High-strength high-flux anti-fouling hollow fiber membrane and method for preparing the same

Abstract

This invention provides a high-strength, high-flux, antifouling hollow fiber membrane and its preparation method. The membrane comprises, by weight, 16-22 parts polyvinylidene fluoride resin, 65-78 parts organic solvent, 5-12 parts pore-forming agent, 0.02-0.06 parts silicone ether type A modifier, and 0.03-0.06 parts defoamer. This hollow fiber membrane exhibits excellent mechanical properties, water permeability, and antifouling performance. The preparation process is stable and yields a high product rate. Using polyvinylidene fluoride resin as the core raw material, a special organic solvent and pore-forming agent are compounded, and a quantitative amount of silicone ether type A modifier and defoamer 237 are added. The hollow fiber membrane is prepared via a solvent-free phase inversion method, solving the problems of low fiber strength, low flux, easy fouling, and numerous preparation defects in existing membranes. The resulting membrane product has excellent mechanical properties, high water permeability, strong antifouling ability, and a stable and controllable process.

Description

Technical Field

[0001] This invention relates to the field of hollow fiber membrane preparation, and more specifically, to a high-strength, high-flux, anti-fouling hollow fiber membrane and its preparation method. Background Technology

[0002] Polyvinylidene fluoride (PVDF) is a high-performance polymer membrane material with excellent chemical stability, acid and alkali corrosion resistance, thermal stability, mechanical toughness, and film-forming properties. It is the preferred raw material for preparing hollow fiber ultrafiltration and microfiltration membranes and is widely used in the membrane separation industry.

[0003] Currently, conventional PVDF hollow fiber membranes generally suffer from the following technical defects in practical applications: First, insufficient mechanical strength. PVDF membrane fibers are relatively brittle, and are prone to breakage and damage during operation, backwashing, and aeration, shortening the service life of the membrane module. Second, low water flux. PVDF material itself is hydrophobic, and the membrane surface has poor hydrophilicity, resulting in high resistance to water molecule permeation and rapid flux decay over long-term operation. Third, poor antifouling performance. The hydrophobic membrane surface easily adsorbs pollutants such as organic matter, colloids, and microorganisms from wastewater, causing membrane pore blockage, high cleaning frequency, and increased operating costs. Fourth, conventional membrane fabrication processes are prone to generating bubbles in the membrane-forming solution, and defects and pores easily appear inside the membrane fibers, resulting in poor fiber uniformity and unstable separation performance. Existing PVDF hollow fiber membrane preparation technologies mostly employ a single pore-regulating agent to control the membrane pore structure, which can only achieve single performance improvement and cannot simultaneously address the mechanical strength of the membrane fibers, water flux, and antifouling performance. At the same time, the lack of efficient defoaming and synergistic modification agents during the membrane preparation process results in poor stability of the membrane preparation solution and a high defect rate in the finished membrane, making it difficult to simultaneously meet the integrated application requirements of high strength, high flux, and antifouling.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The primary objective of this invention is to provide a high-strength, high-flux, and antifouling hollow fiber membrane. This hollow fiber membrane combines excellent mechanical properties, water permeability, and antifouling performance. The preparation process is stable and the yield is high. Using polyvinylidene fluoride resin as the core raw material, a special organic solvent and pore-forming agent are compounded, and a quantitative amount of silicone ether type A modifier and defoamer 237 are added. The hollow fiber membrane is prepared by a solvent-free phase inversion method, which solves the problems of low fiber strength, low flux, easy fouling, and many preparation defects in existing membranes. The resulting membrane product has excellent mechanical properties, high water permeability, strong antifouling ability, and a stable and controllable process.

[0006] The second objective of this invention is to provide a method for preparing the above-mentioned hollow fiber membrane, which produces a hollow fiber membrane with good performance and a wide range of applications.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: This invention provides a high-strength, high-flux, anti-fouling hollow fiber membrane, comprising, by weight, 16-22 parts of polyvinylidene fluoride resin, 65-78 parts of organic solvent, 5-12 parts of pore-forming agent, 0.02-0.06 parts of silicone ether type A modifier, and 0.03-0.06 parts of defoamer.

[0008] Preferably, as a further feasible option, the following components are included by weight: 18-20 parts polyvinylidene fluoride resin, 66-75 parts organic solvent, 6-10 parts pore-forming agent, 0.03-0.06 parts silicone ether type A modifier, and 0.04-0.06 parts defoamer.

[0009] Preferably, as a further feasible option, the mixture comprises 19 parts of polyvinylidene fluoride resin, 70 parts of organic solvent, 8 parts of pore-forming agent, 0.05 parts of silicone ether type A modifier, and 0.05 parts of defoamer.

[0010] Preferably, as a further feasible option, the organic solvent is at least one of dimethylformamide and N,N-dimethylacetamide.

[0011] Preferably, as a further feasible option, the pore-forming agent is at least one of PEG400, PEG600, PEG800, PEG1000, PEG2000, polyvinylpyrrolidone K17, polyvinylpyrrolidone K30, polyvinylpyrrolidone K60 or polyvinylpyrrolidone K90.

[0012] Preferably, as a further feasible option, the polyvinylidene fluoride resin has a molecular weight of 800,000 to 1,200,000.

[0013] Preferably, as a further feasible option, the defoamer is preferably of the type of defoamer 237.

[0014] The present invention also provides a method for preparing the above-mentioned high-strength, high-flux, anti-fouling hollow fiber membrane, comprising the following steps: Add an organic solvent and heat to 80-90℃, then add polyvinylidene fluoride resin and stir until completely dissolved. Add the pore-forming agent, stir at a constant temperature until dissolved, then add the silicone ether type A modifier and defoamer, and stir to disperse evenly; The solution was kept at a constant temperature and vacuum degassed for 12 hours to obtain the spinning casting solution. The solution was then wet-spun using a non-solvent phase inversion method, shaped by an air bath and a pure water coagulation bath, and rinsed and dried.

[0015] Preferably, as a further feasible option, the stirring speed is 300-500 r / min and the spinning temperature is 40-65℃.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) This invention optimizes the internal cross-linking structure of the membrane fibers through the synergistic effect of a special silicone ether type A modifier and the PVDF resin molecular chain, thereby improving the density and flexibility of the membrane fibers, increasing the tensile strength by more than 30%, making the membrane fibers more resistant to tensile stress and aeration erosion, less prone to breakage, significantly extending their service life, and greatly improving their mechanical strength. 2) This invention uniformly regulates the membrane pore structure through the compounding of pore-forming agents, resulting in good pore connectivity, uniform pore size distribution, reduced water permeability resistance, and a pure water flux far exceeding that of conventional PVDF hollow fiber membranes. It also exhibits high operational permeability, slow flux decay, and high water permeability. 3) The hollow fiber membrane of the present invention has excellent antifouling performance. The modifier simultaneously improves the hydrophilicity of the membrane surface and reduces the hydrophobicity of the membrane surface, thereby reducing the adsorption and adhesion of organic matter and colloidal pollutants. The membrane surface is not easily fouled and is easy to clean, and has strong long-term operational stability. 4) The hollow fiber membrane preparation method of the present invention has stable process and excellent defoaming effect: adding quantitative defoamer 237 can quickly eliminate bubbles in the membrane forming solution, avoid pinholes and defects in the membrane fibers, and achieve high yield; the formula ratio is scientific, the amount of additives added is precise and controllable, there is no false ratio, and the process can be industrialized for mass production. 5) The hollow fiber membrane product prepared by this invention has good chemical stability, is resistant to acids and alkalis and aging, and is suitable for various water treatment, separation and purification processes, with a wide range of applications. Attached Figure Description

[0017] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings.

[0018] Figure 1 This is a scanning electron microscope (SEM) image of the cross-section of the membrane fiber in Example 8 of the present invention. Detailed Implementation

[0019] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0020] Example 1 Based on the mass fractions of the casting solution: PVDF resin: 18 parts, DMF organic solvent: 71.9 parts, PVP-K30 pore maker: 10 parts, silicone ether type A modifier: 0.05 parts, defoamer 237: 0.05 parts.

[0021] Preparation steps: (1) Add DMF solvent to the reactor, stir and heat to 80°C, slowly add PVDF resin, and stir until completely dissolved; (2) Add PVP, stir at a constant temperature for 0.5 h until fully dissolved, add silicone ether type A modifier and defoamer 237, and stir for 4 h; (3) Vacuum degassing at 60℃ for 12 hours to remove air bubbles; (4) Control the spinning temperature to 50℃ and the extrusion speed to 1.0m / min. After forming in an air bath and a pure water coagulation bath, rinse with pure water, retain the pores in a glycerol solution, and then air dry at room temperature to obtain a hollow fiber membrane.

[0022] Example 2 Based on the mass fractions of the casting solution: PVDF resin: 16 parts, DMF organic solvent: 78 parts, PVP-K30 pore maker: 5 parts, silicone ether type A modifier: 0.02 parts, defoamer 237: 0.06 parts.

[0023] Preparation steps: (1) Add DMF solvent to the reactor, stir and heat to 85°C, slowly add PVDF resin, and stir until completely dissolved; (2) Add PVP, stir at a constant temperature for 0.5 h until fully dissolved, add silicone ether type A modifier and defoamer 237, and stir for 4 h; (3) Vacuum degassing at 60℃ for 12 hours to remove air bubbles; (4) Control the spinning temperature to 55℃ and the extrusion speed to 1.0m / min. After forming in an air bath and a pure water coagulation bath, rinse with pure water, retain the pores in a glycerol solution, and then air dry at room temperature to obtain a hollow fiber membrane.

[0024] Example 3 Based on the mass fractions of the casting solution: PVDF resin: 22 parts, DMF organic solvent: 65 parts, PVP-K30 pore maker: 12 parts, silicone ether type A modifier: 0.06 parts, defoamer 237: 0.03 parts.

[0025] Preparation steps: (1) Add DMF solvent to the reactor, stir and heat to 90°C, slowly add PVDF resin, and stir until completely dissolved; (2) Add PVP, stir at a constant temperature for 0.5 h until fully dissolved, add silicone ether type A modifier and defoamer 237, and stir for 4 h; (3) Vacuum degassing at 60℃ for 12 hours to remove air bubbles; (4) Control the spinning temperature to 60℃ and the extrusion speed to 1.0m / min. After forming in an air bath and a pure water coagulation bath, rinse with pure water, retain the pores in a glycerol solution, and then air dry at room temperature to obtain a hollow fiber membrane.

[0026] Example 4 Based on the mass fractions of the casting solution: PVDF resin: 18 parts, DMAc organic solvent: 75 parts, PVP-K30 pore maker: 6 parts, silicone ether type A modifier: 0.03 parts, defoamer 237: 0.04 parts.

[0027] Preparation steps: (1) Add DMAc solvent to the reactor, stir and heat to 80°C, slowly add PVDF resin, and stir until completely dissolved; (2) Add PVP, stir at a constant temperature for 0.5 h until fully dissolved, add silicone ether type A modifier and defoamer 237, and stir for 4 h; (3) Vacuum degassing at 60℃ for 12 hours to remove air bubbles; (4) Control the spinning temperature to 60℃ and the extrusion speed to 1.0m / min. After forming in an air bath and a pure water coagulation bath, rinse with pure water, retain the pores in a glycerol solution, and then air dry at room temperature to obtain a hollow fiber membrane.

[0028] Example 5 The preparation steps are the same as in Example 4, except that the constant temperature stirring temperature is 85°C and the spinning temperature is 55°C to obtain the finished film filament.

[0029] Example 6 The preparation steps are the same as in Example 4, except that the constant temperature stirring temperature is 90°C and the spinning temperature is 65°C to obtain the finished film filament.

[0030] Example 7 Based on the total mass of the film-forming solution: PVDF resin: 20 parts, DMF and DMAC mixed organic solvent (mass ratio 3:7): 69.9 parts, PEG-1000 porogen: 10 parts, silicone ether type A modifier: 0.05 parts, defoamer 237: 0.05 parts.

[0031] The preparation steps are the same as in Example 1, with a constant temperature stirring temperature of 80°C and a spinning temperature of 55°C to obtain the finished film filament.

[0032] Example 8 The preparation steps are the same as in Example 7, with a constant stirring temperature of 85°C and a spinning temperature of 55°C to obtain the finished membrane fibers. The specific scanning electron microscope (SEM) image of the obtained membrane product is shown below. Figure 1 As shown.

[0033] Example 9 The preparation steps are the same as in Example 7, with a constant temperature stirring temperature of 90°C and a spinning temperature of 55°C to obtain the finished film filament.

[0034] Experimental Example 1 The performance of the hollow fiber membrane products finally prepared in the above embodiments was tested, and the results are shown in Table 1 below:

[0035] The performance test results in Table 1 above also show that the hollow fiber membrane of the present invention has excellent performance. Conventional membranes only require a ratio of three components: organic solvent, PVDF resin, and pore-forming agent. Compared with conventional membranes, the hollow fiber membrane prepared in the embodiments of the present invention has achieved significant breakthroughs in many key performance indicators.

[0036] In particular, the membrane fibers of Example 8 showed an increase in tensile strength from 2.2N for conventional membranes to 4.6N, indicating a substantial enhancement in their mechanical resilience and tensile strength. This is beneficial for resisting mechanical damage caused by high-pressure scouring and backwashing operations during actual operation, thereby extending their service life. Regarding pure water flux, the value measured in Example 8 at a transmembrane pressure of 0.1MPa jumped from 286LMH to 584LMH, a significant increase reflecting its superior permeation efficiency. This improvement is mainly attributed to the synergistic effect of the PEG-1000 pore-forming agent and the silicone ether type A modifier in the casting solution, combined with optimized thermally induced phase separation conditions, resulting in a more interconnected and uniform pore structure. Correspondingly, the porosity increased from 64.5% to 80%, an increase of 15.5 percentage points, providing more permeation pathways for water molecules. Meanwhile, the surface contact angle decreased from 86° to 52°, a reduction of over 30%, indicating a significant improvement in the hydrophilicity of the membrane surface. This not only effectively reduces the adsorption and adhesion tendency of organic pollutants and biomass on the membrane surface, enhancing antifouling capabilities, but also reduces the frequency and intensity of chemical cleaning during operation, thereby lowering maintenance costs. The above data fully demonstrates that the membrane fibers of Example 8 comprehensively surpass conventional membranes in terms of mechanical strength, permeate flux, pore characteristics, and hydrophilic and antifouling properties. Crucially, its flux (584 LMH) and strength (4.6 N) are significantly improved simultaneously, breaking the traditional trade-off of "high flux often accompanied by low strength" in membrane materials, exhibiting an excellent balance of comprehensive performance. Therefore, Example 8 is particularly suitable for water treatment scenarios with stringent requirements for separation efficiency and operational stability, such as deep reuse of municipal wastewater, industrial wastewater purification, and membrane bioreactors (MBR), possessing significant engineering application potential and economic benefits.

[0037] Although the invention has been illustrated and described with reference to specific embodiments, it should be understood that many other changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, it is intended that all such changes and modifications falling within the scope of the invention be included in the appended claims.

Claims

1. A high-strength, high-flux, anti-fouling hollow fiber membrane, characterized in that, By weight, the composition includes 16-22 parts polyvinylidene fluoride resin, 65-78 parts organic solvent, 5-12 parts pore-forming agent, 0.02-0.06 parts silicone ether type A modifier, and 0.03-0.06 parts defoamer.

2. The high-strength, high-flux, anti-fouling hollow fiber membrane according to claim 1, characterized in that, By weight, the composition is: 18-20 parts polyvinylidene fluoride resin, 66-75 parts organic solvent, 6-10 parts pore-forming agent, 0.03-0.06 parts silicone ether type A modifier, and 0.04-0.06 parts defoamer.

3. The high-strength, high-flux, anti-fouling hollow fiber membrane according to claim 1, characterized in that, The mixture contains 19 parts polyvinylidene fluoride resin, 70 parts organic solvent, 8 parts pore-forming agent, 0.05 parts silicone ether type A modifier, and 0.05 parts defoamer.

4. The high-strength, high-flux, anti-fouling hollow fiber membrane according to claim 1, characterized in that, The organic solvent is at least one of dimethylformamide and N,N-dimethylacetamide.

5. The high-strength, high-flux, anti-fouling hollow fiber membrane according to claim 1, characterized in that, The porogen is at least one of PEG400, PEG600, PEG800, PEG1000, PEG2000, polyvinylpyrrolidone K17, polyvinylpyrrolidone K30, polyvinylpyrrolidone K60 or polyvinylpyrrolidone K90.

6. The high-strength, high-flux, anti-fouling hollow fiber membrane according to claim 1, characterized in that, The polyvinylidene fluoride resin has a molecular weight of 800,000 to 1,200,000.

7. The method for preparing the high-strength, high-flux, anti-fouling hollow fiber membrane according to any one of claims 1-6, characterized in that, Includes the following steps: Add an organic solvent and heat to 80-90℃, then add polyvinylidene fluoride resin and stir until completely dissolved. Add the pore-forming agent, stir at a constant temperature until dissolved, then add the silicone ether type A modifier and defoamer, and stir to disperse evenly; The solution was kept at a constant temperature and vacuum degassed for 12 hours to obtain the spinning casting solution. The solution was then wet-spun using a non-solvent phase inversion method, shaped by an air bath and a pure water coagulation bath, and rinsed and dried.

8. The preparation method according to claim 7, characterized in that, Stirring speed 300-500 r / min, spinning temperature 40-65℃.

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