Polycaffeic acid sandwich MAF-6 based mixed matrix membrane and its preparation method and application

Abstract

The present invention discloses a polycaffeic acid interlayer MAF-6-based mixed matrix membrane and its preparation method and application. The mixed matrix membrane consists of a PVDF base membrane, a polycaffeic acid interlayer with in-situ grown MAF-6, and a polymer matrix layer with dispersed MAF-6 from bottom to top. The membrane material of the present invention can be effectively applied in the field of alcohol / water separation, and has the advantages of simple preparation, environmental friendliness, small required space, high separation efficiency, etc. When applied to ethanol / water separation, it has excellent pervaporation performance and has good application prospects for future bio-alcohol recovery.

Description

Technical Field

[0001] The present invention relates to the field of pervaporation membranes, and in particular to a polycaffeic acid sandwich MAF-6-based mixed matrix membrane, a preparation method thereof, and application of the membrane in ethanol-water separation. Background Art

[0002] Pervaporation membranes are an excellent membrane separation technology, offering advantages such as simple operation, low energy consumption, and environmental friendliness. They offer high separation efficiency for dehydrating organic matter and recovering organic matter from water. Currently, mixed-matrix membranes (MMMs) that incorporate MOFs / COFs and inorganic nanoparticles within a polymer matrix are a hot topic of research. MOFs, due to their high surface area, thermal stability, and preferential adsorption of specific molecules, hold great promise for use in MMMs.

[0003] MAF-6 with RHO topology is a Zn 2+ MAF-6 is a hydrophobic, large-pore MOF with a metal source and 2-ethylimidazole as a ligand. Notably, both the inner pores and the outer crystal surface of MAF-6 are highly hydrophobic, unlike ZIF-8. This high hydrophobicity makes it virtually incapable of adsorbing or being wetted by water, but it readily adsorbs a large number of organic molecules. Furthermore, MAF-6 nanoparticles can be synthesized at room temperature through a rapid solution mixing reaction, resulting in high crystallinity, high purity, large quantities, and high thermal and chemical stability. However, MAF-6 particles in porous polymer membranes still face challenges such as poor adhesion and compatibility with the support and a lack of sufficient nucleation sites. Sol-gel coating is a simple method to improve nucleation sites. Furthermore, organic materials tend to form a continuous and uniform layer on the substrate, and their abundant functional groups facilitate close bonding between the separation layer and the substrate. Caffeic acid is a natural plant polyphenol with a catechol structure and carboxyl groups. Caffeic acid itself can oxidatively polymerize to form a layer of organic macromolecules. Summary of the Invention

[0004] In order to break the trade-off between permeation flux and selectivity, improve pervaporation performance, and prepare a uniform and defect-free membrane, the present invention provides a defect-free mixed matrix membrane with polycaffeic acid as an interlayer to increase MAF-6 nucleation sites, a preparation method thereof, and application in ethanol-water separation.

[0005] The technical solutions of the present invention are as follows:

[0006] A polycaffeic acid interlayer MAF-6-based mixed matrix membrane, which is composed of a PVDF (polyvinylidene fluoride) base membrane, a polycaffeic acid interlayer with in-situ growth of MAF-6, and a polymer matrix layer with dispersed MAF-6 from bottom to top;

[0007] The polymer matrix is ​​selected from the group consisting of: polyether block polyamide, polydimethylsiloxane, preferably polyether block polyamide;

[0008] The polycaffeic acid is prepared by polymerization of caffeic acid, ammonium persulfate and ethylenediamine; preferably, the particle size of the polycaffeic acid is 200 to 1000 nm;

[0009] Specifically, the preparation method of polycaffeic acid is as follows:

[0010] The aqueous solution of caffeic acid, ammonium persulfate and ethylenediamine were mixed evenly, the pH was adjusted to 6-7, and the mixture was stirred at room temperature for 2 hours. The reaction solution was then centrifuged, and the precipitate was collected, washed and dried to obtain polycaffeic acid.

[0011] The molar ratio of caffeic acid, ammonium persulfate and ethylenediamine is 2-4:1-2:1, preferably 2:1:1;

[0012] The concentration of the aqueous solution of caffeic acid is 1 to 5 g / L, preferably 2 g / L.

[0013] The method for preparing the polycaffeic acid sandwich MAF-6-based mixed matrix membrane of the present invention comprises the following steps:

[0014] (1) Dispersing polycaffeic acid uniformly in deionized water, adding zinc hydroxide in ammonia solution to adjust the pH to 6-7, and then adding 2-ethylimidazole organic solution to disperse uniformly to obtain a mixed system; immersing a PVDF substrate in the obtained mixed system, allowing it to stand for 1-4 hours, then taking it out and rinsing it with methanol, and evaporating it at room temperature to obtain a polycaffeic acid membrane with in situ growth of MAF-6;

[0015] The mass ratio of polycaffeic acid, zinc hydroxide and 2-ethylimidazole is 1-20:10-20:10, preferably 10:25:23.75;

[0016] The volume mass ratio of deionized water to polycaffeic acid is 16.7 to 33.3:1, mL / g, preferably 25:1, mL / g;

[0017] In the ammonia solution of zinc hydroxide, the concentration of zinc hydroxide is 40 to 80 g / L, preferably 50 g / L; the concentration of the solvent ammonia is 15 to 28 wt%;

[0018] The organic solution of 2-ethylimidazole has a concentration of 5 to 20 g / L, preferably 11.8 g / L; the solvent is a mixed solvent of methanol and cyclohexane in a volume ratio of 15:1, wherein the cyclohexane is added as a hydrophobic template;

[0019] The content of polycaffeic acid on PVDF base film ranges from 20 to 50 g / m 2 , preferably 23g / m 2 ;

[0020] The pH can be adjusted using 7.5 mol / L hydrochloric acid and 0.1 mol / L sodium hydroxide aqueous solution;

[0021] (2) MAF-6 was dispersed in n-butanol, and then the polymer matrix was added, stirred (80°C, 5 h), and allowed to stand (60°C, 12 h) to obtain a membrane-forming solution;

[0022] The mass ratio of MAF-6, polymer matrix, and n-butanol is 0.01-0.2:1:15-20;

[0023] (3) fixing the polycaffeic acid film of the in situ grown MAF-6 obtained in step (1), applying the membrane-building solution obtained in step (2) by scraping, and drying to obtain the polycaffeic acid sandwich MAF-6-based mixed matrix membrane;

[0024] The coating thickness of the membrane-building liquid is controlled at 50 to 100 μm.

[0025] The polycaffeic acid sandwich MAF-6-based mixed matrix membrane of the present invention can be used for pervaporation recovery of alcohol from an alcohol aqueous solution; the alcohol is preferably ethanol.

[0026] The specific application method is:

[0027] At 40°C, a polycaffeic acid sandwich MAF-6 based mixed matrix membrane was fixed horizontally in a sealed container, and the membrane separated the sealed container into two independent spaces (such as Figure 1 As shown in ), the front side of the membrane is in contact with the alcohol-water solution, and the gas (including air and alcohol) is continuously extracted from the top of the other side and condensed to recover the alcohol;

[0028] The preferred alcohol aqueous solution is ethanol aqueous solution with a concentration of 5 wt %. The ethanol aqueous solution with a concentration of 5 wt % is used as the permeation side feed liquid. The operating conditions of the pervaporation are: temperature 40° C., upper vacuum degree 100 Pa, and feed rate 0.4 L / min.

[0029] Compared with the prior art, the innovation and advantages of the present invention are as follows:

[0030] (1) For the first time, the cheap and readily available caffeic acid was applied to the mixed matrix membrane separation of ethanol / water, which broadened the application field of caffeic acid in membrane separation.

[0031] (2) Caffeic acid was firstly combined with MAF-6, and the multiple phenolic hydroxyl groups and amino groups on caffeic acid were combined with Zn 2+ Cross-linking forms a metal complex-polyphenol network, pre-seeding MAF-6 seeds on the gel layer, enhancing the adhesion of MAF-6 to the gel layer and increasing the nucleation sites.

[0032] (3) After a layer of polymer matrix membrane-building liquid is applied, the hydrophobicity of the membrane surface is improved, and at the same time, it has good compatibility and can greatly reduce the defects of the membrane. It not only effectively improves the separation performance of the membrane, but also controls the thickness of the membrane and increases its permeation flux.

[0033] (4) The polycaffeic acid-sandwiched MAF-6-based mixed matrix membranes described in the present invention can be effectively applied in the field of ethanol / water separation. Compared with other separation methods, they have the advantages of simple preparation, environmental friendliness, small space requirements, and high separation efficiency. The prepared defect-free mixed matrix membranes have good pervaporation performance in ethanol / water separation and have good application prospects for future bio-alcohol recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 : Schematic diagram of the pervaporation device for detecting membrane performance of the present invention. DETAILED DESCRIPTION

[0035] The present invention will be described in detail below with reference to specific embodiments. However, the present invention is not limited to the following embodiments. Without departing from the content and scope of the present invention, any changes should be included in the technical scope of the present invention.

[0036] In the following embodiments:

[0037] The pervaporation performance of the membrane is evaluated by two parameters: permeation flux (J) and separation factor (α), which are calculated using the following formula:

[0038]

[0039] Where m is the total mass collected on the permeate side after t hours, A is the effective membrane area (7 cm 2 ), X and Y are the mass fractions of ethanol in the feed solution and the permeate, respectively.

[0040] In the following examples, the PVDF ultrafiltration membrane used was manufactured by Zhongke Ruiyang Membrane Technology (Beijing) Co., Ltd., with a product number of SG-UF050-8084, a molecular weight cut-off of 50,000 Da, and an area of ​​approximately 10 cm 2 .

[0041] Polyether block polyamide was purchased from Arkema, France, with the product number being PEBAX MH 1657.

[0042] Polydimethylsiloxane was purchased from Jinan Xingchi Chemical Co., Ltd. with a product number of XC-107 and a viscosity of 100,000 cst.

[0043] Example 1:

[0044] (1) Preparation of polycaffeic acid: 1 g of caffeic acid was completely dissolved in deionized water at 80°C to obtain a caffeic acid solution with a concentration of 2 g / L. Then, ammonium persulfate and ethylenediamine were added in sequence with a molar ratio of 2:1:1 for caffeic acid, ammonium persulfate, and ethylenediamine, wherein the mass of ammonium persulfate was 0.633 g and the mass of ethylenediamine was 188 μL, and the mixture was stirred until uniformly mixed. The mixture was then heated to 40°C with hydrochloric acid (7.5 mol·L -1 ) and sodium hydroxide aqueous solution (0.1 mol·L -1 ) was adjusted to a pH of 6-7. The polymerization reaction was stirred at room temperature for 2 hours, followed by centrifugation. The resulting precipitate was filtered, washed with deionized water, and dried at 80°C for 12 hours. The mass of the obtained polycaffeic acid was 0.7834 g.

[0045] Preparation of MAF-6: Completely dissolve 1g of zinc hydroxide in 20ml of 25wt% ammonia water to obtain zinc hydroxide solution A. Dissolve 1.9g of 2-ethylimidazole in a mixture of 150ml of methanol and 10ml of cyclohexane and stir thoroughly to obtain 2-ethylimidazole solution B. Solution A was quickly poured into solution B, stirred at room temperature for 2h, vacuum filtered, washed with methanol, and oven-dried at 80°C for 12h. The resulting MAF-6 mass was 1.170g.

[0046] (2) In situ growth of MAF-6 on a polycaffeic acid film: 0.4 g of polycaffeic acid was dispersed in 10 ml of deionized water; 1 g of zinc hydroxide was dissolved in 20 ml of aqueous ammonia (25 wt%) and stirred to obtain a zinc hydroxide solution C in aqueous ammonia. 0.95 g of 2-ethylimidazole was dissolved in a mixed solution of 75 ml of methanol and 5 ml of cyclohexane and stirred to obtain a 2-ethylimidazole solution D.

[0047] The zinc hydroxide solution C prepared above was slowly added to the polycaffeic acid solution prepared above, and the zinc hydroxide solution C was completely dissolved in ammonia water. -1 ) and sodium hydroxide aqueous solution (0.1 mol·L -1 ) to a pH of 6-7 to obtain a mixed solution. Add 2-ethylimidazole solution D to the prepared mixed solution and stir evenly to obtain 85 mL of solution. Immerse a PVDF base membrane in the above solution and let it stand for 4 hours. Remove the membrane, gently rinse with methanol, and let it stand at room temperature.

[0048] (3) Preparation of the casting solution: 0.1 g of MAF-6 was dispersed in 18.4 g of n-butanol, stirred at 80°C for 6 h (preferably at 800 rpm), and ultrasonicated for 2 h. Subsequently, 1 g of polyether block polyamide was added to obtain a casting solution. The casting solution was stirred at 80°C for 5 h to ensure uniform dispersion of the MAF-6. The solution was then allowed to stand at 60°C for 12 h to remove air bubbles.

[0049] (4) Preparation of a polycaffeic acid-interlayered MAF-6-based mixed matrix membrane: The precursor membrane prepared in step (2) was fixed on a smooth glass plate. The membrane-building solution prepared in step (3) was then slowly poured onto the membrane surface and doctor-coated (the coating was set to a thickness of 60 μm). After doctor-coating, the membrane was placed in a Petri dish and dried in an oven at 80°C for 12 hours. The resulting membrane was the aforementioned polycaffeic acid-interlayered MAF-6-based mixed matrix membrane.

[0050] The prepared polycaffeic acid sandwich MAF-6 based mixed matrix membrane (one side of the membrane coating solution is in contact with the permeate side feed solution) is used in the separation of volatile organic compounds as follows:

[0051] A 5 wt% ethanol / water solution was used as the permeation side feed liquid. The pervaporation operating conditions were a temperature of 40°C, a vacuum of 100 Pa, a feed volume of 1 L, a feed rate of 0.4 L / min, and an operation time of 1 h. The total permeation flux of the membrane prepared under these conditions was 2160 g·m -2 ·h -1 , the separation factor is 15.3.

[0052] Example 2:

[0053] (1) Preparation of polycaffeic acid: 1 g of caffeic acid was completely dissolved in deionized water at 80°C to obtain a caffeic acid solution with a concentration of 2 g / L. Then, ammonium persulfate and ethylenediamine were added in sequence with a molar ratio of 2:1:1 for caffeic acid, ammonium persulfate, and ethylenediamine, wherein the mass of ammonium persulfate was 0.633 g and the mass of ethylenediamine was 188 μL, and the mixture was stirred until uniformly mixed. -1 ) and sodium hydroxide aqueous solution (0.1 mol·L -1 ) was adjusted to a pH of 6-7. The polymerization reaction was stirred at room temperature for 2 hours, followed by centrifugation. The resulting precipitate was filtered, washed with deionized water, and then dried at 80°C for 12 hours. The concentration of the caffeic acid solution was 2 g / L. The mass of the resulting polycaffeic acid was 0.7834 g.

[0054] Preparation of MAF-6: Completely dissolve 1g of zinc hydroxide in 20ml of 25wt% ammonia water to obtain zinc hydroxide solution A. Dissolve 1.9g of 2-ethylimidazole in a mixture of 150ml of methanol and 10ml of cyclohexane and stir thoroughly to obtain 2-ethylimidazole solution B. Solution A was quickly poured into solution B, stirred at room temperature for 2h, vacuum filtered, washed with methanol, and oven-dried at 80°C for 12h. The resulting MAF-6 mass was 1.170g.

[0055] (2) In situ growth of MAF-6 on a polycaffeic acid film: 0.4 g of polycaffeic acid was dispersed in 10 ml of deionized water; 1 g of zinc hydroxide was dissolved in 20 ml of ammonia (25 wt%) and stirred to obtain zinc hydroxide solution C in ammonia. 4 g of 2-ethylimidazole was dissolved in a mixture of 50 ml of methanol and 5 ml of cyclohexane and stirred to obtain 2-ethylimidazole solution D.

[0056] The zinc hydroxide solution C prepared above was slowly added to the polycaffeic acid solution prepared above, and the zinc hydroxide solution C was completely dissolved in ammonia water. -1 ) and sodium hydroxide aqueous solution (0.1 mol·L -1 ) to a pH of 6-7 to obtain a mixed solution. Add 25 mL of 2-ethylimidazole solution D to the prepared mixed solution and stir evenly to obtain 55 mL of solution. Immerse a PVDF base membrane in the above solution and let it stand for 4 hours. Remove the membrane, gently rinse with methanol, and let it stand at room temperature.

[0057] (3) Preparation of the casting solution: 0.15 g of MAF-6 was dispersed in 18.4 g of n-butanol, stirred at 80°C for 6 h (preferably at 800 rpm), and ultrasonicated for 2 h. Subsequently, 1 g of polyether block polyamide was added to obtain a casting solution. The casting solution was stirred at 80°C for 5 h to ensure uniform dispersion of the MAF-6. The solution was then allowed to stand at 60°C for 12 h to remove air bubbles.

[0058] (4) Preparation of a polycaffeic acid-interlayered MAF-6-based mixed matrix membrane: The precursor membrane prepared in step (2) was fixed on a smooth glass plate. The membrane-building solution prepared in step (3) was then slowly poured onto the membrane surface and doctor-coated (the coating was set to a thickness of 60 μm). After doctor-coating, the membrane was placed in a Petri dish and dried in an oven at 80°C for 12 hours. The resulting membrane was the aforementioned polycaffeic acid-interlayered MAF-6-based mixed matrix membrane.

[0059] The prepared polycaffeic acid sandwich MAF-6 based mixed matrix membrane (one side of the membrane coating solution is in contact with the permeate side feed solution) is used in the separation of volatile organic compounds as follows:

[0060] A 5 wt% ethanol / water solution was used as the permeation side feed liquid. The pervaporation operating conditions were a temperature of 40°C, a vacuum of 100 Pa, a feed volume of 1 L, a feed rate of 0.4 L / min, and an operation time of 1 h. The total permeation flux of the membrane prepared under these conditions was 2020 g·m -2 ·h -1 , the separation factor is 15.6.

[0061] Example 3:

[0062] (1) Preparation of polycaffeic acid: 1 g of caffeic acid was completely dissolved in deionized water at 80°C to obtain a caffeic acid solution with a concentration of 2 g / L. Then, ammonium persulfate and ethylenediamine were added in sequence with a molar ratio of 2:1:1 for caffeic acid, ammonium persulfate, and ethylenediamine, wherein the mass of ammonium persulfate was 0.633 g and the mass of ethylenediamine was 188 μL, and the mixture was stirred until uniformly mixed. -1 ) and sodium hydroxide aqueous solution (0.1 mol·L -1 ) was adjusted to a pH of 6-7. The polymerization reaction was stirred at room temperature for 2 hours, followed by centrifugation. The resulting precipitate was filtered, washed with deionized water, and then dried at 80°C for 12 hours. The concentration of the caffeic acid solution was 2 g / L. The mass of the resulting polycaffeic acid was 0.7834 g.

[0063] Preparation of MAF-6: Completely dissolve 1g of zinc hydroxide in 20ml of 25wt% ammonia water to obtain zinc hydroxide solution A. Dissolve 1.9g of 2-ethylimidazole in a mixture of 150ml of methanol and 10ml of cyclohexane and stir thoroughly to obtain 2-ethylimidazole solution B. Solution A was quickly poured into solution B, stirred at room temperature for 2h, vacuum filtered, washed with methanol, and oven-dried at 80°C for 12h. The resulting MAF-6 mass was 1.170g.

[0064] (2) In situ growth of MAF-6 on a polycaffeic acid film: 0.4 g of polycaffeic acid was dispersed in 10 ml of deionized water; 1.6 g of zinc hydroxide was dissolved in 20 ml of ammonia (25 wt%) (the concentration of the zinc hydroxide solution was 80 g / L) and stirred to obtain zinc hydroxide solution C in ammonia. 4 g of 2-ethylimidazole was dissolved in a mixed solution of 50 ml of methanol and 5 ml of cyclohexane and stirred to obtain 2-ethylimidazole solution D.

[0065] The zinc hydroxide solution C prepared above was slowly added to the polycaffeic acid solution prepared above, and the zinc hydroxide solution C was completely dissolved in ammonia water. -1 ) and sodium hydroxide aqueous solution (0.1 mol·L -1 ) to a pH of 6-7 to obtain a mixed solution. Add 25 mL of 2-ethylimidazole solution D to the prepared mixed solution and stir evenly to obtain 55 mL of solution. Immerse a PVDF base membrane in the above solution and let it stand for 4 hours. Remove the membrane, gently rinse with methanol, and let it stand at room temperature.

[0066] (3) Preparation of the casting solution: 0.1 g of MAF-6 was dispersed in 18.4 g of n-butanol, stirred at 80°C for 6 h (preferably at 800 rpm), and ultrasonicated for 2 h. Subsequently, 1 g of polyether block polyamide was added to obtain a casting solution. The casting solution was stirred at 80°C for 5 h to ensure uniform dispersion of the MAF-6. The solution was then allowed to stand at 60°C for 12 h to remove air bubbles.

[0067] (4) Preparation of a polycaffeic acid-interlayered MAF-6-based mixed matrix membrane: The precursor membrane prepared in step (2) was fixed on a smooth glass plate. The membrane-building solution prepared in step (3) was then slowly poured onto the membrane surface and doctor-coated (the coating was set to a thickness of 60 μm). After doctor-coating, the membrane was placed in a Petri dish and dried in an oven at 80°C for 12 hours. The resulting membrane was the aforementioned polycaffeic acid-interlayered MAF-6-based mixed matrix membrane.

[0068] The prepared polycaffeic acid sandwich MAF-6 based mixed matrix membrane (one side of the membrane coating solution is in contact with the permeate side feed solution) is used in the separation of volatile organic compounds as follows:

[0069] A 5 wt% ethanol / water solution was used as the permeate feed solution. The pervaporation operating conditions were a temperature of 40°C, a vacuum of 100 Pa, a feed volume of 1 L, a feed rate of 0.4 L / min, and an operating time of 1 h. The total permeate flux of the membrane prepared under these conditions was 1588 g·m -2 ·h -1 , the separation factor is 16.7.

[0070] Example 4:

[0071] (1) Preparation of polycaffeic acid: 1 g of caffeic acid was completely dissolved in deionized water at 80°C to obtain a caffeic acid solution with a concentration of 2 g / L. Then, ammonium persulfate and ethylenediamine were added in sequence. The molar ratio of caffeic acid, ammonium persulfate, and ethylenediamine was 2:1:1, with 0.633 g of ammonium persulfate and 188 μL of ethylenediamine. Stir until uniformly mixed. -1 ) and sodium hydroxide aqueous solution (0.1 mol·L -1 ) was adjusted to a pH of 6-7. The polymerization reaction was carried out at room temperature for 2 hours, followed by centrifugation. The resulting precipitate was filtered, washed with deionized water, and dried at 80°C for 12 hours. The mass of the resulting polycaffeic acid was 0.7834 g.

[0072] Preparation of MAF-6: Completely dissolve 1g of zinc hydroxide in 20ml of 25wt% ammonia water to obtain zinc hydroxide solution A. Dissolve 1.9g of 2-ethylimidazole in a mixture of 150ml of methanol and 10ml of cyclohexane and stir thoroughly to obtain 2-ethylimidazole solution B. Solution A was quickly poured into solution B, stirred at room temperature for 2h, vacuum filtered, washed with methanol, and oven-dried at 80°C for 12h. The resulting MAF-6 mass was 1.170g.

[0073] (2) In situ growth of MAF-6 on a polycaffeic acid film: Disperse 0.5 g of polycaffeic acid in 10 ml of deionized water; dissolve 1 g of zinc hydroxide in 20 ml of ammonia water and stir evenly to obtain zinc hydroxide solution C in ammonia water. Dissolve 4 g of 2-ethylimidazole in a mixture of 50 ml of methanol and 5 ml of cyclohexane and stir evenly to obtain 2-ethylimidazole solution D.

[0074] The zinc hydroxide solution C prepared above was slowly added to the polycaffeic acid solution prepared above, and the zinc hydroxide solution C was completely dissolved in ammonia water. -1 ) and sodium hydroxide aqueous solution (0.1 mol·L -1 ) to a pH of 6-7 to obtain a mixed solution. Add 25 mL of 2-ethylimidazole solution D to the prepared mixed solution and stir evenly to obtain 55 mL of solution. Immerse a PVDF base membrane in the above solution and let it stand for 4 hours. Remove the membrane, gently rinse with methanol, and let it stand at room temperature.

[0075] (3) Preparation of the casting solution: 0.1 g of MAF-6 was dispersed in 18.4 g of n-butanol, stirred at 80°C for 6 h (preferably at 800 rpm), and ultrasonicated for 2 h. Subsequently, 1 g of polyether block polyamide was added to obtain a casting solution. The casting solution was stirred at 80°C for 5 h to ensure uniform dispersion of the MAF-6. The solution was then allowed to stand at 60°C for 12 h to remove air bubbles.

[0076] (4) Preparation of a polycaffeic acid-interlayered MAF-6-based mixed matrix membrane: The precursor membrane prepared in step (2) was fixed on a smooth glass plate. The membrane-building solution prepared in step (3) was then slowly poured onto the membrane surface and doctor-coated (the coating was set to a thickness of 60 μm). After doctor-coating, the membrane was placed in a Petri dish and dried in an oven at 80°C for 12 hours. The resulting membrane was the aforementioned polycaffeic acid-interlayered MAF-6-based mixed matrix membrane.

[0077] The prepared polycaffeic acid sandwich MAF-6 based mixed matrix membrane (one side of the membrane coating solution is in contact with the permeate side feed solution) is used in the separation of volatile organic compounds as follows:

[0078] A 5 wt% ethanol / water solution was used as the permeate feed solution. The pervaporation operating conditions were a temperature of 40°C, a vacuum of 100 Pa, a feed volume of 1 L, a feed rate of 0.4 L / min, and an operating time of 1 h. The total permeate flux of the membrane prepared under these conditions was 2347 g·m -2 ·h -1 , the separation factor is 13.

[0079] Example 5:

[0080] (1) Preparation of polycaffeic acid: 1 g of caffeic acid was completely dissolved in deionized water at 80°C to obtain a caffeic acid solution with a concentration of 2 g / L. Then, ammonium persulfate and ethylenediamine were added in sequence with a molar ratio of 2:1:1 for caffeic acid, ammonium persulfate, and ethylenediamine, wherein the mass of ammonium persulfate was 0.633 g and the mass of ethylenediamine was 188 μL, and the mixture was stirred until uniformly mixed. -1 ) and sodium hydroxide aqueous solution (0.1 mol·L -1 ) was adjusted to a pH of 6-7. The polymerization reaction was carried out at room temperature for 2 hours, followed by centrifugation. The resulting precipitate was filtered, washed with deionized water, and dried at 80°C for 12 hours. The mass of the resulting polycaffeic acid was 0.7834 g.

[0081] Preparation of MAF-6: Completely dissolve 1g of zinc hydroxide in 20ml of 25wt% ammonia water to obtain zinc hydroxide solution A. Dissolve 1.9g of 2-ethylimidazole in a mixture of 150ml of methanol and 10ml of cyclohexane and stir thoroughly to obtain 2-ethylimidazole solution B. Solution A was quickly poured into solution B, stirred at room temperature for 2h, vacuum filtered, washed with methanol, and oven-dried at 80°C for 12h. The resulting MAF-6 mass was 1.170g.

[0082] (2) In situ growth of MAF-6 on a polycaffeic acid film: Disperse 0.4 g of polycaffeic acid in 10 ml of deionized water; dissolve 1 g of zinc hydroxide in 20 ml of ammonia water and stir evenly to obtain zinc hydroxide solution C in ammonia water. Dissolve 4 g of 2-ethylimidazole in a mixture of 50 ml of methanol and 5 ml of cyclohexane and stir evenly to obtain 2-ethylimidazole solution D.

[0083] The zinc hydroxide solution C prepared above was slowly added to the polycaffeic acid solution prepared above, and the zinc hydroxide solution C was completely dissolved in ammonia water. -1 ) and sodium hydroxide aqueous solution (0.1 mol·L -1) to a pH of 6-7 to obtain a mixed solution. Add 25 mL of 2-ethylimidazole solution D to the prepared mixed solution and stir evenly to obtain 55 mL of solution. Immerse a PVDF base membrane in the above solution and let it stand for 4 hours. Remove the membrane, gently rinse with methanol, and let it stand at room temperature.

[0084] (3) Preparation of membrane-forming solution: 0.855 g of polydimethylsiloxane was dispersed in 5 ml of the organic solvent n-heptane. After sufficient dispersion, 0.855 g of MAF-6 prepared in (1) was added and stirred for 30 min. 92 μL of silane coupling agent and 0.0085 g of catalyst were added in sequence. The mixture was stirred at room temperature for 4 h. The resulting polymer matrix was allowed to stand for degassing to obtain a membrane-forming solution. The crosslinking agent was tetraethyl orthosilicate; the catalyst was dibutyltin dilaurate; and the mass ratio of polydimethylsiloxane, crosslinking agent, and catalyst was 100:10:1.

[0085] (4) Preparation of a polycaffeic acid-interlayered MAF-6-based mixed matrix membrane: The precursor membrane prepared in step (2) was fixed on a smooth glass plate. The membrane-building solution prepared in step (3) was then slowly poured onto the membrane surface and doctor-coated (the coating was set to a thickness of 60 μm). After doctor-coating, the membrane was placed in a Petri dish and dried in an oven at 80°C for 12 hours. The resulting membrane was the aforementioned polycaffeic acid-interlayered MAF-6-based mixed matrix membrane.

[0086] The prepared polycaffeic acid sandwich MAF-6 based mixed matrix membrane (one side of the membrane coating solution is in contact with the permeate side feed solution) is used in the separation of volatile organic compounds as follows:

[0087] A 5 wt% ethanol / water solution was used as the permeation side feed liquid. The pervaporation operating conditions were a temperature of 40°C, a vacuum of 100 Pa, a feed volume of 1 L, a feed rate of 0.4 L / min, and an operation time of 1 h. The total permeation flux of the membrane prepared under these conditions was 1807 g·m -2 ·h -1 , the separation factor is 15.1.

[0088] Comparative Example 1:

[0089] (1) Preparation of membrane casting solution: Weigh 18.4 g of n-butanol solution and add 1 g of polyether block polyamide to obtain a membrane casting solution. Stir the membrane casting solution at 80°C for 5 h and let it stand at 60°C for 12 h to remove bubbles.

[0090] (2) Membrane Preparation: A PVDF base membrane was fixed on a smooth glass plate. The membrane-building solution prepared in (1) was then slowly poured onto the membrane surface and applied by blade coating (the coating was set to a thickness of 60 μm). After blade coating, the membrane was placed in a Petri dish and dried in an oven at 80°C for 12 h. The resulting membrane was a polyether block polyamide matrix pervaporation membrane.

[0091] The prepared polyether block polyamide matrix pervaporation membrane (one side of the membrane coating liquid contacts the permeation side feed liquid) is used in the separation of volatile organic compounds as follows:

[0092] A 5 wt% ethanol / water solution was used as the permeation side feed liquid. The pervaporation operating conditions were a temperature of 40°C, a vacuum of 100 Pa, a feed volume of 1 L, a feed rate of 0.4 L / min, and an operation time of 1 h. The total permeation flux of the membrane prepared under these conditions was 1390 g·m -2 ·h -1 , the separation factor is 8.8.

[0093] This phenomenon is due to the fact that the membrane is composed of only one layer of polyether block polyamide, the hydrophobicity of the membrane surface is insufficient, and at the same time, there are relatively few transmission paths for alcohol molecules. By adding highly hydrophobic MAF-6 and a polycaffeic acid interlayer, the selectivity for alcohol preferential permeation can be increased. At the same time, the high specific surface area of ​​MAF-6 itself provides more paths for ethanol molecules to pass through, thereby improving the permeation flux.

[0094] Comparative Example 2:

[0095] (1) Preparation of polycaffeic acid: 1 g of caffeic acid was completely dissolved in deionized water at 80°C to obtain a caffeic acid solution with a concentration of 2 g / L. Then, ammonium persulfate and ethylenediamine were added in sequence with a molar ratio of 2:1:1 for caffeic acid, ammonium persulfate, and ethylenediamine, wherein the mass of ammonium persulfate was 0.633 g and the mass of ethylenediamine was 188 μL, and the mixture was stirred until uniformly mixed. -1 ) and sodium hydroxide solution (0.1 mol·L -1 ) was adjusted to a pH of 6-7. The polymerization reaction was carried out at room temperature for 2 hours, followed by centrifugation. The resulting precipitate was filtered, washed with deionized water, and dried at 80°C for 12 hours. The mass of the resulting polycaffeic acid was 0.7834 g.

[0096] (2) Preparation of a casting solution: 0.1 g of polycaffeic acid was dispersed in 18.4 g of n-butanol solution, stirred at 80°C for 6 h (preferably at 800 rpm), and ultrasonicated for 2 h. Subsequently, 1 g of polyether block polyamide was added to obtain a casting solution, which was stirred at 80°C for 5 h. The solution was then allowed to stand at 60°C for 12 h to remove bubbles.

[0097] (3) Membrane Preparation: A PVDF base film was fixed on a smooth glass plate. The membrane-building solution prepared in (1) was then slowly poured onto the membrane surface and applied by doctor blade coating (the coating was set to a thickness of 60 μm). After doctor blade coating, the membrane was placed in a Petri dish and dried in an oven at 80°C for 12 h. The resulting membrane was a polycaffeic acid-doped mixed matrix membrane.

[0098] The prepared polycaffeic acid-doped pervaporation membrane (one side of the membrane coating liquid is in contact with the permeation side feed liquid) is used in the separation of volatile organic compounds as follows:

[0099] A 5 wt% ethanol / water solution was used as the permeation side feed liquid. The pervaporation operating conditions were a temperature of 40°C, a vacuum degree of 100-150 Pa, a feed volume of 1 L, a feed rate of 0.4 L / min, and an operation time of 1 h. The total permeation flux of the membrane prepared under these conditions was 1580 g·m -2 ·h -1 , the separation factor is 7.7.

[0100] After adding polycaffeic acid, the hydroxyl groups in the polycaffeic acid increase the membrane surface's affinity for water molecules, slightly increasing the permeate flux. However, due to the hydrophilicity of polycaffeic acid, the separation factor decreases. Adding highly hydrophobic MAF-6 can effectively increase the hydrophobicity of the membrane surface and improve the separation factor.

[0101] Comparative Example 3:

[0102] (1) Preparation of MAF-6 nanoparticles: 1.9 g of 2-ethylimidazole was dissolved in a mixture of 150 ml of methanol and 10 ml of cyclohexane to obtain a 2-ethylimidazole solution. 1 g of zinc hydroxide was dissolved in 20 ml of aqueous ammonia to obtain a zinc hydroxide solution. The zinc hydroxide solution was quickly added to the 2-ethylimidazole solution and stirred at room temperature for 2 hours. The resulting white precipitate was centrifuged and filtered with methanol. The precipitate was then dried in an oven at 80°C for 12 hours. 1.170 g of MAF-6 particles with a particle size of 400-500 nm were obtained.

[0103] (2) Preparation of the casting solution: 0.1 g of MAF-6 was dispersed in 18.4 g of n-butanol solution, stirred at 80°C for 6 h (preferably at 800 rpm), and ultrasonicated for 2 h. Subsequently, 1 g of polyether block polyamide was added to obtain a casting solution. The casting solution was stirred at 80°C for 5 h to ensure uniform dispersion of the MAF-6. The solution was then allowed to stand at 60°C for 12 h to remove bubbles.

[0104] (3) Membrane Preparation: A PVDF base film was fixed on a smooth glass plate. The membrane-building solution prepared in (2) was then slowly poured onto the membrane surface and applied by doctor blade coating (the coating was set to a thickness of 60 μm). After doctor blade coating, the membrane was placed in a Petri dish and dried in an oven at 80°C for 12 h. The resulting membrane was a MAF-6-doped mixed matrix membrane.

[0105] The prepared MAF-6 doped mixed matrix membrane was applied in the separation of volatile organic compounds as follows:

[0106] A 5 wt% ethanol / water solution was used as the permeation side feed liquid. The pervaporation operating conditions were a temperature of 40°C, a vacuum of 100 Pa, a feed volume of 1 L, a feed rate of 0.4 L / min, and an operation time of 1 h. The total permeation flux of the membrane prepared under these conditions was 1500 g·m -2 ·h -1 , the separation factor is 12.5.

[0107] The addition of MAF-6 significantly improves the membrane separation factor. However, due to the high hydrophobicity of the inner and outer pores of MAF-6, MAF-6 has a significant repulsion for water molecules, so the permeation flux is lower than that of Example 1.

[0108] Comparative Example 4:

[0109] (1) Preparation of MAF-6 nanoparticles: 1.9 g of 2-ethylimidazole was dissolved in a mixture of 150 ml of methanol and 10 ml of cyclohexane to obtain a 2-ethylimidazole solution. 1 g of zinc hydroxide was dissolved in 20 ml of aqueous ammonia to obtain a zinc hydroxide solution. The zinc hydroxide solution was quickly added to the 2-ethylimidazole solution and stirred at room temperature for 2 hours. The resulting white precipitate was centrifuged and filtered with methanol. The precipitate was then dried in an oven at 80°C for 12 hours. 1.170 g of MAF-6 particles with a particle size of 400-500 nm were obtained.

[0110] (2) Preparation of polycaffeic acid: Preparation of polycaffeic acid: 1 g of caffeic acid was completely dissolved in deionized water at 80°C to obtain a caffeic acid solution with a concentration of 2 g / L. Then, ammonium persulfate and ethylenediamine were added in sequence with a molar ratio of caffeic acid, ammonium persulfate, and ethylenediamine of 2:1:1, wherein the mass of ammonium persulfate was 0.633 g and the mass of ethylenediamine was 188 μL, and the mixture was stirred until uniformly mixed. -1 ) and sodium hydroxide solution (0.1 mol·L -1 ) was adjusted to a pH of 6-7. The polymerization reaction was carried out at room temperature for 2 hours, followed by centrifugation. The resulting precipitate was filtered, washed with deionized water, and dried at 80°C for 12 hours. The mass of the resulting polycaffeic acid was 0.7834 g.

[0111] (3) Preparation of the casting solution: 0.1 g MAF-6 and 0.1 g polycaffeic acid were dispersed in 18.4 g n-butanol solution, stirred at 80°C for 6 h (preferably at 800 rpm), and ultrasonicated for 2 h. Subsequently, 1 g polyether block polyamide was added to obtain a casting solution. The casting solution was stirred at 80°C for 5 h to ensure uniform dispersion of the MAF-6. The solution was then allowed to stand at 60°C for 12 h to remove bubbles.

[0112] (4) Membrane Preparation: A PVDF base film was fixed on a smooth glass plate, and the membrane-building solution prepared in (1) was slowly poured onto the membrane surface and applied by blade coating (the coating was set to a thickness of 60 μm). After blade coating, the membrane was placed in a Petri dish and dried in an oven at 80°C for 12 h. The resulting membrane was a polycaffeic acid and MAF-6 co-doped mixed matrix membrane.

[0113] The prepared polycaffeic acid and MAF-6 co-doped mixed matrix membrane was applied in the separation of volatile organic compounds as follows:

[0114] A 5 wt% ethanol / water solution was used as the permeate feed solution. The pervaporation operating conditions were a temperature of 40°C, a vacuum of 100 Pa, a feed volume of 1 L, a feed rate of 0.4 L / min, and an operating time of 1 h. The total permeate flux of the membrane prepared under these conditions was 1876 g·m -2 ·h -1 , the separation factor is 13.

[0115] Although the addition of MAF-6 and polycaffeic acid particles improves the membrane's separation factor, simple mechanical mixing can cause MAF-6 to agglomerate within the membrane, which can easily lead to surface defects and compromise membrane performance. By pre-laying a polycaffeic acid interlayer and then in-situ growing MAF-6 on the polycaffeic acid's hydroxyl groups, the uniform distribution of MAF-6 is promoted, forming a continuous layer that effectively improves the separation factor and permeate flux.

Claims

1. A polycaffeic acid sandwich MAF-6 based mixed matrix membrane, characterized in that From bottom to top, it consists of a PVDF base membrane, a polycaffeic acid interlayer with in-situ grown MAF-6, and a polymer matrix layer with MAF-6 dispersed therein.

2. The polycaffeic acid sandwich MAF-6 based mixed matrix membrane according to claim 1, characterized in that The polymer matrix is ​​selected from the group consisting of: polyether block polyamide, polydimethylsiloxane.

3. The polycaffeic acid sandwich MAF-6 based mixed matrix membrane according to claim 1, characterized in that The polycaffeic acid is prepared by polymerization reaction of caffeic acid, ammonium persulfate and ethylenediamine. The particle size of the polycaffeic acid is 200-1000 nm.

4. The polycaffeic acid sandwich MAF-6 based mixed matrix membrane according to claim 3, characterized in that The preparation method of polycaffeic acid is as follows: The aqueous solution of caffeic acid, ammonium persulfate and ethylenediamine were mixed evenly, the pH was adjusted to 6-7, and the mixture was stirred at room temperature for 2 hours. The reaction solution was then centrifuged, and the precipitate was collected, washed and dried to obtain polycaffeic acid. The molar ratio of caffeic acid, ammonium persulfate and ethylenediamine is 2-4:1-2:1; The concentration of the aqueous solution of caffeic acid is 1 to 5 g / L.

5. The method for preparing a polycaffeic acid sandwich MAF-6 based mixed matrix membrane according to claim 1, wherein: The preparation method comprises the following steps: (1) Dispersing polycaffeic acid uniformly in deionized water, adding zinc hydroxide in ammonia solution to adjust the pH to 6-7, and then adding 2-ethylimidazole organic solution to disperse uniformly to obtain a mixed system; immersing a PVDF substrate in the obtained mixed system, allowing it to stand for 1-4 hours, then taking it out and rinsing it with methanol, and evaporating it at room temperature to obtain a polycaffeic acid membrane with in situ growth of MAF-6; (2) MAF-6 was dispersed in n-butanol, and then the polymer matrix was added, stirred, and allowed to stand to obtain a membrane-forming solution; (3) Fixing the polycaffeic acid film of the in situ grown MAF-6 obtained in step (1), scraping the membrane-building solution obtained in step (2), and drying to obtain the polycaffeic acid sandwich MAF-6-based mixed matrix membrane.

6. The preparation method according to claim 5, wherein In step (1), the volume mass ratio of deionized water to polycaffeic acid is 16.7-33.3:1, mL / g; the mass ratio of polycaffeic acid, zinc hydroxide, and 2-ethylimidazole is 1-20:10-20:

10.

7. The preparation method according to claim 5, wherein In step (1), the concentration of zinc hydroxide in the ammonia solution is 40-80 g / L, and the concentration of the solvent ammonia solution is 15-28 wt %; the concentration of 2-ethylimidazole in the organic solution is 5-20 g / L, and the solvent is a mixed solvent of methanol and cyclohexane in a volume ratio of 15:

1.

8. The preparation method according to claim 5, wherein In step (2), the mass ratio of MAF-6, polymer matrix and n-butanol is 0.01-0.2:1:15-20.

9. The polycaffeic acid sandwich MAF-6-based mixed matrix membrane as claimed in claim 1 is used for recovering alcohol from alcohol aqueous solution by pervaporation.

10. The use according to claim 9, characterized in that The alcohol is ethanol.

Images