A method for producing a hollow fiber composite membrane

Abstract

This invention discloses a method for preparing a hollow fiber composite membrane, comprising the following steps: Step 1: Weaving fiber filaments into hollow braided tubes using two-dimensional braiding technology, followed by alkaline washing and drying; Step 2: Thoroughly wetting the hollow braided tubes prepared in Step 1 with an aqueous solution of an organic solvent, uniformly coating the outside of the hollow braided tubes with a casting solution preferably through a concentric spinning spinneret, then immersing them in a coagulation bath for double diffusion, solidifying and then cleaning to obtain a nascent hollow fiber membrane; Step 3: Sealing one end of the nascent hollow fiber membrane filaments to form a component, evacuating the inside of the hollow fiber, placing it in a sealed container containing pyrrole, and chemically depositing it to form a polypyrrole separation layer, followed by cleaning and drying to obtain the hollow fiber membrane composite membrane. The prepared fluoropolymer-based hollow fiber composite membrane exhibits excellent chemical stability, high interfacial bonding strength, high pressure resistance, and stable hydrophilicity and separation performance.

Description

Technical Field

[0001] This invention relates to the field of membrane technology, specifically to a method for preparing a hollow fiber composite membrane. Background Technology

[0002] Membrane separation technology, as a highly efficient and environmentally friendly new separation technology, has become a supporting, leading, and forward-looking high-tech field in environmental protection, energy conservation and emission reduction, selective and precise separation of substances at different scales, and deep purification and recycling. It is also one of the key common technologies for solving major global problems such as the energy crisis, water resource crisis, and air pollution. Among them, hollow fiber membranes, as an important type of separation membrane, have advantages in industrial applications due to their good self-support, large specific surface area, high membrane module packing density, compact equipment, simple operation, and high separation efficiency.

[0003] Fluoropolymers such as polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and polyvinylidene fluoride-chlorotrifluoroethylene (PVDF-CTFE) copolymer possess excellent chemical corrosion resistance, high temperature resistance, oxidation resistance, and good mechanical strength, making them ideal membrane materials with a wide range of applications. However, currently, most micro / ultrafiltration membranes on the market are represented by PVDF, and their separation accuracy needs further improvement. Chinese patents CN105617875A and CN201410607043.6 mention using PVDF microporous filter membranes as base membranes to form nanofiltration membranes through an interfacial polymerization process involving immersion in an aqueous phase followed by an oil phase. However, fluoropolymer materials have low surface energy and poor hydrophilicity. When used as base membranes for nanofiltration / loose nanofiltration membranes, the separation layer is prone to discontinuity on the base membrane surface, insufficient bonding strength with the base membrane, and long-term stability cannot be guaranteed, leading to easy peeling. Chinese patents CN101524626 and CN111644077B combine PVDF membranes with hydrophilic polymers to improve the hydrophilicity of PVDF and prepare nanofiltration membranes. However, the modified layer has limited temperature and solvent resistance, which weakens the overall performance of PVDF. Furthermore, membranes prepared by traditional non-solvent-induced phase separation or thermally induced phase separation have poor strength and pressure resistance, resulting in nanofiltration / loose nanofiltration membranes with poor pressure resistance and insufficient membrane structural stability. Therefore, developing new methods to obtain PVDF nanofiltration / loose nanofiltration membrane products with high separation accuracy, good interfacial stability, and high pressure resistance is of great significance. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing hollow fiber composite membranes. The method of this invention is simple to operate, suitable for industrial production, and the prepared fluoropolymer-based hollow fiber composite membrane has excellent chemical stability, high interfacial bonding strength, high pressure resistance, and stable hydrophilicity and separation performance.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0006] This invention uses fluoropolymers as the film-forming polymer. First, a high-strength, pressure-resistant composite hollow braided tube is prepared using two-dimensional braiding technology. Then, a fluoropolymer-based membrane is prepared using a concentric circular composite spinning method. During double diffusion in the coagulation bath, an oxidant enters the membrane, forming a nascent hollow fiber membrane with a gradient concentration of oxidant. This membrane is then in-situ polymerized with pyrrole monomers to form a fluoropolymer-based low-pressure nanofiltration membrane product. The hollow fiber composite membrane includes a fluoropolymer-based membrane and a polypyrrole separation layer formed in-situ on the fluoropolymer-based membrane. The fluoropolymer-based membrane also includes a fluoropolymer layer and a composite fiber braided tube.

[0007] As a preferred embodiment, a method for preparing a hollow fiber composite membrane includes the following steps:

[0008] Step 1: The fiber filaments are woven into hollow braided tubes using two-dimensional braiding technology. Preferably, the braiding parameters are a braiding pitch of 0.5-2 mm and a braiding speed of 500-1000 rpm. The hollow braided tubes are then treated with alkali and dried for later use.

[0009] The fiber filament is made of two kinds of fibers. One of the blended filaments is a fluorinated polymer, preferably polyvinylidene fluoride (PVDF) or polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) fiber filament, and the other is a poly(m-phenylene isophthalamide) or polyimide (PI) fiber filament.

[0010] Step 2: Optional (optional means that the impregnation step can or can not be performed) the hollow braided tube prepared in step 1 is fully impregnated with an aqueous solution of organic solvent. The casting solution is preferably uniformly coated on the outside of the hollow braided tube through a concentric spinning spinneret with an aperture of 1.7-2.3 mm. Then, it is immersed in a coagulation bath to undergo double diffusion. After solidification and shaping, it is cleaned to obtain the nascent hollow fiber membrane.

[0011] Step 3: Seal one end of the nascent hollow fiber membrane to form a component. Vacuum the inside of the hollow fiber and place it in a sealed container containing pyrrole. After chemical deposition, a polypyrrole separation layer is formed. After cleaning and drying, a hollow fiber membrane composite membrane is obtained.

[0012] In this invention, in step 1, the ratio of the two types of fibers in the braiding process is 1-4:4-1. The hollow braided tube serves as the support for the hollow fiber membrane, improving the strength and pressure resistance of the membrane filaments. The hybrid braiding process introduces a second type of high-strength, high-modulus fiber filament, giving the braided tube superior strength. Simultaneously, both types of hybrid fiber filaments are soluble in a co-solvent, solving the technical problems of low interfacial bonding strength in heterogeneous reinforced membranes and the tendency for homogeneous reinforced membranes to form dense regions, thus improving the interfacial bonding strength of the reinforced membrane.

[0013] In this invention, step 1, the alkaline washing treatment, involves drawing the braided tubing into a solution of NaOH at a temperature of 40–90°C and a concentration of 5–15 wt%.

[0014] After soaking in the solution for 10–30 minutes, it is dried with hot air.

[0015] In this invention, step 2 involves a casting solution comprising 5-22 wt% fluoropolymer resin, 5-12 wt% pore-forming agent, 1-5 wt% additive, and 61-89 wt% solvent, prepared according to a 100% total content of all components, and fully dissolved to obtain a homogeneous solution for later use. Preferably, the pore-forming agent is one or more of polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), sodium chloride (NaCl), lithium chloride (LiCl), and glycerol, with PEG, PVP, or LiCl being preferred. The solvent is one or more of triethyl phosphate (TEP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and N-methylpyrrolidone (NMP), with low-toxicity solvents such as TEP and DMSO being preferred. The additive is one or more of Tween-20, Tween-60, and Tween-80. The addition of additives to the casting solution regulates phase separation time and slows down the curing rate. The fluoropolymer resin is one or more of PVDF, PVDF-HFP, and PVDF-CTFE.

[0016] In this invention, in step 2, the organic solvent is one or more of N,N-dimethylacetamide (DMAc) and N,N-dimethylformamide (DMF), preferably with a concentration of 15-30 wt%.

[0017] In this invention, in step 2, the hollow braided tube coated with the liquid is immersed in a coagulation bath at 20-70°C for 0.2-5 minutes under the traction of a winding roller at 0.5-5.0 m / min to solidify and form the tube.

[0018] Preferably, the coagulation bath comprises water, solvent, alcohol, oxidant, and additives. Further, the alcohol is one or more of ethanol, n-butanol, and isopropanol, with a content of 3-15 wt%, preferably ethanol. The oxidant is one or more of ferric chloride, ferric sulfate, ferric nitrate, and ferric perchlorate, with a content of 1-10 wt%, preferably ferric chloride. The additive is one or more of toluenesulfonic acid, sodium benzenesulfonate, and camphorsulfonic acid, with a content of 0.05-1 wt%. The solvent is the same as the solvent used in the casting solution, with a content of 10-30 wt%, and the remainder is water. As a preferred embodiment, in this invention, the oxidant in the coagulation bath enters the membrane interior through a double diffusion between the non-solvent (in the coagulation bath) and the solvent (in the casting solution). After solidification, it is firmly loaded onto the membrane. Through the interaction between the alcohol in the coagulation bath and the additives in the casting solution, the oxidant is distributed in a gradient from the outer surface to the interior, improving the dispersion performance of the oxidant while enhancing the stability of the oxidant loading, and avoiding problems such as uneven dispersion and membrane pore blockage caused by traditional impregnation methods. The hydrophilicity of the preferred additive sulfonate slows down the subsequent pyrrole polymerization reaction, which is beneficial to the uniform distribution of the polypyrrole layer.

[0019] Preferably, before coating the hollow braided tube with the casting solution, the hollow braided tube is pre-impregnated. A solution of DMAc or DMF mixed with water is used to fully impregnate the hollow braided tube prepared in step (1). The impregnation temperature is 50–65°C, and the impregnation time is 0.5–10 min. DMAc or DMF can simultaneously swell and etch the two types of mixed braided fibers, thereby increasing its roughness and improving the bonding strength between the braided tube and the surface coating layer. The preferred solvent concentration is 5–30 wt%.

[0020] In step 3 of this invention, the vacuum degree is 0.05–0.09 MPa, the temperature is 25–90°C, and the chemical deposition time is 20–180 min. Drying is performed in an oven at 60–80°C for 3–5 h. The temperature in the sealed container is 50–90°C. The amount of pyrrole used is 1–10 ml per 1 m of membrane fiber.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The hollow braided tube of the support is prepared by a mixed weaving process. It is obtained by mixing homogeneous fibers with high-strength, high-temperature resistant, and hydrophilic heterogeneous fibers with the same film-forming material and then weaving them in two dimensions. The co-solvent of the two fibers gives the fluoropolymer hollow fiber membrane support and surface separation layer a strong bonding strength. The heterogeneous fibers avoid the formation of dense areas, while improving the membrane strength and pressure resistance, and improving the membrane hydrophilicity.

[0023] (2) By adopting vapor deposition and in-situ growth, the polypyrrole layer is uniformly deposited on the surface and inside of the hollow fiber membrane, forming a dense external and loose internal structure, which not only improves the separation accuracy and hydrophilicity, but also avoids clogging the membrane pores. The separation layer is firmly anchored inside the base membrane, with high interfacial bonding strength and good stability, thus solving the problem of poor uniformity of the separation layer caused by the high curvature radius of the hollow fiber membrane in traditional coating methods.

[0024] (3) The hollow fiber membrane separation layer and the base membrane prepared by this method have good high temperature resistance and corrosion resistance, and the separation performance reaches the nanofiltration level, which can effectively expand the application field of fluoropolymer hollow fiber membrane. Attached Figure Description

[0025] Figure 1 This is a scanning electron microscope image of the outer surface of the hollow fiber composite membrane prepared in Example 1.

[0026] Figure 2 This is a scanning electron microscope image of the cross-section of the hollow fiber membrane prepared in Example 1.

[0027] Figure 3 This is a schematic diagram illustrating the evolution of the hollow fiber composite membrane structure in Example 1.

[0028] Figure 4 The image shows the static water contact angle of the outer surface of the hollow fiber composite membrane prepared in Example 1.

[0029] Figure 5 The image shows a scanning electron microscope image of the outer surface of the hollow fiber membrane prepared for Comparative Example 1. Detailed Implementation

[0030] The hollow fiber composite membrane and its preparation method according to the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The specific embodiments are only used to further illustrate the present invention and do not limit the scope of protection of the claims of this application.

[0031] The sources of raw materials in the examples and comparative examples are as follows:

[0032] Polyvinylidene fluoride (PVDF, Solvay, Belgium, 6010);

[0033] Vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, Arkema, Kynar 2500);

[0034] Polyvinylidene fluoride-chlorotrifluoroethylene copolymer (PVDF-CTFE, Solvay, Belgium, 31508);

[0035] Polyvinylpyrrolidone (PVP, Aladdin Reagent (China) Co., Ltd., M) w =30000);

[0036] Polyethylene glycol (PEG), Aladdin Reagent (China) Co., Ltd., M n =2000);

[0037] Unless otherwise specified, all other raw materials and reagents are commercially available conventional chemical reagents.

[0038] The hollow fiber composite membrane was evaluated mainly by water contact angle test, pure water flux test and dye separation performance test.

[0039] (1) Water / oil contact angle test:

[0040] The static water contact angle of the hollow fiber composite membrane was tested using an OCA25 optical contact angle meter from Dataphysics, Germany. The hollow fiber composite membrane was fixed to a glass slide with double-sided tape and placed on the testing platform. The contact time between the droplet and the membrane surface was set to 30 seconds. After stabilization, each sample was tested five times, and the average value was taken.

[0041] (2) Pure water flux and rejection test

[0042] The pure water flux of a 10cm long membrane fiber was tested at 25℃ using the external pressure method. First, the membrane was pre-pressurized for 30 minutes. Then, different membrane samples were tested under constant pressure. The pure water flux was calculated using the following formula:

[0043] J = V / (A·T)

[0044] Where J is the pure water flux of the membrane (L·m -2 ·h -1 V is the permeate volume (L), and A is the effective area of ​​the membrane (m²). 2 ); T is the test time (h).

[0045] The dye retention performance of the hollow fiber composite membrane was evaluated by testing its dye retention effect. Before testing, the membrane was pre-pressed for 30 minutes. After the flux stabilized, a prepared 20 mg / L dye solution was used as the stock solution, and the filtrate was collected for testing. The absorbance of the feed solution and the permeate was measured using a Shanghai Yuanxi X-3 UV spectrophotometer. The absorbance was converted to concentration based on the relationship between absorbance and concentration, and the retention rate was calculated using the following formula:

[0046] R(%)=(1-C p / C f 100%

[0047] Where R is the retention rate, C f and C p These represent the dye concentrations in the raw material solution and the filtrate, respectively.

[0048] Example 1

[0049] 1) Preparation of hybrid fiber hollow braided tubes:

[0050] PVDF filaments and PMIA filaments were twisted together and braided into hollow tubes with an outer diameter of 1.8 mm using a 24-spindle two-dimensional braiding machine (model GBJ-90, Xuzhou Heng Hui Braiding Machinery Co., Ltd.), with a braiding pitch of 2 mm and a rotation speed of 800 rpm. The resulting braided tubes were immersed in a 5 wt% sodium hydroxide solution and treated at 40°C for 20 min, followed by washing with deionized water and drying at 60°C.

[0051] 2) Preparation of casting solution:

[0052] PVDF, DMSO, PEG2000 and Tween-80 were mixed at 15wt%, 79wt%, 5wt% and 1wt% respectively, and heated in a water bath at 70℃, mechanically stirred for 5 hours, and degassed completely to obtain a uniform casting solution.

[0053] 3) Preparation of nascent hollow fiber membranes:

[0054] The hollow braided tube was immersed in a 20wt% DMAc aqueous solution at 50℃ for 3 minutes. The casting solution was uniformly coated on the outside of the hollow braided tube through a concentric spinning spinneret with an aperture of 2.3 mm. Under the traction of the winding roller at 1 m / min, it was immersed in a coagulation bath at 50℃ with a composition of 12wt% ethanol, 2wt% ferric chloride, 0.5wt% sodium benzoate, 10wt% DMSO and 75.5wt% water for 2 minutes to solidify and form the nascent hollow fiber membrane.

[0055] 4) Preparation of hollow fiber membrane composite membrane:

[0056] One end of the nascent hollow fiber membrane filament is sealed to form a component. The hollow fiber is then evacuated to 0.05 MPa and placed in a sealed container at 80°C containing pyrrole. After chemical deposition for 60 minutes, a polypyrrole separation layer is formed. 5 ml of pyrrole is used per 1 m of membrane filament. The membrane is then dried in a 60°C oven for 5 hours and then washed and dried with water to form a PVDF hollow fiber composite membrane.

[0057] After testing, as shown in the attached document Figure 1 The obtained PVDF hollow fiber composite membrane has a uniformly deposited polypyrrole layer on its surface, and the membrane cross-section is shown in the figure. Figure 2 As shown, the bonding is good, and there is no dense region formed by the dissolution of the braided tube. The structural evolution diagram is as follows. Figure 3 As shown. The tensile strength of the membrane was tested using a tensile testing machine (model JBDL-200N, Yangzhou Jingbo Testing Machinery Co., Ltd.) (the membrane filaments were held at a clamping length of 10 cm, and the tensile rate was 5 mm·min). -1The membrane tensile strength was tested to be greater than 200 MPa, and the water contact angle test results were as follows: Figure 4 As shown, the water contact angle is 64°, and the flux is 125 L·m at 0.5 MPa. -2 ·h -1 The membrane fibers were not flattened, and the interfacial bonding was good. The membrane fibers had a rejection rate of more than 98% for both methylene blue and Congo red, and a rejection rate of 19% for NaCl. The separation of dyes and salts could be achieved. After repeated washing tests, the membrane flux and rejection performance remained basically unchanged.

[0058] Example 2

[0059] 1) Preparation of hybrid fiber hollow braided tubes:

[0060] PVDF filaments and PI filaments are twisted together and braided into a hollow braided tube with an outer diameter of 1.6 mm using a 24-spindle two-dimensional braiding machine with a braiding pitch of 1 mm and a rotation speed of 600 rpm. The resulting braided tube is immersed in an 8 wt% sodium hydroxide solution and treated at 40 °C for 20 min. It is then washed with deionized water and dried at 60 °C.

[0061] 2) Preparation of casting solution:

[0062] PVDF, TEP, PVP30000 and Tween-80 were mixed at 17wt%, 73wt%, 8wt%, and 2wt%, respectively. The mixture was heated in a 70℃ water bath, mechanically stirred for 5 hours, and degassed completely to obtain a uniform casting solution.

[0063] 3) Preparation of nascent hollow fiber membranes:

[0064] The hollow braided tube was immersed in a 10wt% DMF aqueous solution at 50℃ for 3 minutes. The casting solution was uniformly coated on the outside of the hollow braided tube through a concentric spinning spinneret with an aperture of 1.7mm. Under the traction of the winding roller at 0.5m / min, it was immersed in a coagulation bath at 50℃ with a composition of 10wt% ethanol, 2wt% ferric sulfate, 0.1wt% sodium benzenesulfonate, 15wt% TEP, and 72.9wt% water for 3 minutes to solidify and form the nascent hollow fiber membrane.

[0065] 4) Preparation of hollow fiber composite membrane:

[0066] One end of the nascent hollow fiber membrane filament is sealed to form a component. The hollow fiber is then evacuated to 0.09 MPa and placed in a sealed container at 80°C containing pyrrole. After chemical deposition for 80 minutes, a polypyrrole separation layer is formed. 10 ml of pyrrole is used per 1 m of membrane filament. The membrane is then dried in a 60°C oven for 5 hours, followed by washing and drying to obtain a PVDF hollow fiber composite membrane.

[0067] Testing revealed that the obtained PVDF hollow fiber composite membrane exhibited a uniformly deposited polypyrrole layer on its surface, without any dense areas formed by the dissolution of the braided tube. Its tensile strength exceeded 200 MPa, its water contact angle was 58°, and its flux at 0.5 MPa was 102 L·m⁻². -2 ·h -1 The membrane fibers were not flattened, and the interfacial bonding was good. The membrane fibers had a rejection rate of more than 97% for both methylene blue and Congo red, and a rejection rate of 21% for NaCl. The separation of dyes and salts could be achieved. After repeated washing tests, the membrane flux and rejection performance remained basically unchanged.

[0068] Example 3

[0069] 1) Preparation of hybrid fiber hollow braided tubes:

[0070] PVDF-HFP filaments and PMIA filaments were twisted together and braided into a hollow braided tube with an outer diameter of 1.8 mm using a 24-spindle two-dimensional braiding machine with a braiding pitch of 2 mm and a rotation speed of 700 rpm. The resulting braided tube was immersed in a 5 wt% sodium hydroxide solution and treated at 40 °C for 20 min. It was then washed with deionized water and dried at 60 °C.

[0071] 2) Preparation of casting solution:

[0072] PVDF-HFP, DMSO, PEG2000 and Tween-20 were mixed at 15wt%, 79wt%, 5wt%, and 1wt%, respectively. The mixture was heated in a water bath at 70℃, mechanically stirred for 5 hours, and degassed completely to obtain a uniform casting solution.

[0073] 3) Preparation of nascent hollow fiber membranes:

[0074] The hollow braided tube was immersed in a 20wt% DMAc aqueous solution at 50℃ for 3 minutes. The casting solution was uniformly coated on the outside of the hollow braided tube through a concentric spinning spinneret with an aperture of 2.1 mm. Under the traction of the winding roller at 0.5 m / min, it was immersed in a coagulation bath at 50℃ with a composition of 12wt% isopropanol, 2wt% ferric chloride, 0.5wt% sodium benzoate, 10wt% DMSO and 75.5wt% water for 2 minutes to solidify and form the nascent hollow fiber membrane.

[0075] 4) Preparation of hollow fiber composite membrane:

[0076] One end of the nascent hollow fiber membrane filament is sealed to form a component. The hollow fiber is then evacuated to 0.05 MPa and placed in a sealed container at 80°C containing pyrrole. After chemical deposition for 30 minutes, a polypyrrole separation layer is formed. 2 ml of pyrrole is used per 1 m of membrane filament. The membrane is then dried in a 60°C oven for 5 hours, followed by washing and drying to obtain the PVDF-HFP hollow fiber composite membrane.

[0077] Testing revealed that the obtained PVDF-HFP hollow fiber composite membrane exhibited a uniformly deposited polypyrrole layer on its surface, without any dense areas formed by the dissolution of the braided tube. Its tensile strength exceeded 200 MPa, its water contact angle was 57°, and its flux at 0.5 MPa was 131 L·m⁻¹. -2 ·h -1 The membrane fibers were not flattened, and the interfacial bonding was good. The membrane fibers had a rejection rate of more than 92% for both methylene blue and Congo red, and a rejection rate of 16% for NaCl. It can achieve the separation of dyes and salts. After repeated washing tests, the membrane flux and rejection performance remained basically unchanged.

[0078] Example 4

[0079] 11) Preparation of hybrid fiber hollow braided tubes:

[0080] PVDF-HFP filaments and PI filaments are twisted together and braided into a hollow braided tube with an outer diameter of 2.0 mm using a 24-spindle two-dimensional braiding machine with a braiding pitch of 2 mm and a rotation speed of 600 rpm. The resulting braided tube is immersed in an 8 wt% sodium hydroxide solution and treated at 40°C for 20 min. It is then washed with deionized water and dried at 60°C.

[0081] 2) Preparation of casting solution:

[0082] PVDF-HFP, TEP, PVP30000 and Tween-80 were mixed at 17wt%, 73wt%, 8wt%, and 2wt%, respectively. The mixture was heated in a 70℃ water bath, mechanically stirred for 5 hours, and degassed completely to obtain a uniform casting solution.

[0083] 3) Preparation of nascent hollow fiber membranes:

[0084] The hollow braided tube was immersed in a 10wt% DMAc aqueous solution at 50℃ for 3 minutes. The casting solution was uniformly coated on the outside of the hollow braided tube through a concentric spinning spinneret with an aperture of 1.7mm. Under the traction of the winding roller at 0.5m / min, it was immersed in a coagulation bath at 50℃ with a composition of 10wt% isopropanol, 2wt% ferric sulfate, 0.1wt% camphor sulfonic acid, 15wt% TEP, and 72.9wt% water for 3 minutes to solidify and form the nascent hollow fiber membrane.

[0085] 4) Preparation of hollow fiber composite membrane:

[0086] One end of the nascent hollow fiber membrane filament is sealed to form a component. The hollow fiber is then evacuated to 0.09 MPa and placed in a sealed container at 80°C containing pyrrole. After chemical deposition for 120 minutes, a polypyrrole separation layer is formed. 10 ml of pyrrole is used per 1 m of membrane filament. The membrane is then dried in a 60°C oven for 5 hours and then washed and dried with water to form a PVDF hollow fiber composite membrane.

[0087] Testing revealed that the obtained PVDF-HFP hollow fiber composite membrane exhibited a uniformly deposited polypyrrole layer on its surface, without any dense areas formed by the dissolution of the braided tube. Its tensile strength exceeded 200 MPa, its water contact angle was 60°, and its flux at 0.5 MPa was 89 L·m⁻¹. -2 ·h -1 The membrane fibers were not flattened, and the interfacial bonding was good. The membrane fibers had a rejection rate of more than 99% for both methylene blue and Congo red, and a rejection rate of 31% for NaCl, which can achieve the separation of dyes and salts.

[0088] Comparative Example 1

[0089] PVDF hollow fiber membranes were prepared using the method described in Example 1, except that ferric chloride was not added to the coagulation bath in step 3, and step 4 was omitted. The resulting PVDF hollow fiber membranes have the surface morphology shown in the attached figure. Figure 5 As shown, a large number of microporous structures are visible on the surface, the water contact angle is 79°, and the membrane fibers have virtually no retention effect on methylene blue and Congo red.

[0090] Comparative Example 2

[0091] The PVDF hollow fiber composite membrane was prepared using the method described in Example 1, except that the hollow braided tube was made of polyethylene terephthalate (PET). When the PVDF hollow fiber composite membrane was prepared, the membrane fibers were flattened under 0.5 MPa, and the separation layer detached from the braided tube.

[0092] In summary, the hollow fiber composite membranes prepared in Examples 1-4 all exhibit better overall performance than the separation membranes prepared in Comparative Examples 1-2. The resulting membranes show significantly improved hydrophilicity and separation accuracy, enhanced interfacial stability, and effectively extended membrane lifespan.

[0093] The present invention has been described in detail above with reference to the embodiments. However, those skilled in the art will understand that, without departing from the spirit of the present invention, various specific parameters in the above embodiments can be changed to form multiple specific embodiments, all of which are common variations of the present invention, and will not be described in detail here.

Claims

1. A method for preparing a hollow fiber composite membrane, characterized in that, The method includes the following steps: Step 1: The fiber filaments are braided into hollow braided tubes using two-dimensional braiding technology. The hollow braided tubes are then treated with alkali washing and dried for later use. The fiber filament is made of two kinds of fibers, one of which is a fluoropolymer and the other is one of poly(m-phenylene isophthalamide) or polyimide fiber filament. Step 2: The casting solution is uniformly coated on the outside of the hollow braided tube, and then immersed in the coagulation bath to undergo double diffusion. After solidification and shaping, it is cleaned to obtain the nascent hollow fiber membrane. The coagulation bath contains solvent, alcohol, oxidant, additive and water. The oxidant is one or more of ferric chloride, ferric sulfate, ferric nitrate and ferric perchlorate. The additive is one or more of toluenesulfonic acid, sodium benzenesulfonate and camphorsulfonic acid. Step 3: Seal one end of the nascent hollow fiber membrane to form a component. Vacuum the inside of the hollow fiber and place it in a sealed container containing pyrrole. After chemical deposition, a polypyrrole separation layer is formed. After cleaning and drying, a hollow fiber composite membrane is obtained.

2. The preparation method according to claim 1, characterized in that, In step 1, the weaving parameters are a weaving pitch of 0.5–2 mm and a weaving speed of 500–1000 rpm.

3. The preparation method according to claim 1, characterized in that, In step 1, one of the fluoropolymers in the blended filaments is one of polyvinylidene fluoride or polyvinylidene fluoride-hexafluoropropylene copolymer fiber filaments.

4. The preparation method according to claim 1, characterized in that, In step 1, the blending ratio of the two fibers is 1-4:4-1; and / or, the alkaline washing treatment involves immersing the hollow braided tube in a NaOH solution with a temperature of 40-90°C and a concentration of 5-15 wt% for 10-30 minutes.

5. The preparation method according to claim 1, characterized in that, Step 2 involves thoroughly wetting the hollow braided tube prepared in Step 1 with an aqueous solution of an organic solvent before coating it with a casting solution.

6. The preparation method according to claim 5, characterized in that, In step 2, the temperature of the aqueous solution of the organic solvent is 50-65℃, and the soaking time is 0.5-10 min.

7. The preparation method according to claim 1, characterized in that, In step 2, the casting solution is uniformly coated onto the outside of the hollow braided tube through a concentric spinning spinneret with an aperture of 1.7 to 2.3 mm.

8. The preparation method according to claim 1, characterized in that, In step 2, the alcohol in the coagulation bath is one or more selected from ethanol, n-butanol, and isopropanol, with a content of 3-15 wt%; and / or, The oxidant content is 1–10 wt%; and / or, The additive content is 0.05–1 wt%; and / or, The solvent is the same as the solvent used in the casting solution, and its content is 10-30 wt%.

9. The preparation method according to claim 1, characterized in that, In step 2, the casting solution contains 5-22 wt% fluoropolymer resin, 5-12 wt% pore-forming agent, 1-5 wt% additive, and 61-89 wt% solvent.

10. The preparation method according to claim 9, characterized in that, The fluoropolymer resin in the casting solution in step 2 is one or more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, and polyvinylidene fluoride-trifluorochloroethylene.

11. The preparation method according to claim 9, characterized in that, The additives in the casting solution in step 2 are one or more of Tween-20, Tween-60, and Tween-80; and / or the pore-forming agent is one or more of polyethylene glycol, polyvinylpyrrolidone, polyvinyl alcohol, sodium chloride, lithium chloride, and glycerol.

12. The preparation method according to claim 9, characterized in that, The solvent in the casting solution in step 2 is one or more of the following: triethyl phosphate, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone.

13. The preparation method according to claim 5, characterized in that, The organic solvent in the aqueous solution of the organic solvent in step 2 is one or more of N,N-dimethylacetamide and N,N-dimethylformamide.

14. The preparation method according to claim 13, characterized in that, The concentration of the organic solvent aqueous solution in step 2 is 15-30 wt%.

15. The preparation method according to any one of claims 1-14, characterized in that, In step 2, the hollow braided tube coated with casting solution is immersed in a coagulation bath at 20-70℃ under the traction of a winding roller at 0.5-5.0 m / min to undergo double diffusion. The immersion time in the coagulation bath is 0.2-5 min.

16. The preparation method according to claim 1, characterized in that, In step 3, the vacuum degree is 0.05-0.09 MPa, the chemical deposition time is 20-180 min, and / or, drying is carried out in an oven at 60-80℃ for 3-5 h; the temperature in the sealed container is 50-90℃.

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