JP2011000509A - Hollow fiber filtration membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hollow fiber filtration membrane capable of mitigating the non-uniformity of the filtration performance thereof in the longitudinal direction caused when being actually used, thereby more stabilizing the separation performance thereof, to provide a hollow fiber filter capable of mitigating the non-uniformity of the filtration performance by packing the hollow fiber filtration membrane, and to provide a method for filtering a liquid to be treated by using the hollow fiber filter.SOLUTION: The porous hollow fiber filtration membrane is characterized in that when the hollow fiber filtration membrane is divided into three equal portions in the longitudinal direction and the water permeability of each of cut fibers in the three equal portions is measured, the cut fiber in the central portion C has the intrinsic water permeability higher than those of both of the cut fiber in the end portion A and the cut fiber in the end portion B.

Description

The present invention relates to a porous hollow fiber filtration membrane. More specifically, the present invention relates to a hollow fiber filtration membrane having a central portion having a higher water permeability than both ends.
The present invention also relates to a hollow fiber filter incorporating the hollow fiber filter membrane and a method for filtering a liquid to be treated using the hollow fiber filter.

Hollow fiber filtration membranes are incorporated as functional elements for separating, concentrating, and purifying target products from liquids or gases to be processed in industrial process filters, water filters, physics / test filters, blood purifiers, etc. It is used for a wide range of applications in various fields.
In these hollow fiber filtration membranes, studies have been made from various viewpoints in order to enhance the capability as a functional element. Especially for permeation performance, improved permeation performance (unit time, filtration rate per unit area, etc.), excellent selective separation (sharp molecular weight fractionation, etc.) or stability over time (lifetime, etc.) In order to achieve this, element factors such as the material, composition, physical properties, shape, and structure of the film, as well as methods for obtaining the desired film by arbitrarily combining or controlling each element factor (for example, film forming method, post-processing method) Alternatively, reforming methods, etc.) are also being studied.

Regarding the permeation performance of the hollow fiber filtration membrane, usually, bundles of a plurality of to tens of thousands of hollow fiber filtration membranes are filled into a cylindrical container, and the bundle is configured in consideration of the usage form used as a hollow fiber filter. The uniformity of the individual hollow fiber filtration membranes is important. Specifically, it is important that there is no variation in permeation performance between the hollow fiber filtration membranes in the bundle, and that each hollow fiber filtration membrane can contribute to filtration without excess or deficiency in the entire length direction.
Regarding the uniformity in the former bundle, for example, when the bundle is dried, a technique (Patent Document 1) for reducing the difference in permeation performance generated in the membrane at the center portion and the peripheral portion of the bundle, or a hollow fiber filtration membrane is used. Techniques for improving graft polymerization unevenness that occurs when the surface is modified in a state, that is, non-uniformity of hydrophilicity are disclosed (Patent Documents 2 and 3).

On the other hand, with regard to the uniformity in the length direction of the latter, when the hollow fiber filtration membrane is surface-modified to improve the permeability, the reaction gas is sucked from one direction of the bundle, so that the reaction can be performed in the length direction. The technique to make is disclosed (patent document 4). In addition, although not specifically cited, a film that has undergone a continuous process without being cut in the middle from film formation to drying is longer in the length direction and in the bundle than a film that is cut in the middle and batch-processed. It is well known that the uniformity is high.
Thus, in the hollow fiber filtration membrane, in order to maximize the permeation performance of the membrane, the viewpoint of homogenization between the membranes in the bundle and in the length direction of the membrane has been emphasized, Attention has been paid to obtaining a hollow fiber filtration membrane having uniform permeation performance.

However, when the filtration is actually performed using a hollow fiber filter, a phenomenon peculiar to the hollow fiber filtration membrane occurs. That is, generally, when water is passed through a hollow fiber membrane having an inner diameter of several hundred μm to several mm and a length of several tens of centimeters or more, the hollow portion is caused by the flow resistance of the liquid flowing through the hollow portion. Pressure loss occurs in the length direction. As a result, since the transmembrane pressure difference also decreases in the length direction, the actual filtration amount decreases in the length direction of the hollow fiber.
As in the prior art, the amount of filtration obtained by measuring the entire hollow fiber filtration membrane or hollow fiber filter is merely looking at the average value in the length direction. This means that there is a shortage and a shortage. In addition to the above, this non-uniformity pattern varies depending on internal pressure filtration, external pressure filtration, dead-end filtration, and crossflow filtration. Is not obtained. Due to this phenomenon, in a region where filtration is excessive, clogging may cause a local decrease in the lifetime, or an object that is originally difficult to permeate may partially permeate with a large filtration flux. On the other hand, in a region where filtration is insufficient, an object to be permeated may not sufficiently permeate.

JP 2002-239348 A JP 2004-244501 A JP-A-4-293939 Japanese Patent Laid-Open No. 05-209071

Even if the inventors pursued uniform permeation performance only at the stage of designing and manufacturing a hollow fiber filtration membrane as in the prior art, the uniformity is sufficiently utilized in actual use. I realized that there was no problem, so I decided to solve it.
Accordingly, an object of the present invention is to obtain a hollow fiber filtration membrane that can further stabilize the separation performance by alleviating the non-uniformity of the filtration performance that occurs in the length direction when the hollow fiber filtration membrane is actually used. To do.
In addition, the present invention provides a hollow fiber filter that can alleviate non-uniformity in filtration performance by filling such a hollow fiber filtration membrane, and a method for filtering a liquid to be treated using the hollow fiber filter. The purpose is to do.

  As a result of intensive studies to solve the above problems, the inventors of the present invention have determined that the intrinsic water permeability at the center when the porous hollow fiber membrane is divided into three equal parts in the length direction is the intrinsic water permeability at both ends. The present inventors have found that the above-mentioned problems can be solved by using a higher hollow fiber filtration membrane, thereby completing the present invention.

That is, the present invention is as follows.
A porous hollow fiber filtration membrane, wherein the intrinsic water permeability at the center when the hollow fiber filtration membrane is divided into three equal parts in the length direction is higher than the intrinsic water permeability at both ends.

  The reason why the problem is solved by the present invention is not clear, but in the hollow fiber filtration membrane of the present invention, by designing the inherent water permeation amount to be “low → high → low” in the length direction, the membrane Although it is estimated that the influence of non-uniformity of the intermediate pressure is canceled and the non-uniformity of the filtration performance is mitigated, it is not limited to this.

  According to the present invention, it is possible to prevent the occurrence of excessive filtration in the hollow fiber filtration membrane, to reduce the local lifetime due to clogging, and to prevent an object that is originally difficult to permeate with a large filtration flux. It is possible to prevent partial transmission.

It is sectional drawing which shows an example of the hollow fiber filter of this invention. It is sectional drawing which shows an example of the hollow fiber filter which measures the effective water permeability of a hollow fiber filtration membrane. It is sectional drawing which shows an example of the partition means of the hollow fiber filter for effective water permeability measurement. It is a figure which shows an example of the flow-path structure of the filtration apparatus which performs the filtration method of this invention. It is a schematic diagram which shows distribution when a hollow fiber filter filters dead-end internal pressure, and a water permeability. It is a mimetic diagram showing distribution of a pressure and water permeability when carrying out cross flow external pressure filtration of a hollow fiber filter. It is a graph which shows the natural water permeability of a hollow fiber filtration membrane.

  As the hollow fiber filtration membrane of the present invention, any material can be used as long as it is made of a polymer material that forms a porous structure and can form the pore size of ultrafiltration or microfiltration membrane. it can. For example, olefin resins such as polyethylene and polypropylene, polyester resins such as polyethylene terephthalate and polyethylene terephthalate, polyamide resins such as nylon 6 and nylon 66, fluorine-containing resins such as polyvinylidene fluoride and polychlorotrifluoroethylene, polystyrene, polysulfone, Amorphous resins such as polyethersulfone and polycarbonate can be used.

  The hollow fiber filtration membrane of the present invention preferably has a maximum pore size of 10 to 100 nm, more preferably 10 to 70 nm, and most preferably 10 to 50 nm. If the maximum pore size is less than 10 nm, the permeability and filtration rate of physiologically active substances such as globulins tend to be low. On the other hand, when the thickness exceeds 100 nm, it is not possible to remove the fine particles to be removed such as viruses at a practical level by blocking membrane permeation. The maximum pore diameter referred to here is a value measured by a bubble point method based on ASTM F316-86.

  The hollow fiber filtration membrane of the present invention preferably has a length of 0.1 to 0.7 m, more preferably 0.15 to 0.5 m, and particularly preferably 0.2 to 0.4 m. . When the length of the hollow fiber filtration membrane is less than 0.1 m, the water permeability distribution in the length direction is difficult to occur during filtration or becomes a negligible level so that the effect of the present invention cannot be exhibited. Moreover, the handleability at the time of shape | molding to a hollow fiber type filter is bad, and production efficiency is also not good. On the other hand, when the length exceeds 0.7 m, it becomes difficult to control the effective water permeability described later.

  The hollow fiber filtration membrane of the present invention may have an inner diameter that is common in ultrafiltration membranes and microfiltration membranes. Considering the magnitude of pressure loss in the hollow part during production or filtration, any inner diameter may be used as long as the inner diameter is larger than 100 μm. Preferably it is 100-2000 micrometers, More preferably, it is 200-1000 micrometers, Especially preferably, it is 300-500 micrometers. When the inner diameter is larger than 2000 μm, the bulk of the filter increases when molding a hollow fiber filter having the same membrane area, which is not preferable from the viewpoint of practicality.

  From the above description, in the hollow fiber filtration membrane of the present invention, L / D (−), which is the ratio of the length L (mm) to the inner diameter D (mm), is preferably 50 to 7000. If it is an elongated shape like this, when it is assembled into a hollow fiber filter as a bundle of thousands to tens of thousands, it becomes a compact size for a large membrane area and is very convenient to use. Moreover, since there exists a tendency which can ensure a high linear velocity when filtering, especially in crossflow filtration, fouling can be suppressed and it is excellent in filtration efficiency. A more preferable range of L / D is 150 to 2500, and particularly preferably 400 to 1333.

  The hollow fiber filtration membrane of the present invention needs to have a higher intrinsic water permeability at the center than at both ends when it is divided into three equal parts in the length direction. In the prior art, in order to make the permeation performance of the hollow fiber filtration membrane uniform, it has been required to be uniform in the length direction (= water permeability is almost constant). It is assumed to be uniform.

The inherent water permeation amount is measured by using the entire hollow fiber filtration membrane as in the prior art, and the average water permeation amount without the concept of the length direction (the water permeation amount of the entire hollow fiber filtration membrane). ) Rather than “the water permeability permeated partially by introducing the concept of the length direction” (water permeability of a specific portion in the length direction of the hollow fiber filtration membrane).
Specifically, the intrinsic water permeability of the center part and the end part is measured as follows. First, the hollow fiber filtration membrane is divided into three equal parts in the length direction, filled into a cylindrical container having a filtrate outlet, and then both ends are potted. Next, header caps having inlets (outlets) for the liquid to be treated communicating with the hollow interior of the hollow fiber filtration membrane were attached to both sides of the cylindrical container, and both ends and the center of the hollow fiber filtration membrane were filled. Create different types of mini-modules. The structure of the mini module is the same as the structure of the hollow fiber filter of the present invention shown in FIG. Next, in a state where one of the header caps attached to both sides of each mini-module is closed, pure water is introduced from the other end to perform constant pressure dead-end internal pressure filtration. Based on the permeation amount of the obtained pure water, the inherent water permeation amounts at three locations in the length direction are calculated based on the following equation (1).
Specific water permeability (m ³ / m ² · s · Pa)
= Permeation amount (m ³ ) / (membrane area (m ² ) × filtration time (m ² ) × filtration pressure (Pa)) (1)

In the present invention, it is necessary that the central portion has a higher intrinsic water permeability than both end portions. In the hollow fiber filtration membrane having a pore size and water permeability suitable for ultrafiltration and microfiltration, by designing the inherent water permeability so that it becomes `` low → high → low '' in the length direction in advance, The following advantages (a) to (c) are produced.
(A) When a hollow fiber filtration membrane is used for internal pressure filtration, a high transmembrane pressure difference is usually generated on the inlet side of the liquid to be treated of the hollow fiber filtration membrane, resulting in excessive filtration (FIG. 5A). If the specific water permeability is designed as in the present invention, the pressure difference between the membranes is high on the inlet side but the water permeability is low. The amount of filtration can be made equal (see FIG. 5 (B)). By doing so, the fall of local lifetime is improved by the clogging which has conventionally occurred at a site where filtration is excessive.
(B) When a hollow fiber filtration membrane is used for external pressure filtration, usually a high transmembrane pressure difference is generated on the filtrate outlet side of the hollow fiber filtration membrane (both ends of the hollow fiber filtration membrane), resulting in excessive filtration. (See FIG. 5 (A)), if the inherent water permeability is designed as in the present invention, the pressure difference between the membranes is high on the outlet side, but the water permeability is low. The amount of filtration at the outlet side end portion and the central portion can be made equal (see FIG. 6 (B)). By doing so, the fall of local lifetime is improved by the clogging which has conventionally occurred at a site where filtration is excessive.
(C) In both cases of the internal pressure filtration and the external pressure filtration, the permeation rate is small, and an object that should be almost prevented from permeating the membrane partially permeates with a large filtration flux locally. The fear of end will be dispelled.

  It is preferable that the intrinsic water permeability of the central portion is higher than the intrinsic water permeability of at least one end by more than 10% (that is, the intrinsic water permeability of the central portion> the intrinsic water permeability of at least one end × 110/100 ). If a difference is provided in this degree, it is easy to adjust the flow rate of the pump and the flow rate adjusting valves when actually filtering. More preferably, it is higher than 15%, particularly preferably higher than 20%. The upper limit is not particularly limited, but if the difference is larger than necessary, the pressure difference between the liquid to be treated and the membrane during actual use will be extremely increased, which may affect the solute in the filtration membrane and liquid to be treated. . Therefore, the upper limit of the intrinsic water permeability at the center may be about 200% of the intrinsic water permeability at the end.

  In the present invention, it is only necessary that the central portion has a higher intrinsic water permeability than both end portions, and the height relationship between the end portions is not limited. However, if the intrinsic water permeation amount at both ends is equal (no statistically significant difference), the hollow fiber filtration membrane is symmetrical in the length direction, so that there is an advantage of excellent handleability. For example, in the manufacturing process of a hollow fiber filter using the membrane, the labor of confirming the directionality of the end portion when filling the hollow container with a hollow fiber filtration membrane (yarn bundle) is saved. Excellent in properties. Moreover, since it is not necessary to confirm the directionality of the filter even after filling the hollow fiber filter, the handleability is excellent. Therefore, it is more preferable that the natural water permeation amounts at both ends are equal.

The hollow fiber filtration membrane according to the present invention has an effective water permeation amount F _AE , F _BE, and F _CE at the end A, the end B, and the center C when the cylindrical container is filled and subjected to dead end internal pressure filtration. It is preferable that the relationship is as follows: (a) F _AE ≧ F _CE > F _BE or (b) F _CE > F _AE > F _BE (however, the central part C is the effective filtration part of the hollow fiber filtration membrane. The portion corresponding to the central portion in the case of being equally divided into three in the length direction, and the end portions A and B are respectively the end portions located on the treatment liquid introduction side from the central portion C of the hollow fiber filtration membrane, (It shall mean the end portion located on the opposite side of the treated liquid introduction side from the central portion C of the hollow fiber filtration membrane).
The effective filtration part means a part where the surface of the hollow fiber filtration membrane is exposed.

The effective water permeability is the water permeability of a specific portion in the length direction of the hollow fiber filtration membrane in a state where it is actually used. That is, as in the prior art, it is measured by using the entire hollow fiber filtration membrane in actual use, not “the concept of length direction, averaged water permeability”, but “actually used”. In this state, the concept of the length direction is introduced and the water permeability is seen partially.
Specifically, the effective water permeability of the end A, the center C, and the end B is measured as follows. First, as shown in FIGS. 2 and 3, a hollow fiber filtration membrane (yarn bundle) 3 is filled into a split-type effective water permeability measuring container 2, which is partitioned into three chambers, without liquid leakage. After potting both ends of the hollow fiber filtration membrane so that it can be filtered, header caps with inlets (outlets) for the liquid to be treated communicating with the hollow interior of the hollow fiber filtration membrane are attached to both sides of the cylindrical container. The hollow fiber filter 1 for measuring the effective water permeability is created. The container 2 includes a split-type outer cylinder 2A and an outer cylinder 2B. The outer cylinder 2A and the outer cylinder 2B are engaged with each other while sandwiching the yarn bundle 3 therebetween to form an integral container. The container is fitted with filtrate outlets (5A, 5C and 5B) communicating with the respective chambers. On the inner walls of the outer cylinder 2A and the outer cylinder 2B, partition means 4 are provided at positions corresponding to the boundary portions of the end portion A and the center portion C of the hollow fiber filtration membrane and the center portion C and the end portion B, respectively. The interior is divided into three rooms. The partition means 4 is not particularly limited as long as it closes the gap between the outer peripheral portion of the yarn bundle and the inner peripheral portion of the container, and a plate-like body, a string-like object, a swellable resin or the like may be used.
Next, of the header caps attached to both sides of the hollow fiber filter for measuring effective water permeability, pure water is introduced from the other end with one end closed, and constant pressure dead end internal pressure filtration is performed. At this time, in order to make the introduction pressure of the liquid to be treated constant, the minimum inner diameter of the introduction port is set to 4.0 mm. Based on the permeation amount of pure water obtained from the three filtrate outlets 5A, 5C and 5B, the effective water permeation amount at three locations in the length direction is calculated based on the following equation (2).
Effective water permeability (m ³ / m ² · s · Pa)
= Permeation amount (m ³ ) / (membrane area (m ² ) × filtration time (s) × filtration pressure (Pa)) (2)

  In addition, when the hollow fiber filtration membrane has already been assembled into a normal hollow fiber filter, the outer tube portion is carefully cut off, and the hollow fiber filtration membrane with the resin layer portions at both ends attached (bundle of ). Thereafter, the hollow fiber filtration membrane (bundle) is filled into an effective water permeability measuring container, and the gap is liquid-tightly sealed and measured.

The effective water permeation amount of the hollow fiber filtration membrane is determined by the relationship between the effective water permeation amounts F _AE , F _BE, and F _CE of the end A, the end B, and the center C when performing constant pressure dead end internal pressure filtration. It is preferable that “ _AE ≧ F _CE > F _BE ”. If each effective water permeation amount is in this relationship, it can be said that excessive filtration due to a high transmembrane pressure difference on the inlet side of the liquid to be treated is reduced.
Further, the relationship between the effective water permeability F _AE , F _BE and F _CE may be “F _CE > F _AE > F _BE ”. If each effective water permeation amount has this relationship, it can be said that the excess filtration due to the high transmembrane pressure difference on the inlet side of the liquid to be treated is offset without being insufficient.
In any of the above cases, it is more preferable if the difference between F _AE and F _CE is within ± 10%. When the hollow fiber filtration membrane has such a distribution of the effective water permeability, the local lifetime reduction due to clogging that has conventionally occurred at a site where filtration is excessive is improved. It is particularly preferable that the relationship between the effective water permeabilities is “F _AE = F _CE > F _BE ”.
Here, the difference between F _CE and F _AE is {(F _CE −F _AE ) / F _CE } × 100.

The method for obtaining the hollow fiber filtration membrane having the inherent water permeation amount is not particularly limited, and examples thereof include a treatment method in a membrane formation step and a surface modification method after the membrane formation.
As an example of the former, there is a method in which a plurality of hollow fiber filtration membranes are combined into a yarn bundle, and microwave-dried in a state of being wound with a film or the like so as not to be separated. At this time, if both ends are excessively dried and film shrinkage proceeds, the central portion C in the length direction can have a higher intrinsic water permeability than the end A and the end B.
As an example of the latter, there are methods such as coating a material that lowers the permeation performance of the substrate membrane (for example, a hydrophilic material (monomer, polymer)) on both ends, covalent bonding, or graft polymerization of the monomer. At that time, after the hollow fiber filtration membrane is immersed in the reaction tank in the vertical direction and reacted, the membrane is turned upside down and immersed again to reduce the intrinsic water permeability in the vicinity of both ends. Alternatively, when the hollow fiber filtration membrane is immersed in the reaction tank in the horizontal direction, the reaction proceeds from both ends toward the center, so that the inherent water permeability near both ends can be reduced. For example, when a hydrophilic monomer is hydrophilized by radical-initiated graft polymerization using a hydrophilic monomer, the reaction rate is high, and as a result, it is easy to create a hydrophilic gradient from both ends to the center. This method is particularly preferable because it is easy to give a gradient to the water permeability.

The hollow fiber filter of the present invention is formed by filling one or more hollow fiber filtration membranes in a cylindrical container. An example of such a hollow fiber filter is shown in FIG. As a specific example, one or more hollow fiber filtration membranes (in the case of a plurality of hollow fiber filtration membranes, also referred to as “yarn bundle”) 3 and a filtrate drain for discharging the filtrate to the outside of the container filled with the hollow fiber filtration membranes. A cylindrical container 6 having an outlet 5 (sometimes referred to as a nozzle), and both ends of the hollow fiber filtration membrane are liquid-tightly fixed to both ends of the cylindrical container, and an opening 7 of the hollow fiber filtration membrane is provided. And a potting portion 8 that separates the hollow interior and the hollow exterior, and an inlet (outlet) of the liquid to be treated that is covered by the potting portion and communicates with the hollow interior (sometimes referred to as a nozzle) And a header cap 9 having
In addition, although FIG. 1 shows an example of a crossflow filter having an inlet (outlet) for the liquid to be treated communicating with the hollow interior of the hollow fiber filtration membrane 3 at both ends, When doing so, it is better to mold one end of the communication port into a blind end in advance.

  The detailed structure and manufacturing method of the hollow fiber filter are not particularly limited, and the structure and manufacturing method of a known hollow fiber type industrial filter or hollow fiber type artificial dialyzer can be employed. However, the length of the hollow fiber filter is preferably molded so that the length of the filtration effective portion of the filled hollow fiber filtration membrane is 0.1 to 0.7 m. Moreover, it is more preferable that the filling state of the hollow fiber filtration membrane is filled linearly than the membrane is bent in a U shape.

Next, a method for filtering the liquid to be treated using the hollow fiber filter will be described with reference to the drawings.
FIG. 4 is a drawing showing an example of the flow path configuration of the filtration device 10 and the arrangement of accessory parts. In FIG. 4, the to-be-processed liquid storage part 12 is connected to the to-be-processed liquid introduction | transduction side of the hollow fiber type filter 11 by the inlet side flow path 20, The liquid transfer means 23, An inlet side pressure gauge 22 and an inlet side pressure adjusting means 21 are provided. On the other hand, the filtrate outlet of the hollow fiber type filter 11 is connected to the filtrate storage part 13 by a filtration side flow path 30, and the filtration side pressure gauge 32 and the filtration side pressure adjusting means 31 are connected to the filtration side flow path 30. Is provided.
Here, the liquid transfer means 23 may be any liquid feed pump, and may be appropriately selected according to the liquid feed amount and the type of daily treatment liquid. The inlet side pressure adjusting means 22 may be any open / close valve capable of continuously adjusting the internal resistance in a part of the inlet side flow path, and may be appropriately selected. Examples of the inlet-side pressure gauge 21 include a Bourdon tube pressure gauge and a digital manometer. The same applies to the other pressure adjusting means.

In FIG. 4, a flow path portion indicated by a solid line is an example of a flow path when dead-end filtration is performed. In dead-end filtration, the liquid to be processed in the liquid storage section 12 is transferred by the liquid transfer means 23 and introduced into the liquid to be processed introduction side of the hollow fiber filter 11. At this time, the end of the hollow fiber filter 11 opposite to the treatment liquid introduction side is blinded or blocked so that the entire amount of the introduced treatment liquid is filtered. The introduced liquid to be treated is filtered, and collected from the filtrate discharge port of the hollow fiber filter 11 through the filtration side channel 30 to the filtrate storage unit 13. The flow rate and the filtration amount of the liquid to be introduced are appropriately set by any one or more of the liquid transfer means 23, the inlet side pressure adjustment means 22 and the filtration side pressure adjustment means 32.
On the other hand, when cross-flow filtration is performed, a flow path indicated by a dotted line is added to circulate the liquid to be processed. In that case, the treated liquid outlet side of the hollow fiber filter 11 is connected to the treated storage section 12 by the outlet side flow path 40, and the outlet side pressure gauge 41 and the outlet side pressure are connected to the outlet side flow path 40. Adjustment means 42 is provided. In the cross-flow filtration, the liquid to be processed in the liquid storage section 12 is transferred by the liquid transfer means 23 and introduced to the liquid to be processed introduction side of the hollow fiber filter 11. At this time, a part of the liquid to be treated introduced into the hollow fiber filter 11 is filtered from the filtrate discharge port to the filtration side flow path 30, and the rest is led out from the liquid to be treated to the outlet side flow path 40. Thus, it is adjusted by the balance of the filtration side pressure adjusting means 32 and the outlet side pressure adjusting means 42. A part of the derived liquid to be processed passes through the outlet side flow path 40 and is collected in the liquid to be processed storing section 12, and is filtered while being circulated. The flow rate and the filtration amount to be introduced / derived are appropriately set by any one or more of the liquid transfer means 23, the inlet side pressure adjusting means 22, the outlet side pressure adjusting means 42, and the filtration side pressure adjusting means 32.
Although not shown, the method of directly introducing the liquid to be treated into the hollow interior from one end of the hollow fiber filtration membrane is internal pressure filtration, and the liquid to be treated is permeated into the hollow interior from the outer peripheral surface of the hollow fiber filtration membrane. The method introduced in this way is external pressure filtration.

When carrying out the filtration method of the present invention, the flow rate of the liquid transfer means 23, the opening / closing degree of the inlet side pressure adjusting means 21 and the opening degree of the filtration side pressure adjusting means 32 are adjusted to adjust the hollowness. The difference between the effective water flow rate F _{CE at} the center C of the yarn filtration membrane and the effective water flow rates F _AE and F _BE at the end A and / or the end B can be set to be within ± 10%. . At that time, either the flow rate or the pressure may be sufficient if the effective water permeability can be sufficiently adjusted, and the effective water flow rate may be adjusted by both the flow rate and the pressure as necessary. In the case of cross flow filtration, the opening / closing degree of the outlet side pressure adjusting means 42 may be adjusted.
In addition, in adjusting each effective water permeability, another hollow fiber filtration membrane same as what is actually used is prepared for adjustment. And it is good to fill this hollow fiber filtration membrane in the container for measuring the effective water permeability, check the optimum values of the flow rate and the pressure while measuring each effective water permeability, and set the respective set values in advance.

FIG. 5 is a schematic diagram showing the distribution of pressure and water permeability when dead-end internal pressure filtration is performed using a hollow fiber filter.
FIG. 5A shows the prior art. When a hollow fiber filtration membrane having a uniform water permeation rate in the length direction is used, the pressure difference between the membranes becomes the highest at the inlet side end of the liquid to be treated of the hollow fiber filtration membrane. The effective water permeability at the side end is higher than the effective water permeability at the center. This means that there is a concern that a lifetime is reduced due to clogging at the inlet side end portion of the liquid to be treated and that a substance to be permeated is caused to permeate.

On the other hand, FIG. 5B shows a case where the hollow fiber filtration membrane of the present invention is used. When a hollow fiber filtration membrane having a higher intrinsic water permeability at the center than at both ends is used, the liquid to be treated can be treated even if the pressure difference between the membranes at the inlet side end of the liquid to be treated of the hollow fiber filtration membrane is high. As a result of the low intrinsic water permeability at the inlet side end of the liquid offsetting the increase in effective water permeability, the effective water permeability F at the inlet side end of the liquid to be treated can be made equal to the effective water permeability at the center. . This means that a lifetime is reduced due to clogging at the inlet side end of the liquid to be treated, and a permeation of a substance to be prevented from permeating is suppressed.
In order to reduce the lifetime due to clogging at the inlet side end of the liquid to be treated and to suppress the permeation of the substance to be permeated, the effective water permeation amount F _{CE in} the center C of the hollow fiber filtration membrane, It is preferable to set the difference between the effective water permeability F _AE and F _BE of the end A or the end B within ± 10%.
In addition, in this drawing, although the case of dead end filtration was illustrated, the same tendency as this case is shown also when performing cross flow filtration.

FIG. 6 is a schematic diagram showing the distribution of pressure and water permeability when external pressure filtration is performed using a hollow fiber filter and the filtrate is led out from both ends of the hollow fiber filtration membrane.
FIG. 6A shows the prior art. When a hollow fiber filtration membrane with a uniform water permeability in the length direction is used, the pressure difference between the membranes is the highest at both ends of the hollow fiber filtration membrane (at the outlet side of the filtrate), resulting in an effective water permeability at both ends. It becomes higher than the effective water permeability in the center. This means that there is a concern that the lifetime is reduced due to clogging in the vicinity of both end portions, or that the substance to be permeated is permeated.

On the other hand, FIG. 6B shows a case where the hollow fiber filtration membrane of the present invention is used. When a hollow fiber filtration membrane having a higher intrinsic water permeability at the center in the length direction is used than at both ends, even if the pressure difference between the membranes is higher at both ends (filtrate outlet side) of the hollow fiber filtration membrane, As a result of the low intrinsic water permeability at both ends offsetting the increase in effective water permeability, the effective water permeability at both ends can be made equal to the effective water permeability at the center. This means that the lifetime is reduced due to clogging in the vicinity of both ends, and the permeation of the substance to be prevented from permeating is suppressed.
In order to suppress the lifetime decrease due to clogging at both ends and the permeation of the material to be prevented from permeating, the effective water permeability F _{CE at} the center C of the hollow fiber filtration membrane and the end A and the end B It is preferable to set the difference between the effective water permeability F _AE and F _BE within ± 10%.

As is apparent from FIG. 6, when the filtrate is led out from both ends of the hollow fiber filtration membrane by external pressure filtration using the hollow fiber filtration membrane of the present invention, it can be uniformly filtered over the entire length of the hollow fiber filtration membrane. become. Therefore, the hollow fiber filtration membrane of the present invention is particularly suitable for use in external pressure filtration.
FIG. 6 shows the case where the filtrate is led out from both ends of the hollow fiber filtration membrane. However, when the filtrate is led out from one end (for example, the end A) of the hollow fiber filtration membrane by external pressure filtration, FIG. The filtrate is drained only from the left end.

  As described above, the hollow fiber filtration membrane, the hollow fiber filter, and the filtration method of the present invention are used in an industrial process filter, a water purification filter, a physicochemical / inspection filter, a blood purifier, and the like from a liquid to be treated. It can be used for a wide range of applications in various fields for separating, concentrating and purifying sucrose.

  Hereinafter, the present invention will be described in detail by way of examples. The examples do not limit the invention. The measurement methods used in the examples and comparative examples are as follows.

(1) Inherent water permeability 25 hollow fiber filtration membranes are divided into three equal parts in the length direction, and both ends are potted to create three types of mini modules of 6.5 cm × 25 effective filtration portions (each end Part A, end B and center C). At this time, in order to make the introduction pressure of the liquid to be processed constant, the minimum inner diameter of the inlet of the liquid to be processed is set to 4.0 mm.
Of the header caps attached to both sides of each mini-module, with one port closed, pure water with a temperature of 25 ° C. is introduced from the other end, and constant-pressure dead-end internal pressure filtration with a filtration pressure of 0.294 MPa is performed. Based on the permeation amount of the obtained pure water, the inherent water permeation amounts at three locations in the length direction are calculated based on the above formula (1).

(2) Effective water permeability The effective water permeability measurement is carried out by filling 1100 hollow fiber filtration membranes into a split-type container with three compartments as shown in Fig. 2 and potting both ends. A hollow fiber filter is prepared. At this time, in order to make the introduction pressure of the liquid to be processed constant, the minimum inner diameter of the inlet of the liquid to be processed is set to 4.0 mm.
After the membrane was sufficiently wetted by passing 1 L or more of pure water through the hollow fiber filter, one of the header caps attached to both sides was closed and the temperature was 25 ° C. from the other end. Pure water is introduced and constant-pressure dead-end internal pressure filtration with a filtration pressure of 0.1 MPa is performed. At this time, the filter is fixed so that all the nozzles on the filtrate side face downward. Based on the permeation amount of the obtained pure water, the effective water permeation amount at three locations in the length direction of the hollow fiber filtration membrane is calculated based on the above formula (2).

<Manufacture of hollow fiber substrate membrane>
[Production Example 1]
A composition comprising 49% by weight of a polyvinylidene fluoride resin (manufactured by SOLVAY, SOFEF1012, crystal melting point 173 ° C.) and 53% by weight of dicyclohexyl phthalate (industrial product manufactured by Osaka Organic Chemical Industry Co., Ltd.) at 70 ° C. using a Henschel mixer. After stirring and mixing, the cooled and powdered product was charged from the hopper, and melted and mixed uniformly at 210 ° C. using a twin screw extruder (Toyo Seiki Co., Ltd., Laboplast Mill MODEL 50C 150). .
Subsequently, while spinning, dibutyl phthalate (manufactured by Sanken Chemical Co., Ltd.) having a temperature of 130 ° C. is flowed into the hollow at a rate of 11 ml / min. It was extruded in the form of a hollow fiber at a discharge speed of 17 m / min from the mouth, cooled and solidified in a water bath adjusted to 40 ° C., and wound around a cassette at a speed of 50 m / min.
After that, dicyclohexyl phthalate and dibutyl phthalate were extracted and removed with 99% methanol-modified ethanol (industrial product of Imazu Pharmaceutical Co., Ltd.), and the adhering ethanol was replaced with water, followed by high-pressure steam sterilization while immersed in water. Heat treatment at 125 ° C. was performed for 1 hour using an apparatus (HV-85 manufactured by Hirayama Seisakusho Co., Ltd.). During the heat treatment, the film was fixed in a constant length state to prevent shrinkage. Then, the porous hollow fiber membrane was obtained by drying at the temperature of 60 degreeC in oven.
The obtained porous hollow fiber membrane had a length of 32.5 cm, an inner diameter of 330 μm, and a film thickness of 49 μm (all numerical values are average values of 15). Using this film as a base film, surface modification by graft polymerization described later was performed.

[Production Example 2]
A porous hollow fiber membrane was produced in the same manner as in Production Example 1 except that the flow rate of dibutyl phthalate flowing into the hollow interior was 12 ml / min. The obtained hollow fiber membrane had a length of 32.5 cm, an inner diameter of 350 μm, and a film thickness of 47 μm (all values are average values of 15). Using this film as a base film, surface modification by graft polymerization described later was performed.

<Production of hollow fiber filtration membrane>
The hollow fiber membrane was produced by subjecting the hollow fiber membrane produced in the production example to surface modification by graft polymerization.
[Example 1]
The hollow fiber filtration membrane obtained in Production Example 1 was subjected to a hydrophilic treatment by a graft method.
As a reaction solution, a solution in which hydroxypropyl acrylate was dissolved in a 25% by volume aqueous solution of t-butanol so as to be 8.2% by volume and maintained at 45 ° C. was subjected to nitrogen bubbling for 20 minutes.
First, 1100 hollow fiber filtration membranes obtained in Production Example 1 were end bundles fixed so as not to be separated into yarn bundles. Next, under a nitrogen atmosphere, the yarn bundle was irradiated with 25 kGy using Co60 as a radiation source while cooling the yarn bundle to −60 ° C. with dry ice.
After filling the yarn bundle after γ-ray irradiation into a reaction vessel having a capacity of 35 L, it was confirmed that the yarn bundle was in a horizontal state using a bubble tube leveler. After leaving the reaction vessel inside at a vacuum degree of 100 Pa or less for 10 minutes, the reaction solution 30L is introduced from the storage vessel into the reaction vessel so that the horizontal state of the yarn bundle is not destroyed and the yarn bundle is completely immersed. As a result, the reaction solution was simultaneously introduced into the hollow portion from both ends of the yarn bundle. When introducing the reaction liquid, the storage container side was pressurized to 0.1 MPa. Thereafter, graft polymerization was carried out at 45 ° C. for 60 minutes with the yarn bundle completely immersed in the reaction solution.
After the polymerization, the yarn bundle was washed with isopropyl alcohol and subjected to heat treatment at 125 ° C. for 1 hour using a high-pressure steam sterilizer while immersed in water. Thereafter, vacuum drying at 60 ° C. is performed for 8 hours, and the fixed portion of the yarn bundle is removed, and a hydrophilic hollow fiber filtration membrane having a moderately hydrophilic center portion and an excessively hydrophilic end portion is obtained. Obtained. In addition, while the water permeability of the hollow fiber filtration membrane moderately made hydrophilic is improved, the water permeability of the hollow fiber filtration membrane made excessively hydrophilic is lowered.
The obtained hollow fiber filtration membrane was divided into three equal parts in the length direction, mini-modules of the end part 1, the end part 2 and the central part were prepared, and the respective intrinsic water permeability was measured. As shown in Table 1, the hollow fiber filtration membrane had a higher intrinsic water permeability at the center than at both ends. Such a distribution state of the intrinsic water permeability is shown by a graph in FIG. 7 including Comparative Examples 1 and 2.

[Comparative Example 1]
In the same manner as in Production Example 1, a porous hollow fiber filtration membrane having a length of 70 cm, an inner diameter of 330 μm, and a film thickness of 49 μm was prepared as the base material membrane. This hollow fiber filtration membrane was hydrophilized by the grafting method in the same manner as in Example 1 and vacuum-dried, then cut from 10.0 cm from one end and 27.5 cm from the other end, and a hollow 32.5 cm long A yarn filtration membrane was obtained.
The obtained hollow fiber filtration membrane was divided into three equal parts in the length direction, and end part 1 (side cut by 10.0 cm), end part 2 (side cut by 27.5 cm), and a mini module at the center were prepared. Each intrinsic water permeability was measured. As shown in Table 1, this hollow fiber filtration membrane had an intrinsic water permeability slightly higher at the right end than at the center, but there was no substantial difference in intrinsic water permeability in the length direction).

[Comparative Example 2]
For the hollow fiber filtration membrane obtained in Production Example 1, instead of leaving the inside of the reaction vessel at a vacuum of 100 Pa or less for 10 minutes, nitrogen was blown into the reaction vessel at atmospheric pressure for 10 minutes, and then the atmospheric pressure was maintained. The grafting treatment was carried out in the same manner as in Example 1 except that 30 L of the reaction solution was introduced from the storage container into the reaction container so that the yarn bundle was completely immersed, and only the end portion was appropriately made hydrophilic. A hollow fiber filtration membrane was obtained.
The obtained hollow fiber filtration membrane was divided into three equal parts in the length direction, mini-modules of the end part 1, the end part 2 and the central part were prepared, and the respective intrinsic water permeability was measured. As shown in Table 1, in the hollow fiber filtration membrane, the end portion 1 and the end portion 2 had an intrinsic water permeability that was clearly higher than that of the central portion.

[Example 2]
The hollow fiber filtration membrane shown in FIG. 3 is filled with 1100 hollow fiber filtration membranes obtained in Example 1 (with the end 1 positioned at the end A and the end 2 at the end B, respectively). A yarn filter was created. At this time, the effective length of the filtration was 30 cm. After the hollow fiber filtration membrane is sufficiently wetted, pure water is filtered into the filter from the injection side of the liquid to be treated at a pressure of 0.1 MPa, and the effective filtration part is divided into three equal parts in the length direction. The effective water permeability at the site was measured. However, the measurement was carried out with the permeation side nozzle (filtrate outlet) facing downward. Table 2 shows the effective water permeability at each site when the effective filtration part is divided into three equal parts in the length direction.
It should be noted that the relationship between the intrinsic water permeability at the end 1 and the central part [(F _{edge 1} -F _{central part} ) / F _{central part} × 100 (%)] is -14.7%. And [(F _AE −F _CE ) / F _CE × 100 (%)] = − 9.87%, and the absolute value thereof is small. From this, the intrinsic water permeability of the hollow fiber filtration membrane is set as in the present invention. It was confirmed that the effective water permeation amount can be made uniform in the length direction by designing it in the length direction.

[Example 3]
The end portions of the 500 hollow fiber filtration membranes obtained in Production Example 1 were fixed so as not to be separated into a yarn bundle. Next, the same grafting treatment as in Example 1 was performed except that the yarn bundle was irradiated with 25 kGy using Co60 as a radiation source while the yarn bundle was cooled to −60 ° C. with dry ice in a nitrogen atmosphere. Here, the intrinsic water permeability of the end part 1, the end part 2 and the central part is 3.40 × 10 ⁻¹¹ , 3.32 × 10 ⁻¹¹ and 3.93 × 10 ⁻¹¹ [m ³ / m ² · s · Pa], respectively. there were.
Next, a hollow fiber filter was prepared in the same manner as in Example 2 except that this hollow fiber filtration membrane was used, and the effective water permeability at each part when the effective filtration part was divided into three equal parts in the length direction was determined. It was measured. Table 2 shows the effective water permeability at each site when the effective filtration part is divided into three equal parts in the length direction.
It should be noted that the relationship between the intrinsic water permeability at the end 1 and the central part [(F _{edge 1} -F _{central part} ) / F _{central part} × 100 (%)] is -13.49%. And [(F _AE −F _CE ) / F _CE × 100 (%)] = 9.70%, and the sign is reversed. From this, the inherent water permeability of the hollow fiber filtration membrane is set as in the present invention. By designing, it was confirmed that the effective water permeability can be made uniform in the length direction.

[Example 4]
The end portions of the 1250 hollow fiber filtration membranes obtained in Production Example 1 were fixed so as not to be separated into a yarn bundle. Next, the same grafting treatment as in Example 1 was performed except that the yarn bundle was irradiated with 25 kGy using Co60 as a radiation source while the yarn bundle was cooled to −60 ° C. with dry ice in a nitrogen atmosphere. Here, the intrinsic water permeability of the end part 1, the end part 2 and the central part is 8.30 × 10 ⁻¹¹ , 7.85 × 10 ⁻¹¹ and 9.60 × 10 ⁻¹¹ [m ³ / m ² · s · Pa], respectively. there were.
Next, a hollow fiber filter was prepared in the same manner as in Example 2 except that this hollow fiber filtration membrane was used, and the effective water permeability at each part when the effective filtration part was divided into three equal parts in the length direction was determined. It was measured. Table 2 shows the effective water permeability at each site when the effective filtration part is divided into three equal parts in the length direction.
It should be noted that the relationship between the intrinsic water permeability at the end 1 and the central part [(F _{edge 1} -F _{central part} ) / F _{central part} × 100 (%)] is -13.54%. And [(F _AE −F _CE ) / F _CE × 100 (%)] = 4.77%, and the sign is reversed, and from this, the intrinsic water permeability of the hollow fiber filtration membrane is set as in the present invention. It was confirmed that the effective water permeability can be made uniform in the length direction by designing.

[Example 5]
The ends of the 1200 hollow fiber filtration membranes obtained in Production Example 1 were fixed so as not to be separated into a yarn bundle. Next, the same grafting treatment as in Example 1 was performed except that the yarn bundle was irradiated with 25 kGy using Co60 as a radiation source while the yarn bundle was cooled to −60 ° C. with dry ice in a nitrogen atmosphere. Here, the intrinsic water permeability of the end part 1, the end part 2 and the central part is 7.60 × 10 ⁻¹¹ , 7.22 × 10 ⁻¹¹ and 8.85 × 10 ⁻¹¹ [m ³ / m ² · s · Pa], respectively. there were.
A hollow fiber filter was prepared in the same manner as in Example 2 except that this hollow fiber filtration membrane was used, and the effective water permeability at each part when the effective filtration part was divided into three equal parts in the length direction was measured. . Table 2 shows the effective water permeability at each site when the effective filtration part is divided into three equal parts in the length direction.

[Comparative Example 3]
A hollow fiber filter was prepared in the same manner as in Example 2 except that 1100 hollow fiber filtration membranes obtained in Comparative Example 1 were filled in a cylindrical container, and the effective filtration part was divided into three equal parts in the length direction. The effective water permeability at each part was measured. Table 2 shows the effective water permeability at each site when the effective filtration part is divided into three equal parts in the length direction.

[Comparative Example 4]
A hollow fiber filter was prepared in the same manner as in Example 2 except that 1100 hollow fiber filtration membranes obtained in Comparative Example 2 were filled in a cylindrical container, and the effective filtration part was divided into three equal parts in the length direction. The effective water permeability at each part was measured. Table 2 shows the effective water permeability at each site when the effective filtration part is divided into three equal parts in the length direction.

  The hollow fiber filtration membrane of the present invention is an industrial process filter, a water purification filter, a physicochemical / inspection filter, a blood purifier, etc., in various fields such as separating, concentrating, and purifying a target product from a liquid to be treated. It can be used for a wide range of applications.

2 Effective water permeability measurement container 2A Outer cylinder 2B Outer cylinder 3 Hollow fiber filtration membrane 4 Partition means 5 Filtrate outlet 5A Filtrate outlet 5B Filtrate outlet 5C Filtrate outlet 6 Tubular container 8 Potting section 9 Header cap 10 Filtration device 11 Hollow fiber filter 12 Processed liquid storage part 13 Filtrate storage part 20 Inlet side flow path 21 Inlet side pressure adjustment means 22 Inlet side pressure gauge 23 Liquid transfer means 30 Filtration side flow path 31 Filtration side pressure adjustment means 32 Filtration side pressure Total 40 Outlet side channel 41 Outlet side pressure gauge 42 Outlet side pressure adjusting means

Claims (10)

  A porous hollow fiber filtration membrane, wherein the intrinsic water permeability at the center when the hollow fiber filtration membrane is divided into three equal parts in the length direction is higher than the intrinsic water permeability at both ends. The relationship between the effective water permeability F _AE , F _BE, and F _CE at the end A, the end B, and the center C when the cylindrical container is filled and dead-end internal pressure filtration is performed is the following (a) or ( The hollow fiber filtration membrane according to claim 1, which is b).
(A) F _AE ≧ F _CE > F _BE
(B) F _CE > F _AE > F _BE
However, the center part C refers to the part corresponding to the center part when the effective filtration part of the hollow fiber filtration membrane is equally divided into three in the length direction, and the end parts A and B are the hollow fiber filtration membranes, respectively. The end portion located on the treatment liquid introduction side from the central portion C of the above, and the end portion located on the opposite side of the treatment liquid introduction side from the central portion C of the hollow fiber filtration membrane. The hollow fiber filtration membrane according to claim 2, wherein a difference between the effective water permeability F _AE and F _CE is within ± 10%.   The hollow fiber filtration membrane according to any one of claims 1 to 3, wherein the effective filtration portion has a length of 0.1 to 0.7 m and an inner diameter of 100 to 2000 µm.   The hollow fiber filtration membrane according to any one of claims 1 to 4, which is obtained by surface modification.   A hollow fiber filter formed by filling one or more hollow fiber filtration membranes according to any one of claims 1 to 5 in a cylindrical container. Liquid storage part to be processed,
An inlet-side flow path that connects the liquid storage part to be processed and the liquid-introducing side of the filter to be processed;
Liquid transfer means and inlet side pressure adjusting means provided in the inlet side flow path;
A filtration-side flow path connecting the filtrate outlet of the filter and the filtrate reservoir,
A filtration side pressure gauge and filtration side pressure adjusting means provided in the filtration side flow path;
In a method for filtering a liquid to be treated using a filtration device comprising:
Using the hollow fiber filter according to claim 6 as a filter,
By adjusting one or more of the flow rate of the liquid transfer means, the opening / closing degree of the inlet side pressure adjusting means, and the opening degree of the filtration side pressure adjusting means, the effective water permeability F _{CE in} the central portion C of the hollow fiber filtration membrane A filtration method in which the difference between at least one of the effective water permeability F _AE and F _BE at the end A and the end B is set within ± 10%.
However, the center part C refers to the part corresponding to the center part when the effective filtration part of the hollow fiber filtration membrane is equally divided into three in the length direction, and the end parts A and B are the hollow fiber filtration membranes, respectively. The end portion located on the treatment liquid introduction side from the central portion C of the above, and the end portion located on the opposite side of the treatment liquid introduction side from the central portion C of the hollow fiber filtration membrane. Liquid storage part to be processed,
An inlet-side flow path that connects the liquid storage part to be processed and the liquid-introducing side of the filter to be processed;
Liquid transfer means and inlet side pressure adjusting means provided in the inlet side flow path;
A filtration-side flow path connecting the filtrate outlet of the filter and the filtrate reservoir,
A filtration side pressure gauge and filtration side pressure adjusting means provided in the filtration side flow path;
An outlet-side flow path for connecting the liquid to be processed and the liquid discharge side of the filter;
Liquid transfer means and outlet side pressure adjustment means provided in the outlet side flow path,
In a method for filtering a liquid to be treated using a filtration device comprising:
Using the hollow fiber filter according to claim 6 as a filter,
Adjusting one or more of the flow rate of the liquid transfer means, the opening / closing degree of the inlet side pressure adjusting means, the opening degree of the outlet side pressure adjusting means, and the opening degree of the filtration side pressure adjusting means, A filtration method in which the difference between the effective water permeability F _CE of the central portion C and at least one of the effective water permeability F _AE and F _BE of the end A and the end B is set within ± 10%.
However, the center part C refers to the part corresponding to the center part when the effective filtration part of the hollow fiber filtration membrane is equally divided into three in the length direction, and the end parts A and B are the hollow fiber filtration membranes, respectively. The end portion located on the treatment liquid introduction side from the central portion C of the above, and the end portion located on the opposite side of the treatment liquid introduction side from the central portion C of the hollow fiber filtration membrane.   The filtration method according to claim 7 or 8, wherein the filtration method is an internal pressure filtration method.   The filtration method according to claim 7 or 8, wherein the filtration method is an external pressure filtration method.