JP4941865B2 - Tube for support of porous multilayer hollow fiber membrane and porous multilayer hollow fiber membrane using the same - Google Patents

Description

  The present invention relates to a tube for a support of a porous multi-layer hollow fiber membrane and a porous multi-layer hollow fiber membrane using the same. It improves the permeation flow rate of the porous multilayer hollow fiber membrane used and improves the filtration performance.

  A porous body made of polytetrafluoroethylene (hereinafter referred to as “PTFE”) is excellent in chemical resistance, heat resistance, weather resistance, nonflammability, etc., and has properties such as non-adhesiveness and low friction coefficient. is doing. In addition, it has a porous structure and has a fine fibrous skeleton in which flexible fibers are connected in a three-dimensional network, and has a large number of pores surrounded by the fibrous skeleton, and has permeability, flexibility, Excellent flexibility and fine particle collection / filterability. Therefore, the porous body made of PTFE has a tube shape or a sheet shape, and is used in a wide range of fields such as filtration of fine chemicals and filters for wastewater treatment.

Among them, a large number of porous expanded PTFE tubes are converged and modularized to be used as a filtration module for performing a solid-liquid separation process.
As a filter medium made of porous PTFE used for such a filtration module or the like, the applicant of the present invention disclosed in JP-A-2006-7224 (Patent Document 1) a support layer made of a porous expanded PTFE tube, PTFE, A filtration layer comprising a porous sheet made of a resin selected from polyolefin resin, polyimide, and polyvinylidene fluoride resin is provided, and the filtration layer sheet is wound around and integrated with the outer surface of the tube of the support layer. And a porous multilayer hollow fiber membrane in which the pores of the support layer and the filtration layer are communicated with each other three-dimensionally.

  In the porous multilayer hollow fiber membrane of Patent Document 1, the solid particles are contained in the filtration layer and the pores in the support layer by making the pores surrounded by the fibrous skeleton of the filtration layer smaller than the pores in the support layer. Prevent entry. 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. Since no clogging occurs and the air holes are not blocked, it is possible to effectively prevent a decrease in permeation flow rate with time.

JP 2006-7224 A

  As described above, the porous multilayer hollow fiber membrane of Patent Document 1 has high particle trapping properties and has excellent filtration performance. However, since the porous multi-layer hollow fiber membrane is usually formed from two layers, a dense filtration layer and a porous tube forming a support layer, the transmembrane pressure difference tends to increase, and the permeate flow rate can be secured. There are limits. In particular, this tendency is remarkable when used in a high-concentration / high-turbidity solution such as a membrane separation activated sludge method. Therefore, a porous multilayer hollow fiber membrane having a smaller transmembrane pressure difference and an increased permeation flow rate is desired.

  The present invention has been made in view of the above problems, and in a porous multilayer hollow fiber membrane having a filtration layer made of a porous sheet on the outer surface, while maintaining high particle trapping properties, it is more permeable than before. The challenge is to increase the flow rate.

In order to solve the above-mentioned problems, the present invention provides, as a first invention, a tube for a support of a porous multilayer hollow fiber membrane comprising a filtration layer made of a porous sheet on the outer surface, and its porosity Is 75% to 90%, IPA bubble point is 2 to 12 kPa, inner diameter is 0.3 to 10 mm, wall thickness is 0.1 to 10 mm, and differential pressure is 20 kPa. There is provided a support tube characterized by comprising a porous stretched polytetrafluoroethylene tube having a / average film thickness) of 40 to 100 ml / min / cm ² / mm.

  The IPA permeability coefficient is the difference between the inside of the tube membrane and pure isopropyl alcohol prepared as a specimen having an effective length of 100 mm so that the pressure is uniformly applied, set on a pressure holder and loaded with internal pressure. The pressure is 20 kPa, IPA flowing out from the tube surface within a pressurization time of 1 minute is collected, the flow rate is measured, and the effective membrane area is calculated based on the inner diameter on the supply side of the tube. (Flux), and further divided by the film thickness. This is because the material is almost uniform and the thickness depends on the flux. It shows that it is excellent in the permeability, so that this figure is high.

  The present invention is characterized in that the holes on the outer peripheral surface of the support tube are made larger and the volume ratio of the holes is increased. Thereby, the processed liquid which has passed through the filtration layer of the porous multilayer hollow fiber membrane can be quickly flowed from the outer peripheral surface of the support tube into the tube. Therefore, when the filtration layer is formed from the same porous sheet, the permeate flow rate can be improved as compared with the case where the conventional support tube is used while maintaining high particle capturing ability. Further, the support tube is made of an expanded PTFE tube, has a certain thickness, and has excellent physical properties derived from PTFE, so that the support function of the porous sheet on the outer surface can be sufficiently achieved.

The reason why the ranges of the porosity, IPA bubble point and IPA permeability coefficient of the support tube are good is that the permeability of the hollow fiber membrane can be enhanced while maintaining a balance with the strength.
That is, when the porosity of the support tube exceeds 90%, it tends to collapse against strength, particularly external pressure. On the other hand, when it falls below 75%, the flow rate decreases. The porosity is more preferably 78% to 85%.
The porosity is measured by the method described in ASTM-D-792. It shows that it is excellent in the permeability, so that this figure is high.

In addition, when the IPA bubble point of the support tube exceeds 12 kPa, the pore diameter is too small, and the flow rate tends to decrease. When the IPA bubble point is below 2 kPa, the pore diameter is too large and the strength is insufficient.
The IPA bubble point is measured according to the method described in ASTM-F-316-80. It shows that a hole diameter is so small that this figure is large. As a result of the porosity and the IPA bubble point ensuring the above range, the above IPA permeability coefficient can be expressed.

  The support tube has an inner diameter of 0.3 mm to 10 mm and a wall thickness of 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.

The support tube preferably has a matrix tensile strength (MTS) of 50 to 110 MPa. The matrix tensile strength is the tensile strength of the porous body converted into the strength of the matrix itself, that is, the material itself excluding the pores, in order to compare the tensile strength of samples with different porosities. The tensile strength (tensile strength / cross-sectional area) divided by the porosity, which is shown below.
Matrix tensile strength = tensile strength / (1−porosity (%) / 100)
The reason why the upper limit value of the matrix tensile strength is 110 MPa is that the matrix tensile strength of the conventional support tube used in Patent Document 1 and the like exceeds 110 MPa, so that it can be distinguished from the material. That is, this low matrix strength reflects the physical properties of the PTFE stretched porous material, such that the material having a large pore size and a high porosity as in the present invention exhibits a low level of molecular orientation. Yes. The matrix tensile strength in the above range is sufficient for PTFE support tubes because PTFE itself has excellent strength characteristics.

  As a second invention, there is provided a method for producing a support tube according to the first invention. The production method comprises blending a liquid lubricant with polytetrafluoroethylene fine powder having a number average molecular weight (Mn) of 1,000,000 to 3,000,000, and forming a tube shape by extrusion molding under a condition where the reduction ratio is 500 or more and 2,000 or less. The tube is stretched by 20 to 400% in the axial direction of the tube, and further stretched by 60 to 560% in the axial direction so that the total stretching ratio is 400 to 700%, and is sintered.

In the manufacturing method, a tube for a support is produced from PTFE fine powder having a lower molecular weight than conventional ones as a PTFE raw material and from an appropriate pulling rate in extrusion. Therefore, PTFE molecules are less likely to be oriented in the extrusion direction (take-off direction) than conventional high molecular weight PTFE, and fiber formation due to stretching is suppressed. As a result, an expanded PTFE tube having larger pores than in the past can be obtained. And the permeate flow rate of the porous multilayer hollow fiber membrane can be increased.
In addition, after stretching at the draw ratio, the fibers are also aggregated and integrated by stretching, thereby forming a strong fibrous skeleton while increasing the pore diameter on the surface of the support tube. Can do.

As described above, the method for producing a support tube of the second invention comprises the following first to fourth steps.
In the first step, a paste is prepared by blending a PTFE fine powder with a liquid lubricant.
As the PTFE fine powder, those having a number average molecular weight (Mn) in the range of 1,000,000 to 3,000,000 are used. This is because when the number average molecular weight exceeds 3 million, the hole diameter of the obtained support tube becomes small and the flow rate tends to decrease, and when PTFE fine powder less than 1 million is used, the extrusion orientation is weak and the film is stably stretched. This is because it is difficult.
The number average molecular weight of the PTFE fine powder is preferably 1.5 million to 2.5 million. Moreover, it is preferable that the specific gravity prescribed | regulated to JISK6891 of this PTFE fine powder exceeds 2.180 and is 2.250 or less. The specific gravity is measured according to JIS-K6891.

  As the liquid lubricant, various lubricants conventionally used in paste extrusion methods can be used. For example, petroleum solvents such as solvent naphtha and white oil, hydrocarbon oils such as undecane, aromatic hydrocarbons such as toluol and xylol, alcohols, ketones, esters, silicone oil, fluorochlorocarbon oil, etc. Examples thereof include a solution in which a polymer such as polyisobutylene or polyisoprene is dissolved in the above solvent, a mixture of two or more thereof, water or an aqueous solution containing a surfactant, and the like. Since a single component can be uniformly mixed rather than a mixture, it is preferable.

Using the paste obtained in the second step, a tubular molded body is produced by a paste extrusion method. The paste extrusion method may be performed by a conventionally known method. Usually, a liquid lubricant is mixed in an amount of 10 to 40 parts by mass, preferably 16 to 25 parts by mass with respect to 100 parts by mass of PTFE fine powder, and extrusion molding is performed. However, in the present invention, 18 to 22 parts are particularly desirable. If it is 18 parts or less, mixing with an auxiliary agent may be insufficient due to the particle size of the low molecular weight resin. On the other hand, if it is 22 parts or more, the molecular orientation of the entire thickness is lowered due to the low molecular weight, and it may not be possible to stretch at high magnification.
Molding by paste extrusion is performed at a sintering temperature of PTFE, that is, 327 ° C. or lower, usually around room temperature. Prior to paste extrusion, preforming is usually performed. In the pre-molding, the mixture is compression-molded at a pressure of, for example, about 2 to 5 MPa to form a rod or tube-shaped block.
The molded body obtained by the preliminary molding is extruded by a paste extruder to produce a tube-shaped molded body that can be stretched.

In this extrusion step, the reduction ratio is preferably 500 to 2000. The reduction ratio is a condition for fine powder extrusion, and is a factor that controls the balance between the flowability of the fine powder and the shear load, and indicates the ratio of the cross-sectional area between the extrusion cylinder and the extrudate when extrusion is possible. Conventionally, in the case of this type of resin, an appropriate value is said to be 50 to 500.
However, in the present invention, attention was paid to changing the idea and manufacturing at this high reduction ratio. As a result of intensive studies, it has been found that this reduction ratio is particularly necessary for imparting molecular orientation to the outer surface in order to withstand a high draw ratio. The above range is set as the optimum production range according to the raw material resin having a low molecular weight. If it is 500 or less, it is possible to produce at a low stretching ratio, but it is not possible to provide an outer surface molecular orientation that can withstand stretching at high magnification. On the other hand, if it is 2000 or more, the fluidity of the resin during extrusion deteriorates and uniform extrusion cannot be performed.

The liquid lubricant is removed from the molded body obtained by the extrusion molding. The liquid lubricant may be removed before sintering and may be removed after stretching, but is preferably removed before stretching.
Removal of the liquid lubricant is performed by heating, extraction or dissolution, and is preferably performed by heating. In general, the heating temperature for heating is preferably 200 to 300 ° C. Further, when a liquid lubricant having a relatively high boiling point such as silicone oil or fluorocarbon is used, it is preferably removed by extraction.

  In the third step, the tube molded body is formed into a stretched tube stretched at a magnification of 20% to 400%, preferably 50% to 150%, particularly preferably 80% to 120% in the axial direction of the tube. The stretching temperature is preferably 100 to 400 ° C, more preferably 200 to 300 ° C.

In the fourth step, the stretched tube is stretched again and sintered at the same time. Re-stretching can be performed in two steps to increase stretching uniformity, increase the total stretching ratio, and increase the pore size by roughening the fiber cleavage. wear. The draw ratio is desirably 60% to 560%. The sintering process performed at this time is set to a sintering temperature of 327 ° C. or higher, which is a transition point of PTFE, and a residence time sufficient to obtain a heat capacity necessary for melting in an oven having an atmospheric temperature of 350 to 700 ° C. For example, the heating is performed for about 1 to 20 minutes, or more in some cases.
By performing the sintering, particularly the radial tensile strength of the stretched tube is rapidly increased, and strength can be imparted. This is because the fibers of the stretched molded body that has been made into a fiber are melted together to increase the fiber diameter and make it uniform and increase the strength, while preventing thermal shrinkage and solvent shrinkage. Thus, by extending | stretching at the time of sintering, the fibrous frame | skeleton made high-strength can be formed, expanding the void | hole formed by previous extending | stretching further.

  Furthermore, in the third invention, a method for producing the support tube of the present invention is provided. The production method comprises blending a liquid lubricant with polytetrafluoroethylene fine powder having a number average molecular weight (Mn) of 6 million to 10 million in a weight ratio of 24 parts to 30 parts with respect to at least 100 parts of resin, and extrusion. After the tube exit speed is 15 m / min or more and 30 m / min or less to form a tube by extrusion, the tube is stretched by 50 to 400% in the axial direction of the tube, and further fired while stretching by 60 to 430% in the axial direction. It is characterized by tying.

  In the third invention, the PTFE fine powder used for the production of the support tube has a molecular weight of 6 to 10 million, and the auxiliary compounding ratio is at least 24 parts and the outlet speed of the extruded tube is 15 m / min or more and 30 m / min or less. The reduction ratio at this time is preferably 500 to 2000 as in the second invention. As described above, in the case of a general high molecular weight resin, it is said to be 50 to 500, but in the present invention, the amount of the auxiliary agent is set on the larger side and the extrusion speed is increased, Similarly, the molecular orientation was suppressed, and as a result, the same quality as in the second invention was obtained. The reduction ratio is also manufactured in this range for the same reason as in the second invention. The PTFE fine powder used in the present invention preferably has a specific gravity specified in JIS K 6891 of more than 2.155 and not more than 2.170.

  The support tube of the first invention is preferably obtained from the production method of the second or third invention, but is not limited thereto.

  According to a fourth aspect of the present invention, there is provided a support layer comprising the support tube and a filtration layer comprising a porous sheet integrated on an outer peripheral surface of the support layer, wherein the support layer and the filtration layer are empty. Providing a porous multilayer hollow fiber membrane characterized in that the pores are three-dimensionally communicated with each other and are for external pressure filtration that performs solid-liquid separation from the outer peripheral surface side toward the inner peripheral surface side. Yes.

The support layer made of the support tube and the filtration layer made of a porous sheet are integrated, and the pores of each other are three-dimensionally communicated with each other. It can withstand long-term mechanical loads due to the above.
One or more porous sheets may be used as long as they completely cover the outer peripheral surface of the support tube so as not to leak. For example, it is wound tightly so as to cover the entire outer peripheral surface of the support tube, and can be made into a multilayer or a single layer. If the outer filtration layer has a sheet winding structure, the porous sheet can be easily uniaxially or biaxially stretched, and the shape and size of the surface pores can be easily adjusted. Is easy to stack.
In addition, if the solid particle is cut on the inner peripheral surface of the support tube for the internal pressure filtration when the high pressure solution is filtered, the external multi-layer hollow fiber membrane is hollow. This is because the solid particles are present at a high concentration in the inside, causing a hollow blockage, and the flow rate in the hollow fiber membrane is likely to decrease. Further, when a liquid containing a large amount of fine particles enters the film from the inner surface, the fine particles enter the stitch structure of the support tube having a rough structure, and the flow rate is likely to decrease due to clogging in a short time. On the other hand, in the case of external pressure filtration, the outermost layer having a short fiber pattern and a small pore diameter becomes the filtration surface on the outer surface, so that the fine particles are captured on the surface and can be continuously filtered while suppressing clogging.

  The porous sheet forming the filtration layer is a stretched porous sheet obtained by uniaxially or biaxially stretching the resin composition, and is uniaxial in the axial direction, or biaxial in the axial direction and the circumferential direction. Can do. The draw ratio can be set as appropriate, but can be 50% to 1000% in the longitudinal direction and 50% to 2500% in the lateral direction. In particular, since the porous sheet can be easily stretched in the lateral direction, the strength in the circumferential direction can be improved when wound in a tube shape, and the membrane can be shaken by air diffusing, etc. Durability can be improved.

  The porous sheet is preferably formed of a resin selected from polyolefin resins such as PTFE, PE, and PP, polyimide, and PVDF. This is because the drawing process is easy, the chemical resistance is excellent, and the integral molding with PTFE is possible. In particular, the porous sheet of the filtration layer is also preferably PTFE because of its good moldability with a porous expanded PTFE tube that is a support tube.

Particularly, porous expanded PTFE having an average pore diameter of 0.01 to 1 μm, a thickness of 5 to 100 μm, an IPA bubble point of 50 to 1000 kPa, and an IPA flux at a differential pressure of 100 kPa of 0.05 to 50 ml / min / cm ² . It is preferable to use a sheet.
The average pore diameter is measured by a pore diameter distribution measuring device (a porous material automatic pore diameter distribution measuring system), for example, a palm porometer (model number CFP-1200A) manufactured by PMI.

As the porous multilayer hollow fiber membrane, the characteristics of the PTFE porous sheet to be used can be freely selected, and thereby, those having a wide range of characteristics can be produced. An excellent PTFE porous composite tube can be obtained by using the above-described support tube having a large pore on the surface and a large pore area. In particular, when the porous multilayer hollow fiber membrane used for the support of the present invention is applied to sewage treatment, it is desirable that the support tube satisfies the scope of the present invention and the IPA bubble point is 100 kPa or more. . In particular, as a suitable membrane separation activated sludge treatment known as a combination technique of biological treatment and membrane, an IPA bubble point is present when the MLSS of the activated sludge is in the range of 5,000 to 20,000 mg / l. The IPA permeation flux at 100 kPa to 300 kPa and the differential pressure of 100 kPa is particularly preferably 14 ml / min / cm ² or more at an IPA bubble point of 100 kPa and 1 ml / min / cm ² or more at an IPA bubble point of 300 kPa. For wastewater containing fine particles of 0.1 to 5 microns in general wastewater, the IPA permeation flux at an IPA bubble point of 150 kPa is 8 ml / min at an IPA bubble point of 150 kPa to 300 kPa and a differential pressure of 100 kPa. / Ml ² or more and 1 ml / min / cm ^{2 at} 300 kPa is particularly desirable. Within these ranges, clogging can be kept small and a high throughput can be obtained.

  The IPA bubble point range set above is preferable because the pore size is large when the lower limit value is not reached, and there is a possibility that particle trapping properties may be lost or internal trapping of fine particles may occur. This is because the flow rate cannot be obtained. On the other hand, the preferred range of IPA flux was defined based on the fact that it depends on the pore size.

The size of each hole present in large numbers on the outer peripheral surface of the filtration layer should be smaller than the size of each hole surrounded by the fibrous skeleton present in many in the support tube serving as the support layer. preferable. The size of each pore is defined by the average maximum length of each pore. Specifically, the average length of the pores in the filtration layer is the average length of the pores in the support tube. It is preferable to set it as 1%-30%.
According to this configuration, the pores on the surface of the filtration layer can be made as small as possible to enhance particle trapping properties, while the pores in the support layer can be enlarged to increase the permeability from the outer peripheral surface side to the inner peripheral surface side. .

  The thickness of the filtration layer in the porous multilayer hollow fiber membrane 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, and if it is larger than the above range, it is difficult to expect an effect on the improvement of the filtration performance. On the other hand, the thickness of the support layer is preferably 0.1 mm to 10 mm.

  Furthermore, this invention provides the manufacturing method of the said porous multilayer hollow fiber membrane as 5th invention. In the manufacturing method, after providing irregularities on the outer peripheral surface of the support tube, a porous sheet made of a porous stretched PTFE sheet is wound, and a load is applied simultaneously with or after the winding. And the porous sheet are closely attached, and the support tube and the porous sheet are sintered and integrated.

  In this way, by providing fine irregularities on the outer peripheral surface of the support tube, it is possible to prevent positional displacement between the support tube and the porous sheet, and a load is applied during or after the sheet winding. Therefore, the sheet can be prevented from floating and the adhesion between them can be improved. In addition, as the porous sheet composed of the support tube and the porous expanded PTFE sheet, a completely sintered sheet may be used, or a partially unsintered or unsintered sheet may be used. When each of them is not completely fired, it can be integrated more firmly. Sintering both partially unsintered in good adhesion can provide good adhesion. Thereby, sufficient durability with respect to internal / external pressure, bending, etc. can be obtained. When both the support body tube and the porous sheet are sintered, if they are sintered at a temperature equal to or higher than their melting points, they can be fused and integrated more firmly.

  It is preferable that fine irregularities on the outer peripheral surface of the support tube are provided by flame treatment. Thereby, a favorable uneven state can be obtained without affecting the performance of the 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. Although it is preferable that the fine unevenness is provided on the entire outer peripheral surface of the support tube, it may be provided partially or intermittently, and the height of the unevenness is preferably about 20 to 200 μm.

  As a method of applying a load simultaneously with the winding of the porous sheet or after the winding, there is a method of passing the entire tube through a die after winding the sheet, so that the porous expanded PTFE tube and the porous sheet are not shifted or damaged. It suffices if an appropriate load can be uniformly applied.

  Also, as a sixth invention, there is provided a filtration module characterized by using a converging body in which a plurality of the porous multilayer hollow fiber membranes are bundled and used for external pressure filtration or immersion type external pressure suction filtration. is doing.

  Specifically, a plurality of porous multilayer hollow fiber membranes are bundled to form a converging body, and the gap between the porous multilayer hollow fiber membranes is sealed with a sealing resin. It can be used as a filtration module that is housed in a cylinder and 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 membrane 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.

  The porous multilayer hollow fiber membrane provided with the support tube of the present invention and the filtration module using the same can be generally applied to filtration. In particular, since a high permeate flow rate is obtained, it is effective for the treatment of high turbidity waste water. 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 through a porous multilayer hollow fiber membrane is preferable. In the sewage treatment, as described above, it is suitably used for the membrane separation activated sludge method.

  As is clear from the above explanation, the support tube of the first invention has a pore diameter of 2 to 12 kPa at the IPA bubble point as an alternative characteristic and a porosity of 75 to 90%. The porous multi-layer hollow fiber membrane provided with this can quickly flow the treated liquid that has passed through the filtration layer into the tube, and can improve the permeation flow rate while maintaining high particle trapping properties. it can.

  In the method for manufacturing the support tube of the second and third inventions, since a PTFE fine powder having a lower molecular weight than that of the conventional one is used, an expanded PTFE tube having a large pore diameter can be obtained, and the porous multilayer hollow The permeation flow rate of the thread membrane can be increased. Alternatively, even with a standard molecular weight, the expanded PTFE tube having the same large pore diameter can be obtained by increasing the number of auxiliary components and extruding at a high speed. Moreover, since it extends | stretches also at the time of sintering after extending | stretching by the said draw ratio, a strong fibrous frame | skeleton can be formed, raising the hole area occupation rate of the tube for support bodies.

  Furthermore, the porous multilayer hollow fiber membrane having the support layer made of the support tube of the fourth invention is integrated with the support tube and the porous sheet forming the filtration layer. It can withstand long-term mechanical loads caused by air diffusion. 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.

  Moreover, according to the method for producing a porous multilayer hollow fiber membrane of the fifth invention, the support tube and the stretched PTFE sheet wound around the outer periphery are provided by providing irregularities on the outer periphery of the support tube. And a load is applied during or after the sheet is wound, so that the sheet can be prevented from being lifted. 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, the filtration module using the porous multilayer hollow fiber membrane of the sixth invention is capable of high-precision filtration while obtaining a higher permeate flow rate than the conventional product, particularly in actual waste water, and is durable. And can be suitably used for external pressure filtration or immersion suction filtration.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In FIG. 1, the tube 10 for support bodies of embodiment is shown.
The support tube 10 is used as the support layer 11 of the porous multilayer hollow fiber membrane 1 shown in FIG. 2, and has a two-layer structure including a filtration layer 12 made of a porous sheet on the outer surface 11a. Used as a hollow fiber membrane.

The support tube 10 is made of a porous expanded PTFE tube. As shown in the enlarged schematic view of FIG. 1 (B), the outer peripheral surface 10a is a porous structure having a large number of substantially slit-shaped holes P in a fibrous skeleton formed by connecting flexible fibers F by knots C. It has a quality structure.
Although not shown in the figure, the inside of the support tube 10 also forms a fine fibrous structure in which flexible fibers F are connected in a three-dimensional network, and the pores P are hollow portions of the support tube 10. 10c.

The tube 10 for support bodies is 2-12 kPa by making the hole diameter of the outer peripheral surface 10a used as a contact surface with the said porous sheet into an IPA bubble point. Moreover, the porosity which shows the volume ratio of a void | hole is 75 to 90%. As a result, the IPA permeability coefficient at a differential pressure of 20 kPa is 40 to 100 ml / min / cm ² / mm.
The matrix tensile strength is 50 to 110 MPa. Each measurement of the matrix tensile strength, the IPA bubble point, the IPA permeability coefficient, the porosity and the like is performed by the method described in the examples. The measuring method is described in the examples.

The support tube 10 serving as the outer peripheral surface 11a serving as the contact surface of the porous sheet can quickly flow the treated liquid that has passed through the filtration layer 12 into the tube, and the porous multilayer hollow fiber membrane 1 The permeation flow rate can be improved as compared with the prior art.
Furthermore, the porosity, IPA bubble point, and IPA permeability coefficient in the above ranges are achieved at the same time, and the permeability inside the tube is also superior to that of the conventional support tube.

Hereafter, the manufacturing method of the tube 10 for support bodies of the said 2nd invention is explained in full detail.
In the first step, a liquid lubricant is blended at a ratio of 16 to 23 parts by mass with respect to 100 parts by mass of PTFE unsintered powder (fine powder) and mixed.
As the PTFE fine powder, those having a number average molecular weight (Mn) of 1 million to 3 million, a reduction ratio of 500 to 2000, and a specific gravity of more than 2.18 and not more than 2.25 are used. As the liquid lubricant, petroleum-based solvents such as solvent naphtha and white oil are used.

  In the second step, the obtained mixture is compression-molded by a compression molding machine to form a block-shaped molded body (preliminary molding), and the block-shaped molded body is extruded from a paste extruder at a temperature of room temperature to 50 ° C. Extrude the tube at the mold outlet at a speed of 10 to 20 m / min. Extruded into a tube. The obtained tubular molded body is heated at 200 to 300 ° C. for 1 to 5 minutes to remove the liquid lubricant.

  In the third step, the obtained tubular molded body is stretched at a stretching ratio of 20 to 400% in the axial direction at a stretching temperature of 200 to 300 ° C. and a linear velocity of 3 to 30 m / min. If stretching at a time exceeds 400%, quality unevenness tends to occur. If it is 20% or less, the porosity is low, and stress is applied to the inner surface of the tube when a stimulus such as bending is given during production, and cracks are likely to occur.

  In the fourth step, the stretched tube is sintered. Sintering is performed at a sintering temperature of 350 to 700 ° C., and an appropriate residence time that gives a sufficient amount of heat to reach 345 to 347 ° C., which is the melting point of the material, specifically 1 to 20 minutes in a heating furnace. While heating and stretching the stretched tube in the axial direction by 60% to 560%, the total stretching ratio is set to 400 to 700%. If it is 400% or less, a sufficient porosity cannot be obtained, and if it is 700% or more, stretching unevenness or the like occurs, causing a problem in uniformity.

  According to the said manufacturing method, since the PTFE fine powder of lower molecular weight than before is used, the support tube 10 having a large pore diameter can be obtained, and the permeate flow rate of the porous multilayer hollow fiber membrane 1 is increased. Can do. Further, since the film is stretched at the stretch ratio and then stretched at the time of sintering, a strong fibrous skeleton as shown in FIG. 1 is formed while increasing the hole area occupation ratio of the support tube 10. Can do.

  Next, with reference to FIG. 2 thru | or 4, the porous multilayer hollow fiber membrane 1 provided with the tube 10 for support bodies as the support layer 11 is demonstrated.

As shown in FIG. 2, the porous multilayer hollow fiber membrane 1 includes a support layer 11 composed of a cylindrical support tube 10, and an expanded porous PTFE sheet integrated with an outer peripheral surface 11 a of the support layer 11. It consists of multiple layers with a filtration layer 12 consisting of 13. The pores P of the support layer 11 and the pores (not shown) of the filtration layer 12 are three-dimensionally communicated with each other as shown in FIG. 3, and in the porous multilayer hollow fiber membrane 1, It has permeability from the outer peripheral surface 12a side toward the inner peripheral surface 11b side of the support layer 11, and is used for external pressure filtration that performs solid-liquid separation processing.
In addition, the thickness of the filtration layer 12 of the porous multilayer hollow fiber membrane 1 is 5 to 100 μm, the thickness of the support layer 11 is 0.3 to 1.0 mm, and the tube inner diameter is 0.5 to 2 mm.

As the expanded porous PTFE sheet used for the filtration layer 12, a sheet having pores that are very small compared to the pores P of the support layer 11 is used, and the support layer 11 and the filtration layer 12 have pores. The size is greatly different.
Specifically, as shown in FIG. 4, the filtration layer 12 has an average maximum length (L) of a fibrous skeleton surrounding each hole 12A existing on the outer peripheral surface 12a of 2.5 μm or less, and as trapping particles. The particle trapping rate when a 0.2 μm diameter bead is pressure filtered at a pressure of 0.1 MPa is 90% or more. On the other hand, the average maximum length of the air holes 11A existing in the support layer 11 is about 20 μm to 50 μm.

  The porous multilayer hollow fiber membrane 1 obtained by the production method as a whole has the characteristic that the IPA bubble point is 100 kPa. Since the porous multi-layer hollow fiber membrane 1 has the pores larger than those in the outer peripheral surface 11a and the inside of the support layer 11 due to the use of the support tube 10, high particles due to the filtration layer 12 can be obtained. While maintaining the trapping property, the permeate flow rate is increased and the filtration performance is extremely excellent.

  Hereinafter, the method for producing the porous multilayer hollow fiber membrane of the present invention will be described in detail with reference to FIG.

  First, the support tube 10 described above is prepared. Here, the tube has an outer diameter of 2.5 mm. Flame treatment is performed over the entire outer peripheral surface 10a of the stretched and sintered support tube 10 under conditions of propane gas 1.2 L / min, air 11 L / min, speed 33 m / min, and the entire outer peripheral surface 10a. Are uniformly provided with fine irregularities of about 50 μm.

  A porous expanded PTFE sheet 13 is prepared. This porous expanded PTFE sheet 13 is stretched and sintered at a predetermined stretch ratio. The porous expanded PTFE sheet 13 is slit after production to form a tape having a width of 7.5 to 9.5 mm and a thickness of 5 to 15 μm.

  The porous expanded PTFE sheet 13 is wound while being spirally overlapped on the outer peripheral surface 10 a of the support tube 10. The porous expanded PTFE sheet 13 is wound so as to cover the entire outer peripheral surface 10a of the support tube 10 without omission.

  After winding the sheet, the laminated body 14 of the support tube 10 and the porous expanded PTFE sheet 13 is passed through a die 15 having an inner diameter of φ2.4 mm, and is uniformly distributed on the entire circumferential surface of the laminated body 14 in the radial direction of the tube. Then, a load of about 4.9 N is applied to the support tube 10 and the porous expanded PTFE sheet 13 is brought into close contact therewith.

  In this state, the support tube 10 and the porous expanded PTFE sheet 13 are sintered for 20 minutes at 350 ° C., which is higher than the melting point of the porous expanded PTFE sheet 13 (PTFE melting point is about 327 ° C.). Turn into.

  Since the integrated support tube 10 and the porous expanded PTFE sheet 13 have fine irregularities on the outer peripheral surface 10a of the support tube 10, the support tube 10 and the porous expanded PTFE sheet 13 are provided. There is no misalignment. Further, since the porous stretched PTFE sheet 13 is prevented from being lifted because it is brought into close contact with a load, both can be integrated in a good contact state.

The porous expanded PTFE sheet 13 can be obtained by various conventionally known methods described in the following (1) to (4).
(1) A method in which an unsintered molded body obtained by PTFE paste extrusion is stretched at a temperature equal to or lower than 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 extruding PTFE fine powder 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 used for the production of the porous stretched PTFE sheet 13 preferably has a number average molecular weight of 8 million to 16 million. In the paste extrusion method, 15 to 30 parts by weight of a liquid lubricant is preferably blended with 100 parts by weight of PTFE and extruded.

  The porous stretched PTFE sheet can be stretched mechanically by a normal method. For example, when winding from one roll to another roll, the winding speed can be made larger than the feeding speed, or the two opposing sides of the sheet can be gripped and stretched to widen the gap. it can. 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 conditions such as the stretching temperature, the degree of crystallinity of PTFE, and the stretching ratio, the maximum length of the pores and the like can be adjusted.

  In the above-described embodiment, two sheets are used and wound approximately half a turn. However, 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.

In addition, when the porous 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.

  The porous multi-layer hollow fiber membrane 1 is a filtration membrane for removing dirt components in waste water, and the average particle size of the solid particles S composed of the dirt components collected and separated by solid-liquid separation is 0.1 μm to The thing of about 5 micrometers is assumed.

  Thus, the porous multilayer hollow fiber membrane 1 is a porous filtration tube for external pressure filtration, and the outermost layer is a filtration layer 12 and surrounds many pores 12A existing on the outer peripheral surface 12a of the filtration layer 12. The size of pores (average maximum length (L)) formed by the fibrous skeleton is set as described above. Therefore, most solid particles S in the solution are rebounded on the outer peripheral surface 12a of the filtration layer 12, and the solid particles S are prevented from irreversibly entering the pores 12A and 11A in the filtration layer 12 and the support layer 11. Can do. 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, by using the porous multilayer hollow fiber membrane 1 after a certain period of time, by circulating a fluid from the inner peripheral surface 11b side of the support layer 11 toward the outer peripheral surface 12a side of the filtration layer 12, 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 said embodiment, although the filtration layer is formed from the porous expanded PTFE sheet, it can also be set as resin selected from polyolefin resin, such as PE and PP, a polyimide, and a polyvinylidene fluoride resin. The filtration layer can also be formed from an extruded tube.

FIG. 6 shows an example of a filtration module 20 using a converging body in which a plurality of porous multilayer hollow fiber membranes 1 are bundled.
The filtration module 20 is used for external pressure filtration, and includes a converging body 21 in which a plurality of porous multilayer hollow fiber membranes 1 are bundled. The converging body 21 is accommodated in the outer cylinder 22, and the gap between the porous multilayer hollow fiber membranes 1 is sealed with a sealing resin 23 at both ends 21 </ b> A and 21 </ b> B of the converging body 21. Further, the gap between the end 21 </ b> A of the focusing body 21 and the outer cylinder 22 is similarly sealed with a sealing resin 23. On the other hand, the end 21B is not bonded to the outer cylinder, and a certain space is provided between the end 21B and the inner wall of the outer cylinder.

The upper end of the filtration module 20 is opened, and the liquid to be treated (raw solution) to be subjected to the solid-liquid separation process is supplied from the bottom surface of the outer cylinder 22 and flows toward the upper end 21A of the converging body 21 as indicated by arrows in the figure. While being filtered through the porous multilayer hollow fiber membrane 1, the filtrate from which the solid particles have been removed flows through the inner peripheral side of the porous multilayer hollow fiber membrane 1 and is led out from the upper end 21 </ b> A side of the focusing body 21. .
Each hollow fiber membrane at the lower end of the filtration module 20 is sealed. Further, all of the turbid liquid containing solid particles or the like passes through the membrane, or a part thereof is discharged from an outlet provided in the outer cylinder 22 as indicated by an arrow in the figure.

Since the filtration module 20 includes a plurality of the porous multilayer hollow fiber membranes 1 described above, it is possible to perform filtration with very high accuracy and high permeation flow rate.
When the filtration module 20 is used for a high turbidity solution in addition to water purification treatment, the transmembrane pressure difference (filtration pressure) can be greatly reduced as compared with the conventional case, which is particularly effective.

7A, 7B, and 7C show a filtration module 30 that is used for immersion type external pressure suction filtration.
As shown in FIG. 7A, the submerged external pressure suction filtration module 30 is formed by bundling a plurality of porous multilayer hollow fiber membranes into a converging body 31, and converging and integrating one end side 31a with an epoxy resin 32. It is a module. As shown in FIGS. 7B and 7C, the other end side 31 b folds the hollow fiber membrane 1 into a U shape via a rod 33. In addition, a sufficient gap between the porous multilayer hollow fiber membranes 1 is secured.

  If it is an immersion type module with the above form, a simple air diffuser such as a perforated tube can be provided below, and bubbles and raw water can be supplied to the entire membrane using the spread of bubbles, Particularly effective for high turbidity solutions such as MLSS of 5,000 to 20,000 mg / L in the membrane separation activated sludge method.

  Examples and comparative examples are described below. In addition, this invention is not limited only to these Examples.

Example 1
Asahi Glass Co., Ltd. "Fluon (registered trademark) PTFE fine powder CD-1" (number average molecular weight 2 million) 100 parts by mass and solvent naphtha (Idemitsu Supersol FP25) 20 parts by mass were mixed. The resulting composition was pressed and hardened by applying a pressure of 2 MPa, and then extruded into a tube shape by a paste extruder having a cylinder diameter of 90 mmΦ, a die diameter of 3.5 mm, and a core pin diameter of 1.7 mm at an extrusion ram speed of 11 mm / min. did. At this time, the speed of the tubular product at the outlet was 10 m / min. The obtained tube was dried at 200 ° C. for 10 hours, and then stretched by 100% in the longitudinal direction under dry heat at 300 ° C. under a condition of a supply linear speed of 10 m / min.
Next, in a heating furnace at 650 ° C., 200% stretching was performed in the longitudinal direction under the condition of a supply line speed of 5 m / min to obtain a support tube.
The obtained support tube had an outer diameter of 2.50 mm, an inner diameter of 1.20 mm, and a thickness of 0.65 mm.

(Example 2)
A composition was prepared by mixing 100 parts by mass of “Fluon (registered trademark) PTFE fine powder CD-145” (number average molecular weight 8 million) manufactured by Asahi Glass Co., Ltd. and 26 parts by mass of solvent naphtha (Idemitsu Supersol FP25). The obtained composition was pressed and solidified by applying a pressure of 2 MPa, and then extruded into a tube shape by a paste extruder at an extrusion ram speed of 22 mm / min using the same size cylinder, die, and core pin size as in Example 1. . At this time, the speed of the tubular product at the outlet was 20 m / min.
Example 2 was carried out in the same manner as in Example 1 except that the supply linear velocity during drying of the support tube was 20 m / min. The obtained support tube had an outer diameter of 2.48 mm, an inner diameter of 1.18 mm, and a thickness of 0.65 mm, almost the same as in Example 1.

(Comparative Example 1)
Using Asahi Glass'"Fluon (registered trademark) PTFE fine powder CD-145" (number average molecular weight 8 million), except that 100 parts by mass and 22 parts by mass of Solvent Naphtha (Idemitsu Supersol FP25) were prepared. Was the same as in Example 1. The obtained support tube had an outer diameter of 2.45 mm, an inner diameter of 1.15 mm, and a thickness of 0.65 mm, almost the same as in Examples 1 and 2.

  The evaluation shown in Table 1 was performed on the support tubes of Examples and Comparative Examples thus obtained. It shows in Table 1 with the difference in manufacturing conditions.

  Further, scanning electron micrographs of the outer peripheral surface and inner peripheral surface of the support tube of Examples 1 and 2 and Comparative Example 1 were taken. Photographs taken are shown in FIGS. 8 to 10, respectively.

Next, the porous multilayer hollow fiber membrane 1 was produced using the support tube 10 of Examples and Comparative Examples.
As a porous sheet to be wound around the support tube, Sumitomo Electric Fine Polymer Co., Ltd. “Poreflon (registered trademark) HP-045-15”, which is a porous expanded PTFE sheet, was used. This porous expanded PTFE sheet has a thickness of 15 μm, a porosity of 60%, an IPA bubble point of 110 kPa, an IPA permeation flux at a differential pressure of 100 kPa of 30 ml / cm ² / min, and average / maximum fiber length (surrounding pores) When the average maximum length (L) of the fibrous skeleton is 2.5 μm, the filtration pressure is 0.1 MPa, and particles having a particle size (X) of 0.2 μm are used as trapping particles, the particle collection rate is 90%. is there.

The support tube and the porous expanded PTFE sheet were set in a dedicated wrapping apparatus. A tube for support was flowed at a line speed of 4 m / min, and a 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-sealing through a tunnel furnace set at an atmospheric temperature of 350 ° C., to obtain a porous multilayer hollow fiber membrane. The characteristics of the obtained porous multilayer hollow fiber membrane are shown in Table 1.

The above-described support tube and porous multilayer hollow fiber membrane were evaluated by the following methods.
(1) Porosity: Based on ASTM-D-792, it is a value obtained from the specific gravity (apparent specific gravity) obtained in water and the specific gravity of tetrafluoroethylene resin, and the larger this value, the better the permeability. .
(2) Average pore diameter: Measured with a palm porometer manufactured by PMI (model number CFP-1200A).
(3) IPA bubble point: Measured using isopropyl alcohol by a method based on ASTM-F-316-80.
(4) IPA flow rate:
Tube: The support tube was measured with a differential pressure of 20 kPa, and the porous multilayer tube was measured with a differential pressure of 100 kPa with isopropyl alcohol (IPA) at 20 ° C. In either case, an internal pressure was applied to the tube to ensure a differential pressure, and IPA flowing out from the outer surface of the hollow fiber membrane was collected per minute and the amount thereof was measured. The larger this value, the better the transparency.
Sheet: Measured by the method of ASTM-F-317, the differential pressure was 70 cmHg, and the pressure was corrected to a 100 kPa equivalent value.
(5) IPA permeation flux: The value obtained by dividing (4) by the effective membrane area was used. The effective membrane area was calculated based on the inner diameter of the support tube and the outer diameter of the porous multilayer hollow fiber membrane.
(6) IPA permeability coefficient: The value obtained by further dividing the permeation flux of (5) by the average film thickness of the sample.
(7) Matrix tensile strength: Based on JIS K 7161, the tensile velocity during the test was 100 mm / min, and the distance between the marked lines was calculated using the following formula using the values measured.
Matrix tensile strength = tensile strength / (1−porosity (%) / 100)

  As shown in FIGS. 8 to 10, it was confirmed that the first and second examples had larger outer surface voids than the first comparative example. Moreover, it was confirmed from Table 1 that the value of the IPA bubble point is small and has large holes. As a result, the IPA flow rate indicating the permeation flow rate was larger in Example 1 than in Comparative Example 1, and the permeation flow rate was excellent.

  Moreover, since the porous multilayer hollow fiber membrane formed from the support tube of Example 1 and Comparative Example 1 is wrapped by the same porous sheet, the IPA bubble point indicating the pore diameter is 87 to 93 kPa at the same level. It became the value of. However, the IPA flow rate was slightly larger in Example 1 than in Comparative Example 1, and excellent in permeability. That is, although the pore size was the same and the particle size that could be excluded was the same, the example had better permeation flow rate than the comparative example.

Next, using the porous multilayer hollow fiber membrane provided with the support tube of Example 1 and Comparative Example 1, the module for external pressure filtration 20 was replaced with the support tube of Example 2 and Comparative Example 1. Using the porous multilayer hollow fiber membrane provided, submerged external pressure suction filtration modules 30 were respectively produced.
Specifically, the external pressure filtration module 20 is a module having the configuration shown in FIG. 6 described above, and 900 pieces of the porous multilayer hollow fiber membranes 1 are bundled to form the converging body 21.
On the other hand, the immersion type external pressure suction filtration module 30 is a module having the form shown in FIG. 7, and 330 bundles of porous multilayer hollow fiber membranes are folded back into a U shape to form a converging body 31.

  Next, the pressure-type filtration experiment apparatus 40 shown in FIG. 11 was assembled by the filtration module 20 for external pressure filtration. In the filtration experiment apparatus 40, the stock solution 41 to be processed is pressurized and supplied to the inside of the outer cylinder of the filtration module 20 by the liquid feed pump 43, and the filtered filtrate is discharged from both ends of the filtration module 20. 44 is stored. In order to remove the solid content deposited on the surface of the hollow fiber membrane, backwashing was possible from the permeate tank using the pump 45. At that time, it was possible to discharge from the bottom of the module to the outside of the system. In addition, after backwashing, air was sent from the blower 46 to the module lower pipe to vibrate the membrane, and unfiltered raw water discharged from the side surface of the outer cylinder was returned to the tank 41.

Moreover, the immersion type filtration experiment apparatus 50 shown in FIG. 12 was assembled by the filtration module 30 for immersion type external pressure suction filtration.
In the immersion type filtration experiment apparatus 50, the filtration module 30 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 30 is sucked by a suction pump 53. In this configuration, the filter tank 52 is discharged. A vacuum gauge 54 was installed between the suction pump 53 and the filtration module 30. 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.

  Using the filtration experiment devices 40 and 50, filtration experiments were performed under the following conditions. The average value of filtration pressure (20 ° C. correction value) for 14 days in each experiment was determined and shown in Table 2.

(Experiment 1)
PAC (polyaluminum chloride) as a small amount of flocculant was added to the raw water before purification treatment collected from the water purification facility as a liquid to be treated using the filtration experimental apparatus 40 so that the effective AL was 1 mg / l. The filtration conditions were a constant flow rate operation with the permeate flow rate set to 2.5 m ³ / m ² / day.

As shown in Table 2, Example 1 was able to obtain better permeability than Comparative Example 1 even when the raw water collected from the water purification facility was filtered using a pressure filtration device. That is, the filtration pressure necessary to obtain the permeation flow rate (2.5 m ³ / m ² / day) started to increase from the beginning of operation in Comparative Example 1, and was about 59 kPa after 14 days. Then, after 14 days, it was almost the same as the initial operation and was reduced to about 29 kPa, about a half.

(Experiment 2)
Using the filtration experiment apparatus 50, the module 30 was immersed in activated sludge having a MLSS of 10,000 mg / L as the liquid to be treated, and the relationship between the elapsed days of the filtration experiment and the filtration pressure (suction pressure) was examined. A constant flow rate operation was performed, and the pressure was adjusted so that the permeation flux (0.6 m ³ / m ² / day) was constant. The other filtration conditions were such that the water temperature was 10 ° C. to 12 ° C. (the graphs of FIGS. 13 to 15 described later are 20 ° C. correction values based on the viscosity correction coefficient of water), and the suction filtration was performed for 9 minutes and 1 minute off. Backwashing was not performed, and the air diffused condition was always air diffused with an air amount of 50 L / min.

As shown in Example 1 in FIG. 13, Example 2 in FIG. 14, and Comparative Example 1 in FIG. 15, Example 2 can achieve the same permeate flow rate with a lower filtration pressure than Comparative Example 1. It was.
Specifically, as shown in Table 2, the filtration pressure required for the permeate flow rate (0.6 m ³ / m ² / day) was 23 kPa in Comparative Example 1 after 20 ° C. correction value · 14 days. On the other hand, in Example 2, it was 11 kPa and a half, and the Example was more excellent in permeability.
In addition, the filtered water which performed the filtration process obtained the clean filtered water whose turbidity is 0.1 NTU or less, and coliform group is zero in both Example and Comparative Example.

The porous multilayer hollow fiber membrane provided with the tube for a support of the present invention and the filtration module provided with a plurality of the membranes are in the field of environmental conservation such as normal water purification treatment, high turbidity wastewater treatment, waste acid / waste alkali treatment, etc. In addition, it can be suitably used in the fields of medicine, fermentation, food, etc., such as sterilization and turbidity (enzyme / amino acid purification) of fermentation processes, and culture filtration of animal cells.
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, foods, etc., filtration of water and dye solutions in 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.

The support tube of the present invention is shown, (A) is a schematic perspective view, (B) is an enlarged schematic view of the outer peripheral surface of the support tube. The porous multilayer hollow fiber membrane provided with the tube for supports of FIG. 1 is shown, (A) is sectional drawing, (B) shows a perspective block diagram. It is a figure which shows the filtration condition by a porous multilayer hollow fiber membrane. 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. (A) (B) (C) (D) is explanatory drawing of the manufacturing method of a porous multilayer hollow fiber membrane. It is a figure which shows the structure of a pressurization type filtration module. (A) shows the structure of the filtration module for immersion type suction filtration, (B) (C) is a figure which shows the principal part. It is the photograph which showed the electron micrograph of the tube for support bodies of Example 1, and expanded the outer peripheral surface 1000 times. It is the photograph which showed the electron micrograph of the tube for support bodies of Example 2, and expanded the outer peripheral surface 1000 times. It is the photograph which showed the electron micrograph of the tube for support bodies of comparative example 1, and expanded the outer peripheral surface 1000 times. FIG. 3 is a schematic configuration diagram of a filtration experiment apparatus of Experiment 1. It is a schematic block diagram of the filtration experiment apparatus of Experiment 2. It is a graph which shows the result of the filtration experiment of Example 1, and shows the relationship between elapsed days and filtration pressure. It is a graph which shows the result of the filtration experiment of Example 2, and shows the relationship between elapsed days and filtration pressure. It is a graph which shows the result of the filtration experiment of the comparative example 1, and shows the relationship between elapsed days and filtration pressure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Porous multilayer hollow fiber membrane 10 Support tube 10a Outer peripheral surface 11 Support layer 11a Outer peripheral surface 12 Filtration layer 12a Outer peripheral surface 13 Expanded porous PTFE sheet 20, 30 Filtration module F Fiber P Hole C Knot

Claims (9)

A porous multi-layer hollow fiber membrane support tube comprising a filtration layer comprising a porous sheet on the outer surface, having a porosity of 75% to 90%, an IPA bubble point of 2 to 12 kPa, and an inner diameter of IPA permeability coefficient (flow rate per unit membrane area of inner diameter reference / average film thickness) at 40 to 100 ml / min / cm ² / mm when 0.3 to 10 mm, wall thickness is 0.1 to 10 mm, and differential pressure is 20 kPa A support tube comprising a porous stretched polytetrafluoroethylene tube.   The tube for a support according to claim 1, wherein the matrix tensile strength is 50 to 110 MPa. A method for manufacturing the support tube according to claim 1 or 2,
After blending a liquid lubricant with polytetrafluoroethylene fine powder having a number average molecular weight (Mn) of 1,000,000 to 3,000,000 and making it into a tube shape by extrusion molding under a condition where the reduction ratio is 500 or more and 2,000 or less, the axial direction of the tube A method for producing a tube for a support, comprising: stretching 20 to 400%, further stretching 60 to 560% in the axial direction, setting the total stretching ratio to 400 to 700%, and sintering. A method for manufacturing the support tube according to claim 1 or 2,
A liquid lubricant is blended in a polytetrafluoroethylene fine powder having a number average molecular weight (Mn) of 6 million to 10 million at a weight ratio of 24 parts to 30 parts with respect to at least 100 parts of the resin, and the exit speed of the extruded tube is After being formed into a tube shape by extrusion at a speed of 15 m / min to 30 m / min, it is stretched by 50 to 400% in the axial direction of the tube and then sintered while being further stretched by 60 to 430% in the axial direction. A method for producing a tube for a support.   A support layer comprising the support tube according to claim 1 and a filtration layer comprising a porous sheet integrated on an outer peripheral surface of the support layer, wherein the support layer and the pores of the filtration layer are provided. Are porous three-dimensional hollow fiber membranes that are three-dimensionally connected to each other and are used for external pressure filtration that performs solid-liquid separation from the outer peripheral surface side toward the inner peripheral surface side.   The porous multilayer hollow fiber membrane according to claim 5, wherein the porous sheet is a porous stretched polytetrafluoroethylene sheet.   The porous multilayer hollow fiber membrane according to claim 6, wherein the IPA bubble point is 100 kPa or more. A method for producing the porous multilayer hollow fiber membrane according to claim 6 or 7,
A porous sheet made of a porous stretched polytetrafluoroethylene sheet is wound on the outer peripheral surface of the support tube, and the support tube and the porous sheet are in close contact with each other by applying a load simultaneously with or after the winding. And producing a porous multilayer hollow fiber membrane by sintering and integrating the support tube and the porous sheet.   A bundle of a plurality of porous multilayer hollow fiber membranes according to any one of claims 6 to 8 is used as a bundle, and is used for external pressure filtration or immersion type external pressure suction filtration. A filtration module.