Ultrafiltration membrane preparation method and membrane separation equipment

Abstract

The invention belongs to the technical field of ultrafiltration membrane preparation methods, and discloses an ultrafiltration membrane preparation method and a membrane separation device.The ultrafiltration membrane preparation method comprises the following steps that carboxyl is introduced into modified PVDF, the modified PVDF is mixed with graphene oxide, carbon nanotubes and additives, ethanediamine promotes amide to react to be connected with a nanometer material, after cleaning and drying, the mixture is dissolved into a membrane casting solution, and the membrane casting solution is obtained; according to the preparation method, carboxyl functional groups are introduced into the PVDF and composite modification of the nano material is carried out, so that the mechanical strength of the ultrafiltration membrane is improved, and through the chemical bonding effect between the nano material of the graphene oxide and the carbon nano tube with the oxygen-containing groups and the modified PVDF, the performance of the ultrafiltration membrane is improved, and the performance of the ultrafiltration membrane is improved. The membrane structure is firmer and can bear higher operating pressure and a worse use environment, the hydrophilicity or hydrophobicity of the surface of the membrane is improved, the adsorption of organic matters and microorganisms is effectively resisted, the membrane pollution is reduced, and the service life of the membrane is prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of ultrafiltration membrane preparation methods, and specifically relates to an ultrafiltration membrane preparation method and membrane separation equipment. Background Art

[0002] With the rapid development of membrane separation technology, ultrafiltration membranes are increasingly used in wastewater treatment, separation of biological products, food industry purification and other fields. However, despite the many advantages of ultrafiltration membranes, traditional ultrafiltration membranes still have some significant disadvantages in practical applications, which limit their further performance improvement and wide application. First, the mechanical strength of traditional ultrafiltration membranes is limited, and it is difficult to withstand high operating pressures and harsh operating environments. During high-intensity filtration processes, membrane materials are prone to deformation or rupture, resulting in decreased membrane performance or even failure. This not only affects the treatment efficiency, but also increases the cost of maintenance and replacement of membranes. Secondly, the surface properties of traditional ultrafiltration membranes are relatively single, and it is difficult to meet the needs of multiple applications at the same time. For example, some applications require the membrane surface to have good hydrophilicity to promote the passage of water molecules, while other applications require the membrane surface to have hydrophobicity to repel specific pollutants. Traditional ultrafiltration membranes often find it difficult to achieve an ideal balance in these aspects. Furthermore, traditional ultrafiltration membranes have weak anti-pollution capabilities and are easily adsorbed and deposited by pollutants such as organic matter and microorganisms. The accumulation of these pollutants on the membrane surface can lead to clogging of membrane pores, decreased flux and reduced retention rate. In order to maintain the performance of the membrane, it needs to be cleaned and maintained regularly, which not only increases the operating cost, but also may cause damage to the membrane. In addition, the service life of traditional ultrafiltration membranes is relatively short and cannot meet the needs of long-term stable operation. This is mainly because the membrane material is prone to aging and degradation during long-term use, resulting in a gradual decline in membrane performance. Therefore, an ultrafiltration membrane preparation method and membrane separation equipment are proposed to solve the above problems. Summary of the invention

[0003] The object of the present invention is to provide a method for preparing an ultrafiltration membrane and a membrane separation device to solve the problems raised in the above background technology.

[0004] To achieve the above object, the present invention provides the following technical solution: a method for preparing an ultrafiltration membrane, comprising the following steps: S1: Modify PVDF and introduce carboxyl functional groups through copolymerization to obtain modified PVDF; S2: mixing modified PVDF, graphene oxide, carbon nanotubes having oxygen-containing groups, and additives including polyimide, polyvinyl pyrrolidone, polyethylene glycol, and lithium salt in a solvent in proportion to form a uniformly dispersed mixed system; S3: adding ethylenediamine to the mixed system, and chemically bonding the graphene oxide and the carbon nanotubes to the modified PVDF through an amide reaction between the amino groups at both ends of the ethylenediamine and the carboxyl groups, thereby forming a composite material; S4: cleaning and vacuum drying the composite material; S5: dissolving the dried composite material in a solvent to prepare a casting solution; S6: The casting liquid is evenly coated on the support material by a scraper coating method or a dip coating method, and the casting liquid is solidified and formed by a phase inversion method to obtain an ultrafiltration membrane product.

[0005] Preferably, the mass ratio of the polyimide, polyvinyl pyrrolidone, polyethylene glycol and lithium salt is (0.5-5):(1-5):(1-5):(0.1-2), and the additive accounts for 5% to 20% of the mass of the modified PVDF.

[0006] Preferably, the solvent includes N,N-dimethylformamide or N-methylpyrrolidone, and the amount of the solvent used is 100% to 300% of the mass of the modified PVDF.

[0007] Preferably, the mass ratio of the graphene oxide and the carbon nanotubes having oxygen-containing groups in the mixed system is (1:2) to (2:1).

[0008] Preferably, the S1 specifically comprises the steps of: S11: weighing PVDF powder, carboxyl-containing monomer and initiator; S12: dissolving PVDF powder in a solvent, adding carboxyl-containing monomers and initiators, and stirring to mix the components evenly.

[0009] S13: placing the mixed solution in a reactor, heating it to a preset temperature, and stirring the reaction for a preset time under nitrogen protection, so that the PVDF and the carboxyl-containing monomer undergo a copolymerization reaction to generate a modified PVDF with a carboxyl functional group; S14: After the reaction is completed, the reaction solution is cooled to room temperature, and unreacted monomers and impurities are removed to obtain a pure modified PVDF product; Preferably, the S2 specifically comprises the steps of: S21: weighing modified PVDF, graphene oxide, carbon nanotubes containing oxygen groups and various additives according to a predetermined ratio, dissolving the modified PVDF in a solvent, adding graphene oxide and carbon nanotubes at the same time, and performing dispersion treatment using an ultrasonic or high-speed stirrer; S22: Under continuous stirring, additives such as polyimide, polyvinyl pyrrolidone, polyethylene glycol and lithium salt are added to the solution one by one, and stirring is continued until each component is completely dissolved and mixed evenly.

[0010] Preferably, the S3 specifically comprises the steps of: S31: slowly adding ethylenediamine solution dropwise to the mixed system under stirring; S32: After the addition of ethylenediamine, the reaction system is continuously stirred to allow the amino groups at both ends of the ethylenediamine to react with the carboxyl groups on the modified PVDF and the oxygen-containing groups on the surfaces of the graphene oxide and the carbon nanotubes to form an amide reaction to form a stable chemical bond connection; S33: The reaction progress was monitored by infrared spectroscopy.

[0011] Preferably, the S4 specifically comprises the steps of: S41: pouring the composite material solution after the reaction into a container, and washing it multiple times with a large amount of solvent to remove unreacted ethylenediamine and other impurities; S42: placing the cleaned composite material in a vacuum drying oven and performing vacuum drying treatment at a preset temperature until the solvent in the composite material is completely volatilized to obtain dry composite material powder.

[0012] Preferably, the S5 specifically comprises the steps of: S51: Select the solvent based on the solubility of the composite material and the requirements of the subsequent film-forming process; S52: slowly adding the dried composite material powder into the solvent while stirring, until the composite material is completely dissolved to form a uniform casting solution.

[0013] A membrane separation device comprises a membrane assembly, a liquid inlet system and a liquid outlet system, wherein the membrane assembly is arranged between the liquid inlet system and the liquid outlet system, and the membrane assembly is filled with an ultrafiltration membrane prepared by the ultrafiltration membrane preparation method.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The present invention improves the mechanical strength of the ultrafiltration membrane by introducing carboxyl functional groups into PVDF and performing composite modification of nanomaterials, and through the chemical bonding between the nanomaterials of graphene oxide and carbon nanotubes with oxygen-containing groups and the modified PVDF, the membrane structure is made stronger and can withstand higher operating pressures and harsher use environments, the hydrophilicity or hydrophobicity of the membrane surface is improved, the adsorption of organic matter and microorganisms is effectively resisted, and membrane pollution is reduced. At the same time, the high specific surface area and porosity of the nanomaterials also help to reduce the deposition and clogging of pollutants and extend the service life of the membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0016] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0017] See also Figure 1 As shown, the present invention provides the following technical solutions: Implementation

[0018] S1: Accurately weigh 100 g of PVDF powder, 25 g of acrylic acid (AA, carboxyl-containing monomer) and 0.5 g of azobisisobutyronitrile (AIBN, initiator).

[0019] Slowly add PVDF powder into 300 ml of N,N-dimethylformamide (DMF), heat to 50 °C, and stir continuously until PVDF is completely dissolved.

[0020] Acrylic acid and AIBN were added to the above solution and stirred for 30 minutes to mix the components evenly. Subsequently, the reaction system was heated to 85°C and stirred for 10 hours under nitrogen protection to ensure that PVDF and acrylic acid fully copolymerized to generate modified PVDF with carboxyl functional groups.

[0021] After the reaction, the reaction solution was cooled to room temperature, and unreacted acrylic acid and impurities were removed by filtration and multiple washings. Finally, the modified PVDF product was vacuum dried at 60°C for 24 hours to obtain pure modified PVDF powder.

[0022] S2: Accurately weigh each component according to a predetermined ratio (e.g., modified PVDF: graphene oxide: oxygen-containing carbon nanotubes = 80:35:45). Dissolve the modified PVDF in 400 ml of N,N-dimethylacetamide (DMAc), and add graphene oxide and carbon nanotubes at the same time.

[0023] The mixed solution was dispersed using an ultrasonic processor with a power setting of 300 W and a processing time of 60 min to ensure that the nanomaterials were evenly dispersed in the solvent.

[0024] Under continuous stirring, polyimide (2 g), polyvinyl pyrrolidone (4 g), polyethylene glycol (4 g) and lithium salt (0.8 g) were added to the solution in sequence. Stirring was continued for 3 hours until all additives were completely dissolved and mixed evenly.

[0025] S3: While stirring, use a precision dropping funnel to slowly add 15 ml of ethylenediamine solution to the mixed system. The dropping speed is controlled at about 1 ml per minute to avoid excessive local concentration.

[0026] After the addition of ethylenediamine, the temperature of the reaction system was raised to 60°C, and the reaction was continued with stirring for 6 hours. During this process, the amino groups at both ends of the ethylenediamine reacted with the carboxyl groups on the modified PVDF and the oxygen-containing groups on the surface of the nanomaterial to form an amide reaction, forming a stable chemical bond connection.

[0027] The infrared spectrometer was used to regularly monitor the infrared spectrum changes of the reaction system to confirm the occurrence and completion of the amide reaction.

[0028] S4: Pour the reacted composite material solution into a beaker and wash it several times (at least 3 times) with a large amount of DMAc to remove unreacted ethylenediamine and other impurities. Stir continuously during the washing process to ensure sufficient washing.

[0029] The cleaned composite material was placed in a vacuum drying oven, set at 80°C, and vacuum dried for 24 hours until the solvent in the composite material was completely volatilized to obtain a dry composite material powder.

[0030] S5: Select a suitable solvent (such as DMAc) according to the solubility of the composite material and the requirements of the subsequent film-forming process. Slowly add the dried composite material powder into the solvent while stirring until the composite material is completely dissolved to form a uniform casting solution.

[0031] S6: Use the doctor blade method to evenly coat the casting solution on the pre-prepared support material (such as polyester non-woven fabric). The coating thickness is adjusted according to specific needs. Subsequently, the coated membrane is placed in a water bath for phase inversion treatment to solidify the casting solution. Finally, an ultrafiltration membrane product with excellent performance is obtained. Implementation

[0032] S1: This step is similar to implementation mode 1, but methyl methacrylate (MMA) is used as the comonomer to explore the effect of different carboxylate groups on membrane properties.

[0033] S2-S6: remain the same as in the first embodiment, but adjust the reaction conditions and subsequent treatments caused by the change of the comonomer. Implementation

[0034] S1: This step is the same as implementation mode 1; S2: Polyethylene glycol dimethacrylate (PEGDMA) was introduced as a cross-linking agent to further enhance the structural stability and anti-fouling property of the membrane. PEGDMA was mixed evenly with the mixed system before adding ethylenediamine.

[0035] S3-S6: Adjust accordingly to accommodate the addition of PEGDMA. Implementation

[0036] S1: This step is the same as the first embodiment.

[0037] S2: Keep the proportion of nanomaterials, but use nano-titanium dioxide (TiO2) to replace part of the graphene oxide to study the effects of different nanomaterials on the photocatalytic and antibacterial properties of the membrane.

[0038] S3-S6: Make corresponding adjustments to accommodate changes in nanomaterials. Implementation

[0039] S1: This step is similar to the first embodiment, but in the preparation of modified PVDF, ultraviolet light is used to initiate polymerization to reduce the use of chemical initiators and potential environmental impact.

[0040] S2-S6: Adjust the reaction conditions and subsequent processing steps according to the characteristics of UV-induced polymerization. Implementation

[0041] S1: This step is similar to the first embodiment, but in the preparation of modified PVDF, supercritical carbon dioxide is used as a solvent to achieve a green and environmentally friendly polymerization process.

[0042] S2-S6: The preparation of mixed systems and chemical bond connection under supercritical carbon dioxide conditions requires special attention to the control of temperature and pressure. Implementation

[0043] S1-S2: This step is the same as the first implementation mode and remains unchanged.

[0044] S3: Use enzyme-catalyzed reactions instead of traditional chemical catalysis to improve the specificity and mildness of the reaction. Select appropriate enzymes and optimize their reaction conditions.

[0045] S4-S6: Adjust the washing and drying steps to remove the enzyme catalyst. Implementation

[0046] S1-S2: This step is the same as the first implementation mode and remains unchanged.

[0047] S3: In the chemical bonding step, click chemistry reactions (such as copper-catalyzed azide-alkyne cycloaddition reaction) are introduced.

[0048] S4-S6: Adjust the subsequent processing steps according to the characteristics of the click chemistry reaction. Implementation

[0049] S1: This step is similar to the first embodiment, but in the preparation of modified PVDF, a block copolymerization method is used to introduce polymer segments with different properties into PVDF to improve the comprehensive performance of the membrane.

[0050] S2-S6: Adjust the steps of preparing the mixed system and chemical bonding according to the characteristics of the block copolymer. Implementation

[0051] S1-S2: This step is the same as the first implementation mode and remains unchanged.

[0052] S3: In the chemical bond connection step, multilayer assembly technology (such as layer-by-layer self-assembly) is introduced to construct a multilayer nanostructure on the membrane surface through physical or chemical forces such as electrostatic interactions and hydrogen bonds to improve the separation performance and anti-fouling properties of the membrane.

[0053] S4-S6: Adjust the cleaning and drying steps to remove impurities and solvents that may be introduced during the assembly process.

[0054] Implementation method eleven: S1-S2: This step is the same as the first implementation mode and remains unchanged.

[0055] S3: After the chemical bond connection step, a post-crosslinking treatment is introduced. The membrane is placed in a solution containing a crosslinking agent, and a crosslinking reaction is initiated by heat treatment or irradiation treatment to further enhance the network structure and performance stability of the membrane.

[0056] S4-S6: The cleaning and drying steps after the post-crosslinking treatment require special attention to remove the crosslinker and unreacted crosslinker monomers.

[0057] A membrane separation device comprises a membrane assembly, a liquid inlet system and a liquid outlet system, wherein the membrane assembly is arranged between the liquid inlet system and the liquid outlet system, and the membrane assembly is filled with an ultrafiltration membrane prepared by the ultrafiltration membrane preparation method.

[0058] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an ultrafiltration membrane, characterized in that: The steps include: S1: Modify PVDF and introduce carboxyl functional groups through copolymerization to obtain modified PVDF; S2: mixing modified PVDF, graphene oxide, carbon nanotubes having oxygen-containing groups, and additives including polyimide, polyvinyl pyrrolidone, polyethylene glycol, and lithium salt in a solvent in proportion to form a uniformly dispersed mixed system; S3: adding ethylenediamine to the mixed system, and chemically bonding the graphene oxide and the carbon nanotubes to the modified PVDF through an amide reaction between the amino groups at both ends of the ethylenediamine and the carboxyl groups, thereby forming a composite material; S4: cleaning and vacuum drying the composite material; S5: dissolving the dried composite material in a solvent to prepare a casting solution; S6: The casting liquid is evenly coated on the support material by a scraper film forming method or a dip coating method, and the casting liquid is solidified and formed by a phase inversion method to obtain an ultrafiltration membrane product.

2. The method for preparing an ultrafiltration membrane according to claim 1, characterized in that: The mass ratio of the polyimide, polyvinyl pyrrolidone, polyethylene glycol and lithium salt is (0.5-5):(1-5):(1-5):(0.1-2), and the additive accounts for 5% to 20% of the mass of the modified PVDF.

3. The method for preparing an ultrafiltration membrane according to claim 1, characterized in that: The solvent includes N,N-dimethylformamide or N-methylpyrrolidone, and the amount of the solvent used is 100% to 300% of the mass of the modified PVDF.

4. The method for preparing an ultrafiltration membrane according to claim 1, characterized in that: The mass ratio of the graphene oxide and the carbon nanotubes having oxygen-containing groups in the mixed system is (1:2) to (2:1).

5. The method for preparing an ultrafiltration membrane according to claim 1, characterized in that: The S1 specifically comprises the steps of: S11: weighing PVDF powder, carboxyl-containing monomer and initiator; S12: dissolving PVDF powder in a solvent, adding a carboxyl-containing monomer and an initiator, and stirring to mix the components uniformly; S13: placing the mixed solution in a reactor, heating it to a preset temperature, and stirring the reaction for a preset time under nitrogen protection, so that the PVDF and the carboxyl-containing monomer undergo a copolymerization reaction to generate a modified PVDF with a carboxyl functional group; S14: After the reaction is completed, the reaction solution is cooled to room temperature, and unreacted monomers and impurities are removed to obtain a pure modified PVDF product.

6. The method for preparing an ultrafiltration membrane according to claim 1, characterized in that: The S2 specifically includes the steps of: S21: weighing modified PVDF, graphene oxide, carbon nanotubes containing oxygen groups and various additives according to a predetermined ratio, dissolving the modified PVDF in a solvent, adding graphene oxide and carbon nanotubes at the same time, and performing dispersion treatment using an ultrasonic or high-speed stirrer; S22: Under continuous stirring, additives such as polyimide, polyvinyl pyrrolidone, polyethylene glycol and lithium salt are added to the solution one by one, and stirring is continued until each component is completely dissolved and mixed evenly.

7. The method for preparing an ultrafiltration membrane according to claim 1, characterized in that: The S3 specifically includes the steps of: S31: slowly adding ethylenediamine solution dropwise to the mixed system under stirring; S32: After the addition of ethylenediamine, the reaction system is continuously stirred to allow the amino groups at both ends of the ethylenediamine to react with the carboxyl groups on the modified PVDF and the oxygen-containing groups on the surfaces of the graphene oxide and the carbon nanotubes to form an amide reaction to form a stable chemical bond connection; S33: The reaction progress was monitored by infrared spectroscopy.

8. The method for preparing an ultrafiltration membrane according to claim 1, characterized in that: The S4 specifically comprises the steps of: S41: pouring the composite material solution after the reaction into a container, and washing it multiple times with a large amount of solvent to remove unreacted ethylenediamine and other impurities; S42: placing the cleaned composite material in a vacuum drying oven and performing vacuum drying treatment at a preset temperature until the solvent in the composite material is completely volatilized to obtain dry composite material powder.

9. The method for preparing an ultrafiltration membrane according to claim 1, characterized in that: The S5 specifically includes the steps of: S51: Select the solvent based on the solubility of the composite material and the requirements of the subsequent film-forming process; S52: slowly adding the dried composite material powder into the solvent while stirring, until the composite material is completely dissolved to form a uniform casting solution.

10. A membrane separation device, characterized in that: The invention comprises a membrane assembly, a liquid inlet system and a liquid outlet system, wherein the membrane assembly is arranged between the liquid inlet system and the liquid outlet system, and the membrane assembly is filled with an ultrafiltration membrane prepared by the ultrafiltration membrane preparation method according to any one of claims 1 to 9.

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