Polyvinylidene fluoride hollow fiber porous separation membrane, preparation method and application thereof

Abstract

The present application relates to a kind of polyvinylidene fluoride hollow fiber porous separation membrane and preparation method and application, preparation method is: 1) polyvinylidene fluoride resin, the mixed solvent consisting of the strong solvent and weak solvent of polyvinylidene fluoride resin, the specific surface area of 150 ~ 300 m 2 / g Hydrophobic modified inorganic additive, and optional adjuvant are mixed uniformly, to obtain casting film mixture;2) the casting film mixture of step 1) is added to extruder melt, then extruded through hollow fiber spinneret, cooling setting, 1.1 ~ 1.5 times of stretching, to obtain hollow fiber membrane filament;3) the hollow fiber membrane filament of step 2) is carried out heat setting treatment, then solvent and inorganic additive in membrane filament are removed by extraction, to obtain the polyvinylidene fluoride hollow fiber porous separation membrane.The obtained polyvinylidene fluoride porous membrane is high in strength, large in flux, uniform in surface pore size distribution, simple in manufacturing process, environment-friendly, easy to industrial production.The membrane is preferably used in material separation field.

Description

Technical Field

[0001] This invention belongs to the field of microfiltration membrane technology, specifically relating to a polyvinylidene fluoride hollow fiber porous separation membrane, its preparation method, and its application. Background Technology

[0002] Currently, with technological advancements, microfiltration membranes have become widely used in industry and are considered a new type of industrial unit operation. They can be used for the separation, concentration, and purification of biological products, pharmaceuticals, and the food industry; they can also be used as terminal treatment devices in blood processing, wastewater treatment, and ultrapure water preparation.

[0003] In recent years, with water scarcity, global demand for high-quality water, growth in the biopharmaceutical and food processing industries, microfiltration membranes have become increasingly popular as a viable alternative to heat treatment in reducing bacteria and extending the shelf life of dairy products. The market for microfiltration membranes is experiencing rapid growth due to increasing application demands. In particular, the proactive adoption of microfiltration membrane technology in industrial ecosystems, such as the cost-effectiveness of continuous fermentation compared to batch processing, will further positively impact the growth of the microfiltration membrane market.

[0004] Because biopharmaceutical, food processing, and bio-fermentation industries have high requirements for product quality, microfiltration membrane products used in industrial systems typically need to have characteristics such as uniform pore size distribution, high flux, stable performance, good chemical resistance, and long lifespan in order to ensure product quality.

[0005] Existing microfiltration membrane products generally use polysulfone or polyvinylidene fluoride materials, which are prepared using non-solvent-induced phase separation methods. These materials fail to meet the requirements of current industrial applications in terms of alkali resistance, membrane strength, and uniformity of pore size distribution. Therefore, there is an urgent need to develop a microfiltration membrane product with superior performance in all aspects.

[0006] Regarding methods for preparing microfiltration membranes made of different materials, patent JP2017136555A discloses a method for preparing a hollow fiber membrane with high water permeability, excellent tensile strength, and excellent elongation at break. This membrane can achieve a particle rejection rate of over 99% for particles of 0.26-0.34 μm and an elongation at break of over 50%. The membrane material is a polysulfone-based material, and the hollow fiber membrane is prepared by adding a hydrophilic polymer using solvent-induced phase separation. The patent does not disclose the pore size and distribution of the membrane, only that it achieves good water permeability while ensuring tensile strength and elongation at break.

[0007] Patent CN1458859A discloses a method for preparing a hollow fiber membrane made of polyvinylidene fluoride (PVDF). This method involves mixing an organic pore-forming agent and inorganic fine powder into PVDF resin, melting and molding the mixture at a temperature up to 250°C, and then extracting the organic pore-forming agent and inorganic fine powder to form a membrane. The inorganic fine powder added to the formulation is prone to agglomeration, leading to the formation of relatively large voids in the extracted membrane. This widens the pore size distribution of the membrane and reduces its ability to retain pollutants.

[0008] The microfiltration membranes prepared by the above-mentioned existing technologies all have the following problems during use: wide pore size distribution, making it difficult to maintain high flux while ensuring retention effect, and poor membrane pressure resistance or low strength. Summary of the Invention

[0009] In view of this, the present invention aims to provide a polyvinylidene fluoride (PVDF) hollow fiber porous separation membrane and its preparation method. This method is based on PVDF resin, employs a thermally induced phase separation method, utilizes a hydrophobically modified inorganic material with a high specific surface area, and combines a strong solvent and a weak solvent for PVDF, along with a subsequent stretching process, to prepare a porous separation membrane. The PVDF hollow fiber porous separation membrane prepared in this way is a microfiltration membrane product with uniform pore size distribution, excellent performance, and good dimensional consistency.

[0010] Meanwhile, the present invention also aims to provide the application of the polyvinylidene fluoride hollow fiber porous separation membrane in material separation systems, specifically applicable to fields such as bio-fermentation, chemical pharmaceuticals, active pharmaceutical ingredients, biopharmaceuticals, and food industry, which can achieve the separation or concentration of substances with a particle size of 0.1 μm or larger in the system.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0012] This invention provides a method for preparing a polyvinylidene fluoride hollow fiber porous separation membrane, comprising the following steps:

[0013] 1) Polyvinylidene fluoride resin, a mixed solvent consisting of a strong solvent and a weak solvent for polyvinylidene fluoride resin, and a specific surface area of ​​150–300 m². 2 / g of hydrophobically modified inorganic additives and optional auxiliaries are mixed evenly to obtain a casting film mixture;

[0014] 2) The casting mixture from step 1) is added to an extruder to melt, then extruded through a hollow fiber spinneret, cooled and shaped, and stretched to obtain hollow fiber membrane filaments;

[0015] 3) The hollow fiber membrane fibers from step 2) are subjected to heat setting treatment, and then the solvent and inorganic additives in the membrane fibers are removed by extraction to obtain the polyvinylidene fluoride hollow fiber porous separation membrane.

[0016] In one specific implementation, step 1) comprises the following raw material weight percentage composition:

[0017] The polyvinylidene fluoride resin is 30% to 50%, for example, 30%, 35%, 40%, 45%, 50%, etc., preferably 35% to 45%;

[0018] A mixed solvent consisting of 30% to 50% strong and weak solvents of polyvinylidene fluoride resin, for example, 30%, 35%, 40%, 45%, 50%, etc.

[0019] The amount of hydrophobically modified inorganic additives is 15% to 40%, such as 15%, 20%, 25%, 30%, 35%, 40%, etc., preferably 20% to 35%.

[0020] The optional additives are 0-5%, such as 0%, 1%, 2%, 3%, 4%, 5%, etc., preferably 0-3%;

[0021] The sum of the weight percentages of all raw materials is 100%.

[0022] In one specific implementation, the polyvinylidene fluoride resin in step 1) can be a homopolymer or copolymer of polyvinylidene fluoride;

[0023] Preferably, the polyvinylidene fluoride resin has a weight-average molecular weight of 200,000 to 700,000, such as 200,000, 300,000, 400,000, 500,000, 600,000, 700,000, etc., and more preferably 300,000 to 600,000.

[0024] In one specific embodiment, the mixed solvent in step 1) is composed of a strong solvent and a weak solvent of polyvinylidene fluoride resin, wherein the mass ratio of the strong solvent to the weak solvent in the mixed solvent is 0.1 to 2, for example, 0.1, 0.3, 0.5, 0.8, 1, 1.3, 1.5, 1.8, 2;

[0025] It should be noted that in this invention, strong solvents and weak solvents are distinguished based on their solubility in polyvinylidene fluoride (PVDF) resin. Specifically, a strong solvent refers to a solvent in which the dissolution temperature of 20 wt% PVDF resin is completely dissolved is 10-20% lower than the melting point of PVDF resin itself. A weak solvent refers to a solvent in which the dissolution temperature of 20 wt% PVDF resin is less than 10% lower than the melting point of PVDF resin itself. Here, 20 wt% PVDF resin means that the concentration of PVDF resin in the mixture with the solvent is 20 wt%. This can be understood as follows: When the melting point of polyvinylidene fluoride resin is A, a strong solvent (the solvent at which 20 wt% of polyvinylidene fluoride resin is completely dissolved) is a solvent at a temperature 10-20% lower than A, and a weak solvent (the solvent at which 20 wt% of polyvinylidene fluoride resin is completely dissolved) is a solvent at a temperature less than 10% lower than A. To further illustrate this, the melting point of polyvinylidene fluoride resin is typically 170-175℃. For example, taking polyvinylidene fluoride resin with a melting point of 170℃, a strong solvent (the solvent at which 20 wt% of polyvinylidene fluoride resin is completely dissolved) is a solvent at a temperature 136-153℃ (10-20% lower than 170℃), and a weak solvent (the solvent at which 20 wt% of polyvinylidene fluoride resin is completely dissolved) is a solvent at a temperature less than 170℃ and greater than 153℃ (less than 10% lower than 170℃).

[0026] Preferably, the strong solvent of the polyvinylidene fluoride resin is one or a mixture of several of the following: dibutyl phthalate, benzoate, sebacic acid ester, adipate, phosphate ester, tributyl acetylacetonate, trioctyl trimellitate, ethylene bis-stearamide, and γ-butyrolactone; more preferably, it is one or a mixture of several of the following: dibutyl phthalate, dibutyl sebacic acid ester, dibutyl adipate, dioctyl adipate, tributyl phosphate, tributyl acetylacetonate, and γ-butyrolactone.

[0027] Preferably, the weak solvent of the polyvinylidene fluoride resin is one or a mixture of several of the following: dioctyl phthalate, diethyl phthalate, triacetyl glycerol, benzophenone, soybean oil, diphenyl carbonate, castor oil, glyceryl monoacetate, and diphenylmethane; more preferably, it is one or a mixture of several of the following: dioctyl phthalate, diethyl phthalate, triacetyl glycerol, soybean oil, and castor oil.

[0028] The preparation method of this invention uses a combination of strong and weak solvents of the above-mentioned polyvinylidene fluoride resin, which can better adjust the phase separation temperature of the resin, make the phase separation more uniform, and the resulting membrane has a more consistent pore size.

[0029] In one specific embodiment, the hydrophobically modified inorganic additive in step 1) has a concentration of 150–300 mg. 2 High specific surface area per g, for example, 150 m² 2 / g、180m 2 / g、200m 2 / g、220m 2 / g、250m 2 / g、280m 2 / g、300m 2 / g, preferably 170-250m 2 / g; High specific surface area inorganic additives are used, which typically have smaller particle sizes, are more abundant at the same addition ratio, and have better dispersibility in the system. Therefore, during the stretching process, highly dispersed inorganic additives can serve as the core (which can also be understood as the separation point during stretching), providing more stretching separation points, resulting in denser pores, which is beneficial for improving the flux and porosity of porous membranes.

[0030] Preferably, the hydrophobically modified inorganic additive is nano-silica; wherein the hydrophobic modifying group is preferably one or more of hexamethyldisilazane, dimethyldichlorosilane, octamethylcyclotetrasiloxane, etc.

[0031] The hydrophobically modified inorganic additives described in this invention are known products in the field, and their sources are not limited. They can be commercially available products, such as Evonik's AEROSIL R974 and R812S; or they can be prepared by self-production according to existing disclosed methods, for example, by referring to the method disclosed in patent IN253288B.

[0032] In one specific embodiment, the optional additive mentioned in step 1) is a conventional additive in the field, including one or more of antioxidants, heat stabilizers, ultraviolet absorbers, and anti-aging agents. In specific applications, conventional selection of various additives in the field can be used, and the present invention does not have any particular requirements. For example...

[0033] The antioxidant can be one or more of antioxidants such as 1330, 1010, and 626;

[0034] The heat stabilizer can be one or more of zinc stearate, zinc-calcium composite stabilizers, etc.

[0035] The ultraviolet absorber can be one or more of UV-3030, UV-360, UV-1600, etc.

[0036] The anti-aging agent can be one or more of 445, 2246, MB, etc.

[0037] In this invention, in step 1), each raw material is preferably mixed evenly using a high-speed mixing device to obtain a casting film mixture.

[0038] In one specific implementation, step 2) involves the melting process performed by an extruder, which is a conventional operation in the field, for example, controlling the temperature range to be 220-280°C, such as 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, etc.; the extruder is a twin-screw extruder.

[0039] In one specific implementation, during the extrusion process via the hollow fiber spinneret in step 2), high-temperature nitrogen gas is introduced into the hollow fiber spinneret. The simultaneous introduction of high-temperature nitrogen gas during the extrusion process can help the porous membrane form its pore diameter.

[0040] Preferably, the nitrogen temperature is 80–200°C, such as 80°C, 100°C, 120°C, 140°C, 160°C, 180°C, 200°C, etc.; preferably, the high-temperature nitrogen flow rate is 70–100 mL / min.

[0041] Preferably, the hollow fiber spinneret can be a conventional type in the field, such as a ring-shaped spinneret, and there are no special requirements in this invention; preferably, the ring-shaped spinneret has an outer diameter of 2.0 to 2.4 mm and an inner diameter of 1.0 to 1.6 mm.

[0042] In one specific implementation, the stretching in step 2) is a low-ratio stretching of 1.1 to 1.5 times in the length direction. During the stretching process, the outer diameter of the membrane filament is tested by a diameter gauge, and then it is wound up. Specifically, a laser diameter gauge is added during the stretching process to test the outer diameter of the membrane filament during the spinning process and adjust it according to the data. This can make the membrane filament specifications more uniform and more effectively achieve the stability of membrane filament performance.

[0043] Since the stretching effect is centered on the core, separating the core from the resin, if the number of cores is insufficient or the stretching ratio is too high, stretching pores will appear on the surface of the polymer itself. These pores are tear pores, generally quite long and thin. Although they can increase throughput, the retention effect will be significantly reduced. In the preparation method of this invention, a low-ratio stretching is used, and the stretching process uses hydrophobically modified inorganic additives as the core, which can avoid the above-mentioned problems, expand the pore size, and improve throughput and porosity.

[0044] In one specific implementation, the heat setting treatment in step 3) is carried out at a temperature of 110 to 150°C, such as 110°C, 120°C, 130°C, 140°C, 150°C, etc., and for a time of 1 to 5 hours, such as 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, etc.

[0045] In one specific implementation, step 3) involves extracting and removing solvents and inorganic additives from the membrane fibers, which includes extraction to remove solvents and extraction to remove inorganic additives.

[0046] The solvent removal process uses an extractant selected from one or more of the following: n-hexane, cyclohexane, gasoline, ethanol, N,N-dimethylformamide, N,N-dimethylacetamide, dichloromethane, chloroform, and isopropanol.

[0047] Preferably, the extraction temperature is 40-80℃, such as 40℃, 50℃, 60℃, 70℃, 80℃, etc., and the extraction time is 4-10 hours, such as 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, etc.

[0048] The extraction process removes inorganic additives, and the extractant used is selected from sodium hydroxide solution, preferably a 5-10 wt% sodium hydroxide aqueous solution.

[0049] Preferably, the extraction temperature is 40-80℃, such as 40℃, 50℃, 60℃, 70℃, 80℃, etc., and the extraction time is 4-10 hours, such as 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, etc.

[0050] This invention provides a polyvinylidene fluoride hollow fiber porous separation membrane, which is prepared by the method described above.

[0051] The polyvinylidene fluoride hollow fiber porous separation membrane has an inner diameter of 1.0–2.0 mm, a wall thickness of 0.1–0.5 mm, a porosity of 50–80%, an average pore size of 0.1–0.6 μm, and a pure water flux of 2000–10000 L / m³. 2 • hr@0.1MPa, 25℃, tensile breaking strength is 9~20MPa, tensile breaking elongation is 120~300%.

[0052] The polyvinylidene fluoride hollow fiber porous separation membrane of the present invention has the advantages of uniform surface pore size, narrow pore size distribution and high mechanical strength. It can be used in fields such as bio-fermentation, chemical drugs, raw materials, biopharmaceuticals, and food industry, and can realize the separation or concentration of substances with a particle size of 0.1 μm or larger in the system.

[0053] Compared with modern technology, the advantages of the technical solution of this invention are as follows:

[0054] The polyvinylidene fluoride hollow fiber porous separation membrane of the present invention has the advantages of uniform surface pore size distribution, excellent performance, and good specification consistency. The product preparation method is economical and environmentally friendly, and it can be used in the field of material separation. It is very suitable for use in material separation systems to remove substances larger than 0.1μm, such as sterilization and turbidity removal, and has important practical significance and economic benefits. Attached Figure Description

[0055] Figure 1 Scanning electron microscope image of the outer surface of the porous membrane prepared in Example 1;

[0056] Figure 2 Scanning electron microscope (SEM) image of the cross-section of the porous membrane prepared in Example 1;

[0057] Figure 3 A diagram showing the pore size and distribution of the porous membrane prepared in Example 1;

[0058] Figure 4 A scanning electron microscope image of the outer surface of the porous membrane prepared for Comparative Example 1;

[0059] Figure 5 A scanning electron microscope image of the cross-section of the porous membrane prepared for Comparative Example 1;

[0060] Figure 6 The pore size and distribution of the porous membrane prepared for Comparative Example 1 are shown in the figure. Detailed Implementation

[0061] The present invention will be further illustrated below with specific embodiments. These embodiments are merely illustrative and do not limit the scope of the invention.

[0062] The main raw materials used in the various embodiments and comparative examples of this invention are sourced as follows. Unless otherwise specified, other raw materials and reagents were obtained through commercially available channels:

[0063] Polyvinylidene fluoride resin: Solvay, Belgium 6010, 1015, 6020;

[0064] Hydrophobically modified nano-silica: Evonik Degussa (China) Co., Ltd., R974, R812S, R8200;

[0065] Strong solvents, weak solvents, and additives are mostly bulk petrochemical products and can all be obtained commercially. The main membrane performance evaluation methods used in the various embodiments and comparative examples of this invention are as follows.

[0066] (1) Average pore size of the membrane: Measured using a POROLUX 1000 pore size analyzer. The calculation formula based on the test principle is as follows:

[0067] D=4δcosθ / P

[0068] In the formula: D—membrane pore diameter, μm;

[0069] δ—Liquid surface tension, N / m;

[0070] θ—Contact angle between the liquid and the orifice wall, °;

[0071] P—Gas pressure, Pa;

[0072] (2)D 最大:D 最小 (Maximum pore size / Minimum pore size, i.e., pore size distribution): The ratio of the maximum pore size to the minimum pore size of the membrane, measured using a POROLUX 1000 pore size analyzer, is used to characterize the pore size distribution of the membrane. Compared to 1, a larger value indicates a wider pore size distribution, and a smaller value indicates a narrower pore size distribution.

[0073] (3) Pure water flux (LMH) is defined as: the volume of water passing through the effective membrane area per unit time under a certain operating pressure condition. Its calculation formula is:

[0074] J = Q / At

[0075] Where: J—flux, L / m 2 ·hr@0.1MPa;

[0076] Q—Pure water permeation rate, in L;

[0077] A—Filtration area of ​​the membrane, m 2 ;

[0078] t — time to collect permeate, hr;

[0079] (4) Mechanical strength: The breaking strength (MPa) and breaking elongation (%) of the hollow fiber membrane were tested by a single fiber tensile tester at a certain tensile speed (50 mm / min).

[0080]

Example 1

[0081] Weigh out 40% of the polyvinylidene fluoride resin by mass percentage. 1015 (molecular weight 600,000), 25% hydrophobically modified nano-silica (R812S, hydrophobic modification group is hexamethyldisilazane, specific surface area 220±25m²). 2 The mixture of 10% dibutyl phthalate, 24% dioctyl phthalate and 1% antioxidant 1330 was homogenized in a high-speed mixer to obtain a casting film mixture.

[0082] The casting mixture is added to a twin-screw extruder, and the barrel temperature is controlled at 270℃ for mixing and melting. Then, it is passed through a circular hollow fiber spinneret with an outer diameter of 2.0 mm and an inner diameter of 1.2 mm. The nozzle temperature is controlled at 260℃, and nitrogen gas is injected into the inner diameter of the spinneret at a high temperature nitrogen flow rate of 80 mL / min. The extruded hollow fiber membrane filaments are introduced into a 2-meter-long pure water solidification cooling bath pipe with the temperature controlled at 30℃ for forming. After the outer diameter and wall thickness are measured by a diameter gauge, the membrane filaments are stretched in the length direction at a stretching ratio of 1.4 times by a stretching device, and then wound onto a winding wheel.

[0083] The membrane fibers are wound onto a certain number of winding wheels and placed in a heat-setting oven at 120°C for 3 hours for heat setting. The membrane fibers are then removed from the winding wheels and immersed in a 95% ethanol solution at 70°C for 6 hours to extract the solvent from the membrane fibers. The membrane fibers are then extracted with an 8wt% sodium hydroxide aqueous solution at 70°C for 6 hours. Finally, the membrane is washed with water to obtain a polyvinylidene fluoride hollow fiber porous separation membrane.

[0084] The surface and cross-section of the polyvinylidene fluoride hollow fiber porous separation membrane prepared in this embodiment were photographed using a scanning electron microscope, such as... Figure 1 and Figure 2 As shown. A POROLUX 1000 pore size analyzer was used to measure the pore size and distribution of the membrane, such as... Figure 3 As shown.

[0085] Comparative Example 1

[0086] The method is the same as in Example 1, except that 25% of hydrophobically modified nano-silica (R972, with dimethyldichlorosilane as the hydrophobic modification group and a specific surface area of ​​110±20 m²) is used during mixing. 2 / g), with a stretching ratio of 2.5 times, and other operations and conditions remaining unchanged.

[0087] The surface and cross-section of the hollow fiber porous membrane prepared in this embodiment were photographed using a scanning electron microscope, such as... Figure 4 and Figure 5 As shown. A POROLUX 1000 pore size analyzer was used to measure the pore size and distribution of the membrane, such as... Figure 6 As shown.

[0088]

Example 2

[0089] Weigh out 30% of polyvinylidene fluoride resin according to the mass ratio. 6020 (molecular weight 700,000), 40% hydrophobically modified nano-silica (R974, hydrophobic modification group is dimethyldichlorosilane, specific surface area 170±20m²). 2 The mixture of 18% tributyl acetyl citrate and 12% soybean oil was homogenized in a high-speed mixer to obtain a casting film mixture.

[0090] The mixed powder for casting is passed through a twin-screw extruder, and the barrel temperature is controlled at 280℃ for mixing and melting. Then, it is passed through a circular hollow fiber spinneret with an outer diameter of 2.0 mm and an inner diameter of 1.4 mm. The nozzle temperature is controlled at 260℃, and nitrogen gas is injected into the inner diameter of the spinneret at a high temperature of 90 mL / min. The extruded hollow fiber membrane filaments are introduced into a 2-meter-long pure water solidification cooling bath pipe with the temperature controlled at 40℃ for forming. After the outer diameter and wall thickness are measured by a diameter gauge, the membrane filaments are stretched in the length direction at a stretching ratio of 1.1 times by a stretching device, and then wound onto a winding wheel. The membrane fibers are wound onto a certain number of winding wheels and placed in a heat-setting oven at 110°C for 5 hours for heat setting. The membrane fibers are then removed from the winding wheels and immersed in an isopropanol solution at 40°C for 10 hours to extract the solvent from the membrane fibers. The membrane fibers are then extracted by passing them through a 5wt% sodium hydroxide aqueous solution at 80°C for 10 hours. Finally, the membrane fibers are washed with water to obtain a polyvinylidene fluoride hollow fiber porous separation membrane.

[0091] Comparative Example 2

[0092] Referring to the method of Example 2, the difference is that during the spinning process, the yarn is stretched in the length direction by a stretching device at a stretching ratio of 2.2, while other operations and conditions remain unchanged.

[0093]

Example 3

[0094] Weigh out 50% of the polyvinylidene fluoride resin according to the mass ratio. 6010 (molecular weight 320,000), 15% nano-silica (R8200, hydrophobic modification group is hexamethyldisilazane, specific surface area 160±25m²). 2 The mixture of 20% dioctyl adipate, 10% triglyceride, and 5% anti-aging agent 445 was homogenized in a high-speed mixer to obtain a casting film mixture.

[0095] The mixed powder for casting is passed through a twin-screw extruder, and the barrel temperature is controlled at 240℃ for mixing and melting. Then, it is passed through a circular hollow fiber spinneret with an outer diameter of 2.0 mm and an inner diameter of 1.2 mm. The nozzle temperature is controlled at 240℃, and nitrogen gas is injected into the inner diameter of the spinneret at a high temperature of 100 mL / min. The extruded hollow fiber membrane filaments are introduced into a 2-meter-long pure water solidification cooling bath pipe with the temperature controlled at 30℃ for forming. After the outer diameter and wall thickness are measured by a diameter gauge, the membrane filaments are stretched in the length direction at a stretching ratio of 1.5 times and then wound onto a winding wheel. The membrane fibers are wound onto a certain number of winding wheels and placed in a heat-setting oven at 150°C for 1 hour for heat setting. The membrane fibers are then removed from the winding wheels and immersed in a 98% ethanol solution at 60°C for 10 hours to extract the solvent from the membrane fibers. The membrane fibers are then extracted with a 10wt% sodium hydroxide aqueous solution at 40°C for 4 hours. Finally, the membrane is washed with water to obtain a polyvinylidene fluoride hollow fiber porous separation membrane.

[0096]

Example 4

[0097] Weigh out 32% of polyvinylidene fluoride resin according to the mass ratio. 6020 (molecular weight 700,000), 18% hydrophobically modified nano-silica (R812S, hydrophobic modification group is hexamethyldisilazane, specific surface area 220±25m²). 2 The mixture of 20% dibutyl adipate and 30% castor oil is homogenized in a high-speed mixer to obtain a casting film mixture.

[0098] The mixed powder for casting is passed through a twin-screw extruder, and the barrel temperature is controlled at 220℃ for mixing and melting. Then, it is passed through a nozzle die with a 2.0mm outer diameter and a 1.0mm inner diameter annular spinneret, and the nozzle temperature is controlled at 240℃. Nitrogen gas is injected into the inner diameter of the spinneret at a high temperature of 70mL / min. The extruded hollow fiber membrane filaments are introduced into a 2-meter-long pure water solidification cooling bath pipe with the temperature controlled at 30℃ for forming. After the outer diameter and wall thickness are measured by a diameter gauge, the membrane filaments are stretched in the length direction at a stretching ratio of 1.3 times by a stretching device, and then wound onto a winding wheel. The membrane fibers are wound onto a certain number of winding wheels and placed in a heat-setting oven at 130°C for 3 hours for heat setting. The membrane fibers are then removed from the winding wheels and immersed in a cyclohexane solution at 40°C for 8 hours to extract the solvent from the membrane fibers. The membrane fibers are then extracted with a 6wt% sodium hydroxide aqueous solution at 60°C for 6 hours. Finally, the membrane is washed with water to obtain a polyvinylidene fluoride hollow fiber porous separation membrane.

[0099]

Example 5

[0100] Weigh out 42% of polyvinylidene fluoride resin according to the mass ratio. 6010 (molecular weight 320,000), 20% hydrophobically modified nano-silica (R974, hydrophobic modification group is dimethyldichlorosilane, specific surface area 170±20m²). 2 The mixture of 5% dibutyl phthalate, 30% dioctyl phthalate and 3% UV absorber UV-3030 was mixed evenly in a high-speed mixer to obtain a casting film mixture.

[0101] The mixed powder for casting is passed through a twin-screw extruder, and the barrel temperature is controlled at 250℃ for mixing and melting. Then, it is passed through a nozzle die with a 2.4mm outer diameter and 1.6mm inner diameter annular spinneret, and the nozzle temperature is controlled at 240℃. Nitrogen gas is injected into the inner diameter of the spinneret at a high temperature of 70mL / min. The extruded hollow fiber membrane filaments are introduced into a 2-meter-long pure water solidification cooling bath pipe with the temperature controlled at 30℃ for forming. After the outer diameter and wall thickness are measured by a diameter gauge, the membrane filaments are stretched in the length direction at a stretching ratio of 1.2 times and then wound onto a winding wheel. The membrane fibers are wound onto a certain number of winding wheels and placed in a heat-setting oven at 125°C for 3.5 hours for heat setting. The membrane fibers are then removed from the winding wheels and immersed in an N,N-dimethylacetamide solution at 80°C for 4 hours to extract the solvent from the membrane fibers. The membrane fibers are then extracted with a 7wt% sodium hydroxide aqueous solution at 65°C for 7 hours. Finally, the membrane fibers are washed with water to obtain a polyvinylidene fluoride hollow fiber porous separation membrane.

[0102]

Example 6

[0103] Weigh out 45% of polyvinylidene fluoride resin according to the mass ratio. 6010 (molecular weight 320,000), 21% hydrophobically modified nano-silica (R974, hydrophobic modification group is dimethyldichlorosilane, specific surface area 170±20m²). 2 The mixture of 12% tributyl phosphate and 22% diethyl phthalate was homogenized in a high-speed mixer to obtain a casting film mixture.

[0104] The casting mixture is added to a twin-screw extruder, and the barrel temperature is controlled at 260℃ for mixing and melting. Then, it is passed through a circular hollow fiber spinneret with an outer diameter of 2.0 mm and an inner diameter of 1.2 mm. The nozzle temperature is controlled at 260℃, and nitrogen gas is injected into the inner diameter of the spinneret at a high temperature nitrogen flow rate of 80 mL / min. The extruded hollow fiber membrane filaments are introduced into a 2-meter-long pure water solidification cooling bath pipe with the temperature controlled at 30℃ for forming. After the outer diameter and wall thickness are measured by a diameter gauge, the membrane filaments are stretched in the length direction at a stretching ratio of 1.5 times and then wound onto a winding wheel.

[0105] The membrane fibers are wound onto a certain number of winding wheels and placed in a heat-setting oven at 120°C for 4 hours for heat setting. The membrane fibers are then removed from the winding wheels and immersed in a 90% ethanol solution at 68°C for 8 hours to extract the solvent from the membrane fibers. The membrane fibers are then extracted with a 6wt% sodium hydroxide aqueous solution at 70°C for 7 hours. Finally, the membrane is washed with water to obtain a polyvinylidene fluoride hollow fiber porous separation membrane.

[0106] Comparative Example 3

[0107] The method is the same as in Example 1, except that 34% dibutyl phthalate is used for mixing (i.e., no weak solvent is added, only a strong solvent is used), while other operations and conditions remain unchanged.

[0108] Comparative Example 4

[0109] The method is the same as in Example 1, except that 34% dioctyl phthalate is used for mixing (i.e., no strong solvent is used, only a weak solvent is used), while other operations and conditions remain unchanged.

[0110] Comparative Example 5

[0111] The method is the same as in Example 1, except that the hydrophobically modified nano-silica is replaced with an equal amount of nano-silica (200, unmodified, with a specific surface area of ​​200±25m²). 2 / g), other operations and conditions remain unchanged. The spinning process is normal, but the surface of the film filament is very rough, it is very easy to break when stretched, it cannot be properly filamented, and there are large void defects on the surface.

[0112] The separation performance of the hollow fiber porous separation membranes prepared in Examples 1-6 and Comparative Examples 1-5 was evaluated mainly by three characteristic parameters: the average pore size of the membrane, the pure water flux, and the mechanical strength. The results are shown in Table 1.

[0113] Table 1. Performance test results of porous separation membranes

[0114]

[0115] The performance test results of the porous membranes prepared for material separation in Examples 1-6 and Comparative Examples 1-5 show that the porous membranes prepared by the above method have an outer diameter of 1.52-2.01 mm, an inner diameter of 1.13-1.60 mm, a pore size of 0.08-0.44 μm, and a pure water flux of 2284-8427 L / m³. 2 At 0.1 mPa and 25℃, the tensile breaking strength ranged from 9.25 to 12.69 MPa, and the tensile elongation at break ranged from 136% to 238%. It can be seen that the porous membranes prepared using this method have higher flux, more uniform pore size distribution, higher strength, and better elongation.

[0116] In addition, in comparison Figure 1 and 4 It can be seen that the hollow fiber porous membrane prepared in Example 1 of this invention has a more uniform surface pore size and more consistent surface pores, without the defect of large pores. In contrast, the membrane prepared in the comparative example has large pores to a certain extent and a wider pore size distribution. Figure 3 and 6 It can also be seen that the porous membranes prepared in the examples have better batch stability compared to the comparative examples. This is important in practical applications.

[0117] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A method for producing a polyvinylidene fluoride hollow fiber porous separation membrane, characterized by, The method comprises the following steps: 1) mixing polyvinylidene fluoride resin, a mixed solvent composed of a strong solvent and a weak solvent for polyvinylidene fluoride resin, a hydrophobically modified inorganic additive having a specific surface area of 150 to 300 m2 / g, and, optionally, an auxiliary agent uniformly to obtain a cast film mixture; 2 / g, a hydrophobically modified inorganic additive having a specific surface area of 150 to 300 m2 / g, and, optionally, an auxiliary agent uniformly to obtain a cast film mixture; 2) melt the casting mixture of step 1) in an extruder, then extrude through a hollow fiber spinneret, cool and set, stretch 1.1-1.5 times, to obtain a hollow fiber membrane filament; 3) heat set the hollow fiber membrane filament of step 2), then extract the solvent and inorganic additive in the membrane filament to obtain the polyvinylidene fluoride hollow fiber porous separation membrane; In step 1), the weight average molecular weight of the polyvinylidene fluoride resin is 300,000-600,000; The mass ratio of the strong solvent to the weak solvent in the mixed solvent is 0.1-2; the strong solvent refers to a solvent in which 20wt% of the polyvinylidene fluoride resin is completely dissolved at a temperature that is 10-20% lower than the melting point of the polyvinylidene fluoride resin; and the weak solvent refers to a solvent in which 20wt% of the polyvinylidene fluoride resin is completely dissolved at a temperature that is 10% or less lower than the melting point of the polyvinylidene fluoride resin.

2. The production method according to claim 1, characterized by, The raw material weight percentage composition in step 1) comprises: 30-50% of polyvinylidene fluoride resin; 30-50% of mixed solvent composed of strong solvent and weak solvent of polyvinylidene fluoride resin; a specific surface area of 150 to 300 m 2 15 to 40 % of a hydrophobically modified inorganic additive having a specific surface area of 150 to 300 m 0-5% of optional auxiliary agent; The sum of the weight percentages of the raw materials is 100%.

3. The production method according to claim 2, characterized by, In the raw material weight percentage composition in step 1), the polyvinylidene fluoride resin is 35-45%; a specific surface area of 150 to 300 m 2 20 to 35 % of a hydrophobically modified inorganic additive having a specific surface area of 150 to 300 m 0-3% of optional auxiliary agent.

4. The preparation method according to claim 1, characterized in that, The polyvinylidene fluoride resin in step 1) is a homopolymer or copolymer of polyvinylidene fluoride.

5. The preparation method according to claim 1, characterized in that, The strong solvent of the polyvinylidene fluoride resin in step 1) is a mixture of one or more of dibutyl phthalate, benzoate, sebacate, adipate, phosphate, acetyl tributyl citrate, trioctyl trimellitate, ethylene bis-stearamide, and γ-butyrolactone.

6. The production method according to claim 5, wherein The strong solvent of the polyvinylidene fluoride resin is a mixture of one or more of dibutyl phthalate, dibutyl sebacate, dibutyl adipate, dioctyl adipate, tributyl phosphate, acetyl tributyl citrate, and γ-butyrolactone.

7. The preparation method according to claim 1, characterized in that, The weak solvent of the polyvinylidene fluoride resin in step 1) is a mixture of one or more of dioctyl phthalate, diethyl phthalate, glycerol triacetate, benzophenone, soybean oil, diphenyl carbonate, castor oil, and glycerol monoacetate.

8. The production method according to claim 7, characterized by, The weak solvent of the polyvinylidene fluoride resin is a mixture of one or more of dioctyl phthalate, diethyl phthalate, glycerol triacetate, and soybean oil.

9. The method of claim 1, wherein, Step 1) the hydrophobically modified inorganic additive has a specific surface area of 170 to 250 m 2 / g.

10. The method of claim 1, wherein, The hydrophobically modified inorganic additive in step 1) is nano-silicon dioxide.

11. The method of claim 1, wherein, In the hydrophobically modified inorganic additive in step 1), the hydrophobic modification group is selected from one or more of hexamethyldisilazane, dimethyldichlorosilane, and octamethylcyclotetrasiloxane.

12. The method of claim 1, wherein, In the melting process in step 2) performed in an extruder, the temperature is controlled in the range of 220-280°C; and the extruder is a double-screw extruder.

13. The method of claim 1, wherein, In the process of extruding through a hollow fiber spinneret in step 2), high-temperature nitrogen gas is passed through the inside of the hollow fiber spinneret.

14. The method of claim 13, wherein, The temperature of the nitrogen gas is 80-200°C.

15. The preparation method according to claim 13, characterized in that, The flow rate of the high-temperature nitrogen gas is 70-100 mL / min.

16. The method of claim 1, wherein, In the heat setting process in step 3), the temperature is 110-150°C, and the time is 1-5 hours.

17. The method of claim 1, wherein, Step 3) the extraction removes the solvent and inorganic additives in the membrane filaments, wherein the extraction removing the solvent and the extraction removing the inorganic additives are included; The extraction removing the solvent uses an extractant selected from one or more of n-hexane, cyclohexane, gasoline, ethanol, N,N-dimethylformamide, N,N-dimethylacetamide, dichloromethane, trichloromethane and isopropyl alcohol; The extraction removing the inorganic additives uses an extractant selected from a sodium hydroxide solution.

18. The method of claim 17, wherein, The extraction removing the solvent is performed at a temperature of 40-80℃ for 4-10 hours.

19. The method of claim 17, wherein, The extraction removing the inorganic additives is performed at a temperature of 40-80℃ for 4-10 hours.

20. The method of claim 17, wherein, The sodium hydroxide solution is a 5-10wt% sodium hydroxide aqueous solution.

21. A polyvinylidene fluoride hollow fiber porous separation membrane prepared by the method of any one of claims 1-20.

22. The polyvinylidene fluoride hollow fiber porous separation membrane prepared by the method of any one of claims 1-20 or the polyvinylidene fluoride hollow fiber porous separation membrane of claim 21 is applied in the fields of bio-fermentation, chemical medicine, raw medicine, biological medicine and food industry, and can realize the separation or concentration of substances with a particle size of 0.1 μm or above in the system.

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