JPH09117643A - Hollow fiber membrane module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve water permeability, mechanical strength, and durability, in the case that hollow fiber membranes are arranged in an expanded sheet-like form, by employing a composite micro-porous hollow fiber membrane of polyolefin comprising at least two micro-porous layers each having pores with different diameters. SOLUTION: A structural member 1 having water collecting function is provided to support the whole hollow fiber membrane module, and an opening of the member 1 is formed into an elongated, nearly rectangular shape so as to receive an elongated, nearly rectangular fixing member 2. The member 2 fixes ends of openings of a large number of composite micro-porous hollow fiber membrans 3, which are arranged in an expanded sheet-like form at the opening of the member 1, in such a manner that the ends of openings of the membranes 3 are kept open and bundled, and to cause the membranes 3 to function as filter membranes, the member 2 functions so as to separate water to be treated and treated water in a sealed manner. And in the membrane 3, two or more micro-porous layers of polyolefin having pores with different diameters are layered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hollow fiber membrane module, and more particularly to a hollow fiber membrane module suitable for filtering a liquid having a high pollutant (particularly a pollutant of organic matter).

[0002]

2. Description of the Related Art Conventionally, hollow fiber membrane modules have been constructed using sterile water,
It has been widely used in the field of so-called microfiltration such as drinking water, tap water, high-purity water production, and air purification, but in recent years, secondary treatment, tertiary treatment, and
Solid-liquid separation in septic tanks, solid-liquid separation of ss (floating suspended solids) in industrial wastewater, direct filtration of river water in water treatment plants,
Various studies have been conducted for use in highly polluted water treatment applications such as industrial tap water filtration and pool water filtration.

However, the hollow fiber membrane module conventionally used in these fields is a cylinder in which hollow fiber membranes are bundled in a cylindrical shape or concentric circles which are used in the field of microfiltration and arranged in a cylindrical container. Most of them were shaped. Further, even if these hollow fiber membrane modules are improved, many of them only change the filling rate or the filling form of the hollow fiber membranes.

Using such a conventional hollow fiber membrane module, highly polluted water (for example, ss ≧ 50 ppm, TOC ≧ 1)
(00 ppm), the hollow fiber membranes are fixed (adhered) and integrated with each other through the deposits such as organic substances adhered to the surface of the hollow fiber membranes during use, and thus the module is formed. The effective membrane area of the hollow fiber membrane inside decreased, and the filtration flow rate was drastically reduced. In particular, this phenomenon was remarkable in the hollow fiber membrane in the central part of the cylindrical module, and was more remarkable in the larger size. Further, even when the hollow fiber membrane module in which the hollow fiber membranes are fixed and integrated in this way is regularly subjected to membrane surface cleaning or backwashing, the function of the module once fixed and integrated is not easy, A decrease in cleaning efficiency was seen.

In order to solve such a problem, a flat type hollow fiber membrane in which hollow fiber membranes arranged and expanded in a sheet shape are fixed by a fixing member in a structural material having an opening having an elongated rectangular cross section. Module has been developed
-220356).

[0006]

In this type of hollow fiber membrane module, the hollow fiber membranes are unlikely to adhere to each other due to contaminants in the water during use, and the membrane surface cleaning of the hollow fiber membranes is performed in parallel with filtration. However, it is difficult to increase the membrane area of the hollow fiber membrane of the module, and it is difficult to make a module having a large water permeation rate. One method is to use a hollow fiber membrane having a large pore diameter to make a module having an increased water permeation amount, but there is a drawback that the filtration efficiency of contaminants is reduced. Further, a module having a large water permeability can be made by using a hollow fiber membrane having a smaller film thickness, but in that case, the mechanical strength of the hollow fiber membrane tends to be insufficient. Therefore, it is necessary to use a large number of hollow fiber membrane modules in order to process a large amount of liquid.

The inventors of the present invention have made extensive studies as to the development of a porous hollow fiber membrane suitable for producing a hollow fiber membrane module having high flux, good mechanical strength and good handleability. By forming a composite microporous hollow fiber membrane in which a microporous membrane having micropores capable of separating particles having a particle diameter of 10 μm is joined to a microporous membrane having micropores having a predetermined ratio larger than that, The inventors have found that a composite porous hollow fiber membrane having sufficient strength without increasing the thickness and having a significantly improved water permeation amount can be produced, and completed the present invention.

An object of the present invention is to provide a hollow fiber membrane module having a large amount of water permeation, good mechanical strength and excellent durability.

Another object of the present invention is to provide a hollow fiber with high recovery of filtration characteristics, even when it is used for filtering highly polluted water, the surface of the hollow fiber membrane in the module can be efficiently cleaned in parallel with the filtration. It is to provide a membrane module.

[0010]

Means for Solving the Problems That is, the present invention provides a hollow fiber membrane which is arranged in a sheet form and spread, and a fixing member which fixes the hollow fiber membrane while keeping the end portions of the hollow fiber membrane open.
A hollow fiber membrane module comprising a structural member that supports and houses the fixing member, and a cross section of the fixing member that is perpendicular to the hollow fiber membrane is elongated and substantially rectangular. A hollow fiber membrane module comprising a polyolefin composite microporous hollow fiber membrane having at least two microporous layers.

Further, according to the present invention, the hollow fiber membranes arranged side by side in a sheet form are arranged, a fixing member for fixing the hollow fiber membranes while keeping the ends of the hollow fiber membranes open, and a supporting member for the fixing member. A hollow fiber membrane module comprising a structural material to be housed and having a substantially rectangular elongated cross section perpendicular to the hollow fiber membrane of the fixing member, and as the hollow fiber membrane, a microporous layer having a separation function. A composite microporous hollow fiber membrane made of polyolefin in which a microporous b layer having a reinforcing function is laminated on at least one side of an a layer, and the membrane structure has a plurality of micro layers in which each of the a layer and the b layer is oriented in the fiber axis direction. It is composed of a laminated body of elliptical micropores composed of a knotted portion of a stack lamella that is bonded at both ends of a fibril bundle and a microfibril bundle,
The micropores are communicated from one surface of the hollow fiber membrane toward the other surface, and the microfibril bundles and the nodules of the stacked lamellae forming the micropores of the hollow fiber membrane are composite microporous hollow. 3 to 100% by weight of thread film precursor
Between the average distance Da between the micropore bundles of micropores which are covered with the hydrophilic copolymer of 30% by weight and exist in the a layer, and between the microfibril bundles of micropores present in the b layer. The ratio to the average distance Db is 1.3 ≦ Db / Da ≦
A hollow fiber membrane module characterized by using a composite microporous hollow fiber membrane in a range of 4.0.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The hollow fiber membrane module of the present invention comprises:
As shown in FIGS. 1 and 2, it is basically composed of a structural material 1, a fixing member 2, and a composite microporous hollow fiber membrane 3. In addition to these, various accessory members such as dispersing means may be attached.

The structural member 1 is a member for supporting the entire hollow fiber membrane module, has a water collecting function, and has an opening for accommodating the elongated and substantially rectangular hollow fiber membrane fixing member. 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, etc. can be used. When incineration is required after use, it is preferable to use a hydrocarbon resin that can be completely burned without producing toxic gas by burning.

The opening of the structural member 1 is a substantially rectangular shape which can accommodate and fix a fixing member for filling and fixing the opening end of a large number of composite microporous hollow fiber membranes spread in a sheet shape therein. It is preferable that the length of the short side of this rectangle is 30 mm or less, from the viewpoint of increasing the water permeability of the hollow fiber membrane module of the present invention and enhancing the cleaning efficiency of the membrane surface, and it is preferably 15 mm or less. Particularly preferred. In this way, by deploying the arrangement mode of the composite microporous hollow fiber membrane in the form of a flat sheet, it is possible to prevent the effective membrane area of the hollow fiber membrane from rapidly decreasing. Further, even if the hollow fiber membrane is contaminated with the pollutant, the hollow fiber membrane is arranged in the form of a sheet, so that the contamination can be easily washed and recovered. The length of the long side of the rectangle is not particularly limited, but if it is too short, it is not preferable because the number of hollow fiber membranes that can be arranged in one hollow fiber membrane module decreases, while if it is too long, its handleability is reduced. Is not preferable because it deteriorates. Usually, the long side length is 100 to 200
It is about 0 mm.

The fixing member 2 is filled and fixed in the opening portion of the structural material 1, and each end portion of a large number of composite microporous hollow fiber membranes 3 arranged in a sheet form is bundled and fixed while keeping the opening state. In addition, in order to make this hollow fiber membrane function as a filtration membrane, it functions as a member that liquid-tightly separates the water to be treated from the treated water. The fixing member 2 is usually formed by curing a liquid resin such as epoxy resin, unsaturated polyester resin or polyurethane.

The composite microporous hollow fiber membrane used in the hollow fiber membrane module of the present invention has a composite structure in which two or more polyolefin microporous layers having micropores having different pore sizes are laminated, that is, The microporous layer b layer having a large pore size, which has a reinforcing function, is laminated on at least one surface of the microporous layer a layer having a small pore size, which has a separating function. Therefore, the structure of the hollow fiber membrane may be, for example, a two-layer structure in which the b layer is laminated on one surface of the a layer,
A three-layer structure in which the b layer is laminated on both surfaces of the a layer may be used. The composite microporous 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 practice. On the other hand, when it is larger than 5000 μm, the degree of integration of the hollow fiber membrane is lowered, so that the water permeability per unit volume is remarkably lowered. The total film thickness is preferably 5 to 500 μm, more preferably 30 to 200 μm.
If the total film thickness is less than 5 μm, the mechanical strength is weak and the hollow fiber is deformed flat. If it is larger than 200 μm, it becomes difficult to obtain high water permeability.

The layers a and b have micropores arranged in the fiber axis direction, and the micropores are in the layer a and b.
The micropores that communicate with each other in the layers and between the ab layers form a layered communication from one surface of the hollow fiber membrane to the other surface.

The micropores formed in the layer a are formed of microfibril bundles arranged in the fiber axis direction and knots of the stacked lamellae arranged in the direction perpendicular to the fiber axis.
The gap between the microfibril bundle and the nodule is an elliptical micropore.

The size of the micropores in the layer a is preferably 0.2 to 0.5 μm, more preferably 0.3 to 0.4 μm in terms of the average distance Da between the microfibril bundles. preferable. A hollow fiber membrane having an average distance Da between the microfibril bundles of 0.2 μm or more has a particularly large water permeability, and a membrane having a Da of 0.5 μm or less has good fine particle blocking ability, that is, a high fractionation membrane. Has become.

The thickness of the layer a is preferably 0.5 to 20 μm, more preferably 3 to 12 μm. When the thickness of the a layer is less than 0.5 μm, pinhole defects tend to occur in the a layer, while when the thickness of the a layer exceeds 20 μm, the water permeability of the hollow fiber membrane decreases. Tend to do. Further, the film thickness of the layer a is preferably 1/3 or less of the total film thickness, and it becomes difficult to effectively obtain high water permeability with a hollow fiber membrane thicker than this.

The microporous layer b layer has a reinforcing function of supporting the microporous layer a layer which has a separating function in the composite hollow fiber membrane. Like the layer a, the layer b also has a laminated structure of micropores oriented in the fiber axis direction, and the micropores are formed by microfibril bundles and knots of the stacked lamellae. The size of the micropores in the b layer is preferably 0.2 to 1 μm, and more preferably 0.4 to 0.5 μm in terms of the average distance Db between the microfibril bundles. A hollow fiber membrane having a b-layer with micropores having a Db of less than 0.2 μm tends to have a reduced water permeation rate, while when Db exceeds 1 μm, a hollow-fiber membrane having a b-layer having the micropores. Mechanical strength tends to decrease.

The average distance Lb between the nodules of the stacked lamella in the layer b is preferably 0.4 to 4.0 μm, more preferably 0.7 to 2.0 μm. The water permeation rate tends to decrease in a hollow fiber membrane having a b-layer composed of micropores having Lb of less than 0.4 μm.
When it exceeds 4.0 μm, the mechanical strength of the hollow fiber membrane tends to decrease.

In the hollow fiber membrane used in the present invention, Db and Da
The ratio is preferably 1.3 ≦ Db / Da ≦ 4.0. A hollow fiber membrane having Db / Da of less than 1.3 is not preferable because it is difficult to form a membrane having a high fraction and a large water permeability. On the other hand, when Db / Da exceeds 4.0, the difference in the physical properties of the polyolefins adjacent to each other increases, and spinning or drawing stability tends to decrease.

In the composite microporous hollow fiber membrane used in the hollow fiber membrane module of the present invention, the maximum pore size of the membrane determined by the bubble point method is preferably in the range of 0.05 to 1.0 μm. A hollow fiber membrane having a maximum pore size of less than 0.05 μm tends to have a reduced water permeation rate, and a hollow fiber membrane having a maximum pore size of more than 1.0 μm has a reduced mechanical strength.

The polyolefins used as the material for forming the composite hollow fiber membrane are, for example, polyethylene, polypropylene, poly-3-methylbutene-1, poly-4-methylpentene-1, polyvinylidene fluoride alone or a mixture of these polymers. Can be used. The MI value (melt index value) of polyolefins measured by ASTM D-1238 is preferably in the range of 0.1 to 50, more preferably in the range of 0.3 to 15. Since the melt viscosity of a polyolefin having an MI value of 0.1 or higher is too high, it is difficult to shape it and it is difficult to form a desired microporous membrane. On the other hand, a polyolefin having an MI value of more than 50 has a too low melt viscosity, which makes it difficult to perform stable shaping. The preferred density of the polyolefin varies depending on the material used, but for example, in the case of polyethylene, it is preferably 0.95 g / cm ³ or more, and in the case of polypropylene, it is preferably 0.91 g / cm ³ or more.

In making this composite microporous hollow fiber membrane,
When the MI value MIa of the polyolefin for forming the a layer and the MI value MIb of the polyolefin for forming the b layer are selected such that MIa <MIb, the density ρa of the polyolefin for forming the a layer and the polyolefin ρb for forming the b layer are almost equal to each other. They can be manufactured evenly. Conversely, if each polyolefin is selected so that ρa <ρb, MIa,
This composite microporous hollow fiber membrane can be obtained even if the MIb is almost the same. It is preferable to select the respective polyolefins so as to satisfy both the relations of MIa <MIb and ρa <ρb, because this composite microporous hollow fiber membrane can be efficiently produced.

The average distance between the microfibril bundles of micropores referred to in the present invention is measured as follows. That is, a 6500-times transmission electron microscope photograph of a sample obtained by cutting an ultrathin section from the hollow fiber membrane in the fiber axis direction is taken into a CRT screen of an image processing device (Fig. 3 is a schematic diagram of this image). Indicates). From the top side of the captured image to the direction perpendicular to the fiber axis direction, to the bottom side,
Sequentially draw the first to nth scanning lines at a pitch of 0.052 μm. Excluding the portion where the average distance between the microfibril bundles indicated by α cannot be measured, each distance of the line segments passing through the hole portion in the first scanning line, for example, the sum of a ₁ to a ₅ Then, the sum of b ₁ to b ₆ is similarly calculated for the second scanning line, and the sum of n ₁ to n ₆ of the nth scanning line is sequentially calculated to obtain the sum (distance sum). Next, the number of fine holes (1
(5 for the second scan line, 6 for the second scan line, 6 for the nth scan line)
Then, the sum of distances / the sum of numbers is determined as the average intervals Da and Db.

In order to manufacture the composite microporous hollow fiber membrane used in the hollow fiber membrane module of the present invention, first, an intermediate composite microporous hollow fiber membrane precursor is prepared, and then a coating treatment with a hydrophilic copolymer is carried out. Just go. In order to make a precursor, it is necessary to select a polyolefin that satisfies the above conditions, perform melt composite spinning using a nozzle that has two or more annular discharge ports that are concentrically arranged, and obtain a multilayer body. It is achieved by performing heat treatment and stretching accordingly.

The means for imparting a difference in pore size to the layers adjacent to each other is achieved by compounding polyolefins having different densities and MI values. When polyethylene is used as the polyolefin, the density of the polyethylene used is 0.95 according to the measurement method specified in JIS K6760.
It is preferably 5 g / cm ³ or more, and more preferably 0.960 g / cm ³ or more. Density is 0.95
If it is less than 5 g / cm ³ , the formation of fine pores by stretching is not uniform, which is not preferable. The MI value is JISK.
It is preferably in the range of 0.05 to 20.0 g / 10 minutes as measured by 6760, more preferably 0.1 to 20.0 g / 10 minutes.
The range is 5.0 g / 10 minutes. MI value is 0.05 g /
If it is less than 10 minutes, the polymer viscosity is so high that melt spinning becomes difficult, which is not preferable. Furthermore, 20.0 g / 10
If it exceeds the limit, the crystal orientation of the multilayer body becomes insufficient, and a uniform fine pore structure cannot be obtained. The micropores formed by the melt spinning or drawing method are a composite microporous hollow in which two or more microporous layers having different pore sizes used in the present invention are laminated by arranging polyethylene whose density or MI value is adjusted. A thread film can be obtained.

The density or MI value of polyethylene described above can be freely adjusted by setting polymerization conditions, blending, etc., and can be selected as required.

The spinning temperature is not lower than the melting point of the polyolefin (preferably 10 to 100 ° C. higher than the melting point), and the discharged product is 0.1 to 3 m in an atmosphere of 10 to 40 ° C.
The multilayered body obtained by taking up at a take-up speed of / sec was heat-treated as it was or at a temperature not higher than the melting point of the polyolefin (preferably 5 to 50 ° C. lower than the melting point) to form a stacked lamella. After that, the multi-layer body is stretched and subjected to an opening treatment. As for stretching, it is preferable to carry out hot stretching after cold stretching. Cold stretching is a process of causing structural destruction of a multilayer body at a relatively low temperature to generate microcracks between stacked lamellas, and the cold stretching is performed in a range of 0 ° C. to 50 ° C. lower than the melting point of the polymer. It is preferable to carry out. When polyethylene is used as the polyolefin, the cold stretching temperature is in the range of 0 to 80 ° C, preferably 10 to 50 ° C. The cold stretching ratio is preferably 5 to 200%. When it is 5% or less, the generation of microcracks becomes insufficient, and it becomes difficult to obtain a target pore size. Also, 200
If it exceeds%, deformation of the stack lamella occurs and the porosity of each microporous layer decreases, which is not preferable.

The subsequent hot stretching is a process of expanding the microcracks generated in the multilayer body and forming microfibrils between the stacked lamellae to form a porous film having slit-like micropores. The hot stretching temperature is preferably as high as possible within the range not exceeding the melting point of the polyolefin. The heat draw ratio may be appropriately selected depending on the target pore size, but is 50 to 2000.
%, Preferably 100 to 1000%, in terms of process stability.

Further, in order to obtain the dimensional stability of the obtained composite porous membrane precursor, heat setting is performed under a fixed length or in a state where the membrane is slightly relaxed. In order to effectively perform heat setting, the heat setting temperature is preferably the stretching temperature or higher and the melting point temperature or lower.

As described above, by melt-composite spinning and stretch porosification, a large number of microfibrils in which the a-layer and the b-layer are oriented in the stretching axis direction of each layer and a knotted portion of a stacked lamella bonded at both ends of the microfibrils. A hollow fiber membrane-shaped precursor is obtained which is constituted by a slit-shaped laminated body constituted by, and the micropores penetrate from one surface of the membrane to the other surface.

Next, a step of imparting permanent hydrophilicity to the obtained multilayer composite film precursor is applied. The hydrophilic copolymer used here is preferably a copolymer containing 20 mol% or more of ethylene and 10 mol% or more of a hydrophilic monomer,
These copolymers may be any type of copolymers such as random copolymers, block copolymers and graft copolymers. The ethylene content in the copolymer is 2
If it is less than 0 mol%, the copolymer has a weak affinity for the precursor, and the precursor is dipped in the hydrophilic copolymer solution and the hydrophilic copolymer is added at a ratio of 3 to 30% by weight to 100% by weight of the precursor. It is not preferable because it becomes difficult to coat the polymer.

Examples of the hydrophilic monomer used when polymerizing the hydrophilic copolymer include vinyl alcohol and
(Meth) acrylic acid and its salts, hydroxyethyl (meth) acrylate, polyethylene glycol (meth) acrylic acid ester, vinylpyrrolidone, vinyl compounds such as acrylamide can be mentioned, and one or more of these hydrophilic monomers may be contained. However, vinyl alcohol may be mentioned as a particularly preferable monomer. Further, this 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, vinyl alcohol formal compound and butyral compound.

The coating amount of the hydrophilic copolymer on the composite porous membrane precursor is in the range of 3 to 30% by weight in terms of the precursor weight. A microporous membrane having a hydrophilic copolymer coating amount of less than 3% by weight has a poor affinity for water and insufficient water permeability to the microporous membrane, while the hydrophilic copolymer coating amount is insufficient. Three
If it exceeds 0% by weight, the pores of the microporous membrane are likely to be clogged with the copolymer, and the water permeability thereof is likely to decrease.

The solvent of 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 raised. These solvents can be used alone, but a mixture with water is more preferable because it has a strong solubility in the hydrophilic copolymer. Also, the ease of making a vapor-containing atmosphere of the solvent used in drying the microporous membrane coated with the hydrophilic copolymer, that is,
From the viewpoint of low vapor pressure of the solvent and low toxicity to the human body, it is particularly preferable to use an alcohol having a boiling point of less than 100 ° C., for example, a mixed solvent of water with methanol, ethanol, isopropyl alcohol and the like. The mixing ratio of the water-miscible organic solvent and water may be within a range that does not impair the permeability to the precursor and does not reduce the dissolution of the copolymer,
When ethanol is used as the organic solvent, the ethanol / water ratio is preferably in the range of 90/10 to 30/70 (vol%), although it varies depending on the type of the copolymer used.

The concentration of the hydrophilic copolymer solution is 0.1 to 1
It is about 0% by weight, preferably 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 if the concentration exceeds 10% by weight, the solution viscosity becomes too large. When treated, the micropores of the multi-layer composite hollow fiber membrane are blocked with the copolymer. As a method of immersing the precursor in the hydrophilic copolymer solution, the precursor solution may be dipped twice or more in the copolymer solution having the same concentration, or may be dipped twice or more in the solutions having different concentrations.

The higher the temperature of the hydrophilic copolymer solution to be subjected to the dipping treatment, the lower the viscosity thereof, and the better the permeability of leaching to the precursor, which is preferable, but from the viewpoint of safety, it should be below the boiling point of the solution. Is preferred.

The dipping treatment time varies depending on the film thickness, fine pore diameter and porosity of the precursor used, but it is preferably in the range of several seconds to several minutes.

The precursor is soaked in a hydrophilic polymer solution and before being subjected to a drying treatment, the organic solvent vapor is contained in an amount of 3 vol% or more, and the temperature is raised from room temperature to a temperature not higher than the boiling point of the solvent. It is necessary to stay for 30 seconds or more and perform the setting process.

The purpose of this treatment step is to prevent the clogging of the micropores by forming a coating film of the hydrophilic copolymer on the surface of the knots between the microfibrils and the stacked lamella forming the precursor. Another object is to bind the microfibrils and increase the diameter of the slit-shaped micropores to form elliptical micropores to increase the amount of water permeation and increase the affinity with the treated water.

In order to prevent the film formation of the hydrophilic copolymer on the precursor surface during the setting step, it is necessary to prevent the rapid drying on the precursor surface. For that purpose, the precursor surface of the copolymer solution is required. It is necessary to suppress the evaporation rate at the same time and to keep the precursor surface wet with the solvent. From this viewpoint, the atmosphere of the setting process should be 3 vol% or more of the water-miscible organic solvent vapor. Will be required.

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 close to the saturated vapor concentration of the solvent. Further, in order to slow down the evaporation of the solvent on the precursor surface in this step, it is better to lower the setting temperature, but if it is too low, the phenomenon that the solvent removal in the setting step does not proceed is not preferable. Therefore, the temperature of the atmosphere is preferably room temperature or higher and not higher than the boiling point of the water-miscible solvent.

The precursor after immersion is raised in the atmosphere from the immersion bath, but the angle of rise is preferably in the range of 45 ° to 90 °. By starting up, a part of the copolymer solution attached to the precursor is drained from the precursor by its own weight. The amount of the liquid removed depends on the speed at which the precursor rises from the bath surface, the viscosity of the immersion solution, the height at which the precursor rises from the bath surface, and the like. Wiping off of the solution on the surface of the precursor by means of guides, slits or the like may be used as an auxiliary means for enhancing the liquid removal effect in the setting step.

This setting time is at least 30
Seconds are required, during which the copolymer solution is concentrated as the solvent evaporates from the precursor and the membrane is homogenized by migration on the microfibrils and the surface of the stacked lamella. In particular, when the precursor is continuously treated with the hydrophilic copolymer solution, the setting time must be at least 30 seconds or longer. If the setting is less than 30 seconds, the concentration due to the evaporation of the solvent is insufficient, and drying is performed with the excess solution attached to the precursor, and the hydrophilic copolymer causes blockage of micropores. At the same time, the uniform adhesion of the copolymer within the membrane structure becomes insufficient, and it is difficult to obtain a microporous hollow fiber membrane having good water permeability and fractionation performance.

The evaporation amount of the solvent from the precursor when the setting time is 30 seconds is preferably about 15 to 30% of the hydrophilic copolymer solution used. As a method of controlling the evaporation amount of the solvent from the precursor in the setting step, there may be mentioned a setting atmosphere temperature, a method of blowing a gas such as air or an inert gas into the atmosphere.

The drying step is to cover the microfibrils forming the innumerable slit-shaped micropores obtained by the stretching method with a hydrophilic copolymer to converge and change the structure into elliptical micropores to enlarge the pore diameter. This is an important step for fixing. Further, since the hollow fiber membrane shrinks at the same time as the drying, the shrinkage is taken into consideration, and the yarn feeding speed before the drying step is made higher than the winding speed after the drying. By making the particles hydrophilic while sufficiently shrinking them, it is possible to increase the pore size and improve 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, slackening of the yarn occurs before drying and the process stability deteriorates. On the contrary, when the feeding speed is equal to the winding speed without considering the shrinkage of the hollow fiber membrane, the yarn is pulled against the shrinkage of the yarn in the drying process and processed under high tension, so As it is, the treatment is performed without expanding the hole diameter to an elliptical shape, and sufficient water permeability cannot be obtained. Therefore, it is necessary to adjust the feeding and winding speeds before and after drying, depending on the degree of shrinkage of the hollow fiber membrane to be treated.

The precursor which has been set may be dried by a known drying method such as vacuum drying or hot air drying. The drying temperature may be a temperature at which the composite microporous hollow fiber membrane is not deformed by heat. For example, in the case of a polyethylene composite microporous hollow fiber membrane, drying at a temperature of 120 ° C or lower is preferable, and drying at a temperature of 40 to 70 ° C is particularly preferable. The drying time varies depending on the pore size of the fine pores, the film thickness, the processing speed, etc., but it may be about 1 to 10 minutes as long as the hollow fiber membrane is sufficiently dried.

The amount of the hydrophilic copolymer attached to the composite microporous hollow fiber membrane is about 3 to 3 with respect to the weight of the composite microporous hollow fiber membrane precursor, which is a substrate, in view of filtration characteristics.
It is 30% by weight, preferably 3 to 15% by weight.

The final adhesion rate of the ethylene copolymer to the porous membrane can be adjusted by appropriately setting the concentration of the hydrophilizing solution, the conditions of the liquid removal treatment, and the like.

By the coating treatment with the hydrophilic copolymer, the microfibrils of the microporous hollow fiber membrane precursor are converged into a microfibril bundle, and the slit-like micropores are elliptical micropores.

The method for producing the hollow fiber membrane module of the present invention is not particularly limited, but the following method is preferable. First, a knitted fabric (which may be a woven fabric) in which a hollow fiber membrane as shown in FIG. 4 is used as a weft and a normal yarn is used as a warp 5 is prepared. As the type of the normal yarn used for the warp, all of those used for the warp of a normal knitted fabric or a woven fabric can be used, but the warp should not be hard so as not to damage the hollow fiber membrane during the production or handling of the knitted fabric. Is preferable, and it is preferable to use a multifilament, spun yarn or processed yarn. A method for producing a knitted fabric is disclosed in, for example, JP-A-62-5796.
No. 5 and Japanese Patent Laid-Open No. 1-266258. This sheet-shaped knitted fabric is cut into an appropriate length and used as one sheet or as a laminate of several sheets.
Here, the term “lamination of knitted fabric” also includes a fabric obtained by folding and knitting a knitted fabric to an appropriate length without cutting it. One side of the laminated body of the knitted fabric is housed in a structural material having an elongated rectangular opening, and the housing is cured and fixed with a liquid resin, and then the cured resin is cut so that the open end of the hollow fiber membrane appears. To do.

The warp yarns of the knitted fabric are generally present only in the vicinity of both ends of the hollow yarn which is a weft yarn, but may be present in the middle of the weft yarn at a certain fixed interval. In the case of a module having no warp in the middle, when the hollow fiber membrane is washed with water flow or bubbling, it may not be possible to maintain uniform dispersion of the hollow fiber. A module having warps in the middle is effective in maintaining uniform dispersion in such a case. Moreover, the hollow fiber membrane knitted fabric may be used or the warp yarn may be completely removed from the knitted fabric. That is, the warp may be contained in the fixing member, or may be cut off together with the discarding portion of the fixing member when forming the open end of the hollow fiber membrane.

In the above, the fixing member as shown in FIG. 1 is disposed on one side (one end) of the hollow fiber membrane knitted fabric, and the hollow fiber membrane is
The hollow fiber membrane module formed by bending the sheet into a letter shape has been described. Regarding the hollow fiber membrane module in which the fixing member and the structural material are respectively disposed in both opposing openings of the sheet-like hollow fiber membrane as shown in FIG. Can be configured in exactly the same way. This type of module has the characteristics of high treatment efficiency of polluted water and high treatment efficiency by air scrubbing. In these figures, 5 represents a water intake (permeate outlet).

Generally, in 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 this reason, it is necessary to clean the film surface by removing the deposit by water flow, air scrubbing, vibration, ultrasonic treatment, or the like. When the washing is not performed, the organic substances deposited on the surface of the membrane cause the clogging of the membrane, leading to a reduction in filtration life. As a specific cleaning method, a so-called cross-flow filtration in which a water flow is caused to flow in parallel to a sheet-like membrane surface, a method of generating a water flow with a pump or a motor in a membrane module dipping tank, a bubbling method using an upward flow of air, Examples thereof include a method of vibrating the module itself and a method of vibrating the water to be treated with ultrasonic waves. The hollow fiber membrane module of the present invention has a form suitable for performing these membrane surface washings in parallel with filtration. Therefore, when using the hollow fiber membrane module of the present invention, it is preferable to wash the membrane surface of the hollow fiber membrane in parallel with filtration. The cleaning of the film surface may be performed continuously or intermittently depending on the degree of progress of blockage of the film surface.

As a function recovery treatment method other than the membrane surface cleaning which is carried out in parallel with the filtration when the hollow fiber membrane module of the present invention is used, the backwashing method can be simply carried out as in the case of the ordinary module. Also, a method using ultrasonic waves or the like can be efficiently implemented due to the physical form of the module.

When the hollow fiber membrane module of the type shown in FIG. 5 is used, the hollow fiber membrane is arranged in the filtration tank so that the fiber axes of the hollow fiber membrane are oriented in the horizontal direction, and the air scrubbing device is arranged below the hollow fiber membrane. It is recommended to use a fiber membrane filter. In particular, when the hollow fiber membranes arranged in the horizontal direction are held in a substantially loose state, the cleaning of the membrane surface by air scrubbing can be performed very effectively.

When carrying out filtration using the hollow fiber membrane module of the present invention, a so-called pressure filtration method is also used in which the module is placed in a closed container and the water to be treated is pressurized to permeate the hollow fiber membrane. However, the hollow fiber membrane module is preferably immersed in an activated sludge tank, a sedimentation tank, or the like and used in a suction filtration method in which the inside of the hollow fiber membrane for collecting the treated water that has permeated the hollow fiber membrane is sucked.

The hollow fiber membrane module of the present invention is particularly suitable for filtration of highly polluted water.
River water filtration, industrial tap water filtration, solid-liquid separation of drainage,
Wastewater treatment (for example, treatment in a combined septic tank) can be mentioned.

[0063]

EXAMPLES The composite microporous hollow fiber membrane used in the hollow fiber membrane module of the present invention will be described in more detail with reference to production examples, and examples of hollow fiber membrane modules using these hollow fiber membranes will be shown. The various measurements and evaluations in the production examples were carried out by the following methods. 1. The ethanol concentration in the atmosphere was measured using a gas detector tube (Gastec detector tube, trade name, manufactured by Gastec Co., Ltd.). 2. The coating amount of the hydrophilic copolymer was calculated according to the following formula.

[0064]

(Equation 1) 3. Water permeability of the membrane to produce a mini-module having an effective membrane area 70~90cm ^2, differential pressure 1 kg / cm ² was filtered deionized water was measured water permeability of the time. 4. Fractions particle diameter, 0.1 wt% surfactant in membrane area of the hollow fiber membrane of about 50 cm ² module (polyethylene glycol -
(p-isooctylphenyl ether) aqueous solution was used to replace the air in the membrane, and then polystyrene latex particles with a predetermined particle size of 0.1% and a single dispersion particle size were filtered at a pressure of 0.7 kg / cm ² to obtain a filtrate. The concentration of the latex particles was measured with a Hitachi spectrophotometer (U-3400) at a wavelength of 320 nm to determine the particle size at a capture rate of 90%.

Production Example 1 67% by weight of high density polyethylene (HB530, manufactured by Mitsubishi Chemical Corporation) having a density of 0.967 g / cm ³ and an MI value of 0.3
And 33% by weight of high-density polyethylene (HB430, manufactured by Mitsubishi Chemical Corporation) having a density of 0.962 g / cm ³ and an MI value of 0.3 were melt-kneaded to obtain a density of 0.965 g / cm ³ , MI.
A blended polymer with a value of 0.3 was obtained.

Next, using a hollow fiber producing nozzle having two concentrically arranged circular tubular ejection ports, the blended polymer was fed from the inner ejection port and the density was 0.967 g / percent from the outer ejection port. High density polyethylene having a cm ³ and an MI value of 0.3 was discharged and melt-spun. At this time, the discharge temperature was 170 ° C., the inner layer side discharge amount was 0.56 g / min, the outer layer side discharge amount was 2.24 g / min, the inner layer / outer layer discharge amount ratio was 1/4, the discharge linear velocity was 47 cm / min, and the draft ratio was 75. It was discharged so as to become. Furthermore, the temperature of the yarn discharged from the nozzle is
The powder was wound at a winding speed of 35 m / min while uniformly applying a cooling wind of 1 ° C. and a wind speed of 1 m / sec to the periphery of the yarn to obtain an unstretched composite hollow fiber.

The obtained unstretched hollow fiber was heat-treated for 16 hours in the air heated to 125 ° C. with a constant length. Furthermore, this heat treated yarn is put between rollers kept at 30 ° C for 25
% Cold stretching, followed by hot stretching in a heating furnace at 119 ° C. so that the total stretching amount becomes 500%, and further 120
Heat setting was performed in a heating furnace at ℃ while keeping the length constant to obtain a composite microporous hollow fiber membrane precursor composed of two layers.

Next, an ethylene-vinyl alcohol copolymer (Soarnol DC320) having an ethylene content of 32 mol% was used.
3. Nippon Synthetic Chemical Industry Co., Ltd.) was dissolved in an ethanol / water = 60/40 vol% mixed solution at 70 ° C. in an amount of 1.0% by weight to prepare a hydrophilic copolymer agent solution. 10 parts of the above composite porous hollow fiber membrane precursor was added to this hydrophilic copolymer solution.
After soaking for 0 second, the precursor was pulled up, and a part of the hydrophilizing agent solution excessively attached to the surface was squeezed out by a guide. Continuing, ethanol vapor concentration 40 vol%, 6
After standing up in a 0 ° C. atmosphere at a rising angle of 90 ° and staying for 100 seconds to evenly attach the hydrophilic agent to the inner surfaces of the precursor micropores, 10% overfeed with hot air at 70 ° C. The solvent was dried. The ethylene-vinyl alcohol copolymer adhesion rate of the obtained hydrophilicized composite hollow fiber membrane was 10.5% by weight.

When the obtained composite microporous hollow fiber membrane was observed with a scanning electron microscope, the inner and outer surfaces and the inner surfaces of the micropores of the composite microporous hollow fiber membrane were thin films of ethylene-vinyl alcohol copolymer. The average distance (Da) between the microfibril bundles of the micropores in the inner layer (a layer) is 0.35.
The average distance (Db) between the microfibril bundles of the micropores of the outer layer (layer b) was 0.47 μm. At this time, D
b / Da = 1.34, the thickness of the inner layer that is the separation functional layer is 1
It was 2 μm. The characteristics of the obtained hollow fiber membrane are shown in Table 1.

Production Example 2 The polymer used in the inner layer and the polymer used in the outer layer in Production Example 1 were reversed, and the blended polymer was discharged from the outer outlet.
Except that the high-density polyethylene having a density of 0.967 and an MI value of 0.3 was discharged from the inner discharge port at an outer layer side discharge rate of 0.56 g / min and an outer layer side discharge rate of 2.24 g / min, and was melt-spun. A composite microporous hollow fiber membrane was produced under the same conditions as in Production Example 1. The obtained composite microporous hollow fiber membrane has an outer layer (a layer).
The average distance (Da) between the micropore bundles of the micropores in the inside is 0.34 μm, the average distance between the microfibril bundles of the micropores in the inner layer (layer b) is 0.48 μm, and Db / Da =
1.41, the film thickness of the outer layer which was the separation functional layer was 12 μm. The characteristics of the obtained hollow fiber membrane are shown in Table 1.

Comparative Production Example 1 The blend polymer used on the inner layer side in Production Example 1 was discharged at a discharge rate of 2.8 g / min and melt-spun, using a hollow fiber manufacturing nozzle having a single tubular discharge port. The discharge temperature at that time was 170 ° C., and the film was wound at a winding speed of 35 m / min. The obtained unstretched hollow fiber was heat-treated, stretched and hydrophilized under the same conditions as in Production Example 1 to obtain a uniform microporous membrane having the same fraction particle size as in Production Example 1. The membrane characteristics of the obtained composite microporous hollow fiber membrane are shown in Table 1.

[0072]

[Table 1] Examples 1 and 2 and Comparative Examples Various composite microporous hollow fiber membranes and microporous hollow fiber membranes prepared in Production Examples and Comparative Production Examples are arranged in a sheet shape, and opening portions at both ends thereof are epoxy resin potting materials. A hollow fiber membrane module of the same type as that shown in FIG. 5 was prepared in which the (fixing member) was connected to the structural material. MLSS does this about 5
As an aeration tank hollow fiber membrane filtering device for wastewater treatment of 000 ppm, it is immersed together with a water collection pipe, the water collection pipe is connected to a decompression pump, and the hollow fiber membrane is in a tightly stretched state in the structural material, and the hollow fiber membrane is horizontal. It was arranged as shown in FIG. Suction filtration was performed while air scrubbing was performed using this hollow fiber membrane filtration device. The suction filtration amount was measured at the initial stage and after 50 days, and the results are shown in Table 2.
It was shown to.

[0073]

[Table 2]

[0074]

INDUSTRIAL APPLICABILITY The hollow fiber membrane module of the present invention has a significantly increased water permeation rate and durability as compared with the case where a conventional hollow fiber membrane having the same fractionation performance is used in the same membrane area. It was excellent. In addition, even when used with a high water permeation rate in suction filtration of highly polluted water, the hollow fiber membranes are less likely to be fixed and integrated, and the characteristic of this form of the hollow fiber membrane module that the water permeation rate does not decrease over time is maintained did it.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a hollow fiber membrane module of the present invention.

FIG. 2 is a partially cutaway perspective view of a hollow fiber membrane module according to another embodiment of the present invention.

FIG. 3 is a schematic diagram for explaining a method of measuring an average distance between microfibril bundles of micropores.

FIG. 4 is a plan view showing a hollow fiber membrane knitted fabric.

FIG. 5 is a perspective view showing another embodiment of the hollow fiber membrane module of the present invention.

FIG. 6 is a perspective view showing an example of a method for supporting a hollow fiber membrane module in a filtration method using the sheet-shaped flat hollow fiber membrane module of the present invention.

[Explanation of symbols]

 1 Structural Material 2 Fixing Member 3 Hollow Fiber Membrane 4 Warp 5 Water Intake 6 Diffuser

Claims (4)

[Claims] 1. A hollow fiber membrane which is arranged in a sheet form and is spread, a fixing member for fixing the hollow fiber membrane while keeping the end portions of the hollow fiber membrane open, and a structural material for supporting and housing the fixing member. And a hollow fiber membrane module having a substantially rectangular elongated cross section perpendicular to the hollow fiber membrane of the fixing member, wherein the hollow fiber membrane has at least two microporous layers having different pore diameters. A hollow fiber membrane module comprising a composite microporous hollow fiber membrane made of polyolefin. 2. A hollow fiber membrane arranged in a sheet-like manner and arranged, a fixing member for fixing the hollow fiber membrane while keeping the end portions of the hollow fiber membrane open, and a structural material for supporting and housing the fixing member. A hollow fiber membrane module having a substantially rectangular elongated cross section perpendicular to the hollow fiber membrane of the fixing member, the hollow fiber membrane being at least a microporous layer a layer having a separation function. A composite microporous hollow fiber membrane made of polyolefin in which a microporous b layer having a reinforcing function is laminated on one surface, and the membrane structure has a plurality of microfibril bundles and micro layers in which each of the a layer and the b layer is oriented in the fiber axis direction. It is composed of a laminated body of elliptical micropores composed of knots of a stacked lamella that are bonded at both ends of the fibril bundle, and the micropores communicate from one surface of the hollow fiber membrane to the other surface. And the micropores of the hollow fiber membrane The microfibril bundles and the knotted portions of the stacked lamellae constituting the above are covered with 3 to 30% by weight of a hydrophilic copolymer with respect to 100% by weight of the composite microporous hollow fiber membrane precursor, and a layer a The average distance Da between the microfibril bundles of the micropores present therein,
It is characterized by using a composite microporous hollow fiber membrane having a ratio of the average distance Db between the microfibril bundles of the micropores present in layer b to 1.3 ≦ Db / Da ≦ 4.0. Hollow fiber membrane module. 3. The hollow fiber membrane module according to claim 1 or 2, wherein the composite microporous hollow fiber membranes are arranged in a sheet form and structural members are provided at both ends thereof. A hollow fiber membrane filtering device, characterized in that the shaft is arranged horizontally and an air scrubbing device is arranged below the hollow fiber membrane. 4. The hollow fiber membrane filtering device according to claim 3, wherein the hollow fiber membranes arranged in the horizontal direction are held in a substantially loose state.