Braided tube reinforced hollow fiber membrane and preparation method thereof

Abstract

The invention relates to a braided tube reinforced hollow fiber membrane and a preparation method thereof. Comprising the following steps: mixing polyvinylidene fluoride resin, a pore-foaming agent, a solvent and an anionic surfactant, standing and defoaming to obtain a spinning solution; spinning by adopting a dry-wet spinning process, enabling a braided tube to penetrate through a spinneret plate, injecting a spinning solution into the spinneret plate, sequentially pulling the braided tube to an air bath and a pure water bath, then sequentially soaking the braided tube in pure water and glycerol, taking out the braided tube, and airing the braided tube to obtain the braided tube enhanced hollow fiber membrane with a convex structure on the surface; the preparation method of the braided tube enhanced hollow fiber membrane is used for solving the technical problems of complex preparation method and poor interception and flux performance of the hollow fiber micro-filtration membrane in the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of hollow fiber microfiltration membranes, and in particular to a woven tube reinforced hollow fiber membrane and a preparation method thereof. Background Art

[0002] Rejection rate, flux and fouling resistance are several of the most important indicators of membrane materials, but there are also certain restrictive relationships among them. It is often difficult to simultaneously improve the permeability, selective permeability and fouling resistance of hollow fiber membranes. It is easy to simply reduce the pore size to improve rejection, but at the same time, it will lead to low flux. Increasing the flux through large pores is likely to result in poor membrane rejection and poor fouling resistance due to pore blockage by impurities. In the current research on hollow fiber membranes, there are few reports on comprehensively improving rejection performance, flux and fouling resistance.

[0003] The literature "Composite PVDF ultrafiltration membrane tailored by sandwich-like GO@UiO-66 nanoparticles for breaking the trade-off between permeability and selectivity" assembled sandwich-like GO@UiO-66 by the solvothermal method, mixed it with the polyvinylidene fluoride (PVDF) bulk membrane, and prepared a nanocomposite membrane by the non-solvent induced phase separation method. When the incorporation amount of the nanocomposite was 1.0 wt% GO@UiO-66, both the rejection rate of BSA and the water flux increased. The literature "Synthesis of patterned PVDF ultrafiltration membranes: spray-modified non-solvent induced phase separation" synthesized a patterned membrane of polyvinylidene fluoride (PVDF) by the spray-modified non-solvent induced phase separation (s-NIPS) technique. In the filtration of proteins, compared with the corresponding flat membrane, the water permeability of the patterned membrane increased sharply (+140%), while the rejection of BSA decreased slightly from 90% to 71%. The literature "Preparation and Application of Patterned Membranes for Wastewater Treatment" introduced a patterned morphology on the membrane surface using a photolithography method, and proved that the patterned surface increased the water flux in proportion to the roughness of the patterned membrane, and the type of pattern had no substantial effect on the average pore size of the patterned surface. In a membrane bioreactor (MBR), due to the local turbulence caused by the hydrodynamics at the vertices of the patterned surface, the deposition of microbial cells on the patterned membrane was significantly reduced, proving the potential of the patterned membrane for anti-fouling. The above research on the performance of membrane materials has improved in a certain performance, but the improvement of the comprehensive performance is not obvious, and the raw materials and processes of the research are complex, remaining in the laboratory research field and not applicable to large-scale production.

[0004] Surfactants, as commonly used additives in industrial production, play roles such as dispersion, solubilization, emulsification, and penetration. Surfactants are classified into ionic and non-ionic types according to the type of hydrophilic group. Ionic surfactants are further divided into cationic, anionic, and amphiphilic surfactants. In addition, mixed surfactants are also included. Due to the special amphiphilic structure of surfactants, when their content reaches a certain concentration, micelles with different arrangements are formed in the solution or at the solution interface, as shown in Figure 1。In recent years, there have been many reports on the interaction between surfactants and polymer materials, but the research mainly focuses on the interaction between surfactants and dilute aqueous solutions of hydrophilic polymers. For example, the interaction between surfactants and aqueous solutions of hydrophilic polymer materials such as PVP, PEG, and PAA will also form some special structures, as shown in Figure 2 。

[0005] There is relatively little research on the mechanism of the interaction between surfactants and polymer materials in non-aqueous solutions. In the field of water treatment membranes, as a commonly used additive, surfactants have been reported in a large number of literatures and patents for the research on the preparation of different kinds of filtration membranes. In the research on hollow fiber membranes, the research focuses on non-ionic surfactants (such as OP-10, FS-30, Brij 58, Tween series, etc.) or amphiphilic macromolecular additives (Pluronic F127, block copolymers). There are also some mentions of anionic and cationic surfactants. Adding surfactants to the membrane-making formula can achieve the purpose of adjusting the pore size and porosity.

[0006] The patent "A Hollow Woven Reinforced Polyvinylidene Fluoride Mesoporous Fiber Ultrafiltration Membrane and Its Preparation Method" prepares an ultrafiltration membrane by adding various surfactants to the formula. The flux is between 300 - 2000 LMH. During the process, a mixed solution of DMAC and PEG400 with different ratios is required as a gel bath, and some formulas need to be cleaned with sodium hypochlorite solution. The process is complex, and whether the rejection performance and membrane fouling performance decrease while the flux changes is not explored in this patent.

[0007] The patent "A High-Flux Polyvinylidene Fluoride Hollow Fiber Membrane and Its Preparation Method" adds nanomaterials and surfactants to the membrane-making formula to prepare a self-supporting hollow fiber membrane with a flux between 500 - 6000 LMH. Using inorganic materials in the organic membrane formula will undoubtedly increase the production operability and risk. At the same time, this patent also does not mention whether the rejection performance and membrane fouling resistance are affected while the surfactant affects the flux.

[0008] Therefore, in view of the above problems, the present invention urgently needs to provide a woven tube-reinforced hollow fiber membrane and its preparation method. Summary of the Invention

[0009] The purpose of the present invention is to provide a woven tube-reinforced hollow fiber membrane and its preparation method, and to solve the technical problems of complex preparation methods of hollow fiber microfiltration membranes and poor rejection and flux performance in the prior art through the preparation method of the woven tube-reinforced hollow fiber membrane.

[0010] A preparation method of a woven tube-reinforced hollow fiber membrane provided by the present invention is characterized in that it includes the following steps:

[0011] Mix polyvinylidene fluoride resin, pore former, solvent and anionic surfactant, let it stand for degassing to obtain a spinning solution;

[0012] Use the dry-wet spinning process for spinning. The braided tube passes through the spinneret, and the spinning solution is injected into the spinneret. After successively pulling the braided tube to the air bath and pure water bath, soak it successively in pure water and glycerol, take it out and dry it to obtain a braided tube-reinforced hollow fiber membrane with a convex structure on the surface;

[0013] Among them, the surface of the hollow fiber membrane has protrusions.

[0014] Preferably, by weight percentage, it includes 18-23 parts of polyvinylidene fluoride resin, 22-28 parts of pore former, 45-65 parts of solvent; the addition amount of anionic surfactant is 2%-8% of the total weight of polyvinylidene fluoride resin, pore former and solvent.

[0015] Preferably, the addition amount of anionic surfactant is 5% of the total weight of polyvinylidene fluoride resin, pore former and solvent.

[0016] Preferably, the anionic surfactant is one of sodium lauryl sulfate or sodium dodecylbenzenesulfonate.

[0017] Preferably, the solvent is N,N-dimethylacetamide.

[0018] Preferably, the pore former includes one or more of polyvinylpyrrolidone, polyethylene glycol, polyoxyethylene, polyethylene oxide, polyvinyl alcohol, methyl cellulose, ethylene glycol, propylene glycol, glycerol, acetone, lithium chloride, diethylene glycol.

[0019] Preferably, the mass concentration of glycerol is 20wt%, and soak it in glycerol for 0.5-1h.

[0020] Preferably, the dry-wet spinning process parameters: the height of the air bath is 5cm, the temperature of the pure water bath is 60-80°C, and the spinning speed is 20m / min; control the outer diameter of the membrane filament to be 2.0±0.1mm, and the membrane thickness to be 80μm±20μm.

[0021] Preferably, the molecular weight of the polyvinylidene fluoride resin is 300,000-800,000.

[0022] The present invention also provides a braided tube-reinforced hollow fiber membrane obtained by the preparation method of the braided tube-reinforced hollow fiber membrane described in any one of the above.

[0023] A braided tube-reinforced hollow fiber membrane and its preparation method provided by the present invention have the following improvements compared with the prior art:

[0024] 1. The woven tube - reinforced hollow fiber membrane of the present invention adds an anionic surfactant to the spinning solution formula. During the phase - inversion contact with the hydrogel bath, a solid - liquid interface is generated between the spinning solution and water. The surfactant aggregates on the surface and arranges directionally at the two - phase interface. On the one hand, the hydrophilic group faces the hydrogel bath side, and the hydrophobic chain segments interact with the polymer chain segments to form micelles with a convex shape. It is equivalent to the hydrophobic groups of the surfactant wrapping the polymer to form protrusions, so that a large number of protrusion structures also exist on the surface of the final product. On the other hand, the special amphiphilic structure of the anionic surfactant affects the phase - separation pore - forming process of the spinning solution, promoting smaller pore sizes and higher porosity on the membrane surface. This hollow fiber membrane has both high - retention and high - flux performance. The surface protrusion structure is beneficial to the long - term stable operation of the membrane and slows down membrane fouling resistance.

[0025] 2. The raw materials for preparation are the raw materials commonly used in membrane preparation, and the process conditions are mild. Conventional dry - wet spinning equipment can meet the membrane - making requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0027] Figure 1 is the micelle shape in the background technology;

[0028] Figure 2 is the schematic diagram of the structure formed by the interaction between the surfactant and the polymer material in the background technology;

[0029] Figure 3 is the scanning electron microscope image of the woven tube - reinforced hollow fiber membrane obtained in Example 1 of the present invention;

[0030] Figure 4 is the scanning electron microscope image of the woven tube - reinforced hollow fiber membrane obtained in Example 2 of the present invention;

[0031] Figure 5 is the scanning electron microscope image of the woven tube - reinforced hollow fiber membrane obtained in Example 3 of the present invention;

[0032] Figure 6 is the scanning electron microscope image of the woven tube - reinforced hollow fiber membrane obtained in Comparative Example 1 of the present invention;

[0033] Figure 7 is the fouling - resistance operation test result diagram of the woven tube - reinforced hollow fiber membranes obtained in Example 1, Example 2, and Comparative Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work fall within the scope of protection of the present invention.

[0035] A method for preparing a woven tube-reinforced hollow fiber membrane, characterized by comprising the following steps:

[0036] Mix polyvinylidene fluoride resin, pore-forming agent, solvent and anionic surfactant, and stand for defoaming to obtain a spinning solution;

[0037] Use the dry-wet spinning process for spinning. The woven tube passes through the spinneret, the spinning solution is injected into the spinneret, and after the woven tube is drawn to a pure water bath and an air bath, it is successively immersed in pure water and glycerol, taken out and dried to obtain a woven tube-reinforced hollow fiber membrane with a convex structure on the surface;

[0038] Among them, the surface of the hollow fiber membrane has protrusions.

[0039] Specifically, by weight percentage, it includes 18-23 parts of polyvinylidene fluoride resin, 22-28 parts of pore-forming agent, and 45-65 parts of solvent; the addition amount of anionic surfactant is 2%-8% of the total weight of polyvinylidene fluoride resin, pore-forming agent and solvent.

[0040] Specifically, the addition amount of anionic surfactant is 5% of the total weight of polyvinylidene fluoride resin, pore-forming agent and solvent.

[0041] Specifically, the anionic surfactant is one of sodium lauryl sulfate or sodium dodecylbenzenesulfonate.

[0042] Specifically, the solvent is N,N-dimethylacetamide.

[0043] Specifically, the pore-forming agent includes one or more of polyvinylpyrrolidone, polyethylene glycol, polyethylene oxide, polyethylene oxide, polyvinyl alcohol, methyl cellulose, ethylene glycol, propylene glycol, glycerol, acetone, lithium chloride, and diethylene glycol.

[0044] Specifically, the mass concentration of glycerol is 20wt%, and it is immersed in glycerol for 0.5-1h.

[0045] Specifically, the dry-wet spinning process parameters: the height of the air bath is 5 cm, the temperature of the pure water bath is 60-80°C, and the spinning speed is 20 m / min; the outer diameter of the membrane filament is controlled at 2.0±0.1 mm, and the membrane thickness is 80μm±20μm.

[0046] Specifically, the molecular weight of the polyvinylidene fluoride resin is 300,000 - 800,000.

[0047] The present invention also provides a braided tube reinforced hollow fiber membrane obtained by the preparation method of the braided tube reinforced hollow fiber membrane as described in any one of the above.

[0048] For the braided tube reinforced hollow fiber membrane of the present invention, an anionic surfactant is added to the spinning solution formulation. During the phase inversion contact with the hydrogel bath, a solid-liquid interface will be generated between the spinning solution and water. The surfactant aggregates on the surface and arranges directionally at the two-phase interface. On the one hand, the hydrophilic group faces the hydrogel bath side, and the hydrophobic chain segments interact with the polymer chain segments to form micelles in a convex shape. It is equivalent to the hydrophobic group of the surfactant wrapping the polymer to form a convex shape, so that a large number of convex structures also exist on the surface of the final product. On the other hand, the special amphiphilic structure of the anionic surfactant affects the phase separation and pore formation process of the spinning solution, promoting smaller pore sizes and higher porosity on the membrane surface. This hollow fiber membrane has both high rejection and high flux performance. The surface convex structure is beneficial to the long-term stable operation of the membrane and slows down the membrane fouling resistance.

[0049] The raw materials for preparation are the raw materials used in conventional membrane preparation, the process conditions are mild, and conventional dry-wet spinning equipment can meet the membrane preparation requirements.

[0050] Example 1

[0051] Preparation method of braided tube reinforced hollow fiber membrane

[0052] Mix 18 parts of polyvinylidene fluoride resin, 22 parts of pore former and 45 parts of solvent, add an anionic surfactant, and the addition amount of the anionic surfactant is 2% of the total mass of the polyvinylidene fluoride resin, pore former and solvent to obtain a mixed solution;

[0053] Use the dry-wet spinning process for spinning. The braided tube passes through the spinneret, the spinning solution is injected into the spinneret, and then the braided tube is sequentially pulled to the air bath and pure water bath, and then soaked in pure water and glycerol in sequence, taken out and dried to obtain a braided tube reinforced hollow fiber membrane with a convex structure on the surface;

[0054] Dry-wet spinning process parameters: the height of the air bath is 5 cm, the temperature of pure water soaking is 60 °C, and the spinning speed is 20 m / min; control the outer diameter of the membrane filament to be 2.0 ± 0.1 mm and the membrane thickness to be 80 μm.

[0055] Specifically, the anionic surfactant is sodium dodecyl sulfate.

[0056] Specifically, the solvent is N,N-dimethylacetamide.

[0057] Specifically, the pore former is polyvinylpyrrolidone.

[0058] Specifically, the molecular weight of the polyvinylidene fluoride resin is 300,000 - 800,000.

[0059] Example Two

[0060] Preparation method of a braided tube - reinforced hollow fiber membrane

[0061] Mix 18 parts of polyvinylidene fluoride resin, 28 parts of pore - forming agent, and 45 parts of solvent, add an anionic surfactant, and the addition amount of the anionic surfactant is 8% of the total mass of the polyvinylidene fluoride resin, pore - forming agent, and solvent to obtain a mixed solution.

[0062] Use the dry - wet spinning process for spinning. The braided tube passes through the spinneret, the spinning solution is injected into the spinneret, and then the braided tube is successively drawn into an air bath and a pure water bath, and then successively soaked in pure water and glycerol, taken out, and dried to obtain a braided tube - reinforced hollow fiber membrane with a convex structure on the surface.

[0063] Among them, the surface of the hollow fiber membrane has protrusions.

[0064] Dry - wet spinning process parameters: the height of the air bath is 5 cm, the temperature of soaking in pure water is 60 °C, and the spinning speed is 20 m / min; control the outer diameter of the membrane fiber to be 2.0 ± 0.1 mm and the membrane thickness to be 80 μm.

[0065] Specifically, the anionic surfactant is sodium lauryl sulfate.

[0066] Specifically, the solvent is N,N - dimethylacetamide.

[0067] Specifically, the pore - forming agent is polyvinylpyrrolidone.

[0068] Specifically, the molecular weight of the polyvinylidene fluoride resin is 300,000 - 800,000.

[0069] Example Three

[0070] Preparation method of a braided tube - reinforced hollow fiber membrane

[0071] Mix 23 parts of polyvinylidene fluoride resin, 28 parts of pore - forming agent, and 65 parts of solvent, add an anionic surfactant, and the addition amount of the anionic surfactant is 8% of the total mass of the polyvinylidene fluoride resin, pore - forming agent, and solvent to obtain a mixed solution.

[0072] Use the dry - wet spinning process for spinning. The braided tube passes through the spinneret, the spinning solution is injected into the spinneret, and then the braided tube is successively drawn into an air bath and a pure water bath, and then successively soaked in pure water and glycerol, taken out, and dried to obtain a braided tube - reinforced hollow fiber membrane with a convex structure on the surface.

[0073] Among them, the surface of the hollow fiber membrane has protrusions.

[0074] Dry-wet spinning process parameters: air bath height 5 cm, pure water immersion temperature 80 °C, spinning speed 20 m / min; control the outer diameter of the membrane fiber to be 2.0 ± 0.1 mm and the membrane thickness to be 100 μm.

[0075] Specifically, the anionic surfactant is sodium cetylbenzenesulfonate.

[0076] Specifically, the solvent is N,N-dimethylacetamide.

[0077] Specifically, the pore-forming agent is polyethylene glycol.

[0078] Specifically, the molecular weight of the polyvinylidene fluoride resin is 300,000 - 800,000.

[0079] Example 4

[0080] Preparation method of a braided tube-reinforced hollow fiber membrane

[0081] Mix 18 parts of polyvinylidene fluoride resin, 28 parts of pore-forming agent and 54 parts of solvent, add an anionic surfactant, and the addition amount of the anionic surfactant is 5% of the total mass of the polyvinylidene fluoride resin, pore-forming agent and solvent to obtain a mixed solution;

[0082] Use the dry-wet spinning process for spinning. Pass the braided tube through the spinneret, inject the spinning solution into the spinneret, sequentially draw the braided tube to the air bath and pure water bath, then soak it in pure water and glycerol in sequence, take it out and dry it to obtain a braided tube-reinforced hollow fiber membrane with a convex structure on the surface;

[0083] Among them, the surface of the hollow fiber membrane has protrusions.

[0084] Dry-wet spinning process parameters: air bath height 5 cm, pure water immersion temperature 70 °C, spinning speed 20 m / min; control the outer diameter of the membrane fiber to be 2.0 ± 0.1 mm, inner diameter 1.0 ± 0.1 mm; membrane thickness 80 μm.

[0085] Specifically, the anionic surfactant is sodium cetyl sulfate.

[0086] Specifically, the solvent is N,N-dimethylacetamide.

[0087] Specifically, the pore-forming agent is polyvinylpyrrolidone and glycerol.

[0088] Specifically, the molecular weight of the polyvinylidene fluoride resin is 300,000 - 800,000.

[0089] Comparative Example 1

[0090] Prepare the spinning solution:

[0091] By mass fraction, 18 parts of polyvinylidene fluoride (PVDF) resin, 28 parts of pore former, and 54 parts of solvent are mixed evenly, then left to stand for degassing to obtain a spinning solution;

[0092] Dry-wet spinning process is used for spinning. The braided tube passes through the spinneret, and the spinning solution is injected into the spinneret. After sequentially pulling the braided tube to the air bath and pure water bath, it is then sequentially soaked in pure water and glycerol, taken out, and dried to obtain a braided tube reinforced hollow fiber membrane;

[0093] Dry-wet spinning process parameters: air bath height is 5 cm, pure water soaking temperature is 70 °C, spinning speed is 20 m / min; the outer diameter of the membrane filament is controlled at 2.0 ± 0.1 mm, and the membrane thickness is 80 μm.

[0094] Comparative Example 2

[0095] Prepare a spinning solution:

[0096] By mass fraction, 18 parts of polyvinylidene fluoride (PVDF) resin, 28 parts of pore former, and 54 parts of solvent are taken, and a surfactant is added. The addition amount of the surfactant is 2% of the total mass of the polyvinylidene fluoride resin, pore former, and solvent to obtain a mixed solution;

[0097] Dry-wet spinning process is used for spinning. The braided tube passes through the spinneret, and the spinning solution is injected into the spinneret. After sequentially pulling the braided tube to the air bath and pure water bath, it is then sequentially soaked in pure water and glycerol, taken out, and dried to obtain a braided tube reinforced hollow fiber membrane.

[0098] Among them, the surfactant is sodium dodecyl sulfate.

[0099] Comparative Example 3

[0100] Prepare a spinning solution:

[0101] By mass fraction, 18 parts of polyvinylidene fluoride (PVDF) resin, 22 parts of pore former, and 60 parts of solvent are mixed evenly, then left to stand for degassing to obtain a spinning solution;

[0102] Dry-wet spinning process is used for spinning. The braided tube passes through the spinneret, and the spinning solution is injected into the spinneret. After sequentially pulling the braided tube to the air bath and pure water bath, it is then sequentially soaked in pure water and glycerol, taken out, and dried to obtain a braided tube reinforced hollow fiber membrane;

[0103] Dry-wet spinning process parameters: air bath height is 5 cm, pure water soaking temperature is 70 °C, spinning speed is 20 m / min; the outer diameter of the membrane filament is controlled at 2.0 ± 0.1 mm, and the membrane thickness is 80 μm.

[0104] Perform performance evaluation on the braided tube reinforced hollow fiber membranes obtained in Example 1, Example 2, Example 3, Example 4, Comparative Example 1, and Comparative Example 2. Specifically,

[0105] 1) Testing of membrane filament flux: 3 - 5 filaments of 35 cm each for each sample, with an effective length of 30 cm; tested with pure water at 0.1 MPa and 25 °C, and the calculation formula is as follows: Flux (L / ㎡×h) = (Flow rate L × 3600 S / h) / (3.14 × Outer diameter m × Effective length m × Time s).

[0106] 2. Bubble point and burst bubble point: Take a 50 - cm membrane filament, seal one end, connect the other end to compressed air, immerse the whole filament in alcohol, continuously pressurize, and record the initial bubble point and the number of the membrane filament.

[0107] 3. Retention testing: Prepare a 200,000 - PEO (Polyethylene Oxide PEO) solution with a concentration of 1000 ppm, stir magnetically until there is no flocculation; take 3 membrane filaments about 40 cm for testing, apply negative pressure suction for about 20 min during testing, then sample 30 - 40 mL, make good marks; immediately send the sample for TOC testing after sampling.

[0108] Table 1 Physical properties of the braided - tube - reinforced hollow - fiber membrane

[0109]

[0110]

[0111] Compared with Comparative Example 1, in Example 1, due to the addition of an anionic surfactant, the rejection rate is significantly improved, and the burst bubble point pressure is greater than 0.40 Mpa. At the same time, the rejection rates and burst bubble point pressures of the braided - tube - reinforced hollow - fiber membranes obtained in Example 2, Example 3, and Example 4 are all higher than those of Comparative Example 1 to Comparative Example 3.

[0112] In Comparative Example 2, when preparing the membrane after adding the surfactant sodium dodecyl sulfate, compared with the anionic surfactant sodium hexadecyl sulfate added in Example 1, the mechanical properties of the braided - tube - reinforced hollow - fiber membrane obtained in the present invention are higher than those of Comparative Example 2 (the burst bubble point pressure is less than 0.40 Mpa). At the same time, the retention performance of Comparative Example 2 has no obvious improvement, indicating that sodium dodecyl sulfate is not very good for improving the overall performance, and the pore structure of the membrane in Comparative Example 2 is loose.

[0113] Take the braided - tube - reinforced hollow - fiber membranes obtained in Example 1, Example 2, Example 3, and Comparative Example 1 for scanning electron microscope testing, and the results are shown in Figure 3 、 Figure 4 、 Figure 5 and Figure 6 ; It can be seen from Figure 6 that the pores on the membrane surface in Comparative Example 1 are relatively large, basically about 0.2 μm, Figure 3 、 Figure 4 and Figure 5As shown, in Example 1, Example 2, and Example 3, after adding the surfactant, the membrane surface shows a granular convex structure, and there are small holes around the convex structure. The pore diameter is basically below 100 nm. The small pore diameter is conducive to surface screening, directly promoting the improvement of the rejection rate. The high porosity of the small holes improves the flux, and at the same time, the convex structure improves the anti-fouling performance.

[0114] Take the woven tube-reinforced hollow fiber membranes obtained from Comparative Example 1, Example 1, and Example 2, and conduct small MBR anti-fouling operation tests respectively; the operation fluxes are 30, 40, and 50 LMH, and a total of 5 cycles are run. The operation data are shown in Figure 7 ; From Figure 7 it can be seen that when operating at a low flux of 30 LMH, the woven tube-reinforced hollow fiber membranes prepared in Comparative Example 1, Example 1, and Example 2 are all relatively stable, and the operating pressure is basically stable between 3 - 5 kPa. Example 1 and Example 2 perform the best, and the operating pressure is basically 3 kPa; when the operating pressure is increased to 40 LMH, the operating pressure of Comparative Example 1 increases from 5 kPa to 8 kPa, the operating pressure of Example 1 remains around 5 kPa, and Example 2 has been operating at a pressure of 3 kPa; when the operating flux is increased to 50 LMH, the operating pressure of Comparative Example 1 increases from 5 kPa to 11 kPa, and Example 1 and Example 2 are respectively operating at low pressures of 5 kPa and 3 kPa. From the small MBR anti-fouling operation data, Comparative Example 1 is not suitable for operating at high fluxes. In Example 1 and Example 2, due to the addition of the surfactant, a small convex structure is generated on the membrane surface, accompanied by small holes, and the overall membrane structure is also improved, ultimately resulting in the improvement of the anti-fouling performance of this microfiltration membrane.

[0115] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a braided tube reinforced hollow fiber membrane, characterized in that: The steps include: The polyvinylidene fluoride resin, the porogen, the solvent and the anionic surfactant are mixed and allowed to stand for degassing to obtain a spinning solution; The spinning is carried out by a dry-wet spinning process. The braided tube passes through the spinneret, the spinning solution is injected into the spinneret, the braided tube is pulled to an air bath and a pure water bath in turn, then immersed in pure water and glycerin in turn, taken out, and dried to obtain a braided tube reinforced hollow fiber membrane with a convex structure on the surface.

2. The method for preparing a braided tube reinforced hollow fiber membrane according to claim 1, characterized in that: The anionic surfactant is one of sodium hexadecyl sulfate or sodium hexadecylbenzenesulfonate.

3. The method for preparing a braided tube reinforced hollow fiber membrane according to claim 2, characterized in that: According to weight percentage, it comprises 18-23 parts of polyvinylidene fluoride resin, 22-28 parts of porogen and 45-65 parts of solvent; the added amount of anionic surfactant is 2%-8% of the total weight of polyvinylidene fluoride resin, porogen and solvent.

4. The method for preparing a braided tube reinforced hollow fiber membrane according to claim 3, characterized in that: The added amount of the anionic surfactant is 5% of the total weight of the polyvinylidene fluoride resin, the porogen and the solvent.

5. The method for preparing a braided tube reinforced hollow fiber membrane according to claim 1, characterized in that: The solvent is dimethylacetamide.

6. The method for preparing a braided tube reinforced hollow fiber membrane according to claim 1, characterized in that: The porogen includes one or more of polyvinyl pyrrolidone, polyethylene glycol, polyoxyethylene, polyethylene oxide, polyvinyl alcohol, methyl cellulose, ethylene glycol, propylene glycol, glycerol, acetone, lithium chloride, and diethylene glycol.

7. The method for preparing a braided tube reinforced hollow fiber membrane according to claim 1, characterized in that: The mass concentration of glycerol is 20wt%, and the mixture is immersed in glycerol for 0.5-1h.

8. The method for preparing a braided tube reinforced hollow fiber membrane according to claim 1, characterized in that: The dry-wet spinning process parameters are as follows: the air bath height is 5 cm, the temperature of the pure water bath is 60-80°C, and the spinning speed is 20 m / min; the outer diameter of the membrane fiber is controlled to be 2.0±0.1 mm, and the thickness of the membrane fiber is 80 μm±20 μm.

9. The method for preparing a braided tube reinforced hollow fiber membrane according to claim 1, characterized in that: The molecular weight of polyvinylidene fluoride resin is 300,000-800,000.

10. A braided tube reinforced hollow fiber membrane obtained based on the method for preparing a braided tube reinforced hollow fiber membrane according to any one of claims 1 to 9.

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