JP7694278B2 - Hollow fiber membrane module - Google Patents

Description

This disclosure relates to hollow fiber membrane modules.

For various purposes such as wastewater treatment, hollow fiber membranes, which are porous bodies formed into cylindrical shapes with a relatively small diameter, are sometimes used as a type of filtration membrane to filter the water being treated and remove solid matter.

For example, a hollow fiber membrane module equipped with such a hollow fiber membrane has been proposed, which is an ozone-resistant membrane module that is equipped with a hollow fiber membrane made of fluororesin and end sealing parts having a silicone-based resin obtained by curing liquid silicone rubber, and is less susceptible to deterioration even when exposed to the strong oxidizing power of ozone, and is capable of stable water treatment for a long period of time (see JP 6-296836 A).

Japanese Patent Application Publication No. 6-296836

In the hollow fiber membrane module described above, there is a risk that the hollow fiber membrane may come off from the end seals when an external force is applied. In particular, when the hollow fiber membrane is made of polytetrafluoroethylene, polytetrafluoroethylene has lower adhesion to other materials compared to other resins, so the hollow fiber membrane is likely to come off from the fixing parts that fix the hollow fiber membrane, such as the end seals. If the hollow fiber membrane comes off from the fixing parts, it will lead to a decrease in filtration performance.

Therefore, the objective is to provide a hollow fiber membrane module in which the hollow fiber membrane is less likely to come off from its fixed portion.

The hollow fiber membrane module according to one aspect of the present disclosure, which has been made to solve the above problems, comprises a plurality of hollow fiber membranes whose main component is polytetrafluoroethylene, and a fixing portion in which the ends of the plurality of hollow fiber membranes are embedded, the fixing portion being made of a resin composition whose main component is silicone resin, and at least a portion of the outer surface side of the region of the hollow fiber membrane that is embedded in the fixing portion is impregnated with the resin composition.

This disclosure provides a hollow fiber membrane module in which the hollow fiber membrane is less likely to come off from its fixed portion.

FIG. 1 is a schematic diagram showing the configuration of a wastewater treatment device equipped with a hollow fiber membrane module according to one embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of the hollow fiber membrane module of FIG. FIG. 3 is a schematic cross-sectional view partially showing the hollow fiber membranes and fixing parts of the hollow fiber membrane module of FIG. 2. FIG. 4 is a schematic partial cross-sectional view of a hollow fiber membrane of the hollow fiber membrane module of FIG. FIG. 5 is an electron microscope photograph (1000x) showing the outer peripheral surface of the surface-treated end of the hollow fiber membrane of Example 1. FIG. 6 is an electron microscope photograph (magnification: 5000) showing the outer peripheral surface of the surface-treated end portion of the hollow fiber membrane of Example 1. FIG. 7 is an electron microscope photograph (1000x) showing the outer peripheral surface of the end portion of the hollow fiber membrane of Comparative Example 1 that has not been surface-treated. FIG. 8 is an electron microscope photograph (5000x) showing the outer peripheral surface of the end portion of the hollow fiber membrane of Comparative Example 1 that was not surface-treated.

[Description of the embodiments of the present disclosure]
A hollow fiber membrane module according to one embodiment of the present disclosure comprises a plurality of hollow fiber membranes composed primarily of polytetrafluoroethylene and a fixing portion in which ends of the plurality of hollow fiber membranes are embedded, the fixing portion being made of a resin composition composed primarily of a silicone resin, and at least a portion of an outer surface side of the region of the hollow fiber membranes embedded in the fixing portion being impregnated with the resin composition.

As mentioned above, PTFE has relatively low adhesion to other materials, and therefore the adhesion of the hollow fiber membrane, which is mainly composed of PTFE, to other components is also relatively low. However, by impregnating the outer surface side of the hollow fiber membrane, which is mainly composed of PTFE, with the resin composition that constitutes the fixing part, the adhesion between the hollow fiber membrane and the fixing part is increased. Therefore, in this hollow fiber membrane module, the hollow fiber membrane is less likely to come off from the fixing part.

It is preferable that the hollow fiber membrane includes a porous structure having a plurality of fibers whose main component is polytetrafluoroethylene and a plurality of nodes connected to each other by these fibers, and that the fibers in the region embedded in the fixing part of the hollow fiber membrane are partially cut. By partially cutting the fibers in the region embedded in the fixing part, the voids impregnated (filled) with the resin composition constituting the fixing part become larger in the region embedded in the fixing part, so that the adhesion between the hollow fiber membrane and the fixing part is more reliably improved.

It is preferable that the average depth of impregnation of the resin composition in the region embedded in the fixing part is 0.3% or more of the average thickness of the hollow fiber membrane. By making the impregnation depth satisfy the above range, the adhesion between the hollow fiber membrane and the fixing part can be further improved.

It is preferable that the ratio of the isopropyl alcohol bubble point of the region of the hollow fiber membrane that is embedded in the fixing portion to the region of the hollow fiber membrane that is not embedded in the fixing portion is 0.4 to 0.8. By having the isopropyl alcohol bubble point ratio in the above range, the adhesion between the hollow fiber membrane and the fixing portion can be further improved.

Here, "main component" refers to the component with the largest content, for example, the component with a content of 50% by mass or more. "Impregnated with the resin composition constituting the fixing part" means that the region of the fixing part facing the outer peripheral surface of the hollow fiber membrane is impregnated with the resin composition constituting the fixing part. "Isopropyl alcohol bubble point (hereinafter also referred to as "IPA-BP")" refers to a value measured in accordance with JIS-K3832 (1990) using isopropyl alcohol, and is an index corresponding to the maximum pore size of the pores (for example, the porous structure described below) of the hollow fiber membrane.

[Details of the embodiment of the present disclosure]
Hereinafter, an embodiment of the hollow fiber membrane module according to the present disclosure will be described in detail with reference to the drawings, taking as an example a case in which the hollow fiber membrane module is provided in a wastewater treatment device.

[Wastewater treatment device]
As shown in Fig. 1, a wastewater treatment device including a hollow fiber membrane module according to an embodiment of the present disclosure includes a treated water tank T for storing treated water containing activated sludge, and one or more hollow fiber membrane modules 1 disposed in the treated water tank T. The hollow fiber membrane module 1 functions as a filtration module. The wastewater treatment device further includes a pump 2 for sucking out the treated water in the treated water tank T through the hollow fiber membrane module 1.

The wastewater treatment device may also have an aeration device for supplying air (oxygen) to the activated sludge, a carrier to which the activated sludge adheres in high concentration, a bubbling device for supplying air bubbles for cleaning the hollow fiber membrane module 1, a sludge extraction device for discharging excess activated sludge, a frame for supporting other components in the treatment tank T, a control device, etc., all of which are not shown.

The wastewater treatment device uses activated sludge, which is an aerobic microorganism, to decompose organic matter in the water to be treated, such as domestic wastewater, sewage, or industrial wastewater, and separates and discharges impurities using a hollow fiber membrane module 1. That is, in this embodiment, the wastewater treatment device is a device that treats wastewater using the membrane separation activated sludge method.

[Treatment tank]
The treated water tank T stores the water to be treated so that the hollow fiber membrane module 1 can be immersed therein. The treated water tank T may be made of a material such as resin, metal, or concrete.

[Hollow fiber membrane module]
The hollow fiber membrane module 1 includes a plurality of hollow fiber membranes 3 mainly composed of PTFE, and a pair of fixing parts 7 in which both ends of the hollow fiber membranes 3 are embedded and which fix both ends of the hollow fiber membranes 3. The fixing parts 7 are composed of a resin composition mainly composed of a silicone resin. At least a part of the outer surface side of the region of the hollow fiber membranes embedded in the fixing parts 7 is impregnated with the resin composition constituting the fixing parts 7. In this embodiment, as shown in FIG. 2, the hollow fiber membrane module 1 includes a plurality of hollow fiber membranes 3 held in a state of being aligned in one direction (up and down), a pair of fixing parts 7 that respectively fix both ends of the plurality of hollow fiber membranes 3, and a pair of holding parts (first holding part 4 and second holding part 5) that hold the hollow fiber membranes 3 fixed by each fixing part 7.

<Hollow fiber membrane>
The hollow fiber membrane 3 is formed of a resin composition mainly composed of PTFE. The lower limit of the PTFE content in the hollow fiber membrane 3 is 50% by mass, preferably 90% by mass, more preferably 95% by mass, and more preferably 99% by mass. The upper limit of the PTFE content in the hollow fiber membrane 3 may be 100% by mass. In addition, the resin composition forming the hollow fiber membrane 3 may contain additives such as resins other than polytetrafluoroethylene and lubricants.

The lower limit of the average outer diameter of the hollow fiber membrane 3 is preferably 1 mm, more preferably 1.5 mm, and even more preferably 2 mm. On the other hand, the upper limit of the average outer diameter of the hollow fiber membrane 3 is preferably 6 mm, more preferably 5 mm, and even more preferably 4 mm. If the average outer diameter of the hollow fiber membrane 3 is less than the above lower limit, the mechanical strength of the hollow fiber membrane 3 may be insufficient. On the other hand, if the average outer diameter of the hollow fiber membrane 3 exceeds the above upper limit, the ratio of the surface area to the cross-sectional area of the hollow fiber membrane 3 may be reduced, and the filtration efficiency may be reduced.

The lower limit of the average inner diameter of the hollow fiber membrane 3 is preferably 0.3 mm, more preferably 0.5 mm, and even more preferably 0.9 mm. On the other hand, the upper limit of the average inner diameter of the hollow fiber membrane 3 is preferably 4 mm, and more preferably 3 mm. If the average inner diameter of the hollow fiber membrane 3 is less than the above lower limit, the pressure loss when discharging the treated water in the hollow fiber membrane 3 may become too large. On the other hand, if the average inner diameter of the hollow fiber membrane 3 exceeds the above upper limit, the thickness of the hollow fiber membrane 3 may become too small, resulting in insufficient mechanical strength and impurity permeation prevention effect.

The lower limit of the ratio of the average inner diameter to the average outer diameter of the hollow fiber membrane 3 is preferably 3/10, more preferably 2/5. On the other hand, the upper limit of the ratio of the average inner diameter to the average outer diameter of the hollow fiber membrane 3 is preferably 4/5, more preferably 3/5. If the ratio of the average inner diameter to the average outer diameter of the hollow fiber membrane 3 does not meet the above lower limit, the thickness of the hollow fiber membrane 3 may become too large, and the water permeability of the hollow fiber membrane 3 may decrease. On the other hand, if the ratio of the average inner diameter to the average outer diameter of the hollow fiber membrane 3 exceeds the above upper limit, the thickness of the hollow fiber membrane 3 may become too small, and the mechanical strength and the effect of preventing the permeation of impurities may become insufficient.

In the hollow fiber membrane module 1, the lower limit of the average effective length along the central axis of the hollow fiber membranes 3 is preferably 1 m, more preferably 2 m. On the other hand, the upper limit of the average effective length of the hollow fiber membranes 3 is preferably 8 m, more preferably 7 m. If the average effective length of the hollow fiber membranes 3 does not meet the above lower limit, the volumetric efficiency of the hollow fiber membrane module 1 may become too small. On the other hand, if the average effective length of the hollow fiber membranes 3 exceeds the above upper limit, the hollow fiber membranes 3 may bend too much due to their own weight, or the hollow fiber membrane module 1 may become less easy to handle when installed, etc.

The lower limit of the average thickness (wall thickness) of the hollow fiber membrane 3 is preferably 100 μm, more preferably 200 μm, and even more preferably 300 μm. On the other hand, the upper limit of the average thickness is preferably 600 μm, more preferably 500 μm, and even more preferably 400 μm. If the average thickness is less than the lower limit, the strength of the hollow fiber membrane 3 may be insufficient. On the other hand, if the average thickness exceeds the upper limit, the filtration efficiency may be too low.

The hollow fiber membrane 3 preferably includes a porous structure having a plurality of fibers (fibrils) whose main component is PTFE, and a plurality of nodes connected to each other by these fibers. The hollow fiber membrane 3 having such a porous structure is formed by a stretch molding method. The size of the pores can be adjusted by adjusting the stretch temperature, stretch ratio, etc. in the stretch molding.

The hollow fiber membrane 3 may be a single-layer tubular hollow fiber membrane or a tubular hollow fiber membrane having multiple layers in the radial direction.

Figure 3 shows an example of a hollow fiber membrane 3 having multiple layers. The hollow fiber membrane 3 shown in Figure 3 has a porous support layer 3a formed in a tubular shape and a porous filtration layer 3b laminated on the outer surface of the support layer 3a. As shown in Figure 4, the support layer 3a has a first porous structure 31 having a plurality of first fibers 32 mainly composed of PTFE and a plurality of first nodes 33 connected to each other by these first fibers 32, and the filtration layer 3b has a second porous structure 34 having a plurality of second fibers 35 mainly composed of PTFE and a second node 36 connected to each other by these second fibers 35.

The lower limit of the average thickness of the support layer 3a is preferably 0.3 mm, more preferably 0.5 mm. On the other hand, the upper limit of the average thickness of the support layer 3a is preferably 1.0 mm, more preferably 0.8 mm. If the average thickness of the support layer 3a is less than the lower limit, the strength of the support layer 3a and therefore the hollow fiber membrane 3 may be insufficient. On the other hand, if the average thickness of the support layer 3a exceeds the upper limit, the inner diameter of the hollow fiber membrane 3 may become too small, and the pressure loss when discharging the treated water may become too large.

The lower limit of the average pore size of the support layer 3a is preferably 1 μm, more preferably 1.5 μm. On the other hand, the upper limit of the average pore size of the support layer 3a is preferably 3 μm, more preferably 2.5 μm. If the average pore size of the support layer 3a is less than the lower limit, the hollow fiber membrane 3 may have insufficient water permeability. On the other hand, if the average pore size of the support layer 3a exceeds the upper limit, the permeation of impurities may not be sufficiently prevented. The average pore size of the support layer 3a is measured by a pore diameter distribution measuring device (for example, PMI's palm porometer "CFP-1200A").

The lower limit of the porosity of the support layer 3a is preferably 40%, more preferably 50%. On the other hand, the upper limit of the porosity of the support layer 3a is preferably 90%, more preferably 85%. If the porosity of the support layer 3a is less than the lower limit, the water permeability of the hollow fiber membrane 3 may be insufficient. On the other hand, if the porosity of the support layer 3a is more than the upper limit, the strength of the hollow fiber membrane 3 may be insufficient. Note that "porosity" refers to the ratio of the total volume of the pores to the volume of the hollow fiber membrane, and is obtained by measuring the actual volume (apparent volume) of the hollow fiber membrane, calculating the true volume of the hollow fiber membrane (calculated from the dry mass and true density of the hollow fiber membrane), and calculating the percentage of the difference obtained by subtracting the true volume from the actual volume.

The lower limit of the average thickness of the filtration layer 3b is preferably 10 μm, more preferably 12 μm. On the other hand, the upper limit of the average thickness of the filtration layer 3b is preferably 100 μm, more preferably 80 μm. If the average thickness of the filtration layer 3b is less than the lower limit, the permeation of impurities may not be sufficiently prevented. On the other hand, if the average thickness of the filtration layer 3b exceeds the upper limit, the water permeability of the hollow fiber membrane 3 may be insufficient.

The lower limit of the average pore size of the filtration layer 3b is preferably 0.01 μm, more preferably 0.05 μm. On the other hand, the upper limit of the average pore size of the filtration layer 3b is preferably 0.45 μm, more preferably 0.3 μm. If the average pore size of the filtration layer 3b is less than the lower limit, the permeability of the hollow fiber membrane 3 may be insufficient. On the other hand, if the average pore size of the filtration layer 3b exceeds the upper limit, the permeation of impurities may not be sufficiently prevented. The length L in FIG. 4 indicates the maximum length of the second porous structure 34 of the filtration tank 3b. The maximum length of the second porous structure 34 indicates the maximum length when the length of the pore structure is measured at any position, and the smaller this maximum length, the smaller the average pore size of the filtration tank 3b. The average pore size of the filtration layer 3b is measured by a pore diameter distribution measuring device (for example, PMI's palm porometer "CFP-1200A").

The lower limit of the porosity of the filtration layer 3b is preferably 40%, more preferably 50%. On the other hand, the upper limit of the porosity of the filtration layer 3b is preferably 80%, more preferably 70%. If the porosity of the filtration layer 3b is less than the lower limit, the water permeability of the hollow fiber membrane 3 may be insufficient. On the other hand, if the porosity of the filtration layer 3b exceeds the upper limit, the pore size of the hollow fiber membrane 3 may be non-uniform.

(Roughened part of hollow fiber membrane)
The hollow fiber membrane 3 has a roughened portion 8 that has been roughened (treated to roughen the surface) on the outer surface side of the region embedded in the fixing portion 7. The roughened portion 8 of the hollow fiber membrane 3 has a large pore size due to the roughening treatment. At least a portion of the roughened portion 8 is impregnated (more specifically, impregnated and solidified) with the resin composition that constitutes the fixing portion 7. In the embodiment shown in FIG. 3, the roughened portion 8 and the region impregnated with the resin composition coincide with each other.

Methods for roughening the surface of the hollow fiber membrane 3 to form the roughened portion 8 include conventionally known methods, such as a method of burning the outer surface of the hollow fiber membrane 3 with a burner, a method of blasting the hollow fiber membrane 3, a method of plasma treating the hollow fiber membrane 3, and a method of treating the hollow fiber membrane 3 with a treatment liquid. Examples of the treatment liquid used in the treatment liquid treatment method include a metallic sodium-naphthalene complex solution. An example of the metallic sodium-naphthalene complex solution is Tetra-Etch (registered trademark), which is a commercially available product. The operating conditions in these methods may be appropriately set so that the hollow fiber membrane 3 is difficult to remove from the solidified portion 7. For example, in the treatment liquid treatment method, the pore size of the roughened portion 8 can be made larger than that of the region of the hollow fiber membrane 3 that is not embedded in the fixed portion 7 (unroughened portion) by adjusting the time for which the hollow fiber membrane is immersed in the treatment liquid. Of these methods, the treatment liquid treatment method is preferred because it is easy to adjust the pore size of the roughened portion 8.

When the resin composition constituting the fixing part 7 is impregnated into the roughened part 8, the PTFE in the roughened part 8 and the siloxane group of the silicone resin in the fixing part 7 are chemically bonded by a chemical reaction, and the roughened part 8 and the resin composition constituting the fixing part 7 are interlocked to form a physical bond. Here, depending on the type of water to be treated by the hollow fiber membrane module 1, the above-mentioned chemical bond may be destroyed. For example, when the water to be treated is an oxidizing (oxidizing) water to be treated, such as an aqueous solution containing sodium hypochlorite (NaClO), hydrogen peroxide (H ₂ O ₂ ), etc., the above-mentioned chemical bond tends to be destroyed due to contact with the water to be treated. However, since the roughened part 8 and the fixing part 7 are bonded not only by chemical bonds but also by physical bonds, the bond between the roughened part 8 and the fixing part 7 is maintained by physical bonds in the case where the chemical bond is weakened. Therefore, by impregnating the resin composition constituting the fixing part 7 into the roughened part 8, the adhesion between the hollow fiber membrane 3 and the fixing part 7 is improved.

In addition, the roughened portion 8 of the hollow fiber membrane 3 has higher wettability with silicone resin than the non-roughened portion. Therefore, by having the roughened portion 8 of the hollow fiber membrane 3, it becomes easier to impregnate the roughened portion 8 with the resin composition that constitutes the fixing portion 7, thereby improving the manufacturability of the hollow fiber membrane module 1.

When the hollow fiber membrane 3 has the above-mentioned porous structure, it is preferable that the fibers in the above-mentioned porous structure in the roughened portion 8 are partially cut. By partially cutting the above-mentioned fibers in the roughened portion 8, the gaps impregnated with the resin composition constituting the fixing portion 7 become larger in the roughened portion 8 compared to the unroughened portion, so that the adhesion between the hollow fiber membrane 3 and the fixing portion 7 is more reliably improved.

When the hollow fiber membrane 3 has a support layer 3a and a filtration layer 3b as described above, the average pore size and porosity of the support layer 3a in the roughened portion 8 may be the same as those in the unroughened portion. The lower limit of the average pore size of the filtration layer 3b in the roughened portion 8 is preferably 0.05 μm, more preferably 0.08 μm. On the other hand, the upper limit of the average pore size of the filtration layer 3b in the roughened portion 8 is preferably 0.5 μm, more preferably 0.4 μm. The lower limit of the porosity of the filtration layer 3b in the roughened portion 8 is preferably 45%, more preferably 55%. On the other hand, the upper limit of the porosity of the filtration layer 3b in the roughened portion 8 is preferably 95%, more preferably 85%.

The lower limit of the IPA-BP of the roughened portion 8 is preferably 60 kPa, more preferably 80 kPa. On the other hand, the upper limit of the IPA-BP of the roughened portion 8 is preferably 200 kPa, more preferably 180 kPa. If the IPA-BP is less than the lower limit, a part of the solidified portion 7 may be excessively impregnated with the resin composition up to the hollow portion of the hollow fiber membrane 3 (i.e., the hollow portion inside the support layer 3a). On the other hand, if the IPA-BP exceeds the upper limit, it may become difficult for the resin composition to be impregnated.

On the other hand, the lower limit of the IPA-BP in the region of the hollow fiber membrane 3 that is not embedded in the fixing portion 7 is preferably 60 kPa, more preferably 80 kPa. On the other hand, the upper limit of the IPA-BP is preferably 200 kPa, more preferably 180 kPa. If the IPA-BP is less than the lower limit, impurities may not be sufficiently separated. On the other hand, if the IPA-BP exceeds the upper limit, the water permeability of the hollow fiber membrane 3 may be insufficient.

The lower limit of the ratio of the isopropyl alcohol bubble point of the region embedded in the fixing portion to the region not embedded in the fixing portion in the hollow fiber membrane 3 is preferably 0.4, more preferably 0.5. On the other hand, the upper limit of the isopropyl alcohol bubble point ratio is preferably 0.8, more preferably 0.6. If the isopropyl alcohol bubble point ratio does not meet the lower limit, a part of the solidified portion 7 may be excessively impregnated with the resin composition up to the hollow portion of the hollow fiber membrane 3 (i.e., the hollow portion inside the support layer 3a). On the other hand, if the isopropyl alcohol bubble point ratio exceeds the upper limit, the resin composition may be difficult to impregnate.

(Fixed part)
The fixing parts 7 fix the outer periphery of the roughened part 8 at both ends in the central axis direction of the hollow fiber membrane 3, and fill the gap between the first holding part 4 and the second holding part 5 and the hollow fiber membrane 3. In this embodiment, both ends of the hollow fiber membrane 3 are fixed by the fixing parts 7, respectively, but only one of the ends may be fixed by the fixing part 7. In this embodiment, both ends of the hollow fiber membrane 3 are fixed by the respective fixing parts 7 so that these ends are open, but at least one opening of the hollow fiber membrane 3 may be sealed by at least one fixing part 7.

The fixing part 7 is formed from a resin composition mainly composed of a silicone resin. The silicone resin may be a fluorinated silicone resin. The lower limit of the content of the silicone resin in the fixing part 7 is 50% by mass, preferably 90% by mass, more preferably 95% by mass, and more preferably 99% by mass. The upper limit of the content of the silicone resin in the fixing part 7 may be 100% by mass. In addition, the resin composition forming the fixing part 7 may contain additives such as resins other than the silicone resin and lubricants.

The resin composition constituting the fixing portion 7 is impregnated into at least a part of the roughened portion 8 of the hollow fiber membrane 3. The lower limit of the average depth of impregnation of the resin composition in the roughened portion 8 is preferably 0.3%, more preferably 0.5%, and even more preferably 1.0% of the average thickness of the hollow fiber membrane 3. On the other hand, the upper limit of the average depth of impregnation is preferably 3%, more preferably 2%, and even more preferably 1.4% of the average thickness of the hollow fiber membrane 3. If the average depth of impregnation does not meet the lower limit, the adhesion between the hollow fiber membrane 3 and the fixing portion 7 may be insufficient. On the other hand, if the average depth of impregnation exceeds the upper limit, the strength of the hollow fiber membrane 3 may be reduced. The "average depth of impregnation" is the average value of the measured values obtained by measuring the impregnation depth at five points after cross-sectional processing of the impregnated portion of the hollow fiber membrane 3 with a laser and observing the cut surface with a scanning electron microscope (SEM).

The lower limit of the pull-out strength of the hollow fiber membrane 3 from the fixed part 7 is, for example, preferably 0.2 MPa, and more preferably 0.3 MPa. When the pull-out strength is equal to or greater than the lower limit, the hollow fiber membrane 3 is more reliably prevented from coming off the fixed part 7. On the other hand, the greater the pull-out strength, the more preferable it is, and is not particularly limited, but may be, for example, 2 MPa, 1 MPa, or 0.5 MPa. "Pull-out strength" refers to the tensile strength when the fixed part and hollow fiber membrane are pulled by a tensile tester and the hollow fiber membrane is pulled out from the fixed part. The "pull-out strength" is the average of the measured values obtained by chucking the fixing part 7 and the hollow fiber membrane 3 with a chuck distance of 100 mm using a tensile tester, pulling them in the longitudinal direction at a speed of 100 mm/min, and measuring the tensile strength three times (three cases) when the hollow fiber membrane 3 is pulled out from the fixing part 3 so that the length (effective length) of the hollow fiber membrane 3 from the fixing part 7 is 100 mm.

When the hollow fiber membrane 3 has the support layer 3a and the filtration layer 3b as described above, the upper limit of the impregnation depth is preferably equal to or less than the maximum thickness of the filtration layer 3b, and more preferably equal to the maximum thickness of the filtration layer 3b. Here, as described above, since the average pore size of the support layer 3a is larger than the average pore size of the filtration layer 3b, it is more difficult for the resin composition constituting the fixing part 7 to impregnate the filtration layer 3b than the support layer 3a. Therefore, by having the impregnation depth be equal to or less than the average thickness of the filtration layer 3b, it becomes possible to impregnate the filtration part 3a, which is relatively difficult to impregnate, with the resin composition constituting the fixing part 7, and the superiority of the hollow fiber membrane module 1 is enhanced.

The fixing portion 7 is formed by embedding both ends of multiple hollow fiber membranes 3 in an uncured resin composition whose main component is silicone resin, and then curing the composition, using a conventional method.

<Upper holding member>
The first holding part 4 holds the upper ends of the multiple hollow fiber membranes 3 fixed by the upper fixing part 7 in Fig. 2. This first holding part 4 forms an internal space communicating with the inner cavity of the hollow fiber membranes 3 it holds, and has a drain nozzle 10 that discharges the treated water filtered by the hollow fiber membranes 3 from this internal space. That is, the pump 2 is connected to the drain nozzle 10 of the first holding part 4.

<Lower holding member>
The second holding part 5 holds the lower ends of the hollow fiber membranes 3 fixed by the fixing part 7 on the lower side of Fig. 2. The second holding part 5 may form an internal space like the above-mentioned first holding part 4, or may hold the lower ends of the hollow fiber membranes 3 in a manner that closes the openings of the hollow fiber membranes 3. The second holding part 5 may be a member configured to fold back the hollow fiber membranes 3. That is, in the hollow fiber membrane module 1, adjacent hollow fiber membranes 3 may be formed with their lower ends folded back.

〔advantage〕
In this hollow fiber membrane module, at least a portion of the outer surface side of the region embedded in the fixing part in the hollow fiber membrane mainly composed of PTFE is impregnated with the resin composition that constitutes the fixing part, thereby increasing the adhesion between the hollow fiber membrane and the fixing part, and therefore the hollow fiber membrane is less likely to come off from the fixing part.

[Other embodiments]
The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is not limited to the configurations of the above-described embodiments, but is indicated by the claims, and is intended to include all modifications within the meaning and scope of the claims.

The hollow fiber membrane module is not limited to an immersion type in which the water to be treated is permeated to the inner surface side by negative pressure on the inner surface side, but can be of any type, such as an external pressure type in which high pressure is applied to the outer surface side of the hollow fiber membrane to permeate the water to be treated to the inner surface side of the hollow fiber membrane, or an internal pressure type in which high pressure is applied to the inner surface side of the hollow fiber membrane to permeate the water to be treated to the outer surface side of the hollow fiber membrane.

The hollow fiber membrane module may be used to filter water to be treated other than water containing activated sludge.

The wastewater treatment device equipped with the hollow fiber membrane module may further include, in addition to the treatment water tank in which the hollow fiber membrane module is disposed, a tank for precipitating suspended solids in the water to be treated, a tank for exclusively decomposing organic matter using activated sludge, etc.

In the above embodiment, the hollow fiber membrane module does not have an outer tube and is directly disposed in the treatment tank of the wastewater treatment device for wastewater treatment. However, other configurations, for example, the hollow fiber membrane module may have an outer tube and be used for water purification treatment. In this configuration, for example, the hollow fiber membrane module includes an outer tube that houses the hollow fiber membrane with one end fixed by the fixing part and the other end sealed with a known sealing material, a first cap part attached to the end of the outer tube on the side of the fixing part, and a second cap part attached to the end of the outer tube on the opposite side (sealing side) from the fixing part, and the second cap part has an opening for introducing the water to be treated into the outer tube, and the first cap part has an opening for leading the treated water to the outside of the outer tube. In this configuration, for example, the hollow fiber membrane module is arranged so that the second cap part is located below and the first cap part is located above, an inlet pipe for introducing the water to be treated is connected to the opening of the second cap part, and an outlet pipe for discharging the treated water is connected to the opening of the first cap part. The water to be treated is introduced from the inlet pipe through the second cap into the inside of the outer cylinder, and the water to be treated introduced into the outer cylinder is treated by passing through the hollow fiber membrane from the outside to the inside, and the treated water is discharged from the inside of the hollow fiber membrane through the first cap part to the outlet pipe, thereby performing water purification treatment. A circulation pipe for circulating the water to be treated that has not passed through the hollow fiber membrane may be connected to the outer cylinder.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[Example 1]
A hollow fiber membrane was prepared by laminating a tubular support layer (average outer diameter: 2.3 mm, average inner diameter: 1.1 mm, average pore size: 2 μm) made of polytetrafluoroethylene and a tubular filtration layer (average pore size: 0.1 μm, average thickness: 15 μm) laminated on the outer peripheral surface of the support layer. The IPA-BP of the hollow fiber membrane was 140 kPa and the porosity was 80%.

Both ends of the hollow fiber membrane were immersed in a metallic sodium-naphthalene complex solution (Tetra-Etch (registered trademark)) at atmospheric pressure for 5 seconds to perform a surface treatment (roughening treatment), and the complex solution was then dried to form the roughened portions.

The outer peripheral surface of the roughened portion treated as described above was embedded in an uncured resin composition mainly composed of silicone resin, and the resin composition was then impregnated into the porous portion of the roughened portion while being cured to form the fixing portion.

When the average depth of the impregnated portion of the silicone resin-based resin composition impregnated into the roughened portion was measured using the above-mentioned measurement method, it was 15 μm, and the ratio of the average depth of the impregnated portion to the average thickness of the hollow fiber membrane was 2.5%. The results are shown in Table 1. Figure 5 (1000x) and Figure 6 (5000x) show the results of electron microscopy of the outer periphery of the end treated with the above complex solution in Example 1 (before the formation of the fixing portion).

[Comparative Example 1]
As shown in Table 1, a hollow fiber membrane module of Comparative Example 1 was produced in the same manner as in Example 1, except that the hollow fiber membranes were not treated with the above complex solution. The average depth of impregnation was measured as in Example 1 and found to be 0 μm. Moreover, the results of photographing the outer circumferential surface of the end portion not treated with the above complex solution (before the formation of the fixing portion) with an electron microscope are shown in Figure 7 (1000x) and Figure 8 (5000x).

[Comparative Example 2]
As shown in Table 1, a hollow fiber membrane module of Comparative Example 2 was produced in the same manner as Comparative Example 1 (without immersion in the complex solution) except that polyvinylidene fluoride (PVDF) was used as the main component instead of the hollow fiber membrane mainly composed of PTFE. The average depth of impregnation was measured in the same manner as in Example 1 and was found to be 0 μm.

(evaluation)
[Isopropyl alcohol bubble point]
For the hollow fiber membrane obtained in Example 1, the isopropyl alcohol bubble point of the region of the hollow fiber membrane that was not embedded in the fixing portion (non-roughened portion) and the isopropyl alcohol bubble point of the region of the hollow fiber membrane that was embedded in the fixing portion (roughened portion) were measured, and the ratio of the isopropyl alcohol bubble point of the roughened portion to the non-roughened portion was determined.

[Pull-out test]
For the hollow fiber membranes of Example 1, Comparative Example 1, and Comparative Example 2 fixed at the fixing part, the pull-out strength (initial pull-out strength) of the hollow fiber membrane from the fixing part was measured as follows. That is, the hollow fiber membrane and the fixing part were chucked with a chuck interval of 100 mm by an autograph as a tensile tester so that the length (effective length) of the hollow fiber membrane from the fixing part was 30 mm, and the membrane was pulled in the longitudinal direction at a speed of 100 mm/min, and the tensile strength was measured three times (three cases) when the hollow fiber membrane was pulled out from the fixing part. The average value of the obtained measured values was calculated as the pull-out strength. The results are shown in Table 1.

As an example of oxidizing water to be treated, ozone water containing 3 ppm of ozone was used with reference to Patent Document 1. The hollow fiber membrane fixed at the fixing part of Example 1 was immersed in the ozone water for 4 weeks, and the pull-out strength of the hollow fiber membrane from the fixing part was measured in the same manner as above. The results are shown in Table 1.

Comparing Figures 5 and 6, which show the outer peripheral surface of the end treated with the complex solution in Example 1, with Figures 7 and 8, which show the outer peripheral surface of the end not treated with the complex solution in Comparative Example 1, it was shown that in the roughened portion of Example 1, the fibers of the porous structure of the hollow fiber membrane are cut, and the voids (pores) are larger than in the surface of Comparative Example 1. It is clear that the surface of the portion of the hollow fiber membrane of Example 1 that is not treated with the complex solution (unroughened portion) is as shown in Figures 7 and 8 of Comparative Example 1.

As shown in Table 1, it was found that Example 1, which was treated with the above complex solution and had a roughened portion, had a much higher pull-out strength of the hollow fiber membrane than Comparative Example 1, which was not treated with the above complex solution and did not have a roughened portion, and Comparative Example 2, which was mainly composed of PVDF. In addition, in Example 1, no significant decrease in the degree of pull-out was observed even after immersion in ozone water for 4 weeks. Thus, the oxidation resistance of the hollow fiber membrane module of Example 1 was demonstrated. Note that, although the pull-out strength after immersion in ozone water for 4 weeks was not confirmed in Comparative Example 1 and Comparative Example 2, the initial pull-out strengths of Comparative Example 1 and Comparative Example 2 were much smaller than that of Example 1, so it is presumed that the pull-out strengths of Comparative Example 1 and Comparative Example 2 after immersion in ozone water for 4 weeks are much smaller than that of Example 1.
In addition, in the case of a hollow fiber membrane mainly composed of PVDF, no roughened portion is formed even when immersed in the above complex solution, and it is presumed that the effect of increasing the pull-out strength by the surface treatment of the hollow fiber membrane is unique to hollow fiber membranes mainly composed of PTFE.

These results show that the hollow fiber membrane module is less likely to come off from the fixed part of the hollow fiber membrane.

The present invention can be suitably used in wastewater treatment equipment, water purification facilities, etc.

Reference Signs List 1 Hollow fiber membrane module 2 Pump 3 Hollow fiber membrane 3a Support layer 3b Filtration layer 31 First porous structure 32 First fiber 33 First node 34 Second porous structure 35 Second fiber 36 Second node 4 First holding portion 5 Second holding portion 7 Fixing portion 8 Roughing portion 10 Drain nozzle T Treatment water tank

Claims (3)

A plurality of hollow fiber membranes mainly composed of polytetrafluoroethylene;
and a fixing portion in which the ends of the plurality of hollow fiber membranes are embedded,
The fixing part is made of a resin composition containing a silicone resin as a main component,
The end of the hollow fiber membrane is roughened,
The ratio of the isopropyl alcohol bubble point of the end portion to the region other than the end portion in the hollow fiber membrane is 0.4 to 0.8,
A hollow fiber membrane module, wherein at least a part of the outer surface side of the region of the hollow fiber membrane embedded in the fixing portion is impregnated with the resin composition. The hollow fiber membrane includes a porous structure having a plurality of fibers mainly composed of polytetrafluoroethylene and a plurality of nodes connected to each other by these fibers,
2. The hollow fiber membrane module according to claim 1, wherein the fibers in the region embedded in the fixing portion are partially cut. The hollow fiber membrane module according to claim 1 or 2, wherein the average depth of the portion impregnated with the resin composition in the region embedded in the fixing portion is 0.3% or more of the average thickness of the hollow fiber membrane.

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