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

Abstract

The invention relates to a polyvinylidene fluoride hollow fiber porous separation membrane as well as a preparation method and application thereof, and the preparation method comprises the following steps: 1) uniformly mixing polyvinylidene fluoride resin, a mixed solvent consisting of a strong solvent and a weak solvent of the polyvinylidene fluoride resin, a hydrophobically modified inorganic additive with the specific surface area of 150-300m < 2 > / g and an optional auxiliary agent, obtaining a casting membrane mixture; (2) adding the membrane casting mixture obtained in the step (1) into an extruder for melting, then extruding through a hollow fiber spinning nozzle, cooling and shaping, and stretching by 1.1-1.5 times to obtain hollow fiber membrane filaments; and (3) carrying out heat setting treatment on the hollow fiber membrane filaments in the step (2), and extracting to remove the solvent and the inorganic additive in the membrane filaments, so as 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 and environmentally friendly. The industrial production is easy. The membrane is preferably used in the field of material separation.

Description

Technical Field

[0001] The invention belongs to the technical field of microfiltration membranes, and in particular relates to a polyvinylidene fluoride hollow fiber porous separation membrane and a preparation method and application thereof. Background Art

[0002] At present, with the advancement of technology, the industrial application of microfiltration membranes has been very extensive and has become one of the new industrial unit operations. It can be used for separation, concentration, purification of biological products, pharmaceutical products and food industry; it can also be used in terminal treatment devices in blood treatment, wastewater treatment and ultrapure water preparation.

[0003] In recent years, with the shortage of water resources, the global demand for high-quality water, the growth of the biopharmaceutical industry, and the growth of the food processing industry, microfiltration membranes have become increasingly popular as a viable alternative to thermal treatment in reducing bacteria and improving the shelf life of dairy products. With the increasing demand for applications, the market for microfiltration membranes is growing rapidly. In particular, as the industrial ecosystem actively applies microfiltration membrane technology, such as continuous fermentation is more cost-effective than batch processing, this will also have a better positive impact on the growth of the microfiltration membrane market.

[0004] Since the fields of biopharmaceuticals, food processing, and biological fermentation have high requirements for product quality, in order to ensure product quality, microfiltration membrane products used in industrial systems usually need to have uniform pore size distribution, high flux, stable performance, good chemical resistance, and long life.

[0005] Existing microfiltration membrane products generally use polysulfone or polyvinylidene fluoride materials, which are prepared by non-solvent induced phase separation methods. They are difficult to meet the needs of existing industrial applications in terms of alkali resistance, membrane strength, and uniformity of pore size distribution. Therefore, it is urgent to develop a microfiltration membrane product with better performance.

[0006] Regarding the preparation method of microfiltration membranes of different materials, the patent JP2017136555A discloses a method for preparing a hollow fiber membrane with high water permeability, excellent breaking strength and breaking elongation. This membrane can achieve a particle interception rate of more than 99% for 0.26-0.34μm and a breaking elongation of more than 50%. The membrane material uses a polysulfone-based material, and a hollow fiber membrane is prepared by adding a hydrophilic polymer and using non-solvent induced phase separation. The patent does not disclose the pore size and distribution of the membrane, and can only have good water permeability while ensuring the breaking strength and elongation.

[0007] Patent CN1458859A discloses a method for preparing polyvinylidene fluoride hollow fiber membranes, in which organic pore formers and inorganic fine powders are mixed in polyvinylidene fluoride resins, melt-formed at a temperature as high as 250°C, and then the organic pore formers and inorganic fine powders are extracted to form membranes. Such inorganic fine powders added to the ingredients are prone to agglomeration, which makes it easy to form relatively large void defects in the membrane after extraction, widens the pore size distribution of the membrane, and reduces its interception effect on pollutants.

[0008] The microfiltration membranes prepared by the above-mentioned prior art have a wide pore size distribution during use, making it difficult to maintain a high flux while ensuring the interception effect. At the same time, there are problems such as 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 hollow fiber porous separation membrane and a preparation method thereof, which is based on polyvinylidene fluoride resin, through a thermally induced phase separation method, using a hydrophobically modified inorganic material with a high specific surface area, and a combination of a strong solvent and a weak solvent for polyvinylidene fluoride, and a subsequent stretching process to prepare a porous separation membrane. The polyvinylidene fluoride hollow fiber porous separation membrane prepared in this way is a microfiltration membrane product with uniform pore size distribution, excellent performance, and good specification consistency.

[0010] At the same time, the purpose of the present invention is also to provide the application of the polyvinylidene fluoride hollow fiber porous separation membrane in a material separation system, which can be specifically applied to the fields of biological fermentation, chemical drugs, raw materials, biopharmaceuticals, food industry, etc., and can achieve the separation or concentration of substances with a particle size of more than 0.1 μm in the system.

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

[0012] The present 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 to 300 m 2 / g of hydrophobically modified inorganic additives and optional auxiliary agents are mixed uniformly to obtain a casting film mixture;

[0014] 2) adding the cast membrane mixture of step 1) into an extruder to melt, and then extruding through a hollow fiber spinneret, cooling and shaping, and stretching to obtain a hollow fiber membrane;

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

[0016] In a specific embodiment, the weight percentage composition of the raw materials in step 1) includes:

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

[0018] 30-50% of a mixed solvent consisting of a strong solvent and a weak solvent for polyvinylidene fluoride resin, such as 30%, 35%, 40%, 45%, 50%, etc.;

[0019] 15-40% of hydrophobically modified inorganic additives, such as 15%, 20%, 25%, 30%, 35%, 40%, etc., preferably 20-35%;

[0020] Optional auxiliary agent 0-5%, such as 0%, 1%, 2%, 3%, 4%, 5%, etc., preferably 0-3%;

[0021] The sum of the weight percentages of each raw material is 100%.

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

[0023] Preferably, the weight average molecular weight of the polyvinylidene fluoride resin is 200,000 to 700,000, for example, 200,000, 300,000, 400,000, 500,000, 600,000, 700,000, etc., preferably 300,000 to 600,000.

[0024] In a specific embodiment, in step 1), the mixed solvent composed of a strong solvent and a weak solvent for polyvinylidene fluoride resin, 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 the strong solvent and the weak solvent in the present invention are distinguished based on the solubility strength of the polyvinylidene fluoride resin. Specifically, the strong solvent refers to a solvent in which the dissolution temperature of 20wt% of the polyvinylidene fluoride resin can be lower than 10-20% of the melting point of the polyvinylidene fluoride resin itself when 20wt% of the polyvinylidene fluoride resin is completely dissolved in the solvent. The weak solvent refers to a solvent in which the dissolution temperature of 20wt% of the polyvinylidene fluoride resin can be lower than 10% of the melting point of the polyvinylidene fluoride resin itself when 20wt% of the polyvinylidene fluoride resin is completely dissolved in the solvent; wherein 20wt% of the polyvinylidene fluoride resin means that the concentration of the polyvinylidene fluoride resin in the mixture with the solvent is 20wt%. It can be understood that: when the melting point of the polyvinylidene fluoride resin itself is A, the temperature at which a strong solvent completely dissolves 20wt% of the polyvinylidene fluoride resin is 10-20% lower than A, and the temperature at which a weak solvent completely dissolves 20wt% of the polyvinylidene fluoride resin is 10% or less lower than A; for ease of understanding, further examples are given, the melting point of the polyvinylidene fluoride resin itself is generally 170-175°C, for example, taking a polyvinylidene fluoride resin with a melting point of 170°C, the temperature at which a strong solvent completely dissolves 20wt% of the polyvinylidene fluoride resin is 136-153°C (10-20% lower than 170°C), and the temperature at which a weak solvent completely dissolves 20wt% of the polyvinylidene fluoride resin is <170°C and >153°C (less than 10% lower than 170°C).

[0026] Preferably, the strong solvent of the polyvinylidene fluoride resin is a mixture of one or more of dibutyl phthalate, benzoates, sebacic acid esters, adipates, phosphates, acetyl tributyl citrate, trioctyl trimellitate, ethylene bis stearic acid amide, and γ-butyrolactone, more preferably a mixture of one or more of dibutyl phthalate, dibutyl sebacic acid ester, dibutyl adipate, dioctyl adipate, tributyl phosphate, acetyl tributyl citrate, and γ-butyrolactone;

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

[0028] The preparation method of the present invention uses a strong solvent and a weak solvent for the polyvinylidene fluoride resin in combination, which can better adjust the phase separation temperature of the resin, make the phase separation more uniform, and obtain a more consistent pore size of the membrane.

[0029] In a specific embodiment, the hydrophobically modified inorganic additive in step 1) has a molecular weight of 150 to 300 m 2 / g high specific surface area, such as 150m 2 / g, 180m 2 / g, 200m 2 / g, 220m 2 / g, 250m 2 / g, 280m 2 / g、300m 2 / g, etc., preferably 170 to 250 m 2 / g; Inorganic additives with high specific surface area are usually smaller in particle size, with more in number at the same addition ratio, and better in dispersion in the system. Therefore, during the stretching process, highly dispersed inorganic additives can be used as the core (also understood as the separation point in the stretching), providing more stretching separation points, forming denser pores, which is beneficial to improving the flux and porosity of the porous membrane.

[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 the present invention are known products in the art, and their sources are not limited. They can be commercially available products, such as Evonik's AEROSIL R974, R812S, etc.; they can also be prepared in-house according to existing published methods, for example, by referring to the method disclosed in patent IN253288B.

[0032] In a specific embodiment, the optional auxiliary agent in step 1) is a conventional additive in the field, including one or more of an antioxidant, a heat stabilizer, an ultraviolet absorber, and an anti-aging agent. In specific applications, conventional selections of various auxiliary agents in the field can be adopted. The present invention has no special requirements here. For example,

[0033] The antioxidant may be one or more of antioxidants 1330, 1010, 626, etc.;

[0034] The heat stabilizer can be one or more of zinc stearate, zinc-calcium composite stabilizer, 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 and the like.

[0037] In the present invention, in step 1), all raw materials are preferably mixed evenly using a high-speed mixing device to obtain a casting film mixture.

[0038] In a specific embodiment, the melting process of adding the extruder in step 2) is a conventional operation in the field, for example, the temperature is controlled in the range of 220-280°C, for example, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, etc.; and the extruder is a twin-screw extruder.

[0039] In a specific embodiment, during the extrusion through the hollow fiber spinneret in step 2), high-temperature nitrogen is passed through the hollow fiber spinneret, and the high-temperature nitrogen is passed through the hollow fiber spinneret during the extrusion process to help the porous membrane form the inner diameter of the pores;

[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 an annular spinneret, and the present invention has no special requirements; preferably, the annular 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 a specific embodiment, 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 the membrane is rolled up. Specifically, a laser diameter gauge is added during the stretching process, and the outer diameter of the membrane filament is tested during the spinning process and adjusted according to the data. This can make the specifications of the formed membrane filaments more uniform and more effectively achieve the stability of the membrane filament performance.

[0043] Since the effect of stretching is to separate the core from the resin with the core as the center, if the number of cores is insufficient or the stretching ratio is too high, stretching holes of the polymer itself will appear on the surface. These holes are tear holes, which are generally long and thin. Although the flux can be increased, the interception effect will be greatly reduced. In the preparation method of the present invention, low-ratio stretching is adopted, and the stretching process uses a hydrophobically modified inorganic additive as the core, which can avoid the above problems, expand the pore size, and improve the flux and porosity.

[0044] In a specific embodiment, the heat setting treatment in step 3) has a temperature of 110-150°C, for example 110°C, 120°C, 130°C, 140°C, 150°C, etc., and a time of 1-5 hours, for example 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, etc.

[0045] In a specific embodiment, the step 3) extracting and removing the solvent and inorganic additives in the membrane fibers includes extracting and removing the solvent and extracting and removing the inorganic additives;

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

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

[0048] The extraction to remove the inorganic additives uses an extractant selected from a sodium hydroxide solution, preferably a 5-10 wt% sodium hydroxide aqueous solution;

[0049] Preferably, the extraction temperature is 40-80°C, for example 40°C, 50°C, 60°C, 70°C, 80°C, etc., and the extraction time is 4-10 hours, for example 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, etc.

[0050] The present 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 to 2.0 mm, a wall thickness of 0.1 to 0.5 mm, a porosity of 50 to 80%, an average pore size of 0.1 to 0.6 μm, and a pure water flux of 2000 to 10000 L / m 2 ·hr@0.1MPa,25℃,tensile strength at break is 9~20MPa,tensile elongation at break 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, high mechanical strength, etc., and can be used in the fields of biological fermentation, chemical drugs, raw materials, biopharmaceuticals, food industry, etc., and can achieve the separation or concentration of substances with a particle size of more than 0.1 μm in the system.

[0053] Compared with modern technologies, the technical solution of the present invention has the following beneficial effects:

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

[0055] Figure 1 This is a scanning electron microscope photograph of the outer surface of the porous membrane prepared in Example 1;

[0056] Figure 2 A scanning electron microscope photograph of a cross section of the porous membrane prepared in Example 1;

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

[0058] Figure 4 This is a scanning electron microscope photograph of the outer surface of the porous membrane prepared in Comparative Example 1;

[0059] Figure 5 This is a scanning electron microscope photograph of the cross section of the porous membrane prepared in Comparative Example 1;

[0060] Figure 6 The pore size and distribution diagram of the porous membrane prepared in Comparative Example 1. DETAILED DESCRIPTION

[0061] The present invention is further described below by means of specific examples. The examples described in the present invention are only used to illustrate the present invention and do not limit the scope of the present invention.

[0062] In the embodiments and comparative examples of the present invention, the sources of the main raw materials used are as follows. Unless otherwise specified, other raw materials and reagents were purchased from commercial sources:

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

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

[0065] Strong solvents, weak solvents and additives are basically bulk petrochemical products and can be obtained through commercial channels. The main performance evaluation methods used in the embodiments and comparative examples of the present invention are as follows:

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

[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 liquid and pore 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 pores tested by the POROLUX1000 pore size analyzer is used to characterize the pore size distribution of the membrane pore size. Compared with 1, the larger the value, the wider the pore size distribution, and the smaller the value, the narrower the pore size distribution.

[0073] (3) Pure water flux (LMH) is defined as the volume of water that passes through the effective membrane area per unit time under certain operating pressure conditions. The calculation formula is:

[0074] J=Q / At

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

[0076] Q—pure water permeation, L;

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

[0078] t—time for collecting 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 machine at a certain pulling speed (50 mm / min).

[0080] [Example 1]

[0081] Weigh 40% of polyvinylidene fluoride resin ( 1015, molecular weight 600,000), 25% hydrophobically modified nano-silica (R812S, hydrophobic modification group is hexamethyldisilazane, specific surface area 220±25m 2 / g), 10% of dibutyl phthalate, 24% of dioctyl phthalate and 1% of antioxidant 1330 were mixed uniformly in a high-speed mixer to obtain a film casting mixture.

[0082] The casting mixture is added into a twin-screw extruder, and the barrel temperature is controlled at 270°C for mixing and melting. It is then 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°C for the nozzle mold, and nitrogen 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 pipeline controlled at 30°C for molding. The outer diameter and wall thickness are tested by a caliper, and then stretched in the length direction by a stretching device at a stretching ratio of 1.4 times, and then the membrane filaments are wound onto a winding wheel.

[0083] The membrane filaments are wound onto a certain number of winding wheels and placed in a heat-setting oven at 120°C for heat setting for 3 hours. The membrane filaments are removed from the winding wheel and immersed in a 95% ethanol solution at 70°C for extraction for 6 hours to extract the solvent in the membrane filaments. The membrane filaments are then extracted with an 8wt% sodium hydroxide aqueous solution at 70°C for 6 hours and finally 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 example were photographed by scanning electron microscopy. Figure 1 and Figure 2 The pore size and distribution of the membrane were measured using the POROLUX1000 pore size analyzer, as shown in Figure 3 shown.

[0085] [Comparative Example 1]

[0086] The method of Example 1 is referred to, except that 25% of hydrophobically modified nano-silica (R972, the hydrophobic modification group is dimethyldichlorosilane, the specific surface area is 110±20m 2 / g), the stretching ratio was 2.5 times, and other operations and conditions remained unchanged.

[0087] The surface and cross section of the hollow fiber porous membrane prepared in this example were photographed by scanning electron microscopy. Figure 4 and Figure 5 The pore size and distribution of the membrane were measured using the POROLUX1000 pore size analyzer, as shown in Figure 6 shown.

[0088] [Example 2]

[0089] Weigh 30% of polyvinylidene fluoride resin ( 6020, molecular weight 700,000), 40% hydrophobically modified nano-silica (R974, hydrophobic modification group is dimethyldichlorosilane, specific surface area 170±20m 2 / g), 18% of acetyl tributyl citrate and 12% of soybean oil are uniformly mixed in a high-speed mixer to obtain a mixture for film casting.

[0090] The mixed powder for casting membrane is passed through a twin-screw extruder, and the cylinder temperature is controlled at 280°C for mixing and melting. It is then 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°C in a nozzle mold, and nitrogen is injected into the inner diameter of the spinneret at a high-temperature nitrogen flow rate of 90 mL / min. The extruded hollow fiber membrane filaments are introduced into a 2-meter-long pure water solidification cooling bath pipeline controlled at 40°C for molding. The outer diameter and wall thickness are tested with a caliper, and then stretched in the length direction with a stretching ratio of 1.1 times by a stretching device, and then the membrane filaments are wound onto a winding wheel. The membrane filaments are wound onto a certain number of winding wheels and placed in a heat-setting oven at 110°C for heat setting for 5 hours. The membrane filaments are removed from the winding wheel and immersed in an isopropanol solution controlled at 40°C for 10 hours to extract the solvent in the membrane filaments. The membrane filaments are then extracted with a 5wt% sodium hydroxide aqueous solution at 80°C for 10 hours and finally washed with water to obtain a polyvinylidene fluoride hollow fiber porous separation membrane.

[0091] [Comparative Example 2]

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

[0093] [Example 3]

[0094] Weigh 50% of polyvinylidene fluoride resin ( 6010, molecular weight 320,000), 15% nano-silica (R8200, hydrophobic modification group is hexamethyldisilazane, specific surface area 160±25m 2 / g), 20% of dioctyl adipate, 10% of triacetin and 5% of antioxidant 445 are mixed uniformly in a high-speed mixer to obtain a mixture for film casting.

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

[0096] [Example 4]

[0097] Weigh 32% of polyvinylidene fluoride resin ( 6020, molecular weight 700,000), 18% hydrophobically modified nano-silica (R812S, hydrophobic modification group is hexamethyldisilazane, specific surface area 220±25m 2 / g), 20% of dibutyl adipate, and 30% of castor oil are uniformly mixed in a high-speed mixer to obtain a mixture for film casting.

[0098] The mixed powder for casting membrane is passed through a twin-screw extruder, and the barrel temperature is controlled at 220°C for mixing and melting. It is then passed through a circular spinneret with an outer diameter of 2.0 mm and an inner diameter of 1.0 mm. The nozzle temperature is controlled at 240°C in a nozzle mold, and nitrogen is injected into the inner diameter of the spinneret at a high-temperature nitrogen flow rate of 70 mL / min. The extruded hollow fiber membrane filaments are introduced into a 2-meter-long pure water solidification cooling bath pipeline controlled at 30°C for molding. The outer diameter and wall thickness are tested with a caliper, and then stretched in the length direction by a stretching device at a stretching ratio of 1.3 times, and then the membrane filaments are wound onto a winding wheel. The film is wound onto a certain number of winding wheels and placed in a heat-setting oven at 130°C for heat setting for 3 hours. The membrane filament is removed from the winding wheel and immersed in a cyclohexane solution controlled at 40°C for extraction for 8 hours to extract the solvent in the membrane filament. The film is then extracted with a 6wt% sodium hydroxide aqueous solution at 60°C for 6 hours and finally washed with water to obtain a polyvinylidene fluoride hollow fiber porous separation membrane.

[0099] [Example 5]

[0100] Weigh 42% of polyvinylidene fluoride resin ( 6010, molecular weight 320,000), 20% hydrophobically modified nano-silica (R974, hydrophobic modification group is dimethyldichlorosilane, specific surface area 170±20m 2 / g), 5% of dibutyl phthalate, 30% of dioctyl phthalate and 3% of ultraviolet absorber UV-3030 are mixed uniformly in a high-speed mixer to obtain a mixture for film casting.

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

[0102] [Example 6]

[0103] Weigh 45% of polyvinylidene fluoride resin ( 6010, molecular weight 320,000), 21% hydrophobically modified nano-silica (R974, hydrophobic modification group is dimethyldichlorosilane, specific surface area 170±20m 2 / g), 12% of tributyl phosphate and 22% of diethyl phthalate are uniformly mixed in a high-speed mixer to obtain a film casting mixture.

[0104] The casting mixture is added into a twin-screw extruder, the barrel temperature is controlled at 260°C for mixing and melting, and then 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°C for the nozzle mold, and nitrogen 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 pipeline controlled at 30°C for molding. The outer diameter and wall thickness are tested by a caliper, and then stretched in the length direction by a stretching device at a stretching ratio of 1.5 times, and then the membrane filaments are wound onto a winding wheel.

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

[0106] [Comparative Example 3]

[0107] Refer to the method of Example 1, except that 34% of dibutyl phthalate is used in the mixing (that is, no weak solvent is added, only a strong solvent is used), and other operations and conditions remain unchanged.

[0108] [Comparative Example 4]

[0109] Refer to the method of Example 1, except that 34% of dioctyl phthalate is used during mixing (ie, no enhanced solvent is used, only weak solvent is used), and other operations and conditions remain unchanged.

[0110] [Comparative Example 5]

[0111] Refer to the method of Example 1, except that the hydrophobically modified nano-silica is replaced by an equal amount of nano-silica (200, not hydrophobically modified, with a specific surface area of ​​200±25m 2 / g), other operations and conditions remain unchanged. The spinning process is normal, but the surface of the membrane fiber is very rough, the fiber is easily broken when stretched, and the fiber cannot be collected normally. There are large pores 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, namely, the average pore size of the membrane, pure water flux and mechanical strength. The results are shown in Table 1.

[0113] Table 1 Porous separation membrane performance test results

[0114]

[0115] From the performance test results of the porous membranes prepared in Examples 1 to 6 and Comparative Examples 1 to 5 for material separation, it can be seen that the outer diameter of the porous membrane prepared by the above method is 1.52 to 2.01 mm, the inner diameter is 1.13 to 1.60 mm, the membrane pore size is 0.08 to 0.44 μm, and the pure water flux is 2284 to 8427 L / m 2 h@0.1mPa, 25℃, tensile strength at break is 9.25~12.69Mpa, and tensile elongation at break is 136~238%. It can be seen that the porous membrane prepared by this method has a larger flux, a more uniform pore size distribution, a higher strength, and a better elongation.

[0116] In addition, compared Figure 1 and 4 It can be seen that the surface pore size of the hollow fiber porous membrane prepared by Example 1 of the present invention is more uniform, the surface pores are more consistent, and there is no defect of large pores, while the surface pores of the membrane prepared in the comparative example will have large pores to a certain extent and a wide pore size distribution. Figure 3 and 6 It can also be seen that the batch stability of the porous membrane prepared in the embodiment is also better than that in the comparative example, which is very important in practical applications.

[0117] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this field can make several improvements and supplements without departing from the method of the present invention. These improvements and supplements should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a polyvinylidene fluoride hollow fiber porous separation membrane, characterized in that: The following steps are involved: 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 to 300 m 2 / g of hydrophobically modified inorganic additives and optional auxiliary agents are mixed uniformly to obtain a casting film mixture; 2) adding the cast membrane mixture of step 1) into an extruder to melt, and then extruding through a hollow fiber spinneret, cooling and shaping, and stretching by 1.1 to 1.5 times to obtain a hollow fiber membrane; 3) The hollow fiber membrane filaments of step 2) are subjected to heat setting treatment, and then the solvent and inorganic additives in the membrane filaments are removed by extraction to obtain the polyvinylidene fluoride hollow fiber porous separation membrane.

2. The preparation method according to claim 1, characterized in that: Step 1) The raw materials are composed by weight percentage: Polyvinylidene fluoride resin 30-50%, preferably 35-45%; 30-50% of a mixed solvent consisting of a strong solvent and a weak solvent for polyvinylidene fluoride resin; Specific surface area is 150~300m 2 / g of hydrophobically modified inorganic additives 15-40%, preferably 20-35%; Optional auxiliary agent 0-5%, preferably 0-3%; The sum of the weight percentages of each raw material is 100%.

3. The preparation method according to claim 1 or 2, characterized in that: Step 1) The polyvinylidene fluoride resin is a homopolymer or copolymer of polyvinylidene fluoride; Preferably, the weight average molecular weight of the polyvinylidene fluoride resin is 200,000 to 700,000, preferably 300,000 to 600,000.

4. The preparation method according to claim 1 or 2, characterized in that: Step 1) the mixed solvent composed of a strong solvent and a weak solvent for polyvinylidene fluoride resin, wherein the mass ratio of the strong solvent to the weak solvent in the mixed solvent is 0.1 to 2; Preferably, the strong solvent of the polyvinylidene fluoride resin is a mixture of one or more of dibutyl phthalate, benzoates, sebacic acid esters, adipates, phosphates, acetyl tributyl citrate, trioctyl trimellitate, ethylene bis stearic acid amide, and γ-butyrolactone, more preferably a mixture of one or more of dibutyl phthalate, dibutyl sebacic acid ester, dibutyl adipate, dioctyl adipate, tributyl phosphate, acetyl tributyl citrate, and γ-butyrolactone; Preferably, the weak solvent of the polyvinylidene fluoride resin is a mixture of one or more of dioctyl phthalate, diethyl phthalate, triacetin, benzophenone, soybean oil, diphenyl carbonate, castor oil, glycerol monoacetate, and diphenylmethane, and more preferably a mixture of one or more of dioctyl phthalate, diethyl phthalate, triacetin, soybean oil, and castor oil.

5. The preparation method according to claim 1 or 2, characterized in that: Step 1) The specific surface area of ​​the hydrophobically modified inorganic additive is 150 to 300 m 2 / g, preferably 170 to 250 m 2 / g; Preferably, the hydrophobically modified inorganic additive is nano-silica; wherein the hydrophobic modifying group is preferably one or more of hexamethyldisilazane, dimethyldichlorosilane, and octamethylcyclotetrasiloxane.

6. The preparation method according to claim 1, characterized in that: Step 2) adding the melt to the extruder, controlling the temperature in the range of 220-280° C.; the extruder is a twin-screw extruder; and / or In step 2), during the extrusion through the hollow fiber spinneret, high-temperature nitrogen is passed through the hollow fiber spinneret; Preferably, the nitrogen temperature is 80-200° C.; preferably, the high-temperature nitrogen flow rate is 70-100 mL / min.

7. The preparation method according to claim 1, characterized in that: The stretching in step 2) is performed by stretching the film 1.1 to 1.5 times in the length direction.

8. The preparation method according to claim 1, characterized in that: Step 3) the heat setting treatment is performed at a temperature of 110 to 150° C. for 1 to 5 hours; and / or Step 3) extracting and removing the solvent and inorganic additives in the membrane fibers, including extracting and removing the solvent and extracting and removing the inorganic additives; The extraction and removal of solvent uses an extractant selected from one or more of n-hexane, cyclohexane, gasoline, ethanol, N,N-dimethylformamide, N,N-dimethylacetamide, dichloromethane, chloroform and isopropanol; Preferably, the extraction temperature is 40 to 80°C and the extraction time is 4 to 10 hours; The extraction to remove the inorganic additives uses an extractant selected from a sodium hydroxide solution, preferably a 5-10 wt% sodium hydroxide aqueous solution; Preferably, the extraction temperature is 40 to 80° C., and the extraction time is 4 to 10 hours.

9. A polyvinylidene fluoride hollow fiber porous separation membrane prepared by the method according to any one of claims 1 to 8.

10. The polyvinylidene fluoride hollow fiber porous separation membrane prepared by the method according to any one of claims 1 to 8 or the polyvinylidene fluoride hollow fiber porous separation membrane according to claim 9 can be used in the fields of biological fermentation, chemical drugs, raw materials, biopharmaceuticals, and food industries to separate or concentrate substances with a particle size of 0.1 μm or more in the system.

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