JP4200157B2 - Porous multilayer hollow fiber and filtration module provided with the porous multilayer hollow fiber - Google Patents

Description

  The present invention relates to a porous multi-layer hollow fiber and a filtration module including the porous multi-layer hollow fiber, and more specifically, a filtration device that performs solid-liquid separation processing in the field of environmental conservation such as sewage treatment, and in the field of medicine and food. It improves the filtration performance of a porous multilayer hollow fiber composed of a porous tube such as PTFE.

  Conventionally, a porous body made of PTFE (tetrafluoroethylene resin) is excellent in chemical resistance, heat resistance, weather resistance, nonflammability and the like, and has characteristics such as non-adhesiveness and low friction coefficient. . Further, since it has a porous structure, it is excellent in permeability, flexibility, flexibility, fine particle collection / filterability, and the like. For this reason, materials made of PTFE are used in a wide range of fields such as fine chemical filtration and wastewater treatment filters.

  Specifically, porous PTFE has a fine fibrous structure in which flexible fibers are connected in a three-dimensional network, and there are a large number of pores surrounded by a fibrous skeleton. Alternatively, it is molded into a sheet shape and used for various filters, deaeration membranes, waterproof membranes and the like. Moreover, it can also be used as a filtration module which performs a solid-liquid separation process by bundling many tubes etc. which consist of these porous PTFE, and making it modular.

  Various proposals have been made to obtain high filtration performance as a filtration material made of porous PTFE used for such a filtration module.

  For example, in Japanese Examined Patent Publication No. 4-75044, a PTFE continuous porous film is wound and coated on the outer peripheral surface of a PTFE continuous porous tube to obtain filtration performance with the film and to improve the strength of the tube. Furthermore, a tubular filter medium having a filter function capable of removing fine particles having a porous film of 0.1 μm or more has been proposed.

  Moreover, in Japanese Utility Model Publication No. 4-3607, a filtering material for filtering fluid from the inside to the outside of the tube, the filtering material is provided on the outer surface of the porous PTFE tube with porous PTFE having a pore diameter smaller than that of the tube. A tubular filter medium has been proposed which is wound in a spiral shape with respect to the axial direction, and further provided with a reinforcing layer made of a PTFE yarn mesh assembly on the outer surface of the wound film layer.

  Furthermore, the present applicant proposed in Japanese Patent No. 3221095 a porous multilayer hollow fiber in which a fluid-permeable sheet such as a porous PTFE sheet is integrally fixed to the inner surface of a porous PTFE tube by heat fusion. ing.

Japanese Patent Publication 4-75044

Reality No. 4-3607

Japanese Patent No. 3221095

  However, although Japanese Patent Publication No. 4-75044 has a filter function that can remove fine particles of 0.1 μm or more, the film is gradually clogged in the film by using for a long time, and the filtration performance is over time. There is a problem of decreasing with. That is, instead of removing fine particles on the surface of the porous film, the pore size is set to be somewhat large in order to obtain a certain flow rate, and when the fine particles pass through the porous film, The particles are trapped in the porous film, and the entire porous film can remove 0.1 μm fine particles. For this reason, although it is excellent in the filtration performance at the initial stage of use, clogging occurs with the passage of time, so that there is a problem that good filtration performance cannot be maintained for a long time. In particular, when a high turbidity solution is filtered, there is a problem that rapid clogging is likely to occur.

  In this way, this kind of porous material constitutes pores by entanglement of fibers, and since the shape and size of the pores are diverse, it is difficult to define the pore diameter of the pores. The performance of the porous material is regulated by the filtration accuracy based on the particle collection rate.

  Further, in Japanese Utility Model Publication No. 4-3607, filtration is performed from the inner surface toward the outer surface, and preliminary filtration is performed with a tube having a large pore to ensure the accuracy of filtration in the wound film layer. However, when a liquid with high turbidity is filtered, large particles cannot escape to the outer surface side, and the pores are blocked with particles entering the pores of the porous tube of the inner layer where preliminary filtration is performed. There is a problem of end up. As a result, there is a problem that clogging occurs and liquid permeability deteriorates. Further, although a netting made of yarn is provided in the outermost layer for reinforcing the strength, it does not exert an effect on filtration performance, and there is a problem that particles or the like enter the netting and the flow rate decreases.

  Thus, in the filtration membrane using a porous body, a decrease in flow rate due to clogging of solid particles after the passage of time becomes a problem together with the initial flow rate, and it is important to prevent this. That is, the filtration performance in a steady state after a certain amount of time has elapsed is important.

  Furthermore, in Patent No. 3221095, in the internal pressure type filtration that filters from the inner surface toward the outer surface, the filtration performance is improved by wrapping and integrating a sheet having a small pore diameter and high porosity on the inner surface, but the inner surface is hollowly closed. In the case of filtering a liquid with high turbidity, the filtration performance is not sufficiently improved, and there is still room for improvement.

  Further, in such filtration using a porous PTFE tube, in order to extend the filtration life, it is a common practice to remove particles adhering to the inner peripheral surface of the tube, the pores of the tube, and the like by back washing. However, when the particles are captured not by the surface of the filtration layer but by the entire filtration layer including the thickness of the tube etc., the particles that have entered the pores of the porous tube can be easily removed even by performing reverse cleaning. There is a problem that it is difficult to recover the filtration performance.

  In order to prevent particles from entering into the pores of a porous tube or the like, it is conceivable to reduce the pores on the surface. At that time, the porosity is also reduced to reduce the draw ratio. Therefore, there is a problem that the permeability of the fluid is deteriorated.

  Further, the porous PTFE tube simply has a PTFE sheet wound around a smooth PTFE tube, and therefore has insufficient durability against internal and external pressure, bending, and the like. Although braided and reinforced to improve durability, there is a problem that if reinforced, particles (SS component: suspended particles) accumulate there, and the flow rate decreases.

  The present invention has been made in view of the above problems, and even when a highly turbid solution is filtered, solid particles or the like are not clogged in the pores of the porous material, and the flow rate decreases with time. It is an object of the present invention to provide a porous multi-layer hollow fiber and a filtration module that can prevent filtration and can easily recover filtration performance by backwashing and maintain good filtration performance over a long period of time.

In order to solve the above problems, the present invention is a porous multilayer hollow fiber for external pressure filtration that performs solid-liquid separation from the outer peripheral surface side toward the inner peripheral surface side,
The support layer composed of a porous PTFE tube and a multi-layer comprising a filtration layer on the outer surface of the support layer, and the pores surrounded by the fibrous skeleton of the filtration layer are the pores of the support layer Smaller and
Particle size of trapped particles when the average maximum length (L) of the fibrous skeleton surrounding the pores on the outer surface of the filtration layer is 90% or higher when the particle trap rate is filtered under a pressure of 0.1 MPa If the value divided by the diameter (X) is the RFL value (Y), that is, (Y = L / X),
(L) is set so that (X) and (Y) exist in a region surrounded by connecting the following 10 points on the XY plane in order: Hollow fiber.
(X, Y) = (0.055,2) (1,1.5) (2,1) (5,0.5) (10,0.3) (10,4) (5,6) ( 2,10) (1,15) (0.055,25)

  As a result of diligent research, the present inventor has found that the problem of clogging of solid particles or the like into the pores of the porous body is each surrounded by a fibrous skeleton present in large numbers on the filtration surface which is the outermost surface of the filtration layer. It has been found that it depends greatly on the maximum length of the pores. In addition, in order to obtain good filtration performance in the long term, it has been found that the flow rate in a steady state after a certain period of time is particularly important together with the initial flow rate.

  That is, the stretched porous body such as PTFE has a fine fibrous structure in which flexible fibers are connected in a three-dimensional network, and there are a large number of pores surrounded by a fibrous skeleton. Since the pores surrounded by the fibrous skeleton are often elongated such as slits, it is not specified by the average pore diameter or porosity of the pores present in the filtration layer in order to reliably separate the solid liquid. It was found that the maximum length of the holes should be specified. In particular, the maximum length of pores on the outer peripheral surface of the filtration layer is important, and solid particles can be cut on the surface of the filtration layer. The maximum length of the hole is the maximum transverse length of the space part constituting the hole, that is, the maximum value of the distance connecting the two points on the outer periphery of the hole formed by the resin part and the fiber connected to the resin part. Point to.

  Specifically, conventionally, by providing a certain amount of thickness to the filtration layer, particles were trapped as a whole layer including the thickness of the filtration layer within the three-dimensional network pores. As time elapses, particles gradually accumulate in the pores, causing clogging, and the flow rate of the entire filtration layer decreases. However, in the present invention, in the porous multilayer hollow fiber for external pressure filtration, the outer layer is a filtration layer, and the average maximum length (L) of the fibrous skeleton surrounding the pores existing in large numbers on the outer surface of the filtration layer is determined. A small length that is set as described above and can be easily removed by backwashing, etc., in the steady state after the initial stage of the solid-liquid separation process, without separating the solid particles to be irreversibly trapped in the pores. Is set. That is, irreversible particle trapping in the pores in the filtration layer and the support layer is substantially achieved in the steady state after the flow rate reduction in the initial stage of the solid-liquid separation process performed at the optimum filtration pressure and backwash pressure. It is set so as not to occur. For this reason, most solid particles can be rebounded on the outer peripheral surface of the filtration layer, clogging does not occur, and liquid permeability can be maintained.

  That is, when the average maximum length (L) (μm) of the fibrous skeleton surrounding each pore on the outer surface of the filtration layer is subjected to pressure filtration at a pressure of 0.1 MPa, the particle capture rate is 90% or more. The value divided by the particle size (X) (μm) of the trapped particles is defined as the RFL value (Y), which defines the configuration of the filtration layer. As a result of accumulating earnest experiments, the present inventor, as shown in FIG. 1, is a region M in which the above (X) and (Y) are surrounded by sequentially connecting the following 10 points A to J on the XY plane. (L) is set so as to exist in (X, Y) = A (0.055, 2), B (1, 1.5), C (2, 1), D (5, 0.5), E (10, 0.3), F (10, 4), G (5, 6), H (2, 10), I (1, 15), J (0.055, 25). As a result, it has been found that in a steady state after the initial stage of the solid-liquid separation process, the solid particles to be separated are not trapped in the pores and the filtration performance can be improved.

  Even when a highly turbid solution is filtered, a large number of solid particles can be cut on the outer surface of the filtration layer, and the solid particles do not enter the pores in the filtration layer and the support layer. Without clogging, only the filtrate can permeate into the filtration layer and the support layer, and the flow rate with time can be prevented from decreasing. Therefore, there is little change in the flow rate between the initial state and the steady state, and good filtration performance can be stably maintained over a long period of time after reaching the steady state.

  In addition, even if some solid particles may adhere to the surface of the filtration layer, the solid particles do not enter the filtration layer and the support layer. The particles can be easily removed, and the filtration performance can be easily recovered.

  Each hole surrounded by the fibrous skeleton is generally slit-like and elongated in one direction such as the axial direction, but may be a mesh, rhombus, ellipse, circle, etc. It can be changed appropriately according to the law. The average maximum length refers to the average value of the maximum lengths of the pores on the outer peripheral surface of the filtration layer, and can be measured on an SEM image in which the outer peripheral surface of the filtration layer is enlarged.

  When filtering the high turbidity solution, the solid particles are filtered into the hollow of the porous multilayer hollow fiber when the solid pressure is cut on the inner peripheral surface of the inner layer. This is because it exists at a high concentration, causing hollow clogging and decreasing the flow rate in the hollow fiber.

  The filtration layer is composed of a porous sheet obtained by uniaxially or biaxially stretching the resin, and the porous sheet is wound in close contact with the outer peripheral surface of the porous expanded PTFE tube. preferable.

  The outer layer of the filtration layer has a sheet winding structure. The porous sheet is easy to perform both uniaxial stretching and biaxial stretching, and the shape and size of the surface pores can be easily adjusted. This is because stacking with is easy. By using an extruded tube as the inner support layer, the moldability is good, the thickness is certain, the strength is sufficient, and the porosity is easily increased. Both the support layer and the filtration layer need only be stretched in at least one axial direction, and can be stretched in the axial direction, circumferential direction, radial direction, or the like of the tube. One axis such as the axial direction, or two axes in the axial direction and the circumferential direction can be used. The draw ratio can be set as appropriate. In the case of an extruded tube, it is 50% to 700% in the axial direction, 5% to 100% in the circumferential direction, and 50% in the longitudinal direction in the case of a porous sheet. ˜1000%, and in the lateral direction 50% ˜2500%. In particular, when a porous sheet is used, it is easy to stretch in the transverse direction, so when wound in a tube shape, the strength in the circumferential direction can be improved. Durability against pressure load can be improved.

  Furthermore, since the support layer and the filtration layer made of a porous expanded PTFE tube are integrated and the respective pores communicate with each other in three dimensions, good permeability can be obtained. The porous sheet is wound so as to cover the entire outer peripheral surface of the porous expanded PTFE tube, and can be multi-layered or single-layered so that there is no leakage using one or a plurality of sheets. What is necessary is just to completely cover the outer peripheral surface of the tube made of porous expanded PTFE.

  The filtration layer is preferably formed from a resin selected from polyolefin resins such as PTFE, PE, and PP, polyimide, and polyvinylidene fluoride resin. It is possible to use the above resin that is easy to stretch, has excellent chemical resistance, and can be integrally formed with PTFE. In particular, from the viewpoint of moldability with porous expanded PTFE as a support layer, the filter layer is also preferably PTFE which is the same material as the support layer.

  It is preferable that the average maximum length of each pore present in large numbers on the outer peripheral surface of the filtration layer is smaller than the average maximum length of each pore surrounded by a fibrous skeleton present in the support layer. Specifically, the average length of the pores in the filtration layer is preferably 1% to 30% of the average length of the pores in the support layer, and is preferably as small as possible. Thereby, the permeability | transmittance from the outer peripheral surface side to an inner peripheral surface side can be improved.

  In the outer surface of the filtration layer, the area occupation ratio of the pores with respect to the total surface area of the outer surface is preferably 40% to 60% by, for example, image processing. Even if the maximum length of the holes is small, if the area occupation ratio of the holes is large to some extent, the flow rate is not reduced and the filtration performance can be improved efficiently.

  The porosity of the filtration layer is preferably 50% to 80%, and the porosity of the support layer is preferably 50% to 85%. Thereby, the permeability | transmittance from the outer peripheral surface side of a hollow fiber to an inner peripheral surface side can further be improved, maintaining a balance with intensity | strength. If the porosity is too small, the flow rate tends to decrease, and if the porosity is too large, the strength tends to decrease.

  The thickness of the filtration layer is preferably 5 μm to 100 μm. This is because if it is smaller than the above range, it is difficult to form a filtration layer. The thickness of the support layer is preferably 0.1 mm to 10 mm. As a result, good strength can be obtained in any of the axial direction, radial direction, and circumferential direction, and durability against internal / external pressure, bending, and the like can be improved. In addition, it is preferable that the internal diameter of a support layer is 0.3 mm-10 mm.

  In addition, the present invention provides a filtration module comprising the bundling body in which a plurality of porous multilayer hollow fibers according to the present invention are bundled, and used for external pressure filtration or immersion type external pressure suction filtration. is doing.

  Specifically, a plurality of porous multilayer hollow fibers are bundled into a bundle, and the gap between the porous multilayer hollow fibers is sealed with a sealing resin. Can be used as a filtration module in which the gap between at least one end of the focusing body and the outer cylinder is sealed with a sealing resin in the same manner as described above. Since the porous multilayer hollow fiber of the present invention is used, it can be suitably used for external pressure filtration or immersion type external pressure suction filtration. The condensing body accommodated in the outer cylinder is used for external pressure filtration, and the one without the outer cylinder and made only of the converging body is used for immersion type external pressure suction filtration.

  Specifically, it can be applied to filtration in general and is particularly effective for wastewater treatment with a high turbidity. For example, in water purification treatment, it can be used in combination with powdered activated carbon. A configuration in which very fine dissolved organic matter is adsorbed by powdered activated carbon and the powdered activated carbon after adsorbing the dissolved organic matter is filtered with a porous multilayer hollow fiber is preferable. In the sewage treatment, the bacterial cells are propagated in the tank, and the sewage is introduced into the tank, so that the bacterial cells decompose and clean the contaminated components in the sewage. Then, the structure which filters this microbial cell with a porous multilayer hollow fiber is suitable. In the oil / water separation, the removed oil is present as oil droplets in the washing waste water (cleaning liquid) of various machines and devices. Some of them are mixed with a surfactant and emulsified. These are preferably filtered through a porous multilayer hollow fiber and recovered and reused.

  Furthermore, the present invention provides the porous stretched PTFE tube and the porous material by applying a load at the same time as or after winding the porous stretched resin sheet after providing irregularities on the outer peripheral surface of the porous stretched PTFE tube. There is provided a method for producing a porous multilayer hollow fiber, wherein a porous stretched resin sheet is brought into close contact, and the porous stretched PTFE tube and the porous stretched resin sheet are sintered and integrated.

  In this way, by providing fine irregularities on the outer peripheral surface of the porous expanded PTFE tube, it is possible to prevent positional displacement between the porous expanded PTFE tube and the porous expanded resin sheet, and to load during or after winding the sheet. Therefore, since the sheet can be prevented from floating, the adhesion between the two can be improved. Further, the porous stretched PTFE tube and the porous stretched resin sheet may be fired or unfired. When each of them is not completely fired, it can be integrated more firmly. When both partially fired parts are sintered in a good contact state, a good contact state can be obtained. As described above, sufficient durability against internal / external pressure, bending, and the like can be obtained. In addition, since a reinforcing layer such as a net assembly is not used, solid particles are not clogged in the net assembly and the flow rate does not decrease with the passage of time.

  By sintering at a temperature equal to or higher than the melting point of the porous stretched PTFE tube and the porous stretched resin sheet, both can be fused and integrated more firmly.

  The fine irregularities on the outer peripheral surface of the porous expanded PTFE tube are preferably given by flame treatment. Thereby, it can obtain with a favorable uneven | corrugated state, without affecting the performance of a tube. In addition, adhesion may be improved by applying physical means such as laser irradiation, plasma irradiation, or application of fluororesin dispersion such as PFA or FEP, or chemical means. The fine irregularities are preferably applied to the entire outer peripheral surface of the porous expanded PTFE tube, but may be applied partially or intermittently, and preferably about 20 to 200 μm.

  As a method of applying a load simultaneously with winding of the porous stretched resin sheet or after winding, a method of passing the entire tube through a die after winding the sheet, the porous stretched PTFE tube and the porous stretched resin sheet may be misaligned. What is necessary is just to be able to apply an appropriate load uniformly so as not to break.

  As is clear from the above description, according to the present invention, in the porous multilayer hollow fiber for external pressure filtration, the outer layer is a filtration layer, and the maximum length of pores existing on the outer peripheral surface of the filtration layer is increased. As described above, in a steady state after the initial stage of the solid-liquid separation process, the solid particles to be separated are not irreversibly trapped in the pores and can be easily removed by backwashing or the like. It is set. That is, the maximum length of the pores is configured such that a large number of solid particles in the solution can be cut on the surface of the filtration layer, and the solid particles do not enter the pores in the filtration layer and the support layer. For this reason, most solid particles can be rebounded on the outer peripheral surface of the filtration layer, and solid particles can be prevented from entering the pores in the filtration layer and the support layer.

  Therefore, even if a high turbidity solution containing a solid content of various shapes and a wide distribution of the solid content, particularly a solution containing solid particles having a large average particle diameter, is filtered, the solid particles enter the pores. Without clogging and no clogging of the pores, so it is possible to prevent a decrease in flow rate over time,

  As a result, there is little change in the flow rate between the initial state and the steady state, and good filtration performance can be maintained for a long time even after reaching the steady state. Moreover, since the adhering solid particles can be easily removed, the filtration performance can be easily recovered by performing reverse cleaning, aeration, chemical cleaning, or the like. Therefore, it is particularly suitable for a filter that is used for several months or years.

  Furthermore, the support layer and the filtration layer are firmly fused and integrated, and can withstand mechanical loads due to backwashing, air diffusion and the like for a long time. Moreover, since it is formed of a material excellent in chemical resistance such as PTFE, it can be applied to strong acid, strong alkaline solution, and the like. Excellent heat resistance.

  In addition, according to the manufacturing method of the present invention, by providing irregularities on the outer peripheral surface of the porous expanded PTFE tube, it is possible to prevent displacement between the tube and the sheet wound around the outer periphery, and at the time of winding the sheet or winding Since a load is applied later, the sheet can be prevented from floating. Furthermore, since the both partially fired parts are sintered at a temperature equal to or higher than the melting point in a state in which the adhesiveness between them is improved, both can be firmly fused and integrated. Therefore, sufficient durability against internal / external pressure, bending, and the like can be obtained.

  Furthermore, since the filtration module of the present invention uses the porous multilayer hollow fiber of the present invention, high-precision filtration is possible, and it has excellent durability, and is used for external pressure filtration or immersion suction filtration. Can be suitably used. Therefore, in the field of medicine / fermentation / food such as sterilization / turbidation (enzyme / amino acid purification) of animal fermentation process, culture filtration of animal cells, etc. It can be used suitably.

  Specifically, solid-liquid separation in sewage treatment, industrial wastewater treatment (solid-liquid separation), industrial tap water filtration, pool water filtration, river water filtration, seawater filtration, water filtration in food industry, and product clarification filtration , Filtration of liquor, beer, wine, etc. (especially raw products), separation of bacterial cells from fermenters in pharmaceuticals and foods, filtration of water and dissolved dyes in the dyeing industry, pure water production process in RO membrane (desalination of seawater Can be suitably used for pretreatment filtration in a process using an ion exchange membrane, pretreatment filtration in a pure water production process using an ion exchange resin, and the like.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
2 to 6 show the porous multilayer hollow fiber 10 according to the first embodiment of the present invention.
The porous multilayer hollow fiber 10 is composed of a multilayer having a filtration layer 12 on an outer peripheral surface 11a of a support layer 11 made of a cylindrical porous expanded PTFE tube. Specifically, a filtration layer 12 formed by closely attaching a porous stretched PTFE sheet to an outer peripheral surface 11a of a support layer 11 made of an extruded porous stretched PTFE tube is integrally formed as an outermost layer. It has a two-layer structure in preparation. The porous multilayer hollow fiber 10 is used for external pressure filtration that performs solid-liquid separation from the outer peripheral surface 12 a side of the filtration layer 12 toward the inner peripheral surface 11 b side of the support layer 11.

  Since the filtration layer 12 and the support layer 11 are both porous bodies made of PTFE, the filtration layer 12 and the support layer 11 have a fine fibrous structure in which flexible fibers f are connected in a three-dimensional network, and are surrounded by a fibrous skeleton. There are holes 11A and 12A. The filtration layer 12 and the support layer 11 are integrated, and the pores 11A and 12A communicate with each other three-dimensionally. In the porous multilayer hollow fiber 10, the support layer 11 is formed from the outer peripheral surface 12a side of the filtration layer 12. The inner peripheral surface 11b side has a transparent structure.

  FIG. 3 is an enlarged photograph (100 times) of the axial cross section and inner peripheral surface of the porous multilayer hollow fiber 10. The thinnest outermost layer on the photograph is the cross section of the filtration layer 12, and the lower layer is the cross section of the support layer 11. The lower part of the photograph is the inner peripheral surface 11 b of the support layer 11. FIG. 4 is a further enlarged photograph (500 times) of the cross section in the axial direction of the porous multilayer hollow fiber 10. The upper part of the photograph shows the cross section of the filtration layer 12, and the lower part of the photograph shows the cross section of the support layer 11. As can be seen from the figure, it can be seen that the support layer 11 has a higher porosity, the size of the pores is larger, and the pores of the filtration layer 12 are much smaller.

  Each hole 11A, 12A surrounded by the fibrous skeleton has various shapes such as a slit shape and an elliptical shape, but the PTFE tube and the PTFE sheet constituting the support layer 11 and the filtration layer 12 are both stretched. Therefore, there are mainly slit-shaped ones that are larger in the length direction than in the width direction. Specifically, the PTFE tube is stretched uniaxially by 500% in the axial direction of the tube, and the PTFE sheet is stretched biaxially by 200% in the axial direction and 1000% in the lateral direction.

  In the present invention, the particle capture rate when the average maximum length (L) (μm) of the fibrous skeleton surrounding each hole 12A on the outer peripheral surface 12a of the filtration layer 12 is filtered under a pressure of 0.1 MPa is 90. The value obtained by dividing the particle size (X) (μm) of the trapped particles in the case of% or more is defined as the RFL value (Y), that is, (Y = L / X), thereby defining the configuration of the filtration layer 12.

As shown in FIG. 1, the above (X) and (Y) are present in a region M (hatched portion in the figure) surrounded by connecting the following 10 points A to J on the XY plane in order. (L) is set. (X, Y) = point A (0.055,2), point B (1,1.5), point C (2,1), point D (5,0.5), point E (10,0) .3), point F (10, 4), point G (5, 6), point H (2, 10), point I (1, 15), point J (0.055, 25).
Thereby, in the steady state after the initial stage of the solid-liquid separation process, the length is set so that the solid particles to be separated are not trapped in the air holes 12A. That is, the average maximum length (L) of the fibrous skeleton surrounding each hole 12A on the outer peripheral surface 12a of the filtration layer 12 is such that a large number of solid particles in the solution can be cut by the outer peripheral surface 12a of the filtration layer 12. Is set so as not to irreversibly enter the pores 12A and 11A in the filtration layer 12 and the support layer 11. The maximum length of the fibrous skeleton refers to the maximum transverse length of the space portion constituting the pores, that is, the maximum value of the distance connecting two points on the outer periphery of the pores constituted by the fibers connected to each other. .

  That is, the average maximum length (L) of the fibrous skeleton surrounding each hole 12A existing on the outer peripheral surface 12a of the filtration layer 12 is 2.5 μm or less, and the filtration layer 12 has a particle size (X) as trapped particles. Since the particle capture rate when 0.2 μm beads are filtered under pressure at a pressure of 0.1 MPa is 90%, the RFL value (Y) is 12.5. (X, Y) = (0.2, 12.5) exists in the region M.

  Further, in the outer peripheral surface 12a of the filtration layer 12, the area occupation ratio of the air holes 12A with respect to the entire peripheral area of the outer peripheral surface 12a is set to 50%. Furthermore, the average maximum length of the air holes 11A existing in the support layer 11 is set to about 20 μm to 50 μm. The area occupation ratio and the average maximum length of the fibrous skeleton are calculated by hand calculation from an electron micrograph or image processing software.

  The porosity of the filtration layer 12 is 60%, and the porosity of the support layer 11 is 80%. The thickness of the filtration layer 12 is 60 μm, the thickness of the support layer 11 is 0.5 mm, and the tube inner diameter is 1 mm.

  The porous multilayer hollow fiber 10 according to the first embodiment is a filtration membrane for removing dirt components in waste water, and has an average particle diameter of solid particles composed of dirt components collected and separated by solid-liquid separation. Is assumed to be about 0.1 μm to 5 μm.

  Thus, the porous multilayer hollow fiber 10 is a porous tube for pressure filtration, the outermost layer is the filtration layer 12, and the fibrous skeleton surrounding many pores 12A existing on the outer peripheral surface 12a of the filtration layer 12 Since the average maximum length (L) is set as described above, most of the solid particles S in the solution bounce off the outer peripheral surface 12a of the filtration layer 12, and the solid particles S are in the filtration layer 12 and the support layer 11. It is possible to prevent irreversible entry into the holes 12A and 11A. Therefore, without causing clogging, only the filtrate can be permeated into the filtration layer 12 and the support layer 11, the flow rate can be prevented from decreasing with time, and the flow rate between the initial state and the steady state can be prevented. There is little change, and good filtration performance can be sustained over a long period of time.

  In addition, after using for a certain period, in the porous multilayer hollow fiber 10, fluid is circulated from the inner peripheral surface 11 b side of the support layer 11 toward the outer peripheral surface 12 a side of the filtration layer 12, and back washing is performed. The solid particles S adhering to the outer peripheral surface 12a and the like of the filtration layer 12 can be easily removed, and the filtration performance can be easily recovered.

  In the above embodiment, the resin constituting the filtration layer is PTFE. However, a resin selected from polyolefin resins such as PE and PP, polyimide, and polyvinylidene fluoride resins may be used. Further, both the support layer and the filtration layer need only be stretched in at least one axial direction, and can be appropriately stretched in one axis, two axes, etc. in consideration of the stretching balance in the axial direction or circumferential direction of the tube. The filtration layer can also be an extruded tube.

FIG. 7 shows a filtration module 20 using a converging body in which a plurality of porous multilayer hollow fibers 10 are bundled.
The filtration module 20 is used for external pressure filtration, and includes a bundling body 21 by bundling a plurality of porous multilayer hollow fibers 10. The converging body 21 is accommodated in the outer cylinder 22, and the gap between the porous multilayer hollow fibers 10 is sealed with a sealing resin 23 at both ends 21 </ b> A and 21 </ b> B of the converging body 21. Further, the gaps between both ends 21A and 21B of the focusing body 21 and the outer cylinder 22 are similarly sealed with a sealing resin 23.

  Both ends of the filtration module 20 are opened, and the stock solution to be subjected to the solid-liquid separation process is supplied from the side surface of the outer cylinder 22 as shown by arrows in the figure, and the upper end 21A side of the focusing body 21 and the lower end of the focusing body 21 The filtrate from which the solid particles have been removed by flowing through the porous multilayer hollow fiber 10 while flowing toward the 21B side circulates on the inner peripheral side of the porous multilayer hollow fiber 10, and the upper end 21A side of the converging body 21 and Derived from the lower end 21B side of the focusing body 21. Moreover, the turbid liquid containing solid particles and the like is discharged from an outlet provided in the outer cylinder 22 as indicated by an arrow in the figure. In addition, it can also be set as the filtration module for immersion type external pressure suction filtration using the bundling body which bundled the porous multilayered hollow fiber 10 in multiple numbers.

  Thus, since the filtration module 20 includes a plurality of porous multilayer hollow fibers 10 of the present invention, very high-precision filtration is possible, particularly for external pressure filtration or immersion suction filtration. Preferably used.

Hereinafter, as shown in FIG. 8, the manufacturing method of the porous multilayer hollow fiber of this invention is explained in full detail.
First, a porous expanded PTFE tube 30 obtained by extrusion molding is prepared. The outer peripheral surface 30a of the porous stretched PTFE tube 30 is stretched at a predetermined stretch ratio without being completely fired.

  Next, under the conditions of propane gas 1.2 L / min, air 11 L / min, and speed 1.7 m / min over the entire outer peripheral surface 30 a of the porous expanded PTFE tube 30 that has been stretched with the outer peripheral surface 30 a unfired. Then, a flame treatment is performed, and fine irregularities of about 100 μm are evenly provided on the entire outer peripheral surface 30a.

  And the porous stretched resin sheet 31 is prepared. The porous stretched resin sheet 31 is stretched at a predetermined stretch ratio without being completely fired. The porous stretched resin sheet 31 has a width of 10 mm and a thickness of 30 μm, has an elongated rectangular shape, and is made of PTFE.

  Thereafter, the unfired porous stretched resin sheet 31 is wound around the outer peripheral surface 30a of the porous stretched PTFE tube 30 while being spirally overlapped. The porous stretched resin sheet 31 is wound so as to cover the entire outer peripheral surface 30a of the porous stretched PTFE tube 30 without omission.

  After winding the sheet, the laminate 32 of the porous stretched PTFE tube 30 and the porous stretched resin sheet 31 is passed through a die 35 having an inner diameter of φ1.8 mm, and the tube diameter is uniformly distributed over the entire circumferential surface of the laminate 32. A load of about 0.5 kgf is applied in the direction. The porous stretched PTFE tube 30 and the porous stretched resin sheet 31 are brought into close contact with each other by applying a load.

  In this state, the porous stretched PTFE tube 30 and the porous stretched resin sheet 31 are sintered at 350 ° C., which is higher than the melting point of the porous stretched resin sheet 31 (the melting point of PTFE is about 327 ° C.) for 20 minutes, and both are fused. Integrate.

  As described above, since fine irregularities are provided on the outer peripheral surface 30a of the porous expanded PTFE tube 30, there is no positional displacement between the porous expanded PTFE tube 30 and the porous expanded resin sheet 31, and a load is applied. Therefore, the porous stretched resin sheet 31 can be prevented from floating, and both can be integrated in a good contact state.

  The porous expanded PTFE tube is, for example, blended with PTFE fine powder with a liquid lubricant such as naphtha and formed into a tube shape by extrusion molding or the like, and without removing the liquid lubricant or at least after dry removal. Stretch in a uniaxial direction. When the stretched structure is sintered and fixed by heating to a sintering temperature of about 327 ° C. or higher in a heat shrinkage-preventing state, a porous expanded PTFE tube having an improved pore size of about 0.1 to 10 μm is obtained. Can do. The porous stretched PTFE tube and the porous stretched resin sheet may be fired.

  The porous expanded PTFE sheet can be obtained by various conventionally known methods as described below. (1) A method in which an unsintered molded body obtained by PTFE paste extrusion is stretched at a temperature below the melting point and then sintered. (2) A method in which a sintered PTFE compact is gradually cooled to enhance crystallization, and then uniaxially stretched to a predetermined stretch ratio. (3) Differential scanning of an unsintered molded body obtained by PTFE fine powder paste extrusion at a temperature not higher than the melting point of the powder of the fine powder and not lower than the melting point of the molded product (sintered body) obtained from the fine powder. After heat treatment so that the endothermic peak of the fine powder does not change on the crystal melting diagram in a calorimeter (DSC) and the specific gravity of the compact is 2.0 or more, the melting point of the powder is below the melting point. A method of stretching at a temperature. (4) A method in which a molded body obtained by paste extrusion of PTFE fine powder having a number average molecular weight of 1,000,000 or less is sintered and heat-treated to increase the crystallinity, and then stretched in at least one axial direction. Thus, it can be formed into a sheet by extruding with a paste extruder, rolling with a calender roll or the like, or extruding and rolling. Even when other resins are used, a porous expanded PTFE sheet can be obtained by the same method.

  The PTFE fine powder has a number average molecular weight of 500,000 or more, preferably 2 million to 20 million. In the paste extrusion method, 15 to 40 parts by weight of a liquid lubricant is preferably blended with 100 parts by weight of PTFE and extruded.

  Stretching can be performed by mechanically stretching a sheet-like or tube-like porous body by an ordinary method. For example, in the case of a sheet, when winding from one roll to another roll, the winding speed is made larger than the feed speed, or the two opposing sides of the sheet are gripped and stretched to widen the interval. Can be stretched. In the case of a tube, it is easy to stretch in the length direction (axial direction). In addition, it can be stretched by various stretching methods such as multistage stretching, sequential biaxial stretching, and simultaneous biaxial stretching. The stretching temperature is usually performed at a temperature not higher than the melting point of the sintered body (about 0 ° C. to 300 ° C.). In order to obtain a porous body having a relatively large pore diameter and a high porosity, stretching at low temperature is good, and in order to obtain a dense porous body having relatively small pore diameter, stretching at high temperature is good. . The stretched porous body may be used as it is, and when high dimensional stability is required, the stretched porous body is kept under tension by fixing the stretched ends and the like. Heat treatment may be performed at a temperature for about 1 to 30 minutes. Further, the dimensional stability can be further enhanced by holding and sintering for about several tens of seconds to several minutes in a heating furnace maintained at a temperature equal to or higher than the melting point of the fine powder, for example, about 350 ° C. to 550 ° C. By combining the stretching temperature, the crystallinity of PTFE, the stretching ratio, and the like as described above, the maximum length of the holes can be adjusted.

  In the above embodiment, two sheets are used and wound approximately half a turn, but the number of sheets may be one or two or more. In addition, the sheet may be wound approximately once or twice around the outer periphery of the tube, and the filtration layer can be formed by laminating single or multiple sheets.

  Moreover, if the porous stretched resin sheet is uniaxially stretched in the axial direction of the tube, it becomes easy to wind it around the outer peripheral surface of the tube. In addition, the shape of the porous stretched resin sheet can also be set according to the winding state, and may be wound spirally with respect to the axial direction of the tube.

  Moreover, in the said embodiment, although the load is applied after winding a sheet | seat, you may apply a load simultaneously with winding by applying tension | tensile_strength to a sheet | seat.

Hereinafter, the Example of the porous multilayer hollow fiber of this invention and a comparative example are explained in full detail.
(Example 1)
It was set as the porous multilayer hollow fiber of this invention.
A porous expanded PTFE tube having an inner diameter of 1 mm, an outer diameter of 2 mm, a porosity of 80%, and an average / maximum fiber length of 40 μm was used as a support layer. The collection performance of the support layer was 90% when beads having a particle size of 2 μm were used as capture particles at a filtration pressure of 0.1 MPa.
Further, a porous expanded PTFE sheet having a thickness of 30 μm, a width of 10 mm, a porosity of 60%, and an average / maximum fiber length (average maximum length (L) of the fibrous skeleton surrounding the pores) of 2.5 μm is used as a filtration layer. did. The collection performance of the filtration layer was 90% when beads having a filtration size of 0.1 MPa and a particle size (X) of 0.2 μm were used as capture particles. That is, the RFL value (Y) is 12.5, and (X, Y) = (0.2, 12.5) exists in the region M.

The porous expanded PTFE tube and the porous expanded PTFE sheet were set in a dedicated wrapping apparatus. A porous expanded PTFE tube was flowed at a line speed of 2 m / min, and the porous expanded PTFE sheet was continuously wrapped while tension control was performed thereon. Wrapping was done by half wrap.
Thereafter, the porous stretched PTFE tube and the porous stretched PTFE sheet were integrated by heat fusion by passing through a tunnel furnace set at an atmospheric temperature of 350 ° C. to obtain a porous multilayer hollow fiber. The porosity of the entire porous multilayer hollow fiber after molding was 68%. The average and maximum fiber length of the outer surface measured by SEM was 2.5 μm. The characteristics of the obtained porous multilayer hollow fiber are shown in Table 1 below.

(Example 2)
It was set as the porous multilayer hollow fiber of this invention.
A porous expanded PTFE tube having an inner diameter of 1 mm, an outer diameter of 2 mm, a porosity of 80%, and an average / maximum fiber length of 40 μm was used as a support layer. The collection performance of the support layer was 90% when beads having a particle size of 2 μm were used as capture particles at a filtration pressure of 0.1 MPa.
A porous expanded PTFE sheet having a thickness of 30 μm, a width of 10 mm, a porosity of 75%, and an average / maximum fiber length (average maximum length (L) of the fibrous skeleton surrounding the pores) of 15 μm was used as a filtration layer. The collection performance of the filtration layer was 90% when beads with a particle size (X) of 5 μm were used as capture particles at a filtration pressure of 0.1 MPa. That is, the RFL value (Y) is 3, and (X, Y) = (5, 3) exists in the region M.

(Comparative Example 1)
The porous expanded PTFE tube is a uniform membrane having an inner diameter of 1 mm, an outer diameter of 2 mm, and an average / maximum fiber length (average maximum length of the fibrous skeleton surrounding the pores (L)) of 15 μm. It was 90% when beads having a particle size (X) of 0.2 μm were used as trapping particles at 1 MPa. That is, the RFL value (Y) was 75, and (X, Y) = (0.2, 75) was outside the range of the region M.

(Comparative Example 2)
The porous expanded PTFE tube is collected as a uniform membrane with an inner diameter of 1 mm, an outer diameter of 2 mm, a porosity of 80%, and an average / maximum fiber length (average maximum length (L) of the fibrous skeleton surrounding the pores) of 60 μm. The performance was 90% when beads with a particle size (X) of 5 μm were used as trapping particles at a filtration pressure of 0.1 MPa. That is, the RFL value (Y) was 12, and (X, Y) = (5, 12) was out of the range of the region M.

  FIG. 9 shows the relationship between the value of (X, Y) and the region M in each example and comparative example. It can be seen that Examples 1 and 2 exist in the region M.

  As shown in FIG. 10, a filtration module 43 was obtained by bundling 20 porous multi-layer hollow fibers 40 of Table 1 to form a converging body 41 and converging and integrating one end side 41a with an epoxy resin 42 to obtain a filtration module 43. . The other end side 41 b was sealed with a heat seal 44.

  A filtration experiment was conducted on the filtration module 43 using each porous multilayer hollow fiber 40 by the filtration experiment apparatus 50 shown in FIG. In the filtration experiment apparatus 50, a filtration module 43 is immersed in a filtration tank 52 in which a stock solution 51 to be processed is supplied and stored, and the filtrate filtered by the filtration module 43 is sucked by a suction pump 53 and is filtered. It is configured to be discharged from. A vacuum gauge 54 is installed between the suction pump 53 and the filtration module 43. In addition, an air diffuser 56 connected to the blower 55 is immersed in the filtration tank 52 so that the air can be diffused into the stock solution 51 of the filtration tank 52.

(Experiment 1) (Example 1, Comparative Example 1)
The filtration conditions were such that the set filtration flow rate was 0.3 m / day. The water temperature was 20 ° C. to 28 ° C. (the graph of FIG. 12 described later is a 25 ° C. correction value). Further, back washing was performed at a frequency of once / 30 minutes, a pressure of 100 kPa, and a condition of 30 seconds. The air diffusion conditions were an air amount of 20 L / min and 1 time / 30 minutes.

(Stock solution)
Filtration processing was performed in a state where powdered activated carbon for adsorbing dissolved organic matter in raw water was added to the raw water before purification treatment collected from the water purification facility so as to be 10 mg / L. The particle size of the powdered activated carbon was 5 to 10 μm. Further, an aqueous sodium hypochlorite solution (30 mg / L) was intermittently added to prevent the bacterial cells from growing.

  FIG. 12 shows the relationship between the elapsed days of the filtration experiment using the filtration module of Example 1 and Comparative Example 1 and the transmembrane pressure difference (suction pressure). A constant flow rate operation was performed and the pressure was adjusted so that the flow rate (0.3 m / day) was constant. When clogging occurs, the value of the transmembrane pressure difference increases. As properties of the treated water, the raw water had a turbidity of 15, and the filtered water subjected to the filtration treatment had a turbidity of 0.

  As shown in Table 1 and FIG. 12, in Example 1, the average maximum length (L) of the fibrous skeleton surrounding the pores on the outer peripheral surface of the filtration layer is 2.5 μm, and the flow rate is reduced at the initial stage. Since the length is set so that irreversible particle trapping in the pores in the filtration layer does not substantially occur in the finished steady state, until the first 8 to 10 days from the start of filtration. Although the value of the transmembrane pressure difference is somewhat large, the transmembrane pressure difference is almost constant at 20 kPa after that, and stable and good filtration performance is realized after a certain period of time. Was confirmed.

  On the other hand, in Comparative Example 1, since the average maximum length (L) of the fibrous skeleton surrounding the pores was as large as 15 μm, the solid particles entered the pores, and as the number of days elapsed, the value of the transmembrane pressure difference The clogging gradually became worse over time, and the filtration performance was greatly deteriorated. Further, Example 1 also had a larger bubble point value than Comparative Example 1.

(Experiment 2) (Example 2, Comparative Example 2)
The filtration conditions were such that the set filtration flow rate was 0.6 m / day. The water temperature was 25 ° C. to 27 ° C. (the graph of FIG. 13 described later is a 25 ° C. correction value). Further, back washing was performed at a frequency of once / 30 minutes, a pressure of 100 kPa, and a condition of 30 seconds. The air diffusion condition was always an air amount of 20 L / min.

(Stock solution)
Activated sludge for wastewater treatment (MLSS 10,000 mg / L) was used.

  FIG. 13 shows the relationship between the elapsed days of the filtration experiment using the filtration modules of Example 2 and Comparative Example 2 and the transmembrane pressure difference (suction pressure). A constant flow rate operation was performed and the pressure was adjusted so that the flow rate (0.6 m / day) was constant. When clogging occurs, the value of the transmembrane pressure difference increases. As properties of the treated water, the raw water had a turbidity of 20, and the filtered water subjected to the filtration treatment had a turbidity of 0.

  As shown in Table 1 and FIG. 13, in Example 1, the average maximum length (L) of the fibrous skeleton surrounding the pores on the outer peripheral surface of the filtration layer was 15 μm, and the flow rate reduction at the initial stage was finished. Since the length is set so that irreversible particle trapping in the pores in the filtration layer does not substantially occur in the steady state, the first 8 days to about 10 days after the filtration is started, Although the value of the transmembrane pressure is large, the transmembrane pressure is almost constant at 30 kPa after that, confirming that stable filtration performance has been achieved after a certain time. did it.

  On the other hand, in Comparative Example 2, since the average maximum length (L) of the fibrous skeleton surrounding the pores was as large as 40 μm, the solid particles entered the pores, and as the number of days elapsed, the value of the transmembrane pressure difference The clogging gradually became worse over time, and the filtration performance was greatly deteriorated. Further, Example 1 also had a larger bubble point value than Comparative Example 1.

Particle size of trapped particles when the average maximum length (L) of the fibrous skeleton surrounding the pores on the outer surface of the filtration layer is pressure filtered at a pressure of 0.1 MPa and the particle trapping rate is 90% or more It is a figure which shows the relationship between said (X), said (Y), and the area | region M when the value divided by (X) is made into RFL value (Y). (A) (B) is a schematic block diagram of a porous multilayer hollow fiber. It is an expanded photograph (100 times) of the cross section of an axial direction of a porous multilayer hollow fiber, and an internal peripheral surface. It is an enlarged photograph (500 times) of the cross section of the axial direction of a porous multilayer hollow fiber. It is a figure which shows the solid particle by which solid-liquid separation processing is carried out, and the maximum length of the void | hole of the outer peripheral surface of a filtration layer. It is a figure which shows the filtration condition by the porous multilayer hollow fiber of this invention. It is a figure which shows the structure of a filtration module. (A) (B) (C) (D) is explanatory drawing of the manufacturing method of the porous multilayer hollow fiber of this invention. It is a figure which shows the relationship between (X, Y) and the area | region M of an Example and a comparative example. It is the schematic of the filtration module used by the Example and the comparative example. It is a schematic block diagram of a filtration experiment apparatus. It is a graph which shows the result of the filtration experiment of Example 1 and Comparative Example 1, and shows the relationship between elapsed days and transmembrane pressure difference. It is a graph which shows the result of the filtration experiment of Example 2 and Comparative Example 2, and shows the relationship between elapsed days and transmembrane pressure difference.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Porous multilayer hollow fiber 11 Support layer 11A, 12A Hole 12 Filtration layer 12a Outer peripheral surface 20 Filtration module L Average maximum length S of the fibrous skeleton surrounding the hole S Solid particle f Fiber

Claims (10)

A porous multilayer hollow fiber that performs a solid-liquid separation process from the outer peripheral surface side toward the inner peripheral surface side,
A support layer comprising a porous expanded PTFE tube, and a filtration layer comprising a resin porous sheet selected from polyolefin resin, polyimide, and polyvinylidene fluoride resin, and the outer surface of the support layer tube And a plurality of layers in which the support layer and the pores of the filtration layer communicate with each other three-dimensionally.
The size of each pore on the outer surface of the filtration layer is set to a size such that the trapping rate of particles to be filtered under pressure is 90% or more, and the average length of the pores in the filtration layer is set to A porous multilayer hollow fiber characterized in that the average length of pores is 1% to 30%.   The porous multilayer hollow fiber according to claim 1, wherein an area occupation ratio of pores with respect to a total surface area of the outer surface of the filtration layer is 40 to 60%.   The porosity of the whole filtration layer and the whole support layer is in the range of 50 to 85%, respectively, and the porosity of the support layer is larger than the porosity of the filtration layer. Porous multi-layer hollow fiber.   The porous multilayer hollow fiber according to any one of claims 1 to 3, wherein the filtration layer has a thickness of 5 µm to 100 µm, and the support layer has a thickness of 0.1 mm to 10 mm.   The porous multi-layer hollow fiber according to any one of claims 1 to 4, wherein the filtration layer is made of a stretched porous sheet made of PTFE made of the same material as the support layer.   The porous multilayer hollow fiber according to any one of claims 1 to 5, wherein particles having an average particle diameter of 0.1 µm to 5 µm are captured on an outer surface of the filtration layer.   A bundling body in which a plurality of porous multilayer hollow fibers according to any one of claims 1 to 6 are bundled, and is used for external pressure filtration or immersion type external pressure suction filtration. Filtration module.   The filtration module according to claim 7, wherein the plurality of porous multilayer hollow fibers are connected by sealing gaps at both ends with sealing resin.   The filtration module according to claim 7 or 8, which is used for waste water treatment.   The filtration module according to claim 9, which is used for sewage treatment.