A high-throughput DTRO reverse osmosis membrane and its preparation method

Abstract

The present invention discloses a high-throughput DTRO reverse osmosis membrane and a preparation method thereof, belonging to the field of water treatment. The disk membrane sheet includes a polyacrylonitrile (PAN) base membrane layer, and a polyethersulfone (PES) pre-coating containing nano-titanium dioxide (TiO2) particles is coated on the surface of the base membrane layer. 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-fouling performance); the active separation layer of the membrane sheet is a polyamide composite layer containing zwitterionic monomers, and the zwitterionic monomers account for 0.8% of the mass ratio of the aqueous solution. At the same time, the attachment of pollutants is reduced through charge repulsion, and the thickness of the active separation layer is 1.5 μm; through the modification of the polyamide composite layer with zwitterionic monomers and the pre-coating process, the present invention effectively reduces the solute retention resistance and significantly improves the water flux; at the same time, through the hydrophilic treatment of the material surface and the optimization of the flow channel, it is ensured that the membrane module maintains a stable filtration efficiency during long-term operation.

Description

Technical Field

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

[0002] Due to advantages such as an open channel and strong anti-pollution ability, the disk tube reverse osmosis membrane (DTRO) is widely used in the treatment of high-concentration wastewater. However, the existing preparation methods for DTRO membranes have the following defects:

[0003] Imbalance between flux and anti-pollution performance: Traditional DTRO membranes rely on the design of the 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. Before the interfacial polymerization reaction of the reverse osmosis membrane, an additive for regulating the interfacial tension is coated on the surface of the base membrane in the form of a diluted hydrogel. During the interfacial polymerization process, the additive can be continuously released into the water phase to adjust the interfacial polymerization reaction process, avoiding too fast reaction rate and 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;

[0004] However, this patent only improves the flux by regulating the interfacial tension and does not combine with the channel characteristics of the DTRO membrane column, making it difficult to achieve performance breakthroughs.

[0005] Insufficient coordination between structure and material: The existing technologies mostly focus on the modification of membrane sheet materials or the design of the flow guide disk structure, lacking systematic optimization of material-structure-process, and it is difficult to operate stably for a long time in high-suspended solid and high-salt environments.

[0006] Poor adaptability to complex water quality: Colloids and organic substances in high-concentration wastewater are easily adsorbed on the membrane surface. The 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.

[0007] 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 the treatment of high-concentration wastewater, and has significant economic benefits and environmental value. Summary of the Invention

[0008] In view of the deficiencies of the prior art, 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.

[0009] 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, which includes a disc membrane, a flow guide disc and a central pull rod:

[0010] The disc membrane includes a polyacrylonitrile (PAN) base film layer, and the surface of the base film layer is coated with a polyethersulfone (PES) pre-coating containing nano-titanium dioxide (TiO2) 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);

[0011] The active separation layer of the disc membrane is a polyamide composite layer containing zwitterionic monomers, and 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, and the thickness of the active separation layer is 1.5 μm;

[0012] The flow guide disc is made of polypropylene (PP), and the surface is provided with a streamline bump array with a height of 0.4 mm and a spacing of 1.5 mm (the bump array of this size can make the feed liquid form a high-efficiency turbulent flow), and 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;

[0013] The central pull 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.

[0014] 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.

[0015] Furthermore, the dispersion particle size of the nano-titanium dioxide particles in the polyethersulfone pre-coating is 10 nm.

[0016] Furthermore, the streamline bump of the flow guide disc is parabolic, and the radius of curvature of the parabola is 1 mm.

[0017] According to another aspect of the present invention, more specifically, a high-flux DTRO reverse osmosis membrane and a preparation method, which includes the above-mentioned high-flux DTRO reverse osmosis membrane, and the method includes the following steps:

[0018] S1. Preparation of disc membrane:

[0019] a. Cut the PAN ultrafiltration membrane into circular membrane sheets and immerse them in deionized water containing 5% glycerol for 2 hours (this pretreatment can effectively improve the surface wettability of the membrane sheets, which is beneficial to the adhesion of subsequent coatings), then drain after soaking.

[0020] b. Dissolve PES and nano-TiO₂ particles in N-methylpyrrolidone (NMP) at a mass ratio of 9:1 to prepare a 15% concentration casting solution. Coating a pre-coating with a thickness of 8 μm on the surface of the base membrane through a film scraping machine. 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.

[0021] c. Immerse the pre-coated base membrane in an aqueous solution containing 2% m-phenylenediamine and 0.8% zwitterionic monomer, drain 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 sheet with deionized water to remove residual reagents.

[0022] S2. Processing of the flow guide disk:

[0023] 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 channels.

[0024] b. Inject and mold a PP flow guide disk 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 disk to avoid scratching the membrane sheet.

[0025] S3. Membrane column assembly: Stack in the order of "flow guide disk → membrane sheet → O-ring rubber gasket", fix with a central pull rod. The membrane sheet spacing is optimized to be 2.5 mm, and seal and test for 30 minutes under a pressure of 10 bar to ensure the integrity of the system under high pressure.

[0026] 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).

[0027] 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).

[0028] Furthermore, the initial water flux of the membrane sheet ≥ 45 L / (m²·h), and the flux decay rate ≤ 15% after running in 5000 ppm NaCl solution for 50 hours, showing good high-flux performance and stability.

[0029] Further, the zwitterionic monomer is potassium 3-sulfopropyl methacrylate or methacryloyloxyethyl trimethyl ammonium chloride.

[0030] Further, in step b of preparing the disc membrane, the scraping speed of the film scraper is 5 mm / s.

[0031] Further, in the membrane column assembly step, the O-ring rubber gasket is made of ethylene-propylene rubber.

[0032] The beneficial effects of the high-flux DTRO reverse osmosis membrane and its preparation method of the present invention are as follows:

[0033] (1) By modifying the polyamide composite layer and the pre-coating process with zwitterionic monomers, the present invention effectively reduces the solute retention resistance and significantly improves the water flux; at the same time, through the hydrophilic treatment of the material surface and the optimization of the flow channel, it ensures that the membrane module maintains a stable filtration efficiency during long-term operation.

[0034] (2) The streamlined bump array design of the flow guide disc in the present invention promotes the efficient turbulence of the feed liquid. Combining the nano-titanium dioxide pre-coating and the charge repulsion effect of zwitterions, it 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.

[0035] (3) The open flow channel structure in the present invention balances the flux and pressure loss and adapts to wastewater with a high suspended solid content; through the charge characteristic regulation of zwitterionic monomers, it can specifically reduce the attachment of different pollutants (such as colloids, organic matters, etc.) and improve the treatment ability for high-salt and high-organic matter wastewater.

[0036] (4) The preparation process parameters of the present invention are clearly controllable. Key steps such as pre-coating and interfacial polymerization reaction ensure the stable membrane performance; the membrane column structure is common with the existing DTRO module, and no additional equipment modification is required, which is applicable to high-difficulty treatment scenarios such as landfill leachate and coal chemical wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The present invention will be further described in detail below with reference to the drawings and specific implementation methods.

[0038] Figure 1 It is a structural schematic diagram of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0039] 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 in the present application and the features in the embodiments can be combined with each other.

[0040] 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.

[0041] Reference Figure 1 A high-flux DTRO reverse osmosis membrane, comprising a disc membrane, a flow guide disc and a central pull rod:

[0042] The disc membrane comprises a polyacrylonitrile (PAN) base membrane layer, and the surface of the base membrane layer is coated with a polyethersulfone (PES) precoat containing nano-titanium dioxide (TiO2) particles, and the thickness of the precoat is 8 μm (the 8 μm thickness can not only ensure the effective adhesion of the precoat, but also exert its best anti-fouling performance);

[0043] The active separation layer of the membrane is a polyamide composite layer containing zwitterionic monomers, and 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, and the thickness of the active separation layer is 1.5 μm;

[0044] The flow guide disc is made of polypropylene (PP), and the surface is provided with a streamline bump array with a height of 0.4 mm and a pitch of 1.5 mm (the bump array of this size can make the feed liquid form a high-efficiency turbulent flow), and the flow guide disc and the membrane are alternately stacked to form an open channel with a width of 2.5 mm, and this channel width can balance the flux and pressure loss and adapt to wastewater with a suspended solid content ≤ 500 mg / L;

[0045] The central pull rod is made of stainless steel 316L, has good corrosion resistance, can adapt to the high-salt and high-pollution wastewater treatment environment, and prevent corrosion during use, affecting the overall structural stability of the membrane module.

[0046] According to another aspect of the present invention, more specifically, a high-flux DTRO reverse osmosis membrane and a preparation method, including a high-flux DTRO reverse osmosis membrane, comprising the following steps:

[0047] S1. Preparation of disc membrane:

[0048] a. Cut the PAN ultrafiltration membrane into circular membranes, immerse them in deionized water containing 5% glycerol and soak for 2 hours (this pretreatment can effectively improve the surface wettability of the membranes), which is beneficial to the subsequent attachment of the coating, and drain after soaking;

[0049] b. Dissolve PES and nano-TiO2 particles in N-methylpyrrolidone (NMP) according to a mass ratio of 9:1, prepare a casting solution with a concentration of 15%, and coat a precoat with a thickness of 8 μm on the surface of the base membrane through a film scraping machine. During the coating process, strictly control the temperature and humidity to ensure the uniformity of the precoat, and dry it in an oven at 60 °C for 30 minutes to form a precoat;

[0050] c. Immerse the pre-coated base film in an aqueous solution containing 2% m-phenylenediamine and 0.8% zwitterionic monomer, drain 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 residual reagents;

[0051] S2. Flow guide disk processing:

[0052] a. Prepare bump molds 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 channels;

[0053] b. Injection mold a PP flow guide disk at 230 °C. The injection temperature within this range can ensure good molding performance of the PP material. After demolding, smooth the edges of the flow guide disk to avoid scratching the membrane;

[0054] S3. Membrane column assembly: Stack in the order of "flow guide disk → membrane → O-ring rubber gasket", fix with a central pull rod, optimize the membrane spacing to 2.5 mm, and conduct a sealing test at 10 bar for 30 minutes to ensure the integrity of the system under high pressure;

[0055] 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).

[0056] Preferably, the zwitterionic monomer is potassium 3-sulfopropyl methacrylate or methacryloyloxyethyl trimethyl ammonium chloride (these two zwitterionic monomers have significant effects in improving membrane performance). The initial water flux of the membrane 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.

[0057] Example 1

[0058] According to the above preparation method, complete the preparation of the disk membrane, flow guide disk processing, membrane column assembly and surface hydrophilic treatment in sequence. Among them, the zwitterionic monomer is selected as potassium 3-sulfopropyl methacrylate. After testing, the initial water flux of the membrane 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, and the chemical cleaning cycle is extended to 16 days.

[0059] It is applicable to wastewater mainly containing cationic pollutants (such as metal ions).

[0060] Example 2

[0061] Using methacryloyloxyethyl trimethyl ammonium chloride as the zwitterionic monomer, other preparation parameters are the same as those in Example 1. The test results show that the initial water flux of the membrane 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;

[0062] It is suitable for water quality mainly containing anionic pollutants (such as humic acid, colloid).

[0063] 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 on 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 modifications 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 shall be subject to the appended claims.

Claims

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

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

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

4. A high-throughput DTRO reverse osmosis membrane according to claim 1, characterized in that, The streamline bumps of the flow guide disc are parabolic, and the curvature radius of the parabola is 1 mm.

5. A preparation method of a high-flux DTRO reverse osmosis membrane, including the high-flux DTRO reverse osmosis membrane described in claim 1, characterized in that, It includes the following steps: 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, and drain them after soaking; b. Dissolve PES and nano-TiO₂ particles in N-methylpyrrolidone 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 scraping machine, 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, and 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 residual reagents; S2. Processing of 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; b. Inject and mold a PP flow guide disc at 230 °C, and smooth the edge of the flow guide disc after demolding; S3. Membrane column assembly: Stack according to "flow guide disc → membrane → O-ring", fix the central pull rod, and the membrane spacing is optimized to be 2.5 mm, and seal and test for 30 minutes under a pressure of 10 bar; S4. Surface hydrophilic treatment: Immerse the membrane column in an aqueous solution containing 0.1% polyvinylpyrrolidone and soak at 40 °C for 1 hour.

6. The preparation method of a high-flux DTRO reverse osmosis membrane according to claim 5, characterized in that, The zwitterionic monomer is potassium 3-sulfopropyl methacrylate or methacryloyloxyethyl trimethyl ammonium chloride.

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

8. The preparation method of 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-ring is ethylene propylene rubber.

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