TW202005709A - Hollow polymer fibres as filtration membranes - Google Patents

Abstract

The invention concerns a porous hollow fibre comprising a copolymer comprising repeating units derived from vinylidene fluoride and repeating units derived from at least one second comonomer, and having a Young"s modulus of less than 40 MPa. The invention also concerns a filtration module comprising said hollow fibre, a method for manufacturing said hollow fibre, the use of said hollow fibre to treat effluent, and a method for defouling said hollow fibre.

Description

Hollow polymer fiber as filter membrane

Field of invention The present invention relates to a porous hollow polymer fiber useful as a filter membrane, especially for microfiltration or ultramicrofiltration; and a method for manufacturing the hollow fiber.

Background of the invention Membrane filtration, especially ultrafiltration, plays an important part in the treatment of natural water or aqueous effluent. For example, it makes it possible to remove clay particles and microorganisms contained in river water, thus creating clear, disinfected water. In the field of water treatment, especially the use of hollow fiber type polymer membranes for filtration.

However, the accumulation of objects retained by the film will gradually cause the film to become dirty and cause a reduction in its production capacity. Therefore, the film must be regularly decontaminated and cleaned. There are typically two types of deposits that stain the film: deposits loosely attached to the film, also known as reversible dirt, which are usually removed by physical cleaning, such as backwashing; and strongly adhered or adsorbed on the film The deposits on the film, also known as irreversible dirt, must be treated by chemical cleaning.

In order to improve the physical cleaning by backwashing, different solutions have been conceived.

For example, the paper by Y. Ye et al., Evolution of fouling deposition and removal on hollow fibre membrane during filtration with periodical backwash, Desalination, vol. 283, pp. 198-205, 2011, which teaches the use of an air flushing method combined with backwashing To increase the effectiveness of the latter, especially because the dirt removed by backwashing will be entrained away from the surface of the film, thus limiting the immediate redeposition of the dirt on the film.

Document WO 2016/011128 describes a membrane module comprising a non-woven substrate and an elastic microfiltration membrane, for example, a polyurethane based on polyether and surrounded by two porous support members.

Document US 4,816,160 describes a filtration method using elastic hollow fiber membranes in polypropylene, in which the hollow fibers of the membrane are cooled before receiving the purified liquid and then countercurrent to the gas.

Document US 5,643,455 describes a method of filtering on elastic hollow fiber membranes in polypropylene, which includes removing the remaining in the fiber by passing a pressurized liquid and then a pressurized gas through the pores of the fiber Solid steps.

Document US 6,159,373 discloses a gas backwashing method that expels dirt in and on the elastic hollow fibers of the membrane by generating explosive decompression.

Other strategies are to improve the resistance of the film to chemical cleaning.

For example, the document US 2009/0101600 describes a film with high resistance to chemical products used in chemical cleaning. The main components of these films are PVDF (polyvinylidene fluoride) resins with a special degree of crystallinity and specific surface area.

There is a real need to provide a filter membrane that makes it possible to improve the removal of reversible dirt and in particular to increase the effectiveness of backwashing.

Summary of the invention The invention first relates to a porous hollow fiber comprising a copolymer comprising units derived from vinylidene fluoride and units derived from at least one second comonomer and having a Young's modulus of less than 40 MPa.

In some embodiments, the present invention relates to a porous hollow fiber, which includes a copolymer comprising units derived from vinylidene fluoride and units derived from at least one second comonomer, the hollow fibers having Young's The modulus is 2 to 30 MPa, and the ratio of its average outer diameter to its average inner diameter is 1.2 to 2.

In certain embodiments, the hollow fiber consists essentially of or consists of a copolymer comprising units derived from vinylidene fluoride and units derived from at least one second comonomer.

In some specific examples, the second co-monomer system is selected from the group consisting of hexafluoropropylene, trifluoroethylene, chlorotrifluoroethylene, 1-chloro-1-fluoroethylene, tetrafluoroethylene and Its combination; the second comonomer is preferably hexafluoropropylene.

In certain embodiments, the unit derived from vinylidene fluoride is present in the copolymer in a weight amount of at least 50% by weight, preferably at least 75% by weight, more preferably at least 85% by weight and up to 99% by weight.

In some specific examples, the hollow fiber has a Young's modulus of 1 to 30 MPa, preferably 2 to 20 MPa, and more preferably 3 to 10 MPa.

In some specific examples, the hollow fiber has a Young's modulus of 3 to 13 MPa and a ratio of its average outer diameter to its average inner diameter of 1.4 to 1.8.

In some specific examples, the hollow fiber has pores with an average diameter of 1 nanometer to 2 micrometers, preferably 1 nanometer to 100 nanometers.

In some specific examples, the hollow fiber has an average outer diameter of 500 to 2000 microns, preferably 800 microns to 1400 microns.

The invention also relates to a filtration module, which contains at least one hollow fiber such as described above.

The invention further relates to a method for manufacturing hollow fibers such as described above, which comprises: Dissolving a copolymer comprising units derived from vinylidene fluoride and units derived from at least one second comonomer in a solvent to form a cotton wool; Forming the glue cotton into a hollow fiber; Glue cotton formed by agglomeration.

In some embodiments, the coagulation of the formed wadding is performed by contacting the formed wadding with a non-solvent coagulation solution including the copolymer.

In some specific examples, the coagulation of the formed wadding is carried out by changing the temperature of the formed wadding, preferably the temperature is lowered.

The invention further relates to the use of hollow fibers such as described above or filter modules such as described above which are used to treat effluent.

The invention further relates to a method for decontaminating hollow fibers such as described above, which comprises: Subject the hollow fiber to mechanical stress so as to cause deformation of the hollow fiber; The hollow fiber is selectively backwashed.

In some embodiments, the mechanical stress is caused by the pressure applied by the backwash liquid and/or the stretching of the hollow fiber.

The invention further relates to a method for filtering effluent, which comprises: Let the effluent come into contact with hollow fibers such as described above; The decontamination of the hollow fiber is performed using a decontamination method such as described above.

The present invention satisfies the needs expressed above. More specifically, it provides a hollow fiber that can be reversibly deformed, which allows the membrane to be physically cleaned more efficiently, thus allowing increased productivity of the filtration method and reduced operating costs, in particular, the consumption of previously filtered water and Consumption of chemical cleaning products.

This is achieved by the presence of a copolymer containing units derived from vinylidene fluoride and units derived from at least one second comonomer in the hollow fiber, and through the specific Young's modulus of the fiber. This reversibly deformable fiber allows the surface of the fiber to undergo macroscopic deformation under the effect of mechanical stress. The deformation of the surface of the fiber causes shear at the interface between the fiber and the dirt deposit covering it, thus promoting the separation of dirt (and dirt not only present in pores) adhering to the surface of the fiber. In addition, the elastic nature of the fiber allows the fiber hole to reversibly expand in diameter under the effect of the mechanical stress, thus improving the displacement of dirt present in the hole. The reversible expansion of the hole can also allow the use of a stronger backwash flow.

In other specific examples, when the hollow fiber according to the present invention is deformed under the effect of mechanical stress, its hole diameter is still fixed or almost fixed. This prevents the hole from potentially expanding irreversibly over time so that it can maintain good film selectivity over time. This can obviously be achieved by incorporating a specific Young's modulus (2 to 30 MPa) and a specific average outer diameter/average inner diameter ratio (1.2 to 2) in the fiber.

The present invention also has one or preferably several of the following excellent features: The deformation of the fiber is reversible, so in some specific examples, when the mechanical stress stops, the holes will restore their original size, which allows maintaining good fiber properties in terms of separation properties; When the mechanical stress stops, the fiber returns to its original shape; The hole size is well controlled; The fiber has high water permeability; The fiber has high long-term resistance to chemical products used in chemical cleaning.

Detailed description of the preferred embodiment The following provides a more detailed, non-limiting description of the invention.

Unless otherwise described, all percentages related to quantity are weight percentages.

In this application, the term «copolymer containing units derived from vinylidene fluoride and units derived from at least one second comonomer» is intended to be interpreted as «one or more units containing units derived from vinylidene fluoride and The meaning of a copolymer derived from units of at least one second comonomer».

In the present application, the copolymer comprising units derived from vinylidene fluoride and units derived from at least one second comonomer is also referred to as «vinylidene fluoride copolymer». Hollow fiber and filter module

The first object of the present invention consists of a pair of porous hollow fibers useful for filtration. The hollow fiber comprises a copolymer comprising units derived from vinylidene fluoride and units derived from at least one second comonomer. It has a Young's modulus of less than 40 MPa. This Young's modulus gives the fiber the ability to deform under relatively weak stress.

More particularly, the fiber has a Young's modulus of preferably 2 to 30 MPa and the ratio of its average outer diameter to its average inner diameter is 1.2 to 2. This Young's modulus grants the fiber the ability to deform under relatively weak stress while keeping the hole diameter almost fixed.

The Young's modulus can be measured by performing a tensile test on a 50 mm hollow fiber test piece. Then, the stress-strain curve of the hollow fiber is determined. Stress (expressed in pressure units) is the ratio between the tension of the test piece and the cross-sectional surface, and strain (dimensionless) is the relative tension of the test piece. The Young's modulus is provided by the initial slope of the stress-strain curve (ie, the slope of the elastic section).

Preferably, the second co-monomer system is selected from the group consisting of hexafluoropropylene, vinyl fluoride or vinyl fluoride, vinyl chloride (1-chloro-1-fluoroethylene and 1-chloro -2-fluoroethylene), trifluoroethylene, chlorodifluoroethylene (especially, 1-chloro-2,2-difluoroethylene), 1-bromo-2,2-difluoroethylene, bromotrifluoroethylene, Chlorotrifluoroethylene, tetrafluoroethylene, trifluoropropene (especially, 3,3,3-trifluoropropene), tetrafluoropropene (especially, 2,3,3,3-tetrafluoropropene or 1, 3,3,3-tetrafluoropropene), chlorotrifluoropropenes (especially, 2-chloro-3,3,3-trifluoropropene), pentafluoropropenes (especially, 1,1,3,3 ,3-pentafluoropropene or 1,2,3,3,3-pentafluoropropene); a perfluoroalkyl vinyl ether of the general formula Rf-O-CF-CF ₂ , Rf is an alkyl group, preferably C1 To C4, especially PPVE (perfluoropropyl vinyl ether) and PMVE (perfluoromethyl vinyl ether); and combinations thereof. In a particularly preferred mode, the copolymer is a copolymer of vinylidene fluoride and hexafluoropropylene (ie, a copolymer formed of units derived from vinylidene fluoride and units derived from hexafluoropropylene).

Advantageously, the copolymer comprises at least 50% by weight, preferably at least 75% by weight, preferably at least 85% by weight units derived from vinylidene fluoride, and up to 99% by weight derived from vinylidene fluoride Unit. These copolymers can be obtained using known polymerization methods, such as solution, emulsion or suspension polymerization. In some specific examples, the copolymer is prepared in the emulsion method in the absence of fluorinated surfactants.

The hollow fiber may have a Young's modulus of less than 1 MPa, or a range of 1 to 5 MPa, or 5 to 10 MPa, or 10 to 15 MPa, or 15 to 20 MPa, or 20 to 25 MPa, or 25 to 30 MPa, or 30 to 35 MPa, or 35 to 40 MPa. The range that may be mentioned is 1 to 30 MPa, or 2 to 20 MPa, or 3 to 10 MPa.

In a more excellent manner, the hollow fiber has a Young's modulus ranging from 2 to 5 MPa; or 5 to 10 MPa, or 10 to 15 MPa, or 15 to 20 MPa, or 20 to 25 MPa, or 25 to 30 MPa . The range of 3 to 13 MPa, or 4 to 80 MPa is particularly preferable.

The hollow fiber of the present invention preferably has an average outer diameter of 500 microns to 600 microns, or 600 microns to 700 microns, or 700 microns to 800 microns, or 800 microns to 900 microns, or 900 microns to 1000 microns, or 1000 microns to 1100 microns, or 1100 microns to 1200 microns, or 1200 microns to 1300 microns, or 1300 microns to 1400 microns, or 1400 microns to 1500 microns, or 1500 microns to 1600 microns, or 1600 microns to 1700 microns, or 1700 microns to 1800 Microns, or 1800 microns to 1900 microns, or 1900 microns to 2000 microns. Preferably, the fiber has an average outer diameter of 500 to 2000 microns, more preferably 800 to 1400 microns, or 1000 to 1400 microns. The average outer diameter can be measured in a photograph obtained with a scanning electron microscope or an optical microscope on a cross section of a hollow fiber that has previously been freeze-ruptured.

The hollow fiber of the present invention preferably has an average inner diameter of 20 microns to 100 microns, or 100 microns to 200 microns, or 200 microns to 300 microns, or 300 microns to 400 microns, or 400 microns to 500 microns, or 500 microns to 600 microns, or 600 microns to 700 microns, or 700 microns to 800 microns, or 800 microns to 900 microns, or 900 microns to 1000 microns, or 1000 microns to 1100 microns, or 1100 microns to 1200 microns, or 1200 microns to 1300 Microns, or 1300 microns to 1400 microns, or 1400 microns to 1500 microns, or 1500 microns to 1600 microns. The average inner diameter can be measured in a photograph obtained with a scanning electron microscope or an optical microscope on a hollow fiber cross-section that has previously been freeze-ruptured.

The average wall thickness of the fiber is advantageously 10 microns to 50 microns, or 50 microns to 100 microns, or 100 microns to 150 microns, or 150 microns to 200 microns, or 200 microns to 250 microns, or 250 microns to 300 microns, Or 300 microns to 350 microns, or 350 microns to 400 microns, or 400 microns to 450 microns, or 450 microns to 500 microns. Preferably, the average wall thickness of the fiber is 100 to 400 microns, more preferably 150 to 250 microns. The average wall thickness of the fiber can be measured in a photograph, where the photograph is obtained with a scanning electron microscope or an optical microscope on a hollow fiber section that has previously been freeze-ruptured.

The ratio of the average outer diameter of the hollow fiber to the average inner diameter of the hollow fiber may be 1.08 to 2.5, more preferably 1.6 to 2. In some specific examples, the ratio of the average outer diameter of the hollow fiber to the average inner diameter of the hollow fiber is 1.08 to 1.1, or 1.1 to 1.2, or 1.2 to 1.3, or 1.3 to 1.4, or 1.4 to 1.5, or 1.5 to 1.6, or 1.6 to 1.7, or 1.7 to 1.8, or 1.8 to 1.9, or 1.9 to 2, or 2 to 2.1, or 2.2 to 2.3, or 2.3 to 2.4, or 2.4 to 2.5.

More preferably, the ratio of the average outer diameter of the hollow fiber to the average inner diameter of the hollow fiber is 1.2 to 2, more preferably 1.4 to 1.8. In some specific examples, the ratio of the average outer diameter of the hollow fiber to the average inner diameter of the hollow fiber is 1.2 to 1.3, or 1.3 to 1.4, or 1.4 to 1.5, or 1.5 to 1.6, or 1.6 to 1.7, or 1.7 to 1.8, or 1.8 to 1.9, or 1.9 to 2.

Preferably, the hollow fiber has a Young's modulus of 3 to 13 MPa and a ratio of its average outer diameter to its average inner diameter of 1.4 to 1.8, and more preferably a Young's modulus of 4 to 8 MPa and its average The ratio of the outer diameter to its average inner diameter is about 1.6. In some specific examples, the hollow fiber has a Young's modulus system of 6 to 30 MPa and a ratio of its average outer diameter to its average inner diameter of 1.2 to 1.4; or a Young's modulus system of 4 to 13 MPa and its average The ratio of the outer diameter to the average inner diameter is 1.4 to 1.6; or the Young's modulus is 3 to 8 MPa and the ratio of the average outer diameter to the average inner diameter is 1.6 to 1.8; or the Young's modulus is 2 to 6 The ratio of MPa and its average outer diameter to its average inner diameter is 1.8 to 2.

The hollow fiber of the present invention may include pores having an average diameter ranging from 1 nanometer to 2 micrometers, and particularly 1 nanometer to 5 nanometers, or 5 nanometers to 10 nanometers, or 10 nanometers to 20 nanometers, or 20 nm to 50 nm, or 50 nm to 80 nm, or 80 nm to 100 nm, or 100 nm to 200 nm, or 200 nm to 300 nm, or 300 nm to 400 Nanometer, or 400 nanometer to 500 nanometer, or 500 nanometer to 600 nanometer, or 600 nanometer to 700 nanometer, or 700 nanometer to 800 nanometer, or 800 nanometer to 900 nanometer, or 900 Nanometer to 1 micrometer, or 1 micrometer to 1.5 micrometers, or 1.5 micrometers to 2 micrometers. In a particularly preferred manner, the hollow fiber may contain pores having an average diameter ranging from 1 to 100 nanometers, for example, when the hollow fiber is to be used as an ultrafiltration membrane. The hollow fiber may also advantageously contain pores having an average diameter of 100 nanometers to 1 micrometer, for example, when the hollow fiber is intended to be used as a microfiltration membrane. The average diameter of the hole can be measured in a photo, where the photo is obtained with a scanning electron microscope on the outer surface of the fiber.

The copolymer comprising units derived from vinylidene fluoride and units derived from at least one second comonomer may be the sole polymer composition of the hollow fiber.

Alternatively, the hollow fiber may contain another polymer. In this case, the vinylidene fluoride copolymer is preferably present in an amount of at least 50% by weight relative to the total weight of the polymer, preferably at least 60% by weight, more preferably at least 70% by weight. Examples of other polymers that can be used alone or in combination are polyvinylpyrrolidone (PVP) and/or polyethylene glycol (PEG), especially as pore forming and/or hydrophilic agents; homopolymerization of acrylic polymers Substances or copolymers; and fluorinated polymers, for example, homopolymers of polyvinylidene fluoride.

In a particularly preferred manner, the hollow fiber consists essentially of or consists of a copolymer comprising units derived from vinylidene fluoride and units derived from at least one second comonomer.

«Hollow fiber consisting essentially of a copolymer comprising units derived from vinylidene fluoride and units derived from at least one second comonomer» means that the hollow fiber contains at least 80% by weight of vinylidene fluoride copolymer It is preferably at least 90% by weight, or at least 95% by weight or at least 99% by weight.

In other specific examples, the hollow fiber contains at least 50% by weight, preferably at least 60% by weight, and more preferably at least 70% by weight of the vinylidene fluoride copolymer relative to the total weight of the hollow fiber.

The hollow fiber may contain one or more additives, especially selected from the group consisting of polymethyl methacrylate (PMMA), polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), partial Saponified polyvinyl alcohols; inorganic salts such as lithium chloride (LiCl), magnesium chloride (MgCl ₂ ), zinc chloride (ZnCl ₂ ); oligomers, polymers (such as those cited above), surfactants, Amphiphilic block copolymers, metal and/or ceramic (nano) particles, carbon nanotubes, or a combination thereof. These additives are preferably present in the fiber in an amount of 0 to 50% by weight, more preferably 0 to 40% by weight, further preferably 0 to 30% by weight, and most preferably 0 to 20% by weight, or 0 To 10% by weight, or 0 to 5% by weight.

In another aspect, the present invention relates to a filter module, particularly a filter module for microfiltration or ultramicrofiltration, which contains at least one hollow fiber such as described above. The filter module may contain 1 to 1,000,000 hollow fibers. The filter module may be a bundle module, a flat module or a plate module; or it may have any other form.

A further object of the invention is to use a hollow fiber or filter module such as described above to treat the effluent, especially water. The filtration is preferably performed from the outside of the fiber toward the inside of the fiber.

A further object of the invention is a method for decontaminating hollow fibers such as described above, which includes subjecting the hollow fibers to mechanical stress in order to cause deformation of the hollow fibers. The decontamination method may also include backwashing of the hollow fiber. This backwashing is preferably performed simultaneously with the step of subjecting the hollow fiber to mechanical stress. The backwashing includes passing a fluid, preferably liquid, from the inside of the fiber toward the outside of the fiber.

The mechanical stress can be of any type. For example, it may be composed of, for example, the pressure applied by a fluid, preferably a liquid, more preferably a backwash liquid; and/or the stretching of the fiber.

The pressure applied by the liquid may be 0.01 to 0.5 MPa, preferably 0.03 to 0.2 MPa. In some specific examples, the pressure applied by the liquid is 0.01 MPa to 0.05 MPa, or 0.05 MPa to 0.1 MPa, or 0.1 MPa to 0.15 MPa, or 0.15 MPa to 0.2 MPa, or 0.2 MPa to 0.25 MPa, or 0.25 MPa to 0.3 MPa, or 0.3 MPa to 0.35 MPa, or 0.35 MPa to 0.4 MPa, or 0.4 MPa to 0.45 MPa, or 0.45 MPa to 0.5 MPa.

When drawn, the fiber may have a draw of 1% to 20%, preferably 3 to 7%.

A further object of the invention is a method for filtering effluent, which comprises: Let the effluent come into contact with hollow fibers such as described above; The decontamination of the hollow fiber is performed using a decontamination method such as described above. Manufacturing method

The hollow fiber of the present invention can be prepared using a one-phase conversion method.

Therefore, a further object of the present invention is a method for preparing fibers such as described above, which includes: Dissolving a copolymer containing vinylidene fluoride units and units derived from at least one second monomer in a solvent to form a cotton wool; Forming the glue cotton into a hollow fiber; Glue cotton formed by agglomeration.

Suitable solvents are, for example, dimethylacetamide (DMAc), N-methyl-pyrrolidone (NMP), dimethylformamide (DMF), dimethylsulfone (DMSO ₂ ), dimethylmethylene Ash (DMSO), trialkyl phosphate, tetrahydrofuran (THF), acetone, benzaldehyde, acetophenone, diphenyl ketone, hexamethylphosphoramide (HMPA), tetramethylurea (TMU), triethyl phosphate Ester (TEP), trimethyl phosphate (TMP) or a combination thereof. However, the solvent may be any other solvent or combination of solvents capable of dissolving the vinylidene fluoride copolymer.

After the vinylidene fluoride copolymer is dissolved, the rubber wool preferably contains 10 to 40% by weight of the vinylidene fluoride copolymer.

The cotton wool may contain additives, preferably in a weight amount of 0% to 50%. For example, these additives may be polymethyl methacrylate (PMMA), polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), partially saponified polyvinyl alcohol; inorganic salts such as lithium chloride (LiCl) , Magnesium chloride (MgCl ₂ ), zinc chloride (ZnCl ₂ ). They can also be non-solvents for vinylidene fluoride copolymers, for example, water, ethanol, methanol, glycerol or propylene glycol; oligomers, polymers, surfactants, amphiphilic block copolymers, metals and/or ceramics (Nano) Particle type additives, or carbon nanotubes. They can also be a combination of two or more of the above additives.

The forming of the cotton wool into hollow fibers is preferably performed by extruding the rubber wool through a ring die. For example, the ring die may have an outer diameter of 0.25 to 5 mm, preferably 0.5 to 2.5 mm; and an inner diameter of 0.1 to 2 mm, preferably 0.2 to 1 mm. The flow rate may be between 0.1 and 72 ml/min, more particularly between 6 and 11 ml/min. Advantageously, a solution called the internal liquid and capable of forming the internal volume of the hollow fiber and the cotton wool are co-extruded. The internal liquid is preferably a non-solvent including the vinylidene fluoride copolymer, such as water, methanol, ethanol, glycerin, propylene glycol; and if necessary, one or more solvents of the vinylidene fluoride copolymer, preferably The same as those included in the rubber cotton, for example, NMP by weight between 0 and 100%, especially between 15 and 70%; and one or more additives such as LiCl or PEG. The temperature can be between 10 and 100°C, especially between 30 and 80°C. The extrusion rate can be between 0.1 and 18 ml/min, more particularly between 1 and 7 ml/min.

Advantageously, the formation of the hollow fiber of the rubber wool is aided by drawing the fiber. If it is not possible to modify the formation by stretching, the stretching speed is equal to the extrusion rate of the cotton wool. If modification is made to form rayon by stretching, the stretching speed is different from the extrusion rate, especially higher than the extrusion rate. The stretching speed may be between 1 and 40 meters/minute, more particularly between 7 and 23 meters/minute.

The coagulated cotton formed by the coagulation is preferably performed by contacting the formed crystalline cotton with a non-solvent coagulation solution including the copolymer. This non-solvent can be in liquid form, vapor form, or sequentially in vapor and then liquid form. In particular, it may be water, methanol, ethanol, glycerin and/or propylene glycol. The coagulation solution may also include one or more solvents of the vinylidene fluoride copolymer, preferably the same as those included in the rubber wool, for example, NMP with a weight concentration between 0 and 50% by weight, in particular Between 0 and 10% by weight; and one or more additives, such as LiCl or PEG.

Optionally or in addition to non-solvent treatment, the agglomeration of the formed cotton wool can be carried out by changing the temperature of the formed cotton wool, preferably by lowering its temperature. As for the embodiments, the temperature of the rubber wool may be particularly between 10 and 130°C, more particularly between 50 and 80°C; in particular, the temperature of the coagulation tank may be between 0 and 100°C, more particularly between 40 and Between 70℃.

Generally speaking, during the manufacture of the fiber, the ratio of the average outer diameter of the hollow fiber to the average inner diameter of the hollow fiber can be reduced by the following: Reduce the flow rate of rubber wool; Increase the internal liquid flow rate; Combining reducing the flow rate of rubber wool and increasing the internal liquid flow rate; Combining increased internal liquid flow rate and increased stretching speed; Combined to reduce the flow rate of rubber wool and increase the stretching speed; Generally speaking, during the manufacture of the fiber, the Young's modulus of the hollow fiber can be reduced by reducing the drawing speed; Increase the porosity of the film, for example, by reducing the amount of vinylidene fluoride copolymer or by increasing the amount of additive in the rubber wool. Examples

The following examples illustrate but do not limit the invention. Preparation of hollow fiber

By phase inversion, hollow fibers were prepared from a copolymer of vinylidene fluoride and hexafluoropropylene containing 11% by weight of hexafluoropropylene.

The operating conditions used to manufacture these fibers are as follows: Rubber wool composition: 20% of the copolymer of vinylidene fluoride and hexafluoropropylene containing 11% by weight of hexafluoropropylene 12% by weight average molecular weight Mw = 10,000 g‧ Mole ^-1 polyethylene glycol 68% dimethyl sulfite (DMSO) Internal liquid composition: water condensate tank composition: water temperature: rubber wool: T=50°C internal liquid: T=49°C condensate tank ：T=49℃ Flow rate: Glue wool: Q=6.24ml‧min- ¹ Internal liquid: Q=6.0ml‧min- ¹ Stretching speed: 22m‧min- ¹ jet-stretch ratio : 1.39 Air gap: 20 cm.

The membrane module is formed by clustering 7 hollow fibers together in a bundle (hereinafter referred to as "elastic membrane").

The Young's modulus of this film is 7MPa. The breaking load of the film is 0.56 Newton and the breaking stress is 1.46 MPa.

A reference film (hereinafter referred to as "reference film") was also manufactured. The hollow fiber is a homopolymer of polyvinylidene fluoride, prepared by forming a cotton wool containing 15% by weight of polyvinylidene fluoride homopolymer, 3% by weight of lithium chloride and 82% of NMP .

The operating conditions used to manufacture the reference fiber are as follows: Glue cotton composition: 15% polyvinylidene fluoride homopolymer (Kynar® PVDF HSV900) 3% lithium chloride (LiCl) 82% N-methyl -2-Pyrrolidone (NMP) Internal liquid composition: 85% water 15% N-methyl-2-pyrrolidone coagulation tank composition: Water temperature: Glue cotton: T=50℃ Internal liquid: T= 49℃ Coagulation tank: T=49℃ Flow rate: Glue cotton: Q=8.5ml‧min- ¹ Internal liquid: Q=2.1ml‧min- ¹ Stretching speed: 8m‧min- ¹ Spray head stretching ratio: 1.14 Air gap: 18 cm.

The Young's modulus of this film is 55 MPa. The breaking load of this film is 2 Newton and the breaking stress is 8 MPa.

反洗研究The properties of the elastic film and reference film are summarized in the following table:

Backwash study

The elastic film and the reference film are used to filter the suspension of bentonite in water, so as to form the same deposit on different fibers of the two films. Filtering from the outside of the fiber toward the inside, dirt is deposited on the outer surface of the fiber.

Then, the two films were simultaneously backwashed: the water system passed from the inside to the outside of the fiber at a pressure of 0.9 bar, and the removal of dirt from the fiber was observed over time with a video camera.

Photos from the video acquired by the camera at different backwashing times are provided in FIGS. 1A to 1F. The elastic film is on the left of the photo, and the reference film is on the right. The dirt is separated from the hollow fiber in the form of filaments.

It can be seen at t=0 seconds (Figure 1A), only two fiber bundles can be seen, and no decontamination is observed.

At t=3 seconds (Figure 1B), a few dirt filaments began to separate from the fibers of the elastic film. The reference film did not separate dirt filaments.

Between t=6 seconds and t=12 seconds (Figures 1C, 1D, and 1E), some dirt filaments continued to separate from the fibers of the elastic film, but no decontamination was observed in the reference film.

At t=15 seconds (Fig. 1F), there were continued thin filaments separating from the elastic film, but the deposit on the reference film still adhered.

Therefore, it can be seen that the hollow fiber of the present invention decontaminates faster and more efficiently than the rigid polyvinylidene fluoride homopolymer fiber.

Furthermore, the backwash of the elastic film, that is, the water permeability and the outer diameter of the fiber from the inside to the outside of the fiber are measured as a function of the applied backwash pressure.

The results are provided in the table below.

The relative pore radius is provided relative to the pore radius at a backwash pressure of 0.3 bar, and is estimated by permeability measurement by considering that the permeability system is proportional to the radius to the fourth power.

It can be seen that, generally speaking, the fiber outer diameter of the elastic film increases with the backwash pressure but the hole diameter is still almost fixed.

FIGS. 1A to 1F are photographs taken from the video recorded by the video camera during the backwashing described in the following embodiments. These photos correspond to different times when the backwash started: Figure 1A at 0 seconds; Figure 1B at 3 seconds; Figure 1C at 6 seconds; Figure 1D at 9 seconds; Figure 1E at 12 seconds; Figure 1F at 15 seconds.

In all of these photos, hollow fiber bundles of polyvinylidene fluoride homopolymer (reference film) are on the right of the photo, and hollow fiber bundles of copolymers of vinylidene fluoride and hexafluoropropylene (elastic films of the invention) ) Is on the left of the photo.

Claims (15)

A porous hollow fiber comprising a copolymer comprising units derived from vinylidene fluoride and units derived from at least one second comonomer, the hollow fibers having a Young's modulus of 2 to 30 MPa and The ratio of its average outer diameter to its average inner diameter is 1.2 to 2. The hollow fiber as claimed in claim 1, which consists of or consists essentially of a copolymer comprising units derived from vinylidene fluoride and units derived from at least one second comonomer. The hollow fiber according to claim 1 or 2, wherein the second co-monomer system is selected from the group consisting of hexafluoropropylene, trifluoroethylene, chlorotrifluoroethylene, 1-chloro-1-fluoroethylene, Tetrafluoroethylene and combinations thereof; the second comonomer is preferably hexafluoropropylene. The hollow fiber according to any one of claims 1 to 3, wherein the unit derived from vinylidene fluoride is present in the copolymer in a weight amount of at least 50% by weight, preferably at least 75% by weight, more preferably It is at least 85% by weight and at most 99% by weight. The hollow fiber according to any one of claims 1 to 4, which has a Young's modulus of 3 to 13 MPa and a ratio of its average outer diameter to its average inner diameter of 1.4 to 1.8. The hollow fiber according to any one of claims 1 to 5, which contains pores having an average diameter of 1 nm to 2 μm, preferably 1 nm to 100 nm. The hollow fiber according to any one of claims 1 to 6, which has an average outer diameter of 500 to 2000 microns, preferably 800 microns to 1400 microns. A filtration module comprising at least one hollow fiber as in any one of claims 1 to 7. A method for manufacturing the hollow fiber according to any one of claims 1 to 7, which comprises: Dissolving a copolymer in a solvent to form a cotton wool, the copolymer comprising units derived from vinylidene fluoride and units derived from at least one second comonomer; Hollow fiber is formed from the rubber wool; Glue cotton formed by agglomeration. The method of claim 9, wherein the coagulation of the formed wadding is performed by contacting the formed wadding with a non-solvent coagulation solution including the copolymer. The method according to claim 9 or 10, wherein the coagulation of the formed wadding is carried out by changing the temperature of the formed wadding, preferably the temperature is lowered. A use of the hollow fiber as claimed in any one of claims 1 to 7 or the filter module as claimed in 8, which is used to treat effluent. A method for decontaminating hollow fibers as claimed in any one of claims 1 to 7, comprising: Subject the hollow fiber to mechanical stress so as to cause deformation of the hollow fiber; The hollow fiber is selectively backwashed. The decontamination method according to claim 13, wherein the mechanical stress is the pressure applied by the backwash liquid and/or the stretching of the hollow fiber. A method for filtering effluent, which includes: Let the effluent come into contact with the hollow fiber according to any one of claims 1 to 7; Decontaminate the hollow fiber using the decontamination method as in claim 13 or 14.

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