High-flux DTRO reverse osmosis membrane and preparation method thereof

Abstract

The invention discloses a high-flux DTRO reverse osmosis membrane and a preparation method, and belongs to the field of water treatment.The high-flux DTRO reverse osmosis membrane comprises a disc type membrane, the disc type membrane comprises a polyacrylonitrile (PAN) base membrane layer, and the surface of the base membrane layer is coated with a polyether sulfone (PES) pre-coating layer containing nanometer titanium dioxide (TiO2) particles; the thickness of the pre-coating layer is 8 microns (the thickness of the pre-coating layer is 8 microns, so that the effective adhesion of the pre-coating layer can be ensured, and the optimal anti-pollution performance can be exerted); an active separation layer of the membrane is a polyamide composite layer containing zwitterionic monomers, the zwitterionic monomers account for 0.8% of the mass of a water-phase solution, meanwhile, pollutant attachment is reduced through charge repulsion, and the thickness of the active separation layer is 1.5 microns; through the zwitterionic monomer modified polyamide composite layer and the pre-coating process, the solute interception resistance is effectively reduced, and the water flux is remarkably improved; meanwhile, through material surface hydrophilization treatment and runner optimization, it is ensured that the stable filtering efficiency of the membrane assembly is kept in long-term operation.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, and in particular to a high-flux DTRO reverse osmosis membrane and a preparation method thereof. Background Art

[0002] Disk tube reverse osmosis membrane (DTRO) is widely used in high-concentration wastewater treatment due to its advantages such as open flow channels and strong anti-pollution ability. However, the existing preparation methods for DTRO membranes have the following defects: Imbalance between flux and anti-pollution performance: Traditional DTRO membranes rely on the design of the flow channel structure to improve the anti-pollution ability, but the membrane sheet materials are not optimized specifically, resulting in limited improvement in water flux. For example, the existing patent CN202111283014.5 discloses a preparation method of a high-flux reverse osmosis membrane. By coating an additive for regulating the interfacial tension on the surface of the base membrane in the form of a diluted hydrogel before the interfacial polymerization reaction of the reverse osmosis membrane, the additive can be continuously released into the water phase during the interfacial polymerization process, regulating the interfacial polymerization reaction process, avoiding too fast reaction rate, and at the same time ensuring the completeness of the reaction, so that the prepared reverse osmosis membrane has better water flux while maintaining the rejection rate. At the same time, by introducing an ester compound for regulating the interfacial tension into the oil phase, it also ensures the reduction of the interfacial tension and better salt rejection rate during the interfacial reaction process; However, this patent only improves the flux by regulating the interfacial tension and does not combine with the flow channel characteristics of the DTRO membrane column, making it difficult to achieve a performance breakthrough.

[0003] Insufficient coordination between structure and material: Existing technologies mostly focus on the modification of membrane sheet materials or the design of the flow guiding disk structure, lacking systematic optimization of materials-structure-process, and it is difficult to operate stably for a long time in an environment with high suspended solids and high salinity.

[0004] Poor adaptability to complex water quality: Colloids and organic substances in high-concentration wastewater are easily adsorbed on the membrane surface. Existing methods do not improve the anti-pollution ability by regulating the surface charge of the material or nano-modification, resulting in a high frequency of chemical cleaning and a short membrane life.

[0005] Therefore, a high-flux DTRO reverse osmosis membrane and a preparation method thereof are needed. It solves the problem that it is difficult to balance the flux and anti-pollution performance of the existing DTRO membrane, provides an efficient and stable technical solution for high-concentration wastewater treatment, and has significant economic benefits and environmental value. Summary of the Invention

[0006] In view of the deficiencies of the existing technology, the present invention provides a high-flux DTRO reverse osmosis membrane and a preparation method thereof, which solve the problems raised in the above background art.

[0007] Technical solution: To solve the above technical problems, according to one aspect of the present invention, more specifically, a high-flux DTRO reverse osmosis membrane includes a disc membrane, a flow guide disc and a central tie rod: The disc membrane includes a polyacrylonitrile (PAN) base membrane layer, and the surface of the base membrane layer is coated with a polyethersulfone (PES) pre-coating containing nano-titanium dioxide (TiO 2 ) particles, and the thickness of the pre-coating is 8 μm (the 8 μm thickness can not only ensure the effective adhesion of the pre-coating, but also exert its best anti-pollution performance); The active separation layer of the disc membrane is a polyamide composite layer containing zwitterionic monomers. The zwitterionic monomers account for 0.8% of the mass ratio of the aqueous solution (a loose polyamide network with negative charges can be formed under this ratio, effectively reducing the solute retention resistance), and at the same time, the attachment of pollutants is reduced by charge repulsion. The thickness of the active separation layer is 1.5 μm; The flow guide disc is made of polypropylene (PP) material, and a streamline bump array with a height of 0.4 mm and a pitch of 1.5 mm is provided on the surface (the bump array of this size can make the feed liquid form an efficient turbulent flow). The flow guide disc and the membrane are alternately stacked to form an open channel with a width of 2.5 mm. This channel width can balance the flux and pressure loss and adapt to wastewater with a suspended solid content ≤ 500 mg / L; The central tie rod is made of stainless steel 316L, which has good corrosion resistance and can adapt to the high-salt and high-pollution wastewater treatment environment to prevent corrosion during use and affect the overall structural stability of the membrane module.

[0008] The initial water flux of the membrane is ≥ 45 L / (m²·h), and the flux decay rate is ≤ 15% after running in 5000 ppm NaCl solution for 50 hours.

[0009] Furthermore, the dispersion particle size of the nano-titanium dioxide particles in the polyethersulfone pre-coating is 10 nm.

[0010] Furthermore, the streamline bumps of the flow guide disc are parabolic, and the curvature radius of the parabola is 1 mm.

[0011] According to another aspect of the present invention, more specifically, a high-flux DTRO reverse osmosis membrane and a preparation method include the above-mentioned high-flux DTRO reverse osmosis membrane, and the steps are as follows: S1. Preparation of disc membrane: a. Cut the PAN ultrafiltration membrane into circular membranes, immerse them in deionized water containing 5% glycerol for 2 hours (this pretreatment can effectively improve the surface wettability of the membranes), which is beneficial to the attachment of subsequent coatings, and drain after immersion; b. Mix PES and nano-TiO 2The particles are dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 9:1 to prepare a casting solution with a concentration of 15%. A pre-coating layer with a thickness of 8 μm is coated on the surface of the base film by a film scraping machine. During the coating process, the temperature and humidity are strictly controlled to ensure the uniformity of the pre-coating layer. Then, it is dried in an oven at 60 °C for 30 minutes to form the pre-coating layer; c. Immerse the pre-coated base film into an aqueous solution containing 2% m-phenylenediamine and 0.8% zwitterionic monomer. After 5 minutes, drain it, and then immerse it into a n-hexane oil phase solution containing 0.1% trimesoyl chloride for 2 minutes to form a polyamide composite layer. Finally, rinse the membrane with deionized water to remove the residual reagents; S2. Processing of the flow guiding disc: a. Use 3D printing to prepare the bump mold. Through high-precision 3D printing technology, the height error of the bumps can be controlled within ±0.05 mm to ensure the uniformity of the flow channels; b. Inject and mold the PP flow guiding disc at 230 °C. The injection temperature within this range can ensure the good molding performance of the PP material. After demolding, smooth the edge of the flow guiding disc to avoid scratching the membrane; S3. Assembly of the membrane column: Stack in the order of "flow guiding disc → membrane sheet → O-ring rubber gasket", fix it with a central pull rod. The distance between the membrane sheets is optimized to be 2.5 mm, and seal and test it under a pressure of 10 bar for 30 minutes to ensure the integrity of the system under high pressure; S4. Surface hydrophilic treatment: Immerse the membrane column into an aqueous solution containing 0.1% polyvinylpyrrolidone (PVP) and soak it at 40 °C for 1 hour (which can significantly improve the hydrophilicity of the membrane surface and reduce the adsorption of organic substances such as proteins).

[0012] Furthermore, the zwitterionic monomer is potassium 3-sulfopropyl methacrylate or methacryloyloxyethyl trimethyl ammonium chloride (these two zwitterionic monomers have significant effects in improving the membrane performance).

[0013] Furthermore, the initial water flux of the membrane sheet is ≥45 L / (m²·h), and the flux decay rate is ≤15% after running in a 5000 ppm NaCl solution for 50 hours, showing good high-flux performance and stability.

[0014] Furthermore, the zwitterionic monomer is potassium 3-sulfopropyl methacrylate or methacryloyloxyethyl trimethyl ammonium chloride.

[0015] Furthermore, in step b of the preparation of the disc membrane sheet, the film scraping speed of the film scraping machine is 5 mm / s.

[0016] Furthermore, in the membrane column assembly step, the material of the O-ring rubber gasket is ethylene propylene rubber.

[0017] The beneficial effects of the high-flux DTRO reverse osmosis membrane and its preparation method of the present invention are: (1) The present invention effectively reduces the solute retention resistance and significantly improves the water flux through the modification of the polyamide composite layer with zwitterionic monomers and the pre-coating process. At the same time, through the hydrophilic treatment of the material surface and the optimization of the flow channel, the membrane module can maintain a stable filtration efficiency during long-term operation.

[0018] (2) The streamlined bump array design of the flow guiding disc in the present invention promotes efficient turbulent flow of the feed liquid. Combining the nano-titanium dioxide pre-coating and the charge repulsion of zwitterions reduces the deposition and adsorption of pollutants on the membrane surface, extends the chemical cleaning cycle, and improves the service life of the membrane module.

[0019] (3) The open-channel structure in the present invention balances the flux and pressure loss and is suitable for wastewater with a high suspended solid content. Through the regulation of the charge characteristics of zwitterionic monomers, the attachment of different pollutants (such as colloids, organic substances, etc.) can be specifically reduced, and the treatment capacity for high-salt and high-organic wastewater is improved.

[0020] (4) The preparation process parameters of the present invention are clearly controllable. Key steps such as pre-coating and interfacial polymerization reactions ensure stable membrane performance. The membrane column structure is common with existing DTRO modules, and no additional equipment modification is required, making it suitable for high-difficulty treatment scenarios such as landfill leachate and coal chemical wastewater. Description of the Drawings

[0021] The present invention will be further described in detail below with reference to the drawings and specific implementation methods.

[0022] Figure 1 It is a schematic structural diagram of the present invention. Specific Embodiments

[0023] The present invention will be described in detail below with reference to the drawings and embodiments. It should be noted that, without conflict, the embodiments and features in the present application can be combined with each other.

[0024] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0025] Referring to Figure 1 , a high-flux DTRO reverse osmosis membrane includes a disc-shaped membrane, a flow guiding disc, and a central pull rod: The disc-shaped membrane includes a polyacrylonitrile (PAN) base membrane layer, and the surface of the base membrane layer is coated with a polyethersulfone (PES) pre-coating containing nano-titanium dioxide (TiO 2 ) particles, and the thickness of the pre-coating is 8 μm (the 8 μm thickness can not only ensure the effective attachment of the pre-coating but also exert its best anti-pollution performance); The active separation layer of the diaphragm is a polyamide composite layer containing zwitterionic monomers. The zwitterionic monomers account for 0.8% of the mass of the aqueous solution (a loose polyamide network with negative charges can be formed under this ratio, effectively reducing the solute retention resistance), and at the same time, pollutant attachment is reduced through charge repulsion. The thickness of the active separation layer is 1.5 μm; The flow guide disc is made of polypropylene (PP), and a streamline bump array with a height of 0.4 mm and a spacing of 1.5 mm is provided on the surface (such a bump array of this size can make the feed liquid form efficient turbulence). The flow guide discs and the diaphragms are stacked alternately to form an open channel with a width of 2.5 mm. This channel width can balance the flux and pressure loss and adapt to wastewater with a suspended solid content ≤ 500 mg / L; The central pull rod is made of stainless steel 316L, which has good corrosion resistance and can adapt to the environment of high-salt and highly polluted wastewater treatment, preventing corrosion during use and affecting the overall structural stability of the membrane module. According to another aspect of the present invention, more specifically, it is a high-flux DTRO reverse osmosis membrane and a preparation method, including a high-flux DTRO reverse osmosis membrane, which comprises the following steps: S1. Preparation of the disc membrane: a. Cut the PAN ultrafiltration membrane into circular membranes, immerse them in deionized water containing 5% glycerol for 2 hours (this pretreatment can effectively improve the surface wettability of the membranes), which is beneficial to the attachment of subsequent coatings, and drain them after soaking; b. Dissolve PES and nano-TiO 2 particles in N-methylpyrrolidone (NMP) according to a mass ratio of 9:1 to prepare a casting solution with a concentration of 15%. Coat a pre-coating with a thickness of 8 μm on the surface of the base membrane through a film coater. During the coating process, strictly control the temperature and humidity to ensure the uniformity of the pre-coating, and dry it in an oven at 60 °C for 30 minutes to form a pre-coating; c. Immerse the pre-coated base membrane in an aqueous solution containing 2% m-phenylenediamine and 0.8% zwitterionic monomers, drain it after 5 minutes, then immerse it in a n-hexane oil phase solution containing 0.1% trimesoyl chloride and react for 2 minutes to form a polyamide composite layer. Finally, rinse the membrane with deionized water to remove the residual reagents; S2. Processing of the flow guide disc: a. Prepare a bump mold by 3D printing. Through high-precision 3D printing technology, the height error of the bumps can be controlled within ±0.05 mm to ensure the uniformity of the flow channel; b. Inject and mold the PP flow guide disc at 230 °C. The injection temperature within this range can ensure the good molding performance of the PP material. After demolding, smooth the edge of the flow guide disc to avoid scratching the membrane; S3. Membrane column assembly: Stack in the order of "flow guiding disc → membrane sheet → O-ring rubber gasket", fix the central pull rod, and the membrane sheet spacing is optimized to be 2.5 mm. Conduct a sealing test for 30 minutes under a pressure of 10 bar to ensure the integrity of the system under high pressure; S4. Surface hydrophilic treatment: Immerse the membrane column in an aqueous solution containing 0.1% polyvinylpyrrolidone (PVP) and soak at 40 °C for 1 hour (which can significantly improve the hydrophilicity of the membrane surface and reduce the adsorption of organic substances such as proteins). Preferably, the zwitterionic monomer is potassium 3-sulfopropyl methacrylate or methacryloyloxyethyl trimethyl ammonium chloride (these two zwitterionic monomers are remarkable in enhancing the membrane performance). The initial water flux of the membrane sheet is ≥ 45 L / (m²·h), and the flux decay rate is ≤ 15% after running in a 5000 ppm NaCl solution for 50 hours, showing good high-flux performance and stability.

[0026] Example 1

[0027] According to the above preparation method, complete the preparation of the disc membrane sheet, the processing of the flow guiding disc, the membrane column assembly and the surface hydrophilic treatment in sequence. Among them, potassium 3-sulfopropyl methacrylate is selected as the zwitterionic monomer. After testing, the initial water flux of the membrane sheet is 48 L / (m²·h), the flux decay rate is 12% after running in a 5000 ppm NaCl solution for 50 hours, the pollutant deposition amount is reduced by 38% compared with the traditional membrane sheet, and the chemical cleaning cycle is extended to 16 days.

[0028] It is applicable to wastewater mainly containing cationic pollutants (such as metal ions).

[0029] Example 2

[0030] Using methacryloyloxyethyl trimethyl ammonium chloride as the zwitterionic monomer, and other preparation parameters are the same as those in Example 1. The test results show that the initial water flux of the membrane sheet is 46 L / (m²·h), the flux decay rate is 14%, the pollutant deposition amount is reduced by 42%, and the chemical cleaning cycle can reach 17 days; It is suitable for water quality mainly containing anionic pollutants (such as humic acid, colloid).

[0031] The above embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation to the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims

1. A high-flux DTRO reverse osmosis membrane, comprising a disc-type membrane, a guide plate, and a central tie rod, characterized in that: The disc-type diaphragm comprises a polyacrylonitrile-based membrane layer, the surface of which is coated with a polyethersulfone pre-coating layer containing nano-titanium dioxide particles, and the thickness of the pre-coating layer is 8 μm; The active separation layer of the disc-type membrane is a polyamide composite layer containing zwitterionic monomers, wherein the zwitterionic monomers account for 0.8% of the mass ratio of the aqueous phase solution, and the thickness of the active separation layer is 1.5 μm; The guide plate is made of polypropylene, and the surface is provided with a streamlined convex array with a height of 0.4mm and a spacing of 1.5mm. The guide plate and the diaphragm are alternately stacked to form an open flow channel with a width of 2.5mm, which is suitable for wastewater with a suspended matter content of ≤500mg / L; The material of the central pull rod is stainless steel 316L.

2. A high flux DTRO reverse osmosis membrane according to claim 1, characterized in that: The initial water flux of the membrane is ≥45L / (m²·h), and the flux attenuation rate is ≤15% after running in a 5000ppm NaCl solution for 50 hours.

3. A high flux DTRO reverse osmosis membrane according to claim 1, characterized in that: The dispersed particle size of the nano titanium dioxide particles in the polyethersulfone pre-coating layer is 10 nm.

4. A high flux DTRO reverse osmosis membrane according to claim 1, characterized in that: The streamlined convex point of the guide plate is parabolic, and the curvature radius of the parabola is 1 mm.

5. A method for preparing a high-flux DTRO reverse osmosis membrane, comprising the high-flux DTRO reverse osmosis membrane according to claim 1, characterized in that: The steps include: S1. Preparation of disc diaphragm: a. Cut the PAN ultrafiltration membrane into circular membrane pieces, immerse them in deionized water containing 5% glycerol for 2 hours, and drain them after immersion; b. PES and nano-TiO2 particles were dissolved in N-methylpyrrolidone at a mass ratio of 9:1 to prepare a 15% concentration of a casting solution, and a pre-coating layer with a thickness of 8 μm was applied on the surface of the base film by a scraper, and dried in an oven at 60 ° C for 30 minutes to form a pre-coating layer; c. Immerse the pre-coated base film in an aqueous solution containing 2% m-phenylenediamine and 0.8% zwitterionic monomer, drain after 5 minutes, and then immerse in an oily solution of n-hexane containing 0.1% trimesoyl chloride for 2 minutes to form a polyamide composite layer, and finally rinse the film with deionized water to remove residual reagents; S2. Guide plate processing: a. The bump mold is prepared by 3D printing. Through high-precision 3D printing technology, the bump height error can be controlled within ±0.05mm; b. Injection mold the PP guide plate at 230℃, and smooth the edge of the guide plate after demoulding; S3, membrane column assembly: stack according to "guide plate → diaphragm → O-type rubber gasket", fix with central tie rod, the diaphragm spacing is optimized to be 2.5mm, and seal test is carried out at 10bar pressure for 30 minutes; S4. Surface hydrophilization treatment: immerse the membrane column in an aqueous solution containing 0.1% polyvinyl pyrrolidone at 40°C for 1 hour.

6. The method for preparing a high-flux DTRO reverse osmosis membrane according to claim 5, characterized in that: The zwitterionic monomer is 3-sulfonate propyl methacrylate potassium or methacryloyloxyethyl trimethylammonium chloride.

7. The method for preparing a high-flux DTRO reverse osmosis membrane according to claim 5, characterized in that: In the step b of preparing the disc-type membrane, the scraping speed of the scraping machine is 5 mm / s.

8. The method for preparing a high-flux DTRO reverse osmosis membrane according to claim 5, characterized in that: In the membrane column assembly step, the material of the O-type rubber gasket is ethylene propylene rubber.

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