JPH11262640A - Hollow fiber membrane module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hollow fiber membrane module which has high fractional performance and is good in mechanical strength and is hardly clogged, and in which while long life is kept, sufficient permeated quantity of water is secured even with compact equipment to improve a filtered flow rate and to lessen a differential pressure rise, and which excels in durability. SOLUTION: This hollow fiber membrane module 30 is provided with an element 34 in which plural knitting cloths 32 each consisting of a hollow fiber membrane are arranged along one direction and at least one end of the hollow fiber membrane is fixed by a fixing member 44 keeping its open state, a housing body 40 for housing the element, a gas supply member 36 for supplying gas into the housing body, and a gas dispersing body 38 for dispersing and leading gas from the gas supply member. In this case, as the hollow fiber membrane, a composite hollow fiber membrane is used in which three or more layers of membranes of three-dimensional mesh structure having plural fine pores are laminated and as an intermediate layer positioned between an outermost layer and an innermost layer of the membrane, a dense layer the average pore diameter of whose fine pores is smaller than the average pore diameter of the fine pores of the outermost and innermost layers is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a water purification treatment at a water purification plant, a filtration of river water, lake water and marsh water, a filtration of industrial water, a drainage treatment,
The present invention relates to a hollow fiber membrane module suitable for filtering highly polluting liquids such as pretreatment for desalination of seawater.

[0002]

2. Description of the Related Art Hollow fiber membrane modules are used in the field of microfiltration such as the production of sterile water, high-purity water, drinking water, and air purification, as well as secondary and tertiary treatment in sewage treatment plants, and septic tanks. It has also been applied to the field of highly polluting water treatment such as solid-liquid separation. In highly polluting water treatment,
Since the hollow fiber membrane module is very clogged during filtration, after filtering for a certain period of time, air is sent from the bottom of the hollow fiber membrane module to vibrate the hollow fiber membrane to clean the membrane surface, or in the direction opposite to the filtration direction. Membrane washing such as backwashing in which water is passed through is repeated. However, when a hollow fiber membrane module, which is formed by concentrating hollow fiber membrane knitted fabrics used in conventional microfiltration in a cylindrical shape or concentrically, is used for high-pollutant water treatment, the membrane time increases with the treatment time. The hollow fiber membranes adhere to each other due to deposits such as organic substances attached to the surface, the effective area of the hollow fiber membrane in the hollow fiber membrane module is reduced, and the filtration flow rate is sharply reduced. Even if the membrane is washed, the membrane function is not easily restored, and the filtration efficiency is significantly reduced.

As a solution to the reduction of the effective area and the reduction of the washing efficiency, a hollow fiber membrane knitted fabric is fixed to a frame while keeping the hollow fiber membrane at one end or both ends open while the knitted fabric is spread in a sheet shape. A rectangular flat-type hollow fiber membrane module has been proposed, and by arranging the hollow fiber membrane modules at appropriate intervals, the membrane surface can be easily washed and a decrease in filtration efficiency can be suppressed. However, when a flat type hollow fiber membrane module is used for storage in a cylindrical container, the ratio of the portion other than the hollow fiber membrane increases, resulting in poor volumetric efficiency.
When housed in a rectangular container, the cost is high because a reinforcing member is required to obtain a pressure-resistant structure.

In order to solve these problems, a plurality of flat hollow fiber membrane knitted fabrics are stacked in parallel or folded in a zigzag shape and housed in a hollow fiber membrane module, and air supplied from an air supply member is provided. A hollow fiber membrane module capable of maintaining a high filtration function for a long period of time by performing scrubbing according to JP-A-5-261254 and Japanese Patent Application No. 7-325274 has been proposed. Further, Japanese Patent Application No. 9-199041 discloses that the drift of supplied air and a plurality of air bubbles become large bubbles during the ascending, that the entire surface of the hollow fiber membrane is insufficiently washed, and that the recovery of the filtration function is insufficient. For the following problems, in the case of a flat hollow fiber membrane module housed in a cylindrical container, perform uniform and efficient cleaning by surely supplying air for scrubbing between hollow fiber membrane knitted fabrics. Thus, there has been proposed a hollow fiber membrane module that maintains a high filtration function for a long time and easily recovers the filtration function. In this type of hollow fiber membrane module, the hollow fiber membranes are less likely to be fixed and integrated due to pollutants in the water at the time of use, and the membrane surface of the hollow fiber membrane can be efficiently cleaned in parallel with the filtration. It is difficult for the drop to occur.

However, it is difficult to increase the membrane area of the hollow fiber membrane of the hollow fiber membrane module, and it is difficult to obtain a hollow fiber membrane module having a large water permeability. Although a hollow fiber membrane module having a large pore diameter may be used to obtain a hollow fiber membrane module with an increased water permeability, there is a drawback that the filtration efficiency of pollutants decreases. A hollow fiber membrane module having a large water permeability can be obtained by using a thinner hollow fiber membrane, but in that case, the mechanical strength of the hollow fiber membrane tends to be insufficient. Therefore, in order to treat a large amount of liquid, it was necessary to use many hollow fiber membrane modules.

Japanese Patent Application Laid-Open No. Hei 9-234352 discloses a hollow fiber membrane module using a polyolefin microporous hollow fiber membrane having at least two layers of microporous layers having different pore sizes. A composite microporous hollow fiber membrane in which a microporous membrane having micropores larger by a predetermined ratio is joined to a porous membrane having micropores capable of separating particles of It is disclosed that a composite porous hollow fiber membrane having sufficient strength without drastically improving the water permeability can be produced. That is, by increasing the pore size of the reinforcing functional layer of the composite membrane, it is possible to obtain a high water permeability while maintaining the fractionation performance and improve the durability, as compared with a hollow fiber membrane (uniform membrane) having the same fractionation performance.

[0007]

In recent years, hollow fiber membrane modules have been used for water filtration, liquid filtration, gas filtration and the like for producing high-purity industrial water, ultrapure water, drinking water such as water purifiers, as well as aseptic water and the like. The filter is used for solid-liquid separation including SS (floating suspended solids) such as vertical drainage. In the case of water purification applications, in the purification treatment of water purification plants, as a measure to remove the chlorine-resistant pathogenic protozoa "Cryptosporidium" that cannot be sufficiently removed by the conventional rapid filtration method (coagulation sedimentation + sand filtration), Membrane modules for water purification are also attracting attention because of their advantages such as more compactness, unmanned operation, and improved water quality stability. The membrane module has a filtration performance with a higher flow rate while maintaining the fractionation performance of filtering and removing fine particles, bacteria, etc., further suppressing a rise in differential pressure, a decrease in water permeation, miniaturization, and a long life. , High durability and the like are strongly demanded. To this end, while maintaining the target fractionation performance such as complete capture of bacteria, the water permeability of the membrane is further improved, enabling high flow rate filtration and reducing the amount of membrane housed in the module. There is a need for a membrane material that has the characteristics of being compact, having a long-life membrane structure that is not easily clogged by water filtration, and having pressure resistance in the practical pressure range of the filtration process. Even with the technique described in Japanese Patent Application Laid-Open No. 9-234352, it is not always sufficient to increase the water permeation amount and to make the device compact.

The present invention has been made to solve the above problems, and has a high fractionation performance capable of completely capturing bacteria and the like.
High performance hollow with good mechanical strength, sufficient clogging resistance, long life span, small size, sufficient water permeability, improved filtration flow rate, and high durability with little differential pressure rise It is to provide a thread membrane module. Furthermore, even if it is used for filtration of polluted water, the membrane surface of the hollow fiber membrane in the module can be efficiently washed in parallel with the filtration, and the object is to provide a hollow fiber membrane module with high recovery of filtration characteristics. .

[0009]

Means for Solving the Problems The present inventors have developed a high-performance hollow which has a high fractionation, good mechanical strength, and a long life with little clogging, and further improved filtration flow rate. As a result of intensive studies on the fiber membrane module, a microporous membrane having pores larger by a predetermined ratio than a porous membrane having micropores capable of separating particles of a predetermined particle size was used as the hollow fiber membrane to be used. By adopting the composition of the composite microporous hollow fiber membrane thus obtained, a composite porous hollow fiber membrane with a small decrease in water permeability of the membrane can be obtained irrespective of the increase in the film thickness, and further, the composite porous hollow fiber membrane can be obtained. Considering the position of the dense layer that performs the separation function in the inside, by setting the dense layer position to the middle layer, while maintaining the performance with excellent clogging resistance, not only the uniform film but also the dense layer inner layered composite hollow fiber membrane Hollow fiber membrane with higher water permeability even when compared Found that the joule, which resulted in the completion of the present invention.

That is, in the hollow fiber membrane module of the present invention, a plurality of knitted fabrics composed of hollow fiber membranes are arranged along one direction, and at least one end of the hollow fiber membrane is fixed by a fixing member while maintaining an open state. A hollow fiber membrane module including an element, a housing for housing the element, an air supply member for supplying gas into the housing, and a gas dispersion for dispersing and guiding gas from the air supply member. The hollow fiber membrane is formed by laminating three or more layers of a three-dimensional network structure having a plurality of micropores as an intermediate layer located between the outermost layer and the innermost layer. Characterized in that it is a composite hollow fiber membrane having a dense layer smaller than the average pore diameter of the micropores. Here, the micropores of the composite hollow fiber membrane are formed by a stack dramella and microfibrils bonded to the stack dramella,
The outermost layer and the innermost layer each have a thickness in the range of 20 to 50 μm, the dense layer is thinner than the outermost layer and the innermost layer, and the porosity of the composite hollow fiber membrane as a whole is 75 vol% or more. Is desirable.

The composite hollow fiber membrane desirably has a coating layer made of a hydrophilic copolymer in an amount of 3 to 30% by weight based on the composite hollow fiber membrane. Furthermore, it is desirable that the average distance Da between the microfibril bundles of the micropores of the dense layer and the average distance Db between the microfibril bundles of the micropores of the support layer satisfy the following expression. 1.3 ≦ Db / Da ≦ 4.0

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The hollow fiber membrane module of the present invention will be described in more detail with reference to the drawings. The hollow fiber membrane module 3 shown in FIG. 1, which is an example of the hollow fiber membrane module of the present invention.
0, an element 34 provided with a knitted fabric 32 made of a hollow fiber membrane, an air supply member 36 provided below the element 34, and a gas dispersion member provided between the air supply member 36 and the element 34 38 and a housing body 40 for housing them.

The housing 40 houses the element 34 and the like, and is cylindrical in the illustrated example. The material of the container 40 is not particularly limited as long as it has corrosion resistance to the highly polluted water of the raw water and can withstand the pressure at the time of treatment, but is not limited to synthetic resins such as polycarbonate resin, ABS resin, and polyvinyl chloride resin. And metals such as stainless steel. This container 40 has a treated raw water supply port 5
2, treated water outlet 54, sediment discharge port 56, gas supply port 5
8. A gas outlet 60 is formed. The container 40 is
A structure that can be separated at an appropriate portion may be used. The shape of the container 40 is not limited to a cylindrical shape, and various shapes can be adopted according to a state in which the hollow fiber membrane module is installed.

The element 34 provided in the container 40
5 is, for example, as shown in FIG. 5, in which a plurality of knitted fabrics 32 made of hollow fiber membranes are arranged and fixed to a ring-shaped support member 42 by a fixing member 44. Support member 4
2 has a cylindrical shape, typically a cylindrical shape, if necessary, but may have a cross-sectional shape such as a rectangular shape.
A shape matching the inside shape of 0 is selected. Any material may be used as long as it has mechanical strength and durability,
For example, polycarbonate, polysulfone, polypropylene, acrylic resin, ABS resin, modified PPE resin, stainless steel and the like can be used. If incineration is required after use, it is preferable to use a hydrocarbon resin that can be completely burned without emitting toxic gas by combustion. Alternatively, the knitted fabric 32 made of a hollow fiber membrane may be directly provided inside the container 40 by the fixing member 44 without providing the support member 42, and the container 40 and the element may be of an integrated structure. However, by arranging the element so that it can be detachably installed in the container 40, the element can be easily replaced.

In the knitted fabric 32 composed of a hollow fiber membrane, a hollow fiber membrane described later is disposed on at least one of a warp and a weft,
It may be formed by any knitting method or weaving method as long as the function of the hollow fiber membrane is maintained. For example, as shown in FIG.
And a knitted fabric (or a woven fabric) composed of a warp 48 formed of a thread member is applied. As the yarn member, those used for the warp of ordinary knitted or woven fabrics can be used.However, in order not to damage the hollow fiber membrane at the time of manufacturing or handling the knitted fabric, a non-hard material is preferable. It is preferable to use a spun yarn or a processed yarn. As a method for producing a knitted fabric, a known method, for example, Japanese Patent Application Laid-Open No. 62-579
No. 65, and the method disclosed in JP-A-1-266258 can be applied. Each of the knitted fabrics 32 may be obtained by cutting the sheet-shaped knitted fabric into an appropriate length, or may be used by laminating several sheets.
In addition, the term “lamination of knitted fabric” as used herein includes a case where the knitted fabric is folded and stacked to an appropriate length without being cut. The warp of the knitted fabric generally exists only near both ends of the hollow fiber which is a weft, but the warp 50 may be provided at an arbitrary constant interval in the middle of the weft. By providing the warp 50 in the middle, even when the hollow fiber membrane is washed by water flow or bubbling, uniform dispersion of the hollow fiber can be favorably maintained. Further, it is also possible to completely remove the warp from the knitted fabric by using a hollow fiber membrane knitted fabric. That is, the warp is contained in the fixing member 44,
When forming the open end of the hollow fiber membrane, it may be cut off together with the removed portion of the fixing member 44.

In the knitted fabric 32 shown in FIGS. 1 and 5, one side of the knitted fabric is inserted into the support member 42 and fixed by the fixing member 44 in which the liquid resin is cured. That is, the opening in the support member 42 is filled with a liquid fixing member so that the opening end of the hollow fiber membrane of the knitted fabric 32 is not closed, and is cured.
After fixing and curing the hollow fiber membrane, unnecessary portions may be removed to fix the hollow fiber membrane. At the same time, the fixing member 44
The opening of the support member 42 is sealed. As the fixing member 44, for example, an epoxy resin, an unsaturated polyester resin,
Polyurethane or the like can be used. In the element in which the knitted fabric 32 formed of the hollow fiber membrane is fixed to the support member 42 in this manner, the opening of the hollow fiber membrane is
It becomes 5.

In the case where the hollow fiber membrane is supported only at one end of the element, the knitted fabric 32 made of hollow fiber membrane is bent into a U-shape, and both ends of the hollow fiber membrane are held by the supporting member 42 while maintaining the open state. The hollow fiber membrane is fixed, or only one end of the flat-plate hollow fiber membrane knitted fabric 32 is fixed to the support member 42, and the other end is sealed by, for example, heat sealing or bonding resin. The filtrate taken in is supplied only to the water collecting section 45. As described later, if the hollow fiber membrane is supported on both ends of the element, the water collecting portions are provided on both sides, and thus such sealing treatment is unnecessary. 1
Usually, a plurality of knitted fabrics are arranged in one direction (in the vertical direction in FIG. 1) for one element 34. The arrangement interval of the hollow fiber membrane knitted fabric 32 is preferably 3 to 50 mm, more preferably 5 to 20 mm from the viewpoints of the utilization efficiency of the hollow fiber membrane, the cleaning property, and the volumetric efficiency.

In this hollow fiber membrane module 30,
An air supply member 36 connected to the gas supply port 58 is provided at a lower part in the housing 40. A compressor or the like is connected to the gas supply port 58, and foam-like gas is emitted from the air supply member 36. As the gas to be radiated, in addition to general air, an inert gas such as nitrogen gas can be used. Further, a gas dispersion 38 is provided between the air supply member 36 and the element 34. The gas dispersion 14 is for dispersing the gas emitted from the air supply member 36 and guiding the gas to the knitted fabric 32 made of a hollow fiber membrane. Like the gas dispersion 38,
It is preferable to form the air hold section 62 and temporarily disperse the gas from the air supply member 36 after staying there, since the air can be uniformly dispersed and diffused on the film surface.

Vent hole 64 formed in gas dispersion 14
Is not particularly limited as long as the gas can be dispersed and guided to the hollow fiber membrane. For example, in addition to the slit-shaped vent hole 64 as shown in FIG. 7, a small circular shape as shown in FIG. The slit width and diameter of the slit may be appropriately determined based on the hollow fiber membrane knitted fabric 32 to be used, raw water properties, operating conditions, amount of gas used, and the like.
0 mm is preferable, and 0.5 to 3 mm is more preferable. The material of the gas dispersion 38 is not particularly limited as long as it has corrosion resistance to the highly polluted water of the raw water. However, a synthetic resin such as a polycarbonate resin, an ABS resin, a polyvinyl chloride resin, a metal such as stainless steel, a ceramic, etc. Etc. are preferred.

The gas dispersion 38 is disposed below the lower end of the hollow fiber membrane knitted fabric 32, as shown in FIG. 1, and the hollow fiber is inserted into a vent hole 64, as shown in FIG. It may be arranged so that the lower part of the membrane knitted fabric 32 is inserted. With such a structure, gas can be reliably guided to the hollow fiber membrane knitted fabric 32, and unnecessary deflection and fluctuation of the hollow fiber membrane knitted fabric 32 can be suppressed, and the hollow fiber membrane knitted fabric can be suppressed. The uniformly distributed arrangement of the fabrics 32 can be easily maintained, mutual adhesion and integration can be prevented, the filtration performance can be maintained, and the cleaning efficiency by air scrubbing treatment can be increased.

In this hollow fiber membrane module 30,
The treated raw water is press-fitted into the container 40 from the treated raw water supply port 52, and is pressure-filtered through the hollow fiber membranes of the hollow fiber membrane knitted fabric 32 arranged in a plurality of elements 34. The water passes through the water collecting section 45 and is discharged from the treated water outlet 54. Generally, in the filtration of highly polluted water using a hollow fiber membrane module, a large amount of SS and organic substances are deposited on the membrane surface. For that purpose, it is necessary to remove the deposit by a water flow, air scrubbing, vibration, ultrasonic treatment, or the like to clean the film surface. If the cleaning is not performed, the organic matter deposited on the membrane surface will cause blockage of the membrane, resulting in a reduction in filtration life. Specific cleaning methods include so-called cross-flow filtration in which a water flow is made parallel to the sheet-like membrane surface, a method in which a water flow is generated in a membrane module immersion tank using a pump or a motor, and bubbling using an upward flow of air. Method, a method of vibrating the module itself, a method of vibrating the water to be treated by ultrasonic waves, and the like.

The hollow fiber membrane module of the present invention is suitable for performing the washing of the membrane surface in parallel with the filtration. That is, gas such as air supplied through the gas supply port 58 is diverged from the gas supply member 36, passes through the gas dispersion 38, becomes a bubble, and is uniformly formed on the hollow fiber membrane knitted fabric 32. Then, the hollow fiber membrane knitted fabric 32 is scrubbed, the hollow fiber membrane is washed, and then discharged from the gas discharge port 60. Deposits such as organic substances separated from the hollow fiber membrane surface by scrubbing settle at the lower part of the container 40,
It is taken out from the deposit outlet 56 as appropriate. Such cleaning of the film surface may be performed continuously or intermittently depending on the progress of the blockage of the film surface. When using the hollow fiber membrane module of the present invention, as a function recovery treatment method other than the membrane surface washing performed in parallel with the filtration, a backwashing method can be easily carried out similarly to the case of a normal module.
Also, a method using ultrasonic waves or the like can be efficiently implemented due to the physical form of the module.

The element in which the both ends of the hollow fiber membrane knitted fabric are fixed can also be applied. For example, in the hollow fiber membrane module 68 shown in FIG.
The hollow fiber membrane knitted fabric 32 of the
4 and is fixed to the support member 78 at the lower end by a fixing member 72. The support member 78 is in the form of a container. The gas dispersion 39 is attached to the upper part, and the treated water outlet 74 is provided in a hole formed in the lower end.
And a drain pipe 76 connected to the drainage pipe. The knitted fabric 32 made of a hollow fiber membrane is provided so as to penetrate through the ventilation holes 64 formed in the gas dispersion 39. The support member 7
The gas supply member 37 connected to the gas supply port 58 is connected above the fixing member 72 of No. 8. In the hollow fiber membrane module 68, the raw water introduced into the container 52 from the raw water supply port 52 is filtered by each hollow fiber membrane knitted fabric, and the filtered water passes through the hollow fiber membrane, A part is discharged from the treated water outlet 54 through the water collecting part 45 at the upper end,
Others are discharged from the treated water outlet 74 through the drainage pipe 76 from the water collecting part 45 at the lower end. The treated water discharged from the treated water outlet 54 and the treated water discharged from the treated water outlet 74 are combined as necessary and sent to the next step. Further, the gas from the gas supply port 58 comes into contact with the hollow fiber membrane knitted fabric 32 via the air supply member 37 and passes through the gas dispersion 39 to form a bubble and become uniformly hollow fiber membrane knitted fabric. Guided to 32,
The knitted fabric 32 made of a hollow fiber membrane is scrubbed to clean the surface of the hollow fiber membrane.

Further, a hollow fiber membrane module 80 as shown in FIG. 4 may be used. In this hollow fiber membrane module 80, unlike the above-described hollow fiber membrane module 68,
The water collecting part in the lower supporting member 79 and the upper fixing member 44
A treated water transfer pipe 82 is provided for connecting to the upper water collecting section. Further, a gas transfer pipe 84 connected to the inside of the lower support member 79 is connected to the gas supply port 58 formed above the container 40. In the hollow fiber membrane module 80, the filtrate from the lower end of the hollow fiber membrane knitted fabric 32 that has been pressure-filtered is sent upward from the inside of the support member 79 through the treated water transfer pipe 82, and the container 40 At the upper part of the hollow fiber membrane knitted fabric 32, the water is combined with the filtered water in the water collecting part at the upper part of the hollow fiber membrane, and is discharged from the treated water outlet 54. Further, the gas sent from the gas supply port 58 is sent to the lower supporting member 79 through the gas transfer pipe 84, and is then subjected to an air scrubbing process. The treated water transfer pipe 82 and the gas transfer pipe 84 may have a structure integrated with the element.

The hollow fiber membrane module in which both ends of the hollow fiber membrane knitted fabric 32 are fixed by fixing members as shown in FIGS. It has the feature of high processing efficiency. In performing filtration using the hollow fiber membrane module of the present invention, a suction filtration method in which the element is immersed in the water to be treated and the treated water permeated through the hollow fiber membrane is recovered, and the inside of the hollow fiber membrane is suctioned can be adopted. However, it is preferable to dispose the element in the container and employ a so-called pressure filtration method in which the water to be treated is pressurized and permeated through the hollow fiber membrane because high flow rate treatment can be performed.

The hollow fiber membrane module of the present invention has a great feature in its hollow fiber membrane. The hollow fiber membrane module of the present invention has a configuration in which three or more membranes having a three-dimensional network structure having a plurality of micropores are laminated, and as an intermediate layer located between the outermost layer and the innermost layer, the average pore diameter of the micropores is the largest. A composite hollow fiber membrane having a dense layer smaller than the average pore diameter of the micropores in the outer layer and the innermost layer is used. The composite hollow fiber membrane preferably has an inner diameter in the range of 50 to 5000 μm. If the inner diameter is less than 50 μm, the pressure loss inside the hollow fiber membrane increases, which is not preferable in practical use. On the other hand, when it is larger than 5000 μm, the degree of integration of the hollow fiber membrane is reduced, so that the water permeability per unit volume is significantly reduced. Total film thickness is 5-50
0 μm, more preferably 30 to 2 μm.
It is in the range of 00 μm. If the total thickness is less than 5 μm, the mechanical strength is weak, and flattening deformation of the hollow fiber occurs. Also, 20
When it is larger than 0 μm, it becomes difficult to obtain high water permeability.

The composite hollow fiber membrane according to the present invention comprises an innermost layer located on the innermost side, an outermost layer located on the outermost side,
And an intermediate layer located between them. If the number of intermediate layers is one, the total number of layers is three. If the number of intermediate layers is two or more, the number of layers is four or more. In the present invention, it is essential that both the innermost layer and the outermost layer are support layers mainly having a reinforcing function, and have a dense layer mainly having a separating function as an intermediate layer. Therefore, if the intermediate layer is a single layer, as shown in FIG.
2, the innermost layer 14 and the dense layer 16. When the dense layer is located not on the innermost layer but on the outer intermediate layer, the membrane area of the dense layer can be increased from the form of a hollow fiber membrane. Therefore, on the premise that the flux rate control is a dense layer, it is possible to further increase the flux (filtration flow rate). However, if the dense layer is made the outermost layer, the clogging resistance performance is reduced, so that the position of the dense layer is the intermediate layer. Also,
Since the dense layer has a multilayer structure sandwiched between the support layers as an intermediate layer, even if the filtration is performed from OUT to IN (filtration from the outer surface of the hollow fiber membrane toward the inner layer), conversely, from the inside to the outside. Even if water is filtered through the filter, water will flow from the layer with the larger pore diameter to the layer with the smaller pore size, and the filter will have excellent clogging resistance and long life even when filtered from both directions. be able to. If the filtration operation of the hollow fiber membrane module is performed over a long period of time, or if the pressure difference rises for some reason (such as a sudden change in the raw water composition), a reverse flow such as chemical washing is performed to restore water permeability. There is a need. Also in that case, the hollow fiber membrane having the three-layer structure in which the dense layer is sandwiched between the support layers as the intermediate layer has OUT → IN, IN → O
It is effective from the viewpoint of clogging resistance because it has excellent blocking resistance and backwash recovery properties for bidirectional filtration of UT.

Each layer is made of various thermoplastic resins such as polyamide, and among them, those made of polyolefin are preferable. For example, high-density polyethylene having a high degree of crystallinity and few branches, polypropylene, particularly isotactic polypropylene, poly-4-methyl-1-pentene, poly-3-methylbutene-1, polyvinylidene fluoride, and the like, and mixtures thereof can be mentioned. Above all, in consideration of the ease of workability into a knitted fabric, a hollow fiber membrane such as polyethylene is preferably used from the viewpoint of strong elongation and flexibility. At this time, the density of the polyethylene used is JIS K67.
Is preferably 0.95 g / cm ³ or more in the measurement method shown in 60, more preferably if Dere 0.955 g / cm ³ or more, still more preferably 0.960 g / cm ³ or more. If the density is less than 0.95 g / cm ³ , the formation of fine pores by stretching is not uniform, which is not preferable. In the case of polypropylene, it is preferably 0.91 g / cm ³ or more.
Further, the isotactic polypropylene preferably has a tacticity of 96% or more. With such a density and stereoregularity, it becomes easy to satisfy the crystal orientation degree fc described later in a specific range.

The MI value (melt index value) measured according to ASTM D-1238 is 0.1 to 50 g / 1.
A range of 0 min is preferable, and a range of 0.3 to 15 g / 10 min is more preferable. Since the polyolefin having an MI value of less than 0.1 g / 10 min has too high a melt viscosity, it is difficult to shape the polyolefin and to form a desired microporous membrane. On the other hand, a polyolefin having an MI value of more than 50 g / 10 min has a too low melt viscosity, so that it is difficult to perform stable shaping. The MI value is preferably in the range of 0.05 to 20.0 g / 10 min, more preferably 0.1 to 5.0 g / 10 min according to the measurement method according to JIS K6760.
Range. When the MI value is less than 0.05 g / 10 min, the polymer viscosity is extremely high, and melt spinning becomes difficult, which is not preferable. If it exceeds 20.0 g / 10 min, the crystal orientation of the multilayer body becomes insufficient, and a uniform microporous structure cannot be obtained. Means for providing a difference in pore diameter between adjacent layers can be achieved by compounding polyolefins having different densities and MI values.

The spinning temperature and the spinning draft can be commonly used for the support layer and the intermediate layer having at least the dense layer. Therefore, it is desirable to use the same kind of material, but it is not necessarily limited. Depending on the polymer used,
For example, spinning temperature 170-270 ° C, draft ratio 50-4
000 condition range can be selected. Melt spinning, micropores formed by the drawing method, by arranging polyethylene of which density or MI value is adjusted, the dense layer having a smaller pore diameter of the present invention becomes a support layer having a larger pore diameter of the micropores. A composite hollow fiber membrane having a sandwiched multilayer structure can be obtained. The density or MI value of polyethylene described above can be freely adjusted by setting polymerization conditions, blending, and the like, and can be selected as needed.

Micropores are formed in each of the outermost layer, the intermediate layer and the innermost layer, and the micropores communicate with each other inside or between the layers to filter water from one surface of the hollow fiber membrane to the other surface. While transmitting. As such micropores, those formed by a stack dramella and microfibrils combined with the stack dramella are desirable.

That is, the unstretched melt-spun yarn is subjected to a stretching treatment, and by the stretching treatment, the stress is concentrated on an amorphous portion having a weak structure, and the amorphous chain is selectively elongated in the stretching direction. Cleavage occurs between the stack lamellas, and at the same time, a part of the stack lamellas also exfoliates, and these aggregate to form microfibrils. Then, a portion having a high cohesive force in the stack dramella withstands stress while maintaining its structure, and as shown in FIG. 10, a large number of microfibrils 20, 20,. , Are connected to the joints of the stack lamellae 18, 18,... To form slit-shaped fine holes 22, 22,.

Usually, the hole diameter, that is, the size of the fine holes 22 is
The average value of the length L of the microfibrils 20 (corresponding to the length of the long side of the slit-shaped micropore or the distance between the stack lamellas) L and the average value of the microfibril intervals W are represented by two parameters. In filtration with a hollow fiber membrane, the permeation flow rate mainly depends on the length L of the microfibrils, and the longer the microfibrils, the larger the permeation flow rate. On the other hand, the fractionation accuracy mainly depends on the microfibril interval W, and a smaller microfibril interval can increase the fractionation accuracy. However, in practice, a high permeation flow rate and a fractionation accuracy are maintained while maintaining a high membrane strength. Is very difficult to achieve in a single layer. In the composite hollow fiber membrane of the present invention, a support layer in which fine pores having a relatively large pore diameter are formed is disposed as the outermost layer and the innermost layer, and while maintaining a high membrane strength, a relatively small pore diameter is used as the intermediate layer. By arranging a dense layer in which micropores are formed to improve the filtration performance, it is possible to exhibit both a high permeation flow rate and a high fractionation accuracy while maintaining high membrane strength. That is, in the present invention, the average microfibril length and the average microfibril interval for the micropores formed in the dense layer are respectively smaller than the average microfibril length and the average microfibril interval for the micropores formed in the support layer. small.

In the composite hollow fiber membrane of the present invention, it can be considered that the layer thickness hardly changes before and after the stretching treatment. As the support layer, each layer thickness is 20 to 50 μm. Desirably within the range. 20μm to ensure external pressure durability and prevent deformation
On the other hand, if the thickness is more than 50 μm, cooling takes a long time after spinning, and the degree of crystal orientational order is likely to be disordered in the thickness direction. Is irregular in the thickness direction. As described above, in the composite hollow fiber membrane of the present invention, although the thickness of the support layer is thinner than the conventional one, it has a multi-layer structure of three or more layers.
Even if it is 50 μm or less, sufficient strength can be exhibited as a composite hollow fiber membrane. The layer thickness of the dense layer is desirably smaller than the layer thickness of the support layer, and the permeation flow rate is increased by making the layer thickness of the dense layer smaller than the layer thickness of the support layer.
The filtration life can be improved. The thickness of such a dense layer is preferably from 0.5 to 20 μm,
More preferably, it is 12 μm. When the thickness of the dense layer is less than 0.5 μm, pinhole defects tend to be easily generated in the dense layer, and it is difficult to perform stable melt spinning, while the thickness of the dense layer exceeds 20 μm. Then, the water permeability of the hollow fiber membrane tends to decrease.
In addition, the thickness of the dense layer is preferably 1/3 or less of the total thickness, and a hollow fiber membrane having a thickness larger than this makes it difficult to effectively obtain high water permeability.

In the support layer, the average microfibril length is preferably 0.5 to 10 μm, and the average microfibril interval is preferably 0.1 to 0.6 μm. When the microfibril length is less than 0.5 μm or the microfibril interval is less than 0.1 μm, the permeation flow rate of the entire composite hollow fiber membrane becomes insufficient. On the other hand, when the microfibril length is 10
If it is longer than μm, the elongation at break of the hollow fiber membrane after stretching tends to be insufficient. Also, when the microfibril interval is wider than 0.6 μm, the mechanical strength tends to be insufficient. In the dense layer, the average microfibril length is preferably 0.2 to 5 μm, and the average microfibril interval is 0.02 to 0.3 μm.
Is preferred. If the microfibril length is less than 0.2 μm or the microfibril interval is less than 0.02 μm, the filtration resistance of the dense layer increases, and the permeation flow rate of the entire composite hollow fiber membrane becomes insufficient. On the other hand, if the microfibril length is longer than 5 μm, the mechanical strength of the dense layer tends to be insufficient, and if the microfibril interval is wider than 0.3 μm, the separation accuracy tends to be reduced as a composite hollow fiber membrane. To increase the filtration flow rate of the composite hollow fiber membrane, it is effective to increase the microporous microfibril length of the support layer and reduce the thickness of the dense layer.

In the present invention, the microfibril length and the microfibril (bundle) interval can be measured, for example, as follows. First, the porous membrane to be measured is cut out as an ultrathin section along the stretching direction to obtain a sample, and the sample is subjected to transmission electron microscopy.
The image is taken into the image processing device after being magnified 500 times. And FIG.
As shown in FIG. 4, n scanning lines are drawn at a constant pitch (for example, 0.052 μm) from the captured image. At this time, for each scanning line, the lengths of the line segments on the fine holes 22, for example, a1, a2, a3,... Are summed (total distance). Similarly, for each scanning line, for example, b1, b2, b
3. Sum up. At this time, the length of the line segment on the micropore 22 (microfibril length or microfibril (bundle))
Those for which the distance cannot be measured, for example, the fine holes 22 'may be excluded. Also, the fine holes 2 through which each scanning line has passed
The numbers 2, 22, ... are obtained (sum of numbers). For example, FIG.
Among them, 5 for the first scan line and 6 for the second scan line
For the nth scanning line, the number is six. Then, the total distance is divided by the total number (total distance / total number). In this measurement, if the scanning direction of the scanning line is perpendicular to the stretching direction, the microfibril (bundle) interval is determined. If the scanning direction of the scanning line is parallel to the stretching direction, the microfibril length is determined.

As the intermediate layer, not only one dense layer is formed, but also, for example, as shown in FIG.
12, two dense layers 16 are formed between the outermost layer 12 and the innermost layer 14, or between the outermost layer 12 and the innermost layer 14, between the dense layer 16 and the support layer and the dense layer. A layer 17 having characteristics may be formed, and outside the outermost layer 12,
As long as a layer denser than the outermost layer 12 is not formed, a layer configuration of four or more layers of various patterns can be adopted.

The composite hollow fiber membrane of the present invention has a three-layer structure or a structure of four or more layers, in which a dense layer exhibiting the best filtration function is positioned as an intermediate layer. In a conventional composite hollow fiber membrane having a two-layer structure, clogging is likely to occur when the dense layer is disposed in the outermost layer. However, in the composite hollow fiber membrane of the present invention, the dense layer is the outermost layer. Because it is not placed in Further, in the case of a conventional composite hollow fiber membrane having a two-layer structure, when the dense layer is disposed in the innermost layer, it is difficult to control the degree of crystal orientation within a predetermined range. Although the micropore size to be formed is non-uniform (the pore size distribution is wide) and the fractionation accuracy is low, in the case of the present invention, since the dense layer is arranged as an intermediate layer, Since it is located outside the inner layer, the cooling rate of the dense layer during spinning is increased, the orientation degree order is improved, and the crystal orientation degree is stabilized. As a result, the pore size of the formed fine pores becomes uniform (the pore size distribution is narrow), and the fractionation accuracy is improved. As described above, by configuring the number of layers of three or more layers, the degree of crystal orientational order and control of both the support layer and the dense layer are facilitated, so that micropore control becomes possible, and the filtration life and the separation accuracy are improved. Can be improved together.

The composite hollow fiber membrane of the present invention desirably has a porosity of 75 vol% or more. 75% porosity
%, The filtration life can be prolonged. Furthermore, by increasing the initial membrane permeation flow rate (water permeation amount), preferably, the initial water permeation amount is set to 16 L / (m ² ···
(hr · KPa) or more, the filtration life can be further improved. Initial permeation flow rate (permeate amount)
In the structure of the composite hollow fiber membrane of the present invention, the microfibril length of the micropores in the support layer is made longer and the thickness of the dense layer is made thinner, thereby further improving the structure.

The composite hollow fiber membrane described above is manufactured, for example, as follows. Using a hollow fiber manufacturing die having three or more annular discharge ports arranged concentrically, co-extruding a crystalline molten polymer, cooling and winding up, an intermediate layer including the innermost layer and the outermost layer and a dense layer A composite unstretched hollow fiber (unstretched yarn) having a configuration in which layers are laminated is produced. At this time, a difference in pore diameter is provided by compounding polyolefins having different densities and MI values into the layers adjacent to each other.

The spinning temperature is not lower than the melting point of the polyolefin (preferably, a temperature higher than the melting point by 10 to 100 ° C.).
The resulting multilayer body is subjected to a heat treatment at a temperature equal to or lower than the melting point of the polyolefin (preferably at a temperature lower by 5 to 50 ° C. than the melting point) to form a stacked lamella. At this time, as a spinning condition, when the polymer for the support layer and the polymer for the dense layer are individually extruded and cooled, the degree of crystal orientation fc of the undrawn hollow fiber composed of the polymer for the support layer is 0.8 to 0.9.
9. It is desirable to set the degree of crystal orientation fc of the undrawn hollow fiber made of the polymer for the dense layer to be 0.2 to 0.75. As the degree of crystal orientation fc increases, the size of the lamellar crystal aggregate increases, and the microfibril length after stretching can be increased. Therefore, by subjecting the composite unstretched hollow fiber having such a degree of crystal orientation to a stretching treatment, a composite hollow fiber membrane having a support layer having relatively large micropores and a dense layer having small micropores is provided. And both high water permeability and high fractionation characteristics can be exhibited.

After preparing the composite undrawn hollow fiber, it is subjected to a drawing treatment to perform a pore opening treatment to obtain a porous structure membrane. The stretching treatment is preferably a two-stage stretching of cold stretching at room temperature and a hot stretching under heating, or a multi-stage stretching in which the hot stretching is further divided into multiple stages. By the cold drawing treatment, first, the crystal structure of the highly oriented crystalline undrawn hollow fiber is broken, and uniform and micro cracking occurs. Cold stretching is a process of causing microstructure cracks between stacked lamellae by causing structural destruction of a multilayer body at a relatively low temperature. This cold stretching is performed in a temperature range from 0 ° C. to 50 ° C. lower than the melting point of the polymer. It is preferred to do so. When polyethylene is used as the polyolefin, the cold stretching temperature is 0 to 80 ° C, preferably 1 to 80 ° C.
The range is from 0 to 50 ° C. Also, as the cold stretching ratio,
5-200% is preferred. If the content is 5% or less, the generation of microcracks becomes insufficient, and it becomes difficult to obtain a target pore diameter. On the other hand, if it exceeds 200%, deformation of the stack lamella occurs, and the porosity of each microporous layer decreases, which is not preferable.

Then, the subsequent hot stretching is a process in which the microcracks generated in the multilayer body are enlarged, microfibrils are formed between the stack lamellas, and a porous film having slit-like micropores is formed. is there. The hot stretching temperature is preferably as high as possible without exceeding the melting point of the polyolefin. Further, the heat stretching ratio may be appropriately selected depending on the target pore diameter.
It is good in the point of process stability to make it the range of -2000%, preferably 100-1000%. The cold stretching and the hot stretching may be performed by using a well-known method of making porous. The total stretching ratio (cold stretching ratio × hot stretching ratio) is preferably 5 or more, and more preferably 6 to 8 times. . By setting the stretching ratio to 5 times or more, the porosity of the entire membrane can be 75 vol% or more, and the initial water permeability and the accumulated water permeability can be increased. Although the optimal conditions for the deformation rate of the hot stretching vary depending on the polymer used, it is preferable to perform the deformation in the range of 0.01 to 10 min ^-1 . 0.01 min ^-1 is smaller than, easily yarn breakage of the undrawn yarn is caused, is unsuitable because it is difficult to achieve as large as the porosity than 10min ^-1.
Further, if necessary, in order to relieve the stress of the obtained drawn yarn and obtain dimensional stability, the film may be heat set under a fixed length or in a state in which the film is slightly relaxed to relieve the stress. preferable. In order to perform heat setting effectively, the heat setting temperature is preferably equal to or higher than the stretching temperature and equal to or lower than the melting point temperature. Thus, a composite hollow fiber membrane composed of three or more layers is obtained. By producing by such a melt spinning method and a stretch opening method, a clean and sanitary film containing no solvent, plasticizer, or the like can be obtained.

In the present invention, during the process in which the molten polymer for the support layer and the molten polymer for the dense layer are discharged from the die and cooled under elongational stress, the molecular mobility of the molten polymer molecular chains decreases (the melt viscosity increases). ) And the growth of a folded crystal of a molecular chain (the growth of a lamellar crystal) compete with each other. It is considered that the degree of crystal orientation (degree of orientational order of lamellar crystals) in the composite undrawn hollow fiber is determined when the two phenomena reach an equilibrium with the progress of cooling. In the present invention, the isothermal crystallization time τ is, under isothermal conditions, when the molecular chain crystallizes into a spherulite, the spherulite grows, and when the time when the adjacent spherulites hit each other and the growth stops, the end point, It means 1/2 of the time to reach this end point.

The crystal structure of the composite unstretched hollow fiber of the present invention is a form in which lamellar crystals are stacked in the fiber axis direction, and is not a spherulite structure at the time of isothermal crystallization. This is one index for quantifying the growth rate of the folded crystal. The larger the degree of orientation of the lamellar crystals in the composite undrawn hollow fiber, the larger the size of the ordered lamellar crystal aggregate. In the present invention, it has been found that the size of the lamella crystal corresponds to the size of the microfibril length after stretching, and by satisfying the above-mentioned condition regarding the size of the lamella crystal, the support layer is formed in the hollow fiber after stretching. Can be made longer than the microfibril length of the dense layer.

Although the details are not clear yet, in the crystal growth process under an elongation stress, the degree of lamellar crystal orientation and the size of the lamellar crystal tend to increase as the polymer has a shorter isothermal crystallization time τ. Therefore, by selecting the polymer of each layer so that the crystallization time τp of the polymer for the dense layer is longer than the crystallization time τs of the polymer for the support layer (τp / τs> 1), the size of the lamella crystal in the dense layer is increased. Is smaller than the size of the lamella crystals in the support layer, and thus the length of the microfibrils in the dense layer is shorter than the length of the microfibrils in the support layer. Smaller than the hole. Therefore, both water permeability and fractionation accuracy can be improved. However, if a polymer that crystallizes so rapidly that τp / τs> 100 is used for the support layer, even if the thickness of the support layer is set as described above, the orientational order is disturbed in the thickness direction. The dimensions are also likely to be non-uniform, making such a polymer selection inappropriate.

In order to use the above-mentioned composite hollow fiber membrane for the water filtration treatment, it is desirable to perform a permanent hydrophilization treatment, coat the surface of the micropores with a hydrophilic polymer, and make it easy to wet with water. That is, it is desirable to form a coating layer by coating the knot portion of the stack dramella of the composite hollow fiber membrane and the surface of the microfibril with a hydrophilic polymer.
Hereinafter, the composite hollow fiber membrane that has not been subjected to the hydrophilization treatment is referred to as a precursor.

The hydrophilic copolymer used herein is preferably a copolymer containing at least 20 mol% of ethylene and at least 10 mol% of a hydrophilic monomer, and these copolymers include random copolymers, block copolymers, graft copolymers and the like. Any type of copolymer may be used. If the ethylene content in the copolymer is less than 20 mol%, the copolymer has a weak affinity for the precursor, and sufficiently coats the hydrophilic copolymer even when the precursor is immersed in the hydrophilic copolymer solution. It is difficult to do so, which is not preferable.

The hydrophilic monomer used for polymerizing the hydrophilic copolymer includes, for example, vinyl alcohol,
Examples thereof include vinyl compounds such as (meth) acrylic acid and salts thereof, hydroxyethyl (meth) acrylate, polyethylene glycol (meth) acrylate, vinylpyrrolidone, and acrylamide. When one or more of these hydrophilic monomers are contained. Although vinyl alcohol may be mentioned as a particularly preferred monomer. Specific hydrophilic polymers include ethylene-vinyl alcohol copolymer, polyvinyl alcohol, polyvinylpyrrolidone, and hydrolyzate of polyvinyl acetate. The hydrophilic copolymer may contain one or more third components other than ethylene and the hydrophilic monomer. Examples of the third component include vinyl acetate, (meth) acrylic acid ester, vinyl alcohol fatty acid ester, Formalized or bratylized vinyl alcohol can be mentioned.

The coating amount of the hydrophilic copolymer on the composite hollow fiber membrane precursor is preferably in the range of 3 to 30% by weight in terms of the precursor weight, more preferably 3 to 15% by weight. A composite hollow fiber membrane having a coating amount of a hydrophilic copolymer of less than 3% by weight has poor affinity for water and lacks water permeability to the composite hollow fiber membrane. Quantity is 30
If the amount exceeds the weight percentage, blockage of the pores of the composite hollow fiber membrane by the copolymer tends to occur, and the water permeability tends to decrease. The adhesion rate of the hydrophilic copolymer to the composite hollow fiber membrane can be adjusted by appropriately setting the concentration of the hydrophilizing solution, the conditions for the liquid removal treatment, and the like.

The solvent for the hydrophilic copolymer is preferably a water-miscible organic solvent, and specific examples thereof include alcohols such as methanol, ethanol, n-propanol and isopropyl alcohol, dimethyl sulfoxide, dimethylformamide and the like. Can be mentioned. These solvents can be used alone, but a mixture with water is more preferable because of its high solubility in the hydrophilic copolymer. Further, from the viewpoint of the ease of creating a vapor-containing atmosphere of a solvent used when drying the composite hollow fiber membrane coated with the hydrophilic copolymer, that is, the low vapor pressure of the solvent and the low toxicity to the human body, the boiling point is 100%. It is particularly preferable to use a mixed solvent of an alcohol having a temperature of lower than 0 ° C, for example, methanol, ethanol, isopropyl alcohol and the like, and water. The mixing ratio of the water-miscible organic solvent and water does not impair the permeability to the precursor and may be within a range that does not reduce the dissolution of the copolymer, and varies depending on the type of the copolymer used, When ethanol is used as the organic solvent, the ratio of ethanol / water is preferably in the range of 90/10 to 30/70 (vol%).

The concentration of the hydrophilic copolymer solution is 0.1 to 1
It is about 0% by weight, preferably in the range of 0.5 to 5% by weight. When the precursor is treated with a solution having a concentration of less than 0.1% by weight, it is difficult to uniformly coat the hydrophilic copolymer, and when the concentration exceeds 10% by weight, the solution viscosity becomes too large. If it is treated, the micropores of the composite hollow fiber membrane will be closed by the copolymer. As a coating method, a conventionally known method in which a precursor is immersed in a hydrophilic polymer solution, pulled up, and then the solvent is evaporated and dried by heating and drying can be applied. In that case, the immersion treatment may be performed twice or more in the copolymer solution having the same concentration, or the immersion treatment may be performed twice or more in the solutions having different concentrations.

The higher the temperature of the hydrophilic copolymer solution to be subjected to the immersion treatment, the lower the viscosity thereof, and the better the permeability of the solution to the precursor, which is preferable. However, from the viewpoint of safety, the temperature is preferably lower than the boiling point of the solution. preferable. The immersion time depends on the thickness of the precursor used, the fine pore diameter, and the porosity.
It is preferable to set the range from several seconds to several minutes. The precursor is immersed in the hydrophilic polymer solution, and before being dried, contains an organic solvent vapor of 3 vol% or more, and is started in an atmosphere having a temperature from room temperature to a temperature not higher than the boiling point of the solvent, and is then started for at least 30 seconds or more. It is preferable to carry out a setting step.

The purpose of this treatment step is to spin off the micropores by forming a coating of a hydrophilic copolymer on the surface of the node between the microfibrils and the stack dramella constituting the precursor. Another object of the present invention is to bind microfibrils to increase the diameter of slit-shaped fine holes to form elliptical fine holes, thereby increasing the amount of water permeation, and increasing the affinity with treated water.

In order to prevent the hydrophilic copolymer from forming a film on the precursor surface during the setting step, it is necessary to prevent rapid drying on the precursor surface. It is necessary to suppress the evaporation rate in the process and to keep the precursor surface wet with the solvent. From this viewpoint, it is preferable that the atmosphere in the setting step be an atmosphere in which the vapor of the water-miscible organic solvent is 3 vol% or more.

The evaporation rate of the solvent from the precursor in the setting step is preferably as low as possible, and the atmosphere in the setting step is preferably an atmosphere close to the saturated evaporation concentration of the solvent. Further, in order to delay the evaporation of the solvent on the precursor surface in this step, it is better to lower the setting temperature. However, if the temperature is too low, the phenomenon that the desolvation does not proceed in the setting step undesirably occurs. Therefore, it is preferable that the temperature of the atmosphere be equal to or higher than room temperature and equal to or lower than the boiling point of the water-miscible solvent.

The precursor after immersion is raised from the immersion bath into the atmosphere, and the rising angle is preferably in the range of 45 ° to 90 °. By starting up, a part of the copolymer solution attached to the precursor is removed from the precursor by its own weight. The amount of liquid removed depends on the speed at which the precursor rises from the bath surface, the viscosity of the immersion solution, the height of the precursor rising from the bath surface, and the like. As an auxiliary means for enhancing the drainage effect in this setting step, wiping of the solution on the precursor surface by a guide, a slit or the like may be used together.

The setting time should be at least 30.
Seconds are preferred, during which the concentration of the copolymer solution as the bath agent evaporates from the precursor and homogenization by migration of the microfibrils of the membrane and the surface of the stacked dramellar are carried out. In particular, when the precursor is continuously treated with the hydrophilic copolymer solution, the setting time is as follows:
At least 30 seconds or more are required. If the setting is less than 30 seconds, concentration due to evaporation of the solvent is insufficient,
Drying is performed in a state where the excess solution adheres to the precursor, and pores are blocked by the hydrophilic copolymer, and at the same time, uniform adhesion of the copolymer within the membrane structure becomes insufficient. It is difficult to obtain a composite hollow fiber membrane having good water permeability and fractionation performance.

The amount of evaporation of the solvent from the precursor when the vapor setting time is 30 seconds is preferably about 15 to 30% of the hydrophilic copolymer solution used. Examples of a method for controlling the evaporation amount of the solvent from the precursor in the setting step include a setting atmosphere temperature, a method of blowing a gas such as air or an inert gas into the atmosphere, and the like.

In the drying step, microfibrils forming innumerable slit-like micropores obtained by a stretching method are covered with a hydrophilic copolymer, converged, and the structure is changed into elliptical micropores, and the pore diameter is enlarged. This is an important step of fixing. In addition, since the hollow fiber membrane shrinks at the same time as drying, taking into account the shrinkage, the feeding speed of the yarn before the drying step is higher than the winding speed after drying, and the hollow fiber membrane is adjusted according to the characteristics of the membrane. By performing hydrophilic treatment while sufficiently shrinking, it is possible to increase the pore diameter and increase the water permeability.

If the feeding speed before drying with respect to the winding speed is faster than the shrinkage of the hollow fiber membrane, yarn slack occurs before drying, and the process stability decreases. Conversely, if the feeding speed is equal to the winding speed without considering the shrinkage of the hollow fiber membrane, the yarn is pulled in response to the shrinkage of the yarn in the drying step and is processed under high tension. The treatment is performed without expanding the hole diameter in an elliptical shape as it is, and sufficient water permeability cannot be obtained. Therefore, it is preferable to adjust the supply and take-up speeds before and after drying according to the degree of shrinkage of the hollow fiber membrane to be treated.

The drying of the precursor after the setting is completed may be performed by a known drying method such as vacuum drying and hot air drying. The drying temperature may be a temperature at which the composite hollow fiber membrane is not deformed by heat. For example, in the case of a composite hollow fiber membrane made of polyethylene, it is preferable to dry at a temperature of 120 ° C or lower, and it is particularly preferable to dry at a temperature of 40 to 70 ° C. The drying time varies depending on the diameter of the fine pores, the film thickness, the processing speed, etc., but it is sufficient that the drying time is about 1 minute to 10 minutes as long as the hollow fiber membrane is sufficiently dried. By performing such a hydrophilic treatment, as shown in FIG. 13, a plurality of microfibrils are bound together to form a microfibril bundle 21, and the micropores 22 are changed from a slit shape to an elliptical shape.

In the composite hollow fiber membrane subjected to the hydrophilic treatment, the average distance Da between the microfibril bundles is preferably 0.2 to 0.5 μm with respect to the size of the fine pores in the dense layer. More preferably, it is 0.3 to 0.4 μm. The average distance Da between the microfibril bundles is 0.
A hollow fiber membrane having a diameter of 2 μm or more has a particularly large water permeability, and a hollow fiber membrane having a Da of 0.5 μm or less has a good ability to block fine particles, that is, a high-fractionation membrane. Similarly, with respect to the size of the micropores in the support layer, the average distance Db between the microfibril bundles is preferably 0.2 to 1 μm, and more preferably 0.4 to 0.5 μm. Db is 0.
In a hollow fiber membrane having a support layer composed of micropores of less than 2 μm, the water permeation rate tends to decrease, while Db is 1
If it exceeds μm, the mechanical strength of the hollow fiber membrane tends to decrease. The microfibril length M in the support layer is preferably from 0.4 to 4.0 μm, and 0.7
More preferably, it is 2.0 μm. In a hollow fiber membrane having a support layer having micropores having a microfibril length M of less than 0.4 μm, the water permeation rate tends to decrease, and when the microfibril length M exceeds 4.0 μm, the mechanical properties of the hollow fiber membrane tend to decrease. The strength tends to decrease.

In this composite hollow fiber membrane, the ratio of the microfibril bundle interval Da of the dense layer to the microfibril bundle interval Db of the support layer preferably satisfies 1.3 ≦ Db / Da ≦ 4.0. By setting Db / Da to 1.3 or more, the accuracy of fractionation and the amount of water permeation can be further increased, and the clogging resistance is improved. On the other hand, if Db / Da exceeds 4.0, the difference in physical properties between adjacent polyolefins increases, and the spinning or drawing stability tends to decrease. In the composite hollow fiber membrane, the maximum pore diameter of the membrane determined by the bubble point method is preferably in the range of 0.05 to 1.0 μm.
In a hollow fiber membrane having a maximum pore diameter of less than 0.05 μm, the water permeation rate tends to decrease, and when it exceeds 1.0 μm, the mechanical strength decreases.

With the composite hollow fiber membrane of the present invention, the rejection (that is, fractionation accuracy) for polystyrene latex standard particles having a particle diameter of 0.05 to 0.3 μm can be 90% or more.

The hollow fiber membrane module of the present invention is particularly suitable for applications requiring high flow rate treatment by filtration under pressure, and requiring a long life by performing backwashing regeneration. Is a high level of water purification treatment as a measure against Cryptosporidium in water treatment plants, filtration of river water, lakes and marshes, filtration of industrial water, solid-liquid separation of sewage, wastewater treatment, pretreatment of seawater desalination, etc. For filtering liquids having a high viscosity.

[0067]

EXAMPLE [Hollow Fiber Membrane 1] A density of 0.966 g / cm ³ , MI value was measured from inner and outer discharge ports using a hollow fiber production nozzle having three annular discharge ports arranged concentrically. 1.35 g / 10 min high-density polyethylene (“Suntech HD-B161” manufactured by Asahi Kasei Kogyo Co., Ltd.) was supplied through the middle discharge port at a density of 0.960 g / cm ³ and an MI value of 0.9 g / 10 min.
("Nipolon Hard 5110" manufactured by Tosoh Corporation) was melt-spun to form a polyethylene hollow fiber having a three-layer structure. At this time, the discharge temperature is 170 ° C.
The inner layer side discharge amount is 3.2 cc / min, and the outer layer side discharge amount is 3.2 cc / min.
2 cc / min, middle layer discharge amount 0.65 cc / mi
n, the discharge rate ratio of the inner layer, the intermediate layer and the outer layer is 4.9 / 1 / 4.9,
Discharge was performed at a discharge linear velocity of 6.1 cm / min and a draft ratio of 979. Further, a cooling air having a temperature of 21 ° C. and a wind speed of 1 m / sec was uniformly applied to the yarn discharged from the nozzle at a winding speed of 60 m / min while uniformly surrounding the yarn to obtain a polyethylene multilayer body.

The obtained polyethylene multilayer body was subjected to a heat treatment for 16 hours in the air heated to 115 ° C. while keeping the fixed length.
Further, the multilayer body was placed between a mouth and a roll kept at 30 ° C. for 6 hours.
The film was cold-stretched by 0%, and subsequently hot-stretched in a heating furnace at 111 ° C. so that the total amount of stretching was 550%. At this time,
The heat deformation rate was 1.3 / min. Further, heat setting was performed in a heating furnace at 120 ° C. while keeping the fixed length to obtain a composite hollow fiber membrane precursor. Next, ethylene content 32 mol
% Of an ethylene-vinyl alcohol copolymer (“Soarnol DC3203” manufactured by Nippon Synthetic Chemical Co., Ltd.) in 70% ethanol / water mixed solution (mixing ratio 60/40 vol%).
A 0% by weight dissolved hydrophilic copolymer solution was prepared. After immersing the composite hollow fiber membrane precursor in this hydrophilic copolymer solution for 500 seconds, the precursor was lifted up, and a part of the hydrophilic agent solution excessively attached to the surface was squeezed out by a guide.

Subsequently, an ethanol vapor concentration of 40 vol
%, At a rising angle of 90 ° in an atmosphere of 60 ° C., 5
After allowing the hydrophilic agent to adhere uniformly to the inner surface of the micropores of the precursor for 00 seconds, the solvent was dried while overfeeding by 10% with hot air at 70 ° C. The ethanol concentration in the atmosphere was measured using a gas detector tube ("Gastec detector tube" manufactured by Gastech Co., Ltd.). The coating amount of the ethylene-vinyl alcohol copolymer on the precursor in the obtained hydrophilic composite hollow fiber membrane was 10.9% by weight. In addition, the coating amount of the hydrophilic copolymer was calculated according to the following equation.

(Equation 1) Table 1 shows the membrane characteristics of the obtained composite hollow fiber membrane (three-layer composite membrane [dense layer intermediate layer]).

[Hollow Fiber Membrane 2] Using a hollow fiber production nozzle having two concentrically arranged annular discharge ports, the density was 0.960 g / cm ³ and the MI value was 0.9 from the inner discharge port.
9 g / 10 min high-density polyethylene (“Nipolon Hard 5110” manufactured by Tosoh Corporation) was supplied from the outer discharge port to a high-density polyethylene having a density of 0.966 g / cm ³ and an MI value of 1.35 g / 10 min (“Suntech HD-B161 (Made by Asahi Kasei Kogyo Co., Ltd.) and melt-spun a polyethylene hollow fiber having a two-layer structure. At this time, the discharge temperature was 170 ° C.
Inner layer side discharge rate 1.3 cc / min, outer layer side discharge rate 10.1
Discharge was performed so as to be cc / min, the discharge amount ratio between the inner layer and the outer layer was 1 / 7.7, the discharge linear velocity was 14.3 cm / min, and the draft ratio was 714. Further, a cooling air having a temperature of 21 ° C. and a wind speed of 1 m / sec was uniformly wound around the yarn discharged from the nozzle at a winding speed of 102 m / min while uniformly surrounding the yarn to obtain a polyethylene multilayer body.

The obtained polyethylene multilayer body was subjected to a heat treatment for 16 hours in the air heated at 115 ° C. while keeping the fixed length.
In addition, the multilayer body was placed between rollers maintained at 30 ° C. for 6 hours.
The film was cold-stretched by 0%, and subsequently hot-stretched in a heating furnace at 111 ° C. so that the total stretching amount was 600%. At this time,
The heat deformation rate was 1.1 / min. Further, heat setting was performed in a heating furnace at 120 ° C. while keeping the fixed length to obtain a composite hollow fiber membrane precursor. Next, ethylene content 32 mol
% Of an ethylene-vinyl alcohol copolymer (“Soarnol DC3203” manufactured by Nippon Synthetic Chemical Co., Ltd.) in 70% ethanol / water mixed solution (mixing ratio 60/40 vol%).
A 0% by weight dissolved hydrophilic copolymer solution was prepared. After dipping the above-mentioned composite hollow fiber membrane precursor in this hydrophilic copolymer solution for 500 seconds, the precursor was pulled up, and a part of the hydrophilizing agent solution excessively attached to the surface was squeezed out by a guide.

Subsequently, an ethanol vapor concentration of 40 vol
%, At a rising angle of 90 ° in an atmosphere of 60 ° C., 5
After allowing the hydrophilic agent to adhere uniformly to the inner surface of the micropores of the precursor for 00 seconds, the solvent was dried while overfeeding by 10% with hot air at 70 ° C. The coating amount of the ethylene-vinyl alcohol copolymer on the precursor in the obtained hydrophilized composite hollow fiber membrane was 10.
It was 5% by weight. Table 1 shows the membrane properties of the obtained composite hollow fiber membrane (compact layer-inner layered composite membrane).

[Hollow Fiber Membrane 3] The polymer used for the intermediate layer in the hollow fiber membrane 1 is discharged at a discharge rate of 6.4 cc / min and melted using a hollow fiber manufacturing nozzle having one annular discharge port. Spun. The discharge temperature at that time was 170 ° C,
The film was wound at a winding speed of 60 m / min. The obtained undrawn hollow fiber is subjected to a heat treatment and a drawing treatment under the same conditions as the hollow fiber membrane 1,
A hydrophilic treatment was performed. The coating amount of the ethylene-vinyl alcohol copolymer with respect to the precursor of the obtained hydrophilized composite hollow fiber membrane was 8.0% by weight. Table 1 shows the membrane characteristics of the obtained hollow fiber membrane (uniform membrane).

In Table 1, the porosity of the film was measured using a mercury porosimeter 221 manufactured by Carlo Elba. As for the water permeability of the membrane, a mini-module having an effective membrane area of 70 to 90 cm ² was prepared, ion-exchanged water at a water temperature of 25 ° C. was filtered at a differential pressure of 98 kPa, and the water permeability at that time was measured. The fractionated particle size is a module of a hollow fiber membrane having a membrane area of about 50 cm ² , a monodispersed particle size of a predetermined particle size of a surfactant (polyethylene glycol-p-isooctylphenyl ether) of 0.1 wt%. The polystyrene latex particles are filtered, and the concentration of the latex particles in the filtrate is measured with a spectrophotometer (“U-
3400 "manufactured by Hitachi) at a wavelength of 320 nm,
The particle size at a capture rate of 90% was determined.

[Table 1]

Each of the hollow fiber membranes 1 to 3 is processed into a hollow fiber membrane knitted fabric and arranged in a sheet shape. The openings at both ends are formed by using a urethane resin potting material (fixing member). Was manufactured.
The knitted fabric 32 made of a hollow fiber membrane had an effective length of about 1.2 m and an effective area of about 15 m ² . Using these hollow fiber membrane modules, a suspension solution having a dry yeast concentration of 200 ppm was prepared.
Pressure filtration, reverse cleaning, air scrubbing cleaning, drainage 6
Repeat at 0 minute cycle, and with constant flow filtration, LV =
0.1 m ³ / m ² · hr (flow rate per unit area per hour)
Under the conditions described above, a water-pass filtration test was carried out by total filtration from OUT to IN. At this time, the filtration pressure (transmembrane pressure difference) at the initial stage and after 7 days was measured, and the results are shown in Table 2.

[0076]

[Table 2] From Table 2, it can be seen that the hollow fiber membrane module of this example has a small transmembrane pressure and a small increase due to its use.
OUT → IN filtration can increase the film area of the outer surface of the dense layer portion, and can increase the flux (filtration flow rate) as compared with the case where the dense layer is located at the innermost layer. In addition to a uniform membrane as well as a module with a dense-layer inner-layered composite hollow fiber membrane, it was possible to further increase the water permeability while maintaining a long life and durability with excellent clogging resistance.

[0077]

According to the hollow fiber membrane module of the present invention,
In constant flow rate filtration, the processing pressure is low and the backwash recovery is excellent, so stable long-term stable operation is possible.
Higher filtration efficiency can be maintained over a long period of time. In addition, in the pressure filtration of highly polluted water, even when used with a high water permeability, the hollow fiber membrane has a flat type form in which the adhesion and integration of the hollow fiber membrane are hard to occur, and the water permeability does not decrease with time. The characteristics of the thread membrane module can be maintained. Also,
As compared with the case of using a conventional hollow fiber membrane having the same fractionation performance, it is possible to obtain a higher filtration flow rate while maintaining a high fractionation performance for the purpose of completely removing bacteria and the like,
The amount of film used can be reduced, and as a result, the module can be made compact.

Also, it is excellent in clogging resistance against water flow from both directions OUT → IN and IN → OUT. Further, the thickness of each support layer of the hollow fiber membrane is 20 to 50 μm,
If the layer thickness of the dense layer is smaller than the layer thickness of the support layer,
It has high external pressure durability, is hardly deformed, has high precision of fine pore separation, has a high permeation flow rate, and has a long filtration life. In addition, since the porosity of the composite hollow fiber membrane is 75 vol% or more, the filtration life becomes longer. Furthermore, by forming the coating layer made of a specific amount of the hydrophilic copolymer, affinity with water is increased, and water permeability is improved.
Further, in the composite hollow fiber membrane, the microfibril bundle interval Da of the dense layer and the microfibril bundle interval Db of the support layer are set.
Is in a specific relationship, it is possible to further increase the fractionation accuracy and the amount of water permeation, to improve the clogging resistance, and to stably manufacture.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing an example of a hollow fiber membrane module.

FIG. 2 is a side sectional view showing an example of a hollow fiber membrane module.

FIG. 3 is a side sectional view showing an example of a hollow fiber membrane module.

FIG. 4 is a partially transparent side view showing an example of a hollow fiber membrane module.

FIG. 5 is a perspective view showing an example of an element.

FIG. 6 is a plan view showing a hollow fiber membrane knitted fabric (woven fabric).

FIG. 7 is a perspective view showing an example of a gas dispersion.

FIG. 8 is a perspective view showing an example of a gas dispersion.

FIG. 9 is a partial perspective view showing an example of a composite hollow fiber membrane.

FIG. 10 is an enlarged plan view of a layer constituting the composite hollow fiber membrane.

FIG. 11 is a side sectional view illustrating an example of a layer configuration.

FIG. 12 is a side sectional view illustrating an example of a layer configuration.

FIG. 13 is an enlarged plan view of a layer constituting a composite hollow fiber membrane subjected to a hydrophilic treatment.

FIG. 14 is a plan view showing a method for measuring an average pore diameter of micropores.

[Explanation of symbols]

 Reference Signs List 10 composite hollow fiber membrane 12 outermost layer 14 innermost layer 16 dense layer 18 stack dramella 20 microfibril 21 microfibril bundle 22 micropore 30 hollow fiber membrane module 32 knitted fabric 34 element 36 air supply member 37 air supply member 38 gas dispersion Body 39 Gas dispersion 40 Container 42 Support member 44 Fixing member 68 Hollow fiber membrane module 70 Element 80 Hollow fiber membrane module

Claims (4)

[Claims] 1. A plurality of knitted fabrics comprising a hollow fiber membrane are arranged along one direction, and at least one end of the hollow fiber membrane is kept open to be fixed by a fixing member, and the element is housed. A hollow fiber membrane module including a container, an air supply member for supplying gas into the container, and a gas dispersion for dispersing and guiding the gas from the air supply member, wherein the hollow fiber membrane has a fine structure. Three or more layers of a three-dimensional network structure film having a plurality of holes are laminated, and as an intermediate layer located between the outermost layer and the innermost layer, the average pore size of the fine pores is larger than the average pore size of the outermost layer and the innermost layer. A hollow fiber membrane module comprising a composite hollow fiber membrane having a small dense layer. 2. The composite hollow fiber membrane, wherein the micropores are formed by a stack dramella and microfibrils bonded to the stack dramella, and each of the outermost layer and the innermost layer has a thickness of 20 to 2. The hollow fiber membrane according to claim 1, wherein the dense layer is thinner than each of the outermost layer and the innermost layer, and has a porosity of 75 vol% or more as a whole of the composite hollow fiber membrane. module. 3. The composite hollow fiber membrane according to claim 1, wherein a coating layer comprising a hydrophilic copolymer in an amount of 3 to 30% by weight based on the composite hollow fiber membrane is formed. Or the hollow fiber membrane module according to 2. 4. An average distance Da between microfibril bundles of micropores of said dense layer and an average distance Db between microfibril bundles of micropores of said support layer, wherein: 4. The hollow fiber membrane module according to 3. 1.3 ≦ Db / Da ≦ 4.0