JP2019042735A - Method for producing porous hollow membrane containing separation layer, porous hollow membrane and filtration method - Google Patents

Abstract

To provide a method for producing a porous hollow membrane excellent in chemical resistance and mechanical strength.SOLUTION: A method for producing a porous hollow membrane containing a separation layer includes a step of producing a kneaded product and a step of discharging a kneaded product. The step of producing the kneaded product includes mixing a thermoplastic resin, a nonsolvent and inorganic fine powder, and then melt kneading the mixture, and the nonsolvent does not uniformly dissolve a thermoplastic resin in a mass of 1/4 at a boiling point.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a porous hollow fiber membrane including a separation layer, a porous hollow fiber membrane, and a filtration method.

  A membrane filtration method using a hollow fiber membrane for the operation of removing the liquid to be treated, such as the water treatment and the sewage treatment, is becoming widespread. A thermally induced phase separation method is known as a method for producing a hollow fiber membrane used for membrane filtration.

In the thermally induced phase separation method, a thermoplastic resin and an organic liquid are used. The thermally induced phase separation method using a solvent which does not dissolve the thermoplastic resin at room temperature but dissolves at high temperature as the organic liquid, that is, a latent solvent (poor solvent), kneads the thermoplastic resin and the organic liquid at high temperature The plastic resin is dissolved in an organic liquid and then cooled to room temperature to induce phase separation, and the organic liquid is further removed to produce a porous body. This method has the following advantages.
(A) It is possible to form a film even with a suitable solvent-free polymer such as polyethylene that can be dissolved at room temperature.
(B) Melt at high temperature and then solidify by cooling to form a film, so in particular when the thermoplastic resin is a crystalline resin, crystallization is promoted at the time of film formation and a high strength film is easily obtained.

  From the above advantages, the thermally induced phase separation method is widely used as a method of producing a porous membrane. However, with certain crystalline resins, the film structure tends to be spherulites, and although the strength is high, the elongation is low and fragile, so there is a problem in practical durability. Conventionally, a technique of forming a film using a poor solvent of a thermoplastic resin, which is selected from citric acid esters, is disclosed (see Patent Document 1).

JP, 2011-168741, A

  However, the film produced by the method described in Patent Document 1 also has the problem of having a spherulite structure. The present invention has been made in view of the above circumstances, and provides a porous hollow fiber membrane having a three-dimensional network structure and excellent in chemical resistance and mechanical strength, and a method for producing the same.

That is, the present invention is as follows.
(1)
A method for producing a porous hollow fiber membrane comprising a separation layer, comprising:
Mixing a thermoplastic resin, a non-solvent which does not uniformly dissolve the thermoplastic resin of a mass of 1⁄4 at a boiling point, and an inorganic fine powder, and melt-kneading to prepare a kneaded product;
And discharging the kneaded material. A method for producing a porous hollow fiber membrane including a separation layer, characterized by comprising:
(2)
The non-solvent includes sebacic acid ester, acetyl citric acid ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, fatty acid having 6 to 30 carbon atoms, and epoxy Process for producing a porous hollow fiber membrane comprising the separation layer according to (1), which is at least one selected from hydrogenated vegetable oil (3)
The method for producing a porous hollow fiber membrane including the separation layer according to (1) or (2), wherein the non-solvent is a plasticizer selected from stearic acid ester, phosphoric acid ester, and fatty acid.
(4)
The method for producing a porous hollow fiber membrane comprising the separation layer according to (3), wherein the thermoplastic resin is an ethylene-chlorotrifluoroethylene copolymer.
(5)
The method for producing a porous hollow fiber membrane according to any one of (1) to (4), wherein the inorganic fine powder is at least one selected from silica, lithium chloride, and titanium oxide.
(6)
The porous hollow fiber membrane is a hollow fiber membrane comprising at least two layers including the separation layer, and a method for producing a porous hollow fiber membrane including the separation layer according to any one of (1) to (5) Method.
(7)
(6) The method for producing a porous multilayer hollow fiber membrane including the separation layer according to (6), wherein at least one layer other than the separation layer in the porous hollow fiber membrane is a porous hollow fiber membrane layer made of fluorocarbon resin.
(8)
The porous hollow fiber membrane according to (7), wherein the fluororesin is at least one selected from ethylene-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, and polyvinylidene fluoride. Manufacturing method.
(9)
The method for producing a porous hollow fiber membrane according to any one of (1) to (8), wherein the porous hollow fiber membrane has a tensile elongation at break of 80% or more.
(10)
What is claimed is: 1. A porous hollow fiber membrane comprising: a thermoplastic resin; a non-solvent which does not dissolve uniformly in the thermoplastic resin of a mass of 1/4 at a boiling point; and an inorganic fine powder.
(11)
Ethylene-chlorotrifluoroethylene copolymer,
Sebacic acid ester, acetyl citric acid ester, citric acid ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid, which does not uniformly dissolve the thermoplastic resin having a mass of 1/4 at the boiling point A non-solvent which is at least one selected from an ester, a phosphate ester, a phosphite ester, a fatty acid having 6 to 30 carbon atoms, and an epoxidized vegetable oil,
An inorganic fine powder, and A porous hollow fiber membrane characterized by including.
(12)
The porous hollow fiber membrane according to (10) or (11), having a tensile elongation at break of 80% or more.
(13)
The filtration method which filters using the porous hollow fiber membrane of any one of (10) to (12).

  According to the present invention, a porous hollow fiber membrane is provided, in which the membrane structure forms a three-dimensional network structure, which has good openness, high chemical resistance, and high mechanical strength.

FIG. 1 is an external view of a porous hollow fiber membrane according to an embodiment of the present invention. It is a schematic diagram which shows the film | membrane structure in the porous hollow fiber membrane of FIG. 5 is a schematic view showing a membrane structure of a porous hollow fiber membrane of Comparative Example 1. FIG.

  Embodiments of the present invention will be described in detail. The present invention is not limited to the following embodiments.

<Porous hollow fiber membrane>
Hereinafter, the porous hollow fiber membrane of the present invention will be described. FIG. 1 is an external view of a porous hollow fiber membrane according to the present invention. The porous hollow fiber membrane 10 includes at least the separation layer 11. The porous hollow fiber membrane 10 may be formed only by the separation layer 11, and further, the porous hollow fiber membrane 10 may include the support layer 12. In the present embodiment, the porous hollow fiber membrane 10 has the separation layer 11 and the support layer 12. In the present embodiment, the support layer 12 is formed on the inner surface side of the porous hollow fiber membrane 10. In the present embodiment, the separation layer 11 is formed on the radially outer side of the support layer 12.

  The separation layer 11 contains a thermoplastic resin. In the present embodiment, the separation layer 11 contains an ethylene-chlorotrifluoroethylene copolymer as a thermoplastic resin. The internal structure including the outer surface of the porous hollow fiber membrane 10 in which the separation layer 11 is formed is not a spherulite structure but a three-dimensional network structure as shown in FIG. By taking a three-dimensional network structure, in the porous hollow fiber membrane 10, the tensile elongation at break becomes high, and the resistance to acids, alkalis (such as aqueous sodium hydroxide solution) and oxidizing agents frequently used as a cleaning agent for the membrane Becomes stronger.

  The separation layer 11 contains components (impurity and the like) other than the thermoplastic resin (ethylene-chlorotrifluoroethylene copolymer). The separation layer 11 may contain components other than the thermoplastic resin up to about 5% by mass. For example, as described later, the separation layer 11 contains a non-solvent used at the time of production. The separation layer 11 may further contain a poor solvent. These nonsolvents and poor solvents can be detected by pyrolysis GC-MS (gas chromatography mass spectrometry).

  In the present embodiment, the poor solvent is an organic liquid which does not uniformly dissolve a 1⁄4 mass of a thermoplastic resin at normal temperature, and uniformly dissolves at least at the boiling point. A refractive index etc. can be utilized for judgment of a melt | dissolution state. For example, a thermoplastic resin and an organic liquid are put into a glass test tube, and the same refractive index is in the melted state regardless of which part of the mixed liquid is measured. In the undissolved state, the two layers are separated and show different refractive indices. For example, in the present embodiment, when an ethylene-chlorotrifluoroethylene copolymer is used as a thermoplastic resin, a 1/4 mass of the ethylene-chlorotrifluoroethylene copolymer is not uniformly dissolved at 25 ° C., It is an organic liquid which dissolves uniformly at 100 ° C. or more and the boiling point or less. Examples of such poor solvents include triphenyl phosphate and oleic acid.

  In the present embodiment, the non-solvent is an organic liquid which does not uniformly dissolve the thermoplastic resin having a mass of 1/4 at the boiling point. That is, the non-solvent is an organic liquid which does not uniformly dissolve the thermoplastic resin at the boiling point of the organic liquid in the mixed liquid containing the thermoplastic resin and the organic liquid at a mass ratio of 20:80.

  In the present embodiment, for example, when an ethylene-chlorotrifluoroethylene copolymer is used as a thermoplastic resin, the non-solvent is sebacic acid ester, acetyl citric acid ester, citric acid ester, adipic acid ester, trimellitic acid ester , Oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, phosphorous acid ester, fatty acid having 6 to 30 carbon atoms, and one selected from epoxidized vegetable oils, or a mixture of these. is there. Preferably, when the ethylene-chlorotrifluoroethylene copolymer is used as a thermoplastic resin, the non-solvent is an organic liquid selected from stearic acid ester, phosphoric acid ester, and fatty acid having 6 to 30 carbon atoms.

  Examples of fatty acids having 6 to 30 carbon atoms include capric acid, lauric acid and oleic acid. Examples of epoxidized vegetable oils include epoxy soybean oil and epoxidized linseed oil. The above solvents are compatible with the additives and have low toxicity.

  The separation layer 11 further contains inorganic fine powder as a component other than the thermoplastic resin (ethylene-chlorotrifluoroethylene copolymer). In the present embodiment, examples of the inorganic fine powder include silica, fine powder silica, titanium oxide, lithium chloride, calcium chloride and the like, and among these, fine powder silica is preferable from the viewpoint of cost.

  In the present embodiment, the support layer 12 is a porous body made of a fluorocarbon resin. The fluorine resin may be vinylidene fluoride, a homopolymer or copolymer of hexafluoropropylene, or a mixture thereof, a copolymer of ethylene-tetrafluoroethylene, an ethylene-chlorotrifluoroethylene copolymer, or a mixture of the above-mentioned fluorine resins. It is.

(Physical properties of porous hollow fiber membrane)
Next, physical properties of the porous hollow fiber membrane 10 according to the present embodiment will be described.
The initial value of the tensile elongation at break of the porous hollow fiber membrane 10 is preferably 60% or more, more preferably 80% or more, still more preferably 100% or more, and particularly preferably 120% or more. The tensile elongation at break can be measured by the measuring method in the examples described later.

  The alkali resistance can be evaluated by the ratio of the breaking elongation before and after the alkali immersion. For example, after immersing the porous hollow fiber membrane in a 4% aqueous solution of NaOH for 10 days, the tensile elongation at break ratio, which is the tensile elongation at break after immersion to the initial tensile elongation at break before immersion, is 60% or more Is preferred. The tensile elongation at break ratio is more preferably 65% or more, still more preferably 70% or more.

  From a practical viewpoint, the compressive strength of the porous hollow fiber membrane 10 is 0.2 MPa or more, preferably 0.3 to 1.0 MPa, and more preferably 0.4 to 1.0 MPa. The compressive strength is measured by measuring the pure water permeability by the external pressure, increasing the pressure every 0.05 MPa, judging that the pressure is no longer proportional to the pure water permeability, that the membrane has collapsed, and compressing the pressure just before that It can be measured as intensity.

  The opening ratio (surface opening ratio) of the surface of the porous hollow fiber membrane 10 is 20 to 60%, preferably 25 to 50%, and more preferably 25 to 45%. By using a membrane having an opening ratio of 20% or more on the surface in contact with the liquid to be treated for filtration, both the water permeation performance deterioration due to clogging and the water permeation performance deterioration due to membrane surface abrasion are both reduced, and filtration stability is enhanced. be able to. The aperture ratio can be measured by the measurement method in the example described later.

  Even if the aperture ratio is high, if the hole diameter is too large, the desired separation performance may not be exhibited. Therefore, the pore diameter at the outer surface is 1,000 nm or less, preferably 10 to 800 nm, and more preferably 100 to 700 nm. If the pore diameter is 1,000 nm or less, the component to be blocked contained in the liquid to be treated can be blocked, and if it is 10 nm or more, sufficiently high water permeability can be secured. The pore diameter can be measured by the measurement method in the examples described later.

  In the configuration in which the porous hollow fiber membrane 10 is a single layer membrane of the separation layer 11, the thickness of the porous hollow fiber membrane 10 is preferably 80 to 1,000 μm, and more preferably 100 to 300 μm. When the thickness is 80 μm or more, the strength can be increased. On the other hand, when the thickness is 1,000 μm or less, the pressure loss due to the film resistance can be reduced. Further, in the configuration of the multilayer porous hollow fiber membrane in which the porous hollow fiber membrane 10 further includes the support layer 12, the thickness of the separation layer 11 is 1 to 100 μm, and the thickness of the support layer 12 is 80 to 1, 000 μm is preferred. When the thickness of the separation layer 11 is 1 μm or more, the separation performance is easily exhibited, and when the thickness is 100 μm or less, the water permeability does not easily deteriorate. The thickness of the support layer 12 can increase the strength by being 80 μm or more, and the pressure loss due to the membrane resistance can be reduced by setting the thickness to 1,000 μm or less.

The porosity of the porous hollow fiber membrane 10 is preferably 50 to 80%, more preferably 55 to 65%. When the porosity is 50% or more, the water permeability is high, and when the porosity is 80% or less, the mechanical strength is high. In the present embodiment, the porosity is calculated by the following equation.
Porosity [%] = 100 × {(wet film weight [g]) − (dry film weight [g])} / (film volume [cm ³ ])

In the present embodiment, the wet membrane is a membrane in which the inside of the hole is filled with water but the inside of the hollow part is not filled with water. Specifically, after immersing a sample membrane having a length of 10 to 20 cm in ethanol and filling the inside of the pores with ethanol, the immersion in water is repeated 4 to 5 times to sufficiently replace the inside of the pores with water. A wet membrane is obtained by holding the end of the hollow fiber membrane after replacement by hand and shaking it about 5 times, holding it at the other end and shaking it about 5 times again to remove water in the hollow part. A dry film is obtained by drying to constant weight at 80 ° C. in an oven after weighing the wet film. The membrane volume is determined by membrane volume [cm ³ ] = π × {(outer diameter [cm] / 2) ² − (inner diameter [cm] / 2) ² } × (film length [cm]).

  The shape of the porous hollow fiber membrane 10 may be an annular single layer membrane, but a multilayer membrane having different pore sizes for the separation layer 11 and the support layer 12 supporting the separation layer 11 may be used. Good. In addition, the outer surface and the inner surface may have an irregular cross-sectional structure such as having a protrusion.

(Processing fluid)
The liquid to be treated by the porous hollow fiber membrane 10 is, for example, suspended water and a process liquid. The porous hollow fiber membrane 10 is suitably used in a water purification method including the step of filtering suspended water.

  Suspended water includes natural water, domestic wastewater, and treated water thereof. Natural water includes river water, lake water, underground water, and seawater as examples. Treated water of natural water obtained by subjecting such natural water to treatment such as sedimentation treatment, sand filtration treatment, coagulation sedimentation sand filtration treatment, ozone treatment, and activated carbon treatment is also included in the suspension water to be treated. An example of household drainage is sewage. Primary sewage treatment water subjected to screen filtration and sedimentation treatment, secondary sewage treatment water treated with biological treatment, and coagulation sediment sand filtration, activated carbon treatment, and ozone treatment etc. 3 Next treated (highly treated) water is also included in the suspension water to be treated. These suspended waters include suspended solids (hum colloids, organic colloids, clays, bacteria, etc.) consisting of fine organics, inorganics and organic-inorganic mixtures of the order of μm or less.

  The water quality of the above-mentioned natural water, domestic drainage, and suspended water such as these treated waters can generally be represented by a single or a combination of turbidity and organic substance concentration which are representative water quality indexes. When the water quality is classified according to turbidity (average turbidity instead of instantaneous turbidity), low turbidity water less than turbidity 1, medium turbidity water of turbidity 1 or more and 10 or less, high turbidity water of turbidity 10 or more and less than 50, It can be divided into ultra-high turbidity water with a turbidity of 50 or more. In addition, when the water quality is classified according to the organic matter concentration (Total Organic Carbon (TOC): mg / L) (this is also not an instantaneous value but an average value), the low TOC water less than 1 It can be divided into medium TOC water of 4 or more, high TOC water of 4 to 8 and ultra-high TOC water of 8 or more. Basically, the higher the turbidity or TOC, the easier it is for the filtration membrane to be clogged, so the higher the turbidity or TOC, the greater the effect of using the porous hollow fiber membrane 10.

  A process liquid refers to a liquid to be separated when valuables and non-valuables are separated in, for example, food, pharmaceuticals, and semiconductor manufacturing. In the food production, for example, the porous hollow fiber membrane 10 is used in the case of separating sakes such as sake and wine from yeast. In the manufacture of a medicine, for example, the porous hollow fiber membrane 10 is used for sterilization, etc. when purifying a protein. In semiconductor manufacturing, for example, the porous hollow fiber membrane 10 is used for separation of an abrasive and water from polishing waste water.

<Method of Manufacturing Porous Hollow Fiber Membrane 10 Including Separation Layer 11>
Next, a method of manufacturing the porous hollow fiber membrane 10 including the separation layer 11 will be described. The method for producing the porous hollow fiber membrane 10 including the separation layer 11 comprises the steps of (a) preparing a melt-kneaded product, and (b) supplying the melt-kneaded product to a spinning nozzle having a multiple structure, and melt kneading from the spinning nozzle. And (c) extracting the non-solvent from the hollow fiber membrane, and (d) extracting the inorganic fine powder from the hollow fiber membrane. In the case of producing a porous hollow fiber membrane further including the support layer 12, the separation layer 11 and the support layer 12 respectively include the step (a) and the step (b), and a triple-tube spinning nozzle is used. The melt-kneaded product to be the separation layer 11 and the support layer 12 is extruded to the outermost pipe of the pipe and the central pipe, and is formed into a hollow shape by flowing the hollow portion forming agent to the inner pipe.

  In each of the steps (c) and (d), the non-solvent and the inorganic fine powder are extracted from the hollow fiber membrane, but the non-solvent and the inorganic fine powder are contained as residual components in the hollow fiber membrane after extraction.

  Further, as the extractant used in the step (c), it is preferable to use a liquid such as methylene chloride or various alcohols which does not dissolve the thermoplastic resin but which has a high affinity for the plasticizer.

  Further, it is preferable to use, as the extractant in the step (d), a liquid which can dissolve hot water or additives used such as acid and alkali but not the thermoplastic resin.

Next, details of the step of preparing (a) the melt-kneaded product in the method for producing a porous hollow fiber membrane will be described.
The step (a) includes a step of absorbing the non-solvent into the inorganic fine powder and pulverizing it, and a step of melt-kneading the powder and the thermoplastic resin. Therefore, the melt-kneaded product contains three components of a thermoplastic resin, a non-solvent, and an inorganic fine powder.

  In the present embodiment, as the thermoplastic resin used in the step (a), for example, an ethylene-chlorotrifluoroethylene copolymer is applied as described above. The concentration of the thermoplastic resin in the melt-kneaded product is preferably 20 to 60% by mass, more preferably 25 to 45% by mass, and still more preferably 30 to 45% by mass. A mechanical strength is high in this value being 20 mass% or more, and water permeability is high in it being 60 mass% or less on the other hand.

  In this embodiment, as a non-solvent used in the step (a), sebacic acid ester, citric acid ester, acetyl citric acid ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, Thermoplastic of 1/4 mass in boiling point among at least one selected from phosphoric ester, phosphorous ester, fatty acid having 6 to 30 carbon atoms, and epoxidized vegetable oil or a combination thereof An organic liquid is applied which does not dissolve the resin uniformly. When the ethylene-chlorotrifluoroethylene copolymer is applied as the thermoplastic resin, the non-solvent is more preferably at least one selected from stearic acid ester, phosphite ester, and fatty acid. The concentration of the non-solvent in the melt-kneaded product is preferably 10 to 60% by mass.

  The method for producing the porous hollow fiber membrane 10 having the separation layer 11 in the present embodiment uses a non-solvent of ethylene-chlorotrifluoroethylene copolymer as a raw material. Thus, when a non-solvent is used as the raw material of the membrane, a porous hollow fiber membrane having a three-dimensional network structure can be obtained. The mechanism of action is not necessarily clear, but it is thought that crystallization of the polymer is appropriately inhibited and a three-dimensional network structure is more likely to be obtained if a solvent having a lower solubility is used by mixing a non-solvent. . Since the non-solvent alone is not mixed with the ethylene-chlorofluoroethylene copolymer, after the non-solvent is absorbed by the inorganic fine powder such as silica, it is mixed with the polymer and melt-kneaded.

  Solvents which can dissolve thermoplastic resins at normal temperature, solvents which can not dissolve at normal temperature but organic liquids which can be dissolved at high temperature can not be dissolved even at high temperatures of poor solvents of thermoplastic resins In the present embodiment, the poor solvent and the nonsolvent can be determined by the following method.

  The non-solvent raises the temperature of the first mixed solution to the boiling point in the first mixed solution mixed at a mass of 4 times with respect to the thermoplastic resin which is the ethylene-chlorotrifluoroethylene copolymer in this embodiment. However, it is an organic liquid which does not dissolve the thermoplastic resin uniformly.

  Further, the poor solvent is a temperature of the second mixture liquid in the second mixture liquid in which the mass is four times the mass of the thermoplastic resin which is the ethylene-chlorotrifluoroethylene copolymer in this embodiment. It is an organic liquid which does not dissolve the thermoplastic resin uniformly at ° C and which uniformly dissolves the thermoplastic resin at any temperature within the range of higher than 100 ° C. and not higher than the boiling point.

  Specifically, about 2 g of ethylene-chlorotrifluoroethylene copolymer and about 8 g of an organic liquid are put in a test tube and it is judged by a block heater for test tubes that the concentration is poor solvent and non-solvent. The temperature is raised to the boiling point of the organic liquid, the inside of the test tube is mixed with a spatula or the like, and the solubility is judged in the above temperature range.

  In addition, the boiling point of some specific examples of the said ester listed as a non-solvent is as follows. The boiling point of tributyl acetyl citrate is 343 ° C., dibutyl sebacate is 345 ° C., dibutyl adipate is 305 ° C., diisobutyl adipate is 293 ° C., and bis 2-ethylhexyl adipate is 335 ° C. Diisononyl adipate is at 250 ° C. or higher, diethyl adipate is at 251 ° C., triethyl citrate is at 294 ° C., and triphenylphosphorous acid is at 360 ° C.

  For example, triethyl citrate is applicable as a poor solvent because it dissolves uniformly at about 200 ° C. when ethylene-chlorotrifluoroethylene copolymer is used as the thermoplastic resin and triethyl citrate is used as the organic liquid to be mixed. . On the other hand, when triphenylphosphorous acid or oleic acid is used as the organic liquid, the ethylene-chlorotrifluoroethylene copolymer does not dissolve even at the boiling points thereof, and therefore, it can be applied as a non-solvent.

  In the present embodiment, examples of the inorganic fine powder used in the step (a) include silica, fine powder silica, titanium oxide, lithium chloride and calcium chloride. Among these, fine powder silica is preferable from the viewpoint of cost. .

  The primary particle diameter of the inorganic fine powder contained in the melt-kneaded product is preferably 50 nm or less, more preferably 5 nm or more and less than 30 nm. The above-mentioned "primary particle size of inorganic fine powder" means a value determined from analysis of an electron micrograph. That is, first, a group of inorganic fine powders is pretreated by the method of ASTM D3849. Then, the particle diameter of 3000-5000 pieces copied to the transmission electron micrograph is measured, and the primary particle diameter of inorganic fine powder is computed by carrying out the arithmetic mean of these values. The concentration of the inorganic fine powder in the melt-kneaded product is preferably 10 to 60% by mass.

  Since the above non-solvent as it is is not mixed with the thermoplastic resin, first, the non-solvent is absorbed in the inorganic fine powder to powder the non-solvent, and then mixed with the thermoplastic resin powder. Further, the mixture of the non-solvent, inorganic fine powder and thermoplastic resin can be uniformly mixed by melt-kneading at about 240 ° C., and the thermoplastic resin can be brought into a molten state.

  The inorganic fine powder in a porous hollow fiber membrane can judge the material of the inorganic fine powder by identifying the element which exists by a fluorescent X ray etc.

  By filtering the liquid to be treated using the porous hollow fiber membrane 10 of the present embodiment, filtration can be performed with high efficiency.

  Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited thereto.

Example 1
The melt-kneaded product was extruded using a double-pipe structure spinning nozzle to obtain a porous hollow fiber membrane of Example 1. 40% by mass of ethylene-chlorotrifluoroethylene copolymer (ECTFE) resin (Salvay Specialty Polymers, Halar 901) as a thermoplastic resin, 23% by mass of finely divided silica (R972, manufactured by Nippon Aerosil) as an inorganic fine powder, and as a non-solvent A melt-kneaded product was prepared at 240 ° C. using 37% by mass of triphenylphosphorous acid (TPP, manufactured by Tokyo Chemical Industry Co., Ltd., boiling point 360 ° C.) to prepare a porous hollow fiber membrane.

  The extruded hollow fiber molding was allowed to pass through a free running distance of 120 mm and then solidified in water at 30 ° C. to prepare a porous hollow fiber membrane by a melt film forming method. It was picked up at a speed of 5 m / min and wound up in a skein. The resulting hollow fiber extrudates were immersed in isopropyl alcohol to extract out the nonsolvent. Subsequently, it was immersed in water for 30 minutes to replace the hollow fiber membrane with water. Subsequently, the resultant was immersed in a 20% by mass aqueous NaOH solution at 70 ° C. for 1 hour, and then repeatedly washed with water to extract and remove finely powdered silica. The membrane structure of the porous hollow fiber membrane of Example 1 exhibited a three-dimensional network structure as shown in FIG.

Example 2
A porous hollow fiber membrane was produced in the same manner as in Example 1 except that a melt-kneaded product was prepared using 37% by mass of ethylhexyl stearate (manufactured by Tokyo Chemical Industry Co., Ltd., boiling point 340 ° C.) 37% by mass instead of 37% by mass of TPP as a non-solvent. did.

  The membrane structure of the porous hollow fiber membrane of Example 2 exhibited a three-dimensional network structure as shown in FIG.

[Example 3]
Example except that a melt-kneaded product was prepared using, as a non-solvent, 37% by mass of oleic acid (manufactured by Tokyo Chemical Industry Co., Ltd., boiling point 285 ° C.) instead of 37% by mass of triphenylphosphorous acid (TPP, boiling point 360 ° C.) A porous hollow fiber membrane was produced in the same manner as 1.

  The membrane structure of the porous hollow fiber membrane of Example 3 exhibited a three-dimensional network structure as shown in FIG.

Example 4
The melt-kneaded product was extruded using a triple tube structure spinning nozzle to obtain a multilayer porous hollow fiber membrane of Example 4. 34% by mass of ethylene-chlorotrifluoroethylene copolymer (ECTFE) resin (manufactured by Solvay Specialty Polymers, Halar 901) as thermoplastic resin in outer layer, 25.4% by mass of finely divided silica (R972 manufactured by Nippon Aerosil), as non-solvent 40.6 mass% of triphenyl phosphorous acid (TPP, manufactured by Tokyo Chemical Industry Co., Ltd., boiling point 360 ° C.), 40 mass% of polyvinylidene fluoride (Solvey Specialty Polymers, Solef 6010) as a thermoplastic resin in the inner layer, finely divided silica 23% by mass (R972 manufactured by Nippon Aerosil Co., Ltd.), 31.3% by mass bis-2-ethylhexyl adipate (DOA manufactured by Tokyo Chemical Industry Co., Ltd., boiling point 335 ° C.) as a non-solvent, triethyl acetyl citrate as a poor solvent Company ATBC, boiling point 343 ° C.) 5. A melt-kneaded product was prepared at 240 ° C. using a mixture of% by mass, the outer layer kneaded product was flowed to the outermost part of the triple pipe, the inner layer kneaded product to the middle part, and air was flowed to the inner part to produce a multilayer porous hollow fiber membrane. .

  The extruded hollow fiber molding was allowed to pass through a free running distance of 120 mm and then solidified in water at 30 ° C. to prepare a porous hollow fiber membrane by a melt film forming method. It was picked up at a speed of 5 m / min and wound up in a skein. The resulting two-layer hollow fiber extrudate was immersed in isopropyl alcohol to extract and remove the solvent. Subsequently, it was immersed in water for 30 minutes to replace the hollow fiber membrane with water. Subsequently, the resultant was immersed in a 20% by mass aqueous NaOH solution at 70 ° C. for 1 hour, and then repeatedly washed with water to extract and remove finely powdered silica. The membrane structure in the separation layer of the porous hollow fiber membrane in Example 4 exhibited a three-dimensional network structure as shown in FIG.

[Example 5]
The melt-kneaded product was extruded using a triple tube structure spinning nozzle to obtain a multilayer porous hollow fiber membrane of Example 5. 34% by mass of ethylene-chlorotrifluoroethylene copolymer (ECTFE) resin (manufactured by Solvay Specialty Polymers, Halar 901) as thermoplastic resin in outer layer, 25.4% by mass of finely divided silica (R972 manufactured by Nippon Aerosil), as non-solvent 40.6 mass% of ethylhexyl stearate (manufactured by Tokyo Chemical Industry Co., Ltd., boiling point 340 ° C.), 40% by mass of ethylene-tetrafluoroethylene copolymer (manufactured by Asahi Glass Co., Ltd., TL-081) as a thermoplastic resin in the inner layer 23% by mass of silica (R972 manufactured by Nippon Aerosil), 32.9% by mass of bis-2-ethylhexyl adipate (DOA manufactured by Tokyo Chemical Industry Co., Ltd., boiling point 335 ° C.) as a non-solvent, diisobutyl adipate as a poor solvent Made of DIBA, Boiling point 293 ° C) 4.1% by mass mixture There are prepared melt-kneaded product at 240 ° C., the outer layer kneaded material at the outermost part of the triple pipe, the inner layer kneaded material in the intermediate portion, flowing air to the innermost, was prepared a multi-layer porous hollow fiber membrane.

  The extruded hollow fiber molding was allowed to pass through a free running distance of 120 mm and then solidified in water at 30 ° C. to prepare a porous hollow fiber membrane by a melt film forming method. It was picked up at a speed of 5 m / min and wound up in a skein. The resulting two-layer hollow fiber extrudate was immersed in isopropyl alcohol to extract and remove the solvent. Subsequently, it was immersed in water for 30 minutes to replace the hollow fiber membrane with water. Subsequently, the resultant was immersed in a 20% by mass aqueous NaOH solution at 70 ° C. for 1 hour, and then repeatedly washed with water to extract and remove finely powdered silica. The membrane structure in the separation layer of the porous hollow fiber membrane in Example 5 exhibited a three-dimensional network structure as shown in FIG.

Comparative Example 1
A hollow fiber membrane of Comparative Example 1 was obtained in the same manner as Example 1, except that only DOA was used as a poor solvent for ECTFE resin instead of non-solvent TPP. The membrane structure of the porous hollow fiber membrane of Comparative Example 1 exhibited a spherulite structure as shown in FIG.

  Each physical property value in an Example and a comparative example was calculated by the following methods, respectively.

(1) Outer Diameter and Inner Diameter of Membrane The hollow fiber membrane was thinly sliced with a razor, and the outer diameter and the inner diameter were measured with a 100 × magnifying glass. For one sample, 60 measurements were made at intervals of 30 mm.

(2) Observation of surface aperture ratio, pore diameter, pore structure The electron microscope (SEM) image of the surface and the cross section of the film was photographed at 5000 times with an accelerating voltage of 3 kV using an electron microscope SU8000 series manufactured by HITACHI. Cross-sectional electron microscope samples were obtained by cutting film samples frozen in ethanol into round slices. Next, using the image analysis software Winroof 6.1.3, “de-noising” of the SEM image is performed with the numerical value “6”, and further binarization with a single threshold It has been digitized. The aperture ratio of the film surface was determined by determining the occupied area of the holes in the binarized image thus obtained.

  The pore diameter is determined by adding the pore area of each pore in order from the smaller pore diameter to each pore present on the surface, and the sum is determined by the pore diameter of 50% of the total pore area of each pore did.

  The film structure was observed at 5000 magnifications on the film surface and the cross section, and it was determined that there was no spherulite and the polymer trunk developed a three-dimensionally network structure as a three-dimensional network structure.

(3) Water Permeability After immersion in ethanol, seal one end of a wet hollow fiber membrane of about 10 cm in length that has been repeatedly immersed in pure water several times, insert the injection needle into the hollow part at the other end, The pure water at 25 ° C is injected into the hollow part at a pressure of 0.1 MPa from the injection needle at this time, the amount of pure water transmitted from the outer surface is measured, the pure water flux is determined by the following equation, and the water permeability is evaluated. did.
Pure water flux [L / (m ² × h)] = 60 × (permeate flow rate [L]) / {π × (outer membrane diameter [m]) × (effective membrane length [m]) × (measurement time [min] ])}

  Here, the membrane effective length refers to the net membrane length excluding the portion where the injection needle is inserted.

(4) Tensile elongation at break (%)
The load and displacement at tensile failure were measured under the following conditions.
According to the method of JIS K7161, a hollow fiber membrane was used as it is as a sample.
Measuring instrument: Instron type tensile tester (AGS-5D manufactured by Shimadzu Corporation)
Chuck distance: 5 cm
The tensile elongation at break was calculated according to JIS K7161 from the results obtained for a tensile speed of 20 cm / min.

(5) Permeability retention ratio at the time of suspension water filtration Permeability retention ratio at the time of suspension water filtration is one index for judging the degree of the permeability degradation due to clogging (fouling). For the measurement, a wet hollow fiber membrane, which was immersed in ethanol and then repeatedly immersed in pure water several times, was filtered by an external pressure method with an effective membrane length of 11 cm. First, pure water was filtered at a filtration pressure of 10 m ³ per day per 1 m ^{2 of the} surface area of the membrane, and permeated water was collected for 2 minutes to obtain an initial pure water permeation amount. Next, the natural surface water (Fujikawa surface water: turbidity 2.2, TOC concentration 0.8 ppm), which is natural suspension water, is filtered for 10 minutes at the same filtration pressure as when measuring the initial pure water permeability. The permeated water was collected for 2 minutes from the eighth filtration to the 10th filtration, and used as the water permeability at the time of the filtration of suspended water. The water permeation performance retention rate at the time of suspension water filtration was defined by the following formula. All operations were performed at 25 ° C. and a film surface linear velocity of 0.5 m / sec.
Permeability retention rate at the time of suspension water filtration [%] = 100 × (permeation water filtration amount [g] at suspension water filtration) / (initial pure water water permeability [g])
Each parameter in the equation is calculated by the following equation.
Filtration pressure = {(input pressure) + (output pressure)} / 2
Outer membrane surface area [m ² ] = π × (Yarn outer diameter [m]) × (film effective length [m])
Membrane surface linear velocity [m / s] = 4 × (circulating water volume [m ³ / s]) / {π × (tube diameter [m]) ^2- π × (film outer diameter [m]) ² }

In this measurement, the filtration pressure of the suspension water is not the same for each membrane, and the filtration pressure at which the initial pure water permeability performance (which is also the permeability performance at the start of suspension suspension) is 10m ³ per day per 1 m ^{2 of} surface area Set. This is because, in actual water treatment and sewage treatment, the membrane is usually used in a quantitative filtration operation (a method in which the filtration pressure is adjusted to obtain a constant filtered water volume within a fixed time). Therefore, in the present measurement as well, it is possible to compare the water permeation performance deterioration under the condition as close as possible to the condition of the quantitative filtration operation within the range of measurement using one hollow fiber membrane.

  Tables 1 and 2 show the composition, production conditions and various performances of the porous hollow fiber membranes of the obtained Examples and Comparative Examples.

As shown in Table 1, Examples 1 to 5 have good openness, high chemical resistance, and high mechanical strength by using a non-solvent as a film forming solution in film formation by a melt film forming method. It can be seen that porous hollow fiber membranes are produced.
On the other hand, in Comparative Example 1 in which the non-solvent is not contained, it is understood that the pore structure is a spherulite structure, and the pore resistance, chemical resistance and mechanical strength are inferior.

  According to the present invention, since the porous hollow fiber membrane is formed by containing a non-solvent, it is possible to use an ethylene-chlorotrifluoroethylene copolymer having good openability, high chemical resistance and high mechanical strength. Hollow fiber membranes are provided.

10 porous hollow fiber membrane 11 separation layer 12 support layer

Claims (13)

Mixing a thermoplastic resin, a non-solvent which does not uniformly dissolve the thermoplastic resin having a mass of 1⁄4 at a boiling point, and an inorganic fine powder, and melt-kneading to prepare a kneaded product;
And discharging the kneaded material. A method for producing a porous hollow fiber membrane including a separation layer, characterized by comprising: The non-solvent is sebacic acid ester, acetyl citric acid ester, citric acid ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, phosphoric acid ester, carbon number It is at least 1 sort (s) chosen from 6 or more and 30 or less fatty acid, and an epoxidized vegetable oil. The manufacturing method of the porous hollow fiber membrane containing the isolation | separation layer of Claim 1 characterized by the above-mentioned. The method for producing a porous hollow fiber membrane including the separation layer according to claim 1, wherein the thermoplastic resin is an ethylene-chlorotrifluoroethylene copolymer. The porous hollow fiber according to claim 3, wherein the non-solvent is a plasticizer selected from stearic acid ester, phosphoric acid ester, and fatty acid having 6 to 30 carbon atoms. Production method. The method for producing a porous hollow fiber membrane including the separation layer according to any one of claims 1 to 4, wherein the inorganic fine powder is at least one selected from silica, lithium chloride and titanium oxide. . The porous hollow fiber according to any one of claims 1 to 5, wherein the porous hollow fiber membrane is a hollow fiber membrane comprising at least two layers including the separation layer. Method of producing a membrane The porous hollow fiber membrane according to claim 6, wherein at least one layer other than the separation layer in the porous hollow fiber membrane is a porous hollow fiber membrane layer comprising a fluorocarbon resin. Method. The fluorine resin is at least one selected from ethylene-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, and polyvinylidene fluoride. The separation layer according to claim 7, characterized in that Method of producing porous hollow fiber membrane. The method for producing a porous hollow fiber membrane including a separation layer according to any one of claims 1 to 8, wherein the porous hollow fiber membrane has a tensile elongation at break of 80% or more. A porous hollow fiber membrane comprising: a thermoplastic resin; a non-solvent which does not uniformly dissolve the thermoplastic resin having a mass of 1/4 at a boiling point; and an inorganic fine powder. Ethylene-chlorotrifluoroethylene copolymer,
Sebacic acid ester, acetyl citric acid ester, citric acid ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid, which does not uniformly dissolve the thermoplastic resin having a mass of 1/4 at the boiling point A non-solvent which is at least one selected from an ester, a phosphate ester, a phosphite ester, a fatty acid having 6 to 30 carbon atoms, and an epoxidized vegetable oil,
An inorganic fine powder, and A porous hollow fiber membrane characterized by including. The porous hollow fiber membrane according to claim 10 or 11, wherein the porous hollow fiber membrane has a tensile elongation at break of 80% or more.   The filtration method which filters using the porous hollow fiber membrane of any one of Claims 10-12.