A kind of pervaporation membrane and its preparation method

Abstract

The application discloses a kind of pervaporation membrane and its preparation method, the pervaporation membrane is prepared using blending method, by adding inorganic nanosheet TiO2-ZrO2-ZnO in polyvinyl alcohol matrix, crosslinking solidification is formed.The inorganic nanosheet is prepared using one-step solvothermal method, with two-dimensional sheet structure.The application utilizes the synergistic effect between ternary nanosheet and the hydrogen bond network between PVA matrix and inorganic rigid sheet layer, forms a "fast water channel" in the matrix, significantly improves the mechanical strength, anti-swelling and separation selectivity of the membrane.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to a pervaporation membrane and its preparation method. Background Technology

[0002] Pervaporation is a membrane separation technology driven by chemical potential difference. It achieves the separation of liquid mixtures through the solubility-diffusion selectivity of the membrane for components, and is particularly suitable for the dehydration and purification of azeotropes, near-boiling point substances, and heat-sensitive substances. Compared with traditional separation methods, the pervaporation process is not limited by gas-liquid phase equilibrium and has advantages such as high separation efficiency, low energy consumption, mild operating conditions, and no pollution. In the field of alcohol dehydration, pervaporation technology has been widely used in industrial solvent refining and alcohol-containing wastewater treatment. Polyvinyl alcohol (PVA) has become one of the preferred materials for preparing pervaporation dehydration membranes due to its excellent hydrophilicity, good film-forming properties, chemical resistance, and thermal stability. However, pure PVA membranes are prone to swelling in aqueous systems, leading to decreased membrane dimensional stability and significantly reduced separation selectivity; furthermore, PVA membranes have poor mechanical strength and are prone to deformation during long-term operation.

[0003] To overcome the above problems, researchers have attempted to prepare organic-inorganic hybrid membranes by adding inorganic fillers to polyvinyl alcohol (PVA) membranes. For example, Chinese patent CN106268332A discloses a method for preparing a PVA / graphite-phase carbon nitride pervaporation hybrid membrane, using ammonia-modified graphite-phase carbon nitride as a two-dimensional nanoskeleton filler, which is ultrasonically blended and dispersed into a PVA solution to form a hybrid membrane. However, g-C3N4 has insufficient hydrophilicity and poor interfacial compatibility with the PVA matrix. Chinese patent CN115920672A discloses an MXene nanosheet / PVA mixed matrix pervaporation membrane and its preparation method, which uses high-speed centrifugal coating technology to stack MXene nanosheets layer by layer on the bottom of a PVA matrix, constructing interlayer hydrophilic permeation channels. However, the preparation process of MXene materials is complex; the centrifugal coating process has high equipment requirements, making it difficult to achieve large-scale continuous production.

[0004] Therefore, developing a high-performance pervaporation membrane with simple preparation process, excellent separation performance, and stable structure remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a pervaporation membrane and its preparation method. By introducing TiO2-ZrO2-ZnO ternary nanosheets as inorganic reinforcing materials, the problem of severe swelling, insufficient mechanical strength, and limited separation performance of existing PVA-based pervaporation membranes is solved.

[0006] A method for preparing a pervaporation membrane includes the following steps: (1) Preparation of TiO2-ZrO2-ZnO ternary nanosheets: Weigh titanium source, zirconium source and zinc source in molar ratio Ti:Zr:Zn=(4~6):1:(0.5~2), dissolve them in a mixed solvent of glycerol, anhydrous ethanol and deionized water in volume ratio of 1:(4~5):1, add diethanolamine, stir evenly and transfer to high pressure reactor, react at 180~200°C for 12~24 hours, cool naturally to room temperature after reaction, centrifuge, wash with deionized water and anhydrous ethanol alternately 2-4 times, and vacuum dry at 80°C for 12 hours to obtain TiO2-ZrO2-ZnO nanosheet structure; (2) Preparation of casting solution: Dissolve polyvinyl alcohol in deionized water and stir in a 90°C water bath to prepare a polyvinyl alcohol aqueous solution with a concentration of 5~10 wt%; weigh the TiO2-ZrO2-ZnO nanosheets obtained in step (1) according to 1~6 wt% of the dry weight of polyvinyl alcohol and disperse them in the polyvinyl alcohol aqueous solution, and mix them evenly by ultrasonication to obtain a mixed solution; (3) Crosslinking and film formation: Add crosslinking agent to the mixture obtained in step (2), adjust the pH to 2-4 with acid, stir and react for 30 minutes to obtain casting solution; after the casting solution is allowed to stand to remove bubbles, coat it onto a glass plate with a scraper; place the glass plate coated with casting solution in an oven at 60-80°C for 8-12 hours to obtain pervaporation membrane.

[0007] In a specific embodiment, the titanium source in step (1) is at least one of tetrabutyl titanate, tetraisopropyl titanate, titanium sulfate, or titanium tetrachloride; the zirconium source is at least one of zirconium oxychloride, zirconium nitrate, zirconium n-propoxide, or zirconium isopropoxide; and the zinc source is at least one of zinc nitrate, zinc acetate, zinc chloride, or zinc sulfate.

[0008] In a specific embodiment, the volume ratio of glycerol, anhydrous ethanol, and deionized water in the mixed solvent in step (1) is 1:4:1, and in step (3), the amount of crosslinking agent added is 0.5~3wt% of the mass of polyvinyl alcohol. In a specific embodiment, the molar ratio of diethanolamine to zirconium source in step (1) is (1-2):1.

[0009] In a specific embodiment, the power of ultrasonic dispersion in step (2) is 200~300 W.

[0010] In a specific embodiment, the crosslinking agent in step (3) is at least one of glutaraldehyde, maleic acid, citric acid or glyoxal.

[0011] Compared with the prior art, the present invention has the following beneficial effects: The surface of TiO2-ZrO2-ZnO nanosheets is rich in hydroxyl groups, which can form strong hydrogen bonds with the hydroxyl groups on the PVA molecular chains. This ensures the high uniformity of the nanosheets within the PVA, and the hydrogen bonds also improve the toughness of the film. Furthermore, the abundant hydroxyl groups have a strong affinity for water molecules, forming a preferential adsorption layer.

[0012] The physical barrier effect of two-dimensional nanosheets can effectively improve separation selectivity; in addition, it can effectively improve the mechanical properties of PVA films.

[0013] The one-step solvothermal method for preparing ternary nanosheets avoids complex processes such as multi-step synthesis and high-temperature calcination; the blending method for film formation is simple and conducive to industrial application.

[0014] (4) TiO2-ZrO2-ZnO has excellent photocatalytic performance. Under ultraviolet light irradiation, active oxygen can be generated on the membrane surface, which can decompose organic pollutants adsorbed on the membrane surface. Therefore, the composite membrane of the present invention has additional anti-fouling advantages when treating alcohol-water systems of wastewater, and can extend the cleaning cycle and service life of the membrane. Attached Figure Description

[0015] Appendix Figure 1 This is a SEM image of the TiO2-ZrO2-ZnO from this application. Detailed Implementation

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Example 1

[0018] Weigh out 5.78 g of tetrabutyl titanate, 1.10 g of zirconium oxychloride and 1.01 g of zinc nitrate. Dissolve the above raw materials in a mixed solvent of glycerol, anhydrous ethanol and deionized water in a volume ratio of 1:4:1, wherein 10 mL of glycerol, 40 mL of anhydrous ethanol and 10 mL of deionized water are added, and 0.65 g of diethanolamine is added. Stir for 30 minutes until completely dissolved.

[0019] The mixed solution was transferred to a 100 mL high-pressure reactor lined with polytetrafluoroethylene, sealed, and placed in an oven at 180°C for 16 hours. After the reaction, the mixture was allowed to cool naturally to room temperature, and the precipitate was separated by centrifugation. The precipitate was washed three times each with deionized water and anhydrous ethanol, and then vacuum dried at 80°C for 12 hours to obtain a white powdery product, which is TiO2-ZrO2-ZnO ternary nanosheets.

[0020] Weigh 8.0 g of polyvinyl alcohol and dissolve it in 100 mL of deionized water. Stir and dissolve in an 80°C water bath for 2 hours to obtain a PVA aqueous solution. Weigh 0.32 g of the nanosheets obtained in step (1) and add them to the above PVA aqueous solution. Sonicate to obtain a homogeneous mixture.

[0021] Add 0.58 g of 25% glutaraldehyde aqueous solution to the above mixture, adjust the pH to 3.0 by adding 0.1 mol / L dilute hydrochloric acid dropwise, and stir for 30 minutes. After standing for 45 minutes to remove bubbles, use a doctor blade to coat the casting solution onto a glass plate, controlling the wet film thickness to 200 μm.

[0022] A glass plate coated with casting solution was placed in an 80°C oven for 8 hours. After cooling to room temperature, the membrane was removed to obtain a pervaporation membrane.

[0023] Material characterization and performance testing: Scanning electron microscopy revealed that the product had a two-dimensional sheet-like morphology with a thickness of 15-40 nm and a length and width of 500-800 nm.

[0024] Swelling test: The membrane sample was immersed in a 90 wt% ethanol / water mixture for 24 hours at room temperature. After being removed, the surface moisture was dried, and the swelling degree was calculated by weighing.

[0025] Pervaporation performance testing: A pervaporation evaluation device was used for testing. The feed solution was a 90 wt% ethanol / water mixture, and the downstream pressure of the membrane was maintained at 100 Pa. After the system stabilized, the permeate was collected, weighed, and its composition was analyzed by gas chromatography. The steady-state flux and separation factor were then calculated.

[0026] Mechanical property testing: The tensile strength of the membrane was determined using a universal testing machine. Test conditions: 25°C, tensile rate 10 mm / min, sample width 10 mm, gauge length 20 mm.

[0027] Example 2

[0028] The difference from Example 1 is that the solvent for solvothermal treatment is adjusted to a mixed solvent of glycerol, anhydrous ethanol and deionized water in a volume ratio of 1:5:1, wherein 10 mL of glycerol, 50 mL of anhydrous ethanol and 10 mL of deionized water are used.

[0029] Comparative Example 1 Films were prepared using only a PVA matrix without the addition of TiO2-ZrO2-ZnO nanosheets. Other conditions were the same as in Example 1.

[0030] Comparative Example 2 The difference between this and Example 1 is that only tetrabutyl titanate is added during the solvothermal process, and zirconium oxychloride and zinc nitrate are not added.

[0031] Comparative Example 3 The difference between this and Example 1 is that only tetrabutyl titanate and zirconium oxychloride are added during the solvothermal process, and zinc nitrate is not added.

[0032] Table 1. Comparison of pervaporation membrane performance between each embodiment and the comparative example. Specific embodiments have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the scope of specific implementation methods based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for preparing a pervaporation membrane, characterized in that, Includes the following steps: (1) Preparation of TiO2-ZrO2-ZnO ternary material: Weigh titanium source, zirconium source and zinc source in molar ratio Ti:Zr:Zn=(4~6):1:(0.5~2), dissolve them in a mixed solvent of glycerol, anhydrous ethanol and deionized water in volume ratio of 1:(4~5):1, add diethanolamine, stir evenly and transfer to high pressure reactor, react at 180~200°C for 12~24 hours, cool naturally to room temperature after reaction, centrifuge, wash with deionized water and anhydrous ethanol alternately 2-4 times, and vacuum dry at 80°C to obtain nanosheet structure TiO2-ZrO2-ZnO; (2) Preparation of casting solution: Dissolve polyvinyl alcohol in deionized water and stir in a water bath at 60-90°C to prepare a polyvinyl alcohol aqueous solution with a concentration of 5-10 wt%; weigh the TiO2-ZrO2-ZnO nanosheets obtained in step (1) at 1-6 wt% of the dry weight of polyvinyl alcohol and disperse them in the polyvinyl alcohol aqueous solution, and mix them evenly by ultrasonication to obtain a mixed solution; (3) Crosslinking and film formation: Add crosslinking agent to the mixture obtained in step (2), adjust the pH to 2-4 with acid, stir for a certain time to obtain casting solution; after the casting solution is allowed to stand to remove bubbles, coat it onto a glass plate with a scraper; place the glass plate coated with casting solution in an oven at 60-80°C for 8-12 hours to obtain pervaporation membrane.

2. The preparation method according to claim 1, characterized in that, The titanium source in step (1) is at least one of tetrabutyl titanate, tetraisopropyl titanate, titanium sulfate, or titanium tetrachloride; the zirconium source is at least one of zirconium oxychloride, zirconium nitrate, zirconium n-propoxide, or zirconium isopropoxide; and the zinc source is at least one of zinc nitrate, zinc acetate, zinc chloride, or zinc sulfate.

3. The preparation method according to claim 1, characterized in that, In step (1), the volume ratio of glycerol, anhydrous ethanol and deionized water in the mixed solvent is 1:4:

1. In step (3), the amount of crosslinking agent added is 0.5~3wt% of the mass of polyvinyl alcohol.

4. The preparation method according to claim 1, characterized in that, In step (1), the molar ratio of diethanolamine to zirconium source is (1-2):

1.

5. The preparation method according to claim 1, characterized in that, The ultrasonic dispersion power in step (2) is 200~300 W.

6. The preparation method according to claim 1, characterized in that, The crosslinking agent mentioned in step (3) is at least one of glutaraldehyde, maleic acid, citric acid or glyoxal.

7. A pervaporation membrane prepared by the preparation method according to any one of claims 1-6.

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