-L powder prepared in (1) was taken in an appropriate amount and dissolved in water, and ultrasonic was applied for a period of time to completely dissolve it. A vacuum filtration machine was used to filter it onto a PAN-based membrane, and the filtered PAN-based membrane was placed in a synthesis solution of ZIF-L with the same proportion, and grown in a 30°C water bath for 30 min. It was taken out, washed with deionized water, and dried at room temperature for 8 h.

[0033] (3) Take 1.25 g of sodium alginate and add it to 48.75 g of water, stir for 4 h to obtain a transparent casting solution, and let it stand to remove bubbles. Pour the casting solution onto the ZIF-L layer prepared in step (2), spread it into a thin layer, and then put it into a spin coater to spin coat at a speed of 1400 r / min. The casting solution spreads on the ZIF-L layer to form a thin layer. Treat the bubbles on the surface of the thin layer to make it defect-free, and then put the spin-coated film into a drying rack to dry naturally, thereby obtaining a high-performance membrane for alcohol-water separation and purification.

[0034] The ZIF-L layer structure prepared in Example 1 is disordered, and the pervaporation membrane prepared in Example 1 is tested. The membrane permeation flux is 1200 g / m 2 *h, and the alcohol-water separation coefficient is 720.

[0035] Example 2:

[0036] (1) Take 0.59 g of Co(NO3)2·6H2O and 1.30 g of dimethyl imidazole (Hmim) and dissolve them in 40 mL of water, respectively. After stirring and dissolving, quickly pour the cobalt nitrate solution into the dimethyl imidazole solution and stir at room temperature for 4 h. Centrifuge at a speed of 8000 r per minute for 20 minutes, repeat three times, collect the two-dimensional ZIF-L crystals, and wash them with deionized water for 3 times. Dry under vacuum at 60°C and grind to obtain ZIF-L nanosheets.

[0037] (2) Take an appropriate amount of ZIF-L powder prepared in (1) and dissolve it in a 1 wt% PEI solution. Ultrasonic for a period of time to completely dissolve. Use a vacuum filter to filter it onto a PAN-based membrane, and then put the filtered PAN-based membrane into the same proportion of ZIF-L synthesis solution and grow for 40 min in a 30°C water bath. Take it out, rinse it with deionized water, and dry it at room temperature for 8 h.

[0038] (3) Take 1.25 g of sodium alginate and add it to 48.75 g of water, stir for 4 h to obtain a transparent casting solution, and let it stand to remove bubbles. Pour the casting solution onto the ZIF-L layer prepared in step (2), spread it into a thin layer, and then put it into a spin coater to spin coat at a speed of 1600 r / min. The casting solution spreads on the ZIF-L layer to form a thin layer. Treat the bubbles on the surface of the thin layer to make it defect-free, and then put the spin-coated film into a drying rack to dry naturally, thereby obtaining a high-performance membrane for alcohol-water separation and purification.

[0039] The ZIF-L layer structure prepared in Example 2 is relatively horizontal, and still has some disorder. The pervaporation membrane prepared in Example 2 is tested. The membrane permeation flux is 1300 g / m 2 *h, and the alcohol-water separation coefficient is 1100.

[0040] Example 3:

[0041] (1) Take 0.78g of Co(NO3)2·6H2O and 1.30g of dimethyl imidazole (Hmim) respectively dissolved in 40mL of water, after stirring and dissolving, quickly pour the cobalt nitrate solution into the dimethyl imidazole solution, and stir at room temperature for 4h. Centrifuge at a speed of 7000r per minute for 15 minutes, repeat three times, collect the two-dimensional ZIF-L crystals, wash with deionized water for 3 times, dry at 60℃ under vacuum and grind to obtain ZIF-L nanosheets.

[0042] (2) Take an appropriate amount of ZIF-L powder prepared in (1) and dissolve it in a 1wt% PEI solution, and ultrasonic it for a period of time to completely dissolve it. Use a vacuum filter to filter it onto a PAN-based membrane, and place the filtered PAN-based membrane in the same proportion of ZIF-L synthesis solution, and grow at 30℃ water bath for 40min. Take out and rinse with deionized water, dry at room temperature for 8h.

[0043] (3) Take 1.25g of sodium alginate and add it to 48.75g of water, stir for 4h to obtain a transparent casting solution, and let it stand to degas. Pour the casting solution onto the ZIF-L layer prepared in step (2), spread it into a thin layer, and then put it into a spin coater at a speed of 1600r / min. The casting solution spreads on the ZIF-L layer to form a thin layer. Treat the bubbles on the surface of the thin layer to make it defect-free, and then put the spin-coated membrane into a drying rack to dry naturally, thereby obtaining a high-performance membrane for alcohol-water separation and purification.

[0044] The ZIF-L prepared in Example 3 has a more complete morphology and better dispersion effect. The pervaporation membrane prepared in Example 3 is tested, and the membrane permeation flux is 1600 g / m 2 *h, and the alcohol-water separation coefficient is 1300.

[0045] Example 4:

[0046] (1) Take 0.78g of Co(NO3)2·6H2O and 1.30g of dimethyl imidazole (Hmim) respectively dissolved in 40mL of water, after stirring and dissolving, quickly pour the cobalt nitrate solution into the dimethyl imidazole solution, and stir at room temperature for 4h. Centrifuge at a speed of 7000r per minute for 15 minutes, repeat three times, collect the two-dimensional ZIF-L crystals, and wash with deionized water for 3 times, dry at 60℃ under vacuum and grind to obtain ZIF-L nanosheets.

[0047] (2) Take the ZIF-L powder prepared in (1) and dissolve it in a 1 wt% PEI solution. Ultrasonic it for a period of time until it is completely dissolved. Use a vacuum filtration machine to filter it onto a PAN-based membrane. Place the filtered PAN-based membrane in the same proportion of ZIF-L synthesis solution and grow it at 30°C for 40 minutes. Take it out, rinse it with deionized water, and dry it at room temperature for 8 hours.

[0048] (3) Take 1.25 g of sodium alginate and add it to 48.75 g of water. Stir for 4 hours to obtain a transparent casting solution. Let it stand and degas. Pour the casting solution onto the ZIF-L layer prepared in step (2) and spread it into a thin layer. Place it in a spin coater and spin it at a speed of 1600 r / min. The casting solution spreads on the ZIF-L layer to form a thin layer. Treat the bubbles on the surface of the thin layer to make it defect-free. Place the spin-coated membrane in a drying rack and let it dry naturally. Thus, a high-performance membrane for alcohol-water separation and purification is obtained.

[0049] The ZIF-L layer prepared in Example 4 has a serious stacking of leaves. The pervaporation membrane prepared in Example 4 is tested, and the membrane permeation flux is 1500 g / m 2 *h, and the alcohol-water separation coefficient is 1000.

[0050] Example 5:

[0051] (1) Take 0.78 g of Co(NO3)2·6H2O and 1.30 g of dimethyl imidazole (Hmim) and dissolve them in 40 mL of water, respectively. After stirring and dissolving, quickly pour the cobalt nitrate solution into the dimethyl imidazole solution and stir at room temperature for 4 hours. Centrifuge at a speed of 7000 r per minute for 15 minutes, repeat three times, collect the two-dimensional ZIF-L crystals, and wash them with deionized water for 3 times. Dry them under vacuum at 60°C and grind them to obtain ZIF-L nanosheets.

[0052] (2) Take the ZIF-L powder prepared in (1) and dissolve it in a 2 wt% PEI solution. Ultrasonic it for a period of time until it is completely dissolved. Use a vacuum filtration machine to filter it onto a PAN-based membrane. Place the filtered PAN-based membrane in the same proportion of ZIF-L synthesis solution and grow it in a 30°C water bath for 40 minutes. Take it out, rinse it with deionized water, and dry it at room temperature for 8 hours.

[0053] (3) Take 1.25 g of sodium alginate and add it to 48.75 g of water. Stir for 4 hours to obtain a transparent casting solution. Let it stand and degas. Pour the casting solution onto the ZIF-L layer prepared in step (2) and spread it into a thin layer. Place it in a spin coater and spin it at a speed of 1600 r / min. The casting solution spreads on the ZIF-L layer to form a thin layer. Treat the bubbles on the surface of the thin layer to make it defect-free. Place the spin-coated membrane in a drying rack and let it dry naturally. Thus, a high-performance membrane for alcohol-water separation and purification is obtained.

[0054] The ZIF-L layer prepared in Example 5 has a horizontal orientation degree of 80%, and the pervaporation membrane prepared in Example 5 is tested, and the membrane permeation flux is 1600 g / m 2 * h, and the alcohol-water separation coefficient is 1500.

[0055] Example 6:

[0056] (1) 0.78 g of Co (NO3) 2·6H2O and 1.30 g of dimethyl imidazole (Hmim) were dissolved in 40 mL of water, respectively, and after stirring and dissolving, the cobalt nitrate solution was quickly poured into the dimethyl imidazole solution, and stirred at room temperature for 4 h. Centrifugation was repeated three times at a speed of 7000 r per minute for 15 minutes, and the two-dimensional ZIF-L crystals were collected and washed with deionized water for 3 times, dried at 60°C under vacuum and ground, to obtain ZIF-L nanosheets.

[0057] (2) The ZIF-L powder prepared in (1) was taken and dissolved in 2wt% PDA solution, and ultrasonic was used for a period of time to completely dissolve it. A vacuum filtration machine was used to filter it onto a PAN-based membrane, and the filtered PAN-based membrane was placed in the same proportion of ZIF-L synthesis solution, and grown at 30°C water bath for 40 min. Take out, wash with deionized water, and dry at room temperature for 8 h.

[0058] (3) 1.25 g of sodium alginate was added to 48.75 g of water, stirred for 4 h to obtain a transparent casting solution, and then left to degas. The casting solution was poured onto the ZIF-L layer prepared in step (2), spread into a thin layer, and then placed in a spin coater for spin coating at a speed of 1600 r / min. The casting solution was spread on the ZIF-L layer to form a thin layer. The bubbles on the surface of the thin layer were treated to make it defect-free, and the spin-coated membrane was placed in a drying rack for natural drying, to obtain a high-performance membrane for alcohol-water separation and purification.

[0059] The ZIF-L layer prepared in Example 6 has a horizontal orientation degree of 60%, but there is a certain stacking between the leaves, and the pervaporation membrane prepared in Example 6 is tested, and the membrane permeation flux is 1800 g / m 2 * h, and the alcohol-water separation coefficient is 1200.

[0060] Example 7:

[0061] (1) Take 0.78g of Co(NO3)2·6H2O and 1.30g of dimethyl imidazole (Hmim) respectively dissolved in 40mL of water, after stirring and dissolving, pour the cobalt nitrate solution into the dimethyl imidazole solution quickly, and stir at room temperature for 4h. Centrifuge at a speed of 7000r per minute for 15 minutes, repeat three times, collect the two-dimensional ZIF-L crystals, wash with deionized water for 3 times, dry at 60℃ under vacuum and grind to obtain ZIF-L nanosheets.

[0062] (2) Take the ZIF-L powder prepared in (1) and dissolve it in 2wt% triethylamine solution, ultrasonic for a period of time to completely dissolve. Use a vacuum filter to filter it onto a PAN base film, and put the filtered PAN base film into the same proportion of ZIF-L synthesis solution, grow at 30℃ water bath for 40min. Take out and rinse with deionized water, dry at room temperature for 8h.

[0063] (3) Take 1.25g of sodium alginate and add it to 48.75g of water, stir for 4h to obtain a transparent casting solution, and let it stand to degas. Pour the casting solution onto the ZIF-L layer prepared in step (2), spread it into a thin layer, and then put it into a spin coater at a speed of 1600r / min. The casting solution spreads on the ZIF-L layer to form a thin layer. Treat the bubbles on the surface of the thin layer to make it defect-free, and put the spin-coated film into a drying rack to dry naturally, which obtains the high-performance membrane for alcohol-water separation and purification.

[0064] The horizontal orientation degree of the ZIF-L layer prepared in Example 7 is 50%, and the leaves are seriously stacked. The pervaporation membrane prepared in Example 7 is tested, and the membrane permeation flux is 1400 g / m 2 *h, and the alcohol-water separation coefficient is 1300.

[0065] Example 8:

[0066] (1) Take 0.78g of Co(NO3)2·6H2O and 1.30g of dimethyl imidazole (Hmim) respectively dissolved in 40mL of water, after stirring and dissolving, pour the cobalt nitrate solution into the dimethyl imidazole solution quickly, and stir at room temperature for 4h. Centrifuge at a speed of 7000r per minute for 15 minutes, repeat three times, collect the two-dimensional ZIF-L crystals, and wash with deionized water for 3 times, dry at 60℃ under vacuum and grind to obtain ZIF-L nanosheets.

[0067] (2) Take the ZIF-L powder prepared in (1) and dissolve it in a 2wt% PEI solution. Ultrasonic it for a period of time until it is completely dissolved. Use a vacuum filter to filter it onto a PAN-based film. Place the filtered PAN-based film in the same proportion of ZIF-L synthesis solution in a 30°C water bath for 40 minutes. Take it out and rinse it with deionized water. Dry it at room temperature for 8 hours.

[0068] (3) Take 1.25g of sodium alginate and add it to 48.75g of water. Stir for 4 hours to obtain a transparent casting solution. Place the casting solution on the ZIF-L layer prepared in step (2) and spread it into a thin layer. Place it in a spin coater at a speed of 1600r / min. The casting solution spreads on the ZIF-L layer to form a thin layer. Treat the bubbles on the surface of the thin layer to make it defect-free. Place the spin-coated film in a drying rack and let it dry naturally. This is the high-performance membrane for alcohol-water separation and purification.

[0069] The ZIF-L prepared in Example 8 has a higher aspect ratio of leaf type and more complete material compared to Co 2+ as the central ion. However, there are still 10% of the defective parts. The pervaporation membrane prepared in Example 8 is tested, with a membrane permeation flux of 1900 g / m 2 *h and an alcohol-water separation coefficient of 1600.

[0070] Example 9:

[0071] (1) Take 0.59g of Zn(NO3)2·6H2O and 1.30g of dimethyl imidazole (Hmim) and dissolve them in 40mL of water respectively. After stirring and dissolving, quickly pour the zinc nitrate solution into the dimethyl imidazole solution and stir at room temperature for 4 hours. Centrifuge at a speed of 7000r per minute for 15 minutes, repeat three times, collect the two-dimensional ZIF-L crystals, wash them with deionized water for 3 times, dry them in a vacuum at 60°C and grind them to obtain ZIF-L nanosheets.

[0072] (2) Take the ZIF-L powder prepared in (1) and dissolve it in a 2wt% PEI solution. Ultrasonic it for a period of time until it is completely dissolved. Use a vacuum filter to filter it onto a PAN-based film. Place the filtered PAN-based film in the same proportion of ZIF-L synthesis solution in a 30°C water bath for 40 minutes. Take it out and rinse it with deionized water. Dry it at room temperature for 8 hours.

[0073] (3) Take 1.25 g of sodium alginate and add it to 48.75 g of water, stir for 4 h to obtain a transparent casting solution, and let it stand to remove bubbles. Pour the casting solution onto the ZIF-L layer prepared in step (2), spread it into a thin layer, and then put it into a spin coater to spin coat at a speed of 1600 r / min. The casting solution spreads on the ZIF-L layer to form a thin layer. Treat the bubbles on the surface of the thin layer to make it defect-free, and then put the spin-coated film into a drying rack to dry naturally, thereby obtaining a high-performance membrane for alcohol-water separation and purification.

[0074] The ZIF-L material prepared in Example 9 has a structure with 30% defective parts, and the prepared ZIF-L layer is stacked more seriously. The pervaporation membrane prepared in Example 9 is tested, and the membrane permeation flux is 1600 g / m 2 h, and the alcohol-water separation coefficient is 1300.

[0075] Example 10:

[0076] (1) Take 0.5 g of Zn(NO3)2·6H2O, 0.3 g of Co(NO3)2·6H2O, and 1.30 g of dimethyl imidazole (Hmim), and dissolve them in 40 mL of water, respectively. After stirring and dissolving, quickly pour the nitrate solution into the dimethyl imidazole solution, and stir at room temperature for 4 h. Centrifuge at a speed of 7000 r per minute for 15 minutes, repeat three times, collect the two-dimensional ZIF-L crystals, and wash them with deionized water for 3 times, dry at 60°C under vacuum, and grind to obtain ZIF-L nanosheets.

[0077] (2) Take an appropriate amount of ZIF-L powder prepared in (1) and dissolve it in a 2wt% PEI solution, and ultrasonic it for a period of time to completely dissolve it. Use a vacuum filter to filter it onto a PAN-based membrane, and then put the filtered PAN-based membrane into a synthesis solution of ZIF-L with the same proportion, and grow it in a 40°C water bath for 40 min. Take it out, rinse it with deionized water, and dry it at room temperature for 8 h.

[0078] (3) Take 1.25 g of sodium alginate and add it to 48.75 g of water, stir for 4 h to obtain a transparent casting solution, and let it stand to remove bubbles. Pour the casting solution onto the ZIF-L layer prepared in step (2), spread it into a thin layer, and then put it into a spin coater to spin coat at a speed of 1600 r / min. The casting solution spreads on the ZIF-L layer to form a thin layer. Treat the bubbles on the surface of the thin layer to make it defect-free, and then put the spin-coated film into a drying rack to dry naturally, thereby obtaining a high-performance membrane for alcohol-water separation and purification.

[0079] The ZIF-L material prepared in Example 10 has a full leaf structure with no obvious defects. The ZIF-L layer prepared in Example 10 has a horizontal orientation of 95% and is well dispersed. The pervaporation membrane prepared in Example 10 is tested, and the membrane permeation flux is 2100 g / m 2 *h, and the alcohol-water separation coefficient is 1800.

[0080] Example 11:

[0081] (1) 0.3 g of Zn(NO3)2·6H2O, 0.5 g of Co(NO3)2·6H2O, and 1.30 g of dimethylimidazole (Hmim) were dissolved in 40 mL of water, respectively. After stirring and dissolving, the nitrate solution was quickly poured into the dimethylimidazole solution, and stirred at room temperature for 4 h. Centrifugation was repeated three times at a speed of 7000 r per minute for 15 minutes, and the two-dimensional ZIF-L crystals were collected and washed with deionized water three times, dried at 60°C under vacuum, and ground to obtain ZIF-L nanosheets.

[0082] (2) The ZIF-L powder prepared in (1) was taken and dissolved in a 2wt% PEI solution, and ultrasonic treatment was performed for a period of time to completely dissolve the ZIF-L powder. The ZIF-L powder was filtered onto a PAN-based membrane using a vacuum filter, and the filtered PAN-based membrane was placed in a synthesis solution of the same proportion of ZIF-L, and grown at 40°C for 40 min. The membrane was taken out, washed with deionized water, and dried at room temperature for 8 h.

[0083] (3) 1.25 g of sodium alginate was added to 48.75 g of water, stirred for 4 h to obtain a transparent casting solution, and left to stand to remove bubbles. The casting solution was poured onto the ZIF-L layer prepared in step (2) and spread into a thin layer, and then placed in a spin coater at a speed of 1600 r / min. The casting solution was spread on the ZIF-L layer to form a thin layer. The bubbles on the surface of the thin layer were removed to make it defect-free, and the spin-coated membrane was placed in a drying rack to dry naturally, thereby obtaining a high-performance membrane for alcohol-water separation and purification.

[0084] The ZIF-L material prepared in Example 11 still has some defects and part of the structure is rod-shaped. The pervaporation membrane prepared in Example 11 is tested, and the membrane permeation flux is 1800 g / m 2 *h, and the alcohol-water separation coefficient is 1500.

Claims

1. A method for preparing a continuous directional ordering ZIF-L high-performance membrane for alcohol-water separation, comprising the following specific steps: (1) Synthesis of two-dimensional leafy material ZIF-L: the substances involved in the synthesis of the two-dimensional leafy material ZIF-L are composed of the following mass percentages: 31-69% of the six-nitrate salt of dimethyl imidazole, and the six-nitrate salt is one or both of the six-nitrate salt of cobalt and the six-nitrate salt of zinc; the six-nitrate salt and dimethyl imidazole are dissolved in an appropriate amount of water at room temperature, the six-nitrate salt solution is quickly poured into the dimethyl imidazole solution, and stirring is performed for 2-4 hours; the solution is poured into a centrifuge tube, centrifugation is performed at a speed of 6000r-8000r per minute for 20 minutes, the operation is repeated three times, the supernatant is removed and washed with the solution, and the lower material is collected in a culture dish and dried at 60 degrees Celsius for 5-8 hours; the material is ground into powder in a mortar, and the two-dimensional leafy material ZIF-L is obtained; (2) Preparation of a continuous directional ordering ZIF-L layer: an appropriate amount of ZIF-L powder prepared in step (1) is mixed in an appropriate concentration of a certain solution, and ultrasonic treatment is performed for a period of time to completely dissolve the powder; the solution is filtered onto a PAN-based membrane using a vacuum filtration machine, the filtered PAN-based membrane is placed in the same proportion of the original solution as used in the previous synthesis of ZIF-L, and growth is performed at an appropriate temperature for 30-60 minutes; the membrane is taken out, washed with deionized water, and dried at room temperature for 8-12 hours; (3) Preparation of an alcohol-water separation high-performance membrane: an appropriate amount of sodium alginate is added to water, the ratio of sodium alginate to water is 2-3%, stirring is performed for 3-4 hours to obtain a transparent casting solution, and the solution is left to stand and degas; the casting solution is poured onto the ZIF-L layer prepared in step (2), spread into a thin layer, and placed in a spin coater for spin coating; the casting solution spreads on the ZIF-L layer to form a thin layer; the bubbles on the surface of the thin layer are removed to make it defect-free, and the spin-coated membrane is placed in a drying rack for natural air drying, thereby obtaining an alcohol-water separation and purification high-performance membrane, and the performance of the membrane can be detected using different concentrations of ethanol.

2. The production method according to claim 1, characterized by The solution used for washing after centrifugation in step (1) is one of water, ethanol, and acetone.

3. The method of claim 1, wherein The certain solution in which the powder is mixed in step (2) is one of a PEI solution, a PDA solution, and a triethylamine solution.

4. The method of claim 1, wherein The temperature for growth in step (2) is 30-50 degrees Celsius.

5. The method of claim 1, wherein The rotation speed of the spin coater in step (3) is 1400r-1600r / min.

6. The Pervaporation high performance membrane for alcohol-water separation prepared by the method for preparing a continuous directional ordering ZIF-L high performance membrane for alcohol-water separation according to any one of claims 1-5, characterized in that, The membrane has certain stability and anti-pollution properties.

Images