WO2020059344A1 - 中空糸膜 - Google Patents

中空糸膜 Download PDF

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Publication number
WO2020059344A1
WO2020059344A1 PCT/JP2019/031018 JP2019031018W WO2020059344A1 WO 2020059344 A1 WO2020059344 A1 WO 2020059344A1 JP 2019031018 W JP2019031018 W JP 2019031018W WO 2020059344 A1 WO2020059344 A1 WO 2020059344A1
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WIPO (PCT)
Prior art keywords
peripheral surface
filtration layer
region
pore diameter
outer peripheral
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/JP2019/031018
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English (en)
French (fr)
Japanese (ja)
Inventor
大輝 宮田
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Sumitomo Electric Industries Ltd
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Sumitomo Electric Industries Ltd
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Filing date
Publication date
Application filed by Sumitomo Electric Industries Ltd filed Critical Sumitomo Electric Industries Ltd
Priority to US17/275,380 priority Critical patent/US12115503B2/en
Priority to AU2019341812A priority patent/AU2019341812A1/en
Priority to CN201980059558.8A priority patent/CN112672814B/zh
Priority to JP2020548102A priority patent/JP7205543B2/ja
Publication of WO2020059344A1 publication Critical patent/WO2020059344A1/ja
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/08—Hollow fibre membranes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D39/00—Filtering material for liquid or gaseous fluids
    • B01D39/14—Other self-supporting filtering material ; Other filtering material
    • B01D39/16—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0002—Organic membrane manufacture
    • B01D67/0023—Organic membrane manufacture by inducing porosity into non porous precursor membranes
    • B01D67/0025—Organic membrane manufacture by inducing porosity into non porous precursor membranes by mechanical treatment, e.g. pore-stretching
    • B01D67/0027—Organic membrane manufacture by inducing porosity into non porous precursor membranes by mechanical treatment, e.g. pore-stretching by stretching
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/30—Polyalkenyl halides
    • B01D71/32—Polyalkenyl halides containing fluorine atoms
    • B01D71/36—Polytetrafluoroethylene
    • 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
    • B01D2325/022—Asymmetric membranes
    • B01D2325/0233—Asymmetric membranes with clearly distinguishable layers
    • 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

Definitions

  • the present disclosure relates to hollow fiber membranes.
  • This application claims priority based on Japanese Patent Application No. 2018-175905 filed on Sep. 20, 2018, and incorporates all the contents described in the Japanese application.
  • Hollow fiber membranes for solid-liquid separation in the manufacturing processes of sewage treatment and pharmaceuticals are known.
  • the hollow fiber membrane includes an inorganic membrane and an organic membrane.
  • the organic film has higher water permeability than the inorganic film, and has an advantage that the manufacturing cost and running cost of the entire apparatus can be easily reduced.
  • As this organic film a film mainly composed of polytetrafluoroethylene having excellent mechanical strength, flexibility, chemical resistance and the like has been proposed (see Japanese Patent Application Laid-Open No. 2010-42329).
  • the hollow fiber membrane according to one embodiment of the present disclosure includes a porous and tubular filtration layer having polytetrafluoroethylene as a main component and a fibrous skeleton, and the average pore diameter of the outer peripheral surface of the filtration layer is the filtration layer. And the ratio of the average pore diameter of the inner peripheral surface of the filtration layer to the average pore diameter of the outer peripheral surface of the filtration layer is 2.0 or more and 5.0 or less.
  • FIG. 1 is a schematic perspective view illustrating a hollow fiber membrane according to an embodiment of the present disclosure.
  • FIG. 2 is a sectional view taken along line AA of the hollow fiber membrane of FIG. 1.
  • FIG. 2 is a schematic partial enlarged view of an outer peripheral surface of a filtration layer of the hollow fiber membrane of FIG. 1.
  • FIG. 2 is a schematic partial enlarged view of an inner peripheral surface of a filtration layer of the hollow fiber membrane of FIG. 1.
  • FIG. 2 is a schematic enlarged cross-sectional view of a filtration layer of the hollow fiber membrane in FIG. 1 in a thickness direction.
  • FIG. 2 is a flowchart showing a method for producing the hollow fiber membrane of FIG. 1.
  • FIG. 1 is a schematic perspective view illustrating a hollow fiber membrane according to an embodiment of the present disclosure.
  • FIG. 2 is a sectional view taken along line AA of the hollow fiber membrane of FIG. 1.
  • FIG. 2 is a schematic partial enlarged view of an outer peripheral surface of a filtration layer
  • FIG. 7 is a schematic view showing an apparatus for forming an extruded body in the method for producing a hollow fiber membrane of FIG. 6.
  • No. 1 is an SEM image of an outer peripheral surface of a filtration layer of a hollow fiber membrane of FIG.
  • No. 3 is an SEM image of the inner peripheral surface of the filtration layer of the hollow fiber membrane of FIG.
  • No. 3 is an SEM image of a cross section in the thickness direction of a filtration layer of the hollow fiber membrane of FIG.
  • the upper side is the outer peripheral surface side of the filtration layer
  • the lower side is the inner peripheral surface side of the filtration layer.
  • the hollow fiber membrane described in the above publication includes a filtration layer containing polytetrafluoroethylene as a main component.
  • This filtration layer is formed by winding a porous sheet mainly composed of polytetrafluoroethylene around the outer peripheral surface of a tubular support layer.
  • the pore diameter on the outer peripheral surface side is substantially equal to the pore diameter on the inner peripheral surface side.
  • the pore size of this filtration layer is increased in order to increase water permeability, impurities easily permeate.
  • the pore size of this filtration layer is reduced in order to increase the selectivity (the property of preventing the penetration of impurities), the water permeability is reduced.
  • the present disclosure has been made based on such circumstances, and has an object to provide a hollow fiber membrane having both excellent water permeability and selectivity.
  • the hollow fiber membrane according to one embodiment of the present disclosure has excellent water permeability and selectivity.
  • the hollow fiber membrane according to one embodiment of the present disclosure includes a porous and tubular filtration layer having polytetrafluoroethylene as a main component and a fibrous skeleton, and the average pore diameter of the outer peripheral surface of the filtration layer is the filtration layer. And the ratio of the average pore diameter of the inner peripheral surface of the filtration layer to the average pore diameter of the outer peripheral surface of the filtration layer is 2.0 or more and 5.0 or less.
  • the hollow fiber membrane since the ratio of the average pore diameter of the inner peripheral surface to the average pore diameter of the outer peripheral surface of the filtration layer containing polytetrafluoroethylene as a main component is within the above range, the permeation of impurities is caused by the outer peripheral surface of the filtration layer. Can be sufficiently suppressed, the flow path of the filtered water passing through the outer peripheral surface can be enlarged, and the pressure loss at the time of discharging the filtered water to the inside of the inner peripheral surface can be reduced. Therefore, the hollow fiber membrane is excellent in both water permeability and selectivity.
  • the difference between the average pore diameter on the outer peripheral surface of the filtration layer and the average pore diameter on the inner peripheral surface of the filtration layer is preferably 4 ⁇ m or more and 15 ⁇ m or less.
  • the difference between the average pore diameter of the outer peripheral surface and the average pore diameter of the inner peripheral surface is within the above range, the water permeability and selectivity can be sufficiently improved.
  • the ratio of the average number of pores per unit area of the inner peripheral surface of the filtration layer to the average number of pores per unit area of the outer peripheral surface of the filtration layer is preferably 1.0 or more and 3.0 or less. As described above, the ratio of the average number of holes per unit area of the inner peripheral surface to the average number of holes per unit area of the outer peripheral surface is within the above range, so that the selectivity is maintained while maintaining sufficient water permeability. Can be increased.
  • the average pore diameter of the first region with respect to the average pore diameter of the inner peripheral surface of the filtration layer is determined.
  • the ratio is preferably 0.9 or more and 1.1 or less.
  • the ratio of the average pore diameter of the second region to the average pore diameter of the outer peripheral surface of the filtration layer is 1.0 or more and 2.5 or less. preferable.
  • the selectivity of the hollow fiber membrane is increased, and the flow path of the filtered water permeated through the outer peripheral surface. Is sufficiently large to further increase the water permeability.
  • the first region is a depth region from the inner peripheral surface of the filtration layer to half the average thickness of the filtration layer
  • the second region is a depth region from the outer peripheral surface of the filtration layer to 10 ⁇ m
  • the first region is a first region.
  • the region between the region and the second region is a third region
  • the average number of holes per unit area of the first region and the third region is larger than the average number of holes per unit area of the second region.
  • the ratio is large, and the ratio of the average number of holes per unit area of the first region to the average number of holes per unit area of the third region is 0.7 or more and 1.3 or less.
  • the hollow fiber membrane is preferably composed of a single layer of the filtration layer.
  • the single-layered body of the filtration layer can reduce the thickness of the entire hollow fiber membrane, and can easily increase the water permeability.
  • the production efficiency of the hollow fiber membrane can be increased by using a single layer body of the filtration layer.
  • the “main component” refers to a component having the largest content ratio in terms of mass, for example, a component having a content ratio of 50% by mass or more, preferably 70% by mass or more, more preferably 95% by mass or more.
  • Pore size refers to the diameter of a hole in the longitudinal direction.
  • the “average pore diameter” refers to an average value of the pore diameters of 10 arbitrarily extracted pores.
  • the “average number of holes per unit area” refers to an average value of the number of holes in any five observation regions of 100 ⁇ m ⁇ 100 ⁇ m observed by a scanning electron microscope (SEM).
  • SEM scanning electron microscope
  • Average thickness refers to the average value of the thickness at any 10 points.
  • the hollow fiber membrane shown in FIGS. 1 and 2 is mainly composed of polytetrafluoroethylene (PTFE), and has a porous and tubular filtration layer 1 having a fibrous skeleton.
  • PTFE polytetrafluoroethylene
  • the average pore diameter D1 of the outer peripheral surface 1a of the filtration layer 1 is smaller than the average pore diameter D2 of the inner peripheral surface 1b of the filtration layer 1.
  • the ratio of the average pore diameter D2 of the inner peripheral surface 1b to the average pore diameter D1 of the outer peripheral surface 1a is 2.0 or more and 5.0 or less.
  • the hollow fiber membrane performs filtration by permeating filtered water inside the inner peripheral surface 1b while preventing penetration of impurities from the liquid to be treated existing on the outer peripheral surface 1a side of the filtration layer 1.
  • the hollow fiber membrane is of an external pressure type in which filtered water is transmitted to the inside of the inner peripheral surface 1b by increasing the pressure on the outer peripheral surface 1a side, and the filtered water is transmitted to the inner peripheral surface 1b by the negative pressure on the inner peripheral surface 1b side. It is suitably used for an immersion type (also called a suction type) filtration device.
  • the hollow fiber membrane is excellent in mechanical strength, flexibility, chemical resistance, etc., because the filtration layer 1 is mainly composed of PTFE.
  • the ratio of the average pore diameter D2 of the inner peripheral surface 1b to the average pore diameter D1 of the outer peripheral surface 1a of the filtration layer 1 mainly composed of PTFE is within the above range.
  • the flow path of the filtered water that has passed through the outer peripheral surface 1a can be enlarged while sufficiently suppressing the penetration of impurities, and the pressure loss when the filtered water is discharged to the inner peripheral surface 1b side can be reduced. Therefore, the hollow fiber membrane is excellent in both water permeability and selectivity.
  • the hollow fiber membrane can prevent impurities from penetrating into the fibrous skeleton of the filtration layer 1 because the pore diameter of the outer peripheral surface 1a of the filtration layer 1 is small. Therefore, the hollow fiber membrane can easily prevent a decrease in water permeability due to stagnation of impurities in the fibrous skeleton.
  • the hollow fiber membrane is composed of a single layer of the filtration layer 1. That is, the outer peripheral surface 1a of the filtration layer 1 constitutes the outer peripheral surface of the hollow fiber membrane, and the inner peripheral surface 1b of the filtration layer 1 constitutes the inner peripheral surface of the hollow fiber membrane. Since the hollow fiber membrane is formed of a single layer of the filtration layer 1, the entire thickness can be reduced, and the water permeability can be more easily increased. In addition, the hollow fiber membrane can be formed with a single layer of the filtration layer 1 to increase the production efficiency.
  • the lower limit of the average thickness T of the hollow fiber membrane (that is, the average thickness of the filtration layer 1) is preferably 0.1 mm, more preferably 0.2 mm.
  • the upper limit of the average thickness T of the hollow fiber membrane is preferably 5.0 mm, more preferably 3.0 mm. If the average thickness T is less than the lower limit, the mechanical strength of the hollow fiber membrane may be insufficient. Conversely, if the average thickness T exceeds the upper limit, it may be difficult to sufficiently increase the water permeability of the hollow fiber membrane.
  • the filtration layer 1 has a fibrous skeleton.
  • This fibrous skeleton has a three-dimensional network structure in which particle masses called nodes 11 are connected by fibrous portions called fibrils 12.
  • holes 13 are formed between the fibrils 12 or between the nodes 11 and the fibrils 12.
  • the filtration layer 1 has a plurality of holes 13 communicating with each other in the thickness direction. These holes 13 are formed in a three-dimensional mesh as shown in FIGS.
  • the filtration layer 1 is a tube obtained by extruding a composition for forming a filtration layer containing PTFE. After extrusion, the filtration layer 1 is formed by extending in the axial direction (X direction in FIG. 1). The filtration layer 1 can be enhanced in mechanical strength by being stretched after extrusion.
  • a plurality of fibrils 12 are oriented in the axial direction by the above stretching, and a plurality of holes 13 whose longitudinal directions are oriented in the axial direction are formed between the fibrils 12 and between the node 11 and the fibrils 12. Is done.
  • the longitudinal direction of the plurality of holes 13 is oriented in the axial direction, filtered water that has passed through the holes 13 can be easily sent in the axial direction while reducing pressure loss.
  • the stretching ratio in the axial direction can be, for example, 50% or more and 700% or less.
  • the filtration layer 1 may be formed by extending in the circumferential direction in addition to the axial direction.
  • the stretching ratio in the circumferential direction can be, for example, 5% or more and 100% or less.
  • the size and shape of the pores of the filtration layer 1 can be adjusted by adjusting the stretching conditions such as the stretching temperature and the stretching ratio.
  • the plurality of holes 13 formed in the filtration layer 1 have an elongated shape in which the longitudinal direction is oriented in the axial direction. Further, as described above, in the filtration layer 1, the average pore diameter D1 of the outer peripheral surface 1a is smaller than the average pore diameter D2 of the inner peripheral surface 1b. As described later, the hollow fiber membrane is intended for the composition for forming a filtration layer that forms the outer peripheral surface 1a side of the filtration layer 1 by the inner peripheral surface of the die when the composition for forming a filtration layer is extruded from a die. By applying friction, the average pore diameter on the outer peripheral surface 1a side can be reduced.
  • fibrillation of the filtration layer-forming composition is promoted by intentional friction with the filtration layer-forming composition that forms the outer peripheral surface 1a of the filtration layer 1. It is thought that. Thereby, the gap between the adjacent fibrils 12 and the gap between the node 11 and the fibrils 12 on the outer peripheral surface 1a side of the filtration layer 1 due to the increase in the number of fibrils 12 are reduced, and the average of the outer peripheral surfaces 1a is reduced. It is considered that the hole diameter D1 is smaller than the average hole diameter D2 of the inner peripheral surface 1b.
  • the lower limit of the ratio of the average pore diameter D2 of the inner peripheral surface 1b to the average pore diameter D1 of the outer peripheral surface 1a of the filtration layer 1 is 2.0, preferably 2.5, and more preferably 3.0.
  • the upper limit of the ratio is 5.0 as described above, preferably 4.5, and more preferably 4.0. If the above ratio is less than the above lower limit, it may be difficult to increase both water permeability and selectivity. Conversely, if the ratio exceeds the upper limit, the formation of the filtration layer 1 may be difficult, or the average pore diameter D2 of the inner peripheral surface 1b may be too large, and the strength of the inner peripheral surface 1b of the filtration layer 1 may be reduced. It may be insufficient.
  • the average pore diameter D1 of the outer peripheral surface 1a of the filtration layer 1 can be set according to the use of the hollow fiber membrane, but the lower limit is preferably 0.01 ⁇ m.
  • the upper limit of the average pore diameter D1 is preferably 10.0 ⁇ m, and more preferably 5.0 ⁇ m. If the average pore diameter D1 is less than the lower limit, it may be difficult to sufficiently increase the water permeability of the filtration layer 1. Conversely, when the average pore diameter D1 exceeds the upper limit, the average pore diameter D2 of the inner peripheral surface 1b of the filtration layer 1 becomes too large, and the strength of the inner peripheral surface 1b side of the filtration layer 1 may be insufficient. is there.
  • the lower limit of the difference between the average pore diameter D1 of the outer peripheral surface 1a of the filtration layer 1 and the average pore diameter D2 of the inner peripheral surface 1b is preferably 4 ⁇ m, more preferably 6 ⁇ m.
  • the upper limit of the difference is preferably 15 ⁇ m, more preferably 10 ⁇ m. If the difference is less than the lower limit, it may be difficult to increase both water permeability and selectivity. Conversely, if the difference exceeds the upper limit, the formation of the filtration layer 1 may become difficult, or the average pore diameter D2 of the inner peripheral surface 1b becomes too large, and the strength of the inner peripheral surface 1b side is insufficient. Can be.
  • the average number of holes per unit area of the inner peripheral surface 1b of the filtration layer 1 is preferably larger than the average number of holes per unit area of the outer peripheral surface 1a. Thereby, the flow path of the filtered water that has passed through the outer peripheral surface 1a of the filtration layer 1 is secured, and the water permeability is easily increased.
  • the hollow fiber membrane can promote fibrillation of the composition for forming a filtration layer by intentionally rubbing the composition for forming a filtration layer that forms the outer peripheral surface 1a side of the filtration layer 1. it is conceivable that.
  • the hollow fiber membrane crushes the fibrils adjacent to each other on the outer peripheral surface 1 a side by intentionally rubbing the composition for forming the filtration layer forming the outer peripheral surface 1 a side of the filtration layer 1, thereby integrating the fibrils. It is thought that it can be done.
  • the hollow fiber membrane suppresses an increase in the number of pores due to fibrillation while reducing the average pore diameter D1 of the outer peripheral surface 1a of the filtration layer 1 and relatively reduces the number of pores in the outer peripheral surface 1a. can do.
  • the lower limit of the ratio of the average number of pores per unit area of the inner peripheral surface 1b to the average number of pores per unit area of the outer peripheral surface 1a of the filtration layer 1 is preferably 1.0, and more preferably 1.2.
  • the upper limit of the ratio is preferably 3.0, and more preferably 2.0. If the ratio is less than the lower limit, the flow path of the filtered water that has passed through the outer peripheral surface 1a of the filtration layer 1 cannot be sufficiently secured, and the water permeability may not be sufficiently increased.
  • the number of pores on the outer peripheral surface 1a may be insufficient and it may be difficult to sufficiently increase water permeability, or the number of pores on the inner peripheral surface 1b may be The strength on the peripheral surface 1b side may be insufficient.
  • the average pore number of lower per unit area of the outer peripheral surface 1a of the filtration layer 1 is preferably 20/2500 [mu] m 2, and more preferably 30/2500 [mu] m 2.
  • the upper limit of the average pore number preferably 100/2500 [mu] m 2, and more preferably 70/2500 [mu] m 2. If the average number of holes is less than the lower limit, it may be difficult to sufficiently increase water permeability.
  • the control of the pore size due to friction of the composition for forming a filtration layer may be insufficient, or the number of pores on the inner peripheral surface 1b may be too large and the inner circumference may be too large. The strength on the surface 1b side may be insufficient.
  • the filtration layer 1 has a small average pore diameter and a relatively small number of pores on the outer peripheral surface 1a side.
  • the formation of the filtration layer 1 does not promote the fibrillation of the composition for forming the filtration layer.
  • the average pore diameter is larger than the outer peripheral surface 1a side.
  • the composition for forming a filtration layer that forms the inner peripheral surface side of the filtration layer 1 does not receive intentional friction when forming the filtration layer 1, and thus the number of pores due to the friction hardly increases or decreases.
  • the average pore diameter is larger than that of the inner peripheral surface 1b side due to the effect of fibrillation of the composition for forming the filtration layer on the outer peripheral surface 1a side. Is slightly smaller, but is less susceptible to crushing between adjacent fibrils, and a decrease in the number of holes is suppressed.
  • a first region P is a depth region from the inner peripheral surface 1b of the filtration layer 1 to 1/2 of the average thickness T of the filtration layer 1
  • a second region Q is a depth region from the outer peripheral surface 1a to 10 ⁇ m
  • the region between the first region P and the second region Q is referred to as a third region R, and the average pore diameter and the number of pores inside the filtration layer 1 will be described.
  • the pores of the first region P, the second region Q, and the third region R are all oriented in the axial direction of the filtration layer 1.
  • the average pore diameter D2 of the inner peripheral surface 1b of the filtration layer 1 is substantially equal to the average pore diameter D3 of the first region P.
  • the lower limit of the ratio of the average pore diameter D3 of the first region P to the average pore diameter D2 of the inner peripheral surface 1b of the filtration layer 1 is preferably 0.9, and more preferably 0.95.
  • the upper limit of the ratio is preferably 1.1, and more preferably 1.05. If the above ratio is less than the lower limit, the flow path of the filtered water cannot be sufficiently increased inside the filtration layer 1, and the water permeability may not be sufficiently increased.
  • the average pore size of the first region P and the second and third regions Q and R described later is the average of the pore sizes of the 10 pores arbitrarily extracted from the SEM image of the cross section in the thickness direction of the filtration layer 1. It can be determined by the value.
  • the average number of holes per unit area of the inner peripheral surface 1b of the filtration layer 1 is substantially equal to the number of holes per unit area of the first region P.
  • the lower limit of the ratio of the average number of holes per unit area of the first region P to the average number of holes per unit area of the inner peripheral surface 1b is preferably 0.9, and more preferably 0.95.
  • the upper limit of the ratio is preferably 1.1, and more preferably 1.05. If the above ratio is less than the above lower limit, the flow path of the filtered water cannot be sufficiently secured inside the filtration layer 1, and the water permeability may not be sufficiently increased.
  • the average number of holes per unit area of the first region P and the second region Q and the third region R which will be described later, is an arbitrary number of 100 ⁇ m ⁇ 5 cross sections in the thickness direction of the filtration layer 1 observed by SEM. It can be determined by the average value of the number of holes in the observation region of 100 ⁇ m.
  • the second region Q secures a flow path of filtered water that has passed through the outer peripheral surface 1a.
  • the lower limit of the ratio of the average pore diameter D4 of the second region Q to the average pore diameter D1 of the outer peripheral surface 1a of the filtration layer 1 is preferably 1.0, and more preferably 1.2.
  • the upper limit of the ratio is preferably 2.5, and more preferably 2.0. If the above ratio is less than the lower limit, the pressure loss may increase due to the flow path being narrowed in the permeation direction of the filtered water. Conversely, if the ratio exceeds the upper limit, it becomes difficult to control the hole diameter, and relatively large holes may be partially formed in the outer peripheral surface 1a.
  • the average number of holes per unit area of the outer peripheral surface 1a of the filtration layer 1 is substantially equal to the average number of holes per unit area of the second region Q.
  • the lower limit of the ratio of the average number of holes per unit area of the second region Q to the average number of holes per unit area of the outer peripheral surface 1a is preferably 0.9, and more preferably 0.95. If the above ratio is less than the above lower limit, the pressure loss may increase due to a decrease in the number of flow paths in the permeation direction of the filtered water.
  • the upper limit of the ratio is not particularly limited, but is preferably 1.1, and more preferably 1.05, from the viewpoint of facilitating the production of the filtration layer 1.
  • the average pore diameter D5 of the third region R is smaller than the average pore diameter D2 of the inner peripheral surface 1b of the filtration layer 1.
  • the flow path is increased in the permeation direction of the filtered water from the third region R to the inner peripheral surface 1b. And the water permeability can be increased.
  • the average pore diameter D5 of the third region R is larger than the average pore diameter D1 of the outer peripheral surface 1a of the filtration layer 1.
  • the lower limit of the ratio of the average pore diameter D5 of the third region R to the average pore diameter D1 of the outer peripheral surface 1a of the filtration layer 1 is preferably 1.5, and more preferably 2.0.
  • the upper limit of the ratio is preferably 3.5, and more preferably 3.0. If the ratio is less than the lower limit, the flow path of the filtered water from the outer peripheral surface 1a to the third region R may not be sufficiently large, and the pressure loss may not be sufficiently reduced. Conversely, when the ratio exceeds the upper limit, the production of the filtration layer 1 may not be easy.
  • the filtration layer 1 preferably has a larger average pore diameter in the order of the outer peripheral surface 1a, the second region Q, the third region R, and the first region P. Thereby, the water permeability can be increased by increasing the flow path of the filtered water that has passed through the outer peripheral surface 1a in the transmission direction.
  • the average number of holes per unit area of the first region P is larger than the average number of holes per unit area of the second region Q.
  • the average number of holes per unit area of the third region R is larger than the average number of holes per unit area of the second region Q.
  • the hollow fiber membrane permeated the outer peripheral surface 1a because the average number of holes per unit area of the first region P and the third region R was larger than the average number of holes per unit area of the second region Q. It is possible to increase the water permeability by sufficiently securing the flow path of the filtered water.
  • the lower limit of the ratio of the average number of holes per unit area of the first region P and the third region R to the average number of holes per unit area of the second region Q is preferably 1.2, more preferably 1.4. preferable.
  • the upper limit of the ratio is preferably 2.5, and more preferably 2.0. If the ratio is less than the lower limit, the water permeability may not be sufficiently increased. Conversely, when the ratio exceeds the upper limit, the production of the filtration layer 1 may not be easy.
  • the average number of holes per unit area of the first region P is substantially equal to the average number of holes per unit area of the third region R.
  • the lower limit of the ratio of the average number of holes per unit area of the first region P to the average number of holes per unit area of the third region R is preferably 0.7, and more preferably 0.8.
  • the upper limit of the ratio is preferably 1.3, and more preferably 1.2. If the above ratio is less than the above lower limit, the pressure loss may increase due to a decrease in the number of flow paths in the permeation direction of the filtered water. Conversely, if the ratio exceeds the upper limit, the strength of the inner peripheral surface 1b side of the filtration layer 1 may be insufficient, or the production of the filtration layer 1 may not be easy.
  • the filtration layer 1 may contain other fluororesins and additives in addition to PTFE as long as the desired effects of the present disclosure are not impaired.
  • the additives include pigments for coloring, inorganic fillers for improving abrasion resistance, preventing low-temperature flow, facilitating void generation, metal powder, metal oxide powder, metal sulfide powder, and the like.
  • the method for producing a hollow fiber membrane includes a step of extruding a composition for forming a filtration layer containing powdered PTFE as a main component into a tubular shape, and a step of axially stretching an extruded body extruded in the extruding step. And baking the extruded body after the stretching in the stretching step.
  • the average pore diameter on the outer peripheral surface of the extruded body after the stretching step is smaller than the average pore diameter on the inner peripheral surface of the extruded body.
  • the ratio of the average pore diameter of the inner peripheral surface to the average pore diameter of the outer peripheral surface of the extruded body is 2.0 or more and 5.0 or less.
  • the hollow fiber membrane of FIG. 1 having both excellent water permeability and selectivity can be easily produced.
  • a cylindrical compression-molded product made of a composition for forming a filtration layer mainly composed of powdered PTFE is extruded into a tube.
  • the extruding step is performed at a temperature lower than the melting point of PTFE, and is generally performed at room temperature.
  • a composition in which a liquid lubricant is mixed with powdered PTFE can be used.
  • liquid lubricant various lubricants conventionally used in the paste extrusion method can be used, for example, naphtha, petroleum solvents such as white oil, hydrocarbon oils such as undecane, toluene, xylene and the like. Aromatic hydrocarbons, alcohols, ketones, esters, silicone oils, fluorochlorocarbon oils, solutions of polymers such as polyisobutylene and polyisoprene in these solvents, mixtures of two or more of these, surface activity Water or an aqueous solution containing the agent.
  • the liquid lubricant it is preferable to use a single component because it is easy to uniformly mix the liquid lubricant.
  • the extruding step can be performed using the extruder 21 shown in FIG.
  • the extruder 21 includes a cylinder 22 having a cylindrical internal space, an internal space communicating with the internal space of the cylinder 22, a die 23 provided continuously on an end surface of the cylinder 22 on the extrusion direction side, and a cylinder 23.
  • the mandrel 24 includes a mandrel 24 provided in an internal space of the cylinder 22 and a core pin 25 protruding from an end surface of the mandrel 24 in the extrusion direction and disposed on a central axis of the internal space of the cylinder 22 and the die 23.
  • the die 23 has an opening 23 a at the end on the extrusion direction side that communicates with the internal space of the cylinder 22.
  • the center of the opening 23a is located on the central axis of the internal space of the cylinder 22 and the die 23.
  • the outer peripheral surface 1a side of the filtration layer 1 is formed by adjusting the inclination angle ⁇ of the inclined surface 23b with respect to the center axis of the cylinder 22 and the die 23 and the length L of the inclined surface 23b in the inclined direction.
  • the friction with the composition for forming a filtration layer is adjusted.
  • the method for manufacturing the hollow fiber membrane can control the average pore diameter D1, the average number of pores per unit area, and the like in the outer peripheral surface 1a of the filtration layer 1 within the above-described ranges.
  • the lower limit of the inclination angle ⁇ of the inclined surface 23b is preferably 30 °, and more preferably 31 °.
  • the friction with the composition for forming a filtration layer that forms the outer peripheral surface 1a side of the filtration layer 1 becomes insufficient, and the average pore diameter D1 of the outer peripheral surface 1a of the filtration layer 1 is sufficiently increased. There is a possibility that it cannot be reduced.
  • the upper limit of the inclination angle ⁇ can be set according to a desired hole diameter of the outer peripheral surface 1a, but is preferably 90 °, more preferably 60 °, and even more preferably 40 °.
  • the lower limit of the length L of the inclined surface 23b in the inclined direction is preferably 30 mm, more preferably 35 mm.
  • the upper limit of the length L in the inclined direction is preferably 50 mm, more preferably 45 mm.
  • the length L in the inclined direction is less than the lower limit, the friction against the composition for forming the outer peripheral surface of the filtration layer 1 becomes insufficient, and the average pore diameter D1 of the outer peripheral surface 1a of the filtration layer 1 is insufficient. May not be smaller.
  • the length L in the inclined direction exceeds the upper limit, it may not be easy to control the average pore diameter and the average number of pores per unit area of the outer peripheral surface 1a of the filtration layer 1.
  • Step of stretching In the stretching step, the tubular extruded body extruded in the extruding step is stretched in the axial direction while heating.
  • the stretching step can be performed by winding the extruded body extruded from the die 23 at a speed higher than the speed extruded from the die 23 while heating. Thereby, the liquid lubricant in the extruded body can be volatilized, and the extruded body can be made porous.
  • the lower limit of the stretching ratio of the extruded body in the stretching step is preferably 50%, more preferably 100%.
  • the upper limit of the stretching ratio is preferably 700%, more preferably 400%.
  • the extruded body after the stretching step is heated to a temperature equal to or higher than the melting point of PTFE while maintaining the length, and fixed in a stretched state.
  • the heating temperature in the baking step can be, for example, 350 ° C. or more and 550 ° C. or less.
  • the heating time in the baking step can be, for example, 10 seconds or more and 20 minutes or less.
  • the extruded body after the firing step constitutes the filtration layer 1.
  • the method for producing a hollow fiber membrane may further include a step of cutting the extruded body after the firing step into a desired size.
  • the hollow fiber membrane is preferably formed of a single layer of a filtration layer from the viewpoint of easily and surely controlling the water permeability and selectivity of the entire membrane, but has a layer other than the filtration layer. Is also good.
  • the average pore diameter and the average number of pores per unit area of the first region P to the third region R are not necessarily controlled to satisfy the relationship of the first embodiment.
  • FIG. 7 shows a cylindrical compression-molded product containing “Super Sol FP-25” manufactured by Idemitsu Kosan Co., Ltd. containing PTFE fine powder (“F104” manufactured by Daikin Industries) as a main component and naphtha as a liquid lubricant. And extruded into a tube using the following extruder 21 (extrusion step).
  • the tubular extruded body extruded in the above extruding step is stretched in the axial direction at a heating temperature of 230 ° C., a heating time of 1 minute and a stretching ratio of 150% (stretching step), and the length of the stretched extruded body is maintained. While heating at a heating temperature of 365 ° C. and a heating time of 6 minutes (firing step), No. 1 consisting of a single-layered filtration layer having an average thickness of 0.3 mm was obtained.
  • One hollow fiber membrane was produced.
  • FIG. 8 shows an SEM image of the outer peripheral surface of the hollow fiber membrane
  • FIG. 9 shows an SEM image of the inner peripheral surface
  • FIG. 10 shows a SEM image of a cross section in the thickness direction.
  • the average pore diameter on the outer peripheral surface of the filtration layer is smaller than the average pore diameter on the inner peripheral surface.
  • the average pore diameter of the outer peripheral surface of this filtration layer was 3 ⁇ m
  • the average pore diameter of the inner peripheral surface was 10 ⁇ m
  • the ratio of the average pore diameter of the inner peripheral surface to the average pore diameter of the outer peripheral surface was 3.3.
  • the average number of holes per unit area of the outer peripheral surface of the filtration layer was 50/2500 ⁇ m 2
  • the average number of holes per unit area of the inner peripheral surface was 70/2500 ⁇ m 2 .
  • the filtration layer has a first region from the inner peripheral surface to a depth of ⁇ of the average thickness of the filtration layer, and a second region, a first region and a second region from the outer peripheral surface to a depth of 10 ⁇ m.
  • the region between the two regions was the third region
  • the average pore size of the first region was 10 ⁇ m
  • the average pore size of the second region was 5 ⁇ m
  • the average pore size of the third region was 8 ⁇ m.
  • the average number of holes per unit area of the first region is 70 / 2,500 ⁇ m 2
  • the average number of holes per unit area of the second region is 50 / 2,500 ⁇ m 2
  • the average space per unit area of the third region is The number of holes was 80/2500 ⁇ m 2 .
  • the Gurley second of the hollow fiber membrane No. 1 was measured based on the time required for 100 cm 3 of air to pass through the 6.45 cm 2 laminate at an average pressure difference of 1.22 kPa in accordance with JIS-P8117: 2009. Seconds. From the above measurement results, No. It can be seen that the hollow fiber membrane 1 is excellent in both water permeability and selectivity.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)
  • Artificial Filaments (AREA)
PCT/JP2019/031018 2018-09-20 2019-08-07 中空糸膜 Ceased WO2020059344A1 (ja)

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US17/275,380 US12115503B2 (en) 2018-09-20 2019-08-07 Hollow-fiber membrane
AU2019341812A AU2019341812A1 (en) 2018-09-20 2019-08-07 Hollow-fiber membrane
CN201980059558.8A CN112672814B (zh) 2018-09-20 2019-08-07 中空纤维膜
JP2020548102A JP7205543B2 (ja) 2018-09-20 2019-08-07 中空糸膜

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