JPH09234352A - Hollow fiber membrane module - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a hollow fiber membrane module having a large water permeability and excellent durability. SOLUTION: A polyolefin composite microporous structure having a specific structure, in which a microporous layer having a reinforcing function is laminated on a microporous layer having a separating function, and walls of micropores are covered with a hydrophilic copolymer. A hollow fiber membrane module in which a high-quality hollow fiber membrane is fixedly arranged in a tubular structure.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a hollow fiber membrane module.

[0002]

2. Description of the Related Art Hollow fiber membranes have an excellent filtration function, and thus have been used in water purifiers and the like for producing industrial water, drinking water, sterile water for medical use, etc. having higher purity than ever before. It was

As a structure of a filtration module having a hollow fiber membrane used in these water purifiers, the hollow fiber membrane is formed into a U-shape in a cylindrical structural material or the opening is formed in a thread shape in which one end is sealed. A typical example is a structure having a structure in which the ends are kept open and focused and fixed by a fixing member such as polyurethane.

Further, as a compact hollow fiber membrane module for treating a large amount of water, a filtrate collecting chamber is provided at one end of the module, and a filtrate for collecting the filtrate is combined with the filtrate collected at the other end. A hollow fiber membrane module having a structure in which a liquid delivery pipe is arranged is also known from JP-A-60-244306.

Various membranes have been developed as hollow fiber membranes used in hollow fiber membrane modules. As a typical example, Japanese Patent Laid-Open No. 57-66114 discloses a knotted portion of microfibrils oriented in the long axis direction of a hollow fiber membrane and a stacked lamella oriented in the thickness direction of the hollow fiber membrane. Slit-like micropores formed from and are laminated in the membrane wall of the hollow fiber membrane,
Also disclosed is a polyethylene microporous hollow fiber membrane which penetrates from one surface to the other surface of the membrane and forms a uniform microporous structure in the thickness direction.

This membrane is produced by melt-forming polyethylene and further stretching the shaped product. That is, after polyethylene is shaped under a specific spinning condition, an annealing treatment is performed to form lamella laminated crystals (stacked lamella) in the film wall of the shaped body, and then this shaped body is stretched to form a stack. By separating the lamellas and growing the fibrils connecting the lamella laminated crystals, the microporous film having the above specific structure is formed. This membrane is excellent in mechanical strength because it has the above-mentioned specific microporous structure, and since it does not use a solvent in the manufacturing process, there is little possibility that impurities will be mixed into purified water. have.

[0007]

In the hollow fiber membrane module, in order to increase the water permeation amount per module, the number of the hollow fiber membranes should be increased from the module structure side or the length of the hollow fiber membranes should be increased. It should be long. But,
When the density of the hollow fiber membranes is increased, the amount of water for treatment increases to some extent in proportion to the number of installations. However, when the density of installations becomes too high, the treatment water to the center of the bundle of hollow fiber membranes Since the passage resistance increases, the amount of water permeation does not increase in proportion to the number of installations. Further, the water permeation rate increases even if the length of the hollow fiber membrane is increased to increase the membrane area, but in this case, the hollow fiber is longer than a certain length because of the relationship between the inner diameter of the hollow fiber membrane and the performance of the membrane. The flow resistance inside the membrane was rate-determining, and the amount of water permeation could not be increased.

From the viewpoint of the hollow fiber membrane to be used, selecting one having a large pore diameter from the above-mentioned hollow fiber membranes is also a method of increasing the water permeation amount, but the fractionation performance becomes insufficient and the desired water quality is obtained. Purified water cannot be obtained. Moreover, although the amount of water permeation increases even when a hollow fiber membrane having a small thickness is used, in that case, the mechanical strength of the microporous membrane tends to be insufficient. for that reason,
It was necessary to use a large number of hollow fiber membrane modules to treat a large amount of water.

The inventors of the present invention have made extensive studies as to the development of a porous hollow fiber membrane suitable for use in a hollow fiber membrane module, which has a high fraction, a high flux, and a good mechanical strength. The filtration characteristics of the composite microporous hollow fiber membrane are obtained by combining a microporous membrane having micropores capable of separating particles of The present inventors have found that a composite porous hollow fiber membrane having sufficient mechanical strength and capable of increasing the amount of water permeation can be produced without impairing it, and completed the present invention.

An object of the present invention is to provide a hollow fiber membrane module having a large water permeability, a sufficient mechanical strength and an excellent fractionation property.

Another object of the present invention is to provide a hollow fiber membrane module which can efficiently utilize the entire hollow fiber membrane, is compact and has a large water permeability.

[0012]

That is, the present invention relates to a hollow fiber membrane module in which a large number of hollow fiber membranes are bundled and fixed by a fixing member in a tubular structural material while keeping the ends open. The hollow fiber membrane module is characterized in that, as the hollow fiber membrane, a polyolefin composite microporous hollow fiber membrane having at least two microporous layers having different pore sizes is used.

Further, the present invention provides a hollow fiber membrane module in which a large number of hollow fiber membranes are bundled and fixed by a fixing member while keeping the end of the hollow fiber membranes open in a tubular structural material. Is 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 surface of a microporous layer a having a separating function, and each of the a layer and the b layer has a fiber axis. Composed of a stack of elliptical micropores composed of a plurality of microfibril bundles oriented in the direction and a knotted part of a stack lamella bonded at both ends of the microfibril bundle, the micropores of a hollow fiber membrane The knots of the microfibril bundles and the stack lamellae, which communicate with each other from the outer surface toward the hollow part and constitute the micropores of the hollow fiber membrane, are 3 per 100% by weight of the composite microporous hollow fiber membrane precursor. ~ 30 layers % Of the hydrophilic copolymer, and the average distance Da between the micropore bundles of the micropores present in the a layer and the average distance between the microfibril bundles of the micropores present in the b layer. The ratio with Db is 1.3 ≦ Db /
A hollow fiber membrane module characterized by using a composite microporous hollow fiber membrane in a range of Da ≦ 4.0.

The hollow fiber membrane module of the present invention is the same as the above hollow fiber membrane module, having two structural materials, wherein the hollow fiber membranes are arranged substantially linearly between the structural materials, and the open end surface of the hollow fiber membrane is A filtrate collecting chamber is formed by the partition member on one of the two water collecting surfaces formed by the fixing member and the fixing member, and the filtrate collected in the filtrate collecting chamber is sent to the other water collecting surface. It can be configured as a module in which the filtrate delivery pipe of (1) is disposed between fixing members.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION FIG. 1 is a schematic sectional view showing an example of a hollow fiber membrane module of the present invention. As shown in this figure, the hollow fiber membrane module of the present invention basically comprises a structural material 1, a fixing member 2, and a composite microporous hollow fiber membrane 3. In addition to these, various accessory members may be attached.

The structural material 1 functions as a support member for supporting the entire module when the hollow fiber membrane module is installed in the water purifier device, and has a cylindrical shape, typically a cylindrical shape. It may have a rectangular cross section. Further, regarding the shape of the outer peripheral surface, various shapes can be adopted depending on the state in which the module is installed in a water purifier or the like.

A partition member for concentrating and fixing the composite microporous hollow fiber membrane 3 on the inner surface of the cylindrical structural material and partitioning the water to be treated and the purified water in a liquid-tight manner in order to function as a filtration membrane. The fixing member 2 functioning as is filled and fixed. 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 3 can be arranged in the hollow fiber membrane module of the present invention in various forms such as a U shape and a linear shape, but is fixed by a fixing member to form a water collecting surface. The open state is maintained at the end portions to be opened. The water collecting surface here means a surface on the fixing member where the open ends of the water to be treated permeate from the outside of the hollow fiber membrane to the hollow part and move in the hollow part to be discharged to the open end. Say.

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 filtration flow rate 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 a high filtration flow rate.

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 composed 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 large filtration flow rate, and a membrane having a Da of 0.5 μm or less has a 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 tends to decrease. . The thickness of the layer a is preferably 1/3 or less of the total thickness, and a thicker hollow fiber membrane makes it difficult to obtain a high filtration flow rate.

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 composed of micropores having Db of less than 0.2 μm tends to have a decreased water permeability, while
When Db exceeds 1 μm, the mechanical strength of the hollow fiber membrane provided with the b layer having fine pores 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. A hollow fiber membrane having a b-layer consisting of micropores having Lb of less than 0.4 μm tends to decrease the filtration rate of sake,
When b 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 a 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 permeation rate, and the anti-clogging property is likely to decrease. 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.

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 less than 0.1 is too high, it is difficult to shape the polyolefin 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 producing 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 the micropores in the present invention is measured as follows. That is, a 6 cm square portion of a 6500-times transmission electron micrograph of a sample obtained by cutting an ultrathin section from the hollow fiber membrane in the fiber axis direction is taken into the CRT screen of the image processing apparatus (Fig. 2 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 produce the composite microporous hollow fiber membrane used in the hollow fiber membrane module of the present invention, first, a composite microporous hollow fiber membrane precursor which is an intermediate is prepared and then coated with a hydrophilic copolymer. 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 necessary.

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 the knotted portion of the stacked lamella bonded at both ends of the microfibril 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.

The hydrophilic monomer used when polymerizing this hydrophilic copolymer is, for example, vinyl alcohol,
(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 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 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 vapor of an organic solvent 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 at least. 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 stack 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 formation of a film of the hydrophilic copolymer on the precursor surface during the setting step, it is necessary to prevent 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, and 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 deliquored liquid varies depending 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 performed by covering and converging the microfibrils forming the innumerable slit-shaped fine pores obtained by the stretching method with the hydrophilic copolymer, and changing the structure into elliptical fine pores 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 performing the hydrophilic treatment while sufficiently shrinking, it is possible to secure high-speed filtration performance as well as enlarge the pore size.

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 decreases. 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 precursor, which is the substrate, in terms 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.

FIG. 2 is a schematic sectional view showing another example of the hollow fiber membrane module of the present invention. In this example, the hollow fiber membranes are linearly arranged between the two structural materials, and water collecting surfaces are formed at both ends of the hollow fiber membranes. A partition member 4 is fixed to one of the structural members, and a filtrate collecting chamber 5 for collecting the filtrate is formed on the water collecting surface by the partition member. A filtrate delivery pipe 6 for delivering the filtrate collected in the filtrate collecting chamber and merging it with the filtrate collected on the other water collecting surface.
Are arranged so as to pass through substantially the respective central portions of the two fixing members 2.

In the hollow fiber membrane module having the structure shown in FIG. 3, since the filtrate delivery pipe 6 is installed, the outlet for the purified liquid is hollow only on the water collecting surface where the filtrate collecting chamber 5 is not provided. There is an advantage that the number of connection points between the fiber membrane module and the purified water recovery pipe can be reduced. Further, the entire membrane surface of the hollow fiber membrane arranged in the module is used more efficiently.

FIG. 4 shows an example in which three hollow fiber membrane modules of the type shown in FIG. 3 are connected in series.
As described above, the hollow fiber membrane module of the present invention can also be used as a module assembly having a length of several meters by connecting a plurality of modules in series. Here, the filtrate collecting chamber 7 of the first module (the one on the left side) and the water collecting surface 10 of the second module (the one on the center) are connected, and similarly the second module is used.
The filtrate collecting chamber 8 of the second module and the water collecting surface 11 of the third module (the one on the right side) are connected. In each of these modules, except for the partition members 12 to 14,
The modules are of the same shape, and the partition members 12 and 13 of the first and second modules also serve as connecting members for connecting the modules, respectively, whereas the partition members of the third module are Only the member 14 fulfills only the function of forming the original filtrate collecting chamber 9. Therefore, if each partition member is detachably configured, it is possible to configure a single module or a module connection body by changing only the shape of the partition member in a module having the same shape. is there.

In this example, the connecting member 15 for connecting the module connection body to the water purifier is attachable to and detachable from the structural material 1 of the first module in order to make each module symmetrically the same shape. It is connected to the. In this module connection body, the number of connection points between the module and the purified water recovery pipe can be further reduced, and the installation area of the module in the water purifier can be reduced.

[0061]

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.

[0062]

[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. Regarding the particle size captured by latex standard particles, the air in the membrane was replaced with a 0.1 wt% surfactant (polyethylene glycol-p-isooctylphenyl ether) aqueous solution in a hollow fiber membrane module having a membrane area of about 50 cm ² . After that, polystyrene latex particles having a monodisperse particle diameter of 0.1% with a predetermined particle diameter of 0.1% are filtered at a pressure of 0.7 kg / cm ² , and the concentration of latex particles in the filtrate is determined by Hitachi spectrophotometer (U
-3400) measured at a wavelength of 320 nm to obtain a capture rate of 9
The particle size at 0% was determined.

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 manufacturing nozzle having two concentric circular tubular discharge ports, the blended polymer was discharged from the inner discharge port and the density was 0.967 g / m from the outer discharge 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 composition was wound at a winding speed of 35 m / min while uniformly applying cooling air having a wind speed of 1 m / sec at a temperature of 35 ° C. to obtain an unstretched composite hollow fiber.

The unstretched hollow fiber obtained was heat-treated for 16 hours in 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 having an ethylene content of 32 mol% (Soarnol DC320
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 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 inner layer side discharge rate of 2.24 g / min, and 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 blended 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.

[0070]

[Table 1] Examples 1 and 2 and Comparative Example Various composite microporous hollow fiber membranes and microporous hollow fiber membranes prepared in Production Examples and Comparative Production Examples were converged into a U shape, and the ends thereof were potted with epoxy resin. Material (fixing member)
A hollow fiber membrane module having an effective membrane area of 80 cm ² was prepared in the same manner as shown in FIG. Using these hollow fiber membrane modules, the clad (amorphous iron 80%, α-Fe ₂ O ₃ 20%) concentration 10
A 0 ppb condensate simulated solution was added at 40 ° C and 0.5 kg / cm ²
The entire amount was filtered with the external pressure of 1, and a function recovery process was performed in which, every week, scrubbing in which bubbles were applied from below the module and pressure backwashing were simultaneously performed. In this test, the initial differential pressure and initial water permeability of the module, and the differential pressure and water permeability immediately after the function recovery treatment after 50 days were measured, and the results are shown in Table 2.

[0071]

[Table 2]

[0072]

INDUSTRIAL APPLICABILITY The hollow fiber membrane module of the present invention has a remarkably 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.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a hollow fiber membrane module of the present invention.

FIG. 2 is a schematic diagram for explaining a method of measuring an average distance between microfibril bundles of micropores.

FIG. 3 is a schematic cross-sectional view showing another embodiment of the hollow fiber membrane module of the present invention.

4 shows a hollow fiber membrane module of the type shown in FIG.
It is a schematic cross section which shows the module connection body connected in series.

[Explanation of symbols]

 1 Structural Material 2 Fixing Member 3 Hollow Fiber Membrane 4 Partition Member 5 Filtrate Collecting Chamber 6 Filtrate Liquid Delivery Pipe 7-9 Filtrate Collecting Chamber 10, 11 Water Collection Surface 12-14 Partitioning Member 15 Connection Member

Claims (3)

[Claims] 1. A hollow fiber membrane module in which a large number of hollow fiber membranes are bundled and fixed by a fixing member in a tubular structural material while keeping the end portions of the hollow fiber membranes open. A hollow fiber membrane module comprising a polyolefin composite microporous hollow fiber membrane having at least two different microporous layers. 2. A hollow fiber membrane module comprising a cylindrical structural material, wherein a large number of hollow fiber membranes are bundled and fixed by a fixing member while keeping the end of the hollow fiber membrane open. A microporous hollow fiber membrane made of polyolefin in which a microporous b layer having a reinforcing function is laminated on at least one surface of a microporous layer a layer for supporting a layer, and each layer 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 plurality of microfibril bundles and knots of a stacked lamella joined at both ends of the microfibril bundles, and the micropores are hollow from the outer surface of the hollow fiber membrane. The microfibril bundles and the nodules of the stacked lamellae that are in communication with each other and form the micropores of the hollow fiber membrane are 3 to 30 with respect to 100% by weight of the composite microporous hollow fiber membrane precursor.
It is covered with a hydrophilic copolymer of weight% and
The ratio of the average distance Da between the microfibril bundles of the micropores present in the layer and the average distance Db between the microfibril bundles of the micropores present in layer b is 1.3 ≦ Db / Da ≦ 4.0. A hollow fiber membrane module characterized by using a composite microporous hollow fiber membrane in the range of: 3. A hollow fiber membrane having two structural materials, wherein the hollow fiber membranes are arranged substantially linearly between the structural materials, and one of the two water collecting surfaces formed by the open end surface of the hollow fiber membrane and the fixing member. A filtrate collecting chamber is formed by a partition member on one of the water collecting surfaces, and a filtrate liquid supply pipe for supplying the filtrate collected in the filtrate collecting chamber to the other water collecting surface is arranged between the fixing members. The hollow fiber membrane module according to claim 1 or 2.