WO2018088232A1 - 多孔性中空糸膜及び多孔性中空糸膜の製造方法 - Google Patents
多孔性中空糸膜及び多孔性中空糸膜の製造方法 Download PDFInfo
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- WO2018088232A1 WO2018088232A1 PCT/JP2017/038805 JP2017038805W WO2018088232A1 WO 2018088232 A1 WO2018088232 A1 WO 2018088232A1 JP 2017038805 W JP2017038805 W JP 2017038805W WO 2018088232 A1 WO2018088232 A1 WO 2018088232A1
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- Prior art keywords
- hollow fiber
- fiber membrane
- porous hollow
- filtration
- producing
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- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/26—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a solid phase from a macromolecular composition or article, e.g. leaching out
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- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
- D01F6/00—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof
- D01F6/02—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds
- D01F6/08—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds from polymers of halogenated hydrocarbons
- D01F6/12—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds from polymers of halogenated hydrocarbons from polymers of fluorinated hydrocarbons
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2315/00—Details relating to the membrane module operation
- B01D2315/06—Submerged-type; Immersion type
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2323/00—Details relating to membrane preparation
- B01D2323/08—Specific temperatures applied
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2323/00—Details relating to membrane preparation
- B01D2323/08—Specific temperatures applied
- B01D2323/082—Cooling
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2323/00—Details relating to membrane preparation
- B01D2323/15—Use of additives
- B01D2323/21—Fillers
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2325/00—Details relating to properties of membranes
- B01D2325/02—Details relating to pores or porosity of the membranes
- B01D2325/0283—Pore size
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2325/00—Details relating to properties of membranes
- B01D2325/02—Details relating to pores or porosity of the membranes
- B01D2325/0283—Pore size
- B01D2325/02834—Pore size more than 0.1 and up to 1 µm
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2325/00—Details relating to properties of membranes
- B01D2325/04—Characteristic thickness
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2325/00—Details relating to properties of membranes
- B01D2325/24—Mechanical properties, e.g. strength
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2327/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers
- C08J2327/02—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment
- C08J2327/12—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
- C08J2327/16—Homopolymers or copolymers of vinylidene fluoride
Definitions
- the present invention relates to a porous hollow fiber membrane and a method for producing a porous hollow fiber membrane.
- Porous hollow fiber membranes have a wide range of operating conditions including high blocking performance that can reliably remove bacteria such as Cryptosporidium and turbid components, high water permeability for treating large amounts of water, chemical cleaning and high operating pressure. Three performances of high strength that can be used for a long time are required.
- a filtration method using a porous hollow fiber membrane there are two methods, an internal pressure filtration method for filtering from the inner surface side to the outer surface side of the membrane and an external pressure filtration method for filtering from the outer surface side to the inner surface side.
- an external pressure filtration method that can ensure a large filtration area is mainly used. Therefore, since the hollow fiber membrane is not crushed during the filtration operation, the porous hollow fiber membrane is required to have high strength in the external pressure direction, that is, high compression strength.
- the methods for reducing the resistance during filtration and the pressure loss in the hollow fiber membrane there is a method of reducing the film thickness and increasing the inner diameter of the hollow fiber membrane. It was difficult to achieve both.
- Patent Document 1 discloses a method for producing a porous hollow fiber membrane by a thermally induced phase separation method, but although there is a description of compression resistance strength, the viewpoint of improving the filtration performance by reducing the film thickness is It was difficult to achieve both high filtration performance and compression resistance.
- An object of the present invention is to provide a porous hollow fiber membrane having high strength suitable for filtration and excellent in water permeability, and a method for producing the porous hollow fiber membrane.
- the present invention has sufficient strength to withstand long-term operation, and has improved water permeability by reducing resistance during filtration and pressure loss in the hollow fiber membrane.
- An object of the present invention is to provide a hollow fiber membrane and a method for producing the porous hollow fiber membrane.
- the present invention is as follows.
- the variation coefficient of the thickness of the trunk forming the surface on the filtration side is preferably 80% or less.
- the porosity of the surface on the filtration side is preferably 32% or more.
- the thickness of the trunk forming the filtration side surface is preferably 0.20 ⁇ m or more and 20 ⁇ m or less.
- the inner diameter is preferably 0.75 mm or more, the compression strength is 0.30 MPa or more, and it is preferably a hollow fiber having a three-dimensional network structure.
- the porous hollow fiber membrane of the present invention is preferably composed of at least two layers.
- the porous hollow fiber membrane of the present invention is preferably composed of at least two layers, the porosity of the surface before filtration is 32% to 60%, and the pore diameter is 500 nm or less.
- the hollow fiber membrane module of the present invention is a hollow fiber membrane module having a hollow fiber membrane bundle and fixed portions at both ends of the hollow fiber membrane bundle, wherein one end of the fixed portion is a hollow portion of the hollow fiber membrane.
- the other end of the fixing part is an external pressure type hollow fiber membrane module that opens the hollow part of the hollow fiber membrane and performs filtration from the outside to the inside of the hollow fiber membrane where the hollow fiber membrane is exposed.
- the method for producing a porous hollow fiber membrane of the present invention comprises a porous hollow fiber comprising at least two layers as described above, having a porosity of 32% to 60% on the surface before filtration and having a pore diameter of 500 nm or less.
- a method for producing a membrane wherein ⁇ T is a difference between a discharge temperature at a discharge port of a melt-kneaded material, which is a raw material of a porous hollow fiber membrane, and a temperature in a coagulation bath for solidifying the melt-kneaded product, and the solidification bath from the discharge port
- the temperature drop rate ⁇ T / t is 180 ° C./s or more and 340 ° C./s or less when the time during which the hollow melt-kneaded product passes through the idle running portion up to the liquid level is defined as idle running time t. It is characterized by that.
- the hollow melt-kneaded material passes through a free running portion between the melt-kneaded material discharge port and the liquid level of the coagulation bath for solidifying the melt-kneaded material.
- the idle running time is preferably 0.50 seconds or more.
- the raw material of the melt-kneaded product is preferably three components of a thermoplastic resin, an inorganic fine powder, and a solvent.
- the inorganic fine powder is preferably silica.
- thermoplastic resin is preferably polyvinylidene fluoride (PVDF).
- the melt-kneaded product used for producing a layer including the filtration-side surface in the porous hollow fiber membrane is 35% by mass or more and 48% by mass or less. It is preferable to have a thermoplastic resin concentration.
- the melt-kneaded product used for producing a layer including the surface on the filtration hollow side of the porous hollow fiber membrane is 20% by mass or more and 35% by mass or less. It is preferable to have a thermoplastic resin concentration.
- a solvent satisfying the condition of the parameter P represented by the following formula is used when producing a layer including the surface before filtration in the porous hollow fiber membrane. It is preferable.
- P (( ⁇ dm ⁇ dp) 2 + ( ⁇ pm ⁇ pp) 2 + ( ⁇ hm ⁇ hp) 2 ) 0.5 ⁇ 7.8
- ⁇ dm and ⁇ dp represent the dispersion force terms of the solvent and polyvinylidene fluoride, respectively
- ⁇ pm and ⁇ pp represent the dipole binding force terms of the solvent and polyvinylidene fluoride, respectively
- ⁇ hm and ⁇ hp represent the solvent and polyvinylidene fluoride, respectively.
- Each hydrogen bond term is shown.
- a solvent satisfying the condition of parameter P represented by the following formula is used when producing a layer including the filtration side surface in the porous hollow fiber membrane. It is preferable.
- P (( ⁇ dm ⁇ dp) 2 + ( ⁇ pm ⁇ pp) 2 + ( ⁇ hm ⁇ hp) 2 ) 0.5 > 7.8
- ⁇ dm and ⁇ dp represent the dispersion force terms of the solvent and polyvinylidene fluoride, respectively
- ⁇ pm and ⁇ pp represent the dipole binding force terms of the solvent and polyvinylidene fluoride, respectively
- ⁇ hm and ⁇ hp represent the solvent and polyvinylidene fluoride, respectively.
- Each hydrogen bond term is shown.
- the filtration method of the present invention is characterized by using the porous hollow fiber membrane of the present invention described above.
- a suction filtration method is preferable.
- the present invention it is possible to provide a porous hollow fiber membrane having high strength suitable for filtration and excellent in water permeability, and a method for producing the porous hollow fiber membrane.
- FIG. 4 is an electron micrograph of the surface FA of the porous hollow fiber membrane obtained in Example 3 at a magnification of 10,000 times.
- 4 is an electron micrograph at a magnification of 5000 times the surface FB of the porous hollow fiber membrane obtained in Example 3.
- FIG. 4 is an electron micrograph at a magnification of 1000 times in the vicinity of the boundary between layers in the cross section of the porous hollow fiber membrane obtained in Example 3.
- the porous hollow fiber membrane means a membrane having a hollow annular shape.
- the membrane area per module unit volume can be increased as compared with a planar membrane.
- the porous hollow fiber membrane of this embodiment preferably has a thickness of 0.050 mm or more and 0.25 mm or less.
- the film thickness is 0.050 mm or more, it is possible to have a strength with no practical problem. If it is 0.25 mm or less, the resistance during filtration is small, and in the case of a porous hollow fiber membrane, the inner diameter can be increased while the outer diameter remains constant, so the pressure loss in the porous hollow fiber membrane tube Can be reduced. More preferably, it is 0.10 mm or more and 0.24 mm or less.
- the inner diameter of the porous hollow fiber membrane is preferably 0.75 mm or more and 1.5 mm or less.
- the pressure loss in the porous hollow fiber membrane can be reduced.
- the number of filled containers for storing the porous hollow fiber membrane can be increased.
- they are 0.76 mm or more and 1.4 mm or less.
- the above-mentioned porous hollow fiber membrane has a strength coefficient of 1.7 or more when the strength coefficient is defined as the following formula (1).
- the strength coefficient is based on Timoschenko's thin-walled annular buckling formula. When the hollow fiber membrane is crushed against the force in the external pressure direction, it is often crushed in the same shape as when the thin ring is buckled.
- the constant term of this theoretical formula is defined as a strength coefficient, and if the strength coefficient is 1.7 or more, the compressive strength is high with respect to the film thickness and the inner diameter, and both high strength and high filtration performance can be achieved. It means that it is possible.
- the strength coefficient is preferably 1.8 or more, and more preferably 1.9 or more.
- the strength coefficient is not particularly limited as long as the strength coefficient is high, but is preferably 60 or less, and more preferably 50 or less. More preferably, it is 40 or less.
- the porous hollow fiber membrane described above has a trunk thickness that forms the surface FB when the surface of the raw water side (before filtration) as the medium to be filtered is the surface FA and the other (the surface on the filtration side) is the surface FB.
- the outer surface corresponds to the surface FA and the inner surface corresponds to the surface FB.
- the strength of the porous hollow fiber membrane is deformed starting from the narrow portion of the trunk that forms the porous hollow fiber membrane.
- the variation coefficient of the thickness of the trunk forming the surface FB is 80% or less, the distribution of the trunk thickness is narrow, and the compressive strength of the porous hollow fiber membrane can be kept high. Moreover, even if the film thickness is reduced, the thickness of the trunk is more uniform, so that it can have higher compressive strength than conventional.
- the variation coefficient of the thickness of the trunk forming the surface FB is preferably 70% or less, and more preferably 60% or less.
- the inner surface corresponds to the surface FA and the outer surface corresponds to the surface FB.
- the thickness of the trunk of the surface FB is 0.20 ⁇ m or more and 20 ⁇ m or less, and the hole diameter of the surface FB is 0.30 ⁇ m or more and 10 ⁇ m or less.
- the compressive strength is preferably 0.30 MPa or more from a practical viewpoint.
- the porosity of the surface FB of the porous hollow fiber membrane is preferably 32% or more and 60% or less.
- it is known to increase the open area ratio on the raw water side (for example, Japanese Patent No. 3781679), but by further increasing the open area ratio of the surface FB on the filtered water side, the filtration stability can be improved. This is what we can do. If it is 32% or more, filtered water can pass through the film thickness portion more efficiently, so that the filtration performance can be improved. If it is 60% or less, the strength does not decrease. Preferably they are 33% or more and 50% or less.
- the aperture ratio of the surface FA is 32% or more and 60% or less.
- the pore diameter of the surface FA is 500 nm or less, preferably 30 nm or more and 500 nm or less, more preferably 50 nm or more and 450 nm or less.
- the pure water permeation rate of the porous hollow fiber membrane 1000L / m 2 / hr or more 20000L / m 2 / hr or less. When it is in this range, it is possible to achieve both filtration performance and blocking performance. More preferably less than or equal 1200L / m 2 / hr or more 18000L / m 2 / hr.
- the porous membrane forming the porous hollow fiber membrane preferably has a three-dimensional network structure.
- the three-dimensional network structure referred to in the present application schematically indicates a structure as shown in FIG. It can be seen that the thermoplastic resin a is joined to form a mesh, and the void b is formed. In the three-dimensional network structure, a lump of resin having a so-called spherulite structure is hardly seen.
- gap part b of a three-dimensional network structure is surrounded by the thermoplastic resin a, and each part of the space
- the porous hollow fiber membrane may have a single layer structure or a multilayer structure of two or more layers.
- a layer having the surface FA is referred to as a layer (A)
- a layer having the surface FB is referred to as a layer (B).
- the layer (A) is a so-called blocking layer, the function of blocking the passage of foreign substances contained in the liquid to be treated (raw water) with a small surface pore diameter is exhibited
- the layer (B) is a so-called support layer.
- the support layer ensures high mechanical strength and has a function sharing such that it has a function of reducing water permeability as much as possible.
- the sharing of the functions of the layer (A) and the layer (B) is not limited to the above.
- the thickness of the layer (A) is preferably 1/100 or more and less than 40/100 of the film thickness.
- the thickness of the layer (A) is preferably 1 ⁇ m or more and 100 ⁇ m or less, and more preferably 2 ⁇ m or more and 80 ⁇ m or less.
- thermoplastic resin and an organic liquid are used as the organic liquid.
- organic liquid a solvent that does not dissolve the thermoplastic resin at room temperature but dissolves at a high temperature, that is, a potential solvent is used.
- the thermally induced phase separation method has the following advantages.
- thermoplastic resin is a crystalline resin. In this case, crystallization is promoted during film formation, and a high-strength film is easily obtained. Because of the above advantages, it is widely used as a method for producing a porous membrane (for example, see Non-Patent Documents 1 to 4).
- the manufacturing method of the present embodiment includes a step of discharging a melt-kneaded product containing a thermoplastic resin, an organic liquid, and inorganic fine powder from a spinneret having an annular discharge port to form a hollow fiber-shaped melt-kneaded product, It is characterized by comprising a step of solidifying the kneaded product and then extracting and removing the organic liquid and the inorganic fine powder to produce a porous hollow fiber membrane.
- the melt-kneaded product may be composed of two components of a thermoplastic resin and a solvent, or may be composed of three components of a thermoplastic resin, inorganic fine powder, and a solvent.
- thermoplastic resin used in the method for producing the porous hollow fiber membrane of the present embodiment is a resin that has elasticity at room temperature and does not exhibit plasticity, but exhibits plasticity by appropriate heating and can be molded.
- a thermoplastic resin is a resin that returns to its original elastic body when it cools down and does not undergo any chemical changes such as its molecular structure during that time (for example, “Chemical Dictionary Dictionary Editorial Committee, Chemical Dictionary, 6 reduced edition, Kyoritsu Shuppan, pages 860 and 867, 1963 ").
- thermoplastic resins include resins described in the section of thermoplastics (pages 829 to 882) of 12695 chemical products (Chemical Industry Daily, 1995), and the Chemical Handbook Application Edition, revised 3rd edition (edited by the Chemical Society of Japan). , Maruzen, 1980), pages 809-810.
- specific examples of the thermoplastic resin include polyethylene, polypropylene, polyolefin such as polypropylene, polyvinylidene fluoride, ethylene-vinyl alcohol copolymer, polyamide, polyetherimide, polystyrene, polysulfone, polyvinyl alcohol, polyphenylene ether, polyphenylene sulfide, Cellulose acetate, polyacrylonitrile and the like.
- crystalline thermoplastic resins such as crystalline polyolefin, polyvinylidene fluoride, ethylene-vinyl alcohol copolymer, and polyvinyl alcohol can be suitably used from the viewpoint of strength development. More preferably, polyolefin, polyvinylidene fluoride, or the like, which has high water resistance due to hydrophobicity and can be expected to have durability in the filtration of a normal aqueous liquid, can be used. Particularly preferably, polyvinylidene fluoride having excellent chemical durability such as chemical resistance can be used.
- Examples of the polyvinylidene fluoride include a vinylidene fluoride homopolymer and a vinylidene fluoride copolymer having a vinylidene fluoride ratio of 50 mol% or more.
- Examples of the vinylidene fluoride copolymer include a copolymer of vinylidene fluoride and one or more monomers selected from the group consisting of ethylene tetrafluoride, propylene hexafluoride, ethylene trifluoride chloride and ethylene. Can do.
- a vinylidene fluoride homopolymer is particularly preferable.
- the concentration of the thermoplastic resin in the melt-kneaded product is desirably 35% by mass to 48% by mass. Preferably, it is 36 mass% to 45 mass%. If it is 35 mass% or more, it is easy to ensure mechanical strength, and if it is 48 mass% or less, the water permeability will not deteriorate.
- the concentration of the thermoplastic resin in the layer (B) is desirably 35% by mass to 48% by mass. More preferably, it is 36 mass% to 45 mass%.
- the concentration of the thermoplastic resin in the layer (A) is preferably 20% by mass to 35% by mass, and more preferably 25% by mass to 35% by mass. If it is 20 mass% or more, the surface pore diameter and mechanical strength can be compatible, and if it is 35 mass% or less, the water permeation performance does not deteriorate.
- the organic liquid used is a latent solvent for the thermoplastic resin used in this embodiment.
- the latent solvent refers to a solvent that hardly dissolves the thermoplastic resin at room temperature (25 ° C.) but can dissolve the thermoplastic resin at a temperature higher than room temperature. It may be liquid at the melt kneading temperature with the thermoplastic resin, and does not necessarily need to be liquid at room temperature.
- thermoplastic resin is polyethylene
- examples of organic liquids include dibutyl phthalate, diheptyl phthalate, dioctyl phthalate, di (2-ethylhexyl) phthalate, diisodecyl phthalate, and ditridecyl phthalate; sebacic acid Sebacic acid esters such as dibutyl; adipic acid esters such as dioctyl adipate; trimellitic acid esters such as trioctyl trimellitic acid; phosphoric acid esters such as tributyl phosphate and trioctyl phosphate; propylene glycol dicaprate, propylene Examples thereof include glycerin esters such as glycol dioleate; paraffins such as liquid paraffin; and mixtures thereof.
- thermoplastic resin is polyvinylidene fluoride
- examples of organic liquids include dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dicyclohexyl phthalate, diheptyl phthalate, dioctyl phthalate, and di (2-ethylhexyl) phthalate.
- Phthalates such as methyl benzoate and ethyl benzoate
- phosphate esters such as triphenyl phosphate, tributyl phosphate and tricresyl phosphate
- ⁇ -butyrolactone ethylene carbonate, propylene carbonate, cyclohexanone, And ketones such as acetophenone and isophorone; and mixtures thereof.
- the inorganic fine powder examples include silica, alumina, titanium oxide, zirconia oxide, calcium carbonate and the like, and fine powder silica having an average primary particle diameter of 3 nm to 500 nm is particularly preferable. More preferably, it is 5 nm or more and 100 nm or less. Hydrophobic silica fine powder that is difficult to aggregate and has good dispersibility is more preferable, and hydrophobic silica having a MW (methanol wettability) value of 30% by volume or more is more preferable.
- the MW value here is a value of the volume% of methanol at which the powder is completely wetted.
- the above-mentioned “primary particle size of inorganic fine powder” means a value obtained from analysis of an electron micrograph. That is, first, a group of inorganic fine powders is pretreated by the method of ASTM D3849. Thereafter, the diameter of 3000 to 5000 particles shown in the transmission electron micrograph is measured, and the primary particle diameter of the inorganic fine powder is calculated by arithmetically averaging these values.
- the mass ratio of the inorganic fine powder in the melt-kneaded product is preferably 5% by mass or more and 40% by mass or less. If the proportion of the inorganic fine powder is 5% by mass or more, the effect of the inorganic fine powder kneading can be sufficiently exhibited, and if it is 40% by mass or less, stable spinning can be achieved.
- Melting and kneading can be performed using ordinary melting and kneading means such as an extruder. Although the case where an extruder is used is described below, the means for melt-kneading is not limited to an extruder.
- An example of the manufacturing apparatus used for implementing the manufacturing method of this embodiment is shown in FIG.
- the porous hollow fiber membrane production apparatus shown in FIG. 2 includes an extruder 10, a hollow fiber molding nozzle 20, a coagulation bath 30 in which a solution for coagulating the membrane forming stock solution is stored, and a porous hollow fiber membrane 40.
- a plurality of rollers 50 for conveying and winding are provided.
- a space S shown in FIG. 2 is an idle running portion through which the raw film forming solution discharged from the hollow fiber molding nozzle 20 passes before reaching the solution in the coagulation bath 30.
- a hollow fiber molding nozzle 20 having one or more annular discharge ports arranged concentrically is mounted at the tip of the extruder 10, and the melt-kneaded product is extruded by the extruder 10 to be hollow. It is discharged from the yarn forming nozzle 20.
- a hollow fiber molding nozzle 20 having two or more annular discharge ports is attached to the tip of the extruder 10, and each annular discharge port is melted by a different extruder 10.
- the hollow kneaded extrudates having a multilayer structure can be obtained by joining the melt-kneaded materials supplied to each other at the discharge ports and superimposing them.
- melt-kneaded materials having different compositions from the annular discharge ports adjacent to each other, it is possible to obtain multilayer films having different pore diameters of the layers adjacent to each other.
- the compositions different from each other refer to the case where the constituent materials of the melt-kneaded material are different, or the case where the constituent materials are the same but the constituent ratio is different. Even in the same kind of thermoplastic resin, if the molecular weight and molecular weight distribution are clearly different, the constituent materials are considered different.
- the joining position of the melt-kneaded materials having different compositions may be the lower end surface of the hollow fiber molding nozzle 20 or may be different from the lower end surface of the hollow fiber molding nozzle 20.
- the discharge parameter R (1 / second) is set to a value of 10 or more and 1000 or less, high productivity and spinning stability and high strength can be obtained. Since a film is obtained, it is preferable.
- the spinneret discharge parameter R is a value obtained by dividing the discharge linear velocity V (m / sec) by the slit width d (m) of the discharge port.
- the discharge linear velocity V (m / sec) is a value obtained by dividing the discharge capacity per unit time (m 3 / sec) of the melt-kneaded product by the cross-sectional area (m 2 ) of the discharge port.
- R When R is 10 or more, there is no problem such as pulsation of the yarn diameter of the hollow extrudate, and stable spinning can be performed with high productivity. Moreover, if R is 1000 or less, the breaking elongation which is one of the important strengths of the obtained porous hollow fiber membrane can be maintained sufficiently high.
- the elongation at break is the elongation relative to the original length when pulled in the film longitudinal direction.
- a value obtained by dividing the discharge linear velocity V of the melt-kneaded material laminated after the resin has joined by the slit width d of the discharge port is defined as the spinneret discharge parameter R.
- the range of R is more preferably 50 or more and 1000 or less.
- the hollow fiber melt-kneaded material discharged from the discharge port passes through the refrigerant such as air or water and solidifies, but the desired porous hollow fiber membrane allows the above-mentioned idle running portion S formed of the air layer to pass therethrough.
- the coagulation bath 30 containing water or the like is passed. That is, the idle running portion S is a portion from the discharge port of the hollow fiber molding nozzle 20 to the water surface of the coagulation bath 30.
- a container such as a cylinder may be used for the idle running section S as needed from the discharge port. After passing through the coagulation bath 30, it is wound up on a skein or the like as necessary.
- the time for the melt-kneaded product to pass through the idle running portion S is called idle running time, and the idle running time is preferably 0.50 seconds or more.
- the idle running time is more preferably 0.50 seconds or more and 2.0 seconds or less. If it is 2.0 seconds or less, stable production is possible. Desirably, it is 0.50 second or more and 1.5 second or less, More preferably, it is 0.50 second or more and 1.1 second or less.
- the temperature drop rate ⁇ T / t is 180 ° C./s or more and 340 ° C. / It is preferable that it is s or less. The reason is not clear, but if it is 180 ° C./s or more, the phase separation speed increases, so the phase separation time is shortened, non-uniform trunks are hardly formed, and the strength coefficient is estimated to be improved. . More preferably, it is 185 ° C./s or more and 330 ° C./s or less.
- the variation coefficient of the trunk thickness is 100%.
- the strength coefficient is 0.9.
- the variation coefficient of the trunk thickness is 52% and the strength coefficient is 2.5. .
- a fluid for forming a hollow part such as air is used.
- the polymer-rich partial phase and the organic liquid-rich partial phase are finely separated.
- the fine powder silica is unevenly distributed in the organic liquid-rich partial phase.
- the extraction and removal of the organic liquid and the inorganic fine powder can be performed simultaneously if they can be extracted and removed with the same solvent. Usually extracted and removed separately.
- a liquid suitable for extraction that is miscible with the organic liquid without dissolving or modifying the used thermoplastic resin is used.
- the contact can be performed by a technique such as immersion.
- the liquid is preferably volatile so that it can be easily removed from the hollow fiber membrane after extraction. Examples of the liquid include alcohols and methylene chloride. If the organic liquid is water-soluble, water can also be used as the extraction liquid.
- Extraction and removal of inorganic fine powder is usually performed using an aqueous liquid.
- the inorganic fine powder is silica
- it can be performed by first contacting with an alkaline solution to convert silica to silicate, and then contacting with water to extract and remove the silicate.
- a porous hollow fiber membrane can be obtained by extracting and removing organic liquid and inorganic fine powder from the solidified porous hollow fiber membrane.
- the porous hollow fiber membrane is stretched in the longitudinal direction within a range of 3 times or less in the stretching ratio. be able to.
- the water permeability is improved, but the pressure resistance (rupture strength and compressive strength) is lowered, so that the membrane does not often have a practical strength after stretching.
- the porous hollow fiber membrane obtained by the production method of the present embodiment has high mechanical strength. Therefore, stretching at a draw ratio of 1.1 times to 3.0 times can be performed.
- the water permeability of the porous hollow fiber membrane is improved by stretching.
- the stretched film may be heat-treated to increase the compression resistance.
- the heat treatment temperature is usually preferably below the melting point of the thermoplastic resin.
- PVDF polyvinylidene fluoride
- a method for increasing the porosity there are a method for decreasing the concentration of PVDF and a method for increasing the temperature of the fluid for forming the hollow part as described above.
- a method of forming a film by lowering the PVDF concentration it is necessary to select a solvent that can achieve a high porosity and a small pore size because the pore size also increases.
- the following parameter P is a relational expression between the three-dimensional solubility parameter of PVDF and the three-dimensional solubility parameter of the solvent, and evaluates the solubility of PVDF and the solvent.
- the right side represents the three-dimensional solubility range of the Hansen solubility parameter.
- the distance from the PVDF three-dimensional solubility parameter ( ⁇ dp, ⁇ pp, ⁇ hp) to the solvent three-dimensional solubility parameter ( ⁇ dm, ⁇ pm, ⁇ hm) is quantified. Represent.
- the parameter P between the solvent used for preparing the melt-kneaded material B forming the layer (B) and PVDF is preferably greater than 7.8, more preferably 7.8. To 10, more preferably 7.8 to 9.0. When this value is 7.8 or more, a decrease in water permeability can be suppressed.
- the parameter P between the solvent used and PVDF is preferably 7.8 or less, more preferably 0 to 7.8, still more preferably 3.0 to 7.8.
- this value is 7.8 or less, a high hole area ratio and a small hole diameter can be achieved.
- the type of solvent is not limited to the above combination, and various solvents can be used as appropriate.
- the upper and lower ends of a membrane bundle composed of a number of porous hollow fiber membranes are bonded and fixed, and one or both ends are open.
- the cross-sectional shape of the end portion to be bonded and fixed may be a circle, a triangle, a quadrangle, a hexagon, an ellipse, or the like.
- an opening of the membrane is provided at the upper end, a skirt structure for introducing gas at the lower end (see Japanese Patent Application Laid-Open No. 2003-24751, etc.), and gas introduction for introducing the gas into the outer surface of the porous hollow fiber membrane
- a hollow fiber membrane module having pores is preferred.
- the longitudinal direction of the hollow fiber membrane in the hollow fiber membrane module may be either the vertical direction or the horizontal direction with respect to the ground, but the installation in the vertical direction is particularly preferable.
- the arrangement location of the hollow fiber membrane modules is not particularly limited, but is preferably arranged at the closest packing position where the hold-up amount is minimized.
- the filtration method may be a whole amount filtration method or a cross flow filtration method. As a method for applying the filtration pressure, a suction filtration method or a water head difference method may be used.
- the porous hollow fiber membrane of the present embodiment has a high strength coefficient, a high pure water permeability, and a high surface porosity, a small pressure loss during suction filtration, and continuous operation at a maximum transmembrane pressure of 0.1 MPa. Even if it performs, since the crushing of a film
- the hollow fiber membrane module is immersed in a tank containing the medium to be filtered,
- the filtration of the filtration medium is performed by external pressure filtration, for example.
- the present embodiment will be described more specifically with reference to examples and comparative examples. However, the present embodiment is not limited only to these examples.
- the measuring method used for this Embodiment is as follows. The following measurements are all performed at 25 ° C. unless otherwise specified. Below, after explaining an evaluation method, the manufacturing method and evaluation result of an Example and a comparative example are explained.
- the hollow fiber membrane is thinly cut with a razor or the like in a direction perpendicular to the longitudinal direction of the membrane at intervals of 15 cm, and the major and minor diameters of the inner diameter of the cross section are measured using a microscope.
- the major axis and the minor axis were measured, the inner diameter and the outer diameter were calculated by the following equations (2) and (3), and the value obtained by subtracting the inner diameter from the calculated outer diameter was calculated as the film thickness. Twenty points were measured, and the average value was defined as the inner diameter, outer diameter, and film thickness under the conditions.
- the pressurizing pressure at which the absolute value of the amount of permeated water was maximized was defined as the compressive strength.
- the number of measurements was 10 points, and the average value was defined as the compression resistance strength under the conditions.
- the following method can also be used to determine the boundary. For example, a method for determining the boundary between the layer (A) and the layer (B) in the case of a porous hollow fiber membrane having a two-layer structure will be described. The following is a method when the layer (A) is a blocking layer and the layer (B) is a support layer.
- the above-mentioned electron microscope was used to photograph a cross section of the hollow fiber membrane and use a photograph that can confirm the shape of 20 or more holes. In order to observe the entire cross section, there are a plurality of images. In this example and the comparative example, the measurement was performed at 5000 times.
- a cross-sectional electron microscope sample was obtained by cutting a membrane sample frozen in ethanol into round slices.
- the line L (that is, the line connecting points having the same film thickness) with the same distance from the surface FA 100 thicknesses were drawn at intervals equal to 101, and as shown in FIG. 3B, the length Lh across which the line L crossed the portion corresponding to the hole portion h in the image was measured. The average value of the length Lh that crossed was calculated by arithmetic average, and the cross-sectional hole diameter in each film thickness portion was obtained. When the magnification of the scanning electron micrograph is sufficiently high, lines having the same distance from the surface FA may be approximated by a straight line. Using the maximum value of the obtained cross-sectional hole diameter, standardize the cross-sectional hole diameter in each film thickness portion, and from the surface FA, the point where the normalized value is closest to 0.7 is reached for the first time at the layer boundary Layered.
- FIG. 4 illustrates an example of a measurement location of the thickness of the trunk that forms the surface FB on the filtration side. Some holes have an inclination with respect to the longitudinal direction. In this case, the distance between the holes was a distance connecting points that were shortest in the direction perpendicular to the longitudinal direction of the hollow fiber membrane. The two holes were excluded from the subsequent measurements.
- 100 measurements were performed in order from the vicinity of the center of the image obtained by photographing the thickness of the trunk forming the hollow fiber membrane.
- the thickness of all the trunks was measured with one image, and when it did not reach 100, measurement was performed in the same manner using an image obtained by photographing another position. In this way, measurement was performed using a plurality of images until the number reached 100.
- the arithmetic average of the measured trunk thickness was calculated
- the photo contrast is small and the pores are difficult to recognize on the image processing software, overlay the transparent sheet on the copy of the image, paint the hole area black with a black pen, etc., and then turn the transparent sheet to a blank sheet.
- the hole portion can be clearly distinguished from black and the non-hole portion can be clearly distinguished from white.
- For the hole diameter calculate the equivalent circle diameter for each hole existing on the surface, and add the hole area of each hole in order from the largest hole diameter, and the sum is 50% of the total hole area of each hole. It was determined by the hole diameter of the hole reached.
- Example 1 A vinylidene fluoride homopolymer as a thermoplastic resin, a mixture of di (2-ethylhexyl) phthalate and dibutyl phthalate as an organic liquid, finely divided silica as an inorganic fine powder, and a hollow fiber by an extruder using a hollow fiber molding nozzle The membrane was melt extruded.
- the extruded hollow fiber melt-kneaded product was passed through the air for 0.90 seconds and then led to a coagulation bath containing 30 ° C. water.
- the obtained hollow fiber was immersed in isopropyl alcohol to extract and remove di (2-ethylhexyl) phthalate and dibutyl phthalate, and then dried.
- Silica was extracted and removed to obtain a porous hollow fiber membrane.
- Example 2 A porous hollow fiber membrane having a two-layer structure in which the layer (A) was on the outer surface side of the hollow fiber membrane and the layer (B) was on the inner surface side of the hollow fiber membrane was produced.
- vinylidene fluoride homopolymer as the thermoplastic resin
- a mixture of di (2-ethylhexyl) phthalate and dibutyl phthalate as the organic liquid, and finely divided silica as the inorganic fine powder the composition of the melt-kneaded layer (A) is fluorinated.
- the air kneaded at 170 ° C. was used as the hollow portion forming fluid, and the melt-kneaded product was extruded from a hollow fiber forming nozzle having an outer diameter of 2.00 mm and an inner diameter of 0.92 mm at a discharge temperature of 240 ° C.
- the extruded hollow fiber melt-kneaded product was passed through the air for 0.90 seconds and then led to a coagulation bath containing 30 ° C. water.
- the obtained hollow fiber was immersed in isopropyl alcohol to extract and remove di (2-ethylhexyl) phthalate and dibutyl phthalate, and then dried.
- Silica was extracted and removed to obtain a porous hollow fiber membrane.
- Example 3 A porous hollow fiber membrane was produced in the same manner as in Example 2 except that the melt kneaded product was set at a discharge temperature of 220 ° C.
- the porous hollow fiber membrane of Example 3 an electron micrograph of the surfaces of the raw water side and the filtration side and an electron micrograph of a cross section perpendicular to the longitudinal direction of the hollow fiber membrane were taken.
- FIG. 5 and FIG. 6 are a photograph of an electron microscope at a magnification of 10,000 times of the surface FA of the obtained porous hollow fiber membrane and an electron microscope photograph of the surface FB at a magnification of 5000 times.
- FIG. 7 is an electron micrograph of the obtained porous hollow fiber membrane near the boundary between layers.
- Example 4 A porous hollow fiber membrane was produced in the same manner as in Example 3 except that the melt-kneaded product was set at a discharge temperature of 205 ° C. and the inner diameter of the hollow fiber membrane was 0.78 mm.
- both ends are fixed by a fixing part, the end of one fixing part seals the hollow part of the hollow fiber membrane, and the end of the other fixing part is An external pressure type hollow fiber membrane module was produced in which the hollow portion of the hollow fiber membrane was opened and filtered from the outside to the inside of the hollow fiber membrane where the hollow fiber membrane was exposed.
- a membrane separator was manufactured using the three hollow fiber membrane modules, the first tank, and the second tank.
- the first tank is a tank in which the membrane modules are installed vertically, and has an installation floor area of 0.109 m 2 and an effective water depth of 2.3 m.
- the second tank is a tank for storing the backwash drainage used for the physical cleaning at the upper part of the first tank, and a buffer tank having a bottom area of 0.25 m 2 and an effective water depth of 0.6 m is provided. Yes.
- the water amount after subtracting was 1.36 L / m 2 .
- the to-be-treated water supply water amount into the 1st tank was 12 m ⁇ 3 > / hr.
- the filtration operation is started from the time when the water to be treated reaches half of the membrane length of the hollow fiber membrane as (Step 1), and subsequently (Step 2) for about 26 minutes in the state where the entire hollow fiber membrane is immersed.
- a filtration operation was performed, and further, as (Step 3), a filtration operation was performed until the water to be treated reached half the length of the hollow fiber membrane just before the physical washing step was performed.
- the filtration operation was performed by applying a membrane differential pressure with the secondary side of the hollow fiber membrane as a negative pressure.
- the membrane filtration flow rate in each (Step) of the filtration step is 6 m 3 / hr (2 m 3 / hr per hollow fiber membrane module) in (Step 1) and (Step 3 ), and 12 m 3 / hr in (Step 2). (4 m 3 / hr per hollow fiber membrane module).
- the operation time of the total filtration process from (Step 1) to (Step 3) was about 28 minutes.
- the amount of water supplied into the first tank of the water to be treated in (Step 2) was the same as the membrane filtration flow rate.
- a physical washing step was performed.
- back cleaning and gas cleaning using air were performed simultaneously.
- the backwash flow rate was 12 m 3 / hr (4 m 3 / hr per membrane module), and the air flow rate used for gas cleaning was 12 Nm 3 / hr (4 Nm 3 / hr per membrane module).
- the concentration ratio in the first tank is made 100 times (recovery rate 99.0%), and then the discharge process of discharging the concentrated waste water in the first tank Carried out.
- discharging step of discharging the suspended solids peeled off in the physical washing step discharging was performed by fully opening the arrangement installed at the bottom of the first tank. Furthermore, the concentrated drainage was completely discharged from the first tank by fully opening the valve for 15 seconds after detecting that the water depth in the tank was 0 m by the pressure type liquid level sensor installed at the bottom.
- Example 2 A porous hollow fiber membrane was produced in the same manner as in Example 1 except that the idle running time was 0.4 seconds.
- Example 4 A porous hollow fiber membrane was produced in the same manner as in Example 2 except that the film thickness was 0.28 mm and the idle running time was 1.2 seconds.
- An external pressure type hollow fiber membrane module was manufactured in the same manner as in Examples 1 to 4. As a result, the transmembrane pressure difference reached 75 kPa, and the differential pressure tended to increase. Since the porous hollow fiber membranes of Examples 1 to 4 have a small film thickness, the resistance during filtration is small and the inner diameter can be increased, thereby reducing the pressure loss in the hollow portion of the porous hollow fiber membrane. As a result, a large difference in transmembrane pressure is considered to have occurred.
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Abstract
Description
本発明は外圧濾過、特に吸引濾過の場合に、長期運転に耐え得る十分な強度を有しつつ、濾過時の抵抗や中空糸膜内の圧力損失を減らすことによって透水性能を向上させた多孔性中空糸膜、及び、該多孔性中空糸膜の製造方法を提供することを目的とする。
P=((σdm-σdp)2+(σpm-σpp)2+(σhm-σhp)2)0.5≦7.8
[式中、σdm及びσdpは溶媒及びポリフッ化ビニリデンの分散力項をそれぞれ示し、σpm及びσppは溶媒及びポリフッ化ビニリデンの双極子結合力項をそれぞれ示し、σhm及びσhpは溶媒及びポリフッ化ビニリデンの水素結合項をそれぞれ示す。]
P=((σdm-σdp)2+(σpm-σpp)2+(σhm-σhp)2)0.5>7.8
[式中、σdm及びσdpは溶媒及びポリフッ化ビニリデンの分散力項をそれぞれ示し、σpm及びσppは溶媒及びポリフッ化ビニリデンの双極子結合力項をそれぞれ示し、σhm及びσhpは溶媒及びポリフッ化ビニリデンの水素結合項をそれぞれ示す。]
例えば、層(A)を、いわゆる阻止層とし、小さい表面孔径により被処理液(原水)中に含まれる異物の膜透過を阻止する機能を発揮させ、層(B)をいわゆる支持層とし、この支持層は高い機械的強度を担保すると共に、透水性をできるだけ低下させない機能を有するというような機能分担にする。層(A)と層(B)の機能の分担は前記に限定されるものではない。
本実施形態の多孔性中空膜の製造方法としては、例えば熱誘起相分離法が挙げられる。この製法では熱可塑性樹脂と有機液体を用いる。この有機液体は、該熱可塑性樹脂を室温では溶解しないが、高温では溶解する溶剤、即ち潜在的溶剤となるものを用いる。熱可塑性樹脂と有機液体を高温で混練し、熱可塑性樹脂を有機液体に溶解させた後、室温まで冷却することで相分離を誘発させ、さらに有機液体を除去して多孔体を製造する方法(熱誘起相分離法)は、以下の利点を持つ。
(a)室温で溶解できる適当な溶剤のないポリエチレン等のポリマーでも製膜が可能になる
(b)高温で溶解したのち冷却固化させて製膜するので、特に熱可塑性樹脂が結晶性樹脂である場合、製膜時に結晶化が促進され高強度膜が得られやすい、
上記の利点から、多孔質膜の製造方法として多用されている(例えば非特許文献1~4参照)。
20cm÷10cm=2
P=((σdm-σdp)2+(σpm-σpp)2+(σhm-σhp)2)0.5
[式中、σdm及びσdpは溶媒及びポリフッ化ビニリデンの分散力項をそれぞれ示し、σpm及びσppは溶媒及びポリフッ化ビニリデンの双極子結合力項をそれぞれ示し、σhm及びσhpは溶媒及びポリフッ化ビニリデンの水素結合項をそれぞれ示す。]
なお、上記の考え方はPVDFに限るものではない。
中空糸膜を膜長手方向に15cm間隔で垂直な向きにカミソリなどで薄く切り、顕微鏡を用いて断面の内径の長径と短径、外径の長径と短径を測定し、以下の式(2)、(3)により、それぞれ内径と外径を計算し、その計算した外径から内径を減算した値を膜厚として計算した。20点測定し、その平均値を、その条件における内径、外径、膜厚とした。
中空糸膜を50質量%のエタノール水溶液中に30分間浸漬させた後、水中に30分間浸漬し、中空糸膜を湿潤化した。約10cm長の湿潤中空糸膜の一端を封止し、他端の中空部内へ注射針を入れ、注射針から0.1MPaの圧力にて25℃の純水を中空部内へ注入し、外表面へと透過してくる純水の透過水量を測定し、以下の式により純水透過流束を決定した。ここに膜有効長とは、注射針が挿入されている部分を除いた、正味の膜長を指す。また、測定数は10点とし、その平均値を各条件における純水透水率とした。
約5cm長の湿潤中空糸膜の一端を封止し、他端を大気開放とし、外表面より40℃の純水を加圧し大気開放端より透過水を出した。このとき膜供給水を循環させることなくその全量を濾過する方式、即ち全量濾過方式を取った。加圧圧力を0.10MPaより0.01MPa刻みで昇圧し、各圧力にて15秒間圧力を保持し、この15秒間に大気開放端より出てくる透過水をサンプリングした。中空糸膜の中空部がつぶれないうちは加圧圧力が増すにつれて透過水量(質量)の絶対値も増してゆくが、加圧圧力が中空糸膜の耐圧縮強度を超えると中空部が潰れて閉塞が始まるため、透過水量の絶対値は加圧圧力が増すにも関わらず、低下する。透過水量の絶対値が極大になる加圧圧力を耐圧縮強度とした。各実施例および比較例において、それぞれ測定数を10点とし、その平均値を、その条件における耐圧縮強度とした。
HITACHI製電子顕微鏡SU8000シリーズを使用し、加速電圧3kVで膜の断面を観察する。本実施例および比較例では1000倍にて、層と層の境界近傍を撮影した。撮影した画像により、層と層の間に境界線が判別できる場合は、その境界線を層と層の境界とする。本実施例および比較例における多孔性中空糸膜においても、境界が判別できるため、その境界線を層と層の境界とした。
三次元溶解度パラメータは以下の成書から引用した。Hansen, Charles (2007). Hansen Solubility Parameters: A user's handbook, Second Edition. Boca Raton, Fla: CRC Press.(ISBN 978-0-8493-7248-3)
(4)と同様の電子顕微鏡にて、表面FBを撮影した。20個以上の孔の形状が確認できる倍率で撮影し、本実施例および比較例では5000倍で撮影を行った。
(4)と同様の電子顕微鏡にて、表面FA、FBを撮影した。20個以上の孔の形状が確認できる倍率で撮影し、本実施例および比較例では表面FAを10000倍、表面FBを5000倍で撮影を行った。
実施例および比較例で用いた原材料を下記に示す。
<熱可塑性樹脂>
フッ化ビニリデンホモポリマー(株式会社クレハ製、商品名:KF W#1000)
<有機液体>
フタル酸ビス(2-エチルヘキシル)(DEHP)(シージーエスター株式会社製)
フタル酸ジブチル(DBP)(シージーエスター株式会社製)
<無機微粉>
微粉シリカ(日本アエロジル株式会社製、商品名:R972 一次粒子径16nm)
表1および表2に、得られた実施例1から実施例4、比較例1から5までの多孔性中空糸膜の配合組成及び製造条件並びに各種性能を示す。
熱可塑性樹脂としてフッ化ビニリデンホモポリマー、有機液体としてフタル酸ジ(2-エチルヘキシル)とフタル酸ジブチルとの混合物、無機微粉として微粉シリカを用い、中空糸成型用ノズルを用いて押出機による中空糸膜の溶融押出を行った。溶融混練物として組成がフッ化ビニリデンホモポリマー:フタル酸ジ(2-エチルヘキシル):フタル酸ジブチル:微粉シリカ=40.0:30.8:6.20:23.1(質量比)の溶融混練物を、中空部形成用流体として空気を用い、共に240℃の吐出温度にて、外径2.00mm、内径0.92mmの中空糸成形用ノズルから押し出した。
層(A)を中空糸膜の外表面側とし、層(B)を中空糸膜の内表面側とする、二層構造の多孔性中空糸膜を製造した。熱可塑性樹脂としてフッ化ビニリデンホモポリマー、有機液体としてフタル酸ジ(2-エチルヘキシル)とフタル酸ジブチルとの混合物、無機微粉として微粉シリカを用い、層(A)の溶融混練物の組成をフッ化ビニリデンホモポリマー:フタル酸ジ(2-エチルヘキシル):フタル酸ジブチル:微粉シリカ=34.0:27.1:13.5:25.4(質量比)とし、層(B)の溶融混練物の組成をフッ化ビニリデンホモポリマー:フタル酸ジ(2-エチルヘキシル):フタル酸ジブチル:微粉シリカ=40.0:31.6:5.3:23.1(質量比)とした。中空部形成用流体として170℃に温調した空気を用い、該溶融混練物を240℃の吐出温度にて、外径2.00mm、内径0.92mmの中空糸成形用ノズルから押し出した。
溶融混練物を220℃の吐出温度とした以外は実施例2と同様の方法で多孔性中空糸膜を製造した。実施例3の多孔性中空糸膜では、原水側および濾過側の表面の電子顕微鏡写真および中空糸膜の長手方向に垂直な断面の電子顕微鏡写真を撮影した。
溶融混練物を205℃の吐出温度とし、中空糸膜の内径を0.78mmとした以外は実施例3と同様の方法で多孔性中空糸膜を製造した。
溶融混練物を220℃の吐出温度とし、押出した中空糸状押出物は、1.1秒の空中走行を経た後30℃の水を入れた凝固浴槽へ導いた以外は実施例1と同様の方法で多孔性中空糸膜を製造した。
空走時間を0.4秒とした以外は、実施例1と同様の方法で多孔性中空糸膜を製造した。
溶融混練物を205℃の吐出温度とし、押出した中空糸状押出物は、0.90秒の空中走行を経た後50℃の水を入れた凝固浴槽へ導いた以外は実施例2と同様の方法で多孔性中空糸膜を製造した。
膜厚を0.28mmとし、空走時間を1.2秒とした以外は実施例2と同様の方法で多孔性中空糸膜を製造した。
20 中空糸成型用ノズル
30 凝固浴槽
40 多孔性中空糸膜
50 ローラ
S 空走部
a 熱可塑性樹脂
b 空隙部
Claims (20)
- 熱可塑性樹脂からなる多孔性中空糸膜であって、膜厚が0.050mm以上0.25mm以下であり、強度係数をK=(耐圧縮強度)/((膜厚)/(内径/2))3と定義した場合に、K=1.7以上であることを特徴とする多孔性中空糸膜。
- 濾過側の表面を形成する幹の太さの変動係数が、80%以下であることを特徴とする請求項1記載の多孔性中空糸膜。
- 濾過側の表面の開孔率が、32%以上であることを特徴とする請求項1または2記載の多孔性中空糸膜。
- 濾過側の表面を形成する幹の太さが、0.20μm以上20μm以下であることを特徴とする請求項1から3いずれか1項記載の多孔性中空糸膜。
- 内径が0.75mm以上であり、耐圧縮強度が0.30MPa以上であり、かつ三次元網目構造の中空糸状であることを特徴とする請求項1から4いずれか1項記載の多孔性中空糸膜。
- 少なくとも2層からなる請求項1から5いずれか1項記載の多孔性中空糸膜。
- 少なくとも2層からなり、濾過前側の表面の開孔率が32%~60%であり、かつ、孔径が500nm以下であることを特徴とする請求項1から6いずれか1項記載の多孔性中空糸膜。
- 中空糸膜束と、該中空糸膜束の両端に固定部とを有する中空糸膜モジュールにおいて、
一方の前記固定部の端は前記中空糸膜の中空部を封止し、他方の前記固定部の端は前記中空部を開口し、
前記中空糸膜が露出した該中空糸膜の外側から内側にろ過する外圧式の中空糸膜モジュールであり、
前記中空糸膜が、強度係数をK=(耐圧縮強度)/((膜厚)/(内径/2))3と定義した場合に、K=1.7以上である
ことを特徴とする中空糸膜モジュール。 - 請求項7記載の多孔性中空糸膜の製造方法であって、
前記多孔性中空糸膜の原料である溶融混練物の吐出口における吐出温度と前記溶融混練物を凝固させる凝固浴槽内の温度との差をΔTとし、前記吐出口から前記凝固浴槽の液面までの間の空走部を中空状の前記溶融混練物が通過する時間を空走時間tとした場合に、降温速度ΔT/tが、180℃/s以上340℃/s以下であることを特徴とする多孔性中空糸膜の製造方法。 - 前記溶融混練物の吐出口から前記溶融混練物を凝固させる凝固浴槽の液面までの間の空走部を中空状の前記溶融混練物が通過する空走時間が、0.50秒以上であることを特徴とする請求項9記載の多孔性中空糸膜の製造方法。
- 前記溶融混練物の原材料が、熱可塑性樹脂、無機微粉及び溶媒の3成分である請求項9または10記載の多孔性中空糸膜の製造方法。
- 前記無機微粉がシリカである請求項11記載の多孔性中空糸膜の製造方法。
- 前記熱可塑性樹脂はポリフッ化ビニリデン(PVDF)である請求項9から12いずれか1項記載の多孔性中空糸膜の製造方法。
- 前記多孔性中空糸膜における濾過側の表面を含む層を製造するために用いられる溶融混練物が、35質量%以上48質量%以下の熱可塑性樹脂の濃度を有することを特徴とする請求項9から13いずれか1項記載の多孔性中空糸膜の製造方法。
- 前記多孔性中空糸膜における濾過前側の表面を含む層を製造するために用いられる溶融混練物が、20質量%以上35質量%以下の熱可塑性樹脂の濃度を有することを特徴とする請求項9から14いずれか1項記載の多孔性中空糸膜の製造方法。
- 前記多孔性中空糸膜における濾過前側の表面を含む層を製造する際、下記式で示されるパラメータPの条件を満たす溶媒を使用する請求項9から15いずれか1項記載の多孔性中空糸膜の製造方法。
P=((σdm-σdp)2+(σpm-σpp)2+(σhm-σhp)2)0.5≦7.8
[式中、σdm及びσdpは溶媒及びポリフッ化ビニリデンの分散力項をそれぞれ示し、σpm及びσppは溶媒及びポリフッ化ビニリデンの双極子結合力項をそれぞれ示し、σhm及びσhpは溶媒及びポリフッ化ビニリデンの水素結合項をそれぞれ示す。] - 前記多孔性中空糸膜における濾過側の表面を含む層を製造する際、下記式で示されるパラメータPの条件を満たす溶媒を使用する、請求項9から16いずれか1項記載の多孔性中空糸膜の製造方法。
P=((σdm-σdp)2+(σpm-σpp)2+(σhm-σhp)2)0.5>7.8
[式中、σdm及びσdpは溶媒及びポリフッ化ビニリデンの分散力項をそれぞれ示し、σpm及びσppは溶媒及びポリフッ化ビニリデンの双極子結合力項をそれぞれ示し、σhm及びσhpは溶媒及びポリフッ化ビニリデンの水素結合項をそれぞれ示す。] - 請求項1から7いずれか1項記載の多孔性中空糸膜を用いた濾過方法。
- 吸引濾過方法であることを特徴とする請求項18記載の濾過方法。
- 被濾過媒体を、中空糸膜モジュールで濾過する方法であって、
前記被濾過媒体を有す槽内に、中空糸膜が露出した中空糸膜モジュールを浸漬させる工程と、
前記被濾過媒体を前記中空糸膜の外側から内側へ濾過する工程と、を有し、
前記中空糸膜が、強度係数をK=(耐圧縮強度)/((膜厚)/(内径/2))3と定義した場合に、K=1.7以上である
ことを特徴とする濾過方法。
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